650 research outputs found
Violation of Chandrasekhar Mass Limit: The Exciting Potential of Strongly Magnetized White Dwarfs
We consider a relativistic, degenerate, electron gas under the influence of a
strong magnetic field, which describes magnetized white dwarfs. Landau
quantization changes the density of states available to the electrons, thus
modifying the underlying equation of state. In the presence of very strong
magnetic fields a maximum of either one, two or three Landau level(s) is/are
occupied. We obtain the mass-radius relations for such white dwarfs and their
detailed investigation leads us to propose the existence of white dwarfs having
a mass ~2.3M_Sun, which overwhelmingly exceeds the Chandrasekhar mass limit.Comment: 10 pages including 4 figures; received Honorable Mention for the
Gravity Research Foundation 2012 Awards for Essays on Gravitation; version to
appear in IJMP
Analysis of the Hydrogen-rich Magnetic White Dwarfs in the SDSS
We have calculated optical spectra of hydrogen-rich (DA) white dwarfs with
magnetic field strengths between 1 MG and 1000 MG for temperatures between 7000
K and 50000 K. Through a least-squares minimization scheme with an evolutionary
algorithm, we have analyzed the spectra of 114 magnetic DAs from the SDSS (95
previously published plus 14 newly discovered within SDSS, and five discovered
by SEGUE). Since we were limited to a single spectrum for each object we used
only centered magnetic dipoles or dipoles which were shifted along the magnetic
dipole axis. We also statistically investigated the distribution of
magnetic-field strengths and geometries of our sample.Comment: to appear in the proceedings of the 16th European Workshop on White
Dwarfs, Barcelona, 200
Multiscale imaging of basal cell dynamics in the functionally mature mammary gland
The mammary epithelium is indispensable for the continued survival of more than 5,000 mammalian species. For some, the volume of milk ejected in a single day exceeds their entire blood volume. Here, we unveil the spatiotemporal properties of physiological signals that orchestrate the ejection of milk from alveolar units and its passage along the mammary ductal network. Using quantitative, multidimensional imaging of mammary cell ensembles from GCaMP6 transgenic mice, we reveal how stimulus evoked Ca oscillations couple to contractions in basal epithelial cells. Moreover, we show that Ca-dependent contractions generate the requisite force to physically deform the innermost layer of luminal cells, compelling them to discharge the fluid that they produced and housed. Through the collective action of thousands of these biological positive-displacement pumps, each linked to a contractile ductal network, milk begins its passage toward the dependent neonate, seconds after the command
Social Value of Marine and Coastal Protected Areas in England and Wales.
The U.K. government is committed to establishing a coherent network of marine protected
areas by 2012 and the recentMarine and Coastal Access Act, 2009 will designate
marine conservation zones and provide wider access rights to the coast. To fulfill these
goals, this article argues the need for a clearer, shared understanding of the social
value of protected areas in creating new designations and managing existing ones. Although
marine and coastal environments attract many people and are vitally important
in terms of realized and potential social value, the majority of the public in the United
Kingdom lacks understanding and awareness regarding them. Combined with this, the
social value of marine and coastal protected areas (MCPAs) have been largely ignored
relative to conservation and economics, with the latter invariably taking precedence
in environmental policymaking. Social value reflects the complex, individual responses
that people experience in a given place. Many reasons determine why one area is valued
above another, and this research investigates the social value of MCPAs from a
practitioner’s perspective through a series of interviews. Understanding why we “socially”
value MCPAs will ultimately equip managers with an informed understanding
of these spaces, influence management decisions, and, potentially, policymaking. This
article defines social value in the context of MCPAs in England and Wales from a
practitioner perspective, explores key concepts, and suggests possible improvements in
decision-making
Secretagogue-induced formation of inositol phosphates in rat exocrine pancreas. Implications for a messenger role for inositol trisphosphate
Orbital Ferromagnetism and the Chandrasekhar Mass-Limit
In this paper, using both quantum magnetohydrodynamic (MHD) and
magnetohydrostatic (MHS) models of a relativistically degenerate magnetic
compact star, the fundamental role of Landau orbital ferromagnetism (LOFER) on
the magneto-gravitational stability of such star is revealed. It is shown that
the previously suggested magnetic equation of state for LOFER with some
generalization of form only within the range and leads to magneto-gravitational stability with
distinct critical value governing the
magnetohydrostatic stability of the compact star. Furthermore, the value of the
parameters and is shown to fundamentally control both the quantum
and Chandrasekhar gravitational collapse mechanisms and the previously
discovered mass-limit on white dwarfs. Current findings can help to understand
the origin of magnetism and its inevitable role on the stability of the
relativistically degenerate super-dense magnetized matter encountered in many
white-dwarfs and neutron stars
Structural requirements for class I MHC molecule-mediated antigen presentation and cytotoxic T cell recognition of an immunodominant determinant of the human immunodeficiency virus envelope protein.
