On the Formation of Multiple-Shells Around Asymptotic Giant Branch Stars

Two types of models for the formation of semi-periodic concentric multiple shells (M-shells) around asymptotic giant branch (AGB) stars and in planetary nebulae are compared against observations. Models that attribute the M-shells to processes in an extended wind acceleration zone around AGB stars result in an optically thick acceleration zone, which reduces the acceleration efficiency in outer parts of the extended acceleration zone. This makes such models an unlikely explanation for the formation of M-shells. Models which attribute the M-shell to semi-periodic variation in one or more stellar properties are most compatible with observations. The only stellar variation models on time scales of 50-1500 years that have been suggested are based on an assumed solar-like magnetic cycle. Although ad-hoc, the magnetic cycle assumption fits naturally into the increasingly popular view that magnetic activity plays a role in shaping the wind from upper AGB stars.Comment: 8 pages, Submitted to Ap

Representation in the classroom: The effect of own-race teachers on student achievement

Previous research suggests that there are academic benefits when students and teachers share the same race/ethnicity because such teachers can serve as role models, mentors, advocates, or cultural translators. In this paper, we obtain estimates of achievement changes as students are assigned to teachers of different races/ethnicities from grades 3 through 10 utilizing a large administrative dataset provided by the Florida Department of Education that follows the universe of test-taking students in Florida public schools from 2001–2002 through 2008–2009. We find small but significant positive effects when black and white students are assigned to race-congruent teachers in reading (.004–.005 standard deviations) and for black, white and Asian/Pacific Island students in math (.007–.041 standard deviations). We also examine the effects of race matching by students' prior performance level, finding that lower-performing black and white students appear to particularly benefit from being assigned to a race-congruent teacher.http://sites.bu.edu/marcuswinters/files/2017/09/Egalite-et-al-2015-FLTM_EER.pdfAccepted manuscrip

An Entropy Stable Nodal Discontinuous Galerkin Method for the Two Dimensional Shallow Water Equations on Unstructured Curvilinear Meshes with Discontinuous Bathymetry

We design an arbitrary high-order accurate nodal discontinuous Galerkin spectral element approximation for the nonlinear two dimensional shallow water equations with non-constant, possibly discontinuous, bathymetry on unstructured, possibly curved, quadrilateral meshes. The scheme is derived from an equivalent flux differencing formulation of the split form of the equations. We prove that this discretisation exactly preserves the local mass and momentum. Furthermore, combined with a special numerical interface flux function, the method exactly preserves the mathematical entropy, which is the total energy for the shallow water equations. By adding a specific form of interface dissipation to the baseline entropy conserving scheme we create a provably entropy stable scheme. That is, the numerical scheme discretely satisfies the second law of thermodynamics. Finally, with a particular discretisation of the bathymetry source term we prove that the numerical approximation is well-balanced. We provide numerical examples that verify the theoretical findings and furthermore provide an application of the scheme for a partial break of a curved dam test problem

A Provably Stable Discontinuous Galerkin Spectral Element Approximation for Moving Hexahedral Meshes

We design a novel provably stable discontinuous Galerkin spectral element (DGSEM) approximation to solve systems of conservation laws on moving domains. To incorporate the motion of the domain, we use an arbitrary Lagrangian-Eulerian formulation to map the governing equations to a fixed reference domain. The approximation is made stable by a discretization of a skew-symmetric formulation of the problem. We prove that the discrete approximation is stable, conservative and, for constant coefficient problems, maintains the free-stream preservation property. We also provide details on how to add the new skew-symmetric ALE approximation to an existing discontinuous Galerkin spectral element code. Lastly, we provide numerical support of the theoretical results

Quantitative Electron Probe X-Ray Microanalysis of Lead-Sequestering Organelles in Earthworms: Technical Appraisal of Air-Dried Smears and Freeze-Dried Cryosections

