Low-frequency Modulation Research Articles

The origins of the eastern meridian system

There is no doubt that the mechanical effect on the so-called bioactive points and areas may be extremely useful and leads sometimes to a complete cure for various ailments. The existence and benefits of a reflex therapy are absolutely indisputable. Indeed, from ancient times to the present, the unique experience and empirical knowledge about the meridians connecting the points of influence and the skin with all body systems have been accumulated in the depths of Eastern medicine. Until now, the physical nature of the meridians is unknown and has not been explained by anyone, that’s why the reflex therapy stands apart from standard medicine and is practiced as a semi-legal occupation, despite its obvious benefits and effectiveness. In this paper, an attempt was made to reveal the physical nature of the meridians and, thereby, legalize this ancient and extremely necessary discipline. The authors propose a coherent hypothesis, the main idea of which is the statement that if there is even a slightest wound, the nervous system will immediately send the impulse to increase the blood supply to this spot, in other words, a special address appears, the fresh blood directs that way and causes the healing. The mechanism of redistribution of blood flow is that there is a certain low-frequency modulation of the heart rate, which leads to a local increase in blood flow, as impact zones are characterized by certain reductions in time with the modulations. The corresponding organ in the body also has a similar address (i.e. a certain frequency), and therefore an intensified blood flow rushes there too, providing a vital effect on this organ. As a result, the supported organ more effectively fights the disease. This, in short, is the mechanism of recovery that nature has in place in the presence of heart rhythm modulations that can be made manageable. Naturally, by saturating the blood with exposure agents, we will obtain an increase in their effectiveness due to local penetration directly into the painful area.

Low-frequency unsteadiness in the flow around a square cylinder with critical angle of [formula omitted] at the Reynolds number of [formula omitted

Numerical simulations with high grid resolutions are conducted to investigate the flow past a square cylinder at the Reynolds number of 2.2×104 and the critical angle of attack of 14°. The focus is on the unsteadiness with a much lower frequency than that of von Karman vortex shedding. This study confirms the existence of low-frequency unsteadiness even for the square cylinder. The qualitative and quantitative features of low-frequency unsteadiness are systematically analyzed in terms of forces, vortex shedding and separation bubble. The low frequency with the outstanding peak is much lower than the frequency of von Karman vortex shedding; specifically, it is about 0.14fvK, where fvK is the vortex-shedding frequency. The low-frequency unsteadiness can be “felt” in the time series of forces and in the dynamics of vortex shedding and separation bubble. For both drag and lift, the unsteadiness is manifested by the low-frequency modulation of force amplitude and by the low-frequency periodic variation between the high and low values of the mean drag and lift over a vortex shedding cycle. The smaller force amplitude is accompanied simultaneously by the vortex shedding with longer formation length and weaker spanwise correlation, together with longer separation bubble on the flow-reattachment side of the cylinder.

Modelado numérico de las oscilaciones frontales y ocurrencia de formación de diques de hielo del Glaciar Perito Moreno, Campo de Hielo Patagónico Sur

En el presente estudio, se aborda el diseño y desarrollo de un modelo numérico computacional del comportamiento del ciclo oscilatorio estacional de avance y retroceso del glaciar Perito Moreno, denominado MO-ACAR. Dentro de su comportamiento oscilatorio, en algunos años el glaciar avanza y alcanza la Península de Magallanes formando un dique de hielo. Por ello, el objetivo del MO-ACAR es simular la posición frontal diaria del glaciar y la ocurrencia de eventos de formación de los diques de hielo durante el periodo 1994-2018. El modelo fue calibrado y validado a partir de un proceso de optimización iterativo, basado en la maximización de valores de correlación y minimización de errores de distancia. La simulación de la ocurrencia de la formación de diques de hielo y la oscilación de la posición frontal lograron altas prestaciones, alcanzando óptimos valores de correlación (0,99) y bajos errores de posición (9,56 ± 13,94 m), respectivamente. Los resultados demuestran que la dinámica del glaciar y la formación de los diques de hielo responden a distintas escalas temporales. En periodos cortos-intermedios de tiempo (escalas diarias-estacionales), la ocurrencia depende tanto de las características propias del evento, como de la fase e intensidad del evento previo. En periodos prolongados (escalas mayores a un año), la modulación de baja frecuencia de la velocidad del flujo de hielo, provocada por las variaciones de temperatura del aire, controla los periodos con formación de diques de hielo y libres de éstos.

