Scheduling Electric Buses with Stochastic Driving Times

To try to make the world more sustainable and reduce air pollution, diesel buses are being replaced with electric buses. This leads to challenges in scheduling, as electric buses need recharging during the day. Moreover, buses encounter varying traffic conditions and passenger demands, leading to delays. Scheduling electric buses with these stochastic driving times is also called the Stochastic Vehicle Scheduling Problem. The classical approach to make a schedule more robust against these delays, is to add slack to the driving time. However, this approach doesn\u27t capture the variance of a distribution well, and it doesn\u27t account for dependencies between trips. We use discrete event simulation in order to evaluate the robustness of a schedule. Then, to create a schedule, we use a hybrid approach, where we combine integer linear programming and simulated annealing with the use of these simulations. We show that with the use of our hybrid algorithm, the punctuality of the buses increase, and they also have a more timely arrival. However, we also see a slight increase in operating cost, as we need slightly more buses compared to when we use deterministic driving times

Scheduling Electric Buses with Stochastic Driving Times

To try to make the world more sustainable and reduce air pollution, diesel buses are being replaced with electric buses. This leads to challenges in scheduling, as electric buses need recharging during the day. Moreover, buses encounter varying traffic conditions and passenger demands, leading to delays. Scheduling electric buses with these stochastic driving times is also called the Stochastic Vehicle Scheduling Problem. The classical approach to make a schedule more robust against these delays, is to add slack to the driving time. However, this approach doesn't capture the variance of a distribution well, and it doesn't account for dependencies between trips. We use discrete event simulation in order to evaluate the robustness of a schedule. Then, to create a schedule, we use a hybrid approach, where we combine integer linear programming and simulated annealing with the use of these simulations. We show that with the use of our hybrid algorithm, the punctuality of the buses increase, and they also have a more timely arrival. However, we also see a slight increase in operating cost, as we need slightly more buses compared to when we use deterministic driving times

High incidence of antimicrobial resistant organisms including extended spectrum beta-lactamase producing Enterobacteriaceae and methicillin-resistant Staphylococcus aureus in nasopharyngeal and blood isolates of HIV-infected children from Cape Town, South Africa

<p>Abstract</p> <p>Background</p> <p>There is little information on nasopharyngeal (NP) flora or bacteremia in HIV-infected children. Our aim was to describe the organisms and antimicrobial resistance patterns in children enrolled in a prospective study comparing daily and three times weekly trimethoprim-sulfamethoxazole (TMP-SMX) and isoniazid (INH) or placebo prophylaxis.</p> <p>Methods</p> <p>NP swabs were taken at baseline from HIV-infected children enrolled in the study. Standard microbiological techniques were used. Children were grouped according to previous or current exposure to TMP-SMX and whether enrolled to the study during a period of hospitalization. Blood culture results were also recorded within 12 months of baseline.</p> <p>Results</p> <p>Two hundred and three children, median age 1.8 (Interquartile [IQ]: 0.7–4) years had NP swabs submitted for culture. One hundred and eighty-four (90.7%) had either stage B or C HIV disease. One hundred and forty-one (69.8%) were receiving TMP-SMX and 19 (9.4%) were on antiretroviral therapy. The majority, 168 (82%) had a history of hospitalization and 91 (44.8%) were enrolled during a period of hospitalization. Thirty-two subjects (16.2%) died within 12 months of study entry.</p> <p>One hundred and eighty-one potential pathogens were found in 167 children. The most commonly isolated organisms were <it>Streptococcus pneumoniae </it>(48: 22.2%), Gram-negative respiratory organisms (<it>Haemophilus influenzae </it>and <it>Moraxella catarrhalis</it>) (47: 21.8%), <it>Staphylococcus aureus </it>(44: 20.4%), Enterobacteriaceae 32 (14.8%) and Pseudomonas 5 (2.3%).</p> <p>Resistance to TMP-SMX occurred in > 80% of pathogens except for <it>M. catarrhalis </it>(2: 18.2% of tested organisms). TMP-SMX resistance tended to be higher in those receiving it at baseline (p = 0.065). Carriage of Methicillin resistant <it>S. aureus </it>(MRSA) was significantly associated with being on TMP-SMX at baseline (p = 0.002). Minimal inhibitory concentrations (MIC) to penicillin were determined for 18 <it>S. pneumoniae </it>isolates: 7 (38.9%) were fully sensitive (MIC ≤ 0.06 μg/ml), 9 (50%) had intermediate resistance (MIC 0.12 – 1 μg/ml) and 2 (11.1%) had high level resistance (MIC ≥2 μg/ml). Fifty percent of Enterobacteriaceae produced extended spectrum beta-lactamases (ESBL) (resistant to third generation cephalosporins) and 56% were resistant to gentamicin. Seventy-seven percent of <it>S. aureus </it>were MRSA. Carriage of resistant organisms was not associated with hospitalization.</p> <p>On multivariate logistic regression, risk factors for colonization with Enterobacteriaceae were age ≤ one year (Odds ratio 4.4; 95% Confidence Interval 1.9–10.9; p = 0.0008) and CDC stage C disease (Odds ratio 3.6; 95% Confidence Interval 1.5–8.6; p = 0.005)</p> <p>Nineteen (9.4%) subjects had 23 episodes of bacteremia. Enterobacteriaceae were most commonly isolated (13 of 25 isolates), of which 6 (46%) produced ESBL and were resistant to gentamicin.</p> <p>Conclusion</p> <p>HIV-infected children are colonized with potential pathogens, most of which are resistant to commonly used antibiotics. TMP-SMX resistance is extremely common. Antibiotic resistance is widespread in colonizing organisms and those causing invasive disease. Antibiotic recommendations should take cognizance of resistance patterns. Antibiotics appropriate for ESBL-producing Enterobacteriaceae and MRSA should be used for severely ill HIV-infected children in our region. Further study of antibiotic resistance patterns in HIV-infected children from other areas is needed.</p

