A seismic free field input model for FE-SBFE coupling in time domain

A seismic free field input formulation of the coupling procedure of the finite element (FE) and the scaled boundary finite-element (SBFE) is proposed to perform the unbounded soil-structure interaction analysis in time domain. Based on the substructure technique, seismic excitation of the soil-structure system is represented by the free-field motion of an elastic half-space. To reduce the computational effort, the acceleration unit-impulse response function of the unbounded soil is decomposed into two functions; linear and residual. The latter converges to zero and can be truncated as required. With the prescribed tolerance parameter, the balance between accuracy and efficiency of the procedure can be controlled. The validity of the model is verified by the scattering analysis of a hemi-spherical canyon subjected to plane harmonic P, SV and SH wave incidence. Numerical results show that the new procedure is very efficient for seismic problems within a normal range of frequency. The coupling procedure presented herein can be applied to linear and nonlinear earthquake response analysis of practical structures which are built on unbounded soil. Supproted by: the National Key Basic Research and Development Program under Grant No. 2002CB412709     

Recent advances in study of oceanic vortex

In this paper, the recent advances in the study of oceanic vortex are outlined. Firstly, the previous studies on oceanic vortex are reviewed. Secondly, some prominent features of oceanic vortex in the Gulf Stream, the Kuroshio, the South China Sea and the Japan Sea regions are depicted based upon the observations and numerical modeling results. Generally, the lifetime of these oceanic vortices ranges from several weeks to several months, and their horizontal scales vary from tens of kilometers to hundreds of kilometers. Their vertical scales are on the order of thousands of meters. Finally, some theoretical studies, mainly on the splitting of a cyclonic vortex and the merging of anticyclonic vortices, are introduced.     

Sampling Bias and Class Imbalance in Maximum-likelihood Logistic Regression

Logistic regression is a widely used statistical method to relate a binary response variable to a set of explanatory variables and maximum likelihood is the most commonly used method for parameter estimation. A maximum-likelihood logistic regression (MLLR) model predicts the probability of the event from binary data defining the event. Currently, MLLR models are used in a myriad of fields including geosciences, natural hazard evaluation, medical diagnosis, homeland security, finance, and many others. In such applications, the empirical sample data often exhibit class imbalance, where one class is represented by a large number of events while the other is represented by only a few. In addition, the data also exhibit sampling bias, which occurs when there is a difference between the class distribution in the sample compared to the actual class distribution in the population. Previous studies have evaluated how class imbalance and sampling bias affect the predictive capability of asymptotic classification algorithms such as MLLR, yet no definitive conclusions have been reached.     

Luminescence in Primordial Helium Lines at the Pre-recombination Epoch

The formation of luminescent subordinate He I lines by the absorption of radiation from a source in lines of the main He I series in an expanding Universe is considered. A burst of radiation in continuum is assumed to occur at some instant of time corresponding to redshift z₀. This radiation is partially absorbed at different z < z₀ in lines of the main He I series (different pumping channels) and then is partially converted into radiation in subordinate lines. If ν _ik is the laboratory transition frequency of some subordinate line emerging at some z, then at the present epoch its frequency will be ν = ν _ik /(1 + z). The quantum yield, i.e., the number of photons emitted in the subordinate line per initial excited atom, has been calculated for different z (and, consequently, for different ν). Several pumping channels have been considered. We show that the luminescent lines can be both emission and absorption ones; the same line can be an emission one for one of the pumping channels and an absorption one for another. For example, the 1s2s–1s2p (1S–1P*) line is an emission one for the 1s2–1s2p pumping and an absorption one for the 1s2–1s3p pumping. We show that in the frequency range 30–80 GHz the total quantum yield for the first and second of the above channels can reach +50 and ?50%, respectively.     

Evaluation of geodynamic activity of the Dead Sea transform fault by radon gas concentrations

Twelve radon lines of dosimeters (detectors) were placed across the Jordan Valley active fault, which is a segment of the active Dead Sea transform fault system. Each line of the dosimeters shows one or more peaks of radon anomaly concentrations. Some of these peaks prove the intersection of the fault trace with these lines in areas where the fault plane is inferred. In other lines, the peaks correspond to the arrangement of faults in areas of pull-apart basins (sag ponds) or pressure ridges, formed due to the left or right step of the fault. Sag ponds usually show low radon emanations, because they are the place for the accumulation of very fine sediments, which decreases their porosity and hence the upward migration of the radon gas. The northern part of the Jordan Valley relatively shows high radon emanation, which could be attributed to the presence of a seismic gap in the upper Jordan valley.     

