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Tachycardia: an elevated resting heart rate. In general an electrocardiogram (ECG) is required to identify the type of tachycardia.
Pulsatile This description of the pulse implies the intrinsic physiology of systole and diastole. Scientifically, systole and diastole are forces that expand and contract the pulmonary an... | Pulse | Wikipedia | 102 | 41600 | https://en.wikipedia.org/wiki/Pulse | Biology and health sciences | Medical procedures | null | vital_articles |
Common palpable sites
Sites can be divided into peripheral pulses and central pulses. Central pulses include the carotid, femoral, and brachial pulses.
Upper limb
Axillary pulse: located inferiorly of the lateral wall of the axilla
Brachial pulse: located on the inside of the upper arm near the elbow, frequently us... | Pulse | Wikipedia | 406 | 41600 | https://en.wikipedia.org/wiki/Pulse | Biology and health sciences | Medical procedures | null | vital_articles |
Carotid pulse: located in the neck (carotid artery). The carotid artery should be palpated gently and while the patient is sitting or lying down. Stimulating its baroreceptors with low palpitation can provoke severe bradycardia or even stop the heart in some sensitive persons. Also, a person's two carotid arteries shou... | Pulse | Wikipedia | 302 | 41600 | https://en.wikipedia.org/wiki/Pulse | Biology and health sciences | Medical procedures | null | vital_articles |
Radiometry is a set of techniques for measuring electromagnetic radiation, including visible light. Radiometric techniques in optics characterize the distribution of the radiation's power in space, as opposed to photometric techniques, which characterize the light's interaction with the human eye. The fundamental diffe... | Radiometry | Wikipedia | 477 | 41625 | https://en.wikipedia.org/wiki/Radiometry | Physical sciences | Electromagnetic radiation | Physics | vital_articles |
In geometry, a cycloid is the curve traced by a point on a circle as it rolls along a straight line without slipping. A cycloid is a specific form of trochoid and is an example of a roulette, a curve generated by a curve rolling on another curve.
The cycloid, with the cusps pointing upward, is the curve of fastest des... | Cycloid | Wikipedia | 429 | 41638 | https://en.wikipedia.org/wiki/Cycloid | Mathematics | Two-dimensional space | null | vital_articles |
Galileo originated the term cycloid and was the first to make a serious study of the curve. According to his student Evangelista Torricelli, in 1599 Galileo attempted the quadrature of the cycloid (determining the area under the cycloid) with an unusually empirical approach that involved tracing both the generating ci... | Cycloid | Wikipedia | 306 | 41638 | https://en.wikipedia.org/wiki/Cycloid | Mathematics | Two-dimensional space | null | vital_articles |
In 1658, Blaise Pascal had given up mathematics for theology but, while suffering from a toothache, began considering several problems concerning the cycloid. His toothache disappeared, and he took this as a heavenly sign to proceed with his research. Eight days later he had completed his essay and, to publicize the ... | Cycloid | Wikipedia | 488 | 41638 | https://en.wikipedia.org/wiki/Cycloid | Mathematics | Two-dimensional space | null | vital_articles |
A cycloid segment from one cusp to the next is called an arch of the cycloid, for example the points with and .
Considering the cycloid as the graph of a function , it satisfies the differential equation:
If we define as the height difference from the cycloid's vertex (the point with a horizontal tangent and ), the... | Cycloid | Wikipedia | 169 | 41638 | https://en.wikipedia.org/wiki/Cycloid | Mathematics | Two-dimensional space | null | vital_articles |
This demonstration uses the rolling-wheel definition of cycloid, as well as the instantaneous velocity vector of a moving point, tangent to its trajectory. In the adjacent picture, and are two points belonging to two rolling circles, with the base of the first just above the top of the second. Initially, and coinc... | Cycloid | Wikipedia | 453 | 41638 | https://en.wikipedia.org/wiki/Cycloid | Mathematics | Two-dimensional space | null | vital_articles |
This proves that the tip of a wire initially stretched on a half arch of the lower cycloid and fixed to the upper circle at will follow the point along its path without changing its length because the speed of the tip is at each moment orthogonal to the wire (no stretching or compression). The wire will be at the same... | Cycloid | Wikipedia | 107 | 41638 | https://en.wikipedia.org/wiki/Cycloid | Mathematics | Two-dimensional space | null | vital_articles |
Area
Using the above parameterization , the area under one arch, is given by:
This is three times the area of the rolling circle.
Arc length
The arc length of one arch is given by
Another geometric way to calculate the length of the cycloid is to notice that when a wire describing an involute has been completel... | Cycloid | Wikipedia | 390 | 41638 | https://en.wikipedia.org/wiki/Cycloid | Mathematics | Two-dimensional space | null | vital_articles |
Related curves
Several curves are related to the cycloid.
Trochoid: generalization of a cycloid in which the point tracing the curve may be inside the rolling circle (curtate) or outside (prolate).
Hypocycloid: variant of a cycloid in which a circle rolls on the inside of another circle instead of a line.
