Unity quantum yield of photogenerated charges and band-like transport in quantum-dot solids

Solid films of colloidal quantum dots show promise in the manufacture of photodetectors and solar cells. These devices require high yields of photogenerated charges and high carrier mobilities, which are difficult to achieve in quantum-dot films owing to a strong electron-hole interaction and quantum confinement. Here, we show that the quantum yield of photogenerated charges in strongly coupled PbSe quantum-dot films is unity over a large temperature range. At high photoexcitation density, a transition takes place from hopping between localized states to band-like transport. These strongly coupled quantum-dot films have electrical properties that approach those of crystalline bulk semiconductors, while retaining the size tunability and cheap processing properties of colloidal quantum dots.     

An integrated approach to evaluating the fracture toughness of irradiated nuclear reactor pressure vessels

Current methods of predicting the inservice fracture toughness of nuclear reactor pressure vessels subject to irradiation embrittlement are briefly reviewed, and a new and integrated approach is proposed. This approach is based on the use of a wide variety of information, including the rapidly emerging understanding of the fundamental mechanisms of fracture in the ductile to brittle transition region as well as the microstructurally-mediated processes leading to embrittlement. However, the focus is on advanced, nonintrusive characterization methods for measuring composition, coarse and fine scale microstructure, and mechanical properties using small sample biopsies from operating vessels.     

Towards the fabrication of a UV light source based on CuCl thin films

CuCl is an ionic wide band gap I–VII semiconductor which has a band gap of 3.4 eV (at 300 K) and a large excitonic binding energy of 190 meV compared to other wide band gap semiconductors, e.g. ZnO (60 meV) and GaN (25 meV). It can be useful as a UV source which can emit light in the blue-UV range. The large excitonic binding energy of CuCl should improve the quantum efficiency compared to ZnO or GaN. In room temperature UV–VIS spectroscopy measurements we have observed strong free Z₃ and Z_1,2 excitonic peaks in vacuum-deposited CuCl films incorporated within structures for electroluminescent devices. Using room temperature photoluminescence (PL) we have also observed a strong free excitonic peak which is attributed to Z₃. We also report on the design of a UV source using electrically pumped CuCl thin films on Si and ITO coated glass substrates. This could open up the possibility of fabricating UV/blue light emitters utilizing CuCl.     

A 3-D hybrid finite element/boundary element method for the unifiedradiation and scattering analysis of general infinite periodic arrays

We present a rigorous frequency domain variational 3-D electromagnetic formulation for the general nonself-adjoint infinite periodic array problem. The hybrid method described combines the vector finite element and Floquet boundary element techniques. It is general in the sense that it is applicable to infinite periodic arrays of the open or aperture-types. It is thus effective for modeling both the scattering and radiation performance of diverse FSS, absorber, and phased-array structures. The technique accurately handles arbitrarily complicated 3-D geometries, lossy inhomogeneous media and internal as well as external excitations. These analyses can be applied to general skewed grids under arbitrary scan and polarization conditions     

Implanted polymer junctions obtained with electrogenerated polythiophene films

Using polythiophene films (～5 μm thick) electrogenerated by trapezoidal waves of potential, then partially reduced, we realised metal-polythiophene contacts on the one hand. The electrical characteristics of a steel/polythiophene/gold sandwich structure are presented. We consider that the rectifying contact takes place between steel and p-type polythiophene. On the other hand, we showed that p-type polythiophene could be compensated after an implantation of alkali ions (Cs⁺ or Na⁺) in order to lead to the realisation of PN junctions. We particularly prove that the use of Na⁺ ions results in junctions yielding currents which are higher than with Cs⁺ ions. Current-voltage and capacitance-voltage characteristics have been presented so as to show that the junction effect is due to the efficiency of the doping by ionic implantation. These electrical measurements seem to be stable after several weeks in air.     

Calculation and analysis of electromagnetic scattering by helicopter rotating blades

This paper describes an application of physical optics and the method of equivalent currents to the calculation of radar cross section (RCS) of a helicopter rotor. The problem is treated using a quasi-stationary approach. The calculation can be parameterized as a function of the locations of the radar transmitter and receiver in relation to the rotor center. Therefore, this offers the possibility of monostatic and bistatic simulations in the far field and near field. Blade geometry is taken into account using a triangular meshing generated by the I-DEAS meshing software. Digital applications are presented and the effects on the RCS spectrum of incidence, frequency, blade number, and the near field are analyzed.     

