2,397 research outputs found
Polarization as a Probe to the Production Mechanisms of Charmonium in Collisions
Measurements of the polarization of \jp produced in pion-nucleus collisions
are in disagreement with leading twist QCD prediction where \jp is observed
to have negligible polarization whereas theory predicts substantial
polarization. We argue that this discrepancy cannot be due to poorly known
structure functions nor the relative production rates of \jp and .
The disagreement between theory and experiment suggests important higher twist
corrections, as has earlier been surmised from the anomalous non-factorized
nuclear -dependence of the \jp cross section.Comment: 8 page
Complete spectral energy distribution of the hot, helium-rich white dwarf RX J0503.9-2854
In the line-of-sight toward the DO-type white dwarf RX J0503.9-2854, the
density of the interstellar medium (ISM) is very low, and thus the
contamination of the stellar spectrum almost negligible. This allows us to
identify many metal lines in a wide wavelength range from the extreme
ultraviolet to the near infrared. In previous spectral analyses, many metal
lines in the ultraviolet spectrum of RX J0503.9-2854 have been identified. A
complete line list of observed and identified lines is presented here. We
compared synthetic spectra that had been calculated from model atmospheres in
non-local thermodynamical equilibrium, with observations. In total, we
identified 1272 lines (279 of them were newly assigned) in the wavelength range
from the extreme ultraviolet to the near infrared. 287 lines remain
unidentified. A close inspection of the EUV shows that still no good fit to the
observed shape of the stellar continuum flux can be achieved although He, C, N,
O, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Mn, Fe, Cr, Ni Zn, Ga, Ge, As, Kr, Zr, Mo,
Sn, Xe, and Ba are included in the stellar atmosphere models. There are two
possible reasons for the deviation between observed and synthetic flux in the
EUV. Opacities from hitherto unconsidered elements in the model-atmosphere
calculation may be missing and/or the effective temperature is slightly lower
than previously determined.Comment: 92 pages, 45 figure
Stellar laboratories. IX. New Se V, Sr IV - VII, Te VI, and I VI oscillator strengths and the Se, Sr, Te, and I abundances in the hot white dwarfs G191-B2B and RE 0503-289
To analyze spectra of hot stars, advanced non-local thermodynamic equilibrium
(NLTE) model-atmosphere techniques are mandatory. Reliable atomic data is for
the calculation of such model atmospheres.
We aim to calculate new Sr IV - VII oscillator strengths to identify for the
first time Sr spectral lines in hot white dwarf (WD) stars and to determine the
photospheric Sr abundances. o measure the abundances of Se, Te, and I in hot
WDs, we aim to compute new Se V, Te VI, and I VI oscillator strengths.
To consider radiative and collisional bound-bound transitions of Se V, Sr IV
- VII, Te VI, and I VI in our NLTE atmosphere models, we calculated oscillator
strengths for these ions.
We newly identified four Se V, 23 Sr V, 1 Te VI, and three I VI lines in the
ultraviolet (UV) spectrum of RE0503-289. We measured a photospheric Sr
abundance of 6.5 +3.8/-2.4 x 10**-4 (mass fraction, 9500 - 23800 times solar).
We determined the abundances of Se (1.6 +0.9/-0.6 x 10**-3, 8000 - 20000), Te
(2.5 +1.5/-0.9 x 10**-4, 11000 - 28000), and I (1.4 +0.8/-0.5 x 10**-5, 2700 -
6700). No Se, Sr, Te, and I line was found in the UV spectra of G191-B2B and we
could determine only upper abundance limits of approximately 100 times solar.
