Abstract:

Atom interferometric sensors exploit the wave nature of matter to make highly accurate measurements of inertial forces.  Following major developments in the laser cooling of atoms and in atom interferometry, existing laboratory sensors compete with or surpass the accuracy of state of the art electro-mechanical and electro-optic inertial technology.  However, it is challenging for atom interferometers to operate robustly in dynamic environments (e.g., flight guidance), and their size, weight, and power are typically unsuitable for many applications.  Advances in mobile atom inertial sensing technology, including novel atom optics and compact vacuum cell design, could dramatically reduce the dependence of precision navigation systems on GPS, and enable precise pointing and gravity mapping systems.  This presentation provides an overview of inertial sensing with atom interferometry, discusses topics of current research such as large momentum transfer atom optics and ultracold atom interferometry.

Biography:
David Butts is a physicist in the Electro-Optics and Instruments group of the Guidance Hardware division at the Charles Stark Draper Laboratory.  He currently works on precise inertial sensing with atomic systems.  He received a B.A. in physics from Williams College, and an S.M. and Ph.D. in aeronautics and astronautics from MIT

 Debra R. Rolison

¹Surface Chemistry Branch, Code 6170, Naval Research Laboratory, Washington, DC 20375

Designing high-performance energy-storage devices that combine nanometric feature size with well-wired transport paths and that bridge to the macroscale requires an architectural perspective. We use aerogel-like carbon nanofoam papers as our architectural test-bed because they provide a low cost and scalable nanocomposite that offers an optimal balance of critical architectural features: (1) open, 3D interconnected macropores sized at 20-to-250 nm co-continuous with (2) ~20-nm pore walls of a size that reduces dead weight and volume yet retains mechanical strength and flexibility without compromising electronic conductivity. Charge-storage or catalytic functionality can then be imparted to internal carbon walls simply by transporting reactants within the 3D “plumbing” of the macroporous foam. Self-limiting modification strategies allow us to incorporate conformal, nanoscopic functional “paints” of metal(Mn, Ti, Ru, Fe)oxides or polymer (redox-active or electron insulating) or specifically adsorb metal nanoparticles (Pt, Au, Pd, Ag) throughout the macroscopic thickness (0.07 to 0.3 millimeter) of carbon nanofoam papers. For instance, painting the carbon walls with 10-nm MnOx increases the mass-, geometric-, and volume-normalized capacitance (2- to 10-fold) relative to the native carbon nanofoam without significantly altering its high-rate character. The oxide-modified paper is now a multifunctional electrode structure that can be used in an aqueous asymmetric electrochemical capacitor or as an air cathode in a Zn/air cell to electrocatalyze oxygen reduction and provide pulse power. Our redesign of electrode structures using modified carbon nanofoam papers has catalyzed breakthroughs in our work within a broad range of multifunctional energy storage and conversion, including asymmetric electrochemical capacitors, air cathodes for metal–air batteries, 3-D batteries, and semi-fuel cells.

]]> http://physics.williams.edu/articles/abstract-debra-rolison/feed/ 0 http://physics.williams.edu/articles/abstract-prof-anne-goodsell/ http://physics.williams.edu/articles/abstract-prof-anne-goodsell/#comments Fri, 10 Feb 2012 18:00:45 +0000 Michele Rech http://physics.williams.edu/?p=1513 more » ]]>           Exciting Physics with Excited Atoms

          Physics and Astronomy Combined Colloquium   Friday, April 13th, 2012                                          2:30 PM to 3:30 PM  Thompson Physical Lab 205

Atoms can be excited by light beams, when the energy of each photon matches the energy for a particular atomic transition.  The resonant interaction between light and individual atoms in a gas can make those atoms heat up, cool down, or come to a nearly-complete stop in midair.  With the technique of laster cooling, we can slow atoms from speeds of hundreds of meters per second to just a few centimeters per second.  We are studying how electric fields can steer, manipulate, or capture these slow, laser-cooled atoms.  I will describe the results of our experiments at Harvard in which we have captured and ionized individual atoms interacting with the electric field of a single charged nanotube.  Looking toward the future, I will outline our plan for experiments at Middlebury to re-excite slow atoms and magnify the influence of external electric fields.  Slow atoms in a highly-excited state can be tremendously sensitive probes to investigate the strength of electric fields near the surface of a material.  As atoms in free flight move near a surface, their flight paths will be deflected by the force due to van der Waals attraction or by controlled fields near charged objects.  While an atom in the ground state is fairly insensitive to these disturbances, an excited atom can be significantly influenced by these small fields.

