High-quality Contributions Research Articles

Service Data Analytics and Business Intelligence

With growing economic globalization, the modern service sector is in great need of business intelligence for data analytics and computational statistics. The joint application of big data analytics, computational statistics and business intelligence has great potential to make the engineering of advanced service systems more efficient. The purpose of this COST issue is to publish high- quality research papers (including reviews) that address the challenges of service data analytics with business intelligence in the face of uncertainty and risk. High quality contributions that are not yet published or that are not under review by other journals or peer-reviewed conferences have been collected. The resulting topic oriented special issue includes research on business intelligence and computational statistics, data-driven financial engineering, service data analytics and algorithms for optimizing the business engineering. It also covers implementation issues of managing the service process, computational statistics for risk analysis and novel theoretical and computational models, data mining algorithms for risk management related business applications.

Building knowledge economies in Africa: an introduction

ABSTRACTKnowledge has emerged as a fundamental driver of economic growth and development by inter alia improving the effectiveness and efficiency of economic projects and boosting the process of finding new avenues of addressing developmental policy syndromes. Recent evidence suggests that Africa is on the threshold of significant and sustainable economic growth if its human and material resources can be effectively mobilised to support the process (Asongu & Tchamyou, 2019; Kuada & Mensah, 2018). Consequently, the World Bank’s Knowledge Economy Framework aims to explore and support the extent to which current policies in African countries affect the knowledge development process (and thereby competitiveness) on the continent. A knowledge economy is an economy in which economic prosperity largely depends on the accessibility, quality and quantity of information available, instead of the means of production (Asongu, 2017a, 2017b). This themed issue of Contemporary Social Science-‘Building Knowledge Economies in Africa’ – consists of papers that focus on, but are not limited to, the four dimensions of the World Bank’s Knowledge Economy Index. These are: information and communication technology, education, economic incentives and institutional regime, and innovation (Tchamyou, 2017). The themed issue engages with high quality contributions which, taken together, address the drivers towards knowledge-based economies. This introduction provides a context for understanding the importance of building knowledge economies in Africa and summarises the main contributions to the themed issue. The paper ends by advising scholars and policy makers regarding the risks associated with a colonial view of knowledge- notably the importance of proposing knowledge-based policies while avoiding hegemonic paradigms and hierarchical constructs. In summary, the issue consists of a set of theoretically informed, empirically robust, policy-relevant and accessible articles for both specialists and non-specialists.

Building Knowledge Economies in Africa: An Introduction

Knowledge has emerged as a fundamental driver of economic growth and development by inter alia improving the effectiveness and efficiency of economic projects and boosting the process of finding new avenues of addressing developmental policy syndromes. Recent evidence suggests that Africa is on the threshold of significant and sustainable economic growth if its human and material resources can be effectively mobilised to support the process (Kuada & Mensah, 2017; Asongu & Tchamyou, 2019). Consequently, the World Bank’s Knowledge Economy Framework aims to explore and support the extent to which current policies in African countries affect the knowledge development process (and thereby competitiveness) on the continent. A knowledge economy is an economy in which economic prosperity largely depends on the accessibility, quality and quantity of information available, instead of the means of production (Asongu, 2017a, 2017b). This themed issue of Contemporary Social Science-‘Building Knowledge Economies in Africa’ - consists of papers that focus on, but are not limited to, the four dimensions of the World Bank’s Knowledge Economy Index. These are: information and communication technology, education, economic incentives and institutional regime, and innovation (Tchamyou, 2017). The themed issue engages with high quality contributions which, taken together, address the drivers towards knowledge-based economies. This introduction provides a context for understanding the importance of building knowledge economies in Africa and summarises the main contributions to the themed issue. The paper ends by advising scholars and policy makers regarding the risks associated with a colonial view of knowledge- notably the importance of proposing knowledge-based policies while avoiding hegemonic paradigms and hierarchical constructs. In summary, the issue consists of a set of theoretically informed, empirically robust, policy-relevant and accessible articles for both specialists and non-specialists.

