43 results on '"Teo KL"'
Search Results
2. A review of methods and algorithms for optimizing construction scheduling
- Author
-
Zhou, J, Love, PED, Wang, X, Teo, KL, and Irani, Z
- Published
- 2013
3. Optimal Selection of Feedback Control Parameters
- Author
-
Conference on Control Engineering (5th : 1992 : Perth, W.A.), Lin, XG, and Teo, KL
- Published
- 1992
4. Feedback Controls for Nonlinear Systems
- Author
-
Conference on Control Engineering (5th : 1992 : Perth, W.A.), Jennings, LS, and Teo, KL
- Published
- 1992
5. Minimax portfolio optimization: empirical numerical study
- Author
-
Cai, X, Teo, KL, Yang, XQ, and Zhou, XY
- Subjects
Analysis of variance ,Management science ,Business ,Business, general - Abstract
In this paper, we carry out the empirical numerical study of the [l.sub.[infinity] portfolio selection model where the objective is to minimize the maximum individual risk. We compare the numerical performance of this model with that of the Markowitz's quadratic programming model by using real data from the Stock Exchange of Hong Kong. Our computational results show that the [l.sub.[infinity]]. model has a similar performance to the Markowitz's model and that the [l.sub.[[infinity] model is not sensitive to the data. For the situation with only two assets, we establish that the expected return of the minimum variance model is less than that of the minimum [l.sub.[infinity]]: model when both variance and the return rate of one asset is less than the corresponding values of another asset. Keywords: variance: standard deviation; portfolio selection: risk aversion measures; numerical study.
- Published
- 2004
6. Scaled-Up Inertial Microfluidics: Retention System for Microcarrier-Based Suspension Cultures
- Author
-
Moloudi, R, Oh, S, Yang, C, Teo, KL, Lam, ATL, Ebrahimi Warkiani, M, and Win Naing, M
- Subjects
Microfluidics ,Cell Culture Techniques ,Humans ,Bone Marrow Cells ,Mesenchymal Stem Cells ,Cell Separation ,Microfluidic Analytical Techniques ,Particle Size ,Flow Cytometry ,Biotechnology ,Biological Phenomena - Abstract
© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Recently, particle concentration and filtration using inertial microfluidics have drawn attention as an alternative to membrane and centrifugal technologies for industrial applications, where the target particle size varies between 1 µm and 500 µm. Inevitably, the bigger particle size (>50 µm) mandates scaling up the channel cross-section or hydraulic diameter (DH > 0.5 mm). The Dean-coupled inertial focusing dynamics in spiral microchannels is studied broadly; however, the impacts of secondary flow on particle migration in a scaled-up spiral channel is not fully elucidated. The mechanism of particle focusing inside scaled-up rectangular and trapezoidal spiral channels (i.e., 5–10× bigger than conventional microchannels) with an aim to develop a continuous and clog-free microfiltration system for bioprocessing is studied in detail. Herein, a unique focusing based on inflection point without the aid of sheath flow is reported. This new focusing mechanism, observed in the scaled-up channels, out-performs the conventional focusing scenarios in the previously reported trapezoidal and rectangular channels. Finally, as a proof-of-concept, the utility of this device is showcased for the first time as a retention system for a cell–microcarrier (MC) suspension culture.
- Published
- 2019
7. Control parametrization enhancing technique for optimal discrete-valued control problems
- Author
-
Lee, HWJ, Teo, KL, Rehbock, V., Jennings, LS, Lee, HWJ, Teo, KL, Rehbock, V., and Jennings, LS
- Abstract
In this paper, we consider a class of optimal discrete-valued control problems. Since the range set of the control function is a discrete set and hence not convex. These problems are, in fact, nonlinear combinatorial optimization problems. Using the novel idea of the control parametrization enhancing technique, it is shown that optimal discrete-valued control problems are equivalent to optimal control problems involving a new control function which is piecewise constant with pre-fixed switching points. The transformed problems are essentially optimal parameter selection problems and can hence be readily solved by various existing algorithms. A practical numerical example is solved using the proposed method. (C) 1999 Elsevier Science Ltd. All rights reserved.
- Published
- 1999
8. Iterative Chebyshev approximation method for optimal control problems.
- Author
-
Wu D, Yu C, Wang H, Bai Y, Teo KL, and Toh KC
- Abstract
We present a novel numerical approach for solving nonlinear constrained optimal control problems (NCOCPs). Instead of directly solving the NCOCPs, we start by linearizing the constraints and dynamic system, which results in a sequence of sub-problems. For each sub-problem, we use finite number of Chebyshev polynomials to estimate the control and state vectors. To eliminate the errors at non-collocation points caused by conventional collocation methods, we additionally estimate the coefficient functions involved in the linear constraints and dynamic system by Chebyshev polynomials. By leveraging the characteristics of Chebyshev polynomials, the approximate sub-problem is changed into an equivalent nonlinear optimization problem with linear equality constraints. Consequently, any feasible point of the approximate sub-problem will satisfy the constraints and dynamic system throughout the entire time scale. To validate the efficacy of the new method, we solve three examples and assess the accuracy of the method through the computation of its approximation error. Numerical results obtained show that our approach achieves lower approximation error when compared to the Chebyshev pseudo-spectral method. The proposed method is particularly suitable for scenarios that require high-precision approximation, such as aerospace and precision instrument production., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 ISA. Published by Elsevier Ltd. All rights reserved.)
- Published
- 2024
- Full Text
- View/download PDF
9. MACTFusion: Lightweight Cross Transformer for Adaptive Multimodal Medical Image Fusion.
- Author
-
Xie X, Zhang X, Tang X, Zhao J, Xiong D, Ouyang L, Yang B, Zhou H, Ling BW, and Teo KL
- Abstract
Multimodal medical image fusion aims to integrate complementary information from different modalities of medical images. Deep learning methods, especially recent vision Transformers, have effectively improved image fusion performance. However, there are limitations for Transformers in image fusion, such as lacks of local feature extraction and cross-modal feature interaction, resulting in insufficient multimodal feature extraction and integration. In addition, the computational cost of Transformers is higher. To address these challenges, in this work, we develop an adaptive cross-modal fusion strategy for unsupervised multimodal medical image fusion. Specifically, we propose a novel lightweight cross Transformer based on cross multi-axis attention mechanism. It includes cross-window attention and cross-grid attention to mine and integrate both local and global interactions of multimodal features. The cross Transformer is further guided by a spatial adaptation fusion module, which allows the model to focus on the most relevant information. Moreover, we design a special feature extraction module that combines multiple gradient residual dense convolutional and Transformer layers to obtain local features from coarse to fine and capture global features. The proposed strategy significantly boosts the fusion performance while minimizing computational costs. Extensive experiments, including clinical brain tumor image fusion, have shown that our model can achieve clearer texture details and better visual quality than other state-of-the-art fusion methods.
- Published
- 2024
- Full Text
- View/download PDF
10. Scalable mesenchymal stem cell enrichment from bone marrow aspirate using deterministic lateral displacement (DLD) microfluidic sorting.
