58 research outputs found
First results from the Very Small Array -- I. Observational methods
The Very Small Array (VSA) is a synthesis telescope designed to image faint
structures in the cosmic microwave background on degree and sub-degree angular
scales. The VSA has key differences from other CMB interferometers with the
result that different systematic errors are expected. We have tested the
operation of the VSA with a variety of blank-field and calibrator observations
and cross-checked its calibration scale against independent measurements. We
find that systematic effects can be suppressed below the thermal noise level in
long observations; the overall calibration accuracy of the flux density scale
is 3.5 percent and is limited by the external absolute calibration scale.Comment: 9 pages, 10 figures, MNRAS in press (Minor revisions
Searching for non-Gaussianity in the VSA data
We have tested Very Small Array (VSA) observations of three regions of sky
for the presence of non-Gaussianity, using high-order cumulants, Minkowski
functionals, a wavelet-based test and a Bayesian joint power
spectrum/non-Gaussianity analysis. We find the data from two regions to be
consistent with Gaussianity. In the third region, we obtain a 96.7% detection
of non-Gaussianity using the wavelet test. We perform simulations to
characterise the tests, and conclude that this is consistent with expected
residual point source contamination. There is therefore no evidence that this
detection is of cosmological origin. Our simulations show that the tests would
be sensitive to any residual point sources above the data's source subtraction
level of 20 mJy. The tests are also sensitive to cosmic string networks at an
rms fluctuation level of (i.e. equivalent to the best-fit observed
value). They are not sensitive to string-induced fluctuations if an equal rms
of Gaussian CDM fluctuations is added, thereby reducing the fluctuations due to
the strings network to rms . We especially highlight the usefulness
of non-Gaussianity testing in eliminating systematic effects from our data.Comment: Minor corrections; accepted for publication to MNRA
Estimating the bispectrum of the Very Small Array data
We estimate the bispectrum of the Very Small Array data from the compact and
extended configuration observations released in December 2002, and compare our
results to those obtained from Gaussian simulations. There is a slight excess
of large bispectrum values for two individual fields, but this does not appear
when the fields are combined. Given our expected level of residual point
sources, we do not expect these to be the source of the discrepancy. Using the
compact configuration data, we put an upper limit of 5400 on the value of f_NL,
the non-linear coupling parameter, at 95 per cent confidence. We test our
bispectrum estimator using non-Gaussian simulations with a known bispectrum,
and recover the input values.Comment: 17 pages, 16 figures, replaced with version accepted by MNRAS.
Primordial bispectrum recalculated and figure 11 change
First results from the Very Small Array -- III. The CMB power spectrum
We present the power spectrum of the fluctuations in the cosmic microwave
background detected by the Very Small Array (VSA) in its first season of
observations in its compact configuration. We find clear detections of first
and second acoustic peaks at l~200 and l~550, plus detection of power on scales
up to l=800. The VSA power spectrum is in very good agreement with the results
of the Boomerang, Dasi and Maxima telescopes despite the differing potential
systematic errors.Comment: 10 pages, 6 figure, MNRAS in press. (Minor revisions - accepted 17
December 2002
Divulgación científica: aprender haciendo y coevaluando
[EN] Objective/s: To assess the process of acquiring competence in scientific dissemination among students at
the La Fe School of Nursing in Valencia.
Development of the innovation: Four cycles of group work were implemented. Each group creates scientific
dissemination documents focused on a work topic related to the subject of Physical Activity and Health
Promotion in Nursing. Each work is co-evaluated by peers using an analytical rubric, with 10 learning
domains, and this evaluation is returned before the creation of the next document. At the end of the 4 work
cycles, 8 teachers external to the activity assessed the dissemination papers using the same co-assessment
rubric, anonymously and blinded.
Results: Acquisition of competence in the domains studied showed significant improvements with
repetition of the tasks. The study differentiated by groups shows that learning becomes uniform in 6 of the
10 competencies, showing significant differences in learning between groups in 4 of the domains.
