Secondary school students’ views of nature of science in quantum physics

Epistemological and philosophical issues have always been relevant for the foundations of physics, but usually do not find their way into secondary physics classrooms. As an exception to this, the strangeness of quantum physics (QP) naturally evokes philosophical questions, and learners might have to change their ideas about the nature of science (NOS). In this exploratory mixed-method study, we examined possible connections between upper secondary school students’ QP content knowledge and their ideas about relevant aspects of NOS in the context of QP. We administered a QP concept test to 240 Dutch secondary students (age 17–19) after they attended classes on QP without a focus on NOS. Next, we selected 24 students with a range of test scores for individual semi-structured interviews about their understanding of wave-particle duality and their views on five aspects of NOS. Contrary to NOS studies in other contexts, the interviews showed that all 24 students had well-informed NOS views in the context of QP. We contend that NOS in QP might be more easily accessible than in many other contexts. Our results suggest that QP can have an additional role in the physics curriculum by enhancing students’ understanding of NOS

Why and how teachers use nature of science in teaching quantum physics:Research on the use of an ecological teaching intervention in upper secondary schools

Students at upper secondary and college level in many countries are introduced to quantum physics (QP) in a mostly mathless course. Research shows that addressing epistemological and philosophical aspects would be beneficial for novice students’ conceptual understanding. However, physics teachers seldom address these nature of science (NOS) aspects in their lessons. We take the view that teachers only implement these aspects if this serves their goals. This study explores whether experienced Dutch high school teachers, who are not trained for NOS teaching, address NOS in their QP lessons when provided with NOS-infused teaching resources. We based our framework on literature about pedagogic content knowledge and on the principles of the practicality of educational innovations. Teacher interviews (N=10) supported by classroom observations provided insights into how and why teachers use specific elements from the resources. Our research reveals teachers’ perspectives on teaching QP in secondary schools and why they think NOS aspects can be helpful to reach their teaching goals. Our findings support the view that conceptual QP is valuable for all students because an informed NOS view is vital for everybody in today’s society. Additionally, we expect that an ecological intervention that supports teachers and at the same time recognizes their professionality and environment has potential implications for other fields of science education and could have a significant positive impact in classrooms

Performance Metrics for the Objective Assessment of Capacitive Deionization Systems

In the growing field of capacitive deionization (CDI), a number of performance metrics have emerged to describe the desalination process. Unfortunately, the separation conditions under which these metrics are measured are often not specified, resulting in optimal performance at minimal removal. Here we outline a system of performance metrics and reporting conditions that resolves this issue. Our proposed system is based on volumetric energy consumption (Wh/m$^3$) and throughput productivity (L/h/m$^2$) reported for a specific average concentration reduction, water recovery, and feed salinity. To facilitate and rationalize comparisons between devices, materials, and operation modes, we propose a nominal standard testing condition of removing 5 mM from a 20 mM NaCl feed solution at 50% water recovery for CDI research. Using this separation, we compare the desalination performance of a flow-through electrode (fte-CDI) cell and a flow between membrane (fb-MCDI) device, showing how significantly different systems can be compared in terms of generally desirable desalination characteristics. In general, we find that performance analysis must be considered carefully so to not allow for ambiguous separation conditions or the maximization of one metric at the expense of another. Additionally, for context we discuss a number of important underlying performance indicators and cell characteristics that are not performance measures in and of themselves but can be examined to better understand differences in performance

The Origin of Presolar Silica Grains in AGB Stars

We have found two presolar silica grains in ALH A77307, which exhibit excesses in 17O but are normal in 18O. Silicon-oxide grains probably form during rapid cooling under non-equilibrium conditions in O-rich AGB stars with low Mg/Si ratios.This work was supported by NASA grants NNX07AU8OH, NNX08AI13G and NNXO7AI82G

The Imprint of Nova Nucleosynthesis in Presolar Grains

Infrared and ultraviolet observations of nova light curves have confirmed grain formation in their expanding shells that are ejected into the interstellar medium by a thermonuclear runaway. In this paper, we present isotopic ratios of intermediate-mass elements up to silicon for the ejecta of CO and ONe novae, based on 20 hydrodynamic models of nova explosions. These theoretical estimates will help to properly identify nova grains in primitive meteorites. In addition, equilibrium condensation calculations are used to predict the types of grains that can be expected in the nova ejecta, providing some hints on the puzzling formation of C-rich dust in O>C environments. These results show that SiC grains can condense in ONe novae, in concert with an inferred (ONe) nova origin for several presolar SiC grains.Comment: 42 pages. Accepted for publication in The Astrophysical Journa

SIMS chemical analysis of extended impact features from the trailing edge portion of experiment AO187-2

