2,269 research outputs found
The continuous strength method for the design of circular hollow sections
Circular hollow sections (CHS) are widely used in a range of structural engineering applications. Their design is covered by all major design codes, which currently use elastic, perfectly-plastic material models and cross-section classification to determine cross-secti\on compressive and flexural resistances. Experimental data for stocky sections show that this can result in overly conservative estimates of cross-section capacity. The continuous strength method (CSM) has been developed to reflect better the observed behaviour of structural sections of different metallic materials. The method is deformation based and allows for the rational exploitation of strain hardening. In this paper, the CSM is extended to cover the design of non-slender and slender structural steel, stainless steel and aluminium CHS, underpinned by and validated against 342 stub column and bending test results. Comparisons with the test results show that, overall, the CSM on average offers more accurate and less scattered predictions of axial and flexural capacities than existing design methods
Spontaneous polariton currents in periodic lateral chains
We predict spontaneous generation of superfluid polariton currents in planar
microcavities with lateral periodic modulation of both potential and decay
rate. A spontaneous breaking of spatial inversion symmetry of a polariton
condensate emerges at a critical pumping, and the current direction is
stochastically chosen. We analyse the stability of the current with respect to
the fluctuations of the condensate. A peculiar spatial current domain structure
emerges, where the current direction is switched at the domain walls, and the
characteristic domain size and lifetime scale with the pumping power.Comment: 6+6 pages, 4+1 figures (with supplemental material
Ballistic spin transport in exciton gases
Traditional spintronics relies on spin transport by charge carriers, such as
electrons in semiconductor crystals. This brings several complications: the
Pauli principle prevents the carriers from moving with the same speed; Coulomb
repulsion leads to rapid dephasing of electron flows. Spin-optronics is a
valuable alternative to traditional spintronics. In spin-optronic devices the
spin currents are carried by electrically neutral bosonic quasi-particles:
excitons or exciton-polaritons. They can form highly coherent quantum liquids
and carry spins over macroscopic distances. The price to pay is a finite
life-time of the bosonic spin carriers. We present the theory of exciton
ballistic spin transport which may be applied to a range of systems where
bosonic spin transport has been reported, in particular, to indirect excitons
in coupled GaAs/AlGaAs quantum wells. We describe the effect of spin-orbit
interaction of electrons and holes on the exciton spin, account for the Zeeman
effect induced by external magnetic fields, long range and short range exchange
splittings of the exciton resonances. We also consider exciton transport in the
non-linear regime and discuss the definitions of exciton spin current,
polarization current and spin conductivity.Comment: 16 pages, 10 figures to be published in Phys. Rev.
Energy relaxation of exciton-polariton condensates in quasi-1D microcavities
We present a time-resolved study of energy relaxation and trapping dynamics
of polariton condensates in a semiconductor microcavity ridge. The combination
of two non-resonant, pulsed laser sources in a GaAs ridge-shaped microcavity
gives rise to profuse quantum phenomena where the repulsive potentials created
by the lasers allow the modulation and control of the polariton flow. We
analyze in detail the dependence of the dynamics on the power of both lasers
and determine the optimum conditions for realizing an all-optical polariton
condensate transistor switch. The experimental results are interpreted in the
light of simulations based on a generalized Gross-Pitaevskii equation,
including incoherent pumping, decay and energy relaxation within the
condensate.Comment: 15 pages, 20 figure
Origins of ferromagnetism in transition-metal doped Si
