1,305 research outputs found
On the complexity of curve fitting algorithms
We study a popular algorithm for fitting polynomial curves to scattered data
based on the least squares with gradient weights. We show that sometimes this
algorithm admits a substantial reduction of complexity, and, furthermore, find
precise conditions under which this is possible. It turns out that this is,
indeed, possible when one fits circles but not ellipses or hyperbolas.Comment: 8 pages, no figure
A Hybrid Model for QCD Deconfining Phase Boundary
Intensive search for a proper and realistic equations of state (EOS) is still
continued for studying the phase diagram existing between quark gluon plasma
(QGP) and hadron gas (HG) phases. Lattice calculations provide such EOS for the
strongly interacting matter at finite temperature () and vanishing baryon
chemical potential (). These calculations are of limited use at finite
due to the appearance of notorious sign problem. In the recent past,
we had constructed a hybrid model description for the QGP as well as HG phases
where we make use of a new excluded-volume model for HG and a
thermodynamically-consistent quasiparticle model for the QGP phase and used
them further to get QCD phase boundary and a critical point. Since then many
lattice calculations have appeared showing various thermal and transport
properties of QCD matter at finite and . We test our hybrid
model by reproducing the entire data for strongly interacting matter and
predict our results at finite so that they can be tested in future.
Finally we demonstrate the utility of the model in fixing the precise location,
the order of the phase transition and the nature of CP existing on the QCD
phase diagram. We thus emphasize the suitability of the hybrid model as
formulated here in providing a realistic EOS for the strongly interacting
matter.Comment: 22 pages, 10 figures. corrected version published in Physical Review
D. arXiv admin note: substantial text overlap with arXiv:1201.044
Specific lipid recruitment by the retroviral gag protein upon HIV-1 assembly : from model membranes to infected cells
The retroviral Gag protein targets the plasma membrane of infected cells for viral particle formation and release. The matrix domain (MA) of Gag is myristoylated for membrane anchoring but also contains a highly basic region that recognizes acidic phospholipids. Gag targets lipid molecules at the inner leaflet of the plasma membrane including phosphatidylinositol (4,5) bisphosphate (PI(4,5)P2) and cholesterol. Here, we addressed the question whether HIV-1 Gag was able to trap PI(4,5)P2 and/or other lipids during HIV-1 assembly in silico, in vitro on reconstituted membranes and in cellulo at the plasma membrane of the host CD4+ T cells. In silico, we could observe the first PI(4,5)P2 preferential recruitment by HIV-1 MA or Gag while protein docked on artificial membranes. In vitro, using biophysical techniques, we observed the specific trapping of PI(4,5)P2, and, to a lesser extent, cholesterol and the exclusion of sphingomyelin, during HIV-1 myr(-)Gag self-assembly on LUVs and SLBs. Finally, in infected living CD4+ T cells, we measured lipid dynamics within and away from HIV-1 assembly sites using super-resolution stimulated emission depletion (STED) microscopy coupled with scanning Fluorescence Correlation Spectroscopy (sSTED-FCS). The analysis of HIV-1 infected CD4+ T lymphocytes revealed that, upon virus assembly, HIV-1 is able to specifically trap PI(4,5)P2, and cholesterol but not phosphatidylethanolamine (PE) or sphingomyelin (SM) at the cellular membrane. Furthermore, analyzing CD4+ T cells expressing only HIV-1 Gag protein showed that Gag is the main driving force restricting the mobility of PI(4,5)P2 and cholesterol at the cell plasma membrane. Our data provide the first direct evidence showing that HIV-1 Gag creates its own specific lipid environment for virus assembly by selectively recruiting lipids to generate PI(4,5)P2/cholesterol-enriched nanodomains favoring virus assembly, and that HIV-1 does not assemble on pre-existing lipid domains
The Hagedorn temperature Revisited
The Hagedorn temperature, T_H is determined from the number of hadronic
resonances including all mesons and baryons. This leads to a stable result T_H
= 174 MeV consistent with the critical and the chemical freeze-out temperatures
at zero chemical potential. We use this result to calculate the speed of sound
and other thermodynamic quantities in the resonance hadron gas model for a wide
range of baryon chemical potentials following the chemical freeze-out curve. We
compare some of our results to those obtained previously in other papers.Comment: 13 pages, 4 figure
Transverse hydrodynamics with sudden hadronization -- production of strangeness
We consider a physical scenario for ultra-relativistic heavy-ion collisions
where, at the early stage, only transverse degrees of freedom of partons are
thermalized, while the longitudinal motion is described by free streaming. When
the energy density of the partonic system drops to a certain critical value,
the partons hadronize and the newly formed hadronic system freezes out. This
sudden change is described with the help of the Landau matching conditions
followed by the simulations done with THERMINATOR. The proposed scenario
reproduces well the transverse-momentum spectra, the elliptic flow coefficient
v2, and the HBT radii of pions and kaons studied at RHIC (Au+Au collisions at
the top beam energy). It also reproduces quite well the transverse-momentum
spectra of hyperons.Comment: talk presented by WF at the Strangeness in Quark Matter Conference,
