Elimination of loading reverberation in the split hopkinson torsional bar

The loading reverberation is a multiple wave effect on the specimen in the split Hopkinson torsional bar (SHTB). Its existence intensively destroys the microstructure pattern in the tested material and therefore, interferes with the study correlating the deformed microstructure to the macroscopic stress-strain response. This paper discusses the problem of the loading reverberation and its effects on the post-mortem observations in the SHTB experiment. The cause of the loading reverberation is illustrated by a stress wave analysis. The modification of the standard SHTB is introduced, which involves attaching two unloading bars at the two ends of the original main bar system and adopting a new loading head and a couple of specially designed clutches. The clutches are placed between the main bar system and the unloading bars in order to lead the secondary loading wave out of the main bar system and to cut off the connection in a timely manner. The loading head of the standard torsional bar was redesigned by using a tube-type loading device associated with a ratchet system to ensure the exclusion of the reflected wave. Thus, the secondary loading waves were wholly trapped in the two unloading bars. The wave recording results and the contrasting experiments for examining the post-mortem microstructure during shear banding both before and after the modification highly support the effectiveness of the modified version. The modified SHTB realizes a single wave pulse loading process and will become a useful tool for investigating the relation between the deformed microstructure and the macroscopic stress-strain response. It will play an important role especially in the study of the evolution of the microstructure during the shear banding process. (C) 1995 American Institute of Physics.

Optimal Correction for Guessing in Multiple-Choice Tests

Building on Item Response Theory we introduce students’ optimal behavior in multiple-choice tests. Our simulations indicate that the optimal penalty is relatively high, because although correction for guessing discriminates against risk-averse subjects, this effect is small compared with the measurement error that the penalty prevents. This result obtains when knowledge is binary or partial, under different normalizations of the score, when risk aversion is related to knowledge and when there is a pass-fail break point. We also find that the mean degree of difficulty should be close to the mean level of knowledge and that the variance of difficulty should be high.

On the strategic equivalence of multiple-choice test scoring rules

A disadvantage of multiple-choice tests is that students have incentives to guess. To discourage guessing, it is common to use scoring rules that either penalize wrong answers or reward omissions. These scoring rules are considered equivalent in psychometrics, although experimental evidence has not always been consistent with this claim. We model students' decisions and show, first, that equivalence holds only under risk neutrality and, second, that the two rules can be modified so that they become equivalent even under risk aversion. This paper presents the results of a field experiment in which we analyze the decisions of subjects taking multiple-choice exams. The evidence suggests that differences between scoring rules are due to risk aversion as theory predicts. We also find that the number of omitted items depends on the scoring rule, knowledge, gender and other covariates.

Does the Term Spread play a role in the FED's reaction function? An Empirical Investigation

Using US data for the period 1967:5-2002:4, this paper empirically investigates the performance of a Fed’s reaction function (FRF) that (i) allows for the presence of switching regimes, (ii) considers the long-short term spread in addition to the typical variables, (iii) uses an alternative monthly indicator of general economic activity suggested by Stock and Watson (1999), and (iv) considers interest rate smoothing. The estimation results show the existence of three switching regimes, two characterized by low volatility and the remaining regime by high volatility. Moreover, the scale of the responses of the Federal funds rate to movements in the rate of inflation and the economic activity index depends on the regime. The estimation results also show robust empirical evidence that the importance of the term spread in the FRF has increased over the sample period and the FRF has been more stable during the term of office of Chairman Greenspan than in the pre-Greenspan period.

