A homogeneous nucleus for comet 67P/Churyumov-Gerasimenko from its gravity field.

Cometary nuclei consist mostly of dust and water ice. Previous observations have found nuclei to be low-density and highly porous bodies, but have only moderately constrained the range of allowed densities because of the measurement uncertainties. Here we report the precise mass, bulk density, porosity and internal structure of the nucleus of comet 67P/Churyumov-Gerasimenko on the basis of its gravity field. The mass and gravity field are derived from measured spacecraft velocity perturbations at fly-by distances between 10 and 100 kilometres. The gravitational point mass is GM = 666.2 ± 0.2 cubic metres per second squared, giving a mass M = (9,982 ± 3) × 10(9) kilograms. Together with the current estimate of the volume of the nucleus, the average bulk density of the nucleus is 533 ± 6 kilograms per cubic metre. The nucleus appears to be a low-density, highly porous (72-74 per cent) dusty body, similar to that of comet 9P/Tempel 1. The most likely composition mix has approximately four times more dust than ice by mass and two times more dust than ice by volume. We conclude that the interior of the nucleus is homogeneous and constant in density on a global scale without large voids. The high porosity seems to be an inherent property of the nucleus material.

A permanent, asymmetric dust cloud around the Moon.

Interplanetary dust particles hit the surfaces of airless bodies in the Solar System, generating charged and neutral gas clouds, as well as secondary ejecta dust particles. Gravitationally bound ejecta clouds that form dust exospheres were recognized by in situ dust instruments around the icy moons of Jupiter and Saturn, but have hitherto not been observed near bodies with refractory regolith surfaces. High-altitude Apollo 15 and 17 observations of a 'horizon glow' indicated a putative population of high-density small dust particles near the lunar terminators, although later orbital observations yielded upper limits on the abundance of such particles that were a factor of about 10(4) lower than that necessary to produce the Apollo results. Here we report observations of a permanent, asymmetric dust cloud around the Moon, caused by impacts of high-speed cometary dust particles on eccentric orbits, as opposed to particles of asteroidal origin following near-circular paths striking the Moon at lower speeds. The density of the lunar ejecta cloud increases during the annual meteor showers, especially the Geminids, because the lunar surface is exposed to the same stream of interplanetary dust particles. We expect all airless planetary objects to be immersed in similar tenuous clouds of dust.

Development of the nano-dust analyzer (NDA) for detection and compositional analysis of nanometer-size dust particles originating in the inner heliosphere.

A linear time-of-flight mass spectrometer is developed for the detection and chemical analysis of nanometer-sized particles originating near the Sun. Nano-dust particles are thought to be produced by mutual collisions between interplanetary dust particles slowly spiraling toward the Sun and are accelerated outward to high velocities by interaction with the solar wind plasma. The WAVES instruments on the two STEREO spacecraft reported the detection, strong temporal variation, and potentially high flux of these particles. Here we report on the optimization and the results from the detailed characterization of the instrument's performance using submicrometer sized dust particles accelerated to 8-60 km/s. The Nano Dust Analyzer (NDA) concept is derived from previously developed detectors. It has a 200 cm(2) effective target area and a mass resolution of approximately m/Δm = 50. The NDA instrument is designed to reliably detect and analyze nanometer-sized dust particles while being pointed close to the Sun's direction, from where they are expected to arrive. Measurements by such an instrument will determine the size-dependent flux of the nano-dust particles and its variations, it will characterize the composition of the nano-dust and, ultimately, it may determine their source. The flight version of the NDA instrument is estimated to be <5 kg and requires <10 W for operation.

Dust trajectory sensor: accuracy and data analysis.

