7 research outputs found
The influence of the mass-ratio on the acceleration of particles by filamentation instabilities
Almost all sources of high energy particles and photons are associated with
jet phenomena. Prominent sources of such highly relativistic outflows are
pulsar winds and Active Galactic Nuclei. The current understanding of these
jets assumes diluted plasmas which are best described as kinetic phenomena. In
this kinetic description particle acceleration to ultra-relativistic speeds can
occur in completely unmagnetized and neutral plasmas through insetting effects
of instabilities. Even though the morphology and nature of particle spectra are
understood to a certain extent, the composition of the jets is not known yet.
While Poynting-flux dominated jets are certainly composed of electron-positron
plasmas, the understanding of the governing physics in AGN jets is mostly
unclear. In this article we investigate how the constituting elements of an
electron-positron-proton plasma behave differently under the variation of the
fundamental mass-ratio m_p/m_e. We studied initially unmagnetized
counterstreaming plasmas using fully relativistic three-dimensional
particle-in-cell simulations to investigate the influence of the mass-ratio on
particle acceleration and magnetic field generation in electron-positron-proton
plasmas. We covered a range of mass-ratios m_p/m_e between 1 and 100 with a
particle number composition of n_{p^+}/n_{e^+} of 1 in one stream, only protons
are injected in the other, whereas electrons are present in both to guarantee
charge neutrality in the simulation box. We find that with increasing proton
mass the instability takes longer to develop and for mass-ratios > 20 the
particles seem to be accelerated in two phases which can be accounted to the
individual instabilities of the different species. This means that for high
mass ratios the coupling between electrons/positrons and the heavier protons,
which occurs in low mass-ratios, disappears.Comment: 15 pages, 6 figure
Diagnosis and management of Silver–Russell syndrome: first international consensus statement
This Consensus Statement summarizes recommendations for clinical diagnosis, investigation and management of patients with Silver–Russell syndrome (SRS), an imprinting disorder that causes prenatal and postnatal growth retardation. Considerable overlap exists between the care of individuals born small for gestational age and those with SRS. However, many specific management issues exist and evidence from controlled trials remains limited. SRS is primarily a clinical diagnosis; however, molecular testing enables confirmation of the clinical diagnosis and defines the subtype. A 'normal' result from a molecular test does not exclude the diagnosis of SRS. The management of children with SRS requires an experienced, multidisciplinary approach. Specific issues include growth failure, severe feeding difficulties, gastrointestinal problems, hypoglycaemia, body asymmetry, scoliosis, motor and speech delay and psychosocial challenges. An early emphasis on adequate nutritional status is important, with awareness that rapid postnatal weight gain might lead to subsequent increased risk of metabolic disorders. The benefits of treating patients with SRS with growth hormone include improved body composition, motor development and appetite, reduced risk of hypoglycaemia and increased height. Clinicians should be aware of possible premature adrenarche, fairly early and rapid central puberty and insulin resistance. Treatment with gonadotropin-releasing hormone analogues can delay progression of central puberty and preserve adult height potential. Long-term follow up is essential to determine the natural history and optimal management in adulthood
Diagnosis and management of Silver-Russell syndrome: First international consensus statement
This Consensus Statement summarizes recommendations for clinical diagnosis, investigation and management of patients with Silver-Russell syndrome (SRS), an imprinting disorder that causes prenatal and postnatal growth retardation. Considerable overlap exists between the care of individuals born small for gestational age and those with SRS. However, many specific management issues exist and evidence from controlled trials remains limited. SRS is primarily a clinical diagnosis; however, molecular testing enables confirmation of the clinical diagnosis and defines the subtype. A 'normal' result from a molecular test does not exclude the diagnosis of SRS. The management of children with SRS requires an experienced, multidisciplinary approach. Specific issues include growth failure, severe feeding difficulties, gastrointestinal problems, hypoglycaemia, body asymmetry, scoliosis, motor and speech delay and psychosocial challenges. An early emphasis on adequate nutritional status is important, with awareness that rapid postnatal weight gain might lead to subsequent increased risk of metabolic disorders. The benefits of treating patients with SRS with growth hormone include improved body composition, motor development and appetite, reduced risk of hypoglycaemia and increased height. Clinicians should be aware of possible premature adrenarche, fairly early and rapid central puberty and insulin resistance. Treatment with gonadotropin-releasing hormone analogues can delay progression of central puberty and preserve adult height potential. Long-term follow up is essential to determine the natural history and optimal management in adulthood
