Chronopotentiometric potential-time curves of electron transfer across the interface between two immiscible electrolyte solutions

Theoretical potential-time curves were derived that are mathematical expressions of the electron transfer reaction O1 (w) + R2(non) ? R1(w) + O2(non) proceeding at the interface of two immiscible phases between the redox couple O1/R1 in the aqueous phase (w) and the redox couple O2/R2 in the non-aqueous phase (non) under galvanostatic conditions. Procedures for the determination of the diffusion coefficients of the reactants in the corresponding phase and for the evaluation of thermodynamic and kinetic parameters of the electron transfer reaction from the potential-time curves were suggested.     

Wärmeübertragung bei der Strömung Newton'scher Flüssigkeiten in Rohren mit SchraubeneinheitenHeat transfer to a Newtonian liquid flowing through a pipe with built-in helical elements

The effect of two types of helical elements built in a cylindrical pipe on the heat transfer intensity in a heated Newtonian liquid was investigated.The results express the dependence of the heat transfer coefficient upon flow conditions and upon physical and geometrical properties of the system examined. The resulting dimensionless equations are given in graphic form. The range of Reynolds and Prandtl numbers investigated was from 90 to 5000 and from 6 to 60, respectively.     

Sorption of water vapor by hydrophilic polyurethane-ureas

Segmented polyurethane-ureas were prepared from low-molecular weight homopolymers or triblock (PEP) copolymers of ethylene and propylene oxides and 4,4′-diphenylmethane diisocyanate with hydrazine as chain extender. Equilibrium sorption of water vapor at 23°C was measured at eight to nine values of relative vapor pressure, 0.08 ≤ p/p₀ ≤ 0.97. The effect of the structure (composition and length) of soft segments was studied. Sorption capacities were found to be lower than the reference values computed under the assumption that the contributions to sorption by the chain constituents are additive. This finding was assigned to the shielding effect of hard segment domains on the interaction of water molecules with hydrophilic (ethoxamer) groups of soft segments. © 1993 John Wiley & Sons, Inc.     

UV–VUV spectroscopy of rare earth doped persistent luminescence materials

The electronic and defect energy level structure of polycrystalline SrAl₂O₄:Eu²⁺,R³⁺ persistent luminescence materials were studied with thermoluminescence and UV–VUV synchrotron radiation emission and excitation spectroscopy. Theoretical calculations using the density functional theory (DFT) were carried out simultaneously with the experimental work. The experimental band gap energy (E_g) value of 6.6 eV agrees very well with the DFT value of 6.4 eV. The 4f⁷ → 4f⁶5d¹ excitation bands of Eu²⁺ were found rather similar irrespective of the R³⁺ co-dopant. The trap level energy distribution depended strongly on the R³⁺ co-dopant except for the shallowest trap energy above the room temperature remaining the same, however. The different processes in the mechanism of persistent luminescence from SrAl₂O₄:Eu²⁺,R³⁺ was constructed and discussed.     

Mechanical testing of a FW panel attachment system for ITER

An objective of experiments and finite element simulations was to check the stiffness, the strength and the fatigue resistance of the attachment of the First Wall panels onto a shield block of blanket modules according to the ITER 2001 design. The panel has a poloidal key at the rear side (in so-called option A with the rear access bolting) and it is attached by means of special studs located on a key-way in the shield block. Special device for a test of stud tensile pre-load relaxation during a thermal cycling was developed. True-to-scale panels, the shield block mock-up and simplified studs were fabricated and the assembly was loaded alternatively by radial moment, poloidal force or poloidal moment simulating the loading during off-normal plasma operations. Thermal cycling led to an acceptable stud pre-load relaxation. Mechanical cycling caused neither the pre-load relaxation nor the loss of the contact in the key-way nor a damage of the attachment system. The combination of poloidal moment and radial force during vertical displacement events (VDEs) seems to be a most dangerous case because it could lead to the loss of the key–key-way contact.     

Primary vacuum standard for UHV range — Standing experience and present problems

Accurate calibrations of gauges to ever lower pressures (higher vacuum) are increasingly becoming necessary. The calibrations over the entire ultra high vacuum (UHV) range i.e. up to 10⁻¹⁰ Pa are already sometimes demanded by the users of vacuum measuring devices. Standards covering part of this range are available in some national metrological laboratories while primary standards covering the entire UHV range are under development. However, the most suitable principle of the primary standard for generating such a low pressure is still not clear. In spite of some attempts during the last century no sufficiently accurate absolute (“calibration-free”) gauge for high vacuum (HV) and UHV ranges has been developed to date. Apparatuses for generating gas pressure in a dynamic flow control method will continue to be used as primary standards for the UHV range, but, by virtue of technical difficulties, the equilibrium (Maxwellian velocity distribution) will be severely disturbed during the process of pressure generation that the pressure in the chamber will not be defined as a simple scalar quantity. This principal problem must be solved first by the development of a primary UHV standard. Another serious problem in the design of an apparatusfor generating controlled pressures on the order of 10⁻¹⁰ Pa requires the uncontrolled changes of gas pressure to 10⁻¹² Pa or lower. Hence an extremely high vacuum (XHV) apparatus must be used in which the requirements concerning the pumps and the outgassing rate from the materials are kept very strict.     

Sound Velocity of Kaolin in the Temperature Range from 20 °C to 1100 °C

The sound velocity of Sedlec kaolin during heating from 20 °C to 1100 °C was investigated by modulated force thermomechanical analysis (mf-TMA). In the interval from 20 °C to 250 °C, the sound velocity increases which can be explained by liberation of the water molecules from pores and micropores. Dehydroxylation (450 °C to 650 °C) presents itself with a decrease of the sound velocity. After dehydroxylation, a two-step increase of the sound velocity was observed. The first step of the increase of the sound velocity is due to solid-state sintering at low temperatures. The second step starts at 950 °C as a consequence of the collapse of the metakaolinite structure. After the maximum, a steep increase of the sound velocity follows as a result of solid-state sintering.     

Evaluating of traumatic brain injuries using artificial neural networks

The purpose of this study is to develop a diagnostic system to detect the severity of traumatic brain injuries using artificial neural networks. Three layered back propagation neural network with an input layer of 10 nodes whose output providing the inputs to a hidden layer was used. Thirty-two patients with traumatic brain injuries in different age and gender were taken in the study. Electroencephalography, Trauma and Glasgow coma scores were used for evaluating the data. The results obtained from the system were compared with the findings of neurologists. We found a significant relationship between the findings of neurologists and systems output for normal, mild, moderate and severe electroencephalography tracing data. Getting this system in routine use will lead to make a rapid decision for the degree of trauma with electroencephalography and revised trauma score.     

Polyurethane/multiwalled carbon nanotube nanowebs prepared by an electrospinning process

Polyurethane (PU) and PU/multiwalled carbon nanotube (MWCNT) nanocomposite nanofibers, both with diameters of 350 nm, were prepared by an electrospinning process from PU dimethylformamide solutions. The appearance of nanowebs in PU/MWCNT nanofiber structures containing PU fibers with diameters of 20–40 nm was observed. The existence of these structures could have been based on the occurrence of strong secondary electric fields, which were created between individual conducting MWCNTs (distributed in the PU/MWCNT nanocomposites), which started to behave as the local moving nanoelectrodes promoting the creation of additional very fine nanowebs during the electrospinning processes. To our knowledge, this is the first report describing nanowebs from synthetic polymers prepared by an electrospinning process. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009