105 research outputs found
Angular dependence of domain wall resistivity in SrRuO films
is a 4d itinerant ferromagnet (T 150 K) with
stripe domain structure. Using high-quality thin films of SrRuO we study
the resistivity induced by its very narrow ( nm) Bloch domain walls,
(DWR), at temperatures between 2 K and T as a function of the
angle, , between the electric current and the ferromagnetic domains
walls. We find that which provides the first experimental
indication that the angular dependence of spin accumulation contribution to DWR
is . We expect magnetic multilayers to exhibit a similar
behavior.Comment: 5 pages, 5 figure
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Stand conditions associated with tree regeneration in Sierran mixed-conifer forests
Fire suppression has significantly increased canopy cover, litter depth, and stem density in many
western forests, altering microsite conditions that affect tree seedling establishment. We conducted studies in a
mixed-conifer forest in the Sierra Nevada, California, to determine relationships between established understory
trees and microsite quality, and to examine the effect of fire intensity and shrub cover on seedling establishment.
Most of the conifer species were found on microsites with relatively high soil moisture and relatively low direct
solar radiation. All species had greater frequency under shadier conditions except for Jeffrey pine, which was
found on drier, more open microsites. Although seedlings were more abundant on mineral soil than expected,
intact litter and forest floor was not a barrier to establishment. Mortality of planted seedlings was high,
particularly in exposed areas. Although shrub cover may initially aid survival, few conifer saplings were present
in shrub-dominated patches, possibly because shrubs can be aggressive competitors for soil moisture. The
lack of regeneration, logs, or snags in many openings suggest that large gaps are hostile environments for
tree seedlings. Results suggest that reductions in shrub cover may benefit tree establishment, but increasing
understory light and decreasing surface soil moisture through canopy cover reductions may not. FOR. SCI.
51(3):198 –210.Keywords: Prunus emarginata, Old-growth, Abies magnifica, Natural regeneration, Pinus jeffreyi, Quercus kelloggii, Arctostaphylos patula, Pinus labertiana, Abies concolor, Calocedrus decurrens, Fire, Shrub competition, Ceanothus cordulatus, Microclimat
A Transgenic Marker for Newly Born Granule Cells in Dentate Gyrus
Neurogenesis in the dentate gyrus continues into adulthood, yet little is known about the function of newly born neurons or how they integrate into an existing network of mature neurons. We made transgenic mice that selectively and transiently express enhanced green fluorescent protein (EGFP) in newly born granule cells of the dentate gyrus under the transcriptional control of proopiomelanocortin (POMC) genomic sequences. Analysis of transgenic pedigrees with truncation or deletion mutations indicated that EGFP expression in the dentate gyrus required cryptic POMC promoter regions dispensable for arcuate hypothalamic or pituitary expression. Unlike arcuate neurons, dentate granule cells did not express the endogenous POMC gene. EGFP-positive neurons had immature properties, including short spineless dendrites and small action potentials. Colocalization with bromodeoxyuridine indicated that EGFP-labeled granule cells were 2 weeks postmitotic. EGFP-labeled cells expressed markers for immature granule cells but not the glial marker GFAP. The number of EGFP-labeled neurons declined with age and increased with exercise, paralleling neurogenesis. Our results indicate that POMC-EGFP marks immature granule cells and that adult-generated granule cells integrate quite slowly into the hippocampal circuitry
Genetic Analysis of High Protein Content in ‘AC Proteus’ Related Soybean Populations Using SSR, SNP, DArT and DArTseq Markers
