Micromagnetic simulations of sweep-rate dependent coercivity in perpendicular recording media

The results of micromagnetic simulations are presented which examine the impact of thermal fluctuations on sweep rate dependent coercivities of both single-layer and exchange-coupled-composite (ECC) perpendicular magnetic recording media. M-H loops are calculated at four temperatures and sweep rates spanning five decades with fields applied normal to the plane and at 45 degrees. The impact of interactions between grains is evaluated. The results indicate a significantly weaker sweep-rate dependence for ECC media suggesting more robustness to long-term thermal effects. Fitting the modeled results to Sharrock-like scaling proposed by Feng and Visscher [J. Appl. Phys. 95, 7043 (2004)] is successful only in the case of single-layer media with the field normal to the plane.Comment: 7 pages, 14 figure

Quantum field theoretic approach to neutrino oscillations in matter

We consider neutrino oscillations in non-uniform matter in a quantum field theoretic (QFT) approach, in which neutrino production, propagation and detection are considered as a single process. We find the conditions under which the oscillation probability can be sensibly defined and demonstrate how the properly normalized oscillation probability can be obtained in the QFT framework. We derive the evolution equation for the oscillation amplitude and discuss the conditions under which it reduces to the standard Schr\"odinger-like evolution equation. It is shown that, contrary to the common usage, the Schr\"odinger-like evolution equation is not applicable in certain cases, such as oscillations of neutrinos produced in decays of free pions provided that sterile neutrinos with $\Delta m^2\gtrsim 1$ eV$^2$ exist.Comment: LaTeX, 24 pages + 16 pages of appendices, 1 figure. V2: typos correcte

Mass hierarchy, 2-3 mixing and CP-phase with Huge Atmospheric Neutrino Detectors

We explore the physics potential of multi-megaton scale ice or water Cherenkov detectors with low ($\sim 1$ GeV) threshold. Using some proposed characteristics of the PINGU detector setup we compute the distributions of events versus neutrino energy $E_\nu$ and zenith angle $\theta_z$, and study their dependence on yet unknown neutrino parameters. The $(E_\nu - \theta_z)$ regions are identified where the distributions have the highest sensitivity to the neutrino mass hierarchy, to the deviation of the 2-3 mixing from the maximal one and to the CP-phase. We evaluate significance of the measurements of the neutrino parameters and explore dependence of this significance on the accuracy of reconstruction of the neutrino energy and direction. The effect of degeneracy of the parameters on the sensitivities is also discussed. We estimate the characteristics of future detectors (energy and angle resolution, volume, etc.) required for establishing the neutrino mass hierarchy with high confidence level. We find that the hierarchy can be identified at $3\sigma$ -- $10\sigma$ level (depending on the reconstruction accuracies) after 5 years of PINGU operation.Comment: 39 pages, 21 figures. Description of Fig.3 correcte

Tailoring Gold Nanoparticle Characteristics and the Impact on Aqueous-Phase Oxidation of Glycerol

Poly(vinyl alcohol) (PVA)-stabilized Au nanoparticles (NPs) were synthesized by colloidal methods in which temperature variations (−75 to 75 °C) and mixed H2O/EtOH solvent ratios (0, 50, and 100 vol/vol) were used. The resulting Au NPs were immobilized on TiO2 (P25), and their catalytic performance was investigated for the liquid phase oxidation of glycerol. For each unique solvent system, there was a systematic increase in the average Au particle diameter as the temperature of the colloidal preparation increased. Generation of the Au NPs in H2O at 1 °C resulted in a high observed activity compared with current Au/TiO2 catalysts (turnover frequency = 915 h–1). Interestingly, Au catalysts with similar average particle sizes but prepared under different conditions had contrasting catalytic performance. For the most active catalyst, aberration-corrected high angle annular dark field scanning transmission electron microscopy analysis identified the presence of isolated Au clusters (from 1 to 5 atoms) for the first time using a modified colloidal method, which was supported by experimental and computational CO adsorption studies. It is proposed that the variations in the populations of these species, in combination with other solvent/PVA effects, is responsible for the contrasting catalytic properties

