Comprehensive testing of a defense systems communications satellite

The system level testing of the defense satellite communications system (DSCS) 3 program is reviewed. Concentration is on the results of the systems tests of the DSCS 3 development test model (DTM). The DSCS 3DTM consisted of engineering components interconnected in an open bench layout. The DTM tests were performed to demonstrate satellite electrical performance characteristics and to uncover design deficiencies and interface problems. The availability of the DTM test results prior to the fabrication of the flight model hardware permited the incorporation of necessary design changes with a minimum impact on program costs and schedules

The effects of repetitive news framing on political opinions over time

This study tests how repeated exposure to the same news frame influences political opinions over time. In a survey experiment (N = 296), we repeatedly exposed participants to the same news frame (at the start of the study, after one day, one week, and two weeks) and measured effects on opinions (at the start, after two weeks, and after six weeks). Participants in a control group were exposed only once and the effect was also traced over time. Results show that repetitive framing leads both to stronger and more persistent effects than single exposure. The persistence effects are most evident for individuals with moderate political knowledge. Our study contributes to a more comprehensive model of framing effects in mass communication experiments

In search of a novel way to analyze early communicative behavior

The aim of this study was to develop a coding scheme that enables researchers and practitioners to conduct a detailed analysis of the communicative behavior of young children with significant cognitive and motor developmental delays. Currently, there is a paucity of methods to do conduct such an analysis. For the study, video observations of three different scenarios from 38 children with significant cognitive and motor developmental delays aged between 12 and 54 months, were used. Findings from the video observations served as the primary means for development of the coding scheme, which comprises three main categories – context, partner behavior, and individual behavior – and several subcategories. The coding scheme was used to document the early expressive communicative behavior of persons with significant cognitive and motor developmental delays in a detailed manner. This fine-grained information is necessary to differentiate children based on their communicative abilities, to monitor their communicative development longitudinally, and to inform person-centered communicative interventions

The interface penny-shaped crack reconsidered

The penny-shaped crack at the interface between two bonded dissimilar media is reconsidered on the basis of recent developments on the elimination of oscillatory singularities. This is accomplished by assuming an annular frictionless contact zone at the crack circumference and reducing the problem to a Fredholm integral equation. Expressions for the strain energy, crack opening force and bond stresses are obtained and numerical results given for specific material combinations.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/22767/1/0000322.pd

Analytical study of fundamental nanoindentation test relations for indenters of non-ideal shapes

Nanoindentation techniques provide a unique opportunity to obtain mechanical properties of materials of very small volumes. The load–displacement and load–area curves are the basis for nanoindentation tests, and their interpretation is usually based on the main assumptions of the Hertz contact theory and formulae obtained for ideally shaped indenters. However, real indenters have some deviation from their nominal shapes leading researchers to develop empirical 'area functions' to relate the apparent contact area to depth. We argue that for both axisymmetric and three-dimensional cases, the indenter shape near the tip can be well approximated by monomial functions of radius. In this case problems obey the self-similar laws. Using Borodich's similarity considerations of three-dimensional contact problems and the corresponding formulae, fundamental relations are derived for depth of indentation, size of the contact region, load, hardness, and contact area, which are valid for both elastic and non-elastic, isotropic and anisotropic materials. For loading the formulae depend on the material hardening exponent and the degree of the monomial function of the shape. These formulae are especially important for shallow indentation (usually less than 100 nm) where the tip bluntness is of the same order as the indentation depth. Uncertainties in nanoindentation measurements that arise from geometric deviation of the indenter tip from its nominal geometry are explained and quantitatively described

WTC2005-64085 MODELS OF FRICTION AND WEAR OF DLC FILMS

ABSTRACT Wear and friction of DLC (diamond-like carbon) covered counterparts are under consideration. Experiments showed that abrasion is the leading wear mechanism at the beginning of the wear process. However, the ability of the surface to wear away the counterpart reduces very rapidly, often as a power law function of the cycle numbers. This phenomenon was explained assuming that the initial abrasiveness of a coating is determined by the number of the nano-sharp asperities that were in contact with the counterpart, i.e. by the number of the sharp asperities within the nominal region of contact. On this basis, a model of abrasive wear was developed, using the concept of statistical self-similarity of distribution of the nano-sharp asperities within the current contact region. After the sharp asperities were blunted or removed from the contact region, the wear is related either to phase transformations or to chemical mechanisms. Recent experimental studies of dry sliding between two hydrogenated DLC coated counterparts in low oxygen environment showed that adsorbates have considerable influence on friction and the friction coefficient increases with the increasing of the time interval between contacts. The observed friction phenomena are assumed caused by a reaction between the adsorbate and carbon atoms of the coatings, and when the slider passes a point on the track, it removes mechanically some adsorbate from the surface. The mechanical action leads to re-exposure of the surface to gases in the environment. We assume that there is a transient short-life high temperature field at the vicinities of contacting protuberances that may cause various transformations of the surface. We suppose that first an adsorbate molecule becomes physically adsorbed to the surface and then chemisorbtion may occur between the carbon atoms of the coating and the 'sticky' oxygen atoms. The atoms or molecules of adsorbate interact with the conterpart. Our modeling established a direct connection between this kind of molecular friction and gradual wear. Using the new adsorption-desorption model, the numerical analyses of the friction coefficient were compared with experimental DLC friction results. INTRODUCTION Carbon-containing thin films such as DLC and boron carbide have the ability to enhance the fatigue resistance of heavily loaded steel component

