Showing papers on "Scattering published in 2009"
TL;DR: It is demonstrated that, like their electronic counterparts, electromagnetic CESs can travel in only one direction and are very robust against scattering from disorder; it is found that even large metallic scatterers placed in the path of the propagating edge modes do not induce reflections.
Abstract: One of the most striking phenomena in condensed-matter physics is the quantum Hall effect, which arises in two-dimensional electron systems subject to a large magnetic field applied perpendicular to the plane in which the electrons reside. In such circumstances, current is carried by electrons along the edges of the system, in so-called chiral edge states (CESs). These are states that, as a consequence of nontrivial topological properties of the bulk electronic band structure, have a unique directionality and are robust against scattering from disorder. Recently, it was theoretically predicted that electromagnetic analogues of such electronic edge states could be observed in photonic crystals, which are materials having refractive-index variations with a periodicity comparable to the wavelength of the light passing through them. Here we report the experimental realization and observation of such electromagnetic CESs in a magneto-optical photonic crystal fabricated in the microwave regime. We demonstrate that, like their electronic counterparts, electromagnetic CESs can travel in only one direction and are very robust against scattering from disorder; we find that even large metallic scatterers placed in the path of the propagating edge modes do not induce reflections. These modes may enable the production of new classes of electromagnetic device and experiments that would be impossible using conventional reciprocal photonic states alone. Furthermore, our experimental demonstration and study of photonic CESs provides strong support for the generalization and application of topological band theories to classical and bosonic systems, and may lead to the realization and observation of topological phenomena in a generally much more controlled and customizable fashion than is typically possible with electronic systems.
2,383 citations
TL;DR: DAMMIF, an enhanced and significantly faster implementation of the ab-initio shape-determination program DAMMIN for small-angle scattering data, is presented.
Abstract: DAMMIF, a revised implementation of the ab-initio shape-determination program DAMMIN for small-angle scattering data, is presented. The program was fully rewritten, and its algorithm was optimized for speed of execution and modified to avoid limitations due to the finite search volume. Symmetry and anisometry constraints can be imposed on the particle shape, similar to DAMMIN. In equivalent conditions, DAMMIF is 25–40 times faster than DAMMIN on a single CPU. The possibility to utilize multiple CPUs is added to DAMMIF. The application is available in binary form for major platforms.
1,482 citations
01 May 2009
TL;DR: The theory of the complex angular momentum plane (Regge theory) as discussed by the authors was proposed by Regge in the early 1970s for non-relativistic potential scattering and has been used to classify the many different particles which have been discovered in recent years, to explain the forces between these particles and to predict the results of high-energy scattering experiments.
Abstract: Originally published in 1977, this book presents an extended introduction to the theory of hadrons, the elementary particles which occur in the atomic nucleus. The main emphasis is on the theory of the complex angular momentum plane 'Regge theory', which has grown from Regge's demonstration in 1959 that it is useful to regard angular momentum as a complex variable when discussing solutions of the Schrodinger equation for non-relativistic potential scattering. This theory helps to classify the many different particles which have been discovered in recent years, to explain the forces between these particles and to predict the results of high-energy scattering experiments. Regge theory thus serves as a unifying concept drawing together many different features of high-energy physics. This monograph is intended primarily for research students just beginning to concern themselves with particle physics, but more experienced workers will also find much to interest them in this detailed survey of the basic ideas and results of Regge theory.
912 citations
TL;DR: It is demonstrated that the chiral nature of these states protects the spin of the carriers, potentially useful for spin-based electronics, in which long spin coherence is critical, and also for quantum computing applications, where topological protection can enable fault-tolerant information processing.
