7,739 research outputs found
Gravitational perturbations from oscillons and transients after inflation
We study the scalar and tensor perturbations generated by the fragmentation
of the inflaton condensate into oscillons or transients after inflation, using
nonlinear classical lattice simulations. Without including the backreaction of
metric perturbations, we find that the magnitude of scalar metric perturbations
never exceeds a few , whereas the maximal strength of the
gravitational wave signal today is for standard
post-inflationary expansion histories. We provide parameter scalings for the
-attractor models of inflation, which can be easily applied to other
models. We also discuss the likelihood of primordial black hole formation, as
well as conditions under which the gravitational wave signal can be at
observationally interesting frequencies and amplitudes.
Finally, we provide an upper bound on the frequency of the peak of the
gravitational wave signal, which applies to all preheating scenarios.Comment: 18 pages, 8 figure
The charged inflaton and its gauge fields: preheating and initial conditions for reheating
We calculate particle production during inflation and in the early stages of
reheating after inflation in models with a charged scalar field coupled to
Abelian and non-Abelian gauge fields. A detailed analysis of the power spectra
of primordial electric fields, magnetic fields and charge fluctuations at the
end of inflation and preheating is provided. We carefully account for the Gauss
constraints during inflation and preheating, and clarify the role of the
longitudinal components of the electric field. We calculate the timescale for
the back-reaction of the produced gauge fields on the inflaton condensate,
marking the onset of non-linear evolution of the fields. We provide a
prescription for initial conditions for lattice simulations necessary to
capture the subsequent nonlinear dynamics. On the observational side, we find
that the primordial magnetic fields generated are too small to explain the
origin of magnetic fields on galactic scales and the charge fluctuations are
well within observational bounds for the models considered in this paper.Comment: 48 pages, 6 figures, 2 appendices, v3: references added, minor
changes to text, to appear in JCA
Impact of Si nanocrystals in a-SiOx<Er> in C-Band emission for applications in resonators structures
Si nanocrystals (Si-NC) in a-SiOx were created by high temperature
annealing. Si-NC samples have large emission in a broadband region, 700nm to
1000nm. Annealing temperature, annealing time, substrate type, and erbium
concentration is studied to allow emission at 1550 nm forsamples with erbium.
Emission in the C-Band region is largely reduced by the presence of Si-NC. This
reduction may be due to less efficient energy transfer processes from the
nanocrystals than from the amorphous matrix to the Er3+ ions, perhaps due to
the formation of more centro-symmetric Er3+ sites at the nanocrystal surfaces
or to very different optimal erbium concentrations between amorphous and
crystallized samples.Comment: 3 pages, 4 figure
Part of the D - dimensional Spiked harmonic oscillator spectra
The pseudoperturbative shifted - l expansion technique PSLET [5,20] is
generalized for states with arbitrary number of nodal zeros. Interdimensional
degeneracies, emerging from the isomorphism between angular momentum and
dimensionality of the central force Schrodinger equation, are used to construct
part of the D - dimensional spiked harmonic oscillator bound - states. PSLET
results are found to compare excellenly with those from direct numerical
integration and generalized variational methods [1,2].Comment: Latex file, 20 pages, to appear in J. Phys. A: Math. & Ge
Bayesian Learning Networks Approach to Cybercrime Detection
The growing dependence of modern society on telecommunication and information networks has become inevitable. The increase in the number of interconnected networks to the Internet has led to an increase in security threats and cybercrimes such as Distributed Denial of Service (DDoS) attacks. Any Internet based attack typically is prefaced by a reconnaissance probe process, which might take just a few minutes, hours, days, or even months before the attack takes place. In order to detect distributed network attacks as early as possible, an under research and development probabilistic approach, which is known by Bayesian networks has been proposed. This paper shows how probabilistically Bayesian network detects communication network attacks, allowing for generalization of Network Intrusion Detection Systems (NIDSs). Learning Agents which deploy Bayesian network approach are considered to be a promising and useful tool in determining suspicious early events of Internet threats and consequently relating them to the following occurring activities.Peer reviewe
Effective polar potential in the central force Schrodinger equation
The angular part of the Schrodinger equation for a central potential is
brought to the one-dimensional 'Schrodinger form' where one has a kinetic
energy plus potential energy terms. The resulting polar potential is seen to be
a family of potentials characterized by the square of the magnetic quantum
number m. It is demonstrated that this potential can be viewed as a confining
potential that attempts to confine the particle to the xy-plane, with a
strength that increases with increasing m. Linking the solutions of the
equation to the conventional solutions of the angular equation, i.e. the
associated Legendre functions, we show that the variation in the spatial
distribution of the latter for different values of the orbital angular quantum
number l can be viewed as being a result of 'squeezing' with different
strengths by the introduced 'polar potential'.Comment: This is an author-created, un-copyedited version of an article
accepted for publication in European Journal of Physic
Sharing the Burden of GHG Reductions
Abstract and PDF report are also available on the MIT Joint Program on the Science and Policy of Global Change website (http://globalchange.mit.edu/).The G8 countries propose a goal of a 50% reduction in global emissions by 2050, in an effort that needs to take account of other agreements specifying that developing countries are to be provided with incentives to action and protected from the impact of measures taken by others. To help inform international negotiations of measures to achieve these goals we develop a technique for endogenously estimating the allowance allocations and associated financial transfers necessary to achieve predetermined distributional outcomes and apply it in the MIT Emissions Prediction and Policy Analysis (EPPA) model. Possible burden sharing agreements are represented by different allowance allocations (and resulting financial flows) in a global cap-and-trade system. Cases studied include agreements that allocate the burden based on simple allocation rules found in current national proposals and alternatives that specify national equity goals for both developing and developed countries.
The analysis shows the ambitious nature of this reduction goal: universal participation will be necessary and the welfare costs can be both substantial and wildly different across regions depending on the allocation method chosen. The choice of allocation rule is shown to affect the magnitude of the task and required emissions price because of income effects. If developing countries are fully compensated for the costs of mitigation then the welfare costs to developed countries, if shared equally, are around 2% in 2020, rising to some 10% in 2050, and the implied financial transfers are large—over 3 trillion in 2050. For success in dealing with the climate threat any negotiation of long-term goals and paths to achievement need to be grounded in a full understanding of the substantial amounts at stake.Development of the EPPA model used has been supported by the U.S. Department of Energy, U.S. Environmental Protection Agency and U.S. National Science Foundation, and by a consortium of industry and foundation sponsors of the MIT Joint Program on the Science and Policy of Global Change
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