Effects of the Charge-Dipole Interaction on the Coagulation of Fractal Aggregates

A numerical model with broad applications to complex (dusty) plasmas is presented. The self-consistent N-body code allows simulation of the coagulation of fractal aggregates, including the charge-dipole interaction of the clusters due to the spatial arrangement of charge on the aggregate. It is shown that not only does a population of oppositely charged particles increase the coagulation rate, the inclusion of the charge-dipole interaction of the aggregates as well as the electric dipole potential of the dust ensemble decreases the gelation time by a factor of up to twenty. It is further shown that these interactions can also stimulate the onset of gelation, or "runaway growth," even in a population of particles charged to a monopotential where previously it was believed that like-charged grains would inhibit coagulation. Gelation is observed to occur due to the formation of high-mass aggregates with fractal dimensions greater than two which act as seeds for runaway growth.Comment: 9 page

Resonantly enhanced pair production in a simple diatomic model

A new mechanism for the production of electron-positron pairs from the interaction of a laser field and a fully stripped diatomic molecule in the tunneling regime is presented. When the laser field is turned off, the Dirac operator has resonances in both the positive and the negative energy continua while bound states are in the mass gap. When this system is immersed in a strong laser field, the resonances move in the complex energy plane: the negative energy resonances are pushed to higher energies while the bound states are Stark shifted. It is argued here that there is a pair production enhancement at the crossing of resonances by looking at a simple 1-D model: the nuclei are modeled simply by Dirac delta potential wells while the laser field is assumed to be static and of finite spatial extent. The average rate for the number of electron-positron pairs produced is evaluated and the results are compared to the single nucleus and to the free cases. It is shown that positrons are produced by the Resonantly Enhanced Pair Production (REPP) mechanism, which is analogous to the resonantly enhanced ionization of molecular physics. This phenomenon could be used to increase the number of pairs produced at low field strength, allowing the study of the Dirac vacuum.Comment: 11 pages, 4 figure

Control of drying shrinkage of magnesium silicate hydrate gel cements

Cracks were observed when the magnesium silicate hydrate gel cement (prepared by 40% MgO/60% silica fume) was dried. This drying cracking is believed to be caused when unbound water evaporates from the binder. The shrinkage upon forced drying to 200 °C of mortars made up from a reactive magnesium oxide, silica fume and sand was measured using dilatometry. The magnitude of the drying shrinkage was found to decrease when more sand or less water was added to the mortars and can be as low as 0.16% for a mortar containing 60 wt% sand and a water to cement ratio of 0.5, which is of a similar order of magnitude as observed in Portland cement based mortars and concretes. A simple geometrical interpretation based on packing of the particles in the mortar can explain the observed drying shrinkages and based on this analysis the drying shrinkage of the hydration products at zero added solid is estimated to be 7.3% after 7 days of curing

Excitonic Effects and Optical Spectra of Single-Walled Carbon Nanotubes

Many-electron effects often dramatically modify the properties of reduced dimensional systems. We report calculations, based on an many-electron Green's function approach, of electron-hole interaction effects on the optical spectra of small-diameter single-walled carbon nanotubes. Excitonic effects qualitatively alter the optical spectra of both semiconducting and metallic tubes. Excitons are bound by ~ 1 eV in the semiconducting (8,0) tube and by ~ 100 meV in the metallic (3,3) tube. These large many-electron effects explain the discrepancies between previous theories and experiments.Comment: 6 pages, 3 figures, 2 table

Instability of Glucocorticoid Metabolites in Coyote Scats: Implications for Field Sampling

