Concentration and distribution of heavy metals in urban airborne particulate matter in Frankfurt am Main, Germany

Heavy metal concentrations were measured in airborne dust collected at three sites with different traffic densities from August 2001 to July 2002 in the Frankfurt am Main area. Bulk samples of particulate matter (PM) with an aerodynamic equivalent diameter of <22 microm were collected on cellulose nitrate filters using air filtration devices. Fractionated samples of PM with an aerodynamic equivalent diameter of <10 microm were collected using an eight-stage Andersen impactor. Pb, Cd, Mn, Ni, Zn, V, As, Sb, Cu, Cr, Co, and Ce were determined by inductively coupled plasma sector field mass spectrometry, Pt and Rh were determined by adsorptive voltammetry, and Pd was determined by total reflection X-ray fluorescence analysis. The results show that the highest airborne heavy metal concentrations occurred at the main street with a large volume of traffic. With the exception of Co, V, Ce, and Mn, the heavy metals had an elevated enrichment factor compared to their concentrations in the continental crust. The main street site was especially contaminated with Sb, Zn, Cu, V, and Ni. Motor vehicles are the likely source of emissions. With the exception of Cr, Cu, and Zn, most of the airborne heavy metal concentrations determined for impactor samples deviate slightly from the results for total airborne dust. Heavy metal particle size distributions can be divided into three groups. For metals such as As, Cd, Pb, and V, the main fraction can be found in fine particles with a diameter of <2.1 microm, whereas Ce, Cr, Co, and Ni occur mainly in coarse particles with a diameter of >2.1 microm. Cu, Mn, Sb, Zn, Pt, Pd, and Rh occur in high concentrations in the medium range of the impactor stages (particle diameters of 1.1-4.7 microm). Metal concentrations in fine dust particles are needed to assess the human health risks of their inhalation.     

Eine Stellungnahme zum Beitrag von Sass & Treskatis: “Herstellungs- und Bemessungsgrundlagen für einen verlaufsgesteuerten Trinkwasserbrunnen ...”

Ohne Zusammenfassung Eingang des Beitrages: 14.03.2000 / Eingang des überarbeiteten Beitrages: nicht überarbeitet, nur korrigiert     

n-Type Doping of Vapor–Liquid–Solid Grown GaAs Nanowires

In this letter, n-type doping of GaAs nanowires grown by metal–organic vapor phase epitaxy in the vapor–liquid–solid growth mode on (111)B GaAs substrates is reported. A low growth temperature of 400°C is adjusted in order to exclude shell growth. The impact of doping precursors on the morphology of GaAs nanowires was investigated. Tetraethyl tin as doping precursor enables heavily n-type doped GaAs nanowires in a relatively small process window while no doping effect could be found for ditertiarybutylsilane. Electrical measurements carried out on single nanowires reveal an axially non-uniform doping profile. Within a number of wires from the same run, the donor concentrations N _D of GaAs nanowires are found to vary from 7 × 10¹⁷ cm^-3 to 2 × 10¹⁸ cm^-3. The n-type conductivity is proven by the transfer characteristics of fabricated nanowire metal–insulator-semiconductor field-effect transistor devices.     

Modelling of the borehole filling of double U-pipe heat exchangers

A new model MISOS is proposed for the simulation of the borehole filling (grout) of double U-pipe heat exchangers. When simulating ground-coupled heat pumps, a suitable model of the filling is necessary because the temperature of the filling effects the temperature of the heat carrier fluid. The filling is divided into three elements whose geometry corresponds to the different temperature zones. For each time step, the temperatures of the filling elements can be calculated from energy balances. MISOS is very fast compared to computational fluid dynamics (CFD) algorithms. CFD calculations were performed for different shank spacings, and results compared with those obtained from MISOS. If the pipe shanks are situated between the axis and the wall of the borehole, nearly the same difference of the fluid temperature between inlet and outlet is predicted by MISOS and CFD. For a minimal shank spacing, heating is overpredicted by about 6% for an extraction period of 3 h while an underprediction of about 9% is obtained for maximal shank spacing.     

Correlation between polyethylene topology and melt flow instabilities by determining in-situ pressure fluctuations and applying advanced data analysis

Using three high sensitive pressure transducers located inside a slit-die of a capillary rheometer and applying a set of advanced mathematical tools to process the acquired time dependent pressure signals, we are able to detect in-situ pressure fluctuations associated with sharkskin instabilities. Other distortions, as spurt and gross melt fracture, can also be in-situ detected. This originates from a factor of 10³ and 10² improvement in terms of time and pressure resolution achieved using the new set-up and data analysis that it will be described in detail in this article. Our approach quantifies the effect of polymer topology and shear rate on the characteristic frequency and amplitude of these pressure fluctuations inside the die. Depending on the polymer structure and the shear rate, different instabilities with large deviation in their main properties at melt-state, can be determined. Based on our results, a polymer-independent power law relationship between the characteristic frequency of the instability and the apparent shear stress has been found. Combining this new technique with the advanced mathematical analysis used, clear evidences concerning the origin and location of these instabilities, could be established. According to our analysis, the spurt instability starts in the entrance of the die and it propagates downstream while increasing its velocity along the die. This was confirmed by non-zero-time-lags in the cross-correlation function between the transducers located inside the slit-die. In case of sharkskin instability, pressure fluctuations inside the die indicate that its origin could also be already inside the die instead of being exclusively located at the die-exit region, as stated in earlier investigations.     

Das Sperrmanagement im neuen deutschen Personalausweis

Dieser Artikel beschreibt im Detail die datenschutzfreundliche Ausgestaltung des Sperrmanagements, wie es im neuen deutschen Personalausweis zum Einsatz kommt.     

Parallel FTIR-ATR and gravimetrical in-situ measurements on sodium alanate powder samples during hydrogen desorption

An experimental set-up has been developed to carry out in-situ measurements on hydrogen storage materials. It has been used to perform FTIR–ATR measurements on sodium alanate samples during hydrogen desorption and, in parallel, to perform gravimetrical measurements on the same sample. The ATR spectra showed the typical broad Al–H vibrational features, changing according to the phase change the material undergoes during the load cycle. It is shown that the absorbance of the material at these bands and the hydrogen content correspond to each other in a reproducible way. This behavior may be used to measure the hydrogen mass released by an alanate hydrogen reservoir by measuring the optical absorbance at defined wavelengths. In this paper the results of these experiments that may give rise to the realization of a level sensor in future hydrogen storage applications are presented.     

A comparative study of a vitreous biological composition suitable for coating steel prostheses

A correlation between composition and quality of a biological glass used as a bioglaze and an industrial glaze for sheet-steel coating was carried out. Apart from the extremely different conditions, particularly relative to the temperature for application of the coating to the metallic substrate, it was noted that the compositions are not very much different; this led us to think that the doping of the vitreous system with substances favouring the bonding of glaze to support (according what has been suggested by enamellists) is trustworthy in this case too. Some hypotheses relative to the role of nickel and the fluidity of the vitreous system were made to explain the observations, and to suggest the best way to improve the adhesion of metal to glaze.