Crystals with the warwickite structure

The crystal structure of the mineral warwickite was established in 1950; its chemical composition is based upon very old analyses and is not readily reconciled with the equipoints of the space group. On the basis of powder photographs, Bertaut assigned to this structure certain transition-metal borates whose compositions he represented as B₂O₃ · Fe₂O₃ · 2M₂O, where M is Mg, Fe², Co, or Ni, and also a warwickite-like composition B₂O₃ · TiO₂ · 3MgO, whose composition is also not readily reconciled with the equipoints. The present authors have determined and refined the structure of B₂O₃ · Fe₂O₃ · 2CoO and found that it indeed has the warwickite structure, and propose that its composition is best represented as an iron cobalt oxyborate FeCoO(BO₃). It is shown that Harris and Yackel's Y₂BeO₄ also has a warwickite-like structure, although the authors did not recognize this, probably because they used a different orientation of the space group and a different origin for their structure determination. The composition is better represented as a coupled-substitution isotype of Fe³Co²O(BO₃), specifically Y³(1)Y³(2)O(BeO₃). It is possible that coupled substitutions may extend the warwickite structure from oxyberyllonates and oxyborates to oxycarbonates and even oxynitrates. Of all the possibilities, the two well-worked-out structures are characterized by oxygen atoms on which the electrostatic valence sums are minimums.     

Solving Fredholm integrals of the first kind with tensor productstructure in 2 and 2.5 dimensions

We present an efficient algorithm to solve a class of two- and 2.5-dimensional (2-D and 2.5-D) Fredholm integrals of the first kind with a tensor product structure and nonnegativity constraint on the estimated parameters of interest in an optimization framework. A zeroth-order regularization functional is used to incorporate a priori information about the smoothness of the parameters into the problem formulation. We adapt the Butler-Reeds-Dawson (1981) algorithm to solve this optimization problem in three steps. In the first step, the data are compressed using singular value decomposition (SVD) of the kernels. The tensor-product structure of the kernel is exploited so that the compressed data is typically a thousand fold smaller than the original data. This size reduction is crucial for fast optimization. In the second step, the constrained optimization problem is transformed to an unconstrained optimization problem in the compressed data space. In the third step, a suboptimal value of the smoothing parameter is chosen by the BRD method. Steps 2 and 3 are iterated until convergence of the algorithm. We demonstrate the performance of the algorithm on simulated data     

Mg 2+-doped GaN nanoparticles as blue-light emitters: a method to avoid sintering at high temperatures

Bright blue-light emission at 410 nm is observed from Mg(2+)-doped GaN nanoparticles prepared by the nitridation of Ga(2)MgO(4) nanoparticles at 950 degrees C. The sintering of these nanoparticles during high-temperature nitridation was prevented by mixing the Ga(2)MgO(4) precursor nanoparticles with La(2)O(3) as an inert matrix before the nitridation process. The Mg(2+)-doped GaN nanoparticles were isolated from the matrix by etching with 10 % nitric acid. The Mg(2+)-doped GaN nanoparticles were characterized by photoluminescence, atomic force microscopy, X-ray diffraction, and IR analyses.     

Synthesis of crystalline and amorphous,particle-agglomerated 3-D nanostructures of Al and Si oxides by femtosecond laser and the prediction of these particle sizes

We report a single step technique of synthesizing particle-agglomerated, amorphous 3-D nanostructures of Al and Si oxides on powder-fused aluminosilicate ceramic plates and a simple novel method of wafer-foil ablation to fabricate crystalline nanostructures of Al and Si oxides at ambient conditions. We also propose a particle size prediction mechanism to regulate the size of vapor-condensed agglomerated nanoparticles in these structures. Size characterization studies performed on the agglomerated nanoparticles of fabricated 3-D structures showed that the size distributions vary with the fluence-to-threshold ratio. The variation in laser parameters leads to varying plume temperature, pressure, amount of supersaturation, nucleation rate, and the growth rate of particles in the plume. The novel wafer-foil ablation technique could promote the possibilities of fabricating oxide nanostructures with varying Al/Si ratio, and the crystallinity of these structures enhances possible applications. The fabricated nanostructures of Al and Si oxides could have great potentials to be used in the fabrication of low power-consuming complementary metal-oxide-semiconductor circuits and in Mn catalysts to enhance the efficiency of oxidation on ethylbenzene to acetophenone in the super-critical carbon dioxide.     

Two dimensional N-doped ZnO-graphitic carbon nitride nanosheets heterojunctions with enhanced photocatalytic hydrogen evolution

The effective separation of photogenerated charge carriers, their transport and interfacial contact is of great significance for excellent performance of semiconductor based photocatalysts. Herein, we report the fabrication of two dimensional (2D) nanosheets heterojunction comprising of N-doped ZnO nanosheets loaded over graphitic carbon nitride (g-C₃N₄) nanosheets for enhanced photocatalytic hydrogen evolution. The prepared 2D-2D heterojunctions with varying amount of g-C₃N₄ nanosheets have been characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS) techniques. The optimized heterojunction photocatalyst with 30 wt% of g-C₃N₄ nanosheets (NZCN30) exhibit hydrogen evolution rate of 18836 μmol h^?1 g_cat^?1 in presence of Na₂S and Na₂SO₃ as sacrificial agents under simulated solar light irradiation. The enhanced photocatalytic performance of NZCN30 heterojunction has been supported well by photoluminescence and photoelectrochemical investigations, which shows the minimum recombination rate and high photoinduced current density, respectively. In addition, the existence of 2D-2D interfacial contact plays a major role in enhanced H₂ evolution by high face-to-face contact surface area for separation of photogenerated charge carriers in space which facilitate their transfer for H₂ generation. This work paves way for the development of 2D-2D heterojunctions for diverse applications.     

Localized Aggregation of Diverse Energy Sources for Rural Electrification Using Microgrids

Extension of electrical service to large rural populations in developing nations is a key requirement to realize human development goals set forth by international agencies. This paper presents the case for distributed generation in the form of microgrids, which should be the preferred path towards rural electrification in developing communities and a vital complement to expensive centralized grid expansion. The technical features of frequency and voltage control for distributed generation devices in a microgrid are discussed along with a presentation of their stability attributes. Computer simulation results and experimental results from a laboratory scale microgrid are also presented.     

Optimal replacement time of an equipment via simulation for truncated failure distributions

The optimal replacement time T^* of an equipment for different failure (truncated) distributions is obtained by Monte Carlo simulation and the results verified by analytical methods, whenever possible. The results are illustrated by explicit numerical solutions (wherever feasible) and by simulation runs in all cases.     

Detecting the Origin of Cancer‐Mobile Quantum Probe for Single Cancer Stem Cell Detection

Cancer stem cells (CSC) are believed to be the driving force of cancer metastases and are a rare population of self‐renewing cells that contribute majorly to the poor outcomes of cancer therapy. The detection of CSC is of utmost importance to shed light on the indestructible nature of certain solid tumors and their metastatic ability. However, tumors tend to harbor CSCs in a specialized niche, making the detection process difficult. Currently, there is no method available to detect CSCs. The significance of this work is twofold. First, to the best of the knowledge, it is the first time that the detection of CSC is demonstrated. This approach simultaneously detects both the phenotypic and the metabolic state of the cell, thus enabling universal detection of CSC with high accuracy. Second, to the best of the knowledge, for the first time, light is shed on cell chemistry of CSC in their dedicated niche to facilitate a better understanding of the key players involved in the metabolic rewiring of CSC. This work will enable a better understanding of the fundamentals of CSCs, which are critical for the early diagnosis of cancer and the development of therapies for the cure of cancer.