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Frequency Dependent (frequency + dependent)
Terms modified by Frequency Dependent Selected AbstractsVibrations of thin cylindrical shells with a periodic structurePROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2008Barbara Tomczyk Free vibrations of thin linear,elastic Kirchhoff,Love cylindrical shells, having a periodic structure along one direction tangent to the shell midsurface, is considered. In order to take into account the effect of the periodicity cell size in this problem, a new averaged non,asymptotic model of such shells, proposed by Tomczyk (2006), is applied. The new additional higher,order free vibration frequencies dependent on the microstructure size will be derived and discussed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] In-plane vibrations of shear deformable curved beamsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 11 2001Moshe Eisenberger Abstract This paper presents the exact dynamic stiffness matrix for a circular beam with a uniform cross-section. The stiffness matrix is frequency dependent, and the natural frequencies are those that cause the matrix to become singular. Using this matrix the exact natural frequencies of circular beams with various boundary conditions are calculated and compared with available results in the literature. Copyright © 2001 John Wiley & Sons, Ltd. [source] 20 Questions on Adaptive DynamicsJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 5 2005D. WAXMAN Abstract Adaptive Dynamics is an approach to studying evolutionary change when fitness is density or frequency dependent. Modern papers identifying themselves as using this approach first appeared in the 1990s, and have greatly increased up to the present. However, because of the rather technical nature of many of the papers, the approach is not widely known or understood by evolutionary biologists. In this review we aim to remedy this situation by outlining the methodology and then examining its strengths and weaknesses. We carry this out by posing and answering 20 key questions on Adaptive Dynamics. We conclude that Adaptive Dynamics provides a set of useful approximations for studying various evolutionary questions. However, as with any approximate method, conclusions based on Adaptive Dynamics are valid only under some restrictions that we discuss. [source] Reproductive performance of clonal and sexual bark beetles (Coleoptera: Scolytidae) in the fieldJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 5 2000Løyning In Ips acuminatus (Gyll.) parthenogenetic females occur together with sexual females and with sexual males upon which they depend for sperm. In a reciprocal-transplant experiment, I studied fecundity differences among parthenogenetic and sexual females from two populations that differ dramatically in the proportion of clonal females. In a second experiment, I studied competition between larvae from different mothers and between females from the two source populations. Fecundity measured by the number of eggs per egg tunnel was influenced by the ambient environment at the sites of the experiment as well as the origin of the female, and was generally higher for clonal than for sexual females at both sites. In experimental groups where larvae competed with larvae from their own population (pure treatments), the number of surviving pupae was significantly lower than in groups where females from the two source populations were mixed. The high fecundity of clonal females makes coexistence of the two types of females difficult to explain. It makes the reproductive advantage associated with clonality in I. acuminatus even higher than the two-fold difference due to asexuality per sé. The significant differences in the number of pupae in mixed vs. pure groups suggest ecological divergence between sexual and clonal females. This would make the mortality of larvae not only density dependent, but also frequency dependent, which could explain the coexistence of sexual and clonal females. [source] EFFECT OF COMPOSITION OF GLUTHNIN SUBFRACTIONS ON RHEOLOGICAL PROPERTIES OF WHEATJOURNAL OF FOOD BIOCHEMISTRY, Issue 4 2000S. JOOD ABSTRACT Gluten extracted from defatted flours of cv. Aubaine (extra-strong), Hereward (strong) and Riband (weak) was separated into five different fractions (R2 to R6) by sequential centrifugation and addition of sodium chloride. A seven-minute mixing time was used to carry out fractionation on the basis of depolymerization