Standard Atmospheric Conditions Research Articles

Air density dependence of the PTW 34013 ionization chamber for soft X-ray

Introduction It has been proved that some ionization chambers, when measuring low energy brachytherapy or soft X-ray sources, show a dependence with the air density that it is not entirely corrected with the usual pressure/temperature correction factor, k TP . This is due to the chamber dimensions and materials forming it. Purpose To determine if the response of PTW 34013 chamber, used for dose measurements in superficial radiotherapy, is fully corrected with k TP or a residual air density dependence remains. Materials and methods Measurements for 70 and 200 kVp X-ray beams, generated by a MAXISHOT.200 cabinet, have been performed using a pressurized chamber. Raw data have been corrected with k TP and normalized to its value in standard atmospheric conditions (760 mmHg and 20 °C). Results The corrected measurements for both beams still show a linear dependence with the normalized density ρ / ρ 0 , ρ 0 being the density in standard atmospheric conditions. When the air density is below ρ 0 , k TP undercorrects the measurement, and the contrary occurs when ρ > ρ 0 . In our city, with 700 m AMSL, usual atmospheric conditions will cause 1.2% undercorrection for the 70 kV beam and 2.5% for the 200 kV beam. Conclusion Despite its dimensions, the dependence of the PTW 34013 ionization chamber with the air density is not fully corrected with k TP . The weather or the altitude of the place where measurements are carried out will require an additional correction to reach the accuracy level required in radiotherapy. Disclosure We thank to PTW for material support.

Combustion characteristics of butanol isomers in multiphase droplet configurations

This study reports results of experiments on the isolated droplet burning characteristics of butanol isomers (n-, iso-, sec-, and tert-) under standard atmosphere conditions in an environment that promotes spherical combustion. The data are compared with predictions from a detailed numerical model (DNM) that incorporates complex combustion chemistry, radiative heat transfer, temperature dependent variable fluid properties, and unsteady gas and liquid transport. Computational predictions are generated using the high temperature kinetic models of Sarathy et al. (2012) and Merchant et al. (2013).The experiments were performed in a free-fall facility to reduce the effects of buoyancy and produce spherical droplet flames. Motion of single droplets with diameters ranged from 0.52mm to 0.56mm was eliminated by tethering them to two small-diameter SiC filaments (∼14µm diameter). In all the experiments, minimal sooting was observed, offering the opportunity for direct comparison of the experimental measurements with DNM predictions that neglect soot kinetics.The experimental data showed that the burning rates of iso- and sec-butanol are very close to that of n-butanol, differing only in flame structure. The flame stand-off ratios (FSR) for n-butanol flames are smaller than those for the isomers, while tert-butanol flames exhibited the largest FSR. DNM predictions based upon the kinetic model of Sarathy et al. over-predict the droplet burning rates and FSRs of all the isomers except n-butanol. Predictions using a kinetic model based upon the work of Merchant et al. agree much better with the experimental data, though relatively higher discrepancies are evident for tert-butanol simulation results. Further analyses of the predictions using the two kinetic models and their differences are discussed. It is found that the disparity in transport coefficients for isomer specific species for Sarathy et al. model fosters deviation in computational predictions against these newly acquired droplet combustion data presented in this study.

Effects of Processing Parameters on Zinc Oxide Thin Films Prepared by Single Solution Deposition

ABSTRACTZinc oxide thin films were prepared via the sol-gel spin-coating method with the use of a spin processor. The film’s annealing parameters were varied to study their impact on the final film morphology and electrical properties. Characterization of the structural properties of the samples was carried on a X-ray diffractometer (XRD) and scanning electron microscopy. Electrical characterization was obtained with the use of a four point probe. Optical characterization of the samples was carried on a UV-Vis-NIR Spectrophotometer. Samples annealed under a cover are observed to have a higher transmission percentage on the visible light range while having a very small grain size and small relative resistivity. Samples annealed under standard atmospheric conditions show a larger grain size and resistivity, and correlated to it, a smaller transmission percentage. Samples annealed under vacuum prove to have a much more reduced optical, electrical, and structural properties when compared to the rest of the samples.

