21,508 research outputs found
Laboratory tank studies of a single species of phytoplankton using a remote sensing fluorosensor
Phytoplankton were grown in the laboratory for the purpose of testing a remote fluorosensor. The fluorosensor uses a unique four-wavelength dye laser system to excite phytoplankton bearing chlorophyll and to measure the chlorophyll fluorescence generated by this excitation. Six different species were tested, one at a time, and each was grown two to four times. Fluorescence measured by the fluorosensor provides good quantitative measurement of chlorophyll concentrations for all species tested while the cultures were in log phase growth. Fluorescene cross section ratios obtained in the single species tank tests support the hypothesis that the shape of the fluorescence cross section curve remains constant with the species (differences in fluorescence cross section ratios are a basis for determining composition of phytoplankton according to color group when a multiwavelength source of excitation is used. Linear relationships exist between extracted chlorophyll concentration and fluorescence measured by the remote fluorosensor during the log phase growth of phytoplankton cultures tested
Visible absorbance spectra: A basis for in situ and passive remote sensing of phytoplankton concentration and community composition
The concentration and composition of phytoplankton populations are measured by an optical method which can be used either in situ or remotely. This method is based upon the in vivo light absorption characteristics of phytoplankton. To provide a data base for testing assumptions relative to the proposed method, visible absorbance spectra of pure cultures of 20 marine phytoplankton were obtained under laboratory conditions. Descriptive and analytical statistics were computed for the absorbance spectra and were used to make comparisons between members of major taxonomic groups and between groups. Spectral variation between the members of the major taxonomic groups was observed to be considerably less than the spectral variation between these groups. In several cases the differences between the mean absorbance spectra of major taxonomic groups are significant enough to be detected with passive remote sensing techniques
Experimental wake survey behind Viking 75 entry vehicle at angles of attack of 0 deg, 5 deg, and 10 deg, Mach numbers from 0.20 to 1.20, and longitudinal stations from 1.50 to 11.00 body diameters
An investigation was conducted to obtain flow properties in the wake of a preliminary configuration of the Viking '75 Entry Vehicle at Mach numbers from 0.20 to 1.20 and at angles of attack of 0 deg, 5 deg, and 10 deg. The wake flow properties were calculated from total and static pressures measured with a pressure rake at longitudinal stations varying from 1.50 to 11.00 body diameters, and are presented in tabulated and plotted form. The wake properties were essentially symmetrical about the X-axis at alpha = 0 deg and the profiles were shifted away from the X-axis at angles of attack. An unexpected reduction in wake property ratios occurred as the Mach number increased from 0.60 to 1.00; these ratios then increased as the Mach number increased to 1.20. The reduction was present for all the longitudinal stations of the tests and decreased with increased longitudinal distance
A new approach to mass spectrometer measurements of thermospheric density
The gas sampling problem in satellite and high velocity probes was investigated by applying the theory of a drifting Maxwellian gas. A lens system using a free stream ion source was developed and experimentally evaluated over the pressure range of 0.00001 to 0.01 N/m sq (approx. 10 to the minus 7th power to 0.0001 torr). The source has high beam transparency, which minimizes gas-surface collisions within, or near, the ionization volume. It is shown that for high ion energy (60 eV), the extracted ion beam has an on-axis energy spread of less than 4 eV, and that 90 percent of the ions are within 2.5 deg of the beam axis. It is concluded that the molecular beam mass spectrometer concept, developed for gas density measurements in the upper atmosphere, substantially reduces gas-surface scattering and gas-surface reactions in the sample, and preserves the integrity of the gas sample during the analysis process. Studies show that both the Scout and Delta launch vehicles have adequate volume, control, velocity, and data acquisition capability necessary to obtain thermospheric number density in real time
Development of Replacement Heifers using Combinations of Three Forage Types and Feed Supplements (with or without Broiler Litter)
The proper management of replacement heifers is an essential component of successful cow/calf operations. The level of management and nutrition applied to replacement heifers as calves and yearlings can impact their subsequent reproductive performance and productivity
Quasilocal Energy for a Kerr black hole
The quasilocal energy associated with a constant stationary time slice of the
Kerr spacetime is presented. The calculations are based on a recent proposal
\cite{by} in which quasilocal energy is derived from the Hamiltonian of
spatially bounded gravitational systems. Three different classes of boundary
surfaces for the Kerr slice are considered (constant radius surfaces, round
spheres, and the ergosurface). Their embeddings in both the Kerr slice and flat
three-dimensional space (required as a normalization of the energy) are
analyzed. The energy contained within each surface is explicitly calculated in
the slow rotation regime and its properties discussed in detail. The energy is
a positive, monotonically decreasing function of the boundary surface radius.
