A Comment on Short-Range Structure of Vitreous As_2Se_3 Observed in High Momentum Transfer Region

The short-range structure of vitreous As_2Se_3 was investigated by the measurement of interference function in high momentum transfer region with a pulsed neutron diffractometer combined with an electron linac

On the Anomalous Physical Properties of Liquid Copper Alloys

Magnetic susceptibilities and electrical resistivities of the liquid copper alloys, Cu-Bi, Cu-Sn and Cu-In have been measured as functions of chemical compositions at temperatures in the neighbourhood of 1000℃. In the liquid Cu-Bi alloy, observed magnetic susceptibility and electrical resistivity are well explained in terms of a model which assumes random distribution of Cu and Bi ions in an free electron gas atmosphere. In the liquid Cu-Sn and Cu-In alloys, anomalous behaviours are observed in their magnetic susceptibility and electrical resistivity. It is shown that the observed deep valleys of diamagnetism in the magnetic susceptibility curves of both liquid alloys correspond to the peaks in the curves of the heat of mixing for the respective alloys observed in our previous report. The observed values of magnetic susceptibility are compared with theoretical curves calculated by taking account of a contribution from n_R pseudo-molecules which are formed by association of Cu ions with Sn or In ion. It is found that about two electrons are localized in a pseudo-molecule for both liquid alloys near 1100℃ and that the observed deep diamagnetism originates from the existence of pseudo-molecules. Electrical resistivities for both kinds of liquid alloys are given as the sum of contributions from scattering of conduction electrons by randomly distributed free ions and by pseudo-molecules. The contribution ρ_1 caused by the former mechanism can be estimated in terms of a hard sphere model for the Ashcroft potential, and the latter contribution ρ_2 can be assumed to be in proportion with the distribution function n_R of the pseudo-molecule in the liquid alloy on the bases of its flexible structure. For both kinds of alloys such a proportional relationship is regarded as a reasonable assumption because the n_R curve behaves similarly to that of ρ_2=ρ-ρ_1 versus alloying compositions, where ρ is the observed total resistivity

Structure of Liquid Gallium and Rubidium by Pulsed Neutron Diffraction Using Electron Linac(Physics)

The static structure factors of liquid gallium and rubidium were measured at several temperatures above their melting points using the time of flight neutron diffractometer installed on the 300 MeV Tohoku University electron linac as a pulsed neutron source. The characteristic oscillation of the structure factor of liquid gallium in a high momentum transfer region has been shown to be well understood in terms of a diatomic molecule-like atomic association with the bond length of 2.69A. It has been discussed, however, that the subsidiary maximum on the high momentum transfer side of the first peak in the structure factor of liquid gallium may appear due to the second and subsequent peaks in the pair correlation function to shift to a larger distance in comparison with those of simple liquid metals such as alkali metals

Short-Range Structures of Amorphous and Liquid Iron and Pd_<0.8>-Si_<0.2> Alloy

A comparison has been made on the short-range structures of iron and Pd_-Si_ alloy between the amorphous and the liquid states. It is suggested that the short-range structure of amorphous Fe film has higher degree of ordering in comparison to liquid Fe. The atomic configuration in the nearest neighbour in amorphous Pd_-Si_ alloy is close to that in Pd_3Si crystal and is not completely reproduced by the Percus-Yevick Hard Sphere model with high packing fraction corresponding to instantaneous freezing of the liquid structure

Origins of a cyanobacterial 6-phosphogluconate dehydrogenase in plastid-lacking eukaryotes

BackgroundPlastids have inherited their own genomes from a single cyanobacterial ancestor, but the majority of cyanobacterial genes, once retained in the ancestral plastid genome, have been lost or transferred into the eukaryotic host nuclear genome via endosymbiotic gene transfer. Although previous studies showed that cyanobacterial gnd genes, which encode 6-phosphogluconate dehydrogenase, are present in several plastid-lacking protists as well as primary and secondary plastid-containing phototrophic eukaryotes, the evolutionary paths of these genes remain elusive. ResultsHere we show an extended phylogenetic analysis including novel gnd gene sequences from Excavata and Glaucophyta. Our analysis demonstrated the patchy distribution of the excavate genes in the gnd gene phylogeny. The Diplonema gene was related to cytosol-type genes in red algae and Opisthokonta, while heterolobosean genes occupied basal phylogenetic positions with plastid-type red algal genes within the monophyletic eukaryotic group that is sister to cyanobacterial genes. Statistical tests based on exhaustive maximum likelihood analyses strongly rejected that heterolobosean gnd genes were derived from a secondary plastid of green lineage. In addition, the cyanobacterial gnd genes from phototrophic and phagotrophic species in Euglenida were robustly monophyletic with Stramenopiles, and this monophyletic clade was moderately separated from those of red algae. These data suggest that these secondary phototrophic groups might have acquired the cyanobacterial genes independently of secondary endosymbioses. ConclusionWe propose an evolutionary scenario in which plastid-lacking Excavata acquired cyanobacterial gnd genes via eukaryote-to-eukaryote lateral gene transfer or primary endosymbiotic gene transfer early in eukaryotic evolution, and then lost either their pre-existing or cyanobacterial gene

Structure of Liquid and Amorphous Selenium by Pulsed Neutron Diffraction Using an Electron LINAC(Physics)

Structure factors of liquid and amorphous selenium were measured over a range of the scattering vector as wide as 0.5 to 30 A^ by means of time-of-flight neutron diffraction using hot pulsed neutrons generated by an electron LINAC. Based on experimental observation of the structure factor in the high-scattering-vector region which is mainly attributed to the intramolecular correlation, a disordered-chain model which has both helical- and ring-type arrangements in a single molecule has been proposed for the structure of the molecule in liquid and amorphous selenium

Time-of-Flight Pulsed Neutron Diffraction of Liquids Using an Electron LINAC(Physics)

A time-of-flight pulsed neutron diffractometer for the measurement of liquid and amorphous structures was built using a pulsed neutron source installed at the Tohoku University 300 MeV electron linac. Procedures for converting the scattered neutron intensity observed as a function of the time of flight of neutrons into the structure factor have been given and performances of the diffractometer including energy integration paths, weighting functions and resolutions have also been discussed. The result of CCl_4 liquid is shown as an example of the measurement and the structure of a single CCl_4 molecule in the liquid state is compared with other experimental observations