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排序方式: 共有900条查询结果,搜索用时 15 毫秒
21.
To understand the entrainment process in granular flow, numerical experiments have been conducted using a Discrete Element Method model. A flow channel of 8 m long with \(15^\circ \) slope is setup with monitoring points located in an erodible bed. Particles, ranging from 3 to 4 mm in diameters, are used in the simulations. In the simulations, translational, rotational and average velocities, total volume, shear stresses are calculated in the measurement circles. The sizes of the measurement circles have been varied to see their effects on the results. It is found the minimum size of the measurement circles should include 20–30 particles. An new analytical model has been developed to calculate entrainment in granular flow. Results of the numerical experiment are compared with analytical model. Shear stresses at the interface between flowing particles in motion and the immobile particles in the channel bed, change of depth of erosion and entrainment rate are used to verify the analytical model. It is found that the calculated shear stresses in the PFC model agree well with the shear stresses calculated using Mohr–Coulomb frictional relationship in the analytical model. The calculated depth of erosion using the new analytical model is also compared with that from dynamic and static entrainment model. The results indicates that the analytical model is able to capture the mechanism of erosion and it can be used in granular flow analysis. 相似文献
22.
Single point incremental forming: state-of-the-art and prospects 总被引:1,自引:0,他引:1
Joost R. Duflou Anne-Marie Habraken Jian Cao Rajiv Malhotra Markus Bambach Dave Adams Hans Vanhove Amirahmad Mohammadi Jack Jeswiet 《International Journal of Material Forming》2018,11(6):743-773
Incremental sheet metal forming in general and Single Point Incremental Forming (SPIF) specifically have gone through a period of intensive development with growing attention from research institutes worldwide. The result of these efforts is significant progress in the understanding of the underlying forming mechanisms and opportunities as well as limitations associated with this category of flexible forming processes. Furthermore, creative process design efforts have enhanced the process capabilities and process planning methods. Also, simulation capabilities have evolved substantially. This review paper aims to provide an overview of the body of knowledge with respect to Single Point Incremental Forming. Without claiming to be exhaustive, each section aims for an up-to-date state-of-the-art review with corresponding conclusions on scientific progress and outlook on expected further developments. 相似文献
23.
In automatic speech recognition (ASR) systems, the speech signal is captured and parameterized at front end and evaluated
at back end using the statistical framework of hidden Markov model (HMM). The performance of these systems depend critically
on both the type of models used and the methods adopted for signal analysis. Researchers have proposed a variety of modifications
and extensions for HMM based acoustic models to overcome their limitations. In this review, we summarize most of the research
work related to HMM-ASR which has been carried out during the last three decades. We present all these approaches under three
categories, namely conventional methods, refinements and advancements of HMM. The review is presented in two parts (papers):
(i) An overview of conventional methods for acoustic phonetic modeling, (ii) Refinements and advancements of acoustic models.
Part I explores the architecture and working of the standard HMM with its limitations. It also covers different modeling units,
language models and decoders. Part II presents a review on the advances and refinements of the conventional HMM techniques
along with the current challenges and performance issues related to ASR. 相似文献
24.
Derrick K. Rollins Nidhi Bhandari Jim Kleinedler Kaylee Kotz Amber Strohbehn Lindsay Boland Megan Murphy Dave Andre Nisarg Vyas Greg Welk Warren E. Franke 《Journal of Process Control》2010,20(1):95-107
The goal of this work is to present a causation modeling methodology with the ability to accurately infer blood glucose levels using a large set of highly correlated noninvasive input variables over an extended period of time. These models can provide insight to improve glucose monitoring, and glucose regulation through advanced model-based control technologies. The efficacy of this approach is demonstrated using real data from a type 2 diabetic (T2D) subject collected under free-living conditions over a period of 25 consecutive days. The model was identified and tested using eleven variables that included three food variables as well as several activity and stress variables. The model was trained using 20 days of data and validated using 5 days of data. This gave a fitted correlation coefficient of 0.70 and an average absolute error (AAE) (i.e., the average of the absolute values for the measured glucose concentration minus modeled glucose concentration) of 13.3 mg/dL for the validation data. This AAE result was significantly better than the subject’s personal glucose meter AAE of 15.3 mg/dL for replicated measurements. 相似文献
25.
26.
