135 research outputs found
Atmospheric conditions and their effect on ball-milled magnesium diboride
Magnesium diboride bulk pellets were fabricated from pre-reacted MgB2 powder
ball milled with different amounts of exposure to air. Evidence of increased
electron scattering including increased resistivity, depressed Tc, and enhanced
Hc2 of the milled and heat treated samples were observed as a result of
increased contact with air. These and other data were consistent with alloying
with carbon as a result of exposure to air. A less clear trend of decreased
connectivity associated with air exposure was also observed. In making the case
that exposure to air should be considered a doping process, these results may
explain the wide varibability of "undoped" MgB2 properties extant in the
literature.Comment: Work presented at ASC 2006 in Seattl
Solenoidal Coils Made from Monofilamentary and Multifilamentary MgB2 strands
Three solenoids have been wound and with MgB2 strand and tested for transport
properties. One of the coils was wound with Cu-sheathed monofilamentary strand
and the other two with a seven filament strand with Nb-reaction barriers, Cu
stabilization, and an outer monel sheath. The wires were first S-glass
insulated, then wound onto an OFHC Cu former. The coils were then heat treated
at 675C/30 min (monofilamentary strand) and 700C/20 min (multifilamentary
strand). Smaller (1 m) segments of representative strand were also wound into
barrel-form samples and HT along with the coils. After HT the coils were epoxy
impregnated. Transport Jc measurements were performed at various taps along the
coil lengths. Measurements were made initially in liquid helium, and then as a
function of temperature up to 30 K. Homogeneity of response along the coils was
investigated and a comparison to the short sample results was made. Each coil
contained more than 100 m of 0.84-1.01 mm OD strand. One of the 7 strand coils
reached 222 A at 4.2 K, self field, with a Jc of 300 kA/cm2 in the SC and a
winding pack Je of 23 kA/cm2. At 20 K these values were 175 kA/cm2 and 13.4
kA/cm2. Magnet bore fields of 1.5 T and 0.87 T were achieved at 4.2 K and 20 K,
respectively. The other multifilamentary coil gave similar results.Comment: 22 pages, 8 figures, 2 table
The effects of superconductor-stabilizer interfacial resistance on quench of a pancake coil made out of coated conductor
We present the results of numerical analysis of normal zone propagation in a
stack of coated conductors which imitates a pancake coil.
Our main purpose is to determine whether the quench protection quality of such
coils can be substantially improved by increased contact resistance between the
superconducting film and the stabilizer. We show that with increased contact
resistance the speed of normal zone propagation increases, the detection of a
normal zone inside the coil becomes possible earlier, when the peak temperature
inside the normal zone is lower, and stability margins shrink. Thus, increasing
contact resistance may become a viable option for improving the prospects of
coated conductors for high magnets applications.Comment: 9 pages, 4 figure
Low serum placental lactogen at term is associated with postnatal symptoms of depression and anxiety in women delivering female infants
Background. Placental endocrine insufficiency may increase the risk of depression and anxiety during pregnancy and/or after birth. This study investigated the association between serum human placental lactogen (hPL) and measures of perinatal mental health, accounting for selective serotonin-reuptake inhibitor (SSRI) usage.
Method. Caucasian women with singleton, term pregnancies recruited at their pre-surgical appointment prior to an elective caesarean section (ELCS) were studied. Serum hPL levels in maternal blood collected at recruitment were measured by ELISA. Depression and anxiety scores were derived from Edinburgh Postnatal Depression Scale (EPDS) and the trait subscale of the State-Trait Anxiety Inventory (STAI) questionnaires completed at recruitment and three postnatal time points. Data was analysed by unadjusted and adjusted multiple linear regression.
Results. In adjusted linear regressions, term maternal serum hPL levels were negatively associated with postnatal EPDS and STAI score ten weeks postnatal for mothers who had girls (B= -.367 , p= .022, 95% CI -.679, -.056; and B= -.776, p= .030, 95% CI -1.475, -.077 respectively). Excluding women prescribed SSRIs strengthened the relationship at 10 weeks and uncovered an earlier association between hPL and mood scores within one week of delivery (EPDS B= -.357 , p= .041, 95% CI -.698, -.015; and STAI B= -.737, p= .027, 95% CI -1.387, -.086). In mothers who had boys, there were no associations between hPL and mood scores at any time point.
Conclusion. Low hPL predicted postnatal depression and anxiety symptoms exclusively in mothers of girls. Insufficiency in hPL may contribute to maternal mood symptoms
Maternal care boosted by paternal imprinting in mammals.
