Prescriptive PCA: Dimensionality Reduction for Two-stage Stochastic Optimization

In this paper, we consider the alignment between an upstream dimensionality reduction task of learning a low-dimensional representation of a set of high-dimensional data and a downstream optimization task of solving a stochastic program parameterized by said representation. In this case, standard dimensionality reduction methods (e.g., principal component analysis) may not perform well, as they aim to maximize the amount of information retained in the representation and do not generally reflect the importance of such information in the downstream optimization problem. To address this problem, we develop a prescriptive dimensionality reduction framework that aims to minimize the degree of suboptimality in the optimization phase. For the case where the downstream stochastic optimization problem has an expected value objective, we show that prescriptive dimensionality reduction can be performed via solving a distributionally-robust optimization problem, which admits a semidefinite programming relaxation. Computational experiments based on a warehouse transshipment problem and a vehicle repositioning problem show that our approach significantly outperforms principal component analysis with real and synthetic data sets

Frequency and accuracy of weight comments by others, and the association with weight misperception among Hong Kong adolescents

*Purpose:* To assess the frequency and accuracy of weight comments received from different sources among Chinese adolescents and the relation of weight comments to weight misperception.

*Methods:* In the Hong Kong Student Obesity Surveillance (HKSOS) project 2006-07, 22612 form 1 to 7 students (41.5% boys) completed a questionnaire on obesity. Students were asked if they had received serious "too fat" or "too thin" comments over the past 30 days from family members, peers and professionals, and the accuracy of the comments was assessed against the actual weight status. Weight misperception was defined as discordance between the actual and perceived weight status. Logistic regression was used to calculate adjusted odd ratios (ORs) for weight misperception by weight comments received.

*Results:* One in three students received weight comments, most commonly from mother for both "too fat" and "too thin" comments. Health professional was the most accurate source of weight comments, yet less than half the comments were correct. Receiving incorrect weight comments was significantly associated with weight misperception in all sex-weight status sub-groups, particularly among obese girls. In contrast, student who received correct weight comments were less likely to have weight misperception.

*Conclusions:* Weight comments were commonly received by Chinese adolescents in Hong Kong, yet most of the comments were inaccurate, and such incorrect comments were associated with weight misperception. Family members, peers and professionals should realize the potential adverse effects of their weight comments and adolescents should be taught how to correctly assess their weight status to reduce misperceptions

Service Region Design for Urban Electric Vehicle Sharing Systems

Emerging collaborative consumption business models have shown promise in terms of both generating business opportunities and enhancing the efficient use of resources. In the transportation domain, car sharing models are being adopted on a mass scale in major metropolitan areas worldwide. This mode of servicized mobility bridges the resource efficiency of public transit and the flexibility of personal transportation. Beyond the significant potential to reduce car ownership, car sharing shows promise in supporting the adoption of fuel- efficient vehicles, such as electric vehicles (EVs), due to these vehicles special cost structure with high purchase but low operating costs. Recently, key players in the car sharing business, such as Autolib, Car2Go and DriveNow, have begun to employ EVs in an operations model that accommodates one-way trips. On the one hand (and particularly in free-floating car sharing), the one-way model results in significant improvements in coverage of travel needs and therefore in adoption potential compared with the conventional round-trip-only model (advocated by ZipCar, for example). On the other hand, this model poses tremendous planning and operational challenges. In this work, we study the planning problem faced by service providers in designing a geographical service region in which to operate the service. This decision entails trade-offs between maximizing customer catchment by covering travel needs and controlling fleet operations costs. We develop a mathematical programming model that incorporates details of both customer adoption behavior and fleet management (including EV repositioning and charging) under imbalanced travel patterns. To address inherent planning uncertainty with regard to adoption patterns, we employ a distributionally robust optimization framework that informs robust decisions to overcome possible ambiguity (or lacking) of data. Mathematically, the problem can be approximated by a mixed integer second-order cone program, which is computationally tractable with practical scale data. Applying this approach to the case of Car2Go’s service with real operations data, we address a number of planning questions and suggest that there is potential for the future development of this service

Association between screen viewing duration and sleep duration, Sleep quality, And excessive daytime sleepiness among adolescents in Hong Kong

© 2014 by the authors; licensee MDPI, Basel, Switzerland. Screen viewing is considered to have adverse impacts on the sleep of adolescents. Although there has been a considerable amount of research on the association between screen viewing and sleep, most studies have focused on specific types of screen viewing devices such as televisions and computers. The present study investigated the duration w ith which currently prevalent screen viewing devices (including televisions, personal computers, mobile phones, and portable video devices) are viewed in relation to sleep duration, sleep quality, and daytime sleepiness among Hong Kong adolescents (N = 762). Television and computer viewing remain prevalent, but were not correlated with sleep variables. Mobile phone viewing was correlated with all sleep variables, while portable video device viewing was shown to be correlated only with daytime sleepiness. The results demonstrated a trend of increase in the prevalence and types of screen viewing and their effects on the sleep patterns of adolescents.Link_to_subscribed_fulltex

