Asymmetry In Distribution Research Articles

Unveiling the 3D Morphology of Epitaxial GaAs/AlGaAs Quantum Dots.

Strain-free GaAs/AlGaAs semiconductor quantum dots (QDs) grown by droplet etching and nanohole infilling (DENI) are highly promising candidates for the on-demand generation of indistinguishable and entangled photon sources. The spectroscopic fingerprint and quantum optical properties of QDs are significantly influenced by their morphology. The effects of nanohole geometry and infilled material on the exciton binding energies and fine structure splitting are well-understood. However, a comprehensive understanding of GaAs/AlGaAs QD morphology remains elusive. To address this, we employ high-resolution scanning transmission electron microscopy (STEM) and reverse engineering through selective chemical etching and atomic force microscopy (AFM). Cross-sectional STEM of uncapped QDs reveals an inverted conical nanohole with Al-rich sidewalls and defect-free interfaces. Subsequent selective chemical etching and AFM measurements further reveal asymmetries in element distribution. This study enhances the understanding of DENI QD morphology and provides a fundamental three-dimensional structural model for simulating and optimizing their optoelectronic properties.

Bertrand‐Edgeworth game under oligopoly. General results and comparisons with duopoly

AbstractThis paper studies price competition among a given number of capacity‐constrained producers of a homogeneous commodity under the efficient rationing rule and constant (and identical) marginal cost until full capacity, when demand is a continuous, non‐increasing, and non‐negative function defined on the set of non‐negative prices and is positive, strictly decreasing, twice differentiable and (weakly) concave when positive. The focus is on general properties of equilibria in the region of the capacity space in which no pure strategy equilibria exist. We study how the properties that are known to hold for the duopoly are generalized to the oligopoly and we highlight the new properties that can arise in asymmetric oligopoly, which include the existence of an atom in the support of the equilibrium strategy of a firm smaller than the largest one, the properties that such an atom entails, the existence of gaps in the supports, and asymmetries in the equilibrium distributions of equally‐sized firms smaller than the largest one. Further, we provide results about the boundaries of the supports. Although the characterization of equilibria is far from being complete, this paper provides substantial elements in this direction.

Conventional magnetic resonance imaging key features for distinguishing pathologically confirmed corticobasal degeneration from its mimics: a retrospective analysis of the J-VAC study.

Due to the indistinguishable clinical features of corticobasal syndrome (CBS), the antemortem differentiation between corticobasal degeneration (CBD) and its mimics remains challenging. However, the utility of conventional magnetic resonance imaging (MRI) for the diagnosis of CBD has not been sufficiently evaluated. This study aimed to investigate the diagnostic performance of conventional MRI findings in differentiating pathologically confirmed CBD from its mimics. Semiquantitative visual rating scales were employed to assess the degree and distribution of atrophy and asymmetry on conventional T1-weighted and T2-weighted images. Additionally, subcortical white matter hyperintensity (SWMH) on fluid-attenuated inversion recovery images were visually evaluated. In addition to 19 patients with CBD, 16 with CBD mimics (progressive supranuclear palsy (PSP): 9, Alzheimer's disease (AD): 4, dementia with Lewy bodies (DLB): 1, frontotemporal lobar degeneration with TAR DNA-binding protein of 43kDa(FTLD-TDP): 1, and globular glial tauopathy (GGT): 1) were investigated. Compared with the CBD group, the PSP-CBS subgroup showed severe midbrain atrophy without SWMH. The non-PSP-CBS subgroup, comprising patients with AD, DLB, FTLD-TDP, and GGT, showed severe temporal atrophy with widespread asymmetry, especially in the temporal lobes. In addition to over half of the patients with CBD, two with FTLD-TDP and GGT showed SWMH, respectively. This study elucidates the distinct structural changes between the CBD and its mimics based on visual rating scales. The evaluation of atrophic distribution and SWMH may serve as imaging biomarkers of conventional MRI for detecting background pathologies.