Highlights of Physics

Highlights of Physics

IEEE Access Special Section Editorial: 5G and Beyond Mobile Wireless Communications Enabling Intelligent Mobility

Increasing urbanization is one major trend that shapes tomorrow’s society; by 2050, more than 85% of the developed world’s population will live in a comparatively small number of ever-growing cities. Within such cities and their commuter belts, reliable high-rate wireless communication will not only be required for (quasi-) static users but also for hosts of people moving in public and private transportation networks. Yet, wireless connectivity is not restricted to people; frictionless functioning of such a society in motion is supported by Intelligent Mobility, where each connected transportation vehicle (car, train, bus, ship, aircraft, motorcycle, and bicycle) is expected to be a smart object equipped with a powerful multi-sensor platform, communication capability, computing units, and Internet protocol (IP)-based connectivity, such as to be highly efficient in various vehicular and transportation applications. This vision requires a more pervasive and ubiquitous communications and networking core, which will not be only driven by the existing research on 5G but also enabled by future mobile wireless communications that employ new concepts, such as data analytics, artificial intelligence, machine learning, and cloud computing. Therefore, this IEEE Access Special Section focuses on various theoretical and experimental views on researching and developing the required technological enhancements of 5G and beyond mobile wireless communications, to efficiently support the vision of intelligent mobility, providing mobility as a service, and enabling dependable Internet services. Twenty-three high-quality contributions to this Special Section have been selected in a strict peer-review process supported by reputed international experts.

Preface

The previous 2017 International Conference on Traffic Engineering and Transportation system (ICTETS 2017) have successfully taken place on October 27-29, 2017 in Haikou, China. 2018 2nd International Conference on Traffic Engineering and Transportation System (ICTETS 2018) have successfully taken place on August 17-19, 2018 in Shenzhen, China. All accepted papers were published in IOP Conference Series: Materials Science and Engineering (MSE) (ISSN: 1757-8981) and have been indexed by EI.The Third International Conference on traffic engineering and transportation systems (ICTETS 2019), which was held together with Anhui University, Henan University of science and technology, Henan city construction university and Henan Agricultural University, was held in Henan, China from September 20 to 22, 2019. The theme of the conference is “opportunities and challenges for transportation development”. We are looking forward to face-to-face exchanges with experts in relevant research fields in Colleges and universities to jointly explore key challenges in these fields. Promote the development and application of new theories, technologies, processes and equipment in the field of transportation.The Conference work was carried out in 4 sections:• Transportation system• Vehicle engineering• Logistics Engineering• Engineering ManagementAll contributions collected at the meeting will be strictly reviewed by experts of the meeting committee, and high-quality contributions that have passed the review will be presented and published orally. We would like to thank the reviewers of the conference committee for their contributions to the conference. We would also like to thank the contributors for submitting their papers and patiently revised them according to the suggestions of the designated reviewers. Finally, all the members of the organizing committee hope that all the articles in this conference can provide valuable summary and reference for researchers in this field.The Organizing Committee of ICTETS 2019List of Committee member also available in this pdf.

Wearable Inertial Sensors to Assess Standing Balance: A Systematic Review.

Wearable sensors are de facto revolutionizing the assessment of standing balance. The aim of this work is to review the state-of-the-art literature that adopts this new posturographic paradigm, i.e., to analyse human postural sway through inertial sensors directly worn on the subject body. After a systematic search on PubMed and Scopus databases, two raters evaluated the quality of 73 full-text articles, selecting 47 high-quality contributions. A good inter-rater reliability was obtained (Cohen’s kappa = 0.79). This selection of papers was used to summarize the available knowledge on the types of sensors used and their positioning, the data acquisition protocols and the main applications in this field (e.g., “active aging”, biofeedback-based rehabilitation for fall prevention, and the management of Parkinson’s disease and other balance-related pathologies), as well as the most adopted outcome measures. A critical discussion on the validation of wearable systems against gold standards is also presented.

Preface

We are pleased to introduce the Proceedings of the 25th JUBILEE TECHNICAL AND SCIENTIFIC CONFERENCE “TRANSPORT, ECOLOGY – SUSTAINABLE DEVELOPMENT” EKO Varna 2019. The conference was held from May 16th to May 18th, 2019 in the city of Varna, Bulgaria. It was organised by Transport Engineering and Technologies Department at Technical University of Varna. The conference was attended by scientists and researchers from Bulgaria, Romania, Russia, Ukraine, Poland and Turkey. The opening was attended by representatives of Varna Regional Administration and the City Hall of Varna, as well as by the Rector of Technical University of Varna.The main conference topics were:• Vehicle design and technology• Ecology of transport engines• Bio fuels for internal combustion engines• Road safety• Electric vehicles and charging stationsThe editors would like to thank all authors for their high-quality contributions and the members of the international programme committee for their commitment. We thank also to Academic Management of Technical University of Varna and to our commercial partners and exhibitors.Official conference website: http://ecovarna.orgEditorsR. HristovR. Dimitrov

Foraging strategies of individual silky pocket mice over a boom-bust cycle in a stochastic dryland ecosystem.

