Administrative aspects of poliomyelitis in isolation hospitals

No Abstrac

Epimorphism surjectivity in varieties of Heyting algebras

It was shown recently that epimorphisms need not be surjective in a variety K of Heyting algebras, but only one counter-example was exhibited in the literature until now. Here, a continuum of such examples is identified, viz. the variety generated by the Rieger-Nishimura lattice, and all of its (locally finite) subvarieties that contain the original counter-example K. It is known that, whenever a variety of Heyting algebras has finite depth, then it has surjective epimorphisms. In contrast, we show that for every integer n greater or equal than 2, the variety of all Heyting algebras of width at most n has a non-surjective epimorphism. Within the so-called Kuznetsov-Gerciu variety (i.e., the variety generated by finite linear sums of one-generated Heyting algebras), we describe exactly the subvarieties that have surjective epimorphisms. This yields new positive examples, and an alternative proof of epimorphism surjectivity for all varieties of Goedel algebras. The results settle natural questions about Beth-style definability for a range of intermediate logics

Embedding Kozen-Tiuryn Logic into Residuated One-Sorted Kleene Algebra with Tests

Kozen and Tiuryn have introduced the substructural logic $\mathsf{S}$ for reasoning about correctness of while programs (ACM TOCL, 2003). The logic $\mathsf{S}$ distinguishes between tests and partial correctness assertions, representing the latter by special implicational formulas. Kozen and Tiuryn's logic extends Kleene altebra with tests, where partial correctness assertions are represented by equations, not terms. Kleene algebra with codomain, $\mathsf{KAC}$, is a one-sorted alternative to Kleene algebra with tests that expands Kleene algebra with an operator that allows to construct a Boolean subalgebra of tests. In this paper we show that Kozen and Tiuryn's logic embeds into the equational theory of the expansion of $\mathsf{KAC}$ with residuals of Kleene algebra multiplication and the upper adjoint of the codomain operator

Epimorphisms in varieties of subidempotent residuated structures

A commutative residuated lattice A is said to be subidempotent if the lower bounds of its neutral element e are idempotent (in which case they naturally constitute a Brouwerian algebra A*). It is proved here that epimorphisms are surjective in a variety K of such algebras A (with or without involution), provided that each finitely subdirectly irreducible algebra B in K has two properties: (1) B is generated by lower bounds of e, and (2) the poset of prime filters of B* has finite depth. Neither (1) nor (2) may be dropped. The proof adapts to the presence of bounds. The result generalizes some recent findings of G. Bezhanishvili and the first two authors concerning epimorphisms in varieties of Brouwerian algebras, Heyting algebras and Sugihara monoids, but its scope also encompasses a range of interesting varieties of De Morgan monoids

Natural resource wars in the shadow of the future: Explaining spatial dynamics of violence during civil war

Previous studies on natural resources and civil wars find that the presence of natural resources increases both civil conflict risk and duration. At the same time, belligerents often cooperate over resource extraction, suggesting a temporal variation in the contest over this subnational space. This study argues that parties fight over natural resources primarily when they expect that the conflict is about to end, as the importance of controlling them increases in the post-conflict setting. In contrast, belligerents that anticipate a long war have incentives to avoid fighting near natural resources since excessive violence will hurt the extraction, trade, and subsequent taxation that provide conflict actors with income from the resource. We test our argument using yearly and monthly grid-cell-level data on African civil conflicts for the period 1989–2008 and find support for our expected spatial variation. Using whether negotiations are underway as an indicator about warring parties’ expectations on conflict duration, we find that areas with natural resources in general experience less intense fighting than other areas, but during negotiations these very areas witness most of the violence. We further find that the spatial shift in violence occurs immediately when negotiations are opened. A series of difference-in-difference estimations show a visible shift of violence towards areas rich in natural resources in the first three months after parties have initiated talks. Our findings are relevant for scholarship on understanding and predicting the trajectories of micro-level civil conflict violence, and for policymakers seeking to prevent peace processes being derailed

Ultra-conformal drawn-on-skin electronics for multifunctional motion artifact-free sensing and point-of-care treatment

An accurate extraction of physiological and physical signals from human skin is crucial for health monitoring, disease prevention, and treatment. Recent advances in wearable bioelectronics directly embedded to the epidermal surface are a promising solution for future epidermal sensing. However, the existing wearable bioelectronics are susceptible to motion artifacts as they lack proper adhesion and conformal interfacing with the skin during motion. Here, we present ultra-conformal, customizable, and deformable drawn-on-skin electronics, which is robust to motion due to strong adhesion and ultra-conformality of the electronic inks drawn directly on skin. Electronic inks, including conductors, semiconductors, and dielectrics, are drawn on-demand in a freeform manner to develop devices, such as transistors, strain sensors, temperature sensors, heaters, skin hydration sensors, and electrophysiological sensors. Electrophysiological signal monitoring during motion shows drawn-on-skin electronics' immunity to motion artifacts. Additionally, electrical stimulation based on drawn-on-skin electronics demonstrates accelerated healing of skin wounds. Designing efficient wearable bioelectronics for health monitoring, disease prevention, and treatment, remains a challenge. Here, the authors demonstrate an ultra-conformal, customizable and deformable drawn-on-skin electronics which is robust to motion artifacts and resistant to physical damage

n Studie van die vloei deur lemroosters

Proefskrif (Ph. D. Ing.) -- Universiteit van Stellenbosch, 1966.Full text to be digitised and attached to bibliographic record

Elementary equivalence in positive logic via prime products

We introduce prime products as a generalization of ultraproducts for positive logic. Prime products are shown to satisfy a version of {\L}o\'s's Theorem restricted to positive formulas, as well as the following variant of Keisler Isomorphism Theorem: under the generalized continuum hypothesis, two models have the same positive theory if and only if they have isomorphic prime powers of ultrapowers.Comment: 15 page

One-sorted Program Algebras

Kleene algebra with tests, KAT, provides a simple two-sorted algebraic framework for verifying properties of propositional while programs. Kleene algebra with domain, KAD, is a one-sorted alternative to KAT. The equational theory of KAT embeds into KAD, but KAD lacks some natural properties of KAT. For instance, not each Kleene algebra expands to a KAD, and the subalgebra of tests in each KAD is forced to be the maximal Boolean subalgebra of the negative cone. In this paper we propose a generalization of KAD that avoids these features while still embedding the equational theory of KAT. We show that several natural properties of the domain operator of KAD can be added to the generalized framework without affecting the results. We consider a variant of the framework where test complementation is defined using a residual of the Kleene algebra multiplication