Key message: Several AC Proteus derived genomic regions (QTLs, SNPs) have been identified which may prove useful for further development of high yielding high protein cultivars and allele-specific marker developments. High seed protein content is a trait which is typically difficult to introgress into soybean without an accompanying reduction in seed yield. In a previous study, ‘AC Proteus’ was used as a high protein source and was found to produce populations that did not exhibit the typical association between high protein and low yield. Five high x low protein RIL populations and a high x high protein RIL population were evaluated by either quantitative trait locus (QTL) analysis or bulk segregant analyses (BSA) following phenotyping in the field. QTL analysis in one population using SSR, DArT and DArTseq markers found two QTLs for seed protein content on chromosomes 15 and 20. The BSA analyses suggested multiple genomic regions are involved with high protein content across the five populations, including the two previously mentioned QTLs. In an alternative approach to identify high protein genes, pedigree analysis identified SNPs for which the allele associated with high protein was retained in seven high protein descendants of AC Proteus on chromosomes 2, 17 and 18. Aside from the two identified QTLs (five genomic regions in total considering the two with highly elevated test statistic, but below the statistical threshold and the one with epistatic interactions) which were some distance from Meta-QTL regions and which were also supported by our BSA analysis within five populations. These high protein regions may prove useful for further development of high yielding high protein cultivars
Single-Band Model for Diluted Magnetic Semiconductors: Dynamical and Transport Properties and Relevance of Clustered States
Dynamical and transport properties of a simple single-band spin-fermion
lattice model for (III,Mn)V diluted magnetic semiconductors (DMS) is here
discussed using Monte Carlo simulations. This effort is a continuation of
previous work (G. Alvarez, Phys. Rev. Lett. 89, 277202 (2002)) where the static
properties of the model were studied. The present results support the view that
the relevant regime of J/t (standard notation) is that of intermediate
coupling, where carriers are only partially trapped near Mn spins, and locally
ordered regions (clusters) are present above the Curie temperature T_C. This
conclusion is based on the calculation of the resistivity vs. temperature, that
shows a soft metal to insulator transition near T_C, as well on the analysis of
the density-of-states and optical conductivity. In addition, in the clustered
regime a large magnetoresistance is observed in simulations. Formal analogies
between DMS and manganites are also discussed.Comment: Revtex4, 20 figures. References updated, minor changes to figures and
tex
Exchange anisotropy, disorder and frustration in diluted, predominantly ferromagnetic, Heisenberg spin systems
Motivated by the recent suggestion of anisotropic effective exchange
interactions between Mn spins in GaMnAs (arising as a result of
spin-orbit coupling), we study their effects in diluted Heisenberg spin
systems. We perform Monte Carlo simulations on several phenomenological model
spin Hamiltonians, and investigate the extent to which frustration induced by
anisotropic exchanges can reduce the low temperature magnetization in these
models and the interplay of this effect with disorder in the exchange. In a
model with low coordination number and purely ferromagnetic (FM) exchanges, we
find that the low temperature magnetization is gradually reduced as exchange
anisotropy is turned on. However, as the connectivity of the model is
increased, the effect of small-to-moderate anisotropy is suppressed, and the
magnetization regains its maximum saturation value at low temperatures unless
the distribution of exchanges is very wide. To obtain significant suppression
of the low temperature magnetization in a model with high connectivity, as is
found for long-range interactions, we find it necessary to have both
ferromagnetic and antiferromagnetic (AFM) exchanges (e.g. as in the RKKY
interaction). This implies that disorder in the sign of the exchange
interaction is much more effective in suppressing magnetization at low
temperatures than exchange anisotropy.Comment: 9 pages, 8 figure
Monte Carlo simulations of an impurity band model for III-V diluted magnetic semiconductors
We report the results of a Monte Carlo study of a model of (III,Mn)V diluted
magnetic semiconductors which uses an impurity band description of carriers
coupled to localized Mn spins and is applicable for carrier densities below and
around the metal-insulator transition. In agreement with mean field studies, we
find a transition to a ferromagnetic phase at low temperatures. We compare our
results for the magnetic properties with the mean field approximation, as well
as with experiments, and find favorable qualitative agreement with the latter.
