46,668 research outputs found
Measurement of photons via conversion pairs in \sqrt{s_{NN}} = 200 GeV Au+Au collisions with the PHENIX experiment at RHIC
Thermal photons can provide information on the temperature of the new state
of matter created at RHIC. In the p_T region of 1--3 GeV/c thermal photons are
expected to be the dominant direct photon source. Therefore, a possible excess
compared to a pure decay photon signal due to a thermal photon contribution
should be seen in the double ratio
(\gamma/\gamma(\pi^{0}))_{Measured}/(\gamma/\gamma(\pi^{0}))_{Simulated}, if
sufficient accuracy can be reached. We present a method to reconstruct direct
photons by measuring e^{+}e^{-}--pairs from external photon conversions.Comment: 4 pages, 7 figures. To appear in the proceedings of Hot Quarks 2006:
Workshop for Young Scientists on the Physics of Ultrarelativistic
Nucleus-Nucleus Collisions, Villasimius, Italy, 15-20 May 200
Equivariant Perturbation in Gomory and Johnson's Infinite Group Problem. I. The One-Dimensional Case
We give an algorithm for testing the extremality of minimal valid functions
for Gomory and Johnson's infinite group problem that are piecewise linear
(possibly discontinuous) with rational breakpoints. This is the first set of
necessary and sufficient conditions that can be tested algorithmically for
deciding extremality in this important class of minimal valid functions. We
also present an extreme function that is a piecewise linear function with some
irrational breakpoints, whose extremality follows from a new principle.Comment: 38 pages, 10 figure
Measurement of light mesons at RHIC by the PHENIX experiment
The PHENIX experiment at RHIC has measured a variety of light neutral mesons
(, K, , , , ) via
multi-particle decay channels over a wide range of transverse momentum. A
review of the recent results on the production rates of light mesons in p+p and
their nuclear modification factors in d+Au, Cu+Cu and Au+Au collisions at
different energies is presented.Comment: 5 pages, 4 figures, talk given at Hard Probes 2008 conference in La
Toja, Spain. submitted to EPJ
Beam Coupling Impedances of Obstacles Protruding into Beam Pipe
The beam coupling impedances of small obstacles protruding inside the vacuum
chamber of an accelerator are calculated analytically at frequencies for which
the wavelength is large compared to a typical size of the obstacle. Simple
formulas for a few important particular cases, including both essentially
three-dimensional objects like a post or a mask and axisymmetric irises, are
presented. The analytical results are compared and agree with three-dimensional
computer simulations. These results allow simple practical estimates of the
broad-band impedance contributions from such discontinuities.Comment: 4 pages, LaTeX (REVTeX), 2 figures (eps); corrected and revised,
comparison with simulations added; presented at PAC97 (Vancouver, May 97
Search for the onset of baryon anomaly at RHIC-PHENIX
The baryon production mechanism at the intermediate (2 - 5 GeV/) at
RHIC is still not well understood. The beam energy scan data in Cu+Cu and Au+Au
systems at RHIC may provide us a further insight on the origin of the baryon
anomaly and its evolution as a function of . In 2005 RHIC
physics program, the PHENIX experiment accumulated the first intensive low beam
energy data in Cu+Cu collisions. We present the preliminary results of
identified charged hadron spectra in Cu+Cu at = 22.5 and 62.4
GeV using the PHENIX detector. The centrality and beam energy dependences of
(anti)proton to pion ratios and the nuclear modification factors for charged
pions and (anti)protons are presented.Comment: 5 pages, 9 figures, proceedings for Hot Quarks 2006 workshop,
Villasimius, Sardinia, Italy, May 15 - 20, 2006. Proceedings of the
conference will be published in The European Physical Journal
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
Zero Temperature Limit of Holographic Superconductors
We consider holographic superconductors whose bulk description consists of
gravity minimally coupled to a Maxwell field and charged scalar field with
general potential. We give an analytic argument that there is no "hard gap":
the real part of the conductivity at low frequency remains nonzero (although
typically exponentially small) even at zero temperature. We also numerically
construct the gravitational dual of the ground state of some holographic
superconductors. Depending on the charge and dimension of the condensate, the
infrared theory can have emergent conformal or just Poincare symmetry. In all
cases studied, the area of the horizon of the dual black hole goes to zero in
the extremal limit, consistent with a nondegenerate ground state.Comment: 27 pages, 8 figure
Perfectionism, fear of failure, and affective responses to success and failure: The central role of fear of experiencing shame and embarrassment
