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Physics Conference Room, SB B326
Coffee starts at 12:00 PM and talk starts at 12:15 PM
- Monday, February 4, 2008
ABSTRACT: Due to its unique one-dimensional tubular structure, carbon nanotubes (CNTs) have proven to possess extraordinary physical properties and have emerged as one of the most promising candidates to advance core technologies such as IC miniaturization and others. The current focus of global CNT research is, as it has been since the first CNT discovery, to produce CNTs at desired locations with controlled atomic structures, so that further integration into various nanodevices is enabled. Intensely studied for this purpose is catalytic chemical vapor deposition (CVD) which uses transition metal nanoparticles as catalyst and low-temperature dissociation of hydrocarbon gases as carbon source. I will first introduce various techniques we devised, including electrochemical deposition, thin film dewetting, microsphere self-assembly, interference lithography and nanoporous membrane mask, to fabricate catalyst nanoparticles with desired morphology, areal density, periodicity and texture on large scales, and then discuss a plasma-enhanced chemical vapor deposition (PECVD) process to grow vertically aligned carbon nanotubes as centerpieces for applications in optical antennas, photonic crystals, field emission displays and more.
- Wednesday, February 6, 2008
ABSTRACT: Materials with significant electronic correlations tend to display remarkable and unconventional properties like insulator-to-metal transitions, high temperature superconductivity and colossal magneto-resistance. Many of these exotic properties have defied understanding most likely because the complex interactions in these materials lead to phase segregation on the nano-scale. For example, the driving mechanism for the temperature-induced insulator-to-metal transition (IMT) in vanadium dioxide (VO2) has been debated for several decades. Central to this debate is the relative importance of electron-electron correlations and charge-ordering to the IMT. I report near-field infrared images of VO2 films that directly show coexisting phases in the vicinity of the percolative IMT. In combination with far-field infrared spectroscopy, the new data reveal the Mott transition with divergent optical mass in the metallic puddles that emerge at the onset of the IMT. These results illuminate a new path towards spectroscopic exploration of electronic inhomogeneities in correlated electron systems.
- Monday, February 11, 2008
ABSTRACT: Multiferroics are materials that display an amazing coexistence and interplay of long range ferromagnetic and ferroelectric orders. The magnetization (ferroelectric polarization) of these materials can be altered by applying an external electric (magnetic) field, such cross-correlations between the electric and the magnetic phenomena leading to intense interest in the possibility of novel magnetoelectric devices. It was observed recently that the multiferroics that show the strongest sensitivity of polarization to an applied magnetic field are non-collinear spiral magnets. The spiral magnetic ordering, in which the local magnetization rotates around a direction in space (pitch vector), spontaneously breaks coordinate space inversion symmetry giving rise to the macroscopic polarization. With hints from the theories of some liquid crystals, which bear a family resemblance to these systems, in this talk I shall develop a Ginzburg-Landau description of this new class of materials. The resulting theory will allow us to explain as well as predict many unusual and outstanding experimental observations.
- Wednesday, February 13, 2008
- Wednesday, February 20, 2008
- Monday, March 3, 2008
ABSTRACT: It seems that everywhere one looks as of late one sees new collaborations between unexpected partners to solve interesting problems in Astronomy. The Largest CCD Optical Survey of The Universe (The SDSS) has a query database designed and funded by a Microsoft research group. It's successor (LSST) will have its 30TB/day data processing needs done by Google while Bill Gates and other entrepreneurs contribute to infrastructure costs. I will discuss how such collaborations are made possible today. Then I will focus on how new approaches to Galaxy Photometric Redshift estimation in The SDSS using advanced regression analysis was developed as the result of a collaboration between Astronomers and Computer Scientists at NASA/Ames and Mathematicians at San Jose State University. I will also quickly review the history of regression analysis and give some background on photometric redshift estimation. Time permitting I will demo another joint project from NASA/Ames called viewpoints (http://astrophysics.arc.nasa.gov/viewpoints) Viewpoints can help characterize multivariate data from any discipline, but much of its development took place with the SDSS in mind.
- Monday, March 3, 2008
ABSTRACT: Optical microresonators such as silica spheres exhibit ultra-high quality (Q) factors and small modal volumes which significantly enhance interaction of the optical field with the material. We use this attribute for biosensing, where a single molecule can shift the frequency of a resonant mode. Applications in biology range from label-free analysis of molecular interactions to detection of bacteria and viral particles. Recently, we have also explored a new approach to photon localization in disordered photonic crystal (PhC) structures. We show that the guided modes in line-defect PhC waveguides experience coherent backscattering by superimposed disorder which can lead to Anderson localization. Random optical cavities with Q's ~ 3 x 105 and ultra-small modal volumes were observed and can find applications in optical sensing systems, random nano-lasers and quantum-computing.
