111 research outputs found
Magnetic Collapse of a Neutron Gas: No Magnetar Formation
A degenerate neutron gas in equilibrium with a background of electrons and
protons in a magnetic field exerts its pressure anisotropically, having a
smaller value perpendicular than along the magnetic field. For critical fields
the magnetic pressure may produce the vanishing of the equatorial pressure of
the neutron gas, and the outcome could be a transverse collapse of the star.
This fixes a limit to the fields to be observable in stable pulsars as a
function of their density. The final structure left over after the implosion
might be a mixed phase of nucleons and meson ()
condensate (a strange star also likely) or a black string, but no magnetar at
all.Comment: 5 pages, 1 latex file, 1 encapsulated figure. Submitted to Physical
Review Letters (24/11/2000
Magnetic collapse of a neutron gas: Can magnetars indeed be formed
A relativistic degenerate neutron gas in equilibrium with a background of
electrons and protons in a magnetic field exerts its pressure anisotropically,
having a smaller value perpendicular than along the magnetic field. For
critical fields the magnetic pressure may produce the vanishing of the
equatorial pressure of the neutron gas. Taking it as a model for neutron stars,
the outcome could be a transverse collapse of the star. This fixes a limit to
the fields to be observable in stable neutron star pulsars as a function of
their density. The final structure left over after the implosion might be a
mixed phase of nucleons and meson condensate, a strange star, or a highly
distorted black hole or black "cigar", but no any magnetar, if viewed as a
super strongly magnetized neutron star. However, we do not exclude the
possibility of a supersotrong magnetic fields arising in supernova explosions
which lead directly to strange stars. In other words, if any magnetars exist,
they cannot be neutron stars.Comment: 15 pages, 3 figures. European Physical Journal C in pres
Ischemic Stroke and Epilepsy in a Patient with TouretteÂŽs Syndrome: Association with the Antiphospholipid Syndrome and Good Response to Levetiracetam
The role played by different humoral factors, including antiphospholipid antibodies, in the pathogenesis of Tourette syndrome (TS) is still presently unclear. We present a patient with chronic and severe TS who, at the age of 16 years, presented an ischemic stroke in the left posterior cerebral artery and/or postero-inferior temporal branch of the left medial cerebral artery. A complete study was negative with the exception of a positive lupus anticoagulant. The stroke was related with the primary antiphospholipid syndrome (APS). The stroke manifested visual abnormalities and thereafter by secondary generalized complex partial seizures. The epileptic syndrome was initially difficult to control but responded dramatically to levetiracetam. With this therapy, the manifestations of TS, especially the tics, improved. We conclude that some TS cases may present APS. In addition, levetiracetam may be useful in the management of TS. Further investigations should pursue both these facts
Selective Anion Extraction and Recovery Using a FeII4L4 Cage
Selective anion extraction is useful for the recovery and purification of valuable chemicals, and in the removal of pollutants from the environment. Here we report that FeII4L4 cage 1 is able to extract an equimolar amount of ReO4â, a high-value anion and a nonradioactive surrogate of TcO4â, from water to nitromethane. Importantly, the extraction was efficiently performed even in the presence of 10 other common anions in water, highlighting the high selectivity of 1 for ReO4â. The extracted guest could be released into water as the cage disassembled in ethyl acetate, and then 1 could be recycled by switching the solvent to acetonitrile. The versatile solubility of the cage also enabled complete extraction of ReO4â (as the tetrabutylammonium salt) from an organic phase into water by using the sulfate salt of 1 as the extractant.This work was supported by the UK Engineering and Physical Sciences Research Council (EPSRC EP/M008258/1). The authors thank the Department of Chemistry NMR facility, University of Cambridge for performing some NMR experiments, and the EPSRC UK National Mass Spectrometry Facility at Swansea University for carrying out high resolution mass spectrometry. D. Z. acknowledges the Herchel Smith Research Fellowship from the University of Cambridge
Nonlinear electrodynamics and the surface redshift of pulsars
Currently is argued that the best method of determining the neutron star (NS)
fundamental properties is by measuring the {\it gravitational redshift} ()
of spectral lines produced in the star photosphere. Measurement of at the
star surface provides a unique insight on the NS mass-to-radius relation and
thus on its equation of state (EoS), which reflects the physics of the strong
interaction between particles making up the star. Evidence for such a
measurement has been provided quite recently by Cottam, Paerels & Mendez
(2002), and also by Sanwal et {\it al.} (2002). Here we argue that although the
quoted observations are undisputed for canonical pulsars, they could be
misidentified if the NS is endowed with a super strong as in the so-called
magnetars (Duncan & Thompson 1992) and strange quark magnetars (Zhang 2002), as
in the spectral line discovered by Ibrahim et {\it al.} (2002;2003). The source
of this new "confusion" redshift is related to nonlinear electrodynamics
