Search

The effect of hydrodynamic interactions on the spreading of clusters of colloid particles in a quasi-one-dimensional channel is analyzed both experimentally and theoretically. An n-particle cluster spreading diffusion coefficient is defined, in terms of the displacement Δx(t) in time t, by Dn≡<[∑i=1nΔxi(t)]2>/2nt, where the average is taken over all groups of n adjacent particles. Our study focuses on the n-dependence of Dn with some attention to the dependence of Dn on colloid packing fraction. We find that the ratio of Dn to the infinite dilution self-diffusion coefficient DS0 increases as n increases, eventually saturating for large n. The observed dependence of Dn on n is in satisfactory agreement with the predictions obtained from both Stokesian dynamics simulations and hydrodynamic calculations using the method of reflections. [ABSTRACT FROM AUTHOR]

The poloidal electric filed, which is the drive field of poloidal rotation, has been observed and increases obviously after the injection of electron cyclotron resonance wave in HL-2A experiment, and the amplitude of the poloidal electric field is in the order of 103 V/m. Through theoretical analysis using Stringer rotation model, the observed poloidal electric field is of the same order as the theoretical calculation value. In addition, the magneticpumpdamping whichwould damp the poloidal rotation is calculated numerically and the calculation results showthat the closer to the core plasmas, the stronger the magnetic pump damping will be. Meanwhile, according to the value of the calculated magnetic pump damping, the threshold of the poloidal electric field which could overcome magnetic pump damping and drive poloidal rotation in tokamak plasmas is given out. Finally, the poloidal rotation velocity over time at different minor radius is studied theoretically. [ABSTRACT FROM AUTHOR]

This paper presents a national- and regional-scale urban growth model (NRUGM) of China based on panel data analysis. Through the panel analysis, population growth, road construction, salary increment per capita, and secondary industry product increment were proven to be the major driving factors for national-scale urban expansion. According to Seventh Five-Year Plan, China had been divided into three regions, Eastern China, Middle China, and Western China, by their geographic position and economic development. We studied the relationship between urban expansion and the driving factors for the three regions between 1990 and 2010 in China. The driving factors of urban expansion were different for the different regions and periods. Population growth and road construction were identified as the two major factors driving urban expansion for Eastern China. Secondary industry and economic development had become the major driving factors for urban expansion over the last twenty years in Middle China. Over the same period, for Western China, economic growth had become the major driving factor for urban expansion. Our results have significant policy implications for China. The macrocontrol of the central government should utilize different policies to adjust urban expansion in the different regions. [ABSTRACT FROM AUTHOR]

The wetland ecosystem in the "Three-River Headwaters" (TRH) region plays an irreplaceable role in water source conservation, run-off adjustment and biodiversity maintenance. In recent years, assessment of wetland resources affected by climate changes has aroused enormous attention, since it can further protect wetland resources and provide a scientific basis for decision makers. In this study, wetland changes and its response to climate changes in the TRH region from the early 1990s to 2012 were analyzed by remote sensing (RS) image interpretation and climate change trend analysis. The results showed that wetlands occupied 6.3% of the total land area in 2012, and swamps, streams & rivers and lakes were the dominant wetland types in the TRH region. Since the early 1990s, wetlands have undergone great changes, and total wetland area increased by 260.57 km2 (1.17%). Lakes, reservoir & ponds took on continuous increasing trend, but swamps, streams & rivers had a continuous decreasing trend. On the other hand, the wetland area in the Yangtze River basin showed an overall increasing trend, while in the Yellow River and Langcang River basins, it decreased in general. The climate turned from Warm-Dry to Warm-Wet. The average temperature and precipitation increased by 0.91 °C and 101.99 mm, respectively, from 1990 to 2012, and the average humidity index (HI) increased by 0.06 and showing an upward trend and a shifting of the dividing line towards the northwest in both the areas of semi-humid and semi-arid zone. The correlation analysis of wetland changes with meteorological factors from 1990 to 2012 indicated that the regional humidity differences and the interannual variation trend, caused by the change of precipitation and evaporation, was the main driving factor for the dynamic variation of wetland change in the TRH region. In the general, the increase of HI in the THR region since the 1990s, especially in the western TRH region, contributed to wetland increase continuously. The conclusions of this study will provide some scientific references for the management and protection of wetlands in the TRH region, especially for restoration, reconstruction and conservation of degradation wetland. [ABSTRACT FROM AUTHOR]

