22264 research outputs found
Sort by
Network of vertically c-oriented prismatic InN nanowalls grown on c-GaN/sapphire template by chemical vapor deposition technique
No full textNetworks of vertically c-oriented prism shaped InN nanowalls, are grown on c-GaN/sapphire templates using a CVD technique, where pure indium and ammonia are used as metal and nitrogen precursors. A systematic study of the growth, structural and electronic properties of these samples shows a preferential growth of the islands along [11 (2) over bar0] and [0 0 0 1] directions leading to the formation of such a network structure, where the vertically [0 0 0 1] oriented tapered walls are laterally align along one of the three [11 (2) over bar0]directions. Inclined facets of these walls are identified as semipolar [11 (2) over bar2]-planes of wurtzite InN. Onset of absorption for these samples is observed to be higher than the band gap of InN suggesting a high background carrier concentration in this material. Study of the valence band edge through XPS indicates the formation of positive depletion regions below the surface of the side facets [(1122)-planes] of the walls. This is in contrast with the observation for c-plane InN epilayers, where electron accumulation is often reported below the top surface. (C) 2018 Elsevier B.V. All rights reserved
Complex-Fluid Approach for Determining Rheological Characteristics of Fine-Grained Soils and Clay Minerals
No full textSoft and semisolid states of fine-grained soils and clay minerals (FGS-CMs) are frequently dealt with during execution of infrastructure projects located in the coastal areas, analysis of natural hazards, and mineral processing. In most of these cases, the FGS-CMs flow like a slurry, and hence determination of their rheological characteristics becomes essential. However, test methods and approaches available for determining the rheological behavior of the FGS-CMs when they transform from the solid to the liquid state are yet to evolve. This study uses a parallel-plate rheometer, which is widely used for rheological characterization of complex fluids (i.e., fluids which exhibit yield stress), to determine the rheological parameters (i.e.,yield stress, T-y, and strains) of the FGS-CMs with a consistency near the liquid limit. A critical analysis of the existing protocols that are used to determine T-y and their applicability to FGS-CMs is conducted. The constant shear-rate (CSR) test, when conducted at low shear-rate, yields the most accurate T-y of FGS-CMs. Subsequently, the results are used to develop a generalized relationship which explains the variation of the T-y of the FGS-CM with the consistency represented as water content normalized with respect to the liquid limit. Furthermore, to understand the nature of strains that develop during the preyielding regime of FGS-CMs, creep-relaxation (CR) tests are conducted by imposing stress equivalent to different fractions of T-y. The results from CR tests were utilized in the development of a novel methodology to determine the elastic component of the shear modulus, G(E), of FGS-CMs. This study reveals that FGS-CMs behave as a linear elastoplastic material in the preyield stage, contrary to the much expected purely elastic response, providing a new insight in the realm of contemporary geomechanics. (C) 2018 American Society of Civil Engineers
A Chiral Bipyrimidine-Bridged Dy-2 SMM: A Comparative Experimental and Theoretical Study of the Correlation Between the Distortion o f the DyO6N2 Coordination Sphere and the Anisotropy Barrier
No full textChiral bipyrimidine-bridged dinuclear Ln(III) complexes of general formula [(mu-bipym){((+)-tfacam)(3)Ln}(2)] and [(mu-bipym){((-)-tfacam)(3)Ln}(2)], have been prepared from the assembly of Ln(AcO)(3)center dot nH(2)O (Ln(III) = Dy, Gd), (+)/(-)-3-(trifluoroacetyl)camphor enantiopure ligands ((+)/(-)-Htfacam) and bipyrimidine (bipym). The structure and chirality of these complexes have been supported by single-crystal X-Ray diffraction and circular dichroism. The study of the magnetic properties of the Gd-III complexes revealed a very weak antiferromagnetic interaction between the Gd-III ions through the bipyrimidine bridging ligand. Ab initio CASSCF calculations indicated that the ground Kramers doublet (KD) of both Dy-III centers is almost purely axial with the anisotropy axis located close to the two tfacam ligands at opposite sides of each Dy-III atom, which create an axial crystal field. In keeping with this, ac dynamic measurements indicated slow relaxation of the magnetization at zero field with U-eff = 55.1 K, a pre-exponential factor of tau(o) = 2.17.10(-6) s and tau(QTM) = 8 mu s. When an optimal dc field of 0.1 T is applied, QTM is quenched and U-eff increases to 75.9 K with tau(o) = 6.16 x 10(-7) s. The DyN2O8 coordination spheres and SMM properties of [(mu-bipym){((+)-tfacam)(3)Ln}(2)] and their achiral [(Dy(beta-diketonate)(3))(2)(mu-bpym)]analogous have been compared and a magneto-structural correlation has been established, which has been supported by theoretical calculations. In contrast to the Gd-III compounds, the magnetic exchange interaction between the Dy-III ions has been calculated to be very weak and, generally, ferromagnetic in nature. Relaxation mechanisms for [(mu-bipym){((+)-tfacam)(3)Ln}(2)] and previously reported analogous have been proposed from ab initio calculations. As the magnetic exchange interaction found to be very weak, the observed magnetization blockade in these systems are primarily dictated by the single ion anisotropy of Dy-III ions
