Length mode piezoelectric ultrasonic transducer for inspection of solid objects

The transducer is constructed from individual transducer elements arranged in an array and configured to exhibit a predominant, longitudinal mode transversely to the array. The elements are interconnected through thin flexible sheets. Each element is individually damped, and the transducer as a whole is electrically damped through resonance with the clamped capacitance and dissipation. Electrical control permits inphase operation of all transducer elements or control with preselected phase differences

Advanced propulsion for LEO-Moon transport. 2: Tether configurations in the LEO-Moon system

This brief work discusses a possible application of a tether as a dynamical element in a low Earth orbit (LEO)-Moon transport system, and is a part of the Cal Space study of that transport system. To be specific, that study concentrated on the downward transport of O2 from the Moon to LEO, where it is stored for use as a rocket propellant, thus reducing Earth liftoff mass requirements by a factor of about 8. Moreover, in order to display clearly the role of advanced technology, only one novel technology was introduced at a single node in the transport system, the rest being 'conventional' rocket transport. Tethers were found useful in several different roles: hanging from platforms in lunar orbits, as supports for elevators, spinning in LEO, or spinning in a tether transport orbit, an elliptical orbit with perigee at approximately 600 km. This last use is considered here. Presented are the usefulness of the tether, nature of the tether system, the apparatus needed to support, deploy, and control it, and a discussion of needed developments

Origins of elastic properties in ordered nanocomposites

We predict a diblock copolymer melt in the lamellar phase with added spherical nanoparticles that have an affinity for one block to have a lower tensile modulus than a pure diblock copolymer system. This weakening is due to the swelling of the lamellar domain by nanoparticles and the displacement of polymer by elastically inert fillers. Despite the overall decrease in the tensile modulus of a polydomain sample, the shear modulus for a single domain increases dramatically

Student understanding of the Boltzmann factor

We present results of our investigation into student understanding of the physical significance and utility of the Boltzmann factor in several simple models. We identify various justifications, both correct and incorrect, that students use when answering written questions that require application of the Boltzmann factor. Results from written data as well as teaching interviews suggest that many students can neither recognize situations in which the Boltzmann factor is applicable, nor articulate the physical significance of the Boltzmann factor as an expression for multiplicity, a fundamental quantity of statistical mechanics. The specific student difficulties seen in the written data led us to develop a guided-inquiry tutorial activity, centered around the derivation of the Boltzmann factor, for use in undergraduate statistical mechanics courses. We report on the development process of our tutorial, including data from teaching interviews and classroom observations on student discussions about the Boltzmann factor and its derivation during the tutorial development process. This additional information informed modifications that improved students' abilities to complete the tutorial during the allowed class time without sacrificing the effectiveness as we have measured it. These data also show an increase in students' appreciation of the origin and significance of the Boltzmann factor during the student discussions. Our findings provide evidence that working in groups to better understand the physical origins of the canonical probability distribution helps students gain a better understanding of when the Boltzmann factor is applicable and how to use it appropriately in answering relevant questions

Double wells, scalar fields and quantum phase transitions in ions traps

Since Hund's work on the ammonia molecule, the double well potential has formed a key paradigm in physics. Its importance is further underlined by the central role it plays in the Landau theory of phase transitions. Recently, the study of entanglement properties of many-body systems has added a new angle to the study of quantum phase transitions of discrete and continuous degrees of freedom, i.e., spin and harmonic chains. Here we show that control of the radial degree of freedom of trapped ion chains allows for the simulation of linear and non-linear Klein-Gordon fields on a lattice, in which the parameters of the lattice, the non-linearity and mass can be controlled at will. The system may be driven through a phase transition creating a double well potential between different configurations of the ion crystal. The dynamics of the system are controllable, local properties are measurable and tunnelling in the double well potential would be observable.Comment: 6 pages, 5 figure

Effects of temperature fluctuations of IUE data quality

Analysis of IUE calibration lamp images shows that variation in the temperature of the scientific instrument causes shifts in the location of the spectral format with respect to the reseau grid on the detector and in the location of the reseaux themselves. In high dispersion, a camera head amplifier temperature difference of 6C corresponds to a shift of 4 pixels in the spectral format for LWR and 2 pixels for SWP along the dispersion direction. Shifts perpendicular to the disperson (for the same temperature difference) are less than one pixel for both cameras. In low dispersion spectra, the shifts are similar but orthogonal to those described above with the larger motion lying in the direction perpendicular to the dispersion. In both dispersion modes, the observed shifts are apparently independent of wavelength. In high dispersion, the constant pixel shift mimics a constant velocity error

Towards Zeptosecond-Scale Pulses from X-Ray Free-Electron Lasers

The short wavelength and high peak power of the present generation of free-electron lasers (FELs) opens the possibility of ultra-short pulses even surpassing the present (tens to hundreds of attoseconds) capabilities of other light sources - but only if x-ray FELs can be made to generate pulses consisting of just a few optical cycles. For hard x-ray operation (~0.1nm), this corresponds to durations of approximately a single attosecond, and below into the zeptosecond scale. This talk will describe a novel method to generate trains of few-cycle pulses, at GW peak powers, from existing x-ray FEL facilities by using a relatively short 'afterburner'. Such pulses would enhance research opportunity in atomic dynamics and push capability towards the investigation of electronic-nuclear and nuclear dynamics. The corresponding multi-colour spectral output, with a bandwidth envelope increased by up to two orders of magnitudes over SASE, also has potential applications.Comment: Submitted to 35th International Free Electron Laser Conference, New York, 201

Fixed point scenario in the Two Higgs Doublet Model inspired by degenerate vacua

We consider the renormalisation group flow of Higgs and Yukawa couplings within the simplest non--supersymmetric two Higgs doublet extension of the Standard Model (SM). In this model the couplings are adjusted so that the multiple point principle (MPP) assumption, which implies the existence of a large set of degenerate vacua at some high energy scale $\Lambda$, is realised. When the top quark Yukawa coupling at the scale $\Lambda$ is large, the solutions of RG equations in this MPP inspired 2 Higgs Doublet Model (2HDM) converge to quasi--fixed points. We analyse the Higgs spectrum and couplings in the quasi--fixed point scenario and compute a theoretical upper bound on the lightest Higgs boson mass. When the scale $\Lambda$ is low, the coupling of the SM--like Higgs scalar to the top quark can be significantly larger in the considered model than in the SM, resulting in the enhanced production of Higgs bosons at the LHC.Comment: 16 pages, 3 figures, CERN preprint number added, references update

A numerical study of the correspondence between paths in a causal set and geodesics in the continuum

This paper presents the results of a computational study related to the path-geodesic correspondence in causal sets. For intervals in flat spacetimes, and in selected curved spacetimes, we present evidence that the longest maximal chains (the longest paths) in the corresponding causal set intervals statistically approach the geodesic for that interval in the appropriate continuum limit.Comment: To the celebration of the 60th birthday of Rafael D. Sorki