Wind loads on flat plate photovoltaic array fields (nonsteady winds)

Techniques to predict the dynamic response and the structural dynamic loads of flat plate photovoltaic arrays due to wind turbulence were analyzed. Guidelines for use in predicting the turbulent portion of the wind loading on future similar arrays are presented. The dynamic response and the loads dynamic magnification factor of the two array configurations are similar. The magnification factors at a mid chord and outer chord location on the array illustrated and at four points on the chord are shown. The wind tunnel test experimental rms pressure coefficient on which magnification factors are based is shown. It is found that the largest response and dynamic magnification factor occur at a mid chord location on an array and near the trailing edge. A technique employing these magnification factors and the wind tunnel test rms fluctuating pressure coefficients to calculate design pressure loads due to wind turbulence is presented

An approach to optimization of low-power Stirling cryocoolers

A method for optimizing the design (shape of the displacer) of low power Stirling cryocoolers relative to the power required to operate the systems is described. A variational calculation which includes static conduction, shuttle and radiation losses, as well as regenerator inefficiency, was completed for coolers operating in the 300 K to 10 K range. While the calculations apply to tapered displacer machines, comparison of the results with stepped displacer cryocoolers indicates reasonable agreement

Polymer matrix and graphite fiber interface study

Hercules AS4 graphite fiber, unsized, or with EPON 828, PVA, or polysulfone sizing, was combined with three different polymer matrices. These included Hercules 3501-6 epoxy, Hercules 4001 bismaleimide, and Hexcel F155 rubber toughened epoxy. Unidirectional composites in all twelve combinations were fabricated and tested in transverse tension and axial compression. Quasi-isotropic laminates were tested in axial tension and compression, flexure, interlaminar shear, and tensile impact. All tests were conducted at both room temperature, dry and elevated temperature, and wet conditions. Single fiber pullout testing was also performed. Extensive scanning electron microphotographs of fracture surfaces are included, along with photographs of single fiber pullout failures. Analytical/experimental correlations are presented, based on the results of a finite element micromechanics analysis. Correlations between matrix type, fiber sizing, hygrothermal environment, and loading mode are presented. Results indicate that the various composite properties were only moderately influenced by the fiber sizings utilized

Lysine Requirements of PIC Barrows during Growing-Finishing Period

True digestible lysine requirements of PIC barrows were estimated by using a PUN (plasma urea nitrogen) technique. For the individually penned barrows, daily true digestible lysine requirements were 16.5, 17.8, 19.9, 20.2, 17.4, 16.7, 16.9, and 14.4 grams at the body weights of 33, 52, 69, 72, 87, 93, 106, and 113 kg, respectively. Based on the results, a lysine requirement model of the pigs over the growing and finishing period under an individually penned environment was established. The equation was y = 0.000001x4 - 0.0004x3 + 0.0365x2 - 1.329x + 32.691, in which y is the true digestible lysine requirement in grams /day, and x is the body weight in kilograms. True digest lysine requirements of the pigs under a group-penned environment were determined to be 15.8 and 19.1 g/d, at 32 and 50 kg body weight, respectively

Dietary Available Phosphorus Needs of Pigs Experiencing a Moderate and High Level of Antigen Exposure

Pigs experiencing a moderate and a high level of antigen exposure were self-fed one of six dietary concentrations (.30, .40, .50, .60, .70, .80%) of available phosphorus (AP) from 14 to 60 pounds body weight. Pigs reared via a management scheme that resulted in a moderate level of antigen exposure consumed more feed daily, gained body weight faster, required less feed per unit of gain, and accrued more body protein daily than pigs reared in a high antigen exposure environment. Over the duration of the study, dietary AP concentrations of .6 to .7% and .4 to .5% in the moderate and high antigen exposure pigs, respectively, were needed to maximize daily body weight gains, gain:feed ratios, and body protein deposition. Based on these data, the dietary available phosphorus needs expressed as a percentage of the diet for 14 to 60 pound pigs experiencing a moderate or high level of antigen exposure are about 2.4 and 1.7 times greater, respectively, than current NRC (1988) estimates

A persistent and dynamic East Greenland Ice Sheet over the past 7.5 million years

