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Search Results: 1 - 10 of 401335 matches for " M. Fromm "
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Revisiting strong coupling QCD at finite temperature and baryon density
M. Fromm,Ph. de Forcrand
Physics , 2008, DOI: 10.1016/j.nuclphysa.2009.01.044
Abstract: The strong coupling limit ($\beta_{gauge}=0$) of lattice QCD with staggered fermions enjoys the same non-perturbative properties as continuum QCD, namely confinement and chiral symmetry breaking. In contrast to the situation at weak coupling, the sign problem which appears at finite density can be brought under control for a determination of the full (mu,T) phase diagram by Monte Carlo simulations. Further difficulties with efficiency and ergodicity of the simulations, especially at the strongly first-order, low-T, finite-mu transition, are addressed respectively with a worm algorithm and multicanonical sampling. Our simulations reveal sizeable corrections to the old results of Karsch and Muetter. Comparison with analytic mean-field determinations of the phase diagram shows discrepancies of O(10) in the location of the QCD critical point.
Multi-frequency properties of synthetic blazar radio light curves within the shock-in-jet scenario
C. M. Fromm,L. Fuhrmann,M. Perucho
Physics , 2014, DOI: 10.1051/0004-6361/201424815
Abstract: Blazars are among the most powerful extragalactic objects, as a sub-class of active galactic nuclei. They launch relativistic jets and their emitted radiation shows strong variability across the entire electro-magnetic spectrum. The mechanisms producing the variability are still controversial and different models have been proposed to explain the observed variations in multi-frequency blazar light curves.We investigate the capabilities of the classical shock-in-jet model to explain and reconstruct the observed evolution of flares in the turnover frequency turnover flux density plane and their frequency-dependent light curve parameters. With a detailed parameter space study we provide the framework for future, detailed comparisons of observed flare signatures with the shock-in-jet scenario. Based on the shock model we compute synthetic single-dish light curves at different radio frequencies (2.6 to 345 GHz) and for different physical conditions in a conical jet (e.g. magnetic field geometry and Doppler factor). From those we extract the slopes of the different energy loss stages within the $\nu_\mathrm{m}$-$S_\mathrm{m}$ plane and deduce the frequency-dependence of different light curve parameters such as flare amplitude, time scale and cross-band delays. The evolution of the Doppler factor along the jet has the largest influence on the evolution of the flare and on the frequency-dependent light curve parameters. The synchrotron stage can be hidden in the Compton or in the adiabatic stage, depending mainly on the evolution of the Doppler factor, which makes it difficult to detect its signature in observations. In addition, we show that the time lags between different frequencies can be used as an efficient tool to better constrain the physical properties of these objects.
In vitro Biocompatibility of New Silver(I) Coordination Compound Coated-Surfaces for Dental Implant Applications
Priscilla S. Brunetto,Tünde Vig Slenters,Katharina M. Fromm
Materials , 2011, DOI: 10.3390/ma4020355
Abstract: Biofilm formation on implant materials causes a common problem: resistance to aggressive pharmacological agents as well as host defenses. Therefore, to reduce bacterial adhesion to implant surfaces we propose to use silver(I) coordination networks as it is known that silver is the most powerful antimicrobial inorganic agent. As a model surface, self-assembled monolayers (SAMs) on gold Au(111) was used to permit permanent attachment of our silver(I) coordination networks. The surface coatings showed typical nano-structured surfaces with a good biocompatibility for soft-tissue integration with fibroblast cells.
(E)-1-(4-Methoxyanthracen-1-yl)-2-phenyldiazene
Aurelien Crochet,Katharina M. Fromm,Vanya Kurteva,Liudmil Antonov
Acta Crystallographica Section E , 2011, DOI: 10.1107/s1600536811010932
Abstract: The title compound, C21H16N2O, has an E-conformation about the diazene N=N bond. It is reasonably planar with the phenyl ring being inclined to the mean plane of the anthracene moiety [planar to within 0.077 (3) ] by 6.43 (10)°. The crystal structure is stabilized by C—H...π and weak π–π interactions [centroid–centroid distances of 3.7192 (16) and 3.8382 (15) ], leading to the formation of two-dimensional networks stacking along [001] and lying parallel to (110).
Ethyl 5-methoxy-2-trifluoromethyl-1H-indole-3-carboxylate
Aurelien Crochet,Isak Alimi,Christian G. Bochet,Katharina M. Fromm
Acta Crystallographica Section E , 2013, DOI: 10.1107/s1600536813002614
Abstract: The title compound, C13H12F3NO3, is almost planar if one excludes the F atoms of the –CF3 group [maximum deviation for the other hetero atoms = 0.069 (1) ], and the dihedral angle between the pyrrole and benzene ring of the indole system is 2.54 (8)°. In the crystal, molecules are linked by N—H...O hydrogen bonds, forming chains propagating along the a-axis direction. These chains are linked via C—H...O and C—H...F hydrogen bonds, forming a three-dimensional network.
