Showing papers by "University of Victoria published in 2008"

The Aquarius Project: the subhaloes of galactic haloes

Abstract: We have performed the largest ever particle simulation of a Milky Way sized dark matter halo, and present the most comprehensive convergence study for an individual dark matter halo carried out thus far We have also simulated a sample of six ultrahighly resolved Milky Way sized haloes, allowing us to estimate the halo-to-halo scatter in substructure statistics In our largest simulation, we resolve nearly 300 000 gravitationally bound subhaloes within the virialized region of the halo Simulations of the same object differing in mass resolution by factors of up to 1800 accurately reproduce the largest subhaloes with the same mass, maximum circular velocity and position, and yield good convergence for the abundance and internal properties of dark matter substructures We detect up to four generations of subhaloes within subhaloes, but contrary to recent claims, we find less substructure in subhaloes than in the main halo when regions of equal mean overdensity are compared The overall substructure mass fraction is much lower in subhaloes than in the main halo Extrapolating the main halo's subhalo mass spectrum down to an Earth mass, we predict the mass fraction in substructure to be well below 3 per cent within 100 kpc, and to be below 01 per cent within the solar circle The inner density profiles of subhaloes show no sign of converging to a fixed asymptotic slope and are well fitted by gently curving profiles of Einasto form The mean concentrations of isolated haloes are accurately described by the fitting formula of Neto et al down to maximum circular velocities of 15 km s(-1), an extrapolation over some five orders of magnitude in mass However, at equal maximum circular velocity, subhaloes are more concentrated than field haloes, with a characteristic density that is typically similar to 26 times larger and increases with decreasing distance from halo centre

The Aquarius Project: the subhalos of galactic halos

Abstract: We have performed the largest ever particle simulation of a Milky Way-sized dark matter halo, and present the most comprehensive convergence study for an individual dark matter halo carried out thus far. We have also simulated a sample of 6 ultra-highly resolved Milky-way sized halos, allowing us to estimate the halo-to-halo scatter in substructure statistics. In our largest simulation, we resolve nearly 300,000 gravitationally bound subhalos within the virialized region of the halo. Simulations of the same object differing in mass resolution by factors up to 1800 accurately reproduce the largest subhalos with the same mass, maximum circular velocity and position, and yield good convergence for the abundance and internal properties of dark matter substructures. We detect up to four generations of subhalos within subhalos, but contrary to recent claims, we find less substructure in subhalos than in the main halo when regions of equal mean overdensity are compared. The overall substructure mass fraction is much lower in subhalos than in the main halo. Extrapolating the main halo's subhalo mass spectrum down to an Earth mass, we predict the mass fraction in substructure to be well below 3% within 100 kpc, and to be below 0.1% within the Solar Circle. The inner density profiles of subhalos show no sign of converging to a fixed asymptotic slope and are well fit by gently curving profiles of Einasto form. The mean concentrations of isolated halos are accurately described by the fitting formula of Neto et al. down to maximum circular velocities of 1.5 km/s, an extrapolation over some 5 orders of magnitude in mass. However, at equal maximum circular velocity, subhalos are more concentrated than field halos, with a characteristic density that is typically ~2.6 times larger and increases towards the halo centre.

Metallicity Calibrations and the Mass-Metallicity Relation for Star-forming Galaxies