The Dust Trajectory Sensor (DTS) instrument is developed for the measurement of the velocity vector of cosmic dust particles. The trajectory information is imperative in determining the particles' origin and distinguishing dust particles from different sources. The velocity vector also reveals information on the history of interaction between the charged dust particle and the magnetospheric or interplanetary space environment. The DTS operational principle is based on measuring the induced charge from the dust on an array of wire electrodes. In recent work, the DTS geometry has been optimized [S. Auer, E. Grün, S. Kempf, R. Srama, A. Srowig, Z. Sternovsky, and V Tschernjawski, Rev. Sci. Instrum. 79, 084501 (2008)] and a method of triggering was developed [S. Auer, G. Lawrence, E. Grün, H. Henkel, S. Kempf, R. Srama, and Z. Sternovsky, Nucl. Instrum. Methods Phys. Res. A 622, 74 (2010)]. This article presents the method of analyzing the DTS data and results from a parametric study on the accuracy of the measurements. A laboratory version of the DTS has been constructed and tested with particles in the velocity range of 2-5 km/s using the Heidelberg dust accelerator facility. Both the numerical study and the analyzed experimental data show that the accuracy of the DTS instrument is better than about 1% in velocity and 1° in direction.

Large area mass analyzer instrument for the chemical analysis of interstellar dust particles.

A new instrument to analyze the chemical composition of dust particles in situ in space has been developed. The large target area ( approximately 0.2 m(2)) makes this instrument well suited for detecting a statistically significant number of interstellar dust grains or other dust particles with a low flux. The device is a reflectron-type time-of-flight mass spectrometer that uses only flat electrodes for the generation of the parabolic potential. The instrument analyzes the ions from the impact generated plasma due to hypervelocity dust impacts onto a solid target surface. The SIMION ion optics software package is used to investigate different potential field configurations and optimize the mass resolution and focusing of the ions. The cylindrically symmetric instrument operates with six ring electrodes and six annular electrodes biased to different potentials to create the potential distribution of the reflectron. The laboratory model of the instrument has been fabricated and tested. Hypervelocity dust impacts are simulated by laser ablation using a frequency doubled Nd:YAG laser with approximately 8 ns pulse length. The experimental data show typical mass resolution m/Deltam approximately 200.

[The stability of progesterone in feces of different wild animal species kept in a zoological garden]. / Untersuchungen zur Stabilität des Progesterons im Kot bei verschiedenen im Zoo gehaltenen Wildtierarten.

Methodical investigations were carried out to monitor especially in what respect external factors (dry mass of faeces, time point of freezing, duration of storage of the frozen samples, multiple defrosting of the samples) influence the progesterone concentration of the faeces of several wild animal species (Baringo giraffe, Black rhinoceros, Dama gazelle, Mountain goat) living in a zoological garden. With reference to one animal species the dry mass of the faeces showed only small variations. Therefore, it is possible to estimate comparable progesterone levels in several faecal samples of the same animal species without drying the samples. In all cases the progesterone concentration was increased after 24 and 48 hour storage of the faecal samples at room temperature compared with samples frozen directly (significant differences for giraffes and rhinoceroses). Samples of rhinoceroses and gazelles showed no significant changes of their progesterone concentration after a long time of storage (one and three months) in the freezing state (-20 degrees C). On the other hand, in faeces of giraffes with high progesterone levels a significant decrease of the initial level was pointed out. In comparison of single and multiple defrosting of the faecal samples, the latter caused a decrease of the progesterone concentration of the faeces of all animal species investigated (significant differences for rhinoceroses and gazelles).

[Content of minerals (Na,K,Ca,Mg) and of trace elements (Fe,Cu and Zn) in 13 different tissues of fallow deer (Dama dama L.) of various ages]. / Der Gehalt an Mineralstoffen (Na, K, Ca, Mg) und Spurenelementen (Fe, Cu, Zn) in 13 verschiedenen Geweben vom Damwild (Dama dama L.) unterschiedlichen Alters.

At male deer in the age of 15 and 27 months, at experimentally induced cryptorchids and at castrated animals analyses of the content of Na, K, Ca, Mg, Fe, Cu and Zn in 13 different tissues were performed. In the liver of newborn animals solely the content of Fe, Cu and Zn was determined. The significance of the content of the mentioned elements in the various tissues is described. In the liver of the newborn animals stores of Fe, Cu an Zn were identified. The values can be used as a basis for analyses at deer with a growth inhibition caused by a lack of sodium chloride Fe, Cu and Zn.

