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Colloquia Archive

Colloquium TBD

Thursday, May 23, 2013 @ 3:30 PM
Disque Hall Room 919



Colloquium

Thursday, May 16, 2013 @ 3:30 PM
Disque Hall Room 919

Speaker: Dr. Haw Yang, Princeton University

Host: Dr. Jian-Min Yuan



Colloquium

Thursday, May 9, 2013 @ 3:30 PM
Disque Hall Room 919

Speaker: Dr. John Straub, Boston University
 
Host: Dr. Brigita Urbanc


Colloquium TBD

Thursday, May 2, 2013 @ 3:30 PM
Disque Hall Room 919



Colloquium TBD

Thursday, April 25, 2013 @ 3:30 PM
Disque Hall Room 919



Colloquium TBD

Thursday, April 18, 2013 @ 3:30 PM
Disque Hall Room 919



Colloquium TBD

Thursday, April 11, 2013 @ 3:30 PM
Disque Hall Room 919



Higgs Results from the CMS Experiment

Thursday, March 14, 2013 @ 3:30 PM
Disque Hall Room 919

Speaker: Dr. Toyoko Orimoto, Northeastern University

Host: Dr. Michelle Dolinski



Colloquium TBD

Thursday, March 7, 2013 @ 3:30 PM
Disque Hall Room 919



Colloquium TBD

Thursday, February 28, 2013 @ 3:30 PM
Disque Hall Room 919



Colloquium TBD

Thursday, February 21, 2013 @ 3:30 PM
Disque Hall Room 919



Colloquium TBD

Thursday, February 14, 2013 @ 3:30 PM
Disque Hall Room 919



Colloquium

Thursday, February 7, 2013 @ 3:30 PM
Disque Hall Room 919

Speaker: Dr. Ophelia Tsui, Boston University

Host: Dr. Brigita Urbanc



Colloquium TBD

Thursday, January 31, 2013 @ 3:30 PM
Disque Hall Room 919



Colloquium TBD

Thursday, January 24, 2013 @ 3:30 PM
Disque Hall Room 919



Colloquium

Thursday, January 17, 2013 @ 3:30 PM
Disque Hall Room 919

Speaker: Dr. Naoko Kurahashi Neilson, University of Wisconsin-Madison
 
Host: Dr. Michelle Dolinski


Nanopore Graphene-based Electronic Devices

Thursday, December 6, 2012 @ 3:30 PM
Disque Hall Room 919

Speaker: Dr. Marija Drndic, University of Pennsylvania

Abstract: Graphene is an exceptional material for high-speed electronics, as well as a revolutionary membrane material due to its strength and atomic thickness. Nanopores in suspended graphene membranes are currently regarded as candidates for ultrafast DNA sequencing. When a single DNA molecule passes through a nanopore, it blocks the field-driven ions passing through the pore and is detected by measuring the ion current reduction. Due to the thin nature of graphene membranes and reduced pore resistance, we observe larger current signals than in the case of traditional solid-state nanopores. Use of graphene as a membrane material opens the door to a new class of nanopore devices in which electronic sensing and control are performed directly at the pore.

Host: Dr. Alexey Aprelev


First Light and Reionization

Thursday, November 29, 2012 @ 3:30 PM
Disque Hall Room 919

Speaker: Dr. Adam Lidz, University of Pennsylvania

Abstract: An exciting frontier in observational and theoretical cosmology is to understand the properties of the Universe between the ages of 400,000 years and 1 billion years, compared to its present 14 billion years of age.  A confluence of data sets from a variety of wavebands will allow us to probe the latter part of this frontier in the next few years, constraining the Universe's properties a few hundred million years after the Big Bang. We expect that around this time, the first galaxies turned on, emitted ultraviolet light, and ionized "bubbles" of  hydrogen gas around them. These bubbles grew, merged, and eventually filled the entire volume of the Universe with ionized hydrogen, in a process known as reionization. Understanding this process will constrain the properties of the first luminous sources, and fill in a significant gap in our story of structure formation, whereby the Universe transitions from simple initial conditions to its present day complexity.  Towards this end, I will describe both recent efforts to theoretically model cosmic reionization, as well as the prospects for observing it.

Host: Dr. Gordon Richards



Women in Physics: Why So Few?

Thursday, November 15, 2012 @ 3:30 PM
Disque Hall Room 919

Speaker: Dr. Meg Urry, Yale University

Abstract: Many people agree there are too few women and minorities in science but disagree about why, and what to do about it. Fortunately, social science research has addressed this issue extensively. I will review gender statistics in different STEM (science, engineering, math and technology) fields, highlighting differences in critical points along the career path. I then describe some of the social science experiments on unconscious bias, including a recent study conducted on STEM faculty. I conclude with a set of steps for improving gender equity in STEM fields.

Host: Dr. Gordon Richards



Skeletons and Core Structures in Oscillatory Gene Regulatory Networks

Thursday, November 8, 2012 @ 3:30 PM
Disque Hall Room 919

Speaker: Dr. Gang Hu, Beijing Normal University
 
Abstract: In the recent two decades the topic of complex networks has attracted great attention due to its theoretical interest and significant applications in wide fields. Complex networks often have complicated topological structures. It is thus useful to explore some simple reduced core structures (if they exist) which play key roles determining different functions of networks. In this talk a midel of oscillatory gene regulatory networks (GRNs) is considered. From the data of network oscillations we are able to reveal some skeletons of interactions and core subnetworks which essentially determine the oscillations of the whole networks. The core subnetworks are often much smaller than the original GRNs. A method of dominant phase-advanced driving (DPAD) analysis is proposed to quantitatively measure the importance of various interactions and to identify the related skeletons and core subnetworks of the given oscillatory GRNs.
 
