Colloquium Chair: Ingrid Wilke

Spring 2008

January 30

Speaker: Emily Liu (Rensselaer Polytechnic Institute)

Where: CII 3051
When: 4 p.m. (Refreshments at 3:30)

Hosts: Ingrid Wilke/Gwo-Ching Wang

High resolution quasi-elastic neutron scattering (QENS) spectroscopy is an up-to-date technique to explore the single particle dynamics of hydrogen containing molecules in liquid or solid states. It is capable of micro-electron-volts resolution studies of slow dynamics of glassy liquids. Phenomena that can be investigated include translational and rotational diffusion processes, which provide information about time scales, length scales and effects of geometrical constraints; the ability to access a wide range of wave vector transfers, with good energy resolution, is key to the success of such investigations.

The behavior of shear viscosity h or equivalently the structural relaxation time t of a supercooled liquid as it approaches the glass transition temperature is called ‘fragile’ if it exhibits non-Arrhenius temperature dependence; on the other hand, if h or t obeys Arrhenius law, the behavior is called ‘strong’. The fragile behavior is typical to systems with ionic and van der Waals type interactions. In contrast, a liquid characterized by strong behavior has its structural makeup controlled by a strong covalent bond, or by a directional hydrogen bond, which results in an open tetrahedral structure.

It has been predicted by Molecular Dynamics simulations of various phenomenological water models that there is a liquid-liquid transition between two structurally distinct states of water at low temperature: the high-density liquid (HDL) and the low-density liquid (LDL). The end point of this first-order liquid-liquid coexistence line is the proposed second low-temperature critical point of water as opposed to the well-known high temperature gas-liquid critical point. Up to now, the proposed second critical point was never found experimentally because it lies in the inaccessible supercooled temperature range of water. By confining water in nano-pores of silica glass MCM-41-S, we succeeded in bypassing the crystallization process and were able to study the dynamics of water in this inaccessible range of temperatures.

February 13

Speaker: David Weitz (Harvard University) "Dripping, Jetting, Drops and Wetting: The Magic of Microfluidics"

Where: CII 3051
When: 4 p.m. (Refreshments at 3:30)

Hosts: Ingrid Wilke/Sang-Kee Eah

This talk will discuss some of the new opportunities that arise by precisely controlling fluid flow and mixing using microfluidic devices.  I describe studies to elucidate the instabilities that lead to drop formation and use these to create new materials that are difficult to achieve with any other method.  I also show how the exquisite control afforded by the microfluidic devices provides enabling technology to use droplets as nanoreactors to qualitatively increase the rate of screening of biological reactions, and will demonstrate how this can be used in new applications relevant for biotechnology.

February 20

Speaker: Joel Geidt (Rensselaer Polytechnic Institute) "Glueballs, Gluinoballs and Other Supersymmetric Exotica at the CCNI"

Where: CII 3051
When: 4 p.m. (Refreshments at 3:30)

Hosts: Ingrid Wilke

Whereas supersymmetric particle theories have been studied extensively for over 30 years, the corresponding spectra of particles (comparable to hadrons) is completely unknown. These composite states will be determined at Rensselaer by a first-ever application of so-called Domain Wall Fermions to the problem. Such a study require facilities of the scale of the CCNI,
which is why it has not been previously performed. It is explained how particle masses are obtained by computing ensemble averages generated from Monte Carlo simulations. Lattice field theory simulation tools developed for the study of Quantum Chromodynamics (QCD) are being exploited for the present project, and will be described.

February 27: Canceled. Will be rescheduled.

Speaker: Michael Meyer (University of Arizona) "Formation and Evolution of Planetary Systems: The Makings of an Epicurean Feast"

Where: CII 3051
When: 4 p.m. (Refreshments at 3:30)

Hosts: Ingrid Wilke/Wayne Roberge

In the 4th century B.C. Epicurus and his followers speculated that with an infinity of possibilities, everything that could happen, eventually would. Assuming that life arises on planets that orbit sources of energy, we will review the prospects for life in our galaxy. We will summarize the observed mass distributions of stars as the sources of the energy, as well as our current understanding of planet formation around stars of various mass. We will focus on: 1) current observational constraints concerning the formation and evolution of planetary systems; 2) the need to estimate luminosities and temperatures of planets from direct detection to test theories of planet formation; and 3) the prospects for the next generation of ground- and space-based telescopes to obtain the required data. Given the apparent diversity in observed planetary systems, it appears that Epicurus was onto something.

