Decrease In Amplitude Of Oscillations Research Articles

Wave resistance of slender body in unsteady motion under an ice sheet

   The paper is devoted to the theoretical study of the rectilinear unsteady movement of a slender body in a liquid near the free surface and an ice sheet. Water is an ideal incompressible liquid, and the motion of the liquid is potential. The ice cover is modeled by a floating viscoelastic plate. The viscoelastic properties of ice are described using the Kelvin–Voigt model. A slender body of a given shape in the liquid flow is modeled by the flow of the source-sink system. Various modes of body movement are considered: acceleration, deceleration, movement at a given speed. The effect of the ice sheet, acceleration and deceleration of the body on its wave resistance is analyzed. It is obtained that unsteady modes of motion (acceleration and deceleration) significantly affect the wave resistance of a slender body. Motion with low initial acceleration makes it possible to reduce amplitude of the first-time hump of wave resistance. During body deceleration to a full stop, the curve of wave resistance has an oscillations. Reduction of deceleration coefficient results in decrease of oscillation amplitude of wave resistance curve. The presence of the ice cover smoothes the hump of wave resistance during acceleration and reduces the number of oscillations and their amplitude during deceleration.

Analysis of oscillatory processes in the cardiovascular system in response to local heating in patients with type 2 diabetes mellitus

A comprehensive spectral analysis was used to assess heart rate variability and skin perfusion pattern of limbs in patients with type 2 diabetes mellitus in response to local heating and to identify significant predictors of physiological and pathological changes in the cardiovascular system. An electrocardiogram and skin perfusion on the forearm and foot were measured using Laser Doppler flowmetry at rest and during local heating in both healthy volunteers and patients with type 2 diabetes. The wavelet analysis was applied to Laser Doppler signals and heart rate variability (based on electrocardiogram signals). ROC analysis was used to evaluate significant predictors. The analysis results of patients with type 2 diabetes were compared with healthy controls. The following changes were observed in patients 1) impairment of skin blood flow reserve on the foot during heating, 2) lower amplitude oscillations in heart rate at rest and during heating, 3) an increase in amplitude of oscillations in the skin blood flow from the forearm in intervals related to respiration and heart activity at rest and during heating, 4) a decrease in amplitude of oscillations in the skin blood flow on the foot in the interval related to myogenic activity at rest and in cardiointerval during heating. The parameters of cardiovascular system (energies of heart rate variability at low-frequencies recorded by laser Doppler flowmetry on forearm in intervals related to respiration activity) with high discriminative power were revealed to distinguish patients from healthy subjects in response to local heating; these parameters can be used as markers for early diagnosis of microvascular disorders.

Numerical study on the integration of supersonic turbine guide vanes and three-dimensional hydrogen/air rotating detonation combustor

Hydrogen/air rotating detonation turbine engine is expected to become a new generation of aerospace power plant because of its compact structure, high cycle thermal efficiency, and superior thrust performance. It can also reduce fuel consumption, save energy, and reduce carbon emissions. However, the highly unsteady oscillation characteristics of the outlet flow of the rotating detonation combustor make it difficult to integrate the supersonic turbine with the rotating detonation combustor. In this paper, the supersonic turbine guide vanes are designed by the method of characteristics and Bessel parameterization and are integrated with three-dimensional hydrogen/air rotating detonation combustors for numerical studies. The effects of aligned mode and misaligned mode on the coupling of supersonic turbine guide vanes and rotating detonation combustor are discussed carefully. The results show that the supersonic turbine guide vanes can make the rotating detonation wave change from a single-wave mode to a double-wave alternating strength and weak propagation mode. It can effectively suppress the oscillation of the combustion chamber outlet airflow. In the aligned mode, the peak pressure at the outlet of the supersonic turbine is about 70% lower than that at the cascade inlet, the pressure oscillation amplitude is reduced by 93.33%, and the temperature amplitude is reduced by 23.81%; the average total pressure loss coefficient of the cascade is 11.63%. In the misaligned mode, compared with the cascade inlet, the peak value of the pressure signal at the cascade outlet decreases by about 50%, while the pressure oscillation amplitude decreases by about 33.33%, and the temperature oscillation amplitude decreases by 11.11%; the average total pressure loss coefficient of the cascade is 4.83%. The supersonic turbine guide vanes have a better suppression effect on the oscillation signal in the aligned mode, but the relative total pressure loss is relatively large. This is because that the oblique shock wave, channel shock wave, and supersonic turbine guide vanes interact to generate more complex wave system and secondary flow in the aligned mode. These features provide important reference information for the coupling of supersonic turbines and rotating detonation combustors.

