33 research outputs found
Relativistic Dyson Rings and Their Black Hole Limit
In this Letter we investigate uniformly rotating, homogeneous and
axisymmetric relativistic fluid bodies with a toroidal shape. The corresponding
field equations are solved by means of a multi-domain spectral method, which
yields highly accurate numerical solutions. For a prescribed, sufficiently
large ratio of inner to outer coordinate radius, the toroids exhibit a
continuous transition to the extreme Kerr black hole. Otherwise, the most
relativistic configuration rotates at the mass-shedding limit. For a given
mass-density, there seems to be no bound to the gravitational mass as one
approaches the black-hole limit and a radius ratio of unity.Comment: 13 pages, 1 table, 5 figures, v2: some discussion and two references
added, accepted for publication in Astrophys. J. Let
Black Holes Surrounded by Uniformly Rotating Rings
Highly accurate numerical solutions to the problem of Black Holes surrounded
by uniformly rotating rings in axially symmetric, stationary spacetimes are
presented. The numerical methods developed to handle the problem are discussed
in some detail. Related Newtonian problems are described and numerical results
provided, which show that configurations can reach an inner mass-shedding limit
as the mass of the central object increases. Exemplary results for the full
relativistic problem for rings of constant density are given and the
deformation of the event horizon due to the presence of the ring is
demonstrated. Finally, we provide an example of a system for which the angular
momentum of the central Black Hole divided by the square of its mass exceeds
one.Comment: 12 pages, 14 figures, revtex, v4: minor changes, Eq. (17) corrected,
corresponds to version in PR
Equilibrium configurations of fluids and their stability in higher dimensions
We study equilibrium shapes, stability and possible bifurcation diagrams of
fluids in higher dimensions, held together by either surface tension or
self-gravity. We consider the equilibrium shape and stability problem of
self-gravitating spheroids, establishing the formalism to generalize the
MacLaurin sequence to higher dimensions. We show that such simple models, of
interest on their own, also provide accurate descriptions of their general
relativistic relatives with event horizons. The examples worked out here hint
at some model-independent dynamics, and thus at some universality: smooth
objects seem always to be well described by both ``replicas'' (either
self-gravity or surface tension). As an example, we exhibit an instability
afflicting self-gravitating (Newtonian) fluid cylinders. This instability is
the exact analogue, within Newtonian gravity, of the Gregory-Laflamme
instability in general relativity. Another example considered is a
self-gravitating Newtonian torus made of a homogeneous incompressible fluid. We
recover the features of the black ring in general relativity.Comment: 42 pages, 11 Figures, RevTeX4. Accepted for publication in Classical
and Quantum Gravity. v2: Minor corrections and references adde
Natural Variation of Model Mutant Phenotypes in Ciona intestinalis
BACKGROUND: The study of ascidians (Chordata, Tunicata) has made a considerable contribution to our understanding of the origin and evolution of basal chordates. To provide further information to support forward genetics in Ciona intestinalis, we used a combination of natural variation and neutral population genetics as an approach for the systematic identification of new mutations. In addition to the significance of developmental variation for phenotype-driven studies, this approach can encompass important implications in evolutionary and population biology. METHODOLOGY/PRINCIPAL FINDINGS: Here, we report a preliminary survey for naturally occurring mutations in three geographically interconnected populations of C. intestinalis. The influence of historical, geographical and environmental factors on the distribution of abnormal phenotypes was assessed by means of 12 microsatellites. We identified 37 possible mutant loci with stereotyped defects in embryonic development that segregate in a way typical of recessive alleles. Local populations were found to differ in genetic organization and frequency distribution of phenotypic classes. CONCLUSIONS/SIGNIFICANCE: Natural genetic polymorphism of C. intestinalis constitutes a valuable source of phenotypes for studying embryonic development in ascidians. Correlating genetic structure and the occurrence of abnormal phenotypes is a crucial focus for understanding the selective forces that shape natural finite populations, and may provide insights of great importance into the evolutionary mechanisms that generate animal diversity
ECMO for COVID-19 patients in Europe and Israel
