Search for ionisation density effects in the radiation absorption stage in LiF:Mg,Ti

Optical absorption (OA) dose-response of LiF:Mg,Ti (TLD-100) is studied as a function of electron energy (ionisation density) and irradiation dose. Contrary to the situation in thermoluminescence dose-response where the supralinearity is strongly energy-dependent, no dependence of the OA dose filling constants on energy is observed. This result is interpreted as indicating a lack of competitive process in the radiation absorption stage. The lack of an energy dependence of the dose filling constant also suggests that the charge carrier migration distances are sufficiently large to smear out the differences in the non-uniform distribution of ionisation events created by the impinging gamma/electron radiation of various energies.     

Giant electric-field-induced strains in lead-free ceramics for actuator applications – status and perspective

In response to the current environmental regulations against the use of lead in daily electronic devices, a number of investigations have been performed worldwide in search for alternative piezoelectric ceramics that can replace the market-dominating lead-based ones, representatively Pb(Zr _x Ti_1-x )O₃ (PZT)-based solid solutions. Selected systems of potential importance such as chemically modified and/or crystallographically textured (K, Na)NbO₃ and (Bi_1/2Na_1/2)TiO₃-based solid solutions have been developed. Nevertheless, only few achievements have so far been introduced to the marketplace. A recent discovery has greatly extended our tool box for material design by furnishing (Bi_1/2Na_1/2)TiO₃-based ceramics with a reversible phase transition between an ergodic relaxor state and a ferroelectric with the application of electric field. This paired the piezoelectric effect with a strain-generating phase transition and extended opportunities for actuator applications in a completely new manner. In this contribution, we will present the status and perspectives of this new class of actuator ceramics, aiming at covering a wide spectrum of topics, i.e., from fundamentals to practice.     

Improved upper contacts PMMA on P3HT PTFTS using photolithographic processes

In this work we present a new polymeric thin film transistor (PTFT), fabrication process where standard photolithographic and dry etching techniques are used to place gate contact on the upper surface of the device, and to access in an easy and reliable way the buried bottom drain and source contacts from the upper surface of the device. This fabrication technique benefits of all the advantages that photolithographic processes report, as device isolation, patterning of small dimensions and possibility of device integration on both rigid and flexible substrates. We also show that, since PMMA is placed as the outermost polymeric layer, it serves both as dielectric and as protective layer, allowing devices to work in ambient conditions with significantly less degradation than other PTFTs structures previously reported. Electrical characterization of the devices showed that this technological approach provides mobility values an order of magnitude higher than those previously reported by us, using the same polymeric layers, but with buried drain and source contacts.     

Thermal-stability of electric field-induced strain and energy storage density in Nb-doped BNKT-ST piezoceramics

In this work, the relationship between the structural mechanisms and macroscopic electrical properties of the Nb-modified 0.96(Bi_0.5Na_0.84K_0.16TiO₃)–0.04SrTiO₃ (BNKT–ST) system were elucidated by using temperature dependent and in situ synchrotron X-ray diffraction (XRD) techniques. For the composition x?=?0.0175, a large-signal piezoelectric coefficient (S_max/E_max?=?d₃₃*) of 735 pm?V^?1 at 6?kV mm^?1 was observed at room temperature. Interestingly, at a higher temperature of 110?°C, the sample still showed a large d₃₃* of 570 pm V^?1. Furthermore, the temperature-invariant electrostrictive coefficient for this sample was found to be 0.0285?m⁴?C^?2 over the temperature range of 25–170?°C. Moreover, the energy density for x?=?0.030 sample was ～1.0?J?cm^?3 with an energy storage efficiency of ?70% in the temperature range of 25–135?°C. These results suggest that the synthesized Nb-modified BNKT–ST system is promising for the design of ceramic actuators as well as capacitor applications.     

Sensei: Enforcing secure coding guidelines in the integrated development environment

We discuss the potential benefits, requirements, and implementation challenges of a security-by-design approach in which an integrated development environment plugin assists software developers to write code that complies with secure coding guidelines. We discuss how such a plugin can enable a company's policy-setting security experts and developers to pass their knowledge on to each other more efficiently, and to let developers more effectively put that knowledge into practice. This is achieved by letting the team members develop customized rule sets that formalize coding guidelines and by letting the plugin check the compliance of code being written to those rule sets in real time, similar to an as-you-type spell checker. Upon detected violations, the plugin suggests options to quickly fix them and offers additional information for the developer. We share our experience with proof-of-concept designs and implementations rolled out in multiple companies, and present some future research and development directions.     

