Using ordinary multiplication to do relativistic velocity addition

Relativistic addition of velocities in one dimension, though a mainstay of introductory physics, contributes much less physical insight than it could. For such calculations, we propose the use of velocity factors (two-way doppler factors). Velocities can easily, often by inspection, be turned into velocity factors, and vice versa. Velocity factors compose by ordinary multiplication. This simple device considerably extends the kinds of questions that can be asked and answered in an introductory course.Comment: 6 page

Microstructural and Isotopic Constraints on WL Rim Formation

Coordinated microanalyses of Wark-Lovering (WL) rims are needed to best understand their origin and to decipher their subsequent evolution both in the nebular and parent body settings. Here we present the mineralogy, petrology, microstructures, O isotopic compositions, and Al-Mg systematics of a WL rim on a Type B CAI, Big Guy, from the reduced CV3 chondrite Vigarano [1]. Our SEM and TEM study reveals seven distinct mineral layers in the WL rim that include: (1) gehlenite with rare grossite, (2) hibonite, (3) spinel with minor hibonite and perovskite, (4) zoned melilite (k(sub ~0-10)), (5) anorthite, (6) zoned diopside grading outwards from Al,Ti-rich to Al,Tipoor, and (7) forsterite intergrown with diopside. We infer a two-stage history in which WL rim formation was initiated by flash melting and extensive evaporation of the original inclusion edge, followed by subsequent condensation under highly dynamic conditions. The outermost edge of the CAI mantle is mineralogically and texturally distinct compared to the underlying mantle that is composed of coarse, zoned melilite (k(sub ~10-60)) grains. The mantle edge contains finegrained gehlenite with hibonite and rare grossite that likely formed by rapid crystallization from a Ca,Al-rich melt produced during a flash vaporization event [2]. These gehlenite and hibonite layers are surrounded by successive layers of spinel, melilite, diopside, and forsterite, indicating their sequential gas-solid reactions onto hibonite. Anorthite occurs as a discontinuous layer that corrodes adjacent melilite and Al-diopside, and appears to have replaced them [3,4], probably even later than the forsterite layer formation. All the WL rim minerals analyzed using the JSC NanoSIMS 50L are 16O-rich (17O 23), indicating their formation in an 16O-rich gas reservoir. Our data are in contrast with many CV CAIs that show heterogeneous 17O values across their WL rims [5]. Our Al-Mg data obtained using the UCLA ims-1290 ion microprobe of the CAI interior and the WL rim define a well-correlated isochron with (26Al/27Al)(sub 0) = 4.94 10(exp 5), indicating their synchronous formation 5 10(exp 4) years after the canonical CAI value. In contrast, no 26Mg excesses are observed in the WL rim anorthite, which suggests its later formation or later isotopic resetting in an 16O-rich gas reservoir, after 26Al had decayed

Systemdynamische Betrachtungen zur Sturzdynamik und -prophylaxe: Entwicklung eines deterministischen Modells

Zusammenfassung: Hintergrund: Stürze älterer Personen ist derzeit eine große Public-Health-Herausforderung. Da Instrumente zur Erkennung sturzgefährdeter Personen wenig genaue Vorhersagen machen, wurde ein deterministisches systemdynamisches Modell der Sturzdynamik entwickelt. Methoden: Unter Verwendung bekannter Sturzrisikofaktoren, quantitativer Forschungsergebnisse und Abschätzungen, Ursachen- und Wirkbeziehungen wurde ein deterministisches Modell simuliert. Ergebnisse: Grundvoraussetzungen für Stürze sind Bewegung oder Bewegungsabsichten ("Mobilität im Alltag"), ein Sturzrisiko und ein Ungleichgewicht zwischen Gehanforderungen und Gehfähigkeit. Kraft, Koordination und Gleichgewicht wurden als Speichergrößen definiert und Ursache-Wirkungs-Zusammenhänge ins Modell integriert. Zahlreiche andere bekannte Sturzrisikofaktoren wurden ins Modell aufgenommen und quantifiziert. Die Simulation einer Fixierung zeigte, dass die Sturzwahrscheinlichkeit unmittelbar nach der Fixierung erhöht ist. Das Modell zeigt in der Simulation systemdynamische Aspekte wie Verzögerung, Rückkoppelung und Nicht-Linearität. Schlussfolgerung: Mit Hilfe der Systemdynamik konnte ein deterministisches systemdynamisches Modell der Sturzdynamik und -prophylaxe für eine Pflegeheimpopulation unter Einbeziehung bekannter Sturzrisikofaktoren entwickelt werden, das von Praktikern als plausibel beurteilt wird und das "richtungssicher" reagier

