4,104 research outputs found
ΠΠΎΠ»ΡΡΠ΅Π½ΠΈΠ΅ ΠΏΠΎΡΠΈΡΡΡΡ ΠΏΠΎΠ»ΠΈΠΌΠ΅ΡΠ½ΡΡ ΠΊΠΎΠΌΠΏΠΎΠ·ΠΈΡΠΎΠ²
Π Π΄Π°Π½Π½ΠΎΠΉ ΡΠ°Π±ΠΎΡΠ΅ ΠΌΡ ΡΠΊΡΠΏΠ΅ΡΠΈΠΌΠ΅Π½ΡΠ°Π»ΡΠ½ΠΎ ΡΠ±Π΅Π΄ΠΈΠ»ΠΈΡΡ Π² ΡΠ΅Π»Π΅ΡΠΎΠΎΠ±ΡΠ°Π·Π½ΠΎΡΡΠΈ ΠΈΡΠΏΠΎΠ»ΡΠ·ΠΎΠ²Π°Π½ΠΈΡ ΠΌΠ΅ΡΠΎΠ΄Π° ΠΏΡΠ΅ΡΡΠΎΠ²Π°Π½ΠΈΡ ΡΠΎΡΠΌ ΠΈΠ· ΠΊΠΎΠΌΠΏΠΎΠ·ΠΈΡΠ° Ρ ΠΏΡΠΈΠΌΠ΅ΡΡΡ NaCl Ρ ΠΏΠΎΡΠ»Π΅Π΄ΡΡΡΠΈΠΌ ΡΠ΄Π°Π»Π΅Π½ΠΈΠ΅ΠΌ ΡΠΎΠ»ΠΈ Π΄Π»Ρ ΠΏΠΎΠ»ΡΡΠ΅Π½ΠΈΡ ΠΏΠΎΡΠΈΡΡΠΎΠΉ ΡΡΡΡΠΊΡΡΡΡ ΠΊΠΎΠΌΠΏΠΎΠ·ΠΈΡΠΎΠ²
Inversionless light amplification and optical switching controlled by state-dependent alignment of molecules
We propose a method to achieve amplification without population inversion by
anisotropic molecules whose orientation by an external electric field is
state-dependent. It is based on decoupling of the lower-state molecules from
the resonant light while the excited ones remain emitting. The suitable class
of molecules is discussed, the equation for the gain factor is derived, and the
magnitude of the inversionless amplification is estimated for the typical
experimental conditions. Such switching of the sample from absorbing to
amplifying via transparent state is shown to be possible both with the aid of
dc and ac control electric fields.Comment: AMS-LaTeX v1.2, 4 pages with 4 figure
Optical properties, electron-phonon coupling, and Raman scattering of vanadium ladder compounds
The electronic structure of two V-based ladder compounds, the quarter-filled
NaVO in the symmetric phase and the iso-structural half-filled
CaVO is investigated by ab initio calculations. Based on the
bandstructure we determine the dielectric tensor of these
systems in a wide energy range. The frequencies and eigenvectors of the fully
symmetric A phonon modes and the corresponding electron-phonon and
spin-phonon coupling parameters are also calculated from first-principles. We
determine the Raman scattering intensities of the A phonon modes as a
function of polarization and frequency of the exciting light.
All results, i.e. shape and magnitude of the dielectric function, phonon
frequencies and Raman intensities show very good agreement with available
experimental data.Comment: 11 pages, 10 figure
Effect of transient pinning on stability of drops sitting on an inclined plane
We report on new instabilities of the quasi-static equilibrium of water drops
pinned by a hydrophobic inclined substrate. The contact line of a statically
pinned drop exhibits three transitions of partial depinning: depinning of the
advancing and receding parts of the contact line and depinning of the entire
contact line leading to the drop's translational motion. We find a region of
parameters where the classical Macdougall-Ockrent-Frenkel approach fails to
estimate the critical volume of the statically pinned inclined drop
Characteristic length for pinning force density in
The pinning force density (where is the
critical current density, is applied magnetic field) is one of main
quantities which characterizes the resilience of a superconductor to carry
dissipative-free transport current in applied magnetic field. Kramer (1973 J.
Appl. Phys. 44 1360) and Dew-Hughes (1974 Phil. Mag. 30 293) proposed a widely
used scaling law for the pinning force density amplitude:
,
where , , , and are free-fitting parameters.
Since late 1970-s till now, several research groups reported experimental data
for the dependence of on the average grain size, , in
-based conductors. Godeke (2006 Supercond. Sci. Techn. 19 R68)
proposed that the dependence obeys the law . However, this scaling law has several problems, for instance, the
logarithm is taken from a non-dimensionless variable, and for large grain sizes and for . Here we reanalysed full inventory of publicly available
data for conductors and found that the dependence
can be described by law, where the
characteristic length, , is varying within a remarkably narrow range,
i.e. , for samples fabricated by different
technologies. The interpretation of the result is based on an idea that the
in-field supercurrent is flowing within a thin surface layer (the thickness of
) near the grain boundary surfaces. Alternative interpretation is
that represents characteristic length for the exponentially decay
flux pinning potential from dominant defects in superconductors,
which are grain boundaries.Comment: 22 pages, 8 figure
Charge ordering in quarter-filled ladder systems coupled to the lattice
We investigate charge ordering in the presence of electron-phonon coupling
for quarter-filled ladder systems by using Exact Diagonalization. As an example
we consider NaV2O5 using model parameters obtained from first-principles
band-structure calculations. The relevant Holstein coupling to the lattice
considerably reduces the critical value of the nearest-neighbor Coulomb
repulsion at which formation of the zig-zag charge-ordered state occurs, which
is then accompanied by a static lattice distortion. Energy and length of a
kink-like excitation on the background of the distorted lattice are calculated.
