120 research outputs found
Capacity Estimation for Vehicle-to-Grid Frequency Regulation Services with Smart Charging Mechanism
Due to various green initiatives, renewable energy will be massively
incorporated into the future smart grid. However, the intermittency of the
renewables may result in power imbalance, thus adversely affecting the
stability of a power system. Frequency regulation may be used to maintain the
power balance at all times. As electric vehicles (EVs) become popular, they may
be connected to the grid to form a vehicle-to-grid (V2G) system. An aggregation
of EVs can be coordinated to provide frequency regulation services. However,
V2G is a dynamic system where the participating EVs come and go independently.
Thus it is not easy to estimate the regulation capacities for V2G. In a
preliminary study, we modeled an aggregation of EVs with a queueing network,
whose structure allows us to estimate the capacities for regulation-up and
regulation-down, separately. The estimated capacities from the V2G system can
be used for establishing a regulation contract between an aggregator and the
grid operator, and facilitating a new business model for V2G. In this paper, we
extend our previous development by designing a smart charging mechanism which
can adapt to given characteristics of the EVs and make the performance of the
actual system follow the analytical model.Comment: 11 pages, Accepted for publication in IEEE Transactions on Smart Gri
Pricing Link by Time
The combination of loss-based TCP and drop-tail routers
often results in full buffers, creating large queueing delays. The challenge with parameter tuning and the drastic consequence of improper tuning have discouraged network administrators from enabling AQM even when routers support
it. To address this problem, we propose a novel design principle for AQM, called the pricing-link-by-time (PLT) principle. PLT increases the link price as the backlog stays above a threshold β, and resets the price once the backlog goes below β. We prove that such a system exhibits cyclic behavior that is robust against changes in network environment and protocol parameters. While β approximately controls the level of backlog, the backlog dynamics are invariant for β across a wide range of values. Therefore, β can be chosen to reduce delay without undermining system performance. We validate these analytical results using packet-level simulation
with Science Classics
Abstract In Dialogue with Nature is a compulsory course on reading science-related classic texts for all students in the Chinese University of Hong Kong. The course aims to provide an opportunity for students to be familiar with the nature of science and develop their critical thinking skills. As the students are from diversified academic background, this situation has provided both positive and negative effects on the pedagogical strategies in this general education foundation course. For instance, while the course has provided a cross-disciplinary environment to stimulate the students to think beyond their own academic specialty, it has been speculated that students without prior scientific knowledge in high school could be disadvantaged in their academic performance. The intention of this paper is to report the current situation of this course and investigate the effectiveness of providing supplementary materials specifically to the non-science students. The preliminary analysis shows positive indicators on the effect
Oscillations of Highly Magnetized Non-rotating Neutron Stars
Highly magnetized neutron stars are promising candidates to explain some of
the most peculiar astronomical phenomena, for instance, fast radio bursts,
gamma-ray bursts, and superluminous supernovae. Pulsations of these highly
magnetized neutron stars are also speculated to produce detectable
gravitational waves. In addition, pulsations are important probes of the
structure and equation of state of the neutron stars. The major challenge in
studying the pulsations of highly magnetized neutron stars is the demanding
numerical cost of consistently solving the nonlinear Einstein and Maxwell
equations under minimum assumptions. With the recent breakthroughs in numerical
solvers, we investigate pulsation modes of non-rotating neutron stars which
harbour strong purely toroidal magnetic fields of G through
two-dimensional axisymmetric general-relativistic magnetohydrodynamics
simulations. We show that stellar oscillations are insensitive to magnetization
effects until the magnetic to binding energy ratio goes beyond 10%, where the
pulsation mode frequencies are strongly suppressed. We further show that this
is the direct consequence of the decrease in stellar compactness when the
extreme magnetic fields introduce strong deformations of the neutron stars
Routing with QoS Information Aggregation in Hierarchical Networks
Abstract-In this paper, we consider the problem of routing with two additive constraints in the hierarchical networks, such as the Internet. In order for scalability, the supported QoS information in the hierarchical networks has to be aggregated. We propose a novel method for aggregating the QoS information. To the best of our knowledge, our approach is the first study to use the area-minimization optimization, the de facto optimization problem of the QoS information aggregation. We use a set of real numbers to approximate the supported QoS between different domains. The size of the set is predefined so that advertisement overhead and the space requirement will not grow exponentially as the network size grows. The simulation results show that the proposed method outperforms the existing methods
Effectiveness of a technology-based injury prevention program for enhancing mothers’ knowledge of child safety: protocol for a randomized controlled trial
Background: Provision of anticipatory guidance for parents is recommended as an effective strategy to prevent injuries among young children. Technology-based anticipatory guidance has been suggested to reinforce the effectiveness of injury prevention and improve parents’ knowledge of child safety.
Objective: This study aims to examine the effectiveness of a technology-based injury prevention program with parental anticipatory guidance for enhancing mothers’ knowledge of child safety.
Methods: In this randomized controlled trial, 308 mothers will be recruited from the antenatal clinics and postnatal wards of two major public hospitals in Hong Kong. Participating mothers will be randomly assigned into intervention and control groups. Mothers in the intervention group will be given free access to a technology-based injury prevention program with anticipatory guidance, whereas mothers in the control group will be given a relevant booklet on parenting. The injury prevention program, available as a website or on a mobile app, includes behavioral components based on the Theory of Planned Behavior. The primary outcome measure will be the change in the mother’s knowledge of child safety. The secondary outcome measures will be age-appropriate domestic safety knowledge, attitudes, intentions, perceived behavioral control, and self-reported behavior related to home safety practice. We will also determine dose-response relationships between the outcome measures and the website and mobile app usage.
Results: Enrolment of participants will begin in October 2016. Results are expected by June 2018.
Conclusions: Parents will be able to easily access the domestic injury prevention website to find information regarding child injury prevention. It is anticipated that the technology-based intervention will help parents improve their knowledge of child safety and raise their awareness about the consequences of domestic injuries and the importance of prevention.
Trial Registration: Clinicaltrials.gov
Clinicaltrials.gov NCT02835768; http://clinicaltrials.gov/ct2/show/NCT02835768 (Archived by WebCite at http://www.webcitation/6lbXYM6b9)
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