Effects of three types of free-stall surfaces on preferences and stall usage by dairy cows

One important criterion in choosing appropriate housing systems for dairy cattle is that the freestall provides a comfortable surface for the cow. This paper describes two experiments testing the effects of commonly used lying surfaces on stall preference and stall usage by Holstein cows. In both experiments, 12 cows were housed individually in separate pens. Each pen contained three free stalls with a different surface: deep-bedded sawdust, deep-bedded sand, and a geotextile mattress covered with 2 to 3 cm of sawdust. The animals were restricted to each surface in turn, in a random order for either 2 (Experiment 1) or 3 d (Experiment 2). Both before and after this restriction phase, the animals were allowed access to all three surfaces, and preference was determined, based on lying times. Of the 12 cows used in Experiment 1, 10 preferred sawdust before and nine after the restriction phase. During the restriction phase, average lying times and number of lying events during the restriction phase were significantly lower for the sand-bedded stalls (P < or = 0.05), and standing times were higher on mattresses (P < or = 0.05), compared with sawdust. Although these cows had some experience with all three surfaces during the experiment, they had been housed in sawdust-bedded stalls during their previous lactation. Cows used in Experiment 2 had spent their previous lactation in sand bedded stalls. In this experiment, about half the cows preferred sand and half sawdust, after the restriction phase. During the restriction phase of experiment, lying times and number of lying events were lower, and standing times were higher when the animals were restricted to the mattresses compared to either sand or sawdust (P < or = 0.05). These results indicate that (1) free stall surface can affect both stall preferences and stall usage, and (2) mattresses are less preferred.     

Free-stall dimensions: effects on preference and stall usage

In 2 experiments, free-stall dimensions were examined to determine how they affected stall preference, usage, cleanliness, and milk production in Holstein dairy cattle. In experiment 1, stall width (112 or 132 cm) and stall length (229 and 274 cm from curb to wall) were compared in a 2 x 2 factorial arrangement of stall treatments using 15 individually housed, non-lactating animals. Cows showed no clear preference for stall size as measured by lying time. When animals had no choice between stalls, average lying time was higher in the wide stalls than in the narrow stalls (10.8 vs. 9.6+/-0.3 h/24 h). Both length and width affected time spent standing with only the front hooves in the stall; total stall area is best explained by the variation associated with this behavior. In experiment 2, 27 lactating dairy cattle were alternately housed with access to stalls of 106, 116, or 126 cm in width using a cross-over design with exposure to each treatment lasting 3 wk. Animals spent an additional 42 min/24 h lying in stalls measuring 126 cm in width compared with stalls with only 106 cm between partitions. Free-stall width influenced the time spent standing with the front 2 hooves in the stall; animals averaged 58 min/24 h in the widest stalls and 85 min/24 h in the narrowest stalls. The amount of time spent standing with all 4 hooves in the stall tended to be longer in wider stalls, and these stalls were also most likely to become soiled with feces. Stall width did not affect the number of lying events or milk production. In conclusion, animals spent more time lying down, and less time was spent standing with only the front hooves in larger stalls, but larger stalls were also more likely to become soiled.     

Characterization of saccharides in size-fractionated ambient particulate matter and aerosol sources: the contribution of primary biological aerosol particles (PBAPs) and soil to ambient particulate matter

Size-fractionated (equivalent to ambient PM2.5 and PM10) local soil, plant, and spore samples were collected in the Sonoran Desert near Phoenix, AZ and measured for saccharide content with the goal of characterizing ambient particulate matter sources including soil and primary biological aerosol particles (PBAPs) from plants and fungi. Different saccharide compositions were observed among soil, plant, and spore samples and between PM2.5 and PM10 fractions. The total measured nonlevoglucosan saccharide content relative to PM mass in ambient aerosols collected in a Phoenix suburb (Higley) was much higher compared to the local soil samples but much lower compared to the PBAP. The enrichment of saccharides from two saccharide-dominated PM source factors resolved by a positive matrix factorization model is also higher than the saccharide content in the size-fractionated local soil samples, but lower than that measured in the size-segregated PBAP samples. This indicates that ambient concentration of particulate saccharides at Higley was dominated by contributions from PBAPs directly injected into the atmosphere from plants and spores rather than from soil and associated biota. Our results also suggest the contribution to the fine size fraction of ambient PM from the primary biologically derived sources may be greater than previously acknowledged.     

