calculating the expected values of many microscopic quantities. we add the quantity artificially to the microstate energies ( or, in the language of quantum mechanics, to the hamiltonian ), calculate the new partition function and expected value, and then set λ to zero in the final expression. this is analogous to the source field method used in the path integral formulation of quantum field theory. relation to thermodynamic variables in this section, we will state the relationships between the partition function and the various thermodynamic parameters of the system. these results can be derived using the method of the previous section and the various thermodynamic relations. as we have already seen, the thermodynamic energy is the variance in the energy ( or " energy fluctuation " ) is the heat capacity is the entropy is partition functions of subsystems suppose a system is subdivided into n sub - systems with negligible interaction energy, that is, we can assume the particles are essentially non - interacting. if the partition functions of the sub - systems are ζ1, ζ2,..., ζn, then the partition function of the entire system is the product of the individual partition functions : if the sub - systems have the same physical properties, then their partition functions are equal, ζ1 = ζ2 =... = ζ, in which case however, there is a well - known exception to this rule. if the sub - systems are actually identical particles, in the quantum mechanical sense that they are impossible to distinguish even in principle, the total partition function must be divided by a n! ( n factorial ) : this is to ensure that we do not " over - count " the number of microstates. while this may seem like a strange requirement, it is actually necessary to preserve the existence of a thermodynamic limit for such systems. this is known as the gibbs paradox. grand canonical partition function we can define a grand canonical partition function for a grand canonical ensemble, which describes the statistics of a constant - volume system that can exchange both heat and particles with a reservoir. the reservoir has a constant temperature t, and a chemical potential μ. the grand canonical partition function, denoted by, is the following sum over microstates here, each microstate is labelled by, and has total particle number and total energy. this partition function is closely related to the grand potential,, by the relation this can be contrasted to the canonical partition function above, which is related instead to the helmhol


microstate is labelled by, and has total particle number and total energy. this partition function is closely related to the grand potential,, by the relation this can be contrasted to the canonical partition function above, which is related instead to the helmholtz free energy. it is important to note that the number of microstates in the grand canonical ensemble may be much larger than in the canonical ensemble, since here we consider not only variations in energy but also in particle number. again, the utility of the grand canonical partition function is that it is related to the probability that the system is in state : an important application of the grand canonical ensemble is in deriving exactly the statistics of a non - interacting many - body quantum gas ( fermi - dirac statistics for fermions, bose - einstein statistics for bosons ), however it is much more generally applicable than that. the grand canonical ensemble may also be used to describe classical systems, or even interacting quantum gases. see also - j. r. klauder, b. - s. skagerstam, coherent states - - - applications in physics and mathematical physics, world scientific, 1985, p. 71 - 73. - huang, kerson, " statistical mechanics ", john wiley & sons, new york, 1967. - a. isihara, " statistical physics ", academic press, new york, 1971. - kelly, james j, ( lecture notes ) - l. d. landau and e. m. lifshitz, " statistical physics, 3rd edition part 1 ", butterworth - heinemann, oxford, 1996. - vu - quoc, l., configuration integral, 2008


a survey of brdf representation for computer graphics cs348c, winter 1997 whether they are generated from theoretical models or measured, brdfs for computer graphics need efficient representations. we examine the representations that have been proposed, including data tables, analytic models, splines, spherical harmonics, wavelets, and zernike polynomials. this evaluation suggests that most are lacking in flexibility, compactness, or computational efficiency. we propose some approaches to improving on these methods by making greater use of the symmetry of brdfs. historically, the reflection properties modeled by computer graphics renderers have been limited. despite their physical inaccuracy, simple models such as the phong model remain popular. true photorealism, however, requires more sophisticated and elaborate models of surface properties. it is difficult to establish exactly how far one should go in elaborating the surface model. a truly complete representation of the reflective behavior of a surface might take into account such phenomena as polarization, scattering, fluorescence, and phosphorescence, all of which might vary with position on the surface. therefore, the variables in this complete function would be : once we have eliminated all these variables, we are left with a reflectance function of the angles of the incident and reflected angles only. this function is called the bidirectional reflectance distribution function ( brdf ). the brdf is defined on the cross product of two hemispheres, and is therefore a function of four ( scalar ) variables : where e is the irradiance, that is the incident flux per unit area, and l is the reflected radiance, or the reflected flux per unit area per unit solid angle. the units of brdf are thus inverse steradians. intuitively the brdf represents, for each incoming angle, the amount of light that is scattered in each outgoing angle. for a lambertian ( perfectly diffuse ) surface, for example, the brdf is constant, and equal to ( the factor of pi is necessary so that the brdf is correctly normalized. ) more complicated brdfs will, of course, have angular dependence. brdfs to be used in rendering may either be obtained from theoretical models of reflection at a surface, or may be measured directly. each of these presents its own set of challenges. in either case, however, the result is a four - dimensional function ( ignoring color for the moment ), and efficient methods of storing and computing this function must be found. there are many methods presented in the literature,


