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Search Results: 1 - 10 of 10458 matches for " Steven Cook "
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Unit root testing in the presence of innovation variance breaks: a simple solution with increased power
Steven Cook
Journal of Applied Mathematics , 2002, DOI: 10.1155/s1110757x02107029
Abstract: The Dickey-Fuller unit root test is known to suffer severe oversizing in the presence of innovation variance breaks. In this paper, forward and reverse Dickey-Fuller regressions are proposed as a means of correcting this size distortion. The results of Monte Carlo experimentation show such an approach to result in both satisfactory size properties and increased power relative to previously suggested solutions.
An International Perspective on Business Cycle Asymmetry: Evidence from Non-parametric Analysis
Steven Cook
Journal of Applied Sciences , 2004,
Abstract: A cross-country comparison of business cycle asymmetry is conducted. The present analysis extends the existing literature in two ways. First, the 152 economies examined allows a larger cross-country comparison than presented in previous studies. Second, a new non-parametric test is employed which, unlike the typically applied test of asymmetry, is robust to outliers. The results obtained show asymmetric behaviour over the course of the business cycle to exist for a large number of economies. The implications of these findings for the implementation of economic policy and the specification of econometric models are noted.
Wound Botulism in Injection Drug Users: Time to Antitoxin Correlates with Intensive Care Unit Length of Stay
Offerman, Steven R,Schaefer, Melissa,Thundiyil, Joseph,Cook, Matthew D
Western Journal of Emergency Medicine : Integrating Emergency Care with Population Health , 2009,
Abstract: Objectives: We sought to identify factors associated with need for mechanical ventilation (MV), length of intensive care unit (ICU) stay, length of hospital stay, and poor outcome in injection drug users (IDUs) with wound botulism (WB).Methods: This is a retrospective review of WB patients admitted between 1991-2005. IDUs were included if they had symptoms of WB and diagnostic confirmation. Primary outcome variables were the need for MV, length of ICU stay, length of hospital stay, hospital-related complications, and death.Results: Twenty-nine patients met inclusion criteria. Twenty-two (76%) admitted to heroin use only and seven (24%) admitted to heroin and methamphetamine use. Chief complaints on initial presentation included visual changes, 13 (45%); weakness, nine (31%); and difficulty swallowing, seven (24%). Skin wounds were documented in 22 (76%). Twenty-one (72%) patients underwent mechanical ventilation (MV). Antitoxin (AT) was administered to 26 (90%) patients but only two received antitoxin in the emergency department (ED). The time from ED presentation to AT administration was associated with increased length of ICU stay (Regression coefficient = 2.5; 95% CI 0.45, 4.5). The time from ED presentation to wound drainage was also associated with increased length of ICU stay (Regression coefficient = 13.7; 95% CI = 2.3, 25.2). There was no relationship between time to antibiotic administration and length of ICU stay.Conclusion: MV and prolonged ICU stays are common in patients identified with WB. Early AT administration and wound drainage are recommended as these measures may decrease ICU length of stay.[West J Emerg Med. 2009;10(4):251-256.]
Investor Na?veté and Asset Prices  [PDF]
Jonathan Cook
Journal of Mathematical Finance (JMF) , 2013, DOI: 10.4236/jmf.2013.34047
Abstract:

This paper describes strategic behavior in a nonequilibrium model of asset pricing with heterogeneous sophistication. Both risk and return are increasing in the na?veté of investors in the market. Optimal investment involves in considering the effect that na?e investors have on the market. Further, we derive a simple characterization of the asset price dynamics that results from an arbitrary combination of a countably infinite set of investor types.

Prevalence, Causes and Socio-Economic Determinants of Vision Loss in Cape Town, South Africa
Nicky Cockburn, David Steven, Karin Lecuona, Francois Joubert, Graeme Rogers, Colin Cook, Sarah Polack
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0030718
Abstract: Purpose To estimate the prevalence and causes of blindness and visual impairment in Cape Town, South Africa and to explore socio-economic and demographic predictors of vision loss in this setting. Methods A cross sectional population-based survey was conducted in Cape Town. Eighty-two clusters were selected using probability proportionate to size sampling. Within each cluster 35 or 40 people aged 50 years and above were selected using compact segment sampling. Visual acuity of participants was assessed and eyes with a visual acuity less than 6/18 were examined by an ophthalmologist to determine the cause of vision loss. Demographic data (age, gender and education) were collected and a socio-economic status (SES) index was created using principal components analysis. Results Out of 3100 eligible people, 2750 (89%) were examined. The sample prevalence of bilateral blindness (presenting visual acuity <3/60) was 1.4% (95% CI 0.9–1.8). Posterior segment diseases accounted for 65% of blindness and cataract was responsible for 27%. The prevalence of vision loss was highest among people over 80 years (odds ratio (OR) 6.9 95% CI 4.6–10.6), those in the poorest SES group (OR 3.9 95% CI 2.2–6.7) and people with no formal education (OR 5.4 95% CI 1.7–16.6). Cataract surgical coverage was 68% in the poorest SES tertile (68%) compared to 93% in the medium and 100% in the highest tertile. Conclusions The prevalence of blindness among people ≥50 years in Cape Town was lower than expected and the contribution of posterior segment diseases higher than previously reported in South Africa and Sub Saharan Africa. There were clear socio-economic disparities in prevalence of vision loss and cataract surgical coverage in this setting which need to be addressed in blindness prevention programs.
