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Microfluidic manipulation of particles usually relies on their cross-stream migration. A center- or wall-directed motion has been reported for particles leading or lagging the Poiseuille flow of viscoelastic polyethylene oxide (PEO) solution via positive or negative electrophoresis. Such electro-elastic migration is exactly opposite to the electro-inertial migration of particles in a Newtonian fluid flow. We demonstrate here through the top- and side-view imaging that the leading and lagging particles in the electro-hydrodynamic flow of PEO solution migrate toward the centerline and corners of a rectangular microchannel, respectively. Each of these electro-elastic particle migrations is reduced in the PEO solution with shorter polymers though neither of them exhibits a strong dependence on the particle size. Both phenomena can be reasonably explained by the theory in terms of the ratios of the forces involved in the process. Decreasing the PEO concentration causes the particle migration to shift from the viscoelastic mode to the Newtonian mode, for which the magnitude of the imposed electric field is found to play an important role.

 

Abstract High-sensitivity interstellar scintillation and polarization observations of PSR B0656+14 made at three epochs over a year using the Five-hundred-meter Aperture Spherical radio Telescope (FAST) show that the scattering is dominated by two different compact regions. We identify the one nearer to the pulsar with the shell of the Monogem Ring, thereby confirming the association. The other is probably associated with the Local Bubble. We find that the observed position angles of the pulsar spin axis and the spatial velocity are significantly different, with a separation of 19.°3 ± 0.°8, inconsistent with a previously published near-perfect alignment of 1° ± 2°. The two independent scattering regions are clearly defined in the secondary spectra, which show two strong forward parabolic arcs. The arc curvatures imply that the scattering screens corresponding to the outer and inner arcs are located approximately 28 pc from PSR B0656+14 and 185 pc from the Earth, respectively. Comparison of the observed Doppler profiles with electromagnetic simulations shows that both scattering regions are mildly anisotropic. For the outer arc, we estimate the anisotropy A R to be approximately 1.3, with the scattering irregularities aligned parallel to the pulsar velocity. For the outer arc, we compare the observed delay profiles with delay profiles computed from a theoretical strong-scattering model. Our results suggest that the spatial spectrum of the scattering irregularities in the Monogem Ring is flatter than Kolmogorov, but further observations are required to confirm this. 

Fast radio bursts (FRBs) are millisecond-time-scale radio transients, the origins of which are predominantly extragalactic and likely involve highly magnetized compact objects. FRBs undergo multipath propagation, or scattering, from electron density fluctuations on sub-parsec scales in ionized gas along the line of sight. Scattering observations have located plasma structures within FRB host galaxies, probed Galactic and extragalactic turbulence, and constrained FRB redshifts. Scattering also inhibits FRB detection and biases the observed FRB population. We report the detection of scattering times from the repeating FRB 20190520B that vary by up to a factor of 2 or more on minutes to days-long time-scales. In one notable case, the scattering time varied from 7.9 ± 0.4 ms to less than 3.1 ms ($95{{\ \rm per\ cent}}$ confidence) over 2.9 min at 1.45 GHz. The scattering times appear to be uncorrelated between bursts or with dispersion and rotation measure variations. Scattering variations are attributable to dynamic, inhomogeneous plasma in the circumsource medium, and analogous variations have been observed from the Crab pulsar. Under such circumstances, the frequency dependence of scattering can deviate from the typical power law used to measure scattering. Similar variations may therefore be detectable from other FRBs, even those with inconspicuous scattering, providing a unique probe of small-scale processes within FRB environments.

 

The repeating fast radio burst FRB 20190520B is localized to a galaxy atz= 0.241, much closer than expected given its dispersion measure DM = 1205 ± 4 pc cm⁻³. Here we assess implications of the large DM and scattering observed from FRB 20190520B for the host galaxy’s plasma properties. A sample of 75 bursts detected with the Five-hundred-meter Aperture Spherical radio Telescope shows scattering on two scales: a mean temporal delayτ(1.41 GHz) = 10.9 ± 1.5 ms, which is attributed to the host galaxy, and a mean scintillation bandwidth Δν_d(1.41 GHz) = 0.21 ± 0.01 MHz, which is attributed to the Milky Way. Balmer line measurements for the host imply an Hαemission measure (galaxy frame) EM_s= 620 pc cm⁻⁶× (T/10⁴K)^0.9, implying DM_Hαof order the value inferred from the FRB DM budget,${\mathrm{DM}}_{\mathrm{h}}={1121}_{-138}^{+89}$pc cm⁻³for plasma temperatures greater than the typical value 10⁴K. Combiningτand DM_hyields a nominal constraint on the scattering amplification from the host galaxy$\tilde{F}G={1.5}_{-0.3}^{+0.8}{({\mathrm{pc}}^2\mathrm{km})}^{-1/3}$, where$\tilde{F}$describes turbulent density fluctuations andGrepresents the geometric leverage to scattering that depends on the location of the scattering material. For a two-screen scattering geometry whereτarises from the host galaxy and Δν_dfrom the Milky Way, the implied distance between the FRB source and dominant scattering material is ≲100 pc. The host galaxy scattering and DM contributions support a novel technique for estimating FRB redshifts using theτ–DM relation, and are consistent with previous findings that scattering of localized FRBs is largely dominated by plasma within host galaxies and the Milky Way.

