Effect of Polyvinyl Alcohol Modified Silica Particles on the Physical and Gas Separation Properties of the Polyurethane Mixed Matrix Membranes

Silicon - Silicon based particles were prepared using tetraethoxysilane (TEOS) as a silica monomer, and low concentration of polyethylene oxide-polypropylene oxide block copolymer (pluronic) with...     

Quality Assessment of Tiger Tooth Croaker (Otolithes ruber) During Ice Storage

Quality and shelf life of tiger tooth croaker (Otolithes ruber) during 19 days of iced storage were investigated in terms of sensory, chemical (total volatile basic nitrogen (TVB-N), thiobarbituric values (TBA), peroxide value (PV), free fatty acid (FFA), and pH) and microbiological (total viable count, TVC and total psychrotrophic count. TPC) aspects. Acceptability quality of Tiger tooth croaker determined by panelists was 15–17 days. Limiting factors for acceptability were eye, gills, peritoneum, smell of gills and abdominal cavity, internal organs and flesh. Bacterial loads in samples were higher than limiting level (3 × 10⁶ CFU g^?1) between 15–17 days of ice storage. Of the chemical indicators of spoilage, the initial value of pH was 6.71 and increased to 7.35 at the end of storage. TVB-N content was 15.31mg N/100g on day 0 and reached to 36.52 on day 19. The acceptability of tiger tooth croaker decreased as FFA, PV and TBA values increased (P < 0.05). The release of FFA increased from an initial value of 4.15 (expressed as % of oleic acid) to a final value of 12.75 during the storage period. The initial PV value was 11.69 meq/kg and it increased to 50.75 meq/kg on day 12 and then started to decrease to 35.82 meq/kg at the end of storage period. The initial and final values of TBA were 0.83 and 3.75, respectively.     

Kinetic,thermodynamic and equilibrium studies on the removal of copper ions from aqueous solutions by natural and modified clinoptilolites

This paper presents the adsorption of Cu(II) ions from aqueous solution on Na and Fe-modified clinoptilolite. The copper adsorption experiments were performed in a batch system considering an optimum contact time of 24 h. Changes in the surfaces and structure were characterized by SEM data. According to the SEM results, it was anticipated that the removal efficiency of Fe-modified clinoptilolite was the highest compared with the natural and Na-modified clinoptilolites. Adsorption of Cu(II) ions by modified clinoptilolites was investigated as a function of the initial Cu(II) concentration, solution pH, and temperature. According to the results, the maximum adsorbed Cu amount onto Fe-modified was 19.40mg/l at the optimum operating condition with a pH value of 5.5 and temperature of 60 °C. According to the thermodynamic evaluations, positive ΔS and negative ΔG were found for the adsorption process showing that the adsorption reaction is a spontaneous process and more favorable at high temperatures. Sorption data have been interpreted in terms of Langmuir and Freundlich, Temkin and Dubinin-Radushkevich. The adsorption equilibrium was best described by the Langmuir adsorption isotherm. In addition, according to the Sips model, the sorption of Cu(II) ions on the Fe-modified clinoptilolite was found to be heterogeneous. The kinetic study showed that the Fe-modified clinoptilolite followed the pseudo-second order model. The results indicated that the clinoptilolite-rich tuff in its iron oxide form could be efficiently used for the removal of copper from aqueous solutions.     

Structural and transport properties of polydimethylsiloxane based polyurethane/silica particles mixed matrix membranes for gas separation

Mixed matrix membranes of synthesized polyurethane (PU) based on toluene diisocyanate (TDI), polydimethylsiloxane (PDMS) and polytetramethylene glycol (PTMG) with polyvinyl alcohol based polar silica particles were prepared by solution casting technique. The homogeneity and thermal properties of the prepared PDMS-PU/silica membranes were characterized using scanning electron microscope (SEM), differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). The SEM micrographs confirmed the distribution of silica particles in the polymer matrix without agglomerations. Gas permeation properties of membranes with different silica contents were studied for pure CO₂, CH₄, O₂, He and N₂ gases. The obtained results indicated the permeability of the condensable and polar CO₂ gas was enhanced whereas permeability of other gases decreased upon increasing the silica content of the mixed matrix membranes. The permeability of CO₂ and its selectivity over N₂ was increased from 68.4 Barrer and 22 in pure PDMS-PU to 96.7 Barrer and 64.4 in the mixed matrix membranes containing 10 wt% of the silica particles.     

