bluuebunny/crossref_metadata_2025 huggingface dataset:
Models of Reflection Nebulae
Authors: Roark T. P. , Mayo Greenberg J.
Published: June 2019

A Feasibility Study For an Observational Program was made to investigate models of reflection nebulae. Specifically, for a relatively simple model of an interstellar dust cloud with a source of illumination nearby, predictions of the color of the nebula, relative to the source color, at points along any radial direction from the source are sought. Furthermore, from these color differences, the possibility is studied of discriminating between the effects produced by the cloud-source-observer geometry and those due to the assumed optical properties of the scattering particles. If such discrimination is feasible, the types of observations that would be most useful in separating the effects must be known to the investigator.

Plane-parallel slab models similar to those of reference 1 in which the scattering particles are distributed isotropically and homogeneously were used. The scattering properties of the particles were assumed to be those obtained by using the Mie theory of electromagnetic scattering.
Scattered Light in H II Regions
Authors: O'Dell C. R.
Published: June 2019

The Possible Role of Interstellar Particles in the determination of the ionization structure of H II regions, the transfer of the Lyman line radiation, and the early stages of stellar contraction have stimulated an investigation of the properties and relative abundance of the scattering particles that exist within the boundaries of a number of bright galactic diffuse nebulae. It is interesting to note that the conclusion reached in reference 1, based on crude observations, was that there does not seem to be any scattered light in the bright H II regions; this conclusion is in contradiction to the results of the study presented herein. Results of the present investigation show that, in general, dust is an important constituent of the diffuse nebulae; that certain anomalies in the gas-to-dust ratio can be explained in a straightforward manner through the interaction of the particles and stellar radiation; and that the anomalies are closely related to the deviations known to exist in the interstellar reddening law.
Diffuse Interstellar Lines and Chemical Characterization of Interstellar Dust
Authors: Johnson Fred M.
Published: June 2019

The Problem of Chemical Identification of the interstellar dust grains has vexed astronomers for over three decades. The earliest evidence for the mere presence of interstellar dust was deduced from the observation of stars (via star counts) in the Milky Way. The best presently available clues for possible chemical identification are spectroscope data, particularly the diffuse (hitherto unidentified) interstellar absorption lines. This paper is concerned primarily with a discussion of new theoretical interpretations of the spectroscopic data.

Much related information on the dust grains was obtained from observations of space reddening, its wavelength dependence, and from interstellar polarization. Furthermore, correlation of space reddening and the strength of some of the diffuse lines is important to the discussion of possible chemical identification of the dust.
Interferometric Techniques Applied to High Resolution Observation of the Solar Granulation
Authors: Aime Claude
Published: June 2019

Michelson,one-dimensional, and two-dimensional apertures are used to obtain the statistical properties of the solar granulation. The calibration of the power spectrum is performed via Michelson stellar interferometry as well as by the use of changes in seeing conditions during speckle-interferometric measurements. The correction of 40 analyses, determined with Fried's parameter ro ranging between 2.5 cm and 11.5 cm, provides satisfactory convergence for frequencies up to 3 cycles per arc second
Rotation-Shearing Interferometry
Authors: Roddier Frangois
Published: June 2019

Holograms of incoherent objects can be recorded with a rotation-shearing interferometer allowing corrections of wavefront errors. Holographic images taken in our laboratory, either through aberrated optics or atmospheric turbulence, have been successfully restored. A stellar hologram is presented.
Absolute Photoionization Cross Section for O I (3P) → O II (4S°)
Authors: Kohl J. L. , Lafayetis G. , Polenius H. P. , Parkinson W. H.
Published: June 2019

Measurements of the absolute cross section for photoionization from the 2p4 3P ground state of atomic oxygen will be described for wavelengths between the 4S° (91.2 nm) and 2D° (73.2 nm) limits. The cross section is determined from the absorption spectrum of shock heated mixtures of neon and oxygen at temperatures near 12000 K. The measured cross section will be compared to theoretical predictions and to earlier experimental work. Similar measurements of the photoionization cross section of H I which demonstrated the reliability of our windowless shock tube apparatus will be discussed briefly.
4d → 4f Excitation in Lanthanide Vapours
Authors: Radtke E. R.
Published: June 2019

Since the last VUV conference in Hamburg, there has been speculation on the possible occurrence of collective effects in the 4d-f excitation channels of the lanthanide sequence. However, the data available so far has been restricted to solids, with the exceptions of Barium and Europium, due to the need for a high temperature absorption cell.

In the present paper we report the first observation of the 4d-f ‘Giant Resonance’ for the atomic vapours of Lanthanum, Samarium and Cerium using a 42 cm long induction furnace working up to 2700 K. The spectra were calibrated by superposing the emission lines from a Garton flash tube.
Calibration of the Echelle-Vidicon Combination of the Buss-Instrument
Authors: Kampermann T. M.
Published: June 2019

For both observations and laboratory measurements the use of television-type detectors is increasing. The Space Research Laboratory at Utrecht is, in collaboration with Johnson Space Center at Houston, carrying out high resolution spectroscopy from a balloon borne observatory using an echelle spectrograph and a SEC-vidicon detector. The calibration of such a system is not trivial. This paper deals with the procedures required to achieve a proper intensity calibration of the system in use.
Theoretical Ultraviolet Spectra of B Type Stars : Uncertainties in gf Values
Authors: Burger Marijke
Published: June 2019

Theoretical spectra have been computed (in LTE) for B type stars, in the wavelength range 2000-3000 Å. The results show a good agreement with observations (S59 and Copernicus).

