Life considerations of the shuttle orbiter densified-tile thermal protection system

The Shuttle orbiter themal protection system (TPS) incorporates ceramic reusable surface insulation tiles bonded to the orbiter substructure through a strain isolation pad. Densification of the bonding surface of the tiles increases the static strength of the tiles. The densification proces does not, however, necessarily lead to an equivalent increase in fatigue strength. Investigation of the expected lifetime of densified tile TPS under both sinusoidal loading and random loading simulating flight conditions indicates that the strain isolation pads are the weakest components of the TPS under fatigue loading. The felt pads loosen under repetitive loading and, in highly loaded regions, could possibly cause excessive step heights between tiles causing burning of the protective insulation between tiles. A method of improving the operational lifetime of the TPS by using a strain isolation pad with increased stiffness is presented as is the consequence of the effect of increased stiffness on the tile inplane strains and transverse stresses

Fatigue properties of shuttle thermal protection system

Static and cyclic load tests were conducted to determine the static and fatigue strength of the RIS tile/SIP thermal protection system used on the orbiter of the space shuttle. The material systems investigated include the densified and undensified LI-900 tile system on the .40 cm thick SIP and the densified and undensified LI-2200 tile system on the .23 cm (.090 inch) thick SIP. The tests were conducted at room temperature with a fully reversed uniform cyclic loading at 1 Hertz. Cyclic loading causes a relatively large reduction in the stress level that each of the SIP/tile systems can withstand for a small number of cycles. For example, the average static strength of the .40 cm thick SIP/LI-900 tile system is reduced from 86 kPa to 62 kPa for a thousand cycles. Although the .23 cm thick SIP/LI-2200 tile system has a higher static strength, similar reductions in the fatigue strength are noted. Densifying the faying surface of the RSI tile changes the failure mode from the SIP/tile interface to the parent RSI or the SIP and thus greatly increases the static strength of the system. Fatigue failure for the densified tile system, however, occurs due to complete separation or excessive elongation of the SIP and the fatigue strength is only slightly greater than that for the undensified tile system

Phosphorus indexing for cropland: Overview and basic concepts of the Iowa phosphorus index

Excessive phosphorus (P) loss from soils impairs surface water resources. An assessment tool or index has been proposed to identify fields with high potential risk of P delivery. The P index integrates P source and transport factors into a decision making process that may lead to changes in current P management and soil conservation practices. The index recognizes that a single soil P threshold alone is not an appropriate evaluation factor because of the varying conditions across fields. Although most indices being developed in the United States include similar factors, source and transport characteristics are considered in various ways to best address the variable conditions across regions. The Iowa P index reflects conditions that predominate under grain-crop production systems, considers source factors in a multiplicative manner within three main transport mechanisms, and approximates loads of P likely to enter and become available to aquatic ecosystems. An erosional component considers sheet and rill erosion, P enrichment, total soil P, buffers, sediment delivery, distance to a stream, and the long term biotic availability of particulate P in lake ecosystems. A runoff component considers water runoff based on a modification of the runoff curve number (RCN), soil-test P (STP), rate, time, and method of P application. An internal drainage component considers the presence of tiles, water flow to tile lines, subsurface recharge from subsurface flow, and soil-test P. When the erosion risk is high, the index weighs particulate P loss heavily compared with dissolved P loss, and emphasizes long-term processes comparatively more than short-term processes. This P assessment tool helps identify alternative P and soil conservation management options for reducing total P delivery from fields to surface water resources

Cold Molecule Spectroscopy for Constraining the Evolution of the Fine Structure Constant

We report precise measurements of ground-state, $\lambda$-doublet microwave transitions in the hydroxyl radical molecule (OH). Utilizing slow, cold molecules produced by a Stark decelerator we have improved over the precision of the previous best measurement by twenty-five-fold for the F' = 2 $\to$ F = 2 transition, yielding (1 667 358 996 $\pm$ 4) Hz, and by ten-fold for the F' = 1 $\to$ F = 1 transition, yielding (1 665 401 803 $\pm$ 12) Hz. Comparing these laboratory frequencies to those from OH megamasers in interstellar space will allow a sensitivity of 1 ppm for $\Delta\alpha/\alpha$ over $\sim$$10^{10}$ years.Comment: This version corrects minor typos in the Zeeman shift discussio

