An instrument for manufacturing zone-plates by using a lathe

A laser writing system is developed in order to manufacture precise and inexpensive zone-plates. The zone-plates are a key component of an interferometer that measures shape error of spherical or aspherical mirrors on an ultrapecision lathe. The laser writer is mounted on the sliding table of the lathe. A glass plate coated with photoresist is attached to a chuck of the lathe and rotated. The zone-plate grating is written on the glass plate by a focused laser beam. Zone-plate writing is sped up by reducing the necessary number of computer instructions, causing no loss in the accuracy of the zone-plate. The accuracy of the zone-plate obtained by this inexpensive method is 0.1 μm and the same as that achieved by an electron beam writer.     

Photodegradation of polymer materials containing flame-cut agents

Photodegradation of incombustible materials [polystyrene (PSt) and polypropyrene (PP) containing 2 wt% of decabromodiphenyl oxide (DBDE) or tetrabromobisphenol-A (TBA) as a flame-cut agent] were studied using Okazaki Large Spectrograph (OLS). Samples were irradiated in air at 23°C with monochromatic light of wavelengths at 260, 280, 300, 320, 340, and 360 nm, UV-visible spectra and FTIR spectra were measured to identify the chemical structural changes of the polymers. Number of chain scissions, which is a measure of the polymer degradation, was estimated from the results of GPC measurements. It was found that the photostability of PP and PSt was reduced by the addition of DBDE or TBA. Photodegradation of these polymers took place by the irradiation of the light of wavelengths lower than 320 and 360 nm for the polymers containing TBA and DBDE, respectively. The most effective irradiation wavelengths for main chain scission are found to be 260–280 and 300 nm for PP or PSt–TBA samples and PP or PSt–DBDE samples, respectively. © 1993 John Wiley & Sons, Inc.     

In situ quantitative analysis of etching process of human teeth by atomic force microscopy

Etching is one of the most fundamental steps in the restoration of teeth by adhesion of composite resin in dental clinics. Atomic force microscope (AFM) was used for the in situ observation of the etching process of human enamel, dentin and synthetic hydroxyapatite in the three different acid agents, 2% phosphoric acid, 10% citric acid and 10% polyacrylic acid. To measure the absolute depth from the initial level before etching and to correlate the surface height between the changing AFM images obtained, the depth profiles were recorded with etching time by carrying out the line scan consecutively at the representative place of the observed area. These chronological series of depth profiles enabled us to perform quantitative analysis of etched amount in addition to the surface roughness obtained from relative depth profile within one image. The course of etching process from the dissolution of smear layer, appearance of enamel prizms or dentinal tubules to progress of demineralization could clearly be observed. The depth profile, surface roughness, etching amount, etching rate and smear layer thickness could then be evaluated. The different etching characteristics of three acid agents and the effect of surface roughness produced by different mechanical prepolish were compared and discussed.     

A new method for separating HFC-134a from gas mixtures using clathrate hydrate formation

A new separation method using gas hydrate formation is proposed for separating HFC-134a from gas mixtures containing N2 and HFC-134a. The feasibility of this separation method was investigated from various points of view. First, to determine the mixed hydrate stability region, three-phase equilibria of hydrate (H), liquid water (Lw), and vapor (V) for HFC-134a + N2 + water mixtures with various HFC-134a vapor compositions were closely examined in the temperature and pressure ranges of 275-285 K and 0.1-2.7 MPa, respectively. Second, the compositions of the hydrate and vapor phases at a three-phase equilibrium state were analyzed for identical mixtures at 278.15 and 282.15 K to confirm the actual separation efficiency. Third, kinetic experiments were performed to monitor the composition change behavior of the vapor phase and to determine the time required for an equilibrium state to be reached. Furthermore, X-ray diffraction confirmed that the mixed HFC-134a + N2 hydrates were structure II. Through an overall investigation of the experimental results, it was verified that more than 99 mol % HFC-134a could be obtained from gas mixtures after hydrate formation and subsequent dissociation processes. Separation of HFC-134a using hydrate formation can be carried out at mild temperature and low-pressure ranges. No additive is needed to lower the hydrate formation pressure.     

