312 research outputs found
Disparate MgII Absorption Statistics towards Quasars and Gamma-Ray Bursts : A Possible Explanation
We examine the recent report by Prochter et al. (2006) that gamma-ray burst
(GRB) sight lines have a much higher incidence of strong MgII absorption than
quasar sight lines. We propose that the discrepancy is due to the different
beam sizes of GRBs and quasars, and that the intervening MgII systems are
clumpy with the dense part of each cloudlet of a similar size as the quasars,
i.e. < 10^16 cm, but bigger than GRBs. We also discuss observational
predictions of our proposed model. Most notably, in some cases the intervening
MgII absorbers in GRB spectra should be seen varying, and quasars with smaller
sizes should show an increased rate of strong MgII absorbers. In fact, our
prediction of variable MgII lines in the GRB spectra has been now confirmed by
Hao et al. (2007), who observed intervening FeII and MgII lines at z=1.48 to be
strongly variable in the multi-epoch spectra of z=4.05 GRB060206.Comment: 12 pages, 2 figures; substantially revised model calculation;
accepted for publication in Astrophysics & Space Science as a Lette
More is the Same; Phase Transitions and Mean Field Theories
This paper looks at the early theory of phase transitions. It considers a
group of related concepts derived from condensed matter and statistical
physics. The key technical ideas here go under the names of "singularity",
"order parameter", "mean field theory", and "variational method".
In a less technical vein, the question here is how can matter, ordinary
matter, support a diversity of forms. We see this diversity each time we
observe ice in contact with liquid water or see water vapor, "steam", come up
from a pot of heated water. Different phases can be qualitatively different in
that walking on ice is well within human capacity, but walking on liquid water
is proverbially forbidden to ordinary humans. These differences have been
apparent to humankind for millennia, but only brought within the domain of
scientific understanding since the 1880s.
A phase transition is a change from one behavior to another. A first order
phase transition involves a discontinuous jump in a some statistical variable
of the system. The discontinuous property is called the order parameter. Each
phase transitions has its own order parameter that range over a tremendous
