The role of Rayleigh-Taylor instabilities in filament threads

Many solar filaments and prominences show short-lived horizontal threads lying parallel to the photosphere. In this work the possible link between Rayleigh-Taylor instabilities and thread lifetimes is investigated. This is done by calculating the eigenmodes of a thread modelled as a Cartesian slab under the presence of gravity. An analytical dispersion relation is derived using the incompressible assumption for the magnetohydrodynamic (MHD) perturbations. The system allows a mode that is always stable, independently of the value of the Alfv\'en speed in the thread. The character of this mode varies from being localised at the upper interface of the slab when the magnetic field is weak, to having a global nature and resembling the transverse kink mode when the magnetic field is strong. On the contrary, the slab model permits another mode that is unstable and localised at the lower interface when the magnetic field is weak. The growth rates of this mode can be very short, of the order of minutes for typical thread conditions. This Rayleigh-Taylor unstable mode becomes stable when the magnetic field is increased, and in the limit of strong magnetic field it is essentially a sausage magnetic mode. The gravity force might have a strong effect on the modes of oscillation of threads, depending on the value of the Alfv\'en speed. In the case of threads in quiescent filaments, where the Alfv\'en speed is presumably low, very short lifetimes are expected according to the slab model. In active region prominences, the stabilising effect of the magnetic tension might be enough to suppress the Rayleigh-Taylor instability for a wide range of wavelengths

Peak expiratory flow rates produced with the Laerdal and Mapleson-C bagging circuits

This study compared the peak expiratory flow rates (PEFR) at different inspiratory pause pressures (IPP) produced by the Mapleson-C circuit and the Laerdal self-inflating resuscitator.The difference in PEFR produced by the two circuits was significantly different at the lowest and the highest IPP studied (I3 and 38cm H20). The greatest differences in the mean expiratory flow rates produced was, however, only 0.07 litre sec-7. The authors suggest that the choice of bagging circuit should depend on the experience and familiarity of the therapist with the circuit

Peer Evaluation of Video Lab Reports in a Blended Introductory Physics Course

The Georgia Tech blended introductory calculus-based mechanics course emphasizes scientific communication as one of its learning goals, and to that end, we gave our students a series of four peer-evaluation assignments intended to develop their abilities to present and evaluate scientific arguments. Within these assignments, we also assessed students' evaluation abilities by comparing their evaluations to a set of expert evaluations. We summarize our development efforts and describe the changes we observed in student evaluation behavior.Comment: 4 pages, 1 table, 2 figures, submitted to Summer 2014 PERC Proceeding

The Initial State of Students Taking an Introductory Physics MOOC

As part of a larger research project into massively open online courses (MOOCs), we have investigated student background, as well as student participation in a physics MOOC with a laboratory component. Students completed a demographic survey and the Force and Motion Conceptual Evaluation at the beginning of the course. While the course is still actively running, we have tracked student participation over the first five weeks of the eleven-week course.Comment: Accepted to PERC Proceedings 201

The effect of the solar corona on the attenuation of small-amplitude prominence oscillations. I. Longitudinal magnetic field

Context. One of the typical features shown by observations of solar prominence oscillations is that they are damped in time and that the values of the damping times are usually between one and three times the corresponding oscillatory period. However, the mechanism responsible for the attenuation is still not well-known. Aims. Thermal conduction, optically thin or thick radiation and heating are taken into account in the energy equation, and their role on the attenuation of prominence oscillations is evaluated. Methods. The dispersion relation for linear non-adiabatic magnetoacoustic waves is derived considering an equilibrium made of a prominence plasma slab embedded in an unbounded corona. The magnetic field is orientated along the direction parallel to the slab axis and has the same strength in all regions. By solving the dispersion relation for a fixed wavenumber, a complex oscillatory frequency is obtained, and the period and the damping time are computed. Results. The effect of conduction and radiation losses is different for each magnetoacoustic mode and depends on the wavenumber. In the observed range of wavelengths the internal slow mode is attenuated by radiation from the prominence plasma, the fast mode by the combination of prominence radiation and coronal conduction and the external slow mode by coronal conduction. The consideration of the external corona is of paramount importance in the case of the fast and external slow modes, whereas it does not affect the internal slow modes at all. Conclusions. Non-adiabatic effects are efficient damping mechanisms for magnetoacoustic modes, and the values of the obtained damping times are compatible with those observed.Comment: Accepted in A&

