ALBERT

Notes: Cathode spots on arc-cleaned copper and molybdenum electrodes in vacuum were studied by fast image converter framing and streak camera photography with high temporal and spatial resolution. The frame exposure time was 20 ns and the interframe period was 200 ns; the streak sweep time was between 200 ns and 1 μs. Spatial structures with a resolution of 5 μm could be determined by observing the spot movement with a small slit at the streak camera and a high sweep speed. Strong fluctuations of the light emission of the spot were found with characteristic times of 50–100 ns. When the spot moved out of the slit field of view a stepwise decrease occurred in the measured light, indicating an internal substructure of the spot with distances between fragments less than 10 μm and even smaller fragment diameters. The current per fragment was estimated to be 20–40 A. The frames confirm the short time constants of the spot. From frame to frame a spot motion was observed in most cases, yielding spot residence times 〈200 ns.

Notes: Abstract The construction of theoretical models in biology, situated at the cross-roads of biology, mathematics and computer science, often leads to a tool as final product. Its genesis can be named ‘Infogenesis’. The procedure of the resolution of theoretical problems is analyzed on examples of practical purposes taken from plant biology. The first example deals with mineral plant nutrition, explaining a way to go from theoretical ionic balances to the experimental realization of nutritional solutions with macro-element components. The balanced concentrations of ions are expressed in terms of concentrations of electrical charges (milli-equivalent per litre). The neutral combination of anions and cations results from salts, acids or bases introduced in water. To achieve this combination, a table lines up concentrations in cations in the last column and concentrations of anions in the bottom line, their sums being equal. The obtained quantities of salts appear at the intersections of lines and columns. An expected ionic equilibrium is equivalent to the filling up of the table considered as a mathematical matrix. The algorithm constructing the table permits e.g. to use fewer salts or some salts preferentially. The procedure minimizing the values of elements corresponding to non-desired salts is presented. A prior order, which is the reverse to the use of preferential anion/cation pairs, is required for the successive treatments of the elements. An algorithm of “successive splittings” respects the weights of sums in lines and columns. It mainly looks for the maximal quantity that can be taken from a chosen box in the table i.e. from the salts, and carries out its splitting. The repetition of this operation takes into account the impossibility to add a positive value to a minimized term. Therefore, during the operation, some lines and columns have to be “frozen”, i.e. their values are considered as unchangeable. The number of rewritings of the table by the splitting method depends on the order of treatment of the elements, their number and the weight of lines and columns. The method gives a global approach of the mineral nutrition in terms of ion concentrations. An initial chemical definition of the problem leads to the constructions of algorithm on the basis of the successive splitting method. It is resolved mathematically and computerized via a dynamic arrangement of elements in the table. The determination of salts formulas from the known ionic concentrations is the practical objective and the filling up of the table is the computerized means. Initial data is the sums in lines and columns. The resolution is accomplished by the weighted redistribution of the values taken from each box in the table. The realization is done within a loop of calculations, rewriting the terms of the grid according to a predefined preferential order. In a second example, a procedure opening the way to the construction of the form for a plant from empirical data is discussed. The study of the vegetative development of woody ornamental plants is necessary to manage the production of commercial varieties during the plants breeding process. The aspect of the plant, regularly recorded, can be reconstructed by image synthesis. Additionally, knowledge about the underlying biological mechanisms becomes accessible if the synthesis images are ordered by the algorithmic formulation of hypotheses on the development. Non-destructive recording of data during the growth of the aerial living branching system is based on elementary units of construction, each unit including a leaf, an axillary bud, a node and an internode. Each elementary unit is referred to by a unique address describing the way from the plant root up to the considered node. The coding of the address is the AF type which is compared to the lexicographical type. Coding, ordering the constituents of the plant and the spatial links (dimensions, orientations in space) together constitute a numerical memory of the development (NMD). The visualization of the enhanced shape is given by a graphical representation. The modelization of plant growth by an algorithm approach uses a set of production rules that contains the complete topological structure. The construction of the associated drawings allows a comparative study of the morphological structure. Branching systems generated by L-Systems or the proposed PL-System, are discussed. The NMD is a possible interface for the comparison of a measured tree structure and a generated tree structure. In the PL-System a segment is characterized by indexes indicating the potentiality of the total branch length and the effective rank of the segment on the axis. A system of linear equations (in matrix form) calculates the indexes of the axes produced by a bifurcation. Where a corresponding L-System would be more concise, the PL-System opens a theoretical way to study relationships between plant forms. As it produces automatically the addresses of the NMD, comparisons with experimental data are easy, especially if highlighted by computerized graphical representations of the branching systems. Biology contributes to the detailed description of the development of woody plants, both by data records and growth models. Computer science structures the NMD and produces the associated shape and volume. The resolution is based on a drawing algorithm managing the multiplication of the elementary units. The realization is a stepwise animation of related graphical blocks. A second biological objective is the comparison of the observed shape and the shape generated by PL-Systems. It is realized by a comparison between observed and theoretical NMDs generated by grammars. Biology, mathematics and computer science fuse in a same objective of modelization. An accurate definition of the biological objectives, separating data from the resolution scheme, is necessary, distinguishing between items that relate to the resolution algorithm or to the mathematical formulation and those which refer to the implementation on a computer.

Notes: Summary In this article the writer suggests an explanation for the germicide effect of compressed oxygen. The production of poisonous products of metabolism can be ignored, because the bacterial development is normal after removal of the pressure. Lack of nutritive material through inhibition of metabolism and permanent damage to the enzymes is also not a satisfactory explanation. The possibility is discussed that oxygen as an acceptor of electrones creates an ionisation of important parts of the cell and resulting in the death of the bacteria. The effect seems to be similar but weaker than that of H2O2.

Notes: Summary The origin of the polarographic peak between 0 and −0.2 V caused by oxidized fats and by different peroxides, especially diacyl peroxides dissolved in LiCl in methanol/benzene, has been investigated with a cathode ray polarograph. This peak is caused by a reduction of Hg-ions. Certain peroxides favour the oxidation of the Hg-metal of the electrode to Hg-ions; thereby the diffusion current is proportional to the peroxide concentration. An addition of Hg-ions to the peroxide solution increases the peak height. Hg2+- and Hg+-solutions without peroxide yield a similar peak.

Notes: Abstract In order to check the predictions of 0D-models experimentally, a small coaxial discharge configuration for the generation of homogeneous high pressure glow discharges (diameter 11 mm, length 20 mm) in rare gas halogen excimer laser gas mixtures under accurately controlled conditions has been developed. It uses X-ray preionization and a special pulse-forming network (PFN) delivering fast rising (8 ns) single square pulses (U 0=25 kV; I=300 A; ∝=100 ns). Discharge current and voltage are measured precisely by a capacitive voltage divider and a shunt integrated into the discharge chamber. All circuit data needed for the model calculations have been evaluated. Interferometric and spectroscopic diagnostics of the bulk of the discharge and of the cathode sheath have been performed. First results for Ne/Xe/HCl mixtures are compared with model calculations.

Notes: Abstract An improved 0-dimensional model for XeCl high-pressure glow discharges is presented. Calculated discharge voltages are compared with precise measurements at a small, very homogeneous discharge. Excellent agreement in a wide parameter field demonstrates that this model may serve as a reference for simpler models describing the ionization kinetics.

Notes: [Auszug] The pits, which are etched on to the front of dielectric track detectors, are a result of primary ionisation, and the diameter of each pit therefore provides a measure of energy. Unfortunately, however, the properties of the material used and the etching conditions also influence the diameter of ...