627 research outputs found
Core-Core Dynamics in Spin Vortex Pairs
We investigate magnetic nano-pillars, in which two thin ferromagnetic
nanoparticles are separated by a nanometer thin nonmagnetic spacer and can be
set into stable spin vortex-pair configurations. The 16 ground states of the
vortex-pair system are characterized by parallel or antiparallel chirality and
parallel or antiparallel core-core alignment. We detect and differentiate these
individual vortex-pair states experimentally and analyze their dynamics
analytically and numerically. Of particular interest is the limit of strong
core-core coupling, which we find can dominate the spin dynamics in the system.
We observe that the 0.2 GHz gyrational resonance modes of the individual
vortices are replaced with 2-6 GHz range collective rotational and vibrational
core-core resonances in the configurations where the cores form a bound pair.
These results demonstrate new opportunities in producing and manipulating spin
states on the nanoscale and may prove useful for new types of ultra-dense
storage devices where the information is stored as multiple vortex-core
configurations
Relativistic Description of Exclusive Semileptonic Decays of Heavy Mesons
Using quasipotential approach, we have studied exclusive semileptonic decays
of heavy mesons with the account of relativistic effects. Due to more complete
relativistic description of the quark more precise expressions for
semileptonic form factors are obtained. Various differential distributions in
exclusive semileptonic decays of heavy mesons are calculated. It is argued that
consistent account of relativistic effects and HQET motivated choice of the
parameters of quark-antiquark potential allow to get reliable value for the
ratio in the decay as well as the
ratio~. All calculated branching
ratios are in accord with available experimental data.Comment: 18 pages, LATEX, 2 figures inclosed + 4 Postscript figure
The driver’s visual perception research to analyze pedestrian safety at twilight
Road traffic movement at nightfall (twilight) is characterizing by a reduction of light time of the day and the rapid nightfall onset, thus the driver's eyes have less time to adapt to rapid sudden changes in illumination. The visual perception and the reaction time of the driver in conditions when pedestrians appear in nightfall conditions on the street and road network in a city is considered in the paper. Researched was conducted in uncontrolled pedestrian crossings in nightfall conditions on Ukrainian roads. Regularities of the vehicle’s driver and pedestrians’ interaction in nightfall conditions are obtained. Road traffic accidents occurrence probabilities at the twilight time considering the driver’s reaction time and the car’s movement parameters was analyzed. As a result, a model for estimating the variation the reaction time of the driver when a pedestrian appears in the nightfall (twilight) conditions was calibrated
Rare radiative B decays to orbitally excited K mesons
The exclusive rare radiative B meson decays to orbitally excited axial-vector
mesons K_1^*(1270), K_1(1400) and to the tensor meson K_2^*(1430) are
investigated in the framework of the relativistic quark model based on the
quasipotential approach in quantum field theory. These decays are considered
without employing the heavy quark expansion for the s quark. Instead the s
quark is treated to be light and the expansion in inverse powers of the large
recoil momentum of the final K^{**} meson is used to simplify calculations. It
is found that the ratio of the branching fractions of rare radiative B decays
to axial vector K^*_1(1270) and K_1(1400) mesons is significantly influenced by
relativistic effects. The obtained results for B decays to the tensor meson
K_2^*(1430) agree with recent experimental data from CLEO.Comment: 17 pages, revte
Exclusive semileptonic B decays to radially excited D mesons
Exclusive semileptonic B decays to radially excited charmed mesons are
investigated at the first order of the heavy quark expansion. The arising
leading and subleading Isgur-Wise functions are calculated in the framework of
the relativistic quark model. It is found that the 1/m_Q corrections play an
important role and substantially modify results. An interesting interplay
between different corrections is found. As a result the branching ratio for the
B-> D'e\nu decay is essentially increased by 1/m_Q corrections, while the one
for B-> D*'e\nu is only slightly influenced by them.Comment: 19 pages, revtex, 6 figures, uses rotating.st
Decay constants of the heavy-light mesons from the field correlator method
Meson Green's functions and decay constants in different
channels are calculated using the Field Correlator Method. Both,
spectrum and , appear to be expressed only through universal
constants: the string tension , , and the pole quark masses.
For the -wave states the calculated masses agree with the experimental
numbers within MeV. For the and mesons the values of are equal to 210(10) and 260(10) MeV, respectively, and their ratio
=1.24(3) agrees with recent CLEO experiment. The values MeV are obtained for the , , and mesons
with the ratio =1.19(2) and =1.14(2). The decay constants
for the first radial excitations as well as the decay constants
in the vector channel are also calculated. The difference of
about 20% between and , and directly follows
from our analytical formulas.Comment: 37 pages, 10 tables, RevTeX
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