297 research outputs found
The Interstellar Medium and Star Formation in Edge-On Galaxies. I. NGC 891
We analyze images of BIMA 12CO (J = 1 --> 0), VLA HI, and Spitzer 3.6 and 24
\mum emission toward the edge-on galaxy NGC 891 and derive the radial and
vertical distributions of gas and the radial distributions of stellar mass and
recent star formation. We describe our method of deriving radial profiles for
edge-on galaxies, assuming circular motion, and verify basic relationships
between star formation rate and gas and stellar content, and between the
molecular-to-atomic ratio and hydrostatic midplane pressure, that have been
found in other galaxy samples. The Schmidt law index we find for the total gas
(H2 + H I) is 0.85\pm0.55, but the Schmidt law provides a poor description of
the SFR in comparison to a model that includes the influence of the stellar
disk. Using our measurements of the thickness of the gas disk and the
assumption of hydrostatic equilibrium, we estimate volume densities and
pressures as a function of radius and height in order to test the importance of
pressure in controlling the {\rho}H2/{\rho}HI ratio. The gas pressure in two
dimensions P(r, z) using constant velocity dispersion does not seem to
correlate with the {\rho}H2/{\rho}HI ratio, but the pressure using varying
velocity dispersion appears to correlate with the ratio. We test the importance
of gravitational instability in determining the sites of massive star
formation, and find that the Q parameter using a radially varying gas velocity
dispersion is consistent with self-regulation (Q - 1) over a large part of the
disk.Comment: 19 pages, 19 figures, accepted for publication in A
Dependence of Interstellar Turbulent Pressure on Supernova Rate
Feedback from massive stars is one of the least understood aspects of galaxy
formation. We perform a suite of vertically stratified local interstellar
medium (ISM) simulations in which supernova rates and vertical gas column
densities are systematically varied based on the Schmidt-Kennicutt law. Our
simulations have a sufficiently high spatial resolution (1.95 pc) to follow the
hydrodynamic interactions among multiple supernovae that structure the ISM. At
a given supernova rate, we find that the mean mass-weighted sound speed and
velocity dispersion decrease as the inverse square root of gas density,
indicating that both thermal and turbulent pressures are nearly constant in the
midplane, so the effective equation of state is isobaric. In contrast, across
our four models having supernova rates that range from one to 512 times the
Galactic supernova rate, the mass-weighted velocity dispersion remains in the
range 4-6 km/s. Hence, gas averaged over ~100 pc regions follows an effective
equation of state that is close to isothermal. Simulated H I emission lines
have widths of 10-18 km/s, comparable to observed values. In our highest
supernova rate model, superbubble blow-outs occur, and the turbulent pressure
on large scales is >~4 times higher than the thermal pressure. We find a tight
correlation between the thermal and turbulent pressures averaged over ~100 pc
regions in the midplane of each model, as well as across the four ISM models.
We construct a subgrid model for turbulent pressure based on analytic arguments
and explicitly calibrate it against our stratified ISM simulations. The subgrid
model provides a simple yet physically motivated way to include supernova
feedback in cosmological simulations.Comment: 13 pages incl. 8 figures; accepted for publication in ApJ; contains a
new model of starburst galaxy showing superbubble blow-ou
Effectiveness of AS03 adjuvanted pandemic H1N1 vaccine: case-control evaluation based on sentinel surveillance system in Canada, autumn 2009
Objective To assess the effectiveness of the pandemic influenza A/H1N1 vaccine used in Canada during autumn 2009
Randomized controlled ferret study to assess the direct impact of 2008-09 trivalent inactivated influenza vaccine on A(H1N1)pdm09 disease risk
During spring-summer 2009, several observational studies from Canada showed increased risk of medically-attended, laboratory-confirmed A(H1N1)pdm09 illness among prior recipients of 2008-09 trivalent inactivated influenza vaccine (TIV). Explanatory hypotheses included direct and indirect vaccine effects. In a randomized placebo-controlled ferret study, we tested whether prior receipt of 2008-09 TIV may have directly influenced A(H1N1)pdm09 illness. Thirty-two ferrets (16/group) received 0.5 mL intra-muscular injections of the Canadian-manufactured, commercially-available, non-adjuvanted, split 2008-09 Fluviral or PBS placebo on days 0 and 28. On day 49 all animals were challenged (Ch0) with A(H1N1)pdm09. Four ferrets per group were randomly selected for sacrifice at day 5 post-challenge (Ch+5) and the rest followed until Ch+14. Sera were tested for antibody to vaccine antigens and A(H1N1)pdm09 by hemagglutination inhibition (HI), microneutralization (MN), nucleoprotein-based ELISA and HA1-based microarray assays. Clinical characteristics and nasal virus titers were recorded pre-challenge then post-challenge until sacrifice when lung virus titers, cytokines