Epicycloi... | Cycloid | Wikipedia | 384 | 41638 | https://en.wikipedia.org/wiki/Cycloid | Mathematics | Two-dimensional space | null | vital_articles |
In physics and electrical engineering the reflection coefficient is a parameter that describes how much of a wave is reflected by an impedance discontinuity in the transmission medium. It is equal to the ratio of the amplitude of the reflected wave to the incident wave, with each expressed as phasors. For example, it... | Reflection coefficient | Wikipedia | 455 | 41641 | https://en.wikipedia.org/wiki/Reflection%20coefficient | Physical sciences | Optics | Physics | vital_articles |
In the accompanying figure, a signal source with internal impedance possibly followed by a transmission line of characteristic impedance is represented by its Thévenin equivalent, driving the load . For a real (resistive) source impedance , if we define using the reference impedance then the source's maximum power ... | Reflection coefficient | Wikipedia | 461 | 41641 | https://en.wikipedia.org/wiki/Reflection%20coefficient | Physical sciences | Optics | Physics | vital_articles |
The complex reflection coefficient (in the region , corresponding to passive loads) may be displayed graphically using a Smith chart. The Smith chart is a polar plot of , therefore the magnitude of is given directly by the distance of a point to the center (with the edge of the Smith chart corresponding to ). Its evol... | Reflection coefficient | Wikipedia | 474 | 41641 | https://en.wikipedia.org/wiki/Reflection%20coefficient | Physical sciences | Optics | Physics | vital_articles |
Resonance is a phenomenon that occurs when an object or system is subjected to an external force or vibration that matches its natural frequency. When this happens, the object or system absorbs energy from the external force and starts vibrating with a larger amplitude. Resonance can occur in various systems, such as m... | Resonance | Wikipedia | 430 | 41660 | https://en.wikipedia.org/wiki/Resonance | Physical sciences | Waves | null | vital_articles |
Resonance occurs when a system is able to store and easily transfer energy between two or more different storage modes (such as kinetic energy and potential energy in the case of a simple pendulum). However, there are some losses from cycle to cycle, called damping. When damping is small, the resonant frequency is appr... | Resonance | Wikipedia | 459 | 41660 | https://en.wikipedia.org/wiki/Resonance | Physical sciences | Waves | null | vital_articles |
Linear systems
Resonance manifests itself in many linear and nonlinear systems as oscillations around an equilibrium point. When the system is driven by a sinusoidal external input, a measured output of the system may oscillate in response. The ratio of the amplitude of the output's steady-state oscillations to the inp... | Resonance | Wikipedia | 444 | 41660 | https://en.wikipedia.org/wiki/Resonance | Physical sciences | Waves | null | vital_articles |
The general solution of Equation () is the sum of a transient solution that depends on initial conditions and a steady state solution that is independent of initial conditions and depends only on the driving amplitude F0, driving frequency ω, undamped angular frequency ω0, and the damping ratio ζ. The transient soluti... | Resonance | Wikipedia | 486 | 41660 | https://en.wikipedia.org/wiki/Resonance | Physical sciences | Waves | null | vital_articles |
Consider a circuit consisting of a resistor with resistance R, an inductor with inductance L, and a capacitor with capacitance C connected in series with current i(t) and driven by a voltage source with voltage vin(t). The voltage drop around the circuit is
Rather than analyzing a candidate solution to this equation l... | Resonance | Wikipedia | 493 | 41660 | https://en.wikipedia.org/wiki/Resonance | Physical sciences | Waves | null | vital_articles |
Here, the resonance corresponds physically to having a relatively large amplitude for the steady state oscillations of the voltage across the capacitor compared to its amplitude at other driving frequencies.
Voltage across the inductor
The resonant frequency need not always take the form given in the examples above. ... | Resonance | Wikipedia | 505 | 41660 | https://en.wikipedia.org/wiki/Resonance | Physical sciences | Waves | null | vital_articles |
The resonant frequency that maximizes this gain is
and the gain is one at this frequency, so the voltage across the resistor resonates at the circuit's natural frequency and at this frequency the amplitude of the voltage across the resistor equals the input voltage's amplitude.
Antiresonance
Some systems exhibit an... | Resonance | Wikipedia | 465 | 41660 | https://en.wikipedia.org/wiki/Resonance | Physical sciences | Waves | null | vital_articles |
Relationships between resonance and frequency response in the RLC series circuit example
These RLC circuit examples illustrate how resonance is related to the frequency response of the system. Specifically, these examples illustrate:
How resonant frequencies can be found by looking for peaks in the gain of the transf... | Resonance | Wikipedia | 486 | 41660 | https://en.wikipedia.org/wiki/Resonance | Physical sciences | Waves | null | vital_articles |
Peaks in the gain at certain frequencies correspond to resonances between that transfer function's input and output, assuming the system is stable.
Each transfer function Hij(s) can also be written as a fraction whose numerator and denominator are polynomials of s.