Prevalence and Correlates of Video and Internet Gaming Addiction among Hong Kong Adolescents: A Pilot Study

This pilot study investigated the patterns of video and internet gaming habits and the prevalence and correlates of gaming addiction in Hong Kong adolescents. A total of 503 students were recruited from two secondary schools. Addictive behaviors of video and internet gaming were assessed using the Game Addiction Scale. Risk factors for gaming addiction were examined using logistical regression. An overwhelming majority of the subjects (94%) reported using video or internet games, with one in six (15.6%) identified as having a gaming addiction. The risk for gaming addiction was significantly higher among boys, those with poor academic performance, and those who preferred multiplayer online games. Gaming addiction was significantly associated with the average time spent gaming per week, frequency of spending money on gaming, period of spending money on gaming, perceived family disharmony, and having more close friends. These results suggest that effective educational and preventative programs or strategies are needed

Hong Kong dentists' preparedness for medical emergency in dental clinics

Aim: The aim of this study was to investigate the Hong Kong dentists’ and dental clinics’ preparedness for medical emergency in the dental clinic. Methods: Two custom designed questionnaires were developed, one for dentists and another for dental clinics, to collect the required information. The sampling frame for participants was the list of registered dentists published by the Hong Kong Dental Council on its website in January 2016. A total of 434 dentists and 143 dental clinics were selected from the list by systematic random sampling. The latter sample was supplemented by 10 randomly selected government dental clinics. The questionnaires were mailed the selected dentists together with a cover letter and a stamped return envelope. A reminder letter and another copy of the questionnaire were sent out two weeks after the first mailing. Results: 167 (38%) completed dentist questionnaires and 53 (35%) clinic questionnaires were collected. Most of the respondent dentists had some deficient knowledge on basic life support (BLS), their mean score was 3.5 out of a maximum of 5. Most (>60%) of the respondents thought they were competent in performing medical emergency procedures except giving intravenous injection. Moreover, most (>60%) of them held positive attitude towards having immediate availability of essential medical emergency equipment and drugs in their clinic. Dentists who were more recent graduates, those with postgraduate qualifications, and those who work with accompaniment generally had higher mean BLS knowledge scores. In the dental clinics, the most commonly kept medical emergency equipment/drug was instant glucose (70%) and followed by antihistamine (62%). Only a quarter of the clinics were equipped with AED, and 45% were equipped with oxygen cylinder. For 8 out of the 11 items, a higher proportion of the bigger clinics (>2 dental chairs) than the smaller clinics had the medical emergency equipment/drug available (Chi-square test, p<0.05). Conclusion: Hong Kong dentists have a moderate level of knowledge on BLS which should be enhanced through regular attendance at CE courses. Their knowledge level is affected by a number of their background and professional activities factors. Most dental clinics in Hong Kong have only few of the essential medical emergency equipment and drugs while the larger clinics are better equipped than the smaller clinics.published_or_final_versio

Lack of Evidence for Human-to-Human Transmission of Avian Influenza A (H9N2) Viruses in Hong Kong, China 19991

In April 1999, isolation of avian influenza A (H9N2) viruses from humans was confirmed for the first time. H9N2 viruses were isolated from nasopharyngeal aspirate specimens collected from two children who were hospitalized with uncomplicated, febrile, upper respiratory tract illnesses in Hong Kong during March 1999. Novel influenza viruses have the potential to initiate global pandemics if they are sufficiently transmissible among humans. We conducted four retrospective cohort studies of persons exposed to these two H9N2 patients to assess whether human-to-human transmission of avian H9N2 viruses had occurred. No serologic evidence of H9N2 infection was found in family members or health-care workers who had close contact with the H9N2-infected children, suggesting that these H9N2 viruses were not easily transmitted from person to person

Reactivation of Epstein–Barr virus by a dual-responsive fluorescent EBNA1-targeting agent with Zn2+-chelating function

EBNA1 is the only Epstein–Barr virus (EBV) latent protein responsible for viral genome maintenance and is expressed in all EBV-infected cells. Zn2+ is essential for oligomerization of the functional EBNA1. We constructed an EBNA1 binding peptide with a Zn2+ chelator to create an EBNA1-specific inhibitor (ZRL5P4). ZRL5P4 by itself is sufficient to reactivate EBV from its latent infection. ZRL5P4 is able to emit unique responsive fluorescent signals once it binds with EBNA1 and a Zn2+ ion. ZRL5P4 can selectively disrupt the EBNA1 oligomerization and cause nasopharyngeal carcinoma (NPC) tumor shrinkage, possibly due to EBV lytic induction. Dicer1 seems essential for this lytic reactivation. As can been seen, EBNA1 is likely to maintain NPC cell survival by suppressing viral reactivation