Kinetic Study of Radical Polymerization VIII. A Comprehensive Study of Solution Copolymerization of Vinyl Acetate and Methyl Acrylate by 1H‐NMR Spectroscopy

Radical copolymerization reaction of vinyl acetate (VA) and methyl acrylate (MA) was performed in a solution of benzene‐d₆ using benzoyl peroxide (BPO) as the initiator at 60°C. Kinetic studies of this copolymerization reaction were investigated by on‐line ¹H‐NMR spectroscopy. Individual monomer conversions vs. reaction time, which was followed by this technique, were used to calculate the overall monomer conversion, as well as the monomer mixture and the copolymer compositions as a function of time. Monomer reactivity ratios were calculated by various linear and nonlinear terminal models and also by simplified penultimate model with r _2(VA)=0 at low and medium/high conversions. Overall rate coefficient of copolymerization was calculated from the overall monomer conversion vs. time data and k _p  . k _t ^?0.5 was then estimated. It was observed that k _p  . k _t ^?0.5 increases with increasing the mole fraction of MA in the initial feed, indicating the increase in the polymerization rate with increasing MA concentration in the initial monomer mixture. The effect of mole fraction of MA in the initial monomer mixture on the drifts in the monomer mixture and copolymer compositions with reaction progress was also evaluated experimentally and theoretically.     

The Effect of Arg on the Structure Perturbation and Chaperone Activity of α-Crystallin in the Presence of the Crowding Agent,Dextran

α-Crystallin is a protein that is expressed at high levels in all vertebrate eye lenses. It has a molecular weight of 20 kDa and is composed of two subunits: αA and αB. α-Crystallin is a member of the small heat shock protein (sHsps) family that has been shown to prevent protein aggregation. Small molecules are organic compounds that have low molecular weight (<800 Da). Arginin (Arg) is a small molecule and has been shown to prevent protein aggregation through interaction with partially folded intermediates. In this study, the effect of Arg on the chaperone activity of α-crystallin in the presence of dextran, as a crowding agent, against ordered and disordered aggregation of different target proteins (α-lactalbumin, ovotransferrin, and catalase) has been investigated. The experiments were done using visible absorption spectroscopy, ThT-binding assay, fluorescence spectroscopy, and CD spectroscopy. The results showed that in amorphous aggregation and amyloid fibril formation, both in the presence and absence of dextran, Arg had a positive effect on the chaperone action of α-crystallin. However, in the presence of dextran, the effect of Arg on the chaperone ability of α-crystallin was less than in its absence. Thus, our result suggests that crowding interior media decreases the positive effect of Arg on the chaperone ability of α-crystallin. This is a very important issue, since we are trying to find a mechanism to protect living cells against the toxic effect of protein aggregation.     

Multi-Class Cost-Constrained Random Coding for Correlated Sources over the Multiple-Access Channel

This paper studies a generalized version of multi-class cost-constrained random-coding ensemble with multiple auxiliary costs for the transmission of N correlated sources over an N-user multiple-access channel. For each user, the set of messages is partitioned into classes and codebooks are generated according to a distribution depending on the class index of the source message and under the constraint that the codewords satisfy a set of cost functions. Proper choices of the cost functions recover different coding schemes including message-dependent and message-independent versions of independent and identically distributed, independent conditionally distributed, constant-composition and conditional constant composition ensembles. The transmissibility region of the scheme is related to the Cover-El Gamal-Salehi region. A related family of correlated-source Gallager source exponent functions is also studied. The achievable exponents are compared for correlated and independent sources, both numerically and analytically.     

Molecular dynamics simulations of hydrogen adsorption/desorption by palladium decorated single-walled carbon nanotube bundle

Utilising molecular dynamics simulations, the hydrogen molecules adsorption isotherms of the (8,?0) palladium decorated single-walled carbon nanotube (SWNT) were obtained. The hydrogen adsorption was studied on the external, interstial and internal surfaces of the SWNT bundle at several temperatures ranging from 77 to 400?K. The results were compared with the bare single-walled carbon nanotube bundle under the same conditions. The decorated carbon nanotube bundle hydrogen adsorption was significantly higher than that of the bare one. The hydrogen desorption and readsorption were studied using temperature as the readsorption/desorption variable. The rate constants were calculated for the hydrogen desorption at different temperatures. The calculated decorated SWNT bundle hydrogen desorption activation energy was higher than that for the bare SWNT bundle. The calculated activation energies for the hydrogen desorption in both nanotube bundles specified the temperature dependency of hydrogen desorption.     