All identified Se V, Sr V, Te VI, and I VI lines in the UV spectrum of
RE0503-289 were simultaneously well reproduced with our newly calculated
oscillator strengths.Comment: 26 pages, 5 figure
Spatial propagation of excitonic coherence enables ratcheted energy transfer
Experimental evidence shows that a variety of photosynthetic systems can
preserve quantum beats in the process of electronic energy transfer, even at
room temperature. However, whether this quantum coherence arises in vivo and
whether it has any biological function have remained unclear. Here we present a
theoretical model that suggests that the creation and recreation of coherence
under natural conditions is ubiquitous. Our model allows us to theoretically
demonstrate a mechanism for a ratchet effect enabled by quantum coherence, in a
design inspired by an energy transfer pathway in the Fenna-Matthews-Olson
complex of the green sulfur bacteria. This suggests a possible biological role
for coherent oscillations in spatially directing energy transfer. Our results
emphasize the importance of analyzing long-range energy transfer in terms of
transfer between inter-complex coupling (ICC) states rather than between site
or exciton states.Comment: Accepted version for Phys. Rev. E. 14 pages, 7 figure
An infrared study of the double nucleus in NGC3256
We present new resolved near and mid-IR imaging and N-band spectroscopy of
the two nuclei in the merger system NGCA3256, the most IR luminous galaxy in
the nearby universe. The results from the SED fit to the data are consistent
with previous estimates of the amount of obscuration towards the nuclei and the
nuclear star formation rates. However, we also find substantial differences in
the infrared emission from the two nuclei which cannot be explained by
obscuration alone. We conclude that the northern nucleus requires an additional
component of warm dust in order to explain its properties. This suggests that
local starforming conditions can vary significantly within the environment of a
single system.Comment: Accepted for publication (MNRAS
The Precise Formula in a Sine Function Form of the norm of the Amplitude and the Necessary and Sufficient Phase Condition for Any Quantum Algorithm with Arbitrary Phase Rotations
In this paper we derived the precise formula in a sine function form of the
norm of the amplitude in the desired state, and by means of he precise formula
we presented the necessary and sufficient phase condition for any quantum
algorithm with arbitrary phase rotations. We also showed that the phase
condition: identical rotation angles, is a sufficient but not a necessary phase
condition.Comment: 16 pages. Modified some English sentences and some proofs. Removed a
table. Corrected the formula for kol on page 10. No figure
Vibration-enhanced quantum transport
In this paper, we study the role of collective vibrational motion in the
phenomenon of electronic energy transfer (EET) along a chain of coupled
electronic dipoles with varying excitation frequencies. Previous experimental
work on EET in conjugated polymer samples has suggested that the common
structural framework of the macromolecule introduces correlations in the energy
gap fluctuations which cause coherent EET. Inspired by these results, we
present a simple model in which a driven nanomechanical resonator mode
modulates the excitation energy of coupled quantum dots and find that this can
indeed lead to an enhancement in the transport of excitations across the
quantum network. Disorder of the on-site energies is a key requirement for this
to occur. We also show that in this solid state system phase information is
partially retained in the transfer process, as experimentally demonstrated in
conjugated polymer samples. Consequently, this mechanism of vibration enhanced
quantum transport might find applications in quantum information transfer of
qubit states or entanglement.Comment: 7 pages, 6 figures, new material, included references, final
published versio
Influence of Coulomb and Phonon Interaction on the Exciton Formation Dynamics in Semiconductor Heterostructures
A microscopic theory is developed to analyze the dynamics of exciton
formation out of incoherent carriers in semiconductor heterostructures. The
carrier Coulomb and phonon interaction is included consistently. A cluster
expansion method is used to systematically truncate the hierarchy problem. By
including all correlations up to the four-point (i.e. two-particle) level, the
fundamental fermionic substructure of excitons is fully included. The analysis
shows that the exciton formation is an intricate process where Coulomb
correlations rapidly build up on a picosecond time scale while phonon dynamics
leads to true exciton formation on a slow nanosecond time scale.Comment: 18 pages, 7 figure
Explicit Model Realizing Parton-Hadron Duality
We present a model that realizes both resonance-Regge (Veneziano) and
parton-hadron (Bloom-Gilman) duality. We first review the features of the
Veneziano model and we discuss how parton-hadron duality appears in the
Bloom-Gilman model. Then we review limitations of the Veneziano model, namely
that the zero-width resonances in the Veneziano model violate unitarity and
Mandelstam analyticity. We discuss how such problems are alleviated in models
that construct dual amplitudes with Mandelstam analyticity (so-called DAMA
models). We then introduce a modified DAMA model, and we discuss its
properties. We present a pedagogical model for dual amplitudes and we construct
the nucleon structure function F2(x,Q2). We explicitly show that the resulting
structure function realizes both Veneziano and Bloom-Gilman duality.Comment: 11 pages, 8 figure
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