92 research outputs found
DEM simulations of the frictional and frictionless polydisperse packings of spheres under uniaxial compression
The uniaxial compression of polydisperse assemblies of spherical frictional and frictionless particles is modeled with the discrete element method (DEM). The normal particle size distribution with standard deviation of particle mean diameter in the range from 0% to 80% was applied. The series of numerical tests have been conducted to study the micromechanical and macromechanical properties of packings of spheres. The micro-scale analyses included distribution of contact forces and average coordination number, whereas macromechanical study included the elasticity, stress transmission and angle of internal friction in the assemblies. The linear increase in solid fraction was observed for standard deviation of particle mean diameter increasing up to 50% in assemblies of both, frictional and frictionless spheres under pressure of 100kPa. Further increase in particle size heterogeneity decreased solid fraction in systems. The increase in coefficient of interparticle friction resulted in decrease in solid fraction by above 10% in the whole range of variability of SD value due to the different space-filling properties of frictional particles. The stiffness of samples increased with compressive loads increasing, however no clear effect of particle size polydispersity on the effective elastic modulus of mixtures was found in frictional sphere packings. The effective elastic modulus increased with SD value increasing up to 50% in sample composed of smooth particles that decreased for higher SD values. Discrete element method predicted decrease in pressure ratio with standard deviation of particle mean diameter increasing up to 50%. Further increase in particle size polydispersity increased value of the parameter. Increase in coefficient of interparticle friction to 0.4 resulted in about 40% decrease in pressure ratio in sphere packings
Characterization of trace gas emissions at an intermediate port
Growing ship traffic in Atlantic Canada strengthens the local economy but
also plays an important role in greenhouse gas and air pollutant emissions in
this coastal environment. A mobile open-path Fourier transform infrared
(OP-FTIR; acronyms defined in Appendix A) spectrometer was set up in Halifax
Harbour (Nova Scotia, Canada), an intermediate harbour integrated into the
downtown core, to measure trace gas concentrations in the vicinity of marine
vessels, in some cases with direct or near-direct marine combustion plume
intercepts. This is the first application of the OP-FTIR measurement
technique to real-time, spectroscopic measurements of CO2, CO,
O3, NO2, NH3, CH3OH, HCHO,
CH4 and N2O in the vicinity of harbour emissions
originating from a variety of marine vessels, and the first measurement of
shipping emissions in the ambient environment along the eastern seaboard of
North America outside of the Gulf Coast. The spectrometer, its active mid-IR
source and its detector were located on shore while the passive retroreflector
was on a nearby island, yielding a 455 m open path over the ocean
(910 m two-way). Atmospheric absorption spectra were recorded during day, night,
sunny, cloudy and substantially foggy or precipitating conditions, with a
temporal resolution of 1 min or better. A weather station was co-located
with the retroreflector to aid in the processing of absorption spectra and
the interpretation of results, while a webcam recorded images of the harbour once
per minute. Trace gas concentrations were retrieved from spectra by the MALT
non-linear least squares iterative fitting routine. During field measurements
(7 days in JulyâAugust 2016; 12 days in January 2017) AIS information on
nearby ship activity was manually collected from a commercial
website and used to calculate emission rates of shipping combustion products
(CO2, CO, NOx, HC, SO2), which were then
linked to measured concentration variations using ship position and wind
information. During periods of low wind speed we observed extended (ââŒâ9 h)
emission accumulations combined with near-complete O3
titration, both in winter and in summer. Our results compare well with a NAPS
monitoring station ââŒâ1 km away, pointing to the extended spatial scale of
this effect, commonly found in much larger European shipping channels. We
calculated total marine sector emissions in Halifax Harbour based on a
complete AIS dataset of ship activity during the cruise ship season (MayâOctober 2015)
and the remainder of the year (November 2015âApril 2016) and found
trace gas emissions (tonnes) to be 2.8 % higher on average during the
cruise ship season, when passenger ship emissions were found to contribute
18 % of emitted CO2, CO, NOx, SO2
and HC (0.5 % in the off season due to occasional cruise ships arriving, even in
April). Similarly, calculated particulate emissions are 4.1 % higher
during the cruise ship season, when passenger ship emissions contribute
18 % of the emitted particulate matter (PM) (0.5 % in the off season). Tugs were found to make the
biggest contribution to harbour emissions of trace gases in both cruise ship
season (23 % NOx, 24 % SO2) and the off season
(26 % of both SO2 and NOx), followed by container ships
(25 % NOx and SO2 in the off season, 21 %
NOx and SO2 in cruise ship season). In the cruise ship season
cruise ships were observed to be in third place regarding trace gas emissions, whilst tankers were in third place in the off
season, with both being responsible for 18 % of the calculated emissions. While the
concentrations of all regulated trace gases measured by OP-FTIR as well as
the nearby in situ NAPS sensors were well below maximum hourly permissible
levels at all times during the 19-day measurement period, we find that AIS-based
shipping emissions of NOx over the course of 1 year are
4.2 times greater than those of a nearby 500 MW stationary source emitter and
greater than or comparable to all vehicle NOx emissions in
the city. Our findings highlight the need to accurately represent emissions
from the shipping and marine sectors at intermediate ports integrated into
urban environments. Emissions can be represented as pseudo-stationary and/or
pseudo-line sources.</p
Fat perception in the human frontal operculum, insular and somatosensory cortex
