5,730 research outputs found
Winter wheat: A model for the simulation of growth and yield in winter wheat
The basic ideas and constructs for a general physical/physiological process level winter wheat simulation model are documented. It is a materials balance model which calculates daily increments of photosynthate production and respiratory losses in the crop canopy. The partitioning of the resulting dry matter to the active growing tissues in the plant each day, transpiration and the uptake of nitrogen from the soil profile are simulated. It incorporates the RHIZOS model which simulates, in two dimensions, the movement of water, roots, and soluble nutrients through the soil profile. It records the time of initiation of each of the plant organs. These phenological events are calculated from temperature functions with delays resulting from physiological stress. Stress is defined mathematically as an imbalance in the metabolite supply; demand ratio. Physiological stress is also the basis for the calculation of rates of tiller and floret abortion. Thus, tillering and head differentiation are modeled as the resulants of the two processes, morphogenesis and abortion, which may be occurring simulaneously
Flow Coefficient Behavior for Boundary Layer Bleed Holes and Slots
An experimental investigation into the flow coefficient behavior for nine boundary layer bleed orifice configurations is reported. This test was conducted for the purposes of exploring boundary layer control through mass flow removal and does not address issues of stability bleed. Parametric data consist of bleed region flow coefficient as a function of Mach number, bleed plenum pressure, and bleed orifice geometry. Seven multiple hole configurations and two single slot configurations were tested over a supersonic Mach number range of 1.3 to 2.5 (nominal). Advantages gained by using multiple holes in a bleed region instead of a single spanwise slot are discussed and the issue of modeling an entire array of bleed orifices based on the performance of a single orifice is addressed. Preconditioning the flow approaching a 90 degree inclined (normal) hole configuration resulted in a significant improvement in the performance of the configuration. The same preconditioning caused only subtle changes in performance for a 20 degree inclined (slanted) configuration
Flowfield Measurements Inside a Boundary-Layer Bleed Slot
An experimental investigation was conducted to determine the flowfield inside a bleed slot used to control an oblique shock-wave and turbulent boundary-layer interaction. The slot was oriented normal to the primary flow direction and had a width of 1.0 cm (primary flow direction) and a length of 2.54 cm and spanned 16.5 cm. The approach boundary layer upstream of the interaction was nominally 3.0 cm thick. Two operating conditions were studied: M = 1.98 with a shock generator deflection angle of 6 deg and M = 2.46 with a shock generator deflection angle of 8 deg. Measurements include surface and flowfield static pressure, pitot pressure, and total mass flow through the slot. The results show that despite an initially two-dimensional interaction for the zero-bleed-flow case, the slot does not remove mass uniformly in the spanwise direction. Inside the slot, the flow is characterized bv two separation regions, which significantly reduce the effective flow area. The upper separation region acts as an aerodynamic throat, resulting in supersonic flow through much of the slot
Fluoride adsorption onto an acid treated lateritic mineral from Kenya: Equilibrium studies
Adsorption of fluoride (F) ions from water using acid treated lateritic mineral (LM-1) from Kenya was studied by batch experiments. The effect of acid-treatment of adsorbent and change in temperature, mass of LM-1, pH and selected competing ions was evaluated. The adsorption process was strongly influenced by temperature, pH and adsorbent dosage. The percentage F removal increased the presence of the nitrate and the chlorate ions but decreased the presence of sulphates, chloride and phosphate ions. Adsorption isotherms were classified according to Gilesâ classification and the adsorption data validated using Langmuir and Freundlich isotherms. The data correlated to both the Langmuir and Freundlich isotherms although the data fit to the Freundlich model was somehow better. This showed that F adsorption onto LM-1 followed a mixed adsorption mechanism in which physisorption reactions involving intra-particle diffusion of F into mesoporous sites in LM-1 became increasingly important at higher concentrations and temperatures whereas ion-exchange mechanism involving surface OH- appear to dominate at low surface coverage in more alkaline conditions. With maximum adsorption capacity of 10.5 mg/g, LM-1 could be used to remove F water.Key words: Equilibrium analysis, fluoride adsorption, Langmuir and Freundlich isotherms, Lateritic mineral adsorbent, low-cost adsorbents
Far-UV FUSE spectroscopy of the OVI resonance doublet in Sand2 (WO)
We present Far-Ultraviolet Spectroscopic Explorer (FUSE) spectroscopy of Sand
2, a LMC WO-type Wolf-Rayet star, revealing the OVI resonance P Cygni doublet
at 1032-38A. These data are combined with HST/FOS ultraviolet and Mt Stromlo
2.3m optical spectroscopy, and analysed using a spherical, non-LTE,
line-blanketed code. Our study reveals exceptional stellar parameters:
T*=150,000K, v_inf=4100 km/s, log (L/Lo)=5.3, and Mdot=10^-5 Mo/yr if we adopt
a volume filling factor of 10%. Elemental abundances of C/He=0.7+-0.2 and
O/He=0.15(-0.05+0.10) by number qualitatively support previous recombination
line studies. We confirm that Sand 2 is more chemically enriched in carbon than
LMC WC stars, and is expected to undergo a supernova explosion within the next
50,000 yr.Comment: 17 pages, 4 figures, AASTeX preprint format. This paper will appear
in a special issue of ApJ Letters devoted to the first scientific results
from the FUSE missio
The Neon Abundance of Galactic Wolf-Rayet Stars
The fast, dense winds which characterize Wolf-Rayet (WR) stars obscure
their underlying cores, and complicate the verification of evolving
core and nucleosynthesis models. Core evolution can be probed by
measuring abundances of wind-borne nuclear processed elements,
