2,024 research outputs found
Direct photons measured by the PHENIX experiment at RHIC
Results from the PHENIX experiment at RHIC on direct photon production in
p+p, d+Au, and Au+Au collisions at sqrt(s_NN) = 200 GeV are presented. In p+p
collisions, direct photon production at high p_T behaves as expected from
perturbative QCD calculations. The p+p measurement serves as a baseline for
direct photon production in Au+Au collisions. In d+Au collisions, no effects of
cold nuclear matter are found within the large uncertainty of the measurement.
In Au+Au collisions, the production of high p_T direct photons scales as
expected for particle production in hard scatterings. This supports jet
quenching models, which attribute the suppression of high p_T hadrons to the
energy loss of fast partons in the medium produced in the collision. Low p_T
direct photons, measured via e+e- pairs with small invariant mass, are possibly
related to the production of thermal direct photons.Comment: 5 pages, 5 figures, Proceedings of the Hot Quarks 2006 Workshop for
young scientists on the physics of ultra-relativistic nucleus-nucleus
collisions, Villasimius, Sardinia, Italy, May 15--20, 200
Phenotypes of Myopathy-related Actin Mutants in differentiated C2C12 Myotubes
BACKGROUND: About 20 % of nemaline myopathies are thus far related to skeletal muscle alpha-actin. Seven actin mutants located in different parts of the actin molecule and linked to different forms of the disease were selected and expressed as EGFP-tagged constructs in differentiated C2C12 mytoubes. Results were compared with phenotypes in patient skeletal muscle fibres and with previous expression studies in fibroblasts and C2C12 myoblasts/myotubes. RESULTS: Whereas EGFP wt-actin nicely incorporated into endogenous stress fibres and sarcomeric structures, the mutants showed a range of phenotypes, which generally changed upon differentiation. Many mutants appeared delocalized in myoblasts but integrated into endogenous actin structures after 4–6 days of differentiation, demonstrating a poor correlation between the appearance in myotubes and the severity of the disease. However, for some mutants, integration into stress fibres induced aberrant structures in differentiated cells, like thickening or fragmentation of stress fibres. Other mutants almost failed to integrate but formed huge aggregates in the cytoplasm of myotubes. Those did not co-stain with alpha-actinin, a main component of nemaline bodies found in patient muscle. Interestingly, nuclear aggregates as formed by two of the mutants in myoblasts were found less frequently or not at all in differentiated cells. CONCLUSION: Myotubes are a suitable system to study the capacity of a mutant to incorporate into actin structures or to form or induce pathological changes. Some of the phenotypes observed in undifferentiated myoblasts may only be in vitro effects. Other phenotypes, like aberrant stress fibres or rod formation may be more directly correlated with disease phenotypes. Some mutants did not induce any changes in the cellular actin system, indicating the importance of additional studies like functional assays to fully characterize the pathological impact of a mutant
High pT pi0 Production and Angular Correlations in 158 AGeV p+A and Pb+Pb Collisions
Recent results of the WA98 experiment with p and Pb induced reactions at 158
AGeV are presented. Azimuthal gamma-gamma correlations at high pT were studied
in search for a signal of jet-like structures. A clear indication for
back-to-back correlations can be seen in p+A with a strong dependence on the pT
of the photons and the size of the system. In Pb+Pb collisions in plane
elliptic flow has been observed. Results on transverse mass spectra of neutral
pions measured at central rapidity are presented for impact parameter selected
Pb+Pb collisions. In going from peripheral to medium central collisions there
is a nuclear enhancement increasing with transverse mass similar to the Cronin
effect, while for very central collisions this enhancement appears to be weaker
than expected.Comment: 4 pages, 2 figures, Talk presented at Quark Matter 2002, Nantes,
France, July 18-24, 2002. To appear in the proceedings (Nucl. Phys. A
Spin configurations in circular and rectangular vertical quantum dots in a magnetic field: Three-dimensional self-consistent simulation
The magnetic field dependence of the electronic properties of \textit{real}
single vertical quantum dots in circular and rectangular mesas is investigated
within a full three-dimensional multiscale self-consistent approach without any
{\it \'a priori} assumptions about the shape and strength of the confinement
potential. The calculated zero field electron addition energies are in good
agreement with available experimental data for both mesa geometries. Charging
diagrams in a magnetic field for number of electrons up to five are also
computed. Consistent with the experimental data, we found that the charging
curves for the rectangular mesa dot in a magnetic field are flatter and exhibit
less features than for a circular mesa dot. Evolution of the singlet-triplet
energy separation in the two electron system for both dot geometries in
magnetic field was also investigated. In the limit of large field, beyond the
singlet-triplet transition, the singlet-triplet energy difference continues to
become more negative in a circular mesa dot without any saturation within the
range of considered magnetic fields whilst it is predicted to asymptotically
approach zero for the rectangular mesa dot. This different behavior is
attributed to the symmetry "breaking" that occurs in the singlet wave-functions
in the rectangular mesa dot but not in the circular one.Comment: 12 pages, 8 gifure
Genotyping of Environmental and Clinical Stenotrophomonas maltophilia Isolates and their Pathogenic Potential
Magneto Transport of high TCR (temperature coefficient of resistance) La2/3Ca1/3MnO3: Ag Polycrystalline Composites
We report the synthesis, (micro)structural, magneto-transport and
magnetization of polycrystalline La2/3Ca1/3MnO3:Agx composites with x = 0.0,
0.1, 0.2, 0.3 and 0.4. The temperature coefficient of resistance (TCR) near
ferromagnetic (FM) transition is increased significantly with addition of Ag.
The FM transition temperature (TFM) is also increased slightly with Ag
addition. Magneto-transport measurements revealed that magneto-resistance MR is
found to be maximum near TFM. Further the increased MR of up to 60% is seen
above 300 K for higher silver added samples in an applied field of 7 Tesla.
Sharp TCR is seen near TFM with highest value of up to 15 % for Ag (0.4)
sample, which is an order of magnitude higher than as for present pristine
sample and best value yet reported for any polycrystalline LCMO compound.
Increased TCR, TFM and significant above room temperature MR of
La2/3Ca1/3MnO3:Agx composites is explained on the basis of improved grains size
and connectivity with silver addition in the matrix. Better coupled FM domains
and nearly conducting grain boundaries give rise to improved physical
properties of the La2/3Ca1/3MnO3 manganites.Comment: 16 pages Text + Figs. ACCEPTED: Solid State Communications (Sept.
2006
Influence of preload and nonlinearity of railpads on vibration of railway tracks under stationary and moving harmonic loads
In railway track dynamics, the stiffness and damping properties of railpads have a significant effect on track vibration, decay rates as well forces transmitted to the track supporting structure. Many studies have shown that railpads exhibit pronounced nonlinear behaviour, with preload and frequency dependent properties. This paper presents a three parameter railpad model, together with its differential equation of motion and the required model parameters obtained from experimental data. A time domain model of a rail discretely supported on these railpads is then formulated using the finite element method. The model is subjected to static and dynamic loading in order to study the effects of preload and frequency on its dynamic behaviour. Results are shown as time histories and frequency spectra for the track displacements and reaction forces for various preload levels. They emphasise the necessity of accounting for nonlinear behaviour based on the large disparities (up to 20 dB) observed between the linear and nonlinear cases for the parameters used in this study
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