Unitary transformation treatment of a single hole in an Ising antiferromagnet

The behavior of a single hole in a two-dimensional Ising antiferromagnet (t-J ^z model), is studied in the generalized Dyson-Maleev representation, where the spins are mapped on boson operators and the hole is described as a spinless fermion. The formal similarity with Fröhlich's polaron Hamiltonian suggests that thet-J ^z model can be approximately diagonalized by means of two successive unitary transformations, analogous to those used by Lee, Low, and Pines in their intermediate-coupling treatment of the polaron. Our approach yields an upper bound to the exact ground state energy, as well as the corresponding ground state eigenvector. Fork=0 our energy bound is remarkably close to the result of the self-consistent Born approximation over a wide range of the coupling parameter, which includes the range typically assumed for the high-T _c materials. The ground state eigenvector is used to calculate the spatial distribution of bosons (spin deviations) surrounding the hole. Here our results are qualitatively very similar to those obtained in previous work, showing that our ground state eigenvector accounts quite well for the small size of the “spin polaron” in thet-J ^z model.     

Beiträge zur Chemie der Pyrrolpigmente, 70. Mitt.: Zum aktiven Transport mit tripyrrinoiden Liganden

The tripyrrin carboxylic acid6 exhibits a pronounced efficiency for carrier mediated proton driven secondary active transport (counter transport) for a series of toxic or valuable cations in a bulk chloroform membrane. In case of Zn⁺⁺ ions the mechanism including complete concentration profiles forNerst diffusion layers and bulk phase have been established. This compound might be used for detoxification or enrichment of precious metals using membrane separation systems.

Herrn Prof. Dr.A. Neckel mit den besten Wünschen zum 60. Geburtstag gewidmet.     

A microcomputer-controlled titrator for automated individual analysis

A titration unit for automatic analysis systems is described. The titrator performs different titrations specified by strings of digital parameters. It has 4 independent titration stations with individual electrode systems. A multiburette with 20 cylinders provides all stations with the necessary reagents. End-point titrations, and incremental and equilibrium titrations are controlled by a microcomputer. In combination with a sample transport and a desk calculator, the titrator can be used to process automatically samples of different natures which require different treatment.     

Das Verhalten der WÄrmeleitfÄhigkeit von Kautschuk bei der Dehnung

Zusammenfassung Mit einer Me\apparatur, die nach einer Relativmethode die W?rmeleitung in fadenf?rmigen Kautschukvulkanisaten zu messen gestattet, wird der Einflu\ der Dehnung auf die W?rmeleitf?higkeit untersucht. Es ergibt sich ein wesentlicher Anstieg der W?rmeleitung mit der Dehnung bei allen untersuchten Materialien. Bei stark vulkanisiertem Kautschuk ist dieser Anstieg am geringsten, bei Polybutadienen ist er h?her als bei Naturkautschuk. Auf Grund von bekannten Vorstellungen über die Kinetik der hochpolymeren Moleküle bei Dehnung und über die Ausbreitung von W?rmewellen in Festk?rpern werden die Beobachtungsergebnisse gedeutet. Dabei wird festgestellt, da\ der Anstieg der W?rmeleitf?higkeit auf eine zunehmende Ausrichtung von Molekülkettenabschnitten in Dehnungsrichtung — die zugleich Richtung des W?rmestromes ist- und auf eine Abnahme der Zahl der Streuzentren für die W?rmewellen zurückzuführen ist. Auch Unterschiede bezüglich des Betrages des Anstiegs, den die einzelnen Materialien zeigen, k?nnen z. T. auf Grund dieser Vorstellungen erkl?rt werden.     

Continuous flow in open microfluidics using controlled evaporation

This paper presents a method for programming the flow rate of liquids inside open microfluidic networks (MFNs). A MFN comprises a number of independent flow paths, each of which starts with an open filling port, has a sealed microchannel in which assays can be performed, and an open capillary pump (CP). The MFN is placed over Peltier elements and its flow paths initially fill owing to capillary forces when liquids are added to the filling ports. A cooling Peltier element underneath the filling ports dynamically prevents evaporation in all filling ports using the ambient temperature and relative humidity as inputs. Another Peltier element underneath the CPs heats the pumps thereby inducing evaporation in the CPs and setting the flow rate in the microchannels. This method achieves flow rates in the microchannels ranging from approximately 1.2 nL s(-1) to approximately 30 pL s(-1), and is able to keep 90% of a 0.6 microL solution placed in an open filling port for 60 min. This simple and efficient method should be applicable to numerous assays or chemical reactions that require small and precise flow of liquids and reagents inside microfluidics.