Light-activated ionic gelation of common biopolymers

Biopolymers such as alginate and pectin are well known for their ability to undergo gelation upon addition of multivalent cations such as calcium (Ca(2+)). Here, we report a simple way to activate such ionic gelation by UV irradiation. Our approach involves combining an insoluble salt of the cation (e.g., calcium carbonate, CaCO(3)) with an aqueous solution of the polymer (e.g., alginate) along with a third component, a photoacid generator (PAG). Upon UV irradiation, the PAG dissociates to release H(+) ions, which react with the CaCO(3) to generate free Ca(2+). In turn, the Ca(2+) ions cross-link the alginate chains into a physical network, thereby resulting in a hydrogel. Dynamic rheological experiments confirm the elastic character of the alginate gel, and the gel modulus is shown to be tunable via the irradiation time as well as the PAG and alginate concentrations. The above approach is easily extended to other biopolymers such as pectin. Using this approach, a photoresponse can be imparted to conventional biopolymers without the need for any chemical modification of the molecules. Photoresponsive alginate gels may be useful in creating biomaterials or tissue mimics. As a step toward potential applications, we demonstrate the ability to photopattern a thin film of alginate gel onto a glass substrate under mild conditions.     

Stable physically adsorbed coating of poly-vinyl alcohol for the separation of basic proteins

In aqueous capillary electrophoresis, the electroosmotic flow can be strongly suppressed by coating the inner surface of the capillary. In the present work hydrophilic coating of 4% polyvinyl alcohol (PVA) has been used for the analysis of basic proteins. The coating is simple and easy to obtain. The separation of ribonuclease and α-chymotrypsin has been uniquely done with other three basic proteins (lysozyme, cytochrome-c and trypsin) using a buffer 11.60 mM sodium acetate and 18.40 mM acetic acid at pH 4.5 in addition to positive power supply of 20 kV at 25°C. Detection was performed using UV detector at 230 nm. The proposed PVA coated capillary provides reproducible separation of five basic proteins within 10 min with RSD values for mobility bellow 1.4% (n = 6) for all the five basic proteins. The stability of coated capillary has been checked up to 40 runs. The viscosity measurement for 4% PVA have been studied and scanning electron microscope (SEM) images obtained to make it compatible with future micro-chip applications.     

Understanding anomalous current-voltage characteristics in microchannel-nanochannel interconnect devices

The integration of a microchannel with a nanochannel is known to exhibit anomalous nonlinear current-voltage characteristics. In this paper, we perform detailed numerical simulations considering a 2-D nonlinear ion transport model, to capture and explain the underlying physics behind the limiting resistance and the overlimiting current regions, observed predominantly in a highly ion-selective nanochannel. We attribute the overlimiting current characteristics to the redistribution of the space charges resulting in an anomalous enhancement in the ionic concentration of the electrolyte in the induced space charge region, beyond a critical voltage. The overlimiting current with constant conductivity is predicted even without considering the effects of fluidic nonlinearities. We extend our study and report anomalous rectification effects, resulting in an enhancement of current in the non-ohmic region, under the application of combined AC and DC electric fields. The necessary criteria to observe these enhancements and some useful scaling relations are discussed.     

Modeling of 2.5 Gbps-intersatellite link (ISL) in inter-satellite optical wireless communication (IsOWC) system

Free-space optics (FSO) has the combined features of most dominated telecommunication technologies: wireless and fiber optics. Many of the aspects of FSO are related to fiber optics with an important difference of transmission medium which is air/free space rather than the glass of the fiber-optic cable. Inter-satellite optical wireless communication systems (IsOWC), one of the important applications of FSO/WSO technology, will be deployed in space in the near future as such systems provide a high bandwidth, small size, light weight, low power and low cost alternative to present microwave satellite systems. In this paper, we have designed a model of IsOWC system using OPTI-SYSTEM™ simulator to establish an inter-satellite link (ISL) between two satellites estranged by a distance of 1000 km at data rate of 2.5 Gbps which is not reported in previous investigated works.     

Stretch-induced wrinkling of polyethylene thin sheets: Experiments and modeling

This paper presents a study on stretch-induced wrinkling of thin polyethylene sheets when subjected to uniaxial stretch with two clamped ends. Three-dimensional digital image correlation was used to measure the wrinkling deformation. It was observed that the wrinkle amplitude increased as the nominal strain increased up to around 10%, but then decreased at larger strain levels. This behavior is consistent with results of finite element simulations for a hyperelastic thin sheet reported previously (Nayyar et al., 2011). However, wrinkles in the polyethylene sheet were not fully flattened out at large strains (>30%) as predicted for the hyperelastic sheet, but exhibited a residual wrinkle whose amplitude depended on the loading rate. This is attributed to the viscoelastic response of the material. Two different viscoelastic models were adopted in finite element simulations to study the effects of viscoelasticity on wrinkling and to improve the agreement with the experiments, including residual wrinkles and rate dependence. It is found that a parallel network model of nonlinear viscoelasticity is suitable for simulating the constitutive behavior and stretch-induced wrinkling of the polyethylene sheets.     

