Search

Hypothesis Nonaqueous foams are found in a variety of applications, many of which contain volatile components that need to be removed during processing. Sparging air bubbles into the liquid can be used to aid in their removal, but the resulting foam can be stabilized or destabilized by several different mechanisms, the relative importance of which are not yet fully understood. Investigating the dynamics of thin film drainage, four competing mechanisms can be observed, such as solvent evaporation, film viscosification, and thermal and solutocapillary Marangoni flows. Experiments Experimental studies with isolated bubbles and/or bulk foams are needed to strengthen the fundamental knowledge of these systems. This paper presents interferometric measurements of the dynamic evolution of a film formed by a bubble rising to an air-liquid interface to shed light on this situation. Two different solvents with different degrees of volatility were investigated to reveal both qualitative and quantitative details on thin film drainage mechanisms in polymer-volatile mixtures. Findings Using interferometry, we found evidence that solvent evaporation and film viscosification both strongly influence the stability of interface. These findings were corroborated by comparison with bulk foam measurements, revealing a strong correlation between these two systems. [ABSTRACT FROM AUTHOR]

We numerically study a new hardware method for network authentication, using a pair of chaotic lasers subject to the same optical injection from a third chaotic laser, in a close-loop configuration. One laser is in the secure environment, the other is in the unsecure environment, and if their parameters are matched (i.e., they are 'twins'), in suitable operating conditions they synchronize and generate the same pseudo-random amplitude modulation. Access to the secure environment is authorized only if the two responses are found equal. As in other schemes based on Physical Unclonable Functions (PUFs), security relies on unavoidable small differences between nominally identical but physically separate devices: due to the strong sensitivity of chaos to laser parameter dispersion, finding a suitable laser to synchronize is a very difficult task for the Adversary, while the laser of the Authorized user can be selected as a twin of the one in the secure environment. [ABSTRACT FROM AUTHOR]

A nickel‐catalyzed reductive cross‐electrophile coupling between the redox‐active N‐trifluoroethoxyphthalimide and iodoarenes is documented. The protocol reproduces a formal arylation of trifluoroacetaldehyde under mild conditions in high yields (up to 88 %) and with large functional group tolerance (30 examples). A combined computational and experimental investigation revealed a pivotal solvent assisted 1,2‐Hydrogen Atom Transfer (HAT) process to generate a nucleophilic α‐hydroxy‐α‐trifluoromethyl C‐centered radical for the Csp2−Csp3 bond forming process. [ABSTRACT FROM AUTHOR]

A nickel‐catalyzed reductive cross‐electrophile coupling between the redox‐active N‐trifluoroethoxyphthalimide and iodoarenes is documented. The protocol reproduces a formal arylation of trifluoroacetaldehyde under mild conditions in high yields (up to 88 %) and with large functional group tolerance (30 examples). A combined computational and experimental investigation revealed a pivotal solvent assisted 1,2‐Hydrogen Atom Transfer (HAT) process to generate a nucleophilic α‐hydroxy‐α‐trifluoromethyl C‐centered radical for the Csp2−Csp3 bond forming process. [ABSTRACT FROM AUTHOR]

We present an environmentally benign methodology for the covalent functionalization (arylation) of reduced graphene oxide (rGO) nanosheets with arylazo sulfones. A variety of tagged aryl units were conveniently accommodated at the rGO surface via visible‐light irradiation of suspensions of carbon nanostructured materials in aqueous media. Mild reaction conditions, absence of photosensitizers, functional group tolerance and high atomic fractions (XPS analysis) represent some of the salient features characterizing the present methodology. Control experiments for the mechanistic elucidation (Raman analysis) and chemical nanomanipulation of the tagged rGO surfaces are also reported. [ABSTRACT FROM AUTHOR]

A carboxylative Ni-catalyzed tandem C–C σ-bond activation of cyclobutanones followed by CO2-electrophilic trapping is documented as a direct route to synthetically valuable 3-indanone-1-acetic acids. The protocol shows an adequate functional group tolerance and useful chemical outcomes (yield up to 76%) when AlCl3 is adopted as an additive. Manipulations of the targeted cyclic scaffolds and a mechanistic proposal based on experimental evidence complete the investigation. [ABSTRACT FROM AUTHOR]

A new type of ligand-free Ni-nanoparticles supported on rGO (size distribution average d = 9 ± 3 nm) was prepared and fully characterized via morphological (Fe-SEM), structural (P-XRD, HR-TEM), and spectroscopic (ICP-EOS, XPS) analysis tools. The metal composite was effectively employed in the unprecedented heterogeneously Ni-assisted cross-coupling reaction of aryl/vinyl iodides and thiocarboxylates. A range of sulfur-containing aryl as well as vinyl derivatives (15 examples) was achieved in high yields (up to 82%), under mild reaction conditions, and with wide functional group tolerance. [ABSTRACT FROM AUTHOR]

