6,289 research outputs found
Development of neutron activation analysis procedures for the determination of oxygen in potassium final report, period ending 15 dec. 1964
Neutron activation analysis for determination of oxygen in potassiu
Dilepton and Photon Emission Rates from a Hadronic Gas
We analyze the dilepton and photon emission rates from a hadronic gas using
chiral reduction formulas and a virial expansion. The emission rates are
reduced to pertinent vacuum correlation functions, most of which can be
assessed from experiment. Our results indicate that in the low mass region, the
dilepton and photon rates are enhanced compared to most of the calculations
using chiral Lagrangians. The enhancement is further increased through a finite
pion chemical potential. An estimate of the emission rates is also made using
Haag's expansion for the electromagnetic current. The relevance of these
results to dilepton and photon emission rates in heavy-ion collisions is
discussed.Comment: 7 pages, LaTeX using revTeX, 6 figures imbedded in text. Figures
slightly changed, text left unchange
Optimal Renormalization-Group Improvement of R(s) via the Method of Characteristics
We discuss the application of the method of characteristics to the
renormalization-group equation for the perturbative QCD series within the
electron-positron annihilation cross-section. We demonstrate how one such
renormalization-group improvement of this series is equivalent to a closed-form
summation of the first four towers of renormalization-group accessible
logarithms to all orders of perturbation theory
Final Report: Buffalo National River Ecosystems
The objective of this study was to sample the Buffalo River on a seasonal basis for a year, in order to determine whether any potential water quality problems existed
A gauge invariant and string independent fermion correlator in the Schwinger model
We introduce a gauge invariant and string independent two-point fermion
correlator which is analyzed in the context of the Schwinger model (QED_2). We
also derive an effective infrared worldline action for this correlator, thus
enabling the computation of its infrared behavior. Finally, we briefly discuss
possible perspectives for the string independent correlator in the QED_3
effective models for the normal state of HTc superconductors.Comment: 14 pages, LaTe
Medium effect on photon production in ultrarelativistic nuclear collisions
The effect of in-medium vector and axial-vector meson masses on photon
production is studied. We assume that the effective mass of a vector meson in
hot nuclear matter decreases according to a universal scaling law, while that
of an axial-vector meson is given by Weinberg's mass formula. We find that the
thermal production rate of photons increases with reduced masses, and is
enhanced by an order of magnitude at T=160 MeV with MeV. Assuming
a hydrodynamic evolution, we estimate the effect of the reduced masses on
photon production in nucleus-nucleus collisions. The result is compared to
experimental data from the WA80/WA98 collaboration.Comment: 21 pages, REVTEX + 9 figures (ps file
Constraints on Higher-Order Perturbative Corrections in Semileptonic Decays from Residual Renormalization-Scale Dependence
The constraint of a progressive decrease in residual renormalization scale
dependence with increasing loop order is developed as a method for obtaining
bounds on unknown higher-order perturbative corrections to
renormalization-group invariant quantities. This technique is applied to the
inclusive semileptonic process (explicitly known to
two-loop order) to obtain bounds on the three- and four-loop perturbative
coefficients that are not accessible via the renormalization group. Using the
principle of minimal sensitivity, an estimate is obtained for the perturbative
contributions to that incorporates
theoretical uncertainty from as-yet-undetermined higher order QCD corrections.Comment: latex2e using amsmath, 8 pages, 4 embedded eps figures. Revised
version contains an additional figure and accompanying revision
Novel Methods for Determining Effective Interactions for the Nuclear Shell Model
The Contractor Renormalization (CORE) method is applied in combination with
modern effective-theory techniques to the nuclear many-body problem. A
one-dimensional--yet ``realistic''--nucleon-nucleon potential is introduced to
test these novel ideas. It is found that the magnitude of ``model-space''
(CORE) corrections diminishes considerably when an effective potential that
eliminates the hard-momentum components of the potential is first introduced.
