Precision of micromilled x-ray masks and exposures

 Micromechanical milling has been shown to be a rapid and direct method for the fabrication of structures with the geometry and size suitable for use as x-ray mask absorbers. While the micromilling process can not duplicate the size and resolution of absorber patterns created by high energy electron beam or optical lithography methods, micromilling can repeatedly create absorber line widths down to 10 micrometers, or less, with a one-sigma tolerance of 0.5 micrometers. A method for easily characterizing milling tool run out has been adapted so tool change out can be more routine. The milling process leaves some absorber burrs and the absorber is apparently tapered at the machined wall which introduce process biases, both of which add to exposure degradation. Nevertheless, based on work to date, it appears both of these effects can be reduced to acceptable limits. Received: 25 August 1997/Accepted: 3 September 1997     

Effect of moisture and particle size on the extractability of oils from seeds with supercritical CO2

Moisture level and particle size of soybeans, peanuts and cottonseed were correlated with the extraction rate and yield of oil when extracted with supercritical carbon dioxide (SC-CO₂) at a constant temperature (50 C) and pressure (8000 psig). The rate of extraction and ultimate oil yields were quite low with cracked soybeans. However, good extraction rates and nearly theoretical oil yields were obtained from ground or thinly flaked (<0.010″) seeds. Moisture levels between 3% and 12% had little effect on extracability. Oil composition was not influenced by either parameter. Scanning electron microscopy was used to study seed structure before and after extraction with SC-CO₂. Micrographs of SC-CO₂-extracted seeds were similar to hexane-extracted seeds. Presented at the AOCS Meeting, May 1983, Chicago.     

Potential synthetic lubricants: Diol ester of C18-saturated cyclic acids

Monoalkyl esters of linseed-oil-derived C₁₈-saturated cyclic acids (HCal), described in earlier work, showed promise as lubricant base stocks for turbine aircraft as set forth in the military specification MIL-L-7808E. These esters, however, did not exhibit the increased oxidative stability and higher viscosity required by the more recent specification MIL-L-23699. Six diol esters of HCal have now been prepared. Both hindered and unhindered dihydric alcohols were used, including ethylene glycol, 1,4-cyclohexanedimethanol, 1,4-benzenedimethanol, 2,3-dimethyl-1,3-propanediol and 2,2,4,4-tetramethyl-1,3-cyclobutanediol (I). The viscosities of these esters at 210F ranged from 10.1 to 19.6 centistokes and the pour points, from −35 to −62F. Oxidative stabilities at 400F were determined with 0.5% each of phenyl-a-napthylamine (PANA) andp,p’-dioctyldiphenylamine as inhibitors. The esters of the unhindered diols had poor stability, whereas esters of the hindered diols, in particular I, exhibited excellent resistance to the formation of acidic decomposition products and sludge. Although the HCal ester of I by itself is too viscous to meet specification MIL-L-23699, its ASTM slope (0.650) is excellent. Blends of this material with less viscous hindered esters, commercially available, may find application as lubricants for high-performance turbine engines used in various aircraft. Presented at the AOCS Meeting in Los Angeles, 1966. No. Utiliz. Res. Dev. Div., ARS, USDA.     

Cis-Unsaturated fatty acid products by hydrogenation with chromium hexacarbonyl

The use of Cr(CO)₆ was investigated to convert polyunsaturated fats intocis unsaturated products. With methyl sorbate, the same order of selectivity for the formation ofcis-3-hexenoate was demonstrated for Cr(CO)₆ as for the arene-Cr(CO)₃ complexes. With conjugated fatty esters, the stereoselectivity of Cr(CO)₆ toward thetrans, trans diene system was particularly high in acetone. However, this solvent was not suitable at elevated temperatures required to hydrogenatecis, trans- andcis, cis-conjugated dienes (175 C) and nonconjugated soybean oil (200 C). Reaction parameters were analyzed statistically to optimize hydrogenation of methyl sorbate and soybean oil. To achieve acceptable oxidative stability, it is necessary to reduce the linolenate constituent of soybean oil below 1–3%. When this is done commercially with conventional heterogenous catalysts, the hydrogenated products contain more than 15%trans unsaturation. By hydrogenating soybean oil with Cr(CO)₆ (200 C, 500 psi H₂, 1% catalyst in hexane solution), the product contains less than 3% each of linolenate andtrans unsaturation. Recycling of Cr(CO)₆ catalyst by sublimation was carried through three hydrogenations of soybean oil, but, about 10% of the chromium was lost in each cycle by decomposition. The hydrogenation mechanism of Cr(CO)₆ is compared with that of arene-Cr(CO)₃ complexes. Presented in part at Seventh Conference on Catalysis in Organic Syntheses, Chicago, Illinois, June 5–7, 1978.     

