10,920 research outputs found
The role of spatial and temporal radiation deposition in inertial fusion chambers: the case of HiPERÂż
The ïŹrst wall armour for the reactor chamber of HiPER will have to face short energy pulses of 5 to 20 MJ mostly in the form of x-rays and charged particles at a repetition rate of 5â10 Hz. Armour material and chamber dimensions have to be chosen to avoid/minimize damage to the chamber, ensuring the proper functioning of the facility during its planned lifetime. The maximum energy ïŹuence that the armour can withstand without risk of failure, is determined by temporal and spatial deposition of the radiation energy inside the material. In this paper, simulations on the thermal effect of the radiationâarmour interaction are carried out with an increasing deïŹnition of the temporal and spatial deposition of energy to prove their inïŹuence on the ïŹnal results. These calculations will lead us to present the ïŹrst values of the thermo-mechanical behaviour of the tungsten armour designed for the HiPER project under a shock ignition target of 48 MJ. The results will show that only the crossing of the plasticity limit in the ïŹrst few micrometres might be a threat after thousands of shots for the survivability of the armour
The Fluctuations of the Quark Number and of the Chiral Condensate
The distributions of the quark number and chiral condensate over the gauge
fields are computed for QCD in Euclidean space at nonzero quark chemical
potential. As both operators are non-hermitian the distributions are in the
complex plane. Moreover, because of the sign problem, the distributions are not
real and positive. The computations are carried out within leading order chiral
perturbation theory and give a direct insight into the delicate cancellations
that take place in contributions to the total baryon number and the chiral
condensate.Comment: 19 pages, 2 figure
HAMSTRING CONTRACTILE TIMING IN ANTERIOR CRUCIATE LIGAMENT DEFICIENT PATIENTS
The purpose of this research is to examine contractile timing of the hamstrings in patients with anterior cruciate ligament (ACL) deficient knees. Ten patients were tested for hamstring contractile timing using Electromyographic (EMG) recordings during gait speeds of 3km/h and 5km/h on both a level and ten degree incline. An ANOVA analysis was used to demonstrate timing onset differences between the deficient and normal leg for each test condition and muscle onset timing was related to the Lysholm scale for perceived knee function. Significant interaction differences were found for legs and speed variations plus a negative correlation between functional scores and hamstring timing onset
Mapping the dynamic interactions between vortex species in highly anisotropic superconductors
Here we use highly sensitive magnetisation measurements performed using a
Hall probe sensor on single crystals of highly anisotropic high temperature
superconductors to study the dynamic interactions
between the two species of vortices that exist in such superconductors. We
observe a remarkable and clearly delineated high temperature regime that
mirrors the underlying vortex phase diagram. Our results map out the parameter
space over which these dynamic interaction processes can be used to create
vortex ratchets, pumps and other fluxonic devices.Comment: 7 pages, 3 figures, to be published in Supercond. Sci. Techno
Critical Collapse of an Ultrarelativistic Fluid in the Limit
In this paper we investigate the critical collapse of an ultrarelativistic
perfect fluid with the equation of state in the limit of
. We calculate the limiting continuously self similar (CSS)
solution and the limiting scaling exponent by exploiting self-similarity of the
solution. We also solve the complete set of equations governing the
gravitational collapse numerically for and
compare them with the CSS solutions. We also investigate the supercritical
regime and discuss the hypothesis of naked singularity formation in a generic
gravitational collapse. The numerical calculations make use of advanced methods
such as high resolution shock capturing evolution scheme for the matter
evolution, adaptive mesh refinement, and quadruple precision arithmetic. The
treatment of vacuum is also non standard. We were able to tune the critical
parameter up to 30 significant digits and to calculate the scaling exponents
accurately. The numerical results agree very well with those calculated using
the CSS ansatz. The analysis of the collapse in the supercritical regime
supports the hypothesis of the existence of naked singularities formed during a
generic gravitational collapse.Comment: 23 pages, 16 figures, revised version, added new results of
investigation of a supercritical collapse and the existence of naked
singularities in generic gravitational collaps
Band structure in classical field theory
Stability and instability bands in classical mechanics are well-studied in
connection with systems such as described by the Mathieu equation. We examine
whether such band structure can arise in classical field theory in the context
of an embedded kink in 1+1 dimensions. The static embedded kink is unstable to
perturbations but we show that if the kink is dynamic it can exhibit stability
in certain parameter bands. Our results are relevant for estimating the
lifetimes of various embedded defects and, in particular, loops of electroweak
Z-string.Comment: 6 pages, 4 fig. Reference added, Fig. 3 updated with improved
numerical code, minor comments added. Version to be published in Phys. Rev.
Sequence heterogeneity and the dynamics of molecular motors
The effect of sequence heterogeneity on the dynamics of molecular motors is
reviewed and analyzed using a set of recently introduced lattice models. First,
we review results for the influence of heterogenous tracks such as a
single-strand of DNA or RNA on the dynamics of the motors. We stress how the
predicted behavior might be observed experimentally in anomalous drift and
diffusion of motors over a wide range of parameters near the stall force and
discuss the extreme limit of strongly biased motors with one-way hopping. We
then consider the dynamics in an environment containing a variety of different
fuels which supply chemical energy for the motor motion, either on a
heterogeneous or on a periodic track. The results for motion along a periodic
track are relevant to kinesin motors in a solution with a mixture of different
nucleotide triphosphate fuel sources.Comment: To appear in a JPhys special issue on molecular motor
Effective Vortex Pinning in MgB2 thin films
We discuss pinning properties of MgB2 thin films grown by pulsed-laser
deposition (PLD) and by electron-beam (EB) evaporation. Two mechanisms are
identified that contribute most effectively to the pinning of vortices in
randomly oriented films. The EB process produces low defected crystallites with
small grain size providing enhanced pinning at grain boundaries without
degradation of Tc. The PLD process produces films with structural disorder on a
scale less that the coherence length that further improves pinning, but also
depresses Tc
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