4,625 research outputs found
Dust obscuration studies along quasar sight lines using simulated galaxies
We use the results of a set of three-dimensional SPH-Treecode simulations
which model the formation and early evolution of disk galaxies, including the
generation of heavy elements by star formation, to investigate the effects of
dust absorption in quasar absorption line systems.
Using a simple prescription for the production of dust, we have compared the
column density, zinc abundance and optical depth properties of our models to
the known properties of Damped Lyman alpha systems.
We find that a significant fraction of our model galaxy disks have a higher
column density than any observed DLA system. We are also able to show that such
parts of the disk tend to be optically thick, implying that any background
quasar would be obscured through much of the disk. This would produce the
selection effect against the denser absorption systems thought to be present in
observations.Comment: 7 pages, 8 figures, to be published in MNRA
Influences of independency in Milton\u27s early life
My thesis is that Milton did develop in his youth, mainly under the influence or Dr. Gill, a belief in his own reason as an arbitrator in theological disputes. It is this characteristic advanced Protestant view that transcends church and king together with his plea for toleration and his attack on the clergy in Lycidas that place him in this early period already somewhat in the tradition or deism suggested by Toland . When Thomas Paine, the revolutionary deist, wrote in The Age of Reason, My mind is my own church, he was stating a basic belief of Milton. Thomas Jefferson, another famous deist, expressed that same thought in a different manner in a letter to Ezra Styles when he stated, I am a sect by myself, as far as I know. The purpose of this paper is to show how Milton\u27s childhood influences could have guided him to a philosophy of religion which would have made it possible for him to give utterance to the two statements quoted in the preceding paragraph
Solid-State Nuclear Magnetic Resonance Analysis of Cytosine-Methylated DNA Dodecamer
The interaction of deoxyribonucleic acid (DNA) and cellular proteins is absolutely central to any biological understanding of DNA replication, transcription, and even gene regulation. Because an incumbent protein latches not onto the four bases but onto the backbone phosphate groups of the nucleic acid, backbone dynamics directly pertain to an understanding of basic cell processes. Studies have unambiguously proven that DNA exists in a balance of two conformations, BI and BII, defined by the difference in their backbone torsion angles. A given DNA sequence expresses a preference for either BI or BII, though both exist in most samples (and are presented as a ratio). Factors affecting that ratio include flanking sequence and methylation. When a DNA sample is methylated, which occurs at a cytosine, backbone dynamics at that site and perhaps even its neighbors are theoretically quenched due to the steric strain of a large attached group. DNA methylation is implicated in cancer diagnosis by new studies focusing on hypermethylation in CpG islands,
This thesis uses solid-state deuterium NMR to study the backbone dynamics of the Dickerson dodecamer, [d(CGCGAATTCGCG)]2, which was the first synthetic BII conformer successfully crystallized (allowing for analysis in the solid state) and which contains the EcoRI binding site, GAATTC. This molecule is a good model system because a massive amount of information has been gathered on it not only using NMR, both high-resolution and solid-state, but also using x-ray diffraction, electron paramagnetic resonance, and all-atom molecular dynamics simulation. This thesis research shows the quenching of backbone dynamics due to C9 methylation
The Chemical Evolution of the Universe I: High Column Density Absorbers
We construct a simple, robust model of the chemical evolution of galaxies
from high to low redshift, and apply it to published observations of damped
Lyman-alpha quasar absorption line systems (DLAs). The elementary model assumes
quiescent star formation and isolated galaxies (no interactions, mergers or gas
flows). We consider the influence of dust and chemical gradients in the
galaxies, and hence explore the selection effects in quasar surveys. We fit
individual DLA systems to predict some observable properties of the absorbing
galaxies, and also indicate the expected redshift behaviour of chemical element
ratios involving nucleosynthetic time delays.
