Search

We investigate the extreme X-ray variability of a z = 1.608 active galactic nucleus in the 7 Ms Chandra Deep Field-South (XID 403), which showed two significant X-ray brightening events. In the first event, XID 403 brightened by a factor of $>2.5$ in $\lesssim6.1$ rest-frame days in the observed-frame 0.5-5 keV band. The event lasted for $\approx5.0\textrm{-}7.3$ days, and then XID 403 dimmed by a factor of $>6.0$ in $\lesssim6.1$ days. After $\approx1.1\textrm{-}2.5$ years in the rest frame (including long observational gaps), it brightened again with the 0.5-5 keV flux increasing by a factor of $>12.6$. The second event lasted over 251 days and the source remained bright until the end of the 7 Ms exposure. The spectrum is a steep power law (photon index $Γ=2.8\pm0.3$) without obscuration during the second outburst, and the rest-frame 2-10 keV luminosity reaches $1.5^{+0.8}_{-0.5}\times10^{43}$ erg s$^{-1}$; there is no significant spectral evolution within this epoch. The infrared-to-UV spectral energy distribution of XID 403 is dominated by the host galaxy. There is no significant optical/UV variability and $R$-band (rest-frame $\approx2500$ $\unicode{xC5}$) brightening contemporaneous with the X-ray brightening. The extreme X-ray variability is likely due to two X-ray unveiling events, where the line of sight to the corona is no longer shielded by high-density gas clumps in a small-scale dust-free absorber. XID 403 is probably a high-redshift analog of local narrow-line Seyfert 1 galaxies, and the X-ray absorber is a powerful accretion-disk wind. On the other hand, we cannot exclude the possibility that XID 403 is an unusual candidate for tidal disruption events., 23 pages, 9 figures, accepted for publication in ApJ

We study the ensemble X-ray variability properties of Active Galactic Nuclei (AGN) over a large range of timescales (20 ks $\leq T\leq$ 14 yrs), redshift ($0\leq z \lesssim 3$), luminosities ($10^{40}$ erg s$^{-1}\leq L_X\leq 10^{46}$ erg s$^{-1}$) and black hole (BH) masses ($10^6 \leq $M$_\odot \leq 10^9$). We propose the use of the variance-frequency diagram, as a viable alternative to the study of the power spectral density (PSD), which is not yet accessible for distant, faint and/or sparsely sampled AGN. We show that the data collected from archival observations and previous literature studies are fully consistent with a universal PSD form which does not show any evidence for systematic evolution of shape or amplitude with redshift or luminosity, even if there may be differences between individual AGN at a given redshift or luminosity. We find new evidence that the PSD bend frequency depends on BH mass and, possibly, on accretion rate. We finally discuss the implications for current and future AGN population and cosmological studies., Comment: In press on Astronomy and Astrophysics

We present 850um imaging of the XMM-LSS field observed for 170 hours as part of the James Clerk Maxwell Telescope SCUBA-2 Large eXtragalactic Survey (S2LXS). S2LXS XMM-LSS maps an area of 9 square degrees, reaching a moderate depth of 1-sigma ~ 4 mJy/beam. This is the largest contiguous area of extragalactic sky mapped by JCMT at 850um to date. The wide area of the S2LXS XMM-LSS survey allows us to probe the ultra-bright (S_850um > 15 mJy), yet rare submillimetre population. We present the S2LXS XMM-LSS catalogue, which comprises 40 sources detected at >5-sigma significance, with deboosted flux densities in the range of 7 mJy to 48 mJy. We robustly measure the bright-end of the 850um number counts at flux densities >7 mJy, reducing the Poisson errors compared to existing measurements. The S2LXS XMM-LSS observed number counts show the characteristic upturn at bright fluxes, expected to be motivated by local sources of submillimetre emission and high-redshift strongly lensed galaxies. We find that the observed 850um number counts are best reproduced by model predictions that include either strong lensing or source blending from a 15 arcsec beam, indicating that both may make an important contribution to the observed over-abundance of bright single dish 850um selected sources. We make the S2LXS XMM-LSS 850um map and >5-sigma catalogue presented here publicly available., Accepted for publication in MNRAS

