1,721,085 research outputs found
Inferring microevolutionary patterns from allele-size frequency distributions of minisatellite loci: a worldwide study of the APOB 3 ' hypervariable region polymorphism
No full textThe availability of numerous population and molecular data makes the apolipoprotein B 3' hypervariable region (APOB 3' HVR) polymorphism ideal for a pilot study of the relationships between the allele-size frequency distributions (referred to as allele-size distributions) of minisatellite loci and the microevolutionary processes underlying their present-day polymorphism in human populations. In this paper, we present a worldwide APOB 3' HVR study, based on published and unpublished data, which refers to 36 populations. We systematically compare APOB 3' HVR within-group diversity (in terms of heterozygosity, number of alleles, and allele-size variance) in numerous human populations, including African, European, Asian, Amerindian, Australomelanesian, and Polynesian groups. Overall, our analyses indicate a greater APOB 3' HVR diversity in Africans than non-Africans. Then, we compare APOB 3' HVR allele-size distributions. The RPOB 3' HVR allele-size distribution is found to be quasi-unimodal in Africans and bimodal or nonunimodal in non-African populations. The analysis of the distribution of pairwise comparisons suggests that Africans expanded earlier and/or that their ancestral population was larger than other continental groups. As a final step, we examine APOB 3' HVR interpopulational relationships by using three genetic distances. The Fs, genetic distance, which assumes genetic drift as being the agent that differentiates populations, provides results that are more congruent with established anthropological knowledge than mutation-based distances (D-SW and R-ST). We hypothesize that the ancestral population was characterized by a high heterozygosity, an extended range of allele size, and a quasi-unimodal allele-size distribution centered on allele *37, features persisting in examined African populations. Sampling processes during "out-of-Africa" migrations would be responsible for the decrease in APOB 3' HVR gene diversity and the nonunimodal allele-size distribution observed in non-Africans. Some possible confounding factors are discussed and a prospect of how the hypothesis could be refined and tested is given
The Effect of a Top Flexible Restraint on a Two-Bodies Vertical Spanning Wall
No full textIn unreinforced masonry structures, one of the most dangerous events that can occur during earthquakes is an out-of-plane mechanism. This type of response significantly changes if the wall is restrained by a horizontal element, like a floor, a roof or tie rods. The collapse, in this case, could take place for slipping/failure of the connection to the diaphragm or for overturning of the wall, following the formation of a crack at an intermediate height between the base and the top. Further, to evaluate the response of these kind of mechanisms, the assumption of a rigid top support can be too crude especially in case of a timber diaphragm or small diameter and large length tie rods. In this context, in order to capture the complex dynamic behavior of the wall, formed by two stacked rigid bodies (free to rock) connected to a spring, a specific analytical model (updated to account for additional masses active on the wall only during the earthquake) is used. For slender walls connected to a flexible restraint, the flexural out-of-plane mechanism is recurrent. These walls are common in the Emilia-Romagna region of Italy. For this reason, a building portfolio in Emilia is analyzed to derive mean and standard deviation of a log-normal distribution of the main parameters of the system. The variation of relevant parameters is investigated, in order to evaluate the effect of the elastic restraint at the top. The results of the analysis highlighted that stiff diaphragm can significantly reduce the rotations. Additionally, the study on the effect of the wall size pointed out how the top spring causes a reverse scale effect
Displacement-based design procedures for rigid block isolation
Full text linkWhen subjected to earthquakes, many objects or structural elements behave like rocking rigid blocks. Computer servers, medical shelves, art objects, statues, and electrical transformers are frequently included in this category. Protection of these objects is an important task, considering that their value could be inestimable or their operation crucial during earthquakes; base isolation technology has been proven to be a viable option for this purpose. Initially, the dynamic model of a rocking rigid block placed on a base isolation device is reviewed. Then, two equivalent-static displacement-based procedures for designing the isolators for these types of objects are proposed, and the main steps are illustrated. The first procedure aims to determine isolator characteristics to prevent the initiation of rocking motion during the code-level earthquake event. The second procedure is aimed at designing isolators that allow a specified maximum rotation of the block during seismic events. The proposed procedures are validated by means of time-history analyses for a suite of spectrum-compatible accelerograms. The first displacement-based procedure appears particularly suitable for objects of small to medium size. The validation of the second procedure demonstrates that the equal displacement rule can be applied for this kind of systems, despite their softening. The results also indicate that the approach is particularly effective for medium to large structures/objects, if small oscillations are acceptable. The controlled rocking procedure offers a significant advantage by allowing for a reduction in the maximum displacement and period of the isolator, compared to situations where rocking motion must be prevented entirely
Our diversity and the Italian Constitution. Do we really need human races?
