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排序方式: 共有790条查询结果,搜索用时 15 毫秒
61.
Fluorescence spectroscopy coupled with factorial discriminant analysis technique to identify sheep milk from different feeding systems 总被引:1,自引:0,他引:1
Moncef Hammami Hamadi Rouissi Nizar Salah Houcine Selmi Mutlag Al-Otaibi Christophe Blecker Romdhane Karoui 《Food chemistry》2010
Rapid measurements of milk properties and discrimination of milk origin are necessary techniques for quality control of milk products. The present study was undertaken to evaluate the potential of using front face fluorescence spectroscopy (FFFS) and synchronous fluorescence spectroscopy (SFS) for monitoring the quality of forty-five ewe’s milk samples originating from different feeding systems. Physico-chemical analyses and fluorescence spectra were conducted on samples during lactation periods (the first 11 weeks). The principal component analysis (PCA) separately applied to the physico-chemical and fluorescence spectral data showed only small discrimination between milk samples based on lactation periods and diet compositions. Similar results were obtained by separately applying factorial discriminant analysis (FDA) on each technique. In a second step, concatenation technique were applied to FFF spectra acquired after excitation set at 250, 290, 380 nm and emission set at 410 nm. Results obtained showed a good discrimination among milk samples with regard to feeding systems given to the ewes throughout the lactation periods. In addition, a better discrimination was observed with FFFS than with SFS. 相似文献
62.
63.
Salah S. Sedarous 《Ferroelectrics Letters Section》1998,23(5):107-119
The microscopic dynamics of phase transitions in ferroelectric crystals are studied using time-resolved fluorescence spectroscopy. Fluorescence decay times of the molecular probe tryptophan, embedded in the ferroelectric crystals potassium dihydrogen phosphate (KDP) and triglycine sulfate (TGS), are measured over a large temperature range. The dependence of the lifetime data on temperature were different between the two crystals. The magnitude of the fluorescence lifetime shows a rapid change around the phase transition temperature in KDP, while the changes in the lifetime data of the TGS crystal have been smooth. The data indicate that the order of the phase transition in solids (first or second) can be recovered using this technique. Since fluorescence lifetime is related to the dynamic interactions between the chromophore and the environment, insight into the emergence of macroscopic phase transition behavior from microscopic fluctuations near the phase transition region may be realized. 相似文献
64.
MA Bayoumi RM Kamal SF Abd El Aal EI Awad 《International journal of food microbiology》2012,158(3):225-231
Food-borne pathogens may develop certain strategies that enable them to defy harsh conditions such as chemical sanitization. Biofilm formation represents a prominent one among those adopted strategies, by which food-borne pathogens protect themselves against external threats. Thus, bacterial biofilm is considered as a major hazard for safe food production. This study was designed to investigate the adherence and the biofilm formation ability of some food-borne pathogens on stainless steel and polypropylene surfaces using chip assay, and to validate regular sanitizing process (sodium hypochlorite 250mg/L) for effective elimination of those pathogens. Sixteen pathogenic bacterial strains, previously isolated from raw milk and dairy products at Zagazig city, Egypt (9 Staphylococcus aureus, 4 Cronobacter sakazakii and 3 Salmonella enterica serovar Typhimurium), were chosen for this study. Strains showed different patterns of adherence and biofilm formation on tested surfaces with minor significance between surfaces. The ability of sodium hypochlorite to completely eradicate either adhered or biofilm-embedded pathogens varied significantly depending on the strain and type of surface used. Whilst, sodium hypochlorite reduced tested pathogens counts per cm(2) of produced biofilms, but it was not able to entirely eliminate neither them nor adherent Cronobacter sakazakii to stainless steel surface. This study revealed that biofilm is considered as a sustainable source of contamination of dairy products with these pathogens, and also emphasized the need of paying more attention to the cleaning and sanitizing processes of food contact surfaces. 相似文献
65.