A new approach to spherically symmetric junction surfaces and the matching of FLRW regions

We investigate timelike junctions (with surface layer) between spherically symmetric solutions of the Einstein-field equation. In contrast to previous investigations this is done in a coordinate system in which the junction surface motion is absorbed in the metric, while all coordinates are continuous at the junction surface. The evolution equations for all relevant quantities are derived. We discuss the no-surface layer case (boundary surface) and study the behaviour for small surface energies. It is shown that one should expect cases in which the speed of light is reached within a finite proper time. We carefully discuss necessary and sufficient conditions for a possible matching of spherically symmetric sections. For timelike junctions between spherically symmetric space-time sections we show explicitly that the time component of the Lanczos equation always reduces to an identity (independently of the surface equation of state). The results are applied to the matching of FLRW models. We discuss `vacuum bubbles' and closed-open junctions in detail. As illustrations several numerical integration results are presented, some of them indicate that the junction surface can reach the speed of light within a finite time.Comment: new version - corrected boundary surface discussion, improved presentation, and corrected reference 22 pages, many figure

30 days wild: development and evaluation of a large-scale nature engagement campaign to improve well-being

There is a need to increase people’s engagement with and connection to nature, both for human well-being and the conservation of nature itself. In order to suggest ways for people to engage with nature and create a wider social context to normalise nature engagement, The Wildlife Trusts developed a mass engagement campaign, 30 Days Wild. The campaign asked people to engage with nature every day for a month. 12,400 people signed up for 30 Days Wild via an online sign-up with an estimated 18,500 taking part overall, resulting in an estimated 300,000 engagements with nature by participants. Samples of those taking part were found to have sustained increases in happiness, health, connection to nature and pro-nature behaviours. With the improvement in health being predicted by the improvement in happiness, this relationship was mediated by the change in connection to nature

Exciton entanglement in two coupled semiconductor microcrystallites

Entanglement of the excitonic states in the system of two coupled semiconductor microcrystallites, whose sizes are much larger than the Bohr radius of exciton in bulk semiconductor but smaller than the relevant optical wavelength, is quantified in terms of the entropy of entanglement. It is observed that the nonlinear interaction between excitons increases the maximum values of the entropy of the entanglement more than that of the linear coupling model. Therefore, a system of two coupled microcrystallites can be used as a good source of entanglement with fixed exciton number. The relationship between the entropy of the entanglement and the population imbalance of two microcrystallites is numerically shown and the uppermost envelope function for them is estimated by applying the Jaynes principle.Comment: 16 pages, 6 figure

Synthesis of nanocrystals by discharges in liquid nitrogen from Si-Sn sintered electrode

International audienceThe synthesis feasibility of silicon-tin nanocrystals by discharges in liquid nitrogen is studied using a Si-10 at % Sn sintered electrode. Time-resolved optical emission spectroscopy shows that silicon and tin melt almost simultaneously. The presence of both vapours does not lead to the synthesis of alloyed nanocrystals but to the synthesis of separate nanocrystals of silicon and tin with average sizes of 10 nm. These nanocrystals are transformed into amorphous silicon oxide (am-SiO2) and beta-SnO2 by air oxidation, after evaporation of the liquid nitrogen. The synthesis of an am-Si0.95Sn0.05 phase around large silicon crystals (similar to 500 nm) decorated by beta-Sn spheroids is achieved if the current flowing through electrodes is high enough. When the sintered electrode is hit by powerful discharges, some grains are heated and tin diffuses in the large silicon crystals. Next, these grains are shelled and fall into the dielectric liquid

Quantum Sine(h)-Gordon Model and Classical Integrable Equations

We study a family of classical solutions of modified sinh-Gordon equation, $\partial_z\partial_{{\bar z}} \eta-\re^{2\eta}+p(z)\,p({\bar z})\ \re^{-2\eta}=0$with$p(z)=z^{2\alpha}-s^{2\alpha}$. We show that certain connection coefficients for solutions of the associated linear problem coincide with the$Q$-function of the quantum sine-Gordon$(\alpha>0)$or sinh-Gordon$(\alpha<-1)$ models.Comment: 35 pages, 3 figure