1,895 research outputs found
The 5C 6 and 5C 7 surveys of radio sources
5C 6 and 5C 7 continue the series of deep surveys made at 408 and 1407 MHz with the One-Mile telescope at Cambridge. They were intended (1) to provide a sample of faint radio sources suitable for further study; (2) to improve the statistics of source counts N(S) and spectral-index distributions at low flux densities; (3) to study the isotropy of the distribution of faint sources. Each observed field is about 4° in diameter at 408 MHz and 1° in diameter at 1407 MHz, and the field-centres are a α = 02ʰ14ᵐ, δ = 32° (5C 6) and α = 08ᵏ17ᵐ, δ = 27° (5C 7). The synthesized beamwidths (FWHM) are 80 arcsec (408 MHz) and 23 arcsec (1407 MHz). The techniques of observation and data-analysis followed closely those used for 5C 5 (Pearson, T. J., 1975. Mon. Not. R. astr. Soc., 171, 475), with some minor variations which are noted in Section 2
Phonons in MgB2 by Polarized Raman Scattering on Single Crystals
The paper presents detailed Raman scattering study of the unusually broad E2g
phonon mode in MgB2 crystal. For the first time, it is shown by the polarized
Raman scattering on few-micron-size crystallites with natural faces that the
observed broad Raman feature really does obey the selection rules of an E2g
mode. Raman spectra on high quality polycrystalline superconducting MgB2 wires
reveal a very symmetric E2g phonon line near 615 1/cm with the room temperature
linewidth of 260 1/cm only. Additional scattering of different polarization
dependence, observed in certain crystallites is interpreted as weighted phonon
density of states induced by lattice imperfections.Comment: 4 pages + 7 figure
The 5C 6 and 5C 7 surveys of radio sources
5C 6 and 5C 7 continue the series of deep surveys made at 408 and 1407 MHz with the One-Mile telescope at Cambridge. They were intended (1) to provide a sample of faint radio sources suitable for further study; (2) to improve the statistics of source counts N(S) and spectral-index distributions at low flux densities; (3) to study the isotropy of the distribution of faint sources. Each observed field is about 4° in diameter at 408 MHz and 1° in diameter at 1407 MHz, and the field-centres are a α = 02ʰ14ᵐ, δ = 32° (5C 6) and α = 08ᵏ17ᵐ, δ = 27° (5C 7). The synthesized beamwidths (FWHM) are 80 arcsec (408 MHz) and 23 arcsec (1407 MHz). The techniques of observation and data-analysis followed closely those used for 5C 5 (Pearson, T. J., 1975. Mon. Not. R. astr. Soc., 171, 475), with some minor variations which are noted in Section 2
Evidence for the Validity of the Berry-Robnik Surmise in a Periodically Pulsed Spin System
We study the statistical properties of the spectrum of a quantum dynamical
system whose classical counterpart has a mixed phase space structure consisting
of two regular regions separated by a chaotical one. We make use of a simple
symmetry of the system to separate the eigenstates of the time-evolution
operator into two classes in agreement with the Percival classification scheme
\cite{Per}. We then use a method firstly developed by Bohigas et. al.