variety of physical properties. These properties include the density of a
liquid gas transition, the magnetization in a ferromagnet, the size of a
connected cluster in a percolation transition, and a condensate wave function
in a superfluid or superconductor. A continuous transition occurs when that
jump approaches zero. This note is about statistical mechanics and the
development of mean field theory as a basis for a partial understanding of this
phenomenon.Comment: 25 pages, 6 figure
Investigating the effects of vitreous humour (crude extract) on growth and differentiation of rat mesenchymal stem cells (rMSCs) and human NTERA2 cells
It is very well documented that retinoic acid (RA) reduces growth rate by induction of cell differentiation in certain conditions and cell lines. On the other hand, hyaluronic acid (HA) is known for its growth induction on cultured cells. A natural source of HA, rabbit vitreous humour (VH), was previously shown to promote wound repair in model animals. In search for its possible mechanisms, VH extract was tested on the cultured mesenchymal stem cells and NTERA2 as human embryonal carcinoma cells in the presence of RA. Changes in some cellular and molecular markers (A2B5, Oct4, Sox2) showed that VH and possibly HA interfere with differentiating effects of RA. Therefore, this reagent may affect cell proliferation and tissue regeneration by inhibition of cell differentiation.Đ„ĐŸŃĐŸŃĐŸ ОзĐČĐ”ŃŃĐœĐŸ, ŃŃĐŸ ŃĐ”ŃĐžĐœĐŸĐ”ĐČĐ°Ń ĐșĐžŃĐ»ĐŸŃĐ° (RA) ŃĐœĐžĐ¶Đ°Đ”Ń ŃĐ”ĐŒĐżŃ ŃĐŸŃŃĐ°, ĐžĐœĐŽŃŃĐžŃŃŃ ĐŽĐžŃŃĐ”ŃĐ”ĐœŃОаŃĐžŃ ĐșлДŃĐŸŃĐœŃŃ
Đ»ĐžĐœĐžĐč ĐČ ĐŸĐżŃĐ”ĐŽĐ”Đ»Đ”ĐœĐœŃŃ
ŃŃĐ»ĐŸĐČĐžŃŃ
. ĐĐŒĐ”ŃŃĐ” Ń ŃĐ”ĐŒ ОзĐČĐ”ŃŃĐœĐŸ, ŃŃĐŸ гОалŃŃĐŸĐœĐŸĐČĐ°Ń ĐșĐžŃĐ»ĐŸŃĐ° (HA) ĐžĐœĐŽŃŃĐžŃŃĐ”Ń ŃĐŸŃŃ ĐșŃĐ»ŃŃĐžĐČĐžŃŃĐ”ĐŒŃŃ
ĐșлДŃĐŸĐș. Đ Đ°ĐœĐ”Đ” бŃĐ»ĐŸ ĐżĐŸĐșĐ°Đ·Đ°ĐœĐŸ, ŃŃĐŸ Đ”ŃŃĐ”ŃŃĐČĐ”ĐœĐœŃĐč ĐžŃŃĐŸŃĐœĐžĐș ĐĐ, ŃŃĐ”ĐșĐ»ĐŸĐČĐžĐŽĐœĐŸĐ” ŃĐ”Đ»ĐŸ (VH) ĐșŃĐŸĐ»ĐžĐșĐ°, ĐČŃĐ·ŃĐČĐ°Đ”Ń Đ·Đ°Đ¶ĐžĐČĐ»Đ”ĐœĐžĐ” ŃĐ°Đœ Ń ĐŒĐŸĐŽĐ”Đ»ŃĐœŃŃ
жОĐČĐŸŃĐœŃŃ
. Đ ĐżĐŸĐžŃĐșĐ°Ń
ĐČĐŸĐ·ĐŒĐŸĐ¶ĐœĐŸĐłĐŸ ĐŒĐ”Ń
Đ°ĐœĐžĐ·ĐŒĐ° ŃŃĐŸĐłĐŸ ĐżŃĐŸŃĐ”ŃŃĐ° ŃĐșŃŃŃĐ°ĐșŃ ŃŃĐ”ĐșĐ»ĐŸĐČĐžĐŽĐœĐŸĐłĐŸ ŃДла бŃĐ» ĐžŃŃĐ»Đ”ĐŽĐŸĐČĐ°Đœ ĐœĐ° ĐșŃĐ»ŃŃĐžĐČĐžŃŃĐ”ĐŒŃŃ
ĐŒĐ”Đ·Đ”ĐœŃ
ĐžĐŒĐ°Đ»ŃĐœŃŃ
ŃŃĐČĐŸĐ»ĐŸĐČŃŃ
ĐșлДŃĐșĐ°Ń
Đž ĐșлДŃĐșĐ°Ń
NTERA2 ŃĐŒĐ±ŃĐžĐŸĐœĐ°Đ»ŃĐœĐŸĐč ĐșĐ°ŃŃĐžĐœĐŸĐŒŃ ŃĐ”Đ»ĐŸĐČĐ”ĐșĐ° ĐČ ĐżŃĐžŃŃŃŃŃĐČОО RA. ĐĐ·ĐŒĐ”ĐœĐ”ĐœĐžŃ ĐœĐ”ĐșĐŸŃĐŸŃŃŃ
ĐșлДŃĐŸŃĐœŃŃ
Đž ĐŒĐŸĐ»Đ”ĐșŃĐ»ŃŃĐœŃŃ