these are the spherical analogues of sines and cosines, in that they form a smooth orthonormal basis for functions on the sphere, and are localized in the frequency domain. these properties are useful, since it is easy to project a brdf onto the basis of spherical harmonics, and since smooth, simple brdfs will have fewer nonzero ( or at least nonnegligible ) coefficients than complex ones. the most complete treatment to date of using spherical harmonics to represent brdfs is [ westin 92 ]. it turns out that a naive implementation of brdf representation in terms of spherical harmonics has several problems. first, since the brdf is defined on the product of two hemispheres, rather than two spheres, there is the question of how to fill in the missing hemispheres of data. next, truncation of high - frequency coefficients is likely to cause " ringing ", because of the sharp edges in frequency space. finally, even moderately complex brdfs require large numbers of spherical harmonic basis functions to be represented correctly. [ westin 92 ] uses a number of mathematical tricks to overcome some of these limitations. first, the authors choose to fill the " missing " hemispheres with copies of available data, rather than with zeroes. this has the effect of introducing a symmetry into the function, which causes the coefficients of all odd harmonics to be zero. next, instead of representing just the brdf, the function they actually store is this enforces continuity at the " equators " of the spheres, and helps to reduce ringing. they also artificially dampen certain high - frequency coefficients to soften the edges in frequency space, and reduce ringing even further. a final important feature used to simplify the brdf representation and increase its physical correctness is the fact that helmholtz reciprocity is enforced. this principle, arising from the physics of reflection, states that the brdf must remain the same if the angles of incidence and reflection are interchanged. therefore, the ( four - dimensional ) matrix of spherical harmonic coefficients must be symmetric under interchange of incoming and outgoing angles. this not only reduces the storage requirements of the matrix, but also enforces some basic constraints on physical correctness. the spherical harmonic representation is an attractive one for describing brdfs, because of the mathematical and conceptual simplicity of the model. nevertheless, even with westin ' s improvements, the number of coefficients required to represent even moderately complex brdfs is large. very specular surfaces


variation is a term used in genetic science, and concerns the emergence of different varieties, or species. this genetic phenomenon causes individuals or groups within a given species to possess different features from others. for example, all human beings on earth possess essentially the same genetic information. but thanks to the variation potential permitted by that genetic information, some people have round eyes, or red hair, or a long nose, or are short and stocky in stature. darwinists, however, seek to portray variation within a species as evidence for evolution. the fact is, however, that variations constitute no such thing, because variation consists of the emergence of different combinations of genetic information that already exists, and cannot endow individuals with any new genetic information or characteristics. variation is always restricted by existing genetic information. these boundaries are known as the gene pool in genetic science. ( see the gene pool. ) darwin, however, thought that variation had no limits when he proposed his theory267, and he depicted various examples of variation as the most important evidence for evolution in his book the origin of species. all human beings on earth share basically the same genetic information, but thanks to the variation potential permitted by this genetic information, they often look very different from one another. according to darwin, for example, farmers mating different variations of cow in order to obtain breeds with better yields of milk would eventually turn cows into another species altogether. darwin ’ s idea of limitless change stemmed from the primitive level of science in his day. as a result of similar experiments on living things in the 20th century, however, science revealed a principle known as genetic homeostasis. this principle revealed that all attempts to change a living species by means of interbreeding ( forming different variations ) were in vain, and that between species, there were unbreachable walls. in other words, it was absolutely impossible for cattle to evolve into another species as the result of farmers mating different breeds to produce different variations, as darwin had claimed would happen. luther burbank, one of the world ’ s foremost authorities on the subject of genetic hybrids, expresses a similar truth : “ there are limits to the development possible, and these limits follow a law. ” 268 thousands of years of collective experience have shown that the amount of biological change obtained using cross - breeding is always limited, and that there is a limit to the variations that any one species can undergo. indeed, in the introduction to their book natural limits to biological change professor of biology lane p. lester and the molecular biologist raymond g. bohli


