31,133 research outputs found
Stability analysis and simulations of coupled bulk-surface reactionâdiffusion systems
In this article, we formulate new models for coupled systems of bulk-surface reactionâdiffusion equations on stationary volumes. The bulk reactionâdiffusion equations are coupled to the surface reactionâdiffusion equations through linear Robin-type boundary conditions. We then state and prove the necessary conditions for diffusion-driven instability for the coupled system. Owing to the nature of the coupling between bulk and surface dynamics, we are able to decouple the stability analysis of the bulk and surface dynamics. Under a suitable choice of model parameter values, the bulk reactionâdiffusion system can induce patterning on the surface independent of whether the surface reactionâdiffusion system produces or not, patterning. On the other hand, the surface reactionâdiffusion system cannot generate patterns everywhere in the bulk in the absence of patterning from the bulk reactionâdiffusion system. For this case, patterns can be induced only in regions close to the surface membrane. Various numerical experiments are presented to support our theoretical findings. Our most revealing numerical result is that, Robin-type boundary conditions seem to introduce a boundary layer coupling the bulk and surface dynamics
A decentralized motion coordination strategy for dynamic target tracking
This paper presents a decentralized motion planning
algorithm for the distributed sensing of a noisy dynamical
process by multiple cooperating mobile sensor agents. This
problem is motivated by localization and tracking tasks of
dynamic targets. Our gradient-descent method is based on a
cost function that measures the overall quality of sensing. We
also investigate the role of imperfect communication between
sensor agents in this framework, and examine the trade-offs in
performance between sensing and communication. Simulations
illustrate the basic characteristics of the algorithms
Constraining Modular Inflation in the MSSM from Giant Q-Ball Formation
We discuss constraints on which flat directions can have large vacuum
expectation values (VEVs) after inflation. We show that only flat directions
which are not charged under B-L and develop positive pressure due to
renormalization group effects can have large VEVs of order \Mp. For example,
within the MSSM only the flat direction is found to be viable. This
strongly constrains the embedding of a broad class of inflationary models in
the MSSM or some other supersymmetric extension of the SM. For flat directions
with negative pressure, the condensate fragments into very large Q-balls which
we call Q-giants. We discuss the formation, evolution and reheating of these
Q-giants and show that they decay too late. The analysis requires taking into
account new phases of the flat directions, which have been overlooked in the
formation and dynamics of the Q-balls. These constraints may be ameliorated by
invoking a short period of thermal inflation. The latter, however, is viable in
a very narrow window of parameter space and requires fine tuning.Comment: 40 pages, 3 figure
Olig2/Plp-positive progenitor cells give rise to Bergmann glia in the cerebellum.
NG2 (nerve/glial antigen2)-expressing cells represent the largest population of postnatal progenitors in the central nervous system and have been classified as oligodendroglial progenitor cells, but the fate and function of these cells remain incompletely characterized. Previous studies have focused on characterizing these progenitors in the postnatal and adult subventricular zone and on analyzing the cellular and physiological properties of these cells in white and gray matter regions in the forebrain. In the present study, we examine the types of neural progeny generated by NG2 progenitors in the cerebellum by employing genetic fate mapping techniques using inducible Cre-Lox systems in vivo with two different mouse lines, the Plp-Cre-ER(T2)/Rosa26-EYFP and Olig2-Cre-ER(T2)/Rosa26-EYFP double-transgenic mice. Our data indicate that Olig2/Plp-positive NG2 cells display multipotential properties, primarily give rise to oligodendroglia but, surprisingly, also generate Bergmann glia, which are specialized glial cells in the cerebellum. The NG2+ cells also give rise to astrocytes, but not neurons. In addition, we show that glutamate signaling is involved in distinct NG2+ cell-fate/differentiation pathways and plays a role in the normal development of Bergmann glia. We also show an increase of cerebellar oligodendroglial lineage cells in response to hypoxic-ischemic injury, but the ability of NG2+ cells to give rise to Bergmann glia and astrocytes remains unchanged. Overall, our study reveals a novel Bergmann glia fate of Olig2/Plp-positive NG2 progenitors, demonstrates the differentiation of these progenitors into various functional glial cell types, and provides significant insights into the fate and function of Olig2/Plp-positive progenitor cells in health and disease
Theory of superconductor-insulator transition in single Josephson junctions
A non-band theory is developed to describe the superconductor-insulator (SI)
transtition in resistively shunted, single Josephson junctions. The
characteristic is formulated by a Landauer-like formula and evaluated by the
path-integral transfer-matrix method. The result is consistent with the recent
experiments at around 80 . However, the insulator phase shrinks with
decreasing temperature indicating that the single Josephson junction becomes
all superconducting at absolute zero temperature, as long as dissipation is
present.Comment: 4 pages, 3 figure
MSAT-X electronically steered phased array antenna system
A low profile electronically steered phased array was successfully developed for the Mobile Satellite Experiment Program (MSAT-X). The newly invented cavity-backed printed crossed-slot was used as the radiating element. The choice of this element was based on its low elevation angle gain coverage and low profile. A nineteen-way radial type unequal power divider and eighteen three-bit diode phase shifters constitute the beamformer module which is used to scan the beams electronically. A complete hybrid mode pointing system was also developed. The major features of the antenna system are broad coverage, low profile, and fast acquisition and tracking performance, even under fading conditions. Excellent intersatellite isolation (better than 26 dB) was realized, which will provide good quality mobile satellite communication in the future
Adjacency labeling schemes and induced-universal graphs
We describe a way of assigning labels to the vertices of any undirected graph
on up to vertices, each composed of bits, such that given the
labels of two vertices, and no other information regarding the graph, it is
possible to decide whether or not the vertices are adjacent in the graph. This
is optimal, up to an additive constant, and constitutes the first improvement
in almost 50 years of an bound of Moon. As a consequence, we
obtain an induced-universal graph for -vertex graphs containing only
vertices, which is optimal up to a multiplicative constant,
solving an open problem of Vizing from 1968. We obtain similar tight results
for directed graphs, tournaments and bipartite graphs
A Decision-Making Framework for Control Strategies in Probabilistic Search
This paper presents the search problem formulated as a decision problem, where the searcher decides whether the target is present in the search region, and if so, where it is located. Such decision-based search tasks are relevant to many research areas, including mobile robot missions, visual search and attention, and event detection in sensor networks. The effect of control strategies in search problems on decision-making quantities, namely time-to-decision, is investigated in this work. We present a Bayesian framework in which the objective is to improve the decision, rather than the sensing, using different control policies. Furthermore, derivations of closed-form expressions governing the evolution of the belief function are also presented. As this framework enables the study and comparison of the role of control for decision-making applications, the derived theoretical results provide greater insight into the sequential processing of decisions. Numerical studies are presented to verify and demonstrate these results
Do You Imitate Immediately? The Location Choices for Foreign Direct Investment
This study applies recency effect on interfirm imitation behavior to investigate whether recent location choices of peer firms regarding foreign direct investment (FDI) exert imitation pressure on another firmâs FDI location choices. This study examines the FDI data of listed companies in Taiwan. The results confirm the existence of recency effect. This study further indicates that the remote experience peer firms and a firmâs own experience have negative moderating effects on recency effect
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