Spectral analysis using orthonormal functions with a case study on the sea surface topography   总被引：1，自引：0，他引：1  

Cheinway Hwang 《Geophysical Journal International》1993,115(3):1148-1160

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Spherical harmonics are orthonormalized using the Gram-Schmidt process in a function space. The problem of linear dependence of spherical harmonics over the oceans is studied using the Gram matrices and consequently three sets of orthonormal (ON) functions have been constructed. For the process an efficient formula for computing inner products of spherical harmonics has been developed. Important spectral properties of the ON functions are addressed. The ON functions may be used for representing the sea surface topography (SST) in the analysis of satellite altimeter data. The geoid error can be transformed to a representation by the ON functions and hence the comparison of powers of the geoid error and the SST signal only over the oceans is possible, leading to a better way of determining the cut-off frequency of the SST in the simultaneous solution using satellite altimeter data. As a case study, the modified Levitus SST is expanded into the ON functions. The results show that 99.90 per cent of that signal's energy is contained within degree 24 of the orthonormal functions. Such expansions also render better spectral behaviour of oceanic signals as compared to that from spherical harmonic expansions. The study shows that these generalized Fourier functions are suitable for spectral analyses of oceanic signals and they can be applied to future altimetric mission where the geoid and the SST are to be recovered.  相似文献   

Generation of hazard-consistent fragility curves   总被引：1，自引：0，他引：1  

Howard H.M. Hwang  Jun-Rong Huo 《Soil Dynamics and Earthquake Engineering》1994,13(5)

This paper presents an analytical method for generating fragility curves of structures. In the proposed method, seismic sources, path attenuation, local soil conditions, and nonlinear building behavior are systematically considered. The uncertainties in the earthquake-site-structure system are quantified by considering the uncertainties in the seismic, site, and structural parameters that define the system. For an illustration, the proposed method is used to generate fragility curves and a damge probability matrix for Smith Hall on the main campus of The University of Memphis, Memphis, Tennessee.  相似文献   

How are storm time injections different from nonstorm time injections?     

D.-Y. Lee  J.A. Hwang  E.S. Lee  K.W. Min  W.Y. Han  U.W. Nam 《Journal of Atmospheric and Solar》2004,66(18):1715

One of the key elements of storms and substorms is the injection of energetic particles into the region of near geosynchronous orbit, that is, the sudden flux enhancement in the energy range of tens to hundreds of keV. This paper reports the observational results on how such injection features during storm times are different from those of nonstorm times. We particularly focus on the difference between proton injections and electron injections. Based on a number of storm time injection events that meet our strict selection criteria, we find a notable difference between proton injections and electron injections in the energy-spectral dependence of the flux enhancement averaged over the first 30 min after the injection onset: The average flux enhancement of many protons injections tends to be bigger at higher energy channels than at lower energy channels, but electron injections exhibit the opposite tendency for the energy-spectral dependence of flux enhancement, i.e., average flux enhancement decreasing with increasing energy. We show that this feature is almost unique only for the injection events during the storm main and early recovery phase. It is suggested that any successful scenario intended to model storm time injections should be able to explain this difference between proton injections and electron injections.  相似文献   

A simple LMS‐based approach to the structural health monitoring benchmark problem     

J. Geoffrey Chase  K. Leo Hwang  L. R. Barroso  J. B. Mander 《地震工程与结构动力学》2005,34(6):575-594

A structure's health or level of damage can be monitored by identifying changes in structural or modal parameters. However, the fundamental modal frequencies can sometimes be less sensitive to (localized) damage in large civil structures, although there are developing algorithms that seek to reduce this difficulty. This research directly identifies changes in structural stiffness due to modeling error or damage using a structural health monitoring method based on adaptive least mean square (LMS) filtering theory. The focus is on computational simplicity to enable real‐time implementation. Several adaptive LMS filtering based approaches are used to analyze the data from the IASC–ASCE Structural Health Monitoring Task Group Benchmark problem. Results are compared with those from the task group and other published results. The proposed methods are shown to be very effective, accurately identifying damage to within 1%, with convergence times of 0.4–13.0 s for the twelve different 4 and 12 degree of freedom benchmark problems. The resulting modal parameters match to within 1% those from the benchmark problem definition. Finally, the methods developed require 1.4–14.0 Mcycles of computation and therefore could easily be implemented in real time. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Coastal Gravity Anomalies from Retracked Geosat/GM Altimetry: Improvement, Limitation and the Role of Airborne Gravity Data   总被引：6，自引：0，他引：6  

