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Organisationseinheit der BAM
Double-side cooled high-power diode laser bars packaged by different techniques on different types of passive heat sinks are analyzed in terms of packaging-induced strain. Reference data from standard devices being single-side cooled only and packaged by conventional soft and hard soldering are also presented. Thermal profiling across the devices complements the results. The most suitable packaging architecture and technique for double-side cooled bars is identified. Measurements of the laser emission near field and electroluminescence pattern provide direct reference to the functionality of the devices. Furthermore, a type of cross calibration of the methods used for strain analysis is made, since all techniques are applied to the same set of bars. This involves micro photoluminescence, micro Raman, and degree-of-polarization electroluminescence spectroscopy.
On the Applicability of Plasma Assisted Chemical Micropatterning to Different Polymeric Biomaterials
(2002)
A plasma process sequence has been developed to prepare chemical micropatterns on polymeric biomaterial surfaces. These patterns induce a guided localized cell layover at microscopic dimension. Two subsequent plasma steps are applied. In the first functionalization step a microwave ammonia plasma introduces amino groups to obtain areas for very good cell adhesion; the second passivation step combines pattern generation and creation of cell repelling areas. This downstream microwave hydrogen plasma process removes functional groups and changes the linkages of polymer chains at the outermost surfaces. Similar results have been obtained on different polymers including polystyrene (PS), polyhydroxyethylmethacrylate (PHEMA), polyetheretherketone (PEEK), polyethyleneterephthalate (PET) and polyethylenenaphthalate (PEN). Such a rather universal chemical structuring process could widen the availability of biomaterials with specific surface preparations.
To properly understand and assess the long-term behaviour of geosynthetic materials it is necessary to investigate the various types of possible degradation mechanims. This includes both chemical and mechanical behaviour, and sometimes even their interactions with one another. Clearly, chemical degradation of geosynthetics depends on the polymer type. For example, polyolefins are vulnerable to oxidation; polyesters are susceptible to hydrolysis; and plasticizers can leach from polyvinyl chloride. This paper describes the concept of these three types of degradation, but focuses on the oxidation of polyolefins since the majority of the geosynthetics is made from this type of polymer. The methods used to predict the lifetime of antioxidants and service life of the geosynthetic material will be illustrated. Furthermore, the influence of temperature, pressure, and ultraviolet light on the service life are also demonstrated. Finally, the current specifications targeting the longevity of different geosynthetics are presented.
Regarding mechanical degradation, the paper mainly focuses upon the creep deformation of geogrids and stress crack resistance (SCR) of polyethylene geomembranes and geopipe. The method to assess stress crack resistance is described, and the microscopic mechanisms that lead to such failure are explained. For creep evaluation, different acceleration tests are presented and their applicability with respect to the different types of polymers is illustrated. In addition, the long-term shear behaviour of geocomposites and geosynthetic clay liners is presented.
Heavy gases in large quantities are used worldwide in various industries. Past incidents, such as the liquefied gas disaster in Viareggio (2009) have shown that these materials are difficult to handle in a safe manner. According to the German Hazardous Incident Ordinance (StörfallVO 2000 - 12. BIMSchV), plant operators with extended responsibilities must produce a report in which they verify that , in the event of an unintentional gas release, the surrounding area will not be aversely affected. Essential elements of this report are calculations of both the released mass flow and the gas dispersion. Using models such as the VDI guideline 3783 (state of the art in Germany) plant operators are able to predict the characteristics of likely gas dispersions. The presented experimental investigations were carried out at the BAM better understand heavy gas dispersion with high gas concentrations in the air (≥ 1 Vol.-%), as well as concentrations with approximately neutral density characteristics (≤ 3000ppm) in order to test the accuracy of the VDI guideline. The starting point for experimental trials was the heavy gas releases resulting from pipeline, vessel or standard gas bottle leaks, with mass flows of between 20 and 100 g s-1. Investigations on the gas-phase release process focused on the unsteady mass flow associated with releases from standard gas bottles. The experimental results will be used as comparative parameters for future simulations. The goal of these simulations is to develop a model with which calculation of the unsteady mass flow, based on the material characteristics for any gas, is possible.
