A Pedagogical Discussion Concerning the Gravitational Energy Radiated by Keplerian Systems

We first discuss the use of dimensional arguments (and of the quadrupolar emission hypothesis) in the derivation of the gravitational power radiated on a circular orbit. Then, we show how to simply obtain the instantaneous power radiated on a general Keplerian orbit by approximating it locally by a circle. This allows recovering with a good precision, in the case of an ellipse, the highly non trivial dependence on the eccentricity of the average power given by general relativity. The whole approach is understandable by undergraduate students.Comment: A simpler method has been used in the calculations, which requires now only standard knowledge (the radius of curvature is defined by the normal acceleration). Two figures have been added. Concerning the dimensional analysis, the comparison with electromagnetism has been detaile

Amazonian deforestation: Regional and global issues

How does the deforestation of Amazonia affect global and regional climates? What are the roles of these changes on Amazonian ecosystems? We have concluded that the relation between Regional Climate Changes (RCC) and Global Climate Change (GCC) is directly associated with anthropogenic activities and therefore sensitive to social, economical and political interventions. The RCCs are caused by actions within the realm of the Brazilian sociopolitical scenario, and prone to changes through the implementation of public policies regulating the sustained use of the renewable resources. The GCCs belong to an international arena, and are caused by the high emission rates of green house gases by the developed countries. The effects of the RCCs could be abated if the developed countries would endeavor to reduce the present emission levels as documented in IPCC meetings and collaborate in the implementation of a regulation to curb the carbon emissions, in accordance to the Kyoto protocol

How and when of eyelid reconstruction using autologous transplantation

Reconstructive surgery of the eyelid after tumor excision, trauma or other causes can be challenging, especially due to the complexities of the anatomic structures and to the necessity of both functional and aesthetic successful outcomes. The aim of this minireview was to investigate the use of tissue transplantation in eyelid reconstruction. Surgical procedures are various, based on the use of both flaps, pedicled or free, and grafts, in order to guarantee adequate tissue reconstruction and blood supply, which are necessary for correct healing. Common techniques normally include the use of local tissues, combining non-vascularized grafts with a vascularized flap for the two lamellae repair, to attempt a reconstruction similar to the original anatomy. When defects are too wide, vast, deep, and complex or when no adjacent healthy tissues are available, distant area tissues need to be recruited as free flaps or grafts and paired with mucosal layer reconstruction. With regards to the anterior lamella, full thickness skin grafts are commonly preferred. With regards to the reconstruction of posterior lamella, there are different graft options, which include conjunctival or tarsoconjunctival, mucosal or palatal or cartilaginous grafts usually combined with local flaps. Free flap transplantation, normally reserved for rare select cases, include the use of the radial forearm and anterolateral flaps combined with mucosal grafts, which are surgical options currently reported in the literature

Adipose Stem Cells in Modern-Day Ophthalmology

Stem cells (SCs) have evolved as an interesting and viable factor in ophthalmologic patient care in the past decades. SCs have been classified as either embryonic, mesenchymal, tissue-specific, or induced pluripotent cells. Multiple novel management techniques and clinical trials have been established to date. While available publications are predominantly animal-model-based, significant material is derived from human studies and case-selected scenarios. This possibility of explanting cells from viable tissue to regenerate/repair damaged tissue points to an exciting future of therapeutic options in all fields of medicine, and ophthalmology is surely not left out. Adipose tissue obtained from lipo-aspirates has been shown to produce mesenchymal SCs that are potentially useful in different body parts, including the oculo-visual system. An overview of the anatomy, physiology, and extraction process for adipose-tissue-derived stem cells (ADSC) is important for better understanding the potential therapeutic benefits. This review examines published data on ADSCs in immune-modulatory, therapeutic, and regenerative treatments. We also look at the future of ADSC applications for ophthalmic patient care. The adverse effects of this relatively novel therapy are also discussed

On the observability of the neutrino charge radius

It is shown that the probe-independent charge radius of the neutrino is a physical observable; as such, it may be extracted from experiment, at least in principle. This is accomplished by expressing a set of experimental neutrino-electron cross-sections in terms of the finite charge radius and two additional gauge- and renormalization-group-invariant quantities, corresponding to the electroweak effective charge and mixing angle.Comment: 10 pages, 1 figure; a typo in Eq.1 corrected, some comments adde

