Predicting initial erosion during the hole erosion test by using turbulent flow CFD simulation

CFD simulation with enhanced modeling of turbulence and near-wall treatment is used to model water–clay mixtures flowing through a cylindrical pipe domain. Effects on the wall-shear stress resulting from varying water clay content and applied hydraulic gradient are analyzed. Various parametric studies were performed and had shown that the two-dimensional modelling introduced in the present study does not yield a uniform wall-shear stress along the pipe wall and that clay concentration affects significantly the wall-shear stress value. This is in contrast with the common hypothesis used in one-dimensional modeling approaches where this stress is assumed constant and which gives rise to uniform erosion along the pipe wall. The obtained results had enabled predicting more realistically erosion amount and had allowed for understanding the irregular eroded hole wall shape as observed experimentally after performing the standard hole erosion test.     

Correlation between chemical composition and antibacterial activity of essential oils from fifteen Eucalyptus species growing in the Korbous and Jbel Abderrahman arboreta (North East Tunisia)

The essential oils of fifteen Eucalyptus species harvested from the Jbel Abderrahman and Korbous arboreta (North East Tunisia) were screened for their antibacterial activities by the agar disc diffusion method. Eighteen major components as identified by GC/FID and GC/MS were selected for a study of the chemical and biological activity variability. The main one was 1,8-cineole, followed by spathulenol, trans-pinocarveol, α-pinene, p-cymene, globulol, cryptone, β-phellandrene, viridiflorol, borneol, limonene and isospathulenol. The chemical principal component analysis identified five species groups and subgroups, where each group constituted a chemotype, however that of the values of zone diameter of the inhibition (zdi) identified six groups of Eucalyptus oils, characterized by their antibacterial inhibition ability. The strongest activity was shown by E. platypus oil against Enterococcus faecalis and by E. lamannii oil against Staphylococcus aureus, Pseudomonas aeruginosa and Escherichia coli. A correlation between the levels of some major components and the antibacterial activities was observed.     

A ruthenium(II) complex with p‐cymene and (S)‐2‐(anilinomethyl)pyrrolidine

The title compound, [(S)‐2‐(anilino­methyl)­pyrrolidine‐N,N′]‐chloro(η⁶‐para‐cymene)­ruthenium(II) chloride, [RuCl‐(C₁₀H₁₄)(C₁₁H₁₆N₂)]Cl, has been synthesized by the reaction of [RuCl₂(p‐cymene)]₂ (p‐cymene is para‐iso­propyl­toluene) with (S)‐2‐(anilinomethyl)­pyrrolidine in triethyl­amine/2‐propanol. The Ru atom is in a pseudo‐tetrahedral environment coordinated by a chloride ligand, the aromatic hydro­carbon is linked in a η⁶ manner and the amine is linked via its two N atoms. The chloride anion is involved in hydrogen bonding with the di­amine moieties through N—H?Cl interactions, with N?Cl distances of 3.273 (4) and 3.352 (4) Å.     

Non-oscillating/Oscillating Shear Layer over a Large Deep Cavity at Low-Subsonic Speeds

The flow over a deep cavity at low subsonic velocity is considered in the present paper. The cavity length-to-depth aspect ratio is L/H = 0.2. Single hot-wire measurements characterized the incident turbulent boundary layer and show the influence of the cavity on the streamwise statistic components just downstream from the cavity. The streamwise mean and fluctuating velocity profiles are affected by the cavity. PIV measurements reveal the presence for ejection-like events responsible of local perturbations of the skewness and the flatness coefficients. Time-resolved PIV technic is also used to characterize phase properties of shear layer oscillating cycle. It is shown that for deep cavity with first Rossiter mode, only one vortical structure is formed at the cavity leading edge. Then, it grows while convecting downstream along the shear layer. A well-defined ejection process begins after the vortex impact near the cavity downstream corner. A cylinder device placed spanwisely near the cavity leading edge eliminates the resonance and highly modifies the behavior of the shear layer flow. In fact, the shear layer could be divided into upper and lower parts with different structure aspects.     

Activation cross sections for some isotopes of Zr,Mo, Br,Ta and Ce at 14.7 MeV neutrons

The (n,p), (n, ), (n, 2n) and (n, ) reaction cross sections on^90,92Zr,^92,97,98,100Mo,^78,81Br,¹⁸¹Ta,¹⁴⁰Ce target nuclei have been measured forE _n=14.73±0.05 MeV neutrons using the activation technique. The induced -ray activities of the irradiated samples and their monitor foils were measured by using HPGe detector. The cross sections are compared with the existing results. The experimental uncertainties are between 3% and 10% in most cases.     

K2CsYb(PO4)2

The crystal structure of dipotassium caesium ytterbium bis(phosphate) is built up from regular independent PO₄ tetrahedra and YbO₆ octahedra sharing corners and arranged in layers. The structure is, in many respects, similar to that of glaserite.     

Measurement of 14.7 MeV neutron cross sections for several isotopes

The (n,p), (n,), (n,2n), (n,np), and (n,n) reaction cross sections on²⁴Mg, 2²⁷Al,^28,29,30Si,^35,37Cl,⁴⁵Sc,⁴⁶Ti,⁵⁶Fe,^58,61Ni,⁹²Mo,¹⁰⁷Ag,^113,115In and¹⁹⁷Au target nuclei have been measured for E_n=14.73±0.05 MeV neutrons using the activation technique. The induced -ray activities of the irradiated samples and their monitor foils were measured using a HPGe detector. The cross sections are compared with existing results. The experimental uncertainties between 3% and 10% in most cases are generally smaller than those given by other authors.     

A new polymorph of (O‐ethyl dithio­carbonato‐κ2S,S′)­bis­(tri­phenylphosphine‐κP)silver(I)

A new triclinic polymorphic modification of the title compound, [Ag(C₃H₅OS₂)(C₁₈H₁₅P)₂], has been found and compared with the previously known orthorhombic modification [Tiekink (1988). Coord. Chem. 17 , 239–243]. The two polymorphs have the same molecular shape, viz. a distorted tetrahedral geometry, with a chelating di­thio­carbonate (xanthate) and two PPh₃ ligands bonded to the Ag atom. However, in this new polymorph, the xanthate ligand is bonded asymmetrically to the Ag atom, with Ag—S distances of 2.5489 (6) and 2.8055 (7) Å, while for the orthorhombic polymorph these distances are 2.686 (4) and 2.601 (4) Å. The Ag—P distances are similar in both structures.     

Stabilization of linear control systems in Hilbert space with nonlinear feedback

This paper considers the problem of stabilization of linear control systems in Hilbert space with nonlinear feedback. Extensions of known results in the linear feedback case to the nonlinear one are given.     

Nonlinear homogeneous retarded differential equations and population dynamics via translation semigroups

In this paper nonlinear homogeneous retarded differential equations and models from population dynamics and epidemiology are considered and studied by the use of translation semigroup theory. We show that the corresponding solution semigroups are equivalent to appropriate translation semigroups. Existence results for the retarded equations are established by taking the space of initial functions of the form W ^1,p ((-r,0),F) where F is a Banach space, 1≤ p<∈fty and 0<r\le∈fty . June 28, 1999