22,471 research outputs found
Case of Almost Redundant Components in 3 alpha Faddeev Equations
The 3 alpha orthogonality condition model using the Pauli-forbidden bound
states of the Buck, Friedlich and Wheatly alpha alpha potential can yield a
compact 3 alpha ground state with a large binding energy, in which a small
admixture of the redundant components can never be eliminated.Comment: Revtex V4.0, 4 pages, no figure
Mononitration of durene
Reaction conditions under which the nitration of durene give predominantly, and in high yield, mononitrodurene (I), rather than dinitrodurene were found. The nitrating agent was No2+RF6-. Nitration with nitrosulfuric acid also gave mononitrodurene; however, byproducts such as 2.3.5.6-Me4C6HCH2C6H2Me3-2,4,5, were also formed. The NO2 PF6- gave an intermediate additional compound with durene. The reaction carried out with 3.6-dideuterodurene in D2O shows no isotope effect
Quark-Meson Coupling Model for a Nucleon
The quark-meson coupling model for a nucleon is considered. The model
describes a nucleon as an MIT bag, in which quarks are coupled to scalar and
vector mesons. A set of coupled equations for the quark and the meson fields
are obtained and are solved in a self-consistent way. It is shown that the mass
of a nucleon as a dressed MIT bag interacting with sigma- and omega-meson
fields significantly differs from the mass of a free MIT bag. A few sets of
model parameters are obtained so that the mass of a dressed MIT bag becomes the
nucleon mass. The results of our calculations imply that the self-energy of the
bag in the quark-meson coupling model is significant and needs to be considered
in doing the nuclear matter calculations.Comment: 3 figure
Disorder-induced double resonant Raman process in graphene
An analytical study is presented of the double resonant Raman scattering
process in graphene, responsible for the D and D features in the
Raman spectra. This work yields analytical expressions for the D and
D integrated Raman intensities that explicitly show the dependencies
on laser energy, defect concentration, and electronic lifetime. Good agreement
is obtained between the analytical results and experimental measurements on
samples with increasing defect concentrations and at various laser excitation
energies. The use of Raman spectroscopy to identify the nature of defects is
discussed. Comparison between the models for the edge-induced and the
disorder-induced D band intensity suggests that edges or grain boundaries can
be distinguished from disorder by the different dependence of their Raman
intensity on laser excitation energy. Similarly, the type of disorder can
potentially be identified not only by the intensity ratio
, but also by its laser energy
dependence. Also discussed is a quantitative analysis of quantum interference
effects of the graphene wavefunctions, which determine the most important
phonon wavevectors and scattering processes responsible for the D and
D bands.Comment: 10 pages, 4 figure
Energy Anomaly and Polarizability of Carbon Nanotubes
The energy of electron Fermi sea perturbed by external potential, represented
as energy anomaly which accounts for the contribution of the deep-lying states,
is analyzed for massive d = 1+1 Dirac fermions on a circle. The anomaly is a
universal function of the applied field, and is related to known
field-theoretic anomalies. We express transverse polarizability of Carbon
nanotubes via the anomaly, in a way which exhibits the universality and
scale-invariance of the response dominated by pi-electrons and qualitatively
different from that of dielectric and conducting shells. Electron band
transformation in a strong-field effect regime is predicted.Comment: 4 pg
Modeling of gas adsorption on graphene nanoribbons
We present a theory to study gas molecules adsorption on armchair graphene
nanoribbons (AGNRs) by applying the results of \emph{ab} \emph{initio}
calculations to the single-band tight-binding approximation. In addition, the
effect of edge states on the electronic properties of AGNR is included in the
calculations. Under the assumption that the gas molecules adsorb on the ribbon
sites with uniform probability distribution, the applicability of the method is
examined for finite concentrations of adsorption of several simple gas
molecules (CO, NO, CO, NH) on 10-AGNR. We show that the states
contributed by the adsorbed CO and NO molecules are quite localized near the
center of original band gap and suggest that the charge transport in such
systems cannot be enhanced considerably, while CO and NH molecules
adsorption acts as acceptor and donor, respectively. The results of this theory
at low gas concentration are in good agreement with those obtained by