As a result, accurate predictions for the ground-state energy of the there-body
system are made with relatively little computational effort when both
techniques are used in a complementary fashion.Comment: 14 pages, 5 figures and 2 tabl
Isospin Fluctuations in QCD and Relativistic Heavy-Ion Collisions
We address the role of fluctuations in strongly interacting matter during the
dense stages of a heavy-ion collision through its electromagnetic emission.
Fluctuations of isospin charge are considered in a thermal system at rest as
well as in a moving hadronic fluid at fixed proper time within a finite bin of
pseudo-rapidity. In the former case, we use general thermodynamic relations to
establish a connection between fluctuations and the space-like screening limit
of the retarded photon self-energy, which directly relates to the emissivities
of dileptons and photons. Effects of hadronic interactions are highlighted
through two illustrative calculations. In the latter case, we show that a
finite time scale inherent in the evolution of a heavy-ion collision
implies that equilibrium fluctuations involve both space-like and time-like
components of the photon self-energy in the system. Our study of non-thermal
effects, explored here through a stochastic treatment, shows that an early and
large fluctuation in isospin survives only if it is accompanied by a large
temperature fluctuation at freeze-out, an unlikely scenario in hadronic phases
with large heat capacity. We point out prospects for the future which include:
(1) A determination of the Debye mass of the system at the dilute freeze-out
stage of a heavy-ion collision, and (2) A delineation of the role of charge
fluctuations during the dense stages of the collision through a study of
electromagnetic emissivities.Comment: 12 pages ReVTeX incl. 4 ps-fig
Aggregation Prediction in Therapeutic Protein Formulations for Excipient Design
Computational Infrastructure & Informatics Poster SessionA major concern in the development therapeutic protein formulations is protein aggregation. Proteins can interact to form bound groups of protein molecules or aggregates. Aggregates in protein formulations reduce effectiveness and can lead to severe immune responses in patients. Excipients are additive molecules that are not therapeutically active, but can increase the stability of protein formulations. An ideal excipient binds with aggregation prone regions on the protein to limit interaction of that region with another protein molecule. The goal of this project is to predict aggregation prone regions and design excipients to interact with these regions.
Several tools exist to predict which regions on a protein will be most likely to initiate aggregation. Aggrescan (http://bioinf.uab.es/aggrescan/) and SAP (Spatial Aggregation Potential) were used to predict aggregation prone regions on proteins and the results were compared. Aggrescan uses experimental data to assign each amino acid an aggregation propensity score. An aggregation prone region is identified by a sequence of amino acids with high propensities. The three-dimensional structure is not used in the aggregation prediction. SAP uses molecular simulation to determine regions that are hydrophobic and solvent accessible. Each residue is scored and the results are mapped to the three-dimensional protein structure. A successful prediction tool must use parameters that correlate with aggregation potential for a folded protein. The aggregation prone regions predicted by Aggrescan and SAP were compared to experimental data on protein aggregation. Proteins with a high number of predicted regions or large predicted regions were found to have higher experimental percent aggregation. With the regions identified, molecular simulations were performed for protein-excipient systems. A protein and small molecule docking algorithm was used to determine which regions of the protein certain excipients interacted with. Trehalose, poly(vinylpyrrolidone), and guanadine hydrochloride were used. For an excipient to successfully stabilize a protein and prevent aggregation, the excipient should interact with the aggregation prone regions predicted by Aggrescan and SAP. The predicted regions were compared to the regions where the excipient docks in the molecular simulation. The simulation results were compared to experimental data on the percent aggregation observed in several protein-excipient formulations. The excipients that were found to interact with the predicted aggregation prone regions in simulations should also experimentally prohibit aggregation, leading to lower percent aggregation. Hydrogen-deuterium swapping along with FTIR analysis will be performed experimentally to determine exposed regions on the protein. Proteins with a high number of exposed regions are less stable. The exposed regions will be compared to the aggregation prone regions predicted by Aggrescan and SAP
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