488 research outputs found
Confinement and electron correlation effects in photoionization of atoms in endohedral anions: Ne@C60^{z-}
Trends in resonances, termed confinement resonances, in photoionization of
atoms A in endohedral fullerene anions A@C60^{z-} are theoretically studied and
exemplified by the photoionization of Ne in Ne@C{60}^{z-}. Remarkably, above a
particular nl ionization threshold of Ne in neutral Ne@C60 (I_{nl}^{z=0}),
confinement resonances in corresponding partial photoionization cross sections
sigma_{nl} of Ne in any charged Ne@C60^{z-} remain almost intact by a charge z
on the carbon cage, as a general phenomenon. At lower photon energies, omega <
I_{nl}^{z=0}, the corresponding photoionization cross sections develop
additional, strong, z-dependent resonances, termed Coulomb confinement
resonances, as a general occurrence. Furthermore, near the innermost 1s
ionization threshold, the 2p photoionization cross section sigma_{2p} of the
outermost 2p subshell of thus confined Ne is found to inherit the confinement
resonance structure of the 1s photoionization spectrum, via interchannel
coupling. As a result, new confinement resonances emerge in the 2p
photoionization cross section of the confined Ne atom at photoelectron energies
which exceed the 2p threshold by about a thousand eV, i.e., far above where
conventional wisdom said they would exist. Thus, the general possibility for
confinement resonances to resurrect in photoionization spectra of encapsulated
atoms far above thresholds is revealed, as an interesting novel general
phenomenon.Comment: 6 pages, 4 figures, Latex2e, jpconf.cls styl
Diffuse versus square-well confining potentials in modelling @C atoms
Attention: this version- of the manuscript differs from its previously
uploaded version- (arXiv:1112.6158v1) and subsequently published in 2012 J.
Phys. B \textbf{45} 105102 only by a removed typo in Eq.(2) of version-;
there was the erroneous factor "2" in both terms in the right-hand-side of the
Eq.(2) of version-. Now that the typo is removed, Eq.(2) is correct.
A perceived advantage for the replacement of a discontinuous square-well
pseudo-potential, which is often used by various researchers as an
approximation to the actual C cage potential in calculations of
endohedral atoms @C, by a more realistic diffuse potential is
explored. The photoionization of endohedral H@C and Xe@C is
chosen as the case study. The diffuse potential is modelled by a combination of
two Woods-Saxon potentials. It is demonstrated that photoionization spectra of
@C atoms are largely insensitive to the degree of diffuseness
of the potential borders, in a reasonably broad range of 's.
Alternatively, these spectra are found to be insensitive to discontinuity of
the square-well potential either. Both potentials result in practically
identical calculated spectra. New numerical values for the set of square-well
parameters, which lead to a better agreement between experimental and
theoretical data for @C spectra, are recommended for future studies.Comment: 11 pages, 4 figure
Confinement resonances in photoionization of endohedral atoms: a myth or reality?
