535 research outputs found
Biliverdin Reductase: More than a Namesake – The Reductase, Its Peptide Fragments, and Biliverdin Regulate Activity of the Three Classes of Protein Kinase C
The expanse of human biliverdin reductase (hBVR) functions in the cells is arguably unmatched by any single protein. hBVR is a Ser/Thr/Tyr-kinase, a scaffold protein, a transcription factor, and an intracellular transporter of gene regulators. hBVR is an upstream activator of the insulin/IGF-1 signaling pathway and of protein kinase C (PKC) kinases in the two major arms of the pathway. In addition, it is the sole means for generating the antioxidant bilirubin-IXα. hBVR is essential for activation of ERK1/2 kinases by upstream MAPKK-MEK and by PKCδ, as well as the nuclear import and export of ERK1/2. Small fragments of hBVR are potent activators and inhibitors of the ERK kinases and PKCs: as such, they suggest the potential application of BVR-based technology in therapeutic settings. Presently, we have reviewed the function of hBVR in cell signaling with an emphasis on regulation of PKCδ activity
Reasoning mechanism for cardinal direction relations
In the classical Projection-based Model for cardinal directions [6], a two-dimensional Euclidean space relative to an arbitrary single-piece region, a, is partitioned into the following nine tiles: North-West, NW(a); North, N(a); North-East, NE(a); West, W(a); Neutral Zone, O(a);East, E(a); South-West, SW(a); South, S(a); and South-East,SE(a). In our Horizontal and Vertical Constraints Model [9], [10] these cardinal directions are decomposed into sets corresponding to horizontal and vertical constraints. Composition is computed for these sets instead of the typical individual cardinal directions. In this paper, we define several whole and part direction relations followed by showing how to compose such relations using a formula introduced in our previous paper [10]. In order to develop a more versatile reasoning system for direction relations, we shall integrate mereology, topology, cardinal directions and include their negations as well. © 2010 Springer-Verlag
Nanometer Scale Dielectric Fluctuations at the Glass Transition
Using non-contact scanning probe microscopy (SPM) techniques, dielectric
properties were studied on 50 nanometer length scales in poly-vinyl-acetate
(PVAc) films in the vicinity of the glass transition. Low frequency (1/f) noise
observed in the measurements, was shown to arise from thermal fluctuations of
the electric polarization. Anomalous variations observed in the noise spectrum
provide direct evidence for cooperative nano-regions with heterogeneous
kinetics. The cooperative length scale was determined. Heterogeneity was
long-lived only well below the glass transition for faster than average
processes.Comment: 4 pages, 4 embedded PS figures, RevTeX - To appear in Phys. Rev. Let
String-like Clusters and Cooperative Motion in a Model Glass-Forming Liquid
A large-scale molecular dynamics simulation is performed on a glass-forming
Lennard-Jones mixture to determine the nature of dynamical heterogeneities
which arise in this model fragile liquid. We observe that the most mobile
particles exhibit a cooperative motion in the form of string-like paths
(``strings'') whose mean length and radius of gyration increase as the liquid
is cooled. The length distribution of the strings is found to be similar to
that expected for the equilibrium polymerization of linear polymer chains.Comment: 6 pages of RevTex, 6 postscript figures, uses epsf.st
Virilizing Leydig-Sertoli cell ovarian tumor associated with endometrioid carcinoma of the endometrium in a postmenopausal patient: Case report and general considerations
Sertoli-Leydig cell tumors (SLCTs) are rare tumors mostly occurring in young women. Here we report an unusual case of a SLCT with simultaneous occurrence of endometrioid adenocarcinoma of the endometrium in a woman in menopause
Methane and carbon monoxide emissions from asphalt pavement: Measurements and estimates of their importance to global budgets
We measured emissions of methane from asphalt surfaces used in pavement for roadways. Maximum emissions were 22 mg/m2/yr for 1- to 4-week-old pavement during maximum sunlight intensity. Emissions were much smaller at low sunlight intensity and dropped off to negligible amounts at night. Smaller emissions were observed for asphalt pavement of 2.5 to 3 years approximate age under similar conditions. Companion measurements of carbon monoxide emissions resulted in maximum emissions of about 2.6 mg/m2/hr for 1-wk-old pavement. These findings indicate that emissions of CH4 and CO are a function of both sunlight and temperature. Based on our results, methane emissions from asphalt pavement cannot be a significant source of atmospheric methane. -from Author
Growing spatial correlations of particle displacements in a simulated liquid on cooling toward the glass transition
We define a correlation function that quantifies the spatial correlation of
single-particle displacements in liquids and amorphous materials. We show for
an equilibrium liquid that this function is related to fluctuations in a bulk
dynamical variable. We evaluate this function using computer simulations of an
equilibrium glass-forming liquid, and show that long range spatial correlations
of displacements emerge and grow on cooling toward the mode coupling critical
temperature
Microscopic Theory of Heterogeneity and Non-Exponential Relaxations in Supercooled Liquids
Recent experiments and computer simulations show that supercooled liquids
around the glass transition temperature are "dynamically heterogeneous" [1].
