http://nova.newcastle.edu.au/vital/access/services/Feed ${session.getAttribute("locale")} 5 http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:12462 This paper investigates the initial yield surface of a new type of hollow sphere structure (HSS). For this new type, the sphere shell is perforated by several holes in order to open the inner sphere volume and surface. Multi-axial tensile loading is applied to investigate the initial yield surface of perforated HSS with ideal plastic base material properties. The influence of the hole diameters and different geometries of linking elements on the initial yield surface are shown. The results are compared to classical configurations without perforation. It is shown that the initial yield surface can be represented as a cone in the principal stress coordinate system. Increasing of the hole diameter (decreasing of the average density) decreases the diameter of this cone. Compared to the changes for different hole diameters, the shape of the initial yield surface is less sensitive to the geometry of the link between two spheres. In addition, the elastic properties of PHSS, i.e. Young's modulus and Poisson's ratio, are investigated. To this end, three-dimensional finite element analysis is used to investigate primitive cubic unit cell models. 2013-01-22T04:54:45.165Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:11978 An unsaturated soil is not a special type of soil, rather a state of the soil. All soils can be partially saturated with water. A constitutive model should therefore represent the soil behaviour over all possible values of pore pressures and stresses. There are many concepts related to constitutive models for unsaturated soils, e.g., suction, net stress, effective stress, apparent consolidation, loading-collapse yield surface, suction-increase yield surface, etc. These concepts seem to make unsaturated soil modelling very special. This paper gives a critical review of these concepts, in an attempt to clarify some common confusion in constitutive modelling of unsaturated soils. 2012-11-09T05:12:35.637Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:11690 The SFG model (Sheng et al. 2008) provides a consistent explanation of yield stress, shear strength and volume change behaviour of unsaturated soils as functions of suctions. All these functions are based on one single equation that defines the volume change with suction and stress changes. This paper provides a systematic validation of the equation against experimental data. The experimental data used in the paper include those for samples prepared from slurry soils and compacted soils. It is shown that (I) the method currently used to determine yield stresses of unsaturated soils is incorrect and (2) volume change behaviour of unsaturated soils can well be predicted by the SFG model. 2012-10-09T05:15:27.154Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:11171 There are four generally mutually exclusive requirements that plague many mass spectrometric measurements of trace constituents: (1) the small size (limited by the depth probed) of many interesting materials requires high useful yields to simply detect some trace elements, (2) the low concentrations of interesting elements require efficient discrimination from isobaric interferences, (3) it is often necessary to measure the depth distribution of elements with high surface and low bulk contributions, and (4) many applications require precise isotopic analysis. Resonant ionization mass spectrometry has made dramatic progress in addressing these difficulties over the past five years. 2012-08-02T01:11:00.472Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:10446 Typical uniaxial stress-strain curves for different types of bones are shown in Figure 6.1 for the compressive regime. For all the curves, an initial linear elastic behavior can be observed. The common approach is to describe this elastic part on the basis of Hooke's law, cf. Sections 6.3 .1-6.3.4. This elastic range is followed by a strong nonlinear behavior of almost constant stress (so-called stress plateau). At higher strains, some curves show a strong increase in the stress where densification begins. 2012-03-20T00:40:04.473Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:9650 Invertase (INV) hydrolyzes sucrose into glucose and fructose, thereby playing key roles in primary metabolism and plant development. Based on their pH optima and sub-cellular locations, INVs are categorized into cell wall, cytoplasmic, and vacuolar subgroups, abbreviated as CWIN, CIN, and VIN, respectively. The broad importance and implications of INVs in plant development and crop productivity have attracted enormous interest to examine INV function and regulation from multiple perspectives. Here, we review some exciting advances in this area over the last two decades, focusing on (1) new or emerging roles of INV in plant development and regulation at the post-translational level through interaction with inhibitors, (2) cross-talk between INV-mediated sugar signaling and hormonal control of development, and (3) sugar- and INV-mediated responses to drought and heat stresses and their impact on seed and fruit set. Finally, we discuss major questions arising from this new progress and outline future directions for unraveling mechanisms underlying INV-mediated plant development and their potential applications in plant biotechnology and agriculture. 