The central dusty torus in the active nucleus of NGC 1068

Active galactic nuclei (AGNs) display many energetic phenomena--broad emission lines, X-rays, relativistic jets, radio lobes--originating from matter falling onto a supermassive black hole. It is widely accepted that orientation effects play a major role in explaining the observational appearance of AGNs. Seen from certain directions, circum-nuclear dust clouds would block our view of the central powerhouse. Indirect evidence suggests that the dust clouds form a parsec-sized torus-shaped distribution. This explanation, however, remains unproved, as even the largest telescopes have not been able to resolve the dust structures. Here we report interferometric mid-infrared observations that spatially resolve these structures in the galaxy NGC 1068. The observations reveal warm (320 K) dust in a structure 2.1 parsec thick and 3.4 parsec in diameter, surrounding a smaller hot structure. As such a configuration of dust clouds would collapse in a time much shorter than the active phase of the AGN, this observation requires a continual input of kinetic energy to the cloud system from a source coexistent with the AGN.     

The interface between silicon and a high-k oxide

The ability of the semiconductor industry to continue scaling microelectronic devices to ever smaller dimensions (a trend known as Moore's Law) is limited by quantum mechanical effects: as the thickness of conventional silicon dioxide (SiO(2)) gate insulators is reduced to just a few atomic layers, electrons can tunnel directly through the films. Continued device scaling will therefore probably require the replacement of the insulator with high-dielectric-constant (high-k) oxides, to increase its thickness, thus preventing tunnelling currents while retaining the electronic properties of an ultrathin SiO(2) film. Ultimately, such insulators will require an atomically defined interface with silicon without an interfacial SiO(2) layer for optimal performance. Following the first reports of epitaxial growth of AO and ABO(3) compounds on silicon, the formation of an atomically abrupt crystalline interface between strontium titanate and silicon was demonstrated. However, the atomic structure proposed for this interface is questionable because it requires silicon atoms that have coordinations rarely found elsewhere in nature. Here we describe first-principles calculations of the formation of the interface between silicon and strontium titanate and its atomic structure. Our study shows that atomic control of the interfacial structure by altering the chemical environment can dramatically improve the electronic properties of the interface to meet technological requirements. The interface structure and its chemistry may provide guidance for the selection process of other high-k gate oxides and for controlling their growth.     

Physiology: hibernation in a tropical primate

The Madagascan fat-tailed dwarf lemur, Cheirogaleus medius, hibernates in tree holes for seven months of the year, even though winter temperatures rise to over 30 degrees C. Here we show that this tropical primate relies on a flexible thermal response that depends on the properties of its tree hole: if the hole is poorly insulated, body temperature fluctuates widely, passively following the ambient temperature; if well insulated, body temperature stays fairly constant and the animal undergoes regular spells of arousal. Our findings indicate that arousals are determined by maximum body temperatures and that hypometabolism in hibernating animals is not necessarily coupled to a low body temperature.     

The influence of 6-OHDA on hypothermia produced by intrahypothalamically-injected carbachol in the pigeon

Summary The involvement of the noradrenergic system in hypothermia induced by intrahypothalamically-injected carbachol (CCh) was studied by depleting hypothalamic noradrenaline (NA) with the catecholamine neurotoxin 6-hydroxydopamine (6-OHDA) and repeating the CCh injections after 6-OHDA treatment. The results suggest that noradrenergic neurons may be involved in hypothermia produced by CCh in the pigeon.     

Purification of a nuclease from human serum

Summary The purification procedure for a nuclease from human serum is described. It includes ammonium sulfate precipitation, chromatography on DEAE-Sephadex and on Sephacryl-S 200, and preparative electrophoresis. The enzyme, purified about 2000-fold, is homogeneous in a sodium dodecyl sulfate electrophoretic system, where it has a mol. wt of 78,000. The pH optimum lies around pH 6.5; it is a sugar-nonspecific endonuclease.Acknowledgment. This work has been supported by a research grant from Stiftung Volkswagenwerk through the Akademie der Wissenschaften und der Literatur, Mainz. We thank Mrs R. Nehrbass and Mrs C. Wolpert for technical assistance.     

A simple method for cultivating the early chick embryo in vitro

Summary A method for cultivating the early chick embryo in an artificial medium has been developed that permits the determination of the stage at the onset of the treatment and the continuous observation of the embryogenesis.Kungliga Fysiografiska Sällskapet, Lund, supported this work.     

Isolierung der tuberkulinaktiven Proteine aus dem Tuberkulin mit Hilfe von Dextran-Gel

Summary By filtering heated filtrates of the cultures ofMycobacterium tuberculosis human, bovine and avian type respectively through the dextran-gel Sephadex 50, it is possible to separate the tuberculoproteins from the other inactive constituents in a simple manner.     

Distribution of inulin space in the rabbit thoracic aorta

Zusammenfassung Die ganze Länge und Dicke des extrazellulären Raumes der thorakalen Kaninchenaorta wurde gemessen. Der Raum ist unverändert die ganze Länge des Blutgefässes hindurch und entspricht 0,59 ml/g 0,39 ml/g für die Adventitia und die Media. In jeder dieser Tunicae ist der Raum durch ihre ganze Dicke gleichmässig verteilt.

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Supported by grants from The American Medical Association Education and Research Foundation, U.S. Public Health Service (HE-08359) and the Los Angeles County Heart Association (408 IG).     

A star in a 15.2-year orbit around the supermassive black hole at the centre of the Milky Way

Many galaxies are thought to have supermassive black holes at their centres-more than a million times the mass of the Sun. Measurements of stellar velocities and the discovery of variable X-ray emission have provided strong evidence in favour of such a black hole at the centre of the Milky Way, but have hitherto been unable to rule out conclusively the presence of alternative concentrations of mass. Here we report ten years of high-resolution astrometric imaging that allows us to trace two-thirds of the orbit of the star currently closest to the compact radio source (and massive black-hole candidate) Sagittarius A*. The observations, which include both pericentre and apocentre passages, show that the star is on a bound, highly elliptical keplerian orbit around Sgr A*, with an orbital period of 15.2 years and a pericentre distance of only 17 light hours. The orbit with the best fit to the observations requires a central point mass of (3.7 +/- 1.5) x 10(6) solar masses (M(*)). The data no longer allow for a central mass composed of a dense cluster of dark stellar objects or a ball of massive, degenerate fermions.     

Voltage-sensing mechanism is conserved among ion channels gated by opposite voltages

Hyperpolarization-activated cyclic-nucleotide-gated (HCN) ion channels are found in rhythmically firing cells in the brain and in the heart, where the cation current through HCN channels (called I(h) or I(f)) causes these cells to fire repeatedly. These channels are also found in non-pacing cells, where they control resting membrane properties, modulate synaptic transmission, mediate long-term potentiation, and limit extreme hyperpolarizations. HCN channels share sequence motifs with depolarization-activated potassium (Kv) channels, such as the fourth transmembrane segment S4. S4 is the main voltage sensor of Kv channels, in which transmembrane movement of S4 charges triggers the opening of the activation gate. Here, using cysteine accessibility methods, we investigate whether S4 moves in an HCN channel. We show that S4 movement is conserved between Kv and HCN channels, which indicates that S4 is also the voltage sensor in HCN channels. Our results suggest that a conserved voltage-sensing mechanism operates in the oppositely voltage-gated Kv and HCN channels, but that there are different coupling mechanisms between the voltage sensor and activation gate in the two different channels.