Interaction of trapped ions with trapped atoms

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 179-186).In this thesis, I present results from two Paul-trap based ion traps carried out in the Vuletić laboratory: the Atom-Ion trap for collision studies between cold atoms and cold ions, and the Cavity-Array trap for studying the interaction between ionic ensembles and photons. The Atom-Ion trap overlaps a surface-planar ion trap with a magneto-optical trap (MOT) for neutral atoms. The initial results of this system were loading of a shallow surface-planar ion trap at an unprecedented high rate of 4. 105 s-1 and isotopic purity by photoionization from the MOT. We demonstrate the first collisions between trapped atoms and trapped ions in the Langevin collision regime between Yb+ and Yb. A measurement of the Langevin rate constant through charge-exchange collisions between [alpha]Yb+ and [beta]Yb over three orders of magnitude in collision energy down to 3 yueV follows. The measured rate coefficient of 6 - 10-10 cm 3 s-1 is in good agreement with the Langevin model based on theoretical predictions of the polarizability of Yb. The theory and limits of sympathetic cooling of ions by localized cold atoms at low temperature is outlined. Measurements of momentum-transfer collisions between Yb+ and Rb are presented indicating that momentum-transfer collisions affect the ion energy at the Langevin rate. Finally, the fabrication and assembly of the Cavity-Array trap are presented. The Cavity-Array trap overlaps a high-finesse optical cavity with a linear array of Paul traps in order to reach the high co-operativity limit with trapped ions. Initial results from loading of the Cavity- Array trap are shown, indicating successful overlap of the optical cavity mode with the ion trapping region and the ability to load individual sites of the array ion trap.by Andrew T. Grier.Ph.D

Signature-Based Small Molecule Screening Identifies Cytosine Arabinoside as an EWS/FLI Modulator in Ewing Sarcoma

BACKGROUND: The presence of tumor-specific mutations in the cancer genome represents a potential opportunity for pharmacologic intervention to therapeutic benefit. Unfortunately, many classes of oncoproteins (e.g., transcription factors) are not amenable to conventional small-molecule screening. Despite the identification of tumor-specific somatic mutations, most cancer therapy still utilizes nonspecific, cytotoxic drugs. One illustrative example is the treatment of Ewing sarcoma. Although the EWS/FLI oncoprotein, present in the vast majority of Ewing tumors, was characterized over ten years ago, it has never been exploited as a target of therapy. Previously, this target has been intractable to modulation with traditional small-molecule library screening approaches. Here we describe a gene expression–based approach to identify compounds that induce a signature of EWS/FLI attenuation. We hypothesize that screening small-molecule libraries highly enriched for FDA-approved drugs will provide a more rapid path to clinical application. METHODS AND FINDINGS: A gene expression signature for the EWS/FLI off state was determined with microarray expression profiling of Ewing sarcoma cell lines with EWS/FLI-directed RNA interference. A small-molecule library enriched for FDA-approved drugs was screened with a high-throughput, ligation-mediated amplification assay with a fluorescent, bead-based detection. Screening identified cytosine arabinoside (ARA-C) as a modulator of EWS/FLI. ARA-C reduced EWS/FLI protein abundance and accordingly diminished cell viability and transformation and abrogated tumor growth in a xenograft model. Given the poor outcomes of many patients with Ewing sarcoma and the well-established ARA-C safety profile, clinical trials testing ARA-C are warranted. CONCLUSIONS: We demonstrate that a gene expression–based approach to small-molecule library screening can identify, for rapid clinical testing, candidate drugs that modulate previously intractable targets. Furthermore, this is a generic approach that can, in principle, be applied to the identification of modulators of any tumor-associated oncoprotein in the rare pediatric malignancies, but also in the more common adult cancers

Ecological insights from three decades of animal movement tracking across a changing Arctic

The Arctic is entering a new ecological state, with alarming consequences for humanity. Animal-borne sensors offer a window into these changes. Although substantial animal tracking data from the Arctic and subarctic exist, most are difficult to discover and access. Here, we present the new Arctic Animal Movement Archive (AAMA), a growing collection of more than 200 standardized terrestrial and marine animal tracking studies from 1991 to the present. The AAMA supports public data discovery, preserves fundamental baseline data for the future, and facilitates efficient, collaborative data analysis. With AAMA-based case studies, we document climatic influences on the migration phenology of eagles, geographic differences in the adaptive response of caribou reproductive phenology to climate change, and species-specific changes in terrestrial mammal movement rates in response to increasing temperature.</p