The complex roots of the numerator are called zeroes... | Resonance | Wikipedia | 414 | 41660 | https://en.wikipedia.org/wiki/Resonance | Physical sciences | Waves | null | vital_articles |
A physical system can have as many natural frequencies as it has degrees of freedom and can resonate near each of those natural frequencies. A mass on a spring, which has one degree of freedom, has one natural frequency. A double pendulum, which has two degrees of freedom, can have two natural frequencies. As the numbe... | Resonance | Wikipedia | 491 | 41660 | https://en.wikipedia.org/wiki/Resonance | Physical sciences | Waves | null | vital_articles |
A generalization to complex networks of coupled harmonic oscillators shows that such systems have a finite number of natural resonant frequencies, related to the topological structure of the network itself. In particular, such frequencies result related to the eigenvalues of the network's Laplacian matrix. Let be the ... | Resonance | Wikipedia | 455 | 41660 | https://en.wikipedia.org/wiki/Resonance | Physical sciences | Waves | null | vital_articles |
The rocket engines for the International Space Station (ISS) are controlled by an autopilot. Ordinarily, uploaded parameters for controlling the engine control system for the Zvezda module make the rocket engines boost the International Space Station to a higher orbit. The rocket engines are hinge-mounted, and ordinari... | Resonance | Wikipedia | 394 | 41660 | https://en.wikipedia.org/wiki/Resonance | Physical sciences | Waves | null | vital_articles |
An optical cavity, also called an optical resonator, is an arrangement of mirrors that forms a standing wave cavity resonator for light waves. Optical cavities are a major component of lasers, surrounding the gain medium and providing feedback of the laser light. They are also used in optical parametric oscillators and... | Resonance | Wikipedia | 380 | 41660 | https://en.wikipedia.org/wiki/Resonance | Physical sciences | Waves | null | vital_articles |
In celestial mechanics, an orbital resonance occurs when two orbiting bodies exert a regular, periodic gravitational influence on each other, usually due to their orbital periods being related by a ratio of two small integers. Orbital resonances greatly enhance the mutual gravitational influence of the bodies. In most ... | Resonance | Wikipedia | 508 | 41660 | https://en.wikipedia.org/wiki/Resonance | Physical sciences | Waves | null | vital_articles |
Resonance in particle physics appears in similar circumstances to classical physics at the level of quantum mechanics and quantum field theory. Resonances can also be thought of as unstable particles, with the formula in the Universal resonance curve section of this article applying if Γ is the particle's decay rate an... | Resonance | Wikipedia | 457 | 41660 | https://en.wikipedia.org/wiki/Resonance | Physical sciences | Waves | null | vital_articles |
The higher the Q factor, the greater the amplitude at the resonant frequency, and the smaller the bandwidth, or range of frequencies around resonance occurs. In electrical resonance, a high-Q circuit in a radio receiver is more difficult to tune, but has greater selectivity, and so would be better at filtering out sign... | Resonance | Wikipedia | 430 | 41660 | https://en.wikipedia.org/wiki/Resonance | Physical sciences | Waves | null | vital_articles |
A shield is a piece of personal armour held in the hand, which may or may not be strapped to the wrist or forearm. Shields are used to intercept specific attacks, whether from close-ranged weaponry like spears or long ranged projectiles such as arrows. They function as means of active blocks, as well as to provide pass... | Shield | Wikipedia | 433 | 41698 | https://en.wikipedia.org/wiki/Shield | Technology | Armour | null | vital_articles |
Often shields were decorated with a painted pattern or an animal representation to show their army or clan. It was common for Aristocratic officials such and knights, barons, dukes, and kings to have their shields painted with customary designs known as a coat of arms. These designs developed into systematized heraldic... | Shield | Wikipedia | 322 | 41698 | https://en.wikipedia.org/wiki/Shield | Technology | Armour | null | vital_articles |
Size and weight varied greatly. Lightly armored warriors relying on speed and surprise would generally carry light shields (pelte) that were either small or thin. Heavy troops might be equipped with robust shields that could cover most of the body. Many had a strap called a guige that allowed them to be slung over the ... | Shield | Wikipedia | 443 | 41698 | https://en.wikipedia.org/wiki/Shield | Technology | Armour | null | vital_articles |
Typical in the early European Middle Ages were round shields with light, non-splitting wood like linden, fir, alder, or poplar, usually reinforced with leather cover on one or both sides and occasionally metal rims, encircling a metal shield boss. These light shields suited a fighting style where each incoming blow is ... | Shield | Wikipedia | 470 | 41698 | https://en.wikipedia.org/wiki/Shield | Technology | Armour | null | vital_articles |
In Italy, the targa, parma, and rotella were used by common people, fencers and even knights. The development of plate armour made shields less and less common as it eliminated the need for a shield. Lightly armoured troops continued to use shields after men-at-arms and knights ceased to use them. Shields continued in ... | Shield | Wikipedia | 479 | 41698 | https://en.wikipedia.org/wiki/Shield | Technology | Armour | null | vital_articles |
Tactical shields often have a firing port so that the officer holding the shield can fire a weapon while being protected by the shield, and they often have a bulletproof glass viewing port. They are typically employed by specialist police, such as SWAT teams in high risk entry and siege scenarios, such as hostage rescu... | Shield | Wikipedia | 193 | 41698 | https://en.wikipedia.org/wiki/Shield | Technology | Armour | null | vital_articles |
Signal-to-noise ratio (SNR or S/N) is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. SNR is defined as the ratio of signal power to noise power, often expressed in decibels. A ratio higher than 1:1 (greater than 0 dB) indicates more signal than no... | Signal-to-noise ratio | Wikipedia | 499 | 41706 | https://en.wikipedia.org/wiki/Signal-to-noise%20ratio | Technology | Basics_4 | null | vital_articles |
where is root mean square (RMS) amplitude (for example, RMS voltage).
