Aqueous Amino Silane Modification of E-glass Surfaces

The majority of work available in the literature examines the effect of epoxy silane, gamma-aminopropyltrimethoxy silane, and methacrylate silane on E-glass surfaces. As alternatives to the most commonly used silanes, we investigated two novel silanes: gamma-ureidopropyltriethoxy silane and Nbeta(aminoethyl) gamma-aminotrimethoxy silane and additionally an amino-functional polysiloxane. The ureido silane-treated E-glass fibers demonstrated a zeta potential similar to that of the untreated E-glass fibers, which was independent of deposition solution pH over the pH range investigated. A moderately hydrophobic E-glass surface, which was silane concentration dependent, was noted as being due to condensed Si-O-Si bonds at the surface. The diamino silane demonstrated an extremely basic surface at the higher silane concentrations investigated. These outer surface layers were modified by changing the pH and the concentration of the deposition solution. The polysiloxane produced an increase in the hydrophobicity of the E-glass fiber, especially when deposited from extremely basic solutions. At the higher solution concentrations investigated, the silanes and the siloxane was initially deposited in patches and an outer surface or "skin" was formed over these patches, giving the appearance of fully coated fibers. Copyright 2001 Academic Press.     

Synthesis of Enantiomerically Pure Bis(hydroxymethyl)-Branched Cyclohexenyl and Cyclohexyl Purines as Potential Inhibitors of HIV

The synthesis of the enantiomerically pure bis(hydroxymethyl)-branched cyclohexenyl and cyclohexyl purines is described. Racemic trans-4,5-bis(methoxycarbonyl)cyclohexene [(+/-)-6] was reduced with lithium aluminum hydride to give the racemic diol (+/-)-7. Resolution of (+/-)-7 via a transesterification process using lipase from Pseudomonas sp. (SAM-II) gave both diols in enantiomerically pure form. The enantiomerically pure diol (S,S)-7was benzoylated and epoxidized to give the epoxide 9. Treatment of the epoxide 9 with trimethylsilyl trifluoromethanesulfonate and 1,5-diazabicyclo[5.4.0]undec-5-ene followed by dilute hydrochloric acid gave (1R,4S,5R)-4,5-bis[(benzoyloxy)methyl]-1-hydroxycyclohex-2-ene (10). Acetylation of 10 gave (1R,4S,5R)-1-acetoxy-4,5-bis[(benzoyloxy)methyl]cyclohex-2-ene (11). (1R,4S,5R)-1-Acetoxy-4,5-bis[(benzoyloxy)methyl]cyclohex-2-ene (11) was converted to the adenine derivative 12 and guanine derivative 13 via palladium(0)-catalyzed coupling with adenine and 2-amino-6-chloropurine, respectively. Hydrogenation of 12 and 13 gave the correspondning saturated adenine derivative 14 and guanine derivative 15. (1R,4S,5R)-4,5-Bis[(benzoyloxy)methyl]-1-hydroxycyclohex-2-ene (10) was converted to the adenine derivative 16 and guanine derivative 17 via coupling with 6-chloropurine and 2-amino-6-chloropurine, respectively, using a modified Mitsunobu procedure. Hydrogenation of 16 and 17 gave the corresponding saturated adenine derivative 18 and guanine derivative 19. Compounds 12-19 were evaluated for activity against human immunodeficiency virus (HIV), but were found to be inactive. Further biological testings are underway.     

Heuristics for integrated optimization of catheter positioning and dwell time distribution in prostate HDR brachytherapy

High dose-rate (HDR) brachytherapy is one kind of radiotherapy used to treat different forms of cancer, such as prostate cancer. When this treatment is used for prostate cancer, a radioactive source is moved through catheters implanted into the prostate. For each patient, a treatment plan is constructed. This plan determines for example catheter positions and dwell time distribution, that is, where to the radioactive source should stop and for how long.     

Fragmentation dynamics within shear bands--a model for aging tectonic faults?

