1314 search hits
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Measuring shear viscosity using correlations
(2007)
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Sean Gavin
Mohamed Abdel-Aziz
- Measurements of transverse momentum fluctuations can be used to determine the shear viscosity [1]. We use current data to estimate the viscosity-to-entropy ratio in the range from 0.08 to 0.3, and discuss how future measurements can reduce this uncertainty.
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Ion beam analysis based on cellular nonlinear networks
(2011)
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Vanessa Senger
Ronald Tetzlaff
Hermine Reichau
Ulrich Ratzinger
- The development of a non- destructive measurement method for ion beam parameters has been treated in various projects. Although results are promising, the high complexity of beam dynamics has made it impossible to implement a real time process control up to now. In this paper we will propose analysing methods based on the dynamics of Cellular Nonlinear Networks (CNN) that can be implemented on pixel parallel CNN based architectures and yield satisfying results even at low resolutions.
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Analysis of a hybrid TATA box binding protein originating from mesophilic and thermophilic donor organisms
(2010)
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Annette Kopitz
Jörg Soppa
Karin Hauser
- The TATA Box Binding Protein (TBP) is a 20 kD protein that is essential and universally conserved in eucarya and archaea. Especially among archaea, organisms can be found that live below 0°C as well as organisms that grow above 100°C. The archaeal TBPs show a high sequence identity and a similar structure consisting of α-helices and β-sheets that are arranged in a saddle-shape 2-symmetric fold. In previous studies, we have characterized the thermal stability of thermophilic and mesophilic archaeal TBPs by infrared spectroscopy and showed the correlation between the transition temperature (Tm) and the optimal growth temperature (OGT) of the respective donor organism. In this study, a “new” mutant TBP has been constructed, produced, purified and analyzed for a deeper understanding of the molecular mechanisms of thermoadaptation. The β-sheet part of the mutant consists of the TBP from Methanothermobacter thermoautotrophicus (OGT 65°C, MtTBP65) whose α-helices have been exchanged by those of Methanosarcina mazei (OGT 37°C, MmTBP37). The Hybrid-TBP irreversibly aggregates after thermal unfolding just like MmTBP37 and MtTBP65, but the Tm lies between that of MmTBP37 and MtTBP65 indicating that the interaction between the α-helical and β-sheet part of the TBP is crucial for the thermal stability. The temperature stability is probably encoded in the variable α-helices that interact with the highly conserved and DNA binding β-sheets.
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Meteorologische Untersuchungen in Osnabrück 1875 - 1983 : mit 9 Tabellen
(1986)
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Johannes Niemann
Günter Schmidt
- Im Jahre 1871 wurde durch den Naturwissenschaftlichen Verein Osnabrück
(gegründet 1870) eine meteorologische Station eingerichtet. Sie hatte ihren
Standort am Sommerhaus des damaligen Obergerichtsrats JOHANN-VOLLRATH
KETTLER,Osnabrück, Ziegelstraße 7. KETTLER hat 1872 im 1. Jahresbericht des
. Naturwissenschaftlichen Vereins über die "Entstehung, Einrichtung und die ersten
Ergebnisse" berichtet. Dieser Bericht ist hier wiedergegeben, legt er uns
dar, daß alle Messungen exakt und gewissenhaft durchgeführt wurden.
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The QCD phase diagram at zero and small baryon density
(2005)
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Owe Philipsen
- I review recent developments in determining the QCD phase diagram by means of lattice simulations.
Since the invention of methods to side-step the sign problem a few years ago, a number
of additional variants have been proposed, and progress has been made towards understanding
some of the systematics involved. All available techniques agree on the transition temperature
as a function of density in the regime mq/T <~1. There are by now four calculations with signals
for a critical point, two of them at similar parameter values and with consistent results. However,
it also emerges that the location of the critical point is exceedingly quark mass sensitive. At the
same time sizeable finite volume, cut-off and step size effects have been uncovered, demanding
additional investigations with exact algorithms on larger and finer lattices before quantitative conclusions
can be drawn. Depending on the sign of these corrections, there is ample room for the
eventual phase diagram to look as expected or also quite different, with no critical point at all.
