Serum Amyloid P Component (SAP)-Like Protein From Botryllid Ascidians Provides a Clue to Amyloid Function

The HA-1 lectin isolated from Botrylloides leachii has an amino acid composition similar to that of mammalian serum amyloid protein (SAP). SAP is a universal component of mammalian amyloid deposits. Like SAP, HA-1 has a disc ultrastructure, and antibody to HA-1 binds both (a) to amyloidlike fibers deposited between rejected Botrylloides colonies and (b) to cerebral amyloid deposits in Alzheimer's disease brains. Deposition of protochordate amyloid within rejection sites and surrounding fouling organisms implies that these fibers function as barriers to allogeneic and infectious challenge. Similarly, mammalian amyloid may also function to contain inflammatory lesions and to limit the spread of certain infections. Pathological amyloidotic conditions in humans, such as Alzheimer's disease, may result from unregulated expression of this primitive encapsulation response

Defects in SiO2 as the possible origin of near interface traps in the SiC∕SiO2 system: A systematic theoretical study

A systematic study of the level positions of intrinsic and carbon defects in SiO2 is presented, based on density functional calculations with a hybrid functional in an alpha-quartz supercell. The results are analyzed from the point of view of the near interface traps (NIT), observed in both SiC/SiO2 and Si/SiO2 systems, and assumed to have their origins in the oxide. It is shown that the vacancies and the oxygen interstitial can be excluded as the origin of such NIT, while the silicon interstitial and carbon dimers give rise to gap levels in the energy range inferred from experiments. The properties of these defects are discussed in light of the knowledge about the SiC/SiO2 interface

Radiative Correction to the Transferred Polarization in Elastic Electron-Proton Scattering

Model independent radiative correction to the recoil proton polarization for the elastic electron-proton scattering is calculated within method of electron structure functions. The explicit expressions for the recoil proton polarization are represented as a contraction of the electron structure and the hard part of the polarization dependent contribution into cross-section. The calculation of the hard part with first order radiative correction is performed. The obtained representation includes the leading radiative corrections in all orders of perturbation theory and the main part of the second order next-to-leading ones. Numerical calculations illustrate our analytical results.Comment: 14 pages, 4 figure

Measurement and interpretation of the polarization of the x-ray line emission of heliumlike Fe XXV excited by an electron beam

The linear polarization of the 1s2p 1P1→1s2 1S0 resonance line, the 1s2p 3P1,2→1s2 1S0 intercombination lines, and the 1s2s 3S1→1s2 1S0 forbidden line was measured in heliumlike Fe XXV excited near threshold by a monoenergetic electron beam. The measurement was carried out with a high-resolution x-ray spectrometer employing a set of two analyzing crystals that acted as polarizers by selectively reflecting the individual polarization components. A value of +0.56-0.08+0.17 was determined for the polarization of the 1P1 line, -0.53-0.02+0.05 for the 3P2 line, -0.22-0.02+0.05 for the 3P1 line, and -0.076-0.007+0.007 for the 3S1 line. The measurements were compared with results from a relativistic distorted-wave calculation, which was carried out for a number of mid-Z heliumlike ions (Mg10+–Kr34+), and good agreement was found. By contrast, disagreement was noted with predictions based on Coulomb-Born calculations, allowing us to distinguish between theoretical approaches

Electron Impact Excitation Cross Section Measurement for n=3 to n=2 Line Emission in Fe(17+) to Fe(23+)

We have measured the electron impact excitation cross sections for the strong iron L-shell 3 --> 2 lines of Fe XVIII to Fe XXIV at the EBIT-I electron beam ion trap using a crystal spectrometer and NASA-Goddard Space Flight Centers 6 x 6 pixel array microcalorimeter. The cross sections were determined by direct normalization to the well established cross section of radiative electron capture through a sophisticated model analysis which results in the excitation cross section for the strong Fe L-shell lines at multiple electron energies. This measurement is part of a laboratory X-ray astrophysics program utilizing the Livermore electron beam ion traps EBIT-I and EBIT-II

Noise Probe of the Dynamic Phase Separation in La2/3Ca1/3MnO3

Giant Random Telegraph Noise (RTN) in the resistance fluctuation of a macroscopic film of perovskite-type manganese oxide La2/3Ca1/3MnO3 has been observed at various temperatures ranging from 4K to 170K, well below the Curie temperature (TC = 210K). The amplitudes of the two-level-fluctuations (TLF) vary from 0.01% to 0.2%. We use a statistical analysis of the life-times of the TLF to gain insight into the microscopic electronic and magnetic state of this manganite. At low temperature (below 30K) The TLF is well described by a thermally activated two-level model. An estimate of the energy difference between the two states is inferred. At higher temperature (between 60K and 170K) we observed critical effects of the temperature on the life-times of the TLF. We discuss this peculiar temperature dependence in terms of a sharp change in the free energy functional of the fluctuators. We attribute the origin of the RTN to be a dynamic mixed-phase percolative conduction process, where manganese clusters switch back and forth between two phases that differ in their conductivity and magnetization.Comment: 15 pages, PDF only, Phys. Rev. Lett. (in press

Quantum Size Effect transition in percolating nanocomposite films

We report on unique electronic properties in Fe-SiO2 nanocomposite thin films in the vicinity of the percolation threshold. The electronic transport is dominated by quantum corrections to the metallic conduction of the Infinite Cluster (IC). At low temperature, mesoscopic effects revealed on the conductivity, Hall effect experiments and low frequency electrical noise (random telegraph noise and 1/f noise) strongly support the existence of a temperature-induced Quantum Size Effect (QSE) transition in the metallic conduction path. Below a critical temperature related to the geometrical constriction sizes of the IC, the electronic conductivity is mainly governed by active tunnel conductance across barriers in the metallic network. The high 1/f noise level and the random telegraph noise are consistently explained by random potential modulation of the barriers transmittance due to local Coulomb charges. Our results provide evidence that a lowering of the temperature is somehow equivalent to a decrease of the metal fraction in the vicinity of the percolation limit.Comment: 21 pages, 8 figure

Excitation Cross Section Measurement for n=3 to n=2 Line Emission in Fe17+ to Fe23+

The authors report the measurement of electron impact excitation cross sections for the strong iron L-shell 3 {yields} 2 lines of Fe XVIII through Fe XXIV at the EBIT-I electron beam ion trap using a crystal spectrometer and a 6 x 6 pixel array microcalorimeter. The cross sections were determined by direct normalization to the well established cross section of radiative electron capture through a sophisticated model analysis which results in the excitation cross section for 48 lines at multiple electron energies. They also studied the electron density dependent nature of the emission lines, which is demonstrated by the effective excitation cross section of the 3d {yields} 2p transition in Fe XXI