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51.
We build up local, time translation covariant Boundary Quantum Field Theory nets of von Neumann algebras ${\mathcal A_V}$ on the Minkowski half-plane M + starting with a local conformal net ${\mathcal A}$ of von Neumann algebras on ${\mathbb R}$ and an element V of a unitary semigroup ${\mathcal E(\mathcal A)}$ associated with ${\mathcal A}$ . The case V?=?1 reduces to the net ${\mathcal A_+}$ considered by Rehren and one of the authors; if the vacuum character of ${\mathcal A}$ is summable, ${\mathcal A_V}$ is locally isomorphic to ${\mathcal A_+}$ . We discuss the structure of the semigroup ${\mathcal E(\mathcal A)}$ . By using a one-particle version of Borchers theorem and standard subspace analysis, we provide an abstract analog of the Beurling-Lax theorem that allows us to describe, in particular, all unitaries on the one-particle Hilbert space whose second quantization promotion belongs to ${\mathcal E(\mathcal A^{(0)})}$ with ${\mathcal A^{(0)}}$ the U(1)-current net. Each such unitary is attached to a scattering function or, more generally, to a symmetric inner function. We then obtain families of models via any Buchholz-Mack-Todorov extension of ${\mathcal A^{(0)}}$ . A further family of models comes from the Ising model. 相似文献
52.
T. Badapanda V. Senthil S.K. Rout L.S. Cavalcante A.Z. Simões T.P. Sinha S. Panigrahi M.M. de Jesus E. Longo J.A. Varela 《Current Applied Physics》2011,11(6):1282-1293
In this work, we report the Rietveld refinement, microstructure, conductivity and impedance properties of Ba[Zr0.25Ti0.75]O3 ceramic synthesized by solid state reaction. This ceramic was characterized by X-ray diffraction, Rietveld refinement, scanning electron microscopy and energy dispersive X-ray spectrometry. Impedance spectroscopy analyses reveals a non-Debye relaxation phenomenon being its relaxation frequency moving toward to positive side with increase of temperature. A significant shift in impedance loss peaks toward higher frequency side indicates conduction in material and favoring the long range motion of mobile charge carriers. The frequency dependent ac conductivity at different temperatures indicates that the conduction process is thermally activated. The variation of dc conductivity exhibited a negative temperature coefficient of resistance behavior. The ac conductivity data are used to evaluate the density of states at Fermi level and activation energy of this ceramic. The dc electrical and thermal conductivities of grain and grain boundary have been discussed. 相似文献
53.
The relation between two-dimensional conformal quantum field theories with and without a timelike boundary is explored.
Dedicated to Klaus Fredenhagen on the occasion of his 60th birthday 相似文献
54.
Márcia R. S. Silva Mary C. F. Alves S. J. G. Lima L. E. B. Soledade Elaine C. Paris E. Longo A. G. Souza Iêda M. G. Santos 《Journal of Thermal Analysis and Calorimetry》2009,97(2):559-564
Sr(Ti,Nd)O3 was synthesized in order to evaluate the influence of the amount of neodymium on the thermal and structural properties of
SrTiO3. The synthesis was carried out using the polymeric precursor method. A small mass gain was observed for the SrTiO3 and SrTi0.98Nd0.02O3 samples accompanied by an exothermic peak in the DTA curves. Other steps at higher temperatures are assigned to the combustion
of the organic material and carbonate. Elimination of defects by previous calcination of the precursors is responsible by
the short and long range ordering of the perovskite. Cubic phase was obtained for undoped and doped SrTiO3. 相似文献
55.
56.
Unsteady resistance, heave force, pitch moment and free-surface elevations for DTMB 5512 at steady forward speed and in regular
head waves are investigated with different measurement systems for a fairly wide range of test conditions in the IIHR towing
tank. Test data are procured for validation of Reynolds-averaged Navier–Stokes computational fluid dynamics codes and for
understanding the physics of unsteady ship hydrodynamics. The second part of the paper presents the measurement results and
discussions.
Received: 4 October 2000 / Accepted: 23 April 2001 Published online: 29 November 2001 相似文献
57.
Grain shear flow in a rotating drum 总被引:2,自引:0,他引:2
In the present paper we report on the experimental activities carried out on a rotating drum partially filled with grains
or glass beads. The experiments give information about rheology through velocity profiles and through the velocity covariance
tensor structure. We used a LDV system to measure the velocity of the grains at several points along three vertical sections.