The local Mn magnetization below the Curie temperature is found to be spatially
inhomogeneous, and strongly correlated with the local carrier charge density at
the Mn sites. The model contains fermions and classical spins and hence we
introduce a perturbative Monte Carlo scheme to increase the speed of our
simulations.Comment: 17 pages, 24 figures, 2 table
Data to support study of Di-Iron(II) [2+2] Helicates of Bis-(Dipyrazolylpyridine) Ligands – the Influence of the Ligand Linker Group on Spin State Properties
A diiron(II) complex has been crystallised in three different helicate conformations, which differ in the torsions of the butane-1,4-diyl ligand linker groups. The crystals exhibit a range of spin state properties, including stepwise spin-crossover of the two iron atoms. A related ligand with a rigid pyrid-2,6-diyl spacer forms more a distorted, high-spin diiron(II) helicate structure
The structural basis of bacterial manganese import
Metal ions are essential for all forms of life. In prokaryotes, ATP-binding cassette (ABC) permeases serve as the primary import pathway for many micronutrients including the first-row transition metal manganese. However, the structural features of ionic metal transporting ABC permeases have remained undefined. Here, we present the crystal structure of the manganese transporter PsaBC from Streptococcus pneumoniae in an open-inward conformation. The type II transporter has a tightly closed transmembrane channel due to "extracellular gating" residues that prevent water permeation or ion reflux. Below these residues, the channel contains a hitherto unreported metal coordination site, which is essential for manganese translocation. Mutagenesis of the extracellular gate perturbs manganese uptake, while coordination site mutagenesis abolishes import. These structural features are highly conserved in metal-specific ABC transporters and are represented throughout the kingdoms of life. Collectively, our results define the structure of PsaBC and reveal the features required for divalent cation transport.Stephanie L. Neville, Jennie Sjöhamn, Jacinta A. Watts, Hugo MacDermott-Opeskin, Stephen J. Fairweather, Katherine Ganio, Alex Carey Hulyer, Aaron P. McGrath, Andrew J. Hayes, Tess R. Malcolm, Mark R. Davies, Norimichi Nomura, So Iwata, Megan L. O’Mara, Megan J. Maher, Christopher A. McDevit
Protocol for the cultural adaptation of pulmonary rehabilitation and subsequent testing in a randomised controlled feasibility trial for adults with chronic obstructive pulmonary disease in Sri Lanka
Introduction: International guidelines recommend pulmonary rehabilitation (PR) should be offered to adults living with chronic obstructive pulmonary disease (COPD), but PR availability is limited in Sri Lanka. Culturally appropriate PR needs to be designed and implemented in Sri Lanka. The study aims to adapt PR to the Sri Lankan context and determine the feasibility of conducting a future trial of the adapted PR in Sri Lanka.
Methods and analysis: Eligible participants will be identified and will be invited to take part in the randomised controlled feasibility trial, which will be conducted in Central Chest Clinic, Colombo, Sri Lanka. A total of 50 participants will be recruited (anticipated from April 2021) to the trial and randomised (1:1) into one of two groups; control group receiving usual care or the intervention group receiving adapted PR. The trial intervention is a Sri Lankan-specific PR programme, which will consist of 12 sessions of exercise and health education, delivered over 6 weeks. Focus groups with adults living with COPD, caregivers and nurses and in-depth interviews with doctors and physiotherapist will be conducted to inform the Sri Lankan specific PR adaptations. After completion of PR, routine measures in both groups will be assessed by a blinded assessor. The primary outcome measure is feasibility, including assessing eligibility, uptake and completion. Qualitative evaluation of the trial using focus groups with participants and in-depth interviews with PR deliverers will be conducted to further determine feasibility and acceptability of PR, as well as the ability to run a larger future trial.
Ethics and dissemination: Ethical approval was obtained from the ethics review committee of Faculty of Medical Sciences, University of Sri Jayewardenepura, Sri Lanka and University of Leicester, UK. The results of the trial will be disseminated through patient and public involvement events, local and international conference proceedings, and peer-reviewed journals.
Trial registration number ISRCTN1336773
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