7,627 research outputs found
Ant-Colony-Based Multiuser Detection for MC DS-CDMA Systems
Full text linkIn this contribution we present a novel ant colony optimization (ACO) based multi-user detector (MUD) designed for synchronous multi-carrier direct sequence code division multiple access (MC DSCDMA) systems. The operation of the ACO-based MUD is based on the behaviour of the ant colony in nature. The ACO-based MUD aims for achieving the same bit-error-rate (BER) performance as the optimum maximum likelihood (ML) MUD, without carrying out an exhaustive search of the entire MC DS-CDMA search space constituted by all possible combinations of the received multi-user vectors. We will demonstrate that the system is capable of supporting almost as many users as the number of chips in the spreading sequence, while searching only a small fraction of the entire ML search space. It will also be demonstrated that the number of floating point operations per second is a factor of 108 lower for the proposed ACO-based MUD than that of the ML MUD, when supporting K = 32 users in a MC DS-CDMA system employing 31-chip Gold codes as the T-domain spreading sequence
Ant-colony-based multiuser detection for multifunctional-antenna-array-assisted MC DS-CDMA systems
No full textA novel Ant Colony Optimization (ACO) based Multi-User Detector (MUD) is designed for the synchronous Multi-Functional Antenna Array (MFAA) assisted Multi-Carrier Direct-Sequence Code-Division Multiple-Access (MC DS-CDMA) uplink (UL), which supports both receiver diversity and receiver beamforming. The ACO-based MUD aims for achieving a bit-error-rate (BER) performance approaching that of the optimum maximum likelihood (ML) MUD, without carrying out an exhaustive search of the entire MC DS-CDMA search space constituted by all possible combinations of the received multi-user vectors. We will demonstrate that regardless of the number of the subcarriers or of the MFAA configuration, the system employing the proposed ACO based MUD is capable of supporting 32 users with the aid of 31-chip Gold codes used as the T-domain spreading sequence without any significant performance degradation compared to the single-user system. As a further benefit, the number of floating point operations per second (FLOPS) imposed by the proposed ACO-based MUD is a factor of 108 lower than that of the ML MUD. We will also show that at a given increase of the complexity, the MFAA will allow the ACO based MUD to achieve a higher SNR gain than the Single-Input Single-Output (SISO) MC DS-CDMA system. Index Terms—Ant Colony Optimization, Multi-User Detector, Multi-Functional Antenna Array, Multi-Carrier Direct-Sequence Code-Division Multiple-Access, Uplink, Near-Maximum Likelihood Detection
MusicSpace: improving access to musicological data
No full textEfforts over the past decade to digitize scholarly musicological materials has revolutionized the research process, however online research in musicology is now held back by the segregation of data into a plethora of discrete and disparate databases, and the use of legacy or ad hoc metadata specifications that are unsuited to modern demands. Many real-world musicological research questions are rendered effectively intractable because there is insufficient metadata or metadata granularity, and a lack of data source integration. The "musicSpace" project has taken a dual approach to solving this problem: designing back-end services to integrate (and where necessary surface) available (meta)data for exploratory search from musicology's key online data providers; and providing a front-end interface, based on the "mSpace" faceted browser, to support rich exploratory search interaction. We unify our partners' data using a multi-level metadata hierarchy and a common ontology. By using RDF for this, we make use of the many benefits of Semantic Web technologies, such as the facility to create multiple files of RDF at different times and using different tools, assert them into a single graph of a knowledge base, and query all of the asserted files as a whole. In many cases we were able to directly map a record field from a partner's dataset to our combined type hierarchy, but in other cases some light syntactic and/or semantic analysis needed to be performed. This small amount of work in the pre-processing stage adds granularity that significantly enriches the data, allowing for more refined filtering and browsing of records via the search UI. Significantly, although all the data we extract is present in the original records, much of it is neither exposed to nor exploitable by the end-user via our data providers' existing UIs. In musicSpace, however, all data surfaced can be used by the musicologist for the purposes of querying the dataset, and can thus aid the process of knowledge discovery and creation. Our work offers an effective generalizable framework for data integration and exploration that is well suited for Arts and Humanities data. Our benchmarks have been (1) to make tractable previously intractable queries, and thereby (2) to accelerate knowledge discovery
High Pressure Diesel-Like Injections for GDI Engine: Experimental and Numerical Approach
No full textMultihole injectors, working like diesel valve coverage orifice (VCO) or mini-sac nozzle, seem to be the future trend for GDI (Gasoline Direct Injection) applications. The GDI approach through this injector type is very similar to diesel one.
A diesel-like electronically controlled Common Rail injection apparatus has been used for pressure up to 100 MPa. An axially disposed single hole 0.18 mm in diameter and 1.0 mm in length injected a gasoline-like fluid in an optically accessible vessel filled with inert gas (N2) and controlled in pressure up to 1.2 MPa. The jets emerging from the injector hole have been lightened by a pulsed laser sheet at different instant from the start of injection. The images were collected by a CCD camera, synchronized with the light, and processed by professional software to extract the significant parameters of the evolving spray (penetration, cone angle, velocity).
