says costes, " i simulated the optical transformation when imaging events at the nanoscale are viewed with a fluorescent microscope. " one optical transformation is blurring, with the result that, in a real microscope, two nearby radiation - induced foci may blend together and look like one. when such factors were taken into account, costes ' s initial model, following the nasa model, confirmed random distribution of double - strand breaks at the micron scale. the frequency of dsbs was radiation dependent, however : in the case of cosmic rays ( nasa ' s main concern ), which lead to complex double - strand breaks, there was good agreement with the rif frequencies seen in the microscope. but in the case of gamma rays, which lead primarily to sparse and noncomplex dsbs, measured frequencies in real microscope images were lower. this suggests that rif correspond to sites of complex double - strand breaks in dna. moreover focusing on cosmic rays for the nasa project although the dsb frequency was the same as predicted by the models, the rif in real microscope images were distributed very differently. model physics, real biology " for one thing, there is a time effect, " says costes. " just five minutes after cells are exposed to high - energy particles, microscope images already show a nonrandom distribution of rif. " the rif occur along straight lines, as expected for a particle track, but are not randomly distributed along the lines. " even though we have the right foci frequency along a track, many foci appear to repulse each other within the first 30 minutes after irradiation " a suggestion that they might be moving to specific regions of the nucleus. costes and his colleagues applied the same kinds of models and measurements to gamma rays and found that whereas the model predicted that these breaks would occur in a random pattern in three dimensions throughout the nucleus ( not along lines ), in fact, under the microscope, radiation - induced foci caused by gamma rays were also distributed nonrandomly. there were fewer rif due to gamma rays than the model predicted, and they appeared more gradually. the researchers now used a novel technique, " relative dna image measurements, " and analyzed the images to show where the dna was dense, where it was less dense, and where the two densities met. they wanted to see whether, where rif occurred, there was an underlying difference in the nature of the dna. indeed there was. by comparison to the random distribution that might have been


british poet william blake once wrote that a world was contained in a grain of sand. physicists have done one better, finding a surprising link between streams of flowing sand grains and the birth of the universe. a new study in the latest issue of the journal physical review letters finds that flowing sand grains show liquid - like behavior also witnessed in particle - collider experiments that simulate our universe ' s first moments. " nature plays the tricks that it knows how to play over and over again, " said study team member sidney nagel of the university of chicago. macroscopic particles visible to the naked eye and invisible particles smaller than an atom sometimes behave in similar ways. nagel and his colleagues found that flowing sand grains create a cone - shaped " envelope structure " after striking a coin - like small, flat, circular object. similar structures have been observed in the " quark - gluon plasma " experiments conducted at brookhaven national laboratory in new york with the relativistic heavy ion collider ( rhic ). the quark - gluon plasma was a super hot and extremely dense soup of subatomic particles scientists think existed for a few millionths of a second after the big bang. an experiment performed in 1883 that involved shooting water onto a small, circular target found that the water molecules also fan out into a thin cone before surface tension brought them back together to form a shape resembling a bell. " that ' s the amazing thing about physics, " nagel said. " the laws you have at one level really are the same as at other levels, or at least influence what happens at other levels. " nagel says the result of his team ' s experiment could change how scientists interpret the rhic data. © 2012 livescience. com. all rights reserved.


if a rough surface is illuminated by a coherent lightwave of wavelength λ1, it is not possible to determine the surface profile from the phases of the speckle field formed by the scattered light. if the rough surface is illuminated, however, by an additional coherent wave of wavelength λ2, the phase differences between the two speckle fields do contain information about the macroscopic surface profile even if subject to a statistical error. it is shown that ( 1 ) the macroscopic surface profile may be determined from the phase differences if the effective wavelength λ = λ1λ2 / | λ1 - λ2 | is sufficiently larger than the standard deviation of the microscopic profile of the illuminated surface, and ( 2 ) the statistical error is reasonably small if the phase measurements are obtained from speckles of sufficient intensity. using a heterodyne interferometer we demonstrate the feasibility of this technique. in the first experiment we determine the radius of curvature of a rough spherical surface. in the second experiment the macroscopic surface contour on two ophthalmic lenses of the same power variation, one with a grounded surface and the other with a polished surface, was determined. © 1985 optical society of america a. f. fercher, h. z. hu, and u. vry, " rough surface interferometry with a two - wavelength heterodyne speckle interferometer, " appl. opt. 24, 2181 - 2188 ( 1985 )


- the magazine - web exclusives many people are familiar with calibration from the stickers on measuring devices and systems that indicate when calibration was last performed. some people learn about calibration when they go to use a measuring system and find it is not available because it is being calibrated. there is so much information out there about calibration and calibration frequency that it can be confusing. however, it is important to understand the basics of establishing calibration frequency. what is calibration? calibration is the process of determining the numerical relationship between the observed output of a measurement system and the value of the characteristic being measured based on reference standards. calibration also describes any steps required to ensure the accuracy and reliability of the procedure. in reality, the device is considered calibrated if its measurements are within a predetermined range of the known value. if measurements are outside the accepted range, adjustments are usually made to the measuring system to make its readings more closely match the known value. low - cost measuring devices, in which no adjustment is possible, are simply discarded when they become outside of the accepted range. in some cases a deviation chart is generated to “ correct ” the measured value. do i even need to calibrate? i bought this expensive, highly accurate measuring machine because i know it can measure everything i make. why should i ever have to calibrate it? the price of a measuring device has little to do with whether or when to calibrate it. even though manufacturers design systems for stability and long - term accuracy, many factors can affect calibration. simple things such as large temperature swings, rough handling in shipment, workplace accidents and operator error can either be a cause for or justify recalibration. it can be pretty expensive to reject parts because they measured out of specification when the real problem was a measuring device giving wrong readings. an appropriate calibration schedule will prevent these situations. how often should my system be calibrated? any dimensional measuring device, from a simple dial caliper to a large - capacity coordinate measuring machine, has a measurement range and resolution. it also has manufacturer specifications for measurement accuracy, which the device is usually calibrated and verified to before shipment. it needs to be verified that all devices or systems meet purchased specification after receipt and before use. after verification, such devices can be accepted and used, with calibrations performed as recommended or required. recommended or required? so you thought all calibration requirements


to be verified that all devices or systems meet purchased specification after receipt and before use. after verification, such devices can be accepted and used, with calibrations performed as recommended or required. recommended or required? so you thought all calibration requirements were satisfied when you purchased your newest piece of measurement equipment. the equipment was purchased based on the manufacturer ’ s published specifications and a pre - purchase gage repeatability and reproducibility study or similar evaluation of your requirements. your measurement equipment should be looked at as a means to guarantee meeting your specific needs and satisfying all internal and external requirements. what you care about is running smoothly, on schedule and with high confidence. correct scheduling of calibration can directly affect your business. the manufacturer ’ s recommendations for calibration usually are supported by international or industry standards, the manufacturer ’ s years of testing and the inherent quality of the system. however, how you use a system and your historical data help to determine specific requirements for and frequency of calibration. also, there are many other factors that enter into the frequency of calibration, for example, the environment, part tolerances, regulatory agencies and inherent machine stability. system maintenance is important in determining calibration frequency. well - maintained systems will require calibration less often than systems that are poorly maintained or abused. seemingly minor maintenance issues can be factors. for instance, failure to properly lubricate stage mechanisms can cause them to perform differently over time, gradually affecting measurements. failure to keep the measuring device clean can allow debris to contaminate lubricants or obscure optical systems, causing degradation in performance over time. a proper calibration frequency assumes consistent performance of the device, which in turn depends on proper maintenance. developing a calibration frequency processthe frequency of calibrations is important. in the past it was not unusual for the organization that performed the calibration to put a sticker on the machine with a due date for the next calibration. that practice is not allowed according to iso / iec 17025 : 2005 - general requirements for the competence of testing and calibration laboratories. the equipment operator must determine the frequency of calibration. ultimately, calibration frequency depends on how important the measuring device is to the manufacturing process. rarely used measuring machines that are well maintained, kept in a controlled environment and used properly may need calibration once a year. measuring machines used to support production or used for product and process development might need quarterly, monthly or more frequent calibrations.


be extremely helpful for determining system changes and using that information to establish the appropriate calibration frequency. a golden part is a reference sample of the production parts that has been thoroughly measured for all the important dimensions. it is simply a part that closely mimics the dimensional requirements you inspect. after your system has been installed and calibrated, the first step is to measure one of your representative parts with the system. make measurements typical of those you will be taking on a daily basis, ensuring that you include the most critical features. you have just created your initial golden part data. store this data in a golden part folder, in a convenient, protected and accessible place - preferably near your system. make sure you note the part number and material, temperature and temperature change, and conditions of the setup. this is the start of your system history file. the importance of your golden part is that it embodies all the dimensions that are important for manufacturing like parts. rather than interpret how any deviations from a calibration artifact might affect a manufacturing decision, deviations in measurements from those of the golden part have obvious, direct implications. by remeasuring the golden part periodically, you will be able to see how the system is functioning by comparing the measurement data and environmental conditions to your original run. this will enable you to realize when your system is changing, alerting you to the possible need for a recalibration. over time you will see how often to use the golden part. its measurements will help establish a calibration frequency initiative. unscheduled calibrationas important as a regular, scheduled calibration process is, there are times when a calibration may be necessary before it is scheduled. an obvious example of this is when there is a “ crash. ” if a probe or sensor is driven into a part, a stage runs at high speed into its end of travel or the system is subjected to any abrupt operation that is out of the ordinary, recalibration may be necessary. unfortunately, it may not always be as obvious as these examples. a system operator may inadvertently drive a probe into a part, recover and continue measuring as though nothing happened. the indication whether something is wrong should become apparent the next time your golden part is measured. using a golden part in events such as this can help process and manufacturing engineers identify the real source of the change in measurement results.


