Molecular‐dynamics simulations of single‐walled carbon nanotubes (CNTs) embedded in a coarse‐grained amorphous monodisperse polyethylene‐like model system have been carried out. The roles of nanotube diameter and chirality on the physical and structural properties of the composite are thoroughly discussed for several CNTs with different diameter and chirality. It is shown that the glass‐transition temperature of the polymer matrix increases with the diameter of the CNT while chirality effects are negligible. A denser and ordered layered region of polymer matrix is found in the vicinity of the nanotube surface. The density and ordering of this layer increases with the CNT diameter. All simulations indicate that chirality does not affect the atomic structure of the highly ordered layer surrounding the CNTs. Despite the simplicity of the polymer model, results of this study are qualitatively comparable with those obtained from experiments and numerical simulations that consider a chemically specific polymer matrix.
The paper discusses the nonlinear free dynamics of an orbiting string satellite system. The focus is on the transversal oscillations, which are governed by two partial integro-differential equations in two transversal displacement components with quadratic nonlinearities. The system is weakly nonlinear but in practice works in conditions of simultaneous internal resonance. The investigation focuses on nonstationary motions arising from perturbed steady-state nonplanar oscillations. A four-mode model is used to study the problem: two modes are necessary to describe the basic oscillation and at least two other modes are involved in the resonance phenomena when the motion is perturbed. The multiple time scales method is used to obtain the equations that govern the amplitude and phase modulations. For increasing levels of system energy, fundamental and bifurcated paths of fixed points of the seven first-order differential equations are determined and their stability is investigated. The trajectories of motion of periodically modulated amplitude solutions and their stability are also studied. A model with a higher number of modes is used to evaluate the accuracy of the stability analysis of two-mode nonplanar oscillations perturbed by a two-mode disturbance.
Sommario Nel presente lavoro si studia la dinamica libera nonlineare di un sistema filo-satellite. L'attenzione è rivolta alle oscillazioni trasversali, governate da due equazioni integro-differenziali, con nonlinearità quadratiche, nelle due componenti di spostamento. Il sistema è debolmente nonlineare ma praticamente lavora in condizioni di risonanza interna. Lo studio è concentrato sui moti nonstazionari generati da perturbazioni delle oscillazioni stazionarie spaziali. Per studiare il problema è stato sviluppato un modello con quattro modi: due sono necessari per descrivere il moto base mentre almeno altri due sono interessati dai fenomeni di risonanza interna quando il moto viene perturbato. Per ottenere le equazioni nelle ampiezze e fasi è stato utilizzato il metodo delle scale multiple. Del sistema di sette equazioni differenziali del primo ordine ottenuto, sono stati studiati i percorsi fondamentali di equilibrio e i rami biforcati, prendendo come parametro il livello di energia totale. È stata inoltre esaminata la stabilità di questi rami. Sono state studiate le traiettorie dei moti periodicamente modulati e la loro stabilità. Infine, è stato utilizzato un modello con un numero più alto di modi per valutare l'accuratezza dell' analisi di stabilità delle oscillazioni bimodali spaziali, nella quale la perturbazione è stata descritta da due soli modi.
Summary Different forms of the dynamical equations for constrained chain systems are investigated. First Kane's equations with Lagrange's multipliers are deduced from the standard form of d'Alembert's principle. Next it is proved that, even for constrained robotic devices, Euler's equations are equivalent to Kane's equations provided only that relative coordinates are employed. This equivalence yields an outstanding mechanical interpretation of Kane's equations. The possibility of applying the procedure to closed-loop multibody systems is also examined.
Sommario Vengono esaminate diverse formulazioni delle equazioni del moto per catene di corpi rigidi soggette a vincoli. Vengono dedotte le equazioni di Kane con moltiplicatori di Lagrange partendo dalla formulazione usuale del principio di d'Alembert. Viene poi provato che anche per i manipolatori vincolati le equazioni di Eulero sono equivalenti a quelle di Kane, purché vengano usate coordinate relative. Tale equivalenza fornisce una significativa interpretazione meccanica delle equazioni di Kane. Infine viene discussa la possibilità di applicare la procedura a sistemi a molti corpi con catene cinematiche chiuse.
