4,338 research outputs found
Spin injection and detection in copper spin valve structures
We report measurements of spin injection and detection in a mesoscopic copper wire from which the electron spin relaxation time and the spin current polarization in copper can be found. Spin injection is realized by applying a voltage to drive a current from a ferromagnet into the normal metal, while spin detection is done using transport measurements. Precession of the spin of the injected electrons due to an external magnetic field is also studied. The existence of a previously unobserved spin signal which vanishes at low temperatures but increases nonlinearly above 100K is reported and a possible explanation for its origin, based on interfacial spin-flip scattering, is suggested. Multiple cross checks to test the possibility of artifacts as an origin of this signal are discussed.
An alternative spin detection method using magnetic force microscopy (MFM) is also studied. This method measures the magnetic field produced by the injected spins directly, so the spin coherence length and the spin current polarization can be extracted directly without the need of a particular transport model, avoiding issues like contact resistance and interface scattering. The MFM method can also be useful for measuring the spin polarization of currents in semiconductors and semiconductor heterostructures, which is important for the development of spintronics
Distribution of red clump stars does not support the X-shaped Galactic bulge
CONTEXT. Claims of an X-shaped Galactic bulge were based on the assumption of
red clump stars as standard candles in some lines of sight crossing the
off-plane bulge. However, some doubts have been cast on whether the two peaks
in star counts along the line of sight really represent a double peak in the
density distribution, or whether there is something wrong with the assumption
of a unique constant absolute magnitude for all of these stars.
AIMS. With the advent of Gaia-DR2 parallaxes in combination with
near-infrared VISTA-VVV data, we are able to check which of the hypotheses is
correct.
METHODS. We calculated the median absolute magnitude corresponding to
both peaks of putative red clumps in seven lines of sight with the lowest
extinction in the interesting coordinates' range.
RESULTS. The difference between the absolute magnitude of the bright and the
faint peak is . The selected stars in both peaks cannot
be represented by the same red clump giants with constant .
CONCLUSIONS. The hypothesis that the bulge contains an X-shape is based on
the assumption that the faint and bright peaks of the density distribution
towards the bulge are dominated by standard red clump stars. However, we show
that both the faint and bright peaks cannot be dominated by standard red clump
stars simultaneously.Comment: 5 pages, accepted to be published in A&
Low frequency noise characteristics of sub-micron magnetic tunnel junctions
We report that low frequency (up to 200 kHz) noise spectra of magnetic tunnel
junctions with areas ~10^{-10}cm^2$ at 10 Kelvin deviate significantly from the
typical 1/f behavior found in large area junctions at room temperature. In most
cases, a Lorentzian-like shape with characteristic time between 0.1 and 10 ms
is observed, which indicates only a small number of fluctuators contribute to
the measured noise. By investigating the dependence of noise on both the
magnitude and orientation of an applied magnetic field, we find that
magnetization fluctuations in both free and reference layers are the main
sources of noise in these devices. At small fields, where the noise from the
free layer is dominant, a linear relation between the measured noise and
angular magnetoresistance susceptibility can be established.Comment: 3 pages, 2 figure
Characterisation of the bacterial and fungal communities associated with different lesion sizes of Dark Spot Syndrome occurring in the Coral Stephanocoenia intersepta
The number and prevalence of coral diseases/syndromes are increasing worldwide. Dark Spot Syndrome (DSS) afflicts numerous coral species and is widespread throughout the Caribbean, yet there are no known causal agents. In this study we aimed to characterise the microbial communities (bacteria and fungi) associated with DSS lesions affecting the coral Stephanocoenia intersepta using nonculture molecular techniques. Bacterial diversity of healthy tissues (H), those in advance of the lesion interface (apparently healthy AH), and three sizes of disease lesions (small, medium, and large) varied significantly (ANOSIM R = 0.052 p,0.001), apart from the medium and large lesions, which were similar in their community profile. Four bacteria fitted into the pattern expected from potential pathogens; namely absent from H, increasing in abundance within AH, and dominant in the lesions themselves. These included ribotypes related to