Experimental investigation of vortex-induced vibrations of a flexibly mounted cylinder in a shear-thinning fluid

We show experimentally that shear thinning can cause suppression of vortex-induced vibration (VIV). Increasing shear thinning in a fluid flow causes a decrease in the critical Reynolds number at which VIV occurs. VIV occurs within a range of reduced velocity, called the lock-in range. The reduced velocity at which lock-in begins, the width of the lock-in range, and the oscillation amplitude decrease for a shear thinning fluid, and beyond a critical concentration, oscillations are completely suppressed.

Hamiltonian Additional Damping Control for Suppressing Power Oscillation Induced by Draft Tube Pressure Fluctuation

The power oscillation induced by pressure fluctuation in the draft tube of the hydraulic turbine is one of the limiting factors preventing the Francis turbine from operating in the vibration zone. At the present power grid with a high proportion of renewable energy resources, we try to improve the load regulation ability of the hydropower units by extending the stable operation zone to the vibration zone. By the mathematical modelling of pressure fluctuation, this paper gives an analytical expression of the power oscillation. We derive the extended Hamiltonian model of the hydropower unit where power oscillation is external excitation. Secondly, the damping injection method introduces some desired interconnection and damping matrices as the Hamiltonian damping factor into the additional damping control. Finally, through theoretical analysis and experimental simulation, this research discusses the resonance characteristics of pressure fluctuation and power oscillation, the equivalent analysis between the damping factor and equivalent damping coefficient, and the control design of vibration zone crossing during the start-up. Simulation results show that when r25 = 1.3, the minimum power oscillation amplitude is 0.5466, which is equivalent to an increase in D by 20. The maximum oscillation amplitude decreases by 4.6%, and the operation limited zone is reduced by 10.1%. The proposed additional damping control can effectively suppress the power oscillation and expand the regulation range.

Analytical workload dependence of self-heating effect for SOI MOSFETs considering two-stage heating process

Dynamic self-heating effect (SHE) of silicon-on-insulator (SOI) MOSFET is comprehensively evaluated by ultrafast pulsed I–V measurement in this work. It is found for the first time that the SHE complete heating response and cooling response of SOI MOSFETs are conjugated, with two-stage curves shown. We establish the effective thermal transient response model with stage superposition corresponding to the heating process. The systematic study of SHE dependence on workload shows that frequency and duty cycle have more significant effect on SHE in first-stage heating process than in the second stage. In the first-stage heating process, the peak lattice temperature and current oscillation amplitude decrease by more than 25 K and 4% with frequency increasing to 10 MHz, and when duty cycle is reduced to 25%, the peak lattice temperature drops to 306 K and current oscillation amplitude decreases to 0.77%. Finally, the investigation of two-stage (heating and cooling) process provides a guideline for the unified optimization of dynamic SHE in terms of workload. As the operating frequency is raised to GHz, the peak temperature depends on duty cycle, and self-heating oscillation is completely suppressed.

