1,985 research outputs found
16 years of Ulysses Interstellar Dust Measurements in the Solar System: II. Fluctuations in the Dust Flow from the Data
The Ulysses spacecraft provided the first opportunity to identify and study
Interstellar Dust (ISD) in-situ in the Solar System between 1992 and 2007. Here
we present the first comprehensive analysis of the ISD component in the entire
Ulysses dust data set. We analysed several parameters of the ISD flow in a
time-resolved fashion: flux, flow direction, mass index, and flow width. The
general picture is in agreement with a time-dependent focussing/defocussing of
the charged dust particles due to long-term variations of the solar magnetic
field throughout a solar magnetic cycle of 22 years. In addition, we confirm a
shift in dust direction of in 2005, along with a
steep, size-dependent increase in flux by a factor of 4 within 8 months. To
date, this is difficult to interpret and has to be examined in more detail by
new dynamical simulations. This work is part of a series of three papers. This
paper concentrates on the time-dependent flux and direction of the ISD. In a
companion paper (Kr\"uger et al., 2015) we analyse the overall mass
distribution of the ISD measured by Ulysses, and a third paper discusses the
results of modelling the flow of the ISD as seen by Ulysses (Sterken et al.,
2015).Comment: 41 pages, 10 figures, 5 table
Assessing satellite-derived land product quality for earth system science applications: results from the ceos lpv sub-group
The value of satellite derived land products for science applications and research is dependent upon the known accuracy of the data. CEOS (Committee on Earth Observation Satellites), the space arm of the Group on Earth Observations (GEO), plays a key role in coordinating the land product validation process. The Land Product Validation (LPV) sub-group of the CEOS Working Group on Calibration and Validation (WGCV) aims to address the challenges associated with the validation of global land products. This paper provides an overview of LPV sub-group focus area activities, which cover seven terrestrial Essential Climate Variables (ECVs). The contribution will enhance coordination of the scientific needs of the Earth system communities with global LPV activities
Heliospheric modulation of the interstellar dust flow on to Earth
Aims. Based on measurements by the Ulysses spacecraft and high-resolution
modelling of the motion of interstellar dust (ISD) through the heliosphere we
predict the ISD flow in the inner planetary system and on to the Earth. This is
the third paper in a series of three about the flow and filtering of the ISD.
Methods. Micrometer- and sub-micrometer-sized dust particles are subject to
solar gravity and radiation pressure as well as to interactions with the
interplanetary magnetic field that result in a complex size-dependent flow
pattern of ISD in the planetary system. With high-resolution dynamical
modelling we study the time-resolved flux and mass distribution of ISD and the
requirements for detection of ISD near the Earth.
Results. Along the Earth orbit the density, speed, and flow direction of ISD
depend strongly on the Earth's position and the size of the interstellar
grains. A broad maximum of the ISD flux (2x10^{-4}/m^2/s of particles with
radii >~0.3\mu m) occurs in March when the Earth moves against the ISD flow.
During this time period the relative speed with respect to the Earth is highest
(~60 km/s), whereas in September when the Earth moves with the ISD flow, both
the flux and the speed are lowest (<~10 km/s). The mean ISD mass flow on to the
Earth is ~100 kg/year with the highest flux of ~3.5kg/day occurring for about 2
weeks close to the end of the year when the Earth passes near the narrow
gravitational focus region downstream from the Sun. The phase of the 22-year
solar wind cycle has a strong effect on the number density and flow of
sub-micrometer-sized ISD particles. During the years of maximum electromagnetic
focussing (year 2031 +/- 3) there is a chance that ISD particles with sizes
even below 0.1\mu m can reach the Earth.
