Numerical equilibrium analysis for structured consumer resource models

In this paper, we present methods for a numerical equilibrium and stability analysis for models of a size structured population competing for an unstructured resource. We concentrate on cases where two model parameters are free, and thus existence boundaries for equilibria and stability boundaries can be defined in the (two-parameter) plane. We numerically trace these implicitly defined curves using alternatingly tangent prediction and Newton correction. Evaluation of the maps defining the curves involves integration over individual size and individual survival probability (and their derivatives) as functions of individual age. Such ingredients are often defined as solutions of ODE, i.e., in general only implicitly. In our case, the right-hand sides of these ODE feature discontinuities that are caused by an abrupt change of behavior at the size where juveniles are assumed to turn adult. So, we combine the numerical solution of these ODE with curve tracing methods. We have implemented the algorithms for “Daphnia consuming algae” models in C-code. The results obtained by way of this implementation are shown in the form of graphs

Cannibalism as a life boat mechanism

Under certain conditions a cannibalistic population can survive when food for the adults is too scarce to support a non-cannibalistic population. Cannibalism can have this lifeboat effect if (i) the juveniles feed on a resource inaccessible to the adults; and (ii) the adults are cannibalistic and thus incorporate indirectly the inaccessible resource. Using a simple model we conclude that the mechanism works when, at low population densities, the average yield, in terms of new offspring, due to the energy provided by one cannibalized juvenile is larger than one

Forensic psychiatry in Africa: prospects and challenges

Forensic Psychiatry has a history that dates back almost two thousand years, and has evolved into a recognised discipline with a robust background of scientific enquiry, mostly because mental health care has always had an important interface with the law. 1 Nevertheless, even in the developed world there are differences between countries with respect to the extent forensic mental health services have developed. This has been exacerbated by the differences in legal systems, resources and priorities in each country. Consequently comparisons and cooperation between forensic psychiatrists internationally has been difficult. 2-4 In Africa, which is the second largest and most populous continent and containing an immense diversity of languages, religious traditions, ethnic groups and sociopolitical systems forensic psychiatry has largely remained underdeveloped within the context of a pervasive neglect in the provision of mental health services. 5 The situation is compounded by the dearth of information about forensic services on the continent. As described by an eminent African psychiatrist, “the practice of forensic psychiatry in Africa is shrouded in both mystery and confusion”. 6 In addition to the lack of appropriate facilities, most countries in Africa have, on average, one psychiatrist per one million inhabitants. Moreover many psychiatrists have migrated to developed countries, leaving a small number of mental health professionals burdened with large numbers of patients. 6 In most countries there are few coordinated initiatives to involve all stakeholders, such as the police, departments of justice, prisons and hospitals, in the development of forensic mental health services

Implementation conditions for diet and physical activity interventions and policies : an umbrella review

BACKGROUND: This umbrella review aimed at identifying evidence-based conditions important for successful implementation of interventions and policies promoting a healthy diet, physical activity (PA), and a reduction in sedentary behaviors (SB). In particular, we examined if the implementation conditions identified were intervention-specific or policy-specific. This study was undertaken as part of the DEterminants of DIet and Physical Activity (DEDIPAC) Knowledge Hub, a joint action as part of the European Joint Programming Initiative a Healthy Diet for a Healthy Life. METHODS: A systematic review of reviews and stakeholder documents was conducted. Data from nine scientific literature databases were analyzed (95 documents met the inclusion criteria). Additionally, published documentation of eight major stakeholders (e.g., World Health Organization) were systematically searched (17 documents met the inclusion criteria). The RE-AIM framework was used to categorize elicited conditions. Across the implementation conditions 25 % were identified in at least four documents and were subsequently classified as having obtained sufficient support. RESULTS: We identified 312 potential conditions relevant for successful implementation; 83 of these received sufficient support. Using the RE-AIM framework eight implementation conditions that obtained support referred to the reach in the target population; five addressed efficacy of implementation processes; 24 concerned adoption by the target staff, setting, or institutions; 43 referred to consistency, costs, and adaptations made in the implementation process; three addressed maintenance of effects over time. The vast majority of implementation conditions (87.9 %; 73 of 83) were supported by documents referring to both interventions and policies. There were seven policy-specific implementation conditions, which focused on increasing complexities of coexisting policies/legal instruments and their consequences for implementation, as well as politicians' collaboration in implementation. CONCLUSIONS: The use of the proposed list of 83 conditions for successful implementation may enhance the implementation of interventions and policies which pursue identification of the most successful actions aimed at improving diet, PA and reducing SB

Levels of cafestol, kahweol, and related diterpenoids in wild species of the coffee plant coffea

