Knowledge management system on flow and water quality modeling

Author name used in this publication: K. W. Chau2001-2002 > Academic research: refereed > Publication in refereed journalAccepted ManuscriptPublishe

High-power single-mode operation in DFB and FP lasers using diffused quantum-well structure

Distributed feedback (DFB) and Fabry-Perot (FP) semiconductor lasers with step and periodic interdiffusion quantum-well structures are proposed for high-power single-longitudinal-mode operation. It is shown that the phase-adjustment region formed by the diffusion step (i.e., step change in optical gain and refractive index) counteracts the influence of spatial hole burning, especially for DFB lasers with large coupling-length products biased at high injection current. Furthermore, it is found that with careful design of the diffusion grating (i.e., grating period and amount of diffusion extent) of FP lasers, side-mode suppression ratio can be enhanced and threshold current density can be minimized to a satisfied level.published_or_final_versio

Vertical-cavity surface-emitting semiconductor lasers with diffusedquantum wells

A self-consistent dynamic model is developed including the current distribution, carrier diffusion rate and spatial hole burning effects to investigate the modulation response of vertical-cavity surface-emitting lasers with diffused quantum wells structure. It is found that the overall performance including relaxation oscillation frequency and modulation bandwidth is improved.published_or_final_versio

Fabry Perot semiconductor lasers with periodic diffused quantum wells structure

Fabry Perot semiconductor laser with periodic change in the extent of interdiffusion along the longitudinal direction of the quantum well active region is proposed to improve the discrimination between cavity modes.published_or_final_versio

Translational potential of human embryonic and induced pluripotent stem cells for myocardial repair: Insights from experimental models

Heart diseases have been a major cause of death worldwide, including developed countries. Indeed, loss of non-regenerative, terminally differentiated cardiomyocytes (CMs) due to aging or diseases is irreversible. Current therapeutic regimes are palliative in nature, and in the case of end-stage heart failure, transplantation remains the last resort. However, this option is significantly hampered by a severe shortage of donor cells and organs. Human embryonic stem cells (hESCs) can self-renew while maintaining their pluripotency to differentiate into all cell types. More recently, direct reprogramming of adult somatic cells to become pluripotent hES-like cells (a.k.a. induced pluripotent stem cells or iPSCs) has been achieved. The availability of hESCs and iPSCs, and their successful differentiation into genuine human heart cells have enabled researchers to gain novel insights into the early development of the human heart as well as to pursue the revolutionary paradigm of heart regeneration. Here we review our current knowledge of hESC-/iPSC-derived CMs in the context of two fundamental operating principles of CMs (i.e. electrophysiology and Ca2+-handling), the resultant limitations and potential solutions in relation to their translation into clinical (bioartificial pacemaker, myocardial repair) and other applications (e.g. as models for human heart disease and cardiotoxicity screening). © Schattauer 2010.published_or_final_versio

Effect of synthesis conditions on the physiochemical properties of lauric acid coated magnetite nanoparticles

