Anodic passivity of glassy Ni83B17 alloy in sulphuric acid

The anodic passivation of Ni₈₃B₁₇ glassy was investigated in sulphuric acid solutions with respect to the degree of proton hydration and the structure of acid. The possibility of passivation in methanolic solutions of sulphuric acid was also examined. The investigations involved electrochemical measurements, XPS and sulphur dioxide analyses. When acid concentration is low, the passivity of Ni₈₃B₁₇ is a result of the formation of an oxide layer in the presence of “free” water molecules (i.e. not bound to protons). In concentrated sulphuric acid, the passivation may occur as a result of the oxidative ability of acid connected with S⁶⁺ ion reduction. At intermediate acid concentrations a mixed salt-oxide layer is formed. The passivity of Ni₈₃B₁₇ was also observed in methanolic solutions of sulphuric acid, as a result of the oxidising ability of the acid.     

Iron enhances generation of fibrin fibers in human blood: Implications for pathogenesis of stroke

Stroke is associated with the intracerebral formation of fibrin clots which may lead to irreversible brain damage. Thrombolytic therapies employ a variety of natural and/or recombinant plasminogen activators to initiate fibrinolytic degradation of cerebral thrombi. However, such therapies when installed beyond 4‐ to 6‐h window, may fail to achieve the expected outcome. This is due to the hydroxyl radical‐induced modification of fibrin(ogen) molecules rendering them refractory to fibrinolytic degradation, but no cause of the increased free radical generation in stroke was offered. Here, we show by means of electron microscopy that iron ions added to human blood dramatically enhances fibrin fibers formation with thrombin, and significantly delays fibrinolysis during spontaneous clotting of native blood. Iron ions caused the appearance dense matted fibrin deposits, similar, if not identical, to those observed in plasma of patients with stroke. These results may explain a known relationship between thrombotic diseases and the increased body concentrations of free iron and/or hemoglobin derivatives. We conclude that any action resulting in the inhibition of hemostatic abnormalities, as well as in the reduction of body free iron and scavenging of hydroxyl radicals (e.g., by polyphenols) can potentially prevent pathological reactions associated with consequences of stroke. Microsc. Res. Tech. 75:1185–1190, 2012. © 2012 Wiley Periodicals, Inc.     

Time-resolved fluorescence microspectroscopy for characterizing crude oils in bulk and hydrocarbon-bearing fluid inclusions

Time-resolved fluorescence data was collected from a series of 23 bulk crude petroleum oils and six microscopic hydrocarbon-bearing fluid inclusions (HCFI). The data was collected using a diode laser fluorescence lifetime microscope (DLFLM) over the 460-700 nm spectral range using a 405 nm excitation source. The correlation between intensity averaged lifetimes (tau) and chemical and physical parameters was examined with a view to developing a quantitative model for predicting the gross chemical composition of hydrocarbon liquids trapped in HCFI. It was found that tau is nonlinearly correlated with the measured polar and corrected alkane concentrations and that oils can be classified on this basis. However, these correlations all show a large degree of scatter, preventing accurate quantitative prediction of gross chemical composition of the oils. Other parameters such as API gravity and asphaltene, aromatic, and sulfur concentrations do not correlate well with tau measurements. Individual HCFI were analyzed using the DLFLM, and time-resolved fluorescence measurements were compared with tau data from the bulk oils. This enabled the fluid within the inclusions to be classified as either low alkane/high polar or high alkane/low polar. Within the high alkane/low polar group, it was possible to clearly discriminate HCFI from different locales and to see differences in the trapped hydrocarbon fluids from a single geological source. This methodology offers an alternative method for classifying the hydrocarbon content of HCFI and observing small variations in the trapped fluid composition that is less sensitive to fluctuations in the measurement method than fluorescence intensity based methods.     

The design of low noise digital filters with controlled dynamic range

A novel digital filter structure, that allows proper positioning of the zeros of the noise transfer functions to reduce the output roundoff noise, is introduced. Relations between zero locations, roundoff noise and dynamic range are derived and are then utilized in an heuristic optimization method for synthesizing a low noise scaled digital filter structure. Illustrative examples supporting the proposed approach are included.     

