Caltech Authors
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Repository of works by Caltech published authors.

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Mostrando recursos 1 - 20 de 2,642

1.
Projections for Dark Photon Searches at Mu3e - Echenard, Bertrand; Essig, Rouven; Zhong, Yi-Ming
We show that dark photons (A0) with masses ~10-80MeV can be probed in the decay µ^+ → e^+v_ev_µA', A' → e^+e^-, with the upcoming Mu3e experiment at the Paul Scherrer Institute (PSI) in Switzerland. With an expected 10^(15)(5.5 x 10^(16)) muon decays in 2015{2016 (2018 and beyond), Mu3e has the exciting opportunity to probe a substantial fraction of currently unexplored dark photon parameter space, probing kinetic-mixing parameter, є, as low as є^2 10^(-7) (10^(-8)). No modifications of the existing Mu3e setup are required.

2.
Liquid pair correlations in four spatial dimensions: Theory versus simulation - Heinen, M.; Horbach, J.; Löwen, H.
Using liquid integral equation theory, we calculate the pair correlations of particles that interact via a smooth repulsive pair potential in d = 4 spatial dimensions. We discuss the performance of different closures for the Ornstein-Zernike equation, by comparing the results to computer simulation data. Our results are of relevance to understand crystal and glass formation in high-dimensional
systems.

3.
The Momentum-Balance Method in Earthquake Engineering - Housner, George W.
During an earthquake the shaking of the ground
imparts movement to structures which are then stressed by the resulting inertia forces. When the structure is a dam, it experiences additional earthquake forces from the water in the reservoir. The horizontal motion of the ground does not impart movement to the water so the dam accelerates into and away from the water and experiences
dynamic water pressures. The first analysis of this problem was by H. M. Westergaard, Professor of Theoretical and Applied Mechanics at the University of Illinois, his paper [1] appearing in the 1933 Transactions of the American Society of Civil...

4.
ALMA Observations of Warm Dense Gas in NGC 1614 — Breaking of Star Formation Law in the Central kpc - Xu, C. K.; Cao, C.; Lu, N.; Gao, Y.; Díaz-Santos, T.; Herrero-Illana, R.; Meijerink, R.; Privon, G.; Zhao, Y.-H.; Evans, A. S.; König, S.; Mazzarella, J. M.; Aalto, S.; Appleton, P.; Armus, L.; Charmandaris, V.; Chu, J.; Haan, S.; Inami, H.; Murphy, E. J.; Sanders, D. B.; Schulz, B.; van der Werf, P.
We present ALMA Cycle-0 observations of the CO (6-5) line emission and of the 435 μm dust continuum emission in the central kpc of NGC 1614, a local luminous infrared galaxy (LIRG) at a distance of 67.8 Mpc (1" = 329 pc). The CO emission is well resolved by the ALMA beam (0."26×0."20) into a circum-nuclear ring, with an integrated flux of f_(CO (6-5)) = 898 (±153) Jy km s^(-1), which is 63(±12)% of the total CO (6-5) flux measured by Herschel. The molecular ring, located between 100 pc < r < 350 pc from the nucleus, looks clumpy and...

5.
A Machine Learning Method to Infer Fundamental Stellar Parameters from Photometric Light Curves - Miller, A. A.; Bloom, J. S.; Richards, J. W.; Lee, Y. S.; Starr, D. L.; Butler, N. R.; Tokarz, S.; Smith, N.; Eisner, J. A.
A fundamental challenge for wide-field imaging surveys is obtaining follow-up spectroscopic observations: there are > 10^9 photometrically cataloged sources, yet modern spectroscopic surveys are limited to ~few x 10^6 targets. As we approach the Large Synoptic Survey Telescope (LSST) era, new algorithmic solutions are required to cope with the data deluge. Here we report the development of a machine-learning framework capable of inferring fundamental stellar parameters (T_(eff), log g, and [Fe/H]) using photometric-brightness variations and color alone. A training set is constructed from a systematic spectroscopic survey of variables with Hectospec/MMT. In sum, the training set includes ~9000 spectra, for...