Decibels
Because many signals have a very wide dynamic range, signals are often expressed using the logarithmic decibel scale. Based upon the definition of decibel, signal and noise may be expressed in decibels (dB) as
and
In a similar manner, SN... | Signal-to-noise ratio | Wikipedia | 481 | 41706 | https://en.wikipedia.org/wiki/Signal-to-noise%20ratio | Technology | Basics_4 | null | vital_articles |
But in signal processing and communication, one usually assumes that so that factor is usually not included while measuring power or energy of a signal. This may cause some confusion among readers, but the resistance factor is not significant for typical operations performed in signal processing, or for computing pow... | Signal-to-noise ratio | Wikipedia | 504 | 41706 | https://en.wikipedia.org/wiki/Signal-to-noise%20ratio | Technology | Basics_4 | null | vital_articles |
Internal electronic noise of measurement systems can be reduced through the use of low-noise amplifiers.
When the characteristics of the noise are known and are different from the signal, it is possible to use a filter to reduce the noise. For example, a lock-in amplifier can extract a narrow bandwidth signal from bro... | Signal-to-noise ratio | Wikipedia | 471 | 41706 | https://en.wikipedia.org/wiki/Signal-to-noise%20ratio | Technology | Basics_4 | null | vital_articles |
Assuming a full-scale sine wave signal (that is, the quantizer is designed such that it has the same minimum and maximum values as the input signal), the quantization noise approximates a sawtooth wave with peak-to-peak amplitude of one quantization level and uniform distribution. In this case, the SNR is approximately... | Signal-to-noise ratio | Wikipedia | 447 | 41706 | https://en.wikipedia.org/wiki/Signal-to-noise%20ratio | Technology | Basics_4 | null | vital_articles |
Other uses
While SNR is commonly quoted for electrical signals, it can be applied to any form of signal, for example isotope levels in an ice core, biochemical signaling between cells, or financial trading signals. The term is sometimes used metaphorically to refer to the ratio of useful information to false or irrelev... | Signal-to-noise ratio | Wikipedia | 182 | 41706 | https://en.wikipedia.org/wiki/Signal-to-noise%20ratio | Technology | Basics_4 | null | vital_articles |
In physics, a standing wave, also known as a stationary wave, is a wave that oscillates in time but whose peak amplitude profile does not move in space. The peak amplitude of the wave oscillations at any point in space is constant with respect to time, and the oscillations at different points throughout the wave are i... | Standing wave | Wikipedia | 428 | 41741 | https://en.wikipedia.org/wiki/Standing%20wave | Physical sciences | Waves | Physics | vital_articles |
As an example of the second type, a standing wave in a transmission line is a wave in which the distribution of current, voltage, or field strength is formed by the superposition of two waves of the same frequency propagating in opposite directions. The effect is a series of nodes (zero displacement) and anti-nodes (m... | Standing wave | Wikipedia | 504 | 41741 | https://en.wikipedia.org/wiki/Standing%20wave | Physical sciences | Waves | Physics | vital_articles |
To begin, consider a string of infinite length along the x-axis that is free to be stretched transversely in the y direction.
For a harmonic wave traveling to the right along the string, the string's displacement in the y direction as a function of position x and time t is
The displacement in the y-direction for an i... | Standing wave | Wikipedia | 392 | 41741 | https://en.wikipedia.org/wiki/Standing%20wave | Physical sciences | Waves | Physics | vital_articles |
Next, consider a string with fixed ends at and . The string will have some damping as it is stretched by traveling waves, but assume the damping is very small. Suppose that at the fixed end a sinusoidal force is applied that drives the string up and down in the y-direction with a small amplitude at some frequency f. ... | Standing wave | Wikipedia | 480 | 41741 | https://en.wikipedia.org/wiki/Standing%20wave | Physical sciences | Waves | Physics | vital_articles |
Next, consider the same string of length L, but this time it is only fixed at . At , the string is free to move in the y direction. For example, the string might be tied at to a ring that can slide freely up and down a pole. The string again has small damping and is driven by a small driving force at .
In this case, ... | Standing wave | Wikipedia | 498 | 41741 | https://en.wikipedia.org/wiki/Standing%20wave | Physical sciences | Waves | Physics | vital_articles |
where
pmax is the pressure amplitude or the maximum increase or decrease in air pressure due to each wave,
ω is the angular frequency or equivalently 2π times the frequency f,
λ is the wavelength of the wave.
If identical right- and left-traveling waves travel through the pipe, the resulting superposition is described... | Standing wave | Wikipedia | 505 | 41741 | https://en.wikipedia.org/wiki/Standing%20wave | Physical sciences | Waves | Physics | vital_articles |
For the case where one end is closed, n only takes odd values just like in the case of the string fixed at only one end.
