21,559 research outputs found

    On Quillen's calculation of graded KK-theory

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    We adapt Quillen's calculation of graded K-groups of Z-graded rings with support in N to graded K-theory, allowing gradings in a product Z \times G with G an arbitrary group. This in turn allows us to use inductions and calculate graded K-theory of Z^m-graded rings. Here Z is the ring of integers and N positive natural numbers

    A note on the graded K-theory of certain graded rings

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    Following ideas of Quillen it is shown that the graded K-theory of a Z^n-graded ring with support contained in a pointed cone is entirely determined by the K-theory of the subring of degree-0 elements.Comment: 4 page

    A microscopic description of sound absorption in the atmosphere

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    The various mechanisms which contribute to sound absorption in the atmosphere are identified and a technique for computing the contribution from each is presented. The similarities between sound absorption, laser fluorescence measurements, and the opto-acoustic effect are discussed. Finally, experimental sound absorption results are compared to predictions to test the microscopic energy transfer approach

    Nucleus-nucleus collisions at high baryon densities

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    We study central collision of Pb+Pb at 20, 40, 80 and 160 AGeV within the UrQMD transport approach and compare rapidity distributions of pi-, K+, K- and Lambda with the recent measurements from the NA49 Collaboration at 40, 80 and 160 AGeV. It is found that the UrQMD model reasonably describes the data, however, systematically overpredicts the pi- yield by about 20%, whereas the K+ yield is underestimated by about 15%. The K- yields are in a good agreement with the experimental data, the Lambda yields are also in a reasonable correspondence with the data for all energies. We find that hadronic flavour exchange reactions largely distort the information about the initial strangeness production mechanism at all energies considered.Comment: 9 pages, including 3 eps figures, submitted to Phys. Lett.

    The Impact of a Clinical Faculty Institute on Participants\u27 Skills for Mentoring Novice Teachers, Grades K-8

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    A seven-day Clinical Faculty Institute was implemented to increase the skills of mentor teachers and to develop a cadre of Clinical Faculty for the four participating colleges and universities. The 128 participants entered with some conïŹdence in their ability to mentor novice teachers in areas typically taught in methods courses; whereas, they displayed minimal conïŹdence in skills typically taught in supervisory courses. By the end of the Institute, participants showed signiïŹcant changes in their self-perceptions of skills in twenty areas, with post-scores clustering between 3.5 and 3.9 on a four-point scale. Future institutes should focus on supervisory skills and then emphasize more reïŹ‚ection upon the congruence of teaching, with the best practices articulated in national standards

    Splittings of generalized Baumslag-Solitar groups

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    We study the structure of generalized Baumslag-Solitar groups from the point of view of their (usually non-unique) splittings as fundamental groups of graphs of infinite cyclic groups. We find and characterize certain decompositions of smallest complexity (`fully reduced' decompositions) and give a simplified proof of the existence of deformations. We also prove a finiteness theorem and solve the isomorphism problem for generalized Baumslag-Solitar groups with no non-trivial integral moduli.Comment: 20 pages; hyperlinked latex. Version 2: minor change

    Can Momentum Correlations Proof Kinetic Equilibration in Heavy Ion Collisions at 160 AGeV?

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    We perform an event-by-event analysis of the transverse momentum distribution of final state particles in central Pb(160AGeV)+Pb collisions within a microscopic non-equilibrium transport model (UrQMD). Strong influence of rescattering is found. The extracted momentum distributions show less fluctuations in A+A collisions than in p+p reactions. This is in contrast to simplified p+p extrapolations and random walk models.Comment: 9 pages, 3 eps figures, submitted to Phys. Lett.

    Azimuthal correlations of pions in relativistic heavy ion collisions at 1 GeV/nucl.

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    Triple differential cross sections of pions in heavy ion collisions at 1 GeV/nucl. are studied with the IQMD model. After discussing general properties of Δ\Delta resonance and pion production we focus on azimuthal correlations: At projectile- and target-rapidities we observe an anticorrelation in the in-plane transverse momentum between pions and protons. At c.m.-rapidity, however, we find that high ptp_t pions are being preferentially emitted perpendicular to the event-plane. We investigate the causes of those correlations and their sensitivity on the density and momentum dependence of the real and imaginary part of the nucleon and pion optical potential.Comment: 40 pages, 18 eps-figures, uses psfig.sty; complete postscript file available at ftp://th.physik.uni-frankfurt.de/pub/bass/GSI-preprint_95-7.ps.

    PEDIATRÍA: Recientes progresos en el conocimiento de las enfermedades infecciosas en la infancia

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    The Disappearance of Flow

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    We investigate the disappearance of collective flow in the reaction plane in heavy-ion collisions within a microscopic model (QMD). A systematic study of the impact parameter dependence is performed for the system Ca+Ca. The balance energy strongly increases with impact parameter. Momentum dependent interactions reduce the balance energies for intermediate impact parameters b≈4.5b\approx4.5 fm. Dynamical negative flow is not visible in the laboratory frame but does exist in the contact frame for the heavy system Au+Au. For semi-peripheral collisions of Ca+Ca with b≈6.5b\approx6.5 fm a new two-component flow is discussed. Azimuthal distributions exhibit strong collectiv flow signals, even at the balance energy.Comment: 19 pages, 7 eps-figures, uses psfig.sty; complete postscript file available at ftp://th.physik.uni-frankfurt.de/pub/bass/GSI-preprint_95-11.ps.
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