6.
A structural distortion induced magneto-elastic locking in Sr_2IrO_4 revealed through nonlinear optical harmonic generation - Torchinsky, D. H.; Chu, H.; Zhao, L.; Perkins, N. B.; Sizyuk, Y.; Qi, T.; Cao, G.; Hsieh, D.
We report a global structural distortion in Sr_2IrO_4 using spatially resolved optical second and third harmonic generation rotational anisotropy measurements. A symmetry lowering from an I4_1/acd to I4_1/ɑ space group is observed both above and below the Néel temperature that arises from a staggered tetragonal distortion of the oxygen octahedra. By studying an effective super-exchange Hamiltonian that accounts for this lowered symmetry, we find that perfect locking between the octahedral rotation and magnetic moment canting angles can persist even in the presence of large non-cubic local distortions. Our results explain the origin of the forbidden Bragg peaks recently observed in...

7.
Short-time diffusion in concentrated bidisperse hard-sphere suspensions - Wang, Mu; Heinen, Marco; Brady, John F.
Diffusion in bidisperse Brownian hard-sphere suspensions is studied by Stokesian Dynamics (SD) computer simulations and a semi-analytical theoretical scheme for colloidal short-time dynamics, based on Beenakker and Mazur's method [Physica 120A, 388 (1983) & 126A, 349 (1984)]. Two species of hard spheres are suspended in an overdamped viscous solvent that mediates the salient hydrodynamic interactions among all particles. In a comprehensive parameter scan that covers various packing fractions and suspension compositions, we employ numerically accurate SD simulations to compute the initial diffusive relaxation of density modulations at the Brownian time scale, quantified by the partial hydrodynamic functions. A revised version...

8.
Yukawa Bound States of a Large Number of Fermions - Wise, Mark B.; Zhang, Yue
We consider the bound state problem for a field theory that contains a Dirac fermion x that Yukawa couples to a (light) scalar field ø. We are interested in bound states with a large number N of x particles. A Fermi gas model is used to numerically determine the dependence of the radius R of these bound states on N and also the dependence of the binding energy on N. Since scalar interactions with relativistic x's are suppressed two regimes emerge. For modest values of N the state is composed of non-relativistic x particles. In this regime as N increases...

9.
Experimental Study of Environment and Heat Transfer in a Room Fire - Zukoski, E. E.; Kubota, T.
This final report is written in three sections. The first two draw attention to work reported in detail in the Third Quarterly Progress Report and the third Section describes ongoing work which has not been previously discussed in a Progress Report.

10.
Large Structure Dynamics and Entrainment in the Mixing Layer at High Reynolds Number - Dimotakis, Paul E.; Brown, Garry L.
Observations were made on a turbulent mixing layer in a water channel at Reynolds numbers up to 3 x 10^6 . Flow visualization with dyes revealed (once more) large coherent structures and showed their role in the entrainment process; observations of the reaction of a base
and an acid indicator injected on the two sides of the layer, respectively, gave some indication of where molecular mixing occurs. Autocorrelations of streamwise velocity fluctuations, using an LDV, revealed a fundamental
periodicity associated with the large structures. The surprisingly long correlation times suggest time scales much longer than had been supposed; it is argued that...

11.
Informal Progress Report No. 3 on The Incorporation of Bending into the Buckling Delamination Analysis - Chai, H.; Babcock, C. D.; Knauss, W. G.
In a previous report a one dimensional model of buckling-delamination in a column was summarized. The main assumption made in that report was that the unbuckled portions of the column can be assumed to remain straight. The purpose of this report is to investigate the
more general problem in which bending effects are taken into account. We deal here with the case of a single off center delamination in a column. (The case of multi-delaminations in a column can be worked out too
under slight modifications.) Following the general procedure outlined in previous reports, consider the column of unit width shown in...

12.
A Simple Collocation Method for Fitting Viscoelastic Models to Experimental Data - Schapery, R. A.
An easily applied collocation method is discussed for fitting the response of finite-element viscoelastic models to experimental stress-strain curves. It can be used with creep, relaxation, and steady-state oscillation data. The method is illustrated by means of two examples. As the first one, a model is obtained utilizing the dynamic shear compliance of polyisobutylene. In the second example we calculate a model from the tensile relaxation modulus of polymethyl methacrylate. With each case the model's response agreed with the experimental data within graphical accuracy over the entire frequency (or time) scale.

