2,251 research outputs found
A development of logistics management models for the Space Transportation System
A new analytic queueing approach was described which relates stockage levels, repair level decisions, and the project network schedule of prelaunch operations directly to the probability distribution of the space transportation system launch delay. Finite source population and limited repair capability were additional factors included in this logistics management model developed specifically for STS maintenance requirements. Data presently available to support logistics decisions were based on a comparability study of heavy aircraft components. A two-phase program is recommended by which NASA would implement an integrated data collection system, assemble logistics data from previous STS flights, revise extant logistics planning and resource requirement parameters using Bayes-Lin techniques, and adjust for uncertainty surrounding logistics systems performance parameters. The implementation of these recommendations can be expected to deliver more cost-effective logistics support
A rationally designed reversible 'turn-off' sensor for glutathione
Îł-Glutamyl-cysteinyl-glycine (GSH) plays a critical role in maintaining redox homeostasis in biological systems and a decrease in its cellular levels is associated with diseases. Existing fluorescence-based chemosensors for GSH acts as irreversible reaction-based probes that exhibit a maximum fluorescence ('turn-on') once the reaction is complete, regardless of the actual concentration of GSH. A reversible, reaction-based 'turn-off' probe ( 1 ) is reported here to sense the decreasing levels of GSH, a situation known to occur at the onset of various diseases. The more fluorescent merocyanine (MC) isomer of 1 exists in aqueous solution and this reacts with GSH to induce formation of the ring-closed spiropyran (SP) isomer, with a measurable decrease in absorbance and fluorescence ('turn-off'). Sensor 1 has good aqueous solubility and shows an excellent selectivity for GSH over other biologically relevant metal ions and aminothiol analytes. The sensor permeates HEK 293 cells and an increase in fluorescence is observed on adding buthionine sulfoximine, an inhibitor of GSH synthesis.Sabrina Heng, Xiaozhou Zhang, Jinxin Pei and Andrew D. Abel
Small-sample corrections for score tests in Birnbaum-Saunders regressions
In this paper we deal with the issue of performing accurate small-sample
inference in the Birnbaum-Saunders regression model, which can be useful for
modeling lifetime or reliability data. We derive a Bartlett-type correction for
the score test and numerically compare the corrected test with the usual score
test, the likelihood ratio test and its Bartlett-corrected version. Our
simulation results suggest that the corrected test we propose is more reliable
than the other tests.Comment: To appear in the Communications in Statistics - Theory and Methods,
http://www.informaworld.com/smpp/title~content=t71359723
Parental absence in early childhood and onset of smoking and alcohol consumption before adolescence
Background: Parental absence, due to death or separation from a parent, has been associated with smoking and alcohol consumption in adolescence and adulthood. The aim of this study was to investigate whether parental absence in early childhood was associated with smoking and alcohol uptake before adolescence. / Methods: Data on 10,940 children from the UKâs Millennium Cohort Study were used. Logistic regression was used to test associations between parental absence (0-7 years) and reports of smoking and alcohol consumption at age 11. / Results: Children who experienced parental absence were more likely to have smoked (OR=2.58, 95% CI: 1.88, 3.56) and consumed alcohol (OR=1.46, 95% CI: 1.25, 1.72). No differences were found by child sex or age, or parent absent. Children who experienced parental death were less likely to have drunk alcohol but those who had were more likely to have consumed enough to feel drunk. / Conclusions: Parental absence was associated with early uptake of risky health behaviours in a large, nationally representative UK cohort. Children who experience parental absence should be supported in early life in order to prevent smoking and alcohol initiation
Analysis of Toxic Amyloid Fibril Interactions at Natively Derived Membranes by Ellipsometry
There is an ongoing debate regarding the culprits of cytotoxicity associated with amyloid disorders. Although small pre-fibrillar amyloid oligomers have been implicated as the primary toxic species, the fibrillar amyloid material itself can also induce cytotoxicity. To investigate membrane disruption and cytotoxic effects associated with intact and fragmented fibrils, the novel in situ spectroscopic technique of Total Internal Reflection Ellipsometry (TIRE) was used. Fibril lipid interactions were monitored using natively derived whole cell membranes as a model of the in vivo environment. We show that fragmented fibrils have an increased ability to disrupt these natively derived membranes by causing a loss of material from the deposited surface when compared with unfragmented fibrils. This effect was corroborated by observations of membrane disruption in live cells, and by dye release assay using synthetic liposomes. Through these studies we demonstrate the use of TIRE for the analysis of protein-lipid interactions on natively derived lipid surfaces, and provide an explanation on how amyloid fibrils can cause a toxic gain of function, while entangled amyloid plaques exert minimal biological activity
The AMIGA sample of isolated galaxies. V. Quantification of the isolation
The AMIGA project aims to build a well defined and statistically significant
reference sample of isolated galaxies in order to estimate the environmental
effects on the formation and evolution of galaxies. The goal of this paper is
to provide a measure of the environment of the isolated galaxies in the AMIGA
sample, quantifying the influence of the candidate neighbours identified in our
previous work and their potential effects on the evolution of the primary
galaxies. Here we provide a quantification of the isolation degree of the
galaxies in this sample. Our starting sample is the Catalogue of Isolated
Galaxies (CIG). We used two parameters to estimate the influence exerted by the
neighbour galaxies on the CIG galaxy: the local number density of neighbour
galaxies and the tidal strength affecting the CIG galaxy. We show that both
parameters together provide a comprehensive picture of the environment. For
comparison, those parameters have also been derived for galaxies in denser
environments such as triplets, groups and clusters. The CIG galaxies show a
continuous spectrum of isolation, as quantified by the two parameters, from
very isolated to interacting. The fraction of CIG galaxies whose properties are
expected to be influenced by the environment is however low (159 out of 950
galaxies). The isolated parameters derived for the comparsion samples gave
higher values than for the CIG and we found clear differences for the average
values of the 4 samples considered, proving the sensitivity of these
parameters. The environment of the galaxies in the CIG has been characterised,
using two complementary parameters quantifying the isolation degree, the local
number density of the neighbour galaxies and the tidal forces affecting the
isolated galaxies. (Abridged)Comment: 10 pages, 12 figures, proposed for acceptance A&
Patterned Arrays of Supramolecular Microcapsules
Micropatterning of hydrogel has brought innovative
outcomes in fundamental and applied material sciences.
