Hydrophobic Metal–Organic Frameworks

Metal–organic frameworks (MOFs) have diverse potential applications in catalysis, gas storage, separation, and drug delivery because of their nanoscale periodicity, permanent porosity, channel functionalization, and structural diversity. Despite these promising properties, the inherent structural features of even some of the best‐performing MOFs make them moisture‐sensitive and unstable in aqueous media, limiting their practical usefulness. This problem could be overcome by developing stable hydrophobic MOFs whose chemical composition is tuned to ensure that their metal–ligand bonds persist even in the presence of moisture and water. However, the design and fabrication of such hydrophobic MOFs pose a significant challenge. Reported syntheses of hydrophobic MOFs are critically summarized, highlighting issues relating to their design, characterization, and practical use. First, wetting of hydrophobic materials is introduced and the four main strategies for synthesizing hydrophobic MOFs are discussed. Afterward, critical challenges in quantifying the wettability of these hydrophobic porous surfaces and solutions to these challenges are discussed. Finally, the reported uses of hydrophobic MOFs in practical applications such as hydrocarbon storage/separation and their use in separating oil spills from water are summarized. Finally, the state of the art is summarized and promising future developments of hydrophobic MOFs are highlighted.     

Bayesian knowledge tracing,logistic models,and beyond: an overview of learner modeling techniques

Learner modeling is a basis of personalized, adaptive learning. The research literature provides a wide range of modeling approaches, but it does not provide guidance for choosing a model suitable for a particular situation. We provide a systematic and up-to-date overview of current approaches to tracing learners’ knowledge and skill across interaction with multiple items, focusing in particular on the widely used Bayesian knowledge tracing and logistic models. We discuss factors that influence the choice of a model and highlight the importance of the learner modeling context: models are used for different purposes and deal with different types of learning processes. We also consider methodological issues in the evaluation of learner models and their relation to the modeling context. Overall, the overview provides basic guidelines for both researchers and practitioners and identifies areas that require further clarification in future research.     

Apoferritin/Vandetanib Association Is Long-Term Stable But Does Not Improve Pharmacological Properties of Vandetanib

A tyrosine kinase inhibitor, vandetanib (Van), is an anticancer drug affecting the signaling of VEGFR, EGFR and RET protooncogenes. Van is primarily used for the treatment of advanced or metastatic medullary thyroid cancer; however, its usage is significantly limited by side effects, particularly cardiotoxicity. One approach to minimize them is the encapsulation or binding of Van in- or onto a suitable carrier, allowing targeted delivery to tumor tissue. Herein, we constructed a nanocarrier based on apoferritin associated with Van (ApoVan). Based on the characteristics obtained by analyzing the average size, the surface ζ-potential and the polydispersive index, ApoVan nanoparticles exhibit long-term stability and maintain their morphology. Experiments have shown that ApoVan complex is relatively stable during storage. It was found that Van is gradually released from its ApoVan form into the neutral environment (pH 7.4) as well as into the acidic environment (pH 6.5). The effect of free Van and ApoVan on neuroblastoma and medullary thyroid carcinoma cell lines revealed that both forms were toxic in both used cell lines, and minimal differences between ApoVan and Van were observed. Thus, we assume that Van might not be encapsulated into the cavity of apoferritin, but instead only binds to its surface.     

F?rster Resonance Energy Transfer (FRET) between Heterogeneously Distributed Probes: Application to Lipid Nanodomains and Pores

The formation of membrane heterogeneities, e.g., lipid domains and pores, leads to a redistribution of donor (D) and acceptor (A) molecules according to their affinity to the structures formed and the remaining bilayer. If such changes sufficiently influence the Förster resonance energy transfer (FRET) efficiency, these changes can be further analyzed in terms of nanodomain/pore size. This paper is a continuation of previous work on this theme. In particular, it is demonstrated how FRET experiments should be planned and how data should be analyzed in order to achieve the best possible resolution. The limiting resolution of domains and pores are discussed simultaneously, in order to enable direct comparison. It appears that choice of suitable donor/acceptor pairs is the most crucial step in the design of experiments. For instance, it is recommended to use DA pairs, which exhibit an increased affinity to pores (i.e., partition coefficients K_D,A > 10) for the determination of pore sizes with radii comparable to the Förster radius R₀. On the other hand, donors and acceptors exhibiting a high affinity to different phases are better suited for the determination of domain sizes. The experimental setup where donors and acceptors are excluded from the domains/pores should be avoided.     

Acoustic emission monitoring of slow strain rate tensile tests of 304L stainless steel in supercritical water environment

An experimental set-up has been developed to perform slow strain rate tensile (SSRT) tests on tubular 304L stainless steel (SS) specimens in supercritical water (SCW) environment (550 °C, 250 bar). The supercritical water is circulated inside an internally pressurized tubular specimen mounted into a universal mechanical test rig and heated by a single loop resistance heating furnace. The set-up enables in situ monitoring of acoustic emission and electrochemical potential during the SSRT test. The SCW environment is found to significantly influence the mechanical performance of the material as a result of corrosion processes. A correlation between acoustic emission response and change of electrochemical potential is revealed. The findings are compared with preliminary results of tests performed on bulk SS specimens under the same condition in a commercial autoclave. The advantages and potentialities of both set-ups are discussed.     

Generation of variable mixed vortex fields by a single static hologram

Recently, a transfer of information based on application of mixed vortex fields has been proposed and experimentally verified. A dynamical creation of vortex superpositions carrying an actual information code has been realized by the spatial light modulator with a limited repetition rate. In this paper, the optical set-up enabling generation of variable optical vortex superpositions by a single static hologram is proposed and examined. The actual information codes are created by a standard dynamical modulation of an array of point sources illuminating the static optical system.     

Low power switched‐current circuits with low sensitivity to the rise/fall time of the clock

The switched‐current (SI) technique permits realizing analog discrete‐time circuits in standard digital CMOS technology. A very important property of the analog part of a system on a chip is the possibility it offers for realizing some functions of a digital circuit, but with reduced power consumption. In this paper, a low power SI integrator is presented. It is shown that an integrator consuming a fraction of a milliwatt can be designed in 0.35µm CMOS technology with the use of narrow transistor channels, and with the channel length as a design parameter. The impact of the rise/fall time of the clock signal on the integrator operation is observed. It is shown that this effect can be reduced when the proper switch dimensions are taken for the integrator. Analysis and measurements of the integrator noise are presented. The integrator was built with equal size transistors, yielding less sensitivity to variations in production parameters. An experimental chip in 0.35µm CMOS technology was fabricated, and measurements are compared with results obtained during analysis and simulations. In order to verify the properties of the designed integrator experimentally, a first‐order filter is built with the use of elementary cells on the chip. Copyright © 2008 John Wiley & Sons, Ltd.