bluuebunny/crossref_metadata_2025_split huggingface dataset:
Exploring the limits of Phase Referenced VLBI Imaging; a progress report
Authors: Vermeulen R.C. , Conway J.E. 
Published: July 2016

AbstractThe practical limits of phase referenced VLBI imaging are not well known. If it would be feasible to use target-reference separations of a few degrees, most of the sky would be accessible to the technique. Preliminary results at 6 cm using baselines of up to 1000 km are encouraging.
Quantitative assessment of the science return from an Orbiting, Imaging, Optical Interferometer
Authors: Meier David L. , Synnott Stephen P. , Dumont Philip J. , Jones Dayton L. 
Published: July 2016

AbstractWe describe an investigation of the science potential of the filled Mills cross orbiting, imaging, optical interferometer proposed by Synnott et al. and the constraints that science places on the design of the instrument. Imaging simulations were performed with this design in order to determine its capabilities in the area of spatial resolution, dynamic range, and sensitivity. In addition, specific astronomical objects of high interest were chosen as candidate program sources to determine what science was desired for these objects, what spatial resolution, etc. was needed to perform that science, and whether or not this interferometer design could do the science.
Imaging Characteristics of the proposed NRAO MMA, with and without a single large element, and a pointing correction algorithm
Authors: Emerson D. T. 
Published: July 2016

AbstractThis is a continuation of earlier imaging studies for the MMA. Earlier work is confirmed, and the differences in imaging quality resulting from small and larger central antennas used for short-spacing information are investigated. An algorithm is presented which uses interferometer data to correct for an important component of central element pointing errors.
The Canadian Geophysical LBI System: Status and Future Plans
Authors: Petrachenko William T. , Mathieu Pierre , Popelar Joseph , Daniels Micheal 
Published: July 2016

AbstractEmphasis in the design of the Canadian Geophysical LBI (CGLBI) system has been placed on economy, operational efficiency, and performance in geophysical applications. Unique features of the system include the use of modified VHS recorders to store digitized astronomical data and the capability to track delay and fringe rotation during observation. A prototype system has been completed and tested at L-band using the ARO-DRAO interferometer baseline. The prototype system converts a single fixed 12 Mhz wide IF channel to baseband. Since delay resolution with this system is not sufficient for modern geophysical applications a frequency switching capability is being designed to synthesize a wide IF bandwidth while still maintaining the economy of a single channel system. Further improvements include the design of a phase cal detector and an input module compatible with NASA geodetic S/X receivers. Finally, efforts are being coordinated with ISTS so that record terminals developed for the Radioastron project can be interfaced to the CGLBI system.
Non-Linear Oscillations and Beats in the Beta Canis Majoris Stars
Authors: Baranov A. S. 
Published: July 2016

Notwithstanding a great number of hypotheses, suggested for explaining superpositions of the light- and of the velocity variations of the ß Canis Majoris stars, no one of these does it satisfactorily. Possibly it is due to an inadequate elaboration of the non-linearly oscillation theory. Analysis and critical evaluation of the existing hypotheses are given by Mel’nikov and Popov (1970). Our explanation consists in existence of close frequencies corresponding to various oscillation modes which are non-linearly interacting.Equations of motion of an ideal incompressible fluid under condition of preserving the equilibrium figure symmetry with respect to the equatorial plane (lateral oscillations) have the form (Baranov 1988):
Theoretical Modes Fitting on Miras Light Curves
Authors: Barthés D. , Tuchman Y. , Mennessier M. O. , Mattei J. A. 
Published: July 2016

Visual observations of long period variable stars over 20 years were provided by the American Association of Variable Stars Observers, and were analysed as part of the preparation of the HIPPARCOS mission.A set of frequencies is extracted from the light curve by using Fourier transform, preliminary Van Cittert deconvolution and comparison of the results obtained through different kinds of spectral windows. The same procedure is applied to the residual obtained after nonlinear fit of the main frequency. After final comparison of both sets, a nonlinear fit of the common frequencies gives the ‘clean’ power spectrum.Different equilibrium stellar model (i) give theoretical linear nonadiabatic pulsation modes (vj) with their growth rates (ηj)i) (Tuchman 1978). The metallicity is taken between 0.005 and 0.02; the mixing length is λ = 1±0.2; the upper bound is r = 0.7. Assuming two peaks of the power spectrum to be the fundamental (vo) and first overtone (v1) modes, one looks for the corresponding models. The best one is selected by checking the other theoretical overtones they give. So are obtained the mass, the luminosity, the effective temperature and the effective radius of each star.
Period Variation of BW VUL
Authors: Shi-Yang Jiang 
Published: July 2016

