1,920 research outputs found
New geometries for high spatial resolution hall probes
The Hall response function of symmetric and asymmetric planar Hall effect
devices is investigated by scanning a magnetized tip above a sensor surface
while simultaneously recording the topography and the Hall voltage. Hall sensor
geometries are tailored using a Focused Ion Beam, in standard symmetric and new
asymmetric geometries. With this technique we are able to reduce a single
voltage probe to a narrow constriction 20 times smaller than the other device
dimensions. We show that the response function is peaked above the
constriction, in agreement with numerical simulations. The results suggest a
new way to pattern Hall sensors for enhanced spatial resolution.Comment: 12 pages, 5 figures, submitted to Journal of Applied Physic
Large-Order Behavior of Two-coupling Constant -Theory with Cubic Anisotropy
For the anisotropic [u (\sum_{i=1^N {\phi}_i^2)^2+v \sum_{i=1^N
\phi_i^4]-theory with {} we calculate the imaginary parts of the
renormalization-group functions in the form of a series expansion in , i.e.,
around the isotropic case. Dimensional regularization is used to evaluate the
fluctuation determinants for the isotropic instanton near the space dimension
4. The vertex functions in the presence of instantons are renormalized with the
help of a nonperturbative procedure introduced for the simple g{\phi^4-theory
by McKane et al.Comment: LaTeX file with eps files in src. See also
http://www.physik.fu-berlin.de/~kleinert/institution.htm
Infection urinaire à Haemophilus influenzae chez 3 enfants ayant une malformation de l’arbre urinaire
La pyélonéphrite aigue (PNA) est une des infections les plus fréquentes de l’enfant, dans laquelle le genre Haemophilus est très rarement impliqué. De janvier 2010 à octobre 2011, seulement 3 enfants âgés de moins de 15 ans ont été hospitalisés dans notre établissement pour une infection urinaire à Haemophilus influenzae. Les 3 enfants présentaient des tableaux typiques de PNA : fièvre, signes fonctionnels urinaires ou douleurs abdominales. L’examen cytobactériologique des urines (ECBU) montrait à l’examen direct une leucocyturie significative et de nombreux bacilles Gram négatifs. La culture bactériologique standard des urines des 3 patients était négative. H. influenzae a été mis en évidence secondairement après réensemencement des urines sur milieu enrichi. Les 3 enfants présentaient une uropathie : 2 syndromes de la jonction pyélo-urétérale droit et une duplicité urétérale bilatérale avec reflux de haut grade. Pendant la période étudiée, la prévalence des PNA à Haemophilus dans notre établissement a été de 0,02 % dans les infections urinaires de l’enfant. Dans la littérature, les PNA à Haemophilus sont rares (moins de 1 % chez l’enfant), fréquemment associées à une malformation de l’arbre urinaire et difficiles à mettre en évidence. Lorsque l’ECBU montre des bacilles Gram négatifs à l’examen direct non retrouvés à la culture, il faut réensemencer les urines sur gélose au sang cuit, notamment si le patient est porteur d’une uropathie
Surface critical behavior in fixed dimensions : Nonanalyticity of critical surface enhancement and massive field theory approach
The critical behavior of semi-infinite systems in fixed dimensions is
investigated theoretically. The appropriate extension of Parisi's massive field
theory approach is presented.Two-loop calculations and subsequent Pad\'e-Borel
analyses of surface critical exponents of the special and ordinary phase
transitions yield estimates in reasonable agreement with recent Monte Carlo
results. This includes the crossover exponent , for which we obtain
the values and , considerably
lower than the previous -expansion estimates.Comment: Latex with Revtex-Stylefiles, 4 page
Critical Behavior of an Ising System on the Sierpinski Carpet: A Short-Time Dynamics Study
The short-time dynamic evolution of an Ising model embedded in an infinitely
ramified fractal structure with noninteger Hausdorff dimension was studied
using Monte Carlo simulations. Completely ordered and disordered spin
configurations were used as initial states for the dynamic simulations. In both
cases, the evolution of the physical observables follows a power-law behavior.