Paediatric non-progression following grandmother-to-child HIV transmission

Background In contrast to adult HIV infection, where slow disease progression is strongly linked to immune control of HIV mediated by protective HLA class I molecules such as HLA-B*81:01, the mechanisms by which a minority of HIV-infected children maintain normal-for-age CD4 counts and remain clinically healthy appear to be HLA class I-independent and are largely unknown. To better understand these mechanisms, we here studied a HIV-infected South African female, who remained a non-progressor throughout childhood. Results Phylogenetic analysis of viral sequences in the HIV-infected family members, together with the history of grand-maternal breast-feeding, indicated that, unusually, the non-progressor child had been infected via grandmother-to-child transmission. Although HLA-B*81:01 was expressed by both grandmother and grand-daughter, autologous virus in each subject encoded an escape mutation L188F within the immunodominant HLA-B*81:01-restricted Gag-specific epitope TL9 (TPQDLNTML, Gag 180–188). Since the transmitted virus can influence paediatric and adult HIV disease progression, we investigated the impact of the L188F mutant on replicative capacity. When this variant was introduced into three distinct HIV clones in vitro, viral replicative capacity was abrogated altogether. However, a virus constructed using the gag sequence of the non-progressor child replicated as efficiently as wildtype virus. Conclusion These findings suggest alternative sequences of events: the transmission of the uncompensated low fitness L188F to both children, potentially contributing to slow progression in both, consistent with previous studies indicating that disease progression in children can be influenced by the replicative capacity of the transmitted virus; or the transmission of fully compensated virus, and slow progression here principally the result of HLA-independent host-specific factors, yet to be defined

Preliminary outcomes of a paediatric highly active antiretroviral therapy cohort from KwaZulu-Natal, South Africa

