Effect of particle shape on packing fraction and velocity profiles at outlet of a silo

Many studies on how the particle shape affects the discharge flow mainly focus on discharge rates and avalanche statistics. In this study, the effect of the particle shape on the packing fraction and velocities of particles in the silo discharge flow are investigated by using the discrete element method. The time-averaged packing fraction and velocity profiles through the aperture are systematically measured for superelliptical particles with different blockinesses. Increasing the particle blockiness is found to increase resistance to flow and reduce the flow rate. At an identical outlet size, larger particle blockiness leads to lower velocity and packing fraction at the outlet. The packing fraction profiles display evidently the self-similar feature that can be appropriately adjusted by fractional power law. The velocity profiles for particles with different shapes obey a uniform self-similar law that is in accord with previous experimental results, which is compatible with the hypothesis of free fall arch. To further investigate the origin of flow behaviors, the packing fraction and velocity field in the region above the orifice are computed. Based on these observations, the flow rate of superelliptical particles is calculated and in agreement with the simulated data.

Spectro-polarimetric observations at the NVST:I.instrumental polarization calibration and primary measurements

This paper is devoted to the primary spectro-polarimetric observation performed at the New Vacuum Solar Telescope(NVST)of China since 2017,and our aim is to precisely evaluate the real polarimetric accuracy and sensitivity of this polarimetry by using full Stokes spectro-polarimetric observations of the photospheric line Fe I 532.4 nm.In the work,we briefly describe the salient characteristic of the NVST as a polarimeter in terms of technology and then characterize its instrumental polarization based on the operation in 2017 and 2019.It is verified that the calibration method utilizing the instrumental polarization calibration unit(ICU)is stable and credible.The calibration accuracy can reach up to 3×10^-3.Based on the scientific observation of NOAA Active Region 12645 on 2017 April 5,we estimate that the residual cross-talk from Stokes I to Stokes Q,U and V,after the instrumental polarization calibration,is about 4×10^-3 on average,which is consistent with the calibration accuracy and close to the photon noise.The polarimetric sensitivity(i.e.,the detection limit)for polarized light is of the order of 10-3 with an integration time over 20 s.Slow modulation rate is indeed an issue for the present system.The present NVST polarimeter is expected to be integrated with a high-order adaptive optics system and a field scanner to realize 2 D vector magnetic field measurements in the following instrumentation update.

Method of composing two-dimensional scanned spectra observed by the New Vacuum Solar Telescope

In this paper we illustrate the technique used by the New Vacuum Solar Telescope（NVST）to increase the spatial resolution of two-dimensional（2D）solar spectroscopy observations involving two dimensions of space and one of wavelength.Without an image stabilizer at the NVST,large scale wobble motion is present during the spatial scanning,whose instantaneous amplitude can reach 1.3′′due to the Earth’s atmosphere and the precision of the telescope guiding system,and seriously decreases the spatial resolution of 2D spatial maps composed with scanned spectra.We make the following effort to resolve this problem：the imaging system（e.g.,the Ti O-band）is used to record and detect the displacement vectors of solar image motion during the raster scan,in both the slit and scanning directions.The spectral data（e.g.,the Hαline）which are originally obtained in time sequence are corrected and re-arranged in space according to those displacement vectors.Raster scans are carried out in several active regions with different seeing conditions（two rasters are illustrated in this paper）.Given a certain spatial sampling and temporal resolution,the spatial resolution of the composed 2D map could be close to that of the slit-jaw image.The resulting quality after correction is quantitatively evaluated with two methods.A physical quantity,such as the line-of-sight velocities in multiple layers of the solar atmosphere,is also inferred from the re-arranged spectrum,demonstrating the advantage of this technique.

