小波变换用于二次微分交流示波计时电位信号中有用信息的提取

小波分析是８０年代发展起来的一种新的数学分支。由于小波变换具有许多其它的信号处理手段所不具备的优良特性，如正交性，可变的时－频分辨率和可调节的局部支持等，使它成为信号处理的一种强有力的工具。     

小波变换用于示波信号中有用信息提取的研究

示波分析是近年来在我国发展起来的一个新的电化学分析研究领域［１～４］．它根据阴极射线示波器荧光屏上示波图及其变化进行分析测试,从原理上可以将其分为示波电位法和示波计时电位法;从测定方式上可以将其分为示波滴定和示波测定．关于示波电位法的一些理论问题（如...     

Electrodeposition of flattened Cu nanoclusters on a p-GaAs(001) electrode monitored by in situ optical second harmonic generation

In situ optical second harmonic generation (SHG) technique was employed to investigate the shape and density of Cu nanoclusters, which were electrochemically formed on p-GaAs(001) electrode surfaces. Since GaAs is not a centrosymmetric medium, a significant portion of SHG signal arises from the bulk dipole susceptibility, but it was possible to separate a surface-induced signal from a bulk-induced signal by choosing an appropriate experimental geometry and appropriate data processing. The rotational anisotropy (RA) pattern of the SHG signal from a p-GaAs(001) electrode changed in both shape and magnitude during potential cycling in an electrolyte solution containing Cu2+. The surface plasmon-induced SHG signal from Cu nanoclusters deposited on GaAs was attributed to the modulation source for the RA-SHG pattern. More detailed study was carried out with both in situ SHG and ex situ AFM measurements for Cu nanoclusters deposited by potential step. The results showed that the SHG signal at the present optical geometry was sensitive to the number of oblate or flattened Cu nanoclusters with lateral diameter larger than 30 nm and that the SHG enhancement occurred because of resonant coupling between the surface plasmon induced in the flattened Cu nanoclusters and the near-infrared fundamental light.     

Wavelet transform as a new approach to the enhancement of signal-to-noise ratio in anodic stripping voltammetry

De-noising signals is a frequent aim achieved by signal processing in analytical chemistry. The purpose is to enable the detection of trace concentrations of analytes. The limit of detection is defined as the lowest amount of analyte that still causes signals greater than the background noise. Appropriate de-noising decreases only the noise and maintains the measurement signal, so that signal-to-noise ratios are enhanced. One adequate mean of signal processing for this purpose is wavelet transform, which still is not a common tool in analytical chemistry. In this paper, the ability of de-noising by wavelet transform is shown for measurements in anodic stripping voltammetry using a hanging mercury drop electrode. The calculation of limits of detection and signal-to-noise ratios on the basis of peak-to-peak noise is exercised to quantify the performance of de-noising. Furthermore, signal shape with regard of easing the application of base lines is discussed. Different wavelet functions are used, and the results are compared also to Fourier transform. Coiflet2 was found out to reduce noise by the factor of 330 and is proposed as the adequate wavelet function for voltammetric and similar signals.     

Signal processing and detection limits for graphite furnace atomic absorption with Zeeman background correction

The signal handling requirements for graphite furnace atomic absorption are much more demanding than those for flame atomic absorption. Graphite furnace signals change rapidly, background levels are higher, and signal interpretation needs are more extensive.We have identified a number of signal generation and processing factors that are important for success in graphite furnace analyses. These include: use of the transverse, a.c. Zeeman technique with the magnet on the analyte for background correction; production of a series of signal integrals at line frequency to accurately represent the shape of the furnace peak; use of interpolation techniques to better correct for rapidly changing background levels; use of integrated peak absorbance (A.s) signals rather than peak height absorbance for quantitative measurements; use of baseline correction to improve the accuracy of integrated peak absorbance signals; and use of graphical techniques to facilitate data interpretation and methods development.Examples are presented that illustrate the contribution of these factors to precision and detection limit performance. It is possible to improve detection limits over those previously reported by choosing appropriate signal handling parameters.     

