31,336 research outputs found
Effects Of The Flash Welding Process On Mechanical And Microstructural Properties Of Structural Steel Joints Assessed Using Dest
ASTM A529 carbon¿manganese steel angle specimens were joined by flash butt welding and the effects of varying process parameter settings on the resulting welds were investigated. The weld metal and heat affected zones were examined and tested using tensile testing, ultrasonic scanning, Rockwell hardness testing, optical microscopy, and scanning electron microscopy with energy dispersive spectroscopy in order to quantify the effect of process variables on weld quality. Statistical analysis of experimental tensile and ultrasonic scanning data highlighted the sensitivity of weld strength and the presence of weld zone inclusions and interfacial defects to the process factors of upset current, flashing time duration, and upset dimension. Subsequent microstructural analysis revealed various phases within the weld and heat affected zone, including acicular ferrite, Widmanstätten or side-plate ferrite, and grain boundary ferrite. Inspection of the fracture surfaces of multiple tensile specimens, with scanning electron microscopy, displayed evidence of brittle cleavage fracture within the weld zone for certain factor combinations. Test results also indicated that hardness was increased in the weld zone for all specimens, which can be attributed to the extensive deformation of the upset operation. The significance of weld process factor levels on microstructure, fracture characteristics, and weld zone strength was analyzed. The relationships between significant flash welding process variables and weld quality metrics as applied to ASTM A529-Grade 50 steel angle were formalized in empirical process models
Development of a high brightness ultrafast Transmission Electron Microscope based on a laser-driven cold field emission source
We report on the development of an ultrafast Transmission Electron Microscope
based on a cold field emission source which can operate in either DC or
ultrafast mode. Electron emission from a tungsten nanotip is triggered by
femtosecond laser pulses which are tightly focused by optical components
integrated inside a cold field emission source close to the cathode. The
properties of the electron probe (brightness, angular current density,
stability) are quantitatively determined. The measured brightness is the
largest reported so far for UTEMs. Examples of imaging, diffraction and
spectroscopy using ultrashort electron pulses are given. Finally, the potential
of this instrument is illustrated by performing electron holography in the
off-axis configuration using ultrashort electron pulses.Comment: 23 pages, 9 figure
Mechanochemically Synthesized CIGS Nanocrystalline Powder for Solar Cell Application
Copper Indium Gallium Diselenide (CIGS) is a compound semiconductor material from the group of I-III-VI. The material is a solid solution of copper, indium and selenium (CIS) and copper, gallium and selenium with an empirical formula of CuIn(1 – x)GaxSe2, where 0 x 1. CIGS has an exceptionally high absorption coefficient of more than 105 cm – 1 for 1.5 eV. Solar cells prepared from absorber layers of CIGS materials have shown an efficiency higher than 20 %. CuIn(1 – x)GaxSe2 (x 0.3) nanocrystalline compound was mechanochemically synthesized by high-energy milling in a planetary ball mill. The phase identification and crystallite size of milled powders at different time intervals were carried out by X-ray diffraction (XRD). The XRD analysis indicates chalcopyrite structure and the crystallite size of about 10 nm of high-energy milled CIGS powder after two and half hours of milling. An attempt for preparing the thin film from CIGS nanocrystalline powder was carried out using the flash evaporation technique. Scanning electron microscopy (SEM) reveals uniform distribution of CIGS particles in thin film.
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Tracking elusive cargo: Illuminating spatio-temporal type 3 effector protein dynamics using reporters
Type 3 secretion systems (T3SS) form an integral part of the arsenal of many pathogenic bacteria. These injection machines, together with their cargo of subversive effector proteins are capable of manipulating the cellular environment of the host in order to ensure persistence of the pathogen. In order to fully appreciate the functions of Type 3 effectors it is necessary to gain spatio-temporal knowledge of each effector during the process of infection. A number of genetic modifications have been exploited in order to reveal effector protein secretion, translocation and subsequent activity and localisation within host cells. In this review, we will discuss the many available approaches for tracking effector protein dynamics and discuss the challenges faced to improve the current technologies and gain a clearer picture of effector protein function
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