2,417 research outputs found
Field evaluation of seat designs for underground coal mine shuttle cars
No full text"Researchers with the National Institute for Occupational Safety and Health (NIOSH) conducted a systematic study to evaluate seat designs on low- and mid-coal-seam shuttle cars. The purpose was to gather additional data to support earlier findings that NIOSH seats, with unique viscoelastic foam padding, are indeed improved designs for coal mine shuttle cars. This study included a larger sample of shuttle car operators than a prior NIOSH investigation. Eight shuttle car operators participated in evaluating seat designs on the basis of perceived levels of vehicle jarring/jolting and discomfort. Researchers then compared the operators' perceptions with field-measured levels of vehicle jarring/jolting. Seven seat designs were evaluated on low- and mid-coal-seam shuttle cars during production operations at two underground coal mines in southern West Virginia. These seat designs comprised the one already in use on each vehicle and five NIOSH designs. Experimental data were collected using accelerometers, signal conditioning amplifiers, and filters connected to a data recorder, whereas subjective data were gathered via a visual analog scale (VAS) and a questionnaire. Field trials included shuttle cars operating under full and no-load conditions. VAS responses indicated that NIOSH-designed seats performed better relative to comfort and isolation from vehicle jarring/jolting than the existing seats used in the shuttle cars. Both mid- and low-coal-seam shuttle car operators, during no-load and full-load conditions, rated lower levels of jarring/jolting with the NIOSH seat design. Questionnaire responses indicated that shuttle car operators rated NIOSH seat designs as more comfortable. Vehicle operators most frequently suggested the addition of armrests as a way to improve the seats on the mid-seam shuttle car. The quantitative levels of vehicle jarring/jolting for the no-load condition (more severe condition for vehicle operation) showed that NIOSH seats for the mid-coal-seam shuttle car performed better than the existing seat in terms of peak acceleration and crest factor. Similarly, for the low-coal-seam shuttle car, NIOSH seats performed better than the existing seat in terms of peak acceleration, root-mean-square (RMS) acceleration, and crest factor. This research will provide the mining industry with better seat designs for isolating operators from vehicle jarring/jolting. Furthermore, equipment manufacturers are afforded the opportunity to refine and improve the NIOSH seat designs using information gathered from this research study." - NIOSHTIC-
"The 'fightin'est' Canadian general:" Brigadier Christopher Vokes and his approach to military command, June 1942 -- August 1943
No full textThis thesis evaluates the manner in which Brigadier Christopher Yokes dealt with the technical and human aspects of command while commanding the 2nd Canadian Infantry Brigade from 25 June 1942 until the end of the Sicilian campaign in August 1943. It seeks to promote a greater understanding of brigade-level command and to rehabilitate Vokes's reputation as a commander, which has largely been based on certain negative personality traits. The author argues that Yokes was a successful commander because he maintained a good balance between technical skills such as planning and directing operations and his ability to understand, motivate, and lead soldiers, and because his actions were guided by a sound philosophy of command based on personal leadership and teamwork. These elements allowed Christopher Yokes to train and lead a highly effective and cohesive fighting force that defeated some of Germany's best troops in the physically demanding environment of the Sicilian battlefield
"The 'fightin'est' Canadian general:" Brigadier Christopher Vokes and his approach to military command, June 1942 -- August 1943
No full textThis thesis evaluates the manner in which Brigadier Christopher Yokes dealt with the technical and human aspects of command while commanding the 2nd Canadian Infantry Brigade from 25 June 1942 until the end of the Sicilian campaign in August 1943. It seeks to promote a greater understanding of brigade-level command and to rehabilitate Vokes's reputation as a commander, which has largely been based on certain negative personality traits. The author argues that Yokes was a successful commander because he maintained a good balance between technical skills such as planning and directing operations and his ability to understand, motivate, and lead soldiers, and because his actions were guided by a sound philosophy of command based on personal leadership and teamwork. These elements allowed Christopher Yokes to train and lead a highly effective and cohesive fighting force that defeated some of Germany's best troops in the physically demanding environment of the Sicilian battlefield