pure silicon laser debuts technology research news from the university of california at los angeles have made a prototype laser from the stuff of computer chips - - silicon. the laser is tunable, meaning it can lase in a range of wavelengths, or colors, and it works at room temperature. the silicon laser could be used to provide optical wireless communications at a wavelength that is optimal for transmission through air and even fog, to detect chemicals and biological molecules, and to provide an infrared countermeasure capable of jamming heat - seeking missiles, said bahram jalali, a professor of electrical engineering at ucla. the device promises to be compatible with today ' s silicon manufacturing processes because it amplifies light using the natural atomic vibrations of silicon rather than a mix of materials or a particular nanoscale physical structure, said jalali. " this is significant because no special impurity or complicated device structure is needed, and hence the technology is 100 percent compatible with silicon chip manufacturing, " he said. this makes silicon lasers potentially inexpensive. " silicon is the bread and butter material of the... electronics industry, " jalali. " ideally everything should be made in silicon because its combination of technology and economics cannot be matched, " he said. the researchers ' prototype consists of a fiber - optic loop containing a silicon waveguide. a standard laser pumps energy into the loop. a tap channels five percent of the output light from the loop to a detector. the remaining light remains in the loop where it is amplified by the silicon. when the pump laser produces 9 watts or more of power, the prototype produces a laser beam. a laser, short for light amplification by stimulated emission of radiation, works by electrically or optically energizing matter. an atom ' s electrons occupy discrete energy levels, and when an atom absorbs energy its electrons move to higher energy levels around the atom ' s nucleus. when an electron falls back to a lower energy level, the atom emits energy in the form of a photon. this is the natural process of spontaneous light emission. if an atom is already at a higher energy level when it absorbs energy, however, an electron releases two photons as it returns to its low energy level, or ground state. this stimulated emission is the basis of the basic components of a laser are a gain medium - - atoms that emit photons - - contained in a resonator cavity, and an energy source. the cavity can be a pair of parallel mirrors that bounce photons back and forth


of the basic components of a laser are a gain medium - - atoms that emit photons - - contained in a resonator cavity, and an energy source. the cavity can be a pair of parallel mirrors that bounce photons back and forth, or, in the case of the researchers ' prototype, a fiber - optic loop that channels emitted photons back into the gain medium. the energy source - - electricity or another laser - - energizes the atoms, and the resonator cavity causes photons produced by spontaneous emission to be resorbed by the atoms. when more atoms emit photons through stimulated rather than spontaneous emission, the laser produces an intense beam of light at a single wavelength, or color. the wavelength of the beam is determined by the type of gain medium. ordinarily silicon makes a poor gain medium because when its electrons drop to the ground state more energy is channeled into the material as vibrations or heat than is emitted as light. the researchers got around this problem by taking advantage of the raman effect. when photons strike atoms, many are absorbed and some scatter. the scattered photons gain or lose energy depending on whether the atoms they struck are in a high or low energy state. the energy change causes the photons ' wavelength to shift. the amount of wavelength shift, or color change, is determined by the type of atom. this effect is commonly used to identify when a powerful enough laser strikes a material, the scattered photons induce lasing at the raman - shifted wavelength. raman lasers made from glass optical fiber are common. the researchers found that silicon works much better than glass as a raman gain medium because silicon ' s atomic structure is well ordered, which increases photon scattering. the raman effect is 10, 000 times stronger in silicon than in optical fiber, jalali said. the researchers ' silicon raman laser shifts 1, 540 - nanometer wavelengths to 1, 675 - nanometer light, which is in the near - to mid - infrared range. the silicon laser could be a cheaper alternative to the fiber - optic raman lasers currently used to provide light for telecommunication networks, said jalali. " the silicon raman laser would be for more compact [ and ] much lower cost, " he said. the silicon laser could also be used in optical wireless communications devices, which require a wavelength that is optimal for transmission through air and fog, said jalali. " existing communication lasers emit at a wavelength that are ideal for transmission to


first up is a charming preprint by yuriy v. pershin and massimiliano di ventra on “ solving mazes with memristors : a massively - parallel approach. ” the moment i saw the title, i guessed the basic idea behind this work — and i was half right. the part i got right is that you fill the maze with a network of memristors, wiring them together along the corridors but making no connections that cross walls ; then you apply a voltage between the entrance and the exit nodes. current flows only through those nodes that lie along the solution path ; there ’ s no current in any of the dead - end branches. the current passing through the memristors along the path alters their resistance, creating a permanent record of the solution. but there ’ s a complication i missed. a memristor is a polar device : in one direction, current decreases the resistance ; but when current flows the other way, the resistance increases. this wouldn ’ t be a problem if you could just arrange the memristors so that all of them on the solution path are oriented the same way — but if you knew enough to do that, you ’ d already know a great deal about the solution. pershin and di ventra found a way around this problem ; for details, see their paper. ( hint : their strategy depends on the observation that any practical memristor has a maximum resistance, which can ’ t increase even when current flows the “ wrong ” way. ) the illustration above ( reproduced courtesy of pershin and di ventra ) shows the path identified by a ( simulated ) grid of memristors for a maze that has two solutions. the red nodes, with the lowest resistance, are common to both paths ; the blue and green sections differ in resistance because they differ in length. i suppose you could also solve mazes with ordinary resistors. just wire them up in the same way, run a healthy current from entrance to exit, and take a thermal infrared photograph. • • • my second postscript concerns an omission. a comment from mark myatt and a letter from james r. biard both point out that i neglected to mention an important predecessor of the memristor. this was the memistor — note the ever - so - slightly different spelling — invented in 1960 by bernard widrow and marcian e. hoff at stanford in connection with their adaline system of neural networks. the memist


december 7, 2012 3 : 32 pm humans navigate the world predominantly by sight. and yet there are colors and worlds we cannot see. infrared light — light whose wavelength is longer than our eyes can detect — exists all around us. but we do not see it. yet. scientists have engineered some proteins to “ see ” infrared. new scientist writes : the team created 11 different artificial protein structures and used spectrophotometry – a technology that compares the intensity of light going in and out of a sample – to identify which wavelengths they could absorb. chromophores within one particular protein were able to absorb red light with a wavelength of around 644 nanometres – tantalisingly close to the wavelength of infrared light, which starts at around 750 nanometres. this was unexpected since natural chromophores have a maximum absorption of around 560 nanometres. “ we were surprised, ” says borhan. “ but i still don ’ t know if we ’ re at the upper limit of absorption yet. i ’ ve speculated about 10 times and been proved wrong. ” just like we can ’ t see infrared, we can ’ t see all sorts of other wavelengths. causes of color explains : visible light is merely a small part of the full electromagnetic spectrum, which extends from cosmic rays at the highest energies down through the middle range ( gamma rays, x - rays, the ultraviolet, the visible, the infrared, and radio waves ) all the way to induction - heating and electric - power - transmission frequencies at the lowest energies. note that this is the energy per quantum ( photon if in the visible range ) but not the total energy ; the latter is a function of the intensity in a beam. if we could see in infrared, we ’ d be able to detect all sorts of things. well, there would be some problems. new scientist writes : if these proteins were present in the eye you would be able to see red light that is invisible to you now, says co - author james geiger, also at michigan state university. but since objects reflect a mixture of light, the world would not necessarily always appear more red. “ something that looked white before would now look green with your new super red vision, ” he says. artists have been keen on this idea for a little while now. scientist patrick degenaar and design studio superflux have created a concept video combining the edges of optogenetics and lasers. more from smithsonian. com sign up for our free email newsletter and receive the best


an odor is caused by one or more volatilized chemical compounds, generally at a very low concentration, that humans or other animals perceive by the sense of olfaction. odors are also commonly called scents, which can refer to both pleasant and unpleasant odors. the terms fragrance, scent, and aroma are used primarily by the food and cosmetic industry to describe a pleasant odor, and are sometimes used to refer to perfumes. in contrast, malodor, stench, reek, and stink are used specifically to describe unpleasant odors. the sense of smell gives rise to the perception of odors, mediated by the olfactory nerve. the olfactory receptor ( or ) cells are neurons present in the olfactory epithelium, a small patch of tissue in back of the nasal cavity. odor sensation depends on the concentration ( number of molecules ) available to the olfactory receptors. a single odorant stimulus type is typically recognized by multiple receptors, and different odorants are recognized by combinations of receptors, the patterns of neuron signals helping to identify the smell. odors can change due to environmental conditions, for example odors tend to be more distinguishable in cool dry air. for most untrained people, the process of smelling gives little information concerning the specific ingredients of an odor. their smell perception primarily offers information related to the emotional impact. brandecon safely neutralizes biological contamination by restoring the scene to its pre - incident state. we physically disassemble vital structural components of odor causing micro - organisms and eliminate odors at the molecular level.


