Phase-shifting interferometry in the presence of nonlinear phase steps, harmonics, and noise

A phase-shifting piezo device commonly employed in phase-shifting interferometry exhibits a nonlinear response to applied voltage. Hence, a method for estimation of phase distribution in the presence of nonlinear phase steps is presented. The proposed method compensates for the harmonics present in the intensity fringe, allows the use of arbitrary phase-step values between 0 and tau rad, and does not impose constraints on the selection of particular phase-step values for minimizing nonlinearity and compensating for the harmonics. The comparison of the proposed method with other well-known benchmarking algorithms shows that our method is highly efficient and also works well in the presence of noise.     

Chirp estimation in phase-shifting interferometry

We propose a new approach for estimating the phase in the presence of a nonlinear response of a phase-shifting device: a piezoelectric transducer (PZT). The method is complemented well by the high resolution and the maximum likelihood estimation techniques in the estimation of the phase step and the nonlinear coefficient. The advantage of the proposed method is that it can be extended to the extraction of multiple phases in configurations involving multiple PZTs in the presence of nonlinearity. Symmetricity in the phase steps is not required in this method. Hence hysteresis of the PZT does not have any influence on the accuracy of the phase estimation. The effectiveness of the method is shown by experimental results.     

Application of integrated computer simulation approach to solid surfaces and interfaces

The atomistic understanding of the structure, reactivity, and electronic properties of solid surfaces and interfaces are essential for the design of novel catalysts and electronics/photonics devices which have high-performance and unexplored properties. Computational chemistry is expected not only to rationalize the experimental results but also to predict new features. We have applied integrated computer simulation methods including quantum chemistry, periodic density functional theory, molecular dynamics, embedded atom method, and atomic force microscopy simulation to various topics related to solid surfaces and interfaces. In the present paper, we reviewed our recent activities on supported metal catalysts, metal clusters, atomic force microscopy simulation, high-temperature superconductors, tribology, Si semiconductor and V₂O₅ catalysts. Our activities also involve the generation of a lot of new computer simulation codes. We emphasize that the integrated computer simulation system provides not only methods for scientific studies but also a key technology for industrial innovations in research and development.     

Difference Equations Approach for Multi-Server Queueing Models with Removable Servers

Methodology and Computing in Applied Probability - We consider an extended form of the MX/M/c queue with two types of server groups: Static as well as dynamic (which turn on/off in a...     

QCD phase transition in rotating neutron star,neutrino beaming and gamma-ray bursters

We have studied the emission of neutrinos from a rotating hybrid star. We find that the emission is predominantly confined to a very small angle, provided the core of the star is in a mixed phase of quarks and hadrons and the size of such a mixed phase is small. Annihilation of neutrinos to produce gamma rays has been discussed. The estimated duration of the burst is found to be within the observational range.     

Generalized linear prediction method in phase-shifting interferometry in the presence of noise

The effectiveness of phase-shifting interferometry (PSI) techniques employing piezoelectric device PZT in the estimation of phase depends largely on the accuracy with which the phase shifts are imparted to the device and the noise influencing the measurement. Several effective algorithms have been proposed to compute the phase shifts imparted to the device and subsequently obtain the phase using least-squares estimation technique. In this paper, we propose a generalized approach, which accurately estimates the phase shifts in the presence of noise. The method is based on the idea of linear prediction and explores the fact that sampling more data frames yields a reliable phase step estimate in a least-squares sense. We also compare our method with a commonly used generalized phase-shifting method based on histogram analysis and show that our proposed approach is highly effective. We also present simulation and experimental validations of our proposed method.     

Phase shifting interferometry using a robust parameter estimation method

The paper proposes a maximum-likelihood (ML) method based on spectral estimation theory for the estimation of phase distribution in interferometry in the presence of nonsinusoidal waveforms, noise, and the miscalibration of the piezoelectric device. The proposed method also allows the use of arbitrary phase steps. ML estimators are asymptotically efficient for large number of data samples. The method is complemented well by the incorporation of global search algorithm known as Probabilistic Global Search Lausanne for minimizing the ML function. The performance of the proposed method is studied in the presence of noise.     

Generalized phase-shifting interferometry by use of a direct stochastic algorithm for global search

A new phase-shifting interferometric technique that uses an unknown phase step is described in which the phase step is determined by use of an algorithm called Probabilistic Global Search Lausanne (PGSL). One of the main sources of error in phase stepping is piezoelectric device (PZT) nonlinearity. The PGSL algorithm identifies the characteristics of the response of the PZT to the applied voltage through matching predicted and measured responses. The unknown phase step is also calculated with 0.097% error. This approach overcomes the limitations of existing techniques to determine unknown phase steps. Linear regression is subsequently applied for interference phase determination.     

Copper clusters: electronic effect dominates over geometric effect

A minimal parameter tight binding molecular dynamics scheme is used to study Cu _n clusters with . We present results for relaxed configurations of different symmetries, binding energies, relative stabilities and HOMO-LUMO gap energies for these clusters. Detailed comparison for small clusters n = 3-9 with ab initio and available experimental results shows very good agreement. Even-odd alternation due to electron pairing and magic behaviour for Cu₂, Cu₈, Cu₁₈ and Cu₂₀ due to electronic shell closing are found. We found electronic effects, electronic shell closing and electron pairing in the HOMO dominates over the geometrical effect to determine the relative stability of copper clusters. The present results indicate that tight-binding molecular dynamics scheme can be relied on to provide a useful semiempirical scheme in modeling interactions in metallic systems.Received: 3 May 2004, Published online: 26 October 2004PACS: 36.40.Cg Electronic and magnetic properties of clusters - 36.40.Mr Spectroscopy and geometrical structure of clusters - 36.40.Qv Stability and fragmentation of clusters     

Model-based processing of a holographic moiré

A state space model for the determination of dual phase distributions in a holographic moiré in the presence of nonsinusoidal waveforms, random noise, and miscalibration of the piezoelectric (PZT) devices is proposed. The extraction of these phase terms requires incorporating two PZTs into the moiré setup. A Toeplitz approximation method (TAM) is applied for phase determination, and modification to the Toeplitz covariance matrix formed from the phase-shifted moiré fringes by application of a denoising step in the state-feedback matrix is proposed. This step ensures that the phase terms can even be estimated at a signal-to-noise ratio much lower than that of the original TAM or by our previously suggested polynomial based method.