Smooth double barriers in quantum mechanics

Quantum mechanical tunneling across smooth double barrier potentials modeled using Gaussian functions, is analyzed numerically and by using the WKB approximation. The transmission probability, resonances as a function of incident particle energy, and their dependence on the barrier parameters are obtained for various cases. We also discuss the tunneling time, for which we obtain generalizations of the known results for rectangular barriers.Comment: 23 pages, 8 figures, a slightly reduced version to appear in American Journal of Physics, references correcte

Frequency-tunable metamaterials using broadside-coupled split ring resonators

We present frequency tunable metamaterial designs at terahertz (THz) frequencies using broadside-coupled split ring resonator (BC-SRR) arrays. Frequency tuning, arising from changes in near field coupling, is obtained by in-plane horizontal or vertical displacements of the two SRR layers. For electrical excitation, the resonance frequency continuously redshifts as a function of displacement. The maximum frequency shift occurs for displacement of half a unit cell, with vertical displacement resulting in a shift of 663 GHz (51% of f0) and horizontal displacement yielding a shift of 270 GHz (20% of f0). We also discuss the significant differences in tuning that arise for electrical excitation in comparison to magnetic excitation of BC-SRRs

Acid extraction of radionuclides from soil samples using autoclave decomposition

The specifi cs of the nuclear tests carried out on the territory of the former Semipalatinsk test site (STS) led to the emergence of various sites that diff er in levels of radioactive contamination and radionuclide composition. This also led to a signifi cant diff erence in the solubility of radioactive particles. Traditionally, the “Experimental Field” testing ground was characterized by the presence of sparingly soluble, vitrifi ed particles, which was determined by the features inherent in ground tests of nuclear weapons, namely, the interaction of the high-temperature explosion region with soil particles. The presence of such sparingly soluble particles in the soil cover makes it impossible to use 6–8 М HCl and 7–8 М HNO3 solutions which are most often used radiochemical analysis to determine the content of 90Sr and 239+240Pu. This paper considers methods for the acid extraction of anthropogenic radionuclides from soils of the STS using autoclaving. The aim of the research is to develop a method for the acid extraction of anthropogenic radionuclides from enlarged soil samples using autoclave decomposition. A blank soil sample was used to determine the optimal autoclave decomposition parameters; to test the acid extraction method, a soil sample was taken from the territory of the “experimental fi eld” testing ground. The radionuclide 137Cs has been used as the most optimal indicator of acid extraction due to its strong fi xation on clay and mineral soil particles and ease of detection by the gamma radiation. Autoclave decomposition has been carried out by dissolving the studied samples in a mixture of mineral acids (HCl, HNO3, HF, H2SO4). The specifi c activity of radionuclide has been determined on a BE3830 gamma spectrometer with a high-purity germanium detector (Canberra, USA), the amount of undecomposed soil residue has been determined gravimetrically (PA214C analytical balance, Ohaus, USA). The data obtained indicate that the most complete extraction of 137Cs occurs when using concentrated HF solutions (individually or in a mixture with other mineral acids). The degree of extraction of 137Cs varied from 85 to 100%. The worst results have been shown by the use of a mixture of acids 3HCl:HNO3. In this case the degree of extraction of 137Cs did not exceed 20%. The effi ciency of decomposition of soil samples weighing 10 g with a concentrated solution of HF at a temperature of 120 to 160 ºC was ≥95%

Geometry of deformations of branes in warped backgrounds

The `braneworld' (described by the usual worldvolume action) is a D dimensional timelike surface embedded in a N dimensional ($N>D$) warped, nonfactorisable spacetime. We first address the conditions on the warp factor required to have an extremal flat brane in a five dimensional background. Subsequently, we deal with normal deformations of such extremal branes. The ensuing Jacobi equations are analysed to obtain the stability condition. It turns out that to have a stable brane, the warp factor should have a minimum at the location of the brane in the given background spacetime. To illustrate our results we explicitly check the extremality and stability criteria for a few known co-dimension one braneworld models. Generalisations of the above formalism for the cases of (i) curved branes (ii) asymmetrical warping and (iii) higher co-dimension braneworlds are then presented alongwith some typical examples for each. Finally, we summarize our results and provide perspectives for future work along these lines.Comment: 21 pages. Version matching final version. Accepted for publication in Class. Quant. Gra

Can degenerate bound states occur in one dimensional quantum mechanics?

