arXiv subjects

A. Zaslavsky

Publications and source records attributed to A. Zaslavsky.

15 recordsLinked to original sources

arXiv2026

White paper on the relevance of the European Solar Telescope (EST) for the French heliophysics

The project of the European Solar Telescope aims to provide a state-of-the art infrastructure to study the Sun and its interactions with Earth and the heliosphere. This 4.2m aperture telescope will be equipped with multi conjugate adaptive optics, light-polarisation analyser, imaging spectrograph and integral field unit spectrographs. It will provide unprecedented observations of the solar photosphere and chromosphere and of the dynamical events and features that pertains to the low solar atmosphere. The EST project is presently in a phase of crystallisation, aiming at the creation of an European Research Infrastructure Consortium. While the French community has continuously been associated with the development of the EST project, some specific scientific aspects are more particularly relevant for the French astrophysics and heliophysics communities. The present review highlights the scientific research axes of high interest from the French community that shall strongly benefit from EST. The later will not only advance numerous topics of solar physics, as well as solar adaptive optics developments, but will also provide unrivaled datasets of high interest in the framework of space weather. This review also aims to highlight the space weather use that can be done with future EST observations, that will be particularly relevant for French heliophysicists.

astro-ph.IM↗

arXiv2021

Simulations of radio-wave anisotropic scattering to interpret type III radio bursts measurements by Solar Orbiter, Parker Solar Probe, STEREO and Wind

We use multi-spacecraft observations of invididual type III radio bursts in order to calculate the directivity of the radio emission, to be compared to the results of ray-tracing simulations of the radio-wave propagation and probe the plasma properties of the inner heliosphere. Ray-tracing simulations of radio-wave propagation with anisotropic scattering on density inhomogeneities are used to study the directivity of radio emissions. Simultaneous observations of type III radio bursts by four widely-separated spacecraft are used to calculate the directivity and position of the radio sources. The shape of the directivity pattern deduced for individual events is compared to the directivity pattern resulting from the ray-tracing simulations. We show that simultaneous observations of type radio III bursts by 4 different probes provide the opportunity to estimate the radio source positions and the directivity of the radio emission. The shape of the directivity varies from one event to another, and is consistent with anisotropic scattering of the radio-waves.

astro-ph.SR↗

arXiv2021

Solar Orbiter/RPW antenna calibration in the radio domain and its application to type III burst observations

In order to allow for a comparison with the measurements from other antenna systems, the voltage power spectral density measured by the Radio and Plasma waves receiver (RPW) on board Solar Orbiter needs to be converted into physical quantities that depend on the intrinsic properties of the radiation itself.The main goal of this study is to perform a calibration of the RPW dipole antenna system that allows for the conversion of the voltage power spectral density measured at the receiver's input into the incoming flux density. We used space observations from the Thermal Noise Receiver (TNR) and the High Frequency Receiver (HFR) to perform the calibration of the RPW dipole antenna system. Observations of type III bursts by the Wind spacecraft are used to obtain a reference radio flux density for cross-calibrating the RPW dipole antennas. The analysis of a large sample of HFR observations (over about ten months), carried out jointly with an analysis of TNR-HFR data and prior to the antennas' deployment, allowed us to estimate the reference system noise of the TNR-HFR receivers. We obtained the effective length of the RPW dipoles and the reference system noise of TNR-HFR in space, where the antennas and pre-amplifiers are embedded in the solar wind plasma. The obtained $l_{eff}$ values are in agreement with the simulation and measurements performed on the ground. By investigating the radio flux intensities of 35 type III bursts simultaneously observed by Solar Orbiter and Wind, we found that while the scaling of the decay time as a function of the frequency is the same for the Waves and RPW instruments, their median values are higher for the former. This provides the first observational evidence that Type III radio waves still undergo density scattering, even when they propagate from the source, in a medium with a plasma frequency that is well below their own emission frequency.