Such heterogeneity is expected from the random first order transition theory of
the glass transition. Using a microscopic approach based on this theory, we
derive a relation between the departure from Debye relaxation as characterized
by the value of a stretched exponential response function , and the fragility of the liquid. The
value is also predicted to depend on temperature and to vanish as the ideal
glass transition is approached at the Kauzmann temperature.Comment: 4 pages including 3 eps figure
Dynamics of Highly Supercooled Liquids:Heterogeneity, Rheology, and Diffusion
Highly supercooled liquids with soft-core potentials are studied via
molecular dynamics simulations in two and three dimensions in quiescent and
sheared conditions.We may define bonds between neighboring particle pairs
unambiguously owing to the sharpness of the first peak of the pair correlation
functions. Upon structural rearrangements, they break collectively in the form
of clusters whose sizes grow with lowering the temperature . The bond life
time , which depends on and the shear rate \gdot, is on the order
of the usual structural or relaxation time in weak
shear \gdot \tau_{\alpha} \ll 1, while it decreases as 1/\gdot in strong
shear \gdot\tau_{\alpha} \gg 1 due to shear-induced cage breakage.
Accumulated broken bonds in a time interval () closely
resemble the critical fluctuations of Ising spin systems. For example, their
structure factor is well fitted to the Ornstein-Zernike form, which yields the
correlation length representing the maximum size of the clusters composed
of broken bonds. We also find a dynamical scaling relation, , valid for any and \gdot with in two dimensions and
in three dimensions. The viscosity is of order for any and
\gdot, so marked shear-thinning behavior emerges. The shear stress is close
to a limiting stress in a wide shear region. We also examine motion of tagged
particles in shear in three dimensions. The diffusion constant is found to be
of order with for any and \gdot, so
it is much enhanced in strong shear compared with its value at zero shear. This
indicates breakdown of the Einstein-Stokes relation in accord with experiments.
Some possible experiments are also proposed.Comment: 20pages (including figures
Transitions between Inherent Structures in Water
The energy landscape approach has been useful to help understand the dynamic
properties of supercooled liquids and the connection between these properties
and thermodynamics. The analysis in numerical models of the inherent structure
(IS) trajectories -- the set of local minima visited by the liquid -- offers
the possibility of filtering out the vibrational component of the motion of the
system on the potential energy surface and thereby resolving the slow
structural component more efficiently. Here we report an analysis of an IS
trajectory for a widely-studied water model, focusing on the changes in
hydrogen bond connectivity that give rise to many IS separated by relatively
small energy barriers. We find that while the system \emph{travels} through
these IS, the structure of the bond network continuously modifies, exchanging
linear bonds for bifurcated bonds and usually reversing the exchange to return
to nearly the same initial configuration. For the 216 molecule system we
investigate, the time scale of these transitions is as small as the simulation
time scale ( fs). Hence for water, the transitions between each of
these IS is relatively small and eventual relaxation of the system occurs only
by many of these transitions. We find that during IS changes, the molecules
with the greatest displacements move in small ``clusters'' of 1-10 molecules
with displacements of nm, not unlike simpler liquids.
However, for water these clusters appear to be somewhat more branched than the
linear ``string-like'' clusters formed in a supercooled Lennar d-Jones system
found by Glotzer and her collaborators.Comment: accepted in PR
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