Studying physiologic stress responses can assist in understanding the welfare of animals. One method of measuring the physiologic stress response is evaluating concentrations of glucocorticoid metabolites in feces. Previously, using an adrenocorticotropic hormone challenge, we found fecal glucocorticoid metabolite levels were a reliable indicator of physiologic stress response in coyotes (Canis latrans). We determine whether glucocorticoid metabolite concentrations remain stable when collecting feces over a 2-week period, a timeframe commonly used in scat surveys for wild canids. We collected feces from 6 captive coyotes maintained at the U.S. Department of Agriculture, Wildlife Services, National Wildlife Research Center, Predator Research Facility near Millville, Utah, USA, and exposed them to the environment for 13 days during summer (August 26 to September 8, 2011) and winter (January 11–24, 2012). Every 2 days, we collected a sub-sample from each individual scat and then quantified the concentration of fecal glucocorticoid metabolites. We found changes in fecal glucocorticoid metabolite concentrations over the 13-day period, with values increasing 45–79% from day 1 to day 3 of sampling. There was also high variation in fecal glucocorticoid metabolites among individuals over time. We provide evidence that fecal samples collected in the field even 3 days after defecation will not provide reliable measures of fecal glucocorticoid metabolites and thus recommend using only fresh fecal samples. We also recommend that, due to high individual variability in fecal glucocorticoid metabolites, a large number of individuals be sampled when a population-wide assessment is desired

Program evaluation : large-scale and small-scale studies

It is increasingly incumbent upon ministries of education to build evaluation into new programs – especially those programs where substantial amounts of money are being spent. Each new program will usually be accompanied by questions about the impact and effectiveness of the program. For example, ministries may direct increased resources to classrooms and schools. Question: “Have these resources gone where desired and have the increased resources had an effect on student achievement?” Or, a new curriculum may have been introduced. Question: “How was the curriculum introduced and what problems occurred with its implementation?” Or, a new teacher in-service program may have been developed. Question: “Did the teachers learn what they were meant to learn? And, if so, did what the teachers learn have an effect on what students learned in terms of achievement, attitudes, and/or behaviour?” These are some examples for the case of general school education, but the same is true for new programs in pre-schools, in schools for the handicapped, in vocational education, and so on. All education programs need to include an evaluation component if their success is to be determined, and if weaknesses in the programs are to be identified and corrected. When introducing new education programs it is not easy to assess whether they have had an effect on student learning. The kind of research design needed to get at the true cause of changes in student learning will vary according to the type of learning specified in the program goals. At the same time, however, there are some similarities in terms of sound and defensible evaluation designs. For example, it is always important that some measure of student learning be made at the beginning of a program. Education programs cannot be said to be effective if there are no measurable improvements in student learning over time. Similarly, some comparison group, or groups, of teachers and students should be included in the study. If there are measurable changes in student learning over time, but the magnitude of the changes is not different from changes that occur in non-program students, then the program cannot be said to be effective. This booklet is about small-scale and large-scale program evaluation studies. In many cases, both small- and large-scale studies are needed within any one evaluation project. In this booklet the authors argue that there is a need for both kinds of studies – provided that they are conducted according to scientific standards

Genome-Wide Identification of Pseudomonas aeruginosa Virulence-Related Genes Using a Caenorhabditis elegans Infection Model

Pseudomonas aeruginosa strain PA14 is an opportunistic human pathogen capable of infecting a wide range of organisms including the nematode Caenorhabditis elegans. We used a non-redundant transposon mutant library consisting of 5,850 clones corresponding to 75% of the total and approximately 80% of the non-essential PA14 ORFs to carry out a genome-wide screen for attenuation of PA14 virulence in C. elegans. We defined a functionally diverse 180 mutant set (representing 170 unique genes) necessary for normal levels of virulence that included both known and novel virulence factors. Seven previously uncharacterized virulence genes (ABC transporters PchH and PchI, aminopeptidase PepP, ATPase/molecular chaperone ClpA, cold shock domain protein PA0456, putative enoyl-CoA hydratase/isomerase PA0745, and putative transcriptional regulator PA14_27700) were characterized with respect to pigment production and motility and all but one of these mutants exhibited pleiotropic defects in addition to their avirulent phenotype. We examined the collection of genes required for normal levels of PA14 virulence with respect to occurrence in P. aeruginosa strain-specific genomic regions, location on putative and known genomic islands, and phylogenetic distribution across prokaryotes. Genes predominantly contributing to virulence in C. elegans showed neither a bias for strain-specific regions of the P. aeruginosa genome nor for putatively horizontally transferred genomic islands. Instead, within the collection of virulence-related PA14 genes, there was an overrepresentation of genes with a broad phylogenetic distribution that also occur with high frequency in many prokaryotic clades, suggesting that in aggregate the genes required for PA14 virulence in C. elegans are biased towards evolutionarily conserved genes