Corynebacterium (KC190237), Acinetobacter (KC190251), Parvularculaceae (KC19027), and Oscillatoria (KC190271). Furthermore, two Vibrio species, a genus including many proposed coral pathogens, dominated the disease lesion and were absent from H and AH tissues, making them candidates as potential pathogens for DSS. In contrast, other members of bacteria from the same genus, such as V. harveyii were present throughout all sample types, supporting previous studies where potential coral pathogens exist in healthy tissues. Fungal diversity varied significantly as well, however the main difference between diseased and healthy tissues was the dominance of one ribotype, closely related to the plant pathogen, Rhytisma acerinum, a known causal agent of tar spot on tree leaves. As the corals’ symbiotic algae have been shown to turn to a darker pigmented state in DSS (giving rise to the syndromes name), the two most likely pathogens are R. acerinum and the bacterium Oscillatoria, which has been identified as the causal agent of the colouration in Black Band Disease, another widespread coral disease
NRF2-driven miR-125B1 and miR-29B1 transcriptional regulation controls a novel anti-apoptotic miRNA regulatory network for AML survival
Transcription factor NRF2 is an important regulator of oxidative stress. It is involved in cancer progression, and has abnormal constitutive expression in acute myeloid leukaemia (AML). Posttranscriptional regulation by microRNAs (miRNAs) can affect the malignant phenotype of AML cells. In this study, we identified and characterised NRF2-regulated miRNAs in AML. An miRNA array identified miRNA expression level changes in response to NRF2 knockdown in AML cells. Further analysis of miRNAs concomitantly regulated by knockdown of the NRF2 inhibitor KEAP1 revealed the major candidate NRF2-mediated miRNAs in AML. We identified miR-125B to be upregulated and miR-29B to be downregulated by NRF2 in AML. Subsequent bioinformatic analysis identified putative NRF2 binding sites upstream of the miR-125B1 coding region and downstream of the mir-29B1 coding region. Chromatin immunoprecipitation analyses showed that NRF2 binds to these antioxidant response elements (AREs) located in the 5′ untranslated regions of miR-125B and miR-29B. Finally, primary AML samples transfected with anti-miR-125B antagomiR or miR-29B mimic showed increased cell death responsiveness either alone or co-treated with standard AML chemotherapy. In summary, we find that NRF2 regulation of miR-125B and miR-29B acts to promote leukaemic cell survival, and their manipulation enhances AML responsiveness towards cytotoxic chemotherapeutics
A major star formation region in the receding tip of the stellar Galactic bar
We present an analysis of the optical spectroscopy of 58 stars in the
Galactic plane at \arcdeg, where a prominent excess in the flux
distribution and star counts have been observed in several spectral regions, in
particular in the Two Micron Galactic Survey (TMGS) catalog. The sources were
selected from the TMGS, to have a magnitude brighter than +5 mag and be
within 2 degrees of the Galactic plane. More than 60% of the spectra correspond
to stars of luminosity class I, and a significant proportion of the remainder
are very late giants which would also be fast evolving. This very high
concentration of young sources points to the existence of a major star
formation region in the Galactic plane, located just inside the assumed origin
of the Scutum spiral arm. Such regions can form due to the concentrations of
shocked gas where a galactic bar meets a spiral arm, as is observed at the ends
of the bars of face-on external galaxies. Thus, the presence of a massive star
formation region is very strong supporting evidence for the presence of a bar
in our Galaxy.Comment: 13 pages (latex) + 4 figures (eps), accepted in ApJ Let
Enhanced Spin Dependent Shot Noise in Magnetic Tunnel Barriers
We report the observation of enhanced spin dependent shot noise in magnetic
tunnel barriers, suggesting transport through localized states within the
barrier. This is supported by the existence of negative magnetoresistance and
structure in the differential conductance curves. A simple model of tunneling
through two interacting localized states with spin dependent tunneling rates is
used to explain our observations.Comment: 8 pages, 8 figures, submitted to Physica E (proceedings of the
seminar on Quantum Coherence, Noise and Decoherence in Nanostructures
A major star formation region in the receding tip of the stellar Galactic bar. II. Supplementary information and evidence that the bar is not the same structure as the triaxial bulge previouly reported
This paper is the second part of Garzon et al. (1997: ApJ 491, L31) in which
we presented an outline of the analysis of 60 spectra from a follow-up program
to the Two Micron Galactic Survey (TMGS) project in the l=27 deg., b=0 deg.
