Elliptical-hollow-section braces under cyclic axial loading

In this paper, finite element analysis was conducted to simulate the cyclic behaviour of elliptical hollow section (EHS) and circular hollow section (CHS) braces with pin-ended conditions. The aims were to investigate the influence of the cross-section slenderness, member slenderness and cross-section shape on the hysteretic performance. Prior to the numerical simulations, tensile coupon tests and stub column tests had been conducted to obtain material properties and cross-section capacities of the hot-rolled and cold-formed hollow section tubes. Pilot numerical simulation results indicated that the member slenderness affects the ultimate load; the cross-section slenderness would have significant impact on the energy dissipation capacity, and EHS specimens dissipate more energy than their CHS counterparts.Department of Civil and Environmental Engineerin

Ultralow-current-density and bias-field-free spin-transfer nano-oscillator

<br /> The spin-transfer nano-oscillator (STNO) offers the possibility of using the transfer of spin angular momentum via spin-polarized currents to generate microwave signals. However, at present STNO microwave emission mainly relies on both large drive currents and external magnetic fields. These issues hinder the implementation of STNOs for practical applications in terms of power dissipation and size. Here, we report microwave measurements on STNOs built with MgO-based magnetic tunnel junctions having a planar polarizer and a perpendicular free layer, where microwave emission with large output power, excited at ultralow current densities, and in the absence of any bias magnetic fields is observed. The measured critical current density is over one order of magnitude smaller than previously reported. These results suggest the possibility of improved integration of STNOs with complementary metal-oxide-semiconductor technology, and could represent a new route for the development of the next-generation of on-chip oscillators

Strain effects on optical polarisation properties in (11(2)over-bar2) plane GaN films

We present the theoretical results of the electronic band structure of wurtzite GaN films under biaxial strains in the (11 (2) over bar2)-plane The calculations are performed by the kappa p perturbation theory approach through using the effective-mass Hamiltonian for an arbitrary direction The results show that the transition energies decrease with the biaxial strains changing from -0 5% to 0 5% For films of (11 (2) over bar2)-plane, the strains are expected to be anisotropic in the growth plane Such anisotropic strains give rise to valence band mixing which results in dramatic change in optical polarisation property The strain can also result in optical polarisation switching phenomena Finally, we discuss the applications of these properties to the (11 (2) over bar2) plane GaN based light emitting diode and lase diod