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45 results on '"Ho, H.W."'

8. Optimization of multi-type traffic sensor locations for network-wide link travel time estimation with consideration of their covariance

Author

Fu, Hao, Lam, William H.K., Ho, H.W., and Ma, Wei

Abstract

Due to the propagation of traffic congestion from upstream to downstream links and the uncertainty of path choice behaviours, travel times between different links, particularly adjacent links, are highly correlated in a typical period from day to day. To improve the estimation accuracy of both the mean and covariance of link travel times, a novel measurement is proposed to optimize the locations of multi-type traffic sensors for link travel time estimation. Multi-source data from different types of traffic sensors can be integrated to better estimate link travel time in an entire road network. In practice, the allocation of multi-type traffic sensors is constrained by the total financial budget and should be optimized in accordance with measurement errors and the cost ratio. Numerical examples of synthetic and real road networks are conducted to demonstrate the applications and merits of the proposed multi-type sensor location model with covariance effects.

Published
2023
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18. Preliminary study of formaldehyde residue in bacterial vaccine products

Author

Norliza W, Nurulaini R, Rohayu N, Rohaiza Y, Bohari J, Lily Rozita M.H, Megat A.R, Ho H.W, and Abdul Sukor S

Subjects
Alum, Formaldehyde, Hemorrhagic septicemia, medicine.disease, Vaccination, Bacterial vaccine, chemistry.chemical_compound, Residue (chemistry), chemistry, medicine, Potency, Food science, General Pharmacology, Toxicology and Pharmaceutics, Pasteurellosis
Abstract

Inactivated bacterial vaccines may contain residual levels of formaldehyde, which may have adverse effects. Therefore, it is important to determine the residual level of formaldehyde to ensure product safety. A number of assays are available for the determination of residual free formaldehyde in inactivated vaccines, including acetyl acetone titration, ferric chloride titration, and the basic fuchsin test. In the current study, ferric chloride quantitative method was used to evaluate formaldehyde residue on 4 types of vaccine produced in the Bacterial Vaccine section in Veterinary Research Institute (VRI), Ipoh. Four types of vaccines tested were Hemorrhagic Septicemia oil (HS oil), Hemorrhagic Septicemia alum (HS alum) vaccine, Duck vaccine (DV), and Sheep and Goat Pasteurellosis vaccine (SGP). Results revealed formaldehyde residue in vaccines tested was between 1.289 g/L to 2.228 g/L (mean SD ±0.18). According to European Pharmacopeia, when formaldehyde has been used in the preparation, the concentration of free formaldehyde is not greater than 0.5 g/L. While the United States Code of Federal stated that it must not exceed 0.74 g/L unless a higher amount has been shown to be safe. In our study, all the vaccines has been tested for safety and potency test before being used on animals, and therefore, it is safe for vaccination purpose. Formaldehyde residue will be conducted for each batch of vaccines production to ensure its safety.

Published
2019

38. A Continuum Model for Housing Allocation and Transportation Emission Problems in a Polycentric City.

Author

Yin, Jun, Wong, S.C., Sze, N.N., and Ho, H.W.

Subjects
HOUSING & health, MATHEMATICAL models, TRANSPORTATION, HOUSING development, TRAFFIC engineering, CARBON dioxide mitigation, FINITE element method
Abstract

The effect of vehicle emissions on the global climate has prompted increasing concern in the past few decades. Housing development patterns determine people's travel behavior and related vehicle emissions. In this study, we consider a hypothetical city with several central business districts (CBDs) serving several classes of road users, which are continuously distributed over the city. The road network is relatively dense and can be approximated as a continuum. We establish a bi-level model to describe the relationships among housing allocation, traffic volume, and CO2 emissions with a continuum modeling approach. At the lower level, the model achieves the user equilibrium condition of a transport system. At the upper level, it optimizes housing allocation to achieve minimum CO2 emissions. The finite element method, Newton-Raphson algorithm, and convex combination approach are applied to solve the constrained optimization problem established in the bi-level model. A numerical example is then given to illustrate the effectiveness and efficiency of the proposed bi-level approach and solution algorithm in modeling transport demand, traffic intensity, and CO2 emissions with an optimized housing development pattern. [ABSTRACT FROM AUTHOR]

Published
2013
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39. A congestion-pricing problem with a polycentric region and multi-class users: a continuum modelling approach

Author

Ho, H.W., Wong, S.C., and Sumalee, A.

Abstract

Consider a region of arbitrary shape with multiple cities competing for multi-class users that are distributed continuously over the region. Within this region, the road network is represented as a continuum and users patronise in a two-dimensional continuum transportation system to their chosen city. A logit-type distribution function is specified to model the probabilistic destination choices made by the different classes of users. In this article, two different congestion-pricing models for this multi-class and multi-city continuum transportation system are studied. The first model focused on utility maximisation, which determines the optimal toll rates that maximise the total utility of the system, while the second model is a cordon-based congestion-pricing model that offers a sub-optimal but more practical tolling strategy. Both models are solved by finite element method and a promising Newtonian-based solution algorithm. A numerical example is given to show the effectiveness of the mathematical program and solution algorithm.

Published
2013
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45. System optimizing flow and externalities in time-dependent road networks

Author

Chow, A. H. F., Wong, S.C., Hau, T.D., Wang, J.J., Chau, K.W., and Ho, H.W.

Abstract

This paper develops a framework for analysing and calculating system optimizing flow and externalities in time-dependent road networks. The externalities are derived by using a novel sensitivity analysis of traffic models. The optimal network flow is determined by solving a state-dependent optimal control problem, which assigns traffic such that the total system cost of the network system is minimized. This control theoretic formulation can work with general travel time models and cost functions. Deterministic queue is predominantly used in dynamic network models. The analysis in this paper is more general and is applied to calculate the system optimizing flow for Friesz’s whole link traffic model. Numerical examples are provided for illustration and discussion. Finally, some concluding remarks are given.

Published
2006

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