Thermoelectric power measurement in a-ZnSe

Thermoelectric power measurements made as a function of temperature are interpreted on the basis of an energy model obtained by the authors for a-ZnSe. The model includes an identification of the electrical transport processes in the two temperature ranges studied. The results obtained here are consistent with the earlier interpretation of experiments on a-ZnSe.     

Search for isovector giant monopole resonances via the Pb(3He,tp) reaction

The (nat)Pb(3He,tp) reaction at E(3He) = 177 MeV was studied to identify 2Planck's over 2piomega isovector monopole strength in Bi isotopes. Monopole strength was found in the region -45相似文献   

Analogy between unconventional superconductivity and unconventional states of liquid crystals

An analogy is stressed between the order-parameter symmetries of the two-dimensional d-pairing wave superconductors and of liquid-crystal mesophases formed from achiral bent-shaped molecules. It leads to a definition of a class of liquid-crystal states which are the analogs of the unconventional superconducting states, and are characterized by a loss of discrete symmetry operations of the parent state.     

Creatine kinase B deficient neurons exhibit an increased fraction of motile mitochondria

Background  

Neurons require an elaborate system of intracellular transport to distribute cargo throughout axonal and dendritic projections. Active anterograde and retrograde transport of mitochondria serves in local energy distribution, but at the same time also requires input of ATP. Here we studied whether brain-type creatine kinase (CK-B), a key enzyme for high-energy phosphoryl transfer between ATP and CrP in brain, has an intermediary role in the reciprocal coordination between mitochondrial motility and energy distribution. Therefore, we analysed the impact of brain-type creatine kinase (CK-B) deficiency on transport activity and velocity of mitochondria in primary murine neurons and made a comparison to the fate of amyloid precursor protein (APP) cargo in these cells, using live cell imaging.     

Critical petermann K factor for intensity noise squeezing

We investigate the impact of the Petermann-excess-noise factor K>/=1 on the possibility of intensity noise squeezing of laser light below the standard quantum limit. Using an N-mode model, we show that squeezing is limited to a floor level of 2(K-1) times the shot noise limit. Thus, even a modest Petermann factor significantly impedes squeezing, which becomes impossible when K>/=1.5. This appears as a serious limitation for obtaining sub-shot-noise light from practical semiconductor lasers. We present experimental evidence for our theory.     

Conformational flexibility in 2,2'-Dioxybiphenyl-chloro-cyclotetraphosphazenes and its relevance to polyphosphazene analogues

The reaction of the cyclotetraphosphazene, [N4P4Cl8], with the difunctional reagent, 2,2'-biphenol, in the presence of potassium carbonate in acetone produced the spiro-substituted derivatives, 2,2'-dioxybiphenylhexachlorocyclotetraphosphazene, bis(2,2'-dioxybiphenyl)tetrachloro-cyclotetraphosphazene, and tris(2,2'-dioxybiphenyl)dichlorocyclotetraphosphazene. Both cis and trans geometrical isomers of the bis compound are observed. Although chromatographic separation of these was unsuccessful, a sample of the trans isomer was obtained by fractional crystallization. The compounds all show non-first-order 31P NMR spectra which were simulated to extract the spectral parameters. Single-crystal X-ray structures of both the trans bis and the tris compounds show that the cyclophosphazene rings exhibit conformational flexibility which gives rise to different crystalline forms being obtained from the same solvent systems. Crystals of trans-bis(2,2'-dioxybiphenyl)tetrachloro-cyclotetraphosphazene were obtained in two different space groups: Pnna (orthorhombic) and P21/n (monoclinic). In the orthorhombic structure, the dominant (72%) conformation of one phosphazene ring is a chair form, and the other (28%) resembles a boat. While for the monoclinic structure, the ring is virtually flat with an oval shape. In both cases the dioxybiphenyl groups are found in R and S configurations in the same molecule and are pi stacked in columns (Pnna) or involved in pi-pi or pi-H interactions (P21/n), thus anchoring the phosphorus atoms of the cyclotetraphosphazenes but still allowing flexibility in the ring conformations. Three crystalline modifications of tris(2,2'-dioxybiphenyl)dichloro-cyclotetraphosphazene were obtained: two in space group P (triclinic), which contained two molecules of dichloromethane in the unit cell, and one solvent-free form in space group P21/n (monoclinic). The cyclophosphazene rings exhibit puckered conformations with the trans-dioxybiphenyl moieties having opposing RS or SR conformations. DFT calculations were carried out on each of the phosphazene ring conformations in trans-bis(2,2'-dioxybiphenyl)tetrachlorocyclotetraphosphazene identified from the X-ray diffraction analysis. It is concluded that intermolecular interactions (i.e., pi-pi or pi-H) between the dioxybiphenyl groups is a factor that modifies the nature of the potential energy surface between the different conformers. The flexibility of the phosphazene ring is supported computationally through the calculated low-energy barriers and experimentally through the highly disordered phosphazene ring conformations observed in the solid state. The results on 2,2'-dioxybiphenyl-substituted cyclotetraphosphazenes provide evidence that microcrystalline domains in their 2,2'-dioxybiphenyl-substituted polyphosphazene analogues will be generated by similar pi-pi and pi-H interactions.     

Astrotricoumarin, an antiproliferative 4'-hydroxy-2',3'-dihydroprenylated methylcoumarin from an Astrotrichilia sp. from the Madagascar dry forest

Bioassay guided fractionation of the ethanol extract of a new endemic species of the genus Astrotrichilia led to the isolation of the new antiproliferative 3-(4'-hydroxy-2',3'-dihydroprenyl)-4,6-dimethoxy-5-methylcoumarin, named astrotricoumarin (8) with an IC50 value of 6.8 microM against the A2780 cell line. The structure of compound 8 was elucidated on the basis of its physical and spectroscopic data, including extensive 1D- and 2D-NMR analysis.     

Antiproliferative compounds of Artabotrys madagascariensis from the Madagascar rainforest

Bioassay-guided fractionation of an ethanol extract of Artabotrys madagascariensis led to the isolation of the new compound artabotrene (1), two butenolides (2 and 3), and the tetracyclic triterpene polycarpol (4). Structure elucidation was determined on the basis of one and two-dimensional NMR, and absolute configuration of compounds 2-4 was verified by analysis of CD and optical rotation spectra. Two of the isolates, melodorinol (2) and acetylmelodorinol (3), were found to display antiproliferative activity against five different tumour cell lines with IC50 values ranging from 2.4 to 12 microM.     

Two antiproliferative saponins of Tarenna grevei from the Madagascar dry forest [1

Antiproliferative bioassay-guided fractionation of the ethanol extract of the endemic Malagasy Rubiaceous plant Tarenna grevei led to the isolation of two new antiproliferative oxygenated oleanane triterpene saponins. The structures of the two active compounds were elucidated as 23-hydroxylongispinogenin 3-O-beta-D-glucopyranoside (1) and longispinogenin 3-O-beta-D-glucopyranosyl (1 --> 2)-beta-D-glucopyranoside (3) by analyses of their spectral data including 1D- and 2D-NMR spectroscopy and chemical evidence. Compounds 1 and 3 displayed moderate antiproliferative activity against the A2780 ovarian cancer cell line with IC50 values of 7.6 and 4 microM, respectively.