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1.
The UK's vast marine energy resource is mostly located in remote areas west and north of Scotland, and transmission of this energy to the mainland will be required. This may be achieved by using this ‘stranded’ power to generate hydrogen electrolytically, which may in turn be stored or transported using sponge iron technology. This paper reviews the technology and research needed to bring such a process on stream. We propose utilising techniques that have been developed for the oxygen carriers used in chemical looping, and also those used in early processes for hydrogen generation in the chemical industry. We briefly outline the design requirements for an energy efficient sponge iron plant. It is shown that the iron sponge system presents better energy efficiencies than alternative forms of bulk storage such as liquid hydrogen, magnesium hydride slurry, some at least of the metal hydrides, or methylcyclohexane–toluene–hydrogen, provided that requirements can be met for particle durability and reactivity. 相似文献
2.
Dominic D. J. Chandar Jayanarayanan Sitaraman Dimitri Mavriplis 《The Journal of supercomputing》2014,67(1):47-68
The application of graphics processing units (GPU) to solve partial differential equations is gaining popularity with the advent of improved computer hardware. Various lower level interfaces exist that allow the user to access GPU specific functions. One such interface is NVIDIA’s Compute Unified Device Architecture (CUDA) library. However, porting existing codes to run on the GPU requires the user to write kernels that execute on multiple cores, in the form of Single Instruction Multiple Data (SIMD). In the present work, a higher level framework, termed CU++, has been developed that uses object oriented programming techniques available in C++ such as polymorphism, operator overloading, and template meta programming. Using this approach, CUDA kernels can be generated automatically during compile time. Briefly, CU++ allows a code developer with just C/C++ knowledge to write computer programs that will execute on the GPU without any knowledge of specific programming techniques in CUDA. This approach is tremendously beneficial for Computational Fluid Dynamics (CFD) code development because it mitigates the necessity of creating hundreds of GPU kernels for various purposes. In its current form, CU++ provides a framework for parallel array arithmetic, simplified data structures to interface with the GPU, and smart array indexing. An implementation of heterogeneous parallelism, i.e., utilizing multiple GPUs to simultaneously process a partitioned grid system with communication at the interfaces using Message Passing Interface (MPI) has been developed and tested. 相似文献
3.
Retrograde densification of pelletized calcines and glasses having an approximate (Bi,Pb)2 Sr2 Ca2 Cu3 O10 starting stoichiometry and sintered at ∼850°C can be described by first-order rate equations. Retrograde densification in the calcine precursors was largely due to the development of open pores, and was approximately proportional to the concentration of the (Bi,Pb)2 Sr2 CaCu3 O10 phase. In the glasses, retrograde densification is mainly caused by porosity accompanying the growth of a needlelike Sr─Ca─Cu─O phase, together with (Bi,Pb)2 Sr2 Ca2 Cu3 O10 and (Bi,Pb)2 Sr2 CaCu2 O8 . 相似文献
4.
High Conductivity in Molecularly p‐Doped Diketopyrrolopyrrole‐Based Polymer: The Impact of a High Dopant Strength and Good Structural Order 下载免费PDF全文
Yevhen Karpov Tim Erdmann Ivan Raguzin Mahmoud Al‐Hussein Marcus Binner Uwe Lappan Manfred Stamm Kirill L. Gerasimov Tetyana Beryozkina Vasiliy Bakulev Denis V. Anokhin Dimitri A. Ivanov Florian Günther Sibylle Gemming Gotthard Seifert Brigitte Voit Riccardo Di Pietro Anton Kiriy 《Advanced materials (Deerfield Beach, Fla.)》2016,28(28):6003-6010
5.
