1,077 research outputs found
Oil price instability, hedging, and an oil stabilization fund : the case of Venezuela
No full textThe Venezuelan government and PDVSA (Venezuela's state oil companies) are both exposed to oil price instability. Given the existing tax structure, PDVSA has a higher exposure than the government, especially when prices drop below $18-20 a barrel. The authors show that the volatility of prices for crude oil is higher (but not significant) than the volatility of prices for refined oil products. And both prices are highly correlated. So, there is not much strength to the argument that Venezuela, being now mainly an exporter of refined products, faces less volatility than when it was exporting mainly crude oil. The basis risk for hedging Venezuelan crude oil was founded to be higher than for other crudes of comparable quality in the region. One explanation could be the pricing policies Venezuela follows, which leads Venezuelan crude oil prices to deviate for long periods from international prices. The basis risk in Venezuelan refined products is much lower and at acceptable levels for risk management. The issue of liquidity is concentrated in contracts for periods of less than a year. For products, the liquidity is concentrated in the nearest 4-5 months. So, for short-term hedges (6-9 months ahead), there is sufficient liquidity for Venezuela to hedge a substantial part of its exports. For longer-term hedges, the over-the-counter market is the more appropriate vehicle. In either case, it will not usually be the case that all production or exports should be hedged. The authors also examined the issue of an oil stabilization fund. For an oil stabilization fund to be effective several preconditions must be met. Most notably: oil prices should not follow a random walk; financial markets are incomplete; and there are large adjustment costs. These conditions do likely apply in Venezuela. Venezuela's best strategy would be to remove as much short-term oil price risk as possible by using short-dated hedging instruments (such as futures, options, or short-dated swaps) and to also do some longer term hedging (using mainly over-the-counter options and long-dated swaps). They also find that an oil stabilization fund should be complemented by using market-based risk management tools. The oil stabilization fund could then be used to manage any remaining interperiod oil price risk to the extent considered necessary.Markets and Market Access,Environmental Economics&Policies,Oil Refining&Gas Industry,Energy and Environment,Energy Demand
Impact of population structure, effective bottleneck time, and allele frequency on linkage disequilibrium maps
No full textGenetic maps in linkage disequilibrium (LD) units play the same role for association mapping as maps in centimorgans provide at much lower resolution for linkage mapping. Association mapping of genes determining disease susceptibility and other phenotypes is based on the theory of LD, here applied to relations with three phenomena. To test the theory, markers at high density along a 10-Mb continuous segment of chromosome 20q were studied in African-American, Asian, and Caucasian samples. Population structure, whether created by pooling samples from divergent populations or by the mating pattern in a mixed population, is accurately bioassayed from genotype frequencies. The effective bottleneck time for Eurasians is substantially less than for migration out of Africa, reflecting later bottlenecks. The classical dependence of allele frequency on mutation age does not hold for the generally shorter time span of inbreeding and LD. Limitation of the classical theory to mutation age justifies the assumption of constant time in a LD map, except for alleles that were rare at the effective bottleneck time or have arisen since. This assumption is derived from the Malecot model and verified in all samples. Tested measures of relative efficiency, support intervals, and localization error determine the operating characteristics of LD maps that are applicable to every sexually reproducing species, with implications for association mapping, high-resolution linkage maps, evolutionary inference, and identification of recombinogenic sequences
Higher naevus count exhibits a distinct DNA methylation signature in healthy human skin: implications for melanoma
No full textHigh naevus count is the strongest risk factor for melanoma and although gene variants have been discovered for both traits, epigenetic variation is unexplored. We investigated 322 healthy human skin DNA methylomes associated with total body naevi count, incorporating genetic and transcriptomic variation. DNA methylation changes were identified at genes involved in melanocyte biology, such as RAF1 (p = 1.2 x 10(-6)) and CTC1 (region: p = 6.3 x 10(-4)), and other genes including ARRDC1 (p = 3.1 x 10(-7)). A subset exhibited coordinated methylation and transcription changes within the same biopsy. The total analysis was also enriched for melanoma-associated DNA methylation variation (p = 6.33 x 10(-6)). Additionally, we show that skin DNA methylation is associated in cis with known GWAS SNPs for naevus count, at PLA2G6 (p = 1.7 x 10(-49)) and NID1 (p = 6.4 x 10(-14)), as well as melanoma risk, including in or near MC1R, MX2 and TERT/CLPTM1L (p < 1 x 10(-10)). Our analysis using a uniquely large dataset comprising healthy skin DNA methylomes identified known and additional regulatory loci and pathways in naevi and melanoma biology. This integrative study improves our understanding of predisposition to naevi and their potential contribution to melanoma pathogenesis
Genome-wide association study of nevirapine hypersensitivity in a sub-Saharan African HIV-infected population
No full textThe initial GWAS was funded by the International Serious Adverse Events Consortium (iSAEC). The iSAEC is a non-profit organization dedicated to identifying and validating DNA variants useful in predicting the risk of drug-related serious adverse events. The Consortium brings together the pharmaceutical industry, regulatory authorities and academic centres to address clinical and scientific issues associated with the genetics of drug-related serious adverse events. The iSAEC’s current funding members include: Abbott, Amgen, AstraZeneca, Daiichi Sankyo, GlaxoSmithKline, Merck, Novartis, Pfizer, Takeda and the Wellcome Trust.