area. In this second part, we present a more detailed explanation of the
analysis as well a library of the spectra for more complete information for
each of the 60 stars, and further discussions on the implications for the
structure of the Galaxy.
This region contains a prominent excess in the flux distribution and star
counts previously observed in several spectral ranges, notably in the TMGS.
More than 50% of the spectra of the stars detected with m_K<5.0 mag, within a
very high confidence level, correspond to stars of luminosity class I, and a
significant proportion of the remainder are very late giants which must also be
rapidly evolving. We make the case, using all the available evidence, that we
are observing a region at the nearer end of the Galactic bar, where the Scutum
spiral arm breaks away, and that this is powerful evidence for the presence of
the bar. Alternative explanations do not give nearly such a satisfactory
account of the observations.
The space localization of one and, a fortiori, of both ends of the bar allows
us to infer a position angle for the bar of around 75 deg. with respect to the
Sun-Galactic centre line. The angle is different from that given by other
authors for the bar and this, we think, is because they refer to the triaxial
bulge and not to the bar as detected here.Comment: 21 pages, 1 table, 9 figures, accepted in A
Sustainable agricultural practices and their adoption in sub-Saharan Africa: A selected review
Africa is currently only producing about 10% of global agricultural output while estimated to possess 25% of the world’s arable land. That said, the estimated additional available agricultural land is probably lower than what is generally assumed given the trend in rising rural population density, which, in places is comparable to Asian levels. Moreover, most soils are fragile with low nutrients and organic matter concentration.A "great balancing act" is needed between the increasing and diversifying food and nutrition security (FNS) needs and the resources available. More generically, reaching FNS faces both conventional (demographics) and emerging challenges (climate change). The debate on the sustainability of agriculture requires translation into specific approached and practices. The report gathers a conventional literature review of existing publications (Peer-reviewed journals, major reports and relevant project documents). The material consulted was mostly in English with references to French documents particularly for West and Central African experiences. The key databases consulted were Scopus and Google Scholar.The challenges faced by Africa’s agriculture are very diverse considering a sustainable approach in responding to the regions’ FNS needs. As such, there is no single solution (‘silver bullet’) allowing the sector to sustainably increase its contribution to food supply. Ultimately, opting for a coherent set of approaches or more targeted agricultural practices depends on the great diversity of local contexts (environmental, institutional, seasonal, etc.) as well as characteristics and motivation of individual farmers and their communities. Collective action in the uptake of key practices has been recorded as having produced more sustainable benefits. When looking at each newly adapted practice as innovations it is essential to look towards more coherent, and more importantly, effective sustainable production systems. For FNS intervention to be sustainable, intervention would benefit from adopting a landscape framework so that the various objectives of sustainability can be coherently negotiated alongside pure FNS objectives. Considering land sharing could be particularly relevant for areas with potential agriculture frontier (e.g. Sahel countries, RDC) but also to those were forest "encroachment" is the only remaining frontier given the rising population density. Management approaches that could improve soils emerge as a prerequisite to conventional intensification. As it is the case for input-based intensification of agriculture, the results from the different management-based approaches are not universal and absolute responses cannot be derived from the cases reviewed (including the meta-analyses). Careful targeting and local adaptation remain fundamental ingredients for both improved performance and the long-term adoption of any of the principles and associated practices. A general challenge for adoption is that of timing. Any new practice or approach promoted is expected to provide at least a perceivable improvement in the objectives of farmers in the short-term, when they are generally most sensitive to.JRC.D.4-Economics of Agricultur
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