Study on the Influencing Factors of the Response Characteristics of the Slide Valve-Type Direct-Acting Relief Valve with External Orifice

The slide valve-type direct-acting relief valve with external orifice (SVTDARVWEO) is widely used in hydraulic systems, and its response characteristics are influenced by key factors. It is of great significance to carry out research on the influencing factors of the response characteristics of the SVTDARVWEO. The working principle of the SVTDARVWEO is analyzed in the present study. The simulation model of the SVTDARVWEO is established using AMESim. The influence of the orifice diameter, viscosity coefficient, valve element mass, spring stiffness, oil seal length, and valve element diameter on the response characteristics of the SVTDARVWEO is studied. The results show that: (1) The smaller the orifice diameter is, the smaller the oscillation frequency, amplitude and maximum overshoot of pressure, flowrate, displacement and velocity are. (2) When the viscosity coefficient is 50 N/(m/s), 55 N/(m/s) and 60 N/(m/s), the pressure, flowrate, displacement and velocity oscillate periodically, but the amplitude of the oscillation decreases gradually, and the oscillation frequency is 250 Hz. When the viscosity coefficient is 60 N/(m/s), the pressure, flowrate, displacement and velocity will reach their respective stable values earlier. (3) When the valve element mass is 0.01 kg, 0.015 kg and 0.02 kg, the pressure, flowrate, displacement and velocity oscillate periodically, but the amplitude of oscillation decreases gradually. When the valve element mass is 0.01 kg, the pressure, flowrate, displacement and velocity will reach the stable value earlier. (4) The smaller the spring stiffness is, the greater the maximum overshoot of pressure, flowrate, displacement and velocity is, and the higher the number of oscillations to reach the stable value are, in addition to more time being required. (5) With the increase in oil seal length, the maximum overshoot of pressure and velocity, stability value of displacement also increase correspondingly. (6) With the increase in the valve element diameter, the stable value of pressure decreases, and the oscillation frequency of pressure, flowrate, displacement and velocity increase, but the oscillation amplitude decreases.

Analytical Damping Contribution Assessment Method of Multiconverters System Based on Energy Network Model

Multiconverters connected to grid can induce subsynchronous oscillation (SSO). This article proposed an analytical damping contribution assessment method that can explicitly reveal how (positively or negatively) and to which degree each converter in the multiconverters system changes the system stability level. First, the energy network model of the multiconverters system that satisfies energy conservation is proposed. On this basis, a theory proof is presented that the real part of eigenvalue of SSO mode in the multiconverters system is equal to the sum of coefficient in the aperiodic components of the derivative of dynamic energies injected by each converter and dissipation energy of network, which illustrates analytically how the SSO stability level is shaped. The dynamic energy showing a decreasing trend is good for the oscillation to disappear, and the faster the dynamic energy decreases, the faster the oscillation amplitude decreases. Thus, how and to which degree converter changes stability level can be revealed by the changing trend and rate of its dynamic energy, respectively. Moreover, the expression of dynamic energy is brief, which is, thus, readily for online use, and is universal for converters with different control strategies. Finally, hardware in loop tests verifies that, eliminate converters’ rapidly increasing dynamic energy, the unstable SSO converges rapidly, and eliminate converters’ slowly increasing dynamic energy, the unstable SSO converges but slowly, and eliminate converters’ decreasing dynamic energy, unstable SSO diverges more rapidly, which demonstrates that dynamic energy can precisely assess damping contribution of converter.

Slow oscillation density and amplitude decrease across development in pediatric Duchenne and Becker muscular dystrophy.

