Preparation and Characterization of Aluminum Alkoxides and their Application to Ring‐Opening Polymerization of ϵ‐Caprolactones

The reaction of 2‐methoxybenzyl alcohol with one molar equiv of R₂AIX in diethyl ether at 0°C gives [(2‐MeOC₆H₄CH₂‐μ‐O)AlRX]₂ ( 1 : R = Et, X = Cl, 2 : R = X = Et). In addition, 2,4‐di‐tert‐butylphenol reacts with ⁱBu₃Al affording a four‐coordinated aluminum compound [(μ‐2,4‐^tBu₂‐C₆H₄O)Al(ⁱBu)₂]₂ ( 4 ). Single crystal X‐ray structure analysis of 4 shows a C_2h‐symmetry with a planar Al₂O₂ core. Ring‐opening polymerization (ROP) of caprolactones initiated by 1, 4 and [(μ‐OCH₂C₆H₄OMe)Al(ⁱBu)₂]₂ ( 3 ) is performed and polyesters with narrow molecular weight distributions were obtained from the “living” ROP of caprolactones. ¹H NMR spectroscopic studies of PCL reveal that the initiator of 1 and 3 is through the Al‐OAr function, but the initiator of 4 is through the Al‐ ⁱBu group.     

Nurses allocation models for maternal and child health services

Maternal and Child Health (MCH) centres in Hong Kong offer, for children aged below six and women of childbearing age, a comprehensive range of health services regularly performed by nurses of different ranks. While each rank has its specific duties, nurses of a higher rank can step down to the work of a more junior rank when necessary. However, cross-regional deployments of nurses occur less frequently. We develop goal programming models of ‘optimal’ MCH nurses allocation. The presence and absence of nurses’ ‘cross-over’ of work functions are explicitly considered. The results show that more equitable manpower levelling can be achieved, with flexibility (in the longer term) on cross-regional deployment of nurses as a possible way of operational improvement when the entire MCH service is taken as a whole.     

Electrospinning of Hyaluronic Acid (HA) and HA/Gelatin Blends

Summary: In the present study, electrospinning of hyaluronic acid (HA) and hyaluronic acid/gelatin (HA‐GE) blends in N,N‐dimethylformamide (DMF)/water‐mixed solvents have been investigated. When the volume ratio of DMF to water was in the range of 1.5–0.5, HA solutions could be electrospun into fibrous membranes successfully. The average diameter of HA fibers was about 200 nm. The HA‐GE composite nanofibrous membranes with varied HA/GE weight ratio in the range of 100/20–100/100 have also been successfully fabricated. The average diameter of HA‐GE fibers was in the range of 190–500 nm. The decrease in surface tension could promote fiber formation. Thus, an introduction of DMF that could decrease the surface tension distinctively, without significant change or increase in viscosity of the solution, could bypass the use of blowing‐assisted electrospinning. Our postulated picture is that the lower surface tension could help the ejection of stream with relatively high viscosity and reduce or prevent the droplet formation during the spinning process.

HA/GE (100/80) nanofibrous membrane produced by electrospinning.     

A Rapid Process for Producing Cellulose Multi‐Filament Fibers from a NaOH/Thiourea Solvent System

Summary: Cellulose was dissolved rapidly in 9.5 wt.‐% NaOH and 4.5 wt.‐% thiourea aqueous solution pre‐cooled to −5 °C to prepare a transparent solution. Novel cellulose multi‐filament fibers were spun successfully, for the first time, from the cellulose dope on an extended laboratory scale. The results from ¹³C NMR, scanning electron microscopy and wide angle X‐ray diffraction (WAXD) patterns indicated that the fibers exhibited cellulose II character and possessed a circular cross‐section and smooth surface. The tensile strength of the novel fibers reached 1.9–2.2 cN · dtex⁻¹. 2D WAXD and SAXS patterns revealed that, with a drawing progress, the orientation factor increased and mechanical properties were improved.

SEM micrographs of the novel multi‐filament fibers spun from cellulose solution in a NaOH/thiourea aqueous system pre‐cooled to −5 °C on an extended laboratory scale.     

