Hazard rate estimation of a mixture model with censored lifetimes     

S. E. Ahn  C. S. Park  H. M. Kim 《Stochastic Environmental Research and Risk Assessment (SERRA)》2007,21(6):711-716

This paper is intended to compare the hazard rate from the Bayesian approach with the hazard rate from the maximum likelihood estimate (MLE) method. The MLE of a parameter is appropriate as long as there are sufficient data. For various reasons, however, sufficient data may not be available, which may make the result of the MLE method unreliable. In order to resolve the problem, it is necessary to rely on judgment about unknown parameters. This is done by adopting the Bayesian approach. The hazard rate of a mixture model can be inferred from a method called Bayesian estimation. For eliciting a prior distribution which can be used in deriving a Bayesian estimate, a computerized-simulation method is introduced. Finally, a numerical example is given to illustrate the potential benefits of the Bayesian approach.  相似文献   

西安市大降水环流特征分析     

林杨  薛春芳  邓小丽  赵荣 《陕西气象》2007,(4):16-19

病虫害是农业气象灾害衍生灾害，是危害农业生产的重要自然灾害，往往使农作物生长和发育受到抑制和损害，造成农作物产量减少或品质下降。通过对农业病虫害的发生特点及相关农业气象条件进行分析，对农业增产增收、可持续发展具有重要意义。  相似文献   

Characteristics of biomass burning aerosol and its impact on regional air quality in the summer of 2003 at Gwangju, Korea   总被引：1，自引：0，他引：1  

S.Y. Ryu  B.G. Kwon  Y.J. Kim  H.H. Kim  K.J. Chun 《Atmospheric Research》2007,84(4):362-373

The main objective of this study is to investigate the chemical characteristics of biomass burning aerosol and its impact on regional air quality during an agricultural waste burning period in early summer in the rural areas of Korea. A 12-h integrated intensive sampling of biomass burning aerosol in the fine and coarse modes was conducted on 2–20 June 2003 in Gwangju, Korea. The collected samples were analyzed for concentrations of mass, ionic, elemental, and carbonaceous species. Average concentrations of fine and coarse mass were measured to be 67.9 and 18.7 μg m^− 3 during the biomass burning period, 41.9 and 18.8 μg m^− 3 during the haze period, and 35.6 and 13.3 μg m^− 3 during the normal period, respectively. An exceptionally high PM_2.5 concentration of 110.3 μg m^− 3 with a PM_2.5/PM₁₀ ratio of 0.79 was observed on 6 June 2003 during the biomass burning period. The potassium ratio method was used to identify biomass burning samples. The average ratio of potassium in the fine mode to the coarse mode (FK/CK) was 23.8 during the biomass burning period, 6.0 during the haze period, and 4.7 during the normal period, respectively. A FK/CK ratio above 9.2 was considered a criterion for biomass burning event in this study. Particulate matter from the open field burning of agricultural waste has an adverse impact on visibility, human health, and regional air quality.  相似文献   

The origin and evolution of mineralizing fluids in the Cretaceous Gyeongsang Basin, Southeastern Korea   总被引：1，自引：0，他引：1  

S.-G. Choi  S.J. Pak  C.S. Kim  I.-C. Ryu  S.-M. Wee 《Journal of Geochemical Exploration》2006,89(1-3):61

Ferroalloy, base-metal and precious-metal deposits in or around the Gyeongsang Basin, which is located in the Cretaceous volcano-sedimentary terrain at the southeastern Korea, displays a genetic relationship with subvolcanic activities of Late Cretaceous to Tertiary age. Diverse mineralization, which occurs as vein, breccia-pipe, porphyry-style and skarn deposits, took place from 108 to 45 Ma that overlapped with polyphase episodes of igneous activity. Based on the mineralogy, host rock, fluid inclusion and stable isotope data of the deposits, the systematic variation of physicochemical conditions is thought to be due to their relative positions with respect to a magma source that is genetically related to a low to intermediate-sulfidation porphyry system. There appears to be a systematic decrease towards δ¹⁸O_H2O values from copper (-gold) and ferroalloy deposits through polymetallic to precious-metal ones. However, Cu (-Au) or Fe–Mo–W deposits are proximal to a magmatic source, whereas polymetallic or precious-metal deposits are more distal to transitional.  相似文献   

Paleoproductivity evolution off central Chile from the Last Glacial Maximum to the Early Holocene   总被引：1，自引：0，他引：1  

Oscar E. Romero  Jung-Hyn Kim  Dierk Hebbeln 《Quaternary Research》2006,65(3):519-525

A geochemical and paleontological reconstruction of paleoproductivity, upwelling intensity and sea surface temperature (SST) off central Chile at 35°S (GeoB3359-3) reveals marked changes from the Last Glacial Maximum (LGM) through the Early Holocene. Surface-water productivity was determined by the interaction between the atmospheric (the Southern Westerlies) and oceanographic (the Antarctic Circumpolar Current, ACC) systems from the LGM through early Termination I (TI). The northward shift of the climate zones during the LGM brought the ACC, as the main macronutrient source, closer to the GeoB3359-3, SST lowered, and surface water productivity and accumulation rates of biogenic components enhanced. With the poleward return of the Southern Westerlies and the ACC, the subtropical high-pressure system became the dominant atmospheric component southward till 35°S during the late TI and Early Holocene and caused surface water productivity to increase through enhanced upwelling.  相似文献   

Tectonic evolution of Korean Peninsula and adjacent crustal fragments in Asia: Introduction     

Chang Whan Oh  K. Sajeev  Sung Won Kim  M. Santosh 《Gondwana Research》2006,9(1-2):19

  相似文献   

B NMR investigation of boron interaction with mineral surfaces: Results for boehmite, silica gel and illite     