Increased expression of cystine/glutamate antiporter in multiple sclerosis

Background: Glutamate excitotoxicity contributes to oligodendrocyte and tissue damage in multiple sclerosis (MS). Intriguingly, glutamate level in plasma and cerebrospinal fluid of MS patients is elevated, a feature which may be related to the pathophysiology of this disease. In addition to glutamate transporters, levels of extracellular glutamate are controlled by cystine/glutamate antiporter x(c)(-), an exchanger that provides intracellular cystine for production of glutathione, the major cellular antioxidant. The objective of this study was to analyze the role of the system x(c)(-) in glutamate homeostasis alterations in MS pathology. -- Methods: Primary cultures of human monocytes and the cell line U-937 were used to investigate the mechanism of glutamate release. Expression of cystine glutamate exchanger (xCT) was quantified by quantitative PCR, Western blot, flow cytometry and immunohistochemistry in monocytes in vitro, in animals with experimental autoimmune encephalomyelitis (EAE), the animal model of MS, and in samples of MS patients. -- Results and discussion: We show here that human activated monocytes release glutamate through cystine/glutamate antiporter x(c)(-) and that the expression of the catalytic subunit xCT is upregulated as a consequence of monocyte activation. In addition, xCT expression is also increased in EAE and in the disease proper. In the later, high expression of xCT occurs both in the central nervous system (CNS) and in peripheral blood cells. In particular, cells from monocyte-macrophage-microglia lineage have higher xCT expression in MS and in EAE, indicating that immune activation upregulates xCT levels, which may result in higher glutamate release and contribution to excitotoxic damage to oligodendrocytes. -- Conclusions: Together, these results reveal that increased expression of the cystine/glutamate antiporter system x(c)(-) in MS provides a link between inflammation and excitotoxicity in demyelinating diseases.

"I'm on it 24/7 at the moment" : A qualitative examination of multi-screen viewing behaviours among UK 10-11 year olds

Background: Screen-viewing has been associated with increased body mass, increased risk of metabolic syndrome and lower psychological well-being among children and adolescents. There is a shortage of information about the nature of contemporary screen-viewing amongst children especially given the rapid advances in screen-viewing equipment technology and their widespread availability. Anecdotal evidence suggests that large numbers of children embrace the multi-functionality of current devices to engage in multiple forms of screen-viewing at the same time. In this paper we used qualitative methods to assess the nature and extent of multiple forms of screen-viewing in UK children. Methods: Focus groups were conducted with 10-11 year old children (n = 63) who were recruited from five primary schools in Bristol, UK. Topics included the types of screen-viewing in which the participants engaged; whether the participants ever engaged in more than one form of screen-viewing at any time and if so the nature of this multiple viewing; reasons for engaging in multi-screen-viewing; the room within the house where multi-screen-viewing took place and the reasons for selecting that room. All focus groups were transcribed verbatim, anonymised and thematically analysed. Results: Multi-screen viewing was a common behaviour. Although multi-screen viewing often involved watching TV, TV viewing was often the background behaviour with attention focussed towards a laptop, handheld device or smart-phone. There were three main reasons for engaging in multi-screen viewing: 1) tempering impatience that was associated with a programme loading; 2) multi-screen facilitated filtering out unwanted content such as advertisements; and 3) multi-screen viewing was perceived to be enjoyable. Multi-screen viewing occurred either in the child's bedroom or in the main living area of the home. There was considerable variability in the level and timing of viewing and this appeared to be a function of whether the participants attended after-school clubs. Conclusions: UK children regularly engage in two or more forms of screen-viewing at the same time. There are currently no means of assessing multi-screen viewing nor any interventions that specifically focus on reducing multi-screen viewing. To reduce children's overall screen-viewing we need to understand and then develop approaches to reduce multi-screen viewing among children.

The Carr Lake Project: Potential Biophysical Benefits of Conversion to a Multiple-Use Park

The Carr Lake Project aims to convert Carr Lake’s 450 acres of agriculture fields into a regional multi-use park that will benefit flood protection, water quality, and wildlife habitat, while also providing additional recreational areas for the local community. The Project is represented by an informal consortium of interested parties including the Watershed Institute of California State University Monterey Bay, The City of Salinas, 1000 Friends of Carr Lake, and the Big Sur Land Trust. (Document contains 54 pages)