Effects of scandium on rapid solidified hypo-eutectic aluminium copper

ABSTRACT

This paper reports on the characterisation of rapidly solidified Al-4.5?wt% Cu-xSc (x?=?0.1, 0.2 or 0.4?wt %). The effect of micro-additions of Sc (up to 0.4?wt %) was examined through microstructural analysis of rapidly solidified, as well as aged samples, by means of electron microscopy, x-ray and neutron diffraction and microhardness measurements. The effect of micro-additions of Sc on the scale of the rapid solidified microstructure was negligible. The Sc additions were supersaturated mainly in the interdendritic regions. However, upon aging of the samples, directly after rapid solidification, nano-precipitates rich in Sc were observed in the matrix and some Sc was also associated with the θ phase. No W-phase was observed in either as atomised or aged samples. Furthermore, dramatic improvements in mechanical properties (specifically hardness) were achieved. This work highlights the use of various and complementary tools to characterise the effect of micro-additions of Sc to hypoeutectic Al-Cu alloys over a wide range of solidification thermal histories. It also demonstrates the capability of designing alloys and process strategies with unique microstructures and mechanical properties superior to age hardened Al-4.5?wt% Cu alloys.     

An Introduction to the RARC '83 Plan for DBS Systems in the Western Hemisphere

The 1983 Regional Administrative Radio Conference (RARC '83), sponsored by the International Telecommunication Union (ITU), adopted a plan that assigns to each country in ITU Region 2 (the western hemisphere) the frequencies and orbital positions it can use for direct broadcasting satellite (DBS) systems in the 12.2-12.7 GHz band. An earlier ITU conference, the 1977 World Administrative Radio Conference (WARC '77), had already made such a plan for countries of ITU Region 1 (Africa, Europe, the Soviet Union, and Mongolia) and Region 3 (the rest of Asia, Australia, and the southwest Pacific) in the 11.7-12.5 and 11.7-12.2 GHz bands, respectively. In addition to orbital positions and frequencies, both plans specify the satellite polarization, coverage, and maximum radiated power to be used by each country. This paper describes the RARC '83 Plan and compares some of its features to those of the WARC '77 Plan. The reference system parameters used for planning at RARC '83 and WARC '77 are summarized and discussed briefly. The RARC '83 Plan itself is described in terms of the satellite coverage areas; the channelization of the band; and the specific orbital position, frequency, and polarization assignments provided. Further details about the assignments in the plan and an assessment of their impact on the development of DBS systems in Region 2 are also included.     

Carbamoyl phosphate synthetase: a crooked path from substrates to products

The formation of carbamoyl phosphate is catalyzed by a single enzyme using glutamine, bicarbonate and two molecules of ATP via a reaction mechanism that requires a minimum of four consecutive reactions and three unstable intermediates. The recently determined X-ray crystal structure of carbamoyl phosphate synthetase has revealed the location of three separate active sites connected by two molecular tunnels that run through the interior of the protein. It has been demonstrated that the amidotransferase domain within the small subunit of the enzyme from Escherichia coli hydrolyzes glutamine to ammonia via a thioester intermediate with Cys269. The ammonia migrates through the interior of the protein, where it reacts with carboxy phosphate to produce the carbamate intermediate. The carboxy phosphate intermediate is formed by the phosphorylation of bicarbonate by ATP at a site contained within the amino-terminal half of the large subunit. The carbamate intermediate is transported through the interior of the protein to a second site within the carboxy-terminal half of the large subunit, where it is phosphorylated by another ATP to yield the final product, carbamoyl phosphate. The entire journey from substrate to product covers a distance of nearly 100 A.     

Horizontal Eye Movements from Abducens Nerve Stimulation in the Cat

Pulse trains with sinusoidally modulated pulse frequencies (50 to 150 pps) were used to stimulate the abducens nerve of the anesthetized cat. Eye movements, the measured output of the system, were observed to follow the sinusoidal modulating waveform over the modulation frequency range of 0.5 to 25 Hz. The gain and phase characteristics of such eye movements indicated the presence of a first-order system at the end of the oculomotor pathway. A delay between stimulation and eye movement of approximately 12 ms was indicated by the frequency response as well as by the step response of the system.     

Beitrag zur Schwefellöslichkeit in CaO-Al2O3-Schlacken

Untersuchung der Schwefelaufnahme von CaO-Al₂O₃-Schlacken mit 44 bis 68% Tonerde durch Emulgieren in schwefelhaltigen Eisenschmelzen im 1-kg-Vakuuminduktionsofen. Kontinuierliche Messung der Sauerstoffaktivität der Eisenschmelze mit ThO₂-Elektrolyten. Ermittlung der Sauerstoffabhängigkeit der Schwefellöslichkeit sowie der Sulfidkapazität der Schlacken bei Sauerstoffaktivitäten zwischen 0,0002 und 0,0035. Vergleich der Sauerstoffaktivitäten in Abhängigkeit vom Aluminiumgehalt der Eisenschmelze sowie mit und ohne Einwirkung der CaO-Al₂O₃-Schlacken.     