(NLEDs) effects.Comment: 5 pages, emulateapj.sty, accepted for publication in Astrophysical
Journa
Anion Binding in Water Drives Structural Adaptation in an Azaphosphatrane-Functionalized Fe(II)4L4 Tetrahedron
Anion-templated aqueous self-assembly resulted in the formation of an endohedrally functionalized FeL tetrahedron from azaphosphatrane-based subcomponents. This new water-soluble cage is flexible and able to encapsulate anions with volumes ranging from 35 to 219 Ă
via hydrogen bonding and electrostatic interactions. It structurally adapts in response to the size and shape of the template anions, dynamically adopting a conformation either where all four azaphosphatrane P-H vectors point inward, or else where one points outward and the other three inward. The two cage isomers can coexist in solution and interconvert. A shape memory phenomenon was observed during guest displacement because guest exchange occurs more rapidly than structural reconfiguration.This work was supported by the UK Engineering and Physical Sciences Research Council (EPSRC EP/M008258/1). The authors thank the Department of Chemistry NMR facility, University of Cambridge for performing some NMR experiments, and the EPSRC UK National Mass Spectrometry Facility at Swansea University for carrying out high-resolution mass spectrometry. D.Z. acknowledges a grant from the China Scholarship Council, Accueil Doc Bursary from France RhoÌneAlpes Region, and Enveloppe AttractiviteÌFellowship from ENSLyon for Ph.D. studies
Primordial Nucleosynthesis with varying fundamental constants: A semi-analytical approach
Using the semi-analytic method proposed by \citet{Esma91} we calculate the
abundances of the light elements produced during primordial nucleosynthesis
assuming that the gauge coupling constants of the fundamental interactions may
vary. We analyze the dependence of the nucleon masses, nuclear binding energies
and cross sections involved in the calculation of the abundances with the
fundamental constants assuming the chiral limit of QCD. The abundances of light
elements as a function of the fundamental constants are obtained. Finally,
using the observational data of \De, \Het, \He and \Li we estimate
constraints on the variation of the fundamental constants between the
primordial nucleosynthesis and the present. All observational abundances and
the WMAP estimate of the baryon density, can be fitted to the theoretical
predictions with varying coupling constants. The possible systematic errors in
the observational data, precludes from stronger conclusions.Comment: 41 pages, 2 figures, new references added, bounds on the gauge
coupling constants at http://www.df.uba.ar/users/slandau/tablasgauge.pd
Predictive Value of Carcinoembryonic Antigen in Symptomatic Patients without Colorectal Cancer: A Post-Hoc Analysis within the COLONPREDICT Cohort
We aimed to assess the risk of cancer in patients with abdominal symptoms after a complete colonoscopy without colorectal cancer (CRC), according to the carcinoembryonic antigen (CEA) concentration, as well as its diagnostic accuracy. For this purpose, we performed a post-hoc analysis within a cohort of 1431 patients from the COLONPREDICT study, prospectively designed to assess the fecal immunochemical test accuracy in detecting CRC. Over 36.5 +/- 8.4 months, cancer was detected in 115 (8%) patients. Patients with CEA values higher than 3 ng/mL revealed an increased risk of cancer (HR 2.0, 95% CI 1.3-3.1), CRC (HR 4.4, 95% CI 1.1-17.7) and non-gastrointestinal cancer (HR 1.7, 95% CI 1.0-2.8). A new malignancy was detected in 51 (3.6%) patients during the first year and three variables were independently associated: anemia (OR 2.8, 95% CI 1.3-5.8), rectal bleeding (OR 0.3, 95% CI 0.1-0.7) and CEA level >3 ng/mL (OR 3.4, 95% CI 1.7-7.1). However, CEA was increased only in 31.8% (95% CI, 16.4-52.7%) and 50% (95% CI, 25.4-74.6%) of patients with and without anemia, respectively, who would be diagnosed with cancer during the first year of follow-up. On the basis of this information, CEA should not be used to assist in the triage of patients presenting with lower bowel symptoms who have recently been ruled out a CRC
Evidence of paleoecological changes and Mousterian occupations at the Galeria de las Estatuas site, Sierra de Atapuerca, northern Iberian plateau, Spain
Here we present a new site in the Sierra de Atapuerca (Burgos, Spain): Galeria de las Estatuas (GE), which provides new information about Mousterian occupations in the Iberian Plateau. The GE was an ancient entrance to the cave system, which is currently closed and sealed by a stalagmitic crust, below which a detritic sedimentary sequence of more than 2 m is found. This has been divided into five litostratigraphic units with a rich assemblage of faunal and lithic remains of clear Mousterian affinity. Radiocarbon dates provide minimum ages and suggest occupations older than 45 C-14 ka BP. The palynological analysis detected a landscape change to increased tree coverage, which suggests that the sequence recorded a warming episode. The macromammal assemblage is composed of both ungulates (mainly red deer and equids) and carnivores. Taphonomic analysis reveals both anthropic, and to a lesser extent, carnivore activities. The GE was occupied by Neanderthals and also sporadically by carnivores. This new site broadens the information available regarding different human occupations at the Sierra de Atapuerca, which emphasizes the importance of this site-complex for understanding human evolution in Western Europe
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