7,499 research outputs found
Least squares volatility change point estimation for partially observed diffusion processes
A one dimensional diffusion process , with drift
and diffusion coefficient
known up to , is supposed to switch volatility regime at some point
. On the basis of discrete time observations from , the
problem is the one of estimating the instant of change in the volatility
structure as well as the two values of , say and
, before and after the change point. It is assumed that the sampling
occurs at regularly spaced times intervals of length with
. To work out our statistical problem we use a least squares
approach. Consistency, rates of convergence and distributional results of the
estimators are presented under an high frequency scheme. We also study the case
of a diffusion process with unknown drift and unknown volatility but constant
Increased intestinal carbonate precipitate abundance in the sea bream (Sparus aurata L.) in response to ocean acidification
Marine fish contribute to the carbon cycle by producing mineralized intestinal precipitates generated as by-products of their osmoregulation. Here we aimed at characterizing the control of epithelial bicarbonate secretion and intestinal precipitate presence in the gilthead sea bream in response to predicted near future increases of environmental CO2. Our results demonstrate that hypercapnia (950 and 1800 ÎŒatm CO2) elicits higher intestine epithelial HCO3- secretion ex vivo and a subsequent parallel increase of intestinal precipitate presence in vivo when compared to present values (440 ÎŒatm CO2). Intestinal gene expression analysis in response to environmental hypercapnia revealed the up-regulation of transporters involved in the intestinal bicarbonate secretion cascade such as the basolateral sodium bicarbonate co-transporter slc4a4, and the apical anion transporters slc26a3 and slc26a6 of sea bream. In addition, other genes involved in intestinal ion uptake linked to water absorption such as the apical nkcc2 and aquaporin 1b expression, indicating that hypercapnia influences different levels of intestinal physiology. Taken together the current results are consistent with an intestinal physiological response leading to higher bicarbonate secretion in the intestine of the sea bream paralleled by increased luminal carbonate precipitate abundance and the main related transporters in response to ocean acidification.AgĂȘncia financiadora
Fundacao para a Ciencia e a Tecnologia (FCT)
SFRH/BD/113363/2015
PTDC/MAR-BIO/3034/2014
Fundacao para a Ciencia e a Tecnologia (FCT)
UID/Multi/04326/2019
Ministry of Science and Higher Education, Polandinfo:eu-repo/semantics/publishedVersio
SOCIO-ECONOMIC IMPACT OF THE MARITIME EDUCATION UPGRADING PROGRAM
This study endeavored to determine the impact of the Maritime Education Upgrading Program of PIT-KVNR on the socio-economic status of its graduates from school years 2002-2003 to 2007-2008. A descriptive-comparative approach design was used with two groups of respondents and total sample size of 296. It was found out that, before these graduates entered the program, the socio-economic status between parents of the two groups of marine transportation graduates-respondents were already significantly different, while there was no significant difference in the socio-economic status between parents of the two groups of marine engineering graduates-respondents. Furthermore, there were significant differences between groups of marine transportation and marine engineering graduates-respondents on their socio-economic status after they graduated from the program. Moreover, results revealed that the socio-economic status of graduates from all groups of respondents have greatly improved over a short span of time after they graduated from the program. On the other hand, the respondents from both groups also accounted the extent of performance of the Maritime Education Upgrading Program as providing opportunities for the respondents to achieve performance ranging from higher to highest level. 
