3,207 research outputs found
Dynamical constraints on the origin of hot and warm Jupiters with close friends
Gas giants orbiting their host star within the ice line are thought to have
migrated to their current locations from farther out. Here we consider the
origin and dynamical evolution of observed Jupiters, focusing on hot and warm
Jupiters with outer friends. We show that the majority of the observed Jupiter
pairs (twenty out of twenty-four) will be dynamically unstable if the inner
planet was placed at >~1AU distance from the stellar host. This finding is at
odds with formation theories that invoke the migration of such planets from
semi-major axes >~1AU due to secular dynamical processes (e.g., secular chaos,
Lidov-Kozai oscillations) coupled with tidal dissipation. In fact, the results
of N-body integrations show that the evolution of dynamically unstable systems
does not lead to tidal migration but rather to planet ejections and collisions
with the host star. This and other arguments lead us to suggest that most of
the observed planets with a companion could not have been transported from
further out through secular migration processes. More generally, by using a
combination of numerical and analytic techniques we show that the high-e
Lidov-Kozai migration scenario can only account for less than 10% of all gas
giants observed between 0.1-1 AU. Simulations of multi-planet systems support
this result. Our study indicates that rather than starting on highly eccentric
orbits with orbital periods above one year, these "warm" Jupiters are more
likely to have reached the region where they are observed today without having
experienced significant tidal dissipation.Comment: Accepted to AAS journals (AJ). 15 pages, 9 figure
Binary black hole mergers from field triples: properties, rates and the impact of stellar evolution
We consider the formation of binary black hole mergers through the evolution
of field massive triple stars. In this scenario, favorable conditions for the
inspiral of a black hole binary are initiated by its gravitational interaction
with a distant companion, rather than by a common-envelope phase invoked in
standard binary evolution models. We use a code that follows self-consistently
the evolution of massive triple stars, combining the secular triple dynamics
(Lidov-Kozai cycles) with stellar evolution. After a black hole triple is
formed, its dynamical evolution is computed using either the orbit-averaged
equations of motion, or a high-precision direct integrator for triples with
weaker hierarchies for which the secular perturbation theory breaks down. Most
black hole mergers in our models are produced in the latter non-secular
dynamical regime. We derive the properties of the merging binaries and compute
a black hole merger rate in the range (0.3- 1.3) Gpc^{-3}yr^{-1}, or up to
~2.5Gpc^{-3}yr^{-1} if the black hole orbital planes have initially random
orientation. Finally, we show that black hole mergers from the triple channel
have significantly higher eccentricities than those formed through the
evolution of massive binaries or in dense star clusters. Measured
eccentricities could therefore be used to uniquely identify binary mergers
formed through the evolution of triple stars. While our results suggest up to
~10 detections per year with Advanced-LIGO, the high eccentricities could
render the merging binaries harder to detect with planned space based
interferometers such as LISA.Comment: Accepted for publication in ApJ. 10 pages, 6 figure
Reply to ``Comment on `Test of constancy of speed of light with rotating cryogenic optical resonators' ''
An improved analysis of the Michelson-Morley-type experiment by P. Antonini
et al. (Phys. Rev. A. 71, 050101 (2005)) yields the Robertson-Mansouri-Sexl
theory parameter combination and the Standard Model Extension theory parameter
.Comment: 2 page
Sustainability assessment: an integrated approach with inhabitant participation
The research has led us to develop a method for formulating sustainability strategies for neighborhood rehabilitation. This method is targeted to decision-makers in charge of implementing projects for the regeneration of the built environment at various levels within the urban and building scales. The methods and tools suggested here, which have been tested in collaboration with Comune di Bologna –the Bologna City Council- and ACER Bologna –the local Agency for public housing- make use of both technical/objective parameters and a participative approach to address the environmental and social sustainability requirements of citizens, local policies, and EU indications
Test of constancy of speed of light with rotating cryogenic optical resonators
A test of Lorentz invariance for electromagnetic waves was performed by
comparing the resonance frequencies of two optical resonators as a function of
orientation in space. In terms of the Robertson-Mansouri-Sexl theory, we obtain
, a ten-fold improvement compared to
the previous best results. We also set a first upper limit for a so far unknown
parameter of the Standard Model Extension test theory,
.Comment: 4 pages, 2 figures, accepted for publication Phys. Rev. A (2005
Frontal and subcortical contribution to visual hallucinations in dementia with Lewy bodies and Parkinson’s disease
Objectives. Visual hallucinations (VH) are common in Lewy body disease (LBD), and have been associated with cognitive and structural brain alterations. Evidence so far concerns mainly Parkinson’s disease (PD), but little is known about symptom-specific pathophysiological mechanisms across the LBD spectrum, especially related to the presence of dementia. The aim of the present pilot study was to investigate the neuroanatomical, and neuropsychological characteristics related to VH in two forms of LBD, namely dementia with Lewy bodies (DLB) and PD without dementia.
