Chaotic Patterns in Aeroelastic Signals

This work presents the analysis of nonlinear aeroelastic time series from wing vibrations due to airflow separation during wind tunnel experiments. Surrogate data method is used to justify the application of nonlinear time series analysis to the aeroelastic system, after rejecting the chance for nonstationarity. The singular value decomposition (SVD) approach is used to reconstruct the state space, reducing noise from the aeroelastic time series. Direct analysis of reconstructed trajectories in the state space and the determination of Poincare sections have been employed to investigate complex dynamics and chaotic patterns. With the reconstructed state spaces, qualitative analyses may be done, and the attractors evolutions with parametric variation are presented. Overall results reveal complex system dynamics associated with highly separated flow effects together with nonlinear coupling between aeroelastic modes. Bifurcations to the nonlinear aeroelastic system are observed for two investigations, that is, considering oscillations-induced aeroelastic evolutions with varying freestream speed, and aeroelastic evolutions at constant freestream speed and varying oscillations. Finally, Lyapunov exponent calculation is proceeded in order to infer on chaotic behavior. Poincare mappings also suggest bifurcations and chaos, reinforced by the attainment of maximum positive Lyapunov exponents. Copyright (C) 2009 F. D. Marques and R. M. G. Vasconcellos.

UNIQUENESS AND NONUNIQUENESS RESULTS FOR A CERTAIN CLASS OF ALMOST PERIODIC DISTRIBUTIONS

We consider distributions u is an element of S'(R) of the form u(t) = Sigma(n is an element of N) a(n)e(i lambda nt), where (a(n))(n is an element of N) subset of C and Lambda = (lambda n)(n is an element of N) subset of R have the following properties: (a(n))(n is an element of N) is an element of s', that is, there is a q is an element of N such that (n(-q) a(n))(n is an element of N) is an element of l(1); for the real sequence., there are n(0) is an element of N, C > 0, and alpha > 0 such that n >= n(0) double right arrow vertical bar lambda(n)vertical bar >= Cn(alpha). Let I(epsilon) subset of R be an interval of length epsilon. We prove that for given Lambda, (1) if Lambda = O(n(alpha)) with alpha < 1, then there exists epsilon > 0 such that u vertical bar I(epsilon) = 0 double right arrow u 0; (2) if Lambda = O(n) is uniformly discrete, then there exists epsilon > 0 such that u vertical bar I(epsilon) = 0 double right arrow u 0; (3) if alpha > 1 and. is uniformly discrete, then for all epsilon > 0, u vertical bar I(epsilon) = 0 double right arrow u = 0. Since distributions of the above mentioned form are very common in engineering, as in the case of the modeling of ocean waves, signal processing, and vibrations of beams, plates, and shells, those uniqueness and nonuniqueness results have important consequences for identification problems in the applied sciences. We show an identification method and close this article with a simple example to show that the recovery of geometrical imperfections in a cylindrical shell is possible from a measurement of its dynamics.

Power Secant Method applied to natural frequency extraction of Timoshenko beam structures

This work deals with an improved plane frame formulation whose exact dynamic stiffness matrix (DSM) presents, uniquely, null determinant for the natural frequencies. In comparison with the classical DSM, the formulation herein presented has some major advantages: local mode shapes are preserved in the formulation so that, for any positive frequency, the DSM will never be ill-conditioned; in the absence of poles, it is possible to employ the secant method in order to have a more computationally efficient eigenvalue extraction procedure. Applying the procedure to the more general case of Timoshenko beams, we introduce a new technique, named ""power deflation"", that makes the secant method suitable for the transcendental nonlinear eigenvalue problems based on the improved DSM. In order to avoid overflow occurrences that can hinder the secant method iterations, limiting frequencies are formulated, with scaling also applied to the eigenvalue problem. Comparisons with results available in the literature demonstrate the strength of the proposed method. Computational efficiency is compared with solutions obtained both by FEM and by the Wittrick-Williams algorithm.