Abstract: Topological insulators are a new class of insulators in which a bulk gap for electronic excitations is generated because of the strong spin–orbit coupling inherent to these systems. These materials are distinguished from ordinary insulators by the presence of gapless metallic surface states, resembling chiral edge modes in quantum Hall systems, but with unconventional spin textures. A key predicted feature of such spin-textured boundary states is their insensitivity to spin-independent scattering, which is thought to protect them from backscattering and localization. Recently, experimental and theoretical efforts have provided strong evidence for the existence of both two- and three-dimensional classes of such topological insulator materials in semiconductor quantum well structures and several bismuth-based compounds, but so far experiments have not probed the sensitivity of these chiral states to scattering. Here we use scanning tunnelling spectroscopy and angle-resolved photoemission spectroscopy to visualize the gapless surface states in the three-dimensional topological insulator Bi_(1-x)Sb_x, and examine in detail the influence of scattering from disorder caused by random alloying in this compound. We show that, despite strong atomic scale disorder, backscattering between states of opposite momentum and opposite spin is absent. Our observations demonstrate that the chiral nature of these states protects the spin of the carriers. These chiral states are therefore potentially useful for spin-based electronics, in which long spin coherence is critical, and also for quantum computing applications, where topological protection can enable fault-tolerant information processing.
860 citations
TL;DR: It is shown that short-pulse laser-induced classical ripples on dielectrics, semiconductors, and conductors exhibit a prominent "non-classical" characteristic-in normal incidence the periods are definitely smaller than laser wavelengths, which indicates that the simplified scattering model should be revised.
Abstract: We show that short-pulse laser-induced classical ripples on dielectrics, semiconductors, and conductors exhibit a prominent "non-classical" characteristic-in normal incidence the periods are definitely smaller than laser wavelengths, which indicates that the simplified scattering model should be revised. Taking into account the surface plasmons (SPs), we consider that the ripples result from the initial direct SP-laser interference and the subsequent grating-assisted SP-laser coupling. With the model, the period-decreasing phenomenon originates in the admixture of the field-distribution effect and the grating-coupling effect. Further, we propose an approach for obtaining the dielectric constant, electron density, and electron collision time of the high-excited surface. With the derived parameters, the numerical simulations are in good agreement with the experimental results. On the other hand, our results confirm that the surface irradiated by short-pulse laser with damage-threshold fluence should behave metallic, no matter for metal, semiconductor, or dielectric, and the short-pulse laser-induced subwavelength structures should be ascribed to a phenomenon of nano-optics.
735 citations
TL;DR: The experimentally determined scattering spectra of discrete, crystalline, gold nanorod dimers arranged side-to-side, end- to-end, at right angles in different orientations and also with longitudinal offsets are reported along with the electron micrographs of the individual dimers, consistent with the plasmon hybridization model.
Abstract: The experimentally determined scattering spectra of discrete, crystalline, gold nanorod dimers arranged side-to-side, end-to-end, at right angles in different orientations and also with longitudinal offsets are reported along with the electron micrographs of the individual dimers. The spectra exhibit both red- and blue-shifted surface plasmon resonances, consistent with the plasmon hybridization model. However, the plasmon coupling constant for gold dimers with less than a few nanometers separation between the particles does not obey the exponential dependence predicted by the Universal Plasmon Ruler equation. The experimentally determined spectra are compared with electrodynamic calculations and the interactions between the individual rod plasmons in different dimer orientations are elucidated.
727 citations
TL;DR: A review of the GISAXS technique, from experimental issues to the theories underlying the data analysis, with a wealth of examples, can be found in this paper, where the authors introduce the notions of particle form factor and interference function, together with the different cases encountered according to the size/shape dispersion.
717 citations
TL;DR: In this paper, the authors used Mie theory for spherical particles and with more complicated numerical methods for other particle shapes to calculate aerosol light absorption in the atmosphere, which contributes to solar radiative forcing through absorption of solar radiation and heating of the absorbing aerosol layer.
