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- Carl Sagan


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Physics Conference Room, SB B326
Coffee starts at 12:00 PM and talk starts at 12:15 PM
Feb '12
Justin Vazquez-Poritz  -  Monday, February 6, 2012
String theory versus the real world
New York City College of Technology, CUNY
ABSTRACT: Even though string theory is a leading candidate for a theory of everything, it has the rather embarrassing requirement that there are nine dimensions of space. In order for this not to conflict with the fact that we observe only three dimensions of space, six of the dimensions must somehow remain hidden. I will provide a non-technical overview of three different ways of hiding these extra dimensions. This has led to the possibility of unifying all forces within a geometrical framework, new methods for computing quantities in nuclear physics as well as condensed matter systems, and concrete predictions that could potentially falsify certain aspects of string theory.
Feb '12
Hyun-Joong Kim  -  Tuesday, February 21, 2012
ABSTRACT: This lecture addresses fundamental concepts of pressure sensitive adhesives (PSA), and developments in industry. Pressure-sensitive-adhesives (PSA) are distinct from general adhesives, as evidenced by phase separation in the curing process and by modes of failure. PSAs are potentially easier to process, can be reusable and easy to remove, and have application in fields such as electronics, semiconductors, transportation, and health. Recent research is directed at eco-friendly, highly functional materials that meet international regulations.
Mar '12
Slava Rotkin  -  Monday, March 5, 2012
ABSTRACT: New solutions for thermal management have been sought recently due to increasing density of dissipated power in modern sub-50 nm electronic devices. Heat transport in nanostructures is affected both by bulk thermal resistances and by thermal coupling across the interfaces between dissimilar materials. The interface thermal resistance, also known as a Kapitza resistance, is in the focus of this talk. Highest intrinsic thermal conductivity of nano-carbons (such as graphene and nanotubes), closest to or even exceeding the diamond, is not helpful enough until one can efficiently connect the nano-carbon to the substrate. We will show that the near-field radiation, or quantum-electrodynamic Kapitza conductance mechanism is the main term in the heat exchange between the polar substrate and graphene or tubes. Such quantum terms may be anticipated to allow a breakthrough in the existing thermal technologies, and, at least, change our understanding of the heat transport at the nanoscale, still largely based on the classical thermal physics.
Mar '12
Ethan Schonbrun  -  Monday, March 12, 2012
Optofluidics for High Speed Microscopy
Rowland Institute, Harvard University
ABSTRACT: Flow cytometry has become a benchmark technology due to its ability to individually characterize extremely large collections of particles or cells. Despite its impressive throughput, flow cytometry requires labeled objects and typically looses all spatial information of each cell. Instead of just quantifying scattering and absorption cross-sections, as is done in flow cytometry, it would be highly advantageous to capture full two or three-dimensional images of cells at the same throughput. Imaging, and especially fluorescence and three-dimensional imaging, is extremely challenging at these speeds due to the required short exposure time and fast acquisition rates. In this talk I will address some of the strategies that our lab is using to address these problems, primarily parallelization, fluidic manipulation, and alternative optical contrast mechanisms.
Mar '12
Christina Othon   -  Monday, March 19, 2012
ABSTRACT: Biological systems consist of a complex, heterogeneous mixture of proteins, lipids, carbohydrates, water, and a myriad of other small molecules. Structural biologists have long focused on the relationship between protein structure and function in investigating biological processes. Few recognize the essential role the solvent plays in dictating structural transitions and self-assembly. In this talk we discuss two experiments that exploit solvent interactions and organization in order to manipulate protein structure and self-assembly at the molecular level. In the first part of the talk we will discuss fluorination of proteins as a tool to enhance protein stability through alterations in hydration dynamics. In the second part of the talk we will discuss the tools being developed at Wesleyan to investigate lipid phase transitions. Lipid phase stability and clustering are essential to the recognition, insertion, and self-assembly of proteins within the lipid membrane. Using our technique we can resolve these highly dynamic processes to unambiguously identify orientation and dynamic freedom within our membrane model with the highest available temporal resolution, and without the restriction imposed by a supporting substrate.
