StoryGrid [educational computing]

The StoryGrid project undertook studying the role new interface technologies might play in education, particularly at the high school level. Unfortunately, technology often seizes center stage in high school classrooms; i.e., it becomes the topic of instruction. We believe that learning about technology would be most successful when technology is not the topic, but simply a tool used during instruction. StoryGrid, therefore, was designed to support and to enhance existing narrative activity in classrooms by adhering to the following goals: trigger reflection and interpretation, accommodate individual expression and encourage student discourse.     

Augmenting elementary school education with VR

At the University of Illinois at Chicago's Electronic Visualization Laboratory, we use virtual reality technology to complement real-world experiences rather than replace them. For more than two years, we've been deploying ImmersaDesk applications in a Chicago-area elementary school. We want to know whether these virtual environments (VEs) help children make sense of mathematics and scientific phenomena. If so, can educators adapt them to the realities of elementary school learning and teaching? Our experience indicates that VR can successfully augment scientific education as well as help to equalize the learning environment by engaging students of all levels     

The Round Earth Project-collaborative VR for conceptual learning

The Round Earth Project is a collaboration among researchers in computer science, education, and psychology. It investigates two alternative pedagogical strategies for teaching children that the Earth is spherical and the implications of that fact. One strategy, which we term the transformationalist approach, attempts to effect conceptual change by breaking down the children's prior models. In contrast, the selectionist strategy attempts to effect learning in an alternative setting (in our case, a small-diameter asteroid), free of preexisting biases, and to relate that learning back to the target domain-the Earth. Virtual reality (VR) technologies support both pedagogical strategies. In the transformationalist approach, VR simulates the launching of a spacecraft from the Earth's surface and subsequent exploration within a fixed-height orbit. In the selectionist approach, VR simulates a small-diameter asteroid     

Comparisons and improvements of designs of data slicers and clocksynchronization circuits for broadcast teletext decoders operating in amultipath environment

It is shown that multipath propagation imposes a serious performance degradation on broadcast teletext systems designed according to the North American Basic Teletext Specifications. By using both analysis and a comprehensive computer simulation model of the teletext broadcast system, it was found that very significant gains in performance could be obtained by improving slicing level and clock synchronization circuit designs. Several slicing level and clock synchronization (also called bit timing recovery (BTR)) circuits were modeled and simulated and their performances compared. These included peak detecting, averaging, modified averaging, adaptive and ideal slicers. The averaging and adaptive slicers used with the correlator BTR circuit were found to give the best performance, but the complexity and cost of an adaptive slicer reduce the advantages of system implementation     

Who needs antiplatelet therapy?

A series of overviews or meta-analyses of randomized clinical trials prepared by the Antiplatelet Trialists' Collaboration were published in the British Medical Journal in January 1994. They demonstrated that prolonged courses of medium-dose aspirin were very effective at preventing both fatal and non-fatal myocardial infarction and stroke in patients at high risk of occlusive vascular disease. The aim of this review is to provide the general practitioner with a practical guide to the use of aspirin in patients at high and low risk of occlusive vascular disease and to discuss appropriate dosages and contraindications to treatment in the light of all the recent evidence.     

CONSORT: an attempt to improve the quality of publication of clinical trials

The sickling of erythrocytes increases viscosity and reduces the rate of both local circulation and arterio-venous transit time. This causes occlusion of capillaries by "microthrombin". The occlusion is implicated in the multiplicity of vaso-occlusive complications of both acute and chronic nature. Whether or not anticoagulant therapy is warranted in these states has remained debatable. There is no clear evidence that there is an inherent coagulation disorder. Earlier studies indicate that fibrinolysis is normal in steady state sickle cell disease but decreased during sickle cell crisis. We studied fibrinolytic activity or euglobulin clot lysis time (ECLT) in 47 subjects, twenty six of them with homozygous sickle cell (HbSS) disease and 21 healthy controls of whom eighteen had the HbAA and three had the HbAS genotypes. The sex distribution was sixteen males to ten females for the HbSS and 13 males to eight females for the controls. Age range was 17-35 years for the HbSS and 25-35 for the controls. Means for basic haematologic parameters including platelets were also performed. Mean clot lysis time (MCLT) was 3.75 hours for the HbSS and 1.91 hours for the controls (normal range 1 1/2-4 hours). The difference in ECLT between patients and controls was statistically significant (p < 0.001). Fifty three and a half per cent of the HbSS fell above the upper limit of normal MCLT. All the 21 controls fell within normal range. There were also statistically higher values (p < 0.001) in HbSS as compared to the controls with regard to MCV, WBC count, and platelet count.     

