Numerical treatment of a discontinuous top surface in 2D shallow water mixed flow modeling

This paper presents a numerical strategy based on shallow water equations (SWE) coupled with the 2D Preissmann slot model to handle a ceiling step discontinuity in finite volume schemes for mixed flow modeling. In practice, a typical situation would be a closed structure, such as a bridge or culvert, which induces a sudden vertical flow constriction and may even run partly or totally full in high flow conditions. In such case, both the inlet and outlet of the structure involve a discontinuity in the top elevation. This special singularity is topologically represented by inserting a fictitious cell between 2 adjacent computational cells characterized by sharply different ceiling elevation. The 2D SWE are solved by means of a well‐balanced quasi‐conservative Godunov‐type numerical scheme based on the Slope Limiter Centered (SLIC) scheme. The flow variables at each boundary of the fictitious cell are reconstructed by adopting the cross‐sectional shape of the adjoining cell. Accordingly, the dynamic effect of the structure deck on the flow is suitably modeled, and the C‐property for a stationary solution is rigorously satisfied, even when the closed structure is partially full. The capability of the numerical scheme is verified by comparison with both novel analytical solutions of 1D Riemann problems with a ceiling step discontinuity and experimental data of steady and unsteady mixed flows available in literature. Finally, a real‐scale application to a multiple arch bridge is presented. The results show that the method is robust and effective in predicting the 2D features induced by a crossing structure on the flow dynamics.     

A molecular dynamics simulation study of three polysulfones in dry and hydrated states

Molecular dynamics (MD) simulations of three polysulfones (poly(ether sulfone) PESU, poly(phenylene sulfone) PPSU and polysulfone PSU) in dry and hydrated states were undertaken in order to study the specific interactions between water and glassy polymer matrices of the same structural family. Dry polysulfone models were generated using a hybrid pivot Monte Carlo‐MD single‐chain sampling technique and the resulting relaxed densities were found to be in close agreement with experimental data. Hydrated systems are found to reproduce quite well volumetric changes experimentally observed. The concentrations of sulfonic groups can explain qualitatively their different water solubilities. Water is preferentially hydrogen‐bonded to two sites which either link two polymer sites, or one polymer site and another water, or two other waters. A detailed analysis of these water bridges that are formed is presented. Only a small quantity of potential bridging sites are occupied for water contents near the experimental saturation. The free fractional volumes, the probe accessible volumes, the swelling of the polymers, the water‐polymer interactions and the hydrogen bond lifetimes, are also presented for these polysulfones. Water‐water interactions and water clusters are found to be more important in the more hydrophilic PESU in comparison to the less hydrophilic PSU. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Polymeric nanoparticles prepared using salt bridges between [(dimethylamino)propyl]-octadecanamide and poly(N-isopropylacrylamide-co-methacrylic acid)

Polymeric lipid nanoparticles were prepared in 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid buffer (pH 8.0, 10 mM) by taking advantage of salt bridges formed between poly(N-isopropylacrylamide-co-methacrylic acid) (P(NIPAM-co-MAA)) and N-[3-(dimethylamino)propyl]-octadecanamide (DMAPODA). The homogeneous nanoparticles of 200–250 nm were obtained when the copolymer was included in the preparation so that the relative mass of copolymer to lipid was more than 5. However, when the relative amount of copolymer was less than 5, large agglomerates more than 10 μm were observed together with nanoparticles. The protonated amino groups of DMAPODA will attach to the ionized carboxyl groups of P(NIPAM-co-MAA), and they would act as polymeric amphiphiles. It is believed that the hydrophilic copolymer can stabilize the hydrophobic core of the lipid. The critical association concentrations were determined to be 32, 112, and 158 mg/l, when the lipid/copolymer ratios were 1:5, 1:23, and 1:50, respectively.     

Weakly directed self-avoiding walks

We define a new family of self-avoiding walks (SAW) on the square lattice, called weakly directed walks. These walks have a simple characterization in terms of the irreducible bridges that compose them. We determine their generating function. This series has a complex singularity structure and in particular, is not D-finite. The growth constant is approximately 2.54 and is thus larger than that of all natural families of SAW enumerated so far (but smaller than that of general SAW, which is about 2.64). We also prove that the end-to-end distance of weakly directed walks grows linearly. Finally, we study a diagonal variant of this model.     

5-Arylmethylene-2,4-imidazolidinediones and 5-arylmethylene-2-thioxo-4-imidazolidinones derivatives: stereochemistry elucidation by H and C NMR

Derivatives of 5-arylmethylene-2,4-imidazolidinediones and 5-arylmethylene-2-thioxo-4-imidazolidinones were synthesized as potential aldose reductase inhibitors (ARI). The Z/E configuration was elucidated by homonuclear NOE difference spectra and by proton-carbon coupling constant measurement from ¹³C coupled spectra using GATEDEC and SFDEC programs.     

