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The Average Performance Analysis of a Closest Pair Algorithm
No full text[[abstract]]Bentley proposed a divide‐and‐conquer approach to solve the planar closest pair problem. In this paper, we shall show that the average case performance of this algorithm is proportional to the number of poins being examined.[[fileno]]2030256010030[[department]]資訊工程學
The Searching over Separators Strategy to Solve Some NP-hard Problems in Sub-exponential Time
No full text[[abstract]]In this paper we propose a new strategy for designing algorithms, called the searching over separators strategy. Suppose that we have a problem where the divide-and-conquer strategy can not be applied directly. Yet, also suppose that in an optimal solution to this problem, there exists a separator which divides the input points into two parts,A d andC d, in such a way that after solving these two subproblems withA d andC d as inputs, respectively, we can merge the respective subsolutions into an optimal solution. Let us further assume that this problem is an optimization problem. In this case our searching over separators strategy will use a separator generator to generate all possible separators. For each separator, the problem is solved by the divide-and-conquer strategy. If the separator generator is guaranteed to generate the desired separator existing in an optimal solution, our searching over separators strategy will always produce an optimal solution. The performance of our approach will critically depend upon the performance of the separator generator. It will perform well if the total number of separators generated is relatively small. We apply this approach to solve the discrete EuclideanP-median problem (DEPM), the discrete EuclideanP-center problem (DEPC), the EuclideanP-center problem (EPC), and the Euclidean traveling salesperson problem (ETSP). We propose O(no(ÖP ) )O(no(P)) algorithms for the DEPM problem, the DEPC problem, and the EPC problem, and we propose an O(no(Ön ) )O(no(n)) algorithm for the ETSP problem, wheren is the number of input points.[[fileno]]2030256010045[[department]]資訊工程學
The Setting Up of Isotope Dilution Mass Spectrometry for REE Analysis
No full text[[fileno]]2010101010015[[department]]物理
138La Anomaly in the Early Solar System
Get PDF[[abstract]]For every 1100 lanthanum atoms in the solar system, only one is La-138. Relative to this low abundance, even a tiny additional La-138 made by irradiating its more abundant neighboring nuclides with energetic protosolar flare particles would cause a large, hence detectable, percentage increase in La-138. Such early solar irradiation can produce many now-extinct short-lived radio nuclides (e.g., Ca-41, Mn-53, and Al-26) and is the only way to make the newly discovered Be-10 and the possibly detected Be-7, because stars destroy rather than produce Be. The alternative hypothesis to produce extinct nuclides is the injection of freshly synthesized radioactivity from a nearby asymptotic giant branch star or supernovae during solar system formation. Hoping to clarify the origin of extinct nuclides, we have been searching for La-138 excess and its possible correlation with extinct nuclides. Here we report the detection of up to 0.6% (similar to 7.5 sigma) La-138 excesses in five Allende calcium-aluminum-rich inclusions. Surprisingly, they do not correlate with 26Al, thus offering no support for making 26Al by early irradiation. Instead, La-138 excess correlates with Ti-50 excess. Current nucleosynthesis models produce Ti-50 in a rare subset of Type I supernovae whose core underwent significant gravitational collapse before carbon deflagration. Our observed correlation thus suggests that 138La also came from these rare sources, perhaps in the mantle of the white dwarf, by reactions induced by the neutrino burst emitted during core neutronization. After the explosion, La-138 was incorporated into Ti-rich dusts that later became the building material of our solar system.[[fileno]]2010101010031[[department]]物理
Absolute Ca isotopic measurement using an improved double spike technique
No full text[[abstract]]A new vector analytical method has been developed in order to obtain the true isotopic composition of the (42)Ca-(48)Ca double spike. This is achieved by using two different sample-spike mixtures combined with the double spike and natural Ca data. Because the natural sample (two mixtures) and the spike should all lie on a single mixing line, we are able to constrain the true isotopic composition of our double spike using this new approach. Once the isotopic composition of the Ca double spike is established, we are able to obtain the true Ca isotopic composition of the NIST Ca standard SRM915a, (40)Ca/(44)Ca = 46.537 +/- 2 (2 sigma(m), n = 55), (42)Ca/(44)Ca = 0.31031 +/- 1, (43)Ca/(44)Ca = 0.06474 +/- 1, and (48)Ca/(44)Ca = 0.08956 +/- 1. Despite an offset of 1.3% in (40)Ca/(44)Ca between our result and the previously reported value (Russell et al. 1978), Our data indicate all offset of 1.89 parts per thousand in (40)Ca/(44)Ca between SRM915a and seawater, entirely consistent with the published results.[[fileno]]2010101010043[[department]]物理
COLLAPSE OF MAGNETIZED MOLECULAR CLOUD CORES .1. SEMIANALYTICAL SOLUTION
No full text[[abstract]]In this paper we follow the evolution of an unstable magnetized cloud core modeled with the density distribution of a singular isothermal sphere and threaded by a uniform magnetic field. We include neutral-ion slip, and we solve the equations by an expansion about the known self-similar problem without magnetism. We find that the magnetic field does not significantly modify the standard rate of mass infall because of two offsetting effects: the Lorentz force that impedes gravitational collapse, and the increased characteristic speed that causes the initiation of infall to travel outward faster (as a fast magnetohydrodynamic wave rather than an acoustic wave). Strong magnetic pinching forces deflect infalling gas toward the equatorial plane to form a flattened disequilibrium structure (''pseudodisk'') around the central protostar. The perturbative approach allows us to calculate analytically the dependence of the radius of the pseudodisk at small times on the physical parameters of the problem when a dimensionless coefficient of order unity is supplied by a separate numerical calculation for the nonlinear flow in the inner region (Paper II).[[fileno]]2010118010064[[department]]物理
HEATING OF MOLECULAR CLOUD CORES
No full text[[abstract]]Following the work of Chu (1983), the present treatment of the role of ambipolar diffusion in the heating of molecular cloud cores calculates the quasistatic evolution of a plane-parallel self-gravitating slab of slightly ionized gas due to the ambipolar diffusion of the field. The temperature at each point of the cloud is computed in light of the most important heating and cooling processes; the results obtained are found to partially explain the thermal differences between the cores forming low- and high-mass stars.[[fileno]]2010118010087[[department]]物理
Activation of the Carbon-Carbon Bond in the Mn-mediated Cycloaddition Reaction between Disilacyclobutene and Cyclic Conjugated Dienes
No full text[[abstract]]Cycloaddition reactions between 1,1,2,2-tetrafluoro-1,2-disilacyclobutene and cyclic conjugate dienes mediated by CpMn(CO)3 under photochemical conditions generate the products resulting from a C-C cleavage of the cyclic conjugate dienes.[[fileno]]2010311010054[[department]]化學
A Novel Reaction of Ruthenium Carbonyl and Tegrafluorodisila-3,5-cyclohexadiene
No full text[[abstract]]In hexane solution, the decomposition of(1,1,6,6-tetrafluoro-3,4-di-t-butyl-1, 6-disila-2,4-hexadiene)ruthenium (II) tetracarbonyl 2, led to formation of compound (eta(4)-1, 1-difluoro-3,4-di-t-butyl-sila-2,4-cyclopentadiene)ruthenium(O)tricarbonyl 3 and monomeric SiF2 that added to cyclic diene compound 1,1,2,2-tetrafluoro-4,5-di-t-butyl-disila-3, 5-cycIohexadiene 1, to form bicyclic compound 4. SiF2 was for the first time generated at such a low temperature and trapped with a conjugated diene.[[fileno]]2010311010057[[department]]化學