4,035 research outputs found
Selected Parametric Effects on Materials Flammability Limits
NASA-STD-(I)-6001B Test 1 is currently used to evaluate the flammability of materials intended for use in habitable environments of U.S. spacecraft. The method is a pass/fail upward flame propagation test conducted in the worst case configuration, which is defined as a combination of a material s thickness, test pressure, oxygen concentration, and temperature that make the material most flammable. Although simple parametric effects may be intuitive (such as increasing oxygen concentrations resulting in increased flammability), combinations of multi-parameter effects could be more complex. In addition, there are a variety of material configurations used in spacecraft. Such configurations could include, for example, exposed free edges where fire propagation may be different when compared to configurations commonly employed in standard testing. Studies involving combined oxygen concentration, pressure, and temperature on flammability limits have been conducted and are summarized in this paper. Additional effects on flammability limits of a material s thickness, mode of ignition, burn-length criteria, and exposed edges are presented. The information obtained will allow proper selection of ground flammability test conditions, support further studies comparing flammability in 1-g with microgravity and reduced gravity environments, and contribute to persuasive scientific cases for rigorous space system fire risk assessments
The in vitro bioactivity of two novel hydrophilic, partially degradable bone cements
Composite bone cements were prepared with bioactive glasses (MgOâSiO2â3CaO Ă P2O5) of different reactivities. The matrix of these
so-called hydrophilic, partially degradable and bioactive cements was composed of a starch/cellulose acetate blend and poly(2-hydroxyethyl
methacrylate). The addition of 30 wt.% of glasses to this system made them bioactive in acellular medium: a dense apatite layer
formed on the surface after 7 days of immersion in simulated body fluid. This was demonstrated both by microscopic and infrared spectroscopic
techniques. The composition of the glass and, consequently, its structure was found to have important effects on the rate of the
apatite formation. The combination of reactivity obtained by one formulation with the hydrophilic and degradable character of these
cements makes them a very promising alternative to conventional acrylic bone cements, by allowing a better stabilization of the implant
and a stronger adhesion to the bone
Effects of the sex of the perpetrator on victimsâ subsequent sexual behaviors and adulthood sexual orientations
Data from 2,828 female and 1,556 male adult participants from a general population convenience sample were used to measure the effect of the sex of the perpetrator on the adult sexual orientation of the victims of child sexual abuse (CSA) by adult male or female perpetrators and early incest with parents or early incest with siblings. Sexual behaviors with female perpetrators tended to promote an orientation toward sex with females and analogous behaviors with male perpetrators tended to promote an orientation toward sex with males in victims of both sexes. Many forms of incest or CSA increased the likelihood the victims would subsequently engage in behaviors with other partners or begin masturbating using adult male or female images. The subsequent early behaviors with other partners and masturbating using images of both male and female adults significantly enhanced or attenuated the conditioning resulting from interacting with the initial perpetrator. The victimsâ adult sexual orientations could be statistically predicted using regression equations that took into account the sexual behaviors with both adult and underage partners and whether or not the participant had masturbated using images of male or female adults. The results were consistent with conditioning and counter-conditioning theories
How should the completeness and quality of curated nanomaterial data be evaluated
Nanotechnology is of increasing significance. Curation of nanomaterial data into electronic databases offers opportunities to better understand and predict nanomaterialsâ behaviour. This supports innovation in, and regulation of, nanotechnology. It is commonly understood that curated data need to be sufficiently complete and of sufficient quality to serve their intended purpose. However, assessing data completeness and quality is non-trivial in general and is arguably especially difficult in the nanoscience area, given its highly multidisciplinary nature. The current article, part of the Nanomaterial Data Curation Initiative series, addresses how to assess the completeness and quality of (curated) nanomaterial data. In order to address this key challenge, a variety of related issues are discussed: the meaning and importance of data completeness and quality, existing approaches to their assessment and the key challenges associated with evaluating the completeness and quality of curated nanomaterial data. Considerations which are specific to the nanoscience area and lessons which can be learned from other relevant scientific disciplines are considered. Hence, the scope of this discussion ranges from physicochemical characterisation requirements for nanomaterials and interference of nanomaterials with nanotoxicology assays to broader issues such as minimum information checklists, toxicology data quality schemes and computational approaches that facilitate evaluation of the completeness and quality of (curated) data. This discussion is informed by a literature review and a survey of key nanomaterial data curation stakeholders. Finally, drawing upon this discussion, recommendations are presented concerning the central question: how should the completeness and quality of curated nanomaterial data be evaluated
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Perceptions of the Environment and Health Among Members of the Confederated Tribes of the Umatilla Indian Reservation
Indigenous cultures perceive the natural environment as an essential link between traditional cultural
practices, social connectedness, identity, and health. Many tribal communities face substantial health
disparities related to exposure to environmental hazards. Our study used qualitative methods to better
understand the Confederated Tribes of the Umatilla Indian Reservation (CTUIR) membersâ perspectives
about their environment and its connections with their health including views on environmental health
