Microfabrication by X‐ray‐induced polymerization above the lower critical solution temperature

A polymer synthesis method is presented in which chain growth driven by exothermic reaction stimulates a gradual chain collapse. The globular precipitates in such systems can be restrained from coalescing by polymerizing in a quiescent environment. Time‐resolved small‐angle scattering study of the methacrylic acid polymerization kinetics in a quiescent system above its lower critical solution temperature (LCST) in water reveals the following features of this method: (a) growing oligomers remain as rigid chains until a critical chain length is reached, at which they undergo chain collapse, (b) radius of gyration increases linearly with time until a critical conversion is reached, and (c) radius of gyration remains constant after the critical conversion, even while conversion is gradually increasing. Following this self‐stabilizing growth mechanism, we show that nanoparticles can be directly synthesized by polymerizing N‐isopropylacrylamide above its LCST in water. The average size of nanoparticles obtained from a polymer–solvent system is expected to be the maximum extent of reaction spread at that monomer concentration. This hypothesis was then verified by polymerizing N‐isopropylacrylamide above their LCST in water, but by initiating the reaction with X‐rays shielded by a mask. The microfabricated patterns conform well to the size and shape of the mask used confirming that the growing chains do not propagate beyond the exposed regions as long as the reaction temperature is maintained above the LCST. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 429–425, 2006     

Microstructural effects on the tensile properties and deformation behavior of a Ti-48Al gamma titanium aluminide

The effects of microstructure on the tensile properties and deformation behavior of a binary Ti-48Al gamma titanium aluminide were studied. Tensile-mechanical properties of samples with microstructures ranging from near γ to duplex to fine grained, near- and fully-lamellar were determined at a range of temperatures, and the deformation structures in these characterized by transmission electron microscopy (TEM). Microstructure was observed to exert a strong influence on the tensile properties, with the grain size and lamellar volume fraction playing connected, but complex, roles. Acoustic emission response monitored during the tensile test revealed spikes whose amplitude and frequency increased with an increase in the volume fraction of lamellar grains in the microstructure. Analysis of failed samples suggested that microcracking was the main factor responsible for the spikes, with twinning providing a minor contribution in the near-lamellar materials. The most important factor that controls ductility of these alloys is grain size. The ductility, yield stress, and work-hardening rate of the binary Ti-48Al alloy exhibit maximum values between 0.50 and 0.60 volume fraction of the lamellar constituent. The high work-hardening rate, which is associated with the low mobility of dislocations, is the likely cause of low ductility of these alloys. In the near-γ and duplex structures, slip by motion of 1/2<110] unit dislocations and twinning are the prevalent deformation modes at room temperature (RT), whereas twinning is more common in the near- and fully-lamellar structures. The occurrence of twinning is largely dictated by the Schmid factor. The 1/2<110] unit dislocations are prevalent even for grain orientations for which the Schmid factor is higher for <101] superdislocations, though the latter are observed in favorably oriented grains. The activity of both of these systems is responsible for the higher ductility at ambient temperatures compared with Al-rich single-phase γ alloys. A higher twin density is observed in lamellar grains, but their propagation depends on the orientation and geometry of the individual γ lamellae. The increase in ductility at high temperatures correlates with increased activity of 1/2<110] dislocations (including their climb motion) and twin thickening. The role of microstructural variables on strength, ductility, and fracture are discussed. This article is based on a presentation made in the symposium entitled “Fundamentals of Structural Intermetallics,” presented at the 2002 TMS Annual Meeting, February 21–27, 2002, in Seattle, Washington, under the auspices of the ASM and TMS Joint Committee on Mechanical Behavior of Materials.     

Optimal operation of a multibasin reservoir system

A simulation-optimization procedure is presented for evaluating the extent of interbasin transfer of water in the Peninsular Indian river system consisting of 15 reservoirs on four river basins. A system-dependent simulation model is developed incorporating the concept of reservoir zoning to facilitate releases and transfers. The simulation model generates a larger number of solutions which are then screened by the optimization model. The Box complex nonlinear programming algorithm is used for the optimization. The performance of the system is evaluated through simulation with the optimal reservoir zones with respect to four indices, reliability, resiliency, vulnerability and deficit ratio. The results indicate that by operating the system of 15 reservoirs as a single unit the existing utilization of water may be increased significantly.     

Densely connected convolutional networks-based COVID-19 screening model

The extensively utilized tool to detect novel coronavirus (COVID-19) is a real-time polymerase chain reaction (RT-PCR). However, RT-PCR kits are costly and consume critical time, around 6 to 9 hours to classify the subjects as COVID-19(+) or COVID-19(-). Due to the less sensitivity of RT-PCR, it suffers from high false-negative results. To overcome these issues, many deep learning models have been implemented in the literature for the early-stage classification of suspected subjects. To handle the sensitivity issue associated with RT-PCR, chest CT scans are utilized to classify the suspected subjects as COVID-19 (+), tuberculosis, pneumonia, or healthy subjects. The extensive study on chest CT scans of COVID-19 (+) subjects reveals that there are some bilateral changes and unique patterns. But the manual analysis from chest CT scans is a tedious task. Therefore, an automated COVID-19 screening model is implemented by ensembling the deep transfer learning models such as Densely connected convolutional networks (DCCNs), ResNet152V2, and VGG16. Experimental results reveal that the proposed ensemble model outperforms the competitive models in terms of accuracy, f-measure, area under curve, sensitivity, and specificity.

