Search results for "HEE"
showing 10 items of 1797 documents
The filter and calibration wheel for the ATHENA wide field imager
2016
The planned filter and calibration wheel for the Wide Field Imager (WFI) instrument on Athena is presented. With four selectable positions it provides the necessary functions, in particular an UV/VIS blocking filter for the WFI detectors and a calibration source. Challenges for the filter wheel design are the large volume and mass of the subsystem, the implementation of a robust mechanism and the protection of the ultra-thin filter with an area of 160 mm square. This paper describes performed trade-offs based on simulation results and describes the baseline design in detail. Reliable solutions are envisaged for the conceptual design of the filter and calibration wheel. Four different varian…
Laser Ultrasonics Inspection for Defect Evaluation on Train Wheel
2019
Abstract Passengers’ safety and in-service life of wheelset axles play an important role in railway vehicles. For this reason, periodic inspections are necessary. Among non-destructive techniques, ultrasonic ones are widely applied in this field. The main disadvantage of conventional ultrasonic techniques is that the overall inspection of wheels requires the train to be put out-of-service and disassembly each part, which is time-consuming and expensive. In this paper, a non-conventional non-contact laser ultrasonic inspection for train wheels is proposed. The proposed method uses a laser interferometer to receive the ultrasonic wave without contact. The receiving system allows choosing the …
An anomalous wave formation at the Al/Cu interface during magnetic pulse welding
2020
This paper reports an anomalous wave formation at an Al/Cu bimetallic interface produced by magnetic pulse welding. The mechanism of the anomalous wave formation is investigated using both metallurgical characterization and the interface kinematics. It reveals that the anomalous wave is formed with the combination of the intermediate zone and the interdiffusion zone with a thickness of 70 nm, wherein the intermediate zone is caused by the local melting due to the high shear instability, and the interdiffusion zone is formed below the melting point of aluminum combined with ultrahigh heating and cooling rates of about 10^13 °C s^−1. A multiphysics simulation of impact welding has been perfor…
Variable-charge method applied to study coupled grain boundary migration in the presence of oxygen
2009
International audience; One of the important differences between simulation and experiments in grain boundary (GB)-dominated metallic structures is the lack of impurities such as oxygen in computational samples. A modified variable-charge method [Elsener A, Politano O, Derlet PM, Van Swygenhoven H. Modell Simul Mater Sci Eng 2008;16:025006] based on the Streitz and Mintmire approach [Streitz FH, Mintmire JW. Phys Rev B 1994;50:11996] is used to study coupled GB motion in an Al bicrystal with a [1 1 2] symmetrical tilt GB in the presence of substitutional O, and compared with the stick–slip process identified by Cahn and Mishin [Cahn JW, Mishin Y, Suzuki A. Acta Mater 2006;54:4953]. It is found…
Ring opening polymerization of d,l-lactide and ε-caprolactone catalysed by (pyrazol-1-yl)copper(ii) carboxylate complexes
2021
1,2-Bis{(3,5-dimethylpyrazol-1-yl)methyl}benzene (L) reacts with [Cu(OAc)2] and C6H5COOH, 4-OH-C6H4COOH, 2-Cl-C6H4COOH and (3,5-NO2)2-C6H3COOH to afford the copper complexes [Cu2(C6H5COO)4(L)2] (1), [Cu2(4-OH-C6H4COO)4(L)2] (2), [Cu2(2-Cl-C6H4COO)4(L)2]n (3) and [Cu{(3,5-NO2)2-C6H3COO}2L]n (4) which are characterised by IR, mass spectrometry, elemental analyses, and X-ray crystallography. The structural data revealed two geometries that are adopted by the complexes: (i) paddle wheel in 1, 2·7H2O, 3 and (ii) regular chains in 3 and 4. Magnetic studies show strong antiferromagnetic couplings in the paddle wheel complexes and a weak antiferromagnetic coupling in the monometallic chain one. Cat…
Supramolecular Assembly of Organophosphonate Diesters Using Paddle-Wheel Complexes: First Examples in Porphyrin Series
2014
The reactions of dicopper tetrapivalate complex Cu2(μ-OOC-t-Bu)4(NCMe)2 (1) with triphenylphosphine oxide and diethyl phosphite allow paddle-wheel (PW) copper(II) complexes with phosphorus-containing axial ligands (2, 3) to be obtained. When meso-bis(diethoxyphosphoryl)porphyrins 4M were employed in this ligand exchange reaction, a series of one-dimensional (1D) homo- and heterometallic coordination polymers 5M composed of PW subunits and organophosphonate diesters were prepared and characterized by means of single crystal X-ray analysis. Planar porphyrinate 4Pd and nonplanar metalloporphyrinates 4Cu and 4Ni proved to be appropriate molecular structural blocks for assembly of coordination p…
Short-Term Vegetation Recovery after a Grassland Fire in Lithuania: The Effects of Fire Severity, Slope Position and Aspect
2016
In Lithuania, fire is frequently used by farmers as a tool to remove dry grass, improve soil nutrient status and help soil tilling. However, little is known about the ecological impacts of these fires, including vegetation recovery. The objective of this work is to study the impacts of a spring grassland fire on vegetation recuperation on an east-facing (A) and a west-facing slope (B), considering fire severity and slope position, 10, 17, 31 and 46 days after the fire. Because of their effects on fire behaviour, aspect, steepness and heterogeneity of topography favoured higher fire severity on slope B than on slope A. Three different slope positions were identified on slope A – flat top, mi…
Understanding the Origins of Problem Geomagnetic Storms Associated with "Stealth" Coronal Mass Ejections.
2021
Geomagnetic storms are an important aspect of space weather and can result in significant impacts on space- and ground-based assets. The majority of strong storms are associated with the passage of interplanetary coronal mass ejections (ICMEs) in the near-Earth environment. In many cases, these ICMEs can be traced back unambiguously to a specific coronal mass ejection (CME) and solar activity on the frontside of the Sun. Hence, predicting the arrival of ICMEs at Earth from routine observations of CMEs and solar activity currently makes a major contribution to the forecasting of geomagnetic storms. However, it is clear that some ICMEs, which may also cause enhanced geomagnetic activity, cann…
Analysis of drought and vulnerability in the North Darfur region of Sudan
2018
North Darfur of Sudan is located on the edge of the Sahara Desert and endures frequent droughts due to water shortages and high summer temperatures. Monitoring and understanding drought characteristics are essential for integrated drought risk mitigation and prevetion of land degradation. This study evaluates drought conditions in North Darfur by analyzing the spatiotemporal distribution of drought using three drought indices (Standardized Precipitation Index, Vegetation Condition Index, and Soil Moisture Content Index) and their combined drought index (CDI) from 2004 to 2013. Biophysical and socioeconomic indicators are further used to measure vulnerability to drought risk and its three co…
Using hydrological connectivity to detect transitions and degradation thresholds: Applications to dryland systems
2020
In arid and semi-arid ecosystems, shortage of water can trigger changes in landscapes’ structures and function leading to degradation and desertification. Hydrological connectivity is a useful framework for understanding water redistribution and scaling issues associated with runoff and sediment production, since human and/or natural disturbances alter surface water availability and pathways increasing/decreasing connectivity. In this paper, we illustrate the use of the connectivity framework for several examples of dryland systems that are analysed at a variety of spatial and temporal scales. In doing so, we draw particular attention to the analysis of coevolution of system structures and …