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QCD equation of state and dark matter
(2006)
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Mark Hindmarsh
Owe Philipsen
- The QCD equation of state is not often discussed in cosmology. However, the relic density of
weakly interacting massive particles (WIMPs) depends on the entropy and the expansion rate of
the Universe when they freeze out, at a temperature in the range 400 MeV – 40GeV, where QCD
corrections are still important. We use recent analytic and lattice calculations of the QCD pressure
to produce a new equation of state suitable for use in relic density calculations. As an example,
we show that relic densities calculated by the dark matter package DarkSUSY receive corrections
of several per cent, within the observational accuracy of the Planck CMB mission, due for launch
in 2007.
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Strong coupling expansion for Yang-Mills theory at finite temperature
(2007)
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Jens Langelage
Gernot Münster
Owe Philipsen
- Euclidean strong coupling expansion of the partition function is applied to lattice Yang-Mills theory
at finite temperature, i.e. for lattices with a compactified temporal direction. The expansions
have a finite radius of convergence and thus are valid only for b <bc, where bc denotes the nearest
singularity of the free energy on the real axis. The accessible temperature range is thus the
confined regime up to the deconfinement transition. We have calculated the first few orders of
these expansions of the free energy density as well as the screening masses for the gauge groups
SU(2) and SU(3). The resulting free energy series can be summed up and corresponds to a glueball
gas of the lowest mass glueballs up to the calculated order. Our result can be used to fix
the lower integration constant for Monte Carlo calculations of the thermodynamic pressure via
the integral method, and shows from first principles that in the confined phase this constant is
indeed exponentially small. Similarly, our results also explain the weak temperature dependence
of glueball screening masses below Tc, as observed in Monte Carlo simulations. Possibilities and
difficulties in extracting bc from the series are discussed.
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Twisted mass QCD at finite temperature
(2007)
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Ernst-Michael Ilgenfritz
Michael Müller-Preußker
Marcus Petschlies
Karl Jansen
Maria Paola Lombardo
Owe Philipsen
Lars Zeidlewicz
André Sternbeck
- We discuss the use of Wilson fermions with twisted mass for simulations of QCD thermodynamics.
As a prerequisite for a future analysis of the finite-temperature transition making use
of automatic O(a) improvement, we investigate the phase structure in the space spanned by the
hopping parameter k , the coupling b , and the twisted mass parameter m. We present results for
Nf = 2 degenerate quarks on a 163×8 lattice, for which we investigate the possibility of an Aoki
phase existing at strong coupling and vanishing m, as well as of a thermal phase transition at
moderate gauge couplings and non-vanishing m.
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Exploring the QCD phase diagram
(2007)
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Owe Philipsen
- Lattice simulations employing reweighting and Taylor expansion techniques have predicted a
(m;T)-phase diagram according to general expectations, with an analytic quark-hadron crossover
at m =0 turning into a first order transition at some critical chemical potential mE. By contrast, recent
simulations using imgainary m followed by analytic continuation obtained a critical structure
in the fmu;d;ms;T;mg parameter space favouring the absence of a critical point and first order line.
I review the evidence for the latter scenario, arguing that the various raw data are not inconsistent
with each other. Rather, the discrepancy appears when attempting to extract continuum results
from the coarse (Nt =4) lattices simulated so far, and can be explained by cut-off effects. New (as
yet unpublished) data are presented, which for Nf = 3 and on Nt = 4 confirm the scenario without
a critical point. Moreover, simulations on finer Nt = 6 lattices show that even if there is a critical
point, continuum extrapolation moves it to significantly larger values of mE than anticipated on
coarse lattices.
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The finite-temperature phase structure of lattice QCD with twisted-mass Wilson fermions
(2008)
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Ernst-Michael Ilgenfritz
Karl Jansen
Maria Paola Lombardo
Michael Müller-Preussker
Marcus Petschlies
Owe Philipsen
Lars Zeidlewicz
- We report progress in our exploration of the finite-temperature phase structure of two-flavour lattice
QCD with twisted-mass Wilson fermions and a tree-level Symanzik-improved gauge action
for a temporal lattice size Nt = 8. Extending our investigations to a wider region of parameter
space we gain a global view of the rich phase structure. We identify the finite temperature transition/
crossover for a non-vanishing twisted-mass parameter in the neighbourhood of the zerotemperature
critical line at sufficiently high b . Our findings are consistent with Creutz’s conjecture
of a conical shape of the finite temperature transition surface. Comparing with NLO lattice
cPT we achieve an improved understanding of this shape.
