Comparative study of plasticity models for concrete material by using different criteria including Hsieh–Ting–Chen criterion

The purpose of this study is to investigate nonlinear behavior of reinforced concrete (RC) structures with the plasticity modeling. For this aim a nonlinear finite element analysis program is coded in MATLAB. This program contains several yield criteria and stress–strain relationship for compression and tension behavior of concrete. In this paper, the well-known criteria, Drucker-Prager, von Mises, and a new criterion, Hsieh–Ting–Chen, are taken into account. The elastic–perfectly plastic and Park–Paulay stress–strain relationships in compression behavior and tension stiffening in tension behavior of concrete are used with four different yield criteria mentioned above. It is concluded that the proposed models are in good agreement with the experimental and analytical results taken from the literature. It is also concluded that the coded program, the proposed models, and Hsieh–Ting–Chen criterion can be effectively used in the nonlinear analysis of reinforced concrete beams.     

Polysulfone based amphiphilic graft copolymers by click chemistry as bioinert membranes

A series of well-defined amphiphilic graft copolymers with hydrophobic polysulfone (PSU) as backbones and hydrophilic poly(ethylene glycol) (PEG) as side chains were synthesized and characterized. For this purpose, PSUs were converted to azido-functionalized polymers by successive chloromethylation and azidation processes to give clickable PSUs. Then, the ω-hydroxyl function of the commercially available PEG-OH was converted into propargyl functionality by simple esterification process. Ultimately, the alkyne functionalized PEO was successfully grafted onto the PSUs by click chemistry. The final polymers and intermediates at various stages were characterized by ¹H NMR, FT-IR, and GPC techniques. The bioinert character of PEG grafted PSU was confirmed by static protein adsorption and prokaryotic and eukaryotic cell adhesion studies, and compared to that of unmodified PSU.     

The effect of serration on mechanics and stability of milling cutters

The machining behaviour of special serrated milling tools are investigated. These cutters are most commonly used for roughing operations of superalloys such as titanium and nickel based alloys which prevent high cutting speeds due to their high cutting forces and low thermal conductivity. During the experimental study, these drawbacks were avoided with the usage of aluminium alloy that allows more convenient machining circumstances and high tooth passing frequencies compared to the frequencies of the essential vibration modes. By means of a general cutting force model, simulations point out the fact that the serrated cutters require lower drive torque than their non-serrated counterparts, while our corresponding measurements validate our model. A regenerative dynamic model is constructed up directly in the modal space using the modal representation of the tool/toolholder/spindle structure and linear stability analyses are performed by the so-called semi-discretization method. The significantly larger parameter domains of stable cutting and their predicted feed dependency for these serrated mills are confirmed by chatter tests. As a result of these investigations, the practical advantages of the serrated cutters are confirmed: while they remove the same specific amount of materials using lower drive torque, their productivity can also be increased using higher stable depth of cuts compared to their non-serrated counterparts even in case of difficult-to-cut materials like titanium. The constructed mechanical model also provides an adequate tuning of the cutting parameters and the serration waves in order to optimize the process for easy-to-cut materials like aluminium.     

New photoinitiating systems designed for polymer/inorganic hybrid nanocoatings

Conventional UV-curable formulations consist of photoinitiators, multifunctional monomers and oligomers, reactive diluents, pigments, and additives. While photoinitiators are the key components of the formulations and responsible for the absorption of light and relevant performances (e.g., cure speed, high-percent conversion, etc.), the final properties of the cured coating are governed by the other high-volume components. With recent advances in the use of nanomaterials like metals, metal oxides, and silicates in coatings, it is now possible to prepare nanocoatings with enhanced physical, chemical, and biological properties. This is due, in part, to the difference in surface area per unit of volume at the nanoscale. Nanocoatings are usually prepared by UV irradiation of formulations containing dispersed nanoparticles. However, the homogeneous dispersion of these nanoparticles is a key challenge due to their easy agglomeration arising from their high surface-free energy. It is often difficult to obtain well-dispersed formulations providing good transmission of light for a complete cure. In this article, we report several synthetic methodologies for the preparation of epoxy and (meth)acrylate-based nanocoatings containing clay or metal nanoparticles. In the former case, photolysis of intercalated photoinitiator within the layers of montmorillonite clay in the presence of monomers resulted in the in situ formation of exfoliated structures. For the preparation of metal nanocoatings, the formation of silver or gold nanoparticles and crosslinking are accomplished simultaneously by photoinduced electron transfer and polymerization processes. The nanoparticles are homogenously distributed in the network without macroscopic agglomeration. Applicability to both free radical and cationic systems is demonstrated. Moreover, a novel photochemical route for grafting from the self-assembled monolayers on gold is presented.     