To protect the water tower's ecosystem environment and conserve biodiversity, China has been implementing a huge payment program for ecosystem services in the three rivers source region. We explored here the dynamics of grassland degradation and restoration from 1990 to 2012 and its relationships with climate mitigation in the TRSR to provide a definite answer as to the forcing and response of grassland degradation and restoration to climate change. Then we estimated its potential of climate mitigation benefits to address the question of whether ecological restoration could be effective in reversing the decline of ecosystem carbon mitigation service. The trend of average annual temperature and precipitation observed by meteorological stations were approximately increased. Compared before and after 2004, the area of grassland degradation was increased slightly. However, nearly one-third of degraded grassland showed improvement, and the grassland vegetation coverage showed significant increase. Comparing current grassland vegetation coverage with healthy vegetation cover with the same grass type, nearly half of the area still needs to further restore vegetation cover. The grassland degradation resulted in significant carbon emissions, but the restoration to its healthy status has been estimated to be technical mitigation potential. [ABSTRACT FROM AUTHOR]

China has abundant crop residues (CRE) that could be used for bioenergy. The spatiotemporal characteristics of bioenergy production are crucial for high-efficiency use and appropriate management of bioenergy enterprises. In this study, statistical and remote-sensing data on crop yield in China were used to estimate CRE and to analyze its spatiotemporal changes between 1990 and 2010. In 2010, China's CRE) was estimated to be approximately 133.24 Mt, and it was abundant in North and Northeast China, the middle and lower reaches of the Yangtze River, and South China; CRE) was scarce on the Loess and Qinghai-Tibet Plateaus. The quantity of CRE) increased clearly over the 20-year analysis period, mainly from an increase in residues produced on dry land. Changes in cultivated land use clearly influenced the changes in CRE). The expansion of cultivated land, which mainly occurred in Northeast and Northwest China, increased CRE) by 5.18 Mt. The loss of cultivated land, which occurred primarily in North China and the middle and lower reaches of the Yangtze River, reduced CRE) by 3.55 Mt. Additionally, the interconversion of paddy fields and dry land, which occurred mostly in Northeast China, increased CRE) by 0.78 Mt. The findings of this article provide important information for policy makers in formulating plans and policies for crop-residue-based bioenergy development in China, and also for commercial ventures in deciding on locations and production schedules for generation of bioenergy. [ABSTRACT FROM AUTHOR]

We report a study of DNA deformationsusing a coarse-grained mechanicalmodel and quantitatively interpret the allosteric effects in protein–DNAbinding affinity. A recent single-molecule study (Kim et al. Science2013, 339, 816) showedthat when a DNA molecule is deformed by specific binding of a protein,the binding affinity of a second protein separated from the firstprotein is altered. Experimental observations together with moleculardynamics simulations suggested that the origin of the DNA allosteryis related to the observed deformation of DNA’s structure,in particular, the major groove width. To unveil and quantify theunderlying mechanism for the observed major groove deformation behaviorrelated to the DNA allostery, here we provide a simple but effectiveanalytical model where DNA deformations upon protein binding are analyzedand spatial correlations of local deformations along the DNA are examined.The deformation of the DNA base orientations, which directly affectthe major groove width, is found in both an analytical derivationand coarse-grained Monte Carlo simulations. This deformation oscillateswith a period of 10 base pairs with an amplitude decaying exponentiallyfrom the binding site with a decay length lD≈10 base pairs as a result of the balance between two competingterms in DNA base-stacking energy. This length scale is in agreementwith that reported from the single-molecule experiment. Our modelcan be reduced to the worm-like chain form at length scales largerthan lPbut is able to explain DNA’smechanical properties on shorter length scales, in particular, theDNA allostery of protein–DNA interactions. [ABSTRACT FROM AUTHOR]

