Physics Commons^™

A Liquid Xenon Ionization Chamber In An All-Fluoropolymer Vessel, F. Leport, Andrea Pocar, L. Bartoszek, R. Devoe, P. Fierlinger, B. Flatt, G. Gratta, M. Green, T. Koffas, M. Montero Diez, R. Neilson, K. O'Sullivan, S. Waldman, J. Wodin, D. Woisard, E. Baussan, M. Breidenbach, R. Conley, W. Fairbank Jr., J. Farine, C. Hall, K. Hall, D. Hallman, C. Hargrove, J. Hodgson, S. Jeng, D. S. Leonard, D. Mackay, Y. Martin, A. Odian, L. Ounalli, A. Piepke, C. Y. Prescott, P. C. Rowson, K. Skarpaas, D. Schenker, D. Sinclair, V. Stekhanov, V. Strickland, C. Virtue, J.-L. Vuilleumier, K. Wamba, P. Weber

Andrea Pocar

A novel technique has been developed to build vessels for liquid xenon ionization detectors entirely out of an ultra-clean fluoropolymer. One such detector was operated inside a welded, He leak tight, all-fluoropolymer chamber. The measured energy resolution for 570 keV gamma rays is σ/E=5.1% at a drift field of 1.5 kV/cm, in line with the best values obtained for ionization only detectors run in LXe using conventional, metal vessels.

A Role For Huntingtin In Dynein/Dynactin-Mediated Vesicle Trafficking, Jennifer Ross, Juliane P. Caviston, Sheila M. Antony, Mariko Tokito, Erika L.F Holzbaur

Jennifer Ross

Cytoplasmic dynein is a multisubunit microtubule motor complex that, together with its activator, dynactin, drives vesicular cargo toward the minus ends of microtubules. Huntingtin (Htt) is a vesicle-associated protein found in both neuronal and nonneuronal cells that is thought to be involved in vesicular transport. In this study, we demonstrate through yeast two-hybrid and affinity chromatography assays that Htt and dynein intermediate chain interact directly; endogenous Htt and dynein coimmunoprecipitate from mouse brain cytosol. Htt RNAi in HeLa cells results in Golgi disruption, similar to the effects of compromising dynein/dynactin function. In vitro studies reveal that Htt and dynein are …

On The Parameterization Dependence Of The Energy Momentum Tensor And The Metric, N. E. J. Bjerrum-Bohr, John Donoghue, Barry R. Holstein

John Donoghue

We use results by Kirilin to show that in general relativity the nonleading terms in the energy-momentum tensor of a particle depends on the parameterization of the gravitational field. While the classical metric that is calculated from this source, used to define the leading long-distance corrections to the metric, also has a parameteriztion dependence, it can be removed by a coordinate change. Thus the classical observables are parameterization independent. The quantum effects that emerge within the same calculation of the metric also depend on the parameterization and a full quantum calculation requires the inclusion of further diagrams. However, within a …

Soft Spheres Make More Mesophases, Mattew A. Glaser, Gregory M. Granson, Randall D. Kamien, A. Kosmrlj, Christian Santangelo, P. Ziherl

Christian Santangelo

We use both mean-field methods and numerical simulation to study the phase diagram of classical particles interacting with a hard core and repulsive, soft shoulder. Despite the purely repulsive and isotropic interaction, this system displays a remarkable array of aggregate phases arising from the competition between the hard-core and soft-shoulder length scales, including fluid and crystalline phases with micellar, lamellar, and inverse micellar morphology. In the limit of large shoulder width to core size, we argue that this phase diagram has a number of universal features, and classify the set of repulsive shoulders that lead to aggregation at high density. …

Dynamic Reorganization Of Eg5 In The Mammalian Spindle Throughout Mitosis Requires Dynein And Tpx2, Jennifer Ross, C. Fagerstrom, G. Yang, E. S. Collins, N. Ma, N. P. Ferenz, S. Balchand, P. Wadsworth, J. Titus, M. Qiu, A. Gabel

Jennifer Ross

Kinesin-5 is an essential mitotic motor. However, how its spatial-temporal distribution is regulated in mitosis remains poorly understood. We expressed localization and affinity purification-tagged Eg5 from a mouse bacterial artificial chromosome (this construct was called mEg5) and found its distribution to be tightly regulated throughout mitosis. Fluorescence recovery after photobleaching analysis showed rapid Eg5 turnover throughout mitosis, which cannot be accounted for by microtubule turnover. Total internal reflection fluorescence microscopy and high-resolution, single-particle tracking revealed that mEg5 punctae on both astral and midzone microtubules rapidly bind and unbind. mEg5 punctae on midzone microtubules moved transiently both toward and away from …

