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

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

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

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

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

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

An inducible transgene expression system for regulated phenotypic modification of human embryonic stem cells

Self-renewing pluripotent human embryonic stem (hES) cells are capable of regenerating such non-dividing cells as neurons and cardiomyocytes for therapies and can serve as an excellent experimental model for studying early human development. Both the spatial and temporal relationships of gene expression play a crucial role in determining differentiation; to obtain a better understanding of hES cell differentiation, it will be necessary to establish an inducible system in hES cells that enables specific transgene(s) to reversibly and conditionally express (1) at specific levels and (2) at particular time points during development. Using lentivirus (LV)-mediated gene transfer and a tetracycline-controlled trans-repressor (TR), we first established in hES cells a doxycycline (DOX)-inducible expression system of green fluorescent protein (GFP) to probe its reversibility and kinetics. Upon the addition of DOX, the percentage of GFP + hES cells increased time dependently: The time at which 50% of all green cells appeared (T 50 on) was 119.5 ± 3.2 h; upon DOX removal, GFP expression declined with a half-time (T 50 off) of 127.7 ± 3.9 h and became completely silenced at day 8. Both the proportion and total mean fluorescence intensity (MFI) were dose-dependent (EC 50 = 24.5 ± 2.2 ng/ml). The same system when incorporated into murine (m) ES cells similarly exhibited reversible dose-dependent responses with a similar sensitivity (EC 50 =49.5 ± 8.5 ng/ml), but the much faster kinetics (T 50 on = 35.5 ± 5.5 h, T 50 off = 71.5 ± 2.4 hours). DOX-induced expression of the Kir2.1 channels in mES and hES cells led to robust expression of the inwardly rectifying potassium (K +) current and thereby hyperpolarized the resting membrane potential (RMP). We conclude that the LV-inducible system established presents a unique tool for probing differentiation. © 2008 Mary Ann Liebert, Inc.published_or_final_versio

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

MiR-29b negatively regulates cell cycle activity of human embryonic stem cell-derived cardiomyocytes

published_or_final_versionThe 16th Medical Resarch Conference (MRC), The University of Hong Kong, Hong Kong, China, 22 January 2011. In Hong Kong Medical Journal, 2011, v. 17, suppl. 1, p. 50, abstract no. 7

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

Feedback-induced nonlinearity and superconducting on-chip quantum optics

Quantum coherent feedback has been proven to be an efficient way to tune the dynamics of quantum optical systems and, recently, those of solid-state quantum circuits. Here, inspired by the recent progress of quantum feedback experiments, especially those in mesoscopic circuits, we prove that superconducting circuit QED systems, shunted with a coherent feedback loop, can change the dynamics of a superconducting transmission line resonator, i.e., a linear quantum cavity, and lead to strong on-chip nonlinear optical phenomena. We find that bistability can occur under the semiclassical approximation, and photon anti-bunching can be shown in the quantum regime. Our study presents new perspectives for engineering nonlinear quantum dynamics on a chip.Comment: 10 pages, 9 figure