Ambient air pollution has been a worldwide concern with a devastating impact on the health of populations, while increasing the burden on public health systems. Assessing the adverse health effects of air pollution is vital for forming disease control policies. This study investigates the excess risk of 6 air pollutants for 21 disease groups (observed in outpatient visits) through the Poisson regression modeling. Daily air quality data and 1.6 million outpatient visit records from Shenzhen, China are used in the study. The outpatient visits are classified into 21 disease groups according to the International Classification of Diseases, Tenth Revision. The results show that associations between air pollutants and diseases vary across different disease groups. Specifically, the following disease classes are significantly associated with air pollution: blood, metabolic, ophthalmological, circulatory, respiratory, digestive, musculoskeletal, connective tissue, and genitourinary diseases. Nitrogen dioxide, particulate matter less than 10 μm in diameter (PM 10 ), particulate matter less than 2.5 μm in diameter (PM 2.5 ), and air quality index have the most extensive impact on more than ten disease groups. A health effect graph is built to support public health management decision-making and provide residents with information about health effects of air pollution.

In order to determine the domains of Chaboche model of cement concrete fatigue damage under high stress ratios, first, the probability densities of general monotonic random variables including cement concrete fatigue life are deduced. And then, the probability density of Chaboche fatigue damage model is deduced. By virtue of laboratory fatigue test results, the fatigue damage probability density functions of Chaboche model can be obtained, considering different stress ratios. Substituting load cycles into the functions, the cement concrete fatigue reliabilities based on Chaboche model can be acquired through integral operation. Finally, on the basis of cement concrete fatigue reliability analysis, the critical values of load cycle of Chaboche model under different high stress ratios can be made certain and the model's domains corresponding to these stress ratios can be obtained. The obtained results also show that under the same stress ratio, with the increase in the load cycle, the fatigue reliability declines gradually from almost 100% to 0%. No matter under any stress ratio, in the initial stage of load action, there is always a relatively stable phase for fatigue reliability. With the increase in the stress ratio, the phase diminishes gradually and the load cycle corresponding to reliability of 0% also decreases. In descent phase of reliability, the higher stress ratio is, the lower cement concrete reliability is for the same load cycle.

We present an analysis of deep multiwavelength data of z = 0.3–3 starburst galaxies selected by their 70 μm emission in the Extended‐Chandra Deep Field‐South (E‐CDF‐S) and Extended Groth Strip (EGS). We identify active galactic nuclei (AGNs) in these infrared sources through their X‐ray emission and quantify the fraction of sources hosting an AGN. We find that the fraction depends strongly on the star formation rate (SFR, inferred from the 70 μm luminosity after subtracting the estimated AGN contribution), particularly for more luminous AGNs. At the highest SFRs (∼1000 M⊙ yr−1), the fraction of galaxies that host an X‐ray detected AGN with L0.5–8.0 keV≳1043 erg s−1 rises to ∼40%, a value roughly consistent with the AGN fraction found for high‐redshift submillimeter galaxies. The strong dependence of the AGN fraction on SFR implies that the duty cycle of luminous AGN activity relates to the growth rate of the host galaxy.

Myelodysplastic syndrome (MDS) constitutes a heterogeneous group of hematopoietic stem cell disorder characterized by peripheral blood cytopenia(s), in the presence of hypercellular bone marrow with features of ineffective hematopoiesis, and susceptibility to acute leukemia (AL). Although the precise pathogenesis of MDS remains to be clarified, cytogenetic abnormalities seem to be involved in its pathogenesis and are considered as an important factor in diagnosis and predicting clinical outcome.To explore the cytogenetic features of Chinese patients with myelodysplastic syndrome (MDS).Conventional cytogenetic analysis was performed in 88 MDS patients and among them, 34 cases were studied by interphase fluorescence in situ hybridization (I-FISH) with precisely chromosome 8 centromere specific DNA probe and DNA specific probes for 7q32 , 5q31.Of the 88 patients, 45 (51.1%) showed clonal karyotypic abnormalities by CC at diagnosis, including numerical changes (18 cases, 20.5%), structural changes (12 cases, 13.6%), and numerical and structural changes simultaneously(15 cases, 17.0%). Trisomy 8, -5/5q-, and -7/ 7q- account for 20.5%, 15.9%, and 5.7% respectively. Complex karyotypes were observed in 17 patients, the incidence being 19.3% in the whole series of cases. Among 34 MDS patients studied by I-FISH, -5/5q-, -7/7q- and trisomy 8 occurring in 4, 2 and 10 cases respectively for CC were confirmed by I-FISH. 5 cases in 30 cases who did not show -5/5q- by CC displayed this abnormality by I-FISH. 3 cases without -7/7q- by CC presented this aberration by I-FISH. 5 cases with trisomy 8 for I-FISH was not identified this change by CC.The frequent abnormalities are trisomy 8, -5/5q- and -7/ 7q-. FISH is very useful in detecting these alterations in MDS and it is an important complement to CC.

