The Stern-Gerlach experiment and the electron spin: a quasi history example

Nossa proposta neste trabalho é utilizar o conceito de quasi-história como perspectiva de análise para a forma de apresentação didática de conteúdos de física. Pretendemos mostrar as transformações sofridas pelo conhecimento, desde os primeiros registros até a forma como ele aparece nos livros didáticos. O conteúdo a ser trabalhado é o experimento de Stern-Gerlach, geralmente associado à descoberta do spin do elétron, e que desempenhou um importante papel no desenvolvimento da teoria quântica no século XX. Analisando os trabalhos originais e utilizando alguns fatos da história da ciência, discutiremos as modificações sofridas por este conteúdo até a forma em que ele é apresentado nos livros didáticos utilizados nos cursos de graduação em física e engenharias.The aim of this work is to use the concept of quasi history to analyze the form of didactical presentation of the physics contents. We intend to stress the changes made to the knowledge, since the first records by the way it appears in textbooks. The content to work is the experiment of Stern-Gerlach, usually associated with the discovery of the electron spin, and which played an important role in the development of quantum theory in the twentieth century. Analyzing the original work and using some facts of history of science, we will discuss the modifications made by this content to the form in which it is presented in textbooks used in graduate courses in physics and engineering

Rich Socio-Cognitive Agents for Immersive Training Environments: Case of NonKin Village

Demand is on the rise for scientifically based human-behavior models that can be quickly customized and inserted into immersive training environments to recreate a given society or culture. At the same time, there are no readily available science model-driven environments for this purpose (see survey in Sect. 2). In researching how to overcome this obstacle, we have created rich (complex) socio-cognitive agents that include a large number of social science models (cognitive, sociologic, economic, political, etc) needed to enhance the realism of immersive, artificial agent societies. We describe current efforts to apply model-driven development concepts and how to permit other models to be plugged in should a developer prefer them instead. The current, default library of behavioral models is a metamodel, or authoring language, capable of generating immersive social worlds. Section 3 explores the specific metamodels currently in this library (cognitive, socio-political, economic, conversational, etc.) and Sect. 4 illustrates them with an implementation that results in a virtual Afghan village as a platform-independent model. This is instantiated into a server that then works across a bridge to control the agents in an immersive, platform-specific 3D gameworld (client). Section 4 also provides examples of interacting in the resulting gameworld and some of the training a player receives. We end with lessons learned and next steps for improving both the process and the gameworld. The seeming paradox of this research is that as agent complexity increases, the easier it becomes for the agents to explain their world, their dilemmas, and their social networks to a player or trainee

Mechanical Forces Guiding Staphylococcus aureus Cellular Invasion

Staphylococcus aureus can invade various types of mammalian cells, thereby enabling it to evade host immune defenses and antibiotics. The current model for cellular invasion involves the interaction between the bacterial cell surface located fibronectin (Fn)-binding proteins (FnBPA and FnBPB) and the α5β1 integrin in the host cell membrane. While it is believed that the extracellular matrix protein Fn serves as a bridging molecule between FnBPs and integrins, the fundamental forces involved are not known. Using single-cell and single-molecule experiments, we unravel the molecular forces guiding S. aureus cellular invasion, focusing on the prototypical three-component FnBPA-Fn-integrin interaction. We show that FnBPA mediates bacterial adhesion to soluble Fn via strong forces (∼1500 pN), consistent with a high-affinity tandem β-zipper, and that the FnBPA-Fn complex further binds to immobilized α5β1 integrins with a strength much higher than that of the classical Fn-integrin bond (∼100 pN). The high mechanical stability of the Fn bridge favors an invasion model in which Fn binding by FnBPA leads to the exposure of cryptic integrin-binding sites via allosteric activation, which in turn engage in a strong interaction with integrins. This activation mechanism emphasizes the importance of protein mechanobiology in regulating bacterial-host adhesion. We also find that Fn-dependent adhesion between S. aureus and endothelial cells strengthens with time, suggesting that internalization occurs within a few minutes. Collectively, our results provide a molecular foundation for the ability of FnBPA to trigger host cell invasion by S. aureus and offer promising prospects for the development of therapeutic approaches against intracellular pathogens

A Presence- and Performance-Driven Framework to Investigate Interactive Networked Music Learning Scenarios

