Effects of non-uniform crosswind fields on scintillometry measurements

The effects of a non-uniform wind field along the path of a scintillometer are investigated. Theoretical spectra are calculated for a range of scenarios where the crosswind varies in space or time and compared to the ‘ideal’ spectrum based on a constant uniform crosswind. It is verified that the refractive-index structure parameter relation with the scintillometer signal remains valid and invariant for both spatially and temporally-varying crosswinds. However, the spectral shape may change significantly preventing accurate estimation of the crosswind speed from the peak of the frequency spectrum and retrieval of the structure parameter from the plateau of the power spectrum. On comparison with experimental data, non-uniform crosswind conditions could be responsible for previously unexplained features sometimes seen in observed spectra. By accounting for the distribution of crosswind, theoretical spectra can be generated that closely replicate the observations, leading to a better understanding of the measurements. Spatial variability of wind speeds should be expected for paths other than those that are parallel to the surface and over flat, homogenous areas, whilst fluctuations in time are important for all sites.

The influence of Antarctica on the momentum budget of the southern extratropics

The antarctic plateau acts as a strong heat sink for the global climate, cooling the atmosphere and radiating energy to space. A cold dense atmospheric boundary layer is formed. Strong surface winds are formed as the boundary layer drains off the plateau. These drainage winds and the eddy fluxes necessary to maintain them are analysed in a general circulation model (GCM). The drainage flow is well represented in the GCM. The associated mean meridional circulation is analysed in isentropic coordinates. The momentum budget over Antarctica reveals a balance between the Eliassen-Palm flux convergence and the Coriolis torque exerted by the mean meridional mass flux. Both vertical and horizontal components of the Eliassen-Palm flux contribute, the vertical component being the greater.

Comparison of TAMSAT and CPC rainfall estimates with raingauges, for southern Africa

Two different TAMSAT (Tropical Applications of Meteorological Satellites) methods of rainfall estimation were developed for northern and southern Africa, based on Meteosat images. These two methods were used to make rainfall estimates for the southern rainy season from October 1995 to April 1996. Estimates produced by both TAMSAT methods and estimates produced by the CPC (Climate Prediction Center) method were then compared with kriged data from over 800 raingauges in southern Africa. This shows that operational TAMSAT estimates are better over plateau regions, with 59% of estimates within one standard error (s.e.) of the kriged rainfall. Over mountainous regions the CPC approach is generally better, although all methods underestimate and give only 40% of estimates within 1 s.e. The two TAMSAT methods show little difference across a whole season, but when looked at in detail the northern method gives unsatisfactory calibrations. The CPC method does have significant overall improvements by building in real-time raingauge data, but only where sufficient raingauges are available.

Corticospinal tract integrity and lesion volume play different roles in chronic hemiparesis and its improvement through motor practice

Background. Initial evidence suggests that the integrity of the ipsilesional corticospinal tract (CST) after stroke is strongly related to motor function in the chronic state but not the treatment gain induced by motor rehabilitation. Objective. We examined the association of motor status and treatment benefit by testing patients with a wide range of severity of hemiparesis of the left and right upper extremity. Method. Diffusion tensor imaging was performed in 22 patients beyond 12 months after onset of stroke with severe to moderate hemiparesis. Motor function was tested before and after 2 weeks of modified constraint-induced movement therapy. Results. CST integrity, but not lesion volume, correlated with the motor ability measures of the Wolf Motor Function Test and the Motor Activity Log. No differences were found between left and right hemiparesis. Motor performance improved significantly with the treatment regime, and did so equally for patients with left and right arm paresis. However, treatment benefit was not associated with either CST integrity or lesion volume. Conclusion. CST integrity correlated best in this small trial with chronic long-term status but not treatment-induced improvements. The CST may play a different role in the mechanisms mediating long-term outcome compared to those underlying practice-induced gains after a chronic plateau in motor function.

