Multichromic polymers based on pyrene clicked thienylpyrrole

In this study, the effect of pendant pyrene on the optical and electronic properties of poly(2,5‐dithienylpyrrole)s was studied. For this purpose a new pyrene coupled 2,5‐dithienylpyrrole derivative (SNS‐pyrene) was synthesized through click reaction. SNS‐pyrene was electrochemically polymerized and its electrochemical and optical properties were investigated by electrochemical and optical techniques. The polymer had a band gap of 3.36 eV and displayed light green to blue color variation upon oxidation in less than 2.48 s. Additionally, electrochemical copolymerization of SNS‐pyrene with 3,4‐ethylenedioxythiophene was achieved whilst a detailed investigation was performed on the effect of electrochemical polymerization conditions on the optoelectronic properties of the copolymers. Studies revealed that the copolymers exhibit multichromic reversible redox behavior with lower band gaps and shorter switching times than their parent polymer, P(SNS‐pyrene) © 2014 Society of Chemical Industry.     

Determination of optimum pH and temperature for pasteurization of citrus juices by response surface methodology

Summary Optimization of microbial death, enzyme inactivation and vitamin C retention during pasteurization of pH-adjusted orange juice is discussed free of equipmentdependent parameters such as the heating lag. The pH-temperature optimum was determined by response surface methodology in the range of 65° C–75° C and pH 2.5–4.0. The results implied that there was no pectinesterase activity below pH 3.5.Leuconostoc mesenteroides had its maximum and minimum thermal resistance at pH 3.5 and pH 2.7, respectively. For an ideal theoretical process requiring four log cycles of microbial reduction the optimum pasteurization conditions were 12 min at 75° C and pH 2.7.

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Bestimmung der optimalen Temperatur- und pH-Wert-Bedingungen für die Pasteurisierung von Citrussäften mit der response surface-Methode

Zusammenfassung Die Optimierung der mikrobiellen Abtötung, Enzyminaktivierung und Vitamin-C-Retention während der Pasteurisierung von Orangensaft mit verschiedenen pH-Werten wird, frei von Anlageneinflüssen, wie z. B. Erhitzungsverzögerungen, diskutiert. Das Temperatur-pH-Wert-Optimum wurde mit der response surface-Methode im Temperaturbereich von 65 bis 75 °C und pH-Werten zwischen 2,5 und 4,0 untersucht. Die Ergebnisse lassen darauf schließen, daß unter pH 3,5 keine Pectinesteraseaktivität mehr vorliegt.Leuconostoc mesentroides wies bei pH 2,7 minimale und bei pH 3,5 maximale Hitzeresistenz auf. In einem idealen theoretischen Pasteurisierungsprozeß, der eine Reduzierung der mikrobiellen Belastung um vier Größenordnungen erfordert, liegen die optimalen Bedingungen bei 12 min, 75 °C und einem pH-Wert von 2,7.

     

Negative capacitance peculiarities in a-Si:H/c-Si rectifier structure

Nontrivial negative capacitance (NC) effect, observed in a-Si:H/c-Si heterostructure devices, is discussed emphasizing the theoretical interpretation of experimental data. To explain NC effect, we have performed dark current voltage (I-V) and admittance measurements (C-V, G-V, C-f and G-f). The calculated values of series resistance (R_s) and barrier height (Φ_Bo) have the values from 100 to 114.7 Ω and 0.94 to 0.83 eV, respectively. Also, below 50% helium dilution rate, diode ideality factor (n) becomes bigger than 2, because tunneling at junction interface plays a major role. The measured room temperature (294 K) dark I-V result has been used during the fitting process for suggested capacitance model (Eq. (18)). The measured NC values exhibit strongly voltage depended behavior. This unexpected behavior is attributed to the presence of inductively coupled space charge region which might possibly be stemmed from the helium diluted a-Si:H material. It is seen that the measured NC values are well fitted with suggested capacitance model (Eq. (18)). Application of suggested correction formula on to experimental C-V data yields satisfactory results. It is shown that the calculated inductance values of the investigated device range from 10 to 42 μH and after correction, NC values are no longer observed in the C_d-V data.     

