2,497 publications from this institution
A 4-bit 12-GSample/sec A/D converter (GAD) has been fabricated in a 0.25-/spl mu/m CMOS process to investigate the design of an equalized multi-level link. Clocked differential amplifiers were used to sample the input, followed by high-speed comparators with current-summed offset cancellation. Input bandwidth was measured at 2.5 GHz. Eight 1.5-GSample/sec flash A/D converters were interleaved to achieve the aggregate sample rate.
Abstract Recent, high‐profile, large‐scale, preregistered failures to replicate uncover that many highly‐regarded experiments are “false positives”; that is, statistically significant results of underlying null effects. Large surveys of research reveal that statistical power is often low and inadequate. When the research record includes selective reporting, publication bias and/or questionable research practices, conventional meta‐analyses are also likely to be falsely positive. At the core of research credibility lies the relation of statistical power to the rate of false positives. This study finds that high (>50%–60%) median retrospective power (MRP) is associated with credible meta‐analysis and large‐scale, preregistered, multi‐lab “successful” replications; that is, with replications that corroborate the effect in question. When median retrospective power is low (<50%), positive meta‐analysis findings should be interpreted with great caution or discounted altogether.
The excellent article in the Journal by Boffetta et al. (1) on fruit and vegetable intake and cancer risk offers a nice example on why inferences based on P values are problematic in large studies that show associations of very small magnitude. The reported associations between high fruit and vegetable intake and cancer risk reached nominal levels of statistical significance (P = .006 and P < .001, respectively), and the authors conclude that the study “supports the notion of a modest cancer preventive effect of high intake of fruits and vegetables” (1). The respective hazard ratios per 100 g/d intake of fruits and vegetables were 0.99 and 0.98, respectively, and 0.97 per 200 g/d intake of fruits and vegetables combined. The authors are commended for being cautious that residual confounding can affect such hazard ratios of very small magnitude (1). The main problem, however, is that for associations of very small magnitude, P values alone do not suffice to make inferences, even if there is absolutely no residual confounding. The inferences depend critically on how strong the associations are expected to be based on previous results, biological reasoning, or practical considerations, that is, the associations that would be important from a clinical or public health perspective.
Scientific publication is immensely important to the scientific endeavour. There is, however, concern that rewarding scientists chiefly on publication creates a perverse incentive, allowing careless and fraudulent conduct to thrive, compounded by the predisposition of top-tier journals towards novel, positive findings rather than investigations confirming null hypothesis. This potentially compounds a reproducibility crisis in several fields, and risks undermining science and public trust in scientific findings. To date, there has been comparatively little modelling on factors that influence science trustworthiness, despite the importance of quantifying the problem. We present a simple phenomenological model with cohorts of diligent, careless and unethical scientists, with funding allocated by published outputs. This analysis suggests that trustworthiness of published science in a given field is influenced by false positive rate, and pressures for positive results. We find decreasing available funding has negative consequences for resulting trustworthiness, and examine strategies to combat propagation of irreproducible science.
Objective. To evaluate and analyze the existing evidence for the diagnosis and treatment of acute uncomplicated sinusitis in children. Design. A systematic overview and meta-analysis considered all pertinent studies with at least 10 children younger than 18 years with acute symptoms of &lt;30 days and without serious complications. Outcomes. Clinical improvement rates for intervention studies of antibiotics or ancillary measures; concordance of diagnostic tests (expressed as likelihood ratios). Results. Of 1857 citations originally reviewed, we identified 21 qualifying studies, compared with 450 reports on complications of acute sinusitis and 233 nonsystematic reviews of the subject. The qualifying studies included 5 randomized, controlled trials and 8 case series on antibiotic therapy, 3 randomized, controlled trials on ancillary treatments, and 8 studies with information on diagnostic tests (including 3 therapeutic trials). Definitions and inclusion criteria were heterogeneous across studies. The pooled clinical improvement rate with antibiotics was 88% (177/202) in randomized, controlled trials and 92% (318/345) in nonrandomized studies; the improvement rates on no antibiotics were 60% and 80%, respectively. Improvement rates were significantly higher in nonrandomized studies (Mantel-Haenszel odds ratio: 1.79; 95% CI: 1.05–3.04, stratified for use of antibiotics). Data on ancillary measures were sparse and heterogeneous. In studies comparing clinical findings with plain film radiography, the pooled rate of abnormal radiographic findings against a clinical diagnosis of sinusitis was 73% (596/814; range: 55% to 96% between studies). There was poor concordance between clinical criteria, plain radiographs, ultrasonography, computed tomography, and fluid on aspiration in all available paired assessments (all positive likelihood ratios were ≤4 and all negative likelihood ratios were ≥0.2). Conclusions. Good, high-quality evidence for acute uncomplicated sinusitis in children is limited. Diagnostic modalities show poor concordance, and treatment options are based on inadequate data. More evidence is needed for defining the optimal treatment and diagnostic methods for this common condition.
