An existence result for a semipositone problem with a sign changing weight

We establish an existence result on positive solution for a class of reaction-diffusion equation with semipositone structure. In particular, our results apply to the diffusive logistic equation with a class of sign changing weight and constant yield harvesting. We establish the result via the method of subsuper solutions

A discrete inhomogeneous model for the yeast cell cycle

We study the robustness and stability of the yeast cell regulatory network by using a general inhomogeneous discrete model. We find that inhomogeneity, on average, enhances the stability of the biggest attractor of the dynamics and that the large size of the basin of attraction is robust against changes in the parameters of inhomogeneity. We find that the most frequent orbit, which represents the cell-cycle pathway, has a better biological meaning than the one exhibited by the homogeneous model.Comment: 5 pages, 1 figur

Strategic analysis of the obstetric and gynaecological internship in Sudan

Background: The high expectations of the increasingly questioning society lays a great burden on the first line treating doctors in Sudan. This is particularly true in the obstetrics and gynaecology departments. The impact of training of the house-officer in surgical departments was not studied before in Sudan.The aim: To evaluate the gains in knowledge and skills of house-officers in the obstetrics and gynaecology departments as reflected by their activities and their opinions.Methodology: A prospective cohort carried in the period from May 2011 through June 2011. The data was collected from 200 house-officers. Their activities and duties as formulated by their seniors and supervisors and gains in knowledge and skills were noted.Results: All house-officers participated actively in the clinical diagnosis (history, physical examination and relevant investigations) and management of cases of antepartum and postpartum haemorrhages. Of them 186(93%) had duties not more than twice a week. However, 121(60.5%) shared training opportunities in units having seven or less peers. Also, 109(54.5%) had regular seminars and tutorials. In practice, 165(82.5%) performed evacuations, 158(79%) participated in normal deliveries, and 110(55%) were assisted in performing caesarean sections.Conclusion: The overall performance of house-officers in the department of obstetrics and gynaecology in Sudan is good. However, standards of training need to revisited to fill gabs in training if these young doctors are to be dispatched to rural hospital immediately after the internshipperiod.Key words: Internship, preregistration medical graduates duties, house-officers, obstetrics and gynaecology, medical education, and medical responsibility

A Framework to Synergize Partial Order Reduction with State Interpolation

We address the problem of reasoning about interleavings in safety verification of concurrent programs. In the literature, there are two prominent techniques for pruning the search space. First, there are well-investigated trace-based methods, collectively known as "Partial Order Reduction (POR)", which operate by weakening the concept of a trace by abstracting the total order of its transitions into a partial order. Second, there is state-based interpolation where a collection of formulas can be generalized by taking into account the property to be verified. Our main contribution is a framework that synergistically combines POR with state interpolation so that the sum is more than its parts

A Denotational Semantics for First-Order Logic

In Apt and Bezem [AB99] (see cs.LO/9811017) we provided a computational interpretation of first-order formulas over arbitrary interpretations. Here we complement this work by introducing a denotational semantics for first-order logic. Additionally, by allowing an assignment of a non-ground term to a variable we introduce in this framework logical variables. The semantics combines a number of well-known ideas from the areas of semantics of imperative programming languages and logic programming. In the resulting computational view conjunction corresponds to sequential composition, disjunction to ``don't know'' nondeterminism, existential quantification to declaration of a local variable, and negation to the ``negation as finite failure'' rule. The soundness result shows correctness of the semantics with respect to the notion of truth. The proof resembles in some aspects the proof of the soundness of the SLDNF-resolution.Comment: 17 pages. Invited talk at the Computational Logic Conference (CL 2000). To appear in Springer-Verlag Lecture Notes in Computer Scienc

Independence in CLP Languages

Studying independence of goals has proven very useful in the context of logic programming. In particular, it has provided a formal basis for powerful automatic parallelization tools, since independence ensures that two goals may be evaluated in parallel while preserving correctness and eciency. We extend the concept of independence to constraint logic programs (CLP) and prove that it also ensures the correctness and eciency of the parallel evaluation of independent goals. Independence for CLP languages is more complex than for logic programming as search space preservation is necessary but no longer sucient for ensuring correctness and eciency. Two additional issues arise. The rst is that the cost of constraint solving may depend upon the order constraints are encountered. The second is the need to handle dynamic scheduling. We clarify these issues by proposing various types of search independence and constraint solver independence, and show how they can be combined to allow dierent optimizations, from parallelism to intelligent backtracking. Sucient conditions for independence which can be evaluated \a priori" at run-time are also proposed. Our study also yields new insights into independence in logic programming languages. In particular, we show that search space preservation is not only a sucient but also a necessary condition for ensuring correctness and eciency of parallel execution

An assertion language for constraint logic programs

In an advanced program development environment, such as that discussed in the introduction of this book, several tools may coexist which handle both the program and information on the program in different ways. Also, these tools may interact among themselves and with the user. Thus, the different tools and the user need some way to communicate. It is our design principie that such communication be performed in terms of assertions. Assertions are syntactic objects which allow expressing properties of programs. Several assertion languages have been used in the past in different contexts, mainly related to program debugging. In this chapter we propose a general language of assertions which is used in different tools for validation and debugging of constraint logic programs in the context of the DiSCiPl project. The assertion language proposed is parametric w.r.t. the particular constraint domain and properties of interest being used in each different tool. The language proposed is quite general in that it poses few restrictions on the kind of properties which may be expressed. We believe the assertion language we propose is of practical relevance and appropriate for the different uses required in the tools considered

Financing essential HIV services: a new economic agenda.

Anna Vassall and colleagues discuss the need for, and challenges facing, innovative and sustainable financing of the HIV response. Please see later in the article for the Editors' Summary

Constraint rule-based programming of norms for electronic institutions

Peer reviewedPostprin