Energy potential of a tidal fence deployed near a coastal headland

Enhanced tidal streams close to coastal headlands appear to present ideal locations for the deployment of tidal energy devices. In this paper, the power potential of tidal streams near an idealized coastal headland with a sloping seabed is investigated using a near-field approximation to represent a tidal fence, i.e. a row of tidal devices, in a two-dimensional depth-averaged numerical model. Simulations indicate that the power extracted by the tidal fence is limited because the flow will bypass the fence, predominantly on the ocean side, as the thrust applied by the devices increases. For the dynamic conditions, fence placements and headland aspect ratios considered, the maximum power extracted at the fence is not related in any obvious way to the local undisturbed kinetic flux or the natural rate of energy dissipation due to bed friction (although both of these have been used in the past to predict the amount of power that may be extracted). The available power (equal to the extracted power net of vertical mixing losses in the immediate wake of devices) is optimized for devices with large area and small centre-to-centre spacing within the fence. The influence of energy extraction on the natural flow field is assessed relative to changes in the M2 component of elevation and velocity, and residual bed shear stress and tidal dispersion

Modelling tidal energy extraction in a depth-averaged coastal domain

An extension of actuator disc theory is used to describe the properties of a tidal energy device, or row of tidal energy devices, within a depth-averaged numerical model. This approach allows a direct link to be made between an actual tidal device and its equivalent momentum sink in a depth-averaged domain. Extended actuator disc theory also leads to a measure of efficiency for an energy device in a tidal stream of finite Froude number, where efficiency is defined as the ratio of power extracted by one or more tidal devices to the total power removed from the tidal stream. To demonstrate the use of actuator disc theory in a depth-averaged model, tidal flow in a simple channel is approximated using the shallow water equations and the results are compared with the published analytical solutions. © 2010 © The Institution of Engineering and Technology

A logarithmic-depth quantum carry-lookahead adder

We present an efficient addition circuit, borrowing techniques from the classical carry-lookahead arithmetic circuit. Our quantum carry-lookahead (QCLA) adder accepts two n-bit numbers and adds them in O(log n) depth using O(n) ancillary qubits. We present both in-place and out-of-place versions, as well as versions that add modulo 2^n and modulo 2^n - 1. Previously, the linear-depth ripple-carry addition circuit has been the method of choice. Our work reduces the cost of addition dramatically with only a slight increase in the number of required qubits. The QCLA adder can be used within current modular multiplication circuits to reduce substantially the run-time of Shor's algorithm.Comment: 21 pages, 4 color figure

The Case for UHP Conditions in the Cuaba Terrane, Río San Juan Metamorphic Complex, Dominican Republic

From the Cuaba terrane in northern Dominican Republic. Ultrahigh pressure (UHP) conditions are indicated for the Cuaba terrane on the basis of phase relationships in garnet-bearing ultramafic rock. Dikes and orthocumulate textures indicate a magmatic origin. Mineral assemblages define a line of descent controlled by fractional crystallization. The original estimate of the magmatic conditions (P>3.4GPa, T>1550°C) was inferred previously from available high-P melting experiments in the CMAS system and high-P experimental determination of the sapphirine-out reaction in the MAS system. Revised estimates of magmatic conditions (P>3.2GPa, T>1500°C) take into account the influence of other components, especially Fe. We propose an origin in the mantle-wedge above a subduction zone. The rock was delivered to the subduction zone by forced convection in the mantle wedge (corner-flow), coupled with erosion of the hanging wall. Thermobarometry indicates >850°C and >3.4GPa when the ultramafic rock was incorporated into eclogite (deep-subducted oceanic crust). Evidence for UHP conditions in the retrograded eclogite is not obvious. Two types of symplectic intergrowths, plagioclase + clinopyroxene (Sym-I) and plagioclase + epidote (Sym-II), are interpreted as the products of the decomposition of two types of omphacite, Omp-I and Omp-II. Theoretically, Omp-II formed as the result of a retrograde reaction of the form, Omp-II + coesite = Omp-I + kyanite + /- garnet, according to which the maximum pressure for Omp-II is between ~2.8GPa (~850°C) and ~4.2GPa (~950°C), consistent with subsolidus conditions for the garnet-bearing ultramafic rocks. For eclogite, the highest-pressure mineral assemblage would have been Omp-I + kyanite + garnet + coesite

