A non-ideal portal frame energy harvester controlled using a pendulum

A model of energy harvester based on a simple portal frame structure is presented. The system is considered to be non-ideal system (NIS) due to interaction with the energy source, a DC motor with limited power supply and the system structure. The nonlinearities present in the piezoelectric material are considered in the piezoelectric coupling mathematical model. The system is a bi-stable Duffing oscillator presenting a chaotic behavior. Analyzing the average power variation, and bifurcation diagrams, the value of the control variable that optimizes power or average value that stabilizes the chaotic system in the periodic orbit is determined. The control sensitivity is determined to parametric errors in the damping and stiffness parameters of the portal frame. The proposed passive control technique uses a simple pendulum to tuned to the vibration of the structure to improve the energy harvesting. The results show that with the implementation of the control strategy it is possible to eliminate the need for active or semi active control, usually more complex. The control also provides a way to regulate the energy captured to a desired operating frequency.     

The onset of convection of a poorly conducting fluid in a modulated thermal field

The stability of a poorly conducting fluid in a constant electric field of a horizontal capacitor is investigated under a variable temperature gradient. It is assumed that free charge in the fluid is generated only due to the nonhomogeneous conductivity of the fluid. The Floquet theory is used to determine the convection thresholds. The instability boundaries and the characteristics of critical perturbations are determined. In addition to the synchronous and subharmonic responses to an external action, the instability can be attributed to quasiperiodic perturbations. The low-frequency limit of modulation is considered by an asymptotic method. The critical electric Rayleigh number is represented as a function of inverse frequency and heating level.     

Transient modal radiation of axisymmetric sources: Application to loudspeakers

The present study proposes a transient model of the acoustic radiation of axisymmetric structures. The pressure field is approximated by the Rayleigh integral corresponding to a monopole source distribution over the non-planar vibrating surface. The displacement field is expanded on the linear modes of the structure and a change of variables in the Rayleigh integral is then proposed in the case of a monotonic profile function to compute the Spatial Impulse Response associated to each mode of vibration efficiently. The results are compared to the formulation obtained in the case of planar and spherical sources. The method of calculation is then derived in the case of a typical loudspeaker profile (association of a truncated cone with a spherical cap). Finally, the present approach is used to estimate the nonlinear radiation pattern of a prototype loudspeaker and predictions are compared to measurements in anechoic room.     

有限存贮空间内可燃多孔介质流动和传热的研究

对通风条件下可燃多孔介质库房内的流动和传热特性进行了数值模拟,得到了库房有限空间内的温度场和速度场.通过比较不同的来流温度和入口流速,得到的结果表明:可燃多孔介质(弹药)内部发生化学反应并产生热量,其温度由中心向四周逐渐降低;来流流速越大,越有利于弹药的冷却;在来流速度相同的情况下,来流温度越低,越有利于散热,对于可燃多孔介质(弹药)的贮存越安全;在左侧进风口的上下两边以及可燃多孔介质(弹药)的上方,会形成漩涡.     

Shear induced anisotropy in two-dimensional liquids

The behavior of a dense two-dimensional soft disc liquid under shear is studied via nonequilibrium molecular dynamics. The structure factor for the liquid at a given shear rate is evaluated directly by plotting the particle positions, taken at random from the NEMD simulation at that shear, onto photographic film and using light scattering to obtain a diffraction pattern. The pair correlation function of this system is also extracted directly by histogramming the particle positions with respect to a given central particle as a function of separation and angle. The pair correlation function is compared to that approximated by a Fourier series expansion to rank ten. Results are reported as a function of shear rate from a shear rate of 0.1 (when the fluid is essentially Newtonian) to 10 (when the fluid can display a string phase). The appearance of the string phase is discussed and shown to be a consequence of the definition of temperature in the simulation algorithm. A modification of the algorithm is proposed. Comparisons between this work and previous work with three-dimensional liquids are given. The two-dimensional structure factor is compared with that obtained from a real colloidal suspension via light scattering.     

Scattering in the nonlinear Lamb system

We obtain long time asymptotics for the solutions to a string coupled to a nonlinear oscillator: each finite energy solution decays to a sum of a stationary state and a dispersive wave. The asymptotics hold in global energy norm. The dispersive waves are expressed via initial data and solution to an ordinary differential equation. The asymptotics give a mathematical model for the Bohr's transitions between quantum stationary states.     