So far, the wave has been written in terms of its pressure as a function of position x and time. Alternatively, the wave can be written in terms of its longitudinal displacement of air, where air in... | Standing wave | Wikipedia | 497 | 41741 | https://en.wikipedia.org/wiki/Standing%20wave | Physical sciences | Waves | Physics | vital_articles |
This is an eigenvalue problem where the frequencies correspond to eigenvalues that then correspond to frequency-specific modes or eigenfunctions. Specifically, this is a form of the Helmholtz equation and it can be solved using separation of variables. Assume
Dividing the Helmholtz equation by Z,
This leads to two co... | Standing wave | Wikipedia | 420 | 41741 | https://en.wikipedia.org/wiki/Standing%20wave | Physical sciences | Waves | Physics | vital_articles |
So, standing waves inside this fixed rectangular boundary oscillate in time at certain resonant frequencies parameterized by the integers n and m. As they oscillate in time, they do not travel and their spatial variation is sinusoidal in both the x- and y-directions such that they satisfy the boundary conditions. The f... | Standing wave | Wikipedia | 427 | 41741 | https://en.wikipedia.org/wiki/Standing%20wave | Physical sciences | Waves | Physics | vital_articles |
A pure standing wave does not transfer energy from the source to the destination. However, the wave is still subject to losses in the medium. Such losses will manifest as a finite SWR, indicating a travelling wave component leaving the source to supply the losses. Even though the SWR is now finite, it may still be t... | Standing wave | Wikipedia | 477 | 41741 | https://en.wikipedia.org/wiki/Standing%20wave | Physical sciences | Waves | Physics | vital_articles |
X-rays
Interference between X-ray beams can form an X-ray standing wave (XSW) field. Because of the short wavelength of X-rays (less than 1 nanometer), this phenomenon can be exploited for measuring atomic-scale events at material surfaces. The XSW is generated in the region where an X-ray beam interferes with a diffr... | Standing wave | Wikipedia | 406 | 41741 | https://en.wikipedia.org/wiki/Standing%20wave | Physical sciences | Waves | Physics | vital_articles |
Seiches
A seiche is an example of a standing wave in an enclosed body of water. It is characterised by the oscillatory behaviour of the water level at either end of the body and typically has a nodal point near the middle of the body where very little change in water level is observed. It should be distinguished from ... | Standing wave | Wikipedia | 150 | 41741 | https://en.wikipedia.org/wiki/Standing%20wave | Physical sciences | Waves | Physics | vital_articles |
Thermodynamic temperature is a quantity defined in thermodynamics as distinct from kinetic theory or statistical mechanics.
Historically, thermodynamic temperature was defined by Lord Kelvin in terms of a macroscopic relation between thermodynamic work and heat transfer as defined in thermodynamics, but the kelvin was... | Thermodynamic temperature | Wikipedia | 496 | 41789 | https://en.wikipedia.org/wiki/Thermodynamic%20temperature | Physical sciences | Thermodynamics | Physics | vital_articles |
The microscopic property that imbues material substances with a temperature can be readily understood by examining the ideal gas law, which relates, per the Boltzmann constant, how heat energy causes precisely defined changes in the pressure and temperature of certain gases. This is because monatomic gases like helium ... | Thermodynamic temperature | Wikipedia | 421 | 41789 | https://en.wikipedia.org/wiki/Thermodynamic%20temperature | Physical sciences | Thermodynamics | Physics | vital_articles |
Temperature scales are numerical. The numerical zero of a temperature scale is not bound to the absolute zero of temperature. Nevertheless, some temperature scales have their numerical zero coincident with the absolute zero of temperature. Examples are the International SI temperature scale, the Rankine temperature sca... | Thermodynamic temperature | Wikipedia | 404 | 41789 | https://en.wikipedia.org/wiki/Thermodynamic%20temperature | Physical sciences | Thermodynamics | Physics | vital_articles |
Boltzmann constant
The Boltzmann constant and its related formulas describe the realm of particle kinetics and velocity vectors whereas ZPE (zero-point energy) is an energy field that jostles particles in ways described by the mathematics of quantum mechanics. In atomic and molecular collisions in gases, ZPE introduce... | Thermodynamic temperature | Wikipedia | 488 | 41789 | https://en.wikipedia.org/wiki/Thermodynamic%20temperature | Physical sciences | Thermodynamics | Physics | vital_articles |
To convert temperature intervals (a span or difference between two temperatures), the formulas from the preceding paragraph are applicable; for instance, an interval of 5 kelvin is precisely equal to an interval of 9 degrees Rankine.
Modern redefinition of the kelvin
For 65 years, between 1954 and the 2019 revision ... | Thermodynamic temperature | Wikipedia | 492 | 41789 | https://en.wikipedia.org/wiki/Thermodynamic%20temperature | Physical sciences | Thermodynamics | Physics | vital_articles |
The 2019 revision of the SI was primarily for the purpose of decoupling much of the SI system's definitional underpinnings from the kilogram, which was the last physical artifact defining an SI base unit (a platinum/iridium cylinder stored under three nested bell jars in a safe located in France) and which had highly q... | Thermodynamic temperature | Wikipedia | 415 | 41789 | https://en.wikipedia.org/wiki/Thermodynamic%20temperature | Physical sciences | Thermodynamics | Physics | vital_articles |
The thermodynamic temperature of any bulk quantity of a substance (a statistically significant quantity of particles) is directly proportional to the mean average kinetic energy of a specific kind of particle motion known as translational motion. These simple movements in the three X, Y, and Z–axis dimensions of space ... | Thermodynamic temperature | Wikipedia | 479 | 41789 | https://en.wikipedia.org/wiki/Thermodynamic%20temperature | Physical sciences | Thermodynamics | Physics | vital_articles |
While the Boltzmann constant is useful for finding the mean kinetic energy in a sample of particles, it is important to note that even when a substance is isolated and in thermodynamic equilibrium (all parts are at a uniform temperature and no heat is going into or out of it), the translational motions of individual at... | Thermodynamic temperature | Wikipedia | 424 | 41789 | https://en.wikipedia.org/wiki/Thermodynamic%20temperature | Physical sciences | Thermodynamics | Physics | vital_articles |
It is neither difficult to imagine atomic motions due to kinetic temperature, nor distinguish between such motions and those due to zero-point energy. Consider the following hypothetical thought experiment, as illustrated in Fig. 2.5 at left, with an atom that is exceedingly close to absolute zero. Imagine peering thro... | Thermodynamic temperature | Wikipedia | 503 | 41789 | https://en.wikipedia.org/wiki/Thermodynamic%20temperature | Physical sciences | Thermodynamics | Physics | vital_articles |
