Using an additive to control the electrospinning of fibres of poly(ε‐caprolactone)

Electrospinning is a route to polymer fibres with diameters considerably smaller than available from most fibre‐producing techniques. We explore the use of a low molecular weight compound as an effective control additive during the electrospinning of poly(ε‐caprolactone). This approach extends the control variables for the electrospinning of nanoscale fibres from the more usual ones such as the polymer molecular weight, solvent and concentration. We show that through the use of dual solvent systems, we can alter the impact of the additive on the electrospinning process so that finer as well as thicker fibres can be prepared under otherwise identical conditions. As well as the size of the fibres and the number of beads, the use of the additive allows us to alter the level of crystallinity as well as the level of preferred orientation of the poly(ε‐caprolactone) crystals. This approach, involving the use of a dual solvent and a low molar mass compound, offers considerable potential for application to other polymer systems. Copyright © 2010 Society of Chemical Industry     

A study on the behaviour of steel braced barrel vaults

The computer analysis of steel braced barrel vaults is presented. This analysis is compared with the approximate method of analysis suggested by Baer. The drawbacks of Baer's method are discussed. The behaviour of these frames due to the effect of laterals, edge trusses and different types of bracing systems is predicted. Based on this parametric study an economic system of braced barrel vault is suggested for practical applications.     

Detect and avoid: an ultra-wideband/WiMAX coexistence mechanism [Topics in Radio Communications]

Cognitive radios have been advanced as a technology for the opportunistic use of underutilized spectrum wherein secondary devices sense the presence of the primary user and use the spectrum only if it is deemed empty. Spectral cognition of this form can also be used by regulators to facilitate the dynamic coexistence of different service types. An example of this is the operation of ultra-wideband devices in WiMAX bands: UWB devices must detect and avoid WiMAX devices in certain regulatory domains. In this article we start by discussing various options for detection and avoidance. We then describe the obstacles faced in achieving robust detection and avoidance with an on-chip implementation of basic DAA functionality. Finally, we present measurement results for operation of a single UWB device with a WiMAX system. This interaction also highlights the problem of dealing with listen before speak primaries where secondary transmission could interfere by blocking the primary's access to the medium.     

Enhancement of nonlinear optical and thermal properties of polyurethanes by modifying the chromophores with fused heterocyclic and pyrimidine rings

This article describes the synthesis of substituted triazolo[3,4‐b]‐thiadiazole heterocycles based nonlinear optical (NLO) responsive chromophores. To enhance the NLO properties of the chromophores, the pyrimidine ring was introduced with an appropriate π‐bonding. With these chromophores, different series of polyurethanes were prepared by condensation with tolylene‐2,4‐diisocyanate and 3,3′‐dimethoxy‐4,4′‐biphenylene diisocyanate. The structure of the resulting chromophores and polyurethanes was confirmed using Fourier transform infrared, proton nuclear magnetic resonance, and Carbon Hydrogen Nitrogen (CHN) analyzer. The inherent viscosities (η_inh) of the polyurethanes measured by Ubbelohde viscometer were in the range of 0.2324–0.2760 dl/g. Thermal behavior of the polyurethanes was investigated using differential scanning calorimetry and thermogravimetric analysis. The molecular orientation in polyurethane films was induced by a corona poling, and this was ascertained using ultraviolet‐visible spectrophotometer and atomic force microscope. The thicknesses and refractive indices of thin films were determined by an Ellipsometer. Polyurethanes exhibited excellent solubility in most of the common organic solvents. The second harmonic generation (SHG) coefficients (d₃₃) of the poled polyurethanes ranged from 63.20 and 95.32 pm/V at 532 nm. None of the polyurethanes showed SHG decay below 100°C, and retained 95% of the signal even up to 500 h. The resulting enhanced NLO efficiency and longer temporal stability make these polyurethanes as promising candidates for photonic devices. POLYM. ENG. SCI., 59:500–509, 2019. © 2018 Society of Plastics Engineers     

Studies on molecular transport of n‐alkanes through poly(tetrafluoroethylene‐co‐propylene) elastomeric membrane

Molecular transport of a series of n‐alkanes through commercial TFE elastomer (FA 150L) has been studied in the temperature range 30–50 °C using sorption‐gravimetric method. The Fickian diffusion equation was used to calculate the diffusion coefficients, which were dependent on the size of the alkanes and temperature. The diffusion coefficients at 30°C varied from 4.53 × 10^?8 cm²/s (n‐heptane) to 0.18 × 10^?8 cm²/s (n‐hexadecane). The liquid concentration profiles have also been computed using analytical solution of Fick's equation with the appropriate initial and boundary conditions and these were presented as a function of penetration depth of molecular migration and time of immersion. These results have been discussed in terms of molecular size of alkanes as well as temperature. In all the liquid penetrants, the transport phenomenon was found to follow the anomalous behavior. From the temperature dependence of diffusion and permeation coefficients, the Arrhenius activation parameters have been estimated. These parameters do not exhibit any systematic variation with the size of the penetrants. The resulting low diffusion coefficients, contribute to the superior barrier performance of the membrane, is due, in part, to the high glass transition temperature of Aflas? TFE elastomer. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2228–2235, 2006     

Synthesis and characterization of nonlinear optical side-chain polyimides containing the thiadiazole chromophores