Palaeovegetation in China during the late Quaternary: Biome reconstructions based on a global scheme of plant functional types

Two previous reconstructions of palaeovegetation across the whole of China were performed using a simple classification of plant functional types (PFTs). Now a more explicit, global PFT classification scheme has been developed, and a substantial number of additional pollen records have become available. Here we apply the global scheme of PFTs to a comprehensive set of pollen records available from China to test the applicability of the global scheme of PFTs in China, and to obtain a well-founded reconstruction of changing palaeovegetation patterns. A total of 806 pollen surface samples, 188 mid-Holocene (MH, 6000 14C yr BP) and 50 last glacial maximum (LGM, 18,000 14C yr BP) pollen records were used to reconstruct vegetation patterns in China, based on a new global classification system of PFTs and a standard numerical technique for biome assignment (biomization). The biome reconstruction based on pollen surface samples showed convincing agreement with present potential natural vegetation. Coherent patterns of change in biome distribution between MH, LGM and present are observed. In the MH, cold and cool-temperate evergreen needleleaf forests and mixed forests, temperate deciduous broadleaf forest, and warm-temperate evergreen broadleaf and mixed forest in eastern China were shifted northward by 200–500 km. Cold-deciduous forest in northeastern China was replaced by cold evergreen needleleaf forest while in central northern China, cold-deciduous forest was present at some sites now occupied by temperate grassland and desert. The forest–grassland boundary was 200–300 km west of its present position. Temperate xerophytic shrubland, temperate grassland and desert covered a large area on the Tibetan Plateau, but the area of tundra was reduced. Treeline was 300–500 m higher than present in Tibet. These changes imply generally warmer winters, longer growing seasons and more precipitation during the MH. Westward shifts of the forest–shrubland–grassland and grassland–desert boundaries imply greater moisture availability in the MH, consistent with a stronger summer monsoon. During the LGM, in contrast, cold-deciduous forest, cool-temperate evergreen needleleaf forest, cool mixed forests, warm-temperate evergreen broadleaf and mixed forest in eastern China were displaced to the south by 300–1000 km, while temperate deciduous broadleaf forest, pure warm-temperate evergreen forest, tropical semi-evergreen and evergreen broadleaf forests were restricted or absent from the mainland of southern China, implying colder winters than present. Strong shifts of temperate xerophytic shrubland, temperate grassland and desert to the south and east in northern and western China and on the Tibetan Plateau imply drier conditions than present.

Pollen-based biome reconstructions for China at 0 and 6000 years

Biomization provides an objective and robust method of assigning pollen spectra to biomes so that pollen data can be mapped and compared directly with the output of biomgeographic models. We have tested the applicability of this procedure, originally developed for Europe, to assign modern surface samples from China to biomes. The procedure successfully delineated the major vegetation types of China. When the same procedure was applied to fossil pollen samples for 6000 years ago, the reconstructions showed systematic differences from present, consistent with previous interpretations of vegetation changes since the mid-Holocene. In eastern China, the forest zones were systematically shifted northwards, such that cool mixed forests displaced taiga in northeastern China, while broad-leaved evergreen forest extended c. 300 km and temperate deciduous forestc. 500–600 km beyond their present northern limits. In northwestern China, the area of desert and steppe vegetation was reduced compared to present. On the Tibetan Plateau, forest vegetation extended to higher elevations than today and the area of tundra was reduced. These shifts in biome distributions imply significant changes in climate since 6000 years ago that can be interpreted qualitatively as a response to orbital forcing and its secondary effects on the Asian monsoon.

Resonance response of electrorheological fluids in vertical oscillation squeeze flow

The resonance effect of microcrystalline cellulose/castor oil electrorheological (ER) suspensions was studied in a compressed oscillatory squeeze flow under external electric fields. The resonance frequency first increases linearly with increasing external held, and then shift to high-field plateau. The amplitudes of resonance peak increase sharply with the applied fields in the range of 0.17-1.67kV/mm. The phase difference of the reduced displacement relative to the excitation force inverses in the case of resonance. A viscoelasticity model of the ER suspensions, which offers both the equivalent stiffness and the viscous damping, should be responsible for the appearance of resonance. The influence of the electric field on the resonance frequency and the resonance hump is consistent qualitatively with the interpretation of our proposed model. Storage modulus G' was presented for the purpose of investigating this influence.

