4,521 research outputs found
Quantiles for Fractions and Other Mixed Data
This paper studies the estimation of quantile regression for fractional data, focusing on the case where there are mass-points at zero or/and one. More generally, we propose a simple strategy for the estimation of the conditional quantiles of data from mixed distributions, which combines standard results on the estimation of censored and Box-Cox quantile regressions. The implementation of the proposed method is illustrated using a well-known dataset.
Quantiles for Fractions and Other Mixed Data
This paper studies the estimation of quantile regression for fractional data, focusing on the case where there are mass-points at zero or/and one. More generally, we propose a simple strategy for the estimation of the conditional quantiles of data from mixed distributions, which combines standard results on the estimation of censored and Box-Cox quantile regressions. The implementation of the proposed method is illustrated using a well-known dataset
Quantiles for counts
This paper studies the estimation of conditional quantiles of counts. Given the discreteness of the data, some smoothness has to be artificially imposed on the problem. The methods currently available to estimate quantiles of count data either assume that the counts result from the discretization of a continuous process, or are based on a smoothed objective function. However, these methods have several drawbacks. We show that it is possible to smooth the data in a way that allows inference to be performed using standard quantile regression techniques. The performance and implementation of the estimator are illustrated by simulations and an application.
Prevalence and pattern of cognitive impairment in rural and urban populations from Northern Portugal
<p>Abstract</p> <p>Background</p> <p>Despite worldwide recognition of the burden of dementia, no epidemiological data is yet available in Portugal. The objective of this study is to estimate the prevalence and describe the pattern of cognitive impairment with dementia or no dementia (CIND) in rural and urban populations from Northern Portugal.</p> <p>Methods</p> <p>Two random samples of residents aged 55 to 79 years in rural and urban communities were drawn from the health centres registries to be screened for cognitive impairment. The screening criteria for dementia were an abnormal Mini-Mental State Examination (MMSE) score or a Blessed Dementia Scale score. After excluding those who tested positive for dementia, cut-off points for CIND were set at 1 standard deviation below the mean of the MMSE according to educational level. All those who screened positive either for dementia or CIND were examined by a neurologist for establishing a definitive diagnosis.</p> <p>Results</p> <p>The prevalence of cognitive impairment was higher in rural than in urban populations, 16.8% (95% CI: 14.3-19.8%) vs. 12.0% (95%CI: 9.3-15.4%), with a rural/urban prevalence ratio (PR) of 2.16 (95% CI: 1.04-4.50) in the eldest and 2.19 (95% CI: 1.01-4.76) in persons with vascular risk factors. The prevalence of dementia was 2.7% (95% CI: 1.9-3.8%) with a rural/urban PR = 2.1 and the prevalence of CIND was 12.3% (95% CI: 10.4-14.4%) and PR = 1.3. The prevalence of dementia increases exponentially with age and in those with cerebrovascular disease or other comorbid conditions while the prevalence of CIND, besides these factors, is also higher in persons with low levels of education or vascular risk factors. Alzheimer's and vascular disease were equally likely aetiologies of dementia (38.7%), the later more common in men PR(F:M = 0.3) as opposed to the former PR(F:M = 2.0). Vascular CIND, associated either with cerebrovascular disease or vascular risk factors was more frequent (39.7%) then depression (18.4%) or any other aetiology.</p> <p>Conclusions</p> <p>The prevalence of cognitive impairment is higher in rural compared with urban populations. This is shown in the synergy between age and rurality, with the rural/urban prevalence ratio increasing with age. In this relatively young population from Northern Portugal, cerebrovascular disease as well as vascular risk factors account for 48% of overall cognitive impairment.</p