Thermally stable second-order nonlinear optical (NLO) polyimides were synthesized using a standard condensation polymerization technique. The polyimides were prepared from 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and pyromellitic dianhydride (PMDA) with two aromatic azo- and diazo-diamine derivatives as the NLO chromophores. The resulting polyimides were characterized by FTIR, ¹H-NMR, UV-vis spectroscopies, differential scanning calorimetry, thermogravimetric analysis, and gel permeation chromatography. The weight-average molecular weights of polyimides determined by gel permeation chromatography (GPC) were in the range of 32,100 to 39,300 (M_w/M_n = 1.58–1.74). All the polyimides exhibited an excellent solubility in many of the aprotic polar organic solvents, manifesting that these polyimides offer good processability. The glass transition temperature for the resulting polyimides was in the range of 152 to 194°C and most of them showed high thermal stability. Particularly, the polyimides containing diazo group and PMDA backbone showed an enhanced thermal stability and glass transition temperature. The second harmonic generation (SHG) coefficients (d₃₃) of the poled polyimide films range from 43.71 to 80.49 pm/V at 532 nm. Further, it is noticed that there was no SHG decay below 180°C because of the partial main-chain character of the polyimide structure, which is acceptable for nonlinear optical device applications. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Development of cardiac prescreening device for rural population using ultralow-power embedded system

The invention is inspired by the desire to understand the opportunities and expectations of developing economies in terms of healthcare. The designed system is a point-of-care (POC) device that can deliver heart-care services to the rural population and bridge the rural-urban divide in healthcare delivery. The product design incorporates several innovations including the effective use of adaptive and multiresolution signal-processing techniques for acquisition, denoising, segmentation, and characterization of the heart sounds (HS) and murmurs using an ultralow-power embedded Mixed Signal Processor. The device is able to provide indicative diagnosis of cardiac conditions and classify a subject into either normal, abnormal, ischemic, or valvular abnormalities category. Preliminary results demonstrated by the prototype confirm the applicability of the device as a prescreening tool that can be used by paramedics in rural outreach programs. Feedback from medical professionals also shows that such a device is helpful in early detection of common congenital heart diseases. This letter aims to determine a framework for utilization of automated HS analysis system for community healthcare and healthcare inclusion.     

Effect of differential maturity of paddy grains in a panicle on their milling quality

Branches of paddy panicles were divided into four equal parts and grains collected from each part separately. Moisture content at harvest and milling breakage after shade drying of grains to 12 to 13% moisture were determined. Average moisture content of grains gradually increased while milling quality generally suffered in grains from the top first quarter to the last quarter at the bottom. The same trend was found when the grains in the “top” quarter were compared with those from the “rest” of the panicle. The proportion of sun-checked grains was highest in the “top” fractions at all stages of maturity. The grains at the “top” also had a tendency to shed easily from the panicle. At early stages of maturity milling breakage of grains in lower portions of panicles was high perhaps due to immaturity and softness.     

In Vitro Release Study of Verapamil Hydrochloride Through Sodium Alginate Interpenetrating Monolithic Membranes

Polymeric sodium alginate interpenetrating network membranes containing verapamil hydrochloride were fabricated for transdermal application. The membranes were evaluated for their physical properties, weight and thickness uniformity, water vapor transmission, as well as drug content uniformity. All the thin patches were transparent, smooth, and flexible. The drug-loaded membranes were analyzed by X-ray diffraction to understand the drug polymorphism inside the membrane. The transdermal patches were permeable to water vapor, indicating the permeability characteristics of the polymers. The in vitro drug release was performed in distilled water using a Keshary-Chien diffusion cell. The release data were analyzed to understand the mechanism of drug release.     

Modification of highly brittle polystyrene sulfonic acid-co-maleic acid crosslinked sodium alginate membrane into flexible membranes by the incorporation of dibutyl phthalate as a plasticizer for pervaporation separation

To convert highly brittle into flexible membrane, the polystyrene sulfonic acid-co-maleic acid crosslinked sodium alginate (PSSAMA/NaAlg) membrane was modified by incorporating the different weight% of dibutyl phthalate (DBP) as a plasticizer. The effect of DBP content on the physico-chemical properties of the membranes was thoroughly examined. The membranes exhibited lower glass transition temperatures with increasing the plasticizer content in the matrix of PSSAMA/NaAlg. The separation performance of the membranes for water/isopropanol and water/1,4-dioxane was studied at different temperatures. Among the modified membranes, the membrane containing 6 wt% of DBP exhibited the highest separation factors of 24,129 with a flux of 13.57 × 10⁻² kg/m² hr and 23,353 with a flux of 12.99 × 10⁻² kg/m² hr for water/isopropanol and water/1,4-dioxane at 30°C, respectively. From the temperature-dependent diffusion and permeation values, the Arrhenius activation parameters were estimated. The estimated activation energy values for permeation of water (E_pw) and isopropanol (E_pIPA) were, respectively, ranged between 12.09 and 8.79, and 42.52 and 32.79 kJ/mol. A negative heat of sorption (ΔH_s) values was obtained for all the membranes, suggesting that Langmuir's mode of sorption was predominant. Based on the results, it is concluded that the modified membranes demonstrated excellent pervaporation performance for the separation of water/isopropanol and water/1,4-dioxane.