Total scattering descriptions of local and cooperative distortions in the oxide spinel (Mg,Cu)Cr2O4 with dilute Jahn-Teller ions

The normal spinel oxide MgCr2O4 is cubic at room temperature while the normal spinel CuCr2O4 is tetragonal as a consequence of the Jahn-Teller nature of Cu2+ on the tetrahedral sites. Despite different end-member structures, complete solid solutions of Mg_{1-x}Cu_xCr2O4 can be prepared that display a first-order structural transition with composition x = 0.43 at room temperature. Reverse Monte Carlo analysis of total neutron scattering on data acquired between 300 K and 15 K on samples with x = 0.10, 0.20, and 0.43 provides unbiased local and average structure descriptions of the samples, including an understanding of the transition from local Jahn-Teller distortions in the cubic phase to cooperative distortions that result in a tetragonal structure. Distributions of continuous symmetry measures help to understand and distinguish distorted and undistorted coordination around the tetrahedral site in the solid solutions. Magnetic exchange bias is observed in field-cooled hysteresis loops of samples with dilute Cu2+ concentration and in samples with tetragonal--cubic phase coexistence around 300 K.Comment: 10 pages, 14 figure

Relapses of Plasmodium vivax infection usually result from activation of heterologous hypnozoites.

BACKGROUND: Relapses originating from hypnozoites are characteristic of Plasmodium vivax infections. Thus, reappearance of parasitemia after treatment can result from relapse, recrudescence, or reinfection. It has been assumed that parasites causing relapse would be a subset of the parasites that caused the primary infection. METHODS: Paired samples were collected before initiation of antimalarial treatment and at recurrence of parasitemia from 149 patients with vivax malaria in Thailand (n=36), where reinfection could be excluded, and during field studies in Myanmar (n=75) and India (n=38). RESULTS: Combined genetic data from 2 genotyping approaches showed that novel P. vivax populations were present in the majority of patients with recurrent infection (107 [72%] of 149 patients overall [78% of patients in Thailand, 75% of patients in Myanmar {Burma}, and 63% of patients in India]). In 61% of the Thai and Burmese patients and in 55% of the Indian patients, the recurrent infections contained none of the parasite genotypes that caused the acute infection. CONCLUSIONS: The P. vivax populations emerging from hypnozoites commonly differ from the populations that caused the acute episode. Activation of heterologous hypnozoite populations is the most common cause of first relapse in patients with vivax malaria

Universality of residence-time distributions in non-adiabatic stochastic resonance

We present mathematically rigorous expressions for the residence-time and first-passage-time distributions of a periodically forced Brownian particle in a bistable potential. For a broad range of forcing frequencies and amplitudes, the distributions are close to periodically modulated exponential ones. Remarkably, the periodic modulations are governed by universal functions, depending on a single parameter related to the forcing period. The behaviour of the distributions and their moments is analysed, in particular in the low- and high-frequency limits.Comment: 8 pages, 1 figure New version includes distinction between first-passage-time and residence-time distribution

Is the Yb2Ti2O7 pyrochlore a quantum spin ice?

We use numerical linked cluster (NLC) expansions to compute the specific heat, C(T), and entropy, S(T), of a quantum spin ice model of Yb2Ti2O7 using anisotropic exchange interactions recently determined from inelastic neutron scattering measurements and find good agreement with experimental calorimetric data. In the perturbative weak quantum regime, this model has a ferrimagnetic ordered ground state, with two peaks in C(T): a Schottky anomaly signalling the paramagnetic to spin ice crossover followed at lower temperature by a sharp peak accompanying a first order phase transition to the ferrimagnetic state. We suggest that the two C(T) features observed in Yb2Ti2O7 are associated with the same physics. Spin excitations in this regime consist of weakly confined spinon-antispinon pairs. We suggest that conventional ground state with exotic quantum dynamics will prove a prevalent characteristic of many real quantum spin ice materials.Comment: 8 pages (two-column), 9 figure

Towards lensfield: Data management, processing and semantic publication for vernacular e-science