Much of the current knowledge of Pb sequestration in earthworm chloragosome granules stems from quantitative and semi-quantitative Electron Probe X-ray Microanalysis (EPXMA) of unfixed, air-dried tissue smears. Fully quantitative EPXMA was used in this study to assess the validity of smearing by comparison with unfixed, freeze-dried cryosections. Samples were obtained from two earthworm species, Lumbricus rubellus (L.r.) and Dendrobaena rubida (D.r.) collected from a Pb and Zn polluted soil (confirmed by XRF). A number of conclusions emerged :- (a) the element compositions of whole worms, determined by EPXMA of sprayed microdroplets of wet-digested tissues, were different (D.r. : Pb = 29.9, Zn= 33.9, Ca = 207.3, S = 387.9, P = 258.0; L.r. : Pb = 12.3, Zn = 44.4, Ca = 288.1, S = 311.8, P = 354. 9 mM/kg dr.w.); (b) the major proportions of the body burdens of Pb and Zn are located in the chloragogenous tissue; (c) cryosectioned chloragosomes possess a concentric sub-structure, and the chemical composition of individual granules and granule populations is very heterogeneous; (d) smeared and cryosectioned chloragosome preparations revealed significant species-differences in compositional chemistry (e. g., higher Pb and lower Zn in D.r., c.f. with L.r), which reflected their body burdens; (e) the absolute conc. values presented for L.r. cryosectioned granules are systematically higher than equivalent smear data; the overall patterns of the quantitative data obtained from smeared and cryosectioned chloragosomes were substantially similar, suggesting that the simpler technique can be recommended for certain applications, particularly where monitoring a large granule population is paramount

The Contribution of Electron Probe X-Ray Microanalysis (EPXMA) to Pollution Studies

This paper surveys the literature on the use of EPXMA in conjunction with (heavy metal) pollution studies. Metal-accumulating compartments are usually granules or vacuoles of 6 main types (i) extracellular, soluble and fairly pure calcium carbonate granules; (ii) insoluble, calcium and phosphorus-rich granules, of ten containing several metal contaminants; (iii) multifunctional, calcium and phosphorus granules containing a high proportion of rather complex organic molecules; (iv) copper-(and sulphur) rich granules; (v) iron-(and phosphorus) rich granules; (vi) Cd, Zn, Cu and Hg -containing vacuoles, where the metals are presumably complexed with cysteine-rich metallothionein proteins, or their derivatives. With a few exceptions, types (ii)-(vi) are intracellular. Many of these inclusions may be associated with the lysosomal system, and the metals are sequestered by the various compartments due to their ligand-binding properties (i.e., whether they belong to Class A or Class B) and on the availability of pre-existing or inducible ligands within those compartments. Future biochemical analysis may change the categories presented here; for example, some type (iv) granules may well be found to contain metallothionein, and thus they may be more appropriately described as type (vi) inclusions. It is concluded that EPXMA provides unique multi-element information concerning the metabolism of essential and toxic heavy metals within cells. However, this information may be considerably enhanced by the use of complementary experimental methods

Integration of patient-reported outcome measures with key clinical outcomes after immediate latissimus dorsi breast reconstruction and adjuvant treatment

Background: linical evidence on patient-reported outcome measures (PROMS) in breast reconstruction is lacking. The aim of this study was to evaluate PROMs in implant-assisted latissimus dorsi (LDI) or tissue-only autologous latissimus dorsi (ALD) flap reconstruction in relation to complications and adjuvant treatments.Methods: this was a prospective cohort study involving six UK centres. Eligible patients had primary early-stage breast cancer. The European Organization for Research and Treatment of Cancer quality-of-life questionnaire (QLQ)-C30 and QLQ-BR23, Functional Assessment of Cancer Therapy—Breast Cancer scale (FACT-B), Body Image Scale, and Hospital Anxiety and Depression Scale were completed before operation and at 3, 6 and 12 months after surgery.Results: a total of 182 patients (82 LDI and 100 ALD) were recruited between 2007 and 2010 with symptomatic (59·9 per cent) or screen-detected (39·6 per cent) cancers. Some 64·3 per cent had lymph node-negative disease; 30 per cent of the LDI group had radiotherapy, compared with 53·0 per cent in the ALD group (P = 0·004). Early complications up to 3 months after surgery were reported in 66 and 51·0 per cent of patients in the LDI and ALD groups respectively (P = 0·062) and long-term complications (4–12 months) in 48 and 45·0 per cent (P = 0·845). Role functioning and pain (P = 0·002 for both) were adversely affected in the ALD group compared with results in the LDI group, with no significant effects of radiotherapy on any health-related quality of life (HRQL). Chemotherapy and early complications adversely affected HRQL, which improved between 3 and 12 months after surgery (P < 0·010 for all).Conclusion: there is evidence of similar HRQL between types of latissimus dorsi breast reconstruction for up to a year after surgery. There appear to be no overarching effects for radiotherapy after mastectomy on the specific HRQL domains studied in the short term. The identification of variables that affect HRQL is important, including their integration into the analysis of PROM