hazards. Three 90-minute focus group sessions with a total of 27 participants were held to elicit opinions on
meanings of health and how the environment interacts with health. A systematic text analysis was used to
derive themes across focus groups. Participants expressed a holistic view of health that included environmental,
physical, mental, spiritual, and social components. A healthy natural environment was identified
as an essential component of a healthy individual and a healthy community. Participants also
described many environmental health concerns including second-hand smoke, outdoor smoke, diesel
exhaust, mold, pesticides, contaminated natural foods, and toxic wastes from the Hanford nuclear site and
methamphetamine labs. Many believe the identified environmental hazards contribute to diseases in their
community. The natural environment is an important resource to CTUIR members and plays an integral
role in achieving and maintaining health. Knowledge about the values and concerns of the community are
useful to the tribal and federal governments, health professionals, environmental health practitioners, and
community members who seek to achieve sustainable and healthy rural Native communities
Evolution of high pathogenicity of H5 avian influenza virus: haemagglutinin cleavage site selection of reverse-genetics mutants during passage in chickens
Low pathogenicity avian influenza viruses (LPAIVs) are generally asymptomatic in their natural avian hosts. LPAIVs can evolve into highly pathogenic forms, which can affect avian and human populations with devastating consequences. The switch to highly pathogenic avian influenza virus (HPAIV) from LPAIV precursors requires the acquisition of multiple basic amino acids in the haemagglutinin cleavage site (HACS) motif. Through reverse genetics of an H5N1 HPAIV, and experimental infection of chickens, we determined that viruses containing five or more basic amino acids in the HACS motif were preferentially selected over those with three to four basic amino acids, leading to rapid replacement with virus types containing extended HACS motifs. Conversely, viruses harbouring low pathogenicity motifs containing two basic amino acids did not readily evolve to extended forms, suggesting that a single insertion of a basic amino acid into the cleavage site motif of low-pathogenic viruses may lead to escalating selection for extended motifs. Our results may explain why mid-length forms are rarely detected in nature. The stability of the short motif suggests that pathogenicity switching may require specific conditions of intense selection pressure (such as with high host density) to boost selection of the initial mid-length HACS forms
Search for the standard model Higgs boson in the H to ZZ to 2l 2nu channel in pp collisions at sqrt(s) = 7 TeV
A search for the standard model Higgs boson in the H to ZZ to 2l 2nu decay
channel, where l = e or mu, in pp collisions at a center-of-mass energy of 7
TeV is presented. The data were collected at the LHC, with the CMS detector,
and correspond to an integrated luminosity of 4.6 inverse femtobarns. No
significant excess is observed above the background expectation, and upper
limits are set on the Higgs boson production cross section. The presence of the
standard model Higgs boson with a mass in the 270-440 GeV range is excluded at
95% confidence level.Comment: Submitted to JHE
Search for New Physics with Jets and Missing Transverse Momentum in pp collisions at sqrt(s) = 7 TeV
A search for new physics is presented based on an event signature of at least
three jets accompanied by large missing transverse momentum, using a data
sample corresponding to an integrated luminosity of 36 inverse picobarns
collected in proton--proton collisions at sqrt(s)=7 TeV with the CMS detector
at the LHC. No excess of events is observed above the expected standard model
backgrounds, which are all estimated from the data. Exclusion limits are
presented for the constrained minimal supersymmetric extension of the standard
model. Cross section limits are also presented using simplified models with new
particles decaying to an undetected particle and one or two jets
Search for anomalous t t-bar production in the highly-boosted all-hadronic final state
A search is presented for a massive particle, generically referred to as a
Z', decaying into a t t-bar pair. The search focuses on Z' resonances that are
sufficiently massive to produce highly Lorentz-boosted top quarks, which yield
collimated decay products that are partially or fully merged into single jets.
The analysis uses new methods to analyze jet substructure, providing
suppression of the non-top multijet backgrounds. The analysis is based on a
data sample of proton-proton collisions at a center-of-mass energy of 7 TeV,
corresponding to an integrated luminosity of 5 inverse femtobarns. Upper limits
in the range of 1 pb are set on the product of the production cross section and
branching fraction for a topcolor Z' modeled for several widths, as well as for
a Randall--Sundrum Kaluza--Klein gluon. In addition, the results constrain any
enhancement in t t-bar production beyond expectations of the standard model for
t t-bar invariant masses larger than 1 TeV.Comment: Submitted to the Journal of High Energy Physics; this version
includes a minor typo correction that will be submitted as an erratu
Combined search for the quarks of a sequential fourth generation
Results are presented from a search for a fourth generation of quarks
produced singly or in pairs in a data set corresponding to an integrated
luminosity of 5 inverse femtobarns recorded by the CMS experiment at the LHC in
2011. A novel strategy has been developed for a combined search for quarks of
the up and down type in decay channels with at least one isolated muon or
electron. Limits on the mass of the fourth-generation quarks and the relevant
Cabibbo-Kobayashi-Maskawa matrix elements are derived in the context of a
simple extension of the standard model with a sequential fourth generation of
fermions. The existence of mass-degenerate fourth-generation quarks with masses
below 685 GeV is excluded at 95% confidence level for minimal off-diagonal
mixing between the third- and the fourth-generation quarks. With a mass
difference of 25 GeV between the quark masses, the obtained limit on the masses
of the fourth-generation quarks shifts by about +/- 20 GeV. These results
significantly reduce the allowed parameter space for a fourth generation of
fermions.Comment: Replaced with published version. Added journal reference and DO
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