383 research outputs found
Multiwavelength Evidence for Quasi-periodic Modulation in the Gamma-ray Blazar PG 1553+113
We report for the first time a gamma-ray and multi-wavelength nearly-periodic
oscillation in an active galactic nucleus. Using the Fermi Large Area Telescope
(LAT) we have discovered an apparent quasi-periodicity in the gamma-ray flux (E
>100 MeV) from the GeV/TeV BL Lac object PG 1553+113. The marginal significance
of the 2.18 +/-0.08 year-period gamma-ray cycle is strengthened by correlated
oscillations observed in radio and optical fluxes, through data collected in
the OVRO, Tuorla, KAIT, and CSS monitoring programs and Swift UVOT. The optical
cycle appearing in ~10 years of data has a similar period, while the 15 GHz
oscillation is less regular than seen in the other bands. Further long-term
multi-wavelength monitoring of this blazar may discriminate among the possible
explanations for this quasi-periodicity.Comment: 8 pages, 5 figures. Accepted to The Astrophysical Journal Letters.
Corresponding authors: S. Ciprini (ASDC/INFN), S. Cutini (ASDC/INFN), S.
Larsson (Stockholm Univ/KTH), A. Stamerra (INAF/SNS), D. J. Thompson (NASA
GSFC
Search for extended gamma-ray emission from the Virgo galaxy cluster with Fermi-LAT
Galaxy clusters are one of the prime sites to search for dark matter (DM)
annihilation signals. Depending on the substructure of the DM halo of a galaxy
cluster and the cross sections for DM annihilation channels, these signals
might be detectable by the latest generation of -ray telescopes. Here
we use three years of Fermi Large Area Telescope (LAT) data, which are the most
suitable for searching for very extended emission in the vicinity of nearby
Virgo galaxy cluster. Our analysis reveals statistically significant extended
emission which can be well characterized by a uniformly emitting disk profile
with a radius of 3\deg that moreover is offset from the cluster center. We
demonstrate that the significance of this extended emission strongly depends on
the adopted interstellar emission model (IEM) and is most likely an artifact of
our incomplete description of the IEM in this region. We also search for and
find new point source candidates in the region. We then derive conservative
upper limits on the velocity-averaged DM pair annihilation cross section from
Virgo. We take into account the potential -ray flux enhancement due to
DM sub-halos and its complex morphology as a merging cluster. For DM
annihilating into , assuming a conservative sub-halo model
setup, we find limits that are between 1 and 1.5 orders of magnitude above the
expectation from the thermal cross section for
. In a more optimistic scenario, we
exclude
for for the same channel. Finally, we
derive upper limits on the -ray-flux produced by hadronic cosmic-ray
interactions in the inter cluster medium. We find that the volume-averaged
cosmic-ray-to-thermal pressure ratio is less than .Comment: 15 pages, 11 figures, 4 tables, accepted for publication in ApJ;
corresponding authors: T. Jogler, S. Zimmer & A. Pinzk
Nanotechnology researchers' collaboration relationships: A gender analysis of access to scientific information
Women are underrepresented in science, technology, engineering, and mathematics fields, particularly at higher levels of organizations. This article investigates the impact of this underrepresentation on the processes of interpersonal collaboration in nanotechnology. Analyses are conducted to assess: (1) the comparative tie strength of women's and men's collaborations, (2) whether women and men gain equal access to scientific information through collaborators, (3) which tie characteristics are associated with access to information for women and men, and (4) whether women and men acquire equivalent amounts of information by strengthening ties. Our results show that the overall tie strength is less for women's collaborations and that women acquire less strategic information through collaborators. Women and men rely on different tie characteristics in accessing information, but are equally effective in acquiring additional information resources by strengthening ties. This article demonstrates that the underrepresentation of women in science, technology, engineering, and mathematics has an impact on the interpersonal processes of scientific collaboration, to the disadvantage of women scientists.Villanueva-Felez, Ă.; Woolley, RD.; Cañibano SĂĄnchez, C. (2015). Nanotechnology researchers' collaboration relationships: A gender analysis of access to scientific information. Social Studies of Science. 