difference between different mixes of laurax, similar to the way most can distinguish different shades of white. more information : weiss, t. et al., perceptual convergence of multi - component mixtures in olfaction implies an olfactory white. proceedings of the national academy of sciences, november 19, 2012. doi : 10. 1073 / pnas. 1208110109 in vision, two mixtures, each containing an independent set of many different wavelengths, may produce a common color percept termed " white. " in audition, two mixtures, each containing an independent set of many different frequencies, may produce a common perceptual hum termed " white noise. " visual and auditory whites emerge upon two conditions : when the mixture components span stimulus space, and when they are of equal intensity. we hypothesized that if we apply these same conditions to odorant mixtures, " whiteness " may emerge in olfaction as well. we selected 86 molecules that span olfactory stimulus space and individually diluted them to a point of about equal intensity. we then prepared various odorant mixtures, each containing various numbers of molecular components, and asked human participants to rate the perceptual similarity of such mixture pairs. we found that as we increased the number of nonoverlapping, equal - intensity components in odorant mixtures, the mixtures became more similar to each other, despite not having a single component in common. with components, most mixtures smelled alike. after participants were acquainted with a novel, arbitrarily named mixture of equal - intensity components, they later applied this name more readily to other novel mixtures of equal - intensity components spanning stimulus space, but not to mixtures containing fewer components or to mixtures that did not span stimulus space. we conclude that a common olfactory percept, " olfactory white, " is associated with mixtures of or more equal - intensity components that span stimulus space, implying that olfactory representations are of features of molecules rather than of molecular identity. journal reference : proceedings of the national academy of sciences © 2012 medical xpress - wake up and smell the sweat nov 21, 2007 | not rated yet | 0 - how odors are sensed : a complex system clarified apr 12, 2006 | not rated yet | 0 - human ability good in tracking odors aug 29, 2005 | not rated yet | 0 - study shows people can guess personality via body odor dec 05, 2011 | not rated yet


; because reason is always present, while the laws of nature generally require to be laboriously sought out. and so metaphysics floated to the surface like foam, and like foam, too, no sooner was it gathered up than it dissolved, while another mass of it appeared upon the scene which some were always found eager to grasp ; while others, instead of seeking to penetrate the cause of the phenomenon in question, thought themselves wise in laughing at the futile exertions of the former. the essential feature distinguishing pure mathematical knowledge from all other knowledge a priori, is that it does not proceed from conceptions themselves, but always through the construction of conceptions. ( critique, p. 435. ) since, therefore, in its propositions it must pass out of the conception to that containing the corresponding intuition, these can and ought never to arise from the dissection of conceptions, that is, analytically ; in other words, they are, in their entirety, synthetic. i cannot refrain from remarking on the disadvantage resulting to philosophy from a neglect of this simple and apparently insignificant observation. hume, indeed, feeling it a task worthy of a philosopher, cast his eye over the whole field of pure knowledge a priori in which the human understanding claims such extensive possession. he, however, inconsiderately severed from it an entire, and indeed the most important, province, namely, that of pure mathematics, under the impression that its nature, and, so to speak, its constitution, rested on totally different principles, that is, solely on the principle of contradiction ; and although he did not make such a formal and universal division of propositions as is here done by me, or under the same name, yet it was as good as saying, pure mathematics contains simply analytic judgments, but metaphysics, synthetic judgments a priori. now in this he made a great mistake, and this mistake had decidedly injurious consequences on his whole conception. for if he had not made it, he would have extended his question respecting the origin of our synthetic judgments far beyond his metaphysical conception of causality, and comprehended therein the possibility of mathematics a priori ; for he must have regarded this as equally synthetic. but in the latter case he could, under no circumstances, have based his metaphysical propositions on mere experience, as he would then have been obliged to have subordinated the axioms of pure mathematics themselves to experience, a proceeding for which he was much too penetrating. the good company into which metaphysics would then have been brought


