113 research outputs found
The effects of under-sleeper pads on sleeper-ballast interaction
Under-sleeper pads (USPs), typically made from polyurethane, are used by railways in certain
parts of the world to reduce ballast settlement and consequently lengthen the ballast tamping
cycle. The rationale behind this relatively new addition to the conventional ballasted track
structure is that the pad increases the contact area between the angular ballast particles
and the underside of the concrete sleeper, with the effect that ballast breakdown and total
track settlement are reduced. This paper describes two experiments on the effects of USPs
on four aspects of sleeper–ballast interaction, namely contact area, contact pressure, ballast
settlement and ballast breakdown. Static and dynamic tests up to 1 million loading cycles
were performed under controlled laboratory conditions on concrete sleepers with and without
USPs. Sophisticated pressure sensors revealed an increase in contact area from 12% to 35%
for static loading tests, and from 8% to 20% for dynamic tests, with a resulting 70% reduction
in contact pressure. In addition, a 44% reduction in ballast settlement and a 23% reduction in
ballast breakdown were achieved by the introduction of USPs. In conclusion it is argued that the
introduction of USPs specifically on heavy-haul lines would offer significant advantages with
respect to ballast settlement and breakdown. These advantages are most likely to lengthen
general ballast tamping and screening cycles, resulting in significant life cycle cost savings.Transnet Freight Rail is gratefully acknowledged
for financial support to the Chair
in Railway Engineering at the University of Pretoria.http://www.journals.co.za/ej/ejour_civileng.htmlam2016Civil Engineerin
Baseline oxygen consumption decreases with cortical depth
The cerebral cortex is organized in cortical layers that differ in their cellular density, composition, and wiring. Cortical laminar architecture is also readily revealed by staining for cytochrome oxidase—the last enzyme in the respiratory electron transport chain located in the inner mitochondrial membrane. It has been hypothesized that a high-density band of cytochrome oxidase in cortical layer IV reflects higher oxygen consumption under baseline (unstimulated) conditions. Here, we tested the above hypothesis using direct measurements of the partial pressure of O2 (pO2) in cortical tissue by means of 2-photon phosphorescence lifetime microscopy (2PLM). We revisited our previously developed method for extraction of the cerebral metabolic rate of O2 (CMRO2) based on 2-photon pO2 measurements around diving arterioles and applied this method to estimate baseline CMRO2 in awake mice across cortical layers. To our surprise, our results revealed a decrease in baseline CMRO2 from layer I to layer IV. This decrease of CMRO2 with cortical depth was paralleled by an increase in tissue oxygenation. Higher baseline oxygenation and cytochrome density in layer IV may serve as an O2 reserve during surges of neuronal activity or certain metabolically active brain states rather than reflecting baseline energy needs. Our study provides to our knowledge the first quantification of microscopically resolved CMRO2 across cortical layers as a step towards better understanding of brain energy metabolism.publishedVersio
Correlation structure in micro-ECoG recordings is described by spatially coherent components
Electrocorticography (ECoG) is becoming more prevalent due to improvements in fabrication and recording technology as well as its ease of implantation compared to intracortical electrophysiology, larger cortical coverage, and potential advantages for use in long term chronic implantation. Given the flexibility in the design of ECoG grids, which is only increasing, it remains an open question what geometry of the electrodes is optimal for an application. Conductive polymer, PEDOT:PSS, coated microelectrodes have an advantage that they can be made very small without losing low impedance. This makes them suitable for evaluating the required granularity of ECoG recording in humans and experimental animals. We used two-dimensional (2D) micro-ECoG grids to record intra-operatively in humans and during acute implantations in mouse with separation distance between neighboring electrodes (i.e., pitch) of 0.4 mm and 0.2/0.25 mm respectively. To assess the spatial properties of the signals, we used the average correlation between electrodes as a function of the pitch. In agreement with prior studies, we find a strong frequency dependence in the spatial scale of correlation. By applying independent component analysis (ICA), we find that the spatial pattern of correlation is largely due to contributions from multiple spatially extended, time-locked sources present at any given time. Our analysis indicates the presence of spatially structured activity down to the sub-millimeter spatial scale in ECoG despite the effects of volume conduction, justifying the use of dense micro-ECoG grids.Published versio
Abstracts from the 8th International Conference on cGMP Generators, Effectors and Therapeutic Implications
This work was supported by a restricted research grant of Bayer AG
Polyelemental Nanolithography via Plasma Ion Bombardment: From Fabrication to Superior H 2
Directed Reactions within Confined Reaction Environments: Polyadditions in Polyelectrolyte−Surfactant Complexes
The Impact of Halogenated Phenylalanine Derivatives on NFGAIL Amyloid Formation
The hexapeptide hIAPP22–27 (NFGAIL) is known as a crucial amyloid core sequence of the human islet amyloid polypeptide (hIAPP) whose aggregates can be used to better understand the wild-type hIAPP′s toxicity to β-cell death. In amyloid research, the role of hydrophobic and aromatic-aromatic interactions as potential driving forces during the aggregation process is controversially discussed not only in case of NFGAIL, but also for amyloidogenic peptides in general. We have used halogenation of the aromatic residue as a strategy to modulate hydrophobic and aromatic-aromatic interactions and prepared a library of NFGAIL variants containing fluorinated and iodinated phenylalanine analogues. We used thioflavin T staining, transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) to study the impact of side-chain halogenation on NFGAIL amyloid formation kinetics. Our data revealed a synergy between aggregation behavior and hydrophobicity of the phenylalanine residue. This study introduces systematic fluorination as a toolbox to further investigate the nature of the amyloid self-assembly process
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Neurovascular Network Explorer 2.0: A Database of 2-Photon Single-Vessel Diameter Measurements from Mouse SI Cortex in Response To Optogenetic Stimulation.
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