Direct voltage regulation of DC–DC buck converter in a wide range of operation using adaptive input–output linearization

In this paper, an adaptive nonlinear controller is designed for voltage control of the DC–DC buck converter in both continuous and discontinuous conduction modes. The proposed controller is developed based on input–output linearization, which is robust and stable against converter load changes, input voltage variations, and parameter uncertainties. In the proposed approach, all the converter parameters, namely input voltage, load resistance, and other parasitic elements of the power circuit, are assumed to be uncertain and estimated using a suitable Lyapunov function. Using a stand‐alone TMS320F2810 digital signal processor from Texas Instruments, some simulations and experimental results are obtained to verify the proposed control approach. The results are in good agreement and prove the effectiveness and capability of the controller over a wide range of operations. Also, advantages of the designed nonlinear regulator are indicated in comparison with a pulse width modulation (PWM)‐based sliding mode controller. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Selective storage and evolution of hydrogen on nafion/NaCl/graphene quantum dot mixed matrix using tensammetry as power electrochemical technique

Hydrogen storage/evolution behavior of nafion/NaCl/graphene quantum dot (GQD) mixed matrix as selective hydrogen capacitor (power source) was evaluated in detail through an electrochemical process at two independent potential ranges. For this purpose, a three-electrode system included Pt disk as counter electrode, Ag/AgCl as reference electrode and GQD-based mixed matrix-modified Pt disk as working electrode. For hydrogen storage, the deposition potential and time were evaluated to ?1.0 V (vs. Ag/AgCl) and 120 s, respectively under high basic solution generated using NaOH (1.0 M) solution, followed by evolution of hydrogen at +0.8 V (vs. Ag/AgCl) during formation of hydrogen bubbles. The main advantage of this system was the occurrence of hydrogen storage and evolution at two independent potential windows. Both mass transfer and adsorption processes were estimated for the tensammetric peak during the evolution step. The mechanism of hydrogen storage and evolution was obeyed from diffusion and tensammetry, respectively. According to Randles–Sevcik equation using 1.0 mM ${{\text{Fe}\left(\text{CN}\right)}_6}^{3?/4?}$, the active surface area of nafion/NaCl/GQD mixed matrix was ～1906 m²g^?1. Based on the CHN analyses, pressure-concentration temperature as well as hydrogen temperature-programmed desorption, the capacity of the synthesized GQDs for hydrogen storage and evolution was estimated to at least 10.1 and 8.6 wt%, respectively. The stability of the electrode was also estimated during 7000s by chronoamperometry during applying at least 40 cycles in the range from ?1.0 to +1.3 V with reproducible tensammetric peak current (relative standard deviation: 2.54%).     

Non-singular expressions for the vector and the gradient tensor of gravitation in a geocentric spherical frame

The traditional expressions of the gravitational vector (GV) and the gravitational gradient tensor (GGT) have complicated forms depending on the first- and the second-order derivatives of associated Legendre functions (ALF), and also singular terms when approaching the poles. This article presents alternative expressions for the GV and GGT, which are independent of the derivatives, and are also non-singular. By using such expressions, it suffices to compute the ALF to two additional degrees and orders, instead of computing the first and the second derivatives of all the ALF. Therefore, the formulas are suitable for computer programming. Matlab software as well as an output of a numerical computation around the North Pole is also presented based on the derived formulas.     

Lipid characteristics in cooked, chill-reheated fillets of Indo-Pacific king mackerel (Scomberomorous guttatus)

Slices of Scomberomorous guttatus cooked by four different methods (microwave cooking, grilling, steaming and shallow fat frying) were kept chilled at 5 °C for 2 days, reheated by microwave and then evaluated for the changes in the lipid characteristics. The total lipid content for raw sample was 6.0 g/100 g which consist of 49.4 g/100 g saturated (SFA), 6.9 g/100 g monounsaturated (MUFA) and 43.8 g/100 g polyunsaturated fatty acids (PUFA). Upon cooking, the total lipids changed to about 7 (microwave), 11 (grilling), 5 (steaming) and 10 g/100 g (shallow fat frying). These changes are significant, with the exception of steam cooking. Cooking did not significantly affect the percentage of NPL, PL, SFA, MUFA and PUFA in the samples. Frying resulted in the change of the SFA/PUFA ratio more than other cooking methods. A significant (P < 0.05) decrease in the content of EPA was only found in the fried samples. A significant (P < 0.05) decrease in the content of DHA in all cooked samples were also obtained. The n-6/n-3 ratio did not change significantly in all cooked and reheated samples, except for shallow fat fried. Reheating did not significantly affect the NPL and PL contents of the fillets, except for microwave cooked samples. Cooking increases the FFA, PV and TBA of samples; reheating enhances the increase.     

A method to determine stratification efficiency of thermal energy storage processes independently from storage heat losses

A new method for the calculation of a stratification efficiency of thermal energy storages based on the second law of thermodynamics is presented. The biasing influence of heat losses is studied theoretically and experimentally. Theoretically, it does not make a difference if the stratification efficiency is calculated based on entropy balances or based on exergy balances. In practice, however, exergy balances are less affected by measurement uncertainties, whereas entropy balances can not be recommended if measurement uncertainties are not corrected in a way that the energy balance of the storage process is in agreement with the first law of thermodynamics. A comparison of the stratification efficiencies obtained from experimental results of charging, standby, and discharging processes gives meaningful insights into the different mixing behaviors of a storage tank that is charged and discharged directly, and a tank-in-tank system whose outer tank is charged and the inner tank is discharged thereafter. The new method has a great potential for the comparison of the stratification efficiencies of thermal energy storages and storage components such as stratifying devices.