Thesis (M.Ed.)--University of Hong Kong, 1988. / Includes bibliographical references (leaf 135-144). Also available in print.

Uniformly distributed ZnO nanorods with diameter 70-100 nm and 1-2μm long have been successfully grown at low temperatures on GaN by using the inexpensive aqueous solution method. The formation of the ZnO nanorods and the growth parameters are controlled by reactant concentration, temperature and pH. No catalyst is required. The XRD studies show that the ZnO nanorods are single crystals and that they grow along the c axis of the crystal plane. The room temperature photoluminescence measurements have shown ultraviolet peaks at 388nm with high intensity, which are comparable to those found in high quality ZnO films. The mechanism of the nanorod growth in the aqueous solution is proposed. The dependence of the ZnO nanorods on the growth parameters was also investigated. While changing the growth temperature from 60°C to 150°C, the morphology of the ZnO nanorods changed from sharp tip (needle shape) to flat tip (rod shape). These kinds of structure are useful in laser and field emission application. / Singapore-MIT Alliance (SMA)

Solid-phase syntheses of two 14-membered ring peptidomimetics were done to determine whether or not a beta-turn structure can facilitate macrocyclization. NMR methods, together with CD and QMD calculations, do not fully support this assumption. However, cyclizations of more ordered structures like those of compounds 2 were more efficient than those for highly strained ring systems like 1. A small library of 18-membered ring peptidomimetics that accommodate an extra amino acid residue was synthesized on resin. Their syntheses were not complicated by head-to-tail dimer impurity, unlike those for previously synthesized 14-membered systems. These larger macrocycles exhibit beta-turn structures as verified by NMR, CD and QMD techniques. Moreover, two compounds in this series (3a and 3g) were shown to have agonistic properties for TrkC in cell survival assays. Dimerization of monovalent mimics was achieved first by modifying the organic template so that monovalent mimics with requisite functional groups can be synthesized. Second, the monovalent units were dimerized using sequential nucleophilic substitutions on fluorescently labeled dichlorotriazine. Our rationale to make bivalent compounds out of monovalent ones was justified when compound 4 was shown to bind TrkA with a 20 nM affinity. Reactions of amino acids with NH4SCN under acylating conditions produced 2-thiohydantoins in which the nitrogen of the amino acid (N1) was acylated. This was proven by 2-D NMR which showed no cross-peak between the NH signal observed and the Cα±-H of the amino acid. When the compound was deacylated, a new NH signal appeared and the corresponding cross-peak with the Cα±-H was observed. Solution-phase syntheses of non-peptidic mimics were achieved by doing a double substitution on a dihalogenated nitrobenzene scaffold. Sonogashira and SNAr reactions were done to install the required side-chains to give the desired compounds. These non-peptidic compounds can be easily adapted to our DTAF-Inp dimerization protocol since the nitro groups can be easily reduced. Attempts to make a spirotetracyclic peptidomimetic with three side chain mimics were done by synthesizing the spirocyclic diketopiperazine precursor. The synthesis of the DKP was achieved by making the cyclic quaternary amino acid that was coupled to another amino acid via the HOAt-EDC method. This protocol gave dipeptides in high yields. These dipeptides were deprotected and cyclized to the DKP under mildly acidic conditions in toluene.

In this paper we study a class of non-linear singular partial differential equation in complex domain Csub(t) x C n sub(x). Under certain assumptions, we prove the existence and uniqueness of holomorphic solution near origin of Csub(t) x C n sub(x).

The paper deals with a non-linear singular partial differential equation: (E) t∂/∂t = F(t, x, u, ∂u/∂x) in the holomorphic category. When (E) is of Fuchsian type, the existence of the unique holomorphic solution was established by Gérard-Tahara [2]. In this paper, under the assumption that (E) is of totally characteristic type, the authors give a sufficient condition for (E) to have a unique holomorphic solution. The result is extended to higher order case.

In this paper, we discuss the global existence of solutions for Chemotaxis models with saturation growth. If the coe±cients of the equations are all positive smooth T-periodic functions, then the problem has a positive T-periodic solution, and meanwhile we discuss here the stability problems for the T-periodic solutions.

