Forward Hemisphere Research Articles

Dual-wavelength superscattering in plasmonic core-shell nanostructures for transparent structural color

Structural coloration generates some of the most vibrant colors in nature and has numerous applications. Inspired by the recently reported transparent displays relying on wavelength-selective scattering, we address the novel problem of transparent structural color, which requires nanoparticles to have a narrow-band and broad-angle scattering response. Although superscattering beyond the single-channel limit has important prospects for enhancing transparent displays, it has not yet been reported. Here, we propose a simple dielectric-gold core–shell nanoparticle capable of superscattering at blue (λ = 450 nm) and green (λ = 532 nm) wavelengths, along with a dipolar surface plasmon resonance (SPR) at the red wavelength (λ = 640 nm), making it suitable for full-color transparent displays. We demonstrate that the superscattering at λ = 450 nm arises from the overlap of the epsilon-near-zero (ENZ) dipolar and quadrupolar modes. Furthermore, the coupling of conventional quadrupolar and dipolar modes can also enhance the scattering efficiency at λ = 532 nm, breaking the single-channel limit. Lastly, we show that the optimized nanoparticles can confine the scattering light within the forward hemisphere at λ = 450 nm and 532 nm, due to the interaction of quadrupolar and dipolar modes. Additionally, they exhibit dipole far-field radiation characteristics at λ = 640 nm with a wide angular beamwidth > 60°. The simple structural nature and unique scattering properties of proposed dielectric-gold core–shell nanoparticles hold promise applications in full-color transparent displays, spectroscopy, and biomedical imaging.

2-битные метаповерхности Патчаратнама-Берри с генерацией, интерференцией и гашением орбитального углового момента для широкополосного снижения ЭПР

The radar cross-section (RCS) reduction using non-absorbing digital Patcharatnam-Berry (PB) metasurfaces (MSs), consisting of 2-bit modules with generation, interference and cancellation of vortex electromagnetic waves with orbital angular momentum (OAM) is studied. Each module has a helical PB-phase profile and possesses vortex scattering. Module unit cells contain a shielded dielectric substrate and meta-particles in the form of triple-coupled split-ring resonators. The modules are distinguished by 2-bit coding of the initial tilt angle of the meta-particles 0º, 45º, 90º and 135º. The purpose of the work is to numerically analyze the generation of antiphase vortex beams (VBs) by OAM-modules and to assess the influence of interference and cancellation of antiphase vortices on the structure and order of OAM in the resulting field and the RCS reduction of three digital MSs in the form of 2´2 lattice of 2-bit OAM-modules of different sizes with different topological charges. The scattering characteristics are studied using HFSS for normally incident circularly polarized waves using of the finite element method. The simulation showed that the interference of phase vortices of four OAM-modules forms the main axial vortex and N additional interference side near and far vortices (N depends on the size of the MS). Interference vortex beams create phase singularities and zero the resulting far field in N side directions over the entire forward hemisphere. The intense OAM modes of the main vortex beams are of the fourth or eighth order. The OAM modes of adjacent interference VBs, as a rule, differ in sign. The proposed 2-bit MSs provide wider-angle phase cancellation of vortex fields (compared to 1-bit MSs) and, as a consequence, wider-angle diffuse scattering of the resulting field of the MS, which is important for RCS reduction.

Quantum State-Resolved Nonadiabatic Dynamics of the H+NaF → Na+HF Reaction

The H + NaF reaction is investigated at the quantum state-resolved level using the time-dependent wave-packet method based on a set of accurate diabatic potential energy surfaces. Oscillatory structures in the total reaction probability indicate the presence of the short-lived intermediate complex, attributed to a shallow potential well and exothermicity. Ro-vibrational state-resolved integral cross sections reveal the inverted population distributions of the product. The HF product favors an angular distribution in the forward hemisphere of 30°–60° within the collision energy range from the threshold to 0.50 eV, which is related to the nonlinear approach of the H atom to the NaF molecule. Quantum generalized deflection functions show that the low-J partial waves contribute primarily to the backward scattering, while the high-J partial waves govern the forward scattering. The correlation between the partial wave J and the scattering angle ϑ proves that the reaction follows a predominant direct reaction mechanism.

