7,295 research outputs found

    The random component of mixer-based nonlinear vector network analyzer measurement uncertainty

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    The uncertainty, due to random noise, of the measurements made with a mixer-based nonlinear vector network analyzer are analyzed. An approximate covariance matrix corresponding to the measurements is derived that can be used for fitting models and maximizing the dynamic range in the measurement setup. The validity of the approximation is verified with measurements

    Noise considerations when determining phase of large-signal microwave measurements

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    Advances in microwave instrumentation now make it feasible to accurately measure not only the magnitude spectrum, but also the phase spectrum of wide-bandwidth signals. In a practical measurement, the spectrum is measured over a finite window of time. The phase spectrum is related to the position of this window, causing the spectrum to differ between measurements of an identical waveform. It is difficult to compare multiple measurements with different window positions or to incorporate them into a model. Several methods have been proposed for determining the phase spectrum such that multiple measurements can be effectively compared and utilized in models. The methods are reviewed in terms of the information required to determine the phase and compared in terms of their robustness in the presence of measurement noise

    Performance and applications of Gallium-Nitride Monolithic Microwave Integrated Circuits (GaN MMICs)

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    The evolution of wide-bandgap semiconductor transistor technology is placed in historical context with other active device technologies. The relative rapidity of GaN transistor development is noted and is attributed to the great parallel activity in the lighting sector and the historical experience and business model from the III-V compound semiconductor sector. The physical performance expectations for wide-bandgap technologies such as Gallium-Nitride Field-E®ect Transistors (GaN FETs) are reviewed. We present some device characteristics. Challenges met in characterising, and prospects for modeling GaN FETs are described. Reliability is identified as the final remaining hurdle facing would-be foundries. Evolutionary and unsurprising applications as well as novel and revolutionary applications are suggested. Novel applications include wholly monolithic switchmode power supplies, simplified tools for ablation and diathermy in tissue, and very wide dynamic range circuits for audio or low phase noise signal generation. We conclude that now is the time to embark on circuit design of MMICs in wide-bandgap technology. The potential for fabless design groups to capitalise upon design IP without strong geopraphic advantage is noted

    Reproduction in Reptiles, from Genes to Ecology: A Retrospective and Prospective Vision

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    The 6th World Congress of Herpetology (WCH), held in Manaus, Brazil in 2008, provided an excellent venue for a broad, integrative symposium on reproduction in reptiles. This symposium brought together researchers from throughout the world who are working on diverse reptilian species. The symposium’s title “Reproduction in Reptiles from Genes to Ecology,” captures the methodological breadth of contemporary research as well as its integrative nature. This special issue of Herpetological Conservation and Biology presents a series of papers from contributors to that symposium. In this introduction to the special issue, we offer an evolutionary overview of reptilian reproduction and summarize the nature, characteristics, and implications of current research efforts, as represented in the WCH symposium

    Spirituality and attitudes towards nature in the Pacific Islands: insights for enabling climate - change adaptation

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    A sample of 1226 students at the University of the South Pacific, the premier tertiary institution in the Pacific Islands, answered a range of questions intended to understand future island decision-makers’ attitudes towards Nature and concern about climate change. Questions asking about church attendance show that the vast majority of participants have spiritual values that explain their feelings of connectedness to Nature which in turn may account for high levels of pessimism about the current state of the global/Pacific environment. Concern about climate change as a future livelihood stressor in the Pacific region is ubiquitous at both societal and personal levels. While participants exhibited a degree of understanding matching objective rankings about the vulnerability of their home islands/countries, a spatial optimism bias was evident in which ‘other places’ were invariably regarded as ‘worse’. Through their views on climate change concern, respondents also favoured a psychological distancing of environmental risk in which ‘other places’ were perceived as more exposed than familiar ones. Influence from spirituality is implicated in both findings. Most interventions intended to reduce exposure to environmental risk and to enable effective and sustainable adaptation to climate change in the Pacific Islands region have failed to acknowledge influences on decision making of spirituality and connectedness to Nature. Messages that stress environmental conservation and stewardship, particularly if communicated within familiar and respected religious contexts, are likely to be more successful than secular ones