Host: Dr. Jian-Min Yuan


Dusty Galaxies Near and Far

Thursday, November 1, 2012 @ 3:30 PM
Disque Hall Room 919

Speaker: Dr. Anna Sajina, Tufts University
 
Abstract: I will discuss what are dusty galaxies and why they are important to studies of galaxy formation and evolution. I will present recent results based on data from the Spitzer and Herschel Space Telescopes in the infrared as well as the Hubble Space Telescope in the optical showing that dusty galaxies early on in the history of the universe are fundamentally different from their closest analogs today. I will discuss how these findings fit with our changing views on the evolution of galaxies over time.
 
Host: Dr. Gordon Richards


Slow Dynamics and Topological Entanglement in Macromolecular Liquids

Thursday, October 25, 2012 @ 3:30 PM
Disque Hall Room 919

Speaker: Dr. Kenneth Schweizer, University of Illinois
 
Abstract: Concentrated liquids of large synthetic and biological macromolecules display fascinating and unique slow dynamics of great importance in fields as diverse as the materials science and processing of molten plastics to cellular rigidity and biophysics. Two common features of all entangled linear polymers is their ability to interpenetrate (ala a bowl of cooked or uncooked spaghetti) but not dynamically cross each other.  The combined consequences of these factors is called “topological entanglement”, and a fundamental understanding remains a major challenge in physics. I will first discuss key experimental phenomena and the reptation-tube model which postulates that at large enough times long polymers move like snakes corresponding to anisotropic diffusion along their own contour. As distinctive consequences, relaxation, diffusion and flow occurs extremely slowly and rubber-like elasticity (ala silly putty or chewing gum) emerges on intermediate time and length scales. However, the reptation-tube theory lacks a microscopic foundation in terms of forces, and many fundamental questions remain unanswered such as the following. Where does the confining tube due to forces between different polymers really come from ? What is the microscopic origin of the remarkable elasticity ? Are entanglements effectively unbreakable ? Building on our recent advances for understanding slow dynamics in glass-forming liquids, Daniel Sussman and I have developed a fundamental theory for entangled polymers of different shapes (rods, random coils, and star-like branched crosses). The key ideas and new predictions that address the above questions will be described in detail for rigid rods, and quantitative comparisons made with simulations and biopolymer experiments. Time permitting, generalization of the approach to random coil flexible polymer chains will be briefly discussed.
 
 
 
Host: Dr. Sam Bose


Human-designed and Nature-designed Approaches to Self-Assembly: Nanomagnets from Diblock Copolymers and Conducting Bacterial Nanowires

Thursday, October 18, 2012 @ 3:30 PM
Disque Hall Room 919

Speaker: Dr. Mark Tuominen, University of Massachusetts, Amherst
 
Abstract: Recently we have seen a rapid expansion in the understanding and utilization of self-assembly. The research activity is driven in part by the promise of new scalable nanomanufacturing processes relevant for nanoscale materials and devices. I will discuss two specific examples: diblock copolymer nanolithography (human-designed) and bacterial protein nanostructures (nature-designed). Diblock copolymer nanolithography uses the thermodynamically-driven microphase separation of block copolymers to create a periodic nanoscale patterns, which in turn can be transformed into a fabrication template, lithographic mask, or functional material. I will discuss our use of this method to produce ferromagnetic nanostructures to investigate the physics of materials built from single-domain magnets. As a contrasting example, I will describe the emerging topic of conducting self-assembled protein nanofilaments (called “pili”) produced by bacteria. These “natural organic metals” are nanowires produced from amino acids by a common soil bacteria, Geobacter sulfurreducens. Networks of pili can transport electrons over centimeter-long distances, thousands of times the size of a bacterium, and exhibit electronic conductivities comparable to synthetic organic metallic nanostructures. Surprisingly, the temperature and gate-voltage dependence this biological material is similar to quasi-1D disordered synthetic organic metals. Further, the electrical capacitance of the network is comparable to that of synthetic supercapacitors.
 
Host: Dr. Goran Karapetrov


Searching for Planets Orbiting Low-mass Stars

Thursday, October 4, 2012 @ 3:30 PM
Disque Hall Room 919

Speaker: Dr. Cullen Blake, University of Pennsylvania
 
Abstract: The majority of stars in the solar neighborhood are low-mass M dwarfs. However, these small stars have largely been excluded from the Doppler surveys that have identified hundreds of extrasolar planets. Today, the precision of Doppler measurements at optical wavelengths is approaching 1 m/s, but comparable precision has not yet been demonstrated at the near infrared (NIR) wavelengths where low-mass stars are brightest. Low-mass stars are attractive targets for planet searches, particularly when searching for rocky, Earth-like planets orbiting in the so-called Habitable Zones of their hosts. I will review techniques for measuring the radial velocities of low-mass stars in the NIR, including the use of absorption features in Earth's atmosphere (telluric lines) as a "zero velocity" reference. I will discuss ongoing efforts to significantly improve Doppler precision in the NIR and future prospects for  a comprehensive census of planets orbiting nearby low-mass stars. Finally, I will demonstrate how a Global Positioning System receiver can be used to precisely measure water vapor absorption, enabling the generation of the telluric absorption templates that are crucial for NIR Doppler measurements.
 
Host: Dr. Gordon Richards


Big Science, Little Stars: Low-Mass Stellar Science in Large Surveys

Thursday, May 24, 2012 @ 3:30 PM
Disque Hall Room 919

Speaker: Dr. John Bochanski, Penn State University
 
Abstract: Modern sky surveys, such as the Sloan Digital Sky Survey and the Two-Micron All Sky Survey, have revolutionized the study of low–mass stars. With millions of photometric and spectroscopic observations, intrinsic stellar properties can be studied with unprecedented statistical significance.  I highlight the link between the solar neighborhood and larger surveys, as nearby stars provide fundamental calibrations for survey efforts.  Recent SDSS results have extended beyond the solar neighborhood and have sought to place the local low-mass stellar population in a broader Galactic context.   I discuss a recent measurement of the luminosity and mass functions of M dwarfs, using a new technique optimized for large surveys. I also report on ongoing investigations employing M dwarfs as tracers of Galactic kinematics. The highlighted projects demonstrate the advantages and problems with using large data sets and will pave the way for studies with next–generation surveys, such as PanSTARRS and LSST.
 
