Band gap engineering in huge-gap semiconductor SrZrO3 for visible-light photocatalysis

Using SrZrO₃ (SZO, the intrinsic band gap being 5.6 eV) as an example, we have investigated the design principles for huge-gap semiconductors with band gap larger than 5 eV for the application of efficient visible-light driven photocatalysts for splitting water into hydrogen. Based on the hybrid density function calculations, the electronic structures of mono-doped and co-doped SZO are investigated to obtain design principles for improving their photocatalytic activity in hydrogen generation. The cationic–anionic co-doping in SZO could reduce the band gap significantly and its electronic band position is excellent for the visible-light photocatalysis. This work reports a new type of candidate material for visible-light driven photocatalysis, i.e., huge-gap semiconductors with band gap larger than 5 eV. Furthermore, based on the present results we have proposed the design principles for band gap engineering that provides general guideline for other huge-gap semiconductors.     

Second-order numerator-dynamics systems: Effects of initial discontinuities

Linear second-order systems with numerator-dynamics are considered and their transient responses are investigated for discontinuous inputs. Characteristic parameters for second-order systems with numerator dynamics are identified. The solution profiles of these systems depend upon the value of one such parameter relative to that of the others on the number line. Effects of initial jump discontinuities of the inputs on the correctness of the solutions are also treated. A methodology for analysis of discontinuities is presented. Initial discontinuities of the calculated response either get accounted for in the input function or the initial condition of the input function for all but the following case. For the impulse response alone, that too among inherent numerator-dynamics systems only, an initial di scontinuity cannot be accounted for in the input. The value of that discontinuity is thus required for correct solutions of these cases. The results are general and extendable to different inputs and higher order systems.     

A Tensor Approximation Approach to Dimensionality Reduction

Dimensionality reduction has recently been extensively studied for computer vision applications. We present a novel multilinear algebra based approach to reduced dimensionality representation of multidimensional data, such as image ensembles, video sequences and volume data. Before reducing the dimensionality we do not convert it into a vector as is done by traditional dimensionality reduction techniques like PCA. Our approach works directly on the multidimensional form of the data (matrix in 2D and tensor in higher dimensions) to yield what we call a Datum-as-Is representation. This helps exploit spatio-temporal redundancies with less information loss than image-as-vector methods. An efficient rank-R tensor approximation algorithm is presented to approximate higher-order tensors. We show that rank-R tensor approximation using Datum-as-Is representation generalizes many existing approaches that use image-as-matrix representation, such as generalized low rank approximation of matrices (GLRAM) (Ye, Y. in Mach. Learn. 61:167–191, 2005), rank-one decomposition of matrices (RODM) (Shashua, A., Levin, A. in CVPR’01: Proceedings of the 2001 IEEE computer society conference on computer vision and pattern recognition, p. 42, 2001) and rank-one decomposition of tensors (RODT) (Wang, H., Ahuja, N. in ICPR ’04: ICPR ’04: Proceedings of the 17th international conference on pattern recognition (ICPR’04), vol. 1, pp. 44–47, 2004). Our approach yields the most compact data representation among all known image-as-matrix methods. In addition, we propose another rank-R tensor approximation algorithm based on slice projection of third-order tensors, which needs fewer iterations for convergence for the important special case of 2D image ensembles, e.g., video. We evaluated the performance of our approach vs. other approaches on a number of datasets with the following two main results. First, for a fixed compression ratio, the proposed algorithm yields the best representation of image ensembles visually as well as in the least squares sense. Second, proposed representation gives the best performance for object classification. A shorter version of this paper was published at IEEE CVPR 2005 (Wang and Ahuja 2005).     

A comparative study to evaluate the corrosion performance of Zr incorporated Cr3C2-(NiCr) coating at 900 °C

In this study zirconium incorporated Cr₃C₂-(NiCr) coating has been sprayed on three superalloys viz. Superni 718, Superni 600 and Superco 605 using D-gun technique. A comparative study has been carried out to check the cyclic oxidation in air and hot corrosion in simulated incinerator environment (40%Na₂SO₄-40%K₂SO₄-10%NaCl-10%KCl) for the coated specimens at 900 °C for 100 cycles. Oxidation kinetics has been established for all the specimens using weight change measurements. Corrosion products have been characterized using X-ray diffractometer (XRD) and scanning electron microscopy/energy-dispersive analysis (SEM/EDAX). Cr₃C₂-(NiCr) + 0.2%wtZr coating provides very good corrosion resistance in air oxidation for all the three coated superalloys. As all the three coated superalloys shows parabolic behaviour with parabolic rate constant as 0.07 × 10^?10 (g² cm^?4 s^?1) for Superni 718, 0.43 × 10^?10 (g² cm^?4 s^?1) for Superni 600 and 0.3 × 10^?10 (g² cm^?4 s^?1) for Superco 605 This coating is also effective in the molten salt environment but coating on Co-based superalloy Superco 605 did not perform satisfactorily. The parabolic rate constants for coated Superni 718 is 0.61 × 10^?10 (g² cm^?4 s^?1), for coated Superni 600 is 6.72 × 10^?10 (g² cm^?4 s^?1) and for coated Superco 605 is 17.5 × 10^?10 (g² cm^?4 s^?1).     

