4,236 research outputs found
Magnetic-field effects in defect-controlled ferromagnetic Ga_{1-x}Mn_xAs semiconductors
We have studied the magnetic-field and concentration dependences of the
magnetizations of the hole and Mn subsystems in diluted ferromagnetic
semiconductor Ga_{1-x}Mn_xAs. A mean-field approximation to the hole-mediated
interaction is used, in which the hole concentration p(x) is parametrized in
terms of a fitting (of the hole effective mass and hole/local moment coupling)
to experimental data on the Tc critical temperature. The dependence of the
magnetizations with x, for a given temperature, presents a sharply peaked
structure, with maxima increasing with applied magnetic field, which indicates
that application to diluted-magnetic-semiconductor devices would require
quality-control of the Mn-doping composition. We also compare various
experimental data for Tc(x) and p(x) on different Ga_{1-x}Mn_xAs samples and
stress the need of further detailed experimental work to assure that the
experimental measurements are reproducible.Comment: RevTeX 4, 3 two-column pages, 4 colour figures; to appear in J Appl
Phy
Direct fluorescent labelling of clones by DOP PCR
<p>Abstract</p> <p>Background</p> <p>Array Comparative Genomic Hybridisation (array CGH) is a powerful technique for the analysis of constitutional chromosomal anomalies. Chromosomal duplications or deletions detected by array CGH need subsequently to be validated by other methods. One method of validation is Fluorescence <it>in situ </it>Hybridisation (FISH). Traditionally, fluorophores or hapten labelling is performed by nick translation or random prime labelling of purified Bacterial Artificial Chromosome (BAC) products. However, since the array targets have been generated from Degenerate Oligonucleotide Primed (DOP) amplified BAC clones, we aimed to use these DOP amplified BAC clones as the basis of an automated FISH labelling protocol. Unfortunately, labelling of DOP amplified BAC clones by traditional labelling methods resulted in high levels of background.</p> <p>Results</p> <p>We designed an improved labelling method, by means of degenerate oligonucleotides that resulted in optimal FISH probes with low background.</p> <p>Conclusion</p> <p>We generated an improved labelling method for FISH which enables the rapid generation of FISH probes without the need for isolating BAC DNA. We labelled about 900 clones with this method with a success rate of 97%.</p
Large tunable image-charge effects in single-molecule junctions
The characteristics of molecular electronic devices are critically determined
by metal-organic interfaces, which influence the arrangement of the orbital
levels that participate in charge transport. Studies on self-assembled
monolayers (SAMs) show (molecule-dependent) level shifts as well as
transport-gap renormalization, suggesting that polarization effects in the
metal substrate play a key role in the level alignment with respect to the
metal's Fermi energy. Here, we provide direct evidence for an electrode-induced
gap renormalization in single-molecule junctions. We study charge transport in
single porphyrin-type molecules using electrically gateable break junctions. In
this set-up, the position of the occupied and unoccupied levels can be followed
in situ and with simultaneous mechanical control. When increasing the electrode
separation, we observe a substantial increase in the transport gap with level
shifts as high as several hundreds of meV for displacements of a few \aa
ngstroms. Analysis of this large and tunable gap renormalization with
image-charge calculations based on atomic charges obtained from density
functional theory confirms and clarifies the dominant role of image-charge
effects in single-molecule junctions
Quantitative Study of Magnetotransport through a (Ga,Mn)As Single Ferromagnetic Domain
We have performed a systematic investigation of the longitudinal and
transverse magnetoresistance of a single ferromagnetic domain in (Ga,Mn)As. We
find that, by taking into account the intrinsic dependence of the resistivity
on the magnetic induction, an excellent agreement between experimental results
and theoretical expectations is obtained. Our findings provide a detailed and
fully quantitative validation of the theoretical description of
magnetotransport through a single ferromagnetic domain. Our analysis
furthermore indicates the relevance of magneto-impurity scattering as a
mechanism for magnetoresistance in (Ga,Mn)As.Comment: 5 pages, 4 figures; v2: missing references included, figures
recompressed to improve readabilit
Hole spin polarization in GaAlAs:Mn structures
A self-consistent calculation of the electronic properties of GaAlAs:Mn
magnetic semiconductor quantum well structures is performed including the
Hartree term and the sp-d exchange interaction with the Mn magnetic moments.
The spin polarization density is obtained for several structure configurations.
Available experimental results are compared with theory.Comment: 4 page
Effect of annealing on the depth profile of hole concentration in (Ga,Mn)As
The effect of annealing at 250 C on the carrier depth profile, Mn
distribution, electrical conductivity, and Curie temperature of (Ga,Mn)As
layers with thicknesses > 200 nm, grown by molecular-beam epitaxy at low
temperatures, is studied by a variety of analytical methods. The vertical
gradient in hole concentration, revealed by electrochemical capacitance-voltage
profiling, is shown to play a key role in the understanding of conductivity and
magnetization data. The gradient, basically already present in as-grown
samples, is strongly influenced by post-growth annealing. From secondary ion
mass spectroscopy it can be concluded that, at least in thick layers, the
change in carrier depth profile and thus in conductivity is not primarily due
to out-diffusion of Mn interstitials during annealing. Two alternative possible
models are discussed.Comment: 8 pages, 8 figures, to appear in Phys. Rev.
Motivational factors mediate the association of general self-efficacy and performance outcomes in acutely hospitalised older patients
Objectives: To study (i) the association of general self-efficacy (GSE) on the course of subjective (i.e. basic and instrumental activities of daily living (ADLs and IADLs) and objective physical performance outcomes (short physical performance battery (SPPB)) among older persons from discharge up to 3 months post-discharge and (ii) the extent to whether motivational factors such as depressive symptoms, apathy and fatigue mediate this association.Methods: Prospective multi-centre cohort of acutely hospitalised patients aged ≥70 (Hospital-ADL study). Structural equation modelling was used to analyse the structural relationships.Results: The analytic sample included 236 acutely hospitalised patients. GSE had a significant total effect on the course of subjective and objective performance outcomes (ADLs: β = -0.21, P < 0.001, IADLs: β = -0.24, P < 0.001 and SPPB: β = 0.17, P < 0.001). However, when motivational factors as mediator were included into the same model, motivational factors (IADLs: β = 0.51, P < 0.001; SPPB: β = 0.49, P < 0.001) but not GSE remained significantly associated with IADLs (β = -0.06, P = 0.16) and SPPB (β = 0.002, P = 0.97). Motivational factors partially mediated the relationship between GSE and ADLs (β = -0.09, P = 0.04). The percentage of mediation was 55, 74 and 99% for ADLs, IADLs and SPPB, respectively.Conclusions: Motivational factors and GSE are both associated with subjective and objective performance outcomes. However, the relationship between GSE and subjective and objective performance outcomes was highly mediated by motivational factors. Taken together, this suggests that GSE is important to being physically active but not sufficient to becoming more physical active in acutely hospitalised older patients; motivation is important to improving both subjective and objective performance.</p
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