The dynamic structure factor in impurity-doped spin chains

The effects of impurities in spin-1/2 Heisenberg chains are recently experiencing a renewed interest due to experimental realizations in solid state systems and ultra-cold gases. The impurities effectively cut the chains into finite segments with a discrete spectrum and characteristic correlations, which have a distinct effect on the dynamic structure factor. Using bosonization and the numerical Density Matrix Renormalization Group we provide detailed quantitative predictions for the momentum and energy resolved structure factor in doped systems. Due to the impurities, spectral weight is shifted away from the antiferromagnetic wave-vector $k=\pi$ into regions which normally have no spectral weight in the thermodynamic limit. The effect can be quantitatively described in terms of scaling functions, which are derived from a recurrence relation based on bosonization.Comment: submitted version, 12 pages, 2 figures, latest version and more information can be found at https://www.physik.uni-kl.de/eggert/papers/index.htm

Testing the BoP impact assessment framework through assessing socio-economic impact of a health care venture in Afghanistan

This thesis explores impact assessment of a health care venture targeting the base of the pyramid market in Afghanistan. Little research has been conducted on BoP ventures in Afghanistan, and impact assessment represents a gap in the BoP literature. Therefore, to address the assessment gap in the BoP literature, the BoP Impact Assessment Framework was used as a theoretical template for designing the research study as well as generalising results. The study design included empirical, field research in rural Afghanistan, which provided a unique context for testing the existing framework. The case study method was used to conduct research on a single organisation providing health services in Afghanistan, and data was collected from multiple sources of evidence such as archival evidence, interviews and focus groups to triangulate results. The research study incorporated grounded theory procedures and processes to collect, analyse and code raw data. Theoretical sampling, a central grounded theory procedure, facilitated theory development through the discovery and comparison of concepts and categories. Results were developed by theorising about the raw data compiled during data collection and analysed using grounded theory. The final empirical results included three broad categories – “lower health care costs”, “relationships” and “behaviours” – and represent the inductive theory that emerged from the research study. The inductive theory was subsequently generalised against the existing theoretical framework through analytical generalisation. In each case where the inductive theory was compared against the existing theoretical framework, the research study found that the empirical results were generalisable against the existing theory

The Evolution of Legal Personhood for Nonhuman Animals in the United States

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Imperfect Construction of Microclusters

Microclusters are the basic building blocks used to construct cluster states capable of supporting fault-tolerant quantum computation. In this paper, we explore the consequences of errors on microcluster construction using two error models. To quantify the effect of the errors we calculate the fidelity of the constructed microclusters and the fidelity with which two such microclusters can be fused together. Such simulations are vital for gauging the capability of an experimental system to achieve fault tolerance.Comment: 5 pages 2 figure

Costs of Security in the PFS File System

Various principles have been proposed for the design of trustworthy systems. But there is little data about their impact on system performance. A filesystem that pervasively instantiates a number of well-known security principles was implemented and the performance impact of various design choices was analyzed. The overall performance of this filesystem was also compared to a Linux filesystem that largely ignores the security principles.Supported in part by NICECAP cooperative agreement FA8750-07-2-0037 administered by AFRL, AFOSR grant F9550-06-0019, National Science Foundation grants 0430161, 0964409, and CCF-0424422 (TRUST), ONR grants N00014-01-1-0968 and N00014-09-1-0652, and grants from Microsoft

Ultraviolet C II and Si III Transit Spectroscopy and Modeling of the Evaporating Atmosphere of GJ436b

Hydrogen gas evaporating from the atmosphere of the hot-Neptune GJ436b absorbs over 50% of the stellar Ly$\alpha$ emission during transit. Given the planet's atmospheric composition and energy-limited escape rate, this hydrogen outflow is expected to entrain heavier atoms such as C and O. We searched for C and Si in the escaping atmosphere of GJ436b using far-ultraviolet HST COS G130M observations made during the planet's extended H I transit. These observations show no transit absorption in the C II 1334,1335 \AA\ and Si III 1206 \AA\ lines integrated over [-100, 100] km s$^{-1}$, imposing 95% (2$\sigma$) upper limits of 14% (C II) and 60% (Si III) depth on the transit of an opaque disk and 22% (C II) and 49% (Si III) depth on an extended, highly asymmetric transit similar to that of H I Ly$\alpha$. C$^+$ is likely present in the outflow according to a simulation we carried out using a spherically-symmetric, photochemical-hydrodynamical model. This simulation predicts a $\sim$2% transit over the integrated bandpass, consistent with the data. At line center, we predict the C II transit depth to be as high as 19%. Our model predicts a neutral hydrogen escape rate of $1.6\times10^{9}$ g s$^{-1}$ ($3.1\times10^{9}$ g s$^{-1}$ for all species) for an upper atmosphere composed of hydrogen and helium.Comment: 7 pages, 4 figures, 1 table; accepted to ApJ Letter