Superconductivity of compressed platinum powder at very low temperatures

Superconductivity of compressed, high-purity platinum powder (average grain size 2–3 μm) was found by measurements of resistivity, AC susceptibility and magnetization. The transition temperature into the superconducting state T_c and the critical magnetic field B_c strongly depend on the packing fraction f of the samples: we found 0.62T_c(0)1.38 mK and 6.6B_c(0)67 μT for 0.8f0.5, respectively. The temperature dependence of the critical magnetic fields can be described by B_c(T)=B_c(0)(1−(T/T_c)²). The discussion of these results includes possible explanations for the origin of superconductivity in this new superconducting material.     

A general Galois theory for cofunctions and corelations

Cofunctions and corelations are introduced and a corresponding Galois connection is studied in analogy to operations and relations in universal algebra. The Galois closed sets are characterized by local closures of clones of cofunctions and corelations, respectively. As an application concrete characterization problems are considered e.g. for strong bisimulations.     

Perspective on “Semiclassical theory of atom–diatom collisions: path integrals and the classical S matrix”

Miller's papers on classical S-matrix theory had a profound influence on the understanding of inelastic atom–molecule collisions. This perspective discusses the historical background, the content, some applications, and new developments. Received: 26 February 1999 / Accepted: 5 April 1999 / Published online: 21 June 1999     

Optoacoustic sensor head for depth profiling

-1 (for 0.25 mJ/cm²). The response function of the total experimental setup is derived from the optoacoustic signal of a black absorber, which is necessary to correct theoretical calculations with regard to the finite time response of the detection system. In the case of homogeneous samples, the theory of optoacoustic signal generation is verified, qualitative results are achieved with layered samples. Received: 14 October 1998 / Published online: 24 February 1999     

In-situ atomic force microscopy investigation of aerosols exposed to different humidities

In-situ atomic force microscopy (AFM) studies were performed on aerosol samples showing the potential of a topochemical approach for gaining information on chemical and physical aerosol properties. The behavior of single sub-micron particles has been investigated with respect to changing humidity in the surrounding atmosphere. Volume calculations allowed monitoring of these changes on a quantitative basis. As expected these in-situ experiments showed the restructuring of particles with highly agglomerated chain-like structures induced by condensation and evaporation on a nanometer scale. The particle volumes decreased as the branched chain-like structure changed into a more regular clump-like structure. The degree of restructuring was clearly depending on the chemical surface properties as could be proven for soot-like test aerosol particles. The collapse of the chain-like structure on a nanometer scale was found to be significantly more pronounced for soot particles previously exposed to ozone. Furthermore, in-situ studies were performed on ammonium sulfate test aerosol. Though a distinct deliquescence point typical for salts could not be detected, neither in the topography nor in the phase image, ammonium sulfate test aerosol particles seemed to partially dissolve in humid atmosphere and hence to decrease in volume. Thus, the volume decrease induced by purging with humid nitrogen and subsequent drying which was also observed for a considerable fraction of urban aerosol, could be interpreted in terms of composition and surface properties considering the geometrical structure (i.e. state of agglomeration) of the particles.     

Routine analysis of vinicultural relevant fungicides, insecticides and herbicides in soil samples using enhanced solvent extraction (ESE)

Parameters affecting the extraction efficiency of various pesticides from a native contaminated soil sample (C_org = 4.4%) using an enhanced solvent extraction (ESE) technique were investigated. The defined settings of temperature (50/150?°C), pressure (180/240 MPa), static and dynamic extraction time (5/15 min and 0/5 min, respectively) yielded results which did not differ significantly (RSD = 5.9–11.8%). In comparison to a classical shake-out extraction method the yielded quantities were on average 14% higher using ESE. The established method achieved a high precision (RSD = 2.8–9.1%) for the pesticides extracted from native contaminated soil samples. A significant influence of the sample matrix on accuracy was not observed. The RSDs of thirteen pesticides extracted from spiked sea sand varied in a similar range from 1.7 to 9.8% and the recoveries were between 83 and 112%. The method has been applied to soil samples from vineyards routinely.     

The Cross‐Sectional Structure of Vanadium Oxide Nanotubes Studied by Transmission Electron Microscopy and Electron Spectroscopic Imaging

Vanadium oxide nanotubes (VO_x‐NTs) are easily accessible in pure form from vanadium(V) alkoxides and amines by a sol‐gel reaction and a subsequent hydrothermal treatment. The wall structure of VO_x‐NTs containing hexadecylamine or dodecylamine as the structure‐directing template has been characterised by transmission electron microscopy (TEM). A standard method for preparing TEM specimens was modified in order to investigate the cross‐sectional structure of the tubes. The elemental distribution in the layered structure inside the tube walls has been visualised by electron spectroscopic imaging: vanadium oxide builds up the layers that appear with dark contrast in the TEM images while carbon, i. e., the organic template, is present in between. The bent VO_x layers inside the tube walls are preferentially scrolls rather than concentric cylinders. Moreover, some tubes are formed by a combination of both types. The layer structure inside the tube walls is frequently disordered, and several types of defects appear.     

Monoxidised Sulfur and Selenium Derivatives of 1,8‐Bis(diphenylphosphino)naphthalene: Synthesis and Coordination Chemistry

Treatment of 1,8‐bis(diphenylphosphino)naphthalene (dppn, 1 ) with stoichiometric amounts of sulfur or selenium in toluene at 80 °C selectively afforded the diphosphine monochalcogenides 1‐Ph₂P(C₁₀H₆)‐8‐P(:S)Ph₂ (dppnS, 2 a ) and 1‐Ph₂P(C₁₀H₆)‐8‐P(:Se)Ph₂ (dppnSe, 2 b ). The ³¹P{¹H} NMR spectrum of 2 b showed an unusually large ⁵J(P–Se) value, which indicates a significant through‐space coupling component. The monosulfide acted as a bidentate P,S‐ligand towards platinum(II) ( 3 a ), whereas the corresponding monoselenide complex ( 3 b ′) lost elemental selenium with formation of the previously reported complex [PtCl₂(dppn)‐P,P′] ( 3 ). Treatment of dppnSe with [(nor)Mo(CO)₄] (nor = norbornadiene) led to formation of [(dppnSe)Mo(CO)₄‐P,Se] ( 3 b ). Solutions of the latter slowly deposited Se with formation of [(dppn)Mo(CO)₄‐P,P′] ( 4 ) which was also obtained by independent synthesis from 1 and [(nor)Mo(CO)₄]. All isolated new compounds were characterised by a combination of ³¹P, ¹H, ¹³C and ⁷⁷Se ( 2 b ) NMR spectroscopy, IR spectroscopy, mass spectrometry and elemental analysis. Single‐crystal X‐ray structure determinations were performed for dppnSe ( 2 b ), [PtCl₂(dppnS)‐P,S] ( 3 a ), [(dppnSe)Mo(CO)₄‐P,Se] ( 3 b ) and [(dppn)Mo(CO)₄‐P,P′] ( 4 ). In 2 b steric effects cause the naphthalene ring to be distorted and force the phosphorus atoms by 65 and 59 pm to opposite sides of the best naphthalene plane. In the metal complexes 3 a , 3 b and 4 the phosphino‐phosphinochalcogenyl systems act as bidentate ligands through the P and the chalcogen atoms. The naphthalene systems are again distorted. The two independent molecules of 4 differ in their conformations.