Frequency-dependent Changes Research Articles

Characterization of conducting polymer coated fabrics at microwave frequencies

Purpose – The purpose of this paper is to investigate microwave reflection, transmission, and complex permittivity of p‐toluene‐2‐sulfonic acid doped conducting polypyrrole coated nylon‐lycra textiles in the 1‐18 GHz frequency with a view to potential applications in the interaction of electromagnetic radiation with such coated fabrics.Design/methodology/approach – The chemical polymerization of pyrrole is achieved by an oxidant, ferric chloride and doped with p‐toluene sulfonic acid (pTSA) to enhance the conductivity and improve stability. Permittivity of the conducting textile substrates is performed using a free space transmission method accompanied by a mathematical diffraction reduction method.Findings – The real part of permittivity increases with polymerization time and dopant concentration, reaching a plateau at certain dopant concentration and polymerization time. The imaginary part of permittivity shows a frequency dependent change throughout the test range. All the samples have higher values of...

Increasing Heart Rate Decreased Actin-Myosin Interaction in Isolated Beating Rat Whole Heart

Background: Heart rate (HR) is one of the determinant factors of cardiac performance. Failing human myocardium shows negative force frequency relation, whereas normal one shows positive relation. Purpose: To test the effect of HR on actin-myosin interaction (AMI) in beating rat hearts those have negative force-frequency relation by X-ray diffraction (XRD) analysis at third-generation synchrotron facility. Methods: Seven isolated isovolumically contracting rat hearts were paced at 120, 240, and 300bpm after complete heart block, mounted so that the X-ray beam (15.0keV) passed the left ventricular (LV) free wall, and perfused with Tyrode solution bubbled with 100% O2. LV volume were adjusted through water filled thin latex balloon inserted into LV cavity so that end-diastolic LV pressure (LVP) was 0 mmHg. The amount of AMI was evaluated by the minimum value of the intensity ratio of inner (1,0) and outer (1,1) equatorial reflections (Imin) provided by anaysis of XRD. Between three different HRs, we compared the amount of AMI and LVP. We also measured frequency-dependent changes in Ca2+ transient in sliced myocardial preparations at 0.5, 1.0, and 2.0Hz. Results: In all hearts, we did not observe incomplete relaxations. As increasing HR at 120, 240, and 300bpm, LVP significantly decreased (66±18, 51±16, and 47±18mmHg, respectively) and Imin also significantly increased (0.93±0.16, 1.20±0.11, and 1.56±0.18, respectively), indicating a significant decrease of the amount of AMI. The durations of Ca2+ transient at 20% developed level at stimulating frequency of 0.5, 1.0, and 2.0Hz were significantly shortened (233±25, 206±34, and 171±28ms, respectively). Conclusion: Increasing HR reduces the AMI. Absence of incomplete relaxations indicates intact intracellular Ca2+ handling. These results may derive from shortening the period of Ca2+-myofilament interaction with increasing HR.

Indirect Modulation of Nonmagnetic Probes for Force Modulation Atomic Force Microscopy

Frequency-dependent changes for phase and amplitude images are demonstrated with test platforms of organosilane ring patterns, using force modulation atomic force microscopy (FM-AFM) with an alternate instrument configuration. The imaging setup using indirect magnetic modulation (IMM) is based on indirect oscillation of soft, nonmagnetic cantilevers, with spring constants <1 N m(-1). The tip is driven to vibrate by the motion of a tip holder assembly which contains ferromagnetic materials. The entire tip assembly is induced to vibrate with the flux of an external ac electromagnetic field, supplied by a wire coil solenoid placed underneath the sample plate. With the use of IMM, dynamic parameters of the driving frequencies and amplitude of the tip motion can be optimized to sensitively map the elastic response of samples. An advantage of this instrument setup is that a magnetic coating is not required to drive the periodic oscillation of the tip. The instrument configuration for IMM may not be practical for intermittent imaging modes, which often work best with stiff cantilevers. However, indirect actuation provides an effective approach for imaging with low force setpoints and is well-suited for dynamic AFM modes using continuous contact imaging.

