Laser powered heating stage in a scanning electron microscope for microstructural investigations at elevated temperatures

A laser powered heating stage designed for application in high vacuum environment of a scanning electron microscope (SEM) is presented. It was developed to observe and characterize microstructural changes in crystalline materials at elevated temperatures up to 1000 degrees C. The approach utilizes the power output of a commercial infrared diode laser in order to heat up specimens without interference with the electronic system of the SEM. The heating stage can be used in combination with any standard characterization technique applicable for SEMs--electron backscatter diffraction, orientation contrast imaging, x-ray energy dispersive spectrometry, etc. The results of test measurements are presented.     

A consistent muscle activation strategy underlies crawling and swimming in Caenorhabditis elegans

Although undulatory swimming is observed in many organisms, the neuromuscular basis for undulatory movement patterns is not well understood. To better understand the basis for the generation of these movement patterns, we studied muscle activity in the nematode Caenorhabditis elegans. Caenorhabditis elegans exhibits a range of locomotion patterns: in low viscosity fluids the undulation has a wavelength longer than the body and propagates rapidly, while in high viscosity fluids or on agar media the undulatory waves are shorter and slower. Theoretical treatment of observed behaviour has suggested a large change in force–posture relationships at different viscosities, but analysis of bend propagation suggests that short-range proprioceptive feedback is used to control and generate body bends. How muscles could be activated in a way consistent with both these results is unclear. We therefore combined automated worm tracking with calcium imaging to determine muscle activation strategy in a variety of external substrates. Remarkably, we observed that across locomotion patterns spanning a threefold change in wavelength, peak muscle activation occurs approximately 45° (1/8th of a cycle) ahead of peak midline curvature. Although the location of peak force is predicted to vary widely, the activation pattern is consistent with required force in a model incorporating putative length- and velocity-dependence of muscle strength. Furthermore, a linear combination of local curvature and velocity can match the pattern of activation. This suggests that proprioception can enable the worm to swim effectively while working within the limitations of muscle biomechanics and neural control.     

Report: 10th annual workshop,membrane discussions 2000

The 10th Annual Workshop 'Membrane Discussions 2000' was held during July 2000 in Kostroma, Russia. The workshop was organised by research and development company TEKO, together with the Association ASPECT of the Ministry of the Atomic Industry of the Russian Federation. This brief review of the event summarises key presentations, and looks at some of the developing technologies which were discussed.     

Recent Advances in Boron Nitride Nanotubes and Nanosheets

Herein the recent experiments performed by the authors on fabricated multi-walled BN nanotubes and monoatomic BN graphene-like nanosheets are reviewed. The results are presented in several sections, namely: (i) method for high-yield synthesis of thin, defect-free BN nanotubes of only a few-layers, with external diameters below 10 nm; (ii) verification of BN nanotube piezoelectrical behavior and its electrically-induced thermal decomposition under combined resistive heating and electrical charging in a transmission electron microscope; (iii) the first direct measurements of the true tensile strength and Young’s modulus of BN nanotubes, using newly developed nanotensile tests inside an electron microscope; the measured values were found to be ∼30 GPa and ∼900 GPa, respectively; and (iv) diverse kinetic processes taking place within the prepared monoatomic BN sheets (so-called “white graphenes”) affiliated with intensive knock-on B and N atom displacements under high energy electron beam irradiation in an aberration-corrected medium-voltage high-resolution transmission electron microscope.     