, related phenomena. the term " technology transfer " encompasses such a broad range of activities that a general definition brief enough to be useful is impossible to develop. however, operational definitions of technology transfer are easier to devise in a specific context, and are best constructed in terms of specific mechanisms of transfer. a number of different definitions are in use by various institutions and groups, and two of them are included below · the technology transfer society ' s brochure defines technology transfer as " a strategy for achieving organizational goals, as " a process leading to actual transfer. " and as " a discipline involving a multiplicity of skills. " · the american federal laboratory consortium defines technology transfer as " the process by which existing knowledge, facilities or capabilities developed under federal r & d funding are utilized to fulfill public and private needs. " that means " technology transfer consists of efforts and activities intended to result in the application or commercialization of federal laboratory - developed innovations by the private sector, state and local governments, and other domestic users. these activities may include, but are not limited to : o technical / cooperative interactions ( direct technical assistance to private sector users and developers ; personnel exchanges ; resource sharing ; and cooperative research and development agreements ) ; o commercialization activities ( patenting and licensing of innovations and identifying markets and users ) ; and o information exchange ( dissemination to potential technology users of technical information ; papers, articles, reports, seminars, etc. ). "


mit professor ’ s book digs into the eclectic, textually linked reading choices of people in medieval london. imagine a future in which wireless power transfer is feasible : cell phones, household robots, mp3 players, laptop computers and other portable electronics capable of charging themselves without ever being plugged in, freeing us from that final, ubiquitous power wire. some of these devices might not even need their bulky batteries to operate. a team from mit ' s department of physics, department of electrical engineering and computer science, and institute for soldier nanotechnologies ( isn ) has experimentally demonstrated an important step toward accomplishing this vision of the future. the team members are andre kurs, aristeidis karalis, robert moffatt, prof. peter fisher, and prof. john joannopoulos ( francis wright davis chair and director of isn ), led by prof. marin soljacic. realizing their recent theoretical prediction, they were able to light a 60w light bulb from a power source seven feet ( more than two meters ) away ; there was no physical connection between the source and the appliance. the mit team refers to its concept as " witricity " ( as in wireless electricity ). the work will be reported in the june 7 issue of science express, the advance online publication of the journal science. the story starts one late night a few years ago, with soljacic ( pronounced soul - ya - cheech ) standing in his pajamas, staring at his cell phone on the kitchen counter. " it was probably the sixth time that month that i was awakened by my cell phone beeping to let me know that i had forgotten to charge it. it occurred to me that it would be so great if the thing took care of its own charging. " to make this possible, one would have to have a way to transmit power wirelessly, so soljacic started thinking about which physical phenomena could help make this wish a reality. various methods of transmitting power wirelessly have been known for centuries. perhaps the best known example is electromagnetic radiation, such as radio waves. while such radiation is excellent for wireless transmission of information, it is not feasible to use it for power transmission. since radiation spreads in all directions, a vast majority of power would end up being wasted into free space. one can envision using directed electromagnetic radiation, such as lasers, but this is not very practical and can even be dangerous. it requires an uninterrupted line of sight between the source and the device, as well as a sophisticated tracking


. one can envision using directed electromagnetic radiation, such as lasers, but this is not very practical and can even be dangerous. it requires an uninterrupted line of sight between the source and the device, as well as a sophisticated tracking mechanism when the device is mobile. the key : magnetically coupled resonance in contrast, witricity is based on using coupled resonant objects. two resonant objects of the same resonant frequency tend to exchange energy efficiently, while interacting weakly with extraneous off - resonant objects. a child on a swing is a good example of this. a swing is a type of mechanical resonance, so only when the child pumps her legs at the natural frequency of the swing is she able to impart substantial energy. another example involves acoustic resonances : imagine a room with 100 identical wine glasses, each filled with wine up to a different level, so they all have different resonant frequencies. if an opera singer sings a sufficiently loud single note inside the room, a glass of the corresponding frequency might accumulate sufficient energy to even explode, while not influencing the other glasses. in any system of coupled resonators there often exists a so - called " strongly coupled " regime of operation. if one ensures to operate in that regime in a given system, the energy transfer can be very efficient. while these considerations are universal, applying to all kinds of resonances ( e. g., acoustic, mechanical, electromagnetic, etc. ), the mit team focused on one particular type : magnetically coupled resonators. the team explored a system of two electromagnetic resonators coupled mostly through their magnetic fields ; they were able to identify the strongly coupled regime in this system, even when the distance between them was several times larger than the sizes of the resonant objects. this way, efficient power transfer was enabled. magnetic coupling is particularly suitable for everyday applications because most common materials interact only very weakly with magnetic fields, so interactions with extraneous environmental objects are suppressed even further. " the fact that magnetic fields interact so weakly with biological organisms is also important for safety considerations, " kurs, a graduate student in physics, points out. the investigated design consists of two copper coils, each a self - resonant system. one of the coils, attached to the power source, is the sending unit. instead of irradiating the environment with electromagnetic waves, it fills the space around it with a non - radiative magnetic field oscillating at mhz frequencies.


