Arlo U. Landolt has been elected to a term on the Council of the American Association of Variable Star Observers (AAVSO), 2017-2019.
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.
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.)
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.
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].
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.
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.
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.
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.
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.
- 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.
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.
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.
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.
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.
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.
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).
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.
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.
WAFB Chanel 9 interviewed Dr. Chatopoulos's for Solar Eclipse event in LSU.
On August 21, a solar eclipse will pass across the United States, first darkening Oregon and creating a path of totality all the way to South Carolina over the course of a few hours. Everyone along this path will experience a few minutes of complete darkness along with the spectacular features of a total solar eclipse. The rest of the nation will experience a partial solar eclipse. Those not along the path of totality may feel like they are missing out, but NASA’s Eclipse Balloon Project has a solution for that!
August 21, 12-2pm lsu parade ground rain location: union
On Friday, August 4, LSU Physics & Astronomy welcomed 4 new PhD, 3 MS and 4 BS graduates who conferred their degrees at the Marvavich Assembly Center.
Advances in modern electronics has demanded the requisite hardware, transistors, to be smaller in each new iteration. Recent progress in nanotechnology has reduced the size of silicon transistors down to the order of 10 nanometers. However, for such small transistors, other physical effects set in, which limit their functionality. For example, the power consumption and heat production in these devices is creating significant problems for device design. Therefore, novel quantum materials and device concepts are required to develop a new generation of energy-saving information technology. The recent discoveries of topological materials — a new class of relativistic quantum materials — hold great promise for use in energy saving electronics. Researchers in the Louisiana Consortium for Neutron Scattering, or LaCNS, led by LSU Department of Physics & Astronomy Chair and Professor John F. DiTusa and Tulane University Professor Zhiqiang Mao, with collaborators at Oak Ridge National Lab, the National High Magnetic Field Laboratory, Florida State University, and the University of New Orleans, recently reported the first observation of this topological behavior in a magnet, Sr1-yMn1-zSb2 (y, z < 0.1). These results were published this week in Nature Materials (doi:10.1038/nmat4953).
BATON ROUGE - On August 21, 2017, a solar eclipse will be visible across North America, passing through the U.S. from Oregon to South Carolina. A solar eclipse occurs when the Moon's shadow passes over the Earth's surface, temporarily blocking the view of the Sun from the Earth. The last time a total solar eclipse occurred in the continental U.S. was 1979. This year, on Aug. 21, the eclipse will pass over the country again, with an 80% partial eclipse visible in Louisiana. With a grant from the Louisiana Space Grant Consortium (LaSPACE), Dr. Dana Browne, Professor and Associate Chair of the LSU Department of Physics & Astronomy, led a small team of K-12 teachers to develop a website toolkit for educators to teach students about the solar eclipse.
Charge density wave (CDW) is an important concept in condensed matter physics, germane to a number of physical phenomena. But the origin of CDW is still under debate, partly because the origin and properties of CDW are highly material-dependent. The concept of a CDW has been applied to many materials without a clear definition of the fundamental nature of CDW. As a result, misconceptions about CDW can be seen in literature. In this review, we will try to describe and explain the possible existing misconceptions associated with the origin of CDWs.
A team of students and faculty from the Louisiana Space Grant Consortium, LaSPACE, led by LSU and including Delgado Community College, or DCC; Louisiana Tech University, or LaTech; and McNeese State University, or MSU, will launch two high-altitude balloons on Aug. 21 as part of a NASA-sponsored project to live-stream aerial video footage of the “Great American Eclipse.”
Among topological materials, experimental study of topological semimetals that host Dirac/Weyl fermions has just begun, even though these topological concepts were proposed nearly a century ago by Dirac and Weyl. Our work shows magnetic-semimetal BaMnSb2 exhibits nearly zero-mass fermions with high mobility and a non-trivial Berry phase. What is unique is the magnetic ordering, indicating the system is Weyl type due to time-reversal symmetry breaking. Theory shows that the spin order is very fragile, so it is expected that the application of magnetic field or uniaxial pressure could drive the material to be a type-II Weyl semimetal.
Developments in synthesis and characterization of artificially structured materials has greatly advanced the possibility to explore new states of matter in material science. Recent discoveries show that new quantum states can be achieved at hetero-interfaces with various electromagnetic and mechanical boundary conditions. It remains an open question on how to design ultrathin layers with properties inaccessible in bulk phases, which is amenable to technological applications. In this work, we grow heterostructures with extremely high quality interfaces, characterized by state-of-the-art atomically resolved electron microscopy and spectroscopy. This combination allows us to identify an interface-induced structure that stabilizes ferromagnetism. Coupled with theory, we provide conceptually useful recipe to design low-dimensional materials with novel functionalities, in line with the loop of “make, measure, model”.
