Polyhedral Analysis using Parametric Objectives

The abstract domain of polyhedra lies at the heart of many program analysis techniques. However, its operations can be expensive, precluding their application to polyhedra that involve many variables. This paper describes a new approach to computing polyhedral domain operations. The core of this approach is an algorithm to calculate variable elimination (projection) based on parametric linear programming. The algorithm enumerates only non-redundant inequalities of the projection space, hence permits anytime approximation of the output

Probing diffusion barrier integrity on porous silica low-k thin films using positron annihilation lifetime spectroscopy

The technique of positron annihilation lifetime spectroscopy (PALS) has been used to investigate the continuity and thermal stability of thin barrier layers designed to prevent Cu atom diffusion into porous silica, low-dielectric constant (k) films. Nanoglass™ K2.2-A10C (A10C), a porous organosilicate film, is determined to have interconnected pores with an average tubular-pore diameter of (6.9 ± 0.4) nm. Cu deposited directly on the A10C films is observed to diffuse into the porous structure. The minimum necessary barrier thickness for stable continuity of Ta and TaN layers deposited on A10C is determined by detecting the signal of positronium (Ps) escaping into vacuum. It is found that the 25 nm thick layers do not form continuous barriers. This is confirmed by the presence of holes observed in such films using a transmission electron microscope. Although 35 nm and 45 nm Ta and TaN layers perform effectively at room temperature as Ps barriers, only the Ta-capped samples are able to withstand heat treatments up to 500 °C500 °C without breakdown or penetration into the porous film. TaN interdiffusion into the silica pores is indicated by the reduction of the Ps lifetime after high annealing temperatures. The validity of using Ps diffusion to test barrier layers designed to inhibit Cu diffusion is discussed. The procedures to standardize the testing of barrier layer integrity and thermal stability using PALS are proposed. Extension to probing barrier layers in realistic vias and trenches should be straightforward. © 2001 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71187/2/JAPIAU-89-9-5138-1.pd

Tree-ring Isotopes Adjacent to Lake Superior Reveal Cold Winter Anomalies for the Great Lakes Region of North America

Tree-ring carbon isotope discrimination (Δ13C) and oxygen isotopes (δ18O) collected from white pine (Pinus strobus) trees adjacent to Lake Superior show potential to produce the first winter-specific paleoclimate reconstruction with inter-annual resolution for this region. Isotopic signatures from 1976 to 2015 were strongly linked to antecedent winter minimum temperatures (Tmin), Lake Superior peak ice cover, and regional to continental-scale atmospheric winter pressure variability including the North American Dipole. The immense thermal inertia of Lake Superior underlies the unique connection between winter conditions and tree-ring Δ13C and δ18O signals from the following growing season in trees located near the lake. By combining these signals, we demonstrate feasibility to reconstruct variability in Tmin, ice cover, and continental-scale atmospheric circulation patterns (r ≥ 0.65, P \u3c 0.001)

Using the Revised Cardiac Risk Index to predict major postoperative events for people with kidney failure : An external validation and update

Funding Information: T.G.H. is supported by a Kidney Research Scientist Core Education and National Training Program postdoctoral fellowship (cosponsored by the Kidney Foundation of Canada and Canadian Institutes of Health Research) and the Clinician Investigator Program at the University of Calgary. These funding sources had no role in study design, data collection, analysis, reporting, or the decision to submit for publication. Funding Information: Ethics Statement: We followed the Transparent Reporting of a Multivariable Prediction Model for Individual Prognosis or Diagnosis (TRIPOD) checklist19 for prediction-model validation (Supplemental Table S1) and were granted ethics approval by the University of Calgary and the University of Alberta.Preoperative risk-prediction tools that are used to predict risk of perioperative death and CV events, and are supported by North American guidelines, include the revised cardiac risk index (RCRI),5 the American College of Surgeons National Surgical Quality Improvement Program (ACS NSQIP) tool,6,7 and the National Surgical Quality Improvement Program Myocardial Infarction or Cardiac Arrest (NSQIP MICA) tool.8 The RCRI has been recommended over others for use in Canada for all adults over the age of 45 years, and for those aged 18-45 years with CV disease, who are undergoing elective, noncardiac surgery.3 The RCRI incorporates 6 criteria based on surgical and comorbidity characteristics of the patient and derives an estimated probability of postoperative myocardial infarction, cardiac arrest, or death.5 Additionally, the RCRI is used to guide perioperative decision-making.3The Alberta Kidney Disease Network database includes person-level linkages of administrative health data, laboratory data, prescription information, and kidney disease-specific data from the province of Alberta, Canada.17 Alberta has approximately 4.4 million residents, and with universal public health insurance, health data capture is near complete.17,18 From this database, we derived a retrospective cohort of adults with kidney failure who underwent ambulatory or inpatient surgery. We used this cohort to externally validate and examine the performance of the RCRI for this population. We followed the Transparent Reporting of a Multivariable Prediction Model for Individual Prognosis or Diagnosis (TRIPOD) checklist19 for prediction-model validation (Supplemental Table S1) and were granted ethics approval by the University of Calgary and the University of Alberta.Peer reviewedPublisher PD