Colloidal suspensions self-assemble into equilibrium structures ranging from face- and body-centered cubic crystals to binary ionic crystals, and even kagome lattices. When driven out of equilibrium by hydrodynamic interactions, even more diverse structures can be accessed. However, mechanisms underlying out-of-equilibrium assembly are much less understood, though such processes are clearly relevant in many natural and industrial systems. Even in the simple case of hard-sphere colloidal particles under shear, there are conflicting predictions about whether particles link up into string-like structures along the shear flow direction. Here, using confocal microscopy, we measure the shear-induced suspension structure. Surprisingly, rather than flow-aligned strings, we observe log-rolling strings of particles normal to the plane of shear. By employing Stokesian dynamics simulations, we address the mechanism leading to this out-of-equilibrium structure and show that it emerges from a delicate balance between hydrodynamic and interparticle interactions. These results demonstrate a method for assembling large-scale particle structures using shear flows. [ABSTRACT FROM AUTHOR]

We report an analysis of the change in character of the fluid-to-solid transition in a quasi-two-dimensional hard-sphere colloid system as the confining wall separation changes from one to two hard-sphere diameters. Our analysis is based on a study of the bifurcation of solutions of the integral equation for the singlet density, using both direct and pair correlation function representations. Two approximations used in previous bifurcation analyses of freezing are improved in the work reported in this paper. The results of the analysis correctly predict the qualitative change in freezing as a function of the confining wall separation and density, specifically the change from a fluid-to-one-layer hexagonal solid transition to a fluid-to-two-layer square solid transition at a wall separation of 1.6 hard-sphere diameters. The numerical predictions of the theory are in semi-quantitative agreement with simulation data for the density dependence of the liquid–solid transition line for wall separations up to 1.6 hard-sphere diameters. [ABSTRACT FROM AUTHOR]

Investigating the relationship between land surface temperature (LST) and other satellite-derived land surface parameters is beneficial to exploring adaptation and mitigation strategies for urban thermal environment. The article indicates the key parameters influencing LST at regional scale and object scale using comparison of the relationship between LST and land surface parameters based on ordinary least squares (OLS) and Kendall robust linear fit. The results showed that normalized difference moisture index (NDMI) is the most effective and robust parameter interpreting LST, followed by normalized difference buildup index (NDBI). Although normalized difference vegetation index (NDVI) and the albedo of visible light can strongly affect LST, they showed a lack of robustness because of the large gaps between the determination coefficients of the two regression methods at regional scale. At object scale, the average temperature of factories was the highest, followed by business services construction. NDVI and NDMI are the important factors affecting LST for these points of interest (POIs). [ABSTRACT FROM AUTHOR]

Metamaterials are artificial materials that can achieve unusual properties through unique structures. In particular, their "invisibility" property has attracted enormous attention due to its little or negligible disturbance to the background field that avoids detection. This invisibility feature is not only useful for the optical field, but it is also important for any field manipulation that requires minimum disturbance to the background, such as the flow field manipulation inside the human body. There are several conventional invisible metamaterial designs: a cloak can isolate the influence between the internal and external fields, a concentrator can concentrate the external field to form an intensified internal field, and a rotator can rotate the internal field by a specific angle with respect to the external field. However, a multifunctional invisible device that can continuously tune across all these functions has never been realized due to its challenging requirements on material properties. Inside a porous medium flow, however, we overcome these challenges and realize such a multifunctional metamaterial. Our hydrodynamic device can manipulate both the magnitude and the direction of the internal flow and, at the same time, make negligible disturbance to the external flow. Thus, we integrate the functions of the cloak, concentrator, and rotator within one single hydrodynamic metamaterial, and such metamaterials may find potential applications in biomedical areas such as tissue engineering and drug release. [ABSTRACT FROM AUTHOR]

