Fluctuating Elastic Rings: Statics and Dynamics

We study the effects of thermal fluctuations on elastic rings. Analytical expressions are derived for correlation functions of Euler angles, mean square distance between points on the ring contour, radius of gyration, and probability distribution of writhe fluctuations. Since fluctuation amplitudes diverge in the limit of vanishing twist rigidity, twist elasticity is essential for the description of fluctuating rings. We find a crossover from a small scale regime in which the filament behaves as a straight rod, to a large scale regime in which spontaneous curvature is important and twist rigidity affects the spatial configurations of the ring. The fluctuation-dissipation relation between correlation functions of Euler angles and response functions, is used to study the deformation of the ring by external forces. The effects of inertia and dissipation on the relaxation of temporal correlations of writhe fluctuations, are analyzed using Langevin dynamics.Comment: 43 pages, 9 Figure

Comparison of Fixed and Variable Pitch Actuators for Agile Quadrotors

This paper presents the design, analysis and experimental testing of a variable- pitch quadrotor. A custom in-lab built quadrotor with on-board attitude stabi- lization is developed and tested. An analysis of the dynamic di erences in thrust output between a xed-pitch and variable-pitch propeller is given and validated with simulation and experimental results. It is shown that variable-pitch actuation has signi cant advantages over the conventional xed-pitch con guration, includ- ing increased thrust rate of change, decreased control saturation, and the ability to quickly and e ciently reverse thrust. These advantages result in improved quadro-tor tracking of linear and angular acceleration command inputs in both simulation and hardware testing. The bene ts should enable more aggressive and aerobatic ying with the variable-pitch quadrotor than with standard xed-pitch actuation, while retaining much of the mechanical simplicity and robustness of the xed-pitch quadrotor.Aurora Flight Sciences Corp.National Science Foundation (U.S.) (Graduate Research Fellowship Grant 0645960

Role of dynamic Jahn-Teller distortions in Na2C60 and Na2CsC60 studied by NMR

Through 13C NMR spin lattice relaxation (T1) measurements in cubic Na2C60, we detect a gap in its electronic excitations, similar to that observed in tetragonal A4C60. This establishes that Jahn-Teller distortions (JTD) and strong electronic correlations must be considered to understand the behaviour of even electron systems, regardless of the structure. Furthermore, in metallic Na2CsC60, a similar contribution to T1 is also detected for 13C and 133Cs NMR, implying the occurence of excitations typical of JT distorted C60^{2-} (or equivalently C60^{4-}). This supports the idea that dynamic JTD can induce attractive electronic interactions in odd electron systems.Comment: 3 figure

Performance Testing of Aero-Naut CAMFolding Propellers

The increase in popularity of unmanned aerial vehicles (UAVs) has been driven by their use in civilian, education, government, and military applications. However, limited on-board energy storage significantly limits flight time and ultimately usability. The propulsion system plays a critical part in the overall energy consumption of the UAV; therefore, it is necessary to determine the most optimal combination of possible propulsion system components for a given mission profile, i.e. propellers, motors, and electronic speed controllers (ESC). Hundreds of options are available for the different components with little performance specifications available for most of them. By examining a variety of existing long-endurance aircraft, Aero-Naut CAM carbon folding propellers were identified as the most commonly used type of commercial-off-the-shelf propeller. However, no performance data exist in the open literature for the Aero-Naut CAM carbon folding propellers. This paper describes the performance testing of 40 Aero-Naut CAM carbon propellers in 2-blade configuration with diameters of 9 to 16 in with various pitch values. The propellers were tested at rotation rates of 3,000 to 7,000 RPM and advancing flows of 8 to 80 ft/s, depending on the propeller and testing equipment limitations. Results are presented for the 40 propellers tested under static and advancing flow conditions with several key observations being discussed. The data produced will be available for download on the UIUC Propeller Data Site and on the Unmanned Aerial Vehicle Database

Effect of trailing edge shape on the separated flow characteristics around an airfoil at low Reynolds number: A numerical study

Direct numerical simulations of the flow field around a NACA 0012 airfoil at Reynolds number 50 000 and angle of attack 5° with 3 different trailing edge shapes (straight, blunt, and serrated) have been performed. Both time-averaged flow characteristics and the most dominant flow structures and their frequencies are investigated using the dynamic mode decomposition method. It is shown that for the straight trailing edge airfoil, this method can capture the fundamental as well as the subharmonic of the Kelvin-Helmholtz instability that develops naturally in the separating shear layer. The fundamental frequency matches well with relevant data in the literature. The blunt trailing edge results in periodic vortex shedding, with frequency close to the subharmonic of the natural shear layer frequency. The shedding, resulting from a global instability, has an upstream effect and forces the separating shear layer. Due to forcing, the shear layer frequency locks onto the shedding frequency while the natural frequency (and its subharmonic) is suppressed. The presence of serrations in the trailing edge creates a spanwise pressure gradient, which is responsible for the development of a secondary flow pattern in the spanwise direction. This pattern affects the mean flow in the near wake. It can explain an unexpected observation, namely, that the velocity deficit downstream of a trough is smaller than the deficit after a protrusion. Furthermore, the insertion of serrations attenuates the energy of vortex shedding by de-correlating the spanwise coherence of the vortices. This results in weaker forcing of the separating shear layer, and both the subharmonics of the natural frequency and the shedding frequency appear in the spectra

