586 research outputs found
Pion and Kaon Condensation at Finite Temperature and Density
In this paper, we study O(2N)-symmetric -theory at finite temperature
and density using the 2PI-1/N expansion. As specific examples, we consider pion
condensation at finite isospin chemical potential and kaon condensation at
finite chemical potential for hyper charge and isospin charge. We calculate the
phase diagrams and the quasiparticle masses for pions and kaons in the large-N
limit. It is shown that the effective potential and the gap equation can be
renormalized by using local counterterms for the coupling constant and mass
parameter, which are independent of temperature and chemical potentials.Comment: 10 pages. 7 Figures. v2: Better plots and figs. Added significant
number of refs v3: Accepted for publication in PRD. Added a figure and
improved part on renormalization as well as presentatio
Three-dimensional MgB-type superconductivity in hole-doped diamond
We substantiate by calculations that the recently discovered
superconductivity below 4 K in 3% boron-doped diamond is caused by
electron-phonon coupling of the same type as in MgB, albeit in 3
dimensions. Holes at the top of the zone-centered, degenerate -bonding
valence band couple strongly to the optical bond-stretching modes. The increase
from 2 to 3 dimensions reduces the mode-softening crucial for reaching
40 K in MgB Even if diamond had the same \emph{bare} coupling constant
as MgB which could be achieved with 10% doping, would only be 25
K. Superconductivity above 1 K in Si (Ge) requires hole-doping beyond 5% (10%).Comment: revised version, accepted by PR
Mass Expansions of Screened Perturbation Theory
The thermodynamics of massless phi^4-theory is studied within screened
perturbation theory (SPT). In this method the perturbative expansion is
reorganized by adding and subtracting a mass term in the Lagrangian. We
analytically calculate the pressure and entropy to three-loop order and the
screening mass to two-loop order, expanding in powers of m/T. The truncated
m/T-expansion results are compared with numerical SPT results for the pressure,
entropy and screening mass which are accurate to all orders in m/T. It is shown
that the m/T-expansion converges quickly and provides an accurate description
of the thermodynamic functions for large values of the coupling constant.Comment: 22 pages, 10 figure
Screened Perturbation Theory to Three Loops
The thermal physics of a massless scalar field with a phi^4 interaction is
studied within screened perturbation theory (SPT). In this method the
perturbative expansion is reorganized by adding and subtracting a mass term in
the lagrangian. We consider several different mass prescriptions that
generalize the one-loop gap equation to two-loop order. We calculate the
pressure and entropy to three-loop order and the screening mass to two-loop
order. In contrast to the weak-coupling expansion, the SPT-improved
approximations appear to converge even for rather large values of the coupling
constant.Comment: 30 pages, 10 figure
Forsvarets rekvisisjonssystem. Hva kan det nye digitale rekvisisjonssystemet bidra til Sjøforsvaret og hvilke utfordringer vil dette gi for maritime operasjoner i Norge?
Problemstillingen blir besvart ved å innledningsvis drøfte Sjøforsvarets operative behov opp mot nødvendigheten av sivilstøtte. Videre drøftes mulighetene ved å anvende Forsvarets rekvisisjonssystem til å dekke de operative behovene. Deretter ses det på utfordringene knyttet til å benytte sivilstøtte for å understøtte Sjøforsvaret sine operative behov. Basert på oppgavens drøftelse konkluderes det med at Sjøforsvaret enda har behov for sivil understøttelse til maritime operasjoner, både i fredstid, og på krigsfot. I fredstid er dette mulig å dekke gjennom ramme- og strategiske avtaler med sivile partnere. Der burde det tilstrebes å benytte aktører som er registrert i den Nasjonal Ressursdatabasen og for håndsrekvirert. Da får Sjøforsvaret under operasjoner i fredstid, trent og øvd på å benytte og samvirke med sivile systemer, som det planlegges å benytte ved rekvisisjons i krig. Likevel forekommer det flere utfordringer ved å benytte sivil understøttelse og den for håndsrekvirerte struktur. Deriblant nasjonaliteten og lojaliteten til det sivile personellet i krig
Mapping the polysaccharide degradation potential of Aspergillus niger