We report the results of experimental studies of the short-time-long-wavelength behavior of collective particle displacements in quasi-one-dimensional (q 1D) and quasi-two-dimensional (q2D) colloid suspensions. Our results are reported via the q → 0 behavior of the hydrodynamic function H(q) that relates the effective collective diffusion coefficient De(q), with the static structure factor S(q) and the self-diffusion coefficient of isolated particles D0: H (q) = De (q) S (q)/D0. We find an apparent divergence of H(q) as q → 0 with the form H (q) ∝ q-γ (1.7 < γ < 1.9) for both q1D and q2D colloid suspensions. Given that S(q) does not diverge as q 0 we infer that De(q) does. This behavior is qualitatively different from that of the three-dimensional H(q) and D, (q) as q → 0, and the divergence is of a different functional form from that predicted for the diffusion coefficient in one-component one-dimensional and two-dimensional fluids not subject to boundary conditions that define the dimensionality of the system. We provide support for the contention that the boundary conditions that define a confined system play a very important role in determining the long-wavelength behavior of the collective diffusion coefficient from two sources: (i) the results of simulations of H(q) and De{q) in quasi-1D and quasi-2D systems and (ii) verification, using data from the work of Lin, Rice and Weitz [Phys. Rev. E 51,423 (1995)], of the prediction by Bleibel et al., arXiv: 1305.3715, that De(q) for a monolayer of colloid particles constrained to lie in the interface between two fluids diverges as q-1 as q → 0. [ABSTRACT FROM AUTHOR]

From the Global Agro-Ecological Zone (GAEZ) model, changes in the three climate factors (temperature, precipitation, and solar radiation) over the past five decades showed different trends and that production potential was impacted significantly by the geographic heterogeneity of climate change. An increase of approximately 1.58 million tons/decade in production potential correlated with climate change. Regions with increased production potential were located mainly in the Northeast China Plain, the northern arid and semiarid region, and the Huang-Huai-Hai Plain. Regions with decreased production potential were located mainly in the Middle-lower Yangtze Plain and southern China. The climate factors that impacted production potential varied by region. In the Northeast China Plain, increased temperature was the major cause of the increased production potential. In the northern arid and semiarid region, temperature and precipitation were the major factors affecting production potential, but their effects were in opposition to each other. In southern China, increased temperature and decreased solar radiation caused a decreased production potential. In the Middle-lower Yangtze Plain, a decrease in solar radiation was the major factor resulting in decreased production potential. In the Huang-Huai-Hai Plain, changes in temperature and solar radiation had large but opposite effects on production potential. [ABSTRACT FROM AUTHOR]

China policies and Grain-for-Green Project have led to changes in farmland area and grain production. Climate change was also occurring during this period. To analyze the effects of land use and climate change on grain production, the area of farmland in northern China during 1988-2008 was determined from remote sensing images, a moisture index (MI) was calculated from daily meteorological data obtained from weather stations, and unit grain production was obtained from statistical yearbooks. Using statistical and spatial analyses, we determined that MI decreased across most of the study area during this period. This decrease in humidity caused humid zones to decrease and semiarid areas to increase. Combined effects of decreased humid area and conversion of farmland resulted in a decrease in agricultural land in humid areas and an increase in semiarid and arid areas. Increases in unit grain production, machine power, and irrigated farmland area led grain production to increase from 122,799,081 to 188,532,597 ton in humid areas, from 28,875,900 to 115,976,814 in semiarid areas, and from 7,622,100 to 15,490,026 in arid areas, respectively. Increased unit grain production and farmland resulted in increased importance of semiarid areas for grain production. [ABSTRACT FROM AUTHOR]