Optical model of a conifer shoot

Description of the entire structure of a conifer shoot, which forms a radiation scattering pattern, has been challenging, and the previous respective components of radiative transfer models for conifer stands were rather coarse. The progress of 3D scanner technology made it possible to collect high-density point clouds of Norway spruce shoots and describe the shoots’ geometrical shape and parameterization in full detail in this paper. The skeleton of shoots was created using custom clustering of point clouds for detecting separate needles. Needles and shoot twigs were modeled as circular cylinders, with their inclination and azimuth corresponding to the shoot skeleton.Specular reflection of incident radiation on the convex surface of needles in the border stripe of the shoot’s silhouette was found to be directed to the forward hemisphere, which increases the ratio of forward to backward scattering of radiation in a shoot. This allows multiple collisions of incident photons inside the same shoot and in the neighbor shoots in deeper layers of the crown layer in a forest, which increases the probability of incident photons being trapped in shoots and crowns of needle-leaf trees.

Forward-backward multiplicity correlation and fluctuation in 197Au + 197Au collisions at fixed target Elab = 10A, 20A, 30A and 40A GeV in the UrQMD model

We use the ultra-relativistic quantum molecular dynamics (UrQMD) model to study the multiplicity correlations and fluctuations of charged hadrons emitted in the forward and backward rapidity hemispheres in 197Au + 197Au collisions at four different incident beam energies, namely Elab=10A,20A, 30A and 40A GeV. Dependence of the correlation and fluctuation parameters on the incident beam energy, collision centrality, rapidity gap and rapidity window size are examined. Both short and long-ranged correlations contribute to our UrQMD simulated results. In the framework of the UrQMD model the short-ranged correlations can be interpreted in terms of resonance decays and/or cluster formation. The long-ranged correlations on the other hand, perhaps originate from multiple rescattering suffered by the hadrons and decay of longitudinally stretched strings in the rapidity space. Our simulation based analysis can be used to set a reference base-line for any future experimental study on the forward-backward multiplicity correlation for the colliding system and collision energies involved in the present case.

Evaluation of the Impedance Variability Effect of Acoustic Liner on Aircraft Engine Fan Noise in Calculation of Far Field Sound Modes Propagation

The influence of the impedance variability of the acoustic liner of an air intake on aircraft engine fan noise in the far field has been studied. The calculations were carried out in an axisymmetric statement for single modes based on the finite element solution to the Blokhintsev equation for the acoustic potential. The acoustic liner impedance was determined from a well-developed semiempirical model that takes into account the influence of a high sound pressure level (SPL) and grazing flow. A procedure has been developed for calculating the propagation of single sound modes through the air intake of an aircraft engine with a variable liner impedance depending on the flow velocity and SPL at a local point. The calculation procedure has been validated. Calculations were made for single mode propagation into the forward hemisphere for an air intake on the wall of which the following conditions were set: rigid wall, constant impedance (the impedance does not change along the liner) and variable impedance (the impedance changes along the liner depending on the changes in the velocity of the grazing flow and SPL). According to the calculation results, it was found that constant and variable impedances yield different SPL values in the far field; as well, taking into account the impedance variability changes not only the SPL values in the far field, but also the direction of the maximum mode radiation.

