1,157 research outputs found
Ab initio study of magnetism at the TiO2/LaAlO3 interface
In this paper we study the possible relation between the electronic and
magnetic structure of the TiO2/LaAlO3 interface and the unexpected magnetism
found in undoped TiO2 films grown on LaAlO. We concentrate on the role
played by structural relaxation and interfacial oxygen vacancies.
LaAlO3 has a layered structure along the (001) direction with alternating LaO
and AlO2 planes, with nominal charges of +1 and -1, respectively. As a
consequence of that, an oxygen deficient TiO2 film with anatase structure will
grow preferently on the AlO2 surface layer. We have therefore performed
ab-initio calculations for superlattices with TiO2/AlO2 interfaces with
interfacial oxygen vacancies. Our main results are that vacancies lead to a
change in the valence state of neighbour Ti atoms but not necessarily to a
magnetic solution and that the appearance of magnetism depends also on
structural details, such as second neighbor positions. These results are
obtained using both the LSDA and LSDA+U approximations.Comment: Accepted for publication in Journal of Materials Scienc
Simulations of Oligomeric Intermediates in Prion Diseases
We extend our previous stochastic cellular automata based model for areal
aggregation of prion proteins on neuronal surfaces. The new anisotropic model
allow us to simulate both strong beta-sheet and weaker attachment bonds between
proteins. Constraining binding directions allows us to generate aggregate
structures with the hexagonal lattice symmetry found in recently observed in
vitro experiments. We argue that these constraints on rules may correspond to
underlying steric constraints on the aggregation process. We find that monomer
dominated growth of the areal aggregate is too slow to account for some
observed doubling time-to-incubation time ratios inferred from data, and so
consider aggregation dominated by relatively stable but non-infectious
oligomeric intermediates. We compare a kinetic theory analysis of oligomeric
aggregation to spatially explicit simulations of the process. We find that with
suitable rules for misfolding of oligomers, possibly due to water exclusion by
the surrounding aggregate, the resulting oligomeric aggregation model maps onto
our previous monomer aggregation model. Therefore it can produce some of the
same attractive features for the description of prion incubation time data. We
propose experiments to test the oligomeric aggregation model.Comment: 8 pages, 10 figures For larger versions of several figures, see
http://asaph.ucdavis.edu/~dmobley and click on the prion paper lin
Theory of STM Spectroscopy of Kondo Ions on Metal Surfaces
The conduction electron density of states nearby a single magnetic impurity,
as measured recently by scanning tunneling microscopy (STM), is calculated. It
is shown that the Kondo effect induces a narrow Fano resonance as an intrinsic
feature in the conduction electron density of states. The line shape varies
with the distance between STM tip and impurity, in qualitative agreement with
experiments, and is sensitive to details of the band structure. For a Co
impurity the experimentally observed width and shift of the Kondo resonance are
in accordance with those obtained from a combination of band structure and
strongly correlated calculations.Comment: 5 pages, 4 figures, presented at the NATO Advanced Research Workshop
on "Size Dependent Magnetic Scattering", Pecs, Hungary, May 28 - June 1, 200
Diet-induced obesity induces endoplasmic reticulum stress and insulin resistance in the amygdala of rats
FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOInsulin acts in the hypothalamus, decreasing food intake (FI) by the IR/PI3K/Akt pathway. This pathway is impaired in obese animals and endoplasmic reticulum (ER) stress and low-grade inflammation are possible mechanisms involved in this impairment. Here, we highlighted the amygdala as an important brain region for FI regulation in response to insulin. This regulation was dependent on PI3K/AKT pathway similar to the hypothalamus. Insulin was able to decrease neuropeptide Y (NPY) and increase oxytocin mRNA levels in the amygdala via PI3K, which may contribute to hypophagia. Additionally, obese rats did not reduce FI in response to insulin and AKT phosphorylation was decreased in the amygdala, suggesting insulin resistance. Insulin resistance was associated with ER stress and low-grade inflammation in this brain region. The inhibition of ER stress with PBA reverses insulin action/signaling, decreases NPY and increases oxytocin mRNA levels in the amygdala from obese rats, suggesting that ER stress is probably one of the mechanisms that induce insulin resistance in the amygdala. © 2013 The Authors.Insulin acts in the hypothalamus, decreasing food intake (FI) by the IR/PI3K/Akt pathway. This pathway is impaired in obese animals and endoplasmic reticulum (ER) stress and low-grade inflammation are possible mechanisms involved in this impairment. Here, we highlighted the amygdala as an important brain region for FI regulation in response to insulin. This regulation was dependent on PI3K/AKT pathway similar to the hypothalamus. Insulin was able to decrease neuropeptide Y (NPY) and increase oxytocin mRNA levels in the amygdala via PI3K, which may contribute to hypophagia. Additionally, obese rats did not reduce FI in response to insulin and AKT phosphorylation was decreased in the amygdala, suggesting insulin resistance. Insulin resistance was associated with ER stress and low-grade inflammation in this brain region. The inhibition of ER stress with PBA reverses insulin action/signaling, decreases NPY and increases oxytocin mRNA levels in the amygdala from obese rats, suggesting that ER stress is probably one of the mechanisms that induce insulin resistance in the amygdala31443449FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOsem informaçã
Appearance of room temperature ferromagnetism in Cu-doped TiO films
In recent years there has been an intense search for room temperature
ferromagnetism in doped dilute semiconductors, which have many potentially
applications in spintronics and optoelectronics. We report here the unexpected
observation of significant room temperature ferromagnetism in a semiconductor
doped with nonmagnetic impurities, Cu-doped TiO thin films grown by Pulsed
Laser Deposition. The magnetic moment, calculated from the magnetization
curves, resulted surprisingly large, about 1.5 per Cu atom. A large
magnetic moment was also obtained from ab initio calculations using the
supercell method for TiO with Cu impurities, but only if an oxygen vacancy
in the nearest-neighbour shell of Cu was present. This result suggests that the
role of oxygen vacancies is crucial for the appearance of ferromagnetism. The
calculations also predict that Cu doping favours the formation of oxygen
vacancies.Comment: 4 pages, 3 figures, published in Phys. Rev. B (Rapid Comm.
