Low-Frequency Radio Transients in the Galactic Center

We report the detection of a new radio transient source, GCRT J1746-2757, located only 1.1 degrees north of the Galactic center. Consistent with other radio transients toward the Galactic center, this source brightened and faded on a time scale of a few months. No X-ray counterpart was detected. We also report new 0.33 GHz measurements of the radio counterpart to the X-ray transient source, XTE J1748-288, previously detected and monitored at higher radio frequencies. We show that the spectrum of XTE J1748-288 steepened considerably during a period of a few months after its peak. We also discuss the need for a more efficient means of finding additional radio transients

A powerful bursting radio source towards the Galactic Centre

Transient astronomical sources are typically powered by compact objects and usually signify highly explosive or dynamic events. While radio astronomy has an impressive record of obtaining high time resolution observations, usually it is achieved in quite narrow fields-of-view. Consequently, the dynamic radio sky is poorly sampled, in contrast to the situation in the X- and gamma-ray bands in which wide-field instruments routinely detect transient sources. Here we report a new transient source, GCRT J1745-3009, detected in 2002 during a moderately wide-field radio transient monitoring program of the Galactic center (GC) region at 0.33 GHz. The characteristics of its bursts are unlike those known for any other class of radio transient. If located in or near the GC, its brightness temperature (~10^16 K) and the implied energy density within GCRT J1745-3009 vastly exceeds that observed in most other classes of radio astronomical sources, and is consistent with coherent emission processes rarely observed. We conclude that GCRT J1745-3009 is the first member of a new class of radio transient sources, the first of possibly many new classes to be identified through current and upcoming radio surveys.Comment: 16 pages including 3 figures. Appears in Nature, 3 March 200

Pain location and widespread pain in youth with orthopaedic conditions: Exploration of the reliability and validity of a body map

BackgroundPain location and widespread pain are important but underexamined dimensions of paediatric pain. Body map tools to assess pain location in youth have been used for several decades, but few studies have established reliability and validity of these measures. The purpose of this study was to explore the reliability and validity of a pain body map among youth with orthopaedic conditions before surgery.MethodYouth ages 10â 17 years completed the body map and other selfâ reported outcomes at their preoperative clinic visit and at their day of surgery.ResultsMost (91.7%) youth had small discrepancy between body map scores at preoperative clinic visit (baseline) and day of surgery (second assessment), and siteâ toâ site agreement ranged from 78% to 98%. Those with back and lower extremity diagnoses had high correspondence between body map sites and diagnostic sites. Body map scores and widespread pain were associated with other dimensions of pain, as well as other patientâ reported outcomes. Higher pain intensity and widespread pain predicted greater discrepancy between body map scores.ConclusionsThese results support the use of body map tools in further research examining widespread pain among youth by demonstrating adequate reliability, descriptive validity and associative validity.SignificanceThese results contribute to the limited information regarding psychometric properties of paediatric pain body maps, provide novel information about widespread pain among youth undergoing orthopaedic surgeries, and pave the way for improved assessment and treatment of paediatric pain.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/147159/1/ejp1282.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/147159/2/ejp1282_am.pd

Authorsâ reply to the letter to the editor by Sabour

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/147224/1/ejp1345.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/147224/2/ejp1345_am.pd

Time evolution of models described by one-dimensional discrete nonlinear Schr\"odinger equation

The dynamics of models described by a one-dimensional discrete nonlinear Schr\"odinger equation is studied. The nonlinearity in these models appears due to the coupling of the electronic motion to optical oscillators which are treated in adiabatic approximation. First, various sizes of nonlinear cluster embedded in an infinite linear chain are considered. The initial excitation is applied either at the end-site or at the middle-site of the cluster. In both the cases we obtain two kinds of transition: (i) a cluster-trapping transition and (ii) a self-trapping transition. The dynamics of the quasiparticle with the end-site initial excitation are found to exhibit, (i) a sharp self-trapping transition, (ii) an amplitude-transition in the site-probabilities and (iii) propagating soliton-like waves in large clusters. Ballistic propagation is observed in random nonlinear systems. The effect of nonlinear impurities on the superdiffusive behavior of random-dimer model is also studied.Comment: 16 pages, REVTEX, 9 figures available upon request, To appear in Physical Review

A Study of The Formation of Stationary Localized States Due to Nonlinear Impurities Using The Discrete Nonlinear Schr\"odinger Equation

The Discrete Nonlinear Schr$\ddot{o}$dinger Equation is used to study the formation of stationary localized states due to a single nonlinear impurity in a Caley tree and a dimeric nonlinear impurity in the one dimensional system. The rotational nonlinear impurity and the impurity of the form $-\chi \mid C \mid^{\sigma}$ where $\sigma$ is arbitrary and $\chi$ is the nonlinearity parameter are considered. Furthermore, $\mid C \mid$ represents the absolute value of the amplitude. Altogether four cases are studies. The usual Greens function approach and the ansatz approach are coherently blended to obtain phase diagrams showing regions of different number of states in the parameter space. Equations of critical lines separating various regions in phase diagrams are derived analytically. For the dimeric problem with the impurity $-\chi \mid C \mid^{\sigma}$, three values of $\mid \chi_{cr} \mid$, namely, $\mid \chi_{cr} \mid = 2$, at $\sigma = 0$ and $\mid \chi_{cr} \mid = 1$ and $\frac{8}{3}$ for $\sigma = 2$ are obtained. Last two values are lower than the existing values. Energy of the states as a function of parameters is also obtained. A model derivation for the impurities is presented. The implication of our results in relation to disordered systems comprising of nonlinear impurities and perfect sites is discussed.Comment: 10 figures available on reques

