1,515 research outputs found
Stress intensity factors for an infinite plate with radial cracks emanating from an internal hole and subjected to cylindrical bending Progress report
Method for stress intensity factors for infinite plate with radial cracks emanating from internal hole and subjected to cylindrical bendin
Method to measure neutron beam polarization with 2x1 Neutron Spin Filter
A method to measure a beam polarization with the use of polarized 3He gas is
discussed. It is shown that special design of the Neutron Spin Filter cell
allows for a fast and accurate measurement. The accuracy of this method is
analyzed.Comment: 13 pages, 3 figures, submitted to Nucl. Instrum. Methods A on 02
January 200
The failed liberalisation of Algeria and the international context: a legacy of stable authoritarianism
The paper attempts to challenge the somewhat marginal role of international factors in the study of transitions to democracy. Theoretical and practical difficulties in proving causal mechanisms between international variables and domestic outcomes can be overcome by defining the international dimension in terms of Western dominance of world politics and by identifying Western actions towards democratising countries. The paper focuses on the case of Algeria, where international factors are key in explaining the initial process of democratisation and its following demise. In particular, the paper argues that direct Western policies, the pressures of the international system and external shocks influence the internal distribution of power and resources, which underpins the different strategies of all domestic actors. The paper concludes that analysis based purely on domestic factors cannot explain the process of democratisation and that international variables must be taken into more serious account and much more detailed
The GALEX Arecibo SDSS Survey II: The Star Formation Efficiency of Massive Galaxies
We use measurements of the HI content, stellar mass and star formation rates
in ~190 massive galaxies with stellar masses greater than 10^10 Msun, obtained
from the Galex Arecibo SDSS Survey (GASS) described in Paper I (Catinella et
al. 2010) to explore the global scaling relations associated with the
bin-averaged ratio of the star formation rate over the HI mass, which we call
the HI-based star formation efficiency (SFE). Unlike the mean specific star
formation rate, which decreases with stellar mass and stellar mass surface
density, the star formation efficiency remains relatively constant across the
sample with a value close to SFE = 10^-9.5 yr^-1 (or an equivalent gas
consumption timescale of ~3 Gyr). Specifically, we find little variation in SFE
with stellar mass, stellar mass surface density, NUV-r color and concentration.
We interpret these results as an indication that external processes or feedback
mechanisms that control the gas supply are important for regulating star
formation in massive galaxies. An investigation into the detailed distribution
of SFEs reveals that approximately 5% of the sample shows high efficiencies
with SFE > 10^-9 yr^-1, and we suggest that this is very likely due to a
deficiency of cold gas rather than an excess star formation rate. Conversely,
we also find a similar fraction of galaxies that appear to be gas-rich for
their given specific star-formation rate, although these galaxies show both a
higher than average gas fraction and lower than average specific star formation
rate. Both of these populations are plausible candidates for "transition"
galaxies, showing potential for a change (either decrease or increase) in their
specific star formation rate in the near future. We also find that 36+/-5% of
the total HI mass density and 47+/-5% of the total SFR density is found in
galaxies with stellar mass greater than 10^10 Msun. [abridged]Comment: 18 pages, 11 figures. Accepted for publication in MNRAS. GASS
publications and released data can be found at
http://www.mpa-garching.mpg.de/GASS/index.ph
The GALEX Arecibo SDSS Survey. I. Gas Fraction Scaling Relations of Massive Galaxies and First Data Release
We introduce the GALEX Arecibo SDSS Survey (GASS), an on-going large program
that is gathering high quality HI-line spectra using the Arecibo radio
telescope for an unbiased sample of ~1000 galaxies with stellar masses greater
than 10^10 Msun and redshifts 0.025<z<0.05, selected from the SDSS
spectroscopic and GALEX imaging surveys. The galaxies are observed until
detected or until a low gas mass fraction limit (1.5-5%) is reached. This paper
presents the first Data Release, consisting of ~20% of the final GASS sample.
