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Time evolution is the change of state brought about by the passage of time , applicable to systems with internal state (also called stateful systems ). In this formulation, time is not required to be a continuous parameter, but may be discrete or even finite . In classical physics , time evolution of a collection of rigid bodies is governed by the principles of classical mechanics . In their most rudimentary form, these principles express the relationship between forces acting on the bodies and their acceleration given by Newton's laws of motion . These principles can be equivalently expressed more abstractly by Hamiltonian mechanics or Lagrangian mechanics .
The concept of time evolution may be applicable to other stateful systems as well. For instance, the operation of a Turing machine can be regarded as the time evolution of the machine's control state together with the state of the tape (or possibly multiple tapes) including the position of the machine's read-write head (or heads). In this case, time is considered to be discrete steps.
Stateful systems often have dual descriptions in terms of states or in terms of observable values. In such systems, time evolution can also refer to the change in observable values. This is particularly relevant in quantum mechanics where the Schrödinger picture and Heisenberg picture are (mostly) [ clarification needed ] equivalent descriptions of time evolution.
Consider a system with state space X for which evolution is deterministic and reversible . For concreteness let us also suppose time is a parameter that ranges over the set of real numbers R . Then time evolution is given by a family of bijective state transformations
F t , s ( x ) is the state of the system at time t , whose state at time s is x . The following identity holds
To see why this is true, suppose x ∈ X is the state at time s . Then by the definition of F, F t , s ( x ) is the state of the system at time t and consequently applying the definition once more, F u , t (F t , s ( x )) is the state at time u . But this is also F u , s ( x ).
In some contexts in mathematical physics, the mappings F t , s are called propagation operators or simply propagators . In classical mechanics , the propagators are functions that operate on the phase space of a physical system. In quantum mechanics , the propagators are usually unitary operators on a Hilbert space . The propagators can be expressed as time-ordered exponentials of the integrated Hamiltonian. The asymptotic properties of time evolution are given by the scattering matrix . [ 1 ]
A state space with a distinguished propagator is also called a dynamical system .
To say time evolution is homogeneous means that
In the case of a homogeneous system, the mappings G t = F t ,0 form a one-parameter group of transformations of X , that is
For non-reversible systems, the propagation operators F t , s are defined whenever t ≥ s and satisfy the propagation identity
In the homogeneous case the propagators are exponentials of the Hamiltonian.
In the Schrödinger picture , the Hamiltonian operator generates the time evolution of quantum states. If | ψ ( t ) ⟩ {\displaystyle \left|\psi (t)\right\rangle } is the state of the system at time t {\displaystyle t} , then
This is the Schrödinger equation .
If H {\displaystyle H} is independent of time, then a state at some initial time ( t = 0 {\displaystyle t=0} ) can be expressed using the unitary time evolution operator U ( t ) {\displaystyle U(t)} is the exponential operator as
or more generally, for some initial time t 0 {\displaystyle t_{0}} | https://en.wikipedia.org/wiki/Time_evolution |
Within differential calculus , in many applications, one needs to calculate the rate of change of a volume or surface integral whose domain of integration , as well as the integrand , are functions of a particular parameter. In physical applications, that parameter is frequently time t .
The rate of change of one-dimensional integrals with sufficiently smooth integrands, is governed by this extension of the fundamental theorem of calculus :
The calculus of moving surfaces [ 1 ] provides analogous formulas for volume integrals over Euclidean domains , and surface integrals over differential geometry of surfaces , curved surfaces, including integrals over curved surfaces with moving contour boundaries .
Let t be a time-like parameter and consider a time-dependent domain Ω with a smooth surface boundary S . Let F be a time-dependent invariant field defined in the interior of Ω. Then the rate of change of the integral ∫ Ω F d Ω {\displaystyle \int _{\Omega }F\,d\Omega }
is governed by the following law: [ 1 ]
where C is the velocity of the interface . The velocity of the interface C is the fundamental concept in the calculus of moving surfaces . In the above equation, C must be expressed with respect to the exterior normal . This law can be considered as the generalization of the fundamental theorem of calculus .
A related law governs the rate of change of the surface integral
The law reads
where the δ / δ t {\displaystyle {\delta }/{\delta }t} - derivative is the fundamental operator in the calculus of moving surfaces , originally proposed by Jacques Hadamard . B α α {\displaystyle B_{\alpha }^{\alpha }} is the trace of the mean curvature tensor . In this law, C need not be expression with respect to the exterior normal, as long as the choice of the normal is consistent for C and B α α {\displaystyle B_{\alpha }^{\alpha }} . The first term in the above equation captures the rate of change in F while the second corrects for expanding or shrinking area. The fact that mean curvature represents the rate of change in area follows from applying the above equation to F ≡ 1 {\displaystyle F\equiv 1} since ∫ S d S {\displaystyle \int _{S}\,dS} is area:
The above equation shows that mean curvature B α α {\displaystyle B_{\alpha }^{\alpha }} can be appropriately called the shape gradient of area. An evolution governed by
is the popular mean curvature flow and represents steepest descent with respect to area. Note that for a sphere of radius R , B α α = − 2 / R {\displaystyle B_{\alpha }^{\alpha }=-2/R} , and for a circle of radius R , B α α = − 1 / R {\displaystyle B_{\alpha }^{\alpha }=-1/R} with respect to the exterior normal.
Suppose that S is a moving surface with a moving contour γ. Suppose that the velocity of the contour γ with respect to S is c . Then the rate of change of the time dependent integral:
is
The last term captures the change in area due to annexation, as the figure on the right illustrates. | https://en.wikipedia.org/wiki/Time_evolution_of_integrals |
In computational complexity theory , the time hierarchy theorems are important statements about time-bounded computation on Turing machines . Informally, these theorems say that given more time, a Turing machine can solve more problems. For example, there are problems that can be solved with n 2 time but not n time, where n is the input length.
The time hierarchy theorem for deterministic multi-tape Turing machines was first proven by Richard E. Stearns and Juris Hartmanis in 1965. [ 1 ] It was improved a year later when F. C. Hennie and Richard E. Stearns improved the efficiency of the universal Turing machine . [ 2 ] Consequent to the theorem, for every deterministic time-bounded complexity class , there is a strictly larger time-bounded complexity class, and so the time-bounded hierarchy of complexity classes does not completely collapse. More precisely, the time hierarchy theorem for deterministic Turing machines states that for all time-constructible functions f ( n ),
where DTIME ( f ( n )) denotes the complexity class of decision problems solvable in time O ( f ( n )). The left-hand class involves little o notation, referring to the set of decision problems solvable in asymptotically less than f ( n ) time.
In particular, this shows that D T I M E ( n a ) ⊊ D T I M E ( n b ) {\displaystyle {\mathsf {DTIME}}(n^{a})\subsetneq {\mathsf {DTIME}}(n^{b})} if and only if a < b {\displaystyle a<b} , so we have an infinite time hierarchy.
The time hierarchy theorem for nondeterministic Turing machines was originally proven by Stephen Cook in 1972. [ 3 ] It was improved to its current form via a complex proof by Joel Seiferas, Michael Fischer , and Albert Meyer in 1978. [ 4 ] Finally in 1983, Stanislav Žák achieved the same result with the simple proof taught today. [ 5 ] The time hierarchy theorem for nondeterministic Turing machines states that if g ( n ) is a time-constructible function, and f ( n +1) = o ( g ( n )), then
The analogous theorems for space are the space hierarchy theorems . A similar theorem is not known for time-bounded probabilistic complexity classes, unless the class also has one bit of advice . [ 6 ]
Both theorems use the notion of a time-constructible function . A function f : N → N {\displaystyle f:\mathbb {N} \rightarrow \mathbb {N} } is time-constructible if there exists a deterministic Turing machine such that for every n ∈ N {\displaystyle n\in \mathbb {N} } , if the machine is started with an input of n ones, it will halt after precisely f ( n ) steps. All polynomials with non-negative integer coefficients are time-constructible, as are exponential functions such as 2 n .
We need to prove that some time class TIME ( g ( n )) is strictly larger than some time class TIME ( f ( n )). We do this by constructing a machine which cannot be in TIME ( f ( n )), by diagonalization . We then show that the machine is in TIME ( g ( n )), using a simulator machine .
Time Hierarchy Theorem. If f ( n ) is a time-constructible function, then there exists a decision problem which cannot be solved in worst-case deterministic time o ( f ( n )) but can be solved in worst-case deterministic time O ( f ( n )log f ( n )). Thus
Equivalently, if f , g {\displaystyle f,g} are time-constructable, and f ( n ) ln f ( n ) = o ( g ( n ) ) {\displaystyle f(n)\ln f(n)=o(g(n))} , then
D T I M E ( f ( n ) ) ⊊ D T I M E ( g ( n ) ) {\displaystyle {\mathsf {DTIME}}(f(n))\subsetneq {\mathsf {DTIME}}(g(n))}
Note 1. f ( n ) is at least n , since smaller functions are never time-constructible.
Example. D T I M E ( n ) ⊊ D T I M E ( n ( ln n ) 2 ) {\displaystyle {\mathsf {DTIME}}(n)\subsetneq {\mathsf {DTIME}}(n(\ln n)^{2})} .
We include here a proof of a weaker result, namely that DTIME ( f ( n )) is a strict subset of DTIME ( f (2 n + 1) 3 ), as it is simpler but illustrates the proof idea. See the bottom of this section for information on how to extend the proof to f ( n )log f ( n ).
To prove this, we first define the language of the encodings of machines and their inputs which cause them to halt within f
Notice here that this is a time-class. It is the set of pairs of machines and inputs to those machines ( M , x ) so that the machine M accepts within f (| x |) steps.
Here, M is a deterministic Turing machine, and x is its input (the initial contents of its tape). [ M ] denotes an input that encodes the Turing machine M . Let m be the size of the tuple ([ M ], x ).
We know that we can decide membership of H f by way of a deterministic Turing machine R , that simulates M for f ( x ) steps by first calculating f (| x |) and then writing out a row of 0s of that length, and then using this row of 0s as a "clock" or "counter" to simulate M for at most that many steps. At each step, the simulating machine needs to look through the definition of M to decide what the next action would be. It is safe to say that this takes at most f ( m ) 3 operations (since it is known that a simulation of a machine of time complexity T ( n ) for can be achieved in time O ( T ( n ) ⋅ | M | ) {\displaystyle O(T(n)\cdot |M|)} on a multitape machine, where | M | is the length of the encoding of M ), we have that:
The rest of the proof will show that
so that if we substitute 2 n + 1 for m , we get the desired result. Let us assume that H f is in this time complexity class, and we will reach a contradiction.
If H f is in this time complexity class, then there exists a machine K which, given some machine description [ M ] and input x , decides whether the tuple ([ M ], x ) is in H f within
We use this K to construct another machine, N , which takes a machine description [ M ] and runs K on the tuple ([ M ], [ M ]), ie. M is simulated on its own code by K , and then N accepts if K rejects, and rejects if K accepts.
If n is the length of the input to N , then m (the length of the input to K ) is twice n plus some delimiter symbol, so m = 2 n + 1. N' s running time is thus
Now if we feed [ N ] as input into N' and ask the question whether N accepts its N' description as input, we get:
We thus conclude that the machine K does not exist, and so
The reader may have realised that the proof gives the weaker result because we have chosen a simple Turing machine simulation for which we know that
It is known [ 7 ] that a more efficient simulation exists which establishes that
If g ( n ) is a time-constructible function, and f ( n +1) = o ( g ( n )), then there exists a decision problem which cannot be solved in non-deterministic time f ( n ) but can be solved in non-deterministic time g ( n ). In other words, the complexity class NTIME ( f ( n )) is a strict subset of NTIME ( g ( n )).
The time hierarchy theorems guarantee that the deterministic and non-deterministic versions of the exponential hierarchy are genuine hierarchies: in other words P ⊊ EXPTIME ⊊ 2-EXP ⊊ ... and NP ⊊ NEXPTIME ⊊ 2-NEXP ⊊ ....
For example, P ⊊ E X P T I M E {\displaystyle {\mathsf {P}}\subsetneq {\mathsf {EXPTIME}}} since P ⊆ D T I M E ( 2 n ) ⊊ D T I M E ( 2 2 n ) ⊆ E X P T I M E {\displaystyle {\mathsf {P}}\subseteq {\mathsf {DTIME}}(2^{n})\subsetneq {\mathsf {DTIME}}(2^{2n})\subseteq {\mathsf {EXPTIME}}} . Indeed, D T I M E ( 2 n ) ⊆ D T I M E ( o ( 2 2 n 2 n ) ) ⊊ D T I M E ( 2 2 n ) {\displaystyle {\mathsf {DTIME}}\left(2^{n}\right)\subseteq {\mathsf {DTIME}}\left(o\left({\frac {2^{2n}}{2n}}\right)\right)\subsetneq {\mathsf {DTIME}}(2^{2n})} from the time hierarchy theorem.
The theorem also guarantees that there are problems in P requiring arbitrarily large exponents to solve; in other words, P does not collapse to DTIME ( n k ) for any fixed k . For example, there are problems solvable in n 5000 time but not n 4999 time. This is one argument against Cobham's thesis , the convention that P is a practical class of algorithms. If such a collapse did occur, we could deduce that P ≠ PSPACE , since it is a well-known theorem that DTIME ( f ( n )) is strictly contained in DSPACE ( f ( n )).
However, the time hierarchy theorems provide no means to relate deterministic and non-deterministic complexity, or time and space complexity, so they cast no light on the great unsolved questions of computational complexity theory : whether P and NP , NP and PSPACE , PSPACE and EXPTIME , or EXPTIME and NEXPTIME are equal or not.
The gap of approximately log f ( n ) {\displaystyle \log f(n)} between the lower and upper time bound in the hierarchy theorem can be traced to the efficiency of the device used in the proof, namely a universal program that maintains a step-count. This can be done more efficiently on certain computational models. The sharpest results, presented below, have been proved for:
For these models, the theorem has the following form:
If f ( n ) is a time-constructible function, then there exists a decision problem which cannot be solved in worst-case deterministic time f ( n ) but can be solved in worst-case time af ( n ) for some constant a (dependent on f ).
Thus, a constant-factor increase in the time bound allows for solving more problems, in contrast with the situation for Turing machines (see Linear speedup theorem ). Moreover, Ben-Amram proved [ 10 ] that, in the above models, for f of polynomial growth rate (but more than linear), it is the case that for all ε > 0 {\displaystyle \varepsilon >0} , there exists a decision problem which cannot be solved in worst-case deterministic time f ( n ) but can be solved in worst-case time ( 1 + ε ) f ( n ) {\displaystyle (1+\varepsilon )f(n)} . | https://en.wikipedia.org/wiki/Time_hierarchy_theorem |
Time of arrival ( TOA or ToA ) is the absolute time instant when a radio signal emanating from a transmitter reaches a remote receiver.
The time span elapsed since the time of transmission ( TOT or ToT ) is the time of flight (TOF or ToF). Time difference of arrival ( TDOA ) is the difference between TOAs.
Many radiolocation systems use TOA measurements to perform geopositioning via true-range multilateration . The true range or distance can be directly calculated from the TOA as signals travel with a known velocity . TOA from two base stations will narrow a position to a position circle ; data from a third base station is required to resolve the precise position to a single point.
TDOA techniques such as pseudorange multilateration use the measured time difference between TOAs.
The concept may be applied as well with IEEE 802.15.4a CSS as with IEEE 802.15.4aUWB modulation. [ 1 ]
As with TDOA, synchronization of the network base station with the locating reference stations is important. This synchronization can be done in different ways:
Two-way ranging is a cooperative method for determining the range between two radio transceiver units. When synchronisation of the oscillators of the involved transmitters is not viable, hence the clocks differ, then applying the measurement as a two ways travel to the receiver and mirrored back to the transmitter compensates for some of the phase differences between the oscillators involved. This concept is applied with the real-time locating system (RTLS) concept as defined in the international standard ISO/IEC FCD 24730-5. [ 2 ]
Assume a surveillance system calculates the time differences ( τ i {\displaystyle \tau _{i}} for i = 1 , 2 , . . . , m − 1 {\displaystyle i=1,2,...,m-1} ) of wavefronts touching each receiver. The TDOA equation for receivers i {\displaystyle i} and 0 {\displaystyle 0} is (where the wave propagation speed is c {\displaystyle c} and the true vehicle-receiver ranges are R 0 {\displaystyle R_{0}} and R i {\displaystyle R_{i}} )
c τ i = c T i − c T 0 , c τ i = R i − R 0 . {\displaystyle {\begin{aligned}c\,\tau _{i}&=c\,T_{i}-c\,T_{0},\\c\,\tau _{i}&=R_{i}-R_{0}.\end{aligned}}}
The quantity c T i {\displaystyle c\,T_{i}} is often termed a pseudo-range. It differs from the true range between the vehicle and station i {\displaystyle i} by an offset, or bias, which is the same for every signal. Differencing two pseudo-ranges yields the difference of the same two true-ranges.
Figure 4a (first two plots) show a simulation of a pulse waveform recorded by receivers P 0 {\displaystyle P_{0}} and P 1 {\displaystyle P_{1}} . The spacing between E {\displaystyle E} , P 1 {\displaystyle P_{1}} and P 0 {\displaystyle P_{0}} is such that the pulse takes 5 time units longer to reach P 1 {\displaystyle P_{1}} than P 0 {\displaystyle P_{0}} . The units of time in Figure 4 are arbitrary. The following table gives approximate time scale units for recording different types of waves:
The red curve in Figure 4a (third plot) is the cross-correlation function ( P 1 ⋆ P 0 ) {\displaystyle (P_{1}\star P_{0})} . The cross-correlation function slides one curve in time across the other and returns a peak value when the curve shapes match. The peak at time = 5 is a measure of the time shift between the recorded waveforms, which is also the τ {\displaystyle \tau } value needed for equation 3 .
Figure 4b shows the same type of simulation for a wide-band waveform from the emitter. The time shift is 5 time units because the geometry and wave speed is the same as the Figure 4a example. Again, the peak in the cross-correlation occurs at τ 1 = 5 {\displaystyle \tau _{1}=5} .
Figure 4c is an example of a continuous, narrow-band waveform from the emitter. The cross-correlation function shows an important factor when choosing the receiver geometry. There is a peak at time = 5 plus every increment of the waveform period. To get one solution for the measured time difference, the largest space between any two receivers must be closer than one wavelength of the emitter signal. Some systems, such as the LORAN C and Decca mentioned at earlier (recall the same math works for moving receiver and multiple known transmitters), use spacing larger than 1 wavelength and include equipment, such as a phase detector , to count the number of cycles that pass by as the emitter moves. This only works for continuous, narrow-band waveforms because of the relation between phase θ {\displaystyle \theta } , frequency f {\displaystyle f} and time T {\displaystyle T} :
The phase detector will see variations in frequency as measured phase noise , which will be an uncertainty that propagates into the calculated location. If the phase noise is large enough, the phase detector can become unstable.
Navigation systems employ similar, but slightly more complex, methods than surveillance systems to obtain delay differences. The major change is DTOA navigation systems cross-correlate each received signal with a stored replica of the transmitted signal (rather than another received signal). The result yields the received signal time delay plus the user clock's bias (pseudo-range scaled by 1 / c {\displaystyle 1/c} ). Differencing the results of two such calculations yields the delay difference sought ( τ i {\displaystyle \tau _{i}} in equation 3 ).
TOT navigation systems perform similar calculations as TDOA navigation systems. However, the final step, subtracting the results of one cross-correlation from another, is not performed. Thus, the result is m {\displaystyle m} received signal time delays plus the user clock's bias ( T i {\displaystyle T_{i}} in equation 3 ). | https://en.wikipedia.org/wiki/Time_of_arrival |
Time of concentration is a concept used in hydrology to measure the response of a watershed to a rain event. It is defined as the time needed for water to flow from the most remote point in a watershed to the watershed outlet. [ 1 ] It is a function of the topography, geology, and land use within the watershed. A number of methods can be used to calculate time of concentration, including the Kirpich (1940) [ 2 ] and NRCS (1997) [ 3 ] methods.
Time of concentration is useful in predicting flow rates that would result from hypothetical storms, which are based on statistically derived return periods through IDF curves . [ 4 ] [ 5 ] For many (often economic) reasons, it is important for engineers and hydrologists to be able to accurately predict the response of a watershed to a given rain event. This can be important for infrastructure development (design of bridges , culverts , etc.) and management, as well as to assess flood risk such as the ARkStorm -scenario.
This image shows the basic principle which leads to determination of the time of concentration. Much like a topographic map showing lines of equal elevation, a map with isolines can be constructed to show locations with the same travel time to the watershed outlet. In this simplified example, the watershed outlet is located at the bottom of the picture with a stream flowing through it. Moving up the map, we can say that rainfall which lands on all of the places along the first yellow line will reach the watershed outlet at exactly the same time. This is true for every yellow line, with each line further away from the outlet corresponding to a greater travel time for runoff traveling to the outlet.
Furthermore, as this image shows, the spatial representation of travel time can be transformed into a cumulative distribution plot detailing how travel times are distributed throughout the area of the watershed.
Time of Concentration | https://en.wikipedia.org/wiki/Time_of_concentration |
Time of flight ( ToF ) is the measurement of the time taken by an object, particle or wave (be it acoustic, electromagnetic, etc.) to travel a distance through a medium. This information can then be used to measure velocity or path length, or as a way to learn about the particle or medium's properties (such as composition or flow rate). The traveling object may be detected directly (direct time of flight, dToF , e.g., via an ion detector in mass spectrometry) or indirectly (indirect time of flight, iToF , e.g., by light scattered from an object in laser doppler velocimetry ). Time of flight technology has found valuable applications in the monitoring and characterization of material and biomaterials, hydrogels included. [ 1 ] [ 2 ]
In electronics , one of the earliest devices using the principle are ultrasonic distance-measuring devices, which emit an ultrasonic pulse and are able to measure the distance to a solid object based on the time taken for the wave to bounce back to the emitter. The ToF method is also used to estimate the electron mobility . Originally, it was designed for measurement of low-conductive thin films, later adjusted for common semiconductors. This experimental technique is used for metal-dielectric-metal structures [ 3 ] as well as organic field-effect transistors. [ 4 ] The excess charges are generated by application of the laser or voltage pulse.
For magnetic resonance angiography (MRA), ToF is a major underlying method. In this method, blood entering the imaged area is not yet saturated, giving it a much higher signal when using short echo time and flow compensation. It can be used in the detection of aneurysm , stenosis or dissection . [ 5 ]
In time-of-flight mass spectrometry , ions are accelerated by an electrical field to the same kinetic energy with the velocity of the ion depending on the mass-to-charge ratio . Thus the time-of-flight is used to measure velocity, from which the mass-to-charge ratio can be determined. [ 6 ] The time-of-flight of electrons is used to measure their kinetic energy. [ 7 ]
In near-infrared spectroscopy , the ToF method is used to measure the media-dependent optical pathlength over a range of optical wavelengths, from which composition and properties of the media can be analyzed.
In ultrasonic flow meter measurement, ToF is used to measure speed of signal propagation upstream and downstream of flow of a media, in order to estimate total flow velocity. This measurement is made in a collinear direction with the flow.
In planar Doppler velocimetry (optical flow meter measurement), ToF measurements are made perpendicular to the flow by timing when individual particles cross two or more locations along the flow (collinear measurements would require generally high flow velocities and extremely narrow-band optical filters).
In optical interferometry, the pathlength difference between sample and reference arms can be measured by ToF methods, such as frequency modulation followed by phase shift measurement or cross correlation of signals. Such methods are used in laser radar and laser tracker systems for medium-long range distance measurement.
In neutron time-of-flight scattering , a pulsed monochromatic neutron beam is scattered by a sample. The energy spectrum of the scattered neutrons is measured via time of flight.
In kinematics , ToF is the duration in which a projectile is traveling through the air. Given the initial velocity u {\displaystyle u} of a particle launched from the ground, the downward (i.e. gravitational) acceleration a {\displaystyle a} , and the projectile's angle of projection θ (measured relative to the horizontal), then a simple rearrangement of the SUVAT equation
results in this equation
for the time of flight of a projectile.
The time-of-flight principle can be applied for mass spectrometry . Ions are accelerated by an electric field of known strength. This acceleration results in an ion having the same kinetic energy as any other ion that has the same charge. The velocity of the ion depends on the mass-to-charge ratio . The time that it subsequently takes for the particle to reach a detector at a known distance is measured. This time will depend on the mass-to-charge ratio of the particle (heavier particles reach lower speeds). From this time and the known experimental parameters one can find the mass-to-charge ratio of the ion. The elapsed time from the instant a particle leaves a source to the instant it reaches a detector.
An ultrasonic flow meter measures the velocity of a liquid or gas through a pipe using acoustic sensors. This has some advantages over other measurement techniques. The results are slightly affected by temperature, density or conductivity. Maintenance is inexpensive because there are no moving parts .
Ultrasonic flow meters come in three different types: transmission (contrapropagating transit time) flowmeters, reflection (Doppler) flowmeters, and open-channel flowmeters. Transit time flowmeters work by measuring the time difference between an ultrasonic pulse sent in the flow direction and an ultrasound pulse sent opposite the flow direction. Doppler flowmeters measure the doppler shift resulting in reflecting an ultrasonic beam off either small particles in the fluid, air bubbles in the fluid, or the flowing fluid's turbulence. Open channel flow meters measure upstream levels in front of flumes or weirs .
Optical time-of-flight sensors consist of two light beams projected into the fluid whose detection is either interrupted or instigated by the passage of small particles (which are assumed to be following the flow). This is not dissimilar from the optical beams used as safety devices in motorized garage doors or as triggers in alarm systems. The speed of the particles is calculated by knowing the spacing between the two beams. If there is only one detector, then the time difference can be measured via autocorrelation . If there are two detectors, one for each beam, then direction can also be known. Since the location of the beams is relatively easy to determine, the precision of the measurement depends primarily on how small the setup can be made. If the beams are too far apart, the flow could change substantially between them, thus the measurement becomes an average over that space. Moreover, multiple particles could reside between them at any given time, and this would corrupt the signal since the particles are indistinguishable. For such a sensor to provide valid data, it must be small relative to the scale of the flow and the seeding density. MOEMS approaches yield extremely small packages, making such sensors applicable in a variety of situations. [ 8 ]
Usually the time-of-flight tube used in mass spectrometry is praised for simplicity, but for precision measurements of charged low energy particles the electric and the magnetic field in the tube has to be controlled within 10 mV and 1 nT respectively.
The work function homogeneity of the tube can be controlled by a Kelvin probe . The magnetic field can be measured by a fluxgate compass . High frequencies are passively shielded and damped by radar absorbent material . To generate arbitrary low frequencies field the screen is parted into plates (overlapping and connected by capacitors) with bias voltage on each plate and a bias current on coil behind plate whose flux is closed by an outer core. In this way the tube can be configured to act as a weak achromatic quadrupole lens with an aperture with a grid and a delay line detector in the diffraction plane to do angle resolved measurements. Changing the field the angle of the field of view can be changed and a deflecting bias can be superimposed to scan through all angles.
When no delay line detector is used focusing the ions onto a detector can be accomplished through the use of two or three einzel lenses placed in the vacuum tube located between the ion source and the detector.
The sample should be immersed into the tube with holes and apertures for and against stray light to do magnetic experiments and to control the electrons from their start.
A time-of-flight camera (ToF camera), also known as time-of-flight sensor (ToF sensor), is a range imaging camera system for measuring distances between the camera and the subject for each point of the image based on time-of-flight , the round trip time of an artificial light signal, as provided by a laser or an LED . Laser-based time-of-flight cameras are part of a broader class of scannerless LIDAR , in which the entire scene is captured with each laser pulse, as opposed to point-by-point with a laser beam such as in scanning LIDAR systems. [ 9 ]
A time-of-flight (TOF) detector is a particle detector which can discriminate between a lighter and a heavier elementary particle of same momentum using their time of flight between two scintillators . [ 11 ] The first of the scintillators activates a clock upon being hit while the other stops the clock upon being hit. If the two masses are denoted by m 1 {\displaystyle m_{1}} and m 2 {\displaystyle m_{2}} and have velocities v 1 {\displaystyle v_{1}} and v 2 {\displaystyle v_{2}} then the time of flight difference is given by | https://en.wikipedia.org/wiki/Time_of_flight |
In forensic investigation , the time of occurrence of an event (such as time of death, time of incident) is one of the most important things to determine accurately as soon as possible. Sometimes this can only be estimated. [ 1 ] Some indicators that investigators use are rigor mortis , livor mortis , algor mortis , clouding of the corneas , state of decomposition , presence/absence of purged fluids and level of tissue desiccation . [ 2 ]
Pathologists can estimate a time of death by analysing necrophagous diptera . [ 3 ] The odour from decaying flesh attracts different species as the stages of decomposition progress. [ 4 ]
This forensics -related article is a stub . You can help Wikipedia by expanding it .
This law enforcement –related article is a stub . You can help Wikipedia by expanding it .
This death -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Time_of_occurrence |
In psychology and neuroscience , time perception or chronoception is the subjective experience, or sense, of time , which is measured by someone's own perception of the duration of the indefinite and unfolding of events. [ 1 ] [ 2 ] [ 3 ] The perceived time interval between two successive events is referred to as perceived duration . Though directly experiencing or understanding another person's perception of time is not possible, perception can be objectively studied and inferred through a number of scientific experiments. Some temporal illusions help to expose the underlying neural mechanisms of time perception.
The ancient Greeks recognized the difference between chronological time ( chronos ) and subjective time ( kairos ).
Pioneering work on time perception, emphasizing species-specific differences, was conducted by Karl Ernst von Baer . [ 4 ]
Time perception is typically categorized in three distinct ranges, because different ranges of duration are processed in different areas of the brain: [ 5 ]
There are many theories and computational models for time perception mechanisms in the brain. William J. Friedman (1993) contrasted two theories of the sense of time: [ 6 ] [ 7 ] [ 8 ]
Another hypothesis involves the brain's subconscious tallying of "pulses" during a specific interval, forming a biological stopwatch. This theory proposes that the brain can run multiple biological stopwatches independently depending on the type of tasks being tracked. The source and nature of the pulses is unclear. [ 9 ] They are as yet a metaphor whose correspondence to brain anatomy or physiology is unknown. [ 10 ]
The specious present is the time duration wherein a state of consciousness is experienced as being in the present . [ 11 ] The term was first introduced by the philosopher E. R. Clay in 1882 (E. Robert Kelly), [ 12 ] [ 13 ] and was further developed by William James . [ 13 ] James defined the specious present to be "the prototype of all conceived times... the short duration of which we are immediately and incessantly sensible". In "Scientific Thought" (1930), C. D. Broad further elaborated on the concept of the specious present and considered that the specious present may be considered as the temporal equivalent of a sensory datum. [ 13 ] A version of the concept was used by Edmund Husserl in his works and discussed further by Francisco Varela based on the writings of Husserl, Heidegger , and Merleau-Ponty . [ 14 ]
Although the perception of time is not associated with a specific sensory system, psychologists and neuroscientists suggest that humans do have a system, or several complementary systems, governing the perception of time . [ 15 ] Time perception is handled by a highly distributed system involving the cerebral cortex , cerebellum and basal ganglia . [ 16 ] One particular component, the suprachiasmatic nucleus , is responsible for the circadian (or daily) rhythm , while other cell clusters appear to be capable of shorter ( ultradian ) timekeeping. There is some evidence that very short (millisecond) durations are processed by dedicated neurons in early sensory parts of the brain. [ 17 ] [ 18 ]
Warren Meck devised a physiological model for measuring the passage of time. He found the representation of time to be generated by the oscillatory activity of cells in the upper cortex. The frequency of these cells' activity is detected by cells in the dorsal striatum at the base of the forebrain . His model separated explicit timing and implicit timing. Explicit timing is used in estimating the duration of a stimulus . Implicit timing is used to gauge the amount of time separating one from an impending event that is expected to occur in the near future. These two estimations of time do not involve the same neuroanatomical areas. For example, implicit timing often occurs to achieve a motor task, involving the cerebellum , left parietal cortex , and left premotor cortex . Explicit timing often involves the supplementary motor area and the right prefrontal cortex. [ 10 ]
Two visual stimuli, inside someone's field of view , can be successfully regarded as simultaneous up to five milliseconds. [ 19 ] [ 20 ] [ 21 ]
In the popular essay "Brain Time", David Eagleman explains that different types of sensory information (auditory, tactile, visual, etc.) are processed at different speeds by different neural architectures. The brain must learn how to overcome these speed disparities if it is to create a temporally unified representation of the external world:
if the visual brain wants to get events correct timewise, it may have only one choice: wait for the slowest information to arrive. To accomplish this, it must wait about a tenth of a second. In the early days of television broadcasting, engineers worried about the problem of keeping audio and video signals synchronized. Then they accidentally discovered that they had around a hundred milliseconds of slop: As long as the signals arrived within this window, viewers' brains would automatically resynchronize the signals. He goes on to say, "This brief waiting period allows the visual system to discount the various delays imposed by the early stages; however, it has the disadvantage of pushing perception into the past. There is a distinct survival advantage to operating as close to the present as possible; an animal does not want to live too far in the past. Therefore, the tenth-of-a-second window may be the smallest delay that allows higher areas of the brain to account for the delays created in the first stages of the system while still operating near the border of the present. This window of delay means that awareness is retroactive, incorporating data from a window of time after an event and delivering a delayed interpretation of what happened." [ 22 ]
Experiments have shown that rats can successfully estimate a time interval of approximately 40 seconds, despite having their cortex entirely removed. [ 23 ] This suggests that time estimation may be a low-level process. [ 24 ]
In recent history, ecologists and psychologists have been interested in whether and how time is perceived by non-human animals , as well as which functional purposes are served by the ability to perceive time. Studies have demonstrated that many species of animals, including both vertebrates and invertebrates , have cognitive abilities that allow them to estimate and compare time intervals and durations in a similar way to humans . [ 25 ]
There is empirical evidence that metabolic rate has an impact on animals' ability to perceive time. [ 26 ] In general, it is true within and across taxa that animals of smaller size (such as flies ), which have a fast metabolic rate, experience time more slowly than animals of larger size, which have a slow metabolic rate. [ 27 ] [ 28 ] Researchers suppose that this could be the reason why small-bodied animals are generally better at perceiving time on a small scale, and why they are more agile than larger animals. [ 29 ]
In a lab experiment, goldfish were conditioned to receive a light stimulus followed shortly by an aversive electric shock , with a constant time interval between the two stimuli. Test subjects showed an increase in general activity around the time of the electric shock. This response persisted in further trials in which the light stimulus was kept but the electric shock was removed. [ 30 ] This suggests that goldfish are able to perceive time intervals and to initiate an avoidance response at the time when they expect the distressing stimulus to happen.
In two separate studies, golden shiners and dwarf inangas demonstrated the ability to associate the availability of food sources to specific locations and times of day, called time-place learning. [ 31 ] [ 32 ] In contrast, when tested for time-place learning based on predation risk , inangas were unable to associate spatiotemporal patterns to the presence or absence of predators.
In June 2022, researchers reported in Physical Review Letters that salamanders were demonstrating counter-intuitive responses to the arrow of time in how their eyes perceived different stimuli. [ 33 ]
When presented with the choice between obtaining food at regular intervals (with a fixed delay between feedings) or at stochastic intervals (with a variable delay between feedings), starlings can discriminate between the two types of intervals and consistently prefer getting food at variable intervals. This is true whether the total amount of food is the same for both options or if the total amount of food is unpredictable in the variable option. This suggests that starlings have an inclination for risk-prone behavior. [ 34 ]
Pigeons are able to discriminate between different times of day and show time-place learning . [ 35 ] After training, lab subjects were successfully able to peck specific keys at different times of day (morning or afternoon) in exchange for food, even after their sleep/wake cycle was artificially shifted. This suggests that to discriminate between different times of day, pigeons can use an internal timer (or circadian timer ) that is independent of external cues . [ 36 ] However, a more recent study on time-place learning in pigeons suggests that for a similar task, test subjects will switch to a non-circadian timing mechanism when possible to save energy resources . [ 37 ] Experimental tests revealed that pigeons are also able to discriminate between cues of various durations (on the order of seconds), but that they are less accurate when timing auditory cues than when timing visual cues . [ 38 ]
A study on privately owned dogs revealed that dogs are able to perceive durations ranging from minutes to several hours differently. Dogs reacted with increasing intensity to the return of their owners when they were left alone for longer durations, regardless of the owners' behavior. [ 39 ]
After being trained with food reinforcement , female wild boars are able to correctly estimate time intervals of days by asking for food at the end of each interval, but they are unable to accurately estimate time intervals of minutes with the same training method. [ 40 ]
When trained with positive reinforcement , rats can learn to respond to a signal of a certain duration, but not to signals of shorter or longer durations, which demonstrates that they can discriminate between different durations. [ 41 ] Rats have demonstrated time-place learning, and can also learn to infer correct timing for a specific task by following an order of events, suggesting that they might be able to use an ordinal timing mechanism. [ 42 ] Like pigeons, rats are thought to have the ability to use a circadian timing mechanism for discriminating time of day. [ 43 ]
When returning to the hive with nectar , forager honey bees need to know the current ratio of nectar-collecting to nectar-processing rates in the colony. To do so, they estimate the time it takes them to find a food-storer bee, which will unload the forage and store it. The longer it takes them to find one, the busier the food-storer bees are, and therefore the higher the nectar-collecting rate of the colony. [ 44 ] Forager bees also assess the quality of nectar by comparing the length of time it takes to unload the forage : a longer unloading time indicates higher quality nectar. They compare their own unloading time to the unloading time of other foragers present in the hive, and adjust their recruiting behavior accordingly. For instance, honey bees reduce the duration of their waggle dance if they judge their own yield to be inferior. [ 45 ] Scientists have demonstrated that anesthesia disrupts the circadian clock and impairs the time perception of honey bees, as observed in humans. [ 46 ] Experiments revealed that a six-hour-long general anesthesia significantly delayed the start of the foraging behaviour of honeybees if induced during daytime, but not if induced during nighttime. [ 47 ]
Bumble bees can be successfully trained to respond to a stimulus after a certain time interval has elapsed (usually several seconds after the start signal). Studies have shown that they can also learn to simultaneously time multiple interval durations. [ 48 ]
In a single study, colonies from three species of ants from the genus Myrmica were trained to associate feeding sessions with different times. The trainings lasted several days, where each day the feeding time was delayed by 20 minutes compared to the previous day. In all three species, at the end of the training, most individuals were present at the feeding spot at the correct expected times, suggesting that ants are able to estimate the time running, keep in memory the expected feeding time and to act anticipatively. [ 49 ]
A temporal illusion is a distortion in the perception of time. For example:
Some main types of temporal illusions are as follows:
The Kappa effect or perceptual time dilation [ 55 ] is a form of temporal illusion verifiable by experiment. [ 56 ] The temporal duration between a sequence of consecutive stimuli is thought to be relatively longer or shorter than its actual elapsed time, due to the spatial/auditory/tactile separation between each consecutive stimuli. The kappa effect can be displayed when considering a journey made in two parts that each take an equal amount of time. When mentally comparing these two sub-journeys, the part that covers more distance may appear to take longer than the part covering less distance, even though they take an equal amount of time.
The perception of space and time undergoes distortions during rapid saccadic eye movements. [ 57 ] Chronostasis is a type of temporal illusion in which the first impression following the introduction of a new event or task demand to the brain appears to be extended in time. [ 58 ] For example, chronostasis temporarily occurs when fixating on a target stimulus, immediately following a saccade (e.g., quick eye movement ). This elicits an overestimation in the temporal duration for which that target stimulus (i.e., postsaccadic stimulus) was perceived. This effect can extend apparent durations by up to 500 ms and is consistent with the idea that the visual system models events prior to perception. [ 59 ] The most well-known version of this illusion is known as the stopped-clock illusion , wherein a subject's first impression of the second-hand movement of an analog clock, subsequent to one's directed attention (i.e., saccade) to the clock, is the perception of a slower-than-normal second-hand movement rate (the second-hand of the clock may seemingly temporarily freeze in place after initially looking at it). [ 60 ] [ 61 ] [ 62 ] [ 63 ]
The occurrence of chronostasis extends beyond the visual domain into the auditory and tactile domains. [ 64 ] In the auditory domain, chronostasis and duration overestimation occur when observing auditory stimuli. One common example is a frequent occurrence when making telephone calls. If, while listening to the phone's dial tone, research subjects move the phone from one ear to the other, the length of time between rings appears longer. [ 65 ] In the tactile domain, chronostasis has persisted in research subjects as they reach for and grasp objects. After grasping a new object, subjects overestimate the time in which their hand has been in contact with this object. [ 61 ]
In an experiment, participants were told to stare at an "x" symbol on a computer screen whereby a moving blue doughnut-like ring repeatedly circled the fixed "x" point. [ 66 ] [ 67 ] [ 68 ] Occasionally, the ring would display a white flash for a split second that physically overlapped the ring's interior. However, when asked what was perceived, participants responded that they saw the white flash lagging behind the center of the moving ring. In other words, despite the reality that the two retinal images were actually spatially aligned, the flashed object was usually observed to trail a continuously moving object in space — a phenomenon referred to as the flash-lag effect .
The first proposed explanation, called the "motion extrapolation" hypothesis, is that the visual system extrapolates the position of moving objects but not flashing objects when accounting for neural delays (i.e., the lag time between the retinal image and the observer's perception of the flashing object). The second proposed explanation by David Eagleman and Sejnowski, called the "latency difference" hypothesis, is that the visual system processes moving objects at a faster rate than flashed objects. In the attempt to disprove the first hypothesis, David Eagleman conducted an experiment in which the moving ring suddenly reverses direction to spin in the other way as the flashed object briefly appears. If the first hypothesis were correct, we would expect that, immediately following reversal, the moving object would be observed as lagging behind the flashed object. However, the experiment revealed the opposite — immediately following reversal, the flashed object was observed as lagging behind the moving object. This experimental result supports the "latency difference" hypothesis. A recent study tries to reconcile these different approaches by treating perception as an inference mechanism aiming at describing what is happening at the present time. [ 69 ]
Humans typically overestimate the perceived duration of the initial and final event in a stream of identical events. [ 70 ] This oddball effect may serve an evolutionarily adapted "alerting" function and is consistent with reports of time slowing down in threatening situations. The effect seems to be strongest for images that are expanding in size on the retina, i.e. , that are "looming" or approaching the viewer, [ 71 ] [ 72 ] [ 73 ] and the effect can be eradicated for oddballs that are contracting or perceived to be receding from the viewer. [ 72 ] The effect is also reduced [ 71 ] or reversed [ 73 ] with a static oddball presented among a stream of expanding stimuli.
Initial studies suggested that this oddball-induced "subjective time dilation" expanded the perceived duration of oddball stimuli by 30–50% [ 71 ] but subsequent research has reported more modest expansion of around 10% [ 73 ] [ 74 ] [ 75 ] [ 76 ] or less. [ 77 ] The direction of the effect, whether the viewer perceives an increase or a decrease in duration, also seems to be dependent upon the stimulus used. [ 77 ]
Numerous experimental findings suggest that temporal order judgments of actions preceding effects can be reversed under special circumstances. Experiments have shown that sensory simultaneity judgments can be manipulated by repeated exposure to non-simultaneous stimuli. In an experiment conducted by David Eagleman , a temporal order judgment reversal was induced in subjects by exposing them to delayed motor consequences. In the experiment, subjects played various forms of video games. Unknown to the subjects, the experimenters introduced a fixed delay between the mouse movements and the subsequent sensory feedback. For example, a subject may not see a movement register on the screen until 150 milliseconds after they had moved the mouse. Participants playing the game quickly adapted to the delay and felt as though there was less delay between their mouse movement and the sensory feedback. Shortly after the experimenters removed the delay, the subjects commonly felt as though the effect on the screen happened just before they commanded it. This work addresses how the perceived timing of effects is modulated by expectations, and the extent to which such predictions are quickly modifiable. [ 78 ]
In an experiment conducted by Haggard and colleagues in 2002, participants pressed a button that triggered a flash of light at a distance, after a slight delay of 100 milliseconds. [ 79 ] By repeatedly engaging in this act, participants had adapted to the delay (i.e., they experienced a gradual shortening in the perceived time interval between pressing the button and seeing the flash of light). The experimenters then showed the flash of light instantly after the button was pressed. In response, subjects often thought that the flash (the effect) had occurred before the button was pressed (the cause). Additionally, when the experimenters slightly reduced the delay, and shortened the spatial distance between the button and the flash of light, participants had often claimed again to have experienced the effect before the cause.