Lithium storage in amorphous TiNi hydride: Electrode for rechargeable lithium-ion batteries

In this study, amorphous TiNi phase was successfully prepared using mechanically milling for a very short time of 8 h. HRTEM confirms the formation of amorphous phase with the presence of nanocrystalline Fe particles. After hydrogenation (30 bars of H₂ for a duration of 2 h), the electrochemical reaction shows that TiNi hydride/Li cell discharges at a current of one Li for 10 h between 3 V and 0.005 V. The discharge of TiNiH electrode around x = 1 Li corresponds to a capacity of 251 mAh g⁻¹ and a hydride composition of TiNiH_1.0 at an average voltage of 0.4 V. Ex-situ X-ray diffraction pattern collected at the end of the discharge shows a mixture of amorphous TiNi compound and LiH. A general mechanism for the electrochemical reaction is then proposed: α-TiNiH + Li⁺ + e⁻ → α-TiNi + LiH. The results from DFT calculations yield an average cell voltage of 0.396 V, which is in good agreement with the experimental pseudo-plateau occurring at 0.4 V.     

Electronic properties of WC nano-compound: Compton spectroscopy and band structure calculations

We present the electronic properties of tungsten carbide (WC) nano-compound using the Compton scattering technique. We have measured the Compton profile (CP) of nano-powder using our ¹³⁷Cs Compton spectrometer. To determine the theoretical CPs of WC nano-compound, we have employed linear combination of atomic orbitals (LCAO) with Hartree-Fock and density functional theory. Although all the LCAO-based calculations show similar agreement with the experiment, the second-order generalised gradient approximation gives a marginally better agreement with the measured CP data. Layered structures and slight over-lapping in energy bands show a small role of exchange and correlation potentials in case of WC nano-compound, which is in contrast to bulk WC.     

Shape and View Independent Reflectance Map from Multiple Views

We consider the problem of estimating the 3D shape and reflectance properties of an object made of a single material from a set of calibrated views. To model the reflectance, we propose to use the View Independent Reflectance Map (VIRM), which is a representation of the joint effect of the diffuse+specular Bidirectional Reflectance Distribution Function (BRDF) and the environment illumination. The object shape is parameterized using a triangular mesh. We pose the estimation problem as minimizing the cost of matching input images, and the images synthesized using the shape and VIRM estimates. We show that by enforcing a constant value of VIRM as a global constraint, we can minimize the cost function by iterating between the VIRM and shape estimation. Experimental results on both synthetic and real objects show that our algorithm can recover both the 3D shape and the diffuse/specular reflectance information. Our algorithm does not require the light sources to be known or calibrated. The estimated VIRM can be used to predict the appearances of objects with the same material from novel viewpoints and under transformed illumination. The support of National Science Foundation under grant ECS 02-25523 is gratefully acknowledged. Tianli Yu was supported in part by a Beckman Institute Graduate Fellowship.     

Ferromagnetism above room temperature in bulk and transparent thin films of Mn-doped ZnO

The search for ferromagnetism above room temperature in dilute magnetic semiconductors has been intense in recent years. We report the first observations of ferromagnetism above room temperature for dilute (<4 at.%) Mn-doped ZnO. The Mn is found to carry an average magnetic moment of 0.16 mu(B) per ion. Our ab initio calculations find a valance state of Mn(2+) and that the magnetic moments are ordered ferromagnetically, consistent with the experimental findings. We have obtained room-temperature ferromagnetic ordering in bulk pellets, in transparent films 2-3 microm thick, and in the powder form of the same material. The unique feature of our sample preparation was the low-temperature processing. When standard high-temperature (T > 700 degrees C) methods were used, samples were found to exhibit clustering and were not ferromagnetic at room temperature. This capability to fabricate ferromagnetic Mn-doped ZnO semiconductors promises new spintronic devices as well as magneto-optic components.     

Risk Evaluation in Resource Allocation

Conventional resource allocation procedures implicitly assume that the availability of resources is certain. In real life situations, their availability is, at times, uncertain. A Risk Evaluation Model (REM) is proposed to systematically evaluate the uncertainty of resource availability and generate several alternatives having varying project completion time, cost, and performance probability. REM can aid a contractor in “bid∕no‐bid” decision‐making, an entrepreneur in investment decision‐making, and a consultancy organization in corporate planning.