Advance in reversible Zn anodes promoted by 2D materials

With the growing energy demand associated with high safety and low-cost requirement,aqueous zinc-ion batteries(AZIBs)have been considered as one of the most promising next-generation batteries.However,some key issues,such as uncontrollable dendrites growth,severe corrosion,hydrogen evolution and side reactions of Zn anodes during charge/discharge process,have hindered its pragmatic applications.Two-dimensional(2D)materials hold advantages of unique physical and chemical properties,large surface areas and abundant active sites,which have been successfully used to overcome the above shortcomings of Zn anodes in recent years.In this review,the issues and challenges of Zn anodes are outlined.Then,the state-of-the-art progress on Zn anodes modification based on 2D materials such as graphene,2D metal carbides and nitrides(MXenes),2D metal-organic frameworks(MOFs),2D covalent organic frameworks(COFs),2D transition metal compounds and other 2D materials is discussed in detail.Finally,the perspectives of employing 2D materials in highly reversible Zn anodes are summarized and discussed.

Degradation of benzene on Zr-doped TiO_2 photocatalysts with a bimodal pore size distribution

Zr-doped TiO2 was prepared from TiOSO4 and ZrOCO3 by a co-precipitation method using NH3H2O as the precipitation agent. The Zr-doped TiO2 was characterized by X-ray diffraction（XRD）, low temperature N2adsorption–desorption measurement, and UV–Vis diffuse reflectance spectroscopy technology. Appropriate amounts of ZrO2 addition can greatly improve the TiO2 microstructure properties and its photocatalytic activities. In addition, polyethylene glycol（PEG） was used as a surfactant for templating the pore structure of samples. A bimodal pore structure can be controlled using PEG6000 and PEG20000 surfactants simultaneously during the preparation. The rate constant of benzene degradation over the Zr-doped TiO2 linearly decreases with the increase of photocatalytic reaction temperature and decreases in a polynomial relation with the benzene concentration.Moreover, it increases approximately linearly with the increase of the illumination intensity or area.

A De novo Mutation in Dystrophin Causing Muscular Dystrophy in a Female Patient

Background： Duchenne muscular dystrophy （DMD） and Becker muscular dystrophy （BMD） are X-linked recessive neuromuscular diseases resulting from dystrophin （DMD） gene mutations. It has been known that the carrier of DMD mutations may also have symptoms of the disease. While de novo mutation is quite common in BMD/DMD patients, it is rarely reported in the female carriers. Methods： Two sporadic Chinese patients with progressive muscular dystrophy and their familial members were recruited. The targeted next-generation sequencing （NGS） and the multiplex ligation-dependent probe analysis （MLPA） were performed in the proband. Blood tests, electrocardiography, echocardiography, and electromyography were also evaluated. Results： Two novel mutations of DMD gene were identified, c.7318C〉T（p.Q2440＊） in the male proband and c.4983dupA（p.A1662Sfs＊24） in the female carrier. The MLPA analysis did not detect any large rearrangements. The haplotype analysis indicated that the two mutations were derived from de novo mutagenesis. Conclusions： We identified two novel de novo mutations of DMD gene in two Chinese pedigrees, one of which caused a female patient with muscular dystrophy. The mutational analysis is important for DMD patients and carriers in the absence of a family history. The NGS can help detect the mutations in MLPA-negative patients.

A direct coupling analysis method and its application to the Scientific Research and Demonstration Platform

Design of a very large floating structure(VLFS)deployed near islands and reefs,different from those in the open sea,inevitably faces new technical challenges including numerical analysis methods.In this paper,a direct coupling analysis method(DCAM)has been established based on the Boussinesq equations and the three-dimensional hydroelasisity theory with Rankine source method to analyze the responses of a VLFS in shallow sea with complicated geographical environment.Model tests have been carried out to validate the DCAM.To further verify the numerical methods and investigate the performance of such a VLFS,a“Scientific Research and Demonstration Platform(SRDP)”was built and deployed in 2019 at the site about 1000 m off an island with water depth around 40m in South China Sea.It is a simplified small model of a two-module semi-submersible-type VLFS.The numerical simulation of its responses on severe waves with focus on motions and connector forces is conduct by DCAM,and compared with the on-site measurements.Good agreement has been achieved.This approves the DCAM as a feasible tool for design and safety assessment of a VLFS deployed near islands and reefs.