This paper discusses the convenience of using two-dimensional (2-D) coding techniques for the compression of electrocardiogram (ECG) signals. These signals present a very clear periodicity that can be exploited by the use of a 2-D time/frequency transform to decorrelate it as much as possible. A brief theoretical approach is given to justify the use of this technique, and a comparison is made between a 2-D and a one-dimensional (1-D) uniform quantization scenarios. The influence of the error as well as the frame size on the estimation of the fundamental period is studied. 相似文献
Currently there are design barriers inhibiting the implementation of high-precision digital signal processing (DSP) objects with field programmable logic (FPL) devices. This paper explores overcoming these barriers by fusing together the popular distributed arithmetic (DA) method with the residue number system (RNS) for use in FPL-centric designs. The new design paradigm is studied in the context of a high-performance filter bank and a discrete wavelet transform (DWT). The proposed design paradigm is facilitated by a new RNS accumulator structure based on a carry save adder (CSA). The reported methodology also introduces a polyphase filter structure that results in a reduced look-up table (LUT) budget. The 2C-DA and RNS-DA are compared, in the context of a FPL implementation strategy, using a discrete wavelet transform (DWT) filter bank as a common design theme. The results show that the RNS-DA, compared to a traditional 2C-DA design, enjoys a performance advantage that increases with precision (wordlength). 相似文献
Adsorption of Triton X-100 on various silica substrates has been investigated. A number of solids, including a natural quartz, this quartz washed with HCl acid and subsequently heated at 1273 K; two aerosils and one Kieselgel silicas were studied. These solids exhibit surface areas in the range of 5 to 430 m2 g?1. All the Triton adsorption isotherms display an S-shape at the adsorption temperatures studied (298 and 308 K). It has been found that the pretreatments of natural quartz (by water washing, impurities removed by acid and/or high temperature calcination) affect considerably the amounts of TX-100 adsorbed. Measurements of surface composition have been made by X-ray photoelectron spectroscopy (XPS) with particular emphasis on the presence of impurities and on the number of OH groups at the surface of the samples. The nature of the surface hydroxyl has also been studied by infrared spectroscopy. Furthermore, the specific number of hydroxyl groups on the surface of the silica samples has been determined by thermogravimetric analysis. Finally an attempt to correlate solid surface characteristics with adsorption isotherms has been developed. 相似文献
BACKGROUND: The establishment of the nasopharyngeal flora was followed in Costa Rican children from birth to 1 year of age. METHODS: Nasopharyngeal cultures were obtained at 1 (n = 413), 3 (n = 393), 6 (n = 376) and 12 months (n = 356) of age from children representative of the population in the Puriscal district. Weekly cultures were obtained from a subcohort of these children (n = 101). Mother-infant diads (n = 95) and preschool children (n = 208) attending day-care centers were also studied. RESULTS: The estimated proportion of colonized children in the population differed markedly depending on the frequency of culture. Quarterly cultures showed a slow increase in carrier rates from 3.9% for Haemophilus influenzae, 3.1% for Streptococcus pneumoniae and 6.5% for Moraxella catarrhalis at 1 month of age to 10.1% carrying H. influenzae and 19.4% carrying S. pneumoniae by the end of the first year. By quarterly culture the proportion of children colonized at least once was 36% for S. pneumoniae, 26% for H. influenzae and 28% for M. catarrhalis. In contrast weekly sampling showed that 95 to 100% of the children were colonized at least once during the first year of life with H. influenzae, S. pneumoniae or M. catarrhalis. Nasopharyngeal carriage of H. influenzae, S. pneumoniae and M. catarrhalis was low in the mothers, and very few mother-infant pairs carried identical bacteria at the same time. In contrast carrier rates were high in the siblings attending day care (H. influenzae 27.9%, S. pneumoniae 39.4%, both organisms 26.6%). Infants with siblings had significantly higher bacterial carriage at all ages than infants without siblings. CONCLUSIONS: Quarterly nasopharyngeal cultures showed that Costa Rican infants acquire their nasopharyngeal flora at a rate comparable with that for infants in developed countries and that siblings are an important source of the bacteria. Weekly samplings showed that virtually all children were colonized at least once during the first year of life. 相似文献
A CEC-funded project has been performed to tackle the problem of producing an advanced Life Monitoring System (LMS) which would calculate the creep and fatigue damage experienced by high temperature pipework components. Four areas were identified where existing Life Monitoring System technology could be improved:
1. 1. the inclusion of creep relaxation
2. 2. the inclusion of external loads on components
3. 3. a more accurate method of calculating thermal stresses due to temperature transients
4. 4. the inclusion of high cycle fatigue terms.
