1,455 research outputs found
A retrotransposon-inserted VvmybA1a allele has been spread among cultivars of Vitis vinifera but not North American or East Asian Vitis species
Research Note
Phase Transitions of an Oscillator Neural Network with a Standard Hebb Learning Rule
Studies have been made on the phase transition phenomena of an oscillator
network model based on a standard Hebb learning rule like the Hopfield model.
The relative phase informations---the in-phase and anti-phase, can be embedded
in the network. By self-consistent signal-to-noise analysis (SCSNA), it was
found that the storage capacity is given by , which is better
than that of Cook's model. However, the retrieval quality is worse. In
addition, an investigation was made into an acceleration effect caused by
asymmetry of the phase dynamics. Finally, it was numerically shown that the
storage capacity can be improved by modifying the shape of the coupling
function.Comment: 10 pages, 6 figure
Robustness of the noise-induced phase synchronization in a general class of limit cycle oscillators
We show that a wide class of uncoupled limit cycle oscillators can be
in-phase synchronized by common weak additive noise. An expression of the
Lyapunov exponent is analytically derived to study the stability of the
noise-driven synchronizing state. The result shows that such a synchronization
can be achieved in a broad class of oscillators with little constraint on their
intrinsic property. On the other hand, the leaky integrate-and-fire neuron
oscillators do not belong to this class, generating intermittent phase slips
according to a power low distribution of their intervals.Comment: 10 pages, 3 figure
Thermodynamics of impurity-enhanced vacancy formation in metals
Hydrogen induced vacancy formation in metals and metal alloys has been of great interest during the past couple of decades. The main reason for this phenomenon, often referred to as the superabundant vacancy formation, is the lowering of vacancy formation energy due to the trapping of hydrogen. By means of thermodynamics, we study the equilibrium vacancy formation in fcc metals (Pd, Ni, Co, and Fe) in correlation with the H amounts. The results of this study are compared and found to be in good agreement with experiments. For the accurate description of the total energy of the metal-hydrogen system, we take into account the binding energies of each trapped impurity, the vibrational entropy of defects, and the thermodynamics of divacancy formation. We demonstrate the effect of vacancy formation energy, the hydrogen binding, and the divacancy binding energy on the total equilibrium vacancy concentration. We show that the divacancy fraction gives the major contribution to the total vacancy fraction at high H fractions and cannot be neglected when studying superabundant vacancies. Our results lead to a novel conclusion that at high hydrogen fractions, superabundant vacancy formation takes place regardless of the binding energy between vacancies and hydrogen. We also propose the reason of superabundant vacancy formation mainly in the fcc phase. The equations obtained within this work can be used for any metal-impurity system, if the impurity occupies an interstitial site in the lattice. Published by AIP Publishing.Peer reviewe
Oscillator neural network model with distributed native frequencies
We study associative memory of an oscillator neural network with distributed
native frequencies. The model is based on the use of the Hebb learning rule
with random patterns (), and the distribution function of
native frequencies is assumed to be symmetric with respect to its average.
Although the system with an extensive number of stored patterns is not allowed
to get entirely synchronized, long time behaviors of the macroscopic order
parameters describing partial synchronization phenomena can be obtained by
discarding the contribution from the desynchronized part of the system. The
oscillator network is shown to work as associative memory accompanied by
synchronized oscillations. A phase diagram representing properties of memory
retrieval is presented in terms of the parameters characterizing the native
frequency distribution. Our analytical calculations based on the
self-consistent signal-to-noise analysis are shown to be in excellent agreement
with numerical simulations, confirming the validity of our theoretical
treatment.Comment: 9 pages, revtex, 6 postscript figures, to be published in J. Phys.
Thermodynamics of hydrogen vacancies in MgH2 from first-principles calculations and grand-canonical statistical mechanics
Ab initio calculations and statistical mechanics are combined to elucidate
the thermodynamics of H vacancies in MgH2. A general method based on a
grand-canonical ensemble of defect configurations is introduced to model the
exchange of hydrogen between crystalline MgH2 and gas-phase H2. We find that,
at temperatures and hydrogen partial pressures of practical interest, MgH2 is
capable of accommodating only very small concentrations of hydrogen vacancies,
which consist mainly of isolated defects rather than vacancy clusters, contrary
to what is expected from a simple energetic analysis.Comment: 13 pages, 5 figures. Paper accepted in Physical Review
Scaling Limits for Internal Aggregation Models with Multiple Sources
We study the scaling limits of three different aggregation models on Z^d:
internal DLA, in which particles perform random walks until reaching an
unoccupied site; the rotor-router model, in which particles perform
deterministic analogues of random walks; and the divisible sandpile, in which
each site distributes its excess mass equally among its neighbors. As the
lattice spacing tends to zero, all three models are found to have the same
scaling limit, which we describe as the solution to a certain PDE free boundary
problem in R^d. In particular, internal DLA has a deterministic scaling limit.
We find that the scaling limits are quadrature domains, which have arisen
independently in many fields such as potential theory and fluid dynamics. Our
results apply both to the case of multiple point sources and to the
Diaconis-Fulton smash sum of domains.Comment: 74 pages, 4 figures, to appear in J. d'Analyse Math. Main changes in
v2: added "least action principle" (Lemma 3.2); small corrections in section
4, and corrected the proof of Lemma 5.3 (Lemma 5.4 in the new version);
expanded section 6.
MicroRNA regulation of endothelial homeostasis and commitment—implications for vascular regeneration strategies using stem cell therapies
Human embryonic (hESC) and induced pluripotent (hiPSC) stem cells have broad therapeutic potential in the treatment of a range of diseases, including those of the vascular system. Both hESCs and hiPSCs have the capacity for indefinite self-renewal, in addition to their ability to differentiate into any adult cell type. These cells could provide a potentially unlimited source of cells for transplantation and, therefore, provide novel treatments, e.g. in the production of endothelial cells for vascular regeneration. MicroRNAs are short, noncoding RNAs that act posttranscriptionally to control gene expression and thereby exert influence over a wide range of cellular processes, including maintenance of pluripotency and differentiation. Expression patterns of these small RNAs are tissue specific, and changes in microRNA levels have often been associated with disease states in humans, including vascular pathologies. Here, we review the roles of microRNAs in endothelial cell function and vascular disease, as well as their role in the differentiation of pluripotent stem cells to the vascular endothelial lineage. Furthermore, we discuss the therapeutic potential of stem cells and how knowledge and manipulation of microRNAs in stem cells may enhance their capacity for vascular regeneration
Comprehensive Study of Relationship between Electron Distributions and Performances of Microwave and Mirror Devices
First principles simulations of liquid Fe-S under Earth's core conditions
First principles electronic structure calculations, based upon density
functional theory within the generalized gradient approximation and ultra-soft
Vanderbilt pseudopotentials, have been used to simulate a liquid alloy of iron
and sulfur at Earth's core conditions. We have used a sulfur concentration of
wt, in line with the maximum recent estimates of the sulfur
abundance in the Earth's outer core. The analysis of the structural, dynamical
and electronic structure properties has been used to report on the effect of
the sulfur impurities on the behavior of the liquid. Although pure sulfur is
known to form chains in the liquid phase, we have not found any tendency
towards polymerization in our liquid simulation. Rather, a net S-S repulsion is
evident, and we propose an explanation for this effect in terms of the
electronic structure. The inspection of the dynamical properties of the system
suggests that the sulfur impurities have a negligible effect on the viscosity
of Earth's liquid core.Comment: 24 pages (including 8 figures
- …