Despite its simplicity, our `monolithic collapse' model gives a good account
of the distribution and evolution of the metallicity and column density of
DLAs, and of the evolution of the global star formation rate and gas density
below redshifts z 3. However, from the comparison of DLA observations with our
model, it is clear that star formation rates at higher redshifts (z>3) are
enhanced. Galaxy interactions and mergers, and gas flows very probably play a
major role.Comment: 36 pages, 11 figures; accepted by MNRA
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The economics of health
This report presents results from the Economics of Health project funded by the East Midlands Development Agency. The work was undertaken between November 2007 and February 2008. The main aim of the project was to examine the relationship between mental and physical health and employability, labour market participation and economic performance, with specific attention given to the direction of causal relationships
Modeling the radial abundance distribution of the transition galaxy ngc 1313
NGC 1313 is the most massive disk galaxy showing a flat radial abundance
distribution in its interstellar gas, a behavior generally observed in
magellanic and irregular galaxies. We have attempted to reproduce this flat
abundance distribution using a multiphase chemical evolution model, which has
been previously used sucessfully to depict other spiral galaxies along the
Hubble morphological sequence. We found that it is not possible to reproduce
the flat radial abundance distribution in NGC 1313, and at the same time, be
consistent with observed radial distributions of other key parameters such the
surface gas density and star formation profiles. We conclude that a more
complicated galactic evolution model including radial flows, and possibly mass
loss due to supernova explosions and winds, is necessary to explain the
apparent chemical uniformity of the disk of NGC 1313Comment: 14 paginas, 4 figures, to be published in ApJ, apri
Modelling alternative strategies for delivering hepatitis B vaccine in prisons : the impact on the vaccination coverage of the injecting drug user population
Since 2001 hepatitis B vaccination has been offered to prisoners on reception into prisons in
England and Wales. However, short campaigns of vaccinating the entire population of individual
prisons have achieved high vaccination coverage for limited periods, suggesting that short
campaigns may be a preferable way of vaccinating prisoners. A model is used that describes the
flow of prisoners through prisons stratified by injecting status to compare a range of vaccination
scenarios that describe vaccination on prison reception or via regular short campaigns. Model
results suggest that vaccinating on prison reception can capture a greater proportion of the
injecting drug user (IDU) population than the comparable campaign scenarios (63% vs. 55 . 6%
respectively). Vaccination on prison reception is also more efficient at capturing IDUs for
vaccination than vaccination via a campaign, although vaccination via campaigns may have a
role with some infections for overall control
The SCUBA Local Universe Galaxy Survey I: First Measurements of the Submillimetre Luminosity and Dust Mass Functions
We have used SCUBA to observe a complete sample of 104 galaxies selected at
60 microns from the IRAS BGS and we present here the 850 micron measurements.
Fitting the 60,100 and 850 micron fluxes with a single temperature dust model
gives the sample mean temperature T=36 K and beta = 1.3. We do not rule out the
possibility of dust which is colder than this, if a 20 K component was present
then our dust masses would increase by factor 1.5-3. We present the first
measurements of the luminosity and dust mass functions, which were well fitted
by Schechter functions (unlike those 60 microns). We have correlated many
global galaxy properties with the submillimetre and find that there is a
tendancy for less optically luminous galaxies to contain warmer dust and have
greater star formation efficiencies (cf. Young 1999). The average gas-to-dust
ratio for the sample is 581 +/- 43 (using both atomic and molecular hydrogen),
significantly higher than the Galactic value of 160. We believe this
discrepancy is due to a cold dust component at T < 20 K. There is a suprisingly
tight correlation between dust mass and the mass of molecular hydrogen as
estimated from CO measurements, with an intrinsic scatter of ~50%.Comment: 24 pages, 15 figures, 8 tables, accepted for publication in MNRA
Applying insights on categorisation, communication, and dynamic decision-making: A case study of a ‘simple’ maritime military decision
A complete understanding of decision-making in military domains requires gathering insights from several fields of study. To make the task tractable, here we consider a specific example of short-term tactical decisions under uncertainty made by the military at sea. Through this lens, we sketch out relevant literature from three psychological tasks each underpinned by decision-making processes: categorisation, communication, and choice. From the literature, we note two general cognitive tendencies that emerge across all three stages: the effect of cognitive load and individual differences. Drawing on these tendencies, we recommend strategies, tools and future research that could improve performance in military domains—but, by extension, would also generalise to other high-stakes contexts. In so doing, we show the extent to which domain general properties of high order cognition are sufficient in explaining behaviours in domain specific contexts
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