Models and experimental results from the wide aperture Nb-Ti magnets for the LHC upgrade

MQXC is a Nb-Ti quadrupole designed to meet the accelerator quality requirements needed for the phase-1 LHC upgrade, now superseded by the high luminosity upgrade foreseen in 2021. The 2-m-long model magnet was tested at room temperature and 1.9 K. The technology developed for this magnet is relevant for other magnets currently under development for the high-luminosity upgrade, namely D1 (at KEK) and the large aperture twin quadrupole Q4 (at CEA). In this paper we present MQXC test results, some of the specialized heat extraction features, spot heaters, temperature sensor mounting and voltage tap development for the special open cable insulation. We look at some problem solving with noisy signals, give an overview of electrical testing, look at how we calculate the coil resistance during at quench and show that the heaters are not working We describe the quench signals and its timing, the development of the quench heaters and give an explanation of an Excel quench calculation and its comparison including the good agreement with the MQXC test results. We propose an improvement to the magnet circuit design to reduce voltage to ground values by factor 2. The program is then used to predict quench Hot-Spot and Voltages values for the D1 dipole and the Q4 quadrupole.Comment: 8 pages, Contribution to WAMSDO 2013: Workshop on Accelerator Magnet, Superconductor, Design and Optimization; 15 - 16 Jan 2013, CERN, Geneva, Switzerlan

Anomalous Quasiparticle Lifetime in Graphite: Band Structure Effects

We report ab initio calculation of quasiparticle lifetimes in graphite, as determined from the imaginary part of the self-energy operator within the GW aproximation. The inverse lifetime in the energy range from 0.5 to 3.5 eV above the Fermi level presents significant deviations from the quadratic behavior naively expected from Fermi liquid theory. The deviations are explained in terms of the unique features of the band structure of this material. We also discuss the experimental results from different groups and make some predictions for future experiments.Comment: 4 pages, 4 figures, submitted PR

Hyporesponsiveness to social and nonsocial sensory stimuli in children with autism, children with developmental delays, and typically developing children

This cross-sectional study seeks to (a) describe developmental correlates of sensory hyporesponsiveness to social and nonsocial stimuli, (b) determine whether hyporesponsiveness is generalized across contexts in children with autism relative to controls, and (c) test the associations between hyporesponsiveness and social communication outcomes. Three groups of children ages 11-105 months (N = 178; autism = 63, developmental delay = 47, typical development = 68) are given developmental and sensory measures including a behavioral orienting task (the Sensory Processing Assessment). Lab measures are significantly correlated with parental reports of sensory hyporesponsiveness. Censored regression models show that hyporesponsiveness decreased across groups with increasing mental age (MA). Group differences are significant but depend upon two-way interactions with MA and context (social and nonsocial). At a very young MA (e.g., 6 months), the autism group demonstrates more hyporesponsiveness to social and nonsocial stimuli (with larger effects for social) than developmental delay and typically developing groups, but at an older MA (e.g., 60 months) there are no significant differences. Hyporesponsiveness to social and nonsocial stimuli predicts lower levels of joint attention and language in children with autism. Generalized processes in attention disengagement and behavioral orienting may have relevance for identifying early risk factors of autism and for facilitating learning across contexts to support the development of joint attention and language