Tunability of temperature-dependent absorption in a graphene-based hybrid nanostructure cavity

Enhanced absorption is obtained in a hybrid nanostructure composed of graphene and one-dimensional photonic crystal as a cavity in the visible wavelength range thanks to the localized electric field around the defect layers. The temperature-induced wavelength shift is revealed in the absorption spectra in which the peak wavelength is red-shifted by increasing the temperature. This temperature dependence comes from the thermal expansion and thermo-optical effects in the constituent layers of the structure. Moreover, the absorption peaks can be adjusted by varying the incident angle. The results show that absorption is sensitive to TE/TM polarization and its peak values for the TE mode are higher than the TM case. Also, the peak wavelength is blue-shifted by increasing the incident angle for both polarizations. Finally, the possibility of tuning the absorption using the electro-optical response of graphene sheets is discussed in detail. We believe our study may be beneficial for designing tunable graphene-based temperature-sensitive absorbers.     

Reaction kinetics of a novel thermoset nanocomposite: the glycerol diglycidyl ether/3,3-dimethylglutaric anhydride/nano-Al2O3 system

Abstract  

The curing behavior of the glycerol diglycidyl ether/3,3-dimethylglutaric anhydride/nano-alumina system was examined using a dynamic differential scanning calorimetry technique. The activation energy of the system was calculated using the Kissinger, Ozawa, Barrett, and two-parameter Sestak–Berggren models. Under the assumption of a constant activation energy and an autocatalytic mechanism, the activation energy, frequency factor, and total order of reaction were computed. The theoretical reaction rate was also calculated and compared to the experimental results. Good agreement was seen between the experimental and calculated data confirming the autocatalytic mechanism. The effect of triethylamine concentration on the reaction rate was clarified using the Barrett method. Fourier transform infrared spectroscopy (FT-IR) spectroscopy was used to verify the formation of internal ester groups. Scanning electron microscopy (SEM) and X-ray mapping analyses revealed that the nanofiller was homogeneously distributed in the continuous phase.     

Mixed hemimicelle magnetic dispersive solid‐phase extraction using carbon‐coated magnetic nanoparticles for the determination of tramadol in urine samples

Ionic liquid carbon‐coated magnetic nanoparticles were successfully applied as an adsorbent in a mixed hemimicelle magnetic dispersive solid‐phase extraction method for the determination of tramadol from urine samples coupled with high‐performance liquid chromatography with UV‐vis detection. The significant parameters affect the extraction efficiency including type and amount of adsorbent, sample volume, pH, ionic strength, type and amount of elution solvent, time of extraction and desorption, time of ionic liquid loading on the adsorbent and stirring rate were studied and optimized. The proposed method provided a fast, straightforward, environmentally friendly and adsorbent recyclable approach for tramadol analysis. The linear range for the tramadol determination was from 100 to 1500 ng/mL. Precisions and accuracies were within 6%. The applicability of the proposed method in clinical trial was tried successfully on determination of tramadol in addicted subjects under tramadol therapy. The mean percent recovery of the patient samples was 94%. The results proved that the proposed method could be applied in clinical and forensic laboratories for determination of tramadol from biological urine samples.     

InAs/GaSb strained layer superlattice detectors with nBn design

We have investigated the electrical and optical properties of an nBn based Type-II InAs/GaSb strained layer superlattice detector as a function of absorber region background carrier concentration. Temperature-dependent dark current, responsivity and detectivity were measured. At T = 77 K and V_b = 0.1 V, with two orders of magnitude change in doping concentration, the dark current density increased from ～0.3 mA/cm² to ～0.3 A/cm². We attribute this to a depletion region that exists at the AlGaSb barrier and the SLS absorber interface. The device with non-intentionally doped absorption region demonstrated the lowest dark current density (0.3 mA/cm² at 0.1 V) with a specific detectivity D¹ at zero bias equal to 1.2 × 10¹¹ Jones at 77 K. The D¹ value decreased to 6 × 10¹⁰ cm Hz^1/2/W at 150 K. This temperature dependence is significantly different from conventional PIN diodes, in which the D¹ decreases by over two orders of magnitude from 77 K to 150 K, making nBn devices a promising alternative for higher operating temperatures.