Sink Density Research Articles

Competitive interaction between two different spherical sinks.

Competitive interactions within diverse mixed populations of chemically active sites are prevalent throughout nature, science, and engineering. Their effects are readily seen in the distribution of dead and surviving aerobic cells within a thick biofilm and particle shape changes during the growth and coarsening of crystals. Even in the most dilute case, competition for a reactant requires at least two spheres/cells, and the solution of the two-spherical sink problem is of interest for several reasons. The solution accurately describes lower cell concentration behavior (10(8) cells/l), and like the Smoluchowski diffusion-reaction treatment for a single sphere, the analysis is extremely helpful in understanding the fundamental phenomena of the effect on the first spherical sink of the presence of a second different spherical sink. In addition these exact solutions are required for the systematic extension to higher density behavior by rigorous expansions in the spherical sink densities. The method of the twin spherical expansion is used with a formal matrix elimination scheme to generate an exact solution for two distinct spherical sinks of differing sizes and kinetics. The two sinks exist in a medium, which supplies a reactant to the sinks via Fickian diffusion. The two sinks compete for the same reactant with different first-order reactions occurring at the surface of each sink. Earlier work focused on two spherical sinks of the same size with identical surface reaction kinetics. This work has been advanced to allow for diversity in the theory of cellular or reactive sink competition. A number of interesting higher order interactive phenomena are observed in this paper when the different reactive sinks are in close proximity. (c) 2004 American Institute of Physics.

Short-range-ordering Kinetics of Cu—5 At.% Zn Influenced by Solute—Vacancy Complexes and Cold Rolling

A modified first-order kinetic law which takes into account defect decay during an ordering process was employed to predict the short-range-order kinetics of a quenched and a quenched-deformed Cu—5 at.% Zn alloy, in conjunction with experiments performed by isothermal calorimetry. The effective activation energy of point defect migration and its temperature dependence strongly suggest the contribution of bound vacancies to the ordering process. An estimate of 91.2 kJ mol−1 was made for the activation energy of solute—vacancy migration by applying an effective rate constant, a value in very good agreement with that obtained from previous non-isothermal experiments. The isothermal curves were utilized to determine the ordering energy: w=−2.90 kJ mol−1. In conjunction, a parametric study of the defect sink density was performed in order to assess its influence on the calculated isothermal curve profiles.

Static and Dynamic Stability in Dense Medium Separation Processes

Static and dynamic stability in dense medium separation processes are defined, and a model for dynamic DMS systems provides the density differential (a measure of dynamic stability) as a function of the static stability and parameters related to the geometry of separatory vessels and operating conditions. A pilot test rig was installed to: (a) study the behaviour of conical and cylindrical dense medium dynamic separators particularly concerning sink and float densities and density differential under different operating conditions; (b) check the correlation model between density differential and static stability. The results provide an interesting description of the different behaviour of conical and cylindrical vessels, regarding the density differential they exhibit, and help explain the differences between the performance of the two types of separators.

The Effect of Interphase Boundaries on Radiation Resistance of New Low-Activation and Chromium-Nickel Stainless Steels under High-Dose Irradiation up to 200 DPA

This paper deals with the evolution of the dislocation structure, phase composition and vacancy voids in new reactor stainless steels over the temperature interval from 550 to 650 °C under irradiation with krypton ions up to high damaging doses (200 dpa). It is shown that the amount of voids formed in stainless steels exposed to irradiation with high-energy particles can be reduced by producing a high density of direct sinks of point defects in the form of α/γ phase boundaries. Compositions of radiation-resistant alloys, including low-activation ones of the Cr13Mn7W2 type having an austenitic-martensitic lath structure, have been proposed.

Damage behavior in an electron/helium dual-beam irradiated Fe–Cr–Mn(W,V) alloy

Results of dual-beam irradiations with electrons and helium ions indicated that the formation of secondary defects (dislocation loops, dislocation networks, voids) was enhanced in an irradiated Fe–Cr–Mn(W,V) alloy, and in particular, voids formed preferentially on dislocation lines at elevated temperature and that the segregation of Cr, Mn to sinks was suppressed. The reason was that helium strongly interacts with vacancies, which in turn decreases the diffusivity of vacancies and increases the density of sinks in matrix.

Competition between gall aphids and natural plant sinks: plant architecture affects resistance to galling.