of glutenin macropolymers (GMP). Depolymerization of GMP occurred at much higher rates in dough of the weak cultivar compared to the strong and extra-strong cultivars. Polypeptide compositions of different ghttenin fractions were determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis under reduced and non-reduced conditions, followed by densitometric scanning of stained patterns. The amount of HMW-glutenin subunits decreased and LMW-glutenin subunits increased correspondingly in each cultivar with the fractionation from R2 to R6. The rheological behavior of the fractions was analyzed by small deformation rheological tests (strain sweep and frequency tests). The high molecular weight fraction (R2) from extra-strong wheat had a higher vahte of G' and a lower tan , value as compared to strong and weak bread-making wheats. The moduli of HMW glutenin fractions (R2 and R3) were frequency independent and promoted the network properties, whereas moduli of LMW glutenin fractions were frequency dependent and gave rise to a plasticizing effect. Therefore, it was concluded from the present studies that HMW-glutenin subunits are not the only factors governing good bread-making quality but their proportions in relation to low molecular weight glutenin subunits is equally important in sinking a balance between viscous and elastic properties essential for bread making performance. [source] Influence of the frequency parameter on extracellular glutamate and ,-aminobutyric acid in substantia nigra and globus pallidus during electrical stimulation of subthalamic nucleus in ratsJOURNAL OF NEUROSCIENCE RESEARCH, Issue 2 2003François Windels Abstract High-frequency stimulation (HFS) of the subthalamic nucleus (STN) proves to be an efficient treatment for alleviating motor symptoms in Parkinson's disease (PD). However, the mechanisms of HFS underlying these clinical effects remain unknown. Using intracerebral microdialysis, we previously reported that HFS induces, in normal rats, a significant increase of extracellular glutamate (Glu) in the globus pallidus (GP in rats or GPe in primates) and the substantia nigra pars reticulata (SNr), whereas ,-aminobutyric acid (GABA) was increased only in the SNr. Bradykinesia can be improved by STN stimulation in a frequency-dependent manner, a plateau being reached around 130 Hz. The aim of the present study was to determine whether neurochemical changes are also frequency dependent. Electrical STN stimulation was applied at various frequencies (10, 60, 130, and 350 Hz) in normal rats. The results show that, for Glu, the amplitude of increase detected in GP and SNr is maximal at 130 Hz and is maintained at 350 Hz. No modifications of GABA were observed in GP whatever the frequency applied, whereas, in SNr, GABA increased from 60 to 350 Hz. Our results provide new neurochemical data implicating STN target structures in deep-brain-stimulation mechanisms. © 2003 Wiley-Liss, Inc. [source] Intervertebral disc cell response to dynamic compression is age and frequency dependent,JOURNAL OF ORTHOPAEDIC RESEARCH, Issue 6 2009Casey L. Korecki Abstract The maintenance of the intervertebral disc extracellular matrix is regulated by mechanical loading, nutrition, and the accumulation of matrix proteins and cytokines that are affected by both aging and degeneration. Evidence suggests that cellular aging may lead to alterations in the quantity and quality of extracellular matrix produced. The aims of this study were to examine the role of loading and maturation (a subset of aging), and the interaction between these two factors in intervertebral disc cell gene expression and biosynthesis in a controlled 3D culture environment. Cells were isolated from young (4,6 months) and mature (18,24 months) bovine caudal annulus fibrosus and nucleus pulposus tissue. Isolated cells were seeded into alginate and dynamically compressed for 7 days at either 0.1, 1, or 3 Hz or maintained as a free-swelling control. After 7 days, DNA and sulfated glycosaminoglycan contents were analyzed along with real time, quantitative reverse transcription-polymerase chain reaction analysis for collagen types I and II, aggrecan, and matrix metalloproteinase-3 gene expression. Results suggest that maturation plays an important role in intervertebral disc homeostasis and influences the cell response to mechanical loading. While isolated intervertebral disc cells responded to mechanical compression in 3D culture, the effect of loading frequency was minimal. Altered cellular phenotype and biosynthesis rates appear to be an attribute of the cell maturation process, potentially independent of changes in cellular microenvironment associated with lost nutrition and disc degeneration. Mature cells may have a decreased capacity to create or retain extracellular matrix components in response to mechanical loading compared to young cells. