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A. Grigoriev

Publications and source records attributed to A. Grigoriev.

12 recordsLinked to original sources
arXiv2024

Unambiguous detection of mesospheric CO2 clouds on Mars using 2.7 μm absorption band from the ACS/TGO solar occultations

Mesospheric CO2 clouds are one of two types of carbon dioxide clouds known on Mars. We present observations of mesospheric CO2 clouds made by Atmospheric Chemistry Suit (ACS) onboard the ESA-Roscosmos ExoMars Trace Gas Orbiter (TGO). We analyzed 1663 solar occultation sessions of Thermal InfraRed (TIRVIM) and Middle InfraRed (MIR) channels of ACS covering more than two Martian years that contain spectra of 2.7 μm carbon dioxide ice absorption band. That allowed us to unambiguously discriminate carbon dioxide ice aerosols from mineral dust and water ice aerosols, not relying on the information of atmospheric thermal conditions. CO2 clouds were detected in eleven solar occultation observations at altitudes from 39 km to 90 km. In five cases, there were two or three layers of CO2 clouds that were vertically separated by 5-15 km gaps. Effective radius of CO2 aerosol particles is in the range of 0.1-2.2 μm. Spectra produced by the smallest particles indicate a need for a better resolved CO2 ice refractive index. Nadir optical depth of CO2 clouds is in the range 5*10^{-4}-4*10^{-2} at both 2.7 μm and 0.8 μm. Asymmetrical diurnal distribution of detections observed by ACS is potentially due to local time variations of temperature induced by thermal tides. Two out of five cases of carbon dioxide cloud detections made by the TIRVIM instrument reveal the simultaneous presence of CO2 ice and H2O ice aerosols. Temperature profiles measured by the Near InfraRed (NIR) channel of ACS are used to calculate CO2 saturation ratio S at locations of carbon dioxide clouds. Supersaturation S > 1 is detected in only 5 out of 19 cases of CO2 cloud layers; extremely low values of S < 0.1 are found in 9 out of 19 cases.

astro-ph.EP↗
arXiv2022

Thermal structure and aerosols in Mars' atmosphere from TIRVIM/ACS onboard the ExoMars Trace Gas Orbiter : validation of the retrieval algorithm

The Atmospheric Chemistry Suite (ACS) onboard the ExoMars Trace Gas Orbiter (TGO) monitors the Martian atmosphere through different spectral intervals in the infrared light. We present a retrieval algorithm tailored to the analysis of spectra acquired in nadir geometry by TIRVIM, the thermal infrared channel of ACS. Our algorithm simultaneously retrieves vertical profile of atmospheric temperature up to 50 km, surface temperature, and integrated optical depth of dust and water ice clouds. The specificity of the TIRVIM dataset lies in its capacity to resolve the diurnal cycle over a 54 sol period. However, it is uncertain to what extent can the desired atmospheric quantities be accurately estimated at different times of day. Here we first present an Observing System Simulation Experiment (OSSE). We produce synthetic observations at various latitudes, seasons and local times and run our retrieval algorithm on these synthetic data, to evaluate its robustness. Different sources of biases are documented, in particular regarding aerosol retrievals. Atmospheric temperature retrievals are found robust even when dust and/or water ice cloud opacities are not well estimated in our OSSE. We then apply our algorithm to TIRVIM observations in April-May, 2018 and perform a cross-validation of retrieved atmospheric temperature and dust integrated opacity by comparisons with thousands of co-located Mars Climate Sounder (MCS) retrievals. Most differences between TIRVIM and MCS atmospheric temperatures can be attributed to differences in vertical sensitivity. Daytime dust opacities agree well with each other, while biases are found in nighttime dust opacity retrieved from TIRVIM at this season.

astro-ph.EP↗
arXiv2021

Neutrino spin operator and dispersion in moving matter

We found a spin integral of motion for neutrino, which propagates in moving and polarized matter. The operator obtained opens up the possibility of consistent classification of neutrino states in such a medium and, as a consequence, a systematic description of the related physical phenomena. Using the operator, we obtain a dispersion relation for neutrinos and consider its particular cases.

hep-ph↗
arXiv2019

Neutrino spin oscillations in polarized matter

We study the neutrino spin oscillations, i.e., neutrino spin precession caused by the neutrino interaction with matter polarized by external magnetic field (or, equivalently, by the interaction of the induced magnetic moment (IMM) of a neutrino with the magnetic field). In the analysis, we consider realistic conditions inside supernovae and discuss both the Dirac and Majorana cases. We show that due to the interaction with the polarized matter a neutrino flux from a supernova suffers additional attenuation at low neutrino energies. Another possible effect is that when taken together the effects of conventional magnetic moment and polarized matter can cancel each other so that under certain condition the oscillations disappear. We note that this can lead to the appearance of a characteristic maximum in the spectrum of electron neutrinos from supernovae. Accounting for neutrino mixing (in the two-flavor approximation) can significantly increase (almost twice) the effective value of the IMM of the electron neutrino. As a result, electron neutrinos with twice as high energy will be able to participate in the processes of spin conversion. Various feedback mechanisms accompanying the considered phenomena are also discussed.

hep-ph↗
arXiv2014

The effect of plasmon mass on spin light of neutrino in dense matter

We develop the theory of spin light of neutrino in matter ($SLν$) and include the effect of plasma influence on the emitted photon. We use the special technique based on exact solutions of particles wave equations in matter to perform all the relevant calculations, and track how the plasmon mass enters the process characteristics including the neutrino energy spectrum, $SLν$ rate and power. The new feature it induces is the existence of the process threshold for which we have found the exact expression and the dependence of the rate and power on this threshold condition. The $SLν$ spatial distribution accounting for the above effects has been also obtained. These results might be of interest in connection with the recently reported hints of ultra-high energy neutrinos $E = 1 ÷10$ PeV observed by IceCube.

