410 research outputs found
Quantum dot to disordered wire crossover: A complete solution in all length scales for systems with unitary symmetry
We present an exact solution of a supersymmetric nonlinear sigma model
describing the crossover between a quantum dot and a disordered quantum wire
with unitary symmetry. The system is coupled ideally to two electron reservoirs
via perfectly conducting leads sustaining an arbitrary number of propagating
channels. We obtain closed expressions for the first three moments of the
conductance, the average shot-noise power and the average density of
transmission eigenvalues. The results are complete in the sense that they are
nonperturbative and are valid in all regimes and length scales. We recover
several known results of the recent literature by taking particular limits.Comment: 4 page
Far Infrared Slab Lensing and Subwavelength Imaging in Crystal Quartz
We examine the possibility of using negative refraction stemming from the
phonon response in an anisotropic crystal to create a simple slab lens with
plane parallel sides, and show that imaging from such a lens should be possible
at room temperature despite the effects of absorption that are inevitably
present due to phonon damping. In particular, we consider the case of crystal
quartz, a system for which experimental measurements consistent with all-angle
negative refraction have already been demonstrated. Furthermore, we investigate
the possibility of subwavelength imaging from such materials, and show that it
should be possible for certain configurations.Comment: 12 pages, 10 figure
Conductance and Its Variance of Disordered Wires with Symplectic Symmetry in the Metallic Regime
The conductance of disordered wires with symplectic symmetry is studied by a
random-matrix approach. It has been shown that the behavior of the conductance
in the long-wire limit crucially depends on whether the number of conducting
channels is even or odd. We focus on the metallic regime where the wire length
is much smaller than the localization length, and calculate the
ensemble-averaged conductance and its variance for both the even- and
odd-channel cases. We find that the weak-antilocalization correction to the
conductance in the odd-channel case is equivalent to that in the even-channel
case. Furthermore, we find that the variance dose not depend on whether the
number of channels is even or odd. These results indicate that in contrast to
the long-wire limit, clear even-odd differences cannot be observed in the
metallic regime.Comment: 9pages, accepted for publication in JPS
Path Integral Approach to the Scattering Theory of Quantum Transport
The scattering theory of quantum transport relates transport properties of
disordered mesoscopic conductors to their transfer matrix \bbox{T}. We
introduce a novel approach to the statistics of transport quantities which
expresses the probability distribution of \bbox{T} as a path integral. The
path integal is derived for a model of conductors with broken time reversal
invariance in arbitrary dimensions. It is applied to the
Dorokhov-Mello-Pereyra-Kumar (DMPK) equation which describes
quasi-one-dimensional wires. We use the equivalent channel model whose
probability distribution for the eigenvalues of \bbox{TT}^{\dagger} is
equivalent to the DMPK equation independent of the values of the forward
scattering mean free paths. We find that infinitely strong forward scattering
corresponds to diffusion on the coset space of the transfer matrix group. It is
shown that the saddle point of the path integral corresponds to ballistic
conductors with large conductances. We solve the saddle point equation and
recover random matrix theory from the saddle point approximation to the path
integral.Comment: REVTEX, 9 pages, no figure
Treatment of neurocysticercosis with praziquantel
27 pacientes com neurocisticercose foram tratados com praziquantel, utilizado em doses progressivamente crescentes até alcançar 50 mg/kg/dia, por período de 21 dias, associado a dexametasona. Os doentes foram avaliados clínica e laboratorialmente durante o tratamento e, aqueles que completaram um ano de evolução, repetiram os testes imunofluorescência e ELISA neste período. Cefaléia foi o sintoma encontrado mais freqüentemente durante o tratamento, ocorrendo em 37% dos pacientes; 18,5% dos doentes apresentaram hipertensão intracraniana, um deles evoluindo para o óbito; 25,9% dos enfermos tiveram que suspender o praziquantel antes de completar o tratamento, devido ao surgimento de complicações importantes. Nos exames laboratoriais realizados no sétimo dia de tratamento, 33,3% dos pacientes