lab graduate student matthew hirsch to build a prototype, hoping that we would have something to demonstrate within a few months. the grant proposal was rejected for administrative reasons ( i made a paperwork error! ), which meant we had to wait nearly a year to apply again. but those two years didn ' t yield any meaningful results, as our lab components weren ' t designed to be used the way we wanted. after nearly three years of experimental work, the team - - especially postdoctoral associate andreas velten and mit professor moungi bawendi, many students, and several collaborators - - cobbled together pieces of the puzzle and built a software program to create a first demonstration of looking around corners. very soon afterward, we could also start creating surreal movies of light in motion. we call this new imaging technology femto photography because we capture a segment of the image with a flashlight ( in this case, a laser pulse ) on for a few millionths of a billionth of a second ( or a few femtoseconds ) and an exposure time approaching a trillionth of a second. just how fast is femto photography? think of it this way : if we took one - thousandth of a second of footage from the femto camera video output and slowed it down to the speed of 30 seconds per frame - - the approximate speed of a standard tv broadcast - - it would take us a lifetime to watch. photographers know that at very short exposures and even at the most sensitive setting for dark scenes, we will record barely any light. so what about in a trillionth of a second? we actually record and average millions of photos to get enough light, each photo made to look the same via carefully timed synchronization with the light pulse. so even if our exposure time is indeed nearly a trillionth of a second, to get sufficient light we must take an average. thus, as of now, we can only record repeatable events, but this is not a fundamental limitation. unlike conventional cameras, our femto camera captures an image as one thin slice at a time of one - dimensional space using a " streak tube, " a laboratory instrument that is commonly used by chemists to study light passing through chemical samples. we then take hundreds of these narrow videos ( each shot at a slightly different angle ) and create a carefully synchronized, slow - motion composite of the light pulses. it takes about an hour to collect and aggregate the data ( view a demonstration of a light pulse as it travels through an ordinary coca


( each shot at a slightly different angle ) and create a carefully synchronized, slow - motion composite of the light pulses. it takes about an hour to collect and aggregate the data ( view a demonstration of a light pulse as it travels through an ordinary coca - cola bottle ). to see around the corner, we use femto photography to analyze scattered light. we bounce light off of visible parts into hidden parts and then measure the time and direction of returned light. usually the scattering of energy is considered a nuisance - - whether driving in fog or poor reception from a cell phone tower - - and most techniques either try to avoid it ( by turning on fog lights ) or reduce the impact of scattering ( by selecting energy for the phone only from direct paths ). in contrast, we exploit the scattering. for the camera, a laser pulse is fired at a wall, and the impact of hitting the wall causes the particles of light to scatter. some of the scattering particles return to the camera at different times. this is repeated about 60 times per image as the camera measures how long it takes for the light to travel back and where the particles land. an algorithm then crunches the data to reconstruct the hidden image. this technique even allows us to see a three - dimensional object such as a mock - up of running person. as exciting as this work is, don ' t look for this technology to be in practice tomorrow - - we ' re still years away from bringing this to market. but, we can already imagine multiple ways that it could have a significant, positive impact on our everyday lives. by allowing us to " see " around a corner, for example, this technology added to our cars could let us know if there ' s another vehicle approaching around a blind curve. it also could give us a new way to look deep inside our bodies without x - rays, or to look through a window into a burning building from a distance to see if anyone is left inside - - without risking a firefighter ' s life. when i gave a tedglobal talk on femto photography in june, i began with a reference to doc edgerton, a very popular mit professor of electrical engineering who, in 1964, wowed the world with an image of a bullet in midair, having just passed through an apple. he accomplished this by using a strobe light to freeze the action of the bullet at a millionth of a second. what we ' re talking about here - - the speed of light - - is a


, having just passed through an apple. he accomplished this by using a strobe light to freeze the action of the bullet at a millionth of a second. what we ' re talking about here - - the speed of light - - is a million times faster, and is opening the door to a complete rethinking of what we mean by, and can do with, photography. it is a first step toward a new world of imaging that far exceeds human ability, resynthesizing data and depicting it in ways that are within human comprehensibility. follow @ cnnopinion on twitter join us at facebook / cnnopinion the opinions expressed in this commentary are solely those of the author, ramesh raskar, who would like to thank his collaborators : moungi g. bawendi, professor, mit department of chemistry ; andreas velten and christopher barsi, postdoctoral associates, mit media lab ; everett lawson, otkrist gupta, nikhil naik, amy fritz, di wu, mit media lab ; matt o ' toole, kyros kutulakos, university of toronto ; diego gutierrez, belen masia, and elisa amoros, universidad de zaragoza ; kavita bala, shuang zhao, cornell university ; ashok veeraraghavan, rice university. ; thomas willwacher, harvard university.


scintillation is a flash of light produced in a transparent material by the passage of a particle ( an electron, an alpha particle, an ion, or a high - energy photon ). see scintillator and scintillation counter for practical applications. the process of scintillation is one of luminescence whereby light of a characteristic spectrum is emitted following the absorption of radiation. the emitted radiation is usually less energetic than that absorbed. scintillation is an inherent molecular property in conjugated and aromatic organic molecules and arises from their electronic structures. scintillation also occurs in many inorganic materials, including salts, gases, and liquids. scintillation of organic scintillators in organic molecules scintillation is a product of π - orbitals. organic materials form molecular crystals where the molecules are loosely bound by van der waals forces. the ground state of 12c is 1s2 2s2 2p2. in valence bond theory, when carbon forms compounds, one of the 2s electrons is excited into the 2p state resulting in a configuration of 1s2 2s1 2p3. to describe the different valencies of carbon, the four valence electron orbitals, one 2s and three 2p, are considered to be mixed or hybridized in several alternative configurations. for example, in a tetrahedral configuration the s and p3 orbitals combine to produce four hybrid orbitals. in another configuration, known as trigonal configuration, one of the p - orbitals ( say pz ) remains unchanged and three hybrid orbitals are produced by mixing the s, px and py orbitals. the orbitals that are symmetrical about the bonding axes and plane of the molecule ( sp2 ) are known as σ - electrons and the bonds are called σ - bonds. the pz orbital is called a π - orbital. a π - bond occurs when two π - orbitals interact. this occurs when their nodal planes are coplanar. in certain organic molecules π - orbitals interact to produce a common nodal plane. these form delocalized π - electrons that can be excited by radiation. the de - excitation of the delocalized π - electrons results in luminescence. the excited states of π - electron systems can be explained by the perimeter free - electron model ( platt 1949 ). this model is used for describing polycyclic hydrocarbons consisting of condensed systems of benzenoid rings in which no c atom belongs to more than


π - electron systems can be explained by the perimeter free - electron model ( platt 1949 ). this model is used for describing polycyclic hydrocarbons consisting of condensed systems of benzenoid rings in which no c atom belongs to more than two rings and every c atom is on the periphery. the ring can be approximated as a circle with circumference l. the wave - function of the electron orbital must satisfy the condition of a plane rotator : the corresponding solutions to the schrodinger wave equation are : where q is the orbital ring quantum number ; the number of nodes of the wave - function. since the electron can have spin up and spin down and can rotate about the circle in both directions all of the energy levels except the lowest are doubly degenerate. the above shows the π - electronic energy levels of an organic molecule. absorption of radiation is followed by molecular vibration to the s10 state. this is followed by a de - excitation to the s0 state called fluorescence. the population of triplet states is also possible by other means. the triplet states decay with a much longer decay time than singlet states, which results in what is called the slow component of the decay process ( the fluorescence process is called the fast component ). depending on the particular energy loss of a certain particle ( de / dx ), the " fast " and " slow " states are occupied in different proportions. the relative intensities in the light output of these states thus differs for different de / dx. this property of scintillators allows for pulse shape discrimination : it is possible to identify which particle was detected by looking at the pulse shape. of course, the difference in shape is visible in the trailing side of the pulse, since it ' s due to the decay of the excited states.


straightforward, for example : others require a little imagination to justify : still others are rather difficult to justify : question : what do you suppose " q " represents? you should be aware this is becoming more and more commonly used, and you should have the mindset of picking it up as you are exposed to it, rather than resisting. sequences are written with the n - terminal to the left and the c - terminal to the right. although r - groups of some amino acids contain amino and carboxyl groups, branched polypeptides or proteins do not occur. the sequence of monomer units in a macromolecule is called the primary structure of that macromolecule. each specific macromolecule has a unique primary structure. this concludes our consideration of the relationship between the structures of biological polymers and their monomer subunits. biosynthesis of these macromolecules will be covered in subsequent lectures. let ' s now begin to investigate the three - dimensional shapes of these macromolecules in solution and the forces responsible for these shapes. it turns out that the regular repeat of monomer units having the same size and the same bond angles leads to helical ( spiral ) polymers. if these helices can be stabilized by suitable intra - or intermolecular interactions, they will persist in solution, and will be available as elements of more complicated macromolecular structures. just what is a helix? a helical structure consists of repeating units that lie on the wall of a cylinder such that the structure is superimposable upon itself if moved along the cylinder axis. a helix looks like a spiral or a screw. a zig - zag is a degenerate helix. helices can be right - handed or left handed. the difference between the two is that : right - handed helices or screws advance ( move away ) if turned clockwise. helical organization is an example of secondary structure. these helical conformations of macromolecules persist in solution only if they are stabilized. what might carry out this stabilization? starch ( amylose ) exemplifies this structure. the starch helix is not very stable in the absence of other interactions ( iodine, which forms a purple complex with starch, stabilized the starch helix ), and it commonly adopts a random coil conformation in solution. in contrast, beta ( 1 - > 4 ) sequences favor linear structures. cellulose exemplifies this structure. cell


