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In this paper a recess gate AlGaN/GaN HEMT on beta gallium oxide (BGO) is designed and analysed using Silvaco ATLAS TCAD software. The DC and RF performance of the device is compared with a schottky gate AlGaN/GaN HEMT on BGO substrate. For optimizing the gate recess depth, three variations with recess depths 6 nm, 12 nm and 20 nm is also simulated. A highest transconductance of 0.4 mS/ µm is observed for recess gate AlGaN/GaN HEMT on BGO substrate with a recess gate depth of 20 nm with a decrease in current density. The radio frequency performance is also highest for the recess gate AlGaN/GaN HEMT with recess gate depth of 20 nm. The device exhibited a maximum oscillation frequency of 2.6 THZ which is highest till reported.

Online condition monitoring of winding insulation has been proved to be an effective means to improve the reliability of an inverter-fed machine, but little work has been done on the insulation of line-end coil subjected to much higher transient voltage stress with a higher risk of premature insulation break down. In this paper, the inverter self-excited high-frequency switching oscillations are utilized for the line-end coil insulation condition monitoring. To improve the condition monitoring sensitivity and its robustness to dynamic operating conditions, a switching oscillation mode decomposition (SOMD) method is proposed. Firstly, the condition-sensitive mode, i.e. high-frequency common-mode (HFCM) current is selected and separated by the variation mode decomposition (VMD) algorithm among three dominant modes in switching oscillation current. Then, the amplitude-frequency features of HFCM current are extracted for condition monitoring. Finally, the overall insulation condition of three-phase line-end coils and the degree of asymmetric degradation are quantitatively evaluated by the frequency and amplitude features respectively. Experimental work was carried out and the results demonstrate the good performance of high sensitivity, good robustness, and non-contract safety.

In research of the characteristics of the cavity evolution, the pressure, and the liquid spurt in hydrodynamic ram, the experiment of the high-velocity fragment impacting the water-filled container had been conducted. The relationships between the above three characteristics have been researched. The evolution of the cavity can be divided into three processes according to its shape characteristics. The first liquid spurt occurred in Process Ⅱ and the rest of it occurred in Process Ⅲ. The duration of the second liquid spurt is longer than the first liquid spurt. When the impact velocity of the fragment is less than 996 m/s, the velocity of the second liquid spurt is the highest. When the velocity of the fragment is greater than 996 m/s, the velocity of the first liquid spurt is the highest. The maximum velocities of the first and second liquid spurt are 111 m/s and 94 m/s respectively. The pressure fluctuated sharply in Processes Ⅰ and Ⅲ. The maximum peak pressures in the shock and the cavity oscillation phases are 15.51 MPa and 7.96 MPa respectively. The time interval of the two adjacent pressure pulses increases with the increase of the fragment velocity.

The majority of research work on triboelectric energy harvesting is on material science, manufacturing and electric circuit design. There is a lack of in-depth research into structural dynamics which is crucial for power generation in triboelectric energy harvesting. In this paper, a novel triboelectric energy harvester with a compact structure working in sliding mode is developed, which is in the form of a casing and an oscillator inside. Unlike most sliding-mode harvesters using single-unit films, the proposed harvester utilizes grating-patterned films which are much more efficient. A bistable mechanism consisting of two pairs of magnets is employed for broadening the frequency bandwidth. A theoretical model is established for the harvester, which couples the structural dynamics domain and electrical dynamics domain. This paper presents the first study about the nonlinear structural dynamics of a triboelectric energy harvester with grating-patterned films, which is also the first triboelectric energy harvester integrating grating-patterned films with a bistable magnetic system for power performance enhancement. Theoretical studies are carried out from the perspectives of both structural and electrical dynamics. Surface charge density and segment configuration of the films affect whether the electrostatic force influences the structural dynamics, which can be neglected under a low surface charge density. Differences in structural response and electrical output are found between a velocity-dependent model and Coulomb’s model for modelling the friction in the triboelectric energy harvesting system. The bistable mechanism can effectively improve the output voltage under low-frequency excitations. Additionally, the output voltage can also be obviously enhanced through increasing the number of the hollowed-out units of the grating-patterned films, which also results in a slight decrease in the optimal load resistance of the harvester. These findings enable innovative designs for triboelectric energy harvesters and provide fabrication guidelines in practical applications.

Unsteady flow in the hub endwall region has long been a hot topic in the turbomachinery community. However important it is to the performance of the whole engine, the coherent unsteady flow phenomena are still not well understood. In this paper, the complex flow field in the hub endwall of a cantilevered compressor cascade has been investigated through numerical approach. The predicted results were validated by experimental data. To highlight the dominant flow structures among irregular and chaotic motions of various vortices, a Dynamic Mode Decomposition (DMD) method was utilized. The results show that there exist three dominant periodic flow structures: the oscillation of the leakage vortex, a circumferential migration of a Breakdown Induced Vortex (BIV) and the fluctuation of the passage vortex. These three coherent structures all together form a self-sustained closed loop which accounts for the flow unsteadiness of the studied cascade. During this process, the BIV plays a key role in inducing the flow unsteadiness. Only if the BIV is strong enough to affect the passage vortex, the flow unsteadiness occurs. This study expands current knowledge base of flow unsteadiness in a compressor environment, and shows the efficacy of the DMD method for revealing the origin of flow unsteadiness.

The present paper provides a complete databank of bubble plume hydrodynamics in various media characterized by different viscosities in the range 1 – 100 mPa . s . Thus, the influence of the viscosity on bubble plume oscillations and on both liquid and gas velocity fields is studied. The role of the bubble size distribution at different viscosities was also analysed by using two different spargers: a membrane to create ellipsoidal millimetrice bubbles and a slugflow tube to create spherical cap bubbles. Mean velocity profiles, averaged over a large number of plume oscillation periods and corresponding root mean square profiles are discussed, in both phases. Furthermore, void fraction profiles, plume oscillation periods, and bubble size distributions are given for all experimental conditions. Finally, probability density functions and phase averaged profiles in the liquid phase provide additional information. The dependence of bubble plume hydrodynamics on liquid viscosity is huge. At large viscosity, the oscillating plume is damped, regardless of the sparger. Concerning the membrane sparger the viscosity increase modifies the plume oscillation period and its lateral plume expansion, whereas, in the case of the slugflow sparger, only the plume expansion is impacted. Liquid phase hyrdodynamics are weakly affected by the choice of sparger, especially at high viscosities.