- Author
-
Tan Kwan Zen N, Zeming KK, Teo KL, Loberas M, Lee J, Goh CR, Yang DH, Oh S, Hui Hoi Po J, Cool SM, Hou HW, and Han J
- Subjects
- Microfluidics, Stem Cells, Blood Platelets, Bone Marrow, Mesenchymal Stem Cells
- Abstract
The growing interest in regenerative medicine has opened new avenues for novel cell therapies using stem cells. Bone marrow aspirate (BMA) is an important source of stromal mesenchymal stem cells (MSCs). Conventional MSC harvesting from BMA relies on archaic centrifugation methods, often leading to poor yield due to osmotic stress, high centrifugation force, convoluted workflow, and long experimental time (∼2-3 hours). To address these issues, we have developed a scalable microfluidic technology based on deterministic lateral displacement (DLD) for MSC isolation. This passive, label-free cell sorting method capitalizes on the morphological differences between MSCs and blood cells (platelets and RBCs) for effective separation using an inverted L-shaped pillar array. To improve throughput, we developed a novel multi-chip DLD system that can process 2.5 mL of raw BMA in 20 ± 5 minutes, achieving a 2-fold increase in MSC recovery compared to centrifugation methods. Taken together, we envision that the developed DLD platform will enable fast and efficient isolation of MSCs from BMA for effective downstream cell therapy in clinical settings.
- Published
- 2023
- Full Text
- View/download PDF
11. Manipulation of the Topological Ferromagnetic State in a Weyl Semimetal by Spin-Orbit Torque.
- Author
-
Ren L, Liu L, Song X, Zhao T, Xing X, Feng YP, Chen J, and Teo KL
- Abstract
Magnetic Weyl semimetals (MWSMs) exhibit unconventional transport phenomena, such as large anomalous Hall (and Nernst) effects, which are absent in spatial inversion asymmetry WSMs. Compared with its nonmagnetic counterpart, the magnetic state of a MWSM provides an alternative way for the modulation of topology. Spin-orbit torque (SOT), as an effective means of electrically controlling the magnetic states of ferromagnets, may be used to manipulate the topological magnetic states of MWSMs. Here we confirm the MWSM state of high-quality Co
2 MnGa film by systematically investigating the transport measurements and demonstrating that the magnetization and topology of Co2 MnGa can be electrically manipulated. The electrical and magnetic optical measurements further reveal that the current-induced SOT switches the topological magnetic state in a 180-degree manner by applying positive/negative current pulses and in a 90-degree manner by alternately applying two orthogonal current pulses. This work opens up more opportunities for spintronic applications based on topological materials.- Published
- 2023
- Full Text
- View/download PDF
12. Efficient Spin-Orbit Torque Switching in a Perpendicularly Magnetized Heusler Alloy MnPtGe Single Layer.
- Author
-
Ren L, Zhou C, Song X, Seng HT, Liu L, Li C, Zhao T, Zheng Z, Ding J, Feng YP, Chen J, and Teo KL
- Abstract
Electrically manipulating magnetic moments by spin-orbit torque (SOT) has great potential applications in magnetic memories and logic devices. Although there have been rich SOT studies on magnetic heterostructures, low interfacial thermal stability and high switching current density still remain an issue. Here, highly textured, polycrystalline Heusler alloy Mn
x Pty Ge (MPG) films with various thicknesses are directly deposited onto thermally oxidized silicon wafers. The perpendicular magnetization of the MPG single layer can be reversibly switched by electrical current pulses with a magnitude as low as 4.1 × 1010 Am-2 , as evidenced by both the electrical transport and the magnetic optical measurements. The switching is shown to arise from inversion symmetry breaking due to the vertical composition gradient of the films after sample annealing. The SOT effective fields of the samples are analyzed systematically. It is found that the SOT efficiency increases with the film thickness, suggesting a robust bulk-like behavior in the single magnetic layer. Furthermore, a memristive characteristic has been observed due to a multidomain switching property in the single-layer MPG device. Additionally, deterministic field-free switching of magnetization is observed when the electric current flows orthogonal to the direction of the in-plane compositional gradient due to the in-plane symmetry breaking. This work proves that the MPG is a good candidate to be utilized in high-density and efficient magnetoresistive random access memory devices and other spintronic applications.- Published
- 2023
- Full Text
- View/download PDF
13. Human Mesenchymal Stem Cell Processing for Clinical Applications Using a Closed Semi-Automated Workflow.
- Author
-
Lam ATL, Jayaraman P, Becker A, Lim R, Teo KL, Ng J, and Oh S
- Subjects
- Humans, Reproducibility of Results, Workflow, Cell Differentiation, Cell Proliferation, Cells, Cultured, Cell Culture Techniques methods, Mesenchymal Stem Cells
- Abstract
Human mesenchymal stem cells (hMSCs) are currently being explored as a promising cell-based therapeutic modality for various diseases, with more market approvals for clinical use expected over the next few years. To facilitate this transition, addressing the bottlenecks of scale, lot-to-lot reproducibility, cost, regulatory compliance, and quality control is critical. These challenges can be addressed by closing the process and adopting automated manufacturing platforms. In this study, we developed a closed and semi-automated process for passaging and harvesting Wharton's jelly (WJ)-derived hMSCs (WJ-hMSCs) from multi-layered flasks using counterflow centrifugation. The WJ-hMSCs were expanded using regulatory compliant serum-free xeno-free (SFM XF) medium, and they showed comparable cell proliferation (population doubling) and morphology to WJ-hMSCs expanded in classic serum-containing media. Our closed semi-automated harvesting protocol demonstrated high cell recovery (~98%) and viability (~99%). The cells washed and concentrated using counterflow centrifugation maintained WJ-hMSC surface marker expression, colony-forming units (CFU-F), trilineage differentiation potential, and cytokine secretion profiles. The semi-automated cell harvesting protocol developed in the study can be easily applied for the small- to medium-scale processing of various adherent and suspension cells by directly connecting to different cell expansion platforms to perform volume reduction, washing, and harvesting with a low output volume.
- Published
- 2023
- Full Text
- View/download PDF
14. Multi-objective two-stage emergent blood transshipment-allocation in COVID-19 epidemic.
- Author
-
Zhou Y, Cheng J, Wu C, and Teo KL
- Abstract
The problem of blood transshipment and allocation in the context of the COVID-19 epidemic has many new characteristics, such as two-stage, trans-regional, and multi-modal transportation. Considering these new characteristics, we propose a novel multi-objective optimization model for the two-stage emergent blood transshipment-allocation. The objectives considered are to optimize the quality of transshipped blood, the satisfaction of blood demand, and the overall cost including shortage penalty. An improved integer encoded hybrid multi-objective whale optimization algorithm (MOWOA) with greedy rules is then designed to solve the model. Numerical experiments demonstrate that our two-stage model is superior to one-stage optimization methods on all objectives. The degree of improvement ranges from 0.69 to 66.26%., (© The Author(s) 2023.)
