Novel strategies for novolak resin fractionation: Consequences for advanced photoresist applications

The importance of well‐characterized novolak resins in the manufacture of high performance photoresists is paramount. Two novel fractionation methods for novolaks synthesized by solution condensation are reported in this paper. Solid resin solutions in methanol and ethyl lactate were fractionated by ultracentrifugation and liquid‐liquid centrifugation (using water and hexane as non‐solvents). The techniques resulted in high yield, low‐polydispersity (high M_w) resins that exhibited superior dissolution rates and lithographic performance when compared to resins obtained by conventional isolation techniques. The effects of solvent/non‐solvent ratio, temperature, and centrifuge rpm on resist performance were evaluated. It was found that at sufficiently high rpm and at 25°C, the M_w and the polydispersity of the fractionated resin increases and the dissolution rate decreases as the solvent/non‐solvent ratio decreases, Slow dissolution rates and improved lithographic performance characteristics in experimental i‐line formulations were obtained for resin solutions fractionated by liquid‐liquid centrifugation using a 1/2 ratio of ethyl lactate (and/or methanol) to hexane. Scaling laws between dissolution rate and polymer molecular weight were derived and the data seem to support reptation‐type diffusion. The use of appropriate process manipulation in order to precisely control resin properties and to design novel resins is discussed.     

粉末冶金铁基软磁材料的发展与应用

用粉末冶金工艺制作的软磁材料,在电动机、压缩机及其他旋转装置中得到了广泛应用。烧结软磁材料广泛应用于汽车和非汽车领域。为了进一步发展粉末冶金产业,近年来开发了许多材料。新近开发出了具有优良磁感应强度与矫顽力的,高密度软磁材料(AncorLam)。其于880MPa的压力下压制时,生坯密度为7.55g/cm3,矫顽力为310A/m,电阻率为8000micro-ohmcm,及生坯强度为100MPa。这篇文章将讨论这些材料的应用。     

Sequential interpenetrating polymer network based on styrene butadiene rubber and polyalkyl methacrylates

A series of sequential interpenetrating polymer network (IPNs) based on styrene butadiene rubber (SBR) and polyalkyl (methyl, ethyl, and butyl) methacrylates have been prepared by using tetraethylene glycol dimethacrylate as crosslinker. The IPNs were characterized by infrared spectrophotometer, dynamic mechanical analyzer, thermogravimetric analyzer, and swelling study. IPNs have exhibited higher tensile properties compared with pure SBR. IPNs based on PMMA have shown higher tensile strength compared with others. Dynamic mechanical analysis has shown that the IPNs have superior dynamic properties than SBR. Because of IPN formation, tan δ peak shifted inward between SBR and acrylates. Although the magnitude of tan δ decreased, the peaks were broadened because of micro heterogeneous phase separation. At higher concentration of methacrylate, splitting in tan δ peak was noticed because of phase separation. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1120–1126, 2007     

Structure-related insect antifeedant and growth regulating activities of some limonoids

Insect antifeedant and growth-regulating activities of 22 limonoids (both natural and their derivatives) againstSpodoptera litura were studied to understand the structure-related bioactivities of the limonoids. The C-seco limonoids (azadirachtins A, B, D, H, and I) were the most effective compounds as a group, while the intact limonoids (cedrelone and its derivatives) were the least effective. The cyclohexenone A ring and the-hydroxy enone group in the B ring appear to be important for antifeedant activity. The presence of a cyclohexenone or 1,2-epoxide in the A ring coupled with an-hydroxy enone in the B ring correlated well with growth regulatory activity. An acetoxy at C-7 instead of-hydroxy enone and perhaps the carbonyl at C-16 increase growth regulatory activity. Absence of 14–15 epoxide may not drastically reduce antifeedant activity and growth regulatory activity.     

A better sheet-formability test

Instability predictions are important in sheet-metal forming processes, one such instability being splitting failures due to localized necking. The majority of such sheet-metal industrial splitting failures occur near to the plane-strain state. Therefore, sheet-metal industries have always been looking for an “ideal” formability test which allows them to evaluate sheets for their ability to resist splitting failures under near plane-strain conditions. Several formability tests have been developed in the past but none have been very successful. Presently, a new test has been designed, constructed and used to evaluate the formability of different sheet materials. The results from this new test are compared with standard limiting-dome-height (LDH) tests and finite-element simulations. The results show that the new test is more reproducible, more closely follows the desirable plane strain path and takes roughly 1/6 of the time to perform relative to the LDH test. Strain measurements and finite-element simulations have revealed that the improvements are a result of the new test geometry, which produces a more stable and repeatable plane-strain state near to the splitting failure locations. The failure heights in the new tests were predicted using a section analysis finite-element program, SHEET-S.     