From childhood through adolescence, brain rhythms during non-rapid eye movement (NREM) sleep show dramatic development that mirror underlying brain maturation. For example, the function and characteristics of slow oscillations (SOs, <1 Hz) in healthy children are linked to brain development, motor skill, and cognition. However, little is known of possible changes in pediatric populations with neurologic abnormalities. We measured slow oscillations in 28 Duchenne and Becker muscular dystrophy male patients from age 4 to 20 years old during overnight in-lab clinical sleep studies. We compared our pediatric patients by age to evaluate the developmental changes of SOs from childhood to early and late adolescence. Consistent with the current neuro- and physically typical literature, we found greater slow oscillation density (count of SOs per minute of each sleep stage) in NREM N3 than N2, and significantly greater slow oscillation density in frontal compared to central and occipital regions. However, separating patients into age-defined groups (child, early adolescent, and late adolescent) revealed a significant age effect, with a specific decline in the rate and amplitude of SOs. We found that with age, pediatric patients with Duchenne muscular dystrophy show a significant decline in slow oscillation density. Given the role that slow oscillations play in memory formation and retention, it is critical to developmentally characterize these brain rhythms in medically complex populations. Our work converges with previous pediatric sleep literature that promotes the use of sleep electroencephalographic markers as prognostic tools and identifies potential targets to promote our patients' quality of life.

Ulcerative Lesions of the Mucosa Gastro-Duodenal Zone in Victims of the Chernobyl Accident: Some Features of the Etiology, Pathogenesis and Clinical Signs Identified in the Third of the Century After the Disaster

