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Department of Physics & Astronomy at the University of Utah

Dr. John Belz Kicks Off Clark Planetarium's Night School Lecture Series

From the Clark Planetarium's website.

Dr. John Belz
June 21, 2012
Clark Planetarium

Beginning in June, join the Clark Planetarium for their new open format lecture series, Night School. Topics range across a wide spectrum of scientific disciplines and the open format encourages group discussion and exploration.

Dr. John Belz, will launch the Night School series on Thursday, June 21st from 7pm – 8pm, with his talk, “Two Through Your Head Every Second – Cosmic Rays”. High energy cosmic rays are important to our understanding of the universe, and John Belz uncovers what cosmic rays are, their origin, and how they are detected.

Night School sessions are hosted in the Hansen Dome Theater, and are followed by light refreshments in the Third Floor Exhibits area. Admission is $2. Members are free.

More information available here.


William Baker Thesis Defense 06/11/12

Thesis Defense

William J. Baker

Monday, June 11, 2012
10:00am (110 INSCC)

Title: Properties & Applications of Coherently Controlled Spin-Dependent Charge Carrier Transitions in MEH-PPV


This thesis is focused on the investigation of the fundamental physical nature and potential technical applications of spin-dependent charge carrier recombination in poly[2-methoxy-5-(20-ethyl-hexyloxy)-1,4-phenylene vinylene (MEH-PPV), a π-conjugated polymer which has been utilized as organic thin film semiconductor. Pulsed electrically detected magnetic resonance (pEDMR) spectroscopy was used to observe how coherent spin motion of paramagnetic charge carrier states (so called polarons) control the macroscopic conductivity of thin (~100nm) MEH-PPV layers under different charge carrier injection regimes. The pEDMR experiments were conducted at frequencies covering almost three orders of magnitude (~20MHz to ~10GHz) and at temperatures between ~5K and ~300k. The measurements revealed that under balanced bipolar injection, the conductivity of MEH-PPV is influenced at any temperature by the polaron pair (PP) mechanism, a spin-dependent process previously described in the literature. The experiments showed that PPs are weakly exchange- and dipolar-coupled pairs but they are strongly influenced by proton induced hyperfine fields. Electrical detection of coherent polaron-spin motion revealed extraordinary long coherence times (order of μs) at room temperature which could qualify PPs for quantum information applications. The PP mechanism was also demonstrated to work as an extraordinary sensitive, 50 nT Hz-1/2, organic thin film probe which uses the polarons gyromagnetic ratio λ as magnetic field standard. λ was observed to be independent of temperature, device-current, and -bias, and degradation of the MEH-PPV device. In addition to the PP mechanism, another spin-dependent process previously described in the literature was confirmed to significantly influence conductivity in MEH-PPV: Triplet exciton -polaron recombination.


Paul Nunez Thesis Defense 06/4/12

Thesis Defense

Paul Nuñez

Monday, June 4, 2012
3:00pm (334 JFB)

Title: Towards Optical Intensity Interferometry for High Angular Resolution Stellar Astrophysics


Most stars are detected as point sources, and recent developments in high angular resolution astronomy have enabled to image stars as extended objects with complex atmospheres and circumstellar environments. However, most neighboring stars are still beyond the angular resolution reach of current observatories.

Atmospheric Cherenkov Telescopes (ACT) are used in gamma-ray astronomy to investigate violent phenomena in the universe. However, this technique can also be used for stellar astrophysics on some isolated sources. Such is the case with the Xray binary LSI+61 303 which was detected in the TeV range. A gamma-ray attenuation model is developed and applied it to this system. This models allows to place constraints on fundamental properties of the system. However, a much better understanding of this system, and more so of nearby bright stellar systems, could be obtained with high angular resolution techniques.

Light detectors such as ACT, can be used as intensity interferometry receivers in the visible band (400 nm). Optical stellar intensity interferometry with air Cherenkov telescope arrays, composed of nearly 100 telescopes, will provide means to measure fundamental stellar parameters and also open the possibility of model-independent imaging. The phase of the complex degree of coherence is not measured in this technique. However, several model-independent phase reconstruction techniques have been developed. Here we implement a Cauchy-Riemann based algorithm to recover images from simulated data. We find that stellar images can be accurately reconstructed, and results are further improved with post-processing routines.

Finally, experimental efforts to measure intensity correlations are expounded. The functionality of analog and digital correlators is demonstrated. Intensity correlations have been measured for a simulated star emitting pseudo-thermal light, resulting in angular diameter measurements. The StarBase observatory, consisting of a pair of 3 m telescopes separated by 23 m, is described


Transit of Venus

Transit of Venus
Dr. Ben Bromley

Location: Skaggs Biology Building (ASB) Auditorium, Room 220 at the University of Utah
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Talk Date: June 4, 2012, 7:00pm

Venus Transit Date: June 5, 2012

Free event open to the public.

On June 5, 2012, our sister planet Venus will pass in front of the Sun. Venus’ silhouette will appear on the Sun’s face, just for a few hours. This “transit” event is rare! It won’t happen again for more than a century. But astronomers now see distant planets transiting their own stars every day. Come learn how Venus’ transit first helped astronomers map the Solar System and find out about the mysterious “Black Drop.” Hear about the trials and tribulations of the first transit chasers and find out how today’s searches are on the verge of discovering worlds that may harbor life like our own, or creatures very different from us!


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