2,338 research outputs found
Mixed Quantum/Classical Approach for Description of Molecular Collisions in Astrophysical Environments
An efficient and accurate mixed quantum/classical theory approach for computational treatment of inelastic scattering is extended to describe collision of an atom with a general asymmetric-top rotor polyatomic molecule. Quantum mechanics, employed to describe transitions between the internal states of the molecule, and classical mechanics, employed for description of scattering of the atom, are used in a self-consistent manner. Such calculations for rotational excitation of HCOOCH3 in collisions with He produce accurate results at scattering energies above 15 cm–1, although resonances near threshold, below 5 cm–1, cannot be reproduced. Importantly, the method remains computationally affordable at high scattering energies (here up to 1000 cm–1), which enables calculations for larger molecules and at higher collision energies than was possible previously with the standard full-quantum approach. Theoretical prediction of inelastic cross sections for a number of complex organic molecules observed in space becomes feasible using this new computational tool
Anisotropic relaxation in NADH excited states studied by polarization-modulation pump-probe transient spectroscopy
We present the results of experimental and theoretical studies of fast
anisotropic relaxation and rotational diffusion in the first electron excited
state of biological coenzyme NADH in water-ethanol solutions. The experiments
have been carried out by means of a novel polarization-modulation transient
method and fluorescence polarization spectroscopy. For interpretation of the
experimental results a model of the anisotropic relaxation in terms of scalar
and vector properties of transition dipole moments and based on the
Born-Oppenheimer approximation has been developed. The results obtained suggest
that the dynamics of anisotropic rovibronic relaxation in NADH under excitation
with 100~fs pump laser pulses can be characterised by a single vibration
relaxation time laying in the range 2--15~ps and a single rotation
diffusion time laying in the range 100--450~ps a subject of ethanol
concentration. The dependence of the times and on the
solution polarity (static permittivity) and viscosity has been determined and
analyzed. Limiting values of an important parameter describing the rotation of the transition dipole
moment in the course of vibrational relaxation has been determined from
experiment as function of the ethanol concentration and analyzed.Comment: 14 pages, 13 figure
Bootstrap and the physical values of resonance parameters
This is the 6th paper in the series developing the formalism to manage the
effective scattering theory of strong interactions. Relying on the theoretical
scheme suggested in our previous publications we concentrate here on the
practical aspect and apply our technique to the elastic pion-nucleon scattering
amplitude. We test numerically the pion-nucleon spectrum sum rules that follow
from the tree level bootstrap constraints. We show how these constraints can be
used to estimate the tensor and vector coupling constants. At last, we
demonstrate that the tree-level low energy expansion coefficients computed in
the framework of our approach show nice agreement with known experimental data.
These results allow us to claim that the extended perturbation scheme is quite
reasonable from the computational point of view.Comment: 41 pages, 7 figure
Preimage Attack on MD4 Hash Function as a Problem of Parallel Sat-Based Cryptanalysis
In this paper we study the inversion problem of MD4 cryptographic hash function developed by R. Rivest in 1990. By MD4-k we denote a truncated variant of MD4 hash function in which k represents a number of steps used to calculate a hash value (the full version of MD4 function corresponds to MD4-48). H. Dobbertin has showed that MD4-32 hash function is not one-way, namely, it can be inverted for the given image of a random input. He suggested to add special conditions to the equations that describe the computation of concrete steps (chaining variables) of the considered hash function. These additional conditions allowed to solve the inversion problem of MD4-32 within a reasonable time by solving corresponding system of equations. The main result of the present paper is an automatic derivation of “Dobbertin’s conditions” using parallel SAT solving algorithms. We also managed to solve several inversion problems of functions of the kind MD4-k (for k from 31 up to 39 inclusive). Our method significantly outperforms previously existing approaches to solving these problems
Scanning Probe Microscopy of Elastomers with Mineral Fillers
The results of a comprehensive study of the newly synthesized elastomeric composites filled with micro- and nanoscale modified shungite and also taurit, diatomit, and neosyl fillers are presented. The surface structure study of the prepared composites was conducted using scanning probe microscopy. The use of microscopy allowed visualization of the distribution patterns of filler aggregates and agglomerates in composites. The morphology and micro-nanometer size ranges of these aggregates in the synthesized materials are determined. The proposed method of grinding shungite, taurit, diatomit, and neosyl fillers allows significantly increasing the strength characteristics of these composites. The correlation between the reinforcement of the elastic-strength properties and the distribution of the used fillers in the rubber matrix was established
Impact of climate change on the ground thermal regime in the lower Lena region, Arctic central Siberia
This paper presents the results of 30 years of permafrost thermal monitoring in the Tiksi area in the eastern Russian Arctic. At a stone ridge site, the mean annual temperatures in the upper 30 m of the ground have increased by 1–2.4 C compared to the first years of observations, with trends of C/yr. At the same time, its change was uneven. In the last 20 years, the rate of increase has increased compared with the first decade of observations. At wet tundra sites in the foothill plain, the mean annual temperatures at the top of permafrost have increased by 2.4–2.6 C between 2005 and 2022 at rates of 0.11–0.15 C/yr, and the active layer thicknesses have increased at rates of 0.05–0.41 cm/yr
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