A study about the effect of the temperature of hydrogen treatment on the properties of Ru/Al2O3 and Ru/C and their catalytic behavior during 1-heptyne semi-hydrogenation

The 1-heptyne selective hydrogenation carried out at 150 kPa, and at 283 and 303 K using Ru/Al₂O₃ and Ru/C as catalysts, was studied. Catalysts were prepared by the incipient wetness impregnation technique using RuCl₃ as precursor. Ru/Al₂O₃ was treated in hydrogen at 373 or 573 K and Ru/C only at the last temperature. Catalysts were characterized by hydrogen chemisorption, TPR and XPS. Ru dispersion after treatment in hydrogen at the highest temperature is similar for both catalysts. Ru is present as Ru⁰ in Ru/C, while Ru⁰ and Ru electron-deficient species are present on the catalysts surface after hydrogen treatment at the two temperatures using Al₂O₃ as support. The best catalytic behavior was observed for the highest temperature of hydrogen treatment and for 303 K reaction temperature. As a consequence of a shape selectivity effect of the C support, the best conversion is obtained with the alumina supported catalyst.     

Speckle removal from SAR images in the undecimated wavelet domain

Speckle reduction is approached as a minimum mean-square error (MMSE) filtering performed in the undecimated wavelet domain by means of an adaptive rescaling of the detail coefficients, whose amplitude is divided by the variance ratio of the noisy coefficient to the noise-free one. All the above quantities are analytically calculated from the speckled image, the variance and autocorrelation of the fading variable, and the wavelet filters only, without resorting to any model to describe the underlying backscatter. On the test image Lena corrupted by synthetic speckle, the proposed method outperforms Kuan's local linear MMSE filtering by almost 3-dB signal-to-noise ratio. When true synthetic aperture radar (SAR) images are concerned, empirical criteria based on distributions of multiscale local coefficient of variation, calculated in the undecimated wavelet domain, are introduced to mitigate the rescaling of coefficients in highly heterogeneous areas where the speckle does not obey a fully developed model, to avoid blurring strong textures and point targets. Experiments carried out on widespread test SAR images and on a speckled mosaic image, comprising synthetic shapes, textures, and details from optical images, demonstrate that the visual quality of the results is excellent in terms of both background smoothing and preservation of edge sharpness, textures, and point targets. The absence of decimation in the wavelet decomposition avoids typical impairments often introduced by critically subsampled wavelet-based denoising.     

Rydberg and autoionizing triplet states in Helium up to the N = 5 threshold

Energy levels of highly excited bound Rydberg states, the position and widths of autoionizing states, and oscillator strengths are calculated for He ³S, ³P^e, ³P^o, ³D^e and ³D^o symmetries up to the N = 5 He⁺ excitation threshold. The calculations are performed with the K-matrix B-spline method with maximum orbital angular momentum ?_max = 8. Reliable doubly excited-state parameters up to the n = 20 multiplet below each ionization threshold are presented. One thousand and six hundred newly identified bound and metastable states, seven times those available in literature, fill many gaps, reveal a dozen intruder states, and allow new speculations on propensity rules and radiative decays of triplet Rydberg states.     

Fast calculation of co-occurrence matrix parameters for image segmentation

Image segmentation methods based only on grey level information are not suitable for pictures in which regions exhibit almost the same average grey level and differ only for local variations or texture. By extending these methods to textural features, better results are expected. Among textural features, those extracted from co-occurrence matrices are quite effective. A fast algorithm for the calculation of these parameters for windows centred on each pixel of the image is presented.<>     

SVD-Based Techniques for Zero-Padded Block Transmission Over Fading Channels

In this paper, the performance of filter bank transceivers in the presence of a dispersive time-variant channel is investigated. It is well known that filter bank transceivers can be adapted to the channel transfer function to yield intersymbol interference (ISI) cancellation. When the channel is time variant, several problems arise, since the transceiver should be changed whenever the channel evolves. In this paper, we will allow both the transmitter and the receiver to change and satisfy the interference-free condition, under the assumption of a zero-padded block transmission. In this case, the optimum transmitter-receiver pair can be computed by using a singular value decomposition (SVD) of the channel matrix. A fast receiver adaptation based on SVD tracking is presented. Simulation results show that minimum performance loss with respect to the optimum receiver can be achieved for our reduced complexity receiver     

Design of IIR eigenfilters in the frequency domain

The eigenfilter approach is an appealing way of designing digital filters, mainly because of the simplicity of its implementation. In this correspondence, a new method of applying the eigenfilter approach to the design of infinite impulse response (IIR) filters is described. The procedure works in the frequency domain and yields the coefficients of a causal rational transfer function having an arbitrary number of poles and zeros. Some examples of filter design are given to show the effectiveness of the method presented     

Audio decoding with frequency and complexity scalability

The paper describes a technique to design a complexity-scalable audio codec based on the partial reconstruction of the spectrum of a signal. The technique can be applied to any subband coding system based on cosine-modulated filterbanks. In the decoder, only a part of the subband is reconstructed, achieving an output signal with a lower sampling rate. The new synthesis filterbank, with a reduced number of channels and low computational cost, must be suitably designed. Hence, a computational saving is traded for lower quality in the reconstructed signal. The technique can be used to design low-complexity decoders compatible with the MPEG audio standard, i.e. able to decode only a part of an MPEG bit stream. In this way, a single MPEG-coded audio can be decoded by different receivers, i.e. standard and low-complexity ones. The problem of having fixed bit rate streams for all the decoders is discussed.     

Design of IIR linear-phase QMF banks based on complex allpasssections

A new method for the design of two-channel, perfect reconstruction, analysis/synthesis QMF banks is presented. The filters of the banks are IIR, power complementary, linear phase, and are represented by means of complex allpass functions. Design procedures based both on numerical approximation and on a flatness constraint imposed on the frequency responses of the filters are given     

Obtaining silicide free spacers by optimizing sputter etch for deep submicron CMOS processes

In this paper, we have shown that the sputter etch before cobalt deposition during the silicide processing of a deep submicron CMOS device fabrication needs to be optimized in order to eliminate a detrimental origin of gate (G) to source (S)/drain (D) bridging. It is known that Co cannot reduce even a thin layer of native oxide. Therefore, it is necessary to ensure that Co is deposited on a very clean Si surface. To ensure this, an in-situ sputter etch is commonly conducted before Co deposition. It is observed that this sputter etch process can sputter Si from the S/D area and deposit them on the sidewall spacer (SWS). This sputtered Si in turn will react with deposited Co and form silicide. The worst case leakage currents from poly-Si to composite for long (10 m) and narrow (0.18 micron) poly lines are shown to be on the order of milliampere. Transmission electron microscope (TEM) micrographs included show the existence of cobalt silicide layers (/spl sim/8 nm thick) over sidewall spacer. The silicide thickness on the sidewall spacer is correlated with resistance value calculated from current and voltage (I-V) measurements. The need for optimizing the sputter etch recipe has been validated by TEM and I-V measurements.