Band-Like Charge Transport in Phytic Acid-Doped Polyaniline Thin Films

We explore the charge transport properties of phytic acid (PA) doped polyaniline thin films prepared by the surfactant monolayer-assisted interfacial synthesis (SMAIS). Structural and elemental analysis confirms the inclusion of PA in the thin films and reveals a progressive loss of crystallinity with the increase of PA doping content. Charge transport properties are interrogated by time-resolved terahertz (THz) spectroscopy. Notably, independently of doping content and hence crystallinity, the frequency-resolved complex conductivity spectra in the THz region can be properly described by the Drude model, demonstrating band-like charge transport in the samples and state-of-the-art charge carrier mobilities of ≈1 cm²V⁻¹s⁻¹. A temperature-dependent analysis for the conductivity further supports band-like charge transport and suggest that charge carrier mobility is primarily limited by impurity scattering. This work highlights the potential of PA doped polyaniline for organic electronics.     

Direct Observation of Core–Shell Structures in Individual Lead Titanate Ferroelectric Nanostructures by Tip‐Enhanced Refractive Index Mapping

Ferroelectrics undergo a size‐driven phase transition at the nanoscale below which the spontaneous polarization, their defining property, irrevocably ceases. This threshold often referred to as the superparaelectric limit has tremendous technological relevance in an era of progressing integration. Just as the balance of short‐range elastic and long‐range electrostatic ordering in bulk, the critical size depends on temperature. Room‐temperature tip‐enhanced Raman spectroscopy (TERS) imaging of individual lead titanate (PbTiO₃) nanoislands is reported with a spatial resolution of ≈3 nm. Monitoring the spectral shift of the gold‐tip enhanced luminescence, which depends on the local refractive index, images grains composing the nanoislands. The wavelength of the enhanced luminescence shifts between the grains and their boundaries indicating the predicted core–shell structure of ferroelectric and paraelectric phase. The shear force configuration rules out the distance dependence of capacitive plasmonic coupling between tip and substrate as the origin of the observed shift. As the reported temperature‐changes in nonresonant TERS do not account for noticeable thermal effects, the underlying, even though weak, tip‐enhanced Raman spectrum of the grain core reflects PbTiO₃ close to the ferroelectric‐to‐paraelectric phase transition which is primarily related to the finite size of the grains.     

Quantification of regional left ventricular dyssynchrony by magnetic resonance imaging

Cardiac resynchronization therapy is an established treatment in patients with symptomatic heart failure and intraventricular conduction delay. Electrical dyssynchrony is typically adopted to represent myocardial activation dyssynchrony, which should be compensated by cardiac resynchronization therapy. One third of the patients, however, does not respond to the therapy. Therefore, imaging modalities aimed at the mechanical dyssynchrony estimation have been recently proposed to improve patient selection criteria. This paper presents a novel fully automated method for regional mechanical left ventricular dyssynchrony quantification in short-axis magnetic resonance imaging. The endocardial movement is described by time-displacement curves with respect to an automatically determined reference point. Different methods are proposed for time-displacement curve analysis aimed at the regional contraction timing estimation. These methods were evaluated in two groups of subjects with (nine patients) and without (six patients) left bundle branch block. The contraction timing standard deviation showed a significant increase for left bundle branch block patients with all the methods. A novel method based on phase spectrum analysis may be however preferred due to a better specificity (99.7%) and sensitivity (99.0%). In conclusion, this method provides a valuable prognostic indicator for heart failure patients with dyssynchronous ventricular contraction and it opens new possibilities for regional timing analysis.     

Iron-overload in patients on maintenance hemodialysis: diagnostic criteria, indications and treatment by desferrioxamine (author's transl)

33 patients with chronic renal failure were divided into two groups. Group I consisted of 8 non-dialysed patients without any clinical or biochemical sign of liver disturbance nor any iron supplementation. Group II consisted of 25 maintenance hemodialysis (MHD) patients treated from 2 to 13 years. 19 subjects had chronic B hepatitis. Total exogenous iron load parenteral iron and/or blood transfusions) was calculated. Body iron overload (hemosiderosis) was assessed by liver iron concentration (LIC) in needle biopsy specimens according to Barry's method (less than 200 microgram/100 mg dry weight) and serum ferritin levels (less than 360 ng/ml). 4 patients whose serum ferritin was increased with or without hepatic fibrosis and with or without any organ dysfunction due to hemochromatosis received i.v. infusions of desferrioxamine in doses of 2 g at each dialysis. Serum ferritin levels were correlated with LIC (p less than 0.001) and iron load (p less than 0.001). Hemosiderosis was noted in 16 MHD patients (group II) and correlated with iron load. Hemochromatosis was noted in 4 patients (group II). 4 hemodialysed patients with iron overload were treated by desferrioxamine from 6 to 18 months. During this therapy, body iron stores fell and organ dysfunction (heart failure, hepatic cytolysis, anaemia, diabetes mellitus improved. Long-term chelation therapy by desferrioxamine was effective and the chelated iron was readily removed by dialysis. These data show the importance of precise evaluation of iron stores in MHD patients.     

