Materials Literature
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Abstract The geometric and electronic structure of 3,4‐ethylenedioxythiophene oligomers, ranging in size up to the decamer, have been calculated with density functional theory according to Becke's three‐parameter exchange functional and the gradient‐corrected functional of Lee, Yang, and Paar (DFT/B3LYP/6‐31G) and ab…
The relationship of structure to optical spectral properties was determined for five types of fluors in a search for an optimum-wavelength shifter to be used as part of the detection systems for high-energy particles from accelerators. In a search for photostable fluors to serve as waveshifters in plastic fibers it wa…
The design, synthesis, and properties of a new type of poly(borocarbosilane) polymer, 9-borabicyclo[3.3.1]nonane-modified allylhydridopolycarbosilane (AHPCS−9-BBN), that has proven to be an excellent processible single-source precursor to dense silicon carbide ceramics is reported. The polymers were synthesized in hig…
[structure: see text] General methods for the synthesis of novel bifunctional hemithioindigo (HT) compounds, e.g., omega-amino acid derivatives, are presented. The photochromic properties of the photoswitches have been characterized by UV-vis and (1)H NMR spectroscopy.
Macrocyclic glycocluster compounds 2n (n = 2-7) with four alkyl (undecyl) chains and eight oligosaccharide moieties on the opposite sides of the calix[4]resorcarene macrocycle are prepared from the reactions of the corresponding octaamine derivative with maltooligosaccharide lactones. Combined evidence from dynamic li…
A series of meso-meso-linked diporphyrins S(n) strapped with a dioxymethylene group of various length were synthesized by intramolecular Ag(I)-promoted coupling of dioxymethylene-bridged diporphyrins B(n), for n=10, 8, 6, 5, 4, 3, 2, and 1. Shortening of the strap length causes a gradual decrease in the dihedral angle…
Nitrogen assimilation in the methanogenic archaeon Methanococcus maripaludis is regulated by transcriptional repression involving a palindromic 'nitrogen operator' repressor binding sequence. Here we report the isolation of the nitrogen repressor, NrpR, from M. maripaludis using DNA affinity purification. Deletion of…
Incorporation of first row transition metals into stable surface precipitates can play an important role in reducing the bioavailability of these metals in neutral and alkaline soils. Organic coatings may interfere with this sorption mechanism by changing the surface characteristics and by masking the mineral surface…
Understanding the size-dependent electronic, structural and chemical properties of metal clusters on oxide supports is an important aspect of heterogeneous catalysis. Recently model oxide-supported metal catalysts have been prepared by vapour deposition of catalytically relevant metals onto ultra-thin oxide films grow…
The magnetocaloric effect that originates from the martensitic transition in the ferromagnetic Ni-Mn-Ga shape-memory alloy is studied. We show that this effect is controlled by the magnetostructural coupling at both the martensitic variant and magnetic domain length scales. A large entropy change induced by moderate m…
Purification and enhanced processability of carbon nanotubes have previously been achieved through interaction with a conjugated polymer. In particular, microscopy and Raman spectroscopy indicate a selective interaction between single-walled carbon nanotubes and a conjugated polymer. Until now, there has been no exten…
A direct measurement of the length scale of dynamic heterogeneity in supercooled d -sorbitol has been performed using a multidimensional 13 C solid-state NMR experiment. Several models predict that the growth of this length scale is linked to the slowing of dynamics as the glass transition is approached from above. At…
A series of first-principles calculations were performed for ferromagnetic Ni 2 MnGa using density functional theory and PAW potentials. Theoretically, a tetragonal crystal structure homogeneous lattice-distortive strain is stabilized around c / a = 0.94 with respect to the L2 1 structure when, in addition, modulation…
We report a theoretical and experimental investigation of Cr-doped AlN. Density functional calculations predict that the isolated Cr t2 defect level in AlN is 1/3 full, falls approximately at midgap, and broadens into an impurity band for concentrations over 5%. Substitutional Al1-xCrxN random alloys with 0.05 <= x <=…
We show that the electron-phonon coupling in the transition-metal diborides NbB2 and TaB2 is dominated by the longitudinal acoustical (LA) mode, in contrast to the optical E_{2g} mode dominated coupling in MgB2. Our ab initio results, described in terms of phonon dispersion, linewidth, and partial electron-phonon coup…
Theory of current hysteresis for tunneling through a molecular quantum dot (MQD) with strong electron-vibron interactions and attractive electron-electron correlations is developed. The dot is modeled as a d-fold degenerate energy level weakly coupled to the leads. The effective attractive interaction between polarons…
We present a study of the magnetic properties of the electron doped manganites Ca 1− x Y x MnO 3 (for 0 ≤ x ≤ 0.25) in the paramagnetic regime. For the less doped samples ( x ≤ 0.1) the magnetic susceptibility, χ( T ), follows a Curie–Weiss (CW) law only for T > 450 K and, below this temperature, χ −1 ( T ) shows a fe…
A great number of the existing data for electrical transport, the Altshuler Aronov Spivak and Aharonov Bohm effects, as well as the tunneling spectra of individual carbon nanotubes can be well explained by theories of the quantum phase slips in quasi-one-dimensional superconductors. The existing data consistently sugg…
Detailed analyses are made on previously published data for multi-walled carbon nanotubes. The field dependence of the Hall voltage, the temperature dependence of the Hall coefficient, and the magnetoresistance effect (Phys. Rev. Lett. 72, 697 (1994)) can all be consistently explained in terms of the coexistence of ph…
Mineral-bound Fe(II) species represent important natural reductants of pollutants in the anaerobic subsurface. At clay minerals, three types of Fe(II) species in fundamentally different chemical environments may be present simultaneously, i.e., structural Fe(II), Fe(II) complexed by surface hydroxyl groups, and Fe(II)…