Partially-Covered Fractal Induced Turbulence On Fins Thermal Dissipation

The impacts of partially-covered fractal grids induced turbulence on the forced convective heat transfer across plate-fin heat sink at Reynolds number ReDh=22.0×103 were numerically and experimentally investigated. Results showed that partially covered grids rendered a higher thermal dissipation performance, with partially covered square fractal grid (PCSFG) registering an outstanding increase of 43% in Nusselt number relative to the no grid configuration. The analyzation via an in-house developed single particle tracking velocimetry (SPTV) system displayed the findings of unique “Turbulence Annulus” formation, which provided a small degree of predictivity in the periodic annulus oscillations. Further assessments on PCSFG revealed the preferred inter-fin flow dynamics of (i) high flow velocity, (ii) strong turbulence intensity, (iii) vigorous flow fluctuations, (iv) small turbulence length scale, and (v) heightened decelerated flow events. Furthermore, power spectra density unveiled the powerful vortex shedding effect, with PCSFG achieving fluctuation frequency f=18.5Hz close to an optimal magnitude. Such intricate flow structures pave the way for superior thermal transfer capabilities, benefiting the community in developing for higher efficiency heat transfer systems.

An influence of characteristics of amplitude fluctuation on detectability of alert sound of electric powered vehicles

The motor sound on electric powered vehicle is quiet at low speeds. Thus, pedestrians have difficulty detecting the vehicles approaching them under urban noise. Although the vehicles were designed to play an alert sound to solve this problem, it has not been solved yet. Our previous studies found that characteristics of amplitude fluctuation, fluctuation frequency, non-periodic fluctuation and amplitude envelope, are effective to make them detect approaching vehicles. However, those studies were investigated under only a specific actual environment, weren't examined validity of detectability in those studies. Here, this paper investigates under another actual environment, examine the validity. Investigations were carried out by using synthesized complex sounds which were designed to have periodic and non-periodic amplitude fluctuations. Those complex sounds have characteristics of amplitude fluctuations in gasoline powered vehicle. Amplitude envelopes such as modulation wave in amplitude-modulated sound were set for deviations for time and amplitude, and amplitude-modulated complex sounds were synthesized using sine wave, sawtooth wave, and rectangle wave. Then, their effects on detectability by pedestrians were assessed in another actual environment. The results found that amplitude fluctuation enhances the ability with which people detect approaching electric powered vehicles in case of some complex sound.

Response analysis of 3D braided two-stage gear system excited by different frequency signals

The knitting principle of 3D braided gear was studied, and the dynamic model of the two-stage gear system was established. The fourth-order Runge-Kutta method was used to numerically simulate the dynamic characteristics of common gear and 3D braided gear. The results showed that the fundamental frequency ω1 of the static transmission error excitation had the greatest effect on the speed and frequency characteristics of the first-stage gear along the meshing line. The research on frequency characteristics of common gear and 3D braided gear shows that the fundamental frequency ω1 of the static transmission error excitation has a large effect on the speed and frequency characteristics of the first-stage gear along the meshing line. With the reduction of the gear mass and moment of inertia, the amplitude in the low-frequency band increases. The vibration resonance of the system is studied by defining the amplitude gain of the response of the system output at the low-frequency signal ω3. The results show that with the reduction of gear mass and moment of inertia, when the input stage torque fluctuation frequency is Ω > 5, the fluctuation of amplitude gain Q disappears, which indicates that the vibration resistance of the 3D braided gear to high-frequency input stage torque fluctuation frequency is greatly improved.

Comparison of extraocular and intraocular pressure transducers for measurement of transient intraocular pressure fluctuations using continuous wireless telemetry

The optimal approach for continuous measurement of intraocular pressure (IOP), including pressure transducer location and measurement frequency, is currently unknown. This study assessed the capability of extraocular (EO) and intraocular (IO) pressure transducers, using different IOP sampling rates and duty cycles, to characterize IOP dynamics. Transient IOP fluctuations were measured and quantified in 7 eyes of 4 male rhesus macaques (NHPs) using the Konigsberg EO system (continuous at 500 Hz), 12 eyes of 8 NHPs with the Stellar EO system and 16 eyes of 12 NHPs with the Stellar IO system (both measure at 200 Hz for 15 s of every 150 s period). IOP transducers were calibrated bi-weekly via anterior chamber manometry. Linear mixed effects models assessed the differences in the hourly transient IOP impulse, and transient IOP fluctuation frequency and magnitude between systems and transducer placements (EO versus IO). All systems measured 8000–12,000 and 5000–6500 transient IOP fluctuations per hour > 0.6 mmHg, representing 8–16% and 4–8% of the total IOP energy the eye must withstand during waking and sleeping hours, respectively. Differences between sampling frequency/duty cycle and transducer placement were statistically significant (p < 0.05) but the effect sizes were small and clinically insignificant. IOP dynamics can be accurately captured by sampling IOP at 200 Hz on a 10% duty cycle using either IO or EO transducers.

