Violent Fluctuations Research Articles

Design optimization of hydrodynamic cavitation for effectual lipid extraction from wet microalgae

Design optimization of hydrodynamic cavitation (HC) was performed for the sake of maximally extracting internal lipids directly from wet microalgae. Different types of orifice plates (α = 2.5–10%; β = 1–10%) were designed for a HC system and examined in terms of cavity formation; and cavitation effect was demonstrated by way of lipid extraction from microalgae. Basic operating parameters of HC, such as flux, flow rate, and the number of rotation, were examined and based on them, the upper and lower limits of cavitation number identified to be 3.37 ± 0.01 (α = 2.5% and β = 1%) and 1.01 ± 0.00 (α = 7.5% and β = 1%), respectively. The maximum lipid extraction (46.0 ± 3.7%) was obtained at 5% of both α and β. A low β value resulted in high vapor pressure, which has a crucial effect on the cell disruption caused by the creation and extinction of cavities. Also, the number of treatment per minute through the orifice proved to be a crucial factor for cell disruption. On the other hand, a high α value caused a surge pressure driven by violent fluctuation of flow. The cavitation effects of HC were able to be well visualized in terms of pressure variation using CFD. This study showed that the HC is indeed a very promising cell disruptor and its effectiveness can be further enhanced by way of design optimization.

Experimental Investigation on Transient Pressure Characteristics in a Helico-Axial Multiphase Pump

In oil and gas exploitation, the multiphase pump is a vital piece of equipment to guarantee production with high efficiency and stable operation. The complicated pattern of multiphase flow in the multiphase pump affects the pump performance; for this reason, the multiphase performance and the inner flow should be sufficiently investigated. In the present work, a liquid-gas multiphase pump is designed and manufactured, and then tested in a specialized test rig to reveal the transient pressure characteristics of the multiphase pump. Results show that the dominant frequency under water and water-air conditions is the blade passing frequency, which is induced by the rotor stator interaction. In the downstream of the impeller, the pressure fluctuation is obviously weakened, because the splitter-blade design could improve the control ability of flow pattern in the downstream region. In comparison with water condition, the pressure fluctuation of water-air condition greatly increases, and the multiples of impeller rotating frequency are stimulated due to the movement and merging of air bubbles. Finally, the correlation of transient pressure and phase distribution in impeller is revealed by using a high-speed camera. With the gradual pressure rise from impeller inlet to outlet, the relative movement and separation of two phases induce violent pressure fluctuations.

Electrical-thermal transport properties and their applications in graphene nanoribbon with DNA bases

Abstract By applying the density functional theory and the nonequilibrium Green's function formalism, we analyze the thermal, electrical transport properties and their applications of four kinds of bases in DNA sandwiched between two zigzag-edge graphene nanoribbon electrodes. The results show that the currents in different base-sandwiched systems display different current bias voltage characteristics. Conductivity enhancement and negative differential resistance (NDR) behaviors can be observed. The electron transport is relatively smooth, while the phonon transport is depressed obviously. The super-low thermal conductance and the violent fluctuation of electronic transmissions induce the enhanced thermopower.

Time-varying character for short-term capital flow from the interest rate aspect in China

This study investigates the causal link between short-term capital flow and interest rate differential with the bootstrap Granger full-sample causality and sub-sample rolling-window methods. The empirical results indicate that there is a unidirectional link from interest rate differential to short-term capital flow. However, when considering structural breaks in the above series, the full-sample causality test cannot be relied on. Hence, the time-varying rolling-window method is employed to examine the dynamic causal nexus. Being influenced by the U.S. monetary, world economic situation, Chinese intervention policies and other factors, interest rate differential has influences on short-term capital flow in some periods, but the reverse effect does not exist. Therefore, it is important for authorities to focus on specific backgrounds (e.g., economic situation, monetary policies) and further utilise interest rate and capital control to alleviate negative effects from violent fluctuation of short-term capital flow on the Chinese economy.

