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A systematic approach to construct a low-dimensional free energy landscape from a classical molecular dynamics (MD) simulation is presented. The approach is based on the recently proposed dihedral angle principal component analysis (dPCA), which avoids artifacts due to the mixing of internal and overall motions in Cartesian coordinates and circumvents problems associated with the circularity of angular variables. Requiring that the energy landscape reproduces the correct number, energy, and location of the system’s metastable states and barriers, the dimensionality of the free energy landscape (i.e., the number of essential components) is obtained. This dimensionality can be determined from the distribution and autocorrelation of the principal components. By performing an 800 ns MD simulation of the folding of hepta-alanine in explicit water and using geometric and kinetic clustering techniques, it is shown that a five-dimensional dPCA energy landscape is a suitable and accurate representation of the full-dimensional landscape. In the second step, the dPCA energy landscape can be employed (e.g., in a Langevin simulation) to facilitate a detailed investigation of biomolecular dynamics in low dimensions. Finally, several ways to visualize the multidimensional energy landscape are discussed. [ABSTRACT FROM AUTHOR]

This article concentrates on the attitude control problem for the lifting re-entry vehicle with non-minimum phase property. A novel attitude control method is proposed for this kind of lifting re-entry vehicle without assuming the internal dynamics to be measurable. First, an internal dynamics extended state observer is developed to deal with the unmeasurable problem of the internal dynamics. And then, the control scheme which adopts output feedback method is proposed by modifying the traditional output redefinition technique with internal dynamics extended state observer. This control scheme only requires the system output to be measurable, and it can still stabilize the unstable internal dynamics and track attitude commands. Besides, because of the inherent property of extended state observer in rejecting uncertainties and disturbances, the control precision of the proposed controller is higher than the controller designed with traditional output redefinition technique. Finally, the effectiveness and robustness of the proposed attitude controller are demonstrated by the simulation results. [ABSTRACT FROM AUTHOR]

An accurate and efficient evaluation for hypersingular integrals (HIs), strongly singular integrals (SSIs), and weakly singular integrals (WSIs) plays an essential role in the numerical solutions of 3D electromagnetic scattering problems. We derive analytic formulas for WSIs based on Stokes' theorem, which can be expressed in elementary functions. Several numerical examples are presented to validate these analytic formulas. Then, to show the feasibility of the proposed formulations for numerical methods, these formulations are used with the existing analytical expressions of HIs and SSIs to correct the near-field interaction in an iterative physical optics (IPO) scheme. Using IPO, the scattering caused by a dihedral reflector is analyzed and compared with the results of the method of moments and measurement data. [ABSTRACT FROM AUTHOR]

An advanced computational and experimental analysis has been performed upon a conventional aircraft wing with two outboard morphing partitions that are variable in twist and dihedral angles. Results are generated with the intention of drawing meaningful comparisons with initial trends in aerodynamic and structural efficiency that have been observed in previous optimization studies. Computational results are obtained with the DLR , German Aerospace Center TAU computational fluid dynamics code, both for an aircraft wing in high-speed flight and for a wing modeled at low speed with wind-tunnel wall constraints. An experimental testing has been performed at the University of Bristol 7 x 5 ft low-speed wind tunnel. An outer-twist variation of ±3 deg and dihedral angles from planar up to 90 deg C-wing geometries are tested for a range of incidence angles. Results demonstrate varying levels of agreement between each form of analysis method, and offer insight into the aerodynamic and structural tradeoff required to select an optimal configuration. [ABSTRACT FROM AUTHOR]

Proportionally large relative radial clearances can be found within the rear stages of multistage axial compressors of gas turbines and aero engines, with significant impact on their efficiency. A new three-dimensional design for cantilevered stators in axial com-pressors is presented, with the aim of improving the overall efficiency and losses of rear stage vanes with large relative hub clearances. The new vane design comprises an uncon-ventional dihedral, with special consideration to reduce the losses caused by the hub clearance vortex. The design was tested in a 4-stage low speed axial research compressor under rear stage conditions. The results are compared to the nominal design to validate the reduction of hub clearance losses and blockage. For both designs, the hub clearances over the third and fourth stator were varied from 1.5% up to 6.0% of span. Overall per-formance data and flow field traverses upstream and downstream of stator 3 and rotor 4 will be presented in this article in comparison with 3D CFD results [ABSTRACT FROM AUTHOR]