Electrical characterization of Au/Pd/n-GaN/Pd/Au device structure in the radio frequency range by simulation study

GaN based devices are highly promising optoelectronic devices for many years due to their useful applications in photovoltaic energy conversation, fiber optic communication and atmosphere monitoring. GaN based devices such as Schottky barrier, metal–semiconductor–metal and p-i-n structure have been fabricated and characterized so far. A proper understanding of the impedance or admittance spectroscopy result is crucial since it is a powerful tool to calculate the physical and electronic parameters of a device. In this study, temperature dependent dark current–voltage (I–V) and dark impedance spectra of n type GaN based metal–semiconductor–metal device have been studied with current–voltage and impedance spectra by simulation. All current–voltage characteristics exhibited good rectification behavior. The forward and reverse bias capacitance–voltage (C–V) characteristics of the Au/Pd/n-GaN/Pd/Au device were simulated at 2 MHz probing frequency. Nyquist plots of simulated device at 295 K are shown that two-barrier heights can be observable above critical threshold bias point. Frequency depended inverse dielectric loss tangent spectra of Au/Pd/n-GaN/Pd/Au device at different DC bias voltages also shows significant two peaks. This indicates that our simulation is extremely useful for determination of potential barrier numbers.     

Enzymatic production of human milk fat substitutes containing γ-linolenic acid: Optimization of reactions by response surface methodology

Structured lipids resembling human milk fat and containing GLA were synthesized by an enzymatic interesterification between tripalmitin, hazelnut oil FA, and GLA in n-hexane. Commercially immobilized 1,3-specific lipases, lipozyme^® RM IM and Lipozyme^® TL IM, were used as the biocatalysts. The effect of these enzymes on the incorporation levels was investigated. A central composite design with five levels and three factors—substrate ratio, reaction temperature, and time—were used to model and optimize the reaction conditions via response surface methodology. Good quadratic models were obtained for the incorporation of GLA (response 1) and oleic acid (response 2) by multiple regression and backward elimination. The determination coefficient (R ²) values for the models were found to be 0.92 and 0.94 for the reactions catalyzed by Lipozyme RM IM, and 0.92 and 0.88 for the reactions catalyzed by Lipozyme TL IM, respecitively. The optimal conditions generated from the models for the targeted GLA (10%) and oleic acid (45%) incorporation were 14.8 mol/mol, 55°C, and 24 h; 14 mol/mol, 55°C, and 24 h for substrate ratio (moles total FA/mol tripalmitin), temperature and time for the reactions catalyzed by Lipozyme RM IM and Lipozyme TL IM, respectively. Human milk fat substitutes containing GLA that can be included in infant formulas were success-fully produced using both Lipozyme RM IM and Lipozyme TL IM enzymes. The effect of the two enzymes on the incorporation of GLA and oleic acid were found to be similar.     

The Effect of ultra‐high speed twin screw extrusion on ABS/organoclay nanocomposite blend properties

Acrylonitrile butadiene styrene (ABS) nanocomposites containing Cloisite 11 organoclay at 2 wt% were prepared using a 60 L/D ultra‐ high speed twin screw extruder (TSE), with speeds ranging from 400 to 4000 rpm. The purpose of this study was to investigate the effect of high shear melt processing on the intercalation and exfoliation of organoclay in the polymer, as well as the mechanical and rheological properties of the material. X‐ray Diffraction (XRD), and Transmission Electron Microscopy (TEM) results showed better intercalation of the nanofiller with increasing screw speed up to a point, and indicated an exfoliated structure of the nanocomposites extruded at 4000 rpm. Mechanical and rheological testing results indicated that by adding organoclay to ABS, the properties improved with increasing screw speed up to an optimum value of 2000 rpm. However, at the higher screw speeds of 3000 and 4000 rpm, the intense shear history led to a decrease in properties, most likely due to chain scission and molecular weight reduction. Similar trends were observed in rheological properties of the nanocomposite as well. At 2000 rpm, the results indicate that the lowering of the molecular weight due to shear effects is balanced by good intercalation/exfoliation of the organoclay. POLYM. ENG. SCI., 57:60–68, 2017. © 2016 Society of Plastics Engineers     

