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Astronomers Measure the Deceleration of the Universe before Dark Energy

Young Universe Expanded Slowly During Last 14 Billion Years, Expansion Slowed and then Sped Up


Astrophysicist Kyle Dawson stands in front of the 2.5-meter Sloan Telescope at Apache Point Observatory in New Mexico. Photo Credit: Dan Long, Apache Point Observatory

Nov. 12, 2012 – Like a roller coaster that crawls slowly uphill and then zooms downhill, the universe expanded at a much slower rate 11 billion years ago than it has during the past 5 billion years, says a new study co-authored by Kyle Dawson, a University of Utah astrophysicist.

Light from 60,000 super-bright objects known as quasars served as flashlights to illuminate hydrogen gas between Earth and objects in the distant, early universe.

“We reconstructed a 3-D map of the hydrogen gas, and from the map, we learned about the processes by which the universe expanded and grew in the first 3 billion years,” says Dawson, an assistant professor of physics and astronomy at the University of Utah and a member of the third Sloan Digital Sky Survey, or SDSS-III, which conducted the study.

Scientists believe the universe formed some 13.8 billion years ago in a sudden expansion of matter and energy known as the Big Bang. Previous research showed its expansion has been speeding up for the past 5 billion years. The new study – performed using the 2.5-meter Sloan Telescope at Apache Point Observatory in New Mexico – is the first to make measurements showing expansion of the universe was slowing for the first 3 billion years after the Big Bang. The expansion later crested the top of the “roller coaster” and began to expand more rapidly some 5 billion years ago.

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Kamdem Thaddee Thesis Defense 11/5/12

Thesis Defense

Kamdem Thaddee

Monday, November 5, 2012
3:30pm (334 JFB)

Title: No Title

Abstract:

We performed a systematic study of bipolar and unipolar diodes based on MEH-PPV, using electronic and magneto-transport measurements with magnetic field in the range 0–180 mT and admittance spectroscopy in the frequencies varying from 1Hz to 10MHz. The admittance spectra of bipolar devices reveal two relaxation processes with distinct time scales that are influenced by the magnetic field. The slower process, which dominates the device capacitance at frequencies less than 10 Hz, is attributed to the trap-assisted monomolecular recombination. The second faster process is attributed to the electron-hole bimolecular recombination kinetics. decreases by approximately 30% under magnetic field of 30 mT. We observed that at low frequencies, the differential capacitance of bipolar devices is positive at low biases voltages, turns negative at intermediate biases, and becomes positive again at stronger biases. By carefully selecting bias voltage, we were able to tune some bipolar diodes from the state with the negative capacitance to the state with the positive capacitance just by applying magnetic field. The magneto-conductance has a characteristic cutoff frequency that shifts to higher frequencies with increasing bias voltages. In particular, the magneto-conductance at 10 MHz in a bipolar device was measured to be 4.5 % in the magnetic field of magnitude 30 mT. For bipolar devices, the frequency-dependent response of the device admittance to the small magnetic field is identical to the response of the admittance to the small increase in the bias voltage in zero magnetic field. We found that the response of the admittance on the magnetic field is consistent with the polaron-polaron model of OMAR. The admittance of unipolar diodes did not reveal any magnetic field.

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This Week's Colloquium: James Pinfold, Nov. 1, 2012

James Pinfold
University of Alberta

Thursday, Nov. 1, 2012
102 JFB

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

Title: The MoEDAL Experiment at the LHC - Searching for the Highly Ionizing Particle Avatars of New Physics

Abstract:

MoEDAL (the Mo nopole and Exotics Detector at the Lhc) was approved by CERN research board in March 2012. It is the 7th and newest LHC experiment designed to search for highly ionizing particle avatars of New Physics. I will give a brief historical introduction to the search for highly ionizing particles, concentrating on the magnetic monopole, and then describe the experiment and its revolutionary physics potential.

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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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