A new differential scanning calorimetry based approach for the estimation of thermal conductivity of polymer solids and melts

A new concept based on differential scanning calorimetry (DSG) is introduced which enables us to make a rapid estimation of the thermal conductivity of materials. This technique is shown to give reasonable agreement with the literature data and offers unique advantages, e.g. short analysis time, no instrument modification, small thermal radients across the sample, spall sample size requirements, and most importantly it can be applied to polymer melts. Although our data falls within the literature range, it is difficult to comment on its accuracy since the literature itself shows a wide variation. The precision of our measurements is better than ±20 percent which is considered adequate for thermal conductivity evaluation. As a matter of convenience, we have also presented briefly, a background of the thermal conductivity measuring techniques.     

Structure-property relationships in thermoplastic elastomers III. Segmented polyacetal-polyurethanes

Dihydroxy-terminated polyacetals had been synthesized from aldehydes and glycols and used as soft segments to obtain segmented polyurethane block copolymers. For soft segment ≥ 1700 M _n, the T_g ranges from–48 to ?58°C and is insensitive to the structures of diisocyanate and chain extender. The T_g of PacPU with 1350 M _n polyacetals is raised to ?38°C, and none was observed for shorter polyacetal chains. The copolymers can be synthesized to have a broad range of mechanical properties, such as modulus from 0.5 to 130 MPa, stress at break from 0.7 to 21 MPa, and elongation at break from 66 to 1300% through the variation of the constituents and composition. The rheologic properties are only slightly dependent on temperature for symmetrical diisocyanates but quite temperature sensitive with asymmetric diisocyanate copolymers. The polyacetals are selected to build in acid-catalyzed thermal decomposition of the thermoplastic elastomers. The extreme acid sensitivity of the polyacetal block is buffered in the coplymers.     

Performance Analysis of Combined Space Time Block Coding with Generalized Selection Combining in Underlay Cognitive Radio

Wireless Personal Communications - In this paper, we demonstrate the performance analysis of an underlay MIMO cognitive radios employing space time block coding at secondary’s user...     

On the Microstructure and Wear Behavior of Fe–xCr–4Mn–3C Hardfacing Alloys

The present paper describes an investigation aimed at evaluating the microstructural and dry sliding adhesive wear characteristics of Fe–xCr–4Mn–3C hardfacing alloys applied through shielded metal arc welding. The effect of chromium addition on the microstructure of hardfacings was carried out by using optical microscope, field emission scanning electron microscope and X-ray mapping. Dry sliding wear tests were performed on a pin-on-disc wear tribometer. From the experimental results, it was observed that the primary carbides were refined and increased with the increase of chromium content. The morphology of carbides revealed that the primary carbides were rod shaped. The increased chromium content was also found to be beneficial to enhance hardness and wear resistance of hardfacings. The correlation between hardness and wear resistance exhibited the reliability of hardness as an indicator of the wear performance of hardfacings.     

Development and gamma scintigraphy evaluation of gastro retentive calcium ion-based oral formulation: an innovative approach for the management of gastro-esophageal reflux disease (GERD)

Calcium chloride is an essential calcium channel agonist which plays an important role in the contraction of muscles by triggering calcium channel. First time hypothesized about its role in the treatment of GER (gastro-esophageal reflux) and vomiting disorder due to its local action. There are two objectives covered in this study as first, the development and optimization of floating formulation of calcium chloride and another objective was to evaluate optimized formulation through gamma scintigraphy in human subjects. Gastro retentive formulation of calcium chloride was prepared by direct compression method. Thirteen tablet formulations were designed with the help of sodium chloride, HPMC-K4M, and carbopol-934 along with effervescing agent sodium bicarbonate and citric acid. Formulation (F8) fitted best for Korsmeyer–Peppas equation with an R² value of 0.993. The optimized formulation was radiolabelled with ^99mTc-99?m pertechnetate for its evaluation by gamma scintigraphy. Gastric retention (6?h) was evaluated by gamma scintigraphy in healthy human subjects and efficacy of present formulation confirmed in GER positive human subjects. Gamma scintigraphy results indicated its usefulness in order to manage GERD. Stability studies of the developed formulation were carried out as per ICH guidelines for region IV and found out to be stable for 24?months.     

