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  • ASTROPHYSICS  (12)
  • Portability  (1)
  • 1
    Electronic Resource
    Electronic Resource
    A message-passing class library C++ for portable parallel programming (1997)
    Springer
    Engineering with computers 13 (1997), S. 20-34 
    Details
    ISSN: 1435-5663
    Keywords: Message-passing ; Object-oriented programming ; Parallel processing ; Portability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract An object-oriented message-passing class library in C++, called PPI++, for portable parallel programming has been developed. PPI++ (parallel portability interface in C++) is designed to serve as a stable (unchanging) interface between the client parallel code and the rapidly evolving distributed computing environments. By taking advantage of encapsulation, inheritance, and polymorphism supported by C++, PPI++ provides a clean and consistent programming interface, which helps improve the clarity and expressiveness of client parallel codes and hides implementation details and complexity from the user to ease parallel programming tasks. In addition, the use of strong type-checking in C++ allows the detection of potential misuses of the library at compile time, and thus promotes code reliability. This paper describes the object-oriented design and implementation of PPI++. Evaluation of PPI++ on important performance issues, such as portability, ease-of-use, extensibility, and efficiency, is also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01201858
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    Paper (German National Licenses)
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  • 2
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    Comment on the paper 'A cosmological limit on the possible variation of G' (1980)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Keywords: ASTROPHYSICS
    Type: Royal Astronomical Society; vol. 191
    Format: text
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  • 3
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    Case for an open universe (1980)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: The determination of the geometrical structure of the universe through the magnitude-vs-redshift relation in standard cosmology has not been very successful, mainly because of the intrinsic insensitivity of the m-vs-z relation to a deceleration parameter, which determines the spatial curvature and therefore the geometry. By relaxing the assumption usually made, i.e., the identity of gravitational and atomic clocks, sufficient sensitivity is achieved. Existing observational evidence then leads one to conclude that the universe is open.
    Keywords: ASTROPHYSICS
    Type: Physical Review Letters; 44; Mar. 17
    Format: text
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  • 4
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    Cosmological considerations on the diffuse gamma-ray isotropic background (1980)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: Bignami et al (1979) have recently studied the problem of the origin of the diffuse gamma-ray isotropic radiation. They have concluded that within standard cosmology with Lambda = 0 and p = 0, BL Lacertae objects and Seyfert galaxies can account for most of the diffuse radiation if they have not evolved in time. For QSOs, an evolutionary factor is allowed by the data. From the study of radio data, however, it is known that strong evolutionary effects are expected. The discrepancy cannot be explained by changing the geometry of the universe. Contrary to the case of standard cosmology, it is found that in order to fit the diffuse gamma-ray background, the evolutionary function required is almost identical to the one previously determined from the study of the log N-log S relation.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 235
    Format: text
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  • 5
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    Scale covariant gravitation. V - Kinetic theory. VI - Stellar structure and evolution (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A scale covariant kinetic theory for particles and photons is developed. The mathematical framework of the theory is given by the tangent bundle of a Weyl manifold. The Liouville equation is derived, and solutions to corresponding equilibrium distributions are presented and shown to yield thermodynamic results identical to the ones obtained previously. The scale covariant theory is then used to derive results of interest to stellar structure and evolution. A radiative transfer equation is derived that can be used to study stellar evolution with a variable gravitational constant. In addition, it is shown that the sun's absolute luminosity scales as L approximately equal to GM/kappa, where kappa is the stellar opacity. Finally, a formula is derived for the age of globular clusters as a function of the gravitational constant using a previously derived expression for the absolute luminosity.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 248
    Format: text
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  • 6
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    Scale-covariant theory of gravitation and astrophysical applications (1977)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: Generalized Einstein equations invariant under scale transformations are presented, and several astrophysical tests studied. It is assumed that the dynamics of atoms or clocks used as measuring apparatus is given a priori. Connection with gauge fields and broken symmetries is made through the cosmological constant.
