Physics Commons^™

Exotic Statistics For Strings In 4d Bf Theory, John C. Baez, Derek K. Wise, Alissa S. Crans

Alissa Crans

After a review of exotic statistics for point particles in 3d BF theory, and especially 3d quantum gravity, we show that string-like defects in 4d BF theory obey exotic statistics governed by the 'loop braid group'. This group has a set of generators that switch two strings just as one would normally switch point particles, but also a set of generators that switch two strings by passing one through the other. The first set generates a copy of the symmetric group, while the second generates a copy of the braid group. Thanks to recent work of Xiao-Song Lin, we can …

Toy Blocks And Rotational Physics, Gabriele U. Varieschi, Isabel R. Jully

Gabriele Varieschi

Have you ever observed a child playing with toy blocks? A favorite game is to build towers and then make them topple like falling trees. To the eye of a trained physicist this should immediately look like an example of the physics of “falling chimneys,” when tall structures bend and break in mid-air while falling to the ground. The game played with toy blocks can actually reproduce well what is usually seen in photographs of falling towers, such as the one that appeared on the cover of the September 1976 issue of The Physics Teacher.1 In this paper we describe …

Kerr Metric, Geodesic Motion, And Flyby Anomaly In Fourth-Order Conformal Gravity, Gabriele U. Varieschi

Gabriele Varieschi

In this paper we analyze the Kerr geometry in the context of Conformal Gravity, an alternative theory of gravitation, which is a direct extension of General Relativity (GR). Following previous studies in the literature, we introduce an explicit expression of the Kerr metric in Conformal Gravity, which naturally reduces to the standard GR Kerr geometry in the absence of Conformal Gravity effects. As in the standard case, we show that the Hamilton–Jacobi equation governing geodesic motion in a space-time based on this geometry is indeed separable and that a fourth constant of motion—similar to Carter’s constant—can also be introduced in …

Intonation And Compensation Of Fretted String Instruments, Gabriele U. Varieschi, Christina M. Gower

Gabriele Varieschi

We discuss theoretical and physical models that are useful for analyzing the intonation of musical instruments such as guitars and mandolins and can be used to improve the tuning on these instruments. The placement of frets on the fingerboard is designed according to mathematical rules and the assumption of an ideal string. The analysis becomes more complicated when we include the effects of deformation of the string and inharmonicity due to other string characteristics. As a consequence, perfect intonation of all the notes on the instrument cannot be achieved, but complex compensation procedures can be introduced to minimize the problem. …

Simulating A Guitar With A Conventional Sonometer, Zily Burstein, Christina M. Gower, Gabriele U. Varieschi

Gabriele Varieschi

In this paper we present a simple way to convert a conventional sonometer into a simulated fretted instrument, such as a guitar or similar, by adding a fingerboard to the sonometer. In particular, we use this modified apparatus in relation to the problem of the instrument intonation, i.e., how to obtain correctly tuned notes on these string instruments. The experimental procedures presented in this study can become a more structured laboratory activity to be used in general physics courses or acoustics classes.

Astrophysical Tests Of Kinematical Conformal Cosmology In Fourth-Order Conformal Weyl Gravity, Gabriele U. Varieschi

Gabriele Varieschi

In this work we analyze kinematical conformal cosmology (KCC), an alternative cosmological model based on conformal Weyl gravity (CG), and test it against current type Ia supernova (SNIa) luminosity data and other astrophysical observations. Expanding upon previous work on the subject, we revise the analysis of SNIa data, confirming that KCC can explain the evidence for an accelerating expansion of the Universe without using dark energy or other exotic components. We obtain an independent evaluation of the Hubble constant, H0 = 67:53 kms-1 Mpc-1, very close to the current best estimates. The main KCC and CG parameters are re-evaluated and …

Toy Models For The Falling Chimney, Gabriele U. Varieschi, Kaoru Kamiya

Gabriele Varieschi

In this paper we review the theory of the ‘‘falling chimney,’’ which deals with the breaking in mid-air of tall structures when they fall to the ground. We show that these ruptures can be caused by either shear forces typically developing near the base, or by the bending of the structure which is caused primarily by the internal bending moment. In the latter case the breaking is more likely to occur between one-third and one-half of the height of the chimney. Small scale toy models are used to reproduce the dynamics of the falling chimney. By examining photos taken during …

