Manganese–calcium clusters supported by calixarenes

The structure of the oxygen-evolving complex of photosystem II, which contains a cubane-like metal-oxo cluster incorporating four manganese (III,IV) cations, along with a calcium cation, has focussed attention on synthetic analogues of this cluster. Despite this activity, there are relatively few structurally characterised coordination clusters with this combination of metal cations. The calixarenes are synthetically versatile and well established cluster-supporting ligands, which to date have not been reported to support a calcium/manganese cluster. Here we report that p-t-butylthiacalix[4]arene supports CaMn2 and Ca2Mn2 clusters, whereas reactions of p-t-butylcalix[4]arene, p-t-butylsulfinylcalix[4]arene, and p-t-butylsulfonylcalix[4]arene, under the same conditions, produced only homometallic manganese complexes

The Evolution of the Fractions of Quiescent and Star-forming Galaxies as a Function of Stellar Mass Since z=3: Increasing Importance of Massive, Dusty Star-forming Galaxies in the Early Universe

Using the UltraVISTA DR1 and 3D-HST catalogs, we construct a stellar-mass-complete sample, unique for its combination of surveyed volume and depth, to study the evolution of the fractions of quiescent galaxies, moderately unobscured star-forming galaxies, and dusty star-forming galaxies as a function of stellar mass over the redshift interval $0.2 \le z \le 3.0$. We show that the role of dusty star-forming galaxies within the overall galaxy population becomes more important with increasing stellar mass, and grows rapidly with increasing redshift. Specifically, dusty star-forming galaxies dominate the galaxy population with $\log{(M_{\rm star}/M_{\odot})} \gtrsim 10.3$ at $z\gtrsim2$. The ratio of dusty and non-dusty star-forming galaxies as a function of stellar mass changes little with redshift. Dusty star-forming galaxies dominate the star-forming population at $\log{(M_{\rm star}/M_{\odot})} \gtrsim 10.0-10.5$, being a factor of $\sim$3-5 more common, while unobscured star-forming galaxies dominate at $\log{(M_{\rm star}/M_{\odot})} \lesssim 10$. At $\log{(M_{\rm star}/M_{\odot})} > 10.5$, red galaxies dominate the galaxy population at all redshift $z<3$, either because they are quiescent (at late times) or dusty star-forming (in the early universe).Comment: 7 pages, 4 figures, 1 table. Accepted by Astrophysical Journal Letters after minor revisio

Development of control systems for space shuttle vehicles, volume 1

Control of winged two-stage space shuttle vehicles was investigated. Control requirements were determined and systems capable of meeting these requirements were synthesized. Control requirements unique to shuttles were identified. It is shown that these requirements can be satisfied by conventional control logics. Linear gain schedule controllers predominate. Actuator saturations require nonlinear compensation in some of the control systems

Structural Variations in the Complete Series of Lanthanoid Complexes of a Calix[4]arene Trisamide

Lanthanoid picrate (pic) complexes of 5,11,17,23-tetra-tert-butyl-25-hydroxy-26,27,28-tris(diethylcarbamoylmethoxy)calix[4]arene (LH) have been synthesised and structurally characterised, to complete this series for all lanthanoids (other than promethium). From cerium to lutetium, three structural types are observed: Type I, [Ln(L)(O,O'-pic)](pic), Ln = Ce-Dy; Type II, [Ln(L)(O-pic)](pic), Ln = Tb, Ho; Type III, [Ln(L)(HOEt)](pic)2, Ln = Er-Lu. With lanthanum, three different ten-coordinate complexes were characterised; [Ln(L)(O,O'-pic)(HOEt)](pic), [Ln(L)(O,O'-pic)(OH2)](pic), and [Ln(L)(O,O'-pic)(HOMe)](pic). The crystallisation of Type I and II observed for terbium shows that the stability of the different structures are sensitively poised at the transition points. Nevertheless, the structures show that the vacant space in the coordination sphere left by the trisamide L tends to reduce across the series as expected. It is occupied by a bidentate picrate anion and unidentate solvent molecule with lanthanum, a bidentate picrate anion for cerium to dysprosium (Type I), a unidentate picrate anion for terbium and holmium (Type II), and finally a unidentate solvent molecule from erbium to lutetium (Type III). The coordination number thus reduces from 10 to 8 across the series

Gamma ray monitoring of a AGN and galactic black hole candidates by the Compton Gamma Ray Observatory

