45,578 research outputs found
On the connection between accreting X-ray and radio millisecond pulsars
No full textFor many years it has been recognized that the terminal stages of mass transfer in a low-mass X-ray binary (LMXB) should cause the magnetosphere of the accreting neutron star to expand, leading to a braking torque acting on the spinning pulsar. After the discovery of radio millisecond pulsars (MSPs) it was therefore somewhat a paradox (e.g. Ruderman et al. 1989) how these pulsars could retain their fast spins following the Roche-lobe decoupling phase, RLDP. Here I present a solution to this so-called ``turn-off problem'' which was recently found by combining binary stellar evolution models with torque computations (Tauris 2012). The solution is that during the RLDP the spin equilibrium of the pulsar is broken and therefore it remains a fast spinning object. I briefly discuss these findings in view of the two observed spin distributions in the populations of accreting X-ray millisecond pulsars (AXMSPs) and radio MSPs. ..
The construction of Karen Karnak: The multi-author-function
No full textThis thesis is situated within the comparatively recent developments of Web 2.0 and the emergence of interactive WikiMedia, and explores the mode of authorship within a Read/Write culture compared to that of a Read/Only tradition. The hypothesis of this study is that the role of the audience has become merged with the author, and as such, represents new functions and attributes, distinct from a more conventional concept of authorship, in which the roles of audience and author are more separate. Read/Write and participatory culture, as defined by this study, is focused on collaboration, and includes the influences of D.I.Y. culture, Open-Source practices and the production of text by multiple authors. Multi-authorship presents a re-thinking of several concepts which support the notion of the individual author, since the focus of multi-authorship is not on attribution and ownership of a finished text, but on the continued malleability of a text. Modes of multi-authorship, demonstrated in the use of the pseudonyms Alan Smithee and Karen Eliot, represent declarative authors whose names signify multiple origins, whilst concurrently indicating a distinct body of work. The function of these names form an important context to this study, since primary research involves the construction of an experimental mode of multi-authorship utilising WikiMedia technology and the interaction of thirty nine participants, who are invited to create a body of work under the collective pseudonym Karen Karnak. The data generated by this experiment is analysed using aspects of Michel Foucault's author-function to identify and determine power structures inherent in the WikiMedia context. The interplay of power structures, including concepts such as identity, ownership and the body of work, affect the resulting mode of authorship and contribute to the construction of Karen Karnak, suggesting further areas of research into the emerging multi-author
Early neutron star evolution in high-mass X-ray binaries
No full textThe application of standard accretion theory to observations of X-ray binaries provides valuable insights into neutron star (NS) properties, such as their spin period and magnetic field. However, most studies concentrate on relatively old systems, where the NS is in its late propeller, accretor, or nearly spin equilibrium phase. Here, we use an analytic model from standard accretion theory to illustrate the evolution of high-mass X-ray binaries (HMXBs) early in their life. We show that a young NS is unlikely to be an accretor because of the long duration of ejector and propeller phases. We apply the model to the recently discovered ∼4000 yr old HMXB XMMU J051342.6−672412 and find that the system's NS, with a tentative spin period of 4.4 s, cannot be in the accretor phase and has a magnetic field B > a few × 10
13 G, which is comparable to the magnetic field of many older HMXBs and is much higher than the spin equilibrium inferred value of a few × 10
11 G. The observed X-ray luminosity could be the result of thermal emission from a young cooling magnetic NS or a small amount of accretion that can occur in the propeller phase.
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Ultra-stripped supernovae: progenitors and fate
Full text linkThe explosion of ultra-stripped stars in close binaries can lead to ejecta masses <0.1 M⊙ and may explain some of the recent discoveries of weak and fast optical transients. In Tauris et al., it was demonstrated that helium star companions to neutron stars (NSs) may experience mass transfer and evolve into naked ∼1.5 M⊙ metal cores, barely above the Chandrasekhar mass limit. Here, we elaborate on this work and present a systematic investigation of the progenitor evolution leading to ultra-stripped supernovae (SNe). In particular, we examine the binary parameter space leading to electron-capture (EC SNe) and iron core-collapse SNe (Fe CCSNe), respectively, and determine the amount of helium ejected with applications to their observational classification as Type Ib or Type Ic. We mainly evolve systems where the SN progenitors are helium star donors of initial mass MHe = 2.5–3.5 M⊙ in tight binaries with orbital periods of Porb = 0.06–2.0 d, and hosting an accreting NS, but we also discuss the evolution of wider systems and of both more massive and lighter – as well as single – helium stars. In some cases, we are able to follow the evolution until the onset of silicon burning, just a few days prior to the SN explosion. We find that ultra-stripped SNe are possible for both EC SNe and Fe CCSNe. EC SNe only occur for MHe = 2.60–2.95 M⊙ depending on Porb. The general outcome, however, is an Fe CCSN above this mass interval and an ONeMg or CO white dwarf for smaller masses. For the exploding stars, the amount of helium ejected is correlated with Porb – the tightest systems even having donors being stripped down to envelopes of less than 0.01 M⊙. We estimate the rise time of ultra-stripped SNe to be in the range 12 h–8 d, and light-curve decay times between 1 and 50 d. A number of fitting formulae for our models are provided with applications to population synthesis. Ultra-stripped SNe may produce NSs in the mass range 1.10–1.80 M⊙ and are highly relevant for LIGO/VIRGO since most (possibly all) merging double NS systems have evolved through this phase. Finally, we discuss the low-velocity kicks which might be imparted on these resulting NSs at birth
