466 research outputs found
Quantum Kinetic Evolution of Marginal Observables
We develop a rigorous formalism for the description of the evolution of
observables of quantum systems of particles in the mean-field scaling limit.
The corresponding asymptotics of a solution of the initial-value problem of the
dual quantum BBGKY hierarchy is constructed. Moreover, links of the evolution
of marginal observables and the evolution of quantum states described in terms
of a one-particle marginal density operator are established. Such approach
gives the alternative description of the kinetic evolution of quantum
many-particle systems to generally accepted approach on basis of kinetic
equations.Comment: 18 page
Towards Rigorous Derivation of Quantum Kinetic Equations
We develop a rigorous formalism for the description of the evolution of
states of quantum many-particle systems in terms of a one-particle density
operator. For initial states which are specified in terms of a one-particle
density operator the equivalence of the description of the evolution of quantum
many-particle states by the Cauchy problem of the quantum BBGKY hierarchy and
by the Cauchy problem of the generalized quantum kinetic equation together with
a sequence of explicitly defined functionals of a solution of stated kinetic
equation is established in the space of trace class operators. The links of the
specific quantum kinetic equations with the generalized quantum kinetic
equation are discussed.Comment: 25 page
Characterization of acetonitrile ice irradiated by X-rays employing the PROCODA code: II. Desorption processes
In this work, we focus on the study of radiation induced desorption processes
that occurred in acetonitrile ice irradiated by broadband X-rays (6 eV to 2
keV) monitored by FTIR spectroscopy at different radiation fluences. In a
previous work, we used the PROCODA code to derive the chemical evolution of the
ice. Here, we have obtained that the acetonitrile desorbed column density is at
least two orders of magnitude larger than the desorbed column densities of
daughter or granddaughter molecular species at chemical equilibrium stage. This
indicates that total desorption column density is mainly governed by the father
molecule, as also previously hypothesized in experimental studies. This occurs
basically because the acetonitrile column density is larger than the other
ones. In particular, at chemical equilibrium acetonitrile desorption column
density represents almost 98\% of the total, while it is close to 1\% for H, CN
and CH, the species with larger molecular desorption percentages at
chemical equilibrium. Another derived quantity is what we called intrinsic
desorption rate, which is a number per second for individual species. Some of
the larger intrinsic desorption rates were: CHCN (), CN
(), H (), CH ()
and CN (). These results help to put constrain in
astrochemical models and can be also useful to clarify some astronomical radio
observations.Comment: To appear in MNRA
The von Neumann Hierarchy for Correlation Operators of Quantum Many-Particle Systems
The Cauchy problem for the von Neumann hierarchy of nonlinear equations is
investigated. One describes the evolution of all possible states of quantum
many-particle systems by the correlation operators. A solution of such
nonlinear equations is constructed in the form of an expansion over particle
clusters whose evolution is described by the corresponding order cumulant
(semi-invariant) of evolution operators for the von Neumann equations. For the
initial data from the space of sequences of trace class operators the existence
of a strong and a weak solution of the Cauchy problem is proved. We discuss the
relationships of this solution both with the -particle statistical
operators, which are solutions of the BBGKY hierarchy, and with the
-particle correlation operators of quantum systems.Comment: 26 page
Hydrodynamic Equations for Microscopic Phase Densities
The evolution equations for the generalized microscopic phase densities are
introduced. The evolution equations of average values of microscopic phase
densities are derived and a solution of the initial-value problem of the
obtained hydrodynamic type hierarchy is constructed.Comment: 4 page
1-Alkoxyamino-4-dimethylaminopyridinium derivatives as new representatives of O–N–N⁺ geminal systems and their structure
On chemical bonding of Helium with hcp-Beryllium
Chemical inertness is the key property of helium determining its solubility,
distribution and accumulation kinetics in metals. Against all expectations, our
ab initio calculations show a substantial chemical bonding between He and Be
atoms in the hcp-Be matrix when He occupies a non-symmetric position in a basal
plane.Comment: Revised version of manuscript, 4 pages, 4 figure
New approach to N,N-dialkoxy-N'-arylureas and N,N-dialkoxycarbamates
Methanolysis of N-chloro-N-alkoxy-N'-arylureas in the presence of silver trifluoroacetate gives the corresponding N,N-dialkoxy-N'‑arylureas, whereas N-chloro-N-alkoxycarbamates react with alcohols in the presence of silver trifluoroacetate to afford N,N-dialkoxycarbamates
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