ĐŒĐ°ŃĐșĐ”ŃĐŸĐČ (A2B5, Oct4, Sox2) ĐżĐŸĐșазалО, ŃŃĐŸ VH Đž, ĐČĐŸĐ·ĐŒĐŸĐ¶ĐœĐŸ, HA ĐČлОŃŃŃ ĐœĐ° ĐŽĐžŃŃĐ”ŃĐ”ĐœŃĐžŃŃŃŃОД ŃŃŃĐ”ĐșŃŃ RA. йаĐșĐžĐŒ ĐŸĐ±ŃĐ°Đ·ĐŸĐŒ, ŃŃĐŸ ĐČĐ”ŃĐ”ŃŃĐČĐŸ ĐŒĐŸĐ¶Đ”Ń ĐČлОŃŃŃ ĐœĐ° ĐżŃĐŸĐ»ĐžŃĐ”ŃĐ°ŃĐžŃ ĐșлДŃĐŸĐș Đž ŃĐ”ĐłĐ”ĐœĐ”ŃĐ°ŃĐžŃ ŃĐșĐ°ĐœĐ”Đč, ĐžĐœĐłĐžĐ±ĐžŃŃŃ ĐŽĐžŃŃĐ”ŃĐ”ĐœŃОаŃĐžŃ ĐșлДŃĐŸĐș.ĐĐŸĐ±ŃĐ” ĐČŃĐŽĐŸĐŒĐŸ, ŃĐŸ ŃĐ”ŃĐžĐœĐŸŃĐČĐ° ĐșĐžŃĐ»ĐŸŃĐ° (RA) Đ·ĐœĐžĐ¶ŃŃ ŃĐ”ĐŒĐżĐž ŃĐŸŃŃŃ, ŃĐœĐŽŃĐșŃŃŃĐž ĐŽĐžŃĐ”ŃĐ”ĐœŃŃĐ°ŃŃŃ ĐșĐ»ŃŃĐșĐŸĐČĐžŃ
Đ»ŃĐœŃĐč ĐČ ĐżĐ”ĐČĐœĐžŃ
ŃĐŒĐŸĐČĐ°Ń
. Đ Đ°Đ·ĐŸĐŒ Đ· ŃĐžĐŒ ĐČŃĐŽĐŸĐŒĐŸ, ŃĐŸ ĐłŃĐ°Đ»ŃŃĐŸĐœĐŸĐČĐ° ĐșĐžŃĐ»ĐŸŃĐ° (ĐĐ) ŃĐœĐŽŃĐșŃŃ ŃŃŃŃ ĐșŃĐ»ŃŃĐžĐČĐŸ- ĐČĐ°ĐœĐžŃ
ĐșĐ»ŃŃĐžĐœ. Đ Đ°ĐœŃŃĐ” бŃĐ»ĐŸ ĐżĐŸĐșĐ°Đ·Đ°ĐœĐŸ, ŃĐŸ ĐżŃĐžŃĐŸĐŽĐœĐ” ЎжДŃĐ”Đ»ĐŸ ĐĐ, ŃĐșĐ»ĐŸĐżĐŸĐŽŃĐ±ĐœĐ” ŃŃĐ»ĐŸ (VH) ĐșŃĐŸĐ»Ń, ĐČĐžĐșлОĐșĐ°Ń Đ·Đ°ĐłĐŸŃĐœĐœŃ ŃĐ°Đœ Ń ĐŒĐŸĐŽĐ”Đ»ŃĐœĐžŃ
ŃĐČĐ°ŃĐžĐœ. Đ ĐżĐŸŃŃĐșĐ°Ń
ĐŒĐŸĐ¶Đ»ĐžĐČĐŸĐłĐŸ ĐŒĐ”Ń
Đ°ĐœŃĐ·ĐŒŃ ŃŃĐŸĐłĐŸ ĐżŃĐŸŃĐ”ŃŃ Đ”ĐșŃŃŃĐ°ĐșŃ ŃĐșĐ»ĐŸĐżĐŸĐŽŃĐ±ĐœĐŸĐłĐŸ ŃŃла бŃĐČ ĐŽĐŸŃĐ»ŃĐŽĐ¶Đ”ĐœĐžĐč ĐœĐ° ĐșŃĐ»ŃŃĐžĐČĐŸĐČĐ°ĐœĐžŃ
ĐŒĐ”Đ·Đ”ĐœŃ
ŃĐŒĐ°Đ»ŃĐœĐžŃ
ŃŃĐŸĐČбŃŃĐŸĐČĐžŃ
ĐșĐ»ŃŃĐžĐœĐ°Ń
ŃĐ° ĐșĐ»ŃŃĐžĐœĐ°Ń
NTERA2 Đ”ĐŒĐ±ŃŃĐŸĐœĐ°Đ»ŃĐœĐŸŃ ĐșĐ°ŃŃĐžĐœĐŸĐŒĐž Đ»ŃĐŽĐžĐœĐž ĐČ ĐżŃĐžŃŃŃĐœĐŸŃŃŃ RA. ĐĐŒŃĐœĐž ĐŽĐ”ŃĐșĐžŃ
ĐșĐ»ŃŃĐžĐœĐœĐžŃ
ŃĐ° ĐŒĐŸĐ»Đ”ĐșŃĐ»ŃŃĐœĐžŃ
ĐŒĐ°ŃĐșĐ”ŃŃĐČ (A2B5, Oct4, Sox2) ĐżĐŸĐșазалО, ŃĐŸ VH Ń, ĐŒĐŸĐ¶Đ»ĐžĐČĐŸ, ĐĐ ĐČплОĐČĐ°ŃŃŃ ĐœĐ° ĐŽĐžŃĐ”ŃĐ”ĐœŃŃŃŃŃŃ Đ”ŃĐ”ĐșŃĐž RA. йаĐșĐžĐŒ ŃĐžĐœĐŸĐŒ, ŃŃ ŃĐ”ŃĐŸĐČĐžĐœĐ° ĐŒĐŸĐ¶Đ” ĐČплОĐČĐ°ŃĐž ĐœĐ° ĐżŃĐŸĐ»ŃŃĐ”ŃĐ°ŃŃŃ Ń ŃĐ”ĐłĐ”ĐœĐ”ŃĐ°ŃŃŃ ŃĐșĐ°ĐœĐžĐœ, ŃĐœĐłŃбŃŃŃĐž ĐŽĐžŃĐ”ŃĐ”ĐœŃŃĐ°ŃŃŃ ĐșĐ»ŃŃĐžĐœ
Search for a W' boson decaying to a bottom quark and a top quark in pp collisions at sqrt(s) = 7 TeV
Results are presented from a search for a W' boson using a dataset
corresponding to 5.0 inverse femtobarns of integrated luminosity collected
during 2011 by the CMS experiment at the LHC in pp collisions at sqrt(s)=7 TeV.
The W' boson is modeled as a heavy W boson, but different scenarios for the
couplings to fermions are considered, involving both left-handed and
right-handed chiral projections of the fermions, as well as an arbitrary
mixture of the two. The search is performed in the decay channel W' to t b,
leading to a final state signature with a single lepton (e, mu), missing
transverse energy, and jets, at least one of which is tagged as a b-jet. A W'
boson that couples to fermions with the same coupling constant as the W, but to
the right-handed rather than left-handed chiral projections, is excluded for
masses below 1.85 TeV at the 95% confidence level. For the first time using LHC
data, constraints on the W' gauge coupling for a set of left- and right-handed
