Design and test of a prototype scale ejector wing

A two dimensional momentum integral analysis was used to examine the effect of changing inlet area ratio, diffuser area ratio, and the ratio of ejector length to width. A relatively wide range of these parameters was considered. It was found that for constant inlet area ratio the augmentation increases with the ejector length, and for constant length: width ratio the augmentation increases with inlet area ratio. Scale model tests were used to verify these trends and to examine th effect of aspect ratio. On the basis of these results, an ejector configuration was selected for fabrication and testing at a scale representative of an ejector wing aircraft. The test ejector was powered by a Pratt-Whitney F401 engine developing approximately 12,000 pounds of thrust. The results of preliminary tests indicate that the ejector develops a thrust augmentation ratio better than 1.65

Assault on the NLO Wishlist: pp -> tt bb

We present the results of a next-to-leading order calculation of QCD corrections to the production of an on-shell top-anti-top quark pair in association with two flavored b-jets. Besides studying the total cross section and its scale dependence, we give several differential distributions. Where comparable, our results agree with a previous analysis. While the process under scrutiny is of major relevance for Higgs boson searches at the LHC, we use it to demonstrate the ability of our system built around Helac-Phegas to tackle complete calculations at the frontier of current studies for the LHC. On the technical side, we show how the virtual corrections are efficiently computed with Helac-1Loop, based on the OPP method and the reduction code CutTools, using reweighting and Monte Carlo over color configurations and polarizations. As far as the real corrections are concerned, we use the recently published Helac-Dipoles package. In connection with improvements of the latter, we give the last missing integrated dipole formulae necessary for a complete implementation of phase space restriction dependence in the massive dipole subtraction formalism.Comment: 19 pages, 11 figures, 2 tables. References added, version to appear in JHE

Non-Gaussian Geostatistical Modeling using (skew) t Processes

We propose a new model for regression and dependence analysis when addressing spatial data with possibly heavy tails and an asymmetric marginal distribution. We first propose a stationary process with $t$ marginals obtained through scale mixing of a Gaussian process with an inverse square root process with Gamma marginals. We then generalize this construction by considering a skew-Gaussian process, thus obtaining a process with skew-t marginal distributions. For the proposed (skew) $t$ process we study the second-order and geometrical properties and in the $t$ case, we provide analytic expressions for the bivariate distribution. In an extensive simulation study, we investigate the use of the weighted pairwise likelihood as a method of estimation for the $t$ process. Moreover we compare the performance of the optimal linear predictor of the $t$ process versus the optimal Gaussian predictor. Finally, the effectiveness of our methodology is illustrated by analyzing a georeferenced dataset on maximum temperatures in Australi

Development and experimentation of LQR/APF guidance and control for autonomous proximity maneuvers of multiple spacecraft

http://dx.doi.org/10.1016/j.actaastro.2010.08.012This work introduces a novel control algorithm for close proximity multiple spacecraft autonomous maneuvers, based on hybrid linear quadratic regulator/artificial potential function (LQR/APF), for applications including autonomous docking, on-orbit assembly and spacecraft servicing. Both theoretical developments and experimental validation of the proposed approach are presented. Fuel consumption is sub-optimized in real-time through re-computation of the LQR at each sample time, while performing collision avoidance through the APF and a high level decisional logic. The underlying LQR/APF controller is integrated with a customized wall-following technique and a decision logic, overcoming problems such as local minima. The algorithm is experimentally tested on a four spacecraft simulators test bed at the Spacecraft Robotics Laboratory of the NAval Postgraduate School. The metrics to evaluate the control algorithm are: autonomy of the system in making decisions, successful completion of the maneuver, required time, and propellant consumption

Development and experimentation of LQR/APF guidance and control for autonomous proximity maneuvers of multiple spacecraft

http://dx.doi.org/10.1016/j.actaastro.2010.08.012This work introduces a novel control algorithm for close proximity multiple spacecraft autonomous maneuvers, based on hybrid linear quadratic regulator/artificial potential function (LQR/APF), for applications including autonomous docking, on-orbit assembly and spacecraft servicing. Both theoretical developments and experimental validation of the proposed approach are presented. Fuel consumption is sub-optimized in real-time through re-computation of the LQR at each sample time, while performing collision avoidance through the APF and a high level decisional logic. The underlying LQR/APF controller is integrated with a customized wall-following technique and a decision logic, overcoming problems such as local minima. The algorithm is experimentally tested on a four spacecraft simulators test bed at the Spacecraft Robotics Laboratory of the NAval Postgraduate School. The metrics to evaluate the control algorithm are: autonomy of the system in making decisions, successful completion of the maneuver, required time, and propellant consumption