Conclusions: Repetition of the task and co-assessment improves the acquisition of competences in science
popularisation. The moment of greatest evolution occurs between the second and third repetition of the
task, slowing down this benefit between the third and fourth repetition.[ES] Objetivo: Valorar el proceso de adquisición de la competencia en divulgación científica del alumnado de la Escuela de Enfermería de la Fe de Valencia. Desarrollo de la innovación: Se implementaron cuatro ciclos de trabajo grupal. Cada grupo crea documentos de divulgación científica centrados en una temática de trabajo relacionada con la asignatura de Actividad física y Promoción de la salud en Enfermería. Cada trabajo es coevaluado por pares mediante rúbrica analítica, con 10 dominios de aprendizaje, y se devuelve esta evaluación antes de la creación del siguiente documento. Finalizados los 4 ciclos de trabajo, 8 docentes externos a la actividad valoraron los documentos de divulgación utilizando la misma rúbrica de coevaluación, de forma anónima y cegada. Resultados: La adquisición de competencia en los dominios estudiados mostraron mejoras significativas con la repetición de las tareas. En el estudio diferenciado por grupos se muestra que el aprendizaje se vuelve uniformen en 6 de las 10 competencias, mostrando diferencias significativas de aprendizaje entre grupos en 4 de los dominios. Conclusiones: La repetición de la tarea y la coevaluación mejora la adquisición de competencias en divulgación científica. El momento de mayor evolución se produce entre la segunda y tercera repetición de la tarea, ralentizando este beneficio entre la tercera y cuarta repetición.García-Martinez, P.; Saus-Ortega, C.; García-Molina, P.; Balaguer-López, E.; Celda-Belinchón, L.; Sosa-Palanca, E.; Buck Sainz-Rozas, P.... (2022). Divulgación científica: aprender haciendo y coevaluando. Editorial Universitat Politècnica de València. 161-172. https://doi.org/10.4995/INRED2022.2022.1583516117
Cosmological parameter estimation using Very Small Array data out to l=1500
We estimate cosmological parameters using data obtained by the Very Small
Array (VSA) in its extended configuration, in conjunction with a variety of
other CMB data and external priors. Within the flat CDM model, we find
that the inclusion of high resolution data from the VSA modifies the limits on
the cosmological parameters as compared to those suggested by WMAP alone, while
still remaining compatible with their estimates. We find that , , , , and
for WMAP and VSA when no external prior is
included.On extending the model to include a running spectral index of density
fluctuations, we find that the inclusion of VSA data leads to a negative
running at a level of more than 95% confidence (),
something which is not significantly changed by the inclusion of a stringent
prior on the Hubble constant. Inclusion of prior information from the 2dF
galaxy redshift survey reduces the significance of the result by constraining
the value of . We discuss the veracity of this result in the
context of various systematic effects and also a broken spectral index model.
We also constrain the fraction of neutrinos and find that at
95% confidence which corresponds to when all neutrino
masses are the equal. Finally, we consider the global best fit within a general
cosmological model with 12 parameters and find consistency with other analyses
available in the literature. The evidence for is only marginal
within this model
High sensitivity measurements of the CMB power spectrum with the extended Very Small Array
We present deep Ka-band ( GHz) observations of the CMB made
with the extended Very Small Array (VSA). This configuration produces a
naturally weighted synthesized FWHM beamwidth of arcmin which covers
an -range of 300 to 1500. On these scales, foreground extragalactic
sources can be a major source of contamination to the CMB anisotropy. This
problem has been alleviated by identifying sources at 15 GHz with the Ryle
Telescope and then monitoring these sources at 33 GHz using a single baseline
interferometer co-located with the VSA. Sources with flux densities \gtsim 20
mJy at 33 GHz are subtracted from the data. In addition, we calculate a
statistical correction for the small residual contribution from weaker sources
that are below the detection limit of the survey.
The CMB power spectrum corrected for Galactic foregrounds and extragalactic
point sources is presented. A total -range of 150-1500 is achieved by
combining the complete extended array data with earlier VSA data in a compact
configuration. Our resolution of allows the first 3
acoustic peaks to be clearly delineated. The is achieved by using mosaiced
observations in 7 regions covering a total area of 82 sq. degrees. There is
good agreement with WMAP data up to where WMAP data run out of
resolution. For higher -values out to , the agreement in
power spectrum amplitudes with other experiments is also very good despite
differences in frequency and observing technique.Comment: 16 pages. Accepted in MNRAS (minor revisions
First results from the Very Small Array -- II. Observations of the CMB
We have observed the cosmic microwave background temperature fluctuations in
eight fields covering three separated areas of sky with the Very Small Array at
34 GHz. A total area of 101 square degrees has been imaged, with sensitivity on
angular scales 3.6 - 0.4 degrees (equivalent to angular multipoles l=150-900).
We describe the field selection and observing strategy for these observations.
In the full-resolution images (with synthesised beam of FWHM ~ 17 arcmin) the
thermal noise is typically 45 microK and the CMB signal typically 55 microK.
The noise levels in each field agree well with the expected thermal noise level
of the telescope, and there is no evidence of any residual systematic features.
The same CMB features are detected in separate, overlapping observations.
Discrete radio sources have been detected using a separate 15 GHz survey and
their effects removed using pointed follow-up observations at 34 GHz. We
estimate that the residual confusion noise due to unsubtracted radio sources is
less than 14 mJy/beam (15 microK in the full-resolution images), which added in
quadrature to the thermal noise increases the noise level by 6 %. We estimate
that the rms contribution to the images from diffuse Galactic emission is less
than 6 microK. We also present images which are convolved to maximise the
signal-to-noise of the CMB features and are co-added in overlapping areas, in
which the signal-to-noise of some individual CMB features exceeds 8.Comment: 11 pages, 5 figures, accepted for publication in MNRAS. Replaces
original version - more detailed abstract, corrected typo
The CMB power spectrum out to l=1400 measured by the VSA
We have observed the cosmic microwave background (CMB) in three regions of
sky using the Very Small Array (VSA) in an extended configuration with antennas
of beamwidth 2 degrees at 34 GHz. Combined with data from previous VSA
observations using a more compact array with larger beamwidth, we measure the
power spectrum of the primordial CMB anisotropies between angular multipoles l
= 160 - 1400. Such measurements at high l are vital for breaking degeneracies
in parameter estimation from the CMB power spectrum and other cosmological
data. The power spectrum clearly resolves the first three acoustic peaks, shows
the expected fall off in power at high l and starts to constrain the position
and height of a fourth peak.Comment: 6 pages with 5 figures, MNRAS in press (minor corrections
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