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27: 800,806, 2009 [source] Mapping of Atrial Activation Patterns After Inducing Contiguous Radiofrequency Lesions: An Experimental StudyPACING AND CLINICAL ELECTROPHYSIOLOGY, Issue 2 2001FRANCISCO J. CHORRO CHORRO, F.J., et al.: Mapping of Atrial Activation Patterns After Inducing Contiguous Radiofrequency Lesions: An Experimental Study. High resolution mapping techniques are used to analyze the changes in atrial activation patterns produced by contiguous RF induced lesions. In 12 Langendorff-perfused rabbit hearts, left atrial activation maps were obtained before and after RF induction of epicardial lesions following a triple-phase sequential protocol: (phase 1) three separate lesions positioned vertically in the central zone of the left atrial wall; (phase 2) the addition of two lesions located between the central lesion and the upper and lower lesions; and (phase 3) the placement of four additional lesions between those induced in the previous phases. In six additional experiments a pathological analysis of the individual RF lesions was performed. In phase 1 (lesion diameter = 2.8 ± 0.2 mm, gap between lesions = 3 ± 0.8 mm), the activation process bordered the lesions line in two (2.0-ms cycles) and four experiments (1.0-ms cycles). In phase 2, activation bordered the lesions line in eight (2.0-ms cycles, P < 0.01 vs control) and nine experiments (1.0-ms cycles, P < 0.001), and in phase 3 this occurred in all experiments except one (both cycles, P < 0.001 vs control). In the experiments with conduction block, the increment of the interval between activation times proximal and distal to the lesions showed a significant correlation to the length of the lesions (r = 0.68, P < 0.05, 100-ms cycle). In two (17%) experiments, sustained regular tachycardias were induced with reentrant activation patterns around the lesions line. In conclusion, in this acute model, atrial RF lesions with intact tissue gaps of 3 mm between them interrupt conduction occasionally, and conduction block may be frequency dependent. Lesion overlap is required to achieve complete conduction block lines. Tachycardias with reentrant activation patterns around a lesions line may be induced. [source] Unilateral suppression of pharyngeal motor cortex to repetitive transcranial magnetic stimulation reveals functional asymmetry in the hemispheric projections to human swallowingTHE JOURNAL OF PHYSIOLOGY, Issue 2 2007Satish Mistry Inhibitory patterns of repetitive transcranial magnetic stimulation (rTMS) were applied to pharyngeal motor cortex in order to establish its role in modulating swallowing activity and provide evidence for functionally relevant hemispheric asymmetry. Healthy volunteers underwent single pulse TMS before and for 60 min after differing intensities of 1 Hz rTMS (n= 9, 6 male, 3 female, mean age 34 ± 3 years) or theta burst stimulation (TBS) (n= 9, 6 male, 3 female, mean age 37 ± 4 years). Electromyographic responses recorded from pharynx and hand were used as a measure of cortico-motor pathway excitability. Swallowing behaviour was then examined with a reaction time protocol, before and for up to 60 min after the most effective inhibitory protocol (1 Hz) applied to each hemisphere. Interventions were conducted on separate days and compared to sham using ANOVA. Only high intensity 1 Hz rTMS consistently suppressed pharyngeal motor cortex immediately and for up to 45 min (,34 ± 7%, P, 0.001). Adjacent hand and contralateral pharyngeal motor cortex showed no change in response (,15 ± 12%, P= 0.14 and 15 ± 12%, P= 0.45, respectively). When used to unilaterally disrupt each hemisphere, rTMS to pharyngeal motor cortex with the stronger responses altered normal (,12 ± 3%, P, 0.001) and fast (,9 ± 4%, P, 0.009) swallow times, not seen following rTMS to the contralateral cortex or after sham. Thus, suppression of pharyngeal motor cortex to rTMS is intensity and frequency dependent, which when applied to each hemisphere reveals functionally relevant asymmetry in the motor control of human swallowing. [source] | |||||||||||||