Results for the 2023 VIMS Industry Cooperative Surveys of the Mid-Atlantic Bight and Georges Bank Scallop Resource Areas

The Virginia Institute of Marine Science (VIMS) conducted high resolution sea scallop dredge surveys of the Mid-Atlantic Bight (MAB) and Georges Bank (GB) scallop resource areas during May–July 2023

Targeted Bisulfite Pyrosequencing & Amplicon Bisulfite Sequencing Epigenetic Analysis

Targeted Bisulfite Pyrosequencing & Amplicon Bisulfite Sequencing Epigenetic Analysis Charles Tran, Dept. of Biology, with Dr. Karolina Aberg, VCU School of Pharmacy Background: The Great Smoky Mountain Study is a longitudinal study that started in 1992 and includes 1,420 participants that were 9 to 13 years at intake and have since been revisited ~ every 2 years. Participants (and their parents) provided detailed assessment of stressors and health outcomes as well as blood samples at each interview. In a recent methylome-wide association study the samples were used to identify methylation marks associated with childhood trauma. In the current work, we present an investigation to replicate these methylation marks in an independent sample. Objective: Our objective is to optimize and apply epigenomic-specific protocols in order to replicate trauma associated methylation biomarkers in an independent study sample. Materials and Methods: We will use DNA samples extracted from saliva from The Young Adolescent Project, another longitudinal study which has obtained relevant information related to childhood trauma. In this sample we will perform replication of top findings using targeted amplicon bisulfite sequencing in saliva samples where amplicons are amplified with JUNO sequencing platform or Pyromark PCR pyrosequencing. Forward and reverse primers are first designed using Pyromark Assay Design software. Primer set candidates are chosen based off of a score of 100; scores are determined by potential for mispriming, likelihood for primer dimers, etc. Higher scores correlate to better PCR performance. Then, BiSearch, an online primer-design algorithm and search tool is used to check primer sets in order to ameliorate PCR efficiency by avoiding non-specific PCR products due to genomic repetition. PCR product is then examined with 2% agarose gel electrophoresis and Agilent Bioanalyzer chip-based capillary electrophoresis in order to determine if amplicons of the correct size were obtained. (Once primers of sufficient efficacy are designed, they are subject to 5’ biotin tag modifications—this makes purification of proteins and other target molecules easier while utilizing streptavidin-coupled Dynabeads). Methylation sites incompatible with JUNO due to amplicon sites exceeding 200 base pairs would instead be analyzed using Pyromark Pyrosequencing Assay for which it is easier to design assays but is more costly and lower throughput: the output of resulting data being similar in quality. Results: We attempted to design assays for 60 loci. Of these we have designed and validated the quality of 23 assays for JUNO and 3 for the Pyromark Q96 sequencing and quantification platform. PCR analysis followed afterwards. We were not able to design assays for 34 sites due to: amplicon sites having exceeded 200 base pairs, forming of hair pins, forming of primer dimers, amplicon sites being too far from target region, or formation of multiple PCR products, as determined by IDT analysis. The 3 primer sets were incompatible with JUNO due to formation of primer dimer and hairpin formations when 5’ tags were added therefore Pyromark Q96 assay was optimal. Conclusion: In conclusion we have optimized and evaluated 23 assays for the JUNO sequencing platform and 3 primers for Pyromark Q96 that, in the next step, will be used to assess the replication of loci of interest in trauma associated methylation biomarkers from saliva samples.https://scholarscompass.vcu.edu/uresposters/1391/thumbnail.jp