Synchronization and parameter identification of one class of realistic chaotic circuit

In this paper, the synchronization and the parameter identification of the chaotic Pikovsky--Rabinovich (PR) circuits are investigated. The linear error of the second corresponding variables is used to change the driven chaotic PR circuit, and the complete synchronization of the two identical chaotic PR circuits is realized with feedback intensity k increasing to a certain threshold. The Lyapunov exponents of the chaotic PR circuits are calculated by using different feedback intensities and our results are confirmed. The case where the two chaotic PR circuits are not identical is also investigated. A general positive Lyapunov function V, which consists of all the errors of the corresponding variables and parameters and changeable gain coefficient, is constructed by using the Lyapunov stability theory to study the parameter identification and complete synchronization of two non-identical chaotic circuits. The controllers and the parameter observers could be obtained analytically only by simplifying the criterion dV/dt<0 (differential coefficient of Lyapunov function V with respect to time is negative). It is confirmed that the two non-identical chaotic PR circuits could still reach complete synchronization and all the unknown parameters in the drive system are estimated exactly within a short transient period.     

E?ect of Thermal Treatment on Structure and Catalytic Activity of Supported Fischer-Tropsch Nano-Cobalt Catalysts for Clean Fuels

"A series of 15%Co/Al2O3 catalysts were prepared by incipient wetness impregnation under various calcination conditions (90-500 oC), and were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy experiments (XPS), temperature programmed reduction, and catalytic measurements of hydrogenation of carbon monoxide to long-chained hydrocarbons leading to clean fuels (Fischer-Tropsch synthesis). The results of XPS show the presence of incompletely decomposed cobalt nitrate for catalysts calcined at 90-200 oC, and the presence of Co3O4 for catalysts calcined at 200-500 oC. For the four alumina-supported nano cobalt catalysts with different thermal treatment (200-500 oC), XRD and XPS results illustrated that there were mainly nano Co3O4 crystalite phases of 9-10 nm and the size of cobalt nano-particles did almost not change with the different temperature of thermal treatment. This was different from that of silica-supported cobalt catalysts. The supported cobalt catalyst (CoAp340 sample) calcinated at 340 oC presented a better activity for Fischer Tropsch synthesis to clean fuels, at mild conditions like atmospheric pressure (100 kPa), 1800 mL/g/h and 190 oC; rather than high pressure (2 MPa or more)."     

Structural polarization properties of vector Gaussian beam in the far field

Based on the vector angular spectrum representation of optical beam and the method of stationary phase, the analytical TE and TM terms of vector Gaussian beam have been presented in the far field. By using the local polarization matrix, the polarization properties of the TE and TM terms in the far field are investigated, and it is found that the degree of their polarization is only determined by the spatial location. When the source is completely polarized, the TE and TM terms are both completely polarized in the far field. When the source is completely unpolarized, the TE and TM terms in the far field are partially polarized. The whole beam is also partially polarized except on the propagating axis. Moreover, the degrees of polarization of TE and TM terms are both larger than that of the whole beam.[第一段]     

Ar (3P0,2 )与SO2反应产生SO (A″ 3Σ+)的光谱

On the flowing afterglow apparatus, in the energy transfer reaction between Ar (3P0,2) and SO2, two series of spectra were observed at two different downstream optical windows from the discharge region. According to the data obtained in this group’s report on the discharge of the mixture of Ar with SO2 and spectral simulation, the two spectrum progressions in the range of 320 and 600 nm were assigned to SO (A″3Σ+→X 3Σ-) and SO (c 1Σ-→X 3Σ-), respectively. The spectroscopic constants for the new electronic state were obtained by spectral simulation based on the method of the least square and shown as follows: T00 =(30460±18.0) cm-1, ωe′=(685±0.8) cm-1 and ωe′χe′=(7.7±8.0) cm-1.     

Fabrication of Poly(lactic acid) Diacrylate Nanospheres with Double Bonds

Summary: In this paper, unsaturated groups were introduced into poly(lactic acid) (PLA) for fabricating PLA‐based nanospheres with carbon‐carbon double bonds as functional groups. The morphology dependencies on fabrication conditions, including the fabrication time as well as the stirring rate, were also investigated.

SEM‐EDX image of poly(lactic acid) diacrylate nanospheres after exposure to osmium tetroxide vapor for 14 h.     

Wideband multiwavelength erbium-doped fiber ring laser with frequency shifted feedback

Wideband multiwavelength erbium-doped fiber ring lasers with frequency shifted feedback are described. The use of an intra-cavity gain flattening filter (GFF) was proposed in order to increase the lasing spectral bandwidth, leading to a demonstration of 34 lasing wavelengths in 28 nm bandwidth in C-band. The GFF induced spectral output power fluctuation is discussed. Multiwavelength operation was also demonstrated for the first time in L-band, where wideband laser operation was obtained without a GFF. Optical bistability and Kerr effect induced pulsation were determined to be limiting factors to stable operation range in this kind of multiwavelength lasers.