This study investigated how different aspects of perfectionism in athletes (N = 388) related to the different fears of failure proposed by Conroy et al. (2002), and how perfectionism and fears of failure predicted positive and negative affect after imagined success and failure in sports competitions. Results showed that perfectionistic personal standards showed a negative relationship with fear of experiencing shame and embarrassment and a positive relationship with positive affect after success, whereas perfectionistic concern over mistakes and perceived parental pressure showed a positive relationship with fear of experiencing shame and embarrassment and with negative affect after failure. Moreover, fear of experiencing shame and embarrassment fully mediated the relationship between perfectionistic concern and negative affect and between coach pressure and negative affect. The findings demonstrate that fear of experiencing shame and embarrassment is central in the perfectionism-fear of failure relationship and that perfectionistic concern about mistakes and perceived coach pressure are aspects of perfectionism that predict fear of experiencing shame and embarrassment and negative affect after failure
Mortality, protoplasm decay rate, and reliability of staining techniques to recognise 'living' foraminifera: a review.
Non-vital staining, especially with rose Bengal, has been widely used in ecological studies to differentiate between the tests of dead(unstained) foraminifera from those presumed to be living at the time of collection (stained). Doubts have been expressed about staining methods because of the possibility that dead individuals may retain undecayed protoplasm for weeks or months after death; when stained, such individuals would be recorded as living. To assess the importance of such false positives, it is necessary to examine rates of mortality, and the modes of generation of empty tests, i.e., whether due to reproduction, growth stages (leaving empty tests during growth) or death. It can be argued that reproduction, ontogeny, and death through predation lead to tests devoid of protoplasm. Whereas reproduction may affect only a small proportion of the population of each species (due to high pre-reproductive mortality), predation in oxygenated environments may be responsible for the major part of that pre-reproductive mortality. In oxygenated environments, disease or adverse environmental conditions are most likely to lead to dead individuals having tests containing protoplasm. In dysaerobic/anoxic environments, predation by macrofauna may be excluded, so foraminifera die through other causes and thus more tests with dead protoplasm may be potentially available for staining. Therefore, for most other environments, the problem of staining dead individuals is almost certainly overstated. Furthermore, from comparative studies, it seems that the most commonly used technique (staining with rose Bengal) is as reliable as others. Now that new vital staining techniques, especially the use of fluorescent probes, are being introduced, it is timely for further objective comparative studies of all techniques to be made in order to evaluate data already gathered and to develop the best strategies for future ecological studies according to whether they are field-based or experimental
Ranking of vitrified grinding wheel parameters by using analytical hierarchical process (AHP) for surface roughness of work piece in grinding operation
Objective of grinding process is to generate high quality surface finish on work piece. There are many parameters which influence on the work piece roughness. Work piece material and characteristics, grinding wheel specification, grinding conditions and dressing conditions influence on the surface quality of the work piece. Selection of grinding wheel is important aspect for producing good quality of surface finish on the work piece. The main components of grinding wheel are the abrasive grains, bond material and porosity. Selection of correct grinding wheel is necessary for generating better surface finish on the work piece. Analytical Hierarchical Process (AHP) is used for ranking of vitrified bond grinding wheel parameters on surface roughness on the work piece in sub sequent grinding operation. The grit, grade, (Hardness of wheel) structure and type of abrasive are critically assisted in terms of the surface finish produced on work piece in the subsequent grinding operation. Analytic Hierarchy Process (AHP) shows that the abrasive grit of grinding wheel has first rank and grade (hardness) of the wheel has Second rank for the producing surface finish on the work piece after grinding operation. Structure and type of abrasive of wheel have a third and fourth rank respectively. Thus, AHP gives qualitative way of controlling work piece surface roughness in sub-sequent grinding operation by selecting proper grinding wheel of vitrified bond which helps the user to select the correct grinding wheel
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