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Nanometer-scale local structural study of the paraelectric cubic phase of KNbO <sub/>3</sub> by convergent-beam electron diffraction
摘要： Nanometer-scale local structures of the paraelectric cubic phase of potassium niobate (KNbO3) are examined by convergent-beam electron diffraction (CBED) using a nanometer-size electron probe. The breaking of the cubic symmetry has been directly observed in the nanometer-scale areas of the cubic phase of KNbO3. This indicates the existence of local polarization clusters in the cubic phase. Symmetry breaking index maps for the fourfold rotation symmetry are given at different temperatures with the combined use of scanning transmission electron microscopy (STEM) and CBED (STEM–CBED). ? 2017 The Japan Society of Applied Physics
关键词： local polarization clusters,CBED,convergent-beam electron diffraction,STEM,KNbO3,symmetry breaking
更新于2025-09-09 09:28:46
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A new method to assign galaxy cluster membership using photometric redshifts
摘要： We introduce a new effective strategy to assign group and cluster membership probabilities Pmem to galaxies using photometric redshift information. Large dynamical ranges both in halo mass and cosmic time are considered. The method takes into account the magnitude distribution of both cluster and field galaxies as well as the radial distribution of galaxies in clusters using a non-parametric formalism, and relies on Bayesian inference to take photometric redshift uncertainties into account. We successfully test the method against 1208 galaxy clusters within redshifts z = 0.05?2.58 and masses 1013.29?14.80 M(cid:12) drawn from wide field simulated galaxy mock catalogs mainly developed for the forthcoming Euclid mission. Median purity and completeness values of (55+17 ?10)% and (95+5 ?15)% are reached for galaxies brighter than 0.25 L? within r200 of each simulated halo and for a statistical photometric redshift accuracy σ((zs ? zp)/(1 + zs)) = 0.03. The mean values p = 56% and c = 93% are consistent with the median and have negligible sub-percent uncertainties. Accurate photometric redshifts (σ((zs ? zp)/(1 + zs)) (cid:46) 0.05) and robust estimates for the cluster redshift and cluster center coordinates are required. The dependence of the assignments on photometric redshift accuracy, galaxy magnitude and distance from the halo center, and halo properties such as mass, richness, and redshift are investigated. Variations in the mean values of both purity and completeness are globally limited to a few percent. The largest departures from the mean values are found for galaxies associated with distant z (cid:38) 1.5 halos, faint (～0.25 L?) galaxies, and those at the outskirts of the halo (at cluster-centric projected distances ～r200) for which the purity is decreased, ?p (cid:39) 20% at most, with respect to the mean value. The proposed method is applied to derive accurate richness estimates. A statistical comparison between the true (Ntrue) vs. estimated richness (λ = (cid:80) Pmem) yields on average to unbiased results, Log(λ/Ntrue) = ?0.0051 ± 0.15. The scatter around the mean of the logarithmic difference between λ and the halo mass is 0.10 dex for massive halos (cid:38)1014.5 M(cid:12). Our estimates could therefore be useful to constrain the cluster mass function and to calibrate independent cluster mass estimates such as those obtained from weak lensing, Sunyaev-Zel’dovich, and X-ray studies. Our method can be applied to any list of galaxy clusters or groups in both present and forthcoming surveys such as SDSS, CFHTLS, Pan-STARRS, DES, LSST, and Euclid.
关键词： galaxies: clusters: general,galaxies: groups: general,galaxies: statistics
更新于2025-09-09 09:28:46
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X-ray and optical spectroscopy of the massive young open cluster IC 1805
摘要： Context. Very young open clusters are ideal places to study the X-ray properties of a homogeneous population of early-type stars. In this respect, the IC 1805 open cluster is very interesting as it hosts the O4 If+ star HD 15570 thought to be in an evolutionary stage intermediate between a normal O-star and a Wolf-Rayet star. Aims. Such a star could provide a test for theoretical models aiming at explaining the empirical scaling relation between the X-ray and bolometric luminosities of O-type stars. Methods. We have observed IC 1805 with XMM-Newton and further collected optical spectroscopy of some of the O-star members of the cluster. Results. The optical spectra allow us to revisit the orbital solutions of BD+60? 497 and HD 15558, and provide the ?rst evidence of binarity for BD+60? 498. X-ray emission from colliding winds does not appear to play an important role among the O-stars of IC 1805. Notably, the X-ray ?uxes do not vary signi?cantly between archival X-ray observations and our XMM-Newton pointing. The very fast rotator BD+60? 513, and to a lesser extent the O4 If+ star HD 15570 appear somewhat underluminous. Whilst the underluminosity of HD 15570 is only marginally signi?cant, its amplitude is found to be compatible with theoretical expectations based on its stellar and wind properties. A number of other X-ray sources are detected in the ?eld, and the brightest objects, many of which are likely low-mass pre-main sequence stars, are analyzed in detail.