Seasonality Directs Contrasting Food Collection Behavior and Nutrient Regulation Strategies in Ants
Steven C. Cook,Micky D. Eubanks,Roger E. Gold,Spencer T. Behmer
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0025407
Abstract: Long-lived animals, including social insects, often display seasonal shifts in foraging behavior. Foraging is ultimately a nutrient consumption exercise, but the effect of seasonality per se on changes in foraging behavior, particularly as it relates to nutrient regulation, is poorly understood. Here, we show that field-collected fire ant colonies, returned to the laboratory and maintained under identical photoperiod, temperature, and humidity regimes, and presented with experimental foods that had different protein (p) to carbohydrate (c) ratios, practice summer- and fall-specific foraging behaviors with respect to protein-carbohydrate regulation. Summer colonies increased the amount of food collected as the p:c ratio of their food became increasingly imbalanced, but fall colonies collected similar amounts of food regardless of the p:c ratio of their food. Choice experiments revealed that feeding was non-random, and that both fall and summer ants preferred carbohydrate-biased food. However, ants rarely ate all the food they collected, and their cached or discarded food always contained little carbohydrate relative to protein. From a nutrient regulation strategy, ants consumed most of the carbohydrate they collected, but regulated protein consumption to a similar level, regardless of season. We suggest that varied seasonal food collection behaviors and nutrient regulation strategies may be an adaptation that allows long-lived animals to meet current and future nutrient demands when nutrient-rich foods are abundant (e.g. spring and summer), and to conserve energy and be metabolically more efficient when nutritionally balanced foods are less abundant.
Horizontal gene transfer between Wolbachia and the mosquito Aedes aegypti
Lisa Klasson, Zakaria Kambris, Peter E Cook, Thomas Walker, Steven P Sinkins
BMC Genomics , 2009, DOI: 10.1186/1471-2164-10-33
Abstract: We have discovered a case of HGT, involving two adjacent genes, between the genomes of Wolbachia and the currently Wolbachia-uninfected mosquito Aedes aegypti, an important human disease vector. The lower level of sequence identity between Wolbachia and insect, the transcription of all the genes involved, and the fact that we have identified homologs of the two genes in another Aedes species (Ae. mascarensis), suggest that these genes are being expressed after an extended evolutionary period since horizontal transfer, and therefore that the transfer has functional significance. The association of these genes with Wolbachia prophage regions also provides a mechanism for the transfer.The data support the argument that HGT between Wolbachia endosymbiotic bacteria and their hosts has produced evolutionary innovation.Wolbachia pipientis is an intracellular inherited bacterium found in arthropods, where it manipulates host reproduction using phenotypes such as cytoplasmic incompatibility (CI), male killing, parthenogenesis and feminization, and can spread rapidly through insect populations [1]. It is also an obligate mutualist of a number of filarial nematode species [2].Several cases where sections of the Wolbachia genome, sometimes large, have been transferred to the host chromosomes are now known in both insects and nematodes [3-5]. These are either recent events where Wolbachia and host sequences are highly similar or involve extensive pseudogenization [4]. Transcription was reported for 2% of the genes transferred to Drosophila ananassae but the levels were estimated to be 104 to 107 fold lower than for a control gene, act5C [5,6], and it has been argued that this could represent background transcriptional noise (as occurs for many pseudogenes) rather than functional expression [7,8] – translation has yet to be demonstrated. It has therefore been suggested that these fragments are on an evolutionary trajectory to degradation by neutral mutation and play no significan
Computer Assisted Assembly of Connectomes from Electron Micrographs: Application to Caenorhabditis elegans
Meng Xu, Travis A. Jarrell, Yi Wang, Steven J. Cook, David H. Hall, Scott W. Emmons
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0054050
Abstract: A rate-limiting step in determining a connectome, the set of all synaptic connections in a nervous system, is extraction of the relevant information from serial electron micrographs. Here we introduce a software application, Elegance, that speeds acquisition of the minimal dataset necessary, allowing the discovery of new connectomes. We have used Elegance to obtain new connectivity data in the nematode worm Caenorhabditis elegans. We analyze the accuracy that can be obtained, which is limited by unresolvable ambiguities at some locations in electron microscopic images. Elegance is useful for reconstructing connectivity in any region of neuropil of sufficiently small size.
Restoring Washed Out Bridges so ELearners Arrive at Online Course Destinations Successfully  [PDF]
Ruth Gannon Cook
Creative Education (CE) , 2012, DOI: 10.4236/ce.2012.34083
Abstract: This study researched the impact of strategic navigation improvements in an online course selected for the study over one quarter (12 weeks) at a large Midwestern private university. The primary purpose of the study was to see if navigation enhancements and specific graphic enhancements (semiotic tools) in the online course selected for the study could make it easier for adult students to learn new course materials. The study also sought to see if these factors could contribute to increased positive learning experiences and to see whether there might be a higher percentage of completion rates in this enhanced online course than in other online courses at the university. While not generalizable, the findings could provide inferences about which factors could positively influence adult learning in online courses and contribute to increased course completion rates; the study could also provide recommendations on graphic enhancements and online course navigation that positively influence student learning in online courses.
The Worldwide Abalone Industry  [PDF]
Peter A. Cook
Modern Economy (ME) , 2014, DOI: 10.4236/me.2014.513110
Abstract: Global fish production continues to outpace world population growth, and aquaculture remains one of the fastest-growing food producing sectors. In 2012, global aquaculture production was 90.4 million tonnes. Although, in terms of production tonnage, abalone contributes a relatively small proportion of this aquaculture production, it is one of the most highly prized seafood delicacies and, therefore, in terms of the value of production, is very important to many countries. The total volume of worldwide abalone fisheries has declined since the 1970’s, but farm production has increased significantly over the past few years. A huge increase in farm production has occurred, beginning in the 1970s, when farm production was almost negligible, to recent years when increases have been huge. In the 8 years immediately preceding 2010, for example, farm production increased by more than 750% and by 2013, farm production had reached an estimated 103,464 mt. The overall effects of these huge increases on the world market are discussed.
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