bluuebunny/crossref_metadata_2025_split huggingface dataset:
Jovian Dust Bursts
Authors: Zook H. A. , Grün E. , Baguhl M. , Hamilton D. , Linkert G. , Liou J.-C. , Forsyth R. , Phillips J. L. 
Published: June 2019

Six streams of dust were unexpectedly detected by the Ulysses dust detector while this spacecraft was approximately within one AU distance from Jupiter (Grün et al., 1993). Stream durations ranged from hours to days for individual streams. It was clear that the dust in these streams (or bursts), from their directionality of approach to the spacecraft and from the nearness of stream occurrences to Jupiter, emanated from the Jovian system.Following the original report, Baguhl et al. (1994) later relaxed the criteria for differentiating true dust impacts from “noise pulses” and found almost triple the number of dust impacts in the six streams already found. They also found 5 more streams that, except for one stream, clearly emanated from the Jovian system. The criteria were relaxed in such a way as to not introduce “noise events” into the data.
The Physics of Meteors
Authors: Ceplecha Z. 
Published: June 2019

AbstractInteraction of a meteoroid penetrating the atmosphere can be described through its motion, ablation, luminosity, ionization and the geometry of its trajectory. A theoretical description may be based on the so called “single body theory”, generalized to allow for discrete fragmentation. Such a concept is fully able to simulate the motion and ablation (mass loss) of meteoroids from millimeter to meter sizes recorded through photographic techniques (the best precision of such observations is better than ±10 m in observed heights). Observed distances and heights as a function of time can be fit to this model with the intrinsic precision of the geometrical data. The majority of meteoroids follow the “single-body theory” closely: large values of the ablation coefficients derived from observations favor continuous fragmentation under very low dynamical pressures as the main process of ablation. The rest, some 20 to 30%, can be described by one or more discrete fragmentation points in addition to continuous fragmentation. Dynamic pressures at these grossfragmentation points are also very low, if compared with the strength of stony meteorites.On the other hand, luminosity and ionization are not as well understood. Existing detailed spectral records show mostly radiation in form of emission lines of ablated meteoroid material with excitation temperatures in the range of 3000 to 5000 K. Additional theoretical modeling is called for.Photographically documented meteorite falls can be used for computation of luminous efficiencies, because the terminal mass and bulk density are known in these cases. Recently, photographs of the Lost City meteorite fall were remeasured with special attention to visible trails of fragments. The new analysis revealed two main discrete fragmentation points that are in perfect agreement with the geometrically resolved trails based on the dynamics. Moreover, Adolfsson (1996) found an artificial periodic signal originating from the switching shutter and after removing this signal, he was able to find an initial rotation period of 3.3±0.3 s and also the rotation phase of the Lost City meteoroid. A solution for the motion, ablation and rotation of the Lost City meteoroid is now completely self-consistent throughout the whole photographed trajectory and yields an initial mass of m = 163 ± 5 kg. The luminous efficiency was found to be 6.1% at v = 13 km/s (for 4500 K), this is ∼ 10x larger than the values determined from artificial meteors, i.e., from masses of 1 g fired downward from high-altitude rockets by shaped-charge.
The Meteoroid Orbit Facility AMOR: Recent Developments
Authors: Baggaley Jack W. , Bennett R.G.T. 
Published: June 2019

AbstractSome 3 x 105radar meteoroid orbits have been secured to date by the AMOR, project since its inception in 1990. For many types of study it is important to realize a high angular resolution; for example to probe more incisively meteoroid stream orbital structure in order better to determine the rôle of the various processes controlling stream dynamics. The orbital precision of AMOR has been enhanced by developing a new dual spacing interferometer using single channel phase detection. In addition, a Doppler-sensing facility has been incorporated to record simultaneously data concerning middle atmospheric dynamics allowing better interpretation of the individual echo signals.
On the Determination of Velocities of Radar Meteors
Authors: Pecina P. 
Published: June 2019

