Determination of lactate dehydrogenase (LDH) activity in milk by a fluorometric assay

Indigenous L-lactate dehydrogenase (LDH) in milk originates mainly from somatic cells, leucocytes and invading microorganisms. Its activity may be used for detection of mastitis. However, existing methods to measure LDH activity in milk both need pretreatment of the samples and still suffer from methodological problems. The present paper describes a fast, reliable method for determination of LDH activity, suitable for milk samples. The method is based on fluorometric determination of enzyme kinetics when L-lactate is converted to pyruvate. The assay uses raw milk without pretreatment and the method is easily adjustable to large-scale analyses on micro assay plates. Detection is based on (straight line) linear response within 4-7 min of initiation of the reaction. A substrate concentration of 35 mM in the reaction mixture was considered to be optimal for the assay. Intra plate assay precision was approx. 6% (CV) and the inter plate precision approx. 10%. Known inhibitors of LDH activity (oxidative direction), i.e., oxalic acid, oxamate, and pyruvate, were tested in different concentrations in order to verify the specificity of the response. The detailed kinetics of samples analysed indicated that the isoenzyme composition may have differed between milk samples, and that this composition may have been altered in high activity samples.     

Design and atomization properties for an inside-out type effervescent atomizer

Atomization of aqueous polymer solutions is a key step in the formulation of several pharmaceutical products. Droplet size control is essential in order to produce pharmaceutical products with the desired properties. The purpose of this paper is to investigate design issues for an inside-out type of effervescent atomizer used to spray water and aqueous solutions of polyvinylpyrrolidone (Kollidon® K-30) and hydroxypropyl methylcellulose (Pharmacoat® 603). The atomizer was operated at air-to-liquid mass ratios of 0.1, 0.3, and 0.5 and a feed pressure of 1172 kPa. Fluid viscosities ranged from 1 to 47 mPa.s. The influence of several atomizer design features was considered, including exit orifice length-to-diameter ratio, exit orifice diameter, the total area of the air injection holes, the distance between the air injection point and the exit orifice, the diameter of the mixing chamber, and the orientation of both air and liquid flows. Droplet size distributions were shown to vary significantly with the atomizer's exit orifice diameter, air injector design, and air injector distance to the exit orifice. In all cases air-to-liquid mass ratio played a key role in the mean droplet size. The design of the atomizer was shown to have the most pronounced effect on the mean droplet size at the lowest air-to-liquid mass ratios. Optimization of the atomizer design is very important in order to obtain small droplet sizes in pharmaceutical processes where the amount of air/gas should be minimized, e.g., closed-cycle spray drying and agglomeration processes.     

The evolution of Zipf's Law for U.S. cities

Exploiting the hierarchical structure of cities and based on a dataset for U.S. cities between 1840 and 2016, the aim of this paper is to analyze the evolution of the U.S. city size distribution. For that purpose we estimate a general three-parameter Zipf model, which can be traced back to Mandelbrot (1982), and validate our results by means of the hierarchical scaling law. Especially in the second half of the twentieth century, we find a pronounced departure from the exact Zipf's law. The city size distribution has become more equally distributed over time. Besides, the applied estimation method reveals evidence for leading cities dominating the remaining largest cities. Thus, the growing equality of the city sizes can be explained rather by growing smaller cities than by a loss of importance of the largest ones.     

Chemometric analysis of mass spectra of cis and trans fatty acid picolinyl esters

Capillary GC of fatty acid methyl esters with MS detection only yields information about the molecular weight of the compound. However, if picolinyl esters of fatty acids are analysed in this way it is possible to obtain more information about their structure, perhaps even the cis or trans configuration. Picolinyl esters of fatty acids are prepared by adding carbonyl-diimidazole, 3-hydroxymethylpyridine and 4-pyrrolidin-o-pyridine to a solution of free fatty acids in dichloromethane. The picolinyl esters dissolved in heptane are then separated by capillary GC on a CP Sil 88 column equipped with a quadropole MS-detector. The mass spectra clearly show the molecular weight and the position of double bonds in the fatty acids, but whether the configuration is cis or trans is impossible to discern visually. However, with the use of principal component analysis, it is possible to distinguish between cis and trans fatty acids of C16:1, C18:1,n-9, C18:1,n-12, C18:2 and C22:1 in two- and three-dimensional score plots. With Soft Independent Modelling of Class Analogy (SIMCA), it is possible to calculate models that can predict from the mass spectra of unknown fatty acids whether they are of the cis or trans configuration, which is demonstrated for C18:1 trans from hardened margarine and butter.     

Large self-thermal-plastic deformation in a NiTi shape-memory alloy fiber-actuated aluminum metal-matrix composite

The present work reports macroscopic thermal-mechanical and in-situ neutron diffraction measurements from a NiTi fiber-actuated aluminum-matrix composite and homogeneous aluminum control materials. Test specimens were subjected to an initial room-temperature, 5 pct tensile elongation and a subsequent room-temperature-to-393 K unconstrained (external-stress-free) heating process. During the unconstrained heating process, the composite material exhibited a very large (2.2 pct), nonlinear, apparent thermal contraction, while the homogeneous control sample exhibited the expected linear thermal expansion. The large-deformation, self-thermal-plastic behavior of the composite material was clearly the result of a powerful shape-memory response in the NiTi composite fiber actuators.