introduce this strain ) the strain of superhelicity can be relieved by forming a supercoil. the identical phenomenon occurs in retractable telephone headset cords when they get twisted. the twisted circular dna is said to be supercoiled. the supercoil is more compact. it is poised to be unwound, a necessary step in dna and rna synthesis. rna - - most rna is single stranded, but contains regions of self - complementarity. this is exemplified by yeast trna. there are four regions in which the strand is complementary to another sequence within itself. these regions are antiparallel, fulfilling the conditions for stable double helix formation. x - ray crystallography shows that the three dimensional structure of trna contains the expected double helical regions. large rna molecules have extensive regions of self - complementarity, and are presumed to form complex three - dimensional structures spontaneously. hydrophobic r - groups, as in leucine and phenylalanine, normally orient inwardly, away from water or polar solutes. polar or ionized r - groups, as in glutamine or arginine, orient outwardly to contact the aqueous environment. some amino acids, such as glycine, can be accommodated by aqueous or nonaqueous environments. the rules of solubility and the tendency for secondary structure formation determine how the chain spontaneously folds into its final structure. r - ch2 - sh + r ' - ch2 - sh + o2 = r - ch2 - s - s - ch2 - r ' + h2o2 ( under reducing conditions a disulfide bridge can be cleaved to regenerate the - sh groups. ) the disulfide bridge is a covalent bond. it strongly links regions of the polypeptide chain that could be distant in the primary sequence. it forms after tertiary folding has occurred, so it stabilizes, but does not determine tertiary structure. globular proteins are typically organized into one or more compact patterns called domains. this concept of domains is important. in general it refers to a region of a protein. but it turns out that in looking at protein after protein, certain structural themes repeat themselves, often, but not always in proteins that have similar biological functions. this phenomenon of repeating structures is consistent with the notion that the proteins are genetically related, and that they arose from one another or from a common ancestor. in looking at the amino acid sequences, sometimes there are


generally biologically inactive. here are some examples of quaternary structure. quaternary structure in proteins is the most intricate degree of organization considered to be a single molecule. higher levels of organization are multimolecular complexes. many different kinds of compound are found in conjugated proteins. a few examples are : nomenclature : the word " conjugated " is from the latin, cum = with and jugum = yoke. the protein and nonprotein moieties are yoked with one another ( like oxen ) to work together. sometimes other organic or inorganic compounds share metals with proteins. lipoproteins resemble micelles in some respects. the structure of lipoproteins typically includes the following features. their outer surface is coated with polar lipids, with protein intermingled. their interior is a region of randomly oriented neutral lipid. lipoproteins are usually much larger than two molecules across. the role of the polar lipid and protein on the surface is to solubilize the neutral lipid interior. protein interacts with the lipid of lipoproteins through amphipathic helices. alpha - helical regions of apolipoproteins have polar amino acids on one surface, and nonpolar ones on the opposite surface. the helix lies on the surface of the structure, with the polar groups oriented outward toward the water, and the nonpolar groups buried in the lipid. ( recall the four - helix bundle domains of proteins, in which contacts between helices involved hydrophobic residues at the contact points. ) consequence of charged surface : ( not unlike many proteins ) a tendency to stick to things. membrane proteins are lipoprotein - like in that they have nonpolar amino acids in strategic locations to permit interaction with the membrane lipid. proteins of the membrane surface may be structured like the apoproteins of lipoproteins, with amphipathic helices. some membrane proteins transverse the membrane. the region of the protein that is completely immersed in membrane should consist entirely of hydrophobic amino acids. a common structural motif to accomplish this is an alpha - helix consisting of at least 22 hydrophobic amino acyl groups. this makes an alpha - helix long enough to span a membrane. in arrays of membrane - spanning helices, helices in the interior of the array could be shorter. the problem of proline in transmembrane " helices : " mostly you find hydrophobic residues in transmemb


reflection : mirror, mirror on the wall reflection of light is how we ‘ see ’ things at all, regardless of color. light waves from the sun - - which, as it emanates its own light, is known as a luminous source — are reflected by all the objects in their path. all objects, that is, except those that allow light to pass through them, like glass, for example. these objects are called transparent, but the vast majority of matter obstructs light waves, and is called opaque. as these objects obstruct the path of light, it is forced to deviate, i. e. it is forced to change its path as it bounces of the obstruction. this “ bouncing off ” is known as reflection, and when light bounces off opaque objects and enters our eyes, which are then able to “ see ” things once the light sensed is processed and analyzed by the brain. for this demonstration of reflection of light, you will need a laser pointer, a room with no windows with a mirror on the wall and any type of spraying device ( ask mom for some room freshener or window cleaner or use deodorant! ). turn off the lights in the rooms. it is very important to make sure no light enters the room from outside. once it is nice and dark and creepy, take the pointer in your hand and point it towards the mirror. you will find that you can only see the red dot of the pointer at two places — where it hits the mirror, and where it is reflected onto the wall. note that these are the two opaque objects the light has encountered. now equip yourself with the spray can and spray away into the darkness, keeping the laser pointed at the mirror. what do you see? magic? not at all. you have just proved that sight depends on the reflection of light. the spray in the air obstructed the light from the laser, enabling you to see the path of the beam. this is exactly how we see our surroundings! the wall behind you is obstructing sun rays and reflecting them back towards your eyes, and eureka! you can see the wall! ( although that may not seem such a brilliant achievement on your resume ) reflection, however, does follow a set of principles, which explains why you and i when standing in the same position see exactly the same image ( given that our eye lenses are properly functional! ). it is easiest to demonstrate these laws using a plane mirror, as it is a leveled


set of principles, which explains why you and i when standing in the same position see exactly the same image ( given that our eye lenses are properly functional! ). it is easiest to demonstrate these laws using a plane mirror, as it is a leveled, flat surface. there are a few terms we use to describe reflection of light in optical physics. to make things simpler to understand, we choose to demonstrate the reflection of light by a single light ray, although there are thousands in reality. this ray of light which falls on a surface ( in this case, the mirror ) is known as the incident ray. at the point where the incident ray hits the surface, a perpendicular line to the surface is drawn, which we call the normal. the angle formed between the incident ray and the normal is called the angle of incidence. when the incident ray of light hits the mirror, it will be reflected in a specific direction. the resultant ray is known as the reflected ray. the angle that this particular ray forms with the normal is known as the angle of reflection. now that we ’ ve enhanced our vocabularies, let ’ s get down to the hands on part — we ’ re now going to try and prove the law of reflection. you ’ ll need a few supplies for this experiment. first, of course, a plane mirror, then a black surface, a dark room, a lamp, a few pins and a piece of black paper with a white colored pencil to write on it. first take the mirror and place it on top of the black paper, near the edge. you may need a stand for the mirror if it is not thick enough to support itself. with the white pencil, mark the position of the mirror carefully. set up the lamp opposite the mirror, and use thick paper to create a shield around the lamp. cut a slit in the shield so that only a thin line of light escapes. now turn off the lights and turn on the lamp. carefully mark the incident ray ’ s path with two pins on the black paper, and do the same for the reflected ray. then turn on the lights, remove the mirror and the lamp and use the white pencil to connect the pins so that two lines represent the incident and reflected ray. at the point where the incident ray intersects the line marking the position of the mirror, draw a perpendicular with a dotted line. this is your normal. identify the angle of incidence and the angle of reflection, and measure them with a protractor. what do you find? precisely. the angle


ball _ volume _ quad is a fortran90 program which investigates the behavior of a quadrature rule when it is applied to the characteristic function of the unit m - dimensional hyperball, which is a discontinuous function. the program integrates the function over the unit hypercube [ - 1, + 1 ] ^ m, where the spatial dimension m is arbitrary. the value of m is inferred from the user input quadrature rule information. the problem used as example input to the program works in m = 6 dimensions. in that case, the volume of the hypercube is 64 ; the volume of the hyperball is pi ^ 3 / 6, or about 5. 16771. because the integrand is discontinuous, any quadrature rule based on the idea of interpolation will probably be unable to do a good job. a family of quadrature rules, which rely on increasing the order of interpolation to improve accuracy, will probably get increasingly bad answers. by contrast, a basic monte carlo rule, which assumes nothing about the function, integrates this function just as well as it integrates most any other square - integrable function. ( that ' s both the strength and weakness of the blunt instrument we call monte carlo integration. ) the program assumes that the quadrature rule is defined by three text files. the computer code and data files described and made available on this web page are distributed under the gnu lgpl license. ball _ volume _ monte _ carlo, a fortran90 program which applies a monte carlo method to estimate the volume of the unit 6d sphere ; nintlib, a fortran90 library which numerically estimates integrals in multiple dimensions. quadrature _ rules, a dataset directory which contains sets of files that define quadrature rules over various 1d intervals or multidimensional hypercubes. stroud, a fortran90 library which defines quadrature rules for a variety of unusual areas, surfaces and volumes in 2d, 3d and multiple dimensions. test _ nint, a fortran90 library which defines integrand functions for testing multidimensional quadrature routines. testpack, a fortran90 library which defines a set of integrands used to test multidimensional quadrature. you can go up one level to the fortran90 source codes.