SUSY-Breaking Parameters from RG Invariants at the LHC

We study Renormalization Group invariant (RGI) quantities in the Minimal Supersymmetric Standard Model and show that they are a powerful and simple instrument for testing high scale models of supersymmetry (SUSY)-breaking. For illustration, we analyze the frameworks of minimal and general gauge mediated (MGM and GGM) SUSY-breaking, with additional arbitrary soft Higgs mass parameters at the messenger scale. We show that if a gaugino and two first generation sfermion soft masses are determined at the LHC, the RGIs lead to MGM sum rules that yield accurate predictions for the other gaugino and first generation soft masses. RGIs can also be used to reconstruct the fundamental MGM parameters (including the messenger scale), calculate the hypercharge D-term, and find relationships among the third generation and Higgs soft masses. We then study the extent to which measurements of the full first generation spectrum at the LHC may distinguish different SUSY-breaking scenarios. In the case of MGM, although most deviations violate the sum rules by more than estimated experimental errors, we find a 1-parameter family of GGM models that satisfy the constraints and produce the same first generation spectrum. The GGM-MGM degeneracy is lifted by differences in the third generation masses and the messenger scales.Comment: (v1) 30 pages; (v2) mislabeling in figs 2 and 3 corrected, version accepted for publication in Phys. Rev.

Primary health care in the South African context - medical students' perspectives

Background Both the South African Department of Health and the University of Cape Town (UCT) have committed to the primary health care (PHC) approach, which is best captured in the Declaration of Alma Ata. If medical students are to be trained in the PHC approach, it is important that they not only have a good understanding of this approach, but are also aware of the social, economic and political context that they will be working in when they have qualified, so that they can develop realistic expectations of their careers as doctors. From research that was conducted at UCT, this article covers UCT medical students' views of health care in South Africa, including their perceptions of the applicability and implementation of the PHC approach for South Africa, and their perceptions of how the South African government features in issues of health and the PHC approach. Methods Mixed-methods were used, but this article will focus on the qualitative data gathered. One hundred and seventeen medical students (years one to four) were purposively selected to be involved in focus groups and interviews. These focus groups were conducted between February 2004 and March 2005. Results Students acknowledged that the state of health care in South Africa needs to change and showed an awareness of the role that South Africa's history of apartheid has played in the state of health care in these areas and the existence of inequity. They however did not agree on the applicability of the PHC approach to the South African situation. The PHC approach is seen not to be working in South Africa because of various obstacles to its implementation and success, such as disorganisation within the health system, and a lack of infrastructure, finances and resources. There seemed to be a general understanding amongst the students that they will have been trained in the PHC approach but then will be working within a system that has possibly not undergone similar changes. Students agreed on the important role of government in PHC, some maintaining that the government should be at the forefront of its implementation, but were generally dissatisfied with the role the South African government is currently playing in health care. Conclusion It is encouraging that students are generally aware of the reality of health care in South Africa and of the fact that more change needs to take place. However, it may be that many students who have a limited understanding of the impact that apartheid had on health care provision in South Africa, and this could then impact on students' perceptions of the applicability of the current PHC approach for South Africa. Students' views that the PHC approach has not been fully implemented in South Africa are a concern, as it is these types of views that are likely to cause students to lose confidence in the PHC approach, and will most likely widen the disjuncture between theory of the approach and the reality of its implementation. Regarding the political dynamics of the PHC approach, students do need to be aware of political factors that can impact on the success of this approach. Discussion around and research into the social, economic and political context of health care and medical education has particular relevance for South Africa, and it is vital that students' views on these issues are acknowledged so that areas for change can be identified and addressed