Field Intercomparison of Radiometers Used for Satellite Validation in the 400–900 nm Range

An intercomparison of radiance and irradiance ocean color radiometers (the second laboratory comparison exercise—LCE-2) was organized within the frame of the European Space Agency funded project Fiducial Reference Measurements for Satellite Ocean Color (FRM4SOC) May 8–13, 2017 at Tartu Observatory, Estonia. LCE-2 consisted of three sub-tasks: (1) SI-traceable radiometric calibration of all the participating radiance and irradiance radiometers at the Tartu Observatory just before the comparisons; (2) indoor, laboratory intercomparison using stable radiance and irradiance sources in a controlled environment; (3) outdoor, field intercomparison of natural radiation sources over a natural water surface. The aim of the experiment was to provide a link in the chain of traceability from field measurements of water reflectance to the uniform SI-traceable calibration, and after calibration to verify whether different instruments measuring the same object provide results consistent within the expected uncertainty limits. This paper describes the third phase of LCE-2: The results of the field experiment. The calibration of radiometers and laboratory comparison experiment are presented in a related paper of the same journal issue. Compared to the laboratory comparison, the field intercomparison has demonstrated substantially larger variability between freshly calibrated sensors, because the targets and environmental conditions during radiometric calibration were different, both spectrally and spatially. Major differences were found for radiance sensors measuring a sunlit water target at viewing zenith angle of 139° because of the different fields of view. Major differences were found for irradiance sensors because of imperfect cosine response of diffusers. Variability between individual radiometers did depend significantly also on the type of the sensor and on the specific measurement target. Uniform SI traceable radiometric calibration ensuring fairly good consistency for indoor, laboratory measurements is insufficient for outdoor, field measurements, mainly due to the different angular variability of illumination. More stringent specifications and individual testing of radiometers for all relevant systematic effects (temperature, nonlinearity, spectral stray light, etc.) are needed to reduce biases between instruments and better quantify measurement uncertainties

Laboratory Intercomparison of Radiometers Used for Satellite Validation in the 400–900 nm Range

An intercomparison of radiance and irradiance ocean color radiometers (The Second Laboratory Comparison Exercise—LCE-2) was organized within the frame of the European Space Agency funded project Fiducial Reference Measurements for Satellite Ocean Color (FRM4SOC) May 8–13, 2017 at Tartu Observatory, Estonia. LCE-2 consisted of three sub-tasks: 1) SI-traceable radiometric calibration of all the participating radiance and irradiance radiometers at the Tartu Observatory just before the comparisons; 2) Indoor intercomparison using stable radiance and irradiance sources in controlled environment; and 3) Outdoor intercomparison of natural radiation sources over terrestrial water surface. The aim of the experiment was to provide one link in the chain of traceability from field measurements of water reflectance to the uniform SI-traceable calibration, and after calibration to verify whether different instruments measuring the same object provide results consistent within the expected uncertainty limits. This paper describes the activities and results of the first two phases of LCE-2: the SI-traceable radiometric calibration and indoor intercomparison, the results of outdoor experiment are presented in a related paper of the same journal issue. The indoor experiment of the LCE-2 has proven that uniform calibration just before the use of radiometers is highly effective. Distinct radiometers from different manufacturers operated by different scientists can yield quite close radiance and irradiance results (standard deviation s < 1%) under defined conditions. This holds when measuring stable lamp-based targets under stationary laboratory conditions with all the radiometers uniformly calibrated against the same standards just prior to the experiment. In addition, some unification of measurement and data processing must be settled. Uncertainty of radiance and irradiance measurement under these conditions largely consists of the sensor’s calibration uncertainty and of the spread of results obtained by individual sensors measuring the same object

Statistical Optimization and Selective Separation of RDX and HMX Explosives by Using Binary Solvent Mixtures Containing Ethyl Acetate and Water

The present study introduces the application of a binary solvent of ethyl acetate and water for the selective separation of 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX). The effect of temperature and weight percent of ethyl acetate in water on the solubility of RDX and HMX over a temperature range of 273.15 K to 363.15 K and 70.0 wt.% to 100.0 wt.% ethyl acetate in water mixtures were modelled and optimized using a central composite design (CCD) and response surface methodology (RSM) in Minitab (ver. 16) software. Multiple regression analysis and analysis of variance (ANOVA) showed that the predicted results were in good agreement with the experimental data. The enthalpies of dissolution and mixing of the materials were determined experimentally from the solubility data. The experimental results showed that the solubility ratio of RDX to HMX can change 6.53- to 16.55-fold, indicating a much lower solubility of HMX in this binary solvent, for a relatively selective separation of RDX and HMX mixtures. Separation experiments under optimized conditions showed that 98.3% of the RDX impurity in HMX was recovered in the first precipitation with an HMX purity of > 99.5% as characterized by high performance liquid chromatography (HPLC)