One hundred capture cells from the trailing edge, which had lost their cover foils during flight, were optically scanned for extended impact features caused by high velocity projectiles impinging on the cells while the foils were still intact. Of the 53 candidates, 24 impacts were analyzed by secondary ion mass spectroscopy for the chemical composition of the deposits. Projectile material was found in all impacts, and at least 75 percent of them appear to be caused by interplanetary dust particles. Elemental ratios are fractionated, with refractory elements enriched in the impacts relative to interplanetary dust particles collected in the stratosphere. Although this could be due to systematic differences in the compositions, a more likely explanation is volatility fractionation during the impact process

Coordinated Analyses of Presolar Grains in the Allan Hills 77307 and Queen Elizabeth Range 99177 Meteorites

We report the identification of presolar silicates (~177 ppm), presolar oxides (~11 ppm), and one presolar SiO2 grain in the Allan Hills (ALHA) 77307 chondrite. Three grains having Si isotopic compositions similar to SiC X and Z grains were also identified, though the mineral phases are unconfirmed. Similar abundances of presolar silicates (~152 ppm) and oxides (~8 ppm) were also uncovered in the primitive CR chondrite Queen Elizabeth Range (QUE) 99177, along with 13 presolar SiC grains and one presolar silicon nitride. The O isotopic compositions of the presolar silicates and oxides indicate that most of the grains condensed in low-mass red giant and asymptotic giant branch stars. Interestingly, unlike presolar oxides, few presolar silicate grains have isotopic compositions pointing to low-metallicity, low-mass stars (Group 3). The 18O-rich (Group 4) silicates, along with the few Group 3 silicates that were identified, likely have origins in supernova outflows. This is supported by their O and Si isotopic compositions. Elemental compositions for 74 presolar silicate grains were determined by scanning Auger spectroscopy. Most of the grains have non-stoichiometric elemental compositions inconsistent with pyroxene or olivine, the phases commonly used to fit astronomical spectra, and have comparable Mg and Fe contents. Non-equilibrium condensation and/or secondary alteration could produce the high Fe contents. Transmission electron microscopic analysis of three silicate grains also reveals non-stoichiometric compositions, attributable to non-equilibrium or multistep condensation, and very fine scale elemental heterogeneity, possibly due to subsequent annealing. The mineralogies of presolar silicates identified in meteorites thus far seem to differ from those in interplanetary dust particles.Comment: 23 pages, 16 figure

SIMS chemical and isotopic analysis of impact features from LDEF experiments AO187-1 and AO187-2

Previous secondary ion mass spectrometry (SIMS) studies of extended impact features from LDEF capture cell experiment AO187-2 showed that it is possible to distinguish natural and man-made particle impacts based on the chemical composition of projectile residues. The same measurement technique has now been applied to specially prepared gold target impacts from experiment AO187-1 in order to identify the origins of projectiles that left deposits too thin to be analyzed by conventional energy-dispersive x-ray (EDX) spectroscopy. The results indicate that SIMS may be the method of choice for the analysis of impact deposits on a variety of sample surfaces. SIMS was also used to determine the isotopic compositions of impact residues from several natural projectiles. Within the precision of the measurements all analyzed residues show isotopically normal compositions

The effect of aqueous alteration and metamorphism in the survival of presolar silicate grains in chondrites

Relatively small amounts (typically between 2-200 parts per million) of presolar grains have been preserved in the matrices of chondritic meteorites. The measured abundances of the different types of grains are highly variable from one chondrite to another, but are higher in unequilibrated chondrites that have experienced little or no aqueous alteration and/or metamorphic heating than in processed meteorites. A general overview of the abundances measured in presolar grains (particularly the recently identified presolar silicates) contained in primitive chondrites is presented. Here we will focus on the most primitive chondrite groups, as typically the highest measured abundances of presolar grains occur in primitive chondrites that have experienced little thermal metamorphism. Looking at the most aqueously altered chondrite groups, we find a clear pattern of decreasing abundance of presolar silicate grains with increasing level of aqueous alteration. We conclude that the measured abundances of presolar grains in altered chondrites are strongly biased by their peculiar histories. Scales quantifying the intensity of aqueous alteration and shock metamorphism in chondrites could correlate with the content in presolar silicates. To do this it would be required to infer the degree of destruction or homogenization of presolar grains in the matrices of primitive meteorites. To get an unbiased picture of the relative abundance of presolar grains in the different regions of the protoplanetary disk where first meteorites consolidated, future dedicated studies of primitive meteorites, IDPs, and collected materials from sample-return missions (like e.g. the planned Marco Polo) are urgently required.Comment: 15 pages, 3 figures, published in PASA as part of the Proceedings of the 2008 Torino Conference "The Origin of the Elements Heavier than Iron

SEM-EDS analyses of small craters in stardust aluminium foils: implications for the Wild-2 dust distribution

Implications for the Wild-2 dust distribution of the statistical results obtained by SEM-EDS from nearly 300 impact craters on aluminium foils of the Stardust sample tray assembly