Specific Frequency Values Research Articles

High-resolution local seismic zonation by cluster and correlation analysis

Site response analysis is essential for seismic hazard and risk assessment and for providing useful data for land-use planning. However, current regional site amplification models do not always have the resolution required for sites such as alpine valleys, in which site response is characterized by complex effects. In addition, even in local studies, site response is usually computed at a limited number of sites because it requires the recording of earthquakes through the installation of seismological stations. To spatially extend the site response to a denser grid of points inside the investigated area, we used k-means cluster and correlation analyses and Voronoi tessellation. The method was applied to the evaluation of the site response of the lower Sarca Valley on the northern shore of Lake Garda. Earthquakes were recorded at 19 sites to calculate site response in terms of amplification and duration functions of ground motion. The results show high amplification values (up to 10) at low frequencies (at about 0.7 Hz) in the center of the valley, where the sediments reach a thickness of about 420 m. Moderate amplification values and duration lengthening of several seconds in the range of 1–10 Hz are found instead at the edge of the valley on the sedimentary deposits, while a lack of amplification is observed for the sites located on the bedrock. Both the amplification and duration functions were assigned to the area covered by the single-station noise measurements to obtain a zonation of the study area, resulting in three zones to which Fourier amplification factors can be assigned for specific frequency values. The results obtained can be used directly for hazard and risk scenarios and to improve regional maps with lower resolution at the local level.

Experimental study on the irreversible displacement evolution and energy dissipation characteristics of disturbance instability of regular joints

AbstractTo investigate the disturbance‐induced shear instability mechanism of structural catastrophe in the deep rock mass, MTS 815 material testing machine was used to carry out quasi‐static loading tests and disturbance shear tests on symmetrical regular dentate joints of two materials at three undulation angles under specific initial static stress, disturbance frequency, and peak value. The test results indicate that: (i) the total ultimate instability displacement is only related to the intrinsic properties of the joints but not to the initial static stress and disturbance parameters; (ii) the cumulative irreversible displacement required for the disturbance instability conforms to the logistic inverse function relationship with the number of disturbances, displaying the variation trend of “rapid increase in the front, stable in the middle, and sudden increase in the rear”; (iii) the accumulation of plastic deformation energy is consistent with the evolution law of irreversible displacement of joints and the overall proportion of hysteretic energy is not large; (iv) the dissipated energy required for the instability of each group of joints is basically the same under various disturbance conditions, and this energy is mainly controlled by the initial shear stress and has no connection with the disturbance parameters. The stability of the total disturbance deformation and the disturbance energy law of the joints revealed in the tests provide data support for reasonably determining the disturbance instability criterion of joints.

NiCoP selenization for enhanced oxygen evolution reaction in alkaline electrolyte

The electrocatalytic performance of bimetallic NiCo phosphide for oxygen evolution can be boosted via facile selenization by forming a crystal structure of metal phosphide and metal selenide. In the alkaline electrolyte, small overpotentials of 280 mV to drive 10 mA cm−2 were required, much smaller than that of NiCo phosphide and NiCo precursor. The improved performance was attributed to the increased electrochemical surface area that exposed more active sites. The high electrocatalytic efficiency of the active sites was also in line with the enhanced specific activity and turnover frequency values. In addition, high catalytic stability was also observed.

Manufacturing a Biomimetic Biorecator in Cardiac Tissue Engineering

Introduction: The direct approach of cardiac tissue engineering is to mimic the natural tissue of heart, considering the significant role of scaffolding and mechanical simulation. Methods: To achieve this purpose, a composite Polycaprolactone (PCL)/Gelatin electrospun scaffold with a ratio of 70:30 and with the most similarities to the cardiac extracellular matrix was fabricated with aligned nanofibers. The scaffold was evaluated using scanning electron microscopy (SEM), mechanical strength analysis, and contact angle test. To simulate the cardiac contraction, a developed Mechanical Loading Device (Bioreactor) was designed to apply a mechanical load with a specific frequency and tensile rate values in the direction of aligned nanofibers due to simulating natural cardiac tissue. Results: Based on our results from the contact angle and mechanical strength tests, we concluded that our designed scaffold has appropriate adhesion and strength to use as cardiac scaffold and is suitable for imposing the frequency of 1Hz and 10% strain. The Bioreactor also worked properly in producing the required frequency, tensile rate and temperature. Conclusion: Since an essential difference between cardiomyocytes and other cells is their contraction, manufacturing a biomimetic bioreactor to simulate the normal cardiac contraction of cardiomyocytes and their required temperature to be survived in-vitro could be a promising approach in cardiac tissue engineering.