comes about. the usual non - resonant magnetic induction would be almost 1 million times less efficient in this particular system. " old physics, new demand witricity is rooted in such well - known laws of physics that it makes one wonder why no one thought of it before. " in the past, there was no great demand for such a system, so people did not have a strong motivation to look into it, " points out joannopoulos, adding, " over the past several years, portable electronic devices, such as laptops, cell phones, ipods and even household robots have become widespread, all of which require batteries that need to be recharged often. " as for what the future holds, soljacic adds, " once, when my son was about three years old, we visited his grandparents ' house. they had a 20 - year - old phone and my son picked up the handset, asking, ' dad, why is this phone attached with a cord to the wall? ' that is the mindset of a child growing up in a wireless world. my best response was, ' it is strange and awkward, isn ' t it? hopefully, we will be getting rid of some more wires, and also batteries, soon. ' " this work was funded by the army research office ( institute for soldier nanotechnologies ), national science foundation ( center for materials science and engineering ), and the department of energy.


ido perlman, helga kolb and ralph nelson horizontal cells are the interneurons of distal vertebrate retina. they provide the pathways for both local and long range interactions between photoreceptors. these interactions are called feedback signals. feedback signals adjust the gain of photoreceptor synaptic output, both as seen in the horizontal cells themselves and in the adjacent, proximally projecting bipolar cells. in forming a distal, lateral synaptic network, horizontal cells enrich not only their own physiology but that of presynaptic and postsynaptic partners. they generate spatial opponency in both cones and bipolar cells. they also generate color opponency in cones, bipolar cells, and chromatic horizontal - cell subtypes. the actions of horizontal cells propagate forward in the retina, can be identified in the physiology of retinal ganglion cells, and in visual perception. horizontal cell actions are in turn tuned by neuromodulators released by other retinal neurons. the first intracellular, light - evoked responses recorded in the vertebrate retina were slow, negative going changes in membrane potential that lasted for as long as the light stimulus was present ( fig. 1 ). before the morphological source of these responses became clear, they were called simply s - potentials ( 1 ). as shown in figure 1, s - potentials are membrane hyperpolarizations that last for as long as the light stimulus is present. the graded character of the s - potential is evident in figure 1a. the brighter the stimulus, the larger the amplitude of the s - potential until a saturation level is reached. in figure 1b, the duration of a light stimulus of fixed intensity is altered in order to examine the temporal properties of s - potentials. for long stimuli, the s - potential only changes in duration but the amplitude remains constant ( 2 leftmost responses in fig. 1b ). further reduction in the stimulus duration causes a decrease in amplitude ( fig. 1b ). this illustrates the temporal summation of the s - potential, following bloch ’ s law. up to certain stimulus durations, in this case about 10 msec, the amplitude is directly related to the quantal content of the stimulus ( quantal flux multiplied by duration ), while for stimuli of longer duration, the amplitude is related to the quantal flux, that is, the rate of quantal absorption by photoreceptors ( 1 ). in s -


