Asymptotic decay of pair correlations in a Yukawa fluid

We analyse the $r \to \infty$ asymptotic decay of the total correlation function, $h(r)$, for a fluid composed of particles interacting via a (point) Yukawa pair potential. Such a potential provides a simple model for dusty plasmas. The asymptotic decay is determined by the poles of the liquid structure factor in the complex plane. We use the hypernetted-chain closure to the Ornstein-Zernike equation to determine the line in the phase diagram, well-removed from the freezing transition line, where crossover occurs in the ultimate decay of $h(r)$, from monotonic to damped oscillatory. We show: i) crossover takes place via the same mechanism (coalescence of imaginary poles) as in the classical one-component plasma and in other models of Coulomb fluids and ii) leading-order pole contributions provide an accurate description of $h(r)$ at intermediate distances $r$ as well as at long range.Comment: 5 pages, 3 figure

The floristics of Sand Forest in northern KwaZulu-Natal, South Africa

We use multivariate analyses (ordination and classification) to assess both the floristic uniqueness of the woody vegeation of Sand Forest in relation to a range of other forest types in the region, and the range of variation within Sand Forest. Two broad Sand Forest subtypes and related Ecotonal Forests are described and grouped under the term Tropical Dry Forest, distinct from all evergreen forests in South Africa. Sand Forest, a dry semi-deciduous type in northeastern KwaZulu-Natals defined by the presence of the canopy dominant Cleistanthus schlechteri as well as Hymenocardia ulmoides, Psydrax fragrantissima, Croton pseudopulchellus and  Drypetes arguta. Sand Forests form a cohesive group in both DCA and TWINSPAN analyses, with similar composition of canopy dominants at sampled sites. This implies that ecological funcioning is similar across the geographical range in northeastern KwaZulu-Natal. However, turnover of subdominant species between recognisable Sand Forest types emphasizes the need to conserve the full range of extant forests

Strategic Review of Tropical Fisheries Management

This project addresses the constraints to tropical fisheries development with sustainable exploitation through a strategic assessment of tropical fisheries management with the following purposes: (1) To evaluate relevant research methods for the development of assessment models appropriate to the circumstances of tropical coastal fisheries; and (2) To evaluate the utility of existing strategies for the implementation of management advice. The report consists of three substantive chapters. Chapter 2 contains a detailed socio-economic assessment of various instruments and implementation strategies applicable to tropical capture fisheries. In Chapter 3, a detailed assessment of the fisheries for tropical large marine ecosystems has been conducted using a technique developed by FAO (Granger & Garcia 1996). The data used were the FAO statistics published regularly by FAO. This analysis has been conducted for each of the tropical large marine ecosystems and indicates that there is the potential for increased fishing in a number of these ecosystems. One of the clear requirements identified in Chapter 2 and implicit in Chapter 3, is that there is a significant need for simple and robust fisheries assessment methods which can estimate the potential of a particular resource, its capacity in terms of the level of fishing effort and its current status ie whether it is currently exploited sustainably or not. In Chapter 4, these problems are addressed directly and, using two approaches, significant simplification of fishery methods is developed. In the first approach, simple empirical relationships between the life history parameters of a species are used to develop models of potential yield which can be determined by a simple assessment of fish growth. In the second approach, optimal life history theory is applied to the key demographic parameters of exploited fish populations and using estimates of the Beverton & Holt invariants a significant simplifying of the basic stock assessment equations is developed

Change and Aging Senescence as an adaptation

Understanding why we age is a long-lived open problem in evolutionary biology. Aging is prejudicial to the individual and evolutionary forces should prevent it, but many species show signs of senescence as individuals age. Here, I will propose a model for aging based on assumptions that are compatible with evolutionary theory: i) competition is between individuals; ii) there is some degree of locality, so quite often competition will between parents and their progeny; iii) optimal conditions are not stationary, mutation helps each species to keep competitive. When conditions change, a senescent species can drive immortal competitors to extinction. This counter-intuitive result arises from the pruning caused by the death of elder individuals. When there is change and mutation, each generation is slightly better adapted to the new conditions, but some older individuals survive by random chance. Senescence can eliminate those from the genetic pool. Even though individual selection forces always win over group selection ones, it is not exactly the individual that is selected, but its lineage. While senescence damages the individuals and has an evolutionary cost, it has a benefit of its own. It allows each lineage to adapt faster to changing conditions. We age because the world changes.Comment: 19 pages, 4 figure

