Increase In Oscillation Frequency Research Articles

Chemical and rheological properties of proteoglycans from Sarcandra glabra (Thunb.) Nakai.

Two proteoglycans (HPP and LPP) with different ratios of protein/polysaccharide were extracted from S. glabra. The chemical compositions, relative average molecular weights, monosaccharide compositions, FT-IR spectra, and rheological properties of the two proteoglycans were determined. The results exhibited that the two proteoglycans had pseudoplastic fluids properties and displayed shear-thinning behavior. The apparent viscosity of the two proteoglycans both increased with increasing concentrations. The temperature had different effects on the viscosity of the two proteoglycans. As temperature increased from 25 to 85 °C, the viscosity of LPP descended while the HPP's viscosity rose first and then dropped slightly. The effects of CaCl2 addition on the two samples were like that of the temperature. The viscosities of HPP and LPP had different tolerances to acidity and alkalinity. HPP solution was more sensitive to pH changes due to its high protein content. The addition of sucrose increased the viscosities of samples. The modulus G' and G″ of HPP and LPP were increased with the increase of oscillation frequency, while the crossover points of G' and G″ values decreased with the increasing concentrations of HPP and LPP. The above data presented that the two proteoglycans could be promising candidates for food industries and pharmacological applications.

Effect of Piezo-Embedded Inverted Flag in Free Shear Layer Wake

The use of flexible inverted piezo embedded Polyvinylidene Difluoride (PVDF) as a simultaneous energy harvester and as a wake sensor is explored. The oscillation amplitude (characterized by voltage output) and oscillation frequency of the piezo-embedded PDVF was quantified in the wake of a 2D NACA 0012 model and SD7003 model at a Reynolds number of 100,000 and 67,000, respectively. The performance of the sensor was also quantified in the freestream without the presence of the wing. In order to quantify the sensor response to angle of attack and downstream distance, the amplitude and frequency of oscillations were recorded in the wing wake. Increase in angle of attack of the wing resulted in increase in oscillation frequency and amplitude of the PVDF. The results also indicated that the inverted flag configuration performed better in the wake under unsteady conditions when compared to freestream conditions. The results from Particle Image Velocimetry indicated that the wake signature was not affected by the presence of the PVDF in the wake. The root mean square voltage contours in the wake of SD7003 airfoil show remarkable free shear layer wake features such as upper and lower surface stratification and downwash angle which shows the sensitivity of the sensor to the unsteadiness in the wake. The capability of this device to act as a potential energy harvester and as a sensor has serious implications in extending the mission capabilities of small UAVs.

Comparing the Performance Characteristics of Different Positive Expiratory Pressure Devices.

Positive expiratory pressure (PEP) devices are widely used in clinical settings, yet the performance characteristics of these devices remain relatively unknown. This study compared the performance characteristics of 6 airway clearance devices by varying resistance and flow. Mean PEP, peak PEP, oscillation frequency, and amplitude PEP of the Flutter, Pari PEP S, Acapella Choice, Acapella DM, Acapella DH, and Aerobika devices were obtained across flows of 5, 10, 15, 20, 25 and 30 L/min and at low, medium, and high resistance using an experimental apparatus custom-built for this bench study. Performance characteristics of the devices differed across flows and resistance settings (device × flow/resistance interaction; P < .001). At a fixed resistance, increasing flows increased mean PEP produced by the Acapella Choice, Acapella DH, Aerobika, and Pari PEP S. Increasing flow resulted in minimal change in mean PEP produced by the Flutter and Acapella DM. Increasing flow increased peak PEP and amplitude PEP produced by all devices except the Acapella DH and Acapella Choice. Increasing flow maintained or increased oscillation frequency for all devices except the Flutter. At a fixed flow, increasing resistance increased mean PEP produced by all devices except the Acapella Choice. Increasing resistance increased peak PEP produced by the Acapella DM, Aerobika, and Pari PEP S but resulted in minimal change in peak PEP for the Flutter and Acapella Choice. Increasing resistance either maintained or increased oscillation frequency for all devices. Amplitude PEP was either maintained or increased during oscillations when increasing resistance for all devices except the Flutter. PEP devices produced small but statistically significant variations in performance characteristics across a range of flows and resistance settings. There appear to be flow-dependent and non-flow-dependent devices. Varying flow or resistance typically maintained or increased the production of mean, peak, and amplitude PEP and oscillation frequency.