Internal solitary waves in the Red Sea : an unfolding mystery
Author Posting. © The Oceanography Society, 2012. This article is posted here by permission of The Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 25, no. 2 (2012): 96-107, doi:10.5670/oceanog.2012.45.The off-shelf region between 16.0° and 16.5°N in the southern Red Sea is identified as a new hotspot for the occurrence of oceanic internal solitary waves. Satellite observations reveal trains of solitons that, surprisingly, appear to propagate from the center of the Red Sea, where it is deepest, toward the continental shelf, but they do not survive as coherent structures over the shelf. These solitons are characterized by coherent crest lengths exceeding 80 km and crest-to-crest distances of more than 2 km, compatible with signatures of large-amplitude solitary waves. Despite the fact that these Red Sea solitons have large amplitudes, they appear to be generated by very weak surface tides. Tidal current velocity is only about 5 cm sâ1 over the shelf, much weaker than over other ocean shelves where similar solitary waves have been reported. The appearance of these waves over this particular geographical stretch suggests generation by a locally amplified internal tide on the main pycnocline. We consider three possible explanations for soliton generation in the Red Sea: interfacial tide resonance, local generation by internal tidal beams generated at the shelf breaks, and local generation by internal tidal beams generated at the shelf breaks but first amplified by repeated focusing reflections
Cambrian ensialic rift-related magmatism in the Ossa-Morena Zone
The Late Ediacaran (c. 560â550 Ma) SĂ©rie Negra sediments of the ĂvoraâAracena metamorphic belt, Ossa-Morena Zone, SW Iberian Massif,
preserve a record of the erosion of an AvalonianâCadomian magmatic arc and subsequent related turbiditic sedimentation. Detrital zircon from the
SĂ©rie Negra is characterized by predominantly Ediacaran and Cryogenian ages, with few Paleoproterozoic and Archean cores, and a marked lack
of Grenvillian ages. These features, when combined with the metasediments' enrichment in LREE (La/Yb=14), negative Eu-anomalies, low
147Sm/144Nd values (0.121) and negative ΔNd550=â5.5, indicate that the protolith SĂ©rie Negra sediments were derived from a continental
magmatic arc.
A period of Late Cadomian (ca. 560â540 Ma) tectonism was followed by an extended episode of widespread bimodal magmatism related to
Cambrian (ca. 540â500 Ma) rifting. This tectonic inversion is expressed in the geological record by a regional Early Cambrian unconformity.
SHRIMP zircon UâThâPb ages from four felsic orthogneisses from the Ăvora Massif record Cambrian (527±10 Ma, 522±5 Ma, 517±6 Ma
and 505±5 Ma) crystallization ages for their igneous protoliths. This confirms the existence of widespread Lower Paleozoic igneous activity in the
Ossa-Morena Zone: (i) a Lower Cambrian (ca. 535â515 Ma) igneousâfelsic dominatedâsedimentary complex (with calc-alkaline signature and
associated carbonate and siliciclastic deposition), and (ii) a Middle Cambrianâ?Ordovician (ca. 515â490 Ma) igneousâbimodalâsedimentary
complex (with calc-alkaline and tholeiitic signatures and associated dominant siliciclastic deposition, but also carbonate sediments).
The Cambrian felsic magmatism was characterized by negative Eu-anomalies, (La/Lu)N=0.8â11, 147Sm/144Nd=0.1289â0.1447 and ΔNd500
ranging from â1.5 to â0.8. A tendency towards peraluminous compositions suggests late fractionation, low degrees of partial melting, or the
mixing of crustal and mantle-derived material in the magma source region. Some felsic rocks possibly represent the last residual melts of hightemperature,
zircon-undersaturated mafic magmas later affected by crustal contamination, while others indicate partial melting of crustal
metasediments variably contaminated by basaltic liquids.
