Understanding the nature of Dark Matter and Dark Energy is one of the most pressing issues in cosmology and fundamental physics. The purpose of the DUNE (Dark UNiverse Explorer) mission is to study these two cosmological components with high precision, using a space-based weak lensing survey as its primary science driver. Weak lensing provides a measure of the distribution of dark matter in the universe and of the impact of dark energy on the growth of structures. DUNE will also include a complementary supernovae survey to measure the expansion history of the universe, thus giving independent additional constraints on dark energy. The baseline concept consists of a 1.2m telescope with a 0.5 square degree optical CCD camera. It is designed to be fast with reduced risks and costs, and to take advantage of the synergy between ground-based and space observations. Stringent requirements for weak lensing systematics were shown to be achievable with the baseline concept. This will allow DUNE to place strong constraints on cosmological parameters, including the equation of state parameter of the dark energy and its evolution from redshift 0 to 1. DUNE is the subject of an ongoing study led by the French Space Agency (CNES), and is being proposed for ESA's Cosmic Vision programme.

Thin linear-viscoelastic layers such as films and coatings have many applications. Simultaneous measurement of the multiple acoustic properties of a thin layer is of great importance in ensuring its quality. In this paper, a novel technique is proposed for the simultaneous determination of the three acoustic properties of a thin linear-viscoelastic layer, namely the acoustic impedance Z2, the time-of-flight Δt2 and the attenuation coefficient α2. A planar ultrasonic transducer, at normal incidence, is used to interrogate the thin layer, and all the reflections are received by the same transducer. Firstly, an optimal estimate of Z2 is obtained by subtracting the echo from the front surface of the thin layer from all the received echoes. After this determination of the acoustic impedance, optimal estimates for Δt2 and α2 can be found if the echo from the back surface of the thin layer is subtracted without any remainder. This technique avoids the convergence problem that is frequently encountered in the traditional measurement techniques based mainly on fitting the experimental reflection spectrum to a theoretical model. The effectiveness of the new technique is firstly confirmed by numerical simulation and then by experimental application to four thin linear-viscoelastic layers. Experimental results show that Z2 and Δt2 can be obtained accurately while the error in determining of α2 is relatively large due to the insensitivity of the ultrasonic echoes to that property. The relative uncertainties in determining the three acoustic properties Z2, Δt2 and α2 in our experiments are around 1.2%, 1.5%, 5%, respectively, mainly arising from the principle of this measurement technique.

The timber board interlayer is applied as the formwork for the pouring of concrete slab in various practical applications of timber–concrete composite structures, with the rehabilitation of timber buildings, in particular. At present, there are few studies performed to study the shear stiffness of inclined screws in timber–concrete composite beams with timber board interlayer. In this article, eight groups of shear tests were carried out to study the shear stiffness of inclined screws in timber–concrete composite beams with timber board interlayer. The key parameters included the embedment depth of the screw connector into timber, screw diameter, the thickness of concrete slab, and concrete strength. As indicated by the test results, the shear stiffness of the inclined screws was improved as the embedment depth of screw into timber and screw diameter increased. When the embedded depth of screw into concrete remained unchanged, the thickness of concrete slab and concrete strength exhibited no significant impact on the shear stiffness of inclined crossing screws. On the basis of the theory of a beam on a two-dimensional elastic foundation, the calculation method for predicting the shear stiffness of inclined screw in timber–concrete composite beams with interlayer was proposed. The comparisons demonstrated that the shear stiffness of inclined screw can be well predicted using the calculation method.

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