Linear and Nonlinear Bullets of the Bogoliubov-de Gennes Excitations

We report on the focalization of Bogoliubov–de Gennes excitations of the nonlinear Schrödinger equation in the defocusing regime (Gross-Pitaevskii equation for repulsive Bose-Einstein condensates) with a spatially modulated periodic potential. Exploiting the modification of the dispersion relation induced by the modulation, we demonstrate the existence of localized structures of the Bogoliubov–de Gennes excitations, in both the linear and nonlinear regimes (linear and nonlinear “bullets”). These traveling Bogoliubov–de Gennes bullets, localized both spatially and temporally in the comoving reference frame, are robust and propagate remaining stable, without spreading or filamentation. The phenomena reported in this Letter could be observed in atomic Bose-Einstein condensates in the presence of a spatially periodic potential induced by an optical lattice.Peer ReviewedPostprint (published version

Kinetic Modelling for Tar Evolution and Formation in a Downdraft Gasifier

Biomass gasification modeling is a powerful tool used to optimize the design of a gasifier. A detailed kinetic model was built by the current authors [1] to predict the behavior of air blown downdraft gasifier for a wide range of materials within the range of (38≤C≤52) %, (5.2≤H≤7) %, and (21.7≤O≤45) %. The model was verified and showed a good stability for a wide range of working parameters like equivalence ratio and moisture content. In the current research, 4 main tar species are added to the model to represent tar formation using detailed kinetic reactions. The yield of tar species is discussed for different zones of a gasifier based on temperature of each zone. Mass and energy balance are calculated. 18 different kinetic reactions are implemented in the kinetic code to predict the optimum working conditions that leads to the production of higher value producer gas. Results conclude that using ER of 0.3 with moisture content levels lower than 10% will lead to the production of higher yields of syngas with lower amounts of tar

Distribution of Wigner delay time from single channel disordered systems

We consider the scattering of an electron from a semi-infinite one-dimensional random medium. The random medium is characterized by force, -\d V/\d L being the basic random variable. We obtain an analytical expression for the stationary delay time ($\tau$) distribution $P_s(\tau)$ within a random phase approximation. Our result agrees with earlier analytical expressions, where the random potential is taken to be of different kind, indicating universality of the delay time distribution, i.e., delay time distribution is independent of the nature of disorder.Comment: 8 pages RevTeX, no figure

Assessment of Forest Encroachment in Shimoga District of Western Ghats, India, Using Remote Sensing and Gis

Sustainable management of Forest ecosystem is necessary as it serves the important functions such as supplementing human dietary requirements, ecological significance in terms of biodiversity conservation, flood control, water purifica-tion and micro climate regulation etc. Hence, an inventory of reserve forest in a given area is a pre-requisite for their con-servation and management. The present study is focused on RS and GIS based assessment of forest encroachment in Shimoga district of Karnataka for the years 1990, 2000 and 2010 using Landsat TM/MSS/ETM+ for 1990 and 2000, and IRS P6 LISS III for the year 2010. It’s located in the mid south western part of malnad region of Karnataka state, geographically lies between 13°27' and 14°39' N latitudes and 74°38' and 76°4'E longitudes. It covers an area of 8,482.32 km2 a apart of western ghats areas (Sahayadrihill ranges), the densely forested high hilly Malnad in the west and sparsely forested tablelands semi-malnad in the east of Karnataka state with a forest area constituting 32.66% of the total geographical area of the district. The study revealed that the encroachment in reserve forest area accounts for 282.92 km2, 257.27 km2 and 192.43 km2 for the year 2010, 2000 and 1990 respectively. Extension of cultivation is the major cause of large-scale encroachment in the district. There is no proper demarcation of the forest boundaries in some places. This has also resulted in encroachment of for-est land. It has led to forest fragmentation, loss of habitat and corridor for movement of wild animals, etc. The policy mak-ers and judiciary have stressed the need for use of recent satellite data to assess the forest encroachment in Western Ghats region. In this regard, an attempt has been made to study the two decadal forest encroachment patterns of Shimoga district. The extent of encroachment was observed to be 12.13 % in 2010. Encroachment is more prevalent in the moist and dry deciduous forests than the evergreen forests and is seen increasing day by day. This information will help for frontline forest officials to trace and book forest offences occurring in their jurisdiction and also to prevent encroachments

Assessment of Forest Encroachment at Belgaum District of Western Ghats of Karnataka Using Remote Sensing and GIS

The present study focuses on the assessment of forest encroachment in Belgaum district of Karnataka for the year 1975, 1990, 2000 and 2010 using RS and GIS. The study area is located in the north-western part of Karnataka state, with a total area of 13,415 km2.The study revealed that the forest encroachment is 4245.6, 16133.1, 28304.4 and 29010.0 ha for the year 1975, 1990, 2000 and 2010 respectively. The extent of encroachment in 2010 amounted to 9.66 % in evergreen to semi evergreen, 15.84 % moist deciduous and 74.50 % in scrub forests.The highest percentage of encroachment was in Hukkeri taluk with mixed plantation and the major part was scrubland whose average encroached area was 31.38% over the years. The major factors accelerating encroachments were agricultural expansion, population dependency on forest livelihood, limited land for cultivation, lack of grazing land and poverty

