Determination of heavy metals and pesticides in ginseng products.

Medicinal plants may carry residuals of environmentally persistent pesticides or assimilate heavy metals in varying degrees. Several factors may influence contaminant accumulation, including species, level and duration of contaminant exposure, and topography. As part of a program for assessment of the quality of herbal medicines, we have analyzed 21 over-the-counter ginseng (Panax ginseng) products in various dosage forms. Chromium, mercury, and arsenic were undetectable above their limits of detection in both liquid and solid samples; while cadmium, lead, and nickel were present in the majority of samples. The chlorinated pesticide levels varied widely. In most samples, the total concentration of pesticides was below 100 ppb; while in 5 samples the total concentration exceeded 100 ppb.     

Some observations on the kinetics and thermochemistry of the reactions of HO2 radicals with aldehydes and ketones

The rapid, gas phase equilibrium addition of HO₂ radicals to CH₂O to form the peroxy radical HOCH₂OO^? is in agreement with the known thermochemistry of these species. The recent study of the similar addition of HO₂^? to ketones shows no significant reaction, which is again in agreement with known thermochemistry. All these reactions are notable for significant dipole attraction between the reactants ranging from 3 to 7 kcal/mol. The thermochemistry shows that the hydroperoxyl alkoxy species, the primary possible adduct, is not favored by the free energy change for direct addition. This and the observed kinetics favor a concerted addition, H‐atom transfer, as the transition state for the reactions. Kinetic estimates for forward and reverse reactions are in good agreement with observations. A thermochemical examination of the step‐wise addition of HO₂^? to the carbonyl shows that the reaction proceeds through a concerted, cyclic transition state involving simultaneous H‐transfer, 3 + 2 cyclo‐addition of HO₂^? to the carbonyl group. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 509–512, 2001     

Interior-point methods for nonconvex nonlinear programming: regularization and warmstarts

In this paper, we investigate the use of an exact primal-dual penalty approach within the framework of an interior-point method for nonconvex nonlinear programming. This approach provides regularization and relaxation, which can aid in solving ill-behaved problems and in warmstarting the algorithm. We present details of our implementation within the loqo algorithm and provide extensive numerical results on the CUTEr test set and on warmstarting in the context of quadratic, nonlinear, mixed integer nonlinear, and goal programming. Research of the first author is sponsored by ONR grant N00014-04-1-0145. Research of the second author is supported by NSF grant DMS-0107450.     

An Experimental Study of CO<Subscript>2</Subscript> Exsolution and Relative Permeability Measurements During CO<Subscript>2</Subscript> Saturated Water Depressurization

Dissolution of CO₂ into brine is an important and favorable trapping mechanism for geologic storage of CO₂. There are scenarios, however, where dissolved CO₂ may migrate out of the storage reservoir. Under these conditions, CO₂ will exsolve from solution during depressurization of the brine, leading to the formation of separate phase CO₂. For example, a CO₂ sequestration system with a brine-permeable caprock may be favored to allow for pressure relief in the sequestration reservoir. In this case, CO₂-rich brine may be transported upwards along a pressure gradient caused by CO₂ injection. Here we conduct an experimental study of CO₂ exsolution to observe the behavior of exsolved gas under a wide range of depressurization. Exsolution experiments in highly permeable Berea sandstones and low permeability Mount Simon sandstones are presented. Using X-ray CT scanning, the evolution of gas phase CO₂ and its spatial distribution is observed. In addition, we measure relative permeability for exsolved CO₂ and water in sandstone rocks based on mass balances and continuous observation of the pressure drop across the core from 12.41 to 2.76 MPa. The results show that the minimum CO₂ saturation at which the exsolved CO₂ phase mobilization occurs is from 11.7 to 15.5%. Exsolved CO₂ is distributed uniformly in homogeneous rock samples with no statistical correlation between porosity and CO₂ saturation observed. No gravitational redistribution of exsolved CO₂ was observed after depressurization, even in the high permeability core. Significant differences exist between the exsolved CO₂ and water relative permeabilities, compared to relative permeabilities derived from steady-state drainage relative permeability measurements in the same cores. Specifically, very low CO₂ and water relative permeabilities are measured in the exsolution experiments, even when the CO₂ saturation is as high as 40%. The large relative permeability reduction in both the water and CO₂ phases is hypothesized to result from the presence of disconnected gas bubbles in this two-phase flow system. This feature is also thought to be favorable for storage security after CO₂ injection.     

Fabrication of heavy metal fluoride glass, optical planar waveguides by hot-spin casting

Hot-spin casting is further investigated using a customised rig for making optical planar waveguides from inorganic-compound-glasses. The rig enables a controlled mass of core-glass, held above its liquidus, to be gravity-cast onto the top surface of a spinning cladding-glass substrate that has been pre-heated to around its glass transformation temperature. Spinning encourages the cast liquid to spread as a film over the top surface of the glass substrate. The mass of liquid cast is controlled by the timed opening of an orifice in the base of the core-glass melt-crucible. The resulting step index, slab optical waveguides are annealed, then cooled to room temperature; they comprise a higher refractive index, glass film core, on top of a lower refractive index glass substrate cladding. The glass film core is air-clad. at its upper surface. The process is applied to two heavy metal fluoride core/clad. glass pairs, namely ZBLANPb/ZBLAN and ZBLALiYPb/HBLANY (where ZBLANLiYPb is ZrF₄-BaF₂-LaF₃-AlF₃-LiF-YF₃-PbF₂ and H is HfF₄) to give waveguides of small and large numerical aperture (NA) (e.g. at 643.8 nm wavelength, NA is 0.18 and 0.33, respectively). The Hot-Spin-Cast waveguides exhibit a guiding region whose top surface tends to be parallel to the upper surface of the underlying substrate. However, flatness of the top surface of the guiding region is limited by the flatness of the top surface of the underlying substrate. Multimode slab waveguiding is demonstrated for both NA waveguide types for glass film cores of depths ?10 μm.     

Basic and reductive sulfone-directed ring-opening reactions of difluorinated oxa[2.2.1]bicycloheptanes

Phenylsulfenyl chloride reacts with racemic endo Diels-Alder adduct 4 (DEC = CONEt(2)) to afford lactone 8, which can be reduced and protected in a series of high-yielding steps. Key sulfone 10 can be ring opened under strong base conditions to afford vinyl sulfone 11. Attempted desulfonation resulted in the formation of a monofluoroalkene, but a direct desulfonation/eliminative ring opening with strain relief delivered highly functionalized monocyclic species 16. [reaction: see text]     

Very low-pressure pyrolysis (VLPP) of t-butylmethyl ether

The thermal decomposition of t-butylmethyl ether has been studied using the VLPP technique. The recommended Arrhenius parameters for the molecular elimination, reaction (1), are A(800°K) = 10^{1 3, 9} sec^?1 and E_a (800°K) = 59.0 ± 1.0 kcal/mole. No radical reactions occur under the conditions used. These parameters are in good agreement with earlier experimental work and with theoretical estimates of both A and E.