A complete characterization of determinantal quadratic polynomials
No full textThe problem of expressing a multivariate polynomial as the determinant of a monic (definite) symmetric or Hermitian linear matrix polynomial (LMP) has drawn a huge amount of attention due to its connection with optimization problems. In this paper we provide a necessary and sufficient condition for the existence of monic Hermitian determinantal representation as well as monic symmetric determinantal representation of size 2 for a given quadratic polynomial. Further we propose a method to construct such a monic determinantal representation (MDR) of size 2 if it exists. It is known that a quadratic polynomial f (x) = x(T) Ax b(T) x + 1 has a symmetric MDR of size n 1 if A is negative semidefinite. We prove that if a quadratic polynomial f (x) with A which is not negative semidefinite has an MDR of size greater than 2, then it has an MDR of size 2 too. Finally, we characterize all quadratic polynomials that exhibit MDRs of any size. (C) 2017 Elsevier Inc. All rights reserved
Liquid interfaces with pH-switchable nanoparticle arrays
No full textStimuli-responsive 2D nanoscale systems offer intriguing opportunities for creating switchable interfaces. At liquid interfaces, such systems can provide control over interfacial energies, surface structure, and rheological and transport characteristics, which is relevant, for example, to bio- and chemical reactors, microfluidic devices, and soft robotics. Here, we explore the formation of a pH-responsive membrane formed from gold nanoparticles grafted with DNA (DNA-NPs) at a liquid-vapor interface. A DNA-NP 2D hexagonal lattice can be reversibly switched by pH modulation between an expanded state of non-connected nanoparticles at neutral pH and a contracted state of linked nanoparticles at acidic pH due to the AH(+)-H(+)A base pairing between A-motifs. Our in situ surface X-ray scattering studies reveal that the reversible lattice contraction can be tuned by the length of pH-activated linkers, with up to approximate to 71% change in surface area
Model-Based Six-Component Scattering Matrix Power Decomposition
No full textFully polarimetric model-based decompositions are developed by accounting for the physical scattering model and experimental polarimetric SAR data acquisition processes. These decompositions offer the promising straightforward interpretation and highly improved inversion models for visualizing images of scattering scenarios optimally. However, the attempts in existing decompositions to implement the split real and imaginary components of the T-13 element of the coherency matrix have been hampered by the absence of physical models to fit the coherency matrix. In this paper, two additional physical scattering submodels are derived. The real and imaginary parts of T-13 are accounted for by implementing two newly developed physical scattering models. (One is for oriented dipole scattering and the other is for oriented quarter-wave reflection.) Furthermore, this paper is extended by implementing these physical models into a six-component scattering power model-based decomposition. To this date, the developed novel decompositions account for the maximum elements of the coherency matrix in a physical manner compared to the existing model-based decompositions. The proposed novel decomposition is tested on L-band and X-band fully polarimetric SAR data sets of the Advanced Land Observing Satellite-2/Phased Array L-band Synthetic Aperture Radar-2 and the X-band TerraSAR-X, respectively. This new decomposition produces additional two scattering submatrix components. Such scattering components are prevalent in vegetation and urban areas and even dominant over highly oriented urban scenarios. The new method enhances the truly existing double-bounce scattering contributions and reduces the overrated volume scattering from double-bounce scatterers. By comparing the results, it is found that the proposed decomposition considerably enhances the SAR image quality and its more correct visualizing presentation compared to existing decompositions. It is also found to be more robust over the oriented urban areas than the existing decompositions, resulting from the utilization of both the real and imaginary components of T-13 polarimetric information in a physical scattering manner
A new approach to control and optimize the laser surface heat treatment of materials