Fabrication and Characterization of Artificially Designed PZT/LSMO Multiferroics Heterostructure

AbstractHighly oriented and epitaxial bilayers of PbZr0.52Ti0.48O3/La0.67Sr0.33MnO3 (PZT/LSMO) thin films have been grown by pulsed laser deposition on two different substrates (100) - MgO and -LaAlO3 (LAO) respectively. The structural analysis using X-ray diffraction (XRD) evidenced that layered structure was formed without any secondary phase. Atomic force microscopy (AFM) images shown change in the grain size and surface roughness with change of the substrate. Room temperature magnetization-field (M-H) exhibited well-shaped magnetization hysteresis loops, good saturation and low coercivity. The electrical properties of hetrostructure exhibited high remnant polarization (30-54 μC/cm2) and dielectric constant (400-1700) depending upon the different substrate and temperature deposition of FM layer. Frequency dependent change in dielectric constant and loss were observed above metallic ferromagnet to insulator paramagnet transition temperature. It is important to note that the frequency dependent dielectric anomalies are attributed to the change in metallic nature of LSMO bottom electrode and also the bilayer.

Partial discharges in a cavity at variable applied frequency part 1: measurements

In this paper partial discharges (PD) in disc-shaped cavities in polycarbonate are measured at variable frequency (0.01-100 Hz) of the applied voltage. The advantage of PD measurements at variable frequency is that more information about the insulation system may be extracted than from traditional PD measurements at a single frequency (usually 50/60 Hz). The PD activity in the cavity is seen to depend on the applied frequency. Moreover, the PD frequency dependence changes with the applied voltage amplitude, the cavity diameter, and the cavity location (insulated or electrode bounded). It is suggested that the PD frequency dependence is governed by the statistical time lag of PD and the surface charge decay in the cavity. This is the first of two papers addressing the frequency dependence of PD in a cavity. In the second paper a physical model of PD in a cavity at variable applied frequency is presented.

Propagation-induced transition from slow to fast light in highly doped erbium fibers

We analyze the propagation regime of an amplitude-modulated 1536 nm signal when traveling along a highly doped erbium fiber pumped at 977 nm as a function of the fiber length. A propagation-induced transition from superluminal to subluminal propagation takes place along the fiber length which allows a change in regime solely based upon increasing the signal modulation frequency. This peculiar behavior is due to the interplay between pump absorption and pump-power broadening of the spectral hole induced by coherent population oscillations. The effect of ion density on this frequency-dependent regime change has been investigated.

Advantages of a navigation system to create portals for shoulder arthroscopy: a preliminary investigation

Background As shoulder arthroscopy has established its place in orthopaedic surgery for management of shoulder problems, developing the skills needed to perform shoulder arthroscopy has become increasingly important. Shoulder arthroscopy remains difficult for beginners. Navigation and computer-assisted placement techniques have been developed for other orthopaedic procedures. We examined such a system for use in shoulder arthroscopy particularly the creation of anterior and posterior portals. Methods Using an anatomically accurate shoulder model, six orthopaedic residents without experience in shoulder arthroscopy created anterior and posterior portals in the shoulder model under navigation control. A control group of five residents also without experience were asked to create the same portals but without navigation control. Time required for accurate creation of each portal was measured and frequency-dependent changes were evaluated. Results The mean times (seconds) required for anterior and posterior portals decreased significantly from 92.2 to 15.5 and from 107.0 to 32.3 (P < 0.05 for both), respectively, in the group that used navigation. In the control group, the mean times (seconds) required for anterior and posterior portals decreased significantly from 86.4 to 46.8 and from 97.0 to 54.4, respectively (P < 0.05 for both). Significant differences were observed in the time decrease for both portals between the two groups (P < 0.05 for both). Conclusions The shoulder navigation system can dramatically assist beginners ascending the steep learning curve for acquiring basic shoulder arthroscopy techniques.

Effects of primordial chemistry on the cosmic microwave background

Previous works have demonstrated that the generation of secondary CMB anisotropies due to the molecular optical depth is likely too small to be observed. In this paper, we examine additional ways in which primordial chemistry and the dark ages might influence the CMB. We present a detailed and updated chemical network and give an overview of the interactions of molecules with the CMB. We consider the optical depth due to line absorption, photoionization, photodissociation and free-free processes, and estimate the resulting changes in the CMB temperature and its power spectrum. The most promising results are obtained for the negative hydrogen ion \HM and the \HeHII molecule. The free-free process of \HM yields a relative change in the CMB temperature of up to $2\times10^{-11}$, and leads to a frequency-dependent change in the power spectrum of the order $10^{-7}$ at 30 GHz. With a change of the order $10^{-10}$ in the power spectrum, our result for the bound-free process of \HM is significantly below a previous suggestion. \HeHII efficiently scatters CMB photons and smears out primordial fluctuations, leading to a change in the power spectrum of the order $10^{-8}$. Improvements in the accuracy of future CMB experiments may thus help to constrain and finally detect these interesting signals from the dark ages of the universe.

