The Experts below are selected from a list of 7047 Experts worldwide ranked by ideXlab platform
A I Kholkin - One of the best experts on this subject based on the ideXlab platform.
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modelling counter current and dual counter current chromatography using longitudinal mixing cell and eluting counter current distribution models
Journal of Chromatography A, 2007Co-Authors: A E Kostanyan, V V Belova, A I KholkinAbstract:Abstract Two well known approaches are considered to analyze the processes of counter-current and dual counter-current chromatography: the longitudinal mixing cell model and the Craig's counter-current distribution model. The cell model represents perfectly mixed, equally sized cells in series. The number of cells characterizes the rates of longitudinal mixing in the stationary and mobile phases. In the eluting counter-current distribution (CCD) model, the CCC process is considered as a continuous form of Craig's counter-current distribution. For a cascade of equilibrium stages theoretical elution profiles of the CCC process by using the CCD and cell model approaches have been compared. It is shown that in general, distribution functions of the CCD and cell models differ. It is established that the distribution of a solute between two solvent phases in the dual CCC process is determined by the extraction factor c , the total number of equilibrium stages n and the position of the Sample Inlet m by the equation Q x = (1 − c m )/(1 − c n + 1 ) with c = F 2 K D / F 1 ( K D , F 1 , F 2 and Q x are the distribution constant, the phase flow-rates and the portion of solute eluted by the first phase, respectively).
P. W. Seakins - One of the best experts on this subject based on the ideXlab platform.
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Pressure-dependent calibration of the OH and HO2 channels of a FAGE HOx instrument using the Highly Instrumented Reactor for Atmospheric Chemistry (HIRAC)
Copernicus Publications, 2015Co-Authors: F. A. F. Winiberg, S. C. Smith, I. Bejan, C. A. Brumby, T. Ingham, T. L. Malkin, S. C. Orr, D. E. Heard, P. W. SeakinsAbstract:The calibration of field instruments used to measure concentrations of OH and HO2 worldwide has traditionally relied on a single method utilising the photolysis of water vapour in air in a flow tube at atmospheric pressure. Here the calibration of two FAGE (fluorescence assay by gaseous expansion) apparatuses designed for HOx (OH and HO2) measurements have been investigated as a function of external pressure using two different laser systems. The conventional method of generating known concentrations of HOx from H2O vapour photolysis in a turbulent flow tube impinging just outside the FAGE Sample Inlet has been used to study instrument sensitivity as a function of internal fluorescence cell pressure (1.8–3.8 mbar). An increase in the calibration constants CHO and CHO2 with pressure was observed, and an empirical linear regression of the data was used to describe the trends, with ΔCHO = (17 ± 11) % and ΔCHO2 = (31.6 ± 4.4)% increase per millibar air (uncertainties quoted to 2σ). Presented here are the first direct measurements of the FAGE calibration constants as a function of external pressure (440–1000 mbar) in a controlled environment using the University of Leeds HIRAC chamber (Highly Instrumented Reactor for Atmospheric Chemistry). Two methods were used: the temporal decay of hydrocarbons for calibration of OH, and the kinetics of the second-order recombination of HO2 for HO2 calibrations. Over comparable conditions for the FAGE cell, the two alternative methods are in good agreement with the conventional method, with the average ratio of calibration factors (conventional : alternative) across the entire pressure range, COH(conv)/COH(alt) = 1.19 ± 0.26 and CHO2(conv)/CHO2(alt) = 0.96 ± 0.18 (2σ). These alternative calibration methods currently have comparable systematic uncertainties to the conventional method: ~ 28% and ~ 41% for the alternative OH and HO2 calibration methods respectively compared to 35% for the H2O vapour photolysis method; ways in which these can be reduced in the future are discussed. The good agreement between the very different methods of calibration leads to increased confidence in HOx field measurements and particularly in aircraft-based HOx measurements, where there are substantial variations in external pressure, and assumptions are made regarding loss rates on Inlets as a function of pressure
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Pressure-dependent calibration of the OH and HO2 channels of a FAGE HOx instrument using the Highly Instrumented Reactor for Atmospheric Chemistry (HIRAC)