The crystal structure of [Ni(C2H5OCS2)2(C14H12N2)] cis- [Ni(EtXA)2(2,9-dmphen)] (EtXA = ethyl xanthate, 2,9-dmphen = 2,9-dimethyl-1,10-phenanthroline), containing a distorted octahedral NiS4N2 core, is reported. The Ni—S bond lengths range from 2.376 (2) to 2.522 (2) A and the Ni—N bond lengths are 2.107 (4) and 2.153 (3) A, while the N(1)—Ni—N(2) chelate angle is 78.3 (1)°.

The effect of cocrystallization on the welding behavior of semicrystalline polymers was studied by means of T-peel testing at room temperature, using ultrahigh-molecular-weight polyethylene (UHMWPE) as a model polymer. Solution-cast films of UHMWPE have a very special morphology, consisting of regularly stacked, 107 angstroms thick lamellae, which exactly double in thickness upon annealing for 15 min below the melting point at 125 °C. This lamellar doubling process was used to introduce a well-defined amount of cocrystallization across the interface, by annealing two stacked, completely wetted solution-cast films. It was found that doubling of the lamellae across the interface enhances the peel energy to such a level that the films could not be separated anymore. By contrast, reference samples, in which cocrystallization across the interface was prohibited by `preannealing' one side of the film, could still be separated easily. Therefore, it is concluded that cocrystallization across the interface is extremely efficient in enhancing the adhesive fracture energy.

Cytogenetic and molecular studies were made in 4 patients with Ph negative chronic myelogenous leukemia (CML) and 4 patients with CML with unusual Ph translocation. Chromosome analysis was performed on direct preparations and short-term cultures of bone marrow cells by R and G bandings. Southern blot analysis of DNA from leukemia cells was made using 4.5kb bcr-u and 1.5kb bcr-HE probes. Four patients with Ph negative CML had normal karyotypes. Among them, 3 had rearrangement of bcr, and 1 expected germ line pattern only. In the 4 patients with CML with unusual Ph translocation who had bcr rearrangement, one had a masked Ph chromosome originating from a translocation t(3;22) (p22;q11), the other three had one of the following complex Ph translocations: t(9;22;13) (q34;q11;q21), t(3;14;22) (p21;q32;q11) and t(X;9;22;12) (q22; q34; q11; q24). Our data confirmed that Ph negative CML could be divided into two different subsets: Ph-bcr+ CML and Ph-bcr-CML and that whatever the type of translocation may be, CML with unusual Ph translocation and Ph positive CML had a common molecular pathological basis.

This paper reports an interesting case of myelodysplastic syndrome (MDS), whose bone marrow karyotype at diagnosis was 46, XY, t(16;17) (q12;q25). Fourteen months later, the disease transformed into erythroleukemia, and several correlative clones with hyperdiploid appeared at the same time. Thus, we consider that detecting karyotypic evolution may help evaluate the prognosis of MDS.

Cytogenetic studies using Giemsa R-bands after a short term culture of bone marrow or peripheral blood were done in 20 cases of acute promyelocytic leukemia (APL), including three cases of microgranular variant. As a result, t (15;17) cells were found in all the cells, and the percentages of the abnormal cells were 38-100%. In 2 cases, t(15;17) was seen in 88% and 65% of the cells in cultured specimens, whereas no such translocation was seen in direct specimens. Among 6 cases treated with tretinoin, 5 achieved complete remission, and among 14 cases treated by HOAP protocol 2 achieved complete remission. Reexamination of 4 of these cases during the stage of complete remission failed to find t(15;17). These data revealed that t(15;17) may probably be present in all cases of APL, and therefore is a very useful diagnostic criterion, especially in cases of micro granular APL. But the detection rate is determined by methodology, which requires special precaution.