Effects of doping Al2O3/2SiO2 on the structure and properties of magnesium matrix ceramic

To improve the sintering properties and the thermal shock resistance of magnesium matrix ceramic, this work used micron-sized MgO as the main raw material and nano-Al2O3 and SiO2 as additives. Magnesium matrix ceramic was doped with different amounts of Al2O3 and SiO2 (Al2O3 and SiO2 at a molar ratio of 1:2) and sintered under standard atmospheric conditions. The effect of Al2O3/2SiO2 doping amounts on sintering properties, thermal shock resistance, phase composition, and microstructure of composite ceramic materials were investivigated. The results suggested that introducing Al2O3/2SiO2 could improve the sintering properties of magnesium matrix ceramic. The grain boundary migration of its periclase phase could be hindered by the magnesium aluminate spinel and forsterite formed by solid reaction including Al2O3, SiO2 addition, and the MgO itself. Furthermore, according to the mechanism of thermal expansion mismatching, with increasing Al2O3/2SiO2 addition, thermal shock times increased significantly, the number of ceramic internal micro-cracks increased after the thermal shock and the material fracture surface energy was improved. It is found that the way of transgranular combining intergranular fractures can decrease the stress concentration at the crack tips and hinder crack propagation. The secondary phase particles deflected matrix internal micro-cracks and the crack propagation path length thus increased, residual stress field were subjected to interference and energy dissipation mechanisms improved. Meanwhile, thermal shock times for the material were enhanced and the degree of densification increased with increasing sintering temperature.

Nanoparticulated hydrophobic CdO coatings deposited by microwave procedure

A novel and inexpensive way to deposit nanostructured cadmium oxide (CdO) coatings is described. Metallic Cd is evaporated by heating a silicon carbide crucible, via microwave radiation at standard atmosphere conditions. The Cd vapour rises from the crucible and reacts with the atmospheric oxygen depositing on a glass substrate. CdO coating is homogeneously distributed above the glass surface and it presents a well-defined cubic-shaped nanostructure. The as-deposited CdO coatings showed good hydrophobic properties and achieved symmetric contact angles of 112°. The hydrophobic behaviour was lost after a 75 min of heat treatment at 723 K.

Optical emission monitoring for defocusing laser percussion drilling

This paper presents a novel method for controlling the laser-drilling process for a hole by monitoring induced plasma emission. The variation of light brightness from laser-induced plasma is used as an indicator to control laser percussion drilling. Through on-line plasma emission acquisition and analysis, we obtain the positive association between the increased depth and the optical signal output. A coaxial photodiode is used to estimate the brightness levels of laser-induced plasma. The above constitute an inexpensive and practical on-line feedback system that can be easily implemented in the laser systems. All of the processing work is performed in air under standard atmospheric conditions without gas assist. The acquired signal for drilling could also be used as an input to a focus point process control scheme. Moreover, the technology demonstrates the feasibility to develop an automated laser micromachining system. Experimental results show that drilling efficiency was increased 47% by applying the proposed defocusing laser percussion drilling.

Corrosion testing of zirconia, beryllia and magnesia ceramics in molten alkali metal carbonates at 900 °C

An electrochemical cell containing molten Li2CO3–Li2O at 900 °C has been proposed for the conversion of the greenhouse gas CO2 to CO for chemical energy storage. In the current work, we have examined the corrosion resistance of zirconia, beryllia and magnesia ceramics at 900 °C in the Li2CO3–Li2O and Li–Na–K carbonate eutectic mixtures to identify suitable electrically insulating materials. Conclusions regarding material stability were based on elemental analysis of the melt, primarily via X-ray photoelectron spectroscopy, a particularly sensitive technique. It was found that magnesia is completely stable for at least 33 h in a Li2CO3–Li2O melt, while a combined lithium titanate/lithium zirconate layer forms on the zirconia ceramic as detected by XRD. Under the same melt conditions, beryllia shows considerable leaching into solution. In a Li–Na–K carbonate eutectic mixture containing 10.2 mol% oxide at 900 °C under standard atmospheric conditions, magnesia showed no signs of degradation. Stabilization of the zirconia content of the eutectic mixture at 0.01–0.02 at% after 2 h is explained by the formation of a lithium zirconate coating on the ceramic. On the basis of these results, we conclude that only magnesia can be satisfactorily used as an insulating material in electrolysis cells containing Li2CO3–Li2O melts.

