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Avishai Ceder,Stephan Hassold,Christopher Dunlop,Iris Chen 서울시립대학교 도시과학연구원 2013 도시과학국제저널 Vol.17 No.2
This paper deals with the creation of bus timetables using different vehicle sizes. The need for the development of new bus timetables for public transport (PT) stems from the current reliability and efficiency problems that current bus services are facing. These issues arise from the fact that timetables are designed mainly with even headways; however, it is also possible to design timetables with even passenger loads on the vehicles at the maximum load points, but with uneven headways. This paper hopes to bridge the two strategies together through the use of the incorporation of a mixed fleet size, running in conjunction. The timetables were constructed using two key concepts; assigning capacity and shifting departure times. The methodology for the creation of timetables was applied to a real-life example from Auckland, New Zealand. The results of the timetable are promising, validating the methodology of the model. The new timetables lead to a reduction in both passenger waiting time (user perspective) and empty seat time (operator perspective), with only a marginal increase in passenger standee time. The implementation of a mixed fleet of different vehicle sizes shows to be a promising way for achieving both an even headway and an even loading.
Urban mobility and public transport: future perspectives and review
Avishai (Avi) Ceder 서울시립대학교 도시과학연구원 2021 도시과학국제저널 Vol.25 No.4
The purpose of this work is to review urban transportation likely to be offered in the future. Trip-making behaviour has already changed considerably as lifestyles change and they will continue to change in the future. This work reflects and places emphasis on profound thinking about the possibilities, rather than predicting them. Thoughts about possibilities for the future draw upon imagination, perceived and justified feasibility, and lessons gained from the past. This work attempts to capture the possibilities, logistics and travel modes of future urban transportation. A visionary, feasibility-related approach grounded in a realist perspective is proposed, only conceptually, to explore plausible visions for the future. In addition, this work shows the inefficiency of using private cars (PCs) and argues that in the development of autonomous and electric vehicles, PCs cannot provide a solution competitive with the potential that urban transportation systems have for the future. Hence, the solutions for the future must be based on public transport (PT) modes of travel, regardless of whether they are metro, bus, light rail, tram, ridesharing services, an ordinary taxi, personal rapid transit, or any other PT-based future mode. The key principal of operation for the mobility of a smart city will be the ability to optimize the connectivity of movement in order to approach a seamless move, while endowing the phrase door-to-door travel with new meaning. Finally, it would be remiss not to mention the unforeseeable implications of the Covid-19 pandemic for future mobility, more controllable by automation of non-privately owned vehicle, and with the prospect of people demonstrating a greater inclination towards changing their habits, behaviour, and thinking paradigms.
Yoon, Gabin,Moon, Sehwan,Ceder, Gerbrand,Kang, Kisuk American Chemical Society 2018 Chemistry of materials Vol.30 No.19
<P>Metallic lithium (Li) is a promising anode candidate for high-energy-density rechargeable batteries because of its low redox potential and high theoretical capacity. However, its practical application is not imminent because of issues related to the dendritic growth of Li metal with repeated battery operation, which presents a serious safety concern. Herein, various aspects of the electrochemical deposition and stripping of Li metal are investigated with consideration of the reaction rate/current density, electrode morphology, and solid electrolyte interphase (SEI) layer properties to understand the conditions inducing abnormal Li growth. It is demonstrated that the irregular (i.e., filamentary or dendritic) growth of Li metal mostly originates from local perturbation of the surface current density, which stems from surface irregularities arising from the morphology, defective nature of the SEI, and relative asymmetry in the deposition/stripping rates. Importantly, we find that the use of a stripping rate of Li metal that is slower than the deposition rate seriously aggravates the formation of disconnected Li debris from the irregularly grown Li metal. This finding challenges the conventional belief that high-rate stripping/plating of Li in an electrochemical cell generally results in more rapid cell failure because of the faster growth of Li metal dendrites.</P> [FIG OMISSION]</BR>
High-rate performance of a mixed olivine cathode with off-stoichiometric composition.