Glenn Melissa J.; Lehmann Hugo; Mumby Dave G.; Woodside Barbara 《Canadian Metallurgical Quarterly》2005,119(3):806
The authors explored the possibility that there are different neural consequences, beyond the primary site of brain damage, following perirhinal cortex (PRh) lesions made in different ways. Fos expression was used as a marker for neuronal activation and compared across the forebrains of rats that underwent the different types of surgery. Electrolytic and excitotoxic PRh lesions produced dramatic increases in Fos expression in the cortex, and excitotoxic and aspiration PRh lesions increased Fos expression in the dentate gyrus. These data are consistent with the hypothesis that different lesion methods have separable effects on neural function in regions outside the lesion site that could account for inconsistencies in the literature regarding the behavioral effects of PRh lesions on tests of spatial memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
27.
An experimental and theoretical investigation was made to find out the reasons for the drop in shell-and-tube condenser performance when replacing R22 with a zeotropic mixture R407C. Measurements show that at lower condenser loads the reduction in performance can be as large as 70% compared to the full condenser load. Calculation results are compared with experimental results for two different condensers, one with micro-finned tubes and one with 3-D finned tubes. Calculations show that the degree of mixing of the newly formed condensate on a tube and the drained condensate is a factor influential enough to explain the performance drop. 3-D finned tubes seem to have better mixing in the condensate than integral finned tubes. 相似文献
28.
Spriet C Trinel D Waharte F Deslee D Vandenbunder B Barbillat J Héliot L 《Microscopy research and technique》2007,70(2):85-94
Studies of proteins' interaction in cells by FRET can take benefit from two important photo-physical properties describing fluorescent proteins: fluorescence emission spectrum and fluorescence lifetime. These properties provide specific and complementary information about the tagged proteins and their environment. However, none of them taken individually can completely quantify the involved fluorophore characteristics due to their multiparametric dependency with molecular environment, experimental conditions, and interpretation complexity. A solution to get a better understanding of the biological process implied at the cellular level is to combine the spectral and temporal fluorescence data acquired simultaneously at every cell region under investigation. We present the SLiM-SPRC160, an original temporal/spectral acquisition system for simultaneous lifetime measurements in 16 spectral channels directly attached to the descanned port of a confocal microscope with two-photon excitation. It features improved light throughput, enabling low-level excitation and minimum invasivity in living cells studies. To guarantee a fairly good level of accuracy and reproducibility in the measurements of fluorescence lifetime and spectra on living cells, we propose a rigorous protocol for running experiments with this new equipment that preserves cell viability. The usefulness of SLiM approach for the precise determination of overlapping fluorophores is illustrated with the study of known solutions of rhodamine. Then, we describe reliable FRET experiments in imaging mode realized in living cells using this protocol. We also demonstrate the benefit of localized fluorescence spectrum-lifetime acquisitions for the dynamic study of fluorescent proteins. proteins. 相似文献
29.
Holmes RW Anderson BS Phillips BM Hunt JW Crane DB Mekebri A Connor V 《Environmental science & technology》2008,42(18):7003-7009
A statewide investigation of urban creek sediment toxicity was conducted in California in recognition of increased incidences of toxicity linked to pyrethroid pesticides. The goals were to examine the spatial occurrence and magnitude of sediment toxicity in California urban creeks, and to examine the role of pyrethroids in toxic urban creek sediment samples. After a preliminary screening of 90 sites, 30 creeks were sampled in eight geographical regions. Sediment toxicity was assessed using 10 day bioassays with the resident amphipod Hyalella azteca. Bioassays were conducted at two test temperatures of 23 degrees C and at 15 degrees C to provide evidence of the cause of toxicity, and to more accurately reflect ambient environmental temperatures. Twenty-five of 30 samples were toxic when tested at 23 degrees C, and all 30 samples were toxic when tested at 15 degrees C. The magnitude of toxicity increased in samples tested at 15 degrees C suggesting the influence of pyrethroids, which are more toxic at colder temperatures. Pyrethroids were present in all sediment samples and were the only compounds detected at concentrations toxic to H. azteca. Bifenthrin was the pyrethroid of greatest toxicological concern, occurring in all 30 samples at concentrations up to 219 ng/g. Pyrethroid contamination of urban creeks was most severe in the Los Angeles, Central Valley, and San Diego regions, respectively. However, pyrethroids were also linked to urban creek aquatic toxicity in all regions sampled, including the less urbanized areas of the North Coast and Lake Tahoe. 相似文献
30.
采用X射线小角散射法(SAXS)和光子相关谱法(PCS)测试了纳米钨(W)粉的粒度分布。结果表明,采用SAXS测试出的纳米W粉的粒度分布与透射电镜观察和比表面积法测试结果十分接近,能较为准确地表征纳米W粉的一次颗粒的粒度分布;但为了得到可信的结果,所选择的X射线衍射仪的最小可测试角必须足够小。PCS法测试的纳米W粉的粒度随分散条件的变化而变化,所提供的最佳分散条件可用于测定二次颗粒的粒度分布。 相似文献