783 research outputs found
Experimental Impacts into Feldspar Phenocrysts
Meteorite impact craters are the
dominant surface feature on most terrestrial planetary
bodies [1]. The extreme temperatures and pressures
generated by hypervelocity impact events produce a
variety of microscopic shock metamorphic effects in
minerals, as well as non-exclusive shock-related features
such as pervasive fracturing and brecciation.<p></p>
Studies of shock effects in feldspar group minerals
have been limited due to the the comparatively rapid
rate at which feldspars weather, and the complexity of
their microtextures which renders them difficult to
study using conventional optical techniques. However,
feldspars are becoming increasingly investigated for
use as shock barometers due to their importance in
planetary studies and meteoritics, where rocks often
contain little or no quartz [e.g., 2]. This provides the
motivation to examine more closely the effects of
high-velocity impact of a projectile, in the method of
[3], into a feldspathic target, in order to the resultant
microstructural variation.<p></p>
Experimental Impacts into Feldspar Phenocrysts
Meteorite impact craters are the
dominant surface feature on most terrestrial planetary
bodies [1]. The extreme temperatures and pressures
generated by hypervelocity impact events produce a
variety of microscopic shock metamorphic effects in
minerals, as well as non-exclusive shock-related features
such as pervasive fracturing and brecciation.
Studies of shock effects in feldspar group minerals
have been limited due to the the comparatively rapid
rate at which feldspars weather, and the complexity of
their microtextures which renders them difficult to
study using conventional optical techniques. However,
feldspars are becoming increasingly investigated for
use as shock barometers due to their importance in
planetary studies and meteoritics, where rocks often
contain little or no quartz [e.g., 2]. This provides the
motivation to examine more closely the effects of
high-velocity impact of a projectile, in the method of
[3], into a feldspathic target, in order to the resultant
microstructural variation.</p
Proportion of Pelvic Inflammatory Disease caused by Chlamydia trachomatis: consistent picture from different methods
Background.âPelvic inflammatory disease (PID) is a leading cause of both tubal factor infertility and ectopic pregnancy. Chlamydia trachomatis is an important risk factor for PID, but the proportion of PID cases caused by C. trachomatis is unclear. Estimates of this are required to evaluate control measures. Methods.âWe consider 5 separate methods of estimating age-group-specific population excess fractions (PEFs) of PID due to C. trachomatis, using routine data, surveys, case-control studies, and randomized controlled trials, and apply these to data from the United Kingdom before introduction of the National Chlamydia Screening Programme. Results.âAs they are informed by randomized comparisons and national exposure and outcome estimates, our preferred estimates of the proportion of PID cases caused by C. trachomatis are 35% (95% credible interval [CrI], 11%â69%) in women aged 16â24 years and 20% (95% CrI, 6%â38%) in women aged 16â44 years in the United Kingdom. There is a fair degree of consistency between adjusted estimates of PEF, but all have wide 95% CrIs. The PEF decreases from 53.5% (95% CrI, 15.6%â100%) in women aged 16â19 years to 11.5% (95% CrI, 3.0%â25.7%) in women aged 35â44 years. Conclusions.âThe PEFs of PID due to C. trachomatis decline steeply with age by a factor of around 5-fold between younger and older women. Further studies of the etiology of PID in different age groups are required
No-Hair Theorem for Spontaneously Broken Abelian Models in Static Black Holes
The vanishing of the electromagnetic field, for purely electric
configurations of spontaneously broken Abelian models, is established in the
domain of outer communications of a static asymptotically flat black hole. The
proof is gauge invariant, and is accomplished without any dependence on the
model. In the particular case of the Abelian Higgs model, it is shown that the
only solutions admitted for the scalar field become the vacuum expectation
values of the self-interaction.Comment: 8 pages, 2 figures, RevTeX; some changes to match published versio
Vale of York 3-D borehole interpretation and cross-sections study
The Vale of York between Doncaster and Scunthorpe in the south and York and Bugthorpe in
the north is largely underlain by bedrock of the Sherwood Sandstone Group â one of the regions
principal aquifers. Significant superficial deposits of Quaternary age overlie the Sherwood
Sandstone. This study aims to investigate the nature of these superficial deposits with respect to
their relationship with the underlying aquifer.
The Vale of York project area represents a varied glaciated terrain, consisting of pro-glacial finegrained
sediments, coarser glaciofluvilal sediments and extensive glacial tills. These diverse
superficial units vary in thickness throughout the project area. The hydrogeological nature of the
natural superficial sequence is consequently highly variable. Units may be considered as
aquitards, while others may act as aquifers, providing a potential pathway to the underlying
sandstone. The classification of lithologies as aquifer or aquitard is described in detail in this
report.
To investigate the hydrogeological nature of the superficial sequence, six east-west and three
north-south lithostratigraphical cross-sections were constructed. A range of geoscientific
information was considered, including existing geological mapping and over 3000 fully
attributed and coded boreholes. The cross-sections show a subdivision of the superficial
sequence into lithostratigraphical units. Each unit is described in detail in this report.
In addition, a series of thematic maps were generated from the lithological component of the
digital borehole data. Total superficial aquifer and superficial aquitard maps show how the
lithological nature of the superficial sequence varies across the area. Rockhead elevation and
superficial thickness maps indicate where the sandstone aquifer outcrops at the ground surface.