Abstract: We investigate the effect of metallicity calibrations, AGN classification, and aperture covering fraction on the local mass-metallicity relation using 27,730 star-forming galaxies from the Sloan Digital Sky Survey (SDSS) Data Release 4. We analyse the SDSS mass-metallicity relation with 10 metallicity calibrations, including theoretical and empirical methods. We show that the choice of metallicity calibration has a significant effect on the shape and y-intercept(12+log(O/H)) of the mass-metallicity relation. The absolute metallicity scale (y-intercept) varies up to �[log(O/H)] = 0.7 dex, depending on the calibration used, and the change in shape is substantial. These results indicate that it is critical to use the same metallicity calibration when comparing different luminosity-metallicity or mass-metallicity relations. We present new metallicity conversions that allow metallicities that have been derived using different strong-line calibrations to be converted to the same base calibration. These conversions facilitate comparisons between different samples, particularly comparisons between galaxies at different redshifts for which different suites of emission-lines are available. Our new conversions successfully remove the large 0.7 dex discrepancies between the metallicity calibrations, and we reach agreement in the mass-metallicity relation to within 0.03 dex on average. We investigate the effect of AGN classification and aperture covering fraction on the mass-metallicity relation. We find that different AGN classification methods have negligible effect on the SDSS MZ-relation. We compare the SDSS mass-metallicity relation with nuclear and global relations from the Nearby Field Galaxy Survey (NFGS). The turn over of the mass-metallicity relation at M∗ ∼ 10 10 M⊙ depends on aperture covering fraction. We find that a lower redshift limit of z 10 10 M⊙) galaxies. Subject headings: galaxies: starburst—galaxies: abundances—galaxies: fundamental parameters— galaxies: spiral—techniques: spectroscopic

Selecting Empirical Methods for Software Engineering Research

Abstract: Selecting a research method for empirical software engineering research is problematic because the benefits and challenges to using each method are not yet well catalogued. Therefore, this chapter describes a number of empirical methods available. It examines the goals of each and analyzes the types of questions each best addresses. Theoretical stances behind the methods, practical considerations in the application of the methods and data collection are also briefly reviewed. Taken together, this information provides a suitable basis for both understand- ing and selecting from the variety of methods applicable to empirical software engineering.

Impacts of atmospheric anthropogenic nitrogen on the open ocean.

Abstract: Increasing quantities of atmospheric anthropogenic fixed nitrogen entering the open ocean could account for up to about a third of the ocean's external (nonrecycled) nitrogen supply and up to 3% of the annual new marine biological production, 0.3 petagram of carbon per year. This input could account for the production of up to 1.6 teragrams of nitrous oxide (N2O) per year. Although 10% of the ocean's drawdown of atmospheric anthropogenic carbon dioxide may result from this atmospheric nitrogen fertilization, leading to a decrease in radiative forcing, up to about two-thirds of this amount may be offset by the increase in N2O emissions. The effects of increasing atmospheric nitrogen deposition are expected to continue to grow in the future.

The 1981 socioeconomic index for occupations in Canada

Abstract: Nous presentons ici un nouvel index socio-economique des occupations, base sur le recensement de 1981. Il est generalement admis que l'occupation est le meilleur indicateur de statut socio-economique, mais l'importance accordee au prestige, au revenu et a leducation dans la hierarchisation des occupations demeure matiere a debats. Pour cet index, nous avons decide d'accorder un poids egal aux niveaux d’education et de revenu, en rant que composantes additives du statut socio-economique. Aussi, pour fins de continuite, nous avons calibre l ‘index sur la base de l echelle Pineo-Porter de prestige. This article presents a socioeconomic index for the total Canadian labour force, based on 1981 Census data. It also reviews the problems and criticisms of indexes of this kind, and attempts to specify the meaning of socioeconomic scales and the uses to which they may be legitimately put. The present index is most applicable in situations where access to data is limited to occupational titles and where one desires a unidimensional contextual indicator which locates individuals in the Canadian occupational structure at a given point in time. Sociological analysis of structured inequality, however, may be advanced most effectively if, where feasible, a full range of methodological options is considered, including the assessment of conditions on the level of the individual, the use of other contextual levels such as the workplace, and the investigation of occupation, gender and class as interdependent historical products.

What makes a good bug report

Abstract: In software development, bug reports provide crucial information to developers. However, these reports widely differ in their quality. We conducted a survey among developers and users of APACHE, ECLIPSE, and MOZILLA to find out what makes a good bug report.The analysis of the 466 responses revealed an information mismatch between what developers need and what users supply. Most developers consider steps to reproduce, stack traces, and test cases as helpful, which are at the same time most difficult to provide for users. Such insight is helpful to design new bug tracking tools that guide users at collecting and providing more helpful information.Our CUEZILLA prototype is such a tool and measures the quality of new bug reports; it also recommends which elements should be added to improve the quality. We trained CUEZILLA on a sample of 289 bug reports, rated by developers as part of the survey. In our experiments, CUEZILLA was able to predict the quality of 31--48% of bug reports accurately.

