266 research outputs found
Non-invasive Monitoring of Intracranial Pressure Using Transcranial Doppler Ultrasonography: Is It Possible?
Although intracranial pressure (ICP) is essential to guide management of patients suffering from acute brain diseases, this signal is often neglected outside the neurocritical care environment. This is mainly attributed to the intrinsic risks of the available invasive techniques, which have prevented ICP monitoring in many conditions affecting the intracranial homeostasis, from mild traumatic brain injury to liver encephalopathy. In such scenario, methods for non-invasive monitoring of ICP (nICP) could improve clinical management of these conditions. A review of the literature was performed on PUBMED using the search keywords 'Transcranial Doppler non-invasive intracranial pressure.' Transcranial Doppler (TCD) is a technique primarily aimed at assessing the cerebrovascular dynamics through the cerebral blood flow velocity (FV). Its applicability for nICP assessment emerged from observation that some TCD-derived parameters change during increase of ICP, such as the shape of FV pulse waveform or pulsatility index. Methods were grouped as: based on TCD pulsatility index; aimed at non-invasive estimation of cerebral perfusion pressure and model-based methods. Published studies present with different accuracies, with prediction abilities (AUCs) for detection of ICP â„20 mmHg ranging from 0.62 to 0.92. This discrepancy could result from inconsistent assessment measures and application in different conditions, from traumatic brain injury to hydrocephalus and stroke. Most of the reports stress a potential advantage of TCD as it provides the possibility to monitor changes of ICP in time. Overall accuracy for TCD-based methods ranges around ±12 mmHg, with a great potential of tracing dynamical changes of ICP in time, particularly those of vasogenic nature.Cambridge Commonwealth, European & International Trust Scholarship (University of Cambridge) provided financial support in the form of Scholarship funding for DC. Woolf Fisher Trust provided financial support in the form of Scholarship funding for JD. Gates Cambridge Trust provided financial support in the form of Scholarship funding for XL. CNPQ provided financial support in the form of Scholarship funding for BCTC (Research Project 203792/2014-9). NIHR Brain Injury Healthcare Technology Co-operative, Cambridge, UK provided financial support in the form of equipment funding for DC, BC and MC. The sponsors had no role in the design or conduct of this manuscript.This is the final version of the article. It first appeared from Springer via http://dx.doi.org/10.1007/s12028-016-0258-
Non-Gaussian bubbles in the sky
We point out a possible generation mechanism of non-Gaussian bubbles in the
sky due to bubble nucleation in the early universe. We consider a curvaton
scenario for inflation and assume that the curvaton field phi, whose energy
density is subdominant during inflation but which is responsible for the
curvature perturbation of the universe, is coupled to another field sigma which
undergoes false vacuum decay through quantum tunneling. For this model, we
compute the skewness of the curvaton fluctuations due to its interaction with
sigma during tunneling, that is, on the background of an instanton solution
that describes false vacuum decay. We find that the resulting skewness of the
curvaton can become large in the spacetime region inside the bubble. We then
compute the corresponding skewness in the statistical distribution of the
cosmic microwave background (CMB) temperature fluctuations. We find a
non-vanishing skewness in a bubble-shaped region in the sky. It can be large
enough to be detected in the near future, and if detected it will bring us
invaluable information about the physics in the early universe.Comment: 6 pages, 6 figure
High Order Correction Terms for The Peak-Peak Correlation Function in Nearly-Gaussian Models
One possible way to investigate the nature of the primordial power spectrum
fluctuations is by investigating the statistical properties of the local
maximum in the density fluctuation fields. In this work we present a study of
the mean correlation function, , and the correlation function for high
amplitude fluctuations (the peak-peak correlation) in a slighlty non-Gaussian
context. From the definition of the correlation excess, we compute the Gaussian
two-point correlation function and, using an expansion in Generalized Hermite
polynomials, we estimate the correlation of high density peaks in a
non-Gaussian field with generic distribution and power spectrum. We also apply
