Entanglement entropy in quantum spin chains with finite range interaction

We study the entropy of entanglement of the ground state in a wide family of one-dimensional quantum spin chains whose interaction is of finite range and translation invariant. Such systems can be thought of as generalizations of the XY model. The chain is divided in two parts: one containing the first consecutive L spins; the second the remaining ones. In this setting the entropy of entanglement is the von Neumann entropy of either part. At the core of our computation is the explicit evaluation of the leading order term as L tends to infinity of the determinant of a block-Toeplitz matrix whose symbol belongs to a general class of 2 x 2 matrix functions. The asymptotics of such determinant is computed in terms of multi-dimensional theta-functions associated to a hyperelliptic curve of genus g >= 1, which enter into the solution of a Riemann-Hilbert problem. Phase transitions for thes systems are characterized by the branch points of the hyperelliptic curve approaching the unit circle. In these circumstances the entropy diverges logarithmically. We also recover, as particular cases, the formulae for the entropy discovered by Jin and Korepin (2004) for the XX model and Its, Jin and Korepin (2005,2006) for the XY model.Comment: 75 pages, 10 figures. Revised version with minor correction

Digital technology and governance in transition: The case of the British Library

Comment on the organizational consequences of the new information and communications technologies (ICTs) is pervaded by a powerful imagery of disaggregation and a tendency for ?virtual? forms of production to be seen as synonymous with the ?end? of bureaucracy. This paper questions the underlying assumptions of the ?virtual organization?, highlighting the historically enduring, diversified character of the bureaucratic form. The paper then presents case study findings on the web-based access to information resources now being provided by the British Library (BL). The case study evidence produces two main findings. First, radically decentralised virtual forms of service delivery are heavily dependent on new forms of capacity-building and information aggregation. Second, digital technology is embedded in an inherently contested and contradictory context of institutional change. Current developments in the management and control of digital rights are consistent with the commodification of the public sphere. However, the evidence also suggests that scholarly access to information resources is being significantly influenced by the ?information society? objectives of the BL and other institutional players within the network of UK research libraries

Many body physics from a quantum information perspective

The quantum information approach to many body physics has been very successful in giving new insight and novel numerical methods. In these lecture notes we take a vertical view of the subject, starting from general concepts and at each step delving into applications or consequences of a particular topic. We first review some general quantum information concepts like entanglement and entanglement measures, which leads us to entanglement area laws. We then continue with one of the most famous examples of area-law abiding states: matrix product states, and tensor product states in general. Of these, we choose one example (classical superposition states) to introduce recent developments on a novel quantum many body approach: quantum kinetic Ising models. We conclude with a brief outlook of the field.Comment: Lectures from the Les Houches School on "Modern theories of correlated electron systems". Improved version new references adde

The spectral energy distribution of fermi bright blazars

We have conducted a detailed investigation of the broadband spectral properties of the γ-ray selected blazars of the Fermi LAT Bright AGN Sample (LBAS). By combining our accurately estimated Fermi γ-ray spectra with Swift, radio, infra-red, optical, and other hard X-ray/γ-ray data, collected within 3 months of the LBAS data taking period, we were able to assemble high-quality and quasi-simultaneous spectral energy distributions (SED) for 48 LBAS blazars. The SED of these γ-ray sources is similar to that of blazars discovered at other wavelengths, clearly showing, in the usual log ν-log ν Fν representation, the typical broadband spectral signatures normally attributed to a combination of low-energy synchrotron radiation followed by inverse Compton emission of one or more components. We have used these SED to characterize the peak intensity of both the low- and the high-energy components. The results have been used to derive empirical relationships that estimate the position of the two peaks from the broadband colors (i.e., the radio to optical, αro, and optical to X-ray, αox, spectral slopes) and from the γ-ray spectral index. Our data show that the synchrotron peak frequency (νSpeak) is positioned between 1012.5 and 1014.5 Hz in broad-lined flat spectrum radio quasars (FSRQs) and between 10 13 and 1017 Hz in featureless BL Lacertae objects. We find that the γ-ray spectral slope is strongly correlated with the synchrotron peak energy and with the X-ray spectral index, as expected at first order in synchrotron-inverse Compton scenarios. However, simple homogeneous, one-zone, synchrotron self-Compton (SSC) models cannot explain most of our SED, especially in the case of FSRQs and low energy peaked (LBL) BL Lacs. More complex models involving external Compton radiation or multiple SSC components are required to reproduce the overall SED and the observed spectral variability. While more than 50% of known radio bright high energy peaked (HBL) BL Lacs are detected in the LBAS sample, only less than 13% of known bright FSRQs and LBL BL Lacs are included. This suggests that the latter sources, as a class, may be much fainter γ-ray emitters than LBAS blazars, and could in fact radiate close to the expectations of simple SSC models. We categorized all our sources according to a new physical classification scheme based on the generally accepted paradigm for Active Galactic Nuclei and on the results of this SED study. Since the LAT detector is more sensitive to flat spectrum γ-ray sources, the correlation between νSpeak and γ-ray spectral index strongly favors the detection of high energy peaked blazars, thus explaining the Fermi overabundance of this type of sources compared to radio and EGRET samples. This selection effect is similar to that experienced in the soft X-ray band where HBL BL Lacs are the dominant type of blazars. © 2010 The American Astronomical Society