March 19

Speaker: Timothy Newman (Arizona State University) "Stochastic dynamics in biological systems: applications to embryogenesis and biochemical networks"

Where: CII 3051
When: 4 p.m. (Refreshments at 3:30)

Hosts: Ingrid Wilke/Gyorgy Korniss

I will argue that the theory of stochastic processes provides a natural framework for describing biological systems. I will present two applications. The first concerns the development of algorithms capable of modeling large-scale multi-cellular systems, such as the early embryo. I will discuss the Subcellular Element Model (SEM), which is designed to simulate the interactions between thousands of three-dimensional, visco-elastic, deformable cells. The use of the SEM to understand one of the most fundamental embryonic processes - extension of the primitive streak - will be described. The second application is to biological oscillations. I will discuss a new theoretical mechanism which predicts that intrinsic noise can induce oscillations in populations of small to intermediate size. I will illustrate this phenomena at two very different length scales: predator-prey dynamics in ecology and non-linear feedback loops in gene networks.

March 26

Speaker: Yiping Zhao (University of Georgia) "Nanostructures Fabricated by Glancing Angle Deposition and Their Novel Applications"

Where: CII 3051
When: 4 p.m. (Refreshments at 3:30)

Hosts: Ingrid Wilke/Gwo-Ching Wang

Glancing Angle Deposition (GLAD) is a simple nanofabrication technique that combines oblique angle deposition (OAD) with substrate manipulations and source controls in a physical vapor deposition system. The geometry shadowing effect is the dominant growth mechanism resulting in the formation of various nanostructure arrays by programming the substrate rotation in polar and/or azimuthal direction. With recent advance in a multilayer deposition procedure, one can design complex and multifunctional heterogeneous nanostructures. In addition, with a co-deposition system of two or more sources, novel nanocomposites or doped nanostructure arrays can be produced, which results in nanostructures with different morphology. In this talk, I will highlight our recent progress in multi-component nanorod array fabrication. We find that aligned silver nanorod array substrates prepared by OAD can be used as a high sensitive virus and bacteria sensor base on surface enhanced Raman spectroscopy (SERS) principle. This SERS based sensor can be used to detect the molecular fingerprints of several important human respiratory viruses including respiratory syncytial virus (RSV), rhinovirus, adenovirus, human immunodeficiency virus (HIV), influenza virus, and bacteria such as E.coli O157:H7, Salmonella typhimurium, and to discriminate between different virus strains. Using a unique multilayer deposition configuration, catalytically driven nanomotors have been fabricated and demonstrated, which can directly convert chemical energy into mechanical energy. This device holds a great promising to mimic biological motors.  

April 9

The 12th Herta Leng Memorial Lecture

Speaker: Edwin Kellogg '60 (Harvard-Smithsonian Center for Astrophysics) "The New Astronomy: X-rays From the Heart of the Universe"

Where: DCC 324
When: 4 p.m. (Refreshments at 3:30)

Hosts: Heinrich Medicus

Chandra, one of NASA's Great Observatories in space, not only is free of atmospheric image distortions, but observes at X-ray wavelengths, a portion of the spectrum that has been historically hidden from our view until the advent of orbiting telescopes. The culmination of a series of ever more powerful X-ray telescopes developed over forty years, Chandra is revealing amazing new things about every type of object in the Universe that we thought we understood: the Moon, the Solar System, nearby stars, our galaxy, galaxies, clusters of galaxies, quasars and the structure and evolution of the Universe as a whole. The discovery of the first stellar black hole by an X-ray observatory in 1971 has led to the realization that black holes are "everywhere," with masses from a few times that of our Sun to hundreds of millions times greater, powering some of the most luminous objects in the Universe. Chandra observations, together with those of observatories across the entire spectrum, are now being used to unlock the secrets of the recently discovered Dark Energy, that mysterious force that is challenging physicists to a new understanding of the fundamental nature of our Universe.

