Cointegration,error-correction models,and forecasting using realigned foreign exchange rates

This study employs error-correction models (ECMs) to forecast foreign exchange (FX) rates where the data-sampling procedures are consistent with the rules governing the settlement (delivery) of FX contracts in the FX market. The procedure involves thatching (aligning) the forward rate to the 'actual' realized (future) spot rate at the settlement (delivery) date. This approach facilitates the generation of five different sets of sub samples of FX rate series for each currency. For comparative purposes, non-aligned month-end rates are also examined. The results indicate that the moments of the realized forecast errors for the same currency are not similar. Further, the ECMs derived are unstable, and their forecasting performance vary. The forecasting performance of the ECMs appear to be affected by the choice of the interval in which the sets of sub samples are observed. These results are attributed to the observed seasonal variation in FX rates.     

Structure and function of an irreversible agonist-β(2) adrenoceptor complex

G-protein-coupled receptors (GPCRs) are eukaryotic integral membrane proteins that modulate biological function by initiating cellular signalling in response to chemically diverse agonists. Despite recent progress in the structural biology of GPCRs, the molecular basis for agonist binding and allosteric modulation of these proteins is poorly understood. Structural knowledge of agonist-bound states is essential for deciphering the mechanism of receptor activation, and for structure-guided design and optimization of ligands. However, the crystallization of agonist-bound GPCRs has been hampered by modest affinities and rapid off-rates of available agonists. Using the inactive structure of the human β(2) adrenergic receptor (β(2)AR) as a guide, we designed a β(2)AR agonist that can be covalently tethered to a specific site on the receptor through a disulphide bond. The covalent β(2)AR-agonist complex forms efficiently, and is capable of activating a heterotrimeric G protein. We crystallized a covalent agonist-bound β(2)AR-T4L fusion protein in lipid bilayers through the use of the lipidic mesophase method, and determined its structure at 3.5?? resolution. A comparison to the inactive structure and an antibody-stabilized active structure (companion paper) shows how binding events at both the extracellular and intracellular surfaces are required to stabilize an active conformation of the receptor. The structures are in agreement with long-timescale (up to 30?μs) molecular dynamics simulations showing that an agonist-bound active conformation spontaneously relaxes to an inactive-like conformation in the absence of a G protein or stabilizing antibody.     

Caspase signalling controls microglia activation and neurotoxicity

Activation of microglia and inflammation-mediated neurotoxicity are suggested to play a decisive role in the pathogenesis of several neurodegenerative disorders. Activated microglia release pro-inflammatory factors that may be neurotoxic. Here we show that the orderly activation of caspase-8 and caspase-3/7, known executioners of apoptotic cell death, regulate microglia activation through a protein kinase C (PKC)-δ-dependent pathway. We find that stimulation of microglia with various inflammogens activates caspase-8 and caspase-3/7 in microglia without triggering cell death in vitro and in vivo. Knockdown or chemical inhibition of each of these caspases hindered microglia activation and consequently reduced neurotoxicity. We observe that these caspases are activated in microglia in the ventral mesencephalon of Parkinson's disease (PD) and the frontal cortex of individuals with Alzheimer's disease (AD). Taken together, we show that caspase-8 and caspase-3/7 are involved in regulating microglia activation. We conclude that inhibition of these caspases could be neuroprotective by targeting the microglia rather than the neurons themselves.     

A long-lived lunar dynamo driven by continuous mechanical stirring

Lunar rocks contain a record of an ancient magnetic field that seems to have persisted for more than 400 million years and which has been attributed to a lunar dynamo. Models of conventional dynamos driven by thermal or compositional convection have had difficulty reproducing the existence and apparently long duration of the lunar dynamo. Here we investigate an alternative mechanism of dynamo generation: continuous mechanical stirring arising from the differential motion, due to Earth-driven precession of the lunar spin axis, between the solid silicate mantle and the liquid core beneath. We show that the fluid motions and the power required to drive a dynamo operating continuously for more than one billion years and generating a magnetic field that had an intensity of more than one microtesla 4.2 billion years ago are readily obtained by mechanical stirring. The magnetic field is predicted to decrease with time and to shut off naturally when the Moon recedes far enough from Earth that the dissipated power is insufficient to drive a dynamo; in our nominal model, this occurred at about 48 Earth radii (2.7 billion years ago). Thus, lunar palaeomagnetic measurements may be able to constrain the poorly known early orbital evolution of the Moon. This mechanism may also be applicable to dynamos in other bodies, such as large asteroids.     