Nitro‐phenyl maleimide (NPM), is the organic stabilizer for poly (vinyl chloride) (PVC), has been investigated as thermal plasticization for rigid chlorinated poly (vinyl chloride) (CPVC). Dielectric relaxation of CPVC stabilized with 10 wt% of NPM has been studied in temperature and frequency ranges of 300–450 K and 10 kHz–1 MHz, respectively. An analysis of the dielectric constant, ε′ and dielectric loss index, ε″, was performed assuming a plasticization effect of NPM molecules. The plasticization effect of NPM molecules was confirmed by the behavior of the dielectric modulus M′ and M″ spectra. A clear dielectric α‐relaxation process has been obtained in the studied temperature range. The results showed that NPM reduce the glass transition temperature, Tg, of CPVC by about 20 K. This effect has been assigned to the plasticization effect of NPM. At lower temperatures, dielectric modulus spectra reveal that there is a role of the effect of the electrode polarization in the relaxation process. The behavior AC conductivity, σac, indicated that the conduction mechanism in all CPVC samples is hopping type conduction. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers 相似文献
66.
Jan Langer Marian Klasztorny Salah El-Sayed El-Bagalaty' 《International journal for numerical methods in engineering》1992,33(5):889-905
The paper presents a family of methods with postintegration, for numerical integration of non-linear dynamic equations of motion of discrete systems. Both explicit and implicit algorithms of these methods are conditionally stable, but can give solutions of accuracy of a few orders higher than the known methods with preintegration, corresponding to them. A general analysis of stability and accuracy of single-step methods is carried out. The postintegration methods have been tested on a single-degree-of-freedom non-linear system. 相似文献
67.
68.
Research into integrated design and manufacturing based on STEP 总被引:1,自引:1,他引:0
Yaoyao F. Zhao Salah Habeeb Xun Xu 《The International Journal of Advanced Manufacturing Technology》2009,44(5-6):606-624
This paper discusses a typical STEP-compliant manufacturing environment, which effectively integrates two systems. The first generates native data that retain the information needed to machine a part on a particular machine tool, whereas the second carries out optimization for machining parameters using the dispatched information from the first system. The related research work is divided into four areas, feature generation, macro process planning, micro process planning, and machining execution. The main part of the paper is devoted to reviewing the most recent research publications. The publications have been organized into the four areas as mentioned above. The discussion section that follows looks at the STEP-compliant research from the perspectives of industrial adoption, feature recognition for process planning, challenges in STEP-enabled inspection and STEP-NC controllers. 相似文献
69.
Evaluation of Some Nonionic Surfactants Derived From Vanillin as Corrosion Inhibitors for Carbon Steel During Drilling Processes 下载免费PDF全文
Nabel A. Negm Salah M. Tawfik Emad A. Badr Mahmoud I. Abdou Ferial M. Ghuiba 《Journal of surfactants and detergents》2015,18(3):413-420
Four eco‐friendly nonionic surfactants based on vanillin were investigated as corrosion inhibitors against carbon steel dissolution during the drilling process in the oil field. The corrosion inhibition efficiencies of the tested compounds were determined using weight loss, electrochemical polarization, and electrochemical impedance techniques. The data obtained show that the nonionic surfactants prevent the corrosion of drilling tools and their inhibition efficiency increased with an increase in their concentration. Tafel curves revealed that the surfactants under study act as mixed inhibitors. The adsorption of the inhibitors on carbon steel surface decreases the double‐layer capacitance. The inhibition efficiencies of the surfactants were influenced by their chemical structure and surface activity. 相似文献
70.
Synthesis,Structure Characterization and Biological Activity of Co (II), Cu (II), and Zn (II) Complexes with (Z)‐3‐((3‐hydroxybenzylidene)amino)pyridin‐1‐ium 4‐(dodecan‐4‐yl)benzenesulfonate Surfactant 下载免费PDF全文
(Z)‐3‐((3‐hydroxybenzylidene)amino)pyridin‐1‐ium4‐dodecylbenzenesulfonate anionic surfactant and its cobalt, copper and zinc complexes were synthesized (I, I‐Co, I‐Cu and I‐Zn). The chemical structures of it were characterized by elemental analysis, FTIR, 1H‐NMR, UV–Vis spectroscopy and atomic adsorption. The effects of the chemical structures of the synthesized anionic surfactant and the type of transition metals on the surface activity are presented in this paper. The thermodynamic parameters show that adsorption and micellization processes are spontaneous. The results of biological activity measurements showed that the synthesized compounds have a great efficiency against gram positive (Bacillus subtilis and Staphylococcus aureus), gram‐ negative bacteria (Pseudomonas aeruginosa and Escherichia coli) and fungi (Candida albicans and Aspergillus niger) as well as the sulfate reducing bacteria (Desulfomonas pigra). The complexation of the anionic surfactant with Co2+, Cu2+ and Zn2+ increase the antimicrobial activity values. 相似文献