Yeongkyoo Kim  R. James Kirkpatrick 《Geochimica et cosmochimica acta》2006,70(13):3231-3238

Boron is an important micronutrient for plants but is toxic at high pore solution concentrations. Its mobility and migration in many geochemical environments is often controlled by reactions with mineral surfaces, and thus its speciation on mineral surfaces has been extensively investigated. Most previous studies have used IR spectroscopy to characterize the surface B-environments. We present here the first ¹¹B MAS NMR study of surface sorbed boron on minerals. The results demonstrate the capability of this method to effectively probe the local structure of the sorption sites at total B-concentrations in the samples as small as 0.03 wt% and to provide insight into the mechanisms of sorption. Signal is readily resolved for both trigonal (B(3)) and tetrahedral (B(4)) boron exchanged onto boehmite, silica gel and illite, and the resonances are readily assigned on the basis of chemical shift and quadrupole coupling constant. Boron surface densities on illite are approximately order of magnitude greater than on silica gel or boehmite. For boehmite, both B(3) and B(4) occur dominantly as inner-sphere complexes formed by ligand exchange reaction with surface aluminol sites. The B(3)/[B(3) + B(4)] ratio of approximately 0.87 does not vary significantly with pH from 3 to 11, with solution B-concentration, or with washing. The occurrence of B(3) and B(4) as inner-sphere complexes is in agreement with previous suggestions from IR studies of B-sorption on iron hydroxide, allophone, kaolinite, and hydrous ferric oxide. For silica gel, B(3) and B(4) occur principally as outer-sphere complexes or as residual precipitate from un-removed solution. The B(3)/B(4) ratio decreases with increasing pH paralleling the speciation in solution, but the relative abundance of B(4) is greater than in solution. A small fraction of the B(4) occurs as inner-sphere complexes with B(4)-O-Si linkages formed by ligand exchange reaction with silanol sites. For illite, surface boron occurs as outer-sphere B(3) and B(4), as for silica gel, and as inner-sphere B(3) and B(4), as for boehmite. Outer-sphere B(3) and B(4) are dominant at pH 3 and 5, whereas inner-sphere B(3) and B(4) are dominant at pH 9 and 11. The inner-sphere complexes probably form dominantly by ligand exchange reactions involving sites on the broken edges of illite layers.  相似文献   

Effects of surfactants and electrolyte solutions on the properties of soil     

Junboum Park  Cumaraswamy Vipulanandan  Jee Woong Kim  Myoung Hak Oh 《Environmental Geology》2006,49(7):977-989

Biosurfactants are frequently used in petroleum hydrocarbon and dense non-aqueous phase liquids (DNAPLs) remediation. The applicability of biosurfactant use in clayey soils requires an understanding and characterization of their interaction. Comprehensive effects of surfactants and electrolyte solutions on kaolinite clay soil were investigated for index properties, compaction, strength characteristics, hydraulic conductivities, and adsorption characteristics. Sodium dodecyl sulfate (SDS) and NaPO₃ decreased the liquid limit and plasticity index of the test soil. Maximum dry unit weights were increased and optimum moisture contents were decreased as SDS and biosurfactant were added for the compaction tests for mixtures of 30% kaolinite and 70% sand. The addition of non-ionic surfactant, biosurfactant, and CaCl₂ increased the initial elastic modulus and undrained shear strength of the kaolinite–sand mixture soils. Hydraulic conductivities were measured by fixed-wall double-ring permeameters. Results showed that the hydraulic conductivity was not significantly affected, but slightly decreased from 1×10⁻⁷ cm/s (water) to 0.3×10⁻⁷ cm/s for Triton X-100 and SDS. The adsorption characteristics of the chemicals onto kaolinite were also investigated by developing isotherm curves. SDS adsorbed onto soil particles with the strongest bonding strength of the fluids tested. Correlations among parameters were developed for surfactants, electrolyte solutions, and clayey soils.  相似文献   

Infrared Spectroscopy of Comet Hale-Bopp     

Weaver  H. A.  Brooke  T. Y.  Chin  G.  Kim  S. J.  Bockelée-Morvan  D.  Davies  J. K. 《Earth, Moon, and Planets》1997,78(1-3):71-80

High resolution (λ/δλ ∼ 20,000) spectra of comet C/1995 O1 (Hale-Bopp) in the 2–5 μm region were obtained during UT 2–5 March 1997 using CSHELL at the NASA Infrared Telescope Facility (IRTF) on Mauna Kea. The heliocentric and geocentric distances of the comet were ∼1.1 AU and ∼1.5 AU,respectively. We detected emission lines of the gas-phase molecules H₂O, ₄, C₂H₆, C₂H₂, HCN, and CO and derived absolute production rates and relative abundances for all species. We also used the 2-dimensional nature of the CSHELL data to investigate the spatial distribution of the molecules and find evidence that CO was derived at least partly from an extended source in the coma. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

The effect of an electric field induced by a time-dependent ring current on the particle drift motion     

C. S. Wang  J. S. Kim 《Planetary and Space Science》1972,20(12):2039-2044

The effect of an electric field induced by a rapidly decaying ring current on the motion of charged particles in the magnetosphere has been investigated using Euler potentials. For a model consisting of the earth dipole and the symmetric ring current, the electric field satisfies the condition E . B = 0.

Under this circumstance, the E × B drift of the particle can be identified as the motion of the magnetic field lines and vice versa. The time dependent electric field induced can be evaluated in a Spherical polar coordinate system by the formula

where and β are Euler potentials.

A model calculation on the particle drift velocity v_D = E × B/B² shows that the radial component of the drift velocity is in good agreement with those deduced from whistler duct studies.  相似文献