Computing presentations for subgroups of polycyclic groups and of context-free groups

Algorithms for solving uniform decision problems for algebraic structures crucially depend on the chosen finite presentations for the structures under consideration. Rewriting techniques have been used very successfully to solve uniform decision problems, when the presentations considered involve finite, noetherian, and ()-confluent rewriting systems. Whenever the class of algebraic structures considered is closed under the operation of taking finitely generated substructures, then the algorithms for solving the uniform decision problems can be applied to the substructures as well. However, since these algorithms depend on the form of the presentations, this involves the task of constructing a presentation of a certain form for a substructure given a presentation of this form for the structure itself and a finite set of generating elements for the substructure.This problem, which has received a lot of attention in algebra, is here investigated from an algorithmic point of view. The structures considered are the following two classes of groups, which have been studied extensively before: the polycyclic groups and the context-free groups.Finitely generated context-free groups can be presented by finite, monadic, and -confluent string-rewriting systems. Due to their nice algorithmic properties these systems provide a way to effectively solve many decision problems for context-free groups. Since finitely generated subgroups of context-free groups are again contextfree, they can be presented in the same way. Here we describe a process that, from a finite, monadic, and -confluent string-rewriting system presenting a context-free groupG and a finite subsetU ofG, determines a presentation of this form for the subgroup U ofG that is generated byU. For finitely presented polycyclic groups we obtain an analogous result, when we use finite confluent PCP2-presentations to describe these groups.This work was performed while this author was visiting at the Fachbereich Informatik, Universität Kaiserslautern, during his sabbatical 1991/92     

Intradermal and subcutaneous leiomyosarcoma: a clinicopathological and immunohistochemical study of 41 cases

Superficial leiomyosarcomas are rare tumours. The lesions confined to the dermis, contrary to those involving the subcutis, have been reported to carry a favourable prognosis. A retrospective study of 41 consecutive cases of surgically treated intradermal and subcutaneous leiomyosarcomas was undertaken in order to determine the prognostic factors that may influence the survival of these patients. Seven tumours were predominantly intradermal and 34 involved the subcutaneous tissue. Fifty-four percent of the tumours were located in the lower extremities. All cases stained positively for smooth muscle antigen and 66% for desmin. The tumours were classified with regard to tumour grade I (low grade, 3%), II (intermediate, 12%), IIIA (high grade, 46%) and IIIB (high grade, 39%). In all patients, follow-up information was available. Mean follow-up time was 5 years. The patients with intradermal tumours were all alive without signs of recurrence, whereas 14 of those with leiomyosarcomas involving the subcutis have died with pulmonary metastases. Our study confirms that "pure" intradermal leiomyosarcomas independent of tumour grade behave in a benign fashion, probably due to small tumour size. Tumour size > or = 5 cm, deep localization with fascia involvement, and high malignancy grade (IIIB) were found to deteriorate survival based on a univariate analysis. However, in a multivariate analysis only tumour size was found to be an independent prognostic factor.     

Parallel communicating grammar systems with regular control and skeleton preserving FRR automata

Parallel communicating grammar systems with regular control (RPCGS, for short) are introduced, which are obtained from returning regular parallel communicating grammar systems by restricting the derivations that are executed in parallel by the various components through a regular control language. For the class of languages that are generated by RPCGSs with constant communication complexity we derive a characterisation in terms of a restricted type of freely rewriting restarting automaton. From this characterisation we obtain that these languages are semi-linear, and that for RPCGSs with constant communication complexity, the centralised variant has the same generative power as the non-centralised variant.     

Identification of statistical patterns in complex systems via symbolic time series analysis

Identification of statistical patterns from observed time series of spatially distributed sensor data is critical for performance monitoring and decision making in human-engineered complex systems, such as electric power generation, petrochemical, and networked transportation. This paper presents an information-theoretic approach to identification of statistical patterns in such systems, where the main objective is to enhance structural integrity and operation reliability. The core concept of pattern identification is built upon the principles of Symbolic Dynamics, Automata Theory, and Information Theory. To this end, a symbolic time series analysis method has been formulated and experimentally validated on a special-purpose test apparatus that is designed for data acquisition and real-time analysis of fatigue damage in polycrystalline alloys.