Exclusion of a luminous red giant as a companion star to the progenitor of supernova SN 2011fe

Type Ia supernovae are thought to result from a thermonuclear explosion of an accreting white dwarf in a binary system, but little is known of the precise nature of the companion star and the physical properties of the progenitor system. There are two classes of models: double-degenerate (involving two white dwarfs in a close binary system) and single-degenerate models. In the latter, the primary white dwarf accretes material from a secondary companion until conditions are such that carbon ignites, at a mass of 1.38 times the mass of the Sun. The type Ia supernova SN 2011fe was recently detected in a nearby galaxy. Here we report an analysis of archival images of the location of SN 2011fe. The luminosity of the progenitor system (especially the companion star) is 10-100 times fainter than previous limits on other type Ia supernova progenitor systems, allowing us to rule out luminous red giants and almost all helium stars as the mass-donating companion to the exploding white dwarf.     

Chinese deserts and sand fields in Last Glacial Maximum and Holocene Optimum

The Last Glacial Maximum (LGM, c. 26-16 ka) and the Holocene Optimum (HO, c. 9-5 ka) were characterized by cold-dry and warm-wet climates respectively in the recently geological Earth. How Chinese deserts and sand fields responded to these distinctive climatic changes is still not clear, however. To reconstruct environments of the deserts and sand fields during the LGM and HO is helpful to understand the forcing mechanisms of environment change in this arid region, and to test paleoclimatic modeling results. Through our long-term field and laboratory investigations, 400 optically stimulated luminescence (OSL) ages and more than 100 depositional records in the Chinese deserts and sand fields were obtained; on the basis of these data, we reconstruct spatial distributions of the deserts and sand fields during the LGM and HO. Our results show that the sand fields of Mu Us, Hunshandake, Horqin and Hulun Buir in northern and northeastern China had expanded 25%, 37%, 38% and 270%, respectively, during the LGM; the sand fields of Gonghe in the northeastern Qinghai-Tibetan Plateau had expanded 20%, and the deserts of Badain Jaran, Tengger in central northern China had expanded 39% and 29% separately during the LGM; the deserts of Taklimakan, Gurbantünggüt and Kumtag in northwestern China had expanded 10%-20% respectively, compared to their modern areas. On the other hand, all of the sand fields were nearly completely covered by vegetation during the HO; the deserts in northwestern and central northern China were reduced by around 5%-20% in area during this time. Lakes in this arid region were probably expanded during the HO but this conclusion needs more investigation. Compared with the geological distributions of deserts and sand fields, human activity has clearly changed (expanded) the area of active sand dunes at the present time. Our observations show that environmental conditions of Chinese deserts and sand fields are controlled by regional climate together with human activity.     

Distribution and dynamics of waterbird habitat during spring in southern Oregon–northeastern California

The southern Oregon–northeastern California and extreme northwestern Nevada (hereafter “SONEC”) region provides critical spring migration habitat for waterfowl and other waterbirds in the Pacific Flyway. Information on the dynamics and distribution of waterbird habitats in SONEC during spring is needed to guide conservation efforts in the region. We grouped 1992 National Land Cover Data classes into 5 potential waterbird habitat types and used Landsat 5 Thematic Mapper and Landsat 7 Enhanced Thematic Mapper Plus satellite imagery to map flooding of these habitat types in SONEC during February–May, 2002 and 2003. SONEC included 13,727 km 2 of potential waterbird habitat comprised of grasslands (37.1%), pasture/hay (24.6%), marsh (15.9%), open wetland (11.8%), and croplands (10.6%). On average, 11.9% of this potential habitat was flooded during spring; but the percentage, area, and composition varied within and among years and subregions. Total flooding increased from 693 km 2 in February to 2099 km 2 in April during 2002 and from 1630 km 2 in February to 2125 km 2 in May during 2003. Open wetland comprised 58%–74%, marsh 8%–18%, pasture/hay 4%–11%, grassland 4%–17%, and cropland 3%–8% of the flooded habitat in SONEC. Satellite imagery and land-use data provided useful estimates of waterbird habitat availability in SONEC during spring, but other methods should be tested to more accurately measure flooding of densely vegetated habitats such as marsh. With <12% of the potential habitat flooded on average during spring, conservation programs have ample opportunity to improve the SONEC landscape for migrating waterbirds.     

Nest site selection in raptor communities of the eastern Great Basin desert

Measures of niche breadth and overlap were used to compare nest site selection in a community of 10 raptor species and the Raven nesting in the eastern Great Basin Desert. Three variables were examined: nest site type, elevation, and exposure. Results suggest a division of component raptor species into relatively abundant core species that show wide niche breadths and uncommon fringe species with narrow niche breadths. Differences in use of each resource are most pronounced along elevation gradient in which three guilds are evident that correspond to raptor species groupings that nest at higher, middle, and lower elevations. Each guild is comprised of a mix of core and fringe species. Raptor species with highest overlap along one or more nest site variables examined are separated by differences in activity patterns.