A Network Intrusion Detection Method Based on Bagging Ensemble

The problems of asymmetry in information features and redundant features in datasets, and the asymmetry of network traffic distribution in the field of network intrusion detection, have been identified as a cause of low accuracy and poor generalization of traditional machine learning detection methods in intrusion detection systems (IDSs). In response, a network intrusion detection method based on the integration of bootstrap aggregating (bagging) is proposed. The extreme random tree (ERT) algorithm was employed to calculate the weights of each feature, determine the feature subsets of different machine learning models, then randomly sample the training samples based on the bootstrap sampling method, and integrated classification and regression trees (CART), support vector machine (SVM), and k-nearest neighbor (KNN) as the base estimators of bagging. A comparison of integration methods revealed that the KNN-Bagging integration model exhibited optimal performance. Subsequently, the Bayesian optimization (BO) algorithm was employed for hyper-parameter tuning of the base estimators’ KNN. Finally, the base estimators were integrated through a hard voting approach. The proposed BO-KNN-Bagging model was evaluated on the NSL-KDD dataset, achieving an accuracy of 82.48%. This result was superior to those obtained by traditional machine learning algorithms and demonstrated enhanced performance compared with other methods.

Similarity measure method of near-infrared spectrum combined with multi-attribute information

Due to the high-dimensionality, redundancy, and non-linearity of the near-infrared (NIR) spectra data, as well as the influence of attributes such as producing area and grade of the sample, which can all affect the similarity measure between samples. This paper proposed a t-distributed stochastic neighbor embedding algorithm based on Sinkhorn distance (St-SNE) combined with multi-attribute data information. Firstly, the Sinkhorn distance was introduced which can solve problems such as KL divergence asymmetry and sparse data distribution in high-dimensional space, thereby constructing probability distributions that make low-dimensional space similar to high-dimensional space. In addition, to address the impact of multi-attribute features of samples on similarity measure, a multi-attribute distance matrix was constructed using information entropy, and then combined with the numerical matrix of spectral data to obtain a mixed data matrix. In order to validate the effectiveness of the St-SNE algorithm, dimensionality reduction projection was performed on NIR spectral data and compared with PCA, LPP, and t-SNE algorithms. The results demonstrated that the St-SNE algorithm effectively distinguishes samples with different attribute information, and produced more distinct projection boundaries of sample category in low-dimensional space. Then we tested the classification performance of St-SNE for different attributes by using the tobacco and mango datasets, and compared it with LPP, t-SNE, UMAP, and Fisher t-SNE algorithms. The results showed that St-SNE algorithm had the highest classification accuracy for different attributes. Finally, we compared the results of searching the most similar sample with the target tobacco for cigarette formulas, and experiments showed that the St-SNE had the highest consistency with the recommendation of the experts than that of the other algorithms. It can provide strong support for the maintenance and design of the product formula.

Analysis of the Influence of Distributed Photovoltaic Access on the Operation Quality of Asymmetry Distribution Network

Abstract Distributed photovoltaic(PV) power generation, as a highly flexible renewable energy source, is currently developing rapidly and has been widely used. However, due to its uncertainty and randomness, large-scale distributed photovoltaic integration into the distribution network will change the network power flow distribution, which will have a greater impact on the operation quality of the distribution network operation. In order to study the influence of distributed PV access on the operation of asymmetry distribution network, this paper builds a three-phase power flow model of distributed photovoltaic access to distribution network. Based on the IEEE33 node three-phase calculation example data, the impact of distributed photovoltaic access location and capacity on a series of operation indicators such as voltage deviation, three-phase unbalance and network loss under asymmetry operation of the distribution network is studied. Finally, for the asymmetry distribution network operating condition, guidance suggestions for distributed photovoltaic access based on operation quality are given.

