A combined scanning electron micrograph and electrochemical study of the effect of chemical interaction on the cyclability of lithium electrodes in an ionic liquid electrolyte

The effect of storage time on the cyclability of lithium electrodes in an ionic liquid electrolyte, namely 0.5 m LiBF4 in N-methyl-N-propyl pyrrolidinium bis(fluorosulfonyl)imide, [C3mpyr+][FSI–], was investigated. A chemical interaction was observed which is time dependent and results in a morphology change of the Li surface due to build up of passivation products over a 12-day period. The formation of this layer significantly impacts on the Li electrode resistance before cycling and the charging/discharging process for symmetrical Li|0.5 m LiBF4 in [C3mpyr+][FSI–]|Li coin cells. Indeed it was found that introducing a rest period between cycling, and thereby allowing the chemical interaction between the Li electrode and electrolyte to take place, also impacted on the charging/discharging process. For all Li surface treatments the electrode resistance decreased after cycling and was due to significant structural rearrangement of the surface layer. These results suggest that careful electrode pretreatment in a real battery system will be required before operation.

Reusable surface confined semi-conducting metal-TCNQ and metal-TCNQF4 catalysts for electron transfer reactions

The synthesis of organic semiconducting materials based on silver and copper-TCNQ (TCNQ = 7,7,8,8-tetracyanoquinodimethane) and their fluorinated analogues has received a significant amount of attention due to their potential use in organic electronic applications. However, there is a scarcity in the identification of different applications for which these interesting materials may be suitable candidates. In this work, we address this by investigating the catalytic properties of such materials for the electron transfer reaction between ferricyanide and thiosulphate ions in aqueous solution, which to date has been almost solely limited to metallic nanomaterials. Significantly it was found that all the materials investigated, namely CuTCNQ, AgTCNQ, CuTCNQF4 and AgTCNQF4, were catalytically active and, interestingly, the fluorinated analogues were superior. AgTCNQF4 demonstrated the highest activity and was tested for its stability and re-usability for up to 50 cycles without degradation in performance. The catalytic reaction was monitored via UV-vis spectroscopy and open circuit potential versus time measurements, as well as an investigation of the transport properties of the films via electrochemical impedance spectroscopy. It is suggested that morphology and bulk conductivity are not the limiting factors, but rather the balance between the accumulated surface charge from electron injection via thiosulphate ions on the catalyst surface and transfer to the ferricyanide ions which controls the reaction rate. The facile fabrication of re-usable surface confined organic materials that are catalytically active may have important uses for many more electron transfer reactions.

Lateral charge propagation effects during the galvanic replacement of electrodeposited MTCNQ (M= Cu, Ag) microstructures with gold and its influence on catalysed electron transfer reactions

The galvanic replacement of isolated electrodeposited semiconducting CuTCNQ microstructures on a glassy carbon (GC) substrate with gold is investigated. It is found that anisotropic metal nanoparticles are formed which are not solely confined to the redox active sites on the semiconducting materials but are also observed on the GC substrate which occurs via a lateral charge propagation mechanism. We also demonstrate that this galvanic replacement approach can be used for the formation of isolated AgTCNQ/Au microwire composites which occurs via an analogous mechanism. The resultant MTCNQ/Au (M = Cu, Ag) composite materials are characterized by Raman, spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and investigated for their catalytic properties for the reduction of ferricyanide ions with thiosulphate ions in aqueous solution. Significantly it is demonstrated that gold loading, nanoparticle shape and in particular the MTCNQ–Au interface are important factors that influence the reaction rate. It is shown that there is a synergistic effect at the CuTCNQ/Au composite when compared to AgTCNQ/Au at similar gold loadings.

