Robustness of Boolean operations on subdivision-surface models

This work was presented in two parts at Dagstuhl seminar 08021. The two presentations described work in progress, including a ``backward bound\u27\u27 for a combined backward/forward error analysis for the problem mentioned in the title. We seek rigorous proofs that representations of computed sets, produced by algorithms to compute Boolean operations, are well formed, and that the algorithms are correct. Such proofs should eventually take account of the use of finite-precision arithmetic, although the proofs presented here do not. The representations studied are based on subdivision surfaces. Such representations are being used more and more frequently in place of trimmed NURBS representations, and the robustness analysis for these new representations is simpler than for trimmed NURBS. The particular subdivision-surface representation used is based on the Loop subdivision scheme. The analysis is broken into three parts. First, it is established that the input operands are well-formed two-dimensional manifolds without boundary. This can be done with existing methods. Secondly, we introduce the so-called ``limit mesh\u27\u27, and view the limit meshes corresponding to the input sets as defining an approximate problem in the sense of a backward error analysis. The presentations mentioned above described a proof of the corresponding error bound. The third part of the analysis corresponds to the ``forward bound\u27\u27: this remains to be done

Effects of past and current crop management on leaching losses, soil microbial community composition and activity

A lysimeter experiment was conducted to investigate the effect of past and current management practices on soil microbial biomass, activity and community composition. Intact monolith lysimeters were taken from sites of the same soil type that had been under long-term organic and conventional crop management. They were subjected to the same crop rotation and managed according to best organic and conventional practices. Mineral N loss was determined in leachates and soil samples taken before the experiment and after 30 months were analysed for biological soil properties, including microbial diversity. Results indicated that leaching losses were similar for all treatments and that crop was the main influence on microbial biomass composition and size, while microbial activity was determined by management history

Report of the National Science Foundation-Sponsored GeoEngineering Extreme Events Reconnaissance (GEER) Team

The L’Aquila earthquake occurred on April 6 2009 at 03:32:39 local time. The earthquake was located in the central Italy region of Abruzzo. Much of the damage occurred in the capital city of L’Aquila, a city of approximate population 73000, although many small villages in the surrounding regions were significantly damaged including Paganica, Castelnuovo, and Onna. Collapsed and damaged structures in L’Aquila included both older masonry buildings and relatively modern reinforced concrete structures. At the time of this writing, 307 people are known to have died from the earthquake, most in collapsed structures, making this the deadliest earthquake to strike Italy since the 1980 Irpinia earthquake. A number of reconnaissance teams were mobilized to the affected region in the weeks following the earthquake. The national institute of geophysics and volcanology (Istituto Nazionale di Geofisica e Vulcanologia, INGV) mobilized a team of geologists (EMERGEO Working Group) to look for evidence of surface rupture and other effects; some of their findings are discussed in this report. The GEER team was assembled to investigate geological, seismological, and geotechnical engineering aspects of the event. The international GEER team is comprised of members from Italy, Austria, Switzerland, Greece, and the United states. Team members were selected to provide needed expertise in geology, engineering geology, GIS applications, earthquake ground motions, and geotechnical earthquake engineering. The team includes individuals highly experienced in post-earthquake reconnaissance and relatively young professionals investigating their first earthquake. The GEER team did not focus on structural engineering or lifeline aspects of the event, which were investigated by an EERI team. The GEER and EERI activities were closely coordinated to optimize resources in the documentation of the valuable, perishable data associated with the earthquake effects. The GEER team employed a number of innovative technologies to facilitate effective reconnaissance. All teams mobilized for field work had a common GPS unit and laptop with a Google Earth (GE) GIS database activity maintained over the course of the work. The GE database was used to keep track of visited locations, but also contained maps of surface geology, locations of aftershocks, strong motion stations, and other information relevant to investigators in the field. Another valuable use of technology involved LIDAR mapping of a site having significant incidents of ground failure (Lake Sinizzo). This report presents the GEER findings. Following this introduction, Chapter 2 describes the geologic and tectonic setting, moment tensor solutions for the mainshock and several triggered events, analysis of aftershock patterns, and analysis of GPS and InSAR data. Included in Chapter 2 is a preliminary model of the ruptured fault. Chapter 3 describes the ground motions recorded during the mainshock by a digital instrument array. Metadata associated with the recordings is presented, trends in the recorded ground motions are presented, and preliminary comparisons to ground motion prediction equations are made. Chapter 4 presents damage patterns, both within L’Aquila and through comparisons of damage intensities in adjacent villages with similar construction. The results provide valuable insights into possible site effects on ground motion in regions where recordings are not available. Chapter 5 presents our findings on ground failure, defined as permanent ground deformations induced by the earthquake. Observed ground failure included several rockfalls, seismic compression of fill materials, and apparent strength loss of soil materials leading to inward movement of the banks of a lake. Chapter 6 reviews the performance of earth dams and earth retaining structures, both of which generally performed well

Diversity patterns of benthic bacterial communities along the salinity continuum of the Humber estuary (UK)

