Rheological Characterization of Self-Hardening Hydrogel for Tissue Engineering Applications: Gel Point Determination and Viscoelastic Properties

Summary: Silated hydroxypropylmethylcellulose (Si-HPMC) is a modified biopolymer used in biomaterial's domain. A hydroxypropylmethylcellulose (HPMC) was functionalised with silane groups. The macromolecular solution of Si-HPMC (pH 12.9) generates an elastic state at physiological pH (∼7.4). In this work we present the gel formation of Si-HPMC resulting from the condensation of silanol groups. The crosslinked hydrogel was characterized using rheological techniques. With the scalar percolation model the gelation time was determined as a function of Si-HPMC concentration at 37 °C.     

An improved weighted essentially non-oscillatory scheme for hyperbolic conservation laws

In this article we develop an improved version of the classical fifth-order weighted essentially non-oscillatory finite difference scheme of [G.S. Jiang, C.W. Shu, Efficient implementation of weighted ENO schemes, J. Comput. Phys. 126 (1996) 202–228] (WENO-JS) for hyperbolic conservation laws. Through the novel use of a linear combination of the low order smoothness indicators already present in the framework of WENO-JS, a new smoothness indicator of higher order is devised and new non-oscillatory weights are built, providing a new WENO scheme (WENO-Z) with less dissipation and higher resolution than the classical WENO. This new scheme generates solutions that are sharp as the ones of the mapped WENO scheme (WENO-M) of Henrick et al. [A.K. Henrick, T.D. Aslam, J.M. Powers, Mapped weighted essentially non-oscillatory schemes: achieving optimal order near critical points, J. Comput. Phys. 207 (2005) 542–567], however with a 25% reduction in CPU costs, since no mapping is necessary. We also provide a detailed analysis of the convergence of the WENO-Z scheme at critical points of smooth solutions and show that the solution enhancements of WENO-Z and WENO-M at problems with shocks comes from their ability to assign substantially larger weights to discontinuous stencils than the WENO-JS scheme, not from their superior order of convergence at critical points. Numerical solutions of the linear advection of discontinuous functions and nonlinear hyperbolic conservation laws as the one dimensional Euler equations with Riemann initial value problems, the Mach 3 shock–density wave interaction and the blastwave problems are compared with the ones generated by the WENO-JS and WENO-M schemes. The good performance of the WENO-Z scheme is also demonstrated in the simulation of two dimensional problems as the shock–vortex interaction and a Mach 4.46 Richtmyer–Meshkov Instability (RMI) modeled via the two dimensional Euler equations.     

Diastereoselective addition of 2H-2-oxo-1,4,2-oxazaphosphinanes to aldehydes and imines

[reaction: see text] Diastereoselective additions of 2-hydrogeno-2-oxo-1,4,2-oxazaphosphinanes to aldehydes and imines are described. alpha,alpha'-Diaminophosphinic and alpha-amino-alpha'-hydroxyphosphinic derivatives were obtained with de's ranging from 24 to 90%.     

Audiogram of a harbor porpoise (Phocoena phocoena) measured with narrow-band frequency-modulated signals

The underwater hearing sensitivity of a two-year-old harbor porpoise was measured in a pool using standard psycho-acoustic techniques. The go/no-go response paradigm and up-down staircase psychometric method were used. Auditory sensitivity was measured by using narrow-band frequency-modulated signals having center frequencies between 250 Hz and 180 kHz. The resulting audiogram was U-shaped with the range of best hearing (defined as 10 dB within maximum sensitivity) from 16 to 140 kHz, with a reduced sensitivity around 64 kHz. Maximum sensitivity (about 33 dB re 1 microPa) occurred between 100 and 140 kHz. This maximum sensitivity range corresponds with the peak frequency of echolocation pulses produced by harbor porpoises (120-130 kHz). Sensitivity falls about 10 dB per octave below 16 kHz and falls off sharply above 140 kHz (260 dB per octave). Compared to a previous audiogram of this species (Andersen, 1970), the present audiogram shows less sensitive hearing between 2 and 8 kHz and more sensitive hearing between 16 and 180 kHz. This harbor porpoise has the highest upper-frequency limit of all odontocetes investigated. The time it took for the porpoise to move its head 22 cm after the signal onset (movement time) was also measured. It increased from about 1 s at 10 dB above threshold, to about 1.5 s at threshold.     

