14,651 research outputs found
C/C ratio in planetary nebulae from the IUE archives
We investigated the abundance ratio of C/C in planetary nebulae
by examining emission lines arising from \ion{C}{3} 2s2p ^3P_{2,1,0} \to 2s^2
^1S_0. Spectra were retrieved from the International Ultraviolet Explorer
archives, and multiple spectra of the same object were coadded to achieve
improved signal-to-noise. The C hyperfine structure line at 1909.6 \AA
was detected in NGC 2440. The C/C ratio was found to be
1.2. In all other objects, we provide an upper limit for the flux
of the 1910 \AA line. For 23 of these sources, a lower limit for the
C/C ratio was established. The impact on our current
understanding of stellar evolution is discussed.
The resulting high signal-to-noise \ion{C}{3} spectrum helps constrain the
atomic physics of the line formation process. Some objects have the measured
1907/1909 flux ratio outside the low-electron density theoretical limit for
C. A mixture of C with C helps to close the gap somewhat.
Nevertheless, some observed 1907/1909 flux ratios still appear too high to
conform to the presently predicted limits. It is shown that this limit, as well
as the 1910/1909 flux ratio, are predominantly influenced by using the standard
partitioning among the collision strengths for the multiplet --
according to the statistical weights. A detailed calculation for the fine
structure collision strengths between these individual levels would be
valuable.Comment: ApJ accepted: 19 pages, 3 Figures, 2 Table
Full Quantum Analysis of Two-Photon Absorption Using Two-Photon Wavefunction: Comparison with One-Photon Absorption
For dissipation-free photon-photon interaction at the single photon level, we
analyze one-photon transition and two-photon transition induced by photon pairs
in three-level atoms using two-photon wavefunctions. We show that the
two-photon absorption can be substantially enhanced by adjusting the time
correlation of photon pairs. We study two typical cases: Gaussian wavefunction
and rectangular wavefunction. In the latter, we find that under special
conditions one-photon transition is completely suppressed while the high
probability of two-photon transition is maintained.Comment: 6 pages, 4 figure
Infrared spectroscopy of diatomic molecules - a fractional calculus approach
The eigenvalue spectrum of the fractional quantum harmonic oscillator is
calculated numerically solving the fractional Schr\"odinger equation based on
the Riemann and Caputo definition of a fractional derivative. The fractional
approach allows a smooth transition between vibrational and rotational type
spectra, which is shown to be an appropriate tool to analyze IR spectra of
diatomic molecules.Comment: revised + extended version, 9 pages, 6 figure
Anomalous thermal conductivity and local temperature distribution on harmonic Fibonacci chains
The harmonic Fibonacci chain, which is one of a quasiperiodic chain
constructed with a recursion relation, has a singular continuous
frequency-spectrum and critical eigenstates. The validity of the Fourier law is
examined for the harmonic Fibonacci chain with stochastic heat baths at both
ends by investigating the system size N dependence of the heat current J and
the local temperature distribution. It is shown that J asymptotically behaves
as (ln N)^{-1} and the local temperature strongly oscillates along the chain.
These results indicate that the Fourier law does not hold on the harmonic
Fibonacci chain. Furthermore the local temperature exhibits two different
distribution according to the generation of the Fibonacci chain, i.e., the
local temperature distribution does not have a definite form in the
thermodynamic limit. The relations between N-dependence of J and the
frequency-spectrum, and between the local temperature and critical eigenstates
are discussed.Comment: 10 pages, 4 figures, submitted to J. Phys.: Cond. Ma
Loss-Induced Limits to Phase Measurement Precision with Maximally Entangled States
The presence of loss limits the precision of an approach to phase measurement
using maximally entangled states, also referred to as NOON states. A
calculation using a simple beam-splitter model of loss shows that, for all
nonzero values L of the loss, phase measurement precision degrades with
increasing number N of entangled photons for N sufficiently large. For L above
a critical value of approximately 0.785, phase measurement precision degrades
with increasing N for all values of N. For L near zero, phase measurement
precision improves with increasing N down to a limiting precision of
approximately 1.018 L radians, attained at N approximately equal to 2.218/L,
and degrades as N increases beyond this value. Phase measurement precision with
multiple measurements and a fixed total number of photons N_T is also examined.