Monitoring the electroosmotic flow in capillary electrophoresis using contactless conductivity detection and thermal marks

The fundamental aspects and the capillary electrophoresis usage of thermal marks are presented. The so-called thermal mark is a perturbation of the electrolyte concentration generated by a punctual heating of the capillary while the separation electric field is maintained. The heating pulse is obtained by powering tungsten filaments or surface mount device resistors with 5 V during a few tens to hundreds of milliseconds. In the proposed model, the variation of the transport numbers with the rising temperature leads to the formation of low- and high-concentration regions during the heating. After cooling down, the initial mobilities of the species are restored and these regions (the thermal mark) migrate chiefly due to the electroosmotic flow (EOF). The mark may be recorded with a conductivity detector as part of a usual electropherogram and be used to index the analyte peaks and thus compensate for variations of the EOF. In a favorable case, 10 mmol/L KCl solution, the theory suggests that the error in the measurement of EOF mobility by this mean is only -6.5 x 10(-7) cm2 V-1 s-1. The method was applied to the analysis of alkaline ions in egg white, and the relative standard deviations of the corrected mobilities of these ions were smaller than 1%. This is a challenging matrix, because albumin reduces the EOF to 20% of its initial value after 11 runs. The combination of thermal mark, electrolysis separated, and contactless conductivity detection allowed the measurement of the EOF of a silica capillary with unbuffered KCl solution with constant ionic strength. The overall approach is advantageous, because one can easily control the chemical composition of the solution in contact with the inner surface of the capillary.     

Trithiocarbonate-mediated free-radical photopolymerization: improved uniformity in hologram recording

A holographic material based on a photopolymerizable nematic acrylate was improved by the addition of the trithiocarbonate, EtO2CCH2SC(S)SCH2CO2Et, increasing uniformity and reproducibility in the formation of electrically switchable holographic gratings. Diffraction efficiencies as high as 34%, the thin-grating theoretical maximum, were achieved at large (10-14 microm) grating spacings. Improved diffraction efficiency was seen over a range of grating spacings (0.35-10 microm). The exposure window for grating formation was increased by an order of magnitude, resulting in much improved reproducibility.     

Review of the LEED Points Obtained by Canadian Building Projects

The expansion and advancement of businesses, cities, municipalities, and populations in Canada are increasingly demanding the effective usage of land and resources in building development. Companies, organizations, and individuals are seeking to construct more environmentally responsible buildings to help minimize the negative effects that structures place on the natural environment, as well as on the people that have either direct or indirect contact with them. In an effort to set a benchmark for what constitutes a green building, the Canada Green Building Council provides a certification system called Leadership in Energy and Environmental Design (LEED), which is a point scheme that seeks to measure sustainability. Many stakeholders in the construction industry in Canada are increasingly employing this system to validate their achievement in sustainable development. This paper reviews the usage of the LEED system in Canadian building construction and the potential challenges and barriers associated with LEED implementation that specifically pertain to Canadian circumstances. Information from 42 new construction projects across Canada that achieved LEED certification were collected and analyzed. The points most often awarded, as well as those that are granted the least frequently, were tabulated. The percentages of points obtained were compared to American projects. Credit frequency indicators (CFIs), which were used to depict the achievement of credits by each project, can provide decision makers with information on credits awarded in the past and insight into credit implementation in future projects with similar goals. The energy and atmosphere and materials and resources categories proved to have the lowest CFIs, whereas the innovation and design process and water efficiency categories yielded the highest CFIs. The study also found that there were differences in the points obtained by LEED projects in Canada and the United States as some credits are influenced by climate, such as weather and temperature, as well as regional location.     

Negative anticipatory contrast and preference conditioning: Flavor cues support preference conditioning, and environmental cues support contrast.

In 2 experiments, access to a .15% saccharin solution was followed on alternating days by access to a 32% sucrose solution and the same saccharin solution. In Exp 1, rats increased both intake of and preference for a flavored saccharin solution that predicted sucrose, but neither effect was found using a predictive odor cue alone. Exp 2 replicated the predictive flavor results but showed suppression of saccharin intake when environmental cues predicted sucrose. When both flavor and environment predicted sucrose, saccharin intake did not change, but preference for the predictive flavor increased. Discriminative taste cues appear to facilitate the development of preference conditioning, but environmental cues favor negative anticipatory contrast effects. Also, preference conditioning and contrast may develop concurrently and compete for expression. (PsycINFO Database Record (c) 2010 APA, all rights reserved)