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An important feature of the ASAE revised standard practice EP403.3 DEC98 for the design of anaerobic lagoons for animal waste management is the addition of normal runoff and normal precipitation on the lagoon surface between drawdown events in the calculation of runoff volume (ROV). In the previous version of this standard (EP403.2 AUG93), only the runoff and precipitation to the lagoon surface from a 25 yr/24 h-storm event were considered in ROV. Lagoon systems under both standards are designed to contain runoff from a 25 yr/24 h-storm event, although significant rainfall events rarely occur as a single wet day. For Dublin, Texas, the design 24-h, 25-yr rainfall is 18.5 cm. From 86 years with complete precipitation records, the return interval of an 18.5 cm event from consecutive wet days is about 6 years rather than 25. Beyond the additional runoff volume from multiple wet-days, chronic rainfall also considers the preclusion of dewatering due to wet weather conditions. To evaluate the risk of overflow from a one-stage lagoon sized for a 1,000-head dairy considering the recurrence of chronic rainfall events, a simple lagoon water balance model was developed. Actual daily rainfall for 86 years was used to estimate runoff into and precipitation on the lagoon. Drawdown management was based on lagoon level, daily rainfall, and saturated ground. When normal runoff and precipitation was considered in the ROV, the frequency of lagoon overflow events was within expected frequency for the 86 years of record for most sensitivity scenarios. When normal runoff and precipitation was not considered in the ROV, the frequency of overflow events often exceeded the expected frequency emphasizing the importance of considering more than just the 25 yr/24 h-storm event in determining the runoff volume of a lagoon.

A system for measuring water droplet impact energy is described, which consists of piezoelectric film connected to a high-speed data acquisition board in a personal computer. The system converts the impact forces of individual water droplets falling onto the piezoelectric film into an output voltage, which is measured and analyzed. Eight DT3-type piezoelectric films were calibrated under laboratory conditions for kinetic energy values ranging from 0.01 × 10−3 to 1.2 × 10−3 J by releasing water droplets of various sizes from specific heights. The DT3-type piezoelectric film is effective for water droplets smaller than 4.6 mm in diameter. Results were used to produce a general model for the response of this film type. The ease of use and robustness of the system was demonstrated by measuring droplet impact forces under a lateral-move irrigation machine.

Mesophilic (37°C) performance of attached-film anaerobic digesters fed with dairy manure that had been subjected to low temperature (10°C) stress was evaluated. Two digesters packed with limestone gravel, two with pieces cut from non-woven polyester matting, and two with no packing were subjected to a temperature cycle between 37°C and 10°C. Two control reactors without packing were maintained continuously at 37°C. All reactors were operated in the upflow mode, and the reactors without packing operated similarly to upflow anaerobic sludge blanket systems. None of the reactors regained their original performance in terms of biogas and methane production characteristics or pollution abatement after the temperature cycle; however, the control reactors also showed a similar decline in performance during the period of study. The reactors with polyester packing and those with no packing had similar values for biogas productivity and yield, while those with limestone packing had significantly lower values. It was concluded that the lack of complete recovery of reactor performance could not be attributed to the temperature cycle. Variability in the feed composition or uniform decline in microbial activity over the prolonged period of time for which the reactors were operational most likely contributed to this effect.

Retention of microorganisms in anaerobic digesters by providing an attachment medium can potentially increase their productivity at lower operating temperatures. The objective of this work was to investigate the effectiveness of attached-film bioreactors for psychrophilic anaerobic digestion of dairy manure. Eight digesters were maintained in an environmental chamber, with the temperature varied between 37 and 10°C. Two digesters were packed with limestone gravel, two with pieces cut from non-woven polyester matting, two with a combination of limestone gravel and polyester pieces, and two had no packing. Digester operation was initiated at a temperature of 37°C. After the digesters reached stable operation at the initial temperature, the temperature was lowered slowly to 10°C. The temperature was held at 10°C for 5 weeks after stabilizing. The polyester medium with its high porosity and surface to volume ratio had the best overall performance for methane productivity at both 37 and 10°C. The biogas production (ml/d) and methane production (ml/d) were significantly higher for the polyester medium when compared to the limestone and combination media reactors (p < 0.0001 and 0.0002, respectively). At 10°C, the polyester medium reactors performed significantly better than all others for biogas (ml/d) and methane (ml/d) production (p < 0.0001). The polyester medium also yielded the maximum reductions in volatile solids (VS) and chemical oxygen demand (COD) at 37°C.

Four variations of the least-squares regression procedure proposed by Lettau (1971) were used to define a solution envelope containing the soil thermal diffusivity function, a(z), for a soil with a heterogeneous moisture profile. An explicit finite difference model of the one-dimensional heat equation was used to evaluate the four variations of Lettau’s procedure based upon agreement between measured and simulated temperatures over a 24-h temperature cycle. The application of Lettau’s regression procedure to a database containing only temperature data from the cooling cycle portion of the diurnal temperature wave was shown to most faithfully reproduce field temperature measurements.

