Selenium absorption by two-grooved milkvetch and western wheatgrass from selenomethionine, selenocystine, and selenite

Selenium (Se) occurs in various forms in soils, including inorganic selenite and selenate and organic selenomethionine. Plant uptake of the inorganic, but not the organic forms, has been studied extensively. Organic-Se uptake was therefore examined in two-grooved milkvetch (Astragalus bisulcatus (Hook.) Gray), a Se-accumulating forb, and western wheatgrass (Pascopyrum smithii (Rydb.) Löve), a non-Se accumulating grass. Plants were grown for 56 days in nutrient culture enriched with 1 or 2 mg Se liter-1 as sodium selenite or 0.3 or 0.6 mg Se liter-1 as Se-DL-methionine or Se-DL-cystine. Growth was not affected by the Se treatments. Selenium concentrations in shoots were proportional to nutrient-solution concentrations for both species grown in sodium selenite and selenocystine, and for wheatgrass when grown in selenomethionine. Selenium concentrations in milkvetch were not increased by the higher concentration of selenomethionine. Shoots of milkvetch, growing in the low-Se treatment contained 243, 283, and 47 µg Se g-1 , for the sodium selenite, selenomethionine, and selenocystine treatments, respectively, whereas values for the wheatgrass were 20, 32, and 17. Shoot:root Se concentrations were 1.2, 0.7, and 0.4 in milkvetch and 0.1, 0.5, and 0.1 in wheatgrass for the sodium selenite, selenomethionine, and selenocystine, respectively. Selenium is more readily transported to shoots in the accumulator plant, or conversely; there is a barrier to Se movement to shoots in the nonaccumulator plant. Wheatgrass contained sufficient Se to be of concern in animal toxicosis and because of greater dry matter yield accumulated as much or more Se than did the milkvetch

Epidemiological Features of the Selenium Status in Cattle of Northern California

Selenium (Se) is an essential mineral for animal health. Deficiencies result in white muscle disease (WMD), retained placenta, and ill thrift in cattle. These health problems are known to occur in some northern California herds. This survey was initiated to provide knowledge on the epidemiological features of Se deficiency in cattle in this region. Blood samples were drawn from 10 cows on each of 10 ranches in each of the northern 22 counties. Whole blood Se and glutathione peroxidase (GSH-Px) activities were determined, and these values were statistically compared with each other and with data obtained by questionnaire. The latter included information on animal diseases, soils, forages, and general ranch descriptors like elevation and rainfall. The GSH-Px spot test produced either a positive (+), negative (-) or intermediate (+/-) enzyme activity classification for each cow. Herd classification was identified as + or - if > 70% cow-values fell in that class, otherwise it was identified as +/-. The overall geometric mean blood-Se value was 47.6 ng/ml. Regressions of individual and herd GSH-Px-class against blood-Se values produced r = .75 and r = .82, respectively. Significantly low blood-Se levels were recorded in herds with: 1) negative GSH-Px values, 2) past histories of WMD and ill thrift, 3) predominantly hay diet, 4) pregnant and early lactating cows, and 5) pure bred cows. The Se status of herds using Se-salt blocks was not different from non-supplemented herds. Descriptive ranch variables did not reliably assess the Se status of herds in this study

Epidemiological features of the selenium status in cattle of northern California

Selenium (Se) is an essential mineral for animal health. Deficiencies result in white muscle disease (40), retained placenta, and ill thrift in cattle. These health problems are known to occur in some northern California herds. This survey was initiated to provide knowledge on the epidemiological features of Se deficiency in cattle in this region. Blood samples were drawn from 10 cows on each of 10 ranches in each of the northern 22 counties. Whole blood Se and glutathione peroxidase (GBH-Px) activities were determined, and these values were statistically compared with each other and with data obtained by questionnaire. The latter included information on animal diseases, soils, forages, and general ranch descriptors like elevation and rainfall. The GSH-Px spot test produced either a positive (+), negative (-) or intermediate (+/-) enzyme activity classification for each cow. Herd classification was identified as + or - if >70% cow-values fell in that class, otherwise it was identified as +/-. The overall geometric mean blood-Se value was 47.6 ng/ml. Regressions of individual and herd GSH-Px-class against blood-Se values produced r = .75 and r = .82, respectively. Significantly low blood-Se levels were recorded in herds with: 1) negative GSH-Px values, 2) past histories of WMD and ill thrift, 3) predominantly hay diet, 4) pregnant and early lactating cows, and 5) pure bred cows. The Se status of herds using Se-salt blocks was not different from non- supplemented herds. Descriptive ranch variables did not reliably assess the Se status of herds in this study