Observations of vacuum spark dynamics from its X-ray emission

The behavior of a medium energy (~1 kJ) pulse-power-driven vacuum spark is shown to depend on the electrode material and form of the anode in otherwise similar conditions of operation. The dynamical evolution of the discharge is followed from its soft X-ray emission. The electrode materials compared are titanium and aluminum with a form of anode that is tubular or conical. The use of a tubular anode favors a more uniform sheath and a better formation of a dense Z-pinch and the ensuing hot spots are found to be at least twice as bright. The position of the brightest spots differs according to the material and the electrode shape, and is found to coincide with the shape of the sheath. The energy output is measured and the density of the plasma in the hot spots may be calculated     

微型计算机在微弱光谱测试系统中的应用

本文报道了在我们研制的微弱光谱测试系统中微计算机的应用,介绍了数据采集、双机间的DMA传送数据、二维光栅扫描控制、应用微机改善信噪比、应用软件和图形显示等问题。着重讨论如何通过我们所做的研制工作,使性能较低的EG3003微计算机达到OMA系统所要求的水平。     

采用选择激发研究光系统Ⅱ反应中心β-Car的物理特性

光系统Ⅱ反应中心包含有2个去镁叶绿素分子(Pheo),2个β胡萝卜素分子(β-Car)和6个叶绿素a分子(Chla).对反应中心的时间分辨荧光光谱表明,两个β-Car具有不同的吸收光谱,吸收峰分别为489 nm(Car489)和507 nm(Car507),Car489靠近吸收峰为667 nm和675 nm的叶绿素a(Chl a),它的主要功能是保护反应中心免受单态氧的破坏,而不能将激发能传递给光化学反应活性的色素分子P680;Car507靠近吸收峰为669 nm的Chl a分子;能够将激发能传递给P680,进行电荷分离.采用全局优化拟合的方法对荧光光谱进行处理,Car489在61 ps时间内将能量传递给Chl a672, 随后传给Chl a677,处于激发态的Chl a677在3 ns衰减到基态;Car507在274 ps时间内将能量传递给P680,P680＋Pheo-的电荷重组发生在3.8 ns和16 ns.     

Hydrocarbon film formed on the surface of a semiconductor irradiated by an electron beam

The rate of formation of a hydrocarbon film on the surface of a sample subjected to the action of an electron beam is studied at room temperature and in cooling a sample to the liquid nitrogen temperature. The thickness and the optical radiation transmission of such films are measured as functions of the electron beam radiation time, the sample temperature, and the level of vacuum. The film thickness is measured with atomic force microscopy. The absorption of the films is determined by comparing the cathodoluminescence intensities from a pure sample surface and from the surface covered with a film. The experimental results can be used to estimate the film formation rate as a function of the sample temperature and the vacuum and to determine the optical radiation absorption at a wavelength of 300, 360, 550, and 665 nm.     

Effects of molecular geometry on liquid crystalline phase behaviour: isotropic-nematic transition

The effects of range and geometry of a simple attractive square-well on the phase diagram of hard ellipsoids and hard spherocylinders is systematically studied using a simple van der Waals type theory. The orientational single particle distribution function is approximated using the Onsager trial function. The quantitative errors introduced by this are thought to be considerably smaller than the use of the van der Waals approximation, which has been shown to give qualitatively correct phase diagrams for similar models. The phase diagrams obtained for hard ellipsoids and hard spherocylinders of aspect ratios ranging between 3 and 10 with a variety of square-well attractions are found to fall into three general types. The first type shows liquid-vapour coexistence and an isotropic-nematic transition, which meet at a liquid-vapour-nematic triple point. The second type shows a marked widening of the isotropic-nematic biphasic region which pre-empts the liquid-vapour coexistence. The final phase diagram shows a strong destabilization of the nematic phase with respect to the isotropic, which results in a shift of the phase transition to higher densities and pressures as the temperature is lowered.     

Pseudoscalar and pseudovector coupling of a pion to a bound Dirac nucleon

The non-equivalence of pseudoscalar and pseudovector coupling of a pion to a Dirac nucleon in the presence of a scalar-vector potential is analysed and found to be strongly related to the magnitude of spin-orbit splitting. The concept of a Galilean invariant vertex operator turns out to be unjustified for a bound nucleon.     

