7,841 research outputs found
The pulsar force-free magnetosphere linked to its striped wind: time-dependent pseudo-spectral simulations
(abridged) Pulsar activity and its related radiation mechanism are usually
explained by invoking some plasma processes occurring inside the magnetosphere.
Despite many detailed local investigations, the global electrodynamics around
those neutron stars remains poorly described. Better understanding of these
compact objects requires a deep and accurate knowledge of their immediate
electromagnetic surrounding within the magnetosphere and its link to the
relativistic pulsar wind.
The aim of this work is to present accurate solutions to the nearly
stationary force-free pulsar magnetosphere and its link to the striped wind,
for various spin periods and arbitrary inclination. To this end, the
time-dependent Maxwell equations are solved in spherical geometry in the
force-free approximation using a vector spherical harmonic expansion of the
electromagnetic field. An exact analytical enforcement of the divergenceless of
the magnetic part is obtained by a projection method. Special care has been
given to design an algorithm able to look deeply into the magnetosphere with
physically realistic ratios of stellar to light-cylinder \rlight
radius. We checked our code against several analytical solutions, like the
Deutsch vacuum rotator solution and the Michel monopole field. We also retrieve
energy losses comparable to the magneto-dipole radiation formula and consistent
with previous similar works. Finally, for arbitrary obliquity, we give an
expression for the total electric charge of the system. It does not vanish
except for the perpendicular rotator. This is due to the often ignored point
charge located at the centre of the neutron star. It is questionable if such
solutions with huge electric charges could exist in reality except for
configurations close to an orthogonal rotator. The charge spread over the
stellar crust is not a tunable parameter as is often hypothesized.Comment: 16 pages, 13 figures, accepted by MNRA
Liposome‐containing mechanoresponsive hydrogels
The direct injection of a drug into a joint can relieve osteoarthritic pain for a short period of time. The problem is that the drug will not stay at the allocated location. Therefore, a proof-of-concept in situ is designed forming hydrogel containing liposomes that are covalently linked to the hydrogel network. When the liposomes are filled with a cargo, the formed hydrogel is thus loaded with this cargo, too. Due to the link between the hydrogel and the liposomes, a compression or other mechanical force applied to the hydrogel will rupture the liposomes and release a small percentage of the cargo. Overall, a long-term intra-articular drug release is feasible
In-plane and Out-of-plane Plasma Resonances in Optimally Doped La1.84Sr0.16CuO4
We addressed the inconsistency between the electron mass anisotropy ratios
determined by the far-infrared experiments and DC conductivity measurements. By
eliminating possible sources of error and increasing the sensitivity and
resolution in the far-infrared reflectivity measurement on the single
crystalline and on the polycrystalline La1.84Sr0.16CuO4, we have unambiguously
identified that the source of the mass anisotropy problem is in the estimation
of the free electron density involved in the charge transport and
superconductivity. In this study we found that only 2.8 % of the total
doping-induced charge density is itinerant at optimal doping. Our result not
only resolves the mass anisotropy puzzle but also points to a novel electronic
structure formed by the rest of the electrons that sets the stage for the high
temperature superconductivity
Spin Caloritronics
This is a brief overview of the state of the art of spin caloritronics, the
science and technology of controlling heat currents by the electron spin degree
of freedom (and vice versa).Comment: To be published in "Spin Current", edited by S. Maekawa, E. Saitoh,
S. Valenzuela and Y. Kimura, Oxford University Pres
Introducing PHAEDRA: a new spectral code for simulations of relativistic magnetospheres
We describe a new scheme for evolving the equations of force-free
electrodynamics, the vanishing-inertia limit of magnetohydrodynamics. This
pseudospectral code uses global orthogonal basis function expansions to take
accurate spatial derivatives, allowing the use of an unstaggered mesh and the
complete force-free current density. The method has low numerical dissipation
and diffusion outside of singular current sheets. We present a range of one-
and two-dimensional tests, and demonstrate convergence to both smooth and
discontinuous analytic solutions. As a first application, we revisit the
aligned rotator problem, obtaining a steady solution with resistivity localised
in the equatorial current sheet outside the light cylinder.Comment: 23 pages, 18 figures, accepted for publication in MNRA
Transmission electron microscopic observations of nanobubbles and their capture of impurities in wastewater
Unique properties of micro- and nanobubbles (MNBs), such as a high adsorption of impurities on their surface, are difficult to verify because MNBs are too small to observe directly. We thus used a transmission electron microscope (TEM) with the freeze-fractured replica method to observe oxygen (O2) MNBs in solutions. MNBs in pure water and in 1% NaCl solutions were spherical or oval. Their size distribution estimated from TEM images close to that of the original solution is measured by light-scattered methods. When we applied this technique to the observation of O2 MNBs formed in the wastewater of a sewage plant, we found the characteristic features of spherical MNBs that adsorbed surrounding impurity particles on their surface
Multisensory information facilitates reaction speed by enlarging activity difference between superior colliculus hemispheres in rats