Self-Lensing Models of the LMC

All of the proposed explanations for the microlensing events observed towards the LMC have difficulties. One of these proposed explanations, LMC self-lensing, which invokes ordinary LMC stars as the long sought-after lenses, has recently gained considerable popularity as a possible solution to the microlensing conundrum. In this paper, we carefully examine the set of LMC self-lensing models. In particular, we review the pertinent observations made of the LMC, and show how these observations place limits on such self-lensing models. We find that, given current observational constraints, no purely LMC disk models are capable of producing optical depths as large as that reported in the MACHO collaboration 2-year analysis. Besides pure disk, we also consider alternate geometries, and present a framework which encompasses the previous studies of LMC self-lensing. We discuss which model parameters need to be pushed in order for such models to succeed. For example, like previous workers, we find that an LMC halo geometry may be able to explain the observed events. However, since all known LMC tracer stellar populations exhibit disk-like kinematics, such models will have difficulty being reconciled with observations. For SMC self-lensing, we find predicted optical depths differing from previous results, but more than sufficient to explain all observed SMC microlensing. In contrast, for the LMC we find a self-lensing optical depth contribution between 0.47e-8 and 7.84e-8, with 2.44e-8 being the value for the set of LMC parameters most consistent with current observations.Comment: 20 pages, Latex, 14 figures, submitted to Ap

A new look at the cosmic ray positron fraction

The positron fraction in cosmic rays was found to be a steadily increasing in function of energy, above $\sim$ 10 GeV. This behaviour contradicts standard astrophysical mechanisms, in which positrons are secondary particles, produced in the interactions of primary cosmic rays during the propagation in the interstellar medium. The observed anomaly in the positron fraction triggered a lot of excitement, as it could be interpreted as an indirect signature of the presence of dark matter species in the Galaxy. Alternatively, it could be produced by nearby astrophysical sources, such as pulsars. Both hypotheses are probed in this work in light of the latest AMS-02 positron fraction measurements. The transport of the primary and secondary positrons in the Galaxy is described using a semi-analytic two-zone model. MicrOMEGAs is used to model the positron flux generated by dark matter species. The description of the positron fraction from astrophysical sources is based on the pulsar observations included in the ATNF catalogue. We find that the mass of the favoured dark matter candidates is always larger than 500 GeV. The only dark matter species that fulfils the numerous gamma ray and cosmic microwave background bounds is a particle annihilating into four leptons through a light scalar or vector mediator, with a mixture of tau (75%) and electron (25%) channels, and a mass between 0.5 and 1 TeV. The positron anomaly can also be explained by a single astrophysical source and a list of five pulsars from the ATNF catalogue is given. Those results are obtained with the cosmic ray transport parameters that best fit the B/C ratio. Uncertainties in the propagation parameters turn out to be very significant. In the WIMP annihilation cross section to mass plane for instance, they overshadow the error contours derived from the positron data.Comment: 20 pages, 16 figures, accepted for publication in A&A, corresponds to published versio

Low-technology exercise test in the preoperative evaluation of lung resection candidates

Exercise tests are increasingly used in the preoperative functional evaluation of lung resection candidates. Low-technology exercise tests include six minute walking, shuttle walking and stair climbing. Conflicting evidence has been reported regarding 6 minute walking test. This test should not be used to select patients for lung resection. An incremental shuttle walk test is easier to replicate than 6 minute walking test. Most patients achieving 25 shuttles or 400 m have a maximum oxygen consumption measured at cardiopulmonary exercise test greater than 15 l/Kg/min. Although this test tends to underestimate performance at the lower range compared to peak oxygen consumption it can be used a screening test before lung resection. Excluding patients from operation based on this test alone is however not recommended and a formal cardiopulmonary exercise test should be always used in those walking less than 400 m. Stair climbing has been extensively studied in thoracic surgery. Several studies have found that poor performance in this test is indicative of cardiopulmonary complications and mortality after lung resection. In particular, climbing less than 12 m represents very high risk, whereas climbing more than 22 m is associated with a favourable outcome. Recent guidelines recommend referring all patients climbing lower than 22 m to cardiopulmonary exercise test. Stair climbing can be used as a screening test in cases cardiopulmonary exercise test is not readily available. In general, patients climbing more than 22 m can proceed to surgery without further evaluation