Gall forming herbivores induce sinks and act as phloem parasites within their host plants. Their performance on the host plant can depend on the sink-source relationship they establish with the plant. Because sink-source relationships within a plant are reflected in its architecture, we examined how architectural differences among cottonwoods might influence the success of the galling aphid, Pemphigus betae. Using cloned cottonwoods in common garden studies, we found three major patterns. First, there is a significant clonal or genetic component to tree architecture; cloned trees grown in a common garden maintain the architecture of parental trees. Second, resistant tree genotypes have more natural sinks (i.e., buds) relative to sources (i.e., stem volume) than susceptible trees. Third, these differences in architecture result in greater competition among sinks on aphid-resistant trees than on aphid-susceptible trees. Sink competition within a tree was estimated by the Gini coefficient which quantifies the size inequality of a shoot population (i.e., competition among sinks is low when shoots are nearly equal in size, and great when a few shoots are large and most are small). Aphid death through gall abortion increased significantly (r 2 = 0.65) on garden-grown trees as competition among sinks within a tree increased. Based on these observations we proposed the "sink competition hypothesis" to account for the performance of gall formers on their host plants. To test this hypothesis, we experimentally reduced sink densities (i.e., buds) on branches of resistant tree genotypes to resemble the bud densities of susceptible genotypes. By reducing the number of competing sinks, we predicted that aphid survival would increase. As predicted, aphid survival significantly increased. For example, in one removal experiment, aphid survival increased from 20% on control branches to 55% on branches with the highest level of bud removal. Similar bud removals on susceptible trees did not increase aphid survival, indicating that competition is relaxed on susceptible hosts. With the exception of the plant vigor hypothesis, most current hypotheses explaining herbivore distributions in nature focus on the importance to leaf-chewing herbivores of variation in chemistry. We believe that a sink competition model is needed to explain the distributions of the diverse group of herbivores that act as phloem parasites. The sink competition model is more mechanistic than the vigor hypothesis, and may account for apparent contradictions because it more clearly quantifies the resource base and the potential interactions that occur when sinks, either herbivore-induced or natural, compete for sources.

Deformation instability and generation of ordered surface structures by laser radiation

A model is proposed to account for a deformation instability which appears under the action of powerful laser radiation in a system of point defects on the surface of a solid with a high density of sinks. It is shown that the development of this instability under conditions linear in respect of the amplitude creates complex three-dimensional surface structures of coupled strain and defect-density fields (rings, radial arrays, one- and two-dimensional lattices). Dispersion relationships are derived for the growth increment of these structures and their characteristic sizes (grating period, number of rays in a structure) are found.

Assessment of quenched-in order and vacancies using modelling and differential scanning calorimetry

Using a rate vacancy loss equation and an overall rate constant for order establishment, a model for describing the roles of quench temperature, quench rate and vacancy sink density is proposed. This model allows computation of the retained value of the first short-range order parameter of quenched binary alloys and the prediction that the most highly disordered state obtainable occurs with quenches from intermediate temperatures. Numerical results were tested against experimental data based on energetic analysis of differential scanning calorimetric traces pertaining to a reordering process towards the equilibrium state. Kinetic evaluations of these traces yield experimental estimates of quenched-in vacancy concentrations. Good agreement between modelled and experimental assessments was obtained in a Cu-30 at.% Zn alloy.

A magnetization study of the development of short-range order in a concentrated - Mn spin glass

The kinetics of short-range order (SRO) growth in a Cu - 16.4 at.% Mn alloy have been studied by measuring the evolution with time of the low-temperature magnetic properties while aging at temperatures around 100 . This new approach was possible because atomic SRO leads to magnetic clustering at this Mn concentration. Several models, all based on the diffusion of vacancies and their annihilation in fixed sinks, implied that the sink density was higher at 115 than at 100 for identical quenching conditions. It was concluded that the quenched-in vacancies condense in clusters. These act as sinks, halting the growth of SRO when the excess quenched-in vacancies have been absorbed. Quenching faster or aging at a higher temperature nucleates more vacancy clusters, causing earlier vacancy exhaustion. Neutron irradiation was used to continuously supply vacancies, thereby driving the SRO process to equilibrium at about 100 . A much higher magnetic susceptibility was attained than previously reported, some 20 times the as-quenched value at the spin freezing temperature.

Vacancy activation enthalpies of AuFe alloys determined from SRO-induced resistivity changes

The kinetics of atomic short-range ordering (SRO) in Au-14-at.% Fe were investigated by measuring residual resistivity after up-quenching and down-quenching over a suitable temperature interval, thus inducing different initial vacancy concentrations and vacancy mobilities. In addition, resistivity variations of Au-5-, 10-, 14- and 20-at.% Fe were measured during isochronal annealing of mechanically deformed and recrystallised samples. By assuming a certain model for SRO relaxation kinetics, migration and formation enthalpies of vacancies as well as vacancy sink densities (dislocation densities) were determined from experimental results. The parameters determined in this way correspond well with each other and with literature data.

