On oxidative degradation of parchment and its non-destructive characterisation and dating

Historic parchment is an extremely complex material, not only due to the various methods of production used and various past environmental histories of objects, but also due to its inhomogeneous structure. Many traditional methods of characterisation are empirical, but useful since they have gained recognition by the end-users. In this paper, we investigated the shrinkage temperature of collagen and the influence of lipids contained in parchment on the measurements. While the content of lipids does not seem to significantly affect shrinkage temperature measurements themselves, it strongly affects the decrease of shrinkage temperature of collagen during degradation, and thus its thermomechanical properties. This confirms the high importance of lipid peroxidation during degradation of parchment.     

Regularity of Intermittent Bursts in BriggsRauscher Oscillating Systems with Phenol

The intermittency or intermittent bursting as the type of dynamic state when two qualitatively different behaviors replace one another randomly during the course of the reaction, although all the control parameters remain constant, is found in the Briggs? Rauscher oscillating system moderated by a very small amount of phenol. Within a range of phenol concentrations, the oscillation amplitude is diminished considerably, and after oscillations cease, they repeat intermittently, giving several bursts of oscillations. For the concentrations used here, the range of phenol concentrations where intermittent bursting oscillations occur in a closed reactor is ca. 1.8×10^?5 to 3.6×10^?5 M . Bursting also occurs in an open reactor and can be sustained indefinitely at 5.53×10^?5 M concentration. The intermittent bursting behavior is robust, and can be achieved at a variety of conditions.     

Some Remarks concerning Flatness and the Parameterization of the System Variables by a Flat Output

For flat systems, by definition the state- and input variables can be parameterized by the flat output and its time derivatives. In the present contribution, for special classes of flat outputs like e.g. flat outputs that only depend on the state, we derive upper bounds for the number of time derivatives that occur in this parameterization. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Numerical and experimental investigations into the upstream transpiration problem in free convection

The influence of uniform upstream transpiration on downstream heat transfer at a vertical plate in free convection is investigated numerically. The governing equations in their von Mises form are solved using a simple finite difference scheme forPr=0.72, in the blowing parameter range, – 1.9x<1.9. Experiments are conducted to verify the numerical predictions for uniform upstream blowing case.It is found that upstream transpiration effect persists upto a very considerable distance downstream of the discontinuity where transpiration ceases. Upstream suction has (relatively) less influence than upstream blowing. The down-stream heat transfer depends not only on the upstream transpiration velocity, but also on the length over which transpiration is applied.

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Numerische und experimentelle Untersuchungen zur stromaufwärts gerichteten Verdunstung bei freier Konvektion

Zusammenfassung Es wird der Einfluß gleichmäßiger, aufwärts gerichteter Verdunstung auf den Wärmeübergang bei freier Konvektion an einer vertikalen abwärts umströmten Platte numerisch untersucht. Der von Misessche Gleichungssatz wird unter Verwendung einer einfachen finiten Differenzenmethode fürPr=0,72 gelöst. Zur Bestätigung der rechnerischen Vorhersagen werden Experimente durchgeführt, bei denen jedoch eine gleichmäßige Aufwärtsströmung erzwungen wird.Es wurde ein starker Einfluß der aufwärts gerichteten Verdunstung über eine sehr lange Strecke auch noch unterhalb der Stelle festgestellt, wo die Verdunstung beginnt. Die Überlagerung eines Aufwärtssoges hat weniger Einfluß als eine durch Gebläse erzwungene Aufwärtsströmung. Der Wärmeübergang in der Abwärtsströmung hängt nicht nur von der Geschwindigkeit der aufwärts gerichteten Verdunstung, sondern auch von der Länge, über die Ausdampfen erfolgt, ab.

     

An implicit time‐marching algorithm for shallow water models based on the generalized wave continuity equation

Wave equation models currently discretize the generalized wave continuity equation with a three‐time‐level scheme centered at k and the momentum equation with a two‐time‐level scheme centered at k+1/2; non‐linear terms are evaluated explicitly. However in highly non‐linear applications, the algorithm becomes unstable at even moderate Courant numbers. This paper examines an implicit treatment of the non‐linear terms using an iterative time‐marching algorithm. Depending on the domain, results from one‐dimensional experiments show up to a tenfold increase in stability and temporal accuracy. The sensitivity of stability to variations in the G‐parameter (a numerical weighting parameter in the generalized wave continuity equation) was examined; results show that the greatest increase in stability occurs with G/τ=2–50. In the one‐dimensional experiments, three different types of node spacing techniques—constant, variable, and LTEA (Localized Truncation Error Analysis)—were examined; stability is positively correlated to the uniformity of the node spacing. Lastly, a scaling analysis demonstrates that the magnitudes of the non‐linear terms are positively correlated to those that most influence stability, particularly the term containing the G‐parameter. It is evident that the new algorithm improves stability and temporal accuracy in a cost‐effective manner. Copyright © 2001 John Wiley & Sons, Ltd.     

High-Performance Planar Isolated Current Sensor for Power Electronics Applications

A planar current sensor, comprised of a magnetic current transformer and a hall-effect element, is presented. The sensor has a broad frequency bandwidth from dc up to 30 MHz, a high current rating (40-A dc), superior linearity, high EMI immunity, small size, robustness, and low realization cost. The main design formulations are given analytically; simulations and finite-element results are presented for verification. Experimental results of current step response and dv/dt immunity are included.     

IR pulsed laser light interaction with soiled cellulose and paper

Nd:YAG laser irradiation (1064 nm) of cellulose samples does not lead to immediate nor long-term effects on mechanical properties of paper, which renders the method increasingly interesting for cleaning of historical paper artefacts. However, the technique’s usability is so far limited due to discoloration when the treated object’s surface contains carbonaceous dirt. By using diffuse-reflectance Fourier-transform infrared spectroscopy, size-exclusion chromatography and viscometry it is demonstrated that the distinct yellowing is accompanied by formation of ether cross-links and dehydration of the cellulose, as well as its depolymerisation. Furthermore, the origin of the discoloration is discussed and it is proposed that yellow chromophores are formed due to carbon–cellulose interactions during laser irradiation. Received: 10 September 2001 / Accepted: 21 January 2002 / Published online: 3 June 2002     

Transmission electron microscopic study of reduced Ca2UO5

Structural changes of Ca₂UO₅ during reduction in hydrogen were studied by transmission electron microscopy. It was shown that monoclinic Ca₂UO₅ changes into triclinic Ca₄U₂O₉. They are related, respectively, to the fluorite and the CM₂O₃structures, so that the product is a superstructure of the latter. Reduction occurs along the (100)_t planes originating from the (006)_m planes of the parent structure by diminishing the coordination number of the Ca cation from 7 to 6.