A numerical solution of the Navier-Stokes and diffusion equations for two equally sized spheres

Imperial Users onl

Fixing of photorefractive volume holograms in K1-yLiyTa1-xO3

We report the f ixing of photorefractive holographic gratings with high eff iciency in a sample of K1-yLiyTa1-xNbxO3 doped with Cu, V, and Ti. Holograms are thermally fixed through the screening of a photorefractive space-charge field by a nonphotoactive species at elevated temperatures. Fixed holograms are revealed by illumination at lower temperatures. Diffraction efficiencies of 25% in a 0.54-cm-thick sample are measured. Holograms undergo thermal decay with a 0.67-eV activation energy

A Study on the Concept of Mental Health and its Implication for Social Work Education in the Context of Chinese Communities

The recently rapid growth of practice in cross-culture and multi-culture field leads practitioners to facing challenge of having to make choice amid different cultural values. Chinese culture has its own framework in understanding the concept of mental health, which is quite different from the Western’s. On personal level, Chinese culture centers on the individual’s inner cultivation. On self level, it concerns much about the individual’s moral practice. On societal level, it focuses on the social harmony. And on spiritual level, it emphasizes on transcending the life limitations to reach oneness. Therefore, it is necessary for social work educators to help studnts to understand the basic cultural meanings underlying the concept of mental healh when applying it to the context of Chinese communities. Keywords: mental health; Chinese culture; progressive adaptation; limitation inclusionRésumé: La croissance rapide de la pratique dans un contexte inter-culturel et multi-culturel conduit les praticiens à faire face au défi de faire un choix parmi de différentes valeurs culturelles. La culture chinoise a sa propre compréhension de la notion de santé mentale, ce qui est assez différente de celle de l'Occident . Au niveau personnel, la culture chinoise se concentre sur la cultivation interne de l'individu. Au niveau individuel, il s'agit bien de la pratique morale de l'individu. Au niveau communautairel, elle souligne l'harmonie sociale. Et au spirituel, elle met l'accent sur la transcendance des limites de vie pour atteindre l'unité. Par conséquent, il est nécessaire que les éducateurs sociaux aident les étudiants à comprendre les significations culturelles de base propres au concept de santé mentale lors de l'appliquer dans le contexte des communautés chinoises.Mots-clés: santé mentale; culture chinoise; adaptation progressive; inclusion de prescriptio

Stabilized Radiation Pressure Dominated Ion Acceleration from Thin-foil Targets

We study transverse and longitudinal electron heating effects on the target stability and the ion spectra in the radiation pressure dominated regime of ion acceleration by means of multi dimensional particle-in-cell (PIC) simulations. Efficient ion acceleration occurs when the longitudinal electron temperature is kept as low as possible. However, tailoring of the transverse electron temperature is required in view of suppressing the transverse instability, which can keep the target structure intact for longer duration during the acceleration stage. We suggest using the surface erosion of the target to increase the transverse temperature, which improves both the final peak energy and the spectral quality of the ions in comparison with a normal flat target.Comment: 5 pages, 3 picture

Target shape effects on monoenergetic GeV proton acceleration

When a circularly polarized laser pulse interacts with a foil target, there are three stages: pre-hole-boring, hole-boring and the light sail acceleration. We study the electron and ion dynamics in the first stage and find the minimum foil thickness requirement for a given laser intensity. Based on this analysis, we propose to use a shaped foil for ion acceleration, whose thickness varies transversely to match the laser intensity. Then, the target evolves into three regions: the acceleration, transparency and deformation regions. In the acceleration region, the target can be uniformly accelerated producing a mono-energetic and spatially collimated ion beam. Detailed numerical simulations are performed to check the feasibility and robustness of this scheme, such as the influence of shape factors and surface roughness. A GeV mono-energetic proton beam is observed in the three dimensional particle-in-cell simulations when a laser pulse with the focus intensity of 1022W=cm2 is used. The energy conversion efficiency of laser pulse to accelerated proton beam is more than 23%. Synchrotron radiation and damping effects are also checked in the interaction.Comment: 11 pages, 9 figure