Here, we combined magnetic resonance imaging with lesion-symptom mapping in patients with chronic brain lesions to investigate brain representations of sugar and fat perception. Patients and healthy controls rated chocolate milkshakes that only differed in sugar or fat content. As compared to controls, patients showed an impaired fat, but not sugar perception. Impairments in fat perception overlapped with the anterior insula and frontal operculum, together assumed to underpin gustatory processing. We also identified the mid-dorsal insula as well as the primary and secondary somatosensory cortex - regions previously assumed to integrate oral-sensory inputs. These findings suggest that fat perception involves a specific set of brain regions that were previously reported to underpin gustatory processing and oral-sensory integration processes
n-XYTER: A CMOS read-out ASIC for a new generation of high rate multichannel counting mode neutron detectors
For a new generation of 2-D neutron detectors developed in the framework of the EU NMI3 project DETNI [1], the 128-channel frontend chip n-XYTER has been designed. To facilitate the reconstruction of single neutron incidence points, the chip has to provide a spatial coordinate (represented by the channel number), as well as time stamp and amplitude information to match the data of x- and y-coordinates. While the random nature of the input signals calls for self-triggered operation of the chip, on-chip derandomisation and sparsi cation is required to exploit the enormous rate capability of these detectors ( 4 106cm2s1). The chosen architecture implements a preampli er driving two shapers with di erent time constants per channel. The faster shaper drives a single-pulse discriminator with subsequent time-walk compensation. The output of this circuit is used to latch a 14-bit time stamp with a 2 ns resolution and to enable a peak detector circuit fed by the slower shaper branch. The analogue output of the peak detector as well as the time stamp are stored in a 4-stage FIFO for derandomisation. The readout of these FIFOs is accomplished by a token-ring based multiplexer working at 32 MHz, which accounts for further derandomisation, sparsi cation and dynamic bandwidth distribution. The chip was submitted for manufacturing in AMS's C35B4M3 0.35”m CMOS technology in June 2006
Hot topics in allergen immunotherapy, 2023: Current status and future perspective
The importance of allergen immunotherapy (AIT) is multifaceted, encompassing both clinical and qualityâofâlife improvements and costâeffectiveness in the long term. Key mechanisms of allergen tolerance induced by AIT include changes in memory type allergenâspecific Tâ and Bâcell responses towards a regulatory phenotype with decreased Type 2 responses, suppression of allergenâspecific IgE and increased IgG and IgG, decreased mast cell and eosinophil numbers in allergic tissues and increased activation thresholds. The potential of novel patient enrolment strategies for AIT is taking into account recent advances in biomarkers discoveries, molecular allergy diagnostics and mobile health applications contributing to a personalized approach enhancement that can increase AIT efficacy and compliance. Artificial intelligence can help manage and interpret complex and heterogeneous data, including big data from omics and nonâomics research, potentially predict disease subtypes, identify biomarkers and monitor patient responses to AIT. Novel AIT preparations, such as synthetic compounds, innovative carrier systems and adjuvants, are also of great promise. Advances in clinical trial models, including adaptive, complex and hybrid designs as well as realâworld evidence, allow more flexibility and cost reduction. The analyses of AIT costâeffectiveness show a clear longâterm advantage compared to pharmacotherapy. Important research questions, such as defining clinical endpoints, biomarkers of patient selection and efficacy, mechanisms and the modulation of the placebo effect and alternatives to conventional field trials, including allergen exposure chamber studies are still to be elucidated. This review demonstrates that AIT is still in its growth phase and shows immense development prospects
Silicon strip detectors for two-dimensional soft X-ray imaging at normal incidence
A simple prototype system for static two-dimensional soft X-ray imaging using silicon microstrip detectors irradiated at normal incidence is presented. Radiation sensors consist of single-sided silicon detectors made from 300 mum thick wafers, read by RX64 ASICs. Data acquisition and control is performed by a Windows PC workstation running dedicated LabVIEW routines, connected to the sensors through a PCI-DIO-96 interface. Two-dimensional images are obtained by scanning a lead collimator with a thin slit perpendicular to the strip axis, along the whole detector size; the several strip profiles (slices) taken at each position are then put together to form a planar image. Preliminary results are presented, illustrating the high-resolution imaging capabilities of the system with soft X-rays. (C) 2003 Elsevier B.V. All rights reserved.info:eu-repo/semantics/publishedVersio
Comparisons between SCIAMACHY and ground-based FTIR data for total columns of CO, CHâ, COâ and NâO
Total column amounts of CO, CH4, CO2 and N2O retrieved from SCIAMACHY nadir observations in ist near-infrared channels have been compared to data from a ground-based quasi-global network of Fourier-transform infrared (FTIR) spectrometers. The SCIAMACHY data considered here have been produced by three different retrieval algorithms, WFM-DOAS (version 0.5 for CO and CH4 and version 0.4 for CO2 and N2O), IMAP-DOAS (version 1.1 and 0.9 (for CO)) and IMLM (version 6.3) and cover the January to December 2003 time period. Comparisons have been made for individual data, as well as for monthly averages. To maximize the number of reliable coincidences that satisfy the temporal and spatial collocation criteria, the SCIAMACHY data have been compared with a temporal 3rd order polynomial interpolation of the ground-based data. Particular attention has been given to the question whether SCIAMACHY observes correctly the seasonal and latitudinal variability of the target species. The present results indicate that the individual SCIAMACHY data obtained with the actual versions of the algorithms have been significantly improved, but that the quality requirements, for estimating emissions on regional scales, are not yet met. Nevertheless, possible directions for further algorithm upgrades have been identified which should result in more reliable data products in a near future
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CO measurements from the ACE-FTS satellite instrument: data analysis and validation using ground-based, airborne and spaceborne observations
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