Spin and charge spectra on ladders with and without static distortion are
obtained, and the charge gap and the effective spin-spin exchange parameter J
are extracted. J agrees well with experimental results. Analysis of the
dynamical Holstein model, restricted to a small number of phonons, shows that
low frequency lattice vibrations increase the charge order, accompanied by
dynamically produced zig-zag lattice distortions.Comment: 11 pages, 17 figures, revised version as to appear in Phys. Rev.
Economic education of junior schoolchildren
Π ΡΡΠ°ΡΡΠ΅ ΠΎΠ±ΠΎΡΠ½ΠΎΠ²ΡΠ²Π°Π΅ΡΡΡ Π½Π΅ΠΎΠ±Ρ
ΠΎΠ΄ΠΈΠΌΠΎΡΡΡ ΡΠΊΠΎΠ½ΠΎΠΌΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ Π²ΠΎΡΠΏΠΈΡΠ°Π½ΠΈΡ Π΄Π΅ΡΠ΅ΠΉ, ΠΎΡΠΎΠ±ΠΎΠ΅ Π²Π½ΠΈΠΌΠ°Π½ΠΈΠ΅ ΡΠ΄Π΅Π»ΡΠ΅ΡΡΡ ΡΠΎΡΠΌΠΈΡΠΎΠ²Π°Π½ΠΈΡ ΡΠΊΠΎΠ½ΠΎΠΌΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ ΠΌΡΡΠ»Π΅Π½ΠΈΡ Ρ ΠΌΠ»Π°Π΄ΡΠΈΡ
ΡΠΊΠΎΠ»ΡΠ½ΠΈΠΊΠΎΠ². ΠΠ°Π½ΠΎ ΠΎΠΏΡΠ΅Π΄Π΅Π»Π΅Π½ΠΈΠ΅ ΡΠ΅Π»ΠΈ ΠΈ Π·Π°Π΄Π°Ρ ΡΠΊΠΎΠ½ΠΎΠΌΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ Π²ΠΎΡΠΏΠΈΡΠ°Π½ΠΈΡ ΡΡΠ°ΡΠΈΡ
ΡΡ Π½Π°ΡΠ°Π»ΡΠ½ΠΎΠΉ ΡΠΊΠΎΠ»Ρ.The article proves the necessity of economic education of children; special attention is paid to the formation of economic thinking among junior schoolchildren. The definition of the purpose and objectives of the economic education of junior schoolchildren is given
Electrochemical synthesis of nickel-aluminium oxide system from metals obtained by ore processing
Separate and combined electrochemical oxidation of aluminium and nickel has been conducted by alternating current of industrial frequency. Concentration increase of electrolyte solution (sodium chloride) in the range from 3 to 25 wt. % and current density from 0.5 to 1.5 A/cm{2} was found to result in the increasing metal oxidation rate, excluding aluminium oxidation which oxidation rate is independent of the electrolyte solution concentration. At the current density of 1.5 A/cm{2} the products of separate oxidation of nickel and aluminium are nickel oxyhydroxides, nickel hydroxides and aluminium oxyhydroxide (boehmite), respectively. In addition to these compounds, the nickel-aluminium oxide hydrate is included in the products of nickel and aluminium co-oxidation. Its content grows with the increasing electrolyte solution concentration. Varying the concentration and current density within the limits indicated, the nickel-aluminium oxide system with nickel oxide content from 3 to 10 wt. % is produced
The Galactic 26Al Problem and The Close Binary SNIb/c Solution?
The origin of the long-lived radioactive 26Al, which has been observed in the
Galactic interstellar medium from its 1.809 MeV decay gamma-ray line emission,
has been a persistent problem for over twenty years. Wolf-Rayet (WR) winds were
thought to be the most promising source, but their calculated 26Al yields are
not consistent with recent analyses of the 1.809 MeV emission from the nearest
WR star and nearby OB associations. The expected 26Al yield from the WR star
exceeds by as much as a factor of 3, that set by the 2-sigma upper limit on the
1.809 MeV emission, while the WR yields in the OB associations are only about
1/3 of that required by the 1.809 MeV emission. We suggest that a solution to
these problems may lie in 26Al from a previously ignored source: explosive
nucleosynthesis in the core collapse SNIb/c supernovae of WR stars that have
lost most of their mass to close binary companions. Recent nucleosynthetic
calculations of SNIb/c suggest that their 26Al yields depend very strongly on
the final, pre-supernova mass of the WR star, and that those with final masses
around 6 to 8 solar masses are expected to produce as much as 0.01 solar masses
of 26Al per supernova. Such binary SNIb/c make up only a small fraction of the
current SNIb/c and only about 1% of all Galactic core collapse supernovae. They
appear to be such prolific sources that the bulk of the present 26Al in the
Galaxy may come from just a few hundred close binary SNIb/c and the intense
1.809 MeV emission from nearby OB associations may come from just one or two
such supernova.Comment: Accepted for publication in Astrophysical Journal Letters, 611,10
August 200
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