Full text linkThis paper describes a proposal regarding the presence of the word "race" in the Italian Constitution. Three points are worth of note. Firstly, simply removing the word race from the Constitution is of no real help, since we could miss an indispensable hook for laws concerned with racism. Rather, we should be able to introduce an alternative phrase that: (i) can express the concept of diversity without forgetting all the various aspects of its meaning (biological and cultural, above all); (ii) in no way evokes a hierarchy of values. To make it more effective, the amendment must be accompanied by an explicit statement that race has no meaning for the human species and that any discriminatory view based on such an invalid assumption must therefore be rejected. Secondly, overcoming the old, but still existing, dichotomy between “physical” and “cultural” anthropology, is an absolute necessity in every discussion about the ”human races”. In fact, the term race is also used to stigmatize cultural differences, as if they were the product of different intellectual skills or moral predispositions. Achieving a synthesis between the biological and cultural dimensions of race is a preliminary step to effectively counter the dangerous links between new forms of intolerance and the resurgence of genetic determinism. Thirdly and finally, we should be aware that our commitment must not end simply by signing a document. On the contrary, it must start from there. In our educational and training activities, we must seek to involve wider audiences and provide them with the best tools so they can look at human diversity with no preconceptions. It is important to raise awareness of the need for a change among all those who, for various reasons,are involved in scientific and cultural dissemination
Non-linear dynamic model of a two-bodies vertical spanning wall elastically restrained at the top
Full text linkUnderstanding the out-of-plane behavior of unreinforced masonry walls is crucial in seismic assessment of existing buildings. Here, the dynamic response of a vertical spanning strip wall, connected to a flexible diaphragm at the top, is investigated. Despite the simplicity of the model, two rocking rigid bodies elastically restrained at the top, the dynamic response is highly nonlinear. This behavior is due to different phenomena: when in motion the system may assume different configurations, with the transition between them due either to impacts or crack opening caused by ground acceleration. An analytical model capable to capture the complex dynamic response of the system is implemented. The equations of motion are first derived, using variational methods, then the events that the system can undergo during motion are studied. Finally, in order to show the potential of the model, some numerical exemplifications are presented applying an earthquake record and a sine pulse to the system
Vertical spanning wall elastically restrained at the top. Validation and parametric dynamic analysis
Full text linkIn unreinforced masonry structures, among the most dangerous events that can occur during earthquakes are the out-of-plane mechanisms. This type of response significantly changes if the wall is restrained by a horizontal element. The collapse, in this case, could take place for slipping/failure of the diaphragm connection or for overturning of the wall, following the formation of a crack at an intermediate height between the base and the top. A specific analytical model is used to capture the complex dynamic behavior of the wall, formed by two stacked rigid bodies (free to rock) with the top one connected to a flexible diaphragm. The model is calibrated using experimental data available in the literature and it is then used to carry out a dynamic parametric analysis. The variation range of relevant parameters refers to the building features surveyed in Emilia-Romagna region, Italy, and their effect on the global response of the system is investigated. Further, the influence of ground motion is considered, using different ground accelerations. The results of the analysis highlight that, for the considered area and return period, the maximum rotations of the system are significant only for large slenderness values. Further, the investigation shows that the diaphragm plays a crucial role in the dynamic response of the system. The stiffness of the diaphragm can significantly reduce the rotations and consequently the risk of overturning. Additionally, the study on the effect of the wall size pointed out how a top spring causes a reverse scale effect
Base-Isolation of a Rocking Object on a Rocking Pedestal: Response to Pulse-Type Ground Motion
No full textThe rocking response of rigid blocks, such as statues, storage systems, and slender structures in general, was documented both in the field and in the laboratory. These objects/structures must be protected from earthquakes, as their value may be inestimable in some cases. The use of base isolation devices for this structural typology was already studied and successfully applied to real cases. Previous research has focused on the isolation of a single rigid block system, although there are circumstances in which the use of a single block is insufficient to define the response. Configurations in which one block is stacked on top of another, such as ancient Greek and Roman structures composed of large heavy members or statues placed on a pedestal, are examples. In this paper the rocking response of two stacked rigid blocks placed on a seismic isolation device is investigated. The dynamics of this multi-degree of freedom system is briefly summarized, together with the conditions associated to an impact or a change in the rocking configuration. Many parameters govern the response of the system and to understand their influence on the dynamic behavior, analysis of the response to a pulse-type ground motion is carried out. In general, the seismic isolation device is shown to be effective for a wide range of scenarios. However, the study also highlights how, for large period pulses or short period devices, the response of the isolated system can be amplified compared to the scenario where the blocks are placed on a rigid foundation. This phenomenon is due to the amplification of the acceleration of the isolation device for specific ratios between the period of the pulse and that of the isolator; the need of a careful design of the device is evident
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