Viscoelastic properties of human periodontal ligament: Effects of the loading frequency and location.

To determine the viscoelastic properties of the human periodontal ligament (PDL) using dynamic mechanical analysis (DMA). This study was carried out on three human maxillary jaw segments containing six upper central incisors and four lateral incisors. DMA was used to investigate the mechanical response of the human PDL. Dynamic sinusoidal loading was carried out with an amplitude of 3 N and frequencies between 0.5 Hz and 10 Hz. All samples were grouped by tooth positions and longitudinal locations. An increase of oscillation frequency resulted in marked changes in the storage and loss moduli of the PDL. The storage modulus ranged from 0.808 MPa to 7.274 MPa, and the loss modulus varied from 0.087 MPa to 0.891 MPa. The tanδ, representing the ratio between viscosity and elasticity, remained constant with frequency. The trends for storage and loss moduli were described by exponential fits. The dynamic moduli of the central incisor were higher than those of the lateral incisor. The PDL samples from the gingival third of the root showed lower storage and loss moduli than those from the middle third of the root. Human PDL is viscoelastic through the range of frequencies tested: 0.5-10 Hz. The viscoelastic relationship changed with respect to frequency, tooth position, and root level.

Effect of high frequency oscillatory high flow nasal cannula on carbon dioxide clearance in a premature infant lung model: A bench study.

This study compared CO2 clearance in a premature infant lung model connected to a high flow nasal cannula (HFNC) system supplied with oscillatory versus non-oscillatory flow. The lung model was set to compliance 1.0 mL/cmH2 O, RR 60 breaths/min, and 6 mL tidal volume. A 100% CO2 was injected at a constant 15 mL/min. To create oscillation, HFNC flow was interrupted at rates of 4-6-8 and 10 Hz. equilibrated end-tidal CO2 (ETCO2 ) was recorded with and without oscillation at set flows of 2-8 L/min and repeated for each oscillation frequency. Overall ETCO2 decreased significantly (P < 0.001) during both non-oscillatory and oscillatory HFNC as set flow increased from 2 to 8 L/min by 26.3% and 60.8%, respectively. Oscillatory ETCO2 levels decreased linearly compared to non-oscillatory HFNC with negligible difference at 2 L/min and a 48.4% difference at 8 L/min (P < 0.001). There were no differences in ETCO2 levels between oscillation frequencies at any flow except at 6 Hz for which ETCO2 was significantly lower (P < 0.01) than at 4, 8, and 10 Hz for 5-8 L/min HFNC flows. Amplitude of volume oscillations increased with increasing flow from 0.5 mL at 2 L/min to 4.0 mL at 8 L/min (P < 0.001), and decreased with increasing oscillation frequency. Oscillatory HFNC as compared to non-oscillatory was associated with significantly improved CO2 clearance in this premature infant lung model. This simple modification of the HFNC system may prove to be a useful enhancement to this mode of non-invasive respiratory support for preterm infants at high risk for respiratory failure.

Self-Excited Fluidic Oscillators for Gas Turbines Cooling Enhancement: Experimental and Computational Study

Pulsed flow has been shown to enhance heat transfer coefficients of impinging jets. This paper considers the use of pulsed impinging jets, derived from a self-excited fluidic oscillator, for gas turbine cooling. Self-excited oscillatory behavior was demonstrated in simulations over a wide range of inlet to outlet pressure ratios from to for a device with a nozzle throat to splitter length of 10.4 mm. Heat transfer simulations at two test points (460 and 769 Hz) resulted in Nusselt number enhancement of 13 and 15% over corresponding cases with nonperiodic flow at the same time-mean mass flow rate. Increased oscillation frequency was found to increase Nusselt number enhancement. In the range (), the Nusselt number approximately doubled. A computational geometry optimization study was performed to increase oscillation frequency, resulting in a 30% increase. Validation experiments were performed using thin-film gauge (high-frequency) and calorimeter (low-frequency) measurement techniques. Experimental results were broadly in line with numerical results; a Nusselt number enhancement of approximately 20% () was achieved. Despite the enhancement in heat transfer, the fluidic oscillator is far from an ideal solution due to extreme pressure losses inside the device.

