Nitrogen balance for an agroforestry system irrigated with saline, high nitrogen effluent

Land disposal is commonly used for urban and industrial wastewater, largely due to the high costs involved in alternative treatments or disposal systems. However, the viability of such systems depends on many factors, including the composition of the effluent water, soil type, the plant species grown, growth rate, and planting density. The objective of this study is to establish whether land disposal of nitrogen (N) rich effluent using an agroforestry system is sustainable, and determine the effect of irrigation rate and tree planting density on the N cycle and subsequent N removal. We examined systems for the sustainable disposal of a high strength industrial effluent. The challenge was to leach the salt, by using a sufficiently high rate of irrigation, while simultaneously ensuring that N did not leach from the soil profile. We describe the N balance for two plant systems irrigated with effluent, one comprising Eucalyptus tereticornis and Eucalyptus moluccana and a Rhodes grass (Chloris gayana) pasture, and the other, Rhodes grass pasture alone. Nitrogen balance was assessed from N inputs in effluent and rainfall, accumulation of N in the plant biomass, changes in soil N storage, N loss in run-off water, denitrification and N loss to the groundwater by deep-drainage. Biomass production was estimated from allometric relationships derived from yearly destructive harvesting of selected trees. The N content of that biomass was then calculated from measured N content of the various plant parts, and their mass. Approximately 300 kg N/ha/yr was assimilated into tree biomass at a planting density of 2500 tree/ha of E. moluccana. In addition to tree assimilation, pasture growth between the tree rows, which was regularly harvested, contributed substantially to N uptake. If the trees were harvested after two years of growth and grass harvested regularly, biomass removal of N by the mixed system would be about 700 kg N/ha/yr. The results of this study show that the current system of effluent disposal is not sustainable as the nitrate leaching from the soil profile far exceeds standards set out by the ANZECC guidelines. Hence additional means of N removal will need to be implemented. Biological N removal is an area that warrants further studies as it is aimed at reducing N levels in the effluent before irrigation. This will complement the current agroforestry system.

Slow binocular rivalry in bipolar disorder

Background. The rate of binocular rivalry has been reported to be slower in subjects with bipolar disorder than in controls when tested with drifting, vertical and horizontal gratings of high spatial frequency. Method. Here we assess the rate of binocular rivalry with stationary, vertical and horizontal gratings of low spatial frequency in 30 subjects with bipolar disorder, 30 age- and sex-matched controls, 18 subjects with schizophrenia and 18 subjects with major depression. Along with rivalry rate, the predominance of each of the rivaling images was assessed, as was the distribution of normalized rivalry intervals. Results. The bipolar group demonstrated significantly slower rivalry than the control, schizophrenia and major depression groups. The schizophrenia and major depression groups did not differ significantly from the control group. Predominance values did not differ according to diagnosis and the distribution of normalized rivalry intervals was well described by a gamma function in all groups. Conclusions. The results provide further evidence that binocular rivalry is slow in bipolar disorder and demonstrate that rivalry predominance and the distribution of normalized rivalry intervals are not abnormal in bipolar disorder. It is also shown by comparison with previous work, that high strength stimuli more effectively distinguish bipolar from control subjects than low strength stimuli. The data on schizophrenia and major depression suggest the need for large-scale specificity trials. Further study is also required to assess genetic and pathophysiological factors as well as the potential effects of state, medication, and clinical and biological subtypes.

Stress corrosion cracking and hydrogen embrittlement of an Al-Zn-Mg-Cu alloy

The age hardening, stress corrosion cracking (SCC) and hydrogen embrittlement (HE) of an Al-Zn-Mg-Cu 7175 alloy were investigated experimentally. There were two peak-aged states during ageing. For ageing at 413 K, the strength of the second peak-aged state was slightly higher than that of the first one, whereas the SCC susceptibility was lower, indicating that it is possible to heat treat 7175 to high strength and simultaneously to have high SCC resistance. The SCC susceptibility increased with increasing Mg segregation at the grain boundaries. Hydrogen embrittlement (HE) increased with increased hydrogen charging and decreased with increasing ageing time for the same hydrogen charging conditions. Computer simulations were carried out of (a) the Mg grain boundary segregation using the embedded atom method and (b) the effect of Mg and H segregation on the grain boundary strength using a quasi-chemical approach. The simulations showed that (a) Mg grain boundary segregation in Al-Zn-Mg-Cu alloys is spontaneous, (b) Mg segregation decreases the grain boundary strength, and (c) H embrittles the grain boundary more seriously than does Mg. Therefore, the SCC mechanism of Al-Zn-Mg Cu alloys is attributed to the combination of HE and Mg segregation induced grain boundary embrittlement. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Service performance of engineering materials

Corrosion research by Atrens and co-workers has made significant contributions to the understanding of the service performance of engineering materials. This includes: (1) elucidated corrosion mechanisms of Mg alloys, stainless steels and Cu alloys, (2) developed an improved understanding of passivity in stainless steels and binary alloys such as Fe-Cr, Ni-Cr, Co-Cr, Fe-Ti, and Fe-Si, (3) developed an improved understanding of the melt spinning of Cu alloys, and (4) elucidated mechanisms of environment assisted fracture (EAF) of steels and Zr alloys. This paper summarises contributions in the following: (1) intergranular stress corrosion cracking of pipeline steels, (2) atmospheric corrosion and patination of Cu, (3) corrosion of Mg alloys, and (4) transgranular stress corrosion cracking of rock bolts.

