3,992 research outputs found
Apparatus for disintegrating kidney stones
The useful life of the wire probe in an ultrasonic kidney stone disintegration instrument is enhanced and prolonged by attaching the wire of the wire probe to the tip of an ultrasonic transducer by means of a clamping arrangement. Additionally, damping material is applied to the wire probe in the form of a damper tube through which the wire probe passes in the region adjacent the transducer tip. The damper tube extends outwardly from the transducer tip a predetermined distance, terminating in a resilient soft rubber joint. Also, the damper tube is supported intermediate its length by a support member. The damper system thus acts to inhibit lateral vibrations of the wire in the region of the transducer tip while providing little or no damping to the linear vibrations imparted to the wire by the transducer
Measuring the hydrostatic mass bias in galaxy clusters by combining Sunyaev-Zel'dovich and CMB lensing data
The cosmological parameters prefered by the cosmic microwave background (CMB)
primary anisotropies predict many more galaxy clusters than those that have
been detected via the thermal Sunyaev-Zeldovich (tSZ) effect. This tension has
attracted considerable attention since it could be evidence of physics beyond
the simplest CDM model. However, an accurate and robust calibration of
the mass-observable relation for clusters is necessary for the comparison,
which has been proven difficult to obtain so far. Here, we present new
contraints on the mass-pressure relation by combining tSZ and CMB lensing
measurements about optically-selected clusters. Consequently, our galaxy
cluster sample is independent from the data employed to derive cosmological
constrains. We estimate an average hydrostatic mass bias of , with no significant mass nor redshift evolution. This value greatly
reduces the tension between the predictions of CDM and the observed
abundance of tSZ clusters while being in agreement with recent estimations from
tSZ clustering. On the other hand, our value for is higher than the
predictions from hydro-dynamical simulations. This suggests the existence of
mechanisms driving large departures from hydrostatic equilibrium and that are
not included in state-of-the-art simulations, and/or unaccounted systematic
errors such as biases in the cluster catalogue due to the optical selection.Comment: 4 pages, 3 figure
How closely do baryons follow dark matter on large scales?
We investigate the large-scale clustering and gravitational interaction of
baryons and dark matter (DM) over cosmic time using a set of collisionless
N-body simulations. Both components, baryons and DM, are evolved from distinct
primordial density and velocity power spectra as predicted by early-universe
physics. We first demonstrate that such two-component simulations require an
unconventional match between force and mass resolution (i.e. force softening on
at least the mean particle separation scale). Otherwise, the growth on any
scale is not correctly recovered because of a spurious coupling between the two
species at the smallest scales. With these simulations, we then demonstrate how
the primordial differences in the clustering of baryons and DM are
progressively diminished over time. In particular, we explicitly show how the
BAO signature is damped in the spatial distribution of baryons and imprinted in
that of DM. This is a rapid process, yet it is still not fully completed at low
redshifts. On large scales, the overall shape of the correlation function of
baryons and DM differs by 2% at z = 9 and by 0.2% at z = 0. The differences in
the amplitude of the BAO peak are approximately a factor of 5 larger: 10% at z
= 9 and 1% at z = 0. These discrepancies are, however, smaller than effects
expected to be introduced by galaxy formation physics in both the shape of the
power spectrum and in the BAO peak, and are thus unlikely to be detected given
the precision of the next generation of galaxy surveys. Hence, our results
validate the standard practice of modelling the observed galaxy distribution
using predictions for the total mass clustering in the Universe.Comment: 9 pages, 6 figures. Replaced with version published in MNRA
How BAO measurements can fail to detect quintessence
We model the nonlinear growth of cosmic structure in different dark energy
models, using large volume N-body simulations. We consider a range of
quintessence models which feature both rapidly and slowly varying dark energy
equations of state, and compare the growth of structure to that in a universe
with a cosmological constant. The adoption of a quintessence model changes the
expansion history of the universe, the form of the linear theory power spectrum
and can alter key observables, such as the horizon scale and the distance to
last scattering. The difference in structure formation can be explained to
first order by the difference in growth factor at a given epoch; this scaling
also accounts for the nonlinear growth at the 15% level. We find that
quintessence models which feature late , rapid transitions towards
in the equation of state, can have identical baryonic acoustic
oscillation (BAO) peak positions to those in CDM, despite being very
different from CDM both today and at high redshifts .
We find that a second class of models which feature non-negligible amounts of
dark energy at early times cannot be distinguished from CDM using
measurements of the mass function or the BAO. These results highlight the need
to accurately model quintessence dark energy in N-body simulations when testing
cosmological probes of dynamical dark energy.Comment: 10 pages, 7 figures, to appear in the Invisible Univers International
Conference AIP proceedings serie
The One-Loop Matter Bispectrum in the Effective Field Theory of Large Scale Structures
Given the importance of future large scale structure surveys for delivering
new cosmological information, it is crucial to reliably predict their
observables. The Effective Field Theory of Large Scale Structures (EFTofLSS)
provides a manifestly convergent perturbative scheme to compute the clustering
of dark matter in the weakly nonlinear regime in an expansion in , where is the wavenumber of interest and is the
wavenumber associated to the nonlinear scale. It has been recently shown that
the EFTofLSS matches to level the dark matter power spectrum at redshift
zero up to Mpc and Mpc at one
and two loops respectively, using only one counterterm that is fit to data.
Similar results have been obtained for the momentum power spectrum at one loop.
This is a remarkable improvement with respect to former analytical techniques.
Here we study the prediction for the equal-time dark matter bispectrum at one
loop. We find that at this order it is sufficient to consider the same
counterterm that was measured in the power spectrum. Without any remaining free
parameter, and in a cosmology for which is smaller than in the
previously considered cases (), we find that the prediction from
the EFTofLSS agrees very well with -body simulations up to Mpc, given the accuracy of the measurements, which is of order a few
percent at the highest 's of interest. While the fit is very good on average
up to Mpc, the fit performs slightly worse on
equilateral configurations, in agreement with expectations that for a given
maximum , equilateral triangles are the most nonlinear.Comment: 39 pages, 12 figures; v2: JCAP published version, improved numerical
data, added explanation and clarification
Status of superpressure balloon technology in the United States
Superpressure mylar balloon technology in United States - applications, balloon size criteria, and possible improvement
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