696 research outputs found
Capillary-gravity solitary waves on water of finite depth interacting with a linear shear current
The problem of two-dimensional capillary-gravity waves on an inviscid fluid of finite depth interacting with a linear shear current is considered. The shear current breaks the symmetry of the irrotational problem and supports simultaneously counter-propagating waves of different types: Korteweg de-Vries (KdV)-type long solitary waves and wave-packet solitary waves whose envelopes are associated with the nonlinear Schrödinger equation. A simple intuition for the broken symmetry is that the current modifies the Bond number differently for left- and right-propagating waves. Weakly nonlinear theories are developed in general and for two particular resonant cases: the case of second harmonic resonance and long-wave/short-wave interaction. Traveling-wave solutions and their dynamics in the full Euler equations are computed numerically using a time-dependent conformal mapping technique, and compared to some weakly nonlinear solutions. Additional attention is paid to branches of elevation generalized solitary waves of KdV type: although true embedded solitary waves are not detected on these branches, it is found that periodic wavetrains on their tails can be arbitrarily small as the vorticity increases. Excitation of waves by moving pressure distributions and modulational instabilities of the periodic waves in the resonant cases described above are also examined by the fully nonlinear computations
Nonlinear hydroelastic waves on a linear shear current at finite depth
This work is concerned with waves propagating on water of finite depth with a constant-vorticity current under a deformable flexible sheet. The pressure exerted by the sheet is modelled by using the Cosserat thin shell theory. By means of multi-scale analysis, small amplitude nonlinear modulation equations in several regimes are considered, including the nonlinear Schrödinger equation (NLS) which is used to predict the existence of small-amplitude wavepacket solitary waves in the full Euler equations and to study the modulational instability of quasi-monochromatic wavetrains. Guided by these weakly nonlinear results, fully nonlinear steady and time-dependent computations are performed by employing a conformal mapping technique. Bifurcation mechanisms and typical profiles of solitary waves for different underlying shear currents are presented in detail. It is shown that even when small-amplitude solitary waves are not predicted by the weakly nonlinear theory, we can numerically find large-amplitude solitary waves in the fully nonlinear equations. Time-dependent simulations are carried out to confirm the modulational stability results and illustrate possible outcomes of the nonlinear evolution in unstable cases
Wess-Zumino sigma models with non-Kahlerian geometry
Supersymmetry of the Wess-Zumino (N=1, D=4) multiplet allows field equations
that determine a larger class of geometries than the familiar Kahler manifolds,
in which covariantly holomorphic vectors rather than a scalar superpotential
determine the forces. Indeed, relaxing the requirement that the field equations
be derivable from an action leads to complex flat geometry. The
Batalin-Vilkovisky formalism is used to show that if one requires that the
field equations be derivable from an action, we once again recover the
restriction to Kahler geometry, with forces derived from a scalar
superpotential.Comment: 13 pages, Late
N=2 supergravity in five dimensions revisited
We construct matter-coupled N=2 supergravity in five dimensions, using the
superconformal approach. For the matter sector we take an arbitrary number of
vector-, tensor- and hyper-multiplets. By allowing off-diagonal vector-tensor
couplings we find more general results than currently known in the literature.
Our results provide the appropriate starting point for a systematic search for
BPS solutions, and for applications of M-theory compactifications on Calabi-Yau
manifolds with fluxes.Comment: 35 pages; v.2: A sign changed in a bilinear fermion term in (5.7
KP solitons in shallow water
The main purpose of the paper is to provide a survey of our recent studies on
soliton solutions of the Kadomtsev-Petviashvili (KP) equation. The
classification is based on the far-field patterns of the solutions which
consist of a finite number of line-solitons. Each soliton solution is then
defined by a point of the totally non-negative Grassmann variety which can be
parametrized by a unique derangement of the symmetric group of permutations.
Our study also includes certain numerical stability problems of those soliton
solutions. Numerical simulations of the initial value problems indicate that
certain class of initial waves asymptotically approach to these exact solutions
of the KP equation. We then discuss an application of our theory to the Mach
reflection problem in shallow water. This problem describes the resonant
interaction of solitary waves appearing in the reflection of an obliquely
incident wave onto a vertical wall, and it predicts an extra-ordinary four-fold
amplification of the wave at the wall. There are several numerical studies
confirming the prediction, but all indicate disagreements with the KP theory.
