Micromagnetic Simulations on the Dependence of Gilbert Damping on Domain Wall Velocities in Magnetic Nanowires

he dependence of damping on domain wall motion and velocity in Permalloy nanowires is presented. The domain wall motion in isolated two micron long Permalloy nanowires, with a rectangular cross-section 10 nm thick and 100 nm wide, is simulated using the Landau-Lifshitz Gilbert (LLG) simulation.Interpreting LLG dynamics can be difficult due to the dependence of the results on the Gilbert damping parameter alpha. The Walker model also predicts the critical field and domain wall velocity as a function of alpha. For these combined reasons the dependence of the domain wall speeds on the damping parameter is explored

Black Holes with Yang-Mills Hair

In Einstein-Maxwell theory black holes are uniquely determined by their mass, their charge and their angular momentum. This is no longer true in Einstein-Yang-Mills theory. We discuss sequences of neutral and charged SU(N) Einstein-Yang-Mills black holes, which are static spherically symmetric and asymptotically flat, and which carry Yang-Mills hair. Furthermore, in Einstein-Maxwell theory static black holes are spherically symmetric. We demonstrate that, in contrast, SU(2) Einstein-Yang-Mills theory possesses a sequence of black holes, which are static and only axially symmetric.Comment: LaTeX using epsf, aipproc, 10 pages including 9 ps figures, Talk held by Jutta Kunz at the Conference on Particles, Fields and Gravitation in Lodz, Poland, April 199

A late-time transition in the equation of state versus Lambda-CDM

We study a model of the dark energy which exhibits a rapid change in its equation of state w(z), such as occurs in vacuum metamorphosis. We compare the model predictions with CMB, large scale structure and supernova data and show that a late-time transition is marginally preferred over standard Lambda-CDM.Comment: 4 pages, 1 figure, to appear in the proceedings of XXXVIIth Rencontres de Moriond, "The Cosmological Model", March 200

Extremal Charged Rotating Dilaton Black Holes in Odd Dimensions

Employing higher order perturbation theory, we find a new class of charged rotating black hole solutions of Einstein-Maxwell-dilaton theory with general dilaton coupling constant. Starting from the Myers-Perry solutions, we use the electric charge as the perturbative parameter, and focus on extremal black holes with equal-magnitude angular momenta in odd dimensions. We perform the perturbations up to 4th order for black holes in 5 dimensions and up to 3rd order in higher odd dimensions. We calculate the physical properties of these black holes and study their dependence on the charge and the dilaton coupling constant.Comment: 20 pages, 3 figure

One Free Swerve? Requiring Police to Corroborate Anonymous Tips in Order to Establish Reasonable Suspicion for Warrantless Seizure of Alleged Drunk Drivers

The Supreme Court holds that warrantless searches and seizures are presumptively unreasonable. Nonetheless, the Court has carved out exceptions that give law enforcement officials considerable flexibility with which to conduct their day-to-day criminal investigations. One such exception to the warrant requirement is that police may stop and question an individual so long as the detaining officer has a reasonable belief that criminal activity may be taking place. Furthermore, the Court permits this requisite reasonable suspicion to be based on information provided by third-party sources, and has identified specific limits as to the type and quality of information police may use. In Florida v. J.L., the Court unanimously recognized such a limit, finding that reasonable suspicion cannot be based exclusively on a bare-boned anonymous tip. Consequently, the Court established an evidentiary baseline for all future police detentions: in order to use third-party information as the basis for a stop or search, police must first ascertain the informant’s reliability by either discovering the tipster’s identity or verifying sufficient predictive information related to the alleged crime. A reasonable suspicion to detain the subject of the tip can only be formed through independent investigation of the alleged criminal activity. Nevertheless, the Court complicated this general rule by hypothesizing that police might be able to act on a lesser showing of reliability when an anonymous tip alleges a sufficiently great danger, but subsequently declined to expound on what circumstances would present such an extreme danger. Consequently, the Court left unanswered what set of facts would warrant using a bare-boned anonymous tip as the sole basis for initiating a seizure and search. In particular, court decisions involving anonymous tips that allege potentially intoxicated motorists, reveal substantial disagreement as to the role these anonymous tips should play in an officer’s decision to initiate a traffic stop. This issue recently gained national attention when the United States Supreme Court denied certiorari to hear Virginia v. Harris. In that case, a Driving Under the Influence (DUI) conviction was overturned because the arresting officer stopped the defendant’s vehicle solely on the basis of an anonymous tip without corroborating suspicious behavior. In an impassioned dissent from the denial of certiorari, Chief Justice Roberts argued that both the frequency and deadliness of drunk driving accidents might justify allowing stops of allegedly intoxicated motorists solely on the basis of a bare anonymous tip, without corroboration of the tip’s criminal allegations. He contended that declining to hear Harris was effectively giving drunk drivers “one free swerve” before police could initiate a stop, inevitably endangering countless lives. Despite the denial of certiorari, this issue is ripe for review and should be heard to conform this divisive issue to the correct interpretation of the law. In order to establish the reasonable suspicion necessary to initiate an investigatory traffic stop, police should be required to corroborate beyond readily observable innocent details of an anonymous tip alleging erratic driving. Considerable Supreme Court precedent related to warrantless seizures implies that police cannot rely solely on an anonymous tip alleging drunk driving if the tip provides no means to establish the informant’s reliability. Moreover, the threat posed by a potentially intoxicated motorist is inconsistent with the extraordinary danger exception suggested in Florida v. J.L. In Part I of his paper, the author examines the historical development of Fourth Amendment case law as it relates to the use of anonymous tips by law enforcement. Part II addresses how these precedents apply in the context of investigatory traffic stops of allegedly intoxicated motorists, and examines the reasoning of jurisdictions on either side of the issue. Part III presents an analysis of the issue and argues that police must corroborate beyond just innocent information provided by an anonymous tip of dangerous driving. Finally, Part IV concludes by recommending that the appropriate focus should be on reducing the anonymity of anonymous reports of erratic driving, rather than constructing exceptions for such tips under the Fourth Amendment. The author also recommends that the Supreme Court should hear this issue to resolve this discrepancy and provide a uniform law consistent with the traditional application of the Fourth Amendment: when law enforcement cannot establish a caller’s credibility, they should be required to take the relatively minor step of corroborating the allegation to ensure there is a reasonable basis for a seizure before initiating an investigatory traffic stop