Based on this fact, the complete set of critical exponents characteristic of a
second-order phase transition was evaluated. Also, the dynamic exponent of the critical initial increase in magnetization, as well as the critical
temperature, were computed. The exponent exhibits a weak dependence
on the initial (small) magnetization. On the other hand, the dynamic exponent
shows a systematic decrease when the segmentation step is increased, i.e.,
when the system size becomes larger. Our results suggest that the effective
noninteger dimension for the second-order phase transition is noticeably
smaller than the Hausdorff dimension. Even when the behavior of the
magnetization (in the case of the ordered initial state) and the
autocorrelation (in the case of the disordered initial state) with time are
very well fitted by power laws, the precision of our simulations allows us to
detect the presence of a soft oscillation of the same type in both magnitudes
that we attribute to the topological details of the generating cell at any
scale.Comment: 10 figures, 4 tables and 14 page
Interpolation Parameter and Expansion for the Three Dimensional Non-Trivial Scalar Infrared Fixed Point
We compute the non--trivial infrared --fixed point by means of an
interpolation expansion in fixed dimension. The expansion is formulated for an
infinitesimal momentum space renormalization group. We choose a coordinate
representation for the fixed point interaction in derivative expansion, and
compute its coordinates to high orders by means of computer algebra. We compute
the series for the critical exponent up to order twenty five of
interpolation expansion in this representation, and evaluate it using \pade,
Borel--\pade, Borel--conformal--\pade, and Dlog--\pade resummation. The
resummation returns as the value of .Comment: 29 pages, Latex2e, 2 Postscript figure
Critical exponents for 3D O(n)-symmetric model with n > 3
Critical exponents for the 3D O(n)-symmetric model with n > 3 are estimated
on the base of six-loop renormalization-group (RG) expansions. A simple
Pade-Borel technique is used for the resummation of the RG series and the Pade
approximants [L/1] are shown to give rather good numerical results for all
calculated quantities. For large n, the fixed point location g_c and the
critical exponents are also determined directly from six-loop expansions
without addressing the resummation procedure. An analysis of the numbers
obtained shows that resummation becomes unnecessary when n exceeds 28 provided
an accuracy of about 0.01 is adopted as satisfactory for g_c and critical
exponents. Further, results of the calculations performed are used to estimate
the numerical accuracy of the 1/n-expansion. The same value n = 28 is shown to
play the role of the lower boundary of the domain where this approximation
provides high-precision estimates for the critical exponents.Comment: 10 pages, TeX, no figure
New approach to Borel summation of divergent series and critical exponent estimates for an N-vector cubic model in three dimensions from five-loop \epsilon expansions
A new approach to summation of divergent field-theoretical series is
suggested. It is based on the Borel transformation combined with a conformal
mapping and does not imply the exact asymptotic parameters to be known. The
method is tested on functions expanded in their asymptotic power series. It is
applied to estimating the critical exponent values for an N-vector field model,
describing magnetic and structural phase transitions in cubic and tetragonal
crystals, from five-loop \epsilon expansions.Comment: 9 pages, LaTeX, 3 PostScript figure
Topological and Universal Aspects of Bosonized Interacting Fermionic Systems in (2+1)d
General results on the structure of the bosonization of fermionic systems in
d are obtained. In particular, the universal character of the bosonized
topological current is established and applied to generic fermionic current
interactions. The final form of the bosonized action is shown to be given by
the sum of two terms. The first one corresponds to the bosonization of the free
fermionic action and turns out to be cast in the form of a pure Chern-Simons
term, up to a suitable nonlinear field redefinition. We show that the second
term, following from the bosonization of the interactions, can be obtained by
simply replacing the fermionic current by the corresponding bosonized
expression.Comment: 29 pages, RevTe
Critical Exponents of the pure and random-field Ising models
We show that current estimates of the critical exponents of the
three-dimensional random-field Ising model are in agreement with the exponents
of the pure Ising system in dimension 3 - theta where theta is the exponent
that governs the hyperscaling violation in the random case.Comment: 9 pages, 4 encapsulated Postscript figures, REVTeX 3.
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