Experimentelle Untersuchung einer Dampfstrahlkälteanlage mit einem alternativen Treibmedium

In order to determine the increase in efficiency of n‐octane compared to water as a propellant in ejector refrigeration systems, a pilot plant with a cooling capacity of up to 1.5 kW was set up. In both cases, water was used as the suction medium, the so‐called cooling medium. From the pressure and temperature measurement data, the two mass flows, the so‐called motive and suction flow, and from this the mass flow ratios could be obtained. Subsequently, a comparison of the theoretical coefficient of performance for the two propellants was carried out in the case of closed‐loop operation.     

KnowVolution of a Fungal Laccase toward Alkaline pH

To date, commercial laccase preparations are used in the food, textile, and paper and pulp industries (mild pH). Laccases are attractive in the synthesis of dye molecules or oxidative lignin treatment, which take place at high pH (≥8.0). So far, one fungal laccase has been reported to be active at alkaline pH. Herein, engineering of the fungal laccase from Melanocarpus albomyces (MaL) for increased activity toward the substrate 2,6-dimethoxyphenol at pH (≥9.0) is reported. Through a knowledge-gaining directed evolution (KnowVolution) campaign, the key positions Leu365 and Leu513 were identified to increase alkaline tolerance. Both positions are located in close proximity of the T1Cu site. Molecular docking and simulations studies reveal that both substitutions act in a synergic way to stabilize and improve laccase activity at higher pH. Kinetic characterization of the final variant MaL-M1 (L365E/L513M) revealed at pH 9.8 a threefold improved k_cat (k_cat=(6.0±0.2) s⁻¹) compared with that of wild-type M. albomyces laccase (k_cat=(2.11±0.07) s⁻¹).     

General Principles for Yield Optimization of Nucleoside Phosphorylase-Catalyzed Transglycosylations

The biocatalytic synthesis of natural and modified nucleosides with nucleoside phosphorylases offers the protecting-group-free direct glycosylation of free nucleobases in transglycosylation reactions. This contribution presents guiding principles for nucleoside phosphorylase-mediated transglycosylations alongside mathematical tools for straightforward yield optimization. We illustrate how product yields in these reactions can easily be estimated and optimized using the equilibrium constants of phosphorolysis of the nucleosides involved. Furthermore, the varying negative effects of phosphate on transglycosylation yields are demonstrated theoretically and experimentally with several examples. Practical considerations for these reactions from a synthetic perspective are presented, as well as freely available tools that serve to facilitate a reliable choice of reaction conditions to achieve maximum product yields in nucleoside transglycosylation reactions.     

Enhancement of the analytical solution for double torsion test using extended finite element techniques

The double torsion (DT) testing technique is not yet standardized for fracture mechanics characterization of brittle materials because previous analytical solutions are insufficient to represent accurate load