213 research outputs found
Recrystallization in an Mg-Nd alloy processed by high-pressure torsion: a calorimetric analysis
Differential scanning calorimetry (DSC) was used to evaluate the recrystallization temperature and activation energy for an Mg-1.43Nd (wt.%) alloy after severe plastic deformation by high-pressure torsion (HPT) at room temperature up to 10 turns. The recrystallization kinetics were determined from DSC analysis. The results show that the recrystallization temperature increases with increasing heating rate and decreases with increasing numbers of HPT turns. Severe plastic deformation by HPT significantly reduces the recrystallization temperature. The estimated activation energy for recrystallization was in the range of ~ 84-89 kJ mol-1
Hagedorn divergences and tachyon potential
We consider the critical behavior for a string theory near the Hagedorn
temperature. We use the factorization of the worldsheet to isolate the Hagedorn
divergences at all genera. We show that the Hagedorn divergences can be
resummed by introducing double scaling limits, which smooth the divergences.
The double scaling limits also allow one to extract the effective potential for
the thermal scalar. For a string theory in an asymptotic anti-de Sitter (AdS)
spacetime, the AdS/CFT correspondence implies that the critical Hagedorn
behavior and the relation with the effective potential should also arise from
the boundary Yang-Mills theory. We show that this is indeed the case. In
particular we find that the free energy of a Yang-Mills theory contains
``vortex'' contributions at finite temperature. Yang-Mills Feynman diagrams
with vortices can be identified with contributions from boundaries of moduli
space on the string theory side.Comment: 36 pages, 13 figures, uses harvma
An investigation by EXAFS of local atomic structure in an Mg-Nd alloy after processing by high-pressure torsion and ageing.
The local atomic structure of an Mg-1.44Nd (wt.%) alloy was investigated after solution annealing, high-pressure torsion (HPT) processing up to 1 and 10 turns and ageing at 250 °C for 5 h using X-ray absorption fine structure (XAFS) measurements at the Nd LIII-edge. The results show that HPT processing has no effect on the atomic structure around Nd atoms compared to the unprocessed state, whereas ageing at 250 °C for 5 h induces a significant modification in the coordination number and interatomic distances around the Nd atoms. These variations are analyzed based on the correlations between precipitation, defects and atomic mobility of the chemical species
Thermodynamic behavior of IIA string theory on a pp-wave
We obtain the thermal one loop free energy and the Hagedorn temperature of
IIA superstring theory on the pp-wave geometry which comes from the circle
compactification of the maximally supersymmetric eleven dimensional one. We use
both operator and path integral methods and find the complete agreement between
them in the free energy expression. In particular, the free energy in the limit is shown to be identical with that of IIB string theory on
maximally supersymmetric pp-wave, which indicates the universal thermal
behavior of strings in the large class of pp-wave backgrounds. We show that the
zero point energy and the modular properties of the free energy are naturally
incorporated into the path integral formalism.Comment: 25 pages, Latex, JHEP style, v4: revised for clarity without change
in main contents, version to appear in JHE
D-Brane Propagation in Two-Dimensional Black Hole Geometries
We study propagation of D0-brane in two-dimensional Lorentzian black hole
backgrounds by the method of boundary conformal field theory of SL(2,R)/U(1)
supercoset at level k. Typically, such backgrounds arise as near-horizon
geometries of k coincident non-extremal NS5-branes, where 1/k measures
curvature of the backgrounds in string unit and hence size of string worldsheet
effects. At classical level, string worldsheet effects are suppressed and
D0-brane propagation in the Lorentzian black hole geometry is simply given by
the Wick rotation of D1-brane contour in the Euclidean black hole geometry.
