Euclidean thermal spinor Green's function in the spacetime of a straight cosmic string

Within the framework of the quantum field theory at finite temperature on a conical space, we determine the Euclidean thermal spinor Green's function for a massless spinor field. We then calculate the thermal average of the energy-momentum tensor of a thermal bath of massless fermions. In the high-temperature limit, we find that the straight cosmic string does not perturb the thermal bathComment: 11 pages, latex, no figure

Collective Decoherence of Nuclear Spin Clusters

The problem of dipole-dipole decoherence of nuclear spins is considered for strongly entangled spin cluster. Our results show that its dynamics can be described as the decoherence due to interaction with a composite bath consisting of fully correlated and uncorrelated parts. The correlated term causes the slower decay of coherence at larger times. The decoherence rate scales up as a square root of the number of spins giving the linear scaling of the resulting error. Our theory is consistent with recent experiment reported in decoherence of correlated spin clusters.Comment: 4 pages, 4 figure

Electron spin coherence in semiconductors: Considerations for a spin-based solid state quantum computer architecture

We theoretically consider coherence times for spins in two quantum computer architectures, where the qubit is the spin of an electron bound to a P donor impurity in Si or within a GaAs quantum dot. We show that low temperature decoherence is dominated by spin-spin interactions, through spectral diffusion and dipolar flip-flop mechanisms. These contributions lead to 1-100 $\mu$s calculated spin coherence times for a wide range of parameters, much higher than former estimates based on $T_{2}^{*}$ measurements.Comment: Role of the dipolar interaction clarified; Included discussion on the approximations employed in the spectral diffusion calculation. Final version to appear in Phys. Rev.

Influences of the Resistive SFCL on the Incremental Power Frequency Relay of Transmission Lines

The superconducting fault-current limiter (SFCL) has been effective in coping with large fault currents and is expected to be largely applicated in the power system to solve the problem of increasing fault-current level in power grid nowadays. However, the coordination between SFCLs and traditional power system devices such as protective relaying has not been researched enough. This paper studies the influences of the resistive-type SFCL on the incremental power frequency relay of the transmission lines. The resistive SFCL is simulated by using thermal-electric analog method. A model of a 220-kV transmission system with the incremental power frequency relay element was built and simulated with the SIMULINK MATLAB software. Three compensation methods to eliminate the negative effects of the integration of SFCL are proposed and compared. Finally, numerical simulation tests have demonstrated the correctness and validity of theoretical analyses

Electron spin as a spectrometer of nuclear spin noise and other fluctuations

This chapter describes the relationship between low frequency noise and coherence decay of localized spins in semiconductors. Section 2 establishes a direct relationship between an arbitrary noise spectral function and spin coherence as measured by a number of pulse spin resonance sequences. Section 3 describes the electron-nuclear spin Hamiltonian, including isotropic and anisotropic hyperfine interactions, inter-nuclear dipolar interactions, and the effective Hamiltonian for nuclear-nuclear coupling mediated by the electron spin hyperfine interaction. Section 4 describes a microscopic calculation of the nuclear spin noise spectrum arising due to nuclear spin dipolar flip-flops with quasiparticle broadening included. Section 5 compares our explicit numerical results to electron spin echo decay experiments for phosphorus doped silicon in natural and nuclear spin enriched samples.Comment: Book chapter in "Electron spin resonance and related phenomena in low dimensional structures", edited by Marco Fanciulli. To be published by Springer-Verlag in the TAP series. 35 pages, 9 figure

Effect of an inhomogeneous external magnetic field on a quantum dot quantum computer

We calculate the effect of an inhomogeneous magnetic field, which is invariably present in an experimental environment, on the exchange energy of a double quantum dot artificial molecule, projected to be used as a 2-qubit quantum gate in the proposed quantum dot quantum computer. We use two different theoretical methods to calculate the Hilbert space structure in the presence of the inhomogeneous field: the Heitler-London method which is carried out analytically and the molecular orbital method which is done computationally. Within these approximations we show that the exchange energy J changes slowly when the coupled dots are subject to a magnetic field with a wide range of inhomogeneity, suggesting swap operations can be performed in such an environment as long as quantum error correction is applied to account for the Zeeman term. We also point out the quantum interference nature of this slow variation in exchange.Comment: 12 pages, 4 figures embedded in tex