Wormhole Geometries In Fourth-Order Conformal Weyl Gravity, Gabriele U. Varieschi, Kellie L. Ault

Gabriele Varieschi

We present an analysis of the classic wormhole geometries based on conformal Weyl gravity, rather than standard general relativity. The main characteristics of the resulting traversable wormholes remain the same as in the seminal study by Morris and Thorne, namely, that effective super-luminal motion is a viable consequence of the metric. Improving on previous work on the subject, we show that for particular choices of the shape and redshift functions the wormhole metric in the context of conformal gravity does not violate the main energy conditions at or near the wormhole throat. Some exotic matter might still be needed at …

Conformal Gravity And The Alcubierre Warp Drive Metric, Gabriele U. Varieschi, Zily Burstein

Gabriele Varieschi

We present an analysis of the classic Alcubierre metric based on conformal gravity, rather than standard general relativity. The main characteristics of the resulting warp drive remain the same as in the original study by Alcubierre, that is, effective superluminal motion is a viable outcome of the metric. We show that for particular choices of the shaping function, the Alcubierre metric in the context of conformal gravity does not violate the weak energy condition, as was the case of the original solution. In particular, the resulting warp drive does not require the use of exotic matter. Therefore, if conformal gravity …

Foundations Of Wave Phenomena, Charles G. Torre

Charles G. Torre

This is an undergraduate text on the mathematical foundations of wave phenomena. Version 8.2.

Connecting Self-Efficacy And Views About Nature Of Science In Undergraduate Research Experiences, Gina M. Quan, Andrew Elby

Gina Quan

Fluctuations In A Cosmology With A Spacelike Singularity And Their Gauge Theory Dual Description, Robert H. Brandenberger, Elisa G.M. Ferreira, Ian A. Morrison, Yi-Fu Cai, Sumit R. Das, Yi Wang

Ian Morrison

We consider a time-dependent deformation of anti–de Sitter (AdS) space-time which contains a spacelike “singularity”—a spacelike region of high curvature. Making use of the AdS/CFT correspondence we can map the bulk dynamics onto the boundary. The boundary theory has a time dependent coupling constant which becomes small at times when the bulk space-time is highly curved. We investigate the propagation of small fluctuations of a test scalar field from early times before the bulk singularity to late times after the singularity. Under the assumption that the AdS/CFT correspondence extends to deformed AdS space-times, we can map the bulk evolution of …

Hybrid Spatiotemporal Coherent Pulse Addition Of A Picosecond Flashlamp-Pumped Ndyag Laser.Pdf, Ahmad Azim

Ahmad Azim

Femtosecond Pulse Trains Of Polychromatic Inverse Compton Γ-Rays From Designer Electron Beams Produced By Laser-Plasma Acceleration In Plasma Channels, Serge Y. Kalmykov, Isaac Ghebregziabher, X. Davoine, Remi Lehe, Agustin F. Lifschitz, Victor Malka, Bradley A. Shadwick

Serge Youri Kalmykov

Accordion Effect Revisited: Generation Of Comb-Like Electron Beams In Plasma Channels, Serge Y. Kalmykov, X. Davoine, Remi Lehe, Agustin F. Lifschitz, Bradley A. Shadwick

Serge Youri Kalmykov

Examination Of The Nonlinear Dynamics And Possible Chaos Encryption In A Zeroth-Order Acousto-Optic Bragg Modulator With Feedback, Fares S. Almehmadi, Monish Ranjan Chatterjee

Monish R. Chatterjee

Zeroth-order chaos modulation in a Bragg cell is examined such that tracking problems due to spatial deflections of the first-order AO beam at the receiver may be avoided by switching to the undeviated zeroth-order beam.

Anisoplanatic Electromagnetic Image Propagation Through Narrow Or Extended Phase Turbulence Using Altitude-Dependent Structure Parameter, Monish Ranjan Chatterjee, Ali Mohamed

Monish R. Chatterjee

The effects of turbulence on anisoplanatic imaging are often modeled through the use of a sequence of phase screens distributed along the optical path. We implement the split-step wave algorithm to examine turbulence-corrupted images.

