Robust compensation of elastic deformations in ball screw drives

Elastic deformations occur in ball screw drives typically due to inertial forces, guideway friction, and cutting forces. This results in elongation and compression of the ball screw, which deteriorates the dynamic linear positioning accuracy. Closing the control loop with a linear encoder helps to alleviate this problem to a certain extent. However, linear scales cost significantly more than rotary encoders and their installation also brings about additional costs. This paper presents a new strategy for mitigating the detrimental effect of elastic deformations, in order to improve the translational accuracy of ball screw drives when only rotational feedback is available. A simple and physically intuitive model is developed, which is used to offset the position commands that are fed to the servo control law. Compensation is proposed using a closed-loop scheme, which is found to be robust against cutting forces, as well as variations in the table mass and guideway friction. These effects are detected as equivalent disturbances that cause an elastic deformation. The proposed closed-loop compensation strategy has been validated in machining and high-speed tracking experiments, as well as simulations, which demonstrate its effectiveness in terms of improving the ball screw drive’s final translational accuracy.     

Indicators and Aspects of Hydrological Drought in Lebanon

Change in climate conditions has become a global issue that has given a serious concern by many researchers. However, the availability of data in this regard is considered as a major element for optimum comparative analysis. The Mediterranean region is influenced by climate change, which is reflected mainly by its impact on water sources supply and flow regime. In Lebanon, these water sources are witnessing obvious quantitative decrease, thus affected the supply side, the so-called “hydrologic drought”. Therefore, many studies have been made to figure out a comprehensive understanding on water resources in Lebanon and their interrelation with climatic trends, but they often analyze one component of the water cycle. This study involves different indices of surface and subsurface water, thus, followed a comparative analysis of different hydrologic records. This was achieved by applying graphical illustrations of the numerical values adopted from available records. In this regard, different tools of analysis were used, and more certainly remotely sensed data were helpful for monitoring approaches. Therefore, results of the obtained comparative analysis revealed a clear regression in the amount of available water from different sources in Lebanon. These sources, which are under the impact of human like rivers and groundwater, showed a 23–29% decrease in the amounts of water since the last four decades. While sources, with less human interference, like snow cover and precipitation have been decreased by 12–16%. However, in both cases, the status is quite alarming and needs immediate water management plans to conserve water resources in Lebanon.     

Liquefaction of empty palm fruit bunch (EPFB) in alkaline hot compressed water

Effect of alkalis (NaOH, KOH and K₂CO₃) on liquefaction of EPFB (empty palm fruit bunch) biomass liquefaction was investigated under subcritical water conditions in a batch reactor operating at 270 °C and 20 bars for a period of 20 min. Catalytic performance and suitable biomass to water ratio that supported higher EPFB conversion, liquid hydrocarbons yield and lignin degradations were screened. Analytical results indicate that maximum of 68 wt% liquids were produced along with 72.4 wt% EPFB mass conversions and 65.6 wt% lignin degradation under 1.0 M K₂CO₃/2:10 (biomass/water) conditions. In comparison, the experiments that were performed in the absence of alkalis yielded only 30.4 wt% liquids, converted 36 wt% EPFB and degraded 24.3 wt% lignin. Furthermore, biomass to water ratios >2:10 decreased both solid mass conversion and liquid hydrocarbons' yield. The reactivity of the alkalis was in the order of K₂CO₃ > KOH > NaOH. The liquid compositions were dominantly phenols and esters; the highest value of phenol (60.1 wt% of liquid yield) was achieved in the case of K₂CO₃ (1.0 M) with 5 g EPFB/25 ml water ratio while 1.0 M NaOH yielded maximum esters (86.4 wt% of liquid yield). The alkali promoted process assisted with hot water treatments seemed promising for production of bio-oils from EPFB.     

Long-Term Structural Health Monitoring of the San Ysidro Bridge

As part of the Lifecycle Innovative Financing Evaluation initiative, the San Ysidro Bridge along U.S. Route 550 will be monitored throughout a 10?year warranty period to determine changes in deflection, stiffness, and load-carrying capacity. This paper discusses an initial live-load test on the San Ysidro Bridge as well as a subsequent load test on a full-scale single lane test bridge. The two load tests in conjunction with finite element modeling were used to determine the load rating for both shear and moment of the San Ysidro Bridge. This load rating was then compared with the load rating using the distribution factors from the American Association of State Highway and Transportation Officials (AASHTO) Standard and Load and Resistance Factor Design Specifications. According to both AASHTO specifications, the interior girder shear controlled the load rating of the San Ysidro Bridge. Using the finite element modeling scheme of frame and shell elements the interior girder moment was found to control the design. This load rating will be used as a baseline for comparison with future load ratings throughout the warranty period.     

Electrical properties of pre-extended FEF carbon black loaded rubbers

The electrical conduction was investigated in different rubber composites, subjected to various values of longitudinal extension. The study involves styrene-butadiene-rubber (SBR), butadiene-rubber (BR), acrylonitrile-butadiene-rubber (NBR), butyl-rubber (IIR), and natural rubber (NR). Each type was separately blended with 100 phr of fast extruding furnace black. The parameters of the model of Polley and Boonstra are recalculated for a specific example and good fitting is found.     

Matching of DC motors to photovoltaic generators for maximum dailygross mechanical energy

The matching to solar-cell generators of both separately excited and series DC motors driving pumping loads is addressed. It is shown that the maximum gross mechanical power can be obtained at slightly higher voltages and slightly lower currents compared to the maximum electrical-power points on the solar-cell generator characteristics at different insolation levels. Guidelines for constructing the loci of the motor voltage-current points for maximum mechanical power and for determining the optimal motor parameters to match the solar generator are derived in terms of the mechanical load characteristics and the solar array parameters. Results of applying these design criteria to practical case studies enabled the assessment and comparison of both kinds of motors, especially as far as the daily utilizable output mechanical energy is concerned. The superiority of the separately excited motors in such systems is quantitatively indicated. The results are also compared to corresponding information available in the literature     

Plasma L-arginine concentration, oxygenation index, and systemic blood pressure in premature infants

OBJECTIVE: To determine the relationships between plasma L-arginine concentrations and the severity of respiratory distress syndrome (RDS) or systemic blood pressure in premature infants. DESIGN: Prospective, observational study. SETTING: Neonatal intensive care, tertiary referral hospital. SUBJECTS: Fifty-three premature infants. INTERVENTIONS: We measured arginine and nutritional intake, plasma arginine concentration, total amino acid concentrations, and blood pressure on days 3, 7, 14, and 21 of life. In 33 infants who received assisted ventilation, oxygenation index could be calculated to reflect the severity of RDS. The relationships between plasma arginine and oxygenation index or blood pressure were analyzed using multiple linear regression. MEASUREMENTS AND MAIN RESULTS: On day 3, plasma arginine concentrations were decreased compared with normal published values. Arginine concentrations increased with the day of life of measurement (p < .001) and with arginine intake (p < .001). After adjusting for arginine intake and day of life, an inverse relationship was found between oxygenation index and plasma arginine concentrations: (p = .025). No similar relationship was found between oxygenation index and the concentration of total amino acids. A weak positive relationship was found between plasma arginine concentration and systemic blood pressure. CONCLUSIONS: Increments in the oxygenation index, reflective of an increased severity of RDS, are associated with a decrease in plasma arginine concentration. This finding may reflect arginine consumption by the nitric oxide synthase pathway in the lungs of premature infants with RDS, or may be explained by increased arginine catabolism. The lack of a similar relationship between total plasma amino acids and oxygenation index supports the first interpretation.