Uncertainties of size measurements in electron microscopy characterization of nanomaterials in foods

Electron microscopy is a recognized standard tool for nanomaterial characterization, and recommended by the European Food Safety Authority for the size measurement of nanomaterials in food. Despite this, little data have been published assessing the reliability of the method, especially for size measurement of nanomaterials characterized by a broad size distribution and/or added to food matrices. This study is a thorough investigation of the measurement uncertainty when applying electron microscopy for size measurement of engineered nanomaterials in foods. Our results show that the number of measured particles was only a minor source of measurement uncertainty for nanomaterials in food, compared to the combined influence of sampling, sample preparation prior to imaging and the image analysis. The main conclusion is that to improve the measurement reliability, care should be taken to consider replications and matrix removal prior to sample preparation

The Clustering of Extragalactic Extremely Red Objects

We have measured the angular and spatial clustering of 671 K5 Extremely Red Objects (EROs) from a 0.98 square degree sub-region of the NOAO Deep Wide-Field Survey (NDWFS). Our study covers nearly 5 times the area and has twice the sample size of any previous ERO clustering study. The wide field of view and BwRIK passbands of the NDWFS allow us to place improved constraints on the clustering of z=1 EROs. We find the angular clustering of EROs is slightly weaker than in previous measurements, and w(1')=0.25+/-0.05 for K<18.40 EROs. We find no significant correlation of ERO spatial clustering with redshift, apparent color or absolute magnitude, although given the uncertainties, such correlations remain plausible. We find the spatial clustering of K5 EROs is well approximated by a power-law, with r_0=9.7+/-1.1 Mpc/h in comoving coordinates. This is comparable to the clustering of 4L* early-type galaxies at z<1, and is consistent with the brightest EROs being the progenitors of the most massive ellipticals. There is evidence of the angular clustering of EROs decreasing with increasing apparent magnitude, when NDWFS measurements of ERO clustering are combined with those from the literature. Unless the redshift distribution of K>20 EROs is very broad, the spatial clustering of EROs decreases from r_0=9.7+/-1.1 Mpc/h for K20 EROs.Comment: Accepted for publication in the ApJ. 29 pages with 10 figures. The NOAO Deep Wide-Field Survey Bootes data release is available online at http://www.noao.edu/noao/noaodeep

From Stars to Super-planets: the Low-Mass IMF in the Young Cluster IC348

We investigate the low-mass population of the young cluster IC348 down to the deuterium-burning limit, a fiducial boundary between brown dwarf and planetary mass objects, using a new and innovative method for the spectral classification of late-type objects. Using photometric indices, constructed from HST/NICMOS narrow-band imaging, that measure the strength of the 1.9 micron water band, we determine the spectral type and reddening for every M-type star in the field, thereby separating cluster members from the interloper population. Due to the efficiency of our spectral classification technique, our study is complete from approx 0.7 Msun to 0.015 Msun. The mass function derived for the cluster in this interval, dN/dlogM \propto M^{0.5}, is similar to that obtained for the Pleiades, but appears significantly more abundant in brown dwarfs than the mass function for companions to nearby sun-like stars. This provides compelling observational evidence for different formation and evolutionary histories for substellar objects formed in isolation vs. as companions. Because our determination of the IMF is complete to very low masses, we can place interesting constraints on the role of physical processes such as fragmentation in the star and planet formation process and the fraction of dark matter in the Galactic halo that resides in substellar objects.Comment: 37 pages, 16 figs, 6 tables (Table 4 is a separate LaTeX file) Accepted for publication in Astrophysical Journal (Oct 1, 2000 issue

Simultaneous Optical Model Analyses of Elastic Scattering, Breakup, and Fusion Cross Section Data for the 6^{6}He + 209^{209}Bi System at Near-Coulomb-Barrier Energies

Based on an approach recently proposed by us, simultaneous $\chi^{2}$-analyses are performed for elastic scattering, direct reaction (DR) and fusion cross sections data for the $^{6}$He+$^{209}$Bi system at near-Coulomb-barrier energies to determine the parameters of the polarization potential consisting of DR and fusion parts. We show that the data are well reproduced by the resultant potential, which also satisfies the proper dispersion relation. A discussion is given of the nature of the threshold anomaly seen in the potential

172 ks Chandra Exposure of the LALA Bo\"{o}tes Field: X-ray Source Catalog

We present an analysis of a deep, 172 ks Chandra observation of the Large Area Lyman Alpha Survey (LALA) Bo\"{o}tes field, obtained with the Advanced CCD Imaging Spectrometer (ACIS-I) on the Chandra X-ray Observatory. This is one of the deepest Chandra images of the extragalactic sky; only the 2 Ms CDF-N and 1 Ms CDF-S are substantially deeper. A total of 168 X-ray sources were detected. The X-ray source counts were derived and compared with those from other Chandra deep surveys; the hard X-ray source density of the LALA Bo\"{o}tes field is 33% higher than that of CDF-S at the flux level of 2.0E-15 ergs/cm^2/s, confirming the field-to-field variances of the hard band source counts reported by previous studies. The deep exposure resolves > 72% of the 2-10 keV X-ray background. Our primary optical data are R-band imaging from NOAO Deep Wide-Field Survey (NDWFS), with limiting magnitude of R = 25.7 (Vega, 3sigma, 4" diameter aperture). We have found optical counterparts for 152 of the 168 Chandra sources (90%). Among the R-band non-detected sources, not more than 11 of them can possibly be at z > 5, based on the hardness ratios of their X-ray emission and nondetections in bluer bands. The majority (~76%) of the X-ray sources are found to have log(f_X/f_R) within 0.0+-1, which are believed to be AGNs.Most of the X-ray faint/optically bright sources (log(f_X/f_R) < -1.0) are optically extended, which are low-z normal galaxies or low luminosity AGNs. There is also a population of sources which are X-ray overluminous for their optical magnitudes (log(f_X/f_R) > 1.0), which are harder in X-ray and are probably obscured AGNs. (abridged)Comment: AJ accepted, 37 pages, including 10 figures and 1 tabl

The IRAC Shallow Survey

The IRAC shallow survey covers 8.5 square degrees in the NOAO Deep Wide-Field Survey in Bootes with 3 or more 30 second exposures per position. An overview of the survey design, reduction, calibration, star-galaxy separation, and initial results is provided. The survey includes approximately 370,000, 280,000, 38,000, and 34,000 sources brighter than the 5 sigma limits of 6.4, 8.8, 51, and 50 microJy at 3.6, 4.5, 5.8, and 8 microns respectively, including some with unusual spectral energy distributions.Comment: To appear in ApJS, Spitzer special issue. For full resolution see http://cfa-www.harvard.edu/irac/publication