Dielectronic recombination lines of C

The present paper presents atomic data generated to investigate the recombination lines of C ii in the spectra of planetary nebulae. These data include energies of bound and autoionizing states, oscillator strengths and radiative transition probabilities, autoionization probabilities, and recombination coefficients. The R-matrix method of electron scattering theory was used to describe the C²⁺ plus electron system.     

Tertiary aromatic amines as cure reaction promoters for unsaturated polyester resins. II. Low temperature studies

N,N-dimethyl-p-toludine (DMPT), N,N-dimethyl-m-toluidine (DMMT), and their isomeric blends, were compared to N,N-dimethylaniline (DMA) as cure reaction promoters for an unsaturated polyester resin using 1% benzoyl peroxide at 15°C and 10°C. The promoters showed the following order of efficiency (by weight) as indicated by decreased gel and cure times: DMPT > DMPT/DMMT blends > DMMT > DMA. Under these conditions the optimum promoter concentration was 0.3%. At this level or higher, 80/20 and 60/40 DMPT/DMMT blends (wt/wt) performed essentially equal to DMPT but superior to DMMT and DMA. Examination of cured samples using differential scanning calorimetry showed that resins cured with DMPT or isomeric blends of DMPT and DMMT with high DMPT contents displayed higher glass transition temperatures and greater degrees of cure than samples cured using DMMT or DMA.     

Unusual AMP-deaminase solubilization from teleost fish white muscle

A previous study described an unusual influence of neutral salts on the behavior of trout muscle AMP-deaminase (AMPD) in its interactions with subcellular particulate matter (Lushchak and Storey 1994, Fish Physiol. Biochem. 13: 356-368). The present study shows that this behavior is also shared by the muscle enzyme of two other fish species, sea scorpion (Scorpaena porcus) and corb (Sciena umbra), indicating that this describes a principle for AMPD interaction with cellular particulate material. AMPD binding to particulate matter increased with increasing KCl concentration through the physiological range (100-200 mM), but at higher salt concentrations the amount of bound enzyme was reduced. The pattern of binding was not influenced by hydrophobic interactions since addition of the nonionic detergents, Triton X-100 or Tween-80, did not alter the distribution of bound versus free enzyme although both detergents, at low concentrations, enhanced enzyme maximal activity. AMPD binding to particulate matter was also influenced by pH, the amount of free enzyme rising by nearly 3-fold as pH fell within the physiological range from 7.5 to 6.5. It is concluded that neither electrostatic nor hydrophobic forces alone can account for the unusual solubilization of AMPD from fish muscle and it is possible that the effect is also related to ion-induced conformational changes in the structure of AMPD and/or of the myosin to which the enzyme binds.     

Biofilms, thermophilic amoebae and Legionella pneumophila--a quantitative risk assessment for distributed water.

A simplistic quantitative microbial risk assessment (QMRA) based on the maximum risk curve (r = 1) was developed for Legionella within a water distribution system. Both biofilms and a thermophilic isolate of acanthamoebae were shown to increase the resistance of Legionella to conventional thermal disinfection by between one and two logs respectively. The level of risk presented to consumers was shown to exceed the USEPA 10(-4) benchmark in many cases tested. This was caused, in part, by the sensitivity of the risk model but also through a lack of reliable dose-response data for Legionella. Not withstanding this, the current study provided comparative information on the efficacy of conventional disinfection against Legionella. Combined chlorine was shown to reduce the risk of infection by as much as 1-log when compared to free chlorine, although thermal disinfection provided the most effective means of risk reduction. Biofilm detachment and the interaction of Legionella with acanthamoebae were two important ecological factors that significantly increased the risk of legionellosis, and thus should be further considered in the refinement of QMRA models.     

Mortality of Sitophilus oryzae (L.) and S. granarius (L.) in atmospheres produced by an exothermic inert atmosphere generator

The exposure to atmospheres with low O₂ required to kill 50 and 95% of the developing Sitophilus oryzae (L.) and S. granarius (L.) indicated that the earlier and later stages were more susceptible and the middle stages were less susceptible. At 27°C, the duration of exposure required to produce 95% mortality during the 4th instar through early pupal development was about 10 days for S. oryzae and 6 days for S. granarius. The toxicity of the atmosphere produced by an exothermic inert atmosphere generator to each stage of S. oryzae was higher at 27°C than at 21°C. Larvae and pupae of S. granarius were more susceptible to the atmosphere than corresponding stages of S. oryzae. The type of grain in which the S. oryzae were developing did not significantly alter the mortality due to the generated atmosphere.     

Extensive drought negates human influence on nutrients and water quality in estuaries

Impacts of land-use on estuarine environmental parameters and nutrients are well documented, but little is known about these characteristics during extensive periods of low water flow (i.e., drought). Droughts are set to increase in frequency and magnitude with climate change, and understanding their influence on ecosystems is imperative. We investigated differences in environmental parameters and nutrients in urban and rural estuaries during a period of prolonged low flow. Sampling was done along each estuary at multiple times to place small-scale variability in the context of land-use differences. No differences were detected between land-use for environmental parameters or nutrients in mean effects or variance structure. Urban estuaries had reduced variation in nutrients over time compared to rural estuaries, which suggested that their concentrations are more stable. Large differences existed within and between individual estuaries, and over time. Low freshwater flow conditions in estuaries provide a glimpse to future climate change impacts of drought, and a baseline upon which pollution and anthropogenic effects can be assessed.     