We present 0.5-2 keV, 2-8 keV, 4-8 keV, and 0.5-8 keV cumulative and differential number counts (logN-logS) measurements for the recently completed ~4 Ms Chandra Deep Field-South (CDF-S) survey, the deepest X-ray survey to date. We implement a new Bayesian approach, which allows reliable calculation of number counts down to flux limits that are factors of ~1.9-4.3 times fainter than the previously deepest number-counts investigations. In the soft band, the most sensitive bandpass in our analysis, the ~4 Ms CDF-S reaches a maximum source density of ~27,800 deg-2. By virtue of the exquisite X-ray and multiwavelength data available in the CDF-S, we are able to measure the number counts from a variety of source populations (active galactic nuclei [AGNs], normal galaxies, and Galactic stars) and subpopulations (as a function of redshift, AGN absorption, luminosity, and galaxy morphology), and test models that describe their evolution. We find that AGNs still dominate the X-ray number counts down to the faintest flux levels for all bands and reach a limiting soft-band source density of ~14,900 deg-2, the highest reliable AGN source density measured at any wavelength. We find that the normal-galaxy counts rise rapidly near the flux limits, and at the limiting soft-band flux, reach source densities of ~12,700 deg-2 and make up 46+/-5% of the total number counts. The rapid rise of the galaxy counts toward faint fluxes, and significant normal-galaxy contributions to the overall number counts, indicate that normal galaxies will overtake AGNs just below the ~4 Ms soft-band flux limit and will provide a numerically significant new X-ray source population in future surveys that reach below the ~4 Ms sensitivity limit. We show that a future ~10 Ms CDF-S would allow for a significant increase in X-ray detected sources, with many of the new sources being cosmologically distant (z > 0.6) normal galaxies., 24 Pages, 17 Figures, 2 Tables; Accepted for publication in ApJ; Data tables are publicly available at http://www2.astro.psu.edu/users/niel/cdfs/cdfs-chandra.html

The 4 Ms Chandra Deep Field-South (CDF-S) and other deep X-ray surveys have been highly effective at selecting active galactic nuclei (AGN). However, cosmologically distant low-luminosity AGN (LLAGN) have remained a challenge to identify due to significant contribution from the host galaxy. We identify long-term X-ray variability (~month-years, observed frame) in 20 of 92 CDF-S galaxies spanning redshifts z~0.08-1.02 that do not meet other AGN selection criteria. We show that the observed variability cannot be explained by X-ray binary populations or ultraluminous X-ray sources, so the variability is most likely caused by accretion onto a supermassive black hole. The variable galaxies are not heavily obscured in general, with a stacked effective power-law photon index of Gamma_stack~1.93+/-0.13, and are therefore likely LLAGN. The LLAGN tend to lie a factor of ~6-80 below the extrapolated linear variability-luminosity relation measured for luminous AGN. This may be explained by their lower accretion rates. Variability-independent black-hole mass and accretion-rate estimates for variable galaxies show that they sample a significantly different black-hole mass-accretion rate space, with masses a factor of 2.4 lower and accretion rates a factor of 22.5 lower than variable luminous AGN at the same redshift. We find that an empirical model based on a universal broken power-law PSD function, where the break frequency depends on SMBH mass and accretion rate, roughly reproduces the shape, but not the normalization, of the variability-luminosity trends measured for variable galaxies and more luminous AGN., ApJ accepted, 22 pages, 14 figures, 2 tables; the full version of Table 2 may be requested from xuey@astro.psu.edu