We numerically demonstrated the spin transfer torque oscillation (STO) in a magnetic orthogonal configuration by introducing a 90° magnetic coupling. In our model, the multilayer consists of a top layer with in-plane magnetic anisotropy, a nonmagnetic spacer, and a bottom layer with perpendicular magnetic anisotropy. The advantage of utilizing the orthogonal configuration is the high efficiency of spin-transfer torque but it is difficult to stabilize STO. By introducing 90° magnetic coupling into the trilayer of FePt/spacer/Co90Fe10, or Ni80Fe20 or Ni, a stable STO in an orthogonal configuration was realized. When the top layer was Ni with low levels of saturation magnetization, a small damping constant, and a small anisotropy, it exhibited high frequency and low amplitude. This indicates the possibility of controlling the STO frequency. Moreover, the STO frequency was increased by enhancing the 90° coupling. The combination of the orthogonal magnetization structure and 90° magnetic coupling is an effective approach to obtain a stable spin-transfer torque oscillator with high frequency.

The complete set of intrinsic dimensionless parameters of a packaged and fiber-pigtailed distributed feedback (DFB) semiconductor laser are extracted from the non-linear operational stability boundaries of the optical-injection-locking (OIL) architecture. Specifically, this procedure is done by relating the intrinsic parameters to the injection ratios corresponding to the Hopf bifurcation points at zero detuning, as well as the detuning of the Hopf-Saddle-Node point. The bifurcation points of the injected laser's operational space are found by coupling its output into a high-resolution optical spectrum analyzer. This is enabled by establishing a 30 dB side mode suppression ratio between the central mode and Period 1 oscillations to define the boundaries of Stable Locking. Along with the laser's threshold current and free-running relaxation oscillation frequencies, performing these measurements over a range of pumping values allows for the calculation of the laser's linewidth enhancement factor, irrespective of the device packaging. Utilizing a high pump approximation, the remaining dimensionless parameters are extracted after obtaining the photon lifetime. Using this approach, the operational capabilities of an arbitrarily-packaged laser can be determined, allowing for the analysis of an injected laser's operational space for a variety high-frequency and dynamical applications.

Optical microcavity, which can localize light at a certain spot for a short period of time, has a wide range of applications, such as optical signal processing and optical frequency combs. Single crystal CaF2 has excellent optical properties and many research on the manufacturing process to create a microcavity has been done. However, due to its unstable thermal conditions, stable oscillation of Kerr comb could not be done. Single crystal MgF2, which also has excellent optical properties, has stable thermal conditions suitable to create a microcavity. Like CaF2, MgF2 microcavity can only be manufactured by ultra-precision cylindrical turning, yet its appropriate processing conditions is not known. In this study, a method to derive the critical depth of cut theoretically in ductile mode machining was proposed in consideration of specific cutting energy, mechanical properties and slip system of workpiece, and tool geometry. The critical depth of cut calculated by the proposed method roughly agreed with the experimental value on the MgF2 plane. Unlike CaF2, MgF2 has an optical anisotropy; therefore, in order to create a microcavity where the refractive angle is constant, the resonance part needs to be made on a cylinder with (001) plane as end face. Therefore, a microcavity was fabricated according to the critical depth of cut on a cylinder with (001) as end face derived from the proposed method, and the surface integrity was evaluated from the viewpoint of microcavity performance.

High-frequency vibration proves a fundamental step towards scalable growth in colloidal crystals. Various experimentally-replicable vibration mechanisms are hereby devised and exerted on randomly generated silicoid particles to explore geometric and dynamic effects on the induced crystal at equilibrium state. The Discrete Element Method is employed, with inter-particle contact idealized by a linear mass–spring–dashpot system with Coulomb sliding friction. With the vertical (Z) direction determined by gravity, the mechanisms comprise vertical, circular, and angular oscillation, with the latter realized in the plane normal to gravity. Characterization of the generated crystal is quantified by a hybrid machine-learning algorithm developed upon direct correlation between the coordinate data, crystallinity and grain-surface parameters. Parametric analysis is carried out in terms of vibration parameters (frequency, amplitude and duration) and the square-prismatic box aspect ratio. Results manifest optimum values of box aspect ratio, vibration amplitude and frequency, with crystallinity parameters mostly saturating after 2 minutes of vibration.

This paper investigates the dynamic behaviour of a low pressure open natural circulation loop applied to a parabolic trough collector. An in-house experimental setup is developed to perform the test. The experiments are performed on two distinct modes: H-mode and S-mode, corresponding to single-phase and two-phase flow. Three distinct power amplitude modes viz, 250, 325, and 464.3 W with a power step number of 24, 18 and 12 having a duration of 15, 20 and 30 min are considered. A Fast Fourier Transform analysis revealed that the flow in the loops is stable with a maximum decay ratio of 0.726. Instabilities, including Density Wave Oscillation, geysering and flashing, are observed during the test. Moreover, the thermal inertia of the loop has a significant role in the initial stage of power steps. An increase in the power step size conferred a 9.1%–33.4% increase in the outlet temperature of water in H-mode. In S-mode, an increase in power step size delayed the onset of boiling and reduced the duration of boiling by 2.8–14.32% and 8.03–22.02%. The loop can generate a mass flux of 40–42.5 kgm2s−1 in H-mode and up to 400 kgm2s−1 in S-mode, which is significant.

