Emission Angle Dependence Research Articles

Thermal Tides in the Upper Cloud Layer of Venus as Deduced From the Emission Angle Dependence of the Brightness Temperature by Akatsuki/LIR

AbstractThe brightness temperature of the Venus disk obtained by Longwave Infrared Camera (LIR) on board Akatsuki shows clear limb darkening at low and middle latitudes. The profile of limb brightness reflects the vertical distributions of atmospheric temperature and the optical thickness of the cloud particles. Horizontal distributions of brightness temperature obtained by LIR during ∼5.8 Venusian years were analyzed to investigate the vertical structure of the brightness temperature distribution above the cloud tops based on the emission angle dependence of the sensing altitude. Emission angles were converted to sensing altitudes by a radiative transfer calculation with nominal temperature and cloud particle distributions based on past observations. We show a local time‐altitude cross section of the brightness temperature deviation above the cloud tops for three latitudinal zones. The derived vertical amplitude distribution of the diurnal and semidiurnal tides above ∼68 km is mostly explained by the classical theory of thermal tides. A semidiurnal tide in which the phase shifts upstream with altitude is clearly seen in the equatorial region. By applying the dispersion relation of the internal gravity wave to the observed wave structure, it was found that the zonally averaged zonal wind velocity at altitudes of 66–71 km was approximately the same as the known superrotation velocity. By comparing the observed and simulated vertical phase structures, it is suggested that the tidal wave structure seen in the equatorial cloud tops is an aspect of upward propagation of a gravity wave generated in the upper cloud layer by solar heating.

Dataset: Thermal tides in the upper cloud layer of Venus as deduced from the emission angle dependence of the brightness temperature by Akatsuki/LIR

Dataset: Thermal tides in the upper cloud layer of Venus as deduced from the emission angle dependence of the brightness temperature by Akatsuki/LIR

Effects of conduction electron excitation on x-ray magnetic circularly polarized emission in itinerant ferromagnets

This study provides a theoretical method to calculate x-ray magnetic circularly polarized emission spectra at the K${}_{\ensuremath{\alpha}}$ transitions in transition-metal ferromagnets. The method is applied to metallic iron. It reproduces the observed tail structures which originate from the electron excitations on the correlated $d$ bands. Cosinusoidal emission angle dependence of the spectral intensity enables one to elucidate the magnetization directions deep inside of bulk ferromagnets.

Polarization of Λ (Λ[over ¯]) Hyperons along the Beam Direction in Au+Au Collisions at sqrt[s_{NN}]=200 GeV.

The Λ (Λ[over ¯]) hyperon polarization along the beam direction has been measured in Au+Au collisions at sqrt[s_{NN}]=200 GeV, for the first time in heavy-ion collisions. The polarization dependence on the hyperons' emission angle relative to the elliptic flow plane exhibits a second harmonic sine modulation, indicating a quadrupole pattern of the vorticity component along the beam direction, expected due to elliptic flow. The polarization is found to increase in more peripheral collisions, and shows no strong transverse momentum (p_{T}) dependence at p_{T} greater than 1 GeV/c. The magnitude of the signal is about 5 times smaller than those predicted by hydrodynamic and multiphase transport models; the observed phase of the emission angle dependence is also opposite to these model predictions. In contrast, the kinematic vorticity calculations in the blast-wave model tuned to reproduce particle spectra, elliptic flow, and the azimuthal dependence of the Gaussian source radii measured with the Hanbury Brown-Twiss intensity interferometry technique reproduce well the modulation phase measured in the data and capture the centrality and transverse momentum dependence of the polarization signal.

Observation of cavity polaritons in a metal-mirror Fabry-Pérot microcavity containing liquid-crystalline semiconductor based on perylene bisimide units.

We investigate the optical properties of a metal-mirror microcavity containing a liquid-crystalline (LC) perylene tetracarboxylic bisimide (PTCBI) derivative. Measurements of the transmission's incidence angle dependence show that the peaks are split in a complex way and shift as the angle changes. Further, measurements of the photoluminescence spectrum's emission angle dependence show that the peak also shifts with the angle, as in the transmission experiment. We also carry out a theoretical analysis; the theoretical and experimental results are in very good agreement, and we estimate the vacuum Rabi splitting energies to be about 212, 180, and 240 meV. In addition, the peak photoluminescence energy coincides with the lower polariton branch obtained by transmission experiment. Finally, in a time-resolved photoluminescence experiment, we observe a fast relaxation component that is not seen in the bare LC PTCBI film. We believe this is due to cavity effects increasing the spontaneous emission transition rate, indicating that the emissions are due to cavity polaritons.