Small mammals use multiple foraging strategies to compensate for fluctuating resource quality in stochastic environments. These strategies may lead to increased dietary overlap when competition for resources is strong. To quantify temporal contributions of high (C3) versus low quality (C4) resources in diets of silky pocket mice (Perognathus flavus), we used stable carbon isotope (δ13C) analysis of 1391 plasma samples collected over 2years. Of these, 695 samples were from 170 individuals sampled ≥ 3 times across seasons or years, allowing us to assess changes in dietary breadth at the population and individual levels across a boom-bust population cycle. In 2014, the P. flavus population increased to 412 captures compared to 8 captures in prior and subsequent years, while populations of co-occurring small mammals remained stable. As intraspecific competition increased, the population-wide dietary niche of P. flavus did not change, but individual specialization increased significantly. During this period, ~ 27% (41/151) of individuals sampled specialized on C3 resources, which were abundant during the spring and previous fall seasons. Most of the remaining individuals were C3-C4 generalists (64%) (96/151), and only 9% (14/151) specialized on C4 resources. In 2015, P. flavus population density and resource availability declined, individual dietary breadth expanded (84% generalists), no C3 specialists were found, and specialization on C4 resources increased (16%). Our results demonstrate a high degree of inter-individual plasticity in P. flavus foraging strategies, which has implications for how this species will respond to environmental change that is predicted to decrease C3 resources in the future.

Biodiversity of Vegetable Crops, A Living Heritage

Biodiversity is the natural heritage of the planet and is one of the key factors of sustainable development, due to its importance not only for the environmental aspects of sustainability but also for the social and economic ones. The purpose of this Special Issue is to publish high-quality research papers addressing recent progress and perspectives while focusing on different aspects related to the biodiversity of vegetable crops. Original, high-quality contributions that have not yet been published, or that are not currently under review by other journals, have been gathered. A broad range of aspects such as genetic, crop production, environments, customs and traditions were covered. All contributions are of significant relevance and could stimulate further research in this area.

20th International School on Condensed Matter Physics

PREFACEWe are pleased to introduce the Proceedings of the 20th JUBILEE INTERNATIONAL SCHOOL ON CONDENSED MATTER PHYSICS “Physics and Applications of Advanced and Multifunctional Materials (20th ISCMP). The school was held from September 3rd to September 7th, 2018 in Varna, Bulgaria. It was organized by the Institute of Solid State Physics of the Bulgarian Academy of Sciences (ISSP-BAS), and took place at one of the fine resorts on the Bulgarian Black sea “Saints Constantine and Helena”.The aim of this international school is to bring together top experimentalists and theoreticians, with interests in interdisciplinary areas, with the younger generation of scientists, in order to discuss current research and to communicate new forefront ideas. This year special focus was given to advanced organic and inorganic materials and their application in biophysics and sensors. Traditionally covered areas, such as characterization of nanostructured materials and thin films were also discussed. Participants from 16 countries presented 26 invited lectures, 28 short oral presentations and 60 posters.The hope of the organizing committee is that the 20th ISCMP provided enough opportunities for direct scientific contacts, interesting discussions and interactive exchange of ideas between the participants. The nice weather certainly helped a lot in this respect. The editors would like to thank all authors for their high-quality contributions and the members of the international program committee for their commitment.The papers submitted for publication in the Proceedings were refereed according to the publishing standards of the Journal of Physics: Conference Series. The Editorial Committee members are very grateful to the Journal’s staff for the continuous fruitful relations and for giving us the opportunity to present the work from the 20th ISCMP.Prof. DSc Hassan Chamati, Prof. DSc Doriana Dimova-Malinovska, Assoc. Prof. Dr. Julia Genova Prof. DSc Diana Nesheva, and Prof. DSc Albena Paskaleva

Ken Foster and the Genesis of Sports Law: A Personal Perspective

Ken Foster’s work in the field of sports law is of central importance. His sustained, high-quality contributions to sports law scholarship underpin much other work in the area. This intervention makes the case for the importance and centrality of this work, and highlights key contributions. It evidences the development of key themes and perspectives in Ken Foster’s work and its fundamental and foundational significance in the relatively new field of sports law.

