Possible applications of a highly ductile sprayed concrete as a measure for ground support and structural upgrade

The possible impacts to our underground infrastructure that might occur during its operational phase are subsequently correlating with the types of goods we are transporting as well as the overall threats to our society. With that in mind, explosions and huge fires, resulting from terroristic attacks or huge accidents, have become valid threats to our tunnels and underground hubs, especially in countries like Great Britain, the United States or Germany. Unfortunately, there are only a limited amount of measures and technical systems available for the systematic upgrade of such underground facilities, especially when talking about combined scenarios (explosion plus fire). The problem is, that most of these protective systems are based on ultra-high performance concrete approaches with a huge amount of reinforcement and additional additives for increasing the explosion and fire resistance of the concrete. For reasons of manufacturing and fabricating such protective layers and shells, these systems can often only be applied to plane structures with simple geometries and clearly defined boundaries. This is not necessarily a typical description of an underground structure, where arches and curved planes are more or less common. Therefore, a highly ductile sprayed concrete, with high fibre or steel content, could help closing this gap, at least in theory. Please click Additional Files below to see the full abstract

Stochastic binding of Staphylococcus aureus to hydrophobic surfaces

The adhesion of pathogenic bacteria to surfaces is of immense importance for health care applications. Via a combined experimental and computational approach, we studied the initiation of contact in the adhesion process of the pathogenic bacterium Staphylococcus aureus. AFM force spectroscopy with single cell bacterial probes paired with Monte Carlo simulations enabled an unprecedented molecular investigation of the contact formation. Our results reveal that bacteria attach to a surface over distances far beyond the range of classical surface forces via stochastic binding of thermally fluctuating cell wall proteins. Thereby, the bacteria are pulled into close contact with the surface as consecutive proteins of different stiffnesses attach. This mechanism greatly enhances the attachment capability of S. aureus. It, however, can be manipulated by enzymatically/chemically modifying the cell wall proteins to block their consecutive binding. Our study furthermore reveals that fluctuations in protein density and structure are much more relevant than the exact form of the binding potential

Different binding mechanisms of Staphylococcus aureus to hydrophobic and hydrophilic surfaces

Bacterial adhesion to surfaces is a crucial step in initial biofilm formation. In a combined experimental and computational approach, we studied the adhesion of the pathogenic bacterium Staphylococcus aureus to hydrophilic and hydrophobic surfaces. We used atomic force microscopy-based single-cell force spectroscopy and Monte Carlo simulations to investigate the similarities and differences of adhesion to hydrophilic and hydrophobic surfaces. Our results reveal that binding to both types of surfaces is mediated by thermally fluctuating cell wall macromolecules that behave differently on each type of substrate: on hydrophobic surfaces, many macromolecules are involved in adhesion, yet only weakly tethered, leading to high variance between individual bacteria, but low variance between repetitions with the same bacterium. On hydrophilic surfaces, however, only few macromolecules tether strongly to the surface. Since during every repetition with the same bacterium different macromolecules bind, we observe a comparable variance between repetitions and different bacteria. We expect these findings to be of importance for the understanding of the adhesion behaviour of many bacterial species as well as other microorganisms and even nanoparticles with soft, macromolecular coatings, used e.g. for biological diagnostics

A detailed guideline for the fabrication of single bacterial probes used for atomic force spectroscopy

The atomic force microscope (AFM) evolved as a standard device in modern microbiological research. However, its capability as a sophisticated force sensor is not used to its full capacity. The AFM turns into a unique tool for quantitative adhesion research in bacteriology by using “bacterial probes”. Thereby, bacterial probes are AFM cantilevers that provide a single bacterium or a cluster of bacteria as the contact-forming object. We present a step-by-step protocol for preparing bacterial probes, performing force spectroscopy experiments and processing force spectroscopy data. Additionally, we provide a general insight into the field of bacterial cell force spectroscopy

Using Knock-Out Mutants to Investigate the Adhesion of Staphylococcus aureus to Abiotic Surfaces