Abstract: Light absorption by aerosols contributes to solar radiative forcing through absorption of solar radiation and heating of the absorbing aerosol layer. Besides the direct radiative effect, the heating can evaporate clouds and change the atmospheric dynamics. Aerosol light absorption in the atmosphere is dominated by black carbon (BC) with additional, significant contributions from the still poorly understood brown carbon and from mineral dust. Sources of these absorbing aerosols include biomass burning and other combustion processes and dust entrainment. For particles much smaller than the wavelength of incident light, absorption is proportional to the particle volume and mass. Absorption can be calculated with Mie theory for spherical particles and with more complicated numerical methods for other particle shapes. The quantitative measurement of aerosol light absorption is still a challenge. Simple, commonly used filter measurements are prone to measurement artifacts due to particle concentration and modification of particle and filter morphology upon particle deposition, optical interaction of deposited particles and filter medium, and poor angular integration of light scattered by deposited particles. In situ methods measure particle absorption with the particles in their natural suspended state and therefore are not prone to effects related to particle deposition and concentration on filters. Photoacoustic and refractive index-based measurements rely on the heating of particles during light absorption, which, for power-modulated light sources, causes an acoustic signal and modulation of the refractive index in the air surrounding the particles that can be quantified with a microphone and an interferometer, respectively. These methods may suffer from some interference due to light-induced particle evaporation. Laser-induced incandescence also monitors particle heating upon absorption, but heats absorbing particles to much higher temperatures to quantify BC mass from the thermal radiation emitted by the heated particles. Extinction-minus-scattering techniques have limited sensitivity for measuring aerosol light absorption unless the very long absorption paths of cavity ring-down techniques are used. Systematic errors can be dominated by truncation errors in the scattering measurement for large particles or by subtraction errors for high single scattering albedo particles. Remote sensing techniques are essential for global monitoring of aerosol light absorption. While local column-integrated measurements of aerosol light absorption with sun and sky radiometers are routinely done, global satellite measurements are so far largely limited to determining a semi-quantitative UV absorption index.
702 citations
TL;DR: In this article, the authors developed accurate x-ray scattering techniques to measure the physical properties of dense plasmas for applications in high energy density physics, including inertial confinement fusion, material science, or laboratory astrophysics.
Abstract: Accurate x-ray scattering techniques to measure the physical properties of dense plasmas have been developed for applications in high energy density physics. This class of experiments produces short-lived hot dense states of matter with electron densities in the range of solid density and higher where powerful penetrating x-ray sources have become available for probing. Experiments have employed laser-based x-ray sources that provide sufficient photon numbers in narrow bandwidth spectral lines, allowing spectrally resolved x-ray scattering measurements from these plasmas. The backscattering spectrum accesses the noncollective Compton scattering regime which provides accurate diagnostic information on the temperature, density, and ionization state. The forward scattering spectrum has been shown to measure the collective plasmon oscillations. Besides extracting the standard plasma parameters, density and temperature, forward scattering yields new observables such as a direct measure of collisions and quantum effects. Dense matter theory relates scattering spectra with the dielectric function and structure factors that determine the physical properties of matter. Applications to radiation-heated and shock-compressed matter have demonstrated accurate measurements of compression and heating with up to picosecond temporal resolution. The ongoing development of suitable x-ray sources and facilities will enable experiments in a wide range of research areas including inertial confinement fusion,more » radiation hydrodynamics, material science, or laboratory astrophysics.« less
612 citations
TL;DR: The SAXS pipeline combines automated sample handling of microliter volumes, temperature and anaerobic control, rapid data collection and data analysis, and couples structural analysis with automated archiving to create an efficient pipeline enabling high-throughput analysis of protein structure in solution with small angle X-ray scattering.
Abstract: We present an efficient pipeline enabling high-throughput analysis of protein structure in solution with small angle X-ray scattering (SAXS). Our SAXS pipeline combines automated sample handling of microliter volumes, temperature and anaerobic control, rapid data collection and data analysis, and couples structural analysis with automated archiving. We subjected 50 representative proteins, mostly from Pyrococcus furiosus, to this pipeline and found that 30 were multimeric structures in solution. SAXS analysis allowed us to distinguish aggregated and unfolded proteins, define global structural parameters and oligomeric states for most samples, identify shapes and similar structures for 25 unknown structures, and determine envelopes for 41 proteins. We believe that high-throughput SAXS is an enabling technology that may change the way that structural genomics research is done.
604 citations
TL;DR: Defected graphene shows a diverging resistivity at low temperature, indicating insulating behavior, and is best explained by ion-induced formation of lattice defects that result in midgap states.
Abstract: Irradiation of graphene on ${\mathrm{SiO}}_{2}$ by 500 eV Ne and He ions creates defects that cause intervalley scattering as is evident from a significant Raman $D$ band intensity. The defect scattering gives a conductivity proportional to charge carrier density, with mobility decreasing as the inverse of the ion dose. The mobility decrease is 4 times larger than for a similar concentration of singly charged impurities. The minimum conductivity decreases proportional to the mobility to values lower than $4{e}^{2}/\ensuremath{\pi}h$, the minimum theoretical value for graphene free of intervalley scattering. Defected graphene shows a diverging resistivity at low temperature, indicating insulating behavior. The results are best explained by ion-induced formation of lattice defects that result in midgap states.