Contrary to those previous numerical studies, we find that the KP theory
actually provides an excellent model to describe the Mach reflection phenomena
when the higher order corrections are included to the quasi-two dimensional
approximation. We also present laboratory experiments of the Mach reflection
recently carried out by Yeh and his colleagues, and show how precisely the KP
theory predicts this wave behavior.Comment: 50 pages, 25 figure
Asymptotic models for the generation of internal waves by a moving ship, and the dead-water phenomenon
This paper deals with the dead-water phenomenon, which occurs when a ship
sails in a stratified fluid, and experiences an important drag due to waves
below the surface. More generally, we study the generation of internal waves by
a disturbance moving at constant speed on top of two layers of fluids of
different densities. Starting from the full Euler equations, we present several
nonlinear asymptotic models, in the long wave regime. These models are
rigorously justified by consistency or convergence results. A careful
theoretical and numerical analysis is then provided, in order to predict the
behavior of the flow and in which situations the dead-water effect appears.Comment: To appear in Nonlinearit
Characterization of soil erosion indicators using hyperspectral data from a Mediterranean rainfed cultivated region
The determination of surface soil properties is an important application of remotely sensed hyperspectral imagery. Moreover, different soil properties can be associated with erosion processes, with significant implications for land management and agricultural uses. This study integrates hyperspectral data supported by morphological and physico-chemical ground data to identify and map soil properties that can be used to assess soil erosion and accumulation. These properties characterize different soil horizons that emerge at the surface as a consequence of the intensity of the erosion processes, or the result of accumulation conditions. This study includes: 1) field and laboratory characterization of the main soil types in the study area; 2) identification and definition of indicators of soil erosion and accumulation stages (SEAS); 3) compilation of the site-specific MEDiterranean Soil Erosion Stages (MEDSES) spectral library of soil surface characteristics using field spectroscopy; 4) using hyperspectral airborne data to determine a set of endmembers for different SEAS and introducing these into the support vector machine (SVM) classifier to obtain their spatial distribution; and 5) evaluation of the accuracy of the classification applying a field validation protocol. The study region is located within an agricultural region in Central Spain, representative of Mediterranean agricultural uses dominated by a gently sloping relief, and characterized by soils with contrasting horizons. Results show that the proposed method is successful in mapping different SEAS that indicate preservation, partial loss, or complete loss of fertile soils, as well as down-slope accumulation of different soil materials
Cyclosporine A reduces microvascular obstruction and preserves left ventricular function deterioration following myocardial ischemia and reperfusion
Postconditioning and cyclosporine A prevent
mitochondrial permeability transition pore opening providing
cardioprotection during ischemia/reperfusion.
Whether microvascular obstruction is affected by these
interventions is largely unknown. Pigs subjected to coronary
occlusion for 1 h followed by 3 h of reperfusion were
assigned to control (n = 8), postconditioning (n = 9) or
cyclosporine A intravenous infusion 10-15 min before the
end of ischemia (n = 8). Postconditioning was induced by
8 cycles of repeated 30-s balloon inflation and deflation.
After 3 h of reperfusion magnetic resonance imaging,
triphenyltetrazolium chloride/Evans blue staining and histopathology
were performed. Microvascular obstruction
(MVO, percentage of gadolinium-hyperenhanced area) was
measured early (3 min) and late (12 min) after contrast
injection. Infarct size with double staining was smaller in
cyclosporine (46.2 ± 3.1 %, P = 0.016) and postconditioning
pigs (47.6 ± 3.9 %, P = 0.008) versus controls
(53.8 ± 4.1 %). Late MVO was significantly reduced by
cyclosporine (13.9 ± 9.6 %, P = 0.047) but not postconditioning
(23.6 ± 11.7 %, P = 0.66) when compared with
controls (32.0 ± 16.9 %). Myocardial blood flow in the
late MVO was improved with cyclosporine versus controls
(0.30 ± 0.06 vs 0.21 ± 0.03 ml/g/min, P = 0.002) and
was inversely correlated with late-MVO extent ( = 0.93,
P\0.0001). Deterioration of left ventricular ejection
fraction (LVEF) between baseline and 3 h of reperfusion
was smaller with cyclosporine (-7.9 ± 2.4 %, P = 0.008)
but not postconditioning (-12.0 ± 5.5 %, P = 0.22) when
compared with controls (-16.4 ± 5.5 %). In the three
groups, infarct size (\beta = -0.69, P\0.001) and late MVO
(\beta = -0.33, P = 0.02) were independent predictors of
LVEF deterioration following ischemia/reperfusion
(R^{2} = 0.73, P\0.001). Despite both cyclosporine A and
postconditioning reduce infarct size, only cyclosporine A
infusion had a beneficial effect on microvascular damage
and was associated with better preserved LV function when
compared with controls
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