An isotope dilution model for partitioning phenylalanine and tyrosine uptake by the mammary gland of lactating dairy cows

An isotope dilution model for partitioning phenylalanine and tyrosine uptake by the mammary gland of the lactating dairy cow is constructed and solved in the steady state. The model contains four intracellular and four extracellular pools and conservation of mass principles are applied to generate the fundamental equations describing the behaviour of the system. The experimental measurements required for model solution are milk secretion and plasma flow rate across the gland in combination with phenylalanine and tyrosine concentrations and plateau isotopic enrichments in arterial and venous plasma and free and protein bound milk during a constant infusion of [1-(13)C]phenylalanine and [2,3,5,6-(2)H]tyrosine tracer. If assumptions are made, model solution enables determination of steady state flows for phenylalanine and tyrosine inflow to the gland, outflow from it and bypass, and flows representing the synthesis and degradation of constitutive protein and hydroxylation. The model is effective in providing information about the fates of phenylalanine and tyrosine in the mammary gland and could be used as part of a more complex system describing amino acid metabolism in the whole ruminant.

Holocene variations in peatland methane cycling associated with the Asian summer monsoon system

Atmospheric methane concentrations decreased during the early to middle Holocene; however, the governing mechanisms remain controversial. Although it has been suggested that the mid-Holocene minimum methane emissions are associated with hydrological change, direct evidence is lacking. Here we report a new independent approach, linking hydrological change in peat sediments from the Tibetan Plateau to changes in archaeal diether concentrations and diploptene delta C-13 values as tracers for methanogenesis and methanotrophy, respectively. A minimum in inferred methanogenesis occurred during the mid-Holocene, which, locally, corresponds with the driest conditions of the Holocene, reflecting a minimum in Asian monsoon precipitation. The close coupling between precipitation and methanogenesis is validated by climate simulations, which also suggest a regionally widespread impact. Importantly, the minimum in methanogenesis is associated with a maximum in methanotrophy. Therefore, methane emissions in the Tibetan Plateau region were apparently lower during the mid-Holocene and partially controlled by interactions of large-scale atmospheric circulation.

Palaeoenvironmental changes during the Valanginian: new insights from variations in phosphorus contents and bulk- and clay mineralogies in the western Tethys

Paleoenvironmental and paleoclimatic changes during the Valanginian carbon isotopic excursion (CIE) have been investigated in the western Tethys. For this purpose, bulk-rock and clay mineralogies, as well as phosphorus (P) contents were evaluated in a selection of five sections located in the Vocontian Basin (Angles, SE France; Alvier, E Switzerland; Malleval, E France), and the Lombardian Basin (Capriolo, N Italy; Breggia, S Switzerland). Within the CIE interval, bulk-rock and clay mineralogies are inferred to reflect mostly climate change. The onset of the CIE (Busnardoites campylotoxus ammonite Zone) is characterized by higher detrital index (DI: sum of the detrital minerals divided by calcite contents) values and the presence of kaolinite in their clay-mineral assemblages. In the late Valanginian (from the Saynoceras verrucosum Zone up to the end of the Valanginian), the samples show relatively variable DI and lower values or the absence of kaolinite. The variation in the mineralogical composition is interpreted as reflecting a change from a climate characterized by optimal weathering conditions associated with an increase in terrigenous input on the southern European margin during the CIE towards an overall unstable climate associated with drier conditions in the late Valanginian. This is contrasted by a dissymmetry (proximal vs distal) along the studied transect, the northern Tethyan margin being more sensitive to changes in continental input compared to the distal environments. P accumulation rates (PAR) present similar features. In the Vocontian basin, P content variations are associated with changes in terrigenous influx, whereas in the Lombardian basin (i.e. Capriolo and Breggia), PAR values are less well correlated. This is mainly because the deeper part of the Tethys was less sensitive to changes in continental inputs. The onset of the CIE (top of the B. campylotoxus Zone) records a general increase in PAR suggesting an increase in marine nutrient levels. This is linked to higher continental weathering rates and the enhanced influx of nutrients into the ocean. In the period corresponding to the shift itself, P contents show a dissymmetry between the Vocontian and Lombardian basins (proximal vs distal). For the sections of Malleval, Alvier and Angles, a decrease in P concentrations associated to a decrease in detrital input is observed. In Capriolo and Breggia, PAR show maximum values during the plateau, indicating a more complex interaction between different P sources. The time interval including the top of S. verrucosum Zone up to the end of the Valanginian is characterized by variable PAR values, suggesting variable nutrient influxes. These changes are in agreement with an evolution towards seasonally contrasted conditions in the late Valanginian.