Growth and form of planetary seedlings: results from a microgravity aggregation experiment.

The outcome of the first stage of planetary formation, which is characterized by ballistic agglomeration of preplanetary dust grains due to Brownian motion in the free molecular flow regime of the solar nebula, is still somewhat speculative. We performed a microgravity experiment flown onboard the space shuttle in which we simulated, for the first time, the onset of free preplanetary dust accumulation and revealed the structures and growth rates of the first dust agglomerates in the young solar system. We find that a thermally aggregating swarm of dust particles evolves very rapidly and forms unexpected open-structured agglomerates.

Io as a source of the jovian dust streams

Streams of dust emerging from the direction of Jupiter were discovered in 1992 during the flyby of the Ulysses spacecraft, but their precise origin within the jovian system remained unclear. Further data collected by the Galileo spacecraft, which has been orbiting Jupiter since December 1995, identified the possible sources of dust as Jupiter's main ring, its gossamer ring, comet Shoemaker-Levy 9 (ref. 8) and Io. All but Jupiter's gossamer ring and Io have since been ruled out. Here we find that the dominant source of the jovian dust streams is Io, on the basis of periodicities in the dust impact signal. Io's volcanoes, rather than impact ejecta, are the dust sources.

Deflection of the local interstellar dust flow by solar radiation pressure.

Interstellar dust grains intercepted by the dust detectors on the Ulysses and Galileo spacecrafts at heliocentric distances from 2 to 4 astronomical units show a deficit of grains with masses from 1 x 10(-17) to 3 x 10(-16) kilograms relative to grains intercepted outside 4 astronomical units. To divert grains out of the 2- to 4-astronomical unit region, the solar radiation pressure must be 1.4 to 1.8 times the force of solar gravity. These figures are consistent with the optical properties of spherical or elongated grains that consist of astronomical silicates or organic refractory material. Pure graphite grains with diameters of 0.2 to 0.4 micrometer experience a solar radiation pressure force as much as twice the force of solar gravity.

Capture of interplanetary and interstellar dust by the jovian magnetosphere.

Interplanetary and interstellar dust grains entering Jupiter's magnetosphere form a detectable diffuse faint ring of exogenic material. This ring is composed of particles in the size range of 0. 5 to 1.5 micrometers on retrograde and prograde orbits in a 4:1 ratio, with semimajor axes 3 < a < 20 jovian radii, eccentricities 0. 1 < e < 0.3, and inclinations i less, similar 20 degrees or i greater, similar 160 degrees. The size range and the orbital characteristics are consistent with in situ detections of micrometer-sized grains by the Galileo dust detector, and the measured rates match the number densities predicted from numerical trajectory integrations.

Evidence of the existence of alpha 1B-adrenoceptors on hepatocytes of domestic fowl (Gallus domesticus).

In liver cell membranes of laying hens alpha 1-adrenergic receptors were characterized using 3H-prazosin. Specific binding was saturable and indicative of a single class of high-affinity binding sites with a KD of 0.40 +/- 16 nM and a Bmax of 390 +/- 38 fmol/mg membrane protein. Preincubation of membranes with chlorethylclonidine significantly diminished the binding of 3H-prazosin (Bmax = 99 +/- 14 fmol/mg membrane protein). Furthermore, competition experiments revealed a rank order of prazosin >> phentolamine = oxymetazoline >> WB 4101, with Ki values of 0.71 +/- 0.62, 20 +/- 6, 32 +/- 13, and 119 +/- 48 nM, respectively. These results suggest the existence of alpha 1B-adrenergic receptors in hen liver cell membranes.

Pharmacological comparison of transient and persistent [3H]dopamine release from mouse striatal synaptosomes and response to chronic L-nicotine treatment.

