Yuqi Bai

Shear localization and recrystallization in dynamic deformation of 8090 Al-Li alloy

The microstructural evolution in localized shear deformation was investigated in an 8090 Al-Li alloy by split Hopkinson pressure bar (strain rate of approximately 10(3) s(-1)) at ambient temperature and 77 K. The alloy was tested in the peak-, over-, under-, and natural-aged conditions, that provide a wide range of microstructural parameters and mechanical properties. Two types of localized shear bands were distinguished by optical microscopy: the deformed shear band and the white-etching shear band. They form at different stages of deformation during localization. There are critical strains for the occurrence of deformed and white-etching localized shear deformation, at the imposed strain rate. Observations by transmission electron microscopy reveal that the white-etching bands contain fine equiaxed grains; it is proposed that they are the result of recrystallization occurring during localization. The deformed-type bands are observed after testing at 77 K in all heat treatment conditions, but they are not as well defined as those developed at ambient temperature. Cracking often occurs along the localized shear at ambient temperature. The decrement in temperature is favorable for the nucleation, growth and coalescence of the microcracks along the shear bands, inducing fracture

Precise and Continuous Time and Frequency Synchronisation at the 5×10-19 Accuracy Level

The synchronisation of time and frequency between remote locations is crucial for many important applications. Conventional time and frequency dissemination often makes use of satellite links. Recently, the communication fibre network has become an attractive option for long-distance time and frequency dissemination. Here, we demonstrate accurate frequency transfer and time synchronisation via an 80 km fibre link between Tsinghua University (THU) and the National Institute of Metrology of China (NIM). Using a 9.1 GHz microwave modulation and a timing signal carried by two continuous-wave lasers and transferred across the same 80 km urban fibre link, frequency transfer stability at the level of 5×10−19/day was achieved. Time synchronisation at the 50 ps precision level was also demonstrated. The system is reliable and has operated continuously for several months. We further discuss the feasibility of using such frequency and time transfer over 1000 km and its applications to long-baseline radio astronomy.

Dynamic recrystallization induced by plastic deformation at high strain rate in a Monel alloy

An investigation has been made into the plastic deformation behavior of a Monel alloy deformed at high strain rate of 10(5) s(-1) by split Hopkinson bar. The results reveal that there are some equiaxed grains with an average size of 150 nm in diameter in the center of the shear bands, suggesting that this microstructure characteristics be developed by dynamic recrystallization, arising from the deformation and the rapid temperature rise in the band. Analysis shows that the plastic strain rate and the mobile dislocation density play a key role in the new crystallized grain formation and growth. Based on grain boundary energy change and diffusion mechanism, the grain growth kinetics is developed for plastic deformation at a high strain rate.

Use of grid computing for modeling virtual geospatial products

Earth science research and applications usually use Distributed Geospatial Information Processing (DGIP) services and powerful computing capabilities to extract information and knowledge from large volumes of distributed geospatial data. Conceptually, such processing can be abstracted into a logical model that utilizes geospatial domain knowledge to produce new geospatial products. Using this idea, the geo-tree concept and the proposed geospatial Abstract Information Model (AIM) have been used to develop a Grid workflow engine complying with geospatial standards and the Business Process Execution Language. Upon a users request, the engine generates virtual geospatial data/information/knowledge products from existing DGIP data and services. This article details how to (1) define and describe the AIM in XML format, (2) describe the process logically with an AIM, including the geospatial semantic logic, (3) conceptually describe the process of producing a particular geospatial product step by step from raw geospatial data, (4) instantiate AIM as a concrete Grid-service workflow by selecting the optimal service instances and data sets, and (5) design a Grid workflow engine to execute the concrete workflows to produce geospatial products. To verify the advantages and applicability of this Grid-enabled virtual geospatial product system, its performance is evaluated, and a sample application is provided.

Towards a geospatial Catalogue federation Service

As geospatial catalogues are becoming accessible online through public query interfaces, a federation to fulfill distributed and integrated metadata discovery needs to be built. This study investigates the feasibility of federating three distinct geospatial catalogue services: the NASA Earth Observing System (EOS) ClearingHOuse (ECHO), the George Mason University (GMU) OpenGIS Catalogue Service for Web (CSW), and the U.S. Department of Energy (DOE) Earth System Grid (ESG) Simulation Data Catalogue. Challenges and problems in dealing with the metadata conceptual models, query languages, and communication protocols are analyzed. Proposed federation strategies and the operational federation system are introduced. Our results show that protocol adaptation, query dispatching, query criteria translation, and query results integration are the four main challenges in building a catalogue federation. A mediatorwrapper based approach can be adopted to build a federation service. The OpenGIS Catalogue Service specification can be used to define the internal communication protocols between the federation service and the affiliated catalogue services, and between the federation service and its clients.