- Published
- 2023
- Full Text
- View/download PDF
15. Insights into Controlling the Spread of COVID-19: A Study Inspired by Seven of the Earliest Vaccinated Countries.
- Author
-
Teh JKL, Bradley DA, Ang WT, Teo KL, Chook JB, Lai KH, and Peh SC
- Subjects
- COVID-19 Vaccines, Canada epidemiology, Humans, Israel, United States epidemiology, COVID-19 epidemiology, COVID-19 prevention & control, Vaccines
- Abstract
Background: The aim of the study is to derive deeper insights into the control of the spread of COVID-19 during the second half of 2021, from seven countries that are among the earliest to have accelerated the deployment of COVID-19 vaccines. Methodology . This study used data from the Global COVID-19 Index and Google COVID-19 Community Mobility Reports. Data was extracted on the 5
th of each month from July to December 2021. Seven countries were selected-United Kingdom, United States of America, Israel, Canada, France, Italy, and Austria. The sample comprised number of new cases, hospitalisations, ICU admissions and deaths due to COVID-19, government stringency measures, partial and full vaccination coverage, and changes in human mobility. Principal component analysis was conducted, and the results were interpreted and visualized through 2-dimensional and 3-dimensional plots to reveal the systematic patterns of the data., Results: The first three principal components captured around 77.3% of variance in the data. The first component was driven by the spread of COVID-19 (31.6%), the second by mobility activities (transit, retail, and recreational) (24.3%), whereas the third by vaccination coverage, workplace-related mobility, and government stringency measures (21.4%). Visualizations showed lower or moderate levels of severity in COVID-19 during this period for most countries. By contrast, the surge in the USA was more severe especially in September 2021. Human mobility activities peaked in September for most countries and then receded in the following months as more stringent government measures were imposed, and countries began to grapple with a surge in COVID-19 cases., Conclusion: This study delineated the spread of COVID-19, human mobility patterns, widespread vaccination coverage, and government stringency measures on the overall control of COVID-19. While at least moderate levels of stringency measures are needed, high vaccine coverage is particularly important in curbing the spread of this disease., Competing Interests: The authors declare that they have no conflicts of interest., (Copyright © 2022 Jane K. L. Teh et al.)- Published
- 2022
- Full Text
- View/download PDF
16. Thermally Processed Quantum-Dot Polypropylene Composite Color Converter Film for Displays.
- Author
-
Fang F, Wen Z, Chen W, Wang Z, Sun J, Liu H, Tang H, Hao J, Liu P, Xu B, Zhang Z, Wang K, Teo KL, Ertugrul M, Lei W, and Sun XW
- Abstract
Quantum dots (QDs) have attracted much attention as one of the most promising candidates for next-generation display materials. However, stability is still a big challenge for QDs. Herein, we encapsulated QDs in a thermoplastic polypropylene (PP) matrix by thermal processing technology to prepare a stabler color conversion film for the first time. Thermal processing technology expands the packaging materials of QDs from traditional soluble polymers to thermoplastic polymers such as PP with easy processing and a low cost. We showed that the QDs in the PP film exhibited longer-lasting stability than the traditional PMMA film. After 216 h of blue light accelerated aging test, the QDs maintained more than 90% of the initial performance in the PP film but dropped to less than 25% in the PMMA film. Moreover, the reasons for the improved stability have been further discussed. It was found that the PP-H film not only possessed better barriers to moisture and oxygen, but the absence of ester groups also led to a milder environment around the QDs. The results show that ester groups have stronger electronegativity and easily cause the ligands on the surface of QDs to fall off, which lead to performance degradation.
- Published
- 2022
- Full Text
- View/download PDF
17. Multivariate visualization of the global COVID-19 pandemic: A comparison of 161 countries.
- Author
-
Teh JKL, Bradley DA, Chook JB, Lai KH, Ang WT, Teo KL, and Peh SC
- Subjects
- Africa epidemiology, Europe epidemiology, Humans, United States epidemiology, COVID-19 epidemiology, COVID-19 transmission, Global Health, Pandemics, SARS-CoV-2
- Abstract
Background: The aim of the study was to visualize the global spread of the COVID-19 pandemic over the first 90 days, through the principal component analysis approach of dimensionality reduction., Methods: This study used data from the Global COVID-19 Index provided by PEMANDU Associates. The sample, representing 161 countries, comprised the number of confirmed cases, deaths, stringency indices, population density and GNI per capita (USD). Correlation matrices were computed to reveal the association between the variables at three time points: day-30, day-60 and day-90. Three separate principal component analyses were computed for similar time points, and several standardized plots were produced., Results: Confirmed cases and deaths due to COVID-19 showed positive but weak correlation with stringency and GNI per capita. Through principal component analysis, the first two principal components captured close to 70% of the variance of the data. The first component can be viewed as the severity of the COVID-19 surge in countries, whereas the second component largely corresponded to population density, followed by GNI per capita of countries. Multivariate visualization of the two dominating principal components provided a standardized comparison of the situation in the161 countries, performed on day-30, day-60 and day-90 since the first confirmed cases in countries worldwide., Conclusion: Visualization of the global spread of COVID-19 showed the unequal severity of the pandemic across continents and over time. Distinct patterns in clusters of countries, which separated many European countries from those in Africa, suggested a contrast in terms of stringency measures and wealth of a country. The African continent appeared to fare better in terms of the COVID-19 pandemic and the burden of mortality in the first 90 days. A noticeable worsening trend was observed in several countries in the same relative time frame of the disease's first 90 days, especially in the United States of America., Competing Interests: The authors have declared that no competing interests exist.
- Published
- 2021
- Full Text
- View/download PDF
18. Spin-Orbit Torque Switching of a High-Quality Perpendicularly Magnetized Ferrimagnetic Heusler Mn 3 Ge Film.
- Author
-
Ren L, Liu L, Shu X, Lin W, Yang P, Chen J, and Teo KL
- Abstract
Current-induced spin-orbit torque (SOT) switching of magnetization has attracted great interest due to its potential application in magnetic memory devices, which offer low-energy consumption and high-speed writing. However, most of the SOT studies on perpendicularly magnetized anisotropy (PMA) magnets have been limited to heterostructures with interfacial PMA and poor thermal stability. Here, we experimentally demonstrate a SOT magnetization switching for a ferrimagnetic D0
22 -Mn3 Ge film with high bulk PMA and robust thermal stability factor under a critical current density of 6.6 × 1011 A m-2 through the spin Hall effect of an adjacent capping Pt and a buffer Cr layer. A large effective damping-like SOT efficiency of 2.37 mT/1010 A m-2 is determined using harmonic measurements in the structure. The effect of the double-spin source layers and the negative-exchange interaction of the ferrimagnet may explain the large SOT efficiency and the manifested magnetization switching of Mn3 Ge. Our findings demonstrate that D022 -Mn3 Ge is a promising candidate for application in high-density SOT magnetic random-access memory devices.- Published
- 2021
- Full Text
- View/download PDF
19. Suppressing the Spikes in Electroencephalogram via an Iterative Joint Singular Spectrum Analysis and Low-Rank Decomposition Approach.
