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Low Temperature Series Expansions for Lattices of Non-Integral Dimensions
No full text[[abstract]]Low-temperature series expansions for Ising models on lattices of non-integral dimensions are studied. Critical exponents β for various dimensions are extrapolated from series expansions for the generalized equivalent neighbor lattice.[[fileno]]2010111010023[[department]]物理
The Vectorization of the Partition Problem
No full text[[abstract]]This paper describes a vectorized algorithm for the partition problem, a famous NP-complete problem. A set of partition problems that required 518 seconds to be solved on a VAX/8550 computer would require only 2 seconds on the Cyber 205 under the vector mode. A partition problem with n equal to 1000 was solved in only 6.34 seconds.[[fileno]]2030256010082[[department]]資訊工程學
A New Parallel Sorting Algorithm Based upon Min-Mid-Max Operations
No full text[[abstract]]In this paper we propose a new parallel sorting algorithm which is based upon an operation which sorts three elements. This algorithm is similar to the parallel odd-even merge sorting algorithm proposed by Batcher, except in the latter, the basic operation sorts only two elements. The correctness of our algorithm is also proved.[[fileno]]2030256010086[[department]]資訊工程學
Discussions on "the IAEA Guidelines for Assessing Volcanic Hazards at Nuclear Facilities"
No full text[[abstract]]The International Atomic Energy Agency's (IAEA, an agency of the United Nations) guidelines for assessing volcanic hazards at nuclear facilities have been revised recently by McBirney and Godoy (2003). Although these guidelines have considered many important criteria and can be applied to broader aspects of hazard assessment to nuclear power plant (NPP), potential hazards from submarine volcanic activities have been overlooked. We would like to provide some feedback to this important document in order to make it more complete.
The IAEA's guidelines for assessing volcanic hazards at nuclear facilities have focused primarily on the potential risks of inland volcanic activities, although the tsunamis hazard was also discussed. While inland volcanic activities are indeed the primary concern for the potential volcanic hazards for nuclear facilities, we would like to point out that the floating pumice particles of submarine volcanic eruptions is also a potential source of volcanic hazard for nuclear facilities.
In general, nuclear power plant (NPP) needs an abundant supply of clean water for cooling. Considering the cost for the operation of a NPP, ocean water should be one of the best candidates of cooling water. Therefore, any pumices, ash particles, and seawater whose chemical compositions have been altered due to submarine volcanic activities (even a small eruption) are sucked into the cooling system; this could deeply affect the cooling system of the NPP, and which may in turn trigger more catastrophic disasters. As a result, both tsunamis and submarine volcanic activities should be considered as the potential sources of volcanic hazards.[[fileno]]2010101010037[[department]]物理
The "real effect" for thermo-equilibrium Ca isotope fractionation with temperature variation
No full text[[fileno]]2010101010040[[department]]物理
Branch, spur, and feather formation in spiral galaxies
Get PDF[[abstract]]We use hydrodynamic simulations to investigate the response of geometrically thin, self-gravitating, singular isothermal disks of gas to imposed rigidly rotating spiral potentials. By minimizing reflection-induced feedback from boundaries, and by restricting our attention to models where the swing parameter Xsimilar to10, we minimize the swing amplification of global normal modes even in models where Toomre's Q(g)similar to1-2 in the gas disk. We perform two classes of simulations: short-term ones over a few galactic revolutions where the background spiral forcing is large, and long-term ones over many galactic revolutions where the spiral forcing is considerably smaller. In both classes of simulations, the initial response of the gas disk is smooth and mimics the driving spiral field. At late times, many of the models evince substructure akin to the so-called branches, spurs, and feathers observed in real spiral galaxies. We comment on the parts played respectively by ultraharmonic resonances, reflection off internal features produced by nonlinear dredging, and local, transient, gravitational instabilities within spiral arms in the generation of such features. Our simulations reinforce the idea that spiral structure in the gaseous component becomes increasingly flocculent and disordered with the passage of time, even when the background population of old disk stars is a grand-design spiral. We speculate that truly chaotic behavior arises when many overlapping ultraharmonic resonances develop in reaction to an imposed spiral forcing that has itself a nonlinear, yet smooth, wave profile.[[fileno]]2010118010026[[department]]物理
Self-similar champagne flows in HII regions
Get PDF[[abstract]]We consider the idealized expansion of an initially self-gravitating, static, singular, isothermal cloud core. For t greater than or equal to 0, the gas is ionized and heated to a higher uniform temperature by the formation of a luminous but massless star in its center. The approximation that the mass and gravity of the central star are negligible for the subsequent motion of the H II region holds for distances r much greater than similar to100 AU and for the massive cloud cores that give rise to high-mass stars. If the initial ionization and heating are approximated to occur instantaneously at t = 0, then the subsequent flow (for r >> 100 AU) caused by the resulting imbalance between self-gravity and thermal pressure is self-similar. Because of the steep density profile (rho proportional to r(-2)), pressure gradients produce a shock front that travels into the cloud, accelerating the gas to supersonic velocities in what has been called the "champagne phase.'' The expansion of the inner region at t > 0 is connected to the outer envelope of the now ionized cloud core through this shock, whose strength depends on the temperature of the H II gas. In particular, we find a modified Larson-Penston (L-P) type of solution as part of the linear sequence of self-similar champagne outflows. The modification involves the proper insertion of a shock and produces the right behavior at infinity (v --> 0) for an outflow of finite duration, reconciling the long-standing conflict on the correct (inflow or outflow) interpretation for the original L-P solution. For realistic heating due to a massive young central star that ionizes and heats the gas to similar to10(4) K, we show that even the self-gravity of the ionized gas of the massive molecular cloud core can be neglected. We then study the self-similar solutions of the expansion of H II regions embedded in molecular clouds characterized by more general power-law density distributions: rho proportional to r(-n) with 3/2 3. We show that this happens because the model includes an origin where the pressure driving the shock diverges because the enclosed heated mass is infinite. Our results imply that the continued photoevaporation of massive reservoirs of neutral gas (e.g., surrounding disks and/or globules) near the embedded ionizing source is required in order to maintain over a significant timescale the emission measure observed in champagne flows.[[fileno]]2010118010029[[department]]物理
A toy model of giant molecular clouds
Get PDF[[abstract]]We idealize giant molecular clouds as flattened sheets, incorporating the concepts of strong magnetization, star formation from dense cores, and efficient bipolar outflows. This toy model reproduces the observed tendency of molecular clouds to form filaments without the need to invoke large-scale overall gravitational collapse that would yield a rate of star formation far in excess of empirical Galactic values. It yields line width-size relationships that are in rough accord with observations, although better simulations are needed that remove the imposition of periodic boundary conditions and allow for a more systematic treatment of subgrid turbulence. The model lends credence to earlier ideas concerning the self-regulation of star formation by turbulence and photoionization.[[fileno]]2010118010040[[department]]物理
THE DENSE INTERSTELLAR-MEDIUM AND THE BIRTHPLACES OF OB STARS
No full text[[abstract]]A review is presented of Stromgren's research on the relationships among atomic, ionized, and molecular hydrogen in the Galaxy and the spatial distribution and kinematics of OB stars. Particular attention is given to the development of density-wave theory, the implication that the pattern of the formation of OB stars in a spiral galaxy should rotate at a constant angular speed, which differs generally from the mean material speed of the interstellar gas. Other theories involving the mechanical support of molecular clouds; triggered star formation; and the relationships among H2, H I, and H II are discussed.[[fileno]]2010118010077[[department]]物理