Characterization and the hydrogen storage capacity of titania-coated electrospun boron nitride nanofibers

In the present work, titania-coated (TiO₂) boron nitride nanofibers were produced by the electrospinning method, and the effect of heat treatment on the nanofibers was studied. Electrospinning method is often adopted for the synthesis of one-dimensional nanofibers due to high productivity, simplicity, and cost-effectiveness. In this study, boric oxide was deposited on co-electrospun polyacrylonitrile and TiO₂. TiO₂-coated boron nitride nanofibers, with a diameter of 100 nm, were obtained after heat treatment and nitridation. The effects of heat treatment on the morphology, surface area and hydrogen storage capacity were studied extensively. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM) showed long, bead-free nanofibers and the presence of TiO₂ nanoparticles on the nanofibers. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy depicted hexagonal structures of boron nitride. The hydrogen uptake capacities of the nanofibers were investigated by pressure composition isotherm (PCI) in the pressure range of 1–70 bar at room temperature.     

The role of Al and Mg in the hydrogen storage of electrospun ZnO nanofibers

Pure and doped ZnO nanofibers with Al and Mg were successfully synthesized via an electrospinning method using a sol–gel containing Polyvinylpyrrolidone as a spinning aid and a zinc nitrate precursor. Calcination of the doped and undoped electrospun nanofibers was conducted at 500 °C in air, and the resultant structures were analyzed by X-ray diffraction (XRD) and Raman spectroscopy. The diameter of the doped nanofibers decreased with increasing viscosity and conductivity, as measured by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Energy dispersive spectroscopy (EDS) showed that Mg and Al are present in ZnO nanofibers. The pressure composition isotherm (PCI) demonstrated that the capacity of hydrogen storage in pure zinc oxide nanofibers is a factor of two greater than that of zinc oxide nanoparticles. However, Al-doped ZnO nanofibers have the highest capacity of hydrogen storage (2.81 wt%) at room temperature.     

Glass transition and fragility of telluro-vanadate glasses containing antimony oxide

The activation energy (ΔH ^*) of the glass transition and the heating-rate dependence of the glass transition temperature (T _g) of V₂O₅–Sb₂O₃–TeO₂ glasses were determined using differential scanning calorimetry technique. Non-isothermal measurements were performed at different heating rates φ (=3, 6, 9, 10, 13 K/min). The heating rate dependence of T _g was used to investigate the applicability of different theoretical models describing the glass transition. The application of Moynihan and Kissinger et al. models to the present data led to different values of (ΔH ^*) at each different heating-rate regions. This behavior was attributed to the strong heating rate dependence of the activation energy of the process. The fragility parameter (m = ΔH ^*/RT _g) were ≲90, suggesting that these glasses may be classified as strong glasses. The viscosity, η, calculated at a few selected temperatures near the glass transition region increased with increasing Sb₂O₃ content at any given temperature, which is also expected. Also the compositional dependence of T _g and ΔH ^* was investigated.     

A Single Input-Multiple Output Time Reversal UWB Communication System

Time reversal is a promising technique for the improvement of UWB communication systems. Intersymbol interference (ISI) limits the system performance in such wireless systems. This paper presents a general ISI analysis for time reversal UWB communication systems. The time reversal UWB system gives good performance for rates below the coherence bandwidth but at higher data rates the performance of the system is limited by intersymbol interference and bit error rate saturates even for high signal-to-noise ratio. To mitigate the ISI effects, a single input/multiple output (SIMO) time reversal UWB system is used and its performance is analyzed. It is shown that by using a SIMO TR transceiver, ISI reduces and the system capacity increases. Transmitted signal power at SIMO time reversal decreases, therefore in low data rate SISO performance is better than SIMO, But in high rate scenario, SIMO TR suppresses the ISI better than the SISO TR and its performance is better than SISO TR. It is possible to compensate the reduced power by using a receiver with more sensitivity.     

Sulfur removal of gas oil using ultrasound-assisted catalytic oxidative process and study of its optimum conditions

Ultrasound-assisted oxidative desulfurization process (UAOD) was applied to reduce sulfur compounds of gas oil containing various types of sulfur content. The environmental regulation requires a very deep desulfurization to eliminate the sulfur compounds. UAOD is a promising technology with lower operating cost and higher safety and environmental protection. For the first time the typical phase transfer agent (tetraoctyl-ammonium-bromide) was replaced with isobutanol because using isobutanol is much more economical than TOAB, imposing no contamination. The reaction was carried out at optimal point with various temperatures, in single-, two- and three step-procedures, investigating the effect of gradual increase of H₂O₂ and TOAB being used instead of isobutanol. Total sulfur concentration in oil phase was analyzed by ASTM-D3120 method. The highest removal of about 90% for gas oil containing 9,500 mg/kg of sulfur was achieved in three-steps during 17 minutes of process at 62±2 °C when 180.3 mmol of H₂O₂ was used and extraction carried out by methanol.     

The Effect of Nanoparticles on the Mass Transfer in Liquid–Liquid Extraction

This article investigates the effect of nanoparticles on mass transfer in the liquid–liquid extraction for the chemical system of n-butanol–succinic acid–water. For this purpose, nanofluids containing various concentrations of ZnO, carbon nanotubes (CNT), and TiO₂ nanoparticles in water, as base fluid, were prepared. To examine the flow mode effect on mass transfer rate, different fluid modes including dropping and jetting were employed in the process. Results show that mass transfer rate enhancement depends on the kinds and the concentration of nanoparticles and the modes of flow. It was observed that after adding nanoparticles, the mass transfer rate significantly increases up to two-fold for ZnO nanoparticles. Furthermore, the results indicate that under the circumstances in which the mass flow rate is high enough, the effect of nanoparticles on the mass transfer phenomenon is too slight.     

Effect of Channel Estimation Error on Time Reversal UWB Communication System

In this paper, effects of channel estimation error on time reversal (TR) UWB systems are investigated. In time reversal, a signal is prefiltered by using a time reversed complex conjugate of the channel impulse response as a transmitter prefilter. To investigate the effect of channel estimation error, an error function is added to TR-UWB prefilter. Analytical and simulation results show that channel estimation error degrade the performance. The signal-to-interference plus noise ratio decreases with increasing error variance. It is shown that the channel performance is degraded about 0.5 dB in CM1 and 1.3 dB in CM4 channel.     

Macro- and Nanoscale Effect of Ethanol on Bovine Serum Albumin Gelation and Naproxen Release

We report extended ethanol-induced gelation procedures of bovine serum albumin (BSA) at 37 °C and investigate the release behavior of a spin-labeled naproxen derivative (SL-NPX) from these hydrogels. The macroscopic mechanical properties of these gels during formation were studied using rheology, while a nanoscopic, more molecular view was obtained by analyzing the secondary structure of the protein during gelation via infrared (ATR-IR) spectroscopy. To evaluate the potential use of BSA hydrogels in controlled drug delivery, SL-NPX-BSA interaction was investigated in detail by continuous-wave electron paramagnetic resonance (CW EPR) spectroscopy, which provides information on the interaction of the small drug molecules and the hydrogel. In addition to CW EPR spectroscopy, dynamic light scattering (DLS), which provides insight into the size and nature of released components, was applied to characterize the combined influence of incubation time, ethanol, SL-drug, and BSA concentration on release behavior. It was found that the alteration of initial drug loading percentage, hydrogel incubation time as well as BSA and alcohol concentrations affect and thus tune the release rate of SL-NPX from BSA hydrogels. These results lead to the conclusion that BSA hydrogels as controlled release systems offer a remarkable fine-tuning capability for pharmaceutical applications due to the variety of gelation parameters.