- Author
-
Tian Z, Ling BW, Zhou X, Lam RW, and Teo KL
- Subjects
- Humans, Time Factors, Algorithms, Electroencephalography, Signal Processing, Computer-Assisted
- Abstract
The novelty and the contribution of this paper consists of applying an iterative joint singular spectrum analysis and low-rank decomposition approach for suppressing the spikes in an electroencephalogram. First, an electroencephalogram is filtered by an ideal lowpass filter via removing its discrete Fourier transform coefficients outside the wave band, the wave band, the wave band, the wave band and the wave band. Second, the singular spectrum analysis is performed on the filtered electroencephalogram to obtain the singular spectrum analysis components. The singular spectrum analysis components are sorted according to the magnitudes of their corresponding eigenvalues. The singular spectrum analysis components are sequentially added together starting from the last singular spectrum analysis component. If the variance of the summed singular spectrum analysis component under the unit energy normalization is larger than a threshold value, then the summation is terminated. The summed singular spectrum analysis component forms the first scale of the electroencephalogram. The rest singular spectrum analysis components are also summed up together separately to form the residue of the electroencephalogram. Next, the low-rank decomposition is performed on the residue of the electroencephalogram to obtain both the low-rank component and the sparse component. The low-rank component is added to the previous scale of the electroencephalogram to obtain the next scale of the electroencephalogram. Finally, the above procedures are repeated on the sparse component until the variance of the current scale of the electroencephalogram under the unit energy normalization is larger than another threshold value. The computer numerical simulation results show that the spike suppression performance based on our proposed method outperforms that based on the state-of-the-art methods., Competing Interests: The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results”.
- Published
- 2020
- Full Text
- View/download PDF
20. Magnetization switching by magnon-mediated spin torque through an antiferromagnetic insulator.
- Author
-
Wang Y, Zhu D, Yang Y, Lee K, Mishra R, Go G, Oh SH, Kim DH, Cai K, Liu E, Pollard SD, Shi S, Lee J, Teo KL, Wu Y, Lee KJ, and Yang H
- Abstract
Widespread applications of magnetic devices require an efficient means to manipulate the local magnetization. One mechanism is the electrical spin-transfer torque associated with electron-mediated spin currents; however, this suffers from substantial energy dissipation caused by Joule heating. We experimentally demonstrated an alternative approach based on magnon currents and achieved magnon-torque-induced magnetization switching in Bi
2 Se3 /antiferromagnetic insulator NiO/ferromagnet devices at room temperature. The magnon currents carry spin angular momentum efficiently without involving moving electrons through a 25-nanometer-thick NiO layer. The magnon torque is sufficient to control the magnetization, which is comparable with previously observed electrical spin torque ratios. This research, which is relevant to the energy-efficient control of spintronic devices, will invigorate magnon-based memory and logic devices., (Copyright © 2019 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)- Published
- 2019
- Full Text
- View/download PDF
21. Rapid Detection of Senescent Mesenchymal Stromal Cells by a Fluorescent Probe.
- Author
-
Ang J, Lee YA, Raghothaman D, Jayaraman P, Teo KL, Khan FJ, Reuveny S, Chang YT, Kang NY, and Oh S
- Subjects
- Cell Differentiation, Cell Proliferation, Cells, Cultured, Cellular Senescence, Humans, Mesenchymal Stem Cells chemistry, Fluorescein-5-isothiocyanate chemistry, Fluorescent Dyes chemistry, Mesenchymal Stem Cells cytology
- Abstract
Despite intense interest in human mesenchymal stromal cells (MSCs), monitoring of the progressive occurrence of senescence has been hindered by the lack of efficient detection tools. Here, the discovery of a novel MSC senescence-specific fluorescent probe (CyBC9) identified by a high-throughput screen is reported. Compared with the prototypical senescence-associated β-galactosidase (SA-β-gal) staining, the CyBC9 assay is rapid (2 h) and nontoxic and can thus be applied to live cells. It is shown that CyBC9 is able to stain early and late senescent populations both in monolayer- and in microcarrier-based cultures. Finally, to investigate the mechanism of CyBC9, colocalization assays are performed and it is found that CyBC9 is accumulated in the mitochondria of senescent MSCs presumably due to the loss of membrane potential. Taken together, it is expected that CyBC9 will be a useful tool to ameliorate cell therapy through rapid and early screening of senescent phenotypes in clinically relevant MSCs., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)
- Published
- 2019
- Full Text
- View/download PDF
22. Sub-confluent culture of human mesenchymal stromal cells on biodegradable polycaprolactone microcarriers enhances bone healing of rat calvarial defect.
- Author
-
Lam AT, Sim EJ, Shekaran A, Li J, Teo KL, Goggi JL, Reuveny S, Birch WR, and Oh SK
- Subjects
- Animals, Bioreactors, Cell Count, Cell Culture Techniques instrumentation, Cell Differentiation, Cell- and Tissue-Based Therapy methods, Cells, Cultured, Cytokines metabolism, Humans, Male, Mesenchymal Stem Cell Transplantation methods, Mesenchymal Stem Cells physiology, Polyesters chemistry, Rats, Nude, Skull, Biocompatible Materials chemistry, Bone Regeneration physiology, Cell Culture Techniques methods, Mesenchymal Stem Cells cytology, Osteogenesis physiology
- Abstract
In the current emerging trend of using human mesenchymal stromal cell (MSCs) for cell therapy, large quantities of cells are needed for clinical testing. Current methods of culturing cells, using tissue culture flasks or cell multilayer vessels, are proving to be ineffective in terms of cost, space and manpower. Therefore, alternatives such as large-scale industrialized production of MSCs in stirred tank bioreactors using microcarriers (MCs) are needed. Moreover, the development of biodegradable MCs for MSC expansion can streamline the bioprocess by eliminating the need for enzymatic cell harvesting and scaffold seeding for bone-healing therapies. Our previous studies described a process of making regulated density (1.06 g/cm
3 ) porous polycaprolactone biodegradable MCs Light Polycarprolactone (LPCL) (MCs), which were used for expanding MSCs from various sources in stirred suspension culture. Here, we use human early MSCs (heMSCs) expanded on LPCL MCs for evaluation of their osteogenic differentiation potential in vitro as well as their use in vivo calvarial defect treatment in a rat model. In summary, (i) in vitro data show that LPCL MCs can be used to efficiently expand heMSCs in stirred cultures while maintaining surface marker expression; (ii) LPCL MCs can be used as scaffolds for cell transfer for transplantation in vivo; (iii) 50% sub-confluency, mid-logarithmic phase, on LPCL MCs (50% confluent) exhibited higher secretion levels of six cytokines (interleukin [IL]-6, IL-8, Vascular endothelial growth factor (VEGF), Monocyte Chemoattractant Protein-1 (MCP-1), growth-regulated oncogene-α (GRO-α) and stromal cell-derived factor-1α (SDF-1α)) as compared with 100% confluent, stationary phase cultures (100% confluent); (iv) these 50% confluent cultures demonstrated better in vitro osteogenic differentiation capacity as compared with 100% confluent cultures (higher levels of calcium deposition and at earlier stage); the improved bone differentiation capacity of these 50% confluent cultures was also demonstrated at the molecular level by higher expression of early osteoblast genes Runt-related transcription factor 2 (RUNX2), Alkaline phosphatase (ALP), collagen type I, osterix and osteocalcin); and (v) in vivo implantation of biodegradable LPCL MCs covered with 50% heMSCs into rats with calvarial defect demonstrated significantly better bone formation as compared with heMSCs obtained from monolayer cultures (5.1 ± 1.6 mm3 versus 1.3 ± 0.7 mm3 ). Moreover, the LPCL MCs covered with 50% heMSCs supported better in vivo bone formation compared with 100% confluent culture (2.1 ± 1.3 mm3 ). Taken together, our study highlights the potential of implanting 50% confluent MSCs propagated on LPCL MCs as optimal for bone regeneration. This methodology allows for the production of large numbers of MSCs in a three-dimensional (3D) stirred reactor, while supporting improved bone healing and eliminating the need for a 3D matrix support scaffold, as traditionally used in bone-healing treatments., (Copyright © 2019 International Society for Cell and Gene Therapy. Published by Elsevier Inc. All rights reserved.)- Published