No full textLaser heating is often used to perform the surface treatment by modifying local microstructural and mechanical properties of components having complex geometries. In this study, the laser surface heat treatment of a rotating cylindrical work-piece was investigated using both experimental and numerical modeling approaches, with an aim to correlate and predict the temperature distribution during the process. The depth of the laser affected zone was predicted by solving the transient heat transfer with a moving laser heat source, using finite element analysis. The temperatures derived from the microstructural examination of the experimental specimen were found to closely agree with the predicted results from the numerical simulations. The numerical and experimental results have also led to a new observation, indicating a linear variation of the absorptivity with the laser scan speed. The prediction of the cooling curves from simulation suggested the beta -> alpha '' phase transformation and the recovery of the 3 phase, and the existence of new phases were confirmed through electron microscopy. The rapid cooling during the laser surface treatment was found to induce a flake-structure that consisted of both martensite (alpha '') and regained bcc (beta) phase. A new polynomial input power function has been proposed to achieve uniform distribution of the heat penetration along the cylinder axis, saving about 10% of the material wastage
Friction Stir Welding (FSW) of Aged CuCrZr Alloy Plates
No full textFriction Stir Welding (FSW) of Cu-0.80Cr-0.10Zr (in wt pct) alloy under aged condition was performed to study the effects of process parameters on microstructure and properties of the joint. FSW was performed over a wide range of process parameters, like tool-rotation speed (from 800 to 1200 rpm) and tool-travel speed (from 40 to 100 mm/min), and the resulting thermal cycles were recorded on both sides (advancing and retreating) of the joint. The joints were characterized for their microstructure and tensile properties. The welding process resulted in a sound and defect-free weld joint, over the entire range of the process parameters used in this study. Microstructure of the stir zone showed fine and equiaxed grains, the scale of which varied with FSW process parameters. Grain size in the stir zone showed direct correlation with tool rotation and inverse correlation with tool-travel speed. Tensile strength of the weld joints was ranging from 225 to 260 MPa, which is substantially lower than that of the parent metal under aged condition (similar to 400 MPa), but superior to that of the parent material under annealed condition (similar to 220 MPa). Lower strength of the FSW joint than that of the parent material under aged condition can be attributed to dissolution of the precipitates in the stir zone and TMAZ. These results are presented and discussed in this paper. (C) The Minerals, Metals & Materials Society and ASM International 201
Total and differential cross sections of eta-production in proton-deuteron fusion for excess energies between Q(eta)=13 MeV and Q(eta)=81 MeV
No full textNew data on both total and differential cross sections of the production of eta mesons in proton-deuteron fusion to He-3 eta in the excess energy region 13.6 MeV <= Q(eta) <= 80.9 MeV are presented. These data have been obtained with the WASA-at-COSY detector setup located at the Forschungszentrum Julich, using a proton beam at 15 different beam momenta between p(p) = 1.60 GeV/c and p(p) = 1.74 GeV/c. While significant structure of the total cross section is observed in the energy region 20 MeV less than or similar to Q(eta) less than or similar to 60 MeV, a previously reported sharp variation around Q(eta) approximate to 50 MeV cannot be confirmed. Angular distributions show the typical forward- peaking that was noted earlier. For the first time, it is possible to study the development of these angular distributions with rising excess energy over a wide interval. (c) 2018 The Author. Published by Elsevier B.V
Wind Effect Modeling and Analysis for Estimation of Photovoltaic Module Temperature
No full textThe performance of photovoltaic (PV) modules in outdoor field conditions is adversely affected by the rise in module operating temperature. Wind flow around the module affects its temperature significantly, which ultimately influences the module output power. In this paper, a new approach has been presented, for module temperature estimation of different technology PV modules (amorphous Si, hetero-junction with intrinsic thin-layer (HIT) and multicrystalline Si) installed at the site of National Institute of Solar Energy (NISE), India. The model based on presented approach incorporates the effect of wind speed along with wind direction, while considering in-plane irradiance, ambient temperature, and the module efficiency parameters. For all the technology modules, results have been analyzed qualitatively and quantitatively under different wind situations. Qualitative analysis based on the trend of module temperature variation under different wind speed and wind direction along with irradiance and ambient temperature has been presented in detail from experimental data. Quantitative results obtained from presented model showed good agreement with the experimentally measured data for different technology modules. The model based on presented approach showed marked improvement in results with high consistency, in comparison with other models analyzed for different technology modules installed at the site. The improvement was very significant in case of multicrystalline Si technology modules, which is most commonly used and highly temperature sensitive technology. Presented work can be used for estimating the effect of wind on different technology PV modules and for prediction of module temperature, which affects the performance and reliability of PV modules