Wavelength-Dependent Seeing Systematically Changes the Normalized Slope of Telescopic Reflectance Spectra of Mercury

Telescopic observations of Mercury consistently report systematic variations of the normalized spectral slope of visible-to-near-infrared reflectance spectra. This effect was previously assumed to be a photometric property of the regolith, but it is not yet fully understood. After the MESSENGER mission, detailed global spectral maps of Mercury are available that better constrain Mercury’s photometry. So far, wavelength-dependent seeing has not been considered in the context of telescopic observations of Mercury. This study investigates the effect of wavelength-dependent seeing on systematic variations of Mercury’s normalized spectral reflectance slope. Therefore, we simulate the disk of Mercury for an idealized scenario, as seen by four different telescopic campaigns using the Hapke and the Kaasalainen–Shkuratov photometric model, the MDIS global mosaic, and a simple wavelength-dependent seeing model. The simulation results are compared with the observations of previous telescopic studies. We find that wavelength-dependent seeing affects the normalized spectral slope in several ways. The normalized slopes are enhanced near the limb, decrease toward the rim of the seeing disk, and even become negative. The decrease of the normalized spectral slope is consistent with previous observations. However, previous studies have associated the spectral slope variations with photometric effects that correlate with the emission angle. Our study suggests that wavelength-dependent seeing may cause these systematic variations. The combined reflectance and seeing model can also account for slope variations between different measurement campaigns. We report no qualitative differences between results based on the Hapke model or the Kaasalainen–Shkuratov model.

The ABALONE photosensor

The ABALONE is a new type of photosensor produced by PhotonLab, Inc. with cost effective mass production, robustness and high performance. This modern technology provides sensitivity to visible and UV light, exceptional radio-purity and excellent detection performance in terms of intrinsic gain, afterpulsing rate, timing resolution and single-photon sensitivity. For these reasons, the ABALONE can have many fields of application, including particle physics experiments, such as DARWIN, and medical imaging. This new hybrid photosensor, that works as light intensifier, is based on the acceleration in vacuum of photoelectrons generated in a traditional photosensor cathode and guided towards a window of scintillating material that can be read from the outside through a silicon photomultiplier. In this work we present the simulation of the ABALONE and the results from operation at room temperature. The goal of the characterization is the evaluation of the gain, the response in time and the single photoelectron spectrum as a function of the electric field and the photoelectron emission angle. Details of future tests will be also discussed.

Optical Constants Retrieval from a Thin Film at Elevated Temperatures Using Emittance

Refractive index and extinction coefficient (optical constants) are essential in photonic design and thermal radiation utilization. These constants vary with the material phase, temperature, wavelength, and subject dimension. Precisely retrieving these constants of a thin film is thus challenging at elevated temperatures. To tackle this challenge, a methodology for retrieval using emittance at different emission angle θ has been developed here. The method contains four steps and takes advantages of an emissometry. The method is firstly validated using simulation and then demonstrates its feasibility by retrieving optical constants of a phase change germanium-antimony-tellurium (Ge2Sb2Te5, GST) film. Emittance from samples at 100°C, 200°C, 300°C, and 400°C is measured at θ = 0°, 15°, and 30°. The spectral range of retrieval covers from 4 μm to 18 μm where thermal radiation dominates. The investigated film phase considers amorphous, face-centered cubic (FCC), and hexagonal close packed (HCP). The retrieved constants exhibit temperature and substrate independence, but they show up significant phase reliance.

Accurate Refraction Correction—Assisted Bathymetric Inversion Using ICESat-2 and Multispectral Data

Shallow-water depth information is essential for ship navigation and fishery farming. However, the accurate acquisition of shallow-water depth has been a challenge for marine mapping. Combining Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2) bathymetry data with multispectral data, satellite-derived bathymetry is a promising solution through which to obtain bathymetric information quickly and accurately. This study proposes a photon refraction correction method considering sea-surface undulations to address errors in the underwater photons obtained by the ICESat-2. First, the instantaneous sea surface and beam emission angle are integrated to determine the sea-surface incidence angle. Next, the distance of photon propagation in water is determined using sea-surface undulation and Snell’s law. Finally, position correction is performed through geometric relationships. The corrected photons were combined with the multispectral data for bathymetric inversion, and a bathymetric map of the Yongle Atoll area was obtained. A bathymetric chart was created using the corrected photons and the multispectral data in the Yongle Atoll. Comparing the results of different refraction correction methods with the data measured shows that the refraction correction method proposed in this paper can effectively correct bathymetry errors: the root mean square error is 1.48 m and the R2 is 0.86.

Triply Differential Positron and Electron Impact Ionization of Argon: Systematic Features and Scaling

Triply differential data are presented for the 200 eV positron and electron impact ionization of argon. Six electron emission energies between 2.6 and 19 eV, and for scattering angles of 2, 3, and 4 degrees cover a momentum transfer range of 0.16 to 0.31 a.u. The binary and recoil intensities are fitted using a double peak structure in both regions, which, for the present kinematic conditions, are unresolved. The fitted peak intensities and angular positions are shown to have systematic dependences as a function of the momentum transfer and kinematic emission angle, respectively, and illustrate projectile charge effects. A comparison with available theories is made where it is seen that the most notable differences include the fact that for the binary lobe, the observed intensity for emission angles around 100° is absent in the theories, and the theoretical predications overestimate the importance of recoil interactions.