April 16

Speaker: Neer Asherie (Yeshiva University) "The Phase Behavior of Thaumatin"

Where: CII 3051
When: 4 p.m. (Refreshments at 3:30)

Hosts: Ingrid Wilke/Gwo-Ching Wang

The phase behavior of proteins is central to many biophysical problems, such as the crystallization of proteins for structure determination, the treatment of protein condensation diseases, and the industrial processing of proteins. Despite its importance, protein phase behavior is not yet well understood. We cannot predict what will happen to a homogeneous solution of proteins when the conditions are changed. Our long-term goal is to make it possible to predict the phase behavior of protein solutions. 

I will present an overview of both experimental and theoretical aspects of protein phase behavior. As an example of the richness of protein phase behavior, I will discuss our recent results for thaumatin, an intensely sweet globular protein used as a model system in crystallization studies. It is known that the addition of L-tartrate ions leads to the rapid formation of protein crystals, but the available information about the solubility of these crystals is inconsistent. We have produced very pure thaumatin and determined the solubility of thaumatin with L- and D-tartrate ions. We find that crystals with the two additives have different solubilities, habits and intermolecular packing. Our results suggest that the chirality of additives may be another useful tool to alter the phase behavior of proteins.

April 23

Speaker: Jie Shan (Case Western University) "Probing Charge Transport by Terahertz Time-Domain Spectroscopy"

Where: CII 3051
When: 4 p.m. (Refreshments at 3:30)

Hosts: Ingrid Wilke

Light pulses as short as two optical cycles (~ 5 femtoseconds) can now be produced by modelocked lasers. These pulses have dramatically advanced many areas of ultrafast spectroscopy. In this talk I will describe how we may use such pulses to control and measure electric fields on the femtosecond time scale. One important application of these capabilities is the time-domain spectroscopy in the terahertz or far-infrared spectral region. I will illustrate the application of the technique to obtain quantitative data on the conductivity of materials without the need of contacts in systems including photoexcited insulators, nanostructures, and organic semiconductors.  Effects such as polaronic transport in ionic crystals, quantum confinement and many-body interactions in nanostructures and disorder on the transport properties will be discussed.

April 30

Speaker: Zheng-Tian Lu (Argonne National Laboratory) "Simple Atom, Extreme Nucleus: Laser Trapping and Probing of Helium-8"

Where: CII 3051
When: 4 p.m. (Refreshments at 3:30)

Hosts: Ingrid Wilke/Gary Adams

Helium-8 (⁸He) is the most neutron-rich matter to have been synthesized on earth: it consists of two protons and six neutrons, and remains stable for an average of 0.2 seconds. It is often viewed as a ⁴He core with four additional neutrons orbiting at a relatively large distance, forming a halo. Because of its intriguing properties, ⁸He has the potential to reveal new aspects of the fundamental forces among the constituent nucleons. We have recently succeeded in laser trapping and cooling this exotic helium isotope, and have performed precision laser spectroscopy on individual trapped atoms. Based on the atomic frequency differences measured along the isotope chain ³He – ⁴He – ⁶He – ⁸He, the nuclear charge radius of ⁸He has now been determined for the first time. Comparing this result with the values predicted by a number of nuclear structure calculations, we test theoretical understanding of the nuclear forces in the extremely neutron-rich environment.

January 24: Astro Seminar

Speaker: Paul Mayeur (RPI Graduate Student) "Using MatLab to Filter Noise from LIGO Data to Better Find Binary Star Inspirals"

Where: Science Center 1C13
When: 4 p.m.

LIGO is a very sensitive experiment which is trying to measure gravity waves. One source of these gravity waves is binary stars collapsing into each other. LIGO looks for tiny movements caused by these gravity waves; however, these tiny movements can also be caused by other things such as trains or ocean waves hitting the coast many miles away. MatLab can be used to compare known sources of noise with the LIGO data to help us make an informed decision about the possibility of a gravity wave.

