unidentified flying object unidentified flying object ( commonly abbreviated as ufo or u. f. o. ) is the popular term for any aerial phenomenon whose cause cannot be easily or immediately identified. both military and civilian research show that a significant majority of ufo sightings have been identified after further investigation, either explicitly or indirectly through the presence of clear and simple explanatory factors. - some years ago i had a conversation with a layman about flying saucers — because i am scientific i know all about flying saucers! i said " i don ' t think there are flying saucers '. so my antagonist said, " is it impossible that there are flying saucers? can you prove that it ' s impossible? " " no ", i said, " i can ' t prove it ' s impossible. it ' s just very unlikely ". at that he said, " you are very unscientific. if you can ' t prove it impossible then how can you say that it ' s unlikely? " but that is the way that is scientific. it is scientific only to say what is more likely and what less likely, and not to be proving all the time the possible and impossible. to define what i mean, i might have said to him, " listen, i mean that from my knowledge of the world that i see around me, i think that it is much more likely that the reports of flying saucers are the results of the known irrational characteristics of terrestrial intelligence than of the unknown rational efforts of extra - terrestrial intelligence. " it is just more likely. that is all. - richard feynman in the character of physical law ( 1964 ) - anyway, i have to argue about flying saucers on the beach with people, you know. and i was interested in this : they keep arguing that it is possible. and that ' s true. it is possible. they do not appreciate that the problem is not to demonstrate whether it ' s possible or not but whether it ' s going on or not. - richard feynman in the meaning of it all : thoughts of a citizen scientist ( 1998 )


in heat transfer, conduction ( or heat conduction ) is the transfer of heat energy by microscopic diffusion and collisions of particles or quasi - particles within a body due to a temperature gradient. the microscopically diffusing and colliding objects include molecules, electrons, atoms, and phonons. they transfer microscopically disorganized kinetic and potential energy, which are jointly known as internal energy. conduction takes place in all forms of ponderable matter, such as solids, liquids, gases and plasmas. by conduction, as well as by thermal radiation, heat spontaneously flows from a body at a higher temperature to a body at a lower temperature. in the absence of external drivers, temperature differences decay over time, and the bodies approach thermal equilibrium. in conduction, heat flows within and through the body itself. in contrast, in heat transfer by thermal radiation, the transfer is often between bodies. also possible is transfer of heat by a combination of conduction and thermal radiation. in convection, internal energy is carried between bodies by a material carrier. in solids, conduction is mediated by the combination of vibrations and collisions of molecules, of propagation and collisions of phonons, and of diffusion and collisions of free electrons. in gases and liquids, conduction is due to the collisions and diffusion of molecules during their random motion. photons in this context do not collide with one another, and so heat transport by electromagnetic radiation is conceptually distinct from heat conduction by microscopic diffusion and collisions of material particles and phonons. in condensed matter, such as a solid or liquid, the distinction between conduction and radiative transfer of heat is clear in physical concept, but it is often not phenomenologically clear, unless the material is semi - transparent. in a gas the distinction is both conceptually and phenomenologically clear. in the engineering sciences, heat transfer includes the processes of thermal radiation, convection, and sometimes mass transfer. usually more than one of these processes occurs in a given situation. the conventional symbol for the material property, thermal conductivity, is. on a microscopic scale, conduction occurs within a body considered as being stationary ; this means that the kinetic and potential energies of the bulk motion of the body are separately accounted for. internal energy diffuses as rapidly moving or vibrating atoms and molecules interact with neighboring particles, transferring some of their microscopic kinetic and potential energies, these quantities being defined relative to the bulk of the body considered as being stationary. heat is transferred by conduction when adjacent


energy diffuses as rapidly moving or vibrating atoms and molecules interact with neighboring particles, transferring some of their microscopic kinetic and potential energies, these quantities being defined relative to the bulk of the body considered as being stationary. heat is transferred by conduction when adjacent atoms or molecules collide, or as several electrons move backwards and forwards from atom to atom in a disorganized way so as not to form a macroscopic electric current, or as phonons collide and scatter. conduction is the most significant means of heat transfer within a solid or between solid objects in thermal contact. conduction is greater in solids because the network of relatively close fixed spatial relationships between atoms helps to transfer energy between them by vibration. fluids ( and especially gases ) are less conductive. this is due to the large distance between atoms in a gas : fewer collisions between atoms means less conduction. conductivity of gases increases with temperature. conductivity increases with increasing pressure from vacuum up to a critical point that the density of the gas is such that molecules of the gas may be expected to collide with each other before they transfer heat from one surface to another. after this point conductivity increases only slightly with increasing pressure and density. thermal contact conductance is the study of heat conduction between solid bodies in contact. a temperature drop is often observed at the interface between the two surfaces in contact. this phenomenon is said to be a result of a thermal contact resistance existing between the contacting surfaces. interfacial thermal resistance is a measure of an interface ' s resistance to thermal flow. this thermal resistance differs from contact resistance, as it exists even at atomically perfect interfaces. understanding the thermal resistance at the interface between two materials is of primary significance in the study of its thermal properties. interfaces often contribute significantly to the observed properties of the materials. the inter - molecular transfer of energy could be primarily by elastic impact as in fluids or by free electron diffusion as in metals or phonon vibration as in insulators. in insulators the heat flux is carried almost entirely by phonon vibrations. metals ( e. g. copper, platinum, gold, etc. ) are usually good conductors of thermal energy. this is due to the way that metals are chemically bonded : metallic bonds ( as opposed to covalent or ionic bonds ) have free - moving electrons which are able to transfer thermal energy rapidly through the metal. the " electron fluid " of a conductive metallic solid conducts most of the heat flux through the solid. phonon flux is still present


state conduction is reached, the spatial gradient of temperatures along the bar does not change any further, as time proceeds. instead, the temperature at any given section of the rod remains constant, and this temperature varies linearly in space, along the direction of heat transfer. in steady state conduction, all the laws of direct current electrical conduction can be applied to " heat currents ". in such cases, it is possible to take " thermal resistances " as the analog to electrical resistances. in such cases, temperature plays the role of voltage, and heat transferred per unit time ( heat power ) is the analog of electrical current. steady state systems can be modelled by networks of such thermal resistances in series and in parallel, in exact analogy to electrical networks of resistors. see purely resistive thermal circuits for an example of such a network. transient conduction in general, during any period in which temperatures are changing in time at any place within an object, the mode of thermal energy flow is termed transient conduction. another term is " non steady - state " conduction, referring to time - dependence of temperature fields in an object. non - steady - state situations appear after an imposed change in temperature at a boundary of an object. they may also occur with temperature changes inside an object, as a result of a new source or sink of heat suddenly introduced within an object, causing temperatures near the source or sink to change in time. when a new perturbation of temperature of this type happens, temperatures within the system will change in time toward a new equilibrium with the new conditions, provided that these do not change. after equilibrium, heat flow into the system will once again equal the heat flow out, and temperatures at each point inside the system no longer change. once this happens, transient conduction is ended, although steady - state conduction may continue if there continues to be heat flow. if changes in external temperatures or internal heat generation changes are too rapid for equilibrium of temperatures in space to take place, then the system never reaches a state of unchanging temperature distribution in time, and the system remains in a transient state. an example of a new source of heat " turning on " within an object which causes transient conduction, is an engine starting in an automobile. in this case the transient thermal conduction phase for the entire machine would be over, and the steady state phase would appear, as soon as the engine had reached steady - state operating temperature. in this state of steady - state equilibrium, temperatures would vary greatly from the


application of approximation theories, and / or numerical analysis by computer. one popular graphical method involves the use of heisler charts. occasionally transient conduction problems may be considerably simplified if regions of the object being heated or cooled can be identified, in which thermal conductivity is very much greater than that for heat paths leading into the region. in this case, the region with high conductivity can often be treated in the lumped capacitance model, as a " lump " of material with a simple thermal capacitance consisting of its aggregate heat capacity. such regions show no temperature variation across their extent during warming or cooling ( as compared to the rest of the system ) due to their far higher conductance. during transient conduction, therefore, their temperature changes uniformly in space, and as a simple exponential in time. an example of such systems are those which follow " newton ' s law of cooling " during transient cooling ( or the reverse during heating ). the equivalent thermal circuit consists of a simple capacitor in series with a resistor. in such cases, the remainder of the system with high thermal resistance ( comparatively low conductivity ) plays the role of the resistor in the circuit. relativistic conduction the theory of relativistic heat conduction is a model that is compatible with the theory of special relativity. for most of the last century, it was recognized that fourier equation is in contradiction with the theory of relativity because it admits an infinite speed of propagation of heat signals. for example, according to fourier equation, a pulse of heat at the origin would be felt at infinity instantaneously. the speed of information propagation is faster than the speed of light in vacuum, which is physically inadmissible within the framework of relativity. alterations to the fourier model provided for a relativistic model of heat conduction, avoiding this problem. quantum conduction second sound is a quantum mechanical phenomenon in which heat transfer occurs by wave - like motion, rather than by the more usual mechanism of diffusion. heat takes the place of pressure in normal sound waves. this leads to a very high thermal conductivity. it is known as " second sound " because the wave motion of heat is similar to the propagation of sound in air. fourier ' s law the law of heat conduction, also known as fourier ' s law, states that the time rate of heat transfer through a material is proportional to the negative gradient in the temperature and to the area, at right angles to that gradient, through which the heat is flowing.