discovery of a new particle at 125 gev : physics, technology and cyberinfrastructure harvey b newman [ * ] high energy physics experiments at the large hadron collider ( lhc ) have begun to explore the fundamental properties of the forces and symmetries of nature, and the particles that compose the universe in a new energy range. in operation since 2009, the lhc experiments have distributed hundreds of petabytes of data worldwide. many thousands of physicists analyze tens of millions of collisions daily, leading to weekly publications of new results in peer - reviewed journals. the complexity and scope of the experimental detector facilities, the data acquisition, computing and software systems are all unparalleled in the scientific community. many petascale data samples of events are extracted daily from hundreds of trillions of proton - proton collisions and are explored by thousands of physicists and students located at hundreds of sites interlinked by high speed networks around the world searching for new physics signals, supported by many hundreds of computer scientists and engineers. in spite of these challenges both of the two largest experiments, cms and atlas, have optimized their analyses in many channels and produced groundbreaking results with a speed unprecedented in the field. the other major experiments at the lhc, alice and lhcb, also have made great strides and produced a vast array of new results in heavy ion and flavor physics respectively. figure 1 a candidate event for the decay of a higgs boson to two photons, one of the distinctive modes used for the discovery. a major milestone on july 4, 2012 was the simultaneous discovery by atlas and cms of the " higgs " or a " higgs - like " boson, culminating the 40 + year search for such a particle thought to be responsible for the masses of elementary particles. a typical candidate event in the two photon decay channel, illustrated in figure 2, is one of several decay modes analyzed for this discovery. one of the next major steps along this generation - long program of exploration is the determination of whether the new particle is the scalar ( spin zero, positive parity ) higgs boson of the standard model ( sm ) of particle physics, or an " impostor " with somewhat different properties ( spin and other quantum numbers, or its production and decay rates ) opening a new era of physics beyond the standard model. it is also possible that this is the sm higgs, but its production is modified by the existence of undiscovered heavy new particles that contribute to the


or its production and decay rates ) opening a new era of physics beyond the standard model. it is also possible that this is the sm higgs, but its production is modified by the existence of undiscovered heavy new particles that contribute to the gluon - fusion loop diagram that is the dominant production mode. irrespective of the discoveries to come, perhaps as early as this year as the experiments expect to triple their collected data, physicists already know that the sm is incomplete. it cannot explain the nature of dark matter, for example, nor can it hold at the energies that prevailed in the early universe. the leading candidate alternative theory is supersymmetry ( susy ), but direct searches have already ruled out much if not most of the susy parameter space accessible with 8 tev collisions, for the simplest susy models. and a " higgs " of mass 125 gev is difficult to produce in such models. it is nearly " too heavy " to be accommodated, and so particular models with relatively light third - generation susy particles, or other models with multiple higgs particle types or new yet - undiscovered scalar or vector ( spin 1 ) particles have been proposed. for the next decades, cms and atlas and the other lhc experiments will therefore continue to advance their search for a wide variety of new phenomena that could point the way to that more fundamental theory. in addition to the higher energies that will bring greater physics reach, when the lhc moves to 13 - 14 tev in 2015 and onward, there are many other keys to the search and future discoveries : more sophisticated algorithms to cope with the increasingly severe conditions of " pileup " from multiple interactions in a single crossing of proton bunches in the lhc collider and the increasing radiation exposure of the detector elements as the lhc luminosity and energy increase, and the means to cope with ever larger data volumes and more massive computing and networking needs. figure 2 : traditional hierarchical model of the first generation wlcg as the lhc went into operation. computing resources and data channels follow a tiered organization expressed in a grid paradigm, with strict service roles provided at and between each level of the hierarchy. this model has recently given way to a more agile data access and transport model with a richer set of wide area connections among sites in different layers and in different world regions. until now the computing challenges have been met successfully, after years of preparation and field - testing, by the worldwide lhc computing grid ( wlc


transport model with a richer set of wide area connections among sites in different layers and in different world regions. until now the computing challenges have been met successfully, after years of preparation and field - testing, by the worldwide lhc computing grid ( wlcg ), which provides access to the open science grid ( osg ), egi and nordugrid ; the lhc experiments have seamlessly combined the resources of more than a hundred computing centers around the globe. on average, a few hundred thousand jobs run simultaneously, accessing hundreds of petabytes of deployed storage worldwide and utilizing hundreds of gigabits / sec of network bandwidth using a hierarchical grid model depicted in figure 2. scientists access these computing resources transparently through distributed computing systems developed by their collaborations. these distributed software systems are highly flexible and are evolving to meet the needs of thousands of physics users, in many cases by investing them with increasing degrees of intelligence and an increased level of communications performance. even though the distributed computing model for the lhc experiments has proven to be extraordinarily successful, we anticipate that the software stacks will need to be replaced within the next few years. the current system will not scale to the complexity and challenges of exabyte - scale data. human resources needed to operate the hardware and software infrastructure cannot be linearly scaled tenfold along with the data. there are still many barriers to efficient data intensive scientific computing that need to be overcome. the revolutionary changes for the new distributed computing model need to start immediately, to be ready for lhc data - taking at the design energy in 2015 and beyond. sophisticated and robust statistical methods have been developed and used to tease out and fairly gauge the appearance of significant new physics signals from large and potentially overwhelming backgrounds. these so - far - successful methods will not scale as needed in the latter part of this decade, particularly if and when the first experimental hints of a more fundamental theory of nature break. if signs of a new theory do emerge, then rapidly finding and characterizing it, in a vast space of candidate models with millions of possible decay chains and billions of possible parameter sets, each to be compared in many dimensions to massive volumes of data, will require new artificially intelligent methods and new orders of magnitude of computational power. the output of this program will be a new set of predictions to be tested through a new multiyear round of targeted analyses, in order to pin down the new theory. along the way, cms and atlas and the other detectors will undergo major upgrades, which together with larger data


be a new set of predictions to be tested through a new multiyear round of targeted analyses, in order to pin down the new theory. along the way, cms and atlas and the other detectors will undergo major upgrades, which together with larger data volumes and higher collision energies this will provide greater reach in the search for new physics as well as fertile ground to train the next generation of scientists and engineers skilled in one or many disciplines : in new methods of signal extraction and background rejection ; in new methods of hypothesis testing and model selection ( finding that more fundamental theory in a vast theory and in parameter space ) ; learning to create, operate and harness a new level and scale of grid - based systems and the dynamic networks, monitoring systems and control planes that underpin them ; and in developing a new generation of collaboration systems and learning how to use them effectively for cooperative daily work on multiple scales, from small groups working round the clock to daily working meetings to weekly collaboration meetings involving hundreds of sites. [ * ] i have been privileged to contribute to the lhc program, and its successes including the recent " discovery milestone " in many ways. our group in cms works on higgs searches, the search for supersymmetry and many other forms of exotic new physics, as well as the calorimeters that precisely measure electrons, photons, jets and missing energy transverse to the beam line, and the trigger that makes online decisions on which events to keep in real time. beyond that our caltech team has created or made central contributions to major elements of " cyberinfrastructure " including : the initiation of international networking for hep from 1982 on, and us lhcnet since 1995 ; the lhc worldwide computing model from 1998, the evo ( enabling virtual organizations ) global collaboration system since 1994 ; the monalisa monitoring and control system since 2000 ; and the nsf - funded dynes dynamic circuit network project being deployed at 50 campuses as well as the lhc open network environment lhcone program since 2010. harvey newman ( email @ example. com ) is a professor at caltech, a high - energy physics experimentalist and past chair of the fip. he is also engaged in work on digital divide issues in many regions of the world. disclaimer - the articles and opinion pieces found in this issue of the aps forum on international physics newsletter are not peer refereed and represent solely the views of the authors and not necessarily the views of the aps.


environment surrounding these stars is clean of gas that would affect the propagation of radio waves from the pulsar to the observer. these properties ensure that the observable effects of general relativity are stronger within these systems without the complicating factor of a solar wind or accretion disk that can alter the propagation of light. but the crucial feature that makes these systems valuable for testing general relativity is that the radio pulsar is a superb clock. in accurately measuring time over years, pulsars surpass atomic clocks in accuracy. this feature allows astronomers to measure precisely the changes in light travel time from earth to the pulsar as it orbits its companion. two of the basic tests of general relativity within our solar system — the modification of the propagation time of light by the gravitational field and the perihelion drift of mercury — can be performed with the double - neutron - star double pulsars. these effects, along with the gravitational redshift and the doppler shift of radio waves from the pulsar and the propagation time across the binary system, appear to observers as changes in the arrival times of radio pulses from the pulsar. the modification of the pulse arrival time is quite small, of order ( gm / ac2 ) 3 / 2 ( a is the semimajor axis ), which is of order 10−9 for psr b1913 + 16. despite being 3 orders of magnitude smaller than the shift in arrival time caused by the gravitational redshift and the doppler shift, which are of order gm / ac2, the effect is seen by observers. the other test, the periastron drift of a binary pulsar ' s orbit, is a rather large effect, because while the shift per orbit is only of order gm / ac2 = 10−6, the binary pulsar completes of order 1, 000 orbits per year. the periastron of psr b1913 + 16 drifts by 4 degrees per year. the periastron drift of a binary pulsar ' s orbit is much more impressive than that of mercury ' s orbit. beyond providing better tests of general relativistic effects seen in our own solar system, binary pulsars provide us with our only unambiguous confirmation of gravitational radiation. all orbiting systems, whether galaxies, planetary systems, or binary stars, radiate gravitational waves. the gravitational waves carry energy and angular momentum from a system, causing the orbits within the system to decay. in most instances


