Wind braking of magnetars: to understand magnetar's multiwave radiation properties

Magnetars are proposed to be peculiar neutron stars powered by their super strong magnetic field. Observationally, anomalous X-ray pulsars and soft gamma-ray repeaters are believed to be magnetar candidates. While more and more multiwave observations of magnetars are available, unfortunately, we see accumulating failed predictions of the traditional magnetar model. These challenges urge rethinking of magnetar. Wind braking of magnetars is one of the alternative modelings. The release of magnetic energy may generate a particle outflow (i.e., particle wind), that results in both an anomalous X-ray luminosity and significantly high spindown rate. In this wind braking scenario, only strong multipole field is necessary for a magnetar (a strong dipole field is no longer needed). Wind braking of magnetars may help us to understand their multiwave radiation properties, including (1) Non-detection of magnetars in Fermi-LAT observations, (2) The timing behaviors of low magnetic field magnetars, (3) The nature of anti-glitches, (4) The criterion for magnetar's radio emission, etc. In the wind braking model of magentars, timing events of magnetars should always be accompanied by radiative events. It is worth noting that the wind engine should be the central point in the research since other efforts with any reasonable energy mechanism may also reproduce the results.Comment: 6 pages, 1 figure, submitted to conference proceeding of SMFNS2013 (Strong electromagnetic field and neutron stars 2013

The timing behavior of magnetar Swift J1822.3-1606: timing noise or a decreasing period derivative?

The different timing results of the magnetar Swift J1822.3-1606 is analyzed and understood theoretically. It is pointed that different timing solutions are caused not only by timing noise, but also that the period derivative is decreasing after outburst. Both the decreasing period derivative and the large timing noise may be originated from wind braking of the magnetar. Future timing of Swift J1822.3-1606 will help us make clear whether its period derivative is decreasing with time or not.Comment: 5 pages, 1 figure. Accepted by Research in Astronomy and Astrophysic

The optical/UV excess of isolated neutron stars in the RCS model

The X-ray dim isolated neutron stars (XDINSs) are peculiar pulsar-like objects, characterized by their very well Planck-like spectrum. In studying their spectral energy distributions, the optical/UV excess is a long standing problem. Recently, Kaplan et al. (2011) have measured the optical/UV excess for all seven sources, which is understandable in the resonant cyclotron scattering (RCS) model previously addressed. The RCS model calculations show that the RCS process can account for the observed optical/UV excess for most sources . The flat spectrum of RX J2143.0+0654 may due to contribution from bremsstrahlung emission of the electron system in addition to the RCS process.Comment: 6 pages, 2 figures, 1 table, accepted for publication in Research in Astronomy and Astrophysic

Nonlinear stability and ergodicity of ensemble based Kalman filters

The ensemble Kalman filter (EnKF) and ensemble square root filter (ESRF) are data assimilation methods used to combine high dimensional, nonlinear dynamical models with observed data. Despite their widespread usage in climate science and oil reservoir simulation, very little is known about the long-time behavior of these methods and why they are effective when applied with modest ensemble sizes in large dimensional turbulent dynamical systems. By following the basic principles of energy dissipation and controllability of filters, this paper establishes a simple, systematic and rigorous framework for the nonlinear analysis of EnKF and ESRF with arbitrary ensemble size, focusing on the dynamical properties of boundedness and geometric ergodicity. The time uniform boundedness guarantees that the filter estimate will not diverge to machine infinity in finite time, which is a potential threat for EnKF and ESQF known as the catastrophic filter divergence. Geometric ergodicity ensures in addition that the filter has a unique invariant measure and that initialization errors will dissipate exponentially in time. We establish these results by introducing a natural notion of observable energy dissipation. The time uniform bound is achieved through a simple Lyapunov function argument, this result applies to systems with complete observations and strong kinetic energy dissipation, but also to concrete examples with incomplete observations. With the Lyapunov function argument established, the geometric ergodicity is obtained by verifying the controllability of the filter processes; in particular, such analysis for ESQF relies on a careful multivariate perturbation analysis of the covariance eigen-structure.Comment: 38 page

AXPs and SGRs in the outer gap model: confronting Fermi observations

Anomalous X-ray pulsars (AXPs) and soft gamma-ray repeaters (SGRs) are magnetar candidates, i.e., neutron stars powered by strong magnetic field. If they are indeed magnetars, they will emit high-energy gamma-rays which are detectable by Fermi-LAT according to the outer gap model. However, no significant detection is reported in recent Fermi-LAT observations of all known AXPs and SGRs. Considering the discrepancy between theory and observations, we calculate the theoretical spectra for all AXPs and SGRs with sufficient observational parameters. Our results show that most AXPs and SGRs are high-energy gamma-ray emitters if they are really magnetars. The four AXPs 1E 1547.0-5408, XTE J1810-197, 1E 1048.1-5937, and 4U 0142+61 should have been detected by Fermi-LAT. Then there is conflict between out gap model in the case of magnetars and Fermi observations. Possible explanations in the magnetar model are discussed. On the other hand, if AXPs and SGRs are fallback disk systems, i.e., accretion-powered for the persistent emissions, most of them are not high-energy gamma-ray emitters. Future deep Fermi-LAT observations of AXPs and SGRs will help us make clear whether they are magnetars or fallback disk systems.Comment: 15 pages, 3 figures, 1 table, accepted for publication in The Astrophysical Journa

The pharmacokinetics and neuropharmacological action of the new antiepileptic drugs vigabatrin and levetiracetam.

