Memory effect in an ionic liquid matrix containing single-walled carbon nanotubes and polystyrene

We report the use of an ionic liquid (IL) gel matrix containing a blend of single-walled carbon nanotubes (SWNTs) and polystyrene (PS) as a memory device. SWNTs and PS beads were mixed in a room-temperature IL, 1-butyl-3-methyl-hexafluorophosphate ([BMIM][PF(6)]). The composite gel was sandwiched between a bottom ITO glass and a top aluminium electrode. By merely changing the concentrations of SWNTs in the inert insulating PS matrix, we observed several distinct electrical properties of the device, such as an insulator, a memory in terms of switching and negative differential resistance (NDR), and a conductor. The electric bistable switching hops between a higher impedance (OFF) state and a lower impedance (ON) state which is approximately equal to five orders of current decays.     

Organic memory using [6,6]-phenyl-C(61) butyric acid methyl ester: morphology, thickness and concentration dependence studies

We report a simple memory device in which the fullerene-derivative [6,6]-phenyl-C(61) butyric acid methyl ester (PCBM) mixed with inert polystyrene (PS) matrix is sandwiched between two aluminum (Al) electrodes. Transmission electron microscopy (TEM) images of PCBM:PS films showed well controlled morphology without forming any aggregates at low weight percentages (<10?wt%) of PCBM in PS. Energy dispersive x-ray spectroscopy (EDX) analysis of the device cross-sections indicated that the thermal evaporation of the Al electrodes did not lead to the inclusion of Al metal nanoparticles into the active PCBM:PS film. Above a threshold voltage of <3?V, independent of thickness, a consistent negative differential resistance (NDR) is observed in devices in the thickness range from 200 to 350?nm made from solutions with 4-10?wt% of PCBM in PS. We found that the threshold voltage (V(th)) for switching from the high-impedance state to the low-impedance state, the voltage at maximum current density (V(max)) and the voltage at minimum current density (V(min)) in the NDR regime are constant within this thickness range. The current density ratio at V(max) and V(min) is more than or equal to 10, increasing with thickness. Furthermore, the current density is exponentially dependent on the longest tunneling jump between two PCBM molecules, suggesting a tunneling mechanism between individual PCBM molecules. This is further supported with temperature independent NDR down to 240?K.     

Potassium-selective electrodes with stable and geometrically well-defined internal solid contact based on nanoparticles of polyaniline and plasticized poly(vinyl chloride)

Solid contact potassium-selective electrodes with the internal ion-to-electron transduction layer composed of plasticized poly(vinyl chloride) (PVC) and 2-20% (m/m) of polyaniline (PANI) nanoparticles, with the mean particle size of 8 nm, have been studied in this paper. UV-vis measurements in pH buffer solutions between pH 0 and 12 show that the electrically conducting emeraldine salt (ES) form of PANI has exceptionally good pH stability. Membranes of PANI nanoparticles were mainly in the ES form even at pH 12, in contrast to electrochemically prepared PANI(Cl) films, which are converted completely to the nonconducting form already at pH 6. Long-term UV-vis measurements with the PANI membranes in contact with aqueous buffer solution at pH 7.5 showed no degradation of the ES form. The PANI nanoparticles are homogenously mixed in the PVC-based solid contact (SC) layer. Only the uppermost part of the SC layer is to a minor extent dissolved in the outer potassium-selective PVC membrane. This enabled the preparation of geometrically well-defined inner SC layers, thus improving the reproducibility of the solid contact electrodes and resulting in good mechanical strength between the inner and outer membranes.     

Label-free optical detection and tracking of single virions bound to their receptors in supported membrane bilayers

We apply an interferometric optical detection scheme to image and track unlabeled single virions. Individual simian virus 40 virions and uninfectious virus-like particles were imaged on a glass substrate and on a supported membrane bilayer. Moreover, single unlabeled virions were tracked when bound to supported membrane bilayers via the viral receptor, the glycolipid GM1. The technology presented here promises to be generally applicable to studying the motion of unlabeled macromolecules on membranes.     