Host: Dr. Gordon Richards


Nonlinear Light Scattering from Meso-/Nano-scopic Materials & Biological Systems

Thursday, May 17, 2012 @ 3:30 PM
Disque Hall Room 919

Speaker: Dr. Grazia Gonella, Temple University
 
Abstract: Microparticles, nanoparticles, micelles, vesicles, etc. have found application in a broad range of fields, spanning from medicine, pharmacy, and biotechnology to the paint industry, electronics, optics, and the environment. These nano- and micro- colloidal “objects” have optical, structural, and chemical properties that are different from both their building blocks and from the bulk materials themselves. The different physical and chemical properties are mainly due to the high surface-to-volume ratio of these objects. It is therefore of fundamental importance to characterize their surface and its interactions with the surrounding medium.
Second-order nonlinear optical techniques are particularly sensitive to interfaces and can be used to characterize them in situ, even when buried deep in the colloidal environment [1]. In this colloquium I will discuss how size, shape, refractive index and nonlinear optical response affect the NLS behavior of micro- and nano-particles, and how information on the orientational distribution of molecules adsorbed on the particle surface can be obtained by NLS [2]. Information can even be obtained from single molecules in solution [3]. I will conclude by presenting an overview of possible new systems to which the NLS techniques could be successfully applied to, and what kind of information can be gained.
 
[1] S. Roke & G. Gonella Annu. Rev. Phys. Chem. 63 (2012), 353-378 http://prb.aps.org/abstract/PRB/v84/i12/e121402
[2] G. Gonella & H.-L. Dai Phys. Rev. B 84 (2011), 121402(R):1-5 http://prb.aps.org/abstract/PRB/v84/i12/e121402
[3] L. A. Burke, G. Gonella, F. Heirtzler, H.-L. Dai, S. Jones, J. Zubieta & A. J. Roche Chem. Commun. 48 (2012), 1000-1002 http://pubs.rsc.org/en/content/articlelanding/2012/cc/c2cc16199k
 
Host: Dr.  Goran Karapetrov


Operational Dynamic Modeling Transcending Quantum and Classical Mechanics: Applications to Quantum Mechanical Phase-space Representation

Thursday, May 10, 2012 @ 3:30 PM
Disque Hall Room 919

Speakers: Drs. Denys I. Bondar and Renan Cabrera, Department of Chemistry, Princeton University

Abstract: We first introduce Operational Dynamic Modeling (ODM) as a systematic theoretical framework for deducing equations of motion from the evolution of observed average values. Then, it is demonstrated that ODM is capable of encompassing wide ranging dynamics from classical non-relativistic mechanics to quantum field theory.
 
We focus on the applications of ODM to the phase-space representations of quantum mechanics based on the Wigner quasi-probability distribution. Wigner function’s negativity is explained within this framework. We develop numerically efficient Wigner function propagators that unveiled overlooked fundamental features of the quantum mechanical phase-space representation.

Host: Dr. Robert Gilmore



Star and Star Cluster Formation: The Big Picture

Thursday, May 3, 2012 @ 3:30 PM
Disque Hall Room 919

Speaker: Dr. Richard de Grijs, Kavli Institute for Astronomy and Astrophysics, Peking University

Abstract: What has been the most profound discovery, progress or idea that has emerged in astronomy over the last decade? And what will be the most important challenge in astronomical research in the next decade? These questions are at the heart of our discipline, but we rarely venture outside of our own niche areas. I will attempt to focus on the broad picture underlying the field of star formation and discuss the requisite conditions for sustained progress in this field, aided by recent achievements in the context of my group's star cluster research.

Host: Dr. Enrico Vesperini

For background, please visit http://kiaa.pku.edu.cn/~grijs/research.html#science and, for a more technical review, see http://rsta.royalsocietypublishing.org/content/368/1913/693.full



Finding 'Missing' Satellites with Gravitational Lensing

Thursday, April 26, 2012 @ 3:30 PM
Disque Hall Room 919

Speaker: Dr. Ross Fadeley, Haverford College
 
Abstract: On large spatial scales (>1 Mpc), the Cold Dark Matter (CDM) theory provides an excellent explanation for the properties of the observed universe.  On smaller scales, however, there is a tension between predictions of the theory and current observations.  One such sticking point is the 'Missing Satellites Problem' - CDM generally predicts many more small satellite galaxies around the Milky Way (and other galaxies) than are observed.  An explanation to the problem has been developed in recent years, suggesting inefficient star-formation and observational biases can alleviate the problem.  If such a solution is correct, there is a sea of 'dark dwarfs' waiting to be found.  Discovery of these objects remains a crucial test of CDM, and can shed light on the nature of Dark Matter.  Thankfully, gravitational lensing provides a means to find such objects, since it is sensitive to mass only.  I will discuss how lensed quasars allow us to detect such objects, as well as the prospects for finding the smallest satellites with upcoming samples of lenses.
 
Host: Dr. Gordon Richards


The Future of Neutrino Mass Measurements with Tritium Beta Decay

Tuesday, April 17, 2012 @ 4:00 PM
Disque Hall Room 919

Speaker: Dr. Noah Oblath, Laboratory for Nuclear Science, MIT
Abstract: Tritium beta decay experiments provide the most sensitive direct measurement of the neutrino mass scale. There is a long history of this type of experiment, and it continues to be refi ned with two particular projects: the Karlsruhe Tritium Neutrino Experiment (KATRIN), and Project 8. KATRIN is currently being set up at the Karlsruhe Institute of Technology in Karlsruhe, Germany. It seeks to improve the sensitivity to the neutrino mass scale by an order of magnitude over the previous generation of tritium beta-decay experiments. KATRIN will use a high-resolution spectrometer known as a MAC-E filter to carefully measure the beta-decay electron energy spectrum. The resolution of the spectrometer is limited by its physical dimensions, and KATRIN is the largest experiment of this type that can be built in the foreseeable future. Therefore a new approach is needed to further improve the sensitivity to the neutrino mass scale.
Project 8 is an experiment that will use radio-frequency techniques to detect and measure the energies of beta-decay electrons. We will detect the radiation created from the cyclotron motion of the electrons in a strong magnetic fi eld. As this technique involves a measurement of a frequency in a way that is non-destructive to the electron, we can, in principle, achieve a high degree of resolution and a further-improved sensitivity to the neutrino mass.
 