Diacylglycerol regulates acute hypoxic pulmonary vasoconstriction via TRPC6
Background: Hypoxic pulmonary vasoconstriction (HPV) is an essential mechanism of the lung that matches blood perfusion to alveolar ventilation to optimize gas exchange. Recently we have demonstrated that acute but not sustained HPV is critically dependent on the classical transient receptor potential 6 (TRPC6) channel. However, the mechanism of TRPC6 activation during acute HPV remains elusive. We hypothesize that a diacylglycerol (DAG)-dependent activation of TRPC6 regulates acute HPV.
Methods:
We investigated the effect of the DAG analog 1-oleoyl-2-acetyl-sn-glycerol (OAG) on normoxic vascular tone in isolated perfused and ventilated mouse lungs from TRPC6-deficient and wild-type mice. Moreover, the effects of OAG, the DAG kinase inhibitor R59949 and the phospholipase C inhibitor U73122 on the strength of HPV were investigated compared to those on non-hypoxia-induced vasoconstriction elicited by the thromboxane mimeticum U46619.
Results:
OAG increased normoxic vascular tone in lungs from wild-type mice, but not in lungs from TRPC6-deficient mice. Under conditions of repetitive hypoxic ventilation, OAG as well as R59949 dose-dependently attenuated the strength of acute HPV whereas U46619-induced vasoconstrictions were not reduced. Like OAG, R59949 mimicked HPV, since it induced a dose-dependent vasoconstriction during normoxic ventilation. In contrast, U73122, a blocker of DAG synthesis, inhibited acute HPV whereas U73343, the inactive form of U73122, had no effect on HPV.
Conclusion:
These findings support the conclusion that the TRPC6-dependency of acute HPV is induced via DAG
Assessing neuraxial microstructural changes in a transgenic mouse model of early stage Amyotrophic Lateral Sclerosis by ultra‐high field MRI and diffusion tensor metrics
bjective: Cell structural changes are one of the main features observed during the development of amyotrophic lateral sclerosis (ALS). In this work, we propose the useof diffusion tensor imaging (DTI) metrics to assess specific ultrastructural changes in the central nervous system during the early neurodegenerative stages of ALS.Methods: Ultra-high field MRI and DTI data at 17.6T were obtained from fixed, excised mouse brains, and spinal cords from ALS (G93A-SOD1) mice.Results: Changes in fractional anisotropy (FA) and linear, planar, and spherical anisotropy ratios (CL, CP, and CS, respectively) of the diffusion eigenvalues were measured in white matter (WM) and gray matter (GM) areas associated with early axonal degenerative processes (in both the brain and the spinal cord). Specifically, in WM structures (corpus callosum, corticospinal tract, and spinal cord funiculi) as the disease progressed, FA, CL, and CP values decreased, whereas CS values increased.In GM structures (prefrontal cortex, hippocampus, and central spinal cord) FA and CP decreased, whereas the CL a nd C values were unchanged or slightly smaller.Histological studies of a fluorescent mice model (YFP, G93A-SOD1 mouse) corroborated the early alterations in neuronal morphology and axonal connectivity measured by DTI.Conclusions: Changes in diffusion tensor shape were observed in this animal model at the early, nonsymptomatic stages of ALS. Further studies of CL, CP, and CSas imaging biomarkers should be undertaken to refine this neuroimaging tool for future clinical use in the detection of the early stages of ALSFil: Gatto, Rodolfo G.. University Of Illinois. Deparment Of Biological Science; Estados UnidosFil: Weissmann, Carina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Fisiología, Biología Molecular y Neurociencias. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Fisiología, Biología Molecular y Neurociencias; ArgentinaFil: Amin, Manish. University of Florida; Estados UnidosFil: Finkielsztein, Ariel. Northwestern University; Estados UnidosFil: Sumagin, Ronen. Northwestern University; Estados UnidosFil: Mareci, Thomas H.. University of Florida; Estados UnidosFil: Uchitel, Osvaldo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Fisiología, Biología Molecular y Neurociencias. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Fisiología, Biología Molecular y Neurociencias; ArgentinaFil: Magin, Richard L.. University Of Illinois. Deparment Of Biological Science; Estados Unido
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