Introduction. The victims of the Chernobyl accident have a significantly higher morbidity compared to the unaffected population. Ulcerative lesions of the gastric and duodenal mucosa are quite common. The aim of the study. To find out some features of ulcerative lesions of the gastroduodenal zone in the victims of the Chernobyl accident based on the analysis of the causes, pathogenesis, clinical signs, conducted in the third of the century after the disaster. Materials and methods. The study involved 115 patients with ulcerative lesions of the gastroduodenal zone. The experimental group (EG) of 80 patients who suffered as a result of the Chernobyl accident and the comparison group (GC) of 35 patients who were not affected by the Chernobyl disaster. The control group (CG) consisted of 30 conditionally healthy volunteers. Results. In patients affected by the Chernobyl accident, heredity plays a significantly smaller role than in patients with GC (28.7 % patients of EG against 48.6 % of GC, p less than 0.05). Smoking and use of nonsteroidal anti-inflammatory drugs were significantly more relevant in those affected by the Chernobyl disaster (75.0 % of patients with EG and 31.4 % of GC; p less than 0.05). All patients EG were exposed to higher radiation (100.0 % EG and 0.0 % GC). The cytoprotection of the gastroduodenal zone in patients EG with gastric ulcer in both gastric juice and insoluble mucus were significantly lower compared with GC (EG: NANA of gastric juice 0.27 ± 0.01 vs. 0.58 ± 0.02 mg/ml; p less than 0.05; GC: NANA in insoluble mucus 0.45 ± 0.04 vs. 1.16 ± 0.09 mg/ml; p less than 0.05). The cytoprotection of the gastroduodenal zone in patients EG with duodenum ulcer in both gastric juice and insoluble mucus were significantly lower compared with GC (EG: NANA in gastric juice 0.29 ± 0.02 vs. 0.53 ± 0.03 mg/ml; p less than 0.05; GC: NANA in insoluble mucus 0.44 ± 0.07 vs. 1.09 ± 0.08 mg/ml; p less than 0.05). Significant increase in heart rate and decrease in amplitude of heart rhythm oscillations and consequently HRV parameters were observed in patients EG compared to GC in both supine position and orthostatic test. In most patients, who are victims of the Chernobyl accident, a specific pattern of HRV (decrease of heart rhythm oscillations (decrease in SDNN and TP), relatively high level of VLF waves, moderate decrease in LF and dramatic decrease in HF) was observed. All patients were divided into three groups, depending on parameters of lipid peroxidation and activity of AOS (AAOS). Group number 1 (with enhanced LPO), group number 2 (with normal LPO) and group number 3 (with reduced LPO). All groups were divided into subgroups according to the AAOS: AAOS increased (subgroup 0.1.) normal activity AOS (subgroup 0.2.) and reduced AAOS (subgroup 0.3.). Some patterns were found after comparison. The results were different vectors. Number of patients with increased LPO (group 1) was significantly different (96.2 %* of patients EG and 68.6 % of patients GC (p less than 0.05). Indicators of patients with reduced lipid peroxidation show that the lowest incidence of such cases were among patients EG (3.7 %), while in GC in 14.3% of patients (p less than 0.01). During endoscopic examination, we found that ulcers from 1.1 to 2.0 cm, there were more EG patients (60.0 % EG and 31.4 % GC; p less than 0.05), so they also had significantly more concomitant erosive lesions of the mucous membrane of the stomach (50.0 % EG and 20.0 % GC; p less than 0.05) and duodenum (47.5 % EG and 17.1 % GC; p less than 0.05). Patients victims of the Chernobyl accident were significantly more often detected reflux conditions including reflux esophagitis (78.8 % EG and 42.9 % GC; p less than 0.05), duodenal-gastric reflux (68.8 % EG and 34.3 % GC; p less than 0.05). Patients EG significantly more often encountered diffuse chronic gastritis with atrophic changes in the gastric mucosa (57.5 % of the patients in the EG and 28.6 % of the GC; p less than 0.05). The patients (affected by the Chernobyl accident) have multiple complaints with its own characteristics. They were significantly less concerned about the intense pain in gastroduodenal zone (intense abdominal pain in 22.5 % of patients EG and 60.0 % of the patients GC, p less than 0.05; painless ulcer in 30.0 % of patients EG and in 8.6 % patients GC; p less than 0.05). Symptoms of gastric and intestinal dyspepsia, the asthenic-neurotic syndrome are much more often. Conclusions. Ulcerative lesions of the mucosa of gastroduodenal in victims of the Chernobyl accident in the long term after the disaster, according to the analysis of the causes, pathogenesis, clinical signs have certain features, compared with patients who did not suffer from the Chernobyl disaster. All victims of the Chernobyl accident were exposed to ionizing radiation. Smoking and use of ulcerogenic drugs, stress and dietary disorders are significantly more frequent in victims of the Chernobyl accident, but aggravated heredity is less common. In the pathogenesis of important place is occupied by changes in the ratio of peptic-aggressive and cytoprotective factors of gastric contents in the direction of reducing the protection of the mucous membrane of the gastroduodenal zone; in patients, who are victims of the Chernobyl accident, compared with patients control, there is a decrease in heart rate variability, as well as a more pronounced internal redistribution of parameters with a relative predominance of central and humoral-metabolic effects on heart rate and a decrease in the amplitude of waves arising from parasympathetic activity; also revealed multi-vector (increased, within normal limits, decreased) state of lipid peroxidation and activity of the antioxidant system (the number of the Chernobyl patients with enhanced lipid peroxidation and reduced activity of the antioxidant system is relatively greater). The morphological forms of gastric and duodenal lesions are dominated by pangastritis with atrophic changes of the mucous membrane, the presence of ulcerative defects of medium and large size, as well as more frequent reflux esophagitis, duodeno-gastric reflux and concomitant erosive lesions. Features of clinical manifestations are the dominance of astheno-neurotic and dyspeptic syndromes, minimization or absence of typical pain.

Anomalous Decay of Quantum Resistance Oscillations of 2D Helical Electrons in Magnetic Field

Shubnikov de Haas resistance oscillations of highly mobile two dimensional helical electrons propagating on a conducting surface of strained HgTe 3D topological insulator are studied in magnetic fields B tilted by angle θ from the normal to the conducting layer. Strong decrease of oscillation amplitude A is observed with the tilt: {boldsymbol{A}}sim {boldsymbol{e}}{boldsymbol{x}}{boldsymbol{p}}(,-,{boldsymbol{xi }}/{boldsymbol{c}}{boldsymbol{o}}{boldsymbol{s}}({boldsymbol{theta }})), where ξ is a constant. Evolution of the oscillations with temperature T shows that the parameter {boldsymbol{xi }} contains two terms: {boldsymbol{xi }}={{boldsymbol{xi }}}_{1}+{{boldsymbol{xi }}}_{2}{boldsymbol{T}}. The temperature independent term, {{boldsymbol{xi }}}_{{bf{1}}}, signals possible reduction of electron mean free path {l}_{q} and/or enhancement of in-homogeneous broadening of the oscillations in magnetic field B. The temperature dependent term, {{boldsymbol{xi }}}_{{bf{2}}}{boldsymbol{T}}, indicates increase of the reciprocal velocity of 2D helical electrons: delta ({v}_{F}^{-1})sim B suggesting modification of the electron spectrum in magnetic fields. Results are found in good agreement with proposed phenomenological model.