Atmospheric extinction in solar tower plants: absorption and broadband correction for MOR measurements

Abstract. Losses of reflected Direct Normal Irradiance due to atmospheric extinction in concentrated solar tower plants can vary significantly with site and time. The losses of the direct normal irradiance between the heliostat field and receiver in a solar tower plant are mainly caused by atmospheric scattering and absorption by aerosol and water vapor concentration in the atmospheric boundary layer. Due to a high aerosol particle number, radiation losses can be significantly larger in desert environments compared to the standard atmospheric conditions which are usually considered in ray-tracing or plant optimization tools. Information about on-site atmospheric extinction is only rarely available. To measure these radiation losses, two different commercially available instruments were tested, and more than 19 months of measurements were collected and compared at the Plataforma Solar de Almería. Both instruments are primarily used to determine the meteorological optical range (MOR). The Vaisala FS11 scatterometer is based on a monochromatic near-infrared light source emission and measures the strength of scattering processes in a small air volume mainly caused by aerosol particles. The Optec LPV4 long-path visibility transmissometer determines the monochromatic attenuation between a light-emitting diode (LED) light source at 532 nm and a receiver and therefore also accounts for absorption processes. As the broadband solar attenuation is of interest for solar resource assessment for concentrated solar power (CSP), a correction procedure for these two instruments is developed and tested. This procedure includes a spectral correction of both instruments from monochromatic to broadband attenuation. That means the attenuation is corrected for the time-dependent solar spectrum which is reflected by the collector. Further, an absorption correction for the Vaisala FS11 scatterometer is implemented. To optimize the absorption and broadband correction (ABC) procedure, additional measurement input of a nearby sun photometer is used to enhance on-site atmospheric assumptions for description of the atmosphere in the algorithm. Comparing both uncorrected and spectral- and absorption-corrected extinction data from 1-year measurements at the Plataforma Solar de Almería, the mean difference between the scatterometer and the transmissometer is reduced from 4.4 to 0.57 %. Applying the ABC procedure without the usage of additional input data from a sun photometer still reduces the difference between both sensors to about 0.8 %. Applying an expert guess assuming a standard aerosol profile for continental regions instead of additional sun photometer input results in a mean difference of 0.8 %. Additionally, a simulation approach which just uses sun photometer and common meteorological data to determine the on-site atmospheric extinction at surface is presented and corrected FS11 and LPV4 measurements are validated with the simulation results. For T1 km equal to 0.9 and a 10 min time resolution, an uncertainty analysis showed that an absolute uncertainty of about 0.038 is expected for the FS11 and about 0.057 for the LPV4. Combining both uncertainties results in an overall absolute uncertainty of 0.068 which justifies quite well the mean RMSE between both corrected data sets. For yearly averages several error influences average out and absolute uncertainties of 0.020 and 0.054 can be expected for the FS11 and the LPV4, respectively. Therefore, applying this new correction method, both instruments can now be utilized to sufficiently accurately determine the solar broadband extinction in tower plants.

Study on moisture absorption and sweat discharge of honeycomb polyester fiber

The moisture absorption and liberation properties of honeycomb polyester fiber were studied in order to understand its moisture absorption and sweat discharge. Through testing moisture absorption and liberation regains of honeycomb polyester fiber and normal polyester fiber in standard atmospheric conditions, their moisture absorption and liberation curves were depicted, and the regression equations of moisture regains to time during their reaching the balance of moisture absorption and moisture liberation were obtained according to the curves. Their moisture absorption and liberation rate curves were analyzed and the regression equations of the rates to time were obtained. The results shows that the moisture regain of honeycomb polyester fiber is much bigger than the normal polyester fiber's, and the initial moisture absorption and moisture liberation rates of the former are much higher than the latter's, so that the moisture absorbance and sweat discharge of honeycomb polyester fiber are excellent.