Buzios, Brazil, Sept. 27 - oct. 2, 200
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HIV-1 Gag specifically restricts PI(4,5)P2 and cholesterol mobility in living cells creating a nanodomain platform for virus assembly
HIV-1 Gag protein assembles at the plasma membrane of infected cells for viral particle formation. Gag targets lipids, mainly PI(4,5)P2, at the inner leaflet of this membrane. Here, we address the question whether Gag is able to trap specifically PI(4,5)P2 or other lipids during HIV-1 assembly in the host CD4+ T lymphocytes. Lipid dynamics within and away from HIV-1 assembly sites were determined using super-resolution microscopy coupled with scanning fluorescence correlation spectroscopy in living cells. Analysis of HIV-1–infected cells revealed that, upon assembly, HIV-1 is able to specifically trap PI(4,5)P2 and cholesterol, but not phosphatidylethanolamine or sphingomyelin. Furthermore, our data showed that Gag is the main driving force to restrict the mobility of PI(4,5)P2 and cholesterol at the cell plasma membrane. This is the first direct evidence highlighting that HIV-1 creates its own specific lipid environment by selectively recruiting PI(4,5)P2 and cholesterol as a membrane nanoplatform for virus assembly
Charge dependent azimuthal correlations in Pb--Pb collisions at TeV
Separation of charges along the extreme magnetic field created in non-central
relativistic heavy--ion collisions is predicted to be a signature of local
parity violation in strong interactions. We report on results for charge
dependent two particle azimuthal correlations with respect to the reaction
plane for Pb--Pb collisions at TeV recorded in 2010 with
ALICE at the LHC. The results are compared with measurements at RHIC energies
and against currently available model predictions for LHC. Systematic studies
of possible background effects including comparison with conventional
(parity-even) correlations simulated with Monte Carlo event generators of
heavy--ion collisions are also presented.Comment: Published in the proceedings of "Quark Matter 2011", Annecy-Franc
Initiation of a critical pathway for pancreaticoduodenectomy at an academic institution -- the first step in multi-disciplinary team building
Objective: This study was designed to identify quantifiable parameters to track performance improvements brought about by the implementation of a critical pathway for complex alimentary tract surgery.
Background: Pancreaticoduodenectomy (PD) is a complex general surgical procedure performed in varying numbers at many academic institutions. Originally associated with significant perioperative morbidity and mortality, multiple studies have now shown that this operation can be performed quite safely at high volume institutions that develop a particular expertise. Critical pathways are one of the key tools used to achieve consistently excellent outcomes as these institutions. It remains to be determined if implementation of a critical pathway at an academic institution with prior moderate experience with PD will result in performance gains and improved outcomes.
Methods: Between January 1, 2004 and October 15, 2006 135 patients underwent PD, 44 before the implementation of a critical pathway on October 15, 2005, and 91 after. Perioperative and postoperative parameters were analyzed retrospectively to identify those that could be used to track performance improvement and outcomes. Key aspects of the pathway include spending the night of surgery in the intensive care unit with careful attention to fluid balance, early mobilization on post-operative day one, aggressive early removal of encumbrances such as nasogastric tubes and urinary catheters, early post-operative feeding, and targeting discharge for postoperative day 6 or 7.
Results: The pre- and post-pathway implementation groups were not statistically different with regards to age, sex, race, or pathology (malignant versus benign). Perioperative mortality, operative blood loss, and number of transfused units of packed red blood cells were also similar. As compared to the pre-pathway group, the post-pathway group had a significantly shorter postoperative length of stay (13 versus 7 days, P ≤ 0.0001), operative time (435 ± 14 minutes versus 379 ± 12 minutes, P ≤ 0.0001), and in room non-operative time (95 ± 4 minutes versus 76 ± 2 minutes, P ≤ 0.0001). Total hospital charges were significantly reduced from 32,490 versus 4883 (P ≤ 0.0001) after pathway implementation. Postoperative complication rates remained constant (44% pre-pathway versus 37% after, P = NS). Readmission rates were not negatively affected by the reduction in length of stay, with a 7% readmission rate prior to implementation and a 7.7% rate after implementation.
Conclusion: Implementation of a critical pathway for a complex procedure can be demonstrated to improve short-term outcomes at an academic institution. This improvement can be quantified and tracked and has implications for better utilization of resources (greater OR and hospital bed availability) and overall cost containment. With a very conservative estimate of 75 pancreaticoduodenectomies per year by this group, this translates to a savings of 450 hospital days and over $8,550,000 in hospital charges on an annual basis. As we enter the pay for performance era, institutions will be required to generate such data in order to retain patient volumes, attract new patients, and receive incentive payments for high quality services rendered
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