Entrapment of Humic Acid in a Sol-Gel Matrix—A New Tool for Sorption Studies

Humic substances are natural complexed mixtures of organic compounds originated from the decomposition of plant and animal residues. These compounds are ubiquitous in soils, sediments, surface waters and groundwaters. They contain both hydrophobic and hydrophilic moieties, able to interact with hydrophobic organic contaminants and with heavy metals. These sorption interactions play a crucial role in contaminants fate and transport and their understanding and quantification are essential for modeling and predictions. However, sorption analyses frequently suffer from experimental problems. A novel idea presented in this study is to use sol-gel as an inert matrix to immobilize (entrap) specific, well defined, humic molecules which then be used in sorption studies. We developed a successful procedure for the immobilization of humic acid (HA) in a sol-gel matrix. After gelation and drying, the doped gel was crushed and washed several times, yielding a very stable product. It was then used in a series of batch experiments, studying the sorption of several polycyclic aromatic hydrocarbons (PAHs) with Aldrich HA. The sorption coefficients (K _oc) obtained with the immobilized HA were highly correlated with the values expected based on the hydrophobicity of the contaminants. We concluded that the entrapped HA retained its original properties and that it was accessible to the external contaminants through the pore network.     

Scheduling Classes on a College Campus

We consider the problem of scheduling a set of classes to classrooms with the objective of minimizing the number of classrooms used. The major constraint that we must obey is that no two classes can be assigned to the same classroom at the same time on the same day of the week. We present an algorithm that produces a nearly optimal schedule for an arbitrary set of classes. The algorithm's first stage produces a packing of classes using a combination of a greedy algorithm and a non-bipartite matching and the second stage consists of a bipartite matching.First we show that for one variant of the problem our algorithm produces schedules that require a number of classrooms that is always within a small additive constant of optimal. Then we show that for an interesting variant of the problem the same algorithm produces schedules that require a small constant factor more classrooms than optimal. Finally, we report on experimental results of our algorithm using actual data and also show how to create schedules with other desirable characteristics.     

A Modification of an Algorithm by Golub and Plemmons for Large Linear Least Squares in the Context of Doppler Positioning

This paper considers the solution of the geodetic Doppler multi-stationadjustment, i.e. the problem of computing the positions of severalstations observing the Doppler shift on radio frequencies emittedby several artificial satellites passing over the horizon. Amodification of an algorithm due to Golub and Plemmons, forsolving large linear least-squares problems where the observationmatrix has a block dual angular form, is proposed in this framework.This modification is shown to reduce substantially both datatransfer between the tracking stations and the main computingcentre, and the total computational effort required to obtainthe solution of the problem. Preliminary numerical results arediscussed and some further comments presented.     

A new approach to prostanoids

A new asymmetric approach to 11-deoxyprostanoids is presented.     

Fission yields at different fission-product kinetic energies for thermal-neutron-induced fission of 239Pu

At the recoil spectrometer “Lohengrin” of the Institut Laue-Langevin in Grenoble, the yields of the light fission products from the thermal-neutron-induced fission of ²³⁹Pu were measured as a function of A, Z, the kinetic energy E and the ionic charge states q. The nuclear charge and mass distributions summed over all ionic charge states were determined for different light fissionproduct kinetic energies between 93 and 112 MeV. The proton odd-even effect which was measured to be (11.6 ± 0.6)% causes considerable fine structure in the yields. The average kinetic energy of even-Z elements in the light fission-product group is 0.3 ± 0.1 MeV larger than for odd-Z elements. The neutron odd-even effect is (6.5 ± 0.7)%. The comparison with previously published data ¹) for thermal-neutron-induced fission of ²³⁵U reveals a correlation between the proton odd-even effect in the yield and in the kinetic energy of the elements. The dependence of the proton odd-even effect on the fragmentation is very similar for ²³⁵U and ²³⁹Pu when it is considered as a function of the nuclear charge of the heavy fission products. The isobaric variances σ_z². for thermal-neutron fission of ²³⁵U and ²³⁹Pu coincide at all kinetic energies if the influence of the proton odd-even effect is averaged out. This supports the hypothesis that the magnitude of σ_z² is determined only by quantum-mechanical zero-point fluctuations. The influence of the spherical shells Z = 50 and N = 82 on the fragmentation is discussed.     

Ideals contracted from 1-dimensional overrings with an application to the primary decomposition of ideals

We prove that each ideal of a locally formally equidimensional analytically unramified Noetherian integral domain is the contraction of an ideal of a one-dimensional semilocal birational extension domain. We give an application to a problem concerning the primary decomposition of powers of ideals in Noetherian rings. It is shown in an earlier paper by the second author that for each ideal in a Noetherian commutative ring there exists a positive integer such that, for all , there exists a primary decomposition where each contains the -th power of its radical. We give an alternate proof of this result in the special case where is locally at each prime ideal formally equidimensional and analytically unramified.