Photoluminescence properties of Gd:ZnO nano phosphor

Journal of Sol-Gel Science and Technology - Gd (0.1, 0.5, 1.0?mol%) doped ZnO nano phosphor, prepared by wet chemical method followed by sintering in air at 700?°C, was...     

Ionic Assembly,Anion–π, Magnetic,and Electronic Attributes of Ambient Stable Naphthalenediimide Radical Ions

Organic spin-based molecular materials are considered to be attractive for the generation of functional materials with emergent optoelectronic, magnetic, or magneto-conductive properties. However, the major limitations to the utilization of organic spin-based systems are their high reactivity, instability, and propensity for dimerization. Herein, we report the synthesis, characterization, and magnetic and electronic studies of three ambient stable radical ions ( 1 a^.+ , 1 b^.+ , and 1 c^.+ ). The radical ions 1 b^.+ and 1 c^.+ with BPh₄⁻ and BF₄⁻ counter anions, respectively, were synthesized in excellent yields by means of anion metathesis of 1 a^.+ with Br⁻ as its counter anion. Notably, synthesis of 1 a^.+ was achieved in an ecofriendly, solvent-free protocol. The radical ions were characterized by means of single-crystal X-ray diffraction studies, which revealed the discrete nature of the radical ions and extensive hydrogen-bonding interactions within the radical ions and with the counter anions. Thus, radical ions can be organized to form infinite supramolecular arrays using weak noncovalent interactions. In addition, the Br⁻, BF₄⁻, and BPh₄⁻ anions formed diverse types of anion–π interactions with the naphthalene and imide rings of the radical ions. The radical ions were characterized by means of X-band electron paramagnetic resonance (EPR) spectroscopy in solution and in the solid state. Magnetic studies revealed their paramagnetic nature in the range of 10 to 300 K. The radical ions exhibited high resistivity approaching the gigaohm (GΩ) scale. In addition, the radical ions exhibited panchromism.     

Design approach of a density-driven solar water heater system

Energy conservation continues to play a crucial role in social and economic development. With the remarkable increase in oil prices and exploring solutions for the replacement of fossil fuels, an ecofriendly energy resource has become the priority among more and more people. Keeping the intension for reducing the global warming impact and looking for alternative clean source of energy, solar energy applications such as solar thermal systems, solar water heating and cooling are becoming energy-efficient designs. One of the widely used applications of solar energy is solar water heating systems. Low-cost solar water heaters can cover the domestic needs for water in the range of 100–200 l per day. Solar water heating systems are generally more efficient and advantageous in hot areas. However, the application of solar water heating is still a challenge in winter and sub-zero conditions, having low solar irradiance. In such conditions, solar water heating system cannot produce enough energy, which drives a need for evaluating system component design and improves its performance during low ambient conditions. In this study, detailed design methods for solar water heater components are discussed for cold regions like North Dakota, USA. The type of system chosen in this study is natural circulation-based solar water heating system. The study will also compare the experimental data with previously conducted numerical analysis.

     

Electron heating by the magnetic field-aligned electron-cyclotron waves in plasmas

It is shown that resonant nonlinear interactions between the magnetic-field aligned right-hand circularly polarized electromagnetic (CPEM) electron-cyclotron waves and electrons can produce electron temperature anisotropy due to the stochastic electron heating by waves in magnetized plasmas. The present result can thus account for the simultaneous presence of CPEM waves and an anisotropic electron temperature distribution in laboratory and space magnetoplasmas.     

Anomalous reflection and excitation of surface waves in metamaterials

We consider reflection of electromagnetic waves from layered structures with various dielectric and magnetic properties, including metamaterials. Assuming periodic variations in the permittivity, we find that the reflection is in general anomalous. In particular, we note that the specular reflection vanishes and that the incident energy is totally reflected in the backward direction, when the conditions for resonant excitation of leaking surface waves are fulfilled.     

High-temperature impedance and modulus spectroscopy characterization of La/Mn modified PbTiO3 nanoceramics

Nanocrystalline samples of Pb_1−yLa_y(Ti_1−xMn_x)_(1−y/4)O₃ (PLMT) (y=0.06, x=0, 0.04, 0.07 and 0.10) were prepared by mechanical activation process (i.e., ball milling) followed by some annealing. The formation of single phase tetragonal crystal structure is confirmed by high-resolution X-ray diffraction study and by High resolution transmission electron micrographs (HRTEM), nano-scale compounds. The electrical behavior (i.e., impedance (Z) and electrical modulus (M)) of PLMT ceramics was studied by impedance spectroscopy technique in high temperature range. This study was carried out by means of the simultaneous analysis of the complex impedance (Z^?) and electrical modulus (M^*) functions in a wide frequency range (1 kHz-1 MHz). Impedance analysis has shown the grain and grain boundary contributions by an equivalent circuit model. Modulus analysis has provided vast information on charge transport processes. The simultaneous representation of the imaginary part of impedance and electric modulus (Z″, M″) vs. frequency revealed the localization of relaxation. The activation energy obtained from relaxation data may be attributed to oxygen ion vacancies.     

Ion-acoustic solitary waves in a dense pair-ion plasma containing degenerate electrons and positrons

Fully nonlinear propagation of ion-acoustic solitary waves in a collisionless dense/quantum electron–positron–ion plasma is investigated. The electrons and positrons are assumed to follow the Thomas–Fermi density distribution and the ions are described by the hydrodynamic equations. An energy balance-like equation involving a Sagdeev-type pseudo-potential is derived. Finite amplitude solutions are obtained numerically and their characteristics are discussed. The small-but finite-amplitude limit is also considered and an exact analytical solution is obtained. The present studies might be helpful to understand the excitation of nonlinear ion-acoustic solitary waves in a degenerate plasma such as in superdense white dwarfs.     

A novel confocal optical pulse stretcher for laser pulses

We present an analytical and experimental study of a novel confocal optical pulse stretcher (COPS). The simple and passive pulse stretcher consists of two concave mirrors and a scraper beam-splitter and its optical configuration ensures a perfect spatial overlapping of laser pulses at the beam-splitter. The pulse stretcher is compact and suitable for laser pulses of large divergences. The confocal optical pulse stretcher is demonstrated on a pulsed copper vapour laser to convert a 40 ns (1/e² % points) pulse into a 55 ns with reduction of peak power by a factor of 1.375 without loss of pulse energy.