Spark plasma sintering the spark-erosion powders of functional alloys

Various shape memory alloys (Ti-Ni-Hf, Ni-Al and Cu-Al-Ni) were elaborated by spark plasma sintering method from the micron, submicron and nano- sized particles prepared by spark-erosion method in cryogenic liquid from preliminary melted master alloys. These alloys are being developed as one of the alternatives for the intermediate temperature applications (100-900oC). Spark plasma sintering method is express method, which provides lower temperature and shorter holding time of sintering. It makes possible to sinter materials from the pre-alloyed powders and eliminate the intensive grains growth and precipitating processes influencing the mechanical and functional properties of functional materials. The effects of processing parameters on the martensitic transformation and microstructure of the sintered compacts were investigated using XRD and SEM study. Temperatures of sintering were chosen according to the assessed data of the decomposition, oxidation and others processes carrying out in material. Although the precipitating processes were usually not completely depressed, the intensive grain growth was also not found in most cases. Most of the microstructure peculiarities of as processed powder were inherited by the sintered material. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2079

The Role of Nano-sized Fraction on Spark Plasma Sintering the Pre-Alloyed Spark-Erosion Powders

Ti-Ni-Hf, Ni-Al and Cu-Al-Ni shape memory materials were produced by spark plasma sintering method from the micron and nano-sized particles prepared by spark-erosion method in cryogenic liquid from preliminary melted master alloys. The effects of spark plasma sintering processing parameters on the martensitic transformation and microstructure of the sintered compacts were investigated using XRD and SEM methods. Although precipitating processes were usually not completely depressed, the intensive grain growth was also not found in most cases. Most of the microstructure peculiarities of as processed powder were inherited by the sintered material. The contradictory role of the nano-sized fraction of powders is discussed: in most case this fraction promotes the rapid sintering but also the oxidation proceses in sintered compacts. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2489

Microstructure Investigation of the Spark Plasma Sintered Cu—Al—Ni Shape Memory Material

Исследована микроструктура компактов Cu—13,0Al—3,9Ni—0,4Ti—0,2Cr масс.%, спечённых плазменно-искровым методом из электроэрозионных порошков, изготовленных из мастер-сплава в жидком аргоне.Досліджено мікроструктуру компактів Cu—13,0Al—3,9Ni—0,4Ti—0,2Cr ваг.% спечених плазмово-іскровим методом із електроерозійних порошків, виготовлених із мастер-стопу в рідкому арґоні.The microstructure of Cu—13.0Al—3.9Ni—0.4Ti—0.2Cr wt.% compacts sintered by spark plasma method from powders prepared by spark-erosion method in liquid argon from master alloy is investigated

Mechanical Testing of the Shape-Memory Materials Synthesized by a Plasma-Spark Method