Archean to Middle Proterozoic evolution of Baltica subcontinental lithosphere: evidence from combined Sm–Nd and Lu–Hf isotope analyses of the Sandvik ultramafic body,Norway

Combined Sm–Nd and Lu–Hf age and isotope data indicate that Mg- and Cr-rich ultramafic rocks at Sandvik, Western Gneiss Region (WGR), Norway, originated from depleted Archean lithospheric mantle that was chemically and physically modified in Middle Proterozoic time. The Sandvik outcrop consists of garnet peridotite and garnet-olivine pyroxenite and thin garnet pyroxenite layers. These contain two principal mineral assemblages: an earlier porphyroclastic assemblage of grt + opx + cpx ± ol (1,200–1,000°C, 40–50 kbar) and a later kelyphitic assemblage of grt + spl + am ± opx ± ol (700–750°C; 12–18 kbar). A CHUR Hf model age indicates a period of melt extraction at ca. 3.3 Ga for garnet peridotite, reflecting extremely high Lu/Hf ratios and very radiogenic present-day ¹⁷⁶Hf/¹⁷⁷Hf (ε_Hf=+2,165). Lu–Hf garnet-cpx-whole rock ages of two olivine-bearing samples (garnet peridotite and garnet-olivine pyroxenite) from the outcrop are ca. 1,255 Ma, whereas two olivine-free garnet pyroxenites yield Lu–Hf ages of ca. 1,185 Ma. All Sm–Nd garnet-cpx-whole rock ages of these samples are significantly younger (ca. 1,150 Ma for garnet peridotite and ca. 1,120 Ma for garnet pyroxenite). The isotope systematics indicate that the Lu–Hf ages represent cooling from an earlier period of formation/recrystallization for garnet peridotite whereas they probably reflect formation/recrystallization ages of the garnet pyroxenite. The Sm–Nd ages and isotope systematics of the garnet peridotite samples are consistent with an episode of LREE metasomatism, perhaps facilitated by a fluid of carbonatitic composition that strongly decoupled Sm–Nd and Lu–Hf. The Sm–Nd ages of the garnet pyroxenite may represent either LREE metasomatism or cooling, and, like the peridotites, Lu–Hf ages are older than Sm–Nd ages. The age data, as well as the inferred Nd isotope composition of the fluid that affected the olivine-bearing samples, suggest that these rocks were not in contact during the LREE metasomatic event. Moreover, the pyroxenite layers cannot have been emplaced as magmas into the host peridotite. The pyroxenite layers are interpreted to be tectonically juxtaposed with the host olivine-bearing samples sometime after 1,150 Ma but before development of kelyphite.     

The importance of precessional signals in the tropical climate

Past research on the climate response to orbital forcing has emphasized the glacial-interglacial variations in global ice volume, global-mean temperature, and the global hydrologic cycle. This emphasis may be inappropriate in the tropics, where the response to precessional forcing is likely to be somewhat independent of the glacial-interglacial variations, particularly in variables relating to the hydrologic cycle. To illustrate this point, we use an atmospheric general circulation model coupled to a slab ocean model, performing experiments that quantify the tropical climates response to (1) opposite phases of precessional forcing, and (2) Last Glacial Maximum boundary conditions. While the glacially-forced tropical temperature changes are typically more than an order of magnitude larger than those arising from precessional forcing, the hydrologic signals stemming from the two forcings are comparable in magnitude. The mechanisms behind these signals are investigated and shown to be quite distinct for the precessional and glacial forcing. Because of strong dynamical linkages in the tropics, the model results illustrate the impossibility of predicting the local hydrologic response to external forcing without understanding the response at much larger spatial scales. Examples from the paleoclimate record are presented as additional evidence for the importance of precessional signals in past variations of the tropical climate.     

Experimental study on full-scale steel beam-to-column moment connections

Ten full-scale steel beam-to-column moment connections used in moment-resisting frames （MRFs） were tested to study the failure process, failure mode, strength and plastic rotation capacity. The specimens include one traditional welded flange-bolted web connection, one traditional fully welded connection, four beam flange strengthened connections, three beam flange weakened connections, and one through-diaphragm connection. The test results show that the connections with flange cover plates or with partly cut beam flanges satisfy the beam plastic rotation demand for ductile MRFs. From the measured stress profiles along the beam flange and beam web depth, the mechanics of brittle fracture at the end of the beam is discussed. Design recommendations for steel beam-to-column moment connections are proposed.     

Application of Wavelet Transform to Magnetic Data Due to Ruins of the Hittite,Civilization in Turkey

— In the recent years, geophysical methods have been applied successfully in archaeological studies. In this article we have studied the application of wavelet transform to magnetic data in order to estimate boundaries of various synthetic examples and real data. Enhanced Horizontal Derivative (EHD) method is also applied as an alternative method for boundary estimation. The performance of wavelet transform and the EHD method are evaluated using magnetic data of the Sarissa-Kusakli archaeological site. All boundary results are mutually compared. Based on these comparisons, we conclude that the wavelet transform provides reasonable results.This work was supported by the TUBITAK under Project YDABCAG-100Y021.Received: 23 October 2001