Superelastic and pH-Responsive Degradable Dendrimer Cryogels Prepared by Cryo-aza-Michael Addition Reaction

Dendrimers exhibit super atomistic features by virtue of their well-defined discrete quantized nanoscale structures. Here, we show that hyperbranched amine-terminated polyamidoamine (PAMAM) dendrimer G4.0 reacts with linear polyethylene glycol (PEG) diacrylate (575 g/mol) via the aza-Michael addition reaction at a subzero temperature (−20 °C), namely cryo-aza-Michael addition, to form a macroporous superelastic network, i.e., dendrimer cryogel. Dendrimer cryogels exhibit biologically relevant Young’s modulus, high compression elasticity and super resilience at ambient temperature. Furthermore, the dendrimer cryogels exhibit excellent rebound performance and do not show significant stress relaxation under cyclic deformation over a wide temperature range (−80 to 100 °C). The obtained dendrimer cryogels are stable at acidic pH but degrade quickly at physiological pH through self-triggered degradation. Taken together, dendrimer cryogels represent a new class of scaffolds with properties suitable for biomedical applications

The influence of a single defect in composite gate insulators on the performance of nanotube transistors

The current through a carbon nanotube field-effect transistor (CNFET) with cylindrical gate electrode is calculated using the nonequilibrium Greens function method in a tight-binding approximation. The obtained result is in good agreement with the experimental data. The space radiation and nuclear radiation are known to cause defects in solids. The theoretical approach is used to calculate the amplitude of the random-telegraph-signal (RTS) noise due to a single defect in the gate oxide of a long channel p-type CNFET. We investigate how the amplitude of the RTS noise is affected by the composite structure of gate insulators, which contains an inner insulator with a dielectric constant larger than 3.9 and an outer insulator with a dielectric constant of 3.9 (as for SiO2). It is found that the RTS amplitude increases apparently with the decreasing thickness of the inner gate insulator. If the inner insulator is too thin, even though its dielectric constant is as large as 80, the amplitude of the RTS noise caused by the charge of Q = +1e may amount to around 80% in the turn-on region. Due to strong effects of defects in CNFETs, CNFETs have a potential to be used for detecting the space radiation or nuclear radiation.Comment: 8 Figure

Influence of design parameters on the global performances of low-speed counter-rotating axial-flow fans

The present work aims at experimentally investigating the effects of some parameters on the performances of a counter-rotating stage, and on the instationary flow between the rotors. Three counter-rotating fans, which have the same design point, have been designed. These systems differ by the distribution of the loading and of the ratio of angular velocity between the front rotor and the rear rotor. All the configurations have been tested in a normalized test rig, where the ratio of angular velocities and the axial distance between the two rotors can be varied. The influence of these parameters are then addressed by analysing the experimental results of the static pressure rise and static efficiency, as well as of the wall pressure fluctuations registered by a microphone at the wall. The three systems achieve the design point with a high efficiency. The counter-rotating systems lead to at least a 10 percentage points gain in static efficiency at the design flow rate, compared to the typical peak efficiency of a traditional rotor-stator stage. Meanwhile, counter-rotating systems display good working stabilities at very low volume flow rates. In addition, at the design speed ratio, the overall performance decreases almost monotonically with the axial distance. Nevertheless, an optimum in axial distance can be found for higher speed ratios. Finally, the investigations of the wall pressure fluctuations show that the amplitudes of power spectral density corresponding to the blade passing frequency of the rear rotor are significantly higher than that of the front rotor. The interaction peaks are also stronger for an equal distribution of the work on the two rotors

Experimental comparison between a counter-rotating axial-flow fan and a conventional rotor-stator stage

Based on the requirement of energy consumption level and weight and dimension restriction, compact axial machines are highly demanded in many industrial fields. The counter-rotating axial-flow fans could be a promising way to achieve these requirements. Because of the reduction of rotational speed and a better homogenization of the flow downstream of the rear rotor, these machines may have very good aerodynamic performances. However, they are rarely used in subsonic applications, mainly due to poor knowledge of the aerodynamics in the mixing area between the two rotors, where very complex structures are produced by the interaction of highly unsteady flows. The purpose of the present work is to compare the global performances (static pressure rise and static efficiency) and the wall pressure fluctuations downstream of the first rotor for three different stages operating at the same point: a single subsonic axial-flow fan, a conventional rotor-stator stage and a counter-rotating system that have been designed with in-house tools. The counter-rotating system allows large savings of energy with respect to the other two systems, for lower rotation rates and by adjusting the distance between the two rotors, a solution with comparable wall pressure fluctuations levels for the three systems is found