Electrical methods of determining soil moisture content

The electrical permittivity of soils is a useful indicator of soil moisture content. Two methods of determining the permittivity profile in soils are examined. A method due to Becher is found to be inapplicable to this situation. A method of Slichter, however, appears to be feasible. The results of Slichter's method are extended to the proposal of an instrument design that could measure available soil moisture profile (percent available soil moisture as a function of depth) from a surface measurement to an expected resolution of 10 to 20 cm

The Scattering of a Plane Electromagnetic Wave by a Finite Cone

This paper treats the solution of the -vector Helmholtz equation for the case of a plane electromagnetic wave at ’nose-on\u27 incidence, on a perfectly-conducting cone of finite size* The solution presented is exact and in the form of an infinite series of spherical harmonics. The expansion coefficients of the series are determined by a set of an infinite number of equations involving an infinite number of unknowns. A discussion and numerical investigation of the field singularities at the tip and edge of the cone are included* as well as graphs of the associated Legendre functions of non-integral degree, P1(cos θ), and their first derivative

Qualidade sanitária de sementes de pau-cigarra (Senna multijuga).

Resumo 38

A model analysis of the photosynthetic response of Vitis vinifera L. cvs Riesling and Chasselas leaves in the field: I. Interaction of age, light and temperature

The photosynthetic activity (A) of leaves of different ages on primary and secondary shoots of Riesling and Chasselas vines was measured under  field  conditions  in relation to photon flux density  (PFD) at various leaf temperatures. The data sets from 4 years and two locations (Geisenheim, Germany; Changins, Switzerland) were  analysed  using  non-linear  regression models  to determine possible  genetic  and/or  climate-induced differences  in  the  light  and  temperature  response between different  leaf ages. A non-rectangular hyperbola with  physiologically meaningful  parameters was  found  to  adequately describe  the  response to photon  flux density. For both  varieties, maximum photosynthetic  rates were  observed  on  leaves  of primary  shoots,  opposite  to  the  clusters,  at  a  leaf  temperature  of  27-32  °C  and  at  light  saturation. Young leaves  showed  a  less  pronounced  temperature  optimum. The  light  response  curves  of photosynthesis  of the  two  cultivars were  similar  over  a  temperature range  of  20-30  °C. Below  this  temperature, Riesling showed higher values of A than Chasselas in most cases, whereas  it was  the reverse when leaf  temperature exceeded 30 °C. This was particularly evident for leaves on secondary shoots and was related to differences  in the photorespiration rate. Mature Riesling  leaves had higher  apparent quantum  yields  (a)  and  lower  light saturation  indices (Is) than Chasselas at  leaf temperatures below  30-35 °C. Dark  respiration  (RD)  and  the light  compensation  point  (Ic)  responded  strongly  to temperature with differences between leaf ages but no consistent difference between varieties. Leaves on secondary shoots of both cultivars had the highest photo-synthetic  activity  during  the  ripening  period  of  the fruit

Highly anisotropic energy gap in superconducting Ba(Fe0.9_{0.9}Co0.1_{0.1})2_{2}As2_{2} from optical conductivity measurements

We have measured the complex dynamical conductivity, $\sigma = \sigma_{1} + i\sigma_{2}$, of superconducting Ba(Fe$_{0.9}$Co$_{0.1}$)$_{2}$As$_{2}$ ($T_{c} = 22$ K) at terahertz frequencies and temperatures 2 - 30 K. In the frequency dependence of $\sigma_{1}$ below $T_{c}$, we observe clear signatures of the superconducting energy gap opening. The temperature dependence of $\sigma_{1}$ demonstrates a pronounced coherence peak at frequencies below 15 cm$^{-1}$ (1.8 meV). The temperature dependence of the penetration depth, calculated from $\sigma_{2}$, shows power-law behavior at the lowest temperatures. Analysis of the conductivity data with a two-gap model, gives the smaller isotropic s-wave gap of $\Delta_{A} = 3$ meV, while the larger gap is highly anisotropic with possible nodes and its rms amplitude is $\Delta_{0} = 8$ meV. Overall, our results are consistent with a two-band superconductor with an $s_{\pm}$ gap symmetry.Comment: 6 pages, 4 figures, discussion on pair-barking scattering and possible lifting of the nodes is adde

Monopolelike probes for quantitative magnetic force microscopy: calibration and application

A local magnetization measurement was performed with a Magnetic Force Microscope (MFM) to determine magnetization in domains of an exchange coupled [Co/Pt]/Co/Ru multilayer with predominant perpendicular anisotropy. The quantitative MFM measurements were conducted with an iron filled carbon nanotube tip, which is shown to behave like a monopole. As a result we determined an additional in-plane magnetization component of the multilayer, which is explained by estimating the effective permeability of the sample within the \mu*-method.Comment: 3 pages, 3 figure

Estimations of electron-positron pair production at high-intensity laser interaction with high-Z targets

Electron-positron pairs' generation occuring in the interaction of $10^{18}$-$10^{20}$~W/cm$^2$ laser radiation with high-Z targets are examined. Computational results are presented for the pair production and the positron yield from the target with allowance for the contribution of pair production processes due to electrons and bremsstrahlung photons. Monte-Carlo simulations using the PRIZMA code confirm the estimates obtained. The possible positron yield from high-Z targets irradiated by picosecond lasers of power $10^2$-$10^3$~TW is estimated to be $10^9$-$10^{11}$

Spin correlations among the charge carriers in an ordered stripe phase

We have observed a diffuse component to the low-energy magnetic excitation spectrum of stripe-ordered La5/3Sr1/3NiO4 probed by neutron inelastic scattering. The diffuse scattering forms a square pattern with sides parallel and perpendicular to the stripe directions. The signal is dispersive, with a maximum energy of ~10 meV. Probed at 2 meV the scattering decreases in strength with increasing temperature, and is barely visible at 100 K. We argue that the signal originates from dynamic, quasi- one-dimensional, antiferromagnetic correlations among the stripe electrons.Comment: 4 pages, 4 figures. To be published in Physical Review Letter

Electron Spin Dynamics and Hyperfine Interactions in Fe/Al_0.1Ga_0.9As/GaAs Spin Injection Heterostructures

We have studied hyperfine interactions between spin-polarized electrons and lattice nuclei in Al_0.1Ga_0.9As/GaAs quantum well (QW) heterostructures. The spin-polarized electrons are electrically injected into the semiconductor heterostructure from a metallic ferromagnet across a Schottky tunnel barrier. The spin-polarized electron current dynamically polarizes the nuclei in the QW, and the polarized nuclei in turn alter the electron spin dynamics. The steady-state electron spin is detected via the circular polarization of the emitted electroluminescence. The nuclear polarization and electron spin dynamics are accurately modeled using the formalism of optical orientation in GaAs. The nuclear spin polarization in the QW is found to depend strongly on the electron spin polarization in the QW, but only weakly on the electron density in the QW. We are able to observe nuclear magnetic resonance (NMR) at low applied magnetic fields on the order of a few hundred Oe by electrically modulating the spin injected into the QW. The electrically driven NMR demonstrates explicitly the existence of a Knight field felt by the nuclei due to the electron spin.Comment: 19 Figures - submitted to PR