Non-isothermal Studies on the Thermal Decomposition of C4 Explosive Using the TG/DTA Technique

The thermal behaviour of energetic materials is very important for their safe production, storage, handling and even demilitarization. In this work, the thermal behaviour and decomposition kinetics of conventional C4 plastic explosive has been studied experimentally by a non-isothermal thermogravimetric (TG)/differential thermal analysis (DTA) technique at different heating rates (2, 4, 6 and 8 °C·min-1). The kinetic triplet of activation energy, frequency factor and model of thermal decomposition of this compound has been evaluated via model-fitting and model-free methods. The results show a single thermal decomposition process for C4, with the model of integral function (g(α)) of [(1−α)-1/3 −1]2 and differential function (f(α)) of [(1−α)2/3(3α−3)/2(1−α)1/3−2], indicating a 3-dimensional diffusion mechanism. In addition, Ea values of 207.1 ± 17.3, and 241 kJ·mol-1, by using the isoconversional model-free modified Kissinger-Akahira-Sunose (KAS) and the Kissinger method, respectively, were obtained for the conversion interval of 0.3-0.7. The C4 matrix shows a significant effect on the activation energy distribution of pure RDX

Pattern of substance use among schoolchildren in Palestine: a cross-sectional study

Abstract Background Tobacco smoking, alcohol use, and illicit drug use are significant health, psychological, and social problems among youth in Palestine. The aim of this study was to provide insight into the extent and the pattern of psychoactive substance use among schoolchildren in the West Bank in Palestine. A cross-sectional study in 16 schools was conducted in 2016. Eight hundred seventy-seven students of 10th grade were chosen randomly. Modified self-administrated questionnaire from Monitor the Future Study and European school survey project on alcohol and other drugs was used. Results The most current substance used by schoolchildren was tobacco (40.6%), followed by alcohol (3.2%) and illicit drugs (2.0%). Around 59.7, 7.9, and 2.9% of the schoolchildren had tried, at least once in their lifetime, tobacco, alcohol, and illicit drugs, respectively. Moreover, 11.1% of them who had not yet tried a substance intends to smoke tobacco, 1.4% intends to drink alcohol, and 0.3% intends to try illicit drugs. Curiosity and experience was the most frequent motivation for using these substances. The mean age of initiation was 12 years for smoking and 14 years for drinking alcohol or using illicit drugs. Most of the illicit drug users (78.3%) had tried more than one illicit drug or more than one substance at the same time. Cannabis and synthetic cannabinoids followed by amphetamines were the most commonly used drugs. Around 78.8%, 37.6%, and 27.6% agreed that tobacco, alcohol, and illicit drugs, respectively, were easily accessible in their communities. Work was significantly associated with increased risk for substance use across various substances. Conclusion Many factors had determined the danger of using psychoactive substances by Palestinian schoolchildren including the initiation age, the availability, the type of the substances used, and the frequency of the use, and using multiple substances at the same time. Curiosity and experience, peer pressure, families, and working were the most important motives. Health care professionals, clinicians, and ministries of education, health, and labor have key responsibilities in preventing substance use among youth and need to develop more effective prevention and cessation strategies. The Palestinian National Authority needs to make more efforts in smoking legislation regulating the age of access and smoking for youths and adults

A Novel Method for the Prediction of the Impact Sensitivity of Quaternary Ammonium-based Energetic Ionic Liquids

Impact sensitivity is an important safety parameter for the assessment of the hazards of working with new energetic compounds including ionic molecular energetic materials. This paper introduces two novel simple correlations to assess the impact sensitivity of quaternary ammonium-based energetic ionic liquids, which are based on the elemental composition of cations and anions divided by the molecular weight of a desired ionic liquid as well as the contribution of specific cations and anions. For 72 ionic molecular systems as a training set, the root mean square (rms) deviations of predictions for these models relative to experiment are 11 J and 6 J, respectively. The reliability of the models has also been tested for a further three ionic compounds containing complex structures, which give rms deviations of 12 J and 6 J, respectively, with respect to the measured data. The results of the current study indicate that the accuracy of this novel method for the prediction of the impact sensitivity of quaternary ammonium-based energetic ionic liquids is not necessarily enhanced by greater complexity