- Monday, March 10, 2008
ABSTRACT: Mid-infrared is one of the most important segments of the optical spectrum because it contains the "fingerprints" of most biological molecules. An explosion of near-field techniques (e.g., spectroscopy with sub-cellular resolution, labels-free detection) motivates the development of new sub-wavelength imaging tools. Experimental demonstration of a near-field super-lens in the mid-infrared (around 11 microns) range will be described. The lens is implemented using crystalline SiC films that have remarkable infrared properties: they support surface polaritons with less damping than most metals. Two demonstrations of super-lensing with l/20 spatial resolution will be demonstrated: (a) using FTIR microscopy , and (b) by direct near-field probing with NSOM . Both amplitude and phase-sensitive imaging is demonstrated. It is also demonstrated that super-lensing can be used for sub-surface imaging. Applications to biologically-relevant imaging through water in nanofluidic channels will be discussed. In the second half of the talk, I will describe a novel imaging tool in IR/THZ: tapered multi-wire coaxial endoscope. Using a conventional coaxial waveguide (the ultimate sub-wavelength element!) as an inspiration, I will demonstrate how two types of nanoscale imaging applications are enabled: image magnification and radiation focusing. In the first scenario, the tapered wire array acts as a multi-pixel TEM endoscope by capturing a detailed electromagnetic field profile created by deeply sub-wavelength objects at the endoscope's tip and magnifying it for observation. The resulting imaging method is superior to the conventional scanning microscopy because of the parallel nature of the image acquisition by multiple metal wires. In the second scenario, the image of a large mask at the endoscope's base can be projected into a much smaller image at the tip, paving the way to novel lithographic techniques.
 D. Korobkin, Y.Urzhumov, and G.Shvets, "Enhanced Near-Field Resolution in Mid-Infrared Using Metamaterials", JOSA B 23, 467 (2006).
 T. Taubner, D.Korobkin, Y.Urzhumov, G.Shvets, and R.Hillenbrand, "Near-field microscopy through a SiC superlens", Science 313, 1595 (2006).
- Thursday, March 13, 2008
ABSTRACT: The interplay of electronic and mechanical properties of nanoelectromechanical systems (NEMS) has been a focal point of research interest in recent years. In this talk, after providing a brief overview of the experimental realizations of such systems, I will present our analysis of two important NEMS structures, a mechanical oscillator (cantilever) coupled to an electrical tunnel junction and a quantum shuttle. Explicit expressions for the oscillator (shuttle) damping/decoherence rate, fluctuations of the oscillator (shuttle) position, and the nonlinear conductance of these NEMS have been obtained on a microscopic basis and their voltage and temperature dependencies have been determined. I will also outline my future plans for research in this field, discussing the feasibility of realizing a coherent phonon source using the suspended nanobridges, electron transport in manganites, and electromechanical processes in living objects. In the latter case, a novel bio-inspired system, nanorotator, will be discussed. Towards the end of my talk, I will describe other projects in which I am involved, concerning electrical and optical properties of semiconductor nanostructures.
- Monday, March 17, 2008
- Tuesday, March 18, 2008
ABSTRACT: Artificial nanosolids, arrays of nanoscale grains interacting with each other through electron tunneling, offer rich new horizons of novel macroscopic behavior emerging from nanoscale structure and dynamics. Fundamental microscopic phenomena such as Coulomb correlation, disorder and coherence produce dramatically new and programmable bulk behavior when mediated by nanoscale granular structure. Each building block of these new materials can be viewed as a tiny cluster of atoms of metallic, semiconducting or superconducting elements. These clusters are not as small as molecules but not as large as macroscopic objects. I will review our progress made in the last several years in understanding the properties of artificial nanosolids. In particular, I will discuss the following topics:
1) Introduction to physics of artificial nanosolids
2) Novel transport regimes
3) The phase diagram of artificial nanosolids
4) Future opportunities
I. Beloborodov et al., Reviews of Modern Physics, 79, 469 (2007).
- Wednesday, March 19, 2008
ABSTRACT: Multi-nuclear Nuclear Magnetic Resonance (NMR) techniques have been used to investigate the molecular dynamics and structures in ion conducting and polymer materials. Materials studied included various proton and lithium ion conductors that have application in electrochemical devices such as fuel cells and batteries. Also studied were varying concentrations of aqueous solutions of various superacids, the purpose of which was to provide a fundamental understanding of the ions solvation and mobility and how they were affected by acid concentration. Parameters studied included self-diffusion coefficients (D) obtained by the Pulse Gradient Spin-Echo (PGSE) technique, spin lattice relaxation times (T1) obtained by the Inversion Recovery technique, and chemical shifts. These provided information on the translational mass transport, rate of energy transfer between the nuclei and their surroundings, and the local electronic environment surrounding the nuclei, respectively. In addition to this, the development of high-pressure NMR technique and its application to the study of NMR lineshapes of individual polymers and small molecules in polymer will also be discussed.