enlightenmentarticle free pass enlightenment, french siecle des lumieres ( “ age of the enlightened ” ), german aufklarung, a european intellectual movement of the 17th and 18th centuries in which ideas concerning god, reason, nature, and man were synthesized into a worldview that gained wide assent and that instigated revolutionary developments in art, philosophy, and politics. central to enlightenment thought were the use and the celebration of reason, the power by which man understands the universe and improves his own condition. the goals of rational man were considered to be knowledge, freedom, and happiness. a brief treatment of the enlightenment follows. for full treatment, see europe, history of : the enlightenment. the powers and uses of reason had first been explored by the philosophers of ancient greece, who discerned in the ordered regularity of nature the workings of an intelligent mind. rome adopted and preserved much of greek culture, notably including the ideas of a rational natural order and natural law. amid the turmoil of empire, however, a new concern arose for personal salvation, and the way was paved for the triumph of the christian religion. christian thinkers gradually found uses for their greco - roman heritage. the system of thought known as scholasticism, culminating in the work of thomas aquinas, resurrected reason as a tool of understanding but subordinated it to spiritual revelation and the revealed truths of christianity. the intellectual and political edifice of christianity, seemingly impregnable in the middle ages, fell in turn to the assaults made on it by humanism, the renaissance, and the protestant reformation. humanism bred the experimental science of francis bacon, nicolaus copernicus, and galileo and the mathematical rigour of rene descartes, g. w. leibniz, and sir isaac newton. the renaissance rediscovered much of classical culture and revived the notion of man as a creative being, while the reformation, more directly but in the long run no less effectively, challenged the monolithic authority of the roman catholic church. for luther as for bacon or descartes, the way to truth lay in the application of human reason. received authority, whether of ptolemy in the sciences or of the church in matters of the spirit, was to be subject to the probings of unfettered minds. the successful application of reason to any question depended on its correct application — on the development of a methodology of reasoning that would serve as its own guarantee of validity. such a methodology was most spectacularly achieved in the sciences and mathematics, where the logics


field that can be measured and that can influence other objects at a distance. electrostatic discharge is defined as the transfer of charge between bodies at different electrical potentials. electrostatic discharge can change the electrical characteristics of a semiconductor device, degrading or destroying it. electrostatic discharge also may upset the normal operation of an electronic system, causing equipment malfunction or failure. another problem caused by static electricity occurs in clean rooms. charged surfaces can attract and hold contaminants, making removal from the environment difficult. when attracted to the surface of a silicon wafer or a device ' s electrical circuitry, these particulates can cause random wafer defects and reduce product yields. controlling electrostatic discharge begins with understanding how electrostatic charge occurs in the first place. electrostatic charge is most commonly created by the contact and separation of two similar or dissimilar materials. for example, a person walking across the floor generates static electricity as shoe soles contact and then separate from the floor surface. an electronic device sliding into or out of a bag, magazine or tube generates an electrostatic charge as the device ' s case and / or metal leads make multiple contacts and separations with the surface of the container. while the magnitude of electrostatic charge may be different in these examples, static electricity is indeed generated. creating electrostatic charge by contact and separation of materials is known as " triboelectric charging. " it involves the transfer of electrons between materials. the atoms of a material with no static charge have an equal number of positive ( + ) protons in their nucleus and negative ( - ) electrons orbiting the nucleus. in figure 1, material " a " consists of atoms with equal numbers of protons and electrons. material b also consists of atoms with equal ( though perhaps different ) numbers of protons and electrons. both materials are electrically neutral. when the two materials are placed in contact and then separated, negatively charged electrons are transferred from the surface of one material to the surface of the other material. which material loses electrons and which gains electrons will depend on the nature of the two materials. the material that loses electrons becomes positively charged, while the material that gains electrons is negatively charged. this is shown in figure 2. the actual level of charge is measured in coulombs. commonly, however, we speak of the electrostatic potential on an object, which is expressed as voltage. this process of material contact, electron transfer and separation is really a more complex mechanism than described here. the amount of charge created by triboelectric


, however, we speak of the electrostatic potential on an object, which is expressed as voltage. this process of material contact, electron transfer and separation is really a more complex mechanism than described here. the amount of charge created by triboelectric charging is affected by the area of contact, the speed of separation, relative humidity, and other factors. once the charge is created on a material, it becomes an " electrostatic " charge ( if it remains on the material ). this charge may be transferred from the material, creating an electrostatic discharge, or esd, event. an electrostatic charge also may be created on a material in other ways such as by induction, ion bombardment, or contact with another charged object. however, triboelectric charging is the most common. material characteristics - how they affect static charge virtually all materials, including water and dirt particles in the air, can be triboelectrically charged. how much charge is generated, where that charge goes, and how quickly, are functions of the materials ' electrical characteristics. a material that prevents or limits the flow of electrons across its surface or through its volume is called an insulator. insulators have an extremely high electrical resistance. a considerable amount of charge can be generated on the surface of an insulator. because an insulative material does not readily allow the flow of electrons, both positive and negative charges can reside on insulative surface at the same time, although at different locations. the excess electrons at the negatively charged spot might be sufficient to satisfy the absence of electrons at the positively charged spot. however, electrons cannot easily flow across the insulative material ' s surface, and both charges may remain in place for a very long time. a conductive material, because it has low electrical resistance, allows electrons to flow easily across its surface or through its volume. when a conductive material becomes charged, the charge ( i. e., the deficiency or excess of electrons ) will be uniformly distributed across the surface of the material. if the charged conductive material makes contact with another conductive material, the electrons will transfer between the materials quite easily. if the second conductor is attached to an earth grounding point, the electrons will flow to ground and the excess charge on the conductor will be " neutralized. " electrostatic charge can be created triboelectrically on conductors the same way it is created on insulators. as long as the conductor is isolated from other conductors or ground, the static charge will remain on the conductor


calculating quantum vacuum forces in nanostructures february 7, 2013 contact : vladimir aksyuk one of the surprising predictions of quantum mechanics is that uncharged conductors can attract each other over small distances, even in empty space. while the resulting “ casimir force ” has been accurately measured and calculated for simple flat conductors, researchers from the department of energy, indiana university - purdue university indianapolis, and the nist center for nanoscale science and technology have solved the much more complicated problem of calculating this force between metal plates with complicated periodic nanoscale structures on their surfaces. * this type of surface nanostructuring is currently being explored in order to control the casimir force in microscopic mechanical sensors, actuators, and electrical relay devices. the casimir force has been notoriously difficult to calculate for complicated structures because an infinite number of electromagnetic quantum vacuum fluctuations have to be taken into account. previous methods took weeks of computer time to carefully combine the results from numerically solving maxwell ’ s equations ‑ a standard set of equations describing the physics of electromagnetism ‑ thousands of times, and were prone to numerical errors. the researchers have now analytically pre - calculated a series of eigenmodes, or exact solutions for specific cases, that can be combined much more simply to produce the force for any particular periodic nanostructure. this analytical calculation also gives simple insight into how the force behaves in various important situations. the researchers expect the analytical techniques they have developed will have broader applications for calculating other forces induced by fluctuations, including thermal emissions and near - field heat transfer. they are now applying these techniques to understand the results of recent casimir force experiments on nanostructured surfaces. nist publication database journal web site


coming soon : tabletop molecular movies november 5, 2012 contact : joel ullom one of the most urgently sought - after goals in modern science is the ability to observe the detailed dynamics of chemical reactions as they happen – that is, on the spatial scale of molecules, atoms, and electrons, and on the time scale of picoseconds or even shorter. that is a formidable challenge. but as a successful 2010 proposal for an ambitious nist project explains, “ it is critical to the development of next - generation nanomaterials ranging from industrial catalysts to renewable energy devices that harvest sunlight, store electricity, and make hydrogen and other fuels from splitting water or recycling carbon dioxide. ” now a group of researchers from that ongoing project has devised and demonstrated a highly unusual, compact, and relatively inexpensive x - ray source for an imaging system that may soon be employed to produce the kind of “ molecular movies ” that scientists and engineers need. “ i believe that we are going to be able to measure interatomic distances to sub - angstrom accuracy [ 1 angstrom = 10 - 10 m ], ” says joel ullom of the quantum devices group in pml ’ s quantum electronics and photonics division, principal investigator for the collaborative project and head of the team that created the x - ray source. “ and we will be able to watch atomic - scale activity with picosecond resolution during chemical reactions. ” “ joel ' s x - ray source is a novel table - top system that creates picosecond pulses of x - rays, a holy grail among scientists who are trying to elucidate the precise, real - time motion of electrons, atoms, and molecules, ” says marla dowell, leader of pml ’ s sources and detectors group. “ eventually, this table - top approach will be able to compete head - to - head with far more expensive and elaborate synchrotron techniques. ” the operating principle is extraordinary. it begins with a pulsed infrared ( ir ) laser beam, which is split into two parts. the first part is used to photoexcite a material under study, starting a chemical reaction. the second part is routed into a vacuum chamber, above which is a water reservoir that has a tiny aperture leading to the chamber. water is drawn into the chamber in a 0. 2 mm wide jet ( see figure, above right ) and the laser beam is focused onto the streaming water jet target. “ this ignites a plasma on the target, ” ullom says, “ and some


take a gander at this cube. it will probably look weird because your visual system can ’ t decide how to perceive it. this persistent ambiguity is called visual rivalry, and in the case of the necker cube, it results from spatial conflict, or when two objects strike the same place in our retina. most scientists think visual rivalry requires spatial conflict, but the authors of a recent psychological science study have shown that this assumption is not necessarily true. using non - retinal reference frames, which are objects ( e. g., mountains in the background ) that make the world appear stable even when our eyes are moving, the study authors created a scenario in which visual rivalry could occur without spatial conflict. they showed participants different arrangements of four dots placed on three larger white discs ( the reference frames ) that switched back and forth. depending on the scenario, the dots moved either with the discs or in opposition to the discs. after viewing this “ motion quartet, ” participants were asked to indicate whether the dots had moved horizontally or vertically. the researchers found that when there was no spatial conflict between the dots ( i. e., the dots were not positioned to hit the same position on the retina ), the moving discs made it difficult to determine how the dots were moving. with the identification of this new mechanism, the study authors believe that further progress can be made in determining the specific parts of the visual system that contribute to resolving visual conflicts. read “ visual rivalry without spatial conflict ” online. leave a comment below and continue the conversation.