coupling combinations have been placed. These results represent a significant
improvement over previously published limits.Comment: Submitted to Physics Letters B. Replaced with version publishe
Search for the standard model Higgs boson decaying into two photons in pp collisions at sqrt(s)=7 TeV
A search for a Higgs boson decaying into two photons is described. The
analysis is performed using a dataset recorded by the CMS experiment at the LHC
from pp collisions at a centre-of-mass energy of 7 TeV, which corresponds to an
integrated luminosity of 4.8 inverse femtobarns. Limits are set on the cross
section of the standard model Higgs boson decaying to two photons. The expected
exclusion limit at 95% confidence level is between 1.4 and 2.4 times the
standard model cross section in the mass range between 110 and 150 GeV. The
analysis of the data excludes, at 95% confidence level, the standard model
Higgs boson decaying into two photons in the mass range 128 to 132 GeV. The
largest excess of events above the expected standard model background is
observed for a Higgs boson mass hypothesis of 124 GeV with a local significance
of 3.1 sigma. The global significance of observing an excess with a local
significance greater than 3.1 sigma anywhere in the search range 110-150 GeV is
estimated to be 1.8 sigma. More data are required to ascertain the origin of
this excess.Comment: Submitted to Physics Letters
Measurement of the Lambda(b) cross section and the anti-Lambda(b) to Lambda(b) ratio with Lambda(b) to J/Psi Lambda decays in pp collisions at sqrt(s) = 7 TeV
The Lambda(b) differential production cross section and the cross section
ratio anti-Lambda(b)/Lambda(b) are measured as functions of transverse momentum
pt(Lambda(b)) and rapidity abs(y(Lambda(b))) in pp collisions at sqrt(s) = 7
TeV using data collected by the CMS experiment at the LHC. The measurements are
based on Lambda(b) decays reconstructed in the exclusive final state J/Psi
Lambda, with the subsequent decays J/Psi to an opposite-sign muon pair and
Lambda to proton pion, using a data sample corresponding to an integrated
luminosity of 1.9 inverse femtobarns. The product of the cross section times
the branching ratio for Lambda(b) to J/Psi Lambda versus pt(Lambda(b)) falls
faster than that of b mesons. The measured value of the cross section times the
branching ratio for pt(Lambda(b)) > 10 GeV and abs(y(Lambda(b))) < 2.0 is 1.06
