First-principles study of CaCu3B4O12 (B=Co, Rh, Ir)

Employing first-principles density functional theory based calculations we investigated the change in electronic structure of CaCu₃B₄O₁₂ compounds as one moves from 3d (Co) to 4d (Rh) to 5d (Ir) element at B site. Our study sheds light on valences of Cu and B ions as one moves from 3d to 4d to 5d based compounds. The valence of Cu in Co and Rh compound turn out to be that of less known 3+ state, while that in Ir compound turn out to be commonly known 2+ state. Our first-principles study provide microscopic understanding of these different valences of Cu, in terms of changes in the mixing of Cu x ² − y ² and B-a _1g states, driven by changes in the crystal field and spin splitting. The stronger crystal field splitting for 4d and 5d elements compared to 3d at B site drive the low-spin state at Rh and Ir site as opposed to intermediate spin in case of Co.     

A Low-Power, Battery-Free Tag for Body Sensor Networks

The authors describe a low-power, battery-free tag for use in pervasive sensing applications such as wearable patient-monitoring systems and body sensor networks. The tag consists of a custom integrated circuit, an antenna for RF energy harvesting, and several sensors for monitoring important physiological parameters and generating alarms when necessary. They also describe experimental results with phonocardiogram and photoplethysmogram signals and demonstrate tag localization within 0.6 m by using an audio localization scheme.     

Effect of silica doping on the densification and grain growth in zinc oxide

The ability of silica (SiO₂) in controlling the densification and grain growth behavior of nano crystalline zinc oxide (ZnO) has been systematically studied. It has been observed that SiO₂ acts as a sintering inhibitor in the ZnO–SiO₂ system up to 4 wt.% limiting value beyond which densification behavior of the system remains almost unchanged, especially above 1100 °C. The addition of SiO₂ to ZnO retards grain growth which in turn results a finer ultimate grain size as compared to the undoped ZnO. However, stabilization in grain size occurs at ≥4 wt.% SiO₂ addition. It has been observed that SiO₂ incorporation changes the grain growth mechanism up to 4 wt.% addition, beyond which no remarkable changes was noticed. The grain growth (n) shows distinctly different slopes as a function of sintering time for the SiO₂ doped ZnO systems than undoped ZnO. The different slopes tend to indicate that different diffusion mechanisms and probably the formation of a secondary phase (Zn–Si–O) at the grain boundary control the densification and grain growth. The thermal expansion coefficient of the system has been found to decrease substantially beyond 4 wt.% SiO₂ addition to ZnO.     

Dielectric,electrical, and rheological characterization of graphene‐filled polystyrene nanocomposites

A series of nanographene filled polystyrene (GPS) nanocomposites was prepared by in situ polymerization of styrene in the laboratory. The concentration of graphene was changed in the step of 0.25 wt% and a total of eight composites (including control) were prepared to obtain a threshold concentration of graphene. These composites, prepared by in situ polymerization followed by compression moulding, were characterized for their structural (using XRD), morphological (SEM), thermal (DSC, TGA, DTGA), dielectric behavior (ɛ', ɛ''') and DC conductivity. It was observed that the thermal stability as well as electrical and rheological properties of graphene‐polystyrene nanocomposites significantly improved due to the homogeneous dispersion, intercalation and exfoliation of the graphene layers in the Polystyrene matrix. It was also observed that at room temperature dielectric constant (ε′) decreased with increasing concentration of graphene and reached a minimum at a certain filler concentration of 0.25 wt% (PSG025) when frequency is kept constant. Rheological study showed an improvement in the storage modulus (G′) with incorporation of graphene as nanofiller. Loss modulus (G′) and complex viscosity (η*) also increased with increasing graphene weight percentage. Relaxation time also increased at high graphene loading because of the pseudo‐solid like behavior of polymer melt. POLYM. COMPOS., 34:2082–2093, 2013. © 2013 Society of Plastics Engineers     

Influence of pressurized carbon dioxide on ketoprofen-incorporated hot-melt extruded low molecular weight hydroxypropylcellulose

Objectives: The aim of the current research project was to investigate the effect of pressurized carbon dioxide (P-CO₂) on the physico-mechanical properties of ketoprofen (KTP)-incorporated hydroxypropylcellulose (HPC) (Klucel? ELF, EF, and LF) produced using hot-melt extrusion (HME) techniques and to assess the plasticization effect of P-CO₂ on the various polymers tested.

Methods: The physico-mechanical properties of extrudates with and without injection of P-CO₂ were examined and compared with extrudates with the addition of 5% liquid plasticizer of propylene glycol (PG). The extrudates were milled and compressed into tablets. Tablet characteristics of the extrudates with and without injection of P-CO₂ were evaluated.