the stimulus ( quantal flux multiplied by duration ), while for stimuli of longer duration, the amplitude is related to the quantal flux, that is, the rate of quantal absorption by photoreceptors ( 1 ). in s - potentials this ‘ critical duration ’ varies considerably with stimulus conditions ( 2 ). it is likely that s - potentials were named in honor of their discoverer, gunnar svaetichin, although ‘ slow potential ’ is another common interpretation. figure 1. the s - potential of the fish retina. light stimuli of fixed duration and different irradiances ( a ) and light stimuli of fixed irradiance but different durations ( b ) were used to elicit these potentials. lower traces in a and b record light - stimulus duration and provide 100 msec ‘ tick - marks ’. the illustrations are from svaetichin, 1953 ( 1 ). s - potentials puzzled neurophysiologists of the 1950s when they were first described. at that time, neurons were thought only to be depolarized by synaptic inputs ( inside becoming more positive relative to outside ), thus having their inside - negative resting membrane potentials become reduced. this depolarization was thought of as excitation, and if the excitation was large enough, action potentials, or nerve spikes, were generated to transfer signals down the length of the nerve - cell axon. s - potentials, however, were not depolarized by light, but rather hyperpolarized, and did not fire action potentials, even with the brightest light stimuli. at first, the cell type of origin for s - potentials was not really known other than that microelectrode tips were somewhere in the outer retina. in fact, initially svaetichin thought s - potentials arose from cones ( 1 ). however, later intracellular marking techniques, in which dyes were injected from the electrode tips into the cytoplasm of the recorded neuron, revealed that horizontal cells, second order neurons postsynaptic to cones, were the source of the s - potentials ( 3, 4 ). since being first described in fish retinas, s - potentials have been recorded from retinal horizontal cells in all vertebrate classes. these include both cold - blooded vertebrates ( 4 - 13 ), household mammals ( 14 - 20 ) and primates ( 21 - 26 ). horizontal cells have now been studied


). some other definitions of lambda based on empirical curve fitting of data have also been suggested ( 10, 171 ). for models based on electrical current flow in the horizontal - cell syncytium, receptive field size is directly related to lambda, and lambda is directly related to the membrane resistance of the horizontal cell, and inversely related to the coupling resistance between the horizontal cells. the space constant of the cone signal components in a cat a - type horizontal cell ( fig. 16a ) is 250 μm. the space constant for the rod signal component in the same cell is 200 μm ( fig. 16b ). this illustrates the point that even in the same cell, depending on what is being measured ; somewhat different receptive fields can be inferred. the concept of field size is not monolithic. the exceptional width of horizontal - cell receptive fields finds several uses. first, horizontal - cell actions on photoreceptors and bipolar cells, both of which are much narrower in receptive field centers than horizontal cells, can be seen in the distal limbs of area functions in these narrower - field neurons. second, horizontal cell types can be distinguished by the size and properties of receptive fields. in the turtle retina, two types of luminosity horizontal cells were early recognized ; l1 and l2 ( 53 ) or respectively, large receptive field ( lrf ) and small receptive field ( srf ) horizontal cells ( 81 ). the l1 ( lrf ) cells are characterized by receptive fields of large diameter ( > 3 mm ) while the l2 ( srf ) cells have a receptive field diameter of about 2 mm. these two l - type horizontal cells also differ with regards to spectral properties ( 172 ) and responsiveness to surround illumination ( 173 ). the anatomical stains of lrf and srf cells actually reveals that they are two, electrically isolated, parts of the same cell. lrf is the axon terminal of h1, and srf is the cell body ( fig. 2a ) ( 53 ). thus receptive field measurements add further evidence that a single horizontal cell may have 2 independent area summation regions. the horizontal cell syncytium cannot be fully described by static passive electrical models. the resistances within the horizontal cell layer change with illumination and time and therefore, the size of the receptive field ( magnitude of lambda, or the length constant ) changes also ( 169, 174, 175 ). in general, the size of the receptive - field