AbstractThe results of testing the classical method of velocity determination based on the positions of the extrema of Fresnel diffraction patterns (FDP) in radio echo amplitude, is presented. This technique is compared to the method of nonlinear least squares fitting (NLSF) of the theoretical patterns to the observed those. It is shown that while the classical method can fail in yielding correct values for the velocity of radar meteors, the NLSF method always yields good results.
A New Technique for Radar Meteor Speed Determination: Inter-pulse Phase Changes from Head Echoes
Authors: Taylor A.D. , Cervera M.A. , Elford W.G. , Steel D.I. 
Published: June 2019

AbstractWe have implemented a 54 MHz radar located near Adelaide, South Australia, for novel forms of meteor observation. Here we describe a radically new form of meteor speed determination: we measure the rate of phase change for head echoes obtained from meteors propagating down the beam towards the radar. These not only provide speeds of unprecedented precision, but also deliver accurate deceleration measurements, these being of importance in understanding the meteoroid ablation process and exploring the physical parameters of such bodies.
No Meteor Storms Expected from P/Machholz 2
Authors: Asher D.J. , Steel D.I. 
Published: June 2019

AbstractP/1994 P1 Machholz 2 is the first Earth-crossing shortperiod comet to have been observed to have split since 3D/Biela about 150 years ago, and that fragmentation resulted in the Andromedid meteor storms of 1872 and 1885. Thus a pertinent question is whether meteor storms might result from P/Machholz 2 in the foreseeable future. Here we integrate its orbit to ascertain when the node might next occur near a heliocentric distance of 1 AU, and find that this is not anticipated far over 1000yr, although some meteor activity in ∽300yr is possible. On such time-scales the recently-released debris will have dispersed, so that meteor storms are not expected from this comet.
Concepts for Dust Velocity Measurements on a Cometary Orbiter
Authors: Perruchot Sandrine , Lamy Philippe L. , Giovane Frank , Gustafson Bo Å. S. 
Published: June 2019

AbstractWe have studied several optical systems for dust velocity measurements on a cometary orbiter using light scattering to detect particles. Two main concepts are considered. The first relies on trajectory imaging, while the second uses time-of-flight measurements between two or more light sheets. Their merits and disadvantages are discussed. The favored system, time-of-flight between two planes with particle localization, is described.
The Elemental Composition of Interplanetary Dust
Authors: Brownlee D.E. 
Published: June 2019

AbstractAnalyses of recovered samples of interplanetary dust have provided direct data on the bulk elemental composition of interplanetary dust over the 5μm to 1mm size range. The majority of particles have compositions similar to the bulk composition of chondrites although C and some trace volatile elements are often found in excess of CI abundances. Some individual particles have distinctly non-chondritic compositions. In most cases these particles contain large mineral grains.
The Search for Interstellar Components in Interplanetary Dust Particles
Authors: Bradley John , Ireland Trevor 
Published: June 2019

AbstractAmorphous silicate grains known as GEMS have been found in chondritic porous interplanetary dust particles (IDPs) from comets. GEMS are composed of nanometer-sized FeNi metal and Fe-rich sulfide crystals embedded in silicate glass. The properties of GEMS appear to have been shaped primarily by exposure to ionizing radiation and, since the irradiation occurredprior toaccretion of the cometary IDPs, GEMS may have formed either in the solar nebula or presolar interstellar environments. The sizes, shapes, structures, and compositions of GEMS correspond to those of interstellar “amorphous silicate” grains. Nanometer-sized superparamagnetic metal inclusions dispersed throughout GEMS provide a logical explanation for alignment of interstellar silicate grains in the galactic magnetic field. Irrespective of their origins, GEMS are an important class of submicrometersized chondritic objects. If they were formed in the solar nebula, then they are among the oldest known solar nebula solids. If they are presolar, then they are probably examples of the “amorphous silicate” grains which are ubiquitous throughout the interstellar medium.
COBE Observations of Zodiacal Emission
Authors: Hauser Michael G. 
Published: June 2019

