We demonstrate a compact tunable photonic modulator driven by surface acoustic waves (SAWs) in the low GHz frequency range. The device follows a well-known Mach-Zehnder interferometer (MZI) structure with three output channels, built upon multi-mode interference (MMI) couplers. The light continuously switches paths between the central and the side channels, avoiding losses and granting a 180◦-dephasing synchronization between them. The modulator was monolithically fabricated on (Al,Ga)As, and can be used as a building block for more complex photonic functionalities. It can also be implemented in other material platforms such as Silicon or (In,Ga)P. Light modulated at multiples of the fundamental acoustic frequency can be accomplished by adjusting the applied acoustic power. An excellent agreement between theory and experiment is achieved.

The long-term behavior of the UO2 fuel matrix under conditions of the Belgian “Supercontainer design” was investigated by dissolution tests of high burn-up spent nuclear fuel (SNF) in high alkaline solution under 40 bar of (Ar + 8%H2) atmosphere. Four fragments of SNF, obtained from a pellet previously leached during two years, were exposed to young cement water with Ca (YCWCa) under 3.2 bar H2 partial pressure in four single/independent autoclave experiments for a period of 59, 182, 252 and 341 days, respectively. After a decrease of the concentration of dissolved 238U, which is associated with a reduction of U(VI) to U(IV), the concentration of 238U in solution is constant in the experiments running for 252 and 341 days. These observations indicate an inhibition of the matrix dissolution due to the presence of H2. A slight increase in the concentration of 90Sr and 137Cs in the aqueous solution indicates that there is still dissolution of the grain boundaries. These findings are similar to those reported for spent nuclear fuel corrosion in synthetic near neutral pH solutions.

New 1212- type Molybdo-Cuprates of with composition Mo0.5Cu0.5Sr2RECu2O7.5 (RE = Rare Earth) have been prepared by High Pressure and High Temperature (HPHT) synthesis. Their crystal structures are characterized by combining the X-Ray/Neutron powder diffraction and electron diffraction techniques. All the materials show tetragonal symmetry, crystallizing in the P4/mmm space group (S.G.). The chain oxygens are randomly distributed in the two different oxygen sites, which are not completely filled and the defect induced by oxygen vacancies in fact makes the chain fragmented and disordered. The microstructure of these compounds is interpreted by a well-known diagonal cell √2ap × √2ap × 3ap, as confirmed by the Electron diffraction (ED) and transmission electron microscope (TEM). X-ray photoelectron spectroscopy (XPS) studies show the predominance of the non magnetic MoVI state over the MoV one. At the same time oxidation state of copper is found to be dominated by CuII.

A novel pressure sensor is proposed exhibiting generative properties fromdisplacement-induced ionic charge separation in gel electrolytes. Amechano-ionic or ‘piezo-ionic’ effect, in analogy to thewell-known piezoelectric effect, is hypothesized to originate from a differencein mobilities between cationic and anionic species causing a localized ioniccharge gradient upon application of pressure. This gradient can be detected as avoltage or current by using copper electrodes placed at the sides or at regularintervals along a surface of the gel. The voltage generated may be a result ofthe local concentration gradient induced by the deformation of the gel orperhaps is the result of some ions moving faster through the porous gel thanothers. In this work, ionic polymer gels based on Poly(vinylidenefluoride-hexafluoropropylene) (PVDF-HFP) co-polymer were synthesized insitu to incorporate an organic electrolyte consisting ofbis(trifluoromethane)sulfonimide lithium salt in propylene carbonate. With twoelectrodes placed under the gel, the samples were subjected to a sinusoidalmechanical force while open circuit voltage was measured to determine therelationship between electrical signal and mechanical input. The voltagesgenerated are 10’s of mV in magnitude at 1 kPa. Results suggest amaximum sensitivity of 25 µV/Pa at 10 mHz, comparable to the voltagesexpected in piezoelectric polymers such as PVDF (44 µV/Pa for similardimensions). The non-aqueous, solid-state ionic gels presented in this workprovide improved stability and is less prone to evaporation than its aqueous,hydrogel based counterpart. The new mechanism of sensing provides an alternativeto the more rigid and less stretchable piezoelectric sensors.

Efficient water desalination constitutes a major challenge for the next years and reverse osmosis membranes will play a key role to achieve this target. In this work, a high-performance reverse osmosis nanocomposite membrane was prepared by interfacial polymerization in presence of multiwalled carbon nanotubes. The effect of carbon nanotubes on the chlorine resistance, antifouling and desalination performance of the nanocomposite membranes was studied. We found that the addition of carbon nanotubes not only improved the membrane performance in terms of flow and antifouling, but also inhibited the chlorine degradation of these membranes. Several reports have acknowledged the benefits of adding carbon nanotubes to aromatic PA nanocomposite membranes, but little attention has been paid to the mechanisms related to the improvement of flow rate, selectivity and chlorine tolerance. We carried out a comprehensive study of the chemical and physical effects of carbon nanotubes on the fully crosslinked polyamide network. The chemical structure, chlorine resistance and membrane degradation was studied by several analytical techniques, permeation and fouling studies, whereas the microstructure of the nanocomposite was studied by small and wide angle X-ray scattering, high resolution transmission electron microscopy, and molecular dynamics. We found that the addition of the nanotube affects the interfacial polymerization, resulting in a polymer network with smaller pore size and higher sodium and chlorine rejection. We simulated the hydration of the membrane in seawater and found that the radial distribution function of water confined in the pores of the nanocomposite membrane exhibited smaller clusters of water molecules, thus suggesting a dense membrane structure. We analysed the network mobility and found that the nanotube provides mechanical stability to the polymer matrix. This study presents solid evidence towards more efficient and robust reverse osmosis membranes using carbon nanotubes as mechanical reinforcing and chlorine protection additive.

