The SNR G106.3+2.7 and its Pulsar Wind Nebula: relics of triggered star formation in a complex environment

We propose that the pulsar nebula associated with the pulsar J2229+6114 and the supernova remnant (SNR) G106.3+2.7 are the result of the same supernova explosion. The whole structure is located at the edge of an HI bubble with extended regions of molecular gas inside. The radial velocities of both the atomic hydrogen and the molecular material suggest a distance of 800 pc. At this distance the SNR is 14 pc long and 6 pc wide. Apparently the bubble was created by the stellar wind and supernova explosions of a group of stars in its center which also triggered the formation of the progenitor star of G106.3+2.7. The progenitor star exploded at or close to the current position of the pulsar, which is at one end of the SNR rather than at its center. The expanding shock wave of the supernova explosion created a comet shaped supernova remnant by running into dense material and then breaking out into the inner part of the HI bubble. A synchrotron nebula with a shell-like structure (the ``Boomerang'') of length 0.8 pc was created by the pulsar wind interacting with the dense ambient medium. The expanding shock wave created an HI shell of mass 0.4 Msun around this nebula by ionizing the atomic hydrogen in its vicinity.Comment: 10 pages, Latex, with aastex and emulateapj5, 5 figures. ApJ, accepted, scheduled for the v560 n1 p1 Oct 10, 2001 issu

Optimizing adiabaticity in quantum mechanics

A condition on the Hamiltonian of a time-dependent quantum mechanical system is derived which, if satisfied, implies optimal adiabaticity (defined below). The condition is expressed in terms of the Hamiltonian and in terms of the evolution operator related to it. Since the latter depends in a complicated way on the Hamiltonian, it is not yet clear how the condition can be used to extract useful information about the optimal Hamiltonian. The condition is tested on an exactly-soluble time-dependent problem (a spin in a magnetic field), where perfectly adiabatic evolution can be easily identified.Comment: 5 pages, 2 figure

X-ray Observations of the Compact Source in CTA 1

The point source RX J0007.0+7302, at the center of supernova remnant CTA 1, was studied using the X-Ray Multi-mirror Mission. The X-ray spectrum of the source is consistent with a neutron star interpretation, and is well described by a power law with the addition of a soft thermal component that may correspond to emission from hot polar cap regions or to cooling emission from a light element atmosphere over the entire star. There is evidence of extended emission on small spatial scales which may correspond to structure in the underlying synchrotron nebula. No pulsations are observed. Extrapolation of the nonthermal spectrum of RX J0007.0+7302 to gamma-ray energies yields a flux consistent with that of EGRET source 3EG J0010+7309, supporting the proposition that there is a gamma-ray emitting pulsar at the center of CTA 1. Observations of the outer regions of CTA 1 with the Advanced Satellite for Cosmology and Astrophysics confirm earlier detections of thermal emission from the remnant and show that the synchrotron nebula extends to the outermost reaches of the SNR.Comment: 5 pages, including 4 postscript figs.LaTex. Accepted for publication by Ap

Assessing the evolution of primary healthcare organizations and their performance (2005-2010) in two regions of Québec province: Montréal and Montérégie

<p>Abstract</p> <p>Background</p> <p>The Canadian healthcare system is currently experiencing important organizational transformations through the reform of primary healthcare (PHC). These reforms vary in scope but share a common feature of proposing the transformation of PHC organizations by implementing new models of PHC organization. These models vary in their performance with respect to client affiliation, utilization of services, experience of care and perceived outcomes of care.</p> <p>Objectives</p> <p>In early 2005 we conducted a study in the two most populous regions of Quebec province (Montreal and Montérégie) which assessed the association between prevailing models of primary healthcare (PHC) and population-level experience of care. The <b>goal </b>of the present research project is to track the <it>evolution </it>of PHC organizational models and their relative performance through the reform process (from 2005 until 2010) and to assess factors at the organizational and contextual levels that are associated with the transformation of PHC organizations and their performance.</p> <p>Methods/Design</p> <p>This study will consist of three interrelated surveys, hierarchically nested. The first survey is a population-based survey of randomly-selected adults from two populous regions in the province of Quebec. This survey will assess the current affiliation of people with PHC organizations, their level of utilization of healthcare services, attributes of their experience of care, reception of preventive and curative services and perception of unmet needs for care. The second survey is an organizational survey of PHC organizations assessing aspects related to their vision, organizational structure, level of resources, and clinical practice characteristics. This information will serve to develop a taxonomy of organizations using a mixed methods approach of factorial analysis and principal component analysis. The third survey is an assessment of the organizational context in which PHC organizations are evolving. The five year prospective period will serve as a natural experiment to assess contextual and organizational factors (in 2005) associated with migration of PHC organizational models into new forms or models (in 2010) and assess the impact of this evolution on the performance of PHC.</p> <p>Discussion</p> <p>The results of this study will shed light on changes brought about in the organization of PHC and on factors associated with these changes.</p

Thermal disc emission from a rotating black hole: X-ray polarization signatures

Thermal emission from the accretion disc around a black hole can be polarized, due to Thomson scattering in a disc atmosphere. In Newtonian space, the polarization angle must be either parallel or perpendicular to the projection of the disc axis on the sky. As first pointed out by Stark and Connors in 1977, General Relativity effects strongly modify the polarization properties of the thermal radiation as observed at infinity. Among these effects, the rotation of the polarization angle with energy is particularly useful as a diagnostic tool. In this paper, we extend the Stark and Connors calculations by including the spectral hardening factor, several values of the optical depth of the scattering atmosphere and rendering the results to the expected performances of planned X-ray polarimeters. In particular, to assess the perspectives for the next generation of X-ray polarimeters, we consider the expected sensitivity of the detectors onboard the planned POLARIX and IXO missions. We assume the two cases of a Schwarzschild and an extreme Kerr black hole with a standard thin disc and a scattering atmosphere. We compute the expected polarization degree and the angle as functions of the energy as they could be measured for different inclinations of the observer, optical thickness of the atmosphere and different values of the black hole spin. We assume the thermal emission dominates the X-ray band. Using the flux level of the microquasar GRS 1915+105 in the thermal state, we calculate the observed polarization.Comment: 8 pages, 7 figures, accepted by MNRA

