63 research outputs found

    Low thrust propulsion in a coplanar circular restricted four body problem

    Get PDF
    This paper formulates a circular restricted four body problem (CRFBP), where the three primaries are set in the stable Lagrangian equilateral triangle configuration and the fourth body is massless. The analysis of this autonomous coplanar CRFBP is undertaken, which identies eight natural equilibria; four of which are close to the smaller body, two stable and two unstable, when considering the primaries to be the Sun and two smaller bodies of the solar system. Following this, the model incorporates `near term' low-thrust propulsion capabilities to generate surfaces of articial equilibrium points close to the smaller primary, both in and out of the plane containing the celestial bodies. A stability analysis of these points is carried out and a stable subset of them is identied. Throughout the analysis the Sun-Jupiter-Asteroid-Spacecraft system is used, for conceivable masses of a hypothetical asteroid set at the libration point L4. It is shown that eight bounded orbits exist, which can be maintained with a constant thrust less than 1:5 10􀀀4N for a 1000kg spacecraft. This illustrates that, by exploiting low-thrust technologies, it would be possible to maintain an observation point more than 66% closer to the asteroid than that of a stable natural equilibrium point. The analysis then focusses on a major Jupiter Trojan: the 624-Hektor asteroid. The thrust required to enable close asteroid observation is determined in the simplied CRFBP model. Finally, a numerical simulation of the real Sun-Jupiter-624 Hektor-Spacecraft is undertaken, which tests the validity of the stability analysis of the simplied model

    A multistep process for the dispersal of a Y chromosomal lineage in the Mediterranean area

    Get PDF
    Tn this work we focus on a microsatellite-defined Y-chromosomal lineage (network 1.2) identified by us and reported in previous studies, whose geographic distribution and antiquity appear to be compatible with the Neolithic spread of farmers. Here, we set network 1.2 in the Y-chromosomal phylogenetic tree, date it with respect to other lineages associated with the same movements by other authors, examine its diversity by means of tri- and tetranucleotide loci and discuss the implications hi reconstructing the spread of this group of chromosomes in the Mediterranean area. Our results define a tripartite phylogeny wit-bin HG 9 (Rosser et al. 2000) with the deepest branching defined by alleles T (Haplogroup Eu 10) or G (Haplogroup Eu9) at M172 (Semino et al. 2000), and a subsequent branching within Eu9 defined by network 1.2. Population distributions of HG 9 and network 1.2 show that their occurrence in the surveyed area is not due to the spread of people from a single parental population but, rather, to a process punctuated by at least two phases. Our data identify the wide area of the Balkans, Aegean and Anatolia as the possible homeland harbouring the largest variation within network 1.2. The use of recently proposed tests based on the stepwise mutation model suggests that its spread was associated to a population expansion, xvith a high rate of male gene flow in the Turkish Greek area

    Patterns of male-specific inter-population divergence in Europe, West Asia and North Africa

    Get PDF
    We typed 1801 males from 55 locations for the Y-specific binary markers YAP! DYZ3, SRY10831 and the (CA)n microsatellites YCAII and DYS413. Phylogenetic relationships of chromosomes with the same binary haplotype were condensed in seven large one-step networks! which accounted for 95% of all chromosomes. Their coalescence ages were estimated based on microsatellite diversity. The three largest and oldest networks undergo sharp frequency changes in three areas. The more recent network; 3.1A clearly discriminates between Western and Eastern European populations. Pairwise Pst showed an overall increment with increasing geographic distance but with a slope greatly reduced when compared to previous reports. BI sectioning the entire data set according to geographic and linguistic criteria, we found higher Fst-on-distance slopes within Europe than in West Asia or across the tno continents

    Multiple Advantageous Amino Acid Variants in the NAT2 Gene in Human Populations

    Get PDF
    Background: Genetic variation at NAT2 has been long recognized as the cause of differential ability to metabolize a wide variety of drugs of therapeutic use. Here, we explore the pattern of genetic variation in 12 human populations that significantly extend the geographic range and resolution of previous surveys, to test the hypothesis that different dietary regimens and lifestyles may explain inter-population differences in NAT2 variation. Methodology/Principal Findings: The entire coding region was resequenced in 98 subjects and six polymorphic positions were genotyped in 150 additional subjects. A single previously undescribed variant was found (34T>C; 12Y>H). Several aspects of the data do not fit the expectations of a neutral model, as assessed by coalescent simulations. Tajima's D is positive in all populations, indicating an excess of intermediate alleles. The level of between-population differentiation is low, and is mainly accounted for by the proportion of fast vs. slow acetylators. However, haplotype frequencies significantly differ across groups of populations with different subsistence. Conclusions/Significance: Data on the structure of haplotypes and their frequencies are compatible with a model in which slow-causing variants were present in widely dispersed populations before major shifts to pastoralism and/or agriculture. In this model, slow-causing mutations gained a selective advantage in populations shifting from hunting-gathering to pastoralism/agriculture. We suggest the diminished dietary availability of folates resulting from the nutritional shift, as the possible cause of the fitness increase associated to haplotypes carrying mutations that reduce enzymatic activity. © 2008 Luca et al

