Enhancement of silicon solar cell performances due to light trapping by colloidal metal nanoparticles

Photovoltaics is the most promising technology for the future of green energy production. To fully realize the potential use of photovoltaic technology, low manufacturing cost and high working photoconversion efficiency must be obtained. Light trapping by metal nanoparticles is an attractive strategy in thin film as well as in bulk silicon solar cells aimed to confine light within the active layer to promote the photon absorption and therefore achieving higher efficiency. In this paper, we tested the deposition of silver and gold nanoparticles on bulk silicon solar cells by colloidal technique in order to enhance their photovoltaic conversion efficiency by means of Plasmonic Light Scattering by metal nanoparticles. The feasible Plasmonic Light Scattering related enhancement was examined using spectral response and I–V measurements. Relative increases of the total delivered power under simulated solar irradiation were observed for cells both with and without antireflection coating using silver and gold nanoparticles.     

Quantization dimension and temperature function for bi-Lipschitz mappings

The quantization dimension function for a probability measure supported on the limit set generated by a set of contractive bi-Lipschitz mappings is determined. The relationship between the quantization dimension function and the temperature function of the thermodynamic formalism arising in multifractal analysis is established.     

Localization of Dirac-like excitations in graphene in the presence of smooth inhomogeneous magnetic fields

The present paper discusses magnetic confinement of the Dirac excitations in graphene in the presence of inhomogeneous magnetic fields. In the first case a magnetic field directed along the z axis whose magnitude is proportional to 1/r is chosen. In the next case we choose a more realistic magnetic field which does not blow up at the origin and gradually fades away from the origin. The magnetic fields chosen do not have any finite/infinite discontinuity for finite values of the radial coordinate. The novelty of the two magnetic fields is related to the equations which are used to find the excited spectra of the excitations. It turns out that the bound state solutions of the two-dimensional hydrogen atom problem are related to the spectra of graphene excitations in the presence of the 1/r (inverse-radial) magnetic field. For the other magnetic field profile one can use the knowledge of the bound state spectrum of a two-dimensional cutoff Coulomb potential to dictate the excitation spectra of graphene. The spectrum of the graphene excitations in the presence of the inverse-radial magnetic field can be exactly solved while the other case cannot be. In the later case we give the localized solutions of the zero-energy states in graphene.     

Magnetotransport properties of a magnetically modulated two-dimensional electron gas with the spin-orbit interaction

We study the electrical transport properties of a two-dimensional electron gas (2DEG) with the Rashba spin-orbit interaction in the presence of a constant perpendicular magnetic field (B(0)( ?z) which is weakly modulated by B1 = B1 cos(qx) ?z, where B(1) ? B(0) and q = 2π/a with a the modulation period. We obtain the analytical expressions of the diffusive conductivities for spin-up and spin-down electrons. The conductivities for spin-up and spin-down electrons oscillate with different frequencies and produce beating patterns in the amplitude of the Weiss and Shubnikov-de Haas oscillations. We show that the Rashba strength can be determined by analyzing the beating pattern in the Weiss oscillation. We find a simple equation which determines the Rashba spin-orbit interaction strength if the number of Weiss oscillations between any two successive nodes is known from the experiment. We compare our results with the electrically modulated 2DEG with the Rashba interaction. For completeness, we also study the beating pattern formation in the collisional and the Hall conductivities.     

Reversible formation of aryloxenium ions from the corresponding quinols under acidic conditions