We present results of the magnetic, structural and chemical characterizations of Mn<sup>+</sup>-implanted Si displaying <i>n</i>-type semiconducting behavior and ferromagnetic ordering with Curie temperature,T<sub>C</sub> well above room temperature. The temperature-dependent magnetization measured by superconducting quantum device interference (SQUID) from 5 K to 800 K was characterized by three different critical temperatures (T*<sub>C</sub>~45 K, T<sub>C1</sub>~630-650 K and T<sub>C2</sub>~805-825 K). Their origins were investigated using dynamic secondary mass ion spectroscopy (SIMS) and transmission electron microscopy (TEM) techniques, including electron energy loss spectroscopy (EELS), Z-contrast STEM (scanning TEM) imaging and electron diffraction. We provided direct evidences of the presence of a small amount of Fe and Cr impurities which were unintentionally doped into the samples together with the Mn<sup>+</sup> ions, as well as the formation of Mn-rich precipitates embedded in a Mn-poor matrix. The observed T*<sub>C</sub> is attributed to the Mn<sub>4</sub>Si<sub>7</sub> precipitates identified by electron diffraction. Possible origins of and are also discussed. Our findings raise questions regarding the origin of the high ferromagnetism reported in many material systems without a careful chemical analysis
Dynamics of a polariton condensate transistor switch
We present a time-resolved study of the logical operation of a polariton
condensate transistor switch. Creating a polariton condensate (source) in a
GaAs ridge-shaped microcavity with a non-resonant pulsed laser beam, the
polariton propagation towards a collector, at the ridge edge, is controlled by
a second weak pulse (gate), located between the source and the collector. The
experimental results are interpreted in the light of simulations based on the
generalized Gross-Pitaevskii equation, including incoherent pumping, decay and
energy relaxation within the condensate.Comment: 4 pages, 2 figure
Spin Selective Filtering of Polariton Condensate Flow
Spin-selective spatial filtering of propagating polariton condensates, using
a controllable spin-dependent gating barrier, in a one-dimensional
semiconductor microcavity ridge waveguide is reported. A nonresonant laser beam
provides the source of propagating polaritons while a second circularly
polarized weak beam imprints a spin dependent potential barrier, which gates
the polariton flow and generates polariton spin currents. A complete spin-based
control over the blocked and transmitted polaritons is obtained by varying the
gate polarization.Comment: 5 pages, 4 figure
Optical control of spin textures in quasi-one-dimensional polariton condensates
We investigate, through polarization-resolved spectroscopy, the spin
transport by propagating polariton condensates in a quasi one-dimensional
microcavity ridge along macroscopic distances. Under circularly polarized,
continuous-wave, non-resonant excitation, a sinusoidal precession of the spin
in real space is observed, whose phase depends on the emission energy. The
experiments are compared with simulations of the spinor-polariton condensate
dynamics based on a generalized Gross-Pitaevskii equation, modified to account
for incoherent pumping, decay and energy relaxation within the condensate.Comment: 10 pages, 9 figure
MicroRNA29a regulates IL-33-mediated tissue remodelling in tendon disease
MicroRNA (miRNA) has the potential for cross-regulation and functional integration of discrete biological processes during complex physiological events. Utilizing the common human condition tendinopathy as a model system to explore the cross-regulation of immediate inflammation and matrix synthesis by miRNA we observed that elevated IL-33 expression is a characteristic of early tendinopathy. Using in vitro tenocyte cultures and in vivo models of tendon damage, we demonstrate that such IL-33 expression plays a pivotal role in the transition from type 1 to type 3 collagen (Col3) synthesis and thus early tendon remodelling. Both IL-33 effector function, via its decoy receptor sST2, and Col3 synthesis are regulated by miRNA29a. Downregulation of miRNA29a in human tenocytes is sufficient to induce an increase in Col3 expression. These data provide a molecular mechanism of miRNA-mediated integration of the early pathophysiologic events that facilitate tissue remodelling in human tendon after injury
Adoptive T-cell immunotherapy for ganciclovir-resistant CMV disease after lung transplantation
Infections with cytomegalovirus (CMV) can induce severe complications after solid organ transplantation (SOT). The prognosis for ganciclovir-resistant CMV infection and disease is particularly poor. Whereas adoptive transfer of CMV-specific T cells has emerged as a powerful tool in hematopoietic stem cell transplant patients, its translation into the SOT setting remains a significant challenge as underlying immunosuppression inhibits the virus-specific T-cell response in vivo. Here, we demonstrate successful expansion and adoptive transfer of autologous CMV-specific T cells from a seronegative recipient of a seropositive lung allograft with ganciclovir-resistant CMV disease, resulting in the long-term reconstitution of protective anti-viral immunity, CMV infection, disease-free survival and no allograft rejection.Chien-Li Holmes-Liew, Mark Holmes, Leone Beagley, Peter Hopkins, Daniel Chambers Corey Smith and Rajiv Khann
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