5,476 research outputs found
Implementation/validation of a low Reynolds number two-equation turbulence model in the Proteus Navier-Stokes code: Two-dimensional/axisymmetric
The implementation and validation of the Chien low Reynolds number k-epsilon turbulence model in the two dimensional axisymmetric version Proteus, a compressible Navier-Stokes computer code, are presented. The set of k-epsilon equations are solved by marching in time using a coupled alternating direction implicit (ADI) solution procedure with generalized first or second order time differencing. To validate Proteus and the k-epsilon turbulence model, laminar and turbulent computations were done for several benchmark test cases: incompressible fully developed 2-D channel flow; fully developed axisymmetric pipe flow; boundary layer flow over a flat plate; and turbulent Sajben subsonic transonic diffuser flows. Proteus results from these test cases showed good agreement with analytical results and experimental data. Detailed comparisons of both mean flow and turbulent quantities showed that the Chien k-epsilon turbulence model given good results over a wider range of turbulent flow than the Baldwin-Lomax turbulence model in the Proteus code with no significant CPU time penalty for more complicated flow cases
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DNA Rereplication Is Susceptible to Nucleotide-Level Mutagenesis.
The sources of genome instability, a hallmark of cancer, remain incompletely understood. One potential source is DNA rereplication, which arises when the mechanisms that prevent the reinitiation of replication origins within a single cell cycle are compromised. Using the budding yeast Saccharomyces cerevisiae, we previously showed that DNA rereplication is extremely potent at inducing gross chromosomal alterations and that this arises in part because of the susceptibility of rereplication forks to break. Here, we examine the ability of DNA rereplication to induce nucleotide-level mutations. During normal replication these mutations are restricted by three overlapping error-avoidance mechanisms: the nucleotide selectivity of replicative polymerases, their proofreading activity, and mismatch repair. Using lys2InsEA14 , a frameshift reporter that is poorly proofread, we show that rereplication induces up to a 30× higher rate of frameshift mutations and that this mutagenesis is due to passage of the rereplication fork, not secondary to rereplication fork breakage. Rereplication can also induce comparable rates of frameshift and base-substitution mutations in a more general mutagenesis reporter CAN1, when the proofreading activity of DNA polymerase ε is inactivated. Finally, we show that the rereplication-induced mutagenesis of both lys2InsEA14 and CAN1 disappears in the absence of mismatch repair. These results suggest that mismatch repair is attenuated during rereplication, although at most sequences DNA polymerase proofreading provides enough error correction to mitigate the mutagenic consequences. Thus, rereplication can facilitate nucleotide-level mutagenesis in addition to inducing gross chromosomal alterations, broadening its potential role in genome instability
Mechanism of the Enzymic Reduction of N_2: The Binding of Adenosine 5'-Triphosphate and Cyanide to the N_2-reducing System
The in vitro reduction of N_2 is a complex process involving at least six different reactants: two proteins [1,2] for which the names azoferredoxin (AzoFd) and molybdoferredoxin (MoFd) have been proposed[3], an electron source, the electron acceptor, ATP[4], and Mg2+[5-7]. One of the goals of research in this area is to define the orderly and quantitative participation of these reactants leading to the reduction of the electron acceptor with concomitant breakdown of ATP to ADP and inorganic phosphate[7].
The work described in this paper shows that (1) AzoFd reversibly binds both ATP, a reactant in N2 reduction, and ADP, a specific inhibitor of N2 reduction, and (2) MoFd reversibly binds cyanide, which is also reduced by the N_2-reducing system. It is suggested that the binding of ATP and of cyanide are partial reactions of the N_2-reducing system
Failure Mechanism of True 2D Granular Flows
Most previous experimental investigations of two-dimensional (2D) granular
column collapses have been conducted using three-dimensional (3D) granular
materials in narrow horizontal channels (i.e., quasi-2D condition). Our recent
research on 2D granular column collapses by using 2D granular materials (i.e.,
aluminum rods) has revealed results that differ markedly from those reported in
the literature. We assume a 2D column with an initial height of h0 and initial
width of d0, a defined as their ratio (a =h0/d0), a final height of h , and
maximum run-out distance of d . The experimental data suggest that for the low
a regime (a <0.65) the ratio of the final height to initial height is 1.
