Phase diagram of the three-dimensional Anderson model of localization with random hopping

We examine the localization properties of the three-dimensional (3D) Anderson Hamiltonian with off-diagonal disorder using the transfer-matrix method (TMM) and finite-size scaling (FSS). The nearest-neighbor hopping elements are chosen randomly according to $t_{ij} \in [c-1/2, c + 1/2]$. We find that the off-diagonal disorder is not strong enough to localize all states in the spectrum in contradistinction to the usual case of diagonal disorder. Thus for any off-diagonal disorder, there exist extended states and, consequently, the TMM converges very slowly. From the TMM results we compute critical exponents of the metal-insulator transitions (MIT), the mobility edge $E_c$, and study the energy-disorder phase diagram.Comment: 4 pages, 5 EPS figures, uses annalen.cls style [included]; presented at Localization 1999, to appear in Annalen der Physik [supplement

Two-dimensional electron gas in a modulation-doped SrTiO3/Sr(Ti,Zr)O3 heterostructure

A two-dimensional electron gas (2DEG) in SrTiO3 is created via modulation doping by interfacing undoped SrTiO3 with a wider-band-gap material, SrTi1-xZrxO3, that is doped n-type with La. All layers are grown using hybrid molecular beam epitaxy. Using magnetoresistance measurements, we show that electrons are transferred into the SrTiO3, and a 2DEG is formed. In particular, Shubnikov-de Haas oscillations are shown to depend only on the perpendicular magnetic field. Experimental Shubnikov-de Haas oscillations are compared with calculations that assume multiple occupied subbands.Comment: Submitted to Applied Physics Letter

Exploring a cardio-thoracic hospital ward soundscape in relation to restoration

Hospitals can provide stressful experiences for both patients and medical staff. A well-designed hospital soundscape should avoid adding to negative emotional states (e.g. stress), limit any detrimental cognitive effects (e.g. attentional fatigue), and enable restoration. Experiences of the cardio-thoracic ward soundscape, in a UK public University hospital, were explored via semi-structured interviews with 11 patients and 16 nurses. Thematic coding analysis resulted in 11 key themes including notions of restoration and emotional responses. The themes were used to develop a conceptual model to describe the processes involved in the perception and evaluation of the soundscape. The language used by patients and nurses indicated the emotional response to the soundscape was at times stressful and at others potentially restorative. Coping methods of accepting and habituating to individual sounds were noted. The impact of the patients' and nurses' ability to maintain these coping strategies are discussed in relation to restoration and the temporal variation of the soundscape. A period of 'quiet time' was in operation at the hospital and the importance of this was noted through various responses relating to emotion and restoration. The results suggest the soundscape has potentially, a beneficial role in facilitating restoration thus helping patients' recovery and medical staff's ability to remain productive. This research supports the need to study hospital soundscapes further so that design implications can be considered for the production of a more restorative environment, possibly through the masking/removal of unwanted sounds and optimising positive sounds

On large-scale diagonalization techniques for the Anderson model of localization

We propose efficient preconditioning algorithms for an eigenvalue problem arising in quantum physics, namely the computation of a few interior eigenvalues and their associated eigenvectors for large-scale sparse real and symmetric indefinite matrices of the Anderson model of localization. We compare the Lanczos algorithm in the 1987 implementation by Cullum and Willoughby with the shift-and-invert techniques in the implicitly restarted Lanczos method and in the Jacobi–Davidson method. Our preconditioning approaches for the shift-and-invert symmetric indefinite linear system are based on maximum weighted matchings and algebraic multilevel incomplete LDLT factorizations. These techniques can be seen as a complement to the alternative idea of using more complete pivoting techniques for the highly ill-conditioned symmetric indefinite Anderson matrices. We demonstrate the effectiveness and the numerical accuracy of these algorithms. Our numerical examples reveal that recent algebraic multilevel preconditioning solvers can accelerate the computation of a large-scale eigenvalue problem corresponding to the Anderson model of localization by several orders of magnitude

Proposing a conceptual framework to develop the hospital soundscape through visual communication

Sound level measurement is used to assess sound within any environment, never more so than in hospitals. This is due to the negative effects that high sound level can have on patients and staff. However, other ways of exploring sound and the soundscape within the hospital context have been used: sound art has conveyed the experiences of heart transplant patients. Art may act as juxtaposition to objective sound level measurement but the two fundamentally attempt to depict attributes of the soundscape. Using theory from design and concepts from art a framework is presented for designing a positive soundscape experience. This is not through the addition of sound per se but through creatively communicating the information contained within a soundscape to enable the everyday listener to interpret a cacophony of hospital sounds more positively. In representing visual communication of sound as a design object, a new way to explore sound may exist

The Constituency Service Basis of the Personal Vote for U.S. Representatives and British Members of Parliament

Under the guise of the "incumbency advantage" American research of the past decade has devoted heavy emphasis to what may be termed the "personal vote" in Congressional elections. Is this phenomenon a purely American one, or is it something susceptible to comparative treatment? This paper contrasts the personal vote in the 1980 U. S. House elections with that in the 1979 British General Election. The analysis utilizes data from surveys conducted by the Center for Political Studies and British Gallup, respectively, in combination with interviews of House AAs and British MPs and party agents whose constituencies fall in the sampling frames of the mass surveys. The analysis finds an incumbency advantage or personal vote in Britain, much weaker than that in the U. S., but of somewhat greater importance than is commonly believed, As in the U. S. constituency service appears to be an important component of the personal vote

Fluctuating Hall resistance defeats the quantized Hall insulator

Using the Chalker-Coddington network model as a drastically simplified, but universal model of integer quantum Hall physics, we investigate the plateau-to-insulator transition at strong magnetic field by means of a real-space renormalization approach. Our results suggest that for a fully quantum coherent situation, the quantized Hall insulator with R_H approx. h/e^2 is observed up to R_L ~25 h/e^2 when studying the most probable value of the distribution function P(R_H). Upon further increasing R_L ->\infty the Hall insulator with diverging Hall resistance R_H \propto R_L^kappa is seen. The crossover between these two regimes depends on the precise nature of the averaging procedure.Comment: major revision, discussion of averaging improved; 8 pages, 7 figures; accepted for publication in EP

The Images of Incumbents in Great Britain and the United States

Incumbents in single member, simple plurality systems strive to develop name recognition and positive images of themselves. We propose to analyze the images that constituents in Great Britain and the United States have of their MPs and Congressmen and to measure the impact which incumbent activities have on those images. We also examine the normative expectations that constituents in both countries have of their representatives and how these expectations shape their evaluations. The data for this study comes from matching elite and voter surveys in Great Britain and the United States. Our results can be summarized as follows: 1) a large percentage of constituents in both countries believe that casework and protecting district interests are the most important functions of the representative; 2) those from working class, less well educated backgrounds are more inclined to prefer a service role for their representative than a policy role; 3) the evaluations that constituents have of their representatives reflects the importance of constituency service in their priorities as well; and 4) that representatives who undertake high levels of constituency service have better constituent images than other representatives