Scattering Processes with the Emission of Longitudinal Optical Phonons in the Landau Level System In GaAs/AlGaAs Quantum Well

The scattering processes of longitudinal optical phonons in GaAs/AlGaAs quantum wells in a quantizing magnetic field are considered. The time of intrasubband scattering between Landau levels is calculated by using Fermi's golden rule. The dependence of the scattering rate on the magnitude of the magnetic field has been shown and the magnetic field can suppress scattering processes on longitudinal optical phonons. It is found that the scattering time depends linearly on the width of the quantum well.

The First CHIME/FRB Fast Radio Burst Catalog

We present a catalog of 536 fast radio bursts (FRBs) detected by the Canadian Hydrogen Intensity Mapping Experiment Fast Radio Burst (CHIME/FRB) Project between 400 and 800 MHz from 2018 July 25 to 2019 July 1, including 62 bursts from 18 previously reported repeating sources. The catalog represents the first large sample, including bursts from repeaters and nonrepeaters, observed in a single survey with uniform selection effects. This facilitates comparative and absolute studies of the FRB population. We show that repeaters and apparent nonrepeaters have sky locations and dispersion measures (DMs) that are consistent with being drawn from the same distribution. However, bursts from repeating sources differ from apparent nonrepeaters in intrinsic temporal width and spectral bandwidth. Through injection of simulated events into our detection pipeline, we perform an absolute calibration of selection effects to account for systematic biases. We find evidence for a population of FRBs—composing a large fraction of the overall population—with a scattering time at 600 MHz in excess of 10 ms, of which only a small fraction are observed by CHIME/FRB. We infer a power-law index for the cumulative fluence distribution of α = − 1.40 ± 0.11 ( stat. ) − 0.09 + 0.06 ( sys. ) , consistent with the −3/2 expectation for a nonevolving population in Euclidean space. We find that α is steeper for high-DM events and shallower for low-DM events, which is what would be expected when DM is correlated with distance. We infer a sky rate of [ 820 ± 60 ( stat. ) − 200 + 220 ( sys. ) ] / sky / day above a fluence of 5 Jy ms at 600 MHz, with a scattering time at 600 MHz under 10 ms and DM above 100 pc cm−3.

Influence of shape resonances on the angular dependence of molecular photoionization delays

Characterizing time delays in molecular photoionization as a function of the ejected electron emission direction relative to the orientation of the molecule and the light polarization axis provides unprecedented insights into the attosecond dynamics induced by extreme ultraviolet or X-ray one-photon absorption, including the role of electronic correlation and continuum resonant states. Here, we report completely resolved experimental and computational angular dependence of single-photon ionization delays in NO molecules across a shape resonance, relying on synchrotron radiation and time-independent ab initio calculations. The angle-dependent time delay variations of few hundreds of attoseconds, resulting from the interference of the resonant and non-resonant contributions to the dynamics of the ejected electron, are well described using a multichannel Fano model where the time delay of the resonant component is angle-independent. Comparing these results with the same resonance computed in e-NO+ scattering highlights the connection of photoionization delays with Wigner scattering time delays.

Strain derivative of thermoelectric properties as a sensitive probe for nematicity

The nematic instability is an undebatable ingredient of the physics of iron-based superconductors. Yet, its origin remains enigmatic as it involves a fermiology with an intricate interplay of lattice-, orbital-, and spin degrees of freedom. It is well known that thermoelectric transport is an excellent probe for revealing even subtle signatures of instabilities and pertinent fluctuations. In this paper, we report a strong response of the thermoelectric transport properties of two underdoped 1111 iron-based superconductors to a vanishingly small strain. By introducing the strain derivative of the Seebeck and the Nernst coefficients, we provide a description of the nematic order parameter, proving the existence of an anisotropic Peltier-tensor beside an anisotropic conductivity tensor. Our measurements reveal that the transport nematic phenomenology is the result of the combined effect of both an anisotropic scattering time and Fermi surface distortions, pointing out that in a realistic description, abreast of the spin fluctuations also the orbital character is a fundamental ingredient. In addition, we show that nematic fluctuations universally relax in a Curie–Weiss fashion above TS in all the elasto-transport measurements and we provide evidences that nematicity must be band selective.