Fast Padé transform for optimal quantification of time signals from magnetic resonance spectroscopy

The fast Padé transform (FPT) is both a parametric and a nonparametric estimator that is capable of quantifying the input raw time signals without any fitting. The FPT simultaneously interpolates as well as extrapolates, and this is expected to mitigate truncation artifacts. To assess performance, it is necessary to compare the main features of the FPT with the characteristics of other parametric estimators, as well as with the fast Fourier transform (FFT), which can yield only shape spectra. The FPT can also give the shape of a spectrum, but accomplishes this in two totally different ways, with and without computing the spectral parameters (complex frequencies and amplitudes). A number of other parametric estimators used in signal processing are unable to yield shape spectra without prior extraction of the fundamental frequencies and the corresponding amplitudes. The primary goal of the present study is to assess the accuracy, robustness, and efficiency of the FPT for parametric and nonparametric estimations of experimentally measured time signals from in vivo magnetic resonance spectroscopy (MRS). Robustness and steadiness of the FPT are assessed relative to the FFT by monitoring the convergence rates of these two processors through a systematic and gradual decrease of the truncation level of the full signal length. Accuracy of the FPT is verified by performing error analysis of proven validity, using a gold standard, if available. Alternatively, comparison is made between the two complementary variants of the FPT that converge inside and outside the unit circle. Efficiency of the FPT is checked with respect to the FFT for estimation of the shape of a spectrum, as well as relative to other parametric processors, in the case of quantifications. To establish the accuracy, robustness, and efficiency of the FPT within the outlined multi‐level strategy, we use a time signal encoded via MRS at 4T from the brain of a healthy volunteer. We also assess the overall usefulness of the FPT for signal processing of data acquired from patients, in light of the emerging appreciation that spectroscopy of the tissue metabolites offers a number of vital advantages over the corresponding anatomical imaging in diagnostics. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Deductive prediction of measurement precision and optimization of integration time and wavelength in capillary electrophoreses

Summary This paper demonstrates that the relative standard deviation (RSD) of measurements in a capillary electrophoresis system can be predicted theoretically from the baseline and the signal shape at low sample concentration. The only requirements for prediction of the uncertainty are the Fourier transform of the baseline (here 2048 data points) and the observation of signal shape. The micellar electrokinetic chromatography (MEKC) of acetaminophen and caffeine is taken as an example. The optimum is defined here as the condition of the lowest RSD or highest precision. The optimum single wavelength is selected from between 220 and 350 nm for the MEKC system equipped with a photodiode array detector. The optimum time domain of signal integration is shown to be even narrower than the entire signal region, providing an RSD value about half that for integration of the entire region. The theory is in good agreement with observed RSD values.     

Analysis of peak asymmetry in chromatography

The knowledge of the symmetry of chromatographic peaks is extremely important regarding the digital signal processing. The significant deviation of the peak shape from the symmetrical peak makes hardly possible the acquisition of chromatographic signal information, such as the retention time, the peak area, the peak width at half peak height, the peak overlapping, etc. In the literature one can find many methods for the determination of the asymmetry factor. For example it is suitable to calculate the skewness from the third central moment. However in case of noisy baseline the value of the skewness oscillates highly depending on the number of points used for the mathematical calculation. In this work a new method is presented for the determination peak shape asymmetry. We order mathematical function to the chromatographic peaks by fitting, and then symmetrical curve is generated with the same peak maximum position and height, the peak width is fitted. The difference of the two functions is constituted and areas of the data differences are calculated, which are really characteristics of the peak asymmetry. Correlation between the area of the difference signal and the asymmetry factor is established. The method was applied for different types of chromatographic peak shapes and the results were interpreted.     