Volume Component Analysis For Classification Of Lidar Data, Nina M. Varney, Vijayan K. Asari

Vijayan K. Asari

One of the most difficult challenges of working with LiDAR data is the large amount of data points that are produced. Analysing these large data sets is an extremely time consuming process. For this reason, automatic perception of LiDAR scenes is a growing area of research. Currently, most LiDAR feature extraction relies on geometrical features specific to the point cloud of interest. These geometrical features are scene-specific, and often rely on the scale and orientation of the object for classification. This paper proposes a robust method for reduced dimensionality feature extraction of 3D objects using a volume component analysis (VCA) …

Multiple Object Detection In Hyperspectral Imagery Using Spectral Fringe-Adjusted Joint Transform Correlator, Paheding Sidike, Vijayan K. Asari, Mohammad S. Alam

Vijayan K. Asari

Hyperspectral imaging (HSI) sensors provide plenty of spectral information to uniquely identify materials by their reflectance spectra, and this information has been effectively used for object detection and identification applications. Joint transform correlation (JTC) based object detection techniques in HSI have been proposed in the literatures, such as spectral fringe-adjusted joint transform correlation (SFJTC) and with its several improvements. However, to our knowledge, the SFJTC based techniques were designed to detect only similar patterns in hyperspectral data cube and not for dissimilar patterns. Thus, in this paper, a new deterministic object detection approach using SFJTC is proposed to perform multiple …

Directional Ringlet Intensity Feature Transform For Tracking, Evan Krieger, Paheding Sidike, Theus H. Aspiras, Vijayan K. Asari

Vijayan K. Asari

The challenges existing for current intensity-based histogram feature tracking methods in wide area motion imagery include object structural information distortions and background variations, such as different pavement or ground types. All of these challenges need to be met in order to have a robust object tracker, while attaining to be computed at an appropriate speed for real-time processing. To achieve this we propose a novel method, Directional Ringlet Intensity Feature Transform (DRIFT), that employs Kirsch kernel filtering and Gaussian ringlet feature mapping. We evaluated the DRIFT on two challenging datasets, namely Columbus Large Image Format (CLIF) and Large Area Image …

Histogram Of Oriented Phase (Hop): A New Descriptor Based On Phase Congruency, Hussin Ragb, Vijayan K. Asari

Vijayan K. Asari

In this paper we present a low level image descriptor called Histogram of Oriented Phase based on phase congruency concept and the Principal Component Analysis (PCA). Since the phase of the signal conveys more information regarding signal structure than the magnitude, the proposed descriptor can precisely identify and localize image features over the gradient based techniques, especially in the regions affected by illumination changes. The proposed features can be formed by extracting the phase congruency information for each pixel in the image with respect to its neighborhood. Histograms of the phase congruency values of the local regions in the image …

A Robust Fringe-Adjusted Joint Transform Correlator For Efficient Object Detection, Paheding Sidike, Vijayan K. Asari, Mohammad S. Alam

Vijayan K. Asari

The fringe-adjusted joint transform correlation (FJTC) technique has been widely used for real-time optical pattern recognition applications. However, the classical FJTC technique suffers from target distortions due to noise, scale, rotation and illumination variations of the targets in input scenes. Several improvements of the FJTC have been proposed in the literature to accommodate these problems. Some popular techniques such as synthetic discriminant function (SDF) based FJTC was designed to alleviate the problems of scale and rotation variations of the target, whereas wavelet based FJTC has been found to yield better performance for noisy targets in the input scenes. While these …

Mechanical Properties Of Self-Assembled Nanoparticle Membranes: Stretching And Bending, Yifan Wang, Pongsakorn Kanjanaboos, Sean P. Mcbride, Edward Barry, Xiao-Min Lin, Heinrich M. Jaeger

Dr. Sean P. McBride

Monolayers composed of colloidal nanoparticles, with thickness less than ten nanometers, have remarkable mechanical strength and can suspend over micron-sized holes to form free-standing membranes. We discuss experiments probing the tensile strength and bending stiffness of these self-assembled nanoparticle sheets. The fracture behavior of monolayers and multilayers is investigated by attaching them to elastomer substrates which are then stretched. For different applied strain the fracture patterns are imaged down to the scale of single particles. The resulting detailed information about the crack width distribution allows us to relate the measured overall tensile strength to the distribution of local bond strengths …

Viscosity Dependent Liquid Slip At Molecularly Smooth Hydrophobic Surfaces, Sean P. Mcbride, Bruce M. Law

Dr. Sean P. McBride

Colloidal probe atomic force microscopy is used to study the slip behavior of 18 Newtonian liquids from two homologous series, the n-alkanes and n-alcohols, at molecularly smooth hydrophobic n-hexadecyltrichlorosilane coated surfaces. We find that the slip behavior is governed by the bulk viscosity η of the liquid, specifically, the slip length b∼ηx with x∼0.33. Additionally, the slip length was found to be shear rate independent, validating the use of Vinogradova slip theory in this work.