We demonstrate that the structure of confinement resonances in the
photoionization cross section of an endohedral atom is very sensitive to the
mean displacement of the atom from the cage center. The resonances are
strongly suppressed if 2 exceeds the photoelectron half-wavelength. We
explain the results of recent experiments which contradict the earlier
theoretical predictions on the existence of confinement resonances in
particular endohedral systems.Comment: 4 pages, 5 figures, RevTe
Mechanical activation influence on the morphological properties of La[2]O[3]-TiO[2]-B
The influence of mechanical activation of the powder mixture used to obtain the high-perfomance cathode for accelerating engineering with the SHS-method has been explored. The mechanically processed mixtures have been morphologically analyzed. The optimal modes of mechanical activation have been determined for the mixture
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 effects in photoionization time delay near the Cooper minimum of noble-gas atoms
Time delay of photoemission from valence ns, np3/2, and np1/2 subshells of noble-gas atoms is theoretically scrutinized within the framework of the dipole relativistic random phase approximation. The focus is on the variation of time delay in the vicinity of the Cooper minima in photoionization of the outer subshells of neon, argon, krypton, and xenon, where the corresponding dipole matrix element changes its sign while passing through a node. It is revealed that the presence of the Cooper minimum in one photoionization channel has a strong effect on time delay in other channels. This is shown to be due to interchannel coupling
Secure radio communication systems using encoded signal in time, frequency and phase
The original algorithm of transfer 8-bit digital data with use of signal, discretely-encoded in the timing, frequency and phase using the matrix of Costas and of Walsh functions, providing high reserve of work and security from broadband and narrow-band interferences is developed. The algorithms of generation and processing of signals on the receiving side is realized in FPGA of type XC7k325T (Xilinx).A radio communication system on the SDR technology (software defined radio) on the basis of the AD 9361 transceiver (Analog Devices).Π Π°Π·ΡΠ°Π±ΠΎΡΠ°Π½ ΠΎΡΠΈΠ³ΠΈΠ½Π°Π»ΡΠ½ΡΠΉ Π°Π»Π³ΠΎΡΠΈΡΠΌ ΠΏΠ΅ΡΠ΅Π΄Π°ΡΠΈ 8-Π±ΠΈΡ ΡΠΈΡΡΠΎΠ²ΡΡ
Π΄Π°Π½Π½ΡΡ
Ρ ΠΈΡΠΏΠΎΠ»ΡΠ·ΠΎΠ²Π°Π½ΠΈΠ΅ΠΌ ΡΠΈΠ³Π½Π°Π»Π°, Π΄ΠΈΡΠΊΡΠ΅ΡΠ½ΠΎ-ΠΊΠΎΠ΄ΠΈΡΠΎΠ²Π°Π½Π½ΠΎΠ³ΠΎ ΠΏΠΎ Π²ΡΠ΅ΠΌΠ΅Π½ΠΈ, ΡΠ°ΡΡΠΎΡΠ΅ ΠΈ ΡΠ°Π·Π΅ Ρ ΠΏΠΎΠΌΠΎΡΡΡ ΠΌΠ°ΡΡΠΈΡΡ ΠΠΎΡΡΠ°ΡΠ° ΠΈ ΡΡΠ½ΠΊΡΠΈΠΉ Π£ΠΎΠ»ΡΠ°. ΠΠ±Π΅ΡΠΏΠ΅ΡΠΈΠ²Π°Π΅ΡΡΡ Π²ΡΡΠΎΠΊΠ°Ρ ΡΠΊΡΡΡΠ½ΠΎΡΡΡ ΡΠ°Π±ΠΎΡΡ ΠΈ Π·Π°ΡΠΈΡΠ΅Π½Π½ΠΎΡΡΡ ΠΎΡ ΡΠΈΡΠΎΠΊΠΎΠΏΠΎΠ»ΠΎΡΠ½ΡΡ
ΠΈ ΡΠ·ΠΊΠΎΠΏΠΎΠ»ΠΎΡΠ½ΡΡ
ΠΏΠΎΠΌΠ΅Ρ
. ΠΠ»Π³ΠΎΡΠΈΡΠΌΡ ΡΠΎΡΠΌΠΈΡΠΎΠ²Π°Π½ΠΈΡ ΡΠΈΠ³Π½Π°Π»ΠΎΠ² ΠΈ ΠΎΠ±ΡΠ°Π±ΠΎΡΠΊΠΈ ΠΈΡ
Π½Π° ΠΏΡΠΈΠ΅ΠΌΠ½ΠΎΠΉ ΡΡΠΎΡΠΎΠ½Π΅ ΡΠ΅Π°Π»ΠΈΠ·ΠΎΠ²Π°Π½Ρ Π² ΠΠΠΠ‘ ΡΠΈΠΏΠ° XC7k325T (Xilinx). Π‘ΠΈΡΡΠ΅ΠΌΠ° ΡΠ°Π΄ΠΈΠΎΡΠ²ΡΠ·ΠΈ ΡΠ΅Π°Π»ΠΈΠ·ΠΎΠ²Π°Π½Π° ΠΏΠΎ ΡΠ΅Ρ
Π½ΠΎΠ»ΠΎΠ³ΠΈΠΈ SDR (ΠΏΡΠΎΠ³ΡΠ°ΠΌΠΌΠ½ΠΎ ΠΎΠΏΡΠ΅Π΄Π΅Π»ΡΠ΅ΠΌΠΎΠ΅ ΡΠ°Π΄ΠΈΠΎ) Π½Π° ΠΎΡΠ½ΠΎΠ²Π΅ ΡΡΠ°Π½ΡΠΈΠ²Π΅ΡΠ° AD 9361 (Analog Devices)
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