A Practical Split-Window Algorithm for Retrieving Land Surface Temperature from Landsat-8 Data and a Case Study of an Urban Area in China

This paper proposes a practical split-window algorithm (SWA) for retrieving land surface temperature (LST) from Landsat-8 Thermal Infrared Sensor (TIRS) data. This SWA has a universal applicability and a set of parameters that can be applied when retrieving LSTs year-round. The atmospheric transmittance and the land surface emissivity (LSE), the essential SWA input parameters, of the Landsat-8 TIRS data are determined in this paper. We also analysed the error sensitivity of these SWA input parameters. The accuracy evaluation of the proposed SWA in this paper was conducted using the software MODTRAN 4.0. The root mean square error (RMSE) of the simulated LST using the mid-latitude summer atmospheric profile is 0.51 K, improving on the result of 0.93 K from Rozenstein (2014). Among the 90 simulated data points, the maximum absolute error is 0.99 °C, and the minimum absolute error is 0.02 °C. Under the Tropical model and 1976 US standard atmospheric conditions, the RMSE of the LST errors are 0.70 K and 0.63 K, respectively. The accuracy results indicate that the SWA provides an LST retrieval method that features not only high accuracy but also a certain universality. Additionally, the SWA was applied to retrieve the LST of an urban area using two Landsat-8 images. The SWA presented in this paper should promote the application of Landsat-8 data in the study of environmental evolution.

On-line monitoring of laser-drilling process based on coaxial machine vision

This paper presents a novel method for monitoring the laser-drilling process for a hole by using machine vision. Through on-line image acquisition and analysis during the laser-drilling processes, we could simultaneously obtain correlations between the machining processes and the analyzed images. The depths of laser-machined holes could be estimated on-line by using the machine vision method. Therefore, an inexpensive on-line inspection system was developed to increase productivity. All of the processing work was performed in air under standard atmospheric conditions with gas assist. A correlation between the area of radiation emitted from the vaporized material and the depth of the hole was derived. The results indicate that the estimated depths of the laser-drilled holes were linearly proportional to the thresholded image area, with a high degree of confidence. This research provides a novel online machine vision-based method for estimating the depths of laser-drilled holes.

Daytime measurements of atmospheric temperature profiles (2–15 km) by lidar utilizing Rayleigh–Brillouin scattering

In this Letter, we report on a novel method for measuring atmospheric temperature profiles by lidar during daytime for heights of 2-15.3 km, with a vertical resolution of 0.3-2.2 km, using Rayleigh-Brillouin scattering. The measurements are performed by scanning a laser (λ=355 nm) over a 12 GHz range and using a Fabry-Pérot interferometer as discriminator. The temperature is derived by using a new analytical line shape model assuming standard atmospheric pressure conditions. Two exemplary temperature profiles resulting from measurements over 14 and 27 min are shown. A comparison with radiosonde temperature measurements shows reasonable agreement. In cloud-free conditions, the temperature difference reaches up to 5 K within the boundary layer, and is smaller than 2.5 K above. The statistical error of the derived temperatures is between 0.15 and 1.5 K.

Four-dimensional reflectivity data comparison between two ground-based radars: methodology and statistical analysis

A methodology is proposed to compare radar reflectivity data obtained from two partially overlapping ground-based radars in order to explain relative differences in radar-rainfall products and establish sound merging procedures for multi-radar observing networks. To identify radar calibration differences, radar reflectivity is compared for well-matched radar sampling volumes viewing common meteorological targets. Temporal separation and three-dimensional matching of two different sampling volumes were considered based on the original polar coordinates of radar observation. Since the proposed method assumes radar beam propagation under standard atmospheric conditions, anomalous propagation cases were eliminated from the analysis. The reflectivity comparison results show systematic differences over time, but the variability of these differences is surprisingly large due to the sensitive nature of the radar reflectivity measurement.Editor D. Koutsoyiannis/Z.W. Kundzewicz; Guest editor R.J. MooreCitation Seo, B.-C., Krajewski, W.F., and Smith, J.A., 2013. Four-dimensional reflectivity data comparison between two ground-based radars: methodology and statistical analysis. Hydrological Sciences Journal, 59 (7), 1312–1326. http://dx.doi.org/10.1080/02626667.2013.839872

