摘要:

The evolutionary history of star and element formation rates with cosmic epoch is reviewed. The problem of taking proper account of the effects of dust obscuration in optical and ultraviolet observations is emphasised. Recent submillimetre surveys have been used to derive the star formation rate as a function of cosmic epoch independent of dust obscuration. These observations suggest that the star formation rate peaked at redshiftsz∼2–4,similar to the maximum in the evolution of the populations of active galaxies. We describe a general two-parameter family of functions that describe the evolution of the efficiency of star formation in merging galaxies as a function of cosmic epoch. The functions are analytic in the Einstein-de Sitter model. The simple functions we obtained provide excellent fits to observations of the evolution of both optically selected and dust-enshrouded galaxies, and are consistent with observations of the evolution of the abundance of both gas and metals at all epochs. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1291466

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The density budget of the Universe is reviewed, and then specific particle candidates for non-bayonic dark matter are introduced, with emphasis on the relevance of cosmic-ray physics. The sizes of theneutrino massesindicated by recent atmospheric and solar neutrino experiments may be too small to contribute much hot dark matter. My favored candidate for the dominant cold dark matter is thelightest supersymmetric particle, which probably weighs between about 50 GeV and about 600 GeV. Strategies to search for it via cosmic rays due to annihilations in the halo, Sun and Earth, or via direct scattering experiments, are mentioned. Possiblesuperheavy relic particlesare also discussed, in particular metastable string- orM-theorycryptons, that may be responsible for the ultra-high-energy cosmic rays. Finally, it is speculated that a non-zero contribution to thecosmological vacuum energymight result from incomplete relaxation of the quantum-gravitational vacuum. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1291467

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Micron sized, presolar grains of SiC and graphite (as well as other phases not discussed here) found in mineral separates of primitive meteorites constitute a new source of cosmic material. The grains are identified by anomalous isotopic ratios in both major and minor elements. In some cases, these differ from average solar system values by a factor>103.The SiC grains can be separated into distinct isotopic families representing different stellar sources. Only two types are discussed here—“mainstream” SiC grains, constituting ∼98&percent; of the total and less abundant X-grains that constitute <1&percent; of the total. The former have isotopic ratios characteristic of S-process nucleosynthesis and are believed to be condensates formed in the atmospheres of AGB stars. In contrast, X grains have isotopic patterns characteristic of R-process nucleosynthesis and are believed to be supernovae condensates. In addition to giving a wealth of new detail on the nuclear processes in different stars, the grains open up entirely new avenues of research. For example, electron microscope mineralogical/petrographic studies of microtomed grains give insight on the processes of grain growth. Molecules of polycyclic aromatic hydrocarbons (PAHs) are common in the graphite grains. Isotopic measurements demonstrate that some of the PAHs formed from the same suite of atoms as the parent grains and are thus indigenous. The relationship of presolar grains to cosmic ray physics is briefly considered. Overall, the grain work serves to deepen the mystery of the similarity of isotopic ratios measured in cosmic rays to those of Solar System materials. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1291468

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The most dramatic changes in the solar corona occur during coronal mass ejections, or CMEs, during which solar material is propelled outward into the heliosphere from regions in the corona not previously participating in the solar wind expansion. These ejections often produce major solar wind disturbances, large geomagnetic storms, enhancements of moderate energy (MeV) particle fluxes and decreases in the galactic cosmic ray particle flux. This paper provides an overview of the CME phenomenon with emphasis on the CMEs themselves and how they evolve as they propagate out through the heliosphere. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1291469

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

This review covers the sessions SH 3.1–3.5: “Galactic cosmic rays in the heliosphere” of the 26th International Cosmic Ray Conference held in Salt Lake City, Utah, in August 1999. The subtopics are modulation models, long-term variations, gradients, anisotropies, and spectra, composition & charge state. Noteworthy contributions include a number of new models, numerical simulations of transport coefficients—including the first of the drift coefficient—that highlight the continuing problems with perpendicular transport, various other attempts to pin down the spatial and rigidity dependence of the diffusion tensor, charge-dependent modulation and especially the role of the wavy current sheet, and the Gnevyshev gap during solar maximum conditions. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1291470

