We have obtained propagators in the position space as an expansion over Landau levels for the charged scalar particle, fermion, and massive vector boson in a constant external magnetic field. The ...summation terms in the resulting expressions consisted of two factors, one being rotationally invariant in the 2-dimensional Euclidean space perpendicular to the direction of the field, and the other being Lorentz-invariant in the 1+1-dimensional space-time. The obtained representations are unique in the sense that they allow for the simultaneous study of the propagator from both space-time and energetic perspectives which are implicitly connected. These results contribute to the development of position-space techniques in QFT and are expected to be of use in the calculations of loop diagrams.
Solar radio observations provide a unique diagnostic of the outer solar atmosphere. However, the inhomogeneous turbulent corona strongly affects the propagation of the emitted radio waves, so ...decoupling the intrinsic properties of the emitting source from the effects of radio wave propagation has long been a major challenge in solar physics. Here we report quantitative spatial and frequency characterization of solar radio burst fine structures observed with the Low Frequency Array, an instrument with high-time resolution that also permits imaging at scales much shorter than those corresponding to radio wave propagation in the corona. The observations demonstrate that radio wave propagation effects, and not the properties of the intrinsic emission source, dominate the observed spatial characteristics of radio burst images. These results permit more accurate estimates of source brightness temperatures, and open opportunities for quantitative study of the mechanisms that create the turbulent coronal medium through which the emitted radiation propagates.
Nanodiamond (ND) is one of the most attractive allotropic modification of carbon due to their unique physical and chemical properties. In the present review the current state of science and ...technology in the field of NDs is analyzed. ND can be used in various application and in different form e.g. as a dispersion phase in suspension, as a filler in composites, etc., so the sedimentation stability of ND in different media are under scrutiny. Thus, theoretical aspects of ND suspension coagulation mechanisms and the methods avoiding it were considered. The dependence of rheological behavior on particles modification was discussed as well. Various methods for the preparation and modification of NDs to obtain particles of various sizes on a nanometer scale with different physicochemical properties were reviewed. The area of practical application for NDs was considered on the example of polymer composites. The various manufacturing methods, mechanical properties and medical aspects for thermosetting, thermoplastic and elastomer ND composites were summarized.
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•The review presents current state of science in the field of nanodiamonds.•There are several methods for stabilizing of nanodiamond particles in various liquids.•The review contributes to a better understanding the nature of sol-gel transition in nanodiamond suspensions.•Composites filled with nanodiamonds exhibit improved mechanical properties.
This article covers the molecular structure optimization and spectroscopic studies, such as Raman, UV–Vis absorption and FTIR, carried out for novel, biodegradable and biocompatible chitosan-graphene ...oxide (CS-GO) polymer nanocomposites (PNCs), which were synthesized by using simple blending technique followed by ultrasonification treatment. In addition, the structural and electrical properties have also been investigated. Under molecular structure optimization, the structural geometry, electronic structure (HOMO and LUMO) and potential distribution have been computed. X-ray diffraction of PNCs reveals that the crystallized phase of GO dominates over the CS giving modification in crystallite size and presence of micro-strain. FTIR and Raman spectroscopic studies have been carried out to confirm the proper formation of PNCs and presence of functional group in the composites. The surface morphology has been studied with the help of FESEM to confirm proper dispersion of GO sheets. Optical absorption edge and band gap analyzed from UV–Vis analysis reveal the semiconducting nature of PNCs. In addition, the optical band gap is tuned by varying the content of GO in PNCs. This tuning in band gap has also been supported by XRD and computational results. The dielectric constant and dc conductivity are found increased with increasing content of GO in PNCs. Additionally, the I–V characteristics of PNCs shows Ohmic type conduction with rising in current due to incorporation of GO. In view of the results achieved, the usage of CS-GO PNC is suitable for future development of optical and Gas sensors and UV-detectors, and therefore, such composite may be proven as a potential and suitable candidate for the optoelectronic or electrical devices operating at high frequencies.