A maximum information utilization approach in X-ray fluorescence analysis

X-ray fluorescence data bases have significant contradictions, and inconsistencies. We have identified that the main source of the contradictions, after the human factors, is rooted in the signal processing approaches. We have developed signal processors to overcome many of the problems by maximizing the information available to the analyst. These non-paralyzable, fully digital signal processors have yielded improved resolution, line shape, tailing and pile up recognition. The signal processors account for and register all events, sorting them into two spectra, one spectrum for the desirable or accepted events, and one spectrum for the rejected events. The information contained in the rejected spectrum is mandatory to have control over the measurement and to make a proper accounting and allocation of the events. It has established the basis for the application of the fundamental parameter method approach. A fundamental parameter program was also developed. The primary X-ray line shape (Lorentzian) is convoluted with a system line shape (Gaussian) and corrected for the sample material absorption, X-ray absorbers and detector efficiency. The peaks also can have, a lower and upper energy side tailing, including the physical interaction based long range functions. It also employs a peak and continuum pile up and can handle layered samples of up to five layers. The application of a fundamental parameter method demands the proper equipment characterization. We have also developed an inverse fundamental parameter method software package for equipment characterisation. The program calculates the excitation function at the sample position and the detector efficiency, supplying an internally consistent system.     

The effect of heating on background and radiation-induced EPR signals in tooth enamel

The presented study is a continuation of our work performed during participation in the Third International Intercomparison on EPR Tooth Dosimetry. During the process of samples preparation, all 22 enamel samples were accidentally exposed for about 30 min to 150 degrees C temperature. This considerably affected shape of their EPR spectra mainly due to substantial increase in the background signal, which approximately doubled its contribution to the spectra. These effects were studied closer under controlled conditions of the delivered dose and heating temperature using another enamel samples. The observed changes in the spectra shape partially faded within a few days after heating. The heating resulted also in a noticeable generation of a spectral component similar to the dosimetric signal induced in enamel by radiation. The temperature-induced dosimetric component in EPR spectra of the heated samples remained constant for 32 days. Deviations in calculated contributions of the dosimetric signal into total EPR spectra of irradiated sample varied from -12 to +15% of its initial contribution in the non-heated enamel, depending on type of the background spectrum applied in numerical processing of the spectra.     

Evaluating shape memory behavior of polymer under deep-drawing conditions

Thermoplastic polyurethanes (TPU) are a popular family of shape memory polymers (SMP) due to their excellent abrasion & weather resistant, and mechanical strength. However, conventional processing operations or their combination with other polymers by adhesion or blending can affect their unique shape memory behavior. Currently, there are no effective methods to study and quantify the shape memory behavior of SMP based polymer laminates as they would respond to deep drawing operations. In this paper, a new method was introduced to effectively quantify the recovery behavior of TPU based polymer laminates undergoing simultaneous stretching and bending operations at different processing temperatures. The results presented show the value of developing a shape recovery characterization method that resembles the stresses of thermoforming to properly assess formability of shape memory polymers used in laminate constructions.     

Self-powered Biosensor Big Data Intelligent Information Processing System for Real-time Motion Monitoring

A portable self-powered biosensor big data information processing system has been designed to help coaches monitor athlete training performance in real-time. The material system is composed of tetrapod-shaped ZnO nanowires and common textiles. Based on the piezoelectric effect, the device can convert weak shape variables into electrical signals, and the output piezoelectric signal obviously depends on the shape variable, the surrounding humidity and temperature. After attaching the device to the athlete, it can monitor the speed, frequency, angle of an athlete, and surrounding humidity and temperature in real-time without external power supply. API data collected by information processing end, server behavior simulated by Web service, turns the host of integrated web services into a data server, shares to other terminals via LAN to implement the visual charts summary for data-driven views, summarize and analyze charts. This multidisciplinary research can point out the new development direction of sport science and may promote the development of flexible self-powered multifunctional nano-systems.     