AbstractThe COBE Diffuse Infrared Background Experiment has obtained some of the most extensive observations of the interplanetary dust (IPD) cloud ever assembled. For the 10 months of cryogenic operation, the brightness of the entire celestial, sphere was mapped with an 0.7° x 0.7° field of view at wavelengths of 1.25, 2.2, 3.5, 4.9, 12, 25, 60, 100, 140, and 240 μm, and the linear polarization was mapped at 1.25, 2.2, and 3.5 μm. Observations with reduced sensitivity continued at all wavelengths short of 12 μm for over 3 years after cryogen expiration. Throughout these observations, nearly 1/2 of the sky was mapped every day at elongation angles ranging from 64° to 124°. I describe the DIRBE and the general character of the infrared sky, outline the DIRBE team's approach to isolating the IPD signal, and review results of our initial studies of the zodiacal dust bands, the circumsolar dust ring, and the character of IPD cloud particles.
Zodiacal Light - Scattered Fraunhofer Line Profiles
Authors: Clarke David 
Published: June 2019

AbstractThe scattering function of Hong's successful model for the brightness variation with elongation, B(ε), of the Zodiacal Light has been used to calculate profiles of Doppler shifted Fraunhofer lines. Substantial line shape changes with ε are predicted with an indication of a bifurcation at ε < 30°, so offering an explanation for reported F corona observations.
Model Calculations of Near Solar Dust Properties
Authors: Mann I. , Ishimoto H. , Okamoto H. , Mukai T. 
Published: June 2019

AbstractWe discuss efforts to explain the dust distribution, as it was derived from the F-coronal brightness, mainly how to explain a constant number density near the Sun. It is shown that silicate particles have temperatures below the blackbody temperature if the impurity from absorbing material amounts to less than 0.1% in volume. This effect is especially significant for porous particles and may explain why particles can approach to less than 3 R⊙ from the Sun. Another effect may arise from particles on high eccentricity orbits and from the influence of collisional fragments. Whereas on the one hand heat resistant silicate particles may cause a stable dust cloud in the solar vicinity, on the other hand dynamical effects may cause a variation of the number density in the corona in short time scales.
Laboratory Experiments on Carbonaceous and Silicate Materials
Authors: Colangeli L. , Mennella V. , Rotundi A. , Bussoletti E. , Palumbo P. 
Published: June 2019

AbstractGround-based, remote and “in situ” observations show that dust plays an important role in the evolution of interstellar, circumstellar and interplanetary media. Despite the wealth of available astronomical data, a main item to be clarified concerns the actual chemico-physical composition of cosmic dust. A correct interpretation of observations must rely on a systematic comparison with results coming from laboratory simulations. In this paper we present an overview of recent results, obtained in our laboratory, on various forms of carbon-based and silicate grains of possible astrophysical interest.
Dust Evolution in Protoplanetary Disks
Authors: Henning Thomas , Schmitt Wolfgang , Klahr Hubert , Mucha Rastislav 
Published: June 2019

AbstractThe evolution of dust particles in circumstellar disk-like structures around protostars and young stellar objects is discussed. We especially consider the coagulation of grains due to collisional aggregation and the influence of this process on the optical properties of the particles. These dust opacities are important for both the derivation of the circumstellar dust mass from submillimetre continuum observations and the dynamical behaviour of the disks.We present first results of a numerical study of the coagulation of dust grains in a turbulent protoplanetary accretion disk described by a time-dependent one-dimensional (radial) “alpha” model. The influence of grain opacity changes due to dust coagulation on the dynamical evolution of a protostellar disk is investigated. In addition, we consider the grain motion in two-dimensional disks.
Central nervous control of voluntary food intake
Authors: Forbes J. M. , Blundell J. E. 
Published: June 2019

