Provincial Veterinary Services respond to drought in South Africa.

In 2018, Cape Town, South Africa, nearly ran out of water. That this has not yet happened is in large part due to the water-saving efforts of its citizens. It is highly likely that this situation will be repeated in Cape Town and that similar situations will be experienced by major cities in other parts of the world. Efforts to save water should thus continue and the lessons learned in Cape Town should be shared. The functioning of Veterinary Services during a drought is affected in the same way as any business, in terms of running an office, but veterinary professionals face an increased risk of exposure to pathogens, compared to that of many occupations, and of veterinary officials becoming disease vectors. One component of Veterinary Services is veterinary laboratory services. Laboratory procedures rely heavily on water and, without advance planning, a laboratory's function can be severely limited by a restricted water supply. In many cases, innovative water-saving techniques can be used to reduce water use substantially without compromising the quality of the services offered. Here, the authors share their experiences and some lessons learned while working in Veterinary Services in the Western Cape province of South Africa.

En 2018, la ville du Cap en Afrique du Sud a failli manquer d'eau. Si la pénurie totale a pu être évitée, ce fut en grande partie grâce aux efforts déployés par les habitants pour économiser l'eau. Or, il est très probable que cette situation se reproduise au Cap et que des situations analogues surviennent dans nombre de grandes métropoles d'autres régions du monde. C'est pourquoi il convient de poursuivre les efforts d'économie d'eau et de partager avec d'autres les enseignements tirés dans la ville du Cap. L'impact de la sécheresse sur le fonctionnement des Services vétérinaires est similaire à celui de toute organisation en termes de gestion administrative ; en revanche, par rapport à d'autres professionnels, les vétérinaires de terrain sont davantage exposés à des agents pathogènes et au risque de devenir eux-mêmes vecteurs de maladies. Les laboratoires vétérinaires sont l'une des composantes des Services vétérinaires. Les procédures de laboratoire sont amplement tributaires de l'eau ; or, en l'absence d'une planification préalable, les activités d'un laboratoire pourraient être gravement mises à mal par des restrictions de l'approvisionnement en eau. Dans bien des cas, il est possible d'utiliser des techniques innovantes pour économiser l'eau afin d'en diminuer la consommation sans pour autant compromettre la qualité des services rendus. Les auteurs font part de leur expérience et de certains enseignements tirés lorsqu'ils travaillaient dans les Services vétérinaires de la province du Cap-Occidental en Afrique du Sud.

En 2018 faltó poco para que Ciudad del Cabo (Sudáfrica) se quedara sin agua. Si las cosas aún no han llegado a este extremo es, en gran parte, gracias a los esfuerzos de los habitantes por economizar agua. Es muy probable que en el futuro Ciudad del Cabo vuelva a sufrir esta situación y que grandes metrópolis de otras partes del mundo conozcan dificultades parecidas. Por ello hay que perseverar en los esfuerzos de ahorro de agua y se deben compartir las enseñanzas extraídas en Ciudad del Cabo. Durante una sequía, el funcionamiento de los Servicios Veterinarios se ve afectado del mismo modo que cualquier otra actividad, por lo que respecta al trabajo de oficina, pero además los profesionales del ramo, en comparación con los de otros muchos sectores, corren mayor peligro de exposición a patógenos, lo que a su vez entraña el riesgo de que los propios veterinarios ejerzan de vectores de la enfermedad. Uno de los puntales de los Servicios Veterinarios son los laboratorios veterinarios, cuyo quehacer depende en gran medida del uso de agua. Por ello, cuando no se ha planificado con antelación la eventualidad de una penuria de agua, esta puede imponer graves cortapisas a las funciones de laboratorio. En muchos casos es posible emplear innovadoras técnicas de ahorro de agua para reducir sustancialmente las cantidades utilizadas sin menoscabo de la calidad de los servicios dispensados. Los autores comparten su experiencia y algunas de las lecciones que extrajeron de su trabajo en los Servicios Veterinarios de la provincia sudafricana del Cabo Occidental.

Description of an outbreak of highly pathogenic avian influenza in domestic ostriches (Struthio camelus) in South Africa in 2011.

In 2011, the commercial ostrich production industry of South Africa experienced an outbreak of highly pathogenic avian influenza (HPAI), subtype H5N2. Surveillance using antibody and antigen detection revealed 42 infected farms with a between-farm prevalence in the affected area of 16%. The outbreak was controlled using depopulation of infected farms, resulting in the direct loss of 10% of the country's domestic ostrich population. Various factors in the ostrich production system were observed that could have contributed to the spread of the virus between farms, including the large number of legal movements of ostriches between farms, access of wild birds to ostrich camps and delays in depopulation of infected farms. Negative effects on the ostrich industry and the local economy of the ostrich-producing area were observed as a result of the outbreak and the disease control measures applied. Prevention and control measures applied as a result of avian influenza in South Africa were informed by this large outbreak and the insights into epidemiology of avian influenza in ostriches that it provided, resulting in stricter biosecurity measures required on every registered ostrich farm in the country.