conduction, also known as fourier ' s law, states that the time rate of heat transfer through a material is proportional to the negative gradient in the temperature and to the area, at right angles to that gradient, through which the heat is flowing. we can state this law in two equivalent forms : the integral form, in which we look at the amount of energy flowing into or out of a body as a whole, and the differential form, in which we look at the flow rates or fluxes of energy locally. differential form the differential form of fourier ' s law of thermal conduction shows that the local heat flux density,, is equal to the product of thermal conductivity,, and the negative local temperature gradient,. the heat flux density is the amount of energy that flows through a unit area per unit time. where ( including the si units ) - is the local heat flux, w · m−2 - is the material ' s conductivity, w · m−1 · k−1, - is the temperature gradient, k · m−1. the thermal conductivity,, is often treated as a constant, though this is not always true. while the thermal conductivity of a material generally varies with temperature, the variation can be small over a significant range of temperatures for some common materials. in anisotropic materials, the thermal conductivity typically varies with orientation ; in this case is represented by a second - order tensor. in nonuniform materials, varies with spatial location. for many simple applications, fourier ' s law is used in its one - dimensional form. in the x - direction, integral form by integrating the differential form over the material ' s total surface, we arrive at the integral form of fourier ' s law : where ( including the si units ) | : is the amount of heat transferred per unit time ( in w ) and | | : is an oriented surface area element ( in m2 ) | - a is the cross - sectional surface area, - is the temperature difference between the ends, - is the distance between the ends. this law forms the basis for the derivation of the heat equation. where u is the conductance, in w / ( m2 k ). fourier ' s law can also be stated as : the reciprocal of conductance is resistance, r, given by : and it is resistance which is additive when several conducting layers lie between the hot and cool regions, because a and q are the same for all layers. in a multilayer partition, the total conductance is related to the conductance


, given by : and it is resistance which is additive when several conducting layers lie between the hot and cool regions, because a and q are the same for all layers. in a multilayer partition, the total conductance is related to the conductance of its layers by : so, when dealing with a multilayer partition, the following formula is usually used : when heat is being conducted from one fluid to another through a barrier, it is sometimes important to consider the conductance of the thin film of fluid which remains stationary next to the barrier. this thin film of fluid is difficult to quantify, its characteristics depending upon complex conditions of turbulence and viscosity, but when dealing with thin high - conductance barriers it can sometimes be quite significant. intensive - property representation ideally, the formulae for conductance should produce a quantity with dimensions independent of distance, like ohm ' s law for electrical resistance :, and conductance :. from the electrical formula :, where ρ is resistivity, x is length, and a is cross - sectional area, we have, where g is conductance, k is conductivity, x is length, and a is cross - sectional area. where u is the conductance. fourier ' s law can also be stated as : analogous to ohm ' s law : or the reciprocal of conductance is resistance, r, given by : analogous to ohm ' s law : the rules for combining resistances and conductances ( in series and in parallel ) are the same for both heat flow and electric current. cylindrical shells conduction through cylindrical shells ( e. g. pipes ) can be calculated from the internal radius,, the external radius,, the length,, and the temperature difference between the inner and outer wall,. the surface area of the cylinder is when fourier ’ s equation is applied : then the rate of heat transfer is : the thermal resistance is : and, where. it is important to note that this is the log - mean radius. the conduction through a spherical shell with internal radius,, and external radius,, can be calculated in a similar manner as for a cylindrical shell. the surface area of the sphere is : solving in a similar manner as for a cylindrical shell ( see above ) produces : transient thermal conduction interface heat transfer the heat transfer at an interface is considered a transient heat flow. to analyze this problem, the biot number is important to understand how the system will behave. the biot number is determined by : the heat transfer coefficient, h, is introduced


a transient heat transfer process in terms of the time temperature transformation ( ttt ). it is possible to manipulate the cooling process to adjust the phase of a suitable material. for example, appropriate quenching of steel can convert a desirable proportion of its content of austenite to martensite, creating a very tough product. to achieve this it is necessary to quench at the “ nose ” of the ttt diagram. since materials differ in their biot numbers, the time it takes for the material to quench, or the fourier number, will vary in practice. in steel, the quenching temperature range is generally from 600°c to 200°c. to control the quenching time and to select suitable quenching media, it is necessary to determine the fourier number from the desired quenching time, the relative temperature drop, and the relevant biot number. usually the correct figures are read from a standard nomogram. by calculating the heat transfer coefficient from this biot number, we can find a liquid medium suitable for the application. zeroth law of thermodynamics one statement of the so - called zeroth law of thermodynamics is directly focused on the idea of conduction of heat. bailyn ( 1994 ) writes that "... the zeroth law may be stated : - all diathermal walls are equivalent. " a diathermal wall is a connection of contiguity between two bodies that allows the passage of heat by conduction between them. this statement of the ' zeroth law ' belongs to an idealized theoretical discourse, and actual physical walls do not match such generality. but with suitable restrictions, the statement has physical import. for example, the material of the wall must not suffer a phase transition, such as evaporation or fusion, at the temperature at which it has to conduct heat. but when only thermal equilibrium is being considered, and time is not urgent, so that the conductivity of the material does not matter too much, one suitable conductor of heat is as good as another. conversely, another aspect of the zeroth law is that, subject again to suitable restrictions, a given diathermal wall is indifferent to the nature of the heat bath to which it is connected. for example the glass bulb of a thermometer will act as a diathermal wall whether exposed to a gas or to a liquid, provided they do not corrode it or melt it. see also - list of thermal conductivities - electrical conduction - convection


bulb of a thermometer will act as a diathermal wall whether exposed to a gas or to a liquid, provided they do not corrode it or melt it. see also - list of thermal conductivities - electrical conduction - convection diffusion equation - r - value ( insulation ) - heat pipe - fick ' s law of diffusion - relativistic heat conduction - thermomass theory - churchill - bernstein equation - fourier number - biot number - false diffusion - sam zhang ; dongliang zhao ( 19 november 2012 ). aeronautical and aerospace materials handbook. crc press. pp. 304 –. isbn 978 - 1 - 4398 - 7329 - 8. retrieved 7 may 2013. - martin eein ( 2002 ). drop - surface interactions.. springer. pp. 174 –. isbn 978 - 3 - 211 - 83692 - 7. retrieved 7 may 2013. - rajiv asthana ; ashok kumar ; narendra b. dahotre ( 9 january 2006 ). materials processing and manufacturing science. butterworth - heinemann. pp. 158 –. isbn 978 - 0 - 08 - 046488 - 6. retrieved 7 may 2013. - george e. totten ( 2002 ). handbook of residual stress and deformation of steel. asm international. pp. 322 –. isbn 978 - 1 - 61503 - 227 - 3. retrieved 7 may 2013. - bailyn, m. ( 1994 ). a survey of thermodynamics, american institute of physics, new york, isbn 0 - 88318 - 797 - 3, page 23. - dehghani, f 2007, chng2801 – conservation and transport processes : course notes, university of sydney, sydney - john h lienhard iv and john h lienhard v, ' a heat transfer textbook ', third edition, phlogyston press, cambridge massachusetts - heat conduction - thermal - fluidspedia - newton ' s law of cooling by jeff bryant based on a program by stephen wolfram, wolfram demonstrations project. - when will my turkey be done? is an example of applied heat conduction equations similar to newton ' s law of cooling which predict the cooking time of turkeys and other roasts.


