Effect of Model Complexity and Gait Criteria on the Synthesis of Bipedal Locomotion

The control functions, system motions, and other characteristics which are obtained from the mathematical synthesis of ``optimal' bipedal locomotion gaits with respect to locomotion criteria (to be minimized) defined in the paper are considered. Results are presented for three mathematical biped models and several locomotion criteria (objective functions). Optimal walking trajectories and associated control functions are synthesized using the optimal programming method of [1]. In the synthesis approach, the model structure and locomotion criterion determine the optimal controls motion and foot placement parameters. These effects are examined, and qualitative comparisons to human walking patterns are suggested. These studies also provide quantitative information for the design of prostheses and walking machines, for example: ranges of suitable motion patterns (as functions of time) and magnitudes of controlling efforts and energy requirements.     

The influence of electrolyte purity on electrochemical measurements using platinum electrodes

The influence of electrolyte purity on electrochemical processes at low-area platinum electrodes has been studied by a fast potential-step method and by cyclic voltammetry. Pre-purification of the electrolyte had no significant influence on the metal surface area available for H adsorption determined immediately after an electrochemical cleaning step. Maintaining the electrode potential within the ‘double-layer’ region of platinum (at 0.5 V vs rhe) for relatively long periods of time (1–30 min) results in the progressive suppression of H adsorption, owing to the adsorption of impurities blocking active Pt sites. All samples of electrolyte, irrespective of the degree of pre-purification, exhibited this effect. In the determination of current-time transients during the first few hundred milliseconds of the methanol electro-oxidation reaction, impurities in the untreated electrolyte contribute to the measured anodic currents at Pt electrodes working in the potential range of 0.4–0.6 V. The anomalous effects observed within this potential range can be largely eliminated by pre-electrolysis of the H₂SO₄ electrolyte for several days using Pt wire gauze electrodes at 2.1 V.     

Selection and sensitivity of pellet dimensions and operating parameters to maximize production rate

The manufacture of pellets from extruded plastic strands is modeled as a constrained nonlinear programming problem. The objective is to maximize the production rate by choice of pellet dimensions and pelletizing machine operating parameters. A general solution strategy leading to identification of a globally maximum production rate for any numerical case is given. It is shown that increases in the maximum production rate can be obtained by selective relaxation of the constraints. A numerical example is presented and discussed.     

Hypoxia stimulates cytokine production by villous explants from the human placenta

It has been hypothesized that inadequate placentation in the hypertensive disorder of pregnancy known as preeclampsia creates foci of placental ischemia/hypoxia leading to the elaboration of factors that compromise systemic endothelial function to produce disease sequelae. As tumor necrosis factor-alpha (TNF alpha) and interleukin-1 (IL-1) are inflammatory cytokines capable of eliciting endothelial cell dysfunction, we investigated whether the production of these inflammatory cytokines by cultured villous explants from the human placenta was affected by incubation in reduced oxygen (2% O2). The term placenta produced TNF alpha, IL-6, and low levels of IL-1alpha and IL-1beta under standard tissue culture conditions. Hypoxia significantly increased TNF alpha, IL-1alpha, and IL-1beta production by 2-, 6-, and 23-fold, respectively, but did not affect IL-6 production. Further, cytokines were immunolocalized to the syncytiotrophoblast layer as well as to some villous core cells. Hypoxic regulation of placental TNF alpha and IL-1beta production also appeared to differ based on gestational age. Finally, treatment with either cobalt chloride or an iron chelator mimicked the hypoxic response, suggesting that stimulation of placental cytokine production may involve a heme-containing, O2-sensing protein. These results suggest that placental hypoxia can lead to the elaboration of inflammatory cytokines, which may contribute to the pathophysiology of preeclampsia.     