Neurologically Motivated Coupling Functions in Models of Motor Coordination.

We present an analysis of two Haken-Kelso-Bunz (HKB) oscillators coupled by a neurologically motivated function. We study the effect of time delay and weighted self-feedback and mutual feedback on the synchronization behavior of the model. We focus on identifying parameter regimes supporting experimentally observed decrease in oscillation amplitude and loss of anti-phase stability that has inspired the development of the HKB model. We show that a combination of cross-talk and nonlinearity in the coupling, along with physiologically relevant time delay, is able to quantitatively account for both drop in oscillation amplitude and loss of anti-phase stability in a frequency dependent manner. Furthermore, we demonstrate that the transition between discrete and rhythmic movements could be captured by this model. To this end, we carry out theoretical and numerical analysis of the emergence of in-phase and anti-phase oscillations.

Residence time distribution and Peclet number correlation for continuous oscillatory flow reactors

AbstractBACKGROUNDOscillatory baffled reactors have good prospect for use in batch to continuous transition for many industries. For reliable design and scale up it is essential to mathematically describe mixing and flow pattern of oscillatory flow. The aim of this study is to investigate the effects of operating conditions on residence time distribution (RTD) of liquid phase in a continuous oscillatory baffled reactor (COBR) and to propose a correlation that accurately describes the flow pattern.RESULTSAnalysis of results obtained for a wide variety of operating conditions in two geometrically similar reactors show that increase of oscillation frequency and amplitude both decrease axial dispersion, with a more prominent effect of amplitude. Proposed power‐law correlation is in very good agreement with all performed experiments. Peclet numbers predicted by this correlation are in reasonably good agreement with the literature experimental data and is much better than the ones obtained by the commonly used correlation, which contains more fitting parameters.CONCLUSIONResults show that relatively high amplitudes, low frequencies and low to moderate secondary non‐oscillatory flow should be used to ensure effective mixing with a low net flow in COBR. Developed correlation offers a simple, yet reliable way to predict the macroscopic flow pattern of liquid in COBR. © 2017 Society of Chemical Industry

High-speed observation for a better understanding of bubble dynamics in an in vivo -like situation of sonoporation

Sonoporation is a technique to temporally increase the permeability of a biological cell membrane by ultrasound exposure and to transduce a foreign gene or drug that normally has no permeability. The mechanisms of sonoporation have not been fully elucidated yet; however, it is widely accepted that microbubbles oscillating adjacent to cells play an important role to induce membrane damage. Dynamics of microbubbles has strong dependence not only on exposure parameters of ultrasound but also on surrounding conditions of the bubbles. To obtain a better understanding of cell-bubble interactions affected by the surrounding conditions, high-speed observation was carried out. A newly designed chamber was used for observation from a lateral direction, enabling visualization of translational movements of bubbles beside a scaffold and of cell-bubble interaction without hiding the interacting point by the oscillating bubble itself. It was observed that a bubble on a soft scaffold surface moves translationally in a direction separating from the surface, whereas a bubble on a hard scaffold surface remains on the surface. Adhesion of a bubble to the top of a cell caused a considerable decrease in bubble oscillation amplitude, but membrane damage was confirmed in all of the observed cells with attached bubbles, indicating the importance of taking into account the conditions surrounding a bubble in order to understand the mechanisms of sonoporation.