Brittle Fe-Al compounds limit the performance of the steel/aluminum joint. Beam oscillation laser technology was performed to control the thickness, morphology and distribution of intermetallic compounds (IMCs) at interface. The results showed that beam oscillation significantly reduced the thickness of IMC layer. When oscillation frequency was 10 Hz, the needle-like phase embedded in aluminum matrix was obviously passivated in the circular oscillation mode, while the needle-like phase at interface tend to distribute parallel to the layer-like IMC, and formed a “bite” connection effect with aluminum matrix. In the linear oscillation mode, the needle-like phase disappeared, and smooth and flat interface was obtained. Compared with the non-oscillation mode, in the case of circular or linear oscillation mode, the width of molten pool was significantly increased, the crystal grains were refined, and the joint property was increased by 26% and 17% respectively, which were caused by the combined effect of mechanical bonding and metallurgical regulation. The influence mechanism of beam oscillation on the thickness, morphology and distribution of IMC at interface was revealed by high-speed photography and finite element simulation, which provides a new idea for the welding of steel/aluminum dissimilar materials.

Evaluating friction in human skin is important to assess its condition and the effects of skincare cosmetics. In this study, we evaluated the friction dynamics of moisturized skin to show the effects of moisturization on its mechanical properties.Friction force was evaluated using a sinusoidal motion friction evaluation system. The skin of the upper arm of 20 subjects was rubbed using a contact probe. The water content of the stratum corneum and the softness of the skin were measured using a Corneometer and a Cutometer, respectively.When human skin was treated with water or 10 wt% glycerol aqueous solution, the friction coefficients increased by 0.23 ± 0.01 and 0.17 ± 0.14, respectively, and the delay times (normalized by calculating the time interval from contact with the probe to the friction response divided by the friction time for one round trip) increased by 0.048 ± 0.034 and 0.055 ± 0.024, respectively. Three different friction profiles were observed: (a) a stable pattern, in which a smooth profile was observed during the sliding process; (b) an oscillation pattern, in which significant oscillation was obtained; and (c) a stick pattern, in which the friction coefficient increased even during the deceleration process. In the case of untreated skin, the oscillation pattern was observed for the majority of subjects. The appearance rate of the stick pattern increased by 80.3% ± 29.4% after treatment with 10 wt% glycerol aqueous solution. These characteristic friction profiles can be explained by a two-step friction model consisting of two modes: (a) friction at the skin surface and (b) the delayed response due to skin deformation.Moisturizing the skin with water or 10 wt% glycerol aqueous solution increased the friction coefficient and delay time, dramatically changing the friction profile. These changes were considered to be due to the swelling and softening of the stratum corneum and the increased true contact area between the contact probe and the skin surface.Une évaluation des effets de la friction sur la peau humaine demeure importante dans le but de juger de l'état de la peau ou de l'efficacité des produits cosmétiques pour les soins de la peau. Dans cette étude, nous avons évalué les propriétés d'une peau hydratée soumise à une friction afin d'identifier les effets de l'hydratation sur les propriétés mécaniques de la peau. MÉTHODE: Les forces de friction ont été évaluées grâce à un système d'évaluation du frottement par mouvement sinusoïdal. Une sonde de contact a été utilisée pour frotter la peau sur le haut du bras de 20 participants. La teneur en eau de la couche cornée et la souplesse de la peau ont été mesurées respectivement à l'aide d'un cornéomètre et d'un cutomètre. RÉSULTAT: Le traitement de la peau humaine avec de l'eau ou une solution de glycérol à 10% a entraîné une augmentation du coefficient de friction respectivement de 0.23 ± 0.01 et de 0.17 ± 0.14, ainsi que du délai de réaction (normalisé en divisant l'intervalle de temps entre le contact avec la sonde jusqu’à l'apparition de la réaction à la friction, par le temps de friction pour un aller-retour), de 0.048 ± 0.034 et de 0.055 ± 0.024. Trois profils de friction différents ont également été observés : (1) un modèle stable, (2) un modèle avec une grande oscillation, et (3) un modèle « collé-glissé » où le coefficient de friction augmente même pendant la décélération. Lorsque la peau est sèche, le modèle oscillant a été observé chez la majorité des participants. Le taux d'apparition du modèle « collé-glissé » a augmenté de 80.3 ± 29.4% dans le cas où la peau a été traitée avec une solution de glycérol à 10%. Ces profils caractéristiques de friction ont pu être expliqués à partir d'un modèle de friction composé de deux modes, (a) une friction à la surface de la peau et (b) un délai de réaction dû à la déformation de la peau.L'hydratation de la peau avec de l'eau ou une solution de glycérol à 10% a considérablement modifié le profil de friction en raison d'une augmentation du coefficient de friction et du délai de réaction. Nous avons estimé que ces changements sont relatifs au gonflement et à l'assouplissement de la couche cornée, engendrant une augmentation de la surface de contact réel entre la sonde de contact et la surface de la peau.

Single-storey systems with different hysteretic characteristic are subjected to impulse-type short duration and long duration earthquake records to investigate the effects of hysteretic behaviour and ground motion characteristics on the seismic response. EPP, bilinear, Takeda, SINA, and flag-shaped hysteretic models loops are considered and an energy approach is taken to explain the inelastic behaviour. The first part of the work is based on analyses of the single-storey systems without any torsion, however; torsional irregularity is considered in the later analyses. It is shown that structures with the same backbone curve, but different hysteretic characteristics, tend to experience the same maximum response under short duration earthquake records, where there is one major displacement excursion. The likelihood of further displacement in the reverse (i.e. negative) direction is characterized using energy methods and free vibration analyses along with a new proposed “oscillation resistance ratio (ORR)” are employed to improve the understanding of the seismic response. Hysteretic models with low ORR, such as SINA and flag-shaped, are shown to have a greater likelihood of higher absolute displacement response in the negative direction compared with those with fatter hysteretic loops. The understanding of the response in terms of energy reconciles some differences in the ability of initial stiffness versus secant stiffness based methods to predict peak displacement demands with account for different ground motion characteristics. The same peak displacements in the primary direction was also observed for structures with stiffness/strength eccentricities under an impulse-type earthquake record. However, during unloading, the elastic energy stored in the out-of-plane elements is released causing greater displacement on the weak side in the reverse direction.