2011-12-07T04:50:03.557Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:8920 The roof area connected to the rainwater tank is an important determinant for rainwater yield at the household scale. This study monitored the performance of a "Rainwater Harvesting System" that supplies a rainwater tank using an innovative configuration of the downpipe and gutter system that maximises connected roof area. Roof runoff is redirected in the gutter system towards the rainwater tank by closing downpipes during rain events. Roof runoff from non-connected roof areas would otherwise be directed to street drainage. The system was installed on a residential dwelling in Brisbane (QLD, Australia) and the site was continuously monitored for rainfall, water demand and water levels in the rainwater tank (6-minute timesteps). Monitoring data was used to calibrate PURRS (Coombes, 2002) to determine the long term rainwater yield at the allotment scale based on an 83 year rainfall record (Brisbane). Rainwater yield increased from 72 kLyr (with 5 kL tank only) to 142 kL/yr after connected roof area was maximised using the Rainwater Harvesting System. Results also highlight household water demand and connected roof area is more important than the size of the rainwater tank for increasing rainwater yield at the household scale. 2011-09-12T05:50:12.447Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:8069 This paper presents a nonlinear analysis of reinforced concrete structures. Various yield surfaces of concrete are reviewed in the beginning and then a recently proposed yield surface for concrete is introduced. The yield surface considers the behavior of concrete in a three-dimensional stress state. Based on the yield surface, a nonlinear finite element formulation is provided to facilitate a three-dimensional analysis of reinforced concrete structures. An eight-node brick element is used in the analysis. Several numerical examples are given to show the ability of the yield surface in solving nonlinear reinforced concrete problems. 2011-07-05T05:50:09.494Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:7660 The authors thank the discussers for their interest in the paper and for pointing out the error in Equation 5. The discussers compared the bearing capacity factors predicted by different models for a smooth circular footing. However, the comparison indicates that all the methods over-estimate the bearing capacity factor, and the Tresca–Mises method, which includes a greater approximation to the original Tresca plastic potential function, gives a closer prediction to the exact solution. The method proposed by the discussers shows about 7% inaccuracy as compared with the exact solution. It is the view of the authors that this numerical example fails to show how application of a more accurate flow rule in a finite element analyses will result in a better prediction. 2011-05-03T04:40:10.404Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:7624 Flocs were produced by adding three cationic polymers (10% charge density, 3.0 × 10⁵ g/mol molecular weight; 40% charge density, 1.1 × 10⁵ g/mol molecular weight; and 100% charge density, 1.2 × 10⁵ g/mol molecular weight) to 90 nm diameter silica particles. The shear yield stresses of the consolidated sediment beds from settled and centrifuged flocs were determined via the vane technique. The polymer charge density plays an important role in influencing the shear yield stresses of sediment beds. The shear yield stresses of sediment beds from flocs induced by the 10% charged polymer were observed to increase with an increase in polymer dose, initial solid concentration and background electrolyte concentration at all volume fractions. In comparison, polymer dose has a marginal effect on the shear yield stresses of sediment beds from flocs induced by the 40% and 100% charged polymers. The shear yield stresses of sediments from flocs induced by the 40% charged polymer are independent of salt concentration whereas the addition of salt decreases the shear yield stresses of sediments from flocs induced by the 100% charged polymer. When flocculated at the optimum dose for each polymer (12 mg/g silica for the 10% charged polymer at 0.03 M NaCl, 12 mg/g for 40% and 2 mg/g for 100%), shear yield stress increases as polymer charge increases. The effects observed are related to the flocculation mechanism (bridging, patch attraction or charge neutralisation) and the magnitude of the adhesive force. Comparison of shear and compressive yield stresses show that the network is only slightly weaker in shear than in compression. This is different than many other systems (mainly salt and pH coagulation) which have shear yield stress much less than compressive yield stress. The existing models relating the power law exponent of the volume fraction dependence of the shear yield stress to the network fractal structure are not satisfactory to predict all the experimental behaviour. 2011-05-02T06:00:11.801Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:4917 The model recently presented by Sheng, Fredlund, and Gens, known as the SFG model, provides a consistent explanation of yield stress, shear strength, and volume change behaviour of unsaturated soils as functions of suction. All these functions are based on one single equation that defines the volume change with suction and stress changes. This paper provides a systematic validation of the equation and the derived shear strength criterion against experimental data. The experimental data used include those for samples prepared from slurry soils and compacted soils. It is shown that (i) the method currently used to determine yield stresses of unsaturated soils is incorrect, (ii) volume change behaviour of unsaturated soils can be well predicted by the SFG model, and (iii) shear strength behaviour of unsaturated soils can be represented very well by the criterion in the SFG model. 