An approach to detecting duplicate bug reports using natural language and execution information

Abstract: An open source project typically maintains an open bug repository so that bug reports from all over the world can be gathered. When a new bug report is submitted to the repository, a person, called a triager, examines whether it is a duplicate of an existing bug report. If it is, the triager marks it as duplicate and the bug report is removed from consideration for further work. In the literature, there are approaches exploiting only natural language information to detect duplicate bug reports. In this paper we present a new approach that further involves execution information. In our approach, when a new bug report arrives, its natural language information and execution information are compared with those of the existing bug reports. Then, a small number of existing bug reports are suggested to the triager as the most similar bug reports to the new bug report. Finally, the triager examines the suggested bug reports to determine whether the new bug report duplicates an existing bug report. We calibrated our approach on a subset of the Eclipse bug repository and evaluated our approach on a subset of the Firefox bug repository. The experimental results show that our approach can detect 67%-93% of duplicate bug reports in the Firefox bug repository, compared to 43%-72% using natural language information alone.

Did Cooling Oceans Trigger Ordovician Biodiversification? Evidence from Conodont Thermometry

Abstract: The Ordovician Period, long considered a supergreenhouse state, saw one of the greatest radiations of life in Earth9s history. Previous temperature estimates of up to ∼70°C have spawned controversial speculation that the oxygen isotopic composition of seawater must have evolved over geological time. We present a very different global climate record determined by ion microprobe oxygen isotope analyses of Early Ordovician–Silurian conodonts. This record shows a steady cooling trend through the Early Ordovician reaching modern equatorial temperatures that were sustained throughout the Middle and Late Ordovician. This favorable climate regime implies not only that the oxygen isotopic composition of Ordovician seawater was similar to that of today, but also that climate played an overarching role in promoting the unprecedented increases in biodiversity that characterized this period.

The feedback correct-related positivity: sensitivity of the event-related brain potential to unexpected positive feedback.

Abstract: The N200 and the feedback error-related negativity (fERN) are two components of the event-related brain potential (ERP) that share similar scalp distributions, time courses, morphologies, and functional dependencies, which raises the question as to whether they are actually the same phenomenon. To investigate this issue, we recorded the ERP from participants engaged in two tasks that independently elicited the N200 and fERN. Our results indicate that they are, in fact, the same ERP component and further suggest that positive feedback elicits a positive-going deflection in the time range of the fERN. Taken together, these results indicate that negative feedback elicits a common N200 and that modulation of fERN amplitude results from the superposition on correct trials of a positive-going deflection that we term the feedback correct-related positivity.

A new generation of sensors based on extraordinary optical transmission.

Abstract: Plasmonic-based chemical sensing technologies play a key role in chemical, biochemical, and biomedical research, but basic research in this area is still attracting interest. Researchers would like to develop new types of plasmonic nanostructures that can improve the analytical figures of merit, such as detection limits, sensitivity, selectivity, and dynamic range, relative to the commercial systems. They are also tackling issues such as cost, reproducibility, and multiplexing with the goal of providing the best plasmonic-based platform for chemical analysis. In this Account, we will describe recent advances in the optical and spectroscopic properties of nanohole arrays in thin gold films and their applications for chemical sensing. These nanostructures support the unusual phenomenon of “extraordinary optical transmission” (EOT), that is, they are more transparent at certain wavelengths than expected by the classical aperture theory. The EOT is a consequence of surface plasmon (SP) excitations; hence, the...