159, 160, 203, 205 ). although these cells clearly have gaba uptake systems and accumulate gaba, the idea that gaba mediates the negative feedback of horizontal cells to cone photoreceptors has not received universal experimental validation. horizontal - cell gaba could still have a feed - forward action directly upon bipolar cell dendrites or other horizontal - cell processes ( 156, 205 ). alternatively gaba receptors on horizontal cells might simply serve the purpose of limiting transporter - generated membrane depolarizations in the presence of extracellular gaba. figure 21. electron microscopy shows immunolabeling ( dark granules ) for vesicular γ - aminobutryric acid transporter ( vgat ) in mouse ( a ) and rat ( b ) horizontal cell lateral elements ( arrow heads ) in rod spherules. rod synaptic ribbons are indicated by long arrows. the scale bars are 0. 5 μm. the illustration is from cueva et al., 2002 ( 192 ). a further feedback model proposes that elevated proton concentration in the synaptic cleft mediates feedback by inhibiting photoreceptor calcium channels ( 206 ). proton buffers, particularly amino sulfonates like hepes, block feedback ( 207 - 212 ). while there is general agreement that some ph buffers block feedback, there is currently disagreement whether alteration of ph in the synaptic cleft is the mechanism ( 213, 214 ). most feedback models propose that modulation of presynaptic calcium channels in the photoreceptor terminals is the key. using voltage - clamp recordings from cones during illumination with spots or annuli of light, verweij et al ( 1996 ) ( 215 ) suggest that feedback modulates the voltage - dependency of the calcium channels in the cone pedicles ( fig. 22a ). the explanation takes off from an old electrical model ( 5 ) and proposes that horizontal cells can initiate large extracellular current flow through hemi - gap - junction channels into the restricted extracellular space within the triad synapse of the cone ( fig. 22b ) ( 68, 70, 72, 189, 216 ). during light stimulation, the l - type horizontal cells hyperpolarize, increasing the magnitude of the inward flow of cations from extracellular space, through hemi - gap - junction channels, into horizontal cell lateral elements. this causes hyperpolarization of the extracellular space. such hemi - gap - junctions,


increasing the magnitude of the inward flow of cations from extracellular space, through hemi - gap - junction channels, into horizontal cell lateral elements. this causes hyperpolarization of the extracellular space. such hemi - gap - junctions, consisting of connexin cx55. 5, have been demonstrated anatomically in horizontal cell lateral elements in zebrafish retinas ( fig. 3d ). the extracellular hyperpolarization activates voltage dependent calcium channels which sense the change in the same way as intracellular depolarization, leading to calcium entry, and an increase in glutamate release. the idea finds some support because when the hemi - channels are blocked with carbenoxolone ( a specific gap junction blocker ), the feedback signal in the cone is eliminated ( 189, 204 ). figure 22. electrical feedback model. a. the activation range of calcium currents in cone synaptic terminals shifts towards more hyperpolarized values during surround stimuli that hyperpolarize horizontal cells. b. the electrical or ‘ ephaptic ’ feedback model argues that the voltage within the enclosed extracellular space surrounding horizontal - cell invaginated dendritic tips is influenced by horizontal - cell membrane polarization. with surround stimulation, these dendrites hyperpolarize, causing extracellular space to hyperpolarize also. this affects synaptic calcium channels in the same way as would intracellular depolarization of the cone terminal. the more hyperpolarized the horizontal cell dendrite, the more calcium enters the cone terminal, and the more neurotransmitter is released. the effect is opposite to the light - induced closing of cone outer segment cation channels that suppress neurotransmitter release. ( i ) calcium channels ( red ) are located on the cone presynaptic membrane, adjacent to the ribbon. gap junction hemichannels ( blue ), polarize adjacent extracellular space. extracellular current flow hyperpolarizes extracellular space to a greater extent in the light ( ii ) than in the dark ( i ) the illustration is from kamermans and fahrenfort, 2004 ( 216 ). further evidence for the importance of connexin 55. 5 and hemi gap - junctions for feedback comes from a genetic knockout in zebrafish. feedback to cones, behavioral contrast sensitivity, and horizontal - cell color opponency were all weakened in this knockout. as this connexin is only expressed in horizontal cells


the kelvin problem - what packing minimizes the surface area in 3d space? for over 100 years, the kelvin structure composed of truncated octahedrons was believed to be the unit cell, which divided 3d space with minimum surface area. in 1994, the weaire - phelan structure was proposed, which shows 0. 3 % less surface area than the kelvin structure. although monodisperse foams have been used to address this problem and realize the structure, high density difference between gas and liquid and lack of technology to make monodisperse bubbles at micron scale have severely restricted their production and observation. we are studying this problem with monodisperse emulsion drops, instead of foam. microfluidic technique facilitates the production of such small and uniform drops. as continuous phase evaporates, monodisperse drops are densely packed without coalescence, minimizing their interfacial area. therefore, microfluidic approach provides an ideal model system to address kelvin ' s problem. in addition, through polymerization of drops in densely packed state, we can permanently fix the structure and produce monodisperse polyhedron microparticles which are potentially useful as building blocks for assemblies. figure 1 : two layers of monodisperse emulsion drops ( a ) in a low volume fraction of drops ( beehive structure ) and ( b ) in a high volume fraction ( toth structure ). ( c ) polyhedron microparticles templated by toth structure. [ scale bar = 200 microns ] this project is a collaboration with shin - hyun kim.