Cooperative music making in networked environments has been subject of extensive research, scientific and artistic. Networked music performance (NMP) is attracting renewed interest thanks to the growing availability of effective technology and tools for computer-based communications, especially in the area of distance and blended learning applications. We propose a conceptual framework for NMP research and design in the context of classical chamber music practice and learning: presence-related constructs and objective quality metrics are used to problematize and systematize the many factors affecting the experience of studying and practicing music in a networked environment. To this end, a preliminary NMP experiment on the effect of latency on chamber music duos experience and quality of the performance is introduced. The degree of involvement, perceived coherence, and immersion of the NMP environment are here combined with measures on the networked performance, including tempo trends and misalignments from the shared score. Early results on the impact of temporal factors on NMP musical interaction are outlined, and their methodological implications for the design of pedagogical applications are discussed

Immunogenic Properties of Streptococcus agalactiae FbsA Fragments

Several species of Gram-positive bacteria can avidly bind soluble and surface-associated fibrinogen (Fng), a property that is considered important in the pathogenesis of human infections. To gain insights into the mechanism by which group B Streptococcus (GBS), a frequent neonatal pathogen, interacts with Fng, we have screened two phage displayed genomic GBS libraries. All of the Fng-binding phage clones contained inserts encoding fragments of FbsA, a protein displaying multiple repeats. Since the functional role of this protein is only partially understood, representative fragments were recombinantly expressed and analyzed for Fng binding affinity and ability to induce immune protection against GBS infection. Maternal immunization with 6pGST, a fragment containing five repeats, significantly protected mouse pups against lethal GBS challenge and these protective effects could be recapitulated by administration of anti-6pGST serum from adult animals. Notably, a monoclonal antibody that was capable of neutralizing Fng binding by 6pGST, but not a non-neutralizing antibody, could significantly protect pups against lethal GBS challenge. These data suggest that FbsA-Fng interaction promotes GBS pathogenesis and that blocking such interaction is a viable strategy to prevent or treat GBS infections

Extensive Adaptive Changes Occur in the Transcriptome of Streptococcus agalactiae (Group B Streptococcus) in Response to Incubation with Human Blood

To enhance understanding of how Streptococcus agalactiae (group B streptococcus, GBS) adapts during invasive infection, we performed a whole-genome transcriptome analysis after incubation with whole human blood. Global changes occurred in the GBS transcriptome rapidly in response to blood contact following shift from growth in a rich laboratory medium. Most (83%) of the significantly altered transcripts were down-regulated after 30 minutes of incubation in blood, and all functional categories of genes were abundantly represented. We observed complex dynamic changes in the expression of transcriptional regulators and stress response genes that allow GBS to rapidly adapt to blood. The transcripts of relatively few proven virulence genes were up-regulated during the first 90 minutes. However, a key discovery was that genes encoding proteins involved in interaction with the host coagulation/fibrinolysis system and bacterial-host interactions were rapidly up-regulated. Extensive transcript changes also occurred for genes involved in carbohydrate metabolism, including multi-functional proteins and regulators putatively involved in pathogenesis. Finally, we discovered that an incubation temperature closer to that occurring in patients with severe infection and high fever (40°C) induced additional differences in the GBS transcriptome relative to normal body temperature (37°C). Taken together, the data provide extensive new information about transcriptional adaptation of GBS exposed to human blood, a crucial step during GBS pathogenesis in invasive diseases, and identify many new leads for molecular pathogenesis research

Essential versus accessory aspects of cell death: recommendations of the NCCD 2015

Cells exposed to extreme physicochemical or mechanical stimuli die in an uncontrollable manner, as a result of their immediate structural breakdown. Such an unavoidable variant of cellular demise is generally referred to as ‘accidental cell death’ (ACD). In most settings, however, cell death is initiated by a genetically encoded apparatus, correlating with the fact that its course can be altered by pharmacologic or genetic interventions. ‘Regulated cell death’ (RCD) can occur as part of physiologic programs or can be activated once adaptive responses to perturbations of the extracellular or intracellular microenvironment fail. The biochemical phenomena that accompany RCD may be harnessed to classify it into a few subtypes, which often (but not always) exhibit stereotyped morphologic features. Nonetheless, efficiently inhibiting the processes that are commonly thought to cause RCD, such as the activation of executioner caspases in the course of apoptosis, does not exert true cytoprotective effects in the mammalian system, but simply alters the kinetics of cellular demise as it shifts its morphologic and biochemical correlates. Conversely, bona fide cytoprotection can be achieved by inhibiting the transduction of lethal signals in the early phases of the process, when adaptive responses are still operational. Thus, the mechanisms that truly execute RCD may be less understood, less inhibitable and perhaps more homogeneous than previously thought. Here, the Nomenclature Committee on Cell Death formulates a set of recommendations to help scientists and researchers to discriminate between essential and accessory aspects of cell death