- 2019
- Full Text
- View/download PDF
23. Scaled-Up Inertial Microfluidics: Retention System for Microcarrier-Based Suspension Cultures.
- Author
-
Moloudi R, Oh S, Yang C, Teo KL, Lam AT, Ebrahimi Warkiani M, and Win Naing M
- Subjects
- Biological Phenomena, Bone Marrow Cells, Cell Culture Techniques instrumentation, Cell Separation instrumentation, Cell Separation methods, Flow Cytometry, Humans, Mesenchymal Stem Cells, Microfluidic Analytical Techniques instrumentation, Microfluidics instrumentation, Particle Size, Cell Culture Techniques methods, Microfluidic Analytical Techniques methods, Microfluidics methods
- Abstract
Recently, particle concentration and filtration using inertial microfluidics have drawn attention as an alternative to membrane and centrifugal technologies for industrial applications, where the target particle size varies between 1 µm and 500 µm. Inevitably, the bigger particle size (>50 µm) mandates scaling up the channel cross-section or hydraulic diameter (D
H > 0.5 mm). The Dean-coupled inertial focusing dynamics in spiral microchannels is studied broadly; however, the impacts of secondary flow on particle migration in a scaled-up spiral channel is not fully elucidated. The mechanism of particle focusing inside scaled-up rectangular and trapezoidal spiral channels (i.e., 5-10× bigger than conventional microchannels) with an aim to develop a continuous and clog-free microfiltration system for bioprocessing is studied in detail. Herein, a unique focusing based on inflection point without the aid of sheath flow is reported. This new focusing mechanism, observed in the scaled-up channels, out-performs the conventional focusing scenarios in the previously reported trapezoidal and rectangular channels. Finally, as a proof-of-concept, the utility of this device is showcased for the first time as a retention system for a cell-microcarrier (MC) suspension culture., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)- Published
- 2019
- Full Text
- View/download PDF
24. Inertial-Based Filtration Method for Removal of Microcarriers from Mesenchymal Stem Cell Suspensions.
- Author
-
Moloudi R, Oh S, Yang C, Teo KL, Lam AT, Warkiani ME, and Naing MW
- Subjects
- Bioreactors, Cell Line, Filtration methods, Humans, Suspensions, Cell Culture Techniques methods, Mesenchymal Stem Cells cytology
- Abstract
Rapidly evolving cell-based therapies towards clinical trials demand alternative approaches for efficient expansion of adherent cell types such as human mesenchymal stem cells (hMSCs). Using microcarriers (100-300 µm) in a stirred tank bioreactor offers considerably enhanced surface to volume ratio of culture environment. However, downstream purification of the harvested cell product needs to be addressed carefully due to distinctive features and fragility of these cell products. This work demonstrates a novel alternative approach which utilizes inertial focusing to separate microcarriers (MCs) from the final cell suspension. First, we systematically investigated MC focusing dynamics inside scaled-up curved channels with trapezoidal and rectangular cross-sections. A trapezoidal spiral channel with ultra-low-slope (Tan(α) = 0.0375) was found to contribute to strong MC focusing (~300 < Re < ~400) while managing high MC volume fractions up to ~1.68%. Accordingly, the high-throughput trapezoidal spiral channel successfully separated MCs from hMSC suspension with total cell yield~94% (after two passes) at a high volumetric flow rate of ~30 mL/min (Re~326.5).
- Published
- 2018
- Full Text
- View/download PDF
25. Room temperature magnetization switching in topological insulator-ferromagnet heterostructures by spin-orbit torques.
- Author
-
Wang Y, Zhu D, Wu Y, Yang Y, Yu J, Ramaswamy R, Mishra R, Shi S, Elyasi M, Teo KL, Wu Y, and Yang H
- Abstract
Topological insulators with spin-momentum-locked topological surface states are expected to exhibit a giant spin-orbit torque in the topological insulator/ferromagnet systems. To date, the topological insulator spin-orbit torque-driven magnetization switching is solely reported in a Cr-doped topological insulator at 1.9 K. Here we directly show giant spin-orbit torque-driven magnetization switching in a Bi
2 Se3 /NiFe heterostructure at room temperature captured using a magneto-optic Kerr effect microscope. We identify a large charge-to-spin conversion efficiency of ~1-1.75 in the thin Bi2 Se3 films, where the topological surface states are dominant. In addition, we find the current density required for the magnetization switching is extremely low, ~6 × 105 A cm-2 , which is one to two orders of magnitude smaller than that with heavy metals. Our demonstration of room temperature magnetization switching of a conventional 3d ferromagnet using Bi2 Se3 may lead to potential innovations in topological insulator-based spintronic applications.- Published
- 2017
- Full Text
- View/download PDF
26. Color tunable electroluminescence and resistance switching from a ZnO-nanorod-TaOx-p-GaN heterojunction.
- Author
-
Zhao JL, Teo KL, Zheng K, and Sun XW
- Abstract
Well-aligned ZnO nanorods have been prepared on p-GaN-sapphire using a vapor phase transport (VPT) technique. A thin sputtered layer of TaOx is employed as the intermediate layer and an n-ZnO-TaOx-p-GaN heterojunction device has been achieved. The current transport of the heterojunction exhibited a typical resistance switching behavior, which originated from the filament forming and breaking in the TaOx layer. Color controllable electroluminescence (EL) was observed from the biased heterojunction at room temperature. Bluish-white wide band emission is achieved from the forward biased device in both the high resistance and low resistance states, while red emission can only be observed for the reverse biased device in the low resistance state. The correlation between the EL and resistance switching has been analyzed in-depth based on the interface band diagram of the heterojunction.
