396 research outputs found
A failure study of the railway rail serviced for heavy cargo trains
AbstractIn this case study, a failed railway rail which was used for heavy cargo trains was investigated in order to find out its root cause. The macroscopic beach marks and microscopic fatigue striations were not observed by macro and microscopic observations. The chevron patterns were observed by macro observations. The crack origin was at the tip of chevron patterns. The fan-shaped patterns, cleavage step and the river patterns were observed at the crack origin, which demonstrated the feature of cleavage fracture. The metallurgical structures at the crack origin were pearlite and ferrite networks. The crack is supposed to be initiated from the weaker ferrite networks. Given all of that, the failed railway rail is considered to be caused by overload. It is of great importance to improve the welding technology, and control the load of train in order to prevent similar failure in future
Habitable Zones and UV Habitable Zones around Host Stars
Ultraviolet radiation is a double-edged sword to life. If it is too strong,
the terrestrial biological systems will be damaged. And if it is too weak, the
synthesis of many biochemical compounds can not go along. We try to obtain the
continuous ultraviolet habitable zones, and compare the ultraviolet habitable
zones with the habitable zones of host stars. Using the boundary ultraviolet
radiation of ultraviolet habitable zone, we calculate the ultraviolet habitable
zones of host stars with masses from 0.08 to 4.00 \mo. For the host stars with
effective temperatures lower than 4,600 K, the ultraviolet habitable zones are
closer than the habitable zones. For the host stars with effective temperatures
higher than 7,137 K, the ultraviolet habitable zones are farther than the
habitable zones. For hot subdwarf as a host star, the distance of the
ultraviolet habitable zone is about ten times more than that of the habitable
zone, which is not suitable for life existence.Comment: 5 pages, 3 figure
Multiplicity distributions inside parton cascades developing in a medium
The explanation of the suppression of high-pT hadron yields at RHIC in terms
of jet-quenching implies that the multiplicity distributions of particles
inside a jet and jet-like particle correlations differ strongly in
nucleus-nucleus collisions at RHIC or at the LHC from those observed at e+e- or
hadron colliders. We present a framework for describing the medium-induced
modification, which has a direct interpretation in terms of a probabilistic
medium-modified parton cascade, and which treats leading and subleading partons
on an equal footing. We show that our approach can account for the strong
suppression of single inclusive hadron spectra measured in Au-Au collisions at
RHIC, and that this implies a characteristic distortion of the single inclusive
distribution of soft partons inside the jet. We determine, as a function of the
jet energy, to what extent the soft fragments within a jet can be measured
above some momentum cut.Comment: 5 pages, 4 eps-figures; talk given at Hot Quarks 2006, Villasimius
(Sardinia, Italy), May 15-20, 200
Habitable Zones of Host Stars During the Post-MS Phase
A star will become brighter and brighter with stellar evolution, and the
distance of its habitable zone will become farther and farther. Some planets
outside the habitable zone of a host star during the main sequence phase may
enter the habitable zone of the host star during other evolutionary phases. A
terrestrial planet within the habitable zone of its host star is generally
thought to be suited to life existence. Furthermore, a rocky moon around a
giant planet may be also suited to life survive, provided that the planet-moon
system is within the habitable zone of its host star. Using Eggleton's code and
the boundary flux of habitable zone, we calculate the habitable zone of our
Solar after the main sequence phase. It is found that Mars' orbit and Jupiter's
orbit will enter the habitable zone of Solar during the subgiant branch phase
and the red giant branch phase, respectively. And the orbit of Saturn will
enter the habitable zone of Solar during the He-burning phase for about 137
million years. Life is unlikely at any time on Saturn, as it is a giant gaseous
planet. However, Titan, the rocky moon of Saturn, may be suitable for
biological evolution and become another Earth during that time. For low-mass
stars, there are similar habitable zones during the He-burning phase as our
Solar, because there are similar core masses and luminosities for these stars
during that phase.Comment: 6 pages, 7 figures. Accepted by Ap & S