Abstract Specific fatty acids and sterols in food composites from seven countries were analyzed. In the 1960s, groups of 8 to 49 men from 16 cohorts, ages 40–59 years and living in the United States, Finland, the Netherlands, Italy, Greece, the former Yugoslavia, or Japan recorded their food intake. In 1987, we collected food composites representing the average food intake per cohort sample in the 1960s. The foods were transported to the Netherlands, pooled, and centrally analyzed for energy, total fat, 42 fatty acids, cholesterol, and four plant sterols. The fat content ranged from 12% of total daily energy in the Tanushimaru, Japan, cohort to 50% in the U.S. cohort sample, and the polyunsaturated to saturated fat ratio ranged from 0.17 in the east Finland cohort to 1.2 in Tanushimaru. The amount oftransfatty acids with 16 or 18 carbon atoms varied between 0.2 g/day in Corfu, Greece, and 8.6 g/day in Zutphen, Netherlands, and that of -linolenic acid between 0.8 g/day in Rome and 2.5 g/day in east Finland. The sum of eicosapentaenoic and docosahexanoic acid ranged from 0.1 (U.S. railroad) to 2.0 g/day (Ushibuka, Japan), and phytosterols from 170 (U.S. railroad) to 358 mg/day (Corfu, Greece). Thus the intake of various fatty acids and sterols with potential relevance for coronary heart disease occurrence varied 10-fold or more between cohorts. Our data can be used to generate new hypotheses about the causes of differences in incidence of diseases between countries

Random solids and random solidification: What can be learned by exploring systems obeying permanent random constraints?

In many interesting physical settings, such as the vulcanization of rubber, the introduction of permanent random constraints between the constituents of a homogeneous fluid can cause a phase transition to a random solid state. In this random solid state, particles are permanently but randomly localized in space, and a rigidity to shear deformations emerges. Owing to the permanence of the random constraints, this phase transition is an equilibrium transition, which confers on it a simplicity (at least relative to the conventional glass transition) in the sense that it is amenable to established techniques of equilibrium statistical mechanics. In this Paper I shall review recent developments in the theory of random solidification for systems obeying permanent random constraints, with the aim of bringing to the fore the similarities and differences between such systems and those exhibiting the conventional glass transition. I shall also report new results, obtained in collaboration with Weiqun Peng, on equilibrium correlations and susceptibilities that signal the approach of the random solidification transition, discussing the physical interpretation and values of these quantities both at the Gaussian level of approximation and, via a renormalization-group approach, beyond.Comment: Paper presented at the "Unifying Concepts in Glass Physics" workshop, International Centre for Theoretical Physics, Trieste, Italy (September 15-18, 1999

Universality and its Origins at the Amorphous Solidification Transition

Systems undergoing an equilibrium phase transition from a liquid state to an amorphous solid state exhibit certain universal characteristics. Chief among these are the fraction of particles that are randomly localized and the scaling functions that describe the order parameter and (equivalently) the statistical distribution of localization lengths for these localized particles. The purpose of this Paper is to discuss the origins and consequences of this universality, and in doing so, three themes are explored. First, a replica-Landau-type approach is formulated for the universality class of systems that are composed of extended objects connected by permanent random constraints and undergo amorphous solidification at a critical density of constraints. This formulation generalizes the cases of randomly cross-linked and end-linked macromolecular systems, discussed previously. The universal replica free energy is constructed, in terms of the replica order parameter appropriate to amorphous solidification, the value of the order parameter is obtained in the liquid and amorphous solid states, and the chief universal characteristics are determined. Second, the theory is reformulated in terms of the distribution of local static density fluctuations rather than the replica order parameter. It is shown that a suitable free energy can be constructed, depending on the distribution of static density fluctuations, and that this formulation yields precisely the same conclusions as the replica approach. Third, the universal predictions of the theory are compared with the results of extensive numerical simulations of randomly cross-linked macromolecular systems, due to Barsky and Plischke, and excellent agreement is found.Comment: 10 pages, including 3 figures (REVTEX

Daphnia revisited: Local stability and bifurcation theory for physiologically structured population models explained by way of an example

We consider the interaction between a general size-structured consumer population and an unstructured resource. We show that stability properties and bifurcation phenomena can be understood in terms of solutions of a system of two delay equations (a renewal equation for the consumer population birth rate coupled to a delay differetial equation for the resource concentration). As many results for such systems are available, we can draw rigorous conclusions concerning dynamical behaviour from an analysis of a characteristic equation. We derive the characteristic equation for a fairly general class of population models, including those based on the Kooijman-Metz Daphnia model and a model introduced by Gurney-Nisbet and Jones et al., and next obtain various ecological insights by analytical or numerical studies of special cases