- Friday, March 28, 2008
NOTES: Joint Physics - Chemistry Colloquium
- Monday, April 7, 2008
ABSTRACT: Before the space age it was widely believed that the neighboring planets would have many similarities with Earth. But after great technological feats, it became appreciated that natural systems are chaotic. This means that seemingly small differences in the initial states of these worlds led to highly divergent subsequent development. An examination of the physics that led to this divergence, casts Earth as a very special place. As a consequence of this divergent behavior life has flourished on Earth but our planet neighbors have yet to exhibit any signs of life.
- Monday, April 14, 2008
ABSTRACT: Optical imaging and detection of targets embedded in highly scattering turbid media is of interest for a variety of biomedical and remote sensing applications. Salient characteristics of laser light, such as, wavelength, polarization, directionality, coherence, short pulse generation, and ability to probe atomic and molecular transitions provide the basis for imaging, detecting, ranging, and characterization of targets. The talk will review our recent research on ultrashort pulse propagation through turbid media, development of approaches for retrieving image information circumventing the deleterious image blurring effects of light scattering, and present some potential applications.
- Monday, May 5, 2008
ABSTRACT: The research fields of plasmonic crystals and photonic crystals have been attracting increased interest due to the fairly recent observations of new and unexpected optical characteristics in subwavelength size-scale periodic structures. Structures such as two-dimensional hole arrays in metal films and optical transmission gratings have been researched in spectral regions from the ultraviolet to microwave. In this talk, the ability to control light with these and related structures will be discussed. Starting with a discussion of anomalously large optical transmission in transmission gratings, the surface plasmons and other optical modes in these structures are identified and their roles in producing several interesting optical characteristics are discussed. The phenomena of anomalously large optical transmission, light circulation, light weaving and light trapping in these structures and their applications to optoelectronic and photonic devices will be discussed.
- Monday, May 12, 2008
Professor Adam Heller
- Wednesday, May 28, 2008
About 6 billion glucose assays are performed each year by self-monitoring diabetic people. Obtaining the required blood samples was painful until TheraSense, the company founded by Ephraim Heller and Adam Heller reduced the required blood volume to 300 nL, a volume so small that it can be painlessly obtained. The painless assay, based on thin-layer micro-coulometry, is also accurate, because the outcome of the measurement does not does not depend on temperature, viscosity, or activity of the bioelectrocatalyst. TheraSensewas acquired by Abbott Laboratories and the micro-coulometricsystem, named FreeStyle,is available world-wide. With the intent of removing the worry of diabetes, Adam Heller designed a continuous glucose monitoring system, FreeStyleNavigator, in a collaborative project with colleagues at the University of Texasin Austin and TheraSense, then Abbott Diabetes Care. It monitors the glucose concentration amperometrically, the glucose being directly and selectively electro-oxidized on an electrode having a unique bioelectrocatalyst. The catalyst comprises the enzyme glucose oxidaseand an electron-conducting redoxhydrogelelectrically connecting the redoxcenters of the enzyme to an electrode. The turnover of the enzyme is observed as an electrical current. The user replaces the sensor implanted under the skin every five days. The system alerts the user to actual and impending high or low glucose concentrations.
Poster file (pdf)
NOTES: Department of Chemistry and Biochemistry, Queens College of CUNY. Lunch to follow the seminar at The Agora Restaurant.
- Monday, September 15, 2008
ABSTRACT: Understanding the structure and properties of many useful technological materials and, in particular, functional nanomaterials, has always been propelled by their in-depth studies with advanced TEM/STEM methods of the electron microscopy, trying to address their properties behind determination of atomic coordinates and composition. A brief review of some important materials examined with S/TEM methods (Pd-cluster catalysts, 1D-SbCrSe3 and Nd2Fe14B ferromagnets, InGaAsP based IR-lasers/photovoltaics, Ca3Co4O9 -thermoelectrics) will be presented. Phase imaging and phase microscopy, being developed along with conventional TEM/STEM methods, provide higher level of physical information, since they can probe electrostatic and magnetostatic potentials for magnetic materials, nanoparticles and hetero-structures at nanoscale resolution. Practical use of such methods named as Lorentz phase microscopy (LPM/TEM) and potential applications for novel position-sensitive diffractive imaging (PSDI/STEM) will be outlined.