Design and Modeling of Membrane-Based Evaporative Cooling Devices for Thermal Management of High Heat Fluxes

We present a high-heat-flux cooling device for advanced thermal management of electronics. The device incorporates nanoporous membranes supported on microchannels to enable thin-film evaporation. The underlying concept takes advantage of the capillary pressure generated by small pores in the membrane, and minimizes the viscous loss by reducing the membrane thickness. The heat transfer and fluid flow in the device were modeled to determine the effect of different geometric parameters. With the optimization of various parameters, the device can achieve a heat transfer coefficient in excess of 0.05 kW/cm²-K, while dissipating a heat flux of 1 kW/cm². When applied to power electronics, such as GaN high-electron-mobility transistors, this membrane-based evaporative cooling device can lower the near-junction temperature by more than 40 K compared with contemporary single-phase microchannel coolers

A novel pathway producing dimethylsulphide in bacteria is widespread in soil environments

The volatile compound dimethylsulphide (DMS) is important in climate regulation, the sulphur cycle and signalling to higher organisms. Microbial catabolism of the marine osmolyte dimethylsulphoniopropionate (DMSP) is thought to be the major biological process generating DMS. Here we report the discovery and characterisation of the first gene for DMSP-independent DMS production in any bacterium. This gene, mddA, encodes a methyltransferase that methylates methanethiol (MeSH) and generates DMS. MddA functions in many taxonomically diverse bacteria including sediment-dwelling pseudomonads, nitrogen-fixing bradyrhizobia and cyanobacteria, and mycobacteria, including the pathogen Mycobacterium tuberculosis. The mddA gene is present in metagenomes from varied environments, being particularly abundant in soil environments, where it is predicted to occur in up to 76% of bacteria. This novel pathway may significantly contribute to global DMS emissions, especially in terrestrial environments, and could represent a shift from the notion that DMSP is the only significant precursor of DMS

The Bolocam Galactic Plane Survey: Survey Description and Data Reduction

We present the Bolocam Galactic Plane Survey (BGPS), a 1.1 mm continuum survey at 33" effective resolution of 170 square degrees of the Galactic Plane visible from the northern hemisphere. The survey is contiguous over the range -10.5 < l < 90.5, |b| < 0.5 and encompasses 133 square degrees, including some extended regions |b| < 1.5. In addition to the contiguous region, four targeted regions in the outer Galaxy were observed: IC1396, a region towards the Perseus Arm, W3/4/5, and Gem OB1. The BGPS has detected approximately 8400 clumps over the entire area to a limiting non-uniform 1-sigma noise level in the range 11 to 53 mJy/beam in the inner Galaxy. The BGPS source catalog is presented in a companion paper (Rosolowsky et al. 2010). This paper details the survey observations and data reduction methods for the images. We discuss in detail the determination of astrometric and flux density calibration uncertainties and compare our results to the literature. Data processing algorithms that separate astronomical signals from time-variable atmospheric fluctuations in the data time-stream are presented. These algorithms reproduce the structure of the astronomical sky over a limited range of angular scales and produce artifacts in the vicinity of bright sources. Based on simulations, we find that extended emission on scales larger than about 5.9' is nearly completely attenuated (> 90%) and the linear scale at which the attenuation reaches 50% is 3.8'. Comparison with other millimeter-wave data sets implies a possible systematic offset in flux calibration, for which no cause has been discovered. This presentation serves as a companion and guide to the public data release through NASA's Infrared Processing and Analysis Center (IPAC) Infrared Science Archive (IRSA). New data releases will be provided through IPAC IRSA with any future improvements in the reduction.Comment: Accepted for publication in Astrophysical Journal Supplemen

A global assessment of the impact of climate change on water scarcity

This paper presents a global scale assessment of the impact of climate change on water scarcity. Patterns of climate change from 21 Global Climate Models (GCMs) under four SRES scenarios are applied to a global hydrological model to estimate water resources across 1339 watersheds. The Water Crowding Index (WCI) and the Water Stress Index (WSI) are used to calculate exposure to increases and decreases in global water scarcity due to climate change. 1.6 (WCI) and 2.4 (WSI) billion people are estimated to be currently living within watersheds exposed to water scarcity. Using the WCI, by 2050 under the A1B scenario, 0.5 to 3.1 billion people are exposed to an increase in water scarcity due to climate change (range across 21 GCMs). This represents a higher upper-estimate than previous assessments because scenarios are constructed from a wider range of GCMs. A substantial proportion of the uncertainty in the global-scale effect of climate change on water scarcity is due to uncertainty in the estimates for South Asia and East Asia. Sensitivity to the WCI and WSI thresholds that define water scarcity can be comparable to the sensitivity to climate change pattern. More of the world will see an increase in exposure to water scarcity than a decrease due to climate change but this is not consistent across all climate change patterns. Additionally, investigation of the effects of a set of prescribed global mean temperature change scenarios show rapid increases in water scarcity due to climate change across many regions of the globe, up to 2°C, followed by stabilisation to 4°C