Conclusions. We demonstrate that ISD can be effectively detected, analysed,
and collected by space probes at 1 AU distance from the Sun.Comment: 17 pages, 17 figure
Useful ‘junk': Alu RNAs in the human transcriptome
Abstract.: Alu elements are the most abundant repetitive elements in the human genome; they have amplified by retrotransposition to reach the present number of more than one million copies. Alu elements can be transcribed in two different ways, by two independent polymerases. ‘Free Alu RNAs' are transcribed by Pol III from their own promoter, while ‘embedded Alu RNAs' are transcribed by Pol II as part of protein- and non-protein-coding RNAs. Recent studies have demonstrated that both free and embedded Alu RNAs play a major role in post transcriptional regulation of gene expression, for example by affecting protein translation, alternative splicing and mRNA stability. These discoveries illustrate how a part of the ‘junk DNA' content of the human genome has been recruited to important functions in regulation of gene expressio
Peatlands and the carbon cycle: from local processes to global implications - a synthesis
Peatlands cover only 3% of the Earth's land surface but boreal and subarctic peatlands store about 15-30% of the world's soil carbon ( C) as peat. Despite their potential for large positive feedbacks to the climate system through sequestration and emission of greenhouse gases, peatlands are not explicitly included in global climate models and therefore in predictions of future climate change. In April 2007 a symposium was held in Wageningen, the Netherlands, to advance our understanding of peatland C cycling. This paper synthesizes the main findings of the symposium, focusing on (i) small-scale processes, (ii) C fluxes at the landscape scale, and (iii) peatlands in the context of climate change. The main drivers controlling most are related to some aspects of hydrology. Despite high spatial and annual variability in Net Ecosystem Exchange ( NEE), the differences in cumulative annual NEE are more a function of broad scale geographic location and physical setting than internal factors, suggesting the existence of strong feedbacks. In contrast, trace gas emissions seem mainly controlled by local factors. Key uncertainties remain concerning the existence of perturbation thresholds, the relative strengths of the CO2 and CH4 feedback, the links among peatland surface climate, hydrology, ecosystem structure and function, and trace gas biogeochemistry as well as the similarity of process rates across peatland types and climatic zones. Progress on these research areas can only be realized by stronger co-operation between disciplines that address different spatial and temporal scales
Gene induction during differentiation of human monocytes into dendritic cells: an integrated study at the RNA and protein levels
Changes in gene expression occurring during differentiation of human
monocytes into dendritic cells were studied at the RNA and protein levels.
These studies showed the induction of several gene classes corresponding to
various biological functions. These functions encompass antigen processing and
presentation, cytoskeleton, cell signalling and signal transduction, but also
an increase in mitochondrial function and in the protein synthesis machinery,
including some, but not all, chaperones. These changes put in perspective the
events occurring during this differentiation process. On a more technical
point, it appears that the studies carried out at the RNA and protein levels
are highly complementary.Comment: website publisher:
http://www.springerlink.com/content/ha0d2c351qhjhjdm
Extent change of protected mangrove forest and its relation to wave power exposure on Aldabra Atoll
Mangrove forests, vital for the conservation of biodiversity, protection of coastlines, and carbon capture, are decreasing globally at a rate higher than most other tropical forests. They are threatened by sea level rise, drought and storm surge, especially on low-lying islands where forests are directly exposed to the elements and have limited land area. We investigated changes in the spatial extent of mangroves on Aldabra Atoll, Seychelles – a protected area without direct human pressures, over 21 years using Landsat images. Over the 21-year study period, mean mangrove extent was 1283 ha with an overall net increase of 60 ha (0.23% year-1). The majority of extent changes were small (<2 ha) and contiguous to the existing mangrove extent. We then assessed the relation of mangrove cover change along the lagoon coastline with wave power (rate of energy transfer by waves), using fetch measures and local wind data. We found lower wave power values for stable mangrove areas than for areas that had gained or lost mangroves from 1997 to 2018. We identified wave power thresholds of 2.3 W m-1 for stable mangrove and 7.1 W m-1 for mangrove occurrence. These thresholds might be valuable for assessing threats and sites with the greatest potential for mangrove restoration across similar areas worldwide. Our results highlight the importance of quantifying mangrove extent changes at a local scale to assist with planning for the protection and restoration of this ecologically important habitat, given its vulnerability to the pressures associated with climate change
