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Thursday Colloquium: Carsten Rott, Oct. 25, 2012

Carsten Rott
(CCAPP) at The Ohio State University

Thursday, Oct. 25, 2012
102 JFB

Refreshments: 3:30 pm in 219 JFB
Lecture 4:00pm (102 JFB)

Title: Latest Results from the IceCube Neutrino Observatory

Abstract:

The world's largest neutrino observatory IceCube is comprised of more than 5000 photomultiplier tubes on 86 strings installed in the Antarctic ice cap at depths from 1450 to 2450 m. An air shower array, called IceTop, is located at the surface. Construction of this multi-purpose detector was completed in December 2010. The detector has been taking data since the deployment of the first string in January 2005. Data has been analyzed for high energy neutrino events of astro-physical origin, cosmic rays, transient sources, dark matter annihilation signals, and various others. After a review of the latest results, the talk will conclude by giving an outlook for potential upgrades to the IceCube detector.

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Special Colloquium: Alan Drew, Oct 24, 2012.

Alan Drew
Queen Mary, University of London

Thursday, Oct. 24, 2012
102 JFB

Refreshments: 3:30 pm in 219 JFB
Lecture 4:15pm (102 JFB)

Title: Local Probe Investigation of Spin & Charge Dynamics in Organic Semiconductors

Abstract:

Organic semiconductors fall into a class of materials that shows significant potential for future applications and as a result, the field is becoming extremely topical. This is due to their ease of processing, low cost, highly tuneable electronic properties, favorable mechanical properties and long spin coherence times. The latter point makes them extremely promising for future spintronic applications. However, there is a lack of suitable techniques that can yield information on intrinsic spin and charge carrier dynamics in organic materials. For example, many of the experimental techniques available that probe the spin polarization of charge carriers in inorganic spintronic devices/materials are not always applicable to organic materials. Muon spectroscopy is a technique that has rarely been applied to study spintronic problems in inorganic systems, yet is ideally suited to studying them in organic semiconductors.

Low energy muon spin rotation can directly measure the depth resolved spin polarization of charge carriers in organic spin injection devices [1]. After giving a brief introduction to muon spin rotation in the context of these results, I will go on to demonstrate that it is possible to separate out the various contributions to spin decoherence in organic spin valves, differentiating between interface and bulk spacer layer effects [2].

A more exotic application of the muon technique, known as avoided level crossing (ALC) spectroscopy, can be used to probe the spin dynamics in organic semiconductors on a molecular lengthscale [3,4]. After briefly introducing this application of muons, I will go on to present measurements of temperature dependent electron spin relaxation rates, on a series of organic molecules of different morphology and molecular structure. These measurements, when combined with some of the latest results on the mass-dependence of electron spin relaxation rates, offer clues as to the underlying relaxation mechanism in organic semiconductors [4,5].

Finally, taking advantage of the intrinsic spatial sensitive of ALC spectroscopy, I will show how laser excited ALC spectroscopy (a technique I am currently developing) can offer unique insight into electron transfer in organic molecules. Not only is this an important process in organic electronics/spintronics, it also is fundamental to many biological processes, including photosynthesis, DNA repair and cell respiration.

[1] A. J. Drew et al., Nature Materials 8, 109 (2009)
[2] L. Schulz et al., Nature Materials 10, 39 (2011)
[3] A. J. Drew et al., Phys. Rev. Lett. 100, 116601 (2008)
[4] L. Schulz et al., Phys. Rev. B 84, 085209 (2011)
[5] L. Nuccio et al., submitted.

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Astronomy Week


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Monday & Tuesday (Oct 15 & 16): Telescopes in the Park at Liberty Park, 11:00 am - 3:00 pm

Join the University of Utah Astronomy Outreach Group to view the Sun through specialized telescopes! Learn more...

Wednesday, October 17: Star Party, 8:30 pm - 11:30 pm

Let our observatory guides take you on a tour of the night sky! Learn more...

Thursday & Friday (Oct. 18-19) Astronomy Activities at the Natural History Museum of Utah, 12:00 pm - 4:00 pm

Come explore astronomy through hands-on activities and demonstrations! Look through telescopes and meet a "Dark Ranger" from Bryce Canyon National Park! Learn more...

Saturday October 20: Astrofest at Clark Planetarium 1:00 pm - 4:00 pm

Learn more about telescopes and how astronomers make discoveries with a variety of presentations and activities! Learn more...

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Monica Allen Thesis Defense 10/15/12

Thesis Defense

Monica Allen

Monday, October 15, 2012
12:00pm (110 INSCC)

Title: Ultra High Energy Cosmic Ray Energy Spectrum and Composition using Hybrid Analysis with Telescope Array

Abstract:

Cosmic radiation was discovered in 1912. This year, the 100th anniversary of the discovery, marks not only the major progress that has been made in understanding these particles, but also the remaining questions about them. Questions about their sources, acceleration mechanisms, propagation and composition are still unanswered. There are only two experiments currently running which have the ability to study cosmic rays in the Ultra High Energy (E > 1018 eV) regime.

The Telescope Array studies Ultra High Energy Cosmic Rays (UHECRs) using a hybrid detector. Fluorescence telescopes measure the longitudinal development of the extensive air shower generated by a primary cosmic ray particle, while scintillator detectors measure the lateral distribution of secondary particles that hit the ground. The Middle Drum (MD) fluorescence telescope consists of 14 refurbished telescopes from the High Resolution Fly's Eye (HiRes) experiment, providing a direct link back to the HiRes experiment and data. The surface array is comprised of 507 Scintillator Detectors (SD) of a similar design as was used by the Akeno Giant Air Shower Array

(AGASA), providing a link to that experiment as well. Using events observed by both types of detectors improves the geometrical reconstruction of the showers significantly. This provides a more accurate reconstruction of the energy of the primary particle and makes it possible to make a measurement of the cosmic ray chemical composition. The spectral and composition measurements made by this hybrid detector will be presented.

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