Three-dimensional Fourier ghost imaging

Time-of-flight (TOF) three-dimensional (3D) imaging is an effective means for remote sensing and target recognition. Fourier ghost imaging (GI) acquires the Fourier spectrum first, then applies an inverse Fourier transform (IFT) to retrieve the image of interest. The Fourier spectrum can be artificially processed when needed. The Fourier spectrum of some partially transmissive occluders is generally concentrated in high-frequency regions. These occluders can be removed by applying an IFT using the low-frequency spectrum coverage. This strategy is innovative in TOF 3D GI. In a TOF 3D GI system with DMDs, the high repetition rate and short-pulse laser is generally employed, which is mismatched with the lower modulation frequency of grayscale patterns. The grayscale Fourier patterns are decomposed into binary patterns. The detected intensities corresponding to the binary patterns are multiplied by the corresponding weighted coefficients, and are summed to form the Fourier spectrum slices at different distances. Then, an IFT is applied to retrieve the image cubes, furtherly to obtain the depth maps with the image cubes. Two 3D experiments are carried out to evaluate the proposed technique. The results indicate the reflectivity and depth maps can reveal the information of the 3D objects under 25 % spectrum coverage. From an imaging experiment through a partially transmissive occluder, we we find the reflectivity and the depth map obtained by the low-frequency Fourier spectral coverage are significantly better than those obtained reconstructions with complete spectral coverage. These preliminary results indicate TOF 3D Fourier GI has potential advantages in the removal of netting.

Using Gated Recurrent Units for Selective Harmonic Current Mitigation-PWM in Grid-Tied Cascaded H-Bridge Converters

Grid-tied converters become more popular for electric vehicle, renewable energy, and energy storage systems applications. Different modulation techniques such as low-frequency (e.g., selective harmonic elimination-PWM, selective harmonic mitigation-PWM, and selective harmonic current mitigation-PWM (SHCM-PWM)) and high-frequency modulation techniques (e.g., phase shift-PWM and space vector modulation) are used in the literature for grid-tied converters. Low-frequency modulation techniques have a high-efficiency due to the low-switching power losses. One of the main challenges of low-frequency modulation techniques such as SHCM-PWM is how to implement the proposed technique in real-time, due to the transcendental Fourier equations of SHCM-PWM. In this paper, a deep learning technique (i.e., gated recurrent units) is adopted to implement the SHCM-PWM technique in real-time. To evaluate the effectiveness of the proposed learning-based technique, both simulation and experiments are performed for a single-phase 3-cell 7-level CHB converter.

Controlled Chemistry via Contactless Manipulation and Merging of Droplets in an Acoustic Levitator.

A unique, versatile, and material-independent approach to manipulate contactlessly and merge two chemically distinct droplets suspended in an acoustic levitator is reported. Large-amplitude axial oscillations are induced in the top droplet by low-frequency amplitude modulation of the ultrasonic carrier wave, which causes the top sample to merge with the sample in the pressure minimum below. The levitator is enclosed within a pressure-compatible process chamber to enable control of the environmental conditions. The merging technique permits precise control of the substances affecting the chemical reactions, the sample temperature, the volumes of the liquid reactants down to the picoliter range, and the mixing locations in space and time. The performance of this approach is demonstrated by merging droplets of water (H2O) and ethanol (C2H5OH), conducting an acid-base reaction between aqueous droplets of sodium hydroxycarbonate (NaHCO3) and acetic acid (CH3COOH), the hypergolic explosion produced via merging a droplet of an ionic liquid with nitric acid (HNO3), and the coalescence of a solid particle (CuSO4·5H2O) and a water droplet followed by dehydration using a carbon dioxide laser. The physical and chemical changes produced by the merging are traced in real time via complementary Raman, Fourier-transform infrared, and ultraviolet-visible spectroscopies. The concept of the contactless manipulation of liquid droplets and solid particles may fundamentally change how scientists control and study chemical reactions relevant to, for example, combustion systems, material sciences, medicinal chemistry, planetary sciences, and biochemistry.

