Prediction of the thermal radiative properties of an x-ray mu-tomographied porous silica glass

A Monte Carlo ray tracing procedure is proposed to simulate thermal optical processes in heterogeneous materials. It operates within a detailed 3D image of the material, and it can therefore be used to investigate the relationship between the microstructure, the constituent optical properties, and the macroscopic radiative behavior. The program is applied to porous silica glass. A sample was first characterized by 3D x-ray tomography; then, its normal spectral emittance was calculated and compared with the experimental spectrum measured independently by high-temperature infrared emittance spectroscopy. We conclude with a discussion of the light-scattering mechanisms occurring in the sample.     

Analytical methodology for TEX86 paleothermometry by high-performance liquid chromatography/atmospheric pressure chemical ionization-mass spectrometry

The TEX86 is a recently proposed paleothermometer through which ancient seawater temperatures of up to 120 My ago can be reconstructed. It is based on the relative distribution of glycerol dibiphytanyl glycerol tetraethers as measured by high-performance liquid chromatography/atmospheric pressure chemical ionization-mass spectrometry (HPLC/APCI-MS). The aim of this study was to examine and improve several analytical aspects in the determination of this important proxy in environmental matrices. Comparison of TEX86 analysis using single ion mode (SIM) and mass scanning (m/z 950 to 1450) detection, respectively, revealed that SIM is up to 2 orders of magnitude more sensitive and that the TEX86 can be determined with a reproducibility of +/-0.004 or +/-0.3 degrees C using this method. Comparison of TEX86 values obtained with two different HPLC/APCI-MS set-ups revealed no significant differences. In addition, analysis of TEX86 of extracts obtained by Soxhlet, ultrasonic, and accelerated high-pressure extraction techniques also showed no significant differences between the methods. Our results suggest that TEX86 analysis by HPLC/APCI-MS is robust and can be determined with analytical errors comparable to those of other temperature proxies.     

Dispersion state and humic acids concentration-dependent sorption of pyrene to carbon nanotubes

Sonication and humic acids (HA) are known to disperse carbon nanotube (CNT) suspensions, but potential effects on sorption of chemicals to CNTs remain poorly understood. We applied a passive sampling method to investigate the influence of dispersion/aggregation on sorption of pyrene to CNTs. Sonication broke down CNT aggregates and increased pyrene sorption affinity by up to 1.39 orders of magnitude. Sorption surfaces newly exposed by sonication remained available to pyrene even after reaggregation occurred, suggesting an irreversible effect of sonication. The presence of HA decreased sorption of pyrene to CNTs, but at the highest HA concentration investigated (200 mg/L), sorption affinity was still 1.90 orders of magnitude larger than sorption of pyrene to HA alone. Specific interactions between pyrene and CNTs were thus still taking place, in spite of the presence of a HA coating on the CNTs' surface. A greater suppression of sorption by CNTs occurred when the HA addition was combined with a sonication pretreatment. Sorption isotherm fitting indicated that the maximum sorption capacity, sorption affinity, and heterogeneity of the CNT surface were all affected by sonication and the presence of HA at a concentration as low as 1 mg/L. The present results contribute to an improved understanding of the sorption behavior of CNTs in both natural and wastewater systems.     

Effect-directed assessment of the bioaccumulation potential and chemical nature of Ah receptor agonists in crude and refined oils

Recent studies have indicated that in addition to narcosis certain chemicals in crude oils and refined petroleum products may induce specific modes of action, such as aryl hydrocarbon receptor (AhR) agonism. The risks these toxic compounds pose to organisms depend on internal exposure levels, as driven by the chemicals' bioaccumulation potential. Information on this potential however is lacking, as the chemicals' identity mostly is unknown. This study showed that AhR agonists bioaccumulate from oil-spiked sediments into aquatic worms and persist in the worms for at least several weeks. Chemical fractionations of eight pure oils into saturates, aromatics, resins, and asphaltenes (SARA), followed by effect-directed analyses using in vitro reporter gene assays revealed that the agonists predominantly are aromatic and resin-like chemicals. Some of the compounds were easily metabolized in vitro, while others were resistant to biotransformation. HPLC-assisted hydrophobicity profiling subsequently indicated that the AhR-active chemicals had a high to extremely high bioaccumulation potential, considering their estimated logK(ow) values of 4 to >10. Most of the AhR agonism, however, was assigned to compounds with logK(ow) of 5-8. These compounds were present mainly in the mid to high boiling point fractions of the oils (C(14)-C(32) alkane range), which are usually not being considered (the most) toxic in current risk assessment. The fractionations further revealed considerable oil and fraction-dependent antagonism in pure oils and SARA fractions. The results of this study clearly demonstrate that crude oils and refined petroleum products contain numerous compounds that can activate the AhR and which because of their likely persistence and extremely high bioaccumulation potential could be potential PBT (persistent, bioaccumulative and toxic) or vPvB (very persistent and very bioaccumulative) substance candidates. Many chemicals were identified by GC-MS, but the responsible individual compounds could not be exactly identified in the complex mixtures of thousands of compounds. Because this obstructs a classical PBT risk assessment, our results advocate an adapted risk assessment approach for complex mixtures in which low concentrations of very potent compounds are responsible for mixture effects.     