Calculation of overhead and underground cable parameters at harmonic frequencies

This paper presents a new method for the comprehensive calculation of power cable parameters at the fundamental and harmonic frequencies and for the assessment of the power cable’s frequency responses. In spite of its growing technical importance, there seem to be very little information in the open literature about resonances in power cables, particularly, when it comes to the so-called supra-harmonic frequencies, which lie in the range 2–150 kHz. At harmonic frequencies, various phenomena, such as skin effect, ground and metallic return loops, a strong capacitive effect, long-line effects, geometric imbalances and cable cross-bonding have all a marked influence on the responses of both overhead and underground cables. The cable resistances and inductances vary in a nonlinear fashion with frequency, and the latter will cancel out with the cables’ capacitive effects at some specific frequency values giving rise to alternate resonant points along the frequency spectrum. All the relevant construction details of the cable together with its electrical and operational parameters need to be processed by suitable models and methods coded into software for the fast and accurate calculations of the frequency responses of the power cables. A computer program has been developed as part of this research, using the formula and methods outlined in the paper. The usefulness and accuracy of the new methodology are demonstrated by resorting to numerical examples.

DA-DA Dönüştürücü Devreleri için Çeşitli İndüktör Nüve Şekillerinin Elektromanyetik ve Mekanik Etkileri Üzerine Karşılaştırmalı Bir Benzetim

DC-DC power electronics converters are used in many applications such as electrical vehicles, energy storage systems, renewable energy sources. The inductors designed for a specific frequency and current level have significant impact on converter performance. In this study, an inductor is designed for a specific frequency and current value with some common core geometric structures called EE, block, pot and toroidal. Since inductors operate at high frequency values, the Kool-Mu which is a kind of powder core is selected. The Kool-Mu has distributed homogeneous air gaps and is used in inductor designs that saturation is not desired. Inductors are designed for EE core, toroidal core, pot core and block core structures. Electromagnetic modelling of these inductors designed for different core structures are carried out with finite element analysis (FEA), and inductance stability, core and winding losses, mechanical specifications and flux distributions have been reported comparatively. In addition, some suggestions are derived in core structure definitions for DC-DC converter inductor design.

Kinematics optimization of the polishing process of large-sized ceramic slabs

Although large-sized ceramic slabs have become a common market product nowadays, their finishing processes still lack proper analyses and optimizations. The finishing is carried out on energy-consuming polishing machines by a train of rotating abrasive heads, which oscillates in a transverse direction on translating slabs. In this paper, a computational method able to investigate the effect of the kinematics on the texture distribution is proposed. Its algorithms allow to map the number of contacts and the scratching angles, relevant factors in the definition of the polished surface quality, but also, differently from the previous studies, the easy use of any preferred law of motion. After validation, the method is applied to a traditional polishing machine in order to assess the optimal process parameters as the forward motion of the conveyor belt and the transverse oscillation of the beam carrying the rotating head with the fickerts. An enhancement in terms of surface quality and machining process is evident. In particular, results suggest to adopt a specific frequency value for the transverse motion, nearly the half of the original one: in spite of a very similar texture, a significant reduction of energy is permitted. Finally, the optimization of motions and processes may lead to other general benefits, such as a reduction of the tool wear and mitigation of possible issues as mechanical vibrations or noise.

The survey of planetary nebulae in Andromeda (M 31)