A simple model for hourly soil temperatures within 100 mm of the surface, for use in appropriate biophysical development models, was derived from simulations using a physically based, one-dimensional, numerical model for soil temperature and water content in a bare soil. The simple model incorporates the effect of soil water content by assuming that the primary mechanism by which it influences soil temperature is the surface energy balance. Daily surface temperature maxima and minima are estimated from daily meteorological data and, from these, hourly soil temperature is estimated. Results indicate that the simple model adequately estimated hourly soil temperatures during the early spring in College Station, Texas.

The internal wiring of an existing stem or trunk flow gauge was redesigned to obtain greater accuracy of the gauge itself, eliminate errors due to signal loss in connecting cables, and reduce the number of channels and of the computing required of the datalogger Tests of the gauge conducted on bald cypress (Taxodium distichum) and Ficus retusa (L.) Nitida trees, in a greenhouse and in an urban backyard, and under well-watered and dry conditions gave daily sap mass flow rates that were within 5% of those obtained by direct weighing

The canopy temperature function and the crop water stress index were calculated for cotton with differing plot locations and irrigation regimes. Advective influences were noted for the water-stressed cotton.

Infrared (IR) thermometry has not been extensively applied in deciduous tree fruit production to determine water use. The objectives of this study were to a) examine IR measurement techniques for evaluating canopy temperatures in peach [Prunus persica (L.) Batsch.] trees; b) evaluate a foliage-minus-air temperature- (Tc – Ta) based diffusion equation for vapor flux used to predict tree water use; and c) measure the Tc – Ta response of irrigated peach trees over a range of air vapor pressure deficits. The mean Tc – Ta for a tree was similar for readings made from the canopy sides (horizontal orientation of the IR thermometer) or canopy tops (vertical orientation). Peach tree water use from weighing lysimeters was predicted within 9.4% ± 3% using the diffusion equation for vapor flux. Tc – Ta for irrigated peach trees was related to the air vapor pressure deficit (VPD). Data are presented to show that stomatal response to VPD does alter the Tc – Ta nonstressed baseline for peach at VPD > 2 kPa.

THIS study evaluated the effect of varying levels of water stress on leaf resistance, leaf water potential and transpiration of drip irrigated peach [Prunus persica (L.) Batsch]. Leaf resistances were significantly higher for the 1-emitter tree indicating it to be the most severely stressed. Leaf water potential and transpiration rates were also lower in these trees. Leaf resistances decreased exponentially with increasing solar radiation and curvilinearly with increasing vapour deficit. Stomata responded slower in stressed trees. Leaf resistances were lower at leaf water potential above —20 bars and increased at leaf water potential below —21 for the well watered trees. In stressed trees the threshold value was lowered to —25 bars. Leaf resistance and leaf water potential decreased until its threshold value, after which both increased.

Mature peach trees [Prunus persica (L.) Batsch] grown in weighing lysi-meters were subjected to soil moisture stress. Evapotranspiration (ET) was not affected by rapid changes in soil moisture until soil matric potential reached -1500 kPa. When the trees reached permanent wilt, there was a sharp decline in water use.

A large twin weighing lysimeter facility was installed at the Stephenville Agricultural Research and Extension Center, Stephenville, Texas, to measure evapotranspiration of mature peach trees. The system was designed to establish a check lysimeter so effects of irrigations or moisture stress or other treatment on the other lysimeter could be evaluated. Each lysimeter is a 2.44 m diameter cylinder 1.52 m deep. The weighing mechanisms for each lysimeter are three compression strain gage load cells with a sensitivity (hysteresis) of 4.54 kg. The load cell data from each lysimeter and on-site environmental data are automatically recorded on a micrologger with a sensitivity of 0.005 mv, which corresponds to a 4.45 kg weight. The equivalent depth of water for a sensitivity of 5 kg is 1 mm over the surface area of the lysimete.

As Bowden has pointed out in his recent discussion on high resolution lithography, conventional photoresists are not particularly suitable for use in the deep ultraviolet (DUV) regime.' The reasons for this are: (1) the novolac resin is a strong absorber at wavelengths shorter than 300 nm;2 and (2) the products produced upon irradiation of the photoactive compound (PAC) absorb in this region (which prevents the phenomenon known as "photobleaching" from occurring). Of these two difficulties the first appeared, to us, to be the more restrictive. Therefore we chose to investigate alternate resins, more transparent in the DUV region, to substitute for novolac. We initially sought to remain within the realm of the dissolution inhibition mechanism and to utilize conventional PAC's. Although it was possible to prepare resins having improved UV absorbtion characteristics (a maleimidestyrene copolymer will be discussed here) and to formulate positive acting resists from them, we found that the resists were not able to adequately form high resolution images with vertical wall profiles. Examples of this behavior are presented. Because of the apparent inability to obtain satisfactory wall profiles, we abandoned the methods based on the dissolution inhibition mechanism. We then elected to explore the so-called "chemical amplification" approach pioneered by Wilson, Ito, Frechet, and their coworkers. To this end, maleimide styrene copolymer was substituted on the nitrogen atom with the tertbutyloxy carbonyl group. This resin, upon application of heat, reverts to maleimide styrene via a process which is apparently catalyzed in the presence of acid. These observations led us to develop a photoresist based on a mixture of a photoacid and the N-blocked maleimide/styrene resin. Details of the performance of this resist are presented.