After detonation synthesis, primary nanodiamond particles are around 4–6 nm in size. However, they join into agglomerates with larger parameters and weak bonds between particles. The introduction of ...agglomerates into a metal matrix can lead to the weakness of composites. This paper demonstrates the possibility of obtaining a non-agglomerated distribution of nanodiamonds inside a metal matrix. The fabrication method was based on mechanical alloying to create additional stresses and deformations by phase transformations during treatment in a planetary mill. According to the findings, the starting temperature of the reaction between the non-agglomerated nanodiamonds and aluminium matrix reduces to 450 °C. Furthermore, the paper shows that existing methods (annealing for the transformation of a diamond structure into graphitic material and cleaning from this graphitic material) cannot reduce the sizes of nanodiamonds in the agglomerated state. Agglomerated nanodiamonds transform into carbon onions (graphitic material) during annealing in a vacuum in the following way: the nanodiamonds located in the surface layers of the agglomerate are the first to undergo the complete transformation followed by the transformation of nanoparticles in its deeper layers. In the intermediate state, the agglomerate has a graphitic surface layer and a core from nanodiamonds: cleaning from graphite cannot reduce nanodiamond particle size.
The article studies the influence of the level and type of reinforcement of bending elements of reinforced concrete structures on their bearing capacity under the influence of alternating freezing ...and thawing. Strength and deformation characteristics for B30 concrete class were taken according to Construction Rules SP 63.13330.2018, and after exposure to alternating freezing and thawing according to Construction Rules SP 52.105.2009. The study of the stress-strain state and the assessment of the bearing capacity were carried out according to a specially developed program, in which the diagrammatic method was implemented. It is shown that the durability of bent reinforced concrete structures depends on the percentage and type of reinforcement. When reinforcing with longitudinal tensile reinforcement equal to 1%, the decrease in the bearing capacity of a reinforced concrete beam after exposure to alternating freezing and thawing will make up 5.5%, and in case of 2.5% reinforcement it will equal to 20.9%. In addition, the nature of fracture will change and the stress in the tensile reinforcement will not reach the design resistance. If it is impossible to limit the percentage of reinforcement of longitudinal tensile reinforcement, it is recommended to use double reinforcement. Installation of working reinforcement in a compressed zone in a volume of 50% of the stretched one with a reinforcement percentage of 2% will reduce the decrease in bearing capacity to 2.2% after exposure to freezing and thawing cycles and not change the nature of destruction.
Diploma or Dropout - it is argued, whether graduation is more important than a successful startup. Students drop either college or their ideas. A presented exploratory study about the incubation of ...technological startups among students tries to solve this contradiction. The curricula business incubation as the educational discipline inside of the curriculum was offered in opposition to the extracurricular activities of students. There is not a lot of data about this model of student incubation outside of the university's entrepreneurship center and every contribution is valuable. The used research method is Qualitative studies, so the surveys among students are conducted during and after the incubation process on the educational discipline "Startup & Technological Entrepreneurship". At the end of this research, the framework was proposed, a set of actions, for helping students to go all the way from Idea to Product and Techno-Business. The framework is tested on a limited number of students in several universities in developing countries. The experiment is about embedding the syllabus into the Curriculum and measuring of achievements of students. The course is supposed to be elective and only students wishing to develop something are accepted. Later, interviews are conducted with two groups of students: those who passed the offered course and those who tried to develop startups independently. The final aim is to prove whether the inter-curricular framework works and how it overperforms other similar extra-curricular solutions.
One view in the literature is that the East Asian economic model is superior to other models in the Global South (i.e. in the developing world), at least in terms of catch-up development and possibly ...even in innovations beyond the technological frontier. Unlike economic models in Latin America and Sub-Saharan Africa, the East Asian model prioritizes community interests of the work collective, the neighbourhood, the nation-state, and all of humanity over those of individuals, possibly limiting some human rights for the greater benefit of all. Crucial features of the East Asian economic model include relatively low income and wealth inequalities, strong state institutional capacity. The origins of the East Asian economic model can be traced to different trajectories of the development of the Global South since the 16th century.This paper argues that European economic model and the East Asian model have a lot in common. After controlling for the country size and the level of development, it turns out that government consumption as a share of GDP is relatively high in both models, whereas income inequalities are relatively low.