Professor Gabriela González is one of four high-profile speakers invited to share the stage with Stephen Hawking for his 75th birthday public symposium on Sunday July 2, from 7 a.m. to noon (CST). The public event at Cambridge University will be livestreamed by Discover Science on Facebook and YouTube.
Femtosecond broadband sum frequency generation (SFG) spectroscopy is applied to surface studies of the archetypical non-centrosymmetric semiconductor GaAs (001). Azimuthal angular dependence studies in reflection geometry under eight possible polarization configurations reveal strong surface-bulk interference owing to heterodyne amplification. The crystal symmetry and the surface quadrupole contributions need to be considered to properly interpret the resulting nonlinear spectroscopic signals. In addition, over bandgap excitation by one of the incident beams brings the semiconductor surface to a transient excited state, enabling enhanced sensitivity of broadband SFG to probe the surface electronic properties of non-centrosymmetric semiconductors. These findings suggest that this technique can be generally applied to surface studies of other non-centrosymmetric crystals.
Bilayered Sr3Ru2O7 is an unusual metamagnetic metal with inherently antiferromagnetic (AFM) and ferromagnetic (FM) fluctuations. Partial substitution of Ru by Mn results in the establishment of metal-insulator transition (MIT) at TMIT and AFM ordering at TM in Sr3(Ru1-xMnx)2O7. Using elastic neutron scattering we determined the effect of Mn doping on the magnetic structure and in-plane magnetic correlation lengths in Sr3(Ru1-xMnx)2O7 (x = 0.06 and 0.12). With increasing Mn doping (x) from 0.06 to 0.12 or decreasing temperatures for x=0.12, an evolution from an in-plane short-range to long-range double-stripe AFM ground state occurs. For both compounds, the onset of magnetic correlation with an anisotropic behavior coincides with the sharp rise of the electrical resistivity and the specific heat. Since it does not induce measurable lattice distortion, the double-stripe magnetic order with anisotropic spin texture breaks the symmetry from C4v crystal lattice to C2v magnetic sublattice. These observations shed new light on an age-old question of Slater versus Mott-type MIT.
Heteroepitaxial growth of transition-metal oxide films on the open (111) surface of SrTiO3 results in significant restructuring due to the polar mismatch. Monitoring the structural and composition on an atomic scale of LaNiO3/SrTiO3 (111) interface as a function of processing conditions has enabled the avoidance of the expected polar catastrophe. Using atomically resolved transmission electron microscopy and spectroscopy as well as Low energy electron diffraction, the structure of the thin film, from interface to the surface, has been studied. In this paper, we show that the proper processing can lead to a structure that is ordered, coherent with the substrate without intermediate structural phase. Angle-resolved X-ray photoemission spectroscopy shows that the oxygen content of thin films increases with the film thickness, indicating that the polar mismatch is avoided by the presence of oxygen vacancies.
The coupling between the electrical transport properties of L a 2 / 3 S r 1 / 3 Mn O 3 (LSMO) thin films and structural phase transitions of SrTi O 3 (STO) substrates at T s = 105 K has been investigated. We found that the electrical resistivity of LSMO films exhibit a “cusp” at T s , which is greatly amplified by tuning films to the verge of metallic and insulating phases, i.e., to the boundary of two delicate competing electronic states. Our results demonstrate that small amounts of strain can tip the subtle balance of competing interactions and tune the electronic properties in correlated electron materials.
LSU alum Edward Montiel graduated with his PhD from LSU Department of Physics & Astronomy in August, 2016 and is currently a postdoctoral researcher at University of California, Davis. He helps process data for guest investigators using the world's largest flying telescope SOFIA and deliver science-ready data to them for their analyses.
Technology that will improve X-rays and medical imaging is one of the 13 innovations the LSU Board of Supervisors recently selected to support through its innovation and technology transfer grant. LSU Department of Physics & Astronomy Assistant Professor Joyoni Dey, along with a Ph.D. student and colleagues at the LSU Center for Advanced Microstructures and Devices, have established the technology to create more detailed X-rays that will aid doctors analyzing lung and bone joint scans. This technology will also provide higher contrast images for mammograms.
The Newsweek interviewed Jonathan Dowling on the implication of quantum physics:"Cybersecurity Attacks Are a Global Threat. Chinese Scientists Have the Answer: Quantum Mechanics"
Researchers with LSU, UT Asutin, and Forschungszentrum Jülich have completed a study of the Zeeman-mediated superconducting phase diagram in ultrathin crystalline aluminum films.
In a state with the highest obesity rate in the nation - 36 percent - researchers in Louisiana are pushing to find new and better ways to combat this chronic disease. The battle against such a prevalent health problem is no small task. It requires scientists to uncover countless mysteries which still surround how and why our bodies work the way they do before they can begin to develop targeted therapies aimed at preventing and treating obesity.
