Estimating population birth rates of zooplankton when rates of egg deposition and hatching are periodic

I present a general method of computing finite birth and death rates of natural zooplankton populations from changes in the age distribution of eggs and changes in population size. The method is applicable to cases in which eggs hatch periodically owing to variable rates of oviposition. When morphological criteria are used to determine the age distribution of eggs at the beginning and end of a sampling interval, egg mortality can be incorporated in estimates of population birth rate. I raised laboratory populations of Asplanchna priodonta , a common planktonic rotifer, in semicontinuous culture to evaluate my method of computing finite birth rate. The Asplanchna population became synchronized to a daily addition of food but grew by the same amount each day once steady state was achieved. The steady-state rate of growth, which can be computed from the volume-specific dilution rate of the culture, was consistent with the finite birth rate predicted from the population's egg ratio and egg age distribution.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47764/1/442_2004_Article_BF00410359.pd

Grandes variations pour la guitare sur un thème de l’opéra de Sémiramis de Rossini. Oeuv. 22.

9 p. Binder’s title: [Miscellaneous collection of music for guitar by French composers]

Electrical conductivity of iron-bearing silicate glasses and melts. Implications for the mechanisms of iron redox reactions

International audienceThe electrical conductivity of a series of glasses and melts of the system SiO2–CaO–MgO–M2O–“FeO” (M = Li and Na) and of a borosilicate has been measured from room temperature to about 1820 K. For samples with predominantly reduced iron, the conductivity increases markedly upon addition of Na+ and still more of Li+, which is consistent with the increasing order Mg2+, Na+, Li+ order of cation mobility. For the oxidized samples the conductivity is in contrast almost not affected by the presence of alkali cations, which agrees with the low mobility of alkali cations that are then serving as charge compensators of tetrahedrally coordinated Al3+. The conductivity is higher for oxidized than for reduced samples. As indicated by polarization electrode phenomena and complementary continuous current measurements, this difference is due to an important contribution of electronic conduction caused by electronic charge transfer between iron species that exists in the oxidized samples. The diffusivities of oxygen and divalent cations were then determined from Eyring relationship and the measured conductivities, respectively and compared with the redox diffusivies determined for the same samples. The good agreement found between both kinds of data confirms the controlling role of divalent cations and of oxygen species in the redox kinetics near the glass transition and at high temperatures, respectively. In addition it illustrates that describing melt properties in an integrated manner is becoming possible

An experimental protocol for determining ferrous to ferric ratios in glasses with the electron microprobe

International audienc

Quantitative electron microprobe analysis of Fe3+/Fe: Basic concepts and experimental protocol for glasses

International audienc

Kinetics of iron oxidation in silicate melts: a preliminary XANES study.

X-ray Absorption Near Edge Structure (XANES) experiments made between 600 and 700 °C at the Fe K-edge have been used to study the kinetics of iron oxidation in a supercooled melt of Fe-bearing pyroxene composition. To provide a firmer basis to redox determinations, the redox state of a series of samples was first determined from wet chemical, Mössbauer spectroscopy and electron microprobe analyses. The XANES experiments show that variations in relative abundances of ferric and ferrous iron can be determined in situ, even just above the glass transition, and that some information can also be obtained on the structural environment around iron cations. The kinetics of iron oxidation do not vary much with temperature down to the glass transition. This observation suggests that the rate-limiting factor in this process is not oxygen diffusion, which is coupled to relaxation of the silicate network, but, as described by Cooper and coworkers, diffusion of network modifying cations along with a counter flux of electrons