Direct potentiometric immunoelectrodes

A method is described to determine Atrazine and its cross-reacting relatives in water, using a previously described graphite based one-way immunoelectrode and any standard millivoltmeter with low input bias current. The new procedure separates the potential measuring step from the incubation step. In this way, the conditions for highly stable potential measurements and for a most effective formation of the hapten (Atrazine) antibody complex can be optimized separately and all imponderable influence from ions in the analyte water is excluded. The limit of detection of such an electrode is some nanogram per liter.Part III: see [4]     

Some logical aspects of information processing

This paper is concerned with dynamic aspects of knowledge representation. A model for information processing is introduced which is based on acyclic directed graphs with starting points. This approach is combined with ideas from non-monotonic reasoning.     

deAtmosph?rische Luft

Ohne Zusammenfassung     

Structure of salvigenolide,a novel diterpenoid with a rearranged neo-clerodane skeleton from salviafulgens

From the aerial parts of Salvia fulgens Cav. (Labiatae) a new diterpenoid with a rearranged neo-clerodane skeleton was isolated. This novel compound named salvigenolide, showed a six-seven A/B ring system with a trans fussion. A probable biogenetic route is proposed. Its structure and relative stereochemistry as in $\text{1}$, were established by spectroscopic means and X-ray diffraction analysis.     

Determination of total fluorine in vegetables and plants by open-flame ashing and microdiffusion : Comparison with furnace ashing and oxygen-flask combustion

The sample is ashed in a nickel crucible over an open flame with calcium hydroxide as the fixative; fluoride is separated by micro-diffusion and measured with a fluoride-selective electrode. The calcium hydroxide fixative permits a temperature of 800–850°C during the final ashing, so that insoluble silicates are decomposed and fluoride is converted to an acid-soluble form. Other advantages over furnace ashing at 600°C are less contamination and more rapid ashing (20 min compared to 6 h). The interference of aluminium and silica on microdiffusion was studied: perchloric acid was found to be preferable to sulphuric acid as medium. A new way for preparing calcium hydroxide suspension, low in fluoride, is described. The values found by the proposed method generally compare well with those obtained by oxygen flask combustion. Direct diffusion (i.e. without ashing) gave much lower values than the ashing methods, except for tea leaves.     

On the edge-coloring problem for a class of 4-regular maps

A (plane) 4-regular map G is called C-simple if it arises as a superposition of simple closed curves (tangencies are not allowed); in this case σ (G) is the smallest integer k such that the curves of G can be colored with k colors in such a way that no two curves of the same color intersect. We prove that if σ (G) ≤ 4, G is edge colorable with 4 colors. Moreover we show that a similar result for maps G with σ(G) ≤ 5 would imply the Four-Color Theorem.     

Hydrogen on W (100): Electron stimulated desorption and a structural model

Prompted by the peculiar shape of the curve of election-induced H⁺ current versus coverage for hydrogen on W(100) which has been observed before, we have restudied this system by correlated ESD, thermal desorption, and LEED measurements. The maxima in ESD signal and intensity of the half-order LEED spots, and the appearance of a second desorption peak are roughly correlated at $\text{1}\text{4}$ coverage. Using this observation and the exact shape of the ESD curve, a structural model is derived in which two different, but uniform states (i and f) exist, the first, i, being exclusively occupied up to $\text{1}\text{4}$ monolayer, and the second, f, at saturation. A gradual conversion from i to f takes place at $\text{1}\text{4}\text{< θ < 1}$ which is caused by the interaction between adsorbed H atoms. From this model a differential equation for the occupation numbers of i and f states, respectively, is derived and solved numerically; it yields good agreement with the experimental ESD curve. Discussing the possible physical realization of the two states, it can be made probable that they must exist on two different sites and have fourfold (i) and twofold (f) symmetry, so that the conversion is accompanied by a shift of the binding site of the adatom.