23,358 research outputs found
Nuclei embedded in an electron gas
The properties of nuclei embedded in an electron gas are studied within the
relativistic mean-field approach. These studies are relevant for nuclear
properties in astrophysical environments such as neutron-star crusts and
supernova explosions. The electron gas is treated as a constant background in
the Wigner-Seitz cell approximation. We investigate the stability of nuclei
with respect to alpha and beta decay. Furthermore, the influence of the
electronic background on spontaneous fission of heavy and superheavy nuclei is
analyzed. We find that the presence of the electrons leads to stabilizing
effects for both decay and spontaneous fission for high electron
densities. Furthermore, the screening effect shifts the proton dripline to more
proton-rich nuclei, and the stability line with respect to beta decay is
shifted to more neutron-rich nuclei. Implications for the creation and survival
of very heavy nuclear systems are discussed.Comment: 35 pages, latex+ep
Influence of gaseous hydrogen on metals Interim report
Gaseous hydrogen embrittlement in Inconel 718, Inconel 625, AISI 321 stainless steel, Ti-5Al-25Sn ELI, and OFHC coppe
Association Between {HIV}-1 Coreceptor Usage and Resistance to Broadly Neutralizing Antibodies
Background: Recently discovered broadly neutralizing antibodies have revitalized hopes of developing a universal vaccine against HIV-1. Mainly responsible for new infections are variants only using CCR5 for cell entry, whereas CXCR4-using variants can become dominant in later infection stages. Methods: We performed a statistical analysis on two different previously published data sets. The first data set was a panel of 199 diverse HIV-1 isolates for which IC50 neutralization titers were determined for the broadly neutralizing antibodies VRC01, VRC-PG04, PG9, and PG16. The second data set contained env sequences of viral variants extracted from HIV-1–infected humanized mice treated with the antibody PGT128 and from untreated control mice. Results: For the panel of 199 diverse HIV-1 isolates, we found a statistically significant association between viral resistance to PG9 and PG16 and CXCR4 coreceptor usage (P = 0.0011 and P = 0.0010, respectively). Our analysis of viral variants from HIV-1–infected humanized mice under treatment with the broadly neutralizing antibody PGT128 indicated that certain antibodies might drive a viral population toward developing CXCR4 coreceptor usage capability (P = 0.0011 for the comparison between PGT128 and control measurement). Conclusions: These analyses highlight the importance of accounting for a possible coreceptor usage bias pertaining to the effectiveness of an HIV vaccine and to passive antibody transfer as therapeutic approach
Non-Markovian Quantum Trajectories of Many-Body Quantum Open Systems
A long-standing open problem in non-Markovian quantum state diffusion (QSD)
approach to open quantum systems is to establish the non-Markovian QSD
equations for multiple qubit systems. In this paper, we settle this important
question by explicitly constructing a set of exact time-local QSD equations for
-qubit systems. Our exact time-local (convolutionless) QSD equations have
paved the way towards simulating quantum dynamics of many-body open systems
interacting with a common bosonic environment. The applicability of this
multiple-qubit stochastic equation is exemplified by numerically solving
several quantum open many-body systems concerning quantum coherence dynamics
and dynamical control.Comment: 8 pages, 2 figures. manuscript revised and reference update
Electron spin tomography through counting statistics: a quantum trajectory approach
We investigate the dynamics of electron spin qubits in quantum dots.
Measurement of the qubit state is realized by a charge current through the dot.
The dynamics is described in the framework of the quantum trajectory approach,
widely used in quantum optics, and we show that it can be applied successfully
to problems in condensed matter physics. The relevant master equation dynamics
is unravelled to simulate stochastic tunneling events of the current through
the dot.Quantum trajectories are then used to extract the counting statistics
of the current. We show how, in combination with an electron spin resonance
(ESR) field, counting statistics can be employed for quantum state tomography
of the qubit state. Further, it is shown how decoherence and relaxation time
scales can be estimated with the help of counting statistics, in the time
domain. Finally, we discuss a setup for single shot measurement of the qubit
state without the need for spin-polarized leads.Comment: 23 pages, 10 figures, RevTeX4, submitted to PR
Nuclear Magnetic Resonance and Hyperfine Structure
Contains reports on three research projects
Non-Markovian quantum state diffusion for absorption spectra of molecular aggregates
In many molecular systems one encounters the situation where electronic
excitations couple to a quasi-continuum of phonon modes. That continuum may be
highly structured e.g. due to some weakly damped high frequency modes. To
handle such a situation, an approach combining the non-Markovian quantum state
diffusion (NMQSD) description of open quantum systems with an efficient but
abstract approximation was recently applied to calculate energy transfer and
absorption spectra of molecular aggregates [Roden, Eisfeld, Wolff, Strunz, PRL
103 (2009) 058301]. To explore the validity of the used approximation for such
complicated systems, in the present work we compare the calculated
(approximative) absorption spectra with exact results. These are obtained from
the method of pseudomodes, which we show to be capable of determining the exact
spectra for small aggregates and a few pseudomodes. It turns out that in the
cases considered, the results of the two approaches mostly agree quite well.
The advantages and disadvantages of the two approaches are discussed
The effect of uniaxial pressure on the magnetic anomalies of the heavy-fermion metamagnet CeRu2Si2
The effect of uniaxial pressure (P_u) on the magnetic susceptibility (X),
magnetization (M), and magnetoresistance (MR) of the heavy-fermion metamagnet
CeRu2Si2 has been investigated. For the magnetic field along the tetragonal c
axis, it is found that characteristic physical quantities, i.e., the
temperature of the susceptibility maximum (T_max), the pagamagnetic Weiss
temperature (Q_p), 1/X at 2 K, and the magnetic field of the metamagnetic
anomaly (H_M), scale approximately linearly with P_u, indicating that all the
quantities are related to the same energy scale, probably of the Kondo
temperature. The increase (decrease) of the quantities for P_u || c axis (P_u
|| a axis) can be attributed to a decrease (increase) in the nearest Ce-Ru
distance. Consistently in MR and X, we observed a sign that the anisotropic
nature of the hybridization, which is believed to play an important role in the
metamagnetic anomaly, can be controlled by applying the uniaxial pressure.
PACS numbers: 75.20.Hr, 71.27.+a, 74.62.FjComment: 7 pages, ReVTeX, 6 EPS figures : Will appear in Phys. Rev.
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