Materials Literature
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Poly(amidoamine) (PAMAM) dendrimers can be used as a polymeric template/stabilizer/reservoir to prepare stable gold−dendrimer nanocomposites by reducing PAMAM−tetrachloroaurate polysalts using hydrazine. In the gold−dendrimer nanocomposite, the presence of elemental gold is indicated by its characteristic plasmon abso…
Dielectric insulator materials containing nanometer-scale closed-cell pores with low dielectric constants ( k < 2.2), good mechanical properties, and high dielectric breakdown strengths are required for future semiconductor devices. In this paper we present a novel method for preparing nanoporous polyorganosilicate fi…
Powder neutron diffraction has been used to pinpoint the nature of the ferroelectric-paraelectric phase transition in Bi 4 Ti 3 O 12 . Below T c (675 °C) the structure has been refined in orthorhombic space group B 2 cb [at 25 °C a = 5.4444(1) Å, b = 5.4086(1) Å, c = 32.8425(6) Å; at 650 °C a = 5.46183(5) Å, b = 5.448…
A theoretical investigation is made of the dispersion characteristics of plasmons in a two-dimensional periodic system of semiconductor (dielectric) cylinders embedded in a dielectric (semiconductor) background. We consider both square and hexagonal arrangements and calculate extensive band structures for plasmons usi…
We discuss the possibility that, besides roughening, a vicinal surface could display preroughening (PR), and consider the possible mechanisms for its promotion. Within the framework of a terrace-step-kink model, it turns out that a PR transition is possible, and could be induced by a short-range repulsion between para…
We report results of density-functional theory calculations on the structural, magnetic, and electronic properties of (1x1)-structures of Co on Cu(001) for coverages up to two monolayers. In particular we discuss the tendency towards phase separation in Co islands and the possibility of segregation of Cu on top of the…
The order parameters of the magnetic, charge and structural orders at half-doped manganites are identified. A corresponding Landau theory of the phase transitions is formulated. Many structural and thermodynamical behaviors are accounted for and clarified within the framework. In particular, the theory provides a unif…
We propose that a specific spatial configuration of lattice sites that energetically favor {\it 3+} or {\it 4+} Mn ions in moderately doped manganites constitutes approximately a spatially random two-energy-level system. Such an effect results in a mechanism of metal-insulator transitions that appears to be different…
The methods of thermogravimetric analysis (TGA) and differential scanning calorimettry (DSC) have been used to study the thermal decomposition of ammonium perchlorate (AP). TGA curves obtained under both isothermal and nonisothermal conditions show a characteristic slowdown at the extents of conversion, α = 0.30−0.35.…
Power plant piping operating at elevated temperatures is subject to several types of service aging-related degradation, such as softening, spheroidization, embrittlement, and creep. When cracks are found in these components, weld repair is often employed to ensure continued operation. The efficacy of the weld repairs…
Controlled, reversible electrochemical promotion (EP) of a base metal catalyst has been demonstrated for the first time. Electropumping of Na from a β‘ ‘ alumina solid electrolyte to a Cu film catalyst results in large improvements in both activity and selectivity of the latter. In the catalytic reduction of NO by CO,…
Exocyclic tris(bidentate) ligands attached to a cyclotriphosphazene skeleton have been prepared and characterized. The cobalt complexes of the ligand have an unusual structure and demonstrate CoIII/CoII equilibrium over a wide temperature range.
A caged, photocleavable derivative of dioleoylphosphatidylethanolamine (DOPE) called NVOC-DOPE was prepared by reaction of DOPE with 6-nitroveratryloxycarbonyl chloride. In contrast to egg phosphatidylethanolamine (EPE), NVOC-DOPE or its 1:1 mixture with EPE forms liposomes at both pH 7.4 and 5.0. Photolysis (lambda >…
Although the catalytic (C) subunit of cAMP-dependent protein kinase is N-myristylated, it is a soluble protein, and no physiological role has been identified for its myristyl moiety. To determine whether the interaction of the two regulatory (R) subunit isoforms (R(I) and R(II)) with the N-myristylated C subunit affec…
The biodegradability of aliphatic polyesters, which are produced by biosynthesis and chemosynthesis, strongly correlates to the polymer morphology such as crystallinity, molecular orientation, chain packing and crystal surface, in addition to the chemical structure. For elucidation of biodegradation mechanism of cryst…
In this issue of PNAS, Chen et al. (1) show feasibility for producing a highly sensitive biosensor, capable of detecting nanomolar quantities of biologically interesting molecules in “real time.” If the phenomenon can be generalized to other systems, it could have significant implications for a wide variety of fields,…
We study an alloy system where short-ranged, thermally-driven diffusion competes with externally imposed, finite-ranged, athermal atomic exchanges, as is the case in alloys under irradiation. Using a Cahn-Hilliard-type approach, we show that when the range of these exchanges exceeds a critical value, labyrinthine conc…
A tetrasubstituted derivative of 1,4,7,10-tetraazacyclododecane with amide coordinating groups and extended noncoordinating phosphonate groups forms a complex with gadolinium(III) (shown in the picture) which contains one slowly exchanging inner-sphere water molecule (tau(M)=21 µs). The 20-MHz water proton relaxivity…
The preparation, characterization, and X-ray structure are reported for the single-molecule magnet (PPh 4 )[Mn 12 O 12 (O 2 CPh) 16 (H 2 O) 4 ]·8(CH 2 Cl 2 ) ( 2 ). Complex 2 crystallizes in the triclinic space group P 1̄, which at 213 K has a = 17.2329(2), b = 17.8347(2), c = 26.8052(2) Å, α = 90.515(2), β = 94.242(2…
The fluorescence of a polyanionic conjugated polymer can be quenched by extremely low concentrations of cationic electron acceptors in aqueous solutions. We report a greater than million-fold amplification of the sensitivity to fluorescence quenching compared with corresponding "molecular excited states." Using a comb…