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In recent years, the discovery of massive quasars at
has provided a striking challenge to our understanding of the origin and growth of supermassive black holes in the early Universe. Mounting observational and theoretical evidence indicates the viability of massive seeds, formed by the collapse of supermassive stars, as a progenitor model for such early, massive accreting black holes. Although considerable progress has been made in our theoretical understanding, many questions remain regarding how (and how often) such objects may form, how they live and die, and how next generation observatories may yield new insight into the origin of these primordial titans. This review focusses on our present understanding of this remarkable formation scenario, based on the discussions held at the Monash Prato Centre from November 20 to 24, 2017, during the workshop ‘Titans of the Early Universe: The Origin of the First Supermassive Black Holes’.
Export tax reform in Argentina could improve its competitiveness in China’s soybean market, displacing exports from competing countries like Brazil and the United States. We examined the factors that determine China’s demand for imported soybean products and how export taxes could affect exporting countries. Using import demand and vector autoregression estimates, we conducted simulations of China’s import demand assuming the elimination of export taxes in Argentina. Results indicated that Argentine soybean products could realize gains in the Chinese market, but only in the short run. Projected import demand changes in the long run were insignificant for all exporting countries.
Withdrawal from the Trans-Pacific Partnership (TPP) could be costly for U.S. beef exports to Japan given existing trade agreements such as the Japan-Australia Economic Partnership Agreement (JAEPA). We estimate the demand for imported beef in Japan by source and product and assess the impact of tariff reductions on exporting countries. Our results suggest JAEPA will result in considerable increases in Australian beef exports to Japan, largely at the expense of the U.S. beef. However, similar tariff reductions for U.S. beef could eliminate these negative effects and even result in a net increase in beef imports from both countries.
Background: The role of aggressive surgical manipulation with clot evacuation, arachnoid dissection, and papaverine-guided adventitial dissection of large vessels during ruptured aneurysm surgery in reducing vasospasm is controversial. Here we describe a single-institution experience in aneurysm surgery outcomes with and without aggressive surgery. Methods: We performed retrospective analysis of all patients >18 years of age with subarachnoid hemorrhage (SAH) from anterior circulation aneurysms between 2008 and 2013 at the University of New Mexico Hospital. Vasospasm was characterized on days 3 through 14 after SAH based on: (1) angiography, (2) vasospasm requiring angiographic intervention, (3) development of delayed ischemic neurologic deficit (DIND), and (4) radiological appearance of new strokes. Results: Of 159 patients, 114 (71.6%) had “aggressive” and 45 (28.3%) had standard microsurgery. More than 60% of patients presented with a Hunt and Hess score of ≥3 and a Fisher grade (FG) of 4. Compared with standard surgery, there was a statistically significant decrease in the incidence of DIND in patients undergoing aggressive surgery (18.4% vs 37.8%, p=0.01). Moreover, there was a reduction in the number of new strokes by 30% in the aggressive surgery group with moderate or higher degrees of vasospasm (46.0% vs 76.5%, p=0.06). In the same group with FG 4 SAH, however, this difference was more than 50% (30% vs 64.7%, p=0.02). Conclusions: We conclude that aggressive surgical manipulation during aneurysm surgery results in lower incidence of DIND and new strokes. This effect is most pronounced in patients with FG 4 SAH.
Infection surveillance definitions for long-term care facilities (ie, the McGeer Criteria) have not been updated since 1991. An expert consensus panel modified these definitions on the basis of a structured review of the literature. Significant changes were made to the criteria defining urinary tract and respiratory tract infections. New definitions were added for norovirus gastroenteritis and Clostridum difficile infections.
Despite extensive literature on contributing factors to the high commodity prices and volatility in the recent years, few have examined these causal factors together in one analysis. We quantify empirically the relative importance of three factors: global demand, speculation, and energy prices/policy in explaining corn price volatility. A structural vector auto-regression model is developed and variance decomposition is applied to measure the contribution of each factor in explaining corn price variation. We find that speculation is important, but only in the short run. However, in the long run, energy is the most important followed by global demand.
We estimate the demand for imported cotton in China and assess the competitiveness of cotton-exporting countries. Given the assertion that developing countries are negatively affected by U.S. cotton subsidies, our focus is the price competition between the United States and competing exporters (Benin, Burkina Faso, Chad, Mali, India, and Uzbekistan). We further project how U.S. programs affect China's imports by country. Results indicate that if U.S. subsidies make other exporting countries worse off, this effect is lessened when global prices respond accordingly. If subsidies are eliminated, China's cotton imports may not fully recover from the temporary spike in global prices.
The current chapter examines allometric exponents as they apply to the evolution of the size, or mass, of the modern human brain relative to the mass of the body. The mass of the brain is considered as a single level of organisation of the nervous system and is treated separately to other levels of organisation. A comprehensive dataset is used to examine the relationship between brain and body mass in primates and hominids. This analysis allows us to postulate that the evolution of the size of the human brain can, for the most part, be accounted for by scaling with body size. There appears to be a minimum of two potential adaptive events that have led to alterations in the scaling laws that help explain the actual mass of the human brain. These two events occur at the origin of primates and the origin of the hominid lineage. These scaling laws appear to obviate much of the need for adaptationist explanations in terms of the evolution of the mass of the human brain.
In this work, a room temperature spin-polarized LED based on ferromagnetic Ga1-xGdxN is reported. The device was grown by metalorganic chemical vapor deposition (MOCVD) and is the first report of a spin-LED based on Ga1-xGdxN. Electroluminescence from this device had a degree of polarization of 14.6% at 5000 Gauss and retained a degree of polarization of 9.3% after removal of the applied magnetic field. Ga1-xGdxN thin films were grown on 2 μm GaN templates and were co-doped with Si and Mg to achieve n-type and p-type materials. Co-doping of the Ga1-xGdxN films with Si produced conductive n-type material, while co-doping with Mg produced compensated p-type material. Both Si and Mg co-doped films exhibited room temperature ferromagnetism, measured by vibrating sample magnetometry.