Frequency-Dependent Behavior of the Intervertebral Disc in Response to Each of Six Degree of Freedom Dynamic Loading

Nondestructive displacement-controlled dynamic testing of cadaver material, with repeated measures design and randomized sequence of tests. To determine whether the frequency-dependent changes in disc stiffness and phase angle between load and displacement differ between the 6 principal directions of displacement, and whether these differences are greater in deformation directions associated with greater intradiscal fluid flow. Prior studies of time-dependent behavior of discs have focused on compression. Comparing different deformation directions allows effects of fluid flow to be distinguished from effects of the solid phase viscoelasticity. Vertebra-disc-vertebra preparations (N = 9) from human lumbar spines were subjected to each of 3 displacements and 3 rotations (6 degree of freedom) at each of 4 frequencies (0.001, 0.01, 0.1, and 1 Hz) after equilibration overnight under a 0.4 MPa preload in a bath of phosphate buffered saline at 37 degrees C with protease inhibitors. The forces and torques were recorded along with the applied translation or rotation. The stiffness (force/displacement or torque/rotation) and the phase angle (between each force and displacement) were calculated for each degree of freedom from recorded data. Disc stiffness increased linearly with the log-frequency. The increases over the four decades of frequency were 35%, 33%, and 26% for AP shear, lateral shear, and torsion respectively, and were 45%, 29%, 51%, and 83% for compression, lateral bending, flexion, and extension. The phase angle (a measure of energy absorption) averaged 6.2, 5.1, and 5.1 degrees in AP shear, lateral shear, and torsion, respectively, and 7.0, 7.0, and 8.6 degrees for compression, lateral bending, and flexion-extension. There were no consistent variations of phase angle with frequency. The stiffness increase and phase angle decrease with frequency were greater for deformation modes in which fluid flow effects are thought to be greater.

Role of Rac and Rho-GDI Alpha in the Frequency-dependent Expression of h1-calponin in Vascular Smooth Muscle Cells under Cyclic Mechanical Strain

Phenotype transformation of vascular smooth muscle cells (VSMCs) has been reported to be directly influenced by the frequency of mechanical strain. This study explored the effects of different frequencies of mechanical strain on expression of phenotype marker h1-calponin and the possible mechanism. VSMCs were subjected to cyclic strains of 10% elongation at 1 and 2 Hz for 24 h by using a Flexercell strain unit. The protein expression of h1-calponin was assessed by Western blotting and the possible protein kinases involved were evaluated by their specific inhibitor or targeted siRNA 'knock-down.' The results showed that cyclic strains modulated the expressions of h1-calponin, phospho-p38, Rac and Rho-guanine nucleotide dissociation inhibitor alpha (Rho-GDI alpha) in nonlinear frequency-dependent manners. This nonlinear frequency-dependent change of h1-calponin expression could be blocked by a specific p38 inhibitor, SB202190. The changed expression of phospho-p38 induced by the frequencies of cyclic strain was reversed by targeted siRNA 'knock-down' of Rac, while enhanced by targeted siRNA 'knock-down' of Rho-GDI alpha. These results suggest that the frequency-dependent expression of h1-calponin under cyclic strain is mediated at least partly by the regulation of Rac and Rho-GDI alpha expression on the activation of p38 pathway.

Efficient copackaging and cotransport yields postsynaptic colocalization of neuromodulators associated with synaptic plasticity

Recent data suggest that tissue plasminogen activator (tPA) influences long-term plasticity at hippocampal synapses by converting plasminogen into plasmin, which then generates mature brain-derived neurotrophic factor (mBDNF) from its precursor, proBDNF. Motivated by this hypothesis, we used fluorescent chimeras, expressed in hippocampal neurons, to elucidate (1) mechanisms underlying plasminogen secretion from hippocampal neurons, (2) if tPA, plasminogen, and proBDNF are copackaged and cotransported in hippocampal neurons, especially within dendritic spines, and (3) mechanisms mediating the transport of these neuromodulators to sites of release. We find that plasminogen chimeras traffic through the regulated secretory pathway of hippocampal neurons in dense-core granules (DCGs) and that tPA, plasminogen, and proBDNF chimeras are extensively copackaged in DCGs throughout hippocampal neurons. We also find that 80% of spines that contain DCGs contain chimeras of these neuromodulators in the same DCG. Finally, we demonstrate, for the first time, that neuromodulators undergo cotransport along dendrites in rapidly mobile DCGs, indicating that neuromodulators can be efficiently recruited into active spines. These results support the hypothesis that tPA mediates synaptic activation of BDNF by demonstrating that tPA, plasminogen, and proBDNF colocalize in DCGs in spines, where these neuromodulators can undergo activity-dependent release and then interact and/or mediate changes that influence synaptic efficacy. The results also raise the possibility that frequency-dependent changes in extents of neuromodulator release from DCGs influence the direction of plasticity at hippocampal synapses by altering the relative proportions of two proteins, mBDNF and proBDNF, that exert opposing effects on synaptic efficacy.