In vivo magnetic resonance spectroscopy for ovarian cancer diagnostics: quantification by the fast Padé transform

Early-stage ovarian cancer has an excellent prognosis, but due mainly to late detection, ovarian cancer remains a major cause of cancer deaths among women. In vivo magnetic resonance spectroscopy (MRS) would be an excellent candidate for early ovarian cancer detection, being non-invasive, surpassing anatomic imaging to identify metabolic features of cancer, and free of ionizing radiation. However, the present meta-analysis of 13 studies indicates that with conventional Fourier-based processing, in vivo MRS insufficiently distinguished 134 cancerous from 114 benign ovarian lesions. The fast Padé transform (FPT), an advanced signal processor with high-resolution and parametric (quantification-equipped) capabilities is best qualified for MRS time signals from the ovary, as demonstrated in our earlier proof-of-concept studies. We now apply the FPT to MRS time signals encoded in vivo on a 3 T scanner, echo time of 30 ms, from a borderline serous cystic ovarian tumor. The FPT-produced total shape spectrum was better resolved than with Fourier processing. Spectra averaging through the FPT generated a denoised total shape spectrum. Subsequent parametric analysis reconstructed dense component spectra in the “usual” mode: absorption and dispersion components mixed and “ersatz” mode: reconstructed phases set to zero, thus eliminating interference effects. Numerous metabolites, including potential cancer biomarkers, were identified and quantified by the FPT, including isoleucine, valine, lipids, lactate, alanine, lysine, N-acetyl aspartate, N-acetylneuraminic acid, glutamine, choline, phosphocholine, myoinositol. Many of these are difficult or impossible to detect with Fourier plus fitting techniques for in vivo MRS of the ovary. These Padé-generated results are promising, overcoming major barriers hindering MRS from becoming a key method for non-invasively assessing ovarian lesions.     

Protein arrays on high-surface-area plasma-nanotextured poly(dimethylsiloxane)-coated glass slides

Treatment of poly(dimethylsiloxane) (PDMS) surfaces with SF(6) plasma results in the creation of high-surface-area nanotextured surfaces that considerably favour protein adsorption with respect to untreated ones. In order to employ such nanotextured surfaces as substrates for microarrays to be created and analysed using standard instrumentation, we fabricated thin PDMS films on top of standard low-cost microscope glass slides. The properties of both untreated and plasma-treated PDMS-coated slides towards spotting of protein solutions were evaluated in terms of spot signal intensity and homogeneity as well as of spot shape and size. It was found that the plasma-treated PDMS-coated glass slides provided highly homogeneous spots (mean intra-spot variation 7.6%) with spot signal intensity 6-times higher than that obtained using the untreated ones. In addition, comparison with commercially available polystyrene and aminosilanized-glass microarray slides showed that the proposed slides provided 3-times higher spot signal intensity and 2-times lower intra-spot signal variation. In addition, the implementation of long-aged-after-plasma-treatment nanotextured PDMS-coated glass slides provided spots whose shape and size matched those of the spotting tip. As a consequence, denser arrays of variable spot shape can be created using SF(6) plasma-treated PDMS-coated slides instead of standard microarray slides opening new potentials for bioanalytical applications.     

Elucidating the spectral and temporal contributions from the resonant and nonresonant response to femtosecond coherent anti-Stokes Raman scattering

A theoretical expression is developed for femtosecond coherent anti-Stokes Raman scattering (CARS) to quantitatively account for the vibrational line shape in the presence of nonresonant signal. The contributions of the resonant and nonresonant components are extracted from the emitted signal line shape as a function of Stokes wavelength and as a function of the temporal overlap of the two pump pulses (for spectrally resolved femtosecond CARS). The theory is compared to the measured spectra of the oxygen vibrational transition DeltaG(01)=1556.4 cm(-1) for temporal detunings of 0 and 700 fs.     

Current sampling in polarography without synchronization with the drop time

The circuit proposed for sampling of polarographic currents enables oscillations on the recorded curves to be eliminated without distortion of the curve. The apparatus, based on a peak detector, can be used regardless of the shape and character of the curves, and does not require indication of drop disconnection. When the necessary conditions are fulfilled, the output signal is identical with the signal from a Tast polarograph.