- Monday, September 22, 2008
ABSTRACT: For many years now, there has been ongoing interest in the manifestations of many body phenomena in the conductance of strongly-confined, one-dimensional (1D) electron systems. One important aspect of this research has centered on the study of the so-called 0.7 feature in the low-temperature conductance of 1D conductors known as quantum points (QPCs). There have been numerous reports in the literature suggesting that the 0.7 feature should be related to some kind of spontaneous spin polarization in the QPCs, which persists even at zero magnetic field. In this presentation, we review the results of our recent work on this problem, in which we make use of coupled QPCs to probe the properties of transport very close to pinch-off. We observe a resonant interaction between two QPCs whenever one of them pinches off, which we believe is associated with the binding of a single spin to the QPC that is pinching off. A phenomenological theoretical model is developed that relates the observed resonance to a tunnel-induced correlation that arises from the interaction between a presumed bound spin on one QPC and conducting states in the other. Building on these ideas, we use this measurement technique to probe the microscopic properties of the bound spin, finding it to be robustly confined and to show a Zeeman splitting in a magnetic field. The spin binding occurs for stronger gate confinement than the 0.7 feature, and we therefore suggest an alternative scenario for understanding the formation of this feature. In this, one considers the evolution of the self-consistent bound state as the gate potential is weakened from pinch off to allow for electron transmission through the QPC. The suggestion of this work is that a QPC may serve as a naturally-formed single-spin system with electrical readout, a finding that may be useful for the development of future generations of single-spin electronics.
J. P. Bird and Y. Ochiai,Electron spin polarization in nanoscale constrictions, Science 303, 1621 (2004).
Y. Yoon, L. Mourokh, T. Morimoto, N. Aoki, Y. Ochiai, J. L. Reno, and J. P. Bird, Probing the microscopic structure of bound states in quantum point contacts, Phys. Rev. Lett. 99, 136805 (2007).
Work performed in collaboration with: Y. Yoon, T. Morimoto, L. Mourokh, N. Aoki, Y. Ochiai, and J. L. Reno
- Monday, October 6, 2008
- Monday, October 27, 2008
ABSTRACT: Experiments on the low-speed impact of solid objects into granular media have been used both to mimic geophysical events and to probe the unusual nature of the granular state of matter. Observations have been interpreted in terms of conflicting stopping forces: product of powers of projectile depth and speed; linear in speed; constant, proportional to the initial impact speed; and proportional to depth. This is reminiscent of high-speed ballistics impact in the 19th and 20th centuries, when a plethora of empirical rules were proposed. To make progress, we developed a means to measure projectile dynamics with 100 nm and 20 µ s precision. For a 1-inch diameter steel sphere dropped from a wide range of heights into non-cohesive glass beads, we reproduce prior observations either as reasonable approximations or as limiting behaviors. Furthermore, we demonstrate that the interaction between projectile and medium can be decomposed into the sum of velocity-dependent inertial drag plus depth-dependent friction. Thus we achieve a unified description of low-speed impact phenomena and show that the complex response of granular materials to impact, while fundamentally different from that of liquids and solids, can be simply understood. This work was done in collaboration with Dr. Hiroaki Katsuragi.
- Monday, November 3, 2008
- Monday, November 10, 2008
ABSTRACT: We study the decay of an atomic BEC population N(τ) from the leaking boundaries of an Optical Lattice (OL). For a rescaled interatomic interaction strength λ>λb, self-trapped Discrete Breathers (DB's) are created, preventing the atoms from reaching the leaking boundaries. Collisions of other lattice excitations with the outermost DB's, result in avalanches (jumps) in N(τ) which for λb<λ<λ* follow a scale free distribution P(J=δN)≅1/Jα. A theoretical analysis of the mixed phase-space of the system, indicate that 1<α<3 in agreement with our numerical findings. We point out that although our focus is given to atomic BECs, our results are also relevant in a large variety of contexts, most prominently being the light emittance from coupled non-linear optics waveguides
- Monday, November 17, 2008
- Monday, November 24, 2008
- Monday, December 1, 2008
- Monday, December 8, 2008
ABSTRACT: Chirality is important in a variety of chemical, biological, and physical phenomena. I will discuss two new chiral phenomena that we have observed recently. One concerns the dynamics of chiral nanostructures and the other discusses a surprisingly simple way a physicist can realize chirality at the molecular level. The symmetries that physical fields need to have in order to induce chirality will be discussed.
NOTES: Joint Physics/Chemistry Colloquium to be held in Remsen 105
- Monday, December 15, 2008