riding the atomic waves : with the magic of quantum mechanics, an atom goes two ways at once. physicists have added a new trick to their experimental repertoire. in their latest feat, called atom interforometry, they paradoxically divide and recombine re · com · bine to undergo or cause genetic recombination ; form new combinations. single atoms, aided by a beautiful but enigmatic assistant known as quantum mechanics quantum mechanics : see quantum theory. branch of mathematical physics that deals with atomic and subatomic systems. it is concerned with phenomena that are so small - scale that they cannot be described in classical terms, and it is. four teams have recently performed atom interferometry, each using a different technique to accomplish this same bit of seeming magic. unlike real magicians, however, these physicists eagerly explain the mysteries of their craft. in the past few months, all four groups have shared the secrets of their atom interferometers. interferometers are highly sensitive adj. 1. highly sensitive - readily affected by various agents ; " a highly sensitive explosive is easily exploded by a shock " ; " a sensitive colloid is readily coagulated " instrument that provide exact measurements of extremely small distances and physical properties such as wavelength. scientists use them mainly for experimentation, but the devices have several commercial applications as well. laser interferometers, for instance, play a vital part in advanced gyroscopes. in the past, interferometers accomplished their precise measurements by manipulating electrons, neutrons or light. researchers have now made even more sensitive instruments that extend those manipulations to atoms. in the paradoxical world of quantum mechanics, an atom - - like a photon - - can be thought of as both a particle and a wave. but atoms have a great advantage over photons when it comes to interferometry. the wavelenth of an atom, known as its de broglie de broglie. for persons thus named use broglie. wavelenth, is based on its momentum and can be 10, 000 times shorter than that of visible light. the smaller the wavelength used, the greater an interferometer ' s precision. with the new atom interferometers, physicists plan to conduct difficulties tests of atomic properties, general relatively and quantum mechanics. one such device shows promise for measuring gravitational acceleration in physics, gravitational acceleration is the acceleration of an object caused by the force of gravity from another object. an interesting fact is that any object will


difficulties tests of atomic properties, general relatively and quantum mechanics. one such device shows promise for measuring gravitational acceleration in physics, gravitational acceleration is the acceleration of an object caused by the force of gravity from another object. an interesting fact is that any object will accelerate towards a large object at the same rate, regardless of the mass of the object. with record - breaking precision. the key to all types of interferometry lies in quantum mechanics ' wave - particle duality wave - particle duality principle that subatomic particles possess some wavelike characteristics, and that electromagnetic waves, such as light, possess some particlelike characteristics.. the instruments take a particle and break the single wave that represents it into multiple ( usually two ) distinct components. in an atom interferometer, for example, " each atom has been split and is going both ways at once, " explains david e. pritchard of the massachusetts institute of technology massachusetts institute of technology, at cambridge ; coeducational ; chartered 1861, opened 1865 in boston, moved 1916. it has long been recognized as an outstanding technological institute and its sloan school of management has notable programs in business, in cambridge. yet an observer attempting to witness this counterintuitive coun · ter · in · tu · i · tive contrary to what intuition or common sense would indicate : " scientists made clear what may at first seem counterintuitive, that the capacity to be pleasant toward a fellow creature is... split will see only one wave - - a phenomenon arising from the quirks of quantum mechanics. with quantum mechanics, notes pritchard " you beat your intuition into submission. " after traveling their divergent paths, the wave components recombine at an awaiting detector. if their path difference is exactly the particle ' s wavelength or an integer multiple of it, the waves are " in phase " and harmoniously merge with each other - - an effect known as constructive interference. in other words adv. 1. in other words - otherwise stated ; " in other words, we are broke " put differently, the crests and troughs of each wave coincide and reinforce one another. but at other spots on the detector, the path difference amounts to only a fraction of the wavelength, and the components are out of phase. the waves still recombine, but with destructive interference. at these places, where the merging waves are out of alignment, probability dictates that fewer particles will appear. ligth interferometers, for example, often produce an


. the waves still recombine, but with destructive interference. at these places, where the merging waves are out of alignment, probability dictates that fewer particles will appear. ligth interferometers, for example, often produce an interference pattern interference pattern an overall pattern that results when two or more waves interfere with each other, generally showing regions of constructive and of destructive interference. consisting of a series of dark strips, where few photons emerge, and light strips, where many photons are detected. atom interferometers show similar patterns based on the number of atoms at each spot on the detector. in effect, " you get ligth and dark spots of atoms, " pritchard says. careful examination of these interference patterns can reveal the minute fraction of a wavelength by which the atom ' s paths differed ( the phase shift ) and can even reveal the particle ' s wavelength. pritchard ' s team and a german group unveiled their atom interferometers in the may 27 physical review letters physical review letters is one of the most prestigious journals in physics. since 1958, it has been published by the american physical society as an outgrowth of the physical review.. the german researchers, led by jurgen mlynek of the university of konstanz the university of konstanz ( german : universitat konstanz ) is a university in the city of konstanz in baden - wurttemberg, germany. it was founded in 1966, and the main campus on the gießberg was opened in 1972., created their device by adapting the classic double - slit experiment “ slit experiment ” redirects here. for other uses, see diffraction. in the double - slit experiment, light is shone at a solid thin plate that has two slits cut into it. a photographic plate is set up to record what comes through those slits. of english physicist thomas young noun 1. thomas young - british physicist and egyptologist ; he revived the wave theory of light and proposed a three - component theory of color vision ; he also played an important role in deciphering the hieroglyphics on the rosetta stone ( 1773 - 1829 ) young, who in 1802 used photons to demonstrate interference. in mlynek ' s atom interferometer, a supersonic beam of helium atoms passes through a 2 - micrometer - wide opening in a thin gold foil. this " spreads " the atom into a wider wave before it travels through two smaller slits. while passing


' s atom interferometer, a supersonic beam of helium atoms passes through a 2 - micrometer - wide opening in a thin gold foil. this " spreads " the atom into a wider wave before it travels through two smaller slits. while passing through the two smaller slits, the waves scatter again and eventually recombine into the original atom ' s single wave. mlynek and co - worker olivier carnal carnal adjective referring to the flesh, to baser instincts, often referring to sexual “ knowledge ” suggest the device can resolve a phase shift equal to 0. 053 of the atom ' s wavelength. since an atom ' s wavelength is known, the researchers can translate that phase shift into the minute distance by which the wave paths differed. pritchard ' s device - - which uses a thin silicon - nitride membrane with a series of extremely fine slits cut into it for a diffraction grating - - is even more sophisticated. a beam of sodium atoms must travel through three of these diffraction gratings before yielding an interference pattern. this instrument can resolve a phase shift of 0. 016 wavelength, a significant improvement over mlynek ' s device, pritchard says. moreover, the use of sodium allows additional precision, since sodium atoms are heavier than helium atoms and therefore have a shorter de broglie wavelength de broglie wavelength the wavelength γ = h / p associated with a beam of particles ( or with a single particle ) of momentum p ; h = 6. 626 × 1034 joule - second is planck ' s constant.. that precision wasn ' t easy to achieve. to preserve the instrument ' s sensitivity, the mit mit - massachusetts institute of technology researchers had to incorporate a number of features merely to eliminate vibrations and maintain the alignment of the three diffraction gratings. they even included a laser interferometers to continuously monitor the gratings ' alignment. physicists have long used atoms - - in the form of solid objects such as diffraction gratings, mirrors and lenses - - to manipulate light. some of the new interferometers do just the opposite : light - - in the form of laser pulses - - manipulates atoms. in the july 8 physical review letters, two groups describe atom interferometers that accomplish this reversal. in one such device, a calcium atomic beam atomic beam or atom laser is special case of particle beam ; it is the collimated flux ( beam ) of neutral atoms. the