In summary, four main lithostratigraphical units overlie the Sherwood Sandstone Group aquifer
in the project area: a basal sequence of glaciofluvial sand and gravel (interpreted as a superficial
aquifer), glaciolacustrine laminated silt & clay (aquitard), glacial till comprising sandy gravelly
clay (aquitard), and a cover sequence of fluvial and aeolian sand, clay and peat (aquifer /
aquitard). The correlations illustrate that in certain areas, superficial deposits are thin or absent
and that in these areas the Sherwood Sandstone aquifer comes directly to ground surface
Pathways into services for offenders with intellectual disabilities : childhood experience, diagnostic information and offence variables
The patterns and pathways into intellectual disability (ID) offender services were studied through case file review for 477 participants referred in one calendar year to community generic, community forensic, and low, medium, and maximum secure services. Data were gathered on referral source, demographic information, index behavior, prior problem behaviors, diagnostic information, and abuse or deprivation. Community referrers tended to refer to community services and secure service referrers to secure services. Physical and verbal violence were the most frequent index behaviors, whereas contact sexual offenses were more prominent in maximum security. Age at first incident varied with security, with the youngest in maximum secure services. Attention-deficit/hyperactivity disorder or conduct disorder was the most frequently recorded diagnosis, and severe deprivation was the most frequent adverse developmental experience. Fire starting, theft, and road traffic offenses did not feature prominently. Generic community services accepted a number of referrals with forensic-type behavior and had higher proportions of both women and people with moderate or severe ID
Ratios of Elastic Scattering of Pions from 3H and 3He
We have measured the elastic-scattering ratios of normalized yields for
charged pions from 3H and 3He in the backward hemisphere. At 180 MeV, we
completed the angular distribution begun with our earlier measurements, adding
six data points in the angular range of 119 deg to 169 deg in the pi-nucleus
center of mass. We also measured an excitation function with data points at
142, 180, 220, and 256 MeV incident pion energy at the largest achievable angle
for each energy between 160 deg and 170 deg in the pi-nucleus center of mass.
This excitation function corresponds to the energies of our forward-hemisphere
studies. The data, taken as a whole, show an apparent role reversal of the two
charge-symmetric ratios r1 and r2 in the backward hemisphere. Also, for data >
100 deg we observe a strong dependence on the four-momentum transfer squared
(-t) for all of the ratios regardless of pion energy or scattering angle, and
we find that the superratio R data match very well with calculations based on
the forward-hemisphere data that predicts the value of the difference between
the even-nucleon radii of 3H and 3He. Comparisons are also made with recent
calculations incorporating different wave functions and double scattering
models.Comment: RevTex 8pages, 12 figure file
Arrow of time in a recollapsing quantum universe
We show that the Wheeler-DeWitt equation with a consistent boundary condition
is only compatible with an arrow of time that formally reverses in a
recollapsing universe. Consistency of these opposite arrows is facilitated by
quantum effects in the region of the classical turning point. Since
gravitational time dilation diverges at horizons, collapsing matter must then
start re-expanding ``anticausally" (controlled by the reversed arrow) before
horizons or singularities can form. We also discuss the meaning of the
time-asymmetric expression used in the definition of ``consistent histories".
We finally emphasize that there is no mass inflation nor any information loss
paradox in this scenario.Comment: Many conceptual clarifications include
Bomb-<sup>14</sup>C analysis of ecosystem respiration reveals that peatland vegetation facilitates release of old carbon
The largest terrestrial-to-atmosphere carbon flux is respired CO<sub>2</sub>. However, the partitioning of soil and plant sources, understanding of contributory mechanisms, and their response to climate change are uncertain. A plant removal experiment was established within a peatland located in the UK uplands to quantify respiration derived from recently fixed plant carbon and that derived from decomposition of soil organic matter, using natural abundance <sup>13</sup>C and bomb-<sup>14</sup>C as tracers. Soil and plant respiration sources were found respectively to contribute ~ 36% and between 41-54% of the total ecosystem CO<sub>2</sub> flux. Respired CO<sub>2</sub> produced in the clipped (âsoilâ) plots had a mean age of ~ 15 years since fixation from the atmosphere, whereas the <sup>14</sup>C content of ecosystem CO<sub>2</sub> was statistically indistinguishable from the contemporary atmosphere. Results of carbon mass balance modelling showed that, in addition to respiration from bulk soil and plant respired CO<sub>2</sub>, a third, much older source of CO<sub>2</sub> existed. This source, which we suggest is CO<sub>2</sub> derived from the catotelm constituted between ~ 10 and 23% of total ecosystem respiration and had a mean radiocarbon age of between several hundred to ~ 2000 years before present (BP). These findings show that plant-mediated transport of CO<sub>2</sub> produced in the catotelm may form a considerable component of peatland ecosystem respiration. The implication of this discovery is that current assumptions in terrestrial carbon models need to be re-evaluated to consider the climate sensitivity of this third source of peatland CO<sub>2</sub>
Iron under Earth's core conditions: Liquid-state thermodynamics and high-pressure melting curve
{\em Ab initio} techniques based on density functional theory in the
projector-augmented-wave implementation are used to calculate the free energy
and a range of other thermodynamic properties of liquid iron at high pressures
and temperatures relevant to the Earth's core. The {\em ab initio} free energy
is obtained by using thermodynamic integration to calculate the change of free
energy on going from a simple reference system to the {\em ab initio} system,
with thermal averages computed by {\em ab initio} molecular dynamics
simulation. The reference system consists of the inverse-power pair-potential
model used in previous work. The liquid-state free energy is combined with the
free energy of hexagonal close packed Fe calculated earlier using identical
{\em ab initio} techniques to obtain the melting curve and volume and entropy
of melting. Comparisons of the calculated melting properties with experimental
measurement and with other recent {\em ab initio} predictions are presented.
Experiment-theory comparisons are also presented for the pressures at which the
solid and liquid Hugoniot curves cross the melting line, and the sound speed
and Gr\"{u}neisen parameter along the Hugoniot. Additional comparisons are made
with a commonly used equation of state for high-pressure/high-temperature Fe
based on experimental data.Comment: 16 pages including 6 figures and 5 table
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