10,470 research outputs found
Why the xE distribution triggered by a leading particle does not measure the fragmentation function but does measure the ratio of the transverse momenta of the away-side jet to the trigger-side jet
Hard-scattering of point-like constituents (or partons) in p-p collisions was
discovered at the CERN-ISR in 1972 by measurements utilizing inclusive single
or pairs of hadrons with large transverse momentum (). It was generally
assumed, following Feynman, Field and Fox, as shown by data from the CERN-ISR
experiments, that the distribution of away side hadrons from a single
particle trigger [with ], corrected for of fragmentation would
be the same as that from a jet-trigger and follow the same fragmentation
function as observed in or DIS. PHENIX attempted to measure the
fragmentation function from the away side
distribution of charged particles triggered by a in p-p collisions at
RHIC and showed by explicit calculation that the distribution is actually
quite insensitive to the fragmentation function. Illustrations of the original
arguments and ISR results will be presented. Then the lack of sensitivity to
the fragmentation function will be explained, and an analytic formula for the
distribution given, in terms of incomplete Gamma functions, for the case
where the fragmentation function is exponential. The away-side distribution in
this formulation has the nice property that it both exhibits scaling and
is directly sensitive to the ratio of the away jet to that of
the trigger jet, , and thus can be used, for example, to measure
the relative energy loss of the two jets from a hard-scattering which escape
from the medium in A+A collisions. Comparisons of the analytical formula to
RHIC measurements will be presented, including data from STAR and PHENIX,
leading to some interesting conclusions.Comment: 6 pages, 5 figures, Proceedings of Poster Session, 19th International
Conference on Ultra-Relativistic Nucleus-Nucleus Collisions (Quark Matter
2006), November 14-20, 2006, Shanghai, P. R. Chin
Elaboração do relatório de gestão da Embrapa Florestas: um processo de melhoria contínua na gestão pela excelência.
Resumo
Nonlinear envelope equation for broadband optical pulses in quadratic media
We derive a nonlinear envelope equation to describe the propagation of
broadband optical pulses in second order nonlinear materials. The equation is
first order in the propagation coordinate and is valid for arbitrarily wide
pulse bandwidth. Our approach goes beyond the usual coupled wave description of
phenomena and provides an accurate modelling of the evolution of
ultra-broadband pulses also when the separation into different coupled
frequency components is not possible or not profitable
Comment on "Why quantum mechanics cannot be formulated as a Markov process"
In the paper with the above title, D. T. Gillespie [Phys. Rev. A 49, 1607,
(1994)] claims that the theory of Markov stochastic processes cannot provide an
adequate mathematical framework for quantum mechanics. In conjunction with the
specific quantum dynamics considered there, we give a general analysis of the
associated dichotomic jump processes. If we assume that Gillespie's
"measurement probabilities" \it are \rm the transition probabilities of a
stochastic process, then the process must have an invariant (time independent)
probability measure. Alternatively, if we demand the probability measure of the
process to follow the quantally implemented (via the Born statistical
postulate) evolution, then we arrive at the jump process which \it can \rm be
interpreted as a Markov process if restricted to a suitable duration time.
However, there is no corresponding Markov process consistent with the
event space assumption, if we require its existence for all times .Comment: Latex file, resubm. to Phys. Rev.
Comparison of Theory and Direct Numerical Simulations of Drag Reduction by Rodlike Polymers in Turbulent Channel Flows
Numerical simulations of turbulent channel flows, with or without additives,
are limited in the extent of the Reynolds number \Re and Deborah number \De.
The comparison of such simulations to theories of drag reduction, which are
usually derived for asymptotically high \Re and \De, calls for some care. In
this paper we present a study of drag reduction by rodlike polymers in a
turbulent channel flow using direct numerical simulation and illustrate how
these numerical results should be related to the recently developed theory
Results from RHIC with Implications for LHC
Results from the PHENIX experiment at RHIC in p-p and Au+Au collisions are
reviewed from the perspective of measurements in p-p collisions at the CERN-ISR
which serve as a basis for many of the techniques used. Issues such as J/Psi
suppression and hydrodynamical flow in A+A collisions require data from
LHC-Ions for an improved understanding. Suppression of high pT particles in
Au+Au collisions, first observed at RHIC, also has unresolved mysteries such as
the equality of the suppression of inclusive pi0 (from light quarks and gluons)
and direct-single electrons (from the decay of heavy quarks) in the transverse
momentum range 4< pT < 9 GeV/c. This disfavors a radiative explanation of
suppression and leads to a fundamental question of whether the Higgs boson
gives mass to fermions. Observation of an exponential distribution of direct
photons in central Au+Au collisions for 1< pT <2 GeV/c where hard-processes are
negligible and with no similar exponential distribution in p-p collisions
indicates thermal photon emission from the medium at RHIC, making PHENIX at the
moment ``the hottest experiment in Physics''.Comment: Invited lectures at the International School of Subnuclear Physics,
47th Course, "The most unexpected at LHC and the status of High Energy
Frontier'', Erice, Sicily, Italy, August 29-September 7. 2009. 32 pages, 22
figure
Aesthetic satisfaction in lip and palate clefts: a comparative study between secondary and tertiary bone grafting
Lip and palate cleft represent one of the most frequently occurring congenital deformity, which includes dental anomalies, such as variation in tooth number and position. In case of hypodontia implant-prosthetic rehabilitation offers significant advantages in terms of function, aesthetics and quality of life and bone graft is usually needed. Secondary bone grafting, generally performed in the mixed dentition phase (years 8-11) seems to be the most successful method to allow for rehabilitation. It's often necessary to perform a tertiary bone grafting in adult age in order to achieve better bone quantity and quality before implant placement. Aim of this retrospective study was to evaluate the aesthetic perception that patients had of themselves comparing dental implants placed in tertiary grafted alveolar cleft sites with a previous secondary grafting to only secondary grafting. Between 2009 and 2012, fourteen alveolar cleft were treated with implant rehabilitation and eleven of them received tertiary bone grafting six months prior to implant placement. All patients were questioned to give a score from 1 to 10 their aesthetic satisfaction of their smile before and after implant rehabilitation and during pre-surgery provisional rehabilitation. At the end of their prosthesis rehabilitation patients who received tertiary bone grafting resulted more satisfied than those who had secondary bone grafting only (9.5 vs 8)
Impossibility of spontaneously breaking local symmetries and the sign problem
Elitzur's theorem stating the impossibility of spontaneous breaking of local
symmetries in a gauge theory is reexamined. The existing proofs of this theorem
rely on gauge invariance as well as positivity of the weight in the Euclidean
partition function. We examine the validity of Elitzur's theorem in gauge
theories for which the Euclidean measure of the partition function is not
positive definite. We find that Elitzur's theorem does not follow from gauge
invariance alone. We formulate a general criterion under which spontaneous
breaking of local symmetries in a gauge theory is excluded. Finally we
illustrate the results in an exactly solvable two dimensional abelian gauge
theory.Comment: Latex 6 page
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