Novel High-Nitrogen Content Energetic Compounds with High Detonation and Combustion Performance for use in Plastic Bonded Explosives (PBXs) and Composite Solid Propellants

Five novel high-nitrogen content (N>50%) derivatives of tetrazole are introduced in the study reported here. The assessment of various properties of these compounds were performed, which include physicothermal properties (crystal density, condensed phase heat of formation, melting point, enthalpy of fusion and entropy of fusion), detonation performance (velocity and pressure of detonation, detonation temperature and power), sensitivity with respect to external stimuli (impact, shock, friction and electric spark) and combustion performance (specific impulse). The predicted results of these compounds are compared with dihydroxylammonium 5,5’-bistetrazole-1,1’-diolate (TKX-50) and octanitro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) as a high performance ionic salt and a neutral explosive, respectively. The novel energetic compounds were found to have higher detonation and combustion performance than either TKX-50 or HMX. The new explosives are therefore good candidates to obtain high detonation and combustion performance in plastic bonded explosives (PBXs) and composite solid propellants, respectively

Modelling of the Effect of Concentrated Nitration Conditions on the Efficiency of the Production of ,7-Dinitro-1,3,5,7-tetraazabicyclo[3,3,1]nonane (DPT)

3,7-Dinitro-1,3,5,7-tetraazabicyclo[3,3,1]nonane (DPT) is one of the most important intermediates in the synthesis of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX). A suitably modified Bachmann process, nitrolysis of solid hexamine in the presence of ammonium nitrate-nitric acid and acetic anhydride on a laboratory scale, is introduced to increase the efficiency, production capacity and purity of the DPT produced. Various quantitative and qualitative analytical methods were used for the identification and quality control of the product. A central composite design (CCD) of experiments was used to optimize the production process, increasing the production capacity, reducing the amount of acetic acid as the reaction medium to a suitable limit, and examining the effects of the main factors impacting on the efficiency of the nitration, e.g. the volume of ammonium nitrate-nitric acid solution, nitration temperature reactor addition time and volume of acetic anhydride. The overall results indicated that DPT was obtained with an efficiency of 64.58% and a production capacity of 20.77 (100 g·mL−1)

Increasing the Efficiency of the Production of 1,3,5,7-Tetranitro-1,3,5,7-tetrazocane (HMX)

This work introduces a suitable method for the optimization of selective synthesis of 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX), as one of the most well-known high explosives, from the aspects of production capacity and efficiency, by nitration of 3,7-dinitro-1,3,5,7-tetraazabicyclo[3,3,1]nonane (DPT). The effective factors in the productive capacity of HMX and the synthesis of a product from raw DPT with high capacity, purity, and efficiency have been identified. The required qualitative and quantitative analyses were performed for the identification and confirmation of the product quality. In order to optimize the process of increasing the capacity of HMX production and evaluation of the effects of different factors on the production capacity, a series of experiments were designed and performed by using central composite design (CCD). Practical studies and statistical analyses showed good conformity between the model presented and the actual results, allowing the selective production of HMX with an efficiency of greater than 70% and a high production capacity

Modelling of the Effect of Concentrated Nitration Conditions on the Efficiency of the Production of 3,7-Dinitro-1,3,5,7-tetraazabicyclo[3,3,1]nonane (DPT)

3,7-Dinitro-1,3,5,7-tetraazabicyclo[3,3,1]nonane (DPT) is one of the most important intermediates in the synthesis of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX). A suitably modified Bachmann process, nitrolysis of solid hexamine in the presence of ammonium nitrate-nitric acid and acetic anhydride on a laboratory scale, is introduced to increase the efficiency, production capacity and purity of the DPT produced. Various quantitative and qualitative analytical methods were used for the identification and quality control of the product. A central composite design (CCD) of experiments was used to optimize the production process, increasing the production capacity, reducing the amount of acetic acid as the reaction medium to a suitable limit, and examining the effects of the main factors impacting on the efficiency of the nitration, e.g. the volume of ammonium nitrate-nitric acid solution, nitration temperature reactor addition time and volume of acetic anhydride. The overall results indicated that DPT was obtained with an efficiency of 64.58% and a production capacity of 20.77 (100 g·mL−1)