A novel multiple species ringdown spectrometer for in situ measurements of methane,carbon dioxide,and carbon isotope

We have developed a standalone, user-friendly, multi-species ringdown spectrometer for in situ measurements of methane (CH₄), carbon dioxide (CO₂), and a carbon dioxide isotope (¹³CO₂). The instrument is based on near-infrared continuous-wave cavity ringdown spectroscopy (NIR cw-CRDS) and engineered to be of approximately 16 kg with dimensions of 50 cm × 40 cm × 15 cm. The instrument design, optical configuration, electronic control, and performance are described. CH₄, CO₂, and ¹³CO₂ are measured at different wavelengths that are obtained through multiplexing two distributed feedback laser diodes with central wavelengths at 1597 and 1650 nm. The spectrometer has low power consumption and runs for 4–6 h when powered by a standard car battery. The instrument is operated either locally by interacting with a 7-inch touch screen or remotely via an Internet connection. The 1-σ detection limits for CH₄ and CO₂ are 0.2 and 120 ppmv, respectively. The measurement uncertainty is better than ±4% of full-scale reading for CH₄ and CO₂ and ±1.5‰ for δ¹³C (part per thousand relative to the Pee Dee Belemnite scale). Measurement of each species is near real-time; switching from measuring one species to another takes less than one minute. This work demonstrates a novel multiple-species CRDS-instrumentation platform, which can be adopted for development of an array of ringdown spectrometers for portable, user-friendly, field analysis of a variety of gases in environmental and industrial applications. Discussion of a future version of the spectrometer with better detection sensitivity, higher accuracy, and a smaller geometry is also presented. PACS  42.62.Fi; 42.55.Px; 33.20.Ea; 07.88.+y; 07.57.Ty     

Nanostructure formation aided by self-organised Bi nanolines on Si(0 0 1)

We provide a mini review of recent theoretical investigations of nanostructure formation aided by self-organised Bi nanolines on the Si(0 0 1) surface. It is suggested that hydrogen-passivated single-domain Si(0 0 1) produced by the formation of defect-free, hundreds of nm long, and 1.2-1.5 nm wide Bi nanolines provides an appealing template with preferential sites for adsorption of other elements. Based on ab initio pseudopotential calculations it is suggested that using the Bi nanoline template it should be possible to grow the following structures: mixed Ge-Si dimer structures on the Si(0 0 1) terrace between two neighbouring Bi nanolines; small In nanoclusters along the nanoline; and line and cluster structures of Fe atoms with novel electronic and magnetic properties.     

Design of an optoelectronic refractometer having an adjustable range of refractive index measurement

A real-time optoelectronic refractometer having an adjustable range of refractive index measurement is presented. The adjustment is achieved by obtaining a shift in the zero-reflected intensity point at the interface following the introduction of a glass plate of refractive index different from that of the constituent prism. The sensitivity remains reasonably high over the enhanced range of refractive index measurement. The experimental results are in qualitative agreement with the theoretical calculations. This refractometer sensor, which is based on the detection of modulation in emergent light intensity, has a sturdy and user-friendly design.     

Structural health monitoring by extraction of coherent guided waves from diffuse fields

This letter points out that, although in the audio signal domain low-pass filtering has been used to prevent aliasing noise from entering the baseband of speech signals, an antialias process in the speech feature domain is still needed to prevent high modulation frequency components from entering the baseband of speech features. The existence of aliasing noise in speech features is revealed via spectral analysis of speech feature streams. A method for suppressing such aliasing noise is proposed. Experiments on large vocabulary speech recognition show that antialias processing of speech features can improve speech recognition, especially for noisy speech.     

A New Solid-State pH Sensor and Its Application in the Construction of all Solid-State Urea Biosensor

A new solid-state pH sensor is developed using neutral poly(3-cyclohexyl thiophene) assembled over a Pt disk electrode. The new sensor is developed following two different approaches; 1) the neutral poly(3-cyclohexyl thiophene) dissolved in chloroform and subsequent coating on to a Pt disk electrode; 2) the neutral polymer is incorporated into plasticized poly(vinyl chloride) matrix membrane. In both cases the polymer modified electrode is sensitive to pH and a reversible super Nernstian behavior is observed. The typical response of the pH sensor and its reversibility are reported. The polymer coated electrode is subsequently used to construct an all solid-state urea sensor. The construction of this new urea sensor involves the following two major steps; a) 20 µL of urease solution (40 mg /mL) is allowed to assemble overnight at 4 °C over neutral poly (3-cyclohexyl thiophene) modified electrode; b) an organically modified sol-gel layer is allowed to form over the urease adsorbed polymer modified electrode. The new solid-state urea sensor provides excellent reproducibility of the measurements and is stable for 3 months when stored at 4 °C under dry condition. The typical response of the solid-state urea sensor and the calibration plot of urea analysis are reported.     

Growth and structural characteristics of the chalcopyrite semiconductor CuInSe2

The growth and structural characteristics of chalcopyrite semiconductor CuInSe₂ have been investigated with particular emphasis on the photovoltaic behaviour of the CdS/CuInSe₂ thin film heterojunction. It has been found that the structural phase of the CuInSe₂ has an important bearing on the photovoltaic behaviour of the heterojunction. Thus the heterojunctions having the sphalerite type cubic CuInSe₂ as one of its component have been found to possess better conversion effciency than those employing the chalcopyrite type tetragonal form of CuInSe₂. Evidences and argument have been put forward to show that the better efficiency with sphalerite phase arises due to smaller lattice mismatch with CdS base. In addition to the type of structural phase, the state of order of CuInSe₂ phase has been found to affect the performance of heterojunctions. The heterojunctions having the disordered sphalerite type CuInSe₂ structure exhibits a much lower efficiency than those embodying the ordered CuInSe₂ phase.     

A Review of Recent Progress in Solid State Fabrication of Composites and Functionally Graded Systems Via Friction Stir Processing

Friction stir processing (FSP) is a rapidly emerging newer solid-state technique for composite fabrication. It involves surface modification which in turn enables successful adaptation of surface properties through plastic deformations in solid state. During initial years of FSP inception, it was primarily employed in development of metal matrix composites of light metal alloys like aluminum. However, recently, it has gained an alluring role in fabrication of composites of various nonferrous and ferrous metal alloys as well as of polymers. In addition to composite fabrication, FSP has evolved as a revolutionary technique in developing functionally graded systems/surfaces (FGS) of metal matrix. This article covers all aspects of FSP in which reinforcement particles are embedded in the base matrix to develop composites and FGS. It presents a critical review on domains of recent developments, effects of different types of reinforcement particles and properties enhancement of composites, and FGS fabrication. In addition to this, various issues, challenges, and future work that demand attention are systematically addressed.     

Study of naturally occurring radioactive material (NORM) in top soil of Punjab State from the North Western part of India

The concentration levels of ²³⁸U, ²³² Th, ⁴⁰K and ¹³⁷Cs in top soils of State of Punjab located in the North Western part of India were measured using conventional low background gamma ray spectrometric setup as well as Compton suppressed gamma ray spectrometric setup. The radioactivity level of ²³⁸U and ²³²Th was found to vary between 15 Bq/kg and 27 Bq/kg and between 16 Bq/kg and 57 Bq/kg respectively. The radioactivity level of ⁴⁰K was found to vary between 266 Bq/kg and 799 Bq/kg. The mean radioactivity level of the NORM in general was found to be similar to what is expected as a result of their normal abundance.