A model for the non-isothermal viscoelastic behavior of polymers

A new constitutive model is derived for the viscoelastic behavior of polymers under non-isothermal loading. The model extends the Tobolsky concept of adaptive links (entanglements) between polymeric molecules to thermoviscoelastic media. Employing this model, we calculate residual stresses built up in an epoxy resin plate under cooling from the rubber-glass transition temperature, analyze the effect of material parameters on residual stresses, and compare results of numerical simulation with experimental data.     

Retrieving seawater-backscattering profiles from coupling Raman and elastic lidar data

We propose a technique for retrieving seawater-backscattering profiles that is based on the joint use of elastic and Raman lidar returns. We suggest using two lidar channels: the Raman channel and the elastic channel with a light frequency equal to a half-sum of initial and Raman-shifted frequencies of the Raman channel. These specific wavelengths provide the same attenuation laws for elastic and Raman signals if absorption and scattering spectra can be approximated by a power law. In particular, seawater supplies such a possibility in the region of 400-500 nm if extremely bioproductive waters are not considered and the chlorophyll absorption peak at 440 nm does not come out of the background of dissolved organic matter absorption. With these specific initial wavelengths, the elastic and Raman lidar returns differ only in the backscattering coefficients. Because the Raman-backscattering coefficient is constant along the profile, the (elastic-to-Raman) ratio of these lidar returns directly produces the profile of the elastic-backscattering coefficient. This technique stays valid even under multiple-scattering conditions, which is of great importance for seawater sounding.     

Equilibrium swelling of thermo-responsive core-shell microgels

Design of new routes for preparation of hydrogels with fast response and enhanced mechanical and physical properties requires adequate modeling of their swelling. A model is developed for the equilibrium swelling of thermo-responsive gels. A characteristic feature of the model is that it accounts for a strong increase in the elastic moduli above the volume phase transition temperature T_c driven by aggregation of hydrophobic segments into clusters that serve as extra physical bonds between chains. The model is applied to the analysis of swelling diagrams on poly(N-isopropylacrylamide) macroscopic gels, microgel latices, and core-shell microgels with rigid cores. Good agreement is shown between the experimental data and results of simulation. It is demonstrated that the elastic moduli of microgels are higher, while their degrees of swelling in the stress-free state are lower compared with those of macroscopic gels.     

Optimization of La2O3-containing diopside based glass-ceramic sealants for fuel cell applications

We report on the optimization of La₂O₃-containing diopside based glass-ceramics (GCs) for sealant applications in solid oxide fuel cells (SOFC). Seven glass compositions were prepared by modifying the parent glass composition, Ca_0.8Ba_0.1MgAl_0.1La_0.1Si_1.9O₆. First five glasses were prepared by the addition of different amounts of B₂O₃ in a systematic manner (i.e. 2, 5, 10, 15, 20 wt.%) to the parent glass composition while the remaining two glasses were derived by substituting SrO for BaO in the glasses containing 2 wt.% and 5 wt.% B₂O₃. Structural and thermal behavior of the glasses was investigated by infrared spectroscopy (FTIR), density measurements, dilatometry and differential thermal analysis (DTA). Liquid–liquid amorphous phase separation was observed in B₂O₃-containing glasses. Sintering and crystallization behavior, microstructure, and properties of the GCs were investigated under different heat treatment conditions (800 and 850 °C; 1–300 h). The GCs with ≥5 wt.% B₂O₃ showed an abnormal thermal expansion behavior above 600 °C. The chemical interaction behavior of the glasses with SOFC electrolyte and metallic interconnects, has been investigated in air atmosphere at SOFC operating temperature. Thermal shock resistance and gas-tightness of GC sealants in contact with 8YSZ was evaluated in air and water. The total electrical resistance of a model cell comprising Crofer 22 APU and 8YSZ plates joined by a GC sealant has been examined by the impedance spectroscopy. Good matching of thermal expansion coefficients (CTE) and strong, but not reactive, adhesion to electrolyte and interconnect, in conjunction with a low level of electrical conductivity, indicate that the investigated GCs are suitable candidates for further experimentation as SOFC sealants.     

Hydrodynamics and heat transfer in swirl flow under conditions of one-side heating. Part 2: Boiling heat transfer. Critical heat fluxes

The paper gives the basic results of experimental investigation of boiling heat transfer in heat-absorbing devices of the ITER thermonuclear reactor, which are subjected to one-side heating. The experimental data on heat transfer at nucleate and film boiling and on critical heat fluxes are obtained in the following range of parameters of water flow: pressure p = 0.7–2.0 MPa, mass flux G = 340–25 000 kg/(m² s), and water temperature at the inlet T_in = 20–60 °C. A twisted tape is inserted in the circular channel in order to form swirling flow of water. The investigations are performed for tapes with different values of flow swirl coefficient, as well for test sections without a tape. Appropriate calculation formulas are derived, which reliably generalize the experimental data.     