Multigeneration exposure of the springtail Folsomia candida to phenanthrone: from dose-response relationships to threshold concentrations

Results of life-cycle toxicity experiments are supposed to be indicative for long-term effects of exposure to toxicants. Several studies, however, have shown that adaptation or extinction of populations exposed for several generations may occur. The aim of this study was therefore to determine if the effects of the PAH phenanthrene on survival and reproduction of the springtail Folsomia candida exposed for 10 consecutive generations to contaminated soil would progressively increase, or, alternatively, if adaptation of the test organisms to the toxicant would occur. LC50 values for the first four generations were similar (171-215 micromol/kg dry soil), as expected for a narcotic compound. In the fourth generation, springtails exposed to a concentration similarto the EC50 for one generation (163 micromol/kg dry soil) showed internal phenanthrene concentrations in the range known to cause mortality; no reproduction took place, and the population went extinct. From the fifth generation onwards, survival and reproduction were not affected by the remaining exposure concentrations. Apparently, up to a certain threshold concentration (above 77 and below 163 micromol/kg dry soil), the springtails were able to metabolize phenanthrene, as shown by the lack of adverse effects and the lack of adaptation. During multigeneration exposure, the graded concentration-response relationship changed into an all-or-nothing response with a defined threshold concentration.Together with the worsening of effects, this raises concerns about the use of single-generation studies to tackle long-term population effects of environmental toxicants.     

3D-Quantification of the distribution of continuous fibres in unidirectionally reinforced composites

Synchrotron microtomography is carried out for continuous C-fibre reinforced aluminium and a continuous C-reinforced polymer. The local volume fraction as well as the orientation distribution of the reinforcement are analysed three dimensionally for both composites using self-developed calculation methods. Representative elements for the analysis of the local volume fraction are determined by using two-point probability functions. The results show that regions with smaller volume fractions tend to form channels along the fibre bundles for both composites. Channels of high volume fractions, representing touching fibres (local volume fraction >55 vol%), are identified for the polymer matrix composite. The regions with high volume fraction >50 vol% tend to form clusters in the case of the metal matrix composite. The orientation of the reinforcement is followed throughout the volume of both composites. The results show preferential orientations within each bundle of the fibre reinforced metal. The orientation of the reinforcement is more homogeneous in the fibre reinforced polymer and the largest misorientations are found within the channels separating fibre bundles. The characterisation methods developed in this work can be used to evaluate quality criteria adopted in the stage of development of the composites.     

Reliable and Efficient Pattern Matching Using an Affine Invariant Metric

We present a new pattern similarity measure that behaves well under affine transformations. Our similarity measure is useful for pattern matching since it is defined on patterns with multiple components, satisfies the metric properties, is invariant under affine transformations, and is robust with respect to perturbation and occlusion. We give an algorithm, based on hierarchical subdivision of transformation space, which minimises our measure under the group of affine transformations, given two patterns. In addition, we present results obtained using an implementation of this algorithm.     

Geometric Spanners for Weighted Point Sets

Let (S,d) be a finite metric space, where each element p∈S has a non-negative weight w (p). We study spanners for the set S with respect to the following weighted distance function:

On the implementation of computed laminography using synchrotron radiation

Hard x rays from a synchrotron source are used in this implementation of computed laminography for three-dimensional (3D) imaging of flat, laterally extended objects. Due to outstanding properties of synchrotron light, high spatial resolution down to the micrometer scale can be attained, even for specimens having lateral dimensions of several decimeters. Operating either with a monochromatic or with a white synchrotron beam, the method can be optimized to attain high sensitivity or considerable inspection throughput in synchrotron user and small-batch industrial experiments. The article describes the details of experimental setups, alignment procedures, and the underlying reconstruction principles. Imaging of interconnections in flip-chip and wire-bonded devices illustrates the peculiarities of the method compared to its alternatives and demonstrates the wide application potential for the 3D inspection and quality assessment in microsystem technology.     

Are Fischer–Tropsch waxes good feedstocks for fluid catalytic cracking units?

The potential of a highly paraffinic Fischer–Tropsch synthesis (FTS) wax as a feedstock for Fluid Catalytic Cracking (FCC) has been evaluated. A once-through microriser reactor was used to mimic realistic FCC conditions. FTS waxes are indeed attractive feedstocks for FCC. As a result of its high paraffinicity an interesting spectrum of products can be obtained by tuning process conditions and catalyst formulations. A high gasoline fraction (70 wt%) with an apparent high-quality motor octane number can be obtained. Also a relatively good diesel is expected. Due to the absence of sulfur and nitrogen in the feed extremely clean transportation fuels can be obtained that are additionally low on aromatics. The combination of an equilibrium catalyst with a steam-deactivated ZSM-5 additive yields high amounts of propene (16 wt%), isobutene (7 wt%) and n-C₄-olefins (8 wt%).