13.
Two Simple Approximate Methods of Laplace Transform Inversion for Viscoelastic Stress Analysis - Schapery, R. A.
Two approximate methods of Laplace transform inversion are given which are simple to use and are particularly applicable to stress analysis problems in quasi-static linear viscoelasticity. Once an associated elastic
solution is known numerically or analytically, the time-dependent viscoelastic response can be easily calculated using realistic material properties,
regardless of how complex the property dependence of the elastic solution may be. The new feature of these methods is that it is necessary to know only 1) an elastic solution numerically for certain ranges of elastic constants and 2) numerical values of the operational moduli or compliances
for real, positive values of the transform...

14.
A Procedure for Predicting Fuel Specific Impulse of Supersonic Combustion Ramjet Engines - Serdengecti, S.
This report presents a procedure in order to portray the effect of design choices on SCRAMJET dynamic performance in the context of real gas effects. Procedure is based on one-dimensional fluid flow analysis. The less
quantifiable aspects of boundary layer transition, mixing, and non-uniform nozzle flow are included in approximate parametric fashion by allowing for parallel flow paths through the engine and nozzle, with possibility of thermal
energy exchange between various flow streams. The effect of finite recombination rates in the nozzle is included by allowing for freezing of the chemical composition at any specified static pressure in the nozzle.
Exploratory results from...

15.
Some Measurements of Flow in a Rectangular Cutout - Roshko, Anatol
The flow in a rectangular cavity, or slot, in the floor or a wind tunnel is described by the results or pressure and velocity measurements. Pressure distributions on the cavity walls as well as measurements of friction are presented. The effects of varying depth-breadth ratio are shown.

16.
On the Development of Turbulent Wakes From Vortex Streets - Roshko, Anatol
Wake development behind circular cylinders at Reynolds numbers from 40 to 10,000 was investigated in a low-speed wind tunnel. Standard hotwire techniques were used to study the velocity fluctuations.
The Reynolds number range of periodic vortex shedding is divided into two distinct subranges. At R = 40 to 150, called the stable range, regular vortex streets are formed and no turbulent motion is developed. The range R = 150 to 300 is a transition range to a regime called the
irregular range, in which turbulent velocity fluctuations accompany the periodic formation of vortices. The turbulence is initiated by laminar-turbulent
transition in the...

17.
Transonic Limits of Linearized Theory - Cole, J. D.
The transonic regime, extending from Mach numbers at which shock waves first appear with the associated drag rise to Mach numbers at which the head shock wave is firmly attached to the nose of the body, is well known. Not so well known, perhaps, is the reason for the failure of linearized theory to describe the flow in this regime, in particular, to permit an accurate calculation of the pressure.

18.
Magnetohydrodynamic Waves - Cole, J. D.
The aim of this paper is to study some special magnetohydrodynamic waves and their connection with the methods of their production, that is, the boundary conditions. Possible wave motions of a fluid
form the underlying structure of the mathematical description; hence a knowledge of their behavior leads to a deeper understanding of fluid dynamical problems. Furthermore there is some evidence that these
waves can be produced in the laboratory and may occur in nature. These waves occur in a model fluid which is an ordinary gas dynamic fluid endowed with a scalar electrical conductivity σ. In practice there is a fairly direct...

19.
Expansion Procedures and Similarity Laws for Transonic Flow Part I. Slender Bodies at Zero Incidence - Cole, J. D.; Messiter, A. F.
The purpose of this report is to provide a detailed and comprehensive account of a transonic approximation as applied to flows past wings and bodies. It is mainly concerned with the derivation of approximate
equations, boundary conditions, etc., rather than with the more difficult problem of the solution of transonic flow problems. Thus the report contains for the most part a re-examination of the basic ideas, as presented for example, in Ref. 1. The essential new point of view
introduced here is to regard the approximate transonic equations as part of a systematic expansion procedure. Thus, it becomes possible, in principle, to...