45(1):100-129. doi:10.1177/0306312714552347S100129451ACKER, J. (1990). HIERARCHIES, JOBS, BODIES: Gender & Society, 4(2), 139-158. doi:10.1177/089124390004002002Aitken, C., Power, R., & Dwyer, R. (2008). A very low response rate in an on-line survey of medical practitioners. Australian and New Zealand Journal of Public Health, 32(3), 288-289. doi:10.1111/j.1753-6405.2008.00232.xAngrist, J. D., & Pischke, J.-S. (2009). Mostly Harmless Econometrics. doi:10.1515/9781400829828Baruch, Y., & Holtom, B. C. (2008). 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MENâS AND WOMENâS NETWORKS: A STUDY OF INTERACTION PATTERNS AND INFLUENCE IN AN ORGANIZATION. Academy of Management Journal, 28(2), 327-343. doi:10.2307/256204Chompalov, I., Genuth, J., & Shrum, W. (2002). The organization of scientific collaborations. Research Policy, 31(5), 749-767. doi:10.1016/s0048-7333(01)00145-7Cook, C., Heath, F., & Thompson, R. L. (2000). A Meta-Analysis of Response Rates in Web- or Internet-Based Surveys. Educational and Psychological Measurement, 60(6), 821-836. doi:10.1177/00131640021970934Durbin, S. (2010). Creating Knowledge through Networks: a Gender Perspective. Gender, Work & Organization, 18(1), 90-112. doi:10.1111/j.1468-0432.2010.00536.xEcklund, E. H., Lincoln, A. E., & Tansey, C. (2012). Gender Segregation in Elite Academic Science. Gender & Society, 26(5), 693-717. doi:10.1177/0891243212451904Ensign, P. C. (2009). Knowledge Sharing among Scientists. doi:10.1057/9780230617131Etzkowitz, H., Kemelgor, C., & Uzzi, B. (2000). Athena Unbound. doi:10.1017/cbo9780511541414Flyvbjerg, B. (2001). Making Social Science Matter. doi:10.1017/cbo9780511810503FOX, M. F. (2001). WOMEN, SCIENCE, AND ACADEMIA. Gender & Society, 15(5), 654-666. doi:10.1177/089124301015005002Fox, M. F. (2010). Women and Men Faculty in Academic Science and Engineering: Social-Organizational Indicators and Implications. American Behavioral Scientist, 53(7), 997-1012. doi:10.1177/0002764209356234Fox, M. F., & Stephan, P. E. (2001). Careers of Young Scientists: Social Studies of Science, 31(1), 109-122. doi:10.1177/030631201031001006Fox, M. F., Sonnert, G., & Nikiforova, I. (2009). Successful Programs for Undergraduate Women in Science and Engineering: Adapting versus Adopting the Institutional Environment. Research in Higher Education, 50(4), 333-353. doi:10.1007/s11162-009-9120-4Friedkin, N. (1980). A test of structural features of granovetterâs strength of weak ties theory. Social Networks, 2(4), 411-422. doi:10.1016/0378-8733(80)90006-4Gaughan, M. (2005). Introduction to the Symposium: Women in Science. The Journal of Technology Transfer, 30(4), 339-342. doi:10.1007/s10961-005-2579-zGaughan, M., & Corley, E. A. (2010). Science faculty at US research universities: The impacts of university research center-affiliation and gender on industrial activities. Technovation, 30(3), 215-222. doi:10.1016/j.technovation.2009.12.001Granovetter, M. S. (1973). The Strength of Weak Ties. American Journal of Sociology, 78(6), 1360-1380. doi:10.1086/225469Hansen, M. T. (1999). The Search-Transfer Problem: The Role of Weak Ties in Sharing Knowledge across Organization Subunits. Administrative Science Quarterly, 44(1), 82. doi:10.2307/2667032Ibarra, H. (1992). Homophily and Differential Returns: Sex Differences in Network Structure and Access in an Advertising Firm. Administrative Science Quarterly, 37(3), 422. doi:10.2307/2393451Islam, N., & Miyazaki, K. (2009). 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Antimicrobial resistance among migrants in Europe: a systematic review and meta-analysis
BACKGROUND: Rates of antimicrobial resistance (AMR) are rising globally and there is concern that increased migration is contributing to the burden of antibiotic resistance in Europe. However, the effect of migration on the burden of AMR in Europe has not yet been comprehensively examined. Therefore, we did a systematic review and meta-analysis to identify and synthesise data for AMR carriage or infection in migrants to Europe to examine differences in patterns of AMR across migrant groups and in different settings. METHODS: For this systematic review and meta-analysis, we searched MEDLINE, Embase, PubMed, and Scopus with no language restrictions from Jan 1, 2000, to Jan 18, 2017, for primary data from observational studies reporting antibacterial resistance in common bacterial pathogens among migrants to 21 European Union-15 and European Economic Area countries. To be eligible for inclusion, studies had to report data