AbstractThe central nervous system is the integrator of most of the actions of the animal and as such plays a vital rôle in the control of voluntary food intake. Much of the work to understand how intake is controlled has been carried out with rats but that which has been done with pigs is included. The first experiments used electrolytic lesions in the designation of the ‘hunger centre’ and the ‘satiety centre’. Recent work has identified the paraventricular nucleus as a sensing site for experimental manipulations. Chemical stimulation of the brain has also been carried out to try to gain understanding of the rôle of neurotransmitters. Noradrenaline (NA) stimulates intake when given into many sites. Serotonin (5-HT) inhibits intake and has been claimed to play a rôle in the selection of macronutrients but 5-HT must now be interpreted in the light of the existence of several different subtypes of 5-HT receptors. Dopamine appears to moderate the hedonic response of eating. Numerous peptides are active in the brain where their rôle as neuromodulators may be quite different from their function in the periphery and at least three types of opioid receptors are implicated with kappa antagonists producing the most potent facilitatory effects. Neuropeptide Y and peptide YY produce massive orexigenic effects which readily overcome peripheral satiety factors. The brain cannot control intake in isolation. It receives inputs in the blood stream, such as glucose, as well as via the nervous system, both from the special senses and from visceral organs such as stomach, intestines and liver. Taste and olfaction are important in diet selection and a specific appetite for protein has been demonstrated in the pig.
3.2 Modelling Sheep Systems
Authors: Sibbald A. R. 
Published: June 2019

At the Hill Farming Research Organization (HFRO), we have been modelling various components of sheep systems and we have also attempted to model, where a need was seen, whole sheep systems at different levels of organization. The sheep systems involved are of course pastoral grazing systems on hill or upland farms. The purpose of this paper is to briefly describe these models, to identify reasons for their existence and to outline some of the problems encountered in their construction.Models have been constructed at HFRO to satisfy particular needs. They cover a spectrum of interests. There are those which are concerned with resource allocation and economic evaluation, those which are built in an attempt to develop more precise operational management procedures and those which describe biological mechanisms and processes which may be conceptual but which provide a better understanding of particular components of an animal production system.The first model (Maxwell, Eadie and Sibbald, 1973) was built to provide answers to the economic questions “Is a particular level of investment in a hill sheep system a viable proposition in both the short and the long term?” and “How does the economic performance of this strategy compare with those of alternatives?”, alternatives being, for example, different levels and rates of flock build-up, with variations in the timing of investments. The model makes year-by-year calculations of cash flow and balance based on Gross Margin, taking account of capital invested, changes in variable costs, tax and interest rates. The Gross Margin is determined from price and cost data and from biological performance. The model also calculates overall economic performance, for a pre-selected project length, as Net Present Value and Internal Rate of Return, taking account of increased stock valuation. These results are used to compare alternative schemes with different rates of investment.
4.3 Integration with Management
Authors: Kilkenny J. B. 
Published: June 2019

Three obvious statements but well worth repeating: “Computers are only an aid to summarizing information for use in assisting management decisions”; “Records are only of any use if they are used — they are not an end in themselves”; and “No point having sophisticated computerized management aids if the basic information is not available and if only decisions at a simple level are to be made”.Amongst dairy and pig producers, the need for keeping records is well established and probably over 40% of all dairy cows and pigs in Britain are involved in an enterprise recording scheme. By contrast, all too few beef and sheep producers currently keep any detailed computerized records in an organized way. It is estimated that only about 2% of all commercial beef and sheep are involved in an enterprise recording scheme. Good basic records are an essential ingredient to any more sophisticated management aid because these need to be based on relevant reliable data for individual situations. The need to use computers and their value on the individual farm is dependent upon having sufficient information to make it worthwhile employing them. The sophistication of management aids required for enterprises will be determined by the level of recording already involved. It is obvious that the requirements for beef and sheep producers are at a much more basic level than for many pig and dairy producers.
Nutritional principles in utilization of waste and by-products
Authors: Ørskov E. R. 
Published: June 2019