This paper studies the dynamic contact response of a piezoelectric half-space under the action of an insulating elastic spherical punch. By means of the perturbation method, the dynamic contact pressure distribution is deduced. Utilizing Hankel transform, the dynamic contact displacement is obtained. Combining the elastic spherical punch oscillation and the piezoelectric half-space motion through contact-displacement boundary conditions, the resonant frequency shift of the elastic sphere is derived. Numerical calculations are given to discuss the influences of the material constant, piezoelectric effect, internal friction and static force on the dynamic contact pressure and resonance frequency shift. The results show that the difference between the dynamic and static contact pressures is small at the center of the contact region, while it is large near the edge of the contact region.

Combustion instability is a common phenomenon in solid rocket motors. Coupling between pressure and heat release rate produces pressure oscillation, which seriously affects the operation and safety of the motors. It is necessary to investigate this mechanism in order to prevent or at least suppress pressure oscillations. A segmented combustor is designed, and a movable flat flame burner is used as the heating source. A stability map is plotted by moving the flat flame burner along the combustor and changing the equivalence ratio. The experimental results are predicted by employing the low-order thermoacoustic network model. When the heat source position is fixed, it is shown that the combustion changes from stable to very unstable and then returns to a stable state, with the increase of equivalence ratio from 0.9 to 1.5. The pressure oscillation is the strongest in the rich combustion region (equivalence ratio is 1.2–1.3), with the amplitude of about 122 dB. The pressure oscillation is strongest and the amplitude is about 125 dB, when the heat source is close to the nozzle exit. The calculation results by thermoacoustic network model agree well with the experimental results. The stability map and limit cycle characteristics of thermoacoustic oscillation can be accurately estimated. It indicates that this experimental method and theoretical model can be used to capture the limit cycle behavior, and provide a new scheme for predictions of thermoacoustic oscillation in solid rocket motors.

Aluminum (Al) particles are regarded as general addictive into solid propellants not only as an extra energy source but also as a metallic damping-carrier on combustion instability. It is possible that the stability in propellant can be improved through partial Al substitution. However, knowledge of unsteady combustion characteristics of Al particles has been insufficient. In order to explore the unsteady combustion and attenuation characteristics of Al particle, a methane micro-combustor is designed. The acoustic oscillation of combustor is found to be excited, regardless of the Al particles mass of diameter. Moreover, the effects of 1) particle size and 2) mass are examined in detail. The burning of micro-sized Al particles in present experiment is attributed to melt dispersion mechanism. The rupture time is in the range of 2.18 ms to 2.81 ms for Al particles with mean diameter of 10 μm, 20 μm and 30 μm. With the increasing of particle size, the sound level of high-frequency oscillation increases from 65 dB to 85 dB. However, the attenuation effect for high-frequency oscillation is weakened for larger particle size. Finally, it is found that the pressure growth rate can be dramatically increased from 1000 Pa/s to 11,000 Pa/s and the peak amplitude of high frequency oscillation is augmented, as the Al particles mass ratio is increased. The present research sheds lights on an effective evaluation of unsteady Al combustion by considering particles parameters.

For fulfilling the demand of durable yet lightweight electrical connections in transportation industries, ultrasonic metal welding (USMW) sees widespread use in these branches. As the ultrasound oscillations utilized in the welding procedure occur at a range of only a few micrometers at frequencies of 20–100 kHz for an overall duration of only 50–1500 ms, it is not possible to observe the compaction behavior with the bare eye. This paper focusses on investigating the oscillation behavior of the horn, the anvil, and the joining partners during the welding procedure by utilizing an array of synchronized laser vibrometers and performing welds with incrementing time stages. The oscillation data is correlated with temperature measurements in the welding zone as well as tensile testing results. Inter alia the formation of sidebands at the fundamental frequency as well as 2nd- and 3rd-order harmonics has been observed for the anvil, terminal, and wire front face when exceeding optimal weld time which would lead to maximum joint strength. Following the assumption of other research groups, the cause of these sidebands could be a change in relative motion of these components. As the terminal is slipping with increasing weld time, it could be assumed that the reason for the sidebands is low-frequency movement of the anvil, modulated onto the fundamental frequency, additionally indicating successful bonding of the stranded wire and the terminal. Furthermore, this slipping of the terminal on the anvil could lead to increased wear of the anvil knurls.

Improving the reliability of electronic devices requires effective heat management, and the key is the relationship between the thermal transport and temperature. Inspired by synthesized T-carbon and H-boron, the 3-X structural models are proposed to unify the two-dimensional (2D) multitriangle materials. Employing structural searches, we identify the stability of the 3-X configuration in 2D boron carbides as 3-9 BC3 monolayer, which, unexpectedly, exhibits a linear thermal conductivity versus temperature, not the traditional ∼1/T trend. We summarize the common characteristics and explore why this behavior is absent in 3-9 AlC3 and graphene via investigating the optical modes. We show that the linear behavior is a direct consequence of the special oscillation modes by the 3-X model associated with the largest group velocity. We find that 2D materials with such behavior usually share a relatively low thermal conductivity. Our work paves the way to deeply understand the lattice thermal transport and to widen nanoelectronic applications.

A temperature sensor named a thermillator (thermo-oscillator) is demonstrated, consisting of a single device with an n+-emitter, p-base and n+-collector. The thermillator with a p-base floating body shows inherent oscillation behavior. The underlying mechanism of the thermillator is based on the single transistor latch (STL). Oscillation originates with the iterative charging and discharging process in the floating p-base, and the oscillation frequency ( $\boldsymbol {f}$ ) is sensitively changed by applied temperature. Compared to a temperature sensor with a circuit-based ring oscillator, the single device-based thermillator has the advantages of small footprint area, low hardware cost, and low power consumption.

