Observability of conduction electron spin resonance (CESR) in superconductors

The condition for the observability of CESR in superconducting thin films is analysed taking into account the finiteness of the flux penetration depth. We have explicitly evaluated the path-dependent phase mixing factor occuring in the expression for power absorption. The calculated line width turns out to be of the order of, or larger than, the nominal resonance frequency for the experimentally realisable choice of parameters.

Electron paramagnetic resonance study of vanadyl ion in K2Zn(SO4)2·6H2O and K2Mg(SO4)2·6H2O

EPR study of the vanadyl ion has been carried out in its paramagnetically dilute form in K2Zn(SO4)2·6H2O and K2Mg(SO4)2·6H2O at room temperature at X-band. The vanadyl ion enters the divalent metal site and preferentially orients itself in the direction of the water molecules forming the octahedron and forms the vanadyl sulfate pentahydrate complex. The g and A tensorscorresponding to the two populous V-O orientations have been analyzed to obtain the principal values and their direction cosines with respect to the crystallographics axes. It is found that the g and A tensor have the same principal frames of reference within the limits of eperimental error. A correlation between the metal-water distance and the populations of the different V-O orientations is observed.

Selectivity in the Interaction of Electron Donor and Acceptor Molecules with Graphene and Single-Walled Carbon Nanotubes

Interaction of electron donor and acceptor molecules with graphene samples prepared by different methods as well as with single-walled carbon nanotubes (SWNTs) has been investigated by isothermal titration calorimetry (ITC). The ITC interaction energies of the graphene samples and SWNTs with electron acceptor molecules are higher than those with electron donor molecules. Thus, tetracyanoethylene (TCNE) shows the highest interaction energy with both graphene and SWNTs. The interaction energy with acceptor molecules varies with the electron affinity as well as with the charge-transfer transition energy for different aromatics. Metallic SWNTs interact reversibly with electron acceptor molecules, resulting in the opening of a gap.

A probabilistic approach to the problem of electron localization in disordered systems and sharpness of the mobility edge

By applying the theory of the asymptotic distribution of extremes and a certain stability criterion to the question of the domain of convergence in the probability sense, of the renormalized perturbation expansion (RPE) for the site self-energy in a cellularly disordered system, an expression has been obtained in closed form for the probability of nonconvergence of the RPE on the real-energy axis. Hence, the intrinsic mobility mu (E) as a function of the carrier energy E is deduced to be given by mu (E)= mu 0exp(-exp( mod E mod -Ec) Delta ), where Ec is a nominal 'mobility edge' and Delta is the width of the random site-energy distribution. Thus mobility falls off sharply but continuously for mod E mod >Ec, in contradistinction with the notion of an abrupt 'mobility edge' proposed by Cohen et al. and Mott. Also, the calculated electrical conductivity shows a temperature dependence in qualitative agreement with experiments on disordered semiconductors.

Three-dimensional reconstruction of black tiger prawn (Penaeus monodon) spermatozoa using serial block-face scanning electron microscopy

Serial Block-Face Scanning Electron Microscopy (SBF-SEM) was used in this study to examine the ultrastructural morphology of Penaeus monodon spermatozoa. SBF-SEM provided a large dataset of sequential electron-microscopic-level images that facilitated comprehensive ultrastructural observations and three-dimensional reconstructions of the sperm cell. Reconstruction divulged a nuclear region of the spermatophoral spermatozoon filled with decondensed chromatin but with two apparent levels of packaging density. In addition, the nuclear region contained, not only numerous filamentous chromatin elements with dense microregions, but also large centrally gathered granular masses. Analysis of the sperm cytoplasm revealed the presence of degenerated mitochondria and membrane-less dense granules. A large electron-lucent vesicle and "arch-like" structures were apparent in the subacrosomal area, and an acrosomal core was found in the acrosomal vesicle. The spermatozoal spike arose from the inner membrane of the acrosomal vesicle, which was slightly bulbous in the middle region of the acrosomal vesicle, but then extended distally into a broad dense plate and to a sharp point proximally. This study has demonstrated that SBF-SEM is a powerful technique for the 3D ultrastructural reconstruction of prawn spermatozoa, that will no doubt be informative for further studies of sperm assessment, reproductive pathology and the spermiocladistics of penaeid prawns, and other decapod crustaceans. J. Morphol., 2016. (c) 2016 Wiley Periodicals, Inc.