Active lactonizing lipase (LipL) efficiently overproduced by Pseudomonas strains as heterologous expression hosts

Pseudomonas sp. strain 109 secretes lactonizing lipase (LipL), which catalyzes efficient intramolecular transesterification of omega-hydroxyfatty acid esters to form macrocyclic lactones. Because Escherichia coli was found to be unsuitable as an expression host due to the predominant formation of inactive LipL-inclusion bodies and a lack of proper secretion machinery which is also required for the formation of active LipL, Pseudomonas strains were surveyed as expression hosts. Pseudomonas sp. strain 109, an original LipL producer, showed a 7.1-fold higher level of active LipL when the lipL gene under the control of tac-lacUV5 tandem promoter was introduced together with a limL gene encoding a LipL-specific chaperon. Pseudomonas aeruginosa ADD 1976 containing a T7 RNA polymerase gene in the chromosome and plasmid-borne lipL-limL genes under the control of T7 promoter showed a 13-fold higher level of active LipL. Several combinations in the number of lipL and/or limL genes on the plasmid were investigated, and (lipL)3-limL was found to be most efficient, yielding a 67-fold greater production of active LipL than that obtained by the wild-type Pseudomonas sp. strain 109.     

Loss Probability for a Finite Buffer Multiplexer with the <Emphasis Type="Italic">M/G/∞</Emphasis> Input Process

This paper studies the impact of long-range-dependent (LRD) traffic on the performance of a network multiplexer. The network multiplexer is characterized by a multiplexing queue with a finite buffer and an M/G/∞ input process. Our analysis expresses the loss probability bounds using a simple relationship between loss probability and buffer full probability. Our analysis also derives an exact expression for the buffer full probability and consequently calculates the loss probability bounds with excellent precision. Through numerical calculations and simulation examples, we show that existing asymptotic analyses lack the precision for calculating the loss probability over realistic ranges of buffer capacity values. We also show that existing asymptotic analyses may significantly overestimate the loss probability and that designing networks using our analysis achieves efficient resource utilization.     

Novolak design concept for high performance positive photoresists

Novolak resins have been optimized for high performance positive photoresists. Low molecular weight novolak resins are the key components for improving resolution capability, sensitivity, and heat resistance of positive photoresists. Various phenolic compounds (monomers) and oligomers of metacresol novolak resins were evaluated as low molecular weight components. It was found that phenolic compounds that have moderate hydrophobicity and azocoupling capability with diazonaphthaoquinone compounds greatly improve positive photoresist performance. This is explained in terms of the Stone wall model for positive photoresist development.     

Polymer complex from copolymers of acrylonitrile and ionic vinyl benzyl compounds

Copolymerization of sodium vinyl benzyl sulfonate (VBS) or vinyl benzyl trimethyl ammonium chloride (VBQ) with acrylonitrile (AN) gave polyelectrolytes of preferable solution viscosities. The blending of these two copolymers in N,N-dimethyl formamide (DMF) produced polymer complexes with ionic linkages, of which the following properties were examined. The maximum in the tan δ temperature was increased by complex formation. Freundlich-type dye adsorption and much better dyeability than on polyacrylonitrile was observed. Electric resistivity decreased with the introduction of ionic moiety. Permeability of water increased with the number of ionic sites. Homogeneous films could be cast from DMF and dimethyl sulfoxide (DMSO) solutions.     

Selective oxidation of Fe-30Cr at low temperatures: 743–823 K

Fe-30 Cr specimens were oxidized for 6×10²–3.6×10⁴ s at 743–823 K in pure oxygen at a pressure of 1.33×10⁴ Pa. Depth profiling of oxidized surfaces was performed with the simultaneous use of Auger electron spectroscopy (AES) and inert gas-ion (Ar⁺ or Xe⁺) sputter-etching technique. Chromium was selectively oxidized, and a chromium-depletion zone was formed in the underlying alloy. The values (10^–16–10^–15 cm² s^–1) of the interdiffusion coefficient, D, of the underlying alloy evaluated from the depth-composition profiles were compared in magnitude with the values extrapolated from lattice diffusion data of the corresponding alloy obtained at high temperature. The apparent activation energy obtained from an Arrhenius plot of the evaluated diffusion coefficient, however, was one-third of the value for the corresponding alloy at high temperatures. Discussion was made on the possible mechanism of selective oxidation at low temperatures.     

On the convergence of a mixed finite element scheme for plate bending

The convergence of a mixed finite element scheme for plate bending, previously proposed by the present authors, is discussed on the basis of functional analysis. First, the outline of the formulation is presented with some mathematical preliminaries. Then, several kinds of energy inequalities are established to assure the stability of the approximate solution. Thus, the rate of convergence may be obtained by the evaluation of the degrees of the completeness and consistency of the employed shape functions. Some remarks are also given with respect to the extension of the method to initial value problems.