Optical Properties of Organic-based Aerosols Produced by Burning Vegetation

The real and imaginary refractive indexes of organic-based nonvolatile aerosols produced by burning vegetation are reported for the infrared spectral region. The data were obtained by an iterative Kramers-Kronig analysis of the transmission spectra (2–25 μm) obtained from thin-film samples deposited on a KBr substrate immersed directly in the smoke plumes of small-scale test fires. The results include samples from fires fueled by lawn grass, alfalfa, mesquite, tumble-weed, pine needles, and mixed twigs, leaves, and weeds. The most significant characteristics of all spectra are as follows: (a) strong absorptions in the 3–5-μm region owing to condensed water and CH₃/CH₂ groups of aliphatic hydrocarbons; (b) characteristic peaks in the 6-, 8-, and 10-μm regions owing to skeletal modes of aromatic and terpenic groups; and (c) relatively little absorption in the 10–12-μm region. The imaginary refractive index of all samples is comparable (～ 0.10–0.30) in the 3–5- and 8–10-μm regions and is 3–10 times lower in the 10–12-μm region. In the 3–5-μm region, most of the absorption takes place in the interval between 3 and 4 μm as opposed to the 4–5-μm interval which shows significantly less absorption. It is also noteworthy that there is insignificant absorption in the 2.0–2.5-μm window region. Results are significantly different from values for elemental carbon which are known to be relatively wavelength independent in these spectral regions and of magnitude between ～ 0.50 and 1.0 for the imaginary index. Theoretical calculations, assuming particle sizes in the Rayleigh scattering regime, yields a mass extinction coefficient (m²/g) for the organic smokes on the order of ～ 0.20 for the 8–10-μm region and as high as 0.40 at 3 μm to near zero at 5 μm in the 3–5-μm window.     

Rapid removal of lead(II) ions from water using iron oxide–tea waste nanocomposite – a kinetic study

Lead (Pb) ions are a major concern to the environment and human health as they are contemplated cumulative poisons. In this study, facile synthesis of magnetic iron oxide–tea waste nanocomposite is reported for adsorptive removal of lead ions from aqueous solutions and easy magnetic separation of the adsorbent afterwards. The samples were characterised by scanning electron microscopy, Fourier transform‐infrared spectroscopy, X‐ray diffraction, and Braunner–Emmet–Teller nitrogen adsorption study. Adsorptive removal of Pb(II) ions from aqueous solution was followed by ultraviolet–visible (UV–Vis) spectrophotometry. About 95% Pb(II) ion removal is achieved with the magnetic tea waste within 10 min. A coefficient of regression R ²  ≃ 0.99 and adsorption density of 18.83 mg g⁻¹ was found when Pb(II) ions were removed from aqueous solution using magnetic tea waste. The removal of Pb(II) ions follows the pseudo‐second‐order rate kinetics. External mass transfer principally regulates the rate‐limiting phenomena of adsorption of Pb(II) ions on iron oxide–tea waste surface. The results strongly imply that magnetic tea waste has promising potential as an economic and excellent adsorbent for the removal of Pb(II) from water.Inspec keywords: visible spectra, scanning electron microscopy, mass transfer, ultraviolet spectra, X‐ray diffraction, nanocomposites, lead, adsorption, magnetic separation, iron compounds, nanofabrication, Fourier transform infrared spectraOther keywords: FeO, Pb, time 10.0 min, X‐ray diffraction, Fourier transform‐infrared spectroscopy, scanning electron microscopy, adsorbent, magnetic separation, rapid removal, Braunner–Emmet–Teller nitrogen adsorption, iron oxide–tea waste surface, magnetic tea waste, aqueous solution, adsorptive removal, magnetic iron oxide–tea waste nanocomposite, lead(II) ions     

Water based simple synthesis of re-dispersible silver nano-particles

Successful experiments with tri-sodium citrate as initial surfactant-cum-reducing agent followed by a secondary reducing agent i.e. sodium formaldehyde sulphoxylate (SFS) to silver nitrate were performed which established a clear large-scale method for the preparation of silver nano-powder of particle size of less than 50 nm. The citrate ions also create hydrophilic capping to in-situ generated zero-valent silver, thus leading to surfactant capped particles. Partial re-dispersion of such nano-powder in aqueous medium leads to colloidal silver which can be loaded in water friendly polymers such as polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP). UV-Visible absorption band at about 275 and 400 nm of colloidal silver in water can be retained even after loading in polymer. Transmission electron microscopy (TEM) of the colloidal solution showed a particle of the size < 30 nm. Particle size distribution by dynamic light scattering technique (DLS) showed that the particles are in the range of 10-40 nm. The elemental composition was studied by energy dispersive analysis of X-rays (EDS).