TL;DR: Various aspects of Scherrer-type grain-size analysis are discussed with regard to the characterization of thin films with grazing-incidence scattering methods utilizing area detectors utilize area detectors.
Abstract: A poor divergence value in the paper by Smilgies [J. Appl. Cryst. (2009), 42, 1030–1034] is corrected.
TL;DR: By studying the voltage-dependent standing wave patterns, the energy dispersion E(k) is determined, which confirms the Dirac cone structure of the topological states, and shows that, very different from the conventional surface states, backscattering of theTopological states by nonmagnetic impurities is completely suppressed.
Abstract: We report direct imaging of standing waves of the nontrivial surface states of topological insulator Bi2Te3 using a scanning tunneling microscope. The interference fringes are caused by the scattering of the topological states off Ag impurities and step edges on the Bi2Te3(111) surface. By studying the voltage-dependent standing wave patterns, we determine the energy dispersion E(k), which confirms the Dirac cone structure of the topological states. We further show that, very different from the conventional surface states, backscattering of the topological states by nonmagnetic impurities is completely suppressed. The absence of backscattering is a spectacular manifestation of the time-reversal symmetry, which offers a direct proof of the topological nature of the surface states.
TL;DR: The present results provide experimental evidence that the extreme differences anticipated in the hydrogen-bonding environment in the deeply supercooled regime surprisingly remain in bulk water even at conditions ranging from ambient up to close to the boiling point.
Abstract: Small-angle X-ray scattering (SAXS) is used to demonstrate the presence of density fluctuations in ambient water on a physical length-scale of ≈1 nm; this is retained with decreasing temperature while the magnitude is enhanced. In contrast, the magnitude of fluctuations in a normal liquid, such as CCl4, exhibits no enhancement with decreasing temperature, as is also the case for water from molecular dynamics simulations under ambient conditions. Based on X-ray emission spectroscopy and X-ray Raman scattering data we propose that the density difference contrast in SAXS is due to fluctuations between tetrahedral-like and hydrogen-bond distorted structures related to, respectively, low and high density water. We combine our experimental observations to propose a model of water as a temperature-dependent, fluctuating equilibrium between the two types of local structures driven by incommensurate requirements for minimizing enthalpy (strong near-tetrahedral hydrogen-bonds) and maximizing entropy (nondirectional H-bonds and disorder). The present results provide experimental evidence that the extreme differences anticipated in the hydrogen-bonding environment in the deeply supercooled regime surprisingly remain in bulk water even at conditions ranging from ambient up to close to the boiling point.
TL;DR: This work identifies spectral singularities of complex scattering potentials with the real energies at which the reflection and transmission coefficients tend to infinity, i.e., they correspond to resonances having a zero width and shows that a waveguide modeled using such a potential operates like a resonator at the frequencies of spectral singularity.
Abstract: Spectral singularities are spectral points that spoil the completeness of the eigenfunctions of certain non-Hermitian Hamiltonian operators. We identify spectral singularities of complex scattering potentials with the real energies at which the reflection and transmission coefficients tend to infinity, i.e., they correspond to resonances having a zero width. We show that a waveguide modeled using such a potential operates like a resonator at the frequencies of spectral singularities. As a concrete example, we explore the spectral singularities of an imaginary PT-symmetric barrier potential and demonstrate the above resonance phenomenon for a certain electromagnetic waveguide.
TL;DR: In this article, it was shown that the Raman spectra are strongly affected by doping, and that this is due to a combination of electron-phonon and electron-electron scattering.
Abstract: Raman spectroscopy is a fast and nondestructive means to characterize graphene samples. In particular, the Raman spectra are strongly affected by doping. While the resulting change in position and width of the $G$ peak can be explained by the nonadiabatic Kohn anomaly at $\ensuremath{\Gamma}$, the significant doping dependence of the $2D$ peak intensity has not been understood yet. Here we show that this is due to a combination of electron-phonon and electron-electron scattering. Under full resonance, the photogenerated electron-hole pairs can scatter not just with phonons but also with doping-induced electrons or holes, and this changes the intensity. We explain the doping dependence and show how it can be used to determine the corresponding electron-phonon coupling. This is higher than predicted by density-functional theory, as a consequence of renormalization by Coulomb interactions.