A CO Adsorption Site Change Induced by Copper Substitution in a Ruthenium Catalyst for Enhanced CO Oxidation Activity

AbstractRu is an important catalyst in many types of reactions. Specifically, Ru is well known as the best monometallic catalyst for oxidation of carbon monoxide (CO) and has been practically used in residential fuel cell systems. However, Ru is a minor metal, and the supply risk often causes violent fluctuations in the price of Ru. Performance‐improved and cost‐reduced solid‐solution alloy nanoparticles of the Cu‐Ru system for CO oxidation are now presented. Over the whole composition range, all of the CuxRu1−x nanoparticles exhibit significantly enhanced CO oxidation activities, even at 70 at % of inexpensive Cu, compared to Ru nanoparticles. Only 5 at % replacement of Ru with Cu provided much better CO oxidation activity, and the maximum activity was achieved by 20 at % replacement of Ru by Cu. The origin of the high catalytic performance was found as CO site change by Cu substitution, which was investigated using in situ Fourier transform infrared spectra and theoretical calculations.

Analytical and experimental investigations of the enhanced mechanical response of cutting deformation compared to progressive folding in AA6061 energy dissipation devices

Traditional axially loaded energy absorbers often dissipate kinetic energy through progressive folding. Both the high probability of transition to global bending and the characteristic, violent fluctuations in load are disadvantages to folding that engineers have rigorously attempted to mitigate and control since the inception of this technology. A novel energy dissipation mechanism developed by researchers at the University of Windsor, referred to as axial cutting, allows extrusions to dissipate energy with minimal fluctuations in load during the deformation process. A previously derived analytical model for the steady-state cutting force was consulted and modified to provide improved predictive capabilities for higher bladed cutting scenarios. A parametric study was conducted using this revised model and an analytical model for the mean crushing force were used to postulate a series of test cases where, for 8 and 10-bladed cutting scenarios, greater total energy absorption could be achieved through axial cutting than with progressive folding of geometrically similar extrusions. The specimens were AA6061 extrusions having T4 and T6 temper conditions with geometries varying from 50.8 mm to 63.5 mm in diameter and 1.0 mm to 2.0 mm in wall thickness. All tests were performed quasi-statically using a universal MTS testing machine at a crushing rate of 50 mm/min. The axially cut extrusions displayed an average increase of 15.8% in energy absorption than their respective axially crushed test specimens with a crush force efficiency greater by a factor of 2. The modified analytical model of the steady-state cutting force was validated using the experimental data and determined to be accurate to within 10% of the experimental mean loads in most cases.

Three-dimensional Eulerian modeling of gas–liquid–solid flow with gas hydrate dissociation in a vertical pipe

The pipe transportation of gas hydrate-bearing sediments (GHBS)1GHBS—gas hydrate-bearing sediments;1 is one of the key problems in mechanical–thermal exploitation of gas hydrate (GH)2GH—gas hydrate.2 in marine stratum. It is a gas–liquid–solid (methane gas–seawater–GHBS particles) three-phase flow, accompanied by GH dissociation. In this study, a three-dimensional Eulerian model combined with the kinetic theory of granular flow (KTGF) was adopted to simulate the gas–liquid–solid flow with GH dissociation. The commercial CFD software FLUENT 16.2 was employed, considering the hydrodynamics, heat and mass transfer, and GH dissociation simultaneously. A kinetic model for GH dissociation in the GHBS particles is presented, considering the influence of multiphase flow on dissociation rate. The model can capture the transition from the initial liquid–solid two-phase flow to gas–liquid–solid three-phase flow, describing the distribution of the phase volume fraction, velocity, temperature, and dissociation rate. The interaction between GH dissociation and multiphase flow is discussed. The simulation results indicate that the continuous production of gas bubbles by GH dissociation leads to more violent fluctuations in the pressure gradient and a more marked elevation of the solid particles compared with the liquid–solid two-phase flow without GH dissociation. In addition, the effect of GH dissociation on the multiphase flow under different hydrate saturations was analyzed.

Improved Point-Line Feature Based Visual SLAM Method for Indoor Scenes

In the study of indoor simultaneous localization and mapping (SLAM) problems using a stereo camera, two types of primary features—point and line segments—have been widely used to calculate the pose of the camera. However, many feature-based SLAM systems are not robust when the camera moves sharply or turns too quickly. In this paper, an improved indoor visual SLAM method to better utilize the advantages of point and line segment features and achieve robust results in difficult environments is proposed. First, point and line segment features are automatically extracted and matched to build two kinds of projection models. Subsequently, for the optimization problem of line segment features, we add minimization of angle observation in addition to the traditional re-projection error of endpoints. Finally, our model of motion estimation, which is adaptive to the motion state of the camera, is applied to build a new combinational Hessian matrix and gradient vector for iterated pose estimation. Furthermore, our proposal has been tested on EuRoC MAV datasets and sequence images captured with our stereo camera. The experimental results demonstrate the effectiveness of our improved point-line feature based visual SLAM method in improving localization accuracy when the camera moves with rapid rotation or violent fluctuation.

