Band Distortion Research Articles

A Neural Approach for Compensation of Effects of PAPR Causing BER Degradations in Hiperlan2

Emergent telecommunication systems use spectral efficient multilevel modulation formats together with multicarrier schemes such as Orthogonal Frequency division multiplexing (OFDM). OFDM transmission is an efficient way to deal with multipath. However one of its major drawbacks is its sensitivity to nonlinear distortions due to its greatly variable envelope and high peak to average power ratio (PAPR). Nonlinear distortions are mainly introduced by high power amplifiers (HPA), cause in band distortions. Misalignments in IQ modulators and demodulators causes imbalance, which results in loss of orthogonality and create intercarrier interference and spectral regrowth in an OFDM system. Nonlinear distortions also cause intermodulation effect. This degrades Bit error rate (BER) performance of the system. This paper introduces the self organization map(SOM) and parameterless self organization map(PLSOM) based and Hiperlan/2 receiver structure used for the compensation of nonlinear distortions. Simulation results presented in this paper clearly indicate the improved performance of the proposed system. Simulations are run for AWGN channel model and for two HPA models namely Travelling wave tube amplifier (TWTA) and Solid state power amplifier (SSPA), with and without SOM and PLSOM neural network blocks.

Line shape distortion effects in infrared spectroscopy

This paper explores different phenomena that cause distortions of infrared absorption spectra by mixing of reflective and absorptive band shape components of infrared spectra, and the resulting distortion of observed band shapes. In the context of this paper, we refer to the line shape of the variations of the refractive index in spectral regions of an absorption maximum (i.e., in regions of "anomalous dispersion") as "dispersive" or "reflective" line shape contributions, in analogy to previous spectroscopic literature. These distortions usually result in asymmetric bands with a negative intensity contribution at the high wavenumber of the band, accompanied by a shift toward lower wavenumber, and confounded band intensities. In extreme cases of band distortions caused by the "resonance Mie" (RMie) mechanism, spectral peaks may be split into doublets of peaks, change from positive to negative peaks, or appear as derivative-shaped features.

A low power sigma-delta modulator for dual-mode wide-band receiver

This work presents a low power cascaded sigma-delta modulator for GSM and WCDMA applications. The proposed modulator has the characteristics of wide bandwidth for WCDMA applications and low distortion in the low frequency band for GSM applications. Low-distortion and interpolative techniques are used in this modulator to enhance the performance. The low-distortion technique has not only the swing-suppressing characteristic, but it can reduce the power consumption. Moreover, the resolution can be improved even under non-linearity effects. An experimental chip is implemented in the standard 0.18-μm 1P6M CMOS technology. The measurements indicate a dynamic range of 76/68 dB and a peak signal to noise plus distortion ratio of 70/61 dB for GSM/WCDMA applications. The core area is 1 × 1.4 mm2 and the power consumption is 10.5/28 mW for GSM/WCDMA at 1.8 V.

Frame-Based Time-Scale Filters for Underwater Acoustic Noise Reduction

Noise reduction for underwater acoustic signals has attracted considerable attention over the last few decades. Among the numerous techniques, wavelet soft-thresholding (STH) has been considered as one of the most effective noise reduction approaches, as it achieves near complete success in minimizing the mean-squared-error (MSE) and eliminating oscillations caused by noise. However, a limitation with STH is its preference towards lower frequency bands, which may cause distortions in the high frequency bands. Few previous research efforts have reported on the reduction of such frequency distortions. By introducing the time-scale filters (TSF), we present a novel technique for underwater noise reduction that improves the standard STH in reducing distortions in the joint time-frequency (TF) space. TSF is an advanced noise reduction algorithm which utilizes the signal's time-scale (TS) support region. It provides smooth reconstructions in both time and frequency spaces. We demonstrate the noise reduction results for two typical underwater noise sources: the snapping shrimp sound and the rainfall sound. We also introduce a TF distortion measurement as a criterion that compares the TF distributions of the denoised signal and the clean signal. For a signal-to-noise ratio (SNR) from -10 to 20 dB, the noise reduction results obtained using TSF have an average of 42.1% lower TF distortion than STH for the snapping shrimp noise, and a 23.3% lower TF distortion for the rainfall noise.