positivism, a scheme of philosophy founded by auguste comte, which limits speculation and knowledge to observed facts, with their constant antecedents, accom paniments, and consequences. it ignores all laws except those of manifest association ; and excludes causes and effects, supernatural and spiritual agencies, hidden forces and immaterial essences. it reduces the intelligible universe to mere phenomena, refusing to search into the essential constitution of things, or to advance beyond the sphere of strictly scientific analysis and construction. it claims thus to pursue purely inductive science, and regards all beyond as not only uncertain but delusive. the system is thus defined by frederick harrison, one of its eminent advocates : " by the positive method of tnought we mean that which would base life and conduct, as well as knowledge, upon evidence that can be referred to logical canons of proof, which would place all that occupies man in a homogeneous system of law. on the other hand it turns aside from hypotheses that cannot be tested by any logical canon familiar to science ; and from ideal standards which profess to transcend the field of law. we say, life and conduct shall stand for us wholly on a basis of law, and must rest entirely in that legion of science ( not physical, but moral and social science ) where we are free to use our intelligence in methods which the intellect can analyze. " to this may be added the original descrip tion of the system by comte himself : " in sue, in the positive state the human mind, recognizing the imposibility of attaining absolute notions, renounces the investigation of the origin arid destination of the universe, and inquiry into the intrinsic causes of phe nomena, and attaches itself instead solely to the discovery, by judicious combination of reasoning and observation, of their invariable relations of succession and re : emblance. the explication of facts thus reduced to its real terms is, thenceforward, nothing more than the connection established between the diverse phenomena and certain general facts whose number is constantly diminished by the progress of science. " notwithstand ing the apparent originality imparted to the system by its modern dress and forms of thought, acute thinkers detect in it a revival of the old dogma that man is the measure of tile universe. the ancient connection between the macrocosm and microcosm is repeated by limiting the intelligible universe to the image that the human mind can obtain by reasoning on the phenomena that the bodily


the integrated circuit ( ic or chip ) is a minaturized electronic circuit. an integrated circuit is an assembly of interconnected components on a small semiconductor chip, usually made of silicon. one chip can contain millions of microscopic components and perform many functions. these components are fabricated together on a slice of silicon crystal ( known as a wafer ) that contains many ics arranged in rows. manufacture of ics involves a succession of processes, including photolithography, high - temperature diffusion, oxidation, and metallisation. the wafer is then separated into chips, which are individually packaged. the ic was invented independently by two researchers. the integrated circuit was invented in the united states in different forms by jack kilby of texas instruments and robert noyce at fairchild semiconductor. with this new semiconductor technology, computers, communications devices, and all sorts of consumer electronics became possible. the integrated circuit controls the functions of the quartz watch. in all quartz watches, the ic makes the quartz crystal oscillate, divides the quartz frequency down to one pulse per second, and drives the display. many more functions can be added using a microprocessor, making today ' s quartz watches more like dedicated microcomputers. both swiss and japanese watch companies were involved in developing ics suitable for use in watches. the first ic used in a watch was developed in the 1960s in a swiss laboratory, ceh. the chip ' s power consumption had to be drastically reduced in order to allow battery life of at least one year. in the first quartz watch, the beta 21, a single ic containing about 110 components managed all electronic functions of the watch, including quartz crystal excitation, frequency division, and motor drive. in 1970 the seiko 36sqc was introduced and was the first quartz watch to use a cmos chip ( a low energy integrated circuit invented at fairchild in 1963 ). today ' s quartz watches all use cmos technology, with chips containing 100, 000 components and more. they combine microprocessor, memory and analog functions, and act like dedicated microcomputers. quartz crystal ~


scale invariance feb 28, 2013 | 4. 8 / 5 ( 10 ) | 14 indeterminism in classical physics 5 hours ago i was reading the roger penrose book emperor ' s new mind and he was explaining the determinism in newtonian mechanics. he says that if we consider... current in two wires 5 hours ago wire a and b, which have the same cross - sectional area are connected in series. there is a p. d. v across the whole wire. suppose the two wires... understanding the dipole model for rayleigh scattering 7 hours ago hello. i am currently studying scattering theory in detail for my bsc thesis, and i ' m starting with rayleigh scattering. i ' m following scattering... question on coriolis effect with drag force 13 hours ago i really need help with this question. a small floating object initially moves with velocity v on the surface of a liquid at latitude λ. the... question of reflection and transmission of tem wave in normal incidenc 19 hours ago suppose tem wave in + z normal to a boundary on xy plane at z = 0. we know * e * & * h * are tangential to the boundary. let # # \ vec e _ i = \ hat x e # #, be the... the rudyak - krasnolutski effective potencial 20 hours ago hi... anyone now how to calculate or the formula of the rudyak - krasnolutski effective potencial? the effective potencial includes the angular... - more from physics forums - classical physics more news stories children with autism showed significant improvement after six months of simple sensory exercises at home using everyday items such as scents, spoons and sponges, according to uc irvine neurobiologists. autism spectrum disorders may 21, 2013 | 3 / 5 ( 1 ) | 0 | research by victoria university phd education graduand larah van der meer highlights the importance of understanding the communication preferences of children with developmental disabilities such as autism. autism spectrum disorders may 14, 2013 | 3. 3 / 5 ( 3 ) | 1 at times, andy shih still finds himself overwhelmed by the groundswell of interest in autism applications he ' s seen in the three years since apple inc. released the first ipad. autism spectrum disorders may 09, 2013 | 2 / 5 ( 1 ) | 0 children with autism see simple movement twice as quickly as other children their age, and


filmy bags of fluid that crawl, extend finger - like protrusions, and engulf smaller objects – living cells exploit engineering principles that physicists would love to understand. but at 10 to 100 µm in size, they ’ re tough to get a handle on. now a team in france has demonstrated how to deduce the material properties of cell membranes from the thermal wobbling of an attached bead. in the february physical review e, they apply their approach to a vesicle, or membrane sphere, which they enmesh in the same protein filaments that reinforce biological membranes. they hope to apply their method to increasingly cell - like architectures. to understand what makes cells simultaneously stiff and oozy – or viscoelastic – biophysicists have mostly relied on large - scale measurements. on the macroscopic scale, they ’ ve deformed gels made from protein filaments and have flexed naked films of lipids, the soap - like molecules that make up cell membranes. on a smaller scale, they ’ ve pressed and pulled on entire cells. but until now, they have not been able to probe the structure of an intact membrane on a scale that cells themselves would consider small – at least not without severely distorting the membrane. emmanuele helfer and her colleagues at the university of strasbourg presented their wobbling - bead methodology in prl in july and their latest paper elaborates on it. the researchers place a coating of sticky molecules on vesicles of about 20 µm diameter and on beads of 1 µm or larger. using a homemade microscope, they manipulate the beads with a steeply focused laser beam known as optical tweezers and immobilize vesicles by rapidly switching the laser between beads stuck to opposite faces. from the jostling of one bead in the weak grip of the tweezers, they compute a power spectrum, a plot of the size of displacements vs. their frequency on a log scale. the team computes spectra for both in - plane bead motions and for motion perpendicular to the plane of the membrane. the paper interprets the spectra with a theory that fred mackintosh of the university of michigan, ann arbor, developed during a sabbatical in strasbourg. the amplitude of the displacements of unattached beads diminishes with a constant slope of - 2, as expected for brownian motion in a viscous medium ( sugar water ). the slope is less steep for the out - of -


the amplitude of the displacements of unattached beads diminishes with a constant slope of - 2, as expected for brownian motion in a viscous medium ( sugar water ). the slope is less steep for the out - of - plane wobbling of a bead stuck to a naked vesicle – indicating partial elasticity – but appears brownian for within - plane motion – consistent with the membrane ’ s liquid crystal structure. for a bead attached to a protein - sheathed vesicle, the slopes for both types of motion are viscoelastic, and the theory accounts for the values of these slopes straightforwardly, assuming that the protein husk acts like actin filaments in a gel. david weitz of harvard university says the properties of other membrane - filament architectures might turn out differently, though he suspects they will not. he cautions that several properties of the protein - lipid system in these vesicles make them unlike those of real cells. also, says weitz, cells often deform over seconds or hours, so he hopes future measurements will probe lower frequencies. weitz characterizes the strasbourg measurements as “ a first step ” – but he also calls them “ cool stuff. ” “ the simple model seems to do a remarkably good job of explaining the data, ” says tom lubensky of the university of pennsylvania, philadelphia. “ they ’ ve shown the technique can be used more generally. ” oliver baker is a freelance science writer based in davis, ca. - e. helfer et al., phys. rev. lett. 85, 457 ( 2000 ).


- encoding induction in correctness proofs of program transformations as a termination problem ( 2012 ) - the diagram - based method to prove correctness of program transformations consists of computing complete set of ( forking and commuting ) diagrams, acting on sequences of standard reductions and program transformations. in many cases, the only missing step for proving correctness of a program transformation is to show the termination of the rearrangement of the sequences. therefore we encode complete sets of diagrams as term rewriting systems and use an automated tool to show termination, which provides a further step in the automation of the inductive step in correctness proofs. - computing overlappings by unification in the deterministic lambda calculus lr with letrec, case, constructors, seq and variable chains ( 2011 ) - correctness of program transformations in extended lambda calculi with a contextual semantics is usually based on reasoning about the operational semantics which is a rewrite semantics. a successful approach to proving correctness is the combination of a context lemma with the computation of overlaps between program transformations and the reduction rules. the method is similar to the computation of critical pairs for the completion of term rewriting systems. we describe an effective unification algorithm to determine all overlaps of transformations with reduction rules for the lambda calculus lr which comprises a recursive let - expressions, constructor applications, case expressions and a seq construct for strict evaluation. the unification algorithm employs many - sorted terms, the equational theory of left - commutativity modeling multi - sets, context variables of different kinds and a mechanism for compactly representing binding chains in recursive let - expressions. as a result the algorithm computes a finite set of overlappings for the reduction rules of the calculus lr that serve as a starting point to the automatization of the analysis of program transformations. - towards correctness of program transformations through unification and critical pair computation ( 2010 ) - correctness of program transformations in extended lambda - calculi with a contextual semantics is usually based on reasoning about the operational semantics which is a rewrite semantics. a successful approach is the combination of a context lemma with the computation of overlaps between program transformations and the reduction rules, which results in so - called complete sets of diagrams. the method is similar to the computation of critical pairs for the completion of term rewriting systems. we explore cases where the computation of these overlaps can be done in a first order way by variants of critical pair computation that use unification algorithms. as


