2,723 research outputs found
Dynamic Hydrostatic Pressure Promotes Differentiation of Human Dental Pulp Stem Cells
The masticatory apparatus absorbs high occlusal forces, but uncontrolled parafunctional or orthodontic forces damage periodontal ligament (PDL), cause pulpal calcification, pulp necrosis and tooth loss. Morphology and functional differentiation of connective tissue cells can be controlled by mechanical stimuli but effects of uncontrolled forces on intra-pulpal homeostasis and ability of dental pulp stem cells (DPSCs) to withstand direct external forces are unclear. Using dynamic hydrostatic pressure (HSP), we tested the hypothesis that direct HSP disrupts DPSC survival and odontogenic differentiation. DPSCs from four teenage patients were subjected to HSP followed by assessment of cell adhesion, survival and recovery capacity based on odontogenic differentiation, mineralization and responsiveness to bone morphogenetic protein-2 (BMP-2). HSP down-regulated DPSC adhesion and survival but promoted differentiation by increasing mineralization, in vivo hard tissue regeneration and BMP-2 responsiveness despite reduced cell numbers. HSP-treated DPSCs displayed enhanced odontogenic differentiation, an indication of favorable recovery from HSP-induced cellular stress
Ferromagnetism in Mn doped GaAs due to substitutional-interstitial complexes
While most calculations on the properties of the ferromagnetic semiconductor
GaAs:Mn have focussed on isolated Mn substituting the Ga site (Mn), we
investigate here whether alternate lattice sites are favored and what the
magnetic consequences of this might be. Under As-rich (Ga-poor) conditions
prevalent at growth, we find that the formation energies are lower for
Mn over interstitial Mn (Mn).As the Fermi energy is shifted towards
the valence band maximum via external -doping, the formation energy of
Mn is reduced relative to Mn. Furthermore, under epitaxial growth
conditions, the solubility of both substitutional and interstitial Mn are
strongly enhanced over what is possible under bulk growth conditions. The high
concentration of Mn attained under epitaxial growth of p-type material opens
the possibility of Mn atoms forming small clusters. We consider various types
of clusters, including the Coulomb-stabilized clusters involving two Mn
and one Mn. While isolated Mn are hole killers (donors), and therefore
destroy ferromagnetism,complexes such as Mn-Mn-Mn) are found
to be more stable than complexes involving Mn-Mn-Mn. The
former complexes exhibit partial or total quenching of holes, yet Mn in
these complexes provide a channel for a ferromagnetic arrangement of the spins
on the two Mn within the complex. This suggests that ferromagnetism in
Mn doped GaAs arises both from holes due to isolated Mn as well as from
strongly Coulomb stabilized Mn-Mn-Mn clusters.Comment: 7 figure
Ultra-Thin Silver Films obtained by Sequential Quench-Anneal Processing
We have used the two-step growth technique, quench condensing followed by an
anneal, to grow ultra thin films of silver on glass substrates. As has been
seen with semiconductor substrates this process produces a metastable
homogeneous covering of silver. By measuring the in situ resistance of the film
during growth we are able to see that the low temperature growth onto
substrates held at 100 Kelvin produces a precursor phase that is insulating
until the film has been annealed. The transformation of the precursor phase
into the final, metallic silver film occurs at a characteristic temperature
near 150K where the sample reconstructs. This reconstruction is accompanied by
a decrease in resistance of up to 10 orders of magnitude
Semirigid Geometry
We provide an intrinsic description of -super \RS s and -\SR\
surfaces. Semirigid surfaces occur naturally in the description of topological
gravity as well as topological supergravity. We show that such surfaces are
obtained by an integrable reduction of the structure group of a complex
supermanifold. We also discuss the \s moduli spaces of -\SR\ surfaces and
their relation to the moduli spaces of -\s\ \RS s.Comment: 29p
Search for NN-decoupled dibaryons using the process below the pion production threshold
The energy spectrum for high energy -rays ( MeV)
from the process emitted at in the laboratory
frame has been measured at an energy below the pion production threshold,
namely, at 216 MeV. The resulting photon energy spectrum extracted from
coincidence events consists of a narrow peak at a photon energy
of about 24 MeV and a relatively broad peak in the energy range of (50 - 70)
MeV. The statistical significances for the narrow and broad peaks are
5.3 and 3.5, respectively. This behavior of the photon energy
spectrum is interpreted as a signature of the exotic dibaryon resonance
with a mass of about 1956 MeV which is assumed to be formed in the
radiative process followed by its electromagnetic
decay via the mode. The experimental spectrum is
compared with those obtained by means of Monte Carlo simulations.Comment: 14 pages, LaTex, 6 eps-figures, accepted for publication in
Phys.Rev.
Trees with Given Stability Number and Minimum Number of Stable Sets
We study the structure of trees minimizing their number of stable sets for
given order and stability number . Our main result is that the
edges of a non-trivial extremal tree can be partitioned into stars,
each of size or , so that every vertex is included in at most two
distinct stars, and the centers of these stars form a stable set of the tree.Comment: v2: Referees' comments incorporate
Quasinormal modes of a Schwarzschild black hole surrounded by free static spherically symmetric quintessence: Electromagnetic perturbations
In this paper, we evaluated the quasinormal modes of electromagnetic
perturbation in a Schwarzschild black hole surrounded by the static spherically
symmetric quintessence by using the third-order WKB approximation when the
quintessential state parameter in the range of . Due to
the presence of quintessence, Maxwell field damps more slowly. And when at
, it is similar to the black hole solution in the ds/Ads
spacetime. The appropriate boundary conditions need to be modified.Comment: 6 pages, 3 figure
Time and Amplitude of Afterpulse Measured with a Large Size Photomultiplier Tube
We have studied the afterpulse of a hemispherical photomultiplier tube for an
upcoming reactor neutrino experiment. The timing, the amplitude, and the rate
of the afterpulse for a 10 inch photomultiplier tube were measured with a 400
MHz FADC up to 16 \ms time window after the initial signal generated by an LED
light pulse. The time and amplitude correlation of the afterpulse shows several
distinctive groups. We describe the dependencies of the afterpulse on the
applied high voltage and the amplitude of the main light pulse. The present
data could shed light upon the general mechanism of the afterpulse.Comment: 11 figure
Transition from tunneling to direct contact in tungsten nanojunctions
We apply the mechanically controllable break junctions technique to
investigate the transition from tunneling to direct contact in tungsten. This
transition is quite different from that of other metals and is determined by
the local electronic properties of the tungsten surface and the relief of the
electrodes at the point of their closest proximity. The conductance traces show
a rich variety of patterns from the avalanche-like jump to a mesoscopic contact
to the completely smooth transition between direct contact and tunneling. Due
to the occasional absence of an adhesive jump the conductance of the contact
can be continuously monitored at ultra-small electrode separations. The
conductance histograms of tungsten are either featureless or show two distinct
peaks related to the sequential opening of spatially separated groups of
conductance channels. The role of surface states of tungsten and their
contribution to the junction conductance at sub-Angstrom electrode separations
are discussed.Comment: 6 pages, 6 figure
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