Performances of dynamic vibration absorbers for beams subjected to moving loads

The goal of this work is a general assessment regarding the performances of linear and nonlinear dynamic vibration absorbers (DVAs) applied to the specific problem of moving loads or vehicles. The problem consists of a simply supported linear Euler–Bernoulli beam excited with a moving load/vehicle; a DVA is connected to the beam in order to reduce the vibrations. The moving vehicle is modeled by a single degree of freedom mass spring system. The partial differential equations governing the beam dynamics is reduced to a set of ordinary differential equations by means of the Bubnov–Galerkin method. A parametric analysis is carried out to find the optimal parameters of the DVA that minimize the maximum vibration amplitude of the beam. For the case of a moving vehicle, the energy absorbed by the DVA is evaluated. Comparisons among the performances of different types of linear and DVAs are carried out. The goal is to clarify if the use of nonlinearities in the DVAs can effectively improve their performances. The study shows that the most effective type of DVA for the test cases considered is the piecewise linear elastic restoring force.     

Experimental investigation of liquid jet injection into Mach 6 hypersonic crossflow

The injection of a liquid jet into a crossing Mach 6 air flow is investigated. Experiments were conducted on a sharp leading edge flat plate with flush mounted injectors. Water jets were introduced through different nozzle shapes at relevant jet-to-air momentum–flux ratios. Sufficient temporal resolution to capture small scale effects was obtained by high-speed recording, while directional illumination allowed variation in field of view. Shock pattern and flow topology were visualized by Schlieren-technique. Correlations are proposed on relating water jet penetration height and lateral extension with the injection ratio and orifice diameter for circular injector jets. Penetration height and lateral extension are compared for different injector shapes at relevant jet-to-air momentum–flux ratios showing that penetration height and lateral extension decrease and increase, respectively, with injector’s aspect ratio. Probability density function analysis has shown that the mixing of the jet with the crossflow is completed at a distance of x/d _j  ~ 40, independent of the momentum–flux ratio. Mean velocity profiles related with the liquid jet have been extracted by means of an ensemble correlation PIV algorithm. Finally, frequency analyses of the jet breakup and fluctuating shock pattern are performed using a Fast Fourier algorithm and characteristic Strouhal numbers of St = 0.18 for the liquid jet breakup and of St = 0.011 for the separation shock fluctuation are obtained.     

Almost Sure Exponential Stability of Large-Scale Stochastic Nonlinear Systems

ABSTRACT

This contribution deals with the study of the almost sure exponential stability of large-scale stochastic systems with multiplicative noises. Under a Lipschitz-like assumption, it is proven that this stability is guaranteed if each “diagonal” subsystem is almost surely exponentially stable.     

Nilpotent and invertible values in semiprime rings with generalized derivations

Let R be a semiprime ring and F be a generalized derivation of R and n??? 1 a fixed integer. In this paper we prove the following: (1) If (F(xy) ? yx) ⁿ is either zero or invertible for all ${x,y\in R}$ , then there exists a division ring D such that either R?=?D or R?=?M ₂(D), the 2?× 2 matrix ring. (2) If R is a prime ring and I is a nonzero right ideal of R such that (F(xy) ? yx) ⁿ ?=?0 for all ${x,y \in I}$ , then [I, I]I?=?0, F(x)?=?ax?+?xb for ${a,b\in R}$ and there exist ${\alpha, \beta \in C}$ , the extended centroid of R, such that (a ? ??)I?=?0 and (b ? ??)I?=?0, moreover ((a?+?b)x ? x)I?=?0 for all ${x\in I}$ .     

Structure of clean and hydrated α-Al2O3 (1102) surfaces: implication on surface charge

Periodic DFT calculations coupled to a first-principle thermodynamic approach have allowed us to establish a surface phase diagram for the different terminations of the α-Al(2)O(3) (1102) surface in various temperature and water pressure conditions. Theoretical results are compared with previous experimental data from the literature. Under a wide range of temperature and water pressure (including ambient conditions) the most stable surface (denoted C2_1H(2)O in this work) is terminated with singly coordinated hydroxyls on four-fold coordinated aluminium (Al(4C)-μ(1)-OH) while most existing surface models are only considering six-fold coordinated surface Al atoms as in the bulk structure of alumina. The presence of more acidic Al(4C)-μ(1)-OH sites helps explain the low Point of Zero Charge (PZC) (between 5 and 6) determined from the onset of Mo oxoanions adsorption on (1102) single crystal wafers. It is also postulated that another termination (corresponding to the hydration of the non-polar, stoichiometric surface, stable in dehydrated conditions) may be observed in aqueous solution depending on the surface preparation conditions.     

