Cooperative Research Centre

About: Cooperative Research Centre is a based out in . It is known for research contribution in the topics: Population & Sea ice. The organization has 7633 authors who have published 8607 publications receiving 429721 citations.

Effects of solidification rate and ageing on the microstructure and mechanical properties of AZ91 alloy

Abstract: Sand-cast plates of a commercial AZ91C alloy have been used for the study. Varying the solidification rate by placing large cast-iron chills in the mould produced a range of secondary dendrite arm spacing (SDAS) within the cast plates. The plates were solution heat-treated. quenched and aged at 165 degreesC for up to 350 h. The SDAS (mum) varied with the solidification time, t(f) (s), as SDAS = 5.3 t(f)(0.43). The tensile ductility in the as-quenched (T4) condition did not depend on the solidification rate whilst in the T6 condition it tended to decrease for slowly solidified material (SDAS > 50 mum). The yield strength and hardness increased and the ductility decreased with ageing. The fracture mode changed from predominantly transgranular in the T4 condition to predominantly intergranular in the T6 condition. The properties of the sand-castings are compared with those of high-pressure diecastings and the possible strengthening mechanisms are discussed. A number of areas that require more research are pointed out. (C) 2002 Elsevier Science B.V. All rights reserved.

Changing Expendable Bathythermograph Fall Rates and Their Impact on Estimates of Thermosteric Sea Level Rise

Abstract: A time-varying warm bias in the global XBT data archive is demonstrated to be largely due to changes in the fall rate of XBT probes likely associated with small manufacturing changes at the factory. Deep-reaching XBTs have a different fall rate history than shallow XBTs. Fall rates were fastest in the early 1970s, reached a minimum between 1975 and 1985, reached another maximum in the late 1980s and early 1990s, and have been declining since. Field XBT/CTD intercomparisons and a pseudoprofile technique based on satellite altimetry largely confirm this time history. A global correction is presented and applied to estimates of the thermosteric component of sea level rise. The XBT fall rate minimum from 1975 to 1985 appears as a 10-yr “warm period” in the global ocean in thermosteric sea level and heat content estimates using uncorrected data. Upon correction, the thermosteric sea level curve has reduced decadal variability and a larger, steadier long-term trend.

Positive-definite Toeplitz completion in DOA estimation for nonuniform linear antenna arrays. II. Partially augmentable arrays

Abstract: This paper considers the problem of direction-of arrival (DOA) estimation for multiple uncorrelated plane waves incident on so-called "fully augmentable" sparse linear arrays. In situations where a decision is made on the number of existing signal sources (m) prior to the estimation stage, we investigate the conditions under which DOA estimation accuracy is effective (in the maximum-likelihood sense). In the case where m is less than the number of antenna sensors (M), a new approach called "MUSIC-maximum-entropy equalization" is proposed to improve DOA estimation performance in the "preasymptotic region" of finite sample size (N) and signal-to-noise ratio. A full-sized positive definite (p.d.) Toeplitz matrix is constructed from the M/spl times/M direct data covariance matrix, and then, alternating projections are applied to find a p.d. Toeplitz matrix with m-variate signal eigensubspace ("signal subspace truncations"). When m/spl ges/M, Cramer-Rao bound analysis suggests that the minimal useful sample size N is rather large, even for arbitrarily strong signals. It is demonstrated that the well-known direct augmentation approach (DAA) cannot approach the accuracy of the corresponding Cramer-Rao bound, even asymptotically (as N/spl rarr//spl infin/) and, therefore, needs to be improved. We present a new estimation method whereby signal subspace truncation of the DAA augmented matrix is used for initialization and is followed by a local maximum-likelihood optimization routine. The accuracy of this method is demonstrated to be asymptotically optimal for the various superior scenarios (m/spl ges/M) presented.

Phosphorus dynamics in the rhizosphere of perennial ryegrass (Lolium perenne L.) and radiata pine (Pinus radiata D. Don.)

Abstract: A short-term glasshouse experiment was carried out with two grassland soils to investigate phosphorus (P) availability and associated processes in the rhizosphere of perennial ryegrass (Lolium perenne L.) and radiata pine (Pinus radiata D. Don.) using a thin slicing technique. Results showed that readily extracted forms of soil inorganic P were depleted by both ryegrass and radiata pine, although depletion zones extended further adjacent to radiata pine (5 mm) compared with ryegrass (3 mm). Accumulation of bicarbonate extractable organic P occurred in rhizosphere soil under both ryegrass and radiata pine, which was related to increased levels of microbial biomass. Enhanced depletion of sodium hydroxide extractable organic P apparent in the rhizosphere of radiata pine compared with ryegrass was related to the presence of greater concentrations of water-soluble organic C, microbial biomass and higher alkaline phosphatase and phosphodiesterase enzyme activities. These results confirmed that microbial and enzyme activities played an important role in the mineralization of soil organic P, particularly under radita pine.