On the Relation of Microstructure and Texture Evolution in an Austenitic Fe-28Mn-0.28C TWIP Steel During Cold Rolling

In the present study, microstructure and texture evolution in an austenitic Fe-28 wt pct Mn-0.28 wt pct C TWIP steel in the range between 10 and 80 pct reduction by cold rolling were systematically analyzed. The formation of the observed microstructural features occurred in three different stages: I (10 to 20 pct)—mainly slip lines, grain elongation, and formation of few twin-matrix lamellae; II (30 to 50 pct)—severe increase of the volume fraction of twins, alignment of twins with the rolling plane, and formation of microshear bands; and III (60 to 80 pct)—further alignment of twins, evolution of a herring bone structure, and macroshear bands. In contrast to most f.c.c. metals, the transition from Copper- to Brass-type texture occurred at low strain levels (30 pct). This behavior is attributed to the early formation of deformation twins in the material and can be related to the SFE of this high manganese steel. At higher reduction levels, microscopic (≥40 pct) and macroscopic shear band formation (≥60 pct) contributed to the increase of randomly oriented grains, mainly at the expense of the Brass component. Furthermore, the formation of the Goss component and of the 〈111〉//ND fiber (γ) is attributed to severe twin formation.     

Comparative study of the stability of sulfide materials encapsulated in and expelled from multi-walled carbon nanotube capsules

A high density of electrical current has been used to induce the abrupt release of a sulfide compound from the interior of electron-beam-welded turbostratic carbon nanotubes. This event did not alter the chemical identity of either the expelled or the encapsulated material. However, upon 30 days of air exposure notable differences in reactivity were observed. It was found that the expelled chalcogenide particles are chemically more unstable than the material protected by the carbon shell.     

Thermodynamic calculation of phase equilibria of the Bi-Sn-Zn system

A thermodynamic assessment of the Bi-Sn-Zn ternary system was carried out by considering the experimental data including the phase equilibria and thermodynamic properties on the basis of the CALPHAD method. A set of optimized thermodynamic parameters has been obtained, which leads to a very good fit between calculation and experiments. In particular, the thermodynamic calculations in the Sn-rich portion are presented in view of the recent progress in Pb-free solder alloys.     

ABS: Adaptive buffer sizing for heterogeneous networks

Most existing criteria [3], [5], [9] for sizing router buffers rely on explicit formulation of the relationship between buffer size and characteristics of Internet traffic. However, this is a non-trivial, if not impossible, task given that the number of flows, their individual RTTs, and congestion control methods, as well as flow responsiveness, are unknown. In this paper, we undertake a completely different approach that uses control-theoretic buffer size tuning in response to traffic dynamics. Motivated by the monotonic relationship between buffer size and loss rate and utilization, we design a mechanism called Adaptive Buffer Sizing (ABS), which is composed of two Integral controllers for dynamic buffer adjustment and two gradient-based components for intelligent parameter training. We demonstrate via ns2 simulations that ABS successfully stabilizes the buffer size at its minimum value under given constraints, scales to a wide spectrum of flow populations and link capacities, exhibits fast convergence rate and stable dynamics in various network settings, and is robust to load changes and generic Internet traffic (including FTP, HTTP, and non-TCP flows). All of these demonstrate that ABS is a promising mechanism for tomorrow’s router infrastructure and may be of significant interest for the ongoing collaborative research and development efforts (e.g., GENI and FIND) in reinventing the Internet.     

Membranes help to produce high-concentration ozone: new challenges

This article briefly looks at current research trends, available technologies, and challenges and possible applications of membrane science for electrocatalytic generation of ozone. It also provides details of research and development work carried out by South African company Dinax Technologies CC, in cooperation with the Chemistry Department at the University of Stellenbosch, and the Water Research Commission of South Africa.     

Analysis of total aerobic viable counts in samples of raw meat using fluorescence-based probe and oxygen consumption assay

A simple test for determining total aerobic viable counts in raw meat is presented. Homogenates of meat samples are prepared in full PBW medium, dispensed in the wells of 96-well plate together with the oxygen-sensing probe, Redlight, covered with oil and monitored on a fluorescent reader at 30 °C. The probe produces characteristic sigmoidal profiles of fluorescence reflecting depletion of sample dissolved oxygen, with onset time indicating the initial microbial load. The test provides rapid and accurate results (1 and 12 h for contamination levels of 10⁸ and 10³ cfu/g, respectively) and correlates well with the ISO:4833:2003 method (r = 0.86), which make it useful as alternative to conventional culture methods for the quick, high throughput determination of TVC (30 °C) in meat samples.