    Keywords: ASTROPHYSICS
    Type: Physical Review Letters; 39; Aug. 22
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  • 7
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    The 3 K blackbody radiation, Dirac's Large Numbers Hypothesis, and scale-covariant cosmology (1978)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: A program is described which is intended to derive a generalized system of gravitational equations that allow (but do not require) G to vary, to use the 3-K blackbody radiation to fix the relation between G and the gauge function, and to employ Dirac's (1937) Large Numbers Hypothesis to derive the geometry of the universe. Einstein's equations are retained in their total integrity, but the specification is made that they are valid only when gravitational units are used. A scale-invariant form of Einstein's equations is obtained, and from this are derived the energy conservation law, the baryon-number conservation law, and the appropriate cosmological equations. Dirac's proposals of 1937 and 1973 are incorporated into the formalism, and a gauge based on consolidation of the 3-K blackbody radiation is presented. A unique solution for the geometry of the universe is determined for zero curvature solely from the 3-K radiation and the Large Numbers Hypothesis; this solution predicts a deceleration parameter exactly equal to unity.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 224
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  • 8
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    Scale covariance and G-varying cosmology. II - Thermodynamics, radiation, and the 3 K background (1979)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: Within the framework of a scale-covariant theory of gravitation, a semiclassical description of particles and photons is given. Thermodynamic relations consistent with the modified conservation equations are derived. Application to a system of radiation shows that the observed 3-K background radiation can be interpreted, within the present framework, as a remnant of equilibrium radiation in the past. As the theory postulates a nonstandard coupling between gravitation and electrodynamics, the assumption that Einstein's theory of gravitation is unchanged forces modifications at the atomic level. The use of Minkowskian spacetime in atomic physics is found to be adequate only over small, but not large, time scales compared with the age of the universe. As a result, a relation between energy and the frequency of a free photon is demonstrated. Possible observational consequences of this relation are discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal Supplement Series; 41; Oct. 197
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  • 9
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    Scale-covariant theory of gravitation and astrophysical applications (1977)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: A scale-covariant theory of gravitation is presented which is characterized by a set of equations that are complete only after a choice of the scale function is made. Special attention is given to gauge conditions and units which allow gravitational phenomena to be described in atomic units. The generalized gravitational-field equations are derived by performing a direct scale transformation, by extending Riemannian geometry to Weyl geometry through the introduction of the notion of cotensors, and from a variation principle. Modified conservation laws are provided, a set of dynamical equations is obtained, and astrophysical consequences are considered. The theory is applied to examine certain homogeneous cosmological solutions, perihelion shifts, light deflections, secular variations of planetary orbital elements, stellar structure equations for a star in quasi-static equilibrium, and the past thermal history of earth. The possible relation of the scale-covariant theory to gauge field theories and their predictions of cosmological constants is discussed.
    Keywords: ASTROPHYSICS
    Type: Physical Review D - Particles and Fields; vol. 16
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  • 10
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    Scale covariance and G-varying cosmology. III - The /m, z/, /theta sub m, z/, /theta sub i, z/, and /N/m/, m/ tests (1979)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: The Einstein gravitational equations in atomic units are fully solved for a matter-dominated universe in the context of a recently proposed scale-covariant cosmology. The magnitude-redshift relation for elliptical galaxies is studied, the evolutionary parameter used in such a study is derived, and the relation between isophotal angular diameters and redshifts is investigated, along with the relation between metric angular diameters and redshifts, the N(m)-magnitude relation for QSOs, and the magnitude-redshift relation for QSOs. Results are presented for four gauges (i.e., relations between G and the scale function beta (t)), and no contradictions are found between the proposed theory and the observational data. It is shown that only an open universe can fit the data if certain gauges suggested by a recent analysis of the time variation of the moon's period are selected and that observations made with atomic instruments do not necessarily yield geometrical parameters unless specific assumptions are made regarding the relation between atomic and gravitational dynamics.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal Supplement Series; 41; Oct. 197
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