Fluids are used for intravenous infusion during practically all surgeries, but several different compositions are available on the market. Crystalloid fluids comprise lactated or acetated Ringer solutions, normal saline, Plasma-Lyte, hypertonic saline, and glucose. They lack allergic properties but are prone to cause peripheral tissue oedema. Their turn­ over is governed by physiological factors such as dehydration and drug effects. Colloid fluids include hydroxyethyl starch, albumin, dextran, and gelatin. These fluids have various degrees of allergic properties and do not promote peripheral oedema. Their half-life is usually about hours. Factors increasing the turnover rate are poorly known but might include inflammatory states. Current debates include the widespread use of normal saline, which should be replaced by Ringer’s or Plasma-Lyte in most situations, and the kidney damage associated with the use of starch in septic patients. New studies show that hypertonic saline does not improve survival or neurological damage in prehospital care.

Water-soluble fullerene containing polymers comprising of poly(2-(dimethylamino) ethyl methacrylate)-fullerene (PDMAEMA-C60) with targeting moieties, poly(oligo(ethylene glycol) methyl ether methacrylate)-C60 (POEGMA-C60), nanocrystalline cellulose-fullerene (NCC-C60) and NCC-C60-POEGMA were synthesized and their solution properties were investigated. PDMAEMA-C60 with galactose targeting moiety was prepared by atom transfer radical polymerization (ATRP) and atom transfer radical addition (ATRA) processes. The self-assembly of galactose functionalized PDMAEMA-C60 structure in aqueous solutions was investigated using dynamic light scattering (DLS) at different pHs. A smaller hydrodynamic radius (Rh) was observed at pH 10 than at pH 3 due to electrostatic repulsion at low pH values. In addition, free PDMAEMA chains induced the demicellization of self-assembled nanostructures caused by the formation of charge transfer complex between PDMAEMA and C60. A well-defined poly(di(ethylene glycol) methyl ether methacrylate–stat-oligo(ethylene glycol) methyl ether methacrylate)-block-poly(di(ethylene glycol) methyl ether methacrylate ((PMEO2MA-stat-POEGMA300)-b-PMEO2) was successfully synthesized at room temperature via a two-step ATRP process. The block copolymer exhibited two thermal transitions at ~ 30 and 45 oC, which was believed to be associated with the formation of micelles and larger aggregates. The Rh of the aggregates increased from 47 to 90 nm, the aggregation number increased from 76 to ~9800 and Rg/Rh increased from 0.75 to 1.2 within the temperature range of 34 to 45oC. Well-defined statistical (PMEO2MA-stat-POEGMA300)-C60 was synthesized via ATRP and ATRA. The lower critical solution temperature (LCST) of (PMEO2MA-stat-POEGMA300)-C60 increased with methanol content in water, exhibiting lower LCSTs than PMEO2MA-stat-POEGMA300 for all methanol/water compositions. Higher critical micelle concentration (CMC) and larger spherical micelles were observed for (PMEO2MA-stat-POEGMA300)-C60 with increasing methanol content. The Rh of the micelles remained constant at temperature below the LCST and increased dramatically at temperature greater than the LCST, and (Rg/Rh) increased from ~ 0.75 to ~ 1.0. Nanocrystalline cellulose (NCC) was modified with water-soluble C60-(β-cyclodextrin) and (PMEO2MA-stat-POEGMA300)-C60) through a radical coupling reaction. NCC-C60-(PMEO2MA-stat-POEGMA300) possessed thermal responsive behavior in water and ~3.5 oC hysteresis associated with the heating/cooling cycles. No observable damage to NCC occurred during the radical coupling reaction as determined by TEM. NCC-C60-(β-cyclodextrin) possessed a similar thermal degradation behavior as NCC except it possessed a broader temperature range. Both NCC-fullerene systems demonstrated a radical scavenging activity when screened with the 2,2-diphenyl-1-picrylhydrazyl (DPPH). In addition, the drug loading and delivery using PDMAEMA-C60 with targeting moieties was explored. Two model drugs, namely fluorescein and pyrene were employed to evaluate the location of drug in the self-assembled structure of PDMAEMA-C60. It was found that the hydrophobic drugs were partitioned between the PDMAEMA shells and the hydrophobic fullerene cores. The drug delivery profiles indicated that PDMAEMA-C60 is an efficient drug carrier, however, it was cytotoxic to cells. The gene transfection efficacy of PDMAEMA-C60 to different cell lines was investigated and the results demonstrated that PDMAEMA-C60 exhibited good gene transfection performance. However, the targeting selectivity to liver cells cannot be determined in both cases. This study demonstrates that nanostructures of stimuli-responsive fullerene polymers can be controlled and manipulated by changing the external environments. Several potential applications, such as in drug and gene delivery, and free radical scavenging can be further explored.

