4,842 research outputs found
Self force via m-mode regularization and 2+1D evolution: foundations and a scalar-field implementation on Schwarzschild
No full textTo model the radiative evolution of extreme mass-ratio binary inspirals (a key target of the LISA mission), the community needs efficient methods for computation of the gravitational self-force (SF) on the Kerr spacetime. Here we further develop a practical “m-mode regularization” scheme for SF calculations, and give the details of a first implementation. The key steps in the method are (i) removal of a singular part of the perturbation field with a suitable “puncture” to leave a sufficiently regular residual within a finite worldtube surrounding the particle’s worldline, (ii) decomposition in azimuthal (m) modes, (iii) numerical evolution of the m modes in 2+1D with a finite-difference scheme, and (iv) reconstruction of the SF from the mode sum. The method relies on a judicious choice of puncture, based on the Detweiler-Whiting decomposition. We give a working definition for the “order” of the puncture, and show how it determines the convergence rate of the m-mode sum. The dissipative piece of the SF displays an exponentially convergent mode sum, while the m-mode sum for the conservative piece converges with a power law. In the latter case, the individual modal contributions fall off at large m as m-n for even n and as m-n+1 for odd n, where n is the puncture order. We describe an m-mode implementation with a 4th-order puncture to compute the scalar-field SF along circular geodesics on Schwarzschild. In a forthcoming companion paper we extend the calculation to the Kerr spacetim
Seven or eight years ago, Dr. Sam Jagoda Jr., a radiologist, saw a picture of junk sculpture in a magazine.
No full textSeven or eight years ago, Dr. Sam Jagoda Jr., a radiologist, saw a picture of junk sculpture in a magazine. Its price tag was in four figures. So Dr. Jagoda got a welder to show him how to use a torch and, that same afternoon, created his first object d'art, a cast-iron owl.
He began combing junkyards for raw material, tearing his car seat covers hauling it home
then welding it into quaint shapes in bis basement. One of his pieces started as a mountain
range and wound up a bird. Another meant to be a penguin, tipped over and became an iguan
Dr. Sam Jagoda Jr. has a rusty thumb.
No full textDr. Sam Jagoda Jr. has a rusty thumb. He drives an old jalopy, which he keeps in excellent running order. And he's a scrap iron sculptor. Some of his object’s d'art are on display in a garden area in front of the Sidewalk Cafe at the Fort Worth Zoo. Dr. Jagoda was delivering one of his pieces of art, which have won acclaim from junk dealers from the Jacksboro Highway to East Handley, in his old jalopy the other day. It was placed on the back seat.
He stopped at a service station for gasoline. The station operator glanced at the piece of sculpture in the back seat and asked: “That fall off your car, Doctor?'' The doctor's work caused a lot of comment among zoo browsers over the Labor Day weekend. “What’s that stuff?” one visitor would ask another.
''I don’t know,'’ the other would answer. “Let's go see the aardvarks.
Self-force via m-mode regularization and 2+1D evolution: III. Gravitational field on Schwarzschild spacetime
No full textThis is the third in a series of papers aimed at developing a practical time-domain method for self-force calculations in Kerr spacetime. The key elements of the method are (i) removal of a singular part of the perturbation field with a suitable analytic "puncture", (ii) decomposition of the perturbation equations in azimuthal (m-)modes, taking advantage of the axial symmetry of the Kerr background, (iii) numerical evolution of the individual -modes in 2+1-dimensions with a finite difference scheme, and (iv) reconstruction of the local self-force from the mode sum. Here we report a first implementation of the method to compute the gravitational self-force. We work in the Lorenz gauge, solving directly for the metric perturbation in 2+1-dimensions. The modes m=0,1$ contain nonradiative pieces, whose time-domain evolution is hampered by certain gauge instabilities. We study this problem in detail and propose ways around it. In the current work we use the Schwarzschild geometry as a platform for development; in a forthcoming paper-the fourth in the series-we apply our method to the gravitational self-force in Kerr geometry
Letter from Hayao (Sam) Chuman to the American Friends Service Committee