关键词： X-rays: stars,open clusters and associations: individual: IC 1805,stars: early-type
更新于2025-09-09 09:28:46
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Constraining ALP-photon coupling using galaxy clusters
摘要： We study photon-ALP conversion by resonance effects in the magnetized plasma of galaxy clusters and compare the predicted distortion of the cosmic microwave background spectrum in the direction of such objects to measurements of the thermal Sunyaev-Zeldovich effect. Using galaxy cluster models based on current knowledge, we obtain upper limits on the photon-ALP coupling constant g of (cid:46) 10?12 GeV?1. The constraints apply to the mass range of 2 · 10?14 eV (cid:46) mALP (cid:46) 3 · 10?12 eV in which resonant photon-ALP conversions can occur. These limits are slightly stronger than current limits, and furthermore provide an independent constraint. We find that a next generation PRISM-like experiment would allow limits down to g (cid:46) 10?14 GeV?1, two orders of magnitude stronger than the currently strongest limits in this mass range.
关键词： axions,Sunyaev-Zeldovich effect,galaxy clusters
更新于2025-09-09 09:28:46
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Monitoring circulating tumor cells in vivo by a confocal microscopy system
摘要： Circulating tumor cells (CTCs) play a key role in cancer metastasis but are very difficult to detect. in vivo monitoring CTCs has been recognized as an important technique for cancer research and clinical diagnosis. Recently, a noninvasive method, in vivo flow cytometry (IVFC) has been developed to enable continuous, real-time, and long-duration detection of CTCs in animal models by detecting CTC fluorescence in blood vessels excited by lasers. In this study, we present a simple optical scheme for direct noninvasive CTC detection using confocal microscopes. We demonstrate that line scanning of confocal microscopy can provide effective and quantitative CTC detection in live mice during cancer development. Rare CTC signals can be acquired at the early stage of the tumor development after implantation of subcutaneous tumor and monitored continuously to the end. Signals from CTC clusters can also be acquired and distinguished from single CTCs. Our results suggest confocal microscopy is a simple and reliable method for biologists and doctors to use for cancer research.
关键词： line scanning,circulating tumor cells,confocal microscopy,CTC clusters
更新于2025-09-04 15:30:14
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Ground-based astrometry with wide field imagers
摘要： High-precision astrometry requires accurate point-spread function modeling and accurate geometric-distortion corrections. This paper demonstrates that it is possible to achieve both requirements with data collected at the high acuity wide-field K-band imager (HAWK-I), a wide-field imager installed at the Nasmyth focus of UT4/VLT ESO 8 m telescope. Our final astrometric precision reaches ～3 mas per coordinate for a well-exposed star in a single image with a systematic error less than 0.1 mas. We constructed calibrated astro-photometric catalogs and atlases of seven fields: the Baade’s window, NGC 6656, NGC 6121, NGC 6822, NGC 6388, NGC 104, and the James Webb Space Telescope calibration field (in the Large Magellanic Cloud). We make these catalogs and images electronically available to the community. Furthermore, as a demonstration of the efficacy of our approach, we combined archival material taken with the optical wide-field imager at the MPI/ESO 2.2 m with HAWK-I observations. We showed that we are able to achieve an excellent separation between cluster members and field objects for NGC 6656 and NGC 6121 with a time base-line of about 8 years. Using both HST and HAWK-I data, we also study the radial distribution of the SGB populations in NGC 6656 and conclude that the radial trend is flat within our uncertainty. We also provide membership probabilities for most of the stars in NGC 6656 and NGC 6121 catalogs and estimate membership for the published variable stars in these two fields.
