Red-emitting LaOF:Eu3+ phosphors: Synthesis, structure and their Judd-Ofelt analysis for LED applications

In the present study, we have synthesized a series of La1-xEuxOF (0.01 <= x <= 0.09) phosphors by the conventional solid-state reaction route at relatively low temperature (500 degrees C) and shorter duration of 2 h. The compounds were crystallized in the rhombohedral structure with the space group R-3m (No. 166). Upon UV excitation (254 nm), the photoluminescence spectra exhibit characteristic luminescence D-5(0) -> F-7(J) (J= 1, 2, 3, and 4) intra-4f shell Eu3+ ion transitions. An intense red emission peak at 610 nm was observed due to electric dipole (D-5(0) -> F-7(2)) transition. Judd-Ofelt theory was employed to evaluate various radiative parameters such as radiative emission rates, lifetime, branching and asymmetry ratios. CIE color coordinates confirmed the red emission of the phosphors. The luminescent results reveal that LaOF:Eu3+ phosphor can be used as potential candidate for developing red component in white LED applications. (C) 2015 Elsevier Ltd. All rights reserved.

Small-Signal Stability Analysis of an Open-Loop Induction Motor Drive Including the Effect of Inverter Deadtime

This paper demonstrates light-load instability in a 100-kW open-loop induction motor drive on account of inverter deadtime. An improved small-signal model of an inverter-fed induction motor is proposed. This improved model is derived by linearizing the nonlinear dynamic equations of the motor, which include the inverter deadtime effect. Stability analysis is carried out on the 100-kW415-V three-phase induction motor considering no load. The analysis brings out the region of instability of this motor drive on the voltage versus frequency (V-f) plane. This region of light-load instability is found to expand with increase in inverter deadtime. Subharmonic oscillations of significant amplitude are observed in the steady-state simulated and measured current waveforms, at numerous operating points in the unstable region predicted, confirming the validity of the stability analysis. Furthermore, simulation and experimental results demonstrate that the proposed model is more accurate than an existing small-signal model in predicting the region of instability.

InN Quantum Dot Based Infra-Red Photodetectors

Self-assembled InN quantum dots (QDs) were grown on Si(111) substrate using plasma assisted molecular beam epitaxy (PA-MBE). Single-crystalline wurtzite structure of InN QDs was confirmed by X-ray diffraction. The dot densities were varied by varying the indium flux. Variation of dot density was confirmed by FESEM images. Interdigitated electrodes were fabricated using standard lithography steps to form metal-semiconductor-metal (MSM) photodetector devices. The devices show strong infrared response. It was found that the samples with higher density of InN QDs showed lower dark current and higher photo current. An explanation was provided for the observations and the experimental results were validated using Silvaco Atlas device simulator.

Mitochondria-Targeting Iron(III) Catecholates for Photoactivated Anticancer Activity under Red Light

Iron(III) catecholates Fe(R-bpa)(R-dopa)Cl] (1, 2) with a triphenylphosphonium (TPP) moiety, where R-bpa is 2-(TPP-N,N-bis((pyridin-2-yl)methyl)ethanamine) chloride (TPPbpa) and R-dopa is 4-{2-(anthracen-9-yl)methylamino]ethyl}benzene-1,2-diol (andopa, 1) or 4-{2-(pyren-1-yl)-methylamino]ethyl}benzene-1,2-diol (pydopa, 2), were synthesized and their photocytotoxicity studied. Complexes 3 and 4 with phenyl-N,N-bis(pyridin-2-yl)methyl]methanamine (phbpa) were used as controls. The catecholate complexes showed an absorption band near 720 nm. The 5e(-) paramagnetic complexes showed a Fe-III/Fe-II irreversible response near -0.45 V and a quasi-reversible catechol/semiquinone couple near 0.5 V versus saturated calomel electrode (SCE) in DMF/0.1 M tetrabutylammonium perchlorate. They showed photocytotoxicity in red/visible light in HeLa, HaCaT, MCF-7, and A549 cells. Complexes 1 and 2 displayed mitochondrial localization, reactive oxygen species (ROS) generation under red light, and apoptotic cell death. Control complexes 3 and 4 exhibited uniform distribution throughout the cell. The complexes showed DNA photocleavage under red light (785 nm), forming hydroxyl radicals as the ROS.

Raman and infra-red microspectroscopy: towards quantitative evaluation for clinical research by ratiometric analysis

Biomolecular structure elucidation is one of the major techniques for studying the basic processes of life. These processes get modulated, hindered or altered due to various causes like diseases, which is why biomolecular analysis and imaging play an important role in diagnosis, treatment prognosis and monitoring. Vibrational spectroscopy (IR and Raman), which is a molecular bond specific technique, can assist the researcher in chemical structure interpretation. Based on the combination with microscopy, vibrational microspectroscopy is currently emerging as an important tool for biomedical research, with a spatial resolution at the cellular and sub-cellular level. These techniques offer various advantages, enabling label-free, biomolecular fingerprinting in the native state. However, the complexity involved in deciphering the required information from a spectrum hampered their entry into the clinic. Today with the advent of automated algorithms, vibrational microspectroscopy excels in the field of spectropathology. However, researchers should be aware of how quantification based on absolute band intensities may be affected by instrumental parameters, sample thickness, water content, substrate backgrounds and other possible artefacts. In this review these practical issues and their effects on the quantification of biomolecules will be discussed in detail. In many cases ratiometric analysis can help to circumvent these problems and enable the quantitative study of biological samples, including ratiometric imaging in 1D, 2D and 3D. We provide an extensive overview from the recent scientific literature on IR and Raman band ratios used for studying biological systems and for disease diagnosis and treatment prognosis.

