Zeitschriftenaufsätze

Time-resolved photoluminescence (TRPL) measurements and the extraction of meaningful parameters involve four key ingredients: a suitable sample such as a semiconductor double heterostructure, a state-of-the-art measurement setup, a kinetic model appropriate for the description of the sample behavior, and a general analysis method to extract the model parameters of interest from the measured TRPL transients. Until now, the last ingredient is limited to single curve fits, which are mostly based on simple models and least-squares fits. These are often insufficient for the parameter extraction in real-world applications. The goal of this article is to give the community a universal method for the analysis of TRPL measurements, which accounts for the Poisson distribution of photon counting events. The method can be used to fit multiple TRPL transients simultaneously using general kinematic models, but should also be used for single transient fits. To demonstrate this approach, multiple TRPL transients of a GaAs/AlGaAs heterostructure are fitted simultaneously using coupled rate equations. It is shown that the simultaneous fits of several TRPL traces supplemented by systematic error estimations allow for a more meaningful and more robust parameter determination. The statistical methods also quantify the quality of the description by the underlying physical model.

In the reservoir computing literature, the information processing capacity is frequently used to characterize the computing capabilities of a reservoir. However, it remains unclear how the information processing capacity connects to the performance on specific tasks. We demonstrate on a set of standard benchmark tasks that the total information processing capacity correlates poorly with task specific performance. Further, we derive an expression for the normalized mean square error of a task as a weighted function of the individual information processing capacities. Mathematically, the derivation requires the task to have the same input distribution as used to calculate the information processing capacities. We test our method on a range of tasks that violate this requirement and find good qualitative agreement between the predicted and the actual errors as long as the task input sequences do not have long autocorrelation times. Our method offers deeper insight into the principles governing reservoir computing performance. It also increases the utility of the evaluation of information processing capacities, which are typically defined on i.i.d. input, even if specific tasks deliver inputs stemming from different distributions. Moreover, it offers the possibility of reducing the experimental cost of optimizing physical reservoirs, such as those implemented in photonic systems.

Electrodeposition is a versatile instrumental technique, already applied in many industrial fields. However, the deposition of silicon and other reactive elements is still challenging and requires further research and improvement. Accomplishing an efficient electrodeposition of silicon at room temperature is very attractive due to the high number of manufacturing technologies that would benefit from this approach. This work provides an overview of the electrochemical approaches for silicon deposition performed in organic electrolytes. The main factors that impact this process are individually discussed and exemplified with appropriately updated literature sources. Furthermore, the previously available research on characterization of electrodeposited silicon containing layers is provided. These studies are presented in the context of better understanding the structure, composition, and functional properties of the deposited silicon material, which may attract the attention of young academic scientists and process engineers.

Muscle fatigue as a defense body mechanism against overload is a result of the products of incomplete oxygen oxidation such as reactive oxygen species. Hence, C60 fullerene as a powerful nanoantioxidant can be used to speed up the muscle recovery process after fatigue. Here, the residual effect of C60 fullerene on the biomechanical and biochemical markers of the development of muscle soleus fatigue in rats for 2 days after 5 days of its application was studied. The known antioxidant N-acetylcysteine (NAC) was used as a comparison drug. The atomic force microscopy to determine the size distribution of C60 fullerenes in an aqueous solution, the tensiometry of skeletal muscles, and the biochemical analysis of their tissues and rat blood were used in this study. It was found that after the cessation of NAC injections, the value of the integrated muscle power is already slightly different from the control (5%-7%) on the first day, and on the second day, it does not significantly differ from the control. At the same time, after the cessation of C60 fullerene injections, its residual effect was 45%-50% on the first day, and 17%-23% of the control on the second one. A significant difference (more than 25%) between the pro- and antioxidant balance in the studied muscles and blood of rats after the application of C60 fullerene and NAС plays a key role in the long-term residual effect of C60 fullerene. This indicates prolonged kinetics of C60 fullerenes elimination from the body, which contributes to their long-term (at least 2 days) compensatory activation of the endogenous antioxidant system in response to muscle stimulation, which should be considered when developing new therapeutic agents based on these nanoparticles.

The input of combustion heat in engines has a major impact on the piston friction and the resulting wear of the piston skirt. The new methodology presented here enables the simulation of combustion heat input during motored operation, and thus a detailed investigation of the piston friction under realistic piston temperature profiles of real engine operation is possible. For this purpose a standardized engine test bench for motored friction evaluations was expanded to include, among other things, a movable high-power diode laser with special defocusing optics. The setup of the test engine is based on the FEV teardown step methodology [1] and has open access to the engine piston from above due to a cylinder head dummy. Thus, the heat input by means of a high-power diode laser into the piston crown can be made. The reduced engine structure also enables a precise and highly accurate evaluation of the piston friction. A previously conducted validation process of the methodology ensures the most accurate possible replication of fired piston temperature profiles. The comparison between the piston temperatures measured in fired operation and those simulated in motored operation for a partial load operating point shows a maximum variance deviation of only 15˚C depending on the measuring point. The new methodology is also used in particular for the evaluation and detection of critical piston friction conditions. Experiments in this context are presented and discussed exemplary by using three measurement series at different operating temperatures and engine speeds. There is a gradual increase in the laser power for each series of measurements and thus in the heat input into the piston. The increase in heat input leads to a significant increase in friction at all operating points due to thermal expansion and the associated decrease reduction in piston clearance. Depending on the operating temperature and the engine speed, a critical piston friction condition is achieved and detected by the level of friction increase. The additional use of ultrasonic sensors and the knock sensor installed as standard makes a simultaneous measurement of the structure-borne sound signals possible. The increase in the acceleration levels of all sensors correlates here with the increase in piston friction. An evaluation of the noise, vibration, and harshness (NVH) measurement in both the frequency range and the crank angle (CA) range shows conspicuous high-frequency excitation levels that occur in the top dead center area. This correlation can be proven for all three measurement series. The results obtained here may open a path to an improved piston cooling strategy in the future.