Several experiments also suggest that temporal order judgment of a pair of tactile stimuli delivered in rapid succession, one to each hand, is noticeably impaired (i.e., misreported) by crossing the hands over the midline. However, congenitally blind subjects showed no trace of temporal order judgment reversal after crossing the arms. These results suggest that tactile signals taken in by the congenitally blind are ordered in time without being referred to a visuospatial representation. Unlike the congenitally blind subjects, the temporal order judgments of the late-onset blind subjects were impaired when crossing the arms to a similar extent as non-blind subjects. These results suggest that the associations between tactile signals and visuospatial representation is maintained once it is accomplished during infancy. Some research studies have also found that the subjects showed reduced deficit in tactile temporal order judgments when the arms were crossed behind their back than when they were crossed in front. [ 80 ] [ 81 ] [ 82 ]
Tachypsychia is a neurological condition that alters the perception of time, usually induced by physical exertion , drug use , or a traumatic event . For someone affected by tachypsychia, time perceived by the individual either lengthens, making events appear to slow down, [ 83 ] or possibly the reverse, with objects appearing as moving in a speeding blur. [ 84 ] [ 85 ]
Research has suggested the feeling of awe has the ability to expand one's perceptions of time availability. Awe can be characterized as an experience of immense perceptual vastness that coincides with an increase in focus. Consequently, it is conceivable that one's temporal perception would slow down when experiencing awe. [ 86 ] The perception of time can differ as people choose between savoring moments and deferring gratification. [ 87 ]
Possibly related to the oddball effect , research suggests that time seems to slow down for a person during dangerous events (such as a car accident, a robbery, or when a person perceives a potential predator or mate ), or when a person skydives or bungee jumps, where they are capable of complex thoughts in what would normally be the blink of an eye (See Fight-or-flight response ). [ 88 ] This reported slowing in temporal perception may have been evolutionarily advantageous because it may have enhanced one's ability to intelligibly make quick decisions in moments that were of critical importance to our survival. [ 89 ] However, even though observers commonly report that time seems to have moved in slow motion during these events, it is unclear whether this is a function of increased time resolution during the event, or instead an illusion created by the remembering of an emotionally salient event. [ 90 ]
A strong time dilation effect has been reported for perception of objects that were looming, but not of those retreating, from the viewer, suggesting that the expanding discs — which mimic an approaching object — elicit self-referential processes which act to signal the presence of a possible danger. [ 91 ] Anxious people, or those in great fear , experience greater "time dilation" in response to the same threat stimuli due to higher levels of epinephrine , which increases brain activity (an adrenaline rush). [ 92 ] In such circumstances, an illusion of time dilation could assist an effective escape. [ 93 ] [ 94 ] When exposed to a threat, three-year-old children were observed to exhibit a similar tendency to overestimate elapsed time. [ 10 ] [ 95 ]
Research suggests that the effect appears only at the point of retrospective assessment, rather than occurring simultaneously with events as they happened. [ 96 ] Perceptual abilities were tested during a frightening experience — a free fall — by measuring people's sensitivity to flickering stimuli. The results showed that the subjects' temporal resolution was not improved as the frightening event was occurring. Events appear to have taken longer only in retrospect, possibly because memories were being more densely packed during the frightening situation. [ 96 ]
Other researchers [ 97 ] [ 98 ] suggest that additional variables could lead to a different state of consciousness in which altered time perception does occur during an event. Research does demonstrate that visual sensory processing [ 99 ] increases in scenarios involving action preparation. Participants demonstrated a higher detection rate of rapidly presented symbols when preparing to move, as compared to a control without movement.
People shown extracts from films known to induce fear often overestimated the elapsed time of a subsequently presented visual stimulus, whereas people shown emotionally neutral clips (weather forecasts and stock market updates) or those known to evoke feelings of sadness showed no difference. It is argued that fear prompts a state of arousal in the amygdala , which increases the rate of a hypothesized "internal clock". This could be the result of an evolved defensive mechanism triggered by a threatening situation. [ 100 ] Individuals experiencing sudden or surprising events, real or imagined (e.g., witnessing a crime, or believing one is seeing a ghost), may overestimate the duration of the event. [ 87 ]
Psychologists have found that the subjective perception of the passing of time tends to speed up with increasing age in humans. This often causes people to increasingly underestimate a given interval of time as they age. This fact can likely be attributed to a variety of age-related changes in the aging brain , such as the lowering in dopaminergic levels with older age; however, the details are still being debated. [ 101 ] [ 102 ] [ 103 ]
Very young children will first experience the passing of time when they can subjectively perceive and reflect on the unfolding of a collection of events. A child's awareness of time develops during childhood, when the child's attention and short-term memory capacities form — this developmental process is thought to be dependent on the slow maturation of the prefrontal cortex and hippocampus . [ 10 ] [ 104 ]
The common explanation is that most external and internal experiences are new for young children but repetitive for adults. Children have to be extremely engaged (i.e. dedicate many neural resources or significant brain power) in the present moment because they must constantly reconfigure their mental models of the world to assimilate it and manage behaviour properly. [ citation needed ]
Adults, however, may rarely need to step outside mental habits and external routines. When an adult frequently experiences the same stimuli, such stimuli may seem "invisible" as a result of having already been sufficiently mapped by the brain. This phenomenon is known as neural adaptation . According to this picture, the rate of new stimuli and new experiences may decrease with age as does the number of new memories created to record them. If one then assumes that the perceived duration of a given interval of time is linked to how many new memories are formed during it, the aging adult may underestimate long stretches of time because, in their recollection, these now contain fewer memory-creating events. [ 105 ] Consequently, the subjective perception is often that time passes by at a faster rate with age.
Let S be subjective time, R be real time, and define both to be zero at birth.
One model proposes that the passage of subjective time relative to actual time is inversely proportional to real time: [ 106 ]
When solved, S 2 − S 1 = K ( log R 2 − log R 1 ) = K log ( R 2 / R 1 ) {\displaystyle S_{2}-S_{1}=K(\log {R_{2}}-\log {R_{1}})=K\log {\left({R_{2}}/{R_{1}}\right)}} .
One day would be approximately 1/4,000 of the life of an 11-year-old, but approximately 1/20,000 of the life of a 55-year-old. This helps to explain why a random, ordinary day may therefore appear longer for a young child than an adult. So a year would be experienced by a 55-year-old as passing approximately five times more quickly than a year experienced by an 11-year-old. If long-term time perception is based solely on the proportionality of a person's age, then the following four periods in life would appear to be quantitatively equal: ages 5–10 (1x), ages 10–20 (2x), ages 20–40 (4x), age 40–80 (8x), as the end age is twice the start age. However, this does not work for ages 0–10, which corresponds to ages 10–∞. [ 106 ] [ 107 ]
Lemlich posits that the passage of subjective time relative to actual time is inversely proportional to total subjective time, rather than the total real time: [ 106 ]
When mathematically solved,
It avoids the issue of infinite subjective time passing from real age 0 to 1 year, as the asymptote can be integrated in an improper integral . Using the boundary conditions S = 0 when R = 0 and K > 0,
This means that time appears to pass in proportion to the square root of the perceiver's real age, rather than directly proportional. Under this model, a 55-year-old would subjectively experience time passing 2 + 1 / 4 times more quickly than an 11-year-old, rather than five times under the previous. This means the following periods in life would appear to be quantitatively equal: ages 0–1, 1–4, 4–9, 9–16, 16–25, 25–36, 36–49, 49–64, 64–81, 81–100, 100–121. [ 106 ] [ 108 ]
In a study, participants consistently provided answers that fit this model when asked about time perception at 1/4 of their age, but were less consistent for 1/2 of their age. Their answers suggest that this model is more accurate than the previous one. [ 106 ]
A consequence of this model is that the fraction of subjective life remaining is always less than the fraction of real life remaining, but it is always more than one half of real life remaining. [ 106 ] This can be seen for 0 < S < S f {\displaystyle 0<S<S_{f}} and 0 < R < R f {\displaystyle 0<R<R_{f}} :
Stimulants such as thyroxine, caffeine, and amphetamines lead to overestimation of time intervals by both humans and rats, while depressants and anesthetics such as barbiturates and nitrous oxide can have the opposite effect and lead to underestimation of time intervals. [ 109 ] The level of activity in the brain of neurotransmitters such as dopamine and norepinephrine may be the reason for this. [ 110 ] [ 111 ] [ 112 ] A research on stimulant-dependent individuals (SDI) showed several abnormal time processing characteristics including larger time differences for effective duration discrimination, and overestimating the duration of a relatively long time interval. Altered time processing and perception in SDI could explain the difficulty SDI have with delaying gratification. [ 113 ] Another research studied the dose-dependent effect in methamphetamine dependents with short term abstinence and its effects on time perception. Results shows that motor timing but not perceptual timing, was altered in meth dependents, which persisted for at least three months of abstinence. Dose-dependent effects on time perception were only observed when short-term abstinent meth abusers processed long time intervals. The study concluded that time perception alteration in meth dependents is task specific and dose dependent. [ 114 ]
The effect of cannabis on time perception has been studied with inconclusive results mainly due to methodological variations and the paucity of research. Even though 70% of time estimation studies report over-estimation, the findings of time production and time reproduction studies remain inconclusive. [ 115 ] [ 116 ] Studies show consistently throughout the literature that most cannabis users self-report the experience of a slowed perception of time. In the laboratory, researchers have confirmed the effect of cannabis on the perception of time in both humans and animals. [ 117 ] Using PET scans it was observed that participants who showed a decrease in cerebellar blood flow (CBF) also had a significant alteration in time sense. The relationship between decreased CBF and impaired time sense is of interest as the cerebellum is linked to an internal timing system. [ 118 ] [ 119 ]
The chemical clock hypothesis implies a causal link between body temperature and the perception of time. [ 120 ]
Past work show that increasing body temperature tends to make individuals experience a dilated perception of time and they perceive durations as shorter than they actually were, ultimately leading them to underestimate time durations. While decreasing body temperature has the opposite effect – causing participants to experience a condensed perception of time leading them to over-estimate time duration – observations of the latter type were rare. [ 121 ] Research establishes a parametric effect of body temperature on time perception with higher temperatures generally producing faster subjective time and vice versa. This is especially seen to be true under changes in arousal levels and stressful events. [ 122 ]
Time perception can be used as a tool in social networks to define the subjective experiences of each node within a system. This method can be used to study characters' psychology in dramas, both film and literature , analyzed by social networks. Each character's subjective time may be calculated, with methods as simple as word counting, and compared to the real time of the story to shed light on their internal states. [ 123 ] [ 124 ] | https://en.wikipedia.org/wiki/Time_perception |
Time resolved crystallography utilizes X-ray crystallography imaging to visualize reactions in four dimensions (x, y, z and time). This enables the studies of dynamical changes that occur in for example enzymes during their catalysis. The time dimension is incorporated by triggering the reaction of interest in the crystal prior to X-ray exposure, and then collecting the diffraction patterns at different time delays. In order to study these dynamical properties of macromolecules three criteria must be met; [ 1 ]
This has led to the development of several techniques that can be divided into two groups, the pump-probe method and diffusion-trapping methods.
In the pump-probe method the reaction is first triggered (pump) by photolysis (most often laser light) and then a diffraction pattern is collected by an X-ray pulse (probe) at a specific time delay. This makes it possible to obtain many images at different time delays after reaction triggering, and thereby building up a chronological series of images describing the events during reaction.
To obtain a reasonable signal to noise ratio this pump-probe cycle has to be performed many times for each spatial rotation of the crystal, and many times for the same time delay. Therefore, the reaction that one wishes to study with pump-probe must be able to relax back to its original conformation after triggering, enabling many measurements on the same sample.
The time resolution of the observed phenomena is dictated by the time width of the probing pulse ( full width at half maximum ). All processes that happen on a faster time scale than that are going to be averaged out by the convolution of the probe pulse intensity in time with the intensity of the actual x-ray reflectivity of the sample.
Diffusion-trapping methods utilizes diffusion techniques to get the substrates into the crystal and thereafter different trapping techniques are applied to get the intermediate of interest to accumulate in the crystal prior to collection of the diffraction pattern. These trapping methods could involve changes in pH , [ 2 ] use of inhibitor [ 3 ] or lowering the temperature in order to slow down the turnover rate or maybe even stop the reaction completely at a specific step. Just starting the reaction and then flash-freeze it, [ 4 ] thereby quenching it at a specific time step, is also a possible method. One drawback with diffusion-trapping methods is that they can only be used to study intermediates that can be trapped, thereby limiting the time resolution one can obtain through the methods as compared to the pump-probe method. | https://en.wikipedia.org/wiki/Time_resolved_crystallography |
Time resolved microwave conductivity ( TRMC ) is an experimental technique used to evaluate the electronic properties of semiconductors . Specifically, it is used to evaluate a proxy for charge carrier mobility and a representative carrier lifetime from light-induced changes in conductance . The technique works by photo-generating electrons and holes in a semiconductor, allowing these charge carriers to move under a microwave field, and detecting the resulting changes in the electric field. TRMC systems cannot be purchased as a single unit, and are generally "home-built" from individual components. One advantage of TRMC over alternative techniques is that it does not require direct physical contact to the material.
While semiconductors have been studied using microwave radiation since the 1950s, [ 1 ] it was not until the late 1970s and early 1980s that John Warman at the Delft University of Technology exploited microwaves for time-resolved measurements of photoconductivity. The first reports used electrons [ 2 ] then photons [ 3 ] to generate charges in fluids. The technique was later refined to study semiconductors by Kunst and Beck at the Hahn Meitner Institute in Berlin. [ 4 ]
Delft remains a significant center for TRMC, [ 5 ] however the technique is now used at a number of institutions around the world, notably the National Renewable Energy Laboratory [ 6 ] and Kyoto University . [ 7 ]
The experiment relies upon the interaction between optically-generated charge carriers and microwave frequency electromagnetic radiation . The most common approach is to use a resonant cavity . [ 8 ] An oscillating voltage is produced using a signal generator such as a voltage controlled oscillator or a Gunn diode . The oscillating current is incident on an antenna , resulting in the emission of microwaves of the same frequency. These microwaves are then directed into a resonant cavity. Because they can transmit microwaves with lower loss than cables, [ 9 ] metallic waveguides are often used to form the circuit. [ 10 ] With the appropriate cavity dimensions and microwave frequency, a standing wave can be formed with 1 full wavelength filing the cavity.
The sample to be studied is placed at a maximum of the electric field component of the standing wave. Because metals act as cavity walls, [ 9 ] the sample needs to have a relatively low free carrier concentration in the dark to be measurable. TRMC is hence best suited to the study of intrinsic or lightly doped semiconductors. Electrons and hole are generated by illuminating the sample with above band gap optical photons. Optical access to the sample is provided by a cavity wall which is both electrically conducting and optically transparent; for example a metallic grating or a transparent conducting oxide .
The photo-generated charge carriers move under the influence of the electric field component of the standing wave, resulting in a change in intensity of microwaves that leave the cavity. The intensity of microwaves out of the cavity is measured as a function of time using an appropriate detector and an oscilloscope . Knowledge of the properties of the cavity can be used [ 8 ] to evaluate photoconductance from changes in microwave intensity.
The reflection coefficient is determined by the coupling between cavity and waveguide. [ 11 ] When the frequency of microwave is resonant frequency, the reflectance , R 0 {\displaystyle R_{0}} , of the cavity is expressed as follows:
Here Q 0 {\displaystyle Q_{0}} is the quality factor of the cavity including the sample, Q e x {\displaystyle Q_{ex}} is the quality factor of the external coupling, which is generally adjusted by iris. The total loaded quality factor of the cavity, Q {\displaystyle Q} , is defined as follows:
The photo-generated charge carriers reduce the quality of the cavity, Q 0 {\displaystyle Q_{0}} . When the change of quality factor is very small, the change of reflected microwave power is approximately proportional to the change of dissipation factor of the cavity. Furthermore, dissipation factor of the cavity is mainly determined by the conductivity of the inside space including the sample. Consequently, the change in the conductivity, Δ σ {\displaystyle \Delta \sigma } , of the cavity contents is proportional to relative changes in microwave intensity: [ 2 ]
Here P {\displaystyle P} is the background (unperturbed) microwave power measured coming out of the cavity and Δ P {\displaystyle \Delta P} is the change in microwave power as a result of the change in cavity conductance. A {\displaystyle A} is the sensitivity factor determined by the quality of the cavity, F {\displaystyle F} is the geometry factor of the sample. A {\displaystyle A} can be derived by Taylor expanding of the reflectance equation:
Here f 0 {\displaystyle f_{0}} is the resonant frequency of the cavity in Hertz unit, ϵ 0 {\displaystyle \epsilon _{0}} is the vacuum permittivity , ϵ r {\displaystyle \epsilon _{r}} is the relative permittivity of the medium inside the cavity. The relative permittivity should be considered only when the cavity is filled by solvent. When the sample is inserted into dry cavity, only vacuum permittivity should be used because most of the inside space is filled by air. The sign of ± {\displaystyle \pm } depends on whether the cavity is in the under-coupled (lower) or over-coupled (upper) regime. So, the negative signal is detected in over-coupled regime, Q 0 > Q e x {\displaystyle Q_{0}>Q_{ex}} , whereas the positive signal is detected in under-coupled regime, Q 0 < Q e x {\displaystyle Q_{0}<Q_{ex}} . No signal can be detected at critical coupling condition, Q 0 = Q e x {\displaystyle Q_{0}=Q_{ex}}
F {\displaystyle F} is determined by the overlap between the electric field and the sample position: [ 10 ]
Here E {\displaystyle E} is the electric field in the cavity. c a v i t y {\displaystyle cavity} and c h a r g e {\displaystyle charge} denote the total inside volume of the cavity and the volume of photo-generated carriers, respectively. If the thickness of the sample is sufficiently thin (below several μm), the electric field to photo-generated carriers would be uniform. In this condition, F {\displaystyle F} is approximately proportional to the thickness of the sample. Above conductivity equation can be expressed as follows:
Here e {\displaystyle e} is the elementary charge , T {\displaystyle T} is the transmittance of the sample at the excitation wavelength, I 0 {\displaystyle I_{0}} is the incident laser fluence, ϕ {\displaystyle \phi } is the quantum yield of photo-carrier generation per absorbed photon, Σ μ {\displaystyle \Sigma \mu } is the sum of the electron and hole mobility, d {\displaystyle d} is the thickness of the sample. Because F {\displaystyle F} is linearly proportional to the thickness, only the fractional absorbance of the semiconductor (between 0 and 1) should be additionally measured to determine the TRMC figure of merit ϕ Σ μ {\displaystyle \phi \Sigma \mu } (e.g. using ultraviolet–visible spectroscopy ):
Knowledge of charge carrier mobility in semiconductors is important for understanding the electronic and materials properties of a system. It is also valuable in device design and optimization. This is particularly true for thin film solar cells and thin film transistors , where charge extraction [ 12 ] and amplification, [ 13 ] respectively, are highly dependent upon mobility. TRMC has been used to study electron and hole dynamics in hydrogenated amorphous silicon , [ 14 ] organic semiconductors , [ 15 ] metal halide perovskites , [ 16 ] metal oxides , [ 17 ] dye sensitized systems , [ 18 ] quantum dots , [ 19 ] carbon nanotubes , [ 20 ] chalcogenides , [ 21 ] metal organic frameworks , [ 22 ] and the interfaces between various systems. [ 23 ]
Because charges are normally generated using a green (~2.3 eV) or ultraviolet (~3 eV) laser, this restricts materials to those with comparable or smaller bandgaps. The technique is hence well suited to the study of solar absorbers , but not to wide bandgap semiconductors such as metal oxides .
While it is very similar, and has the same dimensions, the parameter ϕ Σ μ {\displaystyle \phi \Sigma \mu } is not the same a charge carrier mobility. ϕ Σ μ {\displaystyle \phi \Sigma \mu } contains contributions from both holes and electrons, which cannot conventionally be resolved using TRMC. This is in contrast to Hall Measurements or transistor measurements, where hole and electron mobility can easily be separated. Additionally, the mobility is not directly extracted from the measurements, it is measured multiplied by the carrier generation yield, ϕ {\displaystyle \phi } . The carrier generation yield is the number of electron hole pairs generated per absorbed photon. Because some absorbed photons can lead to bound neutral excitons , not all absorbed photons will lead to detectable free carriers. This can make interpretation of ϕ Σ μ {\displaystyle \phi \Sigma \mu } more complicated than mobility. However, generally both mobility and ϕ {\displaystyle \phi } are parameters which one wishes to maximize when developing solar cells.
As a time-resolved technique, TRMC also provides information on the timescale of carrier recombination in solar cells. Unlike time resolved photoluminescence measurements, TRMC is not sensitive to the lifetime of excitons . | https://en.wikipedia.org/wiki/Time_resolved_microwave_conductivity |
In mathematics and physics , time-reversibility is the property of a process whose governing rules remain unchanged when the direction of its sequence of actions is reversed.
A deterministic process is time-reversible if the time-reversed process satisfies the same dynamic equations as the original process; in other words, the equations are invariant or symmetrical under a change in the sign of time. A stochastic process is reversible if the statistical properties of the process are the same as the statistical properties for time-reversed data from the same process.
In mathematics , a dynamical system is time-reversible if the forward evolution is one-to-one , so that for every state there exists a transformation (an involution ) π which gives a one-to-one mapping between the time-reversed evolution of any one state and the forward-time evolution of another corresponding state, given by the operator equation:
Any time-independent structures (e.g. critical points or attractors ) which the dynamics give rise to must therefore either be self-symmetrical or have symmetrical images under the involution π.
In physics , the laws of motion of classical mechanics exhibit time reversibility, as long as the operator π reverses the conjugate momenta of all the particles of the system, i.e. p → − p {\displaystyle \mathbf {p} \rightarrow \mathbf {-p} } ( T-symmetry ).
In quantum mechanical systems, however, the weak nuclear force is not invariant under T-symmetry alone; if weak interactions are present, reversible dynamics are still possible, but only if the operator π also reverses the signs of all the charges and the parity of the spatial co-ordinates ( C-symmetry and P-symmetry ). This reversibility of several linked properties is known as CPT symmetry .
Thermodynamic processes can be reversible or irreversible , depending on the change in entropy during the process. Note, however, that the fundamental laws that underlie the thermodynamic processes are all time-reversible (classical laws of motion and laws of electrodynamics), [ 1 ] which means that on the microscopic level, if one were to keep track of all the particles and all the degrees of freedom, the many-body system processes are all reversible; However, such analysis is beyond the capability of any human being (or artificial intelligence ), and the macroscopic properties (like entropy and temperature) of many-body system are only defined from the statistics of the ensembles . When we talk about such macroscopic properties in thermodynamics, in certain cases, we can see irreversibility in the time evolution of these quantities on a statistical level. Indeed, the second law of thermodynamics predicates that the entropy of the entire universe must not decrease, not because the probability of that is zero, but because it is so unlikely that it is a statistical impossibility for all practical considerations (see Crooks fluctuation theorem ).
A stochastic process is time-reversible if the joint probabilities of the forward and reverse state sequences are the same for all sets of time increments { τ s }, for s = 1, ..., k for any k : [ 2 ]
A univariate stationary Gaussian process is time-reversible. Markov processes can only be reversible if their stationary distributions have the property of detailed balance :
Kolmogorov's criterion defines the condition for a Markov chain or continuous-time Markov chain to be time-reversible.
Time reversal of numerous classes of stochastic processes has been studied, including Lévy processes , [ 3 ] stochastic networks ( Kelly's lemma ), [ 4 ] birth and death processes , [ 5 ] Markov chains , [ 6 ] and piecewise deterministic Markov processes . [ 7 ]
Time reversal method works based on the linear reciprocity of the wave equation , which states that the time reversed solution of a wave equation is also a solution to the wave equation since standard wave equations only contain even derivatives of the unknown variables. [ 8 ] Thus, the wave equation is symmetrical under time reversal, so the time reversal of any valid solution is also a solution. This means that a wave's path through space is valid when travelled in either direction.
Time reversal signal processing [ 9 ] is a process in which this property is used to reverse a received signal; this signal is then re-emitted and a temporal compression occurs, resulting in a reversal of the initial excitation waveform being played at the initial source. | https://en.wikipedia.org/wiki/Time_reversibility |
Time smearing or time-average smearing is the degradation of the reconstructed image of a celestial body observed by a ground-based interferometer that occurs because of the duration of the observation. Unlike single telescopes or cameras that can compensate for the Earth's rotation in real time using a dedicated mount , the different telescopes of the interferometer are at fixed positions on the Earth. As a result, maps obtained with interferometers feature elongated orthoradial features similar to those of night sky photographs taken with a fixed tripod , unless they use short enough integration times.
The smearing is a problem for long integration times or very separated telescopes. Mostly an issue in radioastronomy , it severely limits the usable field of view of observations in very long baseline interferometry .
This astronomy -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Time_smearing |
Time stretch microscopy , also known as serial time-encoded amplified imaging/microscopy or stretched time-encoded amplified imaging/microscopy' ( STEAM ), is a fast real-time optical imaging method that provides MHz frame rate, ~100 ps shutter speed, and ~30 dB (× 1000) optical image gain. Based on the photonic time stretch technique, STEAM holds world records for shutter speed and frame rate in continuous real-time imaging. STEAM employs the Photonic Time Stretch with internal Raman amplification to realize optical image amplification to circumvent the fundamental trade-off between sensitivity and speed that affects virtually all optical imaging and sensing systems. This method uses a single-pixel photodetector , eliminating the need for the detector array and readout time limitations. Avoiding this problem and featuring the optical image amplification for improvement in sensitivity at high image acquisition rates, STEAM's shutter speed is at least 1000 times faster than the best CCD [ 1 ] and CMOS [ 2 ] cameras. Its frame rate is 1000 times faster than the fastest CCD cameras and 10–100 times faster than the fastest CMOS cameras .
Time stretch microscopy and its application to microfluidics for classification of biological cells was invented at UCLA. [ 3 ] [ 4 ] [ 5 ] [ 6 ] [ 7 ] [ 8 ] [ 9 ] [ 10 ] It combines the concept of spectrally encoded illumination with the photonic time stretch, an ultrafast real-time data acquisition technology developed earlier in the same lab to create a femtosecond real-time single-shot digitizer , [ 11 ] and a single shot stimulated Raman spectrometer. [ 12 ] The first demonstration was a one-dimensional version [ 3 ] and later a two-dimensional version. [ 4 ] Later, a fast imaging vibrometer was created by extending the system to an interferometric configuration. [ 13 ] The technology was then extended to time stretch quantitatve phase imaging ( TS-QPI ) for label free classification of blood cells and combined with artificial intelligence (AI) for classification of cancer cells in blood with over 96% accuracy. [ 14 ] The system measured 16 biophysical parameters of cells simultaneously in a single shot and performed hyper-dimensional classification using a Deep Neural Network (DNN). The results were compared with other machine learning classification algorithms such as logistic regression and naive Bayes with the highest accuracy obtained with deep learning.
This was later extended "Deep Cytometry" [ 15 ] in which the computationally intensive tasks of image processing and feature extraction before deep learning were avoided by directly feeding the time-stretch line scans, each representing a laser pulse into a deep convolutional neural network. This direct classification of raw time-stretched data reduced the inference time by orders of magnitude to 700 micro-seconds on a GPU accelerated processor. At a flow speed of 1 m/s the cells only move less than a millimeter. Therefore, this ultrashort inference time is fast enough for cell sorting.
Fast real-time optical imaging technology is indispensable for studying dynamical events such as shockwaves , laser fusion , chemical dynamics in living cells, neural activity, laser surgery , microfluidics, and MEMS . The usual techniques of conventional CCD and CMOS cameras are inadequate for capturing fast dynamical processes with high sensitivity and speed; there are technological limitations—it takes time to read out the data from the sensor array and there's a fundamental trade-off between sensitivity and speed: at high frame rates, fewer photons are collected during each frame, a problem that affects nearly all optical imaging systems.
The streak camera , used for diagnostics in laser fusion, plasma radiation, and combustion, operates in burst mode only (providing just several frames) and requires synchronization of the camera with the event to be captured. It is therefore unable to capture random or transient events in biological systems. On the other hand, Stroboscopes have a complementary role: they can capture the dynamics of fast events—but only if the event is repetitive, such as rotations, vibrations, and oscillations. They are unable to capture non-repetitive random events that occur only once or do not occur at regular intervals.
The basic principle involves two steps both performed optically. In the first step, the spectrum of a broadband optical pulse is converted by a spatial disperser into a rainbow that illuminates the target. Here the rainbow pulse consists of many subpulses of different colors (frequencies), indicating that the different frequency components (colors) of the rainbow pulse are incident onto different spatial coordinates on the object. Therefore, the spatial information (image) of the object is encoded into the spectrum of the resultant reflected or transmitted rainbow pulse. The image-encoded reflected or transmitted rainbow pulse returns to the same spatial disperser or enters another spatial disperser to combine the colors of the rainbow back into a single pulse. Here STEAM's shutter speed or exposure time corresponds to the temporal width of the rainbow pulse. In the second step, the spectrum is mapped into a serial temporal signal that is stretched in time using dispersive Fourier transform to slow it down such that it can be digitized in real-time. The time stretch happens inside a dispersive fibre that is pumped to create internal Raman amplification. Here the image is optically amplified by stimulated Raman scattering to overcome the thermal noise level of the detector. The amplified time-stretched serial image stream is detected by a single-pixel photodetector and the image is reconstructed in the digital domain. Subsequent pulses capture repetitive frames hence the laser pulse repetition rate corresponds to the frame rate of STEAM. The second is known as the time stretch analogue-to-digital converter , otherwise known as the time stretch recording scope (TiSER).
The simultaneous stretching and amplification is also known as amplified time stretch dispersive Fourier transformation (TS-DFT). [ 16 ] [ 17 ] The amplified time stretch technology was developed earlier to demonstrate analog-to-digital conversion with femtosecond real-time sampling rate [ 11 ] and to demonstrate stimulated Raman spectroscopy in single shot at millions of frames per second. [ 12 ] Amplified time stretch is a process in which the spectrum of an optical pulse is mapped by large group-velocity dispersion into a slowed-down temporal waveform and amplified simultaneously by the process of stimulated Raman scattering . Consequently, the optical spectrum can be captured with a single-pixel photodetector and digitized in real-time. Pulses are repeated for repetitive measurements of the optical spectrum. Amplified time stretch DFT consists of a dispersive fibre pumped by lasers and wavelength-division multiplexers that couple the lasers into and out of the dispersive fibre. Amplified dispersive Fourier transformation was originally developed to enable ultra wideband analog to digital converters and has also been used for high throughput real-time spectroscopy . The resolution of STEAM imager is mainly determined by diffraction limit, the sampling rate of the back-end digitizer, and spatial dispersers. [ 18 ]
Time-stretch quantitative phase imaging ( TS-QPI ) is an imaging technique based on time-stretch technology for simultaneous measurement of phase and intensity spatial profiles. [ 19 ] [ 20 ] [ 21 ] [ 22 ] Developed at UCLA, it has led to the development of time stretch artificial intelligence microscope. [ 19 ]
In time stretched imaging, the object's spatial information is encoded in the spectrum of laser pulses within a pulse duration of sub- nanoseconds . Each pulse representing one frame of the camera is then stretched in time so that it can be digitized in real-time by an electronic analog-to-digital converter (ADC). The ultra-fast pulse illumination freezes the motion of high-speed cells or particles in flow to achieve blur-free imaging. Detection sensitivity is challenged by the low number of photons collected during the ultra-short shutter time (optical pulse width) and the drop in the peak optical power resulting from the time stretch. [ 23 ] These issues are solved in time stretch imaging by implementing a low noise-figure Raman amplifier within the dispersive device that performs time stretching. Moreover, warped stretch transform can be used in time stretch imaging to achieve optical image compression and nonuniform spatial resolution over the field-of-view.
In the coherent version of the time-stretch camera, the imaging is combined with spectral interferometry to measure quantitative phase [ 24 ] [ 25 ] and intensity images in real-time and at high throughput. Integrated with a microfluidic channel, coherent time stretch imaging system measures both quantitative optical phase shift and loss of individual cells as a high-speed imaging flow cytometer, capturing millions of line-images per second in flow rates as high as a few meters per second, reaching up to hundred-thousand cells per second throughput. The time stretch quantitative phase imaging can be combined with machine learning to achieve very accurate label-free classification of the cells.
This method is useful for a broad range of scientific, industrial, and biomedical applications that require high shutter speeds and frame rates. The one-dimensional version can be employed for displacement sensing, [ citation needed ] barcode reading, [ citation needed ] and blood screening; [ 26 ] the two-dimensional version for real-time observation, diagnosis, and evaluation of shockwaves, microfluidic flow, [ 27 ] neural activity, MEMS, [ 28 ] and laser ablation dynamics. [ citation needed ] The three-dimensional version is useful for range detection, [ citation needed ] dimensional metrology, [ citation needed ] and surface vibrometry and velocimetry. [ 29 ]
Big data not only brings opportunity but also a challenge in biomedical and scientific instruments, as acquisition and processing units are overwhelmed by a torrent of data. The need to compress massive volumes of data in real-time has fueled interest in nonuniform stretch transformations – operations that reshape the data according to its sparsity.
Recently researchers at UCLA demonstrated image compression performed in the optical domain and in real-time. [ 30 ] Using nonlinear group delay dispersion and time-stretch imaging, they were able to optically warp the image such that the information-rich portions are sampled at a higher sample density than the sparse regions. This was achieved by restructuring the image before optical-to-electrical conversion followed by a uniform electronic sampler. The reconstruction of the nonuniformly stretched image demonstrates that the resolution is higher where information is rich and lower where information is much less and relatively not important. The information-rich region at the center is well preserved while maintaining the same sampling rates compared to uniform case without down-sampling. Image compression was demonstrated at 36 million frames per second in real time. | https://en.wikipedia.org/wiki/Time_stretch_quantitative_phase_imaging |
A time temperature indicator ( TTI ) is a device or smart label that shows the accumulated time-temperature history of a product. Time temperature indicators are commonly used on food , pharmaceutical , and medical products to indicate exposure to excessive temperature (and time at temperature). [ 1 ]
In contrast, a temperature data logger measures and records the temperatures for a specified time period. The digital data can be downloaded and analyzed.
The basic types of time-temperature indicators include:
Digital temperature data loggers are available to indicate the full temperature history of a shipment to help identify the time period that out-of- tolerance temperatures were encountered. This temperature history can be used to calculate the loss of shelf life or the likelihood of spoilage. These small recorders are also used to identify the time (and thus location) of a shipment when the problem occurred, which allows for corrective action.
There are a large number of different time temperature indicators available in the market, based on different technologies. To the degree that these physical changes in the indicator match the degradation rate of the food, the indicator can help indicate probable food degradation. [ 4 ]
Time-temperature indicators can be used on food products that are dependent on a controlled temperature environment. Certain technologies can also be used for frozen food and the cold chain .
Meals, Ready-to-Eat (MREs) from the US military have included "Fresh-Check" TTIs on the cardboard boxes since 1997 to help estimate their shelf lives. [ 6 ]
Surveys within the European Union projects "Freshlabel" and "Chill-on" have shown positive feedback from consumers on the use of TTIs on food products. As TTIs help assure the cold chain of food products, they are expected to reduce the amount of food waste , [ 7 ] as well as reducing the number of foodborne illnesses . [ 8 ]
The World Health Organization regulates the use of TTIs for certain medical products. There is extensive regulation by the FDA on the use of TTIs on US seafood products. [ 9 ] | https://en.wikipedia.org/wiki/Time_temperature_indicator |
Time to first byte ( TTFB ) is a measurement used as an indication of the responsiveness of a webserver or other network resource.
TTFB measures the duration from the user or client making an HTTP request to the first byte of the page being received by the client's browser. This time is made up of the socket connection time, the time taken to send and the time taken to get the first byte of the page. [ 1 ] Although sometimes misunderstood as a post-DNS calculation, the original calculation of TTFB in networking always includes network latency in measuring the time it takes for a resource to begin loading. [ 2 ] Often, a smaller (faster) TTFB size is seen as a benchmark of a well-configured server application. For example, a lower time to first byte could point to fewer dynamic calculations being performed by the webserver , although this is often due to caching at either the DNS, server, or application level. [ 1 ] More commonly, a very low TTFB is observed with statically served web pages , while larger TTFB is often seen with larger, dynamic data requests being pulled from a database. [ 3 ]
Time to first byte is important to a webpage since it indicates pages that load slowly due to server-side calculations that might be better served as client-side scripting . Often this includes simple scripts and calculations like transitioning images that are not gifs and are transitioned using JavaScript to modify their transparency levels. This can often speed up a website by downloading multiple smaller images through sockets instead of one large image. However this technique is more intensive on the client's computer and on older PCs can slow the webpage down when actually rendering.
TTFB is often used by web search engines like Google and Yahoo to improve search rankings since a website will respond to the request faster and be usable before other websites would be able to. [ 4 ] There are downsides to this metric since a web-server can send only the first part of the header before the content is even ready to send to reduce their TTFB. While this may seem deceptive it can be used to inform the user that the webserver is in fact active and will respond with content shortly. There are several reasons why this deception is useful, including that it causes a persistent connection to be created, which results in fewer retry attempts from a browser or user since it has already received a connection and is now preparing for the content download. [ 5 ]
Load time is how long it takes for a webpage to be loaded and usable by a browser. Often in web page delivery a page is compressed in the Gzip format to make the size of the download smaller. [ 5 ] This practice prevents the first byte from being sent until the compression is complete and increases the TTFB significantly. TTFB can go from 100–200 ms to 1000–20000 ms, but the page will load much faster and be ready for the user in a much smaller amount of time. Many websites see a common 5–10× increase in TTFB but a much faster browser response time garnering 20% load-time decrease. | https://en.wikipedia.org/wiki/Time_to_first_byte |
Time to first fix ( TTFF ) is a measure of the time required for a GPS navigation device to acquire satellite signals and navigation data, and calculate a position solution (called a fix ).
The TTFF is commonly broken down into three more specific scenarios, as defined in the GPS equipment guide:
Many receivers can use as many as twelve channels simultaneously, allowing quicker fixes (especially in a cold case for the almanac download). [ 1 ] Many cell phones reduce the time to first fix by using assisted GPS (A-GPS): they acquire almanac and ephemeris data over a fast network connection from the cell-phone operator rather than over the slow radio connection from the satellites.
The TTFFs for a cold start is typically between 2 and 4 minutes, a warm start is 45 seconds (or shorter), and a hot start is 22 seconds (or only a few seconds). [ 2 ] In older hardware where satellite search is slower, a cold start may take more than the full 12.5 minutes. [ 3 ] | https://en.wikipedia.org/wiki/Time_to_first_fix |
Time triple modular redundancy , also known as TTMR, is a patented single-event upset mitigation technique that detects and corrects errors in a computer or microprocessor. TTMR allows the use of very long instruction word ( VLIW ) style microprocessors in space or other applications where external sources, such as radiation, would cause an elevated rate of errors. TTMR permits triple modular redundancy ( TMR ) protection in a single processor. [ 1 ]
Space Micro Inc developed and patented TTMR. It has been implemented in Space Micro's space qualified single-board computers , such as the Proton200k . | https://en.wikipedia.org/wiki/Time_triple_modular_redundancy |
The time value of money refers to the fact that there is normally a greater benefit to receiving a sum of money now rather than an identical sum later. It may be seen as an implication of the later-developed concept of time preference .
The time value of money refers to the observation that it is better to receive money sooner than later. Money you have today can be invested to earn a positive rate of return, producing more money tomorrow. Therefore, a dollar today is worth more than a dollar in the future. [ 1 ]
The time value of money is among the factors considered when weighing the opportunity costs of spending rather than saving or investing money. As such, it is among the reasons why interest is paid or earned: interest, whether it is on a bank deposit or debt , compensates the depositor or lender for the loss of their use of their money. Investors are willing to forgo spending their money now only if they expect a favorable net return on their investment in the future, such that the increased value to be available later is sufficiently high to offset both the preference to spending money now and inflation (if present); see required rate of return .
The Talmud (~500 CE) recognizes the time value of money. In Tractate Makkos page 3a the Talmud discusses a case where witnesses falsely claimed that the term of a loan was 30 days when it was actually 10 years. The false witnesses must pay the difference of the value of the loan "in a situation where he would be required to give the money back (within) thirty days..., and that same sum in a situation where he would be required to give the money back (within) 10 years...The difference is the sum that the testimony of the (false) witnesses sought to have the borrower lose; therefore, it is the sum that they must pay." [ 2 ]
The notion was later described by Martín de Azpilcueta (1491–1586) of the School of Salamanca .
Time value of money problems involve the net value of cash flows at different points in time.
In a typical case, the variables might be: a balance (the real or nominal value of a debt or a financial asset in terms of monetary units), a periodic rate of interest, the number of periods, and a series of cash flows. (In the case of a debt, cash flows are payments against principal and interest; in the case of a financial asset, these are contributions to or withdrawals from the balance.) More generally, the cash flows may not be periodic but may be specified individually. Any of these variables may be the independent variable (the sought-for answer) in a given problem. For example, one may know that: the interest is 0.5% per period (per month, say); the number of periods is 60 (months); the initial balance (of the debt, in this case) is 25,000 units; and the final balance is 0 units. The unknown variable may be the monthly payment that the borrower must pay.
For example, £100 invested for one year, earning 5% interest, will be worth £105 after one year; therefore, £100 paid now and £105 paid exactly one year later both have the same value to a recipient who expects 5% interest assuming that inflation would be zero percent. That is, £100 invested for one year at 5% interest has a future value of £105 under the assumption that inflation would be zero percent. [ 3 ]
This principle allows for the valuation of a likely stream of income in the future, in such a way that annual incomes are discounted and then added together, thus providing a lump-sum "present value" of the entire income stream; all of the standard calculations for time value of money derive from the most basic algebraic expression for the present value of a future sum, "discounted" to the present by an amount equal to the time value of money. For example, the future value sum F V {\displaystyle FV} to be received in one year is discounted at the rate of interest r {\displaystyle r} to give the present value sum P V {\displaystyle PV} :
Some standard calculations based on the time value of money are:
There are several basic equations that represent the equalities listed above. The solutions may be found using (in most cases) the formulas, a financial calculator, or a spreadsheet . The formulas are programmed into most financial calculators and several spreadsheet functions (such as PV, FV, RATE, NPER, and PMT). [ 7 ]
For any of the equations below, the formula may also be rearranged to determine one of the other unknowns. In the case of the standard annuity formula, there is no closed-form algebraic solution for the interest rate (although financial calculators and spreadsheet programs can readily determine solutions through rapid trial and error algorithms).
These equations are frequently combined for particular uses. For example, bonds can be readily priced using these equations. A typical coupon bond is composed of two types of payments: a stream of coupon payments similar to an annuity, and a lump-sum return of capital at the end of the bond's maturity —that is, a future payment. The two formulas can be combined to determine the present value of the bond.
An important note is that the interest rate i is the interest rate for the relevant period. For an annuity that makes one payment per year, i will be the annual interest rate. For an income or payment stream with a different payment schedule, the interest rate must be converted into the relevant periodic interest rate. For example, a monthly rate for a mortgage with monthly payments requires that the interest rate be divided by 12 (see the example below). See compound interest for details on converting between different periodic interest rates.
The rate of return in the calculations can be either the variable solved for, or a predefined variable that measures a discount rate, interest, inflation, rate of return, cost of equity, cost of debt or any number of other analogous concepts. The choice of the appropriate rate is critical to the exercise, and the use of an incorrect discount rate will make the results meaningless.