Quinols, 1, are products of the hydration of O‐aryloxenium ions, 2, and N‐arylnitrenium ions, 3, and they are being investigated for medical uses. Under acidic conditions (pH 1–3) kinetics and products of Br^– trapping demonstrate that 1a, 4‐phenyl‐4‐hydroxy‐2,5‐cyclohexadienone, and 1b, 4‐p‐tolyl‐4‐hydroxy‐2,5‐cyclohexadienone, generate the corresponding oxenium ions 2a and 2b, respectively, as steady‐state intermediates. Formation and trapping of the oxenium ions occurs in competition with the acid catalyzed dienone–phenol rearrangement. Because oxenium ion formation is reversible, the ion can only be detected by trapping with a nucleophile. Br^– is an efficient trap under acidic conditions because, unlike N₃^–, it is not protonated under those conditions. Attempts to detect the oxenium ions 2a and 2b at pH 4.6 and 7.1 with N₃^– were unsuccessful indicating that oxenium ion formation only occurs under acidic conditions. The oxenium ion 2c could not be detected under acidic conditions from the quinol 1c, 4‐(benzothiazol‐2‐yl)‐4‐hydroxy‐2,5‐cyclohexadienone, by Br^– trapping methods, even though this ion can be detected during hydrolysis of the corresponding ester, 4c. Although the benzothiazol‐2‐yl group is a resonance electron donor that is capable of stabilizing an O‐aryloxenium ion, it is also a strong inductive electron withdrawing group that hinders the formation of 2c from 1c by decreasing the extent of protonation of 1c to generate 1cH⁺ and by destabilizing the transition state for ionization of 1cH⁺. Generation of an oxenium ion from the corresponding quinol is feasible under acidic conditions as long as the 4‐substituent of the quinol is both a resonance and inductive electron donor. Copyright © 2012 John Wiley & Sons, Ltd.     

Portfolio Optimization in a Semi-Markov Modulated Market

We address a portfolio optimization problem in a semi-Markov modulated market. We study both the terminal expected utility optimization on finite time horizon and the risk-sensitive portfolio optimization on finite and infinite time horizon. We obtain optimal portfolios in relevant cases. A numerical procedure is also developed to compute the optimal expected terminal utility for finite horizon problem. This work was supported in part by a DST project: SR/S4/MS: 379/06; also supported in part by a grant from UGC via DSA-SAP Phase IV, and in part by a CSIR Fellowship.     

Comment on “Atomic structure calculations for F-like tungsten” by S. Aggarwal [Chin. Phys B 23(2014) 093203]

Recently, S. Aggarwal [Chin. Phys. B 23 (2014) 093203] reported energy levels, radiative rates, and the lifetimes for the lowest 60 levels belonging to the 2s²2p⁵, 2s2p⁶, and 2s²2p⁴3l configurations of F-like tungsten. There is no discrepancy for his calculated energies for the levels and the radiative rates for the limited number of E1 transitions, but the reported results for the lifetimes are highly inaccurate. According to our calculations, errors in his reported lifetimes are up to 6 orders of magnitude for several levels. Here we report the correct lifetimes for future comparisons and applications, and also explain the reason for the discrepancies.     

Preferential mode of cyclization of tetrahydrofuran amino acids containing peptides: some theoretical insights

Theoretical insights have been provided for the observed preference of cyclodimerization over intramolecular cyclization reactions in linear tripeptides containing “2,5‐cis” (2S,5R)‐tetrahydrofuran amino acid as well as in those containing “2,5‐trans” (2S,5S)‐tetrahydrofuran amino acid, using quantum chemical methods. The geometries of species involved as well as the feasibility of cyclization reactions are studied at the B3LYP/6‐31G(d,p) level of theory in gas phase as well as in solvent phase. Thermodynamic data from Hessian calculations favor the intermolecular cyclization. Analysis of optimized geometries reveals the existence of additional stabilizing hydrogen bonding interactions in intermolecularly cyclized products. The existence of these second‐order interactions is substantiated by topological (atoms in molecules (AIM)) and natural bond orbital (NBO) analyses. Such interactions are absent in the intramolecular cyclization products. Further justification for the presence of stabilizing interactions in intermolecularly cyclized products comes from the molecular electrostatic potentials and electron density surfaces. Kinetic control favoring the intermolecularly cyclized products due to additional entropy of activation in the intramolecular case is surmised. Copyright © 2009 John Wiley & Sons, Ltd.     

Dynamic Coupling at Low Reynolds Number

Collective and emergent behaviors of active colloids provide useful insights into the statistical physics of out‐of‐equilibrium systems. Colloidal suspensions containing microscopic active swimmers have been intensively studied to understand the principles of energy transfer at low Reynolds number conditions. Studies on active enzymes and Ångström‐sized organometallic catalysts have demonstrated that energy can even be transferred by molecules to their surroundings, thereby influencing the overall dynamics of the systems substantially. By monitoring the diffusion of non‐reacting tracers in active solutions, it has been shown that the nature of energy transfer in systems containing different swimmers is surprisingly similar—irrespective of their size, modes of energy transduction, and propulsion strategies. This Review discusses research results obtained so far in this direction, highlighting the common features observed in the dynamic coupling of swimmers with their surroundings.