Magnetic iron oxide nanoparticles have attracted broad interests in many biomedical areas, such as magnetic resonance imaging (MRI) contrast enhancement, magnetic hyperthermia, magnetic bio-sensing, and cell labeling [1]. To avoid nanoparticle aggregation and enhance their colloidal stability, carboxylate surfactants are widely used as coating materials to form steric repulsions between nanoparticles [2]. Lauric acid is one of the classical carboxylate materials, and is already approved for use in pharmaceuticals and food industry, which makes it a very promising coating material for nanoparticles in biomedical application. [3] Various methods, like mechanical milling, microemulsion, co-precipitation, thermal decomposition, etc., have been widely attempted to prepare nanoparticles. However, it is reported that the synthesis route has great impact on the properties of nanoparticle products, such as aluminium oxide nanoparticles, cobalt ferrite nanoparticles, and so on [4, 5]. Therefore, it is worthwhile to investigate the effects of different synthesis methods on the properties of lauric acid coated magnetic iron oxide nanoparticles. The research outcome can enable the synthesis of magnetic nanoparticles with desired features. Here, lauric acid coated iron oxide nanoparticles (LAIONPs) were prepared through two methods, co-precipitation and thermal decomposition. The products were characterized by using transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR), dynamic light scattering (DLS), thermo gravimetric analysis (TGA), and vibrating sample magnetometry (VSM). The iron-oxide-core average size could be tuned from 9 nm (CP-1), 11 nm (CP-2) to 13 nm (CP-3) by using different stirring speed of 1200 rpm, 800 rpm, and 400 rpm, respectively in co-precipitation experiments, while the core average size could be adjusted from 7 nm (TD-1), 11 nm (TD-2) to 17 nm (TD-3) by following different heating process in thermal - ecomposition experiments. (Fig. 1) The nanoparticles obtained through thermal decomposition (LAIONPs-TD) showed more uniform sizes and morphologies than the ones got from co-precipitation (LAIONPs-CP). Higher mass ratio of lauric acid in TD samples than CP samples, as indicated in TGA results (Fig. 2a and 2b), implies higher surface cover density of lauric acid surfactant on LAIONPs-TD than LAIONPs-CP. All the six LAIONPs samples exhibited superparamagnetic behavior at room temperature (Fig. 2c and 2d). The saturated magnetization (Ms) of LAIONPs increased as the particle size increased. Such a trend can be observed in the samples obtained through co-precipitation (CP-1, 54 emu/g; CP-2, 58 emu/g; and CP-3, 63 emu/g) and also in the samples obtained through thermal decomposition (TD-1, 53 emu/g; TD-2, 64 emu/g; TD-3, and 78 emu/g). For the LAIONPs with similar average core size of 11 nm, Ms value of TD-2 obtained by thermal decomposition (64 emu/g) was higher than CP-2 obtained by co-precipitation (58 emu/g). As shown in Fig. 2e, in colloidal solution with solvent of chloroform, smaller mean hydrodynamic sizes and narrower hydrodynamic size distributions were observed on IONPs-TD samples, compared with IONPs-CP samples. This work revealed the influences of two different synthesis methods on the core size, morphology, hydrodynamic size, surfactant coating mass ratio, and magnetic behavior of the final products. Our comparative study provides insights into the influence of synthesis conditions on the geometrical and magnetic properties of lauric acid coated iron oxide nanoparticles.postprin

Experimental observation of chiral phonons in monolayer WSe2

Chirality characterizes an object that is not identical to its mirror image. In condensed matter physics, Fermions have been demonstrated to obtain chirality through structural and time-reversal symmetry breaking. These systems display unconventional electronic transport phenomena such as the quantum Hall effect and Weyl semimetals. However, for bosonic collective excitations in atomic lattices, chirality was only theoretically predicted and has never been observed. We experimentally show that phonons can exhibit intrinsic chirality in monolayer tungsten diselenide, whose lattice breaks the inversion symmetry and enables inequivalent electronic K and -K valley states. The time-reversal symmetry is also broken when we selectively excite the valley polarized holes by circularly polarized light. Brillouin-zone-boundary phonons are then optically created by the indirect infrared absorption through the hole-phonon interactions. The unidirectional intervalley transfer of holes ensures that only the phonon modes in one valley are excited. We found that such photons are chiral through the transient infrared circular dichroism, which proves the valley phonons responsible to the indirect absorption has non-zero pseudo-angular momentum. From the spectrum we further deduce the energy transferred to the phonons that agrees with both the first principle calculation and the double-resonance Raman spectroscopy. The chiral phonons have significant implications for electron-phonon coupling in solids, lattice-driven topological states, and energy efficient information processing

The Origin of Meridians

This article explores the origin of meridians. It suggests that the origin of meridians is closely related to the imageries derived by ancient physicians experiencing the circulation of Qi in their bodies during Qigong practice. Based on the cognitive experience from Qigong practice, as well as the symbolic analogy of the flow of rivers and the irrigation system of agriculture, the meridian theory has constructed a model of Qi and blood circulation. Such model is abstract and yet concrete, dialectic and yet intuitive, definite and yet vague, integrated and yet independent, having profound influence on the overall formation of traditional Chinese medicine theories.published_or_final_versio

An intelligent knowledge processing system on hydrodynamics and water quality modeling

Series: Lecture notes in computer scienceAuthor name used in this publication: K. W. ChauAuthor name used in this publication: O. WaiAuthor name used in this publication: Y. S. Li2001-2002 > Academic research: refereed > Publication in refereed journalAccepted ManuscriptPublishe

Preliminary study on assimilation of significant wave heights from T/P altimeter

2003-2004 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe