HEM Impoundment—A Numerical Prediction Tool for the Water Framework Directive Assessment of Impounded River Reaches

A novel prediction tool is presented as a component of the Habitat Evaluation Model (HEM), which allows the assessment of the ecological status of impounded water bodies based on environmental factors that were shown in literature to correlate with the abundance of benthic macro-invertebrates. Main model parameters are the observed grain sizes and depth-averaged flow velocities obtained from a hydrodynamic simulation. The tool was tested in three Austrian river reaches. It was found that the river lengths predicted to be ecologically affected by the impoundments were substantially shorter for mean flow conditions than previously assessed when employing a physical mapping approach. The differences disappeared for low discharge conditions. The numerical prediction tool allows us to perform a status assessment for discharge conditions, which are potentially more representative of the annual discharge spectrum than those within the in-situ observable range. This property, thus, bears the potential to facilitate the recommendation of sediment management strategies in impounded river reaches in the future.

Fretting Wear and Microstructure of Plasma Carburized TiAl Alloy

A carburized layer is fabricated in the surface of TiAl alloy using plasma carburization at 975 °C. Fretting wear test at ambient temperature was carried out to evaluate wear resistance of carburized TiAl. Glow discharge spectrum, X-ray diffraction and scanning electron microscopy equipped with energy dispersive spectrometry were used to characterize the microstructure of carburized TiAl and its property capability. The experimental results show that the carburized layer with about 5 μm in thickness is mainly composed of Ti2AlC and possesses better fretting wear resistances at ambient temperature. Precipitation of carbides in surface layer leads to a higher surface hardness and compressive stress, causing a surface strengthening of TiAl. Strengthening mechanism of carburized TiAl is also considered in this investigation.

Influence of Temperature on Characteristics of TiAl Plasma Surface Niobiumizing

In this study, plasma niobium alloying of the TiAl based alloys has been carried out at 1050, 1100 and 1150°C. The effect of the alloying temperature on the characteristic of the alloyed layer was investigated by optical microscopy, scanning electronic microscopy (SEM), glow discharge spectrum (GDS) and energy dispersive spectrum (EDS). The results show that the surface roughness, chemical composition and thickness of the alloyed layer increased with the alloying temperature which is dependent on the sheath potential. A deposition layer formed on the TiAl surface at 1150 °C was resulted from the larger sheath potential or the stronger sputtering of source electrode.

CrN Coating on Magnesium Alloy AZ91 by Arc-Glow Plasma Depositing Process

Magnesium alloys exhibit great application potential in industries such as automotive, electronics, aerospace and others. But poor wear resistance and corrosion resistance have restricted their actual uses. In this study, a CrN film had been prepared on magnesium alloy AZ91 by arc-glow plasma depositing. The composition and microstructure of the coating had been analyzed by X-ray diffraction (XRD) and glow discharge spectrum (GDS). The morphology of CrN film has been surveyed through scanning electronic microscopy (SEM) and atom force microscopy (AFM). The wear behavior was investigated through ball-on-disc test. The corrosion behavior in 5 wt% NaCl solution was also studied. The results indicate that the specific wear ratio decreases greatly and the corrosion potential also increases relatively comparing to AZ91 matrix.

High-resolution spectroscopy with a CCD array detector: application to the 2880 Å emission band system in I2

The 2880 Å system in the Tesla discharge spectrum of I2 in Ar is reexamined using a CCD array detector to record spectra for both 127I2 and 129I2. This charge-transfer transition terminates on a weakly bound valence state, giving a highly congested spectrum with fine violet-degraded band structure barely perceivable on a pseudocontinuous background. The superior signal-to-noise capabilities of the array detector permit a great improvement in the precision and number of measured bandheads, as compared with previous results obtained from photographically recorded spectra. The new data span a larger range of vibrational levels in the lower state and lead to a change in the previous ν″ numbering by −3 units. Both states can now be located precisely on the absolute energy axis through least-squares fits in which the lower state energy is represented as a near-dissociation expansion. The primary spectroscopic constants (cm−1) are [Formula: see text] [Formula: see text] [Formula: see text] [Formula: see text] [Formula: see text] [Formula: see text] The lower state has a dissociation energy of 287.5 cm−1 and supports 35 bound levels, subject, however, to possible further revision due to a remaining uncertainty of 1 unit in the ν″ numbering. The previous tentative electronic assignment of this system remains in effect: The upper state is likely the [Formula: see text] state that correlates with I−(1S) + I+(3P1), while the lower state is the [Formula: see text] component of the lowest valence 3Πu multiplet.