Common principles underlie the fluctuation of auditory and visual sustained attention

Sustained attention plays an important role in adaptive behaviours in everyday activities. As previous studies have mostly focused on vision, and attentional resources have been thought to be specific to sensory modalities, it is still unclear how mechanisms of attentional fluctuations overlap between visual and auditory modalities. To reduce the effects of sudden stimulus onsets, we developed a new gradual-onset continuous performance task (gradCPT) in the auditory domain and compared dynamic fluctuation of sustained attention in vision and audition. In the auditory gradCPT, participants were instructed to listen to a stream of narrations and judge the gender of each narration. In the visual gradCPT, they were asked to observe a stream of scenery images and indicate whether the scene was a city or mountain. Our within-individual comparison revealed that auditory and visual attention are similar in terms of the false alarm rate and dynamic properties including fluctuation frequency. Absolute timescales of the fluctuation in the two modalities were comparable, notwithstanding the difference in stimulus onset asynchrony. The results suggest that fluctuations of visual and auditory attention are underpinned by common principles and support models with a more central, modality-general controller.

Stability Analysis of Luo Converter Using State Space Modeling

In this paper, stability of the Luo converter and the effect of circuit elements on the stability and damping fluctuation frequency is investigated. Along with this, the mathematical modeling of positive output (P/O) Luo converter in continuous conduction mode (CCM) is done by using an average state-space method. By using the obtained mathematical model, the transfer function of the Luo converter is extracted, and by using the location of the roots the mentioned transfer function, stability, and effect of circuit elements on converter behavior are studied. Also, its situations are compared with other converters. The analyses are performed through MATLAB based on simulations, which includes both roots location and bodes diagram.

Methane and carbon dioxide dynamics affected by water-level fluctuations in a shallow lake: Implications for wetland restoration

&lt;p&gt;Shallow lake was characterized by distinct hydrology, biochemistry and ecology that influence the carbon balance. This study explored methane and carbon emission responses to water level fluctuation in shallow lake, and also addressed its legacy for wetland restoration. This study used the process-based biogeochemical model, denitrification-decomposition (DNDC) model to simulate the alteration of methane and carbon emission with water level fluctuation in the Baiyangdian Lake (BYD Lake). The results showed: (i) compared with the observed carbon flux, the DNDC model can presented a suitable results in capturing the dynamics of methane and carbon dioxide, and the daily rate of carbon dioxide and methane emission showed sensitive to water fluctuation when it ranged from -10 cm to 10 cm; (ii) for the carbon dioxide, the annual flux showed a decline trend when the duration prolonged from 10 days to 40 days, and then an increasing trend while the duration prolonged to 90 days furtherly, with a lowest flux when the duration is 40 days, while for the methane, annual emission increased with inundation lasting time and the flux changing from -2.27 kg C/ha/y to 1.57 kg C/ha/y; and (iii) The flux of carbon dioxide and methane increased when water level fluctuation frequency increased, for a certain water level fluctuation frequency, carbon dioxide flux is lowest in January and February, and methane flux is negative from December to March of the following year. All of these results indicated that water level fluctuation (e.g., magnitude, duration and frequency) affected the carbon dioxide and methane flux, which will help to reduce the emission of carbon dioxide and methane by regulating ecological water transfer.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Keywords: &lt;/strong&gt;shallow lake, carbon emission; DNDC; water level fluctuation&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Acknowledgments&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;This study was supported by the National Key R&amp;D Program of China (No. 2018ZX07110001, No. 2017YFC0404505) and the National Natural Science Foundation of China (No. 51579008).&lt;/p&gt;

Dynamic Interactions Between the Rolling Element and the Cage in Rolling Bearing Under Rotational Speed Fluctuation Conditions

A nonlinear dynamic model is proposed to investigate the dynamic interactions between the rolling element and cage under rotational speed fluctuation conditions. Discontinuous Hertz contact between the rolling element and the cage and lubrication and interactions between rolling elements and raceways are considered. The dynamic model is verified by comparing simulation result with the published experimental data. Based on this model, the interaction forces and the contact positions between the rolling element and the cage with and without the rotational speed fluctuation are analyzed. The effects of fluctuation amplitude, fluctuation frequency, and cage pocket clearance on the interaction forces between the rolling element and the cage are also investigated. The results show that the fluctuation of the rotational speed and the cage pocket clearance significantly affects the interaction forces between the rolling element and the cage.