Cheinway Hwang  Jinyun Guo  Xiaoli Deng  Hsin-Ying Hsu  Yuting Liu 《Journal of Geodesy》2006,80(4):204-216

We process geophysical and waveform data records of the Geosat/GM (geodetic mission) satellite altimeter mission for waveform retracking and applications. An improved threshold retracker is developed. The performances of the Beta-5, threshold and improved threshold retrackers are assessed over waters around Taiwan. The improved threshold retracker outperforms the other two. The improvement in the accuracy of sea surface height (SSH) is investigated according to marine zone and the distance of waters to the shore. The improvement rate increases closer to the land, with the largest improvement rate of about 20% in waters within 10 km of the shore. Over waters around islands and coasts, there are still retracked SSHs with large errors. Least-squares collocation is used to compute gravity anomalies from the Geosat/GM altimeter data. Use of retracked SSHs improves the accuracy of gravity anomalies by about 11%. Adding airborne gravity data further improves the accuracy, especially in the immediate vicinity of the coasts. Tide model errors over coastal waters remain a problem in altimetry applications, even if the waveforms are properly retracked.  相似文献   

Mineralogy,geochemistry and petrogenesis of the Metters Bore No. 1 lamproite pipe,Calwynyardah Field,West Kimberley Province,Western Australia     

Hwang  P.  Taylor  W. R.  Rocky  N. M. S.  Ramsay  R. R. 《Mineralogy and Petrology》1994,51(2-4):195-226

Summary The Metters Bore No. 1 lamproite (MB1) is a small unexposed pipe located in the Calwynyardah field of the Miocene West Kimberley lamproite province. Microdiamonds have been recovered from bulk sampling of the pipe but no macrodiamonds (>0.8 mm) have been found. The pipe contains both volcaniclastic and magmatic (i.e. non-fragmental, extrusive-to-hypabyssal facies) lamproite. The latter rock is dominantly olivine-leucite-diopside lamproite and comprises phenocrysts and microphenocrysts of diopside, altered olivine ( Fo₉₁), and rare phlogopite, together with phenocrysts and glomeroporphyritic aggregates of altered leucite. These are set in an altered, fine-grained to glassy groundmass including diopside, leucite, priderite, apatite, less abundant chrome-spine', perovskite, interstitial richterite with minor calcic amphibole, ilmenite, sphene and wadeite. Mineral compositions are complex and variable: for example: five compositionally distinct fields can be recognizedamong the diopsides, and three among the phlogopites. The Ti-rich, Al-poor diopsides, Ti-F-rich, Al-poor phlogopites, and potassium titanian richterites all have apparent tetrahedral site deficiencies which can best be explained by tetrahedral substitution of Ti⁴⁺ and/or Mg²⁺; no substitution of Fe³⁺ is indicated. Three major types of spinel are recognized: olivine-included titaniferous magnesiochromite (TMC), xenocrystic aluminous magnesiochromite (AMC) and leucite-included pleonaste. Spinel-olivine-melt oxygen barometry indicates that the TMC spine's crystallized from evolving lamproite magma under low oxygen fugacity conditions (MW to IW). Manganiferous groundmass ilmenite has low calculated Fe₂O₃ (< 1 wt%), also consistent with reduced conditions. The maintenance of a low oxidation state during magmatic crystallization, a feature shared with the Argyle olivine-lamproite, is considered a significant factor in preservation of the MB1 microdiamond population. Xenocrystic minerals encountered in heavy mineral concentrates (HMC) indicate that the MB1 lamproite sampled upper mantle spinel ±garnet lherzolite from >60 km depth and crustal mafic rocks. Geochemically, MB1 is typical of West Kimberley leucite-lamproites, which are characterized by high TiO₂ (> 4 wt%), low CaO (< 5 wt%), MgO < 10wt%, and enrichment in incompatible elements (Rb, Sr, Ba, LREE, etc.). Although MB1 is an olivine-bearing lamproite, it has source-related geochemical features, e.g. mantle-normalized Sc/V and Zr/Nb ratios of < 0.75 and > 0.6, respectively, that are similar to other West Kimberley leucite-lamproites and distinct from olivine-lamproites. Petrogenetically, the bulk composition and low magmatic oxidation state of MB1 supports an origin by melting of phlogopite-bearing harzburgitic source under reduced fO₂ (< MW) conditions.

