UVB Radiation Affects Growth,Reproduction and Tissue Structure of Daphnia magna Across Several Temperatures

We examined the effects of daily exposure to UVB on growth, reproduction and histological characteristics of Daphnia magna over two generations at 20, 22, 25 and 30°C. Animals were exposed to 16 h of UVA and photosynthetically active radiation daily. Treated animals received 6 h of UVB during the light phase. Parental (P) generation growth and reproduction was impaired by exposure to UVB at all temperatures, with the poorest production at 30°C. First brood size decreased with UVB exposure; it was lowest at 30°C. Although F1 length at birth increased with P generation age, F1 produced by UVB‐exposed mothers were smaller at all temperatures. The F1 generation was followed at 20 and 25°C; at both temperatures UVB exposure reduced F1 growth and reproduction. F1 growth and F2 production were lowest when both P and F1 generations were exposed to UVB. UVB exposure damaged ovarian and gut tissue at both 25 and 30°C; the consequences of this exposure were more severe at 30°C. The observed tissue damage may relate directly to the UVB‐induced impairment of growth and reproduction. This study provides new insights into the effects of UVB on an important component of the pelagic zooplankton.     

Fits to new calculations of photoionization cross sections for low-Z elements

Analytical approximations to results of new calculations of partial (i.e. by subshell) photoionization cross sections of elements (2 < Z < 30, Z = 36) are presented which cover the photon energy range from near threshold to 300 keV. The computer program developed by Brysk and Zerby, which is based on the single-electron model and uses screened self-consistent field and Dirac-Slater wave function data furnished by Cromer, Waber and Liberman, was used. Sufficient multipoles were included to calculate the partial cross sections within a few per cent, on the assumed model. Results for several elements are compared with other calculations and measurements of total photoionization cross sections. The results are presented in a form most convenient for calculations of opacities of hot gases.     

'Double redox-activity' in azobenzene-quinonoid palladium(II) complexes: a combined structural, electrochemical and spectroscopic study

Reactions of [(az(-H))Pd(μ-Cl)(2)Pd(az(-H))] (az = azobenzene) with the zwitterionic, p-benzoquinonemonoimine-type ligands 4-(n-butylamino)-6(n-butylimino)-3-oxocyclohexa-1,4-dien-1-olate (Q(1)) or 4-(isopropylamino)-6(isopropylimino)-3-oxocyclohexa-1,4-dien-1-olate) (Q(2)) in the presence of a base leads to the formation of the mononuclear complexes [(az(-H))Pd(Q(1)(-H))] (1) and [(az(-H))Pd(Q(2)(-H))] (2) respectively. Structural characterization of 2 shows an almost square planar coordination geometry around the Pd(II) centre, a short Pd-C bond, a slight elongation of the N=N double bond of the az(-H) ligand and localization of the double bonds within the Q(2)(-H) ligand. Additionally, intermolecular N-H-O interactions exist between the uncoordinated N-H and O groups of two different molecules. Cyclic voltammetry of the complexes reveals an irreversible oxidation and two reversible reduction processes. A combination of electrochemical and UV-vis-NIR and EPR spectroelectrochemical studies are used to show that both coordinated ligands participate successively in the redox processes, thus revealing their non-innocent character.     

Acoustic characterization of ultrasonic transducer materials: I. Blends of rigid and flexible epoxy resins used in piezocomposites

Five different types of Dow epoxy blends were studied with differential scanning calorimetry. Each epoxy blend consists of a flexible epoxy resin, DER 736 or DER 732, with one of four different rigid epoxies, DER 317, DER 331, DER 332 and DEN 431, crosslinked by 1,4-bis (3-aminopropyl)-piperazine (BAPP). Longitudinal and shear wave acoustic properties of these epoxy resin blends as a function of the composition were measured at room temperature and an ultrasonic frequency range. All moduli and Poisson's ratios were calculated by using longitudinal velocity, shear velocity and density. These systems all have similar behavior. By increasing the amount of flexible epoxy in a mixture of hard and flexible epoxies a critical composition was found (∼50% by weight for DER 736 and ∼30% for DER 732), below which the acoustic properties, the elastic moduli and Poisson's ratios kept an almost constant value, and above which the velocities, impedances and all moduli decreased, whereas attenuations and Poisson's ratios increased gradually. Many epoxy materials ranging from soft and flexible to hard and rigid have been obtained by epoxy blend technology. Some of them have been applied to make 1–3 composites for medical ultrasound transducers.     

On the calculation of scattering cross sections from absorption cross sections

A dispersion-type relation between photon scattering and absorption cross sections is derived. It is shown that the relation gives the correct scattering cross section in the low and high frequency limits, and is consistent with the Kramers-Heisenberg formula in the vicinity of a resonance. The practical application of the relation is illustrated by calculations of the scattering cross section and refractive index of He and Ne at STP and dry air at 1200°K from known absorption cross section data. The method is useful for obtaining scattering cross sections, polarizabilities, and refractive indices at elevated temperatures.     

Threshold electron excitation of azulene

Intense energy absorption at 2.44 eV is observed in the threshold electron excitation spectrum of azulene vapor. Direct excitation of triplet states or an electron-molecule resonance may account for this striking feature.     

Age-dependent survival, reproduction and photorepair activity in Daphnia magna (Straus, 1820) after exposure to artificial ultraviolet radiation

We examined age-related vulnerability of Daphnia magna to UV-B (ultraviolet-B radiation, 280-320 nm), the age-related relationships between UV-B dosage and reproduction, and the effects of duration of PRR (photorecovery radiation) on survival and fecundity. Animals were exposed to 0, 6, 9 or 12 h UV-B (peak emission 312 nm) at 1, 2, 3 or 4 days of age and followed to 12 days. Survival decreased with increasing exposure to UV-B, but increased with age at exposure. Duration of UV-B, but not age at exposure, decreased offspring production. Survival increased with an increase in duration of PRR for animals of all ages; however, the effect was not age related. Three-day-old animals were exposed to 6 h of UV-B followed by 0-600 min of PRR. Survival was greatest in controls, lowest in the group that received no PRR and similar for all other groups. Most mortality occurred within the first 72 h postirradiation. Offspring production was highest in light controls, lowest in the UV-B-exposed group that received no PRR and not significantly different among other groups. This study demonstrates the need to consider age when examining the effects of UV-B on zooplankton and the need to monitor responses over a sufficient length of time.     

The Effect of Chronic Exposure to Artificial UVB Radiation on the Survival and Reproduction of Daphnia magna Across Two Generations

We examined the effects of daily (chronic) exposure to artificial UVB radiation on the survival and reproduction of Daphnia   magna over two generations. Control and experimental animals in each generation (parental and F1) were exposed to 16 h of UVA radiation and photosynthetically active radiation daily. In addition, experimental animals were exposed to 6 h of UVB during the middle of the light period. Survival and reproduction were followed for 12 days for each individual. Survival and production of F1 were significantly lower in the UVB exposed parental generation Daphnia than in controls. F1 exposure to UVB significantly decreased F1 survival and reproduction. Reproduction was lowest in UVB exposed F1 animals whose parents were also exposed to UVB. Adverse effects of UVB on offspring production may be magnified in successive generations suggesting that short-term experiments could underestimate the impact of increased UVB exposure on populations.