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

This paper reviews highlights of the 26th ICRC in the area of acceleration and propagation of solar energetic particles (SEPs). New results on SEP charge state and composition, a lively topic during the Conference, are covered in an accompanying paper by Klecker. I begin with a brief historical review of the field to provide context for the key advances/developments on SEP acceleration/propagation presented in Salt Lake City. These include: (1) the use of gamma-ray emissions as diagnostics of the acceleration process(es) and probes of the interaction region; (2) the observation of ∼10 GeV (or higher) protons for the 6 November 1997 ground level event by the Milagrito experiment; (3) observations of coronal Moreton waves as “smoking pistols” of shock acceleration/injection of SEPs; (4) an investigation of the role of proton event spectra in the current “two-class” picture of SEP events; (5) an analysis of the Gnevyshev Gap in SEP activity; (6) a Ulysses-based determination of the dependence of SEP mean free path on radial distance from the Sun and on heliographic latitude, and (7) an examination of the dissipation range in the power spectrum of interplanetary magnetic field fluctuations. I conclude with a discussion of new instrumentation (e.g., Milagro, HESSI) and a look to the expected level of SEP activity for the approaching maximum of solar cycle 23. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1291471

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

This paper is an overview of the contributed papers presented at the SH2.1, SH2.2, SH2.3, and SH3.6 sessions of the 26th International Cosmic Ray Conference (Salt Lake City—Utah, August 17–25, 1999). The main subjects covered are observational features and modeling efforts for transient phenomena in the heliosphere and radiation in the terrestrial environment. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1291472

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

This is a rapporteur paper for the 26th International Cosmic Ray Conference covering the sessions on anomalous cosmic rays (SH 4.1-SH 4.4) and on energetic charged particle composition, spectra, and charge states (SH 1.4). The ACR sessions covered the topics anomalous cosmic ray elemental and isotopic composition and energy spectra, anomalous cosmic ray sources, preacceleration and acceleration, ACR transport, modulation and time variation, the observation of ACRs trapped in the Earth’s magnetic field, and energetic neutral atoms of ACR origin from the outer heliosphere. Among the highlights of the ACR sessions were the discovery of new ACR elements of possibly heliospheric origin, the new high resolution measurements of ACR elemental and isotopic composition with instrumentation onboard ACE, and the first report on energetic neutral hydrogen atoms of ACR origin observed onboard SOHO. Session SH 1.4 covered the elemental and isotopic composition, the energy spectra, and the ionic charge composition of energetic charged particles in gradual and impulsive solar energetic particle events and the signature of a quiet-time interplanetary low-energy component. This brief report will concentrate on compositional variations during individual gradual events and their simulation, on new observations of the event-to event variability of elemental and isotopic composition, and on the determination of the ionic charge composition, using a variety of indirect methods and direct observations. Among the highlights of the SEP session were the new high-resolution measurements of elemental, isotopic, and ionic charge composition with unprecedented sensitivity providing new insight into the characteristic differences between gradual and impulsive events. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1291473

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

This paper summarizes highlights of the OG3.1, 3.2 and 3.3 sessions of the XXVIth International Cosmic Ray Conference in Salt Lake City, which were devoted to issues of origin/composition, acceleration and propagation. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1291474

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Many new results on galactic cosmic ray composition and spectra were presented at the 26th ICRC. The sessions covered in this paper (OG 1.1, OG 4.1, and OG 4.2) include direct measurements of cosmic rays, related work on modeling and interpretation, and plans for future experiments in this area. Approximately thirty active and planned experiments were presented. Highlights of the conference included measurements of elemental and isotopic composition by the Cosmic Ray Isotope Spectrometer (CRIS) aboard the Advanced Composition Explorer (ACE) spacecraft, new data from several magnetic spectrometers and other balloon payloads, and continued progress in the application of passive techniques to studies of rare components of the cosmic rays. Considerable interest in extending direct measurements to higher energies was reflected in the technical sessions. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1291475

出版商:AIP    

年代:1900

数据来源: AIP