logging in or signing up nano robots medicine of the future ashokmateti download post to : url : related presentations : share add to flag embed email send to blogs and networks add to channel uploaded from authorpoint lite insert youtube videos in powerpont slides with as desktop copy embed code : embed : flash ipad copy does not support media & animations wordpress embed customize embed url : copy thumbnail : copy the presentation is successfully added in your favorites. views : 1823 category : science & tech.. license : all rights reserved like it ( 3 ) dislike it ( 1 ) added : march 17, 2011 this presentation is public favorites : 1 presentation description no description available. comments posting comment... premium member presentation transcript slide 1 : medicine of the future ch. poojitha roll no : 12080026 priyadarshini college of pharmaceutical sciences nanorobots 1 presented byslide 2 : nanotechnology nanorobots molecular nanotechnology ( mnt ) how nanorobots will work applications conclusion references contents 2slide 3 : what does nanotechnology mean? nanotechnology is the engineering of functional systems at the molecular scale. it is the study of manipulating matter on an atomic and molecular scale. 3slide 4 : nanorobots a nanorobot is a tiny machine designed to perform a specific task or tasks repeatedly and with precision at nanoscale dimensions, that is, dimensions of a few nanometer s ( nm ) or less, where 1 nm = 10 - 9 meter they are nanodevices that will be used for the purpose of maintaining and protecting the human body against pathogens. 4slide 5 : molecular nanotechnology ( mnt ) the umbrella science of nanomedicine mnt describes engineered nanosystems ( nanoscale machines ) operating on the molecular scale. mnt is especially associated with the molecular assembler, a machine that can produce a desired structure. mnt is based on the ability to build structures to complex, atomic specifications by means of mechanosynthesis. 5slide 6 : what is a chromallocyte? what is a respirocyte? what are the risks of nanoscience? what are the potential benefits of mnt ( molecular nanotechnology )? what are the potential dangers of molecular nanotechnology? related wise geek articles 6slide 7 : a chromallocyte is a lozenge - shaped mobile nanorobot, consisting of about four trillion atoms. what is


- the magazine what can be said about a glaze? plenty! we have all been in the position of trying to describe our favorite glaze to another potter or to ourselves. if the actual glaze is not present, the verbal account can leave a lot to the imagination, which can produce an inaccurate image. the glaze description language is an agreed - upon meaning to the many characteristics found in glazes. it uses several key words and phrases to define a glaze. the idea, as with all languages, is that everyone understands what is meant by the standardized terms that classify a glaze. the glaze description language allows the listener or reader to formulate an accurate mental image of how the fired glaze looks and functions. one area of potential error occurs when writing or describing glazes. many potters still refer to a glaze formula by its popular name. for example, we have all called glazes randy ’ s red or bob ’ s blue. while there is a certain personal and informal quality in referring to glazes in such a manner, it can lead to numerous inaccuracies in exchanging or understanding glaze formulas. just referring to a glaze by its common name does not tell us enough about its characteristics, such as color, texture or light transmission. as an added potential for error, the actual glaze formula for randy ’ s red could have changed many times since randy developed the glaze. identifying glazes only by their names is an inaccurate attempt to transfer information and can indicate a potter ’ s lack of knowledge about glaze formulas. even potters who know better are still drawn into the easy habit of referring to a glaze only by its name. however, there is another method that can transfer information with greater accuracy. once the vocabulary is known, it makes the task of explaining how a glaze looks much easier, faster and more accurate. we ' re not talking about deciphering sanskrit or egyptian hieroglyphics ; just a few simple categories can add to the enjoyment of making and describing ceramic glazes. keep in mind there are no set rules about the number of terms to use in describing a glaze. however, it is critical that any terms used have some universal understanding among potters. in addition, too many descriptive terms can be overly cumbersome to use in actual practice. many potters choose only those descriptions that accurately focus on their particular glaze. listed are several characteristics that will define a glaze in specific terms. firing temperature :