共查询到20条相似文献,搜索用时 109 毫秒
1.
ZHANG Hao WANG Peng-jie LEI Xin-gen YANG Hong-ju ZHANG Lu-da REN Fa-zheng ZHENG Li-min 《光谱学与光谱分析》2013,33(5):1275-1280
The effects of heat treatment (heating temperature and pH) on the structures and emulsifying properties of caseins were systematically studied by spectroscopy. Heat treatment from 60 to 100 ℃ resulted in an increase in their fluorescence intensity, hydrodynamic diameter, turbidity and emulsifying activity index, but decreased the size polydispersity of caseins. In the pH range of 5.5 to 7.0, the fluorescence intensity, hydrodynamic diameter, turbidity and emulsifying properties decreased with increased heating pH, but the size polydispersity of caseins increased with increased pH. The relationship between the surface fluorescence intensity and emulsifying activity was also investigated, revealing a correlation coefficient of 0.90. These results suggested that heat treatment could be used to modify the structures and emulsifying properties of caseins by appropriately selecting heating conditions. 相似文献
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The thermal conductivity of mesoporous material has aroused the great interest of scholars due to its wide applications such as insulation,catalyst,etc.Mesoporous alumina substrate consists of uniformly distributed,unconnected cylindrical pores.Near-field radiative heat transfer cannot be ignored,when the diameters of the pores are less than the characteristic wavelength of thermal radiation.In this paper,near-field radiation across a cylindrical pore is simulated by employing the fluctuation dissipation theorem and Green function.Such factors as the diameter of the pore,and the temperature of the material are further analyzed.The research results show that the radiative heat transfer on a mesoscale is 2~4 orders higher than on a macroscale.The heat flux and equivalent thermal conductivity of radiation across a cylindrical pore decrease exponentially with pore diameter increasing,while increase with temperature increasing.The calculated equivalent thermal conductivity of radiation is further developed to modify the thermal conductivity of the mesoporous alumina.The combined thermal conductivity of the mesoporous alumina is obtained by using porosity weighted dilute medium and compared with the measurement.The combined thermal conductivity of mesoporous silica decreases gradually with pore diameter increasing,while increases smoothly with temperature increasing,which is in good agreement with the experimental data.The larger the porosity,the more significant the near-field effect is,which cannot be ignored. 相似文献
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ZHANGYong-Gang HEYou-Jun LIAi-Zhen 《中国物理快报》2003,20(5):678-681
The transient thermal characteristics of InAlAs/InGaAs/InP mid-infrared quantum cascade lasers in pulse driving conditions have been simulated by using the finite-element method,and evaluated experimentally.The results show that specific heat of the materials and heat capacity of the device should be take into account to simulate the thermal performance of the devices in pulse driving conditions.In this case,good coincidence of the simulation with the measured results has been reached and the much higher apparent thermal resistance of the quantum cascade lasers under pulse driving conditions could be explained. 相似文献
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Investigation of a Microcalorimeter for Thin-Film Heat Capacity Measurement 总被引:1,自引:0,他引:1
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A microcalorimeter is studied for testing heat capacity of thin films. The microcalorimeter is a suspended membrane supported by six microbridges, which is fabricated by the front-side surface micromachining. Compared to the bulk micro-machined one, the microcalorimeter has excellent mechanical strength and precisely controlled pattern size as well as good thermal characteristics that are essential to a microcalorimeter. The heating rate of the microcalorimeter is up to 2 × 10^5Kis with 4.5mW heating power in vacuum, and the heat capacity of the corresponding empty microcalorimeter is about 23.4nJ/K at 30OK. By a pulse calorimetry, the heat capacity of A1 thin films with thickness of 40-1150nm are measured in the temperature range from 300K to 420K in vacuum. The mass of each sample is evaluated and the specific heat capacity is calculated. The results show that specific heat capacity of the 1150-nm A1 film agrees well with the data of bulk A1 reported in the literature. For the thinner films, enhanced heat capacity is observed. 相似文献
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In this paper,the low-temperature properties of the spin-1 two-dimensional frustrated Heisenberg antiferromagnet with the single-ion anisotropy are investigated on a square lattice by using the spin-wave theory.The influence of the frustration and anisotropy is found in the thermodynamics of the model,such as the temperature dependence of the staggered magnetization and specific heat.For some selected values of the frustration and anisotropy parameters,the results for the specific heat are compared with those of existing theories and numerical estimates.Within a spin-wave analysis,we have found the evidence for an intermediate magnetically disorder phase to separate the N′eel and collinear phases. 相似文献
6.
