Experimental investigation of the thermal conductivities of C6D6, C6H6 and C6D12, C6H12 in the gaseous phase

Results of the measurement of the thermal conductivities of C₆D₆, C₆H₆ and C₆D₁₂, C₆H₁₂ in the temperature interval 300–600°K are presented.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 32, No. 3, pp. 406–409, March, 1977.     

Atomic-scale structure of Mo6S6 nanowires

We have studied the atomic-scale structure of the Mo6S6 nanowires using scanning tunneling microscopy and spectroscopy (STM and STS) and density functional theory (DFT). A novel synthesis route based on metallic Mo precursors is presented for the selective formation of elementary pure Mo6S6 nanowires. The Mo6S6 nanowires selectively organize as trimer bundles, and each of the Mo6S6 nanowires consists of an electrically conducting Mo backbone dressed with a sulfur exterior cap. The Mo6S6 nanowires may thus be of interest as novel building blocks in nanoelectronics because the Mo6S6 nanowires exist in a robust, singular structural conformation with uniquely defined electrical (metallic) properties.     

Transport properties of GdB6 and DyB6

The electrical resistance and absolute thermoelectric power (TEP) have been measured for GdB₆ and DyB₆ in the temperature range 2–30 K. The compounds GdB₆ and DyB₆ order antiferromagnetically atT _N 15.2 and 20.3 K, respectively. Above the Néel temperature the resistivity has a small contribution that is linear inT due to electron-phonon scattering, whereas in the same temperature range the spin-disorder TEP (S _spd) has been evaluated and found to be linear inT. A divergence in the temperature derivative of resistance and TEP has been found atT _N that is consistent with the present theories. There is evidence of a low-temperature phase appearing at 7 K in the resistivity and the TEP data of GdB₆. A minimum in the TEP is found in these compounds below 6 K, which is associated mainly with phonon drag and possibly a magnon contribution. A broad peak in the TEP of DyB₆ around 16 K is thought to be due to crystalline electric field effects.     

Röntgenröhren in der Medizintechnik

X‐Ray Tubes in Medical Imaging Applications The application of X‐rays in medical diagnostics has become an essential element in everyday life. Every hospital or imaging center uses X‐ray radiation to get an insight into the human body within shortest time. The technology which is used to take an image of the mandible or to create a full body scan of an emergency patient by computer tomography within a few seconds is the same. This article describes shortly the history of the invention of X‐rays. The creation of X‐rays is explained by a simple schematic. The relevance and function of the cathode to create free electrons is very important. The evolution form simple thermal filaments to electron field emitters is described. The innovation of liquid metal bearings is also essential to realize high power X‐ray tubes by effectively removing the heat from the anode. After a short excursion to the medical applications of X‐Ray imaging a completely new approach of X‐ray source is described.     

化合物DyMn6Sn6的磁晶各向异性及自旋重取向相变研究

采用交换相互作用的分子场理论模型对金属间化合物DyMn6Sn6的自旋重取向相变进行了研究.从理论上计算了DyMn6Sn6的易磁化方向以及Dy和Mn离子磁矩与c轴夹角随温度的变化.基于单离子模型计算了Dy离子的一阶和二阶磁晶各向异性常数K 1R和K 2R随温度的变化.研究表明,为了很好的描述该化合物的自旋重取向相变,必须考虑Dy离子的四阶晶场项及相应的二阶磁晶各向异性常数K 2R、K 2R与K 1R和Mn离子磁各向异性常数K1t之间的相互竞争是导致DyMn6Sn6自旋重取向相变的重要因素.     

PA6/PA6IcoT相容共混物的结晶行为

采用差示扫描量热法研究了熔融共混聚己内酰胺/聚对(间)苯二甲酸己二胺(PA6/PA6IcoT)相容体系的结晶温度、结晶程度以及结晶动力学,并通过热台偏光显微镜、广角X射线衍射仪观察了PA6/PA6IcoT共混体系的结晶相形态和晶体结构。结果表明,共混物的结晶行为与其组成、结晶温度区域密切相关。在非等温结晶时,随着非晶态PA6IcoT含量的增加,PA6相的相对结晶度增加,部分晶体结构由γ晶型转变为较完善的α晶型。在较高温度区域结晶时,少量的PA6IcoT就能使串并的晶核分开,形成大量微小晶粒。当PA6IcoT含量继续增加时,球晶数目会减少但尺寸增大。等温结晶动力学研究发现,结晶速度随PA6IcoT含量的提高而下降,Avrami指数值在4.5～6之间,并随着结晶温度升高而增大。     

Semi-numerical solution to 6/6-Stewart-platform kinematics based on symmetry

The direct and inverse kinematics of the 6/6-Stewart-platform architecture drawn opposite is considered. A fast and self-contained numerical algorithm is designed to compute the kinematic transformations. The design exploits the geometric symmetry of the construction by reducing the involved polynomial equations in a systematic fashion. The two special cases of constant orientation and of constant position are solved in closed form.     