INDIVIDUAL CONTROL CHARTS FOR NON-NORMAL DATA

Individual control charts are a suitable option to consider when the processes being studied change slowly. If obtaining standard samples for Shewhart control charts is expensive or in the case of studying statistical characteristics of the technological process, they are used. Control charts are used to control technological processes in the case of a normal distribution of the possible values of the controlled parameter. Sometimes a quasi-normal distribution of the studied parameter is allowed. In practice, it is often necessary to deal with technological processes in which samples are not distributed according to a normal distribution. In such cases, using individual control charts can lead to type I and II errors. This is because the control limits of the charts are calculated for the mean and standard deviation of the normal distribution. Control charts of individual values are most sensitive to the deviation of the distribution from the normal one since individual values are used to construct the limits, to which the central limit theorem does not apply, as in the case of control charts of mean values. Therefore, it is extremely important to develop methods of applying the individual control charts for random samples, the general population of which is not normally distributed. The study examines the application of individual control charts for a random process that is non-normally distributed. This is achieved by using the normalization method to transform samples of the studied parameter into samples that are distributed normally or quasi-normally. The normalization is performed using the Box-Cox method with further construction of control charts based on the transformed samples. The mathematical apparatus of the individual control chart application for samples with non-normal distribution is described. Numerical modeling of the application of individual control charts for the chi-square distributed samples, which have a significant distribution asymmetry for small values of the shape factor, and for the samples obtained by normalizing the chi-square one, was performed. According to the research findings, the utilization of individual control charts for samples exhibiting a significantly asymmetric distribution results in a higher likelihood of type I errors being detected. However, when the method of sample normalization is employed, this issue is almost entirely eliminated. Modeling process disruption, by changing a certain individual value, also demonstrated the emergence of false signals of process disruption.

Neutron emission from a source moving in a gravitational field

This work is devoted to the problem of neutron field formation near elliptical orbits of space objects equipped with nuclear power plants. The high-energy part of the fission spectrum is not affected by the gravitational field. Radiation safety is ensured by the triad fair for a point source: activity-distance-time. The connection between space object orbit parameters and neutron flux density occurs for the thermal (near-thermal) part of the spectrum. The possibility of formation of a stable neutron trace in the volume of a «torus» around the orbit of a space object is considered. The paper presents theoretical and numerical evidence of the validity of the hypothesis put forward. The introduction considers the separation effect of Galileo's relativity principle in the case of rectilinear uniform motion of a point isotropic neutron source on a plane. The occurrence of angular asymmetry of the neutron distribution in a stationary coordinate system when their relative velocity is close to the transport velocity of the source is illustrated. Under these conditions, a significant velocity dispersion of initially monochromatic neutrons is also recorded. This expected fundamental kinematic effect determines the characteristic distribution of neutrons in the gravitational field when the source moves along the Kepler orbit. The solution of the problem is carried out in the velocity space. It is argued that if the distribution of neutrons in the velocity space is such that their velocities are collinear to the orbital velocity of the source, this indicates the existence of a neutron flux near the orbit. The problem is analysed on the example of one revolution of a hypothetical space station by simulation modelling. For this purpose, thermal neutron packets with isotropic angular distribution were generated at eight points of an elliptical orbit. The neutron and source velocity fluxes at the selected points of the orbit were compared in a coordinate system related to the earth. The obtained data made it possible to calculate the densities of neutron velocity fluxes to the front and rear hemispheres relative to the source orbital motion as a function of the polar angle, while the value of the determinant of the correlation matrix – an indicator of collinearity of neutron velocity vectors in the flux - was fixed. The results of the studies confirm the hypothesis put forward about the possibility of formation of a «trace» in the orbit of a thermal neutron source, which determines the need to take it into account as a significant component of radiation risk.

Comparing the three-dimensional morphological asymmetries in the ejecta of Kepler and Tycho in X-rays

Aims. Recent simulations have shown that asymmetries in the ejecta distribution of supernova remnants (SNRs) may be a reflection of asymmetries left over from the initial supernova explosion. Thus, SNR studies provide a vital means for testing and constraining model predictions in relation to the distribution of heavy elements, which are key to improving our understanding of the explosion mechanisms in Type Ia supernovae. Methods. The use of a novel blind source separation method applied to the megasecond X-ray observations of the historic Kepler and Tycho supernova remnants has revealed maps of the ejecta distribution. These maps are endowed with an unprecedented level of detail and clear separations from the continuum emission. Our method also provides a three-dimensional (3D) view of the ejecta by individually disentangling red- and blueshifted spectral components associated with images of the Si, S, Ar, Ca, and Fe emission. This approach provides insights into the morphology of the ejecta distribution in those two remnants. Results. Those mappings have allowed us to thoroughly investigate the asymmetries in the intermediate-mass elements and Fe distribution in two Type Ia supernova remnants. We also compared the results with the core-collapse Cassiopeia A remnant, which we had studied previously. The images obtained confirm, as expected for Type Ia SNRs, that the Fe distribution is mostly closer to the core than that of intermediate-mass elements. They also highlight peculiar features in the ejecta distribution, such as the Fe-rich southeastern knot in Tycho.

