Impurity induced disordering produced lateral optical confinement in AlGaAs and InGaAs (on GaAs) quantum well waveguides

The impurity induced disordering technique is employed on an AlGaAs/GaAs quantum well optical waveguide to provide lateral optical confinement. The modal propagation constant and field profile are analysed using an improved Fourier decomposition method. The single mode operating region is given in terms of thickness of quantum well layers.published_or_final_versio

Solutions of the quasi-vector wave equation for optical waveguides in a mapped infinite domains by the Galerkin's method

Galerkin's method is employed to analyze the quasi-vector wave equation for optical waveguides with arbitrary refractive index profile in a mapped infinite domains. Results are presented for a range of waveguide structures which include rectangular core, circular core, rib, and multiple quantum well. Solutions are compared favorably to exact vector solution and numerical results using Fourier operator transform method and beam-propagation method.published_or_final_versio

Cutoff frequency of the quasi-vector mode of optical waveguide with arbitrary refractive index profile

Based on the Galerkin's method, a numerical method is developed to analysis the cutoff frequencies of guided modes of optical waveguides with arbitrary refractive index profile. Solutions are presented in the quasi-vector regime. Optical waveguide structures with single core of arbitrary shape are considered in this paper. The calculated results are compared favorably with exact vector solution and circular-harmonic expansion method.published_or_final_versio

Phase modulator defined by impurities induced disordering

Optical waveguide type phase modulators defined by impurities induced disordering (IID) are investigated. To achieve a better optical confinement, a two steps ion implantation process is carried out to introduce additional impurities with respect to depth in the cladding region. A more uniform refractive index profile in deeper lateral confined region is obtained after thermal annealing. The refractive index different between the core and cladding can be adjusted by controlling the extension of interdiffusion in the cladding. This provide tuning of single mode operating region. For present IID phase modulator with 25 period of 100 angstroms/100 angstroms Al0.3Ga0.7As/GaAs multiple quantum wells single mode operating at 0.88 μm, a normalized phase shift of 362°/Vmm, chirping parameter of 47, and absorption loss less than 120 cm-1 are achieved theoretically.published_or_final_versio

Investigation of the hydrodynamic behaviour of particles and aggregates by particle image velocimetry (PIV)

Proceedings of the International Symposium on Sustainable and Safe Water Supplies, Hong Kong, China, 15-17 January 2007.An advanced fluid visualisation technique, particle image velocimetry, was employed to investigate the hydrodynamic properties of particles and aggregates. The experiments were conducted in a settling column filled with a suspension of fluorescent polymeric beads as flow tracers. A thin vertical section of the settling column was illuminated by a laser sheet, while the motions of particles were recorded by a high speed CCD camera. Large solid spheres, flocs of latex microspheres and aggregates of marine diatoms were characterised for their hydrodynamic properties. The trajectories of the tracer particles were tracked when a large particle or aggregate settled through the suspension of the tracers, which gave the streamlines surrounding the falling object. The streamlines demonstrate directly the curvilinear feature of the interaction between approaching particles. However, the available curvilinear model underestimates the collision frequency function of particles by one order of magnitude or two. The collision potentials of the flocs and aggregates are more than an order of magnitude greater than the similar-sized solid spheres. Algal aggregates appear to be highly porous and fractal with a fluid collection efficiency of 10-40%, which would significantly enhance the flocculation between particles and the mass transfer into the aggregates. © IWA Publishing 2007.postprin

Investigation and visualization of internal flow through particle aggregates and microbial flocs using particle image velocimetry

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Activin a protects midbrain neurons in the 6-hydroxydopamine mouse model of Parkinson's disease

© 2015 Stayte et al. Parkinson's disease (PD) is a chronic neurodegenerative disease characterized by a significant loss of dopaminergic neurons within the substantia nigra pars compacta (SNpc) and a subsequent loss of dopamine (DA) within the striatum. Despite advances in the development of pharmacological therapies that are effective at alleviating the symptoms of PD, the search for therapeutic treatments that halt or slow the underlying nigral degeneration remains a particular challenge. Activin A, a member of the transforming growth factor β superfamily, has been shown to play a role in the neuroprotection of midbrain neurons against 6-hydroxydopamine (6-OHDA) in vitro, suggesting that activin A may offer similar neuroprotective effects in in vivo models of PD. Using robust stereological methods, we found that intrastriatal injections of 6-OHDA results in a significant loss of both TH positive and NeuN positive populations in the SNpc at 1, 2, and 3 weeks post-lesioning in drug naive mice. Exogenous application of activin A for 7 days, beginning the day prior to 6-OHDA administration, resulted in a significant survival of both dopaminergic and total neuron numbers in the SNpc against 6-OHDA-induced toxicity. However, we found no corresponding protection of striatal DA or dopamine transporter (DAT) expression levels in animals receiving activin A compared to vehicle controls. These results provide the first evidence that activin A exerts potent neuroprotection in a mouse model of PD, however this neuroprotection may be localized to the midbrain