Fiber Reinforcement in Injection Molded Nylon 6/6 Spur Gears

Injection molded polymer composite gears are being used in many power and or motion transmission applications. In order to widen the utilization of reinforced polymers for precision motion transmission and noise less applications, the accuracy of molded gears should be increased. Since the injection molded gear accuracy is significantly influenced by the material shrinkage behaviour, there is a need to understand the influence of fiber orientation and gate location on part shrinkage behaviour and hence the gear accuracy. Unreinforced and 20% short glass fiber reinforced Nylon 6/6 spur gears were injection molded in the laboratory and computer aided simulations of gear manufacturing was also carried out. Results of the mold flow simulation of gear manufacturing were correlated with the actual fiber orientation and measured major geometrical parameters of the molded gears. Actual orientation of the fibers near the tooth profile, weld line region and injection points of molded gears were observed using optical microscope and correlated with predicted fiber orientation.     

Micro-mechanical modelling of Young’s modulus of semi-crystalline polyamide 6 (PA 6) and elastomer particle-modified-PA 6

In this study semi-crystalline polyamide 6 (PA 6) and its composites consisting of a semi-crystalline PA 6 matrix filled with up to 32.9 vol.% submicron elastomeric copolymer particles are investigated. The aim of this paper is to show how micro-mechanical modelling can predict the elastic behaviour of these composites from the experimentally observed morphology and determined parameters.Semi-crystalline PA 6 possesses a spherulitic morphology, consisting of a radial assembly of amorphous layers and nano-sized crystalline lamellae. In the continuum mechanical representation of semi-crystalline PA 6, nano-sized crystallite lamellae are considered as a phase which is additionally embedded into the amorphous matrix. The 2D self-consistent embedded cell model was chosen to predict the Young’s modulus of the semi-crystalline PA 6 material. In this model a rectangular lamella is surrounded by an amorphous matrix, which is again embedded in the semi-crystalline PA 6 material with the mechanical behaviour to be determined iteratively in a self-consistent manner. The Young’s modulus of PA 6 has been calculated by an appropriate integration of results of all orientations of the crystalline lamellae. The Young’s modulus of PA 6/elastomer composite is also predicted by a 3D self-consistent embedded cell model. In this model a circular inclusion is surrounded by the PA 6 polymer matrix, which is again embedded in the PA 6/elastomer composite. Good agreement is obtained between experiments and the prediction with the self-consistent embedded cell models.     

Critical scattering in the electrical resistance of GdB6 and DyB6

Detailed investigations of the electrical resistance of GdB₆ and DyB₆ near T _N, their antiferromagnetic transition temperatures, and of nonmagnetic LaB₆ are reported. In GdB₆ a recently reported magnetic phase transition around 6 K has been found to be sample dependent. The resistance of this compound shows a very rapid increase at about T _N = 15.15 K and a small maximum near 15.5 K. Analysis of the data using r = r₀ + Bt + A_±t^1–, where t = (T–T _N )/T _N , for –4 × 10^–3 t –7 × 10^–2, yields 0.36. This is in agreement with a renormalization group theory prediction for a system with a three-dimensional lattice (d = 3) that is magnetically isotropic and has six spin degrees of freedom (n = 6). The resistance of DyB₆ shows features of a typical antiferromagnetic transition with electron scattering mainly dominated by fluctuations in short-range spin correlations.Using the above expression for –1.8 × 10^–2 t 4.8 × 10^–2 with the A ₊term when t is positive and A _–when t is negative, we obtain T _N = 20.32 K and = –0.16, which is close to the theoretical value ( = –0.17) for d = 3 and n = 4. The results are discussed in terms of the present theories for critical scattering.This research was supported in part by a grant from the Natural Sciences and Engineering Research Council of Canada.     

纳米HA/PA6复合材料的体外生物活性

研究了PA6和纳米HA/PA6复合材料在模拟体液(SBF)中的行为变化,用IR,XRD,SEM和EDS等手段对材料的表面变化进行了分析,讨论了PA6和纳米HA/PA6复合材料的稳定性、亲水性和生物活性。结果表明:在SBF中PA6的吸水率大概在6%左右,纳米HA/PA6复合材料的吸水率有少量下降,PA6和纳米HA/PA6复合材料出现一定的溶解和降解。在SBF中,PA6表面形成Ca,P化合物中的Ca/P比例为1.12,与HA的理论值1.67有一定的差别;HA/PA6复合材料在其表面形成了HA沉积物和碳酸取代的磷灰石沉积物,Ca/P逐步变化为1.67,表现出较好的生物活性。复合材料表面沉积的HA和原来合成的HA具有相近的结晶形貌,该复合材料可作为优良的骨修复填充材料和组织工程支架材料。      

CHF3/C6H6等离子体中的基团分析

在一个微波电子回旋共振等离子体化学气相沉积系统中，测量了CHF3、C6H6及其混合气体放电的质谱和发射光谱图，分析了等离子体中主要基团的分布及其产生的途径，研究了放电功率和流量对主要基团密度的影响，以及它们与氟化非晶碳薄膜沉积速率和键结构之间的关联。结果表明，提高微波功率会增加CHx、CFx等成膜基团的密度，有利于加大沉积速率；而增加CHF3的进气量则会加大F原子基团的密度，这是由于它控制了薄膜的氟化程度。