Requirements for stress gradient‐based fatigue assessment of notched structures according to theory of critical distance

Notches, local stress raisers within structural components, are one of the most important locations for fatigue crack initiation. It is well known that fatigue is governed by the effective stresses in the vicinity of notches. Within this study, differences in prediction accuracy between different types of theory of critical distance methods, that is, point and line methods, are systematically investigated in conjunction with a sensitivity study regarding mesh refinement, assumed strength hypothesis and material behaviour. For this purpose, a finite element analysis parameter study on notched structures is performed and recommendations for the application of stress gradient methods are presented. Difference in effective stress of up to 30%, and hence a significant difference in fatigue life (e.g., 185% for a slope of S‐N curve of k = 4), is found for typical notch shapes, for example, in welded joints.     

Self-Charging of Quench Condensed Tritium Films

Self-charging of a solid tritium film (T₂) has been discovered by chance in a precision spectroscopy experiment on tritium decay as a shift of the endpoint energy by several eV. The effect was then investigated systematically as a function of film thickness and time by measuring the energy shift of monochromatic conversion electrons from ^{83 m} Kr evaporated onto T₂ films. The steady state is characterized by a practically constant, critical electric field strength E _c 62 MV/m (20 mV/monolayer) over the film, at which the residual positive charges attain sufficient mobility to penetrate the film towards the conducting substrate. This kind of breakthrough behaviour is analyzed in terms of a thermal hopping model, where a trapping potential of ₀175 k _BK is lowered in direction of the electric force by a factor of 3 in order to facilitate hopping at a film temperature of about 1.9 K.     

Exciton polarizability in semiconductor nanocrystals

The response of charge to externally applied electric fields is an important basic property of any material system, as well as one critical for many applications. Here, we examine the behaviour and dynamics of charges fully confined on the nanometre length scale. This is accomplished using CdSe nanocrystals of controlled radius (1-2.5 nm) as prototype quantum systems. Individual electron-hole pairs are created at room temperature within these structures by photoexcitation and are probed by terahertz (THz) electromagnetic pulses. The electronic response is found to be instantaneous even for THz frequencies, in contrast to the behaviour reported in related measurements for larger nanocrystals and nanocrystal assemblies. The measured polarizability of an electron-hole pair (exciton) amounts to approximately 10(4) A(3) and scales approximately as the fourth power of the nanocrystal radius. This size dependence and the instantaneous response reflect the presence of well-separated electronic energy levels induced in the system by strong quantum-confinement effects.     

Sample preparation for the analysis of complex carbohydrates by multicapillary gel electrophoresis with light-emitting diode induced fluorescence detection

This paper evaluates various sample preparation methods for multicapillary gel electrophoresis based glycan analysis to support electrokinetic injection. First the removal of excess derivatization reagent is discussed. Although the Sephadex G10 filled multiscreen 96-well filter plate and Sephadex G10 filled pipet tips enabled increased analysis sensitivity, polyamide DPA-6S pipet tips worked particularly well. In this latter case an automated liquid handling system was used to increase purification throughput, necessary to feed the multicapillary electrophoresis unit. Problems associated with the high glucose content of such biological samples as normal human plasma were solved by applying ultrafiltration. Finally, a volatile buffer system was developed for exoglycosidase-based carbohydrate analysis.     

Loosening quantum confinement: observation of real conductivity caused by hole polarons in semiconductor nanocrystals smaller than the bohr radius

We report on the gradual evolution of the conductivity of spherical CdTe nanocrystals of increasing size from the regime of strong quantum confinement with truly discrete energy levels to the regime of weak confinement with closely spaced hole states. We use the high-frequency (terahertz) real and imaginary conductivities of optically injected carriers in the nanocrystals to report on the degree of quantum confinement. For the smaller CdTe nanocrystals (3 nm < radius < 5 nm), the complex terahertz conductivity is purely imaginary. For nanocrystals with radii exceeding 5 nm, we observe the onset of real conductivity, which is attributed to the increasingly smaller separation between the hole states. Remarkably, this onset occurs for a nanocrystal radius significantly smaller than the bulk exciton Bohr radius a(B) ～ 7 nm and cannot be explained by purely electronic transitions between hole states, as evidenced by tight-binding calculations. The real-valued conductivity observed in the larger nanocrystals can be explained by the emergence of mixed carrier-phonon, that is, polaron, states due to hole transitions that become resonant with, and couple strongly to, optical phonon modes for larger QDs. These polaron states possess larger oscillator strengths and broader absorption, and thereby give rise to enhanced real conductivity within the nanocrystals despite the confinement.