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981.
Miguel B. Furtado Jr. Paulo S. R. Diniz Sergio L. Netto 《Circuits, Systems, and Signal Processing》2003,22(2):193-210
A design procedure for frequency-response masking (FRM) prototype filters
of cosine-modulated filter banks (CMFBs) is proposed. In the given method, we perform
minimization of the maximum attenuation level in the filters stopband, subject to intersymbol
interference (ISI) and intercarrier interference (ICI) constraints. For optimization,
a quasi-Newton algorithm with line search is used, and we provide simplified analytical
expressions to impose the interference constraints, which greatly reduce the computational
complexity of the optimization procedure. The result is lower levels of ISI and ICI for a
predetermined filter order, or a reduced filter complexity for given levels of interferences. It
is then illustrated how the FRM-CMFB structure is suitable for implementing filter banks
with a large number of bands, yielding sharp transition bands and small roll-off factors,
which is an attractive feature for a wide range of practical applications. 相似文献
982.
Region-based wavelet coding methods for digital mammography 总被引:6,自引:0,他引:6
Penedo M Pearlman WA Tahoces PG Souto M Vidal JJ 《IEEE transactions on medical imaging》2003,22(10):1288-1296
Spatial resolution and contrast sensitivity requirements for some types of medical image techniques, including mammography, delay the implementation of new digital technologies, namely, computer-aided diagnosis, picture archiving and communications systems, or teleradiology. In order to reduce transmission time and storage cost, an efficient data-compression scheme to reduce digital data without significant degradation of medical image quality is needed. In this study, we have applied two region-based compression methods to digital mammograms. In both methods, after segmenting the breast region, a region-based discrete wavelet transform is applied, followed by an object-based extension of the set partitioning in hierarchical trees (OB-SPIHT) coding algorithm in one method, and an object-based extension of the set partitioned embedded block (OB-SPECK) coding algorithm in the other. We have compared these specific implementations against the original SPIHT and the new standard JPEG 2000, both using reversible and irreversible filters, on five digital mammograms compressed at rates ranging from 0.1 to 1.0 bit per pixel (bbp). Distortion was evaluated for all images and compression rates by the peak signal-to-noise ratio. For all images, OB-SPIHT and OB-SPECK performed substantially better than the traditional SPIHT and JPEG 2000, and a slight difference in performance was found between them. A comparison applying SPIHT and the standard JPEG 2000 to the same set of images with the background pixels fixed to zero was also carried out, obtaining similar implementation as region-based methods. For digital mammography, region-based compression methods represent an improvement in compression efficiency from full-image methods, also providing the possibility of encoding multiple regions of interest independently. 相似文献
983.
Arturo F. Méndez-Sánchez M. Rosario López-González V. Hugo Rolón-Garrido José Pérez-González Lourdes de Vargas 《Rheologica Acta》2003,42(1-2):56-63
The rheological behavior of a cetylpyridinium chloride 100 mmol l–1/sodium salicylate 60 mmol l–1 aqueous solution was studied in this work under homogeneous (cone and plate) and non-homogeneous flow conditions (vane-bob
and capillary rheometers), respectively. Instabilities consistent with non-monotonic flow curves were observed in all cases
and the solution exhibited similar behavior under the different flow conditions. Hysteresis and the sigmoidal flow curve suggested
as characteristic of systems that show constitutive instabilities were observed when running cycles of increasing and decreasing
stress or shear rate, respectively. This information, together with a detailed determination of steady states at shear stresses
close to the onset of the instabilities, allowed one to show unequivocally that "top and bottom jumping" are the mechanisms
to trigger the instabilities in this micellar system. It is shown in addition that there is not a true plateau region in between
the "top and bottom jumping". Finally, the flow behavior beyond the upturn seemed to be unstable and was found accompanied
by an apparent violation of the no-slip boundary condition. 相似文献
984.
AC-coupled front-end for biopotential measurements 总被引:5,自引:0,他引:5
Spinelli EM Pallàs-Areny R Mayosky MA 《IEEE transactions on bio-medical engineering》2003,50(3):391-395
AC coupling is essential in biopotential measurements. Electrode offset potentials can be several orders of magnitude larger than the amplitudes of the biological signals of interest, thus limiting the admissible gain of a dc-coupled front end to prevent amplifier saturation. A high-gain input stage needs ac input coupling. This can be achieved by series capacitors, but in order to provide a bias path, grounded resistors are usually included, which degrade the common mode rejection ratio (CMRR). This paper proposes a novel balanced input ac-coupling network that provides a bias path without any connection to ground, thus resulting in a high CMRR. The circuit being passive, it does not limit the differential dc input voltage. Furthermore, differential signals are ac coupled, whereas common-mode voltages are dc coupled, thus allowing the closed-loop control of the dc common mode voltage by means of a driven-right-leg circuit. This makes the circuit compatible with common-mode dc shifting strategies intended for single-supply biopotential amplifiers. The proposed circuit allows the implementation of high-gain biopotential amplifiers with a reduced number of parts, thus resulting in low power consumption. An electrocardiogram amplifier built according to the proposed design achieves a CMRR of 123 dB at 50 Hz. 相似文献
985.
