2,551 research outputs found
Exact lattice Ward-Takahashi identity for the N=1 Wess-Zumino model
We consider a lattice formulation of the four dimensional N=1 Wess-Zumino
model that uses the Ginsparg-Wilson relation. This formulation has an exact
supersymmetry on the lattice. We show that the corresponding Ward-Takahashi
identity is satisfied, both at fixed lattice spacing and in the continuum
limit. The calculation is performed in lattice perturbation theory up to order
in the coupling constant. We also show that this Ward-Takahashi identity
determines the finite part of the scalar and fermion renormalization wave
functions which automatically leads to restoration of supersymmetry in the
continuum limit. In particular, these wave functions coincide in this limit.Comment: 19 pages, 6 figure
AscensĂŁo e queda dos cfcs como estudo de caso : diferentes estágios de conscientização acerca de riscos quĂmicos
Ao criar novas substâncias, todo quĂmico precisa lidar com a possibilidade de essas substâncias oferecerem algum tipo de perigo. Este trabalho se apresenta como um estudo de caso, que pode servir aos educadores em quĂmica como motivador de reflexões a respeito do gerenciamento dos riscos ambientais inerentes Ă atividade dos quĂmicos. O estudo Ă© focado na trajetĂłria da preparação, uso e descoberta dos riscos ambientais dos compostos conhecidos como clorofluorocarbonos (CFCs). Para isso foram consultados artigos cientĂficos do perĂodo enfocado, alĂ©m de fontes secundárias em histĂłria e em filosofia da quĂmica. Pode-se classificar as concepções dos quĂmicos a respeito dos riscos oferecidos pelas substâncias produzidas por eles em trĂŞs dimensões: individual, ambiental local e ambiental global – sendo que esta emerge definitivamente na dĂ©cada de 1970
Chronic neural probe for simultaneous recording of single-unit, multi-unit, and local field potential activity from multiple brain sites
Drug resistant focal epilepsy can be treated by resecting the epileptic focus
requiring a precise focus localization using stereoelectroencephalography
(SEEG) probes. As commercial SEEG probes offer only a limited spatial
resolution, probes of higher channel count and design freedom enabling the
incorporation of macro and microelectrodes would help increasing spatial
resolution and thus open new perspectives for investigating mechanisms
underlying focal epilepsy and its treatment. This work describes a new
fabrication process for SEEG probes with materials and dimensions similar to
clinical probes enabling recording single neuron activity at high spatial
resolution. Polyimide is used as a biocompatible flexible substrate into which
platinum electrodes and leads are...
The resulting probe features match those of clinically approved devices.
Tests in saline solution confirmed the probe stability and functionality.
Probes were implanted into the brain of one monkey (Macaca mulatta), trained to
perform different motor tasks. Suitable configurations including up to 128
electrode sites allow the recording of task-related neuronal signals. Probes
with 32 and 64 electrode sites were implanted in the posterior parietal cortex.
Local field potentials and multi-unit activity were recorded as early as one
hour after implantation. Stable single-unit activity was achieved for up to 26
days after implantation of a 64-channel probe. All recorded signals showed
modulation during task execution. With the novel probes it is possible to
record stable biologically relevant data over a time span exceeding the usual
time needed for epileptic focus localization in human patients. This is the
first time that single units are recorded along cylindrical polyimide probes
chronically implanted 22 mm deep into the brain of a monkey, which suggests the
potential usefulness of this probe for human applications
Evaluation of an automatic gas chromatographic system for the identification of bacterial infective agents
The potential clinical application of gas chromatography to
microbial identifcation was evaluated. A completely automated
system, the MIS (Microbial Identification System; Hewlett-
Packard) can analyse and identify pure strains by comparison of
their cellular fatty acids patterns (C9-C20) with the reference
parameters stored in a library. Three hundred and sixty-seven
strains were tested, comparing the gas chromatographic results
with those obtained by the traditional microbiological methods in
the bacteriology laboratory of our Institute. A standardized
extractive procedure was followed to obtain the fatty acid methyl
esters (FAMEs), but some modifications to the recommended
procedure were introduced in the bacterial growth procedures:
colonies harvested not only from the recommended growth media but
also from selective media routinely used in the bacteriology
laboratory were successfully examined. These modifications did not
influence the results but improved the ease for the user; good
agreement with the comparison method was observed as far as
identifications of genus and species are concerned for 238 cases.
The major advantages of this computerized system are a reduction
in the time required to obtain the final results, the elimination of
human errors by using the autosampler and a better inter-laboratory
comparability of results owing to a higher degree of objectivity. On
the other hand, the limited throughput of MIS (only 40 samples in
24 h) prevents its use in a large routine laboratory; this technology
is appropriate in emergency cases, in taxonomic studies and as a
confirmatory method
Monte Carlo simulations and field transformation: the scalar case
We describe a new method in lattice field theory to compute observables at
various values of the parameters lambda_i in the action S[phi,lambda_i].
Firstly one performs a single simulation of a ``reference action'' S[phi^r,
lambda_i^r] with fixed lambda_i^r. Then the phi^r-configurations are
transformed into those of a field phi distributed according to S[phi,lambda_i],
apart from a ``remainder action'' which enters as a \break weight. In this way
we measure the observables at values of lambda_i different from lambda_i^r. We
study the performance of the algorithm in the case of the simplest
renormalizable model, namely the phi^4 scalar theory on a four dimensional
lattice and compare the method with the ``histogram'' technique of which it is
a generalization.Comment: Latex, 23 pgs, 8 eps-figures include
Effective Average Action in N=1 Super-Yang-Mills Theory
For N=1 Super-Yang-Mills theory we generalize the effective average action
Gamma_k in a manifest supersymmetric way using the superspace formalism. The
exact evolution equation for Gamma_k is derived and, introducing as an
application a simple truncation, the standard one-loop beta-function of N=1 SYM
theory is obtained.Comment: 17 pages, LaTeX, some remarks added, misprints corrected, to appear
in Phys. Rev.
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