Synthesis of alkyne‐terminated xanthate RAFT agents and their uses for the controlled radical polymerization of N‐vinylpyrrolidone and the synthesis of its block copolymer using click chemistry

Two new alkyne‐terminated xanthate reversible addition‐fragmentation chain‐transfer (RAFT) agents: (S)‐2‐(Propynyl propionate)‐(O‐ethyl xanthate) (X₃) and (S)‐2‐(Propynyl isobutyrate)‐(O‐ethyl xanthate) (X₄) were synthesized and characterized and used for the controlled radical polymerization of N‐vinylpyrrolidone (NVP). X₃ showed better chain transfer ability in the polymerization at 60°C. Molecular weight of the resulted polymer increased linearly with the increase in monomer loading. Kinetics study with X₃ showed the pseudo‐first order kinetics up to 67% monomer conversion. Molecular weight (M_n) of the resulting polymer increased linearly with the increase in the monomer conversion up to around 67%. With the increase in the monomer conversion, polydispersity of the corresponding poly(NVP)s initially decreased from 1.34 to 1.32 and then increased gradually to 1.58. Chain‐end analysis of the resulting polymer by ¹H‐NMR and FTIR showed clearly that polymerization started with radical forming out of xanthate RAFT agent. Living nature of the polymerization was also confirmed from the successful homo‐chain extension experiment and the hetero‐chain extension experiment involving synthesis of poly(NVP)‐b‐polystyrene amphiphilic diblock copolymer. Formed alkyne‐terminated poly(NVP) also allowed easy conjugation to azide‐terminated polystyrene by click chemistry to prepare well‐defined poly(NVP)‐b‐polystyrene block copolymers. Resulting polymers were characterized by GPC, ¹H‐NMR, FTIR, and thermal study. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Dynamic mechanical properties of high density polyethylene and teak wood flour composites

The dynamic mechanical properties of high density polyethylene (HDPE) and teak wood flour (TWF) composites at varying volume fraction (Φ _f) of TWF from 0.00 to 0.32 have been studied. In HDPE/TWF composites, storage modulus (E′) decreased at Φ _f = 0.05, then increases with Φ _f; however, values were lower than HDPE up to Φ _f = 0.16, due to a pseudolubricating effect of filler. Loss modulus (E″) values were higher than HDPE in β and α relaxation regions while in γ relaxation region values were marginally equal to HDPE. Tan δ value decreases with Φ _f which may be due to enhanced amorphization and decreased crystallinity of HDPE. In presence of maleic anhydride grafted HDPE (HDPE-g-MAH), E′ values were lower than HDPE/TWF composites. In HDPE/TWF/HDPE-g-MAH, E″ were slightly higher than HDPE/TWF due to slippage of HDPE chains facilitated by the extent of degradation of coupling agent. Tan δ were higher for both systems than the rule of mixture.     

Effect of band parameters on interband optical absorption in quantum wire structure of low band gap III–V semiconductors

A generalized theory is presented to study the effect of band parameters on inter band optical absorption in quantum wire structure of III–V compound semiconductors considering the wave-vector ( $\vec{k}$ ) dependence of the optical transition matrix element (OME). The band structures of these low band gap semiconducting materials with sufficiently separated split-off valance band are frequently described by the three energy band model of Kane. This has been adopted to calculate the inter band optical absorption coefficient (IOAC) for a wide range of III–V compound semiconductors like, InAs, InSb, Hg_1?x Cd _x Te and In_1?x Ga _x As _y P_1?y lattice matched to InP, having varied split-off energy band compared to their energy band gap. It has been found that IOAC for quantum wires (QWRs) increases in oscillatory manner with increasing incident photon energy and the positions of peaks of oscillation of the coefficient are more closely spaced in the three band model of Kane than those with parabolic energy band approximations reflecting the direct the influence of band energy constants. This effect of band parameters is better revealed from the study of light polarization dependence of the absorption coefficient.     

Underpinning-based simultaneous extraction of contiguous sections of a thick coal seam under weak and laminated parting

