Physics & Astronomy News
"Shared symmetries of the hydrogen atom and the two-qubit system," by A.R.P. Rau and G. Alber, Topical Review: J. Phys. B : At. Mol. Opt. Phys. 50, 242001 (2017)
The hydrogen atom is the simplest system of atomic and molecular physics, while a two-qubit system is the simplest of quantum information. Remarkably, they share common symmetry aspects which are described in this paper.
Arlo U. Landolt has been elected to a term on the Council of the American Association of Variable Star Observers
Arlo U. Landolt has been elected to a term on the Council of the American Association of Variable Star Observers (AAVSO), 2017-2019.
CALET Makes First Direct Measurements of High Energy Electrons in Space
The CALET Cosmic Ray experiment, led by Professor Shoji Torii from Waseda University in Japan, along with collaborators from LSU and other researchers in the U.S. and abroad, have successfully carried out the high-precision measurement of cosmic-ray electron spectrum up to 3 tera electron volts (TeV) by using the CALorimetric Electron Telescope (CALET) on the Japanese Experimental Module, the Exposed Facility on the International Space Station (ISS). This experiment is the first to make direct measurements of such high energy electrons in space.
Gabriela González on TED: "How LIGO discovered gravitational waves"
More than 100 years after Albert Einstein predicted gravitational waves -- ripples in space-time caused by violent cosmic collisions -- LIGO scientists confirmed their existence using large, extremely precise detectors in Louisiana and Washington. Astrophysicist Gabriela González of the LIGO Scientific Collaboration tells us how this incredible, Nobel-winning discovery happened -- and what it might mean for our understanding of the universe. (In Spanish with English subtitles.)
"Anomalous Acoustic Plasmon Mode from Topologically Protected States" by Xun Jia, E. W. Plummer, Jiandi Zhang, etc.
Plasmons, the collective excitations of electrons in the bulk or at the surface, play an important role in the properties of materials, and have generated the field of “plasmonics.” We report the observation of a highly unusual acoustic plasmon mode on the surface of a three-dimensional topological insulator (TI) Bi2Se3, using momentum resolved inelastic electron scattering. In sharp contrast to ordinary plasmon modes, this mode exhibits almost linear dispersion into the second Brillouin zone and remains prominent with remarkably weak damping not seen in any other systems. This behavior must be associated with the inherent robustness of the electrons in the TI surface state, so that not only the surface Dirac states but also their collective excitations are topologically protected. On the other hand, this mode has much smaller energy dispersion than expected from a continuous media excitation picture, which can be attributed to the strong coupling with surface phonons.
“Reentrance of Insulating Phase of La2/3Sr1/3MnO3(110) Thin Film at Low Temperature” by Lin Li, Zhenyu Diao, Rongying Jin, E. W. Plummer, and Jiandi Zhang etc.
We have studied La2/3Sr1/3MnO3 thin films grown on (3×1)-reconstructed SrTiO3 (110) substrates. Films with thicknesses less than the critical thickness of θc≅8 unit cells are insulating in the measured temperature (T) range (2–400 K). However, films with thicknesses slightly over θc exhibit reentrant nonmetallic behavior at low temperatures in addition to the normally observed metal-insulator transition at higher temperatures. In contrast, the magnetization does not show signs of low-T transitions. Such reentrance of a low-T nonmetallic phase is affected by the film thickness as well as the density of oxygen vacancies. The electrical resistivity analysis reveals that localization effects are responsible for the reentrant nonmetallic behavior, which is enhanced with reduced film thickness. Reentrance of low-temperature nonmetallic phase of L a 2 / 3 S r 1 / 3 Mn O 3 (110) thin films. Available from: https://www.researchgate.net/publication/319241498_Reentrance_of_low-temperature_nonmetallic_phase_of_L_a_2_3_S_r_1_3_Mn_O_3_110_thin_films [accessed Oct 20 2017].
LIGO-Virgo Scientists Detect First Gravitational Waves from Neutron Stars
Discovery made at LIGO Livingston by LSU physicists marks first cosmic event observed in both gravitational waves and light - For the first time, scientists have directly detected gravitational waves — ripples in space and time — in addition to light from the spectacular collision of two neutron stars. This marks the first time that a cosmic event has been viewed in both gravitational waves and light. The discovery was made using the U.S.-based Laser Interferometer Gravitational-Wave Observatory, or LIGO; the Europe-based Virgo detector; and some 70 ground- and space-based observatories.
