The effect of grain size on the twin initiation stress in a TWIP steel

The influence of grain size on the twinning stress of an Fe-15Mn-2Al-2Si-0.7C Twinning Induced Plasticity (TWIP) steel has been investigated. Five grain sizes were obtained using a combination of cold rolling and annealing. Electron backscatter diffraction (EBSD) analysis revealed that the material exhibited a typical cold rolled and annealed texture. Tensile testing showed the yield stress to increase with decreasing grain size, however, the ductility of the material was not substantially affected by a reduction in grain size. Cyclic tensile testing at sub-yield stresses indicated the accumulation of plastic strain with each cycle, consequently the nucleation stress for twinning was determined. The twin stress was found to increase with decreasing grain size. Furthermore, the amount of strain accumulated was greater in the coarser grain material. It is believed that this is due to a difference in the twin thickness, which is influenced by the initial grain size of the material. SEM and TEM analysis of the material deformed to 5% strain revealed thinner primary twins in the fine grain material compared to the coarse grain. TEM examination also showed the dislocation arrangement is affected by the grain size. Furthermore, a larger fraction of stacking faults was observed in the coarse-grained material. It is concluded that the twin nucleation stress and also the thickness of the deformation twins in a TWIP steel, is influenced by the initial grain size of the material. In addition grain refinement results in a boost in strength and energy absorption capabilities in the material

Case-Fatality Ratio of Blood Culture-Confirmed Typhoid Fever in Dhaka, Bangladesh.

With impending rollout of new conjugate typhoid vaccines, better estimates of typhoid case-fatality ratio are needed for countries to set priorities for public health programs. We enrolled 1425 patients of all ages with blood culture-confirmed Salmonella Typhi from laboratory networks serving inpatients and outpatients in Dhaka, Bangladesh. Participants were asked about symptoms and complications including death experienced over a median 3-month period following blood culture diagnosis. Four fatal cases were identified (case-fatality ratio of 0.3% [95% confidence interval, .05%-.55%]). Applying this case-fatality ratio to global typhoid burden estimates would reduce deaths by 70%

Superelastic load cycling of Gum Metal

The superelastic beta titanium alloy, Gum Metal, has been found to accumulate plastic strain during tensile load cycling in the superelastic regime. This is evident from the positive drift of the macroscopic stress vs. strain hysteresis curve parallel to the strain axis and the change in its geometry subsequent to every load-unload cycle. In addition, there is a progressive reduction in the hysteresis loop width and in the stress at which the superelastic transition occurs. In situ synchrotron X-ray diffraction has shown that the lattice strain exhibited the same behaviour as that observed in macroscopic measurements and identified further evidence of plastic strain accumulation. The mechanisms responsible for the observed behaviour have been evaluated using transmission electron microscopy, which revealed a range of different defects that formed during load cycling. The formation of these defects is consistent with the classical mathematical theory for the bcc to orthorhombic martensitic transformation. It is the accumulation of these defects over time that alters its superelastic behaviour

Investigation of the Magnetic Response of a Nanocrystalline High-Frequency Magnetic Link With Multi-Input Excitations

© 2019 IEEE. With the technological advancement of magnetic materials and semiconductor devices, the use of high-frequency magnetic link made of high-saturation induction and low specific core loss nanocrystalline alloy has been gaining popularity to replace the common dc link or ac link specially in integrating multiple renewable sources to the grid. The magnetic integration of multiple renewable sources through a common magnetic link has a number of advantages including galvanic isolation compared with the common dc or ac link. However, the magnetic response of the common magnetic link under multi-input excitations highly affects the energy conversion efficiency. To the best of the authors' knowledge, the magnetic response of an advanced magnetic-material-based magnetic link under multi-input excitations has not been well investigated in the literature. In this paper, a systematic investigation is carried out to interconnect multiple sources through a common magnetic link. The magnetic response and the procedure used in the investigation are also presented and discussed in this paper

Concerns, perceived impacts and preparedness of health care workers in a referral hospital in Egypt in facing influenza (H1N1) epidemic