The internal energy and specific heat of a Heisenberg ferro-
antiferromagnetic double-layer system are studied by using spin-wave theory
and the retarded Green function method at low temperatures.
Numerical results show that the antiferromagnetic intralayer coupling
$J_2 $ has an important influence on internal energy and specific
heat for a four-sublattice system with antiferromagnetic (or
ferrimagnetic) interlayer couplings. 相似文献
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We employ Prasher's non-dimensional form to analyse the size effects on specific heat of Al thin films. Compared the calculation results of pure aluminium film with the experimental data, it is found that the reduction of phonon states is not the main reason of the size effect on the specific heat Al thin films with thickness from lOnm to 37Onm. However, the Al thin film in air usually has an oxidation layer and the specific heat of the layer is smaller than Al. By including the contribution of the oxidation layer to the thin-film specific heat, the calculation results are much closer to the experimental data. This may be a possible reason of the size effects on specific heat of Al thin films. 相似文献
8.
JIANGWei WEIGuo-Zhu DUAn ZHANGQi 《理论物理通讯》2003,40(4):503-506
The spin-1 Ising model with biaxiM crystal-field on the honeycomb lattice is investigated by using the effective-field theory with self-spin correlations and the differential operator technique. The effects of biaxial crystal-field described by two uniaxial anisotropy parameters Dx and Dy on the phase transition and specific heat and susceptibility are studied numerically. Some interesting results are observed in the system such as tricritical behavior depending sensitively on the strength of the biaxial crvstal-field. 相似文献
9.
CHENGNan-Pu CHENZhi-Qian CHEN-Hong 《中国物理快报》2003,20(5):731-734
The thermodynamic properties of an ensemble of metallic nano-particles are affected by the level distribution and the level correlation between the discrete electronic energy levels.We numerically calculate the specific heat of metallic nano-particles in the canonical ensemble with an odd or even number of electrons by considering the effects of the level distribution and the level correlation.The behaviour of the specific heat at low and high temperatures,compared with the average nearest-neighbour level spacing,is also investigated. 相似文献
10.
Theoretical calculations of thermophysical properties of single-wall carbon nanotube bundles
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Carbon nanotube bundles are promising thermal interfacial materials due to their excellent thermal and mechanical characteristics.In this study,the phonon dispersion relations and density of states of the single-wall carbon nanotube bundles are calculated by using the force constant model.The calculation results show that the inter-tube interaction leads to a significant frequency raise of the low frequency modes.To verify the applied calculation method,the specific heat of a single single-wall carbon nanotube is calculated first based on the obtained phonon dispersion relations and the results coincide well with the experimental data.Moreover,the specific heat of the bundles is calculated and exhibits a slight reduction at low temperatures in comparison with that of the single tube.The thermal conductivity of the bundles at low temperatures is calculated by using the ballistic transport model.The calculation results indicate that the inter-tube interaction,i.e.van der Waals interaction,hinders heat transfer and cannot be neglected at extremely low temperatures.For(5,5) bundles,the relative difference of the thermal conductivity caused by ignoring inter-tube effect reaches the maximum value of 26% around 17 K,which indicates the significant inter-tube interaction effect on the thermal conductivity at low temperatures. 相似文献
11.
