Boundary saltation and minimum pressure velocities in particle-gas systems

The saltation velocity is one of the key design parameters in pneumatic conveying systems. The aim of this work is to experimentally study the mechanism of saltation. Experiments were carried out with various spherical and non-spherical particles in a small wind tunnel with very dilute flow. For each velocity the distribution of halted particles along the tunnel bottom was measured. From this length distribution, the median length was determined and used for further analysis. It was found that the median conveying length approaches infinity at a certain threshold velocity. By testing many materials the boundary saltation velocity followed a simple correlation of the modified Reynolds number as a function of the modified Archimedes number. The conveying length was an accumulation of three lengths: the first flight length, the rebound length, which is affected by the coefficient of restitution, and the rolling/sliding length, which is affected by the coefficient of friction. By analyzing these lengths, the total conveying length and the boundary saltation velocity were easily defined. Furthermore, as the velocities at minimum pressure velocities (referred to in the paper as the minimum pressure velocities) have been found to follow the same trend as the boundary saltation velocity if the solid concentration is taken into account, our simple correlation can describe by ± 30% all the relevant experiments found in the literature.     

Boolean logic gates that use enzymes as input signals

Biochemical systems that demonstrate the Boolean logic operations AND, OR, XOR, and InhibA were developed by using soluble compounds, which represent the chemical "devices", and the enzymes glucose oxidase (GOx), glucose dehydrogenase (GDH), alcohol dehydrogenase (AlcDH), and microperoxidase-11 (MP-11), which operated as the input signals that activated the logic gates. The enzymes were used as soluble materials and as immobilized biocatalysts. The studied systems are proposed to be a step towards the construction of "smart" signal-responsive materials with built-in Boolean logic.     

Single yeast cell vacuolar milieu viscosity assessment by fluorescence polarization microscopy with computer image analysis

This study was undertaken to evaluate the apparent viscosity within the vacuoles of single Saccharomyces cerevisiae cells by steady‐state fluorescence anisotropy measurements of quinacrine, using wide‐field fluorescence polarization microscopy combined with computer image analysis. Quinacrine was shown to be rather specifically accumulated within the vacuoles of the cells. This accumulation was effectively reversed by ATP depletion of the cells, with no detectable binding of the dye within the vacuoles. Quinacrine fluorescence anisotropy in the sucrose solutions of various viscosities obeyed the Perrin equation. The fluorescence anisotropy of quinacrine was measured in the vacuoles of 39 cells. From cell to cell, this parameter changed in the range 0.032–0.086. Using the Perrin plot as a calibration curve, apparent viscosity values of the vacuolar milieu were calculated for each cell. The population of the cells studied was heterogeneous with regard to vacuolar viscosity, which was in the range 3.5 ± 0.4–14.06 ± 0.64 cP. There was a characteristic distribution of the frequencies of cells with apparent viscosities within certain limits, and cells with viscosity values in the range 5–6 cP were the most frequent. No relationship was found between the sizes of the vacuoles and their apparent viscosities. Copyright © 2012 John Wiley & Sons, Ltd.     

Homogeneous nucleation and mesophase formation in glassy isotactic polypropylene

Differential fast scanning chip calorimetry has been employed to study nucleation/ordering during annealing the glass of quenched isotactic polypropylene. Initially non-ordered samples were annealed below the glass transition temperature for different periods of time, and the change of structure during isothermal annealing was then analyzed by monitoring the exchange of latent heat on heating. Primary result of this work is the proof of homogeneous nucleation of ordering and mesophase formation in the glassy state. It is suggested that only local non-cooperative mobility of molecular segments is required to form small, ordered domains, and that the classical nucleation theory, which restricts nucleation of the crystallization/ordering process of polymers to temperatures between the equilibrium melting temperature and the glass transition temperature, needs modification.     

In-Situ Vibrational Spectroscopic Studies on Model Catalyst Surfaces at Elevated Pressures

Elucidation of complex heterogeneous catalytic mechanisms at the molecular level is a challenging task due to the complex electronic structure and the topology of catalyst surfaces. Heterogeneous catalyst surfaces are often quite dynamic and readily undergo significant alterations under working conditions. Thus, monitoring the surface chemistry of heterogeneous catalysts under industrially relevant conditions such as elevated temperatures and pressures requires dedicated in situ spectroscopy methods. Due to their photons-in, photons-out nature, vibrational spectroscopic techniques offer a very powerful and a versatile experimental tool box, allowing real-time investigation of working catalyst surfaces at elevated pressures. Infrared reflection absorption spectroscopy (IRAS or IRRAS), polarization modulation-IRAS and sum frequency generation techniques reveal valuable surface chemical information at the molecular level, particularly when they are applied to atomically well-defined planar model catalyst surfaces such as single crystals or ultrathin films. In this review article, recent state of the art applications of in situ surface vibrational spectroscopy will be presented with a particular focus on elevated pressure adsorption of probe molecules (e.g. CO, NO, O₂, H₂, CH₃OH) on monometallic and bimetallic transition metal surfaces (e.g. Pt, Pd, Rh, Ru, Au, Co, PdZn, AuPd, CuPt, etc.). Furthermore, case studies involving elevated pressure carbon monoxide oxidation, CO hydrogenation, Fischer–Tropsch, methanol decomposition/partial oxidation and methanol steam reforming reactions on single crystal platinum group metal surfaces will be provided. These examples will be exploited in order to demonstrate the capabilities, opportunities and the existing challenges associated with the in situ vibrational spectroscopic analysis of heterogeneous catalytic reactions on model catalyst surfaces at elevated pressures.     