For calculations involving annuities, it must be decided whether the payments are made at the end of each period (known as an ordinary annuity), or at the beginning of each period (known as an annuity due). When using a financial calculator or a spreadsheet , it can usually be set for either calculation. The following formulas are for an ordinary annuity. For the answer to the present value of an annuity due, the PV of an ordinary annuity can be multiplied by (1 + i ).
The following formula use these common variables:
The future value ( FV ) formula is similar and uses the same variables.
The present value formula is the core formula for the time value of money; each of the other formulas is derived from this formula. For example, the annuity formula is the sum of a series of present value calculations.
The present value ( PV ) formula has four variables, each of which can be solved for by numerical methods :
The cumulative present value of future cash flows can be calculated by summing the contributions of FV t , the value of cash flow at time t :
Note that this series can be summed for a given value of n , or when n is ∞. [ 8 ] This is a very general formula, which leads to several important special cases given below.
In this case the cash flow values remain the same throughout the n periods. The present value of an annuity (PVA) formula has four variables, each of which can be solved for by numerical methods:
To get the PV of an annuity due , multiply the above equation by (1 + i ).
In this case, each cash flow grows by a factor of (1 + g ). Similar to the formula for an annuity, the present value of a growing annuity (PVGA) uses the same variables with the addition of g as the rate of growth of the annuity (A is the annuity payment in the first period). This is a calculation that is rarely provided for on financial calculators.
Where i ≠ g :
Where i = g :
To get the PV of a growing annuity due , multiply the above equation by (1 + i ).
A perpetuity is payments of a set amount of money that occur on a routine basis and continue forever. When n → ∞, the PV of a perpetuity (a perpetual annuity) formula becomes a simple division.
When the perpetual annuity payment grows at a fixed rate ( g , with g < i ) the value is determined according to the following formula, obtained by setting n to infinity in the earlier formula for a growing perpetuity:
In practice, there are few securities with precise characteristics, and the application of this valuation approach is subject to various qualifications and modifications. Most importantly, it is rare to find a growing perpetual annuity with fixed rates of growth and true perpetual cash flow generation. Despite these qualifications, the general approach may be used in valuations of real estate, equities, and other assets.
This is the well known Gordon growth model used for stock valuation .
The future value (after n periods) of an annuity (FVA) formula has four variables, each of which can be solved for by numerical methods:
To get the FV of an annuity due, multiply the above equation by (1 + i ).
The future value (after n periods) of a growing annuity (FVA) formula has five variables, each of which can be solved for by numerical methods:
Where i ≠ g :
Where i = g :
The following table summarizes the different formulas commonly used in calculating the time value of money. [ 9 ] These values are often displayed in tables where the interest rate and time are specified.
Increasing percentage (g)
F = D ⋅ n ( 1 + i ) n 1 + g {\displaystyle F=D\cdot {\frac {n(1+i)^{n}}{1+g}}} (for i = g )
Increasing percentage (g)
P = D ⋅ n 1 + g {\displaystyle P=D\cdot {\frac {n}{1+g}}} (for i = g )
Notes:
The formula for the present value of a regular stream of future payments (an annuity) is derived from a sum of the formula for future value of a single future payment, as below, where C is the payment amount and n the period.
A single payment C at future time m has the following future value at future time n :
Summing over all payments from time 1 to time n , then reversing the order of terms and substituting k = n − m :
Note that this is a geometric series , with the initial value being a = C , the multiplicative factor being 1 + i , with n terms. Applying the formula for geometric series, we get:
The present value of the annuity (PVA) is obtained by simply dividing by ( 1 + i ) n {\displaystyle (1+i)^{n}} :
Another simple and intuitive way to derive the future value of an annuity is to consider an endowment, whose interest is paid as the annuity, and whose principal remains constant. The principal of this hypothetical endowment can be computed as that whose interest equals the annuity payment amount:
Note that no money enters or leaves the combined system of endowment principal + accumulated annuity payments, and thus the future value of this system can be computed simply via the future value formula:
Initially, before any payments, the present value of the system is just the endowment principal, P V = C i {\displaystyle PV={\frac {C}{i}}} . At the end, the future value is the endowment principal (which is the same) plus the future value of the total annuity payments ( F V = C i + F V A {\displaystyle FV={\frac {C}{i}}+FVA} ). Plugging this back into the equation:
Without showing the formal derivation here, the perpetuity formula is derived from the annuity formula. Specifically, the term:
can be seen to approach the value of 1 as n grows larger. At infinity, it is equal to 1, leaving C i {\displaystyle {C \over i}} as the only term remaining.
Rates are sometimes converted into the continuous compound interest rate equivalent because the continuous equivalent is more convenient (for example, more easily differentiated). Each of the formulas above may be restated in their continuous equivalents. For example, the present value at time 0 of a future payment at time t can be restated in the following way, where e is the base of the natural logarithm and r is the continuously compounded rate:
This can be generalized to discount rates that vary over time: instead of a constant discount rate r, one uses a function of time r ( t ). In that case, the discount factor, and thus the present value, of a cash flow at time T is given by the integral of the continuously compounded rate r ( t ):
Indeed, a key reason for using continuous compounding is to simplify the analysis of varying discount rates and to allow one to use the tools of calculus. Further, for interest accrued and capitalized overnight (hence compounded daily), continuous compounding is a close approximation for the actual daily compounding. More sophisticated analysis includes the use of differential equations , as detailed below.
Using continuous compounding yields the following formulas for various instruments:
These formulas assume that payment A is made in the first payment period and annuity ends at time t . [ 10 ]
Ordinary and partial differential equations (ODEs and PDEs)—equations involving derivatives and one (respectively, multiple) variables—are ubiquitous in more advanced treatments of financial mathematics . While time value of money can be understood without using the framework of differential equations, the added sophistication sheds additional light on time value, and provides a simple introduction before considering more complicated and less familiar situations. This exposition follows ( Carr & Flesaker 2006 , pp. 6–7).
The fundamental change that the differential equation perspective brings is that, rather than computing a number (the present value now ), one computes a function (the present value now or at any point in future ). This function may then be analyzed (how does its value change over time?) or compared with other functions.
Formally, the statement that "value decreases over time" is given by defining the linear differential operator L {\displaystyle {\mathcal {L}}} as:
This states that value decreases (−) over time (∂ t ) at the discount rate ( r ( t )). Applied to a function, it yields:
For an instrument whose payment stream is described by f ( t ), the value V ( t ) satisfies the inhomogeneous first-order ODE L V = f {\displaystyle {\mathcal {L}}V=f} ("inhomogeneous" is because one has f rather than 0, and "first-order" is because one has first derivatives but no higher derivatives)—this encodes the fact that when any cash flow occurs, the value of the instrument changes by the value of the cash flow (if one receives a £10 coupon, the remaining value decreases by exactly £10).
The standard technique tool in the analysis of ODEs is Green's functions , from which other solutions can be built. In terms of time value of money, the Green's function (for the time value ODE) is the value of a bond paying £1 at a single point in time u ; the value of any other stream of cash flows can then be obtained by taking combinations of this basic cash flow. In mathematical terms, this instantaneous cash flow is modeled as a Dirac delta function δ u ( t ) := δ ( t − u ) . {\displaystyle \delta _{u}(t):=\delta (t-u).}
The Green's function for the value at time t of a £1 cash flow at time u is
where H is the Heaviside step function . The notation " ; u {\displaystyle ;u} " is to emphasize that u is a parameter (fixed in any instance—the time when the cash flow will occur), while t is a variable (time). In other words, future cash flows are exponentially discounted (exp) by the sum (integral, ∫ {\displaystyle \textstyle {\int }} ) of the future discount rates ( ∫ t u {\displaystyle \textstyle {\int _{t}^{u}}} for future, r ( v ) for discount rates), while past cash flows are worth 0 ( H ( u − t ) = 1 if t < u , 0 if t > u {\displaystyle H(u-t)=1{\text{ if }}t<u,0{\text{ if }}t>u} ), because they have already occurred. Note that the value at the moment of a cash flow is not well-defined—there is a discontinuity at that point, and one can use a convention (assume cash flows have already occurred, or not already occurred), or simply not define the value at that point.
In case the discount rate is constant, r ( v ) ≡ r , {\displaystyle r(v)\equiv r,} this simplifies to
where ( u − t ) {\displaystyle (u-t)} is "time remaining until cash flow".
Thus for a stream of cash flows f ( u ) ending by time T (which can be set to T = + ∞ {\displaystyle T=+\infty } for no time horizon) the value at time t, V ( t ; T ) {\displaystyle V(t;T)} is given by combining the values of these individual cash flows:
This formalizes time value of money to future values of cash flows with varying discount rates, and is the basis of many formulas in financial mathematics, such as the Black–Scholes formula with varying interest rates . | https://en.wikipedia.org/wiki/Time_value_of_money |
In agile principles , timeboxing allocates a maximum unit of time to an activity, called a timebox , within which a planned activity takes place. It is used by agile principles-based project management approaches and for personal time management.
Timeboxing is used as a project planning technique. The schedule is divided into a number of separate time periods (timeboxes), with each part having its own deliverables, deadline and budget. [ citation needed ] Sometimes referred to as schedule as independent variable (SAIV). [ 1 ] "Timeboxing works best in multistage projects or tasks that take little time and you can fit them in the same time slot. It is also worth implementing in case of duties that have foreseeable time-frames of completion." [ 2 ]
In project management , there are generally considered to be three constraints : time (sometimes schedule ), cost (sometimes budget ), and scope . [ 3 ] [ 4 ] [ 5 ] [ 6 ] [ 7 ] ( Quality is often added as a fourth constraint---represented as the middle of a triangle. [ 8 ] [ 9 ] [ 10 ] ) The assumption is that a change in one constraint will affect the others. [ 6 ]
Without timeboxing, projects usually work to a fixed scope, [ 11 ] in which case when it becomes clear that some deliverables cannot be completed within the planned timescales, either the deadline has to be extended (to allow more time to complete the fixed scope) or more people are involved (to complete the fixed scope in the same time). Often both happen, resulting in delayed delivery, increased costs, and often reduced quality (as per The Mythical Man-Month principle).
With timeboxing, the deadline is fixed, meaning that the scope would have to be reduced. As this means organizations have to focus on completing the most important deliverables first, timeboxing often goes hand-in-hand with a scheme for prioritizing of deliverables (such as with the MoSCoW method ). [ 12 ]
Timeboxes are used as a form of risk management , to explicitly identify uncertain task/time relationships, i.e., work that may easily extend past its deadline. Time constraints are often a primary driver in planning and should not be changed without considering project or sub-project critical paths. That is, it's usually important to meet deadlines. Risk factors for missed deadlines can include complications upstream of the project, planning errors within the project, team-related issues, or faulty execution of the plan. Upstream issues might include changes in project mission or backing/support from management. A common planning error is inadequate task breakdown, which can lead to underestimation of the time required to perform the work. Team-related issues can include trouble with inter-team communication; lack of experience or required cross-functionality; lack of commitment/drive/motivation (i.e. poor team building and management).
To stay on deadline, the following actions against the triple constraints are commonly evaluated:
Many successful software development projects use timeboxing, especially smaller ones. [ 13 ] Adopting timeboxing more than tripled developer productivity at DuPont in the '80s. [ 14 ] In some cases, applications were completely delivered within the time estimated to complete just a specification . [ 14 ] However, Steve McConnell argues that not every product is suitable [ 14 ] and that timeboxing should only be used after the customer agrees to cut features, not quality. [ 14 ] There is little evidence for strong adoption amongst the largest class of projects. [ 13 ]
Timeboxing has been adopted by some notable software development methodologies :
Agile software development advocates moving from plan driven to value driven development. Quality and time are fixed but flexibility allowed in scope. Delivering the most important features first leads to an earlier return on investment than the waterfall model . [ 7 ]
A lack of detailed specifications typically is the result of a lack of time, or the lack of knowledge of the desired end result (solution). In many types of projects, and especially in software engineering, analyzing and defining all requirements and specifications before the start of the realization phase is impossible. Timeboxing can be a favorable type of contracting for projects in which the deadline is the most critical aspect and when not all requirements are completely specified up front. This also allows for new feedback or insights discovered during the project to be reflected in the end result. [ 12 ]
Timeboxing can be used for personal tasks, in which case it uses a reduced scale of time (e.g., thirty minutes) and of deliverables (e.g., a household chore instead of project deliverable), and is often called timeblocking .
Personal timeboxing is also said to act as a life hack to help curb perfectionist tendencies (by setting a firm time and not overcommitting to a task) which can also enhance creativity and focus (by creating a sense of urgency or increased pressure). [ 21 ]
Timeboxing acts as a building block in other personal time management methods: | https://en.wikipedia.org/wiki/Timeboxing |
This is a timeline of Chinese records and investigations in astronomy .
This astronomy -related article is a stub . You can help Wikipedia by expanding it .
This article related to the history of China is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Timeline_of_Chinese_astronomy |
The Mars 2020 mission , consisting of the rover Perseverance and helicopter Ingenuity , was launched on July 30, 2020, and landed in Jezero crater on Mars on February 18, 2021. [ 1 ] As of May 17, 2025, Perseverance has been on the planet for 1508 sols (1549 total days ; 4 years, 88 days ). Ingenuity operated for 1042 sols (1071 total days ; 1 year, 341 days ) until its rotor blades, possibly all four, were damaged during the landing of flight 72 on January 18, 2024, causing NASA to retire the craft. [ 2 ] [ 3 ]
Current weather data on Mars is being monitored by the Curiosity rover and had previously been monitored by the Insight lander. [ 4 ] [ 5 ] The Perseverance rover is also collecting weather data. (See the External links section)
The Mars 2020 mission was announced by NASA on December 4, 2012. In 2017 the three sites ( Jezero crater , Northeastern Syrtis Major Planum , and Columbia Hills ) were chosen as potential landing locations, with Jezero crater selected as the landing location, and launched on July 30th, 2020, from Cape Canaveral .
After arriving on February 18, Perseverance focused on validating its systems. During this phase, it used its science instruments for the first time, [ 6 ] generated oxygen on Mars with MOXIE , [ 7 ] and deployed Ingenuity . Ingenuity began the technology demonstration phase of its mission, completing five flights before transitioning to the operations demonstration phase of its mission.
The Cratered Floor Campaign was the first science campaign. [ 9 ] It began on June 1, 2021, with the goal of exploring the Crater Floor Fractured Rough and Séítah geologic units. To avoid the sand dunes of the Séítah unit, Perseverance mostly traveled within the Crater Floor Fractured Rough geologic unit or along the boundary between the two units. The first nine of Perseverance ' s sample tubes were to be filled during this expedition, including the first three 'witness tubes'. [ 8 ]
After collecting the samples, Perseverance returned to its landing site, before continuing to the delta for its second science campaign. Some of the sample tubes filled during this campaign were later stored in a designated area for the upcoming NASA-ESA Mars Sample Return mission, during the Delta Front Campaign. [ 10 ] While Perseverance embarked on its first science campaign, Ingenuity continued to travel alongside the rover as part of its operations demonstration campaign. [ 11 ] Ingenuity's sixth through twenty-fifth flights were completed during this phase, achieving an at-the-time speed record of 5.5 meters per second. [ 12 ]
The Delta Front Campaign was the second science campaign of the Mars 2020 mission. The campaign began with Ingenuity continuing to travel alongside the rover as part of its operations demonstration campaign, and Perseverance leaving the rapid traverse mode it had entered at the end of the last mission to rapidly reach the delta. [ 13 ] During the campaign, Perseverance would take a further nine samples, in addition to two further witness tubes. Ingenuity would make its 41th flight during this mission. An incident occurred in which Ingenuity was unable to sufficiently charge during the night, leading to a change in how Ingenuity manages its heaters. [ 14 ] The MOXIE experiment continued to run, generating a record amount of oxygen-per-hour on Mars. The campaign concluded with Perseverance reaching the top of the delta and the completion of its first sample depot. [ 15 ]
The Upper Fan Campaign, also called the Delta Top Campaign, was the third science campaign of the Mars 2020 mission. Whereas prior campaigns investigated areas that are believed to have been submerged in an ancient lake, this campaign investigated one of the riverbeds that used to feed into the lake. [ 16 ] [ 17 ] The MOXIE experiment completed its 16th, and final, oxygen generation test during this campaign. [ 18 ] Ingenuity completed its 54th flight during this campaign. The helicopter experienced an anomaly that caused it to land outside the range of the rover, but this was ultimately resolved when the rover moved into a position that allowed contact to be restored. [ 19 ] The campaign ended with Perseverance reaching the margin carbonate geologic unit, [ 20 ] after having taken three further rock samples (and 21 overall). [ 21 ]
The Margin Campaign was the fourth of the Mars 2020 mission. The campaign was expected to last around 8 months, although it lasted closer to a year, after which point Perseverance began the Crater Rim Campaign. [ 22 ] The campaign gets its name from the geological unit it aims to explore - the margin carbonate unit. Rocks in this unit are capable of containing traces of life, and their formation is tied to the presence of liquid water. [ 23 ]
During the campaign, Ingenuity achieved several records, including a max altitude of 24 meters (flight 61) and a maximum groundspeed of 10 meters per second (flight 62). Unfortunately, due to a failure on the 72nd flight, the helicopter blades became too damaged to fly. On January 25th, 2024, NASA declared the end of Ingenuity's mission - the helicopter's final resting place was named Valinor Hills, after a location in the Lord of the Rings franchise. [ 2 ] Despite the loss of Ingenuity's blades, the core of the helicopter remained intact; it will continue to monitor atmospheric conditions for as long as it is able. Perseverance took four further rock samples during this campaign (25 overall). The campaign overlapped with solar conjunction, interfering with the ability to communicate with the rover from Earth. [ 24 ]
Engineers from NASA’s Jet Propulsion Laboratory in Southern California and AeroVironment are completing a detailed assessment of the Ingenuity Mars Helicopter’s final flight on January 18, 2024, the first of its kind on an extraterrestrial planet, concluding that the inability of Ingenuity’s navigation system to provide accurate data during the flight likely caused a chain of events that ended the mission. [ 25 ]
The helicopter’s vision navigation system was designed to track visual features on the surface using a downward-looking camera over well-textured (pebbly) but flat terrain. This limited tracking capability was more than sufficient for carrying out Ingenuity’s first five flights, but by Flight 72 the helicopter was in a region of Jezero Crater filled with steep, relatively featureless sand ripples. [ 25 ]
One of the navigation system’s main requirements was to provide velocity estimates that would enable the helicopter to land within a small envelope of vertical and horizontal velocities. Data sent down during Flight 72 shows that, around 20 seconds after takeoff, the navigation system couldn’t find enough surface features to track. [ 25 ]
Photographs taken after the flight indicate the navigation errors created high horizontal velocities at touchdown. In the most likely scenario, the hard impact on the sand ripple’s slope caused Ingenuity to pitch and roll. The rapid attitude change resulted in loads on the fast-rotating rotor blades beyond their design limits, snapping all four of them off at their weakest point — about a third of the way from the tip. The damaged blades caused excessive vibration in the rotor system, ripping the remainder of one blade from its root and generating an excessive power demand that resulted in loss of communications. [ 25 ]
The Crater Rim Campaign is the fifth, currently ongoing science campaign, and the first new science campaign since the loss of the Ingenuity helicopter. It is expected to last until the end of 2024, and will include a total elevation change of over 1000 feet (~300 meters). The main focuses of the campaign are expected to be at the regions "Pico Turquino" and "Witch Hazel Hill", pictured above. [ 26 ] It is expected to encounter rocks as old as 4 billion years. [ 27 ] [ 28 ] [ 29 ]
In the frame of the NASA-ESA Mars Sample Return around 0.5 kilograms (1.1 lb) of soil samples along with some Martian gas samples from the atmosphere will be cached. Currently, samples are being cached by Mars 2020 Perseverance Rover on the surface of Mars . Out of 43 sample tubes, 8 are igneous rock sample tubes, 12 are sedimentary rock sample tubes, [ 30 ] 1 silica - cemented carbonate rock sample tube, 1 gas sample tube, [ 31 ] 2 regolith sample tubes, 3 "witness tubes", [ 32 ] with 16 tubes remaining unused as of August, 2024. Before launch, 5 of the 43 tubes were designated "witness tubes" and filled with materials that would capture particulates in the ambient environment of Mars. [ 33 ] | https://en.wikipedia.org/wiki/Timeline_of_Mars_2020 |
The Mars Science Laboratory and its rover, Curiosity , were launched from Earth on 26 November 2011. As of May 18, 2025, Curiosity has been in Gale Crater on the planet Mars for 4543 sols (4668 total days ; 12 years, 285 days ) since landing on 6 August 2012. (See Current status .)
In April 2004, the United States National Aeronautics and Space Administration (NASA) called for scientific experiments and instruments proposals for the Mars Science Laboratory and rover mission. [ 2 ] Launch was proposed for September 2009. [ 3 ] [ 4 ] By 14 December 2004, eight proposals were selected, including instruments from Russia and Spain. [ 2 ] [ 4 ]
Testing of components also began in late 2004, including Aerojet 's monopropellant engine with the ability to throttle from 15 to 100 percent thrust with a fixed propellant inlet pressure. [ 2 ] By November 2008 most hardware and software development was complete, and testing continued. [ 5 ] At this point, cost overruns were approximately $400 million. [ 6 ] In December 2008, lift-off was delayed to November 2011 due to insufficient time for testing and integration. [ 7 ] [ 8 ] [ 9 ]
Between 23–29 March 2009, the general public ranked nine finalist rover names ( Adventure, Amelia, Journey, Perception, Pursuit, Sunrise, Vision, Wonder , and Curiosity ) [ 10 ] through a public poll on the NASA website. [ 11 ] On 27 May 2009, the winning name was announced to be Curiosity . The name had been submitted in an essay contest by Clara Ma, a then sixth-grader from Kansas. [ 11 ]
At the first MSL Landing Site workshop, 33 potential landing sites were identified. [ 12 ] By the second workshop in late 2007, the list had grown to include almost 50 sites, [ 13 ] and by the end of the workshop, the list was reduced to six; [ 14 ] [ 15 ] [ 16 ] in November 2008, project leaders at a third workshop reduced the list to these four landing sites: [ 17 ] [ 18 ] [ 19 ]
A fourth landing site workshop was held in late September 2010, [ 25 ] and the fifth and final workshop 16–18 May 2011. [ 26 ] On 22 July 2011, it was announced that Gale Crater had been selected as the landing site of the Mars Science Laboratory mission.
MSL was launched from Cape Canaveral Air Force Station Space Launch Complex 41 on 26 November 2011, at 10:02 EST (15:02 UTC ) aboard an Atlas V 541 provided by United Launch Alliance . [ 28 ] [ 29 ] The first and second rocket stages, along with the rocket motors, were stacked on 9 October 2011, near the launch pad. [ 30 ] The fairing containing the spacecraft was transported to the launch pad on 3 November 2011. [ 31 ]
On 13 December 2011, the rover began monitoring space radiation to aid in planning for future crewed missions to Mars. [ 32 ]
The interplanetary journey to Mars took more than eight months, [ 33 ] time during which, the spacecraft performed four trajectory corrections: on 11 January, 26 March, 26 June and on 28 July. Mission design had allowed for a maximum of 6 trajectory correction opportunities. [ 34 ] [ 35 ]
Curiosity landed in the Gale Crater at 05:17 UTC on 6 August 2012. [ 38 ] [ 39 ] [ 40 ] [ 41 ] Upon reaching Mars, an automated precision landing sequence took over the entire landing events. [ 42 ] A cable cutter separated the cruise stage from the aeroshell and then the cruise stage was diverted into a trajectory for burn-up in the atmosphere. [ 43 ] [ 44 ] Landing was confirmed simultaneously by 3 monitoring Mars orbiters. Curiosity landed on target and only 2.4 km (1.5 mi) from its center. [ 45 ] The coordinates of the landing site (named " Bradbury Landing ") are: 4°35′22″S 137°26′30″E / 4.5895°S 137.4417°E / -4.5895; 137.4417 . [ 46 ] [ 47 ]
Some low resolution Hazcam images were beamed to Earth by relay orbiters confirming the rover's wheels were deployed correctly and on the ground. [ 41 ] [ 48 ] Three hours later, the rover begins to beam detailed data on its systems' status as well as on its entry, descent and landing experience. [ 48 ] Aerial 3-D images of the landing site are available and include: the Curiosity rover and related Parachute ( HiRISE , 10 October 2012).
On 8 August 2012, Mission Control began upgrading the rover's dual computers by deleting the entry-descent-landing software, then uploading and installing the surface operation software; [ 49 ] the switchover was completed by 15 August. [ 50 ]
On 15 August 2012, the rover began several days of instrument checks and mobility tests. [ 51 ] [ 52 ] The first laser testing of the ChemCam by Curiosity on Mars was performed on a rock, N165 ("Coronation" rock) , near Bradbury Landing on 19 August 2012. [ 53 ] [ 54 ] [ 55 ]
The science and operations teams have identified at least six possible routes to the base of Mount Sharp , and estimate about a year studying the rocks and soil of the crater floor while Curiosity slowly makes its way to the base of the mountain. [ 51 ] [ 56 ] The ChemCam team expects to take approximately one dozen compositional measurements of rocks per day. [ 57 ]
Having completed its mobility tests, the rover's first drive began on 29 August 2012, to a place called Glenelg about 400 m (1,300 ft) to the east. [ 58 ] Glenelg is a location where three types of terrain intersect, and is the mission's first major driving destination. The drive across may take up to two months, after which Curiosity will stay at Glenelg for a month. [ 59 ]
On the way, Curiosity studied a pyramidal rock dubbed " Jake Matijevic " after a mathematician-turned-rover-engineer who played a critical role in the design of the six-wheeled rover, but died just days after Curiosity landed in August. [ 60 ] The Jake rock measures about 25 cm (9.8 in) tall and 40 cm (16 in) wide. [ 61 ] It is an igneous rock and may be a mugearite , a sodium rich oligoclase -bearing basaltic trachyandesite . [ 62 ] Afterwards, on 30 September 2012, a finely-grained rock, named " Bathurst Inlet ", was examined by Curiosity 's Mars Hand Lens Imager (MAHLI) and Alpha particle X-ray spectrometer (APXS) . The rock was named after Bathurst Inlet , a deep inlet located along the northern coast of the Canadian mainland. Also, a sand patch , named " Rocknest ", is a test target for the first use of the scoop on the arm of the Curiosity rover . [ 63 ]
On 27 September 2012, NASA scientists announced that the Curiosity rover found evidence for an ancient streambed suggesting a "vigorous flow" of water on Mars . [ 64 ] [ 65 ] [ 66 ]
On 7 October 2012, a mysterious "bright object" ( image ), discovered in the sand at Rocknest , drew scientific interest. Several close-up pictures ( close-up 1 ) ( close-up 2 ) were taken of the object and preliminary interpretations by scientists suggest the object to be "debris from the spacecraft". [ 67 ] [ 68 ] [ 69 ] Nonetheless, further images in the nearby sand have detected other "bright particles" ( image ) ( close-up 1 ). These newly discovered objects are presently thought to be "native Martian material". [ 67 ] [ 70 ] [ 71 ]
On 17 October 2012, at Rocknest , the first X-ray diffraction analysis of Martian soil was performed. The results revealed the presence of several minerals, including feldspar , pyroxenes and olivine , and suggested that the Martian soil in the sample was similar to the weathered basaltic soils of Hawaiian volcanoes . The sample used is composed of dust distributed from global dust storms and local fine sand. So far, the materials Curiosity has analyzed are consistent with the initial ideas of deposits in Gale Crater recording a transition through time from a wet to dry environment. [ 72 ] On 22 November 2012, the Curiosity rover analyzed a rock named " Rocknest 3 " with the APXS and then resumed traveling toward "Point Lake" overlook on its way to Glenelg Intrigue . [ 73 ]
On 3 December 2012, NASA reported that Curiosity performed its first extensive soil analysis , revealing the presence of water molecules , sulfur and chlorine in the Martian soil . [ 74 ] [ 75 ] The presence of perchlorates in the sample seems highly likely. The presence of sulfate and sulfide is also likely because sulfur dioxide and hydrogen sulfide were detected. Small amounts of chloromethane , dichloromethane and trichloromethane were detected. The source of the carbon in these molecules is unclear. Possible sources include contamination of the instrument, organics in the sample and inorganic carbonates . [ 74 ] [ 75 ]
In February 2013, the rover used its drill for the first time. [ 76 ]
In March 2013, NASA reported Curiosity found evidence that geochemical conditions in Gale Crater were once suitable for microbial life after analyzing the first drilled sample of Martian rock , "John Klein" rock at Yellowknife Bay in Gale Crater . The rover detected water , carbon dioxide , oxygen , sulfur dioxide and hydrogen sulfide . [ 77 ] [ 78 ] [ 79 ] Chloromethane and dichloromethane were also detected. Related tests found results consistent with the presence of smectite clay minerals . [ 77 ] [ 78 ] [ 79 ] [ 80 ] [ 81 ] In addition, sandstone beds associated with the Gillespie Lake Member of Yellowknife Bay seem similar to microbially induced sedimentary structures (MISS) found on Earth, according to one study. [ 82 ]
On 8 April 2013, NASA reported that much of the atmosphere of Mars has been lost based on argon isotope ratios studies. [ 83 ] [ 84 ]
On 19 July 2013, NASA scientists published the results of a new analysis of the atmosphere of Mars , reporting a lack of methane around the landing site of the Curiosity rover. In addition, the scientists found evidence that Mars "has lost a good deal of its atmosphere over time", based on the abundance of isotopic compositions of gases, particularly those related to argon and carbon . [ 85 ] [ 86 ] [ 87 ]
On 28 February 2013, NASA was forced to switch to the backup computer due to an issue with the then active computer's flash memory which resulted in the computer continuously rebooting in a loop. The backup computer was turned on in safe mode and was converted to operational status on 19 March 2013. [ 88 ] [ 89 ]
On 18 March 2013, NASA reported evidence of mineral hydration , likely hydrated calcium sulfate , in several rock samples including the broken fragments of "Tintina" rock and "Sutton Inlier" rock as well as in veins and nodules in other rocks like "Knorr" rock and "Wernicke" rock . [ 90 ] [ 91 ] [ 92 ] Analysis using the rover's DAN instrument provided evidence of subsurface water, amounting to as much as 4% water content, down to a depth of 60 cm (2.0 ft), in the rover's traverse from the Bradbury Landing site to the Yellowknife Bay area in the Glenelg terrain. [ 90 ]
Between 4 April – 1 May 2013, Curiosity operated autonomously due to a Martian solar conjunction with Earth. While Curiosity transmitted a beep to Earth each day and the Odyssey spacecraft continued to relay information from the rover, no commands were sent from mission control since there was a possibility of data corruption due to interference from the Sun. Curiosity continued to perform stationary science at Yellowknife Bay for the duration of the conjunction. [ 83 ] [ 93 ]
On 5 June 2013, NASA announced that Curiosity will soon begin a 8 km (5.0 mi) journey from the Glenelg area to the base of Mount Sharp . The trip is expected to take nine months to a year with stops along the way to study the local terrain. [ 94 ] [ 95 ] [ 96 ]
On 16 July 2013, the Curiosity rover reached a milestone in its journey across Mars , having traveled 1 km (0.62 mi), since its landing in 2012; [ 97 ] on 1 August 2013, the rover traveled over one mile: 1.686 km (1.048 mi). [ 98 ]
On 6 August 2013, NASA celebrated Curiosity 's first year on Mars (6 August 2012 to 5 August 2013) by programming the rover to perform the " Happy Birthday " song to itself. [ 99 ] [ 100 ] NASA also released several videos ( video-1 , video-2 ) summarizing the rover's accomplishments over the year. [ 101 ] [ 102 ] Primarily, the mission found evidence of " ancient environments suitable for life " on Mars. The rover drove over one-mile across the Martian terrain, transmitted more than 190 gigabits of data to Earth, including 70,000 images (36,700 full images and 35,000 thumbnails), and the rover's laser fired more than 75,000 times at 2,000 targets. [ 103 ]
On 27 August 2013, Curiosity used autonomous navigation (or "autonav" - the ability of the rover to decide for itself how to drive safely) over unknown Martian ground for the first time. [ 104 ]
On 19 September 2013, NASA scientists, on the basis of further measurements by Curiosity , reported no detection of atmospheric methane with a measured value of 0.18 ± 0.67 ppbv corresponding to an upper limit of only 1.3 ppbv (95% confidence limit) and, as a result, conclude that the probability of current methanogenic microbial activity on Mars is reduced. [ 105 ] [ 106 ] [ 107 ]
On 26 September 2013, NASA scientists reported the Mars Curiosity rover detected "abundant, easily accessible" water (1.5 to 3 weight percent) in soil samples at the Rocknest region of Aeolis Palus in Gale Crater . [ 108 ] [ 109 ] [ 110 ] [ 111 ] [ 112 ] [ 113 ] In addition, NASA reported that the Curiosity rover found two principal soil types: a fine-grained mafic type and a locally derived, coarse-grained felsic type . [ 110 ] [ 112 ] [ 114 ] The mafic type, similar to other Martian soils and Martian dust , was associated with hydration of the amorphous phases of the soil. [ 114 ] Also, perchlorates , the presence of which may make detection of life-related organic molecules difficult, were found at the Curiosity rover landing site (and earlier at the more polar site of the Phoenix lander ) suggesting a "global distribution of these salts". [ 113 ] NASA also reported that Jake M rock , a rock encountered by Curiosity on the way to Glenelg , was a mugearite and very similar to terrestrial mugearite rocks. [ 115 ]
On 17 October 2013, NASA reported, based on analysis of argon in the Martian atmosphere , that certain meteorites found on Earth thought to be from Mars are confirmed to be from Mars. [ 116 ]
On 13 November 2013, NASA announced the names of two features on Mars important to two active Mars exploration rovers in honor of planetary scientist Bruce C. Murray (1931-2013): "Murray Buttes", an entryway the Curiosity rover will traverse on its way to Mount Sharp and "Murray Ridge", an uplifted crater that the Opportunity rover is exploring. [ 117 ]
On 25 November 2013, NASA reported that Curiosity has resumed full science operations, with no apparent loss of capability, after completing the diagnosis of an electrical problem first observed on 17 November. Apparently, an internal short in the rover's power source, the Multi-Mission Radioisotope Thermoelectric Generator , caused an unusual and intermittent decrease in a voltage indicator on the rover. [ 118 ] [ 119 ]
On 27 November 2013, an overview (titled, " The World of Mars ") of current and proposed Mars exploration by John Grotzinger , chief scientist of the Curiosity rover mission, was published in the New York Times . [ 120 ]
On 9 December 2013, NASA reported that the planet Mars had a large freshwater lake (which could have been a hospitable environment for microbial life ) based on evidence from the Curiosity rover studying Aeolis Palus near Mount Sharp in Gale Crater . [ 121 ] [ 122 ]
On 9 December 2013, NASA researchers described, in a series of six articles in the journal Science , many new discoveries from the Curiosity rover. Possible organics were found that could not be explained by contamination. [ 123 ] [ 124 ] Although the organic carbon was probably from Mars, it can all be explained by dust and meteorites that have landed on the planet. [ 125 ] [ 126 ] [ 127 ] Because much of the carbon was released at a relatively low temperature in Curiosity 's Sample Analysis at Mars (SAM) instrument package, it probably did not come from carbonates in the sample. The carbon could be from organisms, but this has not been proven. This organic-bearing material was obtained by drilling 5 centimeters deep in a site called Yellowknife Bay into a rock called " Sheepbed mudstone ". The samples were named John Klein and Cumberland . Microbes could be living on Mars by obtaining energy from chemical imbalances between minerals in a process called chemolithotrophy which means "eating rock." [ 128 ] However, in this process only a very tiny amount of carbon is involved — much less than was found at Yellowknife Bay . [ 129 ] [ 130 ]
Using SAM's mass spectrometer , scientists measured isotopes of helium , neon , and argon that cosmic rays produce as they go through rock. The fewer of these isotopes they find, the more recently the rock has been exposed near the surface. The 4-billion-year-old lakebed rock drilled by Curiosity was uncovered between 30 million and 110 million years ago by winds which sandblasted away 2 meters of overlying rock. Next, they hope to find a site tens of millions of years younger by drilling close to an overhanging outcrop. [ 131 ]
The absorbed dose and dose equivalent from galactic cosmic rays and solar energetic particles on the Martian surface for ~300 days of observations during the current solar maximum was measured. These measurements are necessary for human missions to the surface of Mars, to provide microbial survival times of any possible extant or past life, and to determine how long potential organic biosignatures can be preserved. This study estimates that a 1-meter depth drill is necessary to access possible viable radioresistant microbe cells. The actual absorbed dose measured by the Radiation Assessment Detector (RAD) is 76 mGy/yr at the surface. Based on these measurements, for a round-trip Mars surface mission with 180 days (each way) cruise, and 500 days on the Martian surface for this current solar cycle, an astronaut would be exposed to a total mission dose equivalent of ~1.01 sievert . Exposure to 1 sievert is associated with a 5 percent increase in risk for developing fatal cancer. NASA's current lifetime limit for increased risk for its astronauts operating in low-Earth orbit is 3 percent. [ 132 ] Maximum shielding from galactic cosmic rays can be obtained with about 3 meters of Martian soil . [ 133 ]
The samples examined were probably once mud that for millions to tens of millions of years could have hosted living organisms. This wet environment had neutral pH , low salinity , and variable redox states of both iron and sulfur species. [ 125 ] [ 134 ] [ 135 ] [ 136 ] These types of iron and sulfur could have been used by living organisms. [ 137 ] C , H , O , S , N , and P were measured directly as key biogenic elements, and by inference, P is assumed to have been there as well. [ 128 ] [ 130 ] The two samples, John Klein and Cumberland , contain basaltic minerals, Ca-sulfates, Fe oxide/hydroxides, Fe-sulfides, amorphous material, and trioctahedral smectites (a type of clay). Basaltic minerals in the mudstone are similar to those in nearby aeolian deposits. However, the mudstone has far less Fe- forsterite plus magnetite , so Fe-forsterite (type of olivine ) was probably altered to form smectite (a type of clay) and magnetite . [ 138 ] A Late Noachian /Early Hesperian or younger age indicates that clay mineral formation on Mars extended beyond Noachian time; therefore, in this location neutral pH lasted longer than previously thought. [ 134 ]
On 20 December 2013, NASA reported that Curiosity has successfully upgraded, for the third time since landing , its software programs and is now operating with version 11. The new software is expected to provide the rover with better robotic arm and autonomous driving abilities. Due to wheel wear, a concern to drive more carefully over the rough terrain the rover is currently traveling on to Mount Sharp , was also reported. [ 139 ]
On 24 January 2014, NASA reported that current studies by the Curiosity and Opportunity rovers will now be searching for evidence of ancient life, including a biosphere based on autotrophic , chemotrophic and/or chemolithoautotrophic microorganisms , as well as ancient water, including fluvio-lacustrine environments ( plains related to ancient rivers or lakes ) that may have been habitable . [ 140 ] [ 141 ] [ 142 ] [ 128 ] The search for evidence of habitability , taphonomy (related to fossils ), and organic carbon on the planet Mars is now a primary NASA objective. [ 140 ]
On 11 September 2014 (Sol 746), Curiosity reached the slopes of Aeolis Mons (or Mount Sharp ), the rover mission's long-term prime destination [ 143 ] [ 144 ] and where the rover is expected to learn more about the history of Mars . [ 103 ] Curiosity had traveled an estimated linear distance of 6.9 km (4.3 mi) [ 145 ] to the mountain slopes since leaving its " start " point in Yellowknife Bay on 4 July 2013. [ 145 ]
On 16 December 2014, NASA reported the Curiosity rover detected a "tenfold spike", likely localized, in the amount of methane in the Martian atmosphere . Sample measurements taken "a dozen times over 20 months" showed increases in late 2013 and early 2014, averaging "7 parts of methane per billion in the atmosphere." Before and after that, readings averaged around one-tenth that level. [ 146 ] [ 147 ] In addition, high levels of organic chemicals , particularly chlorobenzene , were detected in powder drilled from one of the rocks, named " Cumberland ", analyzed by the Curiosity rover. [ 146 ] [ 147 ]
On 6 February 2014, the Curiosity rover, in order to reduce wear on its wheels by avoiding rougher terrain, [ 148 ] successfully crossed ( image ) the " Dingo Gap " sand dune and is now expected to travel a smoother route to Mount Sharp . [ 149 ]
On 19 May 2014, scientists announced that numerous microbes , like Tersicoccus phoenicis , may be resistant to methods usually used in spacecraft assembly clean rooms . It's not currently known if such resistant microbes could have withstood space travel and are present on the Curiosity rover now on Mars. [ 150 ]
On 25 May 2014, Curiosity discovered an iron meteorite , and named it " Lebanon " ( image ).
On 3 June 2014, Curiosity observed the planet Mercury transiting the Sun , marking the first time a planetary transit has been observed from a celestial body besides Earth . [ 151 ]
On 24 June 2014, Curiosity completed a Martian year —687 Earth days—after finding that Mars once had environmental conditions favorable for microbial life . [ 152 ]
On 27 June 2014, Curiosity crossed the boundary line of its " 3-sigma safe-to-land ellipse " and is now in territory that may get even more interesting, especially in terms of Martian geology and landscape ( view from space ). [ 153 ]
On 12 July 2014, Curiosity imaged the first laser spark on Mars ( related image ; video (01:07) .)
On 6 August 2014, Curiosity celebrated its second anniversary since landing on Mars in 2012. [ 154 ]
On 11 September 2014, a panel of NASA scientists announced ( video (01:25) ) the arrival of Curiosity at Mount Sharp and discussed future rover plans. [ 144 ]
On 19 October 2014, the Curiosity rover viewed the flyby of Comet C/2013 A1 .
On 8 December 2014, a panel of NASA scientists discussed ( archive 62:03) the latest observations of Curiosity , including findings about how water may have helped shape the landscape of Mars and had a climate long ago that could have produced long-lasting lakes at many Martian locations. [ 155 ] [ 156 ] [ 157 ]
On 16 December 2014, NASA reported detecting an unusual increase, then decrease, in the amounts of methane in the atmosphere of the planet Mars ; in addition, organic chemicals were detected in powder drilled from a rock by the Curiosity rover . Also, based on deuterium to hydrogen ratio studies, much of the water at Gale Crater on Mars was found to have been lost during ancient times, before the lakebed in the crater was formed; afterwards, large amounts of water continued to be lost. [ 146 ] [ 147 ] [ 158 ]
On 21 January 2015, NASA announced a collaborative effort with Microsoft that developed a software project called OnSight which allows scientists to perform virtual work on Mars based on data from the Curiosity rover. [ 159 ]
On 6 March 2015, NASA reported performing tests on the rover to help uncover the reason for intermittent problems with the robotic arm used for rock drilling and analysis. [ 160 ] Results of preliminary tests suggest the intermittent short-circuit problem may be related to the percussion mechanism of the drill. Further tests are planned to verify and adjust to the problem. [ 161 ]
On 24 March 2015, NASA reported the first detection of nitrogen released after heating surface sediments on the planet Mars . The nitrogen, in the form of nitric oxide , was detected by the SAM instrument on the Curiosity rover and can be used by living organisms . The discovery supports the notion that ancient Mars may have been habitable for life . [ 162 ]
On 27 March 2015, NASA reported that the Bradbury Landing , the mission's landing site, was fading from view in the two-and-a-half years since landing in 2012.
