855 research outputs found
Time evolution of spin state of radical ion pair in microwave field: An analytical solution
The paper reports an exact solution for the problem of spin evolution of
radical ion pair in static magnetic and resonant microwave field taking into
account Zeeman and hyperfine interactions and spin relaxation. The values of
parameters that provide one of the four possible types of solution are
analysed. It is demonstrated that in the absence of spin relaxation, besides
the zero field invariant an invariant at large amplitudes of the resonant
microwave field can be found. The two invariants open the possibility for
simple calculation of microwave pulses to control quantum state of the radical
pair. The effect of relaxation on the invariants is analysed and it is shown
that changes in the high field invariant are induced by phase relaxation.Comment: 18 pages, 7 figure
Cytokine gene polymorphisms in preterm infants with necrotising enterocolitis: genetic association study
BACKGROUND The inflammatory cytokine cascade is implicated in the pathogenesis of necrotising enterocolitis (NEC). Genetic association studies of cytokine polymorphisms may help to detect molecular mechanisms that are causally related to the disease process. AIM To examine associations between the common genetic variants in candidate inflammatory cytokine genes and NEC in preterm infants. METHODS Multi-centre case-control and genetic association study. DNA samples were collected from 50 preterm infants with NEC and 50 controls matched for gestational age and ethnic group recruited to a multi-centre case-control study. Ten candidate single-nucleotide polymorphisms in cytokines previously associated with infectious or inflammatory diseases were genotyped. The findings were included in random-effects meta-analyses with data from previous genetic association studies. RESULTS All allele distributions were in Hardy-Weinberg equilibrium. None of the studied cytokine polymorphisms was significantly associated with NEC. Four previous genetic association studies of cytokine polymorphisms and NEC in preterm infants were found. Meta-analyses were possible for several single-nucleotide polymorphisms. These increased the precision of the estimates of effect size but did not reveal any significant associations. CONCLUSIONS The available data are not consistent with more than modest associations between these candidate cytokine variant alleles and NEC in preterm infants. Data from future association studies of these polymorphisms may be added to the meta-analyses to obtain more precise estimates of effects sizes.The study was funded by Tenovus (Scotland)
Understanding hydrogen recombination line observations with ALMA and EVLA
Hydrogen recombination lines are one of the major diagnostics of H II region
physical properties and kinematics. In the near future, the Expanded Very Large
Array (EVLA) and the Atacama Large Millimeter Array (ALMA) will allow observers
to study recombination lines in the radio and sub-mm regime in unprecedented
detail. In this paper, we study the properties of recombination lines, in
particular at ALMA wavelengths. We find that such lines will lie in almost
every wideband ALMA setup and that the line emission will be equally detectable
in all bands. Furthermore, we present our implementation of hydrogen
recombination lines in the adaptive-mesh radiative transfer code RADMC-3D. We
particularly emphasize the importance of non-LTE (local thermodynamical
equilibrium) modeling since non-LTE effects can drastically affect the line
shapes and produce asymmetric line profiles from radially symmetric H II
regions. We demonstrate how these non-LTE effects can be used as a probe of
systematic motions (infall & outflow) in the gas. We use RADMC-3D to produce
synthetic observations of model H II regions and study the necessary conditions
for observing such asymmetric line profiles with ALMA and EVLA.Comment: MNRAS in pres
Towards operational measures of computer security
Ideally, a measure of the security of a system should capture quantitatively the intuitive notion of âthe ability of the system to resist attackâ. That is, it should be operational, reflecting the degree to which the system can be expected to remain free of security breaches under particular conditions of operation (including attack). Instead, current security levels at best merely reflect the extensiveness of safeguards introduced during the design and development of a system. Whilst we might expect a system developed to a higher level than another to exhibit âmore secure behaviourâ in operation, this cannot be guaranteed; more particularly, we cannot infer what the actual security behaviour will be from knowledge of such a level. In the paper we discuss similarities between reliability and security with the intention of working towards measures of âoperational securityâ similar to those that we have for reliability of systems. Very informally, these measures could involve expressions such as the rate of occurrence of security breaches (cf rate of occurrence of failures in reliability), or the probability that a specified âmissionâ can be accomplished without a security breach (cf reliability function). This new approach is based on the analogy between system failure and security breach. A number of other analogies to support this view are introduced. We examine this duality critically, and have identified a number of important open questions that need to be answered before this quantitative approach can be taken further. The work described here is therefore somewhat tentative, and one of our major intentions is to invite discussion about the plausibility and feasibility of this new approach
