Physicists should take an active role in explaining science to the general public. As an example, I will explain why I think nuclear power is (still) a good idea.
Refreshments will be served in CP 179 at 3:15 PM
Abstract: Quantum Field Theory is a universal language to describe a multitude of physical phenomena from elementary particle and condensed matter physics. Often apparent complexity of the described phenomena is attributed to strong coupling in the underlying QFT. Accordingly, understanding strongly-coupled dynamics became a universal theoretical challenge relevant for many areas of contemporary physics. Remarkably, the past decade was characterized by an accelerated development of several original approaches to this problem, leading to a plethora of new results. In my talk I will focus on several non-pertubative methods, most notably holographic correspondence, and describe recent progress and hot research topics. Refreshments will be served in CP 179 at 3:15 PM
A single sheet of sp^2-hybridized carbon atoms, called Graphene, is presently one of the most widely studied materials in the scientific community. Following a bried introduction of Graphene and its unique properties, I will present evidence for the amplification of surface plasmon coupled emission (SPCE) from Graphene-Ag hybrid films. SPCE is a novel analytical technique in which the isotropic emission of a fluorophore is combined with the surface plasma resonance of a Ag (or Au) think film to yield highly directional emission from the so-called plasmaphore, and thus greatly increased sensitivity. In another project, we harnessed the nonlinear optical properties of Graphene in conjunction with those of C_60 to fabricate an all-optical analog of a diode. Our all-carbon optical diode, built from a Graphene and C_60 sandwiched structure, is passive, polarization independent and most importantly has no phase-matching constraints. Evidence for tunable nonreciprocity factor and potentially large bandwidth capability with be presented. This work was done in collaboration with team members from Clemson University, USA (M. Karakaya, R. Podila, K. Lingam), Sri Sathya Sai Institute of Higher Learning, India (P. Mulpur, B. Anand, R. S. Satish) and Raman Research Institute, India (R. Philip).
Refreshments will be served in CP 179 at 3:15 PM
The space we live in -- the space measured in miles, kilometers and parsecs -- has an internal structure of its own. Surprisingly, this structure is intimately related to quantum information theory, a field at the intersection of physics and computer science. To understand this connection, I exploit the holographic duality: an alternative description of the world as a gigantic hologram, which can be deduced from careful reasoning about the physics of black holes. The final conclusion is that the fabric of space encodes streaming compression protocols analogous to the one used by Netflix. Consequences of this assertion range from condensed matter physics to the most fundamental ways in which we conceptualize space and time.
Refreshments will be served in CP 179 at 3:15 PM
A revision of our system of units, the SI, is currently discussed and may be implemented as early as 2018. The new SI is a logical extension of an argument made in 1983 when the meter was redefined to be based on the exact value of the speed of light. In the new SI all units will be derived from seven fundamental reference constants, thus replacing the seven base units of the current system.
For example, the unit of mass, the kilogram, is currently defined by an artifact called the International Prototype of the Kilogram (IPK). In the future we will be able to realize the unit of mass, not just at the kilogram level, from a fixed value of the Planck constant, which has units of kg m^2/s.
One condition for redefinition is agreement between different measurements of the Planck constant. Currently two measurement strategies lead to values with relative uncertainties less than 100 parts per billion (ppb): (1) Avogadro’s number can be determined by estimating the number of atoms in a well characterized crystal. From Avogadro’s number h can be calculated using the Rydberg constant, which is known with much smaller uncertainty (2) A watt balance can be used to measure mechanical power in units of electrical power. Electrical power can be measured as the product of the Planck constant and two frequencies by utilizing the Josephson effect and the Quantum Hall effect. NIST has carried out measurements of h with watt balances for over 20 years. In 2012/13 a new team has performed a largely independent determination of h. I will describe this measurement and measurements from other laboratories.
Refreshments will be served in CP 179 at 3:15 PM
Theory predicts the existence of some peculiar phases of quantum condensed matter systems that have multiple degrees of freedom with very low energy, when localized “defects” are introduced. I shall focus on a class of these phases where each defect has half of a conventional degree of freedom, and the defects may be considered as sites for localized zero-energy states of a “Majorana fermion”. Such defects would also exhibit the intriguing property of “non-Abelian statistics” -- i.e., if various defects can be moved around each other, or if two identical defects can be interchanged, the result is a unitary transformation on the quantum mechanical state that depends on the order in which operations are performed but is insensitive to many other details. In my talk, I will try to explain these various concepts and discuss the attempts to realize them in condensed matter systems.
In this presentation, I will discuss the hypothesis proposed by Francis and Vavrus (2012) that links rapid Arctic warming (so-called Arctic amplification) to changes in the large-scale atmospheric circulation in the northern hemisphere that favors more persistent weather patterns and a higher likelihood of extreme weather events such as droughts, cold spells, flooding, heavy snows, and heat waves. This hypothesis has been a topic of considerable controversy in recent months, particularly regarding its relationship to the unusual weather conditions that persisted in the winter of 2013/2014. I will discuss various aspects of this linkage, what we know and don't know, and present new related research. Refreshments will be served in CP 173 at 3PM
Fundamental scientific research, as a majority federally funded initiative, is becoming more deeply embedded in politics. Since the end of the Space Race, funding of basic physical sciences research as a percent GDP has continuously declined, indicating that policy makers see funding scientific research as less of a priority than they once did. Indeed, a lack of understanding about both science and how science is done amongst members of Congress has led to both reduced prioritization and also to misguided attempts at regulation, such as making peer review a public process and considering Congressional oversight for specific grants. Here we will examine a few current issues in science policy and the need for physicists to effectively weigh in on such policy issues. We will also consider the positive or negative effects such public engagement may have on our scientific careers and ways in which you can get involved.
Refreshments will be served in CP 179 at 3:15 PM
Neutrinos are the most numerous massive particles in the Universe. Their masses are very tiny, no larger than one millionth the mass of the electron. Are they like all the known massive fermions, being four component particles, or are they a new type of fermion never seen before, a two component fermion? Are there only only three neutrinos or are there more species of neutrinos? Of the three neutrinos we know of, we have determined part of the massing pattern but not the completely pattern. Also we have measured some of their mixing parameters with reasonable precision via neutrino oscillation experiments but not all. Do neutrinos violate CP in neutrino oscillations? Can neutrinos help explain the baryon-antibaryon asymmetry of the Universe? I will address many of the important questions about the neutrinos and how the future Fermilab program will address some of these questions.
Refreshments will be served in CP 179 at 3:15 PM
The cosmic ray spectrum spans many orders of magnitude in energy. At the very end of the spectrum (E>10^18 eV) lie the Ultra High Energy cosmic rays (UHECRs). Their origin remains largely unknown and their study is made difficult in part by the very low flux impinging on Earth's atmosphere. The Pierre Auger Observatory, located in the Mendoza province of Argentina, is an array of detectors spread over 3000 km^2 specifically designed to study the properties of the extensive air showers induced by the UHECRs in the atmosphere. The Observatory is fully operational since 2008 and is operated by a collaboration of more than 500 scientists and engineers from 19 countries. In this colloquium, a selection of recent results obtained by the Observatory and the plan for the upcoming upgrade will be presented.