Effects of past climate variability on fire and vegetation in the cerrãdo savanna of the Huanchaca Mesetta, NE Bolivia

Cerrãdo savannas have the greatest fire activity of all major global land-cover types and play a significant role in the global carbon cycle. During the 21st century, temperatures are projected to increase by ∼ 3 ◦C coupled with a precipitation decrease of ∼ 20 %. Although these conditions could potentially intensify drought stress, it is unknown how that might alter vegetation composition and fire regimes. To assess how Neotropical savannas responded to past climate changes, a 14 500-year, high-resolution, sedimentary record from Huanchaca Mesetta, a palm swamp located in the cerrãdo savanna in northeastern Bolivia, was analyzed with phytoliths, stable isotopes, and charcoal. A nonanalogue, cold-adapted vegetation community dominated the Lateglacial–early Holocene period (14 500–9000 cal yr BP, which included trees and C3 Pooideae and C4 Panicoideae grasses. The Lateglacial vegetation was fire-sensitive and fire activity during this period was low, likely responding to fuel availability and limitation. Although similar vegetation characterized the early Holocene, the warming conditions associated with the onset of the Holocene led to an initial increase in fire activity. Huanchaca Mesetta became increasingly firedependent during the middle Holocene with the expansion of C4 fire-adapted grasses. However, as warm, dry conditions, characterized by increased length and severity of the dry season, continued, fuel availability decreased. The establishment of the modern palm swamp vegetation occurred at 5000 cal yr BP. Edaphic factors are the first-order control on vegetation on the rocky quartzite mesetta. Where soils are sufficiently thick, climate is the second-order control of vegetation on the mesetta. The presence of the modern palm swamp is attributed to two factors: (1) increased precipitation that increased water table levels and (2) decreased frequency and duration of surazos (cold wind incursions from Patagonia) leading to increased temperature minima. Natural (soil, climate, fire) drivers rather than anthropogenic drivers control the vegetation and fire activity at Huanchaca Mesetta. Thus the cerrãdo savanna ecosystem of the Huanchaca Plateau has exhibited ecosystem resilience to major climatic changes in both temperature and precipitation since the Lateglacial period.

A Time-Series Analysis of the H alpha Emission Line in V3885 Sagitarii

Flickering is a phenomenon related to mass accretion observed among many classes of astrophysical objects. In this paper we present a study of flickering emission lines and the continuum of the cataclysmic variable V3885 Sgr. The flickering behavior was first analyzed through statistical analysis and the power spectra of lightcurves. Autocorrelation techniques were then employed to estimate the flickering timescale of flares. A cross-correlation study between the line and its underlying continuum variability is presented. The cross-correlation between the photometric and spectroscopic data is also discussed. Periodograms, calculated using emission-line data, show a behavior that is similar to those obtained from photometric datasets found in the literature, with a plateau at lower frequencies and a power-law at higher frequencies. The power-law index is consistent with stochastic events. The cross-correlation study indicates the presence of a correlation between the variability on Ha and its underlying continuum. Flickering timescales derived from the photometric data were estimated to be 25 min for two lightcurves and 10 min for one of them. The average timescales of the line flickering is 40 min, while for its underlying continuum it drops to 20 min.

(40)Ar/(39)Ar ages and Sr-Nd-Pb-Os geochemistry of CAMP tholeiites from Western Maranhao basin (NE Brazil)