January 31: Condensed Matter and Optics Seminar

Speaker: Junrong Zheng (Stanford University) "Ultrafast Chemical Exchange 2D IR Spectroscopy"

Where: Science Center 1C13
When: 2 p.m. - 3 p.m.

Host: Zhongfang Chen 

The ultrafast chemical exchange 2D IR spectroscopy has been developed and applied to the study of formation and dissociation dynamics of weakly hydrogen bonded solute-solvent complexes in liquid solutions at room temperature. The 2D IR technique is akin to the 2D NMR methods but 6 orders of magnitude faster.  The strengths of the solute-solvent hydrogen bonds are adjusted by modifying the chemical structures of the solutes (donors) and solvents (acceptors). For the fourteen samples studied, the formation enthalpies vary from -0.6 kcal/mol to -3.3 kcal/mol, and the dissociation time constants vary from 3 ps to 140 ps. The dissociation rates of the hydrogen bonds are found to be strongly correlated with their formation enthalpies. The correlation can be described with an equation similar to the Arrhenius equation. As another example of chemical exchange spectroscopy, the rate of carbon-carbon single bond rotational isomerization of an ethane derivative in a room temperature liquid solution is measured. The results are compared to simulations of a similar compound and the simulations are in good agreement with the experiments.  Based on the experimental results and density functional theory calculations, the time constant for the ethane internal rotational isomerization under the same conditions is estimated to be ~12 ps.

February 11: Condensed Matter and Optics Seminar

Speaker: Fu Tang (RPI) "Novel Mg Nanoblade Structure for Hydrogen Storage"

Where: Science Center 1C13
When: 4 p.m. - 4:50 p.m.

Host: Zhongfang Chen 

Magnesium is an attractive material candidate for hydrogen storage due to its low density and abundance. Theoretically, magnesium hydride (MgH2) contains 7.6 wt.% of hydrogen, which is above the 6 wt. % system requirement of the US DOE hydrogen plan. However, the hydrogenation/dehydrogenation process of Mg is slow and requires a high temperature (~623 K) thus have prevented the practical use of Mg. Various ways have been used to improve hydrogen adsorption and desorption kinetics. Among them, ball-milling of powder to create nanomaterials with high surface areas and catalysts coating have been demonstrated to accelerate the reaction rate significantly.

In this talk, I will present our preliminary studies of hydrogen storage property of a metal-catalyst system using a unique morphology of Mg, namely, isolated vertically-standing Mg nanoblades with Pd as the catalyst. The temperature desorption spectrum (TDS) has shown that this unique composite nanoblade has a low hydrogen desorption temperature at ~365 K. An in situ reflection high energy electron diffraction (RHEED) was used to monitor the structure transformations such as the reduction of MgH2 and formation of alloys of Mg and Pd as a function of temperature in the dehydrogenation process. Through a combinational microstructure and TDS analyses of Pd/Mg nanoblades it was found that the effect of Pd catalyst on reducing the hydrogen desorption temperature is more significant than the conventionally proposed grain size and strain mechanisms. In addition, morphology change during the hydrogenation/dehydrogenation process will be discussed.

February 21: Astro Seminar

Speaker: Lauren Nicole Smith (RPI) "Progenitors of Type Ia Supernovae"

Where: Science Center 1C13
When: 3 p.m. - 3:30 p.m.

Supernovae have often been used to help solve important problems pertinent to astronomy and astrophysics.  However, the process by which type Ia supernovae are formed is still a bit uncertain.  Current undergraduate research here at RPI is attempting to reproduce the results of recent experiments in order to find the progenitor companion for Tycho's Supernova. The data used is taken from the USNO-B catalog, and searching for the progenitor using both star color and distance from the supernova, the experiment seeks to confirm conclusions previously drawn by Pilar Ruiz-Lapuente.

Speaker: Ben Scaralia (RPI) "Black Holes"

Where: Science Center 1C13
When: 3:30 p.m. - 4 p.m.