BACKGROUND: Few studies address the use of paediatric highly active antiretroviral therapy (HAART) in Africa. METHODS: We performed a retrospective cohort study to investigate preliminary outcomes of all children eligible for HAART at Sinikithemba HIV/AIDS clinic in KwaZulu-Natal, South Africa. Immunologic, virologic, clinical, mortality, primary caregiver, and psychosocial variables were collected and analyzed. RESULTS: From August 31, 2003 until October 31, 2005, 151 children initiated HAART. The median age at HAART initiation was 5.7 years (range 0.3–15.4). Median follow-up time of the cohort after HAART initiation was 8 months (IQR 3.5–13.5). The median change in CD4% from baseline (p < 0.001) was 10.2 (IQR 5.0–13.8) at 6 months (n = 90), and 16.2 (IQR 9.6–20.3) at 12 months (n = 59). Viral loads (VLs) were available for 100 children at 6 months of which 84% had HIV-1 RNA levels ≤ 50 copies/mL. At 12 months, 80.3% (n = 61) had undetectable VLs. Sixty-five out of 88 children (73.8%) reported a significant increase (p < 0.001) in weight after the first month. Eighty-nine percent of the cohort (n = 132) reported ≤ 2 missed doses during any given treatment month (> 95%adherence). Seventeen patients (11.3%) had a regimen change; two (1.3%) were due to antiretroviral toxicity. The Kaplan-Meier one year survival estimate was 90.9% (95%confidence interval (CI) 84.8–94.6). Thirteen children died during follow-up (8.6%), one changed service provider, and no children were lost to follow-up. All 13 deaths occurred in children with advanced HIV disease within 5 months of treatment initiation. In multivariate analysis of baseline variables against mortality using Cox proportional-hazards model, chronic gastroenteritis was associated with death [hazard ratio (HR), 12.34; 95%CI, 1.27–119.71) and an HIV-positive primary caregiver was found to be protective against mortality [HR, 0.12; 95%CI, 0.02–0.88). Age, orphanhood, baseline CD4%, and hemoglobin were not predicators of mortality in our cohort. Fifty-two percent of the cohort had at least one HIV-positive primary caregiver, and 38.4% had at least one primary caregiver also on HAART at Sinikithemba clinic. CONCLUSION: This report suggests that paediatric HAART can be effective despite the challenges of a resource-limited setting

Optimizing for Reliable and Sustainable Public Transport

To make a public transport network efficient, a lot of planning has to be done. This planning leads to complex optimization problems. This thesis is devoted to key issues in the optimization of public transport with the focus on reliability and sustainability. For the optimization for reliability we use historical measurements of run times to develop models for evaluation and optimization of reliability of a public transport network. For the sustainability we include environmental concerns in the optimization: electric vehicles with no exhaust from the engine as well as a mixed fleet with electric vehicles and other vehicles of varying degrees of exhaust. We aim to develop models and optimization methods for these problems which can be used in practice. These methods will be able to handle real-life sized instances and should perform better than currently used algorithms or heuristics. In this thesis, we have investigated four different subjects: Trip Runtime Determination: Based on measured trip runtimes we determine the optimal planned trip runtimes on stops in order to minimize average delay. We developed a new method which leads to a decrease of the average delay at stops with 60 percent. We also optimized on minimal passenger travel time instead of minimal average delay at stops. This halves the average waiting time for a passenger and reduces the average travel duration with up to 5 percent. Robust Vehicle Scheduling: In order to reduce knock-on delays in vehicle schedules, some buffer time is scheduled between trips. When the first trip is delayed, the second trip will leave on time. Usually, a fixed buffer time is used. We investigated this subject and developed a new model for assigning buffer times. We were able to improve the punctuality with up to 3 percent at no cost. Electric vehicles: We have developed a model to schedule electric vehicles, taking into account the State of Charge of the battery. This is because the battery is not large enough to drive during a whole day without recharging. We use a combination of lagrange relaxation and column generation to solve our model. Furthermore, we developed a model for solving the pricing problem in polynomial time, where we are only aware of NP-complete solution methods for this pricing problem. Vehicle scheduling during transition to a more sustainable public transport: We developed models for vehicle scheduling during the transition phase from traditional, diesel vehicles to more sustainable, cleaner vehicles. Typical for this transition phase is the mixture of old and new vehicles that should be used. For a mixture of older, less clean and newer, cleaner vehicles we show that by taking the exhaust characteristics of the different buses in the fleet into account, we can reduce the total exhaust by 15 percent without extra cost. For a mixture of diesel and electric vehicles, we show that taking the different characteristics into account saves up to 4 percent in cost