Polarization of Thermal X-rays from Isolated Neutron Stars

Since the opacity of a magnetized plasma depends on polarization of radiation, the radiation emergent from atmospheres of neutron stars with strong magnetic fields is expected to be strongly polarized. The degree of linear polarization, typically ~10-30%, depends on photon energy, effective temperature and magnetic field. The spectrum of polarization is more sensitive to the magnetic field than the spectrum of intensity. Both the degree of polarization and the position angle vary with the neutron star rotation period so that the shape of polarization pulse profiles depends on the orientation of the rotational and magnetic axes. Moreover, as the polarization is substantially modified by the general relativistic effects, observations of polarization of X-ray radiation from isolated neutron stars provide a new method for evaluating the mass-to-radius ratio of these objects, which is particularly important for elucidating the properties of the superdense matter in the neutron star interiors.Comment: 7 figures, to be published in Ap

Candidate Genes for Expansion and Transformation of Hematopoietic Stem Cells by NUP98-HOX Fusion Genes

BACKGROUND: Hox genes are implicated in hematopoietic stem cell (HSC) regulation as well as in leukemia development through translocation with the nucleoporin gene NUP98. Interestingly, an engineered NUP98-HOXA10 (NA10) fusion can induce a several hundred-fold expansion of HSCs in vitro and NA10 and the AML-associated fusion gene NUP98-HOXD13 (ND13) have a virtually indistinguishable ability to transform myeloid progenitor cells in vitro and to induce leukemia in collaboration with MEIS1 in vivo. METHODOLOGY/PRINCIPAL FINDINGS: These findings provided a potentially powerful approach to identify key pathways mediating Hox-induced expansion and transformation of HSCs by identifying gene expression changes commonly induced by ND13 and NA10 but not by a NUP98-Hox fusion with a non-DNA binding homedomain mutation (N51S). The gene expression repertoire of purified murine bone marrow Sca-1+Lin- cells transduced with retroviral vectors encoding for these genes was established using the Affymetrix GeneChip MOE430A. Approximately seventy genes were differentially expressed in ND13 and NA10 cells that were significantly changed by both compared to the ND13(N51S) mutant. Intriguingly, several of these potential Hox target genes have been implicated in HSC expansion and self-renewal, including the tyrosine kinase receptor Flt3, the prion protein, Prnp, hepatic leukemia factor, Hlf and Jagged-2, Jag2. Consistent with these results, FLT3, HLF and JAG2 expression correlated with HOX A cluster gene expression in human leukemia samples. CONCLUSIONS: In conclusion this study has identified several novel Hox downstream target genes and provides important new leads to key regulators of the expansion and transformation of hematopoietic stem cells by Hox

Weak-Lensing by Large-Scale Structure and the Polarization Properties of Distant Radio-Sources

We estimate the effects of weak lensing by large-scale density inhomogeneities and long-wavelength gravitational waves upon the polarization properties of electromagnetic radiation as it propagates from cosmologically distant sources. Scalar (density) fluctuations do not rotate neither the plane of polarization of the electromagnetic radiation nor the source image. They produce, however, an appreciable shear, which distorts the image shape, leading to an apparent rotation of the image orientation relative to its plane of polarization. In sources with large ellipticity the apparent rotation is rather small, of the order (in radians) of the dimensionless shear. The effect is larger at smaller source eccentricity. A shear of 1% can induce apparent rotations of around 5 degrees in radio sources with the smallest eccentricity among those with a significant degree of integrated linear polarization. We discuss the possibility that weak lensing by shear with rms value around or below 5% may be the cause for the dispersion in the direction of integrated linear polarization of cosmologically distant radio sources away from the perpendicular to their major axis, as expected from models for their magnetic fields. A rms shear larger than 5% would be incompatible with the observed correlation between polarization properties and source orientation in distant radio galaxies and quasars. Gravity waves do rotate both the plane of polarization as well as the source image. Their weak lensing effects, however, are negligible.Comment: 23 pages, 2 eps figures, Aastex 4.0 macros. Final version, as accepted by ApJ. Additional references and some changes in the introduction and conclusion

Status of the connection between unidentified EGRET sources and supernova remnants: The case of CTA 1

In this paper we briefly comment on the observational status of the possible physical association between unidentified EGRET sources and supernova remnants (SNRs) in our Galaxy. We draw upon recent results presented in the review by Torres et al. (Physics Reports, 2003), concerning molecular gas in the vicinity of all 19 SNRs found to be positionally coincident with EGRET sources at low Galactic latitudes. In addition, we present new results regarding the supernova remnant CTA~1. Our findings disfavor the possibility of a physical connection with the nearby (in projection) EGRET source. There remains possible, however, that the compact object produced in the supernova explosion be related with the observed $\gamma$-ray flux.Comment: Presented for the proceedings of the II Workshop on Unidentified Gamma-Ray Sources, Hong Kong, June 1-4, 2004. To appear in Astrophysics and Space Science. Some changes to address referee's and readers' remarks. References added. Results unchange