Functional Femtoliter Droplets for Ultrafast Nanoextraction and Supersensitive Online Microanalysis

A universal femtoliter surface droplet‐based platform for direct quantification of trace of hydrophobic compounds in aqueous solutions is presented. Formation and functionalization of femtoliter droplets, concentrating the analyte in the solution, are integrated into a simple fluidic chamber, taking advantage of the long‐term stability, large surface‐to‐volume ratio, and tunable chemical composition of these droplets. In situ quantification of the extracted analytes is achieved by surface‐enhanced Raman scattering (SERS) spectroscopy by nanoparticles on the functionalized droplets. Optimized extraction efficiency and SERS enhancement by tuning droplet composition enable quantitative determination of hydrophobic model compounds of rhodamine 6G, methylene blue, and malachite green with the detection limit of 10^?9 to 10^?11 m and a large linear range of SERS signal from 10^?9 to 10^?6 m of the analytes. The approach addresses the current challenges of reproducibility and the lifetime of the substrate in SERS measurements. This novel surface droplet platform combines liquid–liquid extraction and highly sensitive and reproducible SERS detection, providing a promising technique in current chemical analysis related to environment monitoring, biomedical diagnosis, and national security monitoring.     

Circular microstrip antenna with off‐centered Y‐slot

A novel dual‐frequency broadband design of a single‐layer single‐feed circular microstrip antenna with an off‐centered Y‐slot is demonstrated in this communication. By selecting a suitable location of the Y‐slot in the circle, the proposed antenna on glass epoxy FR‐4 substrate not only resonates efficiently at two closely spaced frequencies (2.736 and 2.868 GHz) but also offers improved bandwidth (210 MHz or 7.5%) in comparison with a conventional circular microstrip patch antenna (～2%). From the measured results, almost identical broadside radiation patterns are obtained at two resonant frequencies, and the variation of less than 1 dBi in gain values is achieved in the frequency range where broadband behavior is observed. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.     

Experimental investigation into the effect of adhesion properties of PEEK modified by atmospheric pressure plasma and low pressure plasma

High performance polymer, Polyether Ether Ketone (PEEK) (service temperature ?250°C to +300°C, tensile strength: 120 MPa) is gaining significant interest in aerospace and automotive industries. In this investigation, attention is given to understand adhesion properties of PEEK, when surface of the PEEK is modified by two different plasma processes (i) atmospheric pressure plasma and (ii) low pressure plasma under DC Glow Discharge. The PEEK sheets are fabricated by ultra high temperature resistant epoxy adhesive (DURALCO 4703, service temperature ?260°C to +350°C). The surface of the PEEK is modified through atmospheric pressure plasma with 30 and 60 s of exposure and low pressure plasma with 30, 60, 120, 240, and 480 s of exposure. It is observed that polar component of surface energy leading to total surface energy of the polymer increases significantly when exposed to atmospheric pressure plasma. In the case of low pressure plasma, polar component of surface energy leading to total surface energy of the polymer increases with time of exposure up to 120 s and thereafter, it deteriorates with increasing time of exposure. The fractured surface of the adhesively bonded PEEK is examined under SEM. It is observed that unmodified PEEK fails essentially from the adhesive to PEEK interface resulting in low adhesive bond strength. In the case of surface modified PEEK under atmospheric pressure plasma, the failure is entirely from the PEEK and essentially tensile failure at the end of the overlap resulting in significant increase in adhesive bond strength. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Advances in Calibration and Imaging Techniques in Radio Interferometry

This paper summarizes some of the major calibration and image reconstruction techniques used in radio interferometry and describes them in a common mathematical framework. The use of this framework has a number of benefits, ranging from clarification of the fundamentals, use of standard numerical optimization techniques, and generalization or specialization to new algorithms.     

Metallurgical analysis of a corrosion failure

A Nicrofer 6025 HT alloy 602 tube in a furnace, used for the recovery of steel pickling liquors, failed during operation at 1100°C. Metallographic investigations—microstructural and energy dispersive X-ray spectrometry (EDS)—of the failed tube showed evidence of corrosion and the presence of chlorine and sulfur in the corrosion products. The failure of the furnace tube was due to the presence of sulfur dioxide in combination with chlorine.     

Electrical and optical properties of thin films based on poly [2-methoxy-5 (2′-ethyl hexyloxy)-1,4-phenylene vinylene] doped with acridine orange dye with possible photovoltaic applications

Conjugated polymers have high potential for efficient production of low-cost flexible optoelectronics devices such as solar cells, photodiodes and light emitting diodes. In this paper, the interaction between poly [2-methoxy-5 (2′-ethyl hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) and acridine orange (AO) dye has been studied to examine the role of charge pair separation and photocurrent generation in organic photovoltaic films. The AO dye concentration has been optimized on the basis of absorption spectra and photoluminescence (PL) studies carried over the films particularly, for photovoltaic applications. For this purpose, MEH-PPV polymer was dissolved in n-butyl acetate and doped with different concentration of AO dye solution. The Current–Voltage characteristics of MEH-PPV films, prepared by spin-coating technique on ITO-coated glass substrate have been determined as a function of temperature. For the cathode contact, Al was deposited using RF sputtering technique so that the current is predominantly due to holes. The conductivity increases by two orders of magnitude as the AO dye concentration increases to 2.65 mol L⁻¹. In optical properties, we have studied the UV–visible absorption spectra, PL spectra of undoped and doped MEH-PPV films. The absorption studies show that the addition of AO dye does not significantly change (reduce) the absorption, which indicates the suitability of photon absorption. The PL spectra were recorded for MEH-PPV films, which become narrow on increasing the AO dye concentration. The PL studies indicate that up to certain concentration of AO dye in MEH-PPV films, PL intensity decreases as compare to that for undoped MEH-PPV film. The combined effect of increase in conductivity by two orders, decrease in PL intensity and no significant change in absorption makes the material suitable for photovoltaic applications.     

A New Semiblind Scheme Based on Second and Fourth Order Statistics for Decoding of Space–Time Data in Time Selective MIMO Channels

In this paper we propose a novel semiblind scheme based on second and fourth order statistics of Space–Time data in time varying MIMO channels. This scheme combines a new blind estimator of frequency offsets and an iterative decoder. Space–Time Codes have a periodic property which is used to find a simple and efficient blind estimator of carrier offsets. The iterative decoder is a data aided decoder which provides the best estimates of channel, noise co-variance and S–T data in its category. As a result of this the new semiblind scheme performs very efficiently in time-selective channels and is able to reduce the training overhead required by the data-aided estimators to a large extent, and increase the effective throughput.