 
Host: Dr. Charles Lane


Colloquium - Reserved

Thursday, April 12, 2012 @ 3:30 PM
Disque Hall Room 919



Colloquium

Thursday, March 15, 2012 @ 3:30 PM
Disque Hall Room 919

Capturing the Dynamics of Biomolecules: From Protein Folding in a Test Tube to Metal-Ion Transportation in Living Cells
 
Speaker: Dr. Hairong Ma, JILA & Dept. Chemistry and Biochemistry, University of Colorado
 
Abstract: Biomolecules do not hold a static structure; they must move to perform functions. Their motions often involve transitions between multiple minima on a rough energy landscape, with timescales spanning a wide range (fs to s), and amplitudes reflecting the changes from elementary structures to large domains. In the first part of my talk, I will present the characterization of folding dynamics and reconstruction of energy landscape of proteins and nucleic acids using temperature-jump and computational modeling methods. Test tube experiments provide critical insight about the fundamental relationship between structure, dynamics, and energy landscape, yet ultimately, biomolecules carry out functions in living cells. In the second part of my talk, I will present the characterization of FRET-based population heterogeneity and reaction dynamics of metal-ion transportation with single cell resolution using microfluidics technology.
 
Host: Dr. Frank Ferrone


Colloquium -TBD

Thursday, March 8, 2012 @ 3:30 PM
Disque Hall Room 919



17th Kaczmarczik Lecture

Thursday, March 1, 2012 @ 3:00 PM
Main Building Auditorium

"The Accelerating Universe"
 
Speaker: Dr. Brian Schmidt, 2011 Nobel Laureate in Physics
Abstract: In 1998 two teams traced back the expansion of the universe over billions of years and discovered that it was accelerating, a startling discovery that suggests that more than 70% of the cosmos is contained in a previously unknown form of matter, called Dark Energy. The 2011 Nobel Laureate for Physics, Brian Schmidt, leader of the High-Redshift Supernova Search Team, will describe this discovery and explain how astronomers have used observations to trace our universe's history back more than 13 billion years, leading them to ponder the ultimate fate of the cosmos.
 
The Lecture is free and Open to the Public
 


Colloquium - Reserved

Thursday, February 23, 2012 @ 3:30 PM
Disque Hall Room 919



Colloquium - Reserved

Thursday, February 16, 2012 @ 3:30 PM
Disque Hall Room 919



Colloquium

Thursday, February 9, 2012 @ 3:30 PM
Disque Hall Room 919

Molecular-level Simulations of  Protein Aggregation and Fibrillization
 
Speaker: Dr. Carol Hall, North Carolina State University
 
Abstract: The pathological hallmark of more than twenty neurodegenerative diseases, like Alzheimer's, Parkinson's and the prion diseases, is the presence within the brain of plaques containing ordered protein aggregates called fibrils. It is not yet known why these structures form in some individuals and not in others, or whether the plaques are toxic or Nature's way of sequestering toxic species. Dr. Hall will describe current thinking on the scientific underpinnings for this phenomenon, and her computational efforts to contribute to our knowledge of how and why proteins assemble into fibrils.
 
Host: Dr. Brigita Urbanc


Colloquium

Thursday, February 2, 2012 @ 4:00 PM
Disque Hall Room 919

Ask Not For Whom The Coffee Rings, It Rings For Spheres But Not Ellipsoids
 
Speaker: Dr. Arjun Yodh, University of Pennsylvania
 
Abstract: I will discuss recent colloid experiments from my lab.  The first set of experiments employ temperature-sensitive microgel particles to study phonons in glasses and their relation to the mechanical response of disordered solids [1,2].  The second set explores the role of particle shape in affecting particle deposition during evaporation [3], i.e., the affect of particle shape on the coffee ring effect.
 
[1]    Chen, K., Ellenbroek, W.G., Zhang, Z.X., Chen, D.T.N., Yunker, P.J., Henkes, S., Brito, C., Dauchot, O., van Saarloos, W., Liu, A.J., and Yodh, A.G., Low-frequency vibrations of soft colloidal glasses. Physical Review Letters 105, 025501 (2010).
[2]    Chen, K., Manning, M.L., Yunker, P.J., Ellenbroek, W.G., Zhang, Z., Liu, A.J., and Yodh, A.G., Measurement of correlations between low-frequency vibrational modes and particle rearrangements in quasi-two-dimensional colloidal glasses. Physical Review Letters 107, 108301 (2011).
[3] Yunker, P.J., Chen, K., Zhang, Z.X., Ellenbroek, W.G., Liu, A.J., and Yodh, A.G., Rotational and translational phonon modes in glasses composed of ellipsoidal particles. Physical Review E 83, 011403 (2011).
 
Host: Dr. Leonard Finegold


Colloquium

Thursday, January 26, 2012 @ 3:30 PM
Disque Hall Room 919

Science: The Public, Congress and You

Speaker: Dr. Michael Lubell, CCNY & APS

Abstract: Polling of public attitudes toward science contains very mixed results. By a margin of 93 to 7 the public believes the U.S. should be a global leader in science, and 2 out of 3 people approve using taxpayer funds to support research. But 46 percent of the respondents in the sample of 1200 give the federal government a grade of C, D, or F for its efforts to promote technological innovation, and 50 percent believe the federal science budget is too large, with a significant fraction of the respondents naming science as their number one target for cutting. In their actions and public statements Washington policymakers also reflect mixed attitudes. The president has been a champion of science, as have a number of legislators in both political parties. But with deficit reduction occupying center stage in the fiscal arena, science funding could fall victim to major cuts in discretionary spending scheduled to begin in FY 2013. Lawmakers could make science an exception to any planned austerity measures, but whether they choose to do so will depend significantly on public attitudes. The polling data suggest an uncertain road ahead and point to the need for scientists to engage with the public in far more effective ways than the have until now.

