797 research outputs found
Room temperature magnetic stabilization of buried cobalt nanoclusters within a ferromagnetic matrix studied by soft x-ray magnetic circular dichroism
Single dusting layers of size-selected Co nanoclusters (NCs) of sizes ranging from 1.5â5.5 nm have been deposited by a gas-phase aggregation method in ultrahigh vacuum, and embedded within a NiFe matrix. Magnetic hysteresis loops have been obtained using soft x-ray magnetic circular dichroism, which shows that these Co NCs embedded in NiFe exhibit room temperature ferromagnetism with identical coercivity to the surrounding NiFe film. The strong local exchange field at the interface between NiFe and Co NCs, combined with the magnetic anisotropy of the NiFe film, allows stabilization of NC ferromagnetism which persists to room temperature
Functional analysis of epilepsy-associated variants in STXBP1/Munc18-1 using humanised Caenorhabditis elegans
Objective:
Genetic variants in STXBP1 , which encodes the conserved exocytosis protein Munc18â1, are associated with a variety of infantile epilepsy syndromes. We aimed to develop an in vivo Caenorhabditis elegans model that could be used to test the pathogenicity of such variants in a costâeffective manner.
Methods:
The CRISPR/Cas9 method was used to introduce a null mutation into the uncâ18 gene (the C. elegans orthologue of STXBP1 ), thereby creating a paralyzed worm strain. We subsequently rescued this strain with transgenes encoding the human STXBP1/Munc18â1 protein (wildâtype and eight different epilepsyâassociated missense variants). The resulting humanized worm strains were then analyzed via behavioral, electrophysiological, and biochemical approaches.
Results:
Transgenic expression of wildâtype human STXBP1 protein fully rescued locomotion in both solid and liquid media to the same level as the standard wildâtype worm strain, Bristol N2. Six variant strains (E59K, V84D, C180Y, R292H, L341P, R551C) exhibited impaired locomotion, whereas two (P335L, R406H) were no different from worms expressing wildâtype STXBP1. Electrophysiological recordings revealed that all eight variant strains displayed less frequent and more irregular pharyngeal pumping in comparison to wildâtype STXBP1âexpressing strains. Four strains (V84D, C180Y, R292H, P335L) exhibited pentylenetetrazolâinduced convulsions in an acute assay of seizureâlike activity, in contrast to worms expressing wildâtype STXBP1. No differences were seen between wildâtype and variant STXBP1 strains in terms of mRNA abundance. However, STXBP1 protein levels were reduced to 20%â30% of wildâtype in all variants, suggesting that the mutations result in STXBP1 protein instability.
Significance:
The approach described here is a costâeffective in vivo method for establishing the pathogenicity of genetic variants in STXBP1 and potentially other conserved neuronal proteins. Furthermore, the humanized strains we created could potentially be used in the future for highâthroughput drug screens to identify novel therapeutics
Kinetic model of II-VI(001) semiconductor surfaces: Growth rates in atomic layer epitaxy
We present a zinc-blende lattice gas model of II-VI(001) surfaces, which is
investigated by means of Kinetic Monte Carlo (KMC) simulations. Anisotropic
effective interactions between surface metal atoms allow for the description
of, e.g., the sublimation of CdTe(001), including the reconstruction of
Cd-terminated surfaces and its dependence on the substrate temperature T. Our
model also includes Te-dimerization and the potential presence of excess Te in
a reservoir of weakly bound atoms at the surface. We study the self-regulation
of atomic layer epitaxy (ALE) and demonstrate how the interplay of the
reservoir occupation with the surface kinetics results in two different
regimes: at high T the growth rate is limited to 0.5 layers per ALE cycle,
whereas at low enough T each cycle adds a complete layer of CdTe. The
transition between the two regimes occurs at a characteristic temperature and
its dependence on external parameters is studied. Comparing the temperature
dependence of the ALE growth rate in our model with experimental results for
CdTe we find qualitative agreement.Comment: 9 pages (REVTeX), 8 figures (EPS). Content revised, references added,
typos correcte
Mechanisms for slow strengthening in granular materials
Several mechanisms cause a granular material to strengthen over time at low
applied stress. The strength is determined from the maximum frictional force
F_max experienced by a shearing plate in contact with wet or dry granular
material after the layer has been at rest for a waiting time \tau. The layer
strength increases roughly logarithmically with \tau -only- if a shear stress
is applied during the waiting time. The mechanisms of strengthening are
investigated by sensitive displacement measurements and by imaging of particle
motion in the shear zone. Granular matter can strengthen due to a slow shift in
the particle arrangement under shear stress. Humidity also leads to
strengthening, but is found not to be its sole cause. In addition to these time
dependent effects, the static friction coefficient can also be increased by
compaction of the granular material under some circumstances, and by cycling of
the applied shear stress.Comment: 21 pages, 11 figures, submitted to Phys. Rev.
