The structural stability of the MMgH3 (M=Li, Na, K, Rb, Cs) series has been investigated using the density-functional projector-augmented-wave method within the generalized-gradient approximation. Among the 24 structural arrangements used as inputs for the structural optimization calculations, the experimentally known frameworks are successfully reproduced, and positional and unit-cell parameters are found to be in good agreement with the experimental findings. The crystal structure of LiMgH3 has been predicted, the most stable arrangement being the trigonal LiTaO3-type (R3c) structure, which contains highly distorted octahedra. The formation energy for all members of the MMgH3 series is investigated along different reaction pathways. The electronic density of states reveals that the MMgH3 compounds are wide-band-gap insulators. Analyses of chemical bonding in terms of charge density, charge transfer, electron-localization function, Born effective charge, and Mulliken population show that these hydrides are basically saline hydrides similar to the parent alkali-/alkaline-earth mono-/di-hydrides. 相似文献
We present two proactive resource allocation algorithms, RBA*-FT and OBA-FT, for fault-tolerant asynchronous real-time distributed systems. The algorithms consider an application model where task timeliness is specified by Jensen's benefit functions and the anticipated application workload during future time intervals is described by adaptation functions. In addition, we assume that reliability functions of processors are available a priori. Given these models, our objective is to maximize aggregate task benefit and minimize aggregate missed deadline ratio in the presence of processor failures. Since determining the optimal solution is computationally intractable, the algorithms heuristically compute sub-optimal resource allocations, but in polynomial time. Experimental results reveal that RBA*-FT and OBA-FT outperform their non-fault-tolerant counterparts in the presence of processor failures. Furthermore, RBA*-FT performs better than OBA-FT, although OBA-FT incurs better worst-case and amortized computational costs. Finally, we observe that both algorithms robustly withstand errors in the estimation of anticipated failures. 相似文献
Designing hardware often involves several types of modeling and analysis, e.g., in order to check system correctness, to derive performance properties such as throughput, to optimize resource usages (e.g., buffer sizes), and to synthesize parts of a circuit (e.g., control logic). Working directly with low-level hardware models such as finite-state machines (FSMs) to answer such questions is often infeasible, e.g., due to state explosion. Instead, designers often use dataflow models such as SDF and CSDF, which are more abstract than FSMs, and less expensive to use since they come with more efficient analysis algorithms. However, dataflow models are only abstractions of the real hardware, and often omit critical information. This raises the question, when can one say that a certain dataflow model faithfully captures a given piece of hardware? The question is of more than simply academic interest. Indeed, as illustrated in this paper, dataflow-based analysis outcomes may sometimes be defensive (e.g., buffers that are too big) or even incorrect (e.g., buffers that are too small). To answer the question of faithfully capturing hardware using dataflow models, we develop a formal conformance relation between the heterogeneous formalisms of (1) finite-state machines with synchronous semantics, typically used to model synchronous hardware, and (2) asynchronous processes communicating via queues, used as a formal model for dataflow. The conformance relation preserves performance properties such as worst-case throughput and latency. 相似文献
An algorithm for reconstructing a binary array of size NsxN from its forest of quadtree representation is presented. The algorithm traverses each tree of the forest in preorder and maps each ‘black’ node into the spatial domain. The time complexity in mapping is O(log N × Bn + Bp), where Bn is the number of black nodes in the forest and Bp is the number of black pixels in the N × N array. The algorithm has been implemented on an Apple II. 相似文献
From gradient-corrected, all-electron, full-potential, density-functional calculations, including structural relaxation, it is shown that the metal-hydride series RTInH1.333 (R=La, Ce, Pr, or Nd; T=Ni, Pd, or Pt) violate the “2-Å” rule as well as the hole-size requirement. These hydrides possess unusually short H–H separations which in the most extreme case for LaPtInH1.333 is as short as 1.454 Å. These findings have been analyzed in terms of charge density, charge transfer, electron-localization function, crystal-orbital Hamilton population, and density of states analyses. From high-pressure studies it is predicted several successive pressure-induced structural transitions in MgH2 within the 20 GPa range. Calculations have also shown several pressure-induced structural transitions in alkali aluminum tetrahydrides with large volume reductions at the phase-transition points and small energy differences between the ambient-pressure and subsequent high-pressure phases. 相似文献
Electrical conductivity (77–300K) and magnetic susceptibility (4.2–300K) of rutile type polycrystalline samples of CrVNbO6, FeVNbO6 and NiV2Nb2O10 are reported. All three compounds are n-type semiconductors with room termperature resistivities of the order of 102–103 ohm-cm. CrVNbO6 shows ferromagnetic coupling in the high temperature region and orders antiferromagnetically below 10K. FeVNbO6 trans-forms to a spin glass state below 20K. NiV2Nb2O10 shows evidence of weak antiferromagnetic interactions. The transport properties of the compounds are discussed in terms of structural properties and unpaired d electrons present on the respective transition metal ions. 相似文献
This paper surveys the applications of multi-criteria decision making (MCDM) methods to production planning, scheduling, and sequencing problems. The basic structure of the decision models are described by their objectives and the resulting models are classified by decision variables into the areas of Aggregate Production Planning, Disaggregate Production Planning, Production Scheduling, and Single Machine Sequencing. The problem sizes that have been solved are summarized to determine how practical it is to use MCDM. 相似文献
The potential of diet acidification to overcome the digestive insufficiency and postweaning lag in early weaned pigs is examined in the review. A survey of published data on various types of acidifiers reveal considerable variation in response to acidification of weaner diets. Several reasons may be proposed to explain the inconsistencies in response, these include differences in diet type, age of pigs, type and level of acidifier, and existing performance levels. Reducing the gastric pH does not appear to be the primary effect of acidifiers. Acidification, however, consistently suppressed pathogenic coliforms in the gastrointestinal tract. Future developments in the use of acidifiers would be intrinsically linked to the understanding of their mode(s) of action in the animal. 相似文献
Tinker AFB (TAFB) is the prime Air Force rework facility for jet engine parts that support standard engines. The wear and tear on the engine parts of the various aircraft currently produces about 10 million individual requirements annually for part inspection and subsequent discard or rework. Past practices have resulted in extremely long flow times for rework and a burgeoning requirement for conveyor capacity.
A new concept, called the Modular Repair Center (MRC), is being implemented to correct the problem. The MRC's have most of the processes necessary to inspect and repair components of a given engine assembly. They have the advantage of reducing the number of long moves, giving more accountability for quality and better tracking. A large network model of TAFB facility has been developed to determine the required work-in-process storage, conveyor capacity, shortest routes for parts to flow from one MRC to another and the maximum flow along each conveyor section. The model was analyzed using Floyd's shortest route algorithm. It resulted in reducing the “bottlenecks” on certain conveyor sections by rerouting some of the flow along low density traffic links and thus reducing the need for extra conveyor capacity. Simple formulas were designed to estimate the number of pallets generated by disassembly and each MRC to provide the demand requirements for conveyor capacity. 相似文献
A gravimetric method using an eledrodynamic balance was developed for the measurement of transport properties such as the diffusion coefficient, D, solubility, S, and permeability, P, for oxygen into thin layers of asphalt materials deposited on aggregate and glass particles. Glass spheres and aggregate particles in the 14 to 50 μm size range coated with asphalt materials (AAB1, AAG1, and AAK1) were suspended contactless in the balance to measure D, S, and P in the temperature range 21 to 61° C. Transport parameters were determined from the changes in the particle mass due to the uptake of oxygen by the asphalt coating on glass spheres and nonspherical aggregate particles. 相似文献