Oscillation and decay of particle current due to a quench and dephasing in an interacting fermionic system

We study the response of a particle current to dissipative dephasing in an interacting, few body fermionic lattice system. The particles are prepared in the many-body interacting ground state in presence of an artificial magnetic gauge field, which is subsequently quenched to zero. The initial current decays non-trivially in the dissipative environment and we explore the emerging dynamics, time scales and their dependence on the various system parameters.     

Application of PARAFAC to a two-component system exhibiting fluorescence resonance energy transfer: from theoretical prediction to experimental validation

One of the conventionally accepted requirements for parallel factor analysis (PARAFAC) to handle the fluorescence excitation emission matrices (EEMs) is the independence of each component's absorption and emission spectra in simple mixtures of fluorophores. EEMs of samples in which F?rster resonance energy transfer (FRET) occurs between fluorophores seem to fail to meet this requirement. A rigorous theoretical treatment of the steady-state kinetics in the present work indicates that the fluorescence in the presence of FRET, excited by relatively weak excitation light intensity, can be reasonably separated into additive contributions from three parts: donors, acceptors and FRET. This prediction is for the first time verified experimentally in sodium dodecyl sulfate micellar solutions containing biphenyl as the energy donor and 2,5-diphenyloxazole as the energy acceptor. The experimental EEMs were well fitted to three components as predicted. A well accepted diagnostic test called core consistency (CC), specifically designed for modeling simple mixtures of fluorophores with PARAFAC, was found to be negative for the 3-component model in the present study. The simultaneous occurrence of good model fit and significantly negative CC when modeling fluorophore mixtures by conventional PARAFAC would be indicative of the presence of physical/chemical processes (e.g., FRET) that deviate from the conventional working requirements for PARAFAC. The extent of FRET has been independently measured or calculated by three methods: 1) decrease in steady state fluorescence of donor; 2) lifetime measurements with population analysis; and 3) Poisson statistics based on PARAFAC-determined distribution constants. The results of the three methods are consistent. The normalized scores of the three components found by PARAFAC also agree to within a few percent with relative concentrations in aqueous and micelle phases determined from distribution constants for the solutions prepared with nine different combinations of total donor and acceptor concentrations. Our theoretical treatment also for the first time spells out in detail the relationship between the PARAFAC scores and concentrations of components, in terms of photophysical constants of the components and spectral shape factors.     

Sequencing membrane proteins by tandem mass spectrometry

Tandem mass spectrometry (MS/MS) is an attractive technique for sequencing membrane proteins because it can be applied to peptides in mixtures that are difficult to separate chromatographically. To evaluate the suitability of MS/MS sequencing for membrane proteins and to develop protocols for the preparation of the cleaved peptides, we employed the well characterized apoproteins of bacteriorhodopsin and bovine rhodopsin, i.e. bacterioopsin and opsin, respectively. Without separation, nine out of ten peptides resulting from cyanogen bromide cleavage of bacterioopsin were detected by fast atom bombardment MS, the single undetected fragment being a tetrapeptide that was presumably hidden in the low-m/z matrix background. Furthermore, MS/MS was used to confirm the sequence of all the peptides detected with m/z values below 3.5 kDa (40% of the protein). Bovine opsin was analyzed in a similar fashion. Tandem MS/MS has thus allowed the sequencing of substantial portions of two integral membrane proteins by the analysis of unseparated peptide mixtures, demonstrating for the first time that this technique can obviate some of the most serious difficulties associated with sequencing membrane proteins, namely the difficult-to-achieve separation of the ‘sticky’ peptide fragments.     

Effects of dielectric barrier discharge in air on morphological and electrical properties of graphene nanoplatelets and multi-walled carbon nanotubes

Multi-walled carbon nanotubes (MWCNTs) and graphene nanoplatelets (GNPs) have been functionalized by dielectric barrier discharge (DBD) in air. The extent of functionalization of MWCNTs and GNPs reaches a maximum at the delivered discharge energy of 720 and 240 J mg⁻¹, respectively. Further exposure to plasma leads to reduction of functional groups from the surface of the treated nanomaterials. It has also been demonstrated that DBD plasma does not produce dramatic structural changes in MWCNTs, while flakes of the treated GNPs become thinner and smaller in the lateral size. Conductive thin films, obtained by drop casting a solution of the treated nanomaterials in N-methyl-1-pyrrolidone on poly(methyl methacrylate) substrate, show significantly lower sheet resistance.     

Shear induced orientation of phase segregated block copolymer/epoxy blends

In this work a phase segregated blend system consisting of a block copolymer (BCP) and epoxy matrix with cylindrical morphology is considered. Transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS) investigations reveal that long-ranged ordered nanostructures can be obtained under certain preparation conditions. The pre-shearing conditions are the most important factors in order to obtain regular structures.     

Radiation effects on room temperature epoxy adhesive molecular structure: Mechanical tests and correlation with calorimetric and outgassing analyses

In applications like space satellites, high-energy physics experiments, and nuclear power stations, epoxy structural adhesives are normally used in an ionizing radiation environment. To check the effects of γ-irradiation on room temperature epoxy adhesives, mechanical measurements were undertaken for three different resins up to the dose of 3 MGy. Both dumbbell and single-lap shear tests were performed. To correlate the measured radiation effects on these mechanical properties with the molecular modifications of the resins, outgassing and calorimetric tests were performed on one of the tested adhesives. As a result of these tests, the mechanical modifications were associated with the combination of reticulation, network scission, and production of low-weight molecules due to radiation. Differences in shear and tensile strength behaviors were associated with the presence of the adhesive-adherend interface.     

Surface‐enhanced Raman spectroscopy for quantitative measurement of lactic acid at physiological concentration in human serum

Lactic acid is a simple and effective indicator for estimating physiological function. Rapid and sensitive detection of lactic acid is very useful in clinical diagnosis. However, the concentration of lactic acid in the physiological state is too low to be detected using traditional Raman spectroscopy. We applied silver colloidal nanoparticles‐mediated surface‐enhanced Raman spectroscopy (SERS) for rapid identification and quantification of lactic acid. The standard SERS spectra of lactic acid were defined and the 1395 cm⁻¹ band intensity was used for quantification from 0.3 to 2 mM (R² = 0.99). In clinical blood sample measurement, the ultrafiltration (cutoff value 5 kDa) can efficiently reduce background fluorescence to improve SERS performance. We established identical and optimal procedure by adjusting reaction time and volume ratio of serum and nanoparticles to obtain high SERS reproducibility. Finally, we showed that silver colloidal nanoparticles‐mediated SERS technique was successfully applied to detect lactic acid at physiological concentrations in the blood. Copyright © 2010 John Wiley & Sons, Ltd.     

Thermal and chemorheological modelling of the processing of advanced epoxy based composites

A general model for the prediction of the rheological behavior of epoxy resins during the processing of epoxy based laminates is presented. The model is able to predict the temperature and the extent of reaction across the laminate thickness during processing. The model leads the computation of the viscosity inside the composite where experimental measurements are not possible. Thermal characterization of the reacting systems gives the input data necessary for the mathematical modelling. The numerical simulation has confirmed the necessity of a controlled temperature ramp in order to obtain a more homogeneous laminated structure. Moreover, the numerical results indicated that the process variables may present anomalous behavior which may affect the physical properties and durability of the final product.