Validation of 525 nm and 1020 nm aerosol extinction profiles derived from ACE imager data: comparisons with GOMOS, SAGE II, SAGE III, POAM III, and OSIRIS
F. Vanhellemont,C. Tetard,A. Bourassa,M. Fromm
Atmospheric Chemistry and Physics Discussions , 2007,
Abstract: The Canadian ACE (Atmospheric Chemistry Experiment) mission is dedicated to the retrieval of a large number of atmospheric trace gas species using the solar occultation technique in the infrared and UV/visible spectral domain. However, two additional solar disk imagers (at 525 nm and 1020 nm) were added for a number of reasons, including the retrieval of aerosol and cloud products. In this paper, we present the first validation results for these imager aerosol/cloud optical extinction coefficient profiles, by intercomparison with profiles derived from measurements performed by 3 solar occultation instruments (SAGE II, SAGE III, POAM III), one stellar occultation instrument (GOMOS) and one limb sounder (OSIRIS). The results indicate that the ACE imager profiles are of good quality in the upper troposphere/lower stratosphere, although the aerosol extinction for the visible channel at 525 nm contains a significant negative bias at higher altitudes, while the profiles are systematically too high at 1020 nm. Both problems are probably related to ACE imager instrumental issues.
Aerosol extinction profiles at 525 nm and 1020 nm derived from ACE imager data: comparisons with GOMOS, SAGE II, SAGE III, POAM III, and OSIRIS
F. Vanhellemont,C. Tetard,A. Bourassa,M. Fromm
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2008,
Abstract: The Canadian ACE (Atmospheric Chemistry Experiment) mission is dedicated to the retrieval of a large number of atmospheric trace gas species using the solar occultation technique in the infrared and UV/visible spectral domain. However, two additional solar disk imagers (at 525 nm and 1020 nm) were added for a number of reasons, including the retrieval of aerosol and cloud products. In this paper, we present first comparison results for these imager aerosol/cloud optical extinction coefficient profiles, with the ones derived from measurements performed by 3 solar occultation instruments (SAGE II, SAGE III, POAM III), one stellar occultation instrument (GOMOS) and one limb sounder (OSIRIS). The results indicate that the ACE imager profiles are of good quality in the upper troposphere/lower stratosphere, although the aerosol extinction for the visible channel at 525 nm contains a significant negative bias at higher altitudes, while the relative differences indicate that ACE profiles are almost always too high at 1020 nm. Both problems are probably related to ACE imager instrumental issues.
Observations and analysis of polar stratospheric clouds detected by POAM III and SAGE III during the SOLVE II/VINTERSOL campaign in the 2002/2003 Northern Hemisphere winter
J. Alfred,M. Fromm,R. Bevilacqua,G. Nedoluha
Atmospheric Chemistry and Physics Discussions , 2006,
Abstract: The Polar Ozone and Aerosol Measurement and Stratospheric Aerosol and Gas Experiment instruments both observed high numbers of polar stratospheric clouds (PSCs) in the polar region during the second SAGE Ozone Loss and Validation Experiment (SOLVE II) and Validation of INTERnational Satellites and Study of Ozone Loss (VINTERSOL) campaign, conducted during the 2002/2003 Northern Hemisphere winter. Between 15 November 2002 (14 November 2002) and 18 March 2003 (21 March 2003) SAGE (POAM) observed 122 (151) aerosol extinction profiles containing PSCs. PSCs were observed on an almost daily basis, from early December through 15 January, in both instruments. No PSCs were observed from either instrument until 4 February, and sparingly in three periods in mid-and-late February and mid-March. In early December, PSCs were observed in the potential temperature range from roughly 375 K to 750 K. Throughout December the top of this range decreases to near 600 K. In February and March, PSC observations were primarily constrained to potential temperatures below 500 K. The PSC observation frequency as a function of ambient temperature relative to the NAT saturation point was used to infer irreversible denitrification. By late December 38% denitrification was inferred at both the 400–475 K and 475–550 K potential temperature ranges. By early January extensive levels of denitrification near 80% were inferred at both potential temperature ranges, and the air remained denitrified at least through early March.
Extended Iterative Scheme for QCD: Three-point Vertices
L. Driesen,J. Fromm,J. Kuhrs,M. Stingl
Physics , 1998, DOI: 10.1007/s100500050246
Abstract: In the framework of a generalized iterative scheme introduced previously to account for the non-analytic coupling dependence associated with the renormalization-group invariant mass scale Lambda, we establish the self-consistency equations of the extended Feynman rules (Lambda-modified vertices of zeroth perturbative order) for the three-gluon vertex, the two ghost vertices, and the two vertices of massless quarks. Calculations are performed to one-loop-order, in Landau gauge, and at the lowest approximation level (r=1) of interest for QCD. We discuss the phenomenon of compensating poles inherent in these equations, by which the formalism automatically cancels unphysical poles on internal lines, and the role of composite-operator information in the form of equation-of-motion condensate conditions. The observed near decoupling of the four-gluon conditions permits a solution to the 2-and-3-point conditions within an effective one-parameter freedom. There exists a parameter range in which one solution has all vertex coefficients real, as required for a physical solution, and a narrower range in which the transverse-gluon and massless-quark propagators both exhibit complex-conjugate pole pairs.
El Corazón del Hombre
Erich Fromm
Revista Costarricense de Cardiología , 2011,
Abstract:
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