555 research outputs found
Optical read out and feedback cooling of a nanostring optomechanical cavity
Optical measurement of the motion of a 940 kHz mechanical resonance of a
silicon nitride nanostring resonator is demonstrated with a read out noise
imprecision reaching 37 dB below that of the resonator's zero-point
fluctuations. Via intensity modulation of the optical probe laser, radiation
pressure feedback is used to cool and damp the mechanical mode from an initial
room temperature occupancy of (K)
down to a phonon occupation of , representing a
mode temperature of mK. The five decades of cooling is enabled
by the system's large single-photon cooperativity and high
quantum efficiency of optical motion detection ().Comment: 13 pages, 13 figure
2D-FFTLog: Efficient computation of real space covariance matrices for galaxy clustering and weak lensing
Accurate covariance matrices for two-point functions are critical for
inferring cosmological parameters in likelihood analyses of large-scale
structure surveys. Among various approaches to obtaining the covariance,
analytic computation is much faster and less noisy than estimation from data or
simulations. However, the transform of covariances from Fourier space to real
space involves integrals with two Bessel integrals, which are numerically slow
and easily affected by numerical uncertainties. Inaccurate covariances may lead
to significant errors in the inference of the cosmological parameters. In this
paper, we introduce a 2D-FFTLog algorithm for efficient, accurate and
numerically stable computation of non-Gaussian real space covariances for both
3D and projected statistics. The 2D-FFTLog algorithm is easily extended to
perform real space bin-averaging. We apply the algorithm to the covariances for
galaxy clustering and weak lensing for a Dark Energy Survey Year 3-like and a
Rubin Observatory's Legacy Survey of Space and Time Year 1-like survey, and
demonstrate that for both surveys, our algorithm can produce numerically stable
angular bin-averaged covariances with the flat sky approximation, which are
sufficiently accurate for inferring cosmological parameters. The code CosmoCov
for computing the real space covariances with or without the flat sky
approximation is released along with this paper.Comment: MNRAS accepted; 13 pages, 3 figures, 2 tables; fixed a typo in Eq.41;
2DFFTLog code available at https://github.com/xfangcosmo/2DFFTLog ; 3x2pt
covariance code CosmoCov at https://github.com/CosmoLike/CosmoCo
A new third-order cosmic shear statistics: Separating E/B-mode correlations on a finite interval
Decomposing the shear signal into E and B-modes properly, i.e. without
leakage of B-modes into the E-mode signal and vice versa, has been a
long-standing problem in weak gravitational lensing. At the two-point level
this problem was resolved by developing the so-called ring statistics, and
later the COSEBIs; however, extending these concepts to the three-point level
is far from trivial. Currently used methods to decompose three-point shear
correlation functions (3PCFs) into E- and B-modes require knowledge of the 3PCF
down to arbitrary small scales. This implies that the 3PCF needs to be modeled
on scales smaller than the minimum separation of 2 galaxies and subsequently
will be biased towards the model, or, in the absence of a model, the statistics
is affected by E/B-mode leakage (or mixing). In this paper we derive a new
third-order E/B-mode statistic that performs the decomposition using the 3PCF
only on a finite interval, and thereby is free of any E/B-mode leakage while at
the same time relying solely on information from the data. In addition, we
relate this third-order ring statistics to the convergence field, thereby
enabling a fast and convenient calculation of this statistic from numerical
simulations. We note that our new statistics should be applicable to
corresponding E/B-mode separation problems in the CMB polarization field
Leading the Way, but Also Following the Trend : The Slovak National Party
Despite spells outside parliament, with its blend of nationalist and populist appeals the Slovak National Party (SNS) has been a prominent fixture on Slovakia’s political scene for three decades. Unlike some of the newer parties in Slovakia and across the region, partly as a product of the point of its (re-)creation, SNS has a comparable organizational density to most established parties in the country and has invested in party branches and recruiting members. Although ordinary members exercised some power and influence during the fissiparous era of the early 2000s, SNS has been notable for the role played by its leader in decision-making and steering the party. Each leader placed their stamp on the projection, pitch and functioning of the party, both as a decision-making organization and an electoral vehicle. Ordinary members have been largely—but not exclusively—relegated to the role of cheerleaders and campaigners for the party’s tribunes; a situation which has not changed significantly in the era of social media. The pre-eminent position of the leader and the limited options for “voice” has led unsuccessful contenders for top posts and their supporters to opt instead for “exit.” Despite having some of the traits of the mass party and having engaged in some of the activities common for mass parties, especially in the earlier years of its existence, in more recent times in particular, SNS falls short of the mass party model both in aspiration and reality
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