Was ist Entropie? Eine Frage – Zehn Antworten

The intention of the paper is to help all those who asked themselves the question raised in the headline but did not yet get a satisfactory answer as well as those who have been asked this very question but could not give a satisfactory answer. By means of the ten answers it should become clear that there is not one single and simple answer – as often expected. Actually entropy as a newly introduced quantity needs a learning process before its can be included in our vocabulary like familiar words such as temperature and energy.     

Orientation dependent fracture toughness of lamellar bone

The critical energy release rate of human bone was determined for different crack propagation directions with three-point-bending tests using controlled crack extension. The local structure was characterised by small-angle X-ray scattering, SEM and polarised light microscopy and related to the energy required for crack extension. It turns out the collagen angle is decisive for switching the fracture behaviour of bone from brittle to quasi-ductile. A significant increase in the critical energy release rate as well as a change of the appearance of the crack path from straight and smooth to deflected and zig-zag is observed.     

Infrared spectroscopy of the skin: influencing the stratum corneum with cosmetic products

The stratum corneum is the outermost layer of the skin and, as such, represents the decisive barrier between the body and the environment. The combination of horny cells and lamellar lipid layers prevents water loss from the body and protects it against penetration by exogenous substances. For selective investigation of the thin outermost stratum corneum layer ATR-FTIR (attenuated total reflection Fourier transform infrared) spectroscopy has proved itself in practice. It provides information about the sebum content, type of fatty substances, water content and degree of order of the lamellar lipid film in the stratum corneum. Different types of skin (dry, normal and greasy) differ mainly in their sebum content but also in the composition of their fats and the degree of order of their lipids. A comparison with model lipid mixtures shows that the stratum corneum lipids are mainly present in a fixed gel form under physiological conditions. In cleansing processes a large part of the sebum is removed from the skin. The skin reacts to the defatting process by the rapid secretion of sebum. After cleansing with a mild face cleansing emulsion the re-achievement of the same fat status takes longer than with a surfactant shower gel. Skin creams cause alterations to the skin moisture and in the degree of order of the stratum corneum lipids. A lamellar cream with a structure similar to that of the stratum corneum lipids increases the degree of order of the alkyl chains of the skin lipid film (biomimetic principle), whereas a conventional w/o cream reduces this degree of order. Skin moisture increases after the use of the creams.     

Mössbauer Spectroscopy and X-ray Diffraction Study of Fe-Labeled Tetrachloroferrate(III)-Based Magnetic Ionic Liquids

Four ⁵⁷Fe-labeled tetrachloroferrates(III) of organic cations (1-butyl-3-methylimidazolium, 1-allyl-3-methylimidazolium, 1-methyl-1-propylpyrrolidinium, tetraphenylphosphonium) were examined by temperature-dependent Mössbauer spectroscopy. The hyperfine and dynamic parameters of the iron(III) site were determined. Single crystal X-ray diffraction data of [Ph₄P][FeCl₄] were collected at four temperatures (295, 223, 173, and 123 K), and the dynamics of the iron atom inferred from the Mössbauer data and the single crystal U_i,j parameters have been compared.     

An analytic study of a scalable video buffer

In this contribution, we investigate the performance of the output buffer of an ‘on-demand’ video streaming server. The server maintains a local database of stored video clips and movies which can be streamed to the users upon request. We assume that the stored video is encoded in a scalable way, which means that the data streams contain a base layer ensuring a minimum of guaranteed quality and a stack of additional enhancement layers progressively improving the quality of the video. For the purpose of performance analysis, we assume that a video stream is split up in logical units called frames. Every frame consists of a number of packets, each containing information of one layer only. When the output buffer gets congested, one may choose to drop the transmission of some of the layers in a frame, thus reducing the frame transmission time and expediting the restoration of the buffer size to normal levels. A discrete-time finite capacity queueing model with buffer size dependent transmission times is proposed. Using a probability generating function approach, we focus on the characteristics of idle and busy periods. We obtain performance measures such as the frame loss ratio and the average frame transmission time. The latter measure relates to the quality of the video stream. We conclude with some numerical examples, including a realistic case study.     

Performance analysis of a discrete-time queueing system with priority jumps

Supporting multiple types of traffic with different Quality of Service (QoS) requirements is not an easy task in modern communication networks. An efficient priority scheduling scheme is thus of great importance. The static, Head-Of-Line (HOL) priority scheme achieves differentiation between different types of traffic, but may have a too severe impact on the performance level of lower-priority traffic. We therefore propose a priority scheme with priority jumps in this paper: the Head-Of-Line Jump-If-Arrival (HOL-JIA) scheme. We show that the use of probability generating functions (pgfs) is suitable for analytically studying the system, and for illustrating the impact of priority jumps on the performance of the system.     

On the evolution of traffic characteristics inside multistage switching systems

In this paper, a method is developed to analyze the evolution of the traffic characteristics of information streams crossing the consecutive stages of an ATM multistage switching structure. Specifically, we develop a generic model for characterizing the traffic streams at the input of the consecutive stages, based on the assumption that the queueing processes in subsequent stages are independent. In our model, the parameters that determine the arrival process on the inlets of a switching element in a given stage solely depend on the output process on the outlets of the switching elements belonging to the previous stage. As a result, we are able to calculate the mean value and variance, as well as the whole distribution of the buffer contents and the packet delay in a tagged switching element, anywhere in the structure, based on earlier work. Furthermore, we can prove that, under the assumptions of the model, the traffic characteristics converge to a spatial steady state after a few stages in the system, i.e., the traffic parameters reach limiting values which are independent of the characteristics of the traffic sources at the entrance of the first stage. Although the present study focuses on the specific case of ATM switching systems, the authors believe similar results to hold also for more general multistage structures in which routing and multiplexing occurs in each stage.