Ricci-flat deformation of orbifolds and localized tachyonic modes

We study Ricci-flat deformations of orbifolds in type II theory. We obtain a simple formula for mass corrections to the twisted modes due to the deformations, and apply it to originally tachyonic and massless states in several examples. In the case of supersymmetric orbifolds, we find that tachyonic states appear when the deformation breaks all the supersymmetries. We also study nonsupersymmetric orbifolds C^2/Z_{2N(2N+1)}, which is T-dual to N type 0 NS5-branes. For N>=2, we compute mass corrections for states, which have string scale tachyonic masses. We find that the corrected masses coincide to ones obtained by solving the wave equation for the tachyon field in the smeared type 0 NS5-brane background geometry. For N=1, we show that the unstable mode representing the bubble creation is the unique tachyonic mode.Comment: 20 pages, minor collection

Polynuclear growth model, GOE2^2 and random matrix with deterministic source

We present a random matrix interpretation of the distribution functions which have appeared in the study of the one-dimensional polynuclear growth (PNG) model with external sources. It is shown that the distribution, GOE$^2$, which is defined as the square of the GOE Tracy-Widom distribution, can be obtained as the scaled largest eigenvalue distribution of a special case of a random matrix model with a deterministic source, which have been studied in a different context previously. Compared to the original interpretation of the GOE$^2$ as ``the square of GOE'', ours has an advantage that it can also describe the transition from the GUE Tracy-Widom distribution to the GOE$^2$. We further demonstrate that our random matrix interpretation can be obtained naturally by noting the similarity of the topology between a certain non-colliding Brownian motion model and the multi-layer PNG model with an external source. This provides us with a multi-matrix model interpretation of the multi-point height distributions of the PNG model with an external source.Comment: 27pages, 4 figure

Supergiant Barocaloric Effects in Acetoxy Silicone Rubber over a Wide Temperature Range: Great Potential for Solid-state Cooling

Solid-state cooling based on caloric effects is considered a viable alternative to replace the conventional vapor-compression refrigeration systems. Regarding barocaloric materials, recent results show that elastomers are promising candidates for cooling applications around room-temperature. In the present paper, we report supergiant barocaloric effects observed in acetoxy silicone rubber - a very popular, low-cost and environmentally friendly elastomer. Huge values of adiabatic temperature change and reversible isothermal entropy change were obtained upon moderate applied pressures and relatively low strains. These huge barocaloric changes are associated both to the polymer chains rearrangements induced by confined compression and to the first-order structural transition. The results are comparable to the best barocaloric materials reported so far, opening encouraging prospects for the application of elastomers in near future solid-state cooling devices.Comment: 19 pages, 7 figures, 2 table

Development of single cell protectors for sealed silver-zinc cells, phase 1

A single cell protector (SCP) assembly capable of protecting a single silver-zinc (Ag Zn) battery cell was designed, fabricated, and tested. The SCP provides cell-level protection against overcharge and overdischarge by a bypass circuit. The bypass circuit consists of a magnetic-latching relay that is controlled by the high and low-voltage limit comparators. Although designed specifically for secondary Ag-Zn cells, the SCP is flexible enough to be adapted to other rechargeable cells. Eighteen SCPs were used in life testing of an 18-cell battery. The cells were sealed Ag-Zn system with inorganic separators. For comparison, another 18-cell battery was subjected to identical life test conditions, but with battery-level protection rather than cell-level. An alternative approach to the SCP design in the form of a microprocessor-based system was conceptually designed. The comparison of SCP and microprocessor approaches is also presented and a preferred approach for Ag-Zn battery protection is discussed

Exact solution for the stationary Kardar-Parisi-Zhang equation

We obtain the first exact solution for the stationary one-dimensional Kardar-Parisi-Zhang equation. A formula for the distribution of the height is given in terms of a Fredholm determinant, which is valid for any finite time $t$. The expression is explicit and compact enough so that it can be evaluated numerically. Furthermore, by extending the same scheme, we find an exact formula for the stationary two-point correlation function.Comment: 9 pages, 3 figure

S-Duality, SL(2,Z) Multiplets and Killing Spinors

The S-duality transformations in type IIB string theory can be seen as local U(1) transformations in type IIB supergravity. We use this approach to construct the $SL(2,Z)$ multiplets associated to supersymmetric backgrounds of type IIB string theory and the transformation laws of their corresponding Killing spinors.Comment: 13 pages, Harvma

Vertically coupled double quantum dots in magnetic fields

Ground-state and excited-state properties of vertically coupled double quantum dots are studied by exact diagonalization. Magic-number total angular momenta that minimize the total energy are found to reflect a crossover between electron configurations dominated by intra-layer correlation and ones dominated by inter-layer correlation. The position of the crossover is governed by the strength of the inter-layer electron tunneling and magnetic field. The magic numbers should have an observable effect on the far infra-red optical absorption spectrum, since Kohn's theorem does not hold when the confinement potential is different for two dots. This is indeed confirmed here from a numerical calculation that includes Landau level mixing. Our results take full account of the effect of spin degrees of freedom. A key feature is that the total spin, $S$, of the system and the magic-number angular momentum are intimately linked because of strong electron correlation. Thus $S$ jumps hand in hand with the total angular momentum as the magnetic field is varied. One important consequence of this is that the spin blockade (an inhibition of single-electron tunneling) should occur in some magnetic field regions because of a spin selection rule. Owing to the flexibility arising from the presence of both intra-layer and inter-layer correlations, the spin blockade is easier to realize in double dots than in single dots.Comment: to be published in Phys. Rev. B1

A non-linear numerical model for stratified Tsunami waves and its application

A non-linear numerical model is developed for the computation of water level and discharge for the propagation of a unidirectional two-layered tsunami wave. Four governing equations, two for each layer, are derived from Euler’s equations of motion and continuity, assuming a long wave approximation, negligible friction and no interfacial mixing. A numerical model is developed using a staggered Leap-Frog scheme. The developed non- linear model is compared with an existing validated linear model developed earlier by the author for different non-dimensional wave amplitudes. The significance of non-linear terms is discussed. It is found that for simulations of the interface wave amplitude, the effect of non-linear terms is not significant. However, for the simulation of the top surface, the effect of non-linear terms is significant for higher wave amplitudes, and insignificant for lower wave amplitudes. Developed non-linear numerical model is used for the case of a progressive internal wave in an inclined bay. It is found that the effect of an adverse bottom slipe towards the direction of wave propagation is to amplify the wave. This amplification depends on the steepness of slope as well as the ratio of densities of upper layer fluid to lower layer fluid (α). Amplification increases with slope. For higher values of α, amplification of the top and interface surface decreases, which is reasonable. It is also found that even for a 4 percent density difference between upper layer and lower layer, amplification of the top surface will be twenty times higher than amplification in the non-stratified case. The model can be applied confidently to simulate the basic features of different practical problems, similar to those investigated in this study

Development of single-cell protectors for sealed silver-zinc cells

Three design approaches to cell-level protection were developed, fabricated, and tested. These systems are referred to as the single-cell protector (SCP), multiplexed-cell protector(MCP). To evaluate the systems 18-cell battery packs without cell level control were subjected to cycle life test. A total of five batteries were subjected to simulate synchronous orbit cycling at 40% depth of discharge at 22C. Batteries without cell-level protection failed between 345 and 255 cycles. Cell failure in the cell level protected batteries occurred between 412 and 540. It was determined that the cell-level monitoring and protection is necessary to attain the long cycle life of a AgZn battery. The best method of providing control and protection of the AgZn cells depends on the specific application and capability of the user