+/- 0.06 +/- 0.12 nb, and the integrated cross section ratio for
anti-Lambda(b)/Lambda(b) is 1.02 +/- 0.07 +/- 0.09, where the uncertainties are
statistical and systematic, respectively.Comment: Submitted to Physics Letters
Search for new physics in events with opposite-sign leptons, jets, and missing transverse energy in pp collisions at sqrt(s) = 7 TeV
A search is presented for physics beyond the standard model (BSM) in final
states with a pair of opposite-sign isolated leptons accompanied by jets and
missing transverse energy. The search uses LHC data recorded at a
center-of-mass energy sqrt(s) = 7 TeV with the CMS detector, corresponding to
an integrated luminosity of approximately 5 inverse femtobarns. Two
complementary search strategies are employed. The first probes models with a
specific dilepton production mechanism that leads to a characteristic kinematic
edge in the dilepton mass distribution. The second strategy probes models of
dilepton production with heavy, colored objects that decay to final states
including invisible particles, leading to very large hadronic activity and
missing transverse energy. No evidence for an event yield in excess of the
standard model expectations is found. Upper limits on the BSM contributions to
the signal regions are deduced from the results, which are used to exclude a
region of the parameter space of the constrained minimal supersymmetric
extension of the standard model. Additional information related to detector
efficiencies and response is provided to allow testing specific models of BSM
physics not considered in this paper.Comment: Replaced with published version. Added journal reference and DO
Measurement of isolated photon production in pp and PbPb collisions at sqrt(sNN) = 2.76 TeV
Isolated photon production is measured in proton-proton and lead-lead
collisions at nucleon-nucleon centre-of-mass energies of 2.76 TeV in the
pseudorapidity range |eta|<1.44 and transverse energies ET between 20 and 80
GeV with the CMS detector at the LHC. The measured ET spectra are found to be
in good agreement with next-to-leading-order perturbative QCD predictions. The
ratio of PbPb to pp isolated photon ET-differential yields, scaled by the
number of incoherent nucleon-nucleon collisions, is consistent with unity for
all PbPb reaction centralities.Comment: Submitted to Physics Letters
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