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- Donald Knuth
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Physics Conference Room, SB B326
Coffee starts at 12:00 PM and talk starts at 12:15 PM
1
Feb '10
Kostiantyn Bliokh   -  Monday, February 1, 2010
17
Feb '10
Photonics Search Presentation   -  Wednesday, February 17, 2010
To be announced
To be announced
22
Feb '10
Photonics Search Presentation   -  Monday, February 22, 2010
To be announced
To be announced
24
Feb '10
Photonics Search Presentation   -  Wednesday, February 24, 2010
To be announced
To be announced
1
Mar '10
Photonics Search Presentation   -  Monday, March 1, 2010
To be announced
To be announced
3
Mar '10
Photonics Search Presentation   -  Wednesday, March 3, 2010
To be announced
To be announced
8
Mar '10
Photonics Search Presentation   -  Monday, March 8, 2010
To be announced
To be announced
15
Mar '10
Photonics Search Presentation   -  Monday, March 15, 2010
To be announced
To be announced
22
Mar '10
Stephen Holler  -  Monday, March 22, 2010
ABSTRACT: Dielectric microcavities have garnered much interest in recent years to study a myriad of physical phenomena including cavity QED effects, lasing, non-linear processes and sensing. Of particular interest are spherical microcavities which possess a high degree of symmetry and support high-Q whispering gallery modes implicated in a variety of physical phenomena. Whispering Gallery Mode (WGM) resonances are efficient conduits for photon transport and may be used to enhance both linear and non-linear optical processes while simultaneously serving as sensitive probes of the local environment. This presentation will examine the role whispering gallery mode resonances of spherical microcavities have played in our research to elucidate physical phenomena such as intermolecular energy transfer far beyond the Forster range, cavity mode selection as a means for molecular characterization, and fluorescence lifetime modification. In addition, our recent work on ultrasensitive biomolecular sensors has demonstrated an optical tractor beam capable of pulling nano-particles into orbit. This carousel mechanism provides a novel means for particle transport and separation in addition to acting as a tool for surface potential characterization. These advances in microcavity photonics pave the way for a myriad of studies that have the potential to offer new insights into biomolecular systems, result in novel laser and micro-photonic geometries, and enhance Homeland Security and clinical diagnostics through advanced biological and chemical sensor platforms. The broad applicability of microcavity photonic devices to both fundamental and applied areas of research in physics, chemistry, and biology make them truly diverse, interdisciplinary, and important scientific tools.
24
Mar '10
Photonics Search Presentation   -  Wednesday, March 24, 2010
To be announced
To be announced
19
Apr '10
Maria Tamargo  -  Monday, April 19, 2010
ABSTRACT: The thrust of the research efforts at the Molecular Beam Epitaxy (MBE) Lab at CCNY is the development of novel semiconductor nanostructures that offer enhanced materials properties for new device applications and physical phenomena. Two areas on which we have focused during the past few years have been the growth of multi-quantum well structures for intersubband (ISB) devices and the growth of submonolayer type II – quantum dots for enhanced p-type doping of difficult to dope materials. I will describe our recent advances in these two areas. Quantum cascade (QC) lasers are a novel semiconductor laser that relies on ISB transitions. They exhibit many unique advantages over the more typical interband devices, including large independence from materials parameters to tune the emission wavelength, ultra-fast response, and the use of uni-polar structures. In order to reach shorter wavelengths in the IR, which is needed for many sensing applications, we have begun to explore the use of wide bandgap II-VI semiconductors for QC laser applications. We have recently demonstrated QC emission form ZnCdMgSe-based heterostructures, and are actively pursuing lasing. Se-based wide bandgap II-VI's are notoriously difficult to dope p-type, as is the case with many other wide bandgap semiconductors. By contrast, ZnTe is easily doped p-type, while n-type ZnTe is not readily achieved. We recently demonstrated a novel approach by which small doped nanoclusters of ZnTe embedded in a ZnSe matrix produce a new composite material in which p-type doping is enhanced by an order of magnitude compared to that of ZnSe. Other properties, such as band gap of the material are not significantly changed. We have carried out a broad range of experiments to understand the mechanism and elucidate the properties of this new nanocomposite material. Other potential applications, such as photovoltaics, have become apparent from our studies.