Summary In this paper we propose a thermodynamic theory for apolar viscoelastic dielectrics. Within this framework we discuss the
possibility of accounting for the Maxwell effect, i.e., the birefringence phenomenon due to the motion of the continuum in
study. To this end we show that the proposal made by Toupin, in order to account for the Maxwell effect, does not contrast
with the second law of Thermodynamics.
Sommario In questo lavoro viene formulata una teoria termodinamica dei dielettrici viscoelastici apolari. Nell'ambito di tale teoria
viene esaminata la possibilità di descrivere l'effetto Maxwell, ossia il fenomeno della birifrangenza dovuta al moto del continuo.
A questo proposito si mostra che il termine proposto da Toupin per tener conto dell'effetto Maxwell non è in contrasto con
la seconda legge della Termodinamica.
This work was supported by the Gruppo Nazionale per la Fisica Matematica of CNR. 相似文献
Summary In this paper we study in detail one-dimensional linear plane harmonic waves in dissipative fluids within the framework of extended linear irreversible thermodynamics. The results for the acoustic mode are compared with the available experimental data on the dispersion and absorption of sound in monatomic gases.
Sommario Vengono studiate dettagliatamente le onde armoniche piane unidimensionali per i fluidi dissipativi nell'ambito della termodinamica estesa irreversibile lineare. I risultati ottenuti per il modo acustico di propagazione sono raffrontati con i risultati sperimentali sulla dispersione e l'assorbimento del suono nei gas monoatomici.
The contact problem between two orthotropic solids is examined. The problem is solved by using Lodge's method, which permits the transformation of the boundary-value problem of an anisotropic solid to a form identical with the corresponding problem of an isotropic medium. The proposed solution is then compared with known results of certain cases and it is observed that it producesHertz's solution when used for an isotropic case,Lodge's solution when applied to contact between an orthotropic solid and a rigid plane and, finally,Love's solution if the solid is transversely isotropic with the axis of material symmetry perpendicular to the rigid plane of contact. 相似文献
The highly radiopure ≃ 250 kg NaI(Tl) DAMA/LIBRA set-up is running at the Gran Sasso National Laboratory of the INFN. In this
paper the first result obtained by exploiting the model independent annual modulation signature for Dark Matter (DM) particles
is presented. It refers to an exposure of 0.53 ton×yr. The collected DAMA/LIBRA data satisfy all the many peculiarities of
the DM annual modulation signature. Neither systematic effects nor side reactions able to account for the observed modulation
amplitude and to contemporaneously satisfy all the several requirements of this DM signature are available. Considering the
former DAMA/NaI and the present DAMA/LIBRA data all together (total exposure 0.82 ton×yr), the presence of Dark Matter particles
in the galactic halo is supported, on the basis of the DM annual modulation signature, at 8.2 σ C.L.; in particular, in the energy interval (2–6) keV, the modulation amplitude is (0.0131±0.0016) cpd/kg/keV and the phase
and the period are well compatible with June 2nd and one year, respectively. 相似文献
A study is carried out on nonlinear multimodal galloping of suspended cables. A consistent model of a curved cable-beam, geometrically nonlinear and able to torque, recently formulated by the authors, is used. The model accounts for quasi-steady aerodynamic forces, including the effect of static swing of the cable and dynamic twist of the cross-section. Complementary solution methods are employed, namely, finite-difference and Galerkin spatial discretization, followed by numerical time-integration, or Galerkin spatial discretization in conjunction with Multiple Scale perturbation analysis. The different techniques are applied to a cable close to the first cross-over point, at which a number of internal resonances exist. Branches of periodic solutions and their stability are evaluated as functions of wind velocity. The existence of branches of quasi-periodic solutions, originating from narrow unstable intervals and propagating elsewhere, is also proved. Qualitative and quantitative results furnished by the different investigation tools are compared among them, and the importance of the various components of motion, accounted or neglected in the reduced models, is discussed. 相似文献