Electron Spectroscopic Studies of Oxygen and Carbon Dioxide Adsorbed on Metal Surfaces

Adsorption of oxygen on Ni, Cu, Pd, Ag, and Au surfaces has been investigated by employing UV and X-ray photoelectron spectrscopy as well as electron energy loss spectroscopy (EELS). Molecularly chemisorbed (singlet) oxygen is found on Ni, Cu, Ag, and Au surfaces showing features such as stabilization of the rB* orbital, destabilization of the .nu orbital, higher O(1s) binding energy than the atomic species, and a band 2-3 eV below the Fermi level due to metal d-O(2p)u* interaction. 0-0 and metal-oxygen stretching frequencies have been observed in EELS. Physical adsorption of O2 is found to occur on Pd and Ni surfaces, only at high exposures in the latter case. Physical adsorption and multilayer condensation of CO, on metal surfaces are distinguished by characteristic relaxation shifts in UPS as well as O(1s) binding energies. Adsorption of CO on a Ni surface covered with presorbed atomic oxygen gives rise to C02.

An electron spectroscopic study of the surface oxidation of glassy and crystalline Cu-Zr alloys

Surface oxidation of three metglasses in the Cu-Zr system has been investigated by employing X-ray photoelectron spectroscopy and Auger electron spectroscopy with a view to comparing their oxidation behaviour with that of the corresponding crystalline states of the alloys. Surface oxidation of pure Zr metal has also been examined in detail using these techniques. Sub-oxides of Zr are formed during the initial stages of oxidation of Zr (at oxygen exposures <10L), while at higher exposures, ZrO2 is formed together with the highest possible sub-oxide which the authors designate as 'ZrO'. The relative proportion of 'ZrO' goes through a maximum in the range 25-50 L. Both the glassy and the crystalline states of the Cu-Zr alloys exhibit preferential oxidation of Zr. The glassy alloys exhibit a higher rate of oxidation at intermediate exposures compared with the crystalline states of the alloys; the extent of oxidation at higher oxygen exposures is, however, higher for crystalline alloys. Interatomic Auger transitions have been found in the Zr+O2 system as well as in Cu-Zr alloys.

Electron spin resonance study of copper(II) doped ferroelectric ammonium sulphate

Single crystal electron spin resonance studies of Cu2+ doped ferroelectric ammonium sulphate ((NH4)2SO4, Tc = 223 K) are reported at 300 and 77 K. The Cu2+ ion is found to enter the lattice interstitially with a trigonal bipyramidal coordination. Proton superhyperfine interaction is found for magnetic field directions close to the a-axis. Changes are observed in the 77 K recordings indicating a distortion of the trigonal bipyramid consistent with crystal structure data. An increase of the proton superhyperfine constant in the ferroelectric phase is indicative of stronger hydrogen bonding. The Cu2+ ion doped as an impurity in a trigonal bipyramid environment in a diamagnetic host lattice is reported for the first time.

A high gain aluminium electron multiplier

A twenty stage electron multiplier using aluminium as dynode material is described. When operated in DC mode, very stable gains approaching 106 were obtained with input currents of the order of 10-12 A, even after repeated exposures to the atmospheres.

Dielectric and Electron Spin Resonance Spectroscopic Studies of Glassy Crystalline States of Organic Compounds

Dielectric studies of the glassy crystalline states of cyclohexanol, cyclohexanone, and camphor obtained by upercooling the plastic crystalline phase demonstrate the presence of characteristic a- and p-relaxations. The parameters of the a-relaxation fit the Vogel-Tammann-Fulcher (VTF) equation. ESR spin-probe studies of the glassy crystalline phase of cyclohexanol show that there is a marked decrease in the correlation time above the glasslike transition temperature. The present studies suggest the similarity between glassy crystals having long-range orientational disorder and glasses which are known to betra nslationally disordered.