                     Physics and Astronomy Colloquium  Friday, November 4, 2011                        2:30 pm Thompson Physical Laboratory 205

Electrostatic forces drive systems with free charges toward charge neutrality. However, entropy can drive persistent charge separation over nanometer and micrometer length scales.  This is typically manifested as charged molecules or interfaces dressed with a diffuse layer of counterions.  Such charge separation underlies the structure of polymers and proteins, the stability of suspensions and even our nervous system’s ability to process information.

We study electrostatic interactions over short length scales, deep inside the diffuse counterion  cloud.  Our model system consists of micron-sized plastic particles floating in oil.  The surfaces of  these particles spontaneously charge at room temperature under appropriate solvent conditions. We  exploit optical forces and thermal fluctuations to measure femtoNewton scale repulsive electrostatic  forces between the particles. Interestingly, the repulsion between any pair of particles can be  strongly reduced when other particles are nearby.   This many-body effect is not accounted for by the  usual suspects: nonlinearity in the Poisson-Boltzmann equation or counter-ion correlations.    Instead, we can quantitatively predict interparticle forces in a variety of geometries by  simply assuming that the surface charge densities adjust to keep the surface electrostatic potentials  at a fixed value.  Finally, I will describe the curious balance of electrostatic, chemical and entropic  forces that leads to constant surface potentials and discuss implications for the structure and stability of systems with large numbers of particles.

Prof. Peter Clote and Kourosh Zarringham  Physics & Astronomy Colloquium
2:30 p.m., December 2, 2011  Thompson Physical Laboratory 205

An RNA secondary structure is a type of planar graph, consisting of Watson-Crick
and wobble base pairs. From experimental data, it is known that the secondary structure forms quickly and acts as a scaffold for the formation of tertiary structure. While state-of-the-art protein secondary structure (alpha-helices, beta-sheets, etc.) is predicted by machine learning methods, RNA secondary structure can be predicted by dynamic programming using empirically determined free energies for stacked base pairs and various loops.

In this talk, we provide an overview of some thermodynamics-based algorithms developed by our lab. Topics will include how to compute the Boltzmann probability of all structural neighbors at a fixed base-pair distance from a target structure (conformational switches), the application of non-Boltzmannian sampling to approximate the partition function, analysis of kinetically trapped structures, and how to predict secondary structure by integrating chemical/enzymatic footprinting data.

Louisa Guilder
Physics & Astronomy Colloquium
2:30 p.m., October 14, 2011
Thompson Physical Laboratory 205

Heisenberg said that “science is rooted in conversations.” If the conversations aren’t clear, the science can suffer. This is what happened to the foundations of quantum mechanics in the early 1930s—mis-communication derailed progress. I will talk about two examples.

1) At Solvay in 1930, five years before the Einstein-Podolsky-Rosen paper and Bohr’s response to it, Einstein first presented to Bohr the EPR idea. Ehrenfest repeated it to Bohr again by letter in 1931. Bohr seems to have mis-heard both times.

2) In von Neumann’s 1932 Mathematische Grundlagen der Quantenmechanik (as an aside) he offered a proof that hidden variables cannot complete quantum mechanics. In early 1935, after long conversations with Heisenberg, mathematician Grete Hermann published a paper in which (also as an aside) she showed that von Neumann’s proof is based on a faulty assumption. But the proof remained unquestioned by most people until Bell’s final unmasking of it, over thirty years after it was first published.

Louisa Gilder is the author of The Age of Entanglement: When Quantum Physics Was Reborn, one of only five science books on the New York Times Book Review’s 100 Notable Books of 2009.