Archimedean-like colloidal tilings on substrates with decagonal and tetradecagonal symmetry.

Two-dimensional colloidal suspensions subjected to laser interference patterns with decagonal symmetry can form an Archimedean-like tiling phase where rows of squares and triangles order aperiodically along one direction (J. Mikhael et al., Nature 454, 501 (2008)). In experiments as well as in Monte Carlo and Brownian dynamics simulations, we identify a similar phase when the laser field possesses tetradecagonal symmetry. We characterize the structure of both Archimedean-like tilings in detail and point out how the tilings differ from each other. Furthermore, we also estimate specific particle densities where the Archimedean-like tiling phases occur. Finally, using Brownian dynamics simulations we demonstrate how phasonic distortions of the decagonal laser field influence the Archimedean-like tiling. In particular, the domain size of the tiling can be enlarged by phasonic drifts and constant gradients in the phasonic displacement. We demonstrate that the latter occurs when the interfering laser beams are not ideally adjusted.

Critical Casimir effect in classical binary liquid mixtures.

If a fluctuating medium is confined, the ensuing perturbation of its fluctuation spectrum generates Casimir-like effective forces acting on its confining surfaces. Near a continuous phase transition of such a medium the corresponding order parameter fluctuations occur on all length scales and therefore close to the critical point this effect acquires a universal character, i.e., to a large extent it is independent of the microscopic details of the actual system. Accordingly it can be calculated theoretically by studying suitable representative model systems. We report on the direct measurement of critical Casimir forces by total internal reflection microscopy with femtonewton resolution. The corresponding potentials are determined for individual colloidal particles floating above a substrate under the action of the critical thermal noise in the solvent medium, constituted by a binary liquid mixture of water and 2,6-lutidine near its lower consolute point. Depending on the relative adsorption preferences of the colloid and substrate surfaces with respect to the two components of the binary liquid mixture, we observe that, upon approaching the critical point of the solvent, attractive or repulsive forces emerge and supersede those prevailing away from it. Based on the knowledge of the critical Casimir forces acting in film geometries within the Ising universality class and with equal or opposing boundary conditions, we provide the corresponding theoretical predictions for the sphere-planar wall geometry of the experiment. The experimental data for the effective potential can be interpreted consistently in terms of these predictions and a remarkable quantitative agreement is observed.

Direct measurement of critical Casimir forces.

When fluctuating fields are confined between two surfaces, long-range forces arise. A famous example is the quantum-electrodynamical Casimir force that results from zero-point vacuum fluctuations confined between two conducting metal plates. A thermodynamic analogue is the critical Casimir force: it acts between surfaces immersed in a binary liquid mixture close to its critical point and arises from the confinement of concentration fluctuations within the thin film of fluid separating the surfaces. So far, all experimental evidence for the existence of this effect has been indirect. Here we report the direct measurement of critical Casimir force between a single colloidal sphere and a flat silica surface immersed in a mixture of water and 2,6-lutidine near its critical point. We use total internal reflection microscopy to determine in situ the forces between the sphere and the surface, with femtonewton resolution. Depending on whether the adsorption preferences of the sphere and the surface for water and 2,6-lutidine are identical or opposite, we measure attractive and repulsive forces, respectively, that agree quantitatively with theoretical predictions and exhibit exquisite dependence on the temperature of the system. We expect that these features of critical Casimir forces may result in novel uses of colloids as model systems.

Thermodynamics of a colloidal particle in a time-dependent nonharmonic potential.

We study the motion of an overdamped colloidal particle in a time-dependent nonharmonic potential. We demonstrate the first lawlike balance between applied work, exchanged heat, and internal energy on the level of a single trajectory. The observed distribution of applied work is distinctly non-Gaussian in good agreement with numerical calculations. Both the Jarzynski relation and a detailed fluctuation theorem are verified with good accuracy.

Direct measurement of entropic forces induced by rigid rods.

We present the first direct depletion potential measurements for a single colloidal sphere close to a wall in a suspension of rigid colloidal rods. Since all particle interactions are as good as hard-core-like, the depletion potentials are of entirely entropic origin. We developed a density functional theory approach that accurately accounts for this experimental situation. The depletion potentials calculated for different rod number densities are in very good quantitative agreement with the experimental results.