A Multilevel Monte Carlo Evolutionary Algorithm for Robust Aerodynamic Shape Design

The majority of problems in aircraft production and operation require decisions made in the presence of uncertainty. For this reason aerodynamic designs obtained with traditional deterministic optimization techniques seeking only optimality in a specific set of conditions may have very poor off-design performances or may even be unreliable. In this work we present a novel approach for robust optimization of aerodynamic shapes based on the combination of single and multi-objective Evolutionary Algorithms and a Continuation Multi Level Monte Carlo methodology to estimate robust designs, without relying on derivatives and meta-models. Detailed numerical studies are presented for a transonic airfoil design affected by geometrical and operational uncertainties

A cryptic promoter in potato virus X vector interrupted plasmid construction

BACKGROUND: Potato virus X has been developed into an expression vector for plants. It is widely used to express foreign genes. In molecular manipulation, the foreign genes need to be sub-cloned into the vector. The constructed plasmid needs to be amplified. Usually, during amplification stage, the foreign genes are not expressed. However, if the foreign gene is expressed, the construction work could be interrupted. Two different viral genes were sub-cloned into the vector, but only one foreign gene was successfully sub-cloned. The other foreign gene, canine parvovirus type 2 (CPV-2) VP1 could not be sub-cloned into the vector and amplified without mutation (frame shift mutation). RESULTS: A cryptic promoter in the PVX vector was discovered with RT-PCR. The promoter activity was studied with Northern blots and Real-time RT-PCR. CONCLUSION: It is important to recognize the homologous promoter sequences in the vector when a virus is developed as an expression vector. During the plasmid amplification stage, an unexpected expression of the CPV-2 VP1 gene (not in the target plants, but in E. coli) can interrupt the downstream work

Nonlinear Large Deflection Theory with Modified Aeroelastic Lifting Line Aerodynamics for a High Aspect Ratio Flexible Wing

This paper investigates the effect of nonlinear large deflection bending on the aerodynamic performance of a high aspect ratio flexible wing. A set of nonlinear static aeroelastic equations are derived for the large bending deflection of a high aspect ratio wing structure. An analysis is conducted to compare the nonlinear bending theory with the linear bending theory. The results show that the nonlinear bending theory is length-preserving whereas the linear bending theory causes a non-physical effect of lengthening the wing structure under the no axial load condition. A modified lifting line theory is developed to compute the lift and drag coefficients of a wing structure undergoing a large bending deflection. The lift and drag coefficients are more accurately estimated by the nonlinear bending theory due to its length-preserving property. The nonlinear bending theory yields lower lift and span efficiency than the linear bending theory. A coupled aerodynamic-nonlinear finite element model is developed to implement the nonlinear bending theory for a Common Research Model (CRM) flexible wing wind tunnel model to be tested in the University of Washington Aeronautical Laboratory (UWAL). The structural stiffness of the model is designed to give about 10% wing tip deflection which is large enough that could cause the nonlinear deflection effect to become significant. The computational results show that the nonlinear bending theory yields slightly less lift than the linear bending theory for this wind tunnel model. As a result, the linear bending theory is deemed adequate for the CRM wind tunnel model

Aero-Structural Modeling of the Truss-Braced Wing Aircraft Using Potential Method with Correction Methods for Transonic Viscous Flow and Wing-Strut Interference Aerodynamics

This paper describes an aero-structural modeling method for the Transonic Truss-Braced Wing (TTBW) aircraft using VSPAERO. A vortex-lattice model of the TTBW aircraft is developed, and a transonic and viscous flow correction method is implemented in the VSPAERO models to account for transonic and viscous flow effects. A correction method for the wing-strut interference aerodynamics is developed and applied to the VSPAERO solver. Also, a structural dynamic finite-element model of the TTBW aircraft is developed. This finite-element model includes the geometric nonlinear effect due to the tension in the struts which cause a deflection dependent nonlinear stiffness. The VSPAERO models are coupled to the finite-element model to provide a rapid capability for aero-structural modeling and flutter analysis. A flight-optimized jig twist model is being developed and will be applied for the purpose of generating a full flight dynamic model of the TTBW aircraft