194 research outputs found
Evaluation of spacial resolution of a PET scanner through the simulation and experimental measurement of the Recovery coefficient
Purpose: In order to measure spatial resolution of a PET tomograph in clinical conditions, this study describes and
validates a method based on the recovery coefficient, a factor required to compensate underestimation in measured
radioactivity concentration for small structures.
Methods: In a PET image, the recovery factors of radioactive spheres were measured and their comparison with
simulated recovery coefficients yielded the tomographic spatial resolution. Following this methodology, resolution was
determined in different surrounding media and several conditions for reconstruction, including clinical conditions for brain
PET studies. All spatial resolution values were compared with those obtained using classical methods with point and
line sources.
Results: In each considered condition, spatial resolution of the PET image estimated using the recovery coefficient
showed good agreement with classical methods measurements, validating the procedure.
Conclusion: Measurement of the recovery coefficient provides an assessment of tomographic spatial resolution,
particularly in clinical studies conditions
The correlation between C/O ratio, metallicity and the initial WD mass for SNe Ia
In this paper, we want to check whether or not the carbon abundance can be
affected by initial metallicity. We calculated a series of stellar evolution.
We found that when , the carbon abundance is almost independent of
metallicity if it is plotted against the initial WD mass. However, when
, the carbon abundance is not only a function of the initial WD mass,
but also metallicity, i.e. for a given initial WD mass, the higher the
metallicity, the lower the carbon abundance. Based on some previous studies,
i.e. both a high metallicity and a low carbon abundance lead to a lower
production of Ni formed during SN Ia explosion, the effects of the
carbon abundance and the metallicity on the amount of Ni are
enhanced by each other, which may account for the variation of maximum
luminosity of SNe Ia, at least qualitatively. Considering that the central
density of WD before supernova explosion may also play a role on the production
of Ni and the carbon abundance, the metallicity and the central
density are all determined by the initial parameters of progenitor system, i.e.
the initial WD mass, metallicity, orbital period and secondary mass, the amount
of Ni might be a function of the initial parameters. Then, our
results might construct a bridge linking the progenitor model and the explosion
model of SNe Ia.Comment: 7pages, 4 figures, accepted for publication in A&
Euroforgen-NoE collaborative exercise on LRmix to demonstrate standardization of the interpretation of complex DNA profiles
Tomografía por emisión de positrones en el cáncer de mama
PET18FDG is an imaging diagnostic technique that shows changes in glycolitic metabolism that appear at a very early phases in the tumoral process. The main limitation of PET in breast cancer is the detection of small tumor lesions and axillary micrometastases. However it offers important information in the staging of high risk patients, in clinical relapse or in therapeutic evaluation. The new PET-CT devices offer advantages over conventional techniques. It provides a greater precision in the localization of tumoral foci. In spite of current difficulties for clinical applications, fluoro-estradiol (18F-ES) offers the possibilty of studying the presence of estrogenic receptors both in the primary and in the metastases. It may prove to be a useful tool to obtain information about therapeutic management and prognosis of breast cancer
Effects of an exercise program on hepatic metabolism, hepatic fat, and cardiovascular health in overweight/obese adolescents from Bogotá, Colombia (the HEPAFIT study): study protocol for a randomized controlled trial
Background: A considerable proportion of contemporary youth have a high risk of obesity-related disorders such
as cardiovascular disease, metabolic syndrome, or non-alcoholic fatty liver disease (NAFLD). Although there is consistent
evidence for the positive effects of physical activity on several health aspects, most adolescents in Colombia are
sedentary. It is, therefore, important to implement strategies that generate changes in lifestyle. The HEPAFIT study
aims to examine whether a 6-month exercise program has benefits for hepatic fat content and cardiovascular health
outcomes among overweight/obese adolescents from Bogotá, Colombia.
Methods/design: Altogether, 100 hundred overweight/obese, sedentary adolescents (aged 11–17 years) attending two
public schools in Bogotá, Colombia, will be included in a parallel-group randomized controlled trial. Adolescents will be
randomly assigned to an intervention group following one of four curricula: (1) the standard physical education
curriculum (60 min per week of physical activity, n = 25) at low-to-moderate intensity; (2) a high-intensity physical
education curriculum (HIPE, n = 25), consisting of endurance and resistance games and non-competitive activities,
such as running, gymkhanas, lifting, pushing, wrestling, or hauling, for 60-min sessions, three times per week, with
an energy expenditure goal of 300 to 500 kcal/session at 75–85% maximum heart rate (HRmax); (3) a low-to-moderate
intensity physical education curriculum (LIPE, n = 25) consisting of endurance and resistance games and non-competitive
activities (e.g., chasing, sprinting, dribbling, or hopping) for 60-min sessions, three times per week with an energy
expenditure goal of 300 kcal/session at 55–75% HRmax; and (4) a combined HIPE and LIPE curriculum (n = 25).