Triply-Periodic Smectic Liquid Crystals, Christian Santangelo, Randall D. Kamien

Christian Santangelo

Twist-grain-boundary phases in smectics are the geometrical analogs of the Abrikosov flux lattice in superconductors. At large twist angles, the nonlinear elasticity is important in evaluating their energetics. We analytically construct the height function of a π∕2 twist-grain-boundary phase in smectic-A liquid crystals, known as Schnerk’s first surface. This construction, utilizing elliptic functions, allows us to compute the energy of the structure analytically. By identifying a set of heretofore unknown defects along the pitch axis of the structure, we study the necessary topological structure of grain boundaries at other angles, concluding that there exist a set of privileged angles and …

2007 Newsletter, Morton Sternheim

STEM Education Institute Newsletters

NANOTECHNOLOGY Summer 2007 Institute p. 3

EARTH CENTRAL 2007 Ending on a High Note p. 5

PV STEMNET Has a Very Productive Year p. 4

CONFERENCE ON ALTERNATIVE CERTIFICATION FOR SCIENCE TEACHERS: Lessons Learned p. 7

NOYCE SCHOLAR travels to Washington D.C. p. 6

NOYCE SCHOLARS p. 6

STEM RAYS Completes Pilot Phase, Goes Into Full Operation p. 2

IPY STEM Polar Connections p. 4

UMASS K12 ENDS DIALUP SERVICE p. 7

SMET OR STEM: WHAT’S IN A NAME? p. 7

Synthesize A Nanoscale Ferrofluid, Rob Snyder

Nanotechnology Teacher Summer Institutes

The chemical synthesis of a ferrofluid is a nanoscale science activity that originally appears in the Journal of Chemical Education. Access to the following website requires a subscription to the journal. J. Chem. Educ., 76, 943-948 (1999). The article was authored by Jonathan Breitzer and George Lisensky.

Department Of Physics Newsletter: Spring 2007, Calla Cofield, Bob Krotkov, Ken Langley, Gerry Peterson, Monroe Rabin, Hajime Sakai

Physics Newsletters

No abstract provided.

Bold Diagrammatic Monte Carlo Technique: When The Sign Problem Is Welcome, N Prokof'ev, B Svistunov

Physics Department Faculty Publication Series

We introduce a Monte Carlo scheme for sampling a bold-line diagrammatic series specifying an unknown function in terms of itself. The range of convergence of this bold(-line) diagrammatic Monte Carlo (BMC) technique is significantly broader than that of a simple iterative scheme for solving integral equations. With the BMC technique, a moderate “sign problem” turns out to be an advantage in terms of the convergence of the process. For an illustrative purpose, we solve the one-particle s-scattering problem. As an important application, we obtain the T matrix for a Fermi polaron (one spin-down particle interacting with the spin-up fermionic sea).

Superfluidity Of Grain Boundaries In Solid 4he, L Pollet, M Boninsegni, A Kuklov, Nikolai Prokof'ev, Boris Svistunov, M Troyer

Physics Department Faculty Publication Series

By large-scale quantum Monte Carlo simulations we show that grain boundaries in 4He crystals are generically superfluid at low temperature, with a transition temperature of the order of ∼0.5  K at the melting pressure; nonsuperfluid grain boundaries are found only for special orientations of the grains. We also find that close vicinity to the melting line is not a necessary condition for superfluid grain boundaries, and a grain boundary in direct contact with the superfluid liquid at the melting curve is found to be mechanically stable and the grain-boundary superfluidity observed by Sasaki et al. [Science 313, 1098 (2006)] is …

The First Law For Boosted Kaluza-Klein Black Holes, David Kastor, Sourya Ray, Jennie Traschen

Physics Department Faculty Publication Series

We study the thermodynamics of Kaluza-Klein black holes with momentum along the compact dimension, but vanishing angular momentum. These black holes are stationary, but non-rotating. We derive the first law for these spacetimes and find that the parameter conjugate to variations in the length of the compact direction is an effective tension, which generally differs from the ADM tension. For the boosted black string, this effective tension is always positive, while the ADM tension is negative for large boost parameter. We also derive two Smarr formulas, one that follows from time translation invariance, and a second one that holds only …