The increasing awareness of the potential use of by-products and the recycling of waste materials, etc., presents the nutritionist with new and interesting challenges. There are several reasons for this. First, that many waste and by-products, hereafter referred to as waste suitable for animal feeding, are produced in small quantities in differing localities; often availability is very seasonal and composition varies enormously. As a result there may be some reluctance both on the part of producers and government organizations to invest a great deal in a research programme of evaluation. Secondly, the motive of industrial producers for using organic wastes for animal feeding is more often a desire to obtain a positive return by selling wastes rather than paying for their disposal, than a real interest in meeting the requirements of the animals. As a result wastes are often produced with dangerous contaminants which could have been avoided.In many instances, therefore, nutritional advice on the use of waste in animal feeding has to be based on a knowledge of similar known feeding-stuffs and a minimum amount of analysis for basic nutritional qualities and for possible dangerous contaminants. These statements are, however, generalizations as some material, like excreta, are of variable quality and produced in vast quantities. I shall attempt to discuss briefly the nutritional attributes of different classes of waste since they are to be discussed more in detail by others at this meeting. First, a division will be made into mainly nitrogen (N) and mainly energy-yielding products and secondly the feeding systems in which they can most profitably be used will be discussed.
The effects of increased prolificacy on lamb and ewe mortality in an intensive hill sheep system
Authors: Waterhouse A. , Logue D. N. , Roger L. C. 
Published: June 2019

Increased prolificacy is often believed to increase the incidence of both lamb and ewe mortality especially in harsher environments. Fecundin® (Coopers Pittman Moore) is a vaccine which leads to immunization against androstenedione and a resulting increase in prolificacy (Rhind, 1987). The use of this drug gives a method of manipulating prolificacy without confounding any effects with improved nutrition, the most usual means of modifying reproductive success.A programme was commenced in 1985 in which half the ewes in a flock of Scottish Blackface ewes was vaccinated with Fecundin (F), the remainder left unvaccinated (N). In subsequent years ewes were maintained on the same treatment. The data presented here are an analysis of a single age group of ewes completing a full lifetime on each treatment. Eighty-five ewes were allocated at random to each treatment. These were vaccinated in autumn 1985, given a booster vaccination 4 weeks pre-ram joining in 1986, 1987 and 1988 and sold as ‘cast for age’ after lamb weaning in 1989. With the exception of injection with Fecundin, at all times management was independent of treatment.
6.6 Observations on the Variation in the Liver Copper Levels of Lambs
Authors: Adamson A. H. , Shaw W. B. , Dover P. A. 
Published: June 2019

Observations were made, from 1970 to 1975, of the liver copper (Cu) levels of lambs reared on various feeding regimes and of lambs which were stillborn or died within the first 7 days of birth in what was considered to be a normal healthy flock.Artificially reared Finnish Landrace × lambs were fed on reconstituted milk substitute and a concentrate containing 4 and 8 mg Cu/kg DM, respectively. Liver Cu levels were determined when lambs were slaughtered at 4/5 months of age. In one group, liver Cu levels varied from 500 to 1600 mg/kg DM without any evidence of Cu toxicity in any lambs, whilst, in another group, levels ranged from 50 to 600 mg/kg DM.
The management and performance of beef cattle in the hills and uplands
Authors: Gurnett L. R. , Waterhouse A. 
Published: June 2019

AbstractWith no supplementary feed to cow or calf, a suckler cow can produce a calf of 330 kg at 1 year old worth about £380. At 2.5 cows per ha on an upland farm, the system can be self-sufficient for grass and silage. Overall production can be 820 kg live-weight gain per ha with the use of 250 kg N per ha. This is technically an efficient enterprise. It is also profitable, with a gross margin per ha in excess of £800.Work at Liscombe, in parallel with other centres, has developed to establish minimum healthy diets for the suckler cow whilst producing healthy, fast growing calves. The cow must be fertile and have a long life, producing on average 10 calves. This involves the controlled management of the natural ability of the cow to put on weight quickly in the summer and take it off slowly in the winter.The winter diet of the cow can vary from (1) restricted silage alone, (2) silage plus untreated straw, (3) untreated straw plus concentrate supplement, or (4) treated straw alone. As a result, the enterprise is very flexible.On a hill farm, the cow has a major role to control pasture in a subordinate role to sheep. Because of her role in pasture control, a low margin per cow can be accepted as a direct contribution to sheep production.