For L above a critical value of approximately 0.586, the ratio of phase
measurement precision attainable with NOON states to that attainable by
conventional methods using unentangled coherent states degrades with increasing
N, the number of entangled photons employed in a single measurement, for all
values of N. For L near zero this ratio is optimized by using approximately
N=1.279/L entangled photons in each measurement, yielding a precision of
approximately 1.340 sqrt(L/N_T) radians.Comment: Additional references include
Brownian markets
Financial market dynamics is rigorously studied via the exact generalized
Langevin equation. Assuming market Brownian self-similarity, the market return
rate memory and autocorrelation functions are derived, which exhibit an
oscillatory-decaying behavior with a long-time tail, similar to empirical
observations. Individual stocks are also described via the generalized Langevin
equation. They are classified by their relation to the market memory as heavy,
neutral and light stocks, possessing different kinds of autocorrelation
functions
Open Questions in Classical Gravity
We discuss some outstanding open questions regarding the validity and
uniqueness of the standard second order Newton-Einstein classical gravitational
theory. On the observational side we discuss the degree to which the realm of
validity of Newton's Law of Gravity can actually be extended to distances much
larger than the solar system distance scales on which the law was originally
established. On the theoretical side we identify some commonly accepted but
actually still open to question assumptions which go into the formulating of
the standard second order Einstein theory in the first place. In particular, we
show that while the familiar second order Poisson gravitational equation (and
accordingly its second order covariant Einstein generalization) may be
sufficient to yield Newton's Law of Gravity they are not in fact necessary. The
standard theory thus still awaits the identification of some principle which
would then make it necessary too. We show that current observational
information does not exclusively mandate the standard theory, and that the
conformal invariant fourth order theory of gravity considered recently by
Mannheim and Kazanas is also able to meet the constraints of data, and in fact
to do so without the need for any so far unobserved non-luminous or dark
matter.Comment: UCONN-93-1, plain TeX format, 22 pages (plus 7 figures - send
requests to [email protected]). To appear in a special issue of
Foundations of Physics honoring Professor Fritz Rohrlich on the occasion of
his retirement, L. P. Horwitz and A. van der Merwe Editors, Plenum Publishing
Company, N.Y., Fall 199
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Discovery of molecular subtypes in leiomyosarcoma through integrative molecular profiling.
Leiomyosarcoma (LMS) is a soft tissue tumor with a significant degree of morphologic and molecular heterogeneity. We used integrative molecular profiling to discover and characterize molecular subtypes of LMS. Gene expression profiling was performed on 51 LMS samples. Unsupervised clustering showed three reproducible LMS clusters. Array comparative genomic hybridization (aCGH) was performed on 20 LMS samples and showed that the molecular subtypes defined by gene expression showed distinct genomic changes. Tumors from the muscle-enriched cluster showed significantly increased copy number changes (P=0.04). A majority of the muscle-enriched cases showed loss at 16q24, which contains Fanconi anemia, complementation group A, known to have an important role in DNA repair, and loss at 1p36, which contains PRDM16, of which loss promotes muscle differentiation. Immunohistochemistry (IHC) was performed on LMS tissue microarrays (n=377) for five markers with high levels of messenger RNA in the muscle-enriched cluster (ACTG2, CASQ2, SLMAP, CFL2 and MYLK) and showed significantly correlated expression of the five proteins (all pairwise P<0.005). Expression of the five markers was associated with improved disease-specific survival in a multivariate Cox regression analysis (P<0.04). In this analysis that combined gene expression profiling, aCGH and IHC, we characterized distinct molecular LMS subtypes, provided insight into their pathogenesis, and identified prognostic biomarkers
Existence and stability of hole solutions to complex Ginzburg-Landau equations
We consider the existence and stability of the hole, or dark soliton,
solution to a Ginzburg-Landau perturbation of the defocusing nonlinear
Schroedinger equation (NLS), and to the nearly real complex Ginzburg-Landau
equation (CGL). By using dynamical systems techniques, it is shown that the
dark soliton can persist as either a regular perturbation or a singular
perturbation of that which exists for the NLS. When considering the stability
of the soliton, a major difficulty which must be overcome is that eigenvalues
may bifurcate out of the continuous spectrum, i.e., an edge bifurcation may
occur. Since the continuous spectrum for the NLS covers the imaginary axis, and
since for the CGL it touches the origin, such a bifurcation may lead to an
unstable wave. An additional important consideration is that an edge
bifurcation can happen even if there are no eigenvalues embedded in the
continuous spectrum. Building on and refining ideas first presented in Kapitula
and Sandstede (Physica D, 1998) and Kapitula (SIAM J. Math. Anal., 1999), we
show that when the wave persists as a regular perturbation, at most three
eigenvalues will bifurcate out of the continuous spectrum. Furthermore, we
precisely track these bifurcating eigenvalues, and thus are able to give
conditions for which the perturbed wave will be stable. For the NLS the results
are an improvement and refinement of previous work, while the results for the
CGL are new. The techniques presented are very general and are therefore
applicable to a much larger class of problems than those considered here.Comment: 41 pages, 4 figures, submitte
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