Surrogate modeling approximation using a mixture of experts based on EM joint estimation 总被引:1,自引:1,他引:0
Dimitri Bettebghor Nathalie Bartoli Stéphane Grihon Joseph Morlier Manuel Samuelides 《Structural and Multidisciplinary Optimization》2011,43(2):243-259
An automatic method to combine several local surrogate models is presented. This method is intended to build accurate and
smooth approximation of discontinuous functions that are to be used in structural optimization problems. It strongly relies
on the Expectation−Maximization (EM) algorithm for Gaussian mixture models (GMM). To the end of regression, the inputs are
clustered together with their output values by means of parameter estimation of the joint distribution. A local expert is
then built (linear, quadratic, artificial neural network, moving least squares) on each cluster. Lastly, the local experts
are combined using the Gaussian mixture model parameters found by the EM algorithm to obtain a global model. This method is
tested over both mathematical test cases and an engineering optimization problem from aeronautics and is found to improve
the accuracy of the approximation. 相似文献
6.
Approximate policy iteration: a survey and some new methods 总被引:2,自引:0,他引:2
Dimitri P. BERTSEKAS 《控制理论与应用(英文版)》2011,9(3):310-335
We consider the classical policy iteration method of dynamic programming(DP),where approximations and simulation are used to deal with the curse of dimensionality.We survey a number of issues:convergence and rate of convergence of approximate policy evaluation methods,singularity and susceptibility to simulation noise of policy evaluation,exploration issues,constrained and enhanced policy iteration,policy oscillation and chattering,and optimistic and distributed policy iteration.Our discussion of policy evaluation is couched in general terms and aims to unify the available methods in the light of recent research developments and to compare the two main policy evaluation approaches:projected equations and temporal differences(TD),and aggregation.In the context of these approaches,we survey two different types of simulation-based algorithms:matrix inversion methods,such as least-squares temporal difference(LSTD),and iterative methods,such as least-squares policy evaluation(LSPE) and TD(λ),and their scaled variants.We discuss a recent method,based on regression and regularization,which recti?es the unreliability of LSTD for nearly singular projected Bellman equations.An iterative version of this method belongs to the LSPE class of methods and provides the connecting link between LSTD and LSPE.Our discussion of policy improvement focuses on the role of policy oscillation and its effect on performance guarantees.We illustrate that policy evaluation when done by the projected equation/TD approach may lead to policy oscillation,but when done by aggregation it does not.This implies better error bounds and more regular performance for aggregation,at the expense of some loss of generality in cost function representation capability.Hard aggregation provides the connecting link between projected equation/TD-based and aggregation-based policy evaluation,and is characterized by favorable error bounds. 相似文献
7.
Xiaoying Wu Dimitri Theodoratos Calisto Zuzarte 《The VLDB Journal The International Journal on Very Large Data Bases》2010,19(5):661-686
The streaming evaluation is a popular way of evaluating queries on XML documents. Besides its many advantages, it is also
the only option for a number of important XML applications. Unfortunately, existing algorithms focus almost exclusively on
tree-pattern queries (TPQs). Requirements for flexible querying of XML data have motivated recently the introduction of query
languages that are more general and flexible than TPQs. These languages are not supported by existing algorithms. In this
paper, we consider a partial tree-pattern query (PTPQ) language which generalizes and strictly contains TPQs. PTPQs can express
a fragment of XPath which comprises reverse axes and the node identity equality (is) operator, in addition to forward axes, wildcards and predicates. They constitute an important subclass of XPath, which is
very useful in practice. Unfortunately, previous streaming algorithms for TPQs cannot be applied to PTPQs. PTPQs can be represented
as dags enhanced with constraints. We explore this representation to design an original polynomial time streaming algorithm
for PTPQs. Our algorithm aggressively filters incoming data that is irrelevant to the query and wisely avoids processing redundant
query matches (i.e., matches of the query dag that do not contribute to new solutions). Our algorithm is the first one to
support the streaming evaluation of such a broad fragment of XPath. We provide an analysis of it, and conduct an extensive
experimental evaluation of its performance and scalability. Compared to the only known streaming algorithm that supports TPQs
extended with reverse axes, our algorithm performs better by orders of magnitude while consuming a much smaller fraction of
memory space. Current streaming applications have stringent requirements on query response time and memory consumption because
of the large (possibly unbounded) size of data they handle. In order to keep memory usage and CPU consumption low for the
PTPQ streaming evaluation, we design another streaming algorithm called Eager PSX for PTPQs. Its key feature is that it applies an eager evaluation strategy to quickly determine when node matches should
be returned as solutions to the user and also to proactively detect redundant matches. We theoretically analyze Eager PSX, and experimentally test its time and space performance and scalability. We compare it with PSX. Our results show that Eager PSX not only achieves better space performance without compromising time performance, but it also greatly improves query response
time for both simple and complex queries, in many cases, by orders of magnitude. 相似文献
8.
