Compressibility in the Integer Quantum Hall Effect within Hartree-Fock Approximation

Electron-electron interactions seem to play a surprisingly small role in the description of the integer quantum Hall effect, considering that for just slightly different filling factors the interactions are of utmost importance causing the interaction-mediated fractional quantum Hall effect. However, recent imaging experiments by Cobden et al. and Ilani et al. constitute strong evidence for the importance of electron-electron interactions even in the integer effect. The experiments report on measurements of the conductance and electronic compressibility of mesoscopic MOSFET devices that show disagreement with predictions from the single particle model. By diagonalising a random distribution of Gaussian scatterers and treating the interactions in Hartree-Fock approximation we investigate the role of electron-electron interactions for the integer quantum Hall effect and find good agreement with the experimental results.Comment: 4 pages, 4 figures, Proceedings of "Transport in Interacting and Disordered Systems (TIDS11)", submitted for publication in phys. stat. sol. (c), including pss style file

Sparse spatial selection for novelty-based search result diversification

Abstract. Novelty-based diversification approaches aim to produce a diverse ranking by directly comparing the retrieved documents. However, since such approaches are typically greedy, they require O(n 2) documentdocument comparisons in order to diversify a ranking of n documents. In this work, we propose to model novelty-based diversification as a similarity search in a sparse metric space. In particular, we exploit the triangle inequality property of metric spaces in order to drastically reduce the number of required document-document comparisons. Thorough experiments using three TREC test collections show that our approach is at least as effective as existing novelty-based diversification approaches, while improving their efficiency by an order of magnitude.

University of Glasgow at WebCLEF 2005: experiments in per-field normalisation and language specific stemming

We participated in the WebCLEF 2005 monolingual task. In this task, a search system aims to retrieve relevant documents from a multilingual corpus of Web documents from Web sites of European governments. Both the documents and the queries are written in a wide range of European languages. A challenge in this setting is to detect the language of documents and topics, and to process them appropriately. We develop a language specific technique for applying the correct stemming approach, as well as for removing the correct stopwords from the queries. We represent documents using three fields, namely content, title, and anchor text of incoming hyperlinks. We use a technique called per-field normalisation, which extends the Divergence From Randomness (DFR) framework, to normalise the term frequencies, and to combine them across the three fields. We also employ the length of the URL path of Web documents. The ranking is based on combinations of both the language specific stemming, if applied, and the per-field normalisation. We use our Terrier platform for all our experiments. The overall performance of our techniques is outstanding, achieving the overall top four performing runs, as well as the top performing run without metadata in the monolingual task. The best run only uses per-field normalisation, without applying stemming

Productivity Growth in U.S. Agriculture

Innovation and changes in technology have been a driving force for gains in productivity growth in U.S. agriculture. USDA's Economic Research Service has developed annual indexes of agricultural inputs, outputs, and total factor productivity (TFP) for 1948 through 2004. American agriculture relies almost entirely on productivity growth to raise output. By lowering the cost of agricultural commodities, productivity growth benefits not only farmers but also food manufacturers and consumers.Agriculture, productivity, productivity growth, total factor productivity, TFP, labor, farm economy, prices, agricultural research, agricultural output, technology, ERS, USDA, Production Economics, Productivity Analysis,

Reconciliation of Religious Beliefs and Minority Sexual Orientation

This study addresses the issue of how gay men and lesbians reconcile conflicts between their religious beliefs and their sexual orientation. Christian faith traditions have commonly rejected minority sexual orientations as sinful, while modem social science has identified these sexual orientations as a normal part of the variety of human experience. This study consists of structured interviews with seven participants who have sought to resolve this conflict in different ways, namely through accepting their sexual orientation and adapting their religious beliefs or through accepting their religious beliefs and seeking to change their sexual orientation. The population includes three lesbians and two gay men who are actively involved in religious groups and a man and a woman who have sought to change their sexual orientation for religious reasons (these persons commonly call themselves Ex-Gays). One of the gay men and one lesbian also sought to change their sexual orientation at a time in the past. The interviews also address the motivations that the individuals cite for the choices that they made in reconciling religious beliefs and sexual orientation and their level of satisfaction with their current status in relation to these variables. The interviews are analyzed using a hermeneutic methodology adapted from Brown, Tappan, Gilligan, Miller and Argyris (1989). An analysis of the interviews indicates that themes related to the rejection of a minority sexual orientation (MSO) include the belief that homosexuality is wrong or sinful, fear of rejection due to having a minority sexual orientation, and severe emotional distress related to the first two themes. The themes associated with affirmation of a MSO include an awareness of God’s love, the experience of an affirmative religious community, and the development of alternative Biblical interpretations relating to homosexuality. The process of reconciliation of religious beliefs and sexual orientation was characterized by a rejection from a religious community, a period of self- and/or spiritual discovery, the experience of acceptance in a Christian community, a sense of emotional healing, and, for those who came to affirm a MSO, a realization that a change of sexual orientation was not possible and a change in religious beliefs. A proposed model for the reconciliation process includes a personal decision to move toward a desired direction, leaving a community of faith or an identity, an experience of grief at what has been lost, creating a new identity, and reconciliation with what has been lost. The discussion includes implications of this research for the present controversy over the ethics of sexual orientation conversion therapies and implications for counseling

Search For Oxygen in Cool DQ White Dwarf Atmospheres

We report new infrared spectroscopic observations of cool DQ white dwarfs by using Coolspec on the 2.7m Harlan-Smith Telescope. DQs have helium-rich atmospheres with traces of molecular carbon thought to be the result of convective dredge-up from their C/O interiors. Recent model calculations predict that oxygen should also be present in DQ atmospheres in detectable amounts. Our synthetic spectra calculations for He-rich white dwarfs with traces of C and O indicate that CO should be easily detected in the cool DQ atmospheres if present in the expected amounts. Determination of the oxygen abundance in the atmosphere will reveal the C/O ratio at the core/envelope boundary, constraining the important and uncertain ^{12}C(alpha,gamma)^{16}O reaction rate.Comment: 2 pages, 2 figures, to appear in proceedings of the 13th European Workshop on White Dwarf

Bilayer Quantum Hall Systems at Filling Factor \nu=2: An Exact Diagonalisation Study

We present an exact diagonalisation study of bilayer quantum Hall systems at a filling factor of two in the spherical geometry. We find the high-Zeeman-coupling phase boundary of the broken symmetry canted antiferromagnet is given exactly by previous Hartree-Fock mean-field theories, but that the state's stability at weak Zeeman coupling has been qualitatively overestimated. In the absence of interlayer tunneling, degeneracies occur between total spin multiplets due to the Hamiltonian's invariance under independent spin-rotations in top and bottom two-dimensional electron layers.Comment: Some remarks added in the discussion of the phase diagram, and some typos corrected. Version to be published in Phys. Rev. Let