It will be shown that the most important factor that influences the resulting computed spectrum - at a resolution of 1.8 Å or lower - is the completeness of the list of spectral lines used in the computations, owing to the large (number) density of lines in the ultraviolet.

At a resolution of 1.8 Å a large error is tolerated on gf values, while identification of observed line features from the theoretical spectra remains possible.

The accuracy of the gf values becomes increasingly more important if one goes to higher spectral resolution, as will be shown by comparison of theoretical spectra with observations.

Our present knowledge of oscillator strengths is sufficient for. identification of a large number of spectral lines in high resolution spectra; for a detailed analysis more accurate data are preferable in many cases.
X-Ray Spectra of Tokamak Plasma
Authors: Fraenkel B.S.
Published: June 2019

A spectrum covering Fe XXV to Fe XXII x ray lines from a tokamak (PLT) plasma has been obtained. Results indicate similarity with the flare spectrum in this region - the forbidden lines also appear in the PLT spectrum.

Te was about 1.8 keV- a value confirmed by intensity of dielectronic recombination lines. Ti was found to be not more than 0.7 keV, by Doppler width of the He like singlet 1s2 –ls2p 1S0 -1P0. A Johansson crystal was used, with the spectrograph adapted for an extended X-ray source.
The Photometry of Visual Binaries
Authors: Hardie R. H.
Published: June 2019

A substantial part of our understanding of the physical nature of stars rests upon observations of visual binaries. In order to secure a complete interpretation of a binary system we require these data: semi-major axis, parallax, period, magnitudes, colours, spectral types and velocities. It goes without saying that for very few systems are all these desiderata available, largely through technical difficulties of observing two images in close proximity to one another - and these difficulties are particularly serious in carrying out photometry. Nevertheless, the usefulness of photometry of binaries is so great that no effort should be spared in resolving the observational and technical problems.
An Observational Evidence of the Common Envelope Phase
Authors: Sarna Marek J. , Drake Jeremy J.
Published: June 2019

Chandra Low Energy Transmission Grating Spectrograph observations of the pre-cataclysmic binary V471 Tau have been used to estimate the C/N abundance ratio of the K dwarf component for the first time. While the white dwarf component dominates the spectrum longward of 50 Å, at shorter wavelengths the observed X-ray emission is entirely due to coronal emission from the K dwarf. The H-like 2p 2Р3/2, 1/2 → 1s 2S1/2 resonance lines of С and N yield an estimate of their logarithmic abundance ratio relative to the Sun of [C/N]= –0.38 ± 0.15—half of the currently accepted solar value. We interpret this result as the first clear observational evidence for the presumed common envelope phase of this system, during which the surface of the K dwarf was contaminated by CN-cycle processed material dredged up into the red giant envelope
Testing Common Envelope Theories with White Dwarf Binaries
Authors: Nelemans G. , Tout C.A.
Published: June 2019

We determine the possible masses and radii of the progenitors of white dwarfs in binaries from fits to detailed stellar evolution models and use these to reconstruct the mass-transfer phase in which the white dwarf was formed. We confirm the earlier finding that in the first phase of mass transfer in the binary evolution leading to a close pair of white dwarfs, the standard common-envelope formalism based on energy balance in the system, does not work. A formalism based on angular momentum balance can explain the observations. We extend our analysis to all close binaries with at least one white dwarf component. Comparing the two, we show that the formalism based on angular momentum balance can explain all observations at least as well as the energy formalism.
Substellar Secondaries in Zero-Age Cataclysmic Variables
Authors: Politano M.
Published: June 2019

The present-day formation of cataclysmic variables (CVs) with brown dwarf (BD) secondaries is investigated using a population synthesis technique. Results from the latest, detailed models for BDs have been incorporated into the population synthesis code. We find that zero-age CVs (ZACVs) with BD secondaries have orbital periods in the range 46 min to 2.5 hrs, and that they comprise 18% of the total, present-day ZACV population. Consequently, we find that 15% of the present-day ZACV population should have orbital periods shorter than the observed orbital period minimum for CVs. We also investigate the dependence of the present-day formation rate of CVs with BD secondaries on the assumed value of the common envelope efficiency parameter, αCE, for three different assumed mass ratio distributions in ZAMS binaries. We find that the common envelope process must be extremely inefficient (αCE < 0.1) in order for CVs with BD secondaries not to be formed. Finally, we find that the progenitor binaries of ZACVs with BD secondaries have ZAMS orbital separations < 3 AU and ZAMS primary masses between ~1-10 M⊙ , with ~75% of the primary masses less than ~ 1.6 M⊙. Interestingly, these ranges in orbital separation and primary mass place the majority of the progenitor binaries within the so-called “brown dwarf desert.”
Realistic Models for Donors in Ultracompact Binaries
Authors: Deloye C. J. , Bildsten L.
Published: June 2019