LC CMOS voltage-controlled oscillators (VCOs) with tunable inductors are essential for high-performance, multi-band communication systems, such as IoT applications and 5G communication. However, VCOs that use CMOS tunable inductors have difficulty in achieving high RF performance due to the low Q-factor of the inductor. In addition, previously reported CMOS VCOs integrated with MEMS inductors have used CMOS switches for tuning frequency bands, but they also had large signal losses on the switch. Herein, we propose a CMOS VCO that is integrated with a MEMS tunable inductor that tunes the frequency band with three MEMS switches. The proposed MEMS tunable inductor enables us to achieve high RF performance due to the suspended structure, and RF MEMS switches enable lower signal loss than CMOS switches. In this work, we successfully fabricated the proposed CMOS VCO integrated with a MEMS tunable inductor using the flip-chip bonding process, and we measured oscillation frequencies according to the actuation of the three switches. The oscillation powers were measured as − 3.03 dBm @ 1.39 GHz, − 5.80 @ 1.98 GHz, − 7.44 dBm @ 2.81 GHz, and − 8.77 dBm @ 3.68 GHz.

Three-dimensional and oscillatory thermo-capillary flow in a liquid bridge of 5 cSt silicone oil (Pr = 67) has been numerically investigated by performing dynamic mode decomposition (DMD) analysis applied to the time-resolved thermal data generated by the ‘method of snapshots’. For various heat transfer conditions defined on the free surface of the curved liquid bridge, a series of dynamic modes has been extracted to unfold the underlying physical mechanism that governs the considered dynamical system. Unstable and neutral modes primarily accountable for the transition to the supercritical state established in the liquid bridge have been identified by decomposing the acquired temperature disturbances into spatial and temporal coherent structures. Under microgravity conditions, unsteady and three-dimensional computations are carried out in a liquid bridge of different volume ratios (VR = 0.9 and 1.1) using the finite volume method (FVM) to capture the dynamical evolution of temperature disturbances at the onset of oscillatory instability. The present numerical investigation is mainly aimed at providing broader insight into the complex fluid dynamic processes associated with the oscillatory thermal convection by determining the growth/decay rate and frequency of each characteristic mode with the help of DMD spectra. For each oscillation pattern, the dominant behavior of oscillatory thermo-capillary flow is revealed by its coherent structures. The characteristic modes having more energy content (dominant modes) are also analyzed by the norm of modes || ϕ || by demonstrating the frequency spectra of DMD analysis.

Load-sensing steering systems for articulated loaders are prone to large pressure shocks and oscillations during steering operations, affecting the system stability. An optimized structure of the redirector with bypass damping is proposed to improve this phenomenon. In this structure, orifices and throttle grooves are added to the traditional redirector. To control the steering load and working conditions, the steering load of the loader is replaced by a pressure regulating valve. Simulation and experimental results reveal that the redirector with bypass damping has better load-sensing characteristics than the traditional redirector. The peak output pressure shock caused by the load unit step signal decreases from 6.50 to 5.64 MPa, which means the pressure oscillation of the hydraulic system is reduced by 13.4%. The pressure fluctuation time can be reduced from 2.09 to 1.6 s, with a decrease rate of 23.4%. The output pressure oscillation decays swiftly, and the smoothness of the steering operation is improved significantly.

Mixtures of LiAlH4/FeCl2 and LiBH4/FeCl2 were produced in several conditions of stoichiometry, time, and vial-oscillation frequency at cryogenic conditions (−196 °C) by ball milling. The best production conditions were milling for 30 min at −196 °C and 15 Hz of the oscillation frequency of the vial. Temperature-programmed desorption and differential scanning calorimetry experiments indicated that hydrogen release in LiAlH4/FeCl2 mixtures begins at approximately 60 °C and ends at 160 °C. Meanwhile, the LiBH4/FeCl2 mixtures presented dehydrogenation on-set at 40 °C, finishing at about 300 °C. These materials behave as reactive mixtures, where the LiCl formation is considered the driving force of the decomposition reactions. Cryogenic ball-milling has a good effect on the production of the mixtures and low-temperature dehydrogenation of the studied samples.

Sputtered Tb/Cr/Fe structures with a Cr layer (tCr) thickness ranging from 0 to 4 nm were prepared. The coercivity (Hc) of Tb/Cr (tCr)/Fe films with tCr ≥ 1 nm is consistent with that of the corresponding Cr(tCr)/Fe films. At the same time, the addition of the Tb layer results in a large saturation magnetization field (Hs) and even oscillatory relations of Hs on tCr, which might indicate an oscillatory indirect exchange coupling mediated by the spin polarization of the spacer Cr layer. Consistent oscillations are observed in anisotropic magnetoresistance (AMR) originating in spin–orbit coupling and magnetoresistance (MR) associated with interlayer exchange coupling as tCr in Tb/Cr/Fe films increases. The oscillatory MR demonstrates antiferromagnetic coupling, which also implies that it is not ordinary MR, although it is of the same magnitude as a result of the nonsharp interfaces. The value of the antiferromagnetic exchange coupling J as a function of tCr is estimated. Consistent oscillations with those in MR and AMR versus tCr are found, accompanied by a gradually flattened oscillation for films with tCr ≥ 2.5 nm resulting from weak coupling as the thick spacer Cr layer. Compared with the curves of MR, AMR, and J versus tCr, the opposite oscillations observed in the curve of Hc/Hs versus tCr further confirm the oscillatory interlayer exchange coupling in the studied structure, which provides theoretical basis for the adjustment of magnetic properties in spintronics by rare earth elements.

A terahertz (THz) fundamental oscillator IC with high efficiency and compact chip size based on an indium phosphide (InP)-based resonant tunneling diode (RTD) is proposed. The oscillator is designed by utilizing a low-frequency bias stabilizer, along with utilizing a negative differential resistance oscillator topology. The oscillator is fabricated by using an InP monolithic THz integrated circuit multilayer process. The fabricated oscillator shows a high dc-to-RF power efficiency ( η ) of 0.274 % with a low dc power consumption of 3.4 mW and an RF output power of 9.3 μ W at an oscillation frequency of 692 GHz. The IC exhibits a chip size of 300 × 380 μ m2 excluding the measurement pads. The achieved η and chip size are good values among THz oscillators above 500 GHz reported to date.