MONDAY: New Gravitational-wave Discovery to be Announced
The Gravitational Wave Astrophysics conference sponsored by the International Astronomical Union will livestream the LIGO Laboratory, LIGO Scientific Collaboration, National Science Foundation and Virgo Collaboration press conference. Journalists are invited to watch the livestream of the press conference on Monday, Oct. 16, at 9 a.m. (CDT) from the National Press Club in Washington, D.C. The livestreamed press conference will begin with an overview of new findings from LIGO, Virgo and partners that span the globe, followed by details from telescopes that work with the LIGO and Virgo Collaboration to study extreme events in the cosmos.
LSU Physicist Patents Wearable Device to Protect Doctors Who Use X-rays
The invention will enhance protection of radiation workers, such as radiologists. Those who work in radiation fields are at increased risk to develop cataracts, cancer, and other radiation effects. Our device accurately measures, records, and reports exposure to the user in real time, thereby providing the information needed to limit exposures to safe levels.
LIGO Gravitational Wave Detection Wins Nobel Prize - LSU faculty and students critical in this groundbreaking discovery
oday the 2017 Nobel Prize in Physics was awarded to the pioneering leaders of the Laser Interferometer Gravitational-wave Observatory, or LIGO, for the first detection of gravitational waves. The detection confirmed a major prediction of Albert Einstein's 1915 general theory of relativity and opens an unprecedented new window onto the cosmos.
LSU Physicist Awarded New NSF Research Fellowship - Alumna and Assistant Professor Kristina Launey one of 30 to receive fellowship
The National Science Foundation, or NSF, announced new awards for non-tenured researchers through their Established Program to Stimulate Competitive Research, or EPSCoR, Research Infrastructure Improvement Track-4 fellowship program. Kristina Launey, LSU Ph.D. ('03) alumna and assistant professor in the Department of Physics & Astronomy, is one of 30 to receive the NSF Research Fellowship. These fellowships partner researchers with premier research centers, enhancing their ability to work at the frontiers of science and engineering.
LSU Physicist's Research Reveals that the Most Energetic Particles in the Cosmos Originated from Outside our Galaxy
- In a paper published in the journal Science, the Pierre Auger Collaboration reports observational evidence demonstrating that cosmic rays with energies a million times greater than that of the protons accelerated in the Large Hadron Collider come from much further away than from our galaxy. LSU Department of Physics & Astronomy Professor Jim Matthews, former co-spokesperson of the Auger Collaboration, works with more than 500 scientists from 17 countries on the world's leading science project for the exploration of the highest energy cosmic rays to elucidate the origins and properties of the most energetic particles in the Universe. The collaboration is reconstructing the path of the Universe's most energetic cosmic rays, bringing new insights into the origin and nature of this intergalactic phenomenon.
"Cell-shaped silicon-on-insulator microdosimeters: characterization and response to 239PuBe irradiations" by Mazza, Newhauser, etc.
This work tested the feasibility of a silicon-on-insulator microdosimeter, which mimics the size and shape of specific cells within the human body, to determine dose equivalent from neutron irradiation. The microdosimeters were analyzed in terms of their basic diode characteristics, i.e., leakage current as a function of bias voltage. Lineal energy spectra were acquired using two different converter layers placed atop the microdosimeter: a tissue-substitute converter made from high-density polyethylene, and a boron converter consisting of epoxy coated with boron powder. The spectra were then converted into absorbed dose and dose equivalent. Experimental results were compared to Monte Carlo simulations of the neutron irradiations, revealing good agreement. Uncertainty in the dose equivalent determinations was 7.5% when using the cell-shaped microdosimeter with the tissue-substitute converter and 13.1% when using the boron converter. This work confirmed that the SOI approach to cell-mimicking microdosimetry is feasible.
"δ-Doping of oxygen vacancies dictated by thermodynamics in epitaxial SrTiO3 films" by Fengmiao Li, Jiandi Zhang, E. W. Plummer,etc.
Homoepitaxial SrTiO3(110) film is grown by molecular beam epitaxy in ultra-high vacuum with oxygen diffusing from substrate as the only oxidant. The resulted oxygen vacancies (VOs) are found to be spatially confined within few subsurface layers only, forming a quasi-two-dimensional doped region with a tunable high concentration. Such a δ-function distribution of VOs is essentially determined by the thermodynamics associated with the surface reconstruction, and facilitated by the relatively high growth temperature. Our results demonstrate that it is feasible to tune VOs distribution at the atomic scale by controlling the lattice structure of oxide surfaces.