The purpose of this paper is to analyze and discuss the performance and stability of a tailless micro aerial vehicle with flexible articulated wings. The dihedral angles can be varied symmetrically on both wings to control the aircraft peed independently of the angle of attack and flight-path angle, while an asymmetric dihedral setting can be used to control yaw in the absence of a vertical tail. A nonlinear aeroelastic model is derived, and it is used to study the steady- state performance and flight stability of the micro aerial vehicle. The concept of the effective dihedral is introduced, which allows for a unified treatment of rigid and flexible wing aircraft. It also identifies the amount of elasticity that is necessary to obtain tangible performance benefits over a rigid wing. The feasibility of using axial tension to stiffen the wing is discussed, and, at least in the context of a linear model, it is shown that adding axial tension is effective but undesirable. The turning performance of an micro aerial vehicle with flexible wings is compared to an otherwise identical micro aerial vehicle with rigid wings. The wing dihedral alone can be varied asymmetrically to perform rapid turns and regulate sideslip. The maximum attainable turn rate for a given elevator setting, however, does not increase unless antisymmetric wing twisting is employed. [ABSTRACT FROM AUTHOR]

This paper present the effect of morphing on the aircraft turning dynamics for symmetric and asymmetric V-shape changing wings. The aerodynamic forces will be calculated using a 3D aerodynamic model developed that utilizes a modern adaptation of Prandtl's liftingline method which can be used for wings of arbitrary camber, sweep and dihedral. The method will be applied to analyze symmetric and asymmetric V-shaped wing configurations of interest for morphing aircraft applications. The V-shaped wing has two panels, an out-of-plane dihedral panel and a horizontal panel. A study of the lift characteristics for symmetric and asymmetric configurations with and without flap deflection will be presented. An investigation as to how the partial dihedral affects the dynamics of the vehicle, in turning, for wings with asymmetric flap deflection is performed. A comparison of the different turning performance measurements, turning radius, bank angle, load factor, turning rate and roll moment coefficient will be presented. [ABSTRACT FROM AUTHOR]

We partially prove and partially disprove Oka's conjecture on the fundamental group/Alexander polynomial of an irreducible plane sextic. Among other results, we enumerate all irreducible sextics with simple singularities admitting dihedral coverings and find examples of Alexander equivalent Zariski pairs of irreducible sextics. [ABSTRACT FROM PUBLISHER]

Abstract: The breakdown of a longitudinal vortex originating from a three-dimensional dihedral body is examined in the perspective of reducing the aerodynamic drag of bluff bodies. The vortex breakdown is induced by a continuous and uniform blowing distributed on the separation line related to the formation and the development of the vortex. The breakdown is characterized by an abrupt disintegration of the vortical core and the appearance of a recirculation zone. Numerical results obtained with and without blowing show the crucial impact of the Swirl parameter on the vortex breakdown. Drag reductions close to 6% are found. To cite this article: B. Lehugeur et al., C. R. Mecanique 334 (2006). [Copyright &y& Elsevier]

The spectroscopic properties and crystal structures of the gold(I) arylacetylide complexes [(R[sub3]P)- Au(C≡CAr)] (R = Cy, Ar = 4-nitrophenyl, 1; 4-trifluoromethylphenyl, 2; pentafluorophenyl, 3; H = Ph, Ar = 4-nitrophenyl, 4) have been examined. The dipole-allowed and -forbidden transitions of 1 (4 in parentheses) at λ[submax] 340 (336) and Ca. 485 (470) nm in CH[sub2]CI[sub2] solution at 296 K are assigned to the singlet and triplet intraligand charge transfer (ILCT) transitions of the 4-nitrophenylacetylide moiety, whereas 2 (3 in parentheses) shows localized singlet and triplet acetylenic ,ππ transitions at λ[submax] 287 (276) and 426 nm, respectively. Two polymorphs of 1 with contrasting phosphorescent characteristics have been identified. At 298 K, the emissive form of 1, as well as 2-4, are highly phosphorescent with peak maximum at 504, 425, 521, and 495 nm, respectively; the other polymorph of 1 is nonemissive at 298 K but emission is detected at 77 K with peak maximum at 486 nm. Crystallographic studies reveal that the major differences between the emissive and nonemissive forms of 1 are the orientations of the molecular dipoles and the dihedral angles between neighboring 4-nitrophenyl moieties. Crystal 2 is isostructural to the nonemissive form of 1, but does not display polymorphism. The molecular planes of two neighboring lumophores are coplanar in the emissive form of 1, parallel in 4, and nearly perpendicular (78.6°) to each other in the nonemissive form of 1. Both the nature of the excited state and the dihedral angle between adjacent [Au-(C≡CAr)] moieties determine the phosphorescent properties of these molecular crystals. [ABSTRACT FROM AUTHOR]

