50,729 research outputs found
The locust frontal ganglion: a central pattern generator network controlling foregut rhythmic motor patterns
The frontal ganglion (FG) is part of the insect
stomatogastric nervous system and is found in most insect
orders. Previous work has shown that in the desert locust,
Schistocerca gregaria, the FG constitutes a major source of
innervation to the foregut. In an in vitro preparation,
isolated from all descending and sensory inputs, the FG
spontaneously generated rhythmic multi-unit bursts of
action potentials that could be recorded from all its
efferent nerves. The consistent endogenous FG rhythmic
pattern indicates the presence of a central pattern
generator network. We found the appearance of in vitro
rhythmic activity to be strongly correlated with the
physiological state of the donor locust. A robust pattern
emerged only after a period of saline superfusion, if the
locust had a very full foregut and crop, or if the animal
was close to ecdysis. Accordingly, haemolymph collected
at these stages inhibited an ongoing rhythmic pattern
when applied onto the ganglion. We present this novel
central pattern generating system as a basis for future
work on the neural network characterisation and its role
in generating and controlling behaviour
Social Sector Business Ventures: The Critical Factors That Maximize Success
This paper seeks to help social sector leaders understand the factors that they should consider when launching revenue-generating business ventures. Given that much of the research on social sector business ventures is based on the personal experiences of individual practitioners, there is a wide array of advice for organizational leaders who are thinking about launching business ventures. Consequently, we approach the subject of social sector business ventures in a systematic and analytic way in order to determine what organizational leaders really need to know about launching successful ventures. We introduce a framework called "business in a box" that separates the process of thinking about launching business ventures from the organizational characteristics and dynamics that influence these ventures. We assert that organizational leaders who wish to maximize the success of their business ventures must explore (1) what is "inside" the box (The Business and its Context) to understand the business fundamentals of launching a venture and (2) what is "outside" the box (Assets and Internal Destructive Forces) to understand the forces and dynamics within the organizational context that impact these ventures.This publication is Hauser Center Working Paper No. 43. The Hauser Center Working Paper Series was launched during the summer of 2000. The Series enables the Hauser Center to share with a broad audience important works-in-progress written by Hauser Center scholars and researchers
Eulerian Statistically Preserved Structures in Passive Scalar Advection
We analyze numerically the time-dependent linear operators that govern the
dynamics of Eulerian correlation functions of a decaying passive scalar
advected by a stationary, forced 2-dimensional Navier-Stokes turbulence. We
show how to naturally discuss the dynamics in terms of effective compact
operators that display Eulerian Statistically Preserved Structures which
determine the anomalous scaling of the correlation functions. In passing we
point out a bonus of the present approach, in providing analytic predictions
for the time-dependent correlation functions in decaying turbulent transport.Comment: 10 pages, 10 figures. Submitted to Phys. Rev.
Rate of energy absorption by a closed ballistic ring
We make a distinction between the spectroscopic and the mesoscopic
conductance of closed systems. We show that the latter is not simply related to
the Landauer conductance of the corresponding open system. A new ingredient in
the theory is related to the non-universal structure of the perturbation matrix
which is generic for quantum chaotic systems. These structures may created
bottlenecks that suppress the diffusion in energy space, and hence the rate of
energy absorption. The resulting effect is not merely quantitative: For a
ring-dot system we find that a smaller Landauer conductance implies a smaller
spectroscopic conductance, while the mesoscopic conductance increases. Our
considerations open the way towards a realistic theory of dissipation in closed
mesoscopic ballistic devices.Comment: 18 pages, 5 figures, published version with updated ref
Stochastic Cahn-Hilliard equation with double singular nonlinearities and two reflections
We consider a stochastic partial differential equation with two logarithmic
nonlinearities, with two reflections at 1 and -1 and with a constraint of
conservation of the space average. The equation, driven by the derivative in
space of a space-time white noise, contains a bi-Laplacian in the drift. The
lack of the maximum principle for the bi-Laplacian generates difficulties for
the classical penalization method, which uses a crucial monotonicity property.
Being inspired by the works of Debussche, Gouden\`ege and Zambotti, we obtain
existence and uniqueness of solution for initial conditions in the interval
. Finally, we prove that the unique invariant measure is ergodic, and
we give a result of exponential mixing
Interplay of the Chiral and Large N_c Limits in pi N Scattering
Light-quark hadronic physics admits two useful systematic expansions, the
chiral and 1/N_c expansions. Their respective limits do not commute, making
such cases where both expansions may be considered to be especially
interesting. We first study pi N scattering lengths, showing that (as expected
for such soft-pion quantities) the chiral expansion converges more rapidly than
the 1/N_c expansion, although the latter nevertheless continues to hold. We
also study the Adler-Weisberger and Goldberger-Miyazawa-Oehme sum rules of pi N
scattering, finding that both fail if the large N_c limit is taken prior to the
chiral limit.Comment: 10 pages, ReVTe
Creation and detection of a mesoscopic gas in a non-local quantum superposition
We investigate the scattering of a quantum matter wave soliton on a barrier
in a one dimensional geometry and we show that it can lead to mesoscopic
Schr\"odinger cat states, where the atomic gas is in a coherent superposition
of being in the half-space to the left of the barrier and being in the
half-space to the right of the barrier. We propose an interferometric method to
reveal the coherent nature of this superposition and we discuss in details the
experimental feasibility.Comment: 4 pages, 1 figur
Collective Atomic Recoil Laser as a synchronization transition
We consider here a model previously introduced to describe the collective
behavior of an ensemble of cold atoms interacting with a coherent
electromagnetic field. The atomic motion along the self-generated
spatially-periodic force field can be interpreted as the rotation of a phase
oscillator. This suggests a relationship with synchronization transitions
occurring in globally coupled rotators. In fact, we show that whenever the
field dynamics can be adiabatically eliminated, the model reduces to a
self-consistent equation for the probability distribution of the atomic
"phases". In this limit, there exists a formal equivalence with the Kuramoto
model, though with important differences in the self-consistency conditions.
Depending on the field-cavity detuning, we show that the onset of synchronized
behavior may occur through either a first- or second-order phase transition.
Furthermore, we find a secondary threshold, above which a periodic self-pulsing
regime sets in, that is immediately followed by the unlocking of the
forward-field frequency. At yet higher, but still experimentally meaningful,
input intensities, irregular, chaotic oscillations may eventually appear.
Finally, we derive a simpler model, involving only five scalar variables, which
is able to reproduce the entire phenomenology exhibited by the original model
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