Analysis of Optimization Weights for Flow Field of Internal Rotation Stabilizer Coupled with Porous Retaining Wall

In this paper, the flow field of the approximate T-shaped tundish and the removal rate of fine inclusions are improved by changing the parameters of the flow control device of the SCB (stabilizer coupling baffle) structure. Studies have shown that the synergistic effect of the DPRW (double porous retaining wall) structure and the IRS (internal rotation stabilizer) structure has excellent performance in mixing the temperature composition of the molten steel, increasing the average residence time of the molten steel, reducing the volume fraction of the dead zone, and improving the removal rate of fine inclusions. The opening method and diameter of the double-layer retaining wall have a greater impact on the flow field parameters. The larger the diameter, the more conducive to increasing the average residence time, and the smaller the diameter, the more conducive to increasing the removal rate of fine inclusions.

The missing ocean plastic sink: Gone with the rivers

Plastic floating at the ocean surface, estimated at tens to hundreds of thousands of metric tons, represents only a small fraction of the estimated several million metric tons annually discharged by rivers. Such an imbalance promoted the search for a missing plastic sink that could explain the rapid removal of river-sourced plastics from the ocean surface. On the basis of an in-depth statistical reanalysis of updated data on microplastics—a size fraction for which both ocean and river sampling rely on equal techniques—we demonstrate that current river flux assessments are overestimated by two to three orders of magnitude. Accordingly, the average residence time of microplastics at the ocean surface rises from a few days to several years, strongly reducing the theoretical need for a missing sink.

Nucleotide Dynamics During Flossing of Polycation-DNA-Polycation through a Nanopore using Molecular Dynamics

The full potential of solid state nanopores is yet to be realized for genome sequencing. Due to its robustness it can handle strong voltage amplitude and frequency. The effect of strong alternating voltage on the dynamics of nucleotides during translocation has been explored. We proposed a setup consisting of single stranded DNA covalently linked with symmetric polycations at both ends fashioned after the proposal of Kasianowicz. Such a setup allows for repeated back and forth motion of the DNA along the nanopore (1.45 nm diameter and 1.53 nm thick) by simply switching the voltage polarity if the polycation tail is sufficiently long (greater than or equal to 10) and the applied voltage is below 0.72 volts, but the average residence time of the nucleotides are too small to be of any practical use (6-30 ns). When alternating voltage of higher frequency is applied, it enhances the average residence time of the nucleotides by an order of magnitude to approximately 0.1 microseconds relative to direct voltage but the individual trajectories are too stochastic. Since, we are able to collect repeated read on the dynamics of individual nucleotides, we obtained the most probable time of appearance of a nucleotide within the nanopore. With such construct we were able to get almost linear dependence of most probable time versus nucleotide index, after gaussian fitting.

Study on the continuous precipitation of U(IV) oxalate in a vortex precipitator

The effects of feeding location, stirring speed and apparent average residence time on oxalate crystals size and distribution, tackiness of the product on the walls of reactor and stirring paddle were investigated in a vortex continuous precipitator at 45 °C. The results showed agglomeration happened during nucleation and crystals growth of U(IV) oxalate. Both local supersaturations and agglomeration maked the particles size distribution of U(IV) oxalate from 10–100 µm and the average sizes 35–45 µm. On the other hand, when the nucleation process were controlled to happen in the forced vortex zone, two feeding locations: (a) both oxalic acid and U(IV) nitrate solution into the forced vortex zone, (b) oxalic acid into the free vortex and U(IV) nitrate solution into the forced vortex, tackiness of the crystals on the wall of the precipitator could be effectively avoided.

Rate of immune complex cycling in follicular dendritic cell determines the extent of protecting antigen integrity and availability to germinal center B cells1

Follicular Dendritic Cells (FDCs) retain immune complexes (ICs) for prolonged time periods and are important for germinal center (GC) reactions. ICs undergo periodic cycling in FDCs, a mechanism supporting an extended half-life of antigen. Based on experimental data we estimated that the average residence time of Phycoerythrin-ICs (PE-ICs) on FDC surface and interior were 21 and 36 minutes, respectively. GC simulations show that antigen cycling might impact GC dynamics due to redistribution of antigen on the FDC surface and by protecting antigen from degradation. Antigen protection and influence on GC dynamics varied with antigen cycling time and total antigen concentration. Simulations predict that blocking antigen cycling terminates the GC reaction and decreases plasma cell production. Considering that cycling of antigen could be a target for the modulation of GC reactions, our findings highlight the importance of understanding the mechanism and regulation of IC cycling in FDCs.

Effects of Multiple-Hole Baffle Arrangements on Flow Fields in a Five-Strand Asymmetric Tundish

This paper reports on the re-engineering of standard five-strand tundish designs into a five-strand asymmetric tundish, which resulted in a non-uniform rate and bias for each strand. We sought to improve the casting conditions by optimizing the liquid steel flow-field in the tundish. Both a water modelling experiment and a numerical simulation were performed to analyze the flow-field according to various diversion hole diameters and injection angles. The results showed that the average residence time decreased as the diameter of the diversion holes increased. As the injection angle was increased, the average residence time initially decreased and then increased. The liquid steel from the ladle shroud rapidly extended to the #2 and #3 strands in the original tundish, which reduced the likelihood of inclusion collision and coalescence.

Residence Time Analysis of RNA Polymerase Transcription Dynamics: A Bayesian Sticky HMM Approach

ABSTRACTThe time spent by a single RNA polymerase (RNAP) at specific locations along the DNA, termed “residence time”, reports on the initiation, elongation and termination stages of transcription. At the single molecule level, this information can be obtained from dual ultra-stable optical trapping experiments, revealing a transcriptional elongation of RNAP interspersed with residence times of variable duration. Successfully discriminating between long and short residence times was used by previous approaches to learn about RNAP’s transcription elongation dynamics. Here, we propose an approach based on the Bayesian sticky hidden Markov models that treats all residence times, for an E. Coli RNAP, on an equal footing without a priori discriminating between long and short residence times. In addition, our method has two additional advantages, we provide: full distributions around key point statistics; and directly treat the sequence-dependence of RNAP’s elongation rate.By applying our approach to experimental data, we find: no emergent separation between long and short residence times warranted by the data; force dependent average residence time transcription elongation dynamics; limited effects of GreB on average backtracking durations and counts; and a slight drop in the average residence time as a function of applied force in RNaseA’s presence.STATEMENT OF SIGNIFICANCEMuch of what we know about RNA Polymerase, and its associated transcription factors, relies on successfully discriminating between what are believed to be short and long residence times in the data. This is achieved by applying pause-detection algorithms to trace analysis. Here we propose a new method relying on Bayesian sticky hidden Markov models to interpret time traces provided by dual optical trapping experiments associated with transcription elongation of RNAP. Our method does not discriminate between short and long residence times from the offset in the analysis. It allows for DNA site-dependent transition probabilities of RNAP to neighboring sites (thereby accounting for chemical variability in site to site transitions) and does not demand any time trace pre-processing (such as denoising).

Brief communication: Residence time of energy in the atmosphere

In atmospheric chemistry, a parameter called residence time is defined for each gas as T=M/F, where M represents the mass of the gas in the atmosphere and F is the total average influx or outflux, which in time averages are equal. In this brief communication, we extend this concept from matter to energy which is also a conservative quantity and estimate the average residence time of energy in the atmosphere, which amounts to about 58 d. A similar estimation for the residence time of energy in the Sun is of the order of 107 years, which agrees with the Kelvin–Helmholtz timescale.