Uncooperative Objects Pose, Motion and Inertia Tensor Estimation via Stereovision

Autonomous close proximity operations are an arduous and attractive problem in space mission design. In particular, the estimation of pose, motion and inertia properties of an uncooperative object is a challenging task because of the lack of available a priori information. In addition, good computational performance is necessary for real applications. This paper develops a method to estimate the relative position, velocity, angular velocity, attitude and inertia properties of an uncooperative space object using only stereo-vision measurements. The classical Extended Kalman Filter (EKF) and an Iterated Extended Kalman Filter (IEKF) are used and compared for the estimation procedure. The relative simplicity and low computational cost of the proposed algorithm allow for an online implementation for real applications. The developed algorithm is validated by numerical simulations in MATLAB using different initial conditions and uncertainty levels. The goal of the simulations is to verify the accuracy and robustness of the proposed estimation algorithm. The obtained results show satisfactory convergence of the estimation errors for all the considered quantities. An analysis of the computational cost is addressed to confirm the possibility of an onboard application. The obtained results, in several simulations, outperform similar works present in literature. In addition, a video processing procedure is presented to reconstruct the geometrical properties of a body using cameras. This method has been experimentally validated at the ADAMUS (ADvanced Autonomous MUltiple Spacecraft) Lab at the University of Florida

Acoustic Characterization and Quality Assessment of Cremona’s Ponchielli Theater

The Ponchielli theater of Cremona was built in 1808 after a fire destroyed the old wooden structure. The interior, the architecture and the shape of the plan layout are reminiscent of the Teatro alla Scala, Milan, a masterpiece by the architect Piermarini, albeit on a smaller scale. The four orders of balconies crowned by the top gallery are typical features of a 19th Century Italian Opera theater. Acoustic measurements have been undertaken across the stalls and in some selected boxes according to ISO 3382. The main acoustic parameters resulting from the measurements have been used for the acoustic calibration of a 3D model representing the Ponchielli theater. The calibration has been used to compare different scenarios involving the acoustic response of the main hall at 50% and 100% occupancy. The outcomes indicate that no significant change can be detected when the seats are provided with robust upholstery, which can be considered a positive result, especially for the actors who are not forced to change their effort between rehearsal and live performance. In order to contextualize the measured values in relation to the optimal ones, a comparison with other Italian Opera theaters provided with similar architectural characteristics has been carried out. Overall, the findings indicate that the acoustics of the Ponchielli theater are suitable for both music and speech in line with the other selected theaters, as these places were mainly created for multifunctional purposes in the 19th Century

Understanding the role of the anode on the polarization losses in high-temperature polymer electrolyte membrane fuel cells using the distribution of relaxation times analysis

To investigate the role of the anode on the polarization losses of a High-Temperature Polymer Electrolyte Membrane Fuel Cell (HT-PEMFC), we analyzed impedance data using the Distribution of Relaxation Times (DRT) method. Thereby, we varied the operating conditions of the anode (humidification, nitrogen dilution, and carbon monoxide (CO) impurities) to study its impact on Nyquist plot and DRT spectrum. Humidification of the hydrogen was found to dilute phosphoric acid, which is visible in the DRT. Nitrogen dilution of the anode gas slightly increases the Mass Transport (MT) resistance. Furthermore, CO was added to anode gas fed and it impacts the impedance throughout the whole frequency range, specifically the medium and low-frequency range, typically assigned to ORR kinetics and oxygen MT. For a more detailed analysis of the impedance data, a reference electrode was employed to separate the overpotential caused by each electrode. The DRT spectrum of the anode exhibits only one peak at 1 kHz. In the presence of CO, a second peak arises corresponding to side-reactions occurring as the anodic half-cell potential increases. It was found that the cathode is affected by CO on the anode merely by the lowered cell potential and not by CO directly