On 4 April 2015, NASA reported studies, based on measurements by the Sample Analysis at Mars (SAM) instrument on the Curiosity rover , of the Martian atmosphere using xenon and argon isotopes . Results provided support for a "vigorous" loss of atmosphere early in the history of Mars and were consistent with an atmospheric signature found in bits of atmosphere captured in some Martian meteorites found on Earth. [ 163 ]
On 19 August 2015, NASA scientists reported that the Dynamic Albedo of Neutrons (DAN) instrument on the Curiosity rover detected an unusual hydrogen-rich area, at "Marias Pass," on Mars. The hydrogen found seemed related to water or hydroxyl ions in rocks within three feet beneath the rover, according to the scientists. [ 165 ]
On 5 October 2015, possible recurrent slope lineae , wet brine flows, were reported on Mount Sharp near Curiosity . [ 166 ] In addition, on 5 October 2015, NASA reported an estimated 20,000 to 40,000 heat-resistant bacterial spores were on Curiosity at launch, as much as 1,000 times more than that may not have been counted. [ 166 ]
On 8 October 2015, NASA confirmed that lakes and streams existed in Gale crater 3.3 - 3.8 billion years ago delivering sediments to build up the lower layers of Mount Sharp . [ 167 ] [ 168 ]
On 17 December 2015, NASA reported that as Curiosity climbed higher up Mount Sharp, the composition of rocks were changing substantially. For example, rocks found higher up the mountain contained much higher levels of silica than the basaltic rocks found earlier. After further analysis, the silica-rich rocks on Mars were found to be tridymite , a mineral that is not commonly found on Earth. Opal-A , another form of silica, was also found on Mars. [ 169 ]
The second extended mission began on 1 October 2016. [ 171 ] The rover explored a ridge known as the Murray Formation for most of the mission.
As of 3 October 2016, NASA summarized the findings of the mission, thus far, as follows: "The Curiosity mission has already achieved its main goal of determining whether the landing region ever offered environmental conditions that would have been favorable for microbial life, if Mars has ever hosted life. The mission found evidence of ancient rivers and lakes, with a chemical energy source and all of the chemical ingredients necessary for life as we know it." [ 172 ] Plans for the next two years, up to September 2018, include further explorations of the uphill slopes of Mount Sharp , including a ridge rich in the mineral hematite and a region of clay-rich bedrock. [ 172 ]
On 13 December 2016, NASA reported further evidence supporting habitability on Mars as the Curiosity rover climbed higher, studying younger layers, on Mount Sharp. [ 173 ] Also reported, the very soluble element boron was detected for the first time on Mars. [ 173 ] Since landing on Mars in August 2012, Curiosity has driven 15.0 km (9.3 mi) and climbed 165 m (541 ft) in elevation. [ 170 ]
On 17 January 2017, NASA released an image of a rock slab, named "Old Soaker", which may contain mud cracks. Also, somewhat later, it released an animation of sand moving in a nearby area.
On 6 February 2017, NASA reported that rock samples analyzed by the rover have not revealed any significant carbonate . This poses a puzzle to researchers: the same rocks that indicate a lake existed also indicate there was very little carbon dioxide in the air to help keep the lake unfrozen. [ 174 ]
On 27 February 2017, NASA presented the following mission overview: "During the first year after Curiosity's 2012 landing in Gale Crater, the mission fulfilled its main goal by finding that the region once offered environmental conditions favorable for microbial life. The conditions in long-lived ancient freshwater Martian lake environments included all of the key chemical elements needed for life as we know it, plus a chemical source of energy that is used by many microbes on Earth. The extended mission is investigating how and when the habitable ancient conditions evolved into conditions drier and less favorable for life." [ 175 ]
From 3 to 7 May 2017, Curiosity used ChemCam to study what turned out to be manganese oxide deposits on the Sutton Island and Blunts Point layers of the Murray Formation. According to a 2024 paper, the deposits suggest Earth-level amounts of oxygen were present in the very early Martian atmosphere, hinting at microbial life. [ 176 ]
On 1 June 2017, NASA reported that the Curiosity rover provided evidence of an ancient lake in Gale crater on Mars that could have been favorable for microbial life ; the ancient lake was stratified , with shallows rich in oxidants and depths poor in oxidants, particularly silica ; the ancient lake provided many different types of microbe-friendly environments at the same time. NASA further reported that the Curiosity rover will continue to explore higher and younger layers of Mount Sharp in order to determine how the lake environment in ancient times on Mars became the drier environment in more modern times. [ 177 ] [ 178 ] [ 179 ]
Between 22 July – 1 August 2017, few commands were sent from the Earth to Mars since Mars was in conjunction with the sun. [ 180 ]
On 5 August 2017, NASA celebrated the fifth anniversary of the Curiosity rover mission landing, and related exploratory accomplishments, on the planet Mars . [ 181 ] [ 182 ] (Videos: Curiosity 's First Five Years (02:07) ; Curiosity 's POV: Five Years Driving (05:49) ; Curiosity 's Discoveries About Gale Crater (02:54) )
On 5 September 2017, scientists reported that the Curiosity rover detected boron , an essential ingredient for life on Earth , on the planet Mars. Such a finding, along with previous discoveries that water may have been present on ancient Mars, further supports the possible early habitability of Gale Crater on Mars. [ 183 ] [ 184 ]
On 13 September 2017, NASA reported that the Curiosity rover climbed an iron-oxide-bearing ridge called Vera Rubin Ridge (or Hematite Ridge ) and will now start studying the numerous bright veins embedded in the various layers of the ridge, in order to provide more details about the history and habitability of ancient Mars. [ 185 ]
On 30 September 2017, NASA reported radiation levels on the surface of the planet Mars were temporarily doubled , and were associated with an aurora 25-times brighter than any observed earlier, due to a massive, and unexpected, solar storm in the middle of the month. [ 186 ]
On 17 October 2017, NASA announced the testing of its systems on Curiosity in an attempt to better resume drilling. The drilling system had stopped working reliably in December 2016. [ 187 ]
On 2 January 2018, Curiosity captured images of rock shapes that may require further study in order to help better determine whether the shapes are biological or geological. [ 188 ] [ 189 ]
On 22 March 2018, Curiosity had spent 2000 sols (2054 days) on Mars, [ 190 ] and prepares to study a region of clay-bearing rocks.
In June 2018, a local dust storm occurred near the Opportunity rover which may affect Curiosity . [ 191 ] [ 192 ] The first signs of the storm, 1,000 km (620 mi) from Opportunity , were discovered on 1 June 2018, in photographs by the Mars Color Imager (MARCI) camera on the Mars Reconnaissance Orbiter (MRO). More weather reports from the MRO and the MARCI team indicated a prolonged storm. Although this was, at that time, still far away from the rover, it influenced the atmospheric permeability (opacity) at the location. Within days, the storm had spread. As of 12 June 2018, the storm spanned an area of 41 million km 2 (16 million sq mi) - about the area of North America and Russia combined. [ 191 ] [ 193 ] Although such dust storms are not surprising, they rarely occur. They can arise within a short time and then persist for weeks to months. During the southern season of summer, the sunlight heats dust particles and brings them higher into the atmosphere. This creates wind, which in turn stirs up more dust. This results in a feedback loop that scientists are still trying to understand. NASA reported on 20 June 2018, that the dust storm had grown to completely cover the entire planet. [ 194 ] [ 195 ]
On 4 June 2018, NASA announced that Curiosity 's ability to drill has been sufficiently restored by engineers. The rover had experienced drill mechanical problems since December 2016. [ 196 ]
On 7 June 2018, NASA announced a cyclical seasonal variation in atmospheric methane , as well as the presence of kerogen and other complex organic compounds . The organic compounds were from mudstone rocks aged approximately 3.5 billion years old, sampled from two distinct sites in a dry lake in the Pahrump Hills of the Gale crater . The rock samples, when pyrolyzed via the Curiosity ' s Sample Analysis at Mars instrument, released an array of organic molecules; these include sulfur-containing thiophenes , aromatic compounds such as benzene and toluene , and aliphatic compounds such as propane and butene . The concentration of organic compounds are 100-fold higher than earlier measurements. The authors speculate that the presence of sulfur may have helped preserve them. The products resemble those obtained from the breakdown of kerogen , a precursor to oil and natural gas on Earth. NASA stated that these findings are not evidence that life existed on the planet, but that the organic compounds needed to sustain microscopic life were present, and that there may be deeper sources of organic compounds on the planet. [ 197 ] [ 198 ] [ 199 ] [ 200 ] [ 201 ] [ 202 ] [ 203 ] [ 204 ]
Since 15 September 2018, a glitch in Curiosity 's active computer (Side-B) has prevented Curiosity from storing science and key engineering data. [ 205 ] On 3 October 2018, the JPL began operating Curiosity on its backup computer (Side-A). [ 205 ] Curiosity will store science and engineering data normally using its Side-A computer until the cause of the glitch in Side-B is determined and remedied. [ 205 ]
On 4 November 2018, geologists presented evidence, based on studies in Gale Crater by the Curiosity rover , that there was plenty of water on early Mars . [ 206 ] [ 207 ]
On 26 November 2018, Curiosity viewed a shiny object (named, "Little Colonsay") on Mars. [ 208 ] Although possibly a meteorite, further studies are planned to better understand its nature.
On 1 February 2019, NASA scientists reported that the Mars Curiosity rover determined, for the first time, the density of Mount Sharp in Gale crater , thereby establishing a clearer understanding of how the mountain was formed. [ 209 ] [ 210 ]
On 4 April 2019, NASA released images of solar eclipses by the two moons of the planet Mars , Phobos ( animation1 ) and Deimos ( animation2 ), as viewed by the Curiosity rover on the planet Mars in March 2019. [ 211 ] [ 212 ]
On 11 April 2019, NASA announced that the Curiosity rover on the planet Mars drilled into, and closely studied, a " clay-bearing unit " which, according to the rover Project Manager, is a "major milestone" in Curiosity 's journey up Mount Sharp . [ 213 ]
During June 2019, while still studying the clay-bearing unit, Curiosity detected the highest levels of methane gas, 21 parts per billion, compared to the typical 1 part per billion the rover detects as normal background readings. The levels of methane dropped quickly over a few days, leading NASA to call this event one of several methane plumes that they have observed before but without any observable pattern. The rover lacked the necessary instrumentation to determine if the methane was biological or inorganic in nature. [ 214 ] [ 215 ] [ 216 ]
The third extended mission began on 1 October 2019 - the rover's 2544th sol on Mars. [ 217 ] In October 2019, evidence in the form of magnesium sulfate deposits left behind in ways that suggested evaporation, uncovered by the Curiosity rover on Mount Sharp, was reported of a 150 km (93 mi) wide ancient basin in Gale crater that once may have contained a salty lake. [ 218 ] [ 219 ]
In January 2020, a report was presented that compared Curiosity at the time of its landing on Mars in 2012, with the rover over seven years later in 2020. [ 220 ]
In February 2020, scientists reported the detection of thiophene organic molecules by the Curiosity rover on the planet Mars . It is not currently known if the detected thiophenes — usually associated on Earth with kerogen , coal and crude oil — are the result of biological or non-biological processes. [ 221 ] [ 222 ]
In April 2020, scientists began operating the rover remotely from their homes due to the COVID-19 pandemic . [ 223 ]
On 29 August 2020, NASA released several videos taken by the Curiosity rover, including those involving dust devils , as well as very high resolution images of the related local martian terrain. [ 224 ]
In June 2021, scientists determined that the methane concentration around Curiosity varied according to the time of sol, with methane present only at night. This explains the difference in methane levels detected by Curiosity and the Trace Gas Orbiter (an open question since 2016), although it does not explain what is creating the methane or why the methane seems to be more short-lived than current models predict. [ 225 ] On 3 July 2021, the Curiosity rover viewed the " Rafael Navarro Mountain " area.
On 1 November 2021, astronomers reported detecting, in a "first-of-its-kind" process based on SAM instruments , organic molecules , including benzoic acid , ammonia and other related unknown compounds, on the planet Mars by the Curiosity rover. [ 226 ] [ 227 ]
On 17 January 2022, scientists reported finding an unusual signal of carbon isotopes on Mars by the Curiosity rover which may (or may not) be associated with ancient Martian life and suggesting, according to the scientists, that microbes residing underground may have emitted the "enriched carbon as methane gas". However, abiotic sources of the unusual carbon signal have not been completely ruled out. [ 228 ] [ 229 ] [ 230 ]
In April 2022, Mars Science Laboratory was renewed for a fourth extended mission, which will include the exploration of the sulfate-bearing unit. [ 231 ]
The rover began its fourth extended mission on 1 October 2022, which will last until October 2025. [ 232 ]
In January 2023, the Curiosity Rover viewed and studied the "Cacao" meteorite.
In August 2023, Curiosity explored the upper Gediz Vallis Ridge . [ 233 ] [ 234 ] A panoramic view of the ridge is here , and a 3D rendered view is here .
In February 2024, Curiosity completed its 40th successful drilling, [ 235 ] [ 236 ] of a rock named "Mineral King" in Gediz Vallis.
In July 2024, it was announced that, in an analysis of a rock that had been crushed by the rover (one in a series of deposits), elemental pure sulfur had been found on Mars for the first time. [ 237 ] [ 238 ]
In October 2024, the science team behind the SAM experiment onboard the rover announced the results of three years of sampling, which suggested that based on high carbon-13 and oxygen-18 levels in the regolith, the early Martian atmosphere was unlikely to be stable enough to support surface water hospitable to life, with rapid wetting-drying cycles and very high-salinity cryogenic brines providing an explanation. [ 239 ] [ 240 ]
In March 2025 it was published that Curiosity discovered long chain alkanes with up to 12 consecutive carbon atoms, in mudstone in Gale crater. The origin of these molecules is unknown. They could be derived from either abiotic or biological sources. [ 241 ]
In the spring of 2025, NASA announced that Curiosity had found carbonates in the form of crystalline siderite (FeCO3). One rock contained over 10 % of the mineral. These were expected on Mars due to the carbon dioxide atmosphere. Not many carbonated were detected from orbit because they may be obscured by dust. The rocks also were composed of plagioclase with the elements sodium (Na)–, Ca-, and aluminum (Al)–, as well as Ca- and Mg-bearing silicate mineral pyroxene. Other minerals found were calcium sulfates, magnesium sulfates, different amounts of iron oxyhydroxides, and an unidentified X-ray amorphous material. Rover’s Chemistry and Mineralogy (CheMin) instrument uses X-ray diffraction to determine sample mineralogy. The names of the rock formations and drill sites are CA, Canaima; TC, Tapo Caparo; UB, Ubajara; and SQ, Sequoia. [ 242 ]
As of May 18, 2025, Curiosity has been on the planet Mars for 4543 sols (4668 total days ) since landing on 6 August 2012. Since 11 September 2014, Curiosity has been exploring the slopes of Mount Sharp , [ 143 ] [ 144 ] where more information about the history of Mars is expected to be found. [ 103 ] As of 26 January 2021, the rover has traveled over 24.15 km (15.01 mi) and climbed over 327 m (1,073 ft) in elevation [ 145 ] [ 170 ] [ 245 ] to, and around, the mountain base since arriving at Bradbury Landing in August 2012. [ 145 ] [ 170 ]
Since early 2015, the percussive mechanism in the drill that chisels into rock has had an intermittent electrical short circuit . [ 246 ]
In December 2016, the motor inside the drill caused a malfunction that prevented the rover from moving its robotic arm and driving to another location. [ 247 ] The fault is in the drill feed motor - internal debris is suspected. [ 246 ] The fault was determined to be limited to the drill mechanism and the rover started moving again on 9 December. The robotic arm is functional, and the Curiosity team performed diagnostics on the drill mechanism throughout 2017. [ 248 ] On 4 June 2018, NASA announced that Curiosity 's ability to drill has been sufficiently restored by changing the drilling methods. [ 196 ]
Since 15 September 2018, a glitch in Curiosity 's active computer (Side-B) has prevented Curiosity from storing science and key engineering data. [ 205 ] On 3 October 2018, the JPL began operating Curiosity on its backup computer (Side-A). [ 205 ] Curiosity will store science and engineering data normally using its Side-A computer until the cause of the glitch in Side-B is determined and remedied. [ 205 ] | https://en.wikipedia.org/wiki/Timeline_of_Mars_Science_Laboratory |
The following is a timeline of Solar System astronomy and science . It includes the advances in the knowledge of the Earth at planetary scale , as part of it.
Humans ( Homo sapiens ) have inhabited the Earth in the last 300,000 years at least, [ 1 ] and they had witnessed directly observable astronomical and geological phenomena. For millennia, these have arose admiration and curiosity, being admitted as of superhuman nature and scale. Multiple imaginative interpretations were being fixed in oral traditions of difficult dating, and incorporated into a variety of belief systems , as animism , shamanism , mythology , religion and/or philosophy .
Although such phenomena are not " discoveries " per se , as they are part of the common human experience, their observation shape the knowledge and comprehension of the world around us, and about its position in the observable universe , in which the Sun plays a role of outmost importance for us. What today is known to be the Solar System was regarded for generations as the contents of the "whole universe ".
The most relevant phenomena of these kind are:
Along with an indeterminate number of unregistered sightings of rare events: meteor impacts ; novae and supernovae .
The number of currently known, or observed, objects of the Solar System are in the hundreds of thousands. Many of them are listed in the following articles:
Solar System → Local Interstellar Cloud → Local Bubble → Gould Belt → Orion Arm → Milky Way → Milky Way subgroup → Local Group → Local Sheet → Virgo Supercluster → Laniakea Supercluster → Local Hole → Observable universe → Universe Each arrow ( → ) may be read as "within" or "part of". | https://en.wikipedia.org/wiki/Timeline_of_Solar_System_astronomy |
This is a timeline of Solar System exploration ordering events in the exploration of the Solar System by date of spacecraft launch.
It includes:
It does not include:
The dates listed are launch dates, but the achievements noted may have occurred some time later—in some cases, a considerable time later (for example, Voyager 2 , launched 20 August 1977, did not reach Neptune until 1989).
(including MAPP LV1, Micro-Nova, AstroAnt and Yaoki rover)
Solar System → Local Interstellar Cloud → Local Bubble → Gould Belt → Orion Arm → Milky Way → Milky Way subgroup → Local Group → Local Sheet → Virgo Supercluster → Laniakea Supercluster → Local Hole → Observable universe → Universe Each arrow ( → ) may be read as "within" or "part of". | https://en.wikipedia.org/wiki/Timeline_of_Solar_System_exploration |
This timeline lists notable events in the history of research into senescence or biological aging , including the research and development of life extension methods , brain aging delay methods and rejuvenation .
People have long been interested in making their lives longer and healthier. The most anсient Egyptian, Indian and Chinese books contain reasoning about aging. Ancient Egyptians used garlic in large quantities to extend their lifespan. Hippocrates ( c. 460 – c. 370 BCE ), in his Aphorisms , and Aristotle ( 384 – 322 BCE), in On youth and old age , expressed their opinions about reasons for old age and gave advice about lifestyle. Medieval Persian physician Ibn Sina ( c. 980 – 1037), known in the West as Avicenna, summarized the achievements of earlier generations about this issue. [ 1 ] [ 2 ] [ 3 ]
Descriptions of rejuvenation and immortality remedies are often found in the writings of alchemists. But all those remedies did not allow even alchemists themselves to live longer than a hundred years. [ 1 ] [ 2 ] [ 3 ]
Though the average lifespan of people through the past millennia increased significantly, [ 4 ] maximum lifespan almost did not change - even in ancient times there were fairly well and unbiasedly documented cases when some people lived for more than a hundred years (for example, Terentia who lived 103 or 104 years). While among the billions of people of the modern world, there is only one case of life over 120 years ( Jeanne Calment , 122 years). The super-long lives of people that are mentioned in ancient books, apparently, are highly exaggerated, since archaeological data show that even the oldest of the ancient people lived no more than modern supercentenarians . [ 2 ] In some cases the exaggeration, possibly, is not intentional but occurs due to errors in translation between languages and synchronization of chronological systems. The species limit of human life is estimated by scientists at 125–127 years, [ 5 ] [ 6 ] and even in the most ideal conditions a person will not live longer due to aging of the body.
Some scientists believe that, even if medicine learns how to treat all major diseases, that will increase the average lifespan of people in developed countries by only about 10 years. [ 2 ] For example, biogerontologist Leonard Hayflick stated that the natural average lifespan for humans is 92 years. [ 7 ] Meanwhile, the life expectancy for Japanese already now is more than 84 years, [ 8 ] and for Monaco it is reported to be more than 89 years. [ 9 ] It may not be possible to achieve further increases without development of new biomedical technologies and approaches. Searches of various equivalents of the elixir of youth happened yet in ancient times: people hoped to find a miraculous remedy in faraway territories, tried to use magic and alchemy. Scientific and technological attempts began at the end of the 19th century. For their intended purpose, all of them turned out to be inefficient at best, sometimes led to premature death, but they had many useful and sometimes unexpected consequences.
From the end of the 19th century, systematic scientific and technical studies began on the processes of slowing down aging and possible rejuvenation. The period of world history between the two world wars is a very complicated, difficult and ambiguous time of world history. In many spheres of life, there were ideas that were radical-bold, but not always intelligent, ethical and moral from the point of view of modern knowledge, foundations and norms. This also affected the aging research, the spirit of which corresponded to the spirit of that time: attempting bold experiments, often on people, intensively implementing in practice treatments that we may now consider ridiculous. Those attempts had both bad and good consequences. But those researches were already scientific. As it often happens in science, it is often difficult to establish priority considering, who was the first person beginning to use one or another approach. Usually the first experiments are done by enthusiasts and have doubtful positive effects. Some researchers work in parallel. Then at some moment the persons emerge who developed the approaches and made them public.
After World War II , research tools and technologies of another level appeared. Thanks to these technologies, it became understandable what really occurs inside cells and between them (for example, the model of the DNA double helix was created in 1953). At the same time, changed ethical norms did not allow cardinal experiments to be performed on humans, as had been possible in previous decades. Consequently, the influence of different factors could be estimated only indirectly.
The research activity has increased. There is a shift of focus of the scientific community from the passive study of aging and theorizing to research aimed at intervening in the aging process to extend the lives of organisms beyond their genetic limits . Scientific-commercial companies appear, which aim to create practical technologies for measuring the biological age of a person (in contrast to chronological age) and extend the life of people to a greater extend than the healthy lifestyle and preventive medicine can provide. In society and media there are discussions not only about whether a significant prolongation of life is physically possible, but also whether it is appropriate, about the possibility of officially classifying aging as a disease, and about the possibility of mass testing on human volunteers.
Research domains related or part of senescence research currently not fully included in the timeline:
Notable events in these fields of research that relate to life extension and healthspan are currently deliberately not included in this timeline | https://en.wikipedia.org/wiki/Timeline_of_aging_research |
The following is a timeline of key developments of algebra : | https://en.wikipedia.org/wiki/Timeline_of_algebra |
This is a timeline of mathematicians in ancient Greece .
Historians traditionally place the beginning of Greek mathematics proper to the age of Thales of Miletus (ca. 624–548 BC), which is indicated by the green line at 600 BC. The orange line at 300 BC indicates the approximate year in which Euclid 's Elements was first published. The red line at 300 AD passes through Pappus of Alexandria ( c. 290 – c. 350 AD ), who was one of the last great Greek mathematicians of late antiquity . Note that the solid thick black line is at year zero , which is a year that does not exist in the Anno Domini (AD) calendar year system
The mathematician Heliodorus of Larissa is not listed due to the uncertainty of when he lived, which was possibly during the 3rd century AD, after Ptolemy . Also not listed is the 1st century AD mathematician Dionysodorus of Amisene (not to be confused with Dionysodorus of Caunus ), Pandrosion from the 4th century AD, Hermotimus of Colophon (born c. 325 BC), Metrodorus from likely the 6th century AD (though he may have lived as early as the 3rd century AD), and Apollodorus Logisticus and Proclus of Laodicea .
Of these mathematicians, those whose work stands out include:
The conquests of Alexander the Great around c. 330 BC led to Greek culture being spread around much of the Mediterranean region, especially in Alexandria, Egypt . This is why the Hellenistic period of Greek mathematics is typically considered as beginning in the 4th century BC. During the Hellenistic period, many people living in those parts of the Mediterranean region subject to Greek influence ended up adopting the Greek language and sometimes also Greek culture. Consequently, some of the Greek mathematicians from this period may not have been "ethnically Greek" with respect to the modern Western notion of ethnicity , which is much more rigid than most other notions of ethnicity that existed in the Mediterranean region at the time. Ptolemy , for example, was said to have originated from Upper Egypt , which is far South of Alexandria, Egypt . Regardless, their contemporaries considered them Greek. | https://en.wikipedia.org/wiki/Timeline_of_ancient_Greek_mathematicians |
This is the timeline of modern [ clarification needed ] antimicrobial [ clarification needed ] (anti-infective) therapy.
The years show when a given drug was released onto the pharmaceutical
market. This is not a timeline of the development of the antibiotics themselves. | https://en.wikipedia.org/wiki/Timeline_of_antibiotics |
Timeline of astronomical maps , catalogs and surveys | https://en.wikipedia.org/wiki/Timeline_of_astronomical_maps,_catalogs,_and_surveys |
This is a timeline of astronomy . It covers ancient, medieval, Renaissance-era, and finally modern astronomy.
Mayan astronomers discover an 18.7-year cycle in the rising and setting of the Moon . From this they created the first almanacs – tables of the movements of the Sun, Moon, and planets for the use in astrology . In 6th century BC Greece, this was also discovered
Thales of Miletus is said to have predicted a solar eclipse . He said "it will happen today."
Anaxagoras produced a correct explanation for eclipses and then described the Sun as a fiery mass larger than the Peloponnese , as well as attempting to explain rainbows and meteors . He was the first to explain that the Moon shines due to reflected light from the Sun. [ 1 ] [ 2 ] [ 3 ]
Around this date, Babylonians use the zodiac to divide the heavens sexagesimally into twelve equal segments of thirty degrees each, the better to record and communicate information about the position of celestial bodies. [ 4 ]
Plato , a Greek philosopher, founds a school (the Platonic Academy ) that will influence the next 2000 years. Borrowing and expanding from Pythagoreanism , it promotes the idea that everything in the universe moves in harmony and that the Sun, Moon, and planets move around Earth in perfect circles. [ 5 ]
Aristotle , a Greek polymath, described motion of physical objects based on their affinity with one of four classical elements : earth, water, air, or fire. [ 6 ]
The astronomer Shi Shen is believed to have cataloged 809 stars in 122 constellations, and he also made the earliest known observation of sunspots. [ 7 ]
Aristarchus of Samos proposes heliocentrism as an alternative to the Earth-centered universe. His heliocentric model places the Sun at its center, with Earth as just one planet orbiting it. However, there were only a few people who took the theory seriously.
The earliest recorded sighting of Halley's Comet is made by Chinese astronomers. Their records of the comet's movement allow astronomers today to predict accurately how the comet's orbit changes over the centuries.
Hipparchus incidentally discovered of the precession of the equinoxes.
Vitruvius explains that an object’s fall speed depends on their specific gravity . [ 8 ] [ 9 ] [ failed verification ]
Ptolemy publishes his star catalogue , listing 48 constellations and endorses the geocentric (Earth-centered) view of the universe. His views go unquestioned for nearly 1500 years in Europe and are passed down to Arabic and medieval European astronomers in his book the Almagest . He also proposed astronomical calculation of the sidereal revolution of planets.
The Hindu cosmological time cycles explained in the Surya Siddhanta , give the average length of the sidereal year (the length of the Earth's revolution around the Sun) as 365.2563627 days, which is only 1.4 seconds longer than the modern value of 365.256363004 days. [ 10 ] This remains the most accurate estimate for the length of the sidereal year anywhere in the world for over a thousand years.
Indian mathematician-astronomer Aryabhata , in his Aryabhatiya first explain the elliptical model of the planets, where the planets spin on their axis and follow elliptical orbits, the Sun and the Moon revolve around the Earth in epicycles . He also writes that the planets and the Moon do not have their own light but reflect the light of the Sun and that the Earth rotates on its axis causing day and night and also that the Sun rotates around the Earth causing years. [ 11 ]
Indian mathematician-astronomer Brahmagupta , in his Brāhmasphuṭasiddhānta , first recognizes gravity as a force of attraction. He gives methods for calculations of the motions and places of various planets, their rising and setting, conjunctions, and calculations of the solar and lunar eclipses.
The Sanskrit works of Aryabhata and Brahmagupta , along with the Sanskrit text Surya Siddhanta , are translated into Arabic , introducing Arabic astronomers to Indian astronomy .
Muḥammad ibn Ibrāhīm al-Fazārī and Yaʿqūb ibn Ṭāriq translate the Surya Siddhanta and Brahmasphutasiddhanta , and compile them as the Zij al-Sindhind , the first Zij treatise. [ 12 ]
The first major Arabic work of astronomy is the Zij al-Sindh by Muhammad ibn Musa al-Khwarizmi . The work contains tables for the movements of the Sun, the Moon, and the five planets known at the time. The work is significant as it introduced Ptolemaic concepts into Islamic sciences. This work also marks the turning point in Arabic astronomy. Hitherto, Arabic astronomers had adopted a primarily research approach to the field, translating works of others and learning already discovered knowledge. Al-Khwarizmi's work marked the beginning of nontraditional methods of study and calculations. [ 13 ]
al-Farghani wrote Kitab fi Jawani (" A compendium of the science of stars "). The book primarily gave a summary of Ptolemic cosmography. However, it also corrected Ptolemy based on findings of earlier Arab astronomers. Al-Farghani gave revised values for the obliquity of the ecliptic, the precessional movement of the apogees of the Sun and the Moon, and the circumference of the Earth. The books were widely circulated through the Muslim world and even translated into Latin . [ 14 ]
The earliest surviving astrolabe is constructed by astronomer Nastulus . [ 15 ]
Al-Biruni discussed the Indian geocentric theories of Aryabhata , Brahmagupta and Varāhamihira in his Ta'rikh al-Hind ( Indica in Latin). Biruni stated that the followers of Aryabhata consider the Earth to be at the center. In fact, Biruni casually stated that this does not create any mathematical problems. [ 16 ]
Al-Sijzi , a contemporary of Al-Biruni , defended the theory that Earth rotates on its axis.
Chinese astronomers record the sudden appearance of a bright star . Native-American rock carvings also show the brilliant star close to the Moon. This star is the Crab supernova exploding.
Abu Ubayd al-Juzjani published the Tarik al-Aflak . In his work, he indicated the so-called " equant " problem of the Ptolemic model . Al-Juzjani even proposed a solution to the problem. In al-Andalus , the anonymous work al-Istidrak ala Batlamyus (meaning "Recapitulation regarding Ptolemy"), included a list of objections to the Ptolemic astronomy.
One of the most important works in the period was Al-Shukuk ala Batlamyus (" Doubts on Ptolemy "). In this, the author summed up the inconsistencies of the Ptolemic models. Many astronomers took up the challenge posed in this work, namely to develop alternate models that evaded such errors.
Islamic and Indian astronomical works (including Aryabhatiya and Brahma-Sphuta-Siddhanta ) are translated into Latin in Córdoba, Spain in 1126, introducing European astronomers to Islamic and Indian astronomy.
Indian mathematician-astronomer Bhāskara II , in his Siddhanta Shiromani , calculates the longitudes and latitudes of the planets, lunar and solar eclipses, risings and settings, the Moon's lunar crescent , syzygies , and conjunctions of the planets with each other and with the fixed stars , and explains the three problems of diurnal rotation . He also calculates the planetary mean motion , ellipses, first visibilities of the planets, the lunar crescent, the seasons, and the length of the Earth's revolution around the Sun to 9 decimal places.
Nur ad-Din al-Bitruji proposed an alternative geocentric system to Ptolemy's. He also declared the Ptolemaic system as mathematical, and not physical. His alternative system spread through most of Europe during the 13th century, with debates and refutations of his ideas continued to the 16th century. [ 17 ] [ 18 ]
Mu'ayyad al-Din al-Urdi develops the Urdi lemma, which is later used in the Copernican heliocentric model.
Nasir al-Din al-Tusi resolved significant problems in the Ptolemaic system by developing the Tusi-couple as an alternative to the physically problematic equant introduced by Ptolemy. [ 19 ] His Tusi-couple is later used in the Copernican model.
Tusi's student Qutb al-Din al-Shirazi , in his The Limit of Accomplishment concerning Knowledge of the Heavens , discusses the possibility of heliocentrism.
Najm al-Din al-Qazwini al-Katibi , who also worked at the Maraghah observatory, in his Hikmat al-'Ain , wrote an argument for a heliocentric model, though he later abandoned the idea. [ citation needed ]
Ibn al-Shatir (1304–1375), in his A Final Inquiry Concerning the Rectification of Planetary Theory , eliminated the need for an equant by introducing an extra epicycle, departing from the Ptolemaic system in a way very similar to what Copernicus later also did. Ibn al-Shatir proposed a system that was only approximately geocentric, rather than exactly so, having demonstrated trigonometrically that the Earth was not the exact center of the universe. His rectification is later used in the Copernican model.
Nilakantha Somayaji proposes a model very similar to the Tychonic system and his equation for the centre for the planets Mercury and Venus were the most accurate until Johannes Kepler
Nicolaus Copernicus publishes De revolutionibus orbium coelestium containing his theory that Earth travels around the Sun. However, he complicates his theory by retaining Plato's perfect circular orbits of the planets.
A brilliant supernova ( SN 1572 – thought at the time to be a comet) is observed by Tycho Brahe , who proves that it is traveling beyond Earth's atmosphere and therefore provides the first evidence that the heavens can change.
Dutch eyeglass maker Hans Lippershey tries to patent a refracting telescope (the first historical record of one). The invention spreads rapidly across Europe, as scientists make their own instruments. Their discoveries begin a revolution in astronomy.
Johannes Kepler publishes his New Astronomy . In this and later works, he announces his three laws of planetary motion , replacing the circular orbits of Plato with elliptical ones. Almanacs based on Johannes' laws prove to be highly accurate.
Galileo Galilei publishes Sidereus Nuncius describing the findings of his observations with the telescope he built. These include spots on the Sun, craters on the Moon, and four satellites of Jupiter. Proving that not everything orbits Earth, he promotes the Copernican view of a Sun-centered universe.
As the power and the quality of the telescopes increase, Christiaan Huygens studies Saturn and discovers its largest satellite, Titan. He also explains Saturn's appearance, suggesting the planet is surrounded by a thin ring.
Scottish astronomer James Gregory describes his " gregorian " reflecting telescope , using parabolic mirrors instead of lenses to reduce chromatic aberration and spherical aberration , but is unable to build one.
Isaac Newton builds the first reflecting telescope , his Newtonian telescope .
Isaac Newton publishes his first copy of the book Philosophiae Naturalis Principia Mathematica , establishing the theory of gravitation and laws of motion. The Principia explains Kepler's laws of planetary motion and allows astronomers to understand the forces acting between the Sun, the planets, and their moons.
Edmond Halley calculates that the comets recorded at 76-year intervals from 1456 to 1682 are one and the same. He predicts that the comet will return again in 1758. When it reappears as expected, the comet is named in his honor.
French astronomer Nicolas de Lacaille sails to southern oceans and begins work compiling a catalog of more than 10,000 stars in the southern sky. Although Halley and others have observed from the Southern Hemisphere before, Lacaille's star catalog is the first comprehensive one of the southern sky.
Amateur astronomer William Herschel discovers the planet Uranus, although he at first mistakes it for a comet. Uranus is the first planet to be discovered beyond Saturn, which was thought to be the most distant planet in ancient times.
Charles Messier publishes his catalog of star clusters and nebulas. Messier draws up the list to prevent these objects from being identified as comets. However, it soon becomes a standard reference for the study of star clusters and nebulas and is still in use today.
William Herschel splits sunlight through a prism and with a thermometer, measures the energy given out by different colours. He notices a sudden increase in energy beyond the red end of the spectrum , discovering invisible infrared and laying the foundations of spectroscopy.
Italian astronomer Giuseppe Piazzi discovers what appears to be a new planet orbiting between Mars and Jupiter, and names it Ceres . William Herschel proves it is a very small object, calculating it to be only 320 km in diameter, and not a planet. He proposes the name asteroid, and soon other similar bodies are being found. We now know that Ceres is 932 km in diameter, and is now considered to be a dwarf planet.
Joseph von Fraunhofer builds the first accurate spectrometer and uses it to study the spectrum of the Sun's light. He discovers and maps hundreds of fine dark lines crossing the solar spectrum. In 1859 these lines are linked to chemical elements in the Sun's atmosphere. Spectroscopy becomes a method for studying what stars are made of.
Friedrich Bessel successfully uses the method of stellar parallax, the effect of Earth's annual movement around the Sun, to calculate the distance to 61 Cygni , the first star other than the Sun to have its distance from Earth measured. Bessel's is a truly accurate measurement of stellar positions, and the parallax technique establishes a framework for measuring the scale of the universe.
German amateur astronomer Heinrich Schwabe , who had been studying the Sun for the past 17 years, announces his discovery of a regular cycle in sunspot numbers - the first clue to the Sun's internal structure.
Irish astronomer William Parsons, 3rd Earl of Rosse completes the first of the world's great telescopes , with a 180-cm mirror. He uses it to study and draw the structure of nebulas, and within a few months discovers the spiral structure of the Whirlpool Galaxy .
French physicists Jean Foucault and Armand Fizeau take the first detailed photographs of the Sun's surface through a telescope - the birth of scientific astrophotography. Within five years, astronomers produce the first detailed photographs of the Moon. Early film is not sensitive enough to image stars.
A new planet, Neptune , is identified by German astronomer Johann Gottfried Galle while searching in the position suggested by Urbain Le Verrier . Le Verrier has calculated the position and size of the planet from the effects of its gravitational pull on the orbit of Uranus. An English mathematician, John Couch Adams , also made a similar calculation a year earlier.
Astronomers notice a new bright emission line in the spectrum of the Sun's atmosphere during an eclipse. The emission line is caused by an element's giving out light, and British astronomer Norman Lockyer concludes that it is an element unknown on Earth. He calls it helium , from the Greek word for the Sun. Nearly 30 years later, helium is found on Earth.
An American astronomer Henry Draper takes the first photograph of the spectrum of a star (Vega), showing absorption lines that reveal its chemical makeup. Astronomers begin to see that spectroscopy is the key to understanding how stars evolve. William Huggins uses absorption lines to measure the redshifts of stars, which give the first indication of how fast stars are moving.
Konstantin Tsiolkovsky publishes his first article on the possibility of space flight. His greatest discovery is that a rocket, unlike other forms of propulsion, will work in a vacuum. He also outlines the principle of a multistage launch vehicle.
A comprehensive survey of stars, the Henry Draper Catalogue , is published. In the catalog, Annie Jump Cannon proposes a sequence of classifying stars by the absorption lines in their spectra, which is still in use today.
Ejnar Hertzsprung establishes the standard for measuring the true brightness of a star. He shows that there is a relationship between color and absolute magnitude for 90% of the stars in the Milky Way Galaxy. In 1913, Henry Norris Russell published a diagram that shows this relationship. Although astronomers agree that the diagram shows the sequence in which stars evolve, they argue about which way the sequence progresses. Arthur Eddington finally settles the controversy in 1924.
Williamina Fleming publishes her discovery of white dwarf stars.
Henrietta Swan Leavitt discovers the period-luminosity relation for Cepheid variables , where the intrinsic brightness of a star is proportional to its luminosity oscillation period. It opened a whole new branch of possibilities of measuring distances on the universe, and this discovery was the basis for the work done by Edwin Hubble on extragalactic astronomy.
German physicist Karl Schwarzschild uses Albert Einstein 's theory of general relativity to lay the groundwork for black hole theory. He suggests that if any star collapse to a certain size or smaller, its gravity will be so strong that no form of radiation will escape from it.
Edwin Hubble discovers a Cepheid variable star in the "Andromeda Nebula" and proves that Andromeda and other nebulas are galaxies far beyond our own. By 1925, he produces a classification system for galaxies.
Cecilia Payne-Gaposchkin discovers that hydrogen is the most abundant element in the Sun's atmosphere, and accordingly, the most abundant element in the universe by relating the spectral classes of stars to their actual temperatures and by applying the ionization theory developed by Indian physicist Meghnad Saha . This opens the path for the study of stellar atmospheres and chemical abundances, contributing to understand the chemical evolution of the universe.
Robert Goddard launches the first rocket powered by liquid fuel. He also demonstrates that a rocket can work in a vacuum. His later rockets break the sound barrier for the first time.
Edwin Hubble discovered that the universe is expanding and that the farther away a galaxy is, the faster it is moving away from us. Two years later, Georges Lemaître suggests that the expansion can be traced to an initial "Big Bang".
By applying new ideas from subatomic physics, Subrahmanyan Chandrasekhar predicts that the atoms in a white dwarf star of more than 1.44 solar masses will disintegrate, causing the star to collapse violently. In 1933, Walter Baade and Fritz Zwicky describe the neutron star that results from this collapse, causing a supernova explosion.
Clyde Tombaugh discovers the dwarf planet Pluto at the Lowell Observatory in Flagstaff, Arizona. The object is so faint and moving so slowly that he has to compare photos taken several nights apart.
Karl Jansky detects the first radio waves coming from space. In 1942, radio waves from the Sun are detected. Seven years later radio astronomers identify the first distant source – the Crab Nebula, and the galaxies Centaurus A and M87.
German physicist Hans Bethe explains how stars generate energy. He outlines a series of nuclear fusion reactions that turn hydrogen into helium and release enormous amounts of energy in a star's core. These reactions use the star's hydrogen very slowly, allowing it to burn for billions of years.
A team of German scientists led by Wernher von Braun develops the V-2 , the first rocket-powered ballistic missile. Scientists and engineers from Braun's team were captured at the end of World War II and drafted into the American and Soviet rocket programs.
The US sent up the first animals in space although not into orbit, through a V-2 rocket launched from White Sands Missile Range , New Mexico . The animals were fruit flies . [ 20 ] [ 21 ] [ 22 ]
The largest telescope in the world, with a 5.08m (200 in) mirror, is completed at Palomar Mountain in California. At the time, the telescope pushes single-mirror telescope technology to its limits – large mirrors tend to bend under their own weight.
The Soviet Union launches the first artificial satellite, Sputnik 1, into orbit, beginning the space age. The US launches its first satellite, Explorer 1, four months later.
July 29 marks the beginning of the NASA (National Aeronautics and Space Administration), agency newly created by the United States to catch up with Soviet space technologies. It absorbs all research centers and staffs of the NACA (National Advisory Committee for Aeronautics), an organization founded in 1915.
The USSR and the US both launch probes to the Moon, but NASA's Pioneer probes all failed. The Soviet Luna program was more successful. Luna 2 crash-lands on the Moon's surface in September, and Luna 3 returns the first pictures of the Moon's farside in October.
Cornell University astronomer Frank Drake performed the first modern SETI experiment, named " Project Ozma ", after the Queen of Oz in L. Frank Baum 's fantasy books. [ 23 ]
As part of NASA's Mercury-Redstone 2 mission, the chimpanzee Ham becomes the first Hominidae in space. Yuri Gagarin becomes the first person to orbit Earth in April. NASA astronaut Alan Shepard becomes the first American in space a month later, but does not go into orbit. [ 24 ]
John Glenn becomes the first American to orbit Earth. Mariner 2 becomes the first probe to reach another planet, flying past Venus in December. NASA follows this with the successful Mariner 4 mission to Mars in 1965, both the US and the USSR send many more probes to planets through the rest of the 1960s and 1970s.
Dutch-American astronomer Maarten Schmidt measures the spectra of quasars, the mysterious star-like radio sources discovered in 1960. He establishes that quasars are active galaxies, and among the most distant objects in the universe.
Arno Penzias and Robert Wilson announce the discovery of a weak radio signal coming from all parts of the sky. Scientists figure out that this must be emitted by an object at a temperature of −270 °C. Soon it is recognized as the remnant of the very hot radiation from the Big Bang that created the universe 13 billion years ago, see Cosmic microwave background .
Soviet Luna 9 probe makes the first successful soft landing on the Moon in January, while the US lands the far more complex Surveyor missions, which follows up to NASA's Ranger series of crash-landers, scout sites for possible crewed landings.
Jocelyn Bell Burnell and Antony Hewish detected the first pulsar, an object emitting regular pulses of radio waves. Pulsars are eventually recognized as rapidly spinning neutron stars with intense magnetic fields - the remains of a supernova explosion.
NASA's Apollo 8 mission becomes the first human spaceflight mission to enter the gravitational influence of another celestial body and to orbit it.
The US wins the race for the Moon as Neil Armstrong and Buzz Aldrin step onto the lunar surface on July 20. Apollo 11 is followed by five further landing missions, three carrying a sophisticated Lunar Roving Vehicle .