1-[(Z)-1-Bromo-2-(butyldichloro-lambda(4)tellanyl)ethenyl]cyclohex-1-ene

The Te(IV) atom in the title compound, [Te(C(4)H(9))(C(8)H(10)Br)Cl(2)] or C(12)H(19)BrCl(2)Te, is in a distorted psi-trigonal-bipyramidal geometry, with the lone pair of electrons projected to occupy a position in the equatorial plane, and with the Cl atoms being mutually trans [172.48 (4)degrees]. Close intramolecular [Te center dot center dot center dot Br = 3.3444 (18) angstrom] and intermolecular [Te center dot center dot center dot Cl = 3.675 (3) angstrom] interactions are observed. The latter lead to centrosymmetric dimers which assemble into layers in the bc plane. The primary connections between layers are of the type C-H center dot center dot center dot Cl.

Food profitability affects intranidal recruitment behaviour in the stingless bee Nannotrigona testaceicornis

Does the food's sugar concentration affect recruitment behaviour in the stingless bee Nan-notrigona testaceicornis? We recorded intranidal forager behaviour while offering sugar water of constant, increasing, or decreasing concentrations. Running speed was not correlated with sugar concentration but the jostling contacts/sec were. Food profitability also affected the recruiter's thorax vibrations: Pulse duration and duty cycle followed both concentration increases and decreases. Sugar concentration also influenced the number of recruited bees. In comparison to the phylogenetically closely related Scaptotrigona, Nan-notrigona's intranidal recruitment behaviour showed a more elaborate association with food profitability. This is likely to reflect differences in ecology and foraging strategies as Nannotrigona - in contrast to Scaptotrigona - does not lay scent trails to guide recruits to a food source.

Multimode Vibrational Couplings in Resonant Positron Annihilation

The mechanisms for multimode vibrational couplings in resonant positron annihilation are not well understood. We show that these resonances can arise from positron-induced distortions of the potential energy surface (target response to the positron field). Though these distortions can transfer energy into single- and multiquantum vibrations, they have so far been disregarded as a pathway to resonant annihilation. We also compare the existing annihilation theories and show that the currently accepted model can be cast as a special case of the Feshbach annihilation theory.

Adiabatic intramolecular movements for water systems

An effective treatment of the intramolecular degrees of freedom is presented for water, where these modes are decoupled from the intermolecular ones, ""adiabatically"" allowing these coordinates to be positioned at their local minimum of the potential energy surface. We perform ab initio Monte Carlo simulations with the configurational energies obtained via density functional theory. We study a water dimer as a prototype system, and even in this simple case the intramolecular relaxations are very important to properly describe properties such as the dipole moment. We show that rigid simulations do not correctly sample the phase space, resulting in an average dipole moment smaller than the one obtained with the adiabatic model, which is closer to the experimental result. (c) 2008 American Institute of Physics.

1-furfuryl-3-furoylthiourea

The title compound, C11H10N2O3S, was synthesized from furoyl isothiocyanate and furfurylamine in dry acetone. The thiourea group is in the thioamide form. The trans-cis geometry of the thiourea group is stabilized by intramolecular hydrogen bonding between the carbonyl and cis-thioamide and results in a pseudo-S(6) planar ring which makes dihedral angles of 2.5 (3) and 88.1 (2)degrees with the furoyl and furfuryl groups, respectively. There is also an intramolecular hydrogen bond between the furan O atom and the other thioamide H atom. In the crystal structure, molecules are linked by two intermolecular N-H center dot center dot center dot O hydrogen bonds, forming dimers. These dimers are stacked within the crystal structure along the [010] direction.

N-(3-chlorophenyl) maleimide

The title compound, C10H6ClNO2, has a dihedral angle of 46.46 (5)degrees between the benzene and maleimide rings. A short intermolecular halogen-oxygen contact is observed, with a Cl center dot center dot center dot O distance of 3.0966 (13) angstrom. Both CO groups are involved in two C-H center dot center dot center dot O interactions, which gives rise to sheets parallel to (100). In addition, these sheets exhibit a pi-pi stacking interaction between the benzene and maleimide rings [mean interplanar distance of 3.337 (3) angstrom].