No full textA letter from Hayao (Sam) Chuman to the American Friends Service Committee, donating a portion of his redress check from the U.S. government to the Committee.The Chuman (Hayao "Sam" and Toshiko) Papers documents the World War II experiences of Hayao "Sam" and Toshiko Chuman, who were Kibei Nisei born in the United States but grew up and completed school in Japan, and then returned to the U.S. prior to the war. It chronicles the Chuman's incarceration from the Santa Anita Assembly Center, through Jerome, Rohwer, Tule Lake camps, and the Santa Fe and Crystal City internment camps as well as their struggle for restoring their U.S. citizenships in the 1960s. The digital collection consists of mostly textual material, including correspondence, affidavits, incarceration camp records, lease agreements, financial documents, receipts, pamphlets, and booklets
Letter from Hayao (Sam) Chuman to Earl Warren and "Attorney General Clark"
No full textA letter from Hayao (Sam) Chuman to Chief Justice of the Supreme Court Earl Warren and "Attorney General Clark". The letter is a request to regain his citizenship after renouncing his U.S. citizenship and requesting repatriation to Japan during his time incarcerated in World War II.The Chuman (Hayao "Sam" and Toshiko) Papers documents the World War II experiences of Hayao "Sam" and Toshiko Chuman, who were Kibei Nisei born in the United States but grew up and completed school in Japan, and then returned to the U.S. prior to the war. It chronicles the Chuman's incarceration from the Santa Anita Assembly Center, through Jerome, Rohwer, Tule Lake camps, and the Santa Fe and Crystal City internment camps as well as their struggle for restoring their U.S. citizenships in the 1960s. The digital collection consists of mostly textual material, including correspondence, affidavits, incarceration camp records, lease agreements, financial documents, receipts, pamphlets, and booklets
Self-force via m-mode regularization and 2+1D evolution. II. Scalar-field implementation on Kerr spacetime
Get PDFThis is the second in a series of papers aimed at developing a practical time-domain method for self-force calculations in Kerr spacetime. The key elements of the method are (i) removal of a singular part of the perturbation field with a suitable analytic “puncture” based on the Detweiler-Whiting decomposition, (ii) decomposition of the perturbation equations in azimuthal (m-)modes, taking advantage of the axial symmetry of the Kerr background, (iii) numerical evolution of the individual m-modes in 2+1 dimensions with a finite-difference scheme, and (iv) reconstruction of the physical self-force from the mode sum. Here we report an implementation of the method to compute the scalar-field self-force along circular equatorial geodesic orbits around a Kerr black hole. This constitutes a first time-domain computation of the self-force in Kerr geometry. Our time-domain code reproduces the results of a recent frequency-domain calculation by Warburton and Barack, but has the added advantage of being readily adaptable to include the backreaction from the self-force in a self-consistent manner. In a forthcoming paper—the third in the series—we apply our method to the gravitational self-force (in the Lorenz gauge)
Wave propagation and quasinormal mode excitation on Schwarzschild spacetime
No full textTo seek a deeper understanding of wave propagation on the Schwarzschild spacetime, we investigate the relationship between (i) the light cone of an event and its caustics (self-intersections), (ii) the large-l asymptotics of quasinormal modes (QNMs), and (iii) the singular structure of the retarded Green function (GF) for the scalar field. First, we recall that the GF has a (partial) representation as a sum over QNMs. Next, we extend a recently developed expansion method to obtain asymptotic expressions for QNM wave functions and their residues. We employ these asymptotics to show (approximately) that the QNM sum is singular on the light cone, and to obtain approximations for the GF which are valid close to the light cone. These approximations confirm a little-known prediction: the singular part of the GF undergoes a transition each time the light cone passes through a caustic, following a repeating fourfold sequence. We conclude with a discussion of implications and extensions of this work
Sam "Kangaroo"
Get PDFabstract: Sam left Sudan when he was six years old. He also witnessed many people die when they tried to cross the Gilo river.
“Lost Boys Found” is an ongoing, interdisciplinary project that is collecting, recording and archiving the oral histories of the Lost Boys/Girls of Sudan. The collection is a work-in-progress, seeking to record the oral history of as many Lost Boys/Girls as are willing, and will be used in a future book.Age: 23Region: Upper Nile (Bor)This picture and bio was donated to the "Lost Boys Found" oral history project from The Arizona Lost Boys Cente
the beat report piece detailing author Sam Pfeifle\u27s wishes for local music fo
No full textthe beat report piece detailing author Sam Pfeifle\u27s wishes for local music for 2004, mentioning radio stations WCYY and WCLZ, local band 6gig, and the Musicians Resource League
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