The Attractor Mechanism In Gauss-Bonnet Gravity, Mohamed Anber, David Kastor

Physics Department Faculty Publication Series

We study extremal black hole solutions of D = 5 Gauss-Bonnet gravity coupled to a system of gauge and scalar fields. As in Einstein gravity, we find that the values of the scalar fields on the horizon must extremize a certain effective potential that depends on the black hole charges. If the matrix of second derivatives of the effective potential at this extremum has positive eigenvalues, we give evidence, based on a near horizon perturbative expansion, that the attractor mechanism continues to hold in this general class of theories. We numerically construct solutions to a particular simple single scalar field …

Dynamic Critical Behavior Of The Chayes-Machta-Swendsen-Wang Algorithm, Youjin Deng, Timothy M. Garoni, Jonathan Machta, Giovanni Ossola, Marco Polin, Alan D. Sokal

Jonathan Machta

We study the dynamic critical behavior of the Chayes-Machta dynamics for the Fortuin-Kasteleyn random-cluster model, which generalizes the Swendsen-Wang dynamics for the q-state Potts model to noninteger q, in two and three spatial dimensions, by Monte Carlo simulation. We show that the Li-Sokal bound z≥α/ν is close to but probably not sharp in d=2 and is far from sharp in d=3, for all q. The conjecture z≥β/ν is false (for some values of q) in both d=2 and d=3.

Membrane Fluctuations Around Inclusions, Christian Santangelo, Oded Farago

Christian Santangelo

The free energy of inserting a protein into a membrane is determined by considering the variation in the spectrum of thermal fluctuations in response to the presence of a rigid inclusion. Both numerically and through a simple analytical approximation, we find that the primary effect of fluctuations is to reduce the effective surface tension, hampering the insertion at low surface tension. Our results, which should also be relevant for membrane pores, suggest (in contrast to classical nucleation theory) that a finite surface tension is necessary to facilitate the opening of a pore.

Do Killing-Yano Tensors Form A Lie Algebra?, David Kastor, Sourya Ray, Jenny Traschen

David Kastor

Killing-Yano tensors are natural generalizations of Killing vectors. We investigate whether Killing-Yano tensors form a graded Lie algebra with respect to the Schouten-Nijenhuis bracket. We find that this proposition does not hold in general, but that it does hold for constant curvature spacetimes. We also show that Minkowski and (anti)-deSitter spacetimes have the maximal number of Killing-Yano tensors of each rank and that the algebras of these tensors under the SN bracket are relatively simple extensions of the Poincare and (A)dS symmetry algebras.

Geometric Theory Of Columnar Phases On Curved Substrates, Christian Santangelo, Vincenzo Vitelli, Randall D. Kamien, David R. Nelson

Christian Santangelo

We study thin self-assembled columns constrained to lie on a curved, rigid substrate. The curvature presents no local obstruction to equally spaced columns in contrast with curved crystals for which the crystalline bonds are frustrated. Instead, the vanishing compressional strain of the columns implies that their normals lie on geodesics which converge (diverge) in regions of positive (negative) Gaussian curvature, in analogy to the focusing of light rays by a lens. We show that the out of plane bending of the cylinders acts as an effective ordering field.

Reaction- Limited Sintering In Nearly Saturated Environments, Benny Davidovitch, Deniz Ertas, Thomas C. Halsey

Benny Davidovitch

We study the shape and growth rate of necks between sintered spheres with dissolutionprecipitation dynamics in the reaction-limited regime. We determine the critical shape that separates those initial neck shapes that can sinter from those that necessarily dissolve, as well as the asymptotic evolving shape of sinters far from the critical shape. We compare our results with past results for the asymptotic neck shape in closely related but more complicated models of surface dynamics; in particular we confirm a scaling conjecture, originally due to Kuczinsky. Finally, we consider the relevance of this problem to the diagenesis of sedimentary rocks and …