The Uhuru satellite , designed to map the sky at X-ray wavelengths, is launched by NASA. The existence of X-rays from the Sun and a few other stars has already been found using rocket-launched experiments, but Uhuru charts more than 300 X-ray sources, including several possible black holes.
The USSR launches its first space station Salyut 1 into orbit. It is followed by a series of stations, culminating with Mir in 1986. A permanent platform in orbit allows cosmonauts to carry out serious research and to set a series of new duration records for spaceflight.
Charles Thomas Bolton was the first astronomer to present irrefutable evidence of the existence of a black hole .
The Soviet probe Venera 9 lands on the surface of Venus and sends back the first picture of its surface. The first probe to land on another planet, Venera 7 in 1970, had no camera. Both break down within an hour in the hostile atmosphere.
NASA's Viking 1 and Viking 2 space probes arrive at Mars. Each Viking mission consists of an orbiter, which photographs the planet from above, and a lander, which touches down on the surface, analyzes the rocks, and searches unsuccessfully for life.
On August 20 the Voyager 2 space probe launched by NASA to study the Jovian system , Saturnian system , Uranian system , Neptunian system , the Kuiper belt , the heliosphere and the interstellar space .
On September 5 The Voyager 1 space probe launched by NASA to study the Jovian system , Saturnian system and the interstellar medium .
Space Shuttle Columbia , the first of NASA's reusable Space Shuttles , makes its maiden flight, ten years in development, the Shuttle will make space travel routine and eventually open the path for a new International Space Station.
The first infrared astronomy satellite, IRAS , is launched. It must be cooled to extremely low temperatures with liquid helium, and it operates for only 300 days before the supply of helium is exhausted. During this time it completes an infrared survey of 98% of the sky.
NASA's spaceflight program comes to a halt when Space Shuttle Challenger explodes shortly after launch. A thorough inquiry and modifications to the rest of the fleet kept the shuttles on the ground for nearly three years.
The returning Halley's Comet is met by a fleet of five probes from the USSR, Japan, and Europe. The most ambitious is the European Space Agency's Giotto spacecraft, which flies through the comet's coma and photographs the nucleus.
The Magellan probe, launched by NASA, arrives at Venus and spends three years mapping the planet with radar. Magellan is the first in a new wave of probes that include Galileo , which arrives at Jupiter in 1995, and Cassini which arrives at Saturn in 2004.
The Hubble Space Telescope , the first large optical telescope in orbit, is launched using the Space Shuttle , but astronomers soon discovered that it is crippled by a problem with its mirror. A complex repair mission in 1993 allows the telescope to start producing spectacular images of distant stars, nebulae, and galaxies.
The Cosmic Background Explorer satellite produces a detailed map of the background radiation remaining from the Big Bang . The map shows "ripples", caused by slight variations in the density of the early universe – the seeds of galaxies and galaxy clusters.
The 10-meter Keck telescope on Mauna Kea, Hawaii, is completed. The first revolutionary new wave of telescopes, the Keck's main mirror is made of 36 six-sided segments, with computers to control their alignment. New optical telescopes also make use of interferometry – improving resolution by combining images from separate telescopes.
The first exoplanet , 51 Pegasi b , is discovered by Michel Mayor and Didier Queloz .
Construction work on a huge new space station named ISS has begun. A joint venture between many countries, including former space rivals Russia and the US.
The accelerated expansion was discovered during 1998, by two independent projects, the Supernova Cosmology Project and the High-Z Supernova Search Team, which both used distant type Ia supernovae to measure the acceleration.
Space Shuttle Columbia disintegrates upon reentry into Earth's atmosphere
Mike Brown and his team discovered Eris a large body in the outer Solar System [ 25 ] which was temporarily named as (2003) UB 313 . Initially, it appeared larger than Pluto and was called the tenth planet. [ 26 ]
International Astronomical Union (IAU) adopted a new definition of planet . A new distinct class of objects called dwarf planets was also decided. Pluto was redefined as a dwarf planet along with Ceres and Eris , formerly known as (2003) UB 313 . Eris was named after the IAU General Assembly in 2006. [ 27 ] [ 28 ]
2008 TC3 becomes the first Earth-impacting meteoroid spotted and tracked prior to impact.
(May 2) First visual proof of the existence of black holes is published. Suvi Gezari 's team in Johns Hopkins University , using the Hawaiian telescope Pan-STARRS 1, record images of a supermassive black hole 2.7 million light-years away that is swallowing a red giant . [ 29 ]
In October 2013, the first extrasolar asteroid is detected around white dwarf star GD 61 . It is also the first detected extrasolar body which contains water in liquid or solid form. [ 30 ] [ 31 ] [ 32 ]
On July 14, with the successful encounter of Pluto by NASA's New Horizons spacecraft, the United States became the first nation to explore all of the nine major planets recognized in 1981. Later on September 14, LIGO was the first to directly detect gravitational waves. [ 33 ]
Exoplanet Proxima Centauri b is discovered around Proxima Centauri by the European Southern Observatory , making it the closest known exoplanet to the Solar System as of 2016.
In August 2017, a neutron star collision that occurred in the galaxy NGC 4993 produced the gravitational wave signal GW170817 , which was observed by the LIGO / Virgo collaboration. After 1.7 seconds, it was observed as the gamma-ray burst GRB 170817A by the Fermi Gamma-ray Space Telescope and INTEGRAL , and its optical counterpart SSS17a was detected 11 hours later at the Las Campanas Observatory . Further optical observations e.g. by the Hubble Space Telescope and the Dark Energy Camera , ultraviolet observations by the Swift Gamma-Ray Burst Mission , X-ray observations by the Chandra X-ray Observatory and radio observations by the Karl G. Jansky Very Large Array complemented the detection. This was the first instance of a gravitational wave event that was observed to have a simultaneous electromagnetic signal, thereby marking a significant breakthrough for multi-messenger astronomy. [ 34 ] Non-observation of neutrinos is attributed to the jets being strongly off-axis. [ 35 ]
China's Chang'e 4 became the first spacecraft to perform a soft landing on the far side of the Moon .
In April 2019, the Event Horizon Telescope Collaboration obtained the first image of a black hole which was at the center of galaxy M87 , providing more evidence for the existence of supermassive black holes in accordance with general relativity. [ 36 ]
India launched its second lunar probe called Chandrayaan-2 with an orbiter that was successful and a lander called Vikram along with a rover called Pragyan which failed just 2.1 km above the lunar south pole.
NASA launches Mars 2020 to Mars with a Mars rover and a small helicopter that was named Perseverance and Ingenuity by seventh grader Alexander Mather and eleventh grader Vaneeza Rupani respectively in a naming contest. [ 37 ] [ 38 ] First human orbital spaceflight launched by a private company occurred when SpaceX Demo-2 carrying astronauts Bob Behnken and Doug Hurley was launched to the International Space Station . | https://en.wikipedia.org/wiki/Timeline_of_astronomy |
A timeline of atomic and subatomic physics, including particle physics . | https://en.wikipedia.org/wiki/Timeline_of_atomic_and_subatomic_physics |
This timeline of binary prefixes lists events in the history of the evolution, development, and use of units of measure that are germane to the definition of the binary prefixes by the International Electrotechnical Commission (IEC) in 1998, [ 1 ] [ 2 ] used primarily with units of information such as the bit and the byte .
Historically, computers have used many systems of internal data representation, [ 3 ] methods of operating on data elements, and data addressing. Early decimal computers included the ENIAC , UNIVAC 1 , IBM 702 , IBM 705 , IBM 650 , IBM 1400 series , and IBM 1620 . Early binary addressed computers included Zuse Z3 , Colossus , Whirlwind , AN/FSQ-7 , IBM 701 , IBM 704 , IBM 709 , IBM 7030 , IBM 7090 , IBM 7040 , IBM System/360 and DEC PDP series .
Decimal systems typically had memory configured in whole decimal multiples, e.g., blocks of 100 and later 1000 . The unit abbreviation ' K ' or ' k ' if it was used, represented multiplication by 1000 . Binary memory had sizes of powers of two or small multiples thereof. In this context, ' K ' or ' k ' was sometimes used to denote multiples of 1024 units or just the approximate size, e.g., either '64K' or '65K' for 65 536 (2 16 ).
The same data sheet uses MByte in a decimal sense.
Shugart Associates, one of the leading FD companies used k in a decimal sense. | https://en.wikipedia.org/wiki/Timeline_of_binary_prefixes |
The historical application of biotechnology throughout time is provided below in chronological order.
These discoveries, inventions and modifications are evidence of the application of biotechnology since before the common era and describe notable events in the research, development and regulation of biotechnology.
could stop the duplication of bacteria, leading to the first antibiotic : penicillin .
Some of these items may also have potential nonmedical applications and vice versa. | https://en.wikipedia.org/wiki/Timeline_of_biotechnology |
A timeline of calculus and mathematical analysis . | https://en.wikipedia.org/wiki/Timeline_of_calculus_and_mathematical_analysis |
This is a timeline of key developments in computational mathematics . | https://en.wikipedia.org/wiki/Timeline_of_computational_mathematics |
The following timeline starts with the invention of the modern computer in the late interwar period. | https://en.wikipedia.org/wiki/Timeline_of_computational_physics |
This is a timeline of crystallography . | https://en.wikipedia.org/wiki/Timeline_of_crystallography |
The timeline of discovery of Solar System planets and their natural satellites charts the progress of the discovery of new bodies over history. Each object is listed in chronological order of its discovery (multiple dates occur when the moments of imaging, observation, and publication differ), identified through its various designations (including temporary and permanent schemes), and the discoverer(s) listed.
Historically the naming of moons did not always match the times of their discovery. Traditionally, the discoverer enjoys the privilege of naming the new object; however, some neglected to do so ( E. E. Barnard stated he would "defer any suggestions as to a name" [for Amalthea] "until a later paper" [ 1 ] but never got around to picking one from the numerous suggestions he received) or actively declined ( S. B. Nicholson stated "Many have asked what the new satellites [Lysithea and Carme] are to be named. They will be known only by the numbers X and XI, written in Roman numerals, and usually prefixed by the letter J to identify them with Jupiter." [ 2 ] ). The issue arose nearly as soon as planetary satellites were discovered: Galileo referred to the four main satellites of Jupiter using numbers while the names suggested by his rival Simon Marius gradually gained universal acceptance. The International Astronomical Union (IAU) eventually started officially approving names in the late 1970s. With the explosion of discoveries in the 21st century, new moons have once again started to be left unnamed even after their numbering, beginning with Jupiter LI and Jupiter LII in 2010.
In the following tables, planetary satellites are indicated in bold type (e.g. Moon ) while planets and dwarf planets, which directly circle the Sun, are in italic type (e.g. Earth ). The Sun itself is indicated in roman type. The tables are sorted by publication/announcement date. Dates are annotated with the following symbols:
In a few cases, the date is uncertain and is then marked "(?)".
* Note: Moons marked by an asterisk (*) had complicated discoveries, such as being lost and rediscovered. Some of them thus appear multiple times in the list to clarify the situation.
The Sun, the planets , dwarf planets , and their natural satellites are marked in the following colors:
It is not known precisely how many objects in the Solar System are dwarf planets. The nine objects listed in the third column are the ones agreed on by most astronomers, corresponding to a threshold of about 900–1000 km diameter.
If a satellite is named, its name is bolded; if it is unnamed, but has a permanent designation, then its permanent designation is bolded; and if it has neither, then its temporary designation is bolded.
In the 5th century BCE, the Greek philosophers Philolaus and Hicetas speculated separately that the Earth was a sphere revolving daily around some mystical "central fire" that regulated the universe. Anaxagoras proposed that the Sun is a star around 450 BCE. In the 3rd century BCE, Aristarchus of Samos extended this idea by proposing that the Earth and other planets moved around a definite central object, which he believed to be the Sun though this was not widely accepted until the 17th century and not proven until the 19th. [ 3 ]
The Earth's position in the Solar System was correctly described in the heliocentric model proposed by Aristarchus of Samos . [ 6 ]
Together with his previous two discoveries, Cassini named these satellites Sidera Lodoicea .
In his work Kosmotheôros [ 16 ] (published posthumously in 1698), Christiaan Huygens relates "Jupiter you see has his four, and Saturn his five Moons about him, all plac’d in their Orbits."
The numbering of Saturn's moons was adjusted with each new discovery until 1848, in order to continue reflecting their order from their parent planet.
The numbering of Titania and Oberon underwent some confusion, because in 1797, Herschel reported four more satellites of Uranus [ 23 ] that turned out not to exist. Before any more Uranian moons were discovered, William Lassell sometimes adopted Herschel's numbers where Titania and Oberon are respectively Uranus II and IV, [ 24 ] and sometimes called them respectively Uranus I and II. [ 25 ] After he discovered Ariel and Umbriel in 1851, Lassell numbered the four real Uranian satellites then known outward from their parent planet as I (Ariel), II (Umbriel), III (Titania), and IV (Oberon), and this finally stuck. [ 26 ]
The discovery of Amalthea marks the first time the Roman numerals were not adjusted with the discovery of a new satellite; from then on they reflected order of discovery rather than distance from the parent planet.
i: 23 November 2000 p: 5 January 2001
i: 7 September 2010 p: 1 June 2011
i: 28 June 2011 p: 20 July 2011
i: 27 September 2011 p: 29 January 2012
i: 26 June 2012 p: 11 July 2012
i: 6 November 2004 o: 1 July 2013 p: 15 July 2013
i: 27 April 2015 p: 25 April 2016
Solar System → Local Interstellar Cloud → Local Bubble → Gould Belt → Orion Arm → Milky Way → Milky Way subgroup → Local Group → Local Sheet → Virgo Supercluster → Laniakea Supercluster → Local Hole → Observable universe → Universe Each arrow ( → ) may be read as "within" or "part of". | https://en.wikipedia.org/wiki/Timeline_of_discovery_of_Solar_System_planets_and_their_moons |
This timeline lists significant discoveries in physics and the laws of nature, including experimental discoveries, theoretical proposals that were confirmed experimentally, and theories that have significantly influenced current thinking in modern physics. Such discoveries are often a multi-step, multi-person process. Multiple discovery sometimes occurs when multiple research groups discover the same phenomenon at about the same time, and scientific priority is often disputed. The listings below include some of the most significant people and ideas by date of publication or experiment. | https://en.wikipedia.org/wiki/Timeline_of_fundamental_physics_discoveries |
The following is a timeline of key developments of geometry : | https://en.wikipedia.org/wiki/Timeline_of_geometry |
The following is a timeline of gravitational physics and general relativity . | https://en.wikipedia.org/wiki/Timeline_of_gravitational_physics_and_relativity |
The following are notable events in the Timeline of immunology : | https://en.wikipedia.org/wiki/Timeline_of_immunology |
A timeline of events related to information theory , quantum information theory and statistical physics , data compression , error correcting codes and related subjects. | https://en.wikipedia.org/wiki/Timeline_of_information_theory |
Timeline of knowledge about the interstellar medium and intergalactic medium :
This astronomy -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Timeline_of_knowledge_about_the_interstellar_and_intergalactic_medium |
Major innovations in materials technology | https://en.wikipedia.org/wiki/Timeline_of_materials_technology |
A timeline of mathematical logic ; see also history of logic . | https://en.wikipedia.org/wiki/Timeline_of_mathematical_logic |
Timeline of microscope technology | https://en.wikipedia.org/wiki/Timeline_of_microscope_technology |
Edit This timeline of nuclear fusion is an incomplete chronological summary of significant events in the study and use of nuclear fusion . | https://en.wikipedia.org/wiki/Timeline_of_nuclear_fusion |
This timeline of nuclear power is an incomplete chronological summary of significant events in the study and use of nuclear power . This is primarily limited to sustained fission and decay processes, and does not include detailed timelines of nuclear weapons development or fusion experiments . | https://en.wikipedia.org/wiki/Timeline_of_nuclear_power |
A timeline of number theory . | https://en.wikipedia.org/wiki/Timeline_of_number_theory |
This is a timeline of subatomic particle discoveries , including all particles thus far discovered which appear to be elementary (that is, indivisible) given the best available evidence. It also includes the discovery of composite particles and antiparticles that were of particular historical importance.
More specifically, the inclusion criteria are: | https://en.wikipedia.org/wiki/Timeline_of_particle_discoveries |
Timeline of particle physics technology | https://en.wikipedia.org/wiki/Timeline_of_particle_physics_technology |
This article attempts to place key plant innovations in a geological context. It concerns itself only with novel adaptations and events that had a major ecological significance, not those that are of solely anthropological interest. The timeline displays a graphical representation of the adaptations; the text attempts to explain the nature and robustness of the evidence.
Plant evolution is an aspect of the study of biological evolution , predominantly involving evolution of plants suited to live on land, greening of various land masses by the filling of their niches with land plants, and diversification of groups of land plants.
In the strictest sense, the name plant refers to those land plants that form the clade Embryophyta , comprising the bryophytes and vascular plants. However, the clade Viridiplantae or green plants includes some other groups of photosynthetic eukaryotes, including green algae . It is widely believed that land plants evolved from a group of charophytes , most likely simple single-celled terrestrial algae similar to extant Klebsormidiophyceae . [ 1 ]
Chloroplasts in plants evolved from an endosymbiotic relationship between a cyanobacterium , a photosynthesising prokaryote and a non-photosynthetic eukaryotic organism, producing a lineage of photosynthesizing eukaryotic organisms in marine and freshwater environments. These earliest photosynthesizing single-celled autotrophs evolved into multicellular organisms such as the Charophyta , a group of freshwater green algae.
Fossil evidence of plants begins around 3000 Ma with indirect evidence of oxygen-producing photosynthesis in the geological record, in the form of chemical and isotopic signatures in rocks and fossil evidence of colonies of cyanobacteria, photosynthesizing prokaryotic organisms. Cyanobacteria use water as a reducing agent , producing atmospheric oxygen as a byproduct, and they thereby profoundly changed the early reducing atmosphere of the earth to one in which modern aerobic organisms eventually evolved. This oxygen liberated by cyanobacteria then oxidized dissolved iron in the oceans, the iron precipitated out of the sea water, and fell to the ocean floor to form sedimentary layers of oxidized iron called Banded Iron Formations (BIFs). These BIFs are part of the geological record of evidence for the evolutionary history of plants by identifying when photosynthesis originated. This also provides deep time constraints upon when enough oxygen could have been available in the atmosphere to produce the ultraviolet blocking stratospheric ozone layer. The oxygen concentration in the ancient atmosphere subsequently rose, acting as a poison for anaerobic organisms, and resulting in a highly oxidizing atmosphere, and opening up niches on land for occupation by aerobic organisms.
Fossil evidence for cyanobacteria also comes from the presence of stromatolites in the fossil record deep into the Precambrian . Stromatolites are layered structures formed by the trapping, binding, and cementation of sedimentary grains by microbial biofilms , such as those produced by cyanobacteria. The direct evidence for cyanobacteria is less certain than the evidence for their presence as primary producers of atmospheric oxygen. Modern stromatolites containing cyanobacteria can be found on the west coast of Australia and other areas in saline lagoons and in freshwater.
Early plants were small, unicellular or filamentous, with simple branching. The identification of plant fossils in Cambrian strata is an uncertain area in the evolutionary history of plants because of the small and soft-bodied nature of these plants. It is also difficult in a fossil of this age to distinguish among various similar appearing groups with simple branching patterns, and not all of these groups are plants. One exception to the uncertainty of fossils from this age is the group of calcareous green algae, Dasycladales found in the fossil record since the middle Cambrian. These algae do not belong to the lineage that is ancestral to the land plants. Other major groups of green algae had been established by this time, but there were no land plants with vascular tissues until the mid- Silurian .
The evidence of plant evolution changes dramatically in the Ordovician with the first extensive appearance of embryophyte spores in the fossil record. The earliest terrestrial plants lived during the Middle Ordovician around 470 million years ago , based on their fossils found in the form of monads and spores, with resistant polymers in their outer walls, from Turkey , Saudi Arabia and Argentina . [ 3 ] [ 4 ] Individual trilete spores resembling those of modern cryptogamic plants and vascular plants first appeared in the fossil record from the Late Ordovician . [ 5 ] [ 6 ] These plants probably resembled liverworts , [ 4 ] and did not have any conducting tissues. [ 7 ] They were able to reproduce with spores , important dispersal units that have hard protective outer coatings which not only allowed their preservation in the fossil record, but also protected them from the UV light, desiccating environment and possible microorganism attack. [ 4 ]
The first fossil records of vascular plants , that is, land plants with vascular tissues , appeared in the Silurian period . The earliest known representatives of this group (mostly from the northern hemisphere) are placed in the genus Cooksonia . They had very simple branching patterns, with the branches terminated by flattened sporangia. By the end of the Silurian much more complex vascular plants, the zosterophylls , had diversified [ 8 ] and primitive lycopods , such as Baragwanathia (originally discovered in Silurian deposits in Victoria, Australia), [ 9 ] had become widespread.
By the Devonian Period, the colonization of the land by plants was well underway. The bacterial and algal mats were joined early in the period by primitive plants that created the first recognizable soils and harbored some arthropods like mites , scorpions and myriapods . Early Devonian plants did not have roots or leaves like the plants most common today, and many had no vascular tissue at all. They probably relied on arbuscular mycorrhizal symbioses with fungi to provide them with water and mineral nutrients such as phosphorus . [ 10 ] [ 11 ] They probably spread by a combination of vegetative reproduction forming clonal colonies, and sexual reproduction via spores and did not grow much more than a few centimeters tall.
By the Late Devonian, forests of large, primitive plants existed: lycophytes , sphenophytes , ferns , and progymnosperms had evolved . Most of these plants have true roots and leaves, and many were quite tall. The tree-like Archaeopteris , ancestral to the gymnosperms, and the giant cladoxylopsid trees had true wood . These are the oldest known trees of the world's first forests. Prototaxites was the fruiting body of an enormous fungus that stood more than 8 meters tall. By the end of the Devonian, the first seed-forming plants had appeared. This rapid appearance of so many plant groups and growth forms has been called the "Devonian Explosion". The primitive arthropods co-evolved with this diversified terrestrial vegetation structure. The evolving co-dependence of insects and seed-plants that characterizes a recognizably modern world had its genesis in the late Devonian. The development of soils and plant root systems probably led to changes in the speed and pattern of erosion and sediment deposition.
The 'greening' of the continents acted as a carbon dioxide sink , and atmospheric concentrations of this greenhouse gas may have dropped. [ 12 ] This may have cooled the climate and led to a massive extinction event . see Late Devonian extinction .
Also in the Devonian, both vertebrates and arthropods were solidly established on the land.
Early Carboniferous land plants were very similar to those of the preceding Latest Devonian, but new groups also appeared at this time.
The main Early Carboniferous plants were the Equisetales (Horse-tails), Sphenophyllales (scrambling plants), Lycopodiales (Club mosses), Lepidodendrales (arborescent clubmosses or scale trees), Filicales (Ferns), Medullosales (previously included in the " seed ferns ", an artificial assemblage of a number of early gymnosperm groups) and the Cordaitales . These continued to dominate throughout the period, but during late Carboniferous , several other groups, Cycadophyta (cycads), the Callistophytales (another group of "seed ferns"), and the Voltziales (related to and sometimes included under the conifers ), appeared.
The Carboniferous lycophytes of the order Lepidodendrales, which were cousins (but not ancestors) of the tiny club-mosses of today, were huge trees with trunks 30 meters high and up to 1.5 meters in diameter. These included Lepidodendron (with its fruit cone called Lepidostrobus ), Halonia , Lepidophloios and Sigillaria . The roots of several of these forms are known as Stigmaria .
The fronds of some Carboniferous ferns are almost identical with those of living species. Probably many species were epiphytic. Fossil ferns include Pecopteris and the tree ferns Megaphyton and Caulopteris . Seed ferns or Pteridospermatophyta include Cyclopteris , Neuropteris , Alethopteris , and Sphenopteris .
The Equisetales included the common giant form Calamites , with a trunk diameter of 30 to 60 cm and a height of up to 20 meters. Sphenophyllum was a slender climbing plant with whorls of leaves, which was probably related both to the calamites and the modern horsetails.
Cordaites , a tall plant (6 to over 30 meters) with strap-like leaves, was related to the cycads and conifers; the catkin -like inflorescence, which bore yew-like berries, is called Cardiocarpus . These plants were thought to live in swamps and mangroves. True coniferous trees ( Walchia , of the order Voltziales) appear later in the Carboniferous, and preferred higher drier ground.
The Permian began with the Carboniferous flora still flourishing. About the middle of the Permian there was a major transition in vegetation. The swamp-loving lycopod trees of the Carboniferous, such as Lepidodendron and Sigillaria , were replaced by the more advanced conifers, which were better adapted to the changing climatic conditions. Lycopods and swamp forests still dominated the South China continent because it was an isolated continent and it sat near or at the equator. The Permian saw the radiation of many important conifer groups, including the ancestors of many present-day families. The ginkgos and cycads also appeared during this period. Rich forests were present in many areas, with a diverse mix of plant groups. The gigantopterids thrived during this time; some of these may have been part of the ancestral flowering plant lineage, though flowers evolved only considerably later.
On land, the holdover plants included the lycophytes , the dominant cycads , Ginkgophyta (represented in modern times by Ginkgo biloba ) and glossopterids . The spermatophytes , or seed plants came to dominate the terrestrial flora: in the northern hemisphere, conifers flourished. Dicroidium (a seed fern ) was the dominant southern hemisphere tree during the Early Triassic period.
The arid, continental conditions characteristic of the Triassic steadily eased during the Jurassic period, especially at higher latitudes; the warm, humid climate allowed lush jungles to cover much of the landscape. [ 13 ] Conifers dominated the flora, as during the Triassic; they were the most diverse group and constituted the majority of large trees. Extant conifer families that flourished during the Jurassic included the Araucariaceae , Cephalotaxaceae , Pinaceae , Podocarpaceae , Taxaceae and Taxodiaceae . [ 14 ] The extinct Mesozoic conifer family Cheirolepidiaceae dominated low latitude vegetation, as did the shrubby Bennettitales . [ 15 ] Cycads were also common, as were ginkgos and tree ferns in the forest. Smaller ferns were probably the dominant undergrowth. Caytoniaceous seed ferns were another group of important plants during this time and are thought to have been shrub to small-tree sized. [ 16 ] Ginkgo-like plants were particularly common in the mid- to high northern latitudes. In the Southern Hemisphere, podocarps were especially successful, while Ginkgos and Czekanowskiales were rare. [ 15 ] [ 17 ]
Flowering plants, also known as angiosperms , spread during this period, although they did not become predominant until near the end of the period ( Campanian age ). [ 18 ] Their evolution was aided by the appearance of bees ; in fact angiosperms and insects are a good example of coevolution . The first representatives of many modern trees, including figs , planes and magnolias , appeared in the Cretaceous. At the same time, some earlier Mesozoic gymnosperms , like Conifers continued to thrive, although other taxa like Bennettitales died out before the end of the period.
The Cenozoic began at the Cretaceous–Paleogene extinction event with a massive disruption of plant communities . It then became just as much the age of savannas, or the age of co-dependent flowering plants and insects. At 35 Ma, grasses evolved from among the angiosperms.
About ten thousand years ago, humans in the Fertile Crescent of the Middle East develop agriculture. Plant domestication begins with cultivation of Neolithic founder crops. This process of food production, coupled later with the domestication of animals caused a massive increase in human population that has continued to the present. In Jericho (modern Israel), there is a settlement with about 19,000 people. At the same time, Sahara is green with rivers, lakes, cattle, crocodiles and monsoons.
At 8 ka, Common (Bread) wheat ( Triticum aestivum ) originates in southwest Asia due to hybridisation of emmer wheat with a goat-grass, Aegilops tauschii .
At 6.5 ka, two rice species are domesticated: Asian rice, Oryza sativa , and African rice Oryza glaberrima . | https://en.wikipedia.org/wiki/Timeline_of_plant_evolution |
The timeline of quantum mechanics is a list of key events in the history of quantum mechanics , quantum field theories and quantum chemistry . | https://en.wikipedia.org/wiki/Timeline_of_quantum_mechanics |
A timeline of events in the history of thermodynamics . | https://en.wikipedia.org/wiki/Timeline_of_thermodynamics |
In telecommunications and related engineering (including computer networking and programming ), the term timeout or time-out has several meanings, including:
Timeouts allow for more efficient usage of limited resources without requiring additional interaction from the agent interested in the goods that cause the consumption of these resources. The basic idea is that in situations where a system must wait for something to happen, rather than waiting indefinitely, the waiting will be aborted after the timeout period has elapsed. This is based on the assumption that further waiting is useless, and some other action is necessary.
Balancing timeout values in distributed systems and microservices can be tricky: short timeout values can fail healthy requests prematurely, leading to complex workarounds, while long timeout values can result in slow error responses and poor user experiences. The circuit breaker design pattern can be a better alternative, as it can monitor service health, detect failures dynamically and faster, and improve the user experience. [ 1 ]
Specific examples include: | https://en.wikipedia.org/wiki/Timeout_(computing) |
A timer or countdown timer is a type of clock that starts from a specified time duration and stops upon reaching 00:00. It can also usually be stopped manually before the whole duration has elapsed. An example of a simple timer is an hourglass . Commonly, a timer triggers an alarm when it ends. A timer can be implemented through hardware or software . Stopwatches operate in the opposite direction, upwards from 00:00, measuring elapsed time since a given time instant. Time switches are timers that control an electric switch .
Mechanical timers use clockwork to measure time. [ 1 ] Manual timers are typically set by turning a dial to the time interval desired, turning the dial stores energy in a mainspring to run the mechanism. They function similarly to a mechanical alarm clock , the energy in the mainspring causes a balance wheel to rotate back and forth. Each swing of the wheel releases the gear train to move forward by a small fixed amount, causing the dial to move steadily backward until it reaches zero when a lever arm strikes a bell. The mechanical kitchen timer was invented in 1926.
The simplest and oldest type of mechanical timer is the hourglass - which is also known as "the glass of the hour" - in which a fixed amount of sand drains through a narrow opening from one chamber to another to measure a time interval.
Short-period bimetallic electromechanical timers use a thermal mechanism, with a metal finger made of strips of two metals with different rates of thermal expansion sandwiched together, steel and bronze are common. An electric current flowing through this finger causes heating of the metals, one side expands less than the other, and an electrical contact on the end of the finger moves away from or towards an electrical switch contact. The most common use of this type is in the "flasher" units that flash turn signals in automobiles , and sometimes in Christmas lights . This is a non-electronic type of multivibrator .
An electromechanical cam timer uses a small synchronous AC motor turning a cam against a comb of switch contacts. The AC motor is turned at an accurate rate by the alternating current, which power companies carefully regulate. Gears drive a shaft at the desired rate, and turn the cam. The most common application of this timer now is in washers , driers and dishwashers . This type of timer often has a friction clutch between the gear train and the cam, so that the cam can be turned to reset the time.
Electromechanical timers survive in these applications because mechanical switch contacts may still be less expensive than the semiconductor devices needed to control powerful lights, motors and heaters.
In the past, these electromechanical timers were often combined with electrical relays to create electro-mechanical controllers. Electromechanical timers reached a high state of development in the 1950s and 1960s because of their extensive use in aerospace and weapons systems. Programmable electromechanical timers controlled launch sequence events in early rockets and ballistic missiles . As digital electronics has progressed and dropped in price, electronic timers have become more advantageous.
Electronic timers are essentially quartz clocks with special electronics, which can achieve higher precision than mechanical timers. They have digital electronics, but may have an analog or digital display. Integrated circuits have made digital logic so inexpensive that an electronic timer is now less expensive than many mechanical and electromechanical timers. Individual timers are implemented as a simple single-chip computer system, similar to a watch and usually utilizing the same, mass-produced technology.
Nowadays, many timers are implemented in software. Modern controllers use a programmable logic controller (PLC) instead of a box full of electromechanical parts. The logic is usually designed as if it were relays, utilizing a special computer language called ladder logic. In PLCs, timers are usually simulated by the software built into the controller. Each timer is just an entry in a table maintained by the software.
Computer systems typically have at least one hardware timer. These are typically digital counters that either increment or decrement at a fixed frequency, which is often configurable, and which interrupt the processor when reaching zero. An alternative design uses a counter with a sufficiently large word size that it will not reach its overflow limit before the end of life of the system.
More sophisticated timers may have comparison logic to compare the timer value against a specific value set by software, which triggers some action when the timer value matches the preset value. This might be used, for example, to measure events or generate pulse-width modulated waveforms to control the speed of motors (using a class D digital electronic amplifier).
One specialist use of hardware timers in computer systems is as watchdog timers, which are designed to perform a hardware reset of the system if the software fails.
Mission timers have been used to measure the duration of an operation, or used as a countdown to a deadline to complete a mission. Such devices have been used by Space organisations. [ 2 ] [ 3 ]
During World War II, precision and timing were crucial for the success of numerous military operations. This necessity gave birth to the development of specialized mission timers, which were essentially high-precision chronographs designed specifically for military use. These mission timers play a pivotal role in coordinating attacks, navigation, and other critical aspects of military operations.
A mission timer typically features a robust rugged design to withstand the harsh conditions of war and engineered to provide an accurate measurement of short time periods, which are essential for tasks such as bombing runs or submarine dives. The face of the timer are often large and clearly marked, allowing operators to read it quickly and under low-light conditions. The functionality of mission timers extend beyond mere timekeeping; they help in calculating speed, distance, and fuel consumption as well. By enabling precise timing, these devices ensure that complex maneuvers could be executed with a higher degree of coordination and synchronization among allied forces. In essence, mission timers are not just timekeeping tools but instruments that contribute significantly to the strategic effectiveness of military operations during times of war.
These types of timers are not devices nor parts of devices, they exist only as software. They rely on the accuracy of a clock generator usually built into a hardware device that runs the software.
Many timer apps have been developed that mimic an old mechanical timer, but which have also highly sophisticated functions. These apps are also easier to use, because they are available at once, without any need to purchase or carry separate devices. Timers can be software applications phones, smartwatches , or tablets . Some of these apps are countdown timers , stopwatches , etc. These timer apps can be set for a specific time and can be used for tracking working or training time, motivating children to do tasks, replacing an hourglass -form egg timer in board games such as Boggle , or for the traditional purpose of tracking time when cooking.
Apps may be superior to hour glasses, or to mechanical timers. Hour glasses are not precise and clear, and they can jam. Mechanical timers lack the customization that applications support, such as sound volume adjustments for individual needs. Most applications will also offer selectable alarm sounds.
Some timer applications can help children to understand the concept of time, help them to finish tasks in time, and help them to get motivated. [ 4 ] These applications are especially used with children with disabilities like ADHD . [ 5 ] | https://en.wikipedia.org/wiki/Timer |
In computing , timestamping refers to the use of an electronic timestamp to provide a temporal order among a set of events.
Timestamping techniques are used in a variety of computing fields, from network management and computer security to concurrency control . [ 1 ] [ 2 ] For instance, a heartbeat network uses timestamping to monitor the nodes on a high availability computer cluster . [ 3 ]
Timestamping computer files (updating the timestamp in the per-file metadata every time a file is modified) makes it possible to use efficient build automation tools.
This computing article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Timestamping_(computing) |
A timetree is a phylogenetic tree scaled to time. [ 3 ] It shows the evolutionary relationships of a group of organisms in a temporal framework. [ 3 ]
Therefore, if living organisms are represented, the branch length between the base of the tree and all leafs (e.g., species) is identical because the same time has elapsed, although extinct organisms can be shown in a timetree. [ 4 ]
As with a phylogenetic tree, timetrees can be drawn in different shapes: rectangular, circular, [ 3 ] or even spiral. [ 2 ] The only figure in Darwin's On the Origin of Species , [ 5 ] one of the earliest printed evolutionary trees, is a hypothetical timetree. Because the fossil record has always been tightly linked to the geologic record , evolutionary trees of extinct organisms are typically illustrated as timetrees. [ 6 ]
In the past, timetrees were sometimes called " chronograms ," [ 7 ] but that term has been criticized because it is imprecise, referring to any graph that shows time, and not indicating that evolutionary relationships are involved. [ 3 ] The first use of the single word "timetree," in the context of an evolutionary tree scaled to time, was in 2001. [ 8 ] | https://en.wikipedia.org/wiki/Timetree |
Timex Datalink or Timex Data Link is a line of early smartwatches manufactured by Timex and is considered a wristwatch computer. [ 1 ] It is the first watch capable of downloading information wirelessly from a computer. [ 2 ] [ 3 ] As the name implies, datalink watches are capable of data transfer through linking with a computer. [ 4 ] The Datalink line was introduced in 1994 and it was co-developed with Microsoft as a wearable alternative to mainstream PDAs with additional attributes such as water resistance, that PDAs lacked, and easy programmability. [ 5 ] The watch was demonstrated by Bill Gates on 21 June 1994 in a presentation where he downloaded information from a computer monitor using bars of light and then showed to the audience the downloaded appointments and other data. [ 6 ] The early models included models 50, 70, 150 and model 150s (small size). [ 5 ] The model numbers indicated the approximate number of phone numbers that could be stored in the watch memory. [ 7 ] These early models were, at the time of their introduction, the only watches to bear the Microsoft logo. [ 8 ] [ 9 ] The watches have been certified by NASA for space travel and have been used by astronauts and cosmonauts in space missions . There had been an evolution over the years as to the number and type of entries that can be stored in the various watch models as well as the mode of data transfer between computer and watch. At the time of its introduction the watch was considered high-tech . [ 10 ]
There is also the Timex Beepwear Datalink series, featuring wearable pagers using the Timex datalink platform which also function as electronic organisers. [ 4 ] [ 11 ] [ 12 ] [ 13 ] [ 14 ] [ 15 ]
Although there are other watches capable of storing all kinds of data, most had either a small keyboard [ 16 ] or buttons, [ 17 ] which could be used to input data. In most cases data was lost when the battery expired. [ 18 ] Upon introduction of the Timex Datalink models, "data watches" such as those from Casio were noted as selling for "between a third and a half the price" of such models, but the "fiddly little buttons" (having to be pressed repeatedly to select letters from the alphabet) were regarded as less convenient and largely only appealing to those used to "doing things the hard way". The Datalink models also offered water resistance to a depth of 100 metres, Timex's Indiglo backlighting, and "the build quality that helped make Timex a household name", although this robustness was reported as making the product more like "the kind of "chunky, clunky watches that divers prefer", being around one-and-a-half inches in diameter and standing "over half an inch proud of the wrist". [ 19 ]
The Timex Datalink watches downloaded data wirelessly by illuminating a computer screen with a changing display encoding information to transfer, which was detected by the watch's sensor. [ 5 ] [ 20 ] Data to be transferred to Datalink watches was held in a database maintained by the Datalink software running on a Windows-based host computer, with alarms, appointments, anniversaries, phone numbers, reminders (or to-do items) being the supported categories of data for transfer. Textual labels for various categories could be up to 15 characters in length, with such text scrolling across an eight character display. Although the time could be set through normal use of the watch, the software also permitted the time to be updated using the transfer mechanism. Selecting the "Send to Watch" option in the Datalink software and pointing the watch face towards the screen at a distance of between six and twelve inches, guided by beeping sounds from the watch, resulted in the transfer of data at a rate that permitted around 1 KB or 70 entries to be sent in less than a minute. However, the mechanism required the use of a cathode-ray tube monitor, as opposed to a liquid-crystal or other kind of display. Transfer of data from the watch to the computer was also not permitted by this mechanism, but entries could be deleted on the watch or, in the case of to-do items, marked as done. [ 19 ] When the watch's battery expired the data would be transferred again after replacement of the battery. [ 18 ]
The watch had a small lens at the top of its face used for data transmission by visible light. [ 5 ] [ 21 ] Data was transmitted from the CRT of the computer through a series of pulsating horizontal bars, [ 22 ] [ 23 ] that were focused by the lens and written to the watch EEPROM memory through an optoelectronic transducer operating in the visible light spectrum and employing optical scanning technology. [ 24 ] [ 25 ]
The original Timex Datalink software with CRT synchronization support is compatible with Windows versions Windows 3.1 to Windows XP . The watch was compatible with Microsoft's Schedule+ time management software. For the Datalink 70 model, the time needed to download seventy phone numbers was about twenty seconds. [ 22 ] [ 26 ]
On the resin strap of the Timex Datalink 50 model 70301, there is a print with binary numbers which are actually ASCII . The numbers on one half of the strap encode, including capitalization, the text 'Listen To The Light'. [ 27 ] The numbers on other half of the strap encode the text 'If You [ASCII-24] See', which, given that ASCII-24 is the 'Cancel' character or just 'CAN', makes the complete message 'Listen To The Light If You Can See'.
The earlier models were the Datalink 50, Datalink 70, Datalink 150 and Datalink 150s, where the "s" was for small and it was intended to be a lady's watch. [ 5 ] [ 28 ] The 150 and 150s models are essentially the same, except that the 150s, having a smaller display, has different display addresses from the 150, and thus it needs its own programming code. [ 28 ]
The programming code is provided in the Timex Datalink software v 2.1 for all models. [ 28 ] These watches were programmed using the same software and computer GUI . To download the settings to these early models, the user was prompted to choose the relevant watch model number. [ 29 ]
The menu choices were the same for all models. [ 29 ] The only differences were the amount of available memory in the watches, and the quantity of phone numbers, appointments, lists etc. which could be downloaded to each model. [ 30 ]
At the time of their introduction, these watches were known as "PIM" watches, i.e. personal information managers. [ 31 ] Bill Gates was known as an owner of one, [ 31 ] and had also shown the capabilities of the watch on television. [ 32 ] The Datalink 150 was also offered as a mail-in gift upon purchase of Office 95 . [ 3 ]
The model number indicated the maximum number of phone numbers that could be downloaded to the watch. For example, the model 150 could store a maximum of 150 phone numbers if nothing else was stored. [ 29 ] Available storage was shared by phone numbers, appointments, anniversaries, lists, wristapps and watch sounds. [ 29 ] These models lacked countdown timers or chronographs, but a simple chronograph could be added as an external application also known as a wristapp. [ 29 ] The wristapps also included a notepad capable of storing forty words. [ 33 ]
The time and date parts of the digital display of the Datalink watches consisted of two main rows of seven segment displays , while the lower portion was a dot matrix display with scrolling capabilities. In time display mode, the dot matrix portion of the display showed the day of the week to the left, and the time zone to the right. The default time zone was indicated as TZ1 (time zone 1), and was fully user customizable to designate any city in the world, usually using IATA naming conventions. The earlier Datalink models featured dual time zone settings. [ 29 ] The secondary time zone had the option to become the local (primary) time by pressing and holding a button until the changeover was effected. [ 29 ] All Datalink models had the Indiglo night light. [ 10 ]
The earlier models included many PDA-type functions such as anniversaries, appointments and phone directory, but did not have functions such as stopwatch and countdown timer. They had five alarms. [ 29 ]
To add functionality, in 1997 Timex introduced the Ironman Triathlon Datalink series with features of the Ironman series , such as a choice of timers, multi-lap stopwatches , and customisable display appearance. The number of alarms increased to 10 in the new series. [ 34 ] Messages could be displayed during an alarm, and they could be downloaded to the watch or input manually through scrolling characters, activated by two forward/reverse buttons. [ 34 ]
The new features came at the expense of some older ones. For example, the "Anniversary" and "Appointment" modes of the previous Datalink models were no longer available, and the number of phone entries for the Ironman Datalink was reduced to 38, from a maximum of 150 of the older Datalink model 150. [ 29 ] [ 34 ] The "Make a List" function of the Datalink 150 model was also gone. This feature enabled the user to create short lists for various tasks, and import wristapps, special programs with custom applications which could be added to the watch. [ 29 ] [ 34 ]
The optical sensor and the method of data transfer were retained. The display of the new series had the same architecture as that of the older models. As with the earlier models, the Triathlon Datalink included dual time zones with local time selectability. Its battery life was approximately three years under normal use. [ 29 ] [ 34 ]
With the advent of portable computers which use active matrix LCD screens which did not refresh like CRT monitors and therefore could not be used for data transfer, [ 23 ] in 1997, Timex introduced a notebook adapter that incorporated a red LED and connected with the laptop through the serial port . During download, the LED flashed and the flashing programmed the watch much like the horizontal bars of the CRT.