on carriage or infection with laboratory-confirmed antibiotic-resistant organisms in migrant populations. We extracted data from eligible studies and assessed quality using piloted, standardised forms. We did not examine drug resistance in tuberculosis and excluded articles solely reporting on this parameter. We also excluded articles in which migrant status was determined by ethnicity, country of birth of participants' parents, or was not defined, and articles in which data were not disaggregated by migrant status. Outcomes were carriage of or infection with antibiotic-resistant organisms. We used random-effects models to calculate the pooled prevalence of each outcome. The study protocol is registered with PROSPERO, number CRD42016043681. FINDINGS: We identified 2274 articles, of which 23 observational studies reporting on antibiotic resistance in 2319 migrants were included. The pooled prevalence of any AMR carriage or AMR infection in migrants was 25·4% (95% CI 19·1-31·8; I2 =98%), including meticillin-resistant Staphylococcus aureus (7·8%, 4·8-10·7; I2 =92%) and antibiotic-resistant Gram-negative bacteria (27·2%, 17·6-36·8; I2 =94%). The pooled prevalence of any AMR carriage or infection was higher in refugees and asylum seekers (33·0%, 18·3-47·6; I2 =98%) than in other migrant groups (6·6%, 1·8-11·3; I2 =92%). The pooled prevalence of antibiotic-resistant organisms was slightly higher in high-migrant community settings (33·1%, 11·1-55·1; I2 =96%) than in migrants in hospitals (24·3%, 16·1-32·6; I2 =98%). We did not find evidence of high rates of transmission of AMR from migrant to host populations. INTERPRETATION: Migrants are exposed to conditions favouring the emergence of drug resistance during transit and in host countries in Europe. Increased antibiotic resistance among refugees and asylum seekers and in high-migrant community settings (such as refugee camps and detention facilities) highlights the need for improved living conditions, access to health care, and initiatives to facilitate detection of and appropriate high-quality treatment for antibiotic-resistant infections during transit and in host countries. Protocols for the prevention and control of infection and for antibiotic surveillance need to be integrated in all aspects of health care, which should be accessible for all migrant groups, and should target determinants of AMR before, during, and after migration. FUNDING: UK National Institute for Health Research Imperial Biomedical Research Centre, Imperial College Healthcare Charity, the Wellcome Trust, and UK National Institute for Health Research Health Protection Research Unit in Healthcare-associated Infections and Antimictobial Resistance at Imperial College London
Spatial analysis of air pollution and childhood asthma in Hamilton, Canada: comparing exposure methods in sensitive subgroups
<p>Abstract</p> <p>Background</p> <p>Variations in air pollution exposure within a community may be associated with asthma prevalence. However, studies conducted to date have produced inconsistent results, possibly due to errors in measurement of the exposures.</p> <p>Methods</p> <p>A standardized asthma survey was administered to children in grades one and eight in Hamilton, Canada, in 1994â95 (N ~1467). Exposure to air pollution was estimated in four ways: (1) distance from roadways; (2) interpolated surfaces for ozone, sulfur dioxide, particulate matter and nitrous oxides from seven to nine governmental monitoring stations; (3) a kriged nitrogen dioxide (NO<sub>2</sub>) surface based on a network of 100 passive NO<sub>2 </sub>monitors; and (4) a land use regression (LUR) model derived from the same monitoring network. Logistic regressions were used to test associations between asthma and air pollution, controlling for variables including neighbourhood income, dwelling value, state of housing, a deprivation index and smoking.</p> <p>Results</p> <p>There were no significant associations between any of the exposure estimates and asthma in the whole population, but large effects were detected the subgroup of children without hayfever (predominately in girls). The most robust effects were observed for the association of asthma without hayfever and NO<sub>2</sub>LUR OR = 1.86 (95%CI, 1.59â2.16) in all girls and OR = 2.98 (95%CI, 0.98â9.06) for older girls, over an interquartile range increase and controlling for confounders.</p> <p>Conclusion</p> <p>Our findings indicate that traffic-related pollutants, such as NO<sub>2</sub>, are associated with asthma without overt evidence of other atopic disorders among female children living in a medium-sized Canadian city. The effects were sensitive to the method of exposure estimation. More refined exposure models produced the most robust associations.</p