Nimesulide limits kainate-induced oxidative damage in the rat hippocampus
Kainate induces a marked expression of cyclooxygenase-2 after its systemic administration. Because cyclooxygenase-2 activity is associated to the production of reactive oxygen species, we investigated the effects of nimesulide, a selective cyclooxygenase-2 inhibitor, on kainate-induced in vivo oxidative damage in the rat hippocampus. A clinically relevant dose of nimesulide (6 mg/kg, i.p. ) was administered three times following kainate application (9 mg/kg, i.p.). After 24 h of kainate administration, the drastic decrease in hippocampal glutathione content and the significant increase in lipid peroxidation were attenuated in nimesulide-treated rats, suggesting that the induction of cyclooxygenase-2 is involved in kainate-mediated free radicals formation
PERFORMANCE ATTRIBUTES OF DECK AND ENGINE CADETS ONBOARD DUTCH MERCHANT SHIPS
This study was conducted to determine the attributes that influenced the performances of the deck and engine cadets of the Palompon Institute of Technology (PIT) during their apprenticeship training onboard Dutch ships. The study was a descriptive-survey method utilizing a standardized survey instrument provided in the Quality Management System of the Instituteâs College of Maritime Education. The subjects considered were deck and engine cadets who were onboard Dutch ships for their 1 year apprenticeship training. While deck and engine management level officers were the respondents. Results revealed the performances of the cadets were highly influenced by the associated attributes as regards âPersonal Qualitiesâ and âProfessional Knowledge and Skills.â Moreover, as regards to âOutlook/Expectationsâ, majority of deck and engine cadets were expected able to perform their tasks independently as shipâs officers upon completion of the onboard training period of one year; while there were few from both groups that were expected able to perform his/her task independently as shipâs officer only after an additional on board training period. Furthermore, it was found out the academic performance of the deck cadets was satisfactory with high grades while the engine cadets with less satisfactory. Finally, the relationship between the performance attributes and academic performance in both groups of respondents were established. 
Near-IR imaging of T Cha: evidence for scattered-light disk structures at solar system scales
T Chamaeleontis is a young star surrounded by a transitional disk, and a
plausible candidate for ongoing planet formation. Recently, a substellar
companion candidate was reported within the disk gap of this star. However, its
existence remains controversial, with the counter-hypothesis that light from a
high inclination disk may also be consistent with the observed data. The aim of
this work is to investigate the origin of the observed closure phase signal to
determine if it is best explained by a compact companion. We observed T Cha in
the L and K s filters with sparse aperture masking, with 7 datasets covering a
period of 3 years. A consistent closure phase signal is recovered in all L and
K s datasets. Data were fit with a companion model and an inclined
circumstellar disk model based on known disk parameters: both were shown to
provide an adequate fit. However, the absence of expected relative motion for
an orbiting body over the 3-year time baseline spanned by the observations
rules out the companion model. Applying image reconstruction techniques to each
dataset reveals a stationary structure consistent with forward scattering from
the near edge of an inclined disk.Comment: 6 pages, 3 figures, accepted for publication in MNRAS Letter
Time course of oxidative damage in different brain regions following transient cerebral ischemia in gerbils
The time course of oxidative damage in different brain regions was investigated in the gerbil model of transient cerebral ischemia. Animals were subjected to both common carotid arteries occlusion for 5 min. After the end of ischemia and at different reperfusion times (2, 6, 12, 24, 48, 72, 96 h and 7 days), markers of lipid peroxidation, reduced and oxidized glutathione levels, glutathione peroxidase, glutathione reductase, manganese-dependent superoxide dismutase (MnSOD) and copper/zinc containing SOD (Cu/ZnSOD) activities were measured in hippocampus, cortex and striatum. Oxidative damage in hippocampus was maximal at late stages after ischemia (48-96 h) coincident with a significant impairment in glutathione homeostasis. MnSOD increased in hippocampus at 24, 48 and 72 h after ischemia, coincident with the marked reduction in the activity of glutathione-related enzymes. The late disturbance in oxidant-antioxidant balance corresponds with the time course of delayed neuronal loss in the hippocampal CA1 sector. Cerebral cortex showed early changes in oxidative damage with no significant impairment in antioxidant capacity. Striatal lipid peroxidation significantly increased as early as 2 h after ischemia and persisted until 48 h with respect to the sham-operated group. These results contribute significant information on the timing and factors that influence free radical formation following ischemic brain injury, an essential step in determining effective antioxidant intervention
On RĂ©nyi information for ergodic diffusion processes
In this paper we derive explicit formulas of the R\'enyi information, Shannon entropy and Song measure for the invariant density of one dimensional ergodic diffusion processes. In particular, the diffusion models considered include the hyperbolic, the generalized inverse Gaussian, the Pearson, the exponential familiy and a new class of skew-t diffusion
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