Photocurrent growth and decay behavior of crystal violet dye-based photoelectrochemical cell in photovoltaic mode

Crystal violet dye-doped photoelectrochemical cells (PEC) show different and unusual behavior in their electrical and optical characteristics. In this work, we have studied the photocurrent growth and decay behavior of crystal violet dye-based solid-state PEC in photovoltaic mode. Photocurrent growth and decay are studied for different intensities of illumination. They follow a power law relationship with time which is of the form I _ph?～?t ^±α , where I _ph is the photocurrent and α is a constant. The positive and negative signs are used to indicate the growth and decay of the photocurrent, respectively. This power law relation is explained by dispersive transport model which was originally developed by Scher and Montrol and subsequently modified by different workers. The constant, α is termed as dispersion parameter, and it is related to the disorder. It is observed that the value of this parameter depends on the intensity of incident illumination. Dependence of this dispersion parameter on incident intensity is studied in this work. Variations of α with intensity for growth and decay have been discussed. In our system, the value of α is 0.325?±?0.005 for decay whereas, in the growth region, its value varies from 0.55 to 0.33, when intensity varies from minimum to maximum. The value of the disorder parameter, α, decreases as the intensity of illumination increases for growth of current whereas it remains nearly constant for decay of current. This work will be helpful in understanding the charge transport mechanism of dye-based PEC cell.     

Functionalization of edge reconstructed graphene nanoribbons by H and Fe: A density functional study

In this paper, we have studied functionalization of 5–7 edge-reconstructed graphene nanoribbons by ab initio density functional calculations. Our studies show that hydrogenation at the reconstructed edges is favorable in contrast to the case of unreconstructed 6–6 zigzag edges, in agreement with previous theoretical results. Thermodynamical calculations reveal the relative stability of single and dihydrogenated edges under different temperatures and chemical potential of hydrogen gas. From phonon calculations, we find that the lowest optical phonon modes are hardened due to 5–7 edge reconstruction compared to the 6–6 unreconstructed hydrogenated edges. Finally, edge functionalization by Fe atoms reveals a dimerized Fe chain structure along the edges. The magnetic exchange coupling across the edges varies between ferromagnetic and antiferromagnetic ones with the variation of the width of the nanoribbons.     

Surfactant-induced modulation of fluorosensor activity: a simple way to maximize the sensor efficiency

Tuning of the sensory capability of a potentially bioactive indoloquinolizine system, namely, 3-acetyl-4-oxo-6,7-dihydro-12H-indolo-[2,3-a]-quinolizine (AODIQ), is described in a biomimicking micellar nanocage. It has been shown that surfactant concentration dictates the sensing behavior of the fluorophore toward physiologically essential trace metals, such as Cu2+. This is a simple, efficient, and general technique that allows one to utilize the sensor to its maximum efficiency.     

Fluorescence resonance energy transfer from tryptophan in human serum albumin to a bioactive indoloquinolizine system

The interaction between a bioactive molecule, 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine (AODIQ), with human serum albumin (HSA) has been studied using steady-state absorption and fluorescence techniques. A 1:1 complex formation has been established and the binding constant (K) and free energy change for the process have been reported. The AODIQ-HSA complex results in fluorescence resonance energy transfer (FRET) from the tryptophan moiety of HSA to the probe. The critical energy-transfer distance (R ₀) for FRET and the Stern-Volmer constant (K _sv) for the fluorescence quenching of the donor in the presence of the acceptor have been determined. Importantly, K _SV has been shown to be equal to the binding constant itself, implying that the fluorescence quenching arises only from the FRET process. The study suggests that the donor and the acceptor are bound to the same protein at different locations but within the quenching distance.     

Synthesis of Oxygen‐Containing Spirobipyrrolidinium Salts for High Conductivity Room Temperature Ionic Liquids

Synthesis of ionic liquids (IL) based on oxygen‐containing spirobipyrrolidinium salts with BF₄, BF₃C₂F₅, and NTf₂ as counterions was undertaken. Their physical and electrochemical properties were evaluated for suitability for Room Temperature Ionic Liquids (RTIL) application. Reduction in melting point occurred upon exchange of C(2) by an O‐atom of spirobipyrrolidinium, without sacrificing the electrochemical stability; while introduction of alkyl groups between the N‐ and O‐atoms led to incorporation of asymmetry, and hence reduced the melting points, and viscosity.     

