Search

The article explores the declining growth of the U.S. economy despite continuous technological innovation in the 21st century and the dependence of productivity growth on innovation and the rate of increase in physical and human capital.

A numerical model was developed to determine the year-round temperature distribution within liquid manure storages, which is relevant for modelling temperature-dependent greenhouse gas and ammonia emissions. The model considers net short and long-wave radiation, heat conduction through walls and floor, surface convective heat transfer, evaporative heat loss, and manure loading. The model was implemented and validated for a circular concrete storage tank (40 m diameter; 2.5 m depth) on a dairy farm in Ontario, Canada, where it is assumed that heat transfer occurs in horizontal and vertical directions, and is symmetric in the angular direction. Annual root mean square error (RMSE), Nash–Sutcliffe model efficiency, coefficient of determination, and average bias between model estimates and measured values were 2.4 °C, 0.91, 0.95, and 0.12 °C, respectively. The model performed best in summer and autumn (lowest RMSE), which are the most important seasons for modelling temperature, as both temperature and manure volume are highest, leading to the greatest opportunity for gaseous emissions. A sensitivity analysis indicated that the most significant parameters were solar absorptivity, manure depth, incoming manure temperature, emissivity, and wind-speed. For every unit increase in depth (m), incoming manure temperature (°C), or wind-speed (m s −1 ), the peak summer temperature changed by −7.3, 0.3, or −2.4 °C, respectively. Parameters with little effect on temperature were the manure solids content and thermal conductivity of soil around the sides and the bottom of the tank. Results show that heat transfer is primarily 1-dimensional, and a simplified 1-D model would be sufficient for future applications. [ABSTRACT FROM AUTHOR]

Abstract: The goal of this in vitro study was to test the feasibility of using femtosecond (fsec) laser pulses to fistulize the human trabecular meshwork (TM), and to determine the minimum exposure time and energy dosage needed to create an ablation channel. Corneo-scleral rims were obtained from tissue used for penetrating keratoplasty. Four millimeter tissue strips hydrated in Optisol-GS were used to create partial thickness fistulas in the human TM by focusing a Ti:Sapphire laser beam (45fsec, 1kHz, 800nm) with various pulse energies (7·2 and 14·4μJ) and exposure times (0·25, 0·5, 1, and 2sec) on the inner surface of the TM. Two-photon images of the lesions were obtained with a multiphoton microscope, using an ultrafast Ti:Sapphire light source. In addition, sections of fixed tissue were examined by light microscopy. Diameters and lengths of the lesions were determined from the hematoxylin and eosin (H&E) stained sections, and the collagen structure surrounding the lesion was evaluated from the two-photon images. All selected time points (except for 0·25sec) and energies achieved the desired photodisruption of the TM. Incisions created with 0·5sec/14·4μJ irradiation appeared to be the most suitable because they were able to achieve consistent full thickness trabecular ablation. Incisions created at 1sec /14·4μJ/pulse and 2sec/14·4μJ/pulse were deeper than those at shorter time points with the same pulse energy. Longer exposure times and higher pulse energies were usually more variable and associated with deeper and larger incisions and slight collateral damage. Our results indicate that, with appropriate exposure time and pulse energy, fsec photodisruption can be employed to create lesions in the human TM without damaging the surrounding tissues. This study demonstrates that fsec laser treatments may have future potential for the surgical treatment of glaucoma. [Copyright &y& Elsevier]