george polya, the famous stanford math professor, once quipped " i am too good for philosophy and not good enough for physics. mathematics is in between ". amongst the many implications of this quote, polya implies that there is a relationship between philosophy and physics. the intersection of philosophy and physics is an admittedly escoteric subject but a great example of interdisciplinary thought. however, as physics advances and becomes increasingly complex, the challenge is for the philosophers to understand the physics and identify the philosophical questions that must be considered. the discipline that addresses such issues is the philosophy of science. the philosophy of science deals with " what science is, how it works, and the logic through which we build scientific knowledge ". building scientific knowledge requires a theory of epistemology, albeit a somewhat specialized epistemology or theory of knowledge. philosophers were doing a good job of keeping up with the physicists until recently. the guardian newspaper has a great article on the three possible roles for the philosophy of science, as physics and perhaps all science gets increasingly complex. the three possible roles, as defined by peter godfrey - smith, are : - an integrative role, whereby philosophy can assess and connect various fields with an emphasis on generic categories and perspectives ; - an incubator role, where philosophy develops new ideas in a broad and speculative form, which are then pursued in a more focussed and specific way within an individual science ; - an educative role, where philosophy teaches various general skills, including critical and abstract thinking i will leave it to to your own deliberate thinking to decide which role you believe is the right course for the philosophy of science to pursue, although the guardian writer argues for one particular role. now you may be wondering why i wrote this post on a subject for which the term " esoteric " might be an understatement. my three reasons are : - to demonstrate that philosophy is still relevant in the modern world - to show that the complexity of science has many implications, to which i think we are paying insufficient attention - to highlight a great example of interdisciplinary thought - - the philosophy of science


mit team finds that the ratio of component atoms is vital to performance. greeningmit is an occasional series focusing on the broad efforts to improve energy efficiency on campus. employees in a handful of mit buildings might notice what look like slim, fin - tubed radiators in ceiling cavities. these cooling devices are a relatively recent innovation to make its way to the u. s. market. called chilled beams, they use water, not air, to remove heat from a room. if you peek under the cover of a baseboard heater, you ' ll see a pipe studded with many thin fins, looking like a car radiator. chilled beams are based on a similar design, except instead of one long straight pipe, their pipes snake back and forth like the security line at the airport. and instead of heating air with hot water, they cool it with cold water. the potential energy reduction of using chilled beams instead of a traditional air - conditioning system ranges from 20 percent to 50 percent, depending on the type of system, climate and building. the recently completed expansion and renovation to the main group - - the 49, 000 - square - foot infill project of the building 6 courtyard - - is one of the recipients of chilled beams. this energy - efficient air - conditioning system also has been successfully installed in buildings 4, 6 and 8. peter l. cooper, manager of sustainability engineering and utility planning for the department of facilities, notes that chilled beams take one - tenth the volume of fresh air needed for traditional air conditioning - - a along with less ductwork, smaller ducts and smaller fans. when the entire main group expansion and renovation project is completed, energy savings tied to the smaller fans alone is expected to be around $ 400, 000 annually. the new mit sloan school of management expansion and the david h. koch institute for integrative cancer research also will take advantage of some chilled - beam cooling. according to cooper, the beams are useful in offices, laboratories and other spaces where equipment and sunlight generate a significant amount of heat. " one of its advantages over conventional air conditioning is that it can be retrofitted in buildings that can ' t accommodate conventional air - conditioning equipment, " cooper says of the chilled beams technology, which was deployed in buildings 4, 6 and 8 in part because those structures had neither enough ductwork nor enough space for new ductwork. mit will incorporate two types of chilled beams : active and passive. active systems tie into the building ' s air supply ducts, mixing supply air


jason geng, vice president for the ieee its society, reveals a prototype of a true 3d monochrome volumetric display prototype based on projection technology. according to geng, nearly 50 % of the human brain ' s capability is devoted to processing visual information and that " flat images and 2d displays do not harness the brain ' s power effectively ". according to geng, there are four depth cues which the brain uses to process stereoscopic information ; a ) the focus : where the eyes focus on a specific object in a 3d scene, b ) convergence : where the eyes converge so each eye sees the 3d object simultaneously, c ) motion parallax : where speed indicates distance from the eyes ( for example, when you look at the landscape when travelling in a car ) and d ) binocular disparity : the differences between the left and right images. to address each cue, ieee intelligent transportation systems ( its ) society have created a volumetric display – a ‘ true ’ 3d display that uses voxels rather than pixels. each voxel emits light from a physical space so the brain is not being deceived into processing an ' illusion '. it is more akin to looking at a real object, where the focussing and converging muscles can naturally focus on an object at the same time. the reason many people find watching 3d tv and 3d movies in the cinema is because the viewer ' s eyes are being forced to converge and focus on different points ( the focus point will always be the screen but the eyes will be required to converge beyond the screen point for an object in positive space – not a natural experience ). for the scientific amongst you, the dlp / helix volumetric system records 3d object information by projecting light out of source which is reflected by a polarizing beamsplitter cube towards a spatial light modulator ( slm ), whose image patterns are generated by a host personal computer ( pc ). to re - create the 3d image, a helix screen is rotated in sync with the dlp which projects high speed images. when the helix screen intercepts each pixel ( which, due to its shape, will constantly move along the z - axis ), it shows up as a pixel ( voxel ) in space. this process happens so fast that, like the persistence of vision phenomena utilised in regular television, the brain adds the points together over time to see one volumetric 3d image without the need to wear glasses. the unique features of the dlp / helix 3d display design include an inherent parallel


focus on aps topical groups group on few body systems by michael lucibella a notable moment for the aps topical group on few body systems ( gfb ) came at the 1989 aps meeting in baltimore, where the group sponsored a now famous symposium on cold fusion. the subject was all over the media after martin fleischmann and stanley pons controversially claimed to have produced fusion in their lab. at the high profile meeting, eight of the nine speakers refuted the fleischmann - pons claims, roundly rejecting the recent cold fusion assertions. this year marks the 25th anniversary of gfb. the group ’ s main purpose has always been to bring together a broad range of scientists who work on atomic and subatomic systems involving three or more particles. by taking this interdisciplinary approach to research, gfb may be the most scientifically diverse of all topical groups. few body systems can yield some of the most fiendishly complex problems to work with. single and two body systems involve only a small number of variables while much larger systems can be simplified by studying their overall dynamics statistically. that middle range is where the number of variables quickly becomes overwhelming and has often stymied attempts to precisely model atomic and nuclear behavior. but results in this area have led to advances in fusion research and an overall better picture of the universe. few body interactions between hydrogen and helium atoms play an important role throughout the observable cosmos. bringing together a wide variety of scientific disciplines to the group has allowed the sharing of techniques that work across many fields. though the forces acting between different particles may differ, the tools and methods for calculating their properties are often the same. this allows disciplines ranging from atomic physics to physical chemistry to come together and share their knowledge. the group can trace its origins back to several older organizations. starting in 1965, the international few body conferences, typically occurring every two years, served as the major gathering for physicists working on various few body problems and research. nuclear physicists made up the audience of the first two meetings, before other fields began to filter in by 1974. a few years later in 1977 theoretical chemist don kouri and nuclear theorist yeong kim submitted a proposal to the gordon research foundation to create a parallel series of interdisciplinary conferences on few body physics. these conferences laid the groundwork for the later gfb by enthusiastically reaching out to different fields. one of the core principles of these gordon conferences was to keep the presentations on a reasonably technical level so that the chemists could fully understand the physicists ’


concretearticle free pass concrete, in philosophy, such entities as persons, physical objects, and events ( or the terms or names that denote such things ), as contrasted with such abstractions as numbers, classes, states, qualities, and relations. many philosophers, however, add a third category of collective names, or concrete universals, i. e., names of classes or collections of concrete things, distinct from the abstract. the distinction between abstract and concrete, though clear enough in general, is not a very sharp one, and borderline cases may be found. the series of terms “ theory, true proposition, fact, and event ” is an example, as, in theoretical physics, is the series “ conductivity, speed, heat, magnetic field, light, electric charge, electron, molecule, quartz crystal. ” in each case, the series begins with an abstract term ; and it is fairly well agreed that the terms grow successively more concrete. if an absolute separation into abstract and concrete is demanded, however, it is difficult to decide where to draw the line. in existential philosophy, the concreteness of human existence in the world is strongly stressed ; thus, the specific events of an individual ’ s lived - through experience are characterized as concrete in contrast to the lifeless formalisms of logical analysis and the tenuous webs of metaphysical speculation. understood in this sense, a “ turn to the concrete ” emerged as perhaps the most fundamental feature of mid - 20th - century continental european philosophy, as also of the existentialist strands in american philosophy. what made you want to look up " concrete "? please share what surprised you most...