Propagation of Exchange Bias in CoFe/FeMn/CoFe Trilayers

CoFe/FeMn, FeMn/CoFe bilayers and CoFe/FeMn/CoFe trilayers were grown in magnetic field and at room temperature. The exchange bias field $H_{eb}$ depends strongly on the order of depositions and is much higher at CoFe/FeMn than at FeMn/CoFe interfaces. By combining the two bilayer structures into symmetric CoFe/FeMn($t_\mathrm{FeMn}$)/CoFe trilayers, $H_{eb}^t$ and $H_{eb}^b$ of the top and bottom CoFe layers, respectively, are both enhanced. Reducing $t_\mathrm{FeMn}$ of the trilayers also results in enhancements of both $H_{eb}^b$ and $H_{eb}^t$. These results evidence the propagation of exchange bias between the two CoFe/FeMn and FeMn/CoFe interfaces mediated by the FeMn antiferromagnetic order

Fault tolerant actuation for dorado class, AUVS.

This paper describes a new control surface actuating design for the Monterey Bay Aquarium Research Institute (MBARI) Dorado class AUVs. The intent was to increase reliability as part of obtaining the goal to greatly increase access to the Arctic Ocean. The new actuating mechanism is part of creating a robust and economical solution towards increased reliability and fault tolerance. Specifically, as part of developing the ALTEX Autonomous Underwater Vehicle (AUV) for Arctic research with basin scale endurance, the concept for under ice missions was redundancy in critical areas. As the development of the DORADO systems progressed from the original ALTEX concepts, added drivers came from the operations group looking for more useable volume in the aft section. The DORADO vehicle is guided using an articulated tail steering section. The tail is comprised of a ducted propeller acting as control surfaces and propulsion, in contrast with the more traditional fin control surfaces used by most vehicles. This approach was taken to be more robust to impacts as experience using Odyssey IB vehicles showed the control surfaces damaged during launch and recovery were the number one failure by far. As predicted by analysis the design also improved propulsion efficiency. Also worth noting is that this entire tail system stays inside the 21” diameter of the main vehicle body. The new system being developed is unique in that it keeps all of the key propulsion and actuators but eliminates the current gimbaled tail through the use of what we refer to as a false center. While several new components are being developed, the objective is to leverage the existing technology to the degree possible and allow for an inexpensive as well as direct swap into existing systems. The new steering mechanism uses a Three Actuator False Center Control solution. The design was first modeled and tested for feasibility. After passing the preliminaries, the decision was made to build a full-scale sea going unit. We now have that system built and in bench testing, ready to swap in for at sea testing in the very near future. We’ve already demonstrated that the new design offers a superior use of space yielding more useable volume for other equipment. The model demonstrated the added redundancy that we will duplicate at sea. We believe the design is very robust and has a broad range of uses in long duration unattended operations where fault situations must be dealt with by the autonomous system. In this paper we will discuss our progress to date, our current test efforts, and the near term future uses of this new control section for DORADO science vehicles.Peer Reviewe

Longevity and mortality of cats attending primary care veterinary practices in England

Enhanced knowledge on longevity and mortality in cats should support improved breeding, husbandry, clinical care and disease prevention strategies. The VetCompass research database of primary care veterinary practice data offers an extensive resource of clinical health information on companion animals in the UK. This study aimed to characterise longevity and mortality in cats, and to identify important demographic risk factors for compromised longevity. Crossbred cats were hypothesised to live longer than purebred cats. Descriptive statistics were used to characterise the deceased cats. Multivariable linear regression methods investigated risk factor association with longevity in cats that died at or after 5 years of age. From 118,016 cats attending 90 practices in England, 4009 cats with confirmed deaths were randomly selected for detailed study. Demographic characterisation showed that 3660 (91.7%) were crossbred, 2009 (50.7%) were female and 2599 (64.8%) were neutered. The most frequently attributed causes of mortality in cats of all ages were trauma (12.2%), renal disorder (12.1%), non-specific illness (11.2%), neoplasia (10.8%) and mass lesion disorders (10.2%). Overall, the median longevity was 14.0 years (interquartile range [IQR] 9.0–17.0; range 0.0–26.7). Crossbred cats had a higher median longevity than purebred cats (median [IQR] 14.0 years [9.1–17.0] vs 12.5 years [6.1–16.4]; P \u3c0.001), but individual purebred cat breeds varied substantially in longevity. In cats dying at or after 5 years (n = 3360), being crossbred, having a lower bodyweight, and being neutered and non-insured were associated with increased longevity. This study described longevity in cats and identified important causes of mortality and breed-related associations with compromised longevity