Construction of a sandwich-type wound dressing with pain-reliever and pH-responsive antibiotic delivery system

A multifunctional sandwich type wound dressing was designed in which two types of microspheres, one to alleviate the pain (ibuprofen) and the other to protect the wound from infections (Gentamicin or Ciprofloxacin), were embedded into bilayer chitosan sponge. pH of the wound increases from acidic (pH ~ 5) to basic (pH ~ 8) via infection, so pH-dependent antibiotic release system was designed using gelatin B microspheres to respond to increasing pH. Ibuprofen release from chitosan microspheres, on the other hand, was pH-independent not to intervene with pain management in changing pH conditions. Crosslinking with glutaraldehyde (GA) affected both release profile and size distribution of microspheres and 2.5% GA was chosen to obtain pH-responsive gelatin microspheres with narrow size distribution (80% of microspheres in between 15 and 25 μm). The final system was found to be effective against both Staphylococcus aureus and Escherichia coli and changing pH seemed to affect the antimicrobial agent delivery as desired. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48252.     

Effect of potassium ion on the stability and release rate of hydrogen peroxide encapsulated in silica hydrogels

Hydrogen peroxide (H₂O₂) is encapsulated in silica hydrogels using sol‐gel method and the effects of the K⁺ : Na⁺ ion ratio on gelation time, hydrogel structure, stability, and release rate of H₂O₂ were investigated. As the amount of K⁺ ions increased relative to the amount of Na⁺ ions at the same pH, the gel structure became less compact and the pore diameter increased. Hydrogen peroxide retention values up to 90 and 80% were observed at the end of 7 and 20 days, respectively, in the presence of K⁺ ions at low pH values when the initial H₂O₂ concentration was 19.9 wt %. Release rate of hydrogen peroxide decreased with decreasing pH for the two K⁺ : Na⁺ ion ratios studied. This work presents an environmentally friendly, low cost, and easy to scale up method to increase the stability of high initial concentrations of H₂O₂ at room temperature and customize the release rate. © 2016 American Institute of Chemical Engineers AIChE J, 63: 409–417, 2017     

AN EMPIRICAL VIRIAL-LIKE CUBIC EQUATION OF STATE FOR PHASE EQUILIBRIUM CALCULATIONS

An empirical cubic equation of state(EOS) was obtained by truncating the virial expansion in reciprocal of molar volume after the third term. The constants of the EOS was generalized in terms of critical temperature, critical pressure and Pitzer's acentric factor.

In pure component applications the EOS exhibited a performance comparable to Peng-Robinson (1976) EOS in the reduced temperature range of 0.5 to 1. The present EOS tends to predict better saturation liquid volumes at reduced temperatures below 0.8, and better estimations for second virial coefficient at high reduced temperatures.

The EOS was successfully employed for vapor liquid equilibrium calculations for some mixtures of normal or slightly polar fluids with traditional one binary parameter mixing rule at moderately high pressures. At low reduced temperatures, where conventional one adjustable parameter applications of the cubic equations compare unfavorably with dual methods based on excess Gibbs energy functions for the liquid phase, a new two constant mixing rule introduced by Stryjek and Vera (1986) was employed for the present equation of state.     

Epidemiological comparisons of problems and positive qualities reported by adolescents in 24 countries.

In this study, the authors compared ratings of behavioral and emotional problems and positive qualities on the Youth Self-Report (T. M. Achenbach & L. A. Rescorla, 2001) by adolescents in general population samples from 24 countries (N = 27,206). For problem scales, country effect sizes (ESs) ranged from 3% to 9%, whereas those for gender and age ranged from less than 1% to 2%. Scores were significantly higher for girls than for boys on Internalizing Problems and significantly higher for boys than for girls on Externalizing Problems. Bicountry correlations for mean problem item scores averaged .69. For Total Problems, 17 of 24 countries scored within one standard deviation of the overall mean of 35.3. In the 19 countries for which parent ratings were also available, the mean of 20.5 for parent ratings was far lower than the self-report mean of 34.0 in the same 19 countries (d = 2.5). Results indicate considerable consistency across 24 countries in adolescents' self-reported problems but less consistency for positive qualities. (PsycINFO Database Record (c) 2010 APA, all rights reserved)