Quantum phase transition induced by Dzyaloshinskii-Moriya in the kagome antiferromagnet

We argue that the S=1/2 kagome antiferromagnet undergoes a quantum phase transition when the Dzyaloshinskii-Moriya coupling is increased. For $D<D_c$ the system is in a moment-free phase and for $D>D_c$ the system develops antiferromagnetic long-range order. The quantum critical point is found to be $D_c \simeq 0.1J$ using exact diagonalizations and finite-size scaling. This suggests that the kagome compound ZnCu$_3(OH)$_6$Cl$_3$ may be in a quantum critical region controlled by this fixed point.Comment: 5 pages, 4 figures; v2: add. data included, show that D=0.1J is at a quantum critical poin

Supercritical multicomponent solvent coal extraction

The yield of organic extract from the supercritical extraction of coal with larger diameter organic solvents such as toluene is increased by use of a minor amount of from 0.1 to 10% by weight of a second solvent such as methanol having a molecular diameter significantly smaller than the average pore diameter of the coal

Half metallic digital ferromagnetic heterostructure composed of a δ\delta-doped layer of Mn in Si

We propose and investigate the properties of a digital ferromagnetic heterostructure (DFH) consisting of a $\delta$-doped layer of Mn in Si, using \textit{ab initio} electronic-structure methods. We find that (i) ferromagnetic order of the Mn layer is energetically favorable relative to antiferromagnetic, and (ii) the heterostructure is a two-dimensional half metallic system. The metallic behavior is contributed by three majority-spin bands originating from hybridized Mn-$d$ and nearest-neighbor Si-$p$ states, and the corresponding carriers are responsible for the ferromagnetic order in the Mn layer. The minority-spin channel has a calculated semiconducting gap of 0.25 eV. Analysis of the total and partial densities of states, band structure, Fermi surfaces and associated charge density reveals the marked two-dimensional nature of the half metallicity. The band lineup is found to be favorable for retaining the half metal character to near the Curie temperature ($T_{C}$). Being Si based and possibly having a high $T_{C}$ as suggested by an experiment on dilutely doped Mn in Si, the heterostructure may be of special interest for integration into mature Si technologies for spintronic applications.Comment: 4 pages, 4 figures, Revised version, to appear in Phys. Rev. Let

A "kilonova" associated with short-duration gamma-ray burst 130603B

Short-duration gamma-ray bursts (SGRBs) are intense flashes of cosmic gamma-rays, lasting less than ~2 s, whose origin is one of the great unsolved questions of astrophysics today. While the favoured hypothesis for their production, a relativistic jet created by the merger of two compact stellar objects (specifically, two neutron stars, NS-NS, or a neutron star and a black hole, NS-BH), is supported by indirect evidence such as their host galaxy properties, unambiguous confirmation of the model is still lacking. Mergers of this kind are also expected to create significant quantities of neutron-rich radioactive species, whose decay should result in a faint transient in the days following the burst, a so-called "kilonova". Indeed, it is speculated that this mechanism may be the predominant source of stable r-process elements in the Universe. Recent calculations suggest much of the kilonova energy should appear in the near-infrared (nIR) due to the high optical opacity created by these heavy r-process elements. Here we report strong evidence for such an event accompanying SGRB 130603B. If this simplest interpretation of the data is correct, it provides (i) support for the compact object merger hypothesis of SGRBs, (ii) confirmation that such mergers are likely sites of significant r-process production and (iii) quite possibly an alternative, un-beamed electromagnetic signature of the most promising sources for direct detection of gravitational waves.Comment: preprint of paper appearing in Nature (3 Aug 2013

Leptogenesis from Soft Supersymmetry Breaking (Soft Leptogenesis)

Soft leptogenesis is a scenario in which the cosmic baryon asymmetry is produced from a lepton asymmetry generated in the decays of heavy sneutrinos (the partners of the singlet neutrinos of the seesaw) and where the relevant sources of CP violation are the complex phases of soft supersymmetry-breaking terms. We explain the motivations for soft leptogenesis, and review its basic ingredients: the different CP-violating contributions, the crucial role played by thermal corrections, and the enhancement of the efficiency from lepton flavour effects. We also discuss the high temperature regime $T > 10^7$ GeV in which the cosmic baryon asymmetry originates from an initial asymmetry of an anomalous $R$-charge, and soft leptogenesis reembodies in $R$-genesis.Comment: References updated. Some minor corrections to match the published versio

Walk Your Life to Health—Motivating Young Adolescents to Engage in a Brisk Walking Program

Increasing numbers of overweight and obese children resulting from sedentary and abundant lifestyles are a health concern in Hong Kong and other affluent communities around the globe. The importance of physical activity is well documented for health and wellbeing, with sedentary behavior emerging as an independent risk factor for chronic diseases and mortality. In this study, Pender's Health-Promotion Model informed the development of an intervention program aimed to engage junior high school students in increased physical activity, specifically brisk-walking. The model set out to motivate participants to engage in behaviors to enhance their health across the life span, including developing self-efficacy with regard to brisk walking. The intervention featured four stages. First, participants were provided with information about the benefits and in stage two were trained in the technique of brisk walking. Next they engaged in the brisk walking program and in stage four were encouraged to serve as health ambassadors by introducing brisk walking and its associated benefits to others, thereby exercising peer influence to diffuse the practice of brisk walking more widely among members of the community. Motivational strategies were used as incentives in the program, including the involvement of a popular singing band to award certificates at the completion of the program. This 7-week intervention program including a 4-week brisk walking component was conducted in a high school context with 71 participants. Data were collected to enable paired-sample t-tests to be conducted to statistically analyze the data at pre- and post-intervention. Findings indicate significant differences among the mean Body Mass Index (BMI), Waist-to-Hip Ratio (WHR), knowledge and attitudes of the participants at pre- and post-intervention. These findings suggest that the intervention was effective as a strategy to reduce sedentary behavior with the concomitant effect of positive shifts in measurable indicators and attitudes.Full Tex

Properties of Si-SiO2 interface traps due to low-energy Ar+ backsurface bombardment in n-channel nitrided MOSFETs

Flicker noise in backsurface gettered, nitrided n-channel MOSFETs is characterized over a wide range of temperatures and biases. The gettering time ranged from 10 to 40 minutes. The noise power spectra for devices with different gettering times are compared to the ungettered devices which serve as the control. It is found that flicker noise is reduced by backsurface gettering for short gettering times. A rebound in the noise magnitude is observed for long gettering times. Investigations of the temperature dependencies of the noise power spectra indicates that the low-frequency noise arises from thermal activation of carriers to traps at the Si-SiO2 interface. Backsurface gettering results in the modification of the energy distribution of the interface traps, probably due to stress relaxation at the Si-SiO2 interface.published_or_final_versio