    Consent for organ and tissue retention in british law in the light of the human tissue act 2004

    No full text
    The experience from the scandals in hospitals at Liverpool and Bristol in the UK where retention of tissue and organs was undertaken without the consent of the parents and relatives raised serious concerns regarding the efficacy of the existing Human Tissue Act 1961, in England and the operation of the law by medical practitioners. In the aftermath of these damaging scandals a combination of public distrust and government overreaction has led to the enactment of new legislation, the Human Tissue Act 2004, which is aiming to prevent any flirther instances of the retention of organs and tissue from dead children or adults without their next of kin's consent or knowledge. However, scientists have expressed concerns that such changes might seriously endanger several medical research programmes, and also tissue and organ donation for transplantation. The aim of this article is to highlight important issues raised by existing practice in the post-mortem examinations in the UK and the lessons learnt from this and to discuss the benefits and the potential problems arising from the new Act. © YOZMOT 2006

    Legal and ethical issues in robotic surgery

    No full text
    Aim. With the rapid introduction of revolutionary technologies in surgical practice, such as computer-enhanced robotic surgery, the complexity in various aspects, including medical, legal and ethical, will increase exponentially. Our aim was to highlight important legal and ethical implications emerged from the application of robotic surgery. Methods. Search of the pertinent medical and legal literature. Results. Robotic surgery may open new avenues in the near future in surgical practice. However, in robotic surgery, special training and experience along with high quality assessment are required in order to provide normal conscientious care and state-of-the-art treatment. While the legal basis for professional liability remains exactly the same, litigation with the use of robotic surgery may be complex. In case of an undesirable outcome, in addition to physician and hospital, the manufacturer of the robotic system may be sued. In respect to ethical issues in robotic surgery, equipment safety and reliability, provision of adequate information, and maintenance of confidentiality are all of paramount importance. Also, the cost of robotic surgery and the lack of such systems in most of the public hospitals may restrict the majority from the benefits offered by the new technology. Conclusion. While surgical robotics will have a significant impact on surgical practice, it presents challenges so much in the realm of law and ethics as of medicine and health care. [Int Angiol 2010;29:75-9

    Evidence of deregulated cholesterol efflux in abdominal aortic aneurysm

    No full text
    Previous studies indicated that lipids may be associated with abdominal aortic aneurysm (AAA); however the molecular mechanism involved is unclear. Our study aimed to investigate the expression pattern of cholesterol efflux related proteins in AAA. Liver X receptors (LXRα and LXRβ), ATP-binding-cassette transporter A1 (ABCA1), Apolipoprotein AI (ApoAI), smooth muscle α-actin (α-SM) and vimentin expression levels were evaluated in human AAA, atherosclerotic (ATH) and normal abdominal aortic tissues. We found significant differences in LXRα, LXRβ and ABCA1 mRNA expression levels between AAA, ATH and normal whole aortic tissues and also within the AAA, ATH and normal "intima-media" layers. Specifically, LXRα, LXRβ and ABCA1 mRNA levels were decreased in AAA compared to ATH-whole tissues, as well as in AAA "intima-media" compared to ATH and normal "intima-media" layers. Moreover, immunohistochemical evaluation revealed that LXRα and ABCA1 immunoreactivities (IR) were reduced in the AAA media compared to the normal and ATH media layers and that they were also reduced in the intima layer of AAA and ATH tissues, whereas ApoAI-IR was increased in the AAA and ATH aortic walls compared to normal pointing to possible deregulation of the cholesterol efflux mechanism in AAA. Furthermore, double staining for vimentin and α-SM showed vimentin expression in the intima and inner media layer of AAA with sparse vimentin positive SMCs designating possible SMCs phenotype switch from contractile to synthetic form. In addition, histochemical analysis showed excessive lipid accumulation in the AAA wall, while co-staining using Oil Red O with α-SM or CD68 revealed lipid accumulation in SMCs and macrophages, respectively. Our study provides novel evidence for impaired cholesterol efflux in AAA associated with lipid accumulation in SMCs and macrophages, as well as switch of SMCs phenotype from contractile to synthetic form. © 2015 Elsevier GmbH

    Periodic Orbits Relevant for the Formation of Inner Rings in Barred Galaxies

    No full text
    • …
    corecore