The transition from early felsic dominated to later more mafic magmatism suggests the gradual opening of the system to tholeiitic NâE-MORB
products (ThN/TaNb1.0). The as yet undated (Cambrianâ?Ordovician) E-MORB amphibolites have 147Sm/144Nd=0.1478â0.1797 and ΔNd500
values ranging from +6.4 to +7.3, while the N-MORB amphibolites have 147Sm/144Nd=0.1818â0.1979 and ΔNd500 values of +5.8 and +7.0,
reaching a maximum of +9.1. In contrast, other amphibolites have a negative Ta-anomaly (1.35bThN/TaNb2.41) reminiscent of lavas from
âorogenicâ settings or alternatively, typical of crustally-contaminated within-plate magmas. These âVAB-likeâ amphibolites have 147Sm/144Nd
values ranging from 0.1639 to 0.1946 and ΔNd500 values of +3.5 to +5.2, suggesting derivation by crustal assimilation processes. The subalkaline
igneous precursors of the amphibolites were most likely generated in a rift setting by asthenospheric upwelling. These results strengthen the proposed geodynamic scenarios for the SW Iberian Massif by which Cadomian accretion gave rise to an ensialic
rift that developed into a proto-oceanic basin and incipient spreading (opening of the Rheic Ocean?). A similar transition from a convergent to a
divergent plate boundary during the Ediacaran to Cambrianâ?Ordovician has also been reported in other segments of the northern Gondwana
margin
Nemabiome metabarcoding reveals differences between gastrointestinal nematode species infecting co-grazed sheep and goats
Our current understanding of differences in the epidemiology of gastrointestinal nematode (GIN) species in co-grazed sheep and goats is inadequate with reference to the development of sustainable control strategies. The next-generation metabarcoding sequencing method referred to as the ânemabiomeâ allows some of these differences to be explored to describe the intensity of co-infecting GIN species. We applied this platform to study sheep and goats that were co-grazed on Guinea grass pasture in northeastern Brazil. Co-grazed goats and sheep were treated with a monepantel anthelmintic, then exposed to the same gastrointestinal nematode species. Overall, there were differences in the prevalence of GIN species identified in the sheep and goats; Trichostrongylus colubriformis and Teladorsagia circumcincta predominated in goat kids, while Haemonchus contortus predominated in adult does, ewes and lambs once burdens became re-established after anthelmintic treatment. Description of the pattern of re-infection following anthelmintic treatment was prevented by the unpredicted poor efficacy of 2.5âmg/kg and 5âmg/kg, respectively, of monepantel against O. columbianum and T. circumcincta in lambs, and T. circumcincta adult does. Differences in drug efficacy between host age and species groups may be important when considering sustainable GIN control strategies for co-grazed animals. The aggregated FECs of the adult does and goat kids representing re-established GIN burdens, were higher than those of the co-grazed adult ewes and lambs. This implies that there are inherent differences in GIN species adaptation to the two naĂŻve small ruminant host species, and shows the need for better understanding of the factors giving rise to this situation associated with exposure to infective larvae and host responses. At the start of the study, the adult does were co-infected with several GIN species, with the highest intensity of T. circumcincta, contrasting with the situation in the adult ewes, in which H. contortus predominated. However, once burdens became re-established after treatment, H. contortus predominated in both adult does and ewes. This demonstrates the potential for host burdens of H. contortus to establish and predominate after anthelmintic treatment when burdens of co-infecting GIN species are low
Mass spectrometry parameters optimization for the 46 multiclass pesticides determination in strawberries with gas chromatography ion-trap tandem mass spectrometry
Multiclass analysis method was optimized in order to analyze pesticides traces by gas
chromatography with ion-trap and tandem mass spectrometry (GC-MS/MS). The influence of some
analytical parameters on pesticide signal response was explored. Five ion trap mass spectrometry
(IT-MS) operating parameters, including isolation time (IT), excitation voltage (EV), excitation time
(ET),maximum excitation energy or âqâ value (q), and isolationmass window (IMW) were numerically
tested in order to maximize the instrument analytical signal response. For this, multiple linear
regression was used in data analysis to evaluate the influence of the five parameters on the analytical
response in the ion trap mass spectrometer and to predict its response. The assessment of the five
parameters based on the regression equations substantially increased the sensitivity of IT-MS/MS in
the MS/MS mode. The results obtained show that for most of the pesticides, these parameters have a
strong influence on both signal response and detection limit.Using the optimized method, a multiclass
pesticide analysis was performed for 46 pesticides in a strawberry matrix. Levels higher than the limit
established for strawberries by the European Union were found in some samples
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