Effect of particle size on photoluminescence emission intensity in ZnO

This study investigates the relationship between ZnO particle size and green emission photoluminescence intensity. Both commercially available ZnO powder and ZnO nanorods grown by solution processes are examined. Samples with different particle size distributions are prepared by centrifuging commercial powders or by modifying the growth conditions of nanorods. The green emission of powders and nanorods is measured as a function of particle size. A first-principles calculation is used to determine the density of states of the surface and bulk of the particles. This calculation strongly indicates that empty surface levels induce distortion of the energy band and inactivate luminescence centers near the surface. Assuming the existence of a non-luminescent surface layer on ZnO particles, equations relating particle size to emission intensity are constructed and used to describe the experimental data. The thickness of non-luminescent layers could be estimated using these modeling equations. The results from powder samples are similar to those from nanorod samples, supporting the validity of the models. Experimental results also show weak residual emission in the surface layer. The results are expected to provide valuable guidelines for future investigations into the mechanisms behind green emission in ZnO.

Effects of the gradient profile, sample volume and solvent on the separation in very fast gradients, with special attention to the second-dimension gradient in comprehensive two-dimensional liquid chromatography

Gradient elution provides significant improvement in peak capacity with respect to isocratic conditions and therefore should be used in comprehensive two-dimensional LC × LC, both in the first and in the second dimension, where, however, gradients are limited to a short time period available for separation, usually 1 min or less. Gradient conditions spanning over a broad mobile phase composition range in each second-dimension fraction analysis are used with generic “full in fraction” (FIF) gradients. “Segment in fraction” (SIF) gradients cover a limited gradient range adjusted independently to suit changing lipophilicity range of compounds transferred to the second dimension during the first-dimension gradient run and to provide regular coverage of the two-dimensional retention space. Optimization of the gradient profiles is important tool for achieving high two-dimensional peak capacity and savings of the separation time in comprehensive LC × LC. Calculations based on the well-established gradient-elution theory can be used to predict the elution times and bandwidths in fast gradients, taking into account increased probability of pre-gradient or post-gradient elution. The fraction volumes transferred into the second dimension may significantly affect the second-dimension bandwidths, especially at high elution strength of the fraction solvent, which may cause even band distortion or splitting in combined normal-phase (HILIC)–RP systems, but also in some two-dimensional RP–RP systems. In the present work, the effects of the fast gradient profile, of the sample volume and solvent on the elution time and bandwidths were investigated on a short column packed with fused-core porous-shell particles, providing narrow bandwidths and fast separations at moderate operating pressure.

Time-resolved fluorescence spectra of cis-stilbene in hexane and acetonitrile

Transient fluorescence spectra from cis-stilbene in solution are recorded with 0.24 ps instrument response by a Kerr–Shutter upon excitation at 283 and 267 nm. The fluorescence decay shows no dependence on the excitation wavelength and proceeds monoexponentially with 0.21 ps in acetonitrile and 0.75 ps in hexane. No spectral shift or distortion of the fluorescence band is observed during the decay. Fluorescence contribution from 4a,4b-dihydrophenanthrene (DHP), produced in a competing reaction channel, was not detectable. From comparison with trans-fluorescence, the emission oscillator strength of cis-stilbene is determined to be 0.19 in hexane and 0.21 in acetonitrile.

Efficiency improvement in microwave power amplifiers by using Complex Gain Predistortion technique

Power Amplifiers (PAs) are important parts of the transmitters. They amplify the signals that are going to be transmitted. With increasing the input power of the PA, it creates the nonlinearity at the output. The nonlinearity causes out of band distortion and in band distortion. To overcome these effects the power amplifier should be backed off but it will reduce the efficiency of the PA. To increase the efficiency, the Complex Gain Memory Predistortion (CGP) is added to the system. Experimental results with the Mini Circuit power amplifier show an improvement of 7% in Power Added Efficiency (PAE) when the CGP method is applied.