It approaches the Arnowitt-Deser-Misner (ADM) mass at spatial infinity and
reduces to (twice) the irreducible mass at the horizon of the Kerr black hole.
The expressions possess the correct static limit and include negative
contributions due to gravitational binding. The energy at the ergosurface is
compared with the energies at other surfaces. Finally, the difficulties
involved in an estimation of the energy in the fast rotation regime are
discussed.Comment: 22 pages, Revtex, Alberta-Thy-18-94. (the approximations in Section
IV have been improved. To appear in Phys. Rev. D
Spin Transfer Torque for Continuously Variable Magnetization
We report quantum and semi-classical calculations of spin current and
spin-transfer torque in a free-electron Stoner model for systems where the
magnetization varies continuously in one dimension.Analytic results are
obtained for an infinite spin spiral and numerical results are obtained for
realistic domain wall profiles. The adiabatic limit describes conduction
electron spins that follow the sum of the exchange field and an effective,
velocity-dependent field produced by the gradient of the magnetization in the
wall. Non-adiabatic effects arise for short domain walls but their magnitude
decreases exponentially as the wall width increases. Our results cast doubt on
the existence of a recently proposed non-adiabatic contribution to the
spin-transfer torque due to spin flip scattering.Comment: 11 pages, 9 figure
Sources of Error for Ultrasonic Measurements of Steer Compositional Traits in Grazing Studies
Real-time ultrasound technology has potential use for measuring compositional traits in grazing studies. Sources of error with this application must be identified for designing experiments with adequate precision to determine treatment effects. A study was conducted to evaluate breed type (Angus x Brahman, AB; Simmental x [Angus x Brahman], SAB; Simmental x [Brahman x Hereford], SBH), initial body weight, and initial ultrasonic measures as sources of experimental error in the analyses of external fat (EF) depths and longissimus dorsi (ribeye) areas (LDA). Steers were ultrasonically scanned at the initiation and conclusion of a grazing study that examined stocking rate effects on average daily gain (ADG) and body condition of steers grazing a mixture of rye (Secale cereale L.) and ryegrass (Lolium multiflorum L.). Breed type did not affect (P \u3e 0.10) final or increases in EF, and curvilinear trends of increased EF with increasing ADG (P \u3e 0.10) among the breed types over the range of ADG (0.03 kg d-1 to 1.62 kg d-1). The three breed types showed curvilinear increases in LDA as ADG increased, but the trends were different (P \u3c 0.05) for SBH than for the other two types. Final LDA and magnitude of increases in EF and LDA over the experimental period were influenced (P \u3c 0.05) by initial body weight. Results indicated that allotting cattle to pastures based on a combination of breed type and body weight should improve precision in detecting treatment effects
Demagnetization Borne Microscale Skyrmions
Magnetic systems are an exciting realm of study that is being explored on
smaller and smaller scales. One extremely interesting magnetic state that has
gained momentum in recent years is the skyrmionic state. It is characterized by
a vortex where the edge magnetic moments point opposite to the core. Although
skyrmions have many possible realizations, in practice, creating them in a lab
is a difficult task to accomplish. In this work, new methods for skyrmion
generation and customization are suggested. Skyrmionic behavior was numerically
observed in minimally customized simulations of spheres, hemisphere,
ellipsoids, and hemi-ellipsoids, for typ- ical Cobalt parameters, in a range
from approximately 40 nm to 120 nm in diameter simply by applying a field
Thermally activated escape rates of uniaxial spin systems with transverse field
Classical escape rates of uniaxial spin systems are characterized by a
prefactor differing from and much smaller than that of the particle problem,
since the maximum of the spin energy is attained everywhere on the line of
constant latitude: theta=const, 0 =< phi =< 2*pi. If a transverse field is
applied, a saddle point of the energy is formed, and high, moderate, and low
damping regimes (similar to those for particles) appear. Here we present the
first analytical and numerical study of crossovers between the uniaxial and
other regimes for spin systems. It is shown that there is one HD-Uniaxial
crossover, whereas at low damping the uniaxial and LD regimes are separated by
two crossovers.Comment: 4 PR pages, 3 figures, final published versio
- …