1,721,111 research outputs found
Space radiation and hypervelocity impact shielding for low earth orbit space structures using ultrahigh-molecular-weight polyethylene
No full textSpace radiation is defined as particle radiation consisting of protons, heavy ions, and electrons. Space radiation has a catastrophic effect on satellite electronics and reduces its lifespan. It also greatly limits the performance of satellite electronics. It makes it impossible for astronauts to stay in space for long-term because of the potential of various diseases and cancer. Polyethylene is known to perform very well in space radiation shielding. In particular, ultra- high- molecular- weight polyethylene (UHMWPE) has very high mechanical performance. Meanwhile, there are millions of space debris in Earth's orbit now. These debris have hypervelocity impact of several tens of km/s depending on the orbit and thus threaten the survival of space structures. In the case of International Space Station, the concept of Whipple shield, a dual aluminum protection system, is applied to protect the astronaut from impact of space debris. In this study, space radiation shielding and hypervelocity impact performance of proposed space structure system with ultra- high- molecular- weight polyethylene is investigated. Cyclotron was used for proton irradiation test. Also, a two stage light gas gun was used for hypervelocity impact test. The UHMWPE showed better performance in space radiation shielding and hypervelocity impact than Kevlar
Tubular laminated composite structural battery
No full textThis paper introduces a polymer-matrix composite-based structural lithium-ion battery system with tubular morphology. Its shape and closed cross-section, fabricated during the autoclave process, allow for high electrochemical performance by controlling the electrode distance and battery environment. To prevent the degradation of the organic liquid electrolyte within this continuous resin polymer system, extra components such as thermoplastic hot melt film, a double glass load-bearing separator, aluminum film, and polydimethylsiloxane were implanted. The electrochemical properties of this manufactured multi-functional structural battery design, named the tubular laminated composite battery (TLCB), were tested with a galvanic cell testing machine. The initial specific capacity of TLCB was found to be approximately 120-130 mAh/g with good cycling performance and steady coulombic efficiency. Furthermore, mechanical load resistance and correlation with electrochemical performance were also assessed under the four-point bending load condition. These results show that the TLCB has the potential to operate as a subsidiary energy storage for future electric vehicle systems with a certain level of structural specific capacity and load-bearing properties.
Early intraneuronal accumulation and increased aggregation of phosphorylated Abeta in a mouse model of Alzheimer's disease
No full textThe progressive accumulation of extracellular amyloid plaques in the brain is a common hallmark of Alzheimer's disease (AD). We recently identified a novel species of A beta phosphorylated at serine residue 8 with increased propensity to form toxic aggregates as compared to non-phosphorylated species. The age-dependent analysis of A beta depositions using novel monoclonal phosphorylation-state specific antibodies revealed that phosphorylated A beta variants accumulate first inside of neurons in a mouse model of AD already at 2 month of age. At higher ages, phosphorylated A beta is also abundantly detected in extracellular plaques. Besides a large overlap in the spatiotemporal deposition of phosphorylated and non-phosphorylated A beta species, fractionized extraction of A beta from brains revealed an increased accumulation of phosphorylated A beta in oligomeric assemblies as compared to non-phosphorylated A beta in vivo. Thus, phosphorylated A beta could represent an important species in the formation and stabilization of neurotoxic aggregates, and might be targeted for AD therapy and diagnosis
Phosphorylation modifies the molecular stability of beta-amyloid deposits
No full textProtein aggregation plays a crucial role in neurodegenerative diseases. A key feature of protein aggregates is their ubiquitous modification by phosphorylation. Little is known, however, about the molecular consequences of phosphorylation of protein aggregates. Here we show that phosphorylation of beta-amyloid at serine 8 increases the stability of its pathogenic aggregates against high-pressure and SDS-induced dissociation. We further demonstrate that phosphorylation results in an elevated number of hydrogen bonds at the N terminus of beta-amyloid, the region that is critically regulated by a variety of post-translational modifications. Because of the increased lifetime of phosphorylated beta-amyloid aggregates, phosphorylation can promote the spreading of beta-amyloid in Alzheimer pathogenesis. Our study suggests that regulation of the molecular stability of protein aggregates by post-translational modifications is a crucial factor for disease progression in the brain
Phosphorylation Interferes with Maturation of Amyloid-β Fibrillar Structure in the N Terminus
Full text linkNeurodegeneration is characterized by the ubiquitous presence of modifications in protein deposits. Despite their potential significance in the initiation and progression of neurodegenerative diseases, the effects of posttranslational modifications on the molecular properties of protein aggregates are largely unknown. Here, we study the Alzheimer disease-related amyloid-β (Aβ) peptide and investigate how phosphorylation at serine 8 affects the structure of Aβ aggregates. Serine 8 is shown to be located in a region of high conformational flexibility in monomeric Aβ, which upon phosphorylation undergoes changes in local conformational dynamics. Using hydrogen-deuterium exchange NMR and fluorescence quenching techniques, we demonstrate that Aβ phosphorylation at serine 8 causes structural changes in the N-terminal region of Aβ aggregates in favor of less compact conformations. Structural changes induced by serine 8 phosphorylation can provide a mechanistic link between phosphorylation and other biological events that involve the N-terminal region of Aβ aggregates. Our data therefore support an important role of posttranslational modifications in the structural polymorphism of amyloid aggregates and their modulatory effect on neurodegeneration
Polybenzimidazole (PBI) film coating for improved hypervelocity impact energy absorption for space applications
No full textThis paper deals with how the use of Polybenzimidazole (PBI) as a film coating over conventional composite designs could help improve the hypervelocity impact ballistic performance of the system. PBI coated composite samples were studied for resistance to Low Earth Orbit environment conditions like high vacuum, thermal cycling, Atomic Oxygen and Ultraviolet Radiation in a simulation facility. It was observed that the PBI coated composites reduced mass loss and surface erosion compared to the non-coated samples after LEO exposure. Hypervelocity impact experiments were conducted on the PBI coated composites for impact velocities between 2.5 to 3 km/s. The experiments showed that the PBI film coating significantly increased the energy absorption of the composite system. The effect of thickness increase as a result of the film application on energy absorption was also found to be negligible confirming the effectiveness of PBI coating as a hypervelocity shield.N
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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