germanium is a hard, brittle metalloid that was first used about a half century ago as a semiconductor material in radar units and as the material for the first transistors. today, it is used as a polymerization catalyst for polyethylene terephthalate ( pet ), a commercially important plastic ; as a component of glass in telecommunications fiber optics ; as a lens or window in infrared night - vision devices ; and as a semiconductor and substrate in electronic circuitry and solar cells. because of its small band gap, it reponds efficiently to infrared light and is used in infrared spectroscopes for thermal imaging devices. germanium oxide has an index of refraction that makes it useful in wide - angle lenses. ibm uses germanium for the avalanche photodetectors in their zenterprise 196 microprocessor systems. domestic production and use : the major end uses for germanium, worldwide, were estimated to be fiber - optic systems, 30 % ; infrared optics, 25 % ; polymerization catalysts, 25 % ; electronics and solar electric applications, 15 % ; and other ( phosphors, metallurgy, and chemotherapy ), 5 %. domestically, these end uses varied and were estimated to be infrared optics, 50 % ; fiber - optic systems, 30 % ; electronics and solar electric applications, 15 % ; and other ( phosphors, metallurgy, and chemotherapy ), 5 %. germanium is not used in polymerization catalysts in the united states. the estimated value of germanium metal consumed in 2009, based upon the annual average u. s. producer price, was about $ 52. 7 million. recycling : worldwide, about 30 % of the total germanium consumed is produced from recycled materials. during the manufacture of most optical devices, more than 60 % of the germanium metal used is routinely recycled as new scrap. germanium scrap was also recovered from the window blanks in decommissioned tanks and other military vehicles. events, trends, and issues : the global market for germanium metal and germanium dioxide generally weakened through the first 10 months of the year. the estimated market price of germanium metal ( 99. 99 % ) in late september was $ 950 per kilogram, a 33 % decline from that of january, when it was about $ 1, 425 per kilogram. germanium dioxide prices also declined during the year and as of late september, germanium dioxide was selling for about $ 580 per kilogram. slumping demand for germanium


by lynn yarris on december 29, 1959, the late caltech physicist richard feynman presented a lecture at the annual meeting of the american physical society entitled, " there ' s plenty of room at the bottom. " in this talk, the nobel laureate speculated as to what technologies might be achieved if scientists could fabricate devices on the scale of atoms and molecules. he offered up such notions as writing the encyclopedia britannica on the head of a pin using electron beam etching ; building circuits with wires that are only a few atoms in diameter ; and rearranging the atoms on the surface of a material in order to change its properties. it has been reported that some of feynman ' s audience laughed - they thought he was joking. in 1991, the office of technology assessment reported to congress that the wave of miniaturization which swept over the electronics industry starting in the 1960s is on the verge of being supplanted by a second wave as we move into the 21st century. the first wave ushered in the age of microtechnology, which revolutionized the electronics industry and carved out computer markets worth well more than $ 100 billion annually. this second wave, the ota report advised, will usher in devices with features a thousand times smaller than the microcircuits of today, and will most likely create entirely new technologies and open commercial arenas beyond computers that are potentially even more vast. what the ota report was talking about and what feynman so presciently predicted is the age of " nanotechnology, " and it is rapidly coming upon us. the word " nanotechnology " comes from nanometer, which means one billionth of a meter ( about 25 millionths of an inch or 10 angstroms ). given that atoms range between one - tenth and one - half a nanometer in diameter, nanotechnology answers feynman ' s call to work on an atomic - scale. most of the nanostructures now envisioned would have dimensions of about 1 to 100 nanometers, making them roughly equivalent in size to a protein molecule. nanotechnology advocates extol possibilities for engineering constructs so small they sound ripped from the pages of science - fiction novels. for example, the most outspoken of these apostles, scientific maverick and author eric drexler, has foretold of supercomputers that fit in the palm of the hand, molecular machines that fight disease and repair damage from inside the human body, and solar - powered nanofactories


, scientific maverick and author eric drexler, has foretold of supercomputers that fit in the palm of the hand, molecular machines that fight disease and repair damage from inside the human body, and solar - powered nanofactories that patrol the atmosphere, scouring the air of pollutants. though it reads like fiction, the scientific credibility is real enough for the u. s and japanese governments to have begun a major push on nanotechnology research and development. private industry is also weighing in with millions of investment dollars. proponents agree that the ultimate success of nanotechnology will hinge upon the ability of researchers to characterize and control the atomic structure of surfaces and interfaces. a solid material ' s chemical, electronic, and mechanical properties are largely determined by the atoms on its surface, or at the interface where two different solid surfaces meet. this is because the interior atoms of a solid are chemically bonded to neighboring atoms in all directions to form a bulk crystal. on the surface, however, neighboring atoms are missing in at least one direction, which leaves surface atoms more free to react or move around. as the size of a material object shrinks to nanometer levels, the proportion of its atoms that are on the surface or at the interfaces also becomes much greater. there is talk now of future devices so small they become two or even one - dimensional objects - essentially nothing but surfaces and interfaces. two of the most powerful techniques known to researchers for studying solid surfaces are photoelectron spectroscopy and photoelectron diffraction - collectively known as pes / ped. one of the country ' s foremost practitioners of pes / ped is charles fadley, an advanced light source professor of physics with a joint appointment at uc davis and berkeley lab ' s materials sciences division ( msd ). for the past 25 years, fadley has been making pes / ped measurements in laboratories and at major facilities all around the globe. drawing from this deep well of experience, fadley has overseen the installation of what is thought to be the most extensive surface science experimental station ever to be linked to the beamline of a synchrotron - radiation particle accelerator. electrically charged subatomic particles accelerated to speeds near that of light and then forced along a curved path give off light known as synchrotron radiation. fadley ' s new pes / ped experimental station is located at berkeley lab ' s advanced light source ( als ), an electron storage ring equipped with special magnetic devices that enable it


path give off light known as synchrotron radiation. fadley ' s new pes / ped experimental station is located at berkeley lab ' s advanced light source ( als ), an electron storage ring equipped with special magnetic devices that enable it to generate beams of x - ray and ultraviolet light at wavelengths and energies ideal for surface science studies. in talking with fadley, he will tell you that surfaces are both " wonderful and terrible " to study. the potential for bonding with other atoms that makes surfaces the key to chemical activity also creates great difficulty for researchers who would study them. in order to avoid problem - causing contamination from atoms in the surrounding environment, surfaces must be prepared with great care, usually under the difficult working conditions of ultrahigh vacuum. " after the preparation, " fadley says, " special techniques also have to be used to avoid looking at the atoms in the bulk crystal. most techniques that use photons to probe solid materials are bulk probes rather than surface probes, or have to be used in special geometries to enhance their surface sensitivity. the beauty of photoelectron spectroscopy and diffraction is that the only effects measured are those that come from within the first 5 to 10 layers of atoms in a material ( the chemically active layers ). " though the execution is tricky, the principle behind fadley ' s research technique is relatively simple. it is based on the " photoelectric effect " which was first explained by einstein at the turn of the century. it starts with a beam of photons striking the surface of a sample to be studied. electrons in the first few layers of the sample ' s atoms absorb the incoming energy and are ejected from the sample as photoelectrons. in pes these photoelectrons are emitted at energies that can be measured to identify each type of emitting atom, and to determine how many there are and what their chemical or magnetic state is. but the principles of quantum theory also dictate that photoelectrons emitted from the inner shells of an atom must also be treated as outgoing spherical waves that can be scattered by nearby atoms. in ped, these scattered waves in turn produce diffraction patterns that can be analyzed to locate the positions of the atoms. fadley ' s experimental station has been constructed to capitalize on the high quality of light delivered by the als. in addition to its unique pes / ped system, the station also features state - of - the - art sample preparation and characterization equipment. to design and