Comparison of the Emulsion Mixing and In Situ Polymerization Techniques for Synthesis of Water‐Borne Reduced Graphene Oxide/Polymer Composites: Advantages and Drawbacks

Water‐borne reduced graphene oxide (rGO)/polymer composites have been synthesized by emulsion mixing and in situ polymerization. The main challenge is to synthesize colloidally stable hybrid latexes that are able to produce composite films by water evaporation at standard atmospheric conditions for their possible application as electrically conductive coatings. The selected polymer system is composed from poly(methyl metacrylate/butyl acrylate) in 50/50 wt% ratio in order to obtain glass transition temperature of the final film lower than the room temperature. The polymer is joined with rGO stable dispersions, which are prepared by reduction of GO in the presence of polyvynil pyrrolidone (PVP). The latex blends are composed of weakly bonded rGO platelets with polymer particles by the presence of PVP, whereas the covalent bonds between the polymers and the rGO in the in situ hybrid latexes are established. Both procedures result in stable hybrid latexes, from which layered composites are obtained by slow water evaporation. The composite blends present better self‐organization of rGO, tendency of segregated network formation, and electrically conductive properties. The in situ composites present decreased aggregation of rGO, uniformly distributed rGO in the polymeric matrix and lower conductivity.

Dependence with air density of the response of the PTW SourceCheck ionization chamber for low energy brachytherapy sources

Air-communicating well ionization chambers are commonly used to assess air kerma strength of sources used in brachytherapy. The signal produced is supposed to be proportional to the air density within the chamber and, therefore, a density-independent air kerma strength is obtained when the measurement is corrected to standard atmospheric conditions using the usual temperature and pressure correction factor. Nevertheless, when assessing low energy sources, the ionization chambers may not fulfill that condition and a residual density dependence still remains after correction. In this work, the authors examined the behavior of the PTW 34051 SourceCheck ionization chamber when measuring the air kerma strength of (125)I seeds. Four different SourceCheck chambers were analyzed. With each one of them, two series of measurements of the air kerma strength for (125)I selectSeed(TM) brachytherapy sources were performed inside a pressure chamber and varying the pressure in a range from 747 to 1040 hPa (560 to 780 mm Hg). The temperature and relative humidity were kept basically constant. An analogous experiment was performed by taking measurements at different altitudes above sea level. Contrary to other well-known ionization chambers, like the HDR1000 PLUS, in which the temperature-pressure correction factor overcorrects the measurements, in the SourceCheck ionization chamber they are undercorrected. At a typical atmospheric situation of 933 hPa (700 mm Hg) and 20 °C, this undercorrection turns out to be 1.5%. Corrected measurements show a residual linear dependence on the density and, as a consequence, an additional density dependent correction must be applied. The slope of this residual linear density dependence is different for each SourceCheck chamber investigated. The results obtained by taking measurements at different altitudes are compatible with those obtained with the pressure chamber. Variations of the altitude and changes in the weather conditions may produce significant density corrections, and that effect should be taken into account. This effect is chamber-dependent, indicating that a specific calibration is necessary for each particular chamber. To our knowledge, this correction has not been considered so far for SourceCheck ionization chambers, but its magnitude cannot be neglected in clinical practice. The atmospheric pressure and temperature at which the chamber was calibrated need to be taken into account, and they should be reported in the calibration certificate. In addition, each institution should analyze the particular response of its SourceCheck ionization chamber and compute the adequate correction factors. In the absence of a suitable pressure chamber, a possibility for this assessment is to take measurements at different altitudes, spanning a wide enough air density range.