Host: Dr. Leonard Finegold



Star and Star Cluster Formation: The Big Picture

Thursday, January 19, 2012 @ 3:30 PM
Disque Hall Room 919

Speaker: Mordecai-Mark Mac Low, American Museum of Natural History
Abstract: In this talk I consider two questions.  First, I investigate the formation of molecular clouds from diffuse interstellar gas.  It has been argued that the pressure of the interstellar gas controls the fraction of molecular hydrogen present, and thus the star formation rate. Alternatively, I and others have suggested that the gravitational instability of gas in galactic disks controls both.  I present numerical results demonstrating that observed correlations between midplane pressure, molecular hydrogen fraction, and star formation rate can be explained within the gravitational instability picture. Second, I discuss how ionization affects the formation of the most massive stars. Although most distinctive observables of massive stars can be traced back to their ionizing radiation, it does not appear to have a strong effect on their actual formation.  Rather, I present simulations suggesting that stars only ionize large volumes after their accretion has already been throttled by gravitational fragmentation in the accretion flow. At the same time these models can explain many aspects of the observations of ultracompact H II regions.
 
Host: Dr. Steve McMillan


Toy Story: What I Have Learned from Playing with Toys About the Physics of Living Cells

Thursday, December 1, 2011 @ 3:30 PM
Disque Hall Room 919

Speaker: Dr. Robert Austin, Princeton University
 
Abstract: Yogi Berra once noted that "You can observe a lot just by watching." A similar remark can be made about toys: you can learn a lot of physics by playing with certain children's toys, and given that physics also applies to life, you could hope that it would also be possible to learn about the physics of living cells by close observation of toys, loosely defined. I'll start out with a couple of toys, rubber duckies and something called a soliton machine and discuss insights (or failures) in how "energy" moves in biological molecules. I'll bring back the rubber duckies and a toy suggested by one of the eccentrics known to roam the halls of academia to discuss how this lead to studies how cells move and collective aspects of cell movement. Then I'll talk about mazes and how they lead to experiments on evolution and cancer. Hopefully this broad range of toys will show how indeed "You can observe a lot just by watching" about some of the fundamental physics of living cells.
 
Host: Frank Ferrone


Multifunctional Magnetic Vortex Microdisks

Thursday, November 17, 2011 @ 3:30 PM
Disque Hall Room 919

Speaker: Valentyn Novosad, Argonne National Laboratory
 
Abstract: The magnetic ground state of magnetically soft thin film ferromagnets in confined geometries (on the micrometer scale) consists of a curling spin configuration, known as a magnetic vortex state (Fig 1b). The vortex is characterized by an in-plane continuous swirling closure spin structure with a core region (typically ~10 nm in diameter) where the spins tilt out of the plane [1, 2]. The vortex state is stable because it generates minimal stray magnetic fields, with the exception of the core area, which forms to satisfy exchange energy considerations. The vortex state can be described in terms of two quantities: a core polarization that defines whether the out-of plane component of the magnetization points up or down, and a chirality that defines the in-plane curling direction (clockwise or counter-clockwise) of the spins. The characteristic reversal mechanism is via nucleation, displacement and annihilation of the vortex [3, 4]. Magnetic vortices in confined ferromagnets is an important research topic of broad interest due its relevance to the fundamental advancement of our understanding of nanomagnetic systems. Various applications based on magnetic vortex concept include Magnetic Random Access Memories [5], microwave oscillators [6, 7], and magnetic field sensors [8, 9]. In this talk I will focus on our recent work on studying the magnetic vortex microdisks (Fig. 1a) as possible multifunctional magnetic carriers for biomedical applications [10]. In particular, I will report on successful interfacing of ferromagnetic materials with a spin vortex ground state and biomaterials (antibody, whole cell). When an alternating magnetic field is applied the vortices shift, leading to the microdisks oscillation that causes a mechanical force to be transmitted to the cell. Cytotoxicity assays, along with optical and atomic force microscopy studies, show that the spin vortex-mediated stimulus creates two dramatic effects: (a) membrane disturbance and compromising, and (b) cellular signal transduction and amplification, leading to robust DNA fragmentation and, finally, programmed cell death [11]. The experiments reveals that by employing biofunctionalized magnetic vortex microdisks the magnetic fields of low frequency of a few tens of Hz and of small amplitude of < 100 Oe applied during only 10 minutes was sufficient to achieve ~90% cancer cells destruction. For comparison, magnetic fields of few hundreds Oe, running at ~ hundreds kHz are typically needed to achieve another type of cytotoxicity, i.e. hyperthermia treatments using superparamagnetic particles. In other words, an external power supplied to the cell cultures in our experiments is ~100,000s times smaller than that applied to magnetic particles that are presently used in hyperthermia applications. This work and the use of the Center for Nanoscale Materials at Argonne National Laboratory were supported by UChicago Argonne, LLC, Operator of Argonne National Laboratory (``Argonne''). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357. See
 
Host: Goran Karapetrov


Neutrinos in MINOS: Oscillations and Time of Flight Measurements

Thursday, November 10, 2011 @ 3:30 PM
Disque Hall Room 919

Speaker: Mayly Sanchez, Iowa State University
 
Abstract: Since neutrino oscillations were observed and announced to the World in 1998, the field of neutrino physics has been teeming with activity. A forefront contributor is the MINOS experiment, which has been taking beam data since 2005. MINOS analyzes a neutrino beam in two different locations: at Fermilab, close to the beam production, and 735 km downstream in Northern Minnesota. By searching for neutrino disappearance as well as appearance, MINOS has been able to examine some of the neutrino mixing parameters that are a window into the new directions of physics. A brief history of neutrino physics and recent results since the discovery of oscillations will lead us to discuss the challenges of performing neutrino experiments. We will focus on how these challenges have been addressed in MINOS in obtaining the results from the first two years of beam data. We will also briefly look into the future, when other experiments such as NOvA and LBNE will explore and unravel other pieces of the neutrino puzzle.
 
