Nonlinear dynamics of axially moving viscoelastic Timoshenko beam under parametric and external excitations

This investigation focuses on the nonlinear dynamic behaviors in the trans- verse vibration of an axiMly accelerating viscoelastic Timoshenko beam with the external harmonic excitation. The parametric excitation is caused by the harmonic fluctuations of the axial moving speed. An integro-partial-differential equation governing the transverse vibration of the Timoshenko beam is established. Many factors are considered, such as viscoelasticity, the finite axial support rigidity, and the longitudinally varying tension due to the axial acceleration. With the Galerkin truncation method, a set of nonlinear ordinary differential equations are derived by discretizing the governing equation. Based on the numerical solutions, the bifurcation diagrams are presented to study the effect of the external transverse excitation. Moreover, the frequencies of the two excitations are assumed to be multiple. Further, five different tools, including the time history, the Poincaré map, and the sensitivity to initial conditions, are used to identify the motion form of the nonlinear vibration. Numerical results also show the characteristics of the quasiperiodic motion of the translating Timoshenko beam under an incommensurable re- lationship between the dual-frequency excitations.

Motion-Enhanced Quantum Entanglement in the Dynamics of Excitation Transfer

We investigate the dynamics of entanglement in the excitation transfer through a model consisting of three interacting molecules coupled to environments. It is shown that the entanglement can be further enhanced if the distance between the molecules is oscillating. Our results demonstrate that the motional effect plays a constructive role on quantum entanglement in the dynamics of excitation transfer. This mechanism might provide a useful guideline for designing artificial systems to battle against decoherence.

Analysis on Pseudo Excitation of Random Vibration for Structure of Time Flight Counter

Traditional computing method is inefficient for getting key dynamical parameters of complicated structure.Pseudo Excitation Method（PEM）is an effective method for calculation of random vibration.Due to complicated and coupling random vibration in rocket or shuttle launching,the new staging white noise mathematical model is deduced according to the practical launch environment.This deduced model is applied for PEM to calculate the specific structure of Time of Flight Counter（ToFC）.The responses of power spectral density and the relevant dynamic characteristic parameters of ToFC are obtained in terms of the flight acceptance test level.Considering stiffness of fixture structure,the random vibration experiments are conducted in three directions to compare with the revised PEM.The experimental results show the structure can bear the random vibration caused by launch without any damage and key dynamical parameters of ToFC are obtained.The revised PEM is similar with random vibration experiment in dynamical parameters and responses are proved by comparative results.The maximum error is within 9%.The reasons of errors are analyzed to improve reliability of calculation.This research provides an effective method for solutions of computing dynamical characteristic parameters of complicated structure in the process of rocket or shuttle launching.

Ultrafast Excited State Dynamics of Biliverdin Dimethyl Ester Coordinate with Zinc Ions

As one of the biological endogenous pigments,biliverdin(BV)and its dimethyl ester(BVE)have extremely weak uorescence in solution with quantum yield less than 0.01%.However,the situation reverses with the addition of zinc ions.The strength for uorescence of BVE-Zn^2+ complex is greatly enhanced and uorescence quantum yield can increase to5%.Herein,we studied ultrafast excited state dynamics of BVE-Zn^2+ complex in ethanol,npropanol,and DMSO solutions in order to reveal the mechanism of uorescence quantum yield enhancement.The results show that BVE can form a stable coordination complex with zinc with 1:1 stoichiometry in solution.BVE is structurally and energetically more stable in the complex.Using picosecond time-resolve uorescence and femtosecond transient absorption spectroscopy,we show that smaller non-radiative rate constant of BVE-Zn^2+ complex in DMSO is the key to increasing its uorescence quantum yield and the excited state decay mechanism is also revealed.These results provide valuable information about the uorescence property change after BVE binding to metal ions and may provide a guidance for the study of phytochromes or other uorescence proteins in which BV/BVE acts as chromophores.