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Wave extraction in numerical evolutions of distorted black holes
The study of black holes and their interactions and the extraction of gravitational waves become of primary importance from both - the astrophysical and theoretical points of view now that the first gravitational detectors have started operating; gravitational waves, while certainly extremely weak, are also extremely pervasive and thus a novel and very promising way of exploring the universe. Space-times containing highly distorted black holes will generally have strong time-dependent gravitational fields and presumably provide the strongest sources of gravitational waves in the universe. This work focuses on two fundamental problems in modern numerical relativity: (1) Creating valid initial data of non-perturbative distorted black hole space-times for numerical evolution, and (2) extracting the radiation quantities in a coordinate independent way, using the Newman-Penrose formalism. I first consider the initial data for such distorted black hole space-times, prescribing them successfully in a simplified situation of superimposed time symmetric Brill waves, and leading the way to more general initial data which corresponds to rotating black holes. To drop the assumption of time symmetric initial hypersurfaces will be subject of future work. Next I move to the numerical evolution and introduce a simple but stable way to perform excision in spherical coordinates. Finally, I extract the gravitational wave signal from the numerical simulations, using the Newman-Penrose formalism, in particular the Weyl scalars. I adopt a particular frame where the Weyl scalars acquire physical meaning, and can be directly associated with the waveform. Moreover, I derive a formula to calculate the energy carried away by the wave. Comparison of the even and odd parity waveforms of our non-perturbation approach with the metric perturbation approaches such as Regge-Wheeler [1], Zerilli [2] and Teukolsky [3] will partly be discussed and partly be subject of future workPhysic
Disturbed genomic imprinting and its relevance for human reproduction: causes and clinical consequences
Background: human reproductive issues affecting fetal and maternal health are caused by numerous exogenous and endogenous factors, of which the latter undoubtedly include genetic changes. Pathogenic variants in either maternal or offspring DNA are associated with effects on the offspring including clinical disorders and nonviable outcomes. Conversely, both fetal and maternal factors can affect maternal health during pregnancy. Recently, it has become evident that mammalian reproduction is influenced by genomic imprinting, an epigenetic phenomenon that regulates the expression of genes according to their parent from whom they are inherited. About 1% of human genes are normally expressed from only the maternally or paternally inherited gene copy. Since numerous imprinted genes are involved in (embryonic) growth and development, disturbance of their balanced expression can adversely affect these processes.Ojective and rationale: this review summarises current our understanding of genomic imprinting in relation to human ontogenesis and pregnancy and its relevance for reproductive medicine.Search methods: literature databases (Pubmed, Medline) were thoroughly searched for the role of imprinting in human reproductive failure. In particular, the terms ‘multilocus imprinting disturbances, SCMC, NLRP/NALP, imprinting and reproduction’ were used in various combinations.Outcomes: a range of molecular changes to specific groups of imprinted genes are associated with imprinting disorders, i.e. syndromes with recognisable clinical features including distinctive prenatal features. Whereas the majority of affected individuals exhibit alterations at single imprinted loci, some have multi-locus imprinting disturbances (MLID) with less predictable clinical features. Imprinting disturbances are also seen in some nonviable pregnancy outcomes, such as (recurrent) hydatidiform moles, which can therefore be regarded as a severe form of imprinting disorders. There is growing evidence that MLID can be caused by variants in the maternal genome altering the imprinting status of the oocyte and the embryo, i.e. maternal effect mutations. Pregnancies of women carrying maternal affect mutations can have different courses, ranging from miscarriages to birth of children with clinical features of various imprinting disorders.Wider implications: increasing understanding of imprinting disturbances and their clinical consequences have significant impacts on diagnostics, counselling and management in the context of human reproduction. Defining criteria for identifying pregnancies complicated by imprinting disorders facilitates early diagnosis and personalised management of both the mother and offspring. Identifying the molecular lesions underlying imprinting disturbances (e.g. maternal effect mutations) allows targeted counselling of the family and focused medical care in further pregnancies