Sediments from intertidal mudflats are fluctuating environments that support very diverse microbialcommunities. The highly variable physicochemical conditions complicate the understanding of the environmental controls on diversity patterns in estuarine systems. This study investigated bacterial diversity and community composition in surface (0-1 cm) and subsurface (5-10 cm) sediments along the salinity gradient of the Humber estuary (UK) using amplicon sequencing of the 16S rRNA gene, and it correlates variations with environmental variables. The sediment depths sampled were selected based on the local remobilisation frequency patterns. In general, bacterial communities showed similar composition at the different sites and depths, with Proteobacteria being the most abundant phylum. Richness of operationally defined taxonomic units (OTUs) was uniform along the Microbial Diversity of the Humber Estuary salinity gradient. However, Hill numbers, as bacterial diversity measures, showed that the common and dominant OTUs exhibited a decreasing trend from the inner towards the outer estuary sites. Additionally, surface and subsurface bacterial communities were separated by NMDS analysis only in the mid and outer estuary samples, where redox transitions with depth in the sediment profile were more abrupt. Salinity, porewater ammonium concentrations and reduced iron concentrations were the subset of environmental factors that best correlated with community dissimilarities. The analysis of the regional diversity indicated that the dataset may include two potentially distinct communities. These are a near surface community that is the product of regular mixing and transport which is subjected to a wide range of salinity conditions, and thus contains decreasing numbers of common and dominant OTUs seawards, and a bacterial community indigenous to the more reducing subsurface sediments of the mid and outer mudflats of the Humber estuary

Study of the Cir X--1 Broad Band Spectrum at Orbital Phases Close to the Apoastron

We report on the results of a BeppoSAX (1.8--200 keV) observation of the peculiar X-ray binary source Circinus X--1 (Cir X--1) at the orbital phases between 0.61 and 0.63. We find that three components are needed to fit the broad band spectrum: a blackbody component, at a temperature of $\sim 0.6$ keV, a Comptonized component, with a seed-photon temperature of $\sim 1.2$ keV, electron temperature of $\sim 6$ keV and optical depth of $\sim 1.7$, and a power-law component dominating the spectrum at energies higher than 20 keV. We interpret the blackbody as the emission from the accretion disk, while the Comptonized component probably comes from a corona surrounding the inner part of the system. This spectrum is different from that observed at the periastron (Iaria et al. 2001a) because of the presence of the blackbody component. We discuss the implications of this difference and the presence of the power-law component.Comment: 15 pages, 6 figures, accepted by Ap

Paid employment and common mental disorders in 50–64-year olds: analysis of three cross-sectional nationally representative survey samples in 1993, 2000 and 2007

Associations between employment status and mental health are well recognised, but evidence is sparse on the relationship between paid employment and mental health in the years running up to statutory retirement ages using robust mental health measures. In addition, there has been no investigation into the stability over time in this relationship: an important consideration if survey findings are used to inform future policy. The aim of this study is to investigate the association between employment status and common mental disorder (CMD) in 50–64-year old residents in England and its stability over time, taking advantage of three national mental health surveys carried out over a 14-year period. Data were analysed from the British National Surveys of Psychiatric Morbidity of 1993, 2000 and 2007. Paid employment status was the primary exposure of interest and CMD the primary outcome – both ascertained identically in all three surveys (CMD from the revised Clinical Interview Schedule). Multivariable logistic regression models were used. The prevalence of CMD was higher in people not in paid employment across all survey years; however, this association was only present for non-employment related to poor health as an outcome and was not apparent in those citing other reasons for non-employment. Odds ratios for the association between non-employment due to ill health and CMD were 3.05 in 1993, 3.56 in 2000, and 2.80 in 2007, after adjustment for age, gender, marital status, education, social class, housing tenure, financial difficulties, smoking status, recent physical health consultation and activities of daily living impairment. The prevalence of CMD was higher in people not in paid employment for health reasons, but was not associated with non-employment for other reasons. Associations had been relatively stable in strength from 1993 to 2007 in those three cross-sectional nationally representative samples

Leaching behaviour of co-disposed steel making wastes: effects of aeration on leachate chemistry and vanadium mobilisation

Steelmaking wastes stored in landfill, such as slag and spent refractory liners, are often enriched in toxic trace metals (including V). These may become mobile in highly alkaline leachate generated during weathering. Fresh steelmaking waste was characterised using XRD, XRF, and SEM-EDX. Batch leaching tests were performed under aerated, air-excluded and acidified conditions to determine the impact of atmospheric CO2 and acid addition on leachate chemistry. Phases commonly associated with slag including dicalcium silicate, dicalcium aluminoferrite, a wüstite-like solid solution and free lime were identified, as well as a second group of phases including periclase, corundum and graphite which are representative of refractory liners. During air-excluded leaching, dissolution of free lime and dicalcium silicate results in a high pH, high Ca leachate in which the V concentration is low due to the constraint imposed by Ca3(VO4)2 solubility limits. Under aerated conditions, carbonation lowers the leachate pH and provides a sink for aqueous Ca, allowing higher concentrations of V to accumulate. Below pH 10, leachate is dominated by periclase dissolution and secondary phases including monohydrocalcite and dolomite are precipitated. Storage of waste under saturated conditions that exclude atmospheric CO2 would therefore provide the optimal environment to minimise V leaching during weathering

Disordered loops in the two-dimensional antiferromagnetic spin-fermion model

The spin-fermion model has long been used to describe the quantum-critical behavior of 2d electron systems near an antiferromagnetic (AFM) instability. Recently, the standard procedure to integrate out the fermions to obtain an effective action for spin waves has been questioned in the clean case. We show that in the presence of disorder, the single fermion loops display two crossover scales: upon lowering the energy, the singularities of the clean fermionic loops are first cut off, but below a second scale new singularities arise that lead again to marginal scaling. In addition, impurity lines between different fermion loops generate new relevant couplings which dominate at low energies. We outline a non-linear sigma model formulation of the single-loop problem, which allows to control the higher singularities and provides an effective model in terms of low-energy diffusive as well as spin modes.Comment: 22 pages, 8 figure