     

Amyloidogenic Properties of Peptides Derived from the VHL Tumor Suppressor Protein

The von Hippel-Lindau tumor suppressor protein (pVHL) is involved in maintaining cellular oxygen homeostasis through the regulated degradation of HIF-α. The intrinsically disordered nature of pVHL makes it prone to aggregation that impairs its function, and this is further aggravated in mutant versions of the protein, thus promoting tumor development. By using in silico analysis, we predicted six peptide fragments from pVHL to be amyloidogenic. This was verified for two of the peptides by biophysical approaches, which demonstrated self-assembly and formation of β-sheet-rich aggregates, which, under transmission electron microscopy, atomic force microscopy, and X-ray diffraction, displayed typical fibrillar amyloid characteristics. These motifs may serve as proxies for exploring the nature of pVHL aggregation.     

Silicon Nitride Derived from an Organometallic Polymeric Precursor: Preparation and Characterization

Partially crystalline Si₃N₄, with nanosized crystals and a specific surface area greater than 200 m²/g, is obtained by pyrolysis of a commercially available vinylic polysilane in a stream of anhydrous NH₃ to 1000°C. This polymer does not contain N initially. Crystallization to high-purity α-Si₃N₄ proceeds with additional heating above 1400°C under N₂. The changes in crystallinity, powder morphology, infrared spectra, and elemental compositions, for samples annealed from 1000° to 1600°C under N₂, are consistent with an amorphous-to-crystalline transformation. Although macroscopic consolidation and local densification occur at 1400°C, volatilization and accompanying weight loss limit bulk densification. The effect of temperature on specific surface area is examined and related to the sintering process. These results are applicable to pyrolysis, decomposition, and crystallization studies of ceramics synthesized by polymeric precursor routes.     

Cement mortar impregnated with poly(methyl methacrylate-co-styrene)

Polymer-impregnated mortars were prepared by copolymerization of a monomer mixture of methyl methacrylate and styrene in the ratios of 13:87 and 40:60 using Co-60 gamma radiation. The copolymerization characteristics viz. the rate of polymerization, the extent of monomer loss, polymer loading, etc., were studied. The nature and molecular weight of the extractable polymer from the composite were determined. The flexural strength of the copolymer-impregnated composites was found to be better than that of the composites impregnated with component homopolymers.     

Has water-saving irrigation recovered groundwater in the Hebei Province plains of China?

This study performed a quantitative evaluation of the impact of water-saving irrigation on the groundwater regime in the Hebei Province plains area. In this work, the change in groundwater regime and the contributions of precipitation and water-saving irrigation development were investigated. The results indicate that the groundwater overdraft has been mitigated to some extent, mainly due to changes in precipitation and the implementation of water-saving irrigation, with contributions of 64.3% and 35.7%, respectively, when considering only these two factors. Water-saving irrigation is accepted as an important means for reducing groundwater depletion, but should be used in conjunction with other measures.     

Microwave joining and repair of composite materials

A novel technique that uses microwave power for joining and repair of thermoplastic and thermoset composites and ceramics is discussed. Enhanced microwave heating resulting from the use of conducting polymers and chiral microinclusions shows considerable promise for joining and repair of composites. The method is attractive because it produces clean and reliable interfacial joints, it is fast, it does not entail alteration of the bulk materials, and it does not result in volumetric heating. System details, including magnetron, waveguides, circulators, coupling iris, and the applicator for delivering microwave power, are described. Material requirements for the efficient absorption of microwave power are discussed. Microwave heating can be increased by doping the components to be joined or by the use of microwave adhesive films. Recent developments in electromagnetic chirality for microwave absorption are introduced and the design of composite materials for enhanced absorptivity is discussed. Results are presented for the welding and repair of thermoplastic, thermoset, and ceramic components.     

Self-emulsifiable soybean oil phosphate ester polyols for low-VOC corrosion resistant coatings

A series of soybean oil phosphate ester polyols (SOPEP) was prepared by reaction of fully epoxidized soybean oil with phosphoric acid and simultanoeous hydrolysis in the presence of a polar solvent. The polyols were characterized by determination of acid value, oxirane number, hydroxyl value, molecular weight (GPC), and FTIR spectra. These polyols with varying amounts of acid phosphate groups could be self-emulsified to form aqueous dispersions after neutralization with organic base. These aqueous dispersion showed varying degrees of stability and their appearance ranged from opaque dispersions to translucent to clear solutions. Waterborne coating compositions were prepared using these aqueous dispersions as principal components and their thermally cured film properties were studied. it was found that by careful selection and formulation, SOPEPs can be successfully used for low-VOC waterborne coating formulations. SOPEPs with 3.5% phosphate ester content showed visibly superior corrosion resistance properties.