the results obtained to a scale-mixed distribution model, which correspond to a
nearly Gaussian model. The results reveal that, even for a small deviation from
Gaussianity, we can expect high density peaks to be much more correlated than
in a Gaussian field with the same power spectrum. In addition, the calculations
reveal how the amplitude of the peaks in the fluctuations field is related to
the existing correlations. Our results may be used as an additional tool to
investigate the behavior of the N-point correlation function, to understand how
non-Gaussian correlations affect the peak-peak statistics and extract more
information about the statistics of the density field.Comment: Accepted for publication in A&
Wilkinson Microwave Anisotropy Probe 7-yr constraints on fNL with a fast wavelet estimator
A new method to constrain the local non-linear coupling parameter fNL based
on a fast wavelet decomposition is presented. Using a multiresolution wavelet
adapted to the HEALPix pixelization, we have developed a method that is 10^2
times faster than previous estimators based on isotropic wavelets and 10^3
faster than the KSW bispectrum estimator, at the resolution of the Wilkinson
Microwave Anisotropy Probe (WMAP) data. The method has been applied to the WMAP
7-yr V+W combined map, imposing constraints on fNL of -69 < fNL < 65 at the 95
per cent CL. This result has been obtained after correcting for the
contribution of the residual point sources which has been estimated to be fNL =
7 +/- 6. In addition, a Gaussianity analysis of the data has been carried out
using the third order moments of the wavelet coefficients, finding consistency
with Gaussianity. Although the constrainsts imposed on fNL are less stringent
than those found with optimal estimators, we believe that a very fast method,
as the one proposed in this work, can be very useful, especially bearing in
mind the large amount of data that will be provided by future experiments, such
as the Planck satellite. Moreover, the localisation of wavelets allows one to
carry out analyses on different regions of the sky. As an application, we have
separately analysed the two hemispheres defined by the dipolar modulation
proposed by Hoftuft et al. (2009). We do not find any significant asymmetry
regarding the estimated value of fNL in those hemispheres.Comment: 8 pages, 5 figures. Submitted and Accepted for publication in MNRA
Map-making in small field modulated CMB polarisation experiments: approximating the maximum-likelihood method
Map-making presents a significant computational challenge to the next
generation of kilopixel CMB polarisation experiments. Years worth of time
ordered data (TOD) from thousands of detectors will need to be compressed into
maps of the T, Q and U Stokes parameters. Fundamental to the science goal of
these experiments, the observation of B-modes, is the ability to control noise
and systematics. In this paper, we consider an alternative to the
maximum-likelihood method, called destriping, where the noise is modelled as a
set of discrete offset functions and then subtracted from the time-stream. We
compare our destriping code (Descart: the DEStriping CARTographer) to a full
maximum-likelihood map-maker, applying them to 200 Monte-Carlo simulations of
time-ordered data from a ground based, partial-sky polarisation modulation
experiment. In these simulations, the noise is dominated by either detector or
atmospheric 1/f noise. Using prior information of the power spectrum of this
noise, we produce destriped maps of T, Q and U which are negligibly different
from optimal. The method does not filter the signal or bias the E or B-mode
power spectra. Depending on the length of the destriping baseline, the method
delivers between 5 and 22 times improvement in computation time over the
maximum-likelihood algorithm. We find that, for the specific case of single
detector maps, it is essential to destripe the atmospheric 1/f in order to
detect B-modes, even though the Q and U signals are modulated by a half-wave
plate spinning at 5-Hz.Comment: 18 pages, 17 figures, MNRAS accepted v2: content added (inc: table
2), typos correcte
The Rise of Cohabitation in the Southern Cone