Effects of Ropivacaine on Action Potential Configuration and Ion Currents in Isolated Canine Ventricular Cardiomyocytes

Despite the widespread clinical application of ropivacaine, there is little information on the cellular cardiac effects of the drug. In the current study, therefore, the concentration-dependent effects of ropivacaine on action potential morphology and the underlying ion currents were studied and compared with those of bupivacaine in isolated canine ventricular cardiomyocytes. Action potentials were recorded from the enzymatically dispersed cells using sharp microelectrodes. Conventional patch clamp and action potential voltage clamp arrangements were used to study the effects of ropivacaine on transmembrane ion currents. Ropivacaine induced concentration- and frequency-dependent changes in action potential configuration, including shortening of the action potentials, reduction of their amplitude and maximum velocity of depolarization, suppression of early repolarization, and depression of plateau. Reduction in maximum velocity of depolarization was characterized with an EC50 value of 81 +/- 7 microm at 1 Hz. Qualitatively similar results were obtained with bupivacaine (EC50 = 47 +/- 3 microm). Under voltage clamp conditions, a variety of ion currents were blocked by ropivacaine: L-type calcium current (EC50 = 263 +/- 67 microm), transient outward current (EC50 = 384 +/- 75 microm), inward rectifier potassium current (EC50 = 372 +/- 35 microm), rapid delayed rectifier potassium current (EC50 = 303 +/- 47 microm), and slow delayed rectifier potassium current (EC50 = 106 +/- 18 microm). Ropivacaine, similarly to bupivacaine, can modify cardiac action potentials and the underlying ion currents at concentrations higher than the usual therapeutic range. However, in cases of overdose, cardiac complications may be anticipated both during and after anesthesia due to the blockade of various ion currents.

Psychoacoustical correlates of musically induced chills

Music listening is often accompanied by the experience of emotions, sometimes even by so-called “strong experiences of music” (SEMs). SEMs can include such pleasurable reactions as shivers down the spine or goose pimples, which are referred to as “chills”. In the present study, the role of psychoacoustical features was investigated with respect to the experience of chills. Psychoacoustical parameters of short musical segments (total duration: 20 s), characterized as chill- inducing, were analyzed and compared with musical excerpts which did not induce chill responses. A significant increase of loudness in the frequency range between 8 and 18 Bark (920–4400 Hz) was found in those excerpts for which chills were reported. Frequency-dependent changes of loudness seem to play an important role in the induction of chills.

Spectral characteristics and linear–nonlinear synchronization changes of different EEG frequency bands during the CNV

During the CNV recorded in a simple auditory working memory task, task-specific decrease of the relative delta band and a transient increase of the absolute theta band were seen, accompanied by an increase of the absolute alpha1 and alpha2 bands in the posterior region. The decreased delta power probably corresponds to increased task-evoked arousal, whereas the transient theta power increase corresponds to working memory demand and possibly to the orienting response. The increased alpha1 and alpha2 power may be a manifestation of a top-down mechanism revealing control over the execution of a response. The area-specific, task-related, and frequency-dependent changes of EEG complexity measures indicate frontally increasing complexity during the early part of the CNV in the beta frequency bands, which underscores the importance of this region in the mechanisms of anticipatory behavior.

Partial discharges in a cavity at variable applied frequency part 2: measurements and modeling

In this paper partial discharges (PD) in a disc-shaped cavity are measured at variable frequency (0.01 - 100 Hz) of the applied voltage. The measured PD phase and magnitude distributions, as well as the number of PDs per voltage cycle, changed with the varying frequency. A charge consistent model is presented and used to dynamically simulate the sequence of PDs in the cavity. The simulation results show that the properties of the cavity surface, mainly the surface conductivity and the surface emission of electrons, change with the varying applied frequency. This is interpreted as an effect of the difference in time between consecutive PDs at different applied frequencies. This is the second of two papers addressing the frequency dependence of PD in a cavity. The first paper described how the PD frequency dependence changes with the applied voltage amplitude, the cavity size and the cavity location.

