332 research outputs found
Simple mechanics of protein machines
While belonging to the nanoscale, protein machines are so complex that tracing even a small fraction of their cycle requires weeks of calculations on supercomputers. Surprisingly, many aspects of their operation can be however already reproduced by using very simple mechanical models of elastic networks. The analysis suggests that, similar to other self-organized complex systems, functional collective dynamics in such proteins is effectively reduced to a low-dimensional attractive manifold
Towards synthetic molecular motors: a model elastic-network study
Protein molecular motors play a fundamental role in biological cells and development of their synthetic counterparts is a major challenge. Here, we show how a model motor system with the operation mechanism resembling that of muscle myosin can be designed at the concept level, without addressing the implementation aspects. The model is constructed as an elastic network, similar to the coarse-grained descriptions used for real proteins. We show by numerical simulations that the designed synthetic motor can operate as a deterministic or Brownian ratchet and that there is a continuous transition between such two regimes. The motor operation under external load, approaching the stall condition, is also analysed
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Removal of hazardous pharmaceutical from water by photocatalytic treatment
The photocatalytic abatement of hazardous pharmaceuticals has been investigated at very low concentration in the ppb range as found in wastewater and in environmental pollutants. Photocatalytic degradation of tetracycline as a model compound with titania catalysts has been studied using solarium UV-A and black light with differentially applied electric power, tetracycline and catalyst concentration. Abatement of up to 90% has been achieved after 1 hour. Adsorption of tetracycline and photochemical degradation contribute significantly to the abatement of tetracycline resulting in an immediate reduction during the initial period of treatment. Contribution of adsorption is high at very low concentration (500 ppb). Photocatalytic treatment with titania is even highly efficient in the abatement of very small concentrations of tetracycline in drinking water. © 2010 Versita Warsaw and Springer-Verlag Wien
Energy and momentum density of thermal gluon oscillations
In the exact propagator for finite temperature gluons the location of the
transverse and longitudinal poles in the gluon propagator are unknown functions
of wave vector: and . The residues of the poles,
also unknown, fix the normalization of the one gluon vector potential and thus
of the field strength. The naive energy density
\pol{E}\cdot\pol{D}+\pol{B}\cdot\pol{H} is not correct because of dispersion.
By keeping the modulations due to the source currents the energy density is
shown to be and regardless of the functional form
of and . The momentum density is . The
resulting energy-momentum tensor is not symmetric.Comment: 16 pages, RevTex, no figure
Remote Ischemic Preconditioning Neither Improves Survival nor Reduces Myocardial or Kidney Injury in Patients Undergoing Transcatheter Aortic Valve Implantation (TAVI)
BACKGROUND:
Peri-interventional myocardial injury occurs frequently during transcatheter aortic valve implantation (TAVI). We assessed the effect of remote ischemic preconditioning (RIPC) on myocardial injury, acute kidney injury (AKIN) and 6-month mortality in patients undergoing TAVI.
METHODS:
We performed a prospective single-center controlled trial. Sixty-six patients treated with RIPC prior to TAVI were enrolled in the study and were matched to a control group by propensity-score. RIPC was applied to the upper extremity using a conventional tourniquet. Myocardial injury was assessed using high-sensitive troponin-T (hsTnT), and kidney injury was assessed using serum creatinine levels. Data were compared with the Wilcoxon-Rank and McNemar tests. Mortality was analysed with the log-rank test.
RESULTS:
TAVI led to a significant rise of hsTnT across all patients (p < 0.001). No significant inter-group difference in maximum troponin release or areas-under-the-curve was detected. Medtronic CoreValve and Edwards Sapien valves showed similar peri-interventional troponin kinetics and patients receiving neither valve did benefit from RIPC. AKIN occurred in one RIPC patient and four non-RIPC patients (p = 0.250). No significant difference in 6-month mortality was observed. No adverse events related to RIPC were recorded.