This chapter analyses the increase in cohabitation in the Southern Cone (Argentina, Chile and Uruguay) and attempts to determine the extent to which consensual unions and marriages have similar traits or differ in the context of the cohabitation boom (Esteve et al. 2012). The first section of the chapter reviews the historical context of cohabitation in the Southern Cone. The second section uses census and survey data to analyse the trends in conjugal union formation in the three countries during the last 40 years. We analyse the patterns of both childbearing and union formation, as well as the differences between marriage and cohabitation based on educational attainment, labour market participation and household structure. The purpose of this analysis is to better understand whether the behaviour of married and cohabiting women with different characteristics are converging or diverging over time and tentatively, whether more egalitarian gender relationships are emerging in both types of conjugal unions
Cosmological Parameters from the 2003 flight of BOOMERANG
We present the cosmological parameters from the CMB intensity and
polarization power spectra of the 2003 Antarctic flight of the BOOMERANG
telescope. The BOOMERANG data alone constrains the parameters of the
CDM model remarkably well and is consistent with constraints from a
multi-experiment combined CMB data set. We add LSS data from the 2dF and SDSS
redshift surveys to the combined CMB data set and test several extensions to
the standard model including: running of the spectral index, curvature, tensor
modes, the effect of massive neutrinos, and an effective equation of state for
dark energy. We also include an analysis of constraints to a model which allows
a CDM isocurvature admixture.Comment: 18 pages, 10 figures, submitted to Ap
A Measurement of the Angular Power Spectrum of the CMB Temperature Anisotropy from the 2003 Flight of Boomerang
We report on observations of the Cosmic Microwave Background (CMB) obtained
during the January 2003 flight of Boomerang . These results are derived from
195 hours of observation with four 145 GHz Polarization Sensitive Bolometer
(PSB) pairs, identical in design to the four 143 GHz Planck HFI polarized
pixels. The data include 75 hours of observations distributed over 1.84% of the
sky with an additional 120 hours concentrated on the central portion of the
field, itself representing 0.22% of the full sky. From these data we derive an
estimate of the angular power spectrum of temperature fluctuations of the CMB
in 24 bands over the multipole range (50 < l < 1500). A series of features,
consistent with those expected from acoustic oscillations in the primordial
photon-baryon fluid, are clearly evident in the power spectrum, as is the
exponential damping of power on scales smaller than the photon mean free path
at the epoch of last scattering (l > 900). As a consistency check, the
collaboration has performed two fully independent analyses of the time ordered
data, which are found to be in excellent agreement.Comment: 11 pages, 7 figures, 3 tables. High resolution figures and data are
available at http://cmb.phys.cwru.edu/boomerang/ and
http://oberon.roma1.infn.it/boomerang/b2
Non-Gaussianity in braneworld and tachyon inflation
We calculate the bispectrum of single-field braneworld inflation, triggered
by either an ordinary scalar field or a cosmological tachyon, by means of a
gradient expansion of large-scale non-linear perturbations coupled to
stochastic dynamics. The resulting effect is identical to that for single-field
4D standard inflation, the non-linearity parameter being proportional to the
scalar spectral index in the limit of collapsing momentum. If the slow-roll
approximation is assumed, braneworld and tachyon non-Gaussianities are
subdominant with respect to the post-inflationary contribution. However, bulk
physics may considerably strengthen the non-linear signatures. These features
do not change significantly when considered in a non-commutative framework.Comment: 17 pages; v2: added references and previously skipped details in the
derivation of the result; v3: improved discussio
Searching for non Gaussian signals in the BOOMERanG 2003 CMB maps
We analyze the BOOMERanG 2003 (B03) 145 GHz temperature map to constrain the
amplitude of a non Gaussian, primordial contribution to CMB fluctuations. We
perform a pixel space analysis restricted to a portion of the map chosen in
view of high sensitivity, very low foreground contamination and tight control
of systematic effects. We set up an estimator based on the three Minkowski
functionals which relies on high quality simulated data, including non Gaussian
CMB maps. We find good agreement with the Gaussian hypothesis and derive the
first limits based on BOOMERanG data for the non linear coupling parameter f_NL
as -300<f_NL<650 at 68% CL and -800<f_NL<1050 at 95% CL.Comment: accepted for publication in ApJ. Letter
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