The relationship between mechanical properties and microstructure of HT9 steel

Next-generation advanced reactor system designs present new challenges for material design and selection. The structural materials selected for these reactors will need to withstand higher operation temperatures, more neutron irradiation (greater flux), and corrosion from liquid metal coolants. HT9, a ferritic/martensitic alloy, was used in previous fast research reactors (such as EBR-II and FFTF). However, it needs validation before it can be selected for use in the more extreme environments of Gen–IV reactors. This dissertation presents a series of in-situ high-energy synchrotron X-ray diffraction (XRD) tensile tests conducted on alloy HT9. The loading behavior of HT9 was examined using diffraction line profile analysis methods. Analysis of the shift in diffraction peak position during deformation of the specimens allowed for the determination of elastic lattice strains in the two primary constituent phases of the material: the ferritic/martensitic matrix and the Cr23C6 carbide particles. With the initiation of plastic deformation, the samples exhibited a clear load transfer from the matrix phase to the carbide particulate. The evolution of the dislocation density in the material as a result of deformation was characterized by peak broadening analysis. Small scale tensile samples of HT9 were strained at room temperature and at test temperatures from 300 C to 500 C. The Cr23C6 carbide phase in the material is shown to accommodate a significant portion of the load after the ferrite phase yields, despite making up only 3% by volume. A set of irradiation-damaged HT9 samples harvested from a duct irradiated in the FFTF were also examined using in-situ XRD. This unique set of specimens extracted from the ACO–3 duct represents a first set of samples to be irradiated under realistic time-variant conditions, including cyclic temperature and fluence variations

Acute coronary syndrome as a current issue of pediatric cardiology. Outcomes and prognosis: Clinical case

Background. Acute coronary syndrome is widespread in the adult population and has clear diagnostic criteria. In pediatric practice, this pathology is rare, and often implies difficulties in diagnosis. Case description. A 16-year-old male with negative paternal history, hypercholesterolemia, dyslipidemia, and excessive body weight developed myocardial infarction on the background of acute tonsillitis. In the onset of the disease, the adolescent demonstrated clinical signs of acute respiratory infection and coronary spasm. Electrocardiogram revealed ST segment elevation above the baseline in leads I, II, III, aVF, V4–V6 and biochemical markers of myocardial necrosis. Echocardiography revealed signs of focal hypokinesis of the left ventricle, newly detected degree 2 mitral regurgitation. Percutaneous coronary angiography revealed no signs of coronary artery stenosis. The patient received conventional medical treatment of acute myocardial infarction as well as antibacterial therapy. He was discharged in satisfactory condition. After 1 year of follow-up after the myocardial infarction the patient showed no pathologic changes both on stress-echocardiography and electrocardiogram. Three-year catamnesis appeared to be favorable. Conclusion. The presented clinical case demonstrates the individual mechanism of acute coronary syndrome development in children. Pediatricians should be aware of the risk of developing acute coronary syndrome against the background of infectious pathology

Competing Patterns of Signaling Activity in Dictyostelium discoideum

Quantitative experiments are described on spatio-temporal patterns of coherent chemical signaling activity in populations of {\it Dictyostelium discoideum} amoebae. We observe competition between spontaneously firing centers and rotating spiral waves that depends strongly on the overall cell density. At low densities, no complete spirals appear and chemotactic aggregation is driven by periodic concentric waves, whereas at high densities the firing centers seen at early times nucleate and are apparently entrained by spiral waves whose cores ultimately serve as aggregation centers. Possible mechanisms for these observations are discussed.Comment: 10 pages, RevTeX, 4 ps figures, accepted in PR

Streaming instability of slime mold amoebae: An analytical model

During the aggregation of amoebae of the cellular slime mould Dictyostelium, the interaction of chemical waves of the signaling molecule cAMP with cAMP-directed cell movement causes the breakup of a uniform cell layer into branching patterns of cell streams. Recent numerical and experimental investigations emphasize the pivotal role of the cell-density dependence of the chemical wave speed for the occurrence of the streaming instability. A simple, analytically tractable, model of Dictyostelium aggregation is developed to test this idea. The interaction of cAMP waves with cAMP-directed cell movement is studied in the form of coupled dynamics of wave front geometries and cell density. Comparing the resulting explicit instability criterion and dispersion relation for cell streaming with the previous findings of model simulations and numerical stability analyses, a unifying interpretation of the streaming instability as a cAMP wave-driven chemotactic instability is proposed

A Behavioral Odor Similarity “Space” in Larval Drosophila

To provide a behavior-based estimate of odor similarity in larval Drosophila, we use 4 recognition-type experiments: 1) We train larvae to associate an odor with food and then test whether they would regard another odor as the same as the trained one. 2) We train larvae to associate an odor with food and test whether they prefer the trained odor against a novel nontrained one. 3) We train larvae differentially to associate one odor with food, but not the other one, and test whether they prefer the rewarded against the nonrewarded odor. 4) In an experiment like (3), we test the larvae after a 30-min break. This yields a combined task-independent estimate of perceived difference between odor pairs. Comparing these perceived differences to published measures of physicochemical difference reveals a weak correlation. A notable exception are 3-octanol and benzaldehyde, which are distinct in published accounts of chemical similarity and in terms of their published sensory representation but nevertheless are consistently regarded as the most similar of the 10 odor pairs employed. It thus appears as if at least some aspects of olfactory perception are “computed” in postreceptor circuits on the basis of sensory signals rather than being immediately given by them

Does the Potential for Chaos Constrain the Embryonic Cell-Cycle Oscillator?