Model-based spacecraft and mission design for the evaluation of technology

In order to meet the future vision of robotic missions, engineers will face intricate mission concepts, new operational approaches, and technologies that have yet to be developed. The concept of smaller, model driven projects helps this transition by including life-cycle cost as part of the decision making process. For example, since planetary exploration missions have cost ceilings and short development periods, heritage flight hardware is utilized. However, conceptual designs that rely solely on heritage technology will result in estimates that may not be truly representative of the actual mission being designed and built. The Laboratory for Spacecraft and Mission Design (LSMD) at the California Institute of Technology is developing integrated concurrent models for mass and cost estimations. The purpose of this project is to quantify the infusion of specific technologies where the data would be useful in guiding technology developments leading up to a mission. This paper introduces the design-to-cost model to determine the implications of various technologies on the spacecraft system in a collaborative engineering environment. In addition, comparisons of the benefits of new or advanced technologies for future deep space missions are examined

Local light-ray rotation

We present a sheet structure that rotates the local ray direction through an arbitrary angle around the sheet normal. The sheet structure consists of two parallel Dove-prism sheets, each of which flips one component of the local direction of transmitted light rays. Together, the two sheets rotate transmitted light rays around the sheet normal. We show that the direction under which a point light source is seen is given by a Mobius transform. We illustrate some of the properties with movies calculated by ray-tracing software.Comment: 9 pages, 6 figure

Surveillance for Toxoplasma gondii in the white-tailed deer (Odocoileus virginianus) in Ohio

Author Institution: Department of Entomology, The Ohio State UniversitySerum samples from 147 white-tailed deer, Odocoileus virginianus, were collected at deer-check stations and Columbus area metropolitan park deer hunts during November and December of Ohio's 1996-97 and 97-98 hunting seasons. These samples were tested for Toxoplasma gondii antibodies using a modified direct agglutination assay. Forty-four percent (65/147) of the samples tested positive. Sixteen percent had a titer of 25, 16% had a titer of 50, 3% had a titer of 250 and 9% had a titer of >500. Percentage of positive deer varied greatly between geographical locations. Fifty-five percent of 45 serum samples collected from Hocking County were positive while only 6% of the 18 deer sampled from Franklin County tested positive. No significant differences in infection rates were observed between sexes. This is the first report of T. gondii antibodies from a game animal in Ohio. Pregnant women should thoroughly cook venison before it is consumed to avoid complications from this pathogen

Overcharging a Black Hole and Cosmic Censorship

We show that, contrary to a widespread belief, one can overcharge a near extremal Reissner-Nordstrom black hole by throwing in a charged particle, as long as the backreaction effects may be considered negligible. Furthermore, we find that we can make the particle's classical radius, mass, and charge, as well as the relative size of the backreaction terms arbitrarily small, by adjusting the parameters corresponding to the particle appropriately. This suggests that the question of cosmic censorship is still not wholly resolved even in this simple scenario. We contrast this with attempting to overcharge a black hole with a charged imploding shell, where we find that cosmic censorship is upheld. We also briefly comment on a number of possible extensions.Comment: 26 pages, 3 figures, LaTe

Proof Theory, Transformations, and Logic Programming for Debugging Security Protocols

We define a sequent calculus to formally specify, simulate, debug and verify security protocols. In our sequents we distinguish between the current knowledge of principals and the current global state of the session. Hereby, we can describe the operational semantics of principals and of an intruder in a simple and modular way. Furthermore, using proof theoretic tools like the analysis of permutability of rules, we are able to find efficient proof strategies that we prove complete for special classes of security protocols including Needham-Schroeder. Based on the results of this preliminary analysis, we have implemented a Prolog meta-interpreter which allows for rapid prototyping and for checking safety properties of security protocols, and we have applied it for finding error traces and proving correctness of practical examples

Initial stage of plate lifting from a water surface

This study deals with the flow induced by a rigid flat plate of finite length, initially touching a horizontal water surface, when it starts to move upwards with constant acceleration. In the present model, negative hydrodynamic pressures on the lower (wetted) surface of the plate are allowed, and thus, the water follows the plate due to the resulting suction force. The acceleration of the plate and the plate length are such that gravity, surface tension and viscous effects can be neglected during the early stages of the motion. Under these assumptions, the initial two-dimensional, potential flow caused by the plate lifting is obtained by using the small-time expansion of the velocity potential. This small-time solution is not valid close to the plate edges, as it predicts there singular flow velocities and unbounded displacements of the water-free surface. It is shown that close to the plate edges the flow is nonlinear and self-similar to leading order. This nonlinear flow is computed by the boundary-element method combined with a time-marching scheme. The numerical time-dependent solution approaches the self-similar local solution with time