Single phase 21 level hybrid multilevel inverter with reduced power components employing low frequency modulation technique

This paper introduces a new hybrid topology of multilevel inverter capable of generating 21-level output voltage. The proposed topology is built using the combination of cross-switched bridge and a conventional full H-bridge. Compared to the conventional topologies and other hybrid topologies, the newly introduced multilevel inverter has the ability to maximize the number of voltage levels utilizing lower number of DC voltage sources, integrated bipolar transistor (IGBT) switches and gate drivers. A low frequency modulation technique is used to generate the ideal multilevel output voltage and gate pulses. Furthermore, the proposed topology is validated by building a hardware prototype and obtaining relevant experimental results. The acquired simulated and experimental results indicate the proper functioning of the proposed hybrid topology along with the compatibility of the applied modulation technique. Normal 0 false false false MS X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman",serif;}

Imaging Single Bacterial Cells with Electro-optical Impedance Microscopy.

Impedance measurements have been an important tool for biosensor applications, including protein detection, DNA quantification, and cell study. We present here an electro-optical impedance microscopy (EIM) based on the dependence of surface optical transmission on local surface charge density for single bacteria impedance imaging. We applied a potential modulation to bacteria placed on an indium tin oxide-coated slide and simultaneously recorded a sequence of transmitted microscopy images. By performing fast Fourier transform analysis on the image sequences, we obtained the DC component (signal at 0 Hz) for cell morphology imaging and the AC component (signal at the modulation frequency) for the mapping of cell impedance responses with subcellular resolution for the first time. Using this method, we have monitored the viability of Escherichia coli bacterial cells under treatment with two different classes of antibiotics with low-frequency potential modulation. The results showed that the impedance response is sensitive to the antibiotic that targets the bacterial cell membrane as the membrane capacitance dominated at low-frequency modulation. Heterogeneous responses to the antibiotic treatment were observed at a single bacteria level. In addition to the high spatial resolution, EIM is label-free and simple and can be potentially used for the continuous mapping of single bacteria impedance changes under different conditions.

Multilevel inverter with improved basic unit structure for symmetric and asymmetric source configuration

An improved multilevel inverter (MLI) topology using a new basic unit structure with a reduced number of components is proposed in this study. Its single compact module is made up of two basic units connected to the left and right sides of a packed H-bridge. The topology produces 9-Level output when operated symmetrically and 17-Level output when operated asymmetrically. Identical magnitude of DC sources is used for the symmetrical operation, while non-identical magnitudes in a trinary sequence are used for the asymmetrical operation. The low-frequency modulation scheme is applied for the switching control where the switching angles are pre-calculated. The mathematical formulations for the switching are also considered to reduce the total harmonic distortion (THD) at the output. The proposed topology is also found to be superior in terms of the required number of switches per output level and total blocking voltage compared to conventional and recently reported MLIs. With these merits, real-time installation of the proposed topology will potentially require lesser space and become cheaper. The feasibility of the proposed topology is validated for its 9-Level and 17-Level operations through experimental verification on output characteristics, THD, blocking voltage, power-sharing and efficiency.

Ultrastrong Jaynes-Cummings model

We propose a reliable scheme to realize the ultrastrong Jaynes-Cummings (JC) model by simultaneously modulating the resonance frequencies of the two-level system and the bosonic mode in the ultrastrong quantum Rabi model. We find that in both the high- and low-frequency modulation regimes, the counter-rotating terms can be completely suppressed without reducing the coupling strength of the rotating-wave terms, and hence the ultrastrong JC Hamiltonian is achieved. The ultrastrong JC interaction can not only be used to implement ultrafast quantum operations, but also will open up a new route to the demonstration of quantum phase transition associated with the JC Hamiltonian across the deep-strong coupling point. Some discussions on the experimental implementation of this scheme with circuit-QED systems are presented.

Lightness induction enhancements and limitations at low frequency modulations across a variety of stimulus contexts.