Analysis of the factors forming the observed inequality in the income of population in Russia

The article considers the problem of population’s income inequality in the Russian Federation and detection of the factors affecting it. Population’s income differences demonstrate both intrinsic and unavoidable differences among individuals and their groups in terms of their participation in the social processes, and the governmental efforts aimed at reasonable and fair distribution of the national wealth among the citizens. The research objective was to identify the dynamics of the Gini index as acknowledged indicator for population inequality in terms of income and to analyze the factors defining such dynamics. The research was carried out based on the national statistical data. The authors detect close connection between the downturns in economy, especially decrease of the dynamics of average income per capita, and the level of population inequality in terms of income. However, contrary to expectation, the correlation is direct which means that during the periods of slowing of the income growth the values of Gini index being the avowed income inequality indicator also reduced. On the other hand, the authors point out that such connection exists only for time series. While studying the static populations’ income differences in various regions no correlation between the income size and difference values was found. Based on the research results the authors draw the conclusion about undesirability of violent fluctuations in the dynamics of the population’s effective earnings, as well as about justifiability of the efforts of national and regional authorities aimed at the improvements of the income policy.

Effect of alloy element on weld pool dynamics in laser welding of aluminum alloys

In this manuscript, weld pool dynamics in laser welding of various series of aluminum alloys were investigated by the in situ X-ray phase contrast imaging system. The experimental results showed that metal irradiated by laser was evaporated immediately, which generated the keyhole. Then metal surrounding the keyhole was melted gradually with the heat from keyhole. The growth rate of keyhole depth had a positive linear correlation with the total content of low boiling temperature elements (TCE), so did the keyhole depth and diameter at the stable stage. Longitudinal view area of the molten pool had a negative linear correlation with the thermal conductivity of aluminum alloy. The measured laser absorption rate had the same variation trend with the ratio of keyhole depth to diameter, and the highest absorption rate of 58% appeared in laser welding of aluminum alloy with TCE equal to 2.1%. Violent fluctuation in keyhole shape was avoided in aluminum alloy with TCE lower than 2.1%, where the surface tension and recoil pressure of metal vapor were balanced. To sum up, the effect of alloy element on weld pool dynamics in laser welding of aluminum alloys was firstly quantified in this manuscript.

Multiscale fluctuations and complexity synchronization of Bitcoin in China and US markets

Bitcoin appeared as a currency, but it is treated as a speculative product due to its violent fluctuation. The main purpose of this article is to find out the fluctuations similarities and differences between China and US Bitcoin markets, as well as Bitcoin market and stock market by Econophysics. We use the multiscale composite complexity synchronization (MCCS) correlation to study the complexity synchronization of Bitcoin price and stock indices fluctuations in those two markets. And we use the multifractal detrended fluctuation analysis (MFDFA) to analyze the inner fractal features of each time series’s small and large fluctuations. The corresponding shuffled time series are also utilized to do the above two kinds of analysis, in order to distinguish what lead to the complexity synchronization and multifractal properties, the different long-range correlations for the times series’ small and large fluctuations or the probability density functions for fluctuations of those nonstationary times series, or both of them. By this study, we find that small fluctuations have the strong memory and synchronization while big fluctuations possess the weak memory and synchronization, and the Bitcoin market has greater synchronicity than the stock market, and large fluctuations in China financial market are persistent while they are anti-persistent in US market.

Edge-oxidation effects on the thermoelectric properties in graphene nanoribbons

The thermal, electrical and thermoelectric properties in edge modified zigzag graphene nanoribbon are analyzed carefully by nonequilibrium Green's function formalism combined with first principles calculation. Epoxy (-O-) and hydroxyl groups (-OH) are considered for the ZGNR edge modification (ZGNR-O and ZGNR-OH). The results show that ZGNR-O and ZGNR-OH both can suppress obviously the phonon transport, leading to low phonon thermal conductance. While ZGNR-O and ZGNR-OH hardly suppress electron transport within the positive energy, which induces one conductance quantum plateau can be observed in ZGNR-O and ZGNR-OH. At the negative energies, ZGNR-O can suppress obviously the electron transport, which induces violent fluctuation of electronic transmissions, leading to high Seebeck coefficient and enhanced thermopower.