Mar '12
Philip Kim  -  Monday, March 26, 2012
ABSTRACT: The two most important achievements in physics in the 20th century were the discoveries of the theory of relativity and quantum physics. In 1928, Paul Dirac synthesized these two theories and wrote the Dirac equation to describe particles moving close to the speed of light in a quantum mechanical way, and thus initiated the beginning of relativistic quantum mechanics. Graphene, a single atomic layer of graphite discovered only a few years ago, has been provided physicists opportunities to explore an interesting analogy to relativistic quantum mechanics. The unique electronic structure of graphene yields an energy and momentum relation mimicking that of relativistic quantum particles, providing opportunities to explore exotic and exciting science and potential technological applications based on the flat carbon form. As a pure, flawless, single-atom-thick crystal, graphene conducts electricity faster at room temperature than any other substance. While engineers envision a range of products made of graphene, such as ultrahigh-speed transistors and flat panel display, physicists are finding the material enables them to test a theory of exotic phenomena previously thought to be observable only in black holes and high-energy particle accelerators. In this presentation I will discuss the brief history of graphene research and their implications in science and technology.
Apr '12
Francis Starr  -  Monday, April 2, 2012
Apr '12
Fred Cadieu  -  Monday, April 16, 2012
ABSTRACT: When two groups of physicists started to use bright supernova explosions to extend distance measurements to far away objects, they came to the very surprising conclusion that these supernovae were fainter than expected. The only explanation seemed to be that some time ago the rate of expansion of the universe had started to accelerate! This interpretation is based on a confluence of results from many recent Nobel prizes in physics which has led to the field of high precision cosmology. Certain aspects of Type 1A supernova explosions that have allowed these to act as standard candles for extending distance measurements billions of years into the past will be discussed. The most recent results, which revolutionized our current understanding of the universe, will be shown to be consistent with the Big Bang Model.
Apr '12
Stefan Bathe  -  Monday, April 30, 2012
The Hottest Matter on Earth
Baruch College of CUNY
ABSTRACT: A few microseconds after the Big Bang, the Universe was too hot for quarks and gluons to be confined into hadrons. But then, what is the nature of this primordial matter? At the Relativistic Heavy Ion Collider (RHIC), we can recreate the conditions of the early Universe and study this matter in the laboratory. I will review the key findings of the experiments and discuss recent developments of the field.
Sep '12
Yisa Rumala  -  Tuesday, September 4, 2012
ABSTRACT: A common way of imprinting orbital angular momentum on light is by using an ideal spiral phase plate. This is a device consisting of a piece of transparent material with an azimuthally varying thickness. When light goes through the device, it acquires an azimuthally varying phase containing orbital angular momentum. In this talk, I will describe a spiral phase plate which has non-zero reflectivity on both surfaces, such that the rays of light makes multiple reflections with the azimuthally varying surface before exiting the device. In this case, the exiting beam will contain a coherent superposition of orbital angular momentum modes with the appearance of an optical intensity pattern that varies as a function of angle on the output plane of the device. When the laser frequency is changed, the optical intensity pattern is observed to rotate. This is the first time that this effect has been quantified. The work extends the conventional Fabry-Perot etalon to a new geometry, namely the spiral phase plate etalon; and it is expected to have broad applications in optical frequency metrology, quantum optics, and atom optics.
Sep '12
Nicolas Giovambattista  -  Monday, September 10, 2012
ABSTRACT: Most liquids can form a single glass or amorphous state when cooled fast enough, so crystallization is avoided. However, there are a few substances that are relevant to scientific and technological applications that can exist in at least two different amorphous states, a property known as polyamorphism. Examples include silicon, silica, and in particular, water. In the case of water, experiments show the existence of a low-density (LDA) and high-density (HDA) amorphous ice that are separated by a dramatic, first-order like phase transition. It has been argued that the LDA-HDA transformation connects to a first-order liquid-liquid phase transition (LLPT) above the glass transition temperature Tg. However, direct experimental evidence of the LLPT is challenging to obtain, since the LLPT occurs at conditions where water rapidly crystallizes. In this work, we (i) discuss the general phenomenology of polyamorphism in water and its implications, and (ii) explore the effects of a LLPT on the pressure dependence of Tg(P) for LDA and HDA. Our study is based on computer simulations of two water models -- one with a LLPT (ST2 model), and one without (SPC/E model). In the absence of a LLPT, Tg(P) for all glasses nearly coincide. Instead, when there is a LLPT, different glasses exhibit dramatically different Tg(P) loci which are directly linked with the LLPT. Available experimental data for Tg(P) are only consistent with the scenario that includes a LLPT (ST2 model) and hence, our results support the view that a LLCP may exist for the case of water.