Scanning electron microscopic study of microstructure of Gala apples during hot air drying

Microscopic changes occur in plant food materials during drying significantly influence the macroscopic properties and quality factors of the dried food materials. It is very critical to study microstructure to understand the underlying cellular mechanisms to improve performance of the food drying techniques. However, there is very limited research conducted on such microstructural changes of plant food material during drying. In this work, Gala apple parenchyma tissue samples were studied using a scanning electron microscope for gradual microstructural changes as affected by temperature, time and moisture content during hot air drying at two drying temperatures: 57 ℃ and 70 ℃. For fresh samples, the average cellular parameter values were; cell area: 20000 μm2, ferret diameter: 160 μm, perimeter: 600 μm, roundness: 0.76, elongation: 1.45 and compactness: 0.84. During drying, a higher degree of cell shrinkage was observed with cell wall warping and increase in intercellular space. However, no significant cell wall breakage was observed. The overall reduction of cell area, ferret diameter and perimeter were about 60%, 40% and 30%. The cell roundness and elongation showed overall increments of about 5% and the compactness remained unchanged. Throughout the drying cycle, cellular deformations were mainly influenced by the moisture content. During the initial and intermediate stages of drying, cellular deformations were also positively influenced by the drying temperature and the effect was reversed at the final stages of drying which provides clues for case hardening of the material.

Characterisation of the ionic products arising from electron photodetachment of simple dicarboxylate dianions

Much of what we currently understand about the structure and energetics of multiply charged anions in the gas phase is derived from the measurement of photoelectron spectra of simple dicarboxylate dianions. Here we have employed a modified linear ion-trap mass spectrometer to undertake complementary investigations of the ionic products resulting from laser-initiated electron photodetachment of two model dianions. Electron photodetachment (ePD) of the \[M-2H](2-) dianions formed from glutaric and adipic acid were found to result in a significant loss of ion signal overall, which is consistent with photoelectron studies that report the emission of slow secondary electrons (Xing et al., 2010 \[201). The ePD mass spectra reveal no signals corresponding to the intact \[M-2H](center dot-) radical anions, but rather \[M-2H-CO2](center dot-) ions are identified as the only abundant ionic products indicating that spontaneous decarboxylation follows ejection of the first electron. Interestingly however, investigations of the structure and energetics of the \[M-2H-CO2](center dot-) photoproducts by ion-molecule reaction and electronic structure calculation indicate that (i) these ions are stable with respect to secondary electron detachment and (ii) most of the ion population retains a distonic radical anion structure where the radical remains localised at the position of the departed carboxylate moiety. These observations lead to the conclusion that the mechanism for loss of ion signal involves unimolecular rearrangement reactions of the nascent \[M-2H](center dot-) carbonyloxyl radical anions that compete favourably with direct decarboxylation. Several possible rearrangement pathways that facilitate electron detachment from the radical anion are identified and are computed to be energetically accessible. Such pathways provide an explanation for prior observations of slow secondary electron features in the photoelectron spectra of the same dicaboxylate dianions. (C) 2013 Elsevier B.V. All rights reserved.

Ozone-induced dissociation of conjugated lipids reveals significant reaction rate enhancements and characteristic odd-electron product ions

Ozone-induced dissociation (OzID) is an alternative ion activation method that relies on the gas phase ion-molecule reaction between a mass-selected target ion and ozone in an ion trap mass spectrometer. Herein, we evaluated the performance of OzID for both the structural elucidation and selective detection of conjugated carbon-carbon double bond motifs within lipids. The relative reactivity trends for \[M + X](+) ions (where X = Li, Na, K) formed via electrospray ionization (ESI) of conjugated versus nonconjugated fatty acid methyl esters (FAMEs) were examined using two different OzID-enabled linear ion-trap mass spectrometers. Compared with nonconjugated analogues, FAMEs derived from conjugated linoleic acids were found to react up to 200 times faster and to yield characteristic radical cations. The significantly enhanced reactivity of conjugated isomers means that OzID product ions can be observed without invoking a reaction delay in the experimental sequence (i.e., trapping of ions in the presence of ozone is not required). This possibility has been exploited to undertake neutral-loss scans on a triple quadrupole mass spectrometer targeting characteristic OzID transitions. Such analyses reveal the presence of conjugated double bonds in lipids extracted from selected foodstuffs. Finally, by benchmarking of the absolute ozone concentration inside the ion trap, second order rate constants for the gas phase reactions between unsaturated organic ions and ozone were obtained. These results demonstrate a significant influence of the adducting metal on reaction rate constants in the fashion Li > Na > K.

