A numerical investigation on the flow physics of koi carp (Cyprinus carpio koi) burst-and-coast swimming

Abstract—Burst-and-coast is the most common locomotion type in freely routine swimming of koi carps (Cyprinus carpio koi), which consists of a burst phase and a coast phase in each cycle and mostly leads to a straight-line trajectory. Combining with the tracking experiment, the flow physics of koi carp’s burst-andcoast swimming is investigated using a novel integrated CFD method solving the body-fluid interaction problem. The dynamical equations of a deforming body are formulated. Following that, the loose-coupled equations of the body dynamics and the fluid dynamics are numerically solved with the integrated method. The two burst modes, MT (Multiple Tail-beat) and HT (Half Tail-beat), which have been reported by the experiments, are investigated by numerical simulations in this paper. The body kinematics is predicted and the flow physics is visualized, which are in good agreement with the corresponding experiments. Furthermore, the optimization on the energy cost and several critical control mechanisms in burst-and-coast swimming of koi carps are explored, by varying the parameters in its selfpropelled swimming. In this paper, energetics is measured by the two mechanical quantities, total output power CP and Froude efficiency Fr. Results and discussion show that from the standpoint of mechanical energy, burst-and-coast swimming does not actually save energy comparing with steady swimming at the same average speed, in that frequently changing of speed leads to decrease of efficiency.

Nonlinear Dynamic Responses of Tension Leg Platform with Slack-Taut Tether

The slack-taut state of tether is a particular Averse circumstance, which may influence the normal operation stale of tension leg platform (TLP). The dynamic responses of TLP with slack-taut tether are studied with consideration of several nonlinear factors introduced by large amplitude motions. The time histories of stresses of tethers of a typical TLP in slack-taut state are given. In addition, the sensitivities of slack to stiffness and mass are investigated by varying file stiffness of tether and mass of TLP. It is found that slack is sensitive to the mass of TLP. The critical culled surfaces (over which indicates the slack) for the increase of mass are obtained.

EVALUATION OF FILM-SUBSTRATE ADHESION VIA IMPACT USING COATED BULLETS

A method was devised to evaluate the adhesion between a film and a substrate. A front-end coated bullet is accelerated by a gas gun and hits the substrate of the specimen under test. The impact generates a compressive stress pulse that propagates toward the film. After transmission through the interface, part of the pulse is reflected on the free surface of the film, and tensile stress arises at the film-substrate interface, possibly inducing debonding of the film. This dynamic process was demonstrated analytically and simulated numerically by the finite element method. The results validate the initial concept and lay the foundation for further optimization of this method.

On a novel method of impact by a front-end-coated bullet to evaluate the interface adhesion between film and substrate

A preliminary experiment was carried out to validate the feasibility of the method of impact by a front-end-coated bullet to evaluate the interface adhesion between film and substrate. The theoretical description of the initiation, propagation and evolution of the stress pulse during impact was generalized and formulized. The effects of the crucial parameters on the interface stress were further investigated with FEM. The results found the promising prospect of the application of such a method and provided useful guidance for experimental design.

Plume Parameters and Thruster Properties of a Low Power Arcjet

Abstract. A low power arcjet-thruster of 1 kW-class with gas mixture of H2-N2 or pure argon as the propellant is fired at a chamber pressure about 10 Pa. The nozzle temperature is detected with an infrared pyrometer; a plate set perpendicular to the plume axis and connected to a force sensor is used to measure the thrust; a probe with a tapered head is used for measuring the impact pressure in the plume flow; and a double-electrostatic probe system is applied to evaluate the electron temperature. Results indicate that the high nozzle temperature could adversely affect the conversion from enthalpy to kinetic energy. The plume flow deviates evidently from the LTE condition, and the rarefied-gas dynamic effect should be considered under the high temperature and low-pressure condition in analyzing the experimental phenomena.

Universal quantum computation with trapped ions in thermal motion by adiabatic passage

We propose a universal quantum computation scheme for trapped ions in thermal motion via the technique of adiabatic passage, which incorporates the advantages of both the adiabatic passage and the model of trapped ions in thermal motion. Our scheme is immune from the decoherence due to spontaneous emission from excited states as the system in our scheme evolves along a dark state. In our scheme the vibrational degrees of freedom are not required to be cooled to their ground states because they are only virtually excited. It is shown that the fidelity of the resultant gate operation is still high even when the magnitude of the effective Rabi frequency moderately deviates from the desired value.

Optical gain at 1550 nm from colloidal solution of Er3+-Yb3+ codoped NaYF4 nanocubes

We demonstrated optical amplification at 1550 nm with a carbon tetrachloride solution of Er3+-Yb3+ codoped NaYF4 nanocubes synthesized with solvo-thermal route. Upon excitation with a 980 nm laser diode, the nanocube solution exhibited strong near-infrared emission by the I-4(13/2) -> I-4(15/2) transition of Er3+ ions due to energy transfer from Yb3+ ions. We obtained the highest optical gain coefficient at 1550 nm of 0.58 cm(-1) for the solution with the pumping power of 200 mW. This colloidal solution might be a promising candidate as a liquid medium for optical amplifier and laser at the optical communication wavelength. (C) 2009 Optical Society of America

Radiation damping effects on the ultrashort x-ray pulses generated by nonlinear Thomson backscattering

Nonlinear Thomson backscattering of an intense Gaussian laser pulse by a counterpropagating energetic electron is investigated by numerically solving the electron equation of motion taking into account the radiative damping force. The backscattered radiation characteristics are different for linearly and circularly polarized lasers because of a difference in their ponderomotive forces acting on the electron. The radiative electron energy loss weakens the backscattered power, breaks the symmetry of the backscattered-pulse profile, and prolongs the duration of the backscattered radiation. With the circularly polarized laser, an adjustable double-peaked backscattered pulse can be obtained. Such a profile has potential applications as a subfemtosecond x-ray pump and probe with adjustable time delay and power ratio. (c) 2006 American Institute of Physics.