Regulation of ground squirrel Na+K+-ATPase activity by reversible phosphorylation during hibernation

BACKGROUND: Intrauterine growth restriction (IUGR) has been linked to impaired renal function and hypertension, suggesting that an adverse prenatal environment could alter kidney development and renin production. METHODS: Immunohistochemistry and in situ hybridization were employed to localize renin-containing cells (RCCs) in the deep, middle, and superficial zones of autopsy kidney sections, in parallel with histologic maturation, from unexplained stillborn fetuses of normal weight (N = 26) and stillborn fetuses with IUGR (N = 17). RESULTS: In the control group, the number of RCC per 100 glomeruli in the deep zone decreased with advancing gestation from 40 at 20 weeks gestation to five at term (P < 0.001), whereas the opposite change was found in the superficial zone (increase from 5 per 100 to 55 per 100; P < 0.001). In the IUGR group, the density of RCCs in both the superficial and deep zones was similar to the control group at 20 weeks, and no shift in renin gene expression was observed as gestation advanced. Histologic maturation was unaltered. CONCLUSIONS: Renin gene expression persists and predominates in the deep renal cortex of the stillborn IUGR fetus, and could contribute to the pathogenesis of neonatal oliguria and/or hypertension during postnatal life.     

Morphology and mechanical and dynamic mechanical properties of linear and star poly(styrene-b-isobutylene-b-styrene) block copolymers

The morphologies of solution cast linear and star poly(styrene-b-isobutylene-b-styrene) (SIBS) block copolymers, of ∼0.3-0.33 polystyrene (PS) volume fraction, were investigated using transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS) methods. The linear (L) and 4-arm star materials have hexagonal packed cylinder morphologies. TEM indicates more continuous domains for the 3-arm SIBS and SAXS indicates lamellar morphology. The diameters of the PS cylinders are 25-30 nm in all cases, but inter-domain distances increase in the order: L→3-arm star →4-arm star SIBS. Dynamic mechanical analysis shows a decrease of plateau modulus in the order L→3-arm →4-arm star. T_g for the PIB phase is independent of star-branching. T_g increases for the PS block phase from L- to 3-SIBS although T_g(PS) for 4-SIBS is not significantly greater than that of L-SIBS. A high temperature shoulder on the PIB block glass transition peak is associated with sub-Rouse motions. Tensile modulus is essentially the same for L- and 3-SIBS but considerably greater for 4-SIBS. Stress levels and energy-to rupture increase in the order: L-SIBS <3-SIBS <4-SIBS and this behavior is rationalized in terms of the covalent junction points, entanglements, and hard block domain reinforcement. The results of cyclic deformation studies of hysteresis vs. maximum percent strain per cycle are interpreted in terms of irreversible morphological rearrangements, chain slippage through entanglements, and the influence of degree of star branching on motional constraints. There is a permanent set that increases while the stress required to extend the sample to a given strain decreases with each cycle. For cycles of lower maximum strain, and before PS block domains are disrupted, microscopic deformation is viewed as somewhat reversible, accompanied by a measure of energy dissipated as a consequence of slow relaxation kinetics of chain rearrangement vs. rate of bulk deformation. At high strain, a major fraction of the energy loss is attributed to irreversible, longer ranged disruption of the PS domains leading to permanent morphological change and permanent set. Percent hysteresis for all three cases decreases—then increases—with increasing maximum percent strain per cycle. The initial decrease is thought of in terms of a progressive decrease in the entropy of stretched chains with consecutive extensions where the chains are increasingly less able to contribute to hysteresis until the PS domains become disrupted on a large scale, after which the curves begin to rise.     

Synthesis and characterization of A-B-A triblock copolymers derived from chloro-telechelic poly(l-lactide): combining ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP)

Ring-opening polymerization (ROP) of l-lactide was combined with atom transfer radical polymerization (ATRP) to produce well-defined linear block copolymers. Poly(l-lactide) (PLLA) was synthesized via ROP using ethylene glycol as an initiator and stannous octoate as a catalyst. The isolated hydroxy-telechelic PLLA was reacted with thionyl chloride and pyridine in toluene to afford chloro-telechelic PLLA (Cl-PLLA-Cl). The latter was employed as a macroinitiator in the synthesis of A-B-A triblock copolymers having either tert-butyl acrylate or benzyl acrylate outer blocks. Outer-block molecular weight was targeted by the mole ratio of monomer (acrylate) to the PLLA chloride initiating sites. The actual incorporation of acrylate into the triblock copolymer was lower than the molar feed ratio as the copolymer became increasingly less soluble upon conversion of acrylate in all cases.