We present the first realistic set of arbitrarily degenerate stellar models appropriate for donors in ultracompact binaries. The mass-radius M-R relations for these objects are parameterized by the donor's entropy and composition. We highlight how this fact can affect our understanding on the current configuration of ultracompact binaries today and their potential evolutionary tracks.
A Disk Instability Interpretation for the 2001 Outburst of WZ SGE
Authors: Osaki Y.
Published: June 2019

The 2001 outburst of WZ SGE is discussed based on the thermal-tidal instability model (TTI model). It is demonstrated that the overall development of the outburst can be understood by the disk instability model (TTI model) and that no enhanced mass transfer is needed to explain observations.
A Circumstellar Interaction Model for SN 2002IC
Authors: Uenishi T. , Suzuki T. , Nomoto K. , Hachisa I.
Published: June 2019

SN 2002ic is a unique supernova which shows the typical spectral features of Type la supernovae (SNe Ia) near maximum light, but also apparent hydrogen features that have been absent in SNe Ia (Hamuy et al. 2003). We have calculated hydrodynamical models for the interaction between the SN la ejecta and the H-rich circumstellar medium (CSM) to reproduce the observed features of SN 2002ic. Based on our modeling, possible progenitor systems of SN 2002ic are discussed.
Rotating Progenitors of the Wolf-Rayet Binaries HD186943 and HD90657
Authors: Petrovic Jelena , Langer Norbert
Published: June 2019

We present rotating progenitor models for the WR+O binary systems HD186943 and HD90657 (van der Hucht, 2001) calculated with the evolutionary code described by Wellstein (2001). Due to rotation, the effective accretion onto the secondary star is reduced as it is spun-up close to its break-up velocity and thereby undergoes strong mass loss. We investigate the progenitor evolution of the two observed WR+O binary systems through stable mass transfer. We conclude that these systems evolved through Case A mass transfer as they have short orbital periods now (8…10 days), and the progenitor systems must have started with a shorter or equal period. We show that there has to be a significant mass loss from the binary system to produce WR+O systems similar to the observed ones. The accretion efficiency of the secondary star in our rotating models is ~10%. We compare properties of the observed and modelled systems in Table 1.
Hydrodynamical Modelling of T Pyxidis
Authors: García-Segura Guillermo , Low Mordecai-Mark Mac , Shara Michael M.
Published: June 2019

The Hubble Space Telescope observations showed that some nova outbursts may not produce smooth shells of gas, but thousands of gaseous blobs. In the case of T Pyx the blobs are distributed in eight concentric circles around the exploding star, producing a pattern similar to tree rings. We explore here the formation of the tree rings by hydrodynamical simulations.
Possible Density Determination of the Nebular Component of Cataclysmic Variables with the N III 4641/4635 Line Ratio
Authors: Bohigas Joaquín , Pérez-Tijerina Eduardo , Machorro Roberto
Published: June 2019

The dependence of the N III 4641/4635 line ratio on the electron density is presented. It is shown that this ratio may be an important diagnostic tool in cataclysmic variables.

Pérez-Tijerina, Bohigas & Machorro (2001) used the Chianti code and database developed by the U.S. Nautical Observatory (Landi, 200) in order to find density and temperature sensitive line ratios in the conditions occuring in plasmas produced in pulsed laser deposition experiments for thin film deposition, i.e., around 1018 cm 3 and 104 K. Level populations are determined considering only radiative decay and collisional excitation and de-excitation.
Detection of Possible Interstellar Particles by the HITEN Spacecraft
Authors: Svedhem H. , Münzenmayer R. , Iglseder H.
Published: June 2019

The Cosmic Dust experiment on the Hiten spacecraft detected more than 500 events likely to be associated with particle impacts during its three years life in space. An excess of approximately 40% was observed in the direction of 220° ecliptic longitude. This direction corresponds well with the direction of the reported interstellar Helium and interstellar dust seen by other experimenters. In absolute number this is about 20 particles. Since this data was taken during three full years and thus most other effects should be averaged out we believe that these particles are of interstellar origin.
Electromagnetic Escape of Dust from the Solar System
Authors: Hamilton Douglas P. , Grün Eberhard , Baguhl Michael
Published: June 2019

Collisions of asteroids and among Zodiacal cloud particles produce large amounts of submicron-sized debris, much of which is immediately ejected from our solar system by electromagnetic forces. We investigate the trajectories of tiny grains started on circular uninclined orbits within the Zodiacal cloud and find that they reach high ecliptic latitudes during the current configuration of the solar magnetic.field, perhaps accounting for particles detected by the Ulysses spacecraft at latitudes up to 80°. When the solar magnetic field is reversed, particles are more strongly confined to the ecliptic plane and escape the solar system less readily. Both fluxes and spatial densities of sub-micron sized Zodiacal dust particles vary with time through the dependence of orbital dynamics on the 22-year solar cycle.
Dynamical Evolution of Interplanetary Dust due to Gravitational Scattering by Jupiter and the Inner Planets
Authors: Gor'kavyi Nikolai N. , Ozernoy Leonid M. , Mather John C.
Published: June 2019