Rapid urbanization and population growth in China have raised great concerns regarding food security caused by the loss of limited cultivated land. In this study, we used remotely sensed data and an agricultural productivity estimation model to characterize the spatiotemporal patterns of the conversion of cropland into urban land and quantify its impacts on agricultural productivity potential during China's rapid urbanization period, from 1990 to 2010. The results show that urban development has transformed approximately 4.18 Mha, or 2.26%, of the total cropland in China. From 1990 to 2000, approximately 1.50 Mha of cropland was developed, while roughly 1.8 times this amount (2.68 Mha) was converted over the period of 2000 to 2010. Most of the conversion is located in the central and eastern coastal provinces and is mainly concentrated on the periphery of the major urban areas. The transformation has, consequently, caused a 71.45 Tg, or 2.65%, loss of potential light-temperature agricultural productivity (PLTAP); losses were 24.33 Tg in the first decade of the study and 47.11 Tg in the second. At the provincial scale, the largest percentages of PLTAP loss are mainly concentrated in the developed provinces on the eastern coast, such as Shanghai, Beijing, Zhejiang, Tianjin, and Jiangsu. Considering that these areas can accommodate more people and produce higher economic output on unit area of built-up land and, yet, scarce land that can be reclaimed, this study suggests that the dynamic balance of total farmland policy in China should be varied provincially according to the major function of the province. The policy adjustment will help maximize the utilization efficiency of land. [ABSTRACT FROM AUTHOR]

We investigate the response of a dense monodisperse quasi-two-dimensional colloid suspension when a particle is dragged by a constant velocity optical trap. Consistent with microrheological studies of other geometries, the perturbation induces a leading density wave and trailing wake. We also use a hybrid version of Stokesian dynamics simulations to parse direct colloid-colloid and hydrodynamic interactions. We go on to analyze the underlying individual particle-particle collisions in the experimental images. The displacements of particles occur in chains reminiscent of stress propagation in sheared granular materials. From these data, we can reconstruct steady-state dipolar-like flow patterns that were predicted for dilute suspensions and previously observed in granular analogs to our system. The decay of this field differs, however, from point Stokeslet calculations, indicating that the nonzero size of the colloids is important. Moreover, there is a pronounced angular dependence that corresponds to the surrounding colloid structure, which develops in response to the perturbation. Put together, our results show that the response of the complex fluid is highly anisotropic owing to the fact that the effects of the perturbation propagate through the structured medium via chains of colloid-colloid collisions. [ABSTRACT FROM AUTHOR]

Near-field hydrodynamic interactions in active fluids are essential to determine many important emergent behaviors observed, but have not been successfully modeled so far. In this work, we propose an effective model capturing the essence of the nearfield hydrodynamic interactions through a tensorial coefficient of resistance, validated numerically by a pedagogic model system consisting of an Escherichia coli bacterium and a passive sphere. In a critical test case that studies the scattering angle of the bacterium-sphere pair dynamics, we prove that the nearfield hydrodynamics can make a qualitative difference even for this simple two-body system: Calculations based on the proposed model reveal a region in parameter space where the bacterium is trapped by the passive sphere, a phenomenon that is regularly observed in experiments but cannot be explained by any existing model. In the end, we demonstrate that our model also leads to efficient simulation of active fluids with tens of thousands of bacteria, sufficiently large for investigations of many emergent behaviors. [ABSTRACT FROM AUTHOR]

Bacterial suspensions--a premier example of active fluids--show an unusual response to shear stresses. Instead of increasing the viscosity of the suspending fluid, the emergent collective motions of swimming bacteria can turn a suspension into a superfluid with zero apparent viscosity. Although the existence of active superfluids has been demonstrated in bulk rheological measurements, the microscopic origin and dynamics of such an exotic phase have not been experimentally probed. Here, using high-speed confocal rheometry, we study the dynamics of concentrated bacterial suspensions under simple planar shear. We find that bacterial superfluids under shear exhibit unusual symmetric shear bands, defying the conventional wisdom on shear banding of complex fluids, where the formation of steady shear bands necessarily breaks the symmetry of unsheared samples. We propose a simple hydrodynamic model based on the local stress balance and the ergodic sampling of nonequilibrium shear configurations, which quantitatively describes the observed symmetric shear-banding structure. The model also successfully predicts various interesting features of swarming vortices in stationary bacterial suspensions. Our study provides insights into the physical properties of collective swarming in active fluids and illustrates their profound influences on transport processes. [ABSTRACT FROM AUTHOR]

