Eric Sembrat's Test Bonanza

The quantum Hall effect (QHE) observed in two dimensional electron gas at low temperature and under a strong perpendicular magnetic field has revolutionized the resistance metrology since its discovery in 1980 by Klaus von Klitzing. It provides a representation of the ohm based on the Planck constant and the electron charge only. In 2005, graphene, a purely two dimensional arrangement of carbon atoms in a honeycomb lattice, where the charge carriers behave as Dirac fermions, has revealed a new flavor of the QHE. From the metrological point of view the QHE in graphene is very promising since it is much more robust than in conventional semiconductors. It could lead to a more convenient resistance standard operating at higher temperature and lower magnetic induction, which is an advantage for a broader dissemination of a precise standard for industrial end-users.

During this presentation I’ll first present the impact in the QHE regime of line defects such as wrinkles or grain boundaries, ubiquitous in graphene grown by chemical vapor deposition on metal. We will show that these line defects lead to a non conventional dissipation mechanism that jeopardize the quantum Hall effect accuracy, pointing to the use of wrinkle-free monocrystals for further metrological studies.

The second part of my presentation will be focused on monolayer graphene grown by chemical vapor deposition on silicon carbide. We compared in detail the Hall resistance of the graphene sample from 10 T to 19 T at 1.4 K with a GaAs/AlGaAs resistance standard with a discrepancy of (-2± 4)x1010. For the first time a graphene-based standard was able to operate not only in the same temperature and magnetic field conditions as the semiconductor-based standard, but in a magnetic range more than ten times larger. We have carefully studied the dissipation mechanisms taking place in this sample and measured precisely the value of the localization length in the QHE regime. It saturates interestingly at the charge carrier wavelength, opening interesting questions about the close link between Hall quantization and localization physics in graphene grown on SiC.

The extragalactic background light (EBL) that fills the Universe is mainly the result of star formation activity over cosmic time. Therefore, it contains fundamental information on galaxy evolution and cosmology. The detection of the EBL by direct methods is hampered by the strong foregrounds mainly from our own Solar System and Galaxy. Interestingly, there are other indirect methodologies that allows us its study such as observations from deep galaxy surveys and gamma-ray observations of distant sources. The latter methodology is based on the fact that very high energy photons traveling across cosmological distances interact by pair production with EBL photons producing an energy-dependent attenuation of the emitted flux. Knowledge of the EBL is thus fundamental in order to correctly interpret extragalactic observations from Cherenkov telescopes such as HAWC and the future CTA. A summary of our EBL knowledge and current and future lines of work will I will also discuss how the recent progress in the EBL understanding has allowed us to measure the expansion rate of the Universe using multiwavelength observations of blazars, which include Fermi and Cherenkov observations.

The large-scale distribution of galaxies can be explained fairly simply by assuming i) all galaxies are hosted by halos and ii) a cosmological model. This simple framework, called the `halo-model', has been remarkably successful at reproducing the large-scale clustering of galaxies observed in various galaxy redshift surveys. However, none of these studies have truly tested the `halo-model' by carefully modeling the systematics. We present the results from a fully-numerical, accurate `halo-model' framework and show that the theory can not simultaneously reproduce the galaxy projected correlation function and the group multiplicity function in the SDSS main samples. In particular, the bright galaxy sample shows significant tension with theory. We discuss the implications of our findings, as well as how to constrain different aspects of galaxy formation by simultaneously fitting multiple statistics.

In this lecture, Georgia Tech Physics Professor Ed Conrad and Director of Research at the French National Center for Scientific Research (CNRS) Amina Taleb will give a feel for how modern research is conducted in the era of small materials and big machines, showing an example of an international materials research collaboration between Georgia Tech’s School of Physics and researchers at the Synchrotron SOLEIL near Paris.

Freelance professional photographer Vincent Moncorge will share his experience on documenting science. Following a short historical exploration from the late 19th century and French photographer Etienne Jules Marey’s Chronophotograph, he will detail the new modern story-telling strategies the scientific community is facing today. Then, he will share about his own personal experiences with photographing synchrotron daily life to model organisms such as tiny Drosophila flies.

 TBD

The cell can be thought of as an organized collection of molecular machines. As such, many biomolecules can have moving parts, generate, bear and leverage forces, and convert chemical energy to mechanical work and vice versa. In this talk I will use several examples to illustrate how mechanics can regulate biology at the molecular scale.

Great voyages of exploration have always been driven in large part by an insatiable curiosity to know what is beyond the furthest horizon you can see. Five hundred years ago, the European exploration of the globe was a central feature of the expanding scientific and artistic explosion we call the Renaissance and Enlightenment. Today, we are once again witnessing an age of exploration and discovery, as we push beyond the shores of Earth, looking deep into the far reaches of space. You and I live in an age where, for the first time in human history, we are discovering and mapping alien worlds.  Some of those worlds are not far from home, huddled around our own Sun but difficult to travel to.  Some of those worlds are far across the Cosmos, spinning around other suns in other parts of the galaxy. For the first time in history, we are seeing and probing these worlds with the same age old questions in mind: Who are we? What is our place in the Cosmos? Are we alone?

In this talk, we'll talk about this new age of discovery in our own Solar System, and how our understanding of the Solar System has changed over the past 40 years, during the first reconnaissance of the Worlds of the Sun. We'll preview the upcoming visit to Pluto, and use that as motivation to explore how the discovery of exoplanets around other stars is shaping our understanding of whether our home around the Sun is commonplace or unique in the catalogue of planetary systems.