A reexamination is conducted of the formation of dwarf, diffuse, metal-poor galaxies due to supernova-driven winds, in view of data on the systematic properties of dwarfs in the Local Group and Virgo Cluster. The critical condition for global gas loss as a result of the first burst of star formation is that the virial velocity lie below an approximately 100 km/sec critical value. This leads, as observed, to two distinct classes of galaxies, encompassing the diffuse dwarfs, which primarily originate from typical density perturbations, and the normal, brighter galaxies, including compact dwarfs, which can originate only from the highest density peaks. This furnishes a statistical biasing mechanism for the preferential formation of bright galaxies in denser regions, enhancing high surface brightness galaxies' clustering relative to the diffusive dwarfs.

Dwarf galaxies, cold dark matter, and biased galaxy formation

In this paper, the development of a class of depth-integrated, phase-resolving models for surface wave propagation, known as Boussinesq-type models (BTMs), is reviewed. This review concentrates on the extension of the leading order formulation for weakly dispersive waves to include a range of physical effects and considers model applications at a range of scales ranging from surf zone processes to ocean basin–scale tsunami propagation. A brief overview of the connection of BTMs to nonhydrostatic models, in either depth-integrated or three-dimensional form, is included.

Boussinesq Models and Their Application to Coastal Processes across a Wide Range of Scales

The amplitude and phase of the cosmic-ray anisotropy are well established experimentally between 1011 eV and 1014 eV. The study of their evolution in the energy region 1014-1016 eV can provide a significant tool for the understanding of the steepening ("knee") of the primary spectrum. In this Letter, we extend the EAS-TOP measurement performed at E 0 ≈ 1014 eV to higher energies by using the full data set (eight years of data taking). Results derived at about 1014 and 4 × 1014 eV are compared and discussed. Hints of increasing amplitude and change of phase above 1014 eV are reported. The significance of the observation for the understanding of cosmic-ray propagation is discussed.

http://inspirehep.net/record/811274/files/arXiv:0901.2740.pdf

Evolution ofthe cosm ic ray anisotropy above 10 14 eV

A lot of work has been reported to present some numerical results on pair-ion–electron plasmas. However, very few works have reported the corresponding mathematical analytical results in these aspects. In this work, we study a cylindrical Kadomtsev-Petviashvili (CKP) equation, which can be derived from pair-ion–electron plasmas. We further report some interesting mathematical analytical results, including some dynamics of soliton waves, breather waves, and rogue waves in pair-ion–electron plasma via the CKP equation. Using a novel gauge transformation, the Grammian N-soliton solutions of the CKP equation are found analytically. Based on the bilinear transformation method, the breather wave solutions are obtained explicitly under some parameter constraints. Furthermore, we construct the rogue waves using the long wave limit method. In addition, some remarkable characteristics of these soliton solutions are analyzed graphically. According to analytic solutions, the influences of each parameter on the dynamics of the soliton waves, breather waves, and rogue waves are discussed, and the method of how to control such nonlinear phenomena is suggested.

Dynamics of the soliton waves, breather waves, and rogue waves to the cylindrical Kadomtsev-Petviashvili equation in pair-ion-electron plasma

VLA H I observations in both C and D configurations have been made of the active galaxy NGC 3079 and its two companions NGC 3073 and MCG 9-17-9. The dwarf SO galaxy NGC 3073 is found to exhibit an elongated H I tail which is remarkably aligned with the nucleus of NGC 3079. Several scenarios are investigated as to the cause of the tail, including ram pressure and tidal effects. It is suggested that ram pressure due to outflowing gas from NGC 3079 is responsible for the H I tail. 27 references.

