The Influence of Stress Raisers on the Performance of Materials

The publications on fracture of metals emphasize the importance of avoiding so far as possible all causes of local stress concentration, particularly in closely designed, lightweight, highly stressed parts subject to repetitions of large fluctuations of load. In cases where the design considerations make some stress concentration unavoidable, certain precautions can be taken

Microscopic Derivation of Causal Diffusion Equation using Projection Operator Method

We derive a coarse-grained equation of motion of a number density by applying the projection operator method to a non-relativistic model. The derived equation is an integrodifferential equation and contains the memory effect. The equation is consistent with causality and the sum rule associated with the number conservation in the low momentum limit, in contrast to usual acausal diffusion equations given by using the Fick's law. After employing the Markov approximation, we find that the equation has the similar form to the causal diffusion equation. Our result suggests that current-current correlations are not necessarily adequate as the definition of diffusion constants.Comment: 10 pages, 1 figure, Final version published in Phys. Rev.

Singlet-triplet decoherence due to nuclear spins in a double quantum dot

We have evaluated hyperfine-induced electron spin dynamics for two electrons confined to a double quantum dot. Our quantum solution accounts for decay of a singlet-triplet correlator even in the presence of a fully static nuclear spin system, with no ensemble averaging over initial conditions. In contrast to an earlier semiclassical calculation, which neglects the exchange interaction, we find that the singlet-triplet correlator shows a long-time saturation value that differs from 1/2, even in the presence of a strong magnetic field. Furthermore, we find that the form of the long-time decay undergoes a transition from a rapid Gaussian to a slow power law ($\sim 1/t^{3/2}$) when the exchange interaction becomes nonzero and the singlet-triplet correlator acquires a phase shift given by a universal (parameter independent) value of $3\pi/4$ at long times. The oscillation frequency and time-dependent phase shift of the singlet-triplet correlator can be used to perform a precision measurement of the exchange interaction and Overhauser field fluctuations in an experimentally accessible system. We also address the effect of orbital dephasing on singlet-triplet decoherence, and find that there is an optimal operating point where orbital dephasing becomes negligible.Comment: 12 pages, 4 figure

Inkwisatoriese en akkusatoriese elemente in die Amerikaanse pleitonderhandelingsproses: rigtingwyser of waarskuwingsteken?

Uit teks: Dit word algemeen aanvaar dat die prosedure van pleitonderhandelinge die hele strafproses hervorm het en is die belangrikste hiervan dat koste bespaar word en tyd meer effektief gebruik kan word. Dit dien as belangrike middel tot beskikking van die aanklaer en die verdediging. Pleitonderhandelinge kan ook bydra tot uitskakeling van onskuldigbevindings by ’n verhoor op bloot ’n tegniese punt. Die prosedure beperk ook tot ’n groot mate die omvang van regsprekende beamptes se diskresie by vonnisoplegging en bring mee dat die beskuldigde persoonlik ook by die proses betrek word

Focus on adolescents with HIV and AIDS

KMAdolescents living with HIV, including those infected perinatally and non-perinatally, bear a disproportionate burden of the HIV epidemic in South Africa. This article discusses HIV management in adolescents including the following aspects: (i) burden of HIV disease, modes of HIV acquisition and implications for management; (ii) initiation of combination antiretroviral therapy (ART), outcomes and complications of ART in adolescents,including virological failure and switching regimens; (iii) adherence in adolescence, including factors that may contribute to poor adherence and advice to improve adherence; (iv) issues particular to adolescents, including sexual and reproductive health needs, disclosure to adolescents and by adolescents, and transition to adult care. This article aims to provide insights based on the literature and experience to assist the clinician to navigate the difficulties of managing HIV in adolescence and achieving successful transition to adult care

Memory-Controlled Diffusion

Memory effects require for their incorporation into random-walk models an extension of the conventional equations. The linear Fokker-Planck equation for the probability density $p(\vec r, t)$ is generalized to include non-linear and non-local spatial-temporal memory effects. The realization of the memory kernels are restricted due the conservation of the basic quantity $p$. A general criteria is given for the existence of stationary solutions. In case the memory kernel depends on $p$ polynomially the transport is prevented. Owing to the delay effects a finite amount of particles remains localized and the further transport is terminated. For diffusion with non-linear memory effects we find an exact solution in the long-time limit. Although the mean square displacement shows diffusive behavior, higher order cumulants exhibits differences to diffusion and they depend on the memory strength

Asymmetric Quantum Shot Noise in Quantum Dots

We analyze the frequency-dependent noise of a current through a quantum dot which is coupled to Fermi leads and which is in the Coulomb blockade regime. We show that the asymmetric shot noise as function of frequency shows steps and becomes super-Poissonian. This provides experimental access to the quantum fluctuations of the current. We present an exact calculation for a single dot level and a perturbative evaluation of the noise in Born approximation (sequential tunneling regime but without Markov approximation) for the general case of many levels with charging interaction.Comment: 5 pages, 2 figure

Hyperfine interaction in a quantum dot: Non-Markovian electron spin dynamics

We have performed a systematic calculation for the non-Markovian dynamics of a localized electron spin interacting with an environment of nuclear spins via the Fermi contact hyperfine interaction. This work applies to an electron in the s -type orbital ground state of a quantum dot or bound to a donor impurity, and is valid for arbitrary polarization p of the nuclear spin system, and arbitrary nuclear spin I in high magnetic fields. In the limit of p=1 and I=1/2, the Born approximation of our perturbative theory recovers the exact electron spin dynamics. We have found the form of the generalized master equation (GME) for the longitudinal and transverse components of the electron spin to all orders in the electron spin--nuclear spin flip-flop terms. Our perturbative expansion is regular, unlike standard time-dependent perturbation theory, and can be carried-out to higher orders. We show this explicitly with a fourth-order calculation of the longitudinal spin dynamics. In zero magnetic field, the fraction of the electron spin that decays is bounded by the smallness parameter \delta=1/p^{2}N, where N is the number of nuclear spins within the extent of the electron wave function. However, the form of the decay can only be determined in a high magnetic field, much larger than the maximum Overhauser field. In general the electron spin shows rich dynamics, described by a sum of contributions with non-exponential decay, exponential decay, and undamped oscillations. There is an abrupt crossover in the electron spin asymptotics at a critical dimensionality and shape of the electron envelope wave function. We propose a scheme that could be used to measure the non-Markovian dynamics using a standard spin-echo technique, even when the fraction that undergoes non-Markovian dynamics is small.Comment: 22 pages, 8 figure

Chicora research contribution 403

This study reports on an intensive cultural resources survey of a 115 acre tract along the Savannah River in the City of North Augusta, Aiken County, South Carolina. The work, conducted for the City of North Augusta, is meant to assist the city in complying with Section 106 of the National Historic Preservation Act and the regulations codified in 36CFR800