The Laser Interferometer Gravitational-wave Observatory, or LIGO, has made a third detection of gravitational waves, which are ripples in space and time, demonstrating that a new window in astronomy has been firmly opened. As was the case with the first two detections, the waves were generated when two black holes collided to form a larger black hole.
Assistant Professor of Physics & Astronomy Kristina Launey is the recipient of the 2017 Dr. Marion D. “Soc” Socolofsky Award for Teaching Excellence. Launey was presented with the award during a surprise visit to her classroom earlier this month by College of Science Dean Cynthia Peterson and Chair of the LSU Department of Physics & Astronomy John DiTusa.
LSU Department of Physics & Astronomy Assistant Professor Ivan Agullo has received the first place award from the Gravity Research Foundation for his essay titled "Gravity and Handedness of Photons," which he co-authored with his colleagues Adrian del Rio and Jose Navarro-Salas, professors at Spain's Universidad de Valencia.
In this interview, Dr. Plummer shared his decades-long experiences of working with CAS, and his insights on the research future in China.
It has been dubbed the most mysterious star in the galaxy. The star, more than 1,200 light-years away in the constellation Cygnus the Swan, flickers and dims in a way never seen before.
On Friday, December 16, LSU Physics & Astronomy welcomed 4 new PhD, 1 MS and 10 BS graduates who conferred their degrees at the Marvavich Assembly Center and Maddox Fieldhouse. Kundan Kadam, PhD (advisor: Dr. Geoffrey Clayton ) Jiayum Pan, PhD (advisor: Dr. Rongying Jin) Mohammad Saghayezhian, PhD (advisors: Dr. Ward Plummer and Dr. Jiandi Zhang ) Marissa Walker, PhD (advisor: Dr. Gabriela González ) Anthony Ramon Davila, MS Daniel Joseph DiMarco, MS Kyle Joerres, MS Brandon Michael Luckett, MS William Craig Jones, BS Sean Michael Laughlin, BS Lucas Chad Lavoie, BS Simon Gabriel Lorenzo, BS Dylan Beckley Ottea, BS Patrick Lee Quebedeaux, BS Irene Vargas-Salazar, BS
In August 2015, the CALorimetric Electron Telescope (CALET), designed for long exposure observations of high energy cosmic rays, docked with the International Space Station (ISS) and shortly thereafter began to collect data. CALET will measure the cosmic ray electron spectrum over the energy range of 1 GeV to 20 TeV with a very high resolution of 2% above 100 GeV, based on a dedicated instrument incorporating an exceptionally thick 30 radiation-length calorimeter with both total absorption and imaging (TASC and IMC) units.
The LSU College of Science inducted four exceptional individuals into the Hall of Distinction on March 31, 2017, among them Donald Kniffen, 1959 LSU Physics & Astronomy alumnus and NASA research scientist. Kniffen, a magna cum laude graduate, is an accomplished astrophysicist and more than 40-year veteran of the NASA space program. He has been a leader in the national and international high-energy astrophysics community, and is one of the scientists who developed the field of high-energy gamma-ray astronomy. Gamma rays are emitted characteristically by the most energetic and exotic objects in the Universe, and gamma-ray astronomy is now one of the highest priority fields of astronomy.
The National Academy of Sciences announced today that LSU Department of Physics & Astronomy Professor Gabriela González has been elected as a member to the academy. González is one of the 84 new members recognized for her distinguished and continuing achievements in original research. She is an experimental physicist with the Laser Interferometer Gravitational-wave Observatory, or LIGO, who contributed to the detection of gravitational waves in 2015 predicted by Albert Einstein’s Theory of General Relativity.
Krystal Kirby, a third-year PhD student working under Dr. Owen Carmichael at LSU’s Pennington Biomedical Research Center, has been awarded an Economic Development Assistantship by the LSU Graduate School. Kirby is enrolled in the medical physics program in the Department of Physics & Astronomy, and is currently performing her research at the Pennington Biomedical’s Imaging Facility, which was opened in 2014.
We provide the power spectrum of small scalar perturbations propagating in an inflationary scenario within loop quantum cosmology. We consider the hybrid quantization approach applied to a Friedmann-Robertson-Walker spacetime with flat spatial sections coupled to a massive scalar field. We study the quantum dynamics of scalar perturbations on an effective background within this hybrid approach. We consider in our study adiabatic states of different orders. For them, we find that the hybrid quantization is in good agreement with the predictions of the dressed metric approach. We also propose an initial vacuum state for the perturbations, and compute the primordial and the anisotropy power spectrum in order to qualitatively compare with the current observations of Planck mission. We find that our vacuum state is in good agreement with them, showing a suppression of the power spectrum for large scale anisotropies. We compare with other choices already studied in the literature.