In this paper, we numerically evaluate a hardware-based method for authentication using a pair of twin chaotic lasers. This method belongs to the PUF (Physically Unclonable Function) class; however, it does not require storing the response of the hardware in a database, because both users own the same hardware (one of the twin chaotic lasers), producing, on the fly, the same response, i.e., the same chaotic waveform, when subject to the same stimulus (injection from a third laser) in the same working conditions (local injection, pump current). A bit sequence can be easily obtained from the chaotic waveforms by electronic processing, and authentication consists in comparing the sequences produced by the twin lasers. This scheme is proposed above all for authentication of a client in an unsecure environment to a server in a secure environment, but it can be used also for peer-to-peer authentication. Both the case of open- and close-loop chaotic lasers are considered. Simulations are based on the Lang-Kobayashi model. [ABSTRACT FROM AUTHOR]

Insights into the effect of die swell on extrusion foam of thermoplastic polymers are presented. The die swell or Barus effect is the swelling of a viscoelastic material due to a fast elastic recovery after being subjected to stress. The elastic recovery is proportional to the energy stored in the material during the deformation that is released immediately when the material is free to expand. In extrusion foam, the elastic recovery happens at the die exit together with the foaming process (i.e., bubble nucleation and growth). Previous reports on extrusion have focused on modeling the die swell or foaming individually. We investigated the existence of a link between the die swell and foaming that is fundamental in designing the geometry of a die for extrusion foam. Simple and complex dies were used to measure the expansion ratio of a polyethylene blown with isobutane and CO2. It was found that the expansion ratio is anisotropic, the anisotropy in the expansion of the foam is due to the die swell strongly affecting the final shape of the product, and it cannot be neglected in standard application for extrusion foam. Surprisingly, it was found that the foam density changes at a high level of die swell because it is affected by the elastic recovery of the material. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) is experiencing growing interest by synthetic organic chemists as a promoter of chemical transformations. The synergistic role of the multiple functionalities featuring the nanostructured carbon materials and their π‐domains enables the interplay of specific activation modes towards organic compounds that can explore unprecedented chemical modifications. A detailed comprehension of the mechanistic details that govern the transformations guided by GO is a not fully solved task in the field. In this direction, more sophisticated and diversified techniques are employed, providing insights towards intriguing activation modes exerted by the π‐matrix and the oxygenated/sulfonate groups decorating the functionalized nano‐carbon material. The present Minireview accounts for a critical survey of the most recent developments in the area of GO‐mediated organic transformations with a specific focus on mechanist aspects. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) is experiencing growing interest by synthetic organic chemists as a promoter of chemical transformations. The synergistic role of the multiple functionalities featuring the nanostructured carbon materials and their π‐domains enables the interplay of specific activation modes towards organic compounds that can explore unprecedented chemical modifications. A detailed comprehension of the mechanistic details that govern the transformations guided by GO is a not fully solved task in the field. In this direction, more sophisticated and diversified techniques are employed, providing insights towards intriguing activation modes exerted by the π‐matrix and the oxygenated/sulfonate groups decorating the functionalized nano‐carbon material. The present Minireview accounts for a critical survey of the most recent developments in the area of GO‐mediated organic transformations with a specific focus on mechanist aspects. [ABSTRACT FROM AUTHOR]

The site‐selective allylative and allenylative dearomatization of indoles with alcohols was performed under carbocatalytic regime in the presence of graphene oxide (GO, 10 wt % loading) as the promoter. Metal‐free conditions, absence of stoichiometric additive, environmentally friendly conditions (H2O/CH3CN, 55 °C, 6 h), broad substrate scope (33 examples, yield up to 92 %) and excellent site‐ and stereoselectivity characterize the present methodology. Moreover, a covalent activation model exerted by GO functionalities was corroborated by spectroscopic, experimental and computational evidences. Recovering and regeneration of the GO catalyst through simple acidic treatment was also documented. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: The chemodivergent ring‐opening of cyclobutanols is described under the carbocatalytic assistance of graphene oxide (GO). The protocol enables the synthesis of diversely functionalized dienes or indenes (26 examples) based on the amount of GO employed. Spectroscopic (XPS and ssNMR) as well as experimental investigations revealed a direct involvement of the π‐domains of GO in tuning the stability of carbocationic intermediates during the reaction. [ABSTRACT FROM AUTHOR]