Use of medication by young people with attention-deficit/hyperactivity disorder

The document attached has been archived with permission from the editor of the Medical Journal of Australia (26 April 2007). An external link to the publisher’s copy is includedObjectivesTo examine the prevalence of psychotropic medication use by children with attention-deficit/hyperactivity disorder (ADHD) and children without ADHD. To identify factors associated with stimulant use by children in the community.DesignA representative, multistage probability sample of Australian households was conducted in 1998. Parents completed questionnaires assessing children's mental health problems and health-related quality of life. They also completed a structured interview to identify children's psychiatric disorders and their use of medications during the previous six months.ParticipantsParent or main caregiver of 3597 children aged 6-17 years.Main outcome measuresRates of use of stimulants (dexamphetamine and methylphenidate), antidepressants and clonidine by children.ResultsOverall, 1.8% of children (95% CI, 1.5%-2.3%) were receiving stimulant medication. Of those with ADHD, 12.6% (95% CI, 9.8%-16.1%) were being treated with stimulants, 2.3% (95% CI, 1.3%-4.3%) with antidepressants, and 1.9% (95% CI, 1.0%-3.7%) with clonidine. Among children without ADHD, 0.5% (95% CI, 0.3%-0.8%) were receiving stimulant medication. This represented 22.9% (95% CI, 14.6%-34.0%) of all the children who were receiving stimulants. Variables significantly associated with stimulant use were being male, having ADHD, attending a paediatrician, and having higher scores on the Aggressive Behaviour and Attention Problems scales on the Child Behaviour Checklist.ConclusionsAbout 13% of Australian children with ADHD, and a substantial number of children without ADHD, are taking stimulants. The question of whether Australian children are being undertreated or overtreated with stimulant medication depends on the criteria used to assess the appropriateness of stimulant use. Additional information is needed to clarify when stimulants should be used to treat ADHD.Michael G. Sawyer, Joseph M. Rey, Brian W. Graetz, Jennifer J. Clark and Peter A. Baghurs

A Self-Consistent Approach to Neutral-Current Processes in Supernova Cores

The problem of neutral-current processes (neutrino scattering, pair emission, pair absorption, axion emission, \etc) in a nuclear medium can be separated into an expression representing the phase space of the weakly interacting probe, and a set of dynamic structure functions of the medium. For a non-relativistic medium we reduce the description to two structure functions S_A(\o) and S_V(\o) of the energy transfer, representing the axial-vector and vector interactions. $S_V$ is well determined by the single-nucleon approximation while $S_A$ may be dominated by multiply interacting nucleons. Unless the shape of S_A(\o) changes dramatically at high densities, scattering processes always dominate over pair processes for neutrino transport or the emission of right-handed states. Because the emission of right-handed neutrinos and axions is controlled by the same medium response functions, a consistent constraint on their properties from consideration of supernova cooling should use the same structure functions for both neutrino transport and exotic cooling mechanisms.Comment: 33 pages, Te

Exploring enterprise social systems & organisational change: Implementation in a digital age

Information systems (IS), since their introduction into organisations over five decades ago, have promised to streamline business processes, integrate disparate systems, increase innovation, and offer greater competitive advantage. Over the past decades, the evolution of Information Systems have mirrored many of the challenges experienced by our work organisations. For example, throughout the 1980s a primary concern for many organisations was the attainment of competitive advantage within their respective industries (Porter, 1980). The IS field responded by developing systems that sought to provide management with timely information to assist in making better strategic decisions, e.g. executive support and decision support systems. In the 1990s, organisations began to look inwards searching for key strategic resources that would yield unique core competencies (Barney, 1991). Similarly, the IS field responded by building highly integrative enterprise-wide systems (Davenport, 1998), which would unite every pillar of the organisation with a single transparent view of firm competencies and business processes, viz Enterprise Systems. The first decade of the 21st century continued in this vein, with organisations extending their global reach through new and innovative business models (Johnson et al, 2008). Similarly, IS have responded with the emergence of digital technologies and their continued growth as transformative organisational systems enabling boundary-less corporate structures, 24/7 real-time customer-centric communication, collaborative supply chain environments, and virtual IS infrastructures delivered via cloud computing

The Dental Health Status of Pre-Columbian Peruvians: A Study of Dental Caries, Missing Teeth, Attrition, Osteitis, Calculus, and Bone Loss

Prior to the recent reports of Sawyer et al and Elzay et al on the characteristics and dental health status of ancient Peruvian cultures, only Stewart, Leigh, and Goaz and Miller had reported on the dental morphology and pathology of the pre-Columbian Peruvian Indians. The purpose of this study is to evaluate the dental health of these ancient peoples to further our understanding of the development of dental diseases. This paper follows up and expands the report of Elzay et al to include another culture and completely new specimens, with a look at primary dentitions not previously available for study

Morphological Characteristics of the Pre-Columbian Dentition I. Shovel-Shaped Incisors, Carabelli\u27s Cusp, and Protostylid

This Peruvian-American cooperative study of paleopathology of the pre-Columbian Peruvian cultures of Southern Peru began in 1971. The purpose of this study is to evaluate the medical and dental health status of these cultures which date from 600 BC to the Spanish conquest. While several authors such as Leigh, Moodie, Stewart, and Goaz and Miller have studied the dental morphology of Northern Peruvians, the paleodontology and oral paleopathology of the Southern Peruvians has not been recorded. This paper reports dental findings on the morphologic characteristics of the shovel-shaped incisor, Carabelli’s cusp, and protostylid