Baseline design of the filters for the LAD detector on board LOFT

The Large Observatory for X-ray Timing (LOFT) was one of the M3 missions selected for the phase A study in the ESA's Cosmic Vision program. LOFT is designed to perform high-time-resolution X-ray observations of black holes and neutron stars. The main instrument on the LOFT payload is the Large Area Detector (LAD), a collimated experiment with a nominal effective area of ~10 m 2 @ 8 keV, and a spectral resolution of ~240 eV in the energy band 2-30 keV. These performances are achieved covering a large collecting area with more than 2000 large-area Silicon Drift Detectors (SDDs) each one coupled to a collimator based on lead-glass micro-channel plates. In order to reduce the thermal load onto the detectors, which are open to Sky, and to protect them from out of band radiation, optical-thermal filter will be mounted in front of the SDDs. Different options have been considered for the LAD filters for best compromise between high quantum efficiency and high mechanical robustness. We present the baseline design of the optical-thermal filters, show the nominal performances, and present preliminary test results performed during the phase A study.Comment: Proc. SPIE 9144, Space Telescopes and Instrumentation 2014: Ultraviolet to Gamma Ray, 91446

On the Propagation of Slip Fronts at Frictional Interfaces

The dynamic initiation of sliding at planar interfaces between deformable and rigid solids is studied with particular focus on the speed of the slip front. Recent experimental results showed a close relation between this speed and the local ratio of shear to normal stress measured before slip occurs (static stress ratio). Using a two-dimensional finite element model, we demonstrate, however, that fronts propagating in different directions do not have the same dynamics under similar stress conditions. A lack of correlation is also observed between accelerating and decelerating slip fronts. These effects cannot be entirely associated with static local stresses but call for a dynamic description. Considering a dynamic stress ratio (measured in front of the slip tip) instead of a static one reduces the above-mentioned inconsistencies. However, the effects of the direction and acceleration are still present. To overcome this we propose an energetic criterion that uniquely associates, independently on the direction of propagation and its acceleration, the slip front velocity with the relative rise of the energy density at the slip tip.Comment: 15 pages, 6 figure

The Role of Magnetic Field Dissipation in the Black Hole Candidate Sgr A*

The compact, nonthermal radio source Sgr A* at the Galactic Center appears to be coincident with a 2.6 million solar mass point-like object. Its energy source may be the release of gravitational energy as gas from the interstellar medium descends into its potential well. Simple attempts at calculating the spectrum and flux based on this picture have come close to the observations, yet have had difficulty in accounting for the low efficiency in this source. There now appear to be two reasons for this low conversion rate: (1) the plasma separates into two temperatures, with the protons attaining a significantly higher temperature than that of the radiating electrons, and (2) the magnetic field, B, is sub-equipartition, which reduces the magnetic bremsstrahlung emissivity, and therefore the overall power of Sgr A*. We investigate the latter with improvement over what has been attempted before: rather than calculating B based on a presumed model, we instead infer its distribution with radius empirically with the requirement that the resulting spectrum matches the observations. Our ansatz for B(r) is motivated in part by earlier calculations of the expected magnetic dissipation rate due to reconnection in a compressed flow. We find reasonable agreement with the observed spectrum of Sgr A* as long as its distribution consists of 3 primary components: an outer equipartition field, a roughly constant field at intermediate radii (~1000 Schwarzschild radii), and an inner dynamo (more or less within the last stable orbit for a non-rotating black hole) which increases B to about 100 Gauss. The latter component accounts for the observed sub-millimiter hump in this source.Comment: 33 pages including 2 figures; submitted to Ap

Low angular momentum flow model of Sgr A* activity

Sgr A* is the closest massive black hole and can be observed with the highest angular resolution. Nevertheless, our current understanding of the accretion process in this source is very poor. The inflow is almost certainly of low radiative efficiency and it is accompanied by a strong outflow and the flow is strongly variable but the details of the dynamics are unknown. Even the amount of angular momentum in the flow is an open question. Here we argue that low angular momentum scenario is better suited to explain the flow variability. We present a new hybrid model which describes such a flow and consists of an outer spherically symmetric Bondi flow and an inner axially symmetric flow described through MHD simulations. The assumed angular momentum of the matter is low, i.e. the corresponding circularization radius in the equatorial plane of the flow is just above the innermost stable circular orbit in pseudo-Newtonian potential. We compare the radiation spectrum from such a flow to the broad band observational data for Sgr A*.Comment: Proceedings of the AHAR 2008 Conference: The Universe under the Microscope; Astrophysics at High Angular Resolution, Bad Honef

An annotated bibliography of the research on marine organisms and environments at Christmas Island and the Cocos (Keeling) Islands