A critical review of the stress corrosion cracking (SCC) of magnesium alloys

This review aims to provide a foundation for the safe and effective use of magnesium (Mg) alloys, including practical guidelines for the service use of Mg alloys in the atmosphere and/or in contact with aqueous solutions. This is to provide support for the rapidly increasing use of Mg in industrial applications, particularly in the automobile industry. These guidelines should be firmly based on a critical analysis of our knowledge of SCC based on (1) service experience, (2) laboratory testing and (3) understanding of the mechanism of SCC, as well as based on an understanding of the Mg corrosion mechanism.

Formation and mechanical properties of Mg65Cu25Er10 and Mg65Cu15Ag10Er10 bulk amorphous alloys

Mg65Cu25Er10 and Mg65Cu15Ag10Er10 bulk amorphous alloys were produced by a copper mould casting method. The alloys have high glass-forming ability and good thermal stability. The maximum diameter of glass formation (D-c), glass transition temperature (T-g), crystallization onset temperature (T-x), temperature interval of the supercooled region (Delta T-x), melting temperature (T-m), liquidus temperature (T-1) as well as heats of crystallization (Delta H-x) and melting (Delta H-m) are reported for these alloys. Both alloys exhibit high hardness and high strength at room temperature. (c) 2005 Elsevier B.V. All rights reserved.

Section thickness, macrohardness and yield strength in high-pressure diecast magnesium alloy AZ91

The yield strength of high-pressure diecast (hpdc) test bars of alloy AZ91 increases with decreasing section thickness while its hardness remains approximately constant. This behaviour is in contrast with that of the gravity cast alloy, whose hardness scales with the yield strength. Vickers hardness measured on the surface of hpdc test bars using increasing loads shows that the subsurface porosity layer usually found in hpdc material may gradually collapse under the indent, lowering the hardness. However, this is insufficient to explain the lack of correlation between hardness and yield strength. It is argued that the low strain-hardening rate of high-pressure diecast material leads to lower than expected hardness values. In addition, it is shown that the plastic zone under a macro indentation is largely contained by the softer core of the castings, rendering hardness insensitive to the casting thickness. It is concluded that macrohardness is too coarse a tool for a meaningful determination of the strength of hpdc material. (c) 2005 Elsevier B.V. All rights reserved.

Microhardness mapping and the hardness-yield strength relationship in high-pressure diecast magnesium alloy AZ91

Microhardness maps of cross-sections of high-pressure diecast test bars of AZ91 have been determined. Specimens with rectangular cross-sections, 1, 2 and 3 mm thick, or with a circular cross-section 6.4 mm in diameter, have been studied. The hardness is generally higher near the edges in all specimens, and more so near the corners of the rectangular specimens. The hardness at the center of the castings is generally lower, due to a coarser solidification microstructure and the concentration of porosity. The evidence confirms that the surface of the castings is harder than the core, but it does not support the concept of a skin with a sharp. and definable boundary. This harder layer is irregular in hardness and depth and is not equally hard on opposite sides of the casting. The mean hardness obtained by integrating the microhardness maps over the entire cross-section increased with decreasing thickness of the bars, and was found to be in good correlation with each bar's yield strength. (c) 2005 Elsevier B.V. All rights reserved.

Strength-ductility behaviour of Al-Si-Cu-Mg casting alloys in T6 temper

A comparative study of the mechanical properties of 20 experimental alloys has been carried out. The effect of different contents of Si, Cu, Mg, Fe and Mn, as well as solidification rate, has been assessed using a strength-ductility chart and a quality index-strength chart developed for the alloys. The charts show that the strength generally increases and the ductility decreases with an increasing content of Cu and Mg. Increased Fe (at Fe/Mn ratio 0.5) dramatically lowers the ductility and strength of low Si alloys. Increased Si content generally increases the strength and the ductility. The increase in ductility with increased Si is particularly significant when the Fe content is high. The charts are used to show that the cracking of second phase particles imposes a limit to the maximum achievable strength by limiting the ductility of strong alloys. The (Cu + Mg) content (at.%), which determines the precipitation strengthening and the volume fraction of Cu-rich and Mg-rich intermetallics, can be used to select the alloys for given strength and ductility, provided the Fe content stays below the Si-dependent critical level for the formation of pre-eutectic alpha-phase particles or beta-phase plates.