proBDNF inhibits the proliferation and migration of OLN-93 oligodendrocytes
In contrast with mature brain‑derived neurotrophic factor (mBDNF), proBDNF induces cell apoptosis. However, the function of proBDNF in oligodendrocytes remains unclear. In the present study, the OLN‑93 oligodendroglia cell line was utilized as an in vitro model to analyse the functions of proBDNF in oligodendroglia. p75NTR, sortilin and proBDNF were expressed in cultured OLN‑93 cells. It was indicated that proBDNF inhibited OLN‑93 cell proliferation in a dose‑dependent manner as determined using the MTT assay and BrdU staining. Furthermore, proBDNF suppressed the migration of OLN‑93 cells as demonstrated using the scratch assay. proBDNF also decreased cell viability and promoted apoptosis as indicated by activated cysteine‑aspartic acid protease‑3 (caspase‑3) immunocytochemistry. Notably, anti‑proBDNF treatment neutralized the effect of proBDNF and resulted in increased cell proliferation and migration and decreased apoptosis. However, these effects were not observed in the presence of recombinant p75NTR extracellular domain‑human FC fusion protein and p75NTR antibody, indicating that proBDNF imparts its inhibitory effects on oligodendrocytes through the p75NTR signal pathway.Shen Liu, Wei Guo, Hengxing Zhou, Liang Tang, Shiqing Feng, Jin-Hua Zhong, and Xi- Fu Zho
The dihadron fragmentation function and its evolution
Dihadron fragmentation functions and their evolution are studied in the
process of annihilation. Under the collinear factorization
approximation and facilitated by the cut-vertex technique, the two hadron
inclusive cross section at leading order (LO) is shown to factorize into a
short distance parton cross section and a long distance dihadron fragmentation
function. We provide the definition of such a dihadron fragmentation function
in terms of parton matrix elements and derive its DGLAP evolution equation at
leading log. The evolution equation for the non-singlet quark fragmentation
function is solved numerically with a simple ansatz for the initial condition
and results are presented for cases of physical interest.Comment: 27 pages, 2 column, Revtex4, 21 figure
Calculating Quenching Weights
We calculate the probability (``quenching weight'') that a hard parton
radiates an additional energy fraction due to scattering in spatially extended
QCD matter. This study is based on an exact treatment of finite in-medium path
length, it includes the case of a dynamically expanding medium, and it extends
to the angular dependence of the medium-induced gluon radiation pattern. All
calculations are done in the multiple soft scattering approximation
(Baier-Dokshitzer-Mueller-Peign\'e-Schiff--Zakharov ``BDMPS-Z''-formalism) and
in the single hard scattering approximation (N=1 opacity approximation). By
comparison, we establish a simple relation between transport coefficient, Debye
screening mass and opacity, for which both approximations lead to comparable
results. Together with this paper, a CPU-inexpensive numerical subroutine for
calculating quenching weights is provided electronically. To illustrate its
applications, we discuss the suppression of hadronic transverse momentum
spectra in nucleus-nucleus collisions. Remarkably, the kinematic constraint
resulting from finite in-medium path length reduces significantly the
transverse momentum dependence of the nuclear modification factor, thus leading
to consistency with the data measured at the Relativistic Heavy Ion Collider
(RHIC).Comment: 45 pages LaTeX, 20 eps-figure
J/psi suppression in heavy ion collisions by quark momentum diffusion
The momentum diffusion effect of the quark pair due to the multiple
scattering in a nuclear medium is studied to explain the observed J/psi yields
in SPS experiments. The resulting suppression is found to be insufficient to
reproduce the J/psi yield in Pb-Pb collisions at SPS energy.Comment: 2 pages (1 figure
Crossing w=-1 in Gauss-Bonnet Brane World with Induced Gravity
Recent type Ia supernovas data seemingly favor a dark energy model whose
equation of state crosses -1 very recently, which is a much more amazing
problem than the acceleration of the universe. In this paper we show that it is
possible to realize such a crossing without introducing any phantom component
in a Gauss-Bonnet brane world with induced gravity, where a four dimensional
curvature scalar on the brane and a five dimensional Gauss-Bonnet term in the
bulk are present. In this realization, the Gauss-Bonnet term and the mass
parameter in the bulk play a crucial role.Comment: Revtex 16 pages including 10 eps files, references added, to appear
in Comm. Theor. Phy
- …