116,727 research outputs found
Cosmological Imprints of a Generalized Chaplygin Gas Model for the Early Universe
We propose a phenomenological model for the early universe where there is a
smooth transition between an early "quintessence" phase and a radiation
dominated era. The matter content is modelled by an appropriately modified
Chaplygin gas for the early universe. We constrain the model observationally by
mapping the primordial power spectrum of the scalar perturbations to the latest
data of WMAP7. We compute as well the spectrum of the primordial gravitational
waves as would be measured today. We show that the high frequencies region of
the spectrum depends on the free parameter of the model and most importantly
this region of the spectrum can be within the reach of future gravitational
waves detectors.Comment: 10 pages, 8 figures. RevTex
Constraints on millicharged particles with low threshold germanium detectors at Kuo-Sheng Reactor Neutrino Laboratory
Relativistic millicharged particles () have been proposed in various
extensions to the Standard Model of particle physics. We consider the scenarios
where they are produced at nuclear reactor core and via interactions of
cosmic-rays with the earth's atmosphere. Millicharged particles could also be
candidates for dark matter, and become relativistic through acceleration by
supernova explosion shock waves. The atomic ionization cross section of
with matter are derived with the equivalent photon approximation.
Smoking-gun signatures with significant enhancement in the differential cross
section are identified. New limits on the mass and charge of are
derived, using data taken with a point-contact germanium detector with 500g
mass functioning at an energy threshold of 300~eV at the Kuo-Sheng Reactor
Neutrino Laboratory.Comment: 8 pages, 7 figure
Exponential stabilization of driftless nonlinear control systems using homogeneous feedback
This paper focuses on the problem of exponential stabilization of controllable, driftless systems using time-varying, homogeneous feedback. The analysis is performed with respect to a homogeneous norm in a nonstandard dilation that is compatible with the algebraic structure of the control Lie algebra. It can be shown that any continuous, time-varying controller that achieves exponential stability relative to the Euclidean norm is necessarily non-Lipschitz. Despite these restrictions, we provide a set of constructive, sufficient conditions for extending smooth, asymptotic stabilizers to homogeneous, exponential stabilizers. The modified feedbacks are everywhere continuous, smooth away from the origin, and can be extended to a large class of systems with torque inputs. The feedback laws are applied to an experimental mobile robot and show significant improvement in convergence rate over smooth stabilizers
Exact analytical approach to differential equations with variable coefficients
This paper shows how to build a formal analytical solution for a differential
equation of arbitrary order and with variable coefficients. It proofs that the
most known approximated solutions for such a problem can be derived from the
analytical expression presented in the paper. The formalism can be easily
extended to the infinite dimensional case such as the quantum time-dependent
Hamiltonian problem.Comment: 16 pages, 4 figure
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