Host:Jelena Maricic


Functional Nanomaterials with Tailored Structures

Thursday, November 3, 2011 @ 3:30 PM
Disque Hall Room 919

Speaker: Vojislav Stamenkovic, Argonne National Laboratory
 
Abstract: Advancement in development of nanomaterials relies on the capability of altering their properties at the nanoscale. In such effort, the approach that considers well-defined systems is of great importance. The knowledge obtained from bulk materials is utilized to tailor nanoscale properties of the materials that are relevant for energy conversion and storage. It has been demonstrated that employment of multimetallic systems could offer unprecedented benefits in functional properties of materials. The reported synergy between well-defined systems and corresponding and nanoparticles emphasizes an efficient approach in design and synthesis of advanced nanomaterials. Such research effort involves the following steps: 1) characterization of well-defined solid materials by varying their surface structure, composition profile and electronic properties; 2) atomic/molecular level characterization of electrified solid-liquid interfaces; 3) theoretical modeling of structure/function relationship; 4) identification of the most active and stable sites at atomic scale during reaction conditions; 5) bond making and bond breaking processes at the electrochemical interfaces; 6) modification of the surface and subsurface composition by other constituents aimed to improving functionality; 7) design and synthesis of advanced (nano)materials with tailored structures. Novel nanoscale structures show substantial improvement of their functional properties under the real conditions. See
 
Host: Goran Karapetrov


Making the Milky Way -- The Continuing Story

Thursday, October 27, 2011 @ 3:30 PM
Disque Hall Room 919

Speaker: Jay Lockman, NRAO
 
Abstract:In the first part of the talk I will describe the Green Bank 100-meter diameter radio telescope, its origin and capabilities, and some of its recent scientific programs including the search for gravitational radiation, Mercury's molten core, interstellar organic chemistry, and the growth and evolution of galaxies. The second part of the talk will expand on the topic of growth and evolution of galaxies, with a focus on the Milky Way's need for continual accretion of fresh material, and the discovery of a large gas cloud in the process of merging with our galaxy. This unique object holds information on the evolution of the Galaxy, the structure of the gaseous halo,and the existence of dark matter halos.

Host:Gordon Richards



Unveiling Nature’s Deep Secrets with Neutrinos

Thursday, October 20, 2011 @ 3:30 PM
Disque Hall Room 919

Speaker: Jelena Maricic
Abstract: One of nature’s ultimate unexplained secrets is: why and how did matter prevail over anti-matter in the early Universe? Tiny neutrinos may hold the key ingredient to answering this complex question. During the last decade, we have learned that neutrinos have mass and oscillate among three neutrino types with a well understood oscillation pattern. In the three-neutrino-oscillation framework, a single mixing angle and one phase (the so-called CP violation phase) are still unknown. The Double Chooz experiment has been taking data since April 2011 and vigorous data analysis is underway with the goal of measuring the last unknown neutrino mixing angle theta13. The size of the theta13 will determine the prospects of measuring the CP-violation phase in the lepton sector. The value of the CP-violation phase provides an indirect measure of asymmetry between matter and anti-matter. The Long Baseline Neutrino Experiment (LBNE) is currently being designed to measure the CP-violation phase, which could explain the level of matter-antimatter asymmetry observed in our Universe. In my talk, I will present current status, our activities and preliminary results from Double Chooz, followed by the description of LBNE, its prospects and our role in it.


Where's the Matter with Clusters?

Thursday, October 13, 2011 @ 3:15 PM
Disque Hall Room 919

Speaker: David Goldberg
Abstract: Clusters of galaxies are the largest collapsed structures in the universe. Their mass maps reveal properties of the primordial density field, and their mass distribution as a function of time is a sensitive probe of Lambda-CDM cosmology. However, it has been known for nearly a century that the luminous matter in clusters is not necessarily a good indicator of the mass. In this talk, I will describe how to map rich clusters using gravitational lensing, what numerical simulations have led us to expect, and what the differences between observation and theory can tell us about the nature of the universe.



DNA-linked Nanoparticle Assemblies

Thursday, October 6, 2011 @ 3:30 PM
Disque Hall Room 919

Speaker: Francis Starr, Wesleyan University

Abstract:Custom designed nanoparticles (NP) or colloids with specific recognition offer the possibility to control the phase behavior and structure of particle assemblies for a range of applications. One approach to realize these new materials is by attaching single-stranded DNA to a core NP. By appropriate choice of base sequence, the hydbridization of double-stranded DNA will link NP, allowing for control of NP assembly. I will discuss a molecular model for DNA-linked NP. We examine how the number and orientation of strands affects the structure, phase behavior, and dynamics. We show that the NP can form networks with very open structure, due to long DNA linkages relative to core NP size, resulting in a multitude of thermodynamically distinct phases, both amorphous and crystal. We further examine the parameters that control the thermodynamical stability of crystalline NP arrays, since these ordered systems are expected to be important for applications, and are challenging to form experimentally. Finally, we show that existing theoretical framework from polymer physics can be adapted to quantitatively explain the growth and cluster structure from numerical simulations.

Host:Luis Cruz-Cruz



Colloquium

Tuesday, April 12, 2011 @ 3:00 PM
Disque Hall Room 919

Speaker: Jose Huchim Herrera
Host: Teck-Kah Lim
Title:Traditions of the SUN
Abstract: This is a presentation about traditions of the SUN across time and cultures. We feature solar alignments with temples, buildings, and pre-Colombian petroglyphs, which are on rock carvings and paintings. The focus is on the ancient Maya, and the Ancestral Pueblo peoples of the American Southwest. This talk is part of the project “Ancient Observatories, Timeless Knowledge” sponsored by NASA, UC Berkeley, The National Institute of Anthropology and History in Mexico.