Effect of vibration on adaptation of dental composites in simulated tooth cavities

This research investigated the effects of vibration on the rheological properties of dental composites and the adaptation of tooth cavity-composite interfaces. A portable vibratory packing device and two composites, micro-hybrid dental composite (MC) and nano-hybrid dental composite (NC), were evaluated. The frequency and amplitude of the vibratory packing device were measured. Dynamic oscillatory shear tests were conducted with varying frequency to examine the rheological properties of the composites. Twenty identical composite teeth with a Class I cavity were prepared and filled with one of the two composites. The composite was placed into a cavity using the vibratory packing device operating in either ON or OFF mode. After light-curing of the composite, the gap between the tooth and the composite was evaluated using micro-computed tomography. Two-way ANOVA was used to evaluate the effects of vibration and composite type on tooth-composite adaptation. The frequency of the vibratory packing device was 66.8 Hz. The complex viscosity, η*, of NC was higher than that of MC, and η* of both composites significantly decreased with increasing oscillation frequency. However, the application of vibration did not enhance adaptation at the tooth-composite interface.

Quasinormal modes for nh-stu black holes

We compute and investigate the behavior of scalar quasinormal frequencies for static, asymptotically anti de Sitter nh-stu black hole solution of {mathcal {N}}=2, D=4 supergravity. We report their exact expression when the horizon topology is flat. The modes are purely imaginary unless they carry high angular momentum number. These modes for spherical horizon topology were numerically computed by using continued fraction method and found to be of two kinds. One such family consists of purely negative imaginary modes. The other family consists of complex modes with their imaginary part always negative, depicting stability of black holes against scalar perturbations. The complex modes show symmetry about imaginary axis, linear relationship with inverse temperature for large horizon radius and increased oscillation frequency for higher harmonics. Many of these properties are common to a family of black holes which asymptotes to anti de Sitter space, thus pointing to common features of thermalization dynamics of a class of dual holographic theories.

Fair-RTT-DAS: A robust and efficient dynamic adaptive streaming over ICN

To sustain the adequate bandwidth demands over rapidly growing multimedia traffic and considering the effectiveness of Information-Centric Networking (ICN), recently, HTTP based Dynamic Adaptive Streaming (DASH) has been introduced over ICN, which significantly increases the network bandwidth utilisation. However, we identified that the inherent features of ICN also causes new vulnerabilities in the network. In this paper, we first propose a novel attack called as Bitrate Oscillation Attack (BOA), which exploits fundamental ICN characteristics: in-network caching and interest aggregation, to disrupt DASH functionality. In particular, the proposed attack forces the bitrate and resolution of video received by the attacked client to oscillate with high frequency and high amplitude during the streaming process. To detect and mitigate BOA, we design and implement a reactive countermeasure called Fair-RTT-DAS. Our solution ensures efficient bandwidth utilisation and improves the user perceived Quality of Experience (QoE) in the presence of varying content source locations. For this purpose, Fair-RTT-DAS consider DASH’s two significant features: round-trip-time (RTT) and throughput fairness. In the presence of BOA in a network, our simulation results show an increase in the annoyance factor in user’s spatial dimension, i.e., increase in oscillation frequency and amplitude. The results also show that our countermeasure significantly alleviates these adverse effects and makes dynamic adaptive streaming friendly to ICN’s implicit features.

Transition of combustion instability in hybrid rocket by swirl injection

A series of experimental tests was conducted to investigate the effect of swirl injection on the combustion instability in hybrid rocket using combustion visualization technique. As a result, swirl injection seems to modify two main physical processes responsible for the initiation of LFI. First one is the transition of coupling status between two fluctuations of combustion pressure (p') and heat release (q') of 500 Hz band. The transition of p' and q' to negative coupling seems to be a crucial modification for stabilizing the combustion. Another noticeable effect of swirl injection is the gradual increase in the peak frequency of pressure oscillation from its initial value of around 20 Hz–50 Hz band, which is caused by the thermal lag, as the swirl intensity increases. Also, POD (Proper Orthogonal Decomposition) analysis was done to understand flow response to the swirl injection near the fuel surface. The analysis of temporal behavior of mode 1 and 2 suggested that the swirl injection with proper intensity not only suppress the generation of p' of 500 Hz band but induces a shift of low frequency peaks of 20 Hz band by adjusting the turbulent structures in boundary layer. And the shift of low frequency peaks seems to be another contributing factor for combustion stabilization.

