Numerical investigation of austenite grain size distribution in square-diamond pass hot bar rolling

In this study, the austenite grain size (AGS) for hot bar rolling of AISI4135 steel was predicted based on two different AGS evolution models available in the literature. In order to predict the AGS more accurately, both models were integrated with a three-dimensional non-isothermal finite element program by implementing a modified additivity rule. The predicted results based on two models for the square-diamond (S-D) and round-oval (R-O) pass bar rolling processes were compared with the experimental data available in the literature. Then, numerical predictions depending on various process parameters such as interpass time, temperature, and roll speed were made to compare both models and investigate the effect of these parameters on the AGS distributions. Such numerical results were found to be beneficial to understand the effect of the microstructure evolution model on the rolling processes better and control the processes more accurately.

Microstructure evolution modeling of square-diamond pass hot bar rolling of AISI 4135 steel

In this study, kinetics of the static (SRX) and metadynamic recrystallization (MDRX) of AISI4135 steel was investigated using hot torsion tests. Continuous torsion tests were carried out to determine the critical strain for dynamic recrystallization (DRX). The times for 50% recrystallization of SRX and MDRX were determined, respectively, by means of interrupted torsion tests. Furthermore, austenite grain size (AGS) evolution due to recrystallization (RX) was measured by optical microscopy. With the help of the evolution model established, the AGS for hot bar rolling of AISI4135 steel was predicted numerically. The predicted AGS values were compared with the results using the other model available in the literature and experimental results to verify its validity. Then, numerical predictions depending on various process parameters such as interpass time, temperature, and roll speed were made to investigate the effect of these parameters on AGS distributions for square-diamond pass rolling. Such numerical results were found to be beneficial in understanding the effect of processing conditions on the microstructure evolution better and control the rolling processes more accurately.

The impact of external forces on cartel network dynamics : Direct research in the diamond industry

This paper describes the impact of external environmental forces on cartel networks. Using a case research approach, this report examines two leading business networks within one industry, over time. The results suggest that (a) bargaining power of intermediaries increases with the advent of new and powerful actors, (b) process activities that cartels previously controlled are being outsourced to new actors sometimes based in developing countries, (c) other actors are acquiring resources once dominated by a cartel, (d) external forces triggered by the illegal diamond trade, such as international regulatory constraints, no longer favour cartels like De Beers, and (e) over time, these and additional environment factors are forcing actors like De Beers who perform rigid process activities to become more flexible. For example,forces are moving cartels which relied previously on hand-picked intermediaries in highly controlled networks to market their products to adopt a flexible market-focused expansion of operations in retail contexts.

Diamond Dialogue method for the evaluation of personal well-being after a maternal health intervention in Lao PDR

This paper follows the genesis of an evolving tool to measure the impact of development interventions on personal well-being in non-literate and non-numerate communities. The Diamond Dialogue was adapted to evaluate the impact on women of the establishment of 17 one stop maternity waiting home/health promotion/income generating centres (Silk Homes) in Southern Lao PDR. The tool elicited data not accessible by research methods which assume literacy and numeracy and revealed that 86% of women who used the Silk Homes experienced substantial improvements in quality of life. The Diamond Dialogue can be modified to assess the outcomes of development interventions in a myriad of contexts.

Potential of 129Xe NMR spectroscopy of adsorbed xenon for testing the chemical state of the surface of mesoporous carbon materials illustrated by the example of aggregates of diamond and onion-like carbon nanoparticles

The chemical shift in the 129Xe NMR spectrum of adsorbed xenon is very sensitive to the presence of oxygen-containing functional groups on the surface of mesoporous carbon materials. Well-characterized, structurally similar nanodiamond and onion-like carbon samples are considered here as model objects.

Profiling of polar metabolites in biological extracts using diamond hydride-based aqueous normal phase chromatography

Highly polar metabolites, such as sugars and most amino acids are not retained by conventional RP LC columns. Without sufficient retention low concentration compounds are not detected due ion suppression and structural isomers are not resolved. In contrast, hydrophilic interaction chromatography (HILIC) and aqueous normal phase chromatography (ANP) retain compounds based on their hydrophilicity and therefore provides a means of separating highly polar compounds. Here, an ANP method based on the diamond hydride stationary phase is presented for profiling biological small molecules by LC. A rapid separation system based upon a fast gradient that delivers reproducible chromatography is presented. Approximately 1000 compounds were reproducibly detected in human urine samples and clear differences between these samples were identified. This chromatography was also applied to xylem fluid from soyabean (Glycine max) plants to which 400 compounds were detected. This method greatly increases the metabolite coverage over RP-only metabolite profiling in biological samples. We show that both forms of chromatography are necessary for untargeted comprehensive metabolite profiling and that the diamond hydride stationary phase provides a good option for polar metabolite analysis.

