Appearance of the canine meninges in subtraction magnetic resonance images

The canine meninges are not visible as discrete structures in noncontrast magnetic resonance (MR) images, and are incompletely visualized in T1‐weighted, postgadolinium images, reportedly appearing as short, thin curvilinear segments with minimal enhancement. Subtraction imaging facilitates detection of enhancement of tissues, hence may increase the conspicuity of meninges. The aim of the present study was to describe qualitatively the appearance of canine meninges in subtraction MR images obtained using a dynamic technique. Images were reviewed of 10 consecutive dogs that had dynamic pre‐ and postgadolinium T1W imaging of the brain that was interpreted as normal, and had normal cerebrospinal fluid. Image‐anatomic correlation was facilitated by dissection and histologic examination of two canine cadavers. Meningeal enhancement was relatively inconspicuous in postgadolinium T1‐weighted images, but was clearly visible in subtraction images of all dogs. Enhancement was visible as faint, small‐rounded foci compatible with vessels seen end on within the sulci, a series of larger rounded foci compatible with vessels of variable caliber on the dorsal aspect of the cerebral cortex, and a continuous thin zone of moderate enhancement around the brain. Superimposition of color‐encoded subtraction images on pregadolinium T1‐ and T2‐weighted images facilitated localization of the origin of enhancement, which appeared to be predominantly dural, with relatively few leptomeningeal structures visible. Dynamic subtraction MR imaging should be considered for inclusion in clinical brain MR protocols because of the possibility that its use may increase sensitivity for lesions affecting the meninges

Pseudorehearsal in value function approximation

Catastrophic forgetting is of special importance in reinforcement learning, as the data distribution is generally non-stationary over time. We study and compare several pseudorehearsal approaches for Q-learning with function approximation in a pole balancing task. We have found that pseudorehearsal seems to assist learning even in such very simple problems, given proper initialization of the rehearsal parameters

Adaptation and enslavement in endosymbiont-host associations

The evolutionary persistence of symbiotic associations is a puzzle. Adaptation should eliminate cooperative traits if it is possible to enjoy the advantages of cooperation without reciprocating - a facet of cooperation known in game theory as the Prisoner's Dilemma. Despite this barrier, symbioses are widespread, and may have been necessary for the evolution of complex life. The discovery of strategies such as tit-for-tat has been presented as a general solution to the problem of cooperation. However, this only holds for within-species cooperation, where a single strategy will come to dominate the population. In a symbiotic association each species may have a different strategy, and the theoretical analysis of the single species problem is no guide to the outcome. We present basic analysis of two-species cooperation and show that a species with a fast adaptation rate is enslaved by a slowly evolving one. Paradoxically, the rapidly evolving species becomes highly cooperative, whereas the slowly evolving one gives little in return. This helps understand the occurrence of endosymbioses where the host benefits, but the symbionts appear to gain little from the association.Comment: v2: Correction made to equations 5 & 6 v3: Revised version accepted in Phys. Rev. E; New figure adde

Storage capacity of a constructive learning algorithm

Upper and lower bounds for the typical storage capacity of a constructive algorithm, the Tilinglike Learning Algorithm for the Parity Machine [M. Biehl and M. Opper, Phys. Rev. A {\bf 44} 6888 (1991)], are determined in the asymptotic limit of large training set sizes. The properties of a perceptron with threshold, learning a training set of patterns having a biased distribution of targets, needed as an intermediate step in the capacity calculation, are determined analytically. The lower bound for the capacity, determined with a cavity method, is proportional to the number of hidden units. The upper bound, obtained with the hypothesis of replica symmetry, is close to the one predicted by Mitchinson and Durbin [Biol. Cyber. {\bf 60} 345 (1989)].Comment: 13 pages, 1 figur

'Making a Difference': Volunteer Tourism and Development,

Abstract: In recent decades there has been a boom in international volunteer tourism, mainly in the form of the growth of gap-year companies offering placements, linked to conservation and community well-being goals. This paper makes two points: firstly, it argues that the growth of volunteer tourism is in part a product of the politics of the current period – the decline of grand narratives and the growth of ‘life political’ alternative forms of agency. Hence volunteer tourism, motivated by the impulse to ‘make a difference’, tells us something about the way in which development issues are being conceived of by idealistic young people who comprise the majority of volunteer tourists. Secondly, the paper takes issue with the view that today’s volunteer tourists are part of a tradition of colonialism and neo-colonialism that projects western conceptions of modernization onto the Third World societies to the detriment of the latter. Rather, it is argued that the politics behind volunteer tourism is better characterized as a rejection of modernization as development in favour of a post-development influenced approach. Keywords: volunteer tourism; life politics; gap-year; ethical consumption; tourism and development

Re-defining the extent of malaria transmission in South Africa: Implications for chemoprophylaxis

Background. Malaria case numbers reported in South Africa have reduced considerably over the last decade, necessitating a revision of the national risk map to guide malaria prevention, including the use of chemoprophylaxis.Objectives. To update the national malaria risk map based on recent case data and to consider the implications of the new transmission profile for guiding prophylaxis.Methods. The geographical distribution of confirmed malaria cases detected both passively and actively over the last six malaria seasons was used to redefine the geographic distribution and intensity of malaria transmission in the country.Results. The national risk map was revised to reflect zones of transmission reduced both in their extent and their intensity. Most notably, the area of risk has been reduced in the north-western parts of Limpopo Province and is limited to the extreme northern reaches of KwaZulu-Natal Province. Areas previously considered to be of high risk are now regarded to be of moderate risk.Conclusion. Chemoprophylaxis is now only recommended from September to May in the north-eastern areas of Limpopo and Mpumalanga Provinces. The recommended options for chemoprophylaxis have not changed from mefloquine, doxycycline or atovaquone-proguanil

Implementing malaria control in South Africa, Eswatini and southern Mozambique during the COVID-19 pandemic

The COVID-19 pandemic has strained healthcare delivery systems in a number of southern African countries. Despite this, it is imperative that malaria control and elimination activities continue, especially to reduce as far as possible the number and rate of hospitalisations caused by malaria. The implementation of enhanced malaria control/elimination activities in the context of COVID-19 requires measures to protect healthcare workers and the communities they serve. The aim of this review is therefore to present innovative ideas for the timely implementation of malaria control without increasing the risk of COVID-19 to healthcare workers and communities. Specific recommendations for parasite and vector surveillance, diagnosis, case management, mosquito vector control and community outreach and sensitisation are given.http://www.samj.org.zaam2021School of Health Systems and Public Health (SHSPH)Veterinary Tropical Disease