MeV Astrophysical Spectroscopic Surveyor (MASS): A Compton Telescope Mission Concept

We propose a future mission concept, the MeV Astrophysical Spectroscopic Surveyor (MASS), which is a large area Compton telescope using 3D position sensitive cadmium zinc telluride (CZT) detectors optimized for emission line detection. The payload consists of two layers of CZT detectors in a misaligned chessboard layout, with a total geometric area of 4096 cm$^2$ for on-axis observations. The detectors can be operated at room-temperature with an energy resolution of 0.6\% at 0.662 MeV. The in-orbit background is estimated with a mass model. At energies around 1 MeV, a line sensitivity of about $10^{-5}$ photons cm$^{-2}$ s$^{-1}$ can be obtained with a 1 Ms observation. The main science objectives of MASS include nucleosynthesis in astrophysics and high energy astrophysics related to compact objects and transient sources. The payload CZT detectors weigh roughly 40 kg, suggesting that it can be integrated into a micro- or mini-satellite. We have constructed a pathfinder, named as MASS-Cube, to have a direct test of the technique with 4 detector units in space in the near future.Comment: accepted for publication in Experimental Astronom

Constitutive Modeling of Geomaterials: Advances and New Applications

The Second International Symposium on Constitutive Modeling of Geomaterials: Advances and New Applications (IS-Model 2012), is to be held in Beijing, China, during October 15-16, 2012. The symposium is organized by Tsinghua University, the International Association for Computer Methods and Advances in Geomechanics (IACMAG), the Committee of Numerical and Physical Modeling of Rock Mass, Chinese Society for Rock Mechanics and Engineering, and the Committee of Constitutive Relations and Strength Theory, China Institution of Soil Mechanics and Geotechnical Engineering, China Civil Engineering Society. This Symposium follows the first successful International Workshop on Constitutive Modeling held in Hong Kong, which was organized by Prof. JH Yin in 2007.   Constitutive modeling of geomaterials has been an active research area for a long period of time. Different approaches have been used in the development of various constitutive models. A number of models have been implemented in the numerical analyses of geotechnical structures. The objective of the symposium is to provide a forum for researchers and engineers working or interested in the area of constitutive modeling to meet together and share new ideas, achievements and experiences through presentations and discussions. Emphasis is placed on recent advances of constitutive modeling and its applications in both theoretic and experimental aspects.   Six famous scholars have been invited for the plenary speeches of the symposiums. Some prominent scholars have been invited to organize four specialized workshops on hot topics, including “Time-dependent stress-strain behavior of geomaterials”, “Constitutive modeling within critical state soil mechanics”, “Multiscale and multiphysics in geomaterials”, and “Damage to failure in rock structures”. A total of 49 papers are included in the above topics. In addition, 51 papers are grouped under three topics covering “Behaviour of geomaterials”, “Constitutive model”, and “Applications”.   The editors expect that the book can be helpful as a reference to all those in the field of constitutive modeling of geomaterials

Attenuation of photosynthetically available radiation by chlorophyll, chromophoric dissolved organic matter, and tripton in lake Donghu, China

The attenuation coefficient of photosynthetically available radiation [Kd(PAR)] and three water quality parameters [chlorophyll a (chl a)], chromophoric dissolvedorganic matter (CDOM) and tripton) were measured at three stations in shallow, subtropical Lake Donghu from April 2003 to March 2004. The multiple regressionequation of &amp;(PAR) versus chl a, CDOM, and tripton was: Kd(PAR) = 0.44 + 0.019 chla + 1.88 CDOM + 0.016 tripton, which revealed the relative contributions of the threeparameters to Kd(PAR). The effects of water and CDOM on Kd(PAR) were of minor importance (19-26%), while chl a and tripton were the two greatest contributors,accounting collectively for 74-8 1 %.<br/

Constitutive Modeling of GeomaterialsAdvances and New Applications /

XIV, 815 p. 468 illus.online resource

Micromechanics of the critical state of granular materials

The geometrical characteristics of the critical state are studied, using twodimensional Discrete Element Method simulations. Various simulations have been performed in order to study the effect on the critical-state fabric tensor of interparticle friction and of the type of loading. The results for the fabric tensor, from simulations with different material properties and different loading conditions, collapse to a single curve, where high coordination number corresponds to low fabric anisotropy. This suggests that a limiting fabric state exists that has a geometrical origin. Since high confining pressure leads to high coordination number, this then means that the fabric anisotropy is low. As it is well-known that fabric anisotropy is a main factor contributing to shear strength of granular materials, this geometrical effect explains the (weak) decrease of shear strength with increasing pressure. The contact network determines loops of contacts. Based on simplified loop shapes, two theoretical relations are developed for their geometrical description. These two theories are based on orientational exclusion of contacts and constant-volume deformation of the loops, respectively. These theoretical results bracket loop fabric anisotropies that are obtained from the results of the Discrete Element Method simulations

Diel variation of methane fluxes in summer in a eutrophic subtropical lake in China

The summer diel variation of methane (CH4) flux was investigated in a eutrophic, subtropical lake in China. The CH4 concentration was always supersaturated, and the emission rate ranged from 0.24 to 45.51mg m-2 h-1 , The diel variations of CH4 flux in June and August showed a single peak in early afternoon and a minimum in the morning, while the pattern varied irregularly in May. There was a moderate relationship between water and sediment temperature and CH4 emission rate in some months