La recherche de la solution optimale d'un problème combinatoire est souvent très longue puisque, d'une manière générale, le temps de résolution est une fonction exponentielle de la taille de ce problème. Dès l'instant où on se place dans un contexte temps réel, c'est-à-dire chaque fois qu'on impose une limite au temps de calcul alloué, les algorithmes d'optimisation classique s'avèrent, à quelques rares exceptions près , impuissants, et on doit se contenter d'utiliser des méthodes heuristiques. La présente étude porte sur l'évaluation de celles qui sont susceptibles d'apporter une réponse satisfaisante à certains problèmes d'ordonnancement. Trois types d'approches sont étudiées : - les heuristiques non convergentes, - les heuristiques convergentes, - les méthodes d'apprentissage. L'évaluation de leurs performances est réalisée sur le double critère de la qualité de la solution et du temps de calcul nécessaire à leur mise en œuvre.

The capillary surface $u(x,y)$ near a cusp region satisfies the boundary value problem: \begin{eqnarray} \nabla \cdot \frac{\nabla u}{\sqrt{1+\left|\nabla u \right|^2}}&=&\kappa u \qquad \textrm{in }\left\{(x,y): 0<x,f_2(x)<y<f_1(x)\right\}\,, \label{0.1}\\ \nu \cdot \frac{\nabla u}{\sqrt{1+\left|\nabla u \right|^2}}&=& \cos \gamma_1 \qquad \textrm{on } y=f_1(x)\,,\\ \nu \cdot \frac{\nabla u}{\sqrt{1+\left|\nabla u \right|^2}}&=& \cos \gamma_2 \qquad \textrm{on } y=f_2(x)\,, \label{0.3} \end{eqnarray} where $\lim_{x\rightarrow 0}f_1(x),f_2(x)=0$, $\lim_{x\rightarrow 0}f'_1(x),f'_2(x)=0$. It is shown that the capillary surface is unbounded at the cusp and satisfies $u(x,y)=O\left(\frac{1}{f_1(x)-f_2(x)}\right)$, even for types of cusp not investigated previously (e.g. exponential cusps). By using a tangent cylinder coordinate system, we show that the exact solution $v(x,y)$ of the boundary value problem: \begin{eqnarray} \nabla \cdot \frac{\nabla v}{\left|\nabla v \right|}&=&\kappa v \qquad \textrm{in }\left\{(x,y): 0<x,f_2(x)<y<f_1(x)\right\}\,,\\ \nu \cdot \frac{\nabla v}{\left|\nabla v \right|}&=& \cos \gamma_1 \qquad \textrm{on } y=f_1(x)\,,\\ \nu \cdot \frac{\nabla v}{\left|\nabla v \right|}&=& \cos \gamma_2 \qquad \textrm{on } y=f_2(x)\,, \end{eqnarray} exhibits sixth order asymptotic accuracy to the capillary equations~\eqref{0.1}$-$\eqref{0.3} near a circular cusp. Finally, we show that the solution is bounded and can be defined to be continuous at a symmetric cusp ($f_1(x)=-f_2(x)$) with the supplementary contact angles ($\gamma_2=\pi-\gamma_1$). Also it is shown that the solution surface is of the order $O\left(f_1(x)\right)$, and moreover, the formal asymptotic series for a symmetric circular cusp region is derived.