Lensfield is a desktop and filesystem-based tool designed as a “personal data management assistant” for the scientist. It combines distributed version control (DVCS), software transaction memory (STM) and linked open data (LOD) publishing to create a novel data management, processing and publication tool. The application “just looks after” these technologies for the scientist, providing simple interfaces for typical uses. It is built with Clojure and includes macros which define steps in a common workflow. Functions and Java libraries provide facilities for automatic processing of data which is ultimately published as RDF in a web application. The progress of data processing is tracked by a fine-grained data structure that can be serialized to disk, with the potential to include manual steps and programmatic interrupts in largely automated processes through seamless resumption. Flexibility in operation and minimizing barriers to adoption are major design features.This paper was presented at the IEEE eScience conference 2009, hosted by the Oxford eResearch Centre and held at the Kassam Stadium outside Oxford

A statistical model for the intrinsically broad superconducting to normal transition in quasi-two-dimensional crystalline organic metals

Although quasi-two-dimensional organic superconductors such as $\kappa$-(BEDT-TTF)$_2$Cu(NCS)$_2$ seem to be very clean systems, with apparent quasiparticle mean-free paths of several thousand \AA, the superconducting transition is intrinsically broad (e.g $\sim 1$ K wide for $T_c \approx 10$ K). We propose that this is due to the extreme anisotropy of these materials, which greatly exacerbates the statistical effects of spatial variations in the potential experienced by the quasiparticles. Using a statistical model, we are able to account for the experimental observations. A parameter $\bar{x}$, which characterises the spatial potential variations, may be derived from Shubnikov-de Haas oscillation experiments. Using this value, we are able to predict a transition width which is in good agreement with that observed in MHz penetration-depth measurements on the same sample.Comment: 8 pages, 2 figures, submitted to J. Phys. Condens. Matte

Space-time clustering of Burkitt's lymphoma in the West Nile district of Uganda: 1961-1975.

Epidemiological data relating to all 202 patients diagnosed with Burkitt's Lymphoma (BL) in the West Nile District of Uganda in the period 1961 to 1975 have been reviewed and analysed. Statistically significant evidence of space-time clustering of cases, first reported for the period 1961-65, was also present during 1972-73, but not during other periods. The patients involved in such clusters were found to be older than other patients (P less than 0.001). The average annual incidence of BL in the District was 2.45 x 10(-5) and overall there was no change in the incidence during the study period. However, there were statistically significant changes in incidence in different counties, which could not be explained as case-ascertainment artifacts. One sib pair of patients with BL was found and the series also included 7 instances of BL in two cousins. It is suggested that study of variation in the intensity and type of malarial infestation in different areas at different times may help explain the epidemiological findings and suggest what, if any, aspects of this infection are critical for inducing BL

Microwave Kinetic Inductance Detector (MKID) Camera Testing for Submillimeter Astronomy

Developing kilopixel focal planes for incoherent submm- and mm-wave detectors remains challenging due to either the large hardware overhead or the complexity of multiplexing standard detectors. Microwave kinetic inductance detectors (MKIDs) provide a efficient means to produce fully lithographic background-limited kilopixel focal planes. We are constructing an MKID-based camera for the Caltech Submillimeter Observatory with 576 spatial pixels each simultaneously sensitive in 4 bands at 230, 300, 350, and 400 GHz. The novelty of MKIDs has required us to develop new techniques for detector characterization. We have measured quasiparticle lifetimes and resonator Qs for detector bath temperatures between 200 mK and 400 mK. Equivalent lifetime measurements were made by coupling energy into the resonators either optically or by driving the third harmonic of the resonator. To determine optical loading, we use both lifetime and internal Q measurements, which range between 15,000 and 30,000 for our resonators. Spectral bandpass measurements confirm the placement of the 230 and 350 GHz bands. Additionally, beam maps measurements conform to expectations. The same device design has been characterized on both sapphire and silicon substrates, and for different detector geometries. We also report on the incorporation of new shielding to reduce detector sensitivity to local magnetic fields

Chelyabinsk: An Ordinary Chondrite From a Spectacular Fall in Russia

The asteroidal explosion that occurred over Chelyabinsk, Russia on Feb 15, 2013 was the first-witnessed occurrence that caused significant damage to humans and their properties. The bolide responsible for this extraordinary event was estimated to be 17-20 m in diameter, traveling at a speed of ~18 km/s. Although it coincided with the fly-by of 2012DA_(14) (a ~45 m asteroid), the Chelyabinsk bolide has been estimated to be derived from the main asteroid belt. Here, we report our study of two pieces of this meteorite, both completely covered by fusion crust and amounting to a total mass of ~5 g