, two groups describe atom interferometers that accomplish this reversal. in one such device, a calcium atomic beam atomic beam or atom laser is special case of particle beam ; it is the collimated flux ( beam ) of neutral atoms. the imaging systems using the slow atomic beams can use the fresnel zone plate ( fresnel diffraction lens ) of a fresnel diffraction mirror as focusing element. is divided into four wave paths by two laser beams perpendicular to the atoms. a second pair of lasers, aimed in the opposite direction of the first pair of laser beams, redirects the waves to either of two detection areas, where the atoms are counted. both detectors reveal interference patterns, although chance determines which detector will tally a given atom. this complex instrument is sensitive to rotational changes, report jurgen helmcke of the federal agency for technical and scientific research in braunschweig, germany, and his colleagues. by rotating their instrument on a turntable at different speeds, the researchers can influence the paths of the wave components, thereby shifting the resulting interference patterns. the laser gyroscopes on many of today ' s airplanes work by a similar principle, but theory indicates that an atom - based system would offer 10 billion times as much sensitivity, useful for general - relatively experiments. at stanford university stanford university, at stanford, calif. ; coeducational ; chartered 1885, opened 1891 as leland stanford junior univ. ( still the legal name ). the original campus was designed by frederick law olmsted. david starr jordan was its first president., steven chu steven chu ( chinese : 文 ; pinyin : zhu diwen ), born 1948 in st. louis, missouri, is an american experimental physicist. and his colleagues manipulate atoms of a slightly different sort. while other research teams work with fast - moving atomic beams, chu slowly pumps laser - cooled atoms through his interferometer interferometer : see interference under interference as a scientific tool. see also virtual telescope. an instrument that measures the wavelengths of light and distances. with an " atomic fountain " ( sn : 8 / 19 / 89, p. 117 ). the languid atoms spend up to 0. 5 second within the device - - an important consideration in measurements of minute effects. " the sensitivity [ of an interferometer ] increases when you use slow atoms, " chu explains. pritchard agrees and says he plans to try slower atoms in his own devices. he adds, however, that the " brightness


minute effects. " the sensitivity [ of an interferometer ] increases when you use slow atoms, " chu explains. pritchard agrees and says he plans to try slower atoms in his own devices. he adds, however, that the " brightness " of such sources needs improvement. chu ' s fountain can deliver atoms much more slowly than an atomic beam, he says, but it cannot yet match the beam ' s intensity - - the number of atoms delivered. in chu ' s interferometer, lasers not only precool pre · cool tr. v. pre · cooled, pre · cool · ing, pre · cools to reduce the temperature of ( produce or meat, for example ) by artificial means before packaging or shipping. atoms but also lie at the heart of the device. two lasers - - one on each side of the atom ' s path - - provide an initial pulse that splits the atom into a super - position of two different energy states. the higher energy state, recoiling from the laser pulse, moves away from the lower energy state so that the atom appears to be in two places at once. a second pulse reverses the action, causing the atom to reconverge. a third laser pulse ultimately reads the interference pattern. for another experiment, chu directed the lasers along, rather than across, the path of the crawling atoms. as a result, an atom ' s components actually travel the same path at slightly different speeds, so that they move apart from each other in space. this setup should allow the most precise measurement yet of a single atom ' s gravitational acceleration, potentially achieving a resolution of 1 part in 10 billion, the stanford researchers assert. with further refinement, atom interferometers could compete with the laser technology now used in gyroscopes, says pritchard. but these new devices will shine their brightest in probing the minute details of physics, he maintains. for experimental physicists, improving measurements by a single decimal place can represent a life ' s goal - - a goal now achievable with atom interferometers. this added precision should help to test the predictions of general relatively and might finally lay to rest the controversial issue of a fifth force, physicists say. it might also dispel any remaining doubts about the charge neutrality of atoms. to confirm atomic neutrality, experimenters would apply an electric field to only one wave component of an atom. if the atom is not neutral, the field will create a discernible change in the interference pattern.


semiconductor device fabrication semiconductor device fabrication is the process used to create chips, the integrated circuits that are present in everyday electrical and electronic devices. it is a multiple - step sequence of photographic and chemical processing steps during which electronic circuits are gradually created on a wafer made of pure semiconducting material. silicon is the most commonly used semiconductor material today, along with various compound semiconductors. the entire manufacturing process from start to packaged chips ready for shipment takes six to eight weeks and is performed in highly specialized facilities referred to as fabs. a typical wafer is made out of extremely pure silicon that is grown into mono - crystalline cylindrical ingots ( boules ) up to 300 mm ( slightly less than 12 inches ) in diameter using the czochralski process. these ingots are then sliced into wafers about 0. 75 mm thick and polished to obtain a very regular and flat surface. once the wafers are prepared, many process steps are necessary to produce the desired semiconductor integrated circuit. in general, the steps can be grouped into two areas : - front end processing - back end processing in semiconductor device fabrication, the various processing steps fall into four general categories : deposition, removal, patterning, and modification of electrical properties. - deposition is any process that grows, coats, or otherwise transfers a material onto the wafer. available technologies consist of physical vapor deposition ( pvd ), chemical vapor deposition ( cvd ), electrochemical deposition ( ecd ), molecular beam epitaxy ( mbe ) and more recently, atomic layer deposition ( ald ) among others. - removal processes are any that remove material from the wafer either in bulk or selective form and consist primarily of etch processes, both wet etching and dry etching such as reactive ion etch ( rie ). chemical - mechanical planarization ( cmp ) is also a removal process used between levels. - patterning covers the series of processes that shape or alter the existing shape of the deposited materials and is generally referred to as lithography. for example, in conventional lithography, the wafer is coated with a chemical called a “ photoresist ”. the photoresist is exposed by a “ stepper ”, a machine that focuses, aligns, and moves the mask, exposing select portions of the wafer to short wavelength light. the unexposed regions are washed away by a developer solution. after etching or other processing, the remaining photoresist is removed by plasma ashing. - modification of electrical properties has


exposing select portions of the wafer to short wavelength light. the unexposed regions are washed away by a developer solution. after etching or other processing, the remaining photoresist is removed by plasma ashing. - modification of electrical properties has historically consisted of doping transistor sources and drains originally by diffusion furnaces and later by ion implantation. these doping processes are followed by furnace anneal or in advanced devices, by rapid thermal anneal ( rta ) which serve to activate the implanted dopants. modification of electrical properties now also extends to reduction of dielectric constant in low - k insulating materials via exposure to ultraviolet light in uv processing ( uvp ). many modern chips have eight or more levels produced in over 300 sequenced processing steps. front end processing " front end processing " refers to the formation of the transistors directly on the silicon. the raw wafer is engineered by the growth of an ultrapure, virtually defect - free silicon layer through epitaxy. in the most advanced logic devices, prior to the silicon epitaxy step, tricks are performed to improve the performance of the transistors to be built. one method involves introducing a " straining step " wherein a silicon variant such as " silicon - germanium " ( sige ) is deposited. once the epitaxial silicon is deposited, the crystal lattice becomes stretched somewhat, resulting in improved electronic mobility. another method, called " silicon on insulator " technology involves the insertion of an insulating layer between the raw silicon wafer and the thin layer of subsequent silicon epitaxy. this method results in the creation of transistors with reduced parasitic effects. front end surface engineering is followed by : growth of the gate dielectric, traditionally silicon dioxide ( sio2 ), patterning of the gate, patterning of the source and drain regions, and subsequent implantation or diffusion of dopants to obtain the desired complementary electrical properties. in memory devices, storage cells, conventionally capacitors, are also fabricated at this time, either into the silicon surface or stacked above the transistor. once the various semiconductor devices have been created they must be interconnected to form the desired electrical circuits. this " back end of line " ( beol – the latter portion of the front end of wafer fabrication, not to be confused with " back end " of chip fabrication which refers to the package and test stages ) involves creating metal interconnecting wires that are isolated by insulating dielectrics. the


of the front end of wafer fabrication, not to be confused with " back end " of chip fabrication which refers to the package and test stages ) involves creating metal interconnecting wires that are isolated by insulating dielectrics. the insulating material was traditionally a form of sio2 or a silicate glass, but recently new low dielectric constant materials are being used. these dielectrics presently take the form of sioc and have dielectric constants around 2. 7 ( compared to 3. 9 for sio2 ), although materials with constants as low as 2. 2 are being offered to chipmakers. historically, the metal wires consisted of aluminium. in this approach to wiring often called " subtractive aluminium ", blanket films of aluminium are deposited first, patterned, and then etched, leaving isolated wires. dielectric material is then deposited over the exposed wires. the various metal layers are interconnected by etching holes, called " vias, " in the insulating material and depositing tungsten in them with a cvd technique. this approach is still used in the fabrication of many memory chips such as dynamic random access memory ( dram ) as the number of interconnect levels is small, currently no more than four. more recently, as the number of interconnect levels for logic has substantially increased due to the large number of transistors that are now interconnected in a modern microprocessor, the timing delay in the wiring has become significant prompting a change in wiring material from aluminium to copper and from the silicon dioxides to newer low - k material. this performance enhancement also comes at a reduced cost via damascene processing that eliminates processing steps. in damascene processing, in contrast to subtractive aluminium technology, the dielectric material is deposited first as a blanket film and is patterned and etched leaving holes or trenches. in " single damascene " processing, copper is then deposited in the holes or trenches surrounded by a thin barrier film resulting in filled vias or wire " lines " respectively. in " dual damascene " technology, both the trench and via are fabricated before the deposition of copper resulting in formation of both the via and line simultaneously, further reducing the number of processing steps. the thin barrier film, called copper barrier seed ( cbs ), is necessary to prevent copper diffusion into the dielectric. the ideal barrier film is effective, but is barely there. as the presence of excessive barrier film competes