Study of solid 4He in two dimensions. The issue of zero-point defects and study of confined crystal

Defects are believed to play a fundamental role in the supersolid state of 4He. We report on studies by exact Quantum Monte Carlo (QMC) simulations at zero temperature of the properties of solid 4He in presence of many vacancies, up to 30 in two dimensions (2D). In all studied cases the crystalline order is stable at least as long as the concentration of vacancies is below 2.5%. In the 2D system for a small number, n_v, of vacancies such defects can be identified in the crystalline lattice and are strongly correlated with an attractive interaction. On the contrary when n_v~10 vacancies in the relaxed system disappear and in their place one finds dislocations and a revival of the Bose-Einstein condensation. Thus, should zero-point motion defects be present in solid 4He, such defects would be dislocations and not vacancies, at least in 2D. In order to avoid using periodic boundary conditions we have studied the exact ground state of solid 4He confined in a circular region by an external potential. We find that defects tend to be localized in an interfacial region of width of about 15 A. Our computation allows to put as upper bound limit to zero--point defects the concentration 0.003 in the 2D system close to melting density.Comment: 17 pages, accepted for publication in J. Low Temp. Phys., Special Issue on Supersolid

Weber and church governance: religious practice and economic activity

The debate about the relationship between religion and economic activity in the wake of Weber has been cast largely in terms of belief and values. This article suggests an alternative focus on practice. It argues that taken for granted practices of church governance formed to-hand resources for the organization of economic activity. The argument is developed through an examination of the historical development of church governance practices in the Presbyterian Church of Scotland, with particular emphasis on the way in which theological belief gave rise to practices of accountability and record keeping. In turn such practices contributed to a ‘culture of organization’ which had implications for economic activity. A focus on governance practices can help to illuminate enduring patterns of difference in the organization of economic activity

The instrument suite of the European Spallation Source

An overview is provided of the 15 neutron beam instruments making up the initial instrument suite of the European Spallation Source (ESS), and being made available to the neutron user community. The ESS neutron source consists of a high-power accelerator and target station, providing a unique long-pulse time structure of slow neutrons. The design considerations behind the time structure, moderator geometry and instrument layout are presented. The 15-instrument suite consists of two small-angle instruments, two reflectometers, an imaging beamline, two single-crystal diffractometers; one for macromolecular crystallography and one for magnetism, two powder diffractometers, and an engineering diffractometer, as well as an array of five inelastic instruments comprising two chopper spectrometers, an inverse-geometry single-crystal excitations spectrometer, an instrument for vibrational spectroscopy and a high-resolution backscattering spectrometer. The conceptual design, performance and scientific drivers of each of these instruments are described. All of the instruments are designed to provide breakthrough new scientific capability, not currently available at existing facilities, building on the inherent strengths of the ESS long-pulse neutron source of high flux, flexible resolution and large bandwidth. Each of them is predicted to provide world-leading performance at an accelerator power of 2 MW. This technical capability translates into a very broad range of scientific capabilities. The composition of the instrument suite has been chosen to maximise the breadth and depth of the scientific impact o

Electrochemotherapy in the treatment of metastatic malignant melanoma:a prospective cohort study by InspECT

Electrochemotherapy (ECT) is an effective local treatment for cutaneous metastasis. Treatment involves the administration of chemotherapeutic drugs followed by delivery of electrical pulses to the tumour. The aim of this study was to investigate the effectiveness of ECT in cutaneous metastases of melanoma and to identify factors which affect (beneficially or adversely) the outcome

Electronically driven phase transitions in a quasi-one-dimensional adsorbate system

A quasi-1D system is prepared using the Pt(110) surface as a template. The electronic surface resonance structure is studied by angle-resolved photoemission spectroscopy for the clean surface as well as for different Bromine coverages. A Fermi surface mapping reveals saddle points at the Fermi level in the interior of the surface Brillouin zone. Correspondingly, a maximum in the static response function chi(q, 0) at the connecting vector q is expected. With 1/2G(x) < q < 2/3G(x) one observes indeed a 3-fold periodicity around defects and a 2-fold periodicity at low temperature for I similar to(Br) = 0.5 ML. Cooling of a defect-free c(2x2)-Br/Pt(110) preparation counter-intuitively results in a loss of long-range order. Motivated by DFT calculations this is attributed to an anomalous order-order phase transition into the (2x1) phase accompanied by intense, strongly anisotropic fluctuations within a temperature range of similar to 200 K. The peculiar behaviour is rationalised in terms of a competition between inter-adsorbate repulsion and an adsorbate triggered 2k(F) interaction in the substrate