8,719 research outputs found
Renormalized field theory and particle density profile in driven diffusive systems with open boundaries
We investigate the density profile in a driven diffusive system caused by a
plane particle source perpendicular to the driving force. Focussing on the case
of critical bulk density we use a field theoretic renormalization
group approach to calculate the density as a function of the distance
from the particle source at first order in (: spatial
dimension). For we find reasonable agreement with the exact solution
recently obtained for the asymmetric exclusion model. Logarithmic corrections
to the mean field profile are computed for with the result for .Comment: 32 pages, RevTex, 4 Postscript figures, to appear in Phys. Rev.
Counting and Tensorial Properties of Twist-Two Helicity-Flip Nucleon Form Factors
We perform a systematic analysis on the off-forward matrix elements of the
twist-two quark and gluon helicity-flip operators. By matching the allowed
quantum numbers and their crossing channel counterparts (a method developed by
Ji & Lebed), we systematically count the number of independent nucleon form
factors in off-forward scattering of matrix elements of these quark and gluon
spin-flip operators. In particular, we find that the numbers of independent
nucleon form factors twist-2, helicity flip quark (gluon) operators are
() if is odd, and () if is even, with (). We also analysis and write down the tensorial/Lorentz structure and
kinematic factors of the expansion of these operators' matrix elements in terms
of the independent form factors. These generalized form factors define the
off-forward quark and gluon helicity-flip distributions in the literature.Comment: 18 pages, revtex
Self-affine surface morphology of plastically deformed metals
We analyze the surface morphology of metals after plastic deformation over a
range of scales from 10 nm to 2 mm, using a combination of atomic force
microscopy and scanning white-light interferometry. We demonstrate that an
initially smooth surface during deformation develops self-affine roughness over
almost four orders of magnitude in scale. The Hurst exponent of
one-dimensional surface profiles is initially found to decrease with increasing
strain and then stabilizes at . By analyzing their statistical
properties we show that the one-dimensional surface profiles can be
mathematically modelled as graphs of a fractional Brownian motion. Our findings
can be understood in terms of a fractal distribution of plastic strain within
the deformed samples
Surface critical behavior of driven diffusive systems with open boundaries
Using field theoretic renormalization group methods we study the critical
behavior of a driven diffusive system near a boundary perpendicular to the
driving force. The boundary acts as a particle reservoir which is necessary to
maintain the critical particle density in the bulk. The scaling behavior of
correlation and response functions is governed by a new exponent eta_1 which is
related to the anomalous scaling dimension of the chemical potential of the
boundary. The new exponent and a universal amplitude ratio for the density
profile are calculated at first order in epsilon = 5-d. Some of our results are
checked by computer simulations.Comment: 10 pages ReVTeX, 6 figures include
Effects of surfaces on resistor percolation
We study the effects of surfaces on resistor percolation at the instance of a
semi-infinite geometry. Particularly we are interested in the average
resistance between two connected ports located on the surface. Based on general
grounds as symmetries and relevance we introduce a field theoretic Hamiltonian
for semi-infinite random resistor networks. We show that the surface
contributes to the average resistance only in terms of corrections to scaling.
These corrections are governed by surface resistance exponents. We carry out
renormalization group improved perturbation calculations for the special and
the ordinary transition. We calculate the surface resistance exponents
\phi_{\mathcal S \mathnormal} and \phi_{\mathcal S \mathnormal}^\infty for
the special and the ordinary transition, respectively, to one-loop order.Comment: 19 pages, 3 figure
Short-time critical dynamics at perfect and non-perfect surface
We report Monte Carlo simulations of critical dynamics far from equilibrium
on a perfect and non-perfect surface in the 3d Ising model. For an ordered
initial state, the dynamic relaxation of the surface magnetization, the line
magnetization of the defect line, and the corresponding susceptibilities and
appropriate cumulant is carefully examined at the ordinary, special and surface
phase transitions. The universal dynamic scaling behavior including a dynamic
crossover scaling form is identified. The exponent of the surface
magnetization and of the line magnetization are extracted. The impact
of the defect line on the surface universality classes is investigated.Comment: 11figure
Current in the light-front Bethe-Salpeter formalism II: Applications
We pursue applications of the light-front reduction of current matrix
elements in the Bethe-Salpeter formalism. The normalization of the reduced wave
function is derived from the covariant framework and related to non-valence
probabilities using familiar Fock space projection operators. Using a simple
model, we obtain expressions for generalized parton distributions that are
continuous. The non-vanishing of these distributions at the crossover between
kinematic regimes (where the plus component of the struck quark's momentum is
equal to the plus component of the momentum transfer) is tied to higher Fock
components. Moreover continuity holds due to relations between Fock components
at vanishing plus momentum. Lastly we apply the light-front reduction to
time-like form factors and derive expressions for the generalized distribution
amplitudes in this model.Comment: 12 pages, 6 figures, RevTex
Surface critical behavior of random systems at the ordinary transition
We calculate the surface critical exponents of the ordinary transition
occuring in semi-infinite, quenched dilute Ising-like systems. This is done by
applying the field theoretic approach directly in d=3 dimensions up to the
two-loop approximation, as well as in dimensions. At
we extend, up to the next-to-leading order, the previous
first-order results of the expansion by Ohno and Okabe
[Phys.Rev.B 46, 5917 (1992)]. In both cases the numerical estimates for surface
exponents are computed using Pade approximants extrapolating the perturbation
theory expansions. The obtained results indicate that the critical behavior of
semi-infinite systems with quenched bulk disorder is characterized by the new
set of surface critical exponents.Comment: 11 pages, 11 figure
Invasive epilepsy surgery evaluation
Intracranial EEG (iEEG) recordings are widely used for the work up of pharmacoresistant epilepsy. Different iEEG recording techniques namely subdural grids, strips, depth electrodes and stereoencephalography (SEEG) are available with distinct limitations and advantages. Epilepsy centres mastering multiple techniques apply them in an individualised patient approach. These tools are used to map the seizure onset zone which is pivotal in approximating the epileptogenic zone, i.e. the zone which is indispensable for the generation of seizures and when resected will render the patient seizure free. Besides, the implanted electrodes can be used to define eloquent cortex through direct cortical stimulation. Different clinical scenarios exist which favour one iEEG recording technique over the other. Proximity of the presumed epileptogenic zone to eloquent cortex, for example, is a clinical scenario which may favour grid electrodes over SEEG. We here review the indication for iEEG for the work-up of patients suffering from pharmacoresistant epilepsy. In addition, we provide a description of the recording techniques focussing on the main techniques used: grid electrodes, depth electrodes and stereoencephalography. We then outline different clinical scenarios and the preferred technical approach for intracranial recordings in these scenarios. Finally, we highlight which advances have been made in the field of iEEG and which advances are in the pipeline waiting to be established for clinical use. This review provides the clinician with an update on the diagnostic use of intracranial EEG for epilepsy surgery and thus aids in understanding patient selection for this technique which may ultimately improve referral patterns
- …