Linear combinatorial approach to thin film research

We describe high-throughput experimentation of film synthesis by use of a linear tape transport system (similar to a web-coating system). Metal tape is fed continuously in a reel-to-reel transport system inside the vacuum deposition chamber. Ion-beam assisted deposition (IBAD) texturing is used to enable the growth of epitaxial films on flexible, polycrystalline metal tapes which further enhances the capability of this research. The tape that is continuously fed can be used as a sample itself, via the use of IBAD-textured templates on the tape, or can be a carrier of other smaller substrates (even nonflexible ones). Characterization of samples is done by means of in situ monitoring as well as ex situ sequential analysis. We utilize in situ reflection high-energy electron diffraction for high-throughput analysis of samples. Epitaxial films are deposited on heated samples by evaporation and by pulsed laser deposition. Here, we explain the techniques and the methodologies developed for this type of combinatorial experimentation and show some examples of the material research completed.     

Whole atmospheric-turbulence profiling with generalized scidar

Statistical analysis of stellar scintillation on the pupil of a telescope, known as the scidar (scintillation, detection, and ranging) technique, is sensitive only to atmospheric turbulence at altitudes higher than a few kilometers. With the generalized scidar technique, recently proposed and tested under laboratory conditions, one can overcome this limitation by analyzing the scintillation on a plane away from the pupil. We report the first experimental implementation of this technique, to our knowledge, under real atmospheric conditions as a vertical profiler of the refractive-index structure constant C (N)(2) (h). The instrument was adapted to the Nordic Optical Telescope and the William Hershel Telescope at La Palma, Canary Islands. We measure the spatial autocorrelation function of double-star scintillation for different positions of the analysis plane, finding good agreement with theoretical expectations.     

Biodegradable Polyanhydrides as Encapsulation Layers for Transient Electronics

Bioresorbable electronic systems represent an emerging class of technology of interest due to their ability to dissolve, chemically degrade, disintegrate, and/or otherwise physically disappear harmlessly in biological environments, as the basis for temporary implants that avoid the need for secondary surgical extraction procedures. Polyanhydride‐based polymers can serve as hydrophobic encapsulation layers for such systems, as a subset of the broader field of transient electronics, where biodegradation eventually occurs by chain scission. Systematic experimental studies that involve immersion in phosphate‐buffered saline solution at various pH values and/or temperatures demonstrate that dissolution occurs through a surface erosion mechanism, with little swelling. The mechanical properties of this polymer are well suited for use in soft, flexible devices, where integration can occur through a mold‐based photopolymerization technique. Studies of the dependence of the polymer properties on monomer compositions and the rates of permeation on coating thicknesses reveal some of the underlying effects. Simple demonstrations illustrate the ability to sustain operation of underlying biodegradable electronic systems for durations between a few hours to a week during complete immersion in aqueous solutions that approximate physiological conditions. Systematic chemical, physical, and in vivo biological studies in animal models reveal no signs of toxicity or other adverse biological responses.     

Electric field–temperature phase diagram of sodium bismuth titanate-based relaxor ferroelectrics

The electric field–temperature phase diagrams of three bismuth sodium titanate-based relaxor ferroelectrics are reported, namely 0.94(Na_1/2Bi_1/2TiO₃)–0.06(BaTiO₃), 0.80(Na_1/2Bi_1/2TiO₃)–0.20(K_1/2Bi_1/2TiO₃) and 0.75(Na_1/2Bi_1/2TiO₃)–0.25(SrTiO₃). Relaxor behavior is demonstrated by temperature-dependent dielectric permittivity measurements in the unpoled and poled states, as well as by the field-induced phase transition into a ferroelectric phase from the relaxor phase. From temperature-dependent thermometry measurements, we identified the threshold electric field to induce the ferroelectric phase and obtained the released latent heat of the phase transition. We determined the nonergodic and ergodic relaxor phase temperature range based on the absence or presence of reversibility of the relaxor to ferroelectric transition. For all three compositions, the electric field–temperature phase diagram was constructed and a critical point was identified. The constructed electric field–temperature phase diagrams are useful to find optimum operational ranges of ferroelectrics and relaxors for electromechanical and electrocaloric applications.     

The role of grain size in static and cyclic deformation behaviour of a laser reversion annealed metastable austenitic steel

Different grain sizes were created in a metastable 17Cr‐7Mn‐7Ni steel by martensite‐to‐austenite reversion at different temperatures using a laser beam. Two fully reverted material states obtained at 990°C and 780°C exhibited average grain sizes of 7.7 and 2.7 μm, respectively. The third microstructure (610°C) consisted of grains at different stages of recrystallization and deformed austenite. A hot‐pressed, coarse‐grained counterpart was studied for reference. The yield and tensile strengths increased with refined grain size, maintaining reasonable elongation except for the heterogeneous microstructure. Total strain‐controlled fatigue tests revealed increasing initial stress amplitudes but decreasing cyclic hardening and fatigue‐induced α′‐martensite formation with decreasing grain size. Fatigue life was slightly improved for the 2.7‐μm grain size. Contrary, the heterogeneous microstructure yielded an inferior lifetime, especially at high strain amplitudes. Examinations of the cyclically deformed microstructure showed that the characteristic deformation band structure was less pronounced in refined grains.