Founders: Christopher Taylor
No full text\ua9 2021 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group. ‘Founders’ is an intermittent series of short, critical appreciations of scholars, researchers and others whose work and ideas, mainly in Britain, have made particularly sweeping, influential and foundational contributions to the development of historically- and archaeologically-informed landscape studies. This latest addition to the series concerns Christopher Taylor, whose death on 28th May 2021 was noted in the Landscapes editorial in issue 21.2
Pannexin-1 and P2X7-Receptor Are Required for Apoptotic Osteocytes in Fatigued Bone to Trigger RANKL Production in Neighboring Bystander Osteocytes
No full textOsteocyte apoptosis is required to induce intracortical bone remodeling after microdamage in animal models, but how apoptotic osteocytes signal neighboring “bystander” cells to initiate the remodeling process is unknown. Apoptosis has been shown to open pannexin-1 (Panx1) channels to release adenosine diphosphate (ATP) as a “find me” signal for phagocytic cells. To address whether apoptotic osteocytes use this signaling mechanism, we adapted the rat ulnar fatigue-loading model to reproducibly introduce microdamage into mouse cortical bone and measured subsequent changes in osteocyte apoptosis, receptor activator of NF-kB ligand (RANKL) expression and osteoclastic bone resorption in wild-type (WT; C57Bl/6) mice and in mice genetically deficient in Panx1 (Panx1KO). Mouse ulnar loading produced linear microcracks comparable in number and location to the rat model. WT mice showed increased osteocyte apoptosis and RANKL expression at microdamage sites at 3 days after loading and increased intracortical remodeling and endocortical tunneling at day 14. With fatigue, Panx1KO mice exhibited levels of microdamage and osteocyte apoptosis identical to WT mice. However, they did not upregulate RANKL in bystander osteocytes or initiate resorption. Panx1 interacts with P2X7R in ATP release; thus, we examined P2X7R-deficient mice and WT mice treated with P2X7R antagonist Brilliant Blue G (BBG) to test the possible role of ATP as a find-me signal. P2X7RKO mice failed to upregulate RANKL in osteocytes or induce resorption despite normally elevated osteocyte apoptosis after fatigue loading. Similarly, treatment of fatigued C57Bl/6 mice with BBG mimicked behavior of both Panx1 KO and P2X7RKO mice; BBG had no effect on osteocyte apoptosis in fatigued bone but completely prevented increases in bystander osteocyte RANKL expression and attenuated activation of resorption by more than 50%. These results indicate that activation of Panx1 and P2X7R are required for apoptotic osteocytes in fatigued bone to trigger RANKL production in neighboring bystander osteocytes and implicate ATP as an essential signal mediating this process.Peer reviewe
Recombination dynamics in polythiophene:fullerene solar cells
No full textOrganic devices based on polymer:fullerene blend films are attracting extensive
interest as low cost solar cells, with power conversion efficiencies over 5%.
Improvements in performance are dependent on developing a better understanding of
the pertinent loss processes. This in turn requires the ability to reliably determine
charge densities (n) and carrier lifetimes (τn) in real devices under standard operating
conditions. In this thesis, we address the recombination dynamics in organic solar
cells based on blends of poly(3-hexylthiophene) (P3HT) and methanofullerene [6,6]-
phenyl C61-butyric acid methyl ester (PCBM), P3HT:PCBM devices, one of the best
devices to date, using both experimental and modelling studies.
Initially, a drift-diffusion model was used to study the basic principles of solar cell
operation, with particular focus on investigating the ‘corrected photocurrent’, where
the effects of dark injection are removed. We then have employed a series of
experimental techniques – including transient photovoltage and photocurrent,
transient absorption spectroscopy and charge extraction – to determine the carrier
lifetimes and charge densities in standard annealed P3HT:PCBM devices under
operation. The results of our studies for a device under open-circuit conditions show
that the open-circuit voltage (Voc) is primarily governed by a trap dependent
bimolecular recombination process. By applying charge extraction studies on devices
under forward bias in the dark, we show that the dark current is also governed by the
same trap dependent bimolecular recombination mechanism which determines Voc.