Around 12.5 m-thick Zero seam of Chirimiri colliery underneath Bartunga hill of M/s South Eastern Coalfield Limited (SECL) was found in two sections; 3.5 m top and 6.0 m bottom section, with a highly laminated 3.0-m-thick parting between the two sections. The laminated parting, comprised of alternate layers of shale, carbonaceous shale, coal and mudstone, was found to be incompetent for safe and clean underground working of both sections. Both top and bottom sections were developed on superimposed pillars along the floor using roof bolts. Based on laboratory testing and investigations on simulated models, an idea of underpinning was conceived for simultaneous depillaring of both the contiguous sections. Taking advantage of presence of openings in the top section, the laminated parting and roof coal band of bottom section was reinforced simultaneously by a full-column grouted cable bolt of suitable length from the floor of the top section. Underpinning consolidated parting stability through reinforcement and provided additional thickness to the critical parting thickness as the roof coal band of the thick bottom section is stitched together with the parting. Maintaining superimposition of workings in the two sections, pillars of both the sections were extracted by splitting and slicing. Splits and slices of the bottom section did not experience roof instability problems due to the presence of the reinforced overlying roof coal band and parting by underpinning. The roof coal of the bottom section was blasted down on retreat. Consolidation of the multi-layered parting by underpinning did not allow separation and collapse of its mudstone/shale layers resulting in clean coal blasted from the roof. Underpinning-based simultaneous depillaring of the contiguous sections proved its technological feasibility and success through field trials.     

Studies on the influence of lanthanum oxide on the sinterability of chromium(III) oxide

The mechanism of sintering in chromium(III) oxide in the presence of varying amounts of lanthanum oxide under firing conditions which simulate a controlled reducing atmosphere, has been investigated. The investigation is based on isothermal shrinkage measurements at different temperatures. The data suggest that the vapour-phase transport mechanism becomes predominant with evidence of a grain-boundary diffusion process.     

Determination of interface state density of PtSi/strained-Si1-xGex/Si Schottky diodes

PtSi/p-strained-Si_1-xGe_x (x=0.19 and x=0.29) Schottky barrier diodes have been fabricated and characterized for the determination of barrier height, ideality factor and the interface state density distribution with energy. Diodes having an epitaxial layer thickness of 20 and 52 nm were modeled with emphasis on comparison with experiment. To achieve better agreement with experimental data, an interfacial layer and associated series resistance were included in the model. The capacitance–voltage (C–V) technique has been used for the determination of the energy distribution of interface state density. The interface state density distribution for the Si_0.81Ge_0.19 and Si_0.71Ge_0.29 diodes is found to decrease with increasing energy from the valence band edge.     

Oxynitride gate dielectric grown in nitric oxide (NO): the effectof reoxidation on dielectric reliability of the active edge

Reoxidation of an oxynitride gate dielectric grown by NO anneal of thermal oxide has been studied. This process has demonstrated ~3-5X improvement of Q_BD of active edge intensive capacitors in comparison to thermal oxide, N₂O and NO oxynitride. This improvement is believed to be due to the reduction of local thinning of the gate dielectric at the field oxide edge which also reduces local build-up of positive charge near the gate electrode at the isolation edges     

Beta-lactamase inhibitors: agents to overcome bacterial resistance

Parental illness can have a profound impact on family relationships and children's behaviour. The amount and nature of communication between parents and children about the illness can play an important role, both positively and negatively, in mediating the outcomes. When children have a disability, families can be reluctant to communicate with them about family difficulties. They are often concerned about the impact that parental unavailability may have on their child's life. This paper reports on three families in which the mother was diagnosed with breast cancer and one child in the family had a disability. The extent and specific characteristics of their communication about the maternal illness with their children, behavioural changes in the children, explanations of communication strategies and attributions of behavioural changes are described. Family coping strategies are examined with reference to Lazarus's process model of stress and coping and the use of either problem-focused or emotion-focused strategies. Implications for possible clinical interventions are proposed. In particular it is suggested that families be offered consultation about: what children might understand; ways in which to communicate effectively; and strategies for coping with the long-term implications of serious parental illness.     

Electrical properties of Ta/sub 2/O/sub 5/ gate dielectric on strained-Si

High dielectric constant (high-k) thin Ta/sub 2/O/sub 5/ films have been deposited on tensilely strained silicon (strained-Si) layers using a microwave plasma enhanced chemical vapour deposition technique at a low temperature. The deposited Ta/sub 2/O/sub 5/ films show good electrical properties as gate dielectrics and are suitable for microelectronic applications. The feasibility of integration of strained-Si and high-k dielectrics has been demonstrated.     

Influence of state of stress on mixed mode stable crack growth through D16AT aluminium alloy

The stable crack growth through three-point bend (TPB) and stiffened and unstiffened compact tension (CT) specimens of D16AT aluminium alloy has been studied both theoretically and experimentally. The specimen thickness is 8 mm. The variation of load with crack opening displacement, the extent of stable crack growth, the cumulative plastically deformed zone and crack edge profiles have been obtained experimentally. These are also predicted theoretically under the assumption of either a state of plane stress or plane strain using a finite element scheme and the COA criterion. Generally, the experimental results agree well with the predictions based on the plane stress condition. There appears to be no significant variation in size of the experimental cumulative plastic zone across the specimen thickness, thereby indicating that the constraint on the plastic zone does not develop near the mid-thickness region.