Reflectance Anisotropy from MODIS for Albedo Retrieval from a Single Directional Reflectance

Surface reflectance anisotropy and insufficient multi-angular observations are the main challenges in albedo estimation from satellite observations. Numerous studies have been developed for albedo retrieval from a single directional reflectance by associating the anisotropy information extracted from coarse-resolution bidirectional-reflectance distribution function (BRDF) data. The contribution of land-cover type (LCT) and the Normalized Difference Vegetation Index (NDVI) in distinguishing reflectance anisotropy in these methods remains controversial. This study first proposed an approach to extracting a priori BRDF (F) from the MODIS BRDF/albedo product by considering the distribution characteristics of the model parameters. LCT- and NDVI-based F were also extracted from the corresponding subset. Then, the F-based albedo was derived from simulated or satellite directional reflectance and the anisotropic information of F. Finally, the directional reflectance and F-based albedo were compared with the MODIS albedo or ground measurement, in order to show the ability of F to compensate for the effect of reflectance anisotropy in the albedo retrieval process. The method was fully validated by the global and time-series MODIS BRDF data. The results showed that reflectance anisotropy has an aggregated distribution pattern, and F can represent the reflectance anisotropy of most pixels within a tile. The improvement of LCT and NDVI only occurs when the tile contains a large area of vegetated and barren ground. With the exception of the hotspot and large viewing-zenith-angle area in the forward hemisphere, the F-based shortwave albedo has high consistency with the MODIS albedo product. A comparison with the ground measurements and MODIS albedo showed that the F-based albedo from a single directional reflectance generally achieves an absolute accuracy requirement, with a root-mean-square error (RMSE) of 0.027 and 0.036.

Emission characteristics of the target fragments at relativistic energy

In this recent work, we present the characteristic of the emission of the black particles ejected with [Formula: see text] [Formula: see text] [Formula: see text] and [Formula: see text] [Formula: see text][Formula: see text] i.e., in the forward and backward hemispheres, respectively. For the multiplicity variation study of black particles, we have considered the interaction of [Formula: see text]Kr beam with the CNO, AgBr target present in the nuclear emulsion detector. After doing the analysis of the data, we have found that the emission possibility of black particle is greater in the forward hemisphere (FHS) angle whereas in the backward hemisphere (BHS) angle, it is quite low. Along with this, we have also found that the emission probability of black particles does not posses any relation with projectile mass as well as with the incident energy. In this work, we have also studied the characteristics of shower and et al. particles using a new parameter Q (total charge [Formula: see text] of the outgoing projectile fragments emitted in forward cone [Formula: see text], here Z denotes charge, and PF denotes Projectile Fragment) instead of impact parameter to distinguish the different type of collision for two interacting nuclei. The observation from this study suggests that the emission probability of the shower particles as well as gray particles increase as the value of Q decreasing (i.e., as we move from peripheral to central colisions). The results of this work are also compared with the context of other experimental observations and it seems to be relevant.

A Multi-Year Study of GOES-13 Droplet Effective Radius Retrievals for Warm Clouds over South America and Southeast Pacific

Geostationary satellites can retrieve the cloud droplet effective radius (re) but suffer biases from cloud inhomogeneities, internal retrieval nonlinearities, and 3-D scattering/shadowing from neighboring clouds, among others. A 1-D retrieval method was applied to Geostationary Operational Environmental Satellite 13 (GOES-13) imagery, over large areas in South America (5∘ N–30∘ S; 20∘–70∘ W), the Southeast Pacific (5∘ N–30∘ S; 70∘–120∘ W), and the Amazon (2∘ N–7∘ S; 54∘–73∘ W), for four months in each year from 2014–2017. Results were compared against in situ aircraft measurements and the Moderate Resolution Imaging Spectroradiometer cloud product for Terra and Aqua satellites. Monthly regression parameters approximately followed a seasonal pattern. With up to 108,009 of matchups, slope, intercept, and correlation for Terra (Aqua) ranged from about 0.71 to 1.17, −2.8 to 2.5 μm, and 0.61 to 0.91 (0.54 to 0.78, −1.5 to 1.8 μm, 0.63 to 0.89), respectively. We identified evidence for re overestimation (underestimation) correlated with shadowing (enhanced reflectance) in the forward (backscattering) hemisphere, and limitations to illumination and viewing configurations accessible by GOES-13, depending on the time of day and season. A proposition is hypothesized to ameliorate 3-D biases by studying relative illumination and cloud spatial inhomogeneity.

