Pränatale Diagnostik bei intrauteriner Wachstumsrestriktion mittels Tissue Doppler Imaging Echokardiographie

Tissue Doppler Imaging (TDI) ermöglicht eine direkte quantitative Analyse der fetalen Myokardfunktion. In der Studie wurden kardiale TDI-Messungen bei IUGR-Feten (intrauterine growth restriction, intrauterine Wachstumsrestriktion, Schätzgewicht < 5. Perzentile) im Vergleich zu gesunden Feten durchgeführt. Bei den IUGR-Feten fanden sich eine niedrigere maximale systolische Velocity (Vmax) und ein höherer Myocardial Performance Index (MPI') in beiden Ventrikeln, ein niedrigerer Peak Strain im linken Ventrikel sowie eine stark erhöhte interventrikuläre Dyssynchronizität. Vmax im linken Ventrikel korrelierte negativ mit dem Pulsatility Index der A. umbilicalis und war ein Prädiktor für das Outcome. Bei IUGR liegen somit Einschränkungen der Myokardfunktion vor, die mittels TDI sensitiv nachgewiesen werden können. MPI' und interventrikuläre Dyssynchronizität erscheinen dabei geeignet als Frühmarker, Vmax im linken Ventrikel als Verlaufsparameter

The Sub-Surface Structure of a Large Sample of Active Regions

We employ ring-diagram analysis to study the sub-surface thermal structure of active regions. We present results using a large number of active regions over the course of Solar Cycle 23. We present both traditional inversions of ring-diagram frequency differences, with a total sample size of 264, and a statistical study using Principal Component Analysis. We confirm earlier results on smaller samples that sound speed and adiabatic index are changed below regions of strong magnetic field. We find that sound speed is decreased in the region between approximately r=0.99R_sun and r=0.995R_sun (depths of 3Mm to 7Mm), and increased in the region between r=0.97R_sun and r=0.985R_sun (depths of 11Mm to 21Mm). The adiabatic index is enhanced in the same deeper layers that sound-speed enhancement is seen. A weak decrease in adiabatic index is seen in the shallower layers in many active regions. We find that the magnitudes of these perturbations depend on the strength of the surface magnetic field, but we find a great deal of scatter in this relation, implying other factors may be relevant.Comment: 16 pages, 11 figures, accepted for publication in Solar Physic

Percolation and high energy cosmic rays above 101710^{17} eV

In this work we argue that, in the interpretation of the energy dependence of the depth of the shower maximum and of the muon content in high energy cosmic ray showers ($E > 10^{17}$ eV), other variables besides the composition may play an important role, in particular those characterising the first (high energy) hadronic collisions. The role of the inelasticity, of the nature of the leading particle, and of the particle multiplicity are discussed. A consistent interpretation of existing data within a string percolation model implemented in a hybrid, one dimensional simulation method is given.Comment: 15 pages, 6 eps figure

Heterotic Compactification, An Algorithmic Approach

We approach string phenomenology from the perspective of computational algebraic geometry, by providing new and efficient techniques for proving stability and calculating particle spectra in heterotic compactifications. This is done in the context of complete intersection Calabi-Yau manifolds in a single projective space where we classify positive monad bundles. Using a combination of analytic methods and computer algebra we prove stability for all such bundles and compute the complete particle spectrum, including gauge singlets. In particular, we find that the number of anti-generations vanishes for all our bundles and that the spectrum is manifestly moduli-dependent.Comment: 36 pages, Late

Open charm and charmonium production at relativistic energies

We calculate open charm and charmonium production in $Au+Au$ reactions at $\sqrt{s}$ = 200 GeV within the hadron-string dynamics (HSD) transport approach employing open charm cross sections from $pN$ and $\pi N$ reactions that are fitted to results from PYTHIA and scaled in magnitude to the available experimental data. Charmonium dissociation with nucleons and formed mesons to open charm ($D+\bar{D}$ pairs) is included dynamically. The 'comover' dissociation cross sections are described by a simple phase-space model including a single free parameter, i.e. an interaction strength $M_0^2$, that is fitted to the $J/\Psi$ suppression data for $Pb+Pb$ collisions at SPS energies. As a novel feature we implement the backward channels for charmonium reproduction by $D \bar{D}$ channels employing detailed balance. From our dynamical calculations we find that the charmonium recreation is comparable to the dissociation by 'comoving' mesons. This leads to the final result that the total $J/\Psi$ suppression at $\sqrt{s}$ = 200 GeV as a function of centrality is slightly less than the suppression seen at SPS energies by the NA50 Collaboration, where the 'comover' dissociation is substantial and the backward channels play no role. Furthermore, even in case that all directly produced $J/\Psi$ mesons dissociate immediately (or are not formed as a mesonic state), a sizeable amount of charmonia is found asymptotically due to the $D+\bar{D} \to J/\Psi$ + meson channels in central collisions of $Au+Au$ at $\sqrt{s}$ = 200 GeV which, however, is lower than the $J/\Psi$ yield expected from binary scaling of $pp$ collisions.Comment: 42 pages, including 14 eps figures, discussions extended and references added, to be published in Phys. Rev.