Particle Deposition to Protruding Local Sinks Adhering on a Collector Surface

In this paper, we measured the local initial deposition rates of streptococci to adhering actinomyces, acting as protruding local sinks on a glass collector, as a function of the actinomyces density in a parallel plate flow chamber. The local initial deposition rates, i.e., deposition in the vicinity of actinomyces, j(0,1) compared well with values predicted by a model based on convective diffusion perpendicular to the collector surface and convection parallel to the collector surface when the seeding density of adhering actinomyces was below 0.5 x 10(6) cm(-2) (0.03% surface coverage). However, at higher sink densities the model breaks down due to particle depletion of the suspension downstream of a protruding sink.

On the experimental determination of the migrating defect fraction under cascade damage conditions

Information on the fraction of defects surviving intracascade recombination, escaping the cascade volume and migrating until their annihilation (“migrating defect fraction”, MDF) can be obtained from the analysis of radiation enhanced diffusion (RED) or radiation induced segregation (RIS) and maximum swelling rates. RED and RIS yield the ratio of the MDF over the effective sink strength whereas maximum swelling rates give lower bound estimates of the MDF. The basic assumptions made in the previous analysis of RED (RIS) and swelling are critically examined in the light of the present understanding of defect production in displacement cascades. MDF values deduced previously from RED are found to be clearly below the lower bound estimates obtained from maximum swelling rates. The discrepancy becomes even larger if the conventional monodefect dislocation bias is used in the analysis of swelling. Possible reasons for this discrepancy are discussed: (1) differences in the contribution of mobile defect clusters produced in cascades to RED and swelling, and (2) an underestimation of both the sink strength evolving during cascade damage conditions and the driving force for the swelling. We argue that the conventional method to deduce the sink strength from sink densities observed in TEM and the application of the conventional monodefect dislocation bias indeed yield only lower bound estimates for the sink strength and for the swelling rate, respectively. If the MDF were established by some other method RED (or RIS) could be used to measure the sink strength.

Atomic short-range ordering in AuFe alloys: a resistometric study

Kinetics and equilibrium of atomic short-range order (SRO) in Au 1− x − Fe x ( x=0.05, 0.10, 0.14, 0.20) have been investigated by measurement of residual electrical resistivity for a cold-rolled and a well-annealed state. Activation enthalpies of SRO relaxation correspond well to the sum of formation and migration enthalpies of vacancies, both determined separately In contrast to Mössbauer measurements a strong temperature dependence of SRO-induced electrical resistivity was observed. It was found that, because of the high density of vacancy sinks, SRO kinetics in the cold-rolled state in considerably slower than in the well-annealed state. Surprisingly, the as-rolled state for the alloys with 5, 10 and 14 at.% Fe has a high degree of SRO, whereas for Au-0.2.%Fe the initial state is disordered.No indications for precipitation of α-Fe were found for the samples with 5,10 and 14 at.% Fe, for both the cold-rolled and the recrystallized state. For 20 at.% Fe, however, a resistivity drift in the cold-rolled state was observed, which may be caused by precipitation of α-Fe.

Generation of thermal donors in silicon: oxygen aggregation controlled by self-interstitials

The analysis of kinetic data on thermal donors (TDS) leads to a general model of oxygen aggregation: the aggregates which arise differ not only in size but also in the number of emitted self-interstitials, m. Each line of aggregates-of a particular m-may contain a TD family. The well known family of double donors observed in in absorption spectra is most likely to reside at m=2. This family is often a minor one in comparison with another family of double TDS which resides at m=1 and is characterized by somewhat shallower energy levels. Self-interstitials (SiIs) produced by aggregates have a strong effect on the TD generation as (i) the equilibrium concentration ratio between the adjacent lines depends on the SiI concentration, CI, and (ii) oxygen transport is sometimes enhanced by SiIs though oxygen attachment to the aggregates is often controlled not by monomer migration (enhanced or not) but by migration of the aggregates themselves. The dependence of generation rate on CI includes both rising and falling parts as well as plateaux (the classical fourth-power law is an example of such a plateau). The actual value of CI depends on the density of SiI sinks (self-interstitial clusters) which appears to be a most important parameter in the TD kinetics.