and inflammatory scores were determined. Baseline characteristics were similar between the two groups of influenza-naïve animals. Antibody rise to vaccine antigens was evident by ELISA and HA1-based microarray but not by HI or MN assays; virus challenge raised antibody to A(H1N1)pdm09 by all assays in both groups. Beginning at Ch+2, vaccinated animals experienced greater loss of appetite and weight than placebo animals, reaching the greatest between-group difference in weight loss relative to baseline at Ch+5 (7.4% vs. 5.2%; p = 0.01). At Ch+ 5 vaccinated animals had higher lung virus titers (log-mean 4.96 vs. 4.23pfu/mL, respectively; p = 0.01), lung inflammatory scores (5.8 vs. 2.1, respectively; p = 0.051) and cytokine levels (p.0.05). At Ch+14, both groups had recovered. Findings in influenza-naïve, systematically-infected ferrets may not replicate the human experience. While they cannot be considered conclusive to explain human observations, these ferret findings are consistent with direct, adverse effect of prior 2008-09 TIV receipt on A(H1N1)pdm09 illness. As such, they warrant further in-depth investigation and search for possible mechanistic explanations
Search for a massive invisible particle in and decays
We present a search for a non-Standard-Model invisible particle in the
mass range in and
decays. The results are obtained from a data sample that corresponds to pairs,
collected at the resonance with the Belle detector at the KEKB
collider. One meson is fully reconstructed in a hadronic mode to
determine the momentum of the lepton of the signal decay in the rest frame of
the recoiling partner meson. We find no evidence of a signal and set upper
limits on the order of .Comment: 8 pages, 4 figures, 3 table
Belle II Technical Design Report
The Belle detector at the KEKB electron-positron collider has collected
almost 1 billion Y(4S) events in its decade of operation. Super-KEKB, an
upgrade of KEKB is under construction, to increase the luminosity by two orders
of magnitude during a three-year shutdown, with an ultimate goal of 8E35 /cm^2
/s luminosity. To exploit the increased luminosity, an upgrade of the Belle
detector has been proposed. A new international collaboration Belle-II, is
being formed. The Technical Design Report presents physics motivation, basic
methods of the accelerator upgrade, as well as key improvements of the
detector.Comment: Edited by: Z. Dole\v{z}al and S. Un
Novel Avian Influenza H7N3 Strain Outbreak, British Columbia
Genome sequences of chicken (low pathogenic avian influenza [LPAI] and highly pathogenic avian influenza [HPAI]) and human isolates from a 2004 outbreak of H7N3 avian influenza in Canada showed a novel insertion in the HA0 cleavage site of the human and HPAI isolate. This insertion likely occurred by recombination between the hemagglutination and matrix genes in the LPAI virus
Top-quark physics at the CLIC electron-positron linear collider
ABSTRACT: The Compact Linear Collider (CLIC) is a proposed future high-luminosity linear electron-positron collider operating at three energy stages, with nominal centre-of-mass energies √s = 380 GeV, 1.5 TeV, and 3 TeV. Its aim is to explore the energy frontier, providing sensitivity to physics beyond the Standard Model (BSM) and precision measurements of Standard Model processes with an emphasis on Higgs boson and top-quark physics. The opportunities for top-quark physics at CLIC are discussed in this paper. The initial stage of operation focuses on top-quark pair production measurements, as well as the search for rare flavour-changing neutral current (FCNC) top-quark decays. It also includes a top-quark pair production threshold scan around 350 GeV which provides a precise measurement of the top-quark mass in a well-defined theoretical framework. At the higher-energy stages, studies are made of top-quark pairs produced in association with other particles. A study of t̄tH production including the extraction of the top Yukawa coupling is presented as well as a study of vector boson fusion (VBF) production, which gives direct access to high-energy electroweak interactions. Operation above 1 TeV leads to more highly collimated jet environments where dedicated methods are used to analyse the jet constituents. These techniques enable studies of the top-quark pair production, and hence the sensitivity to BSM physics, to be extended to higher energies. This paper also includes phenomenological interpretations that may be performed using the results from the extensive top-quark physics programme at CLIC.the Spanish Ministry of Economy, Industry and Competitiveness under projects MINEICO/FEDER-UE, FPA2015-65652-C4-3-R, FPA2015-71292-C2-1-Pand FPA2015-71956-REDT; and the MECD grant FPA2016-78645-P, Spai
Association between the 2008–09 Seasonal Influenza Vaccine and Pandemic H1N1 Illness during Spring–Summer 2009: Four Observational Studies from Canada
In three case-control studies and a household transmission cohort, Danuta Skowronski and colleagues find an association between prior seasonal flu vaccination and increased risk of 2009 pandemic H1N1 flu
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