The redshift dependence of the structure of massive Λ cold dark matter haloes

Abstract: We use two very large cosmological simulations to study how the density profiles of relaxedCDM dark halos depend on redshift and on halo mass. We confirm that these profiles deviate slightly but systematically from the NFW form and are better approximated by the empirical formula, dlog ρ/dlog r ∝ r � , first used by Einasto to fit star counts in the Milky Way. The best-fit value of the additional shape parameter, α, increases gradually with mass, from α ∼ 0.16 for present-day galaxy halos to α ∼ 0.3 for the rarest and most massive clusters. Halo concentrations depend only weakly on mass at z = 0, and this dependence weakens further at earlier times. At z ∼ 3 the average concentration of relaxed halos does not vary appreciably over the mass range accessible to our simulations (M ∼3×10 11 h −1 M⊙). Furthermore, in our biggest simulation, the average concentration of the most massive, relaxed halos is constant at h c200i ∼ 3.5 to 4 for 0 ≤ z ≤ 3. These results agree well with those of Zhao et al (2003b) and support the idea that halo densities reflect the density of the universe at the time they formed, as proposed by Navarro, Frenk & White (1997). With their original parameters, the NFW prescription overpredicts halo concentrations at high redshift. This shortcoming can be reduced by modifying the definition of halo formation time, although the evolution of the concentrations of Milky Way mass halos is still not reproduced well. In contrast, the much-used revisions of the NFW prescription by Bullock et al. (2001) and Eke, Navarro & Steinmetz (2001) predict a steeper drop in concentration at the highest masses and stronger evolution with redshift than are compatible with our numerical data. Modifying the parameters of these models can reduce the discrepancy at high masses, but the overly rapid redshift evolution remains. These results have important implications for currently planned surveys of distant clusters.

The amphioxus genome illuminates vertebrate origins and cephalochordate biology

Abstract: Cephalochordates, urochordates, and vertebrates evolved from a common ancestor over 520 million years ago To improve our understanding of chordate evolution and the origin of vertebrates, we intensively searched for particular genes, gene families, and conserved noncoding elements in the sequenced genome of the cephalochordate Branchiostoma floridae, commonly called amphioxus or lancelets Special attention was given to homeobox genes, opsin genes, genes involved in neural crest development, nuclear receptor genes, genes encoding components of the endocrine and immune systems, and conserved cis-regulatory enhancers The amphioxus genome contains a basic set of chordate genes involved in development and cell signaling, including a fifteenth Hox gene This set includes many genes that were co-opted in vertebrates for new roles in neural crest development and adaptive immunity However, where amphioxus has a single gene, vertebrates often have two, three, or four paralogs derived from two whole-genome duplication events In addition, several transcriptional enhancers are conserved between amphioxus and vertebrates--a very wide phylogenetic distance In contrast, urochordate genomes have lost many genes, including a diversity of homeobox families and genes involved in steroid hormone function The amphioxus genome also exhibits derived features, including duplications of opsins and genes proposed to function in innate immunity and endocrine systems Our results indicate that the amphioxus genome is elemental to an understanding of the biology and evolution of nonchordate deuterostomes, invertebrate chordates, and vertebrates

Galaxy pairs in the sloan digital sky survey. i. star formation, active galactic nucleus fraction, and the luminosity/mass-metallicity relation