Animals can make faster behavioral responses to multisensory stimuli than to unisensory stimuli. The superior colliculus (SC), which receives multiple inputs from different sensory modalities, is considered to be involved in the initiation of motor responses. However, the mechanism by which multisensory information facilitates motor responses is not yet understood. Here, we demonstrate that multisensory information modulates competition among SC neurons to elicit faster responses. We conducted multiunit recordings from the SC of rats performing a two-alternative spatial discrimination task using auditory and/or visual stimuli. We found that a large population of SC neurons showed direction-selective activity before the onset of movement in response to the stimuli irrespective of stimulation modality. Trial-by-trial correlation analysis showed that the premovement activity of many SC neurons increased with faster reaction speed for the contraversive movement, whereas the premovement activity of another population of neurons decreased with faster reaction speed for the ipsiversive movement. When visual and auditory stimuli were presented simultaneously, the premovement activity of a population of neurons for the contraversive movement was enhanced, whereas the premovement activity of another population of neurons for the ipsiversive movement was depressed. Unilateral inactivation of SC using muscimol prolonged reaction times of contraversive movements, but it shortened those of ipsiversive movements. These findings suggest that the difference in activity between the SC hemispheres regulates the reaction speed of motor responses, and multisensory information enlarges the activity difference resulting in faster responses
Lysophosphatidic acid-3 receptor-mediated feed-forward production of lysophosphatidic acid: an initiator of nerve injury-induced neuropathic pain
<p>Abstract</p> <p>Background</p> <p>We previously reported that intrathecal injection of lysophosphatidylcholine (LPC) induced neuropathic pain through activation of the lysophosphatidic acid (LPA)-1 receptor, possibly via conversion to LPA by autotaxin (ATX).</p> <p>Results</p> <p>We examined <it>in vivo </it>LPA-induced LPA production using a biological titration assay with B103 cells expressing LPA<sub>1 </sub>receptors. Intrathecal administration of LPC caused time-related production of LPA in the spinal dorsal horn and dorsal roots, but not in the dorsal root ganglion, spinal nerve or sciatic nerve. LPC-induced LPA production was markedly diminished in ATX heterozygotes, and was abolished in mice that were deficient in LPA<sub>3</sub>, but not LPA<sub>1 </sub>or LPA<sub>2 </sub>receptors. Similar time-related and LPA<sub>3 </sub>receptor-mediated production of LPA was observed following intrathecal administration of LPA. In an <it>in vitro </it>study using spinal cord slices, LPA-induced LPA production was also mediated by ATX and the LPA<sub>3 </sub>receptor. Intrathecal administration of LPA, in contrast, induced neuropathic pain, which was abolished in mice deficient in LPA<sub>1 </sub>or LPA<sub>3 </sub>receptors.</p> <p>Conclusion</p> <p>These findings suggest that feed-forward LPA production is involved in LPA-induced neuropathic pain.</p
Global Coronal Waves
After the {\em Solar and Heliospheric Observatory} ({\em SOHO}) was launched
in 1996, the aboard Extreme Ultraviolet Imaging Telescope (EIT) observed a
global coronal wave phenomenon, which was initially named "EIT wave" after the
telescope. The bright fronts are immediately followed by expanding dimmings. It
has been shown that the brightenings and dimmings are mainly due to plasma
density increase and depletion, respectively. Such a spectacular phenomenon
sparked long-lasting interest and debates. The debates were concentrated on two
topics, one is about the driving source, and the other is about the nature of
this wavelike phenomenon. The controversies are most probably because there may
exist two types of large-scale coronal waves that were not well resolved before
the {\em Solar Dynamics Observatory} ({\em SDO}) was launched: one is a
piston-driven shock wave straddling over the erupting coronal mass ejection
(CME), and the other is an apparently propagating front, which may correspond
to the CME frontal loop. Such a two-wave paradigm was proposed more than 13
years ago, and now is being recognized by more and more colleagues. In this
paper, we review how various controversies can be resolved in the two-wave
framework and how important it is to have two different names for the two types
of coronal waves.Comment: 14 pages, 6 figures, a review pape
Social norms of cooperation in small-scale societies
Indirect reciprocity, besides providing a convenient framework to address the evolution of moral systems, offers a simple and plausible explanation for the prevalence of cooperation among unrelated individuals. By helping someone, an individual may increase her/his reputation, which may change the pre-disposition of others to help her/him in the future. This, however, depends on what is reckoned as a good or a bad action, i.e., on the adopted social norm responsible for raising or damaging a reputation. In particular, it remains an open question which social norms are able to foster cooperation in small-scale societies, while enduring the wide plethora of stochastic affects inherent to finite populations. Here we address this problem by studying the stochastic dynamics of cooperation under distinct social norms, showing that the leading norms capable of promoting cooperation depend on the community size. However, only a single norm systematically leads to the highest cooperative standards in small communities. That simple norm dictates that only whoever cooperates with good individuals, and defects against bad ones, deserves a good reputation, a pattern that proves robust to errors, mutations and variations in the intensity of selection.This research was supported by Fundacao para a Ciencia e Tecnologia (FCT) through grants SFRH/BD/94736/2013, PTDC/EEI-SII/5081/2014, PTDC/MAT/STA/3358/2014 and by multi-annual funding of CBMA and INESC-ID (under the projects UID/BIA/04050/2013 and UID/CEC/50021/2013 provided by FCT). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.info:eu-repo/semantics/publishedVersio
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