The marine geochemistry of germanium: ekasilicon.

The geochemical behavior of dissolved germanium in rivers, estuaries, and the oceans is similar to that of silicon. It is chemically weathered from continental rocks and transported by rivers to the oceans, where it is taken up by siliceous organisms and deposited in biogenic opal. The ratio of germanium to silicon buried in siliceous oozes must reflect the oceanic input ratios from rivers (crustal weathering) and sea-floor vents (mid-ocean ridge hydrothermal weathering). The opal germanium/silicon ratio may thus monitor relative variations in these weathering processes and provide information about the geochemical history of seawater.

Hydrothermal germanium over the southern East pacific rise.

Germanium enrichment in the oceanic water column above the southern axis of the East Pacific Rise results from hydrothermal solutions emanating from hot springs along the rise crest. This plume signature provides a new oceanic tracer of reactions between seawater and sea floor basalts during hydrothermal alteration. In contrast to the sharp plumes of (3)He and manganese, the germanium plume is broad and diffuse, suggesting the existence of pervasive venting of low-temperature solutions off the ridge axis.

Interstitial nitrate profiles and oxidation of sedimentary organic matter in the eastern equatorial atlantic.

Pore-water nitrate concentrations in six pelagic eastern equatorial Atlantic cores increase from bottom water values (22 micromolar) to 40 micromolar at a depth of about 5 centimeters, then decrease to undetectable levels at depths as shallow as 40 centimeters. These nitrate concentrations and concentration gradients reflect zones of oxygen reduction, nitrate reduction, and sulfate reduction in the sediments. The estimated benthic flux of nitrate to the ocean from our data is much less than the total globalflux of nitrate to deep waters, even though these equatorial sediments underlie a productive upwelling zone. The estimated denitrification rate in our study area suggests that pelagic sediments may be important sites of marine denitrification.

Improved molecular final-state distribution of HeT+ for the beta-decay process of T2

An improved theoretical final-state distribution of HeT+ (and HeH+) resulting from the beta decay of molecular tritium T2 (HT) is presented to accommodate the needs of increased accuracy in the analysis of ongoing and future tritium neutrino-mass experiments. The previously available theoretical spectrum has been improved in many respects, and adopted approximations have been validated.

Hydrogen-antihydrogen collisions

Matter-antimatter interactions are investigated using hydrogen-antihydrogen collisions as an example. Cross sections for elastic scattering and for the antihydrogen loss (either through the rearrangement reaction, resulting in formation of protonium and positronium according to H+&Hmacr;-->p&pmacr;+e(+)e(-), or via annihilation in flight) are calculated for the first time in a fully quantum mechanical approach. Implications for experiments intending to trap and cool antihydrogen are discussed.

Collisions between metastable hydrogen atoms at thermal energies

The complex interaction potentials arising in the approach of two metastable hydrogen 2s atoms are calculated and the cross sections for ionization, excitation transfer, and elastic scattering are predicted. The measured cross section for associative ionization at E = 4.1 meV equals 2x10(-15) cm (2). We calculate a total ionization cross section of 2x10(-13) cm (2), varying as E(-2/3) at higher energies. Thus it appears that dissociative ionization is the major ionization channel. We find also that double excitation transfer into two excited H(2p) atoms is still more probable with the large cross section of 9x10(-12) cm (2) at E = 4.1 meV varying as E(-1/2) at higher energies. The detection of the resulting Lyman alpha photons would provide a diagnostic test of our predictions.

Does sedimentary organic delta 13C record variations in quaternary ocean [CO2(aq)]?

Ocean surface water [CO2(aq)] variations based on glacial/interglacial changes in sediment delta 13Corg are shown to compare favorably with reconstructions based on ice core [CO2]. In particular, an approximate 80 microatmospheres increase in atmospheric pCO2 during the last glacial-interglacial transition is calculated to correspond to a 3-4 micromolar increase in ocean surface water [CO2(aq)] at atmospheric equilibrium. A widespread marine delta 13Corg decrease of 1-2% accompanied this event and was not preceded by an equivalent isotopic change in surface water total dissolved inorganic carbon. These observations support the hypothesis that [CO2(aq)] influences photosynthetic isotope fractionation between marine inorganic and organic carbon pools, and therefore that plankton/sediment delta 13Corg may serve as a proxy for surface water [CO2(aq)].

Chronic catheterization of coronary sinus in large domestic animals.

A technique was developed for long-term catheterization of the coronary sinus in calves and ponies. A catheter with a 10 to 12 cm-long stiff segment was implanted via right lateral thoracotomy. Catheters were kept patent up to 10 weeks after the surgical procedure. At that time, location of the catheter tip was confirmed both by determining oxygen tension of the anaerobically sampled blood and by radiography. Base-line values of oxygen venous blood of non-anesthetized calves and ponies are reported.

[Early manifestations of Tangier disease]. / Les manifestations précoces de la maladie de Tangier.

BACKGROUND: The diagnosis of Tangier disease in childhood is based on the specific aspect of tonsils or by screening relatives of affected subjects. CASE REPORT: A moderately enlarged liver associated with splenomegaly was found upon routine physical examination of a 3 month-old breast-fed boy, born in Turkey from consanguineous parents. Laboratory studies disclosed moderate increase in serum alanine aminotransferase activity (ALAT 52 UI/l, N < 30). The diagnosis of Tangier disease was confirmed by studies of plasma cholesterol and apolipoprotein A. By 8 months of age, the patient had enlarged orange tonsils. Small cervical, axillary and inguinal lymphadenopathies were present. The tonsilar and adenoidal tissues were removed at 18 months of age because the patient suffered from chronic airway obstruction. Colonoscopic examination revealed tiny flat orange spots, 1 to 2 mm in diameter, scattered throughout the rectosigmoidal and colonic mucosa. Survey of the family led to the discovery of one sister, with asymptomatic apolipoprotein Al deficiency and a normal sister, while the parents were heterozygotes for Tangier disease. CONCLUSION: Enlarged liver associated with a moderate level in serum aminotransferase may be an early manifestation of Tangier disease in infants. Rectosigmoidal and colonic lesions may be convenient for biopsy when tonsillectomy is not indicated.

Altered growth patterns and depressed pituitary growth hormone content in young rats: effects of pre- and postnatal thiouracil administration.

The important influence of postnatal thyroid status on development is well recognized, while the effect of prenatal thyroid status on postnatal growth is less understood. The present study was undertaken to assess the effects of pre- and postnatal thiouracil administration on postnatal growth and pituitary grown hormone (GH) content in 25 day old rats. Pups were born to Sprague-Dawley rats fed lab chow mash containing 0.25% thiouracil according to the following schedules: a) during gestation only; b) during lactation only (25 days postpartum); and c) through gestation and lactation. Mothers of euthyroid controls were fed diet without thiouracil for the length of the experiment. Pups were weighed daily through day 21 and decapitated on day 25. Pituitary GH content was measured by densiometric comparison of disc gel column electrophoresed pituitary homogenates with similarly treated rat GH standard. Incorporation of thiouracil into the diet of pregnant and/or lactating rats significantly depressed the body weight and pituitary GH levels in their 25 day old pups. Furthermore, analysis of the daily mean body weight of each litter revealed four significantly different patterns of growth. While previous investigators have reported that prenatal thyroid restriction does not significantly alter the developmental processes of young rodents, the present study indicates that prenatal thyroid status is an important influence on normal postnatal growth.