We introduce the continuity equation written in the coordinate space of the orbital elements (e.g. large semi-axis a vs. eccentricity e, etc.) to explore the density evolution of the zodiacal cloud. Emphasis is on those terms of the continuity equation which describe ‘jumps’ of particles in the (a, e)-space due to gravitational scattering of the interplanetary dust particles by planets, which represents one of the leading factors in the dynamical evolution of the zodiacal cloud. In the remainder (div-terms of the continuity equation), one can incorporate the known analytical expressions for the rates of gradual change of orbital elements due to the Poynting-Robertson and solar wind drags (Liou et al. 1995).
Dynamics of the Leonid Meteoroid Stream: a Numerical Approach
Authors: Brown P. , Jones J.
Published: June 2019

We have simulated the evolution of the Leonid stream via numerical integration of 3 million test particles ejected from 55P/Tempel-Tuttle during five perihelion passages of that comet. Using the Whipple ejection velocity formula and a random ejection spread in true anomaly about the parent comet orbit inside 2.3 AU, we have followed the subsequent evolution of Leonid meteoroids differing by over 5 orders of magnitude in mass under the influence of radiation pressure and planetary perturbations. By comparing the model predictions of Leonid activity on a year by year basis with the available observations we have attempted to determine roughly the time of ejection associated with each Leonid storm occurrence and model the observed mass distribution. On the basis of the demonstrated accuracy of the model we make predictions regarding times of peak activity and relative strengths for the Leonid returns for each year during the latter part of the 1990s.
The First in a New Series of Leonid Outbursts
Authors: Jenniskens P.
Published: June 2019

The Leonids returned with higher than usual rates in November 1994. From an analysis of the available visual and radio forward m teor scatter observations, it is found that the meteor stream activity curve and the magnitude distribution index are similar to those of the outbursts in 1961 and 1965 during the previous return of the parent comet. It is possible that the outburst was due to the same dust component or dust with a similar stream evolution history.
Regular and Stochastic Motion of Meteoroid Streams in Halley-type Orbits
Authors: Emel'yanenko V.V. , Bailey M.E.
Published: June 2019

Despite the complicated structure of old meteoroid streams in Halley-type orbits, the positions of their ecliptic-plane crossings are insensitive to the initial conditions of ejection and have a form determined by resonances due to planetary perturbations. This allows the main observational features of meteor showers such as the η-Aquarids, Orionids, Lyrids and Perseids to be understood. A proportion of the particles ejected into such orbits librate about the centres of mean-motion resonances and produce compact streams which may lead to meteor storms.
Naturally Occurring Selection Effects on the Terrestrial Accretion of Interplanetary Dust Particles
Authors: Kortenkamp Stephen J. , Dermott Stanley F. , Liou J.C.
Published: June 2019

Interplanetary dust particles deposited in the Earth's atmosphere (IDPs) are an important source of extraterrestrial material. The origin of these particles, whether asteroidal or cometary, is a dispute that can be resolved into two separate questions. What are the fractions of the asteroidal and cometary components of the zodiacal cloud? And what fraction of each component is captured by the Earth? Evidence from the structure of the zodiacal cloud, particularly the dust bands and the Earth's resonant circumsolar ring, indicate that about one third of the cloud is asteroidal while two thirds is cometary. The geometry of capture is such that low eccentricity (e), low inclination (I) particles will be preferentially captured over high e, I particles. Two known abundant sources of low e, I particles are the asteroidal families Themis and Koronis, as witnessed by the associated zodiacal dust bands. We show that capture rates of particles from these two families achieve dominance over every other source. This leads to the result that particles from Themis and Koronis may account for over half of all deposited IDPs and that very few of the IDPs deposited in the Earth's atmosphere are of cometary origin. Furthermore, there are dynamical arguments which suggest that the accretion rate of Themis and Koronis dust particles varies with time. Two perodicities occur, a seasonal variation with a period of six months and a long-term variation with a period near 105 years. The amplitude and period of this long-term variation is supported by measurements of extraterrestrial 3He found in deep-sea sediments.
Sources of 10 micron Interplanetary Dust: The Contribution from the Kuiper Belt
Authors: Flynn G. J.
Published: June 2019

Two major sources are observed to contribute to the Zodiacal Cloud: main-belt asteroids and active comets. However, the discovery of 100 km size objects in trans-Neptunian orbits (Jewitt & Luu 1993) coupled with Pioneer 10 measurements showing an essentially constant flux of 10 μm dust from 4 to 18 AU with indications that dust may be in near-circular orbits (Humes 1980) suggests that collisions in the Kuiper Belt may contribute significantly to the Zodiacal Cloud and to the interplanetary dust collected from the Earth's stratosphere. Kuiper Belt dust collected at Earth could be identified by high densities of solar flare tracks, unusually thick amorphous rims, and high concentrations of spallogenic isotopes.
The Contamination of Iapetus by Phoebe Dust
Authors: Burns J. A. , Hamilton D. P. , Mignard Francois , Soter Steven
Published: June 2019