Since March 15th, 2020, 177 centres from Europe and Israel have joined the study, routinely reporting on the ECMO support they provide to COVID-19 patients. The mean annual number of cases treated with ECMO in the participating centres before the pandemic (2019) was 55. The number of COVID-19 patients has increased rapidly each week reaching 1531 treated patients as of September 14th. The greatest number of cases has been reported from France (n = 385), UK (n = 193), Germany (n = 176), Spain (n = 166), and Italy (n = 136) .The mean age of treated patients was 52.6 years (range 16–80), 79% were male. The ECMO configuration used was VV in 91% of cases, VA in 5% and other in 4%. The mean PaO2 before ECMO implantation was 65 mmHg. The mean duration of ECMO support thus far has been 18 days and the mean ICU length of stay of these patients was 33 days. As of the 14th September, overall 841 patients have been weaned from ECMO
support, 601 died during ECMO support, 71 died after withdrawal of ECMO, 79 are still receiving ECMO support and for 10 patients status n.a. . Our preliminary data suggest that patients placed
on ECMO with severe refractory respiratory or cardiac failure secondary to COVID-19 have a reasonable (55%) chance of survival. Further extensive data analysis is expected to provide invaluable information on the demographics, severity of illness, indications and different ECMO management strategies in these patients
SlyD: A novel epitope-presenting thermostable scaffold for the development of highly specific IGF-1/-2 antibodies
Energiesparen und Emissionsminderung in landwirtschaftlichen Betrieben (Moeglichkeiten zur rationellen Energienutzung und zur Minderung der Emissionen klimarelevanter Spurengase landwirtschaftlicher Betriebe) T. 1: Erstellung von Beratungsunterlagen fuer die landwirtschaftliche Betriebsberatung. T. 2: Quantifizierung der Freisetzung von klimarelevanten Gasen aus Guellebehaeltern mit und ohne Strohhaeckselabdeckung. Abschlussbericht
In der vorliegenden Studie werden Moeglichkeiten zur Emissionsminderung und Senkung des Energieverbrauchs analysiert und bewertet. Zu den verschiedenen Themengebieten (Grundlagen der Energienutzung, Bauphysik (Daemmmassnahmen) Stallklima (Lueftung und Heizung), Lagerung und Aufbereitung landwirtschaftlicher Gueter sowie Energieeinsatz in Fuetterungstechnik, Milchproduktion und Aussendtechnik). Grundsaetzlich kann eine Energieeinsparung erreicht werden durch: - Aufdecken energetischer Schwachstellen durch systematische Analyse des Einzelbetriebes - Optimierung der Waermedaemmung in allen beheizten Bereichen - Einsatz intelligenter Regelungstechnik - Verwendung energieeinsparender Technik bei Neuanschaffungen. (orig.)The present study analyses and evaluates ways of cutting emissions and reducing energy consumption. Different subjects (basic elements of energy use, construction physics, controlled environment in the livestock buildings, storing and preparing agricultural produce, energy use and energy saving in feeding, milk production and outdoor operations) are overviewed regarding usual utilization and operations. In this context recommendations how to save energy are given. In principle, energy can be saved by: - Identifying energy weaknesses by a systematic analysis of the individual farm - Optimising thermal insulation in all of the heated ares - Use of intelligent control technology - Use of energy-saving technology with new acquisitions. (orig.)Available from TIB Hannover: RN 8422(1999,38) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Umwelt, Naturschutz und Reaktorsicherheit, Bonn (Germany)DEGerman
Biogeography, Taxonomical Status and Ecology of Alcyonium (Parerythropodium) coralloides (PALLAS, 1766)
La Formazione dei Foglietti Embrionali, L'origine Dell'Epitelio Intestinale e la Determinazione Della Linea Germinale Femminile Nell' Haploembia Solieri
RIASSUNTOIn Haploembia solieri e negli altri Embiotteri esaminati, il foglietto interno si forma per migrazione diffusa di cellule dalla piastra germinativa. E assente un solco gastrulare. Non si hanno abbozzi bipolari entodermici. Costituitosi il mesoderma splancnico, l'epitelio mesenterico si forma per un processo di epibolia, e non di proliferazione, delle cellule della parete ectodermica stomodeale e proctodeale; il processo e piu intenso nel tratto mesenterico proctodeale che non in quello stomodeale. Successivamente le cellule vitelline, tranne alcune, migrano alla periferia assiepandosi sulle pareti. L'assiepamento e assai piu intenso nel quarto anteriore dove le cellule epiteliali di origine stomodeale sono piu rade. Sulla parete i nuclei dei vitellofagi subiscono ripetute divisioni amitotiche disponendosi quindi in un'assisa uniforme tra le preesistenti cellule di origine ectodermica. Al momento della schiusa, l'epitelio mesenterico e quindi di costituzione mista e di derivazione prevalentemente ..