Experimental investigation of self-excited combustion instabilities with injection coupling in a cryogenic rocket combustor

The cryogenic LOX/H2 multi-injector research combustor “BKD” allows the investigation of high-frequency combustion instabilities under realistic conditions. Two different types of self-excited instabilities were observed. For one instability the underlying coupling mechanism was already identified as LOX injection-driven. The second type of combustion instability was experienced for different operating conditions and is characterized by higher amplitudes, more than 75% of the static chamber pressure. Analysis of the pressure data showed that amplitude and frequency of the acoustic field vary strongly over time, which complicates interpretation of the coupling mechanism. A normalization of the shifting frequency shows that the increase of oscillation frequency depends on transverse acoustic velocity. This is an effect that has also been noticed in other experiments and simulations and is explained by improved mixing leading to a reduced length of the combustion zone. This observation suggests that during the large amplitude pressure oscillations the mode shape remains a first tangential (1T) mode with shifting frequency. By using highly resolved information of the acoustic field in the time domain, both from the combustion chamber and the injector volumes, in combination with acoustic modelling of the injector elements, insights into the coupling mechanism could be gained. For periods of lower amplitudes the pressure oscillations are LOX injector-driven, similar to the first type of instability. With increasing amplitude also the frequency of the unstable mode increases and shifts into a region, where interaction with the hydrogen injector 1L mode becomes possible.

RESEARCH ON DYNAMIC TEST TECHNOLOGY FOR WIND TURBINE BLADE AIRFOIL

The dynamic oscillation process of wind turbine blades is usually accompanied by pitching and yaw. Due to the unclear understanding of many dynamic problems previously, a safer design is adopted at the expense of increasing the weight of the blade structure in engineering, usually neglecting the influence of the yaw oscillation. The design of large wind turbines has put forward higher requirements for obtaining more comprehensive and accurate dynamic loads of airfoils. It is of great significance to study the influence of yaw oscillation on the dynamic aerodynamic characteristics of airfoil. In view of this, the dynamic wind tunnel test on yaw oscillation of airfoil is carried out in this paper for the first time. The “electronic cam” technology is used instead of the mechanical cam to realize the stepless adjustment of oscillation frequency and oscillation angle. Based on the designed electronic external trigger device, the real-time measurement of the dynamic flow field is realized. Meanwhile, the synchronous acquisition of wind tunnel flow, model angular displacement and dynamic pressure data is realized. Furthermore, the static pressure measurement, pitching / yaw dynamic pressure measurement, PIV and fluorescent wire test are carried out respectively. The accuracy of the test results is high, and the regular pattern is reasonable. Besides, the influence mechanism of wall interference in dynamic test is analyzed. Research shows that: there is also obvious hysteresis effect on the dynamic aerodynamic parameters of yaw oscillation airfoil with the changing of the angle of attack. And with the increase of oscillation frequency, the aerodynamic hysteresis characteristics of the airfoil under pitching and yaw oscillation are all enhanced. The dynamic stall vortex at the positive stroke is delayed due to the pitching oscillation. The pressure distribution of the airfoil is greatly influenced by the strong three-dimensional effect at the intersection of the wind tunnel wall and the model tip. Overall, the dynamic test technique of yaw oscillation established in this paper can provide technical support for the study of the dynamic swept effect of the wind turbines.

Numerical study of the effect of the oscillation frequency in buttonhole welding

A three-dimensional transient simulation was conducted with comprehensive models of the laser welding process with a combination of wire feeding and one-dimensional sinusoidal beam oscillation. Both a realistic filler wire feeding and simultaneous melting by oscillating laser beam were considered. The buttonhole formation, which was shown in the simulations, was affected by the shape of the molten filler wire, e.g. the length and angle. The buttonholes formed at higher oscillation frequencies and became clearer with increasing oscillation frequency. The so-called chopping frequency of the wire, found in the frequency domain through Fourier analysis, became more dominant with increasing oscillation frequency. The wire chopping process seems to affect the number of multiple reflections, the power absorption, and the buttonhole behavior.

Accuracy of oscillatory pressure measured by mechanical ventilators during high frequency oscillatory ventilation in newborns.

