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We present a numerical analysis of the single particle energy spectra of ballistic condensed matter systems and compare with recent theoretical results. We show that the presence even of weak disorder induces full chaoticity on time scales larger than the elastic disorder scattering time. To disentangle the effect of boundary, respectively disorder scattering on the spectral statistics, different types of correlation functions are introduced and discussed.

Information about the transport time of electrons through a quasi one-dimensional sample is obtained by calculating the energy auto-correlation function of the conductance. Depending on the length of the sample and its coupling to the external device (here modelled by perfectly conducting leads), the transport time undergoes a smooth crossover between two different limiting regimes. In the case of long samples and good coupling it coincides with the diffusion time. In the opposite limit of short and weakly coupled systems, however, the transport time is given by the reciprocal of the quantum mechanical decay width into the leads. The transition between both regimes is discussed in terms of a few model independent concepts.

A gradient mixing device has been designed to pour polyacrylamide gels with a wide-range immobilized pH gradient including a "window" of extremely flattened slope. The device consists of an IBM-compatible personal computer controlling 8 step-motor-driven burettes, with four producing a density gradient from glycerol and delivering acrylamides and catalysts for gel polymerization, two delivering Immobilines for a wide-range pH gradient and the other two burettes responsible for the delivery of Immobilines for a partial pH range inside the wide range. The effect on a complex separation pattern of proteins with a wide range of pI is that resolution can be increased reproducibly to any reasonable extent at any location of the separation pattern.

A program has been developed for the computer-controlled cooperation of 4 commercially available stepmotor-driven burettes to form density gradients in polyacrylamide gels and solute gradients for other purposes such as centrifugation and low pressure chromatography. The slope of the gradients was defined by entering up to 200 endpoints of straight lines with the percentage of the total volume and the concentration of the gradient-forming solute as coordinates. The possible minimum increment of the discontinuous gradients is 0.5 % of the total range. They are mixed at variable flow rate by two burettes containing the high and low density acrylamide solutions and two additional burettes for the admixture of two catalysts at variable volume proportions. Within 10 min gradients with total volumes between 4 and 650 ml can be delivered. Gradient volumes smaller than 4 ml are possible if an average increment of > 0.5 % is accepted. The program meets the requirements of reproducibility for high resolution gradient gel electrophoresis and isoelectric focusing in immobilized pH gradients. All input data for the definition of the gradients can be displayed as a hard copy by a matrix printer and stored on tape. Thus the device meets the requirements of proper documentation of a given gradient in a publication and for reproduction in another laboratory. Other types of gradients for volumes of up to 1.4 liters can be produced by a subprogram converting the 4 burettes into a gradient pump with continuous outflow as used for column chromatography. The speed is variable between 0.4 ml and 5.2 liters per hour with minor pulsation only in the very low range.