Yield responses of crops to changes in environment and management practices: Model sensitivity analysis. I. Maize

YIELD, a parametric crop production model, employs climatic data to calculate actual and potential yield for various crops and includes formulations for specific crop and growth stage effects. The objective was to demonstrate the sensitivity of YIELD for grain corn (maize) to changes in various environmental and decision-making inputs. Five temperature, five solar radiation, six relative humidity regimes, five water application schemes, and four irrigation frequencies were included in this study. The effects of different soil types and wind regimes on crop water requirements were investigated. The model output includes crop yield, water use efficiency, and management efficiency. Among the results, yield decreased on the average by 3.9% per one degree (C) increase in air temperature. A 1% change in solar radiation resulted in an average of 1% change in yield. Similar changes in relative humidity caused a yield change of about 0.8%.     

Tachyarrhythmia in a baboon: a case report

An adult baboon with multiple organ symptomatology and tachycardia was successfully treated with one-time electrical cardioversion. The case is presented to demonstrate the need to include ECG monitoring in diagnostic assessment of primate animals with nonspecific symptoms.     

Three-dimensional strain fields in a uniform osteotomy gap

Stable internal fixation usually results in a unique histological healing pattern which involves direct cortical reconstruction and an absence of periosteal bridging callus. While it has been suggested that longitudinal interfragmentary strain levels control this healing pattern, the complex, multiaxial strain fields in the interfragmentary region are not well understood. Based on an in-vivo study of gap healing in the sheep tibia by Mansmann et al., we used several finite element models of simplified geometry to: explore modeling assumptions on material linearity and deformation kinematics, and examine the strain distribution in a healing fracture gap subjected to known levels of interfragmentary strain. We found that a general nonlinear material, nonlinear geometric analysis is necessary to model an osteotomy gap subjected to a maximum longitudinal strain of 100 percent. The large displacement, large strain conditions which were used in the in-vivo study result in complex, multiaxial strain fields in the gap. Restricting the maximum longitudinal strain to 10 percent allows use of a linear geometric formulation without compromising the numerical results. At this reduced strain level a linear material model can be used to examine the extent of material yielding within a homogeneous osteotomy gap. Severe local strain variations occurred both through the thickness of the gap and radially from the endosteal to periosteal gap surfaces. The bone/gap interface represented a critical plane of high distortional and volumetric change and principal strain magnitudes exceeded the maximum longitudinal strains.     

An investigation of arterial insufficiency in rat hindlimb. A combined 31P-n.m.r. and bloodflow study.

A small animal model of arterial insufficiency is presented which involves unilateral femoral artery ligation and section. Invoked alterations in metabolism and perfusion of the affected muscle mass have been investigated 12 h, 4, 7 and 14 days post-ligation by 31P-n.m.r. and microsphere infusion, both at rest and during isometric muscle contraction at 1 Hz. At rest, the concentration of phosphocreatine was similar to the mean control value (36.0 +/- 1.0 mM) from 4 days post-ligation, but was significantly lower at 12 h (28.5 +/- 3.6 mM). Inorganic phosphate concentrations were significantly elevated for 7 days post-ligation. No significant differences were noted in intramuscular pH. Upon stimulation of the affected muscle mass, a time-dependent improvement in phosphocreatine utilization was observed such that 14 days post-ligation phosphocreatine utilization was not significantly different from mean control values. A similar amelioration was noted for the contraction-induced fall in intramuscular pH. At rest, no significant differences in bloodflow to the muscles of the ligated limb compared with the unaffected contralateral limb were observed. However, isometric contraction of the affected muscle mass resulted in a markedly reduced hyperaemic response 12 h post-ligation. Thereafter, a time-dependent improvement in tissue perfusion during stimulation was observed which paralleled the improvements in phosphocreatine utilization and intramuscular pH changes. The results presented are discussed with respect to the interrelationship between oxygen delivery, high energy phosphate utilization and force maintenance.     

Cold-stage scanning electron microscope measurement of ice morphology in apple tissue as a function of freezing rate

A cold-stage SEM was used to document the morphology of ice in apple tissue and a sucrose solution frozen at rates ranging from 450 to 0.03 degrees K/min. Freezing rates of 3-mm-thick apple discs were measured with a differential thermocouple technique, which gave measurement of the growth velocity and the temperature gradient through the solidified specimen as well as the cooling rate during solidification. Cold-stage SEM micrographs were used to measure the dendritic spacing of the ice structures, and these data were found to correlate linearly with the square root of the cooling rate during solidification as would be predicted by a theoretical analysis of mass transfer in the formation of dendrites. Comparison of freeze-substituted and freeze-dried apple-tissue micrographs with those from a cold-stage SEM showed that the cold-stage SEM technique was the only one which correctly represented ice morphology in apple tissue.