A solar air heater with variable flow passage width

Different designs of solar air heaters with variable width of the flow channels are investigated.

Four possible geometries for the flow passage are considered with the aim to improve the efficienc of the system by maintaining a constant temperature of the absorber plate.

Efficiencies and plate temperatures are calculated for various designs, among them the most efficient is the one with decreasing duct width.     

White Electroluminescence by Supramolecular Control of Energy Transfer in Blends of Organic‐Soluble Encapsulated Polyfluorenes

Here, it is demonstrated that energy transfer in a blend of semiconducting polymers can be strongly reduced by non‐covalent encapsulation of one constituent, ensured by threading of the conjugated strands into functionalized cyclodextrins. Such macrocycles control the minimum intermolecular distance of chromophores with similar alignment, at the nanoscale, and therefore the relevant energy transfer rates, thus enabling fabrication of white‐light‐emitting diodes (CIE coordinates: x = 0.282, y = 0.336). In particular, white electroluminescence in a binary blend of a blue‐emitting, organic‐soluble rotaxane based on a polyfluorene derivative and the green‐emitting poly(9,9‐dioctylfluorene‐alt‐benzothiadiazole ( F8BT ) is achieved. Morphological and structural analyses by atomic force microscopy, fluorescence mapping, µ‐Raman, and fluorescence lifetime microscopy are used to complement optical and electroluminescence characterization, and to enable a deeper insight into the properties of the novel blend.     

A polyfluoroalkyl imidazolium ionic liquid as iodide ion source in dye sensitized solar cells

We report on the use of a fluorinated imidazolium ionic liquid as a source of iodide ions in solvent-based electrolytes for DSSCs. Efficient dye regeneration and fast charge transport in the fluorinated electrolyte result in an overall improvement of the device performances compared to conventional hydrogenated ionic liquids.     

The influence of hydrogen and nitrogen on the formation of Si nanoclusters embedded in sub-stoichiometric silicon oxide layers

This work reports the study concerning the influence of the preparation conditions on the structure of silicon rich oxide (SRO) deposited by PECVD method by which the structural properties of the film are strictly related. In particular we investigated the role of reactant gases N₂O and SiH₄ on the total Si concentration, Si excess concentration, Si clustered concentration and size of nanoclusters formed by high annealing temperature. We payed particular attention on the role of the hydrogen and nitrogen during the Si agglomeration.The presence of hydrogen atoms on the as-deposited specimen, confirmed by the Si–H bonds peak on the FTIR analysis, has been directly correlated to the silicon excess concentration in the layer. The silicon, oxygen and nitrogen atomic density has been calculated from RBS analysis. These information were coupled to the ones obtained using methodology based on electron energy loss spectroscopy combined with energy filtered images, which allowed us to quantify the clustered silicon concentration in annealed sub-stoichiometric silicon oxide layers (SiO_x). We have verified that the nitrogen dissolved in the layer inhibits the Si excess clustering so that the efficiency of silicon agglomeration process decreases as the nitrogen content increases.     

A 5-GHz highly integrated receiver front-end

In this paper a radio front-end for a IEEE 802.11a and HIPERLAN2 sliding-IF receiver is presented. The circuit, implemented in a low-cost 46-GHz-f _T silicon bipolar process, includes a variable-gain low noise amplifier and a double-balanced mixer. Thanks to monolithic LC filters and on-chip single-ended-to-differential conversion of the RF signal, the proposed solution does not require the expensive image rejection filter and an external input balun. The receiver front-end exhibits a 4.3-dB noise figure and a power gain of 21 dB, providing an image rejection ratio higher than 50 dB. By using a 1-bit gain control, it achieves an input 1-dB compression point of −11 dBm, while drawing only 22 mA from a 3-V supply voltage.     

Synthesis optimization and characterization of multiwalled carbon nanotubes

The unique properties of carbon nanotubes (CNTs) have suggested applications in a variety of fields. Multiwalled nanotubes were synthesized using chemical vapor deposition (CVD) procedures and subsequently characterized. Reaction parameters such as catalyst type and carrier gas flow rate were optimized to produce well-aligned multiwalled nanotubes with lengths between a few microns to several millimeters. Characterization was performed with scanning electron microscopy (SEM), transmission electron microscopy (TEM), x-ray diffraction (XRD), energy dispersive x-ray spectroscopy (EDS), thermo-gravimetric analysis, and Raman spectroscopy, focusing on composition and purity. Results show the synthesis of high-purity nanotubes of several millimeters in length from iron, nickel, cobalt, and titanium carbide catalysts with thermal stability to above 550°C.     

Layer‐by‐Layer All‐Inorganic Quantum‐Dot‐Based LEDs: A Simple Procedure with Robust Performance

A novel all‐inorganic electroluminescent device is demonstrated based on highly luminescent CdTe nanocrystals intercalated within a laminar hydrotalcite‐like structure. The laminar scaffold acts to both support and distribute the CdTe nanocrystals. The device is synthesized using simple wet chemical processes at room temperature in ambient conditions. It has high thermal stability, operating continuously up to 90 °C, and a maximum efficiency at J = 0.12 A cm^?2. The device is targeted at the automotive industry.     

Design of Engineered Elastomeric Substrate for Stretchable Active Devices and Sensors

In the field of flexible electronics, emerging applications require biocompatible and unobtrusive devices, which can withstand different modes of mechanical deformation and achieve low complexity in the fabrication process. Here, the fabrication of a mesa‐shaped elastomeric substrate, supporting thin‐film transistors (TFTs) and logic circuits (inverters), is reported. High‐relief structures are designed to minimize the strain experienced by the electronics, which are fabricated directly on the pillars' surface. In this design configuration, devices based on amorphous indium‐gallium‐zinc‐oxide can withstand different modes of deformation. Bending, stretching, and twisting experiments up to 6 mm radius, 20% uniaxial strain, and 180° global twisting, respectively, are performed to show stable electrical performance of the TFTs. Similarly, a fully integrated digital inverter is tested while stretched up to 20% elongation. As a proof of the versatility of mesa‐shaped geometry, a biocompatible and stretchable sensor for temperature mapping is also realized. Using pectin, which is a temperature‐sensitive material present in plant cells, the response of the sensor shows current modulation from 13 to 28 °C and functionality up to 15% strain. These results demonstrate the performance of highly flexible electronics for a broad variety of applications, including smart skin and health monitoring.     

Smashing OpenFlow's “atomic” actions: Programmable data plane packet manipulation in hardware

Recently, with new hardware architectures such as Reconfigurable Match Tables and languages such as P4, the Software Defined Networking community has started to bring line‐rate data plane programmability inside switching chipsets. Starting from the original OpenFlow's match/action abstraction, most of the work has so far focused on key improvements in matching flexibility. Conversely, the “action part,” ie, the set of operations (such as encapsulation or header manipulation) performed on packets after the forwarding decision, has received way less attention. Goal of this paper is to move beyond the idea of “atomic,” preimplemented, actions, and rather make them programmable while retaining high speed multi‐Gbps operation. To this purpose, we propose a domain‐specific HW architecture, called Packet Manipulation Processor (PMP), able to efficiently implement such actions. Both a PMP C++ instruction set simulator and a NetFPGA prototype have been developed. The performances of the PMP have been verified with three nontrivial use cases (tunneling, NAT, and ARP reply generation), showing that also in the worst case the throughput is well above 10 Gbps.