An Electronic Mach-Zehnder Quantum Eraser

We propose an electronic quantum eraser in which the electrons are injected into a mesoscopic conductor at the quantum Hall regime. The conductor is composed of a two-path interferometer which is an electronic analogue of the optical Mach-Zehnder interferometer, and a quantum point contact detector capacitively coupled to the interferometer. While the interference of the output current at the interferometer is shown to be suppressed by the which-path information, we show that the which-path information is erased by the zero-frequency cross correlation measurement between the interferometer and the detector output leads. We also investigate a modified setup in which the detector is replaced by a two-path interferometer.We show that the path distinguishability and the visibility of the joint detection can be controlled in a continuous manner, and satisfy a complementarity relation for the entangled electrons.Comment: 5 pages, 2 figure

Resort Evolution Along the Gulf of Mexico Littoral: Historical, Morphological, and Environmental Aspects.

The development histories of eight coastal resorts along the Gulf of Mexico littoral (Fort Myers Beach, Pensacola Beach, Dauphin Island, Grand Isle, Galveston Island, South Padre Island, Tecolutia, and Progreso) are documented to evaluate variability of temporal, spatial, and environmental aspects of resort development. Temporally, a modified S-curve model of resort evolution is offered to describe the historical development of seaside resorts, and stages of exploration, infrastructural development, and settlement expansion precede each resort\u27s levelling off stage. The upper level of development, or level of maturation, varies among the sites, primarily as a function of demand. Resorts in high demand undergo an additional development stage prior to reaching maturation--landuse intensification. In this stage, a resort becomes characterized by high-density landuse and corollary high levels of visitation and seasonal occupancy. After a resort reaches its level of maturation, it declines in terms of attractiveness to new recreationists and tourists. Spatially, a resort\u27s morphology reflects its stage of development. The initial locus of development at the resort site generally evolves into the recreational core area, or recreational business district, and subsequent growth fans outward from this core. While any pre-existing settlement in the area avoided the exposed beachfront as a locus of construction, recreational development proceeds by a pattern of linear shorefront urbanization and subsequent urban infilling of zones removed from the waterfront. At resorts subject to landuse intensification, high-density development initially takes place at more distal zones within the bounds of the site, but eventually \u27redevelopment\u27 of older properties transforms the beachfront into a highrise landscape. Environmentally, greater variability in degree of human modification is noted. Generally, environmental changes become more widespread with successive stages of development. Dune disturbance, shoreline armoring, and wetlands dredging are extensive during the settlement expansion stage, but preservation efforts are often made as a resort matures. If shoreline erosion constitutes a serious problems for continued resort development, human efforts at stabilization by either \u27hard\u27 or \u27soft\u27 methods may only propel a resort into an early maturation stage. Hurricanes were found to stimulate progression through the development stages, primarily by facilitating landuse intensification via \u27redevelopment\u27

Entanglement, measurement, and conditional evolution of the Kondo singlet interacting with a mesoscopic detector

We investigate various aspects of the Kondo singlet in a quantum dot (QD) electrostatically coupled to a mesoscopic detector. The two subsystems are represented by an entangled state between the Kondo singlet and the charge-dependent detector state. We show that the phase-coherence of the Kondo singlet is destroyed in a way that is sensitive to the charge-state information restored both in the magnitude and in the phase of the scattering coefficients of the detector. We also introduce the notion of the `conditional evolution' of the Kondo singlet under projective measurement on the detector. Our study reveals that the state of the composite system is disentangled upon this measurement. The Kondo singlet evolves into a particular state with a fixed number of electrons in the quantum dot. Its relaxation time is shown to be sensitive only to the QD-charge dependence of the transmission probability in the detector, which implies that the phase information is erased in this conditional evolution process. We discuss implications of our observations in view of the possible experimental realization.Comment: Focus issue on "Interference in Mesoscopic Systems" of New J. Phy