Lightness illusions are often studied under static viewing conditions with figures varying in geometric design, containing different types of perceptual grouping and figure-ground cues. A few studies have explored the perception of lightness induction while modulating lightness illusions continuously in time, where changes in perceived lightness are often linked to the temporal modulation frequency, up to around 2–4 Hz. These findings support the concept of a cut-off frequency for lightness induction. However, another critical change (enhancement) in the magnitude of perceived lightness during slower temporal modulation conditions has not been addressed in previous temporal modulation studies. Moreover, it remains unclear whether this critical change applies to a variety of lightness illusion stimuli, and the degree to which different stimulus configurations can demonstrate enhanced lightness induction in low modulation frequencies. Therefore, we measured lightness induction strength by having participants cancel out any perceived modulation in lightness detected over time within a central target region, while the surrounding context, which ultimately drives the lightness illusion, was viewed in a static state or modulated continuously in time over a low frequency range (0.25–2 Hz). In general, lightness induction decreased as temporal modulation frequency was increased, with the strongest perceived lightness induction occurring at lower modulation frequencies for visual illusions with strong grouping and figure-ground cues. When compared to static viewing conditions, we found that slow continuous surround modulation induces a strong and significant increase in perceived lightness for multiple types of lightness induction stimuli. Stimuli with perceptually ambiguous grouping and figure-ground cues showed weaker effects of slow modulation lightness enhancement. Our results demonstrate that, in addition to the existence of a cut-off frequency, an additional critical temporal modulation frequency of lightness induction exists (0.25–0.5 Hz), which instead maximally enhances lightness induction and seems to be contingent upon the prevalence of figure-ground and grouping organization.

A Displacement Measuring Interferometer Based on a Frequency-Locked Laser Diode with High Modulation Frequency

Laser interferometers can achieve a nanometer-order uncertainty of measurements when their frequencies are locked to the reference frequencies of the atom or molecule transitions. There are three types of displacement-measuring interferometers: homodyne, heterodyne, and frequency modulation (FM) interferometers. Among these types of interferometer, the FM interferometer has many advantageous features. The interference signal is a series of time-dependent harmonics of modulation frequency, so the phase shift can be detected accurately using the synchronous detection method. Moreover, the FM interferometer is the most suitable for combination with a frequency-locked laser because both require frequency modulation. In previous research, low modulation frequencies at some tens of kHz have been used to lock the frequency of laser diodes (LDs). The low modulation frequency for the laser source means that the maximum measurement speed of the FM interferometers is limited. This paper proposes a novel contribution regarding the application of a high-frequency modulation for an LD to improve both the frequency stability of the laser source and the measurement speed of the FM interferometer. The frequency of the LD was locked to an I2 hyperfine component at 1 MHz modulation frequency. A high bandwidth lock-in amplifier was utilized to detect the saturated absorption signals of the I2 hyperfine structure and induce the signal to lock the frequency of the LD. The locked LD was then used for an FM displacement measuring interferometer. Moreover, a suitable modulation amplitude that affected the signal-to-noise ratio of both the I2 absorption signal and the harmonic intensity of the interference signal was determined. In order to verify the measurement resolution of the proposed interferometer, the displacement induced by a piezo electric actuator was concurrently measured by the interferometer and a capacitive sensor. The difference of the displacement results was less than 20 nm. To evaluate the measurement speed, the interferometer was used to measure the axial error of a high-speed spindle at 500 rpm. The main conclusion of this study is that a stable displacement interferometer with high accuracy and a high measurement speed can be achieved using an LD frequency locked to an I2 hyperfine transition at a high modulation frequency.

Large signal analysis of multiple quantum well transistor laser: Investigation of imbalanced carrier and photon density distribution

In this paper, we present a large-signal and switching analysis for the Heterojunction Bipolar Transistor Laser (HBTL) to reveal its optical and electrical behavior under high current injection conditions. Utilizing appropriate models for carrier transport, nonlinear optical gain, and optical confinement factor, we have simulated the large-signal response of the HBTL in relatively low and high modulation frequencies. Our results predict that for multiple quantum well (MQW) structures at low frequencies, there should not be a difference in either the carrier density or the photon density. However, the carrier concentration can be differently distributed between subsequent wells in the case of a high speed yet large-signal input. This leads to increased linewidth instead as it depends on ΔNqw. We show the effect of different structural parameters on the switching behavior by performing a switching analysis of the single quantum well and MQW structures using computationally efficient numerical methods. A set of coupled rate equations are solved to investigate the large-signal and switching behavior of MQW-HBTL. Finally, to have a comprehensive judgment about this optoelectronic device, we introduce a relative performance factor taking into account all the optoelectronic characteristics such as the output power, ac current gain, modulation bandwidth, and base threshold current, as well as turn-on time in order to design a suitable TL for optoelectronic integrated circuits.