Abstract: We present a sample of 1716 galaxies with companions within Δv <500 km s–1, rp < 80 h–1 70 kpc and stellar mass ratio 0.1 < M 1/M 2 < 10 from the Sloan Digital Sky Survey Data Release 4. The galaxy pairs are selected from the Main Galaxy Sample using stringent and well-understood criteria for redshift, spectral quality, available stellar masses, and metallicities. In agreement with previous studies, we find an enhancement in the star-formation rate (SFR) of galaxy pairs at projected separations <30-40 h–1 70 kpc. In addition, we find that this enhancement is highest (and extends to the greatest separations) for galaxies of approximately equal mass, the so-called major pairs. However, SFR enhancement can still be detected for a sample of galaxy pairs whose masses are within a factor of 10 of each other. Based on these results, we define a sample of close pairs (Δv <500 km s–1, rp < 30 h–1 70 kpc, and 0.1 < M 1/M 2 < 10) which we use to investigate interaction-induced effects in the luminosity-metallicity (LZ) relation. In agreement with the one previous study of the LZ relation in paired galaxies, we find an offset to lower metallicities (by ~0.1 dex) for a given luminosity for galaxies in pairs compared to the control sample. We also present the first mass-metallicity (MZ) relation comparison between paired galaxies and the field and again find an offset to lower metallicities (by ~0.05 dex) for a given mass. The smaller offset in the MZ relation indicates that both higher luminosities and lower metallicities may contribute to the shift of pairs relative to the control in the LZ relation. We show that the offset in the LZ relation depends on galaxy half-light radius, rh . Galaxies with rh 3 h–1 70 kpc and with a close companion show a 0.05-0.1 dex downward offset in metallicity compared to control galaxies of the same size. Larger galaxies do not show this offset and have LZ and MZ relations consistent with the control sample. We investigate the physical impetus behind this empirical dependence on rh and consider the galaxy's dynamical time and bulge fractions as possible causes. We conclude that the former is unlikely to be a fundamental driver of the offset in the LZ relation for paired galaxies, but that bulge fraction may play a role. Finally, we study the active galactic nucleus (AGN) fraction in both the pair and control sample and find that whilst selecting galaxies in different cuts of color and asymmetry yields different AGN fractions, the fraction for pairs and the control sample are consistent for a given set of selection criteria. This indicates that if AGNs are ignited as a result of interactions, this activity begins later than the close pairs stage (i.e. once the merger is complete).

Weak Gravitational Lensing and Its Cosmological Applications

Abstract: Weak gravitational lensing is a unique probe of the dark side of the universe: It provides a direct way to map the distribution of dark matter around galaxies and clusters of galaxies as well as on cosmological scales. Furthermore, the measurement of the weak lensing–induced distortions of the shapes of distant galaxies is a potentially powerful probe of dark energy. In this review we discuss how this challenging measurement is made and interpreted. We describe the various systematic effects that can hamper progress and how they may be overcome. We review some of the recent results in weak lensing by galaxies, galaxy clusters, and cosmic shear and discuss the prospects for dark energy measurements from planned surveys.

The Evolution of Galaxy Mergers and Morphology at z<1.2 in the Extended Groth Strip

Abstract: We present the quantitative rest-frame B morphological evolution and galaxy merger fraction at 0.2 1011 L☉ are disk galaxies, and only ~15% are classified as major merger candidates. Edge-on and dusty disk galaxies (Sb-Ir) are almost a third of the red sequence at z ~ 1.1, while E/S0/Sa make up over 90% of the red sequence at z ~ 0.3. Approximately 2% of our full sample are red mergers. We conclude (1) the merger rate does not evolve strongly between 0.2 < z < 1.2; (2) the decrease in the volume-averaged star formation rate density since z ~ 1 is a result of declining star formation in disk galaxies rather than a disappearing population of major mergers; (3) the build-up of the red sequence at z < 1 can be explained by a doubling in the number of spheroidal galaxies since z ~ 1.2.

Mechanisms of neurodegeneration in Huntington's disease.

Abstract: Huntington's disease (HD) is caused by an expansion of cytosine-adenine-guanine (CAG) repeats in the huntingtin gene, which leads to neuronal loss in the striatum and cortex and to the appearance of neuronal intranuclear inclusions of mutant huntingtin. Huntingtin plays a role in protein trafficking, vesicle transport, postsynaptic signaling, transcriptional regulation, and apoptosis. Thus, a loss of function of the normal protein and a toxic gain of function of the mutant huntingtin contribute to the disruption of multiple intracellular pathways. Furthermore, excitotoxicity, dopamine toxicity, metabolic impairment, mitochondrial dysfunction, oxidative stress, apoptosis, and autophagy have been implicated in the progressive degeneration observed in HD. Nevertheless, despite the efforts of a multidisciplinary scientific community, there is no cure for this devastating neurodegenerative disorder. This review presents an overview of the mechanisms that may contribute for HD pathogenesis. Ultimately, a better understanding of these mechanisms will lead to the development of more effective therapeutic targets.

