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排序方式: 共有3172条查询结果,搜索用时 15 毫秒
61.
An approximate formulation is presented for the analysis of sandwich plates consisting of an orthotropic core and two unequal thickness anisotropic face plates. The method uncouples the membrane and bending actions, thereby significantly reducing the effort involved in accurately predicting displacements and stresses. Defining modified stiffnesses, the formulation is valid for relatively thick anisotropic laminated face plates and can be combined with a variety of analysis techniques. Using a series solution, results are generated herein for simply supported sandwich plates with unbalanced cross-ply and angle-ply faces. 相似文献
62.
Tuning PI controllers for stable processes with specifications on gain and phase margins 总被引:2,自引:0,他引:2
Kaya I 《ISA transactions》2004,43(2):297-304
In industrial practice, controller designs are performed based on an approximate model of the actual process. It is essential to design a control system which will exhibit a robust performance because the physical systems can vary with operating conditions and time. Gain and phase margins are well known parameters for evaluating the robustness of a control system. This paper presents a tuning algorithm to design and tune PI controllers for stable processes with a small dead time while meeting specified gain and phase margins. Simulation examples are given to demonstrate that the proposed design method can result, in a closed-loop system, in better performances than existing design methods which are also based on user-specified gain and phase margins. 相似文献
63.
Quality evaluation model using loss function for multiple S-type quality characteristics 总被引:2,自引:2,他引:2
W.M. Chan R.N. Ibrahim P.B. Lochert 《The International Journal of Advanced Manufacturing Technology》2005,26(1-2):98-101
Most of the studies of quality system or product-quality assessment deal with a single quality characteristic to determine the quality loss. Products are often assessed on more than one quality characteristic. For this reason, different multivariate quality loss functions have been proposed. However, these loss functions only consider the nominal-the-best quality characteristics (N-type); they do not consider the condition when the quality characteristics are of the smaller-the-better (S-type). In this article, we present a quality evaluation model using loss function for multiple S-type quality characteristics. A numerical example is illustrated showing that using inappropriate loss functions will lead to inaccurate results that give either an underestimate or overestimate of the expected quality costs. 相似文献
64.
Mohamad Maatouk Ahmad Ibrahim Lucile Pinault Nicholas Armstrong Said Azza Jean-Marc Rolain Fadi Bittar Didier Raoult 《International journal of molecular sciences》2022,23(10)
The increased exploitation of microbial sequencing methods has shed light on the high diversity of new microorganisms named Candidate Phyla Radiation (CPR). CPR are mainly detected via 16S rRNA/metabarcoding analyses or metagenomics and are found to be abundant in all environments and present in different human microbiomes. These microbes, characterized by their symbiotic/epiparasitic lifestyle with bacteria, are directly exposed to competition with other microorganisms sharing the same ecological niche. Recently, a rich repertoire of enzymes with antibiotic resistance activity has been found in CPR genomes by using an in silico adapted screening strategy. This reservoir has shown a high prevalence of putative beta-lactamase-encoding genes. We expressed and purified five putative beta-lactamase sequences having the essential domains and functional motifs from class A and class B beta-lactamase. Their enzymatic activities were tested against various beta-lactam substrates using liquid chromatography-mass spectrometry (LC-MS) and showed some beta-lactamase activity even in the presence of a beta-lactamase inhibitor. In addition, ribonuclease activity was demonstrated against RNA that was not inhibited by sulbactam and EDTA. None of these proteins could degrade single- and double-stranded-DNA. This study is the first to express and test putative CPR beta-lactamase protein sequences in vitro. Our findings highlight that the reduced genomes of CPR members harbor sequences encoding for beta-lactamases known to be multifunction hydrolase enzymes. 相似文献
65.
N. A. Ibrahim S. E. Zayan R. M. Issa G. B. El-Hefnawey 《Advanced Synthesis \u0026amp; Catalysis》1973,315(2):202-210
The U. V. and visible absorption spectra of α-nitroso-β-naphthol and nitroso-R-salt are recorded in solutions of varying pH. The U. V. bands are assigned to π → π* transition within the aromatic system while the visible bands are assigned to intramolecular charge transfer. The pK of both compounds are determined from spectrophotometric and pH measurements. 相似文献
66.
Abdullah Saad Abdullah Ibrahim El Tantawy El Sayed Abdel Moneim A. El-Torgoman Abul Kalam S. Wageh Maher A. Kamel 《International journal of molecular sciences》2022,23(10)
Background: Silymarin (SIL) has long been utilized to treat a variety of liver illnesses, but due to its poor water solubility and low membrane permeability, it has a low oral bioavailability, limiting its therapeutic potential. Aim: Design and evaluate hepatic-targeted delivery of safe biocompatible formulated SIL-loaded chitosan nanoparticles (SCNPs) to enhance SIL’s anti-fibrotic effectiveness in rats with CCl4-induced liver fibrosis. Methods: The SCNPs and chitosan nanoparticles (CNPs) were prepared by ionotropic gelation technique and are characterized by physicochemical parameters such as particle size, morphology, zeta potential, and in vitro release studies. The therapeutic efficacy of successfully formulated SCNPs and CNPs were subjected to in vivo evaluation studies. Rats were daily administered SIL, SCNPs, and CNPs orally for 30 days. Results: The in vivo study revealed that the synthesized SCNPs demonstrated a significant antifibrotic therapeutic action against CCl4-induced hepatic injury in rats when compared to treated groups of SIL and CNPs. SCNP-treated rats had a healthy body weight, with normal values for liver weight and liver index, as well as significant improvements in liver functions, inflammatory indicators, antioxidant pathway activation, and lipid peroxidation reduction. The antifibrotic activities of SCNPs were mediated by suppressing the expression of the main fibrosis mediators TGFβR1, COL3A1, and TGFβR2 by boosting the hepatic expression of protective miRNAs; miR-22, miR-29c, and miR-219a, respectively. The anti-fibrotic effects of SCNPs were supported by histopathology and immunohistochemistry (IHC) study. Conclusions: According to the above results, SCNPs might be the best suitable carrier to target liver cells in the treatment of liver fibrosis. 相似文献
67.
