Search results for "pressure [gas]"
showing 10 items of 99 documents
Calibration of an airborne HO<sub><i>x</i></sub> instrument using the All Pressure Altitude-b…
2020
Abstract. Laser-induced fluorescence (LIF) is a widely used technique for both laboratory-based and ambient atmospheric chemistry measurements. However, LIF instruments require calibrations in order to translate instrument response into concentrations of chemical species. Calibration of LIF instruments measuring OH and HO2 ( HOx ) typically involves the photolysis of water vapor by 184.9 nm light, thereby producing quantitative amounts of OH and HO2 . For ground-based HOx instruments, this method of calibration is done at one pressure (typically ambient pressure) at the instrument inlet. However, airborne HOx instruments can experience varying cell pressures, internal residence times, tempe…
The influence of rock heterogeneity on the scaling properties of simulated and natural stylolites
2009
International audience; Stylolites are among the most prominent deformation patterns in sedimentary rocks that document localized pressure solution. Recent studies revealed that stylolite roughness is characterized by two distinct scaling regimes. The main goal of the present study is to decipher whether this complex scaling behavior of stylolites is caused by the composition of the host-rock, i.e. heterogeneities in the material, or is governed by inherent processes on respective scales, namely the transition from a surface energy to an elastic energy dominated regime, as theoretically predicted. For this purpose we have developed a discrete numerical technique, based on a lattice spring m…
Modelling of stylolite geometries and stress scaling
2012
International audience; In this contribution we present numerical simulations of stylolite growth to decipher the effects of initial rock heterogeneity and stress on their morphology. We show that stylolite growth in a rock with a uniform grain size produces different patterns than stylolite growth in a rock with a bimodal grain size distribution. Strong pinning of large heterogeneities produce stylolite structures that are dominated by pronounced teeth, whereas a uniform grain size leads to spikes and a roughness that shows variable wavelengths. We compare the simulated stylolites with natural examples and show that the model can reproduce the real structures. In addition we show that stro…
Pollen and non-pollen palynomorph evidence of medieval farming activities in southwestern Greenland
2010
International audience; Radiocarbon dating, pollen and non-pollen palynomorph analyses from a lake core were used to establish the timing and effects of farming activities around Lake Igaliku, Eastern Settlement, Greenland. The absence of agro-pastoral impact before the medieval colonization by Europeans provides an opportunity to understand the development of farming activity in a pristine landscape. The results show that the first phase of clearance and grazing pressure, without the expansion of the Norse apophyte (native plant, in habitats created by humans) Rumex acetosa type, could have occurred in the 9–10th century A.D. The presence of Norse settlers and livestock is clearly recorded…
Upgrading landfill gas using a high pressure water absorption process
2014
Abstract The upgrading of landfill gas (methane 54.2 ± 2.0%, carbon dioxide 42.1 ± 2.4% and nitrogen 3.7 ± 1.2%) was studied with a pilot-scale high pressure water absorption system consisting of absorption, desorption and gas drying units. The gas was upgraded in two phases and with two absorption columns operating in sequence in pressures up to 180 bar, and with initial pressures of 8 and 10 bar. This type of high pressure process, where water is used for increasing the gas pressure, does not need a separate compression unit to produce the gas pressure required by gas vehicles. Product gas with a methane contents ranging from 83.0% to 92.1% was achieved with differing process parameters, …
Tidal Volume Estimation during Helmet Noninvasive Ventilation: an Experimental Feasibility Study
2019
AbstractWe performed a bench (BS) and human (HS) study to test the hypothesis that estimation of tidal volume (VT) during noninvasive helmet pressure support ventilation (nHPSV) would be possible using a turbine driven ventilator (TDV) coupled with an intentional leak single-limb vented circuit. During the BS a mannequin was connected to a lung simulator (LS) and at different conditions of respiratory mechanics, positive end expiratory pressure (PEEP) levels and leaks (30, 50 and 80 L/min). All differences were within the 95% limits of agreement (LoA) in all conditions in the Bland-Altman plot. The overall bias (difference between VT measured by TDV and LS) was 35 ml (95% LoA 10 to 57 ml), …
Chest wall mechanics during pressure support ventilation.
2005
Introduction During pressure support ventilation (PSV) a part of the breathing pattern is controlled by the patient, and synchronization of respiratory muscle action and the resulting chest wall kinematics is a valid indicator of the patient's adaptation to the ventilator. The aim of the present study was to analyze the effects of different PSV settings on ventilatory pattern, total and compartmental chest wall kinematics and dynamics, muscle pressures and work of breathing in patients with acute lung injury. Method In nine patients four different levels of PSV (5, 10, 15 and 25 cmH2O) were randomly applied with the same level of positive end-expiratory pressure (10 cmH2O). Flow, airway ope…
Neutron transmission measurements at nELBE
2020
International Conference on Nuclear Data for Science and Technology, ND 2019, Bejing, China, 19 May 2019 - 24 May 2019; The European physical journal / Web of Conferences 239, 01006 (2020). doi:10.1051/epjconf/202023901006
Sensitivity and mode spectrum of a frequency-output silicon pressure sensor
1988
The vibrational mode spectrum of a silicon vibrating pressure sensor is investigated. Particular attention is given to the analysis of the vibration shapes, quality factors and relative sensitivity of the resonance frequencies as a function of pressure. It is shown that a pressure sensitivity of a few parts per million at one atmosphere can be achieved. Some comments are also made regarding an improved design of the device.
On the Angola low interannual variability and its role in modulating ENSO effects in southern Africa
2019
Abstract The Angola low is a summertime low pressure system that affects the convergence of low-level moisture fluxes into southern Africa. Interannual variations of the Angola low reduce the seasonal prediction skills for this region that arise from coupled atmosphere–ocean variability. Despite its importance, the interannual dynamics of the Angola low, and its relationship with El Niño–Southern Oscillation (ENSO) and other coupled modes of variability, are still poorly understood, mostly because of the scarcity of atmospheric data and short-term duration of atmospheric reanalyses in the region. To bypass this issue, we use a long-term (3500 year) run from a 50-km-resolution global coupled…