Radiation from a Charge Supported in a Gravitational Field

We examine whether a charge supported statically in a gravitational field radiates, and find the answer to this question to be positive. Based on our earlier results we find that the important condition for the creation of radiation is the existence of a relative acceleration between the charge and its electric field, where such an acceleration causes the curving of the electric field and the creation of a stress force due to this curvature. This stress force is the reaction force, which creates the radiation. Later we find that this condition do exist for a charge supported statically in a gravitational field, where the electric field of the charge falls in the gravitational field, it curves, and the stress force raised in this curved field, creates electromagnetic radiation.     

Multiple avalanches across the metal-insulator transition of vanadium oxide nanoscaled junctions

The metal-insulator transition of nanoscaled VO2 devices is drastically different from the smooth transport curves generally reported. The temperature driven transition occurs through a series of resistance jumps ranging over 2 decades in magnitude, indicating that the transition is caused by avalanches. We find a power law distribution of the jump sizes, demonstrating an inherent property of the VO2 films. We report a surprising relation between jump magnitude and device size. A percolation model captures the general transport behavior, but cannot account for the statistical behavior.     

A new modular indole synthesis. Construction of the highly strained CDEF parent tetracycle of nodulisporic acids A and B

[reaction: see text] Construction of the highly strained CDEF parent tetracycle, a structural motif found only in the potent ectoparasiticidal agents (+)-nodulisporic acids A and B and related congeners, has been achieved via a new modular indole synthesis, exploiting a sequential Stille cross-coupling/Buchwald-Hartwig union/cyclization tactic. The new indole synthesis holds the promise of rapid assembly of diverse, highly substituted indoles possessing uncommon substitution patterns.     

High-resolution soft X-ray photoelectron spectroscopic studies and scanning auger microscopy studies of the air oxidation of alkylated silicon(111) surfaces

High-resolution soft X-ray photoelectron spectroscopy was used to investigate the oxidation of alkylated silicon(111) surfaces under ambient conditions. Silicon(111) surfaces were functionalized through a two-step route involving radical chlorination of the H-terminated surface followed by alkylation with alkylmagnesium halide reagents. After 24 h in air, surface species representing Si(+), Si(2+), Si(3+), and Si(4+) were detected on the Cl-terminated surface, with the highest oxidation state (Si(4+)) oxide signal appearing at +3.79 eV higher in energy than the bulk Si 2p(3/2) peak. The growth of silicon oxide was accompanied by a reduction in the surface-bound Cl signal. After 48 h of exposure to air, the Cl-terminated Si(111) surface exhibited 3.63 equivalent monoleyers (ML) of silicon oxides. In contrast, after exposure to air for 48 h, CH(3)-, C(2)H(5)-, or C(6)H(5)CH(2)-terminated Si surfaces displayed <0.4 ML of surface oxide, and in most cases only displayed approximately 0.20 ML of oxide. This oxide was principally composed of Si(+) and Si(3+) species with peaks centered at +0.8 and +3.2 eV above the bulk Si 2p(3/2) peak, respectively. The silicon 2p SXPS peaks that have previously been assigned to surface Si-C bonds did not change significantly, either in binding energy or in relative intensity, during such air exposure. Use of a high miscut-angle surface (7 degrees vs < or =0.5 degrees off of the (111) surface orientation) yielded no increase in the rate of oxidation nor change in binding energy of the resultant oxide that formed on the alkylated Si surfaces. Scanning Auger microscopy indicated that the alkylated surfaces formed oxide in isolated, inhomogeneous patches on the surface.     

Total synthesis of (-)-aplaminal

The total synthesis and assignment of absolute configuration of (-)-aplaminal ( 1), a cytotoxic metabolite from a sea hare possessing a triazobicyclo[3.2.1]octane skeleton, has been achieved. The synthesis entailed condensation of a monoprotected diamine ( 3) with dimethyl 2-oxomalonate ( 4) to generate the imidazolidine core ( 2). Introduction of the third nitrogen via Mitsunobu activation and azide displacement, followed by reduction and lactam formation (AlMe 3), furnished (-)-aplaminal ( 1). Overall, the synthesis entailed 9 steps and proceeded in 19% overall yield.     