- Published
- 2016
- Full Text
- View/download PDF
27. Robust Filtering for Nonlinear Nonhomogeneous Markov Jump Systems by Fuzzy Approximation Approach.
- Author
-
Yin Y, Shi P, Liu F, Teo KL, and Lim CC
- Abstract
This paper addresses the problem of robust fuzzy L2-L∞ filtering for a class of uncertain nonlinear discrete-time Markov jump systems (MJSs) with nonhomogeneous jump processes. The Takagi-Sugeno fuzzy model is employed to represent such nonlinear nonhomogeneous MJS with norm-bounded parameter uncertainties. In order to decrease conservation, a polytope Lyapunov function which evolves as a convex function is employed, and then, under the designed mode-dependent and variation-dependent fuzzy filter which includes the membership functions, a sufficient condition is presented to ensure that the filtering error dynamic system is stochastically stable and that it has a prescribed L2-L∞ performance index. Two simulated examples are given to demonstrate the effectiveness and advantages of the proposed techniques.
- Published
- 2015
- Full Text
- View/download PDF
28. Serum-free media formulations are cell line-specific and require optimization for microcarrier culture.
- Author
-
Tan KY, Teo KL, Lim JF, Chen AK, Choolani M, Reuveny S, Chan J, and Oh SK
- Subjects
- Cell Line, Cell Proliferation, Humans, Cell Culture Techniques, Cell- and Tissue-Based Therapy methods, Culture Media, Serum-Free, Mesenchymal Stem Cells cytology
- Abstract
Background Aims: Mesenchymal stromal cells (MSCs) are being investigated as potential cell therapies for many different indications. Current methods of production rely on traditional monolayer culture on tissue-culture plastic, usually with the use of serum-supplemented growth media. However, the monolayer culturing system has scale-up limitations and may not meet the projected hundreds of billions to trillions batches of cells needed for therapy. Furthermore, serum-free medium offers several advantages over serum-supplemented medium, which may have supply and contaminant issues, leading to many serum-free medium formulations being developed., Methods: We cultured seven MSC lines in six different serum-free media and compared their growth between monolayer and microcarrier culture., Results: We show that (i) expansion levels of MSCs in serum-free monolayer cultures may not correlate with expansion in serum-containing media; (ii) optimal culture conditions (serum-free media for monolayer or microcarrier culture) differ for each cell line; (iii) growth in static microcarrier culture does not correlate with growth in stirred spinner culture; (iv) and that early cell attachment and spreading onto microcarriers does not necessarily predict efficiency of cell expansion in agitated microcarrier culture., Conclusions: Current serum-free media developed for monolayer cultures of MSCs may not support MSC proliferation in microcarrier cultures. Further optimization in medium composition will be required for microcarrier suspension culture for each cell line., (Copyright © 2015 International Society for Cellular Therapy. Published by Elsevier Inc. All rights reserved.)
- Published
- 2015
- Full Text
- View/download PDF
29. Gate-tuned quantum oscillations of topological surface states in β-Ag2Te.
- Author
-
Sulaev A, Zhu W, Teo KL, and Wang L
- Abstract
We report the strong experimental evidence of the existence of topological surface states with large electric field tunability and mobility in β-Ag2Te. Pronounced 2D Shubnikov-de Haas oscillations have been observed in β-Ag2Te nanoplates. A Berry phase is determined to be near π using the Landau level fan diagram for a relatively wide nanoplate while the largest electric field ambipolar effect in topological insulator so far (~2500%) is observed in a narrow nanoplate. The π Berry phase and the evolution of quantum oscillations with gate voltage (Vg) in the nanoplates strongly indicate the presence of topological surface states in β-Ag2Te. Moreover, the mobility of the narrow Ag2Te nanoplate is about several thousand cm(2)s(-1)V(-1). Our results suggest that β-Ag2Te has the potential to become an important material in the investigation of topological insulators.
- Published
- 2015
- Full Text
- View/download PDF
30. Analysis of schizophrenia data using a nonlinear threshold index logistic model.
- Author
-
Jiang Z, Du C, Jablensky A, Liang H, Lu Z, Ma Y, and Teo KL
- Subjects
- Case-Control Studies, Genetic Predisposition to Disease, Humans, Logistic Models, Models, Genetic, Polymorphism, Single Nucleotide, Schizophrenia genetics
- Abstract
Genetic information, such as single nucleotide polymorphism (SNP) data, has been widely recognized as useful in prediction of disease risk. However, how to model the genetic data that is often categorical in disease class prediction is complex and challenging. In this paper, we propose a novel class of nonlinear threshold index logistic models to deal with the complex, nonlinear effects of categorical/discrete SNP covariates for Schizophrenia class prediction. A maximum likelihood methodology is suggested to estimate the unknown parameters in the models. Simulation studies demonstrate that the proposed methodology works viably well for moderate-size samples. The suggested approach is therefore applied to the analysis of the Schizophrenia classification by using a real set of SNP data from Western Australian Family Study of Schizophrenia (WAFSS). Our empirical findings provide evidence that the proposed nonlinear models well outperform the widely used linear and tree based logistic regression models in class prediction of schizophrenia risk with SNP data in terms of both Types I/II error rates and ROC curves.
- Published
- 2014
- Full Text
- View/download PDF
31. Spin-polarized wide electron slabs in functionally graded polar oxide heterostructures.
- Author
-
Ye J, Ter Lim S, Bosman M, Gu S, Zheng Y, Tan HH, Jagadish C, Sun X, and Teo KL
- Abstract
We report on the high mobility wide electron slabs with enhanced correlation effects by tailoring the polarization effects in a functionally graded ZnMgO/ZnO heterostructures. The characteristics of three-dimensional (3D) spreading electrons are evidenced by the capacitance-voltage profiling and the quantization of 3D Fermi surface in magneto-transport measurements. Despite the weak spin-orbit interaction, such electron slabs are spin-polarized with a large zero-field spin splitting energy, which is induced by the carrier-mediated ferromagnetism. Our results suggest that the vast majority of electrons are localized at the surface magnetic moment which does not allow spin manipulations, and only in the region visited by the itinerant carriers that the ferromagnetic exchange interactions via coupling to the surface local moments contribute to the spin transport. The host ferromagnetism is likely due to the formation of Zn cation vacancies on the surface regime induced by the stabilization mechanism and strain-relaxation in ZnMgO polar ionic surface.
- Published
- 2012
- Full Text
- View/download PDF
32. Robust stability analysis of guaranteed cost control for impulsive switched systems.
- Author
-
Xu H, Teo KL, and Liu X
- Subjects
- Computer Simulation, Algorithms, Models, Theoretical, Signal Processing, Computer-Assisted
- Abstract
This correspondence is concerned with the robust stability for a class of impulsive switched systems under the LQ guaranteed cost control. Some results on robust stability for this class of impulsive switched systems are obtained. Sufficient conditions for the existence of a guaranteed cost control law are also given. Subject to these sufficient conditions, the closed-loop uncertain impulsive switched system under the guaranteed cost control law is robustly stable with a guaranteed cost value.