Temperature conditions on casting a gel minimizing the band distortion of DGGE

Temperature conditions on casting a gel minimizing the band distortion of DGGE

Chemical and electronic interface structure of spray pyrolysis deposited undoped and Al-doped ZnO thin films on a commercial Cz-Si solar cell substrate

We have studied differences in the interface between undoped and Al-doped ZnO thin films deposited on commercial Si solar cell substrates. The undoped ZnO film is significantly thicker than the Al-doped film for the same deposition time. An extended silicate-like interface is present in both samples. Transmission electron microscopy (TEM) and photoelectron spectroscopy (PES) probe the presence of a zinc silicate and several Si oxides in both cases. Although Al doping improves the conductivity of ZnO, we present evidence for Al segregation at the interface during deposition on the Si substrate and suggest the presence of considerable fixed charge near the oxidized Si interface layer. The induced distortion in the valence band, compared to that of undoped ZnO, could be responsible for considerable reduction in the solar cell performance.

Theory of Fermi-surface pockets and correlation effects in underdopedYBa2Cu3O6.5

The detection of quantum oscillations in the electrical resistivity of $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{6.5}$ provides evidence for the existence of Fermi-surface pockets in an underdoped cuprate. We present a theoretical study of the electronic structure of $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ aimed at establishing the nature of these pockets---i.e., $\mathrm{Cu}{\mathrm{O}}_{2}$ plane vs CuO chain or BaO. We argue that electron correlation effects, such as orbital-dependent band distortions and anisotropic self-energy corrections, must be taken into account to interpret the quantum oscillation experiments.

Frequency domain interpretation of power ratio metric for cognitive radio systems

SoftWare radio (SWR) is an enabling technology for cognitive radio (CR) systems which promises to (de) modulate any signal, at any frequency. SWR signal therefore is composed of different standard's signals, and each standard's signal is either multicarrier or multiplex of single carriers. This combination leads to high temporal fluctuations and thus SWR signal inherits high peak to average power ratio (PAPR) or simply high power ratio (PR). Nonlinear analogue components (amplifiers, converters etc.) cause distortions (in and out of band distortion) for high PR signals which result in system performance degradation. Usually PR problem is addressed in time domain, and here frequency domain interpretation of PR which is more appropriate in SWR context is presented. Gaussian equivalence between SWR signal and orthogonal frequency division multiplexing (OFDM) signal is proved first to accentuate high PR issue in SWR as OFDM suffers the same problem. Then frequency domain interpretation of PR metric is discussed which results in a PR upper bound. This PR upper bound depends only upon spectral values of the signal thus associates spectrum with PR. As a result this bound assists in spectrum access for CR systems by providing PR metric information related to any available bandwidth. Thus bandwidth allocation in a spectrum access scenario under PR constraint is simplified.

Fast Distortion Measurement Using Chord-Length Parameterization Within the Vertex-Based Rate-Distortion Optimal Shape Coding Framework

Existing vertex-based operational rate-distortion (ORD) optimal shape coding algorithms can use a number of different distortion measurement techniques, including the shortest absolute distance (SAD), the distortion band (DB), the tolerance band (TB), and the accurate distortion measurement technique for shape coding (ADMSC). From a computational time perspective, an N-point contour requires O(N2 ) time for DB and TB for both polygon and B-spline-based encoding, while SAD and ADMSC incur O(N) time for polygonal encoding but O(N2 ) for B-spline based encoding, thereby rendering the ORD optimal algorithms computationally inefficient. This letter presents a novel distortion measurement strategy based on chord-length parameterization (DMCLP) of a boundary that incurs order O(N) complexity for both polygon and B-spline-based encoding while preserving a comparable rate-distortion performance to the original ORD optimal shape coding algorithms

Semiconductor–metal transition of pyriteFeS2 under high pressure by full-potential linearized-augmented plane wave calculations

The effects of hydrostatic pressure on the electronic band structure of the semiconductor mineral ironpyrite FeS2 have been investigated theoretically by an ab initio full-potential linearized-augmented planewave (FPLAPW) method within a local approximation (LDA/GGA) to the density functionaltheory. The calculations predict that at a pressure of 94.1 GPa the indirect band gap of pyriteFeS2 vanishes and the material becomes a metal. This is due to the presence of the S–S and Fe–Sbonds, which provide novel energy band distortions in the process of attaining the metallicstate. Analysis indicates that, under increasing high pressure, the conduction bands(3pz ofsulfur and 3dx2−y2+3dxy of iron) intrude downwards into the valence bands, which are predominantly 3d in nature.At normal pressure, the lattice constant, the bulk modulus, sulfur position parameteru, S–S bond length, and the indirect band gap of pyriteFeS2 are calculated using a fully relaxed unit cell and found to be equal to 541.8 pm, 159.7 GPa,u = 0.383, 219.5 pm and 0.45 eV, respectively. Apart from the gap, which is too small (the usual ‘LDAerror’), these results agree well with recent experiments. The effective masses of an electronat selected points in the conduction band are reported.

