非磁性替代原子对Ce_2Co_(17)居里温度和饱和磁化强度的影响

用真空电弧熔炼法制备了Ce2 Co17-xMx(M =Ga ,Al和Si)化合物。通过X射线衍射和磁性测量手段 ,研究了非磁性替代原子Ga,Al和Si的加入对Ce2 Co17化合物的居里温度和饱和磁化强度的影响 ,其中Si在Ce2 Co17化合物中的固溶度最小 ,并使居里温度和饱和磁化强度下降幅度最大。     

THE INFLUENCE OF CYLINDER LUBRICATION ON PISTON SLAP

A model has been developed for determining the time history of piston slap impact force. This model takes into account the influence of the oil film on the impact behaviour, which was found to be an important factor. However, it was also found that entrapped gas bubbles in the oil are equally significant. Three test rigs were designed and built to study these effects on the impact phenomenon and extensive tests were carried out. The impact force time history has been determined using Reynolds' theory. Results have shown that Reynolds' theory for fluid film squeezing can be applied for oil film damping determination. However, the experimental results have also shown that when gas is entrapped during the impact, this theory considerably overpredicts the magnitude of the impact. An eight-degree-of-freedom lumped parameter model was developed through the dynamic analysis of each component of an internal combustion engine's reciprocating system. The effective damping factor derived from this model was found to be inversely proportional to the oil film thickness cubed, as expected from Reynolds' theory. A dynamic model has been proposed, where the oil film mixed with bubbles is considered to be analogous to a serial spring and damping system. By incorporating a spring in series with this damper, the effect of the bubbles can also be predicted.     

由混合激发钠分子—原子系统产生的强度振荡变化的红外受激喇曼散射

本文报道以等频二步激发钠分子-原子系统,观测到强度随泵浦光的调谐而呈振荡变化的3P—4P受激喇曼散射,以及对应4D—4P和4F—3D跃迁的红外受激辐射和由四波混频产生的816.8～822.1nm区内可调谐相干辐射。文中对这些过程进行了分析讨论。     

Electronic surface structure of <Emphasis Type="Italic">n</Emphasis>-ML Ag/Cu(111) and Cs/<Emphasis Type="Italic">n</Emphasis>-ML Ag/Cu(111) as investigated by 2PPE and STS

We investigated the electronic structure of epitaxially grown silver films on Cu(111) with and without adsorption of cesium by means of scanning tunneling spectroscopy and two-photon photoemission. This system has been chosen as a model system to engineer and measure the dynamics of charge-transfer processes between an adsorbate and a heterogeneous substrate. Special emphasis has been laid on the investigation of the energy shift of the Shockley-type surface state and an excited cesium resonance as a function of Ag film thickness. For the cesium resonance we observe an increase in line width with increasing layer thickness. PACS 68.37.Ef; 68.43.-h; 68.55.Jk; 73.20.-r     

A Study of the Oxidation Pathway of Adrenaline by Cyclic Voltammetry: An Undergraduate Analytical Chemistry Laboratory Exercise

An undergraduate laboratory exercise to be used in an undergraduate instrumental methods course is presented for the electrochemical characterization of oxidation products of adrenaline. An objective of this experiment is to use information obtained through cyclic voltammetry and simulation software to develop a qualitative understanding of the oxidation mechanism of adrenaline.     

Thermotropic and lyotropic liquid crystalline behaviour of 4-alkoxyphenyl beta-D-glucopyranosides

The liquid crystalline properties of a series of 4-alkoxyphenyl beta -D-glucopyranosides (methoxy to decyloxy and dodecyloxy) were studied using polarized light microscopy and differential scanning calorimetry. The compounds with the shortest alkoxy substituents are not liquid crystalline. The butoxy derivative displays a monotropic smectic A phase and the higher homologues display enantiotropic smectic A phases. The lyotropic behaviour was studied as a function of concentration and temperature. Hexagonal, cubic and lamellar phases were observed for compounds with alkoxy chains longer than butoxy. The nonyloxy derivative forms long ribbons in dilute solution as revealed by electron microscopy.     

Magnetic hyperfine fields in Heusler alloys Co YZ (Y=Ti,Zr; Z=Al,Ga,Sn)

Magnetic hyperfine fields (mhf) acting on Ta at the Ti and Zr sites have been measured in Heusler alloys Co₂TiAl(Ga,Sn) and Co₂ZrAl(Sn) by the TDPAC technique utilizing the 133–482 keV gamma cascade in¹⁸¹Hf. Curie temperatures of all the alloys have also been measured using a vibrating sample magnetometer. Present data together with the existing results on the Co₂HfAl(Ga,Sn) are discussed and compared with the mhf systematics in Heusler alloys.work partially supported by CNEN and CNPq     

Modelling the growth of soil-borne fungi in response to carbon and nitrogen

Email: Angelique.Lamour{at}medew.fyto.wau.nl Growth of soil-borne fungi is poorly described and understood,largely because non-destructive observations on hyphae in soilare difficult to make. Mathematical modelling can help in theunderstanding of fungal growth. Except for a model by Paustian& Schnürer (1987a), fungal growth models do not considercarbon and nitrogen contents of the supplied substrate, althoughthese nutrients have considerable effects on hyphal extensionin soil. We introduce a fungal growth model in relation to soilorganic matter decomposition dealing with the detailed dynamicsof carbon and nitrogen. Substrate with a certain carbon: nitrogenratio is supplied at a constant rate, broken down and then takenup by fungal mycelium. The nutrients are first stored internallyin metabolic pools and then incorporated into structural fungalbiomass. Standard mathematical procedures were used to obtainoverall-steady states of the variables (implicitly from a cubicequation) and the conditions for existence. Numerical computationsfor a wide range of parameter combinations show that at mostone solution for the steady state is biologically meaningful,specified by the conditions for existence. These conditionsspecify a constraint, namely that the ‘energy’ (interms of carbon) invested in breakdown of substrate should beless than the ‘energy’ resulting from breakdownof substrate, leading to a positive carbon balance. The biologicalinterpretation of the conditions for existence is that for growththe ‘energy’ necessary for production of structuralfungal biomass and for maintenance should be less than the mentionedpositive carbon balance in the situation where all substrateis colonized. In summary, the analysis of this complicated fungalgrowth model gave results with a clear biological interpretation.