The Compton Gamma-Ray Observatory's Burst and Transient Source Experiment (BATSE) has a powerful capability to provide nearly uninterrupted monitoring in the 25 keV-10 MeV range of both active galactic nuclei (AGN) and galactic black hole candidates (GBHC) such as Cygnus X-1, using the occultation of cosmic sources by the Earth. Since the Crab is detected by the BATSE Large Area Detectors with roughly 25(sigma) significance in the 15-125 keV range in a single rise or set, a variation by a factor of two of a source having one-tenth the strength of Cygnus X-1 should be detectable within a day. Methods of modeling the background are discussed which will increase the accuracy, sensitivity, and reliability of the results beyond those obtainable from a linear background fit with a single rise or set discontinuity

Acquired heart block: A possible complication of patent ductus arteriosus in a preterm infant

A large patent ductus arteriosus (PDA) is a frequently encountered clinical problem in extremely low birth weight (ELBW) infants. It leads to an increased pulmonary blood flow and in a decreased or reversed diastolic flow in the systemic circulation, resulting in complications. Here we report a possible complication of PDA not previously published. On day 8 of life, a male ELBW infant (birth weight 650 g) born at a gestational age of 23 weeks and 3 days developed an atrioventricular block (AV block). The heart rate dropped from 168/min to 90/min, and the ECG showed a Wenckebach second-degree AV block and intraventricular conduction disturbances. Echocardiography demonstrated a PDA with a large left-to-right shunt and large left atrium and left ventricle with high contractility. Within several minutes after surgical closure of the PDA, the heart rate increased, and after 30 min the AV block had improved to a 1: 1 conduction ratio. Echocardiography after 2 h revealed a significant decrease of the left ventricular and atrial dimensions. Within 12 h, the AV block completely reversed together with the intraventricular conduction disturbances. We suggest that PDA with a large left-to-right shunt and left ventricular volume overload may lead to an AV block in an ELBW infant. Surgical closure of the PDA may be indicated. Copyright (C) 2007 S. Karger AG, Basel

The Most Luminous z~9-10 Galaxy Candidates yet Found: The Luminosity Function, Cosmic Star-Formation Rate, and the First Mass Density Estimate at 500 Myr

[abridged] We present the discovery of four surprisingly bright (H_160 ~ 26 - 27 mag AB) galaxy candidates at z~9-10 in the complete HST CANDELS WFC3/IR GOODS-N imaging data, doubling the number of z~10 galaxy candidates that are known, just ~500 Myr after the Big Bang. Two similarly bright sources are also detected in a systematic re-analysis of the GOODS-S data set. Three of the four galaxies in GOODS-N are significantly detected at 4.5-6.2sigma in the very deep Spitzer/IRAC 4.5 micron data, as is one of the GOODS-S candidates. Furthermore, the brightest of our candidates (at z=10.2+-0.4) is robustly detected also at 3.6 micron (6.9sigma), revealing a flat UV spectral energy distribution with a slope beta=-2.0+-0.2, consistent with demonstrated trends with luminosity at high redshift. The abundance of such luminous candidates suggests that the luminosity function evolves more significantly in phi_* than in L_* at z>~8 with a higher number density of bright sources than previously expected. Despite the discovery of these luminous candidates, the cosmic star formation rate density for galaxies with SFR >0.7 M_sun/yr shows an order-of-magnitude increase in only 170 Myr from z ~ 10 to z ~ 8, consistent with previous results. Based on the IRAC detections, we derive galaxy stellar masses at z~10, finding that these luminous objects are typically 10^9 M_sun. The cosmic stellar mass density at z~10 is log10 rho_* = 4.7^+0.5_-0.8 M_sun Mpc^-3 for galaxies brighter than M_UV~-18. The remarkable brightness, and hence luminosity, of these z~9-10 candidates highlights the opportunity for deep spectroscopy to determine their redshift and nature, demonstrates the value of additional search fields covering a wider area to understand star-formation in the very early universe, and highlights the opportunities for JWST to map the buildup of galaxies at redshifts much earlier than z~10.Comment: 20 pages, 12 figures, changed to match resubmitted version to Ap

One-step assembly of Re(I) tricarbonyl 2-pyridyltetrazolato metallacalix[3]arene with aqua emission and reversible three-electron oxidation

The reaction of 2-pyridyltetrazolate with [Re(CO)5X] (X = Cl, Br) yielded the formation of an unexpected cyclic metallacalix[3]-arene, as revealed by X-ray structural studies, characterised by aqua emission and reversible three-electron oxidation