Soot concentration and temperature measurements in co-annular, nonpremixed CH4/air laminar flames at pressures up to 4 MPa

Laminar nonpremixed methane-air flames were studied over the pressure range of 0.5 to 4 MPa using a new high-pressure combustion chamber. Flame characterization showed very good flame stability over the range of pressures, with a flame tip rms flicker of less than 1% in flame height. At all pressures, soot was completely oxidized within the visible flame. Spectral soot emission (SSE) and line-of-sight attenuation (LOSA) measurements provided radially resolved measurements of soot volume fraction and soot temperature at pressures from 0.5 to 4.0 MPa. Such measurements provide an improved understanding of the influence of pressure on soot formation and have not been reported previously in laminar nonpremixed flames for pressures above 0.4 MPa. SSE and LOSA soot concentration values typically agree to within 30% and both methods exhibit similar trends in the spatial distribution of soot concentration. Maximum soot concentration depended on pressure according to a power law, where the exponent on pressure is about 2 for the range of pressures between 0.5 and 2.0 MPa, and about 1.2 for 2.0 to 4.0 MPa. Peak carbon conversion to soot also followed a power-law dependence on pressure, where the pressure exponent is unity for pressures between 0.5 and 2.0 MPa and 0.1 for 2.0 to 4.0 MPa. The pressure dependence of sooting propensity diminished at pressures above 2.0 MPa. Soot concentrations measured in this work, when transformed to line-integrated values, are consistent with the measurements of Flower and Bowman for pressures up to 1.0 MPa [Proc. Combust Inst. 21 (1986) 1115-1124] and Lee and Na for pressures up to 0.4 MPa [JSME Int. J. Ser. B 43 (2000) 550-555]. Soot temperature measurements indicate that the overall temperatures decrease with increasing pressure; however, the differences diminish with increasing height in the flame. Low down in the flame, temperatures are about 150 K lower at pressures of 4.0 MPa than those at 0.5 MPa. In the upper half of the flame the differences reduce to 50 K.     

Second law analysis of forced convection in a circular duct for non-Newtonian fluids

The second law characteristics of fluid flow and heat transfer inside a circular duct under fully developed forced convection for non-Newtonian fluids are presented. Heat flux is kept constant at the duct wall. Analytical expressions for dimensionless entropy generation number (_NS$N_{\mathrm{S}}$), irreversibility distribution ratio (Φ  ), and Bejan number (Be$\mathit{Be}$) are obtained as functions of dimensionless radius (R$R$), Peclet number (Pe$\mathit{Pe}$), modified Eckert number (Ec$\mathit{Ec}$), Prandtl number (Pr), dimensionless temperature difference (Ω  ), and fluid index (m$m$ or n$n$). Spatial distributions of local and average entropy generation number, irreversibility ratio, and Bejan number are presented graphically. For a particular value of fluid index, n=1$n=1$ (or m=2$m=2$), the general entropy generation number expression for a non-Newtonian power-law fluid reduces to the expression for Newtonian fluid as expected. Furthermore, entropy generation minimization is applied to calculate an optimum fluid index (_nEGM$n_{\mathrm{EGM}}$). A correlation is proposed that calculates _nEGM$n_{\mathrm{EGM}}$as a function of group parameter (Ec×Pr/Ω$\mathit{Ec}\times \mathit{Pr}/\Omega$) and Peclet number (Pe$\mathit{Pe}$) within ±5% accuracy. Finally, for some selected fluid indices, the governing equations are solved numerically in order to obtain Nusselt number. It is observed that the numerically obtained asymptotic Nusselt number shows excellent agreement with the analytically obtained Nusselt number.     

Brinkman–Forchheimer modeling for porous media thermoacoustic system

In this paper, analytical studies have been conducted on the flow and thermal fields of unsteady compressible viscous oscillating flow through channels filled with porous media representing stacks in thermoacoustic systems. The flow in the porous material is described by the Brinkman–Forchheimer–extended Darcy model. Analytical expressions for oscillating velocity, temperature, and energy flux density are obtained after linearizing and solving the governing differential equations with long wave, short stack, and small amplitude oscillation approximations. Experimental work is also conducted to verify the temperature difference obtained across the porous stack ends. To produce the experimental results, a thermoacoustic heat pump is designed and constructed where reticulated vitreous carbon (RVC) is used as the stack material. A very good agreement is obtained between the modeling and the experimental results. The expression of temperature difference across the stack ends obtained in the present study is also compared with the existing thermoacoustic literature. The proposed expression surpasses the existing expression available in the literature. The system of equations developed in the present study is a helpful tool for thermal engineers and physicist to design porous stacks for thermoacoustic devices.     

Register allocation and exhaustive peephole optimization

Emerging peephole optimizers can relieve code generators of much case analysis, but delaying code generation decisions requires register allocation algorithms that accept object code instead of the more usual intermediate code. This paper describes two programs that implement such algorithms for a retargetable optimizing compiler. In a machine-independent fashion, they allocate and assign registers, eliminate common subexpressions (including often-missed machine-specific ones), identify dead variables, and define windows for the companion peephole optimizer. Their techniques for handling machine-specific data should generalize to other optimizations as well.