L-Nicotine stimulates a biphasic release of [3H]dopamine from mouse striatal synaptosomes which does not persist after agonist is removed. Approximately 80% of the initial release is transient and disappears with a half-time of less than 1 min; the other 20% persists for several minutes (t(1/2), 5-10 min). Both the transient and persistent phases were investigated by 10-min exposures to agonists with an in vitro perfusion technique. A series of nicotinic agonists and antagonists were used to determine the pharmacological relationship of the two phases. Parameters measured included EC50 and Vmax values and desensitization rates for both phases for agonists, Ki values for antagonists and Ki values for low concentrations of agonists. The results are consistent with both phases being mediated by a single type of receptor. In addition, the effects of chronic nicotine treatment on transient and persistent [3H]DA release were measured. For both phases, release was decreased approximately 15% by chronic infusion of 4.0 mg/kg/hr L-nicotine. Correlation of the results with inactivation of a portion of the receptors rather than a reversible desensitization is discussed.

Solar wind magnetic field bending of Jovian dust trajectories.

From September 1991 to October 1992, the cosmic dust detector on the Ulysses spacecraft recorded 11 short bursts, or streams, of dust. These dust grains emanated from the jovian system, and their trajectories were strongly affected by solar wind magnetic field forces. Analyses of the on-board measurements of these fields, and of stream approach directions, show that stream-associated dust grain masses are of the order of 10(-18) gram and dust grain velocities exceed 200 kilometers per second. These masses and velocities are, respectively, about 10(3) times less massive and 5 to 10 times faster than earlier reported.

ST/b and DBA/2 mice differ in brain alpha-bungarotoxin binding and alpha 7 nicotinic receptor subunit mRNA levels: a quantitative autoradiographic analysis.

Inbred mouse strains vary in sensitivity to a number of behavioral and physiological effects produced by nicotine. Differences in sensitivity to nicotine are correlated with variance in the number of brain nicotinic receptors as measured in regionally dissected brain tissue. The studies reported here used quantitative autoradiography and in-situ hybridization methods to measure regional levels of alpha-bungarotoxin (alpha BTX) binding and alpha 7 mRNA levels. Two inbred mouse strains, ST/b and DBA/2, were compared because these strains differ maximally in sensitivity to nicotine-induced seizures and in alpha BTX binding measured in regional brain homogenates. The binding of alpha BTX was significantly greater in the St/b strain in 42 of 127 brain regions that were analyzed, and a trend towards increased binding was seen in many additional brain regions. The most consistent strain differences were found in hippocampal, thalamic and pontine nuclei. Strain differences in alpha 7 mRNA levels were also detected, but these were not as widespread as were the alpha BTX binding differences. The alpha 7 mRNA levels were significantly correlated with alpha BTX binding in both mouse strains which suggests that the strain differences in binding are related, in part, to the levels of alpha 7 mRNA.

Changes in sensitivity to nicotine and brain nicotinic receptors following chronic nicotine and corticosterone treatments in mice.

Chronic nicotine treatment often results in tolerance to nicotine as well as increases in brain [3H]-nicotine binding and [125l]-alpha-bungarotoxin (alpha-BTX) binding. Chronic corticosterone (CCS) treatment also produces tolerance to nicotine, but it does not change [3H]-nicotine binding; decreases in alpha-BTX binding are observed, which suggests that tolerance to nicotine may be related to decreases in the number of this nicotinic receptor subtype. In the studies reported here, C57BL/6 mice were implanted subcutaneously with cholesterol or 60% CCS/40% cholesterol-containing pellets and were infused continuously with saline (control) or nicotine for a total of 9 days. Effects of acute nicotine challenge on Y-maze crossing and rearing activities, heart rate, and body temperature were measured. Both chronic nicotine and CCS treatment resulted in tolerance to nicotine for all of the measures, and some evidence for additivity was seen in the animals that were cotreated with CCS and nicotine. Chronic nicotine infusion increased brain nicotine binding and CCS treatment reduced alpha-BTX binding. Decreases in alpha-BTX binding were not detected in the cotreated animals. The latter finding argues that changes in alpha-BTX binding are not reliable predictors of or a cause of tolerance to nicotine.

