137 research outputs found
Multi-jet cross sections in deep inelastic scattering at next-to-leading order
We present the perturbative prediction for three-jet production cross section
in DIS at the NLO accuracy. We study the dependence on the renormalization and
factorization scales of exclusive three-jet cross section. The perturbative
prediction for the three-jet differential distribution as a function of the
momentum transfer is compared to the corresponding data obtained by the H1
collaboration at HERA.Comment: 5 pages, 3 figure
Ordering variable for parton showers
The parton splittings in a parton shower are ordered according to an ordering
variable, for example the transverse momentum of the daughter partons relative
to the direction of the mother, the virtuality of the splitting, or the angle
between the daughter partons. We analyze the choice of the ordering variable
and conclude that one particular choice has the advantage of factoring softer
splittings from harder splittings graph by graph in a physical gauge.Comment: 28 pages, 5 figure
QCD radiative corrections to prompt diphoton production in association with a jet at hadron colliders
We compute the next-to-leading order corrections in to prompt
diphoton production in association with a jet at hadron colliders. We use a
next-to-leading order general-purpose partonic Monte Carlo event generator that
allows the computation of a rate differential in the produced photons and
hadrons.Comment: 17 pages, 6 figures, JHEP3 documen
Four-jet angular distributions and color charge measurements: leading order versus next-to-leading order
We present the next-to-leading order perturbative QCD prediction to the
four-jet angular distributions used by experimental collaborations at LEP for
measuring the QCD color charge factors. We compare our results to ALEPH data
corrected to parton level. We perform a leading order ``measurement'' of the
QCD color factor ratios by fitting the leading order perturbative predictions
to the next-to-leading order result. Our result shows that in an experimental
analysis for measuring the color charge factors the use of the O()
QCD predictions instead of the O() results may shift the center of
the fit by a relative factor of 1+2\as in the direction.Comment: 14 pages, 10 tables, 5 figures, revtex, eps style
Three-jet cross sections in hadron-hadron collisions at next-to-leading order
We present a new QCD event generator for hadron collider which can calculate
one-, two- and three-jet cross sections at next-to-leading order accuracy. In
this letter we study the transverse energy spectrum of three-jet hadronic
events using the kT algorithm. We show that the next-to-leading order
correction significantly reduces the renormalization and factorization scale
dependence of the three-jet cross section.Comment: 4 pages, 4 figures, REVTEX
General subtraction method for numerical calculation of one-loop QCD matrix elements
We present a subtraction scheme for eliminating the ultraviolet, soft, and
collinear divergences in the numerical calculation of an arbitrary one-loop QCD
amplitude with an arbitrary number of external legs. The subtractions consist
of local counter terms in the space of the four-dimensional loop momentum. The
ultraviolet subtraction terms reproduce MSbar renormalization. The key point in
the method for the soft and collinear subtractions is that, although the
subtraction terms are defined graph-by-graph and the matrix element is also
calculated graph-by-graph, the sum over graphs of the integral of each the
subtraction term can be evaluated analytically and provides the well known
simple pole structure that arises from subtractions from real emission graphs,
but with the opposite sign.Comment: 38 pages, 10 figures, axodraw styl
Next-to-Leading Order Calculation of Four-Jet Shape Variables
We present the next-to-leading order calculation of two four-jet event shape
variables, the D parameter and acoplanarity differential distributions. We find
large, more than 100% radiative corrections. The theoretical prediction for the
D parameter is compared to L3 data obtained at the Z peak and corrected to
hadron level.Comment: 11 pages, latex with aps, epsf, rotate styles 3 tables, 3 figures
typo in eq. 10 corrected, note and reference added, introduction revise
Prehistoric uses of circumpolar mineral resources: Insights and emerging questions from Arctic archaeology
Background. There are little comparative data on catheter ablation of paroxysmal atrial fibrillation (AF) using the contact force radiofrequency (CF-RF) catheter versus the second-generation cryoballoon (CB2). Methods and results. This is a single center, retrospective, nonrandomized study of 98 patients with symptomatic, drug-refractory paroxysmal AF who underwent their first PVI ablation using either the CB2 (n=40) or CF-RF (n=58). The mean age was 60 years with 63% men, a mean LA size of 42 mm. The procedure duration (74±17 versus 120±49 minutes p<0.05) was shorter for CB2 group; the fluoroscopy time (14±17 versus 16±5 minutes, p=0.45) was similar. Complete PVI was achieved in 96% of patients with RF-CF and 98% with CB2. Phrenic nerve palsies (2 transient and 1 persistent) occurred exclusively in the CB2 group and 1 severe, nonlethal complication (pericardial tamponade) occurred in the CF-RF group. At 24-month follow-up, the success rate, defined as freedom from AF/atrial tachycardia (AT) after a single procedure without antiarrhythmic drug, was comparable in CF-RF group and CB2 group (65.5% versus 67%, resp., log rank p=0.54). Conclusion. Both the CB2 and the RF-CF ablation appeared safe; the success rate at 2 years was comparable between both technologies
Isolation of Exosomes from Blood Plasma: Qualitative and Quantitative Comparison of Ultracentrifugation and Size Exclusion Chromatography Methods
BACKGROUND: Exosomes are emerging targets for biomedical research. However, suitable methods for the isolation of blood plasma-derived exosomes without impurities have not yet been described. AIM: Therefore, we investigated the efficiency and purity of exosomes isolated with potentially suitable methods; differential ultracentrifugation (UC) and size exclusion chromatography (SEC). METHODS AND RESULTS: Exosomes were isolated from rat and human blood plasma by various UC and SEC conditions. Efficiency was investigated at serial UC of the supernatant, while in case of SEC by comparing the content of exosomal markers of various fractions. Purity was assessed based on the presence of albumin. We found that the diameter of the majority of isolated particles fell into the size range of exosomes, however, albumin was also present in the preparations, when 1h UC at 4 degrees C was applied. Furthermore, with this method only a minor fraction of total exosomes could be isolated from blood as deduced from the constant amount of exosomal markers CD63 and TSG101 detected after serial UC of rat blood plasma samples. By using UC for longer time or with shorter sedimentation distance at 4 degrees C, or UC performed at 37 degrees C, exosomal yield increased, but albumin impurity was still observed in the isolates, as assessed by transmission electron microscopy, dynamic light scattering and immunoblotting against CD63, TSG101 and albumin. Efficiency and purity were not different in case of using further diluted samples. By using SEC with different columns, we have found that although a minor fraction of exosomes can be isolated without significant albumin content on Sepharose CL-4B or Sephacryl S-400 columns, but not on Sepharose 2B columns, the majority of exosomes co-eluted with albumin. CONCLUSION: Here we show that it is feasible to isolate exosomes from blood plasma by SEC without significant albumin contamination albeit with low vesicle yield
Spin chains from dynamical quadratic algebras
We present a construction of integrable quantum spin chains where local
spin-spin interactions are weighted by ``position''-dependent potential
containing abelian non-local spin dependance. This construction applies to the
previously defined three general quadratic reflection-type algebras:
respectively non-dynamical, semidynamical, fully dynamical.Comment: 12 pages, no figures; v2: corrected formulas of the last sectio
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