Limit laws for random vectors with an extreme component

Models based on assumptions of multivariate regular variation and hidden regular variation provide ways to describe a broad range of extremal dependence structures when marginal distributions are heavy tailed. Multivariate regular variation provides a rich description of extremal dependence in the case of asymptotic dependence, but fails to distinguish between exact independence and asymptotic independence. Hidden regular variation addresses this problem by requiring components of the random vector to be simultaneously large but on a smaller scale than the scale for the marginal distributions. In doing so, hidden regular variation typically restricts attention to that part of the probability space where all variables are simultaneously large. However, since under asymptotic independence the largest values do not occur in the same observation, the region where variables are simultaneously large may not be of primary interest. A different philosophy was offered in the paper of Heffernan and Tawn [J. R. Stat. Soc. Ser. B Stat. Methodol. 66 (2004) 497--546] which allows examination of distributional tails other than the joint tail. This approach used an asymptotic argument which conditions on one component of the random vector and finds the limiting conditional distribution of the remaining components as the conditioning variable becomes large. In this paper, we provide a thorough mathematical examination of the limiting arguments building on the orientation of Heffernan and Tawn [J. R. Stat. Soc. Ser. B Stat. Methodol. 66 (2004) 497--546]. We examine the conditions required for the assumptions made by the conditioning approach to hold, and highlight simililarities and differences between the new and established methods.Comment: Published at http://dx.doi.org/10.1214/105051606000000835 in the Annals of Applied Probability (http://www.imstat.org/aap/) by the Institute of Mathematical Statistics (http://www.imstat.org

A multiple-access satellite relay system for low data rate users

Multiple access satellite relay system for low data rate user

New Firm Growth: Exploring Processes and Paths

This paper provides a new methodology for the diachronic study of new firm growth, theoretically grounded in the work of Penrose (1995). We show that a model of firm growth as an unfolding process makes possible draw simple, measurable inferences from firm level to aggregate evidence on growth paths of new firms, expressed as propositions. Metrics on growth paths of new firms in three longitudinal samples of new firms are examined for evidence at the aggregate level consistent with the dynamic model. Dynamic processes in the early development of young firms result in variations in the timing, magnitude, duration and rate of change of growth as between firms and in the same firm over time. The conceptual and methodological framework in this paper provides a basis for future research aimed at explaining the development of new firms.entrepreneurship;Penrose;growth paths;new firm growth;resource-based perspective

Impact and Cost-Effectiveness of Point-Of-Care CD4 Testing on the HIV Epidemic in South Africa.

Rapid diagnostic tools have been shown to improve linkage of patients to care. In the context of infectious diseases, assessing the impact and cost-effectiveness of such tools at the population level, accounting for both direct and indirect effects, is key to informing adoption of these tools. Point-of-care (POC) CD4 testing has been shown to be highly effective in increasing the proportion of HIV positive patients who initiate ART. We assess the impact and cost-effectiveness of introducing POC CD4 testing at the population level in South Africa in a range of care contexts, using a dynamic compartmental model of HIV transmission, calibrated to the South African HIV epidemic. We performed a meta-analysis to quantify the differences between POC and laboratory CD4 testing on the proportion linking to care following CD4 testing. Cumulative infections averted and incremental cost-effectiveness ratios (ICERs) were estimated over one and three years. We estimated that POC CD4 testing introduced in the current South African care context can prevent 1.7% (95% CI: 0.4% - 4.3%) of new HIV infections over 1 year. In that context, POC CD4 testing was cost-effective 99.8% of the time after 1 year with a median estimated ICER of US$4,468/DALY averted. In healthcare contexts with expanded HIV testing and improved retention in care, POC CD4 testing only became cost-effective after 3 years. The results were similar when, in addition, ART was offered irrespective of CD4 count, and CD4 testing was used for clinical assessment. Our findings suggest that even if ART is expanded to all HIV positive individuals and HIV testing efforts are increased in the near future, POC CD4 testing is a cost-effective tool, even within a short time horizon. Our study also illustrates the importance of evaluating the potential impact of such diagnostic technologies at the population level, so that indirect benefits and costs can be incorporated into estimations of cost-effectiveness

Brain Injury Resources [English and Spanish versions]

A Spanish translation of this publication is available for download under Additional Files below. This issue brief, prepared by the University of Massachusetts Medical School’s Brain Injury Academic Interest Group (BI-AIG), focuses on raising awareness about the extent of this problem both nationwide and among the veteran population. The impact of brain injuries on individuals and their families, as well as treatment challenges, are discussed. Goals of the BI-AIG and a resource list that has been compiled for providers, researchers and individuals with brain injuries are listed