\cite{BoUlTo} to evaluate the fractional measure of states belonging to the
regular class, and finally present the level spacings statistics for each class
which confirm the validity of the Berry-Robnik surmise in our model.Comment: 15 pages, 9 figures available upon request, Latex fil
Hybrid morphology radio sources from FIRST survey
The so-called HYbrid MOrphology Radio Sources (HYMORS) are a class of objects
that appear to have a mixed Fanaroff-Riley (FR) morphology in a single object;
i.e. a HYMORS has an FR I-type lobe on one side of its nucleus and an FR
II-type lobe on the other side. Because of this unique feature and given that
the origin of the FR morphological dichotomy is still unclear, HYMORS may
possibly play a crucial role in our understanding of the FR-dichotomy. As the
number of known HYMORS is quite small, we aimed to increase that number by
inspecting a few areas of the sky covered by the VLA FIRST survey and by
selecting 21 HYMORS candidates based on the morphology shown in the FIRST
images. They were observed with the VLA in B-conf. at 4.9 GHz. Three objects
from the initial sample turned out to be actual HYMORS and two others very
likely to fulfill the criteria. These five were subsequently re-observed with
the VLA in A-conf. at 1.4 GHz. Our results provide strong support to the
findings of Gopal-Krishna & Wiita (2000), namely that there are two different
kinds of jets in HYMORS; consequently, the existence of FR-dichotomy as a whole
is difficult to reconcile with the class of explanations that posit fundamental
differences in the central engine.Comment: 17 pages, 6 figures, matches the version printed in Astronomy &
Astrophysic
The nuclear jets in 3C309.1 & 3C380
8 station VLBI maps of the nuclear jets in 3C309.1 and 3C380 reveal complex, bent, structures which seem hard to reconcile with the concept of ballistic outflow. Together with the observation of “flaring” in the MERLIN/EVN map of the 3C309.1 jet the maps point strongly to the jets being confined fluid flows
Generalized Entanglement as a Natural Framework for Exploring Quantum Chaos
We demonstrate that generalized entanglement [Barnum {\em et al.}, Phys. Rev.
A {\bf 68}, 032308 (2003)] provides a natural and reliable indicator of quantum
chaotic behavior. Since generalized entanglement depends directly on a choice
of preferred observables, exploring how generalized entanglement increases
under dynamical evolution is possible without invoking an auxiliary coupled
system or decomposing the system into arbitrary subsystems. We find that, in
the chaotic regime, the long-time saturation value of generalized entanglement
agrees with random matrix theory predictions. For our system, we provide
physical intuition into generalized entanglement within a single system by
invoking the notion of extent of a state. The latter, in turn, is related to
other signatures of quantum chaos.Comment: clarified and expanded version accepted by Europhys. Let
Computational benchmarking for ultrafast electron dynamics: wavefunction methods vs density functional theory
Attosecond electron dynamics in small- and medium-sized molecules, induced by an ultrashort strong optical pulse, is studied computationally for a frozen nuclear geometry. The importance of exchange and correlation effects on the nonequilibrium electron dynamics induced by the interaction of the molecule with the strong optical pulse is analyzed by comparing the solution of the time-dependent Schrodinger equation based on the correlated field-free stationary electronic states computed with the equation-of-motion coupled cluster singles and doubles and the complete active space multi-configurational self-consistent field methodologies on one hand, and various functionals in real-time time-dependent density functional theory (TD-DFT) on the other. We aim to evaluate the performance of the latter approach, which is very widely used for nonlinear absorption processes and whose computational cost has a more favorable scaling with the system size. We focus on LiH as a toy model for a nontrivial molecule and show that our conclusions carry over to larger molecules, exemplified by ABCU (C10H19N). The molecules are probed with IR and UV pulses whose intensities are not strong enough to significantly ionize the system. By comparing the evolution of the time-dependent field-free electronic dipole moment, as well as its Fourier power spectrum, we show that TD-DFT performs qualitatively well in most cases. Contrary to previous studies, we find almost no changes in the TD-DFT excitation energies when excited states are populated. Transitions between states of different symmetries are induced using pulses polarized in different directions. We observe that the performance of TD-DFT does not depend on the symmetry of the states involved in the transition.Belgian Fonds National de la Recherche Collective through project number 2.4545.12 “Control of attosecond dynamics: applications to molecular reactivity
Shuffling cards, factoring numbers, and the quantum baker's map
It is pointed out that an exactly solvable permutation operator, viewed as
the quantization of cyclic shifts, is useful in constructing a basis in which
to study the quantum baker's map, a paradigm system of quantum chaos. In the
basis of this operator the eigenfunctions of the quantum baker's map are
compressed by factors of around five or more. We show explicitly its connection
to an operator that is closely related to the usual quantum baker's map. This
permutation operator has interesting connections to the art of shuffling cards
as well as to the quantum factoring algorithm of Shor via the quantum order
finding one. Hence we point out that this well-known quantum algorithm makes
crucial use of a quantum chaotic operator, or at least one that is close to the
quantization of the left-shift, a closeness that we also explore
quantitatively.Comment: 12 pgs. Substantially elaborated version, including a new route to
the quantum bakers map. To appear in J. Phys.
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