An aircraft acquisition decision model under stochastic demand

AbstractThis study proposes the probabilistic dynamic programming model to address the stochastic demand issue in aircraft acquisition problem. A probable phenomena is defined to comprehend the uncertain state variables so that the targeted level of service could be achieved profitably by the airline company. The objective function and the constraints have a linear expression with respect to the decision variables, and hence the proposed model is then converted as a linear programming model. The proposed model and the solution method are then examined with an illustrative case study to determine the number and the types of new aircraft that should be purchased at every time period. The results show that the proposed methodology is viable in providing the optimal solution

A Bi-Objective Optimization Approach for Inflight Food Waste Reduction

For airline industry, an excess of inflight food waste has been highlighted as one of the crucial concerns that affecting airline’s profit margin and operations. Furthermore, it may result in environmental issue if excessive food waste is not handled with care. As such, ensuring an optimal inflight catering service is particularly important to airlines. However, the existing literatures focusing on the reduction of inflight food waste is very limited. Correspondingly, this paper develops a bi-objective inflight food waste reduction model, with the aim to minimize inflight food waste while maximizing passengers’ expectation towards inflight catering service. In particular, an optimal strategy of offering inflight meals (comprise standard and light meals) is proposed appropriately to meet the demand of passengers under uncertainty. By examining some international flights, the results of an illustrative case study show that the developed model is viable to reduce airline’s inflight food waste to a greater extent. Besides, the airline would have greater flexibility to meet the expectations of the passengers in a better manner. It is anticipated that the developed model would reveal some useful insights to the airlines in providing inflight catering services profitably and environmentally

Environmental assessment and improvement strategies for electric bus operations

In accordance with worldwide environmental problems and fossil oil dependency concern, green mobility with electric buses is receiving increasing attention as an essential road transport. Environmentally, electric buses emerge as a promising solution in particular to alleviate the emission and noise pollution. Nevertheless, there is no available method on how to quantify green (environmental) performance of electric buses that could provide proper guidance to the bus operators. Therefore, this study aims to construct a green index assessment and improvement framework for electric buses by capturing bus noise, emission and energy consumption level explicitly. The proposed framework, which is capable of quantifying the green level of electric bus operations, plays a vital role in improving the green performance of bus operating system, by considering numerous operational aspects. In order to examine the applicability of the proposed approach, an illustrative case study, focusing on the electric bus operations of Putrajaya (Malaysia), is analyzed accordingly. The resultant findings show that the green performance of electric buses would be different at varying degrees, depending on various inter-correlated factors. It is anticipated that this study may reveal some beneficial insights for the bus operators to operate environmental-friendly electric buses feasibly

Scenario-based electric bus operation: A case study of Putrajaya, Malaysia

Globally, transportation sector has emerged as one of the major sources of air pollution. Correspondingly, green mobility (with electric bus) is gaining increasing attention as an essential step to mitigate emission concern. As such, a proper electric bus network design and fleet planning is important especially for bus operator to acquire an adequate number of electric bus, right on time, in order to operate electric bus system viably. Thus, this paper aims to examine the possibility to operate electric bus as a replacement for the conventional bus operation (with natural gas buses for the study area in Putrajaya, Malaysia). In order to determine a proper-designed electric bus operating system in terms of electric bus route, service frequency and quantity, the proposed methodology is developed with the aid of a traffic modeling software to cater various scenarios. Based on the existing (conventional) traffic and transit system in Putrajaya, the developed electric bus operating model is calibrated accordingly by considering various operational concerns including battery capacity and charging facility. The resultant findings revealed that the developed electric bus operating system in Putrajaya outperforms the conventional bus operation, not only in generating a higher profit margin for the bus operator, but also satisfying the passengers in a better manner (by carrying more passengers per unit of bus with a lower energy consumption)

Evaluation of stool short chain fatty acids profiles in the first year of life with childhood atopy-related outcomes

Introduction: Short chain fatty acids (SCFAs) are the main intestinal intermediate and end products of metabolism of dietary fibers/polyphenols by the gut microbiota. The aim of this study was to evaluate the biological implication of stool SCFA profiles determined in the first year of life on the clinical presentation of allergic outcomes in childhood. Methods: From the Growing Up in Singapore Toward healthy Outcomes (GUSTO) cohort, a sub-cohort of 75 participants was recruited. Scheduled questionnaire data was collected for cumulative prevalence of physician-diagnosed eczema, wheezing with the use of nebuliser, and allergen sensitization till the age of 8 years. Stool samples collected at week 3 and months 3, 6 and 12 were quantitated for 9 SCFAs using LC/MS/MS. SCFA data were grouped into lower (below the 25th) and higher (above the 75th percentiles) categories. Generalized Linear Mixed Models was employed to analyse longitudinal association between SCFAs and atopy-related outcomes. Results: Children with lower stool butyric acid levels (≤25th percentile) over the first 3 time points had higher odds ratio (OR) for wheezing (adjOR = 14.6), eczema (adjOR = 13.2), food sensitization (adjOR = 12.3) and combined outcomes of both wheezing and eczema (adjOR = 22.6) till age 8 years, compared to those with higher levels (≥75 percentile). Additionally, lower longitudinal levels of propionic acid (≤25th percentile) over 4 time points in first year of life was associated with recurrent wheezing (≥2 episodes) till 8 years (adjOR = 7.4) (adj p < 0.05). Conclusion: Our results suggest that relatively low levels of gut SCFAs in early life are associated with increased susceptibility to atopic-related outcomes in childhood

Prenatal diet, plasma micronutrients/metabolome and inflammatory status influence the development of atopic eczema in early childhood

Non peer reviewe