A NOTE ON SMALL GAPS BETWEEN NONZERO FOURIER COEFFICIENTS OF CUSP FORMS

It is shown that there are infinitely many primitive cusp forms f of weight 2 with the property that for all X large enough, every interval (X, X + cX(1/4)), where c > 0 depends only on the form, contains an integer n such that the n-th Fourier coefficient of f is nonzero.

Multiple oligomeric structures of a bacterial small heat shock protein

Small heat shock proteins are ubiquitous molecular chaperones that form the first line of defence against the detrimental effects of cellular stress. Under conditions of stress they undergo drastic conformational rearrangements in order to bind to misfolded substrate proteins and prevent cellular protein aggregation. Owing to the dynamic nature of small heat shock protein oligomers, elucidating the structural basis of chaperone action and oligomerization still remains a challenge. In order to understand the organization of sHSP oligomers, we have determined crystal structures of a small heat shock protein from Salmonella typhimurium in a dimeric form and two higher oligomeric forms: an 18-mer and a 24-mer. Though the core dimer structure is conserved in all the forms, structural heterogeneity arises due to variation in the terminal regions.

A micromechanical damage theory for brittle materials with small cracks

For brittle solids containing numerous small cracks, a micromechanical damage theory is presented which accounts for the interactions between different small cracks and the effect of the boundary of a finite solid, and includes growth of the pre-existing small cracks. The analysis is based on a superposition scheme and series expansions of the complex potentials. The small crack evolution process is simulated through the use of fracture mechanics incorporating appropriate failure criteria. The stress-strain relations are obtained from the micromechanics analysis. Typical examples are given to illustrate the potential capability of the proposed theory. These results show that the present method provides a direct and efficient approach to deal with brittle finite solids containing multiple small cracks. The stress-strain relation curves are evaluated for a rectangular plate containing small cracks.

Effect of liquid bridge volume on the instability in small-Prandtl-number half zones

A perturbation method is used to examine the linear instability of thermocapillary convection in a liquid bridge of floating half-zone filled with a small Prandtl number fluid. The influence of liquid bridge volume on critical Marangoni number and flow features is analyzed. The neutral modes show that the instability is mainly caused by the bulk flow that is driven by the nonuniform thermocapillary forces acting on the free surface. The hydrodynamic instability is dominant in the case of small Prandtl number fluid and the first instability mode is a stationary bifurcation. The azimuthal wave number for the most dangerous mode depends on the liquid bridge volume, and is not always two as in the case of a cylindrical liquid bridge with aspect ratio near 0.6. Its value may be equal to unity when the liquid bridge is relatively slender.

Flow Characteristics of Non-Polar Organic Liquids with Small Molecules in a Microchannel

用去离子水及有机液体在内径约为25μm的石英圆管内进行了流量特性实验.液体分子量范围为18～160,动力黏性系数的范围为0.5～1 mPa.s.实验雷诺数范围为Re<8.所用有机液体为:四氯化碳、乙基苯及环己烷都是非极性液体,其分子结构尺度小于1 nm.实验结果表明,在定常层流条件下,圆管内的液体流量与两端压力差成正比,其压力-流量关系仍符合经典的Hagen-Poiseuille流动.这说明非极性小分子有机液体在本实验所用微米尺度管道中其流动规律仍符合连续介质假设.鉴于微尺度流动实验的特殊性,文中还介绍了微流动实验装置,分析了微尺度流动测量误差来源及提高测量精度的措施.

Fine scale structures from deformation of aluminium containing small alumina particles

Microstructures and mechanical properties have been studied in aluminium containing a fine dispersion of alumina particles, deformed by cold-rolling to strains between 1.4 and 3.5. The microstructure was characterised by TEM. The deformation structures evolved very rapidly, forming a nanostructured material, with fine subgrains about 0.2 μm in diameter and a fraction of high-angle boundaries which was already high at a strain of 1.4, but continued to increase with rolling strain. The yield stress and ductility of the rolled materials were measured in tension, and properties were similar for all materials. Yield stress measurements were correlated with estimates made using microstructural models. The role of small particles in forming and stabilising the deformation structure is discussed. This nanostructured cold-deformed alloy has mechanical properties which are usefully enhanced at comparatively low cost. This gives it, and similar particle-strengthened alloys, good potential for commercial exploitation. © 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.

Squeeze-film Effects in MEMS Devices with Perforated Plates for Small Amplitude Vibration

Squeeze-film effects of perforated plates for small amplitude vibration are analyzed through modified Reynolds equation (MRE). The analytical analysis reckons in most important influential factors: compressibility of the air, border effects, and the resistance caused by vertical air flow passing through perforated holes. It is found that consideration of air compressibility is necessary for high operating frequency and small ratio of the plate width to the attenuation length. The analytical results presented in this paper agree with ANSYS simulation results better than that under the air incompressibility assumption. The analytical analysis can be used to estimate the squeeze-film effects causing damping and stiffness added to the system. Since the value of Reynolds number involved in this paper is low (< 1), inertial effects are neglected.