The adhesion of Staphylococcus aureus to abiotic surfaces is crucial for establishing device related infections. With a high number of single-cell force spectroscopy measurements with geneti cally modified S. aureus cells, this study provides insights into the adhesion process of the pathogen to abiotic surfaces of different wettability. Our results show that S. aureus utilizes different cell wall molecules and interaction mechanisms when binding to hydrophobic and hydrophilic surfaces. We found that covalently bound cell wall proteins strongly interact with hydrophobic substrates, while their contribution to the overall adhesion force is smaller on hydrophilic substrates. Teichoic acids promote adhesion to hydrophobic surfaces as well as to hydrophilic surfaces. This, however, is to a lesser extent. An interplay of electrostatic effects of charges and protein composition on bacterial surfaces is predominant on hydrophilic surfaces, while it is overshadowed on hydrophobic surfaces by the influence of the high number of binding proteins. Our results can help to design new models of bacterial adhesion and may be used to interpret the adhesion of other microorganisms with similar surface properties

Influence of fuel properties on fundamental spray characteristics and soot emissions using different tailor-made fuels from biomass

This work evaluates the potential of some new biomass-derived fuels as candidates for compression ignition operation. Thus, fundamental spray characteristics related to fuel vaporization and fuel/air mixing process for 2-Methyltetrahydrofuran, Di-n-butyl ether and 1-octanol has been studied and compared with conventional EN590 Diesel fuel. For this purpose, OH⁄ chemiluminescence and shadowgraphy measurements in a high pressure chamber as well as 1D simulations with a spray model have been carried out at different operating conditions representative of the NEDC driving cycle. Finally, measured soot emissions in the single-cylinder engine were presented and discussed. Results from the high pressure chamber presented very good agreement in terms of liquid length and vapor penetration with simulation results. Thus, some analytical expressions related to macroscopic spray characteristics have been proposed and validated experimentally for all four fuels. Finally, the single-cylinder engine results confirmed the relevant role of soot formation on final emissions for 1-octanol and 2-MTHF. In addition, DNBE showed greater soot oxidation potential than diesel and other TMFB candidates.This work was performed as part of the Cluster of Excellence "Tailor-Made Fuels from Biomass", which is funded by the Excellence Initiative by the German federal and state governments. Simulation works have been partially funded by Spanish government under the grant "Jose Castillejo" (CAS12/000097).García Martínez, A.; Monsalve Serrano, J.; Heuser, B.; Jakob, M.; Kremer, F.; Pischinger, S. (2016). Influence of fuel properties on fundamental spray characteristics and soot emissions using different tailor-made fuels from biomass. Energy Conversion and Management. 108:243-254. https://doi.org/10.1016/j.enconman.2015.11.010S24325410

Sub-Telomere Directed Gene Expression during Initiation of Invasive Aspergillosis

Aspergillus fumigatus is a common mould whose spores are a component of the normal airborne flora. Immune dysfunction permits developmental growth of inhaled spores in the human lung causing aspergillosis, a significant threat to human health in the form of allergic, and life-threatening invasive infections. The success of A. fumigatus as a pathogen is unique among close phylogenetic relatives and is poorly characterised at the molecular level. Recent genome sequencing of several Aspergillus species provides an exceptional opportunity to analyse fungal virulence attributes within a genomic and evolutionary context. To identify genes preferentially expressed during adaptation to the mammalian host niche, we generated multiple gene expression profiles from minute samplings of A. fumigatus germlings during initiation of murine infection. They reveal a highly co-ordinated A. fumigatus gene expression programme, governing metabolic and physiological adaptation, which allows the organism to prosper within the mammalian niche. As functions of phylogenetic conservation and genetic locus, 28% and 30%, respectively, of the A. fumigatus subtelomeric and lineage-specific gene repertoires are induced relative to laboratory culture, and physically clustered genes including loci directing pseurotin, gliotoxin and siderophore biosyntheses are a prominent feature. Locationally biased A. fumigatus gene expression is not prompted by in vitro iron limitation, acid, alkaline, anaerobic or oxidative stress. However, subtelomeric gene expression is favoured following ex vivo neutrophil exposure and in comparative analyses of richly and poorly nourished laboratory cultured germlings. We found remarkable concordance between the A. fumigatus host-adaptation transcriptome and those resulting from in vitro iron depletion, alkaline shift, nitrogen starvation and loss of the methyltransferase LaeA. This first transcriptional snapshot of a fungal genome during initiation of mammalian infection provides the global perspective required to direct much-needed diagnostic and therapeutic strategies and reveals genome organisation and subtelomeric diversity as potential driving forces in the evolution of pathogenicity in the genus Aspergillus

