For pt.I see ibid., vol.50, no.3, p.267-78 (2003). This paper presents an application of continuous wave ultrasound Doppler velocity measurements to two-phase flow in pipes. In many petroleum wells, the multiphase flow is separated into two phases: the first is a liquid phase and the second is a gas phase with small scatterers. The problem of multiphase velocity profile measurements has not been satisfactorily solved by classical approaches due to the multiphase nature of the fluid and the presence of colored noise, which introduces a significant bias in classical frequency estimators. We propose the use of resolution frequency techniques to overcome the classical limitations. Direct estimation of Doppler frequency then obtained using either time frequency maximum frequency or arguments of poles of the parametric model that identifies the Doppler part of the signal is discussed. The tests made with synthetic Doppler signals and two-phase flow have demonstrated the excellent performance of the high resolution techniques based on reassignment and parametric techniques. 相似文献
Abstract. We consider generalized first-order sentences over < using both ordinary and modular quantifiers. It is known that the languages definable by such sentences are exactly the regular languages whose syntactic monoids contain only solvable groups. We show that any sentence in this logic is equivalent to one using three variables only, and we prove that the languages expressible with two variables are those whose syntactic monoids belong to a particular pseudovariety of finite monoids, namely the wreath product of the pseudovariety DA (which corresponds to the languages definable by ordinary first-order two-variable sentences) with the pseudovariety of finite solvable groups. This generalizes earlier work of Thérien and Wilke on the expressive power of two-variable formulas in which only ordinary quantifiers are present. If all modular quantifiers in the sentence are of the same prime modulus, this provides an algorithm to decide if a regular language has such a two-variable definition. 相似文献
The implementation challenge for new low-cost low-power wireless modem transceivers has continuously been growing with increased
modem performance, bandwidth, and carrier frequency. Up to now we have been designing transceivers in a way that we are able
to keep the analog (RF) problem domain widely separated from the digital signal processing design. However, with today’s deep
sub-micron technology, analog impairments – “dirt effects” – are reaching a new problem level which requires a paradigm shift
in the design of transceivers. Examples of these impairments are phase noise, non-linearities, I/Q imbalance, ADC impairments,
etc. In the world of “Dirty RF” we assume to design digital signal processing such that we can cope with a new level of impairments,
allowing lee-way in the requirements set on future RF sub-systems. This paper gives an overview of the topic and presents
analytical evaluations of the performance losses due to RF impairments as well as algorithms that allow to live with imperfect
RF by compensating the resulting error effects using digital baseband processing. 相似文献
This paper describes realization and characterization of SrTiO3 (STO) high K MIM capacitors above BiCMOS integrated circuit (IC). These capacitances are connected to IC and are used as coupling capacitors in order to realize a high pass filter. Surface capacitance achieved is 10 nF/mm2 with capacitance value of 1.2 nF. The process for STO MIM fabrication does not exceed 400 °C, which is compatible with interconnections. Typical K and dielectric losses values obtained are, respectively 110% and 2%. Yield obtained reaches 83% for capacitors. A functional high pass filter using these STO capacitors was realized in this study. It exhibits a cut-off frequency at 6.5 kHz and a constant gain at higher frequencies of −1.3 dB. 相似文献
Calcium carbonate crystals with various morphologies have been found in a variety of biospecimens and artificially synthesized structures. Usually, the diversity in morphology can be attributed to different types of interactions between the specific crystal faces and the environment or the templates used for the growth of CaCO3 crystals. On the other hand, isotropic amorphous calcium carbonate (ACC) has been recognized as the precursor of other crystalline calcium carbonate forms for both in vivo and in vitro systems. However, here we propose a self-confined amorphous template process leading to the anisotropic growth of single-crystalline calcite nanowires. Initiated by the assembly of precipitated nanoparticles, the calcite nanowires grew via the continuous precipitation of partly crystallized ACC nanodroplets onto their tips. Then, the crystalline domains in the tip, which were generated from the partly crystallized nanodroplets, coalesced in the interior of the nanowire to form a single-crystalline core. The ACC domains were left outside and spontaneously formed a protective shell to retard the precipitation of CaCO3 onto the side surface of the nanowire and thus guided the highly anisotropic growth of nanowires as a template.
Information represents one of the most important factors in the success of any enterprise today. Moreover, confidential information is becoming increasingly integrated into complex info-innovation solutions and is accordingly exposed to novel means of manipulation and theft. The legal requirements concerning information security (IS) policies in organizations are mainly based on reactive approaches that follow the standards applied in this area and are regularly updated every few years. However, a complementary approach that takes into account a fast-changing information/innovation security threats landscape and that is of proactive nature is required. Such an approach is presented in this article by linking the information security field with the field of innovation management. 相似文献
Triangle meshes have been nearly ubiquitous in computer graphics, and a large body of data structures and geometry processing algorithms based on them has been developed in the literature. At the same time, quadrilateral meshes, especially semi‐regular ones, have advantages for many applications, and significant progress was made in quadrilateral mesh generation and processing during the last several years. In this survey we discuss the advantages and problems of techniques operating on quadrilateral meshes, including surface analysis and mesh quality, simplification, adaptive refinement, alignment with features, parametrisation and remeshing. 相似文献
In this article, we propose to revisit the China of April 2008 and ponder on one major event that happened that year: the boycott of the Carrefour stores, which resulted in an unprecedented display of demonstrations and protests. After having proposed an original theoretical framework (the information cascade), we move on to carry out a detailed reading of this case in order to learn from it and have a better understanding of current crises. 相似文献
Winter and summer 7-day low flows of eighteen natural rivers in the St. Lawrence River watershed of Quebec were analyzed over
the period from 1934 to 2000. The rivers were first subdivided into three modes using principal component analysis. Two of
these modes are located on the south shore of the St. Lawrence River, respectively south (Southeast mode) and north (East
mode) of the 47°N, and the third (Southwest mode) is located on the north shore. The Southeast mode shows a significant increase
in 7-day low flows in winter and summer due to increasing summer and fall precipitation, whereas the Southwest mode shows
a significant decrease in summer 7-day low flows due to an increase in evapotranspiration. No significant change in winter
and summer 7-day low flows is observed in the East mode. Results show that the variability of 7-day low flows and their link
with climate indices are mainly seasonally dependent. The North Atlantic Oscillation (NAO) is the only index which is correlated
to 7-day low flows in all three modes. This correlation is positive for north shore rivers and negative for south shore rivers.
Furthermore, only north shore rivers are correlated to NAO in both winter and summer. 相似文献