Sep '12
Mikhail Shneider  -  Monday, September 24, 2012
Molecular ensembles in non-resonant optical lattices
Applied Physics Group, Department of Mechanical and Aerospace Engineering
ABSTRACT: In this talk recent theoretical and experimental results on the interaction of optical lattices with neutral gases will be reviewed. Small gas density perturbations produced by the electrostrictive effects of laser beams (when the optical potential well depth << kT) can be used for powerful nonintrusive diagnostics based on coherent Rayleigh and Rayleigh-Brillouin scattering. Effects such as bulk drift can be induced in a gas by a periodic optical traveling wave (lattice), even when the mean kinetic energy is much greater that the maximum optical potential provided by the field. With increasing laser beam intensities, the optical potential can trap a large fraction of the gas. In this case, acceleration or deceleration of the gas is possible. Gas particles cannot be trapped in the highly collisional regime. Analysis of the trapped and untrapped motion of particles demonstrates that atoms and molecules can be accelerated from room temperature to velocities in the 10 to 100 km/s range over distances of 100s of microns. Recently, such experiment was successfully performed by Dr. Peter Barker's group in Great Britain. The effects of coupling of non-resonant laser radiation to a gas will be discussed. In all cases when a lattice induces a periodic modulation of the gas density, strong Bragg diffraction of light can occur. It can potentially limit the achievable intensities inside the optical lattice limiting the ability to manipulate the gas. The self-consistent evolution of the input laser beams via the light-induced perturbation of the index of refraction can be determined by the solution of the wave equation in the interference region together with the Boltzmann kinetic equation for gas.
Oct '12
Alan Calder  -  Monday, October 15, 2012
ABSTRACT: Supernovae are spectacular explosions that signal the violent death of a star. Supernovae produce and disseminate heavy elements, trigger star formation, and in some cases may be used as distance indicators for cosmological studies. These fascinating events encompass a broad range of physics, and realistically modeling these requires the largest supercomputers. I will give an overview of supernovae and our theoretical understanding of these events and present results from our research into type Ia (thermonuclear) supernovae. Our models and statistical framework allow the systematic study of how properties of the host galaxy can influence the brightness of an event. I will present the results from ensembles of simulations addressing the influence of age and metallicity on the brightness of an event and compare our results to observed trends in brightness with age and color of the host galaxy.
Oct '12
Jon Swaim  -  Monday, October 22, 2012
Plasmonics in the Whispering Gallery
University of Queensland, Australia
ABSTRACT: Whispering gallery mode (WGM) resonators are optical cavities with extremely high quality factors (up to 10^8) in air and water. In this talk I will present results on chip-based microtoroids as nanoparticle sensors and discuss their feasibility as single molecule detectors. I will discuss a variety of approaches for enhancing the sensitivity in the context of biosensing. In particular, we show through numerical modeling that coupling of plasmonic nanoparticles to WGM fields leads to large enhancements in sensitivity which may enable single molecule detection under practical experimental conditions. In addition, we observe experimentally that coupling of plasmonic nanoparticles (39x10 nm gold nanorods) leads to interesting changes in the optical spectra which are currently not fully understood, but related to theoretical predictions in the literature. These effects have the potential for enhanced measurement in sensing both the position and size of nanoscale objects. Lastly, I will present results on the first ever optomechanical magnetometer, with current sensitivity of 400 pT/root Hz; and experiments towards achieving the quantum ground state of vibrational modes in microtoroids, an enabling step towards quantum optomechanics.