Polarized THz Emission from In‐Plane Dipoles in Monolayer Tungsten Disulfide by Linear and Circular Optical Rectification

AbstractRecent advances in the development of polarized terahertz (THz) emission from nanomaterials have not only opened up a new “TeraNano” interdiscipline but also provided a new tool for nonlinear optical process research. Herein, THz radiation mechanism of monolayer tungsten disulfide (WS2) is first investigated by both linear and circular polarization laser excitations at room temperature. The results reveal that polarized THz emission is dominated by the optical rectification based on in‐plane nonlinear dipoles, which is totally different from that of bulk WS2. The mechanism is verified by the azimuthal angle and pump polarization angle dependence of THz emission in both experiment and theory. Furthermore, controllably elliptically polarized THz emission is observed with the maximum ellipticity of ≈0.52 based on nonresonant nonlinear process under the circularly polarized excitation. A clear understanding of THz radiation mechanism of 2D materials will facilitate further design, optimization, and polarization control of integrable 2D THz optoelectronics.

Template-Assisted Preparation of Micrometric Suspended Membrane Lattices of Photoluminescent and Non-Photoluminescent Polymers by Capillarity-Driven Solvent Evaporation: Application to Microtagging

In this work, the bottom-up template-assisted preparation of high-density lattices (up to 11 · 106 membranes/cm2) of suspended polymer membranes with micrometric size (in the order of few μm2) and sub-micrometric thickness (in the order of hundreds of nm) is demonstrated for both photoluminescent and non-photoluminescent polymers by capillarity-driven solvent evaporation. Solvent evaporation of low concentration polymer solutions drop-cast on an array of open-ended micropipes is shown to lead to polymer membrane formation at the inlet of the micropipes thanks to capillarity. The method is proven to be robust with high-yield (>98%) over large areas (1 cm2) and of general validity for both conjugated and non-conjugated polymers, e.g. poly(9,9-di-n-octylfluorene-alt-benzothiadiazole (F8BT), poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV), polystyrene (PS), thus breaking a new ground on the controlled preparation of polymer micro and nanostructures. Angle dependence and thermal stability of photoluminescence emission arising from F8BT membrane lattices was thorough investigated, highlighting a non-Lambertian photoluminescence emission of membrane lattices with respect to F8BT films. The method is eventually successfully applied to the preparation of both photoluminescent and non-photoluminescent micro Quick Response (μQR) codes using different polymers, i.e. F8BT, MDMO-PPV, PS, thus providing micrometric-sized taggants suitable for anti-counterfeiting applications.

MWR: Microwave Radiometer for the Juno Mission to Jupiter

The Juno Microwave Radiometer (MWR) is a six-frequency scientific instrument designed and built to investigate the deep atmosphere of Jupiter. It is one of a suite of instruments on NASA’s New Frontiers Mission Juno launched to Jupiter on August 5, 2011. The focus of this paper is the description of the scientific objectives of the MWR investigation along with the experimental design, observational approach, and calibration that will achieve these objectives, based on the Juno mission plan up to Jupiter orbit insertion on July 4, 2016. With frequencies distributed approximately by octave from 600 MHz to 22 GHz, the MWR will sample the atmospheric thermal radiation from depths extending from the ammonia cloud region at around 1 bar to pressure levels as deep as 1000 bars. The primary scientific objectives of the MWR investigation are to determine the presently unknown dynamical properties of Jupiter’s subcloud atmosphere and to determine the global abundance of oxygen and nitrogen, present in the atmosphere as water and ammonia deep below their respective cloud decks. The MWR experiment is designed to measure both the thermal radiation from Jupiter and its emission-angle dependence at each frequency relative to the atmospheric local normal with high accuracy. The antennas at the four highest frequencies (21.9, 10.0, 5.2, and 2.6 GHz) have ∼12° beamwidths and will achieve a spatial resolution approaching 600 km near perijove. The antennas at the lowest frequencies (0.6 and 1.25 GHz) are constrained by physical size limitations and have 20° beamwidths, enabling a spatial resolution of as high as 1000 km to be obtained. The MWR will obtain Jupiter’s brightness temperature and its emission-angle dependence at each point along the subspacecraft track, over angles up to 60° from the normal over most latitudes, during at least six perijove passes after orbit insertion. The emission-angle dependence will be obtained for all frequencies to an accuracy of better than one part in 10^3, sufficient to detect small variations in atmospheric temperature and absorber concentration profiles that distinguish dynamical and compositional properties of the deep Jovian atmosphere.