Synthesis,characterization, and biological evaluation of new polyester containing Schiff base metal complexes

The production of new biocidal polyester Schiff base metal complexes [PESB–M(II)] via polycondensation reaction between chelated Schiff base diol and adipoyl chloride is reported. The resulting polyesters were characterized by physico-chemical and spectroscopic methods. The analytical data of all the synthesized polyesters were found to be in good agreement with 1:1 molar ratio of chelated Schiff base diol to adipoyl chloride. Thermogravimetric analyses of synthesized polyesters were studied by TG in nitrogen atmosphere up to 1073 K and results indicate that Cu(II) polyester complex exhibited better heat resistant properties than the other polyesters complexes. Magnetic moment and UV–visible spectra were examined to explain the structure of all the polyesters which reveled that Mn(II), Co(II), Ni(II) have octahedral geometry while Cu(II) possess a distorted octahedral geometry. These newly developed polyesters were also tested for their antibacterial activity against several bacteria and fungi. Among all the tested compounds PESB–Cu(II) possess the highest bactericidal and fungicidal activity.     

Synthesis of biosourced polyether-amides from 1,4-3,6-dianhydrohexitols: Characterization by NMR and MALDI–ToF mass spectrometry

New series of polyether-amides were prepared by polycondensation in solution of three diamines based on 1,4-3,6-dianhydrohexitols with two types of diacyl chlorides (sebacoyl and isophtaloyl). Unprecedented diamines based on isomannide and isoidide were elaborated. The corresponding polyether-amides (PeA) were obtained with high yields. They were characterized by different analytical techniques (NMR, MALDI–ToF MS, DSC). The combination of MALDI–ToF MS with NMR spectroscopy allowed us to confirm structure types. DSC measurements revealed an amorphous character for the isophtaloyl family with a high T_g value. The sebacoyl series proved to be semi-crystalline with a high T_m value. Isosorbide-based PeAs demonstrated interesting properties (T_g above 210 °C and T_m above 240 °C) and high viscosity (0.32).     

Novel Photochemical Synthesis of Spiro-1,2,6,8,9 Pentaza-4-thia(4,4)nonane via Rearrangement of Aliphatic Arylazo Compounds

Irradiation of N-phenyl-2-phenylazo-3-oxo-3-[(4-phenyl-5-aryl)-1,2,4-triazol-3-yl)thio]butanamides 4 _a–c gave the corresponding title spiro compounds 5 _a–c as end products via tandem rearrangement and cyclization of 4 _a–c in their excited states.     

Existence Results for Certain Multi-Orders Impulsive Fractional Boundary Value Problem

We derive in this paper some new existence and uniqueness results for a nonlinear multi-orders impulsive differential equation subject to fractional multi-point fractional integral boundary conditions. The obtained results are based on the Banach’s contraction theorem as well as Schauder fixed point theorem. Finally, two illustrative examples are given.     

Spectroscopic and Molecular Modeling Based Approaches to Study on the Binding Behavior of DNA with a Copper (II) Complex

Blocking the division of tumor cells by small-molecules is currently of great interest for the design of new antitumor drugs. The interaction of a new metal complex with DNA was investigated through several techniques. Absorption spectroscopy and gel electrophoresis studies on the interaction of the Cu-complex of (2a-4mpyH)₂ [Cu(pyzdc)₂ (H₂O)₂].6 H₂O with DNA have shown that this complex can bind to CT-DNA with binding constant 3.99?×?10⁵ M^?1. The cyclic voltammetry (CV) responses of the metal complex in the presence of CT-DNA have shown that the metal complex can bind to CT-DNA through partial intercalation mode and this is consistent with molecular docking analysis, quenching process and thermal denaturation experiments. The cytotoxicity of this complex has been evaluated by MTT assay. The results of cell viability assay on DU145 cell line revealed that the metal complex had cytotoxic effects.