On the friction coefficient of straight-chain aggregates

A methodology to calculate the friction coefficient of an aggregate in the continuum regime is proposed. The friction coefficient and the monomer shielding factors, aggregate-average or individual, are related to the molecule-aggregate collision rate that is obtained from the molecular diffusion equation with an absorbing boundary condition on the aggregate surface. Calculated friction coefficients of straight chains are in very good agreement with previous results, suggesting that the friction coefficients may be accurately calculated from the product of the collision rate and an average momentum transfer,the latter being independent of aggregate morphology. Langevin-dynamics simulations show that the diffusive motion of straight-chain aggregates may be described either by a monomer-dependent or an aggregate-average random force, if the shielding factors are appropriately chosen.Comment: 22 pages, 6 figures, revised version. To appear in the Journal of Colloid and Interface Scienc

Performance Assessment of UVAPS: Influence of Fungal Spore Age and Air Exposure

This work focused on two main outcomes. The first was the assessment of the response of the Ultraviolet Aerodynamic Particle Sizer Spectrometer (UVAPS) for two different fungal spore species. The UVAPS response was investigated as a function of fungal age and the frequency of air current that their colonies exposure to. This outcome was achieved through the measurement of fungal spore fluorescent percentage and fluorescent intensity throughout a period of culturing time (three weeks), and the study of their fluorescent percentage as a function of exposure to air currents. The second objective was to investigate the change of fungal spore size during this period, which may be of use as a co-factor in this differentiation. Fungal spores were released by blowing the surface of the culture colonies with continuous filtered flow air. The UVAPS was used to detect and measure auto-fluorescing biomolecules such as riboflavin and nicotinamide adenine dinucleotide phosphate (NAD(P)H) present in the released fungal spores. The study demonstrated an increase in aerodynamic diameter for fungal spores under investigation (Aspergillus niger and Penicillium species) over a period of time. The fluorescent percentage of spores was found to decrease for both fungal genera as they aged. It was also found that the fluorescent percentage for tested fungi decreased with frequency of air exposure. The results showed that, while the UVAPS could discriminate between Aspergillus and Penicillium species under well-controlled laboratory conditions, it is unlikely to be able to do so in the field

Feminism on the Far-Right? How Female PVV Voters make sense of Gender Equality

The PVV’s (Party for Freedom) verzetsspray action is a perfect example of right-wing populist parties (RPPs) taking a progressive stance on gender to further their anti-immigration agenda. This paper looks at the mostly overlooked group of women who vote for the PVV and asks how they think about gender and gender equality. First looking at the literature on the rhetoric from RPPs in The Netherlands, the PVV and the LPF, three discourses are discerned: the culturalisation of gender and gender equality, the normalisation and naturalisation of gender and gender equality in the Netherlands, and individualisation of gender and gender equality. To understand how women who vote for RPPs understand gender, 10 interviews with women who support either the PVV or Leefbaar Rotterdam were conducted. The results show that the participants also participate in the culturalization of gender and gender equality, normalisation and naturalisation of gender and gender equality, and individualisation of gender and gender equality discourses. From the analysis a fourth discourse emerges, focused around responsibility, or responsibilisation of gender and gender equality

Evaluation of existing control measures in reducing health and safety risks of engineered nanomaterials

