The Analysis and Improvement of a Current-Steering DAC's Dynamic SFDR—II: The Output-Dependent Delay Differences

For a current-steering digital-to-analog converter (DAC) without an extra output stage, the variation of the output voltage will result in the variation of the output delay. These output-dependent delay differences will deteriorate the spurious-free dynamic range (SFDR) of a high-speed high-accuracy DAC, especially when glitches exist. In this paper, a convenient mathematical model is presented to analyze during design the impact of this kind of delay differences on the SFDR. The results are verified by comparison to the results of more detailed simulations. Also the impact of glitches on this effect is demonstrated. Possible solutions to reduce this impact are discussed and summarized     

Morphological and stance interpolations in database for simulating bipedalism of virtual humans

We present a computer tool for testing walk hypotheses for human beings. This tool aims to generate plausible walking movements according to anatomical knowledge. To this end, we introduce an interpolation method based, on one hand, on morphological data and, on the other hand, on stance hypotheses and on footprint hypotheses. We want to test these hypotheses for application to the reconstruction of early hominid walking. We interpolate from a specific representation of the movement—a characteristic relative displacement. First, we use a motion capture system to acquire real movements of a walk cycle, and we propose to represent them by using a generic parametric model. Thus, we create a database of movements. The interpolation process produces, thanks to this database, a retargeted motion adapted to the morphology of the considered targeted skeleton. The interpolation is done according to three main hypotheses. The first concerns the reference stance, the second the lateral spacing between the feet, and the third the length of the step. In the introduction, we refer to related work. Then we propose the two following points of our method: the 3D representation of our motion representation and the multidimensional interpolation method applied to this representation. The interpolation method addresses morphological adaptation, and the use of an inverse kinematics solver addresses the computation of skeleton movements. The self-coherent validation process aims to test the coherence of the proposed method. The results propose an application to a virtual skeleton of Lucy (Australopithecus afarensis A.L. 288-1) reconstructed from real data. Finally, the relevance of the method for anthropological investigations and for animation purposes is discussed and future work is discussed with respect to the limitations of the proposed method.     

Three-Dimensional Cell Culture: A Breakthrough in Vivo

Cell culture is an important tool for biological research. Two-dimensional cell culture has been used for some time now, but growing cells in flat layers on plastic surfaces does not accurately model the in vivo state. As compared to the two-dimensional case, the three-dimensional (3D) cell culture allows biological cells to grow or interact with their surroundings in all three dimensions thanks to an artificial environment. Cells grown in a 3D model have proven to be more physiologically relevant and showed improvements in several studies of biological mechanisms like: cell number monitoring, viability, morphology, proliferation, differentiation, response to stimuli, migration and invasion of tumor cells into surrounding tissues, angiogenesis stimulation and immune system evasion, drug metabolism, gene expression and protein synthesis, general cell function and in vivo relevance. 3D culture models succeed thanks to technological advances, including materials science, cell biology and bioreactor design.     

Life cycle emissions analysis of two nZEB concepts

The net-zero emissions building (nZEB) performance is investigated for building operation (EO) and embodied emissions in materials (EE) for Norway's cold climate. nZEB concepts for new residential and office buildings are conceived in order to understand the balance and implications between operational and embodied emissions over the building's life. The main drivers for the CO₂ equivalent (CO₂e) emissions are revealed for both building concepts through a detailed emissions calculation. The influence of the CO₂e factor for electricity is emphasized and it is shown to have significant impact on the temporal evolution of the overall CO₂e emissions balance. The results show that the criterion for zero emissions in operation is easily reached for both nZEB concepts (independent of the CO₂e factor considered). Embodied emissions are significant compared to operational emissions. It was found that an overall emissions balance including both operational and embodied energy is difficult to reach and would be unobtainable in a scenario of low carbon electricity from the grid. In this particular scenario, the net balance of emissions alone is nonetheless not a sufficient performance indicator for nZEB.     

