518 research outputs found
The effect of internal pipe wall roughness on the accuracy of clamp-on ultrasonic flow meters
Clamp-on transit-time ultrasonic flowmeters (UFMs) suffer from poor accuracy compared with spool-piece UFMs due to uncertainties that result from the in-field installation process. One of the important sources of uncertainties is internal pipe wall roughness which affects the flow profile and also causes significant scattering of ultrasound. This paper purely focuses on the parametric study to quantify the uncertainties (related to internal pipe wall roughness) induced by scattering of ultrasound and it shows that these effects are large even without taking into account the associated flow disturbances. The flowmeter signals for a reference clamp-on flowmeter setup were simulated using 2-D finite element analysis including simplifying assumptions (to simulate the effect of flow) that were deemed appropriate. The validity of the simulations was indirectly verified by carrying out experiments with different separation distances between ultrasonic probes. The error predicted by the simulations and the experimentally observed errors were in good agreement. Then, this simulation method was applied on pipe walls with rough internal surfaces. For ultrasonic waves at 1 MHz, it was found that compared with smooth pipes, pipes with only a moderately rough internal surface (with 0.2-mm rms and 5-mm correlation length) can exhibit systematic errors of 2 in the flow velocity measurement. This demonstrates that pipe internal surface roughness is a very important factor that limits the accuracy of clamp on UFMs
Refined architecture of the WASP-8 system: a cautionary tale for traditional Rossiter-McLaughlin analysis
Probing the trajectory of a transiting planet across the disk of its star
through the analysis of its Rossiter-McLaughlin effect can be used to measure
the differential rotation of the host star and the true obliquity of the
system. Highly misaligned systems could be particularly conducive to these
mesurements, which is why we reanalysed the HARPS transit spectra of WASP-8b
using the 'Rossiter-McLaughlin effect reloaded' (reloaded RM) technique. This
approach allows us to isolate the local stellar CCF emitted by the
planet-occulted regions. As a result we identified a 35% variation in the
local CCF contrast along the transit chord, which might trace a deepening of
the stellar lines from the equator to the poles. Whatever its origin, such an
effect cannot be detected when analyzing the RV centroids of the
disk-integrated CCFs through a traditional velocimetric analysis of the RM
effect. Consequently it injected a significant bias into the results obtained
by Queloz et al. (2010) for the projected rotational velocity (1.59 km/s) and the sky-projected
obliquity (-123.0). Using our
technique, we measured these values to be =
1.900.05 km/s and = -143.0. We
found no compelling evidence for differential rotation of the star, although
there are hints that WASP-8 is pointing away from us with the stellar poles
rotating about 25% slower than the equator. Measurements at higher accuracy
during ingress/egress will be required to confirm this result. In contrast to
the traditional analysis of the RM effect, the reloaded RM technique directly
extracts the local stellar CCFs, allowing us to analyze their shape and to
measure their RV centroids, unbiased by variations in their contrast or FWHM.Comment: Accepted for publication in A&A. 12 page
Does A Classroom Website Increase Positive Communication And Relationships Between Parents And Teachers?
The research questions addressed in this project was: Does a classroom website increase positive communication and relationships with teachers and parents? It provides readers research regarding the benefits of different communication strategies that can take place between teachers and parents. The project then narrows down to the focus of building a classroom website that will increase communication and build relationships between parents and teachers. Throughout the different chapters, the author describes the benefits, but also the barriers that come with communicating through a classroom website. It provides readers information on several different types of school website designs and classroom website designs. However the author focused on using Dunn and Pete’s Taxonomy of a Classroom Website design to create the website for parents to visit throughout the school year and to learn about their child’s education
Simultaneous transmission and reception on all elements of an array: binary code excitation
Pulse-echo arrays are used in radar, sonar, seismic, medical and non-destructive evaluation. There is a trend to produce arrays with an ever-increasing number of elements. This trend presents two major challenges: (i) often the size of the elements is reduced resulting in a lower signal-to-noise ratio (SNR) and (ii) the time required to record all of the signals that correspond to every transmit–receive path increases. Coded sequences with good autocorrelation properties can increase the SNR while orthogonal sets can be used to simultaneously acquire all of the signals that correspond to every transmit–receive path. However, a central problem of conventional coded sequences is that they cannot achieve good autocorrelation and orthogonality properties simultaneously due to their length being limited by the location of the closest reflectors. In this paper, a solution to this problem is presented by using coded sequences that have receive intervals. The proposed approach can be more than one order of magnitude faster than conventional methods. In addition, binary excitation and quantization can be employed, which reduces the data throughput by roughly an order of magnitude and allows for higher sampling rates. While this concept is generally applicable to any field, a 16-element system was built to experimentally demonstrate this principle for the first time using a conventional medical ultrasound probe
Understanding Astrophysical Noise from Stellar Surface Magneto-Convection
To obtain cm/s precision, stellar surface magneto-convection must be
disentangled from observed radial velocities (RVs). In order to understand and
remove the convective signature, we create Sun-as-a-star model observations
based on a 3D magnetohydrodynamic solar simulation. From these Sun-as-a-star
model observations, we find several line characteristics are correlated with
the induced RV shifts. The aim of this campaign is to feed directly into future
high precision RV studies, such as the search for habitable, rocky worlds, with
forthcoming spectrographs such as ESPRESSO.Comment: 6 pages, 3 figures; presented at the 18th Cambridge Workshop on Cool
Stars, Stellar Systems, and the Sun (CoolStars18); to appear in the
proceedings of Lowell Observatory (9-13 June 2014), edited by G. van Belle &
H. Harris. Updated with correct y-axis units on righthand plot in figure
The Impact of Stellar Surface Magnetoconvection and Oscillations on the Detection of Temperate, Earth-Mass Planets Around Sun-Like Stars
Detecting and confirming terrestrial planets is incredibly difficult due to
their tiny size and mass relative to Sun-like host stars. However, recent
instrumental advancements are making the detection of Earth-like exoplanets
technologically feasible. For example, Kepler and TESS photometric precision
means we can identify Earth-sized candidates (and PLATO in the future will add
many long-period candidates to the list), while spectrographs such as ESPRESSO
and EXPRES (with an aimed radial velocity precision [RV] near 10 cm/s) mean we
will soon reach the instrumental precision required to confirm Earth-mass
planets in the habitable zones of Sun-like stars. However, many astrophysical
phenomena on the surfaces of these host stars can imprint signatures on the
stellar absorption lines used to detect the Doppler wobble induced by planetary
companions. The result is stellar-induced spurious RV shifts that can mask or
mimic planet signals. This review provides a brief overview of how stellar
surface magnetoconvection and oscillations can impact low-mass planet
confirmation and the best-tested strategies to overcome this astrophysical
noise. These noise reduction strategies originate from a combination of
empirical motivation and a theoretical understanding of the underlying physics.
The most recent predications indicate that stellar oscillations for Sun-like
stars may be averaged out with tailored exposure times, while granulation may
need to be disentangled by inspecting its imprint on the stellar line profile
shapes. Overall, the literature suggests that Earth-analog detection should be
possible, with the correct observing strategy and sufficient data collection.Comment: 14 pages, 10 figures, invited review article for a Special Issue on
the "Detection and Characterization of Extrasolar Planets" in Geosciences,
Guest Editors: M. Oshagh, M. and J. Martinez-Frias, accepted on 17 January
201
Trayectoria asistencial en el Trastorno Bipolar
Tesis Doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Medicina, Departamento de Psiquiatría. Fecha de Lectura: 03-06-202
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