TL;DR: In this article, the authors investigated the physical mechanisms responsible for Seebeck coefficient enhancement in nanocrystalline systems and proposed that carrier trapping in the grain boundaries forms energy barriers that impede the conduction of carriers between grains, essentially filtering charge carriers with energy less than the barrier height.
Abstract: Resistivity, Seebeck coefficient, and Hall measurements were performed on densified nanocrystalline composite materials of undoped and Ag-doped PbTe nanocrystals to investigate the physical mechanisms responsible for Seebeck coefficient enhancement in nanocrystalline systems. The unique temperature dependence of the resistivity and mobility for these PbTe nanocomposites suggests that grain-boundary potential barrier scattering is the dominant scattering mechanism. We propose that carrier trapping in the grain boundaries forms energy barriers that impede the conduction of carriers between grains, essentially filtering charge carriers with energy less than the barrier height. These nanocomposites therefore demonstrate an enhanced Seebeck coefficient as compared to single crystal or polycrystalline PbTe at similar carrier concentrations.
TL;DR: In this article, the effect of impurities in inducing spin-orbit coupling in graphene was studied and it was shown that the spin-flip scattering produced by the impurity leads to spin scattering lengths of the order found in recent experiments.
Abstract: We study the effect of impurities in inducing spin-orbit coupling in graphene. We show that the $s{p}^{3}$ distortion induced by an impurity can lead to a large increase in the spin-orbit coupling with a value comparable to the one found in diamond and other zinc-blende semiconductors. The spin-flip scattering produced by the impurity leads to spin scattering lengths of the order found in recent experiments. Our results indicate that the spin-orbit coupling can be controlled via the impurity coverage.
TL;DR: Temperature-dependent I-V and C-V spectroscopy of single InAs nanowire field-effect transistors were utilized to directly shed light on the intrinsic electron transport properties as a function of nanowires radius, serving as a versatile and powerful platform for in-depth characterization of nanoscale, electronic materials.
Abstract: Temperature-dependent I−V and C−V spectroscopy of single InAs nanowire field-effect transistors were utilized to directly shed light on the intrinsic electron transport properties as a function of nanowire radius. From C−V characterizations, the densities of thermally activated fixed charges and trap states on the surface of untreated (i.e., without any surface functionalization) nanowires are investigated while enabling the accurate measurement of the gate oxide capacitance, therefore leading to the direct assessment of the field-effect mobility for electrons. The field-effect mobility is found to monotonically decrease as the radius is reduced to <10 nm, with the low temperature transport data clearly highlighting the drastic impact of the surface roughness scattering on the mobility degradation for miniaturized nanowires. More generally, the approach presented here may serve as a versatile and powerful platform for in-depth characterization of nanoscale, electronic materials.
TL;DR: An analysis tool is described using relatively inexpensive small angle X-ray scattering (SAXS) measurements to identify flexibility and validate a constructed minimal ensemble of models, which represent highly populated conformations in solution.
Abstract: Flexibility between domains of proteins is often critical for function. These motions and proteins with large scale flexibility in general are often not readily amenable to conventional structural analysis such as X-ray crystallography, nuclear magnetic resonance spectroscopy (NMR) or electron microscopy. A common evolution of a crystallography project, once a high resolution structure has been determined, is to postulate possible sights of flexibility. Here we describe an analysis tool using relatively inexpensive small angle X-ray scattering (SAXS) measurements to identify flexibility and validate a constructed minimal ensemble of models, which represent highly populated conformations in solution. The resolution of these results is sufficient to address the questions being asked: what kinds of conformations do the domains sample in solution? In our rigid body modeling strategy BILBOMD, molecular dynamics (MD) simulations are used to explore conformational space. A common strategy is to perform the MD simulation on the domains connections at very high temperature, where the additional kinetic energy prevents the molecule from becoming trapped in a local minimum. The MD simulations provide an ensemble of molecular models from which a SAXS curve is calculated and compared to the experimental curve. A genetic algorithm is used to identify the minimal ensemble (minimal ensemble search, MES) required to best fit the experimental data. We demonstrate the use of MES in several model and in four experimental examples.
