An initial demonstration of underwater acoustic communication using time reversal   总被引：3，自引：0，他引：3  

Edelmann  G.F. Akal  T. Hodgkiss  W.S. Seongil Kim Kuperman  W.A. Hee Chun Song 《Oceanic Engineering, IEEE Journal of》2002,27(3):602-609

In July 1999, an at-sea experiment to measure the focus of a 3.5-kHz centered time-reversal mirror (TRM) was conducted in three different environments: an absorptive bottom, a reflective bottom, and a sloping bottom. The experiment included a preliminary exploration of using a TRM to generate binary-phase shift keying communication sequences in each of these environments. Broadside communication transmissions were also made, and single-source communications were simulated using the measured-channel response. A comparison of the results is made and time reversal is shown to be an effective approach for mitigating inter-symbol interference caused by channel multipath.  相似文献   

Instrumentation and Numerical Analysis of Cylindrical Diaphragm Wall Movement During Deep Excavation at Coastal Area     

Dong Soo Kim  Byoung Chul Lee 《Marine Georesources & Geotechnology》2005,23(1):117-136

The lateral deflection of a cylindrical diaphragm wall and the associated ground movement induced by deep excavation are analyzed by performing site instrumentations and numerical analyses in the coastal area of Korea. Wall lateral deflection, rebar stress, and pore water pressure were measured and analyzed in eight directions. Variations of soil properties with the decrease of confining pressure are compared by performing various in situ tests before ad after excavation. To calculate the wall lateral deflection accurately, the effects of small strain nonlinearity, confining pressure, and the hysteresis loading/unloading loop developed during excavation are considered in the proposed numerical analysis. By comparing numerical results with measured ones, the importances of considering small strain nonlinearity and confining pressure reduction in the nonlinear (FEM) are emphasized. Also, the effects of wall stiffness on the performance of cylindrical diaphragm walls are studied for future similar excavation in the coastal area.  相似文献   

Identification of constitutive androstane receptor cDNA in northern fur seal (Callorhinus ursinus)     

Hiroki Sakai  Hisato Iwata  Eun-Young Kim  Shinsuke Tanabe  Norihisa Baba 《Marine environmental research》2004,58(2-5):107

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Tephrostratigraphy and paleo-environmental implications of Late Quaternary sediments and interstitial water in the western Ulleung Basin, East/Japan Sea     

M. H. Park  J. H. Kim  I. S. Kim  B. J. Ryu  K. M. Yu 《Geo-Marine Letters》2005,25(1):54-62

Two piston cores, collected from the western Ulleung Basin of the East/Japan Sea, were used to investigate the Late Quaternary tephrostratigraphy, lithology, and mineralogy of the sediments, as well as the elemental composition of both sediments and interstitial water, and their paleo-environmental implications. The cores show two lapilli tephra layers and one rhyolitic ash layer at the boundaries between sedimentary lithofacies units I, II, and III. These layers can be correlated with the well-known Ulleung-Oki (ca. 9.3 ka; boundary of units I/II), Ulleung-Yamato (ca. 25–33 ka), and Aira-Tanzawa (ca. 25.1 ka; boundary of units II/III) layers, respectively. These data suggest that the cores cover the period from the middle stage of marine isotope stage (MIS) 3 to the Holocene. In each core, a so-called dark laminated mud (DLM) layer in unit II commonly has high contents of Si and Al, suggesting that the DLM layer generally contains significant amounts of fine-grained silicates and/or aluminosilicates. In addition, these DLM layers are enriched in Fe relative to Mn, iron being predominantly bound in framboidal pyrite. The size distribution of pyrite in the DLM layers suggests that these have formed under anoxic (euxinic) conditions at times of reduced water circulation in the basin during sea-level lowstand (euxinic environment). The C/N ratios [5–12] suggest that sedimentary organic matter in the cores is predominantly of marine origin. Total organic carbon (TOC) contents increased shortly before Termination I. This could have been caused by an increased flux of marine organic matter in association with sea-level rise. The C and S values of units II and III (Late Pleistocene sediments; C: <2.0%; S: 0.5–2.1%) suggest a more euxinic environment than that of unit I (Holocene sediments; C: 1.0–3.5%; S: <1.0%). Concentrations of SO₄^2– in the interstitial water decrease with increasing burial depth, whereas CH₄ concentrations show the reverse trend. Therefore, it seems that sulfate reduction, probably related to microbial activity, predominates in the upper core sections (<5 m), shifting to methanogenesis in the lower core sections.  相似文献   