MNE Nitrido Bridges with Transition Metal Nitrogen Multiple Bonds and E = Phosphorus,Sulfur, and Chlorine

A compilation is given on new syntheses, properties, and structures of complexes with M≡N—E ? M=N=E nitrido bridges with transition metal nitrogen multiple bonds and participation of the main group elements E of phosporus, sulfur, and chlorine. 1. MNP: This atomic sequence is realized in phosphoraneiminato complexes with transition metals in high oxidation states and termal bond of the (NPR₃^—) ligand. A series of new complexes of this type is reported with M = zirconium, hafnium, molybdenum, tungsten, and rhenium, among these the homoleptic species [Hf(NPPh₃)₄] and [M(NPPh₃)₄]²⁺ with M = Mo and W. Therefrom the isolobal complexes [:N≡Mo(NPPh₃)₃], [:O≡W(NPPh₃)₃]⁺, [(O)₂Mo(NPPh₃)₂], and [(O)₃Re(NPPh₃)] are derived. 2. MNS: Adding to compounds with this atomic sequence, new complexes were developed on the basis of the functional ligand groups thionitrosyl ( a ), dinitridosulphate(II) ( b ), dinitridosulphate(IV) ( c ), and cyclothiazeno ( d ) (cyclo‐3, 5‐dithia‐2, 4, 6‐triazino):

     

Transference Numbers of NaCl in Aqueous Mixtures with Organic Solvents of Moderate to Low Permittivities

Electromotive forces (emf) were measured in the transference cells: AgAgCl- Nacl (m₂) in Z NaCl (m₁) in ZAgClAg and Na_xHg_1-xNaCl (m₁) in Z NaCl (m₂) in ZNa_xHg_1-x (where Na_xHg_1-x denotes a flowing Na–amalgam electrode and Z an aqueous-organic solvent mixture) at various molalities m ₂ > m₁ of NaCl in Z = (ethylene glycol + water), (acetonitrile + water) and (1,4-dioxane + water), with mass fractions of the organic components 0.8. The transference number of Na⁺ in (ethylene glycol + water) and (1,4-dioxane + water) varies little with respect to that in pure water medium, whereas in (acetonitrile + water) it increases remarkably with increasing proportion of acetonitrile so as to approach equitransference, behavior similar to that previously found in (methanol + water) and in (ethanol + water). At acetonitrile mass fraction 0.6 NaCl is sufficiently close to equitransference to emerge as a useful salt bridge, nearly at the same level as the popular aqueous KCl.     

Halfsandwich Complexes Containing the Tetrathiotungstate Chelate Ligand. Crystal and Molecular Structure of Cp*Rh(PMe3)[(μ‐S)2WS2] (Cp* = η5‐Pentamethylcyclopentadienyl)

The reactions of Cp*M(PMe₃)Cl₂ (M = Rh ( 1a ), Ir ( 1b )) with (NEt₄)₂[WS₄] led to the heterodimetallic sulfido‐bridged complexes Cp*M(PMe₃)[(μ‐S)₂WS₂] (M = Rh ( 2a ), Ir ( 2b )), whereas the dimers [Cp*MCl(μ‐Cl)]₂ (M = Rh ( 4a ), Ir ( 4b )) reacted with (NEt₄)₂[WS₄) to give the known trinuclear compounds [Cp*M(Cl)]₂(μ‐WS₄) (M = Rh ( 5a ), Ir ( 5b )). Hydrolysis of the terminal W=S bonds converts 2a, b into Cp*M(PMe₃)[(μ‐S)₂WO₂] (M = Rh ( 3a ), Ir ( 3b )). Salts of a heterodimetallic anion, A[CpMo(I)(NO)(WS₄)] ( 6 ) (A⁺ = NEt₄⁺, NPh₄⁺) were obtained by reactions of [CpMo(NO)I₂]₂ with tetrathiotungstates, A₂[WS₄]. The complexes were characterized by IR and NMR (¹H, ¹³C, ³¹P) spectroscopy, and the X‐ray crystallographic structure of Cp*Rh(PMe₃)[(μ‐S)₂WS₂] ( 2a ) has been determined. The bond lengths and angles in the coordinations spheres of Rh and W in 2a (Rh···W 288.5(1) pm) are compared with related complexes containing terminal [WS₄^2—] chelate ligands.     

Synthese eines funktionalen Aluminiumalkinids,Me3C‐C≡C‐AlBr2, und dessen Reaktionen mit der sperrigen Lithiumverbindung LiCH(SiMe3)2

Synthesis of a Functional Aluminium Alkynide, Me₃C‐C≡C‐AlBr₂, and its Reactions with the Bulky Lithium Compound LiCH(SiMe₃)₂ Treatment of aluminium tribromide with the lithium alkynide (Li)C≡C‐CMe₃ afforded the aluminium alkynide Me₃C‐C≡C‐AlBr₂ ( 1 ) in an almost quantitative yield. 1 crystallizes with trimeric formula units possessing Al₃C₃ heterocycles and the anionic carbon atoms of the alkynido groups in the bridging positions. A dynamic equilibrium was determined in solution which probably comprises trimeric and dimeric formula units. Reaction of 1 with one equivalent of LiCH(SiMe₃)₂ yielded the compound [Me₃C‐C≡C‐Al(Br)‐CH(SiMe₃)₂]₂ ( 2 ), which is a dimer via Al‐C‐Al bridges. Two equivalents of the lithium compound gave a mixture of four main‐products, which could be identified as 2 , Li[Me₃C‐C≡C‐Al{CH(SiMe₃)₂}₃] ( 3 ), Me₃C‐C≡C‐Al[CH(SiMe₃)₂]₂ ( 4 ), and Al[CH(SiMe₃)₂]₃. The lithium atom of 3 is coordinated by the C≡C triple bond and an inner carbon atom of one bis(trimethylsilyl)methyl group. Further interactions were observed to C‐H bonds of methyl groups.