Gas-Phase Transformation of Phosphatidylcholine Cations to Structurally Informative Anions via Ion/Ion Chemistry

Gas-phase transformation of synthetic phosphatidylcholine (PC) monocations to structurally informative anions is demonstrated via ion/ion reactions with doubly deprotonated 1,4-phenylenedipropionic acid (PDPA). Two synthetic PC isomers, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (PC16:0/18:1) and 1-oleoyl-2-palmitoyl-sn-glycero-3-phosphocholine (PC18:1/16:0), were subjected to this ion/ion chemistry. The product of the ion/ion reaction is a negatively charged complex, \[PC + PDPA - H](-). Collisional activation of the long-lived complex causes transfer of a proton and methyl cation to PDPA, generating \[PC - CH3](-). Subsequent collisional activation of the demethylated PC anions produces abundant fatty acid carboxylate anions and low-abundance acyl neutral losses as free acids and ketenes. Product ion spectra of \[PC - CH3](-) suggest favorable cleavage at the sn-2 position over the sn-1 due to distinct differences in the relative abundances. In contrast, collisional activation of PC cations is absent of abundant fatty acid chain-related product ions and typically indicates only the lipid class via formation of the phosphocholine cation. A solution phase method to produce the gas-phase adducted PC anion is also demonstrated. Product ion spectra derived from the solution phase method are similar to the results generated via ion/ion chemistry. This work demonstrates a gas-phase means to increase structural characterization of phosphatidylcholines via ion/ion chemistry. Grant Number ARC/CE0561607, ARC/DP120102922

Rapid quantification of free cholesterol in tears using direct insertion/electron ionization-Mass spectrometry

Purpose. To establish a simple and rapid analytical method, based on direct insertion/electron ionization-mass spectrometry (DI/EI-MS), for measuring free cholesterol in tears from humans and rabbits. Methods. A stable-isotope dilution protocol employing DI/EI-MS in selected ion monitoring mode was developed and validated. It was used to quantify the free cholesterol content in human and rabbit tear extracts. Tears were collected from adult humans (n = 15) and rabbits (n = 10) and lipids extracted. Results. Screening, full-scan (m/z 40-600) DI/EI-MS analysis of crude tear extracts showed that diagnostic ions located in the mass range m/z 350 to 400 were those derived from free cholesterol, with no contribution from cholesterol esters. DI/EI-MS data acquired using selected ion monitoring (SIM) were analyzed for the abundance ratios of diagnostic ions with their stable isotope-labeled analogues arising from the D6-cholesterol internal standard. Standard curves of good linearity were produced and an on-probe limit of detection of 3 ng (at 3:1 signal to noise) and limit of quantification of 8 ng (at 10:1 signal to noise). The concentration of free cholesterol in human tears was 15 ± 6 μg/g, which was higher than in rabbit tears (10 ± 5 μg/g). Conclusions. A stable-isotope dilution DI/EI-SIM method for free cholesterol quantification without prior chromatographic separation was established. Using this method demonstrated that humans have higher free cholesterol levels in their tears than rabbits. This is in agreement with previous reports. This paper provides a rapid and reliable method to measure free cholesterol in small-volume clinical samples. © 2013 The Association for Research in Vision and Ophthalmology, Inc.

Simulations of the spontaneous emission of a quantum dot near a gap plasmon waveguide

In this paper we modeled a quantum dot at near proximity to a gap plasmon waveguide to study the quantum dot-plasmon interactions. Assuming that the waveguide is single mode, this paper is concerned about the dependence of spontaneous emission rate of the quantum dot on waveguide dimensions such as width and height. We compare coupling efficiency of a gap waveguide with symmetric configuration and asymmetric configuration illustrating that symmetric waveguide has a better coupling efficiency to the quantum dot. We also demonstrate that optimally placed quantum dot near a symmetric waveguide with 50 nm x 50 nm cross section can capture 80% of the spontaneous emission into a guided plasmon mode.

