Excitation‐Dependent Photoluminescence from Single‐Carbon Dots

Carbon dots (CDs) are carbon‐based fluorescent nanoparticles that can exhibit excitation‐dependent photoluminescence (PL) “tunable” throughout the entire visible range, interesting for optoelectronic and imaging applications. The mechanism underlying this tunable emission remains largely debated, most prominently being ascribed to dot‐to‐dot variations that ultimately lead to excitation‐dependent ensemble properties. Here, single‐dot spectroscopy is used to elucidate the origin of the excitation‐dependent PL of CDs. It is demonstrated that already single CDs exhibit excitation‐dependent PL spectra, similar to those of the CD ensemble. The single dots, produced by a facile one‐step synthesis from chloroform and diethylamine, exhibit emission spectra with several characteristic peaks differing in emission peak position and spectral width and shape, indicating the presence of distinct emission sites on the CDs. Based on previous work, these emission sites are related to the sp² subregions in the carbon core, as well as the functional groups on the surface. These results confirm that it is possible to integrate and engineer different types of electronic transitions at the nanoscale on a single CD, making these CDs even more versatile than organic dyes or inorganic quantum dots and opening up new routes toward light‐emission engineering.     

Tunable Volatility of Ge2Sb2Te5 in Integrated Photonics

The operation of a single class of optical materials in both a volatile and nonvolatile manner is becoming increasingly important in many applications. This is particularly true in the newly emerging field of photonic neuromorphic computing, where it is desirable to have both volatile (short‐term transient) and nonvolatile (long‐term static) memory operation, for instance, to mimic the behavior of biological neurons and synapses. The search for such materials thus far have focused on phase change materials where typically two different types are required for the two different operational regimes. In this paper, a tunable volatile/nonvolatile response is demonstrated in a photonic phase‐change memory cell based on the commonly employed nonvolatile material Ge₂Sb₂Te₅ (GST). A time‐dependent, multiphysics simulation framework is developed to corroborate the experimental results, allowing us to spatially resolve the recrystallization dynamics within the memory cell. It is then demonstrated that this unique approach to photonic memory enables both data storage with tunable volatility and detection of coincident events between two pulse trains on an integrated chip. Finally, improved efficiency and all‐optical routing with controlled volatility are demonstrated in a ring resonator. These crucial results show that volatility is intrinsically tunable in normally nonvolatile GST which can be used in both regimes interchangeably.     

Explicit reference governor for linear systems

The explicit reference governor is a constrained control scheme that was originally introduced for generic nonlinear systems. This paper presents two explicit reference governor strategies that are specifically tailored for the constrained control of linear time-invariant systems subject to linear constraints. Both strategies are based on the idea of maintaining the system states within an invariant set which is entirely contained in the constraints. This invariant set can be constructed by exploiting either the Lyapunov inequality or modal decomposition. To improve the performance, we show that the two strategies can be combined by choosing at each time instant the least restrictive set. Numerical simulations illustrate that the proposed scheme achieves performances that are comparable to optimisation-based reference governors.     

Secondary nanoparticle emissions during diesel particulate trap regeneration

Two nanostructured mixed oxide catalysts (the CoCr₂O₄ spinel and the LiCrO₂ delafossite) have been recently developed for diesel soot combustion. The catalysts have been deposited via in situ combustion synthesis over SiC wallflow trap by CTI (Salindres, F). Bench tests proved that, after soot loading, both the developed traps enable a faster and more complete regeneration at 550 °C than the non-catalysed trap. However, a specific study on the particles distribution after the SiC trap, carried out via SMPS analysis, showed that secondary nanoparticles (<20 nm) are emitted during the regeneration promoted by the highly-active CoCr₂O₄ catalytic trap, as opposed to the LiCrO₂-catalysed and the virgin counter parts. This phenomenon has been investigated vs. the regeneration temperature and some sampling conditions so as to draw preliminary indications on the nature of these undesired particles.     