As mentioned above, there are other ways molecules can jiggle besides the three translational degrees of freedom that imbue substances with their kinetic temperature. As can be seen in the animation at right, molecules are complex objects; they are a population of atoms and thermal agitation can strain their internal c... | Thermodynamic temperature | Wikipedia | 444 | 41789 | https://en.wikipedia.org/wiki/Thermodynamic%20temperature | Physical sciences | Thermodynamics | Physics | vital_articles |
Different molecules absorb different amounts of internal energy for each incremental increase in temperature; that is, they have different specific heat capacities. High specific heat capacity arises, in part, because certain substances' molecules possess more internal degrees of freedom than others do. For instance, r... | Thermodynamic temperature | Wikipedia | 404 | 41789 | https://en.wikipedia.org/wiki/Thermodynamic%20temperature | Physical sciences | Thermodynamics | Physics | vital_articles |
Translational motion in solids, however, takes the form of phonons (see Fig. 4 at right). Phonons are constrained, quantized wave packets that travel at the speed of sound of a given substance. The manner in which phonons interact within a solid determines a variety of its properties, including its thermal conductivity... | Thermodynamic temperature | Wikipedia | 445 | 41789 | https://en.wikipedia.org/wiki/Thermodynamic%20temperature | Physical sciences | Thermodynamics | Physics | vital_articles |
Thermal radiation is a byproduct of the collisions arising from various vibrational motions of atoms. These collisions cause the electrons of the atoms to emit thermal photons (known as black-body radiation). Photons are emitted anytime an electric charge is accelerated (as happens when electron clouds of two atoms col... | Thermodynamic temperature | Wikipedia | 394 | 41789 | https://en.wikipedia.org/wiki/Thermodynamic%20temperature | Physical sciences | Thermodynamics | Physics | vital_articles |
The kinetic energy of particle motion is just one contributor to the total thermal energy in a substance; another is phase transitions, which are the potential energy of molecular bonds that can form in a substance as it cools (such as during condensing and freezing). The thermal energy required for a phase transition ... | Thermodynamic temperature | Wikipedia | 472 | 41789 | https://en.wikipedia.org/wiki/Thermodynamic%20temperature | Physical sciences | Thermodynamics | Physics | vital_articles |
As stated above, the thermal energy required for a phase transition is called latent heat. In the specific cases of melting and freezing, it is called enthalpy of fusion or heat of fusion. If the molecular bonds in a crystal lattice are strong, the heat of fusion can be relatively great, typically in the range of 6 to ... | Thermodynamic temperature | Wikipedia | 498 | 41789 | https://en.wikipedia.org/wiki/Thermodynamic%20temperature | Physical sciences | Thermodynamics | Physics | vital_articles |
The total energy of all translational and internal particle motions, including that of conduction electrons, plus the potential energy of phase changes, plus zero-point energy of a substance comprise the internal energy of it.
Internal energy at absolute zero
As a substance cools, different forms of internal energy ... | Thermodynamic temperature | Wikipedia | 455 | 41789 | https://en.wikipedia.org/wiki/Thermodynamic%20temperature | Physical sciences | Thermodynamics | Physics | vital_articles |
The above complexities make for rather cumbersome blanket statements regarding the internal energy in = 0 substances. Regardless of pressure though, what can be said is that at absolute zero, all solids with a lowest-energy crystal lattice such those with a closest-packed arrangement (see Fig. 8, above left) contain m... | Thermodynamic temperature | Wikipedia | 470 | 41789 | https://en.wikipedia.org/wiki/Thermodynamic%20temperature | Physical sciences | Thermodynamics | Physics | vital_articles |
Loosely stated, temperature differences dictate the direction of heat between two systems such that their combined energy is maximally distributed among their lowest possible states. We call this distribution "entropy". To better understand the relationship between temperature and entropy, consider the relationship bet... | Thermodynamic temperature | Wikipedia | 503 | 41789 | https://en.wikipedia.org/wiki/Thermodynamic%20temperature | Physical sciences | Thermodynamics | Physics | vital_articles |
With this understanding of , and , mathematically,
But since the first function is not a function of , the product of the final two functions must result in the removal of as a variable. The only way is therefore to define the function as follows:
and
so that
I.e. the ratio of heat exchanged is a function of the... | Thermodynamic temperature | Wikipedia | 451 | 41789 | https://en.wikipedia.org/wiki/Thermodynamic%20temperature | Physical sciences | Thermodynamics | Physics | vital_articles |
Guillaume Amontons (1663–1705) published two papers in 1702 and 1703 that may be used to credit him as being the first researcher to deduce the existence of a fundamental (thermodynamic) temperature scale featuring an absolute zero. He made the discovery while endeavoring to improve upon the air thermometers in use at ... | Thermodynamic temperature | Wikipedia | 451 | 41789 | https://en.wikipedia.org/wiki/Thermodynamic%20temperature | Physical sciences | Thermodynamics | Physics | vital_articles |
Coincident with the death of Anders Celsius in 1744, the botanist Carl Linnaeus (1707–1778) effectively reversed Celsius's scale upon receipt of his first thermometer featuring a scale where zero represented the melting point of ice and 100 represented water's boiling point. The custom-made Linnaeus-thermometer, for us... | Thermodynamic temperature | Wikipedia | 448 | 41789 | https://en.wikipedia.org/wiki/Thermodynamic%20temperature | Physical sciences | Thermodynamics | Physics | vital_articles |
Joseph Louis Gay-Lussac (1778–1850) published work in 1802 (acknowledging the unpublished lab notes of Jacques Charles fifteen years earlier) describing how the volume of gas under constant pressure changes linearly with its absolute (thermodynamic) temperature. This behavior is called Charles's law and is one of the g... | Thermodynamic temperature | Wikipedia | 464 | 41789 | https://en.wikipedia.org/wiki/Thermodynamic%20temperature | Physical sciences | Thermodynamics | Physics | vital_articles |
The above definition fixes the ratios between absolute temperatures, but it does not fix a scale for absolute temperature. For the scale, Thomson proposed to use the Celsius degree, that is, the interval between the freezing and the boiling point of water.
