Computer Tomograph Measurements in Shear and Gravity Particle Flows

The paper reports the recent results obtained on the applicability of cross-sectional digital imaging method to study particle flow characteristics in 3D particle beds forced to move by gravity or shear. X-ray CT imaging technique is widely used in medical diagnostics and, during the last decades, its spatial and temporal resolution has been improved significantly. In this study, an attempt was made to use this technique for engineering purposes. Two experimental set-ups with different types of particle flows were investigated using Siemens Somatom Plus type CT equipment. A series of trials were carried out in a small model hopper with flat bottom and almost cylindrical side wall slightly deviating from verticality. Non steady-state flow was studied during the outflow of particulate material from this vessel, through a central hole at the bottom. Further investigation was fulfilled in a modified Cuette-type shearing device to study steady-state shear flow. This equipment consisted of an almost cylindrical vessel identical to that used for gravity flow measurements, and a smaller inner cylinder rotating within this vessel concentrically, around its vertical axis. The surface of the inner cylinder was notched vertically, i.e. perpendicularly to the direction of rotation to increase wall friction between the particles and the cylinder. Almost spherical sucrose granules, also used for gravity flow measurements, were filled into the gap between the rotating cylinder and the outer wall of the equipment. Movement of particles took place due to shear, generated within the particle bed. By using X-ray CT technique, cross-sectional digital images were obtained in every two seconds for both types of particle flows. For this, the cross-sectional variation of the local Hounsfield density values were measured in a matrix of 0.1x0.1x2.0 mm space elements. It was proved that the applied non-invasive crosssectional imaging technique was suitable to distinguish the stationary and moving particle regions, and by this, to estimate the location of the boundary zone between them

Measurement of ion emission from plasmas obtained with a 600 fs KrF laser

Ion emission from plasmas obtained by the use of a 600 fs, 36 mJ KrF laser operating at 248 nm was measured and analysed for a variety of targets at different laser intensities. The intensity was set by changing the distance between the focusing lens and the target. It was found that the ions emitted originate from impurities and ions from the bulk of the target can be produced only in the subsequent shots. Proton emission was identified from some targets, but the energy of the protons was low (less than 12 keV). A new silicon carbide semiconductor detector proved to be applicable for the collection of the ions

A mathematical model for cell cycle-specific cancer virotherapy

Oncolytic viruses preferentially infect and replicate in cancerous cells, leading to elimination of tumour populations, while sparing most healthy cells. Here, we study the cell cycle-specific activity of viruses such as vesicular stomatitis virus (VSV). In spite of its capacity as a robust cytolytic agent,VSVcannot effectively attack certain tumour cell types during the quiescent, or resting, phase of the cell cycle. In an effort to understand the interplay between the time course of the cell cycle and the specificity of VSV, we develop a mathematical model for cycle-specific virus therapeutics. We incorporate the minimum biologically required time spent in the non-quiescent cell cycle phases using systems of differential equations with incorporated time delays. Through analysis and simulation of the model, we describe how varying the minimum cycling time and the parameters that govern viral dynamics affect the stability of the cancer-free equilibrium, which represents therapeutic success

Structural Toxicity: Hypertrophy Models of Human Pluripotent Stem Cell-Derived Cardiomyocytes

Human pluripotent stem cells (hPSC) are investigated as a source of authentic human cardiac cells for drug discovery and toxicological tests. Cell-based assays performed using an automated fluorescence imaging platform and high-content analysis are valuable in characterizing hypertrophic states that may be induced in hPSC-derived cardiomyocytes upon exposure to cardiotoxic compounds. In high-purity populations of hPSC-derived cardiomyocytes loaded with cell tracer probes and other cell markers, detailed hypertrophic profiles can be assessed based on information captured at cellular and subcellular levels

Mechanistic study of an immobilized molecular electrocatalyst by in situ gap-plasmon-assisted spectro-electrochemistry

Immobilised first-row transition metal complexes are potential low-cost electrocatalysts for selective CO2 conversion to produce renewable fuels. Mechanistic understanding of their function is vital for the development of next-generation catalysts, though poor surface sensitivity of many techniques makes this challenging. Here, a nickel bis(terpyridine) complex is introduced as a CO2 reduction electrocatalyst in a unique electrode geometry, sandwiched by thiol anchoring moieties between two gold surfaces. Gap-plasmon-assisted surface-enhanced Raman scattering spectroscopy coupled with density functional theory calculations reveals the nature of the anchoring group plays a pivotal role in the catalytic mechanism by eliminating ligand loss. Our in-situ spectro-electrochemical measurement enables the detection of as few as 8 molecules undergoing redox transformations in the individual gold-sandwiched nanocavities, together with the calibration of electrical fields via vibrational Stark effects. This advance allows rapid exploration of non-resonant redox reactions at the few-molecule level and provides scope for future mechanistic studies of single-molecules

Strong structuring arising from weak cooperative O-H···π and C-H···O hydrogen bonding in benzene-methanol solution

Weak hydrogen bonds, such as O-H···π and C-H···O, are thought to direct biochemical assembly, molecular recognition, and chemical selectivity but are seldom observed in solution. We have used neutron diffraction combined with H/D isotopic substitution to obtain a detailed spatial and orientational picture of the structure of benzene-methanol mixtures. Our analysis reveals that methanol fully solvates and surrounds each benzene molecule. The expected O-H···π interaction is highly localised and directional, with the methanol hydroxyl bond aligned normal to the aromatic plane and the hydrogen at a distance of 2.30 Å from the ring centroid. Simultaneously, the tendency of methanol to form chain and cyclic motifs in the bulk liquid is manifest in a highly templated solvation structure in the plane of the ring. The methanol molecules surround the benzene so that the O-H bonds are coplanar with the aromatic ring while the oxygens interact with C-H groups through simultaneous bifurcated hydrogen bonds. This demonstrates that weak hydrogen bonding can modulate existing stronger interactions to give rise to highly ordered cooperative structural motifs that persist in the liquid phase

A Counterexample Regarding Labelled Well-Quasi-Ordering

Korpelainen, Lozin, and Razgon conjectured that a hereditary property of graphs which is well-quasi-ordered by the induced subgraph order and defined by only finitely many minimal forbidden induced subgraphs is labelled well-quasi-ordered, a notion stronger than that of n-well-quasi-order introduced by Pouzet in the 1970s. We present a counterexample to this conjecture. In fact, we exhibit a hereditary property of graphs which is well-quasi-ordered by the induced subgraph order and defined by finitely many minimal forbidden induced subgraphs yet is not 2-well-quasi-ordered. This counterexample is based on the widdershins spiral, which has received some study in the area of permutation patterns

Pre-Excitation Studies for Rubidium-Plasma Generation

The key element in the Proton-Driven-Plasma-Wake-Field-Accelerator (AWAKE) project is the generation of highly uniform plasma from Rubidium vapor. The standard way to achieve full ionization is to use high power laser which can assure the over-barrier-ionization (OBI) along the 10 meters long active region. The Wigner-team in Budapest is investigating an alternative way of uniform plasma generation. The proposed Resonance Enhanced Multi Photon Ionization (REMPI) scheme probably can be realized by much less laser power. In the following the resonant pre-excitations of the Rb atoms are investigated, theoretically and the status report about the preparatory work on the experiment are presented.Comment: 8 pages, 6 figures, submitted to Nucl. Inst. and Meth. in Phys. Res.