Enhancing Forecasting Accuracy in Commodity and Financial Markets: Insights from GARCH and SVR Models

The aim of this study is to enhance the understanding of volatility dynamics in commodity returns, such as gold and cocoa, as well as the financial market index S&P500. It provides a comprehensive overview of each model’s efficacy in capturing volatility clustering, asymmetry, and long-term memory effects in asset returns. By employing models like sGARCH, eGARCH, gjrGARCH, and FIGARCH, the research offers a nuanced understanding of volatility evolution and its impact on asset returns. Using the Skewed Generalized Error Distribution (SGED) in model optimization shows how important it is to understand asymmetry and fat-tailedness in return distributions, which are common in financial data. Key findings include the sGARCH model being the preferred choice for Gold Futures due to its lower AIC value and favorable parameter estimates, indicating significant volatility clustering and a slight positive skewness in return distribution. For Cocoa Futures, the FIGARCH model demonstrates superior performance in capturing long memory effects, as evidenced by its higher log-likelihood value and lower AIC value. For the S&P500 Index, the eGARCH model stands out for its ability to capture asymmetry in volatility responses, showing superior performance in both log-likelihood and AIC values. Overall, identifying superior modeling approaches like the FIGARCH model for long memory effects can enhance risk management strategies by providing more accurate estimates of Value-at-Risk (VaR) and Expected Shortfall (ES). Additionally, the out-of-sample evaluation reveals that Support Vector Regression (SVR) outperforms traditional GARCH models for short-term forecasting horizons, indicating its potential as an alternative forecasting tool in financial markets. These findings underscore the importance of selecting appropriate modeling techniques tailored to specific asset classes and forecasting horizons. Furthermore, the study highlights the potential of advanced techniques like SVR in enhancing forecasting accuracy, thus offering valuable implications for portfolio management and risk assessment in financial markets.

Unveiling the mechanisms of Moso bamboo's motor function and internal growth stress.

Bamboo, a renewable resource with rapid growth and an impressive height-to-diameter ratio, faces mechanical instability due to its slender structure. Despite this, bamboo maintains its posture without breaking in its battle against environmental and gravitational forces. But what drives this motor function in bamboo? This study subjected Moso bamboo (Phyllostachys edulis) to gravitational stimulation, compelling it to grow at a 45° angle instead of upright. Remarkably, the artificially inclined bamboo exhibited astonishing shape control and adjustment capabilities. The growth strain was detected at both macroscopic and microscopic levels, providing evidence for the presence of internal stress, namely growth stress. The high longitudinal tensile stress on the upper side, along with a significant asymmetry in stress distribution in tilted bamboo, plays a pivotal role in maintaining its mechanical stability. Drawing upon experimental findings, it can be deduced that the growth stress primarily originates from the broad layers of fiber cells. Bamboo could potentially regulate the magnitude of growth stress by modifying the number of fiber cell layers during its maturation process. Additionally, the microfibril angle and lignin disposition may decisively influence the generation of growth stress.

Enhancing the circular dichroism of chiral dielectric nanostructure through the addition of a symmetric Au cylinder

