Momentum analyticity of the holographic electric polarizability in 2+1 dimensions

The static electric polarization of a holographic field theory dual to the Einstein-Maxwell theory in the background of $AdS_4$ with a Reissner-Nordst\"{o}m (AdS-RN) black hole is investigated. We prove that the holographic polarization is a meromorphic functions in complex momentum plane and locate analytically the asymptotic distribution of the poles along two straight lines parallel to the imaginary axis for a large momentum magnitude. The results are compared with the numerical result on Friedel-like poles of the same holographic model reported in the literature and with the momentum singularities of the one-loop polarization in weak-coupling spinor QED$_3$ and scalar QED$_3$ with the similarities and differences discussed.Comment: 31 pages, 2 figure

Competition between the inter-valley scattering and the intra-valley scattering on magnetoconductivity induced by screened Coulomb disorder in Weyl semimetals

Recent experiments on Weyl semimetals reveal that charged impurities may play an important role. We use a screened Coulomb disorder to model the charged impurities, and study the magneto-transport in a two-node Weyl semimetal. It is found that when the external magnetic field is applied parallel to the electric field, the calculated longitudinal magnetoconductivity shows positive in the magnetic field, which is just the negative longitudinal magnetoresistivity (LMR) observed in experiments. When the two fields are perpendicular to each other, the transverse magnetoconductivities are measured. It is found that the longitudinal (transverse) magnetoconductivity is suppressed (enhanced) sensitively with increasing the screening length. This feature makes it hardly to observe the negative LMR in Weyl semimetals experimentally owing to a small screening length. Our findings gain insight into further understanding on recently actively debated magneto-transport behaviors in Weyl semimetals. Furthermore we studied the relative weight of the inter-valley scattering and the intra-valley scattering. It shows that the former is as important as the latter and even dominates in the case of strong magnetic fields and small screening length. We emphasize that the discussions on inter-valley scattering is out of the realm of one-node model which has been studied.Comment: 14 pages, 5 figure

Cold-Formed Ferritic Stainless Steel Tubular Sections under End-One-Flange Loading Condition

This paper presents experimental and numerical investigations of cold-formed ferritic stainless steel tubular sections under End-One-Flange (EOF) loading condition. A series of web crippling tests was conducted on cold-formed square and rectangular hollow sections of ferritic stainless steel grade EN 1.4003. The web crippling test results were used for the verification of the finite element (FE) model. Upon verification, a parametric study was performed thereafter. The codified web crippling design provisions in American, Australian/New Zealand and European standards for stainless steel structures were assessed. Improved web crippling design rules are proposed for cold-formed ferritic stainless steel tubular sections under EOF loading condition through modifying the design rules of the North American Specification and Direct Strength Method. It is shown that the modified web crippling design rules are able to provide accurate and reliable predictions

Design of concrete-filled high strength steel tubular X-joints subjected to compression

[EN] The structural performance and design of concrete-filled high strength steel tubular X-joints subjected to compression are investigated. A numerical investigation on the behaviour of concrete-filled high strength steel tubular chord members under concentrated bearing load has been performed. The high strength steel tubes had nominal yield stresses of 700 and 900 MPa. The infilled concrete had nominal concrete cylinder strengths of 35 and 100 MPa. In order to avoid the failure of brace members and reveal the true capacity of the X-joints, steel bearing plates were used to simulate the brace members. A finite element model was developed and validated against test results. Furthermore, a parametric study comprised 156 finite element analyses was carried out. The strengths of the concrete-filled high strength steel square and rectangular hollow section X-joints obtained from the parametric study together with available data in the literature were compared with the nominal strengths calculated from the CIDECT Design Guide. It is shown that the CIDECT design predictions exhibit significant scatter and could be unconservative for the concrete-filled tubular joints with chord sidewall slenderness ratio beyond 40 in this study. Hence, new design rules are proposed for concrete-filled high strength steel tubular X-joints subjected to compression. It is shown that the proposed design rules are able to provide reasonably good predictions.The research work described in this paper was supported by a grant from the Research Grants Council of the Hong Kong Special Administrative Region, China (Project No. 17209614).Li, H.; Young, B. (2018). Design of concrete-filled high strength steel tubular X-joints subjected to compression. Editorial Universitat Politècnica de València. 483-490. https://doi.org/10.4995/ASCCS2018.2018.7062OCS48349

Web Crippling of Cold-Formed High Strength Steel Square and Rectangular Hollow Sections under Two-Flange Loading Conditions

The web crippling behavior of cold-formed high strength steel (HSS) square and rectangular hollow sections under End-Two-Flange and Interior-Two-Flange loading conditions is studied. The cold-formed HSS tubular sections had nominal 0.2% proof stresses of 700 and 900 MPa. Finite element (FE) models were developed and validated against test results, showing the capability of replicating the experimental web crippling strengths, failure modes and load-deformation histories. Upon validation of the FE models, an extensive parametric study comprised 112 FE analyses was performed. The web crippling strengths obtained from the experimental and numerical investigations were compared with the nominal strengths calculated from the North American Specification, Australian/New Zealand Standard and European Code for cold-formed steel structures. The comparison results show that the nominal strengths predicted by the existing codified web crippling design provisions are either unconservative or overly conservative. Hence, new design rules are proposed for cold-formed HSS square and rectangular hollow sections by means of Direct Strength Method (DSM). It is shown that the modified DSM is able to provide reasonably good predictions