Parametric Wavelength Conversion From Conventional Near-Infrared to Visible Band

The feasibility of distant wavelength conversion in photonic crystal fiber was explored. The one-pump parametric architecture was used to demonstrate translation from the conventional (1550 nm) to visible (500 nm) band. Experimental results are reported, which demonstrate the conventional-to-visible conversion of single- and multiple-channel signals encoded in the nonreturn-to-zero format     

Improvement in the Low Frequency Performance of Geometric Transition Radar Absorbers Using Square Loop Impedance Layers

A technique is described for improving the low frequency performance of geometric transition (GT) radar absorbers based on lossy foam pyramids. The technique makes use of the fact that at high frequencies, only the geometric transition region of the absorber is utilized whereas at low frequencies, the whole absorber thickness interacts with the incident wave. Hence the low frequency performance may be improved, without compromising that at high frequencies, by electrically loading the absorber base layer using one or more frequency selective surfaces (FSS) whose elements are typically in the form of single or nested loops. Other advantages of this technique include minimal increases in weight and manufacturing costs. The paper includes comparative predictions of unmodified and loaded GT absorber reflectivity at both normal and oblique incidence and discusses the effect on absorber performance of tolerance variations in the dimensions and location of the loading FSS elements. Finally, free-space reflectivity measurements on unmodified and loaded commercial absorber blocks are made over the frequency range 1-10 GHz and these confirm the validity of the technique.     

Efficiency Enhancement of Single‐Walled Carbon Nanotube‐Silicon Heterojunction Solar Cells Using Microwave‐Exfoliated Few‐Layer Black Phosphorus

Carbon nanotube‐silicon (CNT‐Si)‐based heterojunction solar cells (HJSCs) are a promising photovoltaic (PV) system. Herein, few‐layer black phosphorus (FL‐BP) sheets are produced in N‐methyl‐2‐pyrrolidone (NMP) using microwave‐assisted liquid‐phase exfoliation and introduced into the CNTs‐Si‐based HJSCs for the first time. The NMP‐based FL‐BP sheets remain stable after mixing with aqueous CNT dispersion for device fabrication. Due to their unique 2D structure and p‐type dominated conduction, the FL‐BP/NMP incorporated CNT‐Si devices show an impressive improvement in the power conversion efficiency from 7.52% (control CNT‐Si cell) to 9.37%. Our density‐functional theory calculation reveals that lowest unoccupied molecular orbital (LUMO) of FL‐BP is higher in energy than that of single‐walled CNT. Therefore, we observed a reduction in the orbitals localized on FL‐BP upon highest occupied molecular orbital to LUMO transition, which corresponds to an improved charge transport. This study opens a new avenue in utilizing 2D phosphorene nanosheets for next‐generation PVs.     

明年半导体销售额仅会温和增长

据iSuppli公司,由于全经济和电子市场继续复苏,尽管2011年半导体产业不会再现今年预期中的强劲表现,但将继续增长.2011年全球半导体销售额将达到3174亿美元,比今年预期的3020亿美元温和增长5.1%.     

Improved All‐Polymer Solar Cell Performance by Using Matched Polymer Acceptor

By the introduction of different building blocks and side‐chains, a series of donor–acceptor type polymer acceptors containing naphthalene diimide have been successfully prepared. The theoretical and experimental results show that the molecular design effectively tunes the energy levels, solubility, and coplanarity of the acceptor polymers. The intermolecular packing, which has been considered as a key factor in the bulk heterojunction morphology, has been adjusted by changing the coplanarity. As a result of improved morphology and fine‐tuned energy levels, a power conversion efficiency of 6.0% has been demonstrated for the optimized devices, which is among the highest‐efficiencies for reported all‐polymer solar cells. The improved device performance may be attributed to the resemble crystallinity of the donor/acceptor polymers, which can lead to the optimal phase separation morphology balancing both charge transfer and transport.     

Fullerene Additives Convert Ambipolar Transport to p‐Type Transport while Improving the Operational Stability of Organic Thin Film Transistors

Many high charge carrier mobility (μ) active layers within organic field‐effect transistor (OFET) configurations exhibit non‐linear current–voltage characteristics that may drift with time under applied bias and, when applying conventional equations for ideal FETs, may give inconsistent μ values. This study demonstrates that the introduction of electron deficient fullerene acceptors into thin films comprised of the high‐mobility semiconducting polymer PCDTPT suppresses an undesirable “double‐slope” in the current–voltage characteristics, improves operational stability, and changes ambipolar transport to unipolar transport. Examination of other high μ polymers shows general applicability. This study also shows that one can further reduce instability by tuning the relative electron affinity of the polymer and fullerene by creating blends containing different fullerene derivatives and semiconductor polymers. One can obtain hole μ values up to 5.6 cm² V^–1 s^–1 that are remarkably stable over multiple bias‐sweeping cycles. The results provide a simple, solution‐processable route to dictate transport properties and improve semiconductor durability in systems that display similar non‐idealities.     

Resolution versus Speckle Relative to Geologic Interpretability of Spaceborne Radar Images: A Survey of User Preference

A survey was conducted to evaluate user preference for resolution versus speckle relative to the geologic interpretability of spaceborne radar images. Thirteen different resolution/looks combinations were simulated from Seasat synthetic-aperture radar (SAR) data of each of three test sites. The SAR images were distributed with questionnarires for analysis by eighty-five earth scientists. The relative discriminability of geologic targets at each test site for each simulation of resolution and speckle on the images is determined here from a survey of the evaluations. A large majority of the analysts indicate that for most targets a two-look image at the highest simulated resolution is best. For a constant data rate a higher resolution is more important for target discrimination than a greater number of looks. Sand dunes require more looks than other geologic targets. Multiple-look images are preferred over the corresponding single-look image at all resolutions. The number of multiple looks that is optimal for discriminating geologic logic targets is in general inversely related to the simulated resolution.     

Self-esteem in alcoholics and nonalcoholics

Alcoholics scored lower on a test of self-esteem than did nonalcoholics, Alcoholics with lower self-esteem were found to be more willing to seek treatment than those with higher self-esteem.     

Pulmonary function in perlite workers

Pulmonary function was studied in 117 men employed in three plants engaged in the mining and processing of perlite. Of these, 38 had been employed for ten years or more; 18 for 15 years or more and four men for 20 years or more. Review of chest films confirmed previous studies which showed no changes indicative of pneumoconiosis. Measurement of forced vital capacity (FVC) by Jones Pulmonor and by Collins 9-liter spirometer did not show reductions correlated with length of exposure, after effects of cigarette smoking had been taken into account. There was instead a slight increase in FVC associated with years in the perlite industry. The distribution of individuals with FVC below 80% of predicted also showed no association with duration of perlite exposure. Although there were slight reductions in forced expiratory volume in one second (FEV1) and in FEV1/FVC% which were associated with years in the perlite industry and which could not be explained by cigarette smoking, these reductions were not statistically significant. In summary, the population of men available for study in the major perlite-producing area of the United States, who have worked for periods up to 23 years, showed no evidence of pneumoconiosis by chest radiography or by measurement of forced vital capacity. Nevertheless, continued control of dust to ensure exposures below nuisance dust levels is essential. Medical surveillance should also continue with records being retained for periodic reevaluation.