nowadays, electron microscopes are an essential tool, especially in the field of materials science. at tu vienna, electron beams are being created that possess an inner rotation, similarly to a tornado. these " vortex beams " cannot only be used to display objects, but to investigate material - specific properties - with precision on a nanometer scale. a new breakthrough in research now allows scientists to produce much more intense vortex beams than ever before. quantum tornado : the electron as a wave in a tornado, the individual air particles do not necessarily rotate on their own axis, but the air suction overall creates a powerful rotation. the rotating electron beams that have been generated at tu vienna behave in a very similar manner. in order to understand them, we should not think of electrons simply as minuscule points or pellets, as in that case they could at most rotate on their own axis. vortex beams, on the other hand, can only be explained in terms of quantum physics : the electrons behave like a wave, and this quantum wave can rotate like a tornado or a water current behind a ship ' s propeller. " after the vortex beam gains angular momentum, it can also transfer this angular momentum to the object that it encounters ", explained prof. peter schattschneider from the institute of solid state physics at tu vienna. the angular momentum of the electrons in a solid object is closely linked to its magnetic properties. for materials science it is therefore a huge advantage to be able to make statements regarding angular momentum conditions based on these new electron beams. beams rotate - with masks and screens peter schattschneider and michael stoger - pollach ( ustem, tu vienna ) have been working together with a research group from antwerp on creating the most intense, clean and controllable vortex beams possible in a transmission electron microscope. the first successes were achieved two years ago : at the time, the electron beam was shot through a minuscule grid mask, whereby it split into three partial beams : one turning right, one turning left and one beam that did not rotate. now, a new, much more powerful method has been developed : researchers use a screen, half of which is covered by a layer of silicon nitride. this layer is so thin that the electrons can penetrate it with hardly any absorption, however they can be suitably phase - shifted. " after focusing using a specially adapted astigmatic lens, an individual vortex beam is obtained ", explained michael stoger - pollach. this beam is more intense by one


any absorption, however they can be suitably phase - shifted. " after focusing using a specially adapted astigmatic lens, an individual vortex beam is obtained ", explained michael stoger - pollach. this beam is more intense by one order of magnitude than the vortex beams that we have been able to create to date. " firstly, we do not split the beam into three parts, as is the case with a grid mask, but rather, the entire electron stream is set into rotation. secondly, the grid mask had the disadvantage of blocking half of the electrons - the new special screen does not do this ", said stoger - pollach. thanks to the new technology, right and left - rotating beams can now be distinguished in a reliable manner - previously this was only possible with difficulty. if we now add a predetermined angular momentum to each right and left - rotating beam, the rotation of one beam is increased, while the rotation of the other beam decreases. electron microscopes with a twist this new technology was briefly presented by the research team in the " physical review letters " journal. in future, the aim is to apply the method in materials science. magnetic properties are often the focus of attention, particularly in the case of newly developed designer materials. " a transmission electron microscope with vortex beams would allow us to investigate these properties with nanometric precision ", explained peter schattschneider. more exotic applications of vortex beams are also conceivable : in principle, it is possible to set all kinds of objects in rotation - even individual molecules - using these beams, which possess angular momentum. vortex beams could therefore also open new doors in nanotechnology.


twenty numbers in the range from 1 to 100 are happy, and they may be presented in a tree diagram showing the chain of numberswhich takes them to 1. know the time it takes only a few seconds ' reflection to appreciate that once every hour the minute hand and the hour hand must point in precisely opposite directions. but how often in a day will each hand be pointing exactly at a minute division at the same time as the hands are precisely opposite each other? when the surface of a lake or pond is undisturbed, it behaves like a plane horizontal mirror. the laws of reflection of light ( angle of incidence equals angle of reflection ) operate and only the light ( from a point source on the opposite bank ) reflected from a particular point of the surface can enter our eyes. this ensure that we see a clear image of the light source. however, when the surface becomes wavy due to the action of the wind, there are multiple points on it that are so inclined relative to us that they canall reflect the light into our eyes, and we see multiple images. as the waves move, these points also change and the images keep shifting. tractors and buffaloes a heavy crawler tractor is able to operate on soft, muddy ground but the farmer ' s as well as his buffaloes ' feet sink. why? the answer lies in the difference between weight and pressure. although the tractor is much heavier than the farmer or his buffaloes, its weight is distributed over a much larger area of its bottom surface. consequently, the load carried by each square centimetre of its bottom surface ( the " pressure " ) is fairly low. on the other hand, the weight of the farmer or his buffaloes is concentrated over the much smaller area of his feet or the hooves, producing a much higher " pressure ". an object penetrates deeper not because it is heavier but because it exerts a higher pressure ( force per unit area ) on its support. singing kettle boiling water in a kettle is a daily chore for most of us. we are all familiar with the hissing sound ( called the " singing " of the kettle ) that starts a few after the kettle is put on the fire. this sound gradually increases and then suddenly drops when the water starts to boil. in fact, we know from the sudden drops of the sound that the water is ready, boiling. have you ever wondered what causes the kettle to " sing "? it is the bottom layer of the kettle gets heated first. as the temperature rises, steam bubbles (


##ferometer space antenna. lisa is a nasa mission planned for launch in 2025. gravitational waves are envisioned as " ripples in space - time " - - analogous to waves produced on a water surface when disturbed by a passing boat - except the material vibrated by gravitational waves is not water, rather it is the postulated fabric of space - time. the movement of very massive objects creates these space - time waves. lisa should be able to detect mergers of binary supermassive black holes in distant galaxies and binary stellar - sized black holes in our own galaxy. both lisa and ligo are designed detect the space - time disturbances, but in different wavelength ranges. lisa will be sensitive to wavelengths from 10 billion to 3 million kilometers - very long waves indeed. ligo ' s wavelength range is much shorter, from 300, 000 to 300 kilometers. the lisa experiment will consist of three satellites in an equilateral triangle, with sides 5 million kilometers in length. the triad of satellites will orbit at the same distance from the sun as earth, but advanced along earth ' s orbit by 50 million kilometers. the passage of very long gravitational waves causes extremely small variations in the distances between the satellite pairs. since the satellite distances will change due to other forces in the solar system - - planetary gravitational forces and the solar wind - - accurate knowledge of these forces is necessary. a pathfinder mission to demonstrate aspects of lisa ' s design is slated for 2013.


d glossary ( non - normative ) several of the following definitions of terms have been borrowed or modified from similar definitions in documents originating from w3c or standards organizations. see the individual definitions for more - a child of a presentation layout schema. that is, " a is an argument of b " means " a is a child of b and b is a presentation layout schema ". thus, token elements have no arguments, even if they have children ( which can only be - a parameter used to specify some property of an sgml or xml element type. it is defined in terms of an attribute name, attribute type, and a default value. a value may be specified for it on a start - tag for that - the axis is an imaginary alignment line upon which a fraction line is centered. often, operators as well as characters that can stretch, such as parentheses, brackets, braces, summation signs etc., are centered on the axis, and are symmetric with respect to it. - the baseline is an imaginary alignment line upon which a glyph without a descender rests. the baseline is an intrinsic property of the glyph ( namely a horizontal line ). often baselines are aligned ( joined ) - black box - the bounding box of the actual size taken up by the viewable portion ( ink ) of a glyph or expression. - bounding box - the rectangular box of smallest size, taking into account the constraints on boxes allowed in a particular context, which contains some specific part of a rendered display. - a rectangular plane area considered to contain a character or further sub - boxes, used in discussions of rendering for display. it is usually considered to have a baseline, height, depth and width. - cascading style sheets ( css ) - a language that allows authors and readers to attach style ( e. g. fonts, colors and spacing ) to html and xml documents. - a member of a set of identifiers used for the organization, control or representation of text. iso / iec standard 10646 - 1 : 1993 uses the word " data " here instead of " text ". - character data ( cdata ) - a data type in sgml and xml for raw data that does not include markup or entity references. attributes of type cdata may contain entity references. these are expanded by an xml processor before the attribute value is processed as cdata. - character or expression depth - distance between the baseline and bottom edge of the character glyph


- a mathematical object that is applied to arguments using the - operator, an - used to represent ordinary operators, fences, separators in mathml presentation. ( the token element mo is defined in section 3. 2. 5 operator, fence, separator or accent - a general representation language for communicating mathematical objects between application programs. - parsed character data ( pcdata ) - an sgml / xml data type for raw data occurring in a context where text is parsed and markup ( for instance entity references and element start / end tags ) is recognized. - point is often abbreviated " pt ". the value of 1 pt is approximately 1 / 72 inch. points are typically used to specify absolute sizes for font - related objects. - presentation elements - mathml tags and entities intended to express the syntactic structure of mathematical notation ( defined in chapter 3 presentation markup ). - presentation layout schema - a presentation element that can have other mathml elements as - presentation token element - a presentation element that can contain only parsed character data - a mathml content element that is used to specify the value of a specific named parameter in the application of selected pre - defined - a mathml content element used to construct expressions such as a < b. - faithfully translate into application - specific form allowing native application operations to be performed. - schema ( plural : schemata or schemata ). see " presentation layout - scope of a declaration - the portion of a mathml document in which a particular definition is active. - selected sub - expression - the argument of an maction element ( a layout schema defined in section 3. 7 enlivening expressions ) that is ( at any given time ) " selected " within the viewing state of a mathml renderer, or by the selection attribute when the element exists only in mathml data. defined precisely in the aforementioned - space - like ( mathml expression ) - a mathml expression that is ignored by the suggested rendering rules for mathml presentation elements when they determine operator forms and effective operator rendering attributes based on operator positions in mrow elements. defined precisely in section 3. 2. 7 space - standard generalized markup language ( sgml ) - an iso standard ( iso 8879 : 1986 ) that provides a formal mechanism for the definition of document structure via dtds ( document type definitions ), and a notation for the markup of document instances conforming to a dtd. - sub - expression ( of a mathml expression - a