Auralization of Accelerating Passenger Cars Using Spectral Modeling Synthesis

While the technique of auralization has been in use for quite some time in architectural acoustics, the application to environmental noise has been discovered only recently. With road traffic noise being the dominant noise source in most countries, particular interest lies in the synthesis of realistic pass-by sounds. This article describes an auralizator for pass-bys of accelerating passenger cars. The key element is a synthesizer that simulates the acoustical emission of different vehicles, driving on different surfaces, under different operating conditions. Audio signals for the emitted tire noise, as well as the propulsion noise are generated using spectral modeling synthesis, which gives complete control of the signal characteristics. The sound of propulsion is synthesized as a function of instantaneous engine speed, engine load and emission angle, whereas the sound of tires is created in dependence of vehicle speed and emission angle. The sound propagation is simulated by applying a series of time-variant digital filters. To obtain the corresponding steering parameters of the synthesizer, controlled experiments were carried out. The tire noise parameters were determined from coast-by measurements of passenger cars with idling engines. To obtain the propulsion noise parameters, measurements at different engine speeds, engine loads and emission angles were performed using a chassis dynamometer. The article shows how, from the measured data, the synthesizer parameters are calculated using audio signal processing.

The DISR imaging mosaic of Titan’s surface and its dependence on emission angle

The DISR (Descent Image/Spectral Radiometer) imagers took about 300 images during the descent of the Huygens probe in Titan’s atmosphere. We combined them into a photometrically calibrated mosaic of Titan’s surface within 100km of the Huygens landing site with a resolution ranging from 1km at 100km distance from the landing site to 50cm near the landing site. We analyzed how the reflectivity of each location varies with the changing phase angle and emission angle during the descent. We found strong variations with the emission angle but no significant variation of the surface phase function. The latter is possibly obscured by the diffuse nature of illumination by Titan’s sky at visible wavelengths. We constructed a map of this emission angle dependence, which represents a measure of surface reflectivity and roughness of the terrain. Titan’s surface probed by the images shows various terrain types with a small correlation between reflectivity and roughness. We propose that variations in the emission angle dependence might be correlated with average tilt angles of the surface. We detected elevated terrain in the bright highland north of the landing site as published by Soderblom et al. (Soderblom, L.A. et al. [2007]. Planet. Space Sci. 55, 2015–2024), but their high ridges in the lakebed appear mostly flat in our analysis. We integrated the color information from the DISR spectrometers into our mosaic to create a color map. We also compared the features seen in maps of the reflectivity, the emission angle dependence, and color to features seen in Cassini RADAR images. Finally, we provide a refined version of the images from Huygens after landing down to a resolution of 2mm.

Angle-dependent hard X-ray photoemission study of Nb hydride formation in high-pressure supercritical water

Nb hydrides formation in 10-GPa supercritical water has been investigated by angle-dependent micro-beam hard X-ray photoemission spectroscopy. In the Nb 3d core-level spectra, Nb hydride components are found in the slightly high binding energy side of the metallic components, and the oxide ones are observed even though little oxides are recognized in X-ray diffraction patterns. Obtained emission-angle dependence of the Nb 3d core-level spectra of Nb hydride specimens shows that the Nb hydride components increase with the emission angle decreased i.e. the sampling depth increased, while the oxide ones decrease. The bulk valence-band spectrum is obtained by decomposing the measured valence-band spectra into a bulk and surface components with use of the emission-angle dependence of the core-level and valence-band spectra; it consists of two bands. This implies the Nb–H chemical bond formation and Nb in an oxidation state, consistent with reported band structure calculations and the observed core-level chemical shifts. Thus it is confirmed by valence-band and core-level photoelectron spectroscopy that the Nb hydrides are formed inside the specimen, irrespective to the well-known high oxidation ability of supercritical water.