Low-Frequency Content of THz Emission from Two-Color Femtosecond Filament

We experimentally investigate the low-frequency (below 1 THz) spectral content of broadband terahertz (THz) emission from two-color femtosecond filament formed by the 2.7-mJ, 40-fs, 800+400-nm pulse focused into air. For incoherent detection, we screened the Golay cell by the bandpass filters and measured the THz angular distributions at the selected frequencies ν=0.5, 1, 2 and 3 THz. The measured distributions of THz fluence were integrated over the forward hemisphere taking into account the transmittance of the filters, thus providing the estimation of spectral power at the frequencies studied. The spectral power decreases monotonically with the frequency increasing from 0.5 to 3 THz, thus showing that the maximum of THz spectrum is attained at ν≤0.5 THz. The THz waveform measured by electro-optical sampling (EOS) based on ZnTe crystal and transformed into the spectral domain shows that there exists the local maximum of the THz spectral power at ν≈1 THz. This disagrees with monotonic decrease of THz spectral power obtained from the filter-based measurements. We have introduced the correction to the spectral power reconstructed from EOS measurements. This correction takes into account different focal spot size for different THz frequencies contained in the broadband electromagnetic pulse. The corrected EOS spectral power is in semi-quantitative agreement with the one measured by a set of filters.

A Low-Scattering Pixelated Dielectric Rod Waveguide Probe for Near-Field Measurement

A 3.4–3.7 GHz dielectric rod waveguide probe for near-field measurements is proposed for applications on the 5G sub-6 GHz band. By implementing a dielectric-filled waveguide, the probe achieved a higher resolution and low scattering characteristics through a miniaturized aperture compared to the open-ended waveguide (OEWG) used for conventional near-field probes. An <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8\times 8$ </tex-math></inline-formula> pixelated grid structure in the dielectric launcher section of the probe is implemented to further reduce the scattering characteristics of the probe. The proposed probe is fabricated and experimentally verified. A coating of silver is applied to the dielectric during a production process. Measurement shows that the −10 dB reflection coefficient bandwidth meets 3.4–3.7 GHz requirement and that the radiation pattern shows a broadside gain of about 3.8 dBi with no null at the forward hemisphere. The results of a scattering characteristic experiment indicate decreased interferer level of 7.3 dB compared to an OEWG.

Seemingly asymmetric atom-localized electronic densities following laser-dissociation of homonuclear diatomics.

Recent experiments on laser-dissociation of aligned homonuclear diatomic molecules show an asymmetric forward-backward (spatial) electron-localization along the laser polarization axis. Most theoretical models attribute this asymmetry to interference effects between gerade and ungerade vibronic states. Presumably due to alignment, these models neglect molecular rotations and hence infer an asymmetric (post-dissociation) charge distribution over the two identical nuclei. In this paper, we question the equivalence that is made between spatial electron-localization, observed in experiments, and atomic electron-localization, alluded by these theoretical models. We show that (seeming) agreement between these models and experiments is due to an unfortunate omission of nuclear permutation symmetry, i.e., quantum statistics. Enforcement of the latter requires mandatory inclusion of the molecular rotational degree of freedom, even for perfectly aligned molecules. Unlike previous interpretations, we ascribe spatial electron-localization to the laser creation of a rovibronic wavepacket that involves field-free molecular eigenstates with opposite space-inversion symmetry i.e., even and odd parity. Space-inversion symmetry breaking would then lead to an asymmetric distribution of the (space-fixed) electronic density over the forward and backward hemisphere. However, owing to the simultaneous coexistence of two indistinguishable molecular orientational isomers, our analytical and computational results show that the post-dissociation electronic density along a specified space-fixed axis is equally shared between the two identical nuclei-a result that is in perfect accordance with the principle of the indistinguishability of identical particles.

