A Rasch Analysis of Item Quality of the Chemical Literacy Assessment for Investigating Student’s Chemical Literacy on Chemical Rate Concepts

<p style="text-align: justify;">Assessment is a topic that continues to be developed in science education research. Assessment evaluates not only students' cognitive abilities but also their thinking skills. Therefore, in this study, an assessment that could measure students' chemical literacy was developed. Chemical literacy is a thinking skill that students must develop as part of their chemistry learning. The goal of this study was to assess item' quality, as well as student’ chemical literacy on the concept of chemical rate. The Rasch model was employed to analyze the data in this study. The results of this study depict that the developed assessment had sufficient reliability and validity to be used to assess students' chemical literacy. Furthermore, the analysis of the students’ responses to the items revealed that many students did not understand or were unaware of the context presented. These findings suggest that students' chemical literacy in the material for the reaction rate is still lacking and needs to be improved. As a result, the teacher's role in assisting students in improving their chemical literacy through chemistry learning is critical.</p>

Atmospheric phenomena affecting the methane lifetime on Mars

&lt;p&gt;We investigate a range of atmospheric phenomena concerning their potential to address the Martian methane lifetime discrepancy. This refers to the over-estimate of the modelled lifetimes compared to observations by a factor of up to six hundred. We apply a newly developed atmospheric photochemical model where we vary in a Monte Carlo approach the chemical rate and Eddy mixing coefficients within their current uncertainties. We also investigate the effect of air shower events due to galactic cosmic rays and solar cosmic rays. Our results suggest that the current uncertainty in chemical rates and transport together with seasonal changes in the water column can likely account for up to a factor of about thirty in the Mars methane lifetime discrepancy whereas the air shower effects are likely to be of secondary importance.&lt;/p&gt;

Dichotomy between heterotypic and homotypic interactions by a common chemical law

This study introduces a general correction to the classical chemical rate law to avoid overestimating the frequency of homotypic interactions.

Chromatin stability generated by stochastic binding and unbinding of cross-linkers at looping sites revealed by Markov models

Chromatin loops inside the nucleus can be stable for a very long time, which remains poorly understood. Such a time is crucial for chromatin organization maintenance and stability. We explore here several physical scenarios, where loop maintenance is due to diffusing cross-linkers such as cohesin and CTCF that can bind and unbind at the base of chromatin loops. Using a Markov chain approach to coarse-grain the binding and unbinding, we consider that a stable loop disappears when the last cross-linker (CTCF or cohesin molecule) is unbound. We derive expressions for this last passage times that we use to quantify the loop stability for various value parameters, such as the chemical rate constant or the number of cross-linkers. The present analysis suggests that this binding and unbinding mechanism is sufficient to guarantee that there are always cross-linkers in place because they generate a positive feed-back mechanism that stabilizes the loop over long-time. To conclude, we propose that tens to hundreds cross-linkers per loop are sufficient to guarantee the loop stability in the genome over a cell cycle.

Numerical Investigation of the Chemical Effect and Inhibition Effect Improvement of C3H2F3Br (2-BTP) Using the Perfectly Stirred Reactor Model

The overall chemical rate and chemical effect of CF3Br, 2-BTP and 2-BTP/CO2 with hydrocarbon flames are calculated using the perfectly stirred reactor (PSR) model. The chemical effects of CF3Br with CH4/air flames always inhibit combustion. The chemical saturation concentration of CF3Br in stoichiometric and lean (Φ = 0.6) CH4/air flames at 298 K and 1 bar is roughly 2.5% and 0.8%, respectively. The overall chemical rate of 2-BTP with moist C3H8/air flames is always less than the uninhibited condition and fluctuates with sub-inerting agent additions. The net chemical effect variation of 2-BTP is more complicated than experimented and calculated flame speeds with 2-BTP added to lean hydrocarbon flames. There are negative chemical effects (chemical combustion effects) with certain sub-inerting 2-BTP concentrations (0.015 ≤ Xa ≤ 0.034), which result in the experimented unwanted combustion enhancement in lean moist C3H8/air flames. CO2 can obviously improve the inhibition effect of 2-BTP in lean moist C3H8/air flames, driving negative chemical effects (enhance combustion) into positive chemical effects (inhibit combustion) with lean moist C3H8/air flames. No enhanced combustion would occur with the blends (2-BTP/CO2) when CO2 addition is larger than 4% in Φ = 0.6 moist C3H8/air flames at 298 K and 1 bar.