Re-print of “Sputtering of polymers by keV clusters: Microscopic views of the molecular dynamics”

This article reviews the results of molecular dynamics simulations of cluster sputtering of hydrocarbon polymers obtained in the last few years and expand them with unpublished data of Ar cluster bombardment. The targets are molecular solids of linear hydrocarbons, polyethylene and polystyrene, including a polyethylene substrate decorated with adsorbed globular macromolecules. The projectiles are (hydro)carbon and Arn clusters, from small to massive, as well as Bin and Au400 clusters. The study focuses on the dynamics of cratering and sputtering, using a coarse-grained representation of the samples, on the study of molecular fragmentation, crosslinking and free H formation, using a fully atomistic model, and on the conditions of desorption of macromolecules by massive clusters. The results explain the similarities and differences between several cluster types and sizes and, to a large extent, the sputtering yields of Arn clusters and their ‘universal’ dependence on the scaled cluster energy, as observed in the experiments. They also demonstrate the reduction of sample fragmentation and crosslinking when going to larger clusters and the incidence angle dependence of intact macromolecule emission. Recent experimental validations obtained in our laboratory are also introduced and comparisons with data obtained by other groups are discussed in order to present a more complete picture of the physics of cluster bombardment of organic solids and polymers.

Sputtering of polymers by keV clusters: Microscopic views of the molecular dynamics

This article reviews the results of molecular dynamics simulations of cluster sputtering of hydrocarbon polymers obtained in the last few years and expand them with unpublished data of Ar cluster bombardment. The targets are molecular solids of linear hydrocarbons, polyethylene and polystyrene, including a polyethylene substrate decorated with adsorbed globular macromolecules. The projectiles are (hydro)carbon and Arn clusters, from small to massive, as well as Bin and Au400 clusters. The study focuses on the dynamics of cratering and sputtering, using a coarse-grained representation of the samples, on the study of molecular fragmentation, crosslinking and free H formation, using a fully atomistic model, and on the conditions of desorption of macromolecules by massive clusters. The results explain the similarities and differences between several cluster types and sizes and, to a large extent, the sputtering yields of Arn clusters and their ‘universal’ dependence on the scaled cluster energy, as observed in the experiments. They also demonstrate the reduction of sample fragmentation and crosslinking when going to larger clusters and the incidence angle dependence of intact macromolecule emission. Recent experimental validations obtained in our laboratory are also introduced and comparisons with data obtained by other groups are discussed in order to present a more complete picture of the physics of cluster bombardment of organic solids and polymers.

Enhancing the emission directionality of organic light-emitting diodes by using photonic microstructures

We report microstructured organic light-emitting diodes (OLEDs) with directional emission based on efficient solution-processable europium-OLEDs patterned by solvent assisted microcontact molding. The angle dependence of the light emission is characterized for OLEDs with square-array photonic crystals with periods between 275 nm and 335 nm. The microstructured devices have emission patterns strongly modified from the Lambertian emission of planar OLEDs and can approximately double the emitted power in a desired angle range in both s- and p-polarizations. The modified emission is attributed to light diffracted out of the waveguide modes of the OLEDs.

Si 2<i>p</i> Core Level Shifts of the Epitaxial SiON Layer on a SiC(0001), Studied by Photoemissin Spectroscopy

The epitaxial silicon oxynitride (SiON) layer grown on a 6H-SiC(0001) surface is studied with core level photoemission spectroscopy. Si 2p spectra show three spectral components other than the bulk one. Chemical shifts and emission angle dependence of these components are well explained within a framework of a determined structure model of the SiON layer.

Systematic comparison of jet quenching in different fluid-dynamical models

Comparing four different (ideal and viscous) hydrodynamic models for the evolution of the medium created in $200A$ GeV Au-Au collisions, combined with two different models for the path-length dependence of parton energy loss, we study the effects of jet quenching on the emission-angle dependence of the nuclear suppression factor ${R}_{\mathit{AA}}(\ensuremath{\phi})$ and the away-side per-trigger yield ${I}_{\mathit{AA}}(\ensuremath{\phi})$. Each hydrodynamic model was tuned to provide a reasonable description of the single-particle transverse momentum spectra for all collision centralities, and the energy-loss models were adjusted to yield the same pion nuclear suppression factor in central Au-Au collisions. We find that the experimentally measured in-plane versus out-of-plane spread in ${R}_{\mathit{AA}}(\ensuremath{\phi})$ is better reproduced by models that shift the weight of the parton energy loss to later times along its path. Among the models studied here, this is best achieved by energy-loss models that suppress energy loss at early times, combined with hydrodynamic models that delay the dilution of the medium density due to hydrodynamic expansion by viscous heating. We were unable to identify a clear tomographic benefit of a measurement of ${I}_{\mathit{AA}}(\ensuremath{\phi})$ over that of ${R}_{\mathit{AA}}(\ensuremath{\phi})$.