Effect of nanoscale amorphization on dislocation emission from a semi-elliptical surface crack tip in nanocrystalline materials

An impact analysis model is built to describe the effect of nanoscale amorphization on dislocation emission from a surface semi-elliptical crack tip in nanocrystalline materials. The nanoscale amorphization is formed by the splitting transformation of grain boundary(GB)disclinations caused by the motion of GBs. The analytical solution of the model is obtained by using the complex method, and the influence of nanoscale amorphization, dislocation emission angle, crack length, and curvature radius of surface crack tip on the critical stress intensity factor (SIF) of the first dislocation emission is investigated through numerical analysis. The numerical analysis shows that the impact of nanoscale amorphization on the critical SIF corresponding to dislocation emission depends on the dislocation emission angle, the position and the size of the nanoscale amorphous, the curvature radius, and the length of surface crack. As the curvature radius of surface crack tip and the crack length increase, the normalized critical SIF increases. When the nanoscale amorphization size is small, it has a great impact on the critical SIF for dislocation, but when the size is relatively large, the effect becomes small. The effect of the increasing strength of the nanoscale amorphization on dislocation emission from the surface crack tip is related to the distance between the nanoscale amorphization and the crack tip, and there is a critical crack-junction for which the increase of dislocation strength has little effect on dislocation emission.

New insight on the role of localisation in the electronic structure of the Si(111)(7 × 7) surfaces

New angle-resolved photoelectron spectroscopy (ARPES) data, recorded at several different photon energies from the Si(111)(7 × 7) surface, show that the well-known S1 and S2 surface states that lie in the bulk band gap are localised at specific (adatom and rest atom) sites on the reconstructed surface. The variations in the photoemission intensity from these states as a function of polar and azimuthal emission angle, and incident photon energy, are not consistent with Fermi surface mapping but are well-described by calculations of the multiple elastic scattering in the final state. This localisation of the most shallowly bound S1 state is consistent with the lack of significant dispersion, with no evidence of Fermi surface crossing, implying that the surface is not, as has been previously proposed, metallic in character. Our findings highlight the importance of final state scattering in interpreting ARPES data, an aspect that is routinely ignored and can lead to misleading conclusions.

Модель переноса импульса при высокоскоростном ударе

An analytical mechanical model of the ejection arising from a high-velocity impact of a rigid projectile on a semi-infinite target is constructed, and an estimate is given of the ejection mass and the effect of momentum amplification transmitted to the target upon impact. The effect of the momentum amplification is caused by the ejection of target fragments in the 148 direction opposite to the direction of flight of the projectie. At present, there is a steady interest in the study of this effect. This is due, in particular, to the possible use of the effect for deflecting a potentially dangerous object (asteroid) approaching the Earth by means of an impact spacecraft using the effect of momentum amplification. The model presented in this work is constructed in approximation of plane deformation using the minimum number of parameters of the projectiler and target materials. Equations for the mass of the ejection and the increment of the target momentum are obtained, depending on the depth of penetration of the projectile. The model takes into account the dependence of the emission angle of the ejection fragments on the penetration depth of the projectile. It is shown that the model adequately describes the ejection momentum, the rate of change in the ejection momentum, and the ejection mass depending on the penetration depth of the projectile. The possibility of representing the momentum and mass of the ejection by scaling ratios is checked both for the ratio of the densities of the projectile and the target ptρρ, and for the dynamic parameter 20ttVYγρ= (0V - impact velocity, tY - yield stress of the target), in which the proportionality coefficient depends only on the shape of the projectile. It was found that scaling with respect to the dynamic parameter γ takes place at сγγ>, where 330сγ≈ that, e.g., for aluminum gives the value 02.5 km/scV =.

Crosstalk Reduction in Voxels for a See-Through Holographic Waveguide by Using Integral Imaging with Compensated Elemental Images

The representation of three-dimensional volumetric pixels, voxels, is an important issue for the near-to-eye displays (NEDs) to solve the vergence-accommodation conflict problem. Although the holographic waveguides using holographic optical element (HOE) couplers are promising technologies for NEDs with the ultra-thin structure and high transparency, most of them have presented only a single and fixed depth plane. In this paper, we analyze the imaging characteristics of holographic waveguides, particularly to represent the arbitrary voxels and investigate the voxel duplication problem arising from the non-collimated light from the voxels. In order to prevent the image crosstalk arising from the voxel duplication, we propose an adjustment method for the emission angle profile of voxels by using the integral imaging technique. In the proposed method, the sub-regions of elemental images, which correspond to the duplicated voxels, are masked in order to optimize the emission angle of integrated voxels. In the experimental verification, a see-through integral imaging system, based on the organic light-emitting diode display and a holographic waveguide with the thickness of 5 mm, was constructed. The fabricated HOE in the waveguide showed high diffraction efficiency of 72.8 %, 76.6%, and 72.5 % for 460 nm, 532 nm, and 640 nm lasers, respectively. By applying the masked elemental images, the proposed method resulted in a reduced crosstalk in the observed voxels by 2.35 times. The full-color experimental results of see-through holographic waveguide with integral imaging are provided, whereby the observed 3D images are presented clearly without the ghost images due to the voxel duplication problem.