<p>Abstract</p> <p>Background</p> <p>The degradation of plant materials by enzymes is an industry of increasing importance. For sustainable production of second generation biofuels and other products of industrial biotechnology, efficient degradation of non-edible plant polysaccharides such as hemicellulose is required. For each type of hemicellulose, a complex mixture of enzymes is required for complete conversion to fermentable monosaccharides. In plant-biomass degrading fungi, these enzymes are regulated and released by complex regulatory structures. In this study, we present a methodology for evaluating the potential of a given fungus for polysaccharide degradation.</p> <p>Results</p> <p>Through the compilation of information from 203 articles, we have systematized knowledge on the structure and degradation of 16 major types of plant polysaccharides to form a graphical overview. As a case example, we have combined this with a list of 188 genes coding for carbohydrate-active enzymes from <it>Aspergillus niger</it>, thus forming an analysis framework, which can be queried. Combination of this information network with gene expression analysis on mono- and polysaccharide substrates has allowed elucidation of concerted gene expression from this organism. One such example is the identification of a full set of extracellular polysaccharide-acting genes for the degradation of oat spelt xylan.</p> <p>Conclusions</p> <p>The mapping of plant polysaccharide structures along with the corresponding enzymatic activities is a powerful framework for expression analysis of carbohydrate-active enzymes. Applying this network-based approach, we provide the first genome-scale characterization of all genes coding for carbohydrate-active enzymes identified in <it>A. niger</it>.</p
The Equation of State for Dense QCD and Quark Stars
We calculate the equation of state for degenerate quark matter to leading
order in hard-dense-loop (HDL) perturbation theory. We solve the
Tolman-Oppenheimer-Volkov equations to obtain the mass-radius relation for
dense quark stars. Both the perturbative QCD and the HDL equations of state
have a large variation with respect to the renormalization scale for quark
chemical potential below 1 GeV which leads to large theoretical uncertainties
in the quark star mass-radius relation.Comment: 7 pages, 3 figure
Helium in natal HII regions: the origin of the X-ray absorption in gamma-ray burst afterglows
Soft X-ray absorption in excess of Galactic is observed in the afterglows of
most gamma-ray bursts (GRBs), but the correct solution to its origin has not
been arrived at after more than a decade of work, preventing its use as a
powerful diagnostic tool. We resolve this long-standing problem and find that
He in the GRB's host HII region is responsible for most of the absorption. We
show that the X-ray absorbing column density (N_Hx) is correlated with both the
neutral gas column density and with the optical afterglow extinction (Av). This
correlation explains the connection between dark bursts and bursts with high
N_Hx values. From these correlations we exclude an origin of the X-ray
absorption which is not related to the host galaxy, i.e. the intergalactic
medium or intervening absorbers are not responsible. We find that the
correlation with the dust column has a strong redshift evolution, whereas the
correlation with the neutral gas does not. From this we conclude that the
column density of the X-ray absorption is correlated with the total gas column
density in the host galaxy rather than the metal column density, in spite of
the fact that X-ray absorption is typically dominated by metals. The strong
redshift evolution of N_Hx/Av is thus a reflection of the cosmic metallicity
evolution of star-forming galaxies. We conclude that the absorption of X-rays
in GRB afterglows is caused by He in the HII region hosting the GRB. While dust
is destroyed and metals are stripped of all of their electrons by the GRB to
great distances, the abundance of He saturates the He-ionising UV continuum
much closer to the GRB, allowing it to remain in the neutral or singly-ionised
state. Helium X-ray absorption explains the correlation with total gas, the
lack of strong evolution with redshift as well as the absence of dust, metal or
hydrogen absorption features in the optical-UV spectra.Comment: 10 pages, 4 figures, submitted to Ap
Identification of miRNA targets with stable isotope labeling by amino acids in cell culture
miRNAs are small noncoding RNAs that regulate gene expression. We have used stable isotope labeling by amino acids in cell culture (SILAC) to investigate the effect of miRNA-1 on the HeLa cell proteome. Expression of 12 out of 504 investigated proteins was repressed by miRNA-1 transfection. This repressed set of genes significantly overlaps with miRNA-1 regulated genes that have been identified with DNA array technology and are predicted by computational methods. Moreover, we find that the 3′-untranslated region for the repressed set are enriched in miRNA-1 complementary sites. Our findings demonstrate that SILAC can be used for miRNA target identification and that one highly expressed miRNA can regulate the levels of many different proteins
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