Angular dependence of L_{3}-subshell X-ray emission following photoionisation

L₃-subshell alignment of Th and U ionized by 59.5 keV photons has been investigated by evaluating the angular dependence of L{i}(i=l, α, η, β and γ) X-ray lines. The angular dependence measurements were performed by measuring the fluorescence cross section, σ{Li}(i=1, η, α, β and γ) and σ{Ll}/σ{Lγ}, σ{Lη}/σ{Lγ }, σ{Lα}/σ{Lγ } and σ{Lβ}/σ{Lγ} ratios at different angles. It was observed from the measurements that L{i}(i=l and α) X rays for the L₃-subshell depended on the emission angle and had an anisotropic spatial distribution. On the other hand, there was no dependence of emission angle and any significant anisotropy for other L X rays. The both Ll and Lα X-rays originate from the filling of vacancies in states L₃-subshell with J =3/2. The results of measurements indicate that the L₃-subshell vacancy states with J = 3/2 are aligned, whereas L{1}, and L{2}vacancy states with J =1/2 are non-aligned. Integral cross-sections for the L{i}(i=l, η, α, β and γ) X-rays and L subshell fluorescence yields ω{i} (i= 1, 2 and 3) were also determined and results were compared with theoretically calculated values and results of others and fairly good correspondence was observed.

Remarks on Some Reference Materials for Applications in Elastic Peak Electron Spectroscopy

The quantification of results of electron spectroscopies, AES and XPS, requires knowledge of the inelastic mean free path (IMFP) of signal electrons in solids. This parameter determines the surface sensitivity of both techniques. There are two methods of determining the IMFPs that provide these parameters in agreement with the definition: (i) calculations based on the experimental optical data, and (ii) calculations based on measurements of the electron elastic backscattering intensity. The latter method requires the use of some reference material for which the IMFP is known. In 1999, an extensive analysis of the published IMFPs has been performed; the results indicated that there is a very good agreement between the calculated and measured IMFPs for four elemental solids: Ni, Cu, Ag and Au. The averaged IMFPs for these elements are known under the name of the recommended IMFPs. However, no preference among these four elements has been established. In the present work, an attempt is made to select an element for which the recommended IMFPs result in the best agreement between the calculated and measured intensities of elastic electron backscattering. For this purpose, the elastic backscattering intensity has been measured at eight electron energies varying from 200 to 1500 eV. At each energy, the intensity was measured over a wide range of emission angles from 35 degrees to 74 degrees . The experiments were accompanied with Monte Carlo calculations of the elastic backscattering probability for the same energies and experimental configurations. It has been found, from comparison, that the best agreement is observed for Au, and this element is thus recommended as the reference material. It has been shown that the shape of the emission angle dependence of the elastic backscattering intensity is noticeably influenced by the surface energy losses.

Electronic structure of hydrogen-terminated silicon surfaces [H-Si(111)] studied by two-photon photoemission

The surface and bulk electronic states of hydrogen-terminated Si(111)-(1 × 1) [H-Si(111)] were studied by two-photon photoemission (2PPE) spectroscopy. With the polarization and emission-angle dependence of the 2PPE spectra, five series of electronic structures for H-Si(111) can be identified as A, B, C, D, and E in the 2PPE spectra by fine tuning the exciting photon energy, hv, from 4.23 to 4.90 eV. For hv < 4.6 eV, peak A arises from a surface resonance at -1.01 eV from E F , and at the photon energy higher than 4.6 eV, peak A indicates photoemission from an intermediate state, corresponding to an image-potential state at 3.61 eV from E F . Other structures, B, C, and D arise from bulk states, while structure E occurs from an electron-hole excitation process. This work has revealed the surface resonance and the image-potential state on H-Si(111) for the first time.

Monte Carlo analysis of energy dependent anisotropy of bremsstrahlung x‐ray spectra

The energy resolved emission angle dependence of x-ray spectra was analyzed by MCNPX (Monte Carlo N particle Monte Carlo) simulator. It was shown that the spectral photon flux had a maximum at a well-defined emission angle due to the anisotropy of the bremsstrahlung process. The higher the relative photon energy, the smaller the emission angle belonging to the maximum was. The trends predicted by the Monte Carlo simulations were experimentally verified. The Monte Carlo results were compared to both the Institute of Physics and Engineering in Medicine spectra table and the SPEKCALCV1.0 code.