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Mineralogie, geochemie und petrogenese der lamproit-pipe Metters Bore No. 1, Kalwynyardah Field, West Kimberley Provinz, West-Australien

Zusammenfassung Der Lamproit Metters Bore No. 1 (MB1) ist eine kleine, nicht an der Oberfläche aufgeschlossene Pipe im Kalwynyardah Gebiet der miozänen Lamproit-Provinz von West Kimberley. Mikrodiamanten sind bei der Untersuchung von Proben aus der Pipe gefunden worden, jedoch keine Makrodiamanten (> 0.8 mm). Die Pipe enthält sowohl vulkanoklastischen wie magmatischen Lamproit (nicht-fragmentierte extrusive bis hypabyssische Fazies). Bei dem magmatischen lamproit handeltes sich um einen Olivin-Leuzit-Diopsid-Lamproit mit Kristallen und Mikrokristallen von Diopsid, umgewandeltem Olivin ( Fo₉₁), seltener Phlogopit, zusammen mit Kristallen und glomeroporphyritischen Aggregaten von umgewandeltem Leuzit. Diese sitzen in einer umgewandelten, feinkörnigen bis glasigen Grundmasse mit Diopsid, Leuzit, Priderit, Apatit, seltener Chromspinell, Perovskit, Richterit mit geringen Mengen an Kalziumamphibol, Ilmenit, Titanit und Wadeit. Die Mineralzusammensetzungen sind komplex und variabel: so können z.B. fünf der Zusammensetzung nach eindeutig definierte Felder für die Diopside nachgewiesen werden und drei solche für die Phlogopite. Die Ti-reichen Al-armen Diopside, Ti-F-reiche Al-arme Phlogopite und Kalium-Titan-Richterite haben alle reduzierte Besetzungen von Tetraederstellen, die am besten durch tetraedrische Substitution von Ti⁴⁺ und/oder Mg` erklärt werden können. Es gibt keine Hinweise für Substition von Fe³⁺. Drei Haupttypen von Spinellen kommen vor: Titan-führender Magnesiochromit (TMC) als Einschlüsse in Olivin, aluminiumführender Magnesiochromit (AMC) und Pleonast, der in Leuzit eingeschlossen ist. Sauerstoffbarometrie (Spinell-Olivin-Schmelze) zeigt, daß die TMC Spinelle von einem fraktionierten lamproitischen Magma bei niedriger Sauerstofffugazität (MW bis IW) kristallisiert sind. Manganführender Ilmenit der Grundmasse hat niedrige berechnete Fe₂O₃ Gehalte (< 1 %), und auch das entspricht reduzierenden Bedingungen. Die Erhaltung eines niedrigen Oxydationsstatus während der magmatischen Kristallisation ist eine Eigenschaft, die auch im Olivin-Lamproit der Argyle Pipe zu beobachten ist. Dies wird als ein signifikanter Faktor für den Erhalt der Mikrodiamanten in MBI gesehen. Xenokristalle die in Schwermineral-Konzentraten (HMC) vorkommen, weisen darauf hin, daß der MB1 Lamproit Material des oberen Mantels (Spinell ± Granatlherzolit) aus mehr als 60 km Tiefe, sowie mafische Gesteine der Kruste aufgenommen hat. Geochemisch gesehen ist MB1 typisch für die Leuzit-Lamproite von West Kimberley, welche durch hohe TiO₂ (> 4 wt.%), niedrige CaO (< 5 wt.%), MgO (< 10 wt.%) und Anreicherung von inkompatiblen Elementen (Rb, Sr, Ba, LSEE, etc.) charakterisiert werden. Obwohl MB1 ein Olivin-führender Lamproit ist, zeigt er geochemische Eigenschaften, wie Mantel-normalisierte Sc/V und Zr/Nb Verhältnisse von < 0.75 und > als 0.6, die ähnlich anderen Leuzit-Lamproiten von West Kimberley sind und sich von Olivin-Lamproiten unterscheiden. Petrogenetisch gesehen weisen sowohl die Gesamtzusammensetzung als auch der niedrige magmatische Oxydationsstatus von MBI auf eine genese durch Aufschmelzen von Phlogopit-führendem Harzburgit unter reduzierenden f0₂ (< MW) Bedingungen hin.