Magneto-optical polar Kerr effect in a film-substrate system

The problem of electromagnetic reflection at an arbitrary angle of incidence in a system consisting of an isotropic ambient, a magnetic film and a thick magnetic substrate is studied. The magnetizations in both the film and substrate are assumed normal to the planar interfaces. The results are expressed in terms of the reflection matrix which is directly connected to the experimentally observed quantities: ellipsometric ratio and magneto-optical rotation and ellipticity. The general condition for guided wave propagation in the system is obtained. The theory is applied to the special cases of (a) normal incidence, (b) oblique incidence on a uniaxial film on a uniaxial substrate, both optical axes being normal to the interfaces, and (c) oblique incidence on a system consisting of an isotropic ambient, a magnetic film and a thick magnetic substrate assuming the diagonal elements of the permittivity tensor in a particular magnetic medium (film or substrate) equal to each other and the corresponding off-diagonal elements much smaller with respect to them. The possible practical applications of the present analysis are in the optimum design of film-substrate structures in magneto-optic devices and in the optical studies of the surface effects in magnetic materials.     

Stability of a charged drop near a conductor wall

The effect of conductor boundaries on the deformation and stability of a charged drop is presented. The motivation for such a study is the occurrence of a charged conductor drop near a conductor wall in experiments (Millikan-like set-up in studies on Rayleigh break-up) and applications (such as electrospraying, ink-jet printing and ion mass spectroscopy). In the present work, analytical (linear stability analysis (LSA)) and numerical methods (boundary element method (BEM)) are used to understand the instability. Two kinds of boundaries are studied: a spherical, conducting, grounded enclosure (similar to a spherical capacitor) and a planar conducting wall. The LSA of a charged drop placed at the center of a spherical cavity shows that the Rayleigh critical charge (corresponding to the most unstable l = 2 Legendre mode) is reduced as the non-dimensional distance ?d = (b - a)/a decreases, where a and b are the radii of the drop and spherical cavity, respectively. The critical charge is independent of the assumptions of constant charge or constant potential conditions. The trans-critical bifurcation diagram, constructed using BEM, shows that the prolate shapes are subcritically unstable over a much wider range of charge as [Formula: see text] decreases. The study is then extended to the stability of a charged conductor drop near a flat conductor wall. Analytical theory for this case is difficult and the stability as well as the bifurcation diagram are constructed using BEM. Moreover, the induced charges in the conductor wall lead to attraction of the drop to the wall, thereby making it difficult to conduct a systematic analysis. The drop is therefore assumed to be held at its position by an external force such as the electric field. The case when the applied field is much smaller than the field due to inherent charge on the drop ((a(3)ρg)/(3ε(0)Ψ(2)) ? 1 is considered. The wall breaks the fore-aft symmetry in the problem, and equilibrium, predominantly prolate shapes corresponding to the legendre mode, l = 2 , are observed. The deformation increases with increasing charge on the drop. The breakup of the prolate equilibrium shapes is independent of the legendre modes of the initial perturbations. The prolate perturbations are subcritically unstable. Since the equilibrium prolate shapes cannot continuously exchange instability with equilibrium oblate shapes, an imperfect transcritical bifurcation is observed. A variety of highly deformed equilibrium oblate shapes are predicted by the BEM calculations.     

Landau electron in a rotating environment: A general factorization of time evolution

For the Landau problem with a rotating magnetic field and a confining potential in the (changing) direction of the field, we derive a general factorization of the time evolution operator that includes the adiabatic factorization as a special case. The confining potential is assumed to be of a general form and it can correspond to nonlinear Heisenberg equations of motion. The rotation operator associated with the solid angle Berry phase is used to transform the problem to a rotating reference frame. In the rotating reference frame, we derive a natural factorization of the time evolution operator by recognizing the crucial role played by a gauge transformation. The major complexity of the problem arises from the coupling between motion in the direction of the magnetic field and motion perpendicular to the field. In the factorization, this complexity is consolidated into a single operator which approaches the identity operator when the potential confines the particle sufficiently close to a rotating plane perpendicular to the magnetic field. The structure of this operator is clarified by deriving an expression for its generating Hamiltonian. The adiabatic limit and non-adiabatic effects follow as consequences of the general factorization which are clarified using the magnetic translation concept.     

