Segregation Rate Research Articles

Versatile kinetochore components control central spindle assembly

Versatile kinetochore components control central spindle assembly

Nonequilibrium grain-boundary segregation mechanism of hot ductility loss for austenitic and ferritic stainless steels

Abstract

Aurora B/C in Meiosis: Correct Me If I’m Right

In this issue of Developmental Cell, Yoshida et al. (2015) report that during meiosis I in mouse oocytes, the kinase Aurora B/C continuously destabilizes chromosome attachments to spindle microtubules, which potentially provides an explanation for the notably high error rate of chromosome segregation in mammalian oocytes.

Survival of LLSVPs for billions of years in a vigorously convecting mantle: Replenishment and destruction of chemical anomaly

AbstractWe study segregation of the subducted oceanic crust (OC) at the core‐mantle boundary and its ability to accumulate and form large thermochemical piles (such as the seismically observed Large Low Shear Velocity Provinces (LLSVPs)). Our high‐resolution numerical simulations of thermochemical mantle convection suggest that the longevity of LLSVPs for up to three billion years, and possibly longer, can be ensured by a balance in the rate of segregation of high‐density OC material to the core‐mantle boundary (CMB) and the rate of its entrainment away from the CMB by mantle upwellings. For a range of parameters tested in this study, a large‐scale compositional anomaly forms at the CMB, similar in shape and size to the LLSVPs. Neutrally buoyant thermochemical piles formed by mechanical stirring—where thermally induced negative density anomaly is balanced by the presence of a fraction of dense anomalous material—best resemble the geometry of LLSVPs. Such neutrally buoyant piles tend to emerge and survive for at least 3 Gyr in simulations with quite different parameters. We conclude that for a plausible range of values of density anomaly of OC material in the lower mantle—it is likely that it segregates to the CMB, gets mechanically mixed with the ambient material, and forms neutrally buoyant large‐scale compositional anomalies similar in shape to the LLSVPs.

A novel gene amplification causes upregulation of the PatAB ABC transporter and fluoroquinolone resistance in Streptococcus pneumoniae.

Overexpression of the ABC transporter genes patA and patB confers efflux-mediated fluoroquinolone resistance in Streptococcus pneumoniae and is also linked to pneumococcal stress responses. Although upregulation of patAB has been observed in many laboratory mutants and clinical isolates, the regulatory mechanisms controlling expression of these genes are unknown. In this study, we aimed to identify the cause of high-level constitutive overexpression of patAB in M184, a multidrug-resistant mutant of S. pneumoniae R6. Using a whole-genome transformation and sequencing approach, we identified a novel duplication of a 9.2-kb region of the M184 genome which included the patAB genes. This duplication did not affect growth and was semistable with a low segregation rate. The expression levels of patAB in M184 were much higher than those that could be fully explained by doubling of the gene dosage alone, and inactivation of the first copy of patA had no effect on multidrug resistance. Using a green fluorescent protein reporter system, increased patAB expression was ascribed to transcriptional read-through from a tRNA gene upstream of the second copy of patAB. This is the first report of a large genomic duplication causing antibiotic resistance in S. pneumoniae and also of a genomic duplication causing antibiotic resistance by a promoter switching mechanism.

Multiscale simulation of xenon diffusion and grain boundary segregation in UO2

In light water reactor fuel, gaseous fission products segregate to grain boundaries, resulting in the nucleation and growth of large intergranular fission gas bubbles. The segregation rate is controlled by diffusion of fission gas atoms through the grains and interaction with the boundaries. Based on the mechanisms established from earlier density functional theory (DFT) and empirical potential calculations, diffusion models for xenon (Xe), uranium (U) vacancies and U interstitials in UO2 have been derived for both intrinsic (no irradiation) and irradiation conditions. Segregation of Xe to grain boundaries is described by combining the bulk diffusion model with a model for the interaction between Xe atoms and three different grain boundaries in UO2 (Σ5 tilt, Σ5 twist and a high angle random boundary), as derived from atomistic calculations. The present model does not attempt to capture nucleation or growth of fission gas bubbles at the grain boundaries. The point defect and Xe diffusion and segregation models are implemented in the MARMOT phase field code, which is used to calculate effective Xe and U diffusivities as well as to simulate Xe redistribution for a few simple microstructures.