Application of raman spectroscopy and sequential injection analysis for pH measurements with water dispersion of polyaniline nanoparticles

A novel method for pH measurements between pH 7.5 and 10.4 is reported in this paper. The method combines Raman spectroscopy and the automated sequential injection analysis system (SIA) and makes use of the acid-base properties of a commercially available water dispersion of polyaniline (PANI) nanoparticles with a mean particle size of 46 nm. The useful pH range of the PANI nanoparticles is broader than for conventional acid-base indicators, due to the 1:2 reaction stoichiometry of the proton-ligand complex of the nanoparticles. The pH measurements were conducted with the 633-nm laser excitation wavelength by calculating the difference between the Raman intensities of the primary and reference wavenumbers. In this study, the pH-sensitive CH=CH stretching band at 1422 cm-1 and C-H in-plane bending band of the quinoid form at 1163 cm-1 were chosen as the primary wavenumbers. The presented method is fast and allows pH to be measured with a precision of 0.2 pH unit. The advantage of the proposed method is that the hysteresis effect, which is usually observed for PANI films, can be overcome with the PANI nanoparticles, because a fresh nanoparticle solution is used in each measurement. It should be pointed out, that this work is a fundamental study showing the applicability of Raman spectroscopy in combination with the SIA technique for pH measurements in specific applications, where the conventional glass pH electrode cannot be used.     

FlipIt: The Game of “Stealthy Takeover”

Recent targeted attacks have increased significantly in sophistication, undermining the fundamental assumptions on which most cryptographic primitives rely for security. For instance, attackers launching an Advanced Persistent Threat (APT) can steal full cryptographic keys, violating the very secrecy of “secret” keys that cryptographers assume in designing secure protocols. In this article, we introduce a game-theoretic framework for modeling various computer security scenarios prevalent today, including targeted attacks. We are particularly interested in situations in which an attacker periodically compromises a system or critical resource completely, learns all its secret information and is not immediately detected by the system owner or defender. We propose a two-player game between an attacker and defender called FlipIt or The Game of “Stealthy Takeover.” In FlipIt, players compete to control a shared resource. Unlike most existing games, FlipIt allows players to move at any given time, taking control of the resource. The identity of the player controlling the resource, however, is not revealed until a player actually moves. To move, a player pays a certain move cost. The objective of each player is to control the resource a large fraction of time, while minimizing his total move cost. FlipIt provides a simple and elegant framework in which we can formally reason about the interaction between attackers and defenders in practical scenarios. In this article, we restrict ourselves to games in which one of the players (the defender) plays with a renewal strategy, one in which the intervals between consecutive moves are chosen independently and uniformly at random from a fixed probability distribution. We consider attacker strategies ranging in increasing sophistication from simple periodic strategies (with moves spaced at equal time intervals) to more complex adaptive strategies, in which moves are determined based on feedback received during the game. For different classes of strategies employed by the attacker, we determine strongly dominant strategies for both players (when they exist), strategies that achieve higher benefit than all other strategies in a particular class. When strongly dominant strategies do not exist, our goal is to characterize the residual game consisting of strategies that are not strongly dominated by other strategies. We also prove equivalence or strict inclusion of certain classes of strategies under different conditions. Our analysis of different FlipIt variants teaches cryptographers, system designers, and the community at large some valuable lessons:

1. Systems should be designed under the assumption of repeated total compromise, including theft of cryptographic keys. FlipIt provides guidance on how to implement a cost-effective defensive strategy.
2. Aggressive play by one player can motivate the opponent to drop out of the game (essentially not to play at all). Therefore, moving fast is a good defensive strategy, but it can only be implemented if move costs are low. We believe that virtualization has a huge potential in this respect.
3. Close monitoring of one’s resources is beneficial in detecting potential attacks faster, gaining insight into attacker’s strategies, and scheduling defensive moves more effectively.

Interestingly, FlipIt finds applications in other security realms besides modeling of targeted attacks. Examples include cryptographic key rotation, password changing policies, refreshing virtual machines, and cloud auditing.     

