Possible magnetic field variability during the 6.7 GHz methanol maser flares of G09.62+0.20

(Abridged) Recently, the magnetic field induced Zeeman splitting was measured for the strongest known 6.7 GHz methanol maser, which arises in the massive star forming region G09.62+0.20. This maser is one of a handful of periodically flaring methanol masers. The 100-m Effelsberg telescope was used to monitor the 6.7 GHz methanol masers of G09.62+0.20. With the exception of a two week period during the peak of the maser flare, we measure a constant magnetic field of B_||~11+-2 mG in the two strongest maser components of G09.62+0.20 that are separated by over 200 AU. In the two week period that coincides exactly with the peak of the maser flare of the strongest maser feature, we measure a sharp decrease and possible reversal of the Zeeman splitting. The exact cause of both maser and polarization variability is still unclear, but it could be related to either background amplification of polarized emission or the presence of a massive protostar with a close-by companion. Alternatively, the polarization variability could be caused by non-Zeeman effects related to the radiative transfer of polarized maser emission.Comment: 4 pages, 3 figures, accepted for publication Astronomy and Astrophysic

The effect of canopy position on growth and mortality in mixed sapling communities during self-thinning

This research investigates how species in the sapling phase differ in growth and survival depending on light availability (as estimated by canopy position) by means of tree-ring analysis and modelling mortality. We harvested 120 live and 158 dead saplings in self-thinning communities consisting of Silver birch (Betula pendula Roth.), Scots pine (Pinus sylvestris L.), Japanese larch (Larix kaempferi Carr.) and Douglas fir (Pseudotsuga menziesii Mirb. Franco) in the Netherlands. Results are evaluated within the framework of a trade-off between high-light growth and low-growth survival. Radial growth, measured at ground level, generally declined over time. In addition, a decreasing light availability further reduced growth in all species except Douglas fir. Trees died when radial growth was reduced to about 0.5 mm year¿1. Mortality in all species except Scots pine was significantly related to recent growth, but mortality curves were not different. The light-demanding Silver birch and Japanese larch differed from the shade-tolerant Douglas fir in both high-light growth and low-growth mortality, in line with a growth-survival trade-off. The light-demanding Scots pine did not fit this pattern as it was unable to transfer high radial growth into height gain, leaving it in suppressed canopy positions. This indicates the importance of height growth in the growth-survival trade-off. Differences in mortality probabilities affect the potential for coexistence, however, in all species also fast-growing individuals died suggesting additional factors causing mortality during self-thinning, other than direct competition for ligh

VLBA imaging of a periodic 12.2 GHz methanol maser flare in G9.62+0.20E

The class II methanol maser source G9.62+0.20E undergoes periodic flares at both 6.7 and 12.2 GHz. The flare starting in 2001 October was observed at seven epochs over three months using the VLBA at 12.2 GHz. High angular resolution images (beam size $\sim$ 1.7 x 0.6 mas) were obtained, enabling us to observe changes in 16 individual maser components. It was found that while existing maser spots increased in flux density, no new spots developed and no changes in morphology were observed. This rules out any mechanism which disturbs the masing region itself, implying that the flares are caused by a change in either the seed or pump photon levels. A time delay of 1--2 weeks was observed between groups of maser features. These delays can be explained by light travel time between maser groups. The regularity of the flares can possibly be explained by a binary system.Comment: 11 pages, accepted for publication in MNRA

PlotXpress, a webtool for normalization and visualization of reporter expression data [version 1; peer review: 3 approved]

In molecular cell biology, reporter assays are frequently used to investigate gene expression levels. Reporter assays employ a gene that encodes a light-emitting protein, of which the luminescence is quantified as a proxy of gene expression. Commercial parties provide reporter assay kits that include protocols and specialized detection machinery. However, downstream analysis of the output data and their presentation are not standardized. We have developed plotXpress to fill this gap, providing a free, open-source platform for the semi-automated analysis and standardized visualisation of experimental gene reporter data. Users can upload raw luminescence data acquired from a reporter gene assay with an internal control. In plotXpress, the data is corrected for sample variation with the internal control and the average for each condition is calculated. When a reference condition is selected the fold change is calculated for all other conditions, based on the selected reference. The results are shown as dot plots with a statistical summary, which can be adjusted to create publication-grade plots without requiring coding skills. Altogether, plotXpress is an open-source, low-threshold, web-based tool, that promotes a standardized and reproducible analysis while providing an appealing visualization of reporter data. The webtool can be accessed at: https://huygens.science.uva.nl/PlotXpress

KAT-7 Science Verification: Using HI Observations of NGC 3109 to Understand its Kinematics and Mass Distribution

HI observations of the Magellanic-type spiral NGC 3109, obtained with the seven dish Karoo Array Telescope (KAT-7), are used to analyze its mass distribution. Our results are compared to what is obtained using VLA data. KAT-7 is the precursor of the SKA pathfinder MeerKAT, which is under construction. The short baselines and low system temperature of the telescope make it sensitive to large scale low surface brightness emission. The new observations with KAT-7 allow the measurement of the rotation curve of NGC 3109 out to 32', doubling the angular extent of existing measurements. A total HI mass of 4.6 x 10^8 Msol is derived, 40% more than what was detected by the VLA observations. The observationally motivated pseudo-isothermal dark matter (DM) halo model can reproduce very well the observed rotation curve but the cosmologically motivated NFW DM model gives a much poorer fit to the data. While having a more accurate gas distribution has reduced the discrepancy between the observed RC and the MOdified Newtonian Dynamics (MOND) models, this is done at the expense of having to use unrealistic mass-to-light ratios for the stellar disk and/or very large values for the MOND universal constant a0. Different distances or HI contents cannot reconcile MOND with the observed kinematics, in view of the small errors on those two quantities. As for many slowly rotating gas-rich galaxies studied recently, the present result for NGC 3109 continues to pose a serious challenge to the MOND theory.Comment: 25 pages, 20 figures, accepted for publication in Astronomical Journa

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

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