However, for the high a regime (a >0.65), the ratio of a to (d-d0)/d0, h0/h ,
or d/d0 is expressed by power-law relations. In particular, the following
power-function ratios (h0/h=1.42a^2/3 and d/d0=4.30a^0.72) are proposed for
every a >0.65. In contrast, the ratio (d-d0)/d0=3.25a^0.96 only holds for 0.65<
a1.5. In addition,
the influence of ground contact surfaces (hard or soft beds) on the final
run-out distance and destruction zone of the granular column under true 2D
conditions is investigated.Comment: 8 page
Extracting multiword expressions from texts with the aid of online resources
Research in recent years has emphasized the ubiquity and pedagogical significance of multiword expressions (MWEs) (e.g. Siyanova-Chanturia & Pellicer-Sánchez, 2018). However, accumulating a sizeable repertoire of MWEs remains a challenge to language learners.
Aiming to shed light on one potential pedagogical path, this classroom-based research project investigates the effectiveness of ‘text-chunking’, an activity where learners are asked to extract MWEs from authentic texts. The participants were two intact classes of Vietnamese EFL learners in their second tertiary year. Over ten weeks, the experimental group (n=26) engaged in weekly text-chunking practice, while a comparison group (n=30) used the same reading materials for content-related activities. The experimental group was taught to consult online dictionaries and an online corpus to verify their identification of MWEs. Their discussions were audio-recorded every week. A pre-test and two post-tests (immediate and delayed) on the form recall of 52 target items revealed significantly greater learning gains in the experimental group, with a medium effect size. Post-treatment questionnaires also suggested these students’ heightened awareness of MWEs and autonomous learning strategies.
This presentation will highlight these main findings and, more importantly, discuss the implications for language teachers on how to better scaffold learners in their MWE acquisition.
Pedagogical suggestions on how extracting MWEs from texts can be done using online resources to adapt the changes caused by Covid-19 conclude the talk
Folding model study of the charge-exchange scattering to the isobaric analog state and implication for the nuclear symmetry energy
The Fermi transition (\Delta L=\Delta S=0 and \Delta T=1) between the nuclear
isobaric analog states (IAS), induced by the charge-exchange (p,n) or (3He,t)
reaction, can be considered as "elastic" scattering of proton or 3He by the
isovector term of the optical potential (OP) that flips the projectile isospin.
The accurately measured (p,n) or (3He,t) scattering cross-section to the IAS
can be used, therefore, to probe the isospin dependence of the proton or 3He
optical potential. Within the folding model, the isovector part of the OP is
determined exclusively by the neutron-proton difference in the nuclear
densities and the isospin dependence of the effective nucleon-nucleon (NN)
interaction. Because the isovector coupling explicitly links the isovector part
of the proton or 3He optical potential to the cross section of the
charge-exchange (p,n) or (3He,t) scattering to the IAS, the isospin dependence
of the effective (in-medium) NN interaction can be well tested in the folding
model analysis of these charge-exchange reactions. On the other hand, the same
isospin- and density dependent NN interaction can also be used in a
Hartree-Fock calculation of asymmetric nuclear matter, to estimate the nuclear
matter energy and its asymmetry part (the nuclear symmetry energy). As a
result, the fine-tuning of the isospin dependence of the effective NN
interaction against the measured (p,n) or (3He,t) cross sections should allow
us to make some realistic prediction of the nuclear symmetry energy and its
density dependence.Comment: Accepted for publication in European Physical Journal A - "Hadrons
and Nuclei
Structure-specified H∞ loop shaping control for balancing of bicycle robots: A particle swarm optimization approach
In this paper, the particle swarm optimization (PSO) algorithm was used to design the structure-specified H∞ loop shaping controllers for balancing of bicycle robots. The structure-specified H∞ loop shaping controller design normally leads to a complex optimization problem. PSO is an efficient meta-heuristic search which is used to solve multi-objectives and non-convex optimizations. A model-based systematic procedure for designing the particle swarm optimization-based structure-specified H∞ loop shaping controllers was proposed in this research. The structure of the obtained controllers are therefore simpler. The simulation and experimental results showed that the robustness and efficiency of the proposed controllers was gained when compared with the proportional plus derivative (PD) as well as conventional H∞ loop shaping controller. The simulation results also showed a better efficiency of the developed control algorithm compared to the Genetic Algorithm based one
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