Although many of the core components of the embryonic cell-cycle network have been elucidated, the question of how embryos achieve robust, synchronous cellular divisions post-fertilization remains unexplored. What are the different schemes that could be implemented by the embryo to achieve synchronization? By extending a cell-cycle model previously developed for embryos of the frog Xenopus laevis to include the spatial dimensions of the embryo, we establish a novel role for the rapid, fertilization-initiated calcium wave that triggers cell-cycle oscillations. Specifically, in our simulations a fast calcium wave results in synchronized cell cycles, while a slow wave results in full-blown spatio-temporal chaos. We show that such chaos would ultimately lead to an unpredictable patchwork of cell divisions across the embryo. Given this potential for chaos, our results indicate a novel design principle whereby the fast calcium-wave trigger following embryo fertilization synchronizes cell divisions

Reconstruction of cellular variability from spatiotemporal patterns of Dictyostelium discoideum

Variability in cell properties can be an important driving mechanism behind spatiotemporal patterns in biological systems, as the degree of cell-to-cell differences determines the capacity of cells to locally synchronize and, consequently, form patterns on a larger spatial scale. In principle, certain features of spatial patterns emerging with time may be regulated by variability or, more specifically, by certain constellations of cell-to-cell differences. Similarly, measuring variability in a system (i.e. the spatial distribution of cell-cell differences) may help predict properties of later-stage patterns

The evolution of aggregative multicellularity and cell-cell communication in the Dictyostelia

AbstractAggregative multicellularity, resulting in formation of a spore-bearing fruiting body, evolved at least six times independently amongst both eukaryotes and prokaryotes. Amongst eukaryotes, this form of multicellularity is mainly studied in the social amoeba Dictyostelium discoideum. In this review, we summarise trends in the evolution of cell-type specialisation and behavioural complexity in the four major groups of Dictyostelia. We describe the cell–cell communication systems that control the developmental programme of D. discoideum, highlighting the central role of cAMP in the regulation of cell movement and cell differentiation. Comparative genomic studies showed that the proteins involved in cAMP signalling are deeply conserved across Dictyostelia and their unicellular amoebozoan ancestors. Comparative functional analysis revealed that cAMP signalling in D. discoideum originated from a second messenger role in amoebozoan encystation. We highlight some molecular changes in cAMP signalling genes that were responsible for the novel roles of cAMP in multicellular development

Sour Taste Responses in Mice Lacking PKD Channels

The polycystic kidney disease-like ion channel PKD2L1 and its associated partner PKD1L3 are potential candidates for sour taste receptors. PKD2L1 is expressed in type III taste cells that respond to sour stimuli and genetic elimination of cells expressing PKD2L1 substantially reduces chorda tympani nerve responses to sour taste stimuli. However, the contribution of PKD2L1 and PKD1L3 to sour taste responses remains unclear.We made mice lacking PKD2L1 and/or PKD1L3 gene and investigated whole nerve responses to taste stimuli in the chorda tympani or the glossopharyngeal nerve and taste responses in type III taste cells. In mice lacking PKD2L1 gene, chorda tympani nerve responses to sour, but not sweet, salty, bitter, and umami tastants were reduced by 25–45% compared with those in wild type mice. In contrast, chorda tympani nerve responses in PKD1L3 knock-out mice and glossopharyngeal nerve responses in single- and double-knock-out mice were similar to those in wild type mice. Sour taste responses of type III fungiform taste cells (GAD67-expressing taste cells) were also reduced by 25–45% by elimination of PKD2L1.These findings suggest that PKD2L1 partly contributes to sour taste responses in mice and that receptors other than PKDs would be involved in sour detection

The Radish Gene Reveals a Memory Component with Variable Temporal Properties

Memory phases, dependent on different neural and molecular mechanisms, strongly influence memory performance. Our understanding, however, of how memory phases interact is far from complete. In Drosophila, aversive olfactory learning is thought to progress from short-term through long-term memory phases. Another memory phase termed anesthesia resistant memory, dependent on the radish gene, influences memory hours after aversive olfactory learning. How does the radish-dependent phase influence memory performance in different tasks? It is found that the radish memory component does not scale with the stability of several memory traces, indicating a specific recruitment of this component to influence different memories, even within minutes of learning