Mas Chaponda was funded by a 3 year Wellcome Trust training fellowship WT078857MA administered through the University of Liverpool. Malawi-Liverpool-Wellcome Trust Clinical Research Programme is funded through a Core Programme Grant award from the Wellcome Trust. Munir Pirmohamed is a National Institute for Health Research Senior Investigator, and also wishes to thank the MRC Centre for Drug Safety Science for support.
The DART study was supported by the UK Medical Research Council (grant number G0600344), the UK Department for International Development and the Rockefeller Foundation.
Andrew P. Morris is a Wellcome Trust Senior Research Fellow in Basic Biomedical Science (grant number WT098017).
Louise Y. Takeshita is funded by a PhD fellowship from CNPq (National Council for Scientific and Technological Development, Brazil).
Panos Deloukas’ work forms part of the research themes contributing to the translational research portfolio of Barts Cardiovascular Biomedical Research Unit which is supported and funded by the National Institute for Health Research
Hybrid adaptive chassis control for vehicle lateral stability in the presence of uncertainty
No full textTo guarantee the safety of passengers in a wide range of driving situations, vehicle lateral stability should be achieved in the presence of nonlinear dynamics (consequence of critical maneuvers) and uncertainty (consequence of uncertain parameters). This paper designs a hybrid adaptive strategy to attain vehicle stability in these situations. The design is based on a piecewise affine (PWA) description of the vehicle model where partitions describe both the linear and the nonlinear regimes, and where parametric uncertainties are handled by estimators for the control gains that can adapt to different conditions acting on the system. Comparisons with strategies that merely exploits the linear region of the vehicle dynamics are provided for different driving conditions, and performance improvements of the proposed methodology are assessed.Accepted Author ManuscriptTeam Bart De Schutte
Dealing with the coffee crisis in Central America - impacts and strategies
No full textCurrent coffee prices are at record lows and below the cost of production for many producers in Central America. Moreover, the coffee crisis is structural, and changes in supply and demand do not indicate a quick recovery of prices. So, coffee producers in Central America are facing new challenges-as are coffee laborers, coffee exporters, and others linked to the coffee sector. Coffee plays a major economic role in Costa Rica, El Salvador, Guatemala, Honduras, and Nicaragua. The coffee crisis is actually part of a broader rural crisis caused by weather shocks (such as Hurricane Mitch and droughts), low international agricultural commodity prices, and the global recession. These challenges call for new strategies for Central American countries aimed at broad-based sustainable development of their rural economies. The authors deal with the impact of the coffee crisis and strategies to deal with it. They include an analysis of the international coffee situation and country-specific analyses. The authors explore options and constraints for increased competitiveness and diversification, and discuss social, environmental, and institutional dimensions of the crisis. The authors conclude that there are specific solutions that can be pursued for the coffee sector. Some are already being applied, but more can be done in a more systematic way. Also, there is a need for safety nets to deal with the short-term impact of the crisis. Longer-term solutions are to be found in increased competitiveness and diversification in the context of broad-based sustainable rural economic development.Crops&Crop Management Systems,Environmental Economics&Policies,Labor Policies,Economic Theory&Research,Markets and Market Access,Crops&Crop Management Systems,Environmental Economics&Policies,Economic Theory&Research,Access to Markets,Markets and Market Access
The use of New York cotton futures contracts to hedge cotton price risk in developing countries
No full textCotton exports account for a significant share of commodity exports for some developing countries, especially in West Africa and Central Asia. In these countries, dependency on cotton for export revenues has increased in the past 20 years. These countries therefore have a high exposure to cotton price volatility. Cotton-producing developing countries and economies in transition make little use of hedging mechanisms to reduce risk from the volatility of cotton export revenues. Countries in Francophone West Africa use forward sales to hedge but only for a small share of the crop. These countries could use cotton futures and options contracts to hedge against short- to medium-term price volatility, making cotton export revenues more predictable. Cotton futures and options contracts could also make cotton-related commercial transactions more flexible. (Futures could be sold when there are no buyers in the physical market, for example.) In West Africa, futures and options could complement the existing system of forward sales. The authors examine the feasibility of using New York cotton futures and options contracts as hedging instruments. They base their analysis on a portfolio selection problem in which the hedger selects the optimal proportions of unhedged and hedged output to minimize risk. The results suggest that despite the existence of relatively high basis risk (that is, a relatively low correlation between spot and future prices), hedging reduces cotton price volatility by 30 to 70 percent. Moreover, for all varieties of cotton examined, the hedge ratio (the percentage of exports hedged) was below one. Using a hedge ratio of one (naive hedge), at times, increases rather than decreases risk. The results also show that hedging, while reducing risk, also reduces expected returns. Attitudes toward risk that is, the degree of risk aversion - determine how much of this risk-return tradeoff is acceptable. For a risk-averse agent, the main benefit of hedging lies in risk reduction rather than in the potential for increased returns.Insurance&Risk Mitigation,Environmental Economics&Policies,Non Bank Financial Institutions,Financial Intermediation,Insurance Law
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