Y. Xiao X. H. Yan D. L. Wang Y. Zhang 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,62(4):433-438
A detailed analysis of room temperature specific heat of unrelaxed layered
and nonlayered nanotubes is presented. Our results exhibit a close interplay
between surface and quantization contributions of specific heat, i.e.
Csurface and Cquantum. The calculated specific heat of single-layer
and multi-layer layered nanotubes increases with diameter regardless of the
species. However, slowly increasing Cquantum and rapidly decreasing
Csurface with diameter result in the decrease of specific heat of
nonlayered nanotubes. Moreover, our theoretical results are compared with
experimental observation and physical mechanisms are discussed. These
results imply that the existence of surface in nonlayered nanotubes has an
important influence on specific heat. 相似文献
12.
为实现干凝胶法制备惯性约束聚变靶用空心玻璃微球(HGM)炉内成球工艺过程的有效控制,从数值模拟和工艺实验两个方面研究了干凝胶粒子直径、比热容、发泡剂质量分数和辐射吸收系数对干凝胶粒子炉内成球过程及最终HGM性能参数的影响。结果表明,随着干凝胶粒子直径和/或比热容的增大,干凝胶粒子在吸热封装阶段的升温速率显著降低,在炉内成球过程各工艺阶段的停留时间快速下降,尤其是在精炼阶段的停留时间急剧缩短。降低干凝胶粒子的比热容和/或提高干凝胶粒子的发泡剂质量分数,HGM的直径和壁厚均匀性增大,高质量空心球的比例也相应提高。干凝胶粒子的辐射吸收系数变化对炉内成球过程几乎没有影响。 相似文献
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The low-temperature behavior of the specific heat in disordered nanotubes strongly depends on structure changes and is not explained by the phonon contribution. Expression for electronic specific heat is carried out taking into account the multiple elastic electron scattering on impurities and structural inhomogeneities of short-range order type. The calculated electronic specific heat depends on diameter of nanotube, concentration of impurities, parameters of short-range order (structural heterogeneity) and describes the peculiarities of low-temperature behavior of specific heat observed in disordered CNT. 相似文献
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V. E. Keilin P. A. Alekseev I. A. Kovalev S. L. Kruglov V. N. Lazukov M. I. Medvedev D. I. Shutova 《Technical Physics》2007,52(9):1148-1154
The influence of doping intermetallics based on rare-earth elements and ceramics with an extremely high low-temperature specific heat on the stability of combined NbTi superconductors against electromagnetic disturbances is studied experimentally and theoretically. The objects of investigation are standard NbTi conductors (0.85 mm in diameter) in a copper matrix that are soldered to copper wires containing high-specific-heat dopants. CeCu6, HoCu2, CeAl2, and PrB6 intermetallics (at 4.2 K, their specific heat is on average 150 times that of copper) or Cd2O2S ceramics (at 4.2 K, its specific heat is higher than that of copper by 600 times) are introduced into combined superconductor samples in the form of fine powder. The powder is placed into the copper wire either as one thick (0.6 mm in diameter) strand or as 19 thin (0.1 mm in diameter) strands. An undoped reference sample contains a solid conductor. Samples with a transport current placed in an external transverse magnetic field are subjected to longitudinal magnetic disturbances causing pulsed heating of the samples by eddy currents. The disturbance time is varied in a wide range: from 50 μs to 1.2 ms. To compare the critical energy densities of the disturbances in differently shaped samples, a mathematical technique is developed that is based on analytical solution of the equation of electromagnetic diffusion into the sample. It is found that the critical energy density of doped samples is much higher (by several times) than that of the reference sample. Upon direct cooling of the samples by liquid helium in a vertical channel (the most intense heat removal under steady-state conditions), the effect of stability improvement for the doped samples persists. Moreover, it is shown that the high-specific-heat dopants, raising the heat needed to warm the sample, restrict the heat flux into the liquid and thereby increase the energy removed by the coolant during unsteady heat transfer. 相似文献
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