The music of marine seismic: A marine vibrator system based on folded surfaces

Marine vibrators have bespoke geophysical benefits that are yet to be harnessed because of robustness and efficiency issues. We have developed a new marine vibrator source technology that is efficient and stable. The source technology overcomes the historical problems of inefficiency and robustness by using folded surface technology and resonance frequency tuning. We show measured output examples that demonstrate that the folded surface concept combined with small displacements can provide the required output levels. Our source system consists of a low-frequency module covering 1–10 Hz and a high-frequency module covering 10–125 Hz. The source control system has shown high stability and precision and can handle harmonic distortion. With the aid of synthetic data examples, we demonstrate that seismic data acquired using marine vibrators in either intermittent or continuous mode can be processed. Finally, we demonstrate the environmental friendliness of the source in comparison to air gun-based sources.

Space-time modulation of turbulence in co-flow jets

This paper focuses on the effects of a space-time dependent periodic stirring of a moderately turbulent planar co-flow jet configuration. The baseline flow is agitated in time and in space by small-scale turbulent perturbations in combination with large-scale modulation imposed at the inflow plane of a rectangular domain of size L × L × 2L in the x, y and z directions respectively. The prescribed large-scale modulation is characterized by a single modulation frequency ω and modulation wave-number, K. A parametric study at different modulation frequencies and wave-numbers is performed. We evaluate the system response to the external agitation in terms of key dynamic properties of the flow, e.g., the total kinetic energy ET, the global averaged dissipation rate and additional flow mixing properties. For low modulation frequencies, e.g., ω=0.5ω0, where ω0 is the large scale-turn over frequency, ω0=U1/D, with U1 and D being relevant velocity and length scales, and at given wave-number K, we observe that ET follows the imposed oscillation with a periodic amplitude response that is sustained at locations further from the inflow plane, whereas for higher frequencies, the response amplitude rapidly decays. Results of the global dissipation rate show the development of a definite maximum value of the response amplitude at frequencies on the order of ω0 for any modulation wave-number K. To investigate in more detail the effects of modulated turbulence on the jet mixing properties, a passive scalar was injected at the inflow plane. The spreading of the scalar surface in the agitated jet was monitored for a wide range of modulation frequencies. In general, results show enhanced mixing efficiency when the main jet is modulated at frequencies near ω0 and low K values.

Current-Modulation-Based On-Line Resonance Tuning Strategy for Linear Generator Drives

Linear generators (LGs) are frequently used for energy harvesting with free-piston Stirling engines, thermoacoustic engines, and wave energy converters. This article presents a control strategy to track and maintain LG resonance conditions in real time. The algorithm is based on the LG response to a low-frequency amplitude modulation of the current component in phase with the instantaneous position (d-axis). The averaged product of modulated air-gap power and modulation signal is fed into a controller to adjust the d-axis current and restore resonance. The use of air-gap power instead of dc power improves resonance tracking accuracy and eliminates steady-state low-frequency stroke oscillations. This article presents a full theoretical analysis providing accurate steady-state and small-signal models for control synthesis. The broad experimental validation included in the article proves that the control is able to restore resonance even when the force-source introduces significant additional mechanical impedance.

Generation of Noiselike Microwave Signals in Microband Antenna Generators

Abstract—The study investigates the possibility of generating noiselike signals in the centimeter wavelength range using antenna generators built on a log-periodic microstrip antenna integrated with a field-effect transistor. The conditions for the occurrence of noiselike generation are experimentally determined. The possibility of expanding the noiselike spectrum using low-frequency noise modulation is studied. Noiselike generation was experimentally obtained in the centimeter wavelength range with a spectral width of up to 2 GHz.