Methods. Whole brain voxel-based morphometry (VBM) analyses on 3D MRI acquired structural brain scans, and neuropsychological testing were performed on 28 clinically diagnosed DLB (11 with VH, 17 NVH), and 24 PD (9 with VH, and 15 NVH) patients. In order to assess differences in grey matter (GM) regional volumes, and cognitive performance, hallucinating patients for each group were compared with corresponding non-hallucinating ones.
Results. DLB patients with VH presented significantly worse visual attention deficits compared to those without, which persisted even when controlling for visual perception. Whole brain VBM analysis revealed decreased GM volume in DLB with VH in the right superior and medial frontal gyri, putamen, caudate nucleus and insula. Subcortical regional volumes were also significantly associated with visual attention performance. Hallucinating PD patients, instead, presented more severe executive dysfunction, but VBM showed no volumetric differences between the two PD subgroups. Post hoc region of interest analyses revealed striatal GM loss in PD with VH.
Conclusion. Frontal and striatal GM atrophy may contribute to the emergence of VH in DLB, which may be fostered by the more severe attention deficits. Striatal GM loss and executive dysfunction, instead, appeared to underlie VH in PD without dementia
Effect of metabolic and antioxidant supplementation on sperm parameters in oligo-astheno-teratozoospermia, with and without varicocele: a double-blind placebo-controlled study
Since sperm require high energy levels to perform their specialised function, it is vital that essential nutrients are available for spermatozoa when they develop, capacitate and acquire motility. However, they are vulnerable to a lack of energy and excess amounts of reactive oxygen species, which can impair sperm function, lead to immotility, acrosomal reaction impairment, DNA fragmentation and cell death. This monocentric, randomised, double-blind, placebo-controlled trial investigated the effect of 6 months of supplementation with l-carnitine, acetyl-l-carnitine and other micronutrients on sperm quality in 104 subjects with oligo- and/or astheno- and/or teratozoospermia with or without varicocele. In 94 patients who completed the study, sperm concentration was significantly increased in supplemented patients compared to the placebo (p =.0186). Total sperm count also increased significantly (p =.0117) in the supplemented group as compared to the placebo group. Both, progressive and total motility were higher in supplemented patients (p =.0088 and p =.0120, respectively). Although pregnancy rate was not an endpoint of the study, of the 12 pregnancies that occurred during the follow-up, 10 were reported in the supplementation group. In general, all these changes were more evident in varicocele patients. In conclusion, supplementation with metabolic and antioxidant compounds could be efficacious when included in strategies to improve fertility
Effect of facade reflectance on outdoor microclimate: An Italian case study
Global warming affects the built environment with relation to its own characteristics, form, density. Heat waves effects would have limited effects if most of the cities would not be affected by Urban Heat Island that strongly increase their impacts (particularly on urban population). Does the choice of façade colours and materials contribute to this issue? The paper reports a research on a case study in Italy that tries to answer to this question comparing the trend in outdoor temperature increase closed to the building façade with relation to its colour and reflectance variations modelled by using Envi-met software. The outcomes point out that there is a correlation between the building façade reflectance and the temperature trend but this has a very limited influence on outdoor microclimate in open spaces as it varies in a range of less than 1°C
Cellular and molecular mechanisms regulating oocyte quality and the relevance for farm animal reproductive efficiency
The efficiency of breeding schemes is dependent on the high fecundity of the selected individuals. Reproductive technologies are constantly pushing the physiological limits, but while the male reproductive potential is almost fully exploited, female reproductive physiology is the subject of constant research. Since the number of offspring that a female can bring to term each pregnancy cannot be changed, the ideal approach is to remove the potential offspring at the beginning of development and to transfer them to recipients of lesser genetic value. The earlier the collection takes place, the higher the number of descendants that a female can generate, so that now, the number of available oocytes becomes the limiting factor. This article will describe how detailed studies on oocyte physiology are beginning to unravel the complex sequence that transforms a small primordial follicle into a large ovulatory follicle containing a mature oocyte. Progressively, the limits to oocyte manipulation have been recognised and gradually overcome with adequate hormonal treatments in vivo and with specific media supplementation in vitro. This has led to the development of highly efficient reproductive technologies and the promise of even greater advances in the future. Surprising new findings, such as ovarian stem cells that can replenish the follicle population or long term embryonic stem cell lines that can differentiate into oocytes, are rapidly changing our expectations
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