Automatic crosswind flight of tethered wings for airborne wind energy: modeling, control design and experimental results

An approach to control tethered wings for airborne wind energy is proposed. A fixed length of the lines is considered, and the aim of the control system is to obtain figure-eight crosswind trajectories. The proposed technique is based on the notion of the wing's "velocity angle" and, in contrast with most existing approaches, it does not require a measurement of the wind speed or of the effective wind at the wing's location. Moreover, the proposed approach features few parameters, whose effects on the system's behavior are very intuitive, hence simplifying tuning procedures. A simplified model of the steering dynamics of the wing is derived from first-principle laws, compared with experimental data and used for the control design. The control algorithm is divided into a low-level loop for the velocity angle and a high-level guidance strategy to achieve the desired flight patterns. The robustness of the inner loop is verified analytically, and the overall control system is tested experimentally on a small-scale prototype, with varying wind conditions and using different wings.Comment: This manuscript is a preprint of a paper accepted for publication on the IEEE Transactions on Control Systems Technology and is subject to IEEE Copyright. The copy of record is available at IEEEXplore library: http://ieeexplore.ieee.org

Endogeneity in Panel Stochastic Frontier Models: An Application to the Japanese Cotton Spinning Industry

We present a panel stochastic frontier model that handles the endogeneity problem. This model can treat the endogeneity of both frontier and inefficiency variables. We apply our method to examine the technical efficiency of Japanese cotton spinning industry. Our results indicate that market concentration is endogenous, and when its endogeneity is properly handled, it has a larger negative impact on the technical efficiency of cotton spinning plants. We find that the exogenous model substantially overestimates efficiency in concentrated markets

School district consolidation policies: endogenous cost inefficiency and saving reversals

Some education policy studies suggest that consolidation of public school districts saves resources. However, endogeneity in cost models would result in incorrect estimates of the effects of consolidation. We use a new stochastic frontier methodology to examine district expenditures while handling endogeneity. Using the data from California, we find that the effects of student achievement and education market concentration on expenditure per pupil are substantially larger when endogeneity is handled. Our findings are robust to concerns such as instrumental variable adequacy and spatial interactions. Our consolidation simulations indicate that failure to address endogeneity can result in unrealistic expectations of savings

Plankton Community Structure of Traditional and Intensive Brackishwater Ponds in Probolinggo Regency, East Java Province

This experiment aimed to determine the plankton community structure in intensive and traditional ponds of Probolinggo Regency, East Java Province. Plankton collected with plankton net size of 60 μm and preserved with lugol 1%. Water qualities such as temperature, transparancy, salinity, dis-solved oxygen, pH, total organic matter, NO2-N, NO3-N, NH3-N, PO4-P, and total suspended solids were measured and analysed in this study. Planktons were identified using microscopy. Cells were counted using cell counting method. The results showed that in intensive pond we found 16 species of phytoplankton and 7 species of zooplankton with abundance 570-1.808 ind./L, while in traditional ponds, we found 10 species of phytoplankton and 3 species of zooplankton with abundance 134-776 ind./L. The dominant species of phytoplankton in the intensive and traditional ponds were Navicula sp andNitzschia sp, each of Bacillariophyceae class with abundance of 423 ind./L and 198 ind./L, res-pectively. Zooplankton species in intensive pond was copepod sp, while in traditional one was Oitho-na sp, each of Crustaceae class with abundance of 66 ind./L and 37 ind./L, respectively. Diversity and abundance of plankton in intensive pond was higher than in the traditional ponds. The water quality in intensive pond was optimal so that the response to the absorption of N and P inorganic by phyto-plankton was quicker and more effective than in traditional pond producing an increase in plankton communities. The increase value of NO3-N and total suspended solids in intensive pond caused the in-crease abundance of Navicula sp. The high value of NH3-N caused the abundance of Navicula sp to decline. The high values of dissolved oxygen, pH, total suspended solid, and NH3-N in traditional pond can decrease the Nitzschia sp abundance

A Dynamic Stochastic Frontier Model with Threshold Effects: U.S. Bank Size and Efficiency

Common/Single frontier methodologies that are used to analyze bank efficiency and performance can be misleading because of the homogeneous technology assumption. Using the U.S. banking data over 1984-2010, our dynamic methodology identifies a few data-driven thresholds and distinct size groups. Under common frontier assumption, the largest banks appear to be 22% less efficient on average than how they are in our model. Also, in the common frontier model, smaller banks seem to be relatively more efficient compared to their larger counterparts. Hence, common policies or regulations may not be well-balanced about controlling the banks of different sizes on the spectrum

Influence of temperature and relative humidity on the efficacy of diatomaceous earth and Metarhizium anisopliae (Metschinkoff) Sorokin (Hyphomycetes: Deuteromycotina) against Tyrophagus fatimii F. (Astigmata: Acaridae)

The combined as well as the alone effect of diatomaceous earth (DE) and entomopathogenic fungi were evaluated against Tyrophagus fatimii (Astigmata: Acaridae). Two different dose rates of DE (1 g and 1.5 g/kg of wheat) and three of the fungus Metarhizium anisopliae (Hyphomycetes: Deuteromycotina) (3.6 x 107, 3.6 x 108 and 3.6 x 109 conidia/kg of wheat) were taken and studied at 20°C and 25°C with 45% and 55% r.h. under three exposure intervals. It was found that the combined effect of DE diatomaceous earth and M. anisopliae was maximum at 25°C and 55% r.h. which gave 75% adult mortality at their highest dose rates, however, DE alone exhibited the highest mortality (61.3%) at 25°C and 45% r.h. On the other hand, M. anisopliae gave maximum mortality of mites (48.7%) at 20°C and 55% r.h. at 3.6 x 109 conidia/kg of wheat. It was concluded that the efficacy of both DE and M. anisopliae increased with the increase of the exposure interval. Moreover, the increase of dose increased the mortality. In addition, temperature and r.h. are the key factors for determining the effectiveness of both DE and M. anisopliae. Keywords: Diatomaceous earth, Tyrophagus fatimii, Metarhizium anisopliae, Stored wheat

Pancreatic Divisum: An Unusual Cause of Chronic Pancreatitis in a Young Patient

Pancreatic divisum is a condition that occurs in 4-14% of the population. Pancreatic divisum occurs in development when the ventral bud and dorsal bud of the pancreas fail to fuse. Patients with this condition are usually asymptomatic, however, 25-38% of these patients experience recurrent pancreatitis that may further progress to chronic pancreatitis. This case is of a 20-year-old female presenting with abdominal pain in the left and right upper quadrants of the abdomen with a significant history of recurrent pancreatitis since the age of seven. The patient was examined with computed tomography (CT), which identified pancreatitis. Further magnetic resonance cholangiopancreatography (MRCP) assisted in the diagnosis of a type III pancreatic divisum, given the remnant of short communication between the dorsal and ventral duct