Precision Measurements Of The Nucleon Strange Form Factors At Q2∼0.1  Gev^2, A. Acha, K. A. Aniol, D. S. Armstrong, J. Arrington, T. Averett, S. L. Bailey, J. Barber, A. Beck, H. Benaoum, J. Benesch, P. Y. Bertin, P. Bosted, F. Butaru, E. Burtin, G. D. Cates, Y. C. Chao, J. P. Chen, E. Chudakov, E. Cisbani, B. Craver, F. Cusanno, R. De Leo, P. Decowski, A. Deur, R. J. Feuerbach, J. M. Finn, S. Frullani, S. A. Fuchs, K. Fuoti, R. Gilman, L. E. Glesener, K. Grimm, J. M. Grames, J. O. Hansen, J. Hansknecht, D. W. Higinbotham, R. Holmes, T. Holmstrom, H. Ibrahim, C. W. De Jager, X. Jiang, J. Katich, L. J. Kaufman, A. Kelleher, P. M. King, A. Kolarkar, S. Kowalksi, E. Kuchina, Krishna Kumar, L. Lagamba, P. Laviolette, J. Lerose, R. A. Lindgren, D. Lhuillier, N. Liyanage, D. J. Margaziotis, P. Markowitz, D. G. Meekins, Z. E. Meziani, R. Michaels, B. Mofit, S. Nanda, V. Nelyubin, K. Otis, K. D. Paschke, S. K. Phillips, M. Poelker, R. Pomatsalyuk, M. Potokar, Y. Prok, A. Puckett, X. Qian, Y. Qiang, B. Reitz, J. Roche, A. Saha, B. Sawatzky, J. Singh, K. Slifer, S. Sirca, R. Snyder, P. Solvingnon, P. A. Souder, M. L. Stutzman, R. Subedi, R. Suleiman, V. Sulkosky, W. A. Tobias, P. E. Ulmer, G. M. Urciuoli, K. Wang, A. Whitbeck, R. Wilson, B. Wojsekhowsi, H. Yao, Y. Ye, X. Zhan, X. Zheng, S. Zhou, V. Ziskin

Krishna Kumar

We report new measurements of the parity-violating asymmetry APV in elastic scattering of 3 GeV electrons off hydrogen and He4 targets with ⟨θlab⟩≈6.0°. The He4 result is APV=(+6.40±0.23(stat)±0.12(syst))×10−6. The hydrogen result is APV=(−1.58±0.12(stat)±0.04(syst))×10−6. These results significantly improve constraints on the electric and magnetic strange form factors GsE and GsM. We extract GsE=0.002±0.014±0.007 at ⟨Q2⟩=0.077  GeV2, and GsE+0.09GsM=0.007±0.011±0.006 at ⟨Q2⟩=0.109  GeV2, providing new limits on the role of strange quarks in the nucleon charge and magnetization distributions.

Giant Viscosity Enhancement In A Spin-Polarized Fermi Liquid, H Akimoto, Js Xia, D Candela, Wj Mullin, Ed Adams, Ns Sullivan

Physics Department Faculty Publication Series

The viscosity is measured for a Fermi liquid, a dilute 3He-4He mixture, under extremely high magnetic field/temperature conditions (B≤14.8  T, T≥1.5  mK). The spin-splitting energy μB is substantially greater than the Fermi energy kBTF; as a consequence the polarization tends to unity and s-wave quasiparticle scattering is suppressed for T≪TF. Using a novel composite vibrating-wire viscometer an enhancement of the viscosity is observed by a factor of more than 500 over its low-field value. Good agreement is found between the measured viscosity and theoretical predictions based upon a t-matrix formalism.

On-Site Number Statistics Of Ultracold Lattice Bosons, B Capogrosso-Sansone, E Kozik, Nikolai Prokof'ev, Boris Svistunov

Physics Department Faculty Publication Series

We study on-site occupation number fluctuations in a system of interacting bosons in an optical lattice. The ground-state distribution is obtained analytically in the limiting cases of strong and weak interaction, and by means of exact Monte Carlo simulations in the strongly correlated regime. As the interaction is increased, the distribution evolves from Poissonian in the noninteracting gas to a sharply peaked distribution in the Mott-insulator (MI) regime. In the special case of large occupation numbers, we demonstrate analytically and check numerically that there exists a wide interval of interaction strength, in which the on-site number fluctuations remain Gaussian and …

Nonlocal Quantum Effects With Bose-Einstein Condensates, F Laloe, Wj Mullin

Physics Department Faculty Publication Series

Quantum systems in Fock states do not have a phase. When two or more Bose-Einstein condensates are sent into interferometers, they nevertheless acquire a relative phase under the effect of quantum measurements. The usual explanation relies on spontaneous symmetry breaking, where phases are ascribed to all condensates and treated as unknown classical quantities. However, this image is not always sufficient: when all particles are measured, quantum mechanics predicts probabilities that are sometimes in contradiction with it, as illustrated by quantum violations of local realism. In this Rapid communication, we show that interferometers can be used to demonstrate a large variety …

On The Stabilization Of Ion Sputtered Surfaces, B Davidovitch

Physics Department Faculty Publication Series

The classical theory of ion beam sputtering predicts the instability of a flat surface to uniform ion irradiation at any incidence angle. We relax the assumption of the classical theory that the average surface erosion rate is determined by a Gaussian response function representing the effect of the collision cascade, and consider the surface dynamics for other physically motivated response functions. We show that although instability of flat surfaces at any beam angle results from all Gaussian and a wide class of non-Gaussian erosive response functions, there exist classes of modifications to the response that can have a dramatic effect. …

