441 research outputs found
Spectral function of the Bloch-Nordsieck model at finite temperature
In this paper we determine the exact fermionic spectral function of the
Bloch-Nordsieck model at finite temperature. Analytic results are presented for
some special parameters, for other values we have numerical results. The
spectral function is finite and normalizable for any nonzero temperature
values. The real time dependence of the retarded Green's function is power-like
for small times and exhibits exponential damping for large times. Treating the
temperature as an infrared regulator, we can also give a safe interpretation of
the zero temperature result.Comment: 16 pages, 9 figures, revtex4-
Validating the 2PI resummation: the Bloch-Nordsieck example
In this work we provide a numerical method to obtain the Bloch-Nordsieck
spectral function at finite temperature in the framework of the 2PI
approximation. We find that the 2PI results nicely agree with the exact one,
provided we perform a coupling constant matching. In the paper we present the
resulting finite temperature running of the 2PI coupling constant. This result
may apply for the finite temperature behavior of the coupling constant in QED,
too.Comment: 14 pages, 14 figures, uses revtex4-
Resummations in the Bloch-Nordsieck model
We studied different levels of resummations of the exactly solvable
Bloch-Nordsieck model in order to be able to compare the approximations with an
exact result. We studied one-loop perturbation theory, 2PI resummation and
Schwinger-Dyson equations truncated in a way to maintain Ward-identities. At
all levels we carefully performed renormalization. We found that although the
2PI resummation does not exhibit infrared sensitivity at the mass shell (the
one-loop perturbation theory does), but it is still far from the exact
solution. The method of truncated Schwinger-Dyson equations, however, is exact
in this model, so it provides a new way of solving the Bloch-Nordsieck model.
This method can also be generalized to other, more complicated theories.Comment: 12 pages, 3 figures, revtex
From random walk to single-file diffusion
We report an experimental study of diffusion in a quasi-one-dimensional (q1D)
colloid suspension which behaves like a Tonks gas. The mean squared
displacement as a function of time is described well with an ansatz
encompassing a time regime that is both shorter and longer than the mean time
between collisions. This ansatz asserts that the inverse mean squared
displacement is the sum of the inverse mean squared displacement for short time
normal diffusion (random walk) and the inverse mean squared displacement for
asymptotic single-file diffusion (SFD). The dependence of the single-file 1D
mobility on the concentration of the colloids agrees quantitatively with that
derived for a hard rod model, which confirms for the first time the validity of
the hard rod SFD theory. We also show that a recent SFD theory by Kollmann
leads to the hard rod SFD theory for a Tonks gas.Comment: 4 pages, 4 figure
Powdery mildew caused by Golovinomyces cichoracearum on eastern purple coneflower (Echinacea purpurea) in Italy
First Report of Downy Mildew Caused by Peronospora arthurii on Common Evening Primrose (Oenothera biennis) in Italy
Purification and characterization of a milk-clotting protease from Mucor pusillus: Method comparison
Crude enzymatic extract obtained from five fermentations (300 g of wheat bran) was characterized by a clotting activity of 0.34 ± 0.08 UP/ml with a strength ratio of 1/1: 200. The comparative study of the summaries from 2 purification protocols showed that it is possible to recover 6% of the initial proteins with a 44.54% activity after gel filtration (protocol I), which appeared more technically sound when compared to ion-exchange (1.80% of total proteins with a 23% performance) (protocol II). The proteinhomogeneity (a single electrophoretic band) of the monomeric protease was confirmed by both methods after precipitation with 80% saturated ammonium sulphate. Moreover, the fractional precipitation technique with this salt (40 and 80%) was useless in the experimental conditionsemployed and an important loss of activity was observed (28.53%) with a 3-fold purification. In another part of the study, without ammonium sulphate precipitation, the gel filtration enabled the elimination of almost 97% of the inactive proteins and improved the activity performance by 55.13%, while multiplying the specific activity of the coagulant by a factor of 20.88 against a 6.75-fold purification with ionexchange and the appearance of a more or less 20 kDa peptide after electrophoresis. The proteolytic activity of the purified extracts had a similar appearance to a more pronounced kinetic when compared with the reference rennet. The purification protocols did not seem to have an impact on the isolatedprotease activity.Key words: Mucor pusillus, protease, purification, enzymatic performance, electrophoresis, milk clotting,rennet
An inverse relationship between production and export efficiency in the Southern Ocean
Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 40 (2013): 1557–1561, doi:10.1002/grl.50219.In the past two decades, a number of studies have been carried out in the Southern Ocean to look at export production using drifting sediment traps and thorium-234 based measurements, which allows us to reexamine the validity of using the existing relationships between production, export efficiency, and temperature to derive satellite-based carbon export estimates in this region. Comparisons of in situ export rates with modeled rates indicate a two to fourfold overestimation of export production by existing models. Comprehensive analysis of in situ data indicates two major reasons for this difference: (i) in situ data indicate a trend of decreasing export efficiency with increasing production which is contrary to existing export models and (ii) the export efficiencies appear to be less sensitive to temperature in this region compared to the global estimates used in the existing models. The most important implication of these observations is that the simplest models of export, which predict increase in carbon flux with increasing surface productivity, may require additional parameters, different weighing of existing parameters, or separate algorithms for different oceanic regimes.This work was supported by NASA award
number NNX08AB48G.2013-10-2
Monovalent Ion Condensation at the Electrified Liquid/Liquid Interface
X-ray reflectivity studies demonstrate the condensation of a monovalent ion
at the electrified interface between electrolyte solutions of water and
1,2-dichloroethane. Predictions of the ion distributions by standard
Poisson-Boltzmann (Gouy-Chapman) theory are inconsistent with these data at
higher applied interfacial electric potentials. Calculations from a
Poisson-Boltzmann equation that incorporates a non-monotonic ion-specific
potential of mean force are in good agreement with the data.Comment: 4 pages, 4 figure
- …