ICER 2019 call for participation

The fifteenth annual ACM International Computing Education Research (ICER) Conference aims to gather high-quality contributions to the computing education research discipline. ICER will take place in Toronto, Canada, August 11-14, 2019. We invite submissions across a variety of categories for research investigating how people of all ages come to understand computational processes and devices, and empirical evaluation of approaches to improve that understanding in formal and informal learning environments.

Editors' Message

It is our great pleasure to welcome you to this issue of the Proceedings of the ACM on Human Computer Interaction, the second to focus on the contributions from the research community Computer-Supported Cooperative Work and Social Computing (CSCW). This journal model allows for rapid publication of papers shortly after acceptance as well as enabling automatic indexing services, such as Institute for Scientific Information (ISI) indexing. The aim is to increase the visibility of the work of authors in this community, and allow for better comparability with fields outside of Computer Science. This issue contains papers accepted over two iterations of the review process. The call for papers for this second issue, with an initial deadline in Spring 2018, attracted 722 submissions, from all around the world. After the first round of reviewing, 326 (45,2%) papers were invited to the Revise and Resubmit phase. The program committee worked hard over August 2018 to arrive at final decisions, with an online editorial committee meeting held to allow for collective deliberation. In the end, 184 papers (25,5%) were accepted. For some of those papers, authors received further shepherding and guidance by a senior committee member. This shows the commitment of the CSCW community to not only ensure high quality contributions, but also to educate and enable authors to write and present their best work for this community. This issue exists because of the dedicated volunteer effort of 132 senior editorial committee members who served as Associate Chairs (ACs), and 837 external expert reviewers to ensure high quality and insightful reviews for all papers in both rounds.

Materials Technology for Renewable Energies

Global warming and climate change are major challenges facing our society in the 21st century. They are mainly caused by the burning of fossil fuels for energy. The adoption of renewable energies will play a pivotal role in reducing greenhouse gas emissions. Materials technologies are critical for the production, harvesting, storage and transmission of renewable energies to realize sustainable development. This special issue published in collaboration with Advanced Sustainable Systems, presents research outcomes, reviews and discussions on topics related to renewable energy technologies: i) hydrogen storage and antiferroelectrics for energy storage, ii) single nanowire solar cells, iii) advanced lithium-ion batteries and flexible lithium-ion batteries and microsupercapacitors, iv) carbon dioxide reduction, and v) low-cost sodium-based batteries and high-energy lithium-sulfur batteries. Hydrogen is a zero-emission fuel. However, its usage has been restricted by the lack of a suitable storage technology. The review in this issue summarizes nanosized light element hydrides to enable hydrogen storage at ambient conditions. Dielectric capacitors are capable of delivering both high energy densities and power densities. Strategies are discussed for improving the performance of antiferroelectric ceramic based capacitors. Furthermore, nanowire solar cells based on different III-V semiconductor nanowire materials are analysed for fabricating high-efficiency solar cells. Carbon dioxide reduction can produce valuable products. Various catalyst materials are reviewed to reveal their intrinsic microstructure and electronic properties towards electrochemical reduction of carbon dioxide. Lithium-ion batteries are currently dominating power sources for portable electronics and electric vehicles, and also are widely applied for the storage of electricity generated by renewable sources such as solar and wind. In this issue, we revisit the development of high-performance lithium-ion batteries. Plasma enabled synthesis and processing of materials are explored for lithium-ion batteries, including electrode materials, separators and electrolytes. Meanwhile, recent advances in flexible lithium-ion batteries are presented with a focus on flexible electrodes, electrolyte and cell structure. In addition, progress on the fabrication of flexible micro-supercapacitors is also discussed for wearable electronic devices. Low-cost rechargeable batteries are in high demand for large-scale energy storage. The abundance of sodium in nature is driving a renaissance of sodium-ion batteries. Titanium oxides as negative materials for sodium-ion batteries are comprehensively reviewed in this issue with emphasis on sodium storage mechanisms and strategies to improve the cycling stability, Coulombic efficiency and kinetic behaviour. Room-temperature sodium-oxygen batteries not only can maintain low cost, but also can deliver high energy density. In this regard, recent achievements and remaining challenges for rechargeable sodium-oxygen batteries are summarized with detailed discussions on the reaction mechanism, cathode materials, sodium anodes, electrolytes and other key components. Finally, the progress of lithium-sulfur batteries is deliberated to understand the complex sulfur redox chemistry and aims to lay foundations for mechanistic investigations on lithium-sulfur batteries. More articles on renewable energy technologies can be found in the Special Issue published in the sister journal Advanced Sustainable Systems. It has been an absolute joy and pleasure to edit this special issue. I would like to thank the Editor-in-Chief of Advanced Materials Technologies – Dr. Esther Levy, for coordinating the special issue and handling all papers. I would like to sincerely thank all authors for their high-quality contributions to this special issue. Professor Guoxiu Wang is the Director of the Centre for Clean Energy Technology and a Distinguished Professor at University of Technology Sydney (UTS), Australia. He is an expert in materials chemistry, electrochemistry, energy storage and conversion, and battery technologies. He is a member of the Australian Research Council (ARC) College of Experts. His research interests include lithium-ion batteries, lithium-air batteries, sodium-ion batteries, lithium-sulfur batteries, supercapacitors, hydrogen storage materials, fuel cells, graphene and MXenes.