The instability of pressurized dense gas-solid jets in a two-dimensional nozzle is experimentally studied using a high-speed camera, and the effects of the hopper pressure and the particle diameter on instability are considered. As particle velocity rises with hopper pressure, dense gas-solid jets become unstable and display an asymmetric oscillation, which is quasi-periodic and its frequency and evolution are further characterized. For particle diameters of d = 185 μm and 410 μm, the time-average frequencies increase linearly with the exit particle velocities. The asymmetric structures grow along the nozzle, and even undergo deformation and merging. The macroshot of the flow transition region between hopper and nozzle indicates that gas-solid separation generates fluctuations which will propagate both upstream and downstream. In the nozzle, fluctuations are amplified by the enhanced gas-solid interaction, evolving to the asymmetric structures.

The detailed mechanism of supersonic mixing enhancement by a novel device is investigated computationally based on the Navier-Stokes equations. The device is a wall-mounted three-dimensional cavity, several parts of the rear face of which are cut out, and the lower wall of the cut-out part has a slope directed toward the injector from which the injectant is discharged. The flow structures and behaviors observed in the computational results are confirmed in the experimental results. Experimental information about the high-frequency (several tens of kHz) pressure oscillation in the cut-out part is acquired in this study using a pressure-sensitive paint (PSP) responding to rapid change in pressure. The computational results reveal that a hairpin-like vortex is formed inside the cavity. The vortex works on the shear layer across the cavity to deflect it upward. The deflected shear layer shields the injectant from the primary flow, which causes the injectant to penetrate deep into the primary flow. The computational results also clarify that the expansion and compression waves produced in the rectangular part of the cavity are delivered effectively to the injector along the slope of the cut-out part, which is confirmed in the PSP measurement results. The delivered waves actuate the jet issuing from the injector to fluctuate up and down periodically with a large amplitude.

In order to study the fluid–solid coupling dynamic characteristics of parachute-payload system during drop process and analyze the unsteady aerodynamic characteristics under finite mass opening conditions, an adaptive moving fluid mesh method is developed on the basis of the existing arbitrary Lagrangian–Eulerian (ALE) fluid–solid coupling method. The calculation results of open force and drop velocity on the C-9 parachute demonstrate the effectiveness of this method. On this basis, the effect of canopies with three different permeability on parachute-payload system motion characteristic including opening property, steady descent property and stability is studied. Comparative analysis is conducted for structures and characteristics of vortex with different canopy materials, and interference mechanism of unsteady flow for parachute-payload system in unsteady oscillation is revealed. The results show that the adaptive moving fluid mesh method can effectively eliminate restrictions of existing simulation methods for parachute-payload system and significantly reduce calculation time. For the lightweight parachute, permeability has significant effect on kinetic characteristic of parachute-payload system. Canopy with large permeability has small opening load and structural stress in opening stage. After opening, there are mainly small vortexes distributed evenly behind the canopy with good stability. However, canopy with small permeability has obvious breath behavior and oscillation in opening stage. The main vortexes periodically shed off after opening. With the change of permeability from small to large, Parachute-payload system eventually presents three steady descent modes: conical descent, gliding descent and stable vertical descent. Graphical abstract

Stacked nanosheet nFETs considering a six-stack four-finger transistor array are studied and optimized by validated TCAD simulation. Stacked Si nanosheet (NS) nFETs have lower parasitics than nFinFETs in the same six-fin/stack four-finger transistor array layout. With the same electron mobility, back-end-of-line (BEOL), equivalent oxide thickness (EOT) of 1.4 nm, and gate length of 30 nm, the stacked Si NSs have $1.1\times $ cut-off frequency (240 versus 215 GHz) and $1.15\times $ maximum oscillation frequency (290 versus 251 GHz) when compared to FinFETs due to larger transconductance increase than capacitance increase and output conductance decrease. With the optimized EOT of 0.8 nm and gate length of 18 nm, the stacked Si NSs can achieve cut-off frequency of 340 GHz and maximum oscillation frequency of 370 GHz. Furthermore, considering the higher electron mobility on {100} surfaces of NSs than {110} sidewalls of FinFETs as suggested by the ${I} _{D}$ – ${V}_{\text {GS}}$ fitting, the cut-off frequency and maximum oscillation frequency of stacked Si NSs can reach 380 and 390 GHz, respectively.

Objectives: To assess the influence of preheating and sonic oscillation of bulk-fill composite on marginal adaptation of class II restorations. Materials and methods: 30 extracted molars were collected, and standardized compound class II cavities were prepared. Teeth were classified into three groups (n=10) according to placement techniques. Group I, the composite material was placed in bulk to fill the prepared cavity using a plastic filling instrument. Group II, composite syringes were placed in the Therma-Flo device before placement into the cavities. Group III, the composite material was placed in bulk to fill the prepared cavity using a plastic filling instrument then adapted by compothixo oscillating packing instrument. After finishing and polishing, the specimens were subjected to thermocycling. Marginal analysis was carried out using Scanning Electron Microscope at 500 x magnifications. The overall margins were investigated, and the maximum gaps were measured. Results: Although preheated composite produce better marginal adaptation, there was no significant difference between all tested groups. CONCLUSION None of the placement techniques produced gap-free margins. Preheated composite improved marginal adaptation

Oscillation of micron-sized liquid droplet is an interesting and common phenomenon, and is used to measure surface tension and viscosity with the recently developed time-resolved rainbow refractometry. Droplets produced by a monodisperse droplet generator are excited to oscillate at a small amplitude (less than 1%) and high frequency (of the order of 10 kHz) by applying a periodic tiny disturbance. The aspect ratio of a spheroidal droplet is quantified by time-resolved angular shift of rainbow signal. Thus the droplet shape oscillation is quantified by its unsphericity, instead of calculated from the polar radius or the variation of surface area. Experiments on several liquids were conducted to evaluate the validation of the experimental system. The results present that the relative errors of measured values of the surface tension and viscosity are less than 5% and 10%, respectively, promising the great potential of rainbow refractometry for liquid surface properties measurement.

