3,211 research outputs found
Dynamical Screening of Atom Confined by Finite-Width Fullerene
This is an investigation on the dynamical screening of an atom confined
within a fullerene of finite width. The two surfaces of the fullerene lead to
the presence of two surface plasmon eigenmodes. It is shown that, in the
vicinity of these two eigenfrequencies, there is a large enhancement of the
confined atom's photoabsorption rate.Comment: 10 pages, 4 figures correction of figure 2 and equation 1
Assessment of physical health and physical fitness of students of technical specialties of I course
Purpose : identification and assessment of levels of physical health and physical fitness of first-year students of the main group. Material : in the experiment participated 264 students (132 boys and 132 girls). The methods of evaluation: physical health by G.L. Apanasenko and physical preparedness for T. Yu. Krutsevich. Results : It was found that more than 75% of the students are low and lower-middle level of physical health. Revealed a level of physical fitness freshmen. 84.8% of boys and 81.1% girls have an average level of physical fitness. This corresponds to a satisfactory evaluation. Found that almost all the students are at risk of development of somatic diseases. Conclusions : These results confirm the tendency to deterioration of health and physical fitness of young people. This requires the development of a program of physical education with an emphasis on improving orientation
Electron-based crystalline undulator
We discuss the features of a crystalline undulator of the novel type based on
the effect of a planar channeling of ultra-relativistic electrons in a
periodically bent crystals. It is demonstrated that an electron-based undulator
is feasible in the tens of GeV range of the beam energies, which is noticeably
higher than the energy interval allowed in a positron-based undulator.
Numerical analysis of the main parameters of the undulator as well as the
characteristics of the emitted undulator radiation is carried out for 20 and 50
GeV electrons channeling in diamond and silicon crystals along the (111)
crystallographic planes.Comment: 16 pages, 8 figures, Latex, IOP styl
Vacancy decay in endohedral atoms: the role of non-central position of the atom
We demonstrate that the Auger decay rate in an endohedral atom is very
sensitive to the atom's location in the fullerene cage. Two additional decay
channels appear in an endohedral system: (a) the channel due to the change in
the electric field at the atom caused by dynamic polarization of the fullerene
electron shell by the Coulomb field of the vacancy, (b) the channel within
which the released energy is transferred to the fullerene electron via the
Coulomb interaction. % The relative magnitudes of the correction terms are
dependent not only on the position of the doped atom but also on the transition
energy \om. Additional enhancement of the decay rate appears for transitions
whose energies are in the vicinity of the fullerene surface plasmons energies
of high multipolarity. % It is demonstrated that in many cases the additional
channels can dominate over the direct Auger decay resulting in pronounced
broadening of the atomic emission lines. % The case study, carried out for
Sc@C, shows that narrow autoionizing resonances in an
isolated Sc within the range \om = 30... 45 eV are dramatically
broadened if the ion is located strongly off-the-center. % Using the developed
model we carry out quantitative analysis of the photoionization spectrum for
the endohedral complex ScN@C and demonstrate that the additional
channels are partly responsible for the strong modification of the
photoionization spectrum profile detected experimentally by
M\"{u}ller et al. (J. Phys.: Conf. Ser. 88, 012038 (2008)).Comment: 32 pages, 11 figure
Relativistic corrections to isotope shift in light ions
We calculate isotope mass shift for several light ions using Dirac wave
functions and mass shift operator with relativistic corrections of the order of
. Calculated relativistic corrections to the specific mass shift
vary from a fraction of a percent for Carbon, to 2% for Magnesium. Relativistic
corrections to the normal mass shift are typically smaller. Interestingly, the
final relativistic mass shifts for the levels of one multiplet appear to be
even closer than for non-relativistic operator. That can be important for the
astrophysical search for possible -variation, where isotope shift is a
source of important systematic error. Our calculations show that for levels of
the same multiplet this systematics is negligible and they can be used as
probes for -variation.Comment: 7 pages, 5 tables, revtex
Angular distribution of positrons in coherent pair production in deformed crystals
We investigate the angular distribution of positrons in the coherent process
electronpositron pair creation process by high-energy photons in a periodically
deformed single crystal with a complex base. The formula for the corresponding
differential cross-section is derived for an arbitrary deformation field. The
case is considered in detail when the photon enters into the crystal at small
angles with respect to a crystallographic axis. The results of the numerical
calculations are presented for and diamond single crystals
and Moliere parameterization of the screened atomic potentials in the case of
the deformation field generated by the acoustic wave of S-type.Comment: 11 pages, 4 figures, figures and references adde
Channeling of Positrons through Periodically Bent Crystals: on Feasibility of Crystalline Undulator and Gamma-Laser
The electromagnetic radiation generated by ultra-relativistic positrons
channelling in a crystalline undulator is discussed. The crystalline undulator
is a crystal whose planes are bent periodically with the amplitude much larger
than the interplanar spacing. Various conditions and criteria to be fulfilled
for the crystalline undulator operation are established. Different methods of
the crystal bending are described. We present the results of numeric
calculations of spectral distributions of the spontaneous radiation emitted in
the crystalline undulator and discuss the possibility to create the stimulated
emission in such a system in analogy with the free electron laser. A careful
literature survey covering the formulation of all essential ideas in this field
is given. Our investigation shows that the proposed mechanism provides an
efficient source for high energy photons, which is worth to study
experimentally.Comment: 52 pages, MikTeX, 14 figure
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