关键词： globular clusters: general,instrumentation: detectors,Galaxy: bulge,proper motions,astrometry,techniques: image processing
更新于2025-09-04 15:30:14
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Surface photometry of WINGS galaxies with GASPHOT
摘要： Aims. We present the B, V, and K band surface photometry catalogs obtained by running the automatic software GASPHOT on galaxies from the WINGS cluster survey with isophotal areas larger than 200 pixels. The catalogs can be downloaded at the Centre de Données Astronomiques de Strasbourg. Methods. The luminosity growth curves of stars and galaxies in a given catalog relative to a given cluster image were obtained simultaneously by slicing the image with a fixed surface brightness step in several SExtractor runs. Then, using a single Sersic law convolved with a space-varying point spread function (PSF), GASPHOT performed a simultaneous χ2 best-fit of the major- and minor-axis luminosity growth curves of galaxies. We outline the GASPHOT performances and compare our surface photometry with that obtained by SExtractor, GALFIT, and GIM2D. This analysis is aimed at providing statistical information about the accuracy that is generally achieved by the softwares for automatic surface photometry of galaxies. Results. The GASPHOT catalogs provide the parameters of the Sersic law that fit the luminosity profiles for each galaxy and for each photometric band. They are the sky coordinates of the galaxy center (RA, Dec), the total magnitude (m), the semi-major axis of the effective isophote (Re), the Sersic index (n), the axis ratio (b/a), and a flag parameter (QFLAG) that generally indicates the fit quality. The WINGS-GASPHOT database includes 41 463 galaxies in the B band, 42 275 in the V band, and 71 687 in the K band. The bright early-type galaxies have higher Sersic indices and larger effective radii, as well as redder colors in their center. In general, the effective radii increase systematically from the K to the V and B band. Conclusions. The GASPHOT photometry agrees well with the surface photometry obtained by GALFIT and GIM2D, and with the aperture photometry provided by SExtractor. In particular, the direct comparison of structural parameters derived by different softwares for common galaxies indicates that the systematic differences are small in general. The only significant deviations are most likely due to the peculiar (and very accurate) image processing adopted by WINGS for large galaxies. The main advantages of GASPHOT with respect to other tools are (i) the automatic finding of the local PSF; (ii) the short CPU execution time; and (iii) the remarkable stability against the choice of the initial-guess parameters. All these characteristics make GASPHOT an ideal tool for blind surface photometry of large galaxy samples in wide-field CCD mosaics.
关键词： surveys,catalogs,galaxies: clusters: general
更新于2025-09-04 15:30:14
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Observations on Si-based micro-clusters embedded in TaN thin film deposited by co-sputtering with oxygen contamination
摘要： Using scanning electron microscopy (SEM) and high-resolution x-ray photoelectron spectroscopy with the synchrotron radiation we investigated Si-based micro-clusters embedded in TaSiN thin films having oxygen contamination. TaSiN thin films were deposited by co-sputtering on fixed or rotated substrates and with various power conditions of TaN and Si targets. Three types of embedded micro-clusters with the chemical states of pure Si, SiOx-capped Si, and SiO2-capped Si were observed and analyzed using SEM and Si 2p and Ta 4 f core-level spectra were derived. Their different resistivities are presumably due to the different chemical states and densities of Si-based micro-clusters.
关键词： oxygen contamination,HRXPS,TaN thin film,SEM,co-sputtering,Si-based micro-clusters
更新于2025-09-04 15:30:14
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IR and XAFS studies of photoluminescent Ag-type zeolite-A
摘要： We examined the relation between the zeolite framework, Ag clusters, and properties of photoluminescence (PL) using in-situ infrared spectroscopy (IR) and X-ray absorption fine structure (XAFS). The Ag clusters are generated in the cavity of Ag-type zeolite-A that is cooled to room temperature after heating at 500°C for 24 hour under vacuum or in atmosphere. The Ag clusters in the zeolite cavity break down when air is introduced. According to the formation and breakdown of the Ag cluster, the infrared spectrum of the zeolite framework changed slightly. Then, this change was compensated by irradiation of the excitation light. Results suggest that the structural change in the zeolite induced by the formation and breakdown of the Ag clusters is a key point of the PL mechanism.
关键词： infrared spectroscopy,XAFS,Ag clusters,photoluminescence,Ag-type zeolite-A
更新于2025-09-04 15:30:14
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NLTE Stellar Population Synthesis of Globular Clusters Using Synthetic Integrated Light Spectra. II. Expanded Photometry and Sensitivity of Near-IR Spectral Features to Cluster Age and Metallicity
摘要： We present an expanded investigation of the library of globular cluster (GC) synthetic integrated light (IL) spectra of Young & Short, focusing on the impact of non-local thermodynamic equilibrium (NLTE) modeling effects on cluster parameters derived from photometric colors and sensitivity of near-IR spectral features to cluster age and metallicity. Johnson–Cousins–Bessel UBVIJK photometric colors are produced for 910 synthetic IL spectra with two degrees of α enhancement, in both NLTE and local thermodynamic equilibrium (LTE). These color values are used to investigate the GC age–metallicity degeneracy and compare NLTE and LTE derived [M/H] values for NGC 104, NGC 5139, and NGC 6205. For a given age, derived [M/H] values are shown to increase by up to 0.05 dex when modeled in NLTE. A total of 86 spectral lines in the range λ?=?12000–22000 ?, representing 14 different atomic species, were identi?ed as sensitive to either cluster age or metallicity, 12 of which were identi?ed as sensitive to both. Equivalent widths of the lines are measured in NLTE and LTE spectra, with NLTE effects changing the widths by up to 0.15–0.25 ? depending on the atomic species.
关键词： stars: fundamental parameters,globular clusters: general,techniques: photometric,stars: atmospheres,techniques: spectroscopic
更新于2025-09-04 15:30:14