Although there have been many reports on the preparation and applications of various polymer nanofibers with the electrospinning technique, the understanding of synthetic parameters in electrospinning remains limited. In this article, we investigate experimentally the influence of solvents on the morphology of the poly(vinyl pyrrolidone) (PVP) micro/nanofibers prepared by electrospinning PVP solution in different solvents, including ethanol, dichloromethane (MC) and N,N‐dimethylformamide (DMF). Using 4 wt % PVP solutions, the PVP fibers prepared from MC and DMF solvents had a shape like a bead‐on‐a‐string. In contrast, smooth PVP nanofibers were obtained with ethanol as a solvent although the size distribution of the fibers was somewhat broadened. In an effort to prepare PVP nanofibers with small diameters and narrow size distributions, we developed a strategy of using mixed solvents. The experimental results showed that when the ratio of DMF to ethanol was 50:50 (w/w), regular cylindrical PVP nanofibers with a diameter of 20 nm were successfully prepared. The formation of these thinnest nanofibers could be attributed to the combined effects of ethanol and DMF solvents that optimize the solution viscosity and charge density of the polymer jet. In addition, an interesting helical‐shaped fiber was obtained from 20 wt % PVP solution in a 50:50 (w/w) mixed ethanol/DMF solvent. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3721–3726, 2004

Note that the multilayer fabrication by using soft materials such as PDMS would have inherent limits in accuracy due to the irregular distortions of the soft materials used in processing. The distortion in 2P-lTM was investigated by using moiré-fringes metrology, [20] and the relative pattern mismatch was less than ±0.5 lm mm -1. Although the inaccuracy from the distortions would limit the applications of 2P-lTM for large-area high-accuracy devices, it would still be tolerable for many other applications.In conclusion, we developed 2P-lTM to provide a route for the fabrication of highly layered microstructures with high yield and high structural fidelity. We improved the consistency of the fabrication processes by controlling the UV dosage for the photocurable prepolymers. Applying two different prepolymers enable us to separate the bonding and the structural functions accomplished by a single prepolymer in conventional lTM. By separately controlling the chemistry and application of the prepolymers, we achieved both high bonding strength and extremely low capillary wicking. Moreover, exact filling without residues and selective coating of the prepolymer, relying on the differences in the surface energies, were efficiently achieved by WAD. We believe that the advantages of 2P-lTM will improve 3D microfabrication for a variety of applications while preserving the advantages of conventional lTM. Experimental PDMS Molding:We used a photoresist (AZ 5214, Clariant) relief pattern on a silicon wafer as a master pattern for PDMS molding. A two-component elastomeric kit, Sylgard 184 (Dow Corning), was used to make PDMS molds with the standard mixing ratio of base and hardener, 10:1 by weight. The mixture was poured on the master pattern and subsequently cured at 60°C for 4 h. The thickness of the PDMS molds was about 2 mm in order to facilitate the peeling away of the PDMS molds.UV Curing: In the experiment, a 100 W UV lamp was used with a high-pass filter and a beam homogenizer for 366 nm UV light. The UV-exposure system delivered a UV intensity of 1.5 mW cm -2 with a full width at half maximum of 4.8 nm. The ambient temperature of PDMS molds during the UV exposure was sustained at around 30°C.Photoluminescence Measurement: For the dye doping of PA, a red dye (LDS 698, Exciton) was dissolved in ethanol (4 × 10 -3 mol-%). After mixing the ethanol solution of the dye with PA, the mixture was ultrasonically agitated for 5 h. The agitated mixture was purged with argon for 24 h at room temperature to remove ethanol. The doping ratio of the dye was 6 × 10 -3 wt.-% after removal of ethanol. For consistent photoluminescence measurement, a hexagonally packed fiber bundle assembly, with the outer six fibers for excitation and the center fiber for detection, was used. To reduce the ependence of the detected photoluminescence intensity on the distance from a photoluminescence sample to the end tip of the fiber assembly, the distance was selected to be 20 times farther than the diameter of each fiber. Moreover, the distance was kept...

Summary: A controlled fabrication of rod‐like nanostructures of cadmium sulfide (CdS) incorporated into polymer fiber matrices has been developed by an electrospinning method. Here, poly(vinyl pyrrolidone) (PVP) was used as a polymer capping reagent, utilizing the interactions of cadmium ions with the carbonyl groups in the PVP molecules. The formation of CdS nanorods inside the PVP was carried out via the reaction of Cd2+ with H2S. SEM images showed that the electrospun films of PVP/CdS are composed of fibers with a diameter between 100 and 900 nm. TEM proved that most of the CdS nanorods are incorporated in the PVP fibrous film. The diameter of the rod is about 50 nm and the length is from 100 to 300 nm.TEM image of the CdS nanorods formed in the PVP fibrous film.imageTEM image of the CdS nanorods formed in the PVP fibrous film.

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Pseudogenes (Cs), nonfunctional relatives of functional genes, form by duplication or retrotransposition, and loss of gene function by disabling mutations. Evolutionary analysis provides clues to C origins and effects on gene regulation. However, few systematic studies of plant Cs have been conducted, hampering comparative analyses. Here, we examined the origin, evolution, and expression patterns of Cs and their relationships with noncoding sequences in seven angiosperm plants. We identified ;250,000 Cs, most of which are more lineage specific than protein-coding genes. The distribution of Cs on the chromosome indicates that genome recombination may contribute to C elimination. Most Cs evolve rapidly in terms of sequence and expression levels, showing tissue-or stage-specific expression patterns. We found that a surprisingly large fraction of nontransposable element regulatory noncoding RNAs (microRNAs and long noncoding RNAs) originate from transcription of C proximal upstream regions. We also found that transcription factor binding sites preferentially occur in putative C proximal upstream regions compared with random intergenic regions, suggesting that Cs have conditioned genome evolution by providing transcription factor binding sites that serve as promoters and enhancers. We therefore propose that rapid rewiring of C transcriptional regulatory regions is a major mechanism driving the origin of novel regulatory modules.