Due to the large fluctuation of the time of light maxima, in each observational season only very few observations is very dangerous for period variation research. Especially when the observation is not accurate enough such as for the early radial velocity data. Of course parts of the fluctuation are real which are caused by the chaotic behavior of the complicated pulsation. Generally the pulsation is quite periodic but is not like a timer such as the oscillation of the quartz or the rotating of the pulsar, all of these as much simple.The period increasing rate of BW Vul from our results is 0.34 micron days per year which makes a evolution time scale about 3 million years. For a star with mass of 10 solar mass, the life age on the main sequence is about 10 million years. So BW Vul should not be very far away from the main sequence.
Fourier Analysis of the Hydrodynamic Limit-Cycle Models of Pulsating Stars
Authors: Fadeyev YU. A. 
Published: July 2016

AbstractThe pulsation motions of the limit-cycle model can be described as a superposition of the Fourier harmonics, in the adiabatic layers each harmonics being identified with the corresponding standing wave. Near the resonance Π0/Πl = k the harmonics of order k is also identified with the overtone of order l The spectra of the oscillatory moment of inertia obey to the power dependence on the Fourier harmonics order k. In cepheids with periods shorter than 9 days the bump is due to the wave packet generated by the second overtone, whereas at periods longer than 10 days the bump feature is due to the traveling pulse reflected off the stellar core.
A Linear and Nonlinear Study of Mira
Authors: Cox A.N. , Ostlie D. A. 
Published: July 2016

AbstractBoth linear and nonlinear calculations of the 331 day, long period variable star Mira have been undertaken to see what radial pulsation mode is naturally selected. Models are similar to those considered in the linear nonadiabatic stellar pulsation study of Ostlie and Cox (1986). Models are considered with masses near one solar mass, luminosities between 4000 and 5000 solar luminosities, and effective temperatures of approximately 3000 K. These models have fundamental mode periods that closely match the pulsation period of Mira. The equation of state for the stellar material is given by the Stellingwerf (1975ab) procedure, and the opacity is obtained from a fit by Cahn that matches the low temperature molecular absorption data for the Population I Ross-Aller 1 mixture calculated from the Los Alamos Astrophysical Opacity Library. For the linear study, the Cox, Brownlee, and Eilers (1966) approximation is used for the linear theory variation of the convection luminosity. For the nonlinear work, the method described by Ostlie (1990) and Cox (1990) is followed. Results showing internal details of the radial fundamental and first overtone modes behavior in linear theory are presented. Preliminary radial fundamental mode nonlinear calculations are discussed. The very tentative conclusion is that neither the fundamental or first overtone mode is excluded from being the actual observed one.
A Simplified Model for a Nonlinear Tidal Effect on Accretion Disks in CVS
Authors: Zhang Zhong-Yong , Chen Jian-Sheng 
Published: July 2016

AbstractThis paper investigates the tidal effect on accretion disk in CVs and sets up a simplified model in which the secondary’s gravitation is substituted by a mean tidal torque. We find that a linear tidal torque will not be able to maintain an equilibrium disk. By using the result of the radius of the equilibrium disk approximately equals to the tidal radius, which was obtained by using the two dimensional numerical simulation invoking nonlinear tidal effect, we give the modified tidal dissipation function for our simplified model which could be used to interpret the outburst of the dwarf nova with tidal effect. The paper also shows that the radius of an equilibrium disk with a torus is slightly small than the Lubow-Shu radius, and the tidal effect may also cause the cycle of quiescence-superoutburst in addition to the cycle of quiescence-outbursts-superoutburst.
Hydrogen Cyanide Polymers from the Impact of Comet P/Shoemaker-Levy 9 on Jupiter
Authors: Matthews Clifford N. , Pesce-Rodriguez Rose A. , Liebman Shirley A. 
Published: July 2016