In 1859 Macquorn Rankine (1820–1872) proposed a thermodynamic... | Thermodynamic temperature | Wikipedia | 472 | 41789 | https://en.wikipedia.org/wiki/Thermodynamic%20temperature | Physical sciences | Thermodynamics | Physics | vital_articles |
Resolution 3 of the 13th CGPM in 1967/1968 renamed the unit increment of thermodynamic temperature kelvin, symbol K, replacing degree absolute, symbol . Further, feeling it useful to more explicitly define the magnitude of the unit increment, the 13th CGPM also decided in Resolution 4 that "The kelvin, unit of thermody... | Thermodynamic temperature | Wikipedia | 233 | 41789 | https://en.wikipedia.org/wiki/Thermodynamic%20temperature | Physical sciences | Thermodynamics | Physics | vital_articles |
A time standard is a specification for measuring time: either the rate at which time passes or points in time or both. In modern times, several time specifications have been officially recognized as standards, where formerly they were matters of custom and practice. An example of a kind of time standard can be a time s... | Time standard | Wikipedia | 331 | 41799 | https://en.wikipedia.org/wiki/Time%20standard | Technology | Timekeeping | null | vital_articles |
Terminology
The term "time" is generally used for many close but different concepts, including:
instant as an object – one point on the time axis. Being an object, it has no value;
date as a quantity characterising an instant. As a quantity, it has a value which may be expressed in a variety of ways, for example "20... | Time standard | Wikipedia | 463 | 41799 | https://en.wikipedia.org/wiki/Time%20standard | Technology | Timekeeping | null | vital_articles |
Most recently, atomic clocks have been developed that offer improved accuracy. Since 1967, the SI base unit for time is the SI second, defined as exactly "the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom" ... | Time standard | Wikipedia | 485 | 41799 | https://en.wikipedia.org/wiki/Time%20standard | Technology | Timekeeping | null | vital_articles |
Standard time or civil time in a time zone deviates a fixed, round amount, usually a whole number of hours, from some form of Universal Time, usually UTC. The offset is chosen such that a new day starts approximately while the Sun is crossing the nadir meridian. Alternatively the difference is not really fixed, but it... | Time standard | Wikipedia | 490 | 41799 | https://en.wikipedia.org/wiki/Time%20standard | Technology | Timekeeping | null | vital_articles |
TCB is a linear transformation of TDB and TDB differs from TT in small, mostly periodic terms. Neglecting these terms (on the order of 2 milliseconds for several millennia around the present epoch), TCB is related to TT by: TCB − TT = LB × (JD − 2443144.5) × 86400 seconds. The scale difference LB has been defined by th... | Time standard | Wikipedia | 281 | 41799 | https://en.wikipedia.org/wiki/Time%20standard | Technology | Timekeeping | null | vital_articles |
Sidereal time is time by the stars. A sidereal rotation is the time it takes the Earth to make one revolution with rotation to the stars, approximately 23 hours 56 minutes 4 seconds. A mean solar day is about 3 minutes 56 seconds longer than a mean sidereal day, or more than a mean sidereal day. In astronomy, sidereal... | Time standard | Wikipedia | 366 | 41799 | https://en.wikipedia.org/wiki/Time%20standard | Technology | Timekeeping | null | vital_articles |
Greenwich Mean Time was originally mean time deduced from meridian observations made at the Royal Greenwich Observatory (RGO). The principal meridian of that observatory was chosen in 1884 by the International Meridian Conference to be the Prime Meridian. GMT either by that name or as 'mean time at Greenwich' used to ... | Time standard | Wikipedia | 251 | 41799 | https://en.wikipedia.org/wiki/Time%20standard | Technology | Timekeeping | null | vital_articles |
Time standards for planetary motion calculations
Ephemeris time (ET) and its successor time scales described below have all been intended for astronomical use, e.g. in planetary motion calculations, with aims including uniformity, in particular, freedom from irregularities of Earth rotation. Some of these standards are... | Time standard | Wikipedia | 430 | 41799 | https://en.wikipedia.org/wiki/Time%20standard | Technology | Timekeeping | null | vital_articles |
For the calculation of ephemerides, Barycentric Dynamical Time (TDB) was officially recommended to replace ET. TDB is similar to TDT but includes relativistic corrections that move the origin to the barycenter, hence it is a dynamical time at the barycenter. TDB differs from TT only in periodic terms. The difference is... | Time standard | Wikipedia | 249 | 41799 | https://en.wikipedia.org/wiki/Time%20standard | Technology | Timekeeping | null | vital_articles |
In electrical engineering, a transmission line is a specialized cable or other structure designed to conduct electromagnetic waves in a contained manner. The term applies when the conductors are long enough that the wave nature of the transmission must be taken into account. This applies especially to radio-frequency ... | Transmission line | Wikipedia | 484 | 41811 | https://en.wikipedia.org/wiki/Transmission%20line | Technology | Signal transmission | null | vital_articles |
At frequencies of microwave and higher, power losses in transmission lines become excessive, and waveguides are used instead, which function as "pipes" to confine and guide the electromagnetic waves. Some sources define waveguides as a type of transmission line; however, this article will not include them.