apresentaram anormalidades, sendo leucocitose a mais freqüente. No período de um ano, 72,2% dos enfermos tiveram melhora do quadro clínico, enquanto os testes imunológicos tornaram-se não-reagentes no soro em 45,4% dos doentes e no LCR em 42,8%. Entretanto, nem sempre houve coincidência da melhora clínica com a apresentação dos testes imunológicos não-reagentes. No presente trabalho, não é possível afirmar que os testes imunológicos não-reagentes, assim como a melhora clínica dos pacientes, sejam conseqüentes à eficácia do tratamento com o praziquantel. Devido à grande freqüência e gravidade das complicações deste tratamento, os pacientes devem ser avaliados individualmente quanto aos riscos versus os benefícios dele.Twenty seven patients with neurocysticercosis were treated with praziquantel in progressive doses reaching 50 mg/kg/day associated with dexamethasone for 21 days. The patients were followed during and after treatment and those followed up for one year repeated their immunological tests (indirect immunofluorescence and ELISA) at this time. Headache was the most frequent symptom during the treatment, occurring on 37% of patients. During the treatment 18.5% of patients had intracranial hypertension and one died. One year after treatment 72.2% of patients who finished treatment improved. The immunological tests became negative in 45.4% of patients sera and 42.8% of cerebrospinal fluids. There was no correlation between the clinical evolution and immunological, testis. In this study it is not possible to afirm that both negative immunological tests and good clinical evolution were consequents to the efficacy of praziquantel treatment. Due to the great frequency and seriousness of this treatment complications, the patients with neurocysticercosis must be individually evaluated to know the risks and the benefits of the treatment with praziquantel
Scaling and Crossover Functions for the Conductance in the Directed Network Model of Edge States
We consider the directed network (DN) of edge states on the surface of a
cylinder of length L and circumference C. By mapping it to a ferromagnetic
superspin chain, and using a scaling analysis, we show its equivalence to a
one-dimensional supersymmetric nonlinear sigma model in the scaling limit, for
any value of the ratio L/C, except for short systems where L is less than of
order C^{1/2}. For the sigma model, the universal crossover functions for the
conductance and its variance have been determined previously. We also show that
the DN model can be mapped directly onto the random matrix (Fokker-Planck)
approach to disordered quasi-one-dimensional wires, which implies that the
entire distribution of the conductance is the same as in the latter system, for
any value of L/C in the same scaling limit. The results of Chalker and Dohmen
are explained quantitatively.Comment: 10 pages, REVTeX, 2 eps figure
Experiência em capacitação de técnicos da ATER em sistemas agroflorestais.
Neste trabalho são discutidas as metodologias e os resultados de oficinas de capacitação em sistemas agroflorestais oferecidas pela Embrapa Amazônia Ocidental a técnicos da Assistência Técnica e Extensão Rural (ATER) atuantes na capital e no interior do Estado do Amazonas
Fuzzy Method for in Control Acetaldehyde Generation in Resin Pet in the Process of Packaging Pre-Forms of Plastic Injection
In order to control the drying temperature of the PET resin in the silo of the plastic injection molding machine, during the plastic injection process in the industries producing preforms for the manufacture of beverage bottles, care is taken in the ideal temperature regulation for the better performance in controlling the generation of Acetaldehyde (AA), which alters the taste of carbonated or non-carbonated drinks, providing a citrus nuance to the palate and questioning the quality of the packaged products The objective of this work is to develop a tool based on Fuzzy logic to support the control of the drying temperature of PET resin, allowing specialists to make the ideal temperature control decisions necessary to control the generation of Acetaldehyde (AA). For the development of the proposed Fuzzy inference model, we used the Matlab Fuzzy toolbox tool, where the input variables, the fuzzyfication rules and the output variable were implemented based on the data collected from the preform injection process. From the inference model, we obtained a more precise management of the variables that influence the generation of AA, estimating a reduction of $ 240,044.00 in annual costs in the production of preforms
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