Holocene and Pleistocene pluvial periods in Yemen,southern Arabia

Arabia is an important potential pathway for the dispersal of Homo sapiens (“out of Africa”). Yet, because of its arid to hyper-arid climate humans could only migrate across southern Arabia during pluvial periods when environmental conditions were favorable. However, knowledge on the timing of Arabian pluvial periods prior to the Holocene is mainly based on a single and possibly incomplete speleothem record from Hoti Cave in Northern Oman. Additional terrestrial records from the Arabian Peninsula are needed to confirm the Hoti Cave record. Here we present a new speleothem record from Mukalla Cave in southern Yemen. The Mukalla Cave and Hoti Cave records clearly reveal that speleothems growth occurred solely during peak interglacial periods, corresponding to Marine Isotope Stages (MIS) 1 (early to mid-Holocene), 5.1, 5.3, 5.5 (Eemian), 7.1, 7.5 and 9. Of these humid periods, highest precipitation occurred during MIS 5.5 and lowest during early to middle Holocene.     

A new closed‐form solution for analysis of unlined pressure tunnels under seepage forces

In this study, a simplified analytical closed‐form solution, considering plane strain and axial symmetry conditions, for analysis of a circular pressure tunnel excavated underwater table, is developed. The method accounts for the seepage forces with the steady‐state flow and is based on the generalized effective stress law. To examine the effect of pore pressure variations and also the boundary conditions at the ground surface, the formulations are derived for different directions around the tunnel. The proposed method can be applied for analysis and design of pressure tunnels. Illustrative examples are given to demonstrate the performance of the proposed solution and also to examine the effect of seepage forces on the stability of tunnels. The simplified analytical solution derived in this study is compared with numerical analyses. It is concluded that the classic solutions (Lame's thick‐walled solution), considering the internal pressure as a mechanical load applied to the tunnel surface, are not applicable to pervious media and can result in an unsafe design. Copyright © 2012 John Wiley & Sons, Ltd.     

Three‐dimensional finite element study of arching behavior in slope/drilled shafts system

Two‐dimensional slope stability analysis for a slope with a row of drilled shafts needs a mechanism to take into account the three‐dimensional effect of the soil arching due to the spaced drilled shafts on slope. To gain a better understanding of the arching mechanisms in a slope with evenly spaced drilled shafts socketed into a stable stratum (or a rock layer), the three‐dimensional finite element modelling technique was used for a comprehensive parametric study, where the nonlinear and plastic nature of the soil and the elastic behavior of the drilled shafts as well as the interface frictions were modelled. Various factors were varied in the parametric study to include (1) the rigidity of the drilled shafts as influenced by its diameter, modulus of elasticity, and total length; (2) shafts spacing and location on the slope; (3) the material properties of rock and the socket length of shaft; and (4) the soil movement and strength parameters. Evidences of soil arching and reduction in the stresses and displacements through the load transfer mechanisms due to the presence of the drilled shafts were elucidated through the finite element method (FEM) simulation results. Design charts based on regression analysis of FEM simulation results were created to obtain a numerical value of the load transfer factor for the arching mechanism provided by the drilled shafts on the slope. Observations of the arching behavior learned from the FEM simulations provide an insight into the behavior of drilled shafts stabilized slope. Copyright © 2009 John Wiley & Sons, Ltd.     

Alkaline character of Eocene volcanism in the middle part of central Iran and its geodynamic situation

Alkaline volcanic rocks, sometimes feldspathoid bearing, appear in variable stratigraphic positions within the Eocene of the middle part of Central Iran. No magmatic zonation and no K₂O enrichment in both time and space can be found in this volcanic sequence. These facts together with other geochemical and geological features of the Iranian Eocene provinces do not agree with a volcanism related to a subduction zone model.Reversely, a rift model may be applied for the interpretation of the origin of Eocene volcanic rocks and their geodynamic situation. The emissions of alkaline magma are linked with rhythmic opening of a rift zone during Eocene.A mutual contamination between a basaltic magma and a bulky palingenetic acid magma is responsible for the few volcanic rocks with calc-alkaline trend.

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Zusammenfassung Alkali-Gesteine, die manchmal Feldspatoide enthalten, treten in verschiedenen stratigraphischen Stellungen innerhalb des Eozäns des Zentral-Irans auf.In diesen Vulkaniten ist keinerlei magmatische Zonierung und insbesondere keine systematische Variation der Kaligehalte festzustellen. Diese und andere geologische und geochemische Argumente sprechen gegen eine Deutung als Paläosubduktionszone.Als Alternative bietet sich das Modell der Öffnung eines Grabens an: der Alkali-Vulkanismus steht in Zusammenhang mit den verschiedenen Phasen der Entstehung und Entwicklung eines Rifts während des Eozäns.Die seltenen Vulkanite kalk-alkalischer Zusammensetzung erklären sich durch Mischung der Magmen von Alkali-Basalten mit den bedeutenden anatektischen Magmen.

