Papers by Robert T Jantzen
International Advances in Economic Research, 2007
ABSTRACT We show that immigrant managers are substantially more likely to hire immigrants than ar... more ABSTRACT We show that immigrant managers are substantially more likely to hire immigrants than are native managers. The finding holds when comparing establishments in the same 5-digit industry and location, when comparing different establishments within the same firm, when analyzing establishments that change management over time, and when accounting for within-establishment trends in recruitment patterns. The effects are largest for small and owner-managed establishments in the for-profit sector. Separations are more frequent when workers and managers have dissimilar origin, but only before workers become protected by EPL. We also find that native managers are unbiased in their recruitments of former co-workers, suggesting that information deficiencies are important. We find no effects on entry wages. Our findings suggest that a low frequency of immigrant managers may contribute to the observed disadvantages of immigrant workers.
The Tenth Marcel Grossmann Meeting
ABSTRACT
Rotating observers and circular test particle orbits in Minkowski spacetime are used to illustrat... more Rotating observers and circular test particle orbits in Minkowski spacetime are used to illustrate the transport laws and derivative operators needed to define the various “inertial forces” one can introduce using the natural relative observer approach to describing spacetime. Various centripetal accelerations (often called centrifugal forces when multiplied by the mass) are evaluated and compared with the familiar value ν/r of nonrelativistic physics.
The historical origins of Fermi-Walker transport and Fermi coordinates and the construction of Fe... more The historical origins of Fermi-Walker transport and Fermi coordinates and the construction of Fermi-Walker transported frames in black hole spacetimes are reviewed. For geodesics this transport reduces to parallel transport and these frames can be explicitly constructed using Killing-Yano tensors as shown by Marck. For accelerated or geodesic circular orbits in such spacetimes, both parallel and FermiWalker transported frames can be given, and allow one to study circular holonomy and related clock and spin transport effects. In particular the total angle of rotation that a spin vector undergoes around a closed loop can be expressed in a factored form, where each factor is due to a different relativistic effect, in contrast with the usual sum of terms decomposition. Finally the Thomas precession frequency is shown to be a special case of the simple relationship between the parallel transport and Fermi-Walker transport frequencies for stationary circular orbits.
A historical overview is given of the various approaches to splitting spacetime into space-plus-t... more A historical overview is given of the various approaches to splitting spacetime into space-plus-time. These may all be described within a common framework—gravitoelectromagnetism—based on test observer fami-
arXiv: Differential Geometry, 2013
A 3-parameter family of helical tubular surfaces obtained by screw revolving a circle provides a ... more A 3-parameter family of helical tubular surfaces obtained by screw revolving a circle provides a useful pedagogical example of how to study geodesics on a surface that admits a 1-parameter symmetry group, but is not as simple as a surface of revolution like the torus which it contains as a special case. It serves as a simple example of helically symmetric surfaces which are the generalizations of surfaces of revolution in which an initial plane curve is screw-revolved around an axis in its plane. The physics description of geodesic motion on these surfaces requires a slightly more involved effective potential approach than the torus case due to the nonorthogonal coordinate grid necessary to describe this problem. Amazingly this discussion allows one to very nicely describe the geodesics of the surface of the more complicated ridged cavatappi pasta.
Parallel transport around closed circular orbits in the equatorial plane of the Taub-NUT spacetim... more Parallel transport around closed circular orbits in the equatorial plane of the Taub-NUT spacetime is analyzed to reveal the effect of the gravitomagnetic monopole parameter on circular holonomy transformations. Investigating the boost/rotation decomposition of the connection 1-form matrix evaluated along these orbits, one finds a situation that reflects the behavior of the general orthogonally transitive stationary axisymmetric case and indeed along Killing trajectories in general.
arXiv: General Relativity and Quantum Cosmology, 2001
We present an integral formulation of observer-dependent Maxwell's equations in curved spacet... more We present an integral formulation of observer-dependent Maxwell's equations in curved spacetime and give a classical interpretation of them.
York’s splitting of the tangent spaces to the space of Riemannian metrics over a 3-manifold is ex... more York’s splitting of the tangent spaces to the space of Riemannian metrics over a 3-manifold is examined in the context of spatially homogeneous cosmology where it is generally found to have two distinct analogues in the noncompact case. This requires a modification of the theory of minimal distortion shifts as it applies to noncompact cosmology and clarifies the roles played by the « kinematical » and « dynamical » degrees of freedom in the evolution of spatially homogeneous Cauchy data.
The problem of finding the distance from a point to a curve is a standard exercise in calculus. I... more The problem of finding the distance from a point to a curve is a standard exercise in calculus. If the curve is differentiable and has no endpoints, the connecting line segment from the given point to the nearest (farthest) point on the curve must be perpendicular to the tangent line there. One can therefore ask the more general question of how many such points on the curve have this geometric property, i.e. how many “normal line segments” can be drawn from the given point to the curve. If one adopts a parametrization of the curve, then these points correspond to critical points of the distance function. Since a continuous real-valued function on a closed interval always has a maximum and minimum value, there are at least two such normals for any simple differentiable closed curve like the ellipse. For example, if the curve is a circle and the point is not at the center of the circle, then precisely two normal line segments can be drawn (in the line through the given point and the c...