ZnSe nanowires grown on the crystal surface by femtosecond laser ablation in air

Uniform ZnSe nanowires are observed on the ablation crater on ZnSe crystal surface irradiated by femtosecond lasers in air, while other parts of the sample surface are not polluted. The nanowire growth rate is about 5 mu m/s, it is higher than that fabricated by chemical vapor deposition method by a factor of 10(4). The nanowire length and diameter can be controlled by varying laser pulse energy and pulse number. The formation mechanism is studied and found to be self-catalyzed vapor-liquid-solid process. (c) 2006 American Institute of Physics.

Optimization of positions and currents of tokamak poloidal field coils using genetic algorithms

Plasma equilibrium geometry has a great influence on the confinement and magnetohydrodynamic stability in tokamaks. The poloidal field (PF) system of a tokamak should be optimized to support the prescribed plasma equilibrium geometry. In this paper, a genetic algorithm-based method is applied to solve the optimization of the positions and currents of tokamak PF coils. To achieve this goal, we first describe the free-boundary code EQT Based on the EQT code, a genetic algorithm-based method is introduced to the optimization. We apply this new method to the PF system design of the fusion-driven subcritical system and plasma equilibrium geometry optimization of the Experimental Advanced Superconducting Tokamak (EAST). The results indicate that the optimization of the plasma equilibrium geometry can be improved by using this method.

Quantum information processing in the wall of cytoskeletal microtubules

Microtubules (MT) are composed of 13 protofilaments, each of which is a series of two-state tubulin dimers. In the MT wall, these dimers can be pictured as "lattice" sites similar to crystal lattices. Based on the pseudo-spin model, two different location states of the mobile electron in each dimer are proposed. Accordingly, the MT wall is described as an anisotropic two-dimensional (2D) pseudo-spin system considering a periodic triangular "lattice". Because three different "spin-spin" interactions in each cell exist periodically in the whole MT wall, the system may be shown to be an array of three types of two-pseudo-spin-state dimers. For the above-mentioned condition, the processing of quantum information is presented by using the scheme developed by Lloyd.

Intense laser beam guiding in self-induced electron cavitation channel in underdense plasmas

In underdense plasmas, the transverse ponderomotive force of an intense laser beam with Gaussian transverse profile expels electrons radially, and it can lead to an electron cavitation. An improved cavitation model with charge conservation constraint is applied to the determination of the width of the electron cavity. The envelope equation for laser spot size derived by using source-dependent expansion method is extended to including the electron cavity. The condition for self-guiding is given and illuminated by an effective potential for the laser spot size. The effects of the laser power, plasma density and energy dissipation on the self-guiding condition are discussed.

Formation mechanisms of uniform arrays of periodic nanoparticles and nanoripples on 6H-SiC crystal surface induced by femtosecond laser ablation

Uniform arrays of periodic nanoparticles with 80-nm period are formed on 6H-SiC crystal irradiated by circularly polarized 400-nm femtosecond laser pulses. In order to understand the formation mechanism, the morphology evolvement as a function of laser pulse energy and number is studied. Periodic nanoripples are also formed on the sample surface irradiated by linearly polarized 400-, 510- and 800-nm femtosecond laser pulses. All these results support well the mechanism that second-harmonic generation plays an important role in the formation of periodic nanostructures.

Broadband infrared luminescence from transparent glass-ceramics containing Ni2+-doped beta-Ga2O3 nanocrystals

Transparent Ni2+-doped beta-Ga2O3 glass-ceramics were synthesized. The nanocrystal phase in the glass-ceramics was identified to be beta-Ga2O3 and its size was about 3.6 nm. It was confirmed from the absorption spectra that the ligand environment of Ni2+ ions changed from the trigonal bi-pyramid fivefold sites in the as-cast glass to the octahedral sites in the glass-ceramics. The broadband infrared emission centering at 1270 nm with full width at half maximum (FWHM) of more than 250 nm was observed. The fluorescence lifetime was about 1.1 mu s at room temperature. The observed infrared emission could be attributed to the T-3 (2g) (F-3) -> (3)A (2g) (F-3) transition of octahedral Ni2+ ions. It is suggested that the Ni2+-doped transparent beta-Ga2O3 glass-ceramics with broad bandwidth and long lifetime have a potential as a broadband amplification medium.

Precipitation of nanocrystals in glasses by electron irradiation: An alternative path to form glass ceramics?

This letter demonstrates an alternative method to form gallium silicate glass ceramics using high-energy electron irradiation. Compared with glass ceramics obtained from the conventional thermal treatment method, the distribution and crystal sizes of the precipitated Ga2O3 nanoparticles are the same. An advantage of this method is that the spatial distribution of the precipitated nanoparticles can be easily controlled. However, optically active dopants Ni2+ ions do not participate in the precipitation during electron irradiation. (c) 2007 American Institute of Physics.