Delivering zero carbon homes in the UK

The conference paper can be viewed at: http://www.arcom.ac.uk/-docs/proceedings/ar2012-1445-1454_Heffernan_Pan_Liang.pdfIn the UK and internationally, a plethora of voluntary and mandatory energy efficiency standards for new buildings exist, with the common aim of mitigating the impact of new buildings on climate change. However, the take-up of voluntary schemes has been limited and, as a result, many governments have seen the need to introduce mandatory schemes through legislation; from 2016 all new build homes in England and Wales will be required to achieve zero carbon in regulated energy consumption. The international context of voluntary and mandatory building energy efficiency standards is examined through a review of the literature. The review is expanded by a series of semi-structured interviews with construction professionals involved in the delivery of low and zero carbon homes in the UK. In order to establish why zero carbon homes are not being developed, themes of drivers and barriers and challenges in relation to the delivery of zero carbon homes are explored. The drivers which emerged are categorized into four groups: legislative; economic; social responsibility and individual; and the barriers and challenges into a further four groups: skills and knowledge; legislative and governmental; economic and industry. Skills shortages and knowledge gaps for all involved in the delivery of zero carbon homes were seen as the primary barriers and a gap in the literature also exists in this area. Gaining a greater understanding of the skills and knowledge required for the delivery of zero carbon homes is therefore confirmed as the focus for further research

New Firm Growth: Exploring Processes and Paths

This paper provides a new methodology for the diachronic study of new firm growth, theoretically grounded in the work of Penrose (1995). We show that a model of firm growth as an unfolding process makes possible draw simple, measurable inferences from firm level to aggregate evidence on growth paths of new firms, expressed as propositions. Metrics on growth paths of new firms in three longitudinal samples of new firms are examined for evidence at the aggregate level consistent with the dynamic model. Dynamic processes in the early development of young firms result in variations in the timing, magnitude, duration and rate of change of growth as between firms and in the same firm over time. The conceptual and methodological framework in this paper provides a basis for future research aimed at explaining the development of new firms

Nutraceutical Alternatives to Pharmaceutical Analgesics in Osteoarthritis

Chronic pain is a considerable health concern worldwide, effecting almost 30% of all European adults. Osteoarthritis (OA), a progressive pro-inflammatory condition, is one of the leading causes of chronic pain (effecting 13% of all those over 50 years, globally) and is the most common cause of joint pain. The prevalence of non-steroidal anti-inflammatory drug (NSAIDs) and analgesic use has been well studied and is abundant throughout the western world, with women being the greatest users and ibuprofen generally being the most reported NSAID. In the US, 65% of all OA patients are prescribed NSAIDs for pain management and form part of the current recommended strategy for OA clinical management. While some NSAIDs and analgesics are effective at improving pain and physical function, they come with significant and harmful side effects such as gastrointestinal complications, renal disturbances and severe cardiovascular events. Given these side-effects, any reduction in NSAID and analgesia use (and the resulting potentially harmful side effects) is of particular importance to OA public health. As such, a number of non-pharmaceutical alternatives (bioactive nutraceuticals) have been developed that may reduce NSAID and analgesia use while maintaining pain reduction and improvements in physical function. This chapter will discuss select nutraceuticals that are not currently in mainstream use but may have the potential to aid in the treatment of OA

Serum tumor necrosis factor-alpha concentrations are negatively correlated with serum 25(OH)D concentrations in healthy women

<p>Abstract</p> <p>Background</p> <p>Circulating 25 hydroxyvitamin D (25 (OH)D), an accurate measure of vitamin D status, is markedly greater in individuals with increased exposure to ultraviolet B (UVB) light via sunlight or the use of artificial UV light. Aside from the known relationship between vitamin D and bone, vitamin D has also been implicated in immune function and inflammation. Furthermore, a mass of evidence is accumulating that vitamin D deficiency could lead to immune malfunction. Our overall objective was to study the relationship between vitamin D status (as determined by serum 25(OH) D concentrations) and inflammatory markers in healthy women.</p> <p>Methods</p> <p>This observational study included 69 healthy women, age 25–82 years. Women with high UVB exposure and women with minimal UVB exposure were specifically recruited to obtain a wide-range of serum 25(OH)D concentrations. Health, sun exposure and habitual dietary intake information were obtained from all subjects. Body composition was determined by dual-energy-x-ray absorptiometry. A fasting blood sample was collected in the morning and analyzed for serum 25(OH)D, parathyroid hormone (iPTH), estradiol (E₂), cortisol, and inflammatory markers [tumor necrosis factor -alpha (TNF-α), interleukin-6 and -10 (IL-6, IL-10), and C-reactive protein (CRP)].</p> <p>Results</p> <p>Women with regular UVB exposure (Hi-D) had serum 25(OH)D concentrations that were significantly higher (<it>p </it>< 0.0001) and iPTH concentrations that were significantly lower (<it>p </it>< 0.0001) than women without regular UVB exposure (Lo-D). Although IL-6, IL-10, and CRP did not have a statistically significant relationship with 25(OH)D concentrations, linear regression models revealed a significant inverse relationship between serum 25(OH)D and TNF-α concentrations. This relationship remained significant after controlling for potential covariates such as body fat mass, menopausal status, age, or hormonal contraceptive use.</p> <p>Conclusion</p> <p>Serum 25(OH)D status is inversely related to TNF-α concentrations in healthy women, which may in part explain this vitamin's role in the prevention and treatment of inflammatory diseases. Results gleaned from this investigation also support the need to re-examine the biological basis for determining optimal vitamin D status.</p