Испытания на сжатие были выполнены при комнатной температуре для образцов сплавов Ni49,0—Mn28,5—Ga22,5 (ат.%) и Ni63—Al37 (ат.%), как для выплавленных, так и полученных плазменно-искровым методом (ПИМ). Для обеих систем пластичность ПИМ-образцов возрастает более чем на порядок по сравнению с исходными. Прочность на сжатие сплава Ni—Mn—Ga увеличивается от 180—240 МПа для выплавленных образцов до 510—815 МПа для ПИМ-образцов в зависимости от режимов обработки, для сплава Ni—Al – от 760 до 1310 МПа. Напряжение разрушения образцов Ni—Mn—Ga увеличивается от 185—215 до 1170 МПа, а для образцов Ni—Al – от 790 до 1870 МПа. Спечённые образцы обеих систем имеют композитную структуру, образованную из металлических частиц микронных размеров, скреплённых связующей фазой, состоящей из Ni₃Al и Al₂O₃ для сплава Ni—Al и из MnO с небольшим количеством Ni₃Ga для сплава Ni—Mn—Ga. Предполагается, что эта фаза укрепляет границы зёрен. Это вместе с уменьшением размера зерна, а также многосвязной морфологией образцов Ni—Mn—Ga, консолидированных из полых частиц, и наличием пластической γ′-фазы в частицах Ni—Al улучшает механические свойства сплавов, полученных плазменно-искровым методом.Випробування на стиснення було виконано при кімнатній температурі для зразків стопів Ni49,0—Mn28,5—Ga22,5 (ат.%) та Ni63—Al37 (ат.%), як щойно витоплених, так і одержаних плазмово-іскровою методою (ПІМ). Для обох систем пластичність ПІМ-зразків зростає більш ніж на порядок порівняно із вихідними. Міцність на стиск стопу Ni—Mn—Ga збільшується від 180—240 МПа для щойно витоплених зразків до 510—815 МПа для ПІМ-зразків, залежно від режимів оброблення; для стопу Ni—Al – від 760 до 1310 МПа. Напруження руйнування зразків Ni—Mn—Ga збільшується від 185—215 до 1170 МПа, а для зразків Ni—Al – від 790 до 1870 МПа. Спечені зразки обох систем мають композитну структуру, утворену з металевих частинок мікронних розмірів, пов’язаних сполучною фазою, що складається з Ni₃Al і Al₂O₃ для стопу Ni—Al та з MnO з невеликою кількістю Ni₃Ga для стопу Ni—Mn—Ga. Передбачається, що ця фаза зміцнює межі зерен. Це разом із зменшенням розміру зерна, а також багатозв’язною морфологією зразків Ni—Mn-Ga, консолідованих із порожнистих частинок, та наявністю пластичної γ′-фази в частинках Ni—Al покращує механічні властивості стопів, одержаних плазмово-іскровою методою.Compression tests are carried out at room temperature with the as-cast and spark-plasma sintered (SPS) specimens of Ni49.0—Mn28.5—Ga22.5 (at.%) and Ni63—Al37 (at.%) alloys. For both systems, ductility of the SPS compacts increases more than by one order of magnitude. Compressive strength of Ni—Mn—Ga alloy increases from 180—240 MPa for induction melted specimens to 510—815 MPa for spark-plasma sintered specimens, depending on the regimes of processing, and for Ni—Al alloy, from 760 to 1310 MPa. Fracture stress of Ni—Mn—Ga and Ni—Al specimens raise from 185—215 to 1170 MPa and from 790 to 1870 MPa, respectively. The SEM and XRD investigations reveal that sintered samples of both systems have a composite structure, which contains the micron-size metallic particles bound by the binder phase. This phase consists of Ni₃Al and Al₂O₃ phases in case of Ni—Al alloy and consists of MnO with apparently small amount of Ni₃Ga phase in case of Ni—Mn—Ga alloy. As assumed, this phase strengthens the grain boundaries. This one, in conjunction with reduction of the grain size, the manifold morphology of the Ni—Mn—Ga specimens consolidated from the hollow particles, the presence of extra ductile γ′-phase in Ni—Al particles, provides the enhancing mechanical properties of alloys fabricated by means of the SPS method

A multifunctional human monoclonal neutralizing antibody that targets a unique conserved epitope on influenza HA

The high rate of antigenic drift in seasonal influenza viruses necessitates frequent changes in vaccine composition. Recent seasonal H3 vaccines do not protect against swine-origin H3N2 variant (H3N2v) strains that recently have caused severe human infections. Here, we report a human VH1-69 gene-encoded monoclonal antibody (mAb) designated H3v-47 that exhibits potent cross-reactive neutralization activity against human and swine H3N2 viruses that circulated since 1989. The crystal structure and electron microscopy reconstruction of H3v-47 Fab with the H3N2v hemagglutinin (HA) identify a unique epitope spanning the vestigial esterase and receptor-binding subdomains that is distinct from that of any known neutralizing antibody for influenza A H3 viruses. MAb H3v-47 functions largely by blocking viral egress from infected cells. Interestingly, H3v-47 also engages Fcγ receptor and mediates antibody dependent cellular cytotoxicity (ADCC). This newly identified conserved epitope can be used in design of novel immunogens for development of broadly protective H3 vaccines

