Time series modeling and spectrum analysis for chatter mode in endmilling dynamics

To analyze the chatter mechanics, the power spectrum of a time series method was analyzed by considering cutting and structural dynamics. In this study, several time series models such as AR (burg, least square, yule walker, geometric lattice, instrument variable), ARX (arx, iv4), ARMAX, ARMA, Box Jenkins, Output Error were modeled and compared with one another. Finally, it was proved that arx, armax and iv4 are more desirable and reliable algorithms than the others for the calculation of the chatter mode in the endmilling operation. The cutting forces Fx and Fz have more powerful effects on the chatter than Fy in the sense that there is no shifting or pseudo mode in the power spectrum.     

Two-dimensional correlation analysis in application to a kinetic model of parallel reactions

By applying generalized two-dimensional (2D) correlation analysis as reported by Noda, we have systematically studied a kinetic model of parallel reactions. Given the related rate constants and absorption coefficients, the correlation between reactant and products are analyzed. The reactant-reactant, reactant-product, and product-product pairs are found to be synchronously correlated, and their intensities increase with increase of the rate constant and the absorption coefficient. On the other hand, only the reactant-product pairs show in the asynchronous spectra. Their intensities also depend proportionally on the rate constant and the absorption coefficient. The influence of signal-to-noise ratio (S/N) and overlapped spectra are further discussed. The resulting synchronous and asynchronous correlation spectra for the kinetic model appear to be weakly influenced by poor quality of the signal when the reference spectrum is set at zero. The ratio of asynchronous to synchronous correlation intensity yields a coherence spectrum. This spectrum remains a constant intensity for all the correlated peaks, being free from the influence of rate constant and absorption coefficient as well as being weakly disturbed by a small S/N ratio. It also provides a way to evaluate the extent of spectral overlap between two peaks. The coherence spectrum is useful to characterize the type of parallel reactions.     

Hierarchical Indexing Structure for Efficient Similarity Search in Video Retrieval

With the rapid increase in both centralized video archives and distributed WWW video resources, content-based video retrieval is gaining its importance. To support such applications efficiently, content-based video indexing must be addressed. Typically, each video is represented by a sequence of frames. Due to the high dimensionality of frame representation and the large number of frames, video indexing introduces an additional degree of complexity. In this paper, we address the problem of content-based video indexing and propose an efficient solution, called the ordered VA-file (OVA-file) based on the VA-file. OVA-file is a hierarchical structure and has two novel features: 1) partitioning the whole file into slices such that only a small number of slices are accessed and checked during k nearest neighbor (kNN) search and 2) efficient handling of insertions of new vectors into the OVA-file, such that the average distance between the new vectors and those approximations near that position is minimized. To facilitate a search, we present an efficient approximate kNN algorithm named ordered VA-LOW (OVA-LOW) based on the proposed OVA-file. OVA-LOW first chooses possible OVA-slices by ranking the distances between their corresponding centers and the query vector, and then visits all approximations in the selected OVA-slices to work out approximate kNN. The number of possible OVA-slices is controlled by a user-defined parameter delta. By adjusting delta, OVA-LOW provides a trade-off between the query cost and the result quality. Query by video clip consisting of multiple frames is also discussed. Extensive experimental studies using real video data sets were conducted and the results showed that our methods can yield a significant speed-up over an existing VA-file-based method and (distance with high query result quality. Furthermore, by incorporating temporal correlation of video content, our methods achieved much more efficient performance     

Bidirectional deformable matching with application to handwritten character extraction

To achieve integrated segmentation and recognition in complex scenes, the model-based approach has widely been accepted as a promising paradigm. However, the performance is still far from satisfactory when the target object is highly deformed and the level of outlier contamination is high. In this paper, we first describe two Bayesian frameworks, one for classifying input patterns and another for detecting target patterns in complex scenes using deformable models. Then, we show that the two frameworks are similar to the forward-reverse setting of Hausdorff matching and that their matching and discriminating properties are complementary to each other. By properly combining the two frameworks, we propose a new matching scheme called bidirectional matching. This combined approach inherits the advantages of the two Bayesian frameworks. In particular, we have obtained encouraging empirical results on shape-based pattern extraction, using a subset of the CEDAR handwriting database containing handwritten words of highly varying shape.     