The influence of radiation-induced segregation on precipitate stability in austenitic steels

The influence of radiation-induced segregation of major components and silicon in austenitic steels on the stability of M 23C 6, γ' and G phases under irradiation is theoretically studied. The low temperature boundary T L of M 23C 6 carbide stability and the high temperature boundary T H of γ' and G silcides stability are estimated by comparing the steady-state chromium and silicon concentrations at point defect sinks with corresponding solubility limits for these precipitates. It is shown that both T L and T H are decreased with increasing sink density and decreasing point defect generation rate. The value of T L drops with increasing carbon content while the value of T H does with decreasing silicon concentration.

Effect of Solutioning Conditions on Aging Response in Ti–15V–3Cr–3Sn–3Al

An effect of the solutioning conditions on the aging response (precipitation, age hardening) in a β type titanium alloy, Ti–15V–3Cr–3Sn–3Al, is examined.The aging response is strongly affected by the solutioning conditions and closely related to the concentration of quenched-in vacancies, which is a function of the quenching temperature and the density of vacancy sinks such as β grain boundaries, dislocations, etc. For example, the ω (≤250°C) and the α (300∼350°C) precipitations and the age hardening are greatly accelerated in the specimens in which a large amount of quenched-in vacancies are contained, i.e. the specimens quenched from high temperatures and/or with a small density of vacancy sinks. Furthermore, the α phase precipitates very homogeneously inside the β grains at the aging temperatures between 300 and 500°C. However, the precipitation delays and the denuded zones are sometimes observed in the area in which vacancy sinks exist, e.g. in the vicinity of the β grain boundaries or the isolatedly formed twins, or in the area in which dislocations are introduced due to the weak plastic deformation.In the specimens quenched from lower temperatures in the β region and having a smaller β grain size or a slightly higher density of dislocations, the delay of the aging response is significant and the α phase precipitation is heterogeneous. These phenomena are considered to be caused by a stronger effect of small amount of excessive vacancies, which is due to the relatively high density of the vacancy sinks and the lower quenching temperature, rather than the effect of the β grain boundaries and dislocations as precipitation sites.

Jet inflow simulation and its downwash effect on lifting surfaces

SummaryA turbulent hot jet is calculated and its entrainment effect is modelled by a line sink with the objective of estimating the downwash effect on rectangular lifting surfaces of various aspect ratios. The line sink density is determined by numerical solution of the free shear layer equations with a turbulent kinetic energy model. The ‘incompressible equivalent jet’ concept is verified within the context of practical engineering calculations.

The effect of defect clusters formed in cascades on the sink strength of irradiated materials

Defects produced by irradiation with energetic particles are often strongly spatially correlated. Energetic primary recoil atoms produce cascades with vacant lattice sites predominately in the central regions, and interstitial atoms at the periphery. A fraction of the defects produced forms clusters during cascade events. We examine the role of these clusters as defect sinks for high-dose irradiations at moderate temperatures. A population of vacancy and interstitial clusters evolves during irradiation which significantly contributes to the sink density. At temperatures at which thermal evaporation from vacancy clusters can be neglected, the cluster density is characteristic of the primary recoil spectrum, but is independent of temperature or dose rate. Contributions by migrating defects to irradiation-enhanced diffusion or to ion-beam mixing should be temperature and dose-rate independent. When thermal evaporation of vacancies from small defect clusters becomes competitive with absorption of excess interstitials, the cluster population becomes temperature and dose-rate dependent.

Effects of phosphorus, silicon and sulphur on microstructural evolution in austenitic stainless steels during electron irradiation

Fe-18Cr-9Ni-1.5Mn austenitic alloys containing phosphorus, silicon and sulphur were irradiated by 1 MeV electrons at 573–773 K. Phosphorus increased the intersitial loop nucleation and decreased the void swelling by increasing void number density and suppressing void growth. Silicon had a similar effect to phosphorus but its effect was weaker than phosphorus. Sulphur enhanced void swelling through increasing the void density. Nickel enrichment at grain boundaries was suppressed only in the alloy containing phosphorus. These phosphorus effects may be explained by a strong interaction with interstitials resulting in a high density of sinks for point defects.

Ti-15V-3Cr-3Sn-3Alの時効特性におよぼす溶体化処理条件の影響

An effect of the solutioning conditions on the aging response (precipitation, age hardening) in a β type titanium alloy, Ti-15V-3Cr-3Sn-3Al, is examined. The aging response is strongly affected by the solutioning conditions and closely related to the concentration of quenched-in vacancies, which is a function of the quenching temperature and the density of vacancy sinks such as β grain boundaries, dislocations, etc. For example, the ω (≤250 o C) and the α (300-350 o C) precipitations and the age hardening are greatly accelerated in the specimens in which a large amount of quenched-in vacancies are contained, i.e. the specimens quenched from high temperatures and/or with a small density of vacancy sinks