5,200 research outputs found
Computing extinction maps of star nulling interferometers
Herein is discussed the performance of spaceborne nulling interferometers
searching for extra-solar planets, in terms of their extinction maps projected
on-sky. In particular, it is shown that the designs of Spatial Filtering (SF)
and Achromatic Phase Shifter (APS) subsystems, both required to achieve planet
detection and characterization, can sensibly affect the nulling maps produced
by a simple Bracewell interferometer. Analytical relationships involving cross
correlation products are provided and numerical simulations are performed,
demonstrating marked differences in the aspect of extinction maps and the
values of attained fringes contrasts. It is concluded that depending on their
basic principles and designs, FS and APS will result in variable capacities for
serendipitous discoveries of planets orbiting around their parent star. The
mathematical relationships presented in this paper are assumed to be general,
i.e. they should apply to other types of multi-apertures nulling
interferometers.Comment: 10 pages, 5 figure
Fluctuations, dissipation and the dynamical Casimir effect
Vacuum fluctuations provide a fundamental source of dissipation for systems
coupled to quantum fields by radiation pressure. In the dynamical Casimir
effect, accelerating neutral bodies in free space give rise to the emission of
real photons while experiencing a damping force which plays the role of a
radiation reaction force. Analog models where non-stationary conditions for the
electromagnetic field simulate the presence of moving plates are currently
under experimental investigation. A dissipative force might also appear in the
case of uniform relative motion between two bodies, thus leading to a new kind
of friction mechanism without mechanical contact. In this paper, we review
recent advances on the dynamical Casimir and non-contact friction effects,
highlighting their common physical origin.Comment: 39 pages, 4 figures. Review paper to appear in Lecture Notes in
Physics, Volume on Casimir Physics, edited by Diego Dalvit, Peter Milonni,
David Roberts, and Felipe da Rosa. Minor changes, a reference adde
Use of Lagrange multipliers to combine 1D variable kinematic finite elements
This paper deals with finite element problems that require different formulations in different subregions of the problem domain. Attention is focused on a variable kinematic, one-dimensional, finite element formulation which was recently introduced by the first author. Finite elements with different order of expansion over the cross-section plane are employed in different regions of the 1D domain. Lagrange multipliers are used to "mix" different elements. Constraints are imposed on displacement variables at a number of points whose location over the cross-section is a parameter of the method. The number and the location of the connection points can be modified until convergence is reached. The method is first assessed by encompassing sample problems and then it is applied to analyze a number of structures which requires different formulations in different regions. Compact, thin-walled and bridge-like sections are considered to show the effectiveness of the methodology proposed as well as its advantages to solve practical problems
Development of a strontium optical lattice clock for the SOC mission on the ISS
Ultra-precise optical clocks in space will allow new studies in fundamental
physics and astronomy. Within an European Space Agency (ESA) program, the Space
Optical Clocks (SOC) project aims to install and to operate an optical lattice
clock on the International Space Station (ISS) towards the end of this decade.
It would be a natural follow-on to the ACES mission, improving its performance
by at least one order of magnitude. The payload is planned to include an
optical lattice clock, as well as a frequency comb, a microwave link, and an
optical link for comparisons of the ISS clock with ground clocks located in
several countries and continents. Within the EU-FP7-SPACE-2010-1 project no.
263500, during the years 2011-2015 a compact, modular and robust strontium
lattice optical clock demonstrator has been developed. Goal performance is a
fractional frequency instability below 1x10^{-15}, tau^{-1/2} and a fractional
inaccuracy below 5x10^{-17}. Here we describe the current status of the
apparatus' development, including the laser subsystems. Robust preparation of
cold {88}^Sr atoms in a second stage magneto-optical trap (MOT) is achieved.Comment: 27 Pages, 15 figures, Comptes Rendus Physique 201
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