Circular dichroism (CD) spectra play a crucial role in recognition, separation and detection of chiral molecules. Due to the inherent weak CD response of natural chiral molecules, researchers have endeavored to enhance CD signals through various artificial nanostructures. In this study, combining the advantages of both the dielectric and metal materials, we propose a hybrid dielectric-metal nanostructure consisting of a chiral Si nanorod dimer coupled with a symmetric Au cylinder to achieve robust CD responses. Owing to the plasmon resonance of the Au cylinder, the scattering-CD and absorption-CD of the hybrid system have been enhanced, which result in the enhanced extinction-CD response. Furthermore, the distributions of electric field, magnetic field and displacement current density of both the Si dimer and hybrid nanostructure have been meticulously crafted to elucidate the physical mechanisms underlying amplified CD signals. The synergistic coupling between the magnetic fields of dielectric materials and the electric fields of the Au cylinder leads to an increase in the electric field strength and the asymmetry of near-field distributions. Additionally, spatial overlaps between electric and magnetic fields occur. These factors contribute to the enhanced chiral response of the hybrid system. Meanwhile, the CD signal can be flexibly tuned by adjusting the size of the Au cylinder and Si nanorods. This design offers a versatile approach to enhancing the chiral response of dielectric nanostructures.

Study on key parameters of buckling deformation instability and fracture of rock beams and asymmetric distribution law of stope stress.

The moving deformation of the strata and the redistribution of stope stress after mining show asymmetrical characteristics, which do not conform to the symmetrical structural characteristics of the original rock beam fracture. To further analyze the deformation of rock beams and the asymmetry law of stope pressure distribution after strata caving, the detailed process of instability and deformation of composite rock beams before failure was revealed through similar material simulation, theoretical analysis, and numerical simulation. Through similar simulation experiments, the structural characteristics of strata caving were observed. After excavation, the caving angle near the open-off cut side of the model is greater than that on the stop-mining line side. The maximum bending moment of the rock beam is located at the open-off cut side. The rock beam fracture is located on the partial open-off cut side in the middle of the rock beam. The rock beam on the open-off cut side is easy to shear slip and not easy to hinge. The rock beam in front of the advancing direction of the working face is easily hinged. Based on the structural characteristics of strata caving, considering the thickness of the composite rock beam, the two-hinged arch mechanical model for rock beam fracture is established. On this basis, the key parameters of rock beam instability and fracture such as limit load, additional horizontal stress, limit break distance, and break position are analyzed. Based on the deformation characteristics of two hinged arches, the caving structure and the asymmetric distribution mechanism of stress redistribution during the deformation of overburden in stope are explained. Finally, the deformation of rock beam and the asymmetry of stress distribution in stope are verified by numerical calculation. The results show that the concentrated stress value of the coal pillar at the open-off cut side is greater than that in front of the working face. There is a pressure relief area behind the working face, and the pressure relief area has a certain range. The range of stress concentration area, pressure relief area, and stress value tend to be stable, and only the range of the original rock stress zone expands when the working face is advanced to a certain distance. The asymmetric distribution of compaction stress in goaf is related to the buckling deformation of strata.

Functional Patterns and Postural Balance in Young Women With Chronic Non-Specific Low Back Pain and Healthy Individuals

Introduction In the case of chronic low back pain, changes occur at the central nervous system level. It leads to functional limitations, muscle activity, and motor control impairments.Objectives The aim of the study was to analyze the impact of chronic low back pain on the quality of performance functional patterns and postural balance in young women.Material and methods The study involved 60 women with an average of 21.571.07. In Group 1 (n=30), participants reported chronic low back pain, Group 2 (n=30) was the control group. To assess functional efficiency, the Functional Movement Screen was used. Postural stability was evaluated using the FreeMED Posture Base pedobarographic platform. Pain level was determined using the VAS scale, and pelvic anterior tilt was measured using the BROM II.Results In the group of women with chronic low back pain, significantly lower levels of functional efficiency were observed. The length distance covered by the CoP, the area of an ellipse containing the trajectory of the CoP, and the average velocity of the CoP were greater compared to the group of women without pain. In Group 1, significantly greater asymmetry in foot pressure distribution was noted.Conclusions Individuals reported chronic low back pain demonstrate poorer quality of performance functional patterns and postural stability compared to healthy ones. Detecting movement disorders may contribute to a physiotherapist's planning of a therapeutic program that includes the specific movement deficits of patients. It can directly impact the reduction or delay of pain occurrence.