An analysis of localized necking in aluminium alloy tubes during hydroforming using a continuum damage model

In this work, localized necking in aluminium alloy tubes subjected to free hydroforming is analyzed. The main objective is to study the influence of loading conditions, such as prescribed fluid pressure or volume flow rate in conjunction with axial end feed, on the nature of the forming limit curve (FLC). To this end, the strain histories experienced at the tube mid-length, which were computed in an earlier investigation [14] [Varma NSP, Narasimhan R. A numerical study of the effect of loading conditions on tubular hydroforming, Journal of Materials Processing Technology 2005; [Submitted for publication]], are analyzed using the Marciniak–Kuczynski (M–K) method along with an anisotropic version of the Gurson model. The Gurson constitutive parameters are determined following an inverse approach using the sheet FLC for the chosen alloy. The predicted FLC for combined pressure and axial contraction corroborates well with the experimental data obtained in [12] [Kulkarni A, Biswas P, Narasimhan R, Luo A, Stoughton T, Mishra R, Sachdev AK. An experimental and numerical study of necking initiation in aluminium alloy tubes during hydroforming. International Journal of Mechanical Sciences 46:2004;1727–46] and is almost flat, whereas it is akin to the sheet FLC and increases with negative minor strain when fluid volume is specified. The forming limit strains for loading with specified fluid volume are in general higher when compared to those with prescribed fluid pressure. Finally, it is demonstrated that a transition from axial to circumferential necking occurs when high ratios of axial extension to volume flow rate are applied to the tube.     

An experimental and numerical study of necking initiation in aluminium alloy tubes during hydroforming

In this paper, a combined experimental and numerical investigation of free hydroforming of aluminium alloy tubes is conducted. The tubes are subjected to different loading histories involving axial compression and internal pressure. The circumferential and axial strains experienced by the tubes are continuously recorded along with the pressure and axial load. The numerical simulations are carried out using both 2D axisymmetric and 3D finite-element formulations by applying the experimentally recorded axial load and internal pressure. In the latter, a geometric imperfection is introduced in the form of wall thickness reduction at the tube mid-length in order to trigger necking which happens after significant bulging and beyond the stage of peak pressure. The strain histories and peak pressures obtained from the simulations agree well with those determined from the experiments. Further, the forming limit curve predicted by the simulations as well as from a M–K analysis incorporating the computed strain paths corroborate well with the experimental data. The role of nonproportional straining on the mechanics of failure of the tubes due to bulging and necking is studied in detail.     

Biodegradation of nitrilotriacetic acid (NTA) and ferric-NTA complex by aerobic microbial granules

Development of mixed-culture microbial granules under aerobic conditions in a sequencing batch reactor (SBR), capable of completely degrading a recalcitrant metal chelating agent is reported. In laboratory-scale reactor studies, the microbial granules degraded 2mM of free nitrilotriacetic acid (NTA) and Fe(III)-NTA completely in 14 and 40 h, respectively. Free NTA was degraded at a specific rate of 0.7 mM (gMLSS)(-1)h(-1), while Fe(III)-NTA was degraded at a specific rate of 0.37 mM (gMLSS)(-1)h(-1). Achievement of significant degradation rates of NTA and ferric-NTA in double-distilled water suggests that the microbial metabolism is not constrained by lack of essential elements. Efficient degradation of recalcitrant synthetic chelating agents by aerobic microbial granules suggests their potential application in a variety of situations where heavy metals or radionuclides are to be co-disposed with metal chelating agents.     

Neural-based approach for localization of sensors in indoor environment

Location of wireless sensor nodes is an important piece of information for many applications. There are many algorithms present in literature based on Received Signal Strength (RSSI) to estimate the location. However the radio signal propagation is easily influenced by diffraction, reflection and scattering. Therefore algorithms purely based on RSSI may not accurately predict the position of the node. In the present work, an algorithm for estimating the position of mobile nodes is proposed which is based on a combination of Received Signal Strength (RSSI) and Link Quality Indicator (LQI). Artificial Neural Networks are used to establish the relationship between the location of the mobile node and the experimentally obtained values of RSSI and LQI. Two different algorithms namely, Bayesian Regularization and Gradient Descent are used to develop the neural network model. Proposed algorithms improve the localization accuracy and perform better than other state-of-the-art algorithms.     

Electrochemical characterization of oxide formed on chromium containing mild steel alloys in LiOH medium

Flow accelerated corrosion leads to wall thinning of outlet-feeder pipes in the primary heat transport system of pressurized heavy water reactors and can even necessitate enmasse feeder replacement. Replacement of carbon steel 106-grade-B (CS) with chromium containing carbon steel reduces the risk of this failure. This paper discusses the role of small additions of chromium in modifying the properties of the oxide film. CS and chromium containing mild steels viz., A333, 2.25Cr–1Mo and modified 9Cr–1Mo alloy were exposed to primary heat transport (PHT) system chemistry conditions. The oxide films formed were characterized by electrochemical and surface characterization techniques. Mott–Schottky analysis showed donor type of defects. The densities of defects in the oxides of chromium containing alloys were 3–15 times less than that in CS. In presence of ∼200 ppb of dissolved oxygen, the oxides formed were hematite with two orders of magnitude smaller concentration of defects as compared to that formed under reducing conditions. These results suggest that the presence of chromium lowers the defect density of the oxide film and thus ensures a reduced corrosion rate.