Crystallographic and structural transformations of sedimentary chalcedony in flint upon heat treatment

The early occurrence of intentional heat treatment of silica rocks has recently become a key element in the discussion about the cultural modernity of prehistoric populations. Lithic vestiges are the only sources that remain of this process and the understanding of the material’s properties and transformations are essential for reconstructing the conditions and parameters applied during heat treatment. Several models of the structural transformations upon heating have been proposed in the current literature. These models are often contradictory and do not account for the most recent structural and mineralogical data on chalcedony. In order to propose a new model, we elaborated an experimental procedure and applied different techniques involving infrared spectroscopy, solid state NMR, X-ray diffraction and electron microscopy. The results show that the major transformation to happen is the loss of silanole (SiOH) and the creation of new Si-O-Si bonds according to the reaction: Si?OH HO-Si → Si-O-Si + H₂O. This reaction starts between 200 °C and 300 °C and causes an increase in the hardness of the rocks. The maximal annealing temperature and the ramp rate are the functions of the ability of the structure to evacuate newly created H₂O and depend on the size of the specimen and the volume of its porosity. These results also show that the annealing duration at maximum temperature can be relatively short (<50 min) for a sufficiently large amount of transformation to be accomplished.     

微痕考古——从微观信息认识历史过程的科学探索

微痕考古以显微观测与技术分析为基础,通过对自然微观痕迹、人类和其它动物行为痕迹的观察研究,阐释人类与动物的行为模式、生活环境、文化遗址埋藏现象等.并作为一种技术性工作广泛服务于我国的文物保护.微痕考古在工作方向、工作方法和工作结果方面,可以弥补传统考古工作和文物保护技术的不足,使考古工作从微观到宏观、从实验到理念、从局部到整体建立更全面、科学的分析过程.我国微痕考古近年迅速发展,专业队伍扩大、研究理念与实验技术进步、工作领域覆盖面拓宽近年微痕考古的重要收获,包括发现人类最早的戳刺性行为痕迹、人类最早的剥皮屠宰技术及刻划图案等;在玉器制作工艺与鉴定、石器使用痕迹与区域文化特点等方面也取得丰富成果.微痕考占的产生与发展,显示脱胎于自然科学的考古学专业,在与现代应用技术紧密结合下,使考古学在研究理念、分析技术和认知深度等方面正发生深刻变化.     

Experimental and Analytical Investigation on the Corner Failure in Masonry Buildings: Interaction between Rocking-Sliding and Horizontal Flexure

ABSTRACT

The failure mechanism of corners in masonry buildings has frequently been observed in seismic scenarios, but only a few works and no experimental investigations devoted to it are available in the literature. In this aritcle, the experimental behavior of a simple masonry corner is first analyzed, by simulating the seismic horizontal actions through a progressive tilting of the supporting base. Then, the conditions of the onset of two possible failure modes are analytically formulated: they are the rocking-sliding and the horizontal flexure mechanism. A three-dimensional macro-block model with frictional joints is used to analyze these mechanisms, while the crack patterns and the load factors are derived through the kinematic approach of the limit analysis. The evaluation of the in-plane frictional resistances involved by the rocking-sliding mechanism is performed by applying a reliable criterion previously proposed, while for the torsion strength involved in the horizontal flexure mechanism, simplified yield conditions are adopted and a possible criterion is also introduced to take into account the actual reduction of the contact surfaces. Last, the experimental findings are compared and critically interpreted in light of the analytical results and the influence of the main parameters on the prevailing mechanism is highlighted.     

Spatial and temporal dynamics of the urban heat island effect in a small Brazilian city

This study examined the spatial and temporal patterns of the canopy layer urban heat islands (UHI_UCL) in a small city in southeastern Brazil using the local climate zone (LCZ) system. We analysed the influence of weather conditions, LCZs characteristics, and local surface relief on the UHI_UCL magnitudes. Mobile traverses were used to measure air temperatures during representative nights of wet and dry seasons. Daily maximum magnitudes were observed in compact classes (LCZs 3 and 7) under ideal weather conditions (dry, clear skies, and calm) and higher anthropogenic heat release (weekdays). Seasonal effects on LCZ thermal differences were negligible. The peripheral landscapes were warmer than the city centre in both seasons. Among the warmer areas in the city, magnitudes in compact LCZs 3 and 7 were consistently higher than in LCZ 6. In general, representative sites of the main ‘built’ LCZs in the study area exhibit similar inter-zone temperature patterns to those reported for cities of different sizes from tropical and midlatitude regions. Thermal contrasts of ΔT_{LCZ 3 − D} in the study area reveal significant evidence that small cities can have as strong heat islands as bigger cities. These findings highlight the importance of the LCZ system to identify the main controlling factors driving such thermal differences and the need to extend the application of this approach in other South American cities to yield systematic data of UHI_UCL for urban planning given the coming challenges of climate change over the region.     

Testing for the presence of thermal pretreatment of flint in the mesolithic and neolithic of Sweden

Through ethnographic accounts, the method of heat treatment of silica materials to improve the flaking qualities is shown to have been known almost worldwide. Some mesolithic and neolithic flint artifacts from southern Sweden were examined in order to determine if they too were heat treated. From several methods proving or indicating thermal alteration of flint, analysis using scanning electron microscopy was chosen. Two samples were taken from each artifact, one being examined unaltered, the other being heat treated. No two samples from the same artifact had the same kind of surface appearance. Thus these analyses prove that the artifacts examined had not been heat treated.     

Skeletal and Surgical Evidence for Acute Osteomyelitis in Non‐Adult Individuals

Osteomyelitis is a non‐specific infection of the bone and bone marrow. In the past acute osteomyelitis (AO) led to high mortality especially in non‐adults. Nevertheless, its diagnosis in archaeological populations is rare. Documented individuals with known cause of death offer a unique opportunity to study this condition. This article aims to describe the bone lesions in non‐adults diagnosed with AO at the Coimbra University Hospital (CUH) and now belonging to the Coimbra Identified Skeletal Collection (CISC). Moreover, mortality rates and demographic profiles for individuals aged ≤18 years old and diagnosed with AO in the CUH, between 1923 and 1929, were also determined. The 5 (1%) non‐adults in the CISC with AO listed as cause of death were selected for this study, and their bones were analysed macroscopically and radiologically. The skeletal remains of one individual revealed a small area of new bone formation in the shaft of the left femur. Radiography of this bone showed a radio‐opaque area in the diaphysis. The other four individuals show evidence of surgical treatment, responsible for many cases of disability in the past. In the 7‐year period under analysis, 122 juveniles were diagnosed with osteomyelitis and admitted for surgery at the CUH, 43 (35.2%) of which were diagnosed with AO. Sixty‐five per cent of the cases of AO occurred between the ages of 8 and 15 years, with boys twice as frequently affected as girls, and lower limb bones were involved in 91% of AO cases. AO was responsible for 76.9% of the deaths. This study of pre‐antibiotic non‐adults may help to recognize skeletal signs of AO and their surgical treatment in unidentified skeletal remains. Copyright © 2012 John Wiley & Sons, Ltd.