We point out that bound states, degenerate in energy but differing in parity, may form in one dimensional quantum systems even if the potential is non-singular in any finite domain. Such potentials are necessarily unbounded from below at infinity and occur in several different contexts, such as in the study of localised states in brane-world scenarios. We describe how to construct large classes of such potentials and give explicit analytic expressions for the degenerate bound states. Some of these bound states occur above the potential maximum while some are below. Various unusual features of the bound states are described and after highlighting those that are ansatz independent, we suggest that it might be possible to observe such parity-paired degenerate bound states in specific mesoscopic systems.Comment: 10 pages, 2 figures, to appear in Europhysics Letter

TAp73/ΔNp73 influences apoptotic response, chemosensitivity and prognosis in hepatocellular carcinoma

n/

Stringy black holes and energy conditions

The energy condition inequalities for the matter stress energy comprised out of the dilaton and Maxwell fields in the dilaton-Maxwell gravity theories emerging out of string theory are examined in detail. In the simplistic 1+1 dimensional models, $R\le 0$ (where $R$ is the Ricci scalar), turns out to be the requirement for ensuring focusing of timelike geodesics. In 3+1 dimensions, we outline the requirements on matter for pure dilaton theories-these in turn constrain the functional forms of the dilaton. Furthermore, in charged dilaton gravity a curious opposite behaviour of the matter stress energy w.r.t the violation/conservation of the Weak Energy Condition is noted for the electric and magnetic black hole metrics written in the string frame of reference. We also investigate the matter that is necessary for creating certain specific non-asymptotically flat black holes. For the electric and magnetic black hole metrics, strangely, matter satisfies the weak energy condition in the string frame. Finally, the Averaged Null Energy Condition is evaluated along radial null geodesics for each of these black hole spacetimes.Comment: 23 pages, RevTex, no figures, corrected and extended,to appear in Physical Review

Probing liquid surface waves, liquid properties and liquid films with light diffraction

Surface waves on liquids act as a dynamical phase grating for incident light. In this article, we revisit the classical method of probing such waves (wavelengths of the order of mm) as well as inherent properties of liquids and liquid films on liquids, using optical diffraction. A combination of simulation and experiment is proposed to trace out the surface wave profiles in various situations (\emph{eg.} for one or more vertical, slightly immersed, electrically driven exciters). Subsequently, the surface tension and the spatial damping coefficient (related to viscosity) of a variety of liquids are measured carefully in order to gauge the efficiency of measuring liquid properties using this optical probe. The final set of results deal with liquid films where dispersion relations, surface and interface modes, interfacial tension and related issues are investigated in some detail, both theoretically and experimentally. On the whole, our observations and analyses seem to support the claim that this simple, low--cost apparatus is capable of providing a wealth of information on liquids and liquid surface waves in a non--destructive way.Comment: 25 pages, 12 figures, to appear in Measurement Science and Technology (IOP

Braneworlds in six dimensions: new models with bulk scalars

Six dimensional bulk spacetimes with 3-- and 4--branes are constructed using certain non--conventional bulk scalars as sources. In particular, we investigate the consequences of having the phantom (negative kinetic energy) and the Brans--Dicke scalar in the bulk while obtaining such solutions. We find geometries with 4--branes with a compact on--brane dimension (hybrid compactification) which may be assumed to be small in order to realize a 3--brane world. On the other hand, we also construct, with similar sources, bulk spacetimes where a 3--brane is located at a conical singularity. Furthermore, we investigate the issue of localization of matter fields (scalar, fermion, graviton, vector) on these 3-- and 4--branes and conclude with comments on our six dimensional models.Comment: 24 pages, 1 figure, Replaced to match version published in Class. Quant. Gra