Some results of a work in progress aiming to select and validate proper models for the various stages of spray development are also discussed. Four different models have been compared, to evaluate the one that better represents the characteristics of the generated spray. The final goal of the research activity is to set up the KIVA 3V code for its extensive use in the design and development of GDI engines
Interactively using Semantic Web knowledge: Creating scalable abstractions with FacetOntology
No full textThe amount of knowledge accessible on the Semantic Web is growing, and there is a need for a scalable solution to facilitate exploring that data. Currently approaches to exploring Semantic Web data either focus on exploring resources individually, following links during exploration, and making little use of collated data, or take the approach of collating and aligning multiple sources into one store for one purpose, and hand-crafting a specific browsing interface onto it. We present an approach that provides a scalable browsing interface, which can browse knowledge from the Semantic Web at will. Our approach creates abstractions of knowledge, collated into facets, which are described using FacetOntology. FacetOntology facilitates describing facets from RDF data, suitable for use in creating datasets for faceted browsing
Enhancing Uncertainty Assessment of LAI Remote Sensing Products Through Multiple Collocation Methods and Error Separation Techniques
No full textInformation relating to errors in leaf area index (LAI) remote sensing products is crucial for their applications, yet such information is often difficult to obtain due to the limited availability of field measurements for comprehensive validation. This study is the first to evaluate the applicability of the multiple collocation (MC) methods for LAI product validation and further analyzes error correlation strategies for products at the same scale and the impact of the rescaling procedure. Using the MC approach, we assessed the uncertainties of GLASS, MCD15A2H, VNP15A2H, and Copernicus Land Monitoring Service LAI products across different land cover types in the Heihe River Basin. The results show that, first, the MC method with error separation reduces underestimation of product uncertainty and significantly improves fairness and objectivity in practical applications. Second, the introduction of scaled root-mean-square error as an evaluation metric enabled a clear differentiation between the performance of static error handling and the quantification of dynamic errors. Third, the evaluation framework effectively captures the dynamic errors of products, although the rescaling process requires further optimization. The improved error characterization and validation framework presented here offers a more precise and broadly applicable intercomparison method for LAI product validation, thereby guiding the production of more reliable LAI products
Growth Morphologies and Mechanisms of Non-Equilibrium Solidified MC Carbide
No full textGrowth morphologies and mechanisms of the carbide of group IVB and VB elements (MC carbide), a typical faceted crystal, were studied with an estimated cooling rate from 102 to 105 K/s. Results showed that although the growth morphologies of the MC carbide vary remarkably with solidification cooling rate, the solid/liquid interface is always atomically smooth, and the growth mechanisms are always lateral growth. The growth mechanism transition from lateral to continuous growth mode, which was predicted by the classic crystal growth theory, was not observed for the TiC type MC carbide within the estimated cooling rate range of 102?105 K/s
Intertidal meiofaunal communities in relation to salinity gradients in the Ba Lai river, Vietnam: Quần xã động vật đáy cỡ trung bình trong mối liên hệ với độ mặn trên sông Ba Lai, Việt Nam
Full text linkIn order to reveal the characteristics of meiofaunal communities (MC) (specifically freshwater meiofauna) and its relationship with salinity gradients, meiofauna samples were collected in September 2015 in Ba Lai river (BLR), Mekong river, Vietnam. A total of 14 meiofaunal taxa were identified. The most dominant group was Nematoda, followed by Nauplii and Rotifera. The MC (specifically nematodes) in BLR were characterized by high abundances and diversities. The characteristics of MC in the downstream site (marine habitats) may be a considerable difference from those in the upstream site (fresh habitats). Abundances and diversities of nematode communities in the downstream site were much higher than observed in the upstream site, especially for abundances. Regarding MC, their abundance in the downstream site was also considerably higher than those in upstream site, whereas their diversity in the downstream site was lower than estimated in the upstream site. Furthermore, the Ba Lai dam (BLD) has the ability to change salinity gradients in BLR, while MC were a strong correlation with salinity. Therefore, the MC and their correlation with environmental variables can be considered as a good tool for the effects of dams on river’s ecosystems.
Để xác định các đặc điểm của quần xã động vật đáy cỡ trung bình (đặc biệt là nhóm nước ngọt) và mối liên hệ giữa chúng với độ mặn, mẫu động vật đáy được thu thập vào tháng 09 năm 2015 trên sông Ba Lai, thuộc hệ thống sông Mekong, Việt Nam. Tổng cộng 14 nhóm động vật đáy được ghi nhận, ưu thế nhất là Nematoda, sau đó là Nauplii và Rotifera. Quần xã động vật đáy trên sông Ba Lai có mật độ và đa dạng cao và đặc điểm nhóm nước ngọt (trong đập Ba Lai) khác biệt với nhóm nước mặn (ngoài đập). Mật độ và đa dạng của nhóm Nematoda ngoài đập cao hơn trong đập. Trong khi đó, đa dạng quần xã động vật đáy trong đập cao hơn bên ngoài, mật độ thì ngược lại. Ngoài ra, đập Ba Lai làm biến đổi độ mặn trên sông Ba Lai, trong khi độ mặn có tương quan chặc chẽ với quần xã động vật đáy. Cụ thể, mật độ, đa dạng của quần xã tuyến trùng và mật độ của quần xã động vật đáy cỡ trung bình có tương quan thuận với độ mặn. Ngược lại, độ đa dạng quần xã động vật đáy cỡ trung bình có tương quan nghịch với độ mặn. Cho nên, quần xã động vật đáy có thể sử dụng làm chỉ thị cho tác động của đập chắn lên hệ sinh thái thủy vực
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