Segregation of non‐target‐site resistance to herbicides in multiple‐resistant Alopecurus myosuroides plants

SummaryNon‐target‐site resistance (NTSR) comprises a set of mechanisms conferring resistance to multiple modes of action. Investigation of the number of loci involved in NTSR will aid in the understanding of these resistance mechanisms. Therefore, six different multiple herbicide‐resistant Alopecurus myosuroides plants with different herbicide history were crossed in two generations with a susceptible wild type. Seeds from the backcrossing generation were studied for their segregation rate for resistance to five herbicides with four different modes of action (HRAC groups C2, A, B and K3). Taking into account that NTSR is a set of quantitative traits, the numbers of loci controlling NTSR were estimated using a normal mixture model fitted by the NLMIXED procedure of SAS. Each herbicide was controlled by a different number of loci comparing the six plants. In most of the cases, chlorotoluron resistance was controlled by one locus, whereas resistance to fenoxaprop‐P‐ethyl needed one or two loci. Resistance to pinoxaden was in all plants conferred by two loci. Cross‐resistance of fenoxaprop‐P‐ethyl and pinoxaden was found in all backcrossings, indicating that at least one of the two loci is responsible for both resistances. Resistance to mesosulfuron + iodosulfuron was conferred by a minimum of two loci. Results indicated that a minimum of five different loci can be involved in a multiple NTSR plant. Furthermore, the plant‐specific accumulation of NTSR loci was demonstrated. Such behaviour should be taken into account when evaluating the development and further spread of herbicide resistance.

Inclusive education in Australia: rhetoric, reality and the road ahead

Inclusive education (IE) is a term that has been part of the educational discourse in Australia for almost two decades. While there is no overarching definition under which IE operates in that country, it is accepted that the meaning behind the term has shifted from being exclusively about students with a disability to now encompassing the delivery of a high‐quality education to all students. The public education system is carrying the burden of an increasingly diverse student population (Gonski et al., 2011), and as such, each of the eight educational jurisdictions responsible for the schools within their borders have developed policies and increased funding levels in the name of IE (Graham, in press). Despite this, there are currently no standards or guidelines provided at the state or federal level to measure the success (or not) of IE practices within Australian educational sectors. This article aims to do just that, by providing a ‘report card’ on IE in Australia. An extensive review of the current literature and related educational policies and reports was conducted, and Loreman's (2014) three guides for measuring IE – student participation, student achievement and post‐school options – were adopted to evaluate the performance of Australia's public education system. The findings indicate that, despite operating under the same national legislative acts, the eight educational jurisdictions in Australia are managing and enacting IE in different ways, leading to inconsistent levels of access and educational outcomes for students. Rates of segregation and exclusion (through both the provision of education in ‘alternative’ settings and disciplinary action) are on the increase, with disproportionate representation of students from minority groups. This has been exacerbated by the inception of a national testing regime, which some have argued is in breach of the Disability Discrimination Act as it excludes participation by particular groups of students. On the flip side, for the first time Australia has a consistent curriculum that has provided a set of outcomes for all students, and the gap between Indigenous and non‐Indigenous students in the areas of literacy and numeracy is on the decrease, albeit a slow decrease. However, there is still a long way to go, and this paper discusses the need for a national approach to IE to enable the continued development of effective schooling for all students across Australia.

Selective mobility, segregation and neighbourhood effects

Selective mobility, segregation and neighbourhood effects

Selective mobility, segregation and neighbourhood effects

Selective mobility, segregation and neighbourhood effects

Selective mobility, segregation and neighbourhood effects

Selective mobility, segregation and neighbourhood effects

Polymer segregation under confinement: free energy calculations and segregation dynamics simulations.

Monte Carlo simulations are used to study the behavior of two polymers under confinement in a cylindrical tube. Each polymer is modeled as a chain of hard spheres. We measure the free energy of the system, F, as a function of the distance between the centers of mass of the polymers, λ, and examine the effects on the free energy functions of varying the channel diameter D and length L, as well as the polymer length N and bending rigidity κ. For infinitely long cylinders, F is a maximum at λ = 0, and decreases with λ until the polymers are no longer in contact. For flexible chains (κ = 0), the polymers overlap along the cylinder for low λ, while above some critical value of λ they are longitudinally compressed and non-overlapping while still in contact. We find that the free energy barrier height, ΔF ≡ F(0) - F(∞), scales as ΔF/k(B)T ∼ ND(-1.93 ± 0.01), for N ⩽ 200 and D ⩽ 9σ, where σ is the monomer diameter. In addition, the overlap free energy appears to scale as F/k(B)T = Nf(λ/N; D) for sufficiently large N, where f is a function parameterized by the cylinder diameter D. For channels of finite length, the free energy barrier height increases with increasing confinement aspect ratio L/D at fixed volume fraction ϕ, and it decreases with increasing ϕ at fixed L/D. Increasing the polymer bending rigidity κ monotonically reduces the overlap free energy. For strongly confined systems, where the chain persistence length P satisfies D ≪ P, F varies linearly with λ with a slope that scales as F'(λ) ∼ -k(B)TD(-β)P(-α), where β ≈ 2 and α ≈ 0.37 for N = 200 chains. These exponent values deviate slightly from those predicted using a simple model, possibly due to insufficiently satisfying the conditions defining the Odijk regime. Finally, we use Monte Carlo dynamics simulations to examine polymer segregation dynamics for fully flexible chains and observe segregation rates that decrease with decreasing entropic force magnitude, f ≡ |dF/dλ|. For both infinite-length and finite-length channels, the polymers are not conformationally relaxed at later times during segregation.