Xiaoying Wu Dimitri Theodoratos Stefanos Souldatos Theodore Dalamagas Timos Sellis 《World Wide Web》2010,13(4):441-474
Finding the occurrences of structural patterns in XML data is a key operation in XML query processing. Existing algorithms
for this operation focus almost exclusively on path patterns or tree patterns. Current applications of XML require querying
of data whose structure is complex or is not fully known to the user, or integrating XML data sources with different structures.
These applications have motivated recently the introduction of query languages that allow a partial specification of path
patterns in a query. In this paper, we consider partial path queries, a generalization of path pattern queries, and we focus
on their efficient evaluation under the indexed streaming evaluation model. Our approach explicitly deals with repeated labels
(that is, multiple occurrences of the same label in a query). We show that partial path queries can be represented as rooted
dags for which a topological ordering of the nodes exists. We present three algorithms for the efficient evaluation of these
queries. The first one exploits a structural summary of data to generate a set of path patterns that together are equivalent
to a partial path query. To evaluate these path patterns, we extend a previous algorithm for path-pattern queries so that
it can work on path patterns with repeated labels. The second one extracts a spanning tree from the query dag, uses a stack-based
algorithm to find the matches of the root-to-leaf paths in the tree, and merge-joins the matches to compute the answer. Finally,
the third one exploits multiple pointers of stack entries and a topological ordering of the query dag to apply a stack-based
holistic technique. We analyze our algorithms and perform extensive experimental evaluations. Our experimental results show
that the holistic algorithm outperforms the other ones. Our approaches are the first ones to efficiently evaluate this class
of queries in the indexed streaming model. 相似文献
9.
Maarten Houbraken Sofie Demeyer Dimitri Staessens Pieter Audenaert Didier Colle Mario Pickavet 《Natural computing》2013,12(2):277-289
Physarum polycephalum, a true slime mould, is a primitive, unicellular organism that creates networks to transport nutrients while foraging. The design of these natural networks proved to be advanced, e.g. the slime mould was able to find the shortest path through a maze. The underlying principles of this design have been mathematically modelled in literature. As in real life the slime mould can design fault tolerant networks, its principles can be applied to the design of man-made networks. In this paper, an existing model and algorithm are adapted and extended with stimulation and migration mechanisms which encourage formation of alternative paths, optimize edge positioning and allow for automated design. The extended model can then be used to better design fault tolerant networks. The extended algorithm is applied to several national and international network configurations. Results show that the extensions allow the model to capture the fault tolerance requirements more accurately. The resulting extended algorithm overcomes weaknesses in geometric graph design and can be used to design fault tolerant networks such as telecommunication networks with varying fault tolerance requirements. 相似文献
10.
The neuroimaging community heavily relies on statistical inference to explain measured brain activity given the experimental paradigm. Undeniably, this method has led to many results, but it is limited by the richness of the generative models that are deployed, typically in a mass-univariate way. Such an approach is suboptimal given the high-dimensional and complex spatiotemporal correlation structure of neuroimaging data.Over the recent years, techniques from pattern recognition have brought new insights into where and how information is stored in the brain by prediction of the stimulus or state from the data. Pattern recognition is intrinsically multivariate and the underlying models are data-driven. Moreover, the predictive setting is more powerful for many applications, including clinical diagnosis and brain–computer interfacing. This special issue features a number of papers that identify and tackle remaining challenges in this field. The specific problems at hand constitute opportunities for future research in pattern recognition and neurosciences. 相似文献