While the risk management of engineered nanomaterials (ENMs) receives significant attention, there is still a limited understanding of how to select optimal risk management measures (RMMs) for controlling and mitigating the risks associated with exposure to ENMs. Clearly, there exists a need to expand current risk management practices to ensure safe production, handling and use of ENMs. Moreover, the performance of the existing RMMs should be re-evaluated for ENMs since control options that are proven to be effective for preventing or limiting risks associated with traditional particles might give unsatisfactory results in the case of nano-scale particles. This paper has brought together the evidence on the adequacy of traditional controls to minimize potential health and environmental risks resulting from exposure to ENMs. The aim here is to advance our understanding of the risk management approaches relevant for ENMs, and ultimately to support the selection of the most suitable RMMs when handling ENMs. To that end, evaluative evidence collected from the review of relevant literature and survey of nanotechnology institutions are combined and summarised to understand the level of protection offered by each control measure, as well as the relative costs of their implementation. The findings suggest that most relevant risk control options are based on isolating people from hazard through engineering measures (e.g. ventilation and chemical fume hoods) or personal protective equipment (PPE), rather than eliminating hazard at source (e.g. substitution). Although control measures related to the modification of ENMs have high efficiency in the occupational risk control hierarchy, they are not widely employed since there is currently a high degree of uncertainty regarding the impact of manipulating nano-characteristics on the performance of final product. Lastly, despite its low cost, PPE is the least effective category in the occupational risk control hierarchy and should not be used on its own when significant risk reduction is required. Clearly, further quantitative data is needed to fully assess the feasibility and cost-effectiveness of risk control options to prevent risks from exposure to ENMs. When there is little information on the efficiency of control measures specific to ENMs, the default efficiencies can be used for initial assessment purposes although it should not be considered exhaustive

Study of the particle motion induced by a vortex shaker

The behaviour of a traced alumina particle lying on limestone powders with similar features has been studied in a test tube agitated by a vortex shaker aiming at studying dust emissions from powders. PEPT (Positron Emission Particle Tracking) was used for measuring the particle's position. Population densities were computed as the frequency of the particle's presence in different regions dividing the two horizontal axes and the vertical axis, respectively. The velocities of the particle were calculated by filtering out all displacements inferior to a critical distance dcrit so as not to consider spurious movements caused by experimental noise. After its validation, the methodology was applied to the standard condition of a vortex shaker experiment (ω = 1500 rpm, 2 g of powder and open test tube). While the horizontal coordinates and velocity components follow a symmetric distribution, the vertical coordinate is characterised by a large asymmetrical plateau. The heights reached by the particle (up to 24.3 mm) are small in comparison to that of the test tube (150 mm). The greatest velocities are found near the inner wall of the test tube and at the highest heights where the population densities are the lowest. The median velocity of the particle is 0.0613 m.s −1 whereas its median kinetic energy is 8.4E-12 J. The method explicated in the present study is directly applicable to any other sets of data obtained through PEPT, especially if the system is of small dimension

Infrarotspektroskopische Untersuchungen zum Mechanismus der Cytochrom-c-Oxidase

Cytochrome c oxidase is a complex biological machinery, which couples the reduction of oxygen to a vectorial transport of protons across the membrane. To achieve this, the protein takes up eight protons, four electrons, and an oxygen molecule. The electrons and four of the eight protons are used for the reduction of oxygen to produce water. The remaining four protons are pumped across the membrane. In this work, Fourier-transorm infrared spectroscopy was applied to provide insight into the structural and functional relationships of the complex catalytic cycle. To accomplish this, different strategies were applied: The results obtained with the $\textit{fully reduced}$, CO-bound cytochrome c oxidase from bovine heart showed for the first time the possibility of performing difference spectroscopy on this enzyme with a time-resolution of 5 $\mu$s in the range of 2200 to 950 cm$^{-1}$. The evaluation of the data revealed a dynamic link between the transient binding of CO to Cu$_{B}$ and the movement of an amino acid side chain (E286) approximately 12 $\mathring{A}$ away. This amino acid is part of the D-channel and thought to play an important role in guiding the protons either into the binuclear center or through the membrane. The results presented in this work suggest a mechanism in which oxygen binding is controlled via E286. The outcome of the measurements with the $\textit{two electron-reduced}$, CO-bound cytochrome c oxidase from $\textit{Rhodobacter sphaeroides}$ indicate the deprotonation of E286 during electron transfer from heme a$_{3}$ to heme a. This result contradicts the current model of the catalytic-cycle because this deprotonation suggests an uptake of just one proton rather than two through the K-channel. Redox difference spectra of wild type and mutant cytochrome c oxidase obtained with the attenuated total reflection technique pointed out the precise assignment of a band feature. This signal was clearly attributed to a conformational change of the side chain of amino acid E286. For the first time it was possible to record a difference spectrum in the IR of the oxidative part of the catalytic cycle. The F $\textit{minus}$ O spectrum showed an involvement of a tyrosine which undergoes deprotonation