Interstellar Holography
The dynamic spectrum of a radio pulsar is an in-line digital hologram of the
ionised interstellar medium. It has previously been demonstrated that such
holograms permit image reconstruction, in the sense that one can determine an
approximation to the complex electric field values as a function of
Doppler-shift and delay, but to date the quality of the reconstructions has
been poor. Here we report a substantial improvement in the method which we have
achieved by simultaneous optimisation of the thousands of coefficients that
describe the electric field. For our test spectrum of PSR B0834+06 we find that
the model provides an accurate representation of the data over the full 63 dB
dynamic range of the observations: residual differences between model and data
are noise-like. The advent of interstellar holography enables detailed
quantitative investigation of the interstellar radio-wave propagation paths for
a given pulsar at each epoch of observation; we illustrate this using our test
data which show the scattering material to be structured and highly
anisotropic. The temporal response of the medium exhibits a scattering tail out
to beyond 100 microsec and a pulse arrival time measurement at this frequency
and this epoch of observation would be affected by a mean delay of 15 microsec
due to multipath propagation in the interstellar medium.Comment: Submitted to MNRAS, 8 pages, 5 figure
Scintillation arcs in low-frequency observations of the timing-array millisecond pulsar PSR J0437–4715
© 2016. The American Astronomical Society. All rights reserved. Low-frequency observations of pulsars provide a powerful means for probing the microstructure in the turbulent interstellar medium (ISM). Here we report on high-resolution dynamic spectral analysis of our observations of the timing-array millisecond pulsar PSR J0437-4715 with the Murchison Widefield Array (MWA), enabled by our recently commissioned tied-array beam processing pipeline for voltage data recorded from the high time resolution mode of the MWA. A secondary spectral analysis reveals faint parabolic arcs akin to those seen in high-frequency observations of pulsars with the Green Bank and Arecibo telescopes. Data from Parkes observations at a higher frequency of 732 MHz reveal a similar parabolic feature with a curvature that scales approximately as the square of the observing wavelength (?2) to the MWA's frequency of 192 MHz. Our analysis suggests that scattering toward PSR J0437-4715 predominantly arises from a compact region about 115 pc from the Earth, which matches well with the expected location of the edge of the Local Bubble that envelopes the local Solar neighborhood. As well as demonstrating new and improved pulsar science capabilities of the MWA, our analysis underscores the potential of low-frequency pulsar observations for gaining valuable insights into the local ISM and for characterizing the ISM toward timing-array pulsars
Corticolimbic Expression of TRPC4 and TRPC5 Channels in the Rodent Brain
The canonical transient receptor potential (TRPC) channels are a family of non-selective cation channels that are activated by increases in intracellular Ca2+ and Gq/phospholipase C-coupled receptors. We used quantitative real-time PCR, in situ hybridization, immunoblots and patch-clamp recording from several brain regions to examine the expression of the predominant TRPC channels in the rodent brain. Quantitative real-time PCR of the seven TRPC channels in the rodent brain revealed that TRPC4 and TRPC5 channels were the predominant TRPC subtypes in the adult rat brain. In situ hybridization histochemistry and immunoblotting further resolved a dense corticolimbic expression of the TRPC4 and TRPC5 channels. Total protein expression of HIP TRPC4 and 5 proteins increased throughout development and peaked late in adulthood (6–9 weeks). In adults, TRPC4 expression was high throughout the frontal cortex, lateral septum (LS), pyramidal cell layer of the hippocampus (HIP), dentate gyrus (DG), and ventral subiculum (vSUB). TRPC5 was highly expressed in the frontal cortex, pyramidal cell layer of the HIP, DG, and hypothalamus. Detailed examination of frontal cortical layer mRNA expression indicated TRPC4 mRNA is distributed throughout layers 2–6 of the prefrontal cortex (PFC), motor cortex (MCx), and somatosensory cortex (SCx). TRPC5 mRNA expression was concentrated specifically in the deep layers 5/6 and superficial layers 2/3 of the PFC and anterior cingulate. Patch-clamp recording indicated a strong metabotropic glutamate-activated cation current-mediated depolarization that was dependent on intracellular Ca2+and inhibited by protein kinase C in brain regions associated with dense TRPC4 or 5 expression and absent in regions lacking TRPC4 and 5 expression. Overall, the dense corticolimbic expression pattern suggests that these Gq/PLC coupled nonselective cation channels may be involved in learning, memory, and goal-directed behaviors
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