Settling of finite-size particles in isotropically forced, homogeneous turbulence: interface-resolved simulations
No full textWe have simulated the gravity-induced settling of finite-size particles in a turbulent background flow which is forced in a statistically-stationary fashion. The simulations are accurately resolving the solid-fluid interface with the aid of an immersed boundary technique [1]. The parameters of the simulation are (apart from background turbulence) identical to those of reference [2], where particle clustering was observed at a Galileo number of 178 and a solid volume fraction of 0.005. In the present case, it is found that a relative turbulence intensity of 0.24 leads to the disappearance of the clusters; as a consequence, the increase in average particle settling velocity found in [2] also vanishes. [1] M. Uhlmann. An immersed boundary method with direct forcing for the simulation of particulate flows. J. Comput. Phys., 209(2):448–476, 2005. [2] M. Uhlmann and T. Doychev. Sedimentation of a dilute suspension of rigid spheres at intermediate Galileo numbers: the effect of clustering upon the particle motion. J. Fluid Mech., 752:310–348, 2014
Mesophilic-hydrothermal-thermophilic (M-H-T) digestion of green corn straw
No full textMesophilic-hydrothermal (80-160 degrees C, 30 min)-thermophilic (M-H-T) digestion and control tests of mesophilic (M), thermophilic (T), hydrothermal-mesophilic (H-M), and mesophilic-thermophilic digestion (M-T) of green corn straw were conducted for a 20-day fermentation period. The results indicate that M-H-T is an efficient method to improve methane production. A maximum methane yield of 371.74 mL/g volatile solid was obtained by the M (3 days)-H (140 degrees C)-T (17 days) process, which was 20.44%, 16.55%, 31.44%, and 14.31% higher than the yields of the M, T, 140-M, and M-T processes. The enhanced methane production was attributed to (1) the improved hemicellulose degradation and lignin disorganization; (2) prevention of the degradation of soluble sugar, easily hydrolyzed hemicellulose and cellulose into furfural and methylfurfural; and (3) lack of formation of Maillard reaction products during initial hydrothermal treatment. (C) 2015 Elsevier Ltd. All rights reserved
Dr. Glendon Swarthout
No full textHosted by Roger M. Busfield, MSU Assistant Professor of Speech and Theater, Meet the Author is designed to introduce a general audience to a contemporary author and their work through in-depth interviews. This episode features a conversation between Dr. Glendon Swarthout, prolific author and English professor at MSU, and assistant professors Sam S. Baskett and Theodore B. Strandness
Recycling Pulsars: spins, masses and ages
No full textAlthough the first millisecond pulsars (MSPs) were discovered 30 years ago we still do not understand all details of their formation process. Here, we present new results from Tauris, Langer & Kramer (2012) on the recycling scenario leading to radio MSPs with helium or carbon-oxygen white dwarf companions via evolution of low- and intermediate mass X-ray binaries (LMXBs, IMXBs). We discuss the location of the spin-up line in the PṖ-diagram and estimate the amount of accreted mass needed to obtain a given spin period and compare with observations. Finally, we constrain the true ages of observed recycled pulsars via calculated isochrones in the PṖ-diagram. ..
The maternal immune system during pregnancy and its influence on fetal development
No full textThe maternal immune system plays a critical role in the establishment, maintenance, and completion of a healthy pregnancy. However, the specific mechanisms utilized to achieve these goals are not well understood. Various cells and molecules of the immune system are key players in the development and function of the placenta and the fetus. Effector cells of the immune system act to promote and yet limit placental development. The T helper 1 (Th1)/T helper 2 (Th2) immune shift during pregnancy is well established. A fine balance between proinflammatory and anti-inflammatory influences is required. We herein review the evidence regarding maternal tolerance of fetal tissues and the underlying cell-mediated immune and humoral (hormones and cytokines) mechanisms. We also note the many unanswered questions in our understanding of these mechanisms. In addition, we summarize the clinical manifestations of an altered maternal immune system during pregnancy related to susceptibility to common viral, bacterial, and parasitic infections, as well as to autoimmune diseases.Peer reviewe
Erosie door open taludbekledingen. Samenvattend verslag + Bijlage A t/m D
No full textOpen taludbekledingen die bestaan uit in verband geplaatste betonblokken met gaten, bieden de mogelijkheid vegetatie te doen groeien, waardoor mogelijk een milieuvriendelijke oever kan worden verkregen. In het pioniersstadium van de vegetatie is het evenwel ongewenst dat de gatvulling uitspoelt. Teneinde de relatie tussen waterbeweging en erosie van de gatvulling vast te stellen, is door de Dienst Weg- en Waterbouwkunde van Rijkswaterstaat per brief d.d. 16 maart 1987 (kenmerk WB 570), opdracht verleend aan het Waterloopkundig Laboratorium tot het uitvoeren van onderzoek naar de erosie door open taludbekledingen. Het doel van het onderzoek is het ontwikkelen van ontwerprichtlijnen voor taludbekledingen met gaten die groter zijn dan de zand- of filterkorrels eronder. Hiertoe dient de kritieke waterbeweging bij een oever- of dijkbekleding te worden vastgesteld, waarbij nog toelaatbare erosie is te verwachten. De toelaatbare erosie mag daarbij maximaal gelijk zijn aan de hoeveelheid sediment in de gaten. Filter- of basismateriaal gelegen onder de elementen mag dus niet uitspoelen. Bij oeverbekledingen waar vegetatie een rol moet gaan spelen, is de toelaatbare erosie kleiner, dat wil zeggen in de gaten dient sediment achter te blijven.Steenzettingen - TAW/EN
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