Highly anisometric α-chitin nanoparticles isolated by TEMPO-oxidation were investigated as filler for electrorheological fluids. The dimensions of rod-like particles were determined by AFM and ...cryo-TEM methods. The rheological behavior of α-chitin nanoparticles in polydimethylsiloxane changes from viscous to elastic under electric field. The yield stress reaches about 220 Pa at 7 kV/mm for 1.0 wt% fluid. Despite the nanosize of particles, the suspensions sedimentation ratio was found to be low (~23%). The electrorheological behavior of the fluids was discussed in terms of the Mason numbers. The stability of fluids response under switching electric field was shown. The activation energy of polarization processes in suspensions was calculated as 58 ± 2 and 64 ± 1 kJ/mol for 0.5 and 1.0 wt% filler content from the impedance spectra. The high aspect ratio (~70) and dielectric permittivity result in high electrorheological activity of α-chitin suspensions at extremely low concentrations (≤1.0 wt%).
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Based on the principles of elasticity theory, an assessment of the adhesion for bodies stuck together has been carried out by the example of a “particle of sprayed powder–metal substrate.” ...Relationships for determining the shear stresses and separation stresses are obtained. The comparison of the theoretical values of shear stresses and separation stresses with experimental data confirms the validity of using adhesion theory for calculation of the adhesion strength for coatings obtained by means of thermal spraying. The developed theoretical principles make it possible to choose a suitable fraction of the deposited powder material, which can provide the required strength of adhesion between the main coating layer and the metal substrate or sublayer in the course of thermal spraying.
Spin Noise in Birefringent Media Kozlov, V. O.; Kuznetsov, N. S.; Smirnov, D. S. ...
Physical review letters,
08/2022, Letnik:
129, Številka:
7
Journal Article
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•Suspensions of polydimethylsiloxane filled by porous chitosan particles exhibit high electrorheological activity.•The porosity of the filler allows achieving higher yield stress at ...lower content of chitosan.•The porosity of the filler significantly enhances the sedimentation stability of suspensions.•Electrorheological fluids filled by porous chitosan particles well operate in on/off electric field mode.
Novel porous filler for electrorheological fluids was fabricated from chitosan via freeze drying technique. An exceptional electrorheological effect was discovered in suspensions of polydimethylsiloxane (silicone oil) filled by highly porous chitosan particles. The electrorheological activity was studied by rotational rheometry and visualized by optical microscopy. High porosity of the filler allows preparing highly efficient electrorheological fluids at rather low (< 1 wt%) concentration of dispersed phase. The mechanism of chain-like structure formation was considered. The electrorheological behavior of suspensions and the filler structural organization at different concentration were comprehended in terms of dielectric properties. The rheological data were approximated by Bingham and Cho-Choi-Jhon equations. The sedimentation stability of chitosan suspensions in polydimethylsiloxane was significantly affected by particles porosity.
The insufficient data on a structure of the boron-doped diamond (BDD) has frustrated efforts to fully understand the fascinating electronic properties of this material and how they evolve with ...doping. We have employed X-ray diffraction and Raman scattering for detailed study of the large-sized BDD single crystals. We demonstrate a formation of boron-carbon (B-C) nanosheets and bilayers in BDD with increasing boron concentration. An incorporation of two boron atoms in the diamond unit cell plays a key role for the B-C nanosheets and bilayer formation. Evidence for these B-C bilayers which are parallel to {111} planes is provided by the observation of high-order, super-lattice reflections in X-ray diffraction and Laue patterns. B-C nanosheets and bilayers minimize the strain energy and affect the electronic structure of BDD. A new shallow acceptor level associated with B-C nanosheets at ~37 meV and the spin-orbit splitting of the valence band of ~6 meV are observed in electronic Raman scattering. We identified that the superconducting transitions occur in the (111) BDD surfaces only. We believe that the origin of Mott and superconducting transitions is associated with the two-dimensional (2D) misfit layer structure of BDD. A model for the BDD crystal structure, based on X-ray and Raman data, is proposed and confirmed by density functional theoretical calculation.
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