We use this data set to explore the main scaling relations of HI gas fraction
with galaxy structure and NUV-r colour. A large fraction (~60%) of the galaxies
in our sample are detected in HI. We find that the atomic gas fraction
decreases strongly with stellar mass, stellar surface mass density and NUV-r
colour, but is only weakly correlated with galaxy bulge-to-disk ratio (as
measured by the concentration index of the r-band light). We also find that the
fraction of galaxies with significant (more than a few percent) HI decreases
sharply above a characteristic stellar surface mass density of 10^8.5 Msun
kpc^-2. The fraction of gas-rich galaxies decreases much more smoothly with
stellar mass. One of the key goals of GASS is to identify and quantify the
incidence of galaxies that are transitioning between the blue, star-forming
cloud and the red sequence of passively-evolving galaxies. Likely transition
candidates can be identified as outliers from the mean scaling relations
between gas fraction and other galaxy properties. [abridged]Comment: 25 pages, 12 figures. Accepted for publication in MNRAS. Version with
high resolution figures available at
http://www.mpa-garching.mpg.de/GASS/pubs.ph
A model-model and data-model comparison for the early Eocene hydrological cycle
A range of proxy observations have recently provided constraints on how
Earth's hydrological cycle responded to early Eocene climatic changes.
However, comparisons of proxy data to general circulation model (GCM)
simulated hydrology are limited and inter-model variability remains poorly
characterised. In this work, we undertake an intercomparison of GCM-derived
precipitation and <i>P</i> − <i>E</i> distributions within the extended EoMIP ensemble
(Eocene Modelling Intercomparison Project; Lunt et al., 2012), which includes
previously published early Eocene simulations performed using five GCMs
differing in boundary conditions, model structure, and precipitation-relevant
parameterisation schemes.
<br><br>
We show that an intensified hydrological cycle, manifested in enhanced
global precipitation and evaporation rates, is simulated for all Eocene
simulations relative to the preindustrial conditions. This is primarily due to elevated
atmospheric paleo-CO<sub>2</sub>, resulting in elevated temperatures, although the
effects of differences in paleogeography and ice sheets are also important
in some models. For a given CO<sub>2</sub> level, globally averaged precipitation rates
vary widely between models, largely arising from different simulated surface
air temperatures. Models with a similar global sensitivity of precipitation
rate to temperature (d<i>P</i>∕d<i>T</i>) display different regional precipitation responses
for a given temperature change. Regions that are particularly sensitive to
model choice include the South Pacific, tropical Africa, and the Peri-Tethys,
which may represent targets for future proxy acquisition.
<br><br>
A comparison of early and middle Eocene leaf-fossil-derived precipitation
estimates with the GCM output illustrates that GCMs generally underestimate
precipitation rates at high latitudes, although a possible seasonal bias of
the proxies cannot be excluded. Models which warm these regions, either via
elevated CO<sub>2</sub> or by varying poorly constrained model parameter values, are
most successful in simulating a match with geologic data. Further data from
low-latitude regions and better constraints on early Eocene CO<sub>2</sub> are now
required to discriminate between these model simulations given the large
error bars on paleoprecipitation estimates. Given the clear differences
between simulated precipitation distributions within the ensemble, our
results suggest that paleohydrological data offer an independent means by
which to evaluate model skill for warm climates
A self-assembled respiratory chain that catalyzes NADH oxidation by ubiquinone-10 cycling between complex I and the alternative oxidase
Complex I is a crucial respiratory enzyme that conserves the energy from NADH oxidation by ubiquinone-10 (Q10) in proton transport across a membrane. Studies of its energy transduction mechanism are hindered by the extreme hydrophobicity of Q10, and they have so far relied on native membranes with many components or on hydrophilic Q10 analogues that partition into membranes and undergo side reactions. Herein, we present a self-assembled system without these limitations: proteoliposomes containing mammalian complex I, Q10, and a quinol oxidase (the alternative oxidase, AOX) to recycle Q10H2 to Q10. AOX is present in excess, so complex I is completely rate determining and the Q10 pool is kept oxidized under steady-state catalysis. The system was used to measure a fully-defined KM value for Q10. The strategy is suitable for any enzyme with a hydrophobic quinone/quinol substrate, and could be used to characterize hydrophobic inhibitors with potential applications as pharmaceuticals, pesticides, or fungicides
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