We examine whether the dark, orbitally-leading hemisphere of Saturn's satellite Iapetus might be coated by debris from low-albedo Phoebe, which orbits retrograde well exterior to Iapetus. Using simplified analytical models along with more complete numerical integrations, we follow the paths of various-sized particles launched gently off Phoebe following collisions with interplanetary and interstellar meteoroids. Micron grains can quickly reach Iapetus since (due to solar radiation) they trace elliptical orbits; larger grains may only hit after their more-circular orbits collapse due to Poynting-Robertson drag; few very large and very small Phoebe grains strike Iapetus. Despite some inconsistencies with observations, we conclude that Phoebe may possibly be the agent that has darkened Iapetus.
Isotopic Anomalies in Interplanetary Dust Particles
Authors: Messenger S. , Walker R. M.
Published: June 2019

Approximately 1/3 of interplanetary dust particles (IDPs) and some primitive meteorites have large excesses in D and/or 15N compared to terrestrial materials. Constraints on the nature and origin of the carriers of these isotopic anomalies are reviewed. Special attention is given to a recently discovered extremely D-rich cluster IDP.
Search for the Signature of Interstellar Dust in the COBE Data
Authors: Grogan K. , Dermott S.F , Gustafson B.Å.S. , Jayaraman S. , Xu Y.L. , Hamilton D.
Published: June 2019

Impact data from the ULYSSES dust detector at 5 AU from the Sun have been interpreted as a flux of sub-micron interstellar dust particles (Grün et al, 1994) arriving from 252° ecliptic longitude and 2.5° ecliptic latitude. Following the motions of these particles under the influence of solar gravity, radiation pressure and electromagnetic forces, we present results from the modeling of the thermal emission from the resultant particle cloud, and conclude that the chances for the detection of such an interstellar signature in the COBE data are marginal at best.
Clues in Zodiacal Light Observations for a Dust Ring Along the Earth's Orbit
Authors: Renard J.B. , Dumont R , Levasseur-Regourd A.C. , Hadamcik E.
Published: June 2019

The ability of the Earth to trap interplanetary grains into a dust ring lying along the terrestrial orbit was shown by numerical simulations and confirmed by infrared observations (IRAS, COBE). Such a ring could have its signature on the elongation dependence of the zodiacal brightness along the ecliptic, especially near 90° of the Sun. Indeed, the elongation dependence observed at Tenerife by Dumont and Sanchez (1975) shows that the space density of interplanetary dust slightly increases with increasing heliocentric distance, within the 2 or 3 hundredths of AU approaching Earth's orbit.
The Role of Particle Size in Producing the F- Coronal Scattered Brightness
Authors: MacQueen R.M. , Davidson W.C. , Mann I.
Published: June 2019

Motivated by new infrared observations, we examine the contribution of various size intervals of interplanetary dust particles to visible and infrared scattered radiances of the solar F-corona, employing Mie theory and particle size distributions based upon differing interpretations of lunar microcrater evidence and interplanetary flux measurements.
A fragmentation model of dust grains in the inner coma of Halley. A possible explanation of the color effect
Authors: Goidet-Devel B. , Clairemidi J. , Moreels G. , Rousselot P.
Published: June 2019

A model to describe the intensity of dust scattered light observed by the spectrometer TKS during the Vega/Halley encounter is presented. Good agreement is obtained when using a particle radius dependent mass density. The color effect is reproduced if the refractive index of tholin is adopted.
Polarimetric Measurements of Scattered Light by Dust Grains In Earth and Microgravity Conditions. Tentative Interpretation of the Dichotomy between Comets
Authors: Hadamcik E. , Levasseur-Regourd A.C. , Worms J.C.
Published: June 2019

The evolution of the polarization of light scattered by dust particles (e.g. cometary dust) with the phase angle is an indicator of the physical properties of the particles. For grains large compared to the wavelength, the maximum value of polarization Pmaxincreases with increasing size. A dichotomy is pointed out in the cometary poiarimetric phase curves, showing two ranges of values for Pmax. A comparison between laboratory measurements performed under Earth and microgravity conditions is presented. Pmaxand the corresponding αmaxappear to be smaller in microgravity than for ground based measurements. The comparison between ground based, microgravity and cometary results is then tentatively discussed in term of physical properties of the grains.
A Complete and Efficient Multisphere Scattering Theory for Modeling the Optical Properties of Interplanetary Dust
Authors: Xu Yu-lin , Gustafson Bo Å. S.
Published: June 2019

For a long time, the dominant scattering theory used in radiative transfer and scattering calculations has been Mie theory, which is the complete solution to the problems of light scattering by single, isotropic, and homogeneous spheres. However, cosmic dust collections show that most of the largest sized interplanetary dust particles may be porous, inhomogeneous, and aggregated and may have quite different scattering properties. Arbitrary configurations of aggregated spheres may provide a reasonable first approximation to realistic light-scattering models of interplanetary dust particles. In the last few decades, progress has been made in developing light scattering theory for interacting spheres, The development of the addition theorems for scalar and vector spherical wave functions (Friedman & Russek, 1954; Stein, 1961; Cruzan, 1962) opened up a new area in the theoretical study of multisphere scattering problems.
Scattering Properties of Cometary Grains
Authors: Vaidya D. B. , Desai J. N.
Published: June 2019