Ab initio dynamics of cellulose pyrolysis: nascent decomposition pathways at 327 and 600 °c

We modeled nascent decomposition processes in cellulose pyrolysis at 327 and 600 °C using Car-Parrinello molecular dynamics (CPMD) simulations with rare events accelerated with the metadynamics method. We used a simulation cell comprised of two unit cells of cellulose Iβ periodically repeated in three dimensions to mimic the solid cellulose. To obtain initial conditions at reasonable densities, we extracted coordinates from larger classical NPT simulations at the target temperatures. CPMD-metadynamics implemented with various sets of collective variables, such as coordination numbers of the glycosidic oxygen, yielded a variety of chemical reactions such as depolymerization, fragmentation, ring opening, and ring contraction. These reactions yielded precursors to levoglucosan (LGA)-the major product of pyrolysis-and also to minor products such as 5-hydroxy-methylfurfural (HMF) and formic acid. At 327 °C, we found that depolymerization via ring contraction of the glucopyranose ring to the glucofuranose ring occurs with the lowest free-energy barrier (20 kcal/mol). We suggest that this process is key for formation of liquid intermediate cellulose, observed experimentally above 260 °C. At 600 °C, we found that a precursor to LGA (pre-LGA) forms with a free-energy barrier of 36 kcal/mol via an intermediate/transition state stabilized by anchimeric assistance and hydrogen bonding. Conformational freedom provided by expansion of the cellulose matrix at 600 °C was found to be crucial for formation of pre-LGA. We performed several comparison calculations to gauge the accuracy of CPMD-metadynamics barriers with respect to basis set and level of theory. We found that free-energy barriers at 600 °C are in the order pre-LGA < pre-HMF < formic acid, explaining why LGA is the kinetically favored product of fast cellulose pyrolysis.     

Application of homotopy analysis method for fractional Swift Hohenberg equation – Revisited

In this article, the homotopy analysis method is used to obtain the approximate analytical solutions of the non-linear Swift Hohenberg equation with fractional time derivative. The fractional derivative is described in Caputo sense. Numerical results reveal that the method is easy to implement, reliable and accurate when applied to time fractional nonlinear partial differential equations. Effects of parameters of physical importance on the probability density function and the convergence of the approximate series solution using residual error formula with the proper choices of auxiliary parameter for various fractional Brownian motions and standard motion are depicted through graphs and tables for different particular cases.     

Viscosity and excess molar volume of binary mixtures of methanol with n-butylamine and di-n-butylamine at 303.15, 313.15 and 323.15 K. Characterization in terms of ERAS model

The excess molar volume V_m^E, viscosity deviation Δη, and excess Gibbs energy of activation ΔG^?E of viscous flow have been investigated from the density ρ and viscosity η measurements of binary mixtures of methanol with n-butylamine and di-n-butylamine over the entire range of mole fractions at 303.15, 313.15, and 323.15 K. The systems studied exhibit very strong cross association through strong O–H…N bonding between –OH and –NH– groups. As a consequence of this strong intermolecular association, both the systems have very large negative V_m^E and positive Δη and ΔG^?E over entire range of composition and at all the temperatures of investigation. V_m^E of the studied mixtures is consistently described by the ERAS model. The values of cross association constants K_AB illustrate that cross-associates are more pronounced in primary amine mixtures than that in secondary amine.     

Effect of pulse slippage on density transition-based resonant third-harmonic generation of short-pulse laser in plasma

The resonant third-harmonic generation of a self-focusing laser in plasma with a density transition was investigated. Because of self-focusing of the fundamental laser pulse, a transverse intensity gradient was created, which generated a plasma wave at the fundamental wave frequency. Phase matching was satisfied by using a Wiggler magnetic field, which provided additional angular momentum to the third-harmonic photon to make the process resonant. An enhancement was observed in the resonant third-harmonic generation of an intense short-pulse laser in plasma embedded with a magnetic Wiggler with a density transition. A plasma density ramp played an important role in the self-focusing, enhancing the third-harmonic generation in plasma. We also examined the effect of the Wiggler magnetic field on the pulse slippage of the third-harmonic pulse in plasma. The pulse slippage was due to the group-velocity mismatch between the fundamental and third-harmonic pulses.     

Simulative investigation of the impact of EDFA and SOA over BER of a single-tone RoF system

In this paper, we investigate the impact of EDFA and SOA amplifiers over BER and Q-parameter of a Radio-over-Fiber (Rof) system consisting of two different system set-ups using direct- and external-laser modulation techniques. In this work, we also measured and compared the electric Rf power at receiver at different modulating Rf frequencies up to 20 GHz using two different optical amplifiers, i.e. EDFA and SOA. Further, we also compared the received electric Rf power at different optical powers without and with different optical amplifiers. An improvement of −11 dB (approx.) of received Rf power was observed using EDFA with the external modulation technique, on comparing with direct modulation.