Based on the understanding of charge carrier dynamics at Voc and the forward bias
dark current, a simple model has been developed to simulate ‘light’ current-voltage
(J-V) curves. Despite the simplicity of this model, remarkably good agreement was
observed with experimental J-V data
The effects of estrogen deficiency on cortical bone microporosity and mineralization
No full textRecent studies have demonstrated matrix-mineral alterations in bone tissue surrounding osteocytes in estrogen-deficient animals.While cortical bone porosity has been shown to be a contributor to the mechanical properties of bone tissue, little analysis has been done to investigate the effects of estrogen deficiency on bone's microporosities, including the vascular and osteocyte lacunar porosities. In this study we examined alterations in cortical bone microporosity, mineralization, and cancellous bone architecture due to estrogen deficiency in the ovariectomized rat model of postmenopausal osteoporosis. Twenty-week-old female Sprague–Dawley rats were subjected to either ovariectomy or sham surgery. Six weeks post-surgery tibiae were analyzed using high-resolution micro-CT, backscattered electron imaging, nanoindentation, and dynamic histomorphometry. Estrogen deficiency caused an increase in cortical bone vascular porosity, with enlarged vascular pores and little change in tissue mineral density in the proximal tibial metaphysis. Measurements of cancellous architecture corresponded to previous studies reporting a decrease in bone volume fraction, an increase in trabecular separation, and a decrease in trabecular number in the proximal tibia due to estrogen deficiency. Nanoindentation results showed no differences in matrix stiffness in osteocyte-rich areas of the proximal tibia of estrogen-deficient rats, and bone labeling and backscattered electron imaging showed no significant changes in mineralization around the vascular pores. The findings demonstrate local surface alterations of vascular pores due to estrogen deficiency. An increase in cortical vascular porosity may diminish bone strength as well as alter bone mechanotransduction via interstitial fluid flow, both of which could contribute to bone fragility during postmenopausal osteoporosis.Peer reviewe
Development of the TanDEM-X Calibration Concept: Analysis of Systematic Errors
No full textThe TanDEM-X mission, result of the partnership
between the German Aerospace Center (DLR) and Astrium
GmbH, opens a new era in spaceborne radar remote sensing. The first bistatic satellite synthetic aperture radar mission is formed by flying the TanDEM-X and TerraSAR-X in a closely controlled helix formation. The primary mission goal is the derivation of a high-precision global digital elevation model (DEM) according to High-Resolution Terrain Information (HRTI) level 3 accuracy.
The finite precision of the baseline knowledge and uncompensated radar instrument drifts introduce errors that may compromise the height accuracy requirements. By means of a DEM calibration, which uses absolute height references, and the information provided by adjacent interferogram overlaps, these height errors can be minimized. This paper summarizes the exhaustive studies of the nature of the residual-error sources that have been carried out during the development of the DEM calibration concept.
Models for these errors are set up and simulations of the resulting DEM height error for different scenarios provide the basis for the development of a successful DEM calibration strategy for the TanDEM-X mission
Heritability and Linkage Analysis of Appendicitis Utilizing Age at Onset
No full textAppendicitis usually afflicts the young, but there is a large tail in the distribution of onset age. The genetics of this disease are still not well understood. A heritability analysis and genome wide linkage analysis of a large twin dataset was undertaken. Treating age of onset of appendicitis as a censored survival trait revealed a heritability of 0.21, and found evidence of linkage to Chromosome 1p37.3. Author(s): Christopher Oldmeadow 1 * | Kerrie Mengersen 2 | Nicholas Martin 3 | David L. Duffy
Covalent Confinement of Sulfur Copolymers onto Graphene Sheets Affords Ultrastable Lithium–Sulfur Batteries with Fast Cathode Kinetics
No full textLithium–sulfur
(Li–S) batteries have received significant
attention due to the high theoretical specific capacity of sulfur
(1675 mA h g–1). However, the practical applications
are often handicapped by sluggish electrochemical kinetics and the
“shuttle effect” of electrochemical intermediate polysulfides.
Herein, we propose an in-situ copolymerization strategy for covalently
confining a sulfur-containing copolymer onto reduced graphene oxide
(RGO) to overcome the aforementioned challenges. The copolymerization
was performed by heating elemental sulfur and isopropenylphenyl-functionalized
RGO to afford a sulfur-containing copolymer, that is, RGO-g-poly(S-r-IDBI), which is featured by
a high sulfur content and uniform distribution of the poly(S-r-IDBI) on RGO sheets. The covalent confinement of poly(S-r-IDBI) onto RGO sheets not only enhances the Li+ diffusion coefficients by nearly 1 order of magnitude, but also
improves the mechanical properties of the cathodes and suppresses
the shuttle effect of polysulfides. As a result, the RGO-g-poly(S-r-IDBI) cathode exhibits an enhanced sulfur
utilization rate (10% higher than that of an elemental sulfur cathode
at 0.1C), an improved rate capacity (688 mA h g–1 for the RGO-g-poly(S-r-IDBI) cathode
vs 400 mA h g–1 for an elemental sulfur cathode
at 1C), and a high cycling stability (a capacity decay of 0.021% per
cycle, less than one-tenth of that measured for an elemental sulfur
cathode)
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