, to support her continuing research into design rationale, which explores not only the results of design processes but also the reasoning behind design choices. while ai in design may sound esoteric to the uninitiated, brown sees it as a utilitarian tool, grounded in logical reasoning. creativity, after all, " exists as a judgment relative to personal or group norms, " he says. " ai in design looks to take the subjective and make it objective and, therefore, computable. creativity can be modeled in computer code because it includes processes involving knowledge and reasoning. " brown ' s recent writings explore computational creative design. his articles began touching on the subject in the late 1970s, when he explored a natural language graphics project. more recently, brown reported on how the ai in design community is developing definitions of creativity with an eye toward designing and judging products. for example, susan besemer, founder of ideafusion, has shown that people judge the creativity of commercial products by their novelty, resolution ( usefulness and user - friendliness ), and style. brown thinks that computers should also be able to do that. additional characteristics refine those main categories. for example, novelty refers to the use of new processes, new techniques, and new concepts in the product. it also includes the newness of the product within and outside of its field. resolution, the degree to which the product addresses a specific need, " underscores the fact that, for products at least, new but bizarre objects aren ' t seen as creative. " salvador dali ' s surrealist lobster telephone, for instance, is widely accepted as creative in the art realm. but if viewed as a product, the lobster phone would flunk the creativity exam due to its limited utility. as such definitions emerge, brown sees ai in design stimulating creativity by assisting human experts while they toil at complex projects. computational models that grasp the basic processes involved in, say, creating buildings, could provide advice and cautions about potential pitfalls in emerging designs. next - generation computational design systems could also stimulate creativity by alleviating tedium. far more ambitious than brown ' s phd thesis for designing part of a sensor, he suggests that a brave new ai program might look more like an architectural grammar to help create buildings. such a tool would be similar to a language grammar for word processing applications. but instead of piping up when sentences ramble, this lexicon of windows, doorways, materials, and other architectural elements could open imaginations to new ideas for floor plans


of individual device, and this monitoring is used in voting logic. the voting logic is linked to switching that automatically reconfigures components. error detection and correction and the global positioning system ( gps ) are two examples of [ active redundancy ]. electrical power distribution provides an example of active redundancy. several power lines connect each generation facility with customers. each power line includes monitors that detect overload. each power line also includes circuit breakers. the combination of power lines provides excess capacity. circuit breakers disconnect a power line when monitors detect an overload. power is redistributed across the remaining lines. voting logic voting logic uses performance monitoring to determine how to reconfigure individual components so that operation continues without violating specification limitations of the overall system. voting logic often involves computers, but systems composed of items other than computers may be reconfigured using voting logic. circuit breakers are an example of a form of non - computer voting logic. electrical power systems use power scheduling to reconfigure active redundancy. computing systems adjust the production output of each generating facility when other generating facilities are suddenly lost. this prevents blackout conditions during major events such as an earthquake. the simplest voting logic in computing systems involves two components : primary and alternate. they both run similar software, but the output from the alternate remains inactive during normal operation. the primary monitors itself and periodically sends an activity message to the alternate as long as everything is ok. all outputs from the primary stop, including the activity message, when the primary detects a fault. the alternate activates its output and takes over from the primary after a brief delay when the activity message ceases. errors in voting logic can cause both to have all outputs active at the same time, can cause both to have all outputs inactive at the same time, or outputs can flutter on and off. a more reliable form of voting logic involves an odd number of 3 devices or more. all perform identical functions and the outputs are compared by the voting logic. the voting logic establishes a majority when there is a disagreement, and the majority will act to deactivate the output from other device ( s ) that disagree. a single fault will not interrupt normal operation. this technique is used with avionics systems, such as those responsible for operation of the space shuttle. calculating the probability of system failure each duplicate component added to the system decreases the probability of system failure according to the formula : - - - number of components - - probability of component i failing - -


cancer stem cell war was lobbed on the basis of “ fuzzy math ” in 2007 by scott kern, m. d., of johns hopkins medical school, and darryl shibata, at the norris comprehensive cancer center at the university of southern california keck school of medicine. they re - evaluated data from published studies and related claims within awarded u. s. patents. the investigators suggested that the mathematical support for the concept of therapeutically useful stem cells was, at that time, “ weak and may even invalidate the foundations of these publications and patent claims. ” mathematical arguments should be used more consistently, they said, “ because they can serve as a guide for interpreting studies into cancer stem cells of solid tumors. ” the authors concluded that they personally suspected “ tumorigenic behavior might be a varying probabilistic potential for all tumor cells rather than a quantal and deterministic feature of a minority of tumor cells. a definition of ‘ solid tumor stem cells ’ may evade us for some time. ” as long as the definition of a stem cell remains vague, neither proof nor disproof are allowed in the discussion, dr. kern told gen. for example, he said, “ we understand the concept of stem cells in cancer, and it makes a lot of sense, particularly in leukemias, it ’ s clear that there is a cell population that ’ s going to maintain the cancer. “ but what has happened over the last five years is that people have tried to extend this into solid cancers. and at this point, we draw the line ; the evidence is weak once you move to solid tumors. ” the august 19 paper, combining solid experimental evidence and some very unfuzzy math, supports the concept that while it is attractive to think of one cell type in a tumor as the major culprit in tumor survival, the emerging picture of tumor growth, survival, and metastasis is much more complicated. dr. kern noted that what was really being measured is a concept that cell biologists have been aware of for some time : the inherent plasticity of cell populations. ultimately, though, discussions about cell type plasticity in tumors boils down to how best to get rid of all the cells in a tumor and finding therapeutics that can either kill them permanently or prolong the time to tumor progession. while cscs may be moving targets, focusing on them with specific therapies such as anti - csc antibodies or small molecules combined with conventional chemotherapies that kill other cancer cells may


into the other person ' s mind, so to speak, and that exercise is at the heart of learning in general. for, by practicing repeatedly how to create links between my mind and another ' s, i am reaching the very core of the art of learning from the ambient culture. without that skill, i can only learn from direct experience ; with that skill, i can learn from the experience of the whole world. thus, whenever i struggle to explain something to someone else, and succeed in doing so, i am advancing my ability to learn from others, too. learning through explanation this aspect of learning through explanation has been overlooked by most commentators. and that is a shame, because both aspects of learning are what makes the age mixing that takes place in the world at large such a valuable educational tool. younger kids are always seeking answers from older kids - - sometimes just slightly older kids ( the seven - year old tapping the presumed life wisdom of the so - much - more - experienced nine year old ), often much older kids. the older kids love it, and their abilities are exercised mightily in these interactions. they have to figure out what it is that they understand about the question being raised, and they have to figure out how to make their understanding comprehensible to the younger kids. the same process occurs over and over again in the world at large ; this is why it is so important to keep communities multi - aged, and why it is so destructive to learning, and to the development of culture in general, to segregate certain ages ( children, old people ) from others. what went on in the one - room schoolhouse is much like what i have been talking about. in fact, i am not sure that the adult teacher in the one - room schoolhouse was always viewed as the best authority on any given subject! long ago, i had an experience that illustrates that point perfectly. when our oldest son was eight years old, he hung around ( and virtually worshiped ) a very brilliant 13 - year - old named ernie, who loved science. our son was curious about everything in the world. one day he asked me to explain some physical phenomenon that lay within the realm of what we have come to call " physics " ; being a former professor of physics, i was considered a reasonable person to ask. so, i gave him an answer - - the " right " answer, the one he would have found in books. he was greatly annoyed. " that ' s not right! " he shouted, and when i expressed


a trillion components. today we could not do such a thing ( even were we equipped with the necessary knowledge ) if we had to build each component separately. however, if we had a million construction machines that could each build a thousand parts per second, our task would take only minutes. in the decades to come, new fabrication machines will make this possible. most present - day manufacturing is based on shaping bulk materials. in contrast, the field called ' nanotechnology ' aims to build materials and machinery by placing each atom and molecule precisely where we want it. by such methods, we could make truly identical parts - - and thus escape from the randomness that hinders conventionally made machines. today, for example, when we try to etch very small circuits, the sizes of the wires vary so much that we cannot predict their electrical properties. however, if we can locate each atom exactly, then those wires will be indistinguishable. this would lead to new kinds of materials that current techniques could never make ; we could endow them with enormous strength, or novel quantum properties. these products in turn will lead to computers as small as synapses, having unparalleled speed and efficiency. once we can use these techniques to construct a general - purpose assembly machine that operates on atomic scales, further progress should be swift. if it took one week for such a machine to make a copy of itself, then we could have a billion copies in less than a year. these devices would transform our world. for example, we could program them to fabricate efficient solar energy collecting devices and apply these to nearby surfaces, so that they could power themselves. in this way, we could grow fields of micro - factories in much the same way that we now grow trees. in such a future, we will have little trouble attaining wealth, but rather in learning how to control it. in particular, we must always take care when dealing with things ( such as ourselves ) that might be able to reproduce themselves. if we want to consider augmenting our brains, we might first ask how much a person knows today. thomas k. landauer of bell communications research reviewed many experiments in which people were asked to read text, look at pictures, and listen to words, sentences, short passages of music, and nonsense syllables. they were later tested in various ways to see how much they remembered. in none of these situations were people able to learn, and later remember, more than about 2 bits per second, for any extended period. if