Context.The Andromeda (M 31) galaxy subtends nearly 100 square degrees on the sky. Any study of its halo must therefore account for the severe contamination from the Milky Way halo stars whose surface density displays a steep gradient across the entire M 31 field of view.Aims.Our goal is to identify a population of stars firmly associated with the M 31 galaxy. Planetary nebulae (PNe) are one such population that are excellent tracers of light, chemistry, and motion in galaxies. We present a 16 square degree survey of the disc and inner halo of M 31 with the MegaCam wide-field imager at the CFHT to identify PNe, and characterise the luminosity-specific PN number and PN luminosity function (PNLF) in M 31.Methods.PNe were identified via automated detection techniques based on their bright [O III] 5007 Å emission and absence of a continuum. Subsamples of the faint PNe were independently confirmed by matching with resolvedHubbleSpace Telescope sources from the PanchromaticHubbleAndromeda Treasury and spectroscopic follow-up observations with HectoSpec at the MMT.Results.The current survey reaches two magnitudes fainter than the previous most sensitive survey. We thus identify 4289 PNe, of which only 1099 were previously known. By comparing the PN number density with the surface brightness profile of M 31 out to ∼30 kpc along the minor axis, we find that the stellar population in the inner halo has a luminosity-specific PN number value that is seven times higher than that of the disc. We measure the luminosity function of the PN population and find a bright cut-off and a slope consistent with previous determinations. Interestingly, it shows a significant rise at the faint end, present in all radial bins covered by the survey. This rise in the M 31 PNLF is much steeper than that observed for the Magellanic clouds and Milky Way bulge.Conclusions.The significant radial variation of the PN specific frequency value indicates that the stellar population at deprojected minor-axis radii larger than ∼10 kpc is different from that in the disc of M 31. The rise at the faint end of the PNLF is a property of the late phases of the stellar population. M 31 shows two major episodes of star formation and the rise at the faint end of the PNLF is possibly associated with the older stellar population. It may also be a result of varying opacity of the PNe.

Auditory Attention Causes Gain Enhancement and Frequency Sharpening at Successive Stages of Cortical Processing-Evidence from Human Electroencephalography.

Previous findings have suggested that auditory attention causes not only enhancement in neural processing gain, but also sharpening in neural frequency tuning in human auditory cortex. The current study was aimed to reexamine these findings. Specifically, we aimed to investigate whether attentional gain enhancement and frequency sharpening emerge at the same or different processing levels and whether they represent independent or cooperative effects. For that, we examined the pattern of attentional modulation effects on early, sensory-driven cortical auditory-evoked potentials occurring at different latencies. Attention was manipulated using a dichotic listening task and was thus not selectively directed to specific frequency values. Possible attention-related changes in frequency tuning selectivity were measured with an adaptation paradigm. Our results show marked disparities in attention effects between the earlier N1 deflection and the subsequent P2 deflection, with the N1 showing a strong gain enhancement effect, but no sharpening, and the P2 showing clear evidence of sharpening, but no independent gain effect. They suggest that gain enhancement and frequency sharpening represent successive stages of a cooperative attentional modulation mechanism that increases the representational bandwidth of attended versus unattended sounds.

Numerical verification of the dispersion relation of trapezoidally corrugated slow wave structure for backward wave oscillators

The dispersion relation of beam-free trapezoidally corrugated periodic metallic slow wave structure (TCSWS) has been numerically verified using a synthetic technique. The dispersion curves for both the fundamental and the higher order passband modes (TM01–TM03) are computed for an axisymmetric-corrugated structure. The periodic structure resonates at specific frequencies when shorted appropriately at both ends. From the specific frequency values of these resonant peaks, a dispersion curve is determined for each transverse magnetic (TM) mode. The obtained dispersion curve is compared with both the experimental and analytical results using the same number of periods. The comparisons with analytical results and their experimental counterpart agree excellently with a maximum deviation of 1.94% for the TM01 mode, 1.29% for the TM02 mode and 2.38% for the TM03 mode. The radial and longitudinal electromagnetic field patterns of TCSWS are also calculated and compared with analytical field patterns for a six-period slow wave structure. Comparative results validate both the obtained dispersion curves and field patterns of TCSWS.

Carbon supported PdxPty nanoparticles for oxygen reduction. The effect of Pd:Pt ratio

Studies concentrated on the development of carbon supported PdxPty/C electrocatalysts for the oxygen reduction reaction (ORR). The application of the reverse ‘water-in-oil’ microemulsion method allowed to obtain a number of electrocatalysts with metal nanoparticles of ca. 5–6nm in size. Catalysts with the constant metal loading of 10wt% and various Pd:Pt atomic ratios were investigated. The textural features of the PdPt/C catalysts (surface area, morphology) as well as the PdPt phase (metal particle size, bulk composition) were characterized by a number of techniques. A particular attention was paid to the characterization of the surface properties of the PdPt particles using cyclic voltammetry technique. For all Pt contents (5 to 70 at%) a segregation of metal components (Pt, Pd) occurred leading to the Pt enrichment in the top layers. The observed Pt enrichment manifested especially strongly for PdPt catalysts with bulk Pt content below 20 at%. The surface fraction of Pt as high as 0.8 to 0.9 was attained regardless of nominal Pt content, starting from 30 at%. Among the catalysts, those with Pt content of 50 and 70 at% exhibited the highest activity towards ORR in terms of positively shifted half-wave potential, even surpassing that of Pt/C. Moreover, the obtained specific activity and turnover frequency values also suggested similar activities of catalysts with Pt content of 50 and 70 at%. A negligible formation of hydrogen peroxide on these two catalysts, indicated almost exclusively a desired four-electron process leading to water formation. The observed effect of Pt content on ORR activity is discussed in terms of surface properties of the PdPt nanoparticles.