Barbosa PR Barbosa-Filho J de Sá CA Barbosa EC Nadal J 《IEEE transactions on bio-medical engineering》2003,50(1):114-117
This paper proposes a technique to improve the quality of high-resolution electrocardiogram by weighting the coherent average of beats by a function of the energy of the corrupting myoelectric noise, prior to subsequent detection of ventricular late potentials. The results obtained with 20 patients indicate the method requires fewer beats than conventional nonweighted average to achieve the same noise level. 相似文献
986.
Martín-Guerrero JD Camps-Valls G Soria-Olivas E Serrano-López AJ Pérez-Ruixo JJ Jiménez-Torres NV 《IEEE transactions on bio-medical engineering》2003,50(10):1136-1142
The external administration of recombinant human erythropoietin is the chosen treatment for those patients with secondary anemia due to chronic renal failure in periodic hemodialysis. The objective of this paper is to carry out an individualized prediction of the EPO dosage to be administered to those patients. The high cost of this medication, its side-effects and the phenomenon of potential resistance which some individuals suffer all justify the need for a model which is capable of optimizing dosage individualization. A group of 110 patients and several patient factors were used to develop the models. The support vector regressor (SVR) is benchmarked with the classical multilayer perceptron (MLP) and the Autoregressive Conditional Heteroskedasticity (ARCH) model. We introduce a priori knowledge by relaxing or tightening the epsilon-insensitive region and the penalization parameter depending on the time period of the patients' follow-up. The so-called profile-dependent SVR (PD-SVR) improves results of the standard SVR method and the MLP. We perform sensitivity analysis on the MLP and inspect the distribution of the support vectors in the input and feature spaces in order to gain knowledge about the problem. 相似文献
987.
Wang Y Tang Z Correa-Duarte MA Liz-Marzán LM Kotov NA 《Journal of the American Chemical Society》2003,125(10):2830-2831
Indiscriminate adsorption of nanoparticles (NPs) significantly complicates the preparation of mesoscale NP patterns considered as enabling technology for many devices and processes. Instead of selected chemical functionalization of the substrate surface prior to the assembly of nanocolloids, the required optical properties - in our case, high quantum yield luminescence - are imparted to the layer-by-layer assembled films by spatially selected photoactivation. The films are made by sequential adsorption of a positively charged polyelectrolyte and a negatively charged CdSe/CdS aqueous dispersion with an initial quantum yield of 0.5-2%. The photoactivation process takes place in the presence of oxygen and may be accompanied by photoetching. A 50-500-fold increase in the luminescence intensity of CdSe/CdS citrate-stabilized particles (quantum yield 25-45%) after visible light illumination provides excellent pattern contrast. Micron scale luminescence patterns were produced from NPs of various CdSe core diameters with red, yellow, and green emission. It was also demonstrated that different emission colors such as orange and green can be combined in one image by taking advantage of spatially selective photoetching. The presented optical patterning technique significantly simplifies the preparation of luminescence patterns as compared to conventional methods. The high signal-to-noise ratio associated with it is essential for optical devices, information processing, and biophotonics. The most immediate use of this approach is expected in cryptography and cell monitoring. 相似文献
988.
[reaction: see text] A one-step synthesis of enantiomerically pure anti-1,2-amino alcohol derivatives has been achieved by reaction of prochiral oxygenated 2-p-tolylsulfinylbenzyl carbanions with N-sulfinylimines bearing the same configuration at sulfur. 相似文献
989.
[reaction: see text] A one-pot synthesis of C(2)-symmetric di-d-fructose dianhydrides having the 1,6,9,13-tetraoxadispiro [4.2.4.2]tetradecane skeleton has been accomplished via intramolecular aglycon delivery from (6 --> 6) xylylene-tethered fructofuranose precursors. The stereochemical outcome of the glycosylation-spiroketalization process is governed by the geometrical constraints imposed by the rigid tetracyclic structure of the final compound. 相似文献
990.
Certain haloanisoles present at trace levels cause a large part of earthy-musty off-flavor problems in drinking water. These potent odorous chemicals come mainly through biomethylation of their corresponding halopenols. To enable the investigation of both families of compounds, a method involving solid-phase microextraction (SPME) was developed and the main parameters governing SPME were optimized. This method allows the simultaneous quantification of haloanisoles and halophenols at levels ranging from 1 to 100 or 250 ng/l, with detection limits of about 0.5 ng/l and could be applied to potable as well as raw surface waters. 相似文献