In mammals, mothers are the primary caregiver, programmed, in part, by hormones produced during pregnancy. High-quality maternal care is essential for the survival and lifelong health of offspring. We previously showed that the paternally silenced imprinted gene pleckstrin homology-like domain family A member 2 (Phlda2) functions to negatively regulate a single lineage in the mouse placenta called the spongiotrophoblast, a major source of hormones in pregnancy. Consequently, the offspring's Phlda2 gene dosage may influence the quality of care provided by the mother. Here, we show that wild-type (WT) female mice exposed to offspring with three different doses of the maternally expressed Phlda2 gene-two active alleles, one active allele (the extant state), and loss of function-show changes in the maternal hypothalamus and hippocampus during pregnancy, regions important for maternal-care behaviour. After birth, WT dams exposed in utero to offspring with the highest Phlda2 dose exhibit decreased nursing and grooming of pups and increased focus on nest building. Conversely, 'paternalised' dams, exposed to the lowest Phlda2 dose, showed increased nurturing of their pups, increased self-directed behaviour, and a decreased focus on nest building, behaviour that was robustly maintained in the absence of genetically modified pups. This work raises the intriguing possibility that imprinting of Phlda2 contributed to increased maternal care during the evolution of mammals
Multifilamentary, in-situ Route, Cu-stabilized MgB2 Strands
Transport critical current densities and n-values were measured at 4.2 K in
fields up to 15 T on 7, 19, and 37-stack multifilamentary MgB2 strands made
using an in-situ route. Some strands included SiC additions (particle size 30
nm), while in others Mg-rich compositions were used. Two basic multifilamentary
variants were measured, the first had Nb filamentary barriers, the second had
Fe filamentary barriers. All samples incorporated stabilizer in the form of Cu
101. Simple, one-step heat treatments were used, with temperatures ranging from
700-800C, and times from 10-30 minutes. Transport critical current densities of
1.75 x 105 A/cm2 were seen at 4.2 K and 5 T in 37 stack strands.Comment: 10 pages, 3 figs, 2 table
Epidemic protection zones : centred on cases or based on connectivity?
When an exotic infectious disease invades a susceptible environment, protection
zones are enforced. Historically, such zones have been shaped as circles of
equal radius (ER), centred on the location of infected premises. Because the ER
policy seems to assume that epidemic dissemination is driven by a similar
number of secondary cases generated per primary case, it does not consider
whether local features, such as connectivity, influence epidemic dispersal. Here
we explored the efficacy of ER protection zones. By generating a geographically
explicit scenario that mimicked an actual epidemic, we created protection
zones of different geometry, comparing the cost-benefit estimates of ER protection
zones to a set of alternatives, which considered a pre-existing connecting
network (CN) – the road network. The hypothesis of similar number of cases
per ER circle was not substantiated: the number of units at risk per circle differed
up to four times among ER circles. Findings also showed that even a
small area (of <115 km2) revealed network properties. Because the CN policy
required 20% less area to be protected than the ER policy, and the CN-based
protection zone included a 23.8% greater density of units at risk/km2 than the
ER-based alternative, findings supported the view that protection zones are
likely to be less costly and more effective if they consider connecting structures,
such as road, railroad and/or river networks. The analysis of local geographical
factors (contacts, vectors and connectivity) may optimize the efficacy of control
measures against epidemics.http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1865-1682ab2012ab2013 (Author correction
Pushing the Limits of Exoplanet Discovery via Direct Imaging with Deep Learning
Further advances in exoplanet detection and characterisation require sampling a diverse population of extrasolar planets. One technique to detect these distant worlds is through the direct detection of their thermal emission. The so-called direct imaging technique, is suitable for observing young planets far from their star. These are very low signal-to-noise-ratio (SNR) measurements and limited ground truth hinders the use of supervised learning approaches. In this paper, we combine deep generative and discriminative models to bypass the issues arising when directly training on real data. We use a Generative Adversarial Network to obtain a suitable dataset for training Convolutional Neural Network classifiers to detect and locate planets across a wide range of SNRs. Tested on artificial data, our detectors exhibit good predictive performance and robustness across SNRs. To demonstrate the limits of the detectors, we provide maps of the precision and recall of the model per pixel of the input image. On real data, the models can re-confirm bright source detections
Density effect on critical current density and flux pinning properties of polycrystalline SmFeAsO1-xFx superconductor
A series of polycrystalline SmFeAs1-xOx bulks was prepared to systematically
investigate the influence of sample density on flux pinning properties.
Different sample densities were achieved by controlling the pelletizing
pressure. The superconducting volume fraction, the critical current densities
Jcm and the flux pinning force densities Fp were estimated from the
magnetization measurements. Experimental results manifest that: (1) the
superconducting volume fraction decreases with the decreasing of sample
density. (2) The Jcm values have the similar trend except for the sample with
very high density may due to different connectivity and pinning mechanism.
Moreover, The Jcm(B) curve develops a peak effect at approximately the same
field at which the high-density sample shows a kink. (3) The Fp(B) curve of the
high-density sample shows a low-field peak and a high-field peak at several
temperatures, which can be explained by improved intergranular current, while
only one peak can be observed in Fp(B) of the low-density samples. Based on the
scaling behaviour of flux pinning force densities, the main intragranular
pinning is normal point pinning.Comment: 23 pages, 8 figures, 1 tabl
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