Climate models show that ice-sheet melt will dominate sea-level rise over the coming centuries, but our understanding of ice-sheet variations before the last interglacial 125,000 years ago remains fragmentary. This is because terrestrial deposits of ancient glacial and interglacial periods1,2,3 are overrun and eroded by more recent glacial advances, and are therefore usually rare, isolated and poorly dated4. In contrast, material shed almost continuously from continents is preserved as marine sediment that can be analysed to infer the time-varying state of major ice sheets. Here we show that the East Greenland Ice Sheet existed over the past 7.5 million years, as indicated by beryllium and aluminium isotopes (10Be and 26Al) in quartz sand removed by deep, ongoing glacial erosion on land and deposited offshore in the marine sedimentary record5,6. During the early Pleistocene epoch, ice cover in East Greenland was dynamic; in contrast, East Greenland was mostly ice-covered during the mid-to-late Pleistocene. The isotope record we present is consistent with distinct signatures of changes in ice sheet behaviour coincident with major climate transitions. Although our data are continuous, they are from low-deposition-rate sites and sourced only from East Greenland. Consequently, the signal of extensive deglaciation during short, intense interglacials could be missed or blurred, and we cannot distinguish between a remnant ice sheet in the East Greenland highlands and a diminished continent-wide ice sheet. A clearer constraint on the behaviour of the ice sheet during past and, ultimately, future interglacial warmth could be produced by 10Be and 26Al records from a coring site with a higher deposition rate. Nonetheless, our analysis challenges the possibility of complete and extended deglaciation over the past several million years

Comparison of Hydrolyzed Intestinal By-products

Pigs were weaned at 16 to 20 days of age and fed diets containing either dried whey, dried porcine solubles (DPS), or condensed porcine solubles (CPS) for 3 weeks, followed by a common diet for 2 weeks. The results of the trial showed that 5% of either DPS or CPS can replace dried whey protein in diets for weanling with no effect on growth performance up to 5 weeks after weanin

Dried Porcine Solubles and Feed Additives

Pigs were weaned at 16 to 20 days of age and fed diets containing either dried whey or 6% dried porcine solubles (DPS), partially replacing dried whey protein, and one of two combinations of feed additives (either ZnO + CSP 250 or CuSO4 + Mecadox) in a 2 × 2 factorial arrangement. The diets were fed for 2 weeks and followed by a common diet for 3 weeks. Feeding the DPS-containing diet during week 1 and 2 post-weaning improved average daily gain in week 3 after weaning (when no DPS was fed), as well as cumulative average daily gain in weeks 0 to 3. However, it tended to lessen feed utilization in week 4 and 5. Furthermore, it was shown that the combination of ZnO and CSP 250 improved growth performance over CuSO4 and Mecadox in weanlingpig diets. Neither feed-additive combination influenced the utilization of DPS

Wind loads on flat plate photovoltaic array fields

The results of an experimental analysis (boundary layer wind tunnel test) of the aerodynamic forces resulting from winds acting on flat plate photovoltaic arrays are presented. Local pressure coefficient distributions and normal force coefficients on the arrays are shown and compared to theoretical results. Parameters that were varied when determining the aerodynamic forces included tilt angle, array separation, ground clearance, protective wind barriers, and the effect of the wind velocity profile. Recommended design wind forces and pressures are presented, which envelop the test results for winds perpendicular to the array's longitudinal axis. This wind direction produces the maximum wind loads on the arrays except at the array edge where oblique winds produce larger edge pressure loads. The arrays located at the outer boundary of an array field have a protective influence on the interior arrays of the field. A significant decrease of the array wind loads were recorded in the wind tunnel test on array panels located behind a fence and/or interior to the array field compared to the arrays on the boundary and unprotected from the wind. The magnitude of this decrease was the same whether caused by a fence or upwind arrays

Self-Regulation in a Web-Based Course: A Case Study

Little is known about how successful students in Web-based courses self-regulate their learning. This descriptive case study used a social cognitive model of self-regulated learning (SRL) to investigate how six graduate students used and adapted traditional SRL strategies to complete tasks and cope with challenges in a Web-based technology course; it also explored motivational and environmental influences on strategy use. Primary data sources were three transcribed interviews with each of the students over the course of the semester, a transcribed interview with the course instructor, and the students’ reflective journals. Archived course documents, including transcripts of threaded discussions and student Web pages, were secondary data sources. Content analysis of the data indicated that these students used many traditional SRL strategies, but they also adapted planning, organization, environmental structuring, help seeking, monitoring, record keeping, and self-reflection strategies in ways that were unique to the Web-based learning environment. The data also suggested that important motivational influences on SRL strategy use—self-efficacy, goal orientation, interest, and attributions—were shaped largely by student successes in managing the technical and social environment of the course. Important environmental influences on SRL strategy use included instructor support, peer support, and course design. Implications for online course instructors and designers, and suggestions for future research are offered