Zone-plate focusing of Bose-Einstein condensates for atom optics and erasable high-speed lithography of quantum electronic components

We show that Fresnel zone plates, fabricated in a solid surface, can sharply focus atomic Bose-Einstein condensates that quantum reflect from the surface or pass through the etched holes. The focusing process compresses the condensate by orders of magnitude despite inter-atomic repulsion. Crucially, the focusing dynamics are insensitive to quantum fluctuations of the atom cloud and largely preserve the condensates' coherence, suggesting applications in passive atom-optical elements, for example zone plate lenses that focus atomic matter waves and light at the same point to strengthen their interaction. We explore transmission zone-plate focusing of alkali atoms as a route to erasable and scalable lithography of quantum electronic components in two-dimensional electron gases embedded in semiconductor nanostructures. To do this, we calculate the density profile of a two-dimensional electron gas immediately below a patch of alkali atoms deposited on the surface of the nanostructure by zone-plate focusing. Our results reveal that surface-induced polarization of only a few thousand adsorbed atoms can locally deplete the electron gas. We show that, as a result, the focused deposition of alkali atoms by existing zone plates can create quantum electronic components on the 50 nm scale, comparable to that attainable by ion beam implantation but with minimal damage to either the nanostructure or electron gas.Comment: 13 pages, 7 figure

Appreciative inquiry as a method of transforming identity and power in Pakistani women

This paper describes a three-year action research project that used Appreciative Inquiry to work with marginalised Pakistani women living in Sheffield. The research encountered many of the difficulties and dilemmas that have been previously identified in the theory and practice of Appreciative Inquiry. However, it also empowered the participants to develop critical thinking, particularly around issues of power and identity. Through generating authentic and untold stories, Appreciative Inquiry enabled participants to discuss, subvert and challenge the identities that had been constructed for them by sources of power within their community and culture. The paper describes the innovative application of Appreciative Inquiry, offers a theoretical response to criticisms of Appreciative Inquiry and suggests how it may be effective in enabling marginalised people to critically address issues of powe

Continuous Spectrum of Automorphism Groups and the Infraparticle Problem

This paper presents a general framework for a refined spectral analysis of a group of isometries acting on a Banach space, which extends the spectral theory of Arveson. The concept of continuous Arveson spectrum is introduced and the corresponding spectral subspace is defined. The absolutely continuous and singular-continuous parts of this spectrum are specified. Conditions are given, in terms of the transposed action of the group of isometries, which guarantee that the pure-point and continuous subspaces span the entire Banach space. In the case of a unitarily implemented group of automorphisms, acting on a $C^*$-algebra, relations between the continuous spectrum of the automorphisms and the spectrum of the implementing group of unitaries are found. The group of spacetime translation automorphisms in quantum field theory is analyzed in detail. In particular, it is shown that the structure of its continuous spectrum is relevant to the problem of existence of (infra-)particles in a given theory.Comment: 31 pages, LaTeX. As appeared in Communications in Mathematical Physic

Maximal regularity for non-autonomous equations with measurable dependence on time

In this paper we study maximal $L^p$-regularity for evolution equations with time-dependent operators $A$. We merely assume a measurable dependence on time. In the first part of the paper we present a new sufficient condition for the $L^p$-boundedness of a class of vector-valued singular integrals which does not rely on H\"ormander conditions in the time variable. This is then used to develop an abstract operator-theoretic approach to maximal regularity. The results are applied to the case of $m$-th order elliptic operators $A$ with time and space-dependent coefficients. Here the highest order coefficients are assumed to be measurable in time and continuous in the space variables. This results in an $L^p(L^q)$-theory for such equations for $p,q\in (1, \infty)$. In the final section we extend a well-posedness result for quasilinear equations to the time-dependent setting. Here we give an example of a nonlinear parabolic PDE to which the result can be applied.Comment: Application to a quasilinear equation added. Accepted for publication in Potential Analysi