TL;DR: In this article, the authors report recent advances in light out-coupling techniques, such as, substrate modification methods, use of scattering medium, micro-lens arrays, microcavity effect, photonic crystals and nano-particles, nano-structures and surface plasmonenhanced techniques that have been implemented to enhance the external extraction efficiency of organic electro-luminescent devices.
TL;DR: A new scaling rhoAH=f(rho( xx0), rho(xx)) that also involves the residual resistivity has been established which helps identify the intrinsic and extrinsic mechanisms of the anomalous Hall effect.
Abstract: Working with epitaxial films of Fe, we succeeded in independent control of different scattering processes in the anomalous Hall effect. The result clearly exposed the fundamental flaws of the conventional scaling rhoAH=f(rho(xx)) between the anomalous Hall resistivity and longitudinal resistivity. A new scaling rhoAH=f(rho(xx0),rho(xx)) that also involves the residual resistivity has been established which helps identify the intrinsic and extrinsic mechanisms of the anomalous Hall effect.
TL;DR: The localized surface plasmon resonance of a silver nanoparticle is responsible for its ability to strongly absorb and scatter light at specific wavelengths as discussed by the authors, and the absorption and scattering spectra of a particle can be predicted using Mie theory (for a spherical particle) or the discrete dipole approximation method (for particles in arbitrary shapes).
Abstract: The localized surface plasmon resonance of a silver nanoparticle is responsible for its ability to strongly absorb and scatter light at specific wavelengths. The absorption and scattering spectra (i.e., plots of cross sections as a function of wavelength) of a particle can be predicted using Mie theory (for a spherical particle) or the discrete dipole approximation method (for particles in arbitrary shapes). In this review, we briefly discuss the calculated spectra for silver nanoparticles with different shapes and the synthetic methods available to produce these nanoparticles. As validated in recent studies, there is good agreement between the theoretically calculated and the experimentally measured spectra. We conclude with a discussion of new plasmonic and sensing applications enabled by the shape-controlled nanoparticles.
TL;DR: A frequency-dependent phonon scattering rate is computed from perturbation theory and related to a description of the surface through the root-mean-square roughness height Delta and autocovariance length L, and a quadratic dependence of thermal conductivity on diameter and roughness is found.
Abstract: We present a novel approach for computing the surface roughness-limited thermal conductivity of silicon nanowires with diameter D<100 nm. A frequency-dependent phonon scattering rate is computed from perturbation theory and related to a description of the surface through the root-mean-square roughness height Delta and autocovariance length L. Using a full phonon dispersion relation, we find a quadratic dependence of thermal conductivity on diameter and roughness as (D/Delta)(2). Computed results show excellent agreement with experimental data for a wide diameter and temperature range (25-350 K), and successfully predict the extraordinarily low thermal conductivity of 2 W m(-1) K-1 at room temperature in rough-etched 50 nm silicon nanowires.
TL;DR: For the first time, DLS is able to directly and quantitatively measure the binding stoichiometry between a protein-conjugated GNP probe and a target analyte protein in solution.
Abstract: Dynamic light scattering (DLS) is an analytical tool used routinely for measuring the hydrodynamic size of nanoparticles and colloids in a liquid environment. Gold nanoparticles (GNPs) are extraordinary light scatterers at or near their surface plasmon resonance wavelength. In this study, we demonstrate that DLS can be used as a very convenient and powerful tool for gold nanoparticle bioconjugation and biomolecular binding studies. The conjugation process between protein A and gold nanoparticles under different experimental conditions and the quality as well as the stability of the prepared conjugates were monitored and characterized systematically by DLS. Furthermore, the specific interactions between protein A-conjugated gold nanoparticles and a target protein, human IgG, can be detected and monitored in situ by measuring the average particle size change of the assay solution. For the first time, we demonstrate that DLS is able to directly and quantitatively measure the binding stoichiometry between a protein-conjugated GNP probe and a target analyte protein in solution.
IBM1
TL;DR: In this article, the temperature distribution in a biased single-layer graphene transistor using Raman scattering microscopy of the 2D-phonon band was measured, and it was shown that remote scattering by substrate polar surface phonons increases the energy transfer to the substrate and at the same time limits the high-bias electronic conduction of graphene.