On the mechanism of photoinitiated cationic polymerization in the presence of polyols

The photoinitiated polymerization of cyclohexene oxide by using triphenyl sulfonium hexafluoroarsenate in the presence of poly(ε-caprolactone) polyols was studied. The polymerization was suggested to proceed via the activated monomer (AM) mechanism. The polymerization rate tended to decrease with increasing concentration of polyol. The enhanced curing rate observed in the presence of polyols was attributed to the multifunctional nature of the components, i. e., monomers and polyols.     

Synthesis of block copolymers via redox polymerization

Polymerization and copolymerization of vinyl monomers such as acrylamide, acrylonitrile, vinyl acetate, and acrylic acid with a redox system of Ce(IV) and organic reducing agents containing hydroxy groups were studied. The reducing compounds were poly(ethylene glycol)s, halogen‐containing polyols, and depolymerization products of poly(ethylene terephthalate). Copolymers of poly(ethylene glycol)s‐b‐polyacrylonitrile, poly(ethylene glycol)s‐b‐poly(acrylonitrile‐co‐vinyl acetate), poly(ethylene glycol)s‐b‐polyacrylamide, poly(ethylene glycol)s‐b‐poly(acrylamide‐co‐vinyl acetate), poly(1‐chloromethyl ethylene glycol)‐bpoly(acrylonitrile‐co‐vinyl acetate), and bis[poly(ethylene glycol terephthalate)]‐b‐poly(acrylonitrile‐co‐vinyl acetate) were produced. The yield of acrylamide polymerization and the molecular weight of the copolymer increased considerably if about 4% vinyl acetate was added into the acrylamide monomer. However, the molecular weight of the copolymer was decreased when 4% vinyl acetate was added into the acrylonitrile monomer. Physical properties such as solubility, water absorption, resistance to UV light, and viscosities of the copolymers were studied and their possible uses are discussed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1385–1395, 1999     

Type I Interferons Enhance the Repair of Ultraviolet Radiation-Induced DNA Damage and Regulate Cutaneous Immune Suppression

Type I interferons (IFNs) are important enhancers of immune responses which are downregulated in human cancers, including skin cancer. Solar ultraviolet (UV) B radiation is a proven environmental carcinogen, and its exposure contributes to the high prevalence of skin cancer. The carcinogenic effects of UV light can be attributed to the formation of cyclobutane pyrimidine dimers (CPD) and errors in the repair and replication of DNA. Treatment with a single dose of UVB (100 mJ/cm²) upregulated IFNα and IFNβ in the skin of C57BL/6 mice. IFNα and IFNβ were predominantly produced by CD11b+ cells. In mice lacking the type I IFN receptor 1 (IFNAR1), the repair of CPD following cutaneous exposure to a single dose of UVB (100 mJ/cm²) was decreased. UVB induced the expression of the DNA repair gene xeroderma pigmentosum A (XPA) in wild-type (WT) mice. In contrast, such treatment in IFNAR1 (IFNAR1-/-) mice downregulated XPA. A local UVB regimen consisting of UVB radiation (150 mJ/cm²) for 4 days followed by sensitization with hapten 2,4, dinitrofluorobenzene (DNFB) resulted in significant suppression of immune responses in both WT and IFNAR1-/- mice. However, there were significantly higher CD4+CD25+Foxp3+ regulatory T-cells in the draining lymph nodes of IFNAR1-/- mice in comparison to WT mice. Overall, our studies reveal a previously unknown action of type I IFNs in the repair of photodamage and the prevention of UVB-induced immune suppression.     

Effect of Soil Sulphur Levels on Feeding Preference of Brevicoryne brassicae on Brussels Sprouts

Two cultivars of Brussels sprouts, Brassica oleracea var. gemmifera were grown in pots treated with nutrient solutions containing five different levels of soil sulfur. Three replicates, each with 10 pots, were infested with the alate form of the aphid, Brevicoryne brassicae. Another three replicates were not infested with aphids. Total apterae aphids were counted on each leaf of the infested plants four weeks later. At the same time all plants were assayed for total glucosinolates and free thiocyanates. The greatest number of aphids per leaf on infested plants was found for the highest levels of sulfur applied. The highest concentrations of total glucosinolates were found in the leaves of uninfested plants that received the highest levels of sulfur. The lowest level of total glucosinolates was found in the leaves of infested plants that received the highest amount of sulfur, and these leaves had the highest level of free thiocyanates. The results suggest that aphids were attracted in greatest numbers to leaves that had the highest synthesis of glucosinolates and that their presence resulted in reduced glucosinolate levels by a combination of a depression in metabolic rate and a stimulation in myrosinase activity.