Results 1 - 10 of 2085
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[en] The dispersion and landau damping of the dispersive Alfvén waves (DAW) have been studied in the plasma with nonextensive electrons and ions. The conditions for the existence of inertial Alfvén waves (IAW) and kinetic Alfvén waves (KAW) are modified by electrons' nonextensive parameter qe. For IAW, βq ≪ me/mi; for KAW, me/mi ≪ βq ≪ 1, βq is the ratio of the effective thermal pressure to the magnetic pressure. In the plasma with superthermal particles, the frequency of the IAW and KAW will increase with the increase of qe when the effective temperature of the plasma systems keeps invariant. Whereas the damping rates of the IAW and KAW vary inversely with respect to qe for the reason that the phase velocity of KAW is much smaller than the effective thermal velocity, while the phase velocity of IAW is much bigger than the effective thermal velocity
[en] For the extended Rayleigh problem of hydrodynamics stability dealing with homogeneous shear flows with variable cross section, we have obtained a parabolic instability region. This improved parabolic instability region intersects with the semicircular instability region under certain condition. The validity of the result is illustrated with an example of basic flows. Furthermore, we have obtained a bound for the complex part of the phase velocity.
[en] Transverse magnetic (TM) modes with phase velocities at or just below the speed of light, c, are intended to accelerate relativistic particles in hollow-core, photonic band gap (PBG) fibers. These are so-called 'surface defect modes', being lattice modes perturbed by the defect to have their frequencies shifted into the band gap, and they can have any phase velocity. PBG fibers also support so-called 'core defect modes' which are characterized as having phase velocities always greater than c and never cross the light line. In this paper we explore the nature of these two classes of accelerating modes and compare their properties.
[en] The paper presents a numerical study to evaluate the phase velocities and attenuations of the average longitudinal and shear ultrasonic waves resulting from multiple scattering in fiber-reinforced composites. A computational procedure developed in this work is first used to produce a random, yet largely even distribution of fibers. Both the viscoelastic epoxy matrix and lossless randomly distributed graphite fibers are modeled using the mass-spring-dashpot lattice model, with no damping for the latter. By numerically simulating ultrasonic through-transmission tests using this direct model of composites, phase velocities and attenuations of the longitudinal and shear waves through the composite are found as functions of frequency or fiber concentration. The numerical results are observed to generally agree with the corresponding results in the literature. Discrepancies found in some detail aspects, particularly in the attenuation results, are also addressed
[en] Highlights: • A high-speed thermoresponsive bioseparation medium was prepared in two steps. • Non-specific adsorption of proteins on thermoresponsive medium was greatly reduced. • Separation of proteins was achieved by only adjusting column temperature. • It was able to separate proteins at the mobile phase velocity up to 2167 cm h−1. - Abstract: A high-speed thermoresponsive medium was developed by grafting poly(N-isopropylacrylamide-co-butyl methacrylate) (P(NIPAM-co-BMA)) brushes onto gigaporous polystyrene (PS) microspheres via surface-initiated atom transfer radical polymerization (ATRP) technique, which has strong mechanical strength, good chemical stability and high mass transfer rate for biomacromolecules. The gigaporous structure, surface chemical composition, static protein adsorption, and thermoresponsive chromatographic properties of prepared medium (PS–P(NIPAM-co-BMA)) were characterized in detail. Results showed that the PS microspheres were successfully grafted with P(NIPAM-co-BMA) brushes and that the gigaporous structure was robustly maintained. After grafting, the nonspecific adsorption of proteins on PS microspheres was greatly reduced. A column packed with PS–P(NIPAM-co-BMA) exhibited low backpressure and significant thermo-responsibility. By simply changing the column temperature, it was able to separate three model proteins at the mobile phase velocity up to 2167 cm h−1. In conclusion, the thermoresponsive polymer brushes grafted gigaporous PS microspheres prepared by ATRP are very promising in ‘green’ high-speed preparative protein chromatography
[en] We propose and theoretically study a hybrid structure consisting of a photonic crystal waveguide (PhC-wg) and a two-wire metallic transmission line (TL), engineered for efficient transfer of mid-infrared (mid-IR) light between them. An efficiency of 32% is obtained for the coupling from the transverse magnetic (TM) photonic mode to the symmetric mode of the TL, with a predicted intensity enhancement factor of 53 at the transmission line surface. The strong coupling is explained by the small phase velocity mismatch and sufficient spatial overlapping between the modes. This hybrid structure could find applications in highly integrated mid-IR photonic-plasmonic devices for biological and gas sensing, among others
[en] According to the standard theory the mechanism of Landau damping does not work in the case of the transverse electromagnetic mode of homogeneous nonmagnetized infinite plasma because the phase velocity of this mode is above the velocity of light. It is shown that this result of the standard theory is based on the assumption that the electrons and ions of the plasma are point charges. Taking into consideration the finite size, internal structure and polarizability of the ion cores, the dispersion relation must be modified and thus the Landau damping works. (D.Gy.)
[en] In this short communication the phase velocity corresponding to the free electron associated wave for the relativist case is analysed. Employing the kinetic energy of the electrons for its calculation the following result is arrived at vsub(φ)=(c2/v)(1-√(1-v2/c2)) which is less then c. For small velocities this expression leads to the classical value, vsub(φ)=(1/2)v. (author)
[en] The principal goal of this project was to develop a tunable dielectric loaded accelerator (DLA) to allow one to adjust the phase velocity of the DLA after it has been assembled into its final form