Lake restoration in Denmark

Lake restoration in Denmark has involved the use of several different restoration techniques, all aiming to improve lake water quality and establishing clear‐water conditions. The most frequently used method, now used in more than 20 lakes, is the reduction of zooplanktivorous and benthivorous fish (especially roach (Rutilus rutilus) and bream (Abramis brama)) with the objective of improving the growth conditions for piscivores, large‐sized zooplankton species, benthic algae and submerged macrophytes. Piscivore stocking (mainly Esox lucius (pike)), aiming especially at reducing the abundance of young‐of‐the‐year fish, has been used in more than 10 lakes and frequently as a supplement to fish removal. Hypolimnetic oxidation, with oxygen and nitrate, has been undertaken in a few stratified lakes and sediment dredging, with the purpose of diminishing the internal phosphorus loading, has been experimented with in one large, shallow lake. Submerged macrophyte implantation has been conducted in some of the biomanipulated lakes to increase macrophyte abundance and distribution. Overall, the results from lake restoration projects, in the mainly shallow Danish lakes, show that external nutrient loading must be reduced to a level below 0.05–0.1 mg P L^–1 under equilibrium conditions to gain permanent effects on lake water quality. By using fish removal, at least 80% of the fish stock should be removed over a period of not more than 1–2 years to obtain a substantial effect on lower trophic levels and to avoid regrowth of the remaining fish stock. Stocking of piscivores requires high densities (>0.1 individuals m^–2) if an impact on the plankton level is to be obtained and stocking should be repeated yearly until a stable clear‐water state is reached. The experiments with hypolimnetic oxygenation and sediment dredging confirm that internal phosphorus loading can be reduced. Experience from macrophyte implantation experiments indicates that protection against grazing by herbivorous waterfowl may be useful in the early phase of recolonization.     

Optimisation of colour stability of cured ham during packaging and retail display by a multifactorial design

A multifactorial design, including (1) percent residual oxygen, (2) oxygen transmission rate of packaging film (OTR), (3) product to headspace volume ratio, (4) illuminance level and (5) nitrite level during curing, was established to investigate factors affecting light-induced oxidative discoloration of cured ham (packaged in modified atmosphere of 20% carbon dioxide and balanced with nitrogen) during 14 days of chill storage. Univariate statistical analysis found significant effects of all main factors on the redness (tristimulus a-value) of the ham. Subsequently, Response Surface Modelling of the data further proved that the interactions between packaging and storage conditions are important when optimising colour stability. The measured content of oxygen in the headspace was incorporated in the model and the interaction between measured oxygen content in the headspace and the product to headspace volume ratio was found to be crucial. Thus, it is not enough to keep the headspace oxygen level low, if the headspace volume at the same time is large, there will still be sufficient oxygen for colour deteriorating processes to take place.     

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.     

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.