Emilia Pardo

Cell cycle- and differentiation stage-dependent variation of dUTPase activity in higher plant cells

Deoxyuridine triphosphate nucleotidohydrolase (dUTPase), a key enzyme in pyrimidine nucleotide metabolism, specifically hydrolyzes deoxyuridine triphosphate (dUTP) to deoxyuridine monophosphate and inorganic pyrophosphate. This enzyme activity has been studied in cellular extracts from Allium cepa root meristem cells with two specific aims: (i) to determine how the properties of the plant enzyme compare with those of dUTPase purified from other sources, and (ii) to analyze the relationship between dUTPase activity and cell proliferation and cell differentiation. Plant dUTPase is highly specific for dUTP, with an apparent Km of 6 microM, is highly sensitive to EDTA and it is probably a metalloenzyme. Our results demonstrate the presence of high levels of dUTPase in both resting and proliferating root meristem cells. The enzyme activity appears to be tightly regulated during the cell cycle. dUTPase activity increases at the G1/S boundary, remains high throughout S phase, and shows almost undetectable levels during G1 and G2. We have also found that dUTPase activity in differentiated cells, located in the mature portion of the root, is barely detectable. Altogether our results indicate that dUTPase activity is modulated by the proliferation rate and that this activity progressively decreases as cells initiate their differentiation program.

Shift Invariant Wavelet Denoising of Ultrasonic Traces

Basic wavelet denoising techniques rely on a thresholding of the discrete wavelet transform (DWT) coefficients of the noisy signal. Some improvements in noise reduction efficiency can be obtained by the use of shift-invariant undecimated wavelet transforms (UWT). Ultrasonic grain noise is one of the most usual types of noise present in ultrasonic non-destructive evaluation. It comes from reflections in the material structure, and occupies a frequency band very similar to that of the echosignals of interest. In this work, new advances in the application of redundant wavelet transforms to ultrasonic grain noise reduction are presented. Wavelet denoising is applied to several sets of synthetic ultrasonic traces, which are obtained from a model that includes frequency dependent attenuation for both grain and flaw backscattered echoes, frequency dependent scattering from the grains, and an accurate model for the pulse-echo frequency response of the piezoelectric ultrasonic transducer. Two processors based on traditional DWT and alternative a trous UWT denosing have been implemented and compared, using level dependent thresholds (appropriate for correlated noise), soft thresholding, and Universal, SURE and Minimax threshold selection rules. The performances of the two processors are analyzed in terms of the mean value and standard deviation of the signal-to-noise ratio (SNR) of different sets of ultrasonic traces before and after denoising. It is shown that a trous UWT processing provides better results than DWT with a general tendency to higher quality of the resulting traces and greater robustness of the processing. It is also shown that the better performance of the UWT is mainly related to the redundancy of the representation, since there are not significant variations between the threshold values obtained with each processor.

Narrowband Interference Suppression Using Undecimated Wavelet Packets in Direct- Sequence Spread-Spectrum Receivers

A new algorithm for narrowband interference suppression in direct-sequence spread-spectrum (DS-SS) communications is presented. The algorithm combines the undecimated wavelet packet transform (UWPT) with frequency shifts to confine the interference energy in a subband that is subsequently eliminated. Computer simulation shows a robust performance that appears to be independent of the interference frequency

Ultrasonic pulse propagation in a bonded three‐layered structure

Bonded layers are used in the assembly of many critical functional parts of industrial equipment. In this work, ultrasonic pulse propagation in a steel‐rubber‐rubber bonded composite structure is investigated by means of computer simulation and pulse echo experimental evaluation. Ultrasonic pulse propagation is modelled using a 2D time domain finite‐difference software. For the experimental measurements, two test samples were fabricated by bonding a thin layer of steel and two thin layers of rubber, including debonded areas at marked regions of each interface. Several ultrasonic traces were acquired by contact pulse‐echo testing, using a 5 MHz wideband transducer, from the external steel surface. The large acoustic impedance mismatch existing between steel and rubber layers makes that only a very small part of the ultrasonic energy is transmitted through the first (steel‐rubber)interface. The high attenuation in rubber materials and the possible overlapping of multiple echoes are additional characteristics of the complex ultrasonic pulse propagation in this flat structure. Some differences in time and frequency domains, between the received signals from normal bonded areas and completely debonded areas are discussed, looking for defect detection at the first (steel‐rubber) and second (rubber‐rubber) interfaces.

Denoising Ultrasound RF Signals by Wavelet Cycle Spinning Shrinkage

A speckle reduction procedure, based on wavelet Cycle Spinning (CS) Shrinkage, has been applied to radio-frequency RF pulse-echo signals. Several sets of 100 synthetic ultrasonic signals were generated using a model of speckle formation which includes frequency dependent attenuation, frequency dependent scattering, and an accurate model for the pulse-echo response of the broad band ultrasonic transducer. The frequency spectra overlapping of ultrasound signal and speckle noise is shown. The mean and standard deviation of the signal to noise ratio (SNR) of sets of 100 RF signals have been taken as denoising performance indexes. Results of CS denoising have been compared with those of Discrete Wavelet Transform (DWT) denoising, using Universal and SURE decomposition level dependent threshold selection rules. CS overcomes the lack of translation invariance of DWT providing on average a better denoising performance. A preliminary evaluation of the influence of different mother wavelets is also presented.

Wavelet cycle-spinning denoising of ultrasonic traces acquired from austenitic steel

Ultrasonic non-destructive evaluation of austenitic steel components or welded unions usually presents difficulty for small flaw detection, due to complex structure and wave scattering at grain boundaries. Ultrasonic signals from small flaws are masked by grain or structural noise whose frequency band partially overlaps the frequency response of the ultrasonic transducer. The main objective of this work is the application and performance analysis of a cycle-spinning undecimated wavelet transform processor for denoising ultrasonic traces acquired from a test block made of austenitic steel.

Sister-chromatid exchange (SCE) elimination kinetics in BrdUrd-treated cells irradiated with visible light

Abstract In the present paper we have characterized the ability of an irradiation with visible light of BrdUrd-containing chromosomes to induce sister-chromatid exchanges (SCEs). The experimental approach has include the use of post-treatments with oxygen, caffeine or benzamide during the pre-replicative period of the cell cycle in Allium cepa L. root-meristem cells exposed to visible light (VL) during early G1. Cells post-treated with benzamide immediately after VL showed higher SCE levels than those post-treated with either caffeine or oxygen. SCE-inducing DNA damage, repaired by a benzamide-sensitive step, appeared to be eliminated with a very fast kinetics. Thus, 15 min between the end of VL exposure and the beginning of benzamide treatment were enough for the cells to exhibit normal SCE levels. However, for the case of oxygen, that time was shown to be 2–3 h. Since these agents presumably act at different levels of the repair process, our results suggests that different SCE-inducing lesions were produced by VL exposure and/or that they were repaired at different times throughout the G1 phase. Finally, when cells irradiated at the beginning of the G1 phase were treated with either caffeine or benzamide during their G1/S traverse, SCE levels were significantly increased. These results were consistent with the occurrenceof a benzamide- and caffeine-sensitive survey mechanism, acting at the G1/S border, that would tend to reduce the SCE-inducing DNA damage before the S-phase.