A taxonomy of geospatial services for global service discovery and interoperability

Geospatial service taxonomies represent the knowledge about the characteristics of geospatial services from the enterprise, computational, information, engineering, infrastructure, or technology viewpoints. This paper presents a lightweight taxonomy of geospatial services with the aim of promoting the global sharing of and interoperability among geospatial service instances. This taxonomy focuses on the knowledge connected with service interoperability. As a hierarchical taxonomy, it consists of six layers: service category, service type, version, profile, binding and uniform resource name (URN), from the root down to the leaves. Each layer is composed of classification nodes, with each node identifying one classification concept. Each concept, with a concrete semantic meaning, can be used to classify service instances. The application of this classification scheme to the Global Earth Observation System of Systems (GEOSS) Component and Service registry is also introduced. The results of this study may lead to the further development of service taxonomy to thoroughly capture the knowledge about geospatial services. The lessons learned may be useful to others representing and manipulating geoscientific knowledge.

BPELPower-A BPEL execution engine for geospatial web services

The Business Process Execution Language (BPEL) has become a popular choice for orchestrating and executing workflows in the Web environment. As one special kind of scientific workflow, geospatial Web processing workflows are data-intensive, deal with complex structures in data and geographic features, and execute automatically with limited human intervention. To enable the proper execution and coordination of geospatial workflows, a specially enhanced BPEL execution engine is required. BPELPower was designed, developed, and implemented as a generic BPEL execution engine with enhancements for executing geospatial workflows. The enhancements are especially in its capabilities in handling Geography Markup Language (GML) and standard geospatial Web services, such as the Web Processing Service (WPS) and the Web Feature Service (WFS). BPELPower has been used in several demonstrations over the decade. Two scenarios were discussed in detail to demonstrate the capabilities of BPELPower. That study showed a standard-compliant, Web-based approach for properly supporting geospatial processing, with the only enhancement at the implementation level. Pattern-based evaluation and performance improvement of the engine are discussed: BPELPower directly supports 22 workflow control patterns and 17 workflow data patterns. In the future, the engine will be enhanced with high performance parallel processing and broad Web paradigms.

A new research paradigm for global land cover mapping

ABSTRACT In this paper, we introduced major challenges in mapping croplands, settlements, water and wetlands, and discussed challenges in the use of multi-temporal and multi-sensor data. We then summarized some of the on-going efforts in improving qualities of global land cover maps. Existing technologies provide sufficient data for better map making if extra efforts can be made instead of harmonizing and integrating various global land cover products. Developing and selecting better algorithms, including more input variables (new types of data or features) for classification, having representative training samples are among conventional measures generally believed effective in improving mapping accuracies at local scales. We pointed out that data were more important in improving mapping accuracies than algorithms. Finally, we proposed a new paradigm for global land cover mapping, which included a view of vegetation classes based on their types and form, canopy cover and height. The new paradigm suggests that a universally applicable training sample set is not only possible but also effective in improving land cover classification at the continental and global scales. To ensure an easy transition from traditional land cover mapping to the new paradigm, we recommended that an all-in-one data management and analysis system be constructed.

The design and implementation of a grid-enabled catalogue service

Catalogue service is crucial to the sharing and utilizing of geographic information. This paper provides a new architecture and its implementation of a geographic information catalogue service that can effectively manage distributed geographic data and services. The catalogue service is based on the Open Geospatial Consortium (OGC) Catalogue Service for Web Specification and the ebXML Registry Information Model (ebRIM). The ebRIM is extended with ISO 19115 (including draft part 2) and ISO 19119 international standards for better description of geographic information. The adoption of the ebRIM and international standards will greatly advance the interoperability of the catalogue service and the sharing of the abundant geographic information. The catalogue service is Gridenabled to facilitate Grid’s abilities of on-demand, ubiquitous access to distributed computing, data, and services resources. The Grid-enabled catalogue service is GSI-supported which enables it to interoperate with other Grid Services in a secure way. By being integrated with RLS, MDS and other Gridenabled OGC Services, this Grid-enabled catalogue service prototype provides secure discovery, retrieval, and management of geographic data and services.

Improving the Accuracy of Daily PM2.5 Distributions Derived from the Fusion of Ground-Level Measurements with Aerosol Optical Depth Observations, a Case Study in North China

The accuracy in estimated fine particulate matter concentrations (PM2.5), obtained by fusing of station-based measurements and satellite-based aerosol optical depth (AOD), is often reduced without accounting for the spatial and temporal variations in PM2.5 and missing AOD observations. In this study, a city-specific linear regression model was first developed to fill in missing AOD data. A novel interpolation-based variable, PM2.5 spatial interpolator (PMSI2.5), was also introduced to account for the spatial dependence in PM2.5 across grid cells. A Bayesian hierarchical model was then developed to estimate spatiotemporal relationships between AOD and PM2.5. These methods were evaluated through a city-specific 10-fold cross-validation procedure in a case study in North China in 2014. The cross validation R(2) was 0.61 when PMSI2.5 was included and 0.48 when PMSI2.5 was excluded. The gap-filled AOD values also effectively improved predicted PM2.5 concentrations with an R(2) = 0.78. Daily ground-level PM2.5 concentration fields at a 12 km resolution were predicted with complete spatial and temporal coverage. This study also indicates that model prediction performance should be assessed by accounting for monitor clustering due to the potential misinterpretation of model accuracy in spatial prediction when validation monitors are randomly selected.