A multisource energy harvesting utilizing highly efficient ferroelectric PMN-PT single crystal

This paper demonstrates a multi-source energy harvester that is able to utilize simultaneously both piezoelectric and pyroelectric effects in lead magnesium niobate-lead titanate (PMN-PT) single crystal. The paper presents a study of PMN-PT single crystal with a (67:33) composition grown in our laboratory via a vertical gradient freeze method without any flux. The performance of the piezoelectric and pyroelectric energy harvester using unimorph device structure was evaluated via modeling and experiment. The theoretical study was implemented based on a distributed parameter electromechanical model and the modelling procedure was approximated using finite element analysis to predict the electromechanical behavior of the harvester. The maximum power density at a resonance frequency of 50 Hz and optimum resistance of 2 MΩ was 16.7 nW/(g2 cm3) under a 1 g acceleration of vibration. The measured values of electrical output parameters were in good agreement with theoretical and modelling results using MATLAB and COMSOL Multiphysics, respectively. By using the pyroelectric effect along with the piezoelectric effect, the output voltage of the energy harvester was found to be enhanced at the optimum resistance and specific frequency values. It was noticed that the output voltage was increased monotonically with temperature-difference (ΔT) and reaches up to 180 % of its original value under temperature difference of 1.7 °C at a frequency value of 49 Hz.

Partial directed coherence statistical performance characteristics in frequency domain.

In this work we show the asymptotic behavior of information partial directed coherence estimator via the Monte Carlo simulation of a particular toy model taken from the literature. We show that the control of false positive rate tends to the chosen significance level if detection decision is made at specific frequency values.

Development of a bilayer ring system for achieving high strain in commercial rheometers

Mechanical stimulation of cell cultures has been shown be an effective means of enhancing ECM production. ECM produced from vocal fold fibroblast cultures has the potential for therapeutic use for vocal fold repair. However, current bioreactor designs generally fail to produce physiological relevant frequency and strain values. Here we present an approach for using commercial oscillatory rheometers and an elastic ring bilayer system to produce physiologically relevant strain values at frequencies in the range of 20–100Hz. We demonstrate the ability to target specific strain and frequency values by manipulating system parameters, and also show that it is possible to maintain high oscillatory strains for extended periods of time. Such a system could be used to mechanically stimulate cell cultures contained within gel carrier systems and has the potential to be extended to other applications requiring high strains at low frequencies.

Enhancing the absorption of graphene in the terahertz range

We study graphene on a photonic crystal operating in the terahertz (THz) spectral range. We show that the absorption of graphene becomes a modulated function of frequency and can be enhanced by more than three times at specific frequency values, depending on the parameters of the system. The problem of a semi-infinite photonic crystal is also solved.

Switching frequency determination of a bidirectional AC–DC converter to improve both power factor and efficiency

This paper investigates the possibility to optimize both the efficiency and the power factor of energy conversion systems which include power electronic converters. The values of these important power quantities depend on different parameters, such as the switching technique and the switching frequency of the power electronic elements. Comparing the already known and used switching techniques with each other we can conclude that the sPWM method offers the highest values of the efficiency and the power factor simultaneously. However, when using this technique the basic current harmonic lags as to the voltage in case of ohmic inductive loads resulting in the decrease in the power factor. In the present work a new sPWM switching technique is suggested in order to achieve higher power factor and efficiency compared to the traditional sPWM method. The aforementioned switching technique is a modified sPWM method based on an appropriate shifting of the input current to the grid voltage. But, the following question is raised: Is there a switching frequency value in a given converter topology by which both the efficiency and the power factor gain optimal value? Thus, the main aim of the present paper is determine this specific switching frequency value. This is achieved by using a simple method based on a criterion suggested in this work. In order to demonstrate how this specific frequency value can be found, a bidirectional AC–DC converter composed of a single phase bridge and two switching elements at the DC side is used. This proposed converter topology excels in that the total number of the switching elements is minimal. The study of this subject is carried out through Matlab/Simulink simulation and experimentation.

