Phase retrieval for imaging problems

We study convex relaxation algorithms for phase retrieval on imaging problems. We show that exploiting structural assumptions on the signal and the observations, such as sparsity, smoothness or positivity, can significantly speed-up convergence and improve recovery performance. We detail numerical results in molecular imaging experiments simulated using data from the Protein Data Bank.     

Finite element method solution of simultaneous two-dimensional heat and mass transfer in laminar film flow

A finite element solution is given for the coupled heat and mass transfer taking place when a vapour with considerable heat of absorption is absorbed into a laminar film flow. Convection and diffusion parallel and perpendicular to the direction of flow are taken into account. Temperature and mass fraction profiles across the film are given as well as results in film flow direction for several values of the Peclet number. Comparison with a solution based on one-dimensional flow and diffusion perpendicular to the flow, shows that deviations from this case by our two-dimensional solution increase for decreasing Peclet number.     

Kinematic features of the brittle fracture phenomenon

Summary Normal-fracture surfaces of various high-polymers were investigated with the aid of light microscopy. The common fracture pattern is discussed in relation with the kinematic fracture picture introduced bySmekal (1–3). Attention is paid to radial traces and hyperbolic traces, as well as to other morphological features. With the aid of the morphological picture and results of mechanical surface roughness measurements, the three-dimensional density (volume population) of fracture sources could, at polymethylmethacrylate, be roughly estimated. The geometry of fracture sources of polymethylmethacrylate was elucidated by means of electron microscopy. Supplementary experiments performated at normal-fracture surfaces of polymethylmethacrylate showed the effect of a 90°-rotation of the largest principal stress upon the critical condition of inhomogeneities.

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Zusammenfassung Bruchflächen verschiedener Hochpolymeren wurden lichtmikroskopisch untersucht. Die Bruchfiguren werden an Hand des kinematischen Bildes des Bruchvorgangs, wie esSmekal entwickelte, betrachtet. Besondere Aufmerksamkeit wurde den radialen und hyperbolischen Spuren sowie den anderen morphologischen Zügen gewidmet. Mit Hilfe des morphologischen Bildes und der Ergebnisse von mechanischen Messungen der Oberflächenrauhigkeit konnte grob für Polymethylmethacrylat die 3-dimensionale Dichte (Volumenhäufigkeit) der Quellen für den Bruch abgeschätzt werden. Die geometrische Form der Bruchquellen für Polymethylmethacrylat wurde elektronenmikroskopisch geklärt. Ergänzende Experimente an Normal-Bruchflächen von Polymethylmethacrylat zeigen den Effekt einer 90°-Drehung der größten Hauptspannung auf die kritische Inhomogenitätsbedingung.

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Presented at the conference Flow, Fatigue and Failure held in Leeds on January 8th and 9th, 1959, by the British Society of Rheology.     

The principle of virtual work and its dual for contact problems

Summary In the first half of this paper, the variational inequalities of virtual work and its dual, the complementary virtual work are formulated for frictional contact problems with large deformations without restriction on the material properties of the bulk material. Care has been taken to formulate as many as possible terms as variations of a functional. Only the terms involving the frictional traction bound are excepted. Next the significance of the theory for the calculation of frictional contact is discussed.

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Das Prinzip der virtuellen Arbeit und sein Dual für Kontaktprobleme

Übersicht In der 1. Hälfte dieses Aufsatzes werden die Variationsgleichungen der virtuellen Arbeit und ihr Dual, die komplementäre virtuelle Arbeit, formuliert für Reibungskontaktprobleme mit großen Verschiebungen, ohne die materiellen Eigenschaften des Werkstoffes zu berücksichtigen. Möglichst viele Terme werden als Variationen eines Funktionals formuliert. Nur die Terme, welche die Reibungsgrenze enthalten, sind ausgenommen. In der 2. Hälfte wird die Bedeutung der Theorie für die Berechnung des Reibungskontakts hervorgehoben.

     

Fluorescent π‐Conjugated Polymer Dots versus Self‐Assembled Small‐Molecule Nanoparticles: What’s the Difference?

Fluorescent nanoparticles based on π‐conjugated small molecules and polymers are two different classes of π‐conjugated systems that have attracted much interest. To date, both emerging classes have only been studied separately and showed no clear differences in their properties. Herein these nanoparticles are compared on the basis of a fluorene co‐polymer and its corresponding small molecule. Both systems formed nanoparticles with the same diameter, whereas the fluorescence properties clearly differed. In case of the polymer the fluorescence diminished, whereas for the small molecules the fluorescence increased. In addition, the capability of encapsulation and release of a hydrophobic dye from the fluorescent nanoparticles was studied. For the polymer system, encapsulation was highly efficient and no release was observed, whereas for the small molecule system encapsulation was less efficient and release of the dye was observed. These studies show a clear difference between small molecules and polymers which has important implications for the design of fluorescent nanoparticles.     

Waves due to surface charges in a metal

The question of the role of waves due to surface charges in the propagation of electromagnetic waves along a metallic cylinder is considered. The possibility of the existence of two types of waves due to surface charges caused by free and bound electrons is demonstrated. It is established that there is a continuous transition from plasma surface waves to Sommerfeld waves and dipole surface waves. A more systematic theory of the boundary value problem is put forth which accounts for the complete system of boundary conditions and the new degrees of freedom related to the waves due to surface charges.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 98–104, April, 1978.     

TLC Method for Monitoring the Formation and Degradation of Bacterial Exo-Polysaccharides

JPC – Journal of Planar Chromatography – Modern TLC - A simple thin-layer chromatography (TLC) method for continuous determination of metabolism of carbohydrate and production of...     

Dictyostelium Extracellular Vesicles Containing Hoechst 33342 Transfer the Dye into the Nuclei of Living Cells: A Fluorescence Study

Cells of the eukaryotic unicellular microorganism Dictyostelium discoideum are constitutively resistant to vital staining of their nuclei by the DNA-specific dye Hoechst 33342. By studying the mechanisms of this resistance, we evidenced that these cells expel vesicles containing the dye for detoxification (Tatischeff et al., Cell Mol Life Sci, 54: 476-87, 1998). The question to be addressed in the present work is the potential use of these extracellular vesicles as a biological drug delivery tool, using Hoechst 33342 as a model of a DNA-targeting drug. After cell growth with or without the dye, vesicles were prepared from the cell-free growth medium by differential centrifugation, giving rise to two types of vesicles. Negative staining electron microscopy showed their large heterogeneity in size. Using fluorescence techniques, data were obtained on the dye loading and its environment inside the vesicles. By UV video-microscopy, it was demonstrated that the dye-containing vesicles were able to deliver it into the nuclei of naive Dictyostelium cells, thus overcoming their constitutive resistance to the free dye. A vesicle-mediated dye-transfer into the nuclei of living human leukaemia multidrug resistant K562r cells was also observed.