 

Although ammonia is a widely used interstellar thermometer, the estimation of its rotational and kinetic temperatures can be affected by the blended hyperfine components (HFCs). We have developed a new recipe, referred to as the hyperfine group ratio (HFGR), which utilizes only direct observables, namely the intensity ratios between the grouped HFCs. As tested on the model spectra, the empirical formulae in the HFGR can derive the rotational temperature (Trot) from the HFC group ratios in an unambiguous manner. We compared the HFGR with two other classical methods, intensity ratio and hyperfine fitting, based on both simulated spectra and real data. The HFGR has three major improvements. First, it does not require modelling the HFC or fitting the line profiles, so it is more robust against the effect of HFC blending. Second, the simulation-enabled empirical formulae are much faster than fitting the spectra over the parameter space, so both computer time and human time can be saved. Third, the statistical uncertainty of the temperature ΔTrot as a function of the signal-to-noise ratio (S/N) is a natural product of the HFGR recipe. The internal error of the HFGR is ΔTrot ≤ 0.5 K over a broad parameter space of rotational temperature (10-60 K), linewidth (0.3-4 km s-1) and optical depth (0-5). When there is spectral noise, the HFGR can also maintain a reasonable uncertainty level at ΔTrot ≤ 1.0 K when S/N > 4. 

Abstract Motivation Biclustering has emerged as a powerful approach to identifying functional patterns in complex biological data. However, existing tools are limited by their accuracy and efficiency to recognize various kinds of complex biclusters submerged in ever large datasets. We introduce a novel fast and highly accurate algorithm RecBic to identify various forms of complex biclusters in gene expression datasets. Results We designed RecBic to identify various trend-preserving biclusters, particularly, those with narrow shapes, i.e. clusters where the number of genes is larger than the number of conditions/samples. Given a gene expression matrix, RecBic starts with a column seed, and grows it into a full-sized bicluster by simply repetitively comparing real numbers. When tested on simulated datasets in which the elements of implanted trend-preserving biclusters and those of the background matrix have the same distribution, RecBic was able to identify the implanted biclusters in a nearly perfect manner, outperforming all the compared salient tools in terms of accuracy and robustness to noise and overlaps between the clusters. Moreover, RecBic also showed superiority in identifying functionally related genes in real gene expression datasets. Availability and implementation Code, sample input data and usage instructions are available at the following websites. Code: https://github.com/holyzews/RecBic/tree/master/RecBic/. Data: http://doi.org/10.5281/zenodo.3842717. Supplementary information Supplementary data are available at Bioinformatics online. 

A fundamental understanding of the flow of polymer solutions through the pore spaces of porous media is relevant and significant to enhanced oil recovery and groundwater remediation. We present in this work an experimental study of the fluid rheological effects on non-Newtonian flows in a simple laboratory model of the real-world pores—a rectangular sudden contraction–expansion microchannel. We test four different polymer solutions with varying rheological properties, including xanthan gum (XG), polyvinylpyrrolidone (PVP), polyethylene oxide (PEO), and polyacrylamide (PAA). We compare their flows against that of pure water at the Reynolds ( R e ) and Weissenburg ( W i ) numbers that each span several orders of magnitude. We use particle streakline imaging to visualize the flow at the contraction–expansion region for a comprehensive investigation of both the sole and the combined effects of fluid shear thinning, elasticity and inertia. The observed flow regimes and vortex development in each of the tested fluids are summarized in the dimensionless W i − R e and χ L − R e parameter spaces, respectively, where χ L is the normalized vortex length. We find that fluid inertia draws symmetric vortices downstream at the expansion part of the microchannel. Fluid shear thinning causes symmetric vortices upstream at the contraction part. The effect of fluid elasticity is, however, complicated to analyze because of perhaps the strong impact of polymer chemistry such as rigidity and length. Interestingly, we find that the downstream vortices in the flow of Newtonian water, shear-thinning XG and elastic PVP solutions collapse into one curve in the χ L − R e space.