17,208 research outputs found
Effects of the Running of the QCD Coupling on the Energy Loss in the Quark-Gluon Plasma
Finite temperature modifies the running of the QCD coupling alpha_s(k,T) with
resolution k. After calculating the thermal quark and gluon masses
selfconsistently, we determine the quark-quark and quark-gluon cross sections
in the plasma based on the running coupling. We find that the running coupling
enhances these cross sections by factors of two to four depending on the
temperature. We also compute the energy loss dE/dx of a high-energy quark in
the plasma as a function of temperature. Our study suggests that, beside
t-channel processes, inverse Compton scattering is a relevant process for a
quantitative understanding of the energy loss of an incident quark in a hot
plasma.Comment: 14 pages, 6 figure
Viscosity of an ideal relativistic quantum fluid: A perturbative study
We show that a quantized ideal fluid will generally exhibit a small but
non-zero viscosity due to the backreaction of quantum soundwaves on the
background. We use an effective field theory expansion to estimate this
viscosity to first order in perturbation theory. We discuss our results, and
whether this estimate can be used to obtain a more model-independent estimate
of the "quantum bound" on the viscosity of physical systemsComment: Accepted for publication, Phys.Rev.D. Discussion slightly clarified
and extended, references added, error in calculation fixed. COnclusions
unchange
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Native Plasmid-Encoded Mercury Resistance Genes Are Functional and Demonstrate Natural Transformation in Environmental Bacterial Isolates.
Plasmid-mediated horizontal gene transfer (HGT) is a major driver of genetic diversity in bacteria. We experimentally validated the function of a putative mercury resistance operon present on an abundant 8-kbp native plasmid found in groundwater samples without detectable levels of mercury. Phylogenetic analyses of the plasmid-encoded mercury reductases from the studied groundwater site show them to be distinct from those reported in proximal metal-contaminated sites. We synthesized the entire native plasmid and demonstrated that the plasmid was sufficient to confer functional mercury resistance in Escherichia coli Given the possibility that natural transformation is a prevalent HGT mechanism in the low-cell-density environments of groundwaters, we also assayed bacterial strains from this environment for competence. We used the native plasmid-encoded metal resistance to design a screen and identified 17 strains positive for natural transformation. We selected 2 of the positive strains along with a model bacterium to fully confirm HGT via natural transformation. From an ecological perspective, the role of the native plasmid population in providing advantageous traits combined with the microbiome's capacity to take up environmental DNA enables rapid adaptation to environmental stresses.IMPORTANCE Horizontal transfer of mobile genetic elements via natural transformation has been poorly understood in environmental microbes. Here, we confirm the functionality of a native plasmid-encoded mercury resistance operon in a model microbe and then query for the dissemination of this resistance trait via natural transformation into environmental bacterial isolates. We identified 17 strains including Gram-positive and Gram-negative bacteria to be naturally competent. These strains were able to successfully take up the plasmid DNA and obtain a clear growth advantage in the presence of mercury. Our study provides important insights into gene dissemination via natural transformation enabling rapid adaptation to dynamic stresses in groundwater environments
Projective Ring Line of an Arbitrary Single Qudit
As a continuation of our previous work (arXiv:0708.4333) an algebraic
geometrical study of a single -dimensional qudit is made, with being
{\it any} positive integer. The study is based on an intricate relation between
the symplectic module of the generalized Pauli group of the qudit and the fine
structure of the projective line over the (modular) ring \bZ_{d}. Explicit
formulae are given for both the number of generalized Pauli operators commuting
with a given one and the number of points of the projective line containing the
corresponding vector of \bZ^{2}_{d}. We find, remarkably, that a perp-set is
not a set-theoretic union of the corresponding points of the associated
projective line unless is a product of distinct primes. The operators are
also seen to be structured into disjoint `layers' according to the degree of
their representing vectors. A brief comparison with some multiple-qudit cases
is made
Subnormalized states and trace-nonincreasing maps
We investigate the set of completely positive, trace-nonincreasing linear
maps acting on the set M_N of mixed quantum states of size N. Extremal point of
this set of maps are characterized and its volume with respect to the
Hilbert-Schmidt (Euclidean) measure is computed explicitly for an arbitrary N.
The spectra of partially reduced rescaled dynamical matrices associated with
trace-nonincreasing completely positive maps belong to the N-cube inscribed in
the set of subnormalized states of size N. As a by-product we derive the
measure in M_N induced by partial trace of mixed quantum states distributed
uniformly with respect to HS-measure in .Comment: LaTeX, 21 pages, 4 Encapsuled PostScript figures, 1 tabl
Measurement efficiency and n-shot read out of spin qubits
We consider electron spin qubits in quantum dots and define a measurement
efficiency e to characterize reliable measurements via n-shot read outs. We
propose various implementations based on a double dot and quantum point contact
(QPC) and show that the associated efficiencies e vary between 50% and 100%,
allowing single-shot read out in the latter case. We model the read out
microscopically and derive its time dynamics in terms of a generalized master
equation, calculate the QPC current and show that it allows spin read out under
realistic conditions.Comment: 5 pages, 1 figur
Probing a critical length scale at the glass transition
We give evidence of a clear structural signature of the glass transition, in
terms of a static correlation length with the same dependence on the system
size which is typical of critical phenomena. Our approach is to introduce an
external, static perturbation to extract the structural information from the
system's response. In particular, we consider the transformation behavior of
the local minima of the underlying potential energy landscape (inherent
structures), under a static deformation. The finite-size scaling analysis of
our numerical results indicate that the correlation length diverges at a
temperature , below the temperatures here the system can be equilibrated.
Our numerical results are consistent with random first order theory, which
predicts such a divergence with a critical exponent at the Kauzmann
temperature, where the extrapolated configurational entropy vanishes.Comment: 5 pages, 5 figures, to appear in Phys. Rev. Lett. 2010
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