Characteristics of the grey particles emission at relativistic energy

The theme of present analysis is to focus on the emission characteristics of grey particles emitted in 4π angle, forward hemisphere angle (θ < 90°) (FHS) and backward hemisphere angle (θ ≥ 90°) (BHS). We have studied the average multiplicity variation of grey particles for the events emitted from the reaction of projectiles with CNO and AgBr target nuclei of nuclear emulsion. We have also investigated the emission probability of grey particles with projectile mass in between the range of 1 and 207. In this analysis we have observed that the emission probability of grey particles is higher in forward hemisphere angle as compared to backward hemisphere angle. We have also observed that the average multiplicity of grey particles is independent on the projectile mass and incident energy.

Emission Characteristics of the grey particles produced in the interaction of the 84Kr36 with nuclear emulsion detector at 1 A GeV

In the present analysis, we have studied the emission characteristics of grey particles produced from the interaction of 84Kr36 projectile at 1 A GeV with CNO target nuclei and AgBr target nuclei of nuclear emulsion detector emitted in 4π space angle, forward hemisphere (θ < 90°), and backward hemisphere (θ ≥ 90°). We have also studied the emission characteristics of grey particle with black particles. The present studies show that the emission of grey particles depends not only on the interaction of the different targets of nuclear emulsion detector but it also depends on the number of emission of the black particles. The results of the present studies are also compared with others and found to be consistent.

Mechanisms of Forward–Backward Correlations in the Multiplicity of Particles in Ultrarelativistic Heavy-Ion Collisions

The contributions of various effects to correlations of the average multiplicity of particles emitted in the forward hemisphere of heavy-ion collisions with the multiplicity of particles emitted in the backward hemisphere (forward–backward correlations) have been comparatively analyzed. It has been shown that the experimentally observed dependence of the strength of such correlations on the centrality of lead–lead ion collisions at the Large Hadron Collider energy $$\sqrt {{{s}_{{NN}}}} $$ = 2.76 TeV can be reproduced by the HYDJET++ model if the hydrodynamic particle flow, decay of resonances, and production and suppression of high-energy quarks and gluons in hot matter are taken into account. The dominant mechanism of forward–backward correlations for the most central collisions involves the production and fragmentation of quark–gluon jets.

Feasibility of energy adaptive angular meshing for perpendicular and parallel magnetic fields in a grid based Boltzmann solver

Purpose: To develop the enabling algorithmic techniques which allow forward-peaked adaptive angular meshing to be compatible with angular advection of magnetic fields within a deterministic Grid Based Boltzmann Solver (GBBS) for MRI-guided radiotherapy, and establish appropriate energy adaptive meshing schemes which minimize total numerical degrees of freedom while preserving high dosimetric accuracy for parallel and perpendicular magnetic fields. Methods: A framework to independently adapt angular mesh resolution and basis function refinement of forward and backscattering hemispheres is developed, uniquely accommodating angular advection introduced by magnetic fields. Upwind stabilization techniques to accurately transfer fluence between hemispheres having different discretization are established. To facilitate oblique beam and magnetic field orientations, cardinal forward-peaked mesh orientations were devised to balance requirements for acyclic space-angle sweep ordering, while ensuring the beam predominantly overlaps the forward hemisphere. Energy-dependent fluence anisotropy is investigated, leading to adaptive angular meshing schemes for parallel and perpendicular magnetic fields. Calculated dose distributions were validated against GEANT4 Monte Carlo calculations on slab geometry and anthropomorphic phantoms. Results: Forward-peaked and isotropic energy adaptive angular meshing schemes were developed for parallel and perpendicular magnetic fields respectively, which reduce the number of elements solved by 52.8% and 47.7% respectively compared to static discretization using 32 quadratic elements while retaining over 97% of points passing the gamma 1%/1 mm criterion against Monte Carlo. Conclusions: Techniques to preserve angular upwind-stabilization between hemispheres of a forward-peaked mesh and establish an acyclic directed space-angle sweep graph enabled energy-adaptive meshing schemes to be developed while accurately solving for magnetic fields. This substantially reduced the numerical degrees of freedom while retaining excellent dosimetric agreement with Monte Carlo. These algorithmic underpinnings contribute towards a fast deterministic GBBS for MRI-guided radiotherapy.