Taking account of string worldsheet effects, boundary state of the Lorentzian
D0-brane is formally constructible via Wick rotation from that of the Euclidean
D1-brane. However, the construction is subject to ambiguities in boundary
conditions. We propose exact boundary states describing the D0-brane, and
clarify physical interpretations of various boundary states constructed from
different boundary conditions. As it falls into the black hole, the D0-brane
radiates off to the horizon and to the infinity. From the boundary states
constructed, we compute physical observables of such radiative process. We find
that part of the radiation to infinity is in effective thermal distribution at
the Hawking temperature. We also find that part of the radiation to horizon is
in the Hagedorn distribution, dominated by massive, highly non-relativistic
closed string states, much like the tachyon matter. Remarkably, such
distribution emerges only after string worldsheet effects are taken exactly
into account. From these results, we observe that nature of the radiation
distribution changes dramatically across the conifold geometry k=1 (k=3 for the
bosonic case), exposing the `string - black hole transition' therein.Comment: 51 pages, 5 figures, v2: referece added, note added replying the
comment made in hep-th/060206
P-wave excited baryons from pion- and photo-induced hyperon production
We report evidence for , , ,
, , and , and find
indications that might have a companion state at 1970\,MeV. The
controversial is not seen. The evidence is derived from a
study of data on pion- and photo-induced hyperon production, but other data are
included as well. Most of the resonances reported here were found in the
Karlsruhe-Helsinki (KH84) and the Carnegie-Mellon (CM) analyses but were
challenged recently by the Data Analysis Center at GWU. Our analysis is
constrained by the energy independent scattering amplitudes from either
KH84 or GWU. The two amplitudes from KH84 or GWU, respectively, lead to
slightly different branching ratios of contributing resonances but the
debated resonances are required in both series of fits.Comment: 22 pages, 28 figures. Some additional sets of data are adde
A Scheme for the Detection and Tracking of People Tuned for Aerial Image Sequences
Abstract. This paper addresses the problem of detecting and tracking a large number of individuals in aerial image sequences that have been taken from high altitude. We propose a method which can handle the numerous challenges that are associated with this task and demonstrate its quality on several test sequences. Moreover this paper contains several contributions to improve object detection and tracking in other domains, too. We show how to build an effective object detector in a flexible way which incorporates the shadow of an object and enhanced features for shape and color. Furthermore the performance of the detector is boosted by an improved way to collect background samples for the classifier train-ing. At last we describe a tracking-by-detection method that can handle frequent misses and a very large number of similar objects
Centrality Dependence of the High p_T Charged Hadron Suppression in Au+Au collisions at sqrt(s_NN) = 130 GeV
PHENIX has measured the centrality dependence of charged hadron p_T spectra
from central Au+Au collisions at sqrt(s_NN)=130 GeV. The truncated mean p_T
decreases with centrality for p_T > 2 GeV/c, indicating an apparent reduction
of the contribution from hard scattering to high p_T hadron production. For
central collisions the yield at high p_T is shown to be suppressed compared to
binary nucleon-nucleon collision scaling of p+p data. This suppression is
monotonically increasing with centrality, but most of the change occurs below
30% centrality, i.e. for collisions with less than about 140 participating
nucleons. The observed p_T and centrality dependence is consistent with the
particle production predicted by models including hard scattering and
subsequent energy loss of the scattered partons in the dense matter created in
the collisions.Comment: 7 pages text, LaTeX, 6 figures, 2 tables, 307 authors, resubmitted to
Phys. Lett. B. Revised to address referee concerns. Plain text data tables
for the points plotted in figures for this and previous PHENIX publications
are publicly available at
http://www.phenix.bnl.gov/phenix/WWW/run/phenix/papers.htm
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Measurement of Bottom versus Charm as a Function of Transverse Momentum with Electron-Hadron Correlations in p+p Collisions at sqrt(s)=200 GeV
The momentum distribution of electrons from semi-leptonic decays of charm and
bottom for mid-rapidity |y|<0.35 in p+p collisions at sqrt(s)=200 GeV is
measured by the PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC)
over the transverse momentum range 2 < p_T < 7 GeV/c. The ratio of the yield of
electrons from bottom to that from charm is presented. The ratio is determined
using partial D/D^bar --> e^{+/-} K^{-/+} X (K unidentified) reconstruction. It
is found that the yield of electrons from bottom becomes significant above 4
GeV/c in p_T. A fixed-order-plus-next-to-leading-log (FONLL) perturbative
quantum chromodynamics (pQCD) calculation agrees with the data within the
theoretical and experimental uncertainties. The extracted total bottom
production cross section at this energy is \sigma_{b\b^bar}= 3.2
^{+1.2}_{-1.1}(stat) ^{+1.4}_{-1.3}(syst) micro b.Comment: 432 authors, 6 pages text, 3 figures. Submitted to Phys. Rev. Lett.
Plain text data tables for the points plotted in figures for this and
previous PHENIX publications are (or will be) publicly available at
http://www.phenix.bnl.gov/papers.htm
The Earth: Plasma Sources, Losses, and Transport Processes
This paper reviews the state of knowledge concerning the source of magnetospheric plasma at Earth. Source of plasma, its acceleration and transport throughout the system, its consequences on system dynamics, and its loss are all discussed. Both observational and modeling advances since the last time this subject was covered in detail (Hultqvist et al., Magnetospheric Plasma Sources and Losses, 1999) are addressed
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