A multi-functional simulation platform for on-demand ride service operations

On-demand ride services or ride-sourcing services have been experiencing fast development in the past decade. Various mathematical models and optimization algorithms have been developed to help ride-sourcing platforms design operational strategies with higher efficiency. However, due to cost and reliability issues (implementing an immature algorithm for real operations may result in system turbulence), it is commonly infeasible to validate these models and train/test these optimization algorithms within real-world ride sourcing platforms. Acting as a useful test bed, a simulation platform for ride-sourcing systems will be very important to conduct algorithm training/testing or model validation through trails and errors. While previous studies have established a variety of simulators for their own tasks, it lacks a fair and public platform for comparing the models or algorithms proposed by different researchers. In addition, the existing simulators still face many challenges, ranging from their closeness to real environments of ride-sourcing systems, to the completeness of different tasks they can implement. To address the challenges, we propose a novel multi-functional and open-sourced simulation platform for ride-sourcing systems, which can simulate the behaviors and movements of various agents on a real transportation network. It provides a few accessible portals for users to train and test various optimization algorithms, especially reinforcement learning algorithms, for a variety of tasks, including on-demand matching, idle vehicle repositioning, and dynamic pricing. In addition, it can be used to test how well the theoretical models approximate the simulated outcomes. Evaluated on real-world data based experiments, the simulator is demonstrated to be an efficient and effective test bed for various tasks related to on-demand ride service operations

Quantum Stress: Density Functional Theory Formulation and Physical Manifestation

The concept of "quantum stress (QS)" is introduced and formulated within density functional theory (DFT), to elucidate extrinsic electronic effects on the stress state of solids and thin films in the absence of lattice strain. A formal expression of QS (\sigma^Q) is derived in relation to deformation potential of electronic states ({\Xi}) and variation of electron density ({\Delta}n), \sigma^Q = {\Xi}{\Delta}n, as a quantum analog of classical Hook's law. Two distinct QS manifestations are demonstrated quantitatively by DFT calculations: (1) in the form of bulk stress induced by charge carriers; and (2) in the form of surface stress induced by quantum confinement. Implications of QS in some physical phenomena are discussed to underlie its importance.Comment: 5 pages, 4 figure

Circulating tumor DNA clearance predicts prognosis across treatment regimen in a large real-world longitudinally monitored advanced non-small cell lung cancer cohort

Background: Although growth advantage of certain clones would ultimately translate into a clinically visible disease progression, radiological imaging does not reflect clonal evolution at molecular level. Circulating tumor DNA (ctDNA), validated as a tool for mutation detection in lung cancer, could reflect dynamic molecular changes. We evaluated the utility of ctDNA as a predictive and a prognostic marker in disease monitoring of advanced non-small cell lung cancer (NSCLC) patients.Methods: This is a multicenter prospective cohort study. We performed capture-based ultra-deep sequencing on longitudinal plasma samples utilizing a panel consisting of 168 NSCLC-related genes on 949 advanced NSCLC patients with driver mutations to monitor treatment responses and disease progression. The correlations between ctDNA and progression-free survival (PFS)/overall survival (OS) were performed on 248 patients undergoing various treatments with the minimum of 2 ctDNA tests.Results: The results of this study revealed that higher ctDNA abundance (P=0.012) and mutation count (P=8.5x10(-4)) at baseline are associated with shorter OS. We also found that patients with ctDNA clearance, not just driver mutation clearance, at any point during the course of treatment were associated with longer PFS (P=2.2x10(-1)6, HR 0.28) and OS (P=4.5x10(-6), HR 0.19) regardless of type of treatment and evaluation schedule.Conclusions: This prospective real-world study shows that ctDNA clearance during treatment may serve as predictive and prognostic marker across a wide spectrum of treatment regimens

Analysis of multi-modal commute behavior with feeding and competing ridesplitting services