Heavy gases in large quantities are used worldwide in various industries. Past incidents, such as
the liquefied gas disaster in Viareggio (2009) have shown that these materials are difficult to
handle in a safe manner. According to the German Hazardous Incident Ordinance (StörfallVO
2000 - 12. BImSchV) plant operators with 'extended responsibilities' must produce a report in
which they verify that, in the event of an unintentional gas release, the surrounding area will not
be aversely affected. The essential elements of this report include calculations of both released
mass flow and gas dispersion. Using models such as the VDI guideline 3783 (state of the art in
Germany) plant operators are able to predict the characteristics of likely gas dispersions.
Within the framework of the reported experimental trials, the release process of heavy gases
from standard gas cylinders was investigated. Using the results of this investigation a calculation
methodology has been developed which is able to predict the mass flow of a gas-phase release.
As input parameters only the geometry of the gas cylinder, the material properties of the
respective fluid as well as the environmental parameters such as velocity of approach and air
temperature are required. In the course of modeling various approaches for nucleate boiling have
been tested for their applicability. Both the calculation methodology and a comparison between
the calculated and experimental results will be presented.
Within the same framework of experimental trials, the dispersion process of the aforementioned
heavy gases was also investigated. The dispersed gas cloud in this case was considered as originating from a continuous point source under ambient conditions. For the various trials
concentrations both in the heavy gas (≥ 1 vol.-%) and in the neutral gas field (≤ 3000 ppm) were
measured. In the immediate area of the release the length, width and height of the heavy gas
cloud were evaluated. The experimental results, comparison calculations and the measurement
techniques will be presented.
The present paper aims to re-examine the validity of the linear correlation found between AFTLOC, the adiabatic flame temperature at the apex of the flammability range of fuel-air-inert mixtures (where LOC, the Limiting Oxygen Concentration, is measured) and AFTLFL, the adiabatic flame temperature at the lower flammability limit of fuel-air mixtures (LFL). New sets of experimental measurements of LFL and LOC referring to fuel-air mixtures diluted with N2, CO2 and H2O(vap) from trusted literature sources form a comprehensive database for such evaluation. Both the slope and intercept of correlations AFTLOC = a + b*AFTLFL are dependent on the nature of inert gas and on initial temperature. Based on the linear correlation between AFTLOC and AFTLFL, a procedure for calculation of LOC and MIC (Minimum Inert Concentration) of fuel-air-inert mixtures is presented, using measured or calculated LFL of fuel-air mixtures and their corresponding AFT. The method predicts with reasonable accuracy LOC and MIC of fuel-air-inert mixtures (relative deviations ranging between -14 and +17% when calculated and measured LOC and MIC for fuelair-nitrogen and fuel-air-carbon dioxide at ambient initial conditions are examined).
The hazardous potential of accidental heavy gas releases, especially those involving flammable and toxic gases, is widely known. In order to predict the area in which these gases are in hazardous concentrations, an estimation of the dispersion of these gases must be carried out. While the hazardous area for flammable heavy gases is determined by the lower flammability limit (ca. >1 vol%), the release of toxic heavy gases can result in a much larger hazardous area. Toxic gases, even in very low concentrations (ca. <3,000 ppm), have the potential to be highly damaging. State-of-the-art dispersion models, such as the VDI Guideline 3783, can be used to estimate the dispersion of heavy gases. However, VDI 3783 gives no method for the prediction of the height and width of a heavy gas cloud, which are both required for quantitative risk analysis as well as for a possible coupling of a Lagrangian particle model with the VDI 3783 heavy gas dispersion model. Therefore, further calculation methods were used to describe these dimensions and were evaluated against experimental studies of the length, width, and height of the heavy and neutral gas field. In addition to that the influence of the source height on the heavy gas dispersion was also examined