- Published
- 2008
- Full Text
- View/download PDF
33. Exponential stability of impulsive high-order Hopfield-type neural networks with time-varying delays.
- Author
-
Liu X, Teo KL, and Xu B
- Subjects
- Computer Simulation, Time Factors, Algorithms, Models, Statistical, Neural Networks, Computer, Nonlinear Dynamics, Signal Processing, Computer-Assisted
- Abstract
This paper considers the problems of global exponential stability and exponential convergence rate for impulsive high-order Hopfield-type neural networks with time-varying delays. By using the method of Lyapunov functions, some sufficient conditions for ensuring global exponential stability of these networks are derived, and the estimated exponential convergence rate is also obtained. As an illustration, an numerical example is worked out using the results obtained.
- Published
- 2005
- Full Text
- View/download PDF
34. Nonlinear system modeling via knot-optimizing B-spline networks.
- Author
-
Yiu KF, Wang S, Teo KL, and Tsoi AC
- Abstract
In using the B-spline network for nonlinear system modeling, owing to a lack of suitable theoretical results, it is quite difficult to choose an appropriate set of knot points to achieve a good network structure for minimizing, say, a minimum error criterion. In this paper, a novel knot-optimizing B-spline network is proposed to approximate the general nonlinear system behavior. The knot points are considered to be independent variables in the B-spline network and are optimized together with the B-spline expansion coefficients. The simulated annealing algorithm with an appropriate search strategy is used as an optimization algorithm for the training process in order to avoid any possible local minima. Examples involving dynamic systems up to six dimensions in the input space to the network are solved by the proposed method to illustrate the effectiveness of this approach.
- Published
- 2001
- Full Text
- View/download PDF
35. A worst-case optimal parameter selection model of cancer chemotherapy.
- Author
-
Martin RB and Teo KL
- Subjects
- Humans, Neoplasms pathology, Models, Statistical, Neoplasms drug therapy
- Abstract
An optimal parameter selection model of cancer chemotherapy in which two system parameters are unknown is formulated as a worst-case optimal parameter selection model. The model assumes that the unknown parameters lie within a known set. The system constraints must be satisfied over this entire set, and the objective function minimized in the worst case. The continuous dependence of the objective function and the system constraints upon the unknown parameters can be removed, making a numerical solution tractable. For the data considered it is proven that a cure is impossible no matter what the values of the unknown parameters in the parameter set. The optimal policy is shown to be relatively low dose intensity for the majority of the treatment, with the remaining drug delivered towards the end of the treatment interval.
- Published
- 1992
- Full Text
- View/download PDF
36. Low-intensity combination chemotherapy maximizes host survival time for tumors containing drug-resistant cells.
- Author
-
Martin RB, Fisher ME, Minchin RF, and Teo KL
- Subjects
- Animals, Computer Simulation, Drug Resistance, Humans, Models, Biological, Neoplasms pathology, Antineoplastic Combined Chemotherapy Protocols therapeutic use, Neoplasms drug therapy
- Abstract
Recent clinical trials have shown that for some cancers, high-intensity alternating chemotherapy does not significantly improve either survival times or response rates compared with nonalternating therapy. The current study uses optimal control to determine the best way to treat a tumor that contains drug-resistant cells that cannot be destroyed. The delivery of two non-cross-resistant chemotherapeutic agents is limited by bounds on the drug concentration and the dose intensity. This ensures that the drug toxicity stays within a tolerable range. The aim of the therapy is to maximize the host survival time, defined as the time over which the tumor burden can be kept below a fixed bound. The model is posed as a free terminal time, optimal parameter selection problem in which the constraints are continuously parametrized by time and the number of courses of therapy is free to vary. New theory is developed so that the optimal parameter selection problem can be solved as a sequence of fixed terminal time problems using existing optimal control software. Numerical simulations of Gompertz tumor growth showed that a treatment maintaining a high tumor burden doubled and sometimes tripled with survival time under aggressive therapy. When these simulations were repeated using exponential and logistic tumor growth models, the tumor burden during treatment had little influence upon survival time. In all simulations, survival time was not extended by delivering the anticancer drugs concurrently instead of staggering the treatment arms.
- Published
- 1992
- Full Text
- View/download PDF
37. Optimal control of tumor size used to maximize survival time when cells are resistant to chemotherapy.
- Author
-
Martin RB, Fisher ME, Minchin RF, and Teo KL
- Subjects
- Animals, Antineoplastic Agents therapeutic use, Cell Division, Drug Resistance, Feedback, Humans, Models, Biological, Neoplasms drug therapy, Neoplasms pathology
- Abstract
The high failure rates encountered in the chemotherapy of some cancers suggest that drug resistance is a common phenomenon. In the current study, the tumor burden during therapy is used to slow the growth of the drug-resistant cells, thereby maximizing the survival time of the host. Three types of tumor growth model are investigated--Gompertz, logistic, and exponential. For each model, feedback controls are constructed that specify the optimal tumor mass as a function of the size of the resistant subpopulation. For exponential and logistic tumor growth, the tumor burden during therapy is shown to have little impact upon survival time. When the tumor is in Gompertz growth, therapies maintaining a large tumor burden double and sometimes triple the survival time under aggressive therapies. Aggressive therapies aim for a rapid reduction in the sensitive cell subpopulation. These conclusions are not dependent upon the values of the model constants that determine the mass of resistant cells. Since treatments maintaining a high tumor burden are optimal for Gompertz tumor growth and close to optimal for exponential and logistic tumor growth, it may no longer be necessary to know the growth characteristics of a tumor to schedule anticancer drugs.
- Published
- 1992
- Full Text
- View/download PDF
38. A mathematical model of cancer chemotherapy with an optimal selection of parameters.
- Author
-
Martin RB, Fisher ME, Minchin RF, and Teo KL
- Subjects
- Humans, Mathematics, Models, Biological, Antineoplastic Agents administration & dosage, Neoplasms drug therapy
- Abstract
An optimal parameter selection model of cancer chemotherapy is presented which describes the treatment of a tumor over a fixed period of time by the repeated administration of a single drug. The drug is delivered at evenly spaced intervals over the treatment period at doses to be selected by the model. The model constructs a regimen that both minimizes the tumor population at the end of the treatment and satisfies constraints on the drug toxicity and intermediate tumor size. Numerical solutions show that an optimal regimen withholds the bulk of the doses until the end of the treatment period. When a drug used is of either moderate or low effectiveness, an optimal regimen is superior to a schedule that delivers all of the drug at the beginning of the treatment. This study questions whether the current method for the administration of chemotherapy is optimal and suggests that alternative regimens should be considered.