2010-09-27T05:40:02.622Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:1404 High Yield Equity Notes are securities that provide the noteholder with a cash flow stream that comprises a fixed yield and a short position in a European put option on the shares of an Australian company. This paper examines the pricing of these securities and finds apparent overpricing compared with expectations given standard pricing relationships. This apparent overpricing is consistent with the low transaction costs incurred by purchasers of High Yield Equity Notes. 2010-04-27T06:53:10.401Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:1557 In recent years, fine particles have been found to be the cause of various harmful effects on health, and many countries have imposed restrictions on emission of these particles. Fine ash particles are formed during coal combustion in power stations and, if not collected in the air pollution control devices, are emitted into the atmosphere. The fine ash particles can remain airborne for long periods and can result in deleterious health effects when inhaled and deposited in the lungs. Previous studies have shown that combustion of coals of different rank can result in differences in the amount and chemistry of the submicron ash particles. This study examines the variability occurring between the submicron ashes formed from coals of similar rank. Five Australian bituminous coals were burned in a laminar flow drop tube furnace in two different oxygen environments to determine the amount and composition of submicron ash formed. The experimental setup is described and the repeatability of the experiments is discussed. The variability in the submicron ash yield as a percentage of the total ash collected and the submicron ash composition are presented and discussed. This paper presents experimental results rather than a detailed discussion on its interpretation. However, the results indicate that the condensation of evaporated species is responsible for the formation of ash particles smaller than 0.3 μm 2010-04-27T06:27:51.490Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:160 [1] The water table fluctuation method for determining recharge from precipitation and water table measurements was originally developed on an event basis. Here a new multievent time series approach is presented for inferring groundwater recharge from longterm water table and precipitation records. Additional new features are the incorporation of a variable specific yield based upon the soil moisture retention curve, proper accounting for the Lisse effect on the water table, and the incorporation of aquifer drainage so that recharge can be detected even if the water table does not rise. A methodology for filtering noise and non- rainfall- related water table fluctuations is also presented. The model has been applied to 2 years of field data collected in the Tomago sand beds near Newcastle, Australia. It is shown that gross recharge estimates are very sensitive to time step size and specific yield. Properly accounting for the Lisse effect is also important to determining recharge. 2010-04-27T05:56:50.101Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:26 In recent years, fine particles have been found to be the cause of various harmful effects on health, and many countries have imposed restrictions on emission of these particles. Fine ash particles are formed during coal combustion in power stations and, if not collected in the air pollution control devices, are emitted into the atmosphere. The fine ash particles can remain airborne for long periods and can result in deleterious health effects when inhaled and deposited in the lungs. Previous studies have shown that combustion of coals of different rank can result in differences in the amount and chemistry of the submicron ash particles. This study examines the variability occurring between the submicron ashes formed from coals of similar rank. Five Australian bituminous coals were burned in a laminar flow drop tube furnace in two different oxygen environments to determine the amount and composition of submicron ash formed. The experimental setup is described and the repeatability of the experiments is discussed. The variability in the submicron ash yield as a percentage of the total ash collected and the submicron ash composition are presented and discussed. This paper presents experimental results rather than a detailed discussion on its interpretation. However, the results indicate that the condensation of evaporated species is responsible for the formation of ash particles smaller than 0.3 mu m. 2010-04-27T05:37:26.982Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:4629 Although a number of constitutive models for unsaturated soils exist in the literature, some fundamental questions have not been fully answered. There are questions related to (i) the change of the yield stress with soil suction, (ii)modelling slurry soils, and (iii) the smooth transition between saturated and unsaturated soil states. This paper addresses these questions by proposing an alternative modelling approach. The paper first presents a volumetric model for unsaturated soils. This volumetric model is then used to derive the yield surface in the