The preparation and characterization of the following bis-imidazole and bis-pyridine complexes of octamethyltetraphenylporphyrinatoiron(III), Fe(III) OMTPP, octamethyltetraphenylporphyrinatoiron (III), Fe-(III)OETPP, and tetra-β,β-tetramethylenetetraphenylporphyrinatoiron(III), Fe(III)TC[SUB6]TPP, are reported: paral-[FeOMTPP(1-Melm)[SUB2]]Cl, perp-[FeOMTPP(1-Melm)[SUB2]]Cl, [FeOETPP(1-Melm)[SUB2]Cl, [FeTC[SUB6]TPP(l-Melm)[SUB2]]Cl,[FeOMTPP(4Me[SUB2]Npy[SUB2]]Cl, and [FeOMTPP(2-MeHim)[SUB2]]Cl. Crystal structure analysis shows that paral-[FeOMTPP(1-Melm)[SUB2]]Cl has its axial ligands in close to parallel orientation (the actual dihedral angle between the planes of the imidazole ligands is 19.5°), while perp-[FeOMTPP(l-Melm)[SUB2]]Cl has the axial imidazole ligand planes oriented at 90° to each other and 29° away from the closest N[SUBP]-Fe-N[SUBP] axis. [FeOETPP-(1-Melm)[SUB2]]Cl has its axial ligands close to perpendicular orientation (the actual dihedral angle between the planes of the imidazole ligands is 73.1°). In all three cases the porphyrin core adopts relatively purely saddled geometry. The [FeTC[SUB6]TPP1-Melm)[SUB2]]Cl complex is the most planar and has the highest contribution of a ruffled component in the overall saddled structure compared to all other complexes in this study. The estimated numerical contribution of saddled and ruffled components is 0.68:0.32, respectively. Axial ligand planes are perpendicular to each other and 15.3° away from the closest N[SUBP]-Fe-N[SUBP] axis. The Fe-N[SUBP] bond is the longest in the series of octaalkyltetraphenylporphyrinatoiron complexes due to [FeTC[SUB6]TPP-(1-Melm)[SUB2]]Cl having the least distorted porphyrin core. In addition to these three complexes, two crystalline forms each of [FeOMTPP(4-Me[SUB2]NPy)[SUB2]Cl and [FeOMTPP(2-MeHlm)[SUB2]]Cl were obtained. [ABSTRACT FROM AUTHOR]

Numerical investigations have been carried out to study aerodynamics of non-flapping characteristics of bird flight. Commercial software ANSYS Fluent 16.1 has been used for three-dimensional computations by considering four types of wing models. At first, square prisms with built-in side flaps are considered and the effects of Reynolds number (Re), angle of attack and dihedral angle on flow characteristics have been investigated. Thereafter, flow past actual bird wing has been considered for wings of owl, seagull, teal and bat. Role of shear layer formation at mid-span of wings has been illustrated with the help of streamline plots for different values of Re. In addition, pulsating flow is imposed on inlet velocity and the responses are obtained in form of force coefficients, phase portraits, time-dependent signals and their spectra. [ABSTRACT FROM AUTHOR]

It is shown that lifting-line theory closely captures the effects of tail dihedral on the static stability contributions of an aft tail and compares well with experiments. Such computations show that vortex interactions between the lifting surfaces of an aft tail can significantly affect tail performance. For a V-tail, these interactions slightly increase the tail's contribution to pitch stability and substantially decrease its contribution to yaw and roll stability. When horizontal-stabilizer dihedral is used in combination with a vertical stabilizer, it is shown that the tail will provide greater yaw stability if negative dihedral is used in horizontal stabilizers mounted below a vertical stabilizer. Conversely, positive dihedral works best in cases where the horizontal stabilizer is mounted above the vertical stabilizer. [ABSTRACT FROM AUTHOR]