Fabrication,Characterization, and Printing of Conductive Ink Based on Multi Core–Shell Nanoparticles Synthesized by RAPET

In the current research, conductive patterns are deposited on different substrates by direct inkjet printing of conductive inks based on metal@carbon and bimetal@carbon core–shell nanoparticles synthesized by the RAPET (reaction under autogenic pressure at elevated temperatures) technique. Various co‐solvents and additives are examined for production of stable conductive ink. The morphology of the deposited layers is characterized by optical and scanning electron microscopy measurements. The stability of the prepared inks is examined by dynamic light scattering measurements. The electrical resistivity is measured by a four‐point probe system and calculated using the geometric dimensions. The results obtained are very promising and indicate that the conductivity of the deposited layers is close to that of bulk metals and higher than most results published so far. Moreover, the importance and advantages of the protective carbon layer that prevents metal oxidation is demonstrated.     

Gender differences in acute alcohol effects on self-regulation of arousal in response to emotional and alcohol-related picture cues.

Basic mechanisms through which men and women self-regulate arousal have received little attention in human experimental addiction research, although stress-response-dampening and craving theories suggest an important role of emotional arousal in motivating alcohol use. This study examined gender differences in the effects of acute alcohol intoxication on psychophysiological and self-reported arousal in response to emotionally negative, positive, and neutral, and alcohol-related, picture cues. Thirty-six social drinkers (16 women) were randomly assigned to an alcohol, placebo, or control beverage group and exposed to picture cues every 10 s (0.1 Hz presentation frequency). Psychophysiological arousal was assessed via a 0.1-Hz heart rate variability (HRV) index. A statistically significant beverage group-by-gender interaction effect on psychophysiological, but not self-reported, arousal was found. The 0.1-Hz HRV responses to picture cues were suppressed by alcohol only in men. This gender-specific suppression pattern did not differ significantly across picture cue types. There were no significant gender differences in the placebo or control group. Greater dampening of arousal by alcohol intoxication in men, compared with women, may contribute to men’s greater tendency to use alcohol to cope with stress. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of backgating on the field distribution in planar thin-film GaAs structures

The distribution of the electric field in planar film–substrate GaAs structures under backgating is considered. It is shown that backgating can make the film exhibit a long-length region of a low-gradient electric field exceeding the threshold of N-type negative differential mobility, the magnitude of negative differential mobility in this region being high enough. At values of the film doping density and film thickness typical of GaAs transferred-electron devices, this region can be as long as several tens of micrometers. The underlying physical mechanism is discussed.     

Tunable order in colloids of hard magnetic hexaferrite nanoplatelets

Structural ordering in the concentrated magnetic colloids containing 50×5 nm hard magnetic disc-like SrFe₁₂O₁₉ nanoparticles was investigated by cryogenic scanning electron microscopy,optical microscopy,magnetic measurements,and small-angle X-ray scattering.It was revealed that macroscopically homogeneous magnetic liquid consists of dynamic threads of stacked nanoparticles.The threads align into quasiperiodic arrays with the distances between individual threads of a few micrometers.They also can form pseudodomain structures with -90°domain boundaries realized through T-type thread interconnects.The effects of magnetic attraction and electrostatic repulsion on the equilibrium interplatelet distance in the threads were studied.It was demonstrated that this distance can be tuned by the control of the particles charge and electric double layer screening from Stern layer thickness(-1 nm)to tens of nanometers.It was shown that the permanent magnetic field is not able to cause any structural changes in the ordered magnetic liquid phase,while alternating field draws particles apart by their vibrations.External variation of interparticle distance up to 6%was achieved using an alternating magnetic field of low intensity.Experimental data were complemented by the theoretical models of screened electrostatic interactions between spherical and platelike magnetic particles.The last model provides good predictive power and correlates with the experimental data.The stabilization energy of the condensed phase in the order of 1-10 kBT was derived from the model.An approach allows controlling of an equilibrium interparticle distance and interparticle distance distribution by adjusting the magnetization and surface charge of the particles as well as the ionic strength of the solvent.