suctiona- mean stress space. Hysteresis associated with soil-water characteristic curves is then formulated in the same framework of elastoplasticity. It is shown that volume collapse during wetting and plastic shrinkage during initial drying are both direct results of a suction-dependent hardening law. The proposed model seems to be more flexible in modelling different types of unsaturated soils than most models in the literature. The model can be applied to soils that are dried or loaded from initially slurry conditions, for soils that have low to high air-entry values, and for compacted soils as well. 2010-04-27T05:32:21.978Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:4732 Yield surfaces for unsaturated soils are usually non-convex if the size of the yield surface has to increase with increasing suction. An expanding yield surface with increasing suction is crucial for modelling the volume collapse due to wetting. The non-convexity always exists at the transition between saturated and unsaturated states, irrespective of the stress variables used in the model. Some recent models for unsaturated soils also possess a stress path dependent hardening law. The non-convexity and stress-path dependency of the constitutive model make the implementation into finite element codes very challenging. This paper discusses aspects of stress integration schemes for non-convex and stress-path dependent models for unsaturated soils. 2010-04-27T05:31:01.320Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:3472 Three different types of aggregates of submicron alumina particles were produced utilising either polymer, high salt (1.0 M), or low salt (0.075 M) aggregation conditions. All three types of aggregates had similar structural properties (mass fractal dimension = 2.0). The typical size (d[4,3]) of the polymer aggregates was 125 microns, the high salt aggregates 12 microns and the low salt aggregates 4 microns. It was found that smaller aggregates produced higher gel points and higher apparent maximum packing fractions. Larger aggregates produced higher shear and compressive yield stresses at all volume fractions. The relative effect that aggregate size and inter-particle attraction has on the sediment yield stresses was investigated in the salt system. The salt concentration was adjusted so as to produce different size aggregates with the same final salt concentration and thus same level of inter-particle attraction. The size of the aggregates and the magnitude of the inter-particle attraction were found to have similar contributions to the compressive yield stress over the range of size and attraction investigated. 2010-04-27T05:29:46.841Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:4098 The use of rainwater tanks as a supplement to traditional domestic urban water supply systems is becoming increasingly common, especially given growing environmental awareness and ongoing drought conditions. Such tanks must be appropriately configured in order to effectively meet demand. Two important aspects of this configuration are the preset mains trickle topup rate and trickle topup volume. Improper configuration of these parameters can result in ongoing tank failure. As such, there is a need to improve our understanding of how these parameters influence tank performance in various rainfall climates around Australia. This paper reports part of a study undertaken to address this need. For a range of topup volumes, it is shown that tank perfomance is highly dependent on climatic regime and demand, and only very weakly dependent on tank size. Seasonal variations in tank failure are investigated and correlated with rainfall and yield patterns. 2010-04-27T05:10:03.680Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:3385 The effect of adding non-adsorbing polymer, poly(acrylic acid) (PAA), on the rheological properties of concentrated electrostatically-stabilised polystyrene latex suspensions was investigated. The extrapolated yield stress of the depletion-flocculated suspensions was studied as a function of the concentration and the molecular weight of the free polymer. Specifically, the Bingham yield value was observed to increase with either an increase in the weight fraction of the polymer or through the use of a longer chain polyacid. Unlike the sterically stabilised colloidal suspensions studied in the literature, at high polymer concentrations these charge-stabilised latex particles exhibited plateauing in the yield stress for each polyacid. The energy of separating particles within an aggregate into single units was calculated using the yield stress and average particle co-ordination number. In contrast to what was commonly done in the literature, the latter was not assumed to be constant but estimated from the aggregate mass fractal dimension as obtained from static light scattering techniques. It was found that the separation energy showed similar trends to those in the yield stress with both varying the polymer concentration and molecular weight. These trends also bear remarkable similarities to those in the depth of the secondary potential energy well as measured using atomic force microscopy (AFM). 