An evaluation of the silicon spectral range for determination of nutrient content of grape vines

The grape industry relies on in situ crop assessment to aid in the day-to-day and seasonal management of their crop. In the case of soil-plant chemistry interactions, there are six key nutrients of interest to viticulturists in the growing of wine grapes: nitrogen, potassium, phosphorous, magnesium, zinc, and boron. Traditional methods of determining the levels of these nutrients are through collection and chemical analysis of petiole samples from the grape vines themselves. In this study, however, we collected ground-level observations of the spectra of the grape vines using a hyperspectral spectroradiometer (0.4-2.5µm range; 1nm resampled spectral interval) at the same time that petioles samples were harvested. The data were collected for two different grape cultivars, both during bloom and veraison phenological stages to provide analytical variability, while also considering the impact of temporal/seasonal change. The data were interpolated to 1nm bandwidths, yielding a consistent 1nm spectral resolution before comparing it to the nutrient data collected. Spectral reflectance also was resampled to match the 10nm bands used by the Airborne Visible and Infrared Imaging Spectrometer (AVIRIS); this was done to assess the efficacy of nutrient modeling using a more standard, airborne system’s spectral resolution. Our analysis was limited to the silicon photodiode range to increase the utility of the approach for wavelength-specific cameras (via spectral filters) in a low cost unmanned aerial vehicle (UAV) platform. Five different approaches were tested to fit the data to the nutrient data. These were: a narrow-band Normalized Difference Index (NDI) approach using a standard linear fit, step-wise linear regression (SLR) using the silicon range of wavelengths, SLR using the NDI that correlated highly with the nutrient data, SLR using the 1st derivative of the reflectance spectra, and SLR using continuum-removed spectra, applied over the red trough (560-750nm) spectral region. For 1nm reflectance data, these methods generated models for nutrient modeling using between 2-10 wavelengths, and associated coefficients of determination values ranging between R2 = 0.74-0.86 across the six nutrients. In the case of the 10nm resampled spectral data, model fits ranged between R2 = 0.61-0.93 across the six nutrients, using 2-18 unique wavelength bands. These results bode well for eventual non-destructive, accurate and precise assessment of vineyard nutrient status through the use of UAVs

Results of High-Temperature Strain-Fatigue Tests on Reactor-Grade Aluminum- Base Materials

Strain-fatigue tests were conducted on two reactor-grade aluminum-base alloys and a sintered aluminum product at 80 to 900 deg F. The materials are used in reactor components, and one of the aluminum alloys has a potential for use in experimental models. Results of the tests indicate that strain-fatigue behavior at room temperature for the materials was similar to that of other ductile materials. The aluminum-alloy specimens at 600 deg F yielded results of limited value owing to the instability of the specimens. At 900 deg F the sintered aluminum product exhibited a significant loss of ductility with a cyclic life 16% of that at 600 deg F. (auth

Numerical Simulations of Supersonic Flow in a Linear Aerospike Micronozzle

In this study, we numerically examine thrust performance of the linear aerospike nozzle micro-thruster for various nozzle spike lengths and flow parameters in order to identify optimal geometry(s) and operating conditions. Decomposed hydrogen-peroxide is used as the monopropellant in the studies. Performance is characterized for different flow rates (Reynolds numbers) and aerospike lengths, and the impact of micro-scale viscous forces is assessed. It is found that 2-D full micro-aerospike efficiencies can exceed axisymmetric micro-nozzle efficiencies by as much as 10%; however, severe penalties are found to occur for truncated spikes at low Reynolds numbers

Nodes of the Gap Function and Anomalies in Thermodynamic Properties of Superfluid 3^3He

Departures of thermodynamic properties of three-dimensional superfluid $^3$He from the predictions of BCS theory are analyzed. Attention is focused on deviations of the ratios $\Delta(T=0)/T_c$ and $[C_s(T_c)-C_n(T_c)]/C_n(T_c)$ from their BCS values, where $\Delta(T=0)$ is the pairing gap at zero temperature, $T_c$ is the critical temperature, and $C_s$ and $C_n$ are the superfluid and normal specific heats. We attribute these deviations to the momentum dependence of the gap function $\Delta(p)$, which becomes well pronounced when this function has a pair of nodes lying on either side of the Fermi surface. We demonstrate that such a situation arises if the P-wave pairing interaction $V(p_1,p_2)$, evaluated at the Fermi surface, has a sign opposite to that anticipated in BCS theory. Taking account of the momentum structure of the gap function, we derive a closed relation between the two ratios that contains no adjustable parameters and agrees with the experimental data. Some important features of the effective pairing interaction are inferred from the analysis.Comment: 17 pages, 4 figure

