Failure of viral shells

We report a combined theoretical and experimental study of the structural failure of viral shells under mechanical stress. We find that discontinuities in the force-indentation curve associated with failure should appear when the so-called F?ppl-von Kármán (FvK) number exceeds a critical value. A nanoindentation study of a viral shell subject to a soft-mode instability, where the stiffness of the shell decreases with increasing pH, confirms the predicted onset of failure as a function of the FvK number.     

Device reliability study of AlGaN/GaN high electron mobility transistors under high gate and channel electric fields via low frequency noise spectroscopy

A set of different short term stress conditions are applied to AlGaN/GaN high electron mobility transistors and changes in the electronic behaviour of the gate stack and channel region are investigated by simultaneous gate and drain current low frequency noise measurements. Permanent degradation of gate current noise is observed during high gate reverse bias stress which is linked to defect creation in the gate edges. In the channel region a permanent degradation of drain noise is observed after a relatively high drain voltage stress in the ON-state. This is attributed to an increase in the trap density at the AlGaN/GaN interface under the gated part of the channel. It was found that self-heating alone does not cause any permanent degradation to the channel or gate stack. OFF-state stress also does not affect the gate stack or the channel.     

Planar micro-direct methanol fuel cell prototyped by rapid powder blasting

We present a planar micro-direct methanol fuel cell (μ-DMFC) fabricated by rapid prototyping-powder blasting technology. Using an elastomeric mask, we pattern two parallel microfluidic channels in glass. The anode and cathode of the fuel cell are formed by wet spraying Pt-Ru/C and Pt/C catalysts, respectively, onto Au electrodes that are evaporated in the microchannels. Simply clamping a Nafion 117 proton exchange membrane (PEM) using a glass substrate covered with PDMS membrane onto the microchannels completes the fuel cell fabrication. Our μ-DMFC generates a voltage of 0.45 V and can deliver a power up to 0.5 mW/cm² by using 1 M CH₃OH in 0.5 M H₂SO₄ solution as fuel in the anodic channel, and 0.01 M H₂O₂ in 0.5 M H₂SO₄ as oxidant solution in the cathodic channel.     

A density-based segmentation for 3D images,an application for X-ray micro-tomography

Density-based spatial clustering of applications with noise (DBSCAN) is an unsupervised classification algorithm which has been widely used in many areas with its simplicity and its ability to deal with hidden clusters of different sizes and shapes and with noise. However, the computational issue of the distance table and the non-stability in detecting the boundaries of adjacent clusters limit the application of the original algorithm to large datasets such as images. In this paper, the DBSCAN algorithm was revised and improved for image clustering and segmentation. The proposed clustering algorithm presents two major advantages over the original one. Firstly, the revised DBSCAN algorithm made it applicable for large 3D image dataset (often with millions of pixels) by using the coordinate system of the image data. Secondly, the revised algorithm solved the non-stability issue of boundary detection in the original DBSCAN. For broader applications, the image dataset can be ordinary 3D images or in general, it can also be a classification result of other type of image data e.g. a multivariate image.     

Dissolution kinetics of nanodispersed gamma-alumina in aqueous solution at different pH: unusual kinetic size effect and formation of a new phase

The dissolution of a technical, nanodispersed gamma-alumina in water was studied at 25 degrees C in the pH range 3.0 < or = pH < or = 11.0. The obtained kinetic dissolution curves showed a distinct pH dependency, whereas only for pH > or = 4.5 the typical behavior of nanodispersed materials could be observed. X-ray powder diffraction analysis and nitrogen adsorption, as well as IR and UV-Raman spectroscopy, were used to characterize the solid material collected during and at the end of each dissolution experiment. As a result the formation of a new aluminum phase-bayerite-could be proven. The analysis of the equilibrium concentration enabled us to determine the solubility constant of the corresponding phase assuming a pH-dependent species distribution. The rate constants of the dissolution process were evaluated using the model of Gibbs free energy of cluster formation, which considers the size effect, among other things. As a result, we could show that the observed maxima in the concentration profiles are due to a size effect of the starting material having a primary particle radius of 10.1 nm.     

A fluorescent broad-spectrum proteasome inhibitor for labeling proteasomes in vitro and in vivo

The proteasome is an essential evolutionary conserved protease involved in many regulatory systems. Here, we describe the synthesis and characterization of the activity-based, fluorescent, and cell-permeable inhibitor Bodipy TMR-Ahx(3)L(3)VS (MV151), which specifically targets all active subunits of the proteasome and immunoproteasome in living cells, allowing for rapid and sensitive in-gel detection. The inhibition profile of a panel of commonly used proteasome inhibitors could be readily determined by MV151 labeling. Administration of MV151 to mice allowed for in vivo labeling of proteasomes, which correlated with inhibition of proteasomal degradation in the affected tissues. This probe can be used for many applications ranging from clinical profiling of proteasome activity, to biochemical analysis of subunit specificity of inhibitors, and to cell biological analysis of the proteasome function and dynamics in living cells.     

A novel green template for the synthesis of mesoporous silica

Mesoporous pure silicas and functionalized silica with a narrow pore size distribution centered at 3.8 nm were prepared by a novel template, amphiphilic dendritic polyglycerol. The resulting silica materials were characterized by electron microscopy; nitrogen adsorption; (1)H, (13)C, and (29)Si solid-state cross-polarization magic-angle spinning NMR spectroscopy. It was shown that the template could be completely removed from the pure and functionalized silica in an environmentally friendly way by means of a simple water extraction procedure. Furthermore, it was shown that these materials could be easily functionalized, for example, by employing aminopropyl groups. Thus, a new environmentally friendly pathway to this fascinating class of silica material has been opened.     

Synthesis of sugar nucleotides by application of phosphoramidites

A new method for the construction of pyrophosphates is reported based on the coupling of a sugar phosphate and a nucleoside phosphoramidite. The in situ formed phosphate-phosphite intermediate was subsequently oxidized with tBuOOH. Three UDP-N-acetylglucosamine derivatives were prepared using this one-pot procedure in good yields.     

Rapid fluidic exchange microsystem for recording of fast ion channel kinetics in Xenopus oocytes

We present a new lab-on-a-chip system for electrophysiological measurements on Xenopus oocytes. Xenopus oocytes are widely used host cells in the field of pharmacological studies and drug development. We developed a novel non-invasive technique using immobilized non-devitellinized cells that replaces the traditional "two-electrode voltage-clamp" (TEVC) method. In particular, rapid fluidic exchange was implemented on-chip to allow recording of fast kinetic events of exogenous ion channels expressed in the cell membrane. Reducing fluidic exchange times of extracellular reagent solutions is a great challenge with these large millimetre-sized cells. Fluidic switching is obtained by shifting the laminar flow interface in a perfusion channel under the cell by means of integrated poly-dimethylsiloxane (PDMS) microvalves. Reagent solution exchange times down to 20 ms have been achieved. An on-chip purging system allows to perform complex pharmacological protocols, making the system suitable for screening of ion channel ligand libraries. The performance of the integrated rapid fluidic exchange system was demonstrated by investigating the self-inhibition of human epithelial sodium channels (ENaC). Our results show that the response time of this ion channel to a specific reactant is about an order of magnitude faster than could be estimated with the traditional TEVC technique.