A numerical study on the ability to predict the heat release rate using CH* chemiluminescence in non-sooting counterflow diffusion flames

Numerical studies on 1-D, non-sooting counterflow diffusion flames were performed to determine the precision with which the total heat release rate can be calculated using light emission, namely, chemiluminescence, from the reaction zone. A detailed reaction mechanism, incorporating sub-reaction models for excited state radicals (CH* and OH*, where * denotes the excited state), was employed in this study. A set of 1-D, steady state conservation equations was solved under standard atmospheric conditions over a counterflow configuration utilizing the CHEMKIN-PRO package. A variety of fuels (CH4 and C3H8), velocities (0.1m/s − near the extinction condition), diluents (N2, H2O, CO2, and Ar), detailed reaction mechanisms for C1–C3 hydrocarbons (GRI-Mech 3.0, Hai Wang’s-, and San Diego-mechanism), different sub-reaction models for excited radicals, and excited radical transport properties were examined for the current purpose. It was found that a one-to-one correlation between total chemiluminescence from CH* and the total heat release rate cannot be sustained when the flame experiences a relatively high stretch and dilution, even though the condition is still far away from extinction. This trend is consistent with the different types of fuels, and it is understood that the reduction of the ethynyl radical (C2H), a potential precursor of CH*, is the main cause of the one-to-one correlation not being sustained. To this end, it was concluded that the observable light emission can only be used to predict the total heat release rate when non-sooting diffusion flames exist under velocity conditions from 0.1m/s to 1.5m/s. In other words, the chemiluminescence intensity does not always correlate with the total heat release rate of highly stretched flames found in practical combustors.

Aerothermodynamics of a hypersonic projectile with a double-disk aerospike

AbstractThe use of aerospikes at the nose of a hypersonic vehicle can substantially reduce its drag; however, the associated heat flux at the reattachment point is very high for turbulent flows. In this paper, the aerothermodynamics of a generic projectile model represented by a hemisphere- cylinder, fitted axisymmetrically with an aerospike at the nose is investigated numerically with a commercially available Navier Stokes Solver. The base model is a hemisphere-cylinder with a diameter of 40mm and an overall length of 70mm. An aerospike protrudes axisymmetrically at the nose of the base model and has a hemispherical cap from which another aerospike protrudes which again has a hemispherical cap, thus forming a double-disk aerospike. Compressible, axisymmetric Navier-Stokes Equations are solved for turbulent hypersonic flow of thermally perfect air with free stream conditions of Mach No 6·2 at standard sea level atmospheric conditions. The results for the model with double-disk aerospikes are compared with those of hemisphere-cylinder without aerospike. The results suggest that the use of double-disk aerospike can favourably reduce the turbulent reattachment heat flux along with suitable drag reduction of the main body.

Dropwise chains as the elements of water fog spatial structure

Video images of water fog drops were acquired under standard atmospheric conditions with weak turbulence of the environment. Pair correlation functions of the drops were performed and traces of the spatial arrangement of the drops inside the fog determined. The fog structure carriers are the drop chains with a fixed interdroplet distance. The possible influence of the drop chains on the shear viscosity and fog surface tension has been analysed.

Performance Evaluation of Insulators Using Flashover Voltage and Leakage Current

Every few years, some samples of insulators should be taken from overhead lines to monitor their operational condition. Since most insulators are not installed in standard atmospheric conditions, their performance evaluation using flashover voltage needs a correction factor to obtain the real breakdown voltage from test results. In this article, the validity of IEC spark over atmospheric correction factor for this purpose was studied. Moreover, the effect of pollution on the leakage current of silicone rubber insulators has been evaluated. Finally, the results have been analyzed to find appropriate correction factors and to discover the relationship between insulators' leakage current and their status.

External Electric Field-Assisted Laser Percussion Drilling for Highly Reflective Metals

In this study, an external electric field was employed during the laser percussion drilling on highly reflective materials. The laser-produced plasma was sputtered substantially, and the charged ions in the plasma plume were drawn by the electrodes. Different configurations of plate electrodes were proposed and investigated in this work to provide a simple, low-cost method that allows expelling the laser-induced plasma during the percussion drilling process. The electric field resulted from the potential that was applied across the two electrodes. This electrical perturbation produced a uniform electric field when the laser-generated plasma was created in the plane plate-charged capacitor. The electric field with different electrode configurations applied to the charged particles that are carrying the electrons was also simulated in this work. All processing work was performed in air under standard atmospheric conditions and in the absence of assisting process gas. The depth of the holes drilled when various types of electrode configurations were used was measured, and the results were used to evaluate the percussion drilling rate. Results show that vaporized debris is expelled by the applied electric field; hence, in optimal configuration the penetration depth can be increased by up to 91.1%.