Results and conclusion: P-CO₂ acted as a plasticizer for tested polymers, which allowed for the reduction in extrusion processing temperature. The microscopic morphology of the extrudates was changed to a foam-like structure due to the expansion of the CO₂ at the extrusion die. The foamy extrudates demonstrated enhanced KTP release compared with the extrudates processed without P-CO₂ due to the increase of porosity and surface area of those extrudates. Furthermore, the hardness of the tablets prepared by foamy extrudates was increased and the percent friability was decreased. Thus, the good binding properties and compressibility of the extrudates were positively influenced by utilizing P-CO₂ processing.     

Statistical optimization of fermentation conditions for the improved production of poly-β-hydroxybutyrate from Bacillus subtilis

Poly-β-hydroxybutyrate (PHB) has been an effective biodegradable plastic obtained by microbial fermentation. Batch fermentation of Bacillus subtilis features an attractive system for the production of PHB. Identification of appropriate media components and cultivation conditions are extremely important for the optimal production of biomass and/or PHB production. Statistical media design was utilized for the optimization of different fermentation variables (glucose, peptone, sodium chloride, K₂HPO₄, KH₂PO₄, ammonium sulfate, ammonium chloride, sodium sulfate, temperature, inoculum size, and pH). The optimized media predicted the optimal dry cell weight of 7.54?g?L^?1 and PHB production of 77.2?mg?L^?1 at 1?g?L^?1 of peptone, 1.46?g?L^?1 sodium sulfate, and pH 6.8 in 24?h. Glucose utilization, batch growth, and PHB production kinetics of B. subtilis were determined experimentally. The effect of substrate inhibition on specific growth rate was also determined experimentally for B. subtilis. The values of kinetic and substrate inhibition parameters obtained from this study shall be utilized to develop a mathematical model for PHB production for further improving the production of PHB.     

The doping effect on the crystal structure and electrochemical properties of LiMnxM1−xPO4 (M = Mg, V, Fe, Co, Gd)

To substitute minor Mn²⁺ by the transition metal ion M = Mg²⁺, V³⁺, Fe²⁺, Co²⁺, or Gd³⁺, LiMn_0.95M_0.05PO₄ samples are synthesized by a solid-state reaction route. The interpretation of doping effects is complicated by the interrelations between doping microstructure and morphology, because the crystal structure would be affected by the doped elements. The lattice structure and deviation of Li-O bond lengths of the doped LiMnPO₄ are refined by XRD refinement. All the samples present a couple of oxidation and reduction peaks in cyclic voltammetry, corresponding to a redox Mn³⁺/Mn²⁺ reaction coupled with the extraction/reinsertion process of Li⁺ in LiMnPO₄ structure. During charge/discharge process, the electron flowing and Li⁺ cation diffusion in the various doped LiMnPO₄ samples should be different thermodynamic and kinetic process. For further studying which step in thermodynamic and kinetic process would affect or control the electrochemical performance, the initial charge/discharge capacities and cycleability of doped LiMnPO₄ samples are obtained under different voltage range (from 2.7 to the upper cut-off voltage 4.4, 4.6 and 4.8 V, respectively) and different environment temperatures (0, 25, and 50 °C). At relative higher measuring temperature, the discharge capacity of Co-doped LiMnPO₄ shows 151.9 mAh g⁻¹.     

Mathematical model of growth and polyhydroxybutyrate production using microbial fermentation of Bacillus subtilis

Poly-3-hydroxybutyrate (PHB) has been extensively utilized as a biodegradable plastic. The value of substrate inhibition constant (K_I) was also established in shake flask cultures by varying the initial glucose concentration (20–160?g/L) in growth media. Excess carbon source adversely affected the growth of Bacillus subtilis cultures. The production kinetics of PHB was studied using batch fermentation strategy for B. subtilis culture. Batch cultivation was also performed in a 5-L stirred tank bioreactor to obtain a Biomass and PHB yield of 5.25 and 1.6?g/L, respectively. The kinetic data of biomass, PHB production, and substrate consumption was used to estimate the optimized values of the growth and product formation kinetic parameters. Optimal values of kinetic parameters (µ_m value of 0.325, K_S value of 10.53?g/L for glucose, Y value of 0.183?g/g of glucose, K_I value of 105?g/L, m value of 0.12?g/(g h), k₁ of 0.36?g/g, and k₂ value was 0.12?g/(g h)) and the initial values of biomass, substrate and PHB concentration (X?=?0.14?g/L, S?=?9.99?g/L, and P?=?0.13?g/L) were utilized to obtain a modified mathematical model for PHB production. Statistical validity of the mathematical model simulations were measured using F-test. The F-test showed that the statistical validity of the model was more than 95% when compared with experimentally obtained values. This model also predicted that the production of PHB using B. subtilis cultures is mainly growth associated.