'Copernicus GmbH', 2015Co-Authors: Winiberg F, C. A. Brumby, T. L. Malkin, S. C. Orr, D. E. Heard, Smith S, Ingham T, P. W. SeakinsAbstract:The calibration of field instruments used to measure concentrations of OH and HO2 worldwide has traditionally relied on a single method utilising the photolysis of water vapour in air in a flow tube at atmospheric pressure. Here the calibration of two FAGE (fluorescence assay by gaseous expansion) apparatuses designed for HOx (OH and HO2) measurements have been investigated as a function of external pressure using two different laser systems. The conventional method of generating known concentrations of HOx from H2O vapour photolysis in a turbulent flow tube impinging just outside the FAGE Sample Inlet has been used to study instrument sensitivity as a function of internal fluorescence cell pressure (1.8-3.8 mbar). An increase in the calibration constants CHO and CHO2 with pressure was observed, and an empirical linear regression of the data was used to describe the trends, with ΔCHO Combining double low line (17 ± 11) % and ΔCHO2 Combining double low line (31.6 ± 4.4)% increase per millibar air (uncertainties quoted to 2σ). Presented here are the first direct measurements of the FAGE calibration constants as a function of external pressure (440-1000 mbar) in a controlled environment using the University of Leeds HIRAC chamber (Highly Instrumented Reactor for Atmospheric Chemistry). Two methods were used: the temporal decay of hydrocarbons for calibration of OH, and the kinetics of the second-order recombination of HO2 for HO2 calibrations. Over comparable conditions for the FAGE cell, the two alternative methods are in good agreement with the conventional method, with the average ratio of calibration factors (conventional : alternative) across the entire pressure range, COH(conv)/COH(alt) Combining double low line 1.19 ± 0.26 and CHO2(conv)/CHO2(alt) Combining double low line 0.96 ± 0.18 (2σ). These alternative calibration methods currently have comparable systematic uncertainties to the conventional method: ∼ 28% and ∼ 41% for the alternative OH and HO2 calibration methods respectively compared to 35% for the H2O vapour photolysis method; ways in which these can be reduced in the future are discussed. The good agreement between the very different methods of calibration leads to increased confidence in HOx field measurements and particularly in aircraft-based HOx measurements, where there are substantial variations in external pressure, and assumptions are made regarding loss rates on Inlets as a function of pressure
Harald Kunstmann - One of the best experts on this subject based on the ideXlab platform.
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simultaneous multicopter based air sampling and sensing of meteorological variables
Atmospheric Measurement Techniques, 2017Co-Authors: Caroline Brosy, Karina Krampf, Matthias Zeeman, Benjamin Wolf, W Junkermann, Klaus Schafer, Stefan Emeis, Harald KunstmannAbstract:The state and composition of the lowest part of the planetary boundary layer (PBL), i.e., the atmospheric surface layer (SL), reflects the interactions of external forcing, land surface, vegetation, human influence and the atmosphere. Vertical profiles of atmospheric variables in the SL at high spatial and temporal resolution increase our understanding of these interactions, but are still challenging to measure appropriately. Traditional ground-based observations include towers that often cover only few measurement heights on a fixed location. At the same time, remote sensing techniques and aircraft measurements are challenged to achieve sufficient detail close to the ground. Vertical and horizontal sounding of the PBL can be complemented by unmanned aerial vehicles (UAV). Our aim in this case study is to assess the use of a multicopter-type UAV to simultaneously support the spatial sampling of air and the sensing of meteorological variables for the study of the surface exchange processes. To this end, a UAV was equipped with onboard air temperature and humidity sensors, while wind conditions were determined from the UAV’s flight control sensors. Further, the UAV was used to systematically change the location of a Sample Inlet connected to a Sample tube, allowing the observation of methane abundance using a ground-based analyzer. Vertical methane gradients were found during stable atmospheric conditions with a gradient of about 300 ppb. Our results showed that both methane and meteorological conditions were in agreement with other observations at the site during the ScaleX-2015 campaign. The multicopter-type UAV was capable of simultaneous in situ sensing of meteorological state variables and sampling of air up to 50 m above the surface, which extended the vertical profile height of existing tower-based infrastructure by a factor of five.