Theoretical Study of Optimal Positioning of Segregating Component Input into Continuous Mixer of Solids

The objective of the study is to demonstrate theoretically one of the ways of improving the quality of continuous mixing of segregating particulate solids. The objective function of optimization is the standard deviation of segregating component distribution over the mixer's cross-section at the mixer outlet, the optimization parameter being the position of segregating component input. It is shown that the input of the component into the position that is optimized over the length of the mixer allows improving the mixing quality. The gain of optimization depends on the rate of segregation and grows with its increase.

Control of solid–liquid interface morphology and radial composition distribution: TbDyFe single crystal growth

Optical zone melting method was adopted for the crystal growth of TbDyFe giant magnetostrictive alloys. Effects of zone-melting length and growth velocity on the quenched solid–liquid interface bending direction, curvature and corresponding radial composition distribution were investigated both experimentally and theoretically. By increasing the zone-melting length, the solid–liquid interface morphology was evolved from convex to flat and then to concave. In the case of convex solid–liquid interface, the curvature of the interface was decreased by increasing the growth velocity. When the initial interface was flat, changing growth velocity had no effect on the interface morphology under our experimental conditions. Accordingly, quite different radial composition distributions were monitored. A 〈110〉 axial oriented twinned-single crystal of TbDyFe alloy without radial composition segregation was obtained through controlling the solid–liquid interface morphology. Solid–liquid interface curvature functions were proposed with the parameters of zone-melting length, growth velocity, temperature gradient and other thermal physical parameters. Furthermore, functions of corresponding radial composition distribution were also given. The theoretical analysis shows that, the curvature of solid–liquid interface and the rate of radial composition segregation are determined by zone melting length, growth velocity and temperature gradient. Theoretical analysis results matched well with the experiments.

Effects of Aggregate Properties and Concrete Rheology on Stability Robustness of Self-Consolidating Concrete

Compared with ordinary concrete, the segregation resistance of self-consolidating concrete (SCC) are more sensitive to small variations of mix proportions such as dosage of superplasticizer, and the size, volume, and gradation, as well as moisture content of the fine and coarse aggregates. To design a SCC mixture, which is robust against small variations in raw materials, it is critical to understand the mechanism of how mix proportions affect robustness. In this paper, modified segregation probe was used to study the effects of various mixture properties on static stability robustness of SCC. It was found that a static segregation rate equation is helpful to explain how paste rheology and aggregate properties affect robustness. Mixture properties, such as higher paste volume, lower superplasticizer % by weight of cement, lower slump flow, smaller aggregate size, better gradation, and higher aggregate packing density may improve robustness. Among the aggregate properties, smaller aggregate size and better gradation seem to have more significant effects than higher aggregate packing density. As expected, no obvious relationship was observed between concrete rheology and robustness in this study.

Preparation and Application of High Dropping Non Vibration Self-Compacting Concrete

High dropping non vibration concrete is widely used in high-rise steel tube concrete construction. In this paper, a high dropping non vibration self-compacting concrete with high mobility, low slump loss, and good anti-segregation ability is developed by mixing addition of PCA superplasticizer and SCC composite expansive admixture. The test results showed that the admixture and cement used in the test possess sound compatibility. The slump flow of self-compacting concrete prepared are more than 660mm, T500 of 2.8~7.5s, 1h slump flow loss of less than 10%, and the segregation rate of less than 7.5%. Through strictly control production and dropping construction, supplemented by field ultrasonic detection measures, the high dropping self-compacting concrete in steel tube achieved successful application for a high-rise building.