Packing While Traveling: Mixed Integer Programming for a Class of Nonlinear Knapsack Problems

Packing and vehicle routing problems play an important role in the area of supply chain management. In this paper, we introduce a non-linear knapsack problem that occurs when packing items along a fixed route and taking into account travel time. We investigate constrained and unconstrained versions of the problem and show that both are NP-hard. In order to solve the problems, we provide a pre-processing scheme as well as exact and approximate mixed integer programming (MIP) solutions. Our experimental results show the effectiveness of the MIP solutions and in particular point out that the approximate MIP approach often leads to near optimal results within far less computation time than the exact approach

PIV characterisation of flocculation dynamics and floc structure in water treatment

Particle flocculation with chemical flocculant addition is an essential step in water treatment. The performance of flocculation and the property of the flocs formed affect the overall results of the treatment process. In addition to particulate impurities, the presence of organic matter in water, such as natural organic materials (NOM), also influence the effectiveness of chemical flocculation. In this paper, the PIV system was employed to investigate the flocculation dynamics for different flocculants in different model waters. With the PIV and image analysis, the change in particle size distribution could be well recorded. Using the sequence of flocculation, shear breakage and re-flocculation on a jar-test device together with the PIV system, the rate of floc formation, the strength of the flocs, the recovery of broken flocs, and the morphological and structural features of the flocs were characterized. The results indicated that the adsorption of HA on the particle will stabilized the particles, hence hindered the flocculation process. Sweep flocculation using a higher chemical coagulant dosage was an effective means of process enhancement for the removal of particulates and associated organic matter. The dynamics of A-B-R process was characterized by particle size distribution (PSD) measurement with PIV setup. The particle strength and reversibility capability were examined. Strength index showed the HA flocs have comparable strength, while recovery index indicated a less recovery capability with the increasing of HA concentration after exposure to a higher shear, especially for ferric HA flocs. It appears that the bonds holding HA flocs together are not purely physical bonds given the limited regrowth seen. Finally, evolution of floc structure during A-B-R process was analysed by investigated the fractal dimension Db. The results were generally consistent with previous PSD measurements. It suggested that the structure of flocs in breakage became more compact with little permeability. An increase in floc compaction provides a further explanation for the limited regrowth for most of flocs. According to the performances of alum and ferric, it can be noticed that HA flocs have different properties dependent on which chemical coagulant is used. Alum produced larger HA flocs which endured a higher recovery capability after exploring higher shear, hence, compared to ferric, it could be preferred to using in the practical enhanced coagulation unit.postprin

Reversible posterior leukoencephalopathy syndrome in Chinese children induced by chemotherapy: A review of five cases

This is a retrospective review of the clinico-radiological features and neurological outcomes of reversible posterior leukoencephalopathy syndrome episodes in Chinese cancer children receiving chemotherapy in a regional hospital in Hong Kong from 1998 to 2008. Five children (3 males and 2 females) with a mean age of 7 years were identified, four of whom had acute lymphoblastic leukaemia and one had a central nervous system germ cell tumour. Presenting symptoms included seizures (100%), altered mental function (100%), headache (40%), and visual disturbance (60%). The mean systolic blood pressure at presentation was 158 mm Hg. Approximately 80% had typical radiological features of reversible posterior leukoencephalopathy syndrome. All showed complete recovery after the acute stage, but one subsequently developed epilepsy. Two patients ultimately died of refractory malignant disease. Two others were followed up for a mean of 6 years, and remained neurologically normal. This report was the first case review documenting reversible posterior leukoencephalopathy syndrome in Chinese cancer children. The clinico-radiological features and neurological outcomes were similar to those reported in western series. Early recognition of the syndrome is important to facilitate appropriate treatment. The central nervous system damage may not be reversible and thus long-term follow-up is warranted.published_or_final_versio