Oscillatory pressure (ΔP) measurement during high frequency oscillatory ventilation (HFOV) is technically challenging and influenced by all the components of the measurement system. To evaluate the differences between the ΔP delivered at the inlet of the endotracheal tube and those displayed by commercial neonatal mechanical ventilators and monitoring devices and to characterize how the ventilator circuit and the flowmeter proximal to the patient affect these differences. Six devices were evaluated while ventilating three mechanical analogues representing the newborn respiratory system in different disease states. ΔP measured at different points of the ventilator circuit were compared. ΔP accuracy is highly variable and decreases with increasing oscillation frequency and amplitude, independently of the mean airway pressure. At 15 Hz, a ΔP displayed by ventilators of 40 cmH2 O resulted in a ΔP effectively delivered at the tracheal tube ranging from 22 to 49 cmH2 O, depending on the ventilator model, the ventilator circuit, and the patient condition. At these settings, the errors exclusively due to the ventilator circuit and the presence of the flowmeter ranged from 6 to 9 cmH2 O and from 1 to 6 cmH2 O, respectively. The ventilator model, the breathing circuit, the flowmeter, and the patient condition severely impacts ΔP measurement accuracy during HFOV, leading to highly variable performances. This prevents the possibility of using the ΔP required to normalize gas exchange as an indicator of patients' condition, complicates comparison of ventilators performances, and adds a significant element of complexity in clinical management of HFOV.

Aggregation behavior and adsorption properties of salt-free catanionic surfactant mixtures containing tetradecyltrimethyl ammonium salts

ABSTRACTThe aggregation behavior of salt-free catanionic surfactants, tetradecyltrimethyl ammonium hydroxide (TTAOH)/fatty acid (FA) including octanoic acid (OA), decylic acid (DA) and lauric acid (LA) in aqueous solutions were studied. The critical micelle concentration(cmc), surface tension at cmc (γcmc), surface excess (Гmax), mean molecular surface area (Amin), adsorption efficiency (pc20) and surface tension reduction effectiveness (πcmc) were obtained from surface tension isotherms. The influence of temperature on the surface tension of salt-free TTAOH/FA (TTAOF) systems was investigated. Data of adsorption dynamics indicated that at fixed adsorption time, the order of adsorption capacity was TTAOH < TTAOH/OA (TTAOO) < TTAOH/DA (TTAOD) < TTAOH/LA (TTAOL). The adsorption process of salt-free TTAOF was adsorption-controlled. The complex and storage moduli increased with increasing oscillation frequency, however, the loss modulus showed the opposite trend. The complex modulus passed through a maximum value with increasing concentration of salt-free surfactant TTAOF. The adsorbed TTAOF layer was elastic, and the elasticity increased with increasing hydrocarbon chain length of FA.

Spontaneously oscillating menisci: Maximizing evaporative heat transfer by inducing condensation

Understanding the fluid dynamics and the phase change heat transfer process within a thin liquid film is important to improve the performance of many industrial processes like coating or distillation. Studies by our group and other research teams showed that thin liquid films begin to oscillate spontaneously as the heat flux increases. We also found that the oscillation amplitude and frequency increase with increasing heat input. This implies that there is a heat transfer advantage to an oscillating thin film. We developed a numerical model to try and understand if there is an advantage to oscillation and under what conditions that advantage occurs. We found that oscillation can enhance net evaporative heat transfer but only if a short period of condensation exists within each oscillation cycle. Such condensation can be driven by intermolecular forces, capillary forces, Marangoni forces, or combinations of all three as we concluded from recent heat pipe experiments. Condensation increases the liquid film thickness at the contact line, and therefore decreases the disjoining pressure impediment to evaporation. These short condensation periods followed by fast evaporation appear as “spikes” in the liquid film thickness over time. These “spikes” were observed experimentally and mimicked by the simulations. Our calculations also show that the heat transfer efficiency increases with increasing oscillation frequency and amplitude in qualitative agreement with experiments.

Effects of extraction methods on the rheological properties of polysaccharides from onion (Allium cepa L.)

