321 research outputs found
Kinematics Of Spatial Mechanisms
Large scale endeavor of research on spatial mechanisms started about half a century ago. Although significant research work has been done, the underlying framework of the theory of spatial mechanisms still appears weak. In this thesis, a theoretical foundation for the kinematic analysis and design of spatial mechanisms and robots has been developed.;In the last twenty years, the matrix method and the spherical trigonometry method have emerged as the most efficient ones among approximately ten other different methods for the kinematic analysis of spatial mechanisms. In this thesis a new method, the vector algebraic method, has been introduced. In comparison with the two methods, the proposed method has shown advantages on its efficiency, uniformity and simplicity.;The goal of this thesis is to enhance the education, research and application of spatial mechanisms
What's Missing in your Shopping Cart? A Set Based Recommendation Method for "Cold-Start" Prediction
This thesis studies the problem of predicting the missing items in the current user's session when there is no additional side information available. Many recommender systems fail in general to provide a precise set of recommendations to users with limited interaction history. This issue is regarded as the "Cold Start" problem and is typically resolved by switching to content-based approaches which require additional information. In this thesis, we use a dimensionality reduction algorithm, Word2Vec under the framework of Collaborative Filtering to tackle the "Cold Start" problem using only implicit data . We have named this combined method: Embedded Collaborative Filtering ECF. We are able to show that the ECF approach outperforms other popular state-of-the-art approaches in "Cold Start" scenarios by 2-10% regarding recommendation precision. In the experiment, we also show that the proposed method is 10 times faster in generating recommendations comparing to the Collaborative Filtering baseline method
A Machine Learning Based Quantitative Data Analysis for Screening Skin Abnormality Based on Optical Coherence Tomography Angiography (OCTA)
3-Methylquinoxaline-2-carboxylic acid 4-oxide monohydrate
In the crystal structure of the title compound, C10H8N2O3·H2O, molecules are linked via intermolecular O—H⋯O and O—H⋯N hydrogen bonds into a two-dimensional network
Research and experimental verification on low-frequency long-range underwater sound propagation dispersion characteristics under dual-channel sound speed profiles in the Chukchi Plateau
The dual-channel sound speed profiles of the Chukchi Plateau and the Canadian
Basin have become current research hotspots due to their excellent
low-frequency sound signal propagation ability. Previous research has mainly
focused on using sound propagation theory to explain the changes in sound
signal energy. This article is mainly based on the theory of normal modes to
study the fine structure of low-frequency wide-band sound propagation
dispersion under dual-channel sound speed profiles. In this paper, the problem
of the intersection of normal mode dispersion curves caused by the dual-channel
sound speed profile (SSP) has been explained, the blocking effect of seabed
terrain changes on dispersion structures has been analyzed, and the normal
modes has been separated by using modified warping operator. The above research
results have been verified through a long-range seismic exploration experiment
at the Chukchi Plateau. At the same time, based on the acoustic signal
characteristics in this environment, two methods for estimating the distance of
sound sources have been proposed, and the experiment data at sea has also
verified these two methods.Comment: 30 pages, 18 figure
Research and experimental verification on low-frequency long-range sound propagation characteristics under ice-covered and range-dependent marine environment in the Arctic
At present, research on sound propagation under the Arctic ice mainly focuses
on modeling and experimental verification of sound propagation under sea ice
cover and unique sound velocity profiles. Among them, the main research object
of concern is sound transmission loss, and this article will delve into the
time-domain waveform and fine dispersion structure of low-frequency broadband
acoustic signals. Firstly, based on the theory of normal modes, this article
derives the horizontal wavenumber expression and warping transformation
operator for refractive normal modes in the Arctic deep-sea environment.
Subsequently, based on measured ocean environmental parameters and sound field
simulation calculations, this article studied the general laws of low-frequency
long-range sound propagation signals in the Arctic deep-sea environment, and
elucidated the impact mechanism of environmental factors such as seabed terrain
changes, horizontal changes in sound velocity profiles (SSPs), and sea ice
cover on low-frequency long-range sound propagation in the Arctic. This article
validates the above research viewpoint through a sound propagation experiment
conducted in the Arctic with a propagation distance exceeding 1000km. The
marine environment of this experiment has obvious horizontal variation
characteristics. At the same time, this article takes the lead in utilizing the
warping transformation of refractive normal waves in the Arctic waters to
achieve single hydrophone based separation of normal waves and extraction of
dispersion structures, which is conducive to future research on underwater
sound source localization and environmental parameter inversion based on
dispersion structures.Comment: 46 pages, 35 figure
Effect of in vitro gastrointestinal digestion on the chemical composition and antioxidant properties of Ginkgo biloba leaves decoction and commercial capsules
In this study Ginkgo biloba leaves (GBL) decoction and commercial capsules were digested using an in vitro model. Thirty-six active compounds were identified and quantified by HPLC-ESI-MS analysis based on the MS/MS patterns (precursor ions and product ions) and retention times, in comparison with reference standards. Most compounds in GBL showed a significant decrease during intestinal digestion, with an exception of vanillic acid and biflavonoids. Bioaccessibility values of chemical compositions varied between decoction and capsules samples. Also, significant reductions of total flavonoids and total phenolic content was observed after in vitro digestion. Both, 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid (ABTS) scavenging capacity decreased after gastric digestion, but increased during intestinal digestion. Nevertheless, different behaviour was observed in reducing antioxidant power (FRAP) assay. Compared to the pH of digestion, the influence of digestive enzymes on the chemical composition and antioxidant activity of GBL was relatively minor. Overall, these results may help provide a valid foundation for further investigations on bioactive compounds and the pharmacodynamics of GBL
- …