A radiation-hydrodynamics scheme valid from the transport to the diffusion limit

We present in this paper the numerical treatment of the coupling between hydrodynamics and radiative transfer. The fluid is modeled by classical conservation laws (mass, momentum and energy) and the radiation by the grey moment $M_1$ system. The scheme introduced is able to compute accurate numerical solution over a broad class of regimes from the transport to the diffusive limits. We propose an asymptotic preserving modification of the HLLE scheme in order to treat correctly the diffusion limit. Several numerical results are presented, which show that this approach is robust and have the correct behavior in both the diffusive and free-streaming limits. In the last numerical example we test this approach on a complex physical case by considering the collapse of a gas cloud leading to a proto-stellar structure which, among other features, exhibits very steep opacity gradients.Comment: 29 pages, submitted to Journal of Computational physic

Virtual Compton scattering off nuclei in the Δ\Delta-resonance region

Virtual Compton scattering in the $\Delta$-resonance region is considered in the case of a target nucleus. The discussion involves generalized polarizabilities and is developed for zero-spin nuclei, focusing on the new information coming from virtual Compton scattering in comparison with real Compton scattering.Comment: 8 pages, LaTeX, 3 figures available from the author

On Local Approximations to the Nonlinear Evolution of Large-Scale Structure

We present a comparative analysis of several methods, known as local Lagrangian approximations, which are aimed to the description of the nonlinear evolution of large-scale structure. We have investigated various aspects of these approximations, such as the evolution of a homogeneous ellipsoid, collapse time as a function of initial conditions, and asymptotic behavior. As one of the common features of the local approximations, we found that the calculated collapse time decreases asymptotically with the inverse of the initial shear. Using these approximations, we have computed the cosmological mass function, finding reasonable agreement with N-body simulations and the Press-Schechter formula.Comment: revised version with color figures, minor changes, accepted for publication in the Astrophysical Journal, 30 pages, 13 figure

Pengaruh Efisiensi Waktu Pada Sistem Pengairan Satu Titik Sarana Tanam Vertikal Terhadap Perubahan Aktivitas Menyiram Tanaman Oleh Masyarakat Kampung Kota

Dalam pelaksanaan program Kampung Berkebun di Kota Bandung, masyarakat yang sebagian besar berprofesi utama bukan sebagai petani mendapati kendala dalam perawatan tanaman produktif seperti sayuran. Hal ini dikarenakan warga harus meluangkan waktunya untuk menyiram tanaman secara rutin setiap hari. Sedangkan kesediaan waktu luang sebagian besar selepas aktivitas utama selesai, sehingga aktivitas tersebut sering terabaikan. Untuk mempermudah aktivitas tersebut perlu adanya pengembangan sistem penyiraman tanaman yang mengutamakan efisiensi waktu. Pengembangan sistem ini dilakukan melalui uji coba terhadap responden di wilayah studi kasus RT. 2, RW. 2, Kelurahan Kacapiring, Kota Bandung. Hasil dari penelitian menunjukkan sistem pengairan terhubung melalui satu titik lebih efisien dalam konsumsi waktu saat melakukan aktivitas penyiraman tanaman. Pada pengamatan uji coba terlihat adanya Perubahan perilaku warga dari yang sebelumnya tidak rutin melakukan penyiraman tanaman, menjadi lebih rutin

A numerical model for multigroup radiation hydrodynamics

We present in this paper a multigroup model for radiation hydrodynamics to account for variations of the gas opacity as a function of frequency. The entropy closure model (M1) is applied to multigroup radiation transfer in a radiation hydrodynamics code. In difference from the previous grey model, we are able to reproduce the crucial effects of frequency-variable gas opacities, a situation omnipresent in physics and astrophysics. We also account for the energy exchange between neighbouring groups which is important in flows with strong velocity divergence. These terms were computed using a finite volume method in the frequency domain. The radiative transfer aspect of the method was first tested separately for global consistency (reversion to grey model) and against a well established kinetic model through Marshak wave tests with frequency dependent opacities. Very good agreement between the multigroup M1 and kinetic models was observed in all tests. The successful coupling of the multigroup radiative transfer to the hydrodynamics was then confirmed through a second series of tests. Finally, the model was linked to a database of opacities for a Xe gas in order to simulate realistic multigroup radiative shocks in Xe. The differences with the previous grey models are discussed.Comment: 27 pages, 11 figures, Accepted for publication in JQSR

Simulations of protostellar collapse using multigroup radiation hydrodynamics. II. The second collapse