A broadly reactive antibody targeting the N-terminal domain of SARS-CoV-2 spike confers Fc-mediated protection

Most neutralizing anti-SARS-CoV-2 monoclonal antibodies (mAbs) target the receptor binding domain (RBD) of the spike (S) protein. Here, we characterize a panel of mAbs targeting the N-terminal domain (NTD) or other non-RBD epitopes of S. A subset of NTD mAbs inhibits SARS-CoV-2 entry at a post-attachment step and avidly binds the surface of infected cells. One neutralizing NTD mAb, SARS2-57, protects K18-hACE2 mice against SARS-CoV-2 infection in an Fc-dependent manner. Structural analysis demonstrates that SARS2-57 engages an antigenic supersite that is remodeled by deletions common to emerging variants. In neutralization escape studies with SARS2-57, this NTD site accumulates mutations, including a similar deletion, but the addition of an anti-RBD mAb prevents such escape. Thus, our study highlights a common strategy of immune evasion by SARS-CoV-2 variants and how targeting spatially distinct epitopes, including those in the NTD, may limit such escape

Systematic analysis of SARS-CoV-2 infection of an ACE2-negative human airway cell

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike (S) variants govern transmissibility, responsiveness to vaccination, and disease severity. In a screen for new models of SARS-CoV-2 infection, we identify human H522 lung adenocarcinoma cells as naturally permissive to SARS-CoV-2 infection despite complete absence of angiotensin-converting enzyme 2 (ACE2) expression. Remarkably, H522 infection requires the E484D S variant; viruses expressing wild-type S are not infectious. Anti-S monoclonal antibodies differentially neutralize SARS-CoV-2 E484D S in H522 cells as compared to ACE2-expressing cells. Sera from vaccinated individuals block this alternative entry mechanism, whereas convalescent sera are less effective. Although the H522 receptor remains unknown, depletion of surface heparan sulfates block H522 infection. Temporally resolved transcriptomic and proteomic profiling reveal alterations in cell cycle and the antiviral host cell response, including MDA5-dependent activation of type I interferon signaling. These findings establish an alternative SARS-CoV-2 host cell receptor for the E484D SARS-CoV-2 variant, which may impact tropism of SARS-CoV-2 and consequently human disease pathogenesis

Rapid isolation and profiling of a diverse panel of human monoclonal antibodies targeting the SARS-CoV-2 spike protein

Antibodies are a principal determinant of immunity for most RNA viruses and have promise to reduce infection or disease during major epidemics. The novel coronavirus SARS-CoV-2 has caused a global pandemic with millions of infections and hundreds of thousands of deaths to date1,2. In response, we used a rapid antibody discovery platform to isolate hundreds of human monoclonal antibodies (mAbs) against the SARS-CoV-2 spike (S) protein. We stratify these mAbs into five major classes on the basis of their reactivity to subdomains of S protein as well as their cross-reactivity to SARS-CoV. Many of these mAbs inhibit infection of authentic SARS-CoV-2 virus, with most neutralizing mAbs recognizing the receptor-binding domain (RBD) of S. This work defines sites of vulnerability on SARS-CoV-2 S and demonstrates the speed and robustness of advanced antibody discovery platforms

A cultura escolar em conflito: ensino técnico e matemática moderna em Portugal

Disponível em: http://www2.pucpr.br/reol/pb/index.php/dialogo?dd1=16276&dd99=view&dd98=pbO artigo estuda as transformações exigidas às escolas do ensino profissional português durante a reforma da matemática moderna que ocorrem a partir de finais dos anos 1960. Em primeiro lugar, traça um quadro das normas associadas às escolas técnicas portuguesas antes da reforma, recorrendo à legislação fundadora, aos manuais e a artigos de opinião de professores. Em segundo, detalha o debate que antecipou a introdução da reforma recorrendo a artigos e aopiniões expressas durante os cursos preparatórios, onde são notórias as pressões para mudanças na cultura escolar, especialmente nas suas representações, suscitadas pela nova matemática. Finalmente, observar-se como se materializou a reforma nos livros de texto da experiência