Critical Behavior Of The Chayes–Machta–Swendsen–Wang Dynamics, Y Deng, T Garoni, J Machta, G Ossola, M Polin, A Sokal

Physics Department Faculty Publication Series

We study the dynamic critical behavior of the Chayes-Machta dynamics for the Fortuin-Kasteleyn random-cluster model, which generalizes the Swendsen-Wang dynamics for the q-state Potts model to noninteger q, in two and three spatial dimensions, by Monte Carlo simulation. We show that the Li-Sokal bound z≥α/ν is close to but probably not sharp in d=2 and is far from sharp in d=3, for all q. The conjecture z≥β/ν is false (for some values of q) in both d=2 and d=3.

What Makes A Crystal Supersolid?, Nikolai Prokof'ev

Physics Department Faculty Publication Series

For nearly half a century the supersolid phase of matter has remained mysterious, not only eluding experimental observation, but also generating a great deal of controversy among theorists. The recent discovery of what is interpreted as a non-classical moment of inertia at low temperature in solid 4He [E. Kim and M.H.W. Chan, Nature 427 225 (2004a); E. Kim and M.H.W. Chan, Science 305 1941 (2004b); E. Kim and M.H.W. Chan, Phys. Rev. Lett. 97 115302 (2006); A.C. Clark and M.H.W. Chan, J. Low Temp. Phys. 138 853 (2005)] has elicited much excitement as a possible first observation of a supersolid …

Superfluid-Insulator And Roughening Transitions In Domain Walls, S Söyler, Capogrosso-Sansone, Nikolai Prokof'ev, Boris Svistunov

Physics Department Faculty Publication Series

We have performed quantum Monte Carlo simulations to investigate the superfluid behavior of one- and two-dimensional interfaces separating checkerboard solid domains. The system is described by the hard-core Bose-Hubbard Hamiltonian with nearest-neighbor interaction. In accordance with Burovski et al. [Phys. Rev. Lett. 94, 165301 (2005)] we find that (i) the interface remains superfluid in a wide range of interaction strength before it undergoes a superfluid-insulator transition; (ii) in one dimension, the transition is of the Kosterlitz-Thouless type and is accompanied by the roughening transition, driven by proliferation of charge-1∕2 quasiparticles; (iii) in two dimensions, the transition belongs to the three-dimensional …

Phase Diagram And Thermodynamics Of The Three-Dimensional Bose-Hubbard Model, B Capogrosso-Sansone, Nikolai Prokof'ev, Boris Svistunov

Physics Department Faculty Publication Series

We report results of quantum Monte Carlo simulations of the Bose-Hubbard model in three dimensions. Critical parameters for the superfluid-to-Mott-insulator transition are determined with significantly higher accuracy than has been done in the past. In particular, the position of the critical point at filling factor n=1 is found to be at (U∕t)c=29.34(2), and the insulating gap Δ is measured with accuracy of a few percent of the hopping amplitude t. We obtain the effective mass of particle and hole excitations in the insulating state—with explicit demonstration of the emerging particle-hole symmetry and relativistic dispersion law at the transition tip—along with …

Do Killing–Yano Tensors Form A Lie Algebra?, David Kastor, Sourya Ray, Jennie Traschen

Physics Department Faculty Publication Series

Killing–Yano tensors are natural generalizations of Killing vectors. We investigate whether Killing–Yano tensors form a graded Lie algebra with respect to the Schouten–Nijenhuis bracket. We find that this proposition does not hold in general, but that it does hold for constant curvature spacetimes. We also show that Minkowski and (anti)-deSitter spacetimes have the maximal number of Killing–Yano tensors of each rank and that the algebras of these tensors under the SN bracket are relatively simple extensions of the Poincaré and (A)dS symmetry algebras.

The Fine-Tuning Problems Of Particle Physics And Anthropic Mechanisms, John Donoghue

Physics Department Faculty Publication Series

Many of the classic problems of particle physics appear in a very different light when viewed from the perspective of the multiverse. Most importantly the two great ``fine tuning'' problems that motivate the field are far less serious when one accounts for the required anthropic constraints which exist in a multiverse. However, the challenge then becomes to construct a realistic physical theory of the multiverse and test it. I describe some phenomenology of the quark and lepton masses that may provide a window to the theory that underlies the multiverse.