Investigation of the Short-Time Photodissociation Dynamics of Furfural in S2 State by Resonance Raman and Quantum Chemistry Calculations

Raman(resonance Raman,FT-Raman),IR and UV-visible spectroscopy and quantum chemistry calculations were used to investigate the photodissociation dynamics of furfural in S2 state.The resonance Raman(RR)spectra indicate that the photorelaxation dynamics for the S0→S2 excited state is predominantly along nine motions:C=O stretchν5(1667 cm-1),ring C=C antisymmetric stretchν6(1570 cm-1),ring C=C symmetric stretchν7(1472 cm-1),C2-O6-C5 symmetric stretch/C1-H8 rock in planeν8(1389 cm-1),C3-C4 stretch/C1-H8 rock in planeν9(1370 cm-1),C5-O6 stretch in planeν12(1154 cm-1),ring breathν13(1077 cm-1),C3-C4 stretchν14(1020 cm-1),C3-C2-O6 symmetric stretchν16(928 cm-1).Stable structures of S0,S1,S2,T1 and T2 states with Cs point group were optimized at CASSCF method in Franck-Condon region there are S2/S1 conical intersection was found by state average method and RR spectra.

Two-Photon Excited State Dynamics of Dark Rydberg and Bright Valence States in Furan

Two-photon absorption in systems with parity permits access to states that cannot be directly prepared by one-photon absorption. Here we investigate ultrafast internal conversion （IC） dynamics of furan by using this strategy in combination with femtosecond time-resolved photoelectron imaging. The dark Rydberg S1 and bright valence S2 states are simultaneously excited by two photons of 405 nm, and then ionized by two photons of 800nm. The IC from S2 to S1 is clearly observed and extracted from the time dependence of the higher photoelectron kinetic energy （PKE） component. More importantly, the internal conversions to hot So from directly-prepared S1 and secondarily-populated S1 are unambiguously identified by the time-dependence of the lower PKE component. The average lifetime of the S2 and S1 states is measured to be 29 fs. The internal conversions of S2 to S1, S1 to hot So occur on estimated timescales of 15.4 fs and 38 fs, respectively.

Seismic assessment of unanchored steel storage tanks by endurance time method

Liquid storage tanks are essential structures that are often located in residential and industrial areas; thus an assessment of their seismic performance is an important engineering issue. In this paper, the seismic response ofunanchored steel liquid storage tanks is investigated using the endurance time （ET） dynamic analysis procedure and compared to responses obtained for anchored tanks under actual ground motions and intensifying ET records. In most cases, the results from ground motions are properly obtained with negligible differences using ET records. It is observed that uplifting of the tank base, which is closely related to the tank aspect ratio, has the greatest significance in the responses of the tank and can be predicted with reasonable accuracy by using currently available ET records.

Performance of a base isolator with shape memory alloy bars

A new and innovative base isolation device is introduced in this paper based on extensive research carried out by the authors and their co-workers. A prototype of the device was built and experimentally tested on the shaking table. The new base isolation device consists of two disks, one vertical cylinder with an upper enlargement sustained by three horizontal cantilevers, and at least three inclined shape memory alloy （SMA） bars. The role of the SMA bars is to limit the relative motion between the base and the superstructure, to dissipate energy by their super-elastic constitutive law and to guarantee the re-centring of the device. To verify the expected performance, a prototype was built and tested under sinusoidal waves of displacement of increasing frequency with different amplitudes. It is shown that the main feature of the proposed base isolation device is that for cyclic loading, the super-elastic behavior of the alloy results in wide load-displacement loops, where a large amount of energy is dissipated.

Nonlinear aspects of energy dissipation in wood-panel joints

The joints connecting vertical and horizontal elements are the ＂weak link＂ in structural systems assembled from wood panels. If they are too weak, local failures may occur, resulting in performance that is significantly below expectations. If they are too resistant, the joints may be unable to dissipate energy during vibrations, thus possibly initiating a fast progressive failure. This paper re-processes and re-elaborates the results of shaking table tests previously carried out by the author and other co-workers. The goal is to assess the feasibility of a joint which is able to dissipate energy during vibration, without degrading the connection performance.

Nonlinear aspects of energy dissipation in wood-panel joints

We have found some mistakes in the article by Sara Casciati （2007）. The revisions are given below：

A kind of noise-induced transition to noisy chaos in stochastically perturbed dynamical system

We investigate a kind of noise-induced transition to noisy chaos in dynamical systems. Due to similar phenomenological structures of stable hyperbolic attractors excited by various physical realizations from a given stationary random process, a specific Poincar6 map is established for stochastically perturbed quasi-Hamiltonian system. Based on this kind of map, various point sets in the Poincar6＇s cross-section and dynamical transitions can be analyzed. Results from the customary Duffing oscillator show that, the point sets in the Poincare＇s global cross-section will be highly compressed in one direction, and extend slowly along the deterministic period-doubling bifurcation trail in another direction when the strength of the harmonic excitation is fixed while the strength of the stochastic excitation is slowly increased. This kind of transition is called the noise-induced point-overspreading route to noisy chaos.