The data were also used to obtain the grain volume concentration, with encouraging results. Instantaneous velocity data were
elaborated in order to obtain velocity and pseudotemperature profiles for all the experiments; for a subset of the experiments
a large set of data were elaborated to obtain the velocity covariance. The velocity covariance is not collinear with the rate
of deformation tensor. An attempt to justify the rotation of the tensor axes as a consequence of the kinetically induced anisotropy
and of some free surface perturbations slowly moving upstream was partially successful.
Received: 23 April 1999 / Accepted: 15 July 2001 相似文献
58.
Non‐Invasive Salivary Electrochemical Quantification of Paraquat Poisoning Using Boron Doped Diamond Electrode 下载免费PDF全文
Thiago Matheus Guimarães Selva William Reis de Araujo Thiago Regis Longo Cesar da Paixão 《Electroanalysis》2015,27(7):1642-1648
The present work describes the first electrochemical method for quantifying paraquat herbicide poisoning in human saliva samples. Paraquat shows two couples of well‐defined peaks in aqueous solution using a boron doped diamond (BDD) electrode. By using square wave voltammetry (SWV) technique under optimum experimental conditions, a linear analytical curve was obtained for paraquat concentrations ranging from 0.800 to 167 µmol L?1, with a detection limit of 70 nmol L?1. This method was applied to quantify paraquat spikes in human saliva samples and in two different water samples (tap and river). The recovery values obtained ranged from 83.0 to 104 % and 99.1 to 105 %, respectively, which highlight the accuracy of the proposed method. 相似文献
59.
The Reynolds-averaged flow for a solid/free-surface juncture boundary layer and wake is documented. The three mean-velocity
components and five of the Reynolds stresses are measured for a surface-piercing flat plate in a towing tank using a laser-Doppler
velocimeter system for both boundary-layer and wake planes in regions close to the free surface. The experimental method is
described, including the foil-plate model, laser-Doppler velocimeter system, conditions, and uncertainty analysis. The underlying
flow data is in excellent agreement with benchmark data. Inner (near the plate and wake centerplane and below the free surface)
and outer (near the free surface) regions of high streamwise vorticity of opposite sign are observed, which transport, respectively,
high mean velocity and low turbulence from the outer to the inner and low mean velocity and high turbulence from the inner
to the outer portions of the boundary layer and wake. For the wake, the inner region of vorticity is relatively weak. The
physical mechanism for the streamwise vorticity is analyzed with regard to the Reynolds-averaged streamwise vorticity equation.
The anisotropy of the crossplane normal Reynolds stresses closely correlates with the vorticity and, additionally, indicates
similarity, i.e., its nature is such that it only depends on the proximity to the plate and free surface boundaries or wake
centerplane symmetry plane. Free-surface effects on the Reynolds stresses are analyzed with regard to the behavior close to
the free surface of the turbulent kinetic energy and the normal components of the anisotropy tensor and the anisotropy invariants.
Close to the free surface, the turbulent kinetic energy is nearly constant and increases for the inner and outer portions,
respectively, of the boundary layer and wake and the normal components of the anisotropy tensor and the anisotropy invariants
roughly correspond to the limiting values for two-component turbulence. The similarities and differences between the present
results and analysis with those from related studies are discussed. The data and analysis should have practical application
with regard to the development of turbulence models for computational fluid dynamics methods for the Reynolds-averaged Navier–Stokes
equations.
Received: 27 May 1997/Accepted: 1 August 1997 相似文献
60.
D. Melo R. M. M. Marinho F. T. G. Vieira S. J. G. Lima E. Longo A. G. Souza A. S. Maia I. M. G. Santos 《Journal of Thermal Analysis and Calorimetry》2011,106(2):513-517
Perovskite type oxides have been intensively studied due to their interesting optical, electrical, and catalytic properties.
Among perovskites the alkaline earth stannates stand out, being strontium stannates (SrSnO3) the most important material in ceramic technology among them due to their wide application as dielectric component. SrSnO3 has also been applied as stable capacitor and humidity sensor. In the present work, SrSnO3:Cu was synthesized by polymeric precursor method and heat treated at 700, 800, and 900 °C for 4 h. After that, the material
was characterized by thermal analysis (TG/DTA), X-ray diffraction (XRD), infrared spectroscopy, and UV–vis spectroscopy. Results
indicated three thermal decomposition steps and confirmed the presence of strontium carbonate and Cu2+ reduction to Cu+ at higher dopant amounts. XRD patterns indicated that the perovskite crystallization started at 700 °C with strontiatite
(SrCO3) and cassiterite (SnO2) as intermediate phases, disappearing at higher temperatures. The amount of secondary phase was reduced with the increase
in the Cu concentration. 相似文献