W.a.m. Wanniarachchi - One of the best experts on this subject based on the ideXlab platform.
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A novel approach to precise evaluation of carbon dioxide flow behaviour in siltstone under tri-axial drained conditions
Journal of Natural Gas Science and Engineering, 2016Co-Authors: Chengpeng Zhang, Pathegama Gamage Ranjith, Mandadige Samintha Anne Perera, Jian Zhao, Decheng Zhang, W.a.m. WanniarachchiAbstract:Abstract Since the secure storage of CO 2 in any geological sink is largely dependent on its caprock and reservoir rock flow properties, it is necessary to check the permeability of both in assessing geological reservoirs for CO 2 storage. Siltstone is a common rock type in both. On the other hand, the highly complicated thermodynamic properties of CO 2 cause its flow behaviour through any rock mass to become highly complex. This intention of this study is to understand this complexity and to propose an accurate technique to evaluate the apparent permeability of CO 2 through siltstone under laboratory conditions, considering the possible phase transitions of CO 2 inside the rock mass. A series of tri-axial drained experiments on siltstones at room temperature was therefore performed. According to the results, the proposed method accurately predicts permeability through siltstone in tri-axial drained tests, because it more precisely considers the influence of CO 2 phase transition on its flow performance, and the permeability in the Sample is separately evaluated for the liquid and gas CO 2 regions. The new approach shows that the actual CO 2 pressure distribution along the Sample has a curvilinear shape. Consideration of the possible phase transition between the Sample Inlet and the outlet is particularly important for liquid CO 2 injection in tri-axial drained tests, due to the certainty of the occurrence of phase transition under this liquid Inlet and gas outlet condition. According to the test results, the apparent permeability calculated for liquid CO 2 injection using the proposed method is around 50% lower than that evaluated using the traditional method. This suggests the importance of the use of more accurate approaches such as that proposed under such situations. In addition, CO 2 permeability in siltstone is found to be significantly increased with increasing injection pressure, and increasing the injection pressure from 3 to 6 MPa (in the gas CO 2 region) caused the CO 2 permeability in the tested siltstone to be increased from 0.00102 to 0.00228 mD at 15 MPa confining pressure, which is related to the related pore structure modification in siltstone.
F L Eisele - One of the best experts on this subject based on the ideXlab platform.
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atmospheric measurements of sub 20 nm diameter particle chemical composition by thermal desorption chemical ionization mass spectrometry
Aerosol Science and Technology, 2004Co-Authors: James N Smith, Katharine F Moore, Peter H Mcmurry, F L EiseleAbstract:We report the first online measurements of the chemical composition of atmospheric aerosol in the 6–20 nm diameter range. These measurements were performed using the recently developed Thermal Desorption Chemical Ionization Mass Spectrometer (TDCIMS), and were made possible by recent sensitivity enhancements resulting from (a) the development of a unipolar charger optimized for high aerosol flow rates, and (b) an improved flow system in the TDCIMS Sample Inlet. Measurements of atmospheric aerosol in Boulder, CO revealed large concentration variations in most detected compounds. The most dominant observed compounds in the negative ion TDCIMS spectra were nitrate and sulfate, while in the positive ion spectra ammonium dominated all other observed compounds. Comparison with laboratory data suggests that particles are composed primarily of ammonium sulfate during times of relatively low ambient aerosol concentration.