Exotic smooth structures on 4-manifolds with zero signature
For every integer , we construct infinite families of mutually
nondiffeomorphic irreducible smooth structures on the topological -manifolds
and (2k-1)(\CP#\CPb), the connected sums of
copies of and \CP#\CPb.Comment: 6 page
Constructions of generalized complex structures in dimension four
Four-manifold theory is employed to study the existence of (twisted)
generalized complex structures. It is shown that there exist (twisted)
generalized complex structures that have more than one type change loci. In an
example-driven fashion, (twisted) generalized complex structures are
constructed on a myriad of four-manifolds, both simply and non-simply
connected, which are neither complex nor symplectic
A Successful Broad-band Survey for Giant Lya Nebulae I: Survey Design and Candidate Selection
Giant Lya nebulae (or Lya "blobs") are likely sites of ongoing massive galaxy
formation, but the rarity of these powerful sources has made it difficult to
form a coherent picture of their properties, ionization mechanisms, and space
density. Systematic narrow-band Lya nebula surveys are ongoing, but the small
redshift range covered and the observational expense limit the comoving volume
that can be probed by even the largest of these surveys and pose a significant
problem when searching for such rare sources. We have developed a systematic
search technique designed to find large Lya nebulae at 2<z<3 within deep
broad-band imaging and have carried out a survey of the 9.4 square degree NOAO
Deep Wide-Field Survey (NDWFS) Bootes field. With a total survey comoving
volume of ~10^8 h^-3_70 Mpc^3, this is the largest volume survey for Lya
nebulae ever undertaken. In this first paper in the series, we present the
details of the survey design and a systematically-selected sample of 79
candidates, which includes one previously discovered Lya nebula.Comment: Accepted to ApJ after minor revision; 25 pages in emulateapj format;
18 figures, 3 table
Heavy quarkonium: progress, puzzles, and opportunities
A golden age for heavy quarkonium physics dawned a decade ago, initiated by
the confluence of exciting advances in quantum chromodynamics (QCD) and an
explosion of related experimental activity. The early years of this period were
chronicled in the Quarkonium Working Group (QWG) CERN Yellow Report (YR) in
2004, which presented a comprehensive review of the status of the field at that
time and provided specific recommendations for further progress. However, the
broad spectrum of subsequent breakthroughs, surprises, and continuing puzzles
could only be partially anticipated. Since the release of the YR, the BESII
program concluded only to give birth to BESIII; the -factories and CLEO-c
flourished; quarkonium production and polarization measurements at HERA and the
Tevatron matured; and heavy-ion collisions at RHIC have opened a window on the
deconfinement regime. All these experiments leave legacies of quality,
precision, and unsolved mysteries for quarkonium physics, and therefore beg for
continuing investigations. The plethora of newly-found quarkonium-like states
unleashed a flood of theoretical investigations into new forms of matter such
as quark-gluon hybrids, mesonic molecules, and tetraquarks. Measurements of the
spectroscopy, decays, production, and in-medium behavior of c\bar{c}, b\bar{b},
and b\bar{c} bound states have been shown to validate some theoretical
approaches to QCD and highlight lack of quantitative success for others. The
intriguing details of quarkonium suppression in heavy-ion collisions that have
emerged from RHIC have elevated the importance of separating hot- and
cold-nuclear-matter effects in quark-gluon plasma studies. This review
systematically addresses all these matters and concludes by prioritizing
directions for ongoing and future efforts.Comment: 182 pages, 112 figures. Editors: N. Brambilla, S. Eidelman, B. K.
Heltsley, R. Vogt. Section Coordinators: G. T. Bodwin, E. Eichten, A. D.
Frawley, A. B. Meyer, R. E. Mitchell, V. Papadimitriou, P. Petreczky, A. A.
Petrov, P. Robbe, A. Vair
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