A METHOD FOR CALCULATING THE LYAPUNOV EXPONENT SPECTRUM OF A PERIODICALLY EXCITED NON-AUTONOMOUS DYNAMICAL SYSTEM

The relation between the Lyapunov exponent spectrum of a periodically excited non-autonomous dynamical system and the Lyapunov exponent spectrum of the corresponding autonomous system is given and the validity of the relation is verified theoretically and computationally. A direct method for calculating the Lyapunov exponent spectrum of non-autonomous dynamical systems is suggested in this paper, which makes it more convenient to calculate the Lyapunov exponent spectrum of the dynamical system periodically excited. Following the definition of the Lyapunov dimension D-L((A)) of the autonomous system, the definition of the Lyapunov dimension D-L of the non-autonomous dynamical system is also given, and the difference between them is the integer 1, namely, D-L((A)) - D-L = 1. For a quasi-periodically excited dynamical system, similar conclusions are formed.

Structure and Excitation Dynamics of β-Carotene Aggregates in Cetyltrimethylammonium Bromide Micelle

The β-carotene（β-Car） aggregate was prepared by self-assembly in cetyltrimethylammoniuln bromide （CTAB） micelle. The ground state absorption measurement showed that the aggregate has J-type characteristics and resonance Raman spectra gave the intrinsic explanation of molecular interaction in aggregate. Upon excitation at the optical allowed S2 state of aggregate, direct generation of triplet state via singlet fission（SF）mechanism was observed. Excitation dynamics was elucidated by fs-transient absorption spectroscopy and ns-flash photolysis, respectively. The triplet state life time of aggregate was found to be independent of the ambient oxygen molecules.

Triplet excitation dynamics of β-carotene studied in three solvents by ns flash photolysis spectroscopy

Upon anthracene-sensitizing, triplet excitation dynamics of β-carotene（β-Car） were studied in nhexane, in methanol, and in acetonitrile, respectively, by ns flash photolysis spectroscopy. In n-hexane,only the bleaching of the ground state absorption（GSB） and the excitation triplet（^3Car＊） absorption were observed, and there were no cationic species detected. In both methanol and acetonitrile, similar excitation dynamics were observed, i.e.,^3Car＊ having a similar lifetime to that in n-hexane, and the immediate generation of the cation dehydrodimer（^#[Car]2^＋） upon excitation following transformation into the radical cation Car＊^＋, since Car＊^＋ has much longer lifetime in acetonitrile than in methanol. The results prove that both solvent and carotenoid structure determine the triplet excitation mechanism.

Production of cold CN molecules by photodissociating ICN precursors in brute-force field

We theoretically investigate the production of cold CN molecules by photodissociating ICN precursors in a brute-force field. The energy shifts and adiabatic orientation of the rotational ICN precursors are first investigated as a function of the external field strength. The dynamical photofragmentation of ICN precursors is numerically simulated for cases with and without orienting field. The CN products are compared in terms of their velocity distributions. A small portion of the CN fragments are recoiled to near zero speed in the lab frame by appropriately selecting the photo energy for dissociation. With a precursor ICN molecular beam of - 1.5 K in rotational temperature, the production of low speed CN fragments can be improved by more than 5 times when an orienting electrical field of 100 k V/cm is present. The corresponding production rate for decelerated fragments with speeds ≤ 50 m/s is simulated to be about ～2.1×10^-4 and CN number densities of 10^8 –10^10 cm^-3 can be reached with precursor ICN densities of ～10^12 –10^14 cm^-3 from supersonic expansion.

VEHICLE DYNAMIC ANALYSIS SIMULATION－MODELLING THEORY AND ENGINEERING APPLICATION

A computer software named VDAS (Vehicle Dynamic Analysis Simulation) is presented.Based on the mathematical modelling for a military vehicle as a 3-D dynamic system, the softwarecreates random excitation resulting from double side road-surface roughness by statisticalsimulation, and solves for the time series of the system response from the system state equations,and gives out the results in probability statistics as well as performance evaluations.

