Gravitational waves from compact binaries

In this review, I give a summary of the history of our understanding of gravitational waves and how compact binaries were used to transform their status from mathematical artefact to physical reality. I also describe the types of compact (stellar) binaries that LISA will observe as soon as it is switched on. Finally, the status and near future of LIGO, Virgo and GEO are discussed, as well as the expected detection rates for the Advanced detectors, and the accuracies with which binary parameters can be determined when BH/NS inspirals are detected.Comment: 15 pages, 3 figures, 2 tables. To be published in "Evolution of compact binaries", editors: Linda Schmidtobreick, Matthias Schreiber and Claus Tapper

The exclusive (e,e′'p) reaction at high missing momenta

The reduced (e,e$'$p) cross section is calculated for kinematics that probe high missing momenta. The final-state interaction is handled within a non-relativistic many-body framework. One- and two-body nuclear currents are included. Electron distortion effects are treated in an exact distorted wave calculation. It is shown that at high missing momenta the calculated (e,e$'$p) cross sections exhibit a pronounced sensitivity to ground-state correlations of the RPA type and two-body currents. The role of these mechanisms is found to be relatively small at low missing momenta.Comment: 15 pages in REVtex with embedded psfigure

Masses and envelope binding energies of primary stars at the onset of a common envelope

We present basic properties of primary stars that initiate a common envelope (CE) in a binary, while on the giant branch. We use the population-synthesis code described in Politano et al. (2010) and follow the evolution of a population of binary stars up to the point where the primary fills its Roche lobe and initiates a CE. We then collect the properties of each system, in particular the donor mass and the binding energy of the donor's envelope, which are important for the treatment of a CE. We find that for most CEs, the donor mass is sufficiently low to define the core-envelope boundary reasonably well. We compute the envelope-structure parameter {\lambda_\mathrm{env}} from the binding energy and compare its distribution to typical assumptions that are made in population-synthesis codes. We conclude that {\lambda_\mathrm{env}} varies appreciably and that the assumption of a constant value for this parameter results in typical errors of 20--50%. In addition, such an assumption may well result in the implicit assumption of unintended and/or unphysical values for the CE parameter {\alpha_\mathrm{CE}}. Finally, we discuss accurate existing analytic fits for the envelope binding energy, which make these oversimplified assumptions for {\lambda_\mathrm{env}}, and the use of {\lambda_\mathrm{env}} in general, unnecessary.Comment: 6 pages, 3 figures, 1 table; to be published in the proceedings of the conference "Binary Star Evolution", in Mykonos, Greece, held in June 22-25, 201

Analytical expressions for the envelope binding energy of giants as a function of basic stellar parameters

The common-envelope (CE) phase is an important stage in the evolution of binary stellar populations. The most common way to compute the change in orbital period during a CE is to relate the binding energy of the envelope of the Roche-lobe filling giant to the change in orbital energy. Especially in population-synthesis codes, where the evolution of millions of stars must be computed and detailed evolutionary models are too expensive computationally, simple approximations are made for the envelope binding energy. In this study, we present accurate analytic prescriptions based on detailed stellar-evolution models that provide the envelope binding energy for giants with metallicities between Z = 10-4 and Z = 0.03 and masses between 0.8 Msun and 100 Msun, as a function of the metallicity, mass, radius and evolutionary phase of the star. Our results are also presented in the form of electronic data tables and Fortran routines that use them. We find that the accuracy of our fits is better than 15% for 90% of our model data points in all cases, and better than 10% for 90% of our data points in all cases except the asymptotic giant branches for three of the six metallicities we consider. For very massive stars (M > 50 Msun), when stars lose more than ~20% of their initial mass due to stellar winds, our fits do not describe the models as accurately. Our results are more widely applicable - covering wider ranges of metallicity and mass - and are of higher accuracy than those of previous studies

The Formation of Low-Mass Double White Dwarfs through an Initial Phase of Stable Non-Conservative Mass Transfer

Although many double white dwarfs (DWDs) have been observed, the evolutionary channel by which they are formed from low-mass/long-period red-giant-main-sequence (RG-MS) binaries remains uncertain. The canonical explanations involve some variant of double common-envelope (CE) evolution, however it has been found that such a mechanism cannot produce the observed distribution. We present a model for the initial episode of mass transfer (MT) in RG-MS binaries, and demonstrate that their evolution into double white dwarfs need not arise through a double-CE process, as long as the initial primary's core mass (Md,c) does not exceed 0.46M$_{\odot}$. Instead, the first episode of dramatic mass loss may be stable, non-conservative MT. We find a lower bound on the fraction of transferred mass that must be lost from the system in order to provide for MT, and demonstrate the feasibility of this channel in producing observed low-mass (with M$_{d,c}$ < 0.46M$_{\odot}$) DWD systems.Comment: 2 pages, 1 figure, Conference Proceedings for the International Conference on Binaries, Mykonos, Greec

Repensar el proyecto urbano residencial en la ciudad lineal: un estudio urbano arquitectonico sobre la vivienda sustentable en el distrito metropolitano de Quito

