2,148 research outputs found
Experimental observation of two-dimensional fluctuation magnetization in the vicinity of T_c for low values of the magnetic field in deoxygenated YBa_2Cu_3O_{7-x}
We measured isofield magnetization curves as a function of temperature in two
single crystal of deoxygenated YBaCuO with T_c = 52 and 41.5 K. Isofield MvsT
were obtained for fields running from 0.05 to 4 kOe. The reversible region of
the magnetization curves was analyzed in terms of a scaling proposed by Prange,
but searching for the best exponent . The scaling analysis carried
out for each data sample set with =0.669, which corresponds to the
3D-xy exponent, did not produced a collapsing of curves when applied to MvsT
curves data obtained for the lowest fields. The resulting analysis for the Y123
crystal with T_c = 41.5 K, shows that lower field curves collapse over the
entire reversible region following the Prange's scaling with =1,
suggesting a two-dimensional behavior. It is shown that the same data obeying
the Prange's scaling with =1 for crystal with T_c = 41.5 K, as well
low field data for crystal with = 52 K, obey the known two-dimensional
scaling law obtained in the lowest-Landau-level approximation.Comment: 4 pages, 3 figure
Fatigue in disordered media
We obtain the Paris law of fatigue crack propagation in a disordered solid
using a fuse network model where the accumulated damage in each resistor
increases with time as a power law of the local current amplitude. When a
resistor reaches its fatigue threshold, it burns irreversibly. Over time, this
drives cracks to grow until the system is fractured in two parts. We study the
relation between the macroscopic exponent of the crack growth rate -- entering
the phenomenological Paris law -- and the microscopic damage-accumulation
exponent, , under the influence of disorder. The way the jumps of the
growing crack, , and the waiting-time between successive breaks,
, depend on the type of material, via , are also
investigated. We find that the averages of these quantities, and
$/$, scale as power laws of the crack length $a$, $
\propto a^{\alpha}$ and $/ \propto a^{-\beta}$, where is
the average rupture time. Strikingly, our results show, for small values of
, a decrease in the exponent of the Paris law in comparison with the
homogeneous case, leading to an increase in the lifetime of breaking materials.
For the particular case of , when fatigue is exclusively ruled by
disorder, an analytical treatment confirms the results obtained by simulation
Monosegemented flow potentiometric titration for the determination of chloride in milk and wine
An automated flow potentiometric titration procedure for the determination of chloride in milk and wine exploiting the monosegmented flow approach is described. The flow network was designed based on a six-way solenoid valve, controlled by a microcomputer running software written in VisualBasic 3.0, allowing selection of the titration conditions. An Ag2S tubular electrode selective for Cl- and a conventional Ag/AgCl electrode were employed as indicator and reference, respectively. An algorithm based on the potential difference between two subsequent titrant additions was developed, allowing to reach the end point in less than 10 attempts, with a precision better than 1.0%. The proposed system was evaluated by determining chloride in milk and wine, using a standard AgNO3 solution as titrant. Accuracy was ascertained by comparing the results with those obtained using the AOAC procedure. No significant difference at a 95% confidence level was observed.Este trabalho descreve um procedimento automático em fluxo monossegmentado para titulação potenciométrica aplicado à determinação de cloreto em leite e vinho. O sistema de fluxo foi desenvolvido com base em uma válvula solenóide de 6 vias, controlada por um microcomputador através de um programa escrito em VisualBasic 3.0. Um eletrodo indicador tubular de Ag2S seletivo a Cl- e um eletrodo de referência convencional de Ag/AgCl foram empregados. Um algoritmo baseado na diferença de potencial entre duas adições subsequentes de titulante foi desenvolvido, possibilitando a determinação do ponto final da titulação em, no máximo, 10 tentativas, com uma precisão melhor que 1,0%. O sistema proposto foi avaliado pela determinação de cloreto em leite e vinho, usando uma solução padrão de AgNO3 como titulante. A exatidão foi avaliada comparando-se os resultados com aqueles obtidos pelo método da AOAC, não sendo encontradas diferenças significativas ao nÃvel de confiança de 95%.259264Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP
Graphene field-effect transistor array with integrated electrolytic gates scaled to 200 mm
Ten years have passed since the beginning of graphene research. In this period we have witnessed breakthroughs both in fundamental and applied research. However, the development of graphene devices for mass production has not yet reached the same level of progress. The architecture of graphene field-effect transistors (FET) has not significantly changed, and the integration of devices at the wafer scale has generally not been sought. Currently, whenever an electrolyte-gated FET (EGFET) is used, an external, cumbersome, out-of-plane gate electrode is required. Here, an alternative architecture for graphene EGFET is presented. In this architecture, source, drain, and gate are in the same plane, eliminating the need for an external gate electrode and the use of an additional reservoir to confine the electrolyte inside the transistor active zone. This planar structure with an integrated gate allows for wafer-scale fabrication of high-performance graphene EGFETs, with carrier mobility up to 1800 cm2 V−1 s−1. As a proof-of principle, a chemical sensor was achieved. It is shown that the sensor can discriminate between saline solutions of different concentrations. The proposed architecture will facilitate the mass production of graphene sensors, materializing the potential of previous achievements in fundamental and applied graphene research.N.C.S.Vieira acknowledges a Postdoctoral fellowship at INL from FAPESP – SP/Brazil (2014/01663-6). G. Machado Jr. acknowledges a PhD grant (no. 237630/2012-5) from CNPq – Brazil
Short-term add-on therapy with angiotensin receptor blocker for end-stage inotrope-dependent heart failure patients: B-type natriuretic peptide reduction in a randomized clinical trial
OBJECTIVE: We aimed to evaluate angiotensin receptor blocker add-on therapy in patients with low cardiac output during decompensated heart failure. METHODS: We selected patients with decompensated heart failure, low cardiac output, dobutamine dependence, and an ejection fractio
Tailoring Three-Point Functions and Integrability II. Weak/strong coupling match
We compute three-point functions of single trace operators in planar N=4 SYM.
We consider the limit where one of the operators is much smaller than the other
two. We find a precise match between weak and strong coupling in the
Frolov-Tseytlin classical limit for a very general class of classical
solutions. To achieve this match we clarify the issue of back-reaction and
identify precisely which three-point functions are captured by a classical
computation.Comment: 36 pages. v2: figure added, references adde
Finite-gap equations for strings on AdS_3 x S^3 x T^4 with mixed 3-form flux
We study superstrings on AdS_3 x S^3 x T^4 supported by a combination of
Ramond-Ramond and Neveu-Schwarz-Neveu-Schwarz three form fluxes, and construct
a set of finite-gap equations that describe the classical string spectrum.
Using the recently proposed all-loop S-matrix we write down the all-loop Bethe
ansatz equations for the massive sector. In the thermodynamic limit the Bethe
ansatz reproduces the finite-gap equations. As part of this derivation we
propose expressions for the leading order dressing phases. These phases differ
from the well-known Arutyunov-Frolov-Staudacher phase that appears in the pure
Ramond-Ramond case. We also consider the one-loop quantization of the algebraic
curve and determine the one-loop corrections to the dressing phases. Finally we
consider some classical string solutions including finite size giant magnons
and circular strings.Comment: 44 pages, 3 figures. v2: references and a discussion about
perturbative results adde
Fluctuations and Dissipation of Coherent Magnetization
A quantum mechanical model is used to derive a generalized Landau-Lifshitz
equation for a magnetic moment, including fluctuations and dissipation. The
model reproduces the Gilbert-Brown form of the equation in the classical limit.
The magnetic moment is linearly coupled to a reservoir of bosonic degrees of
freedom. Use of generalized coherent states makes the semiclassical limit more
transparent within a path-integral formulation. A general
fluctuation-dissipation theorem is derived. The magnitude of the magnetic
moment also fluctuates beyond the Gaussian approximation. We discuss how the
approximate stochastic description of the thermal field follows from our
result. As an example, we go beyond the linear-response method and show how the
thermal fluctuations become anisotropy-dependent even in the uniaxial case.Comment: 22 page
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