1997 American Urological Association Gallup survey: Changes in diagnosis and management of prostate cancer and benign prostatic hyperplasia, and other practice trends from 1994 to 1997

PURPOSE: The American Urological Association first commissioned the Gallup Organization to conduct a study to assess urologist practice patterns in 1992. We present the results of the 1997 survey, the sixth consecutive Gallup survey performed for the Association. MATERIALS AND METHODS: A random sample of 502 American urologists who had completed urological residency and practiced at least 20 hours weekly in 1996 was interviewed by telephone in February and March 1997. RESULTS: Emerging trends showed significant changes since 1994 in how urologists diagnosed and treated prostate cancer. The survey revealed a significant change in the tests routinely ordered to stage newly diagnosed prostate cancer and for diagnostic evaluation of patients with benign prostatic hyperplasia. CONCLUSIONS: Urologists are becoming more cost conscious and effective in ordering pretreatment testing. Urologists are becoming more oriented toward medical treatment for the management of benign prostatic hyperplasia, and less laser surgery is being performed.     

Effects of dietary boron supplementation on broilers

Two experiments were conducted with a total of 432 broiler chicks to investigate the influence of supplementing different amounts of boron to practical corn-soybean meal diets. The birds were housed in batteries and had free access to feed and water. In Experiment 1, 144 1-day-old broiler chicks were fed a basal diet supplemented with 0, 5, 40, 80, or 120 ppm boron for 21 days. Female body weight was not influenced by the dietary treatments. However, males supplemented with 5 ppm boron were heavier and their tibias resisted more load than the control birds. Overall feed conversion was not influenced by boron. In Experiment 2, 288 1-day-old broiler chicks were fed a basal diet supplemented with 0, 60, 120, 240, or 300 ppm boron for 22 days. Male and female body weights of the 300-ppm group were lower than those of the control birds. Percentage tibia ash was highest with 300 ppm boron. No significant differences were found in intestinal tract weight (grams of intestine per 100 g body weight) among treatments. Boron concentration in the breast muscle and liver increased as dietary concentration of boron increased. Data collected in these two experiments indicated that consumption of diets containing up to 240 ppm boron from hatch to 21 days of age was not detrimental to broiler performance. Data were not conclusive on the need for supplemental boron in broiler diets based on corn and soybean meal.     

Poly(2-aminoadenylic acid): interaction with poly(uridylic acid)

Poly(2-aminoadenylic acid) forms both double and triple helices with poly(uridylic acid) [poly(U)]. The 2-amino group forms a third hydrogen bond, elevating the 2 leads to 1 transition temperature by 33 degrees C. The third strand, however, has about the same stability as poly(A)-2poly(U), as measured by Tm 3 leads to 2. This selective stabilization of the two-stranded helix results in a much greater resolution of the differnt thermal transitions than that observed in analogous polynucleotide systems. In contrast to other A, U systems 3 leads to 1 and 2 leads to 3 transitions are not observed under any conditions, and the triple helix always undergoes a 3 leads to 2 transition even at very high ionic strength. A 1:1 mixture of poly(2NH2A) and poly(U) exhibits no transient formation of 1:2 complex, unlike similar mixtures of poly(A) with poly(U) and poly(T). This difference is evidently due to a more rapid displacement reaction: [poly(2NH2A) + poly(2NH2A)-2poly(U) leads to 2 poly(2NH2A)-poly(U)] With poly(2NH2A) than with poly(A). We describe a method for establishing the combining ratios of polynucleotide complexes which used a computer to calculate the angles of intersection of mixing curves as explicit and continuous functions of the wavelength. The wavelength dispersions of the angles of intersection determine optimum wavelengths for establishing stoichiometry and can also provide reliable negative evidence that presumably plausible complexes are not formed. Analogous computer procedures have been developed to determine wavelengths which are selective for the formation of both 1:1 and 1:2 complexes. Infrared spectra of the 1:1 and 1:2 complexes resemble those of other A, U homoribopolynucleotide helices in having two and three strong bands, respectively, in the region of carbonyl stretching vibrations. CD spectra of the two complexes are unusual in having negative first extrema of moderate intensity. We attribute these extrema to intrastrand interactions of strong, well-resolved transitions at 278 nm (B2u) of the 2-aminoadenine residues. The CD spectra are correlated with those of other polynucleotide helices.