Many researches have been conducted on the topic of the AlSi10Mg alloy, covering different aspects of the selective laser melting fabrication process. However, a database is still lacking much ...information and understanding regarding the properties of the material under different conditions, which will allow a tailoring of suitable properties to the required application. This work aims to provide a correlation between the mechanical properties of vertically built (Z samples) AlSi10Mg specimens subjected to different post-processing conditions and the change in properties in relation to these conditions and the fracture mechanism. Among these is the accepted T5 stress relief treatment, a modified T5 treatment, the as-built condition and a high temperature Hot Isostatic Pressing treatment. A more in-depth analysis of the fracture mode for the vertical build direction is provided with emphasis on the mechanism for each treatment as well as a quantitative analysis of the Full Width at Half Maximum via X-Ray diffraction measurements. The modified T5 treatment suggested was found to result in an increase in strength values beyond those of the as-built condition and a 64% increase in yield stress compared to the typical T5 treatment with a concurrent decrease in elongation values. It is suggested that at 200 °C nano-scale precipitation of Silicon particles occurs, responsible for the strength elevation. Charpy impact test results are provided for each condition and their fracture mode is compared to the tensile tests and discussed.
Implementation of Additive Manufacturing (AM) parts in the growing applications within the automotive and aerospace industries encourages further investigations of the material behavior under various ...strain rates, spanning from quasi-static to the high strain rate regimes. Although mechanical properties of AM-Selective Laser Melting (SLM) AlSi10Mg parts under a static regime have been investigated, the strain rate sensitivity of these materials, to the best of our knowledge, has not been discussed in the literature. In this work, the properties of AM-SLM AlSi10Mg material were systematically investigated under a wide range of strain rates, spanning from 2.77×10−6 to 2.77×10−1 S−1. The AM-SLM AlSi10Mg alloy, as opposed to Al alloys fabricated by conventional methods, was found to be strain rate sensitive with significant changes to the flow stress and strain hardening exponents with an increase in strain rate. The fracture mechanisms of these specimens, built in different orientations, are discussed.
We report that, in the rat hippocampus, learning leads to a significant increase in extracellular lactate levels that derive from glycogen, an energy reserve selectively localized in astrocytes. ...Astrocytic glycogen breakdown and lactate release are essential for long-term but not short-term memory formation, and for the maintenance of long-term potentiation (LTP) of synaptic strength elicited in vivo. Disrupting the expression of the astrocytic lactate transporters monocarboxylate transporter 4 (MCT4) or MCT1 causes amnesia, which, like LTP impairment, is rescued by L-lactate but not equicaloric glucose. Disrupting the expression of the neuronal lactate transporter MCT2 also leads to amnesia that is unaffected by either L-lactate or glucose, suggesting that lactate import into neurons is necessary for long-term memory. Glycogenolysis and astrocytic lactate transporters are also critical for the induction of molecular changes required for memory formation, including the induction of phospho-CREB, Arc, and phospho-cofilin. We conclude that astrocyte-neuron lactate transport is required for long-term memory formation.
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► Learning results in glycogenolysis-dependent lactate increase in the hippocampus ► Inhibiting glycogenolysis in the hippocampus blocks long-term memory and LTP ► Knockdown of astrocytic lactate transporters abolishes long-term memory ► Knockdown of neuronal lactate transporter abolishes long-term memory
Pathological tau leads to dementia and neurodegeneration in tauopathies, including Alzheimer’s disease. It has been shown to disrupt cellular and synaptic functions, yet its effects on the function ...of the intact neocortical network remain unknown. Using in vivo intracellular and extracellular recordings, we measured ongoing activity of neocortical pyramidal cells during various arousal states in the rTg4510 mouse model of tauopathy, prior to significant cell death, when only a fraction of the neurons show pathological tau. In transgenic mice, membrane potential oscillations are slower during slow-wave sleep and under anesthesia. Intracellular recordings revealed that these changes are due to longer Down states and state transitions of membrane potentials. Firing rates of transgenic neurons are reduced, and firing patterns within Up states are altered, with longer latencies and inter-spike intervals. By changing the activity patterns of a subpopulation of affected neurons, pathological tau reduces the activity of the neocortical network.
•Pathological tau disrupts the activity of single cells and neocortical networks•Pathological tau alters neocortical neuronal oscillatory patterns•Pathological tau affects firing patterns of neocortical pyramidal cells
Menkes-Caspi et al. show that the activity of cortical neurons is reduced in tau-transgenic mice, including in neurons without detectable pathological tau. The pathological effects on a group of neurons are amplified and propagated through the entire cortical network.
Noncommutative point sources Stern, A
Physical review letters,
02/2008, Letnik:
100, Številka:
6
Journal Article
Recenzirano
Odprti dostop
We construct a perturbative solution to classical noncommutative gauge theory on R3 minus the origin using the Groenewald-Moyal star product. The result describes a noncommutative point charge. ...Applying it to the quantum mechanics of the noncommutative hydrogen atom gives shifts in the 1S hyperfine splitting which are first order in the noncommutativity parameter.