Multi-scale Mechanical Characterization of Palmetto Wood using Digital Image Correlation to Develop a Template for Biologically-Inspired Polymer Composites

Palmetto wood is garnering growing interest as a template for creating biologically-inspired polymer composites due to its historical use as an energy absorbing material in protective structures. In this study, quasi-static three-point bend tests have been performed to characterize the mechanical behavior of Palmetto wood. Full-field deformation measurements are obtained using Digital Image Correlation (DIC) to elucidate on the strain fields associated with the mechanical response. By analyzing strain fields at multiple length scales, it is possible to study the more homogeneous mechanical behavior at the macro-scale associated with the global load-deformation response; while at the microscale the mechanical behavior is more inhomogeneous due to microstructural failure mechanisms. Thus, it was possible to determine that, despite the presence of discontinuous macro-fiber reinforcement, at the macro-scale the response is associated with classical bending and progressive failure processes that are adequately described by Weibull statistics proceeding from the tensile side of the specimen. At the microscale, however, the failure mechanisms giving rise to the macroscopic response consist of both shear-dominated debonding between the fiber and matrix, and inter-fiber matrix failure due to pore collapse. These microscale mechanisms are present in both the compressive and tensile regions of the specimen, most likely due to local macro-fiber bending, which is independent of the global bending state. The pore collapse mechanism observed during mechanical loading appears to improve the energy absorption of the matrix material, thereby, transferring less energy and shear strain to the macro-fiber-matrix interface for initiation of debonding. However, the pore collapse mechanism can also accumulate substantial shear strain, which results in matrix shear cracking. Through these complex failure mechanisms, Palmetto wood exhibits a high resistance to catastrophic failure after damage initiation, an observation that can be used as inspiration for creating new polymer composite materials.     

Photoperiod regulates lung-associated immunological parameters and melatonin receptor (Mel1a and Mel1b) in lungs of a tropical bird, Perdicula asiatica

We accessed the effects of different photoperiodic regimes, i.e. long (LP; 20L:4D), short (SP; 4L:20D) and natural day photoperiod during reproductively inactive and reproductively active phase on immune parameters of lungs and general immunity of Perdicula asiatica. SP increased bronchus-associated lymphoid tissue (BALT) and non-BALT nodule size, total leukocyte count, lymphocyte count, plasma melatonin level, percent stimulation ratio of lymphocytes and decreased testicular activity (weight and testosterone level). LP during both the reproductive phases decreased the above-mentioned immune parameters suggesting that photoperiod might be regulating lung-associated immune system (LAIS) via melatonin. We also extended our study to note the expression of melatonin receptor types Mel(1a) and Mel(1b) in lung tissue to support our above statement. Western blot analysis showed significant increase in expression of Mel(1a) and Mel(1b) receptor types under SP conditions and decreased expression under LP condition when compared with control group of both reproductive phases. This suggests the probable involvement of Mel(1a) and Mel(1b) receptors in mediation of photoperiodic signals to LAIS. P. asiatica is a photoperiodic bird hence photoperiodically regulated melatonin hormone and its receptors in the lung might be responsible for modulation of lung-associated immunity.     

Fabrication of hollow self-assembled peptide microvesicles and transition from sphere-to-rod structure

This paper presents the construction of hollow peptide microspheres and the mechanism of transition of microspheres to rod-like vesicles at low concentration. The tripeptides Boc-Phe-Maba-Phe-OMe 1 and Boc-Phe-Maba-Tyr-OMe 2, each of them containing a rigid m-aminobenzoic acid (Maba) template at the central position, forms microspheres at a concentration of 1.6 mM in methanol. At low concentration, these vesicular structures are fused through neck formation, and this leads to sphere-to-rod transition of vesicles. Sizes of these microspheres increase with increasing concentration. We have successfully characterized this transition by fluorescence spectroscopy, DLS, and electron microscopic study. The scanning electron microscopy clearly shows that these spheres are hollow. One important property of these microvesicular structures is the encapsulation of a potent anticonvulsant and mood stabilizing drug carbamazepine, which holds future promise to use these microvesicles as delivery vehicles.     

Modeling and Simulation of Rate-Dependent Magneto-Active Polymers

In the present work, the magneto-viscoelastic behavior of MAPs is studied by a thermodynamically consistent constitutive model. A finite deformation based framework of nonlinear magneto-viscoelastic coupling is introduced with a multiplicative decomposition of the deformation gradient. The viscosity is captured by evolution equations of the internal variables introduced. We propose energy functions for pure magnetic and magneto-mechanical coupling such that saturation behavior of the magnetostriction and magnetization is captured. After having established the general framework, the model is studied for homogeneous deformations for the purpose of a least-square-based parameter identification from experimental data. The model predictions of non-linear magneto-mechanical responses with strong rate and field dependency are presented. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)