28,748 research outputs found
Neptune's Migration into a Stirred-Up Kuiper Belt: A Detailed Comparison of Simulations to Observations
Nbody simulations are used to examine the consequences of Neptune's outward
migration into the Kuiper Belt, with the simulated endstates being compared
rigorously and quantitatively to the observations. These simulations confirm
the findings of Chiang et al. (2003), who showed that Neptune's migration into
a previously stirred-up Kuiper Belt can account for the Kuiper Belt Objects
(KBOs) known to librate at Neptune's 5:2 resonance. We also find that capture
is possible at many other weak, high-order mean motion resonances, such as the
11:6, 13:7, 13:6, 9:4, 7:3, 12:5, 8:3, 3:1, 7:2, and the 4:1. The more distant
of these resonances, such as the 9:4, 7:3, 5:2, and the 3:1, can also capture
particles in stable, eccentric orbits beyond 50 AU, in the region of phase
space conventionally known as the Scattered Disk. Indeed, 90% of the simulated
particles that persist over the age of the Solar System in the so-called
Scattered Disk zone never had a close encounter with Neptune, but instead were
promoted into these eccentric orbits by Neptune's resonances during the
migration epoch. This indicates that the observed Scattered Disk might not be
so scattered. This model also produced only a handful of Centaurs, all of which
originated at Neptune's mean motion resonances in the Kuiper Belt. We also
report estimates of the abundances and masses of the Belt's various
subpopulations (e.g., the resonant KBOs, the Main Belt, and the so-called
Scattered Disk), and also provide upper limits on the abundance of Centaurs and
Neptune's Trojans, as well as upper limits on the sizes and abundances of
hypothetical KBOs that might inhabit the a>50 AU zone.Comment: 60 pages, 16 figures. Accepted for publication in the Astronomical
Journa
Squeeze-film dampers for turbomachinery stabilization
A technique for investigating the stability and damping present in centrally preloaded radially symmetric multi-mass flexible rotor bearing systems is presented. In general, one needs to find the eigenvalues of the linearized perturbation equations, though zero frequency stability maps may be found by solving as many simultaneous non-linear equations as there are dampers; and in the case of a single damper, such maps may be found directly, regardless of the number of degrees of freedom. The technique is illustrated for a simple symmetric four degree of freedom flexible rotor with an unpressurized damper. This example shows that whereas zero frequency stability maps are likely to prove to be a simple way to delineate multiple solution possibilities, they do not provide full stability information. Further, particularly for low bearing parameters, the introduction of an unpressurized squeeze film damper may promote instability in an otherwise stable system
FormCalc 8: Better Algebra and Vectorization
We present Version 8 of the Feynman-diagram calculator FormCalc. New features
include in particular significantly improved algebraic simplification as well
as vectorization of the generated code. The Cuba Library, used in FormCalc,
features checkpointing to disk for all integration algorithms.Comment: 7 pages, LaTeX, proceedings contribution to ACAT 2013, Beijing,
China, 16-21 May 201
Addressing the Next Wave of Internet Regulation: The Case For Equal Opportunity
In October 2009, the Federal Communications Commission released a Notice of Proposed Rule Making in which it asked for guidance on how to convert a principle of “nondiscrimination on the Internet” into a practical rule for broadband service providers. The ultimate formulation of the nondiscrimination principle could have a significant economic effect on economic welfare in the short term and on innovation. In this paper, we explain the economics of discrimination and offer a new approach for identifying anticompetitive discrimination. Discrimination raises concerns when it interferes with what is often referred to as “equality of opportunity.” However, the Commission’s proposed nondiscrimination policy, which would limit the ability of service providers and content providers to contract on terms that (1) are mutually agreeable to both parties, (2) are available to all prospective consumers, and (3) do not impose significantly externalities on third parties, is inimical to promoting equality of opportunity. Moreover, given the twosided nature of the Internet access market, a blanket rule forbidding broadband service providers from offering quality of service to content providers (and charging for it) would likely harm endusers and certain content providers.
Magnetic properties of -FeCr alloy as calculated with the charge and spin self-consistent KKR(CPA) method
Magnetic properties of a FeCr alloy calculated with
the charge and spin self- consistent Korringa-Kohn-Rostoker (KKR) and combined
with coherent potential approximation (KKR-CPA) methods are reported.