AbstractHydrogen cyanide polymers – heterogeneous solids ranging in color from yellow to orange to brown to black – may be among the organic macromolecules most readily formed within the Solar System. The non-volatile black crust of comet Halley, for example, as well as the extensive orangebrown streaks in the atmosphere of Jupiter, might consist largely of such polymers synthesized from HCN formed by photolysis of methane and ammonia, the color observed depending on the concentration of HCN involved. Laboratory studies of these ubiquitous compounds point to the presence of polyamidine structures synthesized directly from hydrogen cyanide. These would be converted by water to polypeptides which can be further hydrolyzed to α-amino acids. Black polymers and multimers with conjugated ladder structures derived from HCN could also be formed and might well be the source of the many nitrogen heterocycles, adenine included, observed after pyrolysis. The dark brown color arising from the impacts of comet P/Shoemaker-Levy 9 on Jupiter might therefore be mainly caused by the presence of HCN polymers, whether originally present, deposited by the impactor or synthesized directly from HCN. Spectroscopic detection of these predicted macromolecules and their hydrolytic and pyrolytic by-products would strengthen significantly the hypothesis that cyanide polymerization is a preferred pathway for prebiotic and extraterrestrial chemistry.
Prebiotics on Titan: from Available to Expected Measurements
Authors: Gautier Daniel 
Published: July 2016

AbstractAn intense organic chemistry occurs in the atmosphere of Titan. The detected species are far to be uniformly spatially distributed. Their mixing ratios vary with altitude and latitude. Tentatives to interpret these data are examined. Available photochemical models are discussed and shown to fail to reproduce simultaneously hydrocarbons and nitriles observed abundances., whatever the assumed eddy diffusion coefficient profile. Future models will have to explicitly take into account polymerisation, distributions of aerosols, seasonal effects and atmospheric circulation. The Cassini-Huygens mission, to be launched towards Saturn and Titan in 1997, will provide a tremendous information on the atmospheric composition of organics and on the mapping of the most abundant species. The nature of the aerosols will be investigated. Current theories on the chemical composition of the subnebulae of Saturn in which Titan was formed are discussed. We conclude that billions of like- Titan objects may exist in the Universe.
Direct Detection of Extra-Solar Planetary Systems from Balloon Borne Telescopes
Authors: Terrile Richard J. , Ftaclas Christ 
Published: July 2016

AbstractAnalysis of a 1.5 meter diameter High Altitude Balloon Circumstellar Imaging Telescope (HABCIT) indicates that it offers a fast and low cost path to direct detection of extra-solar planets. Above an altitude of about 30 kilometers, scatter in the visible due to the atmosphere is more than 1000 times smaller than the diffraction sidelobes for a 1.5 meter telescope at 1 arcsecond in the visible. This permits a thousandfold reduction in the total background against which the planet must be detected. By flying a scatter compensated 1.5 meter telescope and high efficiency coronagraph on a balloon platform, a very near term and low cost opportunity exists to achieve exciting scientific results and technology demonstrations. For a thousandfold reduction in the background, a Jupiter like planet could be detected around more than 70 stars with an average integration time of 16 hours. For the very nearest stars complete planetary systems can be characterized down to nearly Earth sized planets, over a range of orbital distances (1-5 AU).
Application of the Strömvil Photometric System for a Search of Solar-Type Stars
Authors: Straižys Vytautas 
Published: July 2016

AbstractThe seven-color photometric system, introduced by Vilnius astronomers in 1963-1967, makes possible a completely photometric determining of spectral classes (and temperatures), absolute magnitudes (and surface gravities), interstellar reddenings and distances of stars of all normal spectral types. Recently it was suggested to join this system with the Stromgren four-color system. The new seven-color system, called the Stromvil system, has the mean wavelengths of the passbands at 350, 375, 411, 467, 516, 547 and 656 nm and half-widths of the order of 20 nm. The system can be effectively used for detection and classification of solar-type stars which are expected to be the best sites for existence of planetary systems and life.
Hydrogen Cyanide Polymers as Prebiotic Sources of Biological Compounds in Terrestrial and Extraterrestrial Environments
Authors: Negrón-Mendoza Alicia , Ramos-Bernal Sergio 
Published: July 2016