A numerical model for packing of fragmenting blocks in a shear band is introduced, and its dynamics is compared with that of a tectonic fault. The shear band undergoes a slow aging process in which the blocks are being grinded by the shear motion and the compression. The dynamics of the model have the same statistical characteristics as the seismic activity in faults. The characteristic magnitude distribution of earthquakes appears to result from frictional slips at small and medium magnitudes, and from fragmentation of blocks at the largest magnitudes. Aftershocks to large-magnitude earthquakes are local recombinations of the fragments before they reach a new quasi-static equilibrium. The aftershocks satisfy Omori's law. Local precursor activity at a few times the normal background level appears at a short time before a major earthquake. Seismic gaps appear as a natural consequence of the aging process of a fault. Explanation of the heat flux and principal stress direction anomalies at the faults both involve the value of fracture stress of the blocks in the gouge. The final form of a tectonic fault is predicted to involve a gouge dominated by fine-grained and rather rounded blocks so that it cannot withstand large shear stresses. Received 26 July 2000     

Invariant Analysis of Turbulent Pipe Flow

The anisotropy analysis of Lumley provides a useful tool to quantify the degree of anisotropy in turbulent flows. Also included in the analysis are relations which may be used to check if the flow is axisymmetric or two-dimensional. However, the method does not provide any scale information about the structures. The analysis has therefore been extended here to Fourier space, which allows scale information to be derived. The method was applied to fully developed pipe flow and it was shown that the large-scale motion is everywhere close to axisymmetric. The intermediate scales are strongly influenced by the restrictions posed by the pipe walls. At the centre line, the flow structure appears axisymmetric at all scales, but the measurement sindicate that true axisymmetry is lost very quickly away from the centre line. The structure of the smallest scales could not be determined reliably due to a singularity in the analysis which develops as the scales go to zero. This revised version was published online in July 2006 with corrections to the Cover Date.     

Mesoscale Clusters in the Crystallisation of Organic Molecules

The early stages of the molecular self-assembly pathway leading to crystal nucleation have a significant influence on the properties and purity of organic materials. This mini review collates the work on organic mesoscale clusters and discusses their importance in nucleation processes, with a particular focus on their critical properties and susceptibility to sample treatment parameters. This is accomplished by a review of detection methods, including dynamic light scattering, nanoparticle tracking analysis, small angle X-ray scattering, and transmission electron microscopy. Considering the challenges associated with crystallisation of flexible and large-molecule active pharmaceutical ingredients, the dynamic nature of mesoscale clusters has the potential to expand the discovery of novel crystal forms. By collating literature on mesoscale clusters for organic molecules, a more comprehensive understanding of their role in nucleation will evolve and can guide further research efforts.     

Anti-Aromatic versus Induced Paratropicity: Synthesis and Interrogation of a Dihydro-diazatrioxa[9]circulene with a Proton Placed Directly above the Central Ring

We present a high-yielding intramolecular oxidative coupling within a diazadioxa[10]helicene to give a dihydro-diazatrioxa[9]circulene. This is the first [n]circulene containing more than eight ortho-annulated rings (n>8). The single-crystal X-ray structure reveals a tight columnar packing, with a proton from a pendant naphthalene moiety centred directly above the central nine-membered ring. This distinct environment induces a significant magnetic deshielding effect on that particular proton as determined by ¹H NMR spectroscopy. The origin of the deshielding effect was investigated computationally in terms of the NICS values. It is established that the deshielding effect originates from an induced paratropic ring current from the seven aromatic rings of the [9]circulene structure, and is not due to the nine-membered ring being antiaromatic. UV/Vis spectroscopy reveals more efficient conjugation in the prepared diazatrioxa[9]circulene compared to the parent helical azaoxa[10]helicenes, and DFT calculations, including energy levels, confirm the experimental observations.     

NMR cryoporometry to study the fiber wall structure and the effect of drying

NMR cryoporometry has been used for investigating the porosity changes of bleached wood pulp upon drying. This NMR method follows the same principles as thermoporosimetry, which has been used for the same purpose during the last decade and makes it possible to investigate porous material in the water-swollen state. In this study bleached softwood kraft pulp was exposed to a series of drying procedures where the decrease in porosity within the fiber cell wall could be characterized for pore radii below 100 nm. This decrease in porosity is called hornification, which is an irreversible collapse of the fiber wall structure during drying and results in decreased uptake of water and reduced swelling of the fiber upon rewetting. Our results have been compared to the traditionally used water retention value (WRV) and correlates well with these. Furthermore, this NMR method could show the reduction of hornification when adsorbing the hemicellulose glucuronoxylan to the fiber.