[en] A theory for the flux-flow voltage noise in a type-II superconductor in the mixed state is developed. The interactions between the vortices are taken into account via a wavevector-dependent interaction matrix. Applied to Johnson noise in a film without flux flow for a special measuring circuit, the theory predicts a suppression of the power spectrum at low frequencies. For flux-flow noise produced when a perfect vortex lattice moves in a superconducting foil or film containing a random array of independent pinning centers, the theory gives two contributions to the power spectrum: one from transverse velocity fluctuations, which has a characteristic frequency determined by the characteristic frequency of the power spectrum of the elementary pinning force; the other from longitudinal density fluctuations, which may have a characteristic frequency determined by the elastic constants and the geometry of the measuring circuit. Both of these frequencies are much higher than experimentally observed values

[en] Diffuse intensity maxima in ZrN_x caused by short-range ordering (SRO) of nitrogen atoms or vacancies are shown in electron diffraction patterns along four different low-index zone-axes. Analysis of the shape of the diffuse intensity was performed using an equation developed by Sauvage and Parthe . Additional {1,1/2,0} diffuse intensity maxima were also observed and these have not been previously reported for interstitial carbides and nitrides with a NaCl-type crystal structure. Both a Kohn construction, which assumes that the positions of 2k_F110 yield the diffuse intensity maxima, and microdomain crystal models based on M₂X or M₄X₃ crystal structures, are presented as possible explanations for the origin of the {1,1/2,0} diffuse intensity maxima. The close relationship between the SRO model and the shape of the Fermi surface indicates that the Fermi surface in ZrN has nearly the same shape as that of TiN

[en] We have measured the sensitivity of three highly conjugated organic compounds to electron irradiation. Using a 200 keV TEM, loss of crystallinity was determined from quantitative electron-diffraction measurements. Degradation of the molecular ring structure was monitored from fading of the 6 eV π-excitation peak in the energy-loss spectrum. Measurements at incident energies between 30 keV and 100 eV were made using a scanning electron microscope (SEM), by recording gradual decay of the cathodoluminescence (CL) signal. Expressed in Grays, the energy dose required for CL decay in coronene is a factor of 30 lower than for destruction of crystallinity and a factor of 300 lower than for destruction of the molecular structure. Below 1 keV, the CL-decay cross section shows no evidence of a threshold effect, indicating that the damage involved is caused by valence-electron (rather than K-shell) excitation. Therefore even relatively radiation-resistant organic materials may undergo some form of damage when examined in a low-energy electron microscope or a low-voltage SEM

[en] Ultrasonic slurry sampling (USS)-electrothermal vaporization (ETV) dynamic reaction cell^TM (DRC) inductively coupled plasma-mass spectrometry (ICP-MS) has been applied to determine Cr, Cu, Cd, Hg and Pb in rice samples. The influences of instrument operating conditions and slurry preparation on the ion signals were reported. Ascorbic acid was used as a modifier to enhance the ion signals. The background ions at the chromium masses were reduced in intensity significantly by using 0.4 ml min^-1 NH₃ as reaction cell gas in the dynamic reaction cell while a q value of 0.6 was used. Since the sensitivities of Cr, Cu, Cd, Hg and Pb in rice flour slurry and aqueous solution were quite different, standard addition and isotope dilution methods were used for the determination of Cr, Cu, Cd, Hg and Pb in these rice samples. This method has been applied to the determination of Cr, Cu, Cd, Hg and Pb in NIST SRM 1568a rice flour reference material and two rice samples purchased from the market. The analytical results for the reference material agreed with the certified values. The results for the rice samples for which no reference values were available were also found to be in good agreement between the isotope dilution and standard addition methods. The method's detection limits estimated from the standard addition plots were about 0.44, 1.7, 0.4, 0.53 and 0.69 ng g^-1 for Cr, Cu, Cd, Hg and Pb, respectively, in the original rice flour

[en] High-resolution transmission electron microscopy (HRTEM), crystallographic analyses and near-coincident-site atom modeling were used to investigate the atomic structure of a planar {<1 1 1}<_ZrN interface between the Zr and ZrN phases in a Zr-33.9 at.% N alloy. The Zr and ZrN phases were found to have a high-index orientation relationship and display poor atomic matching across the {<1 1 1}<_ZrN interface in the HRTEM images and using near-coincident-site atom modeling. These results show that the {<1 1 1}<_ZrN interface is atomically incoherent and suggest that atomic faceting in the ZrN phase, rather than atomic matching at the interface, is the dominant factor in determining the {<1 1 1}<_ZrN interface plane. Both the experimental HRTEM images and atomic model of the interface indicate that six (0 0 2)_Zr planes correspond to nine (0 2 0)_ZrN planes across the interface, so that it is mathematically rational. The interface is faceted at the micrometer-level and contains atomic steps, similar to partly coherent interfaces, indicating that such features cannot be used to define partial coherency at interfaces