Satellite-Measured Chlorophyll and Temperature Variability Off Northern Chile During the 1996-1998 La Niña and El Niño
Time series of satellite measurements are used to describe patterns of surface temperature and chlorophyll associated with the 1996 cold La Nina phase and the 1997-1998 warm El Nino phase of the El Nino - Southern Oscillation cycle in the upwelling region off northern Chile. Surface temperature data are available through the entire study period. Sea-viewing Wide Field-of-view Sensor (SeaWiFS) data first became available in September 1997 during a relaxation in El Nino conditions identified by in situ hydrographic data. Over the time period of coincident satellite data, chlorophyll patterns closely track surface temperature patterns. Increases both in nearshore chlorophyll concentration and in cross-shelf extension of elevated concentrations are associated with decreased coastal temperatures during both the relaxation in El Nino conditions in September-November 1997 and the recovery from EI Nino conditions after March 1998. Between these two periods during austral summer (December 1997 to March 1998) and maximum El Nino temperature anomalies, temperature patterns normally associated with upwelling were absent and chlorophyll concentrations were minimal. Cross-shelf chlorophyll distributions appear to be modulated by surface temperature frontal zones and are positively correlated with a satellite-derived upwelling index. Frontal zone patterns and the upwelling index in 1996 imply an austral summer nearshore chlorophyll maximum, consistent with SeaWiFS data from I 1998-1999, after the El Nino. SeaWiFS retrievals in the data set used here are higher than in situ measurements by a factor of 2-4; however, consistency in the offset suggests relative patterns are valid
Seasonal Climatology of Hydrographic Conditions in the Upwelling Region Off Northern Chile
Over 30 years of hydrographic data from the northern Chile (18 degreesS-24 degreesS) upwelling region are used to calculate the surface and subsurface seasonal climatology extending 400 km offshore. The data are interpolated to a grid with sufficient spatial resolution to preserve cross-shelf gradients and then presented as means within four seasons: austral winter (July-September), spring (October-December), summer (January-March), and fall (April-June). Climatological monthly wind forcing, surface temperature, and sea level from three coastal stations indicate equatorward (upwelling favorable) winds throughout the year, weakest in the north. Seasonal maximum alongshore wind stress is in late spring and summer (December-March). Major water masses of the region are identified in climatological T-S plots and their sources and implied circulation discussed. Surface fields and vertical transects of temperature and salinity confirm that upwelling occurs year-round, strongest in summer and weakest in winter, bringing relatively fresh water to the surface nearshore. Surface geostrophic flow nearshore is equatorward throughout the year. During summer, an anticyclonic circulation feature in the north which extends to at least 200 m depth is evident in geopotential anomaly and in both temperature and geopotential variance fields. Subsurface fields indicate generally poleward flow throughout the year, strongest in an undercurrent near the coast. This undercurrent is strongest in summer and most persistent and organized in the south (south of 21 degreesS), A subsurface oxygen minimum, centered at similar to 250 m, is strongest at lower latitudes. Low-salinity subsurface water intrudes into the study area near 100 m, predominantly in offshore regions, strongest during summer and fall and in the southernmost portion of the region. The climatological fields are compared to features off Baja within the somewhat analogous California Current and to measurements from higher latitudes within the Chile-Peru Current system
Nanogranular MgB2 thin films on SiC buffered Si substrates prepared by in-situ method
MgB2 thin films were deposited on SiC buffered Si substrates by sequential
electron beam evaporation of B-Mg bilayer followed by in-situ annealing. The
application of a SiC buffer layer enables the maximum annealing temperature of
830 C. The Transmission Electron Microscopy analysis confirms the growth of a
nanogranular MgB2 film and the presence of a Mg2Si compound at the surface of
the film. The 150-200 nm thick films show a maximum zero resistance critical
temperature TC0 above 37 K and a critical current density JC ~ 106 A/cm2 at
11K.Comment: 7 pages, 6 figures, submitted to Applied Physics Letter
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