Counterpoint: Lung Impedance Measurements are not More Useful than Simpler Measurements of Lung Function in Animal Models of Pulmonary Disease

Counterpoint: Lung Impedance Measurements are not More Useful than Simpler Measurements of Lung Function in Animal Models of Pulmonary Disease

Frequency-dependent changes in absolute hearing threshold caused by perception of a previous sound

This study investigated effects of a previous sound presentation at the absolute threshold of hearing. Changes in threshold were measured when a pure tone at 60 dB SPL preceded a test tone in the contra- or ipsilateral ear. When the previous and test sounds both had the same frequency of 500 Hz, threshold decreased approximately 2 dB in the contralateral ear, and increased slightly in the ipsilateral ear. On the other hand, when the frequency of the previous sound differed from that of the test sound, the threshold was decreased slightly in the ipsilateral ear.

Amplitude- and Frequency-Dependent Changes in Neuronal Regularity Parallel Changes in Tremor With Thalamic Deep Brain Stimulation

The mechanisms by which deep brain stimulation (DBS) alleviates tremor remain unclear, but successful treatment can be achieved with properly selected frequency and amplitude. The clinical tremor response to thalamic DBS for essential tremor is dependent on the stimulation frequency and amplitude, and for high frequencies (> or = 90 Hz), increasing amplitude suppressed tremor, whereas for low frequencies (< 60 Hz), increasing amplitude aggravated tremor. We studied the effects of stimulation frequency and amplitude on the output of a population of intrinsically active model neurons to test the hypothesis that regularization of neuronal firing patterns is responsible for the clinical effectiveness of DBS. The firing patterns of model thalamocortical neurons were dependent on stimulation frequency and amplitude in a manner similar to the clinical tremor response. Above a critical frequency, increasing amplitude reduced the coefficient of variation (CV) of the neuronal firing pattern, whereas for low frequencies, increasing the amplitude increased the CV of neuronal activity. The correlation between the changes in tremor and the changes in the CV of neuronal firing supports the hypothesis that regularization of neuronal firing pattern during DBS is one of the mechanisms underlying the suppression of tremor.

Modulated charge separation at tetraphenyl porphyrin/Au interfaces

A frequency and temperature dependent change of the sign of modulated surface photovoltage signals from metal-free tetraphenyl porphyrin (H2TPP)∕Au junctions has been observed. The sign of the modulated photovoltage signal could be switched by using continuous (bias) illumination, while the sign depends on the wavelength of the bias light. The light induced modulation of the negative and positive charges in the H2TTP layer can be interpreted in terms of internal photoemission of electrons from Au into H2TTP and of hole escape after exciton dissociation at the H2TPP∕Au junction.

Time-dependent density-matrix-functional theory

Although good progress has been made in the calculation of correlation energies from total energy expressions which are implicit functionals of the one-particle reduced density matrix, and explicit functionals of the natural orbitals (NOs) and their occupation numbers, a formulation of the calculation of excitation energies in this so-called density-matrix-functional theory (DMFT) is still lacking. In this paper we propose a time-dependent density-matrix- functional theory (TDDMFT). It is based on the equation of motion (EOM) for the 1-matrix P(s) (t) in the representation of the stationary NOs. In the final form of the EOM, the rate of change of the P(s) (t), P(s) (t) t, is determined by the commutator of the generalized time-dependent Fock matrix F(s) (t) with P(s) (t) plus an additional term D(s) (t). The matrix F(s) (t) determines the evolution of the NOs in the time-dependent one-electron Schrodinger equations, while D(s) (t) determines the time evolution of the NO occupations. With the neglect of the electron Coulomb correlation, the time-dependent one-electron equations for the NOs reduce to those for the Hartree-Fock (HF) orbitals of time-dependent HF (TDHF) theory. The coupled-perturbed equations of TDDMF response theory (TDDMFRT) are derived for the linear response of the 1-matrix δ P(s) (t) to a time-dependent perturbation δ vext (t) of the external potential. The frequency-dependent changes δ P (s), ij (ω) and δ P (s), kl (ω) are coupled through the coupling matrix Kijkl (ω), which is produced with the derivatives of F(s) (t) and D(s) (t) with respect to Pkl (t′). Based on the response equations, TDDMFRT eigenvalue equations are derived for the electron excitations ωq. © 2007 The American Physical Society.