Fabrication and characterization of freestanding ultrathin diamond-like carbon targets for high-intensity laser applications

Here, we report the fabrication of diamond-like carbon (DLC) thin films using pulsed laser deposition (PLD). PLD is a well-established technique for deposition of high-quality DLC thin films. Carbon tape target was ablated using a KrF (248 nm, 25 ns, 20 Hz) excimer laser to deposit DLC films on soap-coated substrates. A laser fluence between 8.5 and 14 J/cm² and a target to substrate distance of 10 cm was used. These films were then released from substrates to obtain freestanding DLC thin foils. Foil thicknesses from 20 to 200 nm were deposited using this technique to obtain freestanding targets of up to 1-inch square area. Typically, 100-nm-thick freestanding DLC films were characterized using different techniques such as AFM, XPS, and nano-indentation. AFM was used to obtain the film surface roughness of 9 nm rms of the released film. XPS was utilized to obtain 74 % sp², 23 % sp³, and 3 % C–O bond components. Nano-indentation was used to characterize the film hardness of 10 GPa and Young’s modulus of 110 GPa. Damage threshold properties of the DLC foils were studied (1,064 nm, 6 ns) and found to be 7 × 10¹⁰ W/cm² peak intensity for our best ultrathin DLC foils.     

Circulant Double Coverings of a Circulant Graph of Valency Four

Several isomorphism classes of graph coverings of a graph G have been enumerated by many authors (see [3], [8]–[15]). A covering of G is called circulant if its covering graph is circulant. Recently, the authors [4] enumerated the isomorphism classes of circulant double coverings of a certain kind, called typical, and showed that no double covering of a circulant graph of valency 3 is circulant. In this paper, the isomorphism classes of connected circulant double coverings of a circulant graph of valency 4 are enumerated. As a consequence, it is shown that no double covering of a non-circulant graph G of valency 4 can be circulant if G is vertex-transitive or G has a prime power of vertices. The first author is supported by NSF of China (No. 60473019) and by NKBRPC (2004CB318000), and the second author is supported by Com²MaC-KOSEF (R11-1999-054) in Korea.     

Modification of microstructures and physical properties of ultra high molecular weight polyethylene by electron beam irradiation

An ultra high molecular weight polyethylene was irradiated with the electron beam at dose levels ranging from 100 kGY to 1 MGy. The microstructures of the irradiated samples were characterized by FTIR, gel fraction measurement, DSC, and small‐ and wide‐angle X‐ray scattering. For the mechanical properties, a static tensile test and creep experiment were also performed. The crosslinking and the crystal morphology changes were the main microstructural changes to influence the mechanical properties. It was found that 250 kGy appeared to be the optimal dose level to induce crosslinks in the amorphous area and recrystalliztion in the crystal lamellae. At doses above 250 kGy, the electron beam penetrates into the crystal domains, resulting in crosslinks in the crystal domains and reduction in the crystal size and crystallinity. The static mechanical properties (modulus, strength) and the creep resistance were enhanced by the electron beam irradiation. The stiffness rather correlated with the degree of crosslinks while the strength with the crystal morphology. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3019–3029, 2005     

Formation of reissert analogs from benzimidazole and use of carboxylic acids in a retro-reissert reactionReissert Analogs from Benzimidazole

Reissert analogs have been formed in high yields from benzimidazole using trimethylsilyl cyanide and chloroformates. A retro-Reissert reaction can be effected on the products, their carbon-2 alkylated derivatives and benzothiazole analogs, by treatment with hexanoic or benzoic acids.     

A Discrete Effect of the Thermal Lattice BGK Model

In this article, a discrete effect in the thermal Lattice BGK two-speed model is studied. These effects are due to the non-equilibrium state in the particle distribution function, and the non-equilibrium occurs near walls. The mechanism of the LBM counterpart of the thermal creep flow, which appears due to the temperature gradient of the boundary in rarefied gases, is clarified analytically and numerical calculations are performed for some cases. A technique for eliminating this effect is also shown.     

Small sample properties of generalized logit model estimators with bootstrap

The generalized logit model of nominal type with random regressors is studied for bootstrapping. We assess the accuracy of some estimators for our generalized logit model, using a Monte Carlo simulation. That is, we study the finite sample properties containing the consistency and asymptotic normality of the maximum likelihood estimators. Also, we compare Newton Raphson algorithm with BHHH algorithm.     

Generalized vector variational inequality and fuzzy extension

A generalized vector variational inequality (GVVI) is considered. We establish the existence theorem for (GVVI) under assumptions of C-pseudomonotonicity and V-hemicontinuity. From our existence theorem, we obtain the fuzzy extension of a result of Chen and Yang.     

Monitoring process for attributes with quality deterioration and diagnosis errors

The aim of this paper is to present an online economical quality-control procedure for attributes in a process subject to quality deterioration after random shift and misclassification errors during inspections. The process starts in control (State I) and, in a random time, it shifts to out of control (State II). Once at State II, the non-conforming fraction increases according to a non-decreasing function ψ(z), where z is the number of items produced after a shift. The monitoring procedure consists of inspecting a single item at every m produced items, which is examined r times independently to decide its condition. Once an inspected item is declared non-conforming, the process is stopped and adjusted. A direct search technique is used to find the optimum parameters which minimize the expected cost function. The proposed model is illustrated by a numerical example. Copyright © 2007 John Wiley & Sons, Ltd.