Calibration method of quartz accelerometer on dynamic centrifuge

This paper proposes a novel method for calibrating error coefficients of the quartz accelerometer faster on the dynamic centrifuge,which can generate a continuous dynamic acceleration excitation.Firstly,working principle and structure of the dynamic centrifuge are analyzed,the error sources and the uncertainty of the dynamic centrifuge are expounded,and relevant coordinate systems are established.Then,according to the characteristics of the input specific forces and the propagating methods of the error sources,the accurate input specific forces acted on the input reference axes of accelerometer are obtained.Based on the calibration error model of the accelerometer,the corresponding dynamic calibration method is proposed.Finally,the second-order and high-order coefficients of the acceleration error model are calibrated,and the calibration precision of the coefficients is analyzed.Compared with traditional calibration methods,the method proposed in this paper not only greatly enhances the calibration efficiency by reducing the installing positions of the accelerometer,but also separates the centrifuge errors from the outputs of the accelerometer,which improves the accuracy and efficiency of the calibration method simultaneously.

Dynamic evaluation of jack-up platform structure under wave, wind, earthquake and tsunami loads

Nowadays,the demand for using jack-up platforms to carry out a large percentage of deep-water oil and gas exploration is steadily increasing.The response of jack-up platforms to the severe dynamic loads that may be encountered during the structure life is not examined enough.Therefore,this study attempts to investigate the response of jack-up platforms performance under the effect of dynamic loads due to wave,wind,earthquake and tsunami forces using the finite element method for two models with the lowest and highest hull elevations.The jack-up platform is located in the Gulf of Mexico.Earthquake ac-celerations are applied to the model in high and moderate seismic levels.In addition,tsunami waves are applied to the platform in three different directions at 0°,45°and 90°.This study utilised Airy’s linear wave approach to assess the surface elevations and wave kinematics.The reference wind velocity is 10 knots at 10 m over the mean water level.Results indicate that the dynamic response of the structure is affected by the height of the platform and by the increase of the platform hull elevation.The combination of the El-Centro earthquake,dead and live loads provides the major impact on the platform at the lowest(70 m)and highest(85 m)hull elevations.The comparison of all result proves that the jack-up platform hull under high earthquake intensity and tsunami waves with 45°has experienced maximum deforma-tion.Moreover,raising the deck will increase the response of the dynamic load and displacements but will negatively affect the platform.

Dual excited state deactivation pathways in TPZ2:A centrosymmetric dye with both high fluorescence and triplet state quantum yield

In this letter, excited state dynamics of TPZ2, a centrosymmetric PRODAN dye, has been studied by using several time-resolved spectroscopy techniques. Fluorescence quantum yield of TPZ2 is found to be 0.50 in both acetonitrile and ethanol solution. The radiative decay rate of the excited state of TPZ2 is determined to be 2.0×10^8 s^-1. Meanwhile, highly efficient triplet state and singlet oxygen generation have been observed in TPZ2 and the intersystem crossing（ISC） rate is determined to be 2.0×10^8s^-1. The almost identical ISC and non-radiative decay rates indicate that ISC is the only non-radiative decay pathway in TPZ2. Thus, dual excited state（S1） deactivation mechanism（50/50, fluorescence/ISC） of TPZ2 is proposed.Because of this unique property, TPZ2 has the potential to be used as biocompatible imaging and photodynamic therapy agent in the same time.

Vibratile Dihydrophenazines with Controllable Luminescence Enabled by Precise Regulation of π-Conjugated Wings

A series of vibratile π-extended dihydrophenazines(BPs)and a tetrahydrodiphenazine(TP)were synthesized via direct C-N coupling reactions.Structural alterations of the fused acene wings lead to diverse intermolecular packing arrangements as well as tunable photophysical properties.These compounds exhibit intriguing features,including large Stokes shift,multiple emissions,and environmental effects.Notably,a dramatic hypsochromic shift in emission is observed when the acene wing is linearly extended from benzene to naphthalene and anthracene.This unusual π-conjugation length-dependent emission is explained by the close correlation between the calculated fluorescence-emitting energy and the π-conjugation length of the acene subunit.In addition,the TP bearing two flexible units exhibits dynamic photophysical properties resembling those of BPs.Our results reveal a balanced control over π-conjugation and luminescence in vibratile π-systems,thereby providing new insight into the molecular design of organic near-infrared fluorophores with large Stokes shifts and dynamic emissions.