Improved In Situ Spring Constant Calibration For Colloidal Probe Atomic Force Microscopy, Sean P. Mcbride, Bruce M. Law

Dr. Sean P. McBride

In colloidal probe atomic force microscopy (AFM) surface forces cannot be measured without an accurate determination of the cantilever spring constant. The effective spring constant k depends upon the cantilever geometry and therefore should be measured in situ; additionally, k may be coupled to other measurement parameters. For example, colloidal probe AFM is frequently used to measure the slip length b at solid/liquid boundaries by comparing the measured hydrodynamic force with Vinogradova slip theory (V-theory). However, in this measurement k and b are coupled, hence, b cannot be accurately determined without knowing k to high precision. In this paper, a …

Forces At Individual Pseudopod-Filament Adhesive Contacts, Govind Paneru, Prem S. Thapa, Sean P. Mcbride, David Moore-Nichols, Bruce M. Law, Bret N. Flanders

Dr. Sean P. McBride

On-chip cellular force sensors are fabricated from cantilever poly(3,4-ethylene dioxythiophene) filaments that visibly deflect under forces exerted at individual pseudopod-filament adhesive contacts. The shape of the deflected filaments and their ∼3 nN/μm spring constants are predicted by cantilever rod theory. Pulling forces exerted by Dictyostelium discoideumcells at these contacts are observed to reach ∼20 nN without breaking the contact.

Influence Of Line Tension On Spherical Colloidal Particles At Liquid-Vapor Interfaces, Sean P. Mcbride, Bruce M. Law

Dr. Sean P. McBride

Atomic force microscopy (AFM) imaging of isolated submicron dodecyltrichlorosilane coated silica spheres, immobilized at the liquid polystyrene- (PS-) air interface at the PS glass transition temperature, Tg , allows for determination of the contact angle θ versus particle radius R . At Tg , all θ versus R measurements are well described by the modified Young’s equation for a line tension τ=0.93  nN . The AFM measurements are also consistent with a minimum contact angle θmin and minimum radius Rmin , below which single isolated silica spheres cannot exist at the PS-air interface.

Hydrolysis Of P-Nitrophenyl Esters Promoted By Semi-Fluorinated Quaternary Ammonium Polymer Latexes And Films, Baljinder Kaur, Sean P. Mcbride, Warren T. Ford

Dr. Sean P. McBride

Semifluorinated polymer latexes were prepared by emulsion polymerization of 2.5-25% of a fluoroalkyl methacrylate, 25% chloromethylstyrene, 1% styrylmethyl(trimethyl)ammonium chloride, and the remainder 2-ethylhexyl methacrylate under surfactant-free conditions. The chloromethylstyrene units were converted to quaternary ammonium ions with trimethylamine. In aqueous dispersions at particle concentrations of less than 1 mg mL-1 the quaternary ammonium ion latexes promoted hydrolyses of p-nitrophenyl hexanoate (PNPH) in pH 9.4 borate buffer and of diethyl p-nitrophenyl phosphate (Paraoxon) in 0.1 M NaOH at 30 oC with half-lives of less than 10 minutes. Thin 0.7-2 μm films of the latexes on glass promoted fast hydrolysis of Paraoxon …

Electron Acceleration And Generation Of High-Brilliance X-Ray Radiation In Kilojoule, Subpicosecond Laser-Plasma Interactions, Serge Y. Kalmykov, X. Davoine

Serge Youri Kalmykov

Strong Resistance To Bending Observed For Nanoparticle Membranes, Yifan Wang, Jianhui Liao, Sean P. Mcbride, Efi Efrati, Xiao-Min Lin, Heinrich M. Jaeger

Dr. Sean P. McBride

We demonstrate how gold nanoparticle monolayers can be curled up into hollow scrolls that make it possible to extract both bending and stretching moduli from indentation by atomic force microscopy. We find a bending modulus that is 2 orders of magnitude larger than predicted by standard continuum elasticity, an enhancement we associate with nonlocal microstructural constraints. This finding opens up new opportunities for independent control of resistance to bending and stretching at the nanoscale.