Effects of high oxygen concentrations on microbial biosensor signals. Hyperoxygenation by means of perfluorodecalin

Amperometric biosensors register oxygen depletion in response to analyte catabolism, and thus are limited by the availability of dissolved oxygen. Microbial sensors containing immobilized cells of Gluconobacter oxydans were hyperoxygenated to 400% of control levels and the effects on sensor responses to glucose were determined. Oxygenated perfluorodecalin (a completely fluorinated organic substance) was as effective in hyperoxygenation as direct sparging with O2, increasing sensor base medium oxygen concentrations from 9.3 to 37 mg/l. Hyperoxygenation enhanced maximal biosensor response amplitudes, particularly at high cell loading densities. Maximal response rates were also improved, although less dramatically. Results suggest that hyperoxygenation may be a new general approach for modulating biosensor responses.     

The emerging diversity of the electrophoretic types of Vibrio cholerae in the Western Hemisphere

Since the Latin American cholera epidemic began in 1991, 447 isolates of Vibrio cholerae O1 from the Western Hemisphere have been assayed by multilocus enzyme electrophoresis (MEE) to determine allelic variation among 16 enzyme-encoding genes. Two electrophoretic types (ETs) were identified among toxigenic isolates from Latin America: 323 were ET 4, the ET associated with the Latin American epidemic, and 29 were ET 3. Twenty-three of these ET 3 isolates had a distinctive antimicrobial resistance pattern also seen in isolates imported into the United States from Latin America and Southeast Asia. These resistant isolates had an identical ribotype and nearly identical pulsed-field gel electrophoresis (PFGE) patterns. Most nontoxigenic isolates analyzed were not precursors or descendants of toxigenic epidemic strains. MEE provided a population genetic frame-work for the interpretation of PFGE and ribotype data from the isolates in this study. All three methods identified 2 distinct strains of toxigenic V. cholerae O1 currently epidemic in Latin America.     

Formulating Jacobian matrices for the dexterity analysis of parallel manipulators

The condition number of the Jacobian matrix has been commonly used in determining the dexterous regions of a manipulator workspace. This has been successful when applied to manipulators having either solely spherical or solely Cartesian degrees of freedom. However, for manipulators having a mix of both rotational and translational degrees of freedom, i.e., complex degree of freedom manipulators, the condition number of the Jacobian matrix may not be used due to dimensional inconsistencies with its elements. This paper furthers earlier work introduced in obtaining a Jacobian matrix which may be used to determine the dexterity of parallel mechanisms regardless of the number and type of degrees of freedom of the mechanism. The result of the method introduced in this paper is a dimensionally homogeneous Jacobian matrix mapping m actuator velocities to n independent end effector velocities. In the typical case where m = n, the Jacobian matrix is also square. As opposed to earlier works, the singular values of the Jacobian matrix obtained here have an evident physical significance. Furthermore, the ratio of the maximum and minimum singular values, i.e., the condition number may be used to measure the dexterity of the manipulator at a given pose. To illustrate the concepts introduced in this paper, the 3-PRS manipulator is analyzed.     

Ascorbic acid: a review of its chemistry and reactivity in relation to a wine environment

Extensive reviews of research are available on the use of ascorbic acid, and its consequent degradation pathways, in physiological conditions or food matrices. However, very little information can be found for wine-related systems. This review highlights the relevant chemistry and reactivity of ascorbic acid with a focus on its behavior and potential behavior in a wine environment. The review describes the use of ascorbic acid as a complementary antioxidant preservative to sulfur dioxide along with the metal-catalyzed and radical-dependent manner by which it achieves this role. The relevant degradation products of ascorbic acid in aerobic and anaerobic conditions are presented as well as the interaction of these degradation products with sulfur dioxide and other wine-relevant sulfur compounds. Limitations in existing knowledge, especially regarding the crossover between the antioxidant and pro-oxidant roles of ascorbic acid, are identified.     

Nutritional value of soya protein and milk coprecipitates in sausage products

Sausages containing 60% of meat proteins replaced with soybean or milk calcium coprecipitates were prepared. Growth rates and plasma amino acid levels in rats fed diets based on these products, together with vitamin and available amino acid analysis indicated that the nutritional values of the non-meat proteins were similar but were both markedly lower than meat sausages. Nutritional damage to the protein in the sausages during cooking was only apparent in the all-meat sausage.     

Bibliometrics as weapons of mass citation

The allocation of resources for research is increasingly based on so-called 'bibliometrics'. Scientists are now deemed to be successful on the sole condition that their work be abundantly cited. This world-wide trend appears to enjoy support not only by granting agencies (whose task is obviously simplified by extensive recourse to bibliometrics), but also by the scientists themselves (who seem to enjoy their status of celebrities). This trend appears to be fraught with dangers, particularly in the area of social sciences, where bibliometrics are less developed, and where monographs (which are not taken into account in citation indexes) are often more important than articles published in journals. We argue in favour of a return to the values of 'real science', in analogy to the much-promised return to a 'real economy'. While economists may strive towards a more objective evaluation of the prospects of a company, a market, or an industrial sector, we scientists can only base our appraisal on a responsible practice of peer review. Since we fear that decision-takers of granting agencies such as the FNRS, CTI, EPFL, ETHZ, ANR, CNRS, NIH, NSF, DOE, etc. will be too busy to read our humble paper in Chimia, we appeal to scientists of all countries and disciplines to unite against the tyranny of bibliometrics.     

Mechanical properties of interpenetrating polymer network hydrogels based on hybrid ionically and covalently crosslinked networks

Hydrogels are polymer networks swollen in water. Because of their soft and wet nature, and their ability to show large volume changes, hydrogels can be useful in many biomedical and actuator applications. In these applications, it is crucial to tune the mechanical and physical properties of a hydrogel in a controllable manner. Here, interpenetrating polymer networks (IPNs) made of a covalently crosslinked network and an ionically crosslinked network were produced to investigate the effective parameters that control the physical and mechanical properties of an IPN hydrogel. Covalently crosslinked polyacrylamide (PAAm) or poly(acrylic acid) (PAA) networks were produced in the presence of alginate (Alg) that was then ionically crosslinked to produce the IPN hydrogels. The effect of ionic crosslinking, degree of covalent crosslinking, AAm : Alg and AA : Alg ratio on the swelling ratio, tensile properties, indentation modulus, and fracture energy of IPN hydrogels was studied. A hollow cylindrical hydrogel with gradient mechanical properties along its length was developed based on the obtained results. The middle section of this hydrogel was designed as a pH triggered artificial muscle, while each end was formulated to be harder, tougher, and insensitive to pH so as to function as a tendon‐like material securing the gel muscle to its mechanical supports. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2504–2513, 2013