Gut evacuation rate and grazing impact of the krill Thysanoessa raschii and T. inermis

Gut evacuation rates and ingestion rates were measured for the krill Thysanoessa raschii and T. inermis in Godthåbsfjord, SW Greenland. Combined with biomass of the krill community, the grazing potential on phytoplankton along the fjord was estimated. Gut evacuation rates were 3.9 and 2.3 h−1 for T. raschii and T. inermis, respectively. Ingestion rates were 12.2 ± 7.5 µg C mg C−1 day−1 (n = 4) for T. inermis and 4.9 ± 3.2 µg C mg C−1 day−1 (n = 4) for T. raschii, corresponding to daily rations of 1.2 and 0.5 % body carbon day−1. Clearance experiments conducted in parallel to the gut evacuation experiment gave similar results for ingestion rates and daily rations. Krill biomass was highest in the central part of the fjord’s length, with T. raschii dominating. Community grazing rates from krill and copepods were comparable; however, their combined impact was low, estimated as <1 % of phytoplankton standing stock being removed per day during this late spring study

The global dust SED: Tracing the nature and evolution of dust with DustEM

The Planck and Herschel missions are currently measuring the farIR-mm emission of dust, which combined with existing IR data, will for the first time provide the full SED of the galactic ISM dust emission with an unprecedented sensitivity and angular resolution. It will allow a systematic study of the dust evolution processes that affect the SED. Here we present a versatile numerical tool, DustEM, that predicts the emission and extinction of dust given their size distribution and their optical and thermal properties. In order to model dust evolution, DustEM has been designed to deal with a variety of grain types, structures and size distributions and to be able to easily include new dust physics. We use DustEM to model the dust SED and extinction in the diffuse interstellar medium at high-galactic latitude (DHGL), a natural reference SED. We present a coherent set of observations for the DHGL SED. The dust components in our DHGL model are (i) PAHs, (ii) amorphous carbon and (iii) amorphous silicates. We use amorphous carbon dust, rather than graphite, because it better explains the observed high abundances of gas-phase carbon in shocked regions of the interstellar medium. Using the DustEM model, we illustrate how, in the optically thin limit, the IRAS/Planck HFI (and likewise Spitzer/Herschel for smaller spatial scales) photometric band ratios of the dust SED can disentangle the influence of the exciting radiation field intensity and constrain the abundance of small grains relative to the larger grains. We also discuss the contributions of the different grain populations to the IRAS, Planck and Herschel channels. Such information is required to enable a study of the evolution of dust as well as to systematically extract the dust thermal emission from CMB data and to analyze the emission in the Planck polarized channels. The DustEM code described in this paper is publically available.Comment: accepted for publication in A&

Seeking legitimacy through CSR: Institutional Pressures and Corporate Responses of Multinationals in Sri Lanka

Arguably, the corporate social responsibility (CSR) practices of multinational enterprises (MNEs) are influenced by a wide range of both internal and external factors. Perhaps most critical among the exogenous forces operating on MNEs are those exerted by state and other key institutional actors in host countries. Crucially, academic research conducted to date offers little data about how MNEs use their CSR activities to strategically manage their relationship with those actors in order to gain legitimisation advantages in host countries. This paper addresses that gap by exploring interactions between external institutional pressures and firm-level CSR activities, which take the form of community initiatives, to examine how MNEs develop their legitimacy-seeking policies and practices. In focusing on a developing country, Sri Lanka, this paper provides valuable insights into how MNEs instrumentally utilise community initiatives in a country where relationship-building with governmental and other powerful non-governmental actors can be vitally important for the long-term viability of the business. Drawing on neo-institutional theory and CSR literature, this paper examines and contributes to the embryonic but emerging debate about the instrumental and political implications of CSR. The evidence presented and discussed here reveals the extent to which, and the reasons why, MNEs engage in complex legitimacy-seeking relationships with Sri Lankan institutions