Reducing the Biological and Psychological Toxicity of Poverty‐related Stress: Initial Efficacy of the BaSICSIntervention for Early Adolescents

This proof‐of‐concept study tests the initial efficacy of the Building a Strong Identity and Coping Skills (BaSICS) intervention, a selective prevention of internalizing problems program for early adolescents exposed to high levels of poverty‐related stress. Eighty‐four early adolescents (Mage = 11.36 years) residing in very low‐income neighborhoods were randomized to receive the 16‐session intervention (n = 44) or to an assessment‐only control condition (n = 40). BaSICS teaches coping skills, social identity development, and collective social action to empower youth with the ability to connect with members of their communities and cope with poverty‐related stress in positive and collaborative ways. Pretest–posttest analyses showed that intervention adolescents acquired problem‐solving and cognitive‐restructuring skills and reduced their reliance on avoidant coping. In addition, HPA reactivity was significantly reduced in the intervention youth, but not controls. Finally, intervention youth\u27s internalizing and somatic symptoms as reported by both youth and their parents, showed significant reductions over time, whereas control youth had no such changes. Results provide strong support for this approach to strength‐building and symptom reduction in a population of early adolescents exposed to poverty‐related stress

Modulation of N-methyl-N-nitrosourea-induced crypt restricted metallothionein immunopositivity in mouse colon by a non-genotoxic diet-related chemical.

Red meat consumption is associated with endogenous metabolic generation of mutagenic N-nitroso compounds (NOC) and may be implicated in causation of colorectal cancer. Assessment of a biologically relevant dose of NOCs is hampered by imperfect understanding of NOC interactions with other dietary components. This study tests the hypothesis that NOC effects upon mutational biomarkers in mouse colon may be modulated by a non-genotoxic diet-related compound. N-methyl-N-nitrosourea (MNU) and undegraded lambda carrageenan (lambdaCgN) were selected as test chemicals, representing a NOC and a non-genotoxic agent, respectively. Study end-points included (i) DNA adduct formation and (ii) metallothionein (MT) crypt restricted immunopositivity indices (MTCRII) which are considered representative of crypt stem cell mutations. Frequency and size of MT immunopositive foci as well as total number of MT immunopositive crypts were assessed. Biologically effective doses of MNU and lambdaCgN were determined in model validation studies and the agents were then tested alone and in combination. Continuous lambdaCgN treatment for 10 weeks induced significantly greater colonic mucosal injury than a drinking water control. In combined treatment regimens, lambdaCgN treatment did not significantly affect MNU-induced DNA adduct formation. However, combinations of lambdaCgN with MNU significantly increased MTCRII in excess of those induced by MNU alone. Recurrent or continuous lambdaCgN regimens had greater interactive effects with MNU upon MTCRII than short-term lambdaCgN treatment. This study has shown that exposure to a non-genotoxic diet-related compound (lambdaCgN) modulates the effective NOC dosimetry for induction of MT crypt restricted immunopositivity