Raman microscopic analysis of internal stress in boron-doped diamond

Analysis of the induced stress on undoped and boron-doped diamond (BDD) thin films by confocal Raman microscopy is performed in this study to investigate its correlation with sample chemical composition and the substrate used during fabrication. Knowledge of this nature is very important to the issue of long-term stability of BDD coated neurosurgical electrodes that will be used in fast-scan cyclic voltammetry, as potential occurrence of film delaminations and dislocations during their surgical implantation can have unwanted consequences for the reliability of BDD-based biosensing electrodes. To achieve a more uniform deposition of the films on cylindrically-shaped tungsten rods, substrate rotation was employed in a custom-built chemical vapor deposition reactor. In addition to visibly preferential boron incorporation into the diamond lattice and columnar growth, the results also reveal a direct correlation between regions of pure diamond and enhanced stress. Definite stress release throughout entire film thicknesses was found in the OPEN ACCESS current Raman mapping images for higher amounts of boron addition. There is also a possible contribution to the high values of compressive stress from sp2 type carbon impurities, besides that of the expected lattice mismatch between film and substrate.

Prediction of a superhard carbon-rich C-N compound comparable to diamond

Until now, it has been a challenge both in experiment and in theory to design new superhard materials with high hardness values that are comparable to that of diamond. Here, by using first-principles calculations, we have introduced two new phases for a carbon-rich C-N compound with stoichiometry C3N, which is predicted to be energetically stable or metastable with respect to graphite and solid N2 at ambient pressure. It is found that C3N has a layered structure containing graphitic layers sandwiched with freely rotated N2 molecules. The layer-structured C3N is calculated to transform into a three-dimensional C2221 structure at 9 GPa with sp3-hybridized C atoms and sp2-hybridized N atoms. Phonon dispersion and elastic constant calculations reveal the dynamical and mechanical stability of the C2221 phase of C3N at ambient pressure. Significantly, first-principles ideal strength calculations indicate that the C2221 phase of C3N is a superhard material with an estimated Vickers hardness (∼76 GPa) comparable to that of diamond (60-120 GPa). The present results shed strong light on designing new superhard materials in the C-N system.

A diamond-based electrode for detection of neurochemicals in the human brain

Deep brain stimulation (DBS), a surgical technique to treat certain neurologic and psychiatric conditions, relies on pre-determined stimulation parameters in an open-loop configuration. The major advancement in DBS devices is a closed-loop system that uses neurophysiologic feedback to dynamically adjust stimulation frequency and amplitude. Stimulation-driven neurochemical release can be measured by fast-scan cyclic voltammetry (FSCV), but existing FSCV electrodes rely on carbon fiber, which degrades quickly during use and is therefore unsuitable for chronic neurochemical recording. To address this issue, we developed durable, synthetic boron-doped diamond-based electrodes capable of measuring neurochemical release in humans. Compared to carbon fiber electrodes, they were more than two orders-of-magnitude more physically-robust and demonstrated longevity in vitro without deterioration. Applied for the first time in humans, diamond electrode recordings from thalamic targets in patients (n = 4) undergoing DBS for tremor produced signals consistent with adenosine release at a sensitivity comparable to carbon fiber electrodes. (Clinical trials # NCT01705301).

Diamond-based electrode for chronic sensing in deep brain stimulation

This thesis describes the development of a sensing electrode and electronic research platform that enables the measurement of fluctuating levels of neurotransmitters in the human brain. Boron doped diamond electrodes were created via a custom developed chemical vapor deposition reactor for measurement of neurotransmitters using Fast Scan Cyclic Voltammetry.

The impact of external forces on cartel network dynamics: direct research in the diamond industry

This paper describes the impact of external environmental forces on cartel networks. Using a case research approach, this report examines two leading business networks within one industry, over time. The results suggest that (a) bargaining power of intermediaries increases with the advent of new and powerful actors, (b) process activities that cartels previously controlled are being outsourced to new actors sometimes based in developing countries, (c) other actors are acquiring resources once dominated by a cartel, (d) external forces triggered by the illegal diamond trade, such as international regulatory constraints, no longer favour cartels like De Beers, and (e) over time, these and additional environment factors are forcing actors like De Beers who perform rigid process activities to become more flexible. For example, forces are moving cartels which relied previously on hand-picked intermediaries in highly controlled networks to market their products to adopt a flexible market-focused expansion of operations in retail contexts.