18,226 research outputs found
The motion of two masses coupled to a massive spring
We discuss the classical motion of a spring of arbitrary mass coupled to two
arbitrary massive blocks attached at its ends. A general approach to the
problem is presented and some general results are obtained. Examples for which
a simple elastic function can be inferred are discussed and the normal modes
and normal frequencies obtained. An approximation procedure to the evaluation
of the normel frequencies in the case of uniform elastic function and mass
density is also discussed.Comment: Standard Latex file plus three eps figure
Detection of a variable ultra-fast outflow in the Narrow Line Seyfert 1 galaxy PG 1448+273
Relativistically blueshifted absorption features of highly ionised ions, the
so-called ultra-fast outflows (UFOs), have been detected in the X-ray spectra
of a number of accreting supermassive black holes. If these features truly
originate from accretion disc winds accelerated to more than 10 per cent of the
speed of light, their energy budget is very significant and they can contribute
to or even drive galaxy-scale feedback from active galactic nuclei (AGN).
However, the UFO spectral features are often weak due to high ionisation of the
outflowing material, and the inference of the wind physical properties can be
complicated by other spectral features in AGN such as relativistic reflection.
Here we study a highly accreting Narrow Line Seyfert 1 galaxy PG 1448+273. We
apply an automated, systematic routine for detecting outflows in accreting
systems and achieve an unambiguous detection of a UFO in this AGN. The UFO
absorption is observed in both soft and hard X-ray bands with the XMM-Newton
observatory. The velocity of the outflow is (26900 +- 600) km/s (~0.09c), with
an ionisation parameter of log ({\xi} / erg cm s^-1)=4.03_{-0.08}^{+0.10} and a
column density above 10^23 cm^-2. At the same time, we detect weak warm
absorption features in the spectrum of the object. Our systematic outflow
search suggests the presence of further multi-phase wind structure, but we
cannot claim a significant detection considering the present data quality. The
UFO is not detected in a second, shorter observation with XMM-Newton,
indicating variability in time, observed also in other similar AGN.Comment: Accepted for publication in MNRAS. 14 pages, 11 figures, 1 tabl
Coastal bathymetry estimation using an ensemble of synthetic aperture radar images from Sentinel-1
In this study, coastal bathymetry is estimated with a wave ray-tracing algorithm using wave parameters retrieved from Synthetic Aperture Radar (SAR) images acquired by the Sentinel-1 satellites. The method relies on the long swell wave’s detection by SAR imagery and the wave’s properties adjustment to the underwater topography, which can be mathematically related using the linear dispersion relation. The ray-tracing algorithm tracks the shoaling waves until the wave breaking zone, using the wavelength and wave direction retrieved from the 2D directional spectra applied at consecutive sub-images. Then, by inverting the linear wave dispersion relationship, the depth is calculated based on the mean wavelength obtained for each sub-image and maintaining the wave period retrieved at the first offshore position, which is computed using a mean depth from an independent bathymetric source. The output of the algorithm is a bathymetric model that results from the interpolation of the depth computed at each tracking position to a uniform grid and the results are compared with bathymetric information from the General Bathymetric Chart of the Ocean. The use of a monthly ensemble of SAR images, instead of individual ones, to reproduce the bathymetry near Aveiro, Portugal, resulted in a smoother topography with lower relative errors, suggesting that the final bathymetric model retrieved from SAR should result from a combination of SAR images. The methodology presented here to infer the bathymetry using space-borne SAR imagery can be useful to retrieve the mean bottom topography (especially in remote areas where the traditional hydrographic surveying methods are not performed regularly) and to reproduce new underwater structures, such as banks, reefs or bars, which are important to detect for the safety of navigation.Peer Reviewe
Assessment of Cancer-related Cognitive Impairment: Methodological Issues