The Central Atlantic Magmatic Province (CAMP), emplaced at the Triassic-Jurassic (T-J) boundary (-200 Ma), is among the largest igneous provinces on Earth. The Maranhao basin in NE Brazil is located around 700 km inland and 2000 km from the site of the earliest Pangea disruption. The CAMP tholeiites occur only in the western part of the basin and have been described as low and high-Ti. Here we document the occurrence of two sub-groups among the high-Ti tholeiites in the Western Maranhao basin. The major and trace elements and the Sr-Nd-Pb isotopic ratios define three chemical groups corresponding to the low-Ti (TiO(2)< 1.3 wt.%), high-Ti (TiO(2)-2.0 wt.%) and evolved high-Ti (TiO(2 >)3 wt.%) western Maranhao basin tholeiites (WMBT). The new (40)Ar/(39)Ar plateau ages obtained on plagioclase separates for high-Ti (199.7 +/- 2.4 Ma) and evolved high-Ti WMBT (197.2 +/- 0.5 Ma and 198.2 +/- 0.6 Ma) are indistinguishable and identical to those of previously analyzed low-Ti WMBT (198.5 +/- 0.8 Ma) and to the mean (40)Ar/(39)Ar age of the CAMP (199 +/- 2.4 Ma). We also present the first Re-Os isotopic data for CAMP basalts. The low and high-Ti samples display mantle-like initial ((187)Os/(188)Os)(i) ranging from 0.1267 to 0.1299, while the evolved high-Ti samples are more radiogenic (((187)Os/ (188)Os)(i) up to 0.184) We propose that the high-Ti WMBT were derived from the sub-lithospheric asthenosphere, and contaminated during ascent by interaction with the subcontinental lithospheric mantle (SCLM). The evolved high-Ti WMBT were derived from the same asthenospheric source but experienced crustal contamination. The chemical characteristics of the low-Ti group can be explained by partial melting of the most fertile portions of the SCLM metasomatized during paleo-subduction. Alternatively, the low-Ti WMBT could be derived from the sub-lithospheric asthenosphere but the resulting melts may have undergone contamination by the SCLM. The occurrences of high-Ti basalts are apparently not restricted to the area of initial continental disruption which may bring into question previous interpretations such as those relating high-Ti CAMP magmatism to the initiation of Atlantic ridge spreading or as the expression of a deep mantle plume. We propose that the CAMP magmatism in the Maranhao basin may be attributed to local hotter mantle conditions due to the combined effects of edge-driven convection and large-scale mantle warming under the Pangea supercontinent. The involvement of a mantle-plume with asthenosphere-like isotopic characteristics cannot be ruled out either as one of the main source components of the WMBT or as a heat supplier. (C) 2010 Elsevier BM. All rights reserved.

Is bird incidence in Atlantic forest fragments influenced by landscape patterns at multiple scales?

The degree to which habitat fragmentation affects bird incidence is species specific and may depend on varying spatial scales. Selecting the correct scale of measurement is essential to appropriately assess the effects of habitat fragmentation on bird occurrence. Our objective was to determine which spatial scale of landscape measurement best describes the incidence of three bird species (Pyriglena leucoptera, Xiphorhynchus fuscus and Chiroxiphia caudata) in the fragmented Brazilian Atlantic forest and test if multi-scalar models perform better than single-scalar ones. Bird incidence was assessed in 80 forest fragments. The surrounding landscape structure was described with four indices measured at four spatial scales (400-, 600-, 800- and 1,000-m buffers around the sample points). The explanatory power of each scale in predicting bird incidence was assessed using logistic regression, bootstrapped with 1,000 repetitions. The best results varied between species (1,000-m radius for P. leucoptera; 800-m for X. fuscus and 600-m for C. caudata), probably due to their distinct feeding habits and foraging strategies. Multi-scale models always resulted in better predictions than single-scale models, suggesting that different aspects of the landscape structure are related to different ecological processes influencing bird incidence. In particular, our results suggest that local extinction and (re)colonisation processes might simultaneously act at different scales. Thus, single-scale models may not be good enough to properly describe complex pattern-process relationships. Selecting variables at multiple ecologically relevant scales is a reasonable procedure to optimise the accuracy of species incidence models.

Are corridors, fragment size and forest structure important for the conservation of leaf-litter lizards in a fragmented landscape?

To investigate the implications of forest fragmentation for conservation of leaf-litter lizards the importance of fragment size, corridors and forest structure was examined in 20 forest fragments and six localities within a continuous forest in the Atlantic Plateau of Sao Paulo state, Brazil. The fragments were 2-276 ha in area and had different degrees of connectivity depending on the presence or absence of corridors. Two species of lizards were dominant, Ecpleopus gaudichaudii and Enyalius perditus. Variation in forest structure among sites was important only in explaining the abundance of E. perditus. Regardless of variation in forest structure, lizard species composition, total lizard abundance, number of species and abundance of E. perditus were sensitive to fragmentation per se but not to fragment size or corridor linkage. The inhospitable matrix surrounding fragments is probably what determines the presence and abundance of E. perditus and the high er lizard richness in continuous forests. These conditions may have prevented lizard species from recolonizing the forest fragments. Our results emphasize that the conservation of this leaf-litter fauna depends on the maintenance of large tracts of continuous forests and not on the size of fragments or on the presence of forest connections. Strategies for conservation of leaf-litter lizards in such highly fragmented Atlantic Forest landscapes should consider the enlargement of landscape connectivity between fragments and continuous forest, allowing the latter areas to act as a source of individuals for fragments.