Optimization of post polymerization processes of polyolefin elastomers (POE) involving solvents is of considerable industrial interest. To this aim, experimental determination and theoretical interpretation of the thermodynamics and mass transport properties of POE-solvent mixtures is relevant. Sorption behavior of n-hexane vapor in a commercial propylene-ethylene elastomer (V8880 VistamaxxTM from ExxonMobil, Machelen, Belgium) is addressed here, determining experimentally the sorption isotherms at temperatures ranging from 115 to 140 °C and pressure values of n-hexane vapor up to 1 atm. Sorption isotherms have been interpreted using a Non Random Lattice Fluid (NRLF) Equation of State model retrieving, from data fitting, the value of the binary interaction parameter for the n-hexane/V8880 system. Both the cases of temperature-independent and of temperature-dependent binary interaction parameter have been considered. Sorption kinetics was also investigated at different pressures and has been interpreted using a Fick's model determining values of the mutual diffusivity as a function of temperature and of n-hexane/V8880 mixture composition. From these values, n-hexane intra-diffusion coefficient has been calculated interpreting its dependence on mixture concentration and temperature by a semi-empiric model based on free volume arguments. [ABSTRACT FROM AUTHOR]

The tandem catalytic functionalization/carboxylation of double as well as triple carbon‐carbon bonds with CO2 represent an emerging research area in synthetic organic methodology. In particular, the combination of mild reaction conditions, stoichiometric acceptor/donorless conditions (visible light photoredox catalysis) and chiral catalysts contributed to a rapid development of this intriguing research area capable of creating chemical diversity/ complexity from readily available unsaturated hydrocarbons and CO2 as a C1‐buinding block. The most recent developments in the field have been collected in the present review article and organized, based on the different sets of π‐systems/intermediates/reactive partners employed (i.e., nickelalactones, organo‐halides) as well as synthetic strategies (i.e., visible‐light photo redox catalysis). [ABSTRACT FROM AUTHOR]

Background: Cybathlon championship aims at promoting the development of prosthetic and assistive devices capable to meet users' needs. This paper describes and analyses possible exploitation outcomes of our team's (REHAB TECH) experience into the Powered Arm Prosthesis Race of the Cybathlon 2020 Global Edition, with the novel prosthetic system Hannes. In detail, we present our analysis on a concurrent evaluation conducted to verify if the Cybathlon training and competition positively influenced pilot's performance and human-technology integration with Hannes, with respect to a non-runner Hannes user.Methods: Two transradial amputees were recruited as pilots (Pilot 1 and Pilot 2) for the Cybathlon competition and were given the polyarticulated myoelectric prosthetic hand Hannes. Due to COVID-19 emergency, only Pilot 1 was trained for the race. However, both pilots kept Hannes for Home Use for seven weeks. Before this period, they both participated to the evaluation of functionality, embodiment, and user experience (UX) related to Hannes, which they repeated at the end of the Home Use and right after the competition. We analysed Pilot 1's training and race outcomes, as well as changes in the concurrent evaluation, and compared these results with Pilot 2's ones.Results: The Cybathlon training gradually improved Pilot 1's performances, leading to the sixth place with a single error in task 5. In the parallel evaluation, both pilots had an overall improvement over time, whereas Pilot 2 experienced a deterioration of embodiment. In detail, Pilot 1, who followed the training and raced the Cybathlon, improved in greater way.Conclusion: Hannes demonstrated to be a valuable competitor and to perform grasps with human-like behaviors. The higher improvements of Pilot 1, who actively participated in the Cybathlon, in terms of functionality, embodiment and UX, may depend on his training and engagement in the effort of achieving a successful user-prosthesis interaction during the competition. Tasks based on Cybathlon's ones could improve the training phase of a prosthetic user, stimulating dexterity, prosthetic integration, and user perception towards the prosthesis. Likewise, timed races or competitions could facilitate and accelerate the learning phase, improving the efficiency and efficacy of the process. [ABSTRACT FROM AUTHOR]

[Display omitted] Hypothesis: Thin liquid films are important in many scientific fields. In particular, films with both the surface layers exposed to a different fluid phase, known as freestanding films, are relevant in the ambit of foams and emulsions. Hence, there is a great interest in developing novel techniques allowing to form large and stable freestanding liquid films and to follow their dynamics. Experiments: We develop a novel opto-mechanical tool allowing to perform and study the preparation and the capillary leveling flow of axisymmetric bare freestanding liquid films. The tool is composed by a customized motorized iris diaphragm and by an innovative joint imaging setup combining digital holography and white light color interferometry that enables real-time measurement of film thickness over a large field of view. The dynamics of films made of a model Newtonian fluid, i.e., high-viscosity silicone oil, is studied. Direct numerical simulations and a hydrodynamic model based on the lubrication theory are used to support the experimental results. Findings: Iris opening induces the formation of large circular freestanding films with a stepped profile. Once iris opening is stopped, the films undergo a capillary leveling flow tending to flatten their profile. The leveling flow follows the theoretical scaling given by Ilton et al. [1]. We prove through numerical simulations that an equi-biaxial extensional flow occurs at the film center. Furthermore, we observe the formation and dynamics of dimples in bare freestanding films for the first time. [ABSTRACT FROM AUTHOR]