Physical Sciences and Mathematics Commons^™

A Comparative Analysis Of Numerical Approaches To The Mechanics Of Elastic Sheets, Michael Taylor, Benny Davidovitch, Zhanlong Qiu, Katia Bertoldi

Benny Davidovitch

No abstract provided.

A Sheet On Deformable Sphere: "Wrinklogami" Patterns Suppress Curvature-Induced Delamination, Evan Hohlfeld, Benny Davidovitch

Benny Davidovitch

No abstract provided.

Chemical Potential In The First Law For Holographic Entanglement Entropy, David Kastor, Sourya Ray, Jennie Traschen

David Kastor

Entanglement entropy in conformal field theories is known to satisfy a first law. For spherical entangling surfaces, this has been shown to follow via the AdS/CFT correspondence and the holographic prescription for entanglement entropy from the bulk first law for Killing horizons. The bulk first law can be extended to include variations in the cosmological constant Λ, which we established in earlier work. Here we show that this implies an extension of the boundary first law to include varying the number of degrees of freedom of the boundary CFT. The thermodynamic potential conjugate to Λ in the bulk is called …

Innovative Representations Of Light, Behaving As Both Particles And Waves, Among The Paintings Of Monet And Renoir, Charles Smith

Charles Kay Smith

Monet and Renoir, friends collaborating in open air about 1865, discovered that sunlight filtering through a canopy of tree leaves does not produce the splotches and dapples that studio artists conventionally represented at the time but circles of light. Sometimes the circles of light punctuating the shade are clear, separate and crisp, as though light is being propagated as particles, but if the pin-hole gaps between leaves are very close together, they will project compound or superimposed circles that look like the waves that Thomas Young saw in his double slit experiment in 1803-4. Newton’s Opticks published in 1704 had …

Non-Vacuum Ads Cosmologies And The Approach To Equilibrium Of Entanglement Entropy, Sebastian Fischetti, David Kastor, Jennie Traschen

David Kastor

We extend standard results for vacuum asymptotically locally AdS (AlAdS) spacetimes, showing that such spacetimes can be constructed as foliations where the induced metric on each hypersurface satisfies Einstein's equation with stress-energy. By an appropriate choice of stress-energy on the hypersurfaces, the resulting AlAdS spacetime satisfies Einstein's equation with a negative cosmological constant and physical stress tensor. We use this construction to obtain AlAdS solutions whose boundaries are FRW cosmologies sourced by a massless scalar field or by a perfect fluid obeying the strong energy condition. We focus on FRW universes that approach Minkowski spacetime at late times, yielding AlAdS …

Single Molecule Studies Of A Short Rna, Peker Milas

Doctoral Dissertations

The material related with orientation of Cyanine dyes and their behavior at the ends of duplex RNA is also documented in [110]. Cyanine dyes are widely used to study the folding and structural transformations of nucleic acids using fluorescence resonance energy transfer (FRET). The extent to which FRET can be used to extract inter- and intra-molecular distances has been the subject of considerable debate in the literature; the contribution of dye and linker dynamics to the observed FRET signal is particularly troublesome. We used molecular dynamics (MD) simulations to study the dynamics of the indocarbocyanine dyes Cy3 and Cy5 attached …

Introducing The Newton-Poisson-Brillouin Model In The Quest For Plasmons In Metallic Carbon Nanotubes, Richard P. Zannoni

Doctoral Dissertations

A new method is presented to model carbon nanotubes (CNT) of micron length. The Newton-Poisson-Brillouin (NPB) model uses Newtonian physics to model the interaction of a population of thermally excited quasi-particles. The NPB model is self-consistent with Poisson’s equation, and the quasi-particles are confined to the CNT’s band structure. In this work, we explore the parameter space of the model.

Measurement Of The Parity Violating Asymmetry In Elastic Electron Scattering Off 208pb, Jonathan W. Wexler

Doctoral Dissertations

The Lead Radius Experiment (PREX) was carried out in order to provide a model independent measurement of the RMS radius √ < r² >of the neutron distribution in the ²⁰⁸Pb nucleus. The parity-violating scattering asymmetry for longitudinally polarized 1.06 GeV electrons from an unpolarized ²⁰⁸Pb target was measured at Q² = 0.00880 GeV². This measurement was performed by the PREX collaboration in Hall A at Jefferson Laboratory in Newport News, VA, between March and June, 2010. The electron detectors used in this measurement were designed and fabricated by University of Massachusetts-Amherst and Smith College. The resulting …

