342 research outputs found
Chaotic to ordered state transition of cathode-sheath instabilities in DC glow discharge plasmas
Transition from chaotic to ordered state has been observed during the initial
stage of a discharge in a cylindrical dc glow discharge plasma. Initially it
shows a chaotic behavior but increasing the discharge voltage changes the
characteristics of the discharge glow and shows a period substraction of order
7 period 5 period 3 period 1 period i.e. the system goes to
single mode through odd cycle subtraction. On further increasing the discharge
voltage, the system goes through period doubling, like 1 period 2 period
4 period. On further increasing the voltage, the system goes to stable
state without having any oscillations.Comment: chathode-sheath, instabilities, chaos, period-subtraction,
bifurcation, dc-discharg
Exact closed form analytical solutions for vibrating cavities
For one-dimensional vibrating cavity systems appearing in the standard
illustration of the dynamical Casimir effect, we propose an approach to the
construction of exact closed-form solutions. As new results, we obtain
solutions that are given for arbitrary frequencies, amplitudes and time
regions. In a broad range of parameters, a vibrating cavity model exhibits the
general property of exponential instability. Marginal behavior of the system
manifests in a power-like growth of radiated energy.Comment: 17 pages, 7 figure
Stability of stationary states in the cubic nonlinear Schroedinger equation: applications to the Bose-Einstein condensate
The stability properties and perturbation-induced dynamics of the full set of
stationary states of the nonlinear Schroedinger equation are investigated
numerically in two physical contexts: periodic solutions on a ring and
confinement by a harmonic potential. Our comprehensive studies emphasize
physical interpretations useful to experimentalists. Perturbation by stochastic
white noise, phase engineering, and higher order nonlinearity are considered.
We treat both attractive and repulsive nonlinearity and illustrate the
soliton-train nature of the stationary states.Comment: 9 pages, 11 figure
On Correctness of Data Structures under Reads-Write Concurrency
Abstract. We study the correctness of shared data structures under reads-write concurrency. A popular approach to ensuring correctness of read-only operations in the presence of concurrent update, is read-set validation, which checks that all read variables have not changed since they were first read. In practice, this approach is often too conserva-tive, which adversely affects performance. In this paper, we introduce a new framework for reasoning about correctness of data structures under reads-write concurrency, which replaces validation of the entire read-set with more general criteria. Namely, instead of verifying that all read conditions over the shared variables, which we call base conditions. We show that reading values that satisfy some base condition at every point in time implies correctness of read-only operations executing in parallel with updates. Somewhat surprisingly, the resulting correctness guarantee is not equivalent to linearizability, and is instead captured through two new conditions: validity and regularity. Roughly speaking, the former re-quires that a read-only operation never reaches a state unreachable in a sequential execution; the latter generalizes Lamport’s notion of regular-ity for arbitrary data structures, and is weaker than linearizability. We further extend our framework to capture also linearizability. We illus-trate how our framework can be applied for reasoning about correctness of a variety of implementations of data structures such as linked lists.
Coming Back to Life: The Permeability of Past and Present, Mortality and Immortality, Death and Life in the Ancient Mediterranean
The lines between death and life were neither fixed nor finite to the peoples of the ancient Mediterranean. For most, death was a passageway into a new and uncertain existence. The dead were not so much extinguished as understood to be elsewhere, and many perceived the deceased to continue to exercise agency among the living. Even for those more skeptical of an afterlife, notions of coming back to life provided frameworks in which to conceptualize the on-going social, political, and cultural influence of the past. This collection of essays examines how notions of coming back to life shape practices and ideals throughout the ancient Mediterranean. All contributors focus on the common theme of coming back to life as a discursive and descriptive space in which antique peoples construct, maintain, and negotiate the porous boundaries between past and present, mortality and immortality, death and life
A Feature-Driven Active Framework for Ultrasound-Based Brain Shift Compensation
A reliable Ultrasound (US)-to-US registration method to compensate for brain
shift would substantially improve Image-Guided Neurological Surgery. Developing
such a registration method is very challenging, due to factors such as missing
correspondence in images, the complexity of brain pathology and the demand for
fast computation. We propose a novel feature-driven active framework. Here,
landmarks and their displacement are first estimated from a pair of US images
using corresponding local image features. Subsequently, a Gaussian Process (GP)
model is used to interpolate a dense deformation field from the sparse
landmarks. Kernels of the GP are estimated by using variograms and a discrete
grid search method. If necessary, the user can actively add new landmarks based
on the image context and visualization of the uncertainty measure provided by
the GP to further improve the result. We retrospectively demonstrate our
registration framework as a robust and accurate brain shift compensation
solution on clinical data acquired during neurosurgery
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