Cooper minima in high-Z atoms: effects of correlation and relativity on np photoionization

Photoionization dipole transition matrix elements pass through a zero or attain a minimum that leaves imprints on photoionization parameters like the cross-section, angular distribution asymmetry parameter, phase shift, and photoionization time delay. This minimum is commonly known as the ‘Cooper minimum’ (CM). The CM, in general, is strongly affected by relativistic and correlation effects. Previous works investigated CM in the 6p and 5p subshell photoionization up to Z = 100 using the single-particle Dirac-Slater (DS) method. The present work extends the earlier work to Z up to 120 using more accurate methods; Dirac–Hartree–Fock (DHF) which includes the relativistic effects and exchange correlations, and the relativistic random phase approximation (RRPA) which includes both initial and final state electron-electron correlations along with relativistic effects. In addition to the study of photoionization from the 6p and 5p subshells, the 4p subshell has also been investigated in the present work. To demonstrate the prominent effects in the high-Z atoms, Rn (Z = 86), Ra (Z = 88), No (Z = 102), Cn (Z = 112), Og (Z = 118), and Ubn (Z = 120) are investigated.

High-cadence monitoring of the emission properties of magnetar XTE J1810−197 with the Stockert radio telescope

Context. Since the detection of a burst resembling a fast radio burst (FRB) from the Galactic magnetar SGR 1935+2154, magnetars have joined the set of favourable candidates for FRB progenitors. However, the emission mechanism of magnetars remains poorly understood. Aims. Observations of magnetars with a high cadence over extended timescales have allowed for their emission properties to be determined, in particular, their temporal variations. In this work, we present the results of the long-term monitoring campaign of the magnetar XTE J1810−197 since its second observed active phase from December 2018 until November 2021, with the Stockert 25 m radio telescope. Methods. We present a single pulse search method, improving on commonly used neural network classifiers thanks to the filtering of radio frequency interference based on its spectral variance and the magnetar’s rotation. Results. With this approach, we were able to lower the signal to noise ratio (S/N) detection threshold from 8 to 5. This allowed us to find over 115 000 spiky single pulses – compared to 56 000 from the neutral network approach. Here, we present the temporal variation of the overall profile and single pulses. Two distinct phases of different single pulse activity can be identified: phase 1 from December 2018 to mid-2019, with a few single pulses per hour, and phase 2 from September 2020 with hundreds of single pulses per hour (with a comparable average flux density). We find that the single pulse properties and folded profile in phase 2 exhibit a change around mid-March 2021. Before this date, the folded profile consists of a single peak and single pulses, with fluences of up to 1000 Jyms and a single-peaked width distribution at around 10 ms. After mid-March 2021, the profile consists of a two peaks and the single pulse population shows a bimodal width distribution with a second peak at 1 ms and fluences of up to 500 Jyms. We also present asymmetries in the phase-resolved single pulse width distributions beginning to appear in 2020, where the pulses arriving earlier in the rotational phase appear wider than those appearing later. This asymmetry persists despite the temporal evolution of the other single pulse and emission properties. Conclusions. We argue that a drift in the emission region in the magnetosphere may explain this observed behaviour. Additionally, we find that the fluence of the detected single pulses depends on the rotational phase and the highest fluence is found in the centre of the peaks in the profile. While the majority of the emission can be linked to the detected single pulses, we cannot exclude another weak mode of emission. In contrast to the pulses from SGR 1935+2154, we have not found any spectral feature or bursts with energies in the order of magnitude of an FRB during our observational campaign. Therefore, the question of whether this magnetar is capable of emitting such highly energetic bursts remains open.