Considering a certain construction of algebraic varieties
X
endowed with an algebraic action of the group Aut(
F
n
),
n
< ∞, we obtain a criterion for the faithfulness of this action. It gives an ...infinite family
𝔉
of
X
s such that Aut(
F
n
) embeds into Aut(
X
). For
n
≥ 3, this implies nonlinearity, and for
n
≥ 2, the existence of
F
2
in Aut(
X
) (hence nonamenability of the latter) for
X
∈
𝔉
. We find in
𝔉
two infinite subfamilies
𝒩
and
ℜ
consisting of irreducible affine varieties such that every
X
∈
𝒩
is nonrational (and even not stably rational), while every
X
∈
𝔉
is rational and 3
n
-dimensional. As an application, we show that the minimal dimension of affine algebraic varieties
Z
, for which Aut(
Z
) contains the braid group
B
n
on
n
strands, does not exceed 3
n
. This upper bound significantly strengthens the one following from the paper by D. Krammer Kr02, where the linearity of
B
n
was proved (this latter bound is quadratic in
n
). The same upper bound also holds for Aut(
F
n
). In particular, it shows that the minimal rank of the Cremona groups containing Aut(
F
n
), does not exceed 3
n
, and the same is true for
B
n
.
Additive manufacturing (AM) is an alternative metal fabrication technology. The outstanding advantage of AM (3D-printing, direct manufacturing), is the ability to form shapes that cannot be formed ...with any other traditional technology. 3D-printing began as a new method of prototyping in plastics. Nowadays, AM in metals allows to realize not only net-shape geometry, but also high fatigue strength and corrosion resistant parts. This success of AM in metals enables new applications of the technology in important fields, such as production of medical implants. The 3D-printing of medical implants is an extremely rapidly developing application. The success of this development lies in the fact that patient-specific implants can promote patient recovery, as often it is the only alternative to amputation. The production of AM implants provides a relatively fast and effective solution for complex surgical cases. However, there are still numerous challenging open issues in medical 3D-printing. The goal of the current research review is to explain the whole technological and design chain of bio-medical bone implant production from the computed tomography that is performed by the surgeon, to conversion to a computer aided drawing file, to production of implants, including the necessary post-processing procedures and certification. The current work presents examples that were produced by joint work of Polygon Medical Engineering, Russia and by TechMed, the AM Center of Israel Institute of Metals. Polygon provided 3D-planning and 3D-modelling specifically for the implants production. TechMed were in charge of the optimization of models and they manufactured the implants by Electron-Beam Melting (EBM
®
), using an Arcam EBM
®
A2X machine.
The current paper is devoted to classification of powder-bed additive manufacturing (PB-AM) techniques and description of specific features, advantages and limitation of different PB-AM techniques in ...aerospace applications. The common principle of “powder-bed” means that the used feedstock material is a powder, which forms “bed-like” platform of homogeneous layer that is fused according to cross-section of the manufactured object. After that, a new powder layer is distributed with the same thickness and the “printing” process continues. This approach is used in selective laser sintering/melting process, electron beam melting, and binder jetting printing. Additionally, relevant issues related to powder raw materials (metals, ceramics, multi-material composites, etc.) and their impact on the properties of as-manufactured components are discussed. Special attention is paid to discussion on additive manufacturing (AM) of aerospace critical parts made of Titanium alloys, Nickel-based superalloys, metal matrix composites (MMCs), ceramic matrix composites (CMCs) and high entropy alloys. Additional discussion is related to the quality control of the PB-AM materials, and to the prospects of new approaches in material development for PB-AM aiming at aerospace applications.
Hybrid additive manufacturing is a relatively modern trend in the integration of different additive manufacturing techniques in the traditional manufacturing production chain. Here the AM-technique ...is used for producing a part on another substrate part, that is manufactured by traditional manufacturing like casting or milling. Such beneficial combination of additive and traditional manufacturing helps to overcome well-known issues, like limited maximum build size, low production rate, insufficient accuracy, and surface roughness. The current paper is devoted to the classification of different approaches in the hybrid additive manufacturing of steel components. Additional discussion is related to the benefits of Powder Bed Fusion (PBF) and Direct Energy Deposition (DED) approaches for hybrid additive manufacturing of steel components.
PDF