Public transit is an essential travel mode in many urban areas. Emerging dynamic ridesplitting programs provided by transportation network companies (TNCs) can be a double-edged sword to public transit. On the one hand, the program provides convenient services to solve first- and last-mile problems. On the other hand, long-distance ridesplitting services may also draw passengers away from public transit. In this paper, we propose a network model to analyze multi-modal commute behavior with ridesplitting programs as both feeders and competitors to public transit, which is with limited accessibility to passengers. The ridesplitting priority and ridesplitting fare ratio (i.e., ridesplitting fare over non-ridesplitting fare) are incorporated as operational strategies of the TNC. Through numerical studies, we find that a significant number of public transit passengers will shift to long-distance ridesplitting services under low fare ratios; and a high ridesplitting priority can lead to a demand drawback for long-distance ridesplitting, which raises public transit ridership. To maintain public transit ridership, the TNC needs to keep a high fare ratio and a high priority; meanwhile, the number of short-distance ridesplitting orders can also decrease dramatically, which may lead to a loss in unit time revenue of the TNC. We note that a win–win condition can be reached through a separated discount strategy for first- and last-mile ridesplitting services. Such a strategy can both increase the number of short-distance ridesplitting orders for the TNC and boost transit ridership for the government, as well as provide low-cost services to passengers

Constructing multifunctional heterostructure of Fe2O3@Ni3Se4 nanotubes

Heterostructures have attracted increasing attention due to their amazing synergetic effects, which may improve the electrochemical properties, such as good electrical/ionic conductivity, electrochemical activity, and mechanical stability. Herein, novel hierarchical Fe2 O3 @Ni3 Se4 nanotubes are successfully fabricated by a multistep strategy. The nanotubes show length sizes of ≈250-500 nm, diameter sizes of ≈100-150 nm, and wall thicknesses of ≈10 nm. The as-prepared Fe2 O3 @Ni3 Se4 nanotubes with INi:Fe = 1:10 show excellent Li storage properties (897 mAh g-1 high reversible charge capacity at 0.1 A g-1 ), good rate performance (440 mAh g-1 at 5 A g-1 ), and outstanding long-term cycling performance (440 mAh g-1 at 5 A g-1 during the 300th cycle) as an anode material for lithium ion batteries. In addition, the Fe2 O3 @Ni3 Se4 nanotubes with INi:Fe = 1:10 (the atomic ratio between Ni and Fe) show superior electrocatalytic performance toward the oxygen evolution reaction with an overpotential of only 246 mV at 10 mA cm-2 and a low Tafel slope of 51 mV dec-1 in 1 m KOH solution.MOE (Min. of Education, S’pore

O2 plasma and cation tuned nickel phosphide nanosheets for highly efficient overall water splitting

Here we present a novel combined-strategy of cation tuning and surface engineering for the fabrication of highly active, earth-abundant, and robust two-dimensional Ni2P electrocatalyst. The nanosheets have lateral sizes of few hundred nm with thicknesses of ~6 nm. Our theoretical calculations suggest the effectiveness of vanadium doping and oxygen plasma, which do not only enhance the density-of-state at Fermi level, but also make the Ni sites more susceptible to OH− adsorption. The oxygen plasma treatment can increase the wettability of the catalyst toward KOH solution, improving the contact angle from 44.95° to 16.8° and also induce a higher BET surface area; hence, more active sites and lower charge transfer resistance are obtained. As a result, the catalyst requires small overpotentials of 257 and 108 mV to drive ±10 mA cm−2 alongside with modest Tafel slope of 43.5 and 72.3 mV dec−1 for oxygen evolution reaction and hydrogen evolution reaction in 1.0 M KOH solution, respectively. When employed for overall water splitting, the catalyst demonstrates a low voltage of 1.56 V to achieve 10 mA cm−2 with good stability and durability, outperforming the state-of-the-art IrO2 || Pt/C which needs 1.69 V. This work opens a new approach to engineer low-cost monometallic phosphides for highly efficient water splitting.MOE (Min. of Education, S’pore