Visualising the onset of viscous fingering in chromatography columns

Viscous fingering is an important fluid transport phenomenon that manifests itself when two fluids having different viscosities move in the same direction. Their interface is unstable and a complex fingering pattern may arise. This phenomenon is important in chromatography because it may lead to a decrease or even a failure in separations. The onset of viscous fingering was visually observed by packing a glass column with particles having the same refractive index as the mobile phase and injecting plugs of dye solutions having viscosities different from that of the mobile phase. Severe fingering effects are observed if the viscosity difference exceeds 0.17 cP. However, for smaller viscosity differences, band distortions are observed that may affect retention data, band efficiency, and band resolution. Careful attention should be paid to matching the mobile phase viscosity and that of the injection plug when accurate chromatographic information is required.

Effect of sample solvent on the chromatographic peak shape of analytes eluted under reversed-phase liquid chromatogaphic conditions

Peak-shape problems represent the most common troubles in liquid chromatography. Distorted peaks are causes for integration problems, and very often for poor resolutions. Sample and standard solvent different from that of the eluent is one of the possible reasons for anomalous peak-shapes. The injection of a pulse of different viscosity from that of the mobile phase is the underlying cause of distortions in early eluting bands. Strong eluting solvents (of exactly equal viscosity coefficients) are cause of band broadening, not of peak distortions. The goal of the present work is to critically evaluate the significant role of sample solvent upon the chromatographic band distortion. Practical solutions for situations where chromatographic analysis is performed under conditions far from ideal as a result of time constrains related to sample preparation are also discussed.

Small-size planar triangular monopole antenna for UWB WBAN applications

A novel topology, based on the PTMA, is investigated in view of UWB WBAN applications. It is shown that adding carefully placed slots in the antenna offers a lot of advantages. The study presented treats all aspects that are important. First, the specifications in the frequency domain are met for the lower UWB band. Secondly, the design is made such that a small size is obtained. Thirdly, and very important, the presence of the human body is investigated. Finally, the pulse distortion in the frequency band 4-7 GHz is investigated and found to be low. The main conclusion is that this PTMA type is a very good topology for UWB applications in combination with human bodies.

Influence of energy band distortion on the Hall emf in bipolar semiconductors

Influence of energy band distortion on the Hall emf in bipolar semiconductors

High-resolution infrared analysis of seven fundamental bands of gaseous isothiazole between 750 and 1500 cm −1

The gas phase IR spectrum of isothiazole, C 3H 3NS, between 550 and 1700 cm −1 was recorded with a resolution of ca. 0.003 cm −1. The rotational structure of seven fundamental bands in the region 750–1500 cm −1 has been assigned and analysed by the Watson Hamiltonian model. A number of local resonances in the bands have been identified and explained qualitatively in terms of Coriolis interactions. For each band upper state spectroscopic constants, including band center, rotational constants, and quartic centrifugal distortion constants are given. From observed crossings due to resonances we locate the weak bands ν 9( A′) and ν 13( A′) at 1041.9(2) and 642.0(3) cm −1, respectively. The anharmonic frequencies have been determined using a cc-pVTZ basis set, at the MP2 and B3LYP levels; the two theoretical methods give very similar results for rotational constants, anharmonic band center frequencies and distortion constants, and many of these are in good agreement with experiment.

Enhancement and band distortion of the IR absorption spectra of a methanol on silver evaporated thin films in UHV-ATR configuration

Enhanced infrared absorption spectra of methanol adsorbed on evaporated silver films were measured using Kretschmann’s ATR configuration. Whereas the enhanced spectra were recordable using p-polarized radiation alone when the metal film was continuous, it was obtainable using both the p-polarized and s-polarized radiations from island films. Band distortion was also measured for changing incident angle and metal thickness. Furthermore, when film with silver of intermediate thickness was used, great distortion of the absorption band was observed. The relation between the anomalous absorption by the silver film and the band distortion was indicated.