Vortex structure in d-density wave scenario of pseudogap

We investigate the vortex structure assuming the d-density wave scenario of the pseudogap. We discuss the profiles of the order parameters in the vicinity of the vortex, effective vortex charge and the local density of states. We find a pronounced modification of these quantities when compared to a purely superconducting case. Results have been obtained for a clean system as well as in the presence of a nonmagnetic impurity. We show that the competition between superconductivity and the density wave may explain some experimental data recently obtained for high-temperature superconductors. In particular, we show that the d-density wave scenario explains the asymmetry of the gap observed in the vicinity of the vortex core.Comment: 8 pages, 10 figure

Crypto-unitary forms of quantum evolution operators

For the description of quantum evolution, the use of a manifestly time-dependent quantum Hamiltonian $\mathfrak{h}(t) =\mathfrak{h}^\dagger(t)$ is shown equivalent to the work with its simplified, time-independent alternative $G\neq G^\dagger$. A tradeoff analysis is performed recommending the latter option. The physical unitarity requirement is shown fulfilled in a suitable ad hoc representation of Hilbert space.Comment: 15 p

Isospin Effects in Nuclear Multifragmentation

We develop an improved Statistical Multifragmentation Model that provides the capability to calculate calorimetric and isotopic observables with precision. With this new model we examine the influence of nuclear isospin on the fragment elemental and isotopic distributions. We show that the proposed improvements on the model are essential for studying isospin effects in nuclear multifragmentation. In particular, these calculations show that accurate comparisons to experimental data require that the nuclear masses, free energies and secondary decay must be handled with higher precision than many current models accord.Comment: 46 pages, 16 figure

Fragments of equality in representative politics

Deploying a broadly interpretive approach, the article explores the extent to which, and the ways in which, equality is enacted in non-elective as well as elective representation. It argues that the fleeting and fragmentary equalities evident in non-elective representation are democratically significant, and that examining them can enhance understanding of the democratic promise and limits of different modes of representation

The Science of Sungrazers, Sunskirters, and Other Near-Sun Comets

This review addresses our current understanding of comets that venture close to the Sun, and are hence exposed to much more extreme conditions than comets that are typically studied from Earth. The extreme solar heating and plasma environments that these objects encounter change many aspects of their behaviour, thus yielding valuable information on both the comets themselves that complements other data we have on primitive solar system bodies, as well as on the near-solar environment which they traverse. We propose clear definitions for these comets: We use the term near-Sun comets to encompass all objects that pass sunward of the perihelion distance of planet Mercury (0.307 AU). Sunskirters are defined as objects that pass within 33 solar radii of the Sun’s centre, equal to half of Mercury’s perihelion distance, and the commonly-used phrase sungrazers to be objects that reach perihelion within 3.45 solar radii, i.e. the fluid Roche limit. Finally, comets with orbits that intersect the solar photosphere are termed sundivers. We summarize past studies of these objects, as well as the instruments and facilities used to study them, including space-based platforms that have led to a recent revolution in the quantity and quality of relevant observations. Relevant comet populations are described, including the Kreutz, Marsden, Kracht, and Meyer groups, near-Sun asteroids, and a brief discussion of their origins. The importance of light curves and the clues they provide on cometary composition are emphasized, together with what information has been gleaned about nucleus parameters, including the sizes and masses of objects and their families, and their tensile strengths. The physical processes occurring at these objects are considered in some detail, including the disruption of nuclei, sublimation, and ionisation, and we consider the mass, momentum, and energy loss of comets in the corona and those that venture to lower altitudes. The different components of comae and tails are described, including dust, neutral and ionised gases, their chemical reactions, and their contributions to the near-Sun environment. Comet-solar wind interactions are discussed, including the use of comets as probes of solar wind and coronal conditions in their vicinities. We address the relevance of work on comets near the Sun to similar objects orbiting other stars, and conclude with a discussion of future directions for the field and the planned ground- and space-based facilities that will allow us to address those science topics