Very weak lensing in the CFHTLS Wide: Cosmology from cosmic shear in the linear regime

Abstract: Aims. We present an exploration of weak lensing by large-scale structure in the linear regime, using the third-year (T0003) CFHTLS Wide data release. Our results place tight constraints on the scaling of the amplitude of the matter power spectrum σ8 with the matter density Ωm. Methods. Spanning 57 square degrees to i � = 24.5 over three independent fields, the unprecedented contiguous area of this survey permits high signal-to-noise measurements of two-point shear statistics from 1 arcmin to 4 degrees. Understanding systematic errors in our analysis is vital in interpreting the results. We therefore demonstrate the percent-level accuracy of our method using STEP simulations, an E/B-mode decomposition of the data, and the star-galaxy cross correlation function. We also present a thorough analysis of the galaxy redshift distribution using redshift data from the CFHTLS T0003 Deep fields that probe the same spatial regions as the Wide fields. Results. We find σ8(Ωm/0.25) 0.64 = 0.785 ± 0.043 using the aperture-mass statistic for the full range of angular scales for an assumed flat cosmology, in excellent agreement with WMAP3 constraints. The largest physical scale probed by our analysis is 85 Mpc, assuming a mean redshift of lenses of 0.5 and a ΛCDM cosmology. This allows for the first time to constrain cosmology using only cosmic shear measurements in the linear regime. Using only angular scales θ> 85 arcmin, we find σ8(Ωm/0.25) 0.53 lin = 0.837 ± 0.084, which agree with the results from our full analysis. Combining our results with data from WMAP3, we find Ωm = 0.248 ± 0.019 and σ8 = 0.771 ± 0.029.

The SCUBA Legacy Catalogues: Submillimeter-Continuum Objects Detected by SCUBA

Abstract: We present the SCUBA Legacy Catalogues, two comprehensive sets of continuum maps (and catalogs) using data at 850 and 450 μm of the various astronomical objects obtained with the Submillimetre Common User Bolometer Array (SCUBA). The Fundamental Map Data Set contains data only where superior atmospheric opacity calibration data were available. The Extended Map Data Set contains data regardless of the quality of the opacity calibration. Each data set contains 1.2° × 1.2° maps at locations where data existed in the JCMT archive, imaged using the matrix inversion method. The Fundamental Data Set is composed of 1423 maps at 850 μm and 1357 maps at 450 μm. The Extended Data Set is composed of 1547 maps at 850 μm. Neither data set includes high sensitivity, single-chop SCUBA maps of "cosmological fields" nor solar system objects. Each data set was used to determine a respective object catalogue, consisting of objects identified within the respective 850 μm maps using an automated identification algorithm. The Fundamental and Extended Map Object Catalogues contain 5061 and 6118 objects, respectively. Objects are named based on their respective J2000.0 position of peak 850 μm intensity. The catalogues provide for each object the respective maximum 850 μm intensity, estimates of total 850 μm flux and size, and tentative identifications from the SIMBAD Database. Where possible, the catalogues also provide for each object its maximum 450 μm intensity and total 450 μm flux and flux ratios.

Flavor physics of leptons and dipole moments

Abstract: This chapter of the report of the “Flavor in the era of the LHC” Workshop discusses the theoretical, phenomenological and experimental issues related to flavor phenomena in the charged lepton sector and in flavor conserving CP-violating processes. We review the current experimental limits and the main theoretical models for the flavor structure of fundamental particles. We analyze the phenomenological consequences of the available data, setting constraints on explicit models beyond the standard model, presenting benchmarks for the discovery potential of forthcoming measurements both at the LHC and at low energy, and exploring options for possible future experiments.

