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Frequency Modes (frequency + mode)
Selected AbstractsDigital image analysis of the flagellar beat of activated and hyperactivated suncus spermatozoaMOLECULAR REPRODUCTION & DEVELOPMENT, Issue 4 2007Takane Kaneko Abstract The flagellar beat of hyperactivated Suncus spermatozoa was analyzed by digital imaging and was compared to that of the nonhyperactivated (activated) spermatozoa in order to examine the function of the accessory fibers during the flagellar beat and the sliding filament mechanism inducing the motility of the hyperactivated spermatozoa. Unusual large and long characteristics of the accessory fibers were involved in generating the gently curved bends and a low beat frequency. Examination of the motility parameters of the flagellar beat of the activated and hyperactivated spermatozoa attached to a slide glass by their heads revealed that there were two beating modes: a frequency-curvature dependent mode in the activated flagellar beat and a nearly constant frequency mode in the hyperactivated flagellar beat. The hyperactivated flagellar beat was characterized by sharp bends in the proximal midpiece and a low beat frequency. The sharp bends in the proximal midpiece were induced by the increase in the total length of the microtubule sliding at the flagellar base. The rate of microtubule sliding (sliding velocity) in the axoneme remained almost constant in the flagellar beat of both the activated and hyperactivated spermatozoa. Comparison of the sliding velocity in Suncus, golden hamster, monkey, and sea urchin sperm flagella with their stiffness suggests that the sliding velocity is determined by the stiffness at the flagellar base and that the same sliding microtubule system functions in both mammalian and echinoderm spermatozoa. Mol. Reprod. Dev. 74: 478,485, 2007. © 2006 Wiley-Liss, Inc. [source] Dispersion of Dust Acoustic Modes and Perturbations of Plasma Flux BalanceCONTRIBUTIONS TO PLASMA PHYSICS, Issue 3 2007V. Tsytovich Abstract Previous considerations of dust acoustic waves is demonstrated to be inconsistent - the required equilibrium state for perturbations was not defined since balance of plasma fluxes was neglecting. The self-consistent treatment shows that plasma flux perturbations are accompanying any collective waves propagating in dusty plasmas and can play an important role in wave dispersion, wave damping and can create instabilities. This is illustrated by the derivation of dispersion relation for dust acoustic modes taking into account the plasma flux balances and plasma flux perturbations by waves. The result of this approach shows that the dust acoustic waves with linear dependence of wave frequency on the wave number exist only in restricted range of the wave numbers. Only for wave numbers larger than some critical wave number for low frequency modes the frequency can be have approximately a linear dependence on wave number and can be called as dust acoustic wave but the phase velocity of these waves is different from that which can be obtained neglecting the flux balance and depends on grain charge variations which are determined by the balance of fluxes. The presence of plasma fluxes previously neglected is the main typical feature of dusty plasmas. The dispersion relation in the range of small wave numbers is found to be mainly determined by the change of the plasma fluxes and is quite different from that of dust acoustic type, namely it is found to have the same form as the well known dispersion relation for the gravitational instability. This result proves in general way the existence of the collective grain attractions of negatively charged grains for for large distances between them and for any source of ionization. The attraction of grains found from dispersion relation of the dust acoustic branch coincides with that found previously for pair grain interactions using some models for the ionization source. For the existing experiments the effective Jeans length for such attraction is estimated to be about 8 , 10 times larger than the ion Debye length and the effective gravitational constant for the grain attraction is estimated to be several orders of magnitude larger than the usual gravitational constant. The grain attraction at large inter-grain distances described by the gravitationlike grain instability is considered as the simplest explanation for observed dust cloud clustering, formation of dust structures including the plasma crystals. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Adiabatic bond charge model for lattice dynamics of ternary chalcopyrite semiconductorsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 1 2006T. Gürel Abstract The adiabatic bond charge model of Rustagi and Weber is extended to study lattice dynamical properties of ternary chalcopyrite semiconductors AgGaS2, AgGaSe2, CuInS2, CuInSe2, CuGaS2, CuGaSe2, CuAlS2 and CuAlSe2. The new model calculations agree well with the results of Raman/IR and neutron measurements of Brillouin zone center phonon frequencies for both low and high frequency modes which was difficult for other phenomenological lattice dynamical models. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Mechanism of Thermal Transport in Zirconia and Yttria-Stabilized Zirconia by Molecular-Dynamics SimulationJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2001Patrick K. Schelling We present results of molecular-dynamics simulations of the thermal conductivity, ,, of ZrO2 and Y2O3 -stabilized ZrO2 (YSZ). For both pure ZrO2 and YSZ with low concentrations of Y2O3, we find that the high-temperature , is typical of a crystalline solid, with the dominant mechanism being phonon-phonon scattering. With increasing Y2O3 concentration, however, the mechanism changes to one more typical of an amorphous system. In particular, phononlike vibrational modes with well-defined wave vectors appear only at very low frequencies. As in amorphous materials, the vast majority of vibrational modes, while delocalized, do not propagate like ordinary phonon modes but transport energy in a diffusive manner. We also find that the few highest frequency modes are localized and do not contribute to ,. [source] Oscillatory nature of human basal ganglia activity: Relationship to the pathophysiology of Parkinson's diseaseMOVEMENT DISORDERS, Issue 4 2003Peter Brown MD Abstract Alterations of basal ganglia physiology in parkinsonism may consist of two elements, an increase in the firing rate of neurones and a change in the pattern of synchronisation of discharges between neurones. Recent findings suggest the presence of two principal modes of synchronised activity within the human subthalamo-pallidal-thalamo-cortical circuit, at <30 Hz and >60 Hz. These oscillations are dynamically and systematically modulated by task, thereby suggesting a functional role in movement. More importantly, the two frequency modes are inversely affected by movement, consistent with opposing actions, and differentially expressed according to the prevailing level of dopaminergic activity. It is argued that the balance between these modes determines the effects of basal ganglia-thalamocortical projections on the motor areas of the cortex. The lower frequency oscillations facilitate slow idling rhythms in the motor areas of the cortex, whereas synchronisation at high frequency restores dynamic task-related cortical ensemble activity in the gamma band.© 2002 Movement Disorder Society [source] | ||||||||||