Comprehensive assessment of microbial aggregation characteristics of activated sludge bioreactors using fuzzy clustering analysis

Understanding microbial aggregation dynamics in response to the often violent environmental fluctuations is important for activated sludge wastewater biotreatment practice, yet remains poorly understood. We investigated microbial aggregation process of an activated sludge reactor in response to various operating conditions of resource limitations, disinfectant and pH stresses, and quantified aggregation characteristics by employing a fuzzy clustering analysis (FCA) method. The results revealed that the FCA provided a means for comprehensive assessment of microbial aggregation dynamics of the bioreactor relying solely on simple parameter estimation. Proper disinfectant stress (of NaClO 1.00% or 2.00%) is a promising strategy to improve the comprehensive performance of microbial aggregation and sludge settleability. Nitrogen– (of C/N ratio > 40) and dissolved oxygen–limitations (of DO < 0.2 mg/L) had medium influence on the comprehensive performance of the activated sludge system, while little impacts for acidic and alkaline conditions. These quantitative estimations offer insights into the underlying bio–physicochemical processes of an activated sludge bioreactor in response to practical fluctuations that is often beyond typical assessment practice. In addition, it may represent a step towards uncoupling the complex biophysical interactions that is essential for optimized designing and proper engineering practice of biological wastewater treatment reactors.

Heterogeneity and optimal sampe size of soil physicochemical properties in subtropical forest.

Selecting the optimal sample size accurately is important for improving the measurement precision of soil physicochemical properties. In this study, we examined the within-site heterogeneity of soil physical and chemical properties in an evergreen broad-leaved forest and a Chinese fir (Cunninghamia lanceolata) plantation in subtropical China. We applied both traditional and bootstrapping technique to determine the optimal sample size, the number of observation (n), for predicting soil nutrient content with an allowable error of 10% at a 95% confidence level for both forest types. The results showed that soil pH and C/N had low variation, while the soil nutrients had a moderate variation in both forests. The coefficients of variation (CV) of total element concentration in the evergreen broad-leaved forest, such as total carbon and total nitrogen, were significantly larger than those in the Chinese fir plantation, while the CVs of available nutrients were similar between two forests. The evaluation error of all soil properties in two forests showed a stable trend after a sharp decline with the increase of sample size. The mean values also changed from violent fluctuation to stable, and extravagant sample could not effectively improve the accuracy of mean value measurement. The sample sizes of soil water content, total carbon, total nitrogen, nitrate (NO3--N), total potassium, total calcium, and total magnesium in the evergreen broad-leaved forest were signifi-cantly larger than those in the Chinese fir plantation, while the sample size for ammonium (NH4+-N) showed opposite pattern, and the others had no significant difference. In addition, the sample sizes of different soil physicochemical properties varied significantly in the same forest. The available elements, such as NH4+-N and NO3--N, needed a larger sample size than total elements in both forests. Accordingly, we proposed that the heterogeneity and sample size of soil physicochemical properties should be considered before soil survey. An adequate sample size may be varied according to the purpose of sample and the site-specific variation of soil characters.

Experimental investigation of single loop thermosyphons utilized in motorized spindle shaft cooling

In this paper, a shaft cooling structure of a grinding motorized spindle was designed based on loop thermosyphons. The evaporation and condensation sections of the loop thermosyphons were located on the same tube due to the thermal conductivity of the shaft. The experimental studies on both heat transfer performance and start-up characteristics of a single loop thermosyphon were performed under the special condition. Then, the cooling effect on the shaft was simulated depending on the obtained experimental data. Results demonstrated that the optimal liquid filling rate of a loop thermosyphon ranged between 50 and 60% under the special condition. Furthermore, a critical value of heating power between 20 W and 40 W was found. When the heating power exceeded this value, the temperature of the evaporation section increased rapidly without any fluctuation. The violent fluctuation of temperature at the upper evaporation section could be utilized as an indicator for the heat transfer limit. Finally, according to the simulation, the maximum temperature of the motorized spindle was reduced by approximately 28% under the effect of the designed cooling structure.

