Stretching skin: The physiological limit and beyond

The goal of this paper is to establish a novel computational model for skin to characterize its constitutive behavior when stretched within and beyond its physiological limits. Within the physiological regime, skin displays a reversible, highly non-linear, stretch locking, and anisotropic behavior. We model these characteristics using a transversely isotropic chain network model composed of eight wormlike chains. Beyond the physiological limit, skin undergoes an irreversible area growth triggered through mechanical stretch. We model skin growth as a transversely isotropic process characterized through a single internal variable, the scalar-valued growth multiplier. To discretize the evolution of growth in time, we apply an unconditionally stable, implicit Euler backward scheme. To discretize it in space, we utilize the finite element method. For maximum algorithmic efficiency and optimal convergence, we suggest an inner Newton iteration to locally update the growth multiplier at each integration point. This iteration is embedded within an outer Newton iteration to globally update the deformation at each finite element node. To illustrate the characteristic features of skin growth, we first compare the two simple model problems of displacement- and force-driven growth. Then, we model the process of stretch-induced skin growth during tissue expansion. In particular, we compare the spatio-temporal evolution of stress, strain, and area gain for four commonly available tissue expander geometries. We believe that the proposed model has the potential to open new avenues in reconstructive surgery and rationalize critical process parameters in tissue expansion, such as expander geometry, expander size, expander placement, and inflation timing.     

A comparison of absolute cross sections for electro- and photo-induced reactions

Absolute cross sections for electron and positron induced reactions on¹²C,⁶³Cu and¹⁰⁷Ag are compared with cross sections for the corresponding photo-induced reactions in order to test DWBA calculations of the virtual photon spectra. A good agreement is found between the experimental cross sections for the electrodisintegration and those calculated with DWBA spectra and photonuclear cross sections.     

Modelluntersuchungen zur pepsinkatalysierten Peptidsynthese im wäßrig-organischen Zweiphasensystem

The usefulness of biphasic aqueous-organic solvent systems for pepsin-catalyzed synthesis of model peptidesZ-X-Phe-Phe-OMe (X=Ala, Gln, Leu) has been demonstrated by coupling the correspondingZ-X-Phe-OH with H-Phe-OMe. The influence of various organic solvents on pepsin activity was examined. Some examples are given for the influence of nucleophile and enzyme concentration, bufferpH and organic solvent portion on product yield. Tetrachloromethane and mixtures of ethyl acetate/n-hexane proved to be especially useful allowing syntheses in good yields and within comparatively short reaction times of 2–6 hours.     

Basic Principles of Protease-Catalyzed Peptide Bond Formation

The stereospecific formation of peptide bonds under mild conditions and without side reactions is still a formidable task in peptide synthesis. One approach that springs to mind, namely the use of the naturally occurring catalyst involved in the biosynthesis of proteins, the ribosomal peptidyl transferase, cannot be realized in practice. The fact, however, that the natural cleavage of proteins is carried out by other enzymes, namely the proteases, together with the reversibility of these cleavage reactions in principle, has led to an interesting synthetic concept. Proteases normally catalyze the enzymatic degradation of proteins and peptides by hydrolytic cleavage of the peptide bond in an exergonic reaction. The use of physicochemical principles in order to influence the equilibrium, the concentration of products, and the kinetic parameters of the reaction results in the successful application of the catalytic properties of proteases to peptide synthesis. The purpose of this review is to describe and summarize the methods used in such approaches and to attempt a systematic categorization. The principles are applied to the synthesis of such practically relevant products as aspartame and human insulin.     

Magnetosonic waves in antimony

A report is given on the observation of magnetosonic waves propagating through antimony in the Voigt-configuration. The waves were observed from a cut-off field and up to field of the order of 60 kG. The usual Alfvén-wave behavior as well as the influence of non-local effects were observed, the latter at the lower magnetic field values. The non-local effects are analysed in terms of the expressions given by Yokota and by Guthmann et al. It turns out, however, that these expressions are not able to account for the non-linear — in B^-1 — dispersion observed at the lower magnetic field values.     

Double-beam fourier spectroscopy with two inputs and two outputs

A theoretical treatment of double-beam Fourier spectroscopy, with two inputs and two outputs measured by a single detector, is presented. One of the novel features is the use of the radiation that returns to the source in a conventional Fourier spectrometer, i.e., the anti-interferogram beam. The double beam feature allows simultaneous measurement of the difference in the spectra of the sample and a reference standard with optical cancellation of common features. Several versions of spectrometers suited for specific applications are discussed as special cases. Applications include the ability to measure small absorptivity or reflectivity against strong and varying background, to compare the emission spectra of two nearly equal sources, or the sensitivity of two different detectors. Moreover, by suitably chopping the input or output beams, the noise due to fluctuations in source intensity may be strongly reduced.     

A battery-supercapacitor hybrid device composed of metallic zinc,a biodegradable ionic liquid electrolyte and graphite

The integration of a battery-type electrode and of a capacitor-type electrode in a single device by proper design is an effective strategy in developing energy storage devices with high energy and power densities. Herein, we present a battery-supercapacitor hybrid device using metallic zinc as anode, a biodegradable ionic liquid (IL) as electrolyte, and graphite as cathode. The recently developed choline acetate ([Ch]OAc) biodegradable IL-based electrolyte enables reversible deposition/stripping of Zn(II). Spongy-like Zn with a high surface area is obtained, which allows fast charge/discharge at high rates. The adsorption/desorption of ions on the surface of the graphite cathode and intercalation/deintercalation of anions into/from the graphite layers occur at the graphite cathode. Raman spectra and X-ray photoelectron reveal the intercalation of IL into and the adsorption of IL on the graphite. Highly reversible adsorption/desorption of ions on the surface of the graphite electrodes in the [Ch]OAc-based electrolyte was demonstrated by a symmetric cell. The Zn/graphite hybrid device delivers an energy density of 53 Wh kg^?1 at a power density of ~ 145 W kg^?1 and 42 Wh kg^?1 at ~ 400 W kg^?1. The hybrid device also exhibits a long cycle life with ～ 86% specific capacitance retained after 1000 cycles at a current density of 0.5 A g^?1. The combination of well-available zinc, inexpensive graphite, and a biodegradable IL electrolyte in a cell could open new avenues for sustainable energy applications.

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