Previous work has studied the magnetic resistance (Fmr) of high-temperature superconducting (HTS) maglev vehicles operating at a speed lower than 40 km/h, but the characteristics of Fmr at higher operation speeds are still unclear. Based on the high-speed rotating simulation platform, this paper studies the dynamic magnetic resistance of maglev vehicle at a speed up to 250 km/h. By stacking silicon steel sheets on a circular permanent magnet guideway (PMG) to form a periodically fluctuating external magnetic field, the characteristics of the influence of strong magnetic field fluctuations on the magnetic resistance of the maglev vehicle under high-speed movement are obtained. The transient magnetic resistance of the HTS maglev system oscillates with time. The oscillation amplitude increases approximately linearly with the operating speed and is closely related to the initial magnetization state of the HTS superconductor. Due to the asymmetry of the oscillation, there is a net average magnetic resistance, whose value increases linearly with the speed, and the rate of change is dominated by the initial magnetization state of the superconductor. The oscillating characteristics of transient magnetic resistance make the net average magnetic resistance much smaller than the magnetic levitation force. The frequency spectrum of magnetic resistance oscillation shows two characteristic frequencies of 5.3 Hz and 53 Hz, and they are independent of the driving frequency.

This paper explores the impacts of temperature oscillation and Lorentz force on the two-dimensional transient hybrid nanofluid boundary layer motion over a semi-infinite moved vertical sheet with energy transfer. The fluid considered here is viscous and incompressible, and partial differential equations model the problem with appropriate boundary conditions. The implicit finite difference numerical technique is employed to define unconditionally stable computational solutions to this challenge. Variations of thermal and hydrodynamic structures and the corresponding engineering quantities are explored in terms of magnetic parameter, Grashof number, phase angle, and nanoparticles concentration via graphs. It has been found that with an increment of nanoparticle volume fraction φ2, the friction parameter decreases and the strength of energy transport increases. Furthermore, a reduction of friction coefficient Cf and local Nusselt number Nu can be found by increasing the magnetic field parameter M or phase angle ωt. The findings can be applied to a variety of engineering devices, such as thermal exchangers, solar collectors, and bioreactors.

In this paper, a novel recessed T-gate double channel HEMT with InGaN back barrier has been designed and studied. The double channel is formed by the AlN layer's insertion below the InAlN/GaN interface, enhancing the drain current density (2.5A/mm). However, double channel HEMT suffers from a lack of gate controllability, due to which device performance decreases. This problem has been resolved by using the InGaN as a back barrier which enhances the carrier confinement of 2DEG by raising the conduction band for the GaN buffer and significantly enhances the gate controllability over a lower channel. Precisely a brief comparison has been done of the proposed device with conventional double channel HEMT. Performance parameters like drain current (Ids), transconductance (gm), intrinsic gain (Av), output conductance (gd), early voltage (VEA), TGF, parasitic capacitances (Cgs, Cgd), cut-off frequency (fT), maximum oscillation frequency (fmax), gain frequency product (GFP), transconductance frequency product (TFP), and gain transconductance frequency product (GTFP) have been investigated. Further, the improvement in linearity parameters such as VIP2, VIP3, IIP3, and 1-dB compression point has been observed by varying the back barrier distance from the lower channel.

Flow-induced oscillation is an effective way to enhance heat transfer, which requires no extra energy consumption and can prevent fouling and soot formation. To test the flow-induced oscillation effect on the heat transfer of impingement flow, an 18 mm wide and 30 µm thick membrane tape was mounted at the exit of the ejection pipe. As the ejection Reynolds number increased from 5280 to 9827, the oscillating frequency also increased. In addition, three different oscillating regimes were observed, these being quasi-still, 2D-oscillating and 3D-oscillating, with the transition Re depending on the tape length. The heating plate was 3D-printed and electrical heating wires were embedded within it so as to predetermine the local heat flux by numerical analysis, and be able to calculate the heat transfer coefficient (HTC). The results demonstrate that heat transfer enhancement is more prominent in the vertical direction to the tape than in the parallel direction. Moreover, the distinctive heat transfer enhancement effect near the plate center becomes weaker as it goes toward the outside of the plate, and even turns negative with an increasing r/D. Using a longer piece of tape or having smaller intervals between the tape tip and plate was also shown to improve the heat transfer effect. The spontaneous oscillating disturbance method shows great promise for heat transfer regulation in impingement flow.

This paper introduces the photon storage and current oscillation characteristics of a quantum effect photodetector and studies the high-sensitivity characteristics of the detector based on device m...

In high-quality ZnO/MgxZn1 – xO heterojunctions, microwave-induced magnetoresistance oscillations have been investigated using a contactless technique. The basic detection principle relies on the measurements of a signal transmission in the radio frequency range (f ~ 50 MHz) between two T-shaped antennas, capacitively coupled to a two-dimensional electron system. When the sample is exposed to exciting microwave radiation with the frequency $$F = $$ 60–140 GHz in low magnetic fields, at least three oscillations are well resolved in the high-frequency conductivity. The amplitude of the first oscillation is comparable in amplitude to Shubnikov–de Haas oscillations in strong magnetic fields. A significant advantage of this method is the absence of Ohmic contacts or metallization deposited on the sample surface, which provides additional information for understanding the origin of this phenomenon.