Influences of phase delay shifts of light and food restriction on blood pressure and heart rate in telemetry monitored rats

Effects of phase delay shifts (PDS) of light in combination with moderately increased salt intake (SL) (2%) or time restriction of food (FR) during the light-time (passive phase) on heart rate (HR), blood pressure (BP) and locomotor activity (LA) in radiotelemetry-measured rats were evaluated. PDS decreased amplitude and spectral power of circadian oscillations of HR, BP and LA. Moderately increased SL did not interfere with the circadian rhythmicity of HR, BP or LA. A prominent decrease in amplitude and spectral power of circadian oscillations was observed if food was available during the lighttime. Combination of PDS with FR split cardiovascular and behavioural parameters. In conclusion, food availability during the light-time in combination with PDS decreased amplitude and spectral power of circadian oscillations of BP, HR and LA more than PDS only. Different response of cardiovascular and behavioural parameters to photic and non-photic stimuli can have consequences for shift workers.

Numerical modeling of the 3D dynamics of ultrasound contrast agent microbubbles using the boundary integral method

Ultrasound contrast agents (UCAs) are microbubbles stabilized with a shell typically of lipid, polymer, or protein and are emerging as a unique tool for noninvasive therapies ranging from gene delivery to tumor ablation. While various models have been developed to describe the spherical oscillations of contrast agents, the treatment of nonspherical behavior has received less attention. However, the nonspherical dynamics of contrast agents are thought to play an important role in therapeutic applications, for example, enhancing the uptake of therapeutic agents across cell membranes and tissue interfaces, and causing tissue ablation. In this paper, a model for nonspherical contrast agent dynamics based on the boundary integral method is described. The effects of the encapsulating shell are approximated by adapting Hoff’s model for thin-shell, spherical contrast agents. A high-quality mesh of the bubble surface is maintained by implementing a hybrid approach of the Lagrangian method and elastic mesh technique. The numerical model agrees well with a modified Rayleigh-Plesset equation for encapsulated spherical bubbles. Numerical analyses of the dynamics of UCAs in an infinite liquid and near a rigid wall are performed in parameter regimes of clinical relevance. The oscillation amplitude and period decrease significantly due to the coating. A bubble jet forms when the amplitude of ultrasound is sufficiently large, as occurs for bubbles without a coating; however, the threshold amplitude required to incite jetting increases due to the coating. When a UCA is near a rigid boundary subject to acoustic forcing, the jet is directed towards the wall if the acoustic wave propagates perpendicular to the boundary. When the acoustic wave propagates parallel to the rigid boundary, the jet direction has components both along the wave direction and towards the boundary that depend mainly on the dimensionless standoff distance of the bubble from the boundary. In all cases, the jet directions for the coated and uncoated bubble are similar but the jet width and jet velocity are smaller for a coated bubble. The effects of shell thickness and shell viscosity are analyzed and determined to affect the bubble dynamics, including jet development.

EVIDENCE OF THERMONUCLEAR FLAME SPREADING ON NEUTRON STARS FROM BURST RISE OSCILLATIONS

Burst oscillations during the rising phases of thermonuclear X-ray bursts are usually believed to originate from flame spreading on the neutron star surface. However, the decrease of fractional oscillation amplitude with rise time, which provides a main observational support for the flame spreading model, have so far been reported from only a few bursts. Moreover, the non-detection and intermittent detections of rise oscillations from many bursts are not yet understood considering the flame spreading scenario. Here, we report the decreasing trend of fractional oscillation amplitude from an extensive analysis of a large sample of Rossi X-ray Timing Explorer Proportional Counter Array bursts from ten neutron star low-mass X-ray binaries. This trend is 99.99% significant for the best case, which provides, to the best of our knowledge, by far the strongest evidence of such trend. Moreover, it is important to note that an opposite trend is not found from any of the bursts. The concave shape of the fractional amplitude profiles for all the bursts suggests latitude-dependent flame speeds, possibly due to the effects of the Coriolis force. We also systematically study the roles of low fractional amplitude and low count rate for non-detection and intermittent detections of rise oscillations, and attempt to understand them within the flame spreading scenario. Our results support a weak turbulent viscosity for flame spreading, and imply that burst rise oscillations originate from an expanding hot spot, thus making these oscillations a more reliable tool to constrain the neutron star equations of state.