Influence of initial conditions on granular dynamics near the jamming transition

In this paper, we compare the behaviours of two vibrofluidized granular systems, identical in terms of their composition, geometry and driving parameters, differing only in their initial conditions. It is found that, by increasing the strength with which a system is initially excited, considerable differences in system composition and dynamics persist even after the driving is returned to its typical value. The observed changes in particle mobility and packing density are shown to result in marked differences in segregative behaviour for equivalent steady-state systems distinguished only by the history of their driving. The ability to significantly increase the rate of segregation in a granular system simply through the application of a short burst of intense vibration clearly has potential industrial applications.

Chalcophile elemental compositions of MORBs from the ultraslow-spreading Southwest Indian Ridge and controls of lithospheric structure on S-saturated differentiation

Sulfide globules in mid-ocean ridge basalts (MORBs) from the ultra-slow spreading Southwest Indian Ridge (SWIR) are present in olivine crystals and in the matrix glass, indicating S-saturated fractionation during magmatic evolution. Most of the sulfides were in equilibrium with the magmas based on the Ni contents of the sulfides. The major element trends of MORBs from Zone C (48–51°E) of the SWIR define two distinct liquid lines of descent (LLD), including one which is composed of MORBs depleted in HREE. The MORBs have variable PGE concentrations with Pd contents ranging from 0.056 to 1.572ppb. They are PGE-depleted relative to Ni and Cu with high Cu/Pd ratios (55,000–1,785,000). Quantitative modeling using Pd vs. Ni correlations yields relatively low amounts of segregated sulfides for both groups assuming complete equilibration between the sulfides and the melt. However, the correlation of calculated sulfur contents with MgO suggests much higher amounts of segregated sulfides, indicating that the segregated sulfides are incompletely equilibrated with the magma.There are no obvious correlations between PGE concentrations and spreading rates for MORBs globally. MORBs from the SWIR show slowly decreasing PGE contents during magmatic evolution but exhibit higher sulfide segregation rates compared to MORBs from faster-spreading ridges, largely due to the poor equilibration between the segregated sulfides and the magma. Such incomplete equilibration could result from thicker lithosphere and an absence of steady magma chambers and conduits beneath ultra-slow spreading ridges.

Stellar dynamics in gas: the role of gas damping

In this paper, we consider how gas damping affects the dynamical evolution of gas-embedded star clusters. Using a simple three-component (i.e. one gas and two stellar components) model, we compare the rates of mass segregation due to two-body relaxation, accretion from the interstellar medium, and gas dynamical friction in both the supersonic and subsonic regimes. Using observational data in the literature, we apply our analytic predictions to two different astrophysical environments, namely galactic nuclei and young open star clusters. Our analytic results are then tested using numerical simulations performed with the NBSymple code, modified by an additional deceleration term to model the damping effects of the gas. The results of our simulations are in reasonable agreement with our analytic predictions, and demonstrate that gas damping can significantly accelerate the rate of mass segregation. A stable state of approximate energy equilibrium cannot be achieved in our model if gas damping is present, even if Spitzer's Criterion is satisfied. This instability drives the continued dynamical decoupling and subsequent ejection (and/or collisions) of the more massive population. Unlike two-body relaxation, gas damping causes overall cluster contraction, reducing both the core and half-mass radii. If the cluster is mass segregated (and/or the gas density is highest at the cluster centre), the latter contracts faster than the former, accelerating the rate of core collapse.

Beyond race and place: distal sociological determinants of HIV disparities.

Informed behavior change as an HIV prevention tool has yielded unequal successes across populations. Despite decades of HIV education, some individuals remain at high risk. The mainstream media often portrays these risk factors as products of race and national borders; however, a rich body of recent literature proposes a host of complex social factors that influence behavior, including, but not limited to: poverty, income inequality, stigmatizing social institutions and health care access. We examined the relationship between numerous social indicators and HIV incidence across eighty large U.S. cities in 1990 and 2000. During this time, major correlating factors included income inequality, poverty, educational attainment, residential segregation and marriage rates. However, these ecological factors were weighted differentially across risk groups (e.g. heterosexual, intravenous drug use, men who have sex with men (MSM)). Heterosexual risk rose significantly with poor economic indicators, while MSM risk depended more heavily on anti-homosexual stigma (as measured by same-sex marriage laws). HIV incidence among black individuals correlated significantly with numerous economic factors but also with segregation and imbalances in the male:female ratio (often an effect of mass incarceration). Our results support an overall model of HIV ecology where poverty, income inequality and social inequality (in the form of institutionalized racism and anti-homosexual stigma) have over time developed into synergistic drivers of disease transmission in the U.S., inhibiting information-based prevention efforts. The relative weights of these distal factors vary over time and by HIV risk group. Our testable model may be more generally applicable within the U.S. and beyond.