A Strict Inequality for the Random Triangle Model

The random triangle model on a graph G, is a random graph model where the usual i.i.d. measure is perturbed by a factor q ^t(), where q1 is a constant, and t() is the number of triangles in the random subgraph . Here we consider the case where G is the usual two-dimensional triangular lattice, for which there exists a percolation threshold p _c (q) such that the probability of getting an infinite connected component of retained edges is 0 for p<p _c (q), and 1 for p>p _c (q). It has previously been shown that p _c (q) is a decreasing function of q. Here we strengthen this by showing that p _c (q) is strictly decreasing. This confirms a conjecture by Häggström and Jonasson.     

A new method for characterization of low grade gliomas using ultra low field magnetic resonance imaging

Low grade gliomas were studied with ultra low field magnetic resonance imaging (ULF MRI). The tumors exhibited high tissue contrast in both T₁ and T₂-weighted images as compared to normal brain tissue. Moreover they were sharply delineated towards the surrounding brain tissue. When compared with X-ray computed tomography the tumors were more readily detected and delineated by using ultra-low field magnetic imaging. A computerassisted classification procedure was used to define new regions of interest for relaxation time estimation. By using this procedure more accurate estimations of the T₁ and T₂ values were obtained.     

Applications to the magnetic tape storage unit,facit ECM64 (the Carousel Memory)

The magnetic tape storage unit, ECM 64 or the Carousel Memory, has been developed by Facit Electronics AB, Stockholm. The prototype of the Memory has been connected to the Facit EDB 3 computer for one and a half year. The applications to the Carousel Memory related here come from the use of this computer by the Facit Service Bureau in Stockholm. Although being a prototype the Carousel Memory is working 24 hours a day.     

Separation of sugar derivatives by partition chromatography on anion-exchange resins

The separation of a number of sugar derivatives such as methyl, ethyl, benzyl, hydroxyethyl erners and various glycosides has been studied. An efficient separation of most species was obtained in 94% ethanol using an anion-exchange resin in its sulfate form. The eluate concentration was determined automatically using the orcinol method.     

The random-cluster model on a homogeneous tree

Summary The random-cluster model on a homogeneous tree is defined and studied. It is shown that for 1q2, the percolation probability in the maximal random-cluster measure is continuous inp, while forq>2 it has a discontinuity at the critical valuep=p _c (q). It is also shown that forq>2, there is nonuniqueness of random-cluster measures for an entire interval of values ofp. The latter result is in sharp contrast to what happens on the integer lattice Z ^d .Research partially supported by a grant from the Royal Swedish Academy of Sciences     

The π-electron energies ofcis- andtrans-stilbene

-electron energies ofcis- andtrans-stilbene and the benzyl radical have been calculated by use of the semiempirical method proposed byPariser, Parr andPople. Special attention is devoted to differences in total energies between the two isomers and to the steric hindrance in thecis-form.

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Zusammenfassung Mit der PPP-Methode wurden die-Elektronenergien voncis- undtrans-Stilben und dem Benzylradikal berechnet. Spezielle Aufmerksamkeit wurde auf den Unterschied der beiden Isomere bezüglich der Gesamtenergie und der sterischen Hinderung gerichtet.

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Résumé Les énergies des électrons ducis et dutrans-stilbène ainsi que du radical benzyle ont été calculées à l'aide de la méthode semi-empirique de Pariser, Parr et Pople. On étudie particulièrement les différences des énergies totales entre les deux isomères et l'empêchement stérique de la forme cis.

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The work reported in this paper has been sponsored in part by the King Gustaf VI Adolf's 70-Years Fund for Swedish Culture, Knut and Alice Wallenberg's Foundation, and in part by the Aerospace Research Laboratories, OAR, through the European Office of Aerospace Research (OAR), United States Air Force.     

The stable doubly infinite pedigree process of supercritical branching populations

Summary An individual is sampled randomly from a supercritical general branching population and the pedigree process, which centers around this ego-individual, is studied. The process describes not only lineage backwards and forwards, but also the lives of all individuals involved. Under mild conditions and in several senses, the process is shown to stabilize, as time passes. The limit is a doubly infinite population process, which generalizes the stable age distribution of branching processes and demography. It displays a nice independence structure, and can easily be constructed from the original branching law. The results are applied to certain kin-number problems, the process of ego's ancestors' births, and to the FLM-curve of cell kinetics.     

Vectorizing a general purpose molecular dynamics simulation program

A molecular dynamics program for arbitrary molecular mixtures is presented. All intramolecular degrees of freedom are treated explicitly, which means that the program is based on central forces only. A double time step technique has been devised in order to separate rapidly varying, covalent forces from slowly varying ones. Typically, the ratio between the different time steps is about 10, with only a minor computational effort spent in the evaluation of the covalent forces. The program source code is arranged so as to obtain maximal efficiency on a vector processor, while still being portable. On a Cray 1A, a typical simulation of an ion-chelate in aqueous solution with 984 atoms requires a total of 29 μs/interaction with a spherical cutoff distance of 10Å.     

Optical properties of low band gap alternating copolyfluorenes for photovoltaic devices

In a joint experimental and theoretical work the optical response and excited-state character of two novel conjugated polymers for photovoltaic applications are studied. The polymers, alternating polyfluorene (APFO) Green 1 and APFO Green 2, are both copolymers of fluorene, thiophene, and electron accepting groups. The band gaps are extended into the red and near infrared with onsets of 780 and 1000 nm, respectively, due to alternating donor and acceptor moieties along the polymer chain. Spectroscopic ellipsometry and subsequent modeling made it possible to extract the dielectric function in the range of 260-1200 nm. Semiempirical quantum chemical calculations (ZINDO) revealed the character of the main electronic transitions in the studied spectral region. The spectral band just above 400 nm was assigned to a delocalized pi-pi* transition for both polymers. The red band lying at 622 and 767 nm in the two polymers corresponds to an electronic state mainly occupying the acceptor units and having a strong charge-transfer character. We show that the ZINDO transition energies are valuable input to the application of Lorentz oscillators in modeling of the dielectric function of the polymer material.     

Diffusion of water in gelatin studied by a new refractometric method

Summary A refractometric method designed to study the diffusive behaviour of low molecular compounds in solid macromolecular substances in the form of thin layers is described. The layer thickness is determined interferometrically in the apparatus. The system gelatin-water is studied at three different thicknesses, 31 , 40 and 82 , at 25°C. The diffusion process is found to be characterized by a diffusion coefficient which is dependent on concentration only, i. e. independent of time. Also, the concentration at the surface of the layer is found to change instantly from the initial concentration to the equilibrium concentration at the beginning of a diffusion experiment.

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Zusammenfassung Es wird eine refraktometrische Methode zur Untersuchung der Diffusion von niedermolekularen Verbindungen in festen makromolekularen Substanzen in Form dünner Schichten beschrieben. Die Schichtdicke wird im Gerät interferometrisch bestimmt. Das System Gelatine-Wasser ist bei drei verschiedenen Dicken (31 , 40 und 82 ) bei 25°C gemessen. Es zeigt sich, daß der Diffusionskoeffizient allein von der Konzentration, also z. B. u. a. unabhängig von der Zeit ist. Auch wechselt die Konzentration an der Oberflächenschicht augenblicklich von der anfänglichen zur Gleichgewichtskonzentration bei Beginn eines Diffusions-experimentes.

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With 13 figures and 2 tables