Synthesis of polyaniline/Q-CdSe composite via ultrasonically assisted dynamic inverse emulsion polymerization

In this communication, polyaniline/CdSe quantum dots (PANI/Q-CdSe) composite was successfully synthesized via in situ ultrasonically assisted dynamic inverse emulsion polymerization. The synthesized PANI-coated Q-CdSe composite was characterized by field emission transmission electron microscopy showed that the CdSe quantum dots have an average size of around ca. 5 nm were dispersed in the PANI matrix. X-ray diffraction, Fourier transform infrared spectrum (FT-IR) and UV-visible spectrum were used to characterize the structure of the obtained PANI/Q-CdSe composite. FT-IR spectra indicated that the polymer was highly doped and existed in conducting emeraldine salt form. The obtained PANI/Q-CdSe composite showed significant improvement in the thermal behavior as indicated by TGA thermograph. The presented dynamic polymerization process is very fast and produces stable colloidal dispersion. This approach provides a one-step, simple, general, and inexpensive method for the preparation of PANI/Q-CdSe composite.     

Cooperative perfunctionalization and partial labeling of 6-azido-6-deoxy-α-cyclodextrin through copper(I)-catalyzed azide-alkyne cycloaddition

In a microwave and ligand-assisted cyclodextrin click cluster synthesis, we observed the cooperative perfunctionalization in the click reaction of 6-azido-6-deoxy-α-cyclodextrin under our optimized reaction conditions. MALDI-MS data and partial fluorescein labeling via the one-pot/stepwise methods confirmed the occurrence of cooperative perfunctionalization: the fully triazole-functionalized cyclodextrin click cluster became the major product with limited alkyne equivalents. To the best of our knowledge, this work constitutes the first example of a ‘cooperative’ click reaction of an azido-cyclodextrin. This cooperative perfunctionalization of cyclodextrin click clusters offers useful synthetic insights into the partial reporter labeling strategy using azido-cyclodextrin.     

Structured sublinear compressive sensing via belief propagation

Compressive sensing (CS) is a sampling technique designed for reducing the complexity of sparse data acquisition. One of the major obstacles for practical deployment of CS techniques is the signal reconstruction time and the high storage cost of random sensing matrices. We propose a new structured compressive sensing scheme, based on codes of graphs, that allows for a joint design of structured sensing matrices and logarithmic-complexity reconstruction algorithms. The compressive sensing matrices can be shown to offer asymptotically optimal performance when used in combination with orthogonal matching pursuit (OMP) methods. For reduced-complexity greedy reconstruction schemes, we propose a new family of list-decoding belief propagation algorithms, as well as reinforced and multiple-basis belief propagation (BP) algorithms. Our simulation results indicate that reinforced BP CS schemes offer very good complexity–performance tradeoffs for very sparse signal vectors.     

Gas sensor based on nanoporous hematite nanoparticles: Effect of synthesis pathways on morphology and gas sensing properties

The development of a low cost and scalable gas sensor for the detection of toxic and flammable gases with fast response and high sensitivity is extremely important for monitoring environmental pollution. In this work, we introduce two different synthesis pathways for the preparation of scalable Fe₂O₃ nanoparticles for gas sensor applications. One is co-precipitation and the other is hydrothermal method. The gas sensing properties of the α-Fe₂O₃ nanoparticles (NPs) fabricated by different synthesis pathways were studied and compared. The performance of the NPs in the detection of toxic and flammable gases such as carbon dioxide, ammonia, liquefied petroleum gas, ethanol, and hydrogen was evaluated. The Fe₂O₃ NP-based gas sensors exhibited high sensitivity and a response time of less than a minute to analytic gases. However, the NPs fabricated by the one-step direct method exhibited higher sensitivities than those generated by the α-Fe₂O₃ NPs obtained by co-precipitation synthesis possibly because of their nanoporous structure. This performance is attributed to the large specific surface area of the NPs, which results in higher sensitivity.     

Generation of free-travelling four-mode cluster-type entangled coherent states

A new scheme is proposed to generate free-travelling four-mode cluster-type entangled coherent states. Compared with other previously proposed schemes ours is very simple in execution using only one π-cross-Kerr medium, two 50:50 beam-splitters and two π/2-phase-shifters. Despite the setup simplicity, our scheme, unlike the others which are all probabilistic, is efficient with 100% success probability since no measurements are involved at all.     

Effect of chemical composition of PM_(2.5) on visibility in Guangzhou,China,2007 spring

The object of this study was to investigate the correlation of visibility with chemical composition of PM2.5 in Guangzhou. In April 2007, 28 PM2.5 samples were collected daily at the monitoring station of the South China Institute of Environmental Sciences (SCIES), in urban Guangzhou. Water-soluble ionic species (Cl-, NO3-, SO42-, NH4+, K+, Na+, Ca2+, and Mg2+) and carbonaceous contents (OC and EC) of the PM2.5 samples were determined to characterize their impact on visibility impairment. The results showed that sulfate was the dominant species that affected both light scattering and visibility. The average percentage contributions of the visibility-degrading species to light scattering coefficient were 40% for sulfate, 16% for nitrate, 22% for organics, and 22% for elemental carbon. Because of its foremost effect on visibility, sulfate reduction in PM2.5 would effectively improve the visibility of Guangzhou.     

A Legendre‐spectral element method for flow and heat transfer about an accelerating droplet

The problem of flow and heat transfer associated with a spherical droplet accelerated from rest under gravitational force is studied using a Legendre‐spectral element method in conjunction with a mixed time integration procedure to advance the solution in time. An influence matrix technique that exploits the superposition principle is adapted to resolve the lack of vorticity boundary conditions and to decouple the equations from the interfacial couplings. The computed flow and temperature fields, the drag coefficient, the Nusselt number, and the interfacial velocity and vorticity are presented for a drop moving vertically in a quiescent gas of infinite extent to illustrate the evolution of the flow and temperature fields. Comparison of the predicted drag coefficient and the Nusselt number against previous numerical and experimental results indicate good agreement. Copyright © 2000 John Wiley & Sons, Ltd.     

Comments on “vibration of a rotating beam with tip mass”

In diagnostic applications of machinery vibration or noise data it is convenient to describe the whole process by a set of numbers called discriminants. Five discriminants can be constructed and measured for every vibroacoustical process. Two of them have dimensional natures and give information about process amplitude and frequency. Two others, dimensionless, give information about the amplitude and spectral spread of the process. The last one, also dimensionless, characterizes the time fluctuations of the process, and can be used to detect instability of a running machine. Numerical and experimental examples are presented.