The effect of the reduction of carbon content on the toughness of high chromium white irons in the as-cast state

Three high chromium white cast irons were examined in the as-cast state to determine the effect of the carbon content on the fracture toughness. The plane strain fracture toughness K-Ic and the fracture strength were measured for each alloy. X-ray mapping was used to identify the phases on the fracture surfaces. Scanning electron fractography and optical microscopy were used to determine the volume fraction of each phase on the fracture surfaces. It was found that most fracture occurred in the eutectic carbides, but that for the alloys with a reduced volume fraction of eutectic carbides, a small amount of crack propagation occurred in the austenitic dendrites. This change in crack path correlated with an increase in fracture toughness. The Ritchie-Knott-Rice model of brittle fracture was applied. It was found to sensibly predict the critical length for fracture for each alloy. Deep etching was employed to examine the distribution of eutectic carbides. It was found that the eutectic carbides formed a continuous network in each case. (C) 2004 Kluwer Academic Publishers.

Early alterations in serum creatine kinase and total cholesterol following high intensity eccentric muscle actions

Aim. The purpose of this experiment was to assess the levels of muscle soreness, serum total cholesterol (TC) and creatine kinase (CK) in the first 48 hours following fatiguing eccentric exercise performed with the triceps brachii. Methods. Eleven untrained male college students performed a total of 50 eccentric elbow extensions in 8 sets (6x7 and 2x4) with a load equal to 85% of their maximal concentric elbow extension strength. Isometric elbow extension strength, muscle soreness and circumference, and serum CK and TC concentrations were measured before, immediately after, and 2, 24 and 48 hours after the exercise. Results. Statistically reliable changes in isometric strength, serum CK and TC, muscle soreness and upper arm circumference occurred within the first 48 hours following eccentric exercise. Serum TC concentrations exhibited a very rapid (within 2 hours) reduction from pre-exercise values after eccentric exercise to a relatively stable concentration of approximately 85% of baseline. Conclusion. These results suggest that serum TC concentration may follow the time-course of reductions in force generating capacity more closely than other biochemical markers of muscle damage.

Microstructure and mechanical properties of high pressure die cast magnesium alloy AE42 with 1% strontium

The addition of 1 wt-%Sr to AE42 results in an improvement in the tensile strength of the alloy at elevated temperatures of 150 and 175degreesC and an improvement in the constant load creep properties at 175degreesC. The improved elevated temperature tensile and creep strength of the alloy can be attributed to the presence of a strontium-containing phase in the microstructure of the alloy along with an increase in the stability of the microstructure of the alloy at high temperatures. (C) 2004 W. S. Maney Son Ltd.

Relationship between thirty post-thaw spermatozoal characteristics and the field fertility of 11 high-use Australian dairy AI sires

This study determined the relationship between two measures of field fertility of I I high-use Australian artificial insemination (AI) dairy bulls and thirty standard laboratory assessments of spermatozoal post-thaw viability. The two measures of field fertility used, conception rates (cCR) and non-return rates (cNRR), were both corrected for all major non-bull variables. Sperm viability assessments were conducted on semen collected within the same season as that used to derive the field fertility estimates. These assessments measured sperm concentration, motility, morphology and membrane integrity at thawing, after 2 h incubation and after the swim-up sperm selection procedure. Derivations of these measures and in vitro embryo fertilizing and developmental capacity were also determined. The Genstat Statistical Package [Genstat 5 Release 4.2 Reference Manual, VSN International, Oxford, 20001 was used to conduct an analysis of variance on the viability parameters across semen straws and bulls, and to calculate the strength of correlation between each semen parameter, cNRR and cCR in a correlation matrix. Step forward multiple regression identified the combination of semen parameters that were most highly correlated with cCR and with cNRR. The sperm parameters identified as being most predictive of cCR were the percentage of morphologically normal sperm immediately post-thaw (zeroNorm), the number of morphologically normal sperm after the swim-up procedure (nSuNorm), and the rate of zygote cleavage in vitro (Clv); the predictive equation formed by these parameters accounted for 70% of variance. The predictive equation produced for cNRR contained the variables zeroNorm, the proportion of membrane intact sperm after 2 h incubation at 37 degreesC (twoMem) and Clv and accounted for 76.5% of the variation. ZeroNorm was found to be consistent across straws and semen batches within-bull and the sperm parameter with the strongest individual predictive capacity for both cCR (P = 0.1) and cNRR (P = 0.001). Post-thaw sperm parameters can be used to predict field fertility of Australian dairy sires; the calculated predictive equations are particularly useful for identifying and monitoring bulls of very high and very low potential fertility within a group. (C) 2003 Elsevier B.V. All rights reserved.