3
May '10
Yasha Yi   -  Monday, May 3, 2010
ABSTRACT: Nano-scale photonics is one of the key components in future clean renewable energy, which plays the central role in next generation photovoltaics and solar cells. After giving an introduction on the available renewable energy sources on earth, I will talk about next generation solar cells utilizing photonic crystals, and our recent research on optoelectronic properties of composite (structurally designed) materials at nm scale for the applications on energy related materials and devices. Utilizing current microelectronics technology and measurement techniques, it is possible to study these novel energy related materials and devices in ways that were unimaginable a decade or two ago. In order to improve next generation thin film solar cell efficiency(2nd generation solar cell), we have developed a new light-trapping scheme that can tremendously enhance optical path length and make light almost completely absorbed at AM1.5 solar spectrum by using novel photonic materials structure on the backside. It makes incident light strongly bent and reflected almost parallel to the surface of the absorption layer, hence the optical path length can be enhanced more than two orders of magnitude longer than that obtained by conventional light trapping schemes. Furthermore, it provides extremely high reflectivity with large omnidirectional bandgap over several hundred nanometers in the solar spectrum range. As a result, the overall efficiency of the solar cell based on our photonic structure is improved significantly. Lastly, I will talk about many potential challenges and future work to be pursued in clean energy fields that require good control of photons and electrons at nanometer scale. This capability can efficiently convert sunlight energy to electricity and meet our demand for clean and renewable energy in the future.
2
Jun '10
Rajeev Pathak  -  Wednesday, June 2, 2010
ABSTRACT: It is an intriguing question why ordinary matter that interacts through Coulomb 'forces' should remain stable at all and not collapse, unlike its gravitational analogue on the cosmic scale. It turns out that a naive 'explanation' based on the Heisenberg Uncertainty Principle alone turns out to be fallacious! On the other hand, it is the fermionic nature of the electron entailing the Pauli Exclusion Principle that actually endows matter with stability. In this colloquium, following Lieb's monumental work, stability of ordinary matter will be discussed threadbare. Also, an upper bound on the number of bound states for an arbitrary attractive potential will be derived using some simple mathematical inequalities. Once again, following Lieb, an interesting upper bound on the maximal degree of negative ionicity possible will be derived, and impossibility of a neutral atom and positron ever forming, albeit an exotic 'quasi-bound-state', will be established. Stability of polar and non-polar molecules and molecular clusters subjected to high external electric fields will also be examined. While in many cases the external field distorts or decomposes the molecular cluster, in some other selective cases, it can strongly bind two molecules exhibiting an exotic phenomenon of 'field induced covalence'.
9
Jul '10
Matthieu Davy   -  Friday, July 9, 2010
Time Reversal Methods at Microwave Frequencies
Institut Langevin, Laboratoire Ondes et Acoustique, Paris
13
Sep '10
Timothy Paglione  -  Monday, September 13, 2010
Star Formation from the Radio to Gamma-Rays
York College of CUNY, American Museum of Natural History
ABSTRACT: Massive stars are an important driver of much of galaxy evolution. These stars live furiously, greatly affecting their surroundings with their winds and radiation, then die dramatically in giant explosions that enrich the interstellar medium in heavy elements. Their lives are relatively brief as well ("only" 10 million years or less) so their impact is not only profound but immediate. Certain galaxies known as starbursts create numerous clusters of these massive stars in their centers. Starburst galaxies may be studied across all the electromagnetic bands, probing different physical regions and processes, but they are traditionally identified by their radio and infrared emission or optical spectroscopy. I augment these studies by including data from a window only recently opened to us: gamma-rays. The gamma-ray emission effectively ties together nearly the entire spectrum of a galaxy while elucidating the impact of cosmic rays on galaxy evolution.
20
Sep '10
Willam Bialek   -  Monday, September 20, 2010
Critical phenomena and biological networks
Princeton University and CUNY Graduate Center
ABSTRACT: Most of the interesting phenomena of life emerge from interactions among a large network of more basic units: interactions among amino acids stabilize the structure of proteins, interactions among genes define the states of our cells, interactions among neurons determine our thoughts, and interactions among groups of organisms are responsible for beautiful schools of fish or flocks of birds. For decades, physicists have hoped that these emergent biological phenomena could be described using the ideas of statistical mechanics, but the models that emerged from this work often have been a bit abstract, not so well connected to what can be measured. Recently it has been suggested that one can actually construct statistical mechanics models directly from data on these complex systems, using the idea of maximum entropy. I'll explain how this works, illustrate some of the surprising successes of this approach, and then outline the most surprising development that has come out of this work: many different biological networks seemed to be poised near a critical point in their parameter space. Examples will be drawn from protein molecules, neural circuits, and flocks of birds, and I will point to emerging experiments that will test these ideas much more clearly. I also hope to convey the fun of connecting theory and experiment, physics and biology.