"Impact of multileaf collimator configuration parameters on the dosimetric accuracy of 6-MV Intensity-Modulated radiation therapy treatment plans" by Petersen, Perrin, Newhauser and Zhang
The purpose of this study was to evaluate the impact of selected configuration parameters that govern multileaf collimator (MLC) transmission and rounded leaf offset in a commercial treatment planning system (TPS) (Pinnacle3, Philips Medical Systems, Andover, MA, USA) on the accuracy of intensity-modulated radiation therapy (IMRT) dose calculation. The MLC leaf transmission factor was modified based on measurements made with ionization chambers. The table of parameters containing rounded-leaf-end offset values was modified by measuring the radiation field edge as a function of leaf bank position with an ionization chamber in a scanning water-tank dosimetry system and comparing the locations to those predicted by the TPS. The modified parameter values were validated by performing IMRT quality assurance (QA) measurements on 19 gantry-static IMRT plans. Planar dose measurements were performed with radiographic film and a diode array (MapCHECK2) and compared to TPS calculated dose distributions using default and modified configuration parameters. Based on measurements, the leaf transmission factor was changed from a default value of 0.001 to 0.005. Surprisingly, this modification resulted in a small but statistically significant worsening of IMRT QA gamma-index passing rate, which revealed that the overall dosimetric accuracy of the TPS depends on multiple configuration parameters in a manner that is coupled and not intuitive because of the commissioning protocol used in our clinic. The rounded leaf offset table had little room for improvement, with the average difference between the default and modified offset values being −0.2 ± 0.7 mm. While our results depend on the current clinical protocols, treatment unit and TPS used, the methodology used in this study is generally applicable. Different clinics could potentially obtain different results and improve their dosimetric accuracy using our approach.
Solving the Mystery of KIC 8462852—the Most Bizarre Star in the Universe
Since its discovery two years ago, a star that resides around 1,300 light years from Earth has gained a reputation as the most bizarre in the galaxy. Named KIC 8462852, the star gained worldwide attention when scientists suggested its weird behaviour could be explained by the presence of a huge shield built by an advanced alien civilization. Back then Tabetha Boyajian, from Louisiana State University, and her colleagues discovered that KIC 8462852 exhibited huge dips in its brightness at regular intervals using data from the Kepler Space Telescope—sometimes by as much as 20 percent.
Dr. Gabriela Gonzalez: Scientist of the Future
Imagine taking a prediction made a hundred years ago by one of the greatest minds of the 20th century and finding the evidence to prove it to be true today. That’s what an Argentine-born female physicist did as part of a team of scientists in Louisiana. By validating Albert Einstein’s theory of relativity, they are being showered with worldwide acclaim, and the near certainty of a Nobel Prize. John Zarrella spent time with Dr. Gabriela Gonzalez, who insists there is more to come.
"A Clarion Call for Large-Scale Collaborative Studies of Pediatric Proton Therapy" by Gonzalez, A.; Newhauser, W. and Walsh, L. etc.
In 2010, there were 24 proton therapy centers operating around the world. During the past 6 years, 33 new centers have opened, 32 are under construction, and 17 are in the planning phase (1).
LSU Health Physics graduate student replicates 1976 ‘Atomic Man’ incident
A pilot project this summer at Oak Ridge Associated Universities, or ORAU, hearkens back to the organization’s roots ...... A near-certain outcome is that the students will finish their internships with a head start on a project that could become their master’s thesis or doctoral dissertation. Such is the case for Daniel DiMarco from Marrero, La.
Solar Eclipse 2017 on the LSU Parade Ground
On August 21, 2017, more than a thousand astronomy enthusiasts gathered on the LSU Parade Ground to view the Great American Eclipse. Physics & Astronomy Department Chair John DiTusa and WAFB chief meteorologist Jay Grymes emceed the event on the first day of class for the fall semester. While students, faculty and staff shared solar viewing glasses to look at the partial eclipse, faculty talked about the science and history of the eclipse, including Manos Chatzopoulos, Gabriela Gonzalez and Rob Parks. Attendees also experienced alternative ways to view the eclipse with a sun spotter, solar filter disk, pinhole cameras, and even viewing the eclipse on the ground through the oak trees.