Dynamics of the Hubbard model: a general approach by time dependent variational principle

We describe the quantum dynamics of the Hubbard model at semi-classical level, by implementing the Time-Dependent Variational Principle (TDVP) procedure on appropriate macroscopic wavefunctions constructed in terms of su(2)-coherent states. Within the TDVP procedure, such states turn out to include a time-dependent quantum phase, part of which can be recognized as Berry's phase. We derive two new semi-classical model Hamiltonians for describing the dynamics in the paramagnetic, superconducting, antiferromagnetic and charge density wave phases and solve the corresponding canonical equations of motion in various cases. Noticeably, a vortex-like ground state phase dynamics is found to take place for U>0 away from half filling. Moreover, it appears that an oscillatory-like ground state dynamics survives at the Fermi surface at half-filling for any U. The low-energy dynamics is also exactly solved by separating fast and slow variables. The role of the time-dependent phase is shown to be particularly interesting in the ordered phases.Comment: ReVTeX file, 38 pages, to appear on Phys. Rev.

The magnetic moments of 'Lambda_b' and 'Lambda_c' baryons in light cone QCD sum rules

Using the most general form of the interpolating currents of heavy baryons, the magnetic moments of heavy baryons "Lambda_Q (Q=b,c)" are calculated in framework of the light cone QCD sum rules. A comparison of our results on magnetic moments with the existing theoretical results calculated in various other frameworks are presented.Comment: 14 pp, 6 figures (postscript formatted), LaTex formatte

Charmonium from Statistical Hadronization of Heavy Quarks -- a Probe for Deconfinement in the Quark-Gluon Plasma

We review the statistical hadronization picture for charmonium production in ultra-relativistic nuclear collisions. Our starting point is a brief reminder of the status of the thermal model description of hadron production at high energy. Within this framework an excellent account is achieved of all data for hadrons built of (u,d,s) valence quarks using temperature, baryo-chemical potential and volume as thermal parameters. The large charm quark mass brings in a new (non-thermal) scale which is explicitely taken into account by fixing the total number of charm quarks produced in the collision. Emphasis is placed on the description of the physical basis for the resulting statistical hadronization model. We discuss the evidence for statistical hadronization of charmonia by analysis of recent data from the SPS and RHIC accelerators. Furthermore we discuss an extension of this model towards lower beam energies and develop arguments about the prospects to observe medium modifications of open and hidden charm hadrons. With the imminent start of the LHC accelerator at CERN, exciting prospects for charmonium production studies at the very high energy frontier come into reach. We present arguments that, at such energies, charmonium production becomes a fingerprint of deconfinement: even if no charmonia survive in the quark-gluon plasma, statistical hadronization at the QCD phase boundary of the many tens of charm quarks expected in a single central Pb-Pb collision could lead to an enhanced, rather than suppressed production probability when compared to results for nucleon-nucleon reactions scaled by the number of hard collisions in the Pb-Pb system.Comment: review article, 27 pages, Landoldt review volume "Relativistic Heavy Ion Physics", Reinhard Stock, edito

Exact flow equation for bound states

We develop a formalism to describe the formation of bound states in quantum field theory using an exact renormalization group flow equation. As a concrete example we investigate a nonrelativistic field theory with instantaneous interaction where the flow equations can be solved exactly. However, the formalism is more general and can be applied to relativistic field theories, as well. We also discuss expansion schemes that can be used to find approximate solutions of the flow equations including the essential momentum dependence.Comment: 22 pages, references added, published versio

Electromagnetic Probes

A review is presented of dilepton and real photon measurements in relativistic heavy ion collisions over a very broad energy range from the low energies of the BEVALAC up to the highest energies available at RHIC. The dileptons cover the invariant mass range \mll = 0 - 2.5 GeV/c$^2$, i.e. the continuum at low and intermediate masses and the light vector mesons, $\rho, \omega, \phi$. The review includes also measurements of the light vector mesons in elementary reactions.Comment: To be published in Landolt-Boernstein Volume 1-23A; 40 pages, 24 figures. Final version updated with small changes to the text, updated references and updated figure