Polyurethanes and polyesters from lignin

Lignin, obtained through steam explosion from straw, was completely characterized via elemental analysis, gel permeation chromatography, ultraviolet and infrared spectroscopy, and ¹³C and ¹H nuclear magnetic resonance spectrometry. Polyurethanes were obtained by treating steam‐exploded lignin from straw with 4,4′‐methylenebis(phenylisocyanate), 4,4′‐methylenebis(phenylisocyanate) –ethandiol, and poly(1,4‐butandiol)tolylene‐2,4‐diisocyanate terminated. The obtained materials were characterized by using gel permeation chromatography, infrared spectroscopy, and scanning electron microscopy. Differential scanning calorimetry analysis showed a T_g at ?6°C, assigned to the glass transition of the poly(1,4‐butandiol) chains. The presence of ethylene glycol reduced the yields of the polyurethanes. The use of the prepolymer gave the best results in polyurethane formation. Steam‐exploded lignin was used as the starting material in the synthesis of polyesters. Lignin was treated with dodecanoyl dichloride. The products were characterized by using gel permeation chromatography, infrared spectroscopy, ¹³C and ¹H nuclear magnetic resonance spectrometry, and scanning electron microscopy. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1451–1456, 2005     

Using VisTrails and Provenance for Teaching Scientific Visualization

Over the last 20 years, visualization courses have been developed and offered at universities around the world. Many of these courses use established visualization libraries and tools (e.g. VTK, ParaView, AVS, VisIt) as a way to provide students a hands‐on experience, allowing them to prototype and explore different visualization techniques. In this paper, we describe our experiences using VisTrails as a platform to teach scientific visualization. VisTrails is an open‐source system that was designed to support exploratory computational tasks such as visualization and data analysis. Unlike previous scientific workflow and visualization systems, VisTrails provides a comprehensive provenance management infrastructure. We discuss how different features of the system, and in particular, the provenance information have changed the dynamics of the Scientific Visualization course we offer at the University of Utah. We also describe our initial attempts at using the provenance information to better assess our teaching techniques and student performance.     

Uncertainty analysis of high frequency image-based vibration measurements

Image-based vibration measurement techniques allow to remotely measuring the displacement of multiple targets in the field of view, without the need to mount anything on the measurand. In this paper the uncertainty budget of vision systems has been performed in order to both optimize the measurement procedure and identify the potential application fields. Two different types of camera are used in this work, both of them equipped with a 1280 × 1024 px sensor but with two different maximum frame rates at full resolution: 25fps and 2000fps respectively. The uncertainty analysis proposed here is based on a careful identification of the uncertainty sources and on experimental tests on an electro-magnetic shaker, where the displacement measured with the cameras are calibrated by means of the reference measurements provided by state-of-the-art traditional techniques.     

Electrospun PHBV/PEO co-solution blends: Microstructure,thermal and mechanical properties

Blending allows to tailor and modulate the properties of selected polymers. Blends of poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and polyethylene oxide (PEO) were fabricated by electrospinning in different weight ratios i.e. 100:0, 80:20, 70:30, 50:50, 0:100.In order to evaluate the influence of PEO addition on the final properties of PHBV, a complete microstructural, thermal and mechanical characterization of PHBV/PEO blends has been performed. The two neat polymeric membranes were also considered for the sake of comparison. The following characterization techniques were employed: scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), Fourier transform infrared attenuated total reflectance (FTIR-ATR) spectroscopy, simultaneous thermogravimetric and differential analyses (TG-DTA), differential scanning calorimetry (DSC), and uniaxial tensile tests.All electrospun mats consisted of randomly oriented and uniform fibers. It has been observed that the microstructure of PHBV/PEO was remarkably affected by blend composition. The average fiber size ranged between 0.5 μm and 2.6 μm. It resulted that the electrospun polymeric blends consisted of separate crystalline domains associated to an amorphous interdisperse phase. PHBV/PEO blends presented intermediate mechanical properties, in terms of tensile modulus and ultimate tensile stress, with respect to the two neat components.     

A trainable system for grading fish from images

Trainable computer vision systems are receiving increased attention in different application domains for their versatility and flexibility. This paper describes a trainable system capable of determining fish weight from image measurements. A prototype of the proposed system has been experimentally installed as a component of an automatic fish grading device at a fish farm. The image measurements are taken from top and side views of live fish sliding through a transparent channel. After the training stage, in which a support vector machine learns the relation between fish weight and shape parameters from a small number of examples, the system is able to grade fish at the rate of three fish per second. The experimental results obtained thus far and reported in the paper indicate that the system is adequate for the required task.