Introduction: The tobacco epidemic is surging in developing countries. While the determinants of tobacco use are well known, it is less certain whether they are similar in developed and developing countries. This has important ramifications for the implementation of interventions locally. This qualitative study explored the determinants and importance of context on tobacco use in Pakistan. Methods: Focus group discussions were conducted in two districts with doctors, nurses and patients from local tuberculosis clinics. Results: Peer influence, social acceptability, affordability and visibility of tobacco, public understanding and personal perception of risks influence tobacco use. Individual factors, such as personal curiosity, adversity and stress, also affected tobacco uptake and use. Patients were willing to pay for effective cessation treatment provided the costs were comparable to their expenditure on tobacco. Discussion: Factors such as peer and social influences are similar to those reported elsewhere. However, local variations exist in the degree of sociocultural acceptability, visibility of tobacco use, public understanding of risks and individual situational factors that influence tobacco use. Patients are prepared to pay for treatment, but there are gender differences in what can be afforded. For tobacco cessation interventions to be effective, local adaptations are essential to ensure cultural and contextual appropriateness.
The Large Synoptic Survey Telescope (LSST) is an anticipated to undertake a 10–year, 3π steradian survey that promises to observe millions of new periodic variable stars. We report on a study to determine the efficiency of the LSST to recover the light curve properties of RR Lyrae stars. An LSST light curve simulation tool was used to sample input idealized light curves or RR Lyrae stars observed in SDSS Stripe 82 data, returning each as it would have been observed by LSST, including realistic photometric scatter, limiting magnitudes, and telescope downtime. Our results show that the LSST will be capable of mapping the spatial distributions and chemical compositions of halo stellar overdensities using RR Lyrae discovered across 3π steradians and out to nearly 1.5 Mpc. LSST will thus enable the mapping of halo merger streams, the discovery of new dwarf galaxies, and the mapping galactic halos throughout the Local Group galaxies.
This study examines the dynamic effects of grain prices and energy prices on catfish feed prices and the price of food-sized catfish at the farm level. Using the autoregressive distributed lag model and bounds testing procedure, a long-run relationship between feed and farm prices and their determinants was confirmed. Given the effect of corn and soybean meal prices on catfish feed prices, and catfish fish feed prices on farm prices, the long-run responsiveness of feed prices to a percentage increase in U.S. ethanol production is 0.325, and the responsiveness of catfish farm prices is 0.064. Although both feed and farm prices increase with ethanol production, the relatively small responsiveness of farm prices when compared with feed prices suggests that catfish farmers are worse off. Results are conditional on ethanol production causing an increase in grain prices.
The primary objective of this study was to assess the impact of catfish imports and tariffs on the U.S. catfish industry, with particular focus on the U.S. International Trade Commission ruling on Vietnam in 2003. Given the importance of Vietnam to the U.S. catfish market, it was assumed that catfish import prices would increase by 35 percent if the maximum tariff was imposed on catfish from Vietnam. With the tariff, domestic catfish prices at the wholesale level would increase by $0.06 per lb, and farm prices by $0.03 per lb. Processor sales would increase by 1.66 percent. Total welfare at the wholesale level would increase from $69.2 million to $71.7 million, an increase of about 3.63 percent, and processor and farm revenue would increase by 4.4 percent and 5.8 percent, respectively. These results represent the greatest possible benefit and suggest modest gains for the U.S. catfish industry.
Several recent papers have used annual changes and monthly data to estimate demand systems. Such use of overlapping data introduces a moving average error term. This paper shows how to obtain consistent and asymptotically efficient estimates of a demand system using seasonally differenced data. Monte Carlo simulations and an empirical application to the estimation of the U.S. meat demand are used to compare the proposed estimator with alternative estimators. Once the correct estimator is used, there is no advantage to using overlapping data in estimating a demand system.
The generalized dynamic Rotterdam model was used in estimating U.S. demand for disaggregated catfish. The overall goal was to examine habit persistence in consumption and to determine the adjustment process in demand. Results indicated that it took up to 1 month for catfish-product demand to fully adjust to changes in expenditures and prices. Additionally, habit persistence played a role in demand where present consumption of a given product was positively affected by past consumption of that product. Consequently, U.S. catfish demand was significantly more elastic in the long-ran.
GaN and InGaN layers were grown on annealed 20 and 50nm Al2O3/ZnO substrates by metalorganic chemical vapor deposition (MOCVD). GaN was only observed by high resolution x-ray diffraction (HRXRD) on 20 nm Al2O3/ZnO substrates. Room temperature photoluminescence (RT-PL) showed the red shift of the GaN near band-edge emission, which might be from oxygen incorporation forming a shallow donor-related level in GaN. HRXRD measurements revealed that (0002) InGaN layers were also successfully grown on 20nm Al2O3/ZnO substrates. In addition, thick InGaN layers (∼200-300nm) were successfully grown on Al2O3/ZnO and bare ZnO substrates. These results are significant as previous studies showed decomposition of the layer at InGaN thicknesses of 100nm or less.
Estimates of price and scale elasticities for U.S. consumed shrimp are derived using aggregate shrimp data differentiated by source country. Own-price elasticities for all countries had the expected negative signs, were statistically significant, and inelastic. The scale elasticities for all countries were positive and statistically significant at the 1% level with only the United States and Ecuador having scale elasticities of less than one. For the most part, the compensated demand effects showed that most of the cross-price effects were positive. Our results also suggest that despite the countervailing duties imposed by the United States, shrimp demand was fairly stable.