Generic theory of colloidal transport

We discuss the motion of colloidal particles relative to a two component fluid consisting of solvent and solute. Particle motion can result from (i) net body forces on the particle due to external fields such as gravity; (ii) slip velocities on the particle surface due to surface dissipative phenomena. The perturbations of the hydrodynamic flow field exhibits characteristic differences in cases (i) and (ii) which reflect different patterns of momentum flux corresponding to the existence of net forces, force dipoles or force quadrupoles. In the absence of external fields, gradients of concentration or pressure do not generate net forces on a colloidal particle. Such gradients can nevertheless induce relative motion between particle and fluid. We present a generic description of surface dissipative phenomena based on the linear response of surface fluxes driven by conjugate surface forces. In this framework we discuss different transport scenarios including self-propulsion via surface slip that is induced by active processes on the particle surface. We clarify the nature of force balances in such situations.Comment: 22 pages, 1 figur

Smooth vortex precession in superfluid 4He

We have measured a precessing superfluid vortex line, stretched from a wire to the wall of a cylindrical cell. By contrast to previous experiments with a similar geometry, the motion along the wall is smooth. The key difference is probably that our wire is substantially off center. We verify several numerical predictions about the motion, including an asymmetry in the precession signature, the behavior of pinning events, and the temperature dependence of the precession.Comment: 8 pages, 8 figure

Temperature Dependence of Hall Response in Doped Antiferromagnets

Using finite-temperature Lanczos method the frequency-dependent Hall response is calculated numerically for the t-J model on the square lattice and on ladders. At low doping, both the high-frequency RH* and the d.c. Hall coefficient RH0 follow qualitatively similar behavior at higher temperatures: being hole-like for T > Ts~1.5J and weakly electron-like for T < Ts. Consistent with experiments on cuprates, RH0 changes, in contrast to RH*, again to the hole-like sign below the pseudogap temperature T*, revealing a strong temperature variation for T->0.Comment: LaTeX, 4 pages, 4 figures, submitted to PR

Low energy and dynamical properties of a single hole in the t-Jz model

We review in details a recently proposed technique to extract information about dynamical correlation functions of many-body hamiltonians with a few Lanczos iterations and without the limitation of finite size. We apply this technique to understand the low energy properties and the dynamical spectral weight of a simple model describing the motion of a single hole in a quantum antiferromagnet: the $t-J_z$ model in two spatial dimension and for a double chain lattice. The simplicity of the model allows us a well controlled numerical solution, especially for the two chain case. Contrary to previous approximations we have found that the single hole ground state in the infinite system is continuously connected with the Nagaoka fully polarized state for $J_z \to 0$. Analogously we have obtained an accurate determination of the dynamical spectral weight relevant for photoemission experiments. For $J_z=0$ an argument is given that the spectral weight vanishes at the Nagaoka energy faster than any power law, as supported also by a clear numerical evidence. It is also shown that spin charge decoupling is an exact property for a single hole in the Bethe lattice but does not apply to the more realistic lattices where the hole can describe closed loop paths.Comment: RevTex 3.0, 40 pages + 16 Figures in one file self-extracting, to appear in Phys. Rev

The breakdown of the Nagaoka phase in the 2D t-J model

In the limit of weak exchange, J, at low hole concentration, the ground state of the 2D t-J model is believed to be ferromagnetic. We study the leading instability of this Nagaoka state, which emerges with increasing J. Both exact diagonalization of small clusters, and a semiclassical analytical calculation of larger systems show that above a certain critical value of the exchange, Nagaoka's state is unstable to phase separation. In a finite-size system a bubble of antiferromagnetic Mott insulator appears in the ground state above this threshold. The size of this bubble depends on the hole concentration and scales as a power of the system size, N