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Analytical approximation of nonlinear vibration of string with large amplitudes
Mojtaba Parvizi Omran,Amin Amani,Hirpa Gelgele Lemu 대한기계학회 2013 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.27 No.4
Study of nonlinear problems in strings with large amplitude is a very important research area in many fields of physics and engineering. variational approach method (VAM) is in particular selected because the method is appropriate to solve nonlinear vibration of a constanttension string. VAM is an explicit method with high capability for resolving strong nonlinear oscillation system problems. It has been found that VAM is well suited for a range of parameters and the approximate frequencies and periodic solutions show a good agreement with the exact ones. This paper compares the various aspects of VAM in relative to exact approaches and higher-order approximate solutions for the constant-tension string. The comparison indicates that VAM is very fast, effective and convenient. The method does not require any linearization or small perturbation, and it leads to high accuracy of the solutions in a single iteration.
Yousefi, Reza,Ardestani, Susan K.,Saboury, Ali Akbar,Kariminia, Amina,Zeinali, Madjid,Amani, Mojtaba Korean Society for Biochemistry and Molecular Biol 2005 Journal of biochemistry and molecular biology Vol.38 No.4
Calcium and zinc binding protein, calprotectin is a multifunctional protein with broad spectrum antimicrobial and antitumoural activity. It was purified from human neutrophil, using a two-step ion exchange chromatography. Since surface hydrophobicity of calprotectin may be important in membrane anchoring, membrane penetration, subunits oligomerization and some biological roles of protein, in this study attempted to explore the effect of calcium in physiological range on the calprotectin lipophilicity. Incubation of human calprotectin ($50\;{\mu}g/ml$) with different calcium concentrations showed that 1-anilino-8-naphthalene sulfonic acid (ANS) fluorescence intensity of the protein significantly elevates with calcium in a dose dependent manner, suggesting an increase in calprotectin surface hydrophobicity upon calcium binding. Our study also indicates that calcium at higher concentrations (6, 8 and 10 mM) induces aggregation of human calprotectin. Our finding demonstrates that the starting time and the rate constant of calprotectin aggregation depend on the calcium concentration.
Rezaei-Tavirani, Mostafa,Moghaddamnia, Seyed Hassan,Ranjbar, Bijan,Amani, Mojtaba,Marashi, Sayed-Amir Korean Society for Biochemistry and Molecular Biol 2006 Journal of biochemistry and molecular biology Vol.39 No.5
Thermal conformational changes of human serum albumin (HSA) in phosphate buffer, 10 mM at pH = 7 are investigated using differential scanning calorimetric (DSC), circular dichroism (CD) and UV spectroscopic methods. The results indicate that temperature increment from $25^{\circ}C$ to $55^{\circ}C$ induces reversible conformational changes in the structure of HSA. Conformational change of HSA are shown to be a three-step process. Interestingly, melting temperature of the last domain is equal to the maximum value of fever in pathological conditions, i.e. $42^{\circ}C$. These conformational alterations are accompanied by a mild alteration of secondary structures. Study of HSA-SDS (sodium dodecyl sulphate) interaction at $45^{\circ}C$ and $35^{\circ}C$ reveals that SDS affects the HSA structure at least in three steps: the first two steps result in more stabilization and compactness of HSA structure, while the last one induces the unfolding of HSA. Since HSA has a more affinity for SDS at $45^{\circ}C$ compared to $35^{\circ}C$, It is suggested that the net negative charge of HSA is decreased in fever, which results in the decrease of HSA-associated cations and plasma osmolarity, and consequently, heat removal via the increase in urine volume.