Robustness evaluation of cutting tool maintenance planning for soft ground tunneling projects

Tunnel boring machines require extensive maintenance and inspection effort to provide a high availability. The cutting tools of the cutting wheel must be changed timely upon reaching a critical condition. While one possible maintenance strategy is to change tools only when it is absolutely necessary, tools can also be changed preventively to avoid further damages. Such different maintenance strategies influence the maintenance duration and the overall project performance. However, determine downtime related to a particular maintenance strategy is still a challenging task. This paper shows an analysis of the robustness to achieve the planned project performance of a maintenance strategy considering uncertainties of wear behavior of the cutting tools. A simulation based analysis is presented, implementing an empirical wear prediction model. Different strategies of maintenance planning are compared by performing a parameter variation study including Monte-Carlo simulations. The maintenance costs are calculated and evaluated with respect to their robustness. Finally, an improved and robust maintenance strategy has been determined. Keywords: Mechanized tunneling, Maintenance, Wear of cutting tools, Process simulation, Robustness, Uncertainty modelin

Pressure infiltration characteristics of foam for EPB shield tunnelling in saturated sand : part 1 : ‘clean’ foam

Infiltration of pressurised foam into saturated sand was investigated in a laboratory set-up that provided an hydraulic gradient comparable to real tunnels. Four different stages were identified in the infiltration: 'foam spurt' (the foam infiltration into the pores of the sand); water flow with reduced permeability; water flow with increased permeability; and a residual stage. It appears that the infiltration depth of foam into sand decreases with increasing foam expansion ratio (FER) of the foam until a limit FER (approximately 15 for the foaming agent and sand used in this experiment). For higher FERs the permeability remains more or less constant. It was also found that a 'dry' foam (FER = 20) is not essential for formation of a low-permeability layer at the sand surface; even a 'wet' foam (FER = 5) can form a low-permeability layer. Furthermore, a foam-infiltrated zone is essential to achieve a low-permeability layer. In these tests, the flow velocities were lower than the normal excavation velocity of a tunnel-boring machine. Thus there was no foam-infiltrated zone and consequently no zone with low permeability during drilling. By comparing the pore pressures measured using pore pressure transducers with and without hydrophilic filter papers, the capillary pressure in the foam-infiltrated sand was found.Infiltration of pressurised foam into saturated sand was investigated in a laboratory set-up that provided an hydraulic gradient comparable to real tunnels. Four different stages were identified in the infiltration: 'foam spurt' (the foam infiltration into the pores of the sand); water flow with reduced permeability; water flow with increased permeability; and a residual stage. It appears that the infiltration depth of foam into sand decreases with increasing foam expansion ratio (FER) of the foam until a limit FER (approximately 15 for the foaming agent and sand used in this experiment). For higher FERs the permeability remains more or less constant. It was also found that a 'dry' foam (FER = 20) is not essential for formation of a low-permeability layer at the sand surface; even a 'wet' foam (FER = 5) can form a low-permeability layer. Furthermore, a foam-infiltrated zone is essential to achieve a low-permeability layer. In these tests, the flow velocities were lower than the normal excavation velocity of a tunnel-boring machine. Thus there was no foam-infiltrated zone and consequently no zone with low permeability during drilling. By comparing the pore pressures measured using pore pressure transducers with and without hydrophilic filter papers, the capillary pressure in the foam-infiltrated sand was found.A