Various classical solutions to lower dimensional Ishibashi-Kawai-Kitazawa-Tsuchiya–like Lorentzian matrix models are examined in their commutative limit. Poisson manifolds emerge in this limit, and ...their associated induced and effective metrics are computed. Signature change is found to be a common feature of these manifolds when quadratic and cubic terms are included in the bosonic action. In fact, a single manifold may exhibit multiple signature changes. Regions with a Lorentzian signature may serve as toy models for cosmological spacetimes, complete with cosmological singularities, occurring at the signature change. The singularities are resolved away from the commutative limit. Toy models of open and closed cosmological spacetimes are given in two and four dimensions. The four-dimensional cosmologies are constructed from noncommutative complex projective spaces, and they are found to display a rapid expansion near the initial singularity.
Background It is increasingly evident that microbial colonization of the respiratory tract might have a role in the pathogenesis of asthma. Objective We sought to characterize and compare the ...microbiome of induced sputum in asthmatic and nonasthmatic adults. Methods Induced sputum samples were obtained from 10 nonasthmatic subjects and 10 patients with mild active asthma (8/10 were not using inhaled corticosteroids). Total DNA was extracted from sputum supernatants and amplified by using primers specific for the V6 hypervariable region of bacterial 16s rRNA. Samples were barcoded, and equimolar concentrations of 20 samples were pooled and sequenced with the 454 GS FLX sequencer. Sequences were assigned to bacterial taxa by comparing them with 16s rRNA sequences in the Ribosomal Database Project. Results All sputum samples contained 5 major bacterial phyla: Firmicutes, Proteobacteria, Actinobacteria, Fusobacterium, and Bacteroidetes, with the first 3 phyla accounting for more than 90% of the total sequences. Proteobacteria were present in higher proportions in asthmatic patients (37% vs 15%, P < .001). In contrast, Firmicutes (47% vs 63%, P = .17) and Actinobacteria (10% vs 14%, P = .36) were found more frequently in samples from nonasthmatic subjects, although this was not statistically significant. Hierarchical clustering produced 2 significant clusters: one contained primarily asthmatic samples and the second contained primarily nonasthmatic samples. In addition, samples from asthmatic patients had greater bacterial diversity compared with samples from nonasthmatic subjects. Conclusion Patients with mild asthma have an altered microbial composition in the respiratory tract that is similar to that observed in patients with more severe asthma.
Chronic traumatic encephalopathy (CTE) is a form of neurodegeneration believed to result from repeated head injuries. Originally termed dementia pugilistica because of its association with boxing, ...the neuropathology of CTE was first described by Corsellis in 1973 in a case series of 15 retired boxers. CTE has recently been found to occur after other causes of repeated head trauma, suggesting that any repeated blows to the head, such as those that occur in American football, hockey, soccer, professional wrestling, and physical abuse, can also lead to neurodegenerative changes. These changes often include cerebral atrophy, cavum septi pellucidi with fenestrations, shrinkage of the mammillary bodies, dense tau immunoreactive inclusions (neurofibrillary tangles, glial tangles, and neuropil neurites), and, in some cases, a TDP-43 proteinopathy. In association with these pathologic changes, disordered memory and executive functioning, behavioral and personality disturbances (eg, apathy, depression, irritability, impulsiveness, suicidality), parkinsonism, and, occasionally, motor neuron disease are seen in affected individuals. No formal clinical or pathologic diagnostic criteria for CTE currently exist, but the distinctive neuropathologic profile of the disorder lends promise for future research into its prevention, diagnosis, and treatment.
We perform a systematic search for rotationally invariant cosmological solutions to toy matrix models. These models correspond to the bosonic sector of Lorentzian Ishibashi, Kawai, Kitazawa and ...Tsuchiya (IKKT)-type matrix models in dimensions d less than ten, specifically d= 3 and d= 5. After taking a continuum (or commutative) limit they yield d- 1 dimensional Poisson manifolds. The manifolds have a Lorentzian induced metric which can be associated with closed, open, or static space-times. For d= 3, we obtain recursion relations from which it is possible to generate rotationally invariant matrix solutions which yield open universes in the continuum limit. Specific examples of matrix solutions have also been found which are associated with closed and static two-dimensional space-times in the continuum limit. The solutions provide for a resolution of cosmological singularities, at least within the context of the toy matrix models. The commutative limit reveals other desirable features, such as a solution describing a smooth transition from an initial inflation to a noninflationary era. Many of the d= 3 solutions have analogues in higher dimensions. The case of d= 5, in particular, has the potential for yielding realistic four-dimensional cosmologies in the continuum limit. We find four-dimensional de Sitter dS super(4) or anti-de Sitter AdS super(4) solutions when a totally antisymmetric term is included in the matrix action. A nontrivial Poisson structure is attached to these manifolds which represents the lowest order effect of noncommutativity. For the case of AdS super(4), we find one particular limit where the lowest order noncommutativity vanishes at the boundary, but not in the interior.
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