- Published
- 1990
- Full Text
- View/download PDF
39. Serotonin-stimulated prolactin secretion may not involve the dopaminergic system.
- Author
-
Tai MH, Teo KL, and Pan JT
- Subjects
- Animals, Domperidone pharmacology, Female, Haloperidol pharmacology, Methyltyrosines pharmacology, Rats, Rats, Inbred Strains, alpha-Methyltyrosine, Prolactin metabolism, Receptors, Dopamine physiology, Serotonin pharmacology
- Abstract
The possible involvement of the dopaminergic system in the serotonin (5-HT)-stimulated prolactin (PRL) secretion was tested in this study. Adult female rats were ovariectomized for two weeks and treated with estrogen (polyestradiol phosphate, 0.1 mg/rat, sc) for 6 days before use. They either received pretreatment with alpha-methyl-p-tyrosine (250 mg/kg BW, ip), a dopamine (DA) synthesis inhibitor, or two DA antagonists, domperidone and haloperidol (0.1 mg/kg BW, iv) before receiving 5-HT (1 mg/kg BW, iv) or quipazine (1 mg/kg BW, iv), a 5-HT agonist. Blockade of DA synthesis or antagonism of DA action invariably induced elevated plasma PRL levels. 5-HT or quipazine, however, could still induce significant PRL secretion on top of the increased PRL levels. Minor difference was found between the action of domperidone and that of haloperidol. In conclusion, the dopaminergic system may not be involved in the action of 5-HT to stimulate PRL secretion.
- Published
- 1990
40. Small dose of domperidone potentiated the effects of TRH and serotonin on prolactin release in ovariectomized, estrogen-treated rats.
- Author
-
Pan JT and Teo KL
- Subjects
- Animals, Dopamine Antagonists, Dose-Response Relationship, Drug, Female, Ovariectomy, Rats, Rats, Inbred Strains, Domperidone pharmacology, Estradiol physiology, Prolactin blood, Serotonin pharmacology, Thyrotropin-Releasing Hormone pharmacology
- Abstract
A transient antagonism of the dopaminergic action by using a dopamine antagonist, domperidone, plus a dopamine agonist, CB154, has been shown to potentiate the effect of thyrotropin-releasing hormone (TRH) on prolactin (PRL) secretion. In order to test whether the serotonin (5-HT)-induced PRL secretion can also be enhanced in a similar way, we used 5-HT instead of TRH in our first experiment. We found that the dose of domperidone used (10 micrograms/rat) seems to be excessive since it induced a marked and substantial increase in PRL release and the use of CB154 further masked the action of 5-HT. We used a smaller dose of domperidone (1 microgram/rat) without the CB154 and found that it induced a moderate amount of PRL release which lasted for over 1 h. Given TRH (1 microgram/rat) or 5-HT (0.3 mg/rat) 1 h later resulted in a significant increase in plasma PRL which was much higher than that induced by TRH or 5-HT alone. The potentiating effect of domperidone was even more significant for the 5-HT- than the TRH-stimulated PRL secretion. Pretreatment with 5-HT or vasoactive intestinal polypeptide (10 micrograms/rat) were without any effect in potentiating the action of TRH. In conclusion, antagonizing the dopamine action appears to enhance the stimulatory effect of TRH and 5-HT on PRL secretion.
- Published
- 1989
- Full Text
- View/download PDF
41. Optimal insulin infusion resulting from a mathematical model of blood glucose dynamics.
- Author
-
Fisher ME and Teo KL
- Subjects
- Humans, Models, Biological, Blood Glucose metabolism, Insulin Infusion Systems
- Abstract
Mathematical optimization techniques are applied to a simplified mathematical model of blood glucose dynamics to derive insulin infusion programs for the control of blood glucose levels in diabetic individuals. Two particular cases are discussed. First, the insulin infusion program which results in an initially high blood glucose level being reduced to acceptable levels. Second, the control of blood glucose levels following a meal, prior to which blood glucose and net blood-glycemic hormone were at their fasting levels.
- Published
- 1989
- Full Text
- View/download PDF
42. Fentanyl stimulates prolactin release through mu-opiate receptors, but not the serotonergic system.
- Author
-
Pan JT and Teo KL
- Subjects
- Animals, Dose-Response Relationship, Drug, Ergolines pharmacology, Female, Fenclonine pharmacology, Ketanserin pharmacology, Prolactin antagonists & inhibitors, Rats, Serotonin pharmacology, Serotonin Antagonists pharmacology, Fentanyl pharmacology, Prolactin metabolism, Receptors, Opioid physiology, Serotonin metabolism
- Abstract
Both serotonin (5-HT) and opiates exert a stimulatory effect on PRL secretion. Some evidence suggests that the action of opiates may be elicited through serotonergic neurons. We tested this hypothesis in the present study by evaluating the effect of perturbation of the serotonergic system on PRL secretion induced by fentanyl, a potent morphine-like analgesic. Female Sprague-Dawley rats ovariectomized for 3 weeks and given polyestradiol phosphate (0.1 mg/rat) for 1 week were used in the study. Fentanyl, at a dose of 20 micrograms/rat, induced significant PRL secretion that peaked at 10 min and lasted for more than 30 min. Pretreatment with naloxone (0.5 mg/kg BW, ip) did not block the acute phase of PRL secretion, but significantly lowered the PRL level at 30 min. Fentanyl at a smaller dose (5 micrograms/rat, iv) still induced significant PRL release 10, but not 30, min after injection. This effect was significantly blocked by pretreatment with the same dose of naloxone. On the other hand, whereas animals pretreated with ketanserin or LY53857 (both at a dose of 5 mg/kg BW, ip), two specific 5-HT2 receptor antagonists, had no effect on fentanyl-induced PRL secretion, the same treatment significantly blocked 5-HT-induced PRL secretion. Likewise, pretreatment with p-chlorophenylalanine (250 mg/kg BW, ip), a 5-HT synthesis inhibitor, for 2 days had no effect on the action of fentanyl, while 5-HT-induced PRL secretion was significantly augmented. We conclude that fentanyl acts through mu-opiate receptors to stimulate PRL secretion in a process that does not involve the serotonergic system.
- Published
- 1989
- Full Text
- View/download PDF
43. Species preservations in an optimal harvest model with random prices.
- Author
-
Goh CJ and Teo KL
- Subjects
- Animals, Ecology, Fisheries legislation & jurisprudence, Fisheries statistics & numerical data, Fishes, Models, Theoretical, Population Dynamics, Fisheries economics
- Abstract
In this paper, we consider an optimal harvest model in which the objective is to maximize the expected return. The unit price of biomass is assumed constant until a random time when the price increases by a given amount. Furthermore, due to obvious environmental protection requirements, it is assumed that the fishery population is bounded from below for all time so as to reduce the danger of species extinction. Clearly, this problem is an optimal control problem in which a random parameter is involved. However, due to its special structure, it is shown that the problem is convertible into a deterministic optimal control problem and hence is solvable by an existing optimal control software package, MISER. The practical implication of several computed results obtained by this approach is discussed. They are also compared with other related results in the literature.
- Published
- 1989
- Full Text
- View/download PDF
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.