History
Ma... | Transmission line | Wikipedia | 449 | 41811 | https://en.wikipedia.org/wiki/Transmission%20line | Technology | Signal transmission | null | vital_articles |
Some of the power that is fed into a transmission line is lost because of its resistance. This effect is called ohmic or resistive loss (see ohmic heating). At high frequencies, another effect called dielectric loss becomes significant, adding to the losses caused by resistance. Dielectric loss is caused when the in... | Transmission line | Wikipedia | 496 | 41811 | https://en.wikipedia.org/wiki/Transmission%20line | Technology | Signal transmission | null | vital_articles |
The model consists of an infinite series of the elements shown in the figure, and the values of the components are specified per unit length so the picture of the component can be misleading. , , , and may also be functions of frequency. An alternative notation is to use , , and to emphasize that the values are deri... | Transmission line | Wikipedia | 498 | 41811 | https://en.wikipedia.org/wiki/Transmission%20line | Technology | Signal transmission | null | vital_articles |
Alternatively, the complex square root can be evaluated algebraically, to yield:
and
with the plus or minus signs chosen opposite to the direction of the wave's motion through the conducting medium. ( is usually negative, since and are typically much smaller than and , respectively, so is usually positive. is... | Transmission line | Wikipedia | 503 | 41811 | https://en.wikipedia.org/wiki/Transmission%20line | Technology | Signal transmission | null | vital_articles |
Matched load
Another special case is when the load impedance is equal to the characteristic impedance of the line (i.e. the line is matched), in which case the impedance reduces to the characteristic impedance of the line so that
for all and all .
Short
For the case of a shorted load (i.e. ), the input impedance is... | Transmission line | Wikipedia | 498 | 41811 | https://en.wikipedia.org/wiki/Transmission%20line | Technology | Signal transmission | null | vital_articles |
For lossless and lossy transmission lines respectively, the S parameter matrix is as follows, using standard hyperbolic to circular complex translations.
Variable definitions
In all matrix parameters above, the following variable definitions apply:
= characteristic impedance
Zp = port impedance, or termination imp... | Transmission line | Wikipedia | 346 | 41811 | https://en.wikipedia.org/wiki/Transmission%20line | Technology | Signal transmission | null | vital_articles |
Coaxial lines confine virtually all of the electromagnetic wave to the area inside the cable. Coaxial lines can therefore be bent and twisted (subject to limits) without negative effects, and they can be strapped to conductive supports without inducing unwanted currents in them.
In radio-frequency applications up to a ... | Transmission line | Wikipedia | 503 | 41811 | https://en.wikipedia.org/wiki/Transmission%20line | Technology | Signal transmission | null | vital_articles |
A coplanar waveguide consists of a center strip and two adjacent outer conductors, all three of them flat structures that are deposited onto the same insulating substrate and thus are located in the same plane ("coplanar"). The width of the center conductor, the distance between inner and outer conductors, and the rela... | Transmission line | Wikipedia | 449 | 41811 | https://en.wikipedia.org/wiki/Transmission%20line | Technology | Signal transmission | null | vital_articles |
Twin-lead consists of a pair of conductors held apart by a continuous insulator. By holding the conductors a known distance apart, the geometry is fixed and the line characteristics are reliably consistent. It is lower loss than coaxial cable because the characteristic impedance of twin-lead is generally higher than ... | Transmission line | Wikipedia | 479 | 41811 | https://en.wikipedia.org/wiki/Transmission%20line | Technology | Signal transmission | null | vital_articles |
Approximating lumped elements
At higher frequencies, the reactive parasitic effects of real world lumped elements, including inductors and capacitors, limits their usefulness. Therefore, it is sometimes useful to approximate the electrical characteristics of inductors and capacitors with transmission lines at the hig... | Transmission line | Wikipedia | 442 | 41811 | https://en.wikipedia.org/wiki/Transmission%20line | Technology | Signal transmission | null | vital_articles |
The troposphere is the lowest layer of the atmosphere of Earth. It contains 80% of the total mass of the planetary atmosphere and 99% of the total mass of water vapor and aerosols, and is where most weather phenomena occur. From the planetary surface of the Earth, the average height of the troposphere is in the tropic... | Troposphere | Wikipedia | 293 | 41822 | https://en.wikipedia.org/wiki/Troposphere | Physical sciences | Atmosphere: General | Earth science | vital_articles |
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