The HIPE, LIPE, and combined interventions were performed in addition to the standard physical education curriculum.
The primary outcome for effectiveness is liver fat content, as measured by the controlled attenuation parameter 1
week after the end of the intervention program.
Discussion: The translational focus may be suitable for collecting new information in a school setting on the
possible effects of physical activity interventions to reduce liver fat content and to improve metabolic profiles
and the cardiometabolic health of overweight/obese adolescents. This may lead to the more efficient use of
school physical education resources.The HEPAFIT study was carried out with the financial support of Instituto
Colombiano para el Desarrollo de la Ciencia y la Tecnología “Francisco José
de Caldas” COLCIENCIAS (code 59700 and no 122277757900). Katherine
González-Ruíz receive a scholarship from Universidad del Rosario, Colombia,
Escuela de Medicina y Ciencias de la Salud, to do a Doctorate. This article
presents independent research commissioned by COLCIENCIAS under its
Program Grants for Applied Research funding scheme (Convocatoria 777–2017)
Optical and IR observations of SN 2002dj: some possible common properties of fast expanding SNe Ia
As part of the European Supernova Collaboration we obtained extensive
photometry and spectroscopy of the type Ia SN 2002dj covering epochs from 11
days before to nearly two years after maximum. Detailed optical and
near-infrared observations show that this object belongs to the class of the
high-velocity gradient events as indicated by Si, S and Ca lines. The light
curve shape and velocity evolution of SN 2002dj appear to be nearly identical
to SN 2002bo. The only significant difference is observed in the optical to
near-IR colours and a reduced spectral emission beyond 6500 A. For
high-velocity gradient Type Ia supernovae, we tentatively identify a faster
rise to maximum, a more pronounced inflection in the V and R light curves after
maximum and a brighter, slower declining late-time B light curve as common
photometric properties of this class of objects. They also seem to be
characterized by a different colour and colour evolution with respect to
``normal'' SNe Ia. The usual light curve shape parameters do not distinguish
these events. Stronger, more blueshifted absorption features of
intermediate-mass elements and lower temperatures are the most prominent
spectroscopic features of Type Ia supernovae displaying high velocity
gradients. It appears that these events burn more intermediate-mass elements in
the outer layers. Possible connections to the metallicity of the progenitor
star are explored.Comment: Equations A4, A5 and A7 in the appendix section have been corrected.
Part of text in the appendix has been remove
Investigation of the Pu 240 (n,f) reaction at the n_TOF/EAR2 facility in the 9 meV-6 MeV range
Background: Nuclear waste management is considered amongst the major challenges in the field of nuclear energy. A possible means of addressing this issue is waste transmutation in advanced nuclear systems, whose operation requires a fast neutron spectrum. In this regard, the accurate knowledge of neutron-induced reaction cross sections of several (minor) actinide isotopes is essential for design optimization and improvement of safety margins of such systems. One such case is Pu240, due to its accumulation in spent nuclear fuel of thermal reactors and its usage in fast reactor fuel. The measurement of the Pu240(n,f) cross section was previously attempted at the CERN n_TOF facility EAR1 measuring station using the time-of-flight technique. Due to the low amount of available material and the given flux at EAR1, the measurement had to last several months to achieve a sufficient statistical accuracy. This long duration led to detector deterioration due to the prolonged exposure to the high α activity of the fission foils, therefore the measurement could not be successfully completed. Purpose: It is aimed to determine whether it is feasible to study neutron-induced fission at n_TOF/EAR2 and provide data on the Pu240(n,f) reaction in energy regions requested for applications. Methods: The study of the Pu240(n,f) reaction was made at a new experimental area (EAR2) with a shorter flight path which delivered on average 30 times higher flux at fast neutron energies. This enabled the measurement to be performed much faster, thus limiting the exposure of the detectors to the intrinsic activity of the fission foils. The experimental setup was based on microbulk Micromegas detectors and the time-of-flight data were analyzed with an optimized pulse-shape analysis algorithm. Special attention was dedicated to the estimation of the non-negligible counting loss corrections with the development of a new methodology, and other corrections were estimated via Monte Carlo simulations of the experimental setup. Results: This new measurement of the Pu240(n,f) cross section yielded data from 9meV up to 6MeV incident neutron energy and fission resonance kernels were extracted up to 10keV. Conclusions: Neutron-induced fission of high activity samples can be successfully studied at the n_TOF/EAR2 facility at CERN covering a wide range of neutron energies, from thermal to a few MeV
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