Bewertung der GMX/Mailvelope-Ende-zu-Ende-Verschlüsselung

Ende-zu-Ende-verschlüsselte E-Mail-Kommunikation hat seit den Veröffentlichungen von Edward Snowden erneut an Bedeutung gewonnen. Obwohl die entsprechenden Möglichkeiten seit mehr als zwei Jahrzehnten gegeben sind, sind die technischen Umsetzungen für Endanwender häufig schwer zugänglich. Ein wesentlicher Grund dafür ist, wie Studien belegen, deren Nutzerschnittstelle. Mit Mailvelope versuchen die Anbieter GMX und WEB.DE derzeit, Ende-zu-Ende-verschlüsselte E-Mail-Kommunikation in ihren gewohnten Benutzerschnittstellen zu integrieren. Zur Bewertung dieses Ansatzes wurden ein Cognitive Walkthrough durchgeführt und die Sicherheit des Ansatzes bewertet.     

How penultimate monomer unit effects and initiator influence ICAR ATRP of n‐butyl acrylate and methyl methacrylate

The relevance of penultimate monomer unit (PMU) effects and the selection of the correct initiator species under typical reversible deactivation radical copolymerization conditions is illustrated, using matrix‐based kinetic Monte Carlo simulations allowing the visualization of all monomer sequences along individual chains. Initiators for continuous activator regeneration atom transfer radical polymerization (ICAR ATRP) is selected as illustrative polymerization technique with n‐butyl acrylate and methyl methacrylate as comonomers, aiming at the synthesis of well‐defined gradient copolymers. Using literature based model parameters, in particular temperature dependent monomer and radical reactivity ratios, it is demonstrated that PMU effects on propagation and ATRP (de)activation cannot be ignored to identify the most suited ICAR ATRP reactants (e.g., tertiary ATRP initiator) and reaction conditions (e.g., feeding rates under fed‐batch conditions). The formulated insights highlight the need for further research on PMU effects on all reaction steps in radical polymerization. © 2017 American Institute of Chemical Engineers AIChE J, 2017     

Spectroscopic Indications of Tunnel Barrier Charging as the Switching Mechanism in Memristive Devices

Resistive random access memory is a promising, energy‐efficient, low‐power “storage class memory” technology that has the potential to replace both flash storage and on‐chip dynamic memory. While the most widely employed systems exhibit filamentary resistive switching, interface‐type switching systems based on a tunable tunnel barrier are of increasing interest. They suffer less from the variability induced by the stochastic filament formation process and the choice of the tunnel barrier thickness offers the possibility to adapt the memory device current to the given circuit requirements. Heterostructures consisting of a yttria‐stabilized zirconia (YSZ) tunnel barrier and a praseodymium calcium manganite (PCMO) layer are employed. Instead of spatially localized filaments, the resistive switching process occurs underneath the whole electrode. By employing a combination of electrical measurements, in operando hard X‐ray photoelectron spectroscopy and electron energy loss spectroscopy, it is revealed that an exchange of oxygen ions between PCMO and YSZ causes an electrostatic modulation of the effective height of the YSZ tunnel barrier and is thereby the underlying mechanism for resistive switching in these devices.     

Modulating the Ferromagnet/Molecule Spin Hybridization Using an Artificial Magnetoelectric

Spin‐polarized charge transfer at the interface between a ferromagnetic (FM) metal and a molecule can lead to ferromagnetic coupling and to a high spin polarization at room temperature. The magnetic properties of these interfaces can not only alter those of the ferromagnet but can also stabilize molecular spin chains with interesting opportunities toward quantum computing. With the aim to enhance an organic spintronic device's functionality, external control over this spin polarization may thus be achieved by altering the ferromagnet/molecule interface's magnetic properties. To do so, the magnetoelectric properties of an underlying ferroelectric/ferromagnetic interface are utilized. Switching the ferroelectric polarization state of a PbZr_0.2Ti_0.8O₃ (PZT) bottom layer within a PZT/Co/FePc‐based (Pc ‐ phthalocyanine) device alters the X‐ray magnetic circular dichroism of the Fe site within the phthalocyanine molecular top layer. Thus, how to electrically alter the magnetic properties of an interface with high spin polarization at room temperature is demonstrated. This expands electrical control over spin‐polarized FM/molecule interfaces, which is first demonstrated using ferroelectric molecules, to all molecular classes.     

Collective Wetting of a Natural Fibrous System and Its Application in Pump‐Free Droplet Transfer

Novel wetting strategies in plants have inspired numerous notable biomimetic surfaces over the past decade, such as self‐cleaning surfaces mimicking the water repellency of lotus leaves and directional water transport surfaces imitating the slippery surface on carnivorous plants. Here, a new wetting behavior in dandelion seed (genus Taraxacum) is found, characterized by capturing a droplet inside it. The critical conditions required for wetting of the fiber assay in terms of the fibrous geometry and liquid surface tension are identified, and how these factors quantitatively affect the volume of the captured droplet is shown further. More importantly, the reverse process can be triggered by introducing a competitive liquid phase with smaller surface tension to the wetted fiber assay, as it is demonstrated by the release of the captured water droplet in oil. These results enhance the understanding on wetting of fibrous structures and would benefit the design of novel intelligent and responsive devices. This newly identified wetting behavior holds great potential for fine control and micromanipulation of liquid. As a demonstration, it is illustrated that the natural fibrous structure is capable of manipulating a small volume of liquid for droplet‐based multiplexed chemical reaction.     

Incubation phenomena during UV‐pulse excimer laser processing of silicone elastomers

Observations of the interaction of poly(dimethylsiloxane) (PDMS) sheet (210 μm thick) with KrF excimer laser irradiation (λ = 248 nm), with low energy of 50 mJ/pulse are presented. The negative ablation or swelling of the material caused by low frequency pulse irradiation is characterized by optical microscopy, μ‐Raman spectrometry and X‐ray micro‐tomography. The appearance of defected areas in the form of cones inside the sheet and changes of material chemistry are discussed. These phenomena are considered as a precursor of the ablation occurring after passing a threshold of absorbed laser irradiation energy. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44541.     

A Mathematical Description of the Kinetics of the Electrophoretic Deposition Process for Al2O3-Based Suspensions

The yield during electrophoretic deposition is modeled incorporating the changing electric field over the suspension, due to a potential drop over the growing deposit, assessed from on-line measurements of the current flowing through the deposition cell and the conductivity of the suspension during electrophoretic deposition. The kinetic model is validated for Al₂O₃ suspensions with different powder loads based on methylethylketone with n -butylamine and ethanol with polyethyleneimine or HNO₃, suspensions with, respectively, a constant and a decreasing electric field during deposition. The need for a powder concentration correction, even at volume fractions down to 0.03, and the incorporation of a changing electric field is experimentally proven to be essential in order to describe the deposition yield more accurately than predicted from the Hamaker equation.     

Prediction of thermal diffusion in binary mixtures of nonelectrolyte liquids by the use of nonequilibrium thermodynamics

A derivation based on nonequilibrium thermodynamic leads to this expression for the thermal diffusion factor, _T=M ₂(h ₂ ^xs -h ₁ ^xs )/RT ₂, where M ₂ is the molecular weight of the lighter of the two components, h ₁ ^xs is the partial excess enthalpy of component i, J/g, R is 8.314 J · K ^–1 · mol ^–1, T is temperature in K, and ₂ is the thermodynamic correction factor (1 + d ln ₂/d ln X ₂), where ₂ is an activity coefficient and X ₂ is the mole fraction. The correctness of this theoretical prediction is verified for the liquid system ethanol-water at 298 K.Paper submitted to the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.