200 research outputs found
La fabricación del silicato de sodio : su obtención con productos nacionales
No full textFil: Perazzo, Alberto Antonio. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina
La fabricación del silicato de sodio : su obtención con productos nacionales
No full textFil: Perazzo, Alberto Antonio. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina
Perazzo 3-folds and the weak Lefschetz property
No full textWe deal with Perazzo 3-folds in P4, i.e. hypersurfaces X = V(f) subset of P4 of degree d defined by a homogeneous polynomial f(x0, x1, x2, u, v) = p0(u, v)x0 +p1(u, v)x1 + p2(u, v)x2 + g(u, v), where p0, p1, p2 are algebraically dependent but linearly independent forms of degree d - 1 in u, v, and g is a form in u, v of degree d. Perazzo 3-folds have vanishing hessian and, hence, the associated graded Artinian Gorenstein algebra Af fails the strong Lefschetz Property. In this paper, we determine the maximum and minimum Hilbert function of Af and we prove that if Af has maximal Hilbert function it fails the weak Lefschetz Property while it satisfies the weak Lefschetz Property when it has minimum Hilbert function. In addition, we classify all Perazzo 3-folds in P4 such that Af has minimum Hilbert function.(c) 2023 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons .org /licenses /by -nc -nd /4 .0/)
Phase inversion emulsification: Current understanding and applications
No full textThis review is addressed to the phase inversion process, which is not only a common, low-energy route to make stable emulsions for a variety of industrial products spanning from food to pharmaceuticals, but can also be an undesired effect in some applications, such as crude oil transportation in pipelines. Two main ways to induce phase inversion are described in the literature, i.e., phase inversion composition (PIC or catastrophic) and phase inversion temperature (PIT or transitional). In the former, starting from one phase (oil or water) with surfactants, the other phase is more or less gradually added until it reverts to the continuous phase. In PIT, phase inversion is driven by a temperature change without varying system composition. Given its industrial relevance and scientific challenge, phase inversion has been the subject of a number of papers in the literature, including extensive reviews. Due to the variety of applications and the complexity of the problem, most of the publications have been focused either on the phase behavior or the interfacial properties or the mixing process of the two phases. Although all these aspects are quite important in studying phase inversion and much progress has been done on this topic, a comprehensive picture is still lacking. In particular, the general mechanisms governing the inversion phenomenon have not been completely elucidated and quantitative predictions of the phase inversion point are limited to specific systems and experimental conditions. Here, we review the different approaches on phase inversion and highlight some related applications, including future and emerging perspectives
An Analysis of Routing Attacks Against IOTA Cryptocurrency
No full textIOTA is a new type of distributed ledger designed for allowing fee-less and rate-scalable micropayments in Internet of Things applications. Security research on IOTA has focused mainly on attacks involving its cryptographic operations or its consensus algorithm. In this paper, we present a preliminary analysis of the IOTA security with respect to malicious Autonomous Systems (ASes), which can intercept IOTA connections by manipulating routing advertisements (BGP hijacking) or by naturally intercepting traffic. We make the simplifying assumption that the malicious AS can intercept routes between hosts without causing side effects, or without these side effects being noticed by the intercepted hosts. We identify three notable attacks that can lead to permanent money freeze, and to local or global interruptions of the consensus mechanisms. We then analyze the vulnerability of IOTA against malicious ASes on the real Internet topology, and we show that IOTA cryptocurrency is, at the time of writing, pretty susceptible of these attacks because quite centralized from the point of view of BGP routing. We then study the routing-level security of the next version of IOTA (post-coordicide), which has been proposed by the IOTA Foundations to make the cryptocurrency fully distributed
The effect of flow on viscoelastic emulsion microstructure
No full textEmulsions made of oil, water and surfactants are widespread soft materials with complex structures depending on composition and temperature. Emulsion phase behavior at rest has been widely investigated but flow-induced effects, which are very relevant in many applications, can still be further explored towards improved emulsion microstructural design. In this work, we use low energy emulsification processing to create small-sized emulsions. In a previous report, we showed the emulsion morphology development and the effect of flow on the microstructure of a highly viscoelastic attractive emulsion which result in a concentrated nanoemulsion after viscoelastic droplet filaments are disrupted. Here, we show that upon stopping the flow, the filaments slowly buckle, recoil and finally form clusters of randomly flocculated droplets. We thus obtain two completely different emulsion morphologies simply induced by the action of flow, where in both cases attractive interactions play a key role. The emulsion high interfacial area represents a valuable feature for several applications such as upstream operations, microreaction media and drug delivery
Flow-switchable morphology of concentrated emulsions
No full textSoft materials can be switched from a liquid to a gel-like state by structural re-arrangement down to the nanoscale and find application in many fields ranging from biomedical engineering to oil recovery. Here, we show that flow-switchable emulsions of oil, water and surfactants can be obtained by simple low-energy emulsification processing. By dropwise addition of water to the oil-surfactant solution under mild stirring, a striking transition from a transparent, purely viscous Newtonian fluid to a highly viscoelastic translucent material climbing onto the impeller is observed. We show that this transition is associated with the formation of elongated droplets, eventually disrupting into nanodroplets which, upon stopping the flow, slowly relax to a stable gel-like microstructure with noticeable birefringent properties. The two structures (elongated droplets and gel-like microstructure) can be reversibly switched between each other by starting/stopping the flow. This behavior can be attributed to the interplay between the cluster-disruptive effect of flow on one side, and droplets attractive interactions promoting coalescence on the other side. Our results, observed for different systems by changing oil type and surfactants chain length, highlight a flow-switchable emulsion processing method, which can be used to produce concentrated emulsions for a variety of applications
Emulsions in porous media: From single droplet behavior to applications for oil recovery
No full textFlow-induced gelation of microfiber suspensions
No full textThe flow behavior of fiber suspensions has been studied extensively, especially in the limit of dilute concentrations and rigid fibers;
at the other extreme, however, where the suspensions are concentrated and the fibers are highly flexible, much less is understood
about the flow properties.We use a microfluidic method to produce uniform concentrated suspensions of high aspect ratio, flexible
microfibers, and we demonstrate the shear thickening and gelling behavior of such microfiber suspensions, which, to the best of our
knowledge, has not been reported previously. By rheological means, we show that flowing the suspension triggers the irreversible
formation of topological entanglements of the fibers resulting in an entangled water-filled network. This phenomenon suggests
that flexible fiber suspensions can be exploited to produce a new family of flow-induced gelledmaterials, such as porous hydrogels. A
significant consequence of these flow properties is that the microfiber suspension is injectable through a needle, from which it can be
extruded directly as a hydrogel without any chemical reactions or further treatments. Additionally, we show that this fiber hydrogel is
a soft, viscoelastic, yield-stress material
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