18
Oct '10
Fengnian Xia   -  Monday, October 18, 2010
Graphene Nanophotonics and Nanoelectronics
IBM Thomas J. Watson Research Center
ABSTRACT: Graphene, a 2-dimensional carbon based material system, recently attracts world-wide attention from physicists and engineers due to its unique electronic and photonic properties. In this talk, I will first discuss the historical evolvement of electronics and photonics, followed by the potential of graphene in electronics and photonics. A few important developments in graphene photonics will then be presented, including photocurrent imaging, ultrafast (> 40 GHz) photoresponse, and the application of graphene photodetector in a realistic optical communication link. Next, two approaches to create a bandgap, using lateral confinement in single layer graphene and vertical E-field in bi-layer graphene, will be covered in detail. I will show that a transport bandgap of > 130 meV can be realized in biased bilayer graphene. The developments in graphene bandgap engineering may enable a few important applications, such as graphene digital electronics, electron Veselago lens and graphene spin qubit
8
Nov '10
Roman Kezerashvili  -  Monday, November 8, 2010
Solar sail to test fundamental physics
New York City College of Technology of CUNY
ABSTRACT: The motion of the solar sail is determined by the solar radiation pressure as well as the spacetime geometry. The Pioneer anomaly, which is the unexplained acceleration of the Pioneer 10 and 11 spacecraft on escape trajectories from the outer solar system and the effects of general relativity on a solar sail propelled satellite will be discussed. We present deviations from Kepler's third law for heliocentric orbits near the sun. In particular, we consider deviations in the period of circular orbits due to the spacetime curvature near the sun, frame dragging from the rotation of the sun, and the oblateness of the sun. The Poynting-Robertson effect on a nearly-circular heliocentric trajectory of a solar sail is discussed. In addition, for non-Keplerian orbits which are outside of the plane of the sun, we predict an analog of the Lense-Thirring effect for which the orbital plane precesses around the sun. This can be tested by a solar sail propelled satellite.
15
Nov '10
Michael Shlesinger  -  Monday, November 15, 2010
ABSTRACT: This lecture traces the history of probability theory from the throwing of bones, sticks, and dice to modern times. Early 18th century books, Jacob Bernouill's "The Art of Conjecture" and Abraham DeMoivre's "The Doctrine of Chances" were rich with new mathematics, insight and gambling odds. Progress was often made by confronting paradoxes. The first of these confused probabilities with expectations and was explained in the Pascal-Fermat letters of 1654. The St. Petersburg Paradox involved a distribution with an infinite first moment, and Levy discovered a whole class of probabilities with infinite moments that have found a surprising utility in physics. The Bertrand paradox involved measure theory for continuous probabilities, Poisson discovered that adding random variables need not always produce the Gaussian, and Daniel Bernoulli and D'Alembert argued over the probabilities for the safety of smallpox vaccinations. Using these and other anecdotes, this lecture discusses vignettes that have brought us to our modern understanding of probability theory.
22
Nov '10
Hui Cao   -  Monday, November 22, 2010
ABSTRACT: Wave optics is an old field of physics that has experienced rapid advances lately. Thanks to modern nanofabrication technology, complex nanostructures such as photonic crystals and metamaterials can be fabricated. They display unusual optical properties and phenomena, e.g., photonic bandgaps, negative refractive index, optical magnetism and cloaking. In this talk, I will start with a brief introduction of the field of nanophotonics and then focus on our studies of photonic nanostructures of random morphology. I show how we can trap light in such structures to make random lasers. Next, learning from the color generation by nanostructures in bird feathers, we use short-range order to enhance light scattering and confinement in artificial nanostructures. Finally I will talk about our latest work on coherent perfect absorbers which can be considered as time-reversed lasers
29
Nov '10
Michael Sumetsky   -  Monday, November 29, 2010
ABSTRACT: A slightly nonuniform and even an ideally uniform optical fiber can perform as a high Q-factor optical microresonator which hosts different types of strongly localized whispering gallery modes (WGMs). These modes are described theoretically and observed experimentally. First, it is shown that a very long (translationally symmetric) lossy dielectric optical microcylinder possesses localized modes. The Q-factor of these WGMs is only 2.5 times smaller than the Q-factor of WGMs in a spherical microresonator fabricated of the same material. Next, localization of WGMs in a cone with a small half-angle is demonstrated. The cylindrical and conical modes are found to be common in conventional optical fibers. The developed theory of a these modes is in excellent agreement with experiment. Finally, the cylinder and conical modes are compared with bottle WGMs that were investigated previously.
6
Dec '10
Jacob Khurgin   -  Monday, December 6, 2010