5,475 research outputs found
Determining the strange and antistrange quark distributions of the nucleon
The difference between the strange and antistrange quark distributions,
\delta s(x)=s(x)-\sbar(x), and the combination of light quark sea and strange
quark sea, \Delta (x)=\dbar(x)+\ubar(x)-s(x)-\sbar(x), are originated from
non-perturbative processes, and can be calculated using non-perturbative models
of the nucleon. We report calculations of and using
the meson cloud model. Combining our calculations of with
relatively well known light antiquark distributions obtained from global
analysis of available experimental data, we estimate the total strange sea
distributions of the nucleon.Comment: 4 pages, 3 figures; talk given by F.-G. at QNP0
Quantum Entanglement of Moving Bodies
We study the properties of quantum information and quantum entanglement in
moving frames. We show that the entanglement between the spins and the momenta
of two particles can be interchanged under a Lorentz transformation, so that a
pair of particles that is entangled in spin but not momentum in one reference
frame, may, in another frame, be entangled in momentum at the expense of
spin-entanglement. Similarly, entanglement between momenta may be transferred
to spin under a Lorentz transformation. While spin and momentum entanglement
each is not Lorentz invariant, the joint entanglement of the wave function is.Comment: 4 pages, 2 figures. An error was corrected in the numerical data and
hence the discussion of the data was changed. Also, references were added.
Another example was added to the pape
Electron surface layer at the interface of a plasma and a dielectric wall
We study the potential and the charge distribution across the interface of a
plasma and a dielectric wall. For this purpose, the charge bound to the wall is
modelled as a quasi-stationary electron surface layer which satisfies Poisson's
equation and minimizes the grand canonical potential of the wall-thermalized
excess electrons constituting the wall charge. Based on an effective model for
a graded interface taking into account the image potential and the offset of
the conduction band to the potential just outside the dielectric, we
specifically calculate the potential and the electron distribution for
magnesium oxide, silicon dioxide and sapphire surfaces in contact with a helium
discharge. Depending on the electron affinity of the surface, we find two
vastly different behaviors. For negative electron affinity, electrons do not
penetrate into the wall and an external surface charge is formed in the image
potential, while for positive electron affinity, electrons penetrate into the
wall and a space charge layer develops in the interior of the dielectric. We
also investigate how the electron surface layer merges with the bulk of the
dielectric.Comment: 15 pages, 9 figures, accepted versio
General Relativistic Simulations of Slowly and Differentially Rotating Magnetized Neutron Stars
We present long-term (~10^4 M) axisymmetric simulations of differentially
rotating, magnetized neutron stars in the slow-rotation, weak magnetic field
limit using a perturbative metric evolution technique. Although this approach
yields results comparable to those obtained via nonperturbative (BSSN)
evolution techniques, simulations performed with the perturbative metric solver
require about 1/4 the computational resources at a given resolution. This
computational efficiency enables us to observe and analyze the effects of
magnetic braking and the magnetorotational instability (MRI) at very high
resolution. Our simulations demonstrate that (1) MRI is not observed unless the
fastest-growing mode wavelength is resolved by more than about 10 gridpoints;
(2) as resolution is improved, the MRI growth rate converges, but due to the
small-scale turbulent nature of MRI, the maximum growth amplitude increases,
but does not exhibit convergence, even at the highest resolution; and (3)
independent of resolution, magnetic braking drives the star toward uniform
rotation as energy is sapped from differential rotation by winding magnetic
fields.Comment: 21 pages, 11 figures, published in Phys.Rev.
