Planet Candidate Validation in K2 Crowded Fields

The discovery of planets outside of our own solar system has captured the imagination of scientists and the public alike. In just the past decade, more than 3000 planets have been discovered with the groundbreaking NASA telescope missions Kepler and its successor, K2. In just three years, the K2 mission has yielded some remarkable results, with the discovery of over 300 confirmed planets and 480 reported planet candidates to be validated. The K2 mission detects planets by recording any periodic dimming in stars; this dimming often indicates that a planet is in orbit around the star, blocking a portion of its light. A major challenge with the analysis of these data is to identify planets in star-crowded regions, where individual camera pixels overlap multiple stars. In this thesis, I developed, tested, and evaluated a validation process for ruling out false-positive detections of planets in K2 observations of star-crowded regions. Using Markov chain Monte Carlo analysis, I fitted a model to obtain the transit parameters for each candidate planetary system. Later, I used seeing-limited on/off imaging to rule out false positives due to nearby transiting binary star systems. These results were then evaluated using a software program called validation of exoplanet signals using a probabilistic algorithm (VESPA) to estimate the probability of a false-positive detection. Such techniques and results are important tools for conducting candidate validation and follow-up observations for space-based missions, including the upcoming Transiting Exoplanet Survey Satellite (TESS) mission, since its large camera pixels resemble K2 star-crowded fields

Pharmacognostical investigation of Clitoria ternatea L. leaves

Clitoria ternatea L. (Family: Fabaceae) is also commonly known as Aparajita or Shankapushpi. The folklore claims the use of whole plant for curing various ailments. The leaves are used for hepatic problems, otalgia and eruptions. Pharmacognosy is an indispensable aid in standardization of herbal drugs. For the present investigation, pharmacognostical evaluation of C. ternatea L. leaf is carried out for quality standards. The study involves the following parameters like macroscopic, microscopic, histochemical analysis, powder microscopy, preliminary phytochemical screening, and physicochemical analysis. The keystone characteristic of microscopic studies under light and scanning electron microscopy revealed the presence of sclerenchyma ring around the vascular bundle in the midrib region and; two types of non-glandular bicellular trichomes, first type is smooth walled with curved apex, and second type is warty walled with blunt apex. The presence of wax crystalloids on the surface of the leaflets was clearly observed in ESEM. Powder study goes concurrent with microscopy. The physicochemical studies revealed i.e. total ash (8.15 %), water soluble ash (6.58 %), acid insoluble ash (1.88 %) and sulphated ash (9.05%); water soluble extractive value (14.92%) and alcohol soluble extractive values of (9.66%) which are comparatively higher to other solvents. The preliminary phytochemical and histochemical studies showed the presence of alkaloids, saponins, anthraquinone glycosides, terpenoids, flavonoids etc. In the current studies, pharmacopeial standards are laid down for the leaves of C. ternatea L

Food Choice Decision-Making Among School-Going Adolescents Amidst the Nutrition Transition in Urban Accra, Ghana

Like many countries of the world, Ghana is experiencing a nutrition transition and rising non-communicable diseases. Adolescents are susceptible to diet-related health risks as they experience significant physical and psychological changes, which are happening in tandem with food environment changes, including widespread proliferation of large portion and package sizes of energy-dense, nutrient-poor foods. Both local and multinational food and beverage companies have encouraged consumption of their products through various marketing tactics targeted directly to adolescents. Some of these tactics include the use of characters or celebrity endorsement, promotional discounts, and appeal to sociocultural values, including messages about body size preferences. As a result, adolescents may experience conflicting messages from exposure to Western food marketing campaigns promoting abnormally thin bodies by consumption of foods that are known contributors to obesity and chronic diseases. This qualitative study used in-depth interviews to explore perspectives held by 48 public junior high males and female students in six urban districts of the Greater Accra Region of Ghana, with respect to healthy and unhealthy food, portion sizes, body image, and how advertising messages contribute to their food choice decision-making. The first aim sought to understand how adolescents conceptualize healthy and unhealthy foods, food portion sizes and purchasing behaviors. Students had rudimentary knowledge of nutrition, mostly derived from school curricula. However, their food choices were predominantly driven by attitudes and beliefs held by those in their social networks, cost considerations, and health claims on advertisements. Students did not fully understand what portion control and mindful eating was, though they recognized moderation as an important health behavior. The second aim sought to uncover perspectives by these same students regarding body image. Younger students and females felt more body image dissatisfaction and desire to change their current weight status. Body image aspirations were important in food choice decision-making; students alluded to people who they sought to emulate. Students discussed tensions with elders about types and quantities of food to eat and the body sizes that their elders wanted them to be versus what they wanted to look like. The results from this study suggest the need for social network and social marketing interventions that could address healthy eating habits, body dysphoria, as well as deceptive marketing tactics used to promote unhealthy foods for both adolescents and their caregivers

The Sun Remains Relatively Refractory Depleted: Elemental Abundances for 17,412 Gaia RVS Solar Analogs and 50 Planet Hosts