Theory of nuclear induced spectral diffusion: Spin decoherence of phosphorus donors in Si and GaAs quantum dots

We propose a model for spectral diffusion of localized spins in semiconductors due to the dipolar fluctuations of lattice nuclear spins. Each nuclear spin flip-flop is assumed to be independent, the rate for this process being calculated by a method of moments. Our calculated spin decoherence time $T_{M}=0.64$ ms for donor electron spins in Si:P is a factor of two longer than spin echo decay measurements. For $^{31}$P nuclear spins we show that spectral diffusion is well into the motional narrowing regime. The calculation for GaAs quantum dots gives $T_{M}=10-50$ $\mu$s depending on the quantum dot size. Our theory indicates that nuclear induced spectral diffusion should not be a serious problem in developing spin-based semiconductor quantum computer architectures.Comment: 15 pages, 9 figures. Accepted for publication in Phys. Rev.

Avaliação do sêmen fresco e pós-congelado de ovinos da raça Morada Nova na região semiárida do Nordeste.

Resumo: A criopreservação de sêmen permite o armazenamento de material genético por tempo indeterminado, transmitindo características desejáveis. Após o processo de congelação/descongelação ocorre uma redução da taxa de fertilidade relacionada, principalmente, aos danos causados às estruturas e propriedades bioquímicas da membrana dos espermatozóides, podendo comprometer os processos de capacitação espermática e a reação acrossomal. Em relação à espécie ovina e mais precisamente a raça Morada Nova pouco se encontra na literatura trabalhos relacionados aos efeitos do congelamento no sêmen desses animais. Foram utilizados quatro animais onde se coletou o sêmen semanalmente no período mais seco do ano (outubro e novembro/2008) com o objetivo de relacionar as avaliações do sêmen fresco e pós-congelamento de ovinos da raça Morada Nova durante a época mais seca do ano na região semi-árida do Nordeste brasileiro

Challenges at the marketing–operations interface in omni-channel retail environments

To compete in today’s omni-channel business context, it is essential for firms to co-ordinate their activities across channels and across different stages of the customer journey and the product flow. This requires firms to adopt an integrative approach, addressing each omni-channel design decision from a dual demand-side (marketing) and supply-side (operations) perspective. However, both in practice and in academic research, such an integrative approach is still in an immature stage. In this article, a framework is developed with the following key decision areas: (i) assortment & inventory, (ii) distribution & delivery and (iii) returns. These affect both the customer journey and the product flow. As a consequence of the resulting interdependencies between the firm’s functions, addressing the issues that arise in the three decision areas requires an integrated marketing and operations perspective. For each of the areas, the key decisions that affect or involve both the customer journey and product flow are identified first. Next, for each decision, the marketing and operational goals and the tensions that arise when these goals are not perfectly aligned are described. The opportunities for relieving these tensions are also discussed and possible directions for future research aimed at addressing these tensions and opportunities are presented.info:eu-repo/semantics/publishedVersio

Determination of Nicotine in Cigarette Tobacco Smuggled to Brazil by Modified QuEChERS Methodology

The study of cigarette authenticity in Brazil is important due to increasing consumption of contraband cigarettes. Nicotine concentration is an important parameter reflecting the quality of tobacco used in the production of these cigarettes. Simple methods for this determination, which produce reduced waste, are environmentally and industrially important. The nicotine concentration of smuggled cigarette tobacco was determined by the QuEChERS method, requiring some modifications, such as decreasing the volume of the extractor solvent, changes in pH, and removal of the sample hydration step. Quantification was performed by gas chromatography using a flame ionization detector. The Doehlert matrix design was used to optimize the method. The extraction recoveries ranged from 97.5% to 99.6%, with relative standard deviation (RSD) ≤ 2.5% and limits of detection and quantification of 0.6 mg L-1 and 2.5 mg L-1, respectively. The method was sensitive and accurate for the detection and quantification of nicotine. The nicotine concentration in contraband cigarettes was found to be lower than that observed in legal cigarettes. The method was successfully applied to real samples of smuggled and legal cigarettes, providing a robust method for routine analysis and proving the need for more studies on quality control of smuggled cigarettes in Brazil