New parton distributions in fixed flavour factorization scheme from recent deep-inelastic-scattering data
We present our QCD analysis of the proton structure function
to determine the parton distributions at the next-to-leading order (NLO). The
heavy quark contributions to , with = , have been
included in the framework of the `fixed flavour number scheme' (FFNS). The
results obtained in the FFNS are compared with available results such as the
general-mass variable-flavour-number scheme (GM-VFNS) and other prescriptions
used in global fits of PDFs. In the present QCD analysis, we use a wide range
of the inclusive neutral-current deep-inelastic-scattering (NC DIS) data,
including the most recent data for charm , bottom , longitudinal
structure functions and also the reduced DIS cross sections
from HERA experiments. The most recent HERMES data for
proton and deuteron structure functions are also added. We take into account
ZEUS neutral current DIS inclusive jet cross section data from HERA
together with the recent Tevatron Run-II inclusive jet cross section data from
CDF and D{\O}. The impact of these recent DIS data on the PDFs extracted from
the global fits are studied. We present two families of PDFs, {\tt KKT12} and
{\tt KKT12C}, without and with HERA `combined' data sets on DIS. We
find these are in good agreement with the available theoretical models.Comment: 23 pages, 26 figures and 4 tables. V3: Only few comments and
references added in the replaced version, results unchanged. Code can be
found at http://particles.ipm.ir/links/QCD.ht
Multivariate Fitting and the Error Matrix in Global Analysis of Data
When a large body of data from diverse experiments is analyzed using a
theoretical model with many parameters, the standard error matrix method and
the general tools for evaluating errors may become inadequate. We present an
iterative method that significantly improves the reliability of the error
matrix calculation. To obtain even better estimates of the uncertainties on
predictions of physical observables, we also present a Lagrange multiplier
method that explores the entire parameter space and avoids the linear
approximations assumed in conventional error propagation calculations. These
methods are illustrated by an example from the global analysis of parton
distribution functions.Comment: 13 pages, 5 figures, Latex; minor clarifications, fortran program
made available; Normalization of Hessian matrix changed to HEP standar
Switching Mechanism in Single-Layer Molybdenum Disulfide Transistors: an Insight into Current Flow across Schottky Barriers
In this article, we study the properties of metal contacts to single-layer
molybdenum disulfide (MoS2) crystals, revealing the nature of switching
mechanism in MoS2 transistors. On investigating transistor behavior as contact
length changes, we find that the contact resistivity for metal/MoS2 junctions
is defined by contact area instead of contact width. The minimum gate dependent
transfer length is ~0.63 {\mu}m in the on-state for metal (Ti) contacted
single-layer MoS2. These results reveal that MoS2 transistors are Schottky
barrier transistors, where the on/off states are switched by the tuning the
Schottky barriers at contacts. The effective barrier heights for source and
drain barriers are primarily controlled by gate and drain biases, respectively.
We discuss the drain induced barrier narrowing effect for short channel
devices, which may reduce the influence of large contact resistance for MoS2
Schottky barrier transistors at the channel length scaling limit.Comment: ACS Nano, ASAP (2013
Pair production of the T-odd leptons at the LHC
The T-odd leptons predicted by the littlest model with T-parity can
be pair produced via the subprocesses ,
, and (= or
) at the Large Hadron Collider . We estimate the hadronic
production cross sections for all of these processes and give a simply
phenomenology analysis. We find that the cross sections for most of the above
processes are very small. However, the value of the cross section for the
process can reach .Comment: 12 pages, 2 figure
A comprehensive ovine model of blood transfusion
Background: The growing awareness of transfusion-associated morbidity and mortality necessitates investigations into the underlying mechanisms. Small animals have been the dominant transfusion model but have associated limitations. This study aimed to develop a comprehensive large animal (ovine) model of transfusion encompassing: blood collection, processing and storage, compatibility testing right through to post-transfusion outcomes. Materials and methods: Two units of blood were collected from each of 12 adult male Merino sheep and processed into 24 ovine-packed red blood cell (PRBC) units. Baseline haematological parameters of ovine blood and PRBC cells were analysed. Biochemical changes in ovine PRBCs were characterized during the 42-day storage period. Immunological compatibility of the blood was confirmed with sera from potential recipient sheep, using a saline and albumin agglutination cross-match. Following confirmation of compatibility, each recipient sheep (n = 12) was transfused with two units of ovine PRBC. Results: Procedures for collecting, processing, cross-matching and transfusing ovine blood were established. Although ovine red blood cells are smaller and higher in number, their mean cell haemoglobin concentration is similar to human red blood cells. Ovine PRBC showed improved storage properties in saline-adenine-glucose-mannitol (SAG-M) compared with previous human PRBC studies. Seventy-six compatibility tests were performed and 17·1% were incompatible. Only cross-match compatible ovine PRBC were transfused and no adverse reactions were observed. Conclusion: These findings demonstrate the utility of the ovine model for future blood transfusion studies and highlight the importance of compatibility testing in animal models involving homologous transfusions
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