Epilepsy affects approximately 1% of the world population and is the most serious neurological conditions. In the UK, 30-35,000 new cases of epilepsy are diagnosed each year, resulting in a prevalence of 300,000 nationwide. There is significant need for new drug treatments. Yet we have a poor understanding of how many of these drugs mediate their antiepileptic effect, and how and where they are distributed within the brain. This thesis sought to investigate the pharmacokinetic and neuropharmacokinetic inter-relationship and the neuropharmacology of two new antiepileptic drugs, vigabatrin and levetiracetam two drugs with distinct mechanisms of action. Firstly, a freely moving and freely behaving rat model was used to determine the pharmacokinetics of vigabatrin and levetiracetam simultaneously in serum, cerebrospinal fluid (CSF) and brain frontal cortex and hippocampal extracellular fluid (ECF). Secondly, amino acid neurotransmitter concentrations were monitored in CSF (by direct CSF sampling) and brain ECF (by microdialysis) after vigabatrin and levetiracetam administration. Thirdly, the effects of vigabatrin and levetiracetam on paired-pulse inhibition recorded in the dentate gyrus evoked by perforant path stimulation were established. Vigabatrin rapidly entered the blood (serum), CSF and ECF (frontal cortex and hippocampus) compartments with concentrations increasing linearly and dose- dependently. Time to maximum concentration (rmax) was achieved at a mean value of 0.4 0.06 minutes in the blood compartment, 0.9 0.1 minutes in the CSF compartment and 0.8 0.1 minutes in both the frontal cortex and hippocampal ECF compartments. Although the CSF kinetics of vigabatrin paralleled that seen in serum, CSF vigabatrin concentrations represented only 2% of serum vigabatrin concentrations and did not reflect free drug concentrations in serum. Vigabatrin was not protein bound in serum. Furthermore, the efflux of vigabatrin from the CSF compartment was significantly slower (mean terminal half life {lcub}1/2{rcub} values, 2.2-3.3 h) than that suggested by serum values (mean tm values, 1.1-1.4 h). Distribution in the brain ECF was brain region specific vigabatrin concentrations achieved in the frontal cortex were 2-fold greater than concentrations achieved in the hippocampus. However, the efflux of vigabatrin from the two brain regions was essentially identical (mean t a values, 2.4-3.6 h) and indeed was similar to values seen in the CSF compartment. The findings are consistent with an active uptake and elimination of vigabatrin from the CSF and ECF. Levetiracetam rapidly entered the blood (serum) and ECF (frontal cortex and hippocampus) compartments with concentrations increasing linearly and dose- dependently. Mean rmax values were 0.4 - 0.7 minutes in the blood compartment and 1.8 - 2.5 minutes in both the frontal cortex and hippocampal ECF compartments. Levetiracetam was not protein bound in serum. In contrast to vigabatrin, levetiracetam did not exhibit brain region specificity in that its neuropharmacokinetic profiles in frontal cortex and hippocampal ECF were essentially identical. However, the efflux of levetiracetam from the two brain regions was slower (mean t a values, 3.1 - 3.3 h) compared to that which occurred in the blood compartment (mean tm values, 2.2 h). In the CSF compartment, vigabatrin administration was associated with changes in 5 of the 16 amino acid neurotransmitter concentrations measured over time. Thus whilst arginine and tyrosine concentrations decreased, homocarnosine, glycine and taurine concentrations increased. Although gamma-aminobutyric acid (GABA) was not measured in CSF, the fact that homocarnosine (a GABA conjugate) concentrations increased is consistent with a GABAergic action for vigabatrin. In the frontal cortex and hippocampal ECF compartments, vigabatrin administration was associated with significant changes in various amino acid concentrations but the changes did not parallel those seen in CSF. The most profound change was that with GABA. However, whilst ECF GABA concentrations increased 6-fold in the frontal cortex, concentrations in the hippocampus were unaffected. These GABA changes did not parallel the concentration versus time profile of ECF vigabatrin nevertheless vigabatrin concentrations in the frontal cortex were 2-fold higher than those achieved in the hippocampus. These findings indicate that CSF amino acid measurements may be a poor reflection of ECF amino acid changes and that changes in ECF amino acids is regionally specific. That vigabatrin reduced paired pulse inhibition in the dentate gyrus evoked by perforant path stimulation at 20 ms interpulse interval but not at 50 ms and 100 ms intervals would suggest that vigabatrin by increasing extracellular GABA may either desensistise synaptic GABAA receptors or inhibit GABA release through an action on GABAB receptors. In the brain ECF compartment, levetiracetam administration was associated with changes in only two (taurine and glutamate) of the 20 amino acid neurotransmitter concentrations measured over time. The significance of these changes in relation to the mechanism of action of levetiracetam is unknown. (Abstract shortened by UMI.)

Criticism and society: The birth of the modern critical subject in China

Focuses on the creation and establishment of critical theory system in China. Application of imported critical approaches and theoretical formulations; Distortion of Euramerican critical theories; Identification of traditional Chinese criticism; Inseparability of criticism and politics.published_or_final_versio