astro-ph.SR↗

arXiv2021

First dust measurements with the Solar Orbiter Radio and Plasma Wave instrument

Impacts of dust grains on spacecraft are known to produce typical impulsive signals in the voltage waveform recorded at the terminals of electric antennas. Such signals are routinely detected by the Time Domain Sampler (TDS) system of the Radio and Plasma Waves (RPW) instrument aboard Solar Orbiter. We investigate the capabilities of RPW in terms of interplanetary dust studies and present the first analysis of dust impacts recorded by this instrument. We discuss previously developed models of voltage pulses generation after a dust impact onto a spacecraft and present the relevant technical parameters for Solar Orbiter RPW as a dust detector. Then we present the statistical analysis of the dust impacts recorded by RPW/TDS from April 20th, 2020 to February 27th, 2021 between 0.5 AU and 1 AU. The study shows that the dust population studied presents a radial velocity component directed outward from the Sun, the order of magnitude of which can be roughly estimated as $v_{r, dust} \simeq 50$ km.$s^{-1}$. This is consistent with the flux of impactors being dominated by $β$-meteoroids. We estimate the cumulative flux of these grains at 1 AU to be roughly $F_β\simeq 8\times 10^{-5} $ m$^{-2}$s$^{-1}$, for particles of radius $r \gtrsim 100$ nm. The power law index $δ$ of the cumulative mass flux of the impactors is evaluated by two differents methods (direct observations of voltage pulses and indirect effect on the impact rate dependency on the impact speed). Both methods give a result $δ\simeq 0.3-0.4$. Solar Orbiter RPW proves to be a suitable instrument for interplanetary dust studies. These first results are promising for the continuation of the mission, in particular for the in-situ study of the dust cloud outside the ecliptic plane, which Solar Orbiter will be the first spacecraft to explore.

physics.space-ph↗

arXiv2020

Dust impact voltage signatures on Parker Solar Probe: influence of spacecraft floating potential

When a fast dust particle hits a spacecraft, it generates a cloud of plasma some of which escapes into space and the momentary charge imbalance perturbs the spacecraft voltage with respect to the plasma. Electrons race ahead of ions, however both respond to the DC electric field of the spacecraft. If the spacecraft potential is positive with respect to the plasma, it should attract the dust cloud electrons and repel the ions, and vice versa. Here we use measurements of impulsive voltage signals from dust impacts on the Parker Solar Probe (PSP) spacecraft to show that the peak voltage amplitude is clearly related to the spacecraft floating potential, consistent with theoretical models and laboratory measurements. In addition, we examine some timescales associated with the voltage waveforms and compare to the timescales of spacecraft charging physics.

physics.space-ph↗

arXiv2019

Elements of mathematics in problems. Through olympiads and circles to profession

This is a collection of teaching materials used in several Russian universities, schools, and mathematical circles. Most problems are chosen in such a way that in the course of the solution and discussion a reader learns important mathematical ideas and theories. The materials can be used by pupils and students for self-study, and by teachers. This is an abridged pre-copyedit version of the published book submitted with the permission of the publisher. Each included individual material is self-contained and ready-for-use. Solutions to problems are not included intentionally. This collection consolidates updates of several arXiv submissions, e.g., arXiv:1305.2598.

math.HO↗

arXiv2015

On the Effect of the Interplanetary Medium on Nanodust Observations by the Solar Terrestrial Relations Observatory

New measurements using radio and plasma-wave instruments in interplanetary space have shown that nanometer-scale dust, or nanodust, is a significant contributor to the total mass in interplanetary space. Better measurements of nanodust will allow us to determine where it comes from and the extent to which it interacts with the solar wind. When one of these nanodust grains impacts a spacecraft, it creates an expanding plasma cloud, which perturbs the photoelectron currents. This leads to a voltage pulse between the spacecraft body and the antenna. Nanodust has a high charge/mass ratio, and therefore can be accelerated by the interplanetary magnetic field to speeds up to the speed of the solar wind: significantly faster than the Keplerian orbital speeds of heavier dust. The amplitude of the signal induced by a dust grain grows much more strongly with speed than with mass of the dust particle. As a result, nanodust can produce a strong signal, despite their low mass. The WAVES instruments on the twin Solar TErrestrial RElations Observatory spacecraft have observed interplanetary nanodust particles since shortly after their launch in 2006. After describing a new and improved analysis of the last five years of STEREO/WAVES Low Frequency Receiver data, a statistical survey of the nanodust characteristics, namely the rise time of the pulse voltage and the flux of nanodust, is presented. Agreement with previous measurements and interplanetary dust models is shown. The temporal variations of the nanodust flux are also discussed.

astro-ph.SR↗

arXiv2014

Statistical Survey of Type III Radio Bursts at Long Wavelengths Observed by the Solar TErrestrial RElations Observatory (STEREO)/Waves Instruments: Radio Flux Density Variations with Frequency

We have performed a statistical study of $152$ Type III radio bursts observed by Solar TErrestrial RElations Observatory (STEREO)/Waves between May 2007 and February 2013. We have investigated the flux density between $125$kHz and $16$MHz. Both high- and low-frequency cutoffs have been observed in $60\,%$ of events suggesting an important role of propagation. As already reported by previous authors, we observed that the maximum flux density occurs at $1$MHz on both spacecraft. We have developed a simplified analytical model of the flux density as a function of radial distance and compared it to the STEREO/Waves data.