Cognitive decline associated with cancer or its treatment has been addressed in many studies, though with inconsistent findings, which largely reflects the diversity of methods that have been used. In this context, we read with much interest the paper recently published in the Archives of Clinical Neuropsychology (Clapp et al., 2018) about the impact of using different reference populations on breast cancer-related cognitive impairment rates, which was based on a thorough assessment of a large number of cancer patients and non-cancer subjects
Tensor Perturbations in Quantum Cosmological Backgrounds
In the description of the dynamics of tensor perturbations on a homogeneous
and isotropic background cosmological model, it is well known that a simple
Hamiltonian can be obtained if one assumes that the background metric satisfies
Einstein classical field equations. This makes it possible to analyze the
quantum evolution of the perturbations since their dynamics depends only on
this classical background. In this paper, we show that this simple Hamiltonian
can also be obtained from the Einstein-Hilbert lagrangian without making use of
any assumption about the dynamics of the background metric. In particular, it
can be used in situations where the background metric is also quantized, hence
providing a substantial simplification over the direct approach originally
developed by Halliwell and Hawking.Comment: 24 pages, JHEP forma
Novel types of anti-ecloud surfaces
In high power RF devices for space, secondary electron emission appears as
the main parameter governing the multipactor effect and as well as the e-cloud
in large accelerators. Critical experimental activities included development of
coatings with low secondary electron emission yield (SEY) for steel (large
accelerators) and aluminium (space applications). Coatings with surface
roughness of high aspect ratio producing the so-call secondary emission
suppression effect appear as the selected strategy. In this work a detailed
study of the SEY of these technological coatings and also the experimental
deposition methods (PVD and electrochemical) are presented. The coating-design
approach selected for new low SEY coatings include rough metals (Ag, Au, Al),
rough alloys (NEG), particulated and magnetized surfaces, and also graphene
like coatings. It was found that surface roughness also mitigate the SEY
deterioration due to aging processes.Comment: 4 pages, contribution to the Joint INFN-CERN-EuCARD-AccNet Workshop
on Electron-Cloud Effects: ECLOUD'12; 5-9 Jun 2012, La Biodola, Isola d'Elba,
Italy; CERN Yellow Report CERN-2013-002, pp.153-15
Fertility preservation in ovarian tumours
A considerable number of patients with a cancer diagnosis are of childbearing age and have not satisfied their desire for a family. Despite ovarian cancer (OC) usually occurring in older patients, 3%–14% are diagnosed at a fertile age with the overall 5-year survival rate being 91.2% in women ≤44 years of age when it is found at 1A–B stage. In this scenario, testing the safety and the efficacy of fertility sparing strategies in OC patients is very important overall in terms of quality of life. Unfortunately, the lack of randomised trials to validate conservative approaches does not guarantee the safety of fertility preservation strategies. However, evidence-based data from descriptive series suggest that in selected cases, the preservation of the uterus and at least one part of the ovary does not lead to a high risk of relapse. This conservative surgery helps to maintain organ function, giving patients of childbearing age the possibility to preserve their fertility. We hereby analysed the main evidence from the international literature on this topic in order to highlight the selected criteria for conservative management of OC patients, including healthy BRCA mutations carriers
Quantum Cosmology in Scalar-Tensor Theories With Non Minimal Coupling
Quantization in the minisuperspace of non minimal scalar-tensor theories
leads to a partial differential equation which is non separable. Through a
conformal transformation we can recast the Wheeler-DeWitt equation in an
integrable form, which corresponds to the minimal coupling case, whose general
solution is known. Performing the inverse conformal transformation in the
solution so found, we can construct the corresponding one in the original
frame. This procedure can also be employed with the bohmian trajectories. In
this way, we can study the classical limit of some solutions of this quantum
model. While the classical limit of these solutions occurs for small scale
factors in the Einstein's frame, it happens for small values of the scalar
field non minimally coupled to gravity in the Jordan's frame, which includes
large scale factors.Comment: latex, 18 page
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