Biomass production,water use and photosynthesis of Salix clones grown in a wastewater purification system

An objective of the study was to identify leaf morphophysiological characteristics indicative of high aboveground woody biomass production of Salix clones growing in the vegetation filter of a wastewater purification system. It was hypothesized, that in these extra irrigated stands, the characteristics of photosynthesis are stronger determinants of the production than the characteristics of leaf water relations. The biomass production of the clones was correlated with numerous characteristics of leaf water relations and photosynthesis. Significant correlation was found between the biomass production and the following characteristics of top foliage leaves: daily decrease in water potential, stomatal conductance, stomatal sensitivity to increase in light intensity, and hydraulic conductance (positive); daily minimum and maximum water potentials, instantaneous water use efficiency, and stomatal sensitivity to decrease in leaf water potential (negative); maximum rate of photosynthetic electron transport, chlorophyll content, and the partitioning coefficient for leaf nitrogen into bioenergetics associated with electron transport (positive). In the most productive clones, the vertical gradient (through foliage) of values of almost all the characteristics was the smallest. The biomass correlated more strongly with the characteristics of photosynthesis light stage than with the characteristics of water relations. We conclude that the characteristics of photosynthesis light stage – high maximum rate of photosynthetic electron transport, high chlorophyll content, and also flat vertical gradient (through foliage) in values of the characteristics could be the strongest indicators of high biomass production of Salix clones growing in vegetation filter.     

AN ANALYSIS OF CRACK TIP SHIELDING IN ALUMINUM ALLOY 2124: A COMPARISON OF LARGE, SMALL, THROUGH-THICKNESS AND SURFACE FATIGUE CRACKS

Abstract— The development of crack closure during the plane strain extension of large and small fatigue cracks has been investigated in a 2124 aluminum alloy using both experimental and numerical procedures. Specifically, the growth rate and crack closure behavior of long (∼17–38 mm) cracks, through-thickness physically-short (50–400 μm) cracks, and naturally-occurring microstructurally-small (2–400 μm) surface cracks have been examined experimentally from threshold levels to instability (over the range 10–^12–10–⁶m/cycle). Results are compared with those predicted numerically using an elastic-plastic finite element analysis of fatigue crack advance and closure under both plane stress and plane strain conditions. It is shown that both the short through-thickness and small surface cracks propagate below the long crack threshold at rates considerably in excess of long cracks, consistent with the reduced levels of closure developed in their limited wake. Numerical analysis, however, is found consistently to underpredict the magnitude of crack closure for both large and small cracks, particularly at near-threshold levels; an observation attributed to the fact that the numerical procedures can only model contributions from cyclic plasticity, whereas in reality significant additional closure arises from the wedging action of fracture surface asperities and corrosion debris. Although such shielding mechanisms are considered to provide a prominent mechanism for differences in the growth rate behavior of large and small cracks, other factors such as the nature of the stress and strain singularity and the extent of local plasticity are shown to play an important role.     

Complex petrogenetic modeling using spreadsheet software

Continuous melting and open-system fractional crystallization modeling can be performed readily using spreadsheet software. Separate portions of the spreadsheet are used for a distribution coefficient matrix, calculation of the bulk distribution coefficients, and a work area for the entry of data and the calculation of new compositions and mineral mass fractions. The relative ease of creating the models in the spreadsheet format, the ability to recalculate quickly the model when any of the variables are changed, and the graphics capabilities of the software, demonstrate the advantages of this approach as opposed to writing a computer program for the same task.     

Math, verbal, and general academic self-concept: The internal/external frame of reference model and gender differences in self-concept structure.

Tested predictions from H. W. Marsh's (see record 1987-17104-001) internal/external (I/E) frame of reference model (measuring cognitive dimensions of math and verbal self-concepts [S-Cs]), and gender differences in the structure of academic S-C were examined through path analyses of data from 231 Norwegian 6th-grade students (117 boys and 114 girls). Math and verbal S-Cs on a cognitive level were defined as success expectations on defined tasks. No strong support was found for the I/E model: Math and verbal S-Cs were highly correlated, and no significant negative direct effects were found of verbal achievement on math S-C or of math achievement on verbal S-C for boys, although a negative direct effect of verbal achievement on math S-C was found for girls. The results differed from previous research measuring evaluative dimensions of math and verbal S-Cs, suggesting either remarkable cultural differences or that academic S-Cs are more complex than has been assumed. The structure of S-C differed for boys and girls; math and verbal S-Cs related differently to general academic S-C. The gender differences are discussed in terms of sex stereotypes. This study has implications for research on academic S-C and gender differences. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Predominant microflora of downgraded Danish bulk tank milk

The microflora of downgraded Danish bulk tank milk was examined to identify the main causes of increased microbial counts. Seventy-five representative samples with a microbial count exceeding 3.0 x 10(4) cfu/mL were selected for a more detailed microbial examination. A total of 1237 isolates from these samples were identified. Gram-negative, oxidase-positive bacteria were found in 72% of the samples. Coliforms were found in 20% of the samples, and non-coliforms were found in 49% of the samples. Coryneforms, other gram-positive rods, Lactococcus spp., Micrococcus spp., and coagulase-negative Staphylococcus spp. were found in 28 to 53% of the samples. Bacillus spp., Enterococcus spp., Staphylococcus aureus, Streptococcus dysgalactiae, Streptococcus uberis, and yeasts were found in <25% of the samples. Additionally, the isolates were divided into 3 groups, based on the main cause of an elevated microbial count. Microorganisms primarily associated with poor hygiene dominated the microflora in 64% of the samples; bacteria also related to poor hygiene, but in addition associated with growth at low temperatures (psychrotrophic bacteria) dominated the microflora in 28% of the samples; and bacteria mainly associated with mastitis dominated the microflora in 8% of the samples. A bulk tank milk storage period of 48 h instead of 24 h did not affect the proportion of downgraded milk samples and could not be associated with a specific group of microorganisms. Further, no relationship was found between somatic cell counts and the presence of mastitis bacteria.