30 research outputs found
Wave packet dynamics and valley filter in strained graphene
The time evolution of a wavepacket in strained graphene is studied within the
tight-binding model and continuum model. The effect of an external magnetic
field, as well as a strain-induced pseudo-magnetic field, on the wave packet
trajectories and zitterbewegung are analyzed. Combining the effects of strain
with those of an external magnetic field produces an effective magnetic field
which is large in one of the Dirac cones, but can be practically zero in the
other. We construct an efficient valley filter, where for a propagating
incoming wave packet consisting of momenta around the K and K' Dirac points,
the outgoing wave packet exhibits momenta in only one of these Dirac points,
while the components of the packet that belong to the other Dirac point are
reflected due to the Lorentz force. We also found that the zitterbewegung is
permanent in time in the presence of either external or strain-induced magnetic
fields, but when both the external and strain-induced magnetic fields are
present, the zitterbewegung is transient in one of the Dirac cones, whereas in
the other cone the wave packet exhibits permanent spatial oscillations.Comment: 13 pages, 10 figure
Spectra of Quarkonia at Finite Temperature
Finite-temperature spectra of heavy quarkonia are calculated by combining
potential model and thermofield dynamics formalisms. The mass spectra of the
heavy quarkonia with various quark contents are calculated. It is found that
binding mass of the quarkonium decreases as temperature increases.Comment: 12 pages, 1 figure. To appear Mod.Phys.Lett.
Electron loss of fast heavy projectiles in collision with neutral targets
The multiple electron loss of heavy projectiles in fast ion-atom collisions
has been studied in the framework of the sudden perturbation approximation.
Especially, a model is developed to calculate the cross sections for the loss
of any number of electrons from the projectile ion, including the ionization of
a single electron and up to the complete stripping of the projectile. For a
given collision system, that is specified by the (type and charge state of the)
projectile and target as well as the collision energy, in fact, the
experimental cross sections for just three final states of the projectile are
required by this model in order to predict the loss of any number, , of
electrons for the same collision system, or for any similar system that differs
only in the energy or the initial charge state of the projectile ion. The model
is simple and can be utilized for both, the projectile and target ionization,
and without that large computer resources are requested. Detailed computation
have been carried out for the multiple electron loss of Xe and
U projectiles in collision with neutral Ar and Ne gas
targets
Complete population transfer in a degenerate 3-level atom
We find conditions required to achieve complete population transfer, via
coherent population trapping, from an initial state to a designated final state
at a designated time in a degenerate 3-level atom, where transitions are caused
by an external interaction. Complete population transfer from an initially
occupied state 1 to a designated state 2 occurs under two conditions. First,
there is a constraint on the ratios of the transition matrix elements of the
external interaction. Second, there is a constraint on the action integral over
the interaction, or "area", corresponding to the phase shift induced by the
external interaction. Both conditions may be expressed in terms of simple odd
integers.Comment: 22 pages, 4 figure
Competitive complex of machinery and technologies for the production of grain and feed
The current situation in agricultural production is challenging. During the last 2 decades, the agrarian production system has been deteriorating. It concerns crop rotations, moisture accumulation and moisture conservation technologies, ways of increasing soil fertility and growing environmentally friendly grain, reducing production costs and increasing product profitability. But there are forced late sowings and artificial “drought”. All this provides reasons to consider domestic breeding and seed production obsolete and to introduce the foreign analogue, which has planned negative impacts not only on quantitative, but also on qualitative safety. The article provides the solution to this major strategic problem. Under the research program of the Russian Academy of Agricultural Sciences, a highly competitive technology for the production of grain and fodder was developed on the basis of only domestic equipment that 2-5 times predominates over the best foreign analogues in functional indicators. It was confirmed by a number of state tests in 1990-2016 and approved by numerous meetings of the Scientific and Technical Council of the Ministry of Agriculture of the Russian Federation, RAS. The units of domestic tractors and functional machines that can compete with the best foreign counterparts have been developed
Formation of ions by high energy photons
We calculate the electron energy spectrum of ionization by a high energy
photon, accompanied by creation of electron-positron pair. The total cross
section of the process is also obtained. The asymptotics of the cross section
does not depend on the photon energies. At the photon energies exceeding a
certain value this appeares to to be the dominant mechanism of
formation of the ions. The dependence of on the value of nuclear
charge is obtained. Our results are consistent with experimental data.Comment: 16 pages, 6 figure