Accretion geometry of the neutron star low mass X-ray binary Cyg X-2 from X-ray polarization measurements
We report spectro-polarimetric results of an observational campaign of the
bright neutron star low-mass X-ray binary Cyg X-2 simultaneously observed by
IXPE, NICER and INTEGRAL. Consistently with previous results, the broad-band
spectrum is characterized by a lower-energy component, attributed to the
accretion disc with 1 keV, plus unsaturated
Comptonization in thermal plasma with temperature keV and
optical depth , assuming a slab geometry. We measure the
polarization degree in the 2-8 keV band per cent and
polarization angle , consistent with the
previous X-ray polarimetric measurements by OSO-8 as well as with the direction
of the radio jet which was earlier observed from the source. While polarization
of the disc spectral component is poorly constrained with the IXPE data, the
Comptonized emission has a polarization degree per cent and a
polarization angle aligned with the radio jet. Our results strongly favour a
spreading layer at the neutron star surface as the main source of the
polarization signal. However, we cannot exclude a significant contribution from
reflection off the accretion disc, as indicated by the presence of the iron
fluorescence line.Comment: 10 pages, 7 figures, accepted for publication in MNRA
Polarization constraints on the X-ray corona in Seyfert Galaxies: MCG-05-23-16
We report on the first observation of a radio-quiet Active Galactic Nucleus
(AGN) using polarized X-rays: the Seyfert 1.9 galaxy MCG-05-23-16. This source
was pointed with the Imaging X-ray Polarimetry Explorer (IXPE) starting on May
14, 2022 for a net observing time of 486 ks, simultaneously with XMM-Newton (58
ks) and NuSTAR (83 ks). A polarization degree smaller than (at the
99% c.l.) is derived in the 2-8 keV energy range, where emission is dominated
by the primary component ascribed to the hot corona. The broad-band spectrum,
inferred from a simultaneous fit to the IXPE, NuSTAR, and XMM-Newton data, is
well reproduced by a power law with photon index and a
high-energy cutoff keV. A comparison with Monte Carlo
simulations shows that a lamp-post and a conical geometry of the corona are
consistent with the observed upper limit, a slab geometry is allowed only if
the inclination angle of the system is less than 50.Comment: 7 pages, 3 figures, 1 table. Submitted to MNRAS Letter
Discovery of a variable energy-dependent X-ray polarization in the accreting neutron star GX 5-1
We report on the coordinated observations of the neutron star low-mass X-ray binary (NS-LMXB) GX 5â1 in X-rays (IXPE, NICER, NuSTAR, and INTEGRAL), optical (REM and LCO), near-infrared (REM), mid-infrared (VLT VISIR), and radio (ATCA). This Z-source was observed by IXPE twice in March-April 2023 (Obs. 1 and 2). In the radio band the source was detected, but only upper limits to the linear polarization were obtained at a 3Ï level of 6.1% at 5.5 GHz and 5.9% at 9 GHz in Obs. 1 and 12.5% at 5.5 GHz and 20% at 9 GHz in Obs. 2. The mid-IR, near-IR, and optical observations suggest the presence of a compact jet that peaks in the mid- or far-IR. The X-ray polarization degree was found to be 3.7%±0.4% (at 90% confidence level) during Obs. 1 when the source was in the horizontal branch of the Z-track and 1.8%±0.4% during Obs. 2 when the source was in the normal-flaring branch. These results confirm the variation in polarization degree as a function of the position of the source in the color-color diagram, as for previously observed Z-track sources (Cyg X-2 and XTE 1701â462). Evidence of a variation in the polarization angle of âŒ20° with energy is found in both observations, likely related to the different, nonorthogonal polarization angles of the disk and Comptonization components, which peak at different energies
IXPE observation confirms a high spin in the accreting black hole 4U 1957+115
We present the results of the first X-ray polarimetric observation of the
low-mass X-ray binary 4U 1957+115, performed with the Imaging X-ray Polarimetry
Explorer in May 2023. The binary system has been in a high-soft spectral state
since its discovery and is thought to host a black hole. The 571 ks
observation reveals a linear polarisation degree of and a
polarisation angle of in the 2-8 keV energy range.