The elemental abundances of stars, particularly the refractory elements (e.g., Fe, Si, Mg), play an important role in connecting stars to their planets. Most Sun-like stars do not have refractory abundance measurements since obtaining a large sample of high-resolution spectra is difficult with oversubscribed observing resources. In this work we infer abundances for C, N, O, Na, Mn, Cr, Si, Fe, Ni, Mg, V, Ca, Ti, Al, and Y for solar analogs with Gaia RVS spectra (R=11,200) using the Cannon, a data-driven method. We train a linear model on a reference set of 34 stars observed by Gaia RVS with precise abundances measured from previous high resolution spectroscopic efforts (R > 30,000--110,000). We then apply this model to several thousand Gaia RVS solar analogs. This yields abundances with average upper limit precisions of 0.04--0.1 dex for 17,412 stars, 50 of which are identified planet (candidate) hosts. We subsequently test the relative refractory depletion of these stars with increasing element condensation temperature compared to the Sun. The Sun remains refractory depleted compared to other Sun-like stars regardless of our current knowledge of the planets they host. This is inconsistent with theories of various types of planets locking up or sequestering refractories. Furthermore, we find no significant abundance differences between identified close-in giant planet hosts, giant planet hosts, and terrestrial/small planet hosts and the rest of the sample within our precision limits. This work demonstrates the utility of data-driven learning for future exoplanet composition and demographics studies.Comment: 24 pages, 10 figures, 4 tables, 1 appendix. Accepted in ApJ. Tables 1 and 2 available upon reques

Stabilization of SMAR1 mRNA by PGA2 involves a stem–loop structure in the 5′ UTR

Prostaglandins are anticancer agents known to inhibit tumor cell proliferation both in vitro and in vivo by affecting the mRNA stability. Here we report that a MAR-binding protein SMAR1 is a target of Prostaglandin A2 (PGA2) induced growth arrest. We identify a regulatory mechanism leading to stabilization of SMAR1 transcript. Our results show that a minor stem and loop structure present in the 5′ UTR of SMAR1 (ϕ1-UTR) is critical for nucleoprotein complex formation that leads to SMAR1 stabilization in response to PGA2. This results in an increased SMAR1 transcript and altered protein levels, that in turn causes downregulation of Cyclin D1 gene, essential for G1/S phase transition. We also provide evidence for the presence of a variant 5′ UTR SMAR1 (ϕ17-UTR) in breast cancer-derived cell lines. This form lacks the minor stem and loop structure required for mRNA stabilization in response to PGA2. As a consequence of this, there is a low level of endogenous tumor suppressor protein SMAR1 in breast cancer-derived cell lines. Our studies provide a mechanistic insight into the regulation of tumor suppressor protein SMAR1 by a cancer therapeutic PGA2, that leads to repression of Cyclin D1 gene

Single-cell gene expression profiles define self-renewing, pluripotent, and lineage primed States of human pluripotent stem cells

Pluripotent stem cells display significant heterogeneity in gene expression, but whether this diversity is an inherent feature of the pluripotent state remains unknown. Single-cell gene expression analysis in cell subsets defined by surface antigen expression revealed that human embryonic stem cell cultures exist as a continuum of cell states, even under defined conditions that drive self-renewal. The majority of the population expressed canonical pluripotency transcription factors and could differentiate into derivatives of all three germ layers. A minority subpopulation of cells displayed high self-renewal capacity, consistently high transcripts for all pluripotency-related genes studied, and no lineage priming. This subpopulation was characterized by its expression of a particular set of intercellular signaling molecules whose genes shared common regulatory features. Our data support a model of an inherently metastable self-renewing population that gives rise to a continuum of intermediate pluripotent states, which ultimately become primed for lineage specification

UTX mediates demethylation of H3K27me3 at muscle-specific genes during myogenesis

Polycomb (PcG) and Trithorax (TrxG) group proteins act antagonistically to establish tissue-specific patterns of gene expression. The PcG protein Ezh2 facilitates repression by catalysing histone H3-Lys27 trimethylation (H3K27me3). For expression, H3K27me3 marks are removed and replaced by TrxG protein catalysed histone H3-Lys4 trimethylation (H3K4me3). Although H3K27 demethylases have been identified, the mechanism by which these enzymes are targeted to specific genomic regions to remove H3K27me3 marks has not been established. Here, we demonstrate a two-step mechanism for UTX-mediated demethylation at muscle-specific genes during myogenesis. Although the transactivator Six4 initially recruits UTX to the regulatory region of muscle genes, the resulting loss of H3K27me3 marks is limited to the region upstream of the transcriptional start site. Removal of the repressive H3K27me3 mark within the coding region then requires RNA Polymerase II (Pol II) elongation. Interestingly, blocking Pol II elongation on transcribed genes leads to increased H3K27me3 within the coding region, and formation of bivalent (H3K27me3/H3K4me3) chromatin domains. Thus, removal of repressive H3K27me3 marks by UTX occurs through targeted recruitment followed by spreading across the gene

A Hot Saturn Near (but Unassociated with) the Open Cluster NGC 1817

We report on the discovery of a hot Saturn-sized planet (9.916 ± 0.985 R ⊕) around a late F-star, K2-308, observed in Campaign 13 of the K2 mission. We began studying this planet candidate because prior to the release of Gaia DR2, the host star was thought to have been a member (⩾90% membership probability) of the ≈1 Gyr open cluster NGC 1817 based on its kinematics and photometric distance. We identify the host star (among three stars within the K2 photometric aperture) using seeing-limited photometry and rule out false-positive scenarios using adaptive optics imaging and radial velocity observations. We statistically validate K2-308b by calculating a false-positive probability rate of 0.01%. However, we also show using new kinematic measurements provided by Gaia DR2 and our measured radial velocity of the system that K2-308 is unassociated with the cluster NGC 1817. Therefore, the long running search for a giant transiting planet in an open cluster remains fruitless. Finally, we note that our use of seeing-limited photometry is a good demonstration of similar techniques that are already being used to follow up Transiting Exoplanet Survey Satellite (TESS) planet candidates, especially in crowded regions