Previous approaches have mainly been dedicated
to fabricate arrays of bulk hydrogel beads, which have
inherent challenges including loading ability, scalability,
specificity and versatility. Here we present a methodology
to create hollow microcapsule arrays from sessile
microdroplets. The difference in wettability between hydrophilic
and hydrophobic surfaces enables self-partitioning
of liquid into microdroplet arrays, serving as microreservoirs
to load complementarily-functionalized host-guest
polymers, cucurbit[8]uril-threaded highly-branched polyrotaxanes
(HBP-CB[8]) and naphthyl-functionalized hydroxyethyl
cellulose (HEC-Np). The interfacial dynamic complexation
between positively-charged HBP-CB[8] and HECNp
occurred in the presence of negatively-charged surfactants,
resulting in condensed supramolecular hydrogel skins.
The hydrogel microcapsules were uniform in size, and were
developed to encapsulate target cargos in a robust and
well-defined manner. Moreover, the microcapsule substrates
were further used for surface enhanced Raman spectroscopy
(SERS) sensing upon loading of gold nanoparticles. This
facile assembly of microcapsule arrays has potential applications
in controlled cargo delivery, bio-sensing, high
throughput analysis and sorting
Parental nonstandard work schedules during infancy and childrenâs BMI trajectories
BACKGROUND: Empirical evidence has demonstrated adverse associations between parental nonstandard work schedules (i.e., evenings, nights, or weekends) and child developmental outcomes. However, there are mixed findings concerning the relationship between parental nonstandard employment and childrenâs body mass index (BMI), and few studies have incorporated information on paternal work schedules. OBJECTIVE: This paper investigated BMI trajectories from early to middle childhood (ages 3â11) by parental work schedules at 9 months of age, using nationally representative cohort data from the United Kingdom. This study is the first to examine the link between nonstandard work schedules and childrenâs BMI in the United Kingdom. METHODS: We used data from the Millennium Cohort Study (2001â2013, n = 13,021) to estimate trajectories in BMI, using data from ages 3, 5, 7, and 11 years. Joint parental work schedules and a range of biological, socioeconomic, and psychosocial covariates were assessed in the initial interviews at 9 months. RESULTS: Compared to children in two-parent families where parents worked standard shifts, we found steeper BMI growth trajectories for children in two-parent families where both parents worked nonstandard shifts and children in single-parent families whose mothers worked a standard shift. Fathersâ shift work, compared to standard shifts, was independently associated with significant increases in BMI. CONCLUSIONS: Future public health initiatives focused on reducing the risk of rapid BMI gain in childhood can potentially consider the disruptions to family processes resulting from working nonstandard hours. CONTRIBUTION: Children in families in which both parents work nonstandard schedules had steeper BMI growth trajectories across the first decade of life. Fathersâ nonstandard shifts were independently associated with increases in BMI
Clusters and Superclusters in the Las Campanas Redshift Survey
Two-dimensional high-resolution density field of galaxies of the Las Campanas
Redshift Survey (LCRS) with a smoothing length 0.8 Mpc/h is used to extract
clusters and groups of galaxies, and a low-resolution field with a smoothing
length 10 Mpc/h to find superclusters of galaxies. Properties of these density
field (DF) clusters and superclusters are studied and compared with the
properties of Abell clusters and superclusters, and LCRS loose groups. We
calculate the DF-cluster luminosity function, and show that most luminous
clusters in high-density environments are about ten times brighter than most
luminous clusters in low-density environments. We present a catalogue of
DF-superclusters and show that superclusters that contain Abell clusters are
richer and more luminous than superclusters without Abell clusters. A pdf file
of the paper with high-resolution figures is available in Tartu Observatory
web-site (http://www.aai.ee/~maret/cosmoweb.html)Comment: 19 pages LaTeX text, 15 PostScript Figures, submitted to Astronomy
and Astrophysic
A 120-Mpc Periodicity in the Three-Dimensional Distribution of Galaxy Superclusters
Using a new compilation of available data on galaxy clusters and
superclusters we present evidence for a quasiregular three-dimensional network
of rich superclusters and voids, with the regions of high density separated by
about 120 Mpc. We calculate the power spectrum for clusters of galaxies; it has
a peak on the wavelength equal to the step of the network; the excess in the
amplitude of the spectrum over that of the cold dark matter model is by a
factor of 1.4. The probability that the spectrum can be formed within the
framework of the standard cosmogony is very small. If the cluster distribution
reflects the distribution of all matter (luminous and dark), then there must
exists some hithero unknown process that produces regular structure on large
scales.Comment: Tex, 6 pages, 2 PostScript figures embedded, accepted by Nature on
November 19, 199
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