of music, and nonsense syllables. they were later tested in various ways to see how much they remembered. in none of these situations were people able to learn, and later remember, more than about 2 bits per second, for any extended period. if you could maintain that rate for twelve hours every day for 100 years, the total would be about three billion bits - - less than what we can store today on a regular 5 - inch compact disk. in a decade or so, that amount should fit on a single computer chip. although these experiments do not much resemble what we do in real life, we do not have any hard evidence that people can learn more quickly. despite those popular legends about people with ' photographic memories, ' no one seems to have mastered, word for word, the contents of as few as one hundred books - - or of a single major encyclopedia. the complete works of shakespeare come to about 130 million bits. landauer ' s limit implies that a person would need at least four years to memorize them. we have no well - founded estimates of how much information we require to perform skills such as painting or skiing, but i don ' t see any reason why these activities shouldn ' t be similarly limited. the brain is believed to contain the order of a hundred trillion synapses - - which should leave plenty of room for those few billion bits of reproducible memories. someday though it should be feasible to build that much storage space into a package as small as a pea, using nanotechnology. once we know what we need to do, our nanotechnologies should enable us to construct replacement bodies and brains that won ' t be constrained to work at the crawling pace of " real time. " the events in our computer chips already happen millions of times faster than those in brain cells. hence, we could design our " mind - children " to think a million times faster than we do. to such a being, half a minute might seem as long as one of our years, and each hour as long as an entire human lifetime. but could such beings really exist? many thinkers firmly maintain that machines will never have thoughts like ours, because no matter how we build them, they ' ll always lack some vital ingredient. they call this essence by various names - - like sentience, consciousness, spirit, or soul. philosophers write entire books to prove that, because of this deficiency, machines can never feel or understand the sorts of things that people do. however, every proof in each of those books is flawed by


like sentience, consciousness, spirit, or soul. philosophers write entire books to prove that, because of this deficiency, machines can never feel or understand the sorts of things that people do. however, every proof in each of those books is flawed by assuming, in one way or another, the thing that it purports to prove - - the existence of some magical spark that has no detectable properties. i have no patience with such arguments. we should not be searching for any single missing part. human thought has many ingredients, and every machine that we have ever built is missing dozens or hundreds of them! compare what computers do today with what we call " thinking. " clearly, human thinking is far more flexible, resourceful, and adaptable. when anything goes even slightly wrong within a present - day computer program, the machine will either come to a halt or produce some wrong or worthless results. when a person thinks, things constantly going wrong as well - - yet this rarely thwarts us. instead, we simply try something else. we look at our problem a different way, and switch to another strategy. the human mind works in diverse ways. what empowers us to do this? on my desk lies a textbook about the brain. its index has about 6000 lines that refer to hundreds of specialized structures. if you happen to injure some of these, you could lose your ability to remember the names of animals. another injury might leave you unable to make any long range plans. yet another kind of impairment could render you prone to suddenly utter dirty words, because of damage to the machinery that normally censors that sort of expression. we know from thousands of similar facts that the brain contains diverse machinery. thus, your knowledge is represented in various forms that are stored in different regions of the brain, to be used by different processes. what are those representations like? in the brain, we do not yet know. however, in the field of artificial intelligence, researchers have found several useful ways to represent knowledge, each better suited to some purposes than to others. the most popular ones use collections of " if - then " rules. other systems use structures called ' frames ' - - which resemble forms that are filled out. yet other programs use web - like networks, or schemes that resemble tree - like scripts. some systems store knowledge in language - like sentences, or in expressions of mathematical logic. a programmer starts any new job by trying to decide which representation will best accomplish the task at hand. typically then, a computer program


that resemble tree - like scripts. some systems store knowledge in language - like sentences, or in expressions of mathematical logic. a programmer starts any new job by trying to decide which representation will best accomplish the task at hand. typically then, a computer program uses only a single representation and if this should fail, the system breaks down. this shortcoming justifies the common complaint that computers don ' t really " understand " what they ' re doing. but what does it mean to understand? many philosophers have declared that understanding ( or meaning, or consciousness ) must be a basic, elemental ability that only a living mind can possess. to me, this claim appears to be a symptom of " physics envy " - - that is, they are jealous of how well physical science has explained so much in terms of so few principles. physicists have done very well by rejecting all explanations that seem too complicated, and searching, instead, for simple ones. however, this method does not work when we ' re dealing with the full complexity of the brain. here is an abridgment of what i said about understanding in my book, the society of mind. " if you understand something in only one way, then you don ' t really understand it at all. this is because, if something goes wrong, you get stuck with a thought that just sits in your mind with nowhere to go. the secret of what anything means to us depends on how we ' ve connected it to all the other things we know. this is why, when someone learns ' by rote, ' we say that they don ' t really understand. however, if you have several different representations then, when one approach fails you can try another. of course, making too many indiscriminate connections will turn a mind to mush. but well - connected representations let you turn ideas around in your mind, to envision things from many perspectives until you find one that works for you. and that ' s what we mean by thinking! " i think that this flexibility explains why thinking is easy for us and hard for computers, at the moment. inthe society of mind, i suggest that the brain rarely uses only a single representation. instead, it always runs several scenarios in parallel so that multiple viewpoints are always available. furthermore, each system is supervised by other, higher - level ones that keep track of their performance, and reformulate problems when necessary. since each part and process in the brain may have deficiencies, we should expect to find other parts that try


computing in the social sciences could migration models as simple as these ever be made to give reliable and accurate predictions? this is a question not just about the models but also about the system being modeled. similar techniques work quite well in the physical sciences and in some areas of biology — such as the case of the ant - graveyard problem. but we tend to see human habits as more complex and more contingent than any behavior of atoms or ants, and therefore beyond the scope of algorithmic or mathematical rules. after all, ants have been following the same basic impulses for millions of years, and furthermore they don ' t read american scientist articles about ant behavior. our own actions, in contrast, are influenced by familial, social, economic, historical, technological and cultural forces — not to mention sheer orneriness and whim. whatever brings people to small towns today, it seems unlikely to be the same factor that acted on their parents or grandparents. and yet the very survival of all those out - of - the - way communities from one generation to the next argues that human actions are not quite as fluid and contingent as they seem. there must be some regularity or consistency in our choices, even if we are not fully aware of it. a conservation law seems to be at work, or at least a stabilizing feedback principle. computational models may offer our best hope of discovering the structure of such laws. © brian hayes


excessive urination ( polyuria ). diarrhea : a common condition that involves unusually frequent and liquid bowel movements. the opposite of constipation. there are many infectious and noninfectious causes of diarrhea. persistent diarrhea is both uncomfortable and dangerous to the health because it can indicate an underlying infection and may mean that the body is not able to absorb some nutrients due to a problem in the bowels. treatment includes drinking plenty of fluids to prevent dehydration and taking over - the - counter remedies. people with diarrhea that persists for more than a couple days, particularly small children or elderly people, should seek medical attention. dizziness : painless head discomfort with many possible causes including disturbances of vision, the brain, balance ( vestibular ) system of the inner ear, and gastrointestinal system. dizziness is a medically indistinct term which laypersons use to describe a variety of conditions ranging from lightheadedness, unsteadiness to vertigo. drain : a device for removing fluid from a cavity or wound. a drain is typically a tube or wick. as a verb, to allow fluid to be released from a confined area. enzymes : proteins that act as a catalysts in mediating and speeding a specific chemical reaction. erythromycin : erythromycin is a common antibiotic for treating bacterial infection. sold under many brand names, including ees, erycin and erythromia. fats : plural of the word " fat ". see the definition of fat. fda : food and drug administration. fever : although a fever technically is any body temperature above the normal of 98. 6 degrees f. ( 37 degrees c. ), in practice a person is usually not considered to have a significant fever until the temperature is above 100. 4 degrees f ( 38 degrees c. ). flu : short for influenza. the flu is caused by viruses that infect the respiratory tract which are divided into three types, designated a, b, and c. most people who get the flu recover completely in 1 to 2 weeks, but some people develop serious and potentially life - threatening medical complications, such as pneumonia. much of the illness and death caused by influenza can be prevented by annual influenza vaccination. flush : ( 1 ) a redness of the skin, typically over the cheeks or neck. a flush is usually temporary and brought on by excitement, exercise, fever, or embarrassment. flushing