Spectral modelling is consistent with the dominant contribution coming from the
standard accretion disc, while polarimetric data suggest a significant role of
returning radiation: photons that are bent by strong gravity effects and forced
to return to the disc surface, where they can be reflected before eventually
reaching the observer. In this setting, we find that models with a black hole
spin lower than 0.96 and an inclination lower than are disfavoured.Comment: 12 pages, 10 figures, 2 tables, accepted for publication in A&
DEEP MORPHOLOGICAL and SPECTRAL STUDY of the SNR RCW 86 with FERMI-LAT
RCW 86 is a young supernova remnant (SNR) showing a shell-type structure at
several wavelengths and is thought to be an efficient cosmic-ray (CR)
accelerator. Earlier \textit{Fermi} Large Area Telescope results reported the
detection of -ray emission coincident with the position of RCW 86 but
its origin (leptonic or hadronic) remained unclear due to the poor statistics.
Thanks to 6.5 years of data acquired by the \textit{Fermi}-LAT and the new
event reconstruction Pass 8, we report the significant detection of spatially
extended emission coming from RCW 86. The spectrum is described by a power-law
function with a very hard photon index () in the 0.1--500 GeV range and an energy flux above 100 MeV of
( ) erg
cm s. Gathering all the available multiwavelength (MWL) data, we
perform a broadband modeling of the nonthermal emission of RCW 86 to constrain
parameters of the nearby medium and bring new hints about the origin of the
-ray emission. For the whole SNR, the modeling favors a leptonic
scenario in the framework of a two-zone model with an average magnetic field of
10.2 0.7 G and a limit on the maximum energy injected into protons
of 2 10 erg for a density of 1 cm. In addition,
parameter values are derived for the North-East (NE) and South-West (SW)
regions of RCW 86, providing the first indication of a higher magnetic field in
the SW region.The Fermi LAT Collaboration acknowledges generous ongoing support from a number of agencies and institutes that have supported both the development and the operation of the LAT as well as scientific data analysis. These include the National Aeronautics and Space Administration and the Department of Energy in the United States, the Commissariat Ă lâEnergie Atomique and the Centre National de la Recherche Scientifique / Institut National de Physique NuclĂ©aire et de Physique des Particules in France, the Agenzia Spaziale Italiana and the Istituto Nazionale di Fisica Nucleare in Italy, the Ministry of Education, Culture, Sports, Science and Technology (MEXT), High Energy Accelerator Research Organization (KEK) and Japan Aerospace Exploration Agency (JAXA) in Japan, and the K. A. Wallenberg Foundation, the Swedish Research Council and the Swedish National Space Board in Sweden. Additional support for science analysis during the operations phase is gratefully acknowledged from the Istituto Nazionale di Astrofisica in Italy and the Centre National dâĂtudes Spatiales in France. GD and EG are members of CIC-CONICET (Argentina), LD is Fellow of CONICET (Argentina). They are supported through grants from CONICET and ANPCyT (Argentina). We acknowledge to Estela Reynoso and Anne Green who collaborated in the first stages of the HI data acquisition and preocessing.This is the author accepted manuscript. It first appeared from the Institute of Physics via http://dx.doi.org/10.3847/0004-637X/819/2/9
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