AbstractAqueous solutions of cyanides are frequently used in experiments related to prebiotic chemistry. CNcontaining molecules are key compounds in this type of synthesis. This is due to the high chemical reactivity of the CN group, their abundance in the interstellar space, in comets, and the facility of their formation from simulated experiments. Implications for prebiotic chemistry are profound mainly because these polymeric materials upon hydrolysis release compounds of biological significance such as amino acids, purines, carboxylic acids, etc. Since the products formed from a CN-containing compound have different chemical groups, and a great variety of molecular weights, the potentiality and versatility for prebiotic synthesis is enormous. The gamma irradiation of very diluted aqueous solutions of HCN yields oligomeric material among the radiolytic products. These oligomers are constituted of polyamides and substituted ureas. However, radiation-induced polymers have different characteristics than the polymers formed by thermal polymerization.
Violent Primitive Earth Might have Harmonized with the Origin of Life
Authors: Shimizu Mikio 
Published: July 2016

AbstractAt the end of the planetesimal infall on the surface of the primitive earth, hot dry beaches might have been useful for the formation of various activated monomers and oligomers (peptides and small RNAs). We discuss the possibility that a small system composed of small RNAs (∼ 10 mers) and dipeptides might have mimicked the contemporary biosystem, based on experimental results suggesting the presence of previously overlooked weak but specific interactions between three bases and one amino acid (of genetic code type) and also those between a dipeptide and a biosubstrate (of ligase, transferase, hydrolase, lyase, isomerase and dehydrogenase type). The Kms obtained for these dipeptide enzymes were of the order of 1M, in accord with the association constant for the binding of guanosine to cytocine in water. In this oligomer world, the genotype and phenotype evolution was closely coupled, resulting in a very rapid rate of evolution.
Redox Reactions in Lipid Membranes as a Model for Primordial Energy-Conserving Systems
Authors: Di Bernardo Salvatore , Fato Romana , Lenaz Giorgio 
Published: July 2016

AbstractOne of the peculiar aspects of living systems is the production and conservation of energy. This aspect is provided by specialized organelles, such as the mitochondria and chloroplasts, in developed living organisms. In primordial systems lacking specialized enzymatic complexes the energy supply was probably bound to the generation and maintenance of an asymmetric distribution of charged molecules in compartmentalized systems. On the basis of experimental evidence, we suggest that lipophilic quinones were involved in the generation of this asymmetrical distribution of charges through vectorial redox reactions across lipid membranes.
Self-Reproduction of Chemical Structures and the Question of the Transition to Life
Authors: Luisi Pier Luigi 
Published: July 2016

AbstractThe principles which underlay the chemical approach to the origin of life are discussed, beginning with Oparin’s notion of molecular evolution, whereby the minimal living emerged from the non livingviaa natural increase of molecular complexity and organization. The philosophical and methodological difficulties inherent in such a view are briefly examined. The scenario of the origin of life provided by the RNA-world is then reviewed, and the great difficulties inherent in this view are emphasized, particularly the one according to which a RNA family is createdex-novoin an enzymefree world in a way which is capable to self-replicate, mutation is concluded that the view of the RNA world for the origin of life, despite its popularity, is not very realistic at all; however it has a great importance as it has introduced a series of fundamental new concepts into the field of origin of life. Particularly important is the notion of self-reproduction, and in the paper the self-reproduction of vesicles is reviewed, pointing to the fact that it is a thermodynamically driven process based on spontaneously self-assembling macromolecualr aggregates. The possible relevance of these experiments for assessing a prebiotic «pre-RNA» world is discussed.
Results from Project Phoenix: Looking up from down Under
Authors: Tarter Jill C. 
Published: July 2016