Detectability of Gravitons, Non-Quantum Gravity, and the Measurement Problem in Quantum Mechanics

Thursday, March 10, 2011 @ 3:30 PM
Disque Hall Room 919

Speaker: Dr. Stephen Boughn, Haverford College
Abstract: One of the great challenges for 21st century physics is to quantize gravity and generate a theory that will unify gravity with the other three fundamental forces of nature. Currently, there is no complete and consistent quantum theory of gravity and, so far, candidate models of quantum gravity all face major formal and conceptual problems. On the experimental side, at present there is absolutely no observational evidence in support of the quantum nature of gravity and the likelihood of definitive tests in the future is not at all certain. Furthermore, straightforward analyses indicate that that it is virtually impossible (in principle) to directly detect individual gravitons, the fundamental quanta in any quantum theory of gravity. For these reasons, it seems reasonable to at least consider the possibility that gravity is an entirely classical, non-quantum phenomenon. In this talk, I will take this heretical point of view and explore the experimental consequences of such a conjecture including an inevitable link to the perennial, 80 year old measurement problem in quantum mechanics.

For reference, see http://lanl.arxiv.org/PS_cache/arxiv/pdf/0809/0809.4218v3.pdf

Host: Dr. Robert Gilmore



Where, Precisely, is the Dark Matter?

Tuesday, March 8, 2011 @ 3:00 PM
Disque Hall Room 919

Speaker: Dr. David Hogg, NYU
 
Host: Dr. Gordon Richards
 
Abstract: If dark matter interacts with the light sector only gravitationally (that is, if it doesn't reflect or produce photons or other standard-model particles, as now seems likely), then we can measure its properties only through its effects on the dynamics of observable objects, like galaxies and stars. I discuss what we have learned so far about the dark matter from astronomical measurements, and what we might be able to learn in the next decade.


Bananas or Fissile Material? Interrogation Techniques for Special Nuclear Materials

Thursday, March 3, 2011 @ 3:30 PM
Disque Hall Room 919

Speaker: Dr. Diane Markoff, North Carolina Central
Abstract: We are involved in the nuclear physics research and development of active interrogation techniques to efficiently and effectively detect special nuclear materials. I will outline the motivation, goals, requirements and situations of interrogation techniques and present as examples the methods being studied using the Free Electron Laser facility at the Triangle Universities Nuclear Laboratory. I will introduce some interesting fundamental questions in nuclear physics that have arisen as a result of these studies.
Host: Dr. Jelena Maricic


The "Standard" Model of Cosmology ... and Open Questions

Thursday, February 17, 2011 @ 3:30 PM
Disque Hall Room 919

Speaker: Dr. Bharat Ratra, Kansas State University
 
Abstract: Experiments and observations over the last decade have provided strong support for a "standard" model of cosmology that describes the evolution of the universe from an early epoch of inflation to the complex hierarchy of structure seen today. I review the basic physics, astronomy, and history of ideas on which this model is based. I describe the data which persuade cosmologists that (as yet undetected) dark energy and dark matter are by far the main components of the energy budget of the universe. I conclude with a list of open cosmological questions.

Host: Dr. Michael Vogeley


Black Hole Spins of Radio Sources

Thursday, February 10, 2011 @ 3:30 PM
Disque Hall Room 919

Speaker: Dr. Ruth Daly, Penn State
 
Abstract: Powerful extended radio sources often result when supermassive black holes produce jets over prolonged periods of time.  Studies of extended radio emitting regions allow estimates of the beam power of the outflow. The beam power can be combined with the black hole mass to estimate the spin of the supermassive black hole.  Empirically determined properties such as the beam power, spin, and spin evolution of powerful radio sources will be discussed. The spin evolution obtained  is similar to that predicted by chaotic accretion models.
 
Host: Dr. Gordon Richards


Star Formation in Extreme Environments, Including Around the Milky Way's Supermassive Black Hole

Thursday, February 3, 2011 @ 3:30 PM
Disque Hall Room 919

Speaker: Dr. Jessica Lu, Caltech
 
Abstract: The center of the Milky Way galaxy harbors not only a supermassive black hole but also a cluster of young stars within the central parsec. The origin of the young stars is intriguing given that the extreme tidal forces near the black hole will shear apart typical molecular clouds before they can collapse to form stars. To understand how stars form in such extreme environments requires high resolution images at infrared wavelengths. I will present infrared observations from the Keck telescopes that utilize adaptive optics to correct the blurring effects of the atmosphere and provide very high resolution images. We use these observations, to study the center of our Galaxy and other sites of extreme star formation. These observations have yielded information both about the black hole and the nature of the star formation process in such extreme environments.
 
Host: Dr. Leonard Finegold


Quantum Control of Cold Atomic Systems Using Nonlinear Dynamics

Thursday, January 13, 2011 @ 3:30 PM
Disque Hall Room 919

Speaker: Dr. Linda Reichl, UT Austin
 
Abstract: Laser radiation, interacting with an ultra-cold boson system, can create chaos and nonlinear dynamical structures in the underlying classical phase space of the system. These light induced classical dynamical structures determine the phase space structure of the Floquet eigenstates that govern the dynamics of the entangled quantum system. Transitions between these light-induced Floquet states can be controlled by applying carefully chosen radiation pulses using a STIRAP-like process. Floquet analysis allows one to transition through a sequence of light-induced avoided crossings to achieve maximum control of transitions in the boson system and can be used, for example, to achieve coherent acceleration of the boson system.
 
Host: Robert Gilmore


Taking Inventory of the Universe: The Mystery of Dark Matter

Thursday, December 2, 2010 @ 3:30 PM
Disque Hall Room 919

Speaker: Dr. Stanley Seibert, University of Pennsylvania
Abstract: Astronomical observations have produced a tremendous amount of evidence that the gravitational interactions we observe in the universe cannot be produced entirely by the particles in the Standard Model. The dark matter hypothesis can explain this mystery by postulating an additional source of mass that does not interact electromagnetically. But can we detect this new particle in the lab? I will review the current state of experimental results in the search for dark matter, and describe the DEAP/CLEAN family of detectors. Coming online in 2011, MiniCLEAN will use both liquid argon and neon targets to search for weakly interacting massive particles, a favored dark matter candidate. The technology is highly scalable, with a direct development path to 50 ton targets that can be used in both solar neutrino and dark matter studies.
 