    Amount of Time to Eat Lunch Is Associated with Children’s Selection and Consumption of School Meal Entrée, Fruits, Vegetables, and Milk

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    Background There are currently no national standards for school lunch period length and little is known about the association between the amount of time students have to eat and school food selection and consumption. Objective Our aim was to examine plate-waste measurements from students in the control arm of the Modifying Eating and Lifestyles at School study (2011 to 2012 school year) to determine the association between amount of time to eat and school meal selection and consumption. Design We used a prospective study design using up to six repeated measures among students during the school year. Participants/setting One thousand and one students in grades 3 to 8 attending six participating elementary and middle schools in an urban, low-income school district where lunch period lengths varied from 20 to 30 minutes were included. Main outcome measures School food selection and consumption were collected using plate-waste methodology. Statistical analyses performed Logistic regression and mixed-model analysis of variance was used to examine food selection and consumption. Results Compared with meal-component selection when students had at least 25 minutes to eat, students were significantly less likely to select a fruit (44% vs 57%; PPPP Conclusions During the school year, a substantial number of students had insufficient time to eat, which was associated with significantly decreased entrée, milk, and vegetable consumption compared with students who had more time to eat. School policies that encourage lunches with at least 25 minutes of seated time might reduce food waste and improve dietary intake

    Gathering evidence- availability of published information to support zoonotic pathogen prioritization in swine within the Canadian context

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    Efforts to implement control programs for zoonotic pathogens at the farm level are ongoing. However, establishing control programs for pathogens that may derive from multiple food-animal sources and for which there are interventions at various levels of the food chain can be challenging. Prioritizing pathogens for control programs should be based on scientific evidence and transparent decision-making processes. As part of a larger project applying multi-criteria decision analysis for prioritizing pathogens, a systematic review of the literature is being conducted with initial focus on existing published research on the prevalence of 15 zoonotic pathogens in swine populations and in humans, as attributable to swine and pork, within the North American context

    Lymphocytic Esophagitis in Nonachalasia Primary Esophageal Motility Disorders: Improved Criteria, Prevalence, Strength of Association, and Natural History.

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    Lymphocytic esophagitis (LE) is a histologic pattern with no established clinical correlates in the majority of patients. The goal of this study was to evaluate the association between nonachalasia primary esophageal motility disorders (PEMD) and LE. Sixty-nine patients with PEMD and esophageal biopsies, including 22 with nutcracker esophagus, 33 with ineffective motility, and 14 with diffuse spasm, constituted the study group. The control group consisted of 70 patients with severe dysmotility-negative gastroesophageal reflux disease requiring referral for Nissen fundoplication. To improve the criteria for LE, a lymphocyte reference range at different esophageal levels was first established in 17 healthy volunteers. The cutoffs for normal intraepithelial lymphocytes, defined as lymphocyte levels not exceeding mean level±2 SDs, were set at 62, 46, and 41 lymphocytes per high-power field at 0 to 2, 5, and 10 cm above the gastroesophageal junction, respectively. Predominantly focal peripapillary LE was observed in approximately 40% of patients with nutcracker esophagus or diffuse spasm and in 20% of patients with ineffective motility, in comparison with 4% of patients with dysmotility-negative gastroesophageal reflux disease (P<0.035 vs. any subtype of PEMD). Overall, LE was strongly associated with PEMD in multivariate analysis (adjusted odds ratio, 7.93; 95% confidence interval, 2.26-27.9; P=0.001). LE had a chronic course in 56% of the patients with follow-up biopsies. In conclusion, LE has a strong association with PEMD, suggesting the utility of LE in raising the possibility of PEMD
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