Spectrophotometric determination of pH in seawater off Taiaroa Head,Otago, New Zealand: Full-spectrum modelling and prediction of pCO₂ levels     

Shane M. Ohline  Malcolm R. Reid  Shamus L.G. Husheer  Kim I. Currie  Keith A. Hunter 《Marine Chemistry》2007

Accurate measurement of seawater pH has long been sought by marine chemists (for example: [Dickson, A.G. 1993a. The measurement of sea water pH. Marine Chemistry, 44, 131–142, Dickson, A.G. 1993b. pH buffers for sea water media based on the total hydrogen ion concentration scale. Deep-Sea Research, 40, 107–118; Zhang, 1996; Tapp, M., Hunter, K.A., Currie, K. and Macaskill, B. 2000. Apparatus of continuous-flow underway spectrophotometric measurement of surface water pH. Marine Chemistry 72(2–4), 193–202; Friis, K., Koetzinger, A., Wallace, D.W.R. 2004. Spectrophotometric pH measurement in the ocean: Requirements, design and testing of an autonomous charge-coupled device detector system. Limnology and Oceanography: Methods 2, 126–136]. Recently, such attempts have taken on greater significance as anthropogenic carbon dioxide emissions may create rapidly changing oceanic pH. Spectrophotometric techniques have been accepted generally as the best for determination of seawater pH. Here we report a new technique using thymol blue as the indicator dye and fitting the entire spectrum from 400 to 900 nm rather than measuring the absorbance values at only two or three points in the spectrum. This full-spectrum modelling enables a reduction in signal to noise over other techniques. In the laboratory, we find with seawater samples a pH precision increase of five-fold “within” a sample and seven-fold “between” samples when comparing the full spectrum to the three-point method of analysis [Zhang, H., Byrne, R.H. 1996. Spectrophotometric pH measurements of surface seawater at in-situ conditions: absorbance and protonation behaviour of thymol blue. Marine Chemistry 52, 17–25].  相似文献   

Bringing GPS into harsh environments for fully automated deformation monitoring     

Jason Bond  Adam Chrzanowski  Don Kim 《GPS Solutions》2008,12(1):1-11

Engineering projects that require deformation monitoring frequently utilize geodetic sensors to measure displacements of target points located in the deformation zone. In situations where control stations and targets are separated by a kilometer or more, GPS can offer higher precision position updates at more frequent intervals than can normally be achieved using total station technology. For large-scale deformation projects requiring the highest precision, it is therefore advisable to use a combination of the two sensors. In response to the need for high precision, continuous GPS position updates in harsh deformation monitoring environments, a software has been developed that employs triple-differenced carrier-phase measurements in a delayed-state Kalman filter. Two data sets were analyzed to test the capabilities of the software. In the first test, a GPS antenna was displaced using a translation stage to mimic slow deformation. In the second test, data collected at a large open pit mine were processed. It was shown that the delayed-state Kalman filter developed could detect millimeter-level displacements of a GPS antenna. The actual precision attained depends upon the amount of process noise infused at each epoch to accommodate the antenna displacements. Higher process noise values result in quicker detection times, but at the same time increase the noise in the solutions. A slow, 25 mm displacement was detected within 30 min of the full displacement with sigma values in E, N and U of ±10 mm or better. The same displacement could also be detected in less than 5 h with sigma values in E, N and U of ±5 mm or better. The software works best for detecting long period deformations (e.g., 20 mm per day or less) for which sigma values of 1–2 mm are attained in all three solution components. It was also shown that the triple-differenced carrier-phase observation can be used to significantly reduce the effects of residual tropospheric delay that would normally plague double-differenced observations in harsh GPS environments.

Don KimEmail:

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A bootstrap based space–time surveillance model with an application to crime occurrences     

Youngho Kim  Morton O’Kelly 《Journal of Geographical Systems》2008,10(2):141-165

This study proposes a bootstrap-based space–time surveillance model. Designed to find emerging hotspots in near-real time, the bootstrap based model is characterized by its use of past occurrence information and bootstrap permutations. Many existing space–time surveillance methods, using population at risk data to generate expected values, have resulting hotspots bounded by administrative area units and are of limited use for near-real time applications because of the population data needed. However, this study generates expected values for local hotspots from past occurrences rather than population at risk. Also, bootstrap permutations of previous occurrences are used for significant tests. Consequently, the bootstrap-based model, without the requirement of population at risk data, (1) is free from administrative area restriction, (2) enables more frequent surveillance for continuously updated registry database, and (3) is readily applicable to criminology and epidemiology surveillance. The bootstrap-based model performs better for space–time surveillance than the space–time scan statistic. This is shown by means of simulations and an application to residential crime occurrences in Columbus, OH, year 2000.  相似文献   