The cut cone III: On the role of triangle facets

The cut polytopeP _n is the convex hull of the incidence vectors of the cuts (i.e. complete bipartite subgraphs) of the complete graph onn nodes. A well known class of facets ofP _n arises from the triangle inequalities:x _ij +x _ik +x _jk ≤2 andx _ij −x _ik −x _jk ≤0 for 1≤i, j, k≤n. Hence, the metric polytopeM _n , defined as the solution set of the triangle inequalities, is a relaxation ofP _n .We consider several properties of geometric type forP _n , in particular, concerning its position withinM _n . Strengthening the known fact ([3]) thatP _n has diameter 1, we show that any set ofk cuts,k≤log₂ n, satisfying some additional assumption, determines a simplicial face ofMn and thus, also, ofP _n . In particular, the collection of low dimension faces ofP _n is contained in that ofM _n . Among a large subclass of the facets ofP _n , the triangle facets are the closest ones to the barycentrum ofP _n and we conjecture that this result holds in general. The lattice generated by all even cuts (corresponding to bipartitions of the nodes into sets of even cardinality) is characterized and some additional questions on the links between general facets ofP _n and its triangle facets are mentioned.     

Variations in model formulations

Mathematical programming models may contain a great deal of variations in their formulations. The same problem can be modeled as different formulations, or different problems can be modeled as the same formulations. In order to handle these variant formulations efficiently and intelligently, a model management system should be able to eliminate or recognize the variations in model formulations. We analyze possible variations involved in model formulations and categorize them into three types-syntactic, semantic and structural.The first author received support for this work from the 1991 Research Fund at Ajou University.     

Synthesis,spectroscopic characterization and in vitro antitumour activity of di-n-butyltin and diethyltin trimethoxybenzoates: X-ray structure analysis of bis[di-n-butyl(3,4,5-trimethoxybenzoato)tin] oxide

Di-n-butyltin(IV) and diethyltin(IV) 2,3,4-, 2,4,5- and 3,4,5-trimethoxybenzoates [(CH₃O)₃C₆H₂COO]₂SnR [Type a] and {[(CH₃O)₃C₆H₂COO]R₂Sn}₂O [Type b] have been synthesized and characterized spectroscopically. The crystal structure of bis[di-n-butyl(3,4,5- trimethoxybenzoato)tin] oxide has been determined. The triclinic unit cell contains one centrosymmetric dimer; a = 15.919(2) Å, b = 11.711(3) Å, c = 13.475(1) Å, and α = 63.63(2)°, β = 67.49(1)°, γ = 76.61(2)°. The geometry of the dimer is very similar to that of bis[di-n-butyl(5-methoxysalicylatotin] oxide), with two different types of five-coordinate tin atoms and one central planar Sn₂O₂ ring.     

Some advantages of high temperature for the separation of pharmaceutical compounds with mass spectrometry detection

The beneficial effects of high temperature on separation and detection of basic compounds, the detection being performed by MS via ESI, are investigated. The influence of various parameters on both separation and detection performances is studied. These parameters include the mobile phase pH, the temperature, and the type of stationary phase. Experiments are performed under gradient elution conditions. The results obtained with four different supports, silica-, zirconia-, carbon-, and polymer-based columns, are compared by means of different criteria including the elution composition, the peak asymmetry, and the S/N. High temperature liquid chromatography at high pH with volatile buffers suitable for MS detection was shown to be an interesting choice for solutes with basic sites.