Evidence for Ram Pressure Stripping of NGC3073 by Outflowing Gas from NGC3079

Fully nonlinear model equations, including dispersive effects at one-order higher approximation than in the model of Choi & Camassa (J. Fluid Mech., vol. 396, 1999, pp. 1–36), are derived for long internal waves propagating in two spatial horizontal dimensions in a two-fluid system, where the lower layer is of infinite depth. The model equations consist of two coupled equations for the displacement of the interface and the horizontal velocity of the upper layer at an arbitrary elevation, and they are correct to O(μ2) terms, where μ is the ratio of thickness of the upper-layer fluid to a typical wavelength. For solitary waves propagating in one horizontal direction, the two coupled equations reduce to a single equation for the elevation of the interface. Solitary wave profiles obtained numerically from this equation for different wave speeds are in good agreement with computational results based on Euler's equations. A numerical approach for the propagation of solitary waves is provided in the weakly nonlinear case.

Fully nonlinear higher-order model equations for long internal waves in a two-fluid system

From Zakharov’s integral equation a nonlinear evolution equation for broader bandwidth gravity waves in deep water is obtained, which is one order higher than the corresponding equation derived by Trulsen and Dysthe [“A modified nonlinear Schrodinger equation for broader bandwidth gravity waves on deep water,” Wave Motion 24, 281 (1996)]. The instability regions in the perturbed wave-number space for a uniform Stokes wave obtained from this equation are in surprisingly good agreement with the exact results obtained by McLean et al. [“Three dimensional instability of finite amplitude water waves,” Phys. Rev. Lett. 46, 817 (1981)].

A higher-order nonlinear evolution equation for broader bandwidth gravity waves in deep water

For a three-dimensional gravity capillary wave packet in the presence of a thin thermocline in deep water two coupled nonlinear evolution equations correct to fourth order in wave steepness are obtained. Reducing these two equations to a single equation for oblique plane wave perturbation, the stability of a uniform gravity-capillary wave train is investigated. The stability and instability regions are identified. Expressions for the maximum growth rate of instability and the wavenumber at marginal stability are obtained. The results are shown graphically.

/pdf/fourth-order-nonlinear-evolution-equations-for-gravity-1bgnh2jxr3.pdf

Fourth order nonlinear evolution equations for gravity-capillary waves in the presence of a thin thermocline in deep water

Starting from the Zakharov integral equation, two coupled fourth-order nonlinear equations have been derived for the evolution of the amplitudes of two capillary-gravity wave packets propagating in the same direction. The two evolution equations are used to investigate the stability of a uniform capillary-gravity wave train in the presence of another having the same group velocity. The relative changes in phase velocity of each uniform wave train due to the presence of the other one have been shown in figures for different wave numbers. The condition of instability of a wave of greater wavelength in the presence of a wave of shorter wavelength is obtained. It is observed that the instability region for a surface gravity wave train in the presence of a capillary-gravity wave train expands with the increase of wave steepness of the capillary-gravity wave train. It is found that the presence of a uniform capillary-gravity wave train causes an increase in the growth rate of instability of a uniform surface gr...

Fourth-order nonlinear evolution equations for a capillary-gravity wave packet in the presence of another wave packet in deep water

Nonlinear evolution equations are derived in a situation of crossing sea states characterized by water waves having two different spectral peaks. The nonlinear evolution equations derived here are valid for any water depth except for shallow water depth case. These evolution equations are then employed to study the instability properties of two Stokes wave trains considering both unidirectional and bidirectional perturbations. Figures have been plotted showing the growth rate of instability for various depths of water and for different values of the angle of interaction of the two wave systems. All the figures serve as an evidence to the fact that freak waves can be formed as a result of modulational instability in crossing sea states over finite depth water. It is observed that the growth rate of instability in crossing sea states situation over finite depth water is much higher than that for infinite depth case and it increases with the decrease of the depth of water.

Suma Debsarma

Papers

Fully nonlinear higher-order model equations for long internal waves in a two-fluid system

A higher-order nonlinear evolution equation for broader bandwidth gravity waves in deep water

Fourth order nonlinear evolution equations for gravity-capillary waves in the presence of a thin thermocline in deep water

Fourth-order nonlinear evolution equations for a capillary-gravity wave packet in the presence of another wave packet in deep water

Modulational instability in crossing sea states over finite depth water