Estimating hydraulic conductivity using grain-size analyses, aquifer tests, and numerical modeling in a riverside alluvial system in South Korea   总被引：2，自引：0，他引：2  

Jae-Yeol Cheong  Se-Yeong Hamm  Hyoung-Soo Kim  Eun-Joung Ko  Kyounghee Yang  Jeong-Hwan Lee 《Hydrogeology Journal》2008,16(6):1129-1143

Hydraulic conductivity (K) for an alluvial system in a riverbank filtration area in Changwon City, South Korea, has been studied using grain-size distribution, pumping and slug tests, and numerical modeling. The alluvial system is composed of layers: upper fine sand, medium sand, lower fine sand, and a highly conductive sand/gravel layer at the base. The geometric mean of K for the sand/gravel layer (9.89?×?10^?4 m s^?1), as determined by grain-size analyses, was 3.33 times greater than the geometric mean obtained from pumping tests (2.97?×?10^?4 m s^?1). The geometric mean of K estimates obtained from slug tests (3.08?×?10^?6 m s^?1) was one to two orders of magnitude lower than that from pumping tests and grain-size analyses. K estimates derived from a numerical model were compared to those derived from the grain-size methods, slug tests and pumping tests in order to determine the degree of deviation from the numerical model. It is considered that the K estimates determined by the slug tests resemble the uppermost part of the alluvial deposit, whereas the K estimates obtained by grain-size analyses and pumping tests are similar to those from the numerical model for the sand/gravel layer of the riverside alluvial system.  相似文献   

The contact binary system YY Eri     

E. Budding  C-H. Kim  O. Demircan  Z. Müyesseroğlu  K. Saijo  T. Banks 《Astrophysics and Space Science》1996,246(2):229-242

Relatively new and unanalysed photometric data-sets of the contact binary system YY Eri are presented. The light curves have been analysed using information limit optimization techniques, and the Binary Maker program of Bradstreet (1992).Comparison of the results allows insight into determinacy questions affecting the W UMa type of light curve, which relates to our general understanding of contact binaries. A limiting contact configuration cannot be ruled out on the basis of empirical data-analysis alone.Very careful analysis of the photospheric flux distribution over the surface of the Sun may help establish appropriate values of the gravity brightening parameter for cool dwarf stars. At present, however, empirical photometric information on contact binaries is non-discriminatory: i.e. alternative cosmogonies can find alternative support from available evidence. The implication is then for more and better observational data to allow better real independent parameter determination.  相似文献   

Study on the kinetics of iron oxide leaching by oxalic acid   总被引：2，自引：0，他引：2  

Suong Oh Lee  Tam Tran  Yi Yong Park  Seong Jun Kim  Myong Jun Kim   《International Journal of Mineral Processing》2006,80(2-4):144-152

The presence of iron oxides in clay or silica raw materials is detrimental to the manufacturing of high quality ceramics. Although iron has been traditionally removed by physical mineral processing, acid washing has been tested as it is more effective, especially for extremely low iron (of less than 0.1% w/w). However, inorganic acids such as sulphuric or hydrochloric acids easily contaminate the clay products with SO₄²⁻ and Cl⁻, and therefore should be avoided as much as possible. On the other hand, if oxalic acid is used, any acid left behind will be destroyed during the firing of the ceramic products. The characteristics of dissolution of iron oxides were therefore investigated in this study.The dissolution of iron oxides in oxalic acid was found to be very slow at temperatures within the range 25–60 °C, but its rate increases rapidly above 90 °C. The dissolution rate also increases with increasing oxalate concentration at the constant pH values set within the optimum range of pH2.5–3.0. At this optimum pH, the dissolution of fine pure hematite (Fe₂O₃) (105–140 μm) follows a diffusion-controlled shrinking core model. The rate expression expressed as 1 − (2 / 3)x − (1 − x)^2 / 3 where x is a fraction of iron dissolution was found to be proportional to [oxalate]^1.5.The addition of magnetite to the leach liquor at 10% w/w hematite was found to enhance the dissolution rate dramatically. Such addition of magnetite allows coarser hematite in the range 0.5–1.4 mm to be leached at a reasonable rate.  相似文献