Surface change of root canal dentin after the use of irrigation activation protocols: Electron microscopy and an energy‐dispersive X‐ray microanalysis

This study evaluated the mineral contents of root‐canal dentin after treatment with different irrigation activation protocols. One hundred and eight maxillary lateral incisor teeth were randomly divided into eight experimental groups and one control group. Root canals were prepared using ProTaper rotary files, with the exception of the Self‐Adjusting File (SAF) group. Canals were irrigated with 2 mL of 5% sodium hypochlorite (NaOCl) at each instrument change, and received a final flush with 10 mL of 17% ethylenediaminetetraacetic acid (EDTA) and 10 mL of 5% NaOCl for 1 min. The control group was irrigated with distilled water. Group I (GI): Needle syringe irrigation; Group II (GII): NaviTip FX; Group III (GIII): CanalBrush; Group IV (GIV): Manual dynamic activation with gutta‐percha; Group V (GV): Passive ultrasonic irrigation; Group VI (GVI): EndoActivator; Group VII (GVII): EndoVac; Group VIII (GVIII): SAF. The level of elemental composition was analyzed by a scanning electron microscopy and an energy‐dispersive spectrometer (EDS) system. The results were then statistically analyzed by one‐way ANOVA and Tukey tests. Ca/P ratio was changed after treatment with SAF and EndoActivator. The Ca, P, Mg, and S level changes were not statistically significant (P > 0.05). Final irrigation activation protocols did not alter the mineral level of root dentin surface. Microsc. Res. Tech. 76:893–896, 2013. © 2013 Wiley Periodicals, Inc.     

Study of electrolyte effects on electrochemical synthesis and p-doping of poly(thienyl biphenyl) films

The electrochemical synthesis and charging–discharging process of a copolymer consisting of 3-octylthiophene (3-OT) and biphenyl units have been studied in different electrolytic media. The polymer material has been characterized by electrochemical and spectroscopic methods: cyclic voltammetry (CV), electrochemical quartz crystal microbalance (EQCM), chronopotentiometry, chronoamperometry and FTIR spectroscopy. The diffusion coefficients of different ions in poly(thienyl biphenyl) (PTB) films have been determined by chronoamperometry and compared with corresponding values in poly(3-octylthiophene) (POT) and poly(paraphenylene) (PPP). The best electrolytic conditions for synthesis of poly(thienyl biphenyl) concerning the copolymer structure was found to be in 0.1 M lithium hexafluoro arsenate (LiAsF₆) in acetonitrile. In this electrolyte solution, the content of phenylene segments compared to thienylene segments is highest resulting in a higher degree of cross-linking compared with films made in the presence of the other electrolyte salts studied.     

Macroscopically Aligned Ionic Self‐Assembled Perylene‐Surfactant Complexes within a Polymer Matrix

Ionic self‐assembled (ISA) surfactant complexes present a facile concept for self‐assembly of various functional materials. However, no general scheme has been shown to allow their overall alignment beyond local polydomain‐like order. Here we demonstrate that ionic complexes forming a columnar liquid‐crystalline phase in bulk can be aligned within polymer blends upon shearing, taken that the matrix polymers have sufficiently high molecular weight. We use an ISA complex of N,N′‐bis(ethylenetrimethylammonium)perylenediimide/bis(2‐ethylhexyl) phosphate (Pery‐BEHP) blended with different molecular weight polystyrenes (PS). Based on X‐ray scattering studies and transmission electron microscopy the pure Pery‐BEHP complex was found to form a two‐dimensional oblique columnar phase where the perylene units stack within the columns. Blending the complex with PS lead to high aspect ratio Pery‐BEHP aggregates with lateral dimension in the mesoscale, having internal columnar liquid‐crystalline order similar to the pure Pery‐BEHP complex. When the Pery‐BEHP/PS blend was subjected to a shear flow field, the alignment of perylenes can be achieved but requires sufficiently high molecular weight of the polystyrene matrix. The concept also suggests a simple route for macroscopically aligned nanocomposites with conjugated columnar liquid‐crystalline functional additives.     

The relations of majority-minority group status and having an other-religion friend to Indonesian youths' socioemotional functioning.

In this study, the authors examined the relations of Indonesian adolescents' socioemotional functioning to their majority-minority status and the presence of cross-religion friendships and whether sex moderated these relations. At Time 1, 1,254 7th graders and their peers in Bandung, Indonesia, reported on their friendships, prosocial behavior, and peer likability; months later, a selected sample of 250 youths and their teachers and parents rated the youths' social functioning and (mal)adjustment. When controlling for socioeconomic status and initial sociometric status, girls were generally higher in measures of adjustment, whereas majority children were lower in externalizing problems and, for boys, loneliness. For minority children's social competence and prosocial behavior at school, there was evidence of a buffering effect of having a cross-religion friend. (PsycINFO Database Record (c) 2010 APA, all rights reserved)