The Tidal Evolution of Local Group Dwarf Spheroidals

Abstract: We use N-body simulations to study the evolution of dwarf spheroidal galaxies (dSphs) driven by galactic tides. We adopt a cosmologically motivated model where dSphs are approximated by a King model embedded within an NFW halo. We find that these NFW-embedded King models are extraordinarily resilient to tides; the stellar density profile still resembles a King model even after losing more than 99% of the stars. As tides strip the galaxy, the stellar luminosity, velocity dispersion, central surface brightness, and core radius decrease monotonically. Remarkably, we find that the evolution of these parameters is solely controlled by the total amount of mass lost from within the luminous radius. Of all parameters, the core radius is the least affected: after losing 99% of the stars, Rc decreases by just a factor of ~2. Interestingly, tides tend to make dSphs more dark matter-dominated because the tightly bound central dark matter "cusp" is more resilient to disruption than the "cored" King profile. We examine whether the extremely large mass-to-light ratios of the newly discovered ultrafaint dSphs might have been caused by tidal stripping of once-brighter systems. Although dSph tidal evolutionary tracks parallel the observed scaling relations in the luminosity-radius plane, they predict too steep a change in velocity dispersion compared with the observational estimates hitherto reported in the literature. The ultrafaint dwarfs are thus unlikely to be the tidal remnants of systems like Fornax, Draco, or Sagittarius. Despite spanning four decades in luminosity, dSphs appear to inhabit halos of comparable peak circular velocity, lending support to scenarios that envision dSphs as able to form only in halos above a certain mass threshold.

Clues to the Origin of the Mass-Metallicity Relation: Dependence on Star Formation Rate and Galaxy Size

Abstract: We use a sample of 43,690 galaxies selected from the Sloan Digital Sky Survey Data Release 4 to study the systematic effects of specific star formation rate (SSFR) and galaxy size (as measured by the half-light radius, -->rh) on the mass-metallicity relation. We find that galaxies with high SSFR or large -->rh for their stellar mass have systematically lower gas-phase metallicities (by up to 0.2 dex) than galaxies with low SSFR or small -->rh. We discuss possible origins for these dependencies, including galactic winds/outflows, abundance gradients, environment, and star formation rate efficiencies.

Further Notes on the Basic Reproduction Number

Abstract: The basic reproduction number, R0 is a measure of the potential for disease spread in a population. Mathematically, R0 is a threshold for stability of a disease-free equilibrium and is related to the peak and final size of an epidemic. The purpose of these notes is to give a precise definition and algorithm for obtaining R0 for a general compartmental ordinary differential equation model of disease transmission. Several examples of calculating R0 are included, and the epidemiological interpretation of this threshold parameter is connected to the local and global stability of a disease-free equilibrium.

Environmental dependence of masses and coupling constants

Abstract: We construct a class of scalar field models coupled to matter that lead to the dependence of masses and coupling constants on the ambient matter density. Such models predict a deviation of couplings measured on the Earth from values determined in low-density astrophysical environments, but do not necessarily require the evolution of coupling constants with the redshift in the recent cosmological past. Additional laboratory and astrophysical tests of $\ensuremath{\Delta}\ensuremath{\alpha}$ and $\ensuremath{\Delta}({m}_{p}/{m}_{e})$ as functions of the ambient matter density are warranted.

A microfluidic fuel cell with flow-through porous electrodes.

Abstract: A microfluidic fuel cell architecture incorporating flow-through porous electrodes is demonstrated. The design is based on cross-flow of aqueous vanadium redox species through the electrodes into an orthogonally arranged co-laminar exit channel, where the waste solutions provide ionic charge transfer in a membraneless configuration. This flow-through architecture enables improved utilization of the three-dimensional active area inside the porous electrodes and provides enhanced rates of convective/diffusive transport without increasing the parasitic loss required to drive the flow. Prototype fuel cells are fabricated by rapid prototyping with total material cost estimated at 2 USD/unit. Improved performance as compared to previous microfluidic fuel cells is demonstrated, including power densities at room temperature up to 131 mW cm-2. In addition, high overall energy conversion efficiency is obtained through a combination of relatively high levels of fuel utilization and cell voltage. When operated at 1 microL min-1 flow rate, the fuel cell produced 20 mW cm-2 at 0.8 V combined with an active fuel utilization of 94%. Finally, we demonstrate in situ fuel and oxidant regeneration by running the flow-through architecture fuel cell in reverse.