A brief history of black holes will be discusses and will cover John Michell's 18th century prediction of the black hole as well as Einstein's General Relativity which first justified them.  I will describe the formation of black holes and their structure, including the event horizon and spaghettification.  Astronomers group black holes using three main properties: mass, electrical charge, and angular momentum. Mass and charge are less important, but a rotating black hole is very different from a non-rotating one because General relativity predicts that rotating masses further distort spactime. They have an Ergosphere and Ring-shaped singularity as well as the possibility of a wormhole opening.  I will close my discussion with a brief description of the "no hair theorem" and the detection of black holes.

February 28: Astro Seminar

Speaker: Daniel Elton (RPI) “Observational Evidence for Dark Matter”

Where: Science Center 1C13
When: 4 p.m. - 4:30 p.m.

Starting with the "missing mass" problem discovered in 1933, I will discuss the growing evidence for dark matter. I will discuss the anomalies found in galactic rotation curves, and the proposed alternate theories which modify current theories of gravity, leaving no need for the dark matter hypothesis. However, I will discuss how observations using gravitational lensing, most notably of the "Bullet Cluster" convincingly show that there must be non-interacting matter moving among the normal matter. I will discuss dark matter halos and recent findings of "Dark Galaxies" which appear to contain few or no stars. Finally, as a form of indirect evidence I will touch on the role dark matter plays in current theories of early galaxy formation.

Speaker: John Dellomo (RPI) "Radio-Loud Active Galactic Nuclei"

Where: Science Center 1C13
When: 4:30 p.m. - 5 p.m.

Radio Galaxies, Quasars, and Blazars are all Active Galactic Nuclei (AGN) that emit large amounts of radiation in the radio frequency range. The differences between these three types of AGN will be discussed. Also, the current theories on the emission of the large jets that have made these objects famous will be discussed.  Finally, I will describe the current theories on how these AGNs are created.

March 3: Condensed Matter and Optics Seminar

Speaker: Yiyang Sun (RPI) “Metal-Organic Frameworks as a Hydrogen Storage Material”

Where: Science Center 1C13
When: 4 p.m. - 4:50 p.m.

Host: Zhongfang Chen 

Metal-organic frameworks (MOFs) are a porous material that can be mass-produced at low cost and currently considered a promising candidate for on-board vehicle storage of hydrogen fuel. Up to 6.9 wt% H2 uptake on MOF has been reported recently. But, only low temperature (77 K) and high pressure (90 bar) can help hold this amount of H2 in MOF. In this talk, I will introduce our recent studies based on first-principles calculations, which are aiming to understand the difficulties in utilizing MOFs as a hydrogen storage material and to design new MOFs that could overcome these difficulties.

March 20: Astro Seminar

Speaker: Rok Buckley (RPI Senior) "Titan"

Where: Science Center 1C13
When: 4 p.m. - 5 p.m.

Titan, Saturn’s largest moon, creates a lot of curiosity about its atmospheric components. It is the second largest moon in the solar system, and its nitrogen-based atmosphere with methane strongly resembles the early time of Earth. Therefore, many scientists and astronomers are interested in observing the effects of tectonics, formation of complex organic compounds, volcanism, and meteorological activities on Titan. Before understanding all these phenomena, the atmosphere of Titan has to be studied, and to do so, the Composite Infrared Spectrometer (CIRS), which is a Fourier Transform Spectrometer on the Cassini orbiter, is used. It provides three-dimensional maps of temperature, gas composition, and condensates of the atmosphere of Titan by measuring spectra covering a wide range of wave lengths from 7 to 1000. Then, the separation of two different spectra peaks (atmospheric temperature and gas abundance) is required for investigation. These analyzed results unravel some curiosities. The expectation of a warmer temperature at the South Pole is found to be false. Possible winds at the North Pole are detected and are suspected of having a high speed that creates a polar vortex mixing the atmospheric gases.

March 24: Condensed Matter and Optics Seminar

Speaker: Jens Feder (University of Oslo) "Friction, Self-Organized Criticality, and Earthquakes"

Where: Science Center 1C13
When: 4 p.m. - 4:50 p.m.