3 Laser transmission joining in microtechnology

The laser is a joining tool which is particularly suitable for the application in microtechnology. The process variant laser transmission joining can be used both for welding thermoplastics and bonding of silicon and glass. The investigations presented in this paper cover detailed examinations of both processes. Concerning laser transmission welding of plastics it is examined how far the content of carbon black in the material influences the formation of the weld seam. It is shown that the optical depth of penetration, the weld seam width as well as the formation of the weld morphology differ with varying content of carbon black. Selective laser radiation bonding (SLB) is a novel method for joining silicon and glass based on the transmission heating of the interface of both joining partners and the thermo-chemical principles of silicon direct bonding. SLB shows advantages in reference to the thermal load of sensitive components like sensors and to the selectivity of the joining geometry. In this study the principle method of SLB and the latest advances like the integration of the thermal process control in the laser processing head will be presented. Also experimental test results of the process with constant laser power and thermal process control and the comparison of them will be shown.An erratum to this article can be found at     

The Role of Vitamin D in Diabetic Nephropathy: A Translational Approach

According to several animal and human studies, vitamin D appears to play a significant role in the development of diabetic nephropathy. However, the possible renoprotective effect of vitamin D and its influence on the reversal of already existing renal damage remains doubtful. At this moment, there are a few hypotheses concerning the underlying molecular and genetic mechanisms including the link between vitamin D and inflammation, oxidative stress, and extracellular matrix accumulation. The present review aims to investigate the potential role of vitamin D in the development of diabetic kidney disease from a translational approach.     

Robot-based automation system for the flexible preforming of single-layer cut-outs in composite industry

Due to the outstanding material properties the use of carbon fiber reinforced plastics in aerospace applications has grown rapidly during the last years. However, the manual process of creating a preform out of dry cut-outs is still very time-consuming and error-prone and thus limits an efficient use of this technology. Especially the high diversity of variants, the material properties and the complexity of the process limited an automation of the preforming process so far. In this paper an automation system is presented, which consists of a robot-based preforming end-effector and its offline path-planning. The end-effector has a highly modular and flexible design and integrates the three essential functions of the preforming process: gripping, draping and heating. Based on a detailed analysis of the geometric parameters of the preforms and its layers the task-specific layout of the end-effector is conducted. To achieve a preform in high-quality a solution for controlling the end-effector and planning the robot-path is necessary. Hence, a semi-automatic approach is developed, which incorporates the know-how of experts and automatically generates layup-curves with path-synchronous trigger signals for the end-effector. In an experimental set up the feasibility and flexibility of the automation solution could be successfully tested. The evaluation on three industrial moulds showed that the challenging requirements and the high quality standards could be met.     

Nanocrystalline TiC reinforced Ti matrix bulk-form nanocomposites by Selective Laser Melting (SLM): Densification, growth mechanism and wear behavior

Selective Laser Melting (SLM) Additive Manufacturing (AM) process was used to produce nanocrystalline TiC reinforced Ti matrix bulk-form nanocomposites. The influence of “volumetric energy density” (ε) on densification activity, microstructural feature, nanohardness, and wear behavior of SLM-processed parts was studied. The densification levels of TiC/Ti parts remained above 97% as ε ? 120 J/mm³. A further decrease in ε lowered the densification rate, due to the occurrence of balling effect. The TiC reinforcement experienced an interesting morphological change from the coarsened dendritic TiC (360 J/mm³) to the accumulated whisker-structured TiC (180 J/mm³) and to the uniformly dispersed nanoscale lamellar TiC (?120 J/mm³). As ε of 120 J/mm³ was properly settled, the dynamic nanohardness (90.9 GPa) and elastic modulus (256 GPa) of SLM-processed TiC/Ti nanocomposites showed respectively ∼22.7-fold and ∼2.4-fold increase upon that of the unreinforced Ti. A uniform distribution of friction coefficient with a low average value <0.2 was obtained, leading to a considerably reduced wear rate of 1.8 × 10⁻⁷ mm³/(Nm). A disappearance of nanostructured TiC reinforcement at an elevated ε of 360 J/mm³ lowered the mechanical properties of TiC/Ti part consisting of the coarsened dendritic TiC.     

The impact of sociodemographic, environmental, and behavioral factors, and cerebrovascular risk factors as potential predictors of the mattis dementia rating scale

BACKGROUND: Age and education have been found to affect the Mattis Dementia Rating Scale (MDRS) score of elderly normals, but there have been no studies assessing the influence of environmental and behavioral factors on this scale. Their role as potential predictors of the MDRS total score was investigated. METHODS: The MDRS was administered to 1,927 normal elderly subjects in the setting of a stroke prevention study. Results were correlated with 16 sociodemographic, environmental, and behavioral factors, and cerebrovascular risk factors. Study statistics resulted from multiple logistic regression analysis. RESULTS: Results indicated that higher age and arterial hypertension were associated with poorer cognitive performance, while better education and moderate general life stress exerted a positive effect on the participants' test results. CONCLUSIONS: Thus, besides the well-established factors of age and educational level, moderate general life stress and hypertension were identified as relevant predictors in determining the MDRS test performance of elderly normals.