Does the Mark-to-Model Fair Value Measure Make Assets Impairment Noisy?

A strong trend towards the implementation and use of International Financial Reporting Standards (IFRS) changes the accounting reporting model and replaces cost-based measures with market-based measures. Based on the decision-making usefulness, the fair value has become a dominant measurement paradigm. However, among the three levels of the fair value hierarchy, the most controversial is the third one: unobservable inputs for the asset or liability. Regarding this level, fair value is estimated based on management’s expectations and projections. This method of fair value measurement is susceptible to manipulation, having poor verifiability and, therefore, poor reliability. This has raised the question: does the implementation of the mark-to-model fair value measures for asset impairment tests enhance the relevance and reliability of information in the financial reports? After a systematic literature review and a synthesis of high-quality contributions in this field, we conclude that the implementation of asset impairment tests which use mark-to-model fair value measures has not increased the quality and reliability of the information presented in financial statements; unfortunately, research has shown that companies are using that tool to manage their earnings and promote managers’ unethical behaviour. Furthermore, capital markets’ reaction to asset impairment announcements is negative.

Guest editorial for the Special Issue on signal and power integrity of microelectronic networks through modelling and simulation of fields and devices

Today's mobile and interconnected society poses complex and growing challenges to the electronic systems that back emerging big data and Internet of Things technologies. As these systems execute increasingly complex algorithms and programs on vast datasets, ensuring their signal and power integrity (SPI) is essential to safeguarding their functionality and interoperability. The hardware systems that enable these advanced technologies and applications must be wireless, low-power/energy, high-speed, high-bandwidth, ultra-thin/small, scalable, reliable, and inexpensive. The design, optimization, fabrication, and testing of such hardware systems poses a formidable challenge spanning a variety of interdisciplinary fields while requiring the simultaneous modeling of coupled electrical, mechanical, and thermal responses of both passive interconnects and active devices. To further complicate matters, multi-physics models of these devices must be capable of quantifying uncertainty due to random variations in design, fabrication, and test processes, as well as (un)intentional noise in the environment. Ensuring the SPI of such electronic systems often requires high-fidelity (e.g., less than 10−6 field error) and full-wave quantification of the electromagnetic (information) waves. Modeling field propagation in such systems is nontrivial. Indeed, electromagnetic waves in these systems often propagate through multi-port networks of lossy, dispersive, inhomogeneous, multilayer (nonuniform), nonlinear, and multi-scale structures. The smallest features of these structures can range from nanometers on chip, to micrometers on package, to millimeters on system. In addition, the flow of signal and power across the complex spatial and temporal dimensions is influenced by thermal and power management specifications. Analytical methods are useful for modeling electromagnetic fields on simple and symmetric structures. While they oftentimes provide useful insights relating to the system response, used by themselves, they have limited range and scope. To solve problems of practical interest, computational electromagnetic (CEM) methods are indispensable. Although recent advancements in CEM methods have enabled solutions to problems considered nearly impossible only a decade ago, many practical applications remain out of the range of present-day algorithms. As a result, CEM practitioners are often forced to trade accuracy for computational cost (memory and time) while accepting an error that depends on the specific problem, the chosen CEM method, and the simplifying assumptions. This Special Issue provides a glimpse into new CEM trends for SPI problems. A Special Issue on this topic cannot be comprehensive; therefore, the intent is to motivate the reader to further explore the vast SPI literature, and to stimulate the development of novel and exciting research, publications, and tools that define the state-of-the-art in the field. Finally, the hope is to inform and generate awareness in the wider engineering community about the significant interdisciplinary challenges and the proportionally significant opportunities in this important and promising field. I'd like to extend my sincere gratitude to all authors for their high-quality contributions. I also would like to thank all reviewers for their invaluable time and efforts to improve the quality of the papers.

