77 research outputs found
Fracture simulation of constructional steels in two fracture modes
The paper presents a comprehensive study, aiming to provide useful tools for numerically predicting the fracture phenomenon in steel structures. A micro-mechanically-based fracture model is proposed, which comprises two competing and correlated fracture criteria corresponding to the shear and tension fracture modes. Yield-to-fracture strain hardening behaviour of constructional steel is also investigated, and numerical modelling technique for fracture simulation in implicit time integration analysis is addressed. Having setting out all necessary components, coupon tests covering a wide range of stress states are carried out and numerically simulated to calibrate and validate the fracture model. Numerical results agree well with the experimental results, and conclusions are drawn about the suitability of the proposed fracture model and methods for predicting fracture in both shear and tension modes.the National Natural Science Foundation of China; the Australian Research Counci
Deep CFHT Y-band imaging of VVDS-F22 field: I. data products and photometric redshifts
We present our deep -band imaging data of a two square degree field within
the F22 region of the VIMOS VLT Deep Survey. The observations were conducted
using the WIRCam instrument mounted at the Canada--France--Hawaii Telescope
(CFHT). The total on-sky time was 9 hours, distributed uniformly over 18 tiles.
The scientific goals of the project are to select faint quasar candidates at
redshift , and constrain the photometric redshifts for quasars and
galaxies. In this paper, we present the observation and the image reduction, as
well as the photometric redshifts that we derived by combining our -band
data with the CFHTLenS optical data and UKIDSS DXS
near-infrared data. With -band image as reference total 80,000
galaxies are detected in the final mosaic down to -band point
source limiting depth of 22.86 mag. Compared with the 3500 spectroscopic
redshifts, our photometric redshifts for galaxies with and
mag have a small systematic offset of
, 1 scatter ,
and less than 4.0% of catastrophic failures. We also compare to the CFHTLenS
photometric redshifts, and find that ours are more reliable at
because of the inclusion of the near-infrared bands. In particular, including
the -band data can improve the accuracy at because the
location of the 4000\AA-break is better constrained. The -band images, the
multi-band photometry catalog and the photometric redshifts are released at
\url{http://astro.pku.edu.cn/astro/data/DYI.html}.Comment: 16 pages, 12 figures, 4 tables. AJ accepted. Updated access to the
data: https://zenodo.org/record/140003
Behaviour of H-section purlin connections in resisting progressive collapse of roofs
When a truss roof is subjected to sudden local damage, purlins are capable of bridging the damaged truss unit, thereby increasing the robustness of the integrated roof system. To investigate the bridging capacity purlins can provide, experiments were carried out on bolted fin plate connections that join thin-walled H-section purlins to the main truss, investigating their behaviour under a main truss-removal scenario. Eight specimens with varied connection details were tested. Results of all experiments are provided in detail, including the full-range vertical resistance versus displacement curves, the collapse-resisting mechanisms, and the failure modes, being either bolt shear failure or combined bolt bearing and net-section tensile failure. Experimental results showed that better bridging capacity can be achieved by adopting relatively larger diameter bolts, reducing the bolt group height, applying higher preloading force when installing bolts, and increasing the end distance for the bolt holes. Meanwhile, a theoretical model is proposed to predict the vertical resistance versus displacement response of the purlin-to-connection assembly. This model is capable of capturing the slip of bolts, and the gradual yielding and failure of the connection components, and thus gives predictions that are in reasonably good agreement with the experimental results.The National Natural Science Foundation of China; The Australian Research Counci
Recent developments on the Component Method
The Component Method is well established and incorporated in Part 1.8 of Eurocode3 for the design of connections of steel frameworks. It is primarily intended to provide the elastic joint stiffness, although Part 1.8 includes provisions for also determining the inelastic moment-rotation response from the elastic limit to the ultimate moment. The latter provisions are empirical and use an established experimentally-based nonlinear equation to define the inelastic response. The Component Method has been further developed in recent years to determine the inelastic response using bi-linear springs with elastic and inelastic ranges. Procedures have also been developed at the University of Sydney to extend the Method into the post-ultimate range by defining tri-linear springs with elastic, inelastic and softening ranges. As well, recent research at the University of Sydney has produced a simple way to predict the moment-rotation response under fracture of components, thus enabling the Method to capture the full moment-rotation behaviour. The ability of the Method to predict full-range moment-rotation behaviour is especially useful for design by advanced analysis and progressive collapse analysis, as it allows both members and connections to be checked for stiffness and strength as part of the analysis. In parallel, an ongoing joint project between Sydney University and Tongji University on the strength of beam-to-upright connections in rack structures has extended to Component Method to cold-formed steel connections which include tang-connectors and bolts. The paper provides an overview of these recent developments of the Component Method, including the opportunity to incorporate the Method in a fully nonlinear procedure for the direct design of steel frameworks including connections by advanced analysis, also referred to as the Direct Design Method.The Australian Research Counci
Thermosensitive Cu2O-PNIPAM core-shell nanoreactors with tunable photocatalytic activity
We report a facile and novel method for the fabrication of Cu2O@PNIPAM
core-shell nanoreactors using Cu2O nanocubes as the core. The PNIPAM shell not
only effectively protects the Cu2O nanocubes from oxidation, but also improves
the colloidal stability of the system. The Cu2O@PNIPAM core-shell microgels can
work efficiently as photocatalyst for the decomposition of methyl orange under
visible light. A significant enhancement in the catalytic activity has been
observed for the core-shell microgels compared with the pure Cu2O nanocubes.
Most importantly, the photocatalytic activity of the Cu2O nanocubes can be
further tuned by the thermosensitive PNIPAM shell, as rationalized by our
recent theory.Comment: 8 pages, 6 figures (Supporting Information included: 11 pages, 10
figures
Re-visiting the extended Schmidt law: the important role of existing stars in regulating star formation
We revisit the proposed extended Schmidt law (Shi et al. 2011) which points
that the star formation efficiency in galaxies depends on the stellar mass
surface density, by investigating spatially-resolved star formation rates
(SFRs), gas masses and stellar masses of star formation regions in a vast range
of galactic environments, from the outer disks of dwarf galaxies to spiral
disks and to merging galaxies as well as individual molecular clouds in M33. We
find that these regions are distributed in a tight power-law as Sigma_SFR
~(Sigma_star^0.5 Sigma_gas )^1.09, which is also valid for the integrated
measurements of disk and merging galaxies at high-z. Interestingly, we show
that star formation regions in the outer disks of dwarf galaxies with Sigma_SFR
down to 10^(-5) Msun/yr/kpc^2, which are outliers of both Kennicutt-Schmidt and
Silk-Elmegreen law, also follow the extended Schmidt law. Other outliers in the
Kennicutt-Schmidt law, such as extremely-metal poor star-formation regions,
also show significantly reduced deviations from the extended Schmidt law. These
results suggest an important role for existing stars in helping to regulate
star formation through the effect of their gravity on the mid-plane pressure in
a wide range of galactic environments.Comment: 15 pages, 6 figures, 3 tables; ApJ in pres
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