48 resultados para volatility spillover
Resumo:
Unfavorable work characteristics, such as low job control and too high or too low job demands, have been suggested to increase the likelihood of physical inactivity during leisure time, but this has not been verified in large-scale studies. The authors combined individual-level data from 14 European cohort studies (baseline years from 19851988 to 20062008) to examine the association between unfavorable work characteristics and leisure-time physical inactivity in a total of 170,162 employees (50 women; mean age, 43.5 years). Of these employees, 56,735 were reexamined after 29 years. In cross-sectional analyses, the odds for physical inactivity were 26 higher (odds ratio 1.26, 95 confidence interval: 1.15, 1.38) for employees with high-strain jobs (low control/high demands) and 21 higher (odds ratio 1.21, 95 confidence interval: 1.11, 1.31) for those with passive jobs (low control/low demands) compared with employees in low-strain jobs (high control/low demands). In prospective analyses restricted to physically active participants, the odds of becoming physically inactive during follow-up were 21 and 20 higher for those with high-strain (odds ratio 1.21, 95 confidence interval: 1.11, 1.32) and passive (odds ratio 1.20, 95 confidence interval: 1.11, 1.30) jobs at baseline. These data suggest that unfavorable work characteristics may have a spillover effect on leisure-time physical activity.
Resumo:
The problem of model selection of a univariate long memory time series is investigated once a semi parametric estimator for the long memory parameter has been used. Standard information criteria are not consistent in this case. A Modified Information Criterion (MIC) that overcomes these difficulties is introduced and proofs that show its asymptotic validity are provided. The results are general and cover a wide range of short memory processes. Simulation evidence compares the new and existing methodologies and empirical applications in monthly inflation and daily realized volatility are presented.
Resumo:
In this paper, we re-examine two important aspects of the dynamics of relative primary commodity prices, namely the secular trend and the short run volatility. To do so, we employ 25 series, some of them starting as far back as 1650 and powerful panel data stationarity tests that allow for endogenous multiple structural breaks. Results show that all the series are stationary after allowing for endogenous multiple breaks. Test results on the Prebisch–Singer hypothesis, which states that relative commodity prices follow a downward secular trend, are mixed but with a majority of series showing negative trends. We also make a first attempt at identifying the potential drivers of the structural breaks. We end by investigating the dynamics of the volatility of the 25 relative primary commodity prices also allowing for endogenous multiple breaks. We describe the often time-varying volatility in commodity prices and show that it has increased in recent years.
Resumo:
We develop a continuous-time asset price model to capture the timeseries momentum documented recently. The underlying stochastic delay differentialsystem facilitates the analysis of effects of different time horizons used bymomentum trading. By studying an optimal asset allocation problem, we find thatthe performance of time series momentum strategy can be significantly improvedby combining with market fundamentals and timing opportunity with respect tomarket trend and volatility. Furthermore, the results also hold for different timehorizons, the out-of-sample tests and with short-sale constraints. The outperformanceof the optimal strategy is immune to market states, investor sentiment andmarket volatility.
Resumo:
Functionalised pyridinium and ammonium ionic liquids bearing a Michael acceptor are shown to scavenge H2S gas and various thiols, in most cases, without the aid of any added bases. Utilising the effective non-volatility of ionic liquids and ‘tagging’ malodourous substances to an ionic matrix renders them odourless.
Resumo:
The sustainability of cross-border peacebuilding initiatives is increasingly pertinent in a context of reduced public funding (national and European), yet the potential contribution to be made to this from private sector cooperation remains under-explored. This paper brings together quantitative data on cross-border trade with qualitative evidence from business leaders in the Irish border region in order to examine the nature of cross-border cooperation within the private sector and its possible connections to peacebuilding. This evidence is analysed in the light of three theses: spillover, contact and business-based peacebuilding. The first part of this paper assesses the conditions for cross-border business cooperation in Ireland, including funding support for economic development, European integration, and (post-Agreement) institutional change. The second part examines the particular contributions made by the private sector to peace, centring upon consciously non-political motivations (such as pragmatism and profit), networking and leadership.
Resumo:
A basic intuition is that arbitrage is easier when markets are most liquid. Surprisingly, we find that momentum profits are markedly larger in liquid market states. This finding is not explained by variation in liquidity risk, time-varying exposure to risk factors, or changes in macroeconomic condition, cross-sectional return dispersion, and investor sentiment. The predictive performance of aggregate market illiquidity for momentum profits uniformly exceed that of market return and market volatility states. While momentum strategies are unconditionally unprofitable in US, Japan, and Eurozone countries in the last decade, they are substantial following liquid market states.
Resumo:
Increasing installed capacities of wind power in an effort to achieve sustainable power systems for future generations pose problems for system operators. Volatility in generation volumes due to the adoption of stochastic wind power is increasing. Storage has been shown to act as a buffer for these stochastic energy sources, facilitating the integration of renewable energy into a historically inflexible power system. This paper examines peak and off peak benefits realised by installing a short term discharge storage unit in a system with a high penetration of wind power in 2020. A fully representative unit commitment and economic dispatch model is used to analyse two scenarios, one ‘with storage’ and one ‘without storage’. Key findings of this preliminary study show that wind curtailment can be reduced in the storage scenario, with a larger reduction in peak time ramping of gas generators is realised.
Resumo:
Reactivity of supported gold catalysts is a hot topic in catalysis for many years. This communication reports an investigation on the dissociation of molecular hydrogen at the perimeter sites of Au/TiO2 and the spillover of hydrogen atoms from the gold to the support using density functional theory calculations. It is found that the heterolytic dissociation is favoured in comparison with homolytic dissociation of molecular hydrogen at the perimeter sites. However, the surface oxygen of the rutile TiO2(110) surface at these sites can be readily passivated by the formed OH, suggesting that further dissociation of molecular hydrogen may occur at pure gold sites.