For systems without a serial port, a USB to serial adapter can be used to connect the Timex adapter to a USB port . Alternatively, DIY Notebook Adapter emulators can be used with the original and third-party software, like timex-datalink-arduino .
The Datalink USB was introduced in 2003. It included the Timex Ironman Datalink USB (sport edition) and the Timex Datalink USB (dress edition) models. Apart from their external appearance, and the fact that the sport edition is water-resistant to 100 metres, while the dress edition is water resistant to 30 metres, the two models had identical specifications.
Although initially a mild disappointment for the wireless datalink purists, it gained widespread acceptance, because, although now tethered to the computer through the USB port during data transfer, the new watch featured greatly improved data transfer rates, greatly increased memory capacity and many additional and customizable modes of operation, as well as two way communication between the watch and computer. [ 35 ]
Its modes are user customizable, with hundreds of phone numbers, alarms and timer settings. [ 36 ] [ 37 ] It also features three time zones, [ 37 ] each of which can be chosen as the primary time display with the press of a button. [ 35 ] The Datalink USB also introduced data protection through the use of a user generated password , [ 37 ] a feature that the earlier models did not offer. [ 34 ] [ 35 ] The USB models also feature a rotating crown known as the Timex i-control . [ 35 ]
The Datalink USB supports software programs developed specifically for the watch similar to its predecessors. [ 38 ] These programs are called wrist applications or wrist apps for short, and they are created by independent software developers . [ 38 ] Timex has developed an application called WristApp SDK Installer . This application can facilitate the import of any independently developed wrist app into the Datalink USB computer interface, and thus make it part of the downloadable program menu in the GUI of the watch. [ 38 ]
Unlike its predecessors, the display of the USB series features full dot matrix architecture with no seven segment display sections. Only a small section at the top right corner uses a nine-segment display layout. [ 38 ] Many programs have been developed, and their applications include video games, screen savers , golf score keepers, watch display contrast and scrolling speed adjustment, as well as analog watch displays, phase of the moon calculations and associated display graphics and others. [ 38 ] The wristapps are written in assembly language . [ 39 ]
Invasion is an example of a game developed specifically for the watch. [ 38 ] It is designed along the lines of Space Invaders , created by Jordi Perez. [ 40 ] The game has been developed to showcase API instructions for primitive pixel displays such as the one used in the watch. [ 38 ] The term primitive refers to displays of low resolution where one can discern the individual pixels.
Among the many programs and utilities which have been developed for the watch, such as football schedules, weather reports and others, there is also a screen saver which blanks out the display of the watch on the minute or the hour, appropriately called Screen Saver – Blank . [ 38 ]
Another application called Antikythera emulates some of the functions of the Antikythera mechanism by calculating the phase of the moon . It is accurate to within one day in 500 years. In the future, it will also be able to calculate the sun's position in the zodiac and upcoming eclipses . [ 41 ]
Timex Datalink is flight certified by NASA for space missions and is one of four watches qualified by NASA for space travel. [ 43 ] [ 44 ] [ 45 ] The various Datalink models are used both by cosmonauts and astronauts. For instance during Expedition 1 the crew log for January mentions:
We have been working with the Timex software. Many thanks to the folks who got this up to us. It seems we each have a different version of the datalink watch, and of course, the software is different with each. Yuri and Sergei are able to load up a day's worth of alarms, but Shep has the Datalink 150, and this has a 5 alarm limit. So 2/3 of the crew are now happy. All this is a pretty good argument for training like you are going to fly-we should have caught this one ourselves in our training work on the ground. [ 46 ]
In another part of the January log it is mentioned:
Missed a whole comm. pass over White Sands. We need to get the timex watches working so we don't overlook these calls.
while in another segment of the same log:
As 5A is now delayed, we would like to request the "timex" watch software if it is available on the ground-a file that can be uplinked to us. This will help us manage our day as we can load comm. passes into the watches.
and from the February and March crew log of Expedition 1:
We copy the request from Houston on the timex watches. We will keep using the ones we have onboard-there are some workarounds we can apply that will help the limited "alarm" situation. We don't request any more watches be sent up on 5A, but thanks to all the crew equipment folks for asking. As a heads-up to Exp 2, any plans to use the timex download capability should include more laptop IR transmitters. We have 1 onboard, but more will be required if the next crew wants to fully use this capability. [ 47 ]
The laptop IR transmitter mentioned in the February and March crew log is the Timex notebook adapter. "Exp 2" refers to Expedition 2 , and the log mentions they may need more notebook adapters for the upcoming expedition.
Due to its unique features and long tradition of innovation and utility, the Datalink watch line has achieved cult-like status among technically minded people. In addition, many websites are dedicated to the programming and information exchange among its many fans. Yahoo groups also exist for fans and software developers alike, especially for the latest Datalink USB series. [ 48 ] [ 49 ]
The early Datalink 50/150 models received a tongue in cheek "[dis]honorable" mention in PC World 's "25 Worst Tech Products of All Time" list in 2006 and were inducted in "the high tech hall of shame", with the rationale that "It looked like a Casio on steroids " and "To download data to it, you held it in front of your CRT monitor while the monitor displayed a pattern of flashing black-and-white stripes (which, incidentally, also turned you into the Manchurian Candidate )", referring to the earlier, flashing CRT method of data transfer, adding that "Depending on your point of view, it was either seriously cool or deeply disturbing". [ 50 ]
Timex Datalink watches are referred to as "classics" and as "worn by astronauts to the moon" in Jeffery Deaver 's crime thriller novel The Burning Wire . [ 51 ]
They are also featured at the online exhibit of the National Museum of American History . [ 52 ]
The Timex Beepwear Datalink series features wearable pagers , using the Timex datalink platform. These watches also function as electronic organisers. [ 4 ] [ 11 ] [ 12 ] [ 13 ] [ 14 ] [ 15 ] [ 53 ] The Beepware series is patented and was the product of a joint Timex- Motorola effort which resulted in a new company called Beepwear Paging Products . [ 54 ] [ 55 ] [ 56 ] [ 57 ] The Beepwear marketing motto was: "One beeping great watch". [ 58 ] It was the first watch/pager able to receive alphanumeric messages. [ 59 ] [ 60 ] It operates in the 900 MHz band. [ 61 ] Beepware also featured FLEX time which, if supported by the service provider, could synchronise the time of the watch with that of the network. [ 14 ] It could also automatically adjust to the time zone of the wearer. [ 59 ] | https://en.wikipedia.org/wiki/Timex_Datalink |
Time–space compression (also known as space–time compression and time–space distanciation ) is an idea referring to the altering of the qualities of space–time and the relationship between space and time that is a consequence of the expansion of capital . It is rooted in Karl Marx 's notion of the "annihilation of space by time" originally elaborated in the Grundrisse , [ 1 ] and was later articulated by Marxist geographer David Harvey in his book The Condition of Postmodernity . [ 2 ] A similar idea was proposed by Elmar Altvater in an article in PROKLA in 1987, [ 3 ] translated into English as "Ecological and Economic Modalities of Time and Space" and published in Capitalism Nature Socialism in 1990. [ 4 ]
Time–space compression occurs as a result of technological innovations driven by the global expansion of capital that condense or elide spatial and temporal distances, including technologies of communication ( telegraph , telephones , fax machines , Internet ) and travel (rail, cars, trains, jets), driven by the need to overcome spatial barriers, open up new markets, speed up production cycles, and reduce the turnover time of capital.
According to Paul Virilio , time-space compression is an essential facet of capitalist life, saying that "we are entering a space which is speed-space ... This new other time is that of electronic transmission, of high-tech machines, and therefore, man is present in this sort of time, not via his physical presence, but via programming" (qtd. in Decron 71 [ 5 ] ). In Speed and Politics , Virilio coined the term dromology to describe the study of "speed-space". Virilio describes velocity as the hidden factor in wealth and power, where historical eras and political events are effectively speed-ratios. In his view, acceleration destroys space and compresses time in ways of perceiving reality.
Theorists generally identify two historical periods in which time–space compression occurred; the period from the mid-19th century to the beginnings of the First World War , and the end of the 20th century. In both of these time periods, according to Jon May and Nigel Thrift, "there occurred a radical restructuring in the nature and experience of both time and space ... both periods saw a significant acceleration in the pace of life concomitant with a dissolution or collapse of traditional spatial co-ordinates". [ 6 ]
Doreen Massey critiqued the idea of time-space compression in her discussion of globalization and its effect on our society. She insisted that any ideas that our world is "speeding up" and "spreading out" should be placed within local social contexts. "Time-space compression", she argues, "needs differentiating socially": "how people are placed within 'time-space compression' are complicated and extremely varied". In effect, Massey is critical of the notion of "time-space compression" as it represents capital's attempts to erase the sense of the local and masks the dynamic social ways through which places remain "meeting places". [ 7 ]
For Moishe Postone , [ 8 ] Harvey's treatment of space-time compression and postmodern diversity are merely reactions to capitalism . Hence Harvey's analysis remains "extrinsic to the social forms expressed" by the deep structure concepts of capital, value and the commodity . For Postone, the postmodern moment is not necessarily just a one-sided effect of the contemporary form of capitalism but can also be seen as having an emancipatory side if it happened to be part of post-capitalism. And because postmodernism usually neglects its own context of embeddedness it can legitimate capitalism as postmodern, whereas at the level of deep structure it may in fact be more concentrated, with large capitals that accumulate rather than diverge, and with an expansion of commodification niches with fewer buyers.
Postone asserts that one cannot step outside capitalism and declare it a pure evil or as a one-dimensional badness, since the emancipatory content of such things as equal distribution or diversity are potentials of capitalism itself in its abundant and diverse productive powers. This initial perspective misfires however, when forms of society such as modernity and subsequently postmodernism take itself as the true whole of life for being oppositional to capitalism, when in fact they are grounded in the reproduction of the same capitalist relations that created them. | https://en.wikipedia.org/wiki/Time–space_compression |
The time–temperature superposition principle is a concept in polymer physics and in the physics of glass-forming liquids . [ 1 ] [ 2 ] [ 3 ]
This superposition principle is used to determine temperature-dependent mechanical properties of linear viscoelastic materials from known properties at a reference temperature. The elastic moduli of typical amorphous polymers increase with loading rate but decrease when the temperature is increased. [ 4 ] Curves of the instantaneous modulus as a function of time do not change shape as the temperature is changed but appear only to shift left or right. This implies that a master curve at a given temperature can be used as the reference to predict curves at various temperatures by applying a shift operation. The time-temperature superposition principle of linear viscoelasticity is based on the above observation. [ 5 ]
The application of the principle typically involves the following steps:
The translation factor is often computed using an empirical relation first established by Malcolm L. Williams, Robert F. Landel and John D. Ferry (also called the Williams-Landel-Ferry or WLF model). An alternative model suggested by Arrhenius is also used. The WLF model is related to macroscopic motion of the bulk material, while the Arrhenius model considers local motion of polymer chains.
Some materials, polymers in particular, show a strong dependence of viscoelastic properties on the temperature at which they are measured. If you plot the elastic modulus of a noncrystallizing crosslinked polymer against the temperature at which you measured it, you will get a curve which can be divided up into distinct regions of physical behavior. At very low temperatures, the polymer will behave like a glass and exhibit a high modulus. As you increase the temperature, the polymer will undergo a transition from a hard “glassy” state to a soft “rubbery” state in which the modulus can be several orders of magnitude lower than it was in the glassy state. The transition from glassy to rubbery behavior is continuous and the transition zone is often referred to as the leathery zone. The onset temperature of the transition zone, moving from glassy to rubbery, is known as the glass transition temperature , or T g .
In the 1940s Andrews and Tobolsky [ 6 ] showed that there was a simple relationship between temperature and time for the mechanical response of a polymer. Modulus measurements are made by stretching or compressing a sample at a prescribed rate of deformation. For polymers, changing the rate of deformation will cause the curve described above to be shifted along the temperature axis. Increasing the rate of deformation will shift the curve to higher temperatures so that the transition from a glassy to a rubbery state will happen at higher temperatures.
It has been shown experimentally that the elastic modulus (E) of a polymer is influenced by the load and the response time. Time–temperature superposition implies that the response time function of the elastic modulus at a certain temperature resembles the shape of the same functions of adjacent temperatures. Curves of E vs. log(response time) at one temperature can be shifted to overlap with adjacent curves, as long as the data sets did not suffer from ageing effects [ 7 ] during the test time (see Williams-Landel-Ferry equation ).
The Deborah number is closely related to the concept of time-temperature superposition.
Consider a viscoelastic body that is subjected to dynamic loading. If the excitation frequency is low enough [ 8 ] the viscous behavior is paramount and all polymer chains have the time to respond to the applied load within a time period. In contrast, at higher frequencies, the chains do not have the time to fully respond and the resulting artificial viscosity results in an increase in the macroscopic modulus. Moreover, at constant frequency, an increase in temperature results in a reduction of the modulus due to an increase in free volume and chain movement.
Time–temperature superposition is a procedure that has become important in the field of polymers to observe the dependence upon temperature on the change of viscosity of a polymeric fluid. Rheology or viscosity can often be a strong indicator of the molecular structure and molecular mobility. Time–temperature superposition avoids the inefficiency of measuring a polymer's behavior over long periods of time at a specified temperature by utilizing the fact that at higher temperatures and shorter time the polymer will behave the same, provided there are no phase transitions.
Consider the relaxation modulus E at two temperatures T and T 0 such that T > T 0 . At constant strain, the stress relaxes faster at the higher temperature. The principle of time-temperature superposition states that the change in temperature from T to T 0 is equivalent to multiplying the time scale by a constant factor a T which is only a function of the two temperatures T and T 0 . In other words,
The quantity a T is called the horizontal translation factor or the shift factor and has the properties:
The superposition principle for complex dynamic moduli (G* = G ' + i G '' ) at a fixed frequency ω is obtained similarly:
A decrease in temperature increases the time characteristics while frequency characteristics decrease.
For a polymer in solution or "molten" state the following relationship can be used to determine the shift factor:
where η T0 is the viscosity (non-Newtonian) during continuous flow at temperature T 0 and η T is the viscosity at temperature T .
The time–temperature shift factor can also be described in terms of the activation energy ( E a ). By plotting the shift factor a T versus the reciprocal of temperature (in K), the slope of the curve can be interpreted as E a / k , where k is the Boltzmann constant = 8.64x10 −5 eV/K and the activation energy is expressed in terms of eV.
The empirical relationship of Williams-Landel- Ferry , [ 10 ] combined with the principle of time-temperature superposition, can account for variations in the intrinsic viscosity η 0 of amorphous polymers as a function of temperature, for temperatures near the glass transition temperature T g . The WLF model also expresses the change with the temperature of the shift factor.
Williams, Landel and Ferry proposed the following relationship for a T in terms of ( T - T 0 ) :
where log {\displaystyle \log } is the decadic logarithm and C 1 and C 2 are positive constants that depend on the material and the reference temperature. This relationship holds only in the approximate temperature range [T g , T g + 100 °C].
To determine the constants, the factor a T is calculated for each component M′ and M of the complex measured modulus M *. A good correlation between the two shift factors gives the values of the coefficients C 1 and C 2 that characterize the material.
If T 0 = T g :
where C g 1 and C g 2 are the coefficients of the WLF model when the reference temperature is the glass transition temperature.
The coefficients C 1 and C 2 depend on the reference temperature. If the reference temperature is changed from T 0 to T′ 0 , the new coefficients are given by
In particular, to transform the constants from those obtained at the glass transition temperature to a reference temperature T 0 ,
These same authors have proposed the "universal constants" C g 1 and C g 2 for a given polymer system be collected in a table. These constants are approximately the same for a large number of polymers and can be written C g 1 ≈ 15 and C g 2 ≈ 50 K. Experimentally observed values deviate from the values in the table. These orders of magnitude are useful and are a good indicator of the quality of a relationship that has been computed from experimental data.
The principle of time-temperature superposition requires the assumption of thermorheologically simple behavior (all curves have the same characteristic time variation law with temperature). From an initial spectral window [ ω 1 , ω 2 ] and a series of isotherms in this window, we can calculate the master curves of a material which extends over a broader frequency range. An arbitrary temperature T 0 is taken as a reference for setting the frequency scale (the curve at that temperature undergoes no shift).
In the frequency range [ ω 1 , ω 2 ], if the temperature increases from T 0 , the complex modulus E′ ( ω ) decreases. This amounts to explore a part of the master curve corresponding to frequencies lower than ω 1 while maintaining the temperature at T 0 . Conversely, lowering the temperature corresponds to the exploration of the part of the curve corresponding to high frequencies. For a reference temperature T 0 , shifts of the modulus curves have the amplitude log( a T ). In the area of glass transition, a T is described by an homographic function of the temperature.
The viscoelastic behavior is well modeled and allows extrapolation beyond the field of experimental frequencies which typically ranges from 0.01 to 100 Hz .
The WLF-model can be developed from Doolittle's concept of free volume and the thermal expansion coefficient α T E {\displaystyle \alpha _{\rm {TE}}} . α T E {\displaystyle \alpha _{\rm {TE}}} has a discontinuity when going below T g {\displaystyle T_{g}} for these types of materials, which can be seen as a phase shift going to more of a solid state (the glassy region). The WLF-model is inaccurate when the material is in the solid state and an Arrhenius equation can be used instead, see equation ( 1 ). [ 11 ]
The shift factor a T {\displaystyle a_{\rm {T}}} can then be defined, see equation ( 2 ), using equation ( 1 )
where E a {\displaystyle E_{a}} is the activation energy, R {\displaystyle R} is the universal gas constant , T g {\displaystyle T_{g}} is both the glass transition temperature and the reference temperature in kelvin (however, it is possible to use another reference below T g {\displaystyle T_{g}} as well), T ∈ [ 0 , T g ] {\displaystyle T\in [0,T_{g}]} is the variable temperature in kelvin , and c 1 ≈ 2.303 {\displaystyle c_{1}\approx 2.303} which is a conversion factor between the ln {\displaystyle \ln } and log {\displaystyle \log } .
This Arrhenius law, under this glass transition temperature, applies to secondary transitions (relaxation) called β -transitions.
For the superposition principle to apply, the sample must be homogeneous, isotropic and amorphous. The material must be linear viscoelastic under the deformations of interest, i.e., the deformation must be expressed as a linear function of the stress by applying very small strains, e.g. 0.01%.
To apply the WLF relationship, such a sample should be sought in the approximate temperature range [ T g , T g + 100 °C], where α -transitions are observed (relaxation). The study to determine a T and the coefficients C 1 and C 2 requires extensive dynamic testing at a number of scanning frequencies and temperature, which represents at least a hundred measurement points. | https://en.wikipedia.org/wiki/Time–temperature_superposition |
Timing failure is a failure in a time related process in machinery or computing. This can be where timing failures refer to "a situation where the environment in which a system operates does not behave as expected regarding the timing assumptions, that is, the timing constraints are not met." [ 1 ]
In computing, it refers to a timing failure or error in process , or part of a process, in a synchronous distributed system or real-time system to meet limits set on execution time, message delivery, clock drift rate, or clock skew . [ 2 ] [ 3 ] [ 4 ] Asynchronous distributed systems cannot be said to have timing failures as guarantees are not provided for response times .
In engineering and mechanics a timing failure typically refers to an issue with the timing belt of an engine . [ 5 ] [ 6 ]
This computing article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Timing_failure |
Timing margin [ 1 ] is an electronics term that defines the difference between the actual change in a signal and the latest time at which the signal can change in order for an electronic circuit to function correctly. It is used in the design of digital electronics .
In this image, the lower signal is the clock and the upper signal is the data. Data is recognized by the circuit at the positive edge of the clock. There are two time intervals illustrated in this image. One is the setup time , and the other is the timing margin. The setup time is illustrated in red in this image; the timing margin is illustrated in green.
The edges of the signals can shift around in a real-world electronic system for various reasons. If the clock and the data signal are shifted relative to each other, this may increase or reduce the timing margin; as long as the data signal changes before the setup time is entered, the data will be interpreted correctly. If it is known from experience that the signals can shift relative to each other by as much as 2 microseconds, for instance, designing the system with at least 2 microseconds of timing margin will prevent incorrect interpretation of the data signal by the receiver.
If the physical design of the circuit is changed, for example by giving more wire that the clock signal is transmitted on, the edge of the data signal will move closer to the positive edge of the clock signal, reducing the timing margin. If the signals have been designed with enough timing margin, only the correct data will be received.
This electronics-related article is a stub . You can help Wikipedia by expanding it .
This engineering-related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Timing_margin |
Timir Datta is an Indian-American physicist specializing in high transition temperature superconductors and a professor of physics in the department of Physics and Astronomy at the University of South Carolina , in Columbia, South Carolina .
Datta grew up in India along with elder brother Jyotirmoy Datta a noted journalist; his father B.N. Dutt a scion of two land owning families from Khulna and Jessore in south central Bengal (British India) was an eminent sugar-refining engineer and on his mother's side a relative of Michael Madhusudan Dutt , the famed poet. He received a master's degree in theoretical plasma physics from Boston College in 1974 under the direction of Gabor Kalman . [ pub 1 ] Datta also worked at the Jet Propulsion laboratory (JPL) in Pasadena, California, as a pre-doctoral NASA research associate of Robert Somoano. He also collaborated with Carl H. Brans at Loyola University New Orleans on a gravitational problem of frame dragging and worked with John Perdew on the behavior of charge density waves in jellium . Datta is of Bengali origin. [ citation needed ]
Datta was a NSF post-doctoral fellow with Marvin Silver and studied charge propagation in non-crystalline systems [ pub 2 ] at the University of North Carolina in Chapel Hill. At UNC-CH he continued his theoretical interests and worked on retarded Vander Waals potential [ pub 3 ] with L. H. Ford. Since 1982, he has been on the faculty of the University of South Carolina in Columbia. [ citation needed ]
He collaborated with several laboratories involved with the early discoveries of high temperature superconductivity, especially the team at NRL, led by Donald U Gubser and Stuart Wolf. This research group at USC was the also first to observe [ pub 4 ] (i) bulk Meissner effect in Tl-copper oxides and thus confirm the discovery by Allen Herman's team at the University of Arkansas of high temperature superconductivity in these compounds. [ 1 ] He coined the term "triple digit superconductivity", [ 2 ] and his group was the first to observe (ii) fractional quantum hall effect in 3-dimensional carbon. [ pub 5 ] [ pub 6 ]
In a paper with Raphael Tsu he derived the first quantum mechanical wave impedance formula for Schrödinger wave functions. [ pub 7 ] He was also the first to show that Bragg's law of X-ray scattering from crystals is a direct consequence of Euclidean length invariance of the incident wave vector; in fact Max von Laue's three diffraction equations are not independent but related by length conservation. [ pub 8 ]
Datta is an active researcher, with over 100 papers listed in the SAO/NASA Astrophysics Data System (ADS) as of 2014. [ 3 ]
Datta was issued one US patent in 1995: "Flux-trapped superconducting magnets and method of manufacture", with two co-inventors. [ 4 ]
Datta was involved in the university-funded development of a "Gravity Generator" in 1996 and 1997, with then-fellow university researcher Douglas Torr. [ 5 ] According to a leaked document from the Office of Technology Transfer at the University of South Carolina and confirmed to Wired reporter Charles Platt in 1998, the device would create a "force beam" in any desired direction and the university planned to patent and license this device. Neither information about this university research project nor any "Gravity Generator" device was ever made public. [ 6 ]
Despite the apparent less than successful outcome of the "Gravity Generator" development effort with Torr, Datta became interested in the effects of electric fields on gravitation, expanding on Torr's theoretical work on the subject. [ pub 9 ] [ pub 10 ] | https://en.wikipedia.org/wiki/Timir_Datta |
Timken OK Load is a standardised measurement that indicates the possible performance of extreme pressure (EP) additives in a lubricating grease or oil . The units of measurement are pounds-force or kilograms-force . This measurement is performed using a special test machine and standard block and ring test specimens.
The test machine is based on a machine manufactured by the Timken Company from 1935 to 1972, [ 1 ] It is now an industry recognized standard test to compare extreme pressure resistance of greases and oils in a reproducible way.
It is not to be confused with some smaller lubricity testers that are also often erroneously called Timken: the confusion originates from a now obsolete Italian brand TIMPKEN. [ citation needed ]
The test machine consists of a standardized bearing race mounted on a tapered arbour rotating at high speed. The race is brought into contact with a square steel test block under a constant load. The contact area is flooded with the lubricant or grease being tested. The Timken OK Load is the highest standard load at which the spinning bearing race produces no scouring mark on the test block, but only a uniform wear scar. [ 1 ]
Timken OK Loads are listed on grease and oil property charts and are part of many specifications. It was once generally assumed that the measure and the film strength of the lubricant were directly related. Today, the primary purpose of the test is to determine whether EP additives are present and functioning. A measure of 35 pounds (16 kilograms-force or 155 newtons) or more means that EP additives are present and working well. [ 1 ]
The Timken OK Load test methods are ASTM D-2509 for greases and ASTM D-2782 for oils.
There are a few portable versions of smaller testers utilizing similar test methods for public demonstration or for product showcase. | https://en.wikipedia.org/wiki/Timken_OK_Load |
Timothy Williamson (born 6 August 1955) is a British philosopher whose main research interests are in philosophical logic , philosophy of language , epistemology and metaphysics . He is the former Wykeham Professor of Logic at the University of Oxford , and a fellow of New College, Oxford .
Born on 6 August 1955, Williamson's education began at Leighton Park School and continued at Henley Grammar School (now the Henley College ). He then went to Balliol College , Oxford University . He graduated in 1976 with a Bachelor of Arts degree with first-class honours in mathematics and philosophy, and in 1980 with a doctorate in philosophy ( DPhil ) for a thesis entitled The Concept of Approximation to the Truth . [ 1 ]
Williamson was Professor of Logic and Metaphysics at the University of Edinburgh (1995–2000), fellow and lecturer in philosophy at University College, Oxford (1988–1994), and lecturer in philosophy at Trinity College, Dublin (1980–1988). He took up the Wykeham Professorship in 2000 and retired in 2023, when he took up a Senior Research and Teaching Fellowship in Philosophy. [ 2 ]
He has been visiting professor at Yale University , Princeton University , MIT , the University of Michigan , and the Chinese University of Hong Kong .
He was president of the Aristotelian Society from 2004 to 2005.
He is a Fellow of the British Academy (FBA), [ 3 ] the Norwegian Academy of Science and Letters , [ 4 ] Fellow of the Royal Society of Edinburgh (FRSE), and a Foreign Honorary Fellow of the American Academy of Arts & Sciences .
Since 2022 he is visiting professor at the Università della Svizzera Italiana .
Williamson has contributed to analytic philosophy of language , logic , metaphysics and epistemology .
On vagueness , he holds a position known as epistemicism , which states that every seemingly vague predicate (like "bald" or "thin") actually has a sharp cutoff, which is impossible for us to know. For instance, there is some number of hairs such that anyone with that number is bald, and anyone with even one more hair is not. In actuality, this condition will be spelled out only partly in terms of numbers of hairs, but whatever measures are relevant will have some sharp cutoff. This solution to the difficult Sorites paradox was considered an astonishing and unacceptable consequence, but has become a relatively mainstream view since his defence of it. [ 5 ] Williamson is fond of using the statement, "no one knows whether I am thin" to illustrate his view. [ 6 ]
In epistemology , Williamson suggests that the concept of knowledge is unanalysable. This went against the common trend in philosophical literature up to that point, which was to argue that knowledge could be analysed into constituent concepts. (Typically this would be justified true belief plus an extra factor.) He agrees that knowledge entails justification, truth and belief , but argues that it is conceptually primitive. He accounts for the importance of belief by discussing its connections with knowledge, but avoids the disjunctivist position of saying that belief can be analysed as the disjunction of knowledge with some distinct, non- factive mental state. [ 7 ]
Williamson also argues against the traditional distinction of knowing-how and knowing-that . He says that knowledge-how is a type of knowledge-that. Williamson argues that knowledge-how does not relate one's ability. As an example, he gives a ski instructor who knows how to perform a complex move without having the ability to do it himself. [ 8 ]
In metaphysics , Williamson defends necessitism, according to which necessarily everything is necessarily something, in short, that everything exists of necessity. Necessitism is associated with the Barcan formula : it is possible for something to have a property only if there is something which has that property. Thus, since it is possible for Wittgenstein to have had a child, there is something which is a possible child of Wittgenstein. However, Williamson has also developed an ontology of bare possibilia which he argues alleviates the worst consequences of necessitism and of the Barcan formula. It's not that Wittgenstein's possible child is concrete; rather, it is contingently non-concrete.
Williamson has also published more than 120 articles in peer-reviewed scholarly journals. | https://en.wikipedia.org/wiki/Timothy_Williamson |
Tin(II) bromide is a chemical compound of tin and bromine with a chemical formula of SnBr 2 . Tin is in the +2 oxidation state. The stability of tin compounds in this oxidation state is attributed to the inert pair effect . [ 3 ]
In the gas phase SnBr 2 is non-linear with a bent configuration similar to SnCl 2 in the gas phase. The Br-Sn-Br angle is 95° and the Sn-Br bond length is 255pm. [ 4 ] There is evidence of dimerisation in the gaseous phase. [ 5 ] The solid state structure is related to that of SnCl 2 and PbCl 2 and the tin atoms have five near bromine atom neighbours in an approximately trigonal bipyramidal configuration. [ 6 ] Two polymorphs exist: a room-temperature orthorhombic polymorph, and a high-temperature hexagonal polymorph. Both contain (SnBr 2 ) ∞ chains but the packing arrangement differs. [ 1 ]
Tin(II) bromide can be prepared by the reaction of metallic tin and HBr distilling off the H 2 O/HBr and cooling: [ 9 ]
However, the reaction will produce tin (IV) bromide in the presence of oxygen.
SnBr 2 is soluble in donor solvents such as acetone , pyridine and dimethylsulfoxide to give pyramidal adducts. [ 9 ] A number of hydrates are known, 2SnBr 2 ·H 2 O, 3SnBr 2 ·H 2 O & 6SnBr 2 ·5H 2 O which in the solid phase have tin coordinated by a distorted trigonal prism of 6 bromine atoms with Br or H 2 O capping 1 or 2 faces. [ 3 ] When dissolved in HBr the pyramidal SnBr 3 − ion is formed. [ 3 ] Like SnCl 2 it is a reducing agent. With a variety of alkyl bromides oxidative addition can occur to yield the alkyltin tribromide [ 10 ] e.g.
Tin(II) bromide can act as a Lewis acid forming adducts with donor molecules e.g. trimethylamine where it forms NMe 3 ·SnBr 2 and 2NMe 3 ·SnBr 2 [ 11 ] It can also act as both donor and acceptor in, for example, the complex F 3 B·SnBr 2 ·NMe 3 where it is a donor to boron trifluoride and an acceptor to trimethylamine . [ 12 ] | https://en.wikipedia.org/wiki/Tin(II)_bromide |
Tin(II) chloride , also known as stannous chloride , is a white crystalline solid with the formula Sn Cl 2 . It forms a stable dihydrate , but aqueous solutions tend to undergo hydrolysis , particularly if hot. SnCl 2 is widely used as a reducing agent (in acid solution), and in electrolytic baths for tin-plating . Tin(II) chloride should not be confused with the other chloride of tin; tin(IV) chloride or stannic chloride (SnCl 4 ).
SnCl 2 has a lone pair of electrons , such that the molecule in the gas phase is bent. In the solid state, crystalline SnCl 2 forms chains linked via chloride bridges as shown. The dihydrate has three coordinates as well, with one water on the tin and another water on the first. The main part of the molecule stacks into double layers in the crystal lattice , with the "second" water sandwiched between the layers.
Tin(II) chloride dissolves in less than its own mass of water. Dilute solutions are subject to hydrolysis, yielding an insoluble basic salt:
Hydrolysis is prevented in the presence of hydrochloric acid , typically of the same or greater molarity as the stannous chloride. Solutions of SnCl 2 are also unstable towards oxidation by the air:
Oxidation can be prevented by storing the solution over lumps of tin metal. [ 4 ]
Tin(II) chloride acts as a reducing agent for silver and gold salts to the metal, and iron(III) salts to iron(II), for example:
It also reduces copper(II) to copper(I).
Solutions of tin(II) chloride can also serve simply as a source of Sn 2+ ions, which can form other tin(II) compounds via precipitation reactions. For example, reaction with sodium sulfide produces the brown/black tin(II) sulfide :
If alkali is added to a solution of SnCl 2 , a white precipitate of hydrated tin(II) oxide forms initially; this then dissolves in excess base to form a stannite salt such as sodium stannite:
Anhydrous SnCl 2 can be used to make a variety of tin(II) compounds in non-aqueous solvents. For example, the lithium salt of 4-methyl-2,6-di-tert-butylphenol reacts with SnCl 2 in THF to give the yellow linear two-coordinate compound Sn(OAr) 2 (Ar = aryl ). [ 5 ]
Tin(II) chloride also behaves as a weak Lewis acid , forming complexes with ligands such as chloride ion, for example:
Like SnCl 2 (H 2 O) , trichlorostannate ( SnCl − 3 ) ion is pyramidal . Such complexes have a full octet . The lone pair of electrons in such complexes is available for bonding. Therefore, SnCl − 3 itself can serve as a Lewis base or ligand: [ 6 ]
SnCl 2 can be used to make a variety of related compounds containing metal-tin bonds. For example, the reaction with dicobalt octacarbonyl :
Anhydrous SnCl 2 is prepared by the action of dry hydrogen chloride gas on tin metal. The dihydrate is made by a similar reaction, using hydrochloric acid :
The water then carefully evaporated from the acidic solution to produce crystals of SnCl 2 ·2H 2 O. This dihydrate can be dehydrated to anhydration using acetic anhydride . [ 7 ]
A solution of tin(II) chloride containing a little hydrochloric acid is used for the tin-plating of steel, in order to make tin cans . An electric potential is applied, and tin metal is formed at the cathode via electrolysis .
Tin(II) chloride is used as a mordant in textile dyeing because it gives brighter colours with some dyes e.g. cochineal . This mordant has also been used alone to increase the weight of silk.
In recent years, an increasing number of tooth paste brands have been adding Tin(II) chloride as protection against enamel erosion to their formula, e. g. Oral-B or Elmex .
It is used as a catalyst in the production of the plastic polylactic acid (PLA).
It also finds a use as a catalyst between acetone and hydrogen peroxide to form the tetrameric form of acetone peroxide .
Tin(II) chloride also finds wide use as a reducing agent . This is seen in its use for silvering mirrors, where silver metal is deposited on the glass:
A related reduction was traditionally used as an analytical test for Hg 2+ (aq) . For example, if SnCl 2 is added dropwise into a solution of mercury(II) chloride , a white precipitate of mercury(I) chloride is first formed; as more SnCl 2 is added this turns black as metallic mercury is formed.
Stannous chloride is also used by many precious metals refining hobbyists and professionals to test for the presence of gold salts. [ 8 ] When SnCl 2 comes into contact with gold compounds, particularly chloroaurate salts, it forms a bright purple colloid known as purple of Cassius . [ 9 ] A similar reaction occurs with platinum and palladium salts, becoming green and brown respectively. [ 10 ]
When mercury is analyzed using atomic absorption spectroscopy, a cold vapor method must be used, and tin (II) chloride is typically used as the reductant.
In organic chemistry , SnCl 2 is used in the Stephen reduction , whereby a nitrile is reduced (via an imidoyl chloride salt) to an imine which is easily hydrolysed to an aldehyde . [ 11 ]
The reaction usually works best with aromatic nitriles Aryl -CN. A related reaction (called the Sonn-Müller method) starts with an amide, which is treated with PCl 5 to form the imidoyl chloride salt.
The Stephen reduction is less used today, because it has been mostly superseded by diisobutylaluminium hydride reduction.
Additionally, SnCl 2 is used to selectively reduce aromatic nitro groups to anilines . [ 12 ]
SnCl 2 also reduces quinones to hydroquinones .
Stannous chloride is also added as a food additive with E number E512 to some canned and bottled foods, where it serves as a color-retention agent and antioxidant .
SnCl 2 is used in radionuclide angiography to reduce the radioactive agent technetium -99m- pertechnetate to assist in binding to blood cells.
Molten SnCl 2 can be oxidised to form highly crystalline SnO 2 nanostructures. [ 13 ] [ 14 ]
A Stannous reduction is used in nuclear medicine bone scans to remove the negative charge from free pertechnetate when it is bound to MDP for radiopharmaceutical studies. Incomplete reduction due to insufficient tin or accidental insufflation of air leads to the formation of free pertechnetate, a finding which can be seen on bone scans due to its inappropriate uptake in the stomach. [ 15 ]
Stannous Chloride is used for coating SnO 2 Tin Oxide doped conductive iridescent coatings for low e glass. [ 16 ] | https://en.wikipedia.org/wiki/Tin(II)_chloride |
Tin(II) fluoride , commonly referred to commercially as stannous fluoride [ 1 ] [ 2 ] (from Latin stannum , 'tin'), is a chemical compound with the formula SnF 2 . It is a colourless solid used as an ingredient in toothpastes .
Stannous fluoride is an alternative to sodium fluoride for the prevention of cavities ( tooth decay ). It was first released commercially in 1956, in Crest toothpaste. It was discovered and developed by Joseph Muhler and William Nebergall. In recognition of their innovation, they were inducted into the Inventor's Hall of Fame . [ 1 ]
The fluoride in stannous fluoride helps to convert the calcium mineral hydroxyapatite in teeth into fluorapatite , which makes tooth enamel more resistant to bacteria-generated acid attacks. [ 3 ] The calcium present in plaque and saliva reacts with fluoride to form calcium fluoride on the tooth surface; over time, this calcium fluoride dissolves to allow calcium and fluoride ions to interact with the tooth and form fluoride-containing apatite within the tooth structure. [ 4 ] This chemical reaction inhibits demineralisation and can promote remineralisation of tooth decay. The resulting fluoride-containing apatite is more insoluble, and more resistant to acid and tooth decay. [ 4 ]
In addition to fluoride, the stannous ion has benefits for oral health when incorporated in a toothpaste. At similar fluoride concentrations, toothpastes containing stannous fluoride have been shown to be more effective than toothpastes containing sodium fluoride for reducing the incidence of dental caries and dental erosion , [ 5 ] [ 6 ] [ 7 ] [ 8 ] [ 9 ] as well as reducing gingivitis . [ 10 ] [ 11 ] [ 12 ] [ 13 ] [ 14 ] Some stannous fluoride-containing toothpastes also contain ingredients that allow for better stain removal. [ 15 ] [ 16 ] Stabilised stannous fluoride formulations allow for greater bioavailability of the stannous and fluoride ion, increasing their oral health benefits. [ 17 ] [ 18 ] A systematic review revealed stabilised stannous fluoride-containing toothpastes had a positive effect on the reduction of plaque , gingivitis and staining, with a significant reduction in calculus and halitosis (bad breath) compared to other toothpastes. [ 16 ] A specific formulation of stabilised stannous fluoride toothpastes has shown superior protection against dental erosion and dentine hypersensitivity compared to other fluoride-containing and fluoride-free toothpastes. [ 19 ]
Stannous fluoride was once used under the trade name Fluoristan in the original formulation of the toothpaste brand Crest , though it was later replaced with sodium monofluorophosphate under the trade name Fluoristat. Stabilised stannous fluoride is now the active ingredient in Crest/ Oral B Pro-Health brand toothpaste. Although concerns have been previously raised that stannous fluoride may cause tooth staining, this can be avoided by proper brushing and by using a stabilised stannous fluoride toothpaste. [ 15 ] [ 16 ] Any stannous fluoride staining that occurs due to improper brushing is not permanent, and Crest/Oral B Pro-Health states that its particular formulation is resistant to staining.
SnF 2 can be prepared by evaporating a solution of SnO in 40% HF . [ 20 ]
Readily soluble in water, SnF 2 is hydrolysed. At low concentration, it forms species such as SnOH + , Sn(OH) 2 and Sn(OH) 3 − . At higher concentrations, predominantly polynuclear species are formed, including Sn 2 (OH) 2 2+ and Sn 3 (OH) 4 2+ . [ 21 ] Aqueous solutions readily oxidise to form insoluble precipitates of Sn IV , which are ineffective as a dental prophylactic. [ 22 ] Studies of the oxidation using Mössbauer spectroscopy on frozen samples suggests that O 2 is the oxidizing species. [ 23 ]
SnF 2 acts as a Lewis acid . For example, it forms a 1:1 complex (CH 3 ) 3 NSnF 2 and 2:1 complex [(CH 3 ) 3 N] 2 SnF 2 with trimethylamine , [ 24 ] and a 1:1 complex with dimethylsulfoxide , (CH 3 ) 2 SO·SnF 2 . [ 25 ] In solutions containing the fluoride ion, F − , it forms the fluoride complexes SnF 3 − , Sn 2 F 5 − , and SnF 2 (OH 2 ). [ 26 ] Crystallization from an aqueous solution containing NaF produces compounds containing polynuclear anions, e.g. NaSn 2 F 5 or Na 4 Sn 3 F 10 depending on the reaction conditions, rather than NaSnF 3 . [ 20 ] The compound NaSnF 3 , containing the pyramidal SnF 3 − anion, can be produced from a pyridine–water solution. [ 27 ] Other compounds containing the pyramidal SnF 3 − anion are known, such as Ca(SnF 3 ) 2 . [ 28 ]
SnF 2 is a reducing agent , with a standard reduction potential of E o (Sn IV / Sn II ) = +0.15 V. [ 29 ] Solutions in HF are readily oxidised by a range of oxidizing agents (O 2 , SO 2 or F 2 ) to form the mixed-valence compound Sn 3 F 8 (containing Sn II and Sn IV and no Sn–Sn bonds). [ 20 ]
The monoclinic form contains tetramers, Sn 4 F 8 , where there are two distinct coordination environments for the Sn atoms. In each case, there are three nearest neighbours, with Sn at the apex of a trigonal pyramid, and the lone pair of electrons sterically active. [ 30 ] Other forms reported have the GeF 2 and paratellurite structures. [ 30 ]
In the vapour phase, SnF 2 forms monomers, dimers, and trimers. [ 26 ] Monomeric SnF 2 is a non-linear with an Sn−F bond length of 206 pm. [ 26 ] Complexes of SnF 2 , sometimes called difluorostannylene, with an alkyne and aromatic compounds deposited in an argon matrix at 12 K have been reported. [ 31 ] [ 32 ]
Stannous fluoride can cause redness and irritation if it is inhaled or comes into contact with the eyes. If ingested, it can cause abdominal pains and shock. [ 33 ] Rare but serious allergic reactions are possible; symptoms include itching, swelling, and difficulty breathing. Certain formulations of stannous fluoride in dental products may cause mild tooth discoloration ; this is not permanent and can be removed by brushing, or can be prevented by using a stabilised stannous fluoride toothpaste. [ 15 ] [ 16 ] [ 34 ] | https://en.wikipedia.org/wiki/Tin(II)_fluoride |
Tin(II) hydroxide , Sn(OH) 2 , also known as stannous hydroxide , is an inorganic compound tin(II). The only related material for which definitive information is available is the oxy hydroxide Sn 6 O 4 (OH) 4 , but other related materials are claimed. They are all white solids that are insoluble in water.
Crystals of Sn 6 O 4 (OH) 4 has been characterized by X-ray diffraction. This cluster is obtained from solution of basic solutions of tin(II). The compound consists of an octahedron of Sn centers, each face of which is capped by an oxide or a hydroxide. The structure is reminiscent of the Mo 6 S 8 subunit of the Chevrel phases .. [ 2 ] The structure of pure Sn(OH) 2 is not known. [ 3 ]
Sn(OH) 2 has been claimed to arise from the reaction of (CH 3 ) 3 SnOH with SnCl 2 in an aprotic solvent: [ 3 ]
No crystallographic characterization is available on this material.