Desiccant integrated hybrid vapor-compression cooling: Performance sensitivity to outdoor conditions

The performance of a desiccant integrated, hybrid, vapor-compression cooling system is modeled numerically. The concept of hybrid cooling investigated in this paper utilizes the waste heat rejected from a vapor-compression cycle to directly activate a solid desiccant dehumidification cycle. The hybrid system consists of four major components; a compressor, an evaporator and two desiccant integrated condensers/dehumidifiers. The performance sensitivity of a first generation prototype hybrid, vapor-compression cooling system to variable outdoor conditions is reported and compared to the performance of conventional vapor-compression systems.     

Estimated transmission beam pattern of clicks recorded from free-ranging white-beaked dolphins (Lagenorhynchus albirostris)

Recordings were made from white-beaked dolphins in Icelandic waters using a four-hydrophone array in a star configuration. The acoustic signals were amplified and sampled to a hard disk at a rate of 800 kHz per channel. The 3 and 10 dB beamwidths were calculated to be 8 degrees and 10 degrees, respectively, indicating a narrower transmission beam for white-beaked dolphins than that reported for bottlenose dolphins (Tursiops truncatus). The beamwidth was more similar to that found for belugas (Delphinapterus lucas). The measured beam pattern included large side lobes, perhaps due to the inclusion of off-axis clicks, even after applying several criteria to select only on-axis clicks. The directivity index was calculated to be 18 dB when using all data for angles from 0 degrees-50 degrees. The calculated sound radiation from a circular piston with a radius of 6 cm driven by a white-beaked dolphin click had a beam pattern very similar to the measured beam pattern for the main transmission lobe of the white-beaked dolphin. The directivity index was 29 dB. This is the first attempt to estimate the directionality index of dolphins in the field.     

Solar contribution to space heating

Summary The solar contribution to space heating and cooling is evaluated through an analytical procedure. The method used simulates the building as a thermal network in which each node corresponds to the centre of a room and each mesh arm to a wall; building materials and frames are explicitly taken into account. The network is excited by a set of generators corresponding to external excitations (e.g. environmental temperature, solar flux, etc.) which are described by a truncated Fourier series. The network is resolved by an analytical method through the matrix formalism and gives either the time diagrams of indoor temperatures in each room, or the diagrams of the auxiliary energy required to maintain a set room temperature. The application to a residential environment is presented as an example and is discussed in relation to a passive retrofitting design. The results are briefly compared with those obtained through established procedures, to give evidence of the occurrence of strong fluctuations on the average values which significantly influence the conditions of comfort. The method can be implemented at the level of microcomputers.     

Fragmentation experiment and model for falling mercury drops

The experiment consists of counting and measuring the size of the many fragments observed after the fall of a mercury drop on the floor. The size distribution follows a power-law for large enough fragments. We address the question of a possible crossover to a second, different power-law for small enough fragments. Two series of experiments were performed. The first uses a traditional film photographic camera, and the picture is later treated on a computer in order to count the fragments and classify them according to their sizes. The second uses a modern digital camera. The first approach has the advantage of a better resolution for small fragment sizes. The second, although with a poorer size resolution, is more reliable concerning the counting of all fragments up to its resolution limit. Both together clearly indicate the real existence of the quoted crossover.     

Vibro-acoustic control with a distributed sensor network

The purpose of this work is to demonstrate the ability of a distributed control system, based on a smart sensor network, to reduce acoustic radiation from a vibrating structure. The platform from which control is effected consists of a network of smart sensors, each referred to as a node. Each node possesses its own computational capability, sensor, actuator and the ability to communicate with other nodes via a wired or wireless network. The primary focus of this work is to employ existing group management middleware concepts to enable vibro-acoustic control with such a distributed network. Group management middleware is distributed software that provides for the establishment and maintenance of groups of distributed nodes and that provides for the network communication among such groups. The control objective is met by designing distributed feedback compensators that take advantage of node groups in order to effect their control. The node groups are formed based on physical proximity. The global control objective is to minimize the radiated sound power from a rectangular plate. Results of this investigation demonstrate that such a distributed control system can achieve attenuations comparable to those achieved by a centralized controller.