PECVD of diamond-like carbon (a-C:H) from the decomposition of methane in a high-density inductively coupled discharge

The paper describes an experimental investigation of the diamond-like carbon deposition process from methane precursor with an innovative high-density inductively coupled plasma source. It appears that a high plasma density allows a fast growth of diamond-like carbon coatings exhibiting a high hardness. In contrast to what is usually found in the literature, it seems that the ion species participate significantly to the growth of the carbon film when exposed to a high ion flux.     

Low-temperature pyroelectric properties of Li<Subscript>2</Subscript>SO<Subscript>4</Subscript>

The pyroelectric properties of lithium sulfate have been studied theoretically on the hypothesis of a pseudosymmetry of the structure of its polar phase. Analytical expressions are proposed for the temperature dependences of its pyroelectric polarization and pyroelectric coefficient at low temperatures and near the polymorphic transformation. The pyroelectric and piezoelectric coefficients of a polar crystal are shown to be in direct proportion.     

Results of testing a centrifugal bubble singlet-oxygen generator

The results of parametric tests of a centrifugal bubble singlet-oxygen generator based on the reaction of chlorine with an alkaline hydrogen peroxide solution have been given. The utilization of chlorine grows with bubble-layer height, whereas the relative content of O₂(¹Δ) remains constant. Growth in centrifugal acceleration leads to a more efficient utilization of chlorine. A specific oxygen output of more than 1 mmole·cm⁻²·sec⁻¹ from the bubble layer for a degree of chlorine utilization of ∼95% and a singlet-oxygen yield of more than 50% has been attained. It has been shown that a centrifugal bubble singlet-oxygen generator is an efficient energy source for an oxygen-iodine laser. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 80, No. 3, pp. 121–128, May–June, 2007.     

Low loss guided wave propagation in a left-handed microstrip structure using dispersive split ring?rod combination metamaterial

Split ring-rod combination metamaterial is used as a substrate material in a microstrip guided wave structure to determine what the effect is of a material with potentially excessive dispersion or loss or both. A Green's function method readily incorporates the metamaterial permittivity and permeability tensor characteristics. Ab initio calculations are performed to obtain the dispersion diagrams of several complex propagation constant modes of the structure. Analytical analysis is done for the design and interpretation of the results, which demonstrate remarkable potential for realistic use in high frequency electronics, while showing modes with extremely low loss bands.     

Singular Trajectories in Multi-Input Time-Optimal Problems: Application to Controlled Mechanical Systems

This paper deals with the time-optimal control problem for a class of control systems which includes controlled mechanical systems with possible dissipation terms. The Lie algebras associated with such mechanical systems have certain special properties. These properties are explored and used in conjunction with the Pontryagin maximum principle to determine the structure of singular extremals and, in particular, time-optimal trajectories. The theory is illustrated by an application to a time-optimal problem for a class of underwater vehicles.     

Development of Free-Electron x-Ray Lasers on the TESLA Test Accelerator (DESY, Germany)

The program for developing free-electron x-ray lasers at TESLA started in 1994. The plan is to use the TESLA test accelerator to develop an x-ray laser with minimum wavelength 0.1–6 nm. The first phase of the project was successfully completed in 2001. At saturation, the laser produces ultrashort 30–100 fsec, gigawatt, radiation pulses. The wavelength can be tuned smoothly over the range 80–120 nm.     

Inference of message sequence charts

Software designers draw message sequence charts for early modeling of the individual behaviors they expect from the concurrent system under design. Can they be sure that precisely the behaviors they have described are realizable by some implementation of the components of the concurrent system? If so, can we automatically synthesize concurrent state machines realizing the given MSCs? If, on the other hand, other unspecified and possibly unwanted scenarios are "implied" by their MSCs, can the software designer be automatically warned and provided the implied MSCs? In this paper, we provide a framework in which all these questions are answered positively. We first describe the formal framework within which one can derive implied MSCs and then provide polynomial-time algorithms for implication, realizability, and synthesis.     

Itemset trees for targeted association querying

Association mining techniques search for groups of frequently co-occurring items in a market-basket type of data and turn these groups into business-oriented rules. Previous research has focused predominantly on how to obtain exhaustive lists of such associations. However, users often prefer a quick response to targeted queries. For instance, they may want to learn about the buying habits of customers that frequently purchase cereals and fruits. To expedite the processing of such queries, we propose an approach that converts the market-basket database into an itemset tree. Experiments indicate that the targeted queries are answered in a time that is roughly linear in the number of market baskets, N. Also, the construction of the itemset tree has O(N) space and time requirements. Some useful theoretical properties are proven.     

Fatigue Behavior and Retrofit Investigation of Distortion-Induced Web Gap Cracking

This paper studies a Kansas Department of Transportation welded plate girder bridge that developed fatigue cracks at small web gaps close to the girder top flange. Repair had been previously performed by softening the connection plate end with a slot retrofit, but cracks were recently found to have reinitiated at some of the repaired details and are again propagating. A comprehensive finite-element method study was performed to investigate the cracking behavior observed in the bridge and to recommend appropriate measures for future bridge retrofit. The analytical results show that stresses developed at the top flange web gaps could exceed yielding under the loading of an HS15 fatigue truck. The current slot repair used in the bridge was found to have introduced higher magnitude fatigue stresses in the web gap. To achieve a permanent repair of the bridge, it is recommended that a welded connection plate to flange attachment be used during future bridge retrofit. The web gap details should be able to withstand unlimited number of load cycles once this additional repair is performed.     

Challenges in the Application of Stochastic Modal Identification Methods to a Cable-Stayed Bridge

This paper presents an analysis of the data collected in the ambient vibration test of the International Guadiana cable-stayed Bridge, which links Portugal and Spain, based on different output-only identification techniques: peak-picking, frequency domain decomposition, covariance-driven stochastic subspace identification, and data-driven stochastic subspace identification. The purpose of the analysis is to compare the performance of the four techniques and evaluate their efficiency in dealing with specific challenges involved in the modal identification of the tested cable-stayed bridge, namely the existence of closely spaced modes, the perturbation produced by the local vibration of stay-cables, and the variation of modal damping coefficients with wind velocity. The identified natural frequencies and mode shapes are compared with the corresponding modal parameters provided by a previously developed numerical model. Additionally, the variability of some modal damping coefficients is related with the variation of the wind characteristics and associated with a component of aerodynamic damping.