A series of hydrogen explosions were conducted in a real scale container with and without vents. The effects of hydrogen concentration, ignition location, obstacles on the vented hydrogen-air explosions were investigated. Hydrogen explosions with concentration of 12% and 16% were conducted in constant volume container, and the maximum peak overpressure can reach 45 kPa and 175 kPa, respectively. During the vented hydrogen explosions, three overpressure peaks generated by the vent rupture, Helmholtz oscillation, and the thermo-acoustic-vibration coupling, respectively, were recorded. The maximum peak overpressure is about several kilopascal, the pressure reduction can reach 97.1% by comparison with peak overpressure developed in closed container. The obstacles change the way that the flame travel inside the container, and resultantly the flame propagates vertically and increases the flame area, which promotes the reaction and increases the peak overpressure, which also increases with the hydrogen concentration. Three engineering models used to depict the relationship between the vent area and the maximum reduced explosion pressure were assessed. Results show that the these models over-predict the maximum reduced explosion pressure for high-reactivity mixtures. However, for low reactivity, the Molkov’ models show a scatter while the NFPA68 gives a better prediction.

International audience; One prerequisite for high-speed imaging in dynamic-mode atomic force microscopy (AFM) is the fast demod-ulation of the probe signal. In this contribution, we present the amplitude and phase estimation method based on the acquisition of four points per oscillation, with the sampling frequency being phase-locked on the probe actuation. The method is implemented on a RedPitaya platform, with its clock being generated from the actuation signal of the probe. Experimental characterizations using square-modulated sine waves show that latency of 500 ns is achieved with a carrier frequency of 10 MHz, which is ten times faster compared with a state-of-the-art lock-in amplifier. A tracking bandwidth greater than 200 kHz is obtained experimentally. The method is eventually applied to a close-loop AFM scan realized using a 15-MHz AFM probe, showing its suitability for high-frequency oscillating probes. Index Terms-Amplitude and phase demodulation, atomic force microscopy (AFM), field-programmable gate array (FPGA) implementation.

A periodic dielectric meta-surface output window was cold and hot tested to extend the operating bandwidth and suppress the parasitic oscillations for a W-band wideband TE01 mode gyrotron traveling wave tube (gyro-TWT) in this letter. The fabricated beryllium oxide meta-surface dielectric window demonstrates a relative bandwidth of 37.84% with the reflection below −20 dB in the range of 75–110 GHz. The influences of engineering factors and machining errors on the performance are investigated and analyzed. Thermal analysis shows the average power handling capability of the window is over 33 kW within a wide frequency range. Hot test results demonstrate that the meta-surface window is excellent for oscillation suppression and the power handling capability is predicted larger than 20 kW.

Comparative analysis of membrane oscillation and aeration in a photocatalytic membrane reactor is conducted. The investigation involved degradation of methylene blue dye as model pollutant using suspended ZnO photocatalyst and UV illumination. The effect of reactor hydrodynamics and design parameters on the system performance and its relation to the membrane-catalyst retention characteristics is evaluated using flat surface membranes roughed with transverse turbulence promoters (TP). The investigation showed that membrane oscillation is more energy efficient than aeration and can provide higher shear rates and better mixing which decreases both the catalyst agglomeration and deposition on the membrane surface. These, in turn, increase both the suspended catalyst concentration in solution and enhance the membrane flux. Compared to oscillation, achieving high shear rates through aeration is limited due to the adverse effects of high gas flow on photocatalytic reactions. Considering the above together with the small effect of aeration on ZnO photocatalytic kinetics, the need for aeration may be relaxed when using membrane oscillation in a ZnO photocatalytic reactor.

Three Plasma Synthetic Jet Actuators (PSJA) under the high-frequency actuation are used to control the Shock Wave Boundary Layer Interaction (SWBLI), a high-speed schlieren image processing method based on spatial Fourier transform as well as snapshot proper orthogonal decomposition were used to study the control effect of high-frequency plasma synthetic jet on low-frequency unsteadiness of SWBLI. The analysis of the base flow shows that the separated shock wave actually has both large- and small-amplitude vibrations at low frequency. And the results revealed that the PSJA with an operating frequency of 2 kHz has the ability to reduce the energy of low-frequency component of shock wave motion, indicating that the 2 kHz actuation can effectively suppress low-frequency unsteadiness of the separated wave. Compared with the actuation frequency of 2 kHz, the energy of low-frequency component of the shock wave is enhanced under the 8 kHz actuation, which aggravates the low-frequency unsteady motion of the shock wave. It is likely that the actuation frequency is too high, thus the intensity of the precursor shock wave induced by PSJA becomes weaker. Additionally, as the 4 kHz actuation is applied, the pulsation of the separation region was enhanced, it is speculated that the actuation frequency is coupled with the oscillation frequency of the separation region.

Researchers have recently attempted to monitor pool oscillations using the three-dimensional laser vision method. However, the deficiency of simulation software will result in significant capital expenditure. Both simulations and experiments are performed in this study, and the Bessel equation is used to analyze the oscillation mode of a weld pool. The laser dot matrix images of (0, 1), (1, 1), (2, 1), and (0, 2) oscillation modes at different times are obtained via structured laser optical measurement simulation. The oscillation mode of a stationary gas tungsten arc weld pool is analyzed based on laser dot matrix images obtained from a structure laser experiment. Results show that the simulated laser dot matrix images are consistent with the experiment results. The oscillation mode of the weld pool can be recognized based on the laser dot matrix image. This study not only provides conditions for assessing the penetrating state of a weld pool, but also enable a further understanding of the oscillation mode of a weld pool and the development of more effective observation methods and measurement tools to effectively control and improve welding quality.

A device for converting skin temperature oscillations into oscillations of blood filling of peripheral vessels has been developed. The operation of the device is based on the analogy between the thermal properties of the skin and the electrical properties of a low-pass filter. The device uses a Sallen−Key high-pass filter with a nonlinear amplitude and phase response reproducing thermal properties of the human skin. Oscillations in blood filling have been restored from the palm temperature oscillation signal measured at rest and during an occlusion test. The developed device holds promise for use in diagnostics of peripheral hemodynamics impairment within endothelial, neurogenic, and myogenic frequency ranges.