Factors contributing to high performance of sows in free farrowing systems
\ua9 The Author(s) 2024. Background: Pressure to abolish farrowing crates is increasing, and producers are faced with decisions about which alternative system to adopt. For sow welfare, well designed free farrowing systems without close confinement are considered optimal but producers have concerns about increased piglet mortality, particularly crushing by the sow. Reporting accurate performance figures from commercial farms newly operating such systems could inform the transition process. This study investigated performance on three commercial farms operating four different zero-confinement systems, three of which were newly installed. A total of 3212 litters from 2920 sows were followed from farrowing to weaning over a three-year period with key performance indicators (KPIs) recorded. Mixed Models (LMMs, GLMMs) determined the influence of different factors (e.g. farrowing system, sow parity, management aspects) and litter characteristics on performance, including levels and causes of piglet mortality. Results: Piglet mortality was significantly influenced by farm/system. Live-born mortality ranged from 10.3 to 20.6% with stillbirths ranging from 2.5 to 5.9%. A larger litter size and higher parity resulted in higher levels of mortality regardless of system. In all systems, crushing was the main cause of piglet mortality (59%), but 31% of sows did not crush any piglets, whilst 26% crushed only one piglet and the remaining sows (43%) crushed two or more piglets. System significantly influenced crushing as a percentage of all deaths, with the system with the smallest spatial footprint (m2) compared to the other systems, recording the highest levels of crushing. Time from the start of the study influenced mortality, with significant reductions in crushing mortality (by ~ 4%) over the course of the three-year study. There was a highly significant effect of length of time (days) between moving sows into the farrowing accommodation and sows farrowing on piglet mortality (P < 0.001). The less time between sows moving in and farrowing, the higher the levels of piglet mortality, with ~ 3% increase in total mortality every five days. System effects were highly significant after adjusting for parity, litter size, and days pre-farrowing. Conclusion: These results from commercial farms demonstrate that even sows that have not been specifically selected for free farrowing are able, in many cases, to perform well in these zero-confinement systems, but that a period of adaptation is to be expected for overall farm performance. There are performance differences between the farms/systems which can be attributed to individual farm/system characteristics (e.g. pen design and management, staff expertise, pig genotypes, etc.). Higher parity sows and those producing very large litters provide a greater challenge to piglet mortality in these free farrowing systems (just as they do in crate systems). Management significantly influences performance, and ensuring sows have plenty of time to acclimatise between moving in to farrowing accommodation and giving birth is a critical aspect of improving piglet survival
An oral delivery system for controlling white spot syndrome virus infection in shrimp using transgenic microalgae
White spot disease (WSD) is a longstanding and serious viral disease of various shrimp species that has caused high mortality rates for many decades. Currently, there is no practical method to control this disease. Therefore, we have explored the development of a novel vaccine-based method to control this disease using transgenic algae. During infection by white spot syndrome virus (WSSV), the interaction between viral envelope proteins and cell surface protein receptors on target cells is the key step of viral entry and replication. Hence, transgenic lines of the green microalga Chlamydomonas reinhardtii harbouring a WSSV VP28 viral envelope protein were created as an oral delivery system for vaccinating shrimp. Two separate transplastomic lines containing wild-type and codon optimized gene sequences for VP28 were evaluated for recombinant protein levels. Only the codon optimized line gave rise to detectable VP28 in western blot analysis, which demonstrated that optimization for chloroplast codon bias improved the efficiency of expression and that the gene design produced a favourable RNA secondary structure with suitable free energy for translation. In addition, bile salt and acid tolerance tests demonstrated that this transgenic Chlamydomonas can tolerate mildly acidic (pH 5.0) conditions and 0.30% bile salts. These features indicated that algal cells are suitable for delivering viral antigens through a shrimp's digestive system. In WSSV infection experiments, the highest survival rate (87%) was recorded in shrimps fed with the codon optimized VP28 line mixed into their feed, indicating that this line could be employed in the control of WSSV spread in shrimp populations. This algal strategy offers a new, efficient, fast and less labour-intensive method for the control of other diseases in aquatic animals through oral delivery
Spectroscopy of i-Dropout Galaxies with an NB921-Band Depression in the Subaru Deep Field
We report new spectroscopy of two star-forming galaxies with strong Ly_alpha