Studies On The Wrinkling Of Thin Polymer Films Floating On Liquid, Kamil B. Toga

Doctoral Dissertations

This dissertation aims to broaden our understanding on wrinkling instabilities occurring on floating polymeric sheets, and tries to establish innovative methods that exploit these patterns in studies on material behavior and interfacial phenomena. We will address three major topics in this thesis including, i) characterization of the conditions required to buckle an annular disc, ii) characterization of wrinkles occurring around a droplet/bubble placed on a membrane that is kept taut at the liquid-air interface, and iii) using wrinkling patterns as a probe to understand the interfacial behavior and dynamics of ultrathin films. The first project in this thesis is about …

The Impact Of Membrane Tension On Phase Separation And Solid Domain Properties In Model Multicomponent Vesicles, Dong Chen

Doctoral Dissertations

Multicomponent phospholipid membranes provide an ideal model to study the complex phase behavior of biological membranes. Giant unilamellar vesicles (GUV) formed by mixtures of two or more phospholipids have particular merit as model membranes because of their simplicity, operability, and ease of viewing phase separation and testing membrane mechanics. Until the research in this thesis, biochemistry and biophysical studies of phase separation in phospholipid membranes primarily addressed the influence of membrane composition on the transition temperatures and domain shapes. This thesis focuses on a commonly neglected variable - membrane tension, analogous to pressure in bulk materials, as an important parameter …

On The Crumpling Of Thin Sheets, Anne Dominique Cambou

Doctoral Dissertations

The inner walls of mitochondria, cabbage leaves, and even the Himalayas are all examples of thin sheets: objects with a thickness much smaller than their length and width. Despite their differences in size and in material composition, similar patterns emerge when sheets are crumpled or forced into a small three-dimensional space. As the compaction progresses, the deformations focus into increasingly sharper features that look like the network of peaks and creases found on the surface of a balled up piece of paper. In this regime, external forces are straining the membrane, causing the elastic energy to localize while leaving most …

Dissipative Superfluid Mass Flux Through Solid 4he, Ye. Vekhov, Robert Hallock

Robert Hallock

The thermomechanical effect in superfluid helium is used to create an initial chemical potential difference ∆u_0 across a solid 4_He sample. This ∆u_0 causes a flow of helium atoms from one reservoir filled with superfluid helium, through a sample cell filled with solid helium, to another superfluid-filled reservoir until potential equilibrium between the reservoirs is restored. The solid helium sample is separated from each of the reservoirs by Vycor rods that allow only the superfluid component to flow. With an improved technique, measurements of the flow F at several fixed solid helium temperatures T have been made as a function …

Mechanics Of Large Folds In Thin Interfacial Films, Vincent Demery, Benny Davidovitch, Christian D. Santangelo

Benny Davidovitch

A thin film at a liquid interface responds to uniaxial confinement by wrinkling and then by folding; its shape and energy have been computed exactly before self contact. Here, we address the mechanics of large folds, i.e. folds that absorb a length much larger than the wrinkle wavelength. With scaling arguments and numerical simulations, we show that the antisymmetric fold is energetically favorable and can absorb any excess length at zero pressure. Then, motivated by puzzles arising in the comparison of this simple model to experiments on lipid monolayers and capillary rafts, we discuss how to incorporate film weight, selfadhesion …

Direct Measurement Of The Pp Solar Neutrino Interaction Rate In Borexino, Keith Otis

Doctoral Dissertations

This dissertation presents the first direct detection of pp solar neutrinos within Borexino, the underground liquid-scintilator detector located at the Gran Sasso National Labratory(LNGS) in Italy, designed to measure the interaction of neutrinos through neutrino-electron elastic scattering. The rate of scattering in Borexino from the pp solar neutrino spectrum is measured to be 155 +/- 16(stat) +/- 13(sys) counts per day per 100 tonnes. With this measurement we are able to rule out the no oscillation hypothesis at the 2-sigma C.L. and the results agree with Standard Solar Model predictions within 1.1-sigma. These neutrinos are from the keystone proton-proton fusion …

Morphology Characterization Of Low Band Gap Polymer-Based Organic Photovoltaics, Feng Liu

Doctoral Dissertations

In bulk heterojunction (BHJ) thin film organic photovoltaics (OPV), morphology control is critical to obtain good device efficiency. Nanoscale phase separation that creates bicontinuous interpenetrating structure on a size scale commensurate with exciton diffusion length (~10 nm) is thought to be the ideal morphology. Results obtained from this work indicate that morphology can be affected by chemical structure of the polymer, processing conditions, blending ratio and post treatments. Physical properties of the material, such as crystallinity, crystal orientation, material interactions and miscibility, surface energy and particle aggregations are critical for determining the morphology and thus the device performance. Previous investigations …