Kim, Jae Chul,Li, Xin,Kang, Byoungwoo,Ceder, Gerbrand The Royal Society of Chemistry 2015 Chemical communications Vol.51 No.68
<P>We highlight that the off-stoichiometric compositional variation is a simply effective method to improve the power density of LiFe0.6Mn0.4PO4. This strategy does not require a supplementary separate coating and is likely applicable to other compositions given the feasibility of the method.</P>
Zhichao Cao,Ting Xu,Silin Zhang,Avishai (Avi) Ceder,Yuyao Sun 대한토목학회 2022 KSCE Journal of Civil Engineering Vol.26 No.7
Even-headway timetables with easy to memorize departure times are commonly in use in public transport (PT) service. In addition, some PT services are using timetables where their departure times are based on even-passenger-load at the max-load stop along the route. In practice, these two types of timetables are implemented in daily operation plans, allowing for their merits, with the former maintaining the initial, even-interval departure rules and conventions, especially when a new PT line is planned without available demand information, while the latter is demand-oriented, exhibiting fluctuation in time and space. The principles of creating the aforementioned timetables have been presented in the literature, but very few evaluations feasibly attest to performance by means of mathematical analysis. Concentrating on building a modelling framework for PT timetabling problems during the planning stage, this work is taking into account 1) passengers’ service-frequency satisfaction, in terms of waiting times, 2) passengers’ perception of riding comfort, in terms of seat availability, and 3) planned passengers’ load ratio (concerning vehicle’s capacity) linked with operation efficiency. Yielding to the models developed in a theoretical manner, the comparative evaluation is conducted through multiple timetable schemes that include four different dimensions: (A) even-headway departures with same headway throughout the time horizon, (B) even-load departures with same load throughout the time horizon, (C) even-headway departures for each demand-dependent period, and (D) even-load departures for each demand-dependent period. Finally, a case study in Nantong, China examines the comparison performances produced and the best plans for operational timetables. The results indicate that travelers attributed great importance to higher satisfaction preferences on frequency or headway-related experience linked with their waiting time.
Gwon, Hyeokjo,Kim, Sung-Wook,Park, Young-Uk,Hong, Jihyun,Ceder, Gerbrand,Jeon, Seokwoo,Kang, Kisuk American Chemical Society 2014 Inorganic Chemistry Vol.53 No.15
<P>An ion-exchange process can be an effective route to synthesize new quasi-equilibrium phases with a desired crystal structure. Important layered-type battery materials, such as LiMnO<SUB>2</SUB> and LiNi<SUB>0.5</SUB>Mn<SUB>0.5</SUB>O<SUB>2</SUB>, can be obtained through this method from a sodium-containing parent structure, and they often show electrochemical properties remarkably distinct from those of their solid-state synthesized equivalents. However, while ion exchange is generally believed to occur via a simple topotactic reaction, the detailed phase transformation mechanism during the process is not yet fully understood. For the case of layered LiNi<SUB>0.5</SUB>Mn<SUB>0.5</SUB>O<SUB>2</SUB>, we show through ex situ X-ray diffraction (XRD) that the ion-exchange process consists of several sequential phase transformations. By a study of the intermediate phase, it is shown that the residual sodium ions in the final structure may greatly affect the electrochemical (de)lithiation mechanism.</P><P>The ion exchange in NaNi<SUB>0.5</SUB>Mn<SUB>0.5</SUB>O<SUB>2</SUB> is not a simple two-phase process but rather involves several intermediate complex compounds. In the early stage of ion exchange, the intermediate phase, which contains randomly distributed sodium and lithium ions in the lithium layers, forms almost immediately, with extremely fast exchange kinetics. Successively, a rather slower two-phase conversion occurred, involving a structural shuffling process.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/inocaj/2014/inocaj.2014.53.issue-15/ic501069x/production/images/medium/ic-2014-01069x_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ic501069x'>ACS Electronic Supporting Info</A></P>