68,016 research outputs found
Single Inclusive Distribution and Two-Particle Correlations Inside One Jet at "Modified Leading Logarithmic Approximation" of Quantum Chromodynamics II : Steepest Descent Evaluation at Small X
The MLLA single inclusive distribution inside one high energy (gluon) jet at
small x is estimated by the steepest descent method. Its analytical expression
is obtained outside the "limiting spectrum". It is then used to evaluate
2-particle correlations at the same level of generality. The dependence of both
observables on the ratio between the infrared cutoff Q\_0 and Lambda\_QCD is
studied. Fong & Webber's results for correlations are recovered at the limits
when this ratio goes to 1 and when one stays close to the peak of the single
inclusive distribution.Comment: LaTeX, 22 pages, 18 .eps figure
Stabilizing Entangled States with Quasi-Local Quantum Dynamical Semigroups
We provide a solution to the problem of determining whether a target pure
state can be asymptotically prepared using dissipative Markovian dynamics under
fixed locality constraints. Beside recovering existing results for a large
class of physically relevant entangled states, our approach has the advantage
of providing an explicit stabilization test solely based on the input state and
constraints of the problem. Connections with the formalism of frustration-free
parent Hamiltonians are discussed, as well as control implementations in terms
of a switching output-feedback law.Comment: 11 pages, no figure
Improvements in X-band transmitter phase stability through klystron body temperature regulation
This article describes the techniques used and experimental results obtained in improving transmitter stability by control of the klystron body temperature. Related work in the measurement of klystron phase control parameters (pushing factors) is also discussed. The contribution of waveguide temperature excursions to uplink phase stability is presented. Suggestions are made as to the direction of future work in this area
Magnetized strange quark matter and magnetized strange quark stars
Strange quark matter could be found in the core of neutron stars or forming
strange quark stars. As is well known, these astrophysical objects are endowed
with strong magnetic fields which affect the microscopic properties of matter
and modify the macroscopic properties of the system. In this paper we study the
role of a strong magnetic field in the thermodynamical properties of a
magnetized degenerate strange quark gas, taking into account beta-equilibrium
and charge neutrality. Quarks and electrons interact with the magnetic field
via their electric charges and anomalous magnetic moments. In contrast to the
magnetic field value of 10^19 G, obtained when anomalous magnetic moments are
not taken into account, we find the upper bound B < 8.6 x 10^17 G, for the
stability of the system. A phase transition could be hidden for fields greater
than this value.Comment: 9 pages, 9 figure
Two particle correlations inside one jet at "Modified Leading Logarithmic Approximation" of Quantum Chromodynamics; I: exact solution of the evolution equations at small x
We discuss correlations between two particles in jets at high energy
colliders and exactly solve the MLLA evolution equations in the small x limit.
We thus extend the Fong-Webber analysis to the region away from the hump of the
single inclusive energy spectrum. We give our results for LEP, Tevatron and LHC
energies, and compare with existing experimental data.Comment: LaTeX, 49 pages, 57 .eps figures + one log
Towards the use of distance sampling to monitorize mountain ungulates numbers.
Many management actions involving mountain ungulates require unbiased and precise
estimations of their numbers. Topography, among other factors, makes difficult the use of
direct methods and to assess the effective area sampled. On the other hand, social behaviour
of animals increases the risk to violate the assumption that observations must be independent
events. This could be avoided using the group or cluster size as a covariate and estimating
density of animals through the density of clusters. In this paper we revise the increasing
potential of Distance Sampling methodology to estimate mountain ungulate populations. We
address different problems which compromise some of the assumptions and discuss several
topics concerning the importance of assessing effective area sampled, estimation of g(0), and
model selection when attempting to adapt the use of Distance Sampling to a three-dimensional
scenarios, like mountainous habitats and ungulate populations
A hybrid boundary for the prediction of intake wave dynamics in IC engines
This paper concerns the calculation of wave dynamics in the intake systems of naturally aspirated internal combustion (I.C.) engines. In particular it presents a method for improving the boundary conditions required to solve the one-dimensional Euler equations that are commonly used to describe the wave dynamics in time and space.
A number of conclusions are reached in this work. The first relates to the quasi-steady state inflow boundary specified in terms of ingoing and outgoing characteristics that is commonly adopted for engine simulation. This is correctly specified by using the pair of primitive variables pressure (p) and density (Ï) but will be unrealistic at frequencies above a Hemholtz number of 0.1 as only stagnation values po, Ïo are used. For the case of I.C. engine intake simulations this sets a maximum frequency of around 300Hz. Above that frequency the results obtained will become increasingly unrealistic.
Secondly, a hybrid time and frequency domain boundary has been developed and tested against linear acoustic theory. This agrees well with results obtained using a quasi-steady state boundary at low frequencies (Helmholtz number less than 0.1) and should remain realistic at higher frequencies in the range of Helmholtz number 0.1 - 1.84.
Thirdly, the cyclic nature of the operation of the IC engine has been exploited to make use of the inverse Fourier transform to develop an analytical hybrid boundary that functions for non-sinusoidal waves in ducts. The method is self starting, does not rely on iterations over complete cycles and is entirely analytical and therefore is an improvement over earlier hybrid boundaries
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