Emission Characteristics of Charged Particle Production in Interactions of 84Kr with the Nuclear Emulsion Detector at Relativistic Energy

This article focuses on the characteristics of the charged particle produced in nucleus-nucleus collisions at relativistic energy. We have studied the emission behavior of charged particles observed in the forward hemisphere (θ < 90°) and the backward hemisphere (θ ≥ 90°). This study shows that the charged particles produced in the forward hemisphere strongly depend on the mass of the projectile beam whereas in the backward hemisphere, they show an exponential decay behavior and are independent of the mass of the projectile beam. The results are compared with other experimental observations and found to be consistent.

PARAMETERS OF OPTICAL POTENTIAL IN p+11Li ELASTIC SCATTERING AT 62 MeV

This paper is a calculation of the differential cross section for the elastic scattering of hydrogen nuclei on exotic nuclei of a neutron-rich lithium-11 isotope by determining the optimal parameters of optical potential via the FRESCO 2.8 software using the strongly coupled nuclear reaction channel method with the spin-orbit and Coulomb interaction included. For lithium, the JP=3/2−- state was selected. The shapes of the elements of the scattering potential were chosen in the Woods-Saxon form. The selection of the parameters of the potential was based on the data extracted from the p+11Li scattering experiment conducted at 62 MeV in the laboratory coordinate system on the RIKEN cyclotron in Japan in 1992. In this work, it was found that the volume and spin-orbital parts of the potential, as well as the diffusion of the interaction, have values of zero or close to zero. The resulting cross section in the forward hemisphere of scattering is 70–75 times largerтthan the corresponding Rutherford cross section, and in the rear hemisphere, on the contrary, Coulomb forces dominate. The theoretical values confidently coincide with the experimental ones.

Angular distribution of multiple Compton scattered gamma rays of 662 keV in tin

In multiple Compton scattering, the incident gamma photon is scattered more than once due to finite dimensions of the sample. It serves as a noise for the exact evaluation of electron momentum distribution in Compton profile, Compton cross section and non-destructive testing of in-assessable large samples. To overcome these difficulties, there is a need to characterise the contribution of multiple scattering as a function of atomic number, scattering angle and incident gamma photon energy. In the present work, measurements are carried out to investigate the multiple scattering of 662 keV photons with tin sample of different thickness in the forward and backward hemispheres. The scattered photon flux is recorded by a NaI(Tl) scintillation detector and with an HPGe solid-state detector to check for the trend of saturation thickness as a function of resolution of the detector. The number of multiply scattered photons is found to be increasing with the sample thickness up to a particular thickness value called saturation thickness beyond which it remains constant with increase in target thickness. The effect of detector collimator size on multiply scattered photons is also studied. Both the detectors show the same trend of saturation thickness as a function of thickness. Angular distribution of multiply scattered photons shows symmetry around 90° scattering angle. The low energy side of multiple scattered photon spectrums is also characterised as a function of sample thickness and order of scattering. Monte Carlo calculations support the present experimental results.

BREMSSTRAHLUNG OF ELECTRONS AND YIELD OF NEUTRONS FROM THICK CONVERTERS, PASSING OF GAMMA RADIATION AND NEUTRONS THROUGH BIOLOGICAL SHIELDING

In GEANT4 spectral-angular distributions of the bremsstrahlung of medium-energy electrons from amorphous targets of different thickness and atomic charge were calculated. The total yield of gamma quanta in the forward hemisphere and at large scattering angles were determined depending on the converter thickness. The difference in the characteristics of gamma radiation for thin and thick targets was shown. The neutron yield is calculated due to photonuclear reactions for various converters. Numerical estimates of the radiation spectra after passing through the biological shielding for neutron and bremsstrahlung were carried out.