Analysis and design of ribbon cables for high‐speed digital applications

Ribbon cables have been widely used as subsystem interconnections in a large number of digital systems, because they can convey numerous bits of a digital signal simultaneously. In this article, finite difference and finite difference time domain (FDTD) methods are used to analyze and optimize the electrostatic analysis design of ribbon cables, and measurements are used to verify the numerical results. © 2002 Wiley Periodicals, Inc. Int J RF and Microwave CAE 12: 148–158, 2002.     

Modeling and control for a Gough‐Stewart platform CNC machine

In this paper, a complete dynamic model on task space for a 6 degrees of freedom (DOF) Gough‐Stewart platform‐type computer numerical control (CNC) machine is derived. The rotation terms of the legs are included for those inertia effects cannot be negligible in the machine tool applications. The formulation derived by means of the Euler‐Lagrange method is convenient for designing the adaptive control law. Also, the average‐type force model for end milling process is derived and included in the dynamic model and control. A composite adaptive control scheme is developed by use of filtering dynamics technique. An appropriate estimator gain is designed in the parameter adaptation law that is useful for estimating the selected important cutting parameters. Experimental results verify the proposed adaptive control scheme can achieve good tracking performance. © 2004 Wiley Periodicals, Inc.     

Dynamics of multiple parallel boiling channel systems with forced flows

This work investigates the nonlinear dynamics of multiple parallel boiling channels with forced flows by using the Galerkin nodal approximation method. The stability maps for multiple-channel systems subject to a constant total mass flow rate are constructed on the basis of the average heat flux and mass flow rate on the parameter plane of the subcooling and phase change numbers. The limit cycle oscillations for 3-, 4- and 5-channel systems indicate that the most heated channel exhibits the largest magnitude of oscillation, and is out-of-phase with the other channels. Owing to that the boiling assembly contains only a small number of channels, the above system becomes unstable due to channel-to-channel interaction with an increase of the channel number. This work also elucidates the dynamics of a 3-channel system with a periodic total mass flow rate. In addition, complicated nonlinear oscillations are predicted for different operating points with high inlet subcooling numbers in the stable region. The system dynamics are highly sensitive to the frequency of the forcing function. Periodic, quasi-periodic and chaotic oscillations may appear in the forcing function system. Unstable oscillations appear when either the frequency of the forcing function is equal or extremely close to the system’s natural frequency or the two frequencies are frequency-locking.     

Greenhouse gases mitigation by CO<Subscript>2</Subscript> reforming of methane to hydrogen-rich syngas using praseodymium oxide supported cobalt catalyst

This study focuses on the potential of hydrogen-rich syngas production by CO₂ reforming of methane over Co/Pr₂O₃ catalyst. The Co/Pr₂O₃ catalyst was synthesized via wet-impregnation method and characterized for physicochemical properties by TGA, XRD, BET, H₂-TPR, FESEM, EDX, and FTIR. The CO₂ reforming of methane over the as-synthesized catalyst was studied in a tubular stainless steel fixed-bed reactor at feed ratio ranged 0.1–1.0, temperature ranged 923–1023 K, and gas hourly space velocity (GHSV) of 30,000 h^?1 under atmospheric pressure condition. The catalyst activity studies showed that the increase in the reaction temperature from 923 to 1023 K and feed ratio from 0.1 to 1.0 resulted in a corresponding increase in the reactant’s conversion and the product’s yields. At 1023 K and feed ratio of 1.0, the activity of the Co/Pr₂O₃ catalyst climaxed with CH₄ and CO₂ conversions of 41.49 and 42.36 %. Moreover, the catalyst activity at 1023 K and feed ratio of 1.0 resulted in the production of H₂ and CO yields of 40.7 and 40.90 %, respectively. The syngas produced was estimated to have H₂:CO ratio of 0.995, making it suitable as chemical building blocks for the production of oxygenated fuel and other value-added chemicals. The used Co/Pr₂O₃ catalyst which was characterized by TPO, XRD, and SEM-EDX show some evidence of carbon formation and deposition on its surface.     

Optically pumped submillimeter gas lasers and the prospects for constructing space-qualifiable LO systems

An optically pumped submillimeter laser operating in the 500 μm (600 GHz) to 100 μm (3 THz) spectral range is the primary and, at present, the only available local oscillator (LO) source for laboratory and astronomical heterodyne applications for this wavelength region. A short review of the state-of-the-art of submillimeter lasers as LO sources, with an emphasis given to receiver systems designed for airborne heterodyne observations, will be presented. The characteristics and prospects for constructing a spacequalifiable laser LO system will also be given.