Imperial Istanbul: A Traveller's Guide: Jane Taylor

Book reviewed in this article: The Revolt of Afrian Slaves in Iraq in the 3rd/9^th Century: Alexandre Popovic     

Set-up, optimization and first set of samples at the radiocarbon laboratory in Lebanon

A new radiocarbon laboratory has been established recently at the Lebanese Atomic Energy Commission. This laboratory consists of benzene synthesis line and a low background liquid scintillation counter, Tri-Carb 3180 TR/SL for measurements with Bismuth Germanate (BGO) guard detector. The effectiveness of the benzene line was tested firstly by preparing benzene from a wood sample after carbide and acetylene receiving. Normalization and standardization of the liquid scintillation counter was carried out, as well as the Factor of Merit (E2/B) was determined for three different counting regions. To assure accuracy and reliability of results, reference materials were used. Based on z-score and u-score evaluation, as well as Student’s t-test, acceptable data were obtained from travertine and wood samples available through the International Atomic Energy Agency (IAEA-C2 and IAEA-C5), and humic acid (U) and murex shell (R) from the Fifth International Radiocarbon Intercomparison (VIRI). After that, a preliminary study was done, which is the base for future research in order to assess the anthropogenic impact and degree of environmental pollution in terms of radiocarbon isotope ratio (Δ¹⁴C) deduced from the Percent Modern Carbon or PMC. This work represents the results of four reference materials and those of five green grass samples. The Δ¹⁴C of green grass samples collected from two different clean zones were found to be 50‰ and 52‰, while the values of those collected from different polluted zones were 23‰, 7‰ and 15‰.     

Dynamic One-Sided Out-Of-Plane Behavior of Unreinforced-Masonry Wall Restrained by Elasto-Plastic Tie-Rods

Past earthquakes have shown the high vulnerability of existing masonry buildings, particularly to out-of-plane local collapse mechanisms. Such mechanisms can be prevented if façades are restrained by tie rods improving the connections to perpendiculars walls. Whereas in the past only static models have been proposed, herein the nonlinear equation of motion of a monolithic wall restrained by a tie rod is presented. The façade, resting on a foundation and adjacent to transverse walls, rotates only around one base pivot and has one degree of freedom. Its thickness is explicitly accounted for and the tie rod is modeled as a linear elastic—perfectly plastic spring, with limited displacement capacity. The model is used to investigate the response to variations of wall geometry (height/thickness ratio, thickness), tie rod features (vertical position, length, prestress level), and material characteristics (elastic modulus, ultimate elongation, yield strength) typical of historical iron. The most relevant parameter is the steel strength, whereas other characteristics play minor roles allowing to recommend reduced values for pre-tensioning forces. The force-based procedure customary in Italy for tie design is reasonably safe and involves protection also against collapse, although probably not enough as desirable.     

Simulation Of Shake Table Tests on Out-of-Plane Masonry Buildings. Part (II): Combined Finite-Discrete Elements

ABSTRACT

Out-of-plane response of unreinforced masonry elements is frequently the most critical aspect of the seismic performance of existing masonry buildings. The response of such elements is usually governed by equilibrium rather than strength. Hence, it is customary to resort to rigid-body models, accounting for possible rotations, and/or sliding. However, the results of such analyses depend on the initial choice of the mechanism. In this article, the shaking-table experiments on a brick-masonry specimen, and on a stone-masonry specimen have been modeled by resorting to a combined finite-discrete element strategy. Despite the coarse discretization of both discrete and finite elements, the three-dimensional models are able to capture the experimentally observed multi-degree-of-freedom mechanisms, without any a priori assumption on the mechanism. A sensitivity analysis is carried out, addressing eight different parameters. The identification of the mechanism is sufficiently robust, but the assessment of its activation and failure is best done by combining the finite-discrete element model with a simplified model of the recognised mechanism.     

Optimal Facility Location in a One-Dimensional Spatial Market

This paper analyzes properties of the optimal spatial arrangement of what may be interpreted as a class of public facilities. Optimality is defined as cost minimization. Three different optimality criteria are considered, and for each, the necessary and, sufficient conditions, market area size, and production levels, are derived. The relationship between optimal production levels and number of facilities needed is also considered. Next the results of implementing various pricing strategies are analyzed with emphasis given to marginal and uniform pricing. It is shown that, given certain conditions, all facilities incur operating deficits, given marginal pricing. Estimates on the level of the deficits are derived in terms of location rents. Finally, in the appendix, several important results from other studies are derived as special cases of the basic model.     

Process-based models for port evolution and wreck site formation at Mombasa,Kenya

Mombasa Island, settled for almost 2000 years, played a central role in the development of the central seaboard of East Africa, emerging by the 16th century as a centre of sustained port dominance. Marine geoarchaeological surveys were conducted in Mombasa Harbour in 2001 (i) to quantify the nature and extent of the submerged archaeological resource, (ii) to investigate site formation and preservation potential of historic shipwrecks, and (iii) to explore the natural evolution of the Old Port and adjacent basins in the context of hydrodynamic and sedimentary processes. Backscatter and single-beam echo-sounder data were acquired, interpreted and diver-truthed using surface-demand and SCUBA systems. It is proposed that sustained scour processes, resultant from the interaction of ebb and flood tidal currents with bedrock ridges, control the bathymetric evolution of Mombasa Harbour, negating requirement for mechanical dredging. The submerged archaeological resource in the area comprises fish traps and shipwrecks. Physical processes govern shipwreck site formation, with scour and bed-migration dominant, ultimately leading to structural instability and site degradation. The wreck of Santo António de Tanná (1697) has been subject to gravitational collapse and mass down-slope movement of material, concentrating wreck structure and material along the portside stern third of the vessel.     

The origin of deep subsurface microbial communities in the Witwatersrand Basin, South Africa as deduced from apatite fission track analyses

The first fission track analyses of detrital apatite grains from the subsurface of the Kaapvaal Craton were utilized to delineate the thermal history for the northern margin of the Witwatersrand Basin, South Africa, where evidence for subsurface thermophilic and hyperthermophilic microorganisms have been discovered. Fission track apatite ages for core samples ranged from 21 to 422 Ma. The trend of decreasing age with increasing depth parallels a trend previously reported for fission track data from surface samples collected from the higher altitude centre and lower altitude margins of the Kaapvaal Craton, South Africa. These new fission track ages are older than the surface samples of equivalent elevation, indicating that the uplift history and/or the geothermal gradient of the centre of the Kaapvaal Craton is distinct from that of its margins. Modelling of one sample collected from a depth of 3.7 km records cooling from 120°C at 75 Ma at a rate of approximately 1.4°C m.y.^?1 and reaching present day temperatures at 30 Ma. This modelling result when compared to other apatite fission track dates indicate that this cooling trend followed a 90‐Ma thermotectonic event. The fission track data also indicate that heated fluid migration, which is observed today in this region of the Witwatersrand Basin, was also active in the past in order to explain the greater palaeogeothermal gradient (18 versus 8°C km^?1). The fission track results suggest that at approximately 70 Ma only hyperthermophilic microorganisms could have existed at palaeodepths >3.2 km depth in the Witwatersrand Basin, and that the current meso/thermophilic microbial communities living at or beneath the present depth of 1.7 km in the Witwatersrand Basin must have migrated to their current location since 70 Ma. Any hyperthermophilic microorganisms found at the present depths 1.2–3.7 km could be descendents of subsurface hyperthermophiles that colonized the crust since the early Mesozoic to Palaeozoic eras.