Path Integrals, Density Matrices, and Information Flow with Closed Timelike Curves

Two formulations of quantum mechanics, inequivalent in the presence of closed timelike curves, are studied in the context of a soluable system. It illustrates how quantum field nonlinearities lead to a breakdown of unitarity, causality, and superposition using a path integral. Deutsch's density matrix approach is causal but typically destroys coherence. For each of these formulations I demonstrate that there are yet further alternatives in prescribing the handling of information flow (inequivalent to previous analyses) that have implications for any system in which unitarity or coherence are not preserved.Comment: 25 pages, phyzzx, CALT-68-188

Time travel paradoxes, path integrals, and the many worlds interpretation of quantum mechanics

We consider two approaches to evading paradoxes in quantum mechanics with closed timelike curves (CTCs). In a model similar to Politzer's, assuming pure states and using path integrals, we show that the problems of paradoxes and of unitarity violation are related; preserving unitarity avoids paradoxes by modifying the time evolution so that improbable events bewcome certain. Deutsch has argued, using the density matrix, that paradoxes do not occur in the "many worlds interpretation". We find that in this approach account must be taken of the resolution time of the device that detects objects emerging from a wormhole or other time machine. When this is done one finds that this approach is viable only if macroscopic objects traversing a wormhole interact with it so strongly that they are broken into microscopic fragments.Comment: no figure

Simple Quantum Systems in Spacetimes with Closed Timelike Curves

Three simple examples illustrate properties of path integral amplitudes in fixed background spacetimes with closed timelike curves: non-relativistic potential scattering in the Born approximation is non-unitary, but both an example with hard spheres and the exact solution of a totally discrete model are unitary.Comment: 15 pages, CALT-68-180

Diverse lipid conjugates for functional extra-hepatic siRNA delivery in vivo

Small interfering RNA (siRNA)-based therapies are proving to be efficient for treating liver-associated disorders. However, extra-hepatic delivery remains challenging, limiting therapeutic siRNA utility. We synthesized a panel of fifteen lipid-conjugated siRNAs and systematically evaluated the impact of conjugate on siRNA tissue distribution and efficacy. Generally, conjugate hydrophobicity defines the degree of clearance and the liver-to-kidney distribution profile. In addition to primary clearance tissues, several conjugates achieve significant siRNA accumulation in muscle, lung, heart, adrenal glands and fat. Oligonucleotide distribution to extra-hepatic tissues with some conjugates was significantly higher than with cholesterol, a well studied conjugate, suggesting that altering conjugate structure can enhance extra-hepatic delivery. These conjugated siRNAs enable functional gene silencing in lung, muscle, fat, heart and adrenal gland. Required levels for productive silencing vary (5-200 mug/g) per tissue, suggesting that the chemical nature of conjugates impacts tissue-dependent cellular/intracellular trafficking mechanisms. The collection of conjugated siRNA described here enables functional gene modulation in vivo in several extra-hepatic tissues opening these tissues for gene expression modulation. A systemic evaluation of a panel of conjugated siRNA, as reported here, has not previously been investigated and shows that chemical engineering of lipid siRNAs is essential to advance the RNA therapeutic field

Noise propagation issues in Belle II pixel detector power cable

The vertex detector used in the upgrade of High-Energy physics experiment Belle II includes DEPFET pixel detector (PXD) technology. In this complex topology the power supply units and the front-end electronics are connected through a PXD power cable bundle which may propagate the output noise from the power supplies to the vertex area. This paper presents a study of the propagation of noise caused by power converters in the PXD cable bundle based on Multi-conductor Transmission Line (MTL) theory. The work exposes the effect of the complex cable topology and shield connections on the noise propagation, which has an impact on the requirements of the power supplies. This analysis is part of the electromagnetic compatibility based design focused on functional safety to define the shield connections and power supply specifications required to ensure the successful integration of the detector and, specifically, to achieve the designed performance of the front-end electronics

Role of Initial Data in Higher Dimensional Quasi-Spherical Gravitational Collapse

We study the gravitational collapse in ($n+2$)-D quasi-spherical Szekeres space-time (which possess no killing vectors) with dust as the matter distribution. Instead of choosing the radial coordinate `$r$' as the initial value for the scale factor $R$, we consider a power function of $r$ as the initial scale for the radius $R$. We examine the influence of initial data on the formation of singularity in gravitational collapse.Comment: 7 Latex Pages, RevTex Style, No figure

High-Speed Cylindrical Collapse of Two Perfect Fluids

In this paper, the study of the gravitational collapse of cylindrically distributed two perfect fluid system has been carried out. It is assumed that the collapsing speeds of the two fluids are very large. We explore this condition by using the high-speed approximation scheme. There arise two cases, i.e., bounded and vanishing of the ratios of the pressures with densities of two fluids given by $c_s, d_s$. It is shown that the high-speed approximation scheme breaks down by non-zero pressures $p_1, p_2$ when $c_s, d_s$ are bounded below by some positive constants. The failure of the high-speed approximation scheme at some particular time of the gravitational collapse suggests the uncertainity on the evolution at and after this time. In the bounded case, the naked singularity formation seems to be impossible for the cylindrical two perfect fluids. For the vanishing case, if a linear equation of state is used, the high-speed collapse does not break down by the effects of the pressures and consequently a naked singularity forms. This work provides the generalisation of the results already given by Nakao and Morisawa [1] for the perfect fluid.Comment: 11 pages, 1 figure, accepted for publication in Gen. Rel. Gra