density-functional theory calculations.Comment: 7 pages, 6 figure
Observation of Devil's Staircase in the Novel Spin Valve System SrCoO
Using resonant soft x-ray scattering as a function of both temperature and
magnetic field, we reveal a large number of almost degenerate magnetic orders
in SrCo6O11. The Ising-like spins in this frustrated material in fact exhibit a
so-called magnetic devil's staircase. It is demonstrated how a magnetic field
induces transitions between different microscopic spin configurations, which is
responsible for the magnetoresistance of SrCo6O11. This material therefore
constitutes a unique combination of a magnetic devil's staircase and spin valve
effects, yielding a novel type of magnetoresistance system.Comment: 5 pages, 5 figure
Optical matrix elements in tight-binding models with overlap
We investigate the effect of orbital overlap on optical matrix elements in
empirical tight-binding models. Empirical tight-binding models assume an
orthogonal basis of (atomiclike) states and a diagonal coordinate operator
which neglects the intra-atomic part. It is shown that, starting with an atomic
basis which is not orthogonal, the orthogonalization process induces
intra-atomic matrix elements of the coordinate operator and extends the range
of the effective Hamiltonian. We analyze simple tight-binding models and show
that non-orthogonality plays an important role in optical matrix elements. In
addition, the procedure gives formal justification to the nearest-neighbor
spin-orbit interaction introduced by Boykin [Phys. Rev \textbf{B} 57, 1620
(1998)] in order to describe the Dresselahaus term which is neglected in
empirical tight-binding models.Comment: 16 pages 6 figures, to appear in Phys. Rev.
Nonequilibrium quantum-impurities: from entropy production to information theory
Nonequilibrium steady-state currents, unlike their equilibrium counterparts,
continuously dissipate energy into their physical surroundings leading to
entropy production and time-reversal symmetry breaking. This letter discusses
these issues in the context of quantum impurity models driven out of
equilibrium by attaching the impurity to leads at different chemical potentials
and temperatures. We start by pointing out that entropy production is often
hidden in traditional treatments of quantum-impurity models. We then use simple
thermodynamic arguments to define the rate of entropy production. Using the
scattering framework recently developed by the authors we show that the rate of
entropy production has a simple information theoretic interpretation in terms
of the Shannon entropy and Kullback-Leibler divergence of nonequilibrium
distribution function. This allows us to show that the entropy production is
strictly positive for any nonequilibrium steady-state. We conclude by applying
these ideas to the Resonance Level Model and the Kondo model.Comment: 5 pages, 1 figure new version with minor clarification
Properties of solar polar coronal plumes constrained by Ultraviolet Coronagraph Spectrometer data
We investigate the plasma dynamics (outflow speed and turbulence) inside
polar plumes. We compare line profiles (mainly of \ion{O}{6}) observed by the
UVCS instrument on SOHO at the minimum of solar cycle 22-23 with model
calculations. We consider Maxwellian velocity distributions with different
widths in plume and inter-plume regions. Electron densities are assumed to be
enhanced in plumes and to approach inter-plume values with increasing height.
Different combinations of the outflow and turbulence velocity in the plume
regions are considered. We compute line profiles and total intensities of the
\ion{H}{1} Ly and the \ion{O}{6} doublets. The observed profile shapes
and intensities are reproduced best by a small solar wind speed at low
altitudes in plumes that increases with height to reach ambient inter-plume
values above roughly 3-4 R_\sun combined with a similar variation of the
width of the velocity distribution of the scattering atoms/ions. We also find
that plumes very close to the pole give narrow profiles at heights above 2.5
R_\sun, which are not observed. This suggests a tendency for plumes to be
located away from the pole. We find that the inclusion of plumes in the model
computations provides an improved correspondence with the observations and
confirms previous results showing that published UVCS observations in polar
coronal holes can be roughly reproduced without the need for large temperature
anisotropy. The latitude distributions of plumes and magnetic flux
distributions are studied by analyzing data from different instruments on SOHO
and with SOLIS.Comment: 11 figure
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