Effect of hydrogen on the strength and microstructure of selected ceramics

Ceramics in monolithic form and as composite constituents in the form of fibers, matrices, and coatings are currently being considered for a variety of high-temperature applications in aeronautics and space. Many of these applications involve exposure to a hydrogen-containing environment. The compatibility of selected ceramics in gaseous high-temperature hydrogen is assessed. Environmental stability regimes for the long term use of ceramic materials are defined by the parameters of temperature, pressure, and moisture content. Thermodynamically predicted reactions between hydrogen and several monolithic ceramics are compared with actual performance in a controlled environment. Morphology of hydrogen attack and the corresponding strength degradation is reported for silicon carbide, silicon nitride, alumina, magnesia, and mullite

You are here: Building an online interactive map application

As new map applications have increased in popularity the opportunities for gathering geographic data have increased as well. The difficulty that interactive user-driven map applications have is the motivation for user participation. People have become more comfortable contributing to forums, blogs, and sites driven by user content, but user-driven map sites have been slow to cultivate a large amount of user-contributed data. Focusing on a small geographic area can increase user participation within interactive map applications. The design and implementation of an online map applications focused on a small geographic area is presented. The site uses a map interface to gather new spatial data from users, as well as allowing browsing and search. Users can also annotate existing data on the site through the map interface. The final site presents a mix between theory-based design and the inherent limitations of a practical implementation

Preface: conservation of european ponds-current knowledge and future needs

Ponds are common elements of the landscape with an important role in the global processes of biosphere and biodiversity preservation. Recent research indicates that ecological characteristics of ponds are different from other inland water systems, but scientific knowledge is still insufficient and poor compared to lakes and rivers. Therefore, whilst indicators and conservation tools have been developed for most aquatic systems, there is also a gap between existing basic information on pond ecology and applied research. The European Pond Conservation Network (EPCN) with the aim of strengthening the links between basic and applied research and pond management organized its 3rd biennial meeting in Valencia (Spain) with the theme "Pond conservation: from science to practice". We present a selection of papers from this conference, which cover the three main topics of the sessions: (1) Management and conservation in practice, (2) Pond ecology at different scales and (3) Temporary ponds. The articles presented develop techniques for assessing the ecological status of this type of ecosystems, evidence the importance of ponds in a global scale, indicate that their conservation must take into account their spatial arrangement in networks, discuss environmental factors that are relevant to biodiversity conservation and provide information on different research areas such as biogeochemical processes, evolution of aquatic biota and community ecology

Patients’ attitudes about the use of placebo treatments: telephone survey

Objective To examine the attitudes of US patients about the use of placebo treatments in medical care. Design: One time telephone surveys. Setting: Northern California. Participants 853 members of Kaiser Permanente Northern California, aged 18-75, who had been seen by a primary care provider for a chronic health problem at least once in the prior six months. Results The response rate was 53.4% (853/1598) of all members who were eligible to participate, and 73.2% (853/1165) of all who could be reached by telephone. Most respondents (50-84%) judged it acceptable for doctors to recommend placebo treatments under conditions that varied according to doctors’ level of certainty about the benefits and safety of the treatment, the purpose of the treatment, and the transparency with which the treatment was described to patients. Only 21.9% of respondents judged that it was never acceptable for doctors to recommend placebo treatments. Respondents valued honesty by physicians regarding the use of placebos and believed that non-transparent use could undermine the relationship between patients and physicians. Conclusions: Most patients in this survey seemed favorable to the idea of placebo treatments and valued honesty and transparency in this context, suggesting that physicians should consider engaging with patients to discuss their values and attitudes about the appropriateness of using treatments aimed at promoting placebo responses in the context of clinical decision making

Spacelike Branes

Scalar field theories with appropriate potentials in Minkowski space can have time-dependent classical solutions containing topological defects which correspond to S-branes - i.e. branes all of whose tangential dimensions are spacelike. It is argued that such S-branes arise in string theory as time-dependent solutions of the worldvolume tachyon field of an unstable D-brane or D-brane-anti-D-brane pair. Using the known coupling of the spacetime RR fields to the worldvolume tachyon it is shown that these S-branes carry a charge, defined as the integral of a RR field strength over a sphere (containing a time as well as spatial dimensions) surrounding the S-brane. This same charge is carried by SD-branes, i.e. Dirichlet branes arising from open string worldsheet conformal field theories with a Dirichlet boundary condition on the timelike dimension. The corresponding SD-brane boundary state is constructed. Supergravity solutions carrying the same charges are also found for a few cases.Comment: 23 pages, harvmac(b), no figures, v2 references added and minor changes, v4: more references adde

The Relationship between Early Childhood Blood Lead Levels and Performance on End-of-Grade Tests

Background Childhood lead poisoning remains a critical environmental health concern. Low-level lead exposure has been linked to decreased performance on standardized IQ tests for school-aged children. Objective In this study we sought to determine whether blood lead levels in early childhood are related to educational achievement in early elementary school as measured by performance on end-of-grade (EOG) testing. Methods Educational testing data for 4th-grade students from the 2000–2004 North Carolina Education Research Data Center were linked to blood lead surveillance data for seven counties in North Carolina and then analyzed using exploratory and multivariate statistical methods. Results The discernible impact of blood lead levels on EOG testing is demonstrated for early childhood blood lead levels as low as 2 μg/dL. A blood lead level of 5 μg/dL is associated with a decline in EOG reading (and mathematics) scores that is roughly equal to 15% (14%) of the interquartile range, and this impact is very significant in comparison with the effects of covariates typically considered profoundly influential on educational outcomes. Early childhood lead exposures appear to have more impact on performance on the reading than on the mathematics portions of the tests. Conclusions Our emphasis on population-level analyses of children who are roughly the same age linked to previous (rather than contemporaneous) blood lead levels using achievement (rather than aptitude) outcome complements the important work in this area by previous researchers. Our results suggest that the relationship between blood lead levels and cognitive outcomes are robust across outcome measures and at low levels of lead exposure

Qualitative Analysis of Isotropic Curvature String Cosmologies

A complete qualitative study of the dynamics of string cosmologies is presented for the class of isotopic curvature universes. These models are of Bianchi types I, V and IX and reduce to the general class of Friedmann-Robertson-Walker universes in the limit of vanishing shear isotropy. A non-trivial two-form potential and cosmological constant terms are included in the system. In general, the two-form potential and spatial curvature terms are only dynamically important at intermediate stages of the evolution. In many of the models, the cosmological constant is important asymptotically and anisotropy becomes dynamically negligible. There also exist bouncing cosmologies.Comment: Accepted to Classical and Quantum Gravity, 40 pages, 12 figures (uses "graphicx" package for figures

Superconformal Multi-Black Hole Moduli Spaces in Four Dimensions

Quantum mechanics on the moduli space of N supersymmetric Reissner-Nordstrom black holes is shown to admit 4 supersymmetries using an unconventional supermultiplet which contains 3N bosons and 4N fermions. A near-horizon limit is found in which the quantum mechanics of widely separated black holes decouples from that of strongly-interacting, near-coincident black holes. This near-horizon theory is shown to have an enhanced D(2,1;0) superconformal symmetry. The bosonic symmetries are SL(2,R) conformal symmetry and SU(2)xSU(2) R-symmetry arising from spatial rotations and the R-symmetry of N=2 supergravity.Comment: 23 pages, harvmac. v2: many typos fixe