WTC2005-64085 MODELS OF FRICTION AND WEAR OF DLC FILMS

ABSTRACT Wear and friction of DLC (diamond-like carbon) covered counterparts are under consideration. Experiments showed that abrasion is the leading wear mechanism at the beginning of the wear process. However, the ability of the surface to wear away the counterpart reduces very rapidly, often as a power law function of the cycle numbers. This phenomenon was explained assuming that the initial abrasiveness of a coating is determined by the number of the nano-sharp asperities that were in contact with the counterpart, i.e. by the number of the sharp asperities within the nominal region of contact. On this basis, a model of abrasive wear was developed, using the concept of statistical self-similarity of distribution of the nano-sharp asperities within the current contact region. After the sharp asperities were blunted or removed from the contact region, the wear is related either to phase transformations or to chemical mechanisms. Recent experimental studies of dry sliding between two hydrogenated DLC coated counterparts in low oxygen environment showed that adsorbates have considerable influence on friction and the friction coefficient increases with the increasing of the time interval between contacts. The observed friction phenomena are assumed caused by a reaction between the adsorbate and carbon atoms of the coatings, and when the slider passes a point on the track, it removes mechanically some adsorbate from the surface. The mechanical action leads to re-exposure of the surface to gases in the environment. We assume that there is a transient short-life high temperature field at the vicinities of contacting protuberances that may cause various transformations of the surface. We suppose that first an adsorbate molecule becomes physically adsorbed to the surface and then chemisorbtion may occur between the carbon atoms of the coating and the 'sticky' oxygen atoms. The atoms or molecules of adsorbate interact with the conterpart. Our modeling established a direct connection between this kind of molecular friction and gradual wear. Using the new adsorption-desorption model, the numerical analyses of the friction coefficient were compared with experimental DLC friction results. INTRODUCTION Carbon-containing thin films such as DLC and boron carbide have the ability to enhance the fatigue resistance of heavily loaded steel component

Physiotherapy management of joint hypermobility syndrome - a focus group study of patient and health professional perspectives.

OBJECTIVE: To develop an understanding of patient and health professional views and experiences of physiotherapy to manage joint hypermobility syndrome (JHS). DESIGN: An explorative qualitative design. Seven focus groups were convened, audio recorded, fully transcribed and analysed using a constant comparative method to inductively derive a thematic account of the data. SETTING: Four geographical areas of the UK. PARTICIPANTS: 25 people with JHS and 16 health professionals (14 physiotherapists and two podiatrists). RESULTS: Both patients and health professionals recognised the chronic heterogeneous nature of JHS and reported a lack of awareness of the condition amongst health professionals, patients and wider society. Diagnosis and subsequent referral to physiotherapy services for JHS was often difficult and convoluted. Referral was often for acute single joint injury, failing to recognise the long-term multi-joint nature of the condition. Health professionals and patients felt that if left undiagnosed, JHS was more difficult to treat because of its chronic nature. When JHS was treated by health professionals with knowledge of the condition patients reported satisfactory outcomes. There was considerable agreement between health professionals and patients regarding an 'ideal' physiotherapy service. Education was reported as an overarching requirement for patients and health care professionals. CONCLUSIONS: Physiotherapy should be applied holistically to manage JHS as a long-term condition and should address injury prevention and symptom amelioration rather than cure. Education for health professionals and patients is needed to optimise physiotherapy provision. Further research is required to explore the specific therapeutic actions of physiotherapy for managing JHS

Nitrogen activation in a Mars-van Krevelen mechanism for ammonia synthesis on Co3Mo3N

Co3Mo3N is one of the most active catalysts for ammonia synthesis; however, little is known about the atomistic details of N2 adsorption and activation. Here we examine whether N2 can adsorb and activate at nitrogen surface vacancies. We have identified the most favorable sites for surface nitrogen vacancy formation and have calculated vacancy formation free energies (and concentrations) taking into account vacancy configurational entropy and the entropy of N2 at temperature and pressure conditions relevant to ammonia synthesis (380–550 °C, 100 atm) via a semiempirical approach. We show that 3-fold hollow bound nitrogen-containing (111)-surfaces have surprisingly high concentrations (1.6 × 1016 to 3.7 × 1016 cm–2) of nitrogen vacancies in the temperature range for ammonia synthesis. It is shown that these vacancy sites can adsorb and activate N2 demonstrating the potential of a Mars–van Krevelen type mechanism on Co3Mo3N. The catalytically active surface is one where 3f-hollow-nitrogens are bound to the molybdenum framework with a hexagonal array of embedded Co8 cobalt nanoclusters. We find that the vacancy-formation energy (VFE) combined with the adsorption energy can be used as a descriptor in the screening of materials that activate doubly and triply bonded molecules that are bound end-on at surface vacancies