partially overcoming this limitation. Using ground-based mid-infrared
spectroscopy and the 12.81um [NeII] emission line measured in
four Galactic WR stars, we estimate neon abundances and compare to
long-standing predictions from evolved-core models. For the WC star
WR121, this abundance is found to be >~11x the cosmic
value, in good agreement with predictions. For the three less-evolved
WN stars, little neon enhancement above cosmic values is measured, as
expected. We discuss the impact of clumping in WR winds on this
measurement, and the promise of using metal abundance ratios to
eliminate sensitivity to wind density and ionization structure.Comment: Accepted for publication in ApJ; 9 pages, 2 color figures, 4 table
XMM-Newton Detection of Hard X-ray Emission in the Nitrogen-Type Wolf-Rayet Star WR110
We have used the excellent sensitivity of XMM-Newton to obtain the first
high-quality X-ray spectrum of a Wolf-Rayet (WR) star which is not known to be
a member of a binary system. Our target, the nitrogen-type star WR 110 (= HD
165688) was also observed and detected with the VLA at four different
frequencies. The radio data are in excellent agreement with that expected for
free-free wind emission. and the ionized mass-loss rate is derived. The X-ray
emission measure distribution shows a dominant contribution from cool plasma at
kT = 0.5 keV (6 MK) which is only weakly absorbed. We argue that this
cool emission originates at hundreds of radii if the wind is spherical and
homogeneous and derive shock velocities and the X-ray filling factor using
radiative shock models. A surprising result is the unambiguous detection of a
hard X-ray component clearly seen in the hard-band images and the spectra. This
hard component accounts for about half of the observed flux and can be
acceptably fitted by a hot optically thin thermal plasma or a power-law model.
If the emission is thermal, then a temperature kT 3 keV is
derived. Such high temperatures are not predicted by current instability-driven
wind shock models. We examine several alternatives and show that the hard
emission could be accounted for by the WR wind shocking onto a close stellar
companion which has so far escaped detection. However, until persuasive
evidence for binarity is found we are left with the intriguing possibility that
the hard X-ray emission is produced entirely by the Wolf-Rayet star.Comment: 2 tables, 7 figure
Evaluating Different Dimensions of Programme Effectiveness for Private Medicine Retailer Malaria Control Interventions in Kenya
BACKGROUND: Private medicine retailers (PMRs) are key partners in the home management of fevers in many settings. Current evidence on effectiveness for PMR interventions at scale is limited. This study presents evaluation findings of two different programs implemented at moderate scale targeting PMRs for malaria control in the Kisii and Kwale districts of Kenya. Key components of this evaluation were measurement of program performance, including coverage, PMR knowledge, practices, and utilization based on spatial analysis. METHODOLOGY/PRINCIPAL FINDINGS: The study utilized mixed quantitative methods including retail audits and surrogate client surveys based on post-intervention cross-sectional surveys in intervention and control areas and mapping of intervention outlets. There was a large and significant impact on PMR knowledge and practices of the program in Kisii, with 60.5% of trained PMRs selling amodiaquine medicines in adequate doses compared to 2.8% of untrained ones (OR; 53.5: 95% CI 6.7, 428.3), a program coverage of 69.7% targeted outlets, and a potential utilization of about 30,000 children under five. The evaluation in Kwale also indicates a significant impact with 18.8% and 2.3% intervention and control PMRs selling amodiaquine with correct advice, respectively (OR; 9.4: 95% CI 1.1, 83.7), a program coverage of 25.3% targeted outlets, and a potential utilization of about 48,000 children under five. A provisional benchmark of 7.5 km was a reasonable threshold distance for households to access PMR services. CONCLUSIONS/SIGNIFICANCE: This evaluation show that PMR interventions operationalized in the district level settings are likely to impact PMR knowledge and practices and lead to increased coverage of appropriate treatment to target populations. There is value of evaluating different dimensions of public health programs, including quality, spatial access, and implementation practice. This approach strengthens the potential contribution of pragmatic study designs to evaluating public health programs in the real world
Equilibrium Studies of Fluoride Adsorption onto a Ferric Poly 12mineral from Kenya
African countries along the Great Rift Valley are among areas of the
world where excess fluoride in water sources is a major public health
problem. In this work, the removal of fluoride (F) from water solutions
using a ferric poly-mineral (FPM) from Kenya was therefore studied
using batch adsorption experiments. The effect of change in solution
pH, temperature, initial concentration of F, mass of FPM, contact time
and presence of various competing ions on F adsorption onto FPM was
evaluated. Adsorption isotherms were then applied to the adsorption
data to characterize and establish the adsorption capacity of the
mineral. The adsorption of F onto FPM was found to be a fast process
and, at 1000 mg/L initial F concentration at pH 3.32 and 293 K and
using 0.2 g/mL adsorbent dosage, over 90% F removal from solution could
be achieved in 30 min. Based on Giles system of classification of
adsorption isotherms, F adsorption isotherm conformed to L4
Langmuir-type isotherms. This indicated that FPM is composed of a
heterogeneous surface consisting of sites which, during adsorption,
filled-up with F ions in succession. The adsorption data also
correlated to Langmuir and Freundlich models indicating that F
adsorption onto FPM was a mixed process involving chemisorption onto
surface sites followed by gradual intra-particle penetration of F into
mesoporous structure of the mineral. High mean Langmuir adsorption
capacity of 10.8 mg/g, indicate that the mineral could be of use as an
inexpensive substrate for the removal of F from aqueous streams
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