Khaled?ElbassioniEmail author Amr?Elmasry Ibrahim?Kamel 《Distributed and Parallel Databases》2005,17(3):215-249
We consider the problem of indexing a set of objects moving in d-dimensional spaces along linear trajectories. A simple external-memory indexing scheme is proposed to efficiently answer
general range queries. The following are examples of the queries that can be answered by the proposed method: report all moving
objects that will (i) pass between two given points within a specified time interval; (ii) become within a given distance
from some or all of a given set of other moving objects. Our scheme is based on mapping the objects to a dual space, where
queries about moving objects are transformed into polyhedral queries concerning their speeds and initial locations. We then
present a simple method for answering such polyhedral queries, based on partitioning the space into disjoint regions and using
a B+-tree to index the points in each region. By appropriately selecting the boundaries of each region, we guarantee an average
search time that matches a known lower bound for the problem. Specifically, for a fixed d, if the coordinates of a given set of N points are statistically independent, the proposed technique answers polyhedral queries, on the average, in O((N/B)1−1/d⋅(log B N)1/d+K/B) I/O's using O(N/B) space, where B is the block size, and K is the number of reported points. Our approach is novel in that, while it provides a theoretical upper bound on the average
query time, it avoids the use of complicated data structures, making it an effective candidate for practical applications.
The proposed index is also dynamic in the sense that it allows object insertion and deletion in an amortized update cost of
log B(N) I/O's. Experimental results are presented to show the superiority of the proposed index over other methods based on R-trees.
recommend Ahmed Elmagarmid 相似文献
68.
Eslam B. Elkaeed Ibrahim H. Eissa Hazem Elkady Ahmed Abdelalim Ahmad M. Alqaisi Aisha A. Alsfouk Alaa Elwan Ahmed M. Metwaly 《International journal of molecular sciences》2022,23(15)
Among a group of 310 natural antiviral natural metabolites, our team identified three compounds as the most potent natural inhibitors against the SARS-CoV-2 main protease (PDB ID: 5R84), Mpro. The identified compounds are sattazolin and caprolactin A and B. A validated multistage in silico study was conducted using several techniques. First, the molecular structures of the selected metabolites were compared with that of GWS, the co-crystallized ligand of Mpro, in a structural similarity study. The aim of this study was to determine the thirty most similar metabolites (10%) that may bind to the Mpro similar to GWS. Then, molecular docking against Mpro and pharmacophore studies led to the choice of five metabolites that exhibited good binding modes against the Mpro and good fit values against the generated pharmacophore model. Among them, three metabolites were chosen according to ADMET studies. The most promising Mpro inhibitor was determined by toxicity and DFT studies to be caprolactin A (292). Finally, molecular dynamics (MD) simulation studies were performed for caprolactin A to confirm the obtained results and understand the thermodynamic characteristics of the binding. It is hoped that the accomplished results could represent a positive step in the battle against COVID-19 through further in vitro and in vivo studies on the selected compounds. 相似文献
69.
Irshad Ahmad Guanglong Zhu Guisheng Zhou Xudong Song Muhi Eldeen Hussein Ibrahim Ebtehal Gabralla Ibrahim Salih Shahid Hussain Muhammad Usama Younas 《International journal of molecular sciences》2022,23(13)
The presence of phyto-hormones in plants at relatively low concentrations plays an indispensable role in regulating crop growth and yield. Salt stress is one of the major abiotic stresses limiting cotton production. It has been reported that exogenous phyto-hormones are involved in various plant defense systems against salt stress. Recently, different studies revealed the pivotal performance of hormones in regulating cotton growth and yield. However, a comprehensive understanding of these exogenous hormones, which regulate cotton growth and yield under salt stress, is lacking. In this review, we focused on new advances in elucidating the roles of exogenous hormones (gibberellin (GA) and salicylic acid (SA)) and their signaling and transduction pathways and the cross-talk between GA and SA in regulating crop growth and development under salt stress. In this review, we not only focused on the role of phyto-hormones but also identified the roles of GA and SA responsive genes to salt stress. Our aim is to provide a comprehensive review of the performance of GA and SA and their responsive genes under salt stress, assisting in the further elucidation of the mechanism that plant hormones use to regulate growth and yield under salt stress. 相似文献
70.
Polat Cevik Ibrahim Kocaman Abdullah S. Akgul Barbaros Akca 《Journal of Intelligent and Robotic Systems》2013,70(1-4):595-608
At the last two decades, according to UAVs concepts and technological advances, there have been lots of unimagined improvements. Nowadays there are serious works and researches about the usage of UAVs in military operations at electronic warfare (EW) missions. But most of the work on UAV platforms is based upon the advantages of a single, big, expensive, and non-expendable platform. In this study, to get rid off the disadvantages of a stand alone platform a new concept is developed consisting of multiple UAVs with smaller dimensions, at a cheaper price and a wider coverage. According to clarify the study, firstly the EW and RADAR systems and then the swarm UAV concepts are explained. In this manner the current and previous works are pointed out and then the use of the swarm UAVs for EA in military operations is stated. Objectively, the swarm UAV concept’s advantages and some outstanding challenges to the intra-theater space have been put forward regarding the information mentioned above. As a result it is considered that the swarm UAV systems will be tasked important EW missions in the future operation theatres, as soon as the technical handicaps are solved. 相似文献