The creep relaxation problem was solved using stress reduction factors in an analytical in-elastic stress calculation. The stress reduction factors were produced for a number of common geometries and materials by means of non-linear finite element analysis. External loads were catered for by producing influence coefficients from in-elastic analysis of the particular piping system and using them to calculate bending moments at critical positions on the pipework from load and displacement measurements made at the convenient points at the pipework. The thermal stress problem was solved by producing a completely new solution based on Green's Function and Fast Fourier transforms. This allowed the thermal stress in a complex component to be calculated from simple non-intrusive thermocouple measurements made on the outside of the component. The high-cycle fatigue problem was dealt with precalculating the fatigue damage associated with standard transients and adding this damage to cumulative total when a transient occurred.
The site testing provided good practical experience and showed up problems which would not otherwise have been detected. 相似文献
The thermal decomposition properties of Mg–Fe hydrotalcites were studied through in situ 57Fe Mössbauer spectroscopy and in situ X-ray diffraction. Abrupt changes in the quadrupolar splitting measured in the Mössbauer spectra revealed a phase transition from the starting lamellar structure to a new crystalline arrangement. By analyzing the Mössbauer parameters we show that the material is highly disordered in the 300–400 °C temperature range. This hypothesis is confirmed by the X-ray results whose diffractograms indicated the collapse of the lamellar structure and the formation of a solid solution. 相似文献
Summary The effect of molecular weight on the uniaxial orientation process has been analyzed in two samples of thermotropic poly(diethylene
glycol p,p′-bibenzoate), evaluating the influence of that parameter on the type of orientation obtained. Several strain rates and deformation
temperatures have been tested in order to map out the conditions for obtaining the two different kinds of orientation. The
results show that in the lower molecular weight PDEB sample (Mw=31200) it is rather easy to get exclusively perpendicular “anomalous” orientation, with the molecular axes aligned transversely
to the stretching direction. However, it is extremely difficult to obtain 100% parallel “normal” orientation. On the contrary,
either type of orientation or a mixture of them can be easily developed for the higher molecular weight PDEB sample (Mw=102900). 相似文献
A new type of bottom‐emission electroluminescent device is described in which a metal oxide is used as the electron‐injecting contact. The preparation of such a device is simple. It consists of the deposition of a thin layer of a metal oxide on top of an indium tin oxide covered glass substrate, followed by the solution processing of the light‐emitting layer and subsequently the deposition of a high‐workfunction (air‐stable) metal anode. This architecture allows for a low‐cost electroluminescent device because no rigorous encapsulation is required. Electroluminescence with a high brightness reaching 5700 cd m–2 is observed at voltages as low as 8 V, demonstrating the potential of this new approach to organic light‐emitting diode (OLED) devices. Unfortunately the device efficiency is rather low because of the high current density flowing through the device. We show that the device only operates after the insertion of an additional hole‐injection layer in between the light‐emitting polymer (LEP) and the metal anode. A simple model that explains the experimental results and provides avenues for further optimization of these devices is described. It is based on the idea that the barrier for electron injection is lowered by the formation of a space–charge field over the metal‐oxide–LEP interface due to the build up of holes in the LEP layer close to this interface. 相似文献