Abstract: We measure the temperature distribution in a biased single-layer graphene transistor using Raman scattering microscopy of the 2D-phonon band. Peak operating temperatures of 1050 K are reached in the middle of the graphene sheet at 210 KW cm^(-2) of dissipated electric power. The metallic contacts act as heat sinks, but not in a dominant fashion. To explain the observed temperature profile and heating rate, we have to include heat-flow from the graphene to the gate oxide underneath, especially at elevated temperatures, where the graphene thermal conductivity is lowered due to umklapp scattering. Velocity saturation due to phonons with about 50 meV energy is inferred from the measured charge density via shifts in the Raman G-phonon band, suggesting that remote scattering (through field coupling) by substrate polar surface phonons increases the energy transfer to the substrate and at the same time limits the high-bias electronic conduction of graphene.
TL;DR: In this paper, the current status of theoretical calculations of the hadronic light-by-light scattering contribution to the muon anomalous magnetic moment is reviewed and related issues such as OPE constraints and large breaking of chiral symmetry are discussed.
Abstract: We review the current status of theoretical calculations of the hadronic light-by-light scattering contribution to the muon anomalous magnetic moment. Different approaches and related issues such as OPE constraints and large breaking of chiral symmetry are discussed. Combining results of different models with educated guesses on the errors we come to the estimate $$a^{\rm HLbL}=(10.5\pm 2.6)\times 10^{-10}.$$ The text is prepared as a contribution to the {\it Glasgow White Paper on the present status of the Muon Anomalous Magnetic Moment}.
TL;DR: An implementation of the specific reaction parameter (SRP) approach to density functional theory (DFT) that carries the method forward from a semiquantitative to a quantitative description of the molecule-surface interaction is introduced.
Abstract: Methods for accurately computing the interaction of molecules with metal surfaces are critical to understanding and thereby improving heterogeneous catalysis. We introduce an implementation of the specific reaction parameter (SRP) approach to density functional theory (DFT) that carries the method forward from a semiquantitative to a quantitative description of the molecule-surface interaction. Dynamics calculations on reactive scattering of hydrogen from the copper (111) surface using an SRP-DFT potential energy surface reproduce data on the dissociative adsorption probability as a function of incidence energy and reactant state and data on rotationally inelastic scattering with chemical accuracy (within ~4.2 kilojoules per mole).
TL;DR: In this article, the authors use synchrotron radiation FTIR micro-spectroscopy to record spectra of mono-dispersed poly(methyl methacrylate) (PMMA) spheres of systematically varying size and demonstrate that the spectral distortions in the data can be understood in terms of resonant Mie scattering.
Abstract: Infrared spectroscopic cytology is potentially a powerful clinical tool. However, in order for it to be successful, practitioners must be able to extract reliably a pure absorption spectrum from a measured spectrum that often contains many confounding factors. The most intractable problem to date is the, so called, dispersion artefact which most prominently manifests itself as a sharp decrease in absorbance on the high wavenumber side of the amide I band in the measured spectrum, exhibiting a derivative-like line shape. In this paper we use synchrotron radiation FTIR micro-spectroscopy to record spectra of mono-dispersed poly(methyl methacrylate) (PMMA) spheres of systematically varying size and demonstrate that the spectral distortions in the data can be understood in terms of resonant Mie scattering. A full understanding of this effect will enable us to develop strategies for deconvolving the scattering contribution and recovering the pure absorption spectrum, thus removing one of the last technological barriers to the development of clinical spectroscopic cytology.
TL;DR: In this article, the authors demonstrated the effect of the unique morphology of the resonator reducing the phase mismatch between the optical modes and the hypersound wave, and demonstrated that the resonance of an ultrahigh Q calcium fluoride resonator with 3 µW Brillouin lasing threshold can be observed.
Abstract: Stimulated Brillouin scattering with both pump and Stokes beams in resonance with whispering gallery modes of an ultrahigh Q calcium fluoride resonator is demonstrated for the first time. The resonator is pumped with 1064 nm light and has 3 µW Brillouin lasing threshold. The scattering is observed due to the unique morphology of the resonator reducing the phase mismatch between the optical modes and the hypersound wave.