A Vectoring Thrust Coaxial Rotor for Micro Air Vehicle: Modeling, Design and Analysis

The growing interest of rotary wing UAVs, for military and civilian applications, has encouraged designers to consider miniaturized configurations, more efficient in terms of endurance, payload capability and maneuverability. The purpose of this paper is to study a new configuration of coaxial rotor as applied to a micro aerial vehicle (MAV) with the intention to guarantee the vehicle maneuverability while removing unnecessary control surfaces which would increase wind gust sensitivity. Coaxial rotor configurations maximize the available rotor disk surface and allow for torque cancelation. Tilting rotors may allow for the vehicle control

On the positivity of fvs schemes

Over the last ten years, robustness of schemes has raised an increasing interest among the CFD community. One mathematical aspect of scheme robustness is the positivity preserving property. At high Mach numbers, solving the conservative Euler equations can lead to negative densities or internal energy. Some schemes such as the flux vector splitting (FVS) schemes are known to avoid this drawback. In this study, a general method is detailed to analyze the positivity of FVS schemes. As an application, three classical FVS schemes (Van Leer's, Hänel's variant and Steger and Warming's) are proved to be positively conservative under a CFL-like condition. Finally, it is proved that for any FVS scheme, there is an intrinsic incompatibility between the desirable property of positivity and the exact resolution of contact discontinuities

Hybrid micro air vehicle for complex environment missions

Modern urban reconnaissance missions dictate the need for a Micro Air Vehicle (MAV) platform capable of performing a complex mission : rapid and efficient ingress to a target location followed by slow loiter for quality image capture. This may be achieved using a tilt-body fixed-wing vehicle which combines the speed, range, and gust-hardiness of a fixed wing with the loiter and precision capability of a rotorcraft vehicle

A cure for the sonic point glitch

Among the various numerical schemes developed since the '80s for the computation of the compressible Euler equations, the vast majority produce in certain cases spurious pressure glitches at sonic points. This flaw is particularly visible in the computation of transonic expansions and leads to unphysical "expansion shocks" when the flow undergoes rapid change of direction. The analysis of this flaw is presented, based on a series of numerical experiments. For Flux-Vector Splitting methods, it is suggested that it is not the order of differentiability of the numerical flux which is crucial but the way the pressure at an interface is calculated. A new way of evaluating the pressure at the interface is proposed, based upon kinetic theory, and is applied to most current available algorithms including Flux Vector Splitting and Flux-Difference Splitting methods as well as recent hybrid schemes (AUSM, HUS)

Positivity of flux vector splitting schemes

Over the last ten years, robustness of schemes has raised an increasing interest among the CFD community. One mathematical aspect of scheme robustness is the positivity preserving property. At high Mach numbers, solving the conservative Euler equations can lead to negative densities or internal energy. Some schemes such as the flux vector splitting (FVS) schemes are known to avoid this drawback. In this study, a general method is detailed to analyze the positivity of FVS schemes. As an application, three classical FVS schemes (Van Leer's, Hänel's variant, and Steger and Warming's) are proved to be positively conservative under a CFL-like condition. Finally, it is proved that for any FVS scheme, there is an intrinsic incompatibility between the desirable property of positivity and the exact resolution of contact discontinuities

A matrix stability analysis of the carbuncle phenomenon

The carbuncle phenomenon is a shock instability mechanism which ruins all efforts to compute grid-aligned shock waves using low-dissipative upwind schemes. The present study develops a stability analysis for two-dimensional steady shocks on structured meshes based on the matrix method. The numerical resolution of the corresponding eigenvalue problem confirms the typical odd–even form of the unstable mode and displays a Mach number threshold effect currently observed in computations. Furthermore, the present method indicates that the instability of steady shocks is not only governed by the upstream Mach number but also by the numerical shock structure. Finally, the source of the instability is localized in the upstream region, providing some clues to better understand and control the onset of the carbuncle