Non-magnetic state as well as various magnetic orderings were considered, i.e.
ferromagnetic (FM) and more complex anti-parallel (called APM) arrangements for
selected sublattices, as follows from the symmetry analysis. It has been shown
that the Stoner criterion applied to non-magnetic density of states at the
Fermi energy, is satisfied for Fe atoms situated on all five lattice
sites, while it is not fulfilled for all Cr atoms. In FM and APM states, the
values of magnetic moments on Fe atoms occupying various sites are dispersed
between 0 and 2.5 , and they are proportional to the number of Fe atoms
in the nearest-neighbor shell. Magnetic moments of Cr atoms havin much smaller
values were found to be coupled antiparallel to those of Fe atoms. The average
value of the magnetic moment per atom was found to be that
is by a factor of 4 larger than the experimental value found for a
FeCr sample. Conversely, admitting an anti-
parallel ordering (APM model) on atoms situated on C and D sites, according to
the group theory and symmetry analysis results, yielded a substantial reduction
of to 0.20 $\mu_B$. Further diminution of to 0.15 ,
which is very close to the experimental value of 0.14 , has been
achieved with the KKR-CPA calculations by considering a chemical disorder on
sites B, C and D
Extending Hybrid CSP with Probability and Stochasticity
Probabilistic and stochastic behavior are omnipresent in computer controlled
systems, in particular, so-called safety-critical hybrid systems, because of
fundamental properties of nature, uncertain environments, or simplifications to
overcome complexity. Tightly intertwining discrete, continuous and stochastic
dynamics complicates modelling, analysis and verification of stochastic hybrid
systems (SHSs). In the literature, this issue has been extensively
investigated, but unfortunately it still remains challenging as no promising
general solutions are available yet. In this paper, we give our effort by
proposing a general compositional approach for modelling and verification of
SHSs. First, we extend Hybrid CSP (HCSP), a very expressive and process
algebra-like formal modeling language for hybrid systems, by introducing
probability and stochasticity to model SHSs, which is called stochastic HCSP
(SHCSP). To this end, ordinary differential equations (ODEs) are generalized by
stochastic differential equations (SDEs) and non-deterministic choice is
replaced by probabilistic choice. Then, we extend Hybrid Hoare Logic (HHL) to
specify and reason about SHCSP processes. We demonstrate our approach by an
example from real-world.Comment: The conference version of this paper is accepted by SETTA 201
CP violating asymmetry in decays
The CP violating asymmetry from the decay rates of
charged Higgs bosons into the lightest neutral Higgs boson and a boson
is calculated and discussed in the complex MSSM. The contributions from all
complex phases are considered, especially from the top-squark trilinear
coupling, which induces a large contribution to the CP asymmetry.Comment: 19 pages, 10 figures, version published in JHE
Determination of Strong-Interaction Widths and Shifts of Pionic X-Rays with a Crystal Spectrometer
Pionic 3d-2p atomic transitions in F, Na, and Mg have been studied using a bent crystal spectrometer. The pionic atoms were formed in the production target placed in the external proton beam of the Space Radiation Effects Laboratory synchrocyclotron. The observed energies and widths of the transitions are E=41679(3) eV and Γ=21(8) eV, E=62434(18) eV and Γ=22(80) eV, E=74389(9) eV and Γ=67(35) eV, in F, Na, and Mg, respectively. The results are compared with calculations based on a pion-nucleus optical potential
Business, Leadership And Education: A Case For More Business Engagement In Higher Education
Institutions of higher education prepare and develop students for the workforce, and in the coming decade, the challenge of workforce preparation will increase as the current workforce is retiring during a time of economic growth. Traditional higher education practice tasks faculty with developing appropriate curricula for students that will adequately prepare them for employment and leadership within an organization, but often this development lacks direct industry input into course content and design resulting in a gap between industry needs and graduate skills. This study addresses both current and perceived future educational and leadership needs of a workforce in an 11 county region in the north central United States. It explores potential strategies for mitigating the skills gap as it relates to organizational leadership skills, the evolving roles of faculty, and curriculum design and application, and develops a community alliance model for business, leadership, and education
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