emission at z=6.03 and z=6.04 in the Subaru Deep Field. These two objects are
originally selected as i'-dropouts (i'-z' > 1.5) showing an interesting
photometric property, the ``NB921 depression''. The NB921-band (centered at
9196A) magnitude is significantly depressed with respect to the z'-band
magnitude. The optical spectra of these two objects exhibit asymmetric
emission-lines at lambda_obs ~ 8540A and ~ 8560A, suggesting that these objects
are Ly_alpha emitters at z~6. The rest-frame equivalent widths of the Ly_alpha
emission of the two objects are 94A and 236A; the latter one is the Ly_alpha
emitter with the largest Ly_alpha equivalent width at z > 6 ever
spectroscopically confirmed. The spectroscopically measured Ly_alpha fluxes of
these two objects are consistent with the interpretation that the NB921
depression is caused by the contribution of the strong Ly_alpha emission to the
z'-band flux. Most of the NB921-depressed i'-dropout objects are thought to be
strong Ly_alpha emitters at 6.0 < z < 6.5; Galactic L and T dwarfs and
NB921-dropout galaxies at z > 6.6 do not dominate the NB921-depressed
i'-dropout sample. Thus the NB921-depression method is very useful for finding
high-z Ly_alpha emitters with a large Ly_alpha equivalent width over a large
redshift range, 6.0 < z < 6.5. Although the broadband-selected sample at z ~ 3
contains only a small fraction of objects with a Ly_alpha equivalent width
larger than 100A, the i'-dropout sample of the Subaru Deep Field contains a
much larger fraction of such strong Ly_alpha emitters. This may imply a strong
evolution of the Ly_alpha equivalent width from z > 6 to z ~ 3.Comment: 21 pages, 6 figures, to appear in The Astrophysical Journa
On the Optimization of Broad-Band Photometry for Galaxy Evolution Studies
We have derived the uncertainties to be expected in the derivation of galaxy
physical properties (star formation history, age, metallicity, reddening) when
comparing broad-band photometry to the predictions of evolutionary synthesis
models. We have obtained synthetic colors for a large sample (9000) of
artificial galaxies assuming different star formation histories, ages,
metallicities, reddening values, and redshifts. The colors derived have been
perturbed by adopting different observing errors, and compared back to the
evolutionary synthesis models grouped in different sets. The comparison has
been performed using a combination of Monte Carlo simulations, a Maximum
Likelihood Estimator and Principal Component Analysis. After comparing the
input and derived output values we have been able to compute the uncertainties
and covariant degeneracies between the galaxy physical properties as function
of (1) the set of observables available, (2) the observing errors, and (3) the
galaxy properties themselves. In this work we have considered different sets of
observables, some of them including the standard Johnson/Cousins (UBVRI) and
Sloan Digital Sky Survey (SDSS) bands in the optical, the 2 Micron All Sky
Survey (2MASS) bands in the near-infrared, and the Galaxy Evolution Explorer
(GALEX) bands in the UV, at three different redshifts, z=0.0, 0.7, and 1.4.
This study is intended to represent a basic tool for the design of future
projects on galaxy evolution, allowing an estimate of the optimal band-pass
combinations and signal-to-noise ratios required for a given scientific
objective.Comment: 20 pages, 9 postscript figures, 3 tables, accepted for publication in
A
Dense Ionized and Neutral Gas Surrounding Sgr A*
We present high resolution H41a hydrogen recombination line observations of
the 1.2' (3 pc) region surrounding Sgr A* at 92 GHz using the OVRO Millimeter
Array with an angular resolution of 7" x 3" and velocity resolution of 13 km/s.
New observations of H31a, H35a, H41a, and H44a lines were obtained using the
NRAO 12-m telescope, and their relative line strengths are interpreted in terms
of various emission mechanisms. These are the most extensive and most sensitive
observations of recombination line to date. Observations of HCO+ (1 - 0)
transition at 89 GHz are also obtained simultaneously with a 40% improved
angular resolution and 4-15 times improved sensitivity over previous
observations, and the distribution and kinematics of the dense molecular gas in
the circumnuclear disk (CND) are mapped and compared with those of the ionized
gas. The line brightness ratios of the hydrogen recombination lines are
consistent with purely spontaneous emission from 7000 K gas with n_e = 20,000
cm near LTE condition. A virial analysis suggests that the most
prominent molecular gas clumps in the CND have mean densities of 10^7 cm^{-3},
sufficient to withstand the tidal shear in the Galactic Center region.
Therefore, these clumps may survive over several dynamical times, and the CND
may be a dynamically stable structure. We estimate a total gas mass of 3 x 10^5
solar mass for the CND. \Comment: 34 pages including 11 figures (4 jpgs), Latex, uses aastex. The full
pdf format file including high resolution figures is available at
http://www.astro.umass.edu/~myun/papers/SgrA.pdf . To appear in the 20
November 2004 (V616) issue of the Astrophysical Journa
Cost effectiveness of alternative planned places of birth in woman at low risk of complications: evidence from the Birthplace in England national prospective cohort study
Objectives To estimate the cost effectiveness of alternative planned places of birth
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