In order to trace the instantaneous star formation rate (SFR) at high redshift, and thus help in understanding the relation between the different emission mechanisms related to star formation, we combine the recent 4-Ms Chandra X-ray data and the deep Very Large Array radio data in the Extended Chandra Deep Field-South region. We find 268 sources detected both in the X-ray and radio bands. The availability of redshifts for {\tilde}95 per cent of the sources in our sample allows us to derive reliable luminosity estimates and the intrinsic properties from X-ray analysis for the majority of the objects. With the aim of selecting sources powered by star formation in both bands, we adopt classification criteria based on X-ray and radio data, exploiting the X-ray spectral features and time variability, taking advantage of observations scattered across more than 10 years. We identify 43 objects consistent with being powered by star formation. We also add another 111 and 70 star-forming candidates detected only in the radio and X-ray bands, respectively. We find a clear linear correlation between radio and X-ray luminosity in star-forming galaxies over three orders of magnitude and up to z{\tilde} 1.5. We also measure a significant scatter of the order of 0.4 dex, higher than that observed at low redshift, implying an intrinsic scatter component. The correlation is consistent with that measured locally, and no evolution with redshift is observed. Using a locally calibrated relation between the SFR and the radio luminosity, we investigate the L$_{X}$(2-10 keV)-SFR relation at high redshift. The comparison of the SFR measured in our sample with some theoretical models for the Milky Way and M31, two typical spiral galaxies, indicates that, with current data, we can trace typical spirals only at z{\le} 0.2, and strong starburst galaxies with SFRs as high as {\tilde}100 M$_{&sun;}$ yr$^{-1}$, up to z{\tilde} 1.5.

We present the first results of the spectroscopy of distant, obscured AGN as obtained with the ultra-deep (~3.3 Ms) XMM-Newton survey in the Chandra Deep Field South (CDFS). One of the primary goals of the project is to characterize the X-ray spectral properties of obscured and heavily obscured Compton-thick AGN over the range of redhifts and luminosities that are relevant in terms of their contribution to the X-ray background. The ultra-deep exposure, coupled with the XMM detector's spectral throughput, allowed us to accumulate good quality X-ray spectra for a large number of X-ray sources and, in particular, for heavily obscured AGN at cosmological redshifts. Specifically we present the X-ray spectral properties of two high-redshift - z= 1.53 and z=3.70 - sources. The XMM spectra of both are very hard, with a strong iron Kalpha line at a rest-frame energy of 6.4 keV. A reflection-dominated continuum provides the best description of the X-ray spectrum of the z=1.53 source, while the intrinsic continuum of the z=3.70 AGN is obscured by a large column N_H ~ 10^24 cm-2 of cold gas. Compton-thick absorption, or close to it, is unambiguously detected in both sources. Interestingly, these sources would not be selected as candidate Compton thick AGN by some multiwavelength selection criteria based on the mid-infrared to optical and X-ray to optical flux ratios., Comment: 6 pages, 3 figures, 1 table. Minor changes applied to match the published version [A&A 526, L9 (2011)]

[abridged] We present point-source catalogs for the 4Ms Chandra Deep Field-South (CDF-S), which is the deepest Chandra survey to date and covers an area of 464.5 arcmin^2. We provide a main source catalog, which contains 740 X-ray point sources that are detected with wavdetect at a false-positive probability threshold of 1E-5 and also satisfy a binomial-probability source-selection criterion of P75% of the main-catalog sources are AGNs; of the 300 new main-catalog sources, about 35% are likely normal and starburst galaxies, reflecting the rise of normal and starburst galaxies at the very faint flux levels uniquely accessible to the 4Ms CDF-S. Near the center of the 4Ms CDF-S, the observed AGN and galaxy source densities have reached ~9800 and 6900 per square degree, respectively. The 4 Ms CDF-S reaches on-axis flux limits of ~9.1E-18 and 5.5E-17 erg/cm^2/s for the soft and hard bands, respectively. An increase in the CDF-S exposure by a factor of ~2-2.5 would provide further significant gains and probe key unexplored discovery space., 31 pages, 24 figures, 8 tables, ApJS in press. Data and images available at http://www.astro.psu.edu/users/niel/cdfs/cdfs-chandra.html

We use the 4Ms CDF-S survey to place direct X-ray constraints on the ubiquity of z~2 heavily obscured AGNs in K10 keV observatories. On the basis of these analyses we estimate the space density for typical (intrinsic X-ray luminosities of L_X>1E43 erg/s) heavily obscured and Compton-thick AGNs at z~2. Our space-density constraints are conservative lower limits but they are already consistent with the range of predictions from X-ray background models., ApJ in press: 15 pages, 6 figures, 3 tables