4,745 research outputs found
Modeling the Pulse Profiles of Millisecond Pulsars in the Second LAT Catalog of gamma-ray Pulsars
Significant gamma-ray pulsations have been detected from ~40 millisecond
pulsars (MSPs) using 3 years of sky-survey data from the Fermi LAT and radio
timing solutions from across the globe. We have fit the radio and gamma-ray
pulse profiles of these MSPs using geometric versions of slot gap and outer gap
gamma-ray emission models and radio cone and core models. For MSPs with radio
and gamma-ray peaks aligned in phase we also explore low-altitude slot gap
gamma-ray models and caustic radio models. The best-fit parameters provide
constraints on the viewing geometries and emission sites. While the exact
pulsar magnetospheric geometry is unknown, we can use the increased number of
known gamma-ray MSPs to look for significant trends in the population which
average over these uncertainties.Comment: 4 pages, 2 figures, to appear in the proceedings of the 5th
International Symposium on High-Energy Astronom
Uncertainty in Climate Change
This Working Paper reviews the main reasons why definite and conclusive evidence in the field of climate change is almost an impossibility. It analyses the main elements that explain natural climatic change and reflects on the high level of uncertainty in the system, which in many ways is inherent to the system itself, and presents the latest evidence. The following section presents in a stylised fashion the key features of uncertainty and how it relates to climate change. Then, an analysis of how GHG have been measured is followed by a discussion of the different GHG, natural and human-induced events that have a significant bearing on climate change. The Working Paper concludes with an overview of past, present and future climate change and with a summary of the main ideas discussed throughout the text
Electron transport in single wall carbon nanotube weak links in the Fabry-Perot regime
We fabricated reproducible high transparency superconducting contacts
consisting of superconducting Ti/Al/Ti trilayers to gated single-walled carbon
nanotubes (SWCNTs). The reported semiconducting SWCNT have normal state
differential conductance up to and exhibit clear Fabry-Perot
interference patterns in the bias spectroscopy plot. We observed subharmonic
gap structure in the differential conductance and a distinct peak in the
conductance at zero bias which is interpreted as a manifestation of a
supercurrent. The gate dependence of this supercurrent as well as the excess
current are examined and compared to a coherent theory of superconducting point
contacts with good agreement.Comment: 10 pages, 4 figure
Phase correlation of laser waves with arbitrary frequency spacing
The theoretically predicted correlation of laser phase fluctuations in
Lambda-type interaction schemes is experimentally demonstrated. We show, that
the mechanism of correlation in a Lambda scheme is restricted to high frequency
noise components, whereas in a double- scheme, due to the laser phase
locking in closed-loop interaction, it extends to all noise frequencies. In
this case the correlation is weakly sensitive to coherence losses. Thus the
double-Lambda scheme can be used to correlate e.m. fields with carrier
frequency differences beyond the GHz regime.Comment: 4 pages, 4 figure
Advanced process design for re-contouring using a time-domain dynamic material removal simulation
The repair of components often requires the removal of excess weld material. This removal is considered as re-contouring. Re-contouring processes have to be designed individually for each case of damage to fulfil the high quality requirements. Therefore, a prognosis of the machined surface topography is crucial. The material removal simulation introduced in this paper allows the prediction of process stability and surface topography for 5-axis ball end milling including dynamic effects. Different process strategies for re-contouring of Ti-6Al-4V welds are examined. It is shown, that selecting suitable process parameters can lead to high surface quality while maintaining productivity. © 2019 The Author(s)
The mission oriented terminal area simulation facility
The Mission Oriented Terminal Area Simulation (MOTAS) was developed to provide an ATC environment in which flight management and flight operations research studies can be conducted with a high degree of realism. This facility provides a flexible and comprehensive simulation of the airborne, ground-based and communication aspects of the airport terminal area environment. Major elements of the simulation are: an airport terminal area environment model, two air traffic controller stations, several aircraft models and simulator cockpits, four pseudo pilot stations, and a realistic air-ground communications network. MOTAS has been used for one study with the DC-9 simulator and a series of data link studies are planned in the near future
Direct and Inverse Results on Bounded Domains for Meshless Methods via Localized Bases on Manifolds
This article develops direct and inverse estimates for certain finite
dimensional spaces arising in kernel approximation. Both the direct and inverse
estimates are based on approximation spaces spanned by local Lagrange functions
which are spatially highly localized. The construction of such functions is
computationally efficient and generalizes the construction given by the authors
for restricted surface splines on . The kernels for which the
theory applies includes the Sobolev-Mat\'ern kernels for closed, compact,
connected, Riemannian manifolds.Comment: 29 pages. To appear in Festschrift for the 80th Birthday of Ian Sloa
A simple proof of Perelman's collapsing theorem for 3-manifolds
We will simplify earlier proofs of Perelman's collapsing theorem for
3-manifolds given by Shioya-Yamaguchi and Morgan-Tian. Among other things, we
use Perelman's critical point theory (e.g., multiple conic singularity theory
and his fibration theory) for Alexandrov spaces to construct the desired local
Seifert fibration structure on collapsed 3-manifolds. The verification of
Perelman's collapsing theorem is the last step of Perelman's proof of
Thurston's Geometrization Conjecture on the classification of 3-manifolds. Our
proof of Perelman's collapsing theorem is almost self-contained, accessible to
non-experts and advanced graduate students. Perelman's collapsing theorem for
3-manifolds can be viewed as an extension of implicit function theoremComment: v1: 9 Figures. In this version, we improve the exposition of our
arguments in the earlier arXiv version. v2: added one more grap
The Rotating Quantum Vacuum
We derive conditions for rotating particle detectors to respond in a variety
of bounded spacetimes and compare the results with the folklore that particle
detectors do not respond in the vacuum state appropriate to their motion.
Applications involving possible violations of the second law of thermodynamics
are briefly addressed.Comment: Plain TeX, 10 pages (to appear in PRD
The ^(54)Mn Clock and Its Implications for Cosmic Ray Propagation and Fe Isotope Studies
Radioactive ^(54)Mn suggested as a 'clock' for measuring the lifetime of heavy cosmic rays, has a poorly known β-decay half-life estimated to be in the range from ~10^5 to 10 ^7 yr. Some years ago Koch et al. concluded from measurements of the Mn/Fe ratio that a significant fraction of low-energy (<1 GeV/nucleon) ^(54)Mn produced by Fe fragmentation had decayed. Using a propagation code that includes improved fragmentation cross-sections, and recent data from HEAO 3 and a number of other spacecraft, we have reexamined the evidence for ^(54)Mn decay in cosmic rays. We conclude that present cosmic-ray data cannot establish the degree of ^(54)Mn decay, but point out that this question has important implications for studies of the ^(54)Fe abundance in cosmic-ray source material, as well as for cosmic-ray propagation studies
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