The origin of anomalous eutectic structures in undercooled Ag-Cu alloy

A melt encasement (fluxing) method was used to undercool Ag-Cu alloy at its eutectic composition. The recalescence of the undercooled alloy was filmed at a high frame rate. For undercoolings <60 K, a microstructure consisting of mixed anomalous and lamellar eutectic is observed. Analysis of eutectic spacing in the lamellar eutectic reveals little dependence upon the undercooling of the bulk melt and is consistent with growth at an undercooling of 1.5 K. Depending upon undercooling, the progress of the recalescence front may be either continuous or spasmodic, wherein periods of rapid growth are separated by significant interludes in which growth totally arrests. Analysis of spot brightness profiles reveals that, during continuous growth, the recalescence is characteristic of the advancement of a planar, space-filling front, while a double recalescence occurs during spasmodic growth, the first of which is characteristic of the propagation of a dendritic, or non-space-filling, front. It is concluded that, during spasmodic growth, the propagation of two-phase, or eutectic, dendrites is observed, which subsequently remelt to form the anomalous eutectic, while the lamellar eutectic grows during post-recalescence cooling

Cosmology with clusters of galaxies

In this Chapter I review the role that galaxy clusters play as tools to constrain cosmological parameters. I will concentrate mostly on the application of the mass function of galaxy clusters, while other methods, such as that based on the baryon fraction, are covered by other Chapters of the book. Since most of the cosmological applications of galaxy clusters rely on precise measurements of their masses, a substantial part of my Lectures concentrates on the different methods that have been applied so far to weight galaxy clusters. I provide in Section 2 a short introduction to the basics of cosmic structure formation. In Section 3 I describe the Press--Schechter (PS) formalism to derive the cosmological mass function, then discussing extensions of the PS approach and the most recent calibrations from N--body simulations. In Section 4 I review the methods to build samples of galaxy clusters at different wavelengths. Section 5 is devoted to the discussion of different methods to derive cluster masses. In Section 6 I describe the cosmological constraints, which have been obtained so far by tracing the cluster mass function with a variety of methods. Finally, I describe in Section 7 the future perspectives for cosmology with galaxy clusters and the challenges for clusters to keep playing an important role in the era of precision cosmology.Comment: 49 pages, 19 figures, Lectures for 2005 Guillermo Haro Summer School on Clusters, to appear in "Lecture notes in Physics" (Springer

The NEP ROSAT Survey

The Rosat All-Sky Survey (Trümper 1991, Adv. Spce Res., 2, 241) has its largest exposure times, approaching 10 ks, at the ecliptic poles where the scan circles overlap. The North Ecliptic Pole (NEP) region covers a 9° X 9° field, and contains a total of 465 X-ray sources detected at &gt; 4σ in the 0.1-2.4 keV. We are identifying all sources in the field. The principal derivative is a statistically complete sample of galaxy clusters appropriate for more fully characterizing X-ray Luminosity Function (XLF) evolution. We report preliminary results for two subregions which are identified to the 95% level. These subregions are observed to approximately the median NEP survey exposure. They enclose 16% of the survey area and contain 96 X-ray sources representing 21% of the total NEP. The typical mix of sources is consistent with the Einstein Extended Medium Sensisitivity Survey (EMSS; Gioia et al., 1990a, ApJS, 72, 567). In particular there are 56% AGN/ELG (59% in the EMSS), 25% stars (27% in the EMSS) and 14% clusters against 13% clusters in the EMSS.</jats:p

Dust-obscured star formation in the outskirts of XMMU J2235.3-2557, a massive galaxy cluster at z = 1.4

Star formation (SF) in the galaxy populations of local massive clusters is reduced with respect to field galaxies, and tends to be suppressed in the core region. Indications of a reversal of the SF–density relation have been observed in a few z > 1.4 clusters. Using deep imaging from 100–500 μm from Photodetector Array Camera and Spectrometer (PACS) and Spectral and Photometric Imaging REceiver (SPIRE) onboard Herschel, we investigate infrared properties of spectroscopic and photo-z cluster members, and of Hα emitters in XMMU J2235.3−2557, one of the most massive, distant, X-ray selected clusters known. Our analysis is based mostly on fitting of the galaxies spectral energy distribution (SED) in the rest-frame 8–1000 μm. We measure total IR luminosity, deriving star formation rates (SFRs) ranging from 89 to 463 M⊙ yr−1 for 13 galaxies individually detected by Herschel, all located beyond the core region (r >250 kpc). We perform a stacking analysis of nine star-forming members not detected by PACS, yielding a detection with SFR = 48 ± 16 M⊙ yr−1. Using a colour criterion based on a star-forming galaxy SED at the cluster redshift, we select 41 PACS sources as candidate star-forming cluster members. We characterize a population of highly obscured SF galaxies in the outskirts of XMMU J2235.3−2557. We do not find evidence for a reversal of the SF–density relation in this massive, distant cluster

The effects of recombinant human insulin-like growth factor I on growth hormone secretion in adolescents with insulin dependent diabetes mellitus.

OBJECTIVE: It has been proposed that low IGF-I levels and reduced IGF-I bioactivity may lead to elevated GH levels in adolescents with insulin dependent diabetes (IDDM). We have therefore studied the effects of human recombinant insulin-like growth factor I (rhIGF-I) administration on GH levels and GH secretion in adolescents with IDDM. PATIENTS: Nine late pubertal adolescents (four male and five female) with IDDM. DESIGN: A double-blind placebo controlled study of rhIGF-I administered subcutaneously in a dose of 40 micrograms/kg body weight at 1800 h. MEASUREMENTS: IGF-I and GH concentrations were measured at regular intervals throughout the study. Twenty-two hour GH secretory rates were calculated by deconvolution analysis. Overnight GH profiles were analysed by distribution analysis, and Fourier transformations were performed on both overnight GH concentrations and GH secretory rates. RESULTS: Mean IGF-I levels over the 22-hour study period were significantly elevated following rhIGF-I administration (350 +/- 26 vs 205 +/- 21 micrograms/l (mean +/- SEM), P < 0.01). Mean 22-hour GH levels were reduced following rhIGF-I administration (19.4 +/- 4.0 compared with 33.6 +/- 5.8 mU/l; P = 0.01). Distribution analysis demonstrated that the reduction in GH levels was due to changes in the proportion of values at both high and low concentrations. Deconvolution analysis also revealed a significant overall reduction in GH secretory rate following IGF-I administration (1.81 +/- 0.30 vs 2.98 +/- 0.47 mU/min, P = 0.01) which was still apparent during the final 5.5 hours of the study period (1.51 +/- 0.30 vs 2.76 +/- 0.61 mU/min, P = 0.02). The dominant periodicity of GH secretory episodes as determined by Fourier transformation was between 120 and 180 minutes after both IGF-I and placebo. CONCLUSIONS: In late pubertal adolescents with IDDM the rise in IGF-I levels following rhIGF-I administration in a subcutaneous dose of 40 micrograms/kg body weight leads to a significant reduction in GH levels and GH secretory rate. The reduction in GH secretion is due to changes in pulse amplitude rather than frequency. A reduction in GH secretion was apparent at the beginning and also towards the end of the 22-hour study period