Impact of uncertainties in inorganic chemical rate constants on tropospheric composition and ozone radiative forcing

Chemical rate constants determine the composition of the atmosphere and how this composition has changed over time. They are central to our understanding of climate change and air quality degradation. Atmospheric chemistry models, whether online or offline, box, regional or global, use these rate constants. Expert panels evaluate laboratory measurements, making recommendations for the rate constants that should be used. This results in very similar or identical rate constants being used by all models. The inherent uncertainties in these recommendations are, in general, therefore ignored. We explore the impact of these uncertainties on the composition of the troposphere using the GEOS-Chem chemistry transport model. Based on the Jet Propulsion Laboratory (JPL) and International Union of Pure and Applied Chemistry (IUPAC) evaluations we assess the influence of 50 mainly inorganic rate constants and 10 photolysis rates on tropospheric composition through the use of the GEOS-Chem chemistry transport model. We assess the impact on four standard metrics: annual mean tropospheric ozone burden, surface ozone and tropospheric OH concentrations, and tropospheric methane lifetime. Uncertainty in the rate constants for NO2 + OH →M HNO3 and O3 + NO → NO2 + O2 are the two largest sources of uncertainty in these metrics. The absolute magnitude of the change in the metrics is similar if rate constants are increased or decreased by their σ values. We investigate two methods of assessing these uncertainties, addition in quadrature and a Monte Carlo approach, and conclude they give similar outcomes. Combining the uncertainties across the 60 reactions gives overall uncertainties on the annual mean tropospheric ozone burden, surface ozone and tropospheric OH concentrations, and tropospheric methane lifetime of 10, 11, 16 and 16 %, respectively. These are larger than the spread between models in recent model intercomparisons. Remote regions such as the tropics, poles and upper troposphere are most uncertain. This chemical uncertainty is sufficiently large to suggest that rate constant uncertainty should be considered alongside other processes when model results disagree with measurement. Calculations for the pre-industrial simulation allow a tropospheric ozone radiative forcing to be calculated of 0.412 ± 0.062 W m−2. This uncertainty (13 %) is comparable to the inter-model spread in ozone radiative forcing found in previous model–model intercomparison studies where the rate constants used in the models are all identical or very similar. Thus, the uncertainty of tropospheric ozone radiative forcing should expanded to include this additional source of uncertainty. These rate constant uncertainties are significant and suggest that refinement of supposedly well-known chemical rate constants should be considered alongside other improvements to enhance our understanding of atmospheric processes.

Impact of uncertainties in inorganic chemical rate constants on tropospheric composition and ozone radiative forcing

Chemical rate constants determine the composition of the atmosphere and how this composition has changed over time. They are central to our understanding of climate change and air quality degradation. Atmospheric chemistry models, whether online or offline, box, regional or global use these rate constants. Expert panels synthesise laboratory measurements, making recommendations for the rate constants that should be used. This results in very similar or identical rate constants being used by all models. The inherent uncertainties in these recommendations are, in general, therefore ignored. We explore the impact of these uncertainties on the composition of the troposphere using the GEOS-Chem chemistry transport model. Based on the JPL and IUPAC evaluations we assess 50 mainly inorganic rate constants and 10 photolysis rates, through simulations where we increase the rate of the reactions to the 1σ upper value recommended by the expert panels. We assess the impact on 4 standard metrics: annual mean tropospheric ozone burden, surface ozone and tropospheric OH concentrations, and tropospheric methane lifetime. Uncertainty in the rate constants for NO2 + OH M → HNO3, OH + CH4 → CH3O2 + H2O and O3 + NO → NO2 + O2 are the three largest source of uncertainty in these metrics. We investigate two methods of assessing these uncertainties, addition in quadrature and a Monte Carlo approach, and conclude they give similar outcomes. Combining the uncertainties across the 60 reactions, gives overall uncertainties on the annual mean tropospheric ozone burden, surface ozone and tropospheric OH concentrations, and tropospheric methane lifetime of 11, 12, 17 and 17 % respectively. These are larger than the spread between models in recent model inter-comparisons. Remote regions such as the tropics, poles, and upper troposphere are most uncertain. This chemical uncertainty is sufficiently large to suggest that rate constant uncertainty should be considered when model results disagree with measurement. Calculations for the pre-industrial allow a tropospheric ozone radiative forcing to be calculated of 0.412 ± 0.062 Wm−2. This uncertainty (15 %) is comparable to the inter-model spread in ozone radiative forcing found in previous model-model inter-comparison studies where the rate constants used in the models are all identical or very similar. Thus the uncertainty of tropospheric ozone radiative forcing should expanded to include this additional source of uncertainty. These rate constant uncertainties are significant and suggest that refinement of supposedly well known chemical rate constants should be considered alongside other improvements to enhance our understanding of atmospheric processes.