Quantum direct secret sharing with efficient eavesdropping-check and authentication based on distributed fountain codes

We propose to use a simple and effective way to achieve secure quantum direct secret sharing. The proposed scheme uses the properties of fountain codes to allow a realization of the physical conditions necessary for the implementation of no-cloning principle for eavesdropping-check and authentication. In our scheme, to achieve a variety of security purposes, nonorthogonal state particles are inserted in the transmitted sequence carrying the secret shares to disorder it. However, the positions of the inserted nonorthogonal state particles are not announced directly, but are obtained by sending degrees and positions of a sequence that are pre-shared between Alice and each Bob. Moreover, they can confirm that whether there exists an eavesdropper without exchanging classical messages. Most importantly, without knowing the positions of the inserted nonorthogonal state particles and the sequence constituted by the first particles from every EPR pair, the proposed scheme is shown to be secure.

Using the quantum probability ranking principle to rank interdependent documents

A known limitation of the Probability Ranking Principle (PRP) is that it does not cater for dependence between documents. Recently, the Quantum Probability Ranking Principle (QPRP) has been proposed, which implicitly captures dependencies between documents through “quantum interference”. This paper explores whether this new ranking principle leads to improved performance for subtopic retrieval, where novelty and diversity is required. In a thorough empirical investigation, models based on the PRP, as well as other recently proposed ranking strategies for subtopic retrieval (i.e. Maximal Marginal Relevance (MMR) and Portfolio Theory(PT)), are compared against the QPRP. On the given task, it is shown that the QPRP outperforms these other ranking strategies. And unlike MMR and PT, one of the main advantages of the QPRP is that no parameter estimation/tuning is required; making the QPRP both simple and effective. This research demonstrates that the application of quantum theory to problems within information retrieval can lead to significant improvements.

A formalization of logical imaging for information retrieval using quantum theory

In this paper we introduce a formalization of Logical Imaging applied to IR in terms of Quantum Theory through the use of an analogy between states of a quantum system and terms in text documents. Our formalization relies upon the Schrodinger Picture, creating an analogy between the dynamics of a physical system and the kinematics of probabilities generated by Logical Imaging. By using Quantum Theory, it is possible to model more precisely contextual information in a seamless and principled fashion within the Logical Imaging process. While further work is needed to empirically validate this, the foundations for doing so are provided.

Social tagging, guppy effect and the role of interference : a quantum-inspired model for tags combination

Social tagging systems are shown to evidence a well known cognitive heuristic, the guppy effect, which arises from the combination of different concepts. We present some empirical evidence of this effect, drawn from a popular social tagging Web service. The guppy effect is then described using a quantum inspired formalism that has been already successfully applied to model conjunction fallacy and probability judgement errors. Key to the formalism is the concept of interference, which is able to capture and quantify the strength of the guppy effect.

Developing the quantum probability ranking principle

In this work, we summarise the development of a ranking principle based on quantum probability theory, called the Quantum Probability Ranking Principle (QPRP), and we also provide an overview of the initial experiments performed employing the QPRP. The main difference between the QPRP and the classic Probability Ranking Principle, is that the QPRP implicitly captures the dependencies between documents by means of quantum interference". Subsequently, the optimal ranking of documents is not based solely on documents' probability of relevance but also on the interference with the previously ranked documents. Our research shows that the application of quantum theory to problems within information retrieval can lead to consistently better retrieval effectiveness, while still being simple, elegant and tractable.

On the use of complex numbers in quantum models for information retrieval

Quantum-inspired models have recently attracted increasing attention in Information Retrieval. An intriguing characteristic of the mathematical framework of quantum theory is the presence of complex numbers. However, it is unclear what such numbers could or would actually represent or mean in Information Retrieval. The goal of this paper is to discuss the role of complex numbers within the context of Information Retrieval. First, we introduce how complex numbers are used in quantum probability theory. Then, we examine van Rijsbergen’s proposal of evoking complex valued representations of informations objects. We empirically show that such a representation is unlikely to be effective in practice (confuting its usefulness in Information Retrieval). We then explore alternative proposals which may be more successful at realising the power of complex numbers.