CONCLUSION:
Our data do not show a beneficial role of RIPC in TAVI patients for cardio- or renoprotection, or improved survival
Lifetime of quasiparticles in hot QED plasmas
The calculation of the lifetime of quasiparticles in a QED plasma at high
temperature remains plagued with infrared divergences, even after one has taken
into account the screening corrections. The physical processes responsible for
these divergences are the collisions involving the exchange of very soft,
unscreened, magnetic photons, whose contribution is enhanced by the thermal
Bose-Einstein occupation factor. The self energy diagrams which diverge in
perturbation theory contain no internal fermion loops, but an arbitrary number
of internal magnetostatic photon lines. By generalizing the Bloch-Nordsieck
model at finite temperature, we can resum all the singular contributions of
such diagrams, and obtain the correct long time behaviour of the retarded
fermion propagator in the hot QED plasma: , where is the plasma frequency and
.Comment: 13 pages, LaTe
Effective theories for real-time correlations in hot plasmas
We discuss the sequence of effective theories needed to understand the
qualitative, and quantitative, behavior of real-time correlators
in ultra-relativistic plasmas. We analyze in detail the case where A is a
gauge-invariant conserved current. This case is of interest because it includes
a correlation recently measured in lattice simulations of classical, hot,
SU(2)-Higgs gauge theory. We find that simple perturbation theory, free kinetic
theory, linearized kinetic theory, and hydrodynamics are all needed to
understand the correlation for different ranges of time. We emphasize how
correlations generically have power-law decays at very large times due to
non-linear couplings to long-lived hydrodynamic modes.Comment: 28 pages, Latex, uses revtex, epsf macro packages [Revised version: t
-> sqrt{t} in a few typos on p. 10.
Soft Electromagnetic Radiations From Equilibrating Quark-Gluon Plasma
We evaluate the bremsstrahlung production of low mass dileptons and soft
photons from equilibrating and transversely expanding quark gluon plasma which
may be created in the wake of relativistic heavy ion collisions. We use initial
conditions obtained from the self screened parton cascade model. We consider a
boost invariant longitudinal and cylindrically symmetric transverse expansion
of the parton plasma and find that for low mass dileptons ( GeV)
and soft photons ( GeV), the bremsstrahlung contribution is
rather large compared to annihilation process at both RHIC and LHC energies. We
also find an increase by a factor of 15-20 in the low mass dileptons and soft
photons yield as one goes from RHIC to LHC energies.Comment: 8 pages, including 7 figures To appear in Phys. Rev.
On the Quasiparticle Description of Lattice QCD Thermodynamics
We propose a novel quasiparticle interpretation of the equation of state of
deconfined QCD at finite temperature. Using appropriate thermal masses, we
introduce a phenomenological parametrization of the onset of confinement in the
vicinity of the predicted phase transition. Lattice results of the energy
density, the pressure and the interaction measure of pure SU(3) gauge theory
are excellently reproduced. We find a relationship between the thermal energy
density of the Yang-Mills vacuum and the chromomagnetic condensate _T.
Finally, an extension to QCD with dynamical quarks is discussed. Good agreement
with lattice data for 2, 2+1 and 3 flavour QCD is obtained. We also present the
QCD equation of state for realistic quark masses.Comment: 20 pages, 10 eps figure
Landau-Pomeranchuk-Migdal effect in thermal field theory
In recent studies, the production rate of photons or lepton pairs by a quark
gluon plasma has been found to be enhanced due to collinear singularities. This
enhancement pattern is very dependent on rather strict collinearity conditions
between the photon and the quark momenta. It was estimated by neglecting the
collisional width of quasi-particles. In this paper, we study the modifications
of this collinear enhancement when we take into account the possibility for the
quarks to have a finite mean free path. Assuming a mean free path of order
, we find that only low invariant mass photons are
affected. The region where collision effects are important can be interpreted
as the region where the Landau-Pomeranchuk-Migdal effect plays a role in
thermal photon production by bremsstrahlung. It is found that this effect
modifies the spectrum of very energetic photons as well. Based on these results
and on a previous work on infrared singularities, we end this paper by a
reasonable physical picture for photon production by a quark gluon plasma, that
should be useful to set directions for future technical developments.Comment: 28 pages Latex document, 9 postscript figures, typos corrected,
semantics cleanup, final version to appear in Phys. Rev.
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