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Résumé Des roches alcalines, éventuellement à feldspathoïde, existent à des niveaux et dans des secteurs variés de la séquence volcanique éocène de la partie médiane de la zone de l'Iran Central; par ailleurs, dans cette série, on n'a pu mettre en évidence ni zonation magmatique, ni enrichissement en K₂O. Ces faits, joints à d'autres caractères géochimiques et géologiques des provinces éocènes de l'Iran, sont en désaccord avec un volcanisme lié à une zone de subduction.En revanche, un modèle de rift peut être appliqué pour interpréter l'origine des volcanites éocènes et leur situation géodynamique. Les émissions de magma alcalin sont en effet en relation avec l'ouverture rhythmique d'une zone de rift pendant l'Eocène.Quant aux rares roches à tendance calco-alcaline, elles résultent d'une contamination mutuelle entre un magma basaltique et un important magma acide palingénétique.

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A simple method of ground water direction measurement in a single bore hole

A simple technique to find both the magnitude and direction of ground water flow in a single bore hole, sited in a pervious water bearing medium, is described. The experiment may be performed with tracers which may not be radioactive (like inactive potassium bromide).     

Second order adiabatic invariants associated with the two-body problem with slowly varying mass

An adiabatic invariant is characterized by the property that its derivative is small and oscillatory. Therefore, assuming that such a quantity is constant does not lead to a cumulative error as t. In this paper, using action and angle variables, adiabatic invariants to 0(1) and 0() are found for the two-body problem with a slowly varying gravitational constant.     

Trace Element Determination of Single Fluid Inclusions in Quartz by Laser Ablation ICP-MS

Single fluid inclusions in quartz from a Pb-Zn-Ag carbonate replacement deposit were selected for trace element determination by laser ablation ICP-MS. Spikes in element intensities were noted between first breached fluids versus subsequent analyses, suggesting that accurate element concentrations may not be determined in smaller fluid inclusions when only one analysis is obtained before the fluid is exhausted. Elemental concentrations in the fluid inclusions were determined by external standardisation using solutions sealed in microcapillary tubes. Standards and single natural inclusion analyses give repeatabilities (%RSD) of ˜ 20% for Rb and Sr. Rubidium and strontium concentrations range from 0.56-5.07 μg ml^-1 and 1.12-27.4 μg ml^-1, respectively, whereas Zn and Ag are below detection limits (< 10 ng ml^-1). The results suggest that nearly all Zn and Ag are removed by the time hydrothermal fluids precipitate gangue minerals.     

Time-domain two-dimensional site response analysis of non-homogeneous topographic structures by a hybrid BE/FE method

In this paper, an advanced formulation of the time-domain, two-dimensional hybrid finite element–boundary element method (FEM/BEM) is presented, and applied to carry out site response analysis of homogeneous and non-homogeneous topographic structures subjected to incident in-plane motions. Seismic responses of half-plane, horizontally layered site, alluvial valley and ridge sections subjected to incident P and SV waves are analyzed in order to demonstrate the applicability and efficiency of the presented method. The numerical results show that hybrid BE/FE methods require smaller time steps than those needed by BEM schemes. They also show that in case of surface irregularities with height to half-width ratio of up to one, the topography effect could be noticeable, if incident waves have wavelengths of less than approximately eight times the width.     

Watershed modeling of rainfall excess transformation into runoff

In this paper an attempt is made to present a distributed physiographic conceptual model that uses the principles of flow continuity and momentum. For this purpose, the watershed under study is divided into subwatersheds keeping in view the drainage patterns and characteristics. Then the main tributaries are identified and their drainage areas are delineated to form tributary subwatersheds. The main channel subwatersheds have taken care of the remaining area in the vicinity of the main channel. The kinematic wave theory is applied for the overland runoff computations from these subwatersheds. Further, the overland flows are superimposed onto the main channel. The dynamic wave theory is used to route the flows through the main channel to compute the watershed responses at the outlet. The proposed model is tested onto a natural watershed. The computations were performed for few storm events. Comparison of the significant parameters of the computed and the observed hydrographs shows that the maximum relative error in prediction is 5.8%. Thus, the results are satisfactory. Better results can be obtained when measured rainfall-excess data are available or a more realistic loss index is adopted for rainfall-excess separation.     

Time delayed control of structural systems

Time delays are ubiquitous in control systems. They usually enter because of the sensors and actuators used in them. Traditionally, time delays have been thought to have a deleterious effect on both the stability and the performance of controlled systems, and much research has been done in attempting to eliminate them, compensate for them, or nullify their presence. In this paper we take a different view. We investigate whether purposefully injected time delays can be used to improve both the system's stability and performance. Our analytical, numerical, and experimental investigation shows that this can indeed be done. Analytical results of the effects of time delays on collocated and non‐collocated control of classically damped and non‐classically damped systems are given. Experimental and numerical results confirm the theoretical expectations. Issues of system uncertainties and robustness of time delayed control are addressed. The results are of practical value in improving the performance and stability of controllers because these characteristics (performance and stability) improve dramatically with the intentional injection of small time delays in the control system. The introduction of such time delays constitutes a ‘minimal change’ to a controller already installed in a structural system for active control. Hence, from a practical standpoint, time delays can be implemented in a nearly costless and highly reliable manner to improve control performance and stability, an aspect that cannot be ignored when dealing with the economics and safety of large structural systems subjected to strong earthquake ground shaking. Copyright © 2003 John Wiley & Sons, Ltd.