Incentivizing High Quality User Contributions: New Arm Generation in Bandit Learning

We study the problem of incentivizing high quality contributions in user generated content platforms, in which users arrive sequentially with unknown quality. We are interested in designing a content displaying strategy which decides which content should be chosen to show to users, with the goal of maximizing user experience (i.e., the likelihood of users liking the content).This goal naturally leads to a joint problem of incentivizing high quality contributions and learning the unknown content quality. To address the incentive issue, we consider a model in which users are strategic in deciding whether to contribute and are motivated by exposure, i.e., they aim to maximize the number of times their contributions are viewed. For the learning perspective, we model the content quality as the probability of obtaining positive feedback (e.g., like or upvote) from a random user. Naturally, the platform needs to resolve the classical trade-off between exploration (collecting feedback for all content) and exploitation (displaying the best content). We formulate this problem as a multi-arm bandit problem, where the number of arms (i.e., contributions) is increasing over time and depends on the strategic choices of arriving users. We first show that applying standard bandit algorithms incentivizes a flood of low cost contributions, which in turn leads to linear regret. We then propose Rand_UCB which adds an additional layer of randomization on top of the UCB algorithm to address the issue of flooding contributions. We show that Rand_UCB helps eliminate the incentives for low quality contributions, provides incentives for high quality contributions (due to bounded number of explorations for the low quality ones), and achieves sub-linear regrets with respect to displaying the current best arms.

Smart Machines, Remote Sensing, Precision Farming, Processes, Mechatronic, Materials and Policies for Safety and Health Aspects

The purpose of this Special Issue is to publish high-quality research papers, as well as review articles, addressing recent advances on systems, processes, and materials for work safety, health, and environment. Original, high-quality contributions that have not yet been published, or that are not currently under review by other journals or peer-reviewed conferences, have been sought. The main topics have been the protection system aimed to agricultural health and safety especially applied to mechanization sector (harvester, chippers), often involved in accidents at work, in the context of Directive 2006/42/EC, and to other families of risk as the chemical one and issues pertinent to safety. Methodologies for gradual and sustainable safety improvements on farms have been investigated in the vision of preliminary applications. Furthermore, the application of technologies aimed to the improvement and facilitation of operations in the agriculture sector as monitoring, precision farming, internet of things, application of evolved networks and machines of new conception.

Incentive Mechanism and Rating System Design for Crowdsourcing Systems: Analysis, Tradeoffs and Inference

Macrotasking crowdsourcing systems like Elance and Fiverr serve as efficient platforms for requesters to outsource challenging and innovative tasks that require special skills to workers. It is widely practiced in such systems that requesters reward workers based on requesters' assessment on solution quality. The challenge is that requesters' assessment may not be accurate to reflect the intrinsic quality of a solution due to human factors like personal preferences or biases. In this work, we consider answering the following questions: How to design a mechanism to incentivize workers provide high quality solutions in the presence of such human factors? How to formally study the impact of human factors on workers' financial incentive to participate? We design a mechanism to incentivize workers to provide high-quality contributions, which is robust to human factors. Our incentive mechanism consists of a “task bundling scheme” and a “rating system”, which reward workers based on requesters' rating on the solution quality. We propose a probabilistic model to capture human factors, and quantify their impact on the incentive mechanism. We formulate an optimization framework to select appropriate rating system parameters, which can be viewed as a tradeoff between “system efficiency”, i.e., the total number of tasks can be solved given a fixed reward budget, and the “rating system complexity”, which determines the human cognitive cost and time in expressing ratings. We also formulate an optimization framework to select appropriate bundling size, which can tradeoff system efficiency against service delay (i.e., the waiting time to form a task bundle). Finally, we conduct experiments on a dataset from Elance. Experimental results show that our incentive mechanism achieves at least 99.95 percent of the theoretical maximum system efficiency with a service delay of at most 2.3639 hours. Furthermore, we discover that the rating system in Elance is too complex, and it should be simplified to a binary rating system (i.e., two rating points).