Christmas Island and the Cocos (Keeling) Islands represent a unique marine biodiversity hotspot because of the overlap between two major biogeographic provinces (Indian and Pacific Ocean) and the high proportion of endemic species. In this paper, we compile existing scientific literature pertaining to marine organisms and environments at these islands to determine the current state of knowledge and identify major knowledge gaps. In total, 1066 studies have been published, including 582 peer-reviewed journal articles (55% of all publications), 332 reports, 141 books or book chapters, and 11 theses. These studies extend back to 1697, but most (83%) are post-1970. Seabirds have been the most studied group (43% of all publications), followed by land crabs (13%). There has been very little research on plankton (<0.3% of all studies), despite the diversity of marine species that have larval stages (including land crabs) and the importance of plankton to ecosystem function. Most invertebrate groups have received little attention or have not been studied. The taxonomic bias in marine research at these islands means that most of the invertebrates are yet to be documented. Some of these groups (e.g., Polychaeta, Copepoda, and anchialine fauna) are known for their high degree of endemism and are likely to contain new species, thereby increasing the biodiversity value of the islands. That whole families (even phyla) are yet to be studied highlights the infancy in some areas of marine research and adding to species lists for unstudied or understudied groups is one priority that would increase the conservation importance of these islands. Without this knowledge, the ability to monitor, detect or predict anthropogenic impacts on marine species is severely restricted, and therefore limits the development of management strategies aimed at conserving the unique marine biodiversity of these islands. Further studies on functional processes and research related directly to impacts are also needed. Increasing studies that directly relate to management questions will provide guidance to managers charged with protecting the environment. Improved decision making in conservation management will occur through increased directed research and monitoring

Neutralino dark matter vs galaxy formation

Neutralino dark matter may be incompatible with current cold dark matter models with cuspy dark halos, because excessive synchrotron radiation may originate from neutralino annihilations close to the black hole at the galactic center.Comment: 6 pages, 3 figures, talk given at "Sources and detection of dark matter in the Universe", Marina del Rey, CA, February 23-25, 200

Local Rice Production Trend Analyses and Consumption in Benue State, Nigeria: 1980 – 2016

The research examined local rice production trends and factors inhibiting the consumption of local rice from 1980 to 2016 in Benue State. Primary data were collected with the aid of questionnaire in Benue State, while secondary data were obtained from Benue Agricultural and Rural Development Authority (BNARDA) in 2017. Multistage random sampling method was employed in selecting respondents. Primary data were collected from one hundred and fifty six (156) respondents. Descriptive statistics, Z – test, Growth model and Kendal’s coefficient of concordance were used for the analysis. The results revealed that from 1980 to 2016, a total of 9.5mt of local rice was produced in Benue State. The result also shows that the respondents were all married (99%), with household size of 1 - 10 persons (95%) and mean household size of about 8 persons. The result further indicated that majority of respondents’ attained tertiary school level. The result also shows that the respondents had low income (40.3%).  The mean quantity of local rice production was 257,333.06mt per year. The instantaneous growth trends of local rice production and price were 0.00122 and 0.01103, and compound growth rate as 3.72 and 3.76 respectively. The result also indicated that many of the respondents were above the age of 41 years (49%) with the mean age of 47 and all respondents male. The presence of stones, poor aroma, impure rice and broken grain were some of the factors inhibiting consumption of local rice in Benue State. The study recommended that the policies that focus on increasing growth rate of local rice in Benue State should be intensified. Breeders and Scientists should make effort in breeding rice with aroma. The processors of local rice should use modern processing mills like rice polisher and des-stoners to mill quality local rice that will be acceptable to consumers

Quantifying the increasing sensitivity of power systems to climate variability

Large quantities of weather-dependent renewable energy generation are expected in power systems under climate change mitigation policies, yet little attention has been given to the impact of long term climate variability. By combining state-ofthe-art multi-decadal meteorological records with a parsimonious representation of a power system, this study characterises the impact of year-to-year climate variability on multiple aspects of the power system of Great Britain (including coal, gas and nuclear generation), demonstrating why multi-decadal approaches are necessary. All aspects of the example system are impacted by inter-annual climate variability, with the impacts being most pronounced for baseload generation. The impacts of inter-annual climate variability increase in a 2025 wind-power scenario, with a 4-fold increase in the inter-annual range of operating hours for baseload such as nuclear. The impacts on peak load and peaking-plant are comparably small. Less than 10 years of power supply and demand data are shown to be insuffcient for providing robust power system planning guidance. This suggests renewable integration studies - widely used in policy, investment and system design - should adopt a more robust approach to climate characterisation