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Deceased

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With 12 Figures  相似文献   

Attenuation relations of Arias intensity based on the Chi-Chi Taiwan earthquake data   总被引：1，自引：0，他引：1  

H. Hwang  C. K. Lin  Y. T. Yeh  S. N. Cheng  K. C. Chen 《Soil Dynamics and Earthquake Engineering》2004,24(7):509-517

This paper presents a derivation of attenuation relations of Arias intensity for various site conditions based on the strong-motion data recorded in the 1999 Chi-Chi Taiwan earthquake. The data are from the mainshock and three large aftershocks with stations in the footwall area and in the area away from the fault. At each station, Arias intensity is computed from two horizontal acceleration time histories. The Arias intensity data are separated into four groups according to site classes assigned to recording stations. For each site class, the attenuation relation of Arias intensity is derived using a two-step regression analysis method. The attenuation relations established in this study can be used to estimate Arias intensity from a rupture of a thrust fault for sites in the footwall area or in the area away from the fault.  相似文献   

TOPEX/POSEIDON-derived space–time variations of the Kuroshio Current: applications of a gravimetric geoid and wavelet analysis     

Cheinway Hwang  Ricky Kao 《Geophysical Journal International》2002,151(3):835-847

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Dynamics of particle export on the Northwest Atlantic margin     

Jeomshik Hwang  Steven J. Manganini  Daniel B. Montluon  Timothy I. Eglinton 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(10):1792-1803

The Northwest Atlantic margin is characterized by high biological productivity in shelf and slope surface waters. In addition to carbon supply to underlying sediments, the persistent, intermediate depth nepheloid layers emanating from the continental shelves, and bottom nepheloid layers maintained by strong bottom currents associated with the southward flowing Deep Western Boundary Current (DWBC), provide conduits for export of organic carbon over the margin and/or to the interior ocean. As a part of a project to understand dynamics of particulate organic carbon (POC) cycling in this region, we examined the bulk and molecular properties of time-series sediment trap samples obtained at 968 m, 1976 m, and 2938 m depths from a bottom-tethered mooring on the New England slope (water depth, 2988 m). Frequent occurrences of higher fluxes in deep relative to shallower sediment traps and low Δ¹⁴C values of sinking POC together provide strong evidence for significant lateral transport of aged organic matter over the margin. Comparison of biogeochemical properties such as aluminum concentration and flux, and iron concentration between samples intercepted at different depths shows that particles collected by the deepest trap had more complex sources than the shallower ones. These data also suggest that at least two modes of lateral transport exist over the New England margin. Based on radiocarbon mass balance, about 30% (±10%) of sinking POC in all sediment traps is estimated to be derived from lateral transport of resuspended sediment. A strong correlation between Δ¹⁴C values and aluminum concentrations suggests that the aged organic matter is associated with lithogenic particles. Our results suggest that lateral transport of organic matter, particularly that resulting from sediment resuspension, should be considered in addition to vertical supply of organic matter derived from primary production, in order to understand carbon cycling and export over continental margins.  相似文献   

Mitigation of asphaltics deposition during CO₂ flood by enhancing CO₂ solvency with chemical modifiers     

R. J. Hwang  J. Ortiz 《Organic Geochemistry》2000,31(12)

CO₂ injected in the reservoir of McElroy Field, TX, for a CO₂ flood was in the supercritical state. Supercritical CO₂ fluid is capable of extracting light and intermediate hydrocarbons from rocks but is unable to extract heavy hydrocarbons and asphaltics. Therefore, plugging of asphaltics in reservoir rocks and a consequent reduction in injectivity and recovery may result when CO₂ only is used in enhanced oil recovery. By adding common solvents as chemical modifiers, the flooding fluid shows marked improvement in solvency for heavy components of crudes due to its increased density and polarity. Numerous supercritical CO₂ fluid extractions of dolomite rock from the Grayburg Formation containing known amount of spiked McElroy crude oil have been carried out to evaluate extraction efficiencies of CO₂ and CO₂ with chemical modifiers at various temperatures and pressures. All experiments show that extraction efficiency increases with increasing CO₂ pressure but decreases with increasing temperature. Addition of chemical modifiers to CO₂ also shows improved extraction efficiency and reduced asphaltic deposits. Under the pressure and temperature similar to McElroy reservoir conditions; chemically modified CO₂ yielded almost 3 times as much oil extracts as those in extractions with CO₂ only. It also reduced the asphaltics content in extracted rocks to nearly one half; indicating its potential for mitigating asphaltics plugging of formation rocks  相似文献