Seismic diffraction separation in the near-surface: Detection of high contrast voids in unconsolidated soils

Seismic diffractions carry the signature of near-surface high-contrast anomalies and need to be extracted from the data to complement the reflection processing and other geophysical techniques. Since diffractions are often masked by reflections, surface waves and noise, a careful diffraction separation is required as a first step for diffraction imaging. A multiparameter time-imaging method is employed to separate near-surface diffractions. The implemented scheme makes use of the wavefront attributes that are reliable fully data-derived processing parameters. To mitigate the effect of strong noise and wavefield interference in near-surface data, the proposed workflow incorporates two wavefront-based parameters, dip angle and coherence, as additional constraints. The output of the diffraction separation is a time trace-based stacked section that provides the basis for further analysis and applications such as time migration. To evaluate the performance of the proposed wavefront-based workflow, it is applied to two challenging field data sets that were collected over small culverts in very near-surface soft soil environments. The results of the proposed constrained workflow and the existing unconstrained approach are presented and compared. The proposed workflow demonstrates superiority over the existing method by attenuating more reflection and noise, leading to improved diffraction separation. The abundance of unmasked diffractions reveal that the very near-surface is highly scattering. Time migration is carried out to enhance the anomaly detection by focusing of the isolated diffractions. Although strong diffractivity is observed at the approximate location of the targets, there are other diffracting zones observed in the final sections that might bring uncertainties for interpretation.

GRINDING AND FRACTIONATION OF DRIED PLANT MATERIALS

In the absence of large-scale pectin production in Ukraine, pectin-containing powders are an alternative source. They are used as natural additives in the manufacture of health products, due primarily to the presence of pectin, as well as other useful natural components of raw materials. The purpose of the work is to conduct research on the dispersion and fractionation of dried plant materials and to determine the energy-saving regimes of these processes. The task of the research is to develop optimal modes of dispersion of dried plant materials; determine the depend-ence of the micromill performance and power consumption on the rotation speed of the dispersant rotor; to establish the influence of the load on the sieve and the scattering time on the fractionation process. Objects, equipment and research methods. Dried pectin-containing apples and table beets were used as research objects. Studies of the dispersion process were performed on an micromill (8-MM), the coarse part was ground on a disintegrator (ДЕЗІ), the study of the dispersed composition of powders was carried out on the device 029. The paper analyzes the existing methods of grinding and equipment for its implementation. The analysis showed that percussion mills are the most suitable for grinding dried pectin-containing apples and table beets. The dispersed composition of pectin-containing powders is determined in the article. The influence of material loading on the sieve and scattering time on the yield of the fine fraction was investigated. It is proved that the scattering process is more influenced by the scattering time. The paper graphically shows the effect of rotor speed on the equivalent particle diameter and powder dispersion; differential and integral particle distribution curves depending on rotor speed and scattering time for apple and beet powders; the dependence of micromill productivity and power consumption on the speed of the disperser rotor, etc. The optimal operating speed of the rotor is 50 m/s. At this speed, energy consumption for grinding dried materials is minimal. It is proved that the fractionation process almost does not depend on the load on the sieve, but depends on the scattering time. It is impractical to increase the process duration over 3 minutes. Increasing the time to 4 minutes increases the mass of the fine fraction by only 2…5%. The yield of the fine fraction of powders according to the optimal modes of dispersion and separation is: apple – 65...68%, beet – 62...65%. The possibility of re-grinding in order to increase the fine fraction yield is shown. Conclusions. According to the results of the research, the optimal dispersion regimes, the dependence of micromill productivity and power consumption on the dispersant rotor speed, as well as the effect of load on the sieve and scattering time of apple and beet powders on the fractionation process are determined. On the basis of the conducted researches energy-saving conditions of processes of dispersion and fractionation of pectin-containing powders and proper work of the corresponding equipment are defined.

Long wavelength Infrared Detection, Bands Structure and effective mass in InAs/GaSb Nanostructure Superlattice

We have investigated in the bands structure and the effective mass, respectively, along the growth axis and in the plane of InAs (d1=48.5Å)/GaSb(d2=21.5Å) type II superlattice (SL), performed in the envelop function formalism. We studied the semiconductor to semimetal transition and the evolutions of the optical band gap, Eg(Γ), as a function of d1, the valence band offset Λ and the temperature. In the range of 4.2–300 K, the corresponding cutoff wavelength ranging from 7.9 to 12.6 µm, which demonstrates that this sample can be used as a long wavelength infrared detector. The position of the Fermi level, EF = 512 meV, and the computed density of state indicates that this sample is a quasi-two-dimensional system and exhibits n type conductivity. Further, we calculated the transport scattering time and the velocity of electrons on the Fermi surface. These results were compared and discussed with the available data in the literature.

Comparative analysis of room temperature plasmonic graphene hot electron bolometric photodetectors

We appraise a waveguide-integrated plasmonic graphene photodetector based on the hot carrier photo-bolometric effect, with performance characterized simultaneously by high responsivity, on the scale of hundreds of A/W, and high speed on the scale of 100’s of GHz. Performance evaluation is based on a theory of bolometric effect originating from the band nonparabolicity of graphene. Results compare favorably with the state-of-the-art plasmonic bolometric photodetectors, predicting up to two orders of magnitude increase in a responsivity while keeping speed on the same level, defined by the electron-lattice scattering time in graphene.