Stannous hydroxide adds additional hydroxide ligands to form stannites . [ 4 ] Air easily oxidizes stannous hydroxide to stannic oxide (SnO 2 ). | https://en.wikipedia.org/wiki/Tin(II)_hydroxide |
Tin(II) iodide , also known as stannous iodide , is the inorganic compound with the formula SnI 2 . It is a red-orange solid. It reacts with iodine to give tin(IV) iodide . [ 1 ]
Tin(II) iodide can be synthesised by heating metallic tin with a mixture iodine in 2 M hydrochloric acid. [ 2 ] [ 1 ]
It crystallizes in a unique motif. According to X-ray crystallography , some Sn(II) centers are bound to six iodide ligands others Sn(II) sites are distorted. [ 3 ] | https://en.wikipedia.org/wiki/Tin(II)_iodide |
Tin(II) oxide ( stannous oxide ) is a compound with the formula SnO. It is composed of tin and oxygen where tin has the oxidation state of +2. There are two forms, a stable blue-black form and a metastable red form.
Blue-black SnO can be produced by heating the tin(II) oxide hydrate, SnO· x H 2 O ( x < 1) precipitated when a tin(II) salt is reacted with an alkali hydroxide such as NaOH. [ 4 ] Metastable, red SnO can be prepared by gentle heating of the precipitate produced by the action of aqueous ammonia on a tin(II) salt. [ 4 ] SnO may be prepared as a pure substance in the laboratory, by controlled heating of tin(II) oxalate ( stannous oxalate ) in the absence of air or under a CO 2 atmosphere. This method is also applied to the production of ferrous oxide and manganous oxide . [ 5 ] [ 6 ]
Tin(II) oxide burns in air with a dim green flame to form SnO 2 . [ 4 ]
When heated in an inert atmosphere initially disproportionation occurs giving Sn metal and Sn 3 O 4 which further reacts to give SnO 2 and Sn metal. [ 4 ]
SnO is amphoteric , dissolving in strong acid to give tin(II) salts and in strong base to give stannites containing Sn(OH) 3 − . [ 4 ] It can be dissolved in strong acid solutions to give the ionic complexes Sn(OH 2 ) 3 2+ and Sn(OH)(OH 2 ) 2 + , and in less acid solutions to give Sn 3 (OH) 4 2+ . [ 4 ] Note that anhydrous stannites, e.g. K 2 Sn 2 O 3 , K 2 SnO 2 are also known. [ 7 ] [ 8 ] [ 9 ] SnO is a reducing agent and is thought to reduce copper(I) to metallic clusters in the manufacture of so-called "copper ruby glass". [ 10 ]
Black, α-SnO adopts the tetragonal PbO layer structure containing four coordinate square pyramidal tin atoms. [ 11 ] This form is found in nature as the rare mineral romarchite . [ 12 ] The asymmetry is usually simply ascribed to a sterically active lone pair; however, electron density calculations show that the asymmetry is caused by an antibonding interaction of the Sn(5s) and the O(2p) orbitals. [ 13 ] The electronic structure and chemistry of the lone pair determines most of the properties of the material. [ 14 ]
Non-stoichiometry has been observed in SnO. [ 15 ]
The electronic band gap has been measured between 2.5 eV and 3eV. [ 16 ]
The dominant use of stannous oxide is as a precursor in manufacturing of other, typically divalent, tin compounds or salts. Stannous oxide may also be employed as a reducing agent and in the creation of ruby glass . [ 17 ] It has a minor use as an esterification catalyst.
Cerium(III) oxide in ceramic form, together with Tin(II) oxide (SnO) is used for illumination with UV light. [ 18 ] | https://en.wikipedia.org/wiki/Tin(II)_oxide |
Tin(II) sulfate ( Sn S O 4 ) is a chemical compound . It is a white solid that can absorb enough moisture from the air to become fully dissolved, forming an aqueous solution; this property is known as deliquescence . It can be prepared by a displacement reaction between metallic tin and copper(II) sulfate : [ 3 ]
Tin(II) sulfate is a convenient source of tin(II) ions uncontaminated by tin(IV) species.
In the solid state the sulfate ions are linked together by O-Sn-O bridges. The tin atom has three oxygen atoms arranged pyramidally at 226 pm with the three O-Sn-O bond angles of 79°, 77.1° and 77.1°. Other Sn-O distances are longer ranging from 295 - 334pm. [ 3 ] [ 4 ] | https://en.wikipedia.org/wiki/Tin(II)_sulfate |
Tin(II) sulfide is an inorganic compound with the chemical formula is SnS. A black or brown solid, it occurs as the rare mineral herzenbergite (α-SnS).It is insoluble in water but dissolves with degradation in concentrated hydrochloric acid . Tin(II) sulfide is insoluble in ammonium sulfide .
The preparation of tin(II) sulfide has been extensively investigated, and the direct reaction of the elements is inefficient. [ 3 ] Instead, molten potassium thiocyanate reliably reacts with stannic oxide to give SnS at 450 °C: [ 4 ]
SnS also forms when aqueous solutions of tin(II) salts are treated with hydrogen sulfide. [ 5 ] This conversion is a step in qualitative inorganic analysis .
At cryogenic temperatures, stannous chloride dissolves in liquid hydrogen sulfide . It then decomposes to the sulfide, but only slowly. [ 6 ]
At temperatures above 905 K, SnS undergoes a second order phase transition to β-SnS (space group: Cmcm, No. 63). [ 7 ] A new polymorph of SnS exists based upon the cubic crystal system, known as π-SnS (space group: P2 1 3, No. 198). [ 8 ] [ 9 ] [ 10 ] Herzenbergite (α-SnS) can be exfoliated to form layered structure similar to that of black phosphorus , featuring 3-coordinate Sn and S centers. [ 5 ] [ 7 ] Analogous to black phosphorus, tin(II) sulfide can be ultrasonically exfoliated in liquids to produce atomically thin semiconducting SnS sheets that have a wider optical band gap (>1.5 eV) compared to the bulk crystal. [ 11 ]
Tin(II) sulfide has been evaluated as a candidate for thin-film solar cells . Currently, both cadmium telluride and CIGS ( copper indium gallium selenide ) are used as p-type absorber layers, but they are formulated from toxic, scarce constituents. [ 12 ] Tin(II) sulfide, by contrast, is formed from cheap, earth-abundant elements, and is nontoxic. This material also has a high optical absorption coefficient, p-type conductivity, and a mid range direct band gap of 1.3-1.4 eV, required electronic properties for this type of absorber layer. [ 13 ] Based on the a detailed balance calculation using the material bandgap, the power conversion efficiency of a solar cell utilizing a tin(II) sulfide absorber layer could be as high as 32%, which is comparable to crystalline silicon. [ 14 ] Finally, Tin(II) sulfide is stable in both alkaline and acidic conditions. [ 15 ] All aforementioned characteristics suggest tin(II) sulfide as an interesting material to be used as a solar cell absorber layer.
Power conversion efficiencies for tin(II) sulfide thin films in photovoltaic cells are less than 5%. [ 16 ] Barriers for use include a low open circuit voltage and an inability to realize many of the above properties due to challenges in fabrication. [ 14 ] | https://en.wikipedia.org/wiki/Tin(II)_sulfide |
Tin(IV) oxide , also known as stannic oxide , is the inorganic compound with the formula SnO 2 . The mineral form of SnO 2 is called cassiterite , and this is the main ore of tin . [ 9 ] With many other names, this oxide of tin is an important material in tin chemistry. It is a colourless, diamagnetic , amphoteric solid.
Tin(IV) oxide crystallises with the rutile structure. As such the tin atoms are six coordinate and the oxygen atoms three coordinate. [ 9 ] SnO 2 is usually regarded as an oxygen-deficient n-type semiconductor . [ 10 ]
Hydrous forms of SnO 2 have been described as stannic acid . Such materials appear to be hydrated particles of SnO 2 where the composition reflects the particle size. [ 11 ]
Tin(IV) oxide occurs naturally. Synthetic tin(IV) oxide is produced by burning tin metal in air. [ 11 ] Annual production is in the range of 10 kilotons. [ 11 ] SnO 2 is reduced industrially to the metal with carbon in a reverberatory furnace at 1200–1300 °C. [ 12 ]
The reaction from tin(IV) oxide with hot carbon monoxide is practiced on a large scale as this carbothermal reduction is used to obtain tin metal from its ores:
Some other reactions relevant to purifying tin from its ores are: [ 13 ]
SnO 2 converts to the monoxide at 1500 °C: [ 13 ]
SnO 2 is insoluble in water. It dissolves in sulfuric acid and in molten sodium hydroxide. It is not amphoteric . Like rutile, it is not attacked by solutions of acid or base.
Dissolution of SnO 2 in sulfuric acid gives the sulfate: [ 11 ]
The latter compound can add additional hydrogen sulfate ligands to give hexahydrogensulfatostannic acid. [ 14 ]
SnO 2 dissolves in molten alkali to give " stannates ," with the nominal formula Na 2 SnO 3 . [ 11 ] Dissolving the solidified SnO 2 /NaOH melt in water gives Na 2 [Sn(OH) 6 ], "preparing salt," which is used in the dye industry. [ 11 ]
In conjunction with vanadium oxide, it is used as a catalyst for the oxidation of aromatic compounds in the synthesis of carboxylic acids and acid anhydrides. [ 9 ]
SnO 2 is used as pigment in the manufacture of glasses, enamels and ceramic glazes . Thousands of tons of SnO 2 are produced annually for this application. Pure SnO 2 gives a milky white colour; other colours are achieved when mixed with other metallic oxides e.g. V 2 O 5 yellow; Cr 2 O 3 pink; and Sb 2 O 5 grey blue. [ 11 ] [ 15 ] This use probably led to the discovery of the pigment lead-tin-yellow , which was produced using tin(IV) oxide as a compound. [ 16 ] The use of tin(IV) oxide has been particularly common in glazes for earthenware , sanitaryware and wall tiles; see the articles tin-glazing and Tin-glazed pottery . Tin oxide remains in suspension in vitreous matrix of the fired glazes, and, with its high refractive index being sufficiently different from the matrix, light is scattered, and hence increases the opacity of the glaze. The degree of dissolution increases with the firing temperature, and hence the extent of opacity diminishes. [ 17 ] Although dependent on the other constituents the solubility of tin oxide in glaze melts is generally low. Its solubility is increased by Na 2 O, K 2 O and B 2 O 3 , and reduced by CaO, BaO, ZnO, Al 2 O 3 , and to a limited extent PbO. [ 18 ]
SnO 2 coatings are valued as transparent conducting oxides (TCOs). Like other TCOs, SnO 2 has significant electrical conductivity but is transparent, an unusual combination of properties. Windows coated with SnO 2 also reflect infrared radiation , which is relevant to temperature control for smart windows . [ 19 ] Coatings can be applied using chemical vapor deposition , vapour deposition techniques that employ SnCl 4 [ 9 ] or organotin trihalides [ 20 ] e.g. butyltin trichloride as the volatile agent. This technique is used to coat glass bottles with a thin (<0.1 μm) layer of SnO 2 , which helps to adhere a subsequent, protective polymer coating such as polyethylene to the glass. [ 9 ]
Thicker layers doped with Sb or F ions are electrically conducting and used in electroluminescent devices and photovoltaics. [ 9 ]
SnO 2 has been evaluated as sensors of combustible gases including carbon monoxide detectors . In these the sensor area is heated to a constant temperature (few hundred °C) and in the presence of a combustible gas the electrical resistivity drops. [ 21 ]
This oxide of tin has been utilized as a mordant in the dyeing process since ancient Egypt. [ 22 ] A German by the name of Kuster first introduced its use to London in 1533 and by means of it alone, the color scarlet was produced there. [ 23 ]
Tin(IV) oxide for this use is sometimes called as "putty powder" [ 24 ] or "jeweler's putty". [ 1 ]
Tin(IV) oxide can be used as a polishing powder, [ 11 ] sometimes in mixtures also with lead oxide, for polishing glass, jewelry, marble and silver. [ 1 ] | https://en.wikipedia.org/wiki/Tin(IV)_oxide |
Tin-silver-copper ( Sn - Ag - Cu , also known as SAC ), is a lead-free ( Pb-free ) alloy commonly used for electronic solder . It is the main choice for lead-free surface-mount technology (SMT) assembly in the industry, [ 1 ] as it is near eutectic , with adequate thermal fatigue properties, strength, and wettability. [ 2 ] Lead-free solder is gaining much attention as the environmental effects of lead in industrial products is recognized, and as a result of Europe's RoHS legislation to remove lead and other hazardous materials from electronics. Japanese electronics companies have also looked at Pb-free solder for its industrial advantages.
Typical alloys are 3–4% silver , 0.5–0.7% copper , and the balance (95%+) tin . [ 3 ] For example, the common "SAC305" solder is 3.0% silver and 0.5% copper. Cheaper alternatives with less silver are used in some applications, such as SAC105 and SAC0307 (0.3% silver, 0.7% copper), at the expense of a somewhat higher melting point.
In 2000, there were several lead-free assemblies and chip products initiatives being driven by the Japan Electronic Industries Development Association (JEIDA) and Waste Electrical and Electronic Equipment Directive (WEEE). These initiatives resulted in tin-silver-copper alloys being considered and tested as lead-free solder ball alternatives for array product assemblies. [ 4 ]
In 2003, tin-silver-copper was being used as a lead-free solder. However, its performance was criticized because it left a dull, irregular finish and it was difficult to keep the copper content under control. [ 5 ] In 2005, tin-silver-copper alloys constituted approximately 65% of lead-free alloys used in the industry and this percentage has been increasing. [ 1 ] Large companies such as Sony and Intel switched from using lead-containing solder to a tin-silver-copper alloy. [ 6 ]
The process requirements for (Pb-free) SAC solders and Sn-Pb solders are different both materially and logistically for electronic assembly. In addition, the reliability of Sn-Pb solders is well established, while SAC solders are still undergoing study, (though much work has been done to justify the use of SAC solders, such as the iNEMI Lead Free Solder Project).
One important difference is that Pb-free soldering requires higher temperatures and increased process control to achieve the same results as that of the tin-lead method. The melting point of SAC alloys is 217–220 °C, or about 34 °C higher than the melting point of the eutectic tin-lead (63/37) alloy. This requires peak temperatures in the range of 235–245 °C to achieve wetting and wicking . [ 1 ]
Some of the components susceptible to SAC assembly temperatures are electrolytic capacitors , connectors , opto-electronics , and older style plastic components. However, a number of companies have started offering 260 °C compatible components to meet the requirements of Pb-free solders. iNEMI has proposed that a good target for development purposes would be around 260 °C. [ 7 ]
Also, SAC solders are alloyed with a larger number of metals so there is the potential for a far wider variety of intermetallics to be present in a solder joint. These more complex compositions can result in solder joint microstructures that are not as thoroughly studied as current tin-lead solder microstructures. [ 8 ] These concerns are magnified by the unintentional use of lead-free solders in either processes designed solely for tin-lead solders or environments where material interactions are poorly understood. For example, the reworking of a tin-lead solder joint with Pb-free solder. These mixed-finish possibilities could negatively impact the solder's reliability. [ 8 ]
SAC solders have outperformed high-Pb solders C4 joints in ceramic ball grid array (CBGA) systems, which are ball-grid arrays with a ceramic substrate. [ 9 ] The CBGA showed consistently better results in thermal cycling for Pb-free alloys. The findings also show that SAC alloys are proportionately better in thermal fatigue as the thermal cycling range decreases. SAC performs better than Sn-Pb at the less extreme cycling conditions. Another advantage of SAC is that it appears to be more resistant to gold embrittlement than Sn-Pb. In test results, the strength of the joints is substantially higher for the SAC alloys than the Sn-Pb alloy. Also, the failure mode is changed from a partially brittle joint separation to a ductile tearing with the SAC. [ 7 ] | https://en.wikipedia.org/wiki/Tin-silver-copper |
A tin can wall is a wall constructed from tin cans , which are not a common building source. The cans can be laid in concrete , stacked vertically on top of each other, and crushed or cut and flattened to be used as shingles . [ 1 ] They can also be used for furniture.
Tin cans can form the actual fill-in structure (or walls) of a building, as is done with earthships .
Tin cans have not been around for a long time, and neither have their building methods. The two main structural methods for building with tin cans are by laying them horizontally in a concrete matrix and by stacking them vertically.
Tin can building in New Mexico originated in the early 1980s as a response to the massive amounts of trash being discarded and the wasteful nature of common building practices. [ citation needed ] Tin can construction was an attempt to utilize a readily available resource that was normally sent to landfills or recycling centers. This led to various experiments in tin can building, including space-filler between wooden frames in traditional house styles and creating domes and archways using cans and cement. Within time, more simplified and practical methods were developed, such as the earthship tin can wall. The main person behind these efforts was Mike Reynolds , also creator of the earthship building method.
A “traditional” earthship tin can wall is made by horizontally stacking tin cans in a concrete matrix. The cans are laid side by side and in alternating rows, similar to bricks . This is done simply and efficiently, using batches of concrete between the cans. The consistency of the concrete must be relatively thick, so as to hold its form and the tin cans in place. A surprisingly large number of cans are required.
The method for stacking the cans involves creating a row of cans separated by hand-formed “lumps” of concrete. The layout of a row is can, concrete, can, etc. This is then repeated, except that the alternating pattern is reversed, so that every can is laid on top of a concrete “lump” below it. This continues until completed, or the weight of the wall and the hardness of the cement seem questionable in terms of solidity. At that point it would be wise to wait for the wall to harden, but the laying time for cans and concrete is such that by the time a builder makes it back to an area that was recently laid it has had time to set. It is a judgment call as to whether or not the builder should continue, but by the next day or even later in the same day building can resume.
The materials that go into a tin can wall are simple: mainly tin cans and concrete. Tin cans (now aluminum cans as real tin cans are not as readily available) can be acquired from any recycling center or a local bar. Brick mortar may also be used instead of cement.
Once the wall is completed, the cans and the concrete are covered with a layer of cement or adobe mud mixture. What is applied depends on the location of the wall; if it is located in an area where it will be exposed to water (such as in a bathroom or utility room) it will need to be coated with a concrete layer. If it is located in a living room or bedroom, it can be covered with adobe plaster . A tin can wall that has half of its structure outside (such as the wall of an entrance to a building) will be coated with cement on the outside and adobe on the inside. The shape of the cans (their pull-tabs , etc.) and the roughness of the cement will provide a lath -like surface for the cement or adobe to stick to.
This initial layer is “screeded” (scratched with a tool that creates a ridge-like pattern thereby making it easier to apply another coat) and a second layer is added. More layers may be added, but it is up to the builder’s judgment and dependent upon the material being applied. In the case of adobe mud, once the initial layer is applied and allowed to harden it will crack and will need additional coats. With cement fewer layers are needed. The basic rule is: the more coats/layers, the stronger and better-looking the wall will be. This can be overdone however.
When a tin can wall has been sufficiently coated it will then be “finished” with a fine plaster ( lime -based or other), stucco (if the wall is outside), or linseed oil (in the case of adobe). It can also be finished with a clay “slip”, or aliz, [ 2 ] which is an earth-based coat that can have natural pigment and fine grains of mica mixed in to produce a beautiful shimmering and organic-looking surface.
An outside tin can insulating wall is a simple design. It is made out of two tin can walls with a layer of solid insulation in the middle. The insulation can vary in thickness, depending on climate and budget. It can be made out of various “green” or sustainable materials or average run-of-the-mill solid insulation. The exposed sides of the tin can walls (those not facing the insulation) are finished using methods aforementioned. The inside part of the wall can be coated with adobe while the outside is finished with concrete and stucco.
A door frame can be built into the can wall, or rather the can wall is built around the frame. The process involves initially having a door frame set in place (on the foundation ) and stacking cans to either side of the frame until they reach the other walls of the building and the ceiling. The door frame is fastened to the tin can wall by hammering nails partially into the side of the frame that will touch the tin can wall and allowing the concrete to harden around the nails. Short strips of metal lath are also attached to the frame and folded out (perpendicular to the frame) and allowed to set in the can/concrete matrix.
The same method is applied to windows . The only difference is all sides of window are fastened to the tin can wall, while the door frame is fastened to the foundation on one side (bottom) and the can wall on three sides. Metal lath and nails are all that is needed, along with a bubble level or similar device. Once the desired height is reached to install a window frame, the wall is leveled. If any cans stick above the level plane they can be flattened to the desired height. Nails and lath sticking out from under the window frame holds the bottom of it in place, and the sides and top of the frame are fastened in the same fashion as a door frame.
To make a smooth transition from door (or window frame) to tin can wall with plaster , sheets of metal lath are attached to the rim of the frame and folded over the gap between the frame and the can wall. A double-layered wooden frame is therefore required, to give a surface for the metal lath to be nailed to while leaving the inside frame untouched. However, this is not necessarily a necessity.
Electrical wiring is simple, with the wires attached to the cans or fastened to the concrete before the initial coat. If a wire needs to go to the other side of a wall it can be punched directly through a can. Plumbing and pipework can use similar methods. The can wall can always be built around a pipe , or there can be a wooden frame made similar to a window or door to house the pipe.
Tin can walls are not considered load-bearing using this building method, although two-story circular dome structures have been built. The basic rule is that it can support considerable weight but should not be used to hold up much more than its own form and shape. It would not be wise to attach a heavy timber roof to a tin can wall without support beams or frames. The basic function for can walls is in-fill (filling in the space between support beams or the main structure) and the division of space. They work well to separate a living room from a bedroom, and are also used as insulating walls from the outside.
An earthship tin can wall is both an efficient and economical building method. They are mainly composed of aluminum and cement , and can withstand the test of time. They are made from few materials (the coating method can be more complex than building the wall itself). They use recycled materials and require little or no skill to build.
The other tin can wall method that will be briefly described is a system developed by a German artist named Michael Hönes. [ 3 ] He has led community rebuilding efforts in Lesotho , Africa using tin cans to create housing and opportunities for Aids orphans and foster mothers. Known as the TCV (a.k.a. Tin-Can Villages) project, Hönes has created buildings using tin cans, masonite , paint, and wire. The roof is made out of corrugated metal shingles. In this method the cans are stacked vertically, one on top of the other in rows that are placed side by side and secured with wire. They are left exposed and are arranged in a decorative manner. The structures require no foundation, and are said to be able to withstand the Lesotho storms .
A site for the first village in Maseru has been secured and the funding has been sourced. What is lacking is building permits (as of July 2004). The TCV organization, headed by Hönes, has been prefabricating tin can walls so that when the permits pass about one building a week can be constructed.
So far the TCV organization’s efforts have been concentrated on storehouses, offices, a large weaving workshop for the women of the Elelloang Basali Weavers group in Teyateyaneng, and a solar-powered restaurant [ 4 ] that cooks with solar ovens . Michael Hönes also focuses on tin can furniture and has created a stove out of tin cans that uses one-third less wood than what the poor people of the area commonly use, thereby diminishing the firewood crisis in Lesotho. | https://en.wikipedia.org/wiki/Tin_can_wall |
Tin cry is the characteristic sound heard when a bar made of tin is bent. Variously described as a "screaming" or "crackling" sound, the effect is caused by the crystal twinning in the metal. [ 1 ] The sound is not particularly loud, despite terms like "crying" and "screaming". It is very noticeable when a hot-dip tin-coated sheet metal is bent at high speed over rollers during processing.
Tin cry is often demonstrated using a simple science experiment. A bar of tin will "cry" repeatedly when bent until it breaks. The experiment can then be recycled by melting and recrystallizing the metal. The low melting point of tin, 231.9 °C (449.4 °F; 505.0 K), makes re-casting easy. Tin anneals at reasonably low temperature as well, normalizing tin's microstructure of crystallites/grains.
Although the cry is most typical of tin, a similar effect occurs in other metals, such as niobium , [ 2 ] indium , [ 3 ] zinc , [ 2 ] cadmium , [ 4 ] gallium , [ 2 ] and solid mercury . [ 5 ]
This article about materials science is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Tin_cry |
Tin pest is an autocatalytic , allotropic transformation of the element tin , which causes deterioration of tin objects at low temperatures. Tin pest has also been called tin disease , [ 1 ] tin blight , tin plague , [ 2 ] or tin leprosy . [ 3 ] It is an autocatalytic process, accelerating once it begins. It was first documented in the scientific literature in 1851, having been observed in the pipes of pipe organs in medieval churches that had experienced cool climates. [ 4 ]
With the adoption of the Restriction of Hazardous Substances Directive (RoHS) regulations in Europe, and similar regulations elsewhere, traditional lead/tin solder alloys in electronic devices have been replaced by nearly pure tin, introducing tin pest and related problems such as tin whiskers . [ 5 ] [ 6 ]
At 13.2 °C (55.8 °F) and below, pure tin transforms from the silvery, ductile metallic allotrope of β-form white tin to the brittle, nonmetallic, α-form grey tin with a diamond cubic structure. The transformation is slow to initiate due to a high activation energy but the presence of germanium (or crystal structures of similar form and size) or very low temperatures of roughly −30 °C aids the initiation. There is also a large volume increase of about 27% associated with the phase change to the nonmetallic low temperature allotrope. This frequently makes tin objects (like buttons) decompose into powder during the transformation, hence the name tin pest . [ 7 ] The decomposition will catalyze itself, which is why the reaction accelerates once it starts. The mere presence of tin pest leads to more tin pest. Tin objects at low temperatures will simply disintegrate.
In 1910 British polar explorer Robert Scott hoped to be the first to reach the South Pole , but was beaten by Norwegian explorer Roald Amundsen . On foot, the expedition trudged through the frozen deserts of the Antarctic , marching for caches of food and kerosene deposited on the way. In early 1912, at the first cache, there was no kerosene; the cans – soldered with tin – were empty. The cause of the empty tins could have been related to tin pest. [ 8 ] The tin cans were recovered and no tin pest was found when analyzed by the Tin Research Institute. [ 9 ] [ 10 ] Some observers blame poor quality soldering, as tin cans over 80 years old have been discovered in Antarctic buildings with the soldering in good condition. [ citation needed ]
The story is often told of Napoleon 's men freezing in the bitter Russian Winter , their clothes falling apart as tin pest ate the buttons. This appears to be an urban legend , as there is no evidence of any failing buttons, and thus they cannot have been a contributing factor in the failure of the invasion . [ 11 ] Uniform buttons of that era were generally bone for enlisted, and brass for officers. [ 12 ] Critics of the theory point out that any tin that might have been used would have been quite impure, and thus more tolerant of low temperatures. Laboratory tests of the time required for unalloyed tin to develop significant tin pest damage at lowered temperatures is about 18 months, which is more than twice the length of the invasion. [ 8 ] Nevertheless, some of the regiments in the campaign did have tin buttons and the temperature reached sufficiently low values (below −40 °C or °F). [ 11 ] In the event, none of the many survivors' tales mention problems with buttons and it has been suggested that the legend is an amalgamation of reports of blocks of Banca tin completely disintegrated in a customs warehouse in St. Petersburg in 1868, and earlier Russian reports that cast-in buttons for military uniforms also disintegrated, [ 13 ] [ 10 ] and the desperate state of Napoleon's army, having turned soldiers into ragged beggars. [ 11 ] [ 14 ]
With the 2006 adoption of the Restriction of Hazardous Substances Directive (RoHS) regulations in the European Union , California banning most uses of lead , and similar regulations elsewhere, the problem of tin pest has returned, [ 15 ] since some manufacturers which previously used tin/lead alloys now use predominantly tin-based alloys. For example, the leads of some electrical and electronic components are plated with pure tin. In cold environments, this can change to α-modification grey tin , which is not electrically conductive , and falls off the leads. After reheating, it changes back to β-modification white tin , which is electrically conductive. This cycle can cause electrical short circuits and failure of equipment. Such problems can be intermittent as the powdered particles of tin move around. Tin pest can be avoided by alloying with small amounts of electropositive metals or semimetals soluble in tin's solid phase, e.g. antimony or bismuth , which prevent the phase change. | https://en.wikipedia.org/wiki/Tin_pest |
Tin soldiers are miniature toy soldiers that are very popular in the world of collecting . They can be bought finished or in a raw state to be hand-painted. They are generally made of pewter , tin , lead , other metals or plastic . Often very elaborate scale models of battle scenes, known as dioramas , are created for their display.
Tin soldiers were originally almost two-dimensional figures, often called "little Eilerts" or "flats". They were the first toy soldiers to be mass-produced. [ 1 ] Though largely superseded in popularity from the late 19th century by fully rounded three-dimensional lead figures, these flat tin soldiers continue to be produced.
The first mass-produced tin soldiers were made in Germany as a tribute to Frederick the Great [ 2 ] during the 18th century. Johann Gottfried Hilpert (1748–1832) and his brother Johann Georg Hilpert (1733–1811) established an early assembly-line in 1775 for soldiers and other figures; female painters applied a single color on each figurine as it was passed around the workshop. [ 3 ] Hilpert, living in Nuremberg was probably the first to create them as a mass-produced toy. [ 4 ] The world's largest Tin Soldier is located in New Westminster , British Columbia, Canada. [ 5 ]
"Real" tin soldiers, i.e., ones cast from an alloy of tin and lead , can also be home-made. Moulds are available for sale in some hobby shops. Earlier, the moulds were made of metal; currently, they are often made of hard rubber which can stand the temperature of the molten metal, around 250 °C (482 °F).
The best-known tin soldier in literature is the unnamed title character in Hans Christian Andersen 's 1838 fairy tale The Steadfast Tin Soldier . It concerns a tin soldier who had only one leg because "he had been left to the last, and then there was not enough of the melted tin to finish him." He falls in love with a dancer made of paper and after much adventuring, including being swallowed by a fish, the two are consumed together by fire, leaving nothing but tin melted "in the shape of a little tin heart."
Tin soldiers also play a role in "The Nutcracker Suite" as well as "Knight's Castle" by Edward Eager .
Media related to Tin soldiers at Wikimedia Commons | https://en.wikipedia.org/wiki/Tin_soldier |
Tin is an essential metal in the creation of tin- bronzes , and its acquisition was an important part of ancient cultures from the Bronze Age onward. Its use began in the Middle East and the Balkans around 3000 BC. Tin is a relatively rare element in the Earth's crust , with about two parts per million (ppm), compared to iron with 50,000 ppm, copper with 70 ppm, lead with 16 ppm, arsenic with 5 ppm, silver with 0.1 ppm, and gold with 0.005 ppm. [ 1 ] Ancient sources of tin were therefore rare, and the metal usually had to be traded over very long distances to meet demand in areas which lacked tin deposits.
Known sources of tin in ancient times include the southeastern tin belt that runs from Yunnan in China to the Malay Peninsula ; Cornwall and Devon in Britain ; Brittany in France ; the border between Germany and the Czech Republic ; Spain ; Portugal ; Italy ; and central and South Africa . [ 2 ] [ 3 ] Syria and Egypt have been suggested as minor sources of tin, but the archaeological evidence is inconclusive.
Tin extraction and use can be dated to the beginning of the Bronze Age around 3000 BC, during which copper objects formed from polymetallic ores had different physical properties. [ 4 ] The earliest bronze objects had tin or arsenic content of less than 2% and are therefore believed to be the result of unintentional alloying due to trace metal content in copper ores such as tennantite , which contains arsenic. [ 5 ] The addition of a second metal to copper increases its hardness, lowers the melting temperature, and improves the casting process by producing a more fluid melt that cools to a denser, less spongy metal. [ 6 ] This was an important innovation that allowed for the much more complex shapes cast in closed molds of the Bronze Age. Arsenical bronze objects appear first in the Middle East where arsenic is commonly found in association with copper ore, but the health risks were quickly realized and the quest for sources of the much less hazardous tin ores began early in the Bronze Age. [ 7 ] This created the demand for rare tin metal and formed a trade network that linked the distant sources of tin to the markets of Bronze Age cultures .
Cassiterite (SnO 2 ), oxidized tin, most likely was the original source of tin in ancient times. Other forms of tin ores are less abundant sulfides such as stannite that require a more involved smelting process. Cassiterite often accumulates in alluvial channels as placer deposits due to the fact that it is harder, heavier, and more chemically resistant than the granite in which it typically forms. [ 8 ] These deposits can be easily seen in river banks , because cassiterite is usually black or purple or otherwise dark, a feature exploited by early Bronze Age prospectors . It is likely that the earliest deposits were alluvial and perhaps exploited by the same methods used for panning gold in placer deposits.
The importance of tin to the success of Bronze Age cultures and the scarcity of the resource offers a glimpse into that time period's trade and cultural interactions, and has therefore been the focus of intense archaeological studies. However, a number of problems have plagued the study of ancient tin such as the limited archaeological remains of placer mining , the destruction of ancient mines by modern mining operations, and the poor preservation of pure tin objects due to tin disease or tin pest . These problems are compounded by the difficulty in provenancing tin objects and ores to their geological deposits using isotopic or trace element analyses. Current archaeological debate is concerned with the origins of tin in the earliest Bronze Age cultures of the Near East. [ 8 ] [ 9 ] [ 10 ] [ 11 ] [ 3 ] [ 12 ]
Europe has very few sources of tin. Therefore, throughout ancient times it was imported long distances from the known tin mining districts of antiquity. These were the Ore Mountains (Erzgebirge) along the modern border between Germany and the Czech Republic, the Iberian Peninsula , Brittany in modern France, and Cornwall and Devon in southwestern Britain. [ 13 ] [ 14 ] [ 15 ] There are several smaller sources of tin in the Balkans [ 16 ] and another minor source of tin is known to exist at Monte Valerio in Tuscany , Italy. The Tuscan source was exploited by Etruscan miners around 800 BC, but it was not a significant source of tin for the rest of the Mediterranean . [ 17 ] Even at that time, the Etruscans themselves had to import additional tin from the northwest of the Iberian Peninsula, and later from Cornwall. [ 18 ]
It has been claimed that tin was first mined in Europe around 2500 BC in the Erzgebirge, and knowledge of tin bronze and tin extraction techniques spread from there to Brittany and Cornwall around 2000 BC and from northwestern Europe to northwestern Spain and Portugal around the same time. [ 19 ] However, the only Bronze Age object from Central Europe whose tin has been scientifically provenanced is the Nebra sky disk , and its tin (and gold, though not its copper), is shown by tin isotopes to have come from Cornwall. [ 20 ] In addition, a rare find of a pure tin ingot in Scandinavia was provenanced to Cornwall. [ 21 ] Available evidence, though very limited, thus points to Cornwall as the sole early source of tin in Central and Northern Europe.
Cornwall and Devon were important sources of tin for Europe and the Mediterranean throughout ancient times and may have been the earliest sources of tin in Western Europe, with evidence for trade to the Eastern Mediterranean by the Late Bronze Age. [ 22 ] Within recorded history, Cornwall and Devon only dominated the European market for tin from late Roman times , starting around the 3rd century AD, as many Spanish tin mines were exhausted. [ 23 ] Cornwall maintained its importance as a source of tin throughout medieval times and into the modern period. [ 24 ]
Brittany – opposite Cornwall on the Celtic Sea – has significant sources of tin which show evidence of being extensively exploited after the Roman conquest of Gaul during the 50s BC and onwards. [ 25 ] Brittany remained a significant source of tin throughout the medieval period .
A group of 52 bronze artifacts from the late Bronze Age Balkans has been shown to have tin of multiple origins, based on the correlation of tin isotope differences with the different find locations of the artifacts. While the locations of these separate tin sources are uncertain, the larger Serbian group of artifacts is inferred to be derived from tin sources in western Serbia (e.g. Mount Cer ), while the smaller group, largely from western Romania, is inferred to have western Romanian origins. [ 26 ]
Iberian tin was widely traded across the Mediterranean during the Bronze Age, and extensively exploited during Roman times . But Iberian tin deposits were largely forgotten throughout the medieval period, were not rediscovered until the 18th century, and only re-gained importance during the mid-19th century. [ 27 ]
Western Asia has very little tin ore; the few sources that have recently been found are too insignificant to have played a major role during most of ancient history. [ 4 ] However, it is possible that they were exploited at the start of the Bronze Age and are responsible for the development of early bronze manufacturing technology. [ 28 ] [ 3 ] Kestel , in Southern Turkey , is the site of an ancient cassiterite mine that was used from 3250 to 1800 BC. It contains miles of tunnels, some only large enough for a child. A grave with children who were probably workers has been found. It was abandoned, with crucibles and other tools left at the site.
While there are a few sources of cassiterite in Central Asia , namely in Uzbekistan , Tajikistan , and Afghanistan , that show signs of having been exploited starting around 2000 BC, [ 29 ] archaeologists disagree about whether they were significant sources of tin for the earliest Bronze Age cultures of the Middle East. [ 30 ] [ 28 ] [ 31 ] [ 32 ]
In Northern Asia the only tin deposits considered exploitable by ancient peoples occur in the far eastern region of Siberia . [ 33 ] This source of tin appears to have been exploited by the Eurasian Steppe people known as the Seima-Turbino culture around 2000 BC as well as by northern Chinese cultures around the same time. [ 34 ]
Eastern Asia has a number of small cassiterite deposits along the Yellow River which were exploited by the earliest Chinese Bronze Age culture of Erlitou and the Shang dynasty (2500 to 1800 BC). However, the richest deposits for the region, and indeed the world, lie in Southeastern Asia , stretching from Yunnan in China to the Malay Peninsula. The deposits in Yunnan were not mined until around 700 BC, but by the Han dynasty had become the main source of tin in China according to historical texts of the Han, Jin , Tang , and Song dynasties. [ 35 ] Other cultures of Southeast Asia exploited the abundant cassiterite resources sometime between the third and second millennia BC, but due to the lack of archaeological work in the region little else is known about tin exploitation during ancient times in that part of the world.
Tin was used in the Indian subcontinent starting between 1500 and 1000 BC. [ 36 ] [ 37 ] While India does have some small scattered deposits of tin, they were not a major source of tin for Indian Bronze Age cultures as shown by their dependence on imported tin.
While rich veins of tin are known to exist in Central and South Africa, whether these were exploited during ancient times is still debated ( Dayton 2003 , p. 165). However, the Bantu culture of Zimbabwe are known to have actively mined, smelted and traded tin between the 11th and 15th centuries AD. [ 38 ]
Tin deposits exist in many parts of South America , with minor deposits in southern Peru , Colombia , Brazil , and northwestern Argentina , and major deposits of exploitable cassiterite in northern Bolivia . These deposits were exploited as early as 1000 AD in the manufacture of tin bronze by Andean cultures, including the later Inca Empire , which considered tin bronze the "imperial alloy". In North America , the only known exploitable source of tin during ancient times is located in the Zacatecas tin province of north central Mexico which supplied west Mexican cultures with enough tin for bronze production. [ 39 ]
The tin belt of Southeast Asia extends all the way down to Tasmania , but metals were not exploited in Australia until the arrival of Europeans in the 1780s.
Due to the scattered nature of tin deposits around the world and its essential nature for the creation of tin bronze, tin trade played an important role in the development of cultures throughout ancient times. Archaeologists have reconstructed parts of the extensive trade networks of ancient cultures from the Bronze Age to modern times using historical texts, archaeological excavations, and trace element and lead isotope analysis to determine the origins of tin objects around the world. [ 40 ] [ 41 ] [ 31 ]
The earliest sources of tin in the Early Bronze Age in the Near East are still unknown and the subject of much debate in archaeology. [ 10 ] [ 30 ] [ 31 ] [ 28 ] [ 8 ] [ 32 ] [ 42 ] Possibilities include minor now-depleted sources in the Near East, trade from Central Asia, [ 3 ] Sub-Saharan Africa , [ 30 ] Europe, or elsewhere.
It is possible that as early as 2500 BC, the Ore Mountains had begun exporting tin, using the well established Baltic amber trade route to supply Scandinavia as well as the Mediterranean with tin. [ 43 ] By 2000 BC, the extraction of tin in Britain, France, Spain, and Portugal had begun and tin was traded to the Mediterranean sporadically from all these sources. Evidence of tin trade in the Mediterranean can be seen in a number of Bronze Age shipwrecks containing tin ingots such as the Uluburun off the coast of Turkey dated 1300 BC which carried over 300 copper bars weighing 10 tons, and approximately 40 tin bars weighing 1 ton. [ 44 ] Evidence of direct tin trade between Europe and the Eastern Mediterranean has been demonstrated through the analysis of tin ingots dated to the 13th-12th centuries BC from sites in Israel, Turkey and modern-day Greece; tin ingots from Israel, for example, have been found to share chemical composition with tin from Cornwall and Devon (Great Britain). [ 22 ]
While Sardinia does not appear to have much in terms of significant sources of tin, it does have rich copper and other mineral wealth and served as a centre for metals trade during the Bronze Age and likely actively imported tin from the Iberian Peninsula for export to the rest of the Mediterranean. [ 45 ]
By classical Greek times, the tin sources were well established. Greece and the Western Mediterranean appear to have traded their tin from European sources, while the Middle East acquired their tin from Central Asian sources through the Silk Road . [ 46 ] For example, Iron Age Greece had access to tin from Iberia by way of the Phoenicians who traded extensively there, from the Erzgebirge by way of the Baltic Amber Road overland route, or from Brittany and Cornwall through overland routes from their colony at Massalia (modern day Marseilles ) established in the 6th century BC. [ 8 ] In 450 BC, Herodotus described tin as coming from Northern European islands named the Cassiterides along the extreme borders of the world, suggesting very long-distance trade, likely from Britain, northwestern Iberia, or Brittany, supplying tin to Greece and other Mediterranean cultures. [ 15 ] The idea that the Phoenicians went to Cornwall for its tin and supplied it to the whole of the Mediterranean has no archaeological basis and is largely considered a myth. [ 47 ]
The early Roman world was mainly supplied with tin from its Iberian provinces of Gallaecia and Lusitania and to a lesser extent Tuscany. Pliny mentions that in 80 BC, a senatorial decree halted all mining on the Italian Peninsula , stopping any tin mining activity in Tuscany and increasing Roman dependence on tin from Brittany, Iberia, and Cornwall. After the Roman conquest of Gaul, Brittany's tin deposits saw intensified exploitation after the first century BC. [ 25 ] With the exhaustion of the Iberian tin mines, Cornwall became a major supplier of tin for the Romans after the 3rd century AD. [ 24 ]
Throughout the medieval period, demand for tin increased as pewter gained popularity. Brittany and Cornwall remained the major producers and exporters of tin throughout the Mediterranean through to modern times. [ 24 ]
Near Eastern development of bronze technology spread across Central Asia by way of the Eurasian Steppes , and with it came the knowledge and technology for tin prospection and extraction. By 2000 to 1500 BC Uzbekistan, Afghanistan, and Tajikistan appear to have exploited their sources of tin, carrying the resources east and west along the Silk Road crossing Central Asia. [ 29 ] This trade link likely followed an existing trade route of lapis lazuli , a highly prized semi-precious blue gemstone , and chlorite vessels decorated with turquoise from Central Asia that have been found as far west as Egypt and that date to the same period. [ 48 ]
In China, early tin was extracted along the Yellow River in Erlitou and Shang times between 2500 and 1800 BC. By Han and later times, China imported its tin from what is today Yunnan province. This has remained China's main source of tin throughout history and into modern times. [ 49 ]
It is unlikely that Southeast Asian tin from Indochina was widely traded around the world in ancient times as the area was only opened up to Indian, Muslim , and European traders around 800 AD. [ 50 ]
Indo–Roman trade relations are well known from historical texts such as Pliny's Natural History (book VI, 26), and tin is mentioned as one of the resources being exported from Rome to South Arabia , Somaliland , and India. [ 51 ] [ 33 ] | https://en.wikipedia.org/wiki/Tin_sources_and_trade_during_antiquity |
Columbia University
Tina van de Flierdt (born 1973) is a Professor of Isotope Geochemistry at Imperial College London .