探析中国传统植物学知识

<正>约瑟夫·尼达姆[李约瑟](Joseph Needham,1900-1995)曾在《中国科学与文明史》(Science and Civilisation in China)第6卷第1期发表了对中国植物学的专项研究。由此,读者可以了解到:在中国古代医学和     

CFD simulation of particle deposition in a reconstructed human oral extrathoracic airway for air and helium–oxygen mixtures

In order to compare the effects of using helium–oxygen and air in assisted breathing and inhalation therapies, flow and particle deposition results were obtained in a realistic model of human oral extrathoracic (ET) airways using computational fluid dynamics (CFD) and pressure loss measurements. As the main deposition mechanism for pharmaceutical aerosols in the ET is inertial impaction, the ET model was reconstructed from medical images to take into account the complexity of realistic morphological features. Calculations were performed with the CFD software Fluent^®, and pressure losses were measured on a cast based on a stereolithographic fabrication of the model. Results show that ET pressure loss and particle deposition are lower with helium–oxygen as compared to air. Moreover, further simulations were performed with various particle sizes and inspiratory flow rates, which indicate that particle deposition in the ET depends on both the Stokes and Reynolds number.     

Impact of retention on trans‐column velocity biases in packed columns

The heights equivalent to a theoretical plate of a weakly and strongly retained compounds were measured on two packed columns having different average mesopore sizes. The measurements were carried out in two different cases, with access to the mesopores by the sample molecules blocked (filled with n‐nonane) or not. The experimental results demonstrate that the eddy dispersion terms of both columns are significantly smaller for porous than for nonporous particles. Two simultaneous phenomena explain this observation. First, packed columns are radially heterogeneous which causes significant trans‐column velocity biases warping the bands. Second, radial dispersion contributes to mass transfer across the column, relaxing the radial concentration gradients that are caused by these velocity biases. The impact of these biases is minimized when the pores of the particles are not blocked; it decreases with increasing residence time and radial dispersion coefficient of the solutes. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Membrane performance in combined processes including ozonation or advanced oxidation, powdered activated carbon and coagulation — Investigations in pilot scale

In Luxembourg the largest drinking water production plant treating reservoir water with conventional technology including ozonation is in operation since 1969. Its maximum capacity is 64,000 m³/d. After 40 years of operation the need for both modernizing and extension of capacity to 100,000 m³/d emerged. Nowadays, due to new developments in technology and research it is possible to assess the water treatment processes more effectively with regard to current and future requirements. Against this background, membrane processes combined with conventional and advanced processes were identified as potential option and long term pilot-scale tests were started in June 2008. Different treatment process schemes all including membranes are investigated in a one year pilot plant period. Various treatment steps such as different pre- and post-treatment steps, various membranes and membrane materials and also conventional treatment steps are compared and assessed.     

Analyzing and modeling the performance degradation of flash A/D converters due to substrate noise coupling

This paper presents a model to evaluate the impact of substrate noise on a CMOS regenerative comparator and moreover to predict the resulting performance degradation of a flash analog-to-digital (A/D) converter. The proposed approach initially relates substrate noise to the induced timing uncertainty of the comparator by means of an analytical linear model. In particular, the analysis first focuses on analyzing and expressing the resulting non-uniform sampling distortion in regenerative comparators in the presence of a deterministic ground bounce. Two sources of distortion are identified and evaluated: the input-dependent and the substrate noise-dependent one. For each error contributor, the analysis investigates two cases of timing error, based on the frequency correlation of the interfering signal with the sampling clock. The properties (number and power of distortion tones) of the sampling error spectrum are found to be highly dependent on the spectral content of the interfering signal and the sampling clock, while the model captures accurately the induced distortion. Subsequently, the linear model is extended to estimate the degradation of flash A/D converters and is utilized to predict the performance of practical flash and time-interleaved converters in the presence of substrate noise.