Host: Dr. Jelena Maricic


“Putting Your Particle Physics to Work”: X-ray Imaging of the Breast

Thursday, November 18, 2010 @ 3:30 PM
Disque Hall Room 919

Speaker: Predrag Bakic, University of Pennsylvania
Abstract: Breast cancer is the leading cause of non-preventable cancer deaths among US women. Although one in eight women will be diagnosed in her lifetime, early cancer detection offers good chances for long term survival. X-ray mammography is the standard imaging modality for screening asymptomatic women to detect breast cancer as early as possible. In the US, every woman above 40 is recommended to get a yearly mammogram.
X-ray mammography uses the photoelectric effect to produces relative contrast between projections of different tissue structures. Visibility of tumor is affected by the amount of radiation, Compton scatter, and various noise sources, including overlapped projections of normal tissue (called anatomical noise). While the radiation dose is kept low for safety and the introduction of digital detectors has improved the dose efficiency, the projection mammography is still limited by the anatomic noise due to its 2D nature. Approaches to reduce the anatomical noise include 3D imaging and dynamic contrast enhanced imaging. Among alternative modalities, the most likely candidate to replace mammography in breast cancer screening is 3D digital breast tomosynthesis (DBT). Our Radiation Physics Lab at the University of Pennsylvania has been at the forefront of the DBT research; we acquired the first clinical contrast-enhanced DBT images in 2005. In addition, our validation approach based upon the anthropomorphic software breast model has allowed for virtual clinical trials.
The talk will review physical principles of x-ray imaging and illustrate currently available systems for digital mammography and DBT. We will also discuss selection of age to begin mammographic screening, in light of recent controversial recommendations from the US Preventive Services Task Force.
For reference, see:
 
Host: Jelena Maricic


Physical Factors Influencing Protein Conformation and Reactivity within Cellular Microenvironments

Thursday, November 11, 2010 @ 3:30 PM
Disque Hall Room 919

Speaker: Dr. Allen Milton, NIH
Abstract: Nonspecific interactions between a particular macromolecular species and constituents of its immediate surroundings within a particular cellular microenvironment (termed “background interactions”) result in significant size- and shape-dependent effects upon the chemical potential of that species and hence upon its conformation and reactivity. We explore the effects of three types of background interaction: (1) Macromolecular crowding : predominantly repulsive interactions between a macromolecule and surrounding mobile macromolecules; (2) Macromolecular confinement: predominantly repulsive interactions between a macromolecule and large immobile structures, such as membranes and fibers; and (3) Macromolecular adsorption: non-site specific attractive interaction between a macromolecule and large immobile structures. Predictions of observable effects based upon simplified statistical-thermodynamic models for each class of background interaction are followed by presentation of results of experiments testing each prediction.
 
Host: Dr. Frank Ferrone


Merging Black Holes

Thursday, October 28, 2010 @ 3:30 PM
Disque Hall Room 919

Speaker: Dr. Joan Centrella, NASA's Goddard Space Flight Center
Abstract: The final merger of two black holes is expected to be the strongest source of gravitational waves for both ground-based detectors such as LIGO and VIRGO, as well as the space-based LISA. Since the merger takes place in the regime of strong dynamical gravity, computing the resulting gravitational waveforms requires solving the full Einstein equations of general relativity on a computer. For many years, numerical codes designed to simulate black hole mergers were plagued by a host of instabilities. However, recent breakthroughs have conquered these instabilities and opened up this field dramatically. This talk will focus on the resulting gold rush of new results that is revealing the dynamics and waveforms of binary black hole mergers, and their applications in gravitational wave detection, testing general relativity, and astrophysics.
 
Host: Dr. Michel Vallieres


The Age of Entanglement

Thursday, October 21, 2010 @ 3:30 PM
Disque Hall Room 919

Speaker: Louisa Gilder, Science Writer
Abstract: The history of quantum-mechanical entanglement over the last century is a fascinating example of how scientific knowledge actually proceeds. Personalities and personal passions (scientific and otherwise) sometimes hinder and sometimes even help the progress of human knowledge.
Louisa Gilder is the author of The Age of Entanglement, which was named one of only five science books on the New York Times 100 Notable Books of 2009, as well as receiving enthusiastic reviews in Science, Nature, American Journal of Physics, and American Scientist.
 
Host: Dr. Robert Gilmore
 


Effects of Osmotic Stress on DNA Packing and Capsid Stability in Simple Viruses

Thursday, September 23, 2010 @ 3:30 PM
Disque Hall Room 919

Speaker: Rudi Podgornik, University of Ljubljana
Abstract: The ordering and packing of DNA inside the capsids of simple viruses such as bacteriophages is very similar to ordering of a liquid crystal confined to a small sphere. Inside a capsid (a protein "box" filled with virus genetic material) DNA wraps in the form of a coiled elastic spring and is subject to a very high (osmotic) pressure, about ten times bigger that the pressure inside a champagne bottle. By changing the osmotic pressure of the external bathing solution, counteracting the osmotic pressure of the coiled DNA, one can reversibly change its amount inside the capsid. Large osmotic pressure keeps the DNA inside the capsid, and small lets it out. It seems like an osmotic tug-of-war that is particularly important when a bacteriophage is trying to infect a bacterial cell. Using a proper amount of osmotic pressure can keep the DNA inside a virus, completely disabling the infection process. However, if too much external osmotic pressure is used in order to keep DNA inside the capsid, the capsid itself can rupture and the whole bacteriophage collapses just like an aluminum soda can. Even a few years ago it was almost unimaginable that so much simple physics is involved in the life of viruses.

Host: Dr. Brigita Urbanc