Production, Delivery and Application of Vibration Energy in Healthcare

In Rehabilitation Medicine therapeutic application of vibration energy in specific clinical treatments and in sport rehabilitation is being affirmed more and more.Vibration exposure can have positive or negative effects on the human body depending on the features and time of the characterizing wave. The human body is constantly subjected to different kinds of vibrations, inducing bones and muscles to actively modify their structure and metabolism in order to fulfill the required functions. Like every other machine, the body supports only certain vibration energy levels over which long term impairments can be recognized. As shown in literature anyway, short periods of vibration exposure and specific frequency values can determine positive adjustments.

Nanopore membrane-based electrochemical immunoassay

Using nanotechnology in the immunoassay field, Lynntech has developed a nanopore-based sensor with electrochemical signal transduction for the detection of biologically relevant molecular targets. Antibodies of interest were immobilized on the inside wall of nanopores and the antibody–antigen interaction was monitored by measuring the ionic conductance through the nanopores. We have used electrochemical impedance spectroscopy to monitor the changes in the ionic conductance due to the antibody–antigen interaction. To aid the development of a portable, fast immunoassay instrument, we have selected specific impedance frequency values that are very sensitive to the ionic conductance changes. Biomarkers of prostate cancer, prostate-specific antigen and hepsin, were successfully assayed by the nanopore membrane-based electrochemical immunoassay in both phosphate-buffered saline and plasma medium.

NORMAL GLOBULAR CLUSTER SYSTEMS IN MASSIVE LOW SURFACE BRIGHTNESS GALAXIES

We present the results of a study of the globular cluster systems of six massive spiral galaxies, originally cataloged as low surface brightness (LSB) but here shown to span a wide range of surface brightness values, including two intermediate to LSB galaxies. We used the Advanced Camera for Surveys on-board Hubble Space Telescope to obtain photometry in the F475W and F775W bands and select sources with photometric and morphological properties consistent with those of globular clusters. A total of 206 candidates were identified in our target galaxies. From a direct comparison with the Galactic globular cluster system we derive specific frequency values for each galaxy that are in the expected range for late-type galaxies. We show that the globular cluster candidates in all galaxies have properties consistent with globular cluster systems of previously studied galaxies in terms of luminosity, sizes and color. We establish the presence of globular clusters in the two intermediate to LSB galaxies in our sample and show that their properties do not have any significant deviation from the behavior observed in the other sample galaxies, implying that these properties do not evolve with the surface brightness of the galaxies. Our results are broadly consistent with a scenario in which low surface brightness galaxies follow roughly the same evolutionary history as normal (i.e. high surface) brightness galaxies except at a much lower rate, but require the presence of an initial period of star formation intense enough to allow the formation of massive star clusters.

Environment effects on the oscillatory unfolding kinetics of GFP

The chromophore of a green fluorescent protein (GFP) mutant engineered to enhance emission and stability is known to display erratic switchings among a few of its chemical substates and, in particular, between the anionic A and the neutral N substates, whose difference is associated with a proton exchange and a consequent conformation rearrangement. However, when close to unfolding, the A-N switchings suddenly become very regular as shown by fluorescence oscillations that have been recently observed for molecules embedded in wet silica gel. In order to establish whether the matrix hosting the protein is responsible for these oscillations, we investigated the effect of another medium (silanized surfaces), of a different denaturant (urea) and of cosolvents (D(2)O and glycerol). The occurrence of periodic A-N switchings, in the last milliseconds before GFP unfolding, is observed under all investigated conditions, together with three specific frequency values that characterize the pre-unfolding fluorescence. Urea and guanidinium, the denaturants employed in order to unfold GFP, do not lead to appreciable differences in the observed switching parameters, whereas the different media embedding the protein give rise only to frequency shifts that scale with the viscosity of the host. The periodicity of the GFP A-N switchings and their dependence on cosolvents suggest that they could be associated with oscillatory motions between meta-stable conformations of the beta-barrel surrounding the chromophore near protein unfolding.