Imaginary Potential as a Counter of Delay Time for Wave Reflection from a 1D Random Potential

We show that the delay time distribution for wave reflection from a one-dimensional random potential is related directly to that of the reflection coefficient, derived with an arbitrarily small but uniform imaginary part added to the random potential. Physically, the reflection coefficient, being exponential in the time dwelt in the presence of the imaginary part, provides a natural counter for it. The delay time distribution then follows straightforwardly from our earlier results for the reflection coefficient, and coincides with the distribution obtained recently by Texier and Comtet [C.Texier and A. Comtet, Phys.Rev.Lett. {\bf 82}, 4220 (1999)],with all moments infinite. Delay time distribution for a random amplifying medium is then derived . In this case, however, all moments work out to be finite.Comment: 4 pages, RevTeX, replaced with added proof, figure and references. To appear in Phys. Rev. B Jan01 200

Low-energy Compton scattering on the nucleon and sum rules

The Gerasimov-Drell-Hearn and Baldin-Lapidus sum rules are evaluated in the dressed K-matrix model for photon-induced reactions on the nucleon. For the first time the sum $\alpha+\beta$ of the electric and magnetic polarisabilities and the forward spin polarisability $\gamma_0$ are explicitly calculated in two alternative ways -- from the sum rules and from the low-energy expansion of the real Compton scattering amplitude -- within the {\em same} framework. The two methods yield compatible values for $\alpha+\beta$ but differ somewhat for $\gamma_0$. Consistency between the two ways of determining the polarisabilities is a measure of the extent to which basic symmetries of the model are obeyed.Comment: 9 pages, 4 figures, using REVTeX. More concise version, results unchanged. To appear in Phys. Rev.

Turbulent drag on a low-frequency vibrating grid in superfluid He-4 at very low temperatures

We present measurements of the dissipative turbulent drag on a vibrating grid in superfluid He-4 over a wide range of (low) frequencies. At high velocities, the dissipative drag is independent of frequency and is approximately the same as that measured in normal liquid He-4. We present measurements on a similar grid in superfluid He-3-B at low temperatures which shows an almost identical turbulent drag coefficient at low frequencies. However, the turbulent drag in He-3-B is substantially higher at higher frequencies. We also present measurements of the inertial drag coefficient for grid turbulence in He-4. The inertial drag coefficient is significantly reduced by turbulence in both superfluid and normal liquid He-4

Diversity in the Tail of the Intersecting Brane Landscape

Techniques are developed for exploring the complete space of intersecting brane models on an orientifold. The classification of all solutions for the widely-studied T^6/Z_2 x Z_2 orientifold is made possible by computing all combinations of branes with negative tadpole contributions. This provides the necessary information to systematically and efficiently identify all models in this class with specific characteristics. In particular, all ways in which a desired group G can be realized by a system of intersecting branes can be enumerated in polynomial time. We identify all distinct brane realizations of the gauge groups SU(3) x SU(2) and SU(3) x SU(2) x U(1) which can be embedded in any model which is compatible with the tadpole and SUSY constraints. We compute the distribution of the number of generations of "quarks" and find that 3 is neither suppressed nor particularly enhanced compared to other odd generation numbers. The overall distribution of models is found to have a long tail. Despite disproportionate suppression of models in the tail by K-theory constraints, the tail in the distribution contains much of the diversity of low-energy physics structure.Comment: 48 pages, 8 figure

Cloud microphysical effects of turbulent mixing and entrainment

Turbulent mixing and entrainment at the boundary of a cloud is studied by means of direct numerical simulations that couple the Eulerian description of the turbulent velocity and water vapor fields with a Lagrangian ensemble of cloud water droplets that can grow and shrink by condensation and evaporation, respectively. The focus is on detailed analysis of the relaxation process of the droplet ensemble during the entrainment of subsaturated air, in particular the dependence on turbulence time scales, droplet number density, initial droplet radius and particle inertia. We find that the droplet evolution during the entrainment process is captured best by a phase relaxation time that is based on the droplet number density with respect to the entire simulation domain and the initial droplet radius. Even under conditions favoring homogeneous mixing, the probability density function of supersaturation at droplet locations exhibits initially strong negative skewness, consistent with droplets near the cloud boundary being suddenly mixed into clear air, but rapidly approaches a narrower, symmetric shape. The droplet size distribution, which is initialized as perfectly monodisperse, broadens and also becomes somewhat negatively skewed. Particle inertia and gravitational settling lead to a more rapid initial evaporation, but ultimately only to slight depletion of both tails of the droplet size distribution. The Reynolds number dependence of the mixing process remained weak over the parameter range studied, most probably due to the fact that the inhomogeneous mixing regime could not be fully accessed when phase relaxation times based on global number density are considered.Comment: 17 pages, 10 Postscript figures (figures 3,4,6,7,8 and 10 are in reduced quality), to appear in Theoretical Computational Fluid Dynamic