Bosonic super-WIMPs as keV-scale dark matter

Abstract: We consider models of light superweakly interacting cold dark matter, with $\mathcal{O}(10--100)\text{ }\text{ }\mathrm{keV}$ mass, focusing on bosonic candidates such as pseudoscalars and vectors. We analyze the cosmological abundance, the $\ensuremath{\gamma}$ background created by particle decays, the impact on stellar processes due to cooling, and the direct-detection capabilities in order to identify classes of models that pass all the constraints. In certain models, variants of photoelectric (or axioelectric) absorption of dark matter in direct-detection experiments can provide a sensitivity to the superweak couplings to the standard model which is superior to all existing indirect constraints. In all models studied, the annual modulation of the direct-detection signal is at the currently unobservable level of $O({10}^{\ensuremath{-}5})$.

Genome-wide and expression analysis of protein phosphatase 2C in rice and Arabidopsis

Abstract: The protein phosphatase 2Cs (PP2Cs) from various organisms have been implicated to act as negative modulators of protein kinase pathways involved in diverse environmental stress responses and developmental processes. A genome-wide overview of the PP2C gene family in plants is not yet available. A comprehensive computational analysis identified 80 and 78 PP2C genes in Arabidopsis thaliana (AtPP2Cs) and Oryza sativa (OsPP2Cs), respectively, which denotes the PP2C gene family as one of the largest families identified in plants. Phylogenic analysis divided PP2Cs in Arabidopsis and rice into 13 and 11 subfamilies, respectively, which are supported by the analyses of gene structures and protein motifs. Comparative analysis between the PP2C genes in Arabidopsis and rice identified common and lineage-specific subfamilies and potential 'gene birth-and-death' events. Gene duplication analysis reveals that whole genome and chromosomal segment duplications mainly contributed to the expansion of both OsPP2Cs and AtPP2Cs, but tandem or local duplication occurred less frequently in Arabidopsis than rice. Some protein motifs are widespread among the PP2C proteins, whereas some other motifs are specific to only one or two subfamilies. Expression pattern analysis suggests that 1) most PP2C genes play functional roles in multiple tissues in both species, 2) the induced expression of most genes in subfamily A by diverse stimuli indicates their primary role in stress tolerance, especially ABA response, and 3) the expression pattern of subfamily D members suggests that they may constitute positive regulators in ABA-mediated signaling pathways. The analyses of putative upstream regulatory elements by two approaches further support the functions of subfamily A in ABA signaling, and provide insights into the shared and different transcriptional regulation machineries in dicots and monocots. This comparative genome-wide overview of the PP2C family in Arabidopsis and rice provides insights into the functions and regulatory mechanisms, as well as the evolution and divergence of the PP2C genes in dicots and monocots. Bioinformatics analyses suggest that plant PP2C proteins from different subfamilies participate in distinct signaling pathways. Our results have established a solid foundation for future studies on the functional divergence in different PP2C subfamilies.

Prospects for detecting supersymmetric dark matter in the Galactic halo

Abstract: Dark matter is the dominant form of matter in the Universe, but its nature is unknown. It is plausibly an elementary particle, perhaps the lightest supersymmetric partner of known particle species. In this case, annihilation of dark matter in the halo of the Milky Way should produce gamma-rays at a level that may soon be observable. Previous work has argued that the annihilation signal will be dominated by emission from very small clumps (perhaps smaller even than the Earth), which would be most easily detected where they cluster together in the dark matter haloes of dwarf satellite galaxies. Here we report that such small-scale structure will, in fact, have a negligible impact on dark matter detectability. Rather, the dominant and probably most easily detectable signal will be produced by diffuse dark matter in the main halo of the Milky Way. If the main halo is strongly detected, then small dark matter clumps should also be visible, but may well contain no stars, thereby confirming a key prediction of the cold dark matter model.