12,610 research outputs found
The relationship between teachers' educational philosophies and the ability-achievement growth of their elementary school classes.
Thesis (Ed.M.)--Boston Universit
β-cell dysfunctional ERAD/ubiquitin/proteasome system in type 2 diabetes mediated by islet amyloid polypeptide-induced UCH-L1 deficiency.
ObjectiveThe islet in type 2 diabetes is characterized by β-cell apoptosis, β-cell endoplasmic reticulum stress, and islet amyloid deposits derived from islet amyloid polypeptide (IAPP). Toxic oligomers of IAPP form intracellularly in β-cells in humans with type 2 diabetes, suggesting impaired clearance of misfolded proteins. In this study, we investigated whether human-IAPP (h-IAPP) disrupts the endoplasmic reticulum-associated degradation/ubiquitin/proteasome system.Research design and methodsWe used pancreatic tissue from humans with and without type 2 diabetes, isolated islets from h-IAPP transgenic rats, isolated human islets, and INS 832/13 cells transduced with adenoviruses expressing either h-IAPP or a comparable expression of rodent-IAPP. Immunofluorescence and Western blotting were used to detect polyubiquitinated proteins and ubiquitin carboxyl-terminal hydrolase L1 (UCH-L1) protein levels. Proteasome activity was measured in isolated rat and human islets. UCH-L1 was knocked down by small-interfering RNA in INS 832/13 cells and apoptosis was evaluated.ResultsWe report accumulation of polyubiquinated proteins and UCH-L1 deficiency in β-cells of humans with type 2 diabetes. These findings were reproduced by expression of oligomeric h-IAPP but not soluble rat-IAPP. Downregulation of UCH-L1 expression and activity to reproduce that caused by h-IAPP in β-cells induced endoplasmic reticulum stress leading to apoptosis.ConclusionsOur results indicate that defective protein degradation in β-cells in type 2 diabetes can, at least in part, be attributed to misfolded h-IAPP leading to UCH-L1 deficiency, which in turn further compromises β-cell viability
Diffusion rates of Cu adatoms on Cu(111) in the presence of an adisland nucleated at FCC or HCP sites
The surface diffusion of Cu adatoms in the presence of an adisland at FCC or
HCP sites on Cu(111) is studied using the EAM potential derived by Mishin {\it
et al.} [Phys. Rev. B {\bf 63} 224106 (2001)]. The diffusion rates along
straight (with close-packed edges) steps with (100) and (111)-type microfacets
(resp. step A and step B) are first investigated using the transition state
theory in the harmonic approximation. It is found that the classical limit
beyond which the diffusion rates follow an Arrhenius law is reached above the
Debye temperature. The Vineyard attempt frequencies and the (static) energy
barriers are reported. Then a comparison is made with the results of more
realistic classical molecular dynamic simulations which also exhibit an
Arrhenius-like behavior. It is concluded that the corresponding energy barriers
are completely consistent with the static ones within the statistical errors
and that the diffusion barrier along step B is significantly larger than along
step A. In contrast the prefactors are very different from the Vineyard
frequencies. They increase with the static energy barrier in agreement with the
Meyer-Neldel compensation rule and this increase is well approximated by the
law proposed by Boisvert {\it et al.} [Phys. Rev. Lett. {\bf 75} 469 (1995)].
As a consequence, the remaining part of this work is devoted to the
determination of static energy barriers for a large number of diffusion events
that can occur in the presence of an adisland. In particular, it is found that
the corner crossing diffusion process for triangular adislands is markedly
different for the two types of borders (A or B). From this set of results the
diffusion rates of the most important atomic displacements can be predicted and
used as input in Kinetic Monte-Carlo simulations
Quantum electrodynamics of relativistic bound states with cutoffs
We consider an Hamiltonian with ultraviolet and infrared cutoffs, describing
the interaction of relativistic electrons and positrons in the Coulomb
potential with photons in Coulomb gauge. The interaction includes both
interaction of the current density with transversal photons and the Coulomb
interaction of charge density with itself. We prove that the Hamiltonian is
self-adjoint and has a ground state for sufficiently small coupling constants.Comment: To appear in "Journal of Hyperbolic Differential Equation
Spin-dependent electron dynamics and recombination in GaAs(1-x)N(x) alloys at room temperature
We report on both experimental and theoretical study of conduction-electron
spin polarization dynamics achieved by pulsed optical pumping at room
temperature in GaAs(1-x)N(x) alloys with a small nitrogen content (x = 2.1,
2.7, 3.4%). It is found that the photoluminescence circular polarization
determined by the mean spin of free electrons reaches 40-45% and this giant
value persists within 2 ns. Simultaneously, the total free-electron spin decays
rapidly with the characteristic time ~150 ps. The results are explained by
spin-dependent capture of free conduction electrons on deep paramagnetic
centers resulting in dynamical polarization of bound electrons. We have
developed a nonlinear theory of spin dynamics in the coupled system of
spin-polarized free and localized carriers which describes the experimental
dependencies, in particular, electron spin quantum beats observed in a
transverse magnetic field.Comment: 5 pages, 4 figures, Submitted to JETP Letter
Les effets de l'adoption obligatoire des normes IFRS sur les incorporels : le cas de la France.
International audienceCet article examine les effets de l'adoption obligatoire des IFRS sur les incorporels, dans le contexte français. Utilisant un échantillon de 83 entreprises issues du SBF 120, nous recherchons une typologie des pratiques comptables liées aux incorporels à la période de transition aux IFRS. Les résultats font ressortir trois classes d'entreprises affectées différemment par le passage aux normes internationales. La première classe est caractérisée par un changement important avec une forte augmentation du goodwill liée au retraitement d'immobilisations incorporelles comme les parts de marché. Elle permet d'illustrer la spécificité de la réglementation française. La deuxième classe se caractérise par une stabilité s'expliquant par le poids prédominant du goodwill sous référentiel français. Enfin la troisième classe ne subit pas non plus de changement compte tenu de la présence de marques en normes françaises. Le phénomène d'inertie décrit par Nobes (2006) selon lequel les traitements comptables pré-IFRS pourraient perdurer sous IFRS est vérifié
Revealing exciton masses and dielectric properties of monolayer semiconductors with high magnetic fields
In semiconductor physics, many essential optoelectronic material parameters
can be experimentally revealed via optical spectroscopy in sufficiently large
magnetic fields. For monolayer transition-metal dichalcogenide semiconductors,
this field scale is substantial --tens of teslas or more-- due to heavy carrier
masses and huge exciton binding energies. Here we report absorption
spectroscopy of monolayer MoS, MoSe, MoTe, and WS in very high
magnetic fields to 91~T. We follow the diamagnetic shifts and valley Zeeman
splittings of not only the exciton's ground state but also its excited
, , ..., Rydberg states. This provides a direct experimental
measure of the effective (reduced) exciton masses and dielectric properties.
Exciton binding energies, exciton radii, and free-particle bandgaps are also
determined. The measured exciton masses are heavier than theoretically
predicted, especially for Mo-based monolayers. These results provide essential
and quantitative parameters for the rational design of opto-electronic van der
Waals heterostructures incorporating 2D semiconductors.Comment: updated; now also including data on MoTe2. Accepted & in press,
Nature Commu
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