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81.
两年前当高温超导材料出现时,人们的注意力集中于高的临界温度,认为材料有可能在液氮温度(77K)得到应用,不需要使用不便且昂贵的液体氦,前景似乎很美妙.事实上,对实际应用言,更重要的是临界电流密度Jc.科学家们为提高Jc而努力,在薄膜材料中得到了很大的成功,Jc在液氮温度可达 105A/cm2,足以满足大多数电子学方面应用的要求.体材料却相反,最高的Jc值也要比上述结果小100多倍.科学家们发现在提高Jc方面面临着复杂困难的局面,这主要来源于磁通线格子的行为. 早在60年代,人们就发现当电流通过时,超导体中的磁通线会感受到推力.如果磁通线被推… 相似文献
82.
从平均场理论出发,针对有限温度下的玻色-爱因斯坦凝聚态的特点,从正则系综的自由能函数变化的角度,推演并得出了临界温度移动的表达式。为同类实验提供了理论依据. 相似文献
83.
84.
炸药柱非限定热爆炸实验研究 总被引:2,自引:1,他引:2
对HMX/TATB系列配方和PBX 1的10mm 10mm、2 0mm 2 0mm、30mm 30mm炸药柱进行了非限定热爆炸实验 ,探讨HMX/TATB含量和几何尺寸对热爆炸临界温度的影响。结果表明 :TATB含量增加 ,炸药配方的热感度降低 ,炸药柱热爆炸临界温度增加 ,其增加趋势随TATB含量的增加而变得更加明显 ;炸药柱几何尺寸越小 ,影响越明显 ;线性拟合得到非限定炸药柱热爆炸临界参数,药柱半径r和热爆炸临界温度Tm 之间的关系式以及热爆炸延滞期t与临界温度Tm的关系式 ;计算获得PBX 1炸药柱非限定试验 4h不发生热爆炸反应的特征临界温度。 相似文献
85.
温度影响下砂岩的细观破坏及变形场的DSCM表征 总被引:1,自引:0,他引:1
通过扫描电镜(SEM)实时在线观察研究了温度影响下砂岩的细观破坏,观察到砂岩的脆性断裂可同时发生在不同地方、不同矿物可能独立承载和裂纹分叉等现象. 温度低于100°C时,主裂纹附近有许多微裂纹和支裂纹发生;而温度超过150°C之后,表面很少出现支裂纹或二次裂纹. 随着温度的升高,砂岩的断裂韧性有先升高后降低的趋势,150°C左右是断裂韧性变化的临界温度. 随着温度的升高,砂岩的细观断裂机制有由脆性机制向延性机制转变的趋势,抵抗和协调变形的能力都得到增强. 细观尺度下砂岩的破坏机制有沿颗粒断裂、穿颗粒断裂及其混合断裂,其中沿颗粒断裂机制占主导地位,这是由于沿颗粒破坏需要消耗较少的能量,而穿颗粒断裂需消耗较多的能量. 利用数字散斑相关方法(digital speckle correlation method, DSCM)对SEM下砂岩破坏的细观变形场进行了测量,这表明利用DSCM表征岩石的局部变形场的连续式测量是可行的. 相似文献
86.
A new high-T_c (HT_c) rf SQUID working at around 1.3GHz has been developed to avoid electromagnetic interference such as growing mobile communication jamming. This new system works in a frequency range from 1.23 to 1.42GHz (centred at 1.3GHz), which is not occupied by commercial communication. The sensor used in the 1.3GHz rf SQUID is made of a HT_c coplanar superconducting resonator and a large-area HT_c superconducting film concentrator. We have achieved in the 1.3GHz HT_c rf SQUID system a minimal flux noise of 2.5×10^{-5}Φ_0/\sqrt{Hz} and a magnetic field sensitivity of 38fT/\sqrt{Hz} in white noise range, respectively. The effective area of the concentrator fabricated on a 15×15mm^2 substrate is 1.35mm^2. It is shown that the 1.3GHz rf SQUID system has a high field sensitivity. Design and implementation of 1.3GHz HT_c rf SQUID offers a promising direction of rf SQUID development for higher working frequency ranges. 相似文献
87.
研究了具有不同氧含量的Bi2Sr2CaCu2O8 δ单晶超导临界温度的各向异性,通过测量沿ab面和c轴的电阻率发现,在轻欠掺杂到过掺杂区域,单晶沿ab面和c轴的Tc值是比较接近的,但在重欠掺杂区,沿ab面的Tc值比c轴的Tc明显高,从平衡态的相位涨落模型可以得到,由于涨落效应对 c轴的临界电流密度的压制作用比对ab面的要强,导致了Tc的各向异性,但这种模型无法解释重欠掺杂超导体中ab面和c轴的Tc如此大的差别,我们认为重欠掺杂超导体中的相位涨落行为不同于其他掺杂超导体中的行为,实验和理论上都值得进一步深入研究。 相似文献
88.
ZHANG Jing-chang GAO Xi-xin CAO Wei-liang 《高等学校化学研究》2005,21(6):687-691
Supercritical carbon dioxide(SC-CO2 ) is considered in green chemistry as a substitute for conventional solvents in chemical reactions due to its environmentally benign character. Recently we have reported the homogeneous hydroformylation of propylene in supercritical carbon dioxide( SC-CO2 ) , which is an example of this kind of application of carbon dioxide. The determination for the critical parameters of carbon dioxide + butyraldehyde mixtures is necessary for this reaction design which is the focus of the present paper. The critical parameters of the binary systems were determined via the static visual method at a constant volume with the molar fraction of butyraldehyde ranging from 1.0% to 2. 2% and the pressure ranging from 5 to 10 MPa. The experimental results show that the critical pressure and temperature increased with increasing the molar fraction of butyraldehyde. The bubble(dew) temperatures and the bubble (dew) pressures for the binary systems were also determined experimentally. The p-T Figures at different compositions of the binary systems were described. In addition, the critical compressibility factors Zc of the binary systems at different concentrations of n-butyraldehyde were calculated. It was found that the critical compressibility factor values of the binary systems decreased with increasing the molar fraction of n-butyraldehyde in the experimental range. 相似文献
89.
90.
Superconducting properties of barium in three phases under high pressure from first principles 下载免费PDF全文
Electron-phonon coupling (EPC) in the three high-pressure phases of Ba is investigated using a pseudopotential plane-wave method based on density functional perturbation theory. The calculated values of superconducting critical temperature T c of Ba-I and Ba-II under pressure are consistent well with the trends observed experimentally. Moreover, Ba-V is found to be superconducting with a maximum T c exceeding 7.8 K at 45 GPa. With the increase of pressure, the values of T c increase in Ba I and Ba-II but the value of T c decreases in Ba-V. For Ba-I at pressures below 2 GPa, the increases of logarithmic average frequency ω log and electron-phonon coupling parameters λ both contribute to the enhancement of T c . For all the three phases at pressures above 2 GPa, T c is found to be primarily determined by λ . Further investigation reveals that for all the three phases, the change in λ with pressure can be explained mainly by change in the phonon frequency. Thus for Ba-II and Ba-V, although they exhibit completely different superconducting behaviors, their superconductivities have the same origin; the pressure dependence of T c is determined finally by the pressure dependence of phonon frequency. 相似文献