15 pages, 11 figures, accepted for publication in A&AStar formation begins with the gravitational collapse of a dense core inside a molecular cloud. As the collapse progresses, the centre of the core begins to heat up as it becomes optically thick. The temperature and density in the centre eventually reach high enough values where fusion reactions can ignite; the protostar is born. This sequence of events entail many physical processes, of which radiative transfer is of paramount importance. Many simulations of protostellar collapse make use of a grey treatment of radiative transfer coupled to the hydrodynamics. However, interstellar gas and dust opacities present large variations as a function of frequency. In this paper, we follow-up on a previous paper on the collapse and formation of Larson's first core using multigroup radiation hydrodynamics (Paper I) by extending the calculations to the second phase of the collapse and the formation of Larson's second core. We have made the use of a non-ideal gas equation of state as well as an extensive set of spectral opacities in a spherically symmetric fully implicit Godunov code to model all the phases of the collapse of a 0.1, 1 and 10 solar mass cloud cores. We find that, for a same central density, there are only small differences between the grey and multigroup simulations. The first core accretion shock remains supercritical while the shock at the second core border is found to be strongly subcritical with all the accreted energy being transfered to the core. The size of the first core was found to vary somewhat in the different simulations (more unstable clouds form smaller first cores) while the size, mass and temperature of the second cores are independent of initial cloud mass, size and temperature. Our simulations support the idea of a standard (universal) initial second core size of 0.003 AU and mass 0.0014 solar masses

The Excursion Set Theory of Halo Mass Functions, Halo Clustering, and Halo Growth

I review the excursion set theory (EST) of dark matter halo formation and clustering. I recount the Press-Schechter argument for the mass function of bound objects and review the derivation of the Press-Schechter mass function in EST. The EST formalism is powerful and can be applied to numerous problems. I review the EST of halo bias and the properties of void regions. I spend considerable time reviewing halo growth in the EST. This section culminates with descriptions of two Monte Carlo methods for generating halo mass accretion histories. In the final section, I emphasize that the standard EST approach is the result of several simplifying assumptions. Dropping these assumptions can lead to more faithful predictions and a more versatile formalism. One such assumption is the constant height of the barrier for nonlinear collapse. I review implementations of the excursion set approach with arbitrary barrier shapes. An application of this is the now well-known improvement to standard EST that follows from the ellipsoidal-collapse barrier. Additionally, I emphasize that the statement that halo accretion histories are independent of halo environments is a simplifying assumption, rather than a prediction of the theory. I review the method for constructing correlated random walks of the density field in more general cases. I construct a simple toy model with correlated walks and I show that excursion set theory makes a qualitatively simple and general prediction for the relation between halo accretion histories and halo environments: regions of high density preferentially contain late-forming halos and conversely for regions of low density. I conclude with a brief discussion of this prediction in the context of recent numerical studies of the environmental dependence of halo properties. (Abridged)Comment: 62 pages, 19 figures. Review article based on lectures given at the Sixth Summer School of the Helmholtz Institute for Supercomputational Physics. Accepted for Publication in IJMPD. Comments Welcom

Autism and the U.K. secondary school experience

This research investigated the self-reported mainstream school experiences of those diagnosed on the autistic spectrum compared with the typically developing school population. Existing literature identifies four key areas that affect the quality of the school experience for students with autism: social skills, perceived relationships with teaching staff, general school functioning, and interpersonal strengths of the young person. These areas were explored in a mainstream U.K. secondary school with 14 students with autism and 14 age and gender matched students without autism, using self-report questionnaires and semi-structured interviews. Quantitative analyses showed consistent school experiences for both groups, although content analysis of interview data highlighted some differences in the ways in which the groups perceive group work, peers, and teaching staff within school. Implications for school inclusion are discussed, drawing attention to how staff awareness of autism could improve school experience and success for students with autism attending mainstream schools

From a fossil-fuel to a biobased economy : the politics of industrial biotechnology

Industrial biotechnology involves the replacement of petrochemical processes and inputs with more energy-efficient and renewable biological ones. It is already being used in the production of biofuels and bioplastics and has been touted as a means by which modern economies can be shifted toward a more competitive, low-carbon growth model. This paper does two things. First, it outlines the policy framework established in the European Union and the narrative of a knowledge-based bioeconomy (KBBE) underpinning this. Second, it argues that the ‘win – win’ rhetoric contained within the KBBE narrative is misleading. Among the different groups commenting on the use of industrial biotechnology, the paper locates cleavages between farmers and agribusiness, between those convinced and those sceptical of environmental technofixes, and between procorporate and anticorporate NGOs. Taken together, they show the purported transition from a fossil-fuel to a bio-based economy to be a resolutely political one