Peer Reviewe

Move to improve:The effect of physical activity on cognitive control and antisocial behavior

The current thesis investigated the effect of physical activity on antisocial behavior and the possible role of cognitive control in multi-problem young adults. Earlier research uncovered a robust association between impaired cognitive control and antisocial behavior, implying individuals displaying antisocial behavior may benefit from interventions targeting neurocognitive functioning. Impaired cognitive control can severely impact one's life, as it is needed to adequately plan, regulate, and adapt goal-directed behavior. Understandably, deficiencies in these capabilities may sustain or promote antisocial behavior through the impaired ability to anticipate negative consequences, suppress unwanted impulses, and adjust behavior according to social expectations. Physical activity has been previously proposed as an effective intervention for decreasing antisocial behavior in children and adolescents (aged &lt; 18) from the general population and in adult offenders or adults suffering from substance use disorders, yet existing research in young adults (especially clinical or at-risk young adults) is scarce and inconclusive. The observed reduction in antisocial behavior may be the result of an enhancement in neurocognitive functioning, as prior studies indicate robust positive effects on cognitive control following increased physical activity in healthy (but sedentary) youth aged &lt;18 and the elderly. However, to date, the effect of physical activity on cognitive control has not been examined in young adults suffering from multiple problems including aggression, delinquent behavior, frequent substance use, and other externalizing behaviors despite their possible associated executive deficits. To deepen our understanding of the relation between physical activity, antisocial behavior, and cognitive control, we first studied the possible potential of neurobiological and (neuro)behavioral measures of cognitive control in the prediction of and association with real-world behavior, i.e., behavior following a multimodal day treatment and antisocial behavior. We included three indices of neurocognitive functions, i.e., error processing, response inhibition, and interference, using different measurement techniques including functional magnetic resonance imaging and electroencephalographic paradigms in male multi-problem young adults (aged 18 – 27). In the following chapter, we reviewed and quantified the overall effectiveness of previous physical activity interventions in reducing antisocial behavior in a meta-analytic review. Subsequently, in the next two chapters, we discussed the association between physical activity and the impact on behavioral measures of cognitive control using a randomized controlled intervention study. And lastly, we investigated other ways in which physical activity might contribute to the development of positive behavior and the decrease of negative behavior, according to the multi-problem young adults, using a thematic approach. Our findings suggest that overall, increased physical activity may be used to treat antisocial behavior in adults displaying a range of externalizing behaviors. Furthermore, regarding cognitive control, the current results first associated a neurocognitive biomarker (ACC activity during response inhibition) with better outcomes (higher odds of engaging in daytime activities) a year after a multimodal day treatment program in populations displaying antisocial behavior, linking cognitive control to real-world positive behavior. Secondly, our data suggest enhanced neurocognitive functioning following a physical activity program in young adults with impaired cognitive control, who are suffering from multiple problems, including several forms of antisocial behavior. Taken together with prior studies, the results of the current dissertation suggest that a: physical activity interventions and programs may possibly provide an easy-to-implement treatment of antisocial behavior and b: this positive behavioral effect may be partially explained by an exercise-induced enhancement of cognitive control, although future studies including both cognitive control and antisocial behavior are needed to verify this hypothesis

Population synthesis of classical low-mass X-ray binaries in the Galactic Bulge

Aims. We model the present-day population of 'classical' low-mass X-ray binaries (LMXBs) with neutron star accretors, which have hydrogen-rich donor stars. Their population is compared with that of hydrogen-deficient LMXBs, known as ultracompact X-ray binaries (UCXBs). We model the observable LMXB population and compare it to observations. Methods. We combine the binary population synthesis code SeBa with detailed LMXB evolutionary tracks to model the size and properties of the present-day LMXB population in the Galactic Bulge. Whether sources are persistent or transient, and what their instantaneous X-ray luminosities are, is predicted using the thermal-viscous disk instability model. Results. We find a population of ~2.1 x 10^3 LMXBs with neutron star accretors. Of these about 15 - 40 are expected to be persistent (depending on model assumptions), with luminosities higher than 10^35 erg s^-1. About 7 - 20 transient sources are expected to be in outburst at any given time. Within a factor of two these numbers are consistent with the observed population of bright LMXBs in the Bulge. This gives credence to our prediction of the existence of a population of ~1.6 x 10^3 LMXBs with low donor masses that have gone through the period minimum, and have present-day mass transfer rates below 10^-11 Msun yr^-1. Conclusions. Even though the observed population of hydrogen-rich LMXBs in the Bulge is larger than the observed population of (hydrogen-deficient) UCXBs, the latter have a higher formation rate. While UCXBs may dominate the total LMXB population at the present, the majority would be very faint, or may have become detached and produced millisecond radio pulsars. In that case UCXBs would contribute significantly more to the formation of millisecond radio pulsars than hydrogen-rich LMXBs. [abridged]Comment: 8 pages, 10 figures. Accepted for publication in Astronomy and Astrophysics. v2: minor language correction