Itinerant electron ferromagnetism in Sr2+-, Ca2+-, and Ba2+-doped rare-earth orthocobaltites (Ln3+1�xM2+xCoO3)

Electronic and magnetic properties of Ln1�xSrxCoO3 (Ln = Pr, Nd, Sm, Eu, and Gd) systems show that above a critical value of x, the d electrons become itinerant while the materials become ferromagnetic at low temperatures. The ferromagnetic component increases with increase in x and decrease in temperature. The Curie temperature increases with x and decreases with decrease in the size of the rare-earth ion. Incorporation of Ba2+ in LaCoO3 favors itinerant electron ferromagnetism relative to Sr2+ while Ca2+ is less favorable than Sr2+.

Radio frequency emission in electron beam-plasma and beam-beam interaction

A linear excitation of electromagnetic modes at frequencies (n + ı89 in a plasma through which two electron beams are contra-streaming along the magnetic field is investigated. This may be a source of the observed {cote emissions at auroral latitudes.

Low-frequency degenerate surface modes of an electron-hole plasma

The computations of Flahive and Quinn1 of the dispersion curves of low frequency degenerate surface (DS) modes propagating along the magnetic field in an electron-hole plasma are extended to higher values of the wavenumber. We find that beyond a certain value of the wavenumber the DS mode re-enters the allowed region of surface wave propagation and tends to an asymptotic frequency ωR (<ωLH). These low frequency resonances of an electron-hole plasma are discussed with reference to the experimental observations.

Electron and proton transfer in NADH:ubiquinone oxidoreductase (Complex I) from Escherichia coli

Cells of every living organism on our planet − bacterium, plant or animal − are organized in such a way that despite differences in structure and function they utilize the same metabolic energy represented by electrochemical proton gradient across a membrane. This gradient of protons is generated by the series of membrane bound multisubunit proteins, Complex I, II, III and IV, organized in so-called respiratory or electron transport chain. In the eukaryotic cell it locates in the inner mitochondrial membrane while in the bacterial cell it locates in the cytoplasmic membrane. The function of the respiratory chain is to accept electrons from NADH and ubiquinol and transfer them to oxygen resulting in the formation of water. The free energy released upon these redox reactions is converted by respiratory enzymes into an electrochemical proton gradient, which is used for synthesis of ATP as well as for many other energy dependent processes. This thesis is focused on studies of the first member of the respiratory chain − NADH:ubiquinone oxidoreductase or Complex I. This enzyme has a boot-shape structure with hydrophilic and hydrophobic domains, the former of which has all redox groups of the protein, the flavin and eight to nine iron-sulfur clusters. Complex I serves as a proton pump coupling transfer of two electrons from NADH to ubiquinone to the translocation of four protons across the membrane. So far the mechanism of energy transduction by Complex I is unknown. In the present study we applied a set of different methods to study the electron and proton transfer reactions in Complex I from Escherichia coli. The main achievement was the experiment that showed that the electron transfer through the hydrophilic domain of Complex I is unlikely to be coupled to proton transfer directly or to conformational changes in the protein. In this work for the first time properties of all redox centers of Complex I were characterized in the intact purified bacterial enzyme. We also probed the role of several conserved amino acid residues in the electron transfer of Complex I. Finally, we found that highly conserved amino acid residues in several membrane subunits form a common pattern with a very prominent feature – the presence of a few lysines within the membrane. Based on the experimental data, we suggested a tentative principle which may govern the redox-coupled proton pumping in Complex I.

Sonochemical Acceleration of Conversion of 2-Alkoxytetrahydrofurans to y-Butyrolactones Synthesis of (±)-Quercus Lactone-A

Effect of sonochemical irradiation on the conversion of 2-alkoxytetrahydrofurans to γ-butyro-1actores by Jones reagent, and its extension to the highly stereoselective synthesis of quercus lactone a, is reported.