University of California, Santa Cruz

About: University of California, Santa Cruz is a education organization based out in Santa Cruz, California, United States. It is known for research contribution in the topics: Galaxy & Population. The organization has 15541 authors who have published 44120 publications receiving 2759983 citations. The organization is also known as: UCSC & UC, Santa Cruz.

Toward a Deterministic Model of Planetary Formation. II. The Formation and Retention of Gas Giant Planets around Stars with a Range of Metallicities

Abstract: The apparent dependence of detection frequency of extrasolar planets on the metallicity of their host stars is investigated with Monte Carlo simulations using a deterministic core-accretion planet formation model. According to this model, gas giants formed and acquired their mass Mp through planetesimal coagulation followed by the emergence of cores onto which gas is accreted. These protoplanets migrate and attain their asymptotic semimajor axis a through tidal interaction with their nascent disk. Based on the observed properties of protostellar disks, we generate an Mp-a distribution. Our results reproduce the observed lack of planets with intermediate mass Mp = 10-100 M⊕ and a 3 AU and with large mass Mp 103 M⊕ and a 0.2 AU. Based on the simulated Mp-a distributions, we also evaluate the metallicity dependence of the fraction of stars harboring planets that are detectable with current radial velocity surveys. If protostellar disks attain the same fraction of heavy elements as contained in their host stars, the detection probability around metal-rich stars would be greatly enhanced because protoplanetary cores formed in them can grow to several Earth masses prior to their depletion. These large masses are required for the cores to initiate rapid gas accretion and to transform into giant planets. The theoretically extrapolated metallicity dependence is consistent with the observations. This correlation does not arise naturally in the gravitational-instability scenario. We also suggest other metallicity dependences of the planet distributions that can be tested by ongoing observations.

Pulsational Pair-instability Supernovae

Abstract: The final evolution of stars in the mass range 70 - 140 solar masses is explored. Depending upon their mass loss history and rotation rates, these stars will end their lives as pulsational pair-instability supernovae producing a great variety of observational transients with total durations ranging from weeks to millennia and luminosities from 10$^{41}$ to over 10$^{44}$ erg s$^{-1}$. No non-rotating model radiates more than $5 \times 10^{50}$ erg of light or has a kinetic energy exceeding $5 \times 10^{51}$ erg, but greater energies are possible, in principle, in magnetar-powered explosions which are explored. Many events resemble Type Ibn, Icn, and IIn supernovae, and some potential observational counterparts are mentioned. Some PPISN can exist in a dormant state for extended periods, producing explosions millennia after their first violent pulse. These dormant supernovae contain bright Wolf-Rayet stars, possibly embedded in bright x-ray and radio sources. The relevance of PPISN to supernova impostors like Eta Carinae, to super-luminous supernovae, and to sources of gravitational radiation is discussed. No black holes between 52 and 133 solar masses are expected from stellar evolution in close binaries.

Acid-induced folding of proteins

Abstract: The addition of HCl, at low ionic strength, to the native state of apomyoglobin, beta-lactamase, and cytochrome c caused these proteins to adopt an essentially fully unfolded conformation in the vicinity of pH 2. However, contrary to expectation, the addition of further acid resulted in refolding to a compact conformation with the properties of a molten globule. The major factor responsible for the refolding is believed to be the binding of the anion, which minimizes the intramolecular charge repulsion that initially brought about the unfolding.

Shoreline Mapping Techniques

Abstract: Numerous coastal mapping techniques have been developed over the last twenty-seven years (STAFFORD, 1971; DOLAN et al., 1978; FISHER and SIMPSON, 1979; LEATHERMAN, 1983; McBRIDE et al., 1991; THIELER and DANFORTH, 1994a, OVERTON et al., 1996). These techniques, used to measure shoreline erosion, barrier island migration, and dune erosion, vary in approach, accuracy, expense and training/time requirements. Some of the more recent coastal mapping techniques apply advances in cartography and photogrammetry providing high-resolution measurements with less error than manual methods that use a photographic comparator or stereo zoom transfer scope. However, such techniques are expensive, require extensive training, and may take longer than manual methods. While many coastal mapping studies would benefit from these advanced techniques, not all studies require the high resolution these more recent techniques offer. When beginning a coastal mapping project or choosing to upgrade laboratory facilities, researching established coastal mapping techniques before choosing from among them requires extensive literature review. To assist researchers, engineers and planners who wish to undertake a coastal mapping project, this paper provides an overview of the errors associated with shoreline mapping, and a discussion of factors to be considered when selecting a coastal mapping technique.

The determinants of the global digital divide: a cross-country analysis of computer and internet penetration

Abstract: To identify the determinants of cross-country disparities in personal computer and Internet penetration, we examine a panel of 161 countries over the 1999-2001 period. Our candidate variables include economic variables (income per capita, years of schooling, illiteracy, trade openness), demographic variables (youth and aged dependency ratios, urbanization rate), infrastructure indicators (telephone density, electricity consumption), telecommunications pricing measures, and regulatory quality. With the exception of trade openness and the telecom pricing measures, these variables enter in as statistically significant in most specifications for computer use. A similar pattern holds true for Internet use, except that telephone density and aged dependency matter less. The global digital divide is mainly – but by no means entirely – accounted for by income differentials. For computers, telephone density and regulatory quality are of second and third importance, while for the Internet, this ordering is reversed. The region specific explanations for large disparities in computer and Internet penetration are generally very similar. Our results suggest that public investment in human capital, telecommunications infrastructure, and the regulatory infrastructure can mitigate the gap in PC and Internet use.