[en] Ambipolar diffusion redistributes magnetic flux in weakly ionized plasmas and plays a critical role in star formation. Simulations of ambipolar diffusion using explicit MHD codes are prohibitively expensive for the level of ionization observed in molecular clouds (∼< 10^-6) since an enormous number of time steps is required to represent the dynamics of the dominant neutral component with a time step determined by the trace ion component. Here we show that ambipolar diffusion calculations can be significantly accelerated by the 'heavy-ion approximation', in which the mass density of the ions is increased and the collisional coupling constant with the neutrals decreased such that the product remains constant. In this approximation, the ambipolar diffusion time and the ambipolar magnetic Reynolds number remain unchanged. We present three tests of the heavy-ion approximation: C-type shocks, the Wardle instability, and the 1D collapse of a magnetized slab. We show that this approximation is quite accurate provided that (1) the square of the Alfven Mach number is small compared to the ambipolar diffusion Reynolds number for dynamical problems, and that (2) the ion mass density is negligible for quasi-static problems; a specific criterion is given for the magnetized slab problem. The first condition can be very stringent for turbulent flows with large density fluctuations

[en] A high energy resolution (σ≤ 1 MeV) neutron detector has been constructed and tested for neutrons in the energy range 80 MeV to 125 MeV. The detector was designed for exclusive, n-p coincidence, quasifree scattering experiments. The design eliminates the need for long neutron flight paths necessary for comparable energy resolution time of flight (TOF) measurements. Unlike TOF measurements, this design allows for a relatively compact geometry (<3 m flight path) with a comparable efficiency solid angle product. The detector consists of thin organic scintillators in which the neutron elastically scatters from free protons. The scattered protons are tracked by alternating thin X and Y horizontal drift chambers and detected in an array of NaI. Results from a test run will be discussed along with possible extensions of this design for use as a polarimeter

[en] Cr/C composite films with 7.9 and 8.5 at% Cr contents were fabricated by facing-target magnetron sputtering. Cr nanoparticles are embedded in amorphous carbon matrix, and Cr atoms bond with C atoms at the interface. The Cr/C films were found to exhibit ferromagnetism in the temperature range of 2–300 K, which is probably induced by uncompensated spins at the surface of Cr nanoparticles. Spin-dependent magnetoresistance (up to −19.5% at 90 kOe and 2 K) was observed in the Cr/C films. The negative MR originates from the alignment of the uncompensated spins at the interface between nanoparticles and matrix. The spin polarization which comes from the interfacial p–d hybridization was calculated to be 21% and 17% in the Cr/C films with 7.9% and 8.5% Cr, respectively. - Highlights: • Cr/C granular films were fabricated by facing-target magnetron sputtering. • Cr/C films were found to exhibit ferromagnetism in the temperature range of 2–300 K. • Spin-dependent magnetoresistance (up to −19.5%) was observed in the Cr/C films. • Both effects are related to the uncompensated spins of the nanoparticles

[en] Fully epitaxial ZnO(0001)/Fe₃O₄(111) spin injection heterostructures with LaNiO₃(111) conductive buffer layers were fabricated on SrTiO₃(111) by sputtering for the prospective spin injection experiments. Epitaxial growth of Fe₃O₄ can be realized at temperatures higher than 673 K on LaNiO₃(111) substrates. The epitaxial relationship was determined to be ZnO(0001)[112^¯0]∥Fe₃O₄(111)[110]∥LaNiO₃(111)[110]∥SrTiO₃(111)[110]. With the increase of LaNiO₃ growth temperature, the surface of Fe₃O₄ in the hybrid heterostructures becomes flatter whereas the magnetization of ZnO/Fe₃O₄ decreases. A Verwey transition located at ∼ 110 K was observed in all the ZnO/Fe₃O₄ heterostructures, demonstrating the stoichiometry and good crystallinity of Fe₃O₄. - Highlights: ► Epitaxial Fe₃O₄/ZnO bilayers were fabricated on conductive LaNiO₃ by sputtering. ► The surface of Fe₃O₄ becomes flatter with the increase of LaNiO₃ growth temperature. ► The moment jump at Verwey transition decreases with the magnetic field increasing.

[en] Stiffness and stability analysis of spacer grid by finite element method are presented. The three dimensional model for calculating takes into account dimples, springs, fuel rods and guid thimbles. And the effects of each component on the stability and stiffness of the spacer grid are investigated. So these characteristics can be predetermined before manufacturing. (author). 4 refs., 6 figs., 1 tab