I will discuss the historical background and Coulomb's work on failure and on friction. I describe recent experiments on stick-slip friction, and show that they are accurately described by a self-affine joint distribution for magnitude and duration, and show that the measured exponents lead to the conclusion that this stick-slip process is a scale-free self-organized critical (SOC) process. We discuss normal earthquakes and show that they are not SOC. However, recently discovered slow earthquakes have scaling exponents that are in the universality class as our experiments, and therefore SOC.

March 31: Condensed Matter and Optics Seminar

Speaker: Damien West (RPI) "Stocastically Accelerated Molecular Dynamics"

Where: Science Center 1C13
When: 4 p.m. - 4:50 p.m.

The details of the formation of large defects in semiconductors is not well understood. A major reason for this is that the formation of large defect clusters is very difficult to directly simulate. This requires the simulation of large systems with many defects for times scales long enough for the defects to diffuse through the system and find the nucleation site.

Various methods have been directed at this problem of “rare-events”[1-3] These methods are all based at least in part on transition state theory[4] and require knowledge of either the location or energy of the transition state(TS). We have developed a new method of MD acceleration which requires very little knowledge of the TS. The idea is that what happens when a defect has some energy E<E_c is unimportant (provided E_c < E_TS), as it does not lead to a transition of the system to another state. So, instead of simulating the system during these times (in which it oscillates about a local minima), we replace the relatively large amount of time the system spends in such situations by a statistical description. The mean time,dt, between the improbable events in which a defect attains E³E_c can be derived from the steady state solution of the Fokker-Planck equation. While dt generally depends on the shape of the potential energy surface (PES), it is only the shape near the minima of the PES which contributes significantly. This dependence can be accounted for by parameters which are calculated through the course of the simulation.

Preliminary results have been obtained for a variety of 1-D potentials and show very good agreement with direct simulations. Furthermore, the speed-up factors are promising, over 10³ (with T=1000K and E_c=.5eV). Current work is focused on the extension of the theory to three dimensions and its application to the formation of extended defects in semiconductor systems.

[1] A.Voter, Phys. Rev. Lett. 78, 20 (1997).
[2] M. R. Sorensen, A. F. Voter, J. Chem. Phys. 112, 9599 (2000).
[3] G. Henkelman and H. Jónsson, J. Chem. Phys. 115, 9657 (2001).
[4] A. Voter, F. Montalenti, and T. Germann, Annu. Rev. Mater. Res., 2002. 32: 321.

April 3: Astro Seminar

Speaker: Ben Willett (RPI Graduate Student) “Search for the Progenitor of a Cold Stellar Stream in the Galactic Spheroid”

Where: Science Center 1C13
When: 4 p.m. - 4:50 p.m.

Grillmair and Dionatos (2006) announced the detection of a 63 degree cold stellar stream in the Sloan Digital Sky Survey (SDSS). I will discuss using SDSS and Sloan Extension for Galactic Understanding and Evolution (SEGUE) data to constrain the orbit of the stream. An overview of the structure of the Milky Way will be given, and semi-analytic N-body simulations of globular clusters will be presented, in an effort to constrain the parameters of the stream progenitor. This project was funded by the National Science Foundation, AST 06-07618.

April 17: Astro Seminar

Speaker: Natalia Connolly (Hamilton College) "A new determination of the high-redshift Type Ia supernova rates with the Hubble Space Telescope Advanced Camera for Surveys"

Where: Science Center 1C13
When: 4 p.m. - 5 p.m.

I will present a new measurement of the volumetric rate of supernovae (SNe) Ia up to a redshift of 1.7, using the Hubble Space Telescope (HST) GOODS data combined with an additional HST data set covering the GOODS-North field collected in 2004. The measurement employs a novel technique that does not require spectroscopic data for identifying SNe Ia; instead, a Bayesian approach using only photometric data to calculate the probability that an object is an SN Ia is used. This Bayesian technique can easily be modified to incorporate improved priors on SN properties, and it is well-suited for future high-statistics SN searches in which spectroscopic follow-up of all candidates will be impractical (e.g., the Dark Energy Survey, LSST, etc.). We find that the data do not distinguish between a flat rate at redshift >0.5 and a previously proposed model, in which the Type Ia rate peaks at redshift 1 due to a significant delay from star formation to the SN explosion.

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