Creasing Instability Of Hydrogels And Elastomers, Dayong Chen

Doctoral Dissertations

CREASING INSTABILITY OF HYDROGELS AND ELASTOMERS MAY 2014 DAYONG CHEN, B.S., TIANJIN UNIVERISTY M.S., TIANJIN UNIVERSITY M.S., UNIVERSITY OF MASSACHUSETTS AMHERST Ph.D., UNIVERSITY OF MASSACHUSETTS AMHERST Directed by: Professor Ryan C. Hayward Soft polymers placed under compressive stress can undergo an elastic creasing instability in which sharp folds spontaneously form on the free surfaces. This process may play an important role in contexts as diverse as brain morphogenesis, failure of tires, and electrical breakdown of soft polymer actuators. While the creasing instability has been used for collotype printing since as early as the 1850s, the scientific appreciation of this instability …

Optical And Scanning Probe Studies Of Isolated Poly (3-Hexylthiophene) Nanofibers, Mina Baghgarbostanabad

Doctoral Dissertations

Plastic electronics have an essential role in the future technologies owing to their compelling characteristics such as light weight, biocompatibity, low cost fabrication, and tunable optoelectronic properties. However, the performance of polymer-based devices strongly depends on the efficiency of exciton formation and dynamics that are themselves strongly sensitive to polymer molecular packing and structural order. Therefore, the current challenge in achieving high efficiency is establishing a correlation between molecular packing and exciton coupling. P3HT nanofibers represent an attractive platform for studying optical and electronic properties of exciton coupling because their nominal (highly crystalline) internal chain packing structure is known. A …

Roadmap To The Morphological Instabilities Of A Stretched Twisted Ribbon, Julien Chopin, Vincent Demery, Benny Davidovitch

Benny Davidovitch

We address the mechanics of an elastic ribbon subjected to twist and tensile load. Motivated by the classical work of green and a recent experiment that discovered a plethora of morphological instabilities, we introduce a comprehensive theoretical framework through which we construct a 4D phase diagram of this basic system, spanned by the exerted twist and tension as well as the thickness and length of the ribbon. Different types of instabilities appear in various "corners" of this 4D parameter space, and are addressed through distinct types of asymptotic methods. Our theory employs three instruments, whose concerted implementation is necessary to …

Entropy- And Flow- Induced Superfluid States, Johan Carlström, Egor Babaev

Egor Babaev

No abstract provided.

Universal Temperature Dependence, Flux Extinction And The Role Of 3he Impurities In Superfluid Mass Transport Through Solid 4he, Ye. Vekhov, W. J. Mullin, Robert B. Hallock

Robert Hallock

The mass flux, F, carried by as-grown solid 4_He in the range 25.6-26.3 bar rises with falling temperature, and at a concentration-dependent temperature, T_d, the flux decreases sharply within a few mK. We study F as a function of 3_He impurity concentration, χ. We find that T_(d )is an increasing function of increasing χ. At temperatures above T_d the flux has a universal temperature dependence and the flux terminates in a narrow window near a characteristic temperature T_h ≈ 625 mK, which is independent of χ.

Biophysical Studies Of Axonal Transport, Leslie Cyle Conway

Doctoral Dissertations

Intracellular transport provides a mechanism by which cellular material, such as organelles, vesicles, and protein, can be actively transported throughout the cell. This process relies on the activity of the cytoskeletal filament, microtubules, and their associated motor proteins. These motors are able to walk along microtubule tracks while carrying cellular cargos to enable the fast, regulated transport of these cargos. In cells, these microtubule filaments act as a binding platform for numerous different motor species as well as microtubule-associated proteins (MAPs). In addition, these filaments often form higher order structures, such as microtubule bundles. How motors navigate such complex, crowded …

Magnetic Fields In An Expanding Universe, David Kastor, Jennie Traschen

David Kastor

We find a solution to 4D Einstein-Maxwell theory coupled to a massless dilaton field describing a Melvin magnetic field in an expanding universe with 'stiff matter' equation of state parameter w=+1. As the universe expands, magnetic flux becomes more concentrated around the symmetry axis for dilaton coupling a<1/3√ and more dispersed for a>1/3√. An electric field circulates around the symmetry axis in the direction determined by Lenz's law. For a=0 the magnetic flux through a disk of fixed comoving radius is proportional to the proper area of the disk. This result disagrees with the usual expectation based on a test magnetic field that this …

Domain Walls And Their Experimental Signatures In S + Is Superconductors, Julien Garaud, Egor Babaev

Egor Babaev

No abstract provided.