A sting in the spit: widespread cross-infection of multiple RNA viruses across wild and managed bees
Resumo:
Declining populations of bee pollinators are a cause of concern, with major repercussions for biodiversity loss and food security. RNA viruses associated with honeybees represent a potential threat to other insect pollinators, but the extent of this threat is poorly understood. This study aims to attain a detailed understanding of the current and ongoing risk of emerging infectious disease (EID) transmission between managed and wild pollinator species across a wide range of RNA viruses. Within a structured large-scale national survey across 26 independent sites, we quantify the prevalence and pathogen loads of multiple RNA viruses in co-occurring managed honeybee (Apis mellifera) and wild bumblebee (Bombus spp.) populations. We then construct models that compare virus prevalence between wild and managed pollinators. Multiple RNA viruses associated with honeybees are widespread in sympatric wild bumblebee populations. Virus prevalence in honeybees is a significant predictor of virus prevalence in bumblebees, but we remain cautious in speculating over the principle direction of pathogen transmission. We demonstrate species-specific differences in prevalence, indicating significant variation in disease susceptibility or tolerance. Pathogen loads within individual bumblebees may be high and in the case of at least one RNA virus, prevalence is higher in wild bumblebees than in managed honeybee populations. Our findings indicate widespread transmission of RNA viruses between managed and wild bee pollinators, pointing to an interconnected network of potential disease pressures within and among pollinator species. In the context of the biodiversity crisis, our study emphasizes the importance of targeting a wide range of pathogens and defining host associations when considering potential drivers of population decline.
Resumo:
The use of biomass as a source of fuel is on the sharp increase. In parallel with this expansion, new chemical processes and technologies are required to improve efficiency, sustainability, and profitability.
Biocatalytic and chemocatalytic methods can be combined to affect the conversion of bio-alcohols, and convert them to valuable chemical targets in an atom efficient and environmentally benign manor. Fermentation offers a useful first step in biomass conversion, as whole cell biocatalysts can provide sustained activity when fed with crude biomass. Coupling this with homogeneous and/or heterogeneous catalysis enables the preparation of a diverse product range. The transition between biocatalytic and chemocatalytic steps can be assisted by utilising ionic liquids.
Ionic liquids have potential roles in biorefineries that generate alcohols; as an extractant, reaction medium, and catalytic reagent. Underpinning the potential of ionic liquids in this area is: 1. the ability of ionic liquids to solubilize polyols and alcohols; 2. the facility to functionalise ionic liquids and tune properties; 3. the low volatility of ionic liquids.
The FP7 project GRAIL will be highlighted; this project focusses on the utilisation of glycerol formed as a by-product in biodiesel synthesis.
Resumo:
Spillover processes (i.e. the migration of ionic species from the support to the catalyst and vice versa) are known to play a very important role in catalysis and electrocatalysis. These spillover processes can be influenced by impurities (pre-existing on the catalyst surface) and by the catalyst morphology that may differ as a result of the differences in catalyst manufacturing processes. This work investigates the influence of impurities present in three commercial platinum (Pt) precursors. The resulting platinum films studied here were supported on yttria-stabilised-zirconia (YSZ). It was found that the three different catalyst films contained a range of impurities (determined by ICP-OES) that appear to affect the oxygen charge transfer reaction as studied by cyclic voltammetry (CV). © 2012 Elsevier B.V.
Resumo:
A dual chamber membrane reactor was used in order to study the effect of macroscopically applied oxygen chemical potential differences to a platinum catalyst supported on a mixed oxygen ion and electronic conducting membrane. It is believed that the oxygen chemical potential difference imposed by the use of an oxygen sweep in one of the reactor chambers causes the back-spillover of oxygen species from the support onto the catalyst surface, resulting in the modification of the catalytic activity. The use of different sweep gases, such as ethylene and hydrogen was investigated as the means to reverse the rate modification by removing the spilt over species from the catalyst surface and returning the system to its initial state. Oxygen sweep in general had a positive effect on the reaction rate with rate increases up to 20% measured. Experimental results showed that hydrogen is a more potent sweep gas than ethylene in terms of the ability to reverse rate modification. A 10% rate loss was observed when using an ethylene sweep as compared with an almost 60% rate decrease when hydrogen was used as the sweep gas. © 2009 Elsevier Ltd. All rights reserved.
Resumo:
A novel configuration for the in situ control of the catalytic activity of a polycrystalline Pt catalyst supported on a mixed ionic electronic conducting (MIEC) substrate is investigated. The modification of the catalytic activity is achieved by inducing the reverse spillover of oxygen promoting species from the support onto the catalyst surface, thus modifying the chemisorptive bond energy of the gas phase adsorbed reactants. This phenomenon is known as Electrochemical Promotion of Catalysis (EPOC). In this work we investigate the use of a wireless system that takes advantage of the mixed ionic electronic conductivity of the catalyst support (internally short-circuiting the system) in a dual chamber reactor. In this wireless configuration, the reaction takes place in one chamber of the membrane reactor while introduction of the promoting species is achieved by the use of an appropriate sweep gas (and therefore control of the oxygen chemical potential difference across the membrane) on the other chamber. Experimental results have shown that the catalytic rate can be enhanced by using an oxygen sweep, while a hydrogen sweep can reverse the changes. Total rate enhancement ratios of up to 3.5 were measured. © 2008 Elsevier B.V. All rights reserved.