In this work we described the rheological properties of polysaccharides (HBSS, CHSS, DASS, CASS) sequentially extracted from onion (Allium cepa L.). Four onion polysaccharides (ACLPs) solutions resulted into significant differences on their rheological properties. ACLPs solutions showed non-Newtonian shear-thinning behavior over the range of 0.5–2.5%. At concentration of 1%, the apparent viscosity of CHSS was observed to be the highest. The apparent viscosity of ACLPs solutions decreased with the acidic pH (4.0) or alkaline pH (10.0) which was further declined at higher temperature (90 °C). After the addition of various salts, ACLPs had apparent differences on apparent viscosity. The G′ (storage modulus) and G″ (loss modulus) of ACLP solutions were increased with increasing oscillation frequency. Moreover, the crossover value of oscillation frequency gradually decreased with increasing concentration of ACLPs. Our results exhibited that among the ACLPs, CHSS can be used as supplements in the food industry as thickening agent, gelling agent and stabilizer.

A Low-Power Ring Oscillator Using Pull-Up Control Scheme Integrated by Metal–Oxide TFTs

This paper proposes a pull-up control scheme in the pseudo-CMOS inverter to design a low-power ring oscillator (RO) realized by only n-type transistors. For comparing 11-stages, the proposed RO and the conventional RO are both fabricated by metal–oxide thin-film transistors with the etch stop layer structure. It is measured that the power-delay product of the proposed RO is reduced by more than 50% under the same value of supply voltage. At the same oscillation frequency, the power consumption tends to be reduced by 18% as oscillation frequency increases. Furthermore, the peak-to-peak voltage of the proposed RO can almost receive a full swing at any supply voltage.

The rheological behavior of polysaccharides sequential extracted from Polygonatum cyrtonema Hua

The present study investigated the rheological properties of polysaccharides (HBSS, CHSS, DASS, CASS) sequentially extracted from Polygonatum cyrtonema Hua. The monosaccharide, uronic acid, total carbohydrate, protein content of four polysaccharides were analyzed. The total carbohydrate content of PCHPs (HBSS, CHSS, DASS, and CASS) were 78.39, 71.86, 69.99 and 73.73% respectively, containing Rha, Ara, Man, Gal besides uronic acid and protein. The non-Newtonian fluidic nature of PCHPs was affected by the types of polysaccharides, concentration, temperature, pH, types and concentration of salt ions. Specifically, the apparent viscosity of four PCHPs solutions at 1%(w/w) concentration were shown as CHSS>HBSS>CHSS>CASS with increased concentration and shear thinning phenomenon and decreased system temperature. Subsequently, the apparent viscosity of four PCHPs at pH 10 or pH 4 were lower than that at pH 7. The Na+ increased the apparent viscosity of HBSS at increasing concentrations, while, decreased for remaining fractions with increasing Na+ concentration. Moreover, higher Ca2+ concentration was inversely proportional to apparent viscosity of four PCHPs. The oscillatory rheological properties showed that linear viscoelastic region of PCHPs was 1–4% which resulted into viscoelastic material. HBSS, DASS and CASS at 0.1%(w/w) showed more viscous behavior at low frequency and enhanced elastic property with the increasing oscillation frequency.

Design optimization of an articulated frame steering system

The articulated frame-steered vehicles (AFSV) exhibit enhanced maneuverability but reduced yaw stability and greater steering power consumption. Apart from kinematics of the steering system, the dynamics of the actuating system strongly influence the performance of the AFSV, which is generally neglected in the reported studies. In this study, a yaw-plane model of the articulated vehicle coupled with the kinematic and dynamics properties of the steering struts is formulated to identify objective measures of the AFSV under steering inputs. The results suggest that the vehicle yaw oscillation/stability, steering power efficiency and maneuverability can be objectively measured in terms of the strut length, yaw oscillation frequency and damping ratio, steering gain, and steering response rate and overshoot. The layout of steering struts and properties of the steering valve and hydraulic fluid are optimized while employing the weighted-sum method and a combination of pattern search and sequential quadratic programming algorithms. The relative weights of individual performance measures were obtained using the analytic hierarchy process (AHP) model. The solutions of the optimization problem revealed more compact articulated frame steering (AFS) system design with over 20% reduction in strut length and 24% gain in the yaw oscillation frequency. Increasing the fluid bulk modulus resulted in more compact AFS layout and further increase in the yaw oscillation frequency with lower response overshoot. The optimal design based on weighted sum of various performance measures, however, revealed negligible changes in terms of the steering power efficiency.