317 research outputs found
Fundamental groups of toroidal compactifications
We compute the fundamental group of a toroidal compactification of a
Hermitian locally symmetric space , without assuming either that
is neat or that it is arithmetic. We also give bounds for the first
Betti number.Comment: Final version. Fixes error pointed out by M. Roessler, leading to
slightly but significantly changed statements: improved notatio
Reconciling different formulations of viscous water waves and their mass conservation
The viscosity of water induces a vorticity near the free surface boundary.
The resulting rotational component of the fluid velocity vector greatly
complicates the water wave system. Several approaches to close this system have
been proposed. Our analysis compares three common sets of model equations. The
first set has a rotational kinematic boundary condition at the surface. In the
second set, a gauge choice for the velocity vector is made that cancels the
rotational contribution in the kinematic boundary condition, at the cost of
rotational velocity in the bulk and a rotational pressure. The third set
circumvents the problem by introducing two domains: the irrotational bulk and
the vortical boundary layer. This comparison puts forward the link between
rotational pressure on the surface and vorticity in the boundary layer,
addresses the existence of nonlinear vorticity terms, and shows where
approximations have been used in the models. Furthermore, we examine the
conservation of mass for the three systems, and how this can be compared to the
irrotational case.Comment: 32 pages, 5 figure
Stabilization of uni-directional water wave trains over an uneven bottom
We study the evolution of nonlinear surface gravity water wave packets developing from modulational instability over an uneven bottom. A nonlinear Schrödinger equation (NLSE) with coefficients varying in space along propagation is used as a reference model. Based on a low-dimensional approximation obtained by considering only three complex harmonic modes, we discuss how to stabilize a one-dimensional pattern in the form of train of large peaks sitting on a background and propagating over a significant distance. Our approach is based on a gradual depth variation, while its conceptual framework is the theory of autoresonance in nonlinear systems and leads to a quasi-frozen state. Three main stages are identified: amplification from small sideband amplitudes, separatrix crossing and adiabatic conversion to orbits oscillating around an elliptic fixed point. Analytical estimates on the three stages are obtained from the low-dimensional approximation and validated by NLSE simulations. Our result will contribute to understand the dynamical stabilization of nonlinear wave packets and the persistence of large undulatory events in hydrodynamics and other nonlinear dispersive media
Population Characteristics of the Virginia Opossum in the Cross Timbers Experimental Range During Raccoon Removal
Light Filaments Without Self Guiding
An examination of the propagation of intense 200 fs pulses in water reveals
light filaments not sustained by the balance between Kerr-induced self-focusing
and plasma-induced defocusing. Their appearance is interpreted as the
consequence of a spontaneous reshaping of the wave packet form a gaussian into
a conical wave, driven by the requirement of maximum localization, minimum
losses and stationarity in the presence of non-linear absorption.Comment: Submitted to Phys. Rev. Lett. on July 7th, 200
Spectral up- and downshifting of Akhmediev breathers under wind forcing
We experimentally and numerically investigate the effect of wind forcing on
the spectral dynamics of Akhmediev breathers, a wave-type known to model the
modulation instability. We develop the wind model to the same order in
steepness as the higher order modifcation of the nonlinear Schroedinger
equation, also referred to as the Dysthe equation. This results in an
asymmetric wind term in the higher order, in addition to the leading order wind
forcing term. The derived model is in good agreement with laboratory
experiments within the range of the facility's length. We show that the leading
order forcing term amplifies all frequencies equally and therefore induces only
a broadening of the spectrum while the asymmetric higher order term in the
model enhances higher frequencies more than lower ones. Thus, the latter term
induces a permanent upshift of the spectral mean. On the other hand, in
contrast to the direct effect of wind forcing, wind can indirectly lead to
frequency downshifts, due to dissipative effects such as wave breaking, or
through amplification of the intrinsic spectral asymmetry of the Dysthe
equation. Furthermore, the definitions of the up- and downshift in terms of
peak- and mean frequencies, that are critical to relate our work to previous
results, are highlighted and discussed.Comment: 30 pages, 11 figure
Mobile source of high-energy single-cycle terahertz pulses
The Teramobile laser facility was used to realize the first mobile source of high-power THz pulses. The source is based on a tilted-pulse-front pumping THz generation scheme optimized for application of terawatt laser pulses. Generation of 50-μJ single-cycle electromagnetic pulses centered at 0.19 THz with a repetition rate of 10Hz was obtained for incoming 700-fs 120-mJ near-infrared laser pulses. The corresponding laser-to-THz photon conversion efficiency is approximately 100
Economic evaluations of psychosocial interventions in cancer: A systematic review
Objective: Although the effectiveness of many psychosocial interventions for people with cancer has been established, one barrier to implementation in routine clinical care is a lack of data on cost-effectiveness. We conducted a systematic review to assess the cost-effectiveness of psychosocial interventions for improving psychological adjustment among people with cancer. Methods: Systematic review of the literature, study appraisal, and narrative synthesis. Results: Eight studies involving 1,668 patients were identified. Four of these reported outcomes in a cost per quality adjusted life year (QALY) framework. Six studies reported psychosocial interventions to be cost-effective for improving health-related quality of life, mood, pain, distress, or fear of cancer progression, compared to usual care. Of the six psychosocial interventions identified as cost-effective, three were cognitive behavioural therapy based interventions, one was a nurse-delivered telephone follow-up plus educational group program, one was a group-based exercise and psychosocial intervention, and one was a series of 10 face-to-face or telephone-based individual support sessions delivered by a nurse. The quality of studies according to the CHEC-list criteria was good overall; however, some studies were limited by their choice of outcome measure and omission of important categories of costs. Conclusions: Several psychosocial interventions, particularly those based on cognitive behavioural therapy, have been demonstrated to represent good value for money in cancer care. Future research should include a clear definition of the economic question, inclusion of all relevant costs, and consideration of utility-based quality of life measures for QALY estimation. Systematic review registration: PROSPERO Registration Number: CRD42014006370
Modifications of filament spectra by shaped octave-spanning laser pulses
In this paper we examine the spectral changes in a white light laser filament due to different pulse shapes generated by a pulse-shaping setup. We particularly explore how the properties of the filament spectra can be controlled by parametrically tailored white light pulses. The experiments are carried out in a gas cell with up to 9 bars of argon. Plasma generation and self-phase modulation strongly affect the pulse in the spectral and temporal domains. By exploiting these effects we show that the pulse spectrum can be modified in a desired way by either using second-order parametric chirp functions to shift the filament spectrum to higher or lower wavelengths, or by optimizing pulse shapes with a genetic algorithm to generate more complex filament spectra. This paper is an example of the application of complex, parametrically shaped white light pulses
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