Does quality of reports of randomised trials affect estimates of intervention efficacy reported in meta-analyses?

BACKGROUND: Few meta-analyses of randomised trials assess the quality of the studies included. Yet there is increasing evidence that trial quality can affect estimates of intervention efficacy. We investigated whether different methods of quality assessment provide different estimates of intervention efficacy evaluated in randomised controlled trials (RCTs). METHODS: We randomly selected 11 meta-analyses that involved 127 RCTs on the efficacy of interventions used for circulatory and digestive diseases, mental health, and pregnancy and childbirth. We replicated all the meta-analyses using published data from the primary studies. The quality of reporting of all 127 clinical trials was assessed by means of component and scale approaches. To explore the effects of quality on the quantitative results, we examined the effects of different methods of incorporating quality scores (sensitivity analysis and quality weights) on the results of the meta-analyses. FINDINGS: The quality of trials was low. Masked assessments provided significantly higher scores than unmasked assessments (mean 2.74 [SD 1.10] vs 2.55 [1.20]). Low-quality trials (score < or = 2), compared with high-quality trials (score > 2), were associated with an increased estimate of benefit of 34% (ratio of odds ratios [ROR] 0.66 [95% CI 0.52-0.83]). Trials that used inadequate allocation concealment, compared with those that used adequate methods, were also associated with an increased estimate of benefit (37%; ROR=0.63 [0.45-0.88]). The average treatment benefit was 39% (odds ratio [OR] 0.61 [0.57-0.65]) for all trials, 52% (OR 0.48 [0.43-0.54]) for low-quality trials, and 29% (OR 0.71 [0.65-0.77]) for high-quality trials. Use of all the trial scores as quality weights reduced the effects to 35% (OR 0.65 [0.59-0.71]) and resulted in the least statistical heterogeneity. INTERPRETATION: Studies of low methodological quality in which the estimate of quality is incorporated into the meta-analyses can alter the interpretation of the benefit of intervention, whether a scale or component approach is used in the assessment of trial quality.     

An iterative multiuser decoder for near-capacity communications

The combination of forward error correction (FEC) coding and random interleaving is shown to overcome the limitations of multiuser detectors/decoders when the user cross correlations are high. In particular, one can asymptotically achieve single-user performance in a highly correlated multiuser system. In addition, an optimal iterative multiuser detector is derived from iterative techniques for cross-entropy minimization. A practical suboptimal implementation of this algorithm is presented, and simulations demonstrate that, even with highly correlated users, it achieves optimal asymptotic efficiency. The effects of the theoretical limits on channel capacity are evident in many of the simulation results. The complexity of the suboptimal algorithm is approximately (O(2^K)+O(2^κ)) per bit per iteration where K is the number of users and κ is the code constraint length     

Testing the compliance of highly integrated modems

A technique for testing modems to ensure compliance with a standard is given. The approach is intended for highly integrated modems where many or all of the intermediate signals are unavailable for testing. The tests developed are directly applicable to the modem output. The technique is demonstrated and validated for a low data rate modem designed for aerodynamic mobile-satellite applications     

Maximum likelihood sequence estimation of CPM signals transmittedover Rayleigh flat-fading channels

A method for the sequential updating of log-likelihood functions for maximum-likelihood sequence estimation is presented. It is shown that, in a general case, this method can be implemented using Kalman filtering techniques. For the special case of Rayleigh flat fading and continuous phase modulation (CPM) signaling, this approach is shown to lead to an attractive receiver structure. This type of receiver, called the linear predictive receiver, can be implemented in the form of the Viterbi algorithm with the trellis updates being computed using a bank of finite pulse response (FIR) filter and square operations. Simulation results are presented that demonstrate the superiority of the linear predictive receiver over receivers employing differential detection, in the presence of fast fading. It is shown that the optimal linear predictive receiver does not possess an irreducible error rate for a class of Rayleigh fading channels used to model terrestrial mobile channels