Halley probes (Giotto, Vega) have shown that cometary grains can be extremely dark and might have fluffy structures. These probes have also detected submicron sized particles in the coma of the comet. In view of these observations and to interpret the observed data on several other comets we calculate the angular distribution of the scattered intensity, polarization and albedo for porous and compact particles. For these calculations, we apply discrete dipole approximation (DDA) first to the spheroidal particles, assumed to be made of small scattering elements (dipoles). Then we reduce the number of dipoles systematically to model the porous grains. We study the phase function, linear polarization, and albedo as a function of grain size and packing density.
Genetic improvement of meat production in sheep and cattle -current industry schemes and future possibilities
Authors: Simm G , Steane D E
Published: June 2019

Overfatness of lamb and beef carcasses is a problem in many countries. Genetic improvement of carcass composition, particularly in specialised terminal sire (meat) breeds, should lead to permanent, cumulative, and cost-effective improvements. In the past, selection in these breeds has been mainly on liveweight. However, the use of in vivo estimates of carcass composition is expected to lead to higher rates of progress. In ruminants index selection is likely to be most useful, and early results from selection experiments are encouraging. Although schemes for recording performance and estimating breeding values are in operation in many countries, structural problems such as small herd or flock sizes, and lack of comparisons between herds or flocks impede progress. To some extent, these problems could be overcome by cooperation amongst breeders and wider use of new statistical techniques. Genetic improvement of meat production could be further enhanced by improved techniques for in vivo estimation of carcass composition, and by use of embryo transfer to increase “annual selection intensity” of females.
Collection, storage and distribution of information on the value of by-products and wastes in animal feeding
Authors: Haendler H.
Published: June 2019

To use information means to use the experiences of others to make decisions. In fields where experience is lacking it can be gained by conducting experiments. People who have available experience in a special field are called experts. In each field of economics production is subject to changes of several factors such as price and availability of the raw material needed for the special type of production. Animal production depends mainly on the availability and prices of useful feeds, and should be regarded as one type of production among others, the different types being more or less correlated.

From time to time changes in industrial or other types of production occur. New materials, often regarded at first as worthless wastes, may be found to be suitable as feeds, but thousands of tonnes of such a new material may have been destroyed before its feed value was established. In other cases the new material may have been given to animals but without success, causing illness or reducing efficiency. The reason for the failure may be that no previous experience was available, no experiments had been made previously or were known and no expert could be asked. In other words, no information was available about the nutritional value of the specific material.

The situation of deficiency of information is comparable to the situation of deficiency of feeds. If regular feeds are not available in adequate quantum or at acceptable prices, then interest in the use of by-products and wastes increases. If no results from research in that specific field are published and no experience is available, one has to look for ‘by-products’ of knowledge. Anybody anywhere in the world may have analysed a sample of a feed for a specific purpose. The result may have been forgotten after the particular question had been answered. But perhaps some years later this piece of knowledge could be used for a quite different purpose. The experience of others then becomes valuable.
3.2 The Role of Dose-Response Trials in Predicting Trace Element Deficiency Disorders
Authors: Phillippo M.
Published: June 2019

The symptoms of trace element deficiency arise from the combined effects of the different lesions provoked within the animal body. Since a variety of different lesions have been described, many of which affect inter-related systems, it is not surprising that diverse symptoms may arise even from the one trace element deficiency; nor that similar symptoms may be caused by deficiencies of different trace elements. The major effects of trace element deficiencies on body functions have been outlined in Table 3.2.1 (from Underwood, 1980).
3.3 Nutritional Myopathy in Cattle; from a Clinical Problem to Experimental Models for Studying Selenium, Vitamin E and Polyunsaturated Fatty Acids Interactions
Authors: McMurray C. H. , Rice D. A. , Kennedy S.
Published: June 2019

A number of diseases of ruminants are related to deficiencies of vitamin E and selenium (Se). Nutritional myopathy or white muscle disease (Blaxter and Sharman, 1953; Oksanen, 1965; Allen, Bradley, Berrett, Parr, Swannack, Barton and MacPhee, 1975; McMurray and McEldowney, 1977) affects the young bovine. Crawley and Bradley (1978) have described a sudden death syndrome in Se-deficient, bucket-fed, calves, which disappeared when Se was added to the diet.
4.2 Parenteral Methods of Trace Element Supplementation
Authors: Allen W. M. , Moore P. R.
Published: June 2019

Dietary manipulations or other oral treatments are, in many cases, the most efficient solution to the problem of trace element deficiency diseases in farm animals. Such approaches are particularly effective against chronic primary deficiencies where there is simply not enough of the required element in the diet to satisfy the animal's needs.