Van de Flierdt grew up in rural western Germany. [ 1 ] In 2000 van de Flierdt completed a diploma in Geology at the University of Bonn . [ 2 ] She earned a PhD at ETH Zurich in 2003, working with Alexander Halliday . [ 3 ]
Van de Flierdt is interested in the marine-terminating sector of the East Antarctic Ice Sheet during past warm periods. [ 1 ] Her research looks to develop new geochemical and isotopic tracers in marine geochemistry, paleoceanography and paleoclimate, with particular focus on radiogenic isotopes. [ 4 ] She is co-lead of the MAGIC Isotope group in the Department of Earth Sciences at Imperial College London . [ 5 ] She is also a research at the Lamont–Doherty Earth Observatory at Columbia University . [ 6 ] [ 7 ]
She is part of the international Geotraces program. [ 8 ] Part of the Geotraces program is to ensure results for trace elements and isotopes collected on different cruises by different laboratories can be compared in a meaningful way. [ 9 ] Van de Flierdt is building a global database of neodymium in the oceans and researching the implications for paleoceanography research. [ 4 ]
In 2012 she won a Leverhulme Trust grant to research deep sea corals. [ 10 ] She was part of the Natural Environment Research Council project SWEET, Super-Warm Early Eocene Temperatures and climate . [ 11 ] She has led several major NERC grants, totalling well over a £1,000,000 as principal investigator. [ 12 ] Van de Flierdt is a member of the Royal Society 's International Exchange Committee. [ 2 ] She is an editor of Geochimica et Cosmochimica Acta . [ 13 ] She has appeared on the podcast Forecast: Climate Conversations . [ 14 ] | https://en.wikipedia.org/wiki/Tina_van_de_Flierdt |
The tine test is a multiple-puncture tuberculin skin test used to aid in the medical diagnosis of tuberculosis (TB). The tine test is similar to the Heaf test , although the Mantoux test is usually used instead. There are various forms of the tine tests which usually fall into two categories: the old tine test (OT) and the purified protein derivative (PPD) tine test. Common brand names of the test include Aplisol, Aplitest, Tuberculin PPD TINE TEST, and Tubersol. [ 1 ]
This test uses a small "button" that has four to six short needles coated with TB antigens ( tuberculin ), either an old tuberculin or a PPD-tuberculin. The needles are pressed into the skin (usually on the inner side of the forearm), forcing the antigens into the skin. The test is then read 48 to 72 hours later by measuring the size of the largest papule or induration . Indications are usually classified as positive, negative, or doubtful. [ 2 ]
Because it is not possible to control precisely the amount of tuberculin used in the tine test, a positive test should be verified using the Mantoux test . [ 3 ]
Tuberculin is a glycerol extract of the tubercle bacillus. Purified protein derivative (PPD) tuberculin is a precipitate of non-species-specific molecules obtained from filtrates of sterilized, concentrated cultures. It was first described by Robert Koch in 1890 and then Giovanni Petragnani. [ citation needed ] A batch of PPD created in 1939 serves as the US and international standard, called PPD-S. [ 4 ] PPD-S concentration is not standardized for multiple-puncture techniques, and should be designed for the specific multiple-puncture system. [ 5 ]
The American Thoracic Society or Centers for Disease Control and Prevention (CDC) do not recommend the tine test, since the amount of tuberculin that enters the skin cannot be measured. [ 6 ] For this reason, the tine test is often considered to be less reliable. [ citation needed ]
Contrary to this, however, studies have shown that the tine test can give results that correlate well to the Mantoux test. [ 7 ] [ 8 ] If a minor reaction is considered doubtful, the OT test is less accurate and may fail to detect TB, producing a false negative. [ 2 ] If all doubtful indications are instead classified as positive, there is no significant difference between the OT test, the PPD tine test, or the Mantoux test. [ 3 ]
Furthermore, the tine test is faster and easier to administer than the Mantoux test and has been recommended for screening children. [ 9 ] [ 10 ] | https://en.wikipedia.org/wiki/Tine_test |
The fossil Tinguiririca fauna , entombed in volcanic mudflows and ash layers at the onset of the Oligocene , about 33-31.5 million years ago, [ 1 ] represents a unique snapshot of the history of South America 's endemic fauna, which was extinguished when the former island continent was joined to North America by the rising Isthmus of Panama . The fossil-bearing sedimentary layers of the Abanico Formation were first discovered in the valley of the Tinguiririca River , high in the Andes of central Chile . The faunal assemblage lends its name to the Tinguirirican stage in the South American land mammal age (SALMA) classification .
The endemic fauna bridges a massive gap in the history of those mammals that were unique to South America. [ 2 ] Paleontologists knew the earlier sloth and anteater forebears of 40 mya, but no fossils from this previously poorly sampled transitional age had been seen. Fossils of the Tinguiririca fauna include the chinchilla -like earliest rodents discovered in South America, [ 3 ] a wide range of the hoofed herbivores called notoungulates , a shrew-like marsupial and ancestors of today's sloth and armadillos . Many of the herbivores have teeth adapted to grass-eating; though no plant fossils have been recovered, the high-crowned hypsodont teeth, protected by tough enamel well below the gumline, identifies grazers suited to a gritty diet. "The proportion of hypsodont taxa relative to other dental types generally increases with the amount of open habitat," John Flynn explained in Scientific American (May 2007) "and the Tinguiririca level of hysodonty surpasses even that observed for mammals living in modern, open habitats such as the Great Plains of North America." Statistical analyses of the number of species categorized by body size (" cenogram " analysis, an aspect of body size scaling ) and of their broad ecological niches ("macroniche" analysis) bears out the existence of dry grasslands. Previously, no grassland ecosystem anywhere had been identified prior to Miocene systems fifteen million years later than the Tinguiririca fauna. Grasslands spread as the Earth's paleoclimate grew cooler and drier.
New fossils were uncovered of the New World monkeys and caviomorph rodents— the group that includes the capybara — which are known not to have evolved in situ . Some of the new fossils demonstrate by the form of their teeth that they lie closer to African fossil relatives than to the North American ones, which previously had been assumed to have rafted to the island continent. Now it appears that some may have made the crossing of a younger, much narrower Atlantic Ocean . A notable discovery was the miniature skull of a delicate progenitor of New World marmosets and tamarins ; it has been given the name Chilecebus carrascoensis .
The first of the fossils were found in 1988. Since then, in strata representing repeated catastrophic lahar events, more than 1500 individual fossils have been recovered from multiple sites in the region, ranging in age from 40 to 10 mya. The mammal species Archaeotypotherium tinguiriricaense is named after the site. | https://en.wikipedia.org/wiki/Tinguiririca_fauna |
Tinne Hoff Kjeldsen ( Danish pronunciation: [ˈkʰelˀsn̩] ) is a Danish mathematician who works in the Department of Science, Systems and Models (IMFUFA) at Roskilde University , [ 1 ] and in the Department of Science Education at the University of Copenhagen . [ 2 ] Her research interests include the philosophy of mathematics , history of mathematics , and mathematics education .
Kjeldsen earned her doctorate in 1999 from Roskilde University under the supervision of Anders Hede Madsen. It was titled: En kontekstualiseret matematikhistorisk analyse af ikke-lineær programmering: udviklingshistorie og multipel opdagelse (A contextualized mathematical history analysis of nonlinear programming: development history and multiple discovery. [ 3 ]
In 2012, she became one of the fellows of the American Mathematical Society . [ 4 ]
This article about a European mathematician is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Tinne_Hoff_Kjeldsen |
Tinning is the process of thinly coating sheets of wrought iron or steel with tin , and the resulting product is known as tinplate . The term is also widely used for the different process of coating a metal with solder before soldering. [ 1 ]
It is most often used to prevent rust , but is also commonly applied to the ends of stranded wire used as electrical conductors to prevent oxidation (which increases electrical resistance ), and to keep them from fraying or unraveling when used in various wire connectors like twist-ons , binding posts , or terminal blocks , where stray strands can cause a short circuit .
While once more widely used, the primary use of tinplate now is the manufacture of tin cans . Formerly, tinplate was [ clarification needed ] used for cheap pots, pans, and other holloware . This kind of holloware was also known as tinware and the people who made it were tinplate workers.
The untinned sheets employed in the manufacture are known as black plates. They are now made of steel, either Bessemer steel or open-hearth. Formerly iron was used, and was of two grades, coke iron and charcoal iron ; the latter, being the better, received a heavier coating of tin, and this circumstance is the origin of the terms coke plates and charcoal plates by which the quality of tinplate is still designated, although iron is no longer used. Tinplate was consumed in enormous quantities for the manufacture of the tin cans in which preserved meat , fish , fruit , biscuits , cigarettes , and numerous other products are packed, and also for the household utensils of various kinds made by the tinsmith . [ 2 ]
The practice of tinning ironware to protect it against rust is an ancient one. According to Pliny the Elder tinning was invented by the Gallic Bituriges tribe (based near modern Bourges ), who boiled copper objects in a tin solution in order to make them look as if they were made from silver. [ 3 ] The first detailed account of the process appears in Zosimus of Panopolis , Book 6.62, part of a work on alchemy written in Roman Egypt around 300 AD. Aside from an attestation in 14th century England, the process is not attested again in Europe until the description in Lazarus Ercker 's Das Kleine Probierbuch (1556) [ 4 ]
The manufacture of tinplate was long a monopoly of Bohemia , but in about the year 1620 the industry spread to Saxony . [ 2 ] Tinplate was apparently produced in the 1620s at a mill of (or under the patronage of) the Earl of Southampton, but it is not clear how long this continued.
Andrew Yarranton , an English engineer and agriculturist, and Ambrose Crowley (a Stourbridge blacksmith and father of the more famous Sir Ambrose Crowley III ) were commissioned to go to Saxony and if possible discover the methods employed. [ 2 ] They visited Dresden in 1667 and found out how it was made. In doing so, they were sponsored by various local ironmasters and people connected with the project to make the River Stour navigable. In Saxony, the plates were forged, but when they conducted experiments on their return to England, they tried rolling the iron. This led to two of the sponsors, the ironmasters Philip Foley and Joshua Newborough , erecting a new mill, Wolverley Lower Mill (or forge), in 1670. This contained three shops: one being a slitting mill , which would serve as a rolling mill , the others being forges. In 1678 one of these was making frying pans and the other drawing out blooms made in finery forges elsewhere. It is likely that the intention was to roll the plates and then finish them under a hammer, but the plan was frustrated by one William Chamberlaine renewing a patent granted to him and Dud Dudley in 1662. Yarranton described the patent as "trumped up". [ 5 ] [ 6 ]
The slitter at Wolverley was Thomas Cooke. Another Thomas Cooke, perhaps his son, moved to Pontypool and worked there for John Hanbury (1664–1734) . [ 7 ] According to Edward Lhuyd , by 1697, John Hanbury had a rolling mill at Pontypool for making "Pontypoole Plates" machine. [ 8 ] [ 9 ] This has been claimed as a tinplate works, but it was almost certainly only producing (untinned) blackplate . However, this method of rolling iron plates by means of cylinders, enabled more uniform black plates to be produced than was possible with the old plan of hammering , and in consequence the English tinplate became recognised as superior to the German . [ 2 ]
Tinplate first begins to appear in the Gloucester Port Books (which record trade passing through Gloucester , mostly from ports in the Bristol Channel ) in 1725. The tinplate was shipped from Newport, Monmouthshire . [ 10 ] This immediately follows the first appearance (in French ) of Réaumur 's Principes de l'art de fer-blanc , and prior to a report of it being published in England.
Further mills followed a few years later, initially in many ironmaking regions in England and Wales, but later mainly in south Wales. In 1805, 80,000 boxes were made and 50,000 exported. The industry continued to spread steadily in England and especially Wales , and after 1834 its expansion was rapid, Great Britain becoming the chief source of the world's supply. In that year her total production was 180,000 boxes of 108 lb each (around 50 kg, in America a box is 100 lb), in 1848 it was 420,000 boxes, in 1860 it reached 1,700,000 boxes. But subsequently the advance was rapid, and the production reached about 2,236,000 lb in 1891. [ 2 ] One of the greatest markets was the United States of America, but that market was cut off in 1891, when the McKinley tariff was enacted there. This caused a great retrenchment in the British industry and the emigration to America of many of those who could no longer be employed in the surviving tinplate works. [ citation needed ]
In 1891, the United States made 11,000 tons of tinplate and imported 325,100 tons, but in 1899, it made 360,900 tons, importing only 63,500 tons (mostly for re-export). British exports were further hindered by the Dingley tariff, which removed the advantage of Welsh plate on America's Pacific coast, [ 11 ] had by 1900 increased to more than 849,000,000 lb, of which over 141,000,000 lb were terne-plates. The total imports in that year were only 135,264,881 lb. In later years, again, there was a decline in the American production, and in 1907 only 20% of the American tinplate mills were at work, while the British production reached 14 million boxes. [ 2 ]
Despite this blow, the industry continued, but on a smaller scale. Nevertheless, there were still 518 mills in operation in 1937, including 224 belonging to Richard Thomas & Co. However the traditional 'pack mill' had been overtaken by the improved 'strip mill', of which the first in Great Britain was built by Richard Thomas & Co. in the late 1930s. Strip mills rendered the old pack mills obsolete and the last of them closed in about the 1960s.
The pack mill process begins with a tin bar , which is a drawn flat bar that was usually purchased from an ironworks or steel works . The tin bar could be wrought iron or mild steel . The cross-section of the bar needed to be accurate in size as this dictates the length and thickness of the final plates. The bar was cut to the correct length to make the desired size plate. For instance, if a 14 in × 20 in (360 mm × 510 mm) plate is desired the tin bar is cut to a length and width that is divisible by 14 and 20. The bar is then rolled and doubled over, with the number of times being doubled over dependent on how large the tin bar is and what the final thickness is. If the starting tin bar is 20 in × 56 in (510 mm × 1,420 mm) then it must be at least finished on the fours , or doubled over twice, and if a thin gauge is required then it may be finished on the eights , or doubled over three times. The tin bar is then heated to a dull red heat and passed five or six times through the roughing rolls. Between each pass the plate is passed over (or round) the rolls, and the gap between the rolls is narrowed by means of a screw. The plate is then reheated and run through the finishing rolls. [ 12 ]
If the plate is not finished on singles , or without doubling the plate over, it is doubled over in a squeezer . The squeezer was like a table where one half of the surface folds over on top of the other and a press flattens the doubled over plate so the rolled end will fit in the rollers. It is then reheated for another set of rolling. This is repeated until the desired geometry is reached. Note that if the plate needs to be doubled over more than once the rolled end is sheared off. The pack is then allowed to cool. When cool, the pack is sheared slightly undersized from the final dimensions and the plates separated by openers . [ 13 ]
At this point, the plates are covered in scale and must be pickled . This involves dipping the plates in sulfuric acid for five minutes. The pickling turns the scales into a greenish-black slime which is removed via annealing. The plates are annealed for approximately 10 hours and then allowed to slowly cool. At this point the plates are known as pickled and annealed black plates . These plates were commonly sold for stamping and enameling purposes. [ 14 ]
After this, the plates are rough and not straight, so they are cold rolled several times. The rolling lengthens the plates to their final dimension. They are then annealed again to remove any strain hardening . These plates are called black plate pickled, cold rolled, and close annealed (black plate p. cr. and ca.). To attain perfect cleanliness the plates are pickled again in a weak sulfuric acid . Finally they are rinsed and stored in water until ready to be tinned. [ 15 ]
The tinning set consists of at least one pot of molten tin, with a zinc chloride flux on top, and a grease pot. The flux dries the plate and prepares it for the tin to adhere. If a second tin pot is used, called the wash pot , it contains tin at a lower temperature. This is followed by the grease pot, which contains oil and a tinning machine . The tinning machine has two small rollers that are spring-loaded together so that when the tinned plate is inserted the rolls squeeze off any excess tin. The springs on the tinning machine can be set to different forces to give different thicknesses of tin. Finally, the oil is cleaned off with fine bran and dusted clean. [ 16 ] [ 17 ]
What is described here is the process as employed during the 20th century. The process grew somewhat in complexity over time, as it was found that the inclusion of additional procedures improved quality. The practice of hot rolling and then cold rolling evidently goes back to the early days, as the Knight family's tinplate works had (from its foundation in about 1740) two rolling mills, one at Bringewood (west of Ludlow) which made blackplate , and the other the tin mill at Mitton (now part of Stourport , evidently for the later stages. [ 18 ] [ page needed ]
Early hot rolling strip mills did not produce strip suitable for tinning, but in 1929 cold rolling began to be used to reduce the gauge further, which made tinning achievable. The plate was then tinned using the process outlined above. [ citation needed ]
There are two processes for the tinning of the black plates: hot-dipping and electroplating .
Hot tin-dipping is the process of immersing a part into a bath of pure molten tin at a temperature greater than 450 °F or 232 °C.
Tinplate made via hot-dipped tin plating is made by cold rolling steel or iron, pickling to remove any scale , annealing to remove any strain hardening , and then coating it with a thin layer of tin . Originally this was done by producing individual or small packs of plates, which became known as the pack mill process . In the late 1920s strip mills began to replace pack mills, because they could produce the raw plates in larger quantities and more economically.
In electroplating, the item to be coated is placed into a container containing a solution of one or more tin salts. The item is connected to an electrical circuit , forming the cathode (negative) of the circuit while an electrode typically of the same metal to be plated forms the anode (positive). When an electric current is passed through the circuit, metal ions in the solution are attracted to the item. To produce a smooth, shiny surface, the electroplated sheet is then briefly heated above the melting point of tin. Most of the tin-plated steel made today is then further electroplated with a very thin layer of chromium to prevent dulling of the surface from oxidation of the tin. | https://en.wikipedia.org/wiki/Tinning |
Tinofedrine ( INN Tooltip International Nonproprietary Name ; developmental code name D-8955 , proposed brand name Novocebrin ), also known as N -(3,3-di-3-thienyl)-2-propenyl)norephedrine , is a sympathomimetic and cerebral vasodilator of the amphetamine family which was never marketed. [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ] [ 6 ] It is a derivative of norephedrine and an analogue of related agents like oxyfedrine , buphenine (nylidrin), and isoxsuprine . [ 4 ] The drug was first described in the literature by 1978. [ 1 ] [ 6 ]
This pharmacology -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Tinofedrine |
Tinplate consists of sheets of steel coated with a thin layer of tin to impede rusting . Before the advent of cheap mild steel , the backing metal (known as "backplate") was wrought iron . While once more widely used, the primary use of tinplate now is the manufacture of tin cans .
In the tinning process, tinplate is made by rolling the steel (or formerly iron) in a rolling mill , removing any mill scale by pickling it in acid and then coating it with a thin layer of tin . Plates were once produced individually (or in small groups) in what became known as a pack mill . In the late 1920s pack mills began to be replaced by strip mills which produced larger quantities more economically.
Formerly, tinplate was used for tin ceiling , and holloware (cheap pots and pans), also known as tinware. The people who made tinware ( metal spinning ) were tinplate workers.
For many purposes, tinplate has been replaced by galvanised metal, the base being treated with a zinc coating. It is suitable in many applications where tinplate was formerly used, although not for cooking vessels, or in other high temperature situations—when heated, fumes from zinc oxide are given off; exposure to such gases can produce toxicity syndromes such as metal fume fever . [ 1 ] The zinc layer prevents the iron from rusting through sacrificial protection with the zinc oxidizing instead of the iron, whereas tin will only protect the iron if the tin surface remains unbroken.
The practice of tin mining likely began circa 3000 B.C. in Western Asia, British Isles and Europe. Tin was an essential ingredient of bronze production during the Bronze Age. [ 2 ] [ 3 ] [ 4 ] The practice of tinning ironware to protect it against rust is an ancient one. This may have been the work of the whitesmith . This was done after the article was fabricated, whereas tinplate was tinned before fabrication. Tinplate was apparently produced in the 1620s at a mill of (or under the patronage of) the Earl of Southampton, but it is not clear how long this continued.
The first production of tinplate was probably in Bohemia , from where the trade spread to Saxony , and was well-established there by the 1660s. Andrew Yarranton and Ambrose Crowley (a Stourbridge blacksmith and father of the more famous Sir Ambrose ) visited Dresden in 1667 and learned how it was made. In doing so, they were sponsored by various local ironmasters and people connected with the project to make the river Stour navigable. In Saxony, the plates were forged, but when they conducted experiments on their return to England, they tried rolling the iron. This led to the ironmasters Philip Foley and Joshua Newborough (two of the sponsors) in 1670 erecting a new mill, Wolverley Lower Mill (or forge) in Worcestershire . This contained three shops, one being a slitting mill (which would serve as a rolling mill ), and the others were forges. In 1678 one of these was making frying pans and the other drawing out blooms made in finery forges elsewhere. It is likely that the intention was to roll the plates and then finish them under a hammer, but the plan was frustrated by William Chamberlaine renewing a patent granted to him and Dud Dudley in 1662. [ 5 ] [ 6 ]
The slitter at Wolverley was Thomas Cooke. Another Thomas Cooke, perhaps his son, moved to Pontypool and worked there for John Hanbury . [ 7 ] He had a slitting mill there and was also producing iron plates called 'Pontpoole plates'. [ 8 ] Edward Lhuyd reported the existence of this mill in 1697. [ 9 ] This has been claimed as a tinplate works, but it was almost certainly only producing (untinned) backplate.
Tinplate first begins to appear in the Gloucester Port Books (which record trade passing through Gloucester ), mostly from ports in the Bristol Channel in 1725. The tinplate was shipped from Newport, Monmouthshire . [ a ] This immediately follows the first appearance (in French ) of Reamur 's Principes de l'art de fer-blanc , and prior to a report of it being published in England.
Further mills followed a few years later, initially in many iron-making regions in England and Wales, but later mainly in south Wales, most notably the Melingriffith Tin Plate Works , Whitchurch, Cardiff , which was founded some time before 1750. In 1805, 80,000 boxes were made and 50,000 exported. The industry continued to grow until 1891. One of the greatest markets was the United States, but that market was cut off in 1891 when the McKinley tariff was enacted. This caused a great retrenchment in the British industry and the emigration to America of many of those were no longer employed in the surviving tinplate works.
Despite this blow, the industry continued, but on a smaller scale. There were 518 mills in operation in 1937, including 224 belonging to Richard Thomas & Co. The traditional 'pack mill' had been overtaken by the improved 'strip mill', of which the first in Great Britain was built by Richard Thomas & Co. in the late 1930s. Strip mills rendered the old pack mills obsolete and the last of them closed circa the 1960s.
The raw material was bar iron , or (from the introduction of mild steel in the late 19th century), a bar of steel. This was drawn into a flat bar (known as a tin bar) at the ironworks or steel works where it was made. The cross-section of the bar needed to be accurate in size as this would be the cross-section of the pack of plates made from it. The bar was cut to the correct length (being the width of the plates) and heated. It was then passed four or five times through the rolls of the rolling mill, to produce a thick plate about 30 inches long. Between each pass the plate is passed over (or round) the rolls, and the gap between the rolls is narrowed by means of a screw.
This was then rolled until it had doubled in length. The plate was then folded in half ('doubled') using a doubling shear, which was like a table where one half of the surface folds over on top of the other. It is then put into a furnace to be heated until it is well 'soaked'. This is repeated until there is a pack of 8 or 16 plates. The pack is then allowed to cool. When cool, the pack was sheared (using powered shears) and the plates separated by 'openers' (usually women). [ 11 ] Defective plates were discarded, and the rest passed to the pickling department.
In the pickling department, the plates were immersed in baths of acid (to remove scale, i.e., oxide), then in water (washing them). After inspection they were placed in an annealing furnace, where they were heated for 10–14 hours. This was known as 'black pickling' and 'black annealing'. After being removed they were allowed to cool for up to 48 hours. The plates were then rolled cold through highly polished rolls to remove any unevenness and give them a polished surface. They were then annealed again at a lower temperature and pickled again, this being known as 'white annealing' and 'white pickling'. They were then washed and stored in slightly acid water (where they would not rust) awaiting tinning.
The tinning set consisted of two pots with molten tin (with flux on top) and a grease pot. The flux dries the plate and prepares it for the tin to adhere. The second tin pot (called the wash pot) had tin at a lower temperature. This is followed by the grease pot (containing an oil), removing the excess tin. Then follow cleaning and polishing processes. Finally, the tinplates were packed in boxes of 112 sheets ready for sale. Single plates were 20 by 14 inches (51 cm × 36 cm); doubles twice that. A box weighed approximately a hundredweight (cwt; 112 pounds or 51 kilograms). [ 12 ] [ b ]
The strip mill was a major innovation, with the first being erected at Ashland, Kentucky in 1923. This provided a continuous process, eliminating the need to pass the plates over the rolls and to double them. At the end the strip was cut with a guillotine shear or rolled into a coil. Early – hot rolling – strip mills did not produce strip suitable for tinplate, but in 1929 cold rolling began to be used to reduce the gauge further. The first strip mill in Great Britain was opened at Ebbw Vale in 1938 with an annual output of 200,000 imperial tons (203,210 tonnes or 224,000 short tons).
The strip mill had several advantages over pack mills: | https://en.wikipedia.org/wiki/Tinplate |
TinyVM is a small Java Virtual Machine primarily designed for use embedded systems with low memory. [ 1 ] In 2000, the project was forked into LeJOS . [ 2 ]
This software article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/TinyVM |
Tip-enhanced Raman spectroscopy ( TERS ) is a variant of surface-enhanced Raman spectroscopy (SERS) [ 1 ] that combines scanning probe microscopy with Raman spectroscopy. High spatial resolution chemical imaging is possible via TERS, [ 2 ] with routine demonstrations of nanometer spatial resolution under ambient laboratory conditions, [ 3 ] or better [ 4 ] at ultralow temperatures and high pressure.
The maximum resolution achievable using an optical microscope , including Raman microscopes , is limited by the Abbe limit , which is approximately half the wavelength of the incident light. Furthermore, with SERS spectroscopy the signal obtained is the sum of a relatively large number of molecules. TERS overcomes these limitations as the Raman spectrum obtained originates primarily from the molecules within a few tens of nanometers of the tip.
Although the antennas' electric near-field distributions are commonly understood to determine the spatial resolution, recent experiments showing subnanometer-resolved optical images put this understanding into question. [ 2 ] This is because such images enter a regime in which classical electrodynamical descriptions might no longer be applicable and quantum plasmonic [ 5 ] and atomistic [ 6 ] effects could become relevant.
The earliest reports of tip enhanced Raman spectroscopy typically used a Raman microscope coupled with an atomic force microscope . Tip-enhanced Raman spectroscopy coupled with a scanning tunneling microscope (STM-TERS) has also become a reliable technique, since it utilizes the gap mode plasmon between the metallic probe and the metallic substrate. [ 7 ] [ 8 ]
Tip-enhanced Raman spectroscopy requires a confocal microscope , and a scanning probe microscope . The optical microscope is used to align the laser focal point with the tip coated with a SERS active metal. The three typical experimental configurations are bottom illumination, side illumination, and top illumination, depending on which direction the incident laser propagates towards the sample, with respect to the substrate. In the case of STM-TERS, only side and top illumination configurations can be applied, since the substrate is required to be conductive, therefore typically being non-transparent. In this case, the incident laser is usually linearly polarized and aligned parallel to the tip, in order to generate confined surface plasmon at the tip apex. The sample is moved rather than the tip so that the laser remains focused on the tip. The sample can be moved systematically to build up a series of tip enhanced Raman spectra from which a Raman map of the surface can be built allowing for surface heterogeneity to be assessed with up to 1.7 nm resolution. [ 9 ] [ 10 ] Subnanometer resolution has been demonstrated in certain cases allowing for submolecular features to be resolved. [ 11 ] [ 12 ]
In 2019, Yan group and Liu group at University of California, Riverside developed a lens-free nanofocusing technique, which concentrates the incident light from a tapered optical fiber to the tip apex of a metallic nanowire and collects the Raman signal through the same optical fiber. Fiber-in-fiber-out NSOM-TERS has been developed. [ 13 ] [ 14 ]
Several research have used TERS to image single atoms and the internal structure of the molecules. [ 15 ] [ 16 ] [ 17 ] [ 18 ] In 2019, the Ara Apkarian group at the Center for Chemistry at the Space-Time Limit , University of California, Irvine imaged vibrational normal modes of single porphyrin molecules using TERS. [ 19 ] TERS-based DNA sequencing has also been demonstrated. [ 20 ] | https://en.wikipedia.org/wiki/Tip-enhanced_Raman_spectroscopy |
The tip-speed ratio , λ, or TSR for wind turbines is the ratio between the tangential speed of the tip of a blade and the actual speed of the wind, v . The tip-speed ratio is related to efficiency, with the optimum varying with blade design. [ 1 ] Higher tip speeds result in higher noise levels and require stronger blades due to larger centrifugal forces .
The tip speed of the blade can be calculated as ω ⋅ R {\displaystyle \omega \cdot R} , where ω {\displaystyle \omega } is the rotational speed of the rotor and R is the rotor radius. Therefore, we can also write:
where v {\displaystyle v} is the wind speed at the height of the blade hub.
The power coefficient, C p {\displaystyle C_{p}} , expresses what fraction of the power in the wind is being extracted by the wind turbine. It is generally assumed to be a function of both tip-speed ratio and pitch angle. Below is a plot of the variation of the power coefficient with variations in the tip-speed ratio when the pitch is held constant:
Originally, wind turbines were fixed speed. This has the benefit that the rotor speed in the generator is constant, so that the frequency of the AC voltage is fixed. This allows the wind turbine to be directly connected to a transmission system. However, from the figure above, we can see that the power coefficient is a function of the tip-speed ratio. By extension, the efficiency of the wind turbine is a function of the tip-speed ratio.
Ideally, one would like to have a turbine operating at the maximum value of C p at all wind speeds. This means that as the wind speed changes, the rotor speed must change as well such that C p = C p max . A wind turbine with a variable rotor speed is called a variable-speed wind turbine . Whilst this does mean that the wind turbine operates at or close to C p max for a range of wind speeds, the frequency of the AC voltage generator will not be constant. This can be seen in the equation
N = 120 f P , {\displaystyle N={\frac {120f}{P}},}
where N is the rotor's angular speed, f is the frequency of the AC voltage generated in the stator windings, and P is the number of poles in the generator inside the nacelle. Therefore, direct connection to a transmission system for a variable speed is not permissible. What is required is a power converter which converts the signal generated by the turbine generator into DC and then converts that signal to an AC signal with the grid/transmission system frequency.
Variable-speed wind turbines cannot be directly connected to a transmission system. One of the drawbacks of this is that the inertia of the transmission system is reduced as more variable-speed wind turbines are put online. This can result in more significant drops in the transmission system's voltage frequency in the event of the loss of a generating unit. Furthermore, variable-speed wind turbines require power electronics, which increases the complexity of the turbine and introduces new sources of failures. On the other hand, it has been suggested that additional energy capture achieved by comparing a variable-speed wind turbine to a fixed speed wind turbine is approximately 2%. [ 2 ] | https://en.wikipedia.org/wiki/Tip-speed_ratio |
Tip and cue , sometimes referred to as tip and que, tipping and cueing, or tipping and queing, is a method for satellite imagery and reconnaissance satellites to automatically coordinate tracking of objects across different satellites in real or near real-time. [ 1 ] [ 2 ] This technique ensures continuous tracking of targets as they move across different regions by handing them off between satellites, sharing satellite imagery and collateral across discrete satellites. [ 1 ] The coordination between various satellites and their complementary sensors allows for more accurate and efficient data collection. [ 1 ] This system is particularly useful in scenarios requiring real-time monitoring and rapid response; the method significantly improves situational awareness and operational effectiveness. [ 1 ]
Tip and cue techniques involve integrating various sensor systems, each playing a specific role in the tracking process. As a target moves, it is handed off from one satellite to another, ensuring continuous monitoring. This coordination optimizes data collection and analysis, enhancing overall tracking accuracy. The real-time information gathered by these satellites is critical for decision-making in various applications, including defense and surveillance. By leveraging multiple satellites and their sensors, it provides broader coverage and more reliable tracking, and the continuous handoff between satellites ensures there are no gaps in monitoring, essential for high-stakes applications. The real-time data provided by this system allows for timely and informed decisions, improving response times and outcomes. Tip and cue methodologies are a part of geospatial intelligence , or GEOINT. [ 3 ] Robert Cardillo , a former director of the National Geospatial-Intelligence Agency , highlighted the importance of tip and cue methods to their data collection efforts in 2015. [ 4 ]
The concept of tip and cue in satellite monitoring has its origins in early military applications designed to enhance missile detection and tracking systems. During the Cold War , advancements in infrared sensing technologies laid the groundwork for more sophisticated tip and cue techniques. The integration of different sensor types, such as radar and optical sensors, in the 1990s expanded the capabilities of tip and cue systems beyond military applications. These advancements have made tip and cue techniques essential for various civilian uses, including disaster monitoring and environmental surveillance. Significant progress was made with the advent of high-speed data processing and communication technologies in the early 2000s, further refining the method. Advanced algorithms and data fusion techniques have been introduced to better integrate information from multiple sensors. Machine learning technologies now play a crucial role in improving detection and prediction capabilities, allowing for more adaptive and efficient tracking.
Richmond and Brennan of Lockheed Martin , presenting to the annual technical conference of the Maui Space Surveillance Complex (formerly the Air Force Maui Optical Station (AMOS)), discussed the algorithms needed for 'tip and cue', to facilitate "multi- phenomenology data fusion ." [ 5 ] The Space Surveillance Telescope (SST) at Naval Communication Station Harold E. Holt in Australia , operated by the United States Space Force and designed by the Massachusetts Institute of Technology Lincoln Laboratory , was reported by the Defense Advanced Research Projects Agency (DARPA) to be a leader in creating and improving tip and cue techniques, from a large library of orbital object data. [ 6 ]
Tip and cue systems utilize a network of satellites equipped with complementary sensor technologies to track moving objects in real-time. The method involves detecting a target with a primary sensor, such as an infrared or photographic sensor, which then cues secondary sensors on the same or other satellites for more detailed monitoring. This handoff process between discrete systems ensures continuous tracking as the target moves across different areas, leveraging each systems strengths. Data collected by these systems and sensors are rapidly processed and shared among the network, enhancing situational awareness. This coordination optimizes resource usage and improves the accuracy of tracking moving objects over large areas.
The primary sensors detect initial targets based on specific signatures , such as heat or movement, and then cue secondary sensors to gather more precise data. This ensures that each sensor operates within its optimal range, maintaining high tracking accuracy and reliability. The integration of various sensor types, including optical , radar , and infrared , allows the system to function effectively under different conditions and environments. Real-time data processing and communication between satellites and ground stations are crucial for timely and accurate target tracking. Satellites using tip and cue processes may use either passive or active scanning methodoloigies. [ 7 ] These systems may also leverage both orbital and ground-based ELINT (electronic signals intelligence ). [ 7 ]
Tip and cue systems have been extensively utilized in military applications, particularly for missile detection and defense . These systems enable early detection of missile launches using infrared sensors, which then cue other sensors to track the missile's trajectory more accurately. In environmental monitoring, tip and cue techniques help track natural disasters such as wildfires and hurricanes by coordinating various satellite sensors for comprehensive data collection and analysis. Surveillance and reconnaissance operations also benefit from tip and cue systems, which provide continuous and precise tracking of moving objects, enhancing situational awareness . Additionally, these systems are used in maritime surveillance to monitor ship movements and detect illegal activities such as smuggling and piracy . [ 8 ] Tip and cue systems are used in disaster management . For instance, during wildfires, infrared sensors can detect heat signatures, prompting other sensors to gather detailed imagery and data on fire spread and intensity. This coordinated approach allows for real-time monitoring and rapid response, crucial for mitigating damage and saving lives. Similarly, in hurricane tracking, satellites equipped with various sensors can monitor storm development and progression, providing timely information for emergency management agencies. The integration of multiple sensor types ensures accurate and comprehensive coverage of these dynamic and fast-changing events.
In maritime surveillance, or maritime domain awareness (MDA), tip and cue systems enhance the detection and monitoring of vessel movements, contributing to maritime security. [ 8 ] By coordinating satellite sensors, these systems can track ships over vast ocean areas, identifying potential threats or illegal activities such as smuggling, piracy, and illegal fishing . [ 8 ] The ability to maintain continuous surveillance and share data in real-time with maritime authorities improves response times and enforcement capabilities. [ 8 ] This application of tip and cue systems not only aids in law enforcement but also supports environmental conservation efforts by monitoring protected marine areas. Automatic Identification System (AIS) is one of the most important sources of data for the MDA agencies. [ 8 ] AIS is used in order for ships to know each other's whereabouts, they transmit a signal from ship to ship and to shore. [ 8 ] Lately, the system has been developed into satellite system, so called satellite AIS, which makes the system more effective. [ 8 ] All ocean-going vessels above 300 tons, are supposed to use and transmit via AIS according to the International Maritime Organisation. [ 8 ] The satellite constellations help facilitate this with tip and cue methodologies. [ 8 ]
This article incorporates public domain material from websites or documents of the United States government . | https://en.wikipedia.org/wiki/Tip_and_cue |
Tip clearance is the distance between the tip of a rotating airfoil and a stationary part. | https://en.wikipedia.org/wiki/Tip_clearance |
Tip dating is a technique used in molecular dating that allows the inference of time-calibrated phylogenetic trees . Its defining feature is that it uses the ages of the samples to provide time information for the analysis, in contrast with traditional ' node dating ' methods that require age constraints to be applied to the internal nodes of the evolutionary tree.
In tip dating, morphological data and molecular data are typically analysed together to estimate the evolutionary relationships ( tree topology ) and the divergence times among lineages (node times); this approach is also known as 'total-evidence dating'. However, tip dating can also be used to analyse data sets that only comprise morphological characters or that only comprise molecular characters (e.g., data sets that include samples of ancient DNA or of serially sampled viruses ).
Tip dating has been implemented in Bayesian phylogenetic software and typically draws on the fossilised birth-death model for evolution. This is a model of diversification that allows speciation , extinction, and sampling of fossil and extant taxa .
This promising method is not yet fully mature, and there are a number of possible biases or undesirable behaviour that must be taken into account when interpreting its results. [ 1 ]
This evolution -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Tip_dating |
Tip growth is an extreme form of polarised growth of living cells that results in an elongated cylindrical cell morphology with a rounded tip at which the growth activity takes place. Tip growth occurs in algae (e.g., Acetabularia acetabulum ), fungi ( hyphae ) and plants (e.g. root hairs and pollen tubes ).
Tip growth is a process that has many similarities in diverse walled cells such as pollen tubes, root hairs, and hyphae.
Fungal hyphae extend continuously at their extreme tips, where enzymes are released into the environment and where new wall materials are synthesised. The rate of tip extension can be extremely rapid - up to 40 micrometres per minute. It is supported by the continuous movement of materials into the tip from older regions of the hyphae. So, in effect, a fungal hypha is a continuously moving mass of protoplasm in a continuously extending tube. This unique mode of growth - apical growth - is the hallmark of fungi, and it accounts for much of their environmental and economic significance. [ 1 ]
This botany article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Tip_growth |
A tippe top is a kind of top that when spun, will spontaneously invert itself to spin on its narrow stem. It was invented by a German nurse, Helene Sperl in 1898. [ 1 ]
A tippe top usually has a body shaped like a truncated sphere , with a short narrow stem attached perpendicular to the center of the flat circular surface of truncation. The stem may be used as a handle to pick up the top, and is also used to spin the top into motion.
When a tippe top is spun at a high angular velocity , its stem slowly tilts downwards more and more until it suddenly lifts the body of the spinning top off the ground, with the stem now pointing downward. Eventually, as the top's spinning rate slows, it loses stability and eventually topples over, like an ordinary top.
At first glance the top's inversion may mistakenly seem to be a situation where the object spontaneously gains overall energy . This is because the inversion of the top raises the object's center of mass , which means the potential energy has in fact increased. What causes the inversion (and the increase in potential energy) is a torque due to surface friction , which also decreases the kinetic energy of the top, so the total energy does not actually increase. [ 2 ]
Once the top is spinning on its stem, it does not spin in the opposite direction to which its spin was initiated. For example, if the top was spun clockwise , as soon as it is on its stem, it will be spinning clockwise viewed from above. This constant spin direction is due to conservation of angular momentum .
It is usually assumed that the speed of the tippe top at the point of contact with the plane is zero (i.e. there is no slippage). However, as indicated by P. Contensou, [ 3 ] this assumption does not lead to a correct physical description of the top's motion. The unusual behavior of the top can be fully described by considering dry friction forces at the contact point. [ 4 ] [ 5 ] | https://en.wikipedia.org/wiki/Tippe_top |
Tipperary Natural Mineral Water is an Irish brand of mineral water coming from a source at Annerville, Clonmel , County Tipperary , Ireland. Tipperary Water is part of C&C Group , an Irish-owned multinational company. [ 2 ]
Tipperary Natural Mineral Water Company was founded in 1986 by Nicholas and Patrick Cooney. [ 3 ] [ 4 ] The water is pumped from a depth of 100 metres. In 1987, Tipperary Natural Mineral Water was the first Irish bottled water to qualify for the European Union 's Natural Mineral Water status. In 2012, C&C Group acquired Gleeson Group for €12.4m. In 2016, seeking to cut costs C&C closed the water-bottling plant in Borrisoleigh which employed 140 staff. Production was moved to Clonmel County Tipperary. [ 5 ]
In 2019 the former Borrisoleigh water-bottling plant was sold to Oscar Wilde Water, a company owned by entrepreneur John Hegarty . | https://en.wikipedia.org/wiki/Tipperary_Natural_Mineral_Water |
The Tipson–Cohen reaction is a name reaction first discovered by Stuart Tipson and Alex Cohen at the National Bureau of Standards in Washington D.C. [ 1 ] The Tipson–Cohen reaction occurs when two neighboring secondary sulfonyloxy groups in a sugar molecule are treated with zinc dust (Zn) and sodium iodide (NaI) in a refluxing solvent such as N , N -dimethylformamide (DMF) to give an unsaturated carbohydrate. [ 2 ]
Unsaturated carbohydrates are desired as they are versatile building blocks that can be used in a variety of reactions. [ 2 ] For example, they can be used as intermediates in the synthesis of natural products, or as dienophiles in the Diels-Alder reaction, or as precursors in the synthesis of oligosaccharides. [ 3 ] The Tipson–Cohen reaction goes through a syn or anti elimination mechanism to produce an alkene in high to moderate yields. [ 4 ] The reaction depends on the neighboring substituents. A mechanism for glucopyranosides and mannooyranosides is shown below. [ 4 ]
Scheme 1: Syn elimination occurs with the glucopyranosides. Galactopyranosides follows a similar syn mechanism. [ 3 ] Whereas, anti elimination occurs with mannopyranosides. [ 4 ] Note that R could be a methanesulfonyl CH 2 O 2 S (Ms), or a toluenesulfonyl CH 3 C 6 H 4 O 2 S (Ts).
Scheme 3: The scheme illustrates the first displacement, the rate determining step and slowest step, where the starting material is converted to the iodo-intermediate. [ 4 ] The intermediate is not detectable as it is rapidly converted to the unsaturated sugar. Experiments with azide instead of the iodide confirmed attack occurs at the C-3 as nitrogen-intermediates were isolated. The order of reactivity from most reactive to least reactive is: β-glucopyranosides > β-mannopyranosides > α-glucopyranosides> α-mannopyranosides.
The reaction of β–mannopyranosides gives low yields and required longer reaction times than with β-glucopyranosides due to the presence of a neighboring axial substituent (sulfonyloxy) relative to C-3 sulfonyloxy group in the starting material. [ 4 ] The axial substituent increases the steric interactions in the transition state, causing unfavorable eclipsing of the two sulfonyloxy groups. α-Glucopyranosides possess a β- trans -axial substituent relative to C-3 sulfonyloxy (anomeric OCH 3 group) in the starting material. The β- trans -axial substituent influences the transition state by also causing an unfavorable steric interaction between the two groups. In the case of α-mannopyranosides, both a neighboring axial substituent (2-sulfonyloxy group) and a β- trans -axial substituent (anomeric OCH 3 group) are present, therefore significantly increasing the reaction time and decreasing the yield. [ 3 ]
Table 1: Reaction times and yield vary on the substrate. The β-glucopyranoside was found to be the best substrate for the Tipson–Cohen reaction as the reaction time and yield were much superior that any other substrate proposed in the study. [ 3 ]
a Substrates possess benzylidene protecting groups at C-4 and C-6, OMe groups at anomeric position and OTs groups at C-2 and C-3. Reaction temperature 95–100 ˚C | https://en.wikipedia.org/wiki/Tipson–Cohen_reaction |
Tiquinamide is a gastric acid synthesis inhibitor. [ 1 ]
This organic chemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Tiquinamide |
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