Wideband detection of electromagnetic signals by high-Tc Josephson junctions with comparable Josephson and thermal energies

Detection mechanisms in Josephson junctions with energies Ej comparable to thermal energies kT have been studied. The responses ΔV of YBa2Cu3O7−x bicrystal junctions to monochromatic radiation with frequencies f ranging from 94 GHz to 3.1 THz can be described in terms of classical rectification on a static nonlinear V–I curve at low frequencies and frequency modulation of the ac Josephson current at high frequencies, with an interplay between these mechanisms at intermediate frequencies. An electrical noise-equivalent power of (9 ± 3) × 10−15 W/Hz1/2, a responsivity of (3.4 ± 0.5) × 105 V/W, and a dynamic power range of 5 × 104 have been demonstrated for the square-law classical detection of 94 GHz radiation with the junctions at 50 K. The effect of background radiation on the V–I curves of YBa2Cu3O7−x bicrystal junctions was found to have an optical noise-equivalent temperature of ≤30 mK/Hz1/2. The main contribution to the effect comes from the interplay between the classical and Josephson detection mechanisms. The spectral and power dependencies of the responses ΔV of Josephson junctions have been numerically simulated within the resistively shunted junction model at various values of kT/Ej, and the results are in acceptable agreement with the experimental data.

Modeling and performance evaluation of in-line Fabry-Perot photothermal gas sensors with hollow-core optical fibers.

We study photothermal phase modulation in gas-filled hollow-core optical fibers with differential structural dimensions and attempt to develop highly sensitive practical gas sensors with an in-line Fabry-Perot interferometer for detection of the phase modulation. Analytical formulations based on a hollow-capillary model are developed to estimate the amplitude of photothermal phase modulation at low modulation frequencies as well as the -3 dB roll-off frequency, which provide a guide for the selection of hollow-core fibers and the pump modulation frequencies to maximize photothermal phase modulation. Numerical simulation with the capillary model and experiments with two types of hollow-core fibers support the analytical formulations. Further experiments with an Fabry-Perot interferometer made of 5.5-cm-long anti-resonant hollow-core fiber demonstrated ultra-sensitive gas detection with a noise-equivalent-absorption coefficient of 2.3×10-9 cm-1, unprecedented dynamic range of 4.3×106 and <2.5% instability over a period of 24 hours.

Regulation of heat transfer in Rayleigh–Bénard convection in Newtonian liquids and Newtonian nanoliquids using gravity, boundary temperature and rotational modulations

The individual effect of time-periodic gravity modulation, in-phase and out-of-phase temperature modulations and rotational modulation on Rayleigh–Benard convection in twenty-eight nanoliquids is studied in the paper using the two-phase description of the generalized Buongiorno model. The generalized Lorenz model for each modulation problem is derived using the truncated Fourier series representation. The method of multiscales is employed to arrive at the Ginzburg–Landau equations from the Lorenz models, and the solution of Ginzburg–Landau equations is used to quantify the heat transport. The modulation amplitude is considered to be small (of order less than unity) and low frequencies of modulation are considered. The coefficient of the linear term of the algebraic part of the Ginzburg–Landau equations is shown to exclusively hold the information on the amplitude and the frequency of modulation. The influence of nanoparticles (nanotubes) on heat transport in the presence/absence of various modulations is explained. The study reveals that the frequency of modulation is a dominant factor in the case of gravity and rotational modulations whereas in the case of boundary temperature modulation in addition to the frequency of modulation, the phase difference plays an important role. Effect of these three modulations is to enhance/diminish heat transport but depends strongly on the choice of values of frequency of modulation and amplitude. For fixed values of frequency ( $$\omega ^*=5$$ ) and amplitude ( $$\delta _2=0.1$$ ) of various modulations, it is shown that the maximum percentage of heat transport enhancement achieved in glycerin due to 5% of $$\hbox {SWCNTs}$$ is 21.86% for gravity modulation, 17.36% for rotational modulation and 15.63% for boundary temperature modulation (out of phase). The reason for highest heat transport in gravity modulation is explained by finding area under the curves of three modulations. The study reveals that the modulation whose area under the curve is maximum transports maximum heat. The results pertaining to the single-phase model are recovered as a limiting case of the present study. The study shows that the single-phase model under-predicts heat transport compared to the two-phase model. The results obtained in the present study are compared with those of previous investigations and qualitatively good agreement is found.