1Written collectively as “Golden Oldie XXX; each author is signed under his segment. 2Copernicus ... more 1Written collectively as “Golden Oldie XXX; each author is signed under his segment. 2Copernicus Astronomical Center, Polish Academy of Sciences, Warsaw, Poland; e-mail: [email protected] 3Eduard-Steinle-Stra βe 19, 70 619 Stuttgart, Germany. 429 Washington Square West, New York, NY 10011, USA; e-mail: [email protected] 5Jet Propulsion Laboratory, Mail Stop 169-327, 4800 Oak Grove Drive, Pasadena, California 91109, USA 6Jet Propulsion Laboratory, Mail Stop 169-327, 4800 Oak Grove Drive, Pasadena, California 91109, USA; e-mail: [email protected] 7Mathematics Department, University of Cape Town, Rondebosch 7700, Cape Town, South Africa; e-mail: [email protected] 8Department of Mathematical Sciences, Villanova University, Villanova, Pennsylvania 19085, USA; e-mail: [email protected] 9Institut für Astrophysik der Universit ̈ at Bonn, Auf dem H ̈ ugel 71, D-53121 Bonn, Germany; e-mail: [email protected]
General Relativity and Gravitation
Timelike geodesics on a hyperplane orthogonal to the symmetry axis of the Gödel spacetime appear ... more Timelike geodesics on a hyperplane orthogonal to the symmetry axis of the Gödel spacetime appear to be elliptic-like if standard coordinates naturally adapted to the cylindrical symmetry are used. The orbit can then be suitably described through an eccentricity-semi-latus rectum parametrization, familiar from the Newtonian dynamics of a two-body system. However, changing coordinates such planar geodesics all become explicitly circular, as exhibited by Kundt's form of the Gödel metric. We derive here a one-to-one correspondence between the constants of the motion along these geodesics as well as between the parameter spaces of elliptic-like versus circular geodesics. We also show how to connect the two equivalent descriptions of particle motion by introducing a pair of complex coordinates in the 2-planes orthogonal to the symmetry axis, which brings the metric into a form which is invariant Donato Bini Istituto per le Applicazioni del Calcolo "M. Picone," CNR,
Classical and Quantum Gravity
... Donato Bini and Robert T Jantzen§ Istituto per Applicazioni della Matematica CNR, I-8013... more ... Donato Bini and Robert T Jantzen§ Istituto per Applicazioni della Matematica CNR, I-80131 Naples, Italy International Center for Relativistic Astrophysics, University of Rome, I-00185 Rome, Italy § Department of Mathematical Sciences, Villanova University, Villanova ...
Physical Review D
The Wigner rotations arising from the combination of boosts along two different directions are re... more The Wigner rotations arising from the combination of boosts along two different directions are rederived from a relative boost point of view and applied to gyroscope spin precession along timelike geodesics in a Kerr spacetime, clarifying the geometrical properties of Marck's recipe for describing parallel transport along such world lines expressed in terms of the constants of the motion. His final angular velocity isolates the cumulative spin precession angular velocity independent of the spacetime tilting required to keep the spin 4-vector orthogonal to the gyro 4-velocity. As an explicit example the cumulative precession effects are computed for a test gyroscope moving along both bound and unbound equatorial plane geodesic orbits.
Il Nuovo Cimento B Series 11
SummaryThe difficulties with the application of Lagrangian or Hamiltonian formulations to spatial... more SummaryThe difficulties with the application of Lagrangian or Hamiltonian formulations to spatially homogeneous cosmology are examined from a new point of view and a simple explanation is given for the necessary modifications of those formulations. A rather natural restriction on the shift vector field freedom minimizes the extent of the required modifications, leaving the dynamical Einstein equations in the form of a Lagrangian/Hamiltonian system driven by a nonpotential force. The symmetry group of this classical mechanical system is a representation of the diffeomorphism group corresponding to the restricted class of shift vector fields.RiassuntoSi esaminano le difficoltà nell'applicazione di formulazioni lagrangiane o hamiltoniane alla cosmologia spazialmente omogenea, da un punto di vista nuovo e si fornisce una semplice spiegazione delle modifiche necessarie per quelle formulazioni. Un'abbastanza naturale restrizione della libertà di campo vettoriale di spostamento minimizza l'entità delle modifiche richieste, lasciando le equazioni di Einstein dinamiche nella forma di un sistema lagrangiano/hamiltoniano guidato da una forza non potenziale. Il gruppo di simmetria di questo sistema meccanico classico è una rappresentazione del gruppo di diffeomorfismo che corrisponde alla classe ristretta di campi vettoriali di spostamento.РезюмеИсследуются трудности, связанные с применением Лагранжева или Гамильтонова формализмов к пространственио однородной космологии. Предлагается простое объяснение необходимых модификаций этих формализмов. Естественное ограничение на свободу векторного поля смещения минимизирует степень требуемых модификаций, приводя к динамическим уравнениям Эйнштейна с непотенциальной силой. Группа симметрий этой системе в классической механике представляет группу диффеоморфизма, которая соответствует ограниченному классу векторных полей смещения.
General Relativity and Gravitation
General Relativity and Gravitation
... 2. THE TAUB-NUT METRIC The metric of the Taub-NUT spacetime [14] in Boyer-Lindquist-like coo... more ... 2. THE TAUB-NUT METRIC The metric of the Taub-NUT spacetime [14] in Boyer-Lindquist-like coor-dinates is ds2 = − −1 (dt + 2l cos θdφ)2 + ( −1 dr2 + dθ2 + sin2 θ dφ2), (1) ... e0 is interpreted as the 4-velocity of the ZAMOs. The ZAMO dual 1-forms are ...
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Papers by Robert T Jantzen