In some situations, however, notably severe and acute deficiencies, parenteral injections of a supplement provide the best methods of restoring normal mineral concentrations in the deficient animal's tissues. Parenteral supplements are also particularly effective against many secondary deficiences in which factors in the diet convert apparently adequate dietary concentrations of the required element into an unavailable form: their effectiveness arises because absorption from the alimentary canal is bypassed. Injectable trace element supplements have also proved particularly useful for short term supplementation during periods when there is a great demand for the element, for instance during pregnancy. One further advantage of the parenteral route of supplementation is that a known amount of the element is introduced into the animal's system.
5.1 Toxicity Problems associated with Trace Elements in Domestic Animals
Authors: Howell J. McC.
Published: June 2019

The opening sentence of the toxicology section of a recent veterinary pharmacology and therapeutics text reads “Everything is poisonous” (Hatch, 1977). Such a generalization reinforces the fact that this paper is concerned with the toxicity of essential trace elements which are necessary for the proper functioning of body cells and are usually thought of in their role as essential components of a diet. Thus, there is the apparent paradox of certain trace elements being both necessary for and damaging to the proper functioning of cells and of the animals that are composed of these cells. It has been said that there are not any toxic elements but that there are toxic concentrations of elements and the paradox of essentiality and toxicity is resolved if we consider that it is the concentration of the element within the biological system that determines the type of action that occurs. Very low concentrations of trace elements are required for the proper functioning of enzymes, cells and tissues. Increasing concentrations can be tolerated by cells but, at a particular concentration, the homeostatic mechanisms can no longer handle the element and cells are damaged. It has been suggested that there are three zones of action of trace elements, (i) the biological action zone, (ii) the inactive zone and (iii) the pharmacotoxicological action zone (Venchikov, 1974).
1.1 Nitrogen Metabolism in the Rumen
Authors: Buttery P. J. , Lewis D.
Published: June 2019

The concept that the protein reaching the duodenum of a ruminant comprises of two major components, feed and microbial, has been accepted for many years but recently there has been considerable interest in attempts to define and quantify those processes which have an influence on the quantity and quality of this protein. The main reason for this is the desire to predict accurately the total flow of protein to the duodenum when a particular diet is fed. The ability to do this, coupled with a refinement of knowledge on the needs of the animal, are essential steps in improving the efficiency with which ruminants are fed. This review examines some of the factors which control the breakdown of dietary protein and the synthesis of microbial protein in the rumen. The lack of space has prevented discussion of many important topics, for example, the contribution of endogenous proteins to the total protein entering the duodenum. Many reviews have been published in this area (see Egan, 1980; Demeyer and Van Nevel, 1980; others are referred to in the text).
1.2 Post-Ruminal Digestion and the Utilization of Nitrogen
Authors: Lindsay D. B. , Armstrong D. G.
Published: June 2019

The preceding paper has detailed our current understanding of the processes of N digestion in the ruminant animal as they relate to the events occurring within the reticulo-rumen. It is the purpose of this paper to consider the processes of digestion occurring principally within the small intestine and to comment on the significance of events occurring within the caecum and colon in so far as they relate to nitrogen digestion. The fate of amino acids subsequent to their absorption from the gastro-intestinal tract will also be discussed, in particular the way they are catabolized and whether this limits their availability for the synthesis of protein. Reference will also be made to purine and pyrimidine nitrogen; these products arise from the considerable content of nucleic acids in the microbial mass which leaves the reticulo-rumen and undergoes digestion in the small intestine.
7.4 The Effect of Supplementary Starch and Urea on the Digestion of a Heather-Based Diet by Sheep
Authors: Mayes R. W. , Lamb C. S.
Published: June 2019

Sheep grazing heather hills in winter normally ingest a mixture of heather and indigenous herbage, predominantly Agrostis and Festuca spp. Under these conditions during mid-pregnancy, ewes at high stocking rates may lose excessive live weight leading to poor subsequent lambing performance. This undernutrition may be attributed, in part, to low voluntary intakes of herbage and, possibly, to insufficient amino acids being absorbed from the small intestine, since the availability of nitrogen (N) of heather is very low, both in the rumen (Milne, Christie and Russel, 1979) and in the small intestine (MacRae, Milne, Wilson and Spence, 1979). Supplementation could increase the nutrient supply to ewes grazing predominantly heather, since voluntary intake of a heather: Agrostis/Festuca (⅔:⅓) diet was not depressed when a urea and starch supplement was fed (J. A. Milne, A. M. Spence and H. A. Fisher, unpublished). The following experiment was conducted to examine the effects of such a supplement on ruminal digestion and the absorption of non-ammonia nitrogen (NAN) and organic matter (OM) from the small intestine and hind gut.
Land use in the hills and uplands
Authors: Thomas T. H. , Harding D. , Hattey R. , Martin W. D.
Published: June 2019

The paper summarises briefly the current status of the major land using activities in the hills and uplands. The dominant land use roles of agriculture and forestry arc explained, as are other uses of recreation, water provision and wild life and landscape conservation. Land use competition in the hills and uplands is seen as the end result of conflicting policy objectives pursued by the major rural resource planning agencies over the past 50 years. The role of these agencies is analysed, as is their ability to meet their objectives in competition with each other. Finally, an attempt is made to establish a quantitative framework within which the interests of the various groups are recognised and priorities in land use can be determined.
Genotype by environment interactions: experience from Langhill
Authors: Veerkamp R. F. , Simm G. , Oldham J. D.
Published: June 2019