Objective. In Egypt, influenza A(H1N1) cases have been detected and deaths have been reported. The aim of this study was to investigate Concerns, Perceived Impacts and Preparedness of Physicians and Nurses of Chest Specialty Hospital in Cairo (Egypt) concerning Influenza A(H1N1). Methods. A questionnaire was applied to a total of 72 Physicians and 41 Nurses from Chest Specialty Hospital in Cairo (Egypt). Results. More than half of physicians (55.6%) were men, while most of nurses (92.7%) were women. The mean age in years of physicians was 36.6 ± 11.3 compared to 26.5 ± 8 in nurses. Physicians feel that they are at greater risk by their job to the pandemic100% compared to 87.6% among nurses and the difference is highly significant. More than one third of the studied physicians reported that they are not ready to face H1N1 pandemic. Residents feel less ready to face the danger of Influenza A(H1N1) compared with Consultants and Specialists/Assistant Specialists, with no statistical significant difference. In concordance, Residents reported less Personal Protective Equipment training compared with Consultants and Specialists/Assistant Specialists, with no statistical significant difference. All Consultants received Seasonal Influenza Vaccine compared with Specialists/Assistant Specialists (68.2%) and Residents (44.7%). Conclusion. Higher work related and non work related stress was found among physicians compared to nurses, which reflects the demand of more information and training courses for physicians about the pandemic nature and its consequences, complications, and methods infection prevention

The dynamic behaviour of a twinning induced plasticity steel

The influence of strain rate on the twinning behaviour and microstructure of an Fe–15Mn–2Al–2Si–0.7C twinning induced plasticity (TWIP) steel has been investigated. A Hopkinson pressure bar setup was used in addition to blast testing to perform the high strain rate testing. The yield stress exhibited a positive strain rate sensitivity with increasing strain rate. However, the failure strain of the material was relatively unaffected. Post-deformation microscopy indicated that deformation twinning was less profuse at higher strain rates. Electron backscatter diffraction also indicated the activation of multiple twin systems at strain rates below 1000 s−1 although this did not occur at the higher strain rates tested. A large intragranular misorientation was found to exist in the material tested at lower strain rates indicating a relatively larger dislocation density existing in the material tested at lower strain rates. In addition selected grains in the blast tested material exhibited a 'wavy' structure which was determined not to be due to a phase transformation. It is suggested that this was caused by the complex loading experienced by the material during testing. High resolution transmission electron microscopy also indicated a large density of intrinsic stacking faults in the material subjected to blast testing

A Modified Carrier-Based Advanced Modulation Technique for Improved Switching Performance of Magnetic-Linked Medium-Voltage Converters

© 1972-2012 IEEE. The high-frequency magnetic link is gaining popularity due to its lightweight, small volume, and inherent voltage balancing capability. Those features can simplify the utilization of a multilevel converter (MLC) for the integration of renewable energy sources to the grid with compact size and exert economic feasibility. The modulation and control of the MLC are crucial issues, especially for grid-connected applications. To support the grid, the converter may need to operate in an overmodulation (OVM) region for short periods depending upon the loading conditions. This OVM operation of the converter causes increased harmonic losses and adverse effects on the overall system efficiency. On top of that, the size and cost of filtering circuitry become critical to eliminate the unwanted harmonics. In this regard, a modified OVM scheme with phase-disposed carriers for a grid-connected high-frequency magnetic-link-based cascaded H-bridge (CHB) MLC is proposed for the suppression of harmonics and the reduction of converter loss. Furthermore, with the proposed OVM technique, the voltage gain with the modulation index can be increased up to the range which is unlikely to be achieved using the classical ones. Extensive simulations are carried out with a 2.24 MVA permanent magnet synchronous generator based wind energy conversion system, which is connected to the 11 kV ac grid through a high-frequency magnetic-link and a five-level CHB MLC. A scaled down laboratory prototype is implemented to validate the performance of the converter

Identification and characterisation of G-quadruplex DNA-forming sequences in the Pseudomonas aeruginosa genome

A number of Gram-negative bacteria such as Pseudomonas aeruginosa are becoming resistant to front-line antibiotics. Consequently, there is a pressing need to find alternative bio-molecular targets for the development of new drugs. Since non-canonical DNA structures such as guanine-quadruplexes (G4s) have been implicated in regulating transcription, we were interested in determining whether there are putative quadruplex-forming sequences (PQS) in the genome of Pseudomonas aeruginosa. Using bioinformatic tools, we screened 36 genes potentially relevant to drug resistance for the presence of PQS and 10 of these were selected for biophysical characterisation (i.e. circular dichroism and thermal difference UV/Vis spectroscopy). These studies showed that three of these G-rich sequences (linked to murE, ftsB and mexC genes) form stable guanine-quadruplexes which were studied by NMR spectroscopy; detailed analysis of one of the sequences (mexC) confirmed that it adopts a two-quartet antiparallel quadruplex structure in the presence of K+ ions. We also show by FRET melting assays that small molecules can stabilise these three new G4 DNA structures under physiological conditions. These initial results could be of future interest in the development of new antibiotics with alternative bio-molecular targets which in turn would help tackle antimicrobial resistance