Nov '12
Chushun Tian  -  Monday, November 5, 2012
Driven systems: from classical chaos to unusual quantum matter
Institute of Advanced Studies, Tsinghua University
Nov '12
Micha Tomkiewicz   -  Monday, November 26, 2012
Democratization of Climate Change
Brooklyn College of CUNY
ABSTRACT: I will try to outline four major challenges to the democratization of the decision making process that in my view are needed to address the challenges that anthropogenic changes in the chemistry of the atmosphere will pose: Climate Change and the Nature of Science - We are now part of the physical world on planet earth. When we try to investigate global phenomena such as climate change we include us in the system that we investigate. In medical or legal terms this process is called self-diagnosis or self-defense. A common saying is that a lawyer that serves as his own legal adviser got a fool for a client. The same holds true for a doctor that tries to treat himself in a serious medical issue. Doctors and lawyers have the options to hire somebody else. The global human population doesn't. We didn't yet identify an exoplanet that can help. "Hate of Science" - Most of us hate science and students that takes my courses that are identified as science courses, tell me with great pride that they "despise" math We are not prophets - The Popperian scientific method is based on refutability. We develop hypothesis and theories based on everything that we know and we should be able to test the theory based on predictions for observations that we didn't yet make. If the tests fail - we change the theory. This amounts to prediction of future results. Since we are part of the system - failure might mean closing the window that allows us to survive. NIMBY (Not In My Backyard) - Climate Change is a global, collective, phenomena that all of us contribute to and all of us, sooner or later are being affected by. The common denominator in all of these challenges is that in my view all of them can be addressed through the educational system. The instruments that we are developing include a "popular" blog (climatechangefork), a book that was just published titled "Climate Change: The Fork at the End of Now" that was written to serve as a textbook for the general public; development of a multiplayer electronic learning system, built on social/scientific simulations and fed by relevant and timely databases that require students to make choices and examine the consequences of these choices; and a documentary film that documents energy transition in the Sunderban region of India from hunter-gatherer to electrified modern existence.
Dec '12
Morton Denn  -  Monday, December 3, 2012
Paths to Macroscopic Constitutive Equations
Levich Institute, City College, CUNY
ABSTRACT: Complex fluids, including polymer melts and solutions, liquid crystals, colloidal and non-colloidal suspensions, etc., are routinely used in consumer and industrial applications and are present in many natural systems. Experimental rheology gives insight into the behavior of such systems in elementary flows and may point to underlying physical phenomena, but the ability to carry out computations in the complex geometries that are normally of interest requires continuum descriptions that can be integrated into conservation equations. Such constitutive equations may arise from empirical considerations, from microstructural analysis, or from fundamental principles of continuum mechanics. The history of the development of constitutive equations for flexible polymeric systems over six decades involves all three approaches, and there has been a synthesis over time that enables meaningful process calculations, although much remains to be done. Other areas are less developed. Continuum theories for suspensions, in particular, remain at a relatively primitive stage that is reminiscent of the situation for polymers many decades in the past, but it is likely that progress will be more rapid because of the ability to integrate ideas from the polymer community and elsewhere. In this talk we will look first at the development of macroscopic constitutive equations for flexible polymers and then consider the state of development and outstanding issues for suspensions.
Dec '12
Frederick Walter   -  Monday, December 10, 2012
ABSTRACT: The galactic novae are thermonuclear explosions in a degenerate hydrogen layer on the surfaces of white dwarf stars. This is inferred from energetics and plausibility arguments, but the lack of uniformity of the novae shows that they are much more complex, and interesting. Novae are highly dynamic phenomena, involving brightenings by up 20 magnitudes, and velocities of over 5000 km/s in extreme cases. Eight years ago we initiated a project to generate a more-or-less uniform set of spectroscopy and photometry of novae accessible to the SMARTS facilities at the Cerro Tololo InterAmerican Obervatory. The atlas now contains observations of over 60 novae, some observed for as long as 8 years past their eruption. Following a general description of the nova phenomenon, I shall turn to two topics that I am currently engaged in. The first is an attempt to explain the peculiar line profiles of the He-N (or recurrent) novae. These do not resemble the optically thick shells of the Fe II (or classical) novae, but can be modeled as optically-thin accretion disks. If so, this will require a change in our understanding of the inner environs of the novae. The second is an examination of the N III Bowen fluorescence lines, and their relation the He II 4686 line. This mechanism is understood in the static case, but the novae are highly dynamic. The lightcurves of the N III and He II lines and the supersoft X-ray flux suggest an interpretation as a temperature gauge.