The mechanical properties of nanocarbon hybrid films are addressed by means of indentation simulation based on molecular-dynamics. In these films, single-walled carbon nanotubes (SWCNTs) are intercalated parallel to each other between graphene sheets; the SWCNT axes are also parallel to the planes of the sheets. Thus the simulation model is quasi-two-dimensional. The load-deflection curve depends on both the number of the layers and the diameter of SWCNTs. In the range of small forces, the simulation data can be interpolated by a cubic function of the deflection, while in the range of large forces, the data can be expressed in terms of a linear function of the deflection. It is revealed that such a transition corresponds to the structural change of the hybrid film.

In support of a recent surge in research to develop an accident tolerant reactor, accident tolerant fuels and cladding candidates are being investigated. Relative motion between the fuel rods and fuel assembly spacer grids can lead to excessive fuel rod wear and, in some cases, to fuel rod failure. Based on industry data, grid-to-rod-fretting (GTRF) has been the number one cause of fuel failures within the U.S. pressurized water reactor (PWR) fleet, accounting for more than 70% of all PWR leaking fuel assemblies. APMT, an Fe-Cr-Al steel alloy, is being examined for the I2S-LWR project as a possible alternative to conventional fuel cladding in a nuclear reactor due to its favorable performance under LOCA conditions. Tests were performed to examine the reliability of the cladding candidate under simulated fretting conditions of a pressurized water reactor (PWR). The contact is simulated with a rectangular and a cylindrical specimen over a line contact area. A combination of SEM analysis and wear & work rate calculations are performed on the samples to determine their performance and wear under fretting. While APMT can perform favorably in loss of coolant accident scenarios, it also needs to perform well when compared to Zircaloy-4 with respect to fretting wear.

This study uses ab initio quantum molecular dynamics (QMD) simulations to validate multimillion-atom reactive molecular dynamics (RMD) simulations, and predicts unexpected condensation of carbon atoms during high-temperature oxidation of silicon-carbide nanoparticles (nSiC). For the validation process, a small nSiC in oxygen environment is chosen to perform QMD simulation. The QMD results provide the number of Si-O and C-O bonds as a function of time. RMD simulation is then performed under the identical condition. The time evolutions of different bonds are compared between the QMD and RMD simulations. We observe the condensation of large number of C-cluster nuclei into larger C clusters in both simulations, thereby validating RMD. Furthermore, we use the QMD simulation results as an input to a multi-objective genetic algorithm to train the RMD force-field parameters. The resulting force field far better reproduces the ground-truth QMD simulation results.

Three-roll milling (TRM) has proven to be an effective method to disperse 1D nanofillers like carbon nanotubes in polymer resins. However, until now only limited research has been performed on using this method to exfoliate and disperse 2D nanofillers, such as graphene and graphene nanoplatelets (GNP) with preserved lateral dimension. In the present work, a systematic study of TRM processing parameters on final nanocomposite properties is presented, resulting in improved GNP/epoxy nanocomposite properties after the optimization of TRM parameters such as mode, speed, cycles, gap distance, and resin temperature. Electrical conductivity of the final GNP/epoxy nanocomposites is increased by six orders of magnitude, while at the same time a high mechanical reinforcement is achieved as well.

Cobalt doped ZnO (ZnO:Co) films with a 1 at% doping rate have been successfullygrown on (100) oriented p type Si substrates by radiofrequency magnetronsputtering. Post annealing treatments at 973 K for various short periods havebeen carried out and structural, optical and electrical properties of the filmshave been investigated. Upon rapid annealing, the dopant distribution in thefilm has been found homogeneous. The annealing improves the (002) texture of thefilm and the mean column width increases with the annealing duration from 60 nmup to 95 nm. The lattice parameter of the ZnO:Co films decreases upon annealingand approaches that of bulk ZnO. The photoluminescence (PL) study reveals thatthe Co2+ ions can be excited directly or through a transfermechanism from the matrix. The PL intensity decreases with the annealing timesuggesting a diffusion process of the dopant impeding theCo2+ emission. At last, the electrical conductivity reachesvalues compatible with potential electroluminescent applications of the ZnO:Cofilms.

The thermoelectric properties of polycrystalline samples of Sr1-xLa0.67xTiO3-δ and Sr0.20La0.53Ti1−yNbyO3-δ have been investigated. The first series has a gradually increasing amount of A-site vacancies, and charge carriers linked to the oxygen deficiency. The second series has a fixed amount of A-site vacancies (27%) and variation of the Nb content was used to optimise the electrical properties. Maximum power factors of 0.6 mW m-1 K-2 for x = 0.4 and 0.4 mW m-1 K-2 for y = 0.05 were observed at 700 K. Combining these values with thermal conductivity data obtained previously, suggests that maximum figures of merit zT = 0.16 for x = 0.4 and zT = 0.2 for y = 0.05 are possible at 1000 K. This study contributes new insight on the interplay between A-site vacancies and thermoelectric performance in SrTiO3.