On the Asymptotic Performance of IDA*

Since best-first search algorithms such as A* require large amounts of memory, they sometimes cannot run to completion, even on problem instances of moderate size. This problem has led to the development of limited-memory search algorithms, of which the best known is IDA*. This paper presents the following results about IDA and related algorithms: The analysis of asymptotic optimality for IDA* in [10] is incorrect. There are trees satisfying the asymptotic optimality conditions given in [10] for which IDA* is not asymptotically optimal. To correct the above problem, we state and prove necessary and sufficient conditions for asymptotic optimality of IDA* on trees. On trees not satisfying our conditions, we show that no best-first limited-memory search algorithm can be asymptotically optimal. On graphs, IDA* can perform quite poorly. In particular, there are graphs on which IDA* does node expansions where N is the number of nodes expanded by A'. (Also cross-referenced as UMIACS-TR-95-22

Prevalence and barriers to HIV testing among mothers at a tertiary care hospital in Phnom Penh, Cambodia. Barriers to HIV testing in Phnom Penh, Cambodia

<p>Abstract</p> <p>Background</p> <p>One-third of all new HIV infections in Cambodia are estimated to be due to mother-to-child transmission. Although the Ministry of Health adopted a policy of provider-initiated HIV testing and counseling (PITC), nearly a quarter of pregnant mothers were not tested in 2007. Greater acceptance of HIV testing is a challenge despite Cambodia's adoption of the PITC policy.</p> <p>Methods</p> <p>A hospital-based quantitative and cross-sectional survey was conducted to assess the prevalence of and barriers to HIV testing among mothers after delivery at the National Maternal and Child Health Center in Phnom Penh. The Center is one of the largest maternal and child care hospitals in the country to offer PITC services. All 600 eligible mothers who were admitted to the hospital after delivery from October to December 2007 were approached and recruited. Data were collected via a semi-structured questionnaire.</p> <p>Results</p> <p>The prevalence of HIV testing among women who delivered at the hospital was 76%. In multivariate logistic regression, factors such as the perceived need to obtain a partner's permission to be tested (OR=0.27, 95% CI=0.14-0.51, p<0.01), the lack of knowledge about HIV prevention and treatment (OR=0.38, CI=0.22-0.66, p<0.01), and the lack of access to ANC services (OR=0.35, 95% CI=0.21-0.58, p<0.01) were found to be the main barriers to HIV testing.</p> <p>Conclusion</p> <p>To achieve greater acceptance of HIV testing, counseling on HIV prevention and treatment must be provided not only to mothers but also to their partners. In addition, utilization of non-laboratory staff such as midwives to provide HIV testing services in rural health facilities could lead to the greater acceptance of HIV testing.</p

Study of lone working magnetic resonance technologists in Western Australia

Objectives: It is recommended that magnetic resonance (MR) technologists should not work alone due to potential occupational health risks although lone working is legally acceptable. The objective of this study was to investigate the current situation of lone working of MR technologists in Western Australia (WA) and any issue against the regulations. Materials and Methods: A questionnaire regarding the issues of occupational health of lone MR technologists was developed based on relevant literature and distributed to WA MR technologists. Descriptive (percentage of frequency, mean and standard deviation) and inferential statistics (Fisher’s exact, chi-square and t tests, and analysis of variance) were used to analyse the responses of the yes/no, multiple choice and 5 point scale questions from the returned questionnaires.Results: The questionnaire response rate was 65.6% (59/90). It was found that about half of the MR technologists (45.8%, 27/59) experienced lone working. The private magnetic resonance imaging (MRI) centres were more likely to arrange technologists to work alone (p <0.05). The respondents expressed positive views on issues of adequacy of training and arrangement, confidence and comfort towards lone working except immediate assistance for emergency (mean: 3). Factors of existence of MRI safety officer (p < 0.05) and nature of lone working (p < 0.001-0.05) affected MR technologists’ concerns. Conclusions: Lone working of MR technologists is common in WA especially private centres. The training and arrangement provided seem to be adequate for meeting the legal requirements. However, several areas should be improved by the workplaces including enhancement on immediate assistance for emergency and concern relief

Evaluation of individual and ensemble probabilistic forecasts of COVID-19 mortality in the United States

Short-term probabilistic forecasts of the trajectory of the COVID-19 pandemic in the United States have served as a visible and important communication channel between the scientific modeling community and both the general public and decision-makers. Forecasting models provide specific, quantitative, and evaluable predictions that inform short-term decisions such as healthcare staffing needs, school closures, and allocation of medical supplies. Starting in April 2020, the US COVID-19 Forecast Hub (https://covid19forecasthub.org/) collected, disseminated, and synthesized tens of millions of specific predictions from more than 90 different academic, industry, and independent research groups. A multimodel ensemble forecast that combined predictions from dozens of groups every week provided the most consistently accurate probabilistic forecasts of incident deaths due to COVID-19 at the state and national level from April 2020 through October 2021. The performance of 27 individual models that submitted complete forecasts of COVID-19 deaths consistently throughout this year showed high variability in forecast skill across time, geospatial units, and forecast horizons. Two-thirds of the models evaluated showed better accuracy than a naïve baseline model. Forecast accuracy degraded as models made predictions further into the future, with probabilistic error at a 20-wk horizon three to five times larger than when predicting at a 1-wk horizon. This project underscores the role that collaboration and active coordination between governmental public-health agencies, academic modeling teams, and industry partners can play in developing modern modeling capabilities to support local, state, and federal response to outbreaks

The United States COVID-19 Forecast Hub dataset

Academic researchers, government agencies, industry groups, and individuals have produced forecasts at an unprecedented scale during the COVID-19 pandemic. To leverage these forecasts, the United States Centers for Disease Control and Prevention (CDC) partnered with an academic research lab at the University of Massachusetts Amherst to create the US COVID-19 Forecast Hub. Launched in April 2020, the Forecast Hub is a dataset with point and probabilistic forecasts of incident cases, incident hospitalizations, incident deaths, and cumulative deaths due to COVID-19 at county, state, and national, levels in the United States. Included forecasts represent a variety of modeling approaches, data sources, and assumptions regarding the spread of COVID-19. The goal of this dataset is to establish a standardized and comparable set of short-term forecasts from modeling teams. These data can be used to develop ensemble models, communicate forecasts to the public, create visualizations, compare models, and inform policies regarding COVID-19 mitigation. These open-source data are available via download from GitHub, through an online API, and through R packages

Ionospheric gas dynamics of satellites and diagnostic probes

The gas dynamics of interactions of a tenuous ionosphere with moving satellites and probes that have bearings on the diagnostics of the ionosphere are discussed. Emphasis is on the cases where the body is moving at mesothermal speeds, namely intermediate between the thermal speeds of ions and electrons of the ambient ionosphere. Methods of collision-free plasma kinetics with self-consistent field are used. The development of the topics for discussion starts with stationary Langmuir probe which entails the basic mechanism of body-plasma interaction that becomes further intricated as the body moves at a higher and higher speed. Applications of the theory of plasma interaction to meteors which move in the ionosphere are also presented.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43801/1/11214_2004_Article_BF00212707.pd