hep-ph↗
arXiv2010

Cumulene Molecular Wire Conductance from First Principles

We present first principles calculations of current-voltage characteristics (IVC) and conductance of Au(111):S2-cumulene-S2:Au(111) molecular wire junctions with realistic contacts. The transport properties are calculated using full self-consistent ab initio NEGF-DFT methods under external bias. The conductance of the cumulene wires shows oscillatory behavior depending on the number of carbon atoms (double bonds). Among all conjugated oligomers, we find that cumulene wires with odd number of carbon atoms yield the highest conductance with metallic-like ballistic transport behavior. The reason is the high density of states in broad LUMO levels spanning the Fermi level of the electrodes. The transmission spectrum and the conductance depend only weakly on applied bias, and the IVC is nearly linear over a bias region from +1 to -1 V. Cumulene wires are therefore potential candidates for metallic connections in nanoelectronic applications.

cond-mat.mes-hall↗
arXiv2006

Critical Roles of Metal-Molecule Contacts in Electron Transport Through Molecular-wire Junctions

We study the variation of electron transmission through Au-S-benzene-S-Au junctions and related systems as a function of the structure of the Au:S contacts. For junctions with semi-infinite flat Au(111) electrodes, the highly coordinated in-hollow and bridge positions are connected with broad transmission peaks around the Fermi level, due to a broad range of transmission angles from transverse motion, resulting in high conductivity and weak dependence on geometrical variations. In contrast, for (unstable) S-adsorption on top of an Au atom, or in the hollow of a 3-Au-atom island, the transmission peaks narrow up due to suppression of large transmission angles. Such more one-dimensional situations may describe more common types of contacts and junctions, resulting in large variations in conductivity and sensitivity to bonding sites, tilting and gating. In particular, if S is adsorbed in an Au vacancy, sharp spectral features appear near the Fermi level due to essential changes of the level structure and hybridization in the contacts, admitting order-of-magnitude variations of the conductivity. Possibly such a system, can it be fabricated, will show extremely strong non-linear effects and might work as uni- or bi-directional voltage-controlled 2-terminal switches and non-linear mixing elements. Finally, density-functional-theory (DFT) based transport calculations seem relevant, being capable of describing a wide range of transmission peak structures and conductivities. Prediction and interpretation of experimental results probably require more precise modeling of realistic experimental situations.

cond-mat.mes-hall↗
arXiv2005

Quantum Theory of Neutrino Spin-Light in Matter

The quantum theory of the spin light of neutrino ($SLν$) exactly accounting for the effect of the background matter is developed. The $SLν$ rate and power, and also the emitted photon's energy are obtained for the different values of the neutrino momentum and density of matter. The spatial distribution of the radiation power and the dependence of the emitted photon's energy on the direction of radiation are studied. It is also shown that, in a wide range of the neutrino momentum and densities of matter, the $SLν$ radiation is characterized by nearly total circular polarization. Conditions for the effective neutrino spin-light radiation in the electron plasma are discussed.

hep-ph↗
arXiv2004

Nonlinear conductance in molecular devices: molecular length dependence

We theoretically study the electronic transport in the monolayer of dithiolated phenylene vinylene oligomeres coupled to the (111) surfaces of gold electrodes. We use non-equilibrium Green functions (NEGF) and density functional theory(DFT) implemented in the TranSIESTA package to obtain a full ab initio self-consistent description ofthe transport current through the molecular nanostructure with different electrochemical bias potentials. The calculated current-voltage characteristics (IVC) of the systems for the same contact geometry have shown a systematic decrease of the conductivity with the increased length of the molecules. We analyze the results in terms of transmission eigenchannels and find that besides the delocalization of molecular orbitals the distance between gold electrodes also determines the transport properties.

cond-mat.mtrl-sci↗
arXiv2002

Effect of Matter Motion and Polarization in Neutrino Flavour Oscillations

The Lorentz invariant formalism for description of neutrino flavor oscillation in moving and polarized matter is developed. It is shown that the neutrino effective potential, which determines the effective mass difference between neutrinos in matter can be sufficiently changed by relativistic motion of matter. In the case of matter motion parallel to neutrino propagation, matter effects in neutrino flavor oscillations are suppressed. In the case of relativistic motion of matter in the opposite direction sufficient increase of effects of matter in neutrino oscillations is predicted. The dependence of the matter term in neutrino effective potential on the values and correlations of the three vectors, the neutrino and matter speeds and matter polarization, is discussed in details.

hep-ph↗
arXiv2002

The Mikheyev-Smirnov-Wolfenstein Effect in Moving Matter

The Lorentz invariant formalism for description of neutrino flavour oscillations in moving matter is developed. It is shown that the matter motion with relativistic speed can sufficiently change the matter term in the neutrino effective potential. In the case of matter motion parallel to neutrino propagation, matter effects in neutrino flavour oscillations are suppressed. In the case of relativistic motion of matter in the opposite direction in respect to neutrino propagation, sufficient increase of effects of matter in neutrino oscillations is predicted. The effective neutrino flavour oscillation probability, effective mixing angle and oscillation length, as well as the MSW effect resonance condition for the case of moving matter are derived.

hep-ph↗