The use of symmetry in direct Møller-Plesset second-order calculations

Summary An algorithm for utilising abelian point group symmetry in direct MP2 energy calculations is presented. This is based upon the direct MP2 method of Head-Gordon, Pople and Frisch. The method uses the petite atomic orbital integral list as in conventional transformations coupled with a symmetry adaption of the three quarter transformed integrals. Representative calculations for ethylene and benzene are presented which demonstrate the potential of the method.     

High-resolution laser ablation inductively coupled plasma mass spectrometry used to study transport of metallic nanoparticles through collagen-rich microstructures in fibroblast multicellular spheroids

We have efficiently produced collagen-rich microstructures in fibroblast multicellular spheroids (MCSs) as a three-dimensional in vitro tissue analog to investigate silver (Ag) nanoparticle (NP) penetration. The MCS production was examined by changing the seeding cell number (500 to 40,000 cells) and the growth period (1 to 10 days). MCSs were incubated with Ag NP suspensions with a concentration of 5 μg mL⁻¹ for 24 h. For this study, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was used to visualize Ag NP localization quantitatively. Thin sections of MCSs were analyzed by LA-ICP-MS with a laser spot size of 8 μm to image distributions of ¹⁰⁹Ag, ³¹P, ⁶³Cu, ⁶⁶Zn, and ⁷⁹Br. A calibration using a NP suspension was applied to convert the measured Ag intensity into the number of NPs present. The determined numbers of NPs ranged from 30 to 7200 particles in an outer rim of MCS. The particle distribution was clearly correlated with the presence of ³¹P and ⁶⁶Zn and was localized in the outer rim of proliferating cells with a width that was equal to about twice the diameter of single cells. Moreover, abundant collagens were found in the outer rim of MCSs. For only the highest seeding cell number, NPs were completely captured at the outer rim, in a natural barrier reducing particle transport, whereas Eosin (⁷⁹Br) used as a probe of small molecules penetrated into the core of MCSs already after 1 min of exposure.

Fibroblast MCS could build up the barrier only for nanoparticles

     

Phase equilibria, crystal structures, and dielectric anomaly in the BaZrO3-CaZrO3 system

Phase equilibria in the (1−x)BaZrO₃-xCaZrO₃ system were analyzed using a combination of X-ray and neutron powder diffraction, and transmission electron microscopy. The proposed phase diagram features two extended two-phase fields containing mixtures of a Ba-rich cubic phase and a tetragonal, or orthorhombic Ca-rich phase, all having perovskite-related structures. The symmetry differences in the Ca-rich phases are caused by different tilting patterns of the [ZrO₆] octahedra. In specimens quenched from 1650°C, CaZrO₃ dissolves only a few percent of Ba, whereas the solubility of Ca in BaZrO₃ is approximately . The BaZrO₃-CaZrO₃ system features at least two tilting phase transitions, Pm3m→I4/mcm and I4/mcm→Pbnm. Rietveld refinements of the Ba_0.8Ca_0.2ZrO₃ structure using variable-temperature neutron powder diffraction data confirmed that the Pm3m→I4/mcm transition corresponds to a rotation of octahedra about one of the cubic axes; successive octahedra along this axis rotate in opposite directions. In situ variable-temperature electron diffraction studies indicated that the transition temperature increases with increasing Ca-substitution on the A-sites, from approximately −120°C at Ca to 225°C at Ca. Dielectric measurements revealed that the permittivity increases monotonically from 36 for BaZrO₃ to 53 for Ba_0.9Ca_0.1ZrO₃, and then decreases to 50 for Ba_0.8Ca_0.2ZrO₃. This later specimen was the Ca-richest composition for which pellets could be quenched from the single-phase cubic field with presently available equipment. Strongly non-monotonic behavior was also observed for the temperature coefficient of resonant frequency; however, in this case, the maximum occurred at a lower Ca concentration, 0.05?x?0.1. The non-linear behavior of the dielectric properties was attributed to two competing structural effects: a positive effect associated with substitution of relatively small Ca cations on the A-sites, resulting in stretched Ca-O bonds, and a negative effect, related to the distortion of the A-site environment (bond strain relaxation) upon octahedral tilting.