Numerical study on solidification characteristics under pulsed magnetic field

The solidification characteristics under a pulsed magnetic field (PMF) are numerically investigated using a transient two-dimensional axisymmetric mathematical model that couples electromagnetic fields with fluid flow and solidification. The model is firstly validated and then applied to the solidification of Al-5 wt%Cu alloy under a typical PMF. Evolutions of the melt flow, temperature field and mushy zone as well as the solidification rate are studied. The results are compared with those obtained without a magnetic field and with a harmonic magnetic field (HMF) having the same peak current and a normal frequency of 50 Hz. It was shown that both the Lorentz force and Joule heat exhibit a phase difference for different locations in the melt, and their peaks are much greater than those induced by the HMF. The melt velocity is accompanied by a violent fluctuation whose amplitude is greater than that obtained with the HMF. The heat extraction of the melt is dominated by the forced convection during the liquid stage and early stage of solidification; thus, the mushy zone develops quickly. Nevertheless, the end time of solidification is a little longer than that without a magnetic field due to the presence of the Joule heat.

Price Stabilization For Sustainable Agricultural Development With Special Reference To Arecanut

Rapid and violent fluctuations in agricultural prices have many harmful consequences. For example, steep decline in the price of a particular crop in some year can inflict heavy losses on the growers of that crop. This will reduce their income substantially and also dampen their spirits to cultivate the same crop next year. If this happens to be a staple food item of the masses, supply next year will remain considerably below the demand forcing the government to fill the gap by resorting to imports. If, on the other hand, prices of a particular crop soar very high in a particular year, the consumers are likely to suffer. Considering these factors, it becomes necessary to stabiles agricultural prices to safeguard the interest of both producers and consumers. The present study is undertaken to analyse extent of price fluctuation in areca nut and opinion about price stability from areca nut growers. The study has used both primary and secondary data to know about extent of price fluctuation in areca nut and measures taken to stablise its price by various stake holders. Primary data are collected through a structured questionnaire schedule pertaining to the objectives of the study canvassed among the selected areca nut growers in the Dakshina Kannada district. The study suggests that, it is necessary to stabilize areca nut prices to safeguard the interest of both producers and consumers.

Study on spillover effect between international soybean market and China's domestic soybean market

Due to high import dependency, China's domestic soybean market became unstable and soybean production was lingering and declining. It would be better to know the correlation between international and China's domestic soybean market for policy-making and production decision. This study used data of CBOT soybean futures price, imported soybean distribution price at Qingdao port and soybean spot price in China from September 10, 2011 to November 19, 2016 and chose multivariate GARCH model to check the spillover effect and correlation between them. The results showed that price volatilities of three markets had significant clustering effect while GARCH effect was stronger than ARCH effect. The spillover effect and correlations between markets were remarkable. It demonstrated the imported soybean market was significantly affected by the international soybean future market volatility, and such instability then resulted in violent fluctuations of China's domestic soybean spot market. Policies should be made to keep China's soybean industry safe and developed.

Study on the aeroelastic responses of a wind turbine using a coupled multibody-FVW method

Abstract The present study aimed at developing an aeroelastic method of a wind turbine and highlighting the influences of aeroelasticity on both the aerodynamic and the structural performances. System's governing equations considering the aeroelastic effects of large scale wind turbines are derived by coupling a multibody method with a free vortex wake (FVW) method. The resulting differential-algebraic equations (DAE) are transformed to algebraic equations whose Jacobian matrices are difficult to be calculated. Based on an inverse Broyden-Fletcher-Goldfarb-Shanno (BFGS) approach, a quasi-Newton method with a suitable linear search is developed and used to solve those nonlinear equations, thus a new aeroelastic method without Jacobian matrices calculation is proposed. The time domain aeroelastic responses of the NH1500 1.5-MW wind turbine are obtained. The simulation results indicate that aeroelasticity of a blade has significant effects on the wake geometries and structural responses. Flexibility of the tower can cause more violent fluctuations for the power and loads compared with the results of a blade, which can considerably affect the blade fatigue life design.

A Voltage Control Method for a Distributed Line Feeder by means of Multiagent Approach

SUMMARYThis paper proposes a method for the coordinated control of power factor by means of a multiagent approach. The proposed multiagent system consists of two types of agent: single feeder agent (F_AG) and bus agent (B_AG). In the proposed system, an F_AG plays as an important role, which decides the power factors of all distributed generators by executing the load flow calculations repeatedly. The voltage control strategies are implemented as the class definition of Java into the system. In order to verify the performance of the proposed method, it has been applied to a typical distribution model system. The simulation results show that the system is able to control very violent fluctuation of the demands and the photovoltaic (PV) generations.