astro-ph.SR↗

arXiv2013

Interplanetary Nanodust Detection by the Solar Terrestrial Relations Observatory/WAVES Low Frequency Receiver

astro-ph.IM↗

arXiv2008

Electron tunneling spectroscopy of a quantum antidot in the quantum Hall regime

Quantum antidot, a small potential hill introduced into a two-dimensional electron system, presents an attractive tool to study quantum mechanics of interacting electrons.Here, we report experiments on electron resonant tunneling via a quantum antidot on the integer i = 1, 2, 3, 4, 5, and 6 quantum Hall plateaus. Several new features are reported. First, as a function of magnetic field, we observe up to six quasiperiodic resonant tunneling peaks within the fundamental flux period: when flux h/e is added to the area of the antidot there are i peaks on the i-th integer plateau, when i spin-polarized Landau levels are occupied. Corresponding back gate voltage data show one peak per added charge e on all integer plateaus. Second, we observe tunneling dips in four-terminal resistance ("forward scattering") on the even i = 2, 4, and 6 plateaus, when population of both spins is nearly equal. Also, for the first time, we report an internal structure within the h/e period: on the i = 3 spin-split plateau, two of the three resonant tunneling peaks are higher and/or closer than the third. Puzzlingly, in this regime, when back gate voltage is swept, the tunneling peaks are grouped in pairs. These results are attributed to the dominance of the electron-electron Coulomb interaction, effectively mixing Landau level occupation, and to the self-consistent electrostatics of the antidot.

cond-mat.mes-hall↗

arXiv2006

Hopping Conduction in Disordered Carbon Nanotubes

We report electrical transport measurements on individual disordered carbon nanotubes, grown catalytically in a nanoporous anodic aluminum oxide template. In both as-grown and annealed types of nanotubes, the low-field conductance shows as exp[-(T_{0}/T)^{1/2}] dependence on temperature T, suggesting that hopping conduction is the dominant transport mechanism, albeit with different disorder-related coefficients T_{0}. The field dependence of low-temperature conductance behaves an exp[-(xi_{0}/xi)^{1/2}] with high electric field xi at sufficiently low T. Finally, both annealed and unannealed nanotubes exhibit weak positive magnetoresistance at low T = 1.7 K. Comparison with theory indicates that our data are best explained by Coulomb-gap variable range hopping conduction and permits the extraction of disorder-dependent localization length and dielectric constant.

cond-mat.mes-hall↗

arXiv2002

Strain-induced quantum ring hole states in a gated vertical quantum dot

We have experimentally investigated the hole states in a gated vertical strained Si/SiGe quantum dot. We demonstrate the inhomogeneous strain relaxation on the lateral surface creates a ring-like potential near the perimeter of the dot, which can confine hole states exhibiting quantum ring characteristics. The magnetotunneling spectroscopy exhibits the predicted periodicity of energy states in ϕ/\phi0, but the magnitude of the energy shifts is larger than predicted by simple ring theory. Our results suggest a new way to fabricate and study quantum ring structures.

cond-mat.mes-hall↗

arXiv2000

Invariance of Charge of Laughlin Quasiparticles

A Quantum Antidot electrometer has been used in the first direct observation of the fractionally quantized electric charge. In this paper we report experiments performed on the integer i = 1, 2 and fractional f = 1/3 quantum Hall plateaus extending over a filling factor range of at least 27%. We find the charge of the Laughlin quasiparticles to be invariantly e/3, with standard deviation of 1.2% and absolute accuracy of 4%, independent of filling, tunneling current, and temperature.

cond-mat.mes-hall↗

arXiv1998

Document Archiving, Replication and Migration Container for Mobile Web Users

With the increasing use of mobile workstations for a wide variety of tasks and associated information needs, and with many variations of available networks, access to data becomes a prime consideration. This paper discusses issues of workstation mobility and proposes a solution wherein the data structures are accessed in an encapsulated form - through the Portable File System (PFS) wrapper. The paper discusses an implementation of the Portable File System, highlighting the architecture and commenting upon performance of an experimental system. Although investigations have been focused upon mobile access of WWW documents, this technique could be applied to any mobile data access situation.

cs.MA↗

arXiv1998

Finite Element Analysis of Strain Effects on Electronic and Transport Properties in Quantum Dots and Wires

Lattice mismatch in layered semiconductor structures with submicron length scales leads to extremely high nonuniform strains. This paper presents a finite element technique for incorporating the effects of the nonuniform strain into an analysis of the electronic properties of SiGe quantum structures. Strain fields are calculated using a standard structural mechanics finite element package and the effects are included as a nonuniform potential directly in the time independent Schrodinger equation; a k-p Hamiltonian is used to model the effects of multiple valence subband coupling. A variational statement of the equation is formulated and solved using the finite element method. This technique is applied to resonant tunneling diode quantum dots and wires; the resulting densities of states confined to the quantum well layers of the devices are compared to experimental current-voltage I(V) curves.

cond-mat.mtrl-sci↗