Cytoskeletal turnover and Myosin contractility drive cell autonomous oscillations in a model of Drosophila Dorsal Closure

Oscillatory behaviour in force-generating systems is a pervasive phenomenon in cell biology. In this work, we investigate how oscillations in the actomyosin cytoskeleton drive cell shape changes during the process of Dorsal Closure, a morphogenetic event in Drosophila embryo development whereby epidermal continuity is generated through the pulsatile apical area reduction of cells constituting the amnioserosa (AS) tissue. We present a theoretical model of AS cell dynamics by which the oscillatory behaviour arises due to a coupling between active Myosin-driven forces, actin turnover and cell deformation. Oscillations in our model are cell-autonomous and are modulated by neighbour coupling, and our model accurately reproduces the oscillatory dynamics of AS cells and their amplitude and frequency evolution. A key prediction arising from our model is that the rate of actin turnover and Myosin contractile force must increase during DC in order to reproduce the decrease in amplitude and period of cell area oscillations observed in vivo. This prediction opens up new ways to think about the molecular underpinnings of AS cell oscillations and their link to net tissue contraction and suggests the form of future experimental measurements.

Effect of Secondary Regular Microstructure on the Micro-flows in Nano-channel with Low Surface Energy

In order to investigate the property of nano-Poiseuille flow using molecular dynamics simulation, while the channel has secondary regular microstructure and low surface energy. In the simulation, statistical ensemble is set as NVE, LJ/126 model as the potential energy function and rigid-atom model is used to describe the wall and the time/rescale thermostat to keep the temperature of fluid constant. Meanwhile, the potential energy parameter between solid and liquid atoms is adjusted to realize the wall of low surface energy. The results show that when the channel wall has microstructure, the vertical density profiles of fluid appeared two oscillation regions near the wall, namely significant weak oscillation within the microstructure(called second oscillation) and strong oscillation in the channel. With the increase of rectangle microstructure period(T), the oscillation degree of density profile within the secondary microstructure increase, while the oscillation in the channel is decrease. The increase of depth(H) of the rectangle microstructure result in a secondary oscillation amplitude decreases and the starting point of density profile move away the center of channel. The period and depth of the secondary microstructure also has a significant influence on the flow. As T and H increase, the average flux of channel also increase, which suggests that the channels present better drag reduction effect.

Flickering characteristics and temperature field of premixed methane/air flame under the influence of co-flow

The flickering characteristics and the temperature field of an axisymmetric premixed methane/air flame under the influence of co-flow are studied experimentally using the image analysis and the flame reaction technique. The premixed flame is visualized by the alkali metal solution of sodium (Na) for characterizing the flickering characteristics. The temperature measurement of the flame is carried out using the flame reaction technique combined with the relationship between the local intensity of the flame and the temperature from the sodium D-line reversal method, and the influence of the number density distribution of Na on the measured temperature field is corrected by the measurement integrated analysis of the flame with the iterative procedure. This technique is validated by the local temperature measurement in the steady flame under the influence of co-flow using the thermocouple calibrated by the sodium D-line reversal method. The flame visualization and temperature measurement in the flickering flame of the premixed methane/air flame indicates that the flame contour and the temperature field oscillate periodically with the flickering frequency due to the Kelvin–Helmholtz instability of the flame. The oscillation amplitude decreases and the frequency increases gradually with the co-flow velocity increases similar to the observation in the diffusion flame in literature, while the oscillation amplitude grows with the equivalence ratio increases. These changes in the flickering characteristics of the flame are caused by the variations of the temperature field in the premixed flame.