C60 secondary ion Fourier transform ion cyclotron resonance mass spectrometry

Secondary ion mass spectrometry (SIMS) has seen increased application for high spatial resolution chemical imaging of complex biological surfaces. The advent and commercial availability of cluster and polyatomic primary ion sources (e.g., Au and Bi cluster and buckminsterfullerene (C(60))) provide improved secondary ion yield and decreased fragmentation of surface species, thus improving accessibility of intact molecular ions for SIMS analysis. However, full exploitation of the advantages of these new primary ion sources has been limited, due to the use of low mass resolution mass spectrometers without tandem MS to enable enhanced structural identification capabilities. Similarly, high mass resolution and high mass measurement accuracy would greatly improve the chemical specificity of SIMS. Here we combine, for the first time, the advantages of a C(60) primary ion source with the ultrahigh mass resolving power and high mass measurement accuracy of Fourier transform ion cyclotron resonance mass spectrometry. Mass resolving power in excess of 100?000 (m/Δm(50%)) is demonstrated, with a root-mean-square mass measurement accuracy below 1 part-per-million. Imaging of mouse brain tissue at 40 μm pixel size is shown. Tandem mass spectrometry of ions from biological tissue is demonstrated and molecular formulas were assigned for fragment ion identification.     

Synthesis of novel tetracationic asymmetric monomeric monomethine cyanine dyes – highly fluorescent dsDNA probes

Quaternisation of monomethine cyanine dyes bearing haloalkyl chains, with the appropriate monoquaternised 1,4‐diazabicyclo[2.2.2]octane derivatives, yielded novel tetracationic asymmetric monomeric monomethine cyanine dyes belonging to the thiazole orange family. The optimal conditions for this reaction were investigated. The longest wavelength absorption maxima of the studied dyes are in the region 504–507 nm. The molar absorptivities of the target dyes are high, with values between 70 500 and 99 500 l mol^?1 cm^?1. The fluorescence intensity and the fluorescence quantum yields of the free dyes in solution or in the presence of double‐stranded DNA were determined using thiazole orange for comparison. The dyes are suitable for nucleic acid detection and have a high binding affinity, attributable to their four positive charges.     

Elimination of systematic mass measurement errors in liquid chromatography-mass spectrometry based proteomics using regression models and a priori partial knowledge of the sample content

The high mass measurement accuracy and precision available with recently developed mass spectrometers is increasingly used in proteomics analyses to confidently identify tryptic peptides from complex mixtures of proteins, as well as post-translational modifications and peptides from nonannotated proteins. To take full advantage of high mass measurement accuracy instruments, it is necessary to limit systematic mass measurement errors. It is well known that errors in m/z measurements can be affected by experimental parameters that include, for example, outdated calibration coefficients, ion intensity, and temperature changes during the measurement. Traditionally, these variations have been corrected through the use of internal calibrants (well-characterized standards introduced with the sample being analyzed). In this paper, we describe an alternative approach where the calibration is provided through the use of a priori knowledge of the sample being analyzed. Such an approach has previously been demonstrated based on the dependence of systematic error on m/z alone. To incorporate additional explanatory variables, we employed multidimensional, nonparametric regression models, which were evaluated using several commercially available instruments. The applied approach is shown to remove any noticeable biases from the overall mass measurement errors and decreases the overall standard deviation of the mass measurement error distribution by 1.2-2-fold, depending on instrument type. Subsequent reduction of the random errors based on multiple measurements over consecutive spectra further improves accuracy and results in an overall decrease of the standard deviation by 1.8-3.7-fold. This new procedure will decrease the false discovery rates for peptide identifications using high-accuracy mass measurements.     

In-situ redox cycling behaviour of Ni–BaZr0.85Y0.15O3−δ cermet anodes for Protonic Ceramic Fuel Cells

The current work investigates the redox behaviour of peak performing Ni–BaZr_0.85Y_0.15O_3−δ (Ni-BZY) cermet anodes for protonic ceramic fuel cells (PCFCs) by electrochemical impedance measurements, scanning electron microscopy (SEM) and X-ray diffraction (XRD). Peak performing PCFC cermet anodes are documented to require much lower porosity levels than those needed in oxide-ion conducting counterparts. The polarisation behaviour of these optimised PCFC anodes is shown to be drastically impaired by redox cycling, with depletions in performance that correspond to around 80% of the original resistance values noted after the first redox cycle. The ohmic resistance (Rohmic) is also shown to be increased due to delamination at the electrode/electrolyte interface, as confirmed by postmortem microstructural analysis. In-situ measurements by environmental scanning electron microscopy (ESEM) reveal that degradation proceeds due to volume expansion of the nickel phase during the re-oxidation stage of redox cycling. The present study reveals degradation to be very fast for peak performing Ni-BZY cermets of low porosity. Hence, methods to improve redox stability can be considered to be essential before such anodes can be implemented in practical devices.