1-Benzyl-3-(2-furoyl)thiourea

In the title compound, C13H12N2O2S, the dihedral angle between the two aromatic ring planes is 87.52 (12)degrees. The molecule shows an intramolecular N-H center dot center dot center dot O hydrogen bond. The crystal structure is stabilized by intermolecular N-H center dot center dot center dot S and C-H center dot center dot center dot O hydrogen bonding.

1-Furoyl-3-methyl-3-phenylthiourea

The title compound, C13H12N2O2S, crystallizes with two independent molecules in the asymmetric unit. The two molecules differ in the conformation of the thiocarbonyl and carbonyl groups, and show the typical geometric parameters of substituted thiourea derivatives. The crystal structure is mainly stabilized by intermolecular N-H center dot center dot center dot O hydrogen bonding.

Low-temperature study of a new nevirapine pseudopolymorph

The title compound (systematic name: 11-cyclopropyl-4-methyl-5,11-dihydro-6H-dipyrido[3,2-b: 2',3'-e][1,4] diazepin-6-one butanol 0.3-solvate), C15H14N4O center dot 0.3C(4)H(9)OH, was crystallized in a new triclinic pseudopolymorphic form, a butanol solvate, and the crystal structure determined at 150 K. The molecular conformation of this new form differs from that reported previously, although the main intermolecular hydrogen-bond pattern remains the same. N-H center dot center dot center dot O hydrogen bonds [N center dot center dot center dot O = 2.957 (3) angstrom] form centrosymmetric dimers and the crystal packing of this new pseudopolymorph generates infinite channels along the b axis.

2-Benzoylpyridine semicarbazone

The title compound, C13H12N4O, crystallizes with two independent molecules in the asymmetric unit. The compound crystallizes as the ZE isomer, where Z and E refer to the configuration around the C=N and N-C bonds, respectively, with an N-H center dot center dot center dot N-py (py is pyridine) intramolecular hydrogen bond. The dihedral angles between the least-squares planes through the semicarbazone group and the pyridyl ring are 22.70 (9) and 27.26 (9)degrees for the two molecules. There are intermolecular N-H center dot center dot center dot O hydrogen bonds.

N-Benzoyl-N ',N '-dimethylthiourea

In the title compound, C(10)H(12)N(2)OS, the amide NCO group is twisted relative to the thioureido SCN(2) group, forming a dihedral angle of 55.3 (2)degrees. The crystal packing shows intermolecular N-H center dot center dot center dot S and weak C-H center dot center dot center dot O interactions, the former giving rise to the formation of centrosymmetric R(2)(2)(8) dimers.

Increasing the symmetry of drug crystals: a monoclinic conformational polymorph of the platelet antiaggregating agent ticlopidine hydrochloride

Ticlopidine hydrochloride (TICLID (R)) is a platelet antiaggregating agent whose use as a potent antithrombotic pharmaceutical ingredient is widespread, even though this drug has not been well characterized in the solid state. Only the crystal phase used for drug product manufacturing is known. Here, a new polymorph of ticlopidine hydrochloride was discovered and its structure was determined. While the antecedent polymorph crystallizes in the triclinic space group P (1) over bar, the new crystal phase was solved in the monoclinic space group P2(1)/c. Both polymorphs crystallize as racemic mixtures of enantiomeric (ticlopidine)(+) cations. Detailed geometrical and packing comparisons between the crystal structures of the two polymorphs have allowed us to understand how different supramolecular architectures are assembled. It was feasible to conclude that the main difference between the two polymorphs is a rotation of about 120 degrees on the bridging bond between the thienopyridine and o-chlorobenzyl moieties. The differential o-chlorobenzyl conformation is related to changeable patterns of weak intermolecular contacts involving this moiety, such as edge-to-face Cl center dot center dot center dot pi and C-H center dot center dot center dot pi interactions in the new polymorph and face-to-face pi center dot center dot center dot pi contacts in the triclinic crystal phase, leading to a symmetry increase in the ticlopidine hydrochloride solid state form described for the first time in this study. Other conformational features are slightly different between the two polymorphs, such as the thienopyridine puckerings and the o-chlorophenyl orientations. These conformational characteristics were also correlated to the crystal packing patterns.