Wrinkling In Buckling And A Thin Sheet, Narayanan Menon

Patterns Around Us

Module 1: Euler Buckling

Learning Objectives:

• What is an instability? A sudden change in behaviour in response to a small change in conditions.

• Instabilities usually involve a change in symmetry from a more symmetric situation to a less symmetric one

• The mechanism for an instability usually involves two competing forces (one force stabilizing the symmetric state, and the other one destabilizing it), with one suddenly winning the contest

• These competing forces in thin objects are often the forces of compression (destabilizing force - favors buckling or wrinkling) and of bending (stabilizing force).

Understanding by data collapse, the power of using …

Evaluation Report, Alan Peterfreund

STEM Digital

This evaluation report synthesizes the results of evaluation activities conducted by SageFox Consulting Group of the STEM DIGITAL project led by the UMass STEM Ed Institute for its no-cost extension year, covering the period September 2013 to August 2014. The goals of the program are to facilitate the participants’ abilities to stimulate student interest in STEM careers while engaging them in ways to think critically about their environment. Participating teachers incorporated digital cameras and Analyzing Digital Images (ADI) software into lab activities focusing on environmental science. STEM DIGITAL materials focused on three strands related to (1) ozone and air quality, …

2013-2014 Newsletter, Morton Sternheim

STEM Education Institute Newsletters

Patterns Workshop

iCons

New! MassBioEd Seminars

Arsenic: Citizen Science

STEM DIGITAL online

Nanotechnology

Honeycomb, Square, And Kagome Vortex Lattices In Superconducting Systems With Multi-Scale Inter-Vortex Interactions, Qingyou Meng, Christopher N. Varney, Hans Fangohr, Egor Babaev

Egor Babaev

The recent proposal of Romero-Isart et al. [1] to utilize the vortex lattice phases of superconducting materials to prepare a lattice for ultra-cold atoms-based quantum emulators, raises the need to create and control vortex lattices of different symmetries. Here we propose a mechanism by which honeycomb, hexagonal, square, and kagome vortex lattices could be created in superconducting systems with multi-scale inter-vortex interaction. Multiple scales of the inter-vortex interaction can be created and controlled in layered systems made of different superconducting material or with differing interlayer spacing.

Mechanics Of Large Folds In Thin Interfacial Films, Vincent Demery, Benny Davidovitch, Christian Santangelo

Christian Santangelo

A thin film confined to a liquid interface responds to uniaxial compression by wrinkling, and then by folding, that has been solved exactly before self-contact. Here, we address the mechanics of large folds, i.e., folds that absorb a length much larger than the wrinkle wavelength. With scaling arguments and numerical simulations, we show that the antisymmetric fold is energetically favorable and can absorb any excess length at zero pressure. Then, motivated by puzzles arising in the comparison of this simple model to experiments on lipid monolayers or capillary rafts, we discuss how to incorporate film weight, self-adhesion, or energy dissipation.

Nonuniform Growth And Topological Defects In The Shaping Of Elastic Sheets, Nakul Bende, Ryan C. Hayward, Christian Santangelo

Christian Santangelo

We demonstrate that shapes with zero Gaussian curvature, except at singularities, produced by the growth-induced buckling of a thin elastic sheet are the same as those produced by the Volterra construction of topological defects in which edges of an intrinsically flat surface are identified. With this connection, we study the problem of choosing an optimal pattern of growth for a prescribed developable surface, finding a fundamental trade-off between optimal design and the accuracy of the resulting shape which can be quantified by the length along which an edge should be identified.

Comparing Monte Carlo Methods For Finding Ground States Of Ising Spin Glasses: Population Annealing, Simulated Annealing And Parallel Tempering, Wenlong Wang, Jonathan Machta, Helmut G. Katzgraber

Jonathan Machta

Population annealing is a Monte Carlo algorithm that marries features from simulated annealing and parallel tempering Monte Carlo. As such, it is ideal to overcome large energy barriers in the free-energy landscape while minimizing a Hamiltonian. Thus, population annealing Monte Carlo can be used as a heuristic to solve combinatorial optimization problems. We illustrate the capabilities of population annealing Monte Carlo by computing ground states of the three-dimensional Ising spin glass with Gaussian disorder, whilst comparing to simulated annealing and parallel tempering Monte Carlo. Our results suggest that population annealing Monte Carlo is significantly more effiicient than simulated annealing but …