AbstractWe used the Parkes and Mopra antennas of the Australia Telescope National Facility (ATNF) and observed 209 solar-type stars in the Southern hemisphere over much of the frequency range 1200-3000 MHz. The sensitivity of these observations was sufficient to rule out any narrow-band transmitters stronger than 5 × 1012Watts (the power of strong terrestrial radars) broadcasting during our observations. The use of two widely separated antennas, linked together as a pseudo-interferometer, proved to be an extremely effective discriminant against RFI. This mode of observing will be continued by Project Phoenix. Observations begin again in October of 1996, with the 140 foot antenna at NRAO Green Bank linked to an old AT&amp;T Earth Station at Woodbury, Georgia that has been resuscitated by students and faculty at Georgia Tech Research Corporation. Later observations will make use of the Arecibo Observatory and the Nançay Observatory, each linked with a second site.
A Search for Artificial Signals from the Newly Discovered Planetarty Systems
Authors: Biraud François , Heidmann Jean , Tarter Jill C. , Airieau Sabine 
Published: July 2016

AbstractWe conducted a search for narrowband artificial signals from the regions of stars around which planetary companions have been recently found: 51 Pegasi, Gliese 229, 70 Virginis and 47 Ursae Majoris. We used the large Nançay decimetric telescope, with a frequency resolution of 50 Hz, and we scanned over 0.64 MHz and 2.24 MHz respectively around the hydrogen and hydroxyl lines.
A Call for Seti well into the 21st Century S for Search/Survey/Study/Sociology of ExtraTerrestrial Intelligence
Authors: Heidmann Jean 
Published: July 2016

AbstractAs soon as we unravel a first signal (if ever!), this will be the immediate proof that extraterrestrial civilizations are numerous in the cosmos and, within a few years, we should discover tens of them, as this happened often, e.g. for quasars, pulsars, gravitational lenses, and now for extrasolar planets. Then the drive to investigate them, in all of their expected varieties, will get very strong. We shall show that this prodigious perspective raises a large number of long-term issues whose investigations and solutions require an immediate call for collaborations at many interdisciplinary and international levels over the next quarter century. In particular, we witness both a remarkable increase of SETI technology efficiency – which over the last 30 years doubled every 8 months – and a sharp rise of man-made radio frequency interference. Thus we ought to save a dedicated lunar farside locale for the next generation (project SAHA). In addition we propose to use gravitational focuses of the Sun to investigate in tremendous detail some selected interesting extraterrestrial technologies (project FOCAL). We ought to think that SETI, after standing for SEARCH, will mean SURVEY, then STUDY, then SOCIOLOGY of ExtraTerrestrial Intelligences. It is time for some to abandon the idea that in case we do not get a signal «before next election year», SETI should be killed. Humankind is engaged, firmly now, into a long-term and far-sighted enterprise.
Unsolved Problems in Stellar Pulsation Physics
Authors: Cox Arthur N. 
Published: July 2016

AbstractUnsolved problems of theoretical stellar pulsations are briefly reviewed for pulsators in six regions of the Hertzsprung-Russell diagram. Only a small selection is included in the discussion of them, and the emphasis is mostly on theoretical problems. The problem of the pulsations of Mira stars, and the mode in which it pulsates is reviewed in more detail together with some new calculations that illustrate the difficulties. Finally an extensive discussion is made for the pulsation mechanism of the white dwarf (DA and DB) pulsators. A new interpretation is advocated, which unfortunately is not tractable by linear nonadiabatic calculations because during the pulsation cycle it involves the turning off and on of Convection with a short time scale relative to the pulsation period. Most of the theoretical problems involve the time dependence of convection, a topic still without any concise and practical way of convenient implementation.
Tidal Modulation of Radial Oscillations in Components of Circular-Orbit Close Binaries
Authors: Reyniers T. , Smeyers P. 
Published: July 2016

AbstractA theoretical description is presented of the modulation of a radial oscillation in a uniformly rotating star in a close binary that is subject to the tidal action of a companion moving in a circular orbit. The star is assumed to rotate non-synchronously with the companion’s orbital motion. A tidal modulation of a radial oscillation has been observed in the star θ Tucanae by Sterken (1997) and De Mey et al. (1998).
Multiperiodicity in the Line-Profile Variations of the Spectroscopic Binary β Cep Star λ Scorpii
Authors: Uytterhoeven K. , Aerts C. 
Published: July 2016

AbstractA study of the rapid variations of the line profiles of λ Scorpii leads to the following new result: we find evidence for the presence of at least 5 periodicities in the intrinsic variations of λ Scorpii, which seem to be part of an equidistant multiplet. The modes associated to these periodicities are interpreted as non radial pulsation modes.