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Photofission of actinides is studied in the region of nuclear excitation energies that covers the entire giant dipole resonance (GDR) region. The mass distributions of [sup.238]U photofission fragments have been explored theoretically for eight different endpoint bremsstrahlung energies from 11.5 to 67.7 MeV, which correspond to average photon energies of 9.09 to 15.90 MeV. Among these energies, 29.1 MeV corresponds to the average photon energy of 13.7 ± 0.3 MeV, which coincides with the GDR peak for [sup.238]U photofission. The integrated yield of [sup.238]U photofission, as well as charge distribution of photofission products, is calculated and its role in producing nuclei and their neutron-richness is investigated. Key words: photonuclear reactions, photofission, nuclear fissility, GDR, exotic nuclei. Nous etudions la photofission des actinides dans la region des excitations nucleaires couvrant toute la region de la resonance geante dipolaire (RGD). Nous faisons une etude theorique de la distribution de masse des fragments de la photofission de [sup.238]U pour huit differentes imites d'energie du bremsstrahlung de 11.5 a 67.7 MeV, ce qui correspond a des energies moyennes de photons de 9.09 a 15.90 MeV. Parmi ces energies, le 29.1 MeV correspond a un photon de 13.7 ± 0.3 MeV qui coincide avec le pic de la RGD pour la photofission de [sup.238]U. Nous calculons la production integree de la photofission de [sup.238]U ainsi que la distribution de charge des produits de la photofission et nous etudions son role dans la production de noyau et de leur richesse en neutrons. [Traduit par la Redaction] Mots-cles: reactions photo-nucleaires, photofission, fissilite, resonance geante dipolaire (RGD), noyaux exotiques. PACS Nos.: 25.20.-x, 27.90.+b, 25.85.Jg, 25.20.Dc, 29.25.Rm., 1. Introduction Induced fission by neutron, proton, and photon has been studied for several decades. However, there are still areas (e.g., far away from the valley of stability, nuclei having [...]

A novel calcium-dependent potassium current ([K.sub.slow]) that slowly activates in response to a simulated islet burst was identified recently in mouse pancreatic [beta]-cells (Gopel, S.O., T. Kanno, S. Barg, L. Eliasson, J. Galvanovskis, E. Renstrom, and P. Rorsman. 1999. J. Gen. Physiol. 114:759-769). [K.sub.slow] activation may help terminate the cyclic bursts of [Ca.sup.2+]-dependent action potentials that drive [Ca.sup.2+] influx and insulin secretion in [beta]-cells. Here, we report that when [[[Ca.sup.2+]].sub.i] handling was disrupted by blocking [Ca.sup.2+] uptake into the ER with two separate agents reported to block the sarco/endoplasmic calcium ATPase (SERCA), thapsigargin (1-5 [micro]M) or insulin (200 nM), [K.sub.slow] was transiently potentiated and then inhibited. [K.sub.slow] amplitude could also be inhibited by increasing extracellular glucose concentration from 5 to 10 mM. The biphasic modulation of [K.sub.slow] by SERCA blockers could not be explained by a minimal mathematical model in which [[[Ca.sup.2+]].sub.i] is divided between two compartments, the cytosol and the ER, and [K.sub.slow] activation mirrors changes in cytosolic calcium induced by the burst protocol. However, the experimental findings were reproduced by a model in which [K.sub.slow] activation is mediated by a localized pool of [[Ca.sup.2+]] in a subspace located between the ER and the plasma membrane. In this model, the subspace [[Ca.sup.2+]] follows changes in cytosolic [[Ca.sup.2+]] but with a gradient that reflects [Ca.sup.2+] efflux from the ER. Slow modulation of this gradient as the ER empties and fills may enhance the role of [K.sub.slow] and [[Ca.sup.2+]] handling in influencing [beta]-cell electrical activity and insulin secretion. KEY WORDS: islets of Langerhans * KCa channels * ER * insulin * intracellular calcium

Alluvial-derived soils of the Missouri River floodplain of western Iowa have greater amounts of available K (AVK), determined by a slurry method, and exchangeable K (EXK) than major upland soils. This research was conducted to better understand the high K status of these soils. Five soil series from Monona County in western Iowa were investigated. The soils differ in relative age and textural class. Soils formed on the lower geomorphic surface have more AVK than the soils formed on the higher geomorphic surface. The variation in podogenic development of soils on geomorphic surfaces was sufficient to cause differences in the K status of these soils. Correlation coefficient analysis of the data indicates that AVK is related to EXK. Correlation coefficients of AVK and EXK were improved when soils were divided into three textural classes. The improvement of correlation coefficients suggests that particle-size fractions and EXK are controlling factors for the higher AVK content. Sand, silt, and clay contents and EXK were used in developing multiple linear regression equations to predict AVK for these soils. This study suggests that clay contents and EXK should be considered for future K-fertilizer recommendations for alluvial-derived soils of the Missouri River floodplain.

Examination of the depth of the water table, morphological features, and groundwater hydrology in a Mollisol catena of Central Iowa shows that these parameters vary with geomorphic positions in the Mollisol catena. Soils on higher landscapes exhibit higher fluctuations of water than soils on lower landscapes. Soil redoximorphic features exhibit a strong correlation with water table presence and fluctuation.

Byline: A. Rauf, F. A. Khan and M. Aslam ABSTRACT Four levels of salinity (0dSm-1, 3dSm-1, 6dSm-1 and 9dSm-1) were used to evaluate twenty different sunflower (Helianthus annuus L.) accessions. [...]