Long-period Radio Pulsars: Population Study in the Neutron Star and White Dwarf Rotating Dipole Scenarios

© 2024 The Author(s). Published by the American Astronomical Society. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/The nature of two recently discovered radio emitters with unusually long periods of 18min (GLEAM-X J1627-52) and 21min (GPM J1839-10) is highly debated. Their bright radio emission resembles that of radio magnetars, but their long periodicities and lack of detection at other wavelengths challenge the neutron-star interpretation. In contrast, long rotational periods are common in white dwarfs but, although predicted, dipolar radio emission from isolated magnetic white dwarfs has never been unambiguously observed. In this work, we investigate these long-period objects as potential isolated neutron-star or white-dwarf dipolar radio emitters and find that both scenarios pose significant challenges to our understanding of radio emission via pair production in dipolar magnetospheres. We also perform population-synthesis simulations based on dipolar spin-down in both pictures, assuming different initial-period distributions, masses, radii, beaming fractions, and magnetic-field prescriptions, to assess their impact on the ultra-long pulsar population. In the neutron-star scenario, we do not expect a large number of ultra-long period pulsars under any physically motivated (or even extreme) assumptions for the period evolution. On the other hand, in the white-dwarf scenario, we can easily accommodate a large population of long-period radio emitters. However, no mechanism can easily explain the production of such bright coherent radio emission in either scenarios.Peer reviewe

A long-period radio transient active for three decades: population study in the neutron star and white dwarf rotating dipole scenarios

The nature of two recently discovered radio emitters with unusually long periods of 18min (GLEAM-X J1627-52) and 21min (GPM J1839-10) is highly debated. Their bright radio emission resembles that of radio magnetars, but their long periodicities and lack of detection at other wavelengths challenge the neutron-star interpretation. In contrast, long rotational periods are common in white dwarfs but, although predicted, dipolar radio emission from isolated magnetic white dwarfs has never been unambiguously observed. In this work, we investigate these long-period objects as potential isolated neutron-star or white-dwarf dipolar radio emitters and find that both scenarios pose significant challenges to our understanding of radio emission via pair production in dipolar magnetospheres. We also perform population-synthesis simulations based on dipolar spin-down in both pictures, assuming different initial-period distributions, masses, radii, beaming fractions, and magnetic-field prescriptions, to assess their impact on the ultra-long pulsar population. In the neutron-star scenario, we cannot reproduce the large number of expected ultra-long period pulsars under any physically motivated (or even extreme) assumptions. Thus, if GLEAM-X J1627-52 and GPM J1839-10 are confirmed as neutron-star pulsars (even if they are magnetars), this would necessarily call for a significant revision of our understanding of birth parameters at the population level. On the other hand, in the white-dwarf scenario, no mechanism can explain the production of such a bright coherent radio emission in isolated magnetic white dwarf systems (binaries with low mass companions are still viable), although we can easily accommodate a large population of long-period radio emitters.Comment: 8 pages, 4 figures; ApJ Letters submitte

The Alzheimer's Disease-Associated Amyloid β-Protein Is an Antimicrobial Peptide

Background: The amyloid $\beta$-protein (A$\beta$) is believed to be the key mediator of Alzheimer's disease (AD) pathology. A$\beta$ is most often characterized as an incidental catabolic byproduct that lacks a normal physiological role. However, A$\beta$ has been shown to be a specific ligand for a number of different receptors and other molecules, transported by complex trafficking pathways, modulated in response to a variety of environmental stressors, and able to induce pro-inflammatory activities. Methodology/Principal Findings: Here, we provide data supporting an in vivo function for A$\beta$ as an antimicrobial peptide (AMP). Experiments used established in vitro assays to compare antimicrobial activities of A$\beta$ and LL-37, an archetypical human AMP. Findings reveal that A$\beta$ exerts antimicrobial activity against eight common and clinically relevant microorganisms with a potency equivalent to, and in some cases greater than, LL-37. Furthermore, we show that AD whole brain homogenates have significantly higher antimicrobial activity than aged matched non-AD samples and that AMP action correlates with tissue A$\beta$ levels. Consistent with A$\beta$-mediated activity, the increased antimicrobial action was ablated by immunodepletion of AD brain homogenates with anti-A$\beta$ antibodies. Conclusions/Significance: Our findings suggest A$\beta$ is a hitherto unrecognized AMP that may normally function in the innate immune system. This finding stands in stark contrast to current models of A$\beta$-mediated pathology and has important implications for ongoing and future AD treatment strategies