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1.
Dehydration reduces the main phase transition pressure of phospholipids. An analysis based on the Gibbs-Duhem equation shows how the shift of the transition pressure is correlated to the hydration pressure.By using Fourier transform infrared (FT-IR) spectroscopy we determined the hydration-dependent phase transition pressure. The application of our new approach gives hydration pressure values which agree with the values obtained with the osmotic stress method. 相似文献
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On the mechanical characterization of compact bone structure using the homogenization theory 总被引:1,自引:0,他引:1
In a previous paper (Crolet et al., 1993, J. Biomechanics 26, 677–687), a modelling of the mechanical behavior of compact bone was presented, in which the homogenization theory was the basic tool of computation. In this simulation, approximations were used for the modelling of the lamellae and the osteons: the lamella and the osteon were divided into cylindrical sectors, each sector being approximated as a parallelepiped having a periodic structure (fibrous composite for the lamella, superimposition of plates for the osteon). The present study deals with a new model without these approximations. First, it can be proved that the homogenized elasticity tensor for a lamella, which has a non-periodic structure, is obtained at each geometrical point as a homogenized tensor of a periodic problem. Similarly, for the osteonal structure, the components of the homogenized tensor are determined at each point as the result of a periodic homogenization.
The software OSTEON, which is the computational method associated with this model, allows one to obtain a better understanding of the effects of many bony parameters. The obtained results are in accordance with experimental data. 相似文献
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The bifurcations of the periodic solutions of SEIR and SIR epidemic models with sinusoidally varying contact rate are investigated. The analysis is carried out with respect to two parameters: the mean value and the degree of seasonality of the contact rate. The corresponding portraits in the two-parameter space are obtained by means of a numerical continuation method. Codimension two bifurcations (degenerate flips and cusps) are detected, and multiple stable modes of behavior are identified in various regions of the parameter space. Finally, it is shown how the parametric portrait of the SEIR model tends to that of the SIR model when the latent period tends to zero. 相似文献
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本文给出天然林内红松种群年令更替数学模型(1)。通过对(1)进行定性分析,得到主要结论是:系统(1)在第一象限内存在唯一稳定周期解的充要条件是bk-bc-2d>0其生态意义是天然林内红松幼树与母树随时间变化会产生一个有规律、互为消涨的变化特征。 相似文献
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一类三维非线性系统空间周期解的存在性及唯一性 总被引:1,自引:1,他引:0
本文研究了一类描述天然林内红松林种群变化的三维非线性教学模型 相似文献
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Abstract: The combined effect of hydrostatic pressure and heat shock on thermotolerance was examined in the deep-sea hyperthermophilic archaeon Pyrococcus strain ES4. Pressure equivalent to the depth of isolation (22 MPa) enhanced ES4's survival at super-optimal temperatures (101–108°C) relative to low pressure (3 MPa). Pressure also raised the temperature at which a putative heat-shock protein (98 kDa) accumulated. ES4 grown at 95°C and 3 MPa displayed immediate enhanced thermotolerance to 105°C after being shifted to 22 MPa. Cultures grown at 95°C and 22 MPa and then heat shocked at 105°C and 3 MPa retained enhanced thermotolerance after decompression. These results suggest that this deep-sea hyperthermophile has developed pressure-induced responses that include increased survival to hyperthermal conditions. 相似文献
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We present ab-initio periodic Hartree–Fock calculations (crystal program) of small molecules on TiO2 and MgO. The adsorption of the molecules may be molecular or dissociative. This depends on their acid and basic properties in the gas phase. For the molecular adsorption, the molecules are adsorbed as bases on Ti(+IV) sites, the adsorption energies correlate with the proton affinities. The dissociations on the surface correlate with the gas phase cleavages: thus, the dissociation of MeOH leads to a preferential basic cleavage (the fragment HO– is adsorbed on a Ti+4 ion and the fragment Me+ is adsorbed on a O2– ion of the oxide). The opposite result is obtained with MeSH. Another important factor is the adsorbate–adsorbate interaction: favorable cases are a sequence of H-bonds for the hydroxyl groups resulting from the water dissociation and the mode of adsorption for the ammonium ions. Lateral interactions also force the adsorbed CO2 molecules to bend over the surface so that their mutual orientation resembles the geometry of the CO2 dimer. With respect to water adsorption, MgO appears to be a basic oxide. As experimentally observed, NH3 adsorbs preferentially on TiO2 and CO2 on MgO. However, this difference of reactivity should not be expressed in terms of acid vs. basic behaviour but in terms of hard and soft acidity. The MgO surface is a 'soft' acidic surface that reacts preferentially with the soft base, CO2. 相似文献
10.
Winona C. Barker Lynne K. Ketcham Margaret O. Dayhoff 《Journal of molecular evolution》1978,10(4):265-281
Summary We have implemented a routine procedure for screening protein sequences for evidence of intragenic duplications. We tested 163 protein sequences representing 116 superfamilies of unrelated proteins. Twenty superfamilies contain proteins with internal gene duplications. The intragenic duplications detected can be divided into two major types. (1) One or more duplications of all or part of a gene produce a protein with two or several detectable regions of sequence homology. Sequences from 18 superfamilies contained this type of duplication. (2) Repeated reduplication of a small DNA segment can produce a protein that is repetitive over most of its length. Three superfamilies contain such repetitive sequences. We also investigated the limits of detection of ancient duplications using sequences derived by random mutation of a model sequence consisting of ten 10-residue repeats. The original repetitive nature of the sequence was usually detected after 250 point mutations even though the ancestral segment could not be accurately reconstructed. 相似文献