Genotype by environment interaction was investigated for a range of traits. Selection (S) and control line (C) cows, housed and managed at the Langhill Dairy Cattle Research Centre, were offered ad libitum complete mixed diets, with proportions (in total dry matter) of concentrates, silage, brewers’ grains of either 20:5:75 (LC; 1.0 t concentrate per annum) or 45 :5 :50 (HC; 2.5 t concentrate), over a full lactation. No diet X genetic line interactions were observed for a range of traits (production, food intake, live weight and condition score) when compared as means. However, regression coefficients of protein yield (P < 0.05), milk yield (P < 0.10) and protein percentage (P < 0.10) on pedigree index for fat plus protein yield were different between LC and HC. Genetic correlations between HC and LC were high for most traits, and only for fat yield was the value below 0-80. Because the rate of increase in energy output from selection is unlikely to be matched by the rate of increase in intake during the first part of the lactation, it was expected that intake capacity is likely to become more important in the future, regardless of the feeding system. For this reason, it is suggested that selecting for a lower live weight whilst simultaneously selecting for increased yield (an approach which has been advocated in some countries) should be treated cautiously. Especially on low input diets increases in yield as a result of continued selection (on higher input diets) may be limited by the rate, or extent of tissue mobilization; under these circumstances health and fertility problems might be the first indicators of such limits being approached.
Summary policy recommended for eastern and southern Africa: Mbabane, Swaziland, 28 July to 1 August, 1997
Authors: Bunoti C. W.
Published: June 2019

The seminar, the aim of which was to develop policy recommendations to improve the livestock sector in eastern and southern Africa, was held from 28 July to 1 August 1997 in Mbabane, Swaziland. All countries were represented and a wide range of topics were discussed. These included livestock development in Africa, relative to the rest of the world, and meeting the food security needs of each country, for which production must increase at 4% per annum, rather than 2% as at present.

Topics considered included: constraints to livestock development, current status, global and African trends in the livestock sector, human resource needs, animal genetic resources, animal health constraints, data and information, research and extension, private sector contribution, participation and contribution by donors or international organizations and interactions between livestock, environment and wildlife.

Recommendations were made on: livestock, environment and wildlife interactions for extensive production systems and mixed crop and livestock interactions for intensive production systems, animal health and genetic resource constraints and policy information management and communication.

The region under discussion has a tremendous potential for livestock production, which has not been fully realized, and potential internal markets for livestock and livestock products. At present it lacks cohesive livestock development policies at both national and regional levels. The region carries more than 37%, 72%, 63%, 55%, 33% and 39% of Africa's human, cattle, sheep, goat, pig and chicken populations respectively (FAO, 1988).

The purpose of this paper is an attempt to summarize the proceedings of the seminar, highlighting the issues raised and recommendations made.
Inocula differences affect in vitro gas production kinetics
Authors: Mertens D. R. , Weimer P. J. , Waghorn G. M.
Published: June 2019

The kinetics of gas production during ruminal fermentation may provide valuable information about foods that can be used to formulate diets and model animal responses. However, measurement of digestion kinetics is affected by methodology and techniques must be established that provide accurate and precise estimates of kinetic parameters. Because gas production measurements provide the opportunity to estimate the digestion kinetics of both soluble and insoluble matter in foods, it would be desirable to use this technique on a wide variety of forages, grains, supplements, and by-product foods. Applying an in vitro technique to such a wide variety of substrates raises questions about the type of inoculum that should be used. The objective of our study was to evaluate the effects of donor animal and its diet on the measurement of gas production kinetics using both forage and concentrate substrates.
Assessment of fermentation characteristics of ruminant foods using an automated pressure evaluation system
Authors: Davies Z. S. , Brooks A. E. , Griffith G. W. , Theodorou M. K.
Published: June 2019

Gas production from the in vitro digestion of forage with buffered rumen fluid can be measured and used to determine forage digestibility and fermentation kinetics. Rumen micro-organisms ferment carbohydrate to gases (CO2 and CH4) and volatile fatty acids (VFA). The VFA produced also cause CO2 to be released from the C02-bicarbonate buffer. Theodorou et al. (1994) introduced the principle of measuring gas production by pressure increase using an electronic pressure transducer and sealed gas-tight culture bottles. Gases accumulate in the head space of the culture bottles as fermentation proceeds. The gas is measured and then released at regular intervals throughout the fermentation. This procedure was automated (Davies et al., 1995). The automated pressure evaluation system (APES) has advantages over the manual pressure transducer technique (Theodorou et al., 1994) in that it is less labour intensive and has been shown to be more sensitive to food characteristics (Davies et al., 1995). The APES, used in this work, has been improved to include new switches and a filtering system. It has been used here to determine the fermentation characteristics of various ruminant foods: ryegrass, wheat grain and ryegrass silage.