Carlo Michelstaedter: Persuasion and Rhetoric

Carlo Michelstaedter\u27s Persuasion and Rhetoric (1910) is one of best examples of what Massimo Cacciari calls the early twentieth century metaphysics of youth. Persuasion and Rhetoric is the result of Michelstaedter\u27s academic investigation on the concepts of persuasion and rhetoric in Plato and Aristotle. Michelstaedter saw in Plato\u27s corpus the gradual abandonment of Parmenidean being and Socrates\u27 dialogical philosophy. He reinterpreted the notions of persuasion and rhetoric terms of a radical dichotomy, using them to represent two opposed ontological modalities, two epistemological attitudes, and two existential alternatives. If rhetoric comprehends language, institutional knowledge, and all manifestations of empirical life, then persuasion is defined as the unity of the individual with Parmenidean being. Persuasion is an impossible choice: lifeless life. Being a decisive alternative to rhetoric, persuasion - much like Platonic mania - can neither be articulated nor communicated. Nevertheless, Michelstaedter speaks, aware of his inevitable failure: he will not persuade anyone

Equilibrium transition study for a hybrid MAV

Wind tunnel testing was performed on a VTOL aircraft in order to characterize longitudinal flight behavior during an equilibrium transition between vertical and horizontal flight modes. Trim values for airspeed, pitch, motor speed and elevator position were determined. Data was collected by independently varying the trim parameters, and stability and control derivatives were identified as functions of the trim pitch angle. A linear fractional representation model was then proposed, along with several methods to improve longitudinal control of the aircraft

Removal of the calcium-dependent regulation of ATP binding in Synapsin I has distinct effects at excitatory and inhibitory synapses

Synapsins are the most abundant family of neuro-specific phosphoproteins associated with the cytoplasmic surface of the synaptic vesicle membrane. These proteins actively regulate synaptic transmission at the level of the presynaptic terminal by controlling the storage and mobilization of synaptic vesicles within a reserve pool. However, it is hypothesized that synapsins could be involved in other stages of synaptic vesicle dynamics such as trafficking, docking, fusion with the plasma membrane and consequent recycling. Synapsin I (SynI) in particular is expressed two isoforms (Ia and Ib) at the presynaptic compartment of all neurons in the adult brain. Several studies suggest that SynI is also involved in axon elongation and synaptic vesicle fusion kinetics. In human, nonsense and missense mutations of SYN1 gene are related to several diseases such as epilepsy and autism spectrum disorder; in fact, SynI knockout (KO) mice show an epileptic and autism-like phenotype. To carry out its functions, SynI requires to bind ATP in a Ca2+-dependent manner thanks to the coordination of a glutamate residue (E373). As ATP binding regulates SynI oligomerization and SV clustering, we analyzed the effect of E373K mutation on neurotransmitter release and short-term plasticity in excitatory and inhibitory synapses. We coupled electrophysiology (patch-clamp recordings) with electron microscopy in primary SynI KO hippocampal neurons in which either the human wild type or the E373K mutant SynI were re-introduced by infection with lentiviral vectors. Our data indicate that E373K mutation affects predominantly excitatory synapses. The frequency of miniature excitatory postsynaptic currents (mEPSCs) was enhanced, without changes in the amplitude and in the number of excitatory synapses. The increment of mEPSCs frequency was totally abolished after acute injection of BAPTA-AM (a specific Ca2+ chelator), suggesting a possible alteration of Ca2+ homeostasis at the presynaptic terminal. Excitatory E373K-Syn I neurons showed reduced evoked EPSC amplitude attributable to a reduction of the readily releasable pool (RRP), while, on the contrary, inhibitory E373K-Syn I neurons did not show any difference both in miniature, evoked IPSC amplitude and RRP size. While no effects in the dynamics and steady state of depression were detected, both excitatory and inhibitory E373K-Syn I neurons failed to recover after stimulation with long high-frequency trains. No mutation-induced changes were observed in network firing/bursting activity as determined with multi-electrode extracellular recordings. Our data suggest that the Ca2+-dependent regulation of ATP-binding to SynI plays important roles in spontaneous and evoked neurotransmitter release that differentially affect the strength of excitatory and inhibitory transmission