EXCHANGE RATE VOLATILITY OF UKRAINE’S MAIN TRADING PARTNERS

Ukraine, as an open economy under conditions of Russian aggression, is highly vulnerable to the import of exogenous shocks. This is embodied in exchange rate volatility and the emergence of corresponding risks. Most studies are aimed at direct, explicit, or transactional risks. They reflect the negative impact of exchange rate fluctuations on economic entities' cash flows in foreign economic activities. However, changes in currency prices can also affect the subjects oriented to the local market and not carry out operations in foreign currencies by changing competitiveness. One speaks about the indirect, implicit, or economic currency risk in this case. The latter generally arises in the event of volatility in the exchange rates of currencies of importing countries or competitors. The study is devoted to the analysis of indirect currency risks, which reflect potential adaptations of competitiveness due to changes in exchange rates. For this purpose, the currencies of the countries that account for about 80% of Ukraine's trade turnover over the last 10 years, namely the euro, Japanese yen, British pound, Swiss franc, yuan, Indian rupee, Czech krona, Polish zloty, Hungarian forint, and Turkish lira were chosen. The article aims to assess the volatility of exchange rates of Ukraine's main trading partners as a stage of analyzing economic currency risks. The paper uses statistical methods for volatility estimation and distribution characteristics, namely standard deviation, skewness, and kurtosis. The obtained results show that some currencies have a high level of asymmetry and excess, indicating possible unpredictable rate changes. The calculated indicators' generalization allows identifying currencies with relatively high and low risk. The article complements the results of previous studies, as it covers both major reserve currencies and currencies of leading countries whose markets are developing globally and in Europe. Estimates of asymmetry and excess exchange rate distributions are essential for effective currency risk management.

Comparing flows of FENE-P, sPTT, and Giesekus model fluids in a helical static mixer

Helical static mixers are used widely for mixing of non-Newtonian fluid flows in the laminar regime. We study flows of three viscoelastic constitutive models (sPTT, FENE-P, and Giesekus) in the helical static mixer using computational fluid dynamics. These three models have similarities in steady viscometric flows in that they all exhibit shear thinning and their planar extensional viscosities can be matched, but their responses can differ in complex geometries. We observe flow distribution asymmetries at the element intersections for all three models, which hinders the mixing performance of the device. These have previously been observed with the constant shear viscosity FENE-CR model. The asymmetry behaves similarly between the sPTT and Giesekus models, however the FENE-P model behaves in a distinct manner; beyond a critical degree of elasticity, the asymmetry sharply changes direction. This was also observed previously with the FENE-CR model. These results suggest that shear thinning and second-normal stress differences (present in the Giesekus model) do not significantly influence mixing performance in the range of conditions studied. We show that increasing the aspect (length/diameter) ratio of the mixer elements mitigates the poor mixing caused by elasticity. Overall, this study provides insight into the behaviour of these well-used constitutive models in complex, industrially-relevant flows.

Size‐dependent asymmetry of barchans indicates dune growth controlled by basal area or bulk volume

AbstractWe introduce a novel analytical model of the growth of barchan dunes in terms of their two flanks, from which we derive expressions for the size‐dependence of the bilateral asymmetry of these bedforms in three cases where different mechanisms dominate the growth process. Analysis of the morphology of barchans on Mars and Earth suggest that there may exist two distinct attractor states for the asymmetry distribution. By comparing our analytical results with the observations, we show that the growth of barchan dunes appears to be dominated by processes, which are proportional to the basal area or volume of the bedforms, rather than being linear to their width as is typically assumed. We propose hypotheses explaining area‐dominated growth as a result of variable wind regimes and volume‐dominated growth from collisions. These predictions appear to be in line with the available data for the terrestrial swarms and barchan‐like submarine bedforms and offer the potential of predicting patterns in inaccessible wind regimes from data on the morphology of the dunes.

Improving ion rejection by optimizing the structure and charge distribution of the Janus membrane

Due to the asymmetry of charge distribution and geometric structure, the Janus membrane can simultaneously intercept counter-ions and co-ions. This work constructed four Janus membrane configurations using numerical simulation methods. Due to the different potential within the membrane and the selectivity level, there is a significant deviation in the interception performance. The results found that the change in the height of the Janus membrane affects the distribution of anion and cation concentration inside the nanochannel, and the asymmetry of the nanochannel height is more conducive to interception than a uniform nanochannel. The effect of the nanochannel length of the first section on the rejection rate is higher than that of the second section. Considering the design of the membrane, we recommend that the pore length of the first section be set to about 50 nm. Since the flow potential balances the electroviscous force, the optimization of the flow rate for ion transport is often opposite to the interception effect. The Janus membrane has asymmetric pore size and charge distribution characteristics and has excellent retention ability for divalent salts under low-pressure intensity and high-concentration conditions.