Corticosterone reversibly alters brain alpha-bungarotoxin binding and nicotine sensitivity.

Previous studies have shown that chronic corticosterone (CCS) treatment via subcutaneous pellets elicits reduced sensitivity to many actions of nicotine in mice as well as decreased brain alpha-bungarotoxin (alpha-BTX) binding. We report here the time courses of altered sensitivity to nicotine, as measured by acoustic startle, Y-maze crossing and rearing activities, heart rate, and body temperature, and alpha-BTX binding during and after CCS treatment. CCS treatment resulted in rapid decreases in sensitivity to nicotine for four of the five responses that were measured, as well as rapid changes in alpha-BTX binding. Sensitivity to nicotine returned to control levels within 3 days following pellet removal, but alpha-BTX binding returned to control levels in most brain regions 9-11 days after pellet removal. Because the restoration of control sensitivity to nicotine occurred long before alpha-BTX binding returned to control levels, it seems likely that factors other than changes in alpha-BTX binding cause chronic CCS-induced changes in sensitivity to nicotine.

[Artificial lactation induction in 12- to 19-month-old heifers with regard to the behavior of the concentration of sex hormones and lactogenic proteohormones in the blood plasma]. / Untersuchungen zur künstlichen Laktationsinduktion an 12 bis 19 Monate alten Jungrindern unter Berücksichtigung des Verhaltens der Konzentrationen an Sexualhormonen und laktogenen Proteohormonen im Blutplasma.

In 24 prepubertal heifers the lactation was artificially induced by two different methods of hormone application. The changes in milk yield and the concentrations of estradiol-17 beta (E), progesterone (P), prolactin, somatotropin and insulin-like growth factor I in blood plasma during the first 55 days of lactation were analyzed. Depending on the age, the animals were divided in three experimental groups (EG) of eight animals each: 12 months old (EG I), 15 months old (EG II) and 19 months (EG III). Four animals of each EG were treated similarly: group E and P, which was injected by estradiol benzoate and P for 7 days, or group E, which received only estradiol benzoate for 10 days. The oldest heifers (EG III) showed an induction rate of 100% with E and P treatment and of 75% with E alone. On the other hand, in heifers of EG I and EG II the induction rate was only 50% irrespectively of the treatment. The animals of EG III had the highest milk yield. The daily milk yield on the 50th day of lactation was 7.0 kg and 4.0 kg in group E and P or group E, respectively. Comparable levels in 15 months old heifers (EG II) were 4.8 kg and 1.4 kg, and in 12 months old heifers (EG I) 2.5 kg and 2.5 kg. The changes of the concentrations of the hormones in blood plasma are demonstrated in diagrams, their effect on the milk production is discussed.

[The composition of milk after artificial lactation induction in 12- to 19-month-old heifers]. / Untersuchungen über die Zusammensetzung der Milch nach künstlicher Laktationsinduktion bei 12 bis 19 Monate alten Jungrindern.

In 24 prepubertal heifers the composition of milk after an artificial induction of lactation was investigated. Depending on the age, the animals were divided in 3 experimental groups (EG) of 8 animals each: 12 months old (EG I), 15 months old (EG II), and 19 months old (EG III). Four animals of each EG were treated similarly: either with estradiol benzoate and progesterone for 7 days (group E and P) or only with estradiol benzoate for 10 days (group E). During the first 18 days of lactation the protein and lactose content of the milk showed similar changes compared to the period of milk maturation during natural lactation of same duration. However, a typical colostral period with high concentrations of immunoglobulins in the milk was not observed. After the artificial induction of lactation, in the period until to the 53rd day of lactation no age dependent differences in the composition of milk were found, except whey proteins. Formation of milk substances, which are synthesized in the mammary gland, is much more induced by treatment with E and P than by treatment of E alone, with the exception of caseins.