Interface growth morphologies in pulsed laser deposited, room temperature grown multilayer hard coatings

The mechanical behaviour - hardness, elasticity, and adhesion - of multilayer coatings is strongly influenced by the type of the formed interfaces between the different layers. In industrially applied tribological coatings the interface region is predominantly not a perfect sudden change of the chemical composition of the adjacent crystal planes, but a transition zone of a thickness, which is strongly dependent on the energetic conditions during deposition. Multilayer coatings grown by high-energetic deposition techniques always struggle with high atomic mixing of both adjacent coating materials due to high energetic ion implantation.One of these high-energetic deposition techniques is the Pulsed Laser Deposition (PLD), characterized by pulsed and within one pulse alternating high- and low-energetic particle fractions, hitting successively the substrate surface. Such deposition conditions were shown to be highly advantageous for low temperature deposition by the densification of the growth structures due to activated diffusion and re-sputtering, but increases the difficulty in depositing multilayer structures.The current paper addresses these specific growth conditions based on Ti/TiN and Cr/CrN multilayer coatings. High resolution transmission electron microscopy results show that the atomic mixing at the interface is not highly critical for the deposition of multilayer coatings and that extremely dense growth structures are forming even in the interface regions.     

Evaluation of porous 430L stainless steel for SOFC operation at intermediate temperatures

In this paper a 430L porous stainless steel is evaluated for possible SOFC applications. Recently, there are extensive studies related to dense stainless steels for fuel cell purposes, but only very few publications deal with porous stainless steel. In this report porous substrates, which are prepared by die-pressing and sintering in hydrogen of commercially available 430L stainless steel powders, are investigated. Prepared samples are characterized by scanning electron microscopy, X-ray diffractometry and cyclic thermogravimetry in air and humidified hydrogen at 400 °C and 800 °C. The electrical properties of steel and oxide scale measured in air are investigated as well. The results show that at high temperatures porous steel in comparison to dense steel behaves differently. It was found that porous 430L has reduced oxidation resistance both in air and in humidified hydrogen. This is connected to its high surface area and grain boundaries, which after sintering are prone to oxidation. Formed oxide scale is mainly composed of iron oxide after the oxidation in air and chromium oxide after the oxidation in humidified hydrogen. In case of dense substrates only chromium oxide scale usually occurs. Iron oxide is also a cause of relatively high area-specific resistance, which reaches the literature limit of 100 mΩ cm² when oxidizing in air only after about 70 h at 800 °C.     

Power quality event detection based on the divide and conquer principle and innovation concept

The aim of this paper is to introduce a novel real-time digital signal processing technique for power quality disturbance detection. The proposed technique is inspired on the Divide and Conquer Principle and on the Innovation Concept. Essentially, the Divide and Conquer Principle is applied in splitting the monitored disturbance event into stationary and nonstationary components, allowing localized individual signal analysis. Thereafter, the Innovation Concept is introduced for revealing new information not previously observed in the energy of the nonstationary signals and so detecting a new event. In addition, this paper demonstrates a straightforward and feasible way to evaluate the Total Harmonic Distortion (THD) or a distortion measure for voltage signals. Simulation results indicate that the proposed technique is able to accurately detect a variety of voltage disturbances.     

Variations of internal friction in YBa2Cu3Ox superconductors

The internal friction (Q ^–1) spectrum of YBa₂Cu₃O_x superconducting ceramic exhibits several peaks. It has been confirmed that the high-temperature peak (around 240 K) depends on structural changes and varies during subsequent cycles of cooling and heating.Q ^–1 conductivity, X-ray spectra and the shielding effect have been measured on several samples having different superconducting properties obtained by various thermal treatments. Splitting is a characteristic feature of the high-temperature internal friction peak of the sample which exhibits good superconducting properties. In the case of the specimen exhibiting the worst properties the peaks decrease and overlap. In both cases an increase can be observed of this peak with the number of thermal cycles. After ageing at 470 K, the high-temperature peak disappears. Subsequent thermal cycles slightly recover it. Hysteresis of the Young modulus is also observed. The results are interpreted as transition of the 04 oxygen atom between two energy minima in the O4-Cu-O4 chain.