Randomised controlled trials and observational studies are often seen as mutually exclusive, if not opposing, methods of clinical research. Two recent reports, however, identified clinical questions (19 in one report,1 five in the other2) where both randomised trials and observational methods had been used to evaluate the same question, and performed a head to head comparison of them. In contrast to the belief that randomised controlled trials are more reliable estimators of how much a treatment works, both reports found that observational studies did not overestimate the size of the treatment effect compared with their randomised counterparts. The authors say that the merits of well designed observational studies may need to be re-evaluated: case-control and cohort studies may need to assume more respect in assessing medical therapies and largescale observational databases should be better exploited. 1 2 The first claim flies in the face of half a century of thinking, so are these authors right? The combined results from the two reports indeed show a striking concordance between the estimates obtained with the two research designs. A correlation analysis we performed on their combined databases found that the correlation coefficient between the odds ratio of randomised trials and the odds ratio of observational designs is 0.84 (P<0.001). This represents excellent concordance …
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The goal of this project was to improve the performance of large scientific and engineering applications through collaborative hardware and software mechanisms to manage the memory hierarchy of non-uniform memory access time (NUMA) shared-memory machines, as well as their component individual processors. In spite of the programming advantages of shared-memory platforms, obtaining good performance for large scientific and engineering applications on such machines can be challenging. Because communication between processors is managed implicitly by the hardware, rather than expressed by the programmer, application performance may suffer from unintended communication – communication that the programmer did not consider when developing his/her application. In this project, we developed and evaluated a collection of hardware, compiler, languages and performance monitoring tools to obtain high performance on scientific and engineering applications on NUMA platforms by managing communication through alternative coherence mechanisms. Alternative coherence mechanisms have often been discussed as a means for reducing unintended communication, although architecture implementations of such mechanisms are quite rare. This report describes an actual implementation of a set of coherence protocols that support coherent, non-coherent and write-update accesses for a CC-NUMA shared-memory architecture, the Stanford FLASH machine. Such an approach has the advantages of using alternative coherence only where it is beneficial, and also provides an evolutionary migration path for improving application performance. We present data on two computations, RandomAccess from the HPC Challenge benchmarks and a forward solver derived from LS-DYNA, showing the performance advantages of the alternative coherence mechanisms. For RandomAccess, the non-coherent and write-update versions can outperform the coherent version by factors of 5 and 2.5, respectively. In LS-DYNA, we obtain improvements of 18% on average using the non-coherent version. We also present data on the SpecOMP benchmarks, showing that the protocols have a modest overhead of less than 3% in applications where the alternative mechanisms are not needed. In addition to the selective coherence studies on the FLASH machine, in the last six months of this project ISI performed research on compiler technology for the transactional memory (TM) programming model being developed at Stanford. As part of this research ISI developed a compiler that recognizes transactional memory “pragmas” and automatically generates parallel code for the TM programming model
: A 64 by 64 bit iterating multiplier, SPIM (Stanford Pipelined Iterative Multiplier) is presented. The pipelined array consists of a small tree of 4:2 adders. The 4:2 tree is better suited than a Wallace tree for a VLSI implementation because it is a more regular structure. A 4:2 carry save accumulator at the bottom of the array is used to iteratively accumulate partial products, allowing a partial array to be used, which reduces area. SPIM was fabricated in a 1.6 micron CMOS process. It has a core size of 3.8 X 6.5mm and contains 41 thousand transistors. The on chip clock generator runs at an internal clock frequency of 85MHz. The latency for a 64 X 64 bit fractional multiply is under 120ns, with a pipeline rate of one multiply every 47ns.