2010-04-27T05:04:13.116Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:4450 Three cationic polymers with molecular weights and charge density of 3.0 x 10⁵ g/mol and 10% (D 6010), 1.1 x 10⁵ g/mol and 40% (D6040), and 1.2 x 10⁵ g/mol and 100% (D6099) were investigated in aqueous NaCl solutions in the presence of silica. The atomic force microscope (AFM) colloidal probe technique was used to determine silica interparticle interaction forces. which were compared to macroscopic information on the strength of interactions such as compressive yield stress measurements. It was found that in 30 mM NaCl solution the 10% charged polymer produced steric repulsion upon approach and long-range adhesion with multiple pull off events upon retraction at the optimum flocculation concentration. This suggests that the polymer was adsorbed in a conformation where segments extend from the surface, resulting in bridging flocculation. The 40 and 100% charged polymers produced attraction upon approach and strong adhesion with snap out from contact upon separation at optimum polymer dosages. This suggests that these polymers are adsorbed with flat conformations and is typical of charge neutralization or patch attraction. The attractions for 40 and 100% charged polymers measured with the AFM are significantly larger than for the 10% charged polymer. The polymer dose that produced the optimum flocculation and the maximum compressive yield stress typically corresponded to the polymer concentration that produced the maximum adhesion for each polymer. It was found that the magnitude of the adhesive force was more significant in determining the compressive yield stresses of the silica particle sediments than the aggregate size and structure. 2010-04-27T04:58:53.189Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:3352 The zeta potentials and yield stresses of silica suspensions were measured over a wide range of monovalent electrolyte concentrations. The counterions investigated were Li⁺, Na⁺, K⁺, and Cs⁺, while the co-ion was always Cl⁻. The poorly hydrated ions (Cs⁺ and K⁺) adsorb in greater quantity to the silica surface than the well-hydrated ions (Li⁺ and Na⁺) and produce lower magnitude negative zeta potentials at high pH. At high electrolyte concentrations and at low pH the poorly hydrated counterions adsorb in great enough quantity to reverse the sign of the zeta potential from negative to positive. This specific adsorption of counterions shifts the iep to higher values. The shift in the iep is directly related to the hydration of the counterion with the least hydrated ions creating the greatest iep shift. The yield stresses of silica suspensions at high pH were found to increase in the order Li⁺ 2010-04-27T04:54:43.729Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:5229 Flocs were produced by adding three cationic polymers (10% charge density, 3.0×10⁵ g/mol molecular weight; 40% charge density, 1.1×10⁵ g/mol molecular weight; and 100% charge density, 1.2×10⁵ g/mol molecular weight) to 90nm diameter silica particles. The compressive yield stresses of the consolidated sediment beds from settled and centrifuged flocs were determined using the volume fraction profile method. The polymer charge density plays an important role in influencing the compressive yield stresses of sediment beds. The compressive yield stresses of sediment beds fromflocs induced by the 10% charged polymer were observed to increase with an increase in polymer dose, initial solids concentration, and background electrolyte concentration at all volume fraction. In comparison, polymer dose has marginal effect on the compressive yield stresses of sediment beds from flocs induced by 40% and 100% charged polymers. Initial solids concentration has no influence on the compressive yield stresses of sediment beds from flocs induced by either 40% or 100% charged polymers at the polymer doses used. The compressive yield stresses of sediments from flocs induced by the 40% charged polymer are independent of salt concentration whereas the addition of salt decreases the compressive yield stresses of sediments from flocs induced by the 100% charged polymer. It is found that the shear intensity during aggregation only affects the compressive yield stresses of sediments from flocs induced by the 10% charged polymer. When flocculated at the optimum dose for each polymer (12 mg/g silica for the 10% charged polymer at 0.03M NaCl, 12 mg/g for 40% and 2 mg/g for 100%), compressive yield stress increases as polymer charge increases. The effects observed are related to the flocculation mechanism (bridging, patch attraction or charge neutralisation) and the magnitude of the attractive force. 2010-04-27T04:40:47.378Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:5619 A stress update algorithm for elastoplastic models with nonconvex yield surfaces is presented. An explicit algorithm based on the Runge–Kutta embedded method of second-order accuracy is developed. The crossing of the yield surface is properly taken into account by means of a robust intersection-finding algorithm. This algorithm is based on a simple multiple-root-finding technique, which requires the yield function, evaluated along a given secant stress path, to be continuously differentiable to the second order. The accuracy of the intersection-finding algorithm is illustrated through examples using simple yield functions similar to the ones adopted in models for unsaturated soils and the modified Cam clay model yield surface with a nonconvex Argyris et al. failure criterion. Isoerror surfaces and finite element simulations are used to investigate the accuracy and efficiency of the stress update algorithm. It is observed that although the algorithm for nonconvex surfaces is slower than its equivalent for convex surfaces, the accuracy can be controlled locally by means of specified tolerances. 2010-04-27T04:39:14.240Z ]]>