Global warming, which is representatively caused by CO2-based greenhouse gases, has caused widespread concern in the global scientific community and gets the high attention of each government in the world. Human activities impact climate change through greenhouse gas emissions and land use changes. The current study on the impact of urbanization on the annual average temperature of the recent 60 years in Beijing was conducted using 1951-2012 temperature data. Anomaly analysis, quadratic polynomial trend method, and moving average method were employed to indicate the temporal variation of temperature. The results showed that average temperature increased both in urban and rural areas. The temperature of urban Beijing increased during the period from 1951 to 2012, especially from 1971 to 1994. The temperature of rural Beijing showed a faster increase than that of the urban area from 1989 to 1998. However, the rate of temperature increase slowed down in recent years. This type of change was temporally consistent with the process of land use change and urbanization in Beijing. Economic restructuring and improvement of urban planning may have been one of the reasons that the regional warming has been slowed down in the rural area. [ABSTRACT FROM AUTHOR]

Beijing has experienced rapid urbanization and associated urban heat island (UHI) effects. This study aimed at analyzing the impact of urban form on UHI in Beijing using TM/ETM images between 1989 and 2010. Spatial analysis was proposed to explore the relationships between area, compactness ratio, the gravity centers of urban land, and UHI. The UHI in Beijing spatially represented a "NE-SW" spindle. The land surface temperature (LST) was higher in south than in north. Urban Heat Island Ratio Index (URI) was well interrelated with urban land area in different zones. Under the similar urban land area condition, UHI and compactness ratio of urban land were in positive correlation. The moving direction of the UHI gravity center was basically in agreement with urban land sprawl. The encroachment of urban land on suburban land is the leading source of UHI effect. The results suggest that urban design based on urban form would be effective for regulating the thermal environment. [ABSTRACT FROM AUTHOR]

Characterization of spatiotemporal variation of water quality is a basic environmental issue with implications for public health in China. Trends in the temporal and spatial distribution of water quality in the Huai River System (HRS) were analyzed using yearly surface water quality data collected from 1982 to 2009. Results showed that the water quality of the main stream deteriorated in the 1990s and early 2000s but has been ameliorated since 2005. The sections that were classified as severely polluted from the monitoring data were located largely in the middle reach. The water quality of HRS fluctuated during the period 1997-2009; it has improved and stabilized since 2005. In terms of spatialized frequency of serious pollution, heavily polluted regions were mostly concentrated in the area along several tributaries of the Ying, Guo and New Sui Rivers as well as the area north of Nansi Lake. These regions decreased from 1997 to 2009, especially after 2005. Our analysis indicated that water pollution in HRS had a close relation with population and primary industry during the period 1997-2009, and implied that spatiotemporal variation of surface water quality could provide a scientific foundation for human health risk assessment of the Huai River Basin. [ABSTRACT FROM AUTHOR]

This study evaluates ecological vulnerability of the wood-grass ecotone of northeast China integrating the spatial analysis technology with algorithms. An assessment model of ecological vulnerability is developed applying the Analytical Hierarchy Process. The composite evaluation index system is established on the basis of the analysis of contemporary status and potential problems in the study area. By the application of the evaluation model, ecological vulnerability index is calculated between 1990 and 2005.The results show that ecological vulnerability was mostly at a medium level in the study area, however the ecological quality was deteriorating. Through the standard deviational ellipse, the variation of ecological vulnerability can be spatially explicated. It is extremely significative for the prediction of the regions that will easily deteriorate. The deterioration zone was concentrating in the area of Da Hinggan Ling Mountain, including Xingan League, Chifeng, Tongliao, and Chengde, whereas the improvement zone was distributing in the north-central of Hulunbeier. [ABSTRACT FROM AUTHOR]

A correction to the article "Integrated Evaluation of Urban Development Suitability Based on Remote Sensing and GIS Techniques "A Case Study in Jingjinji Area, China" that was published in the 2008 issue is presented.

Land cover data represent a fundamental data source for various types of scientific research. The classification of land cover based on satellite data is a challenging task, and an efficient classification method is needed. In this study, an automatic scheme is proposed for the classification of land use using multispectral remote sensing images based on change detection and a semi-supervised classifier. The satellite image can be automatically classified using only the prior land cover map and existing images; therefore human involvement is reduced to a minimum, ensuring the operability of the method. The method was tested in the Qingpu District of Shanghai, China. Using Environment Satellite 1(HJ-1) images of 2009 with 30 m spatial resolution, the areas were classified into five main types of land cover based on previous land cover data and spectral features. The results agreed on validation of land cover maps well with a Kappa value of 0.79 and statistical area biases in proportion less than 6%. This study proposed a simple semi-automatic approach for land cover classification by using prior maps with satisfied accuracy, which integrated the accuracy of visual interpretation and performance of automatic classification methods. The method can be used for land cover mapping in areas lacking ground reference information or identifying rapid variation of land cover regions (such as rapid urbanization) with convenience. [ABSTRACT FROM AUTHOR]

Enhanced diffusion of passive tracers immersed in active fluids is a universal feature of active fluids and has been extensively studied in recent years. Similar to microrheology for equilibrium complex fluids, the unusual enhanced particle dynamics reveal intrinsic properties of active fluids. Nevertheless, previous studies have shown that the translational dynamics of spherical tracers are qualitatively similar, independent of whether active particles are pushers or pullers--the two fundamental classes of active fluids. Is it possible to distinguish pushers from pullers by simply imaging the dynamics of passive tracers? Here, we investigated the diffusion of isolated ellipsoids in algal C. reinhardtii suspensions--a model for puller-type active fluids. In combination with our previous results on pusher-type E. coli suspensions [Peng et al., Phys. Rev. Lett. 116, 068303 (2016)], we showed that the dynamics of asymmetric tracers show a profound difference in pushers and pullers due to their rotational degree of freedom. Although the laboratory-frame translation and rotation of ellipsoids are enhanced in both pushers and pullers, similar to spherical tracers, the anisotropic diffusion in the body frame of ellipsoids shows opposite trends in the two classes of active fluids. An ellipsoid diffuses fastest along its major axis when immersed in pullers, whereas it diffuses slowest along the major axis in pushers. This striking difference can be qualitatively explained using a simple hydrodynamic model. In addition, our study on algal suspensions reveals that the influence of the near-field advection of algal swimming flows on the translation and rotation of ellipsoids shows different ranges and strengths. Our work provides not only new insights into universal organizing principles of active fluids, but also a convenient tool for detecting the class of active particles. [ABSTRACT FROM AUTHOR]

Active fluids such as swarming bacteria and motile colloids exhibit exotic properties different from conventional equilibrium materials. As a peculiar example, a spherical tracer immersed inside active fluids shows an enhanced translational diffusion, orders of magnitude stronger than its intrinsic Brownian motion. Here, rather than spherical tracers, we investigate the diffusion of isolated ellipsoids in a quasi-two-dimensional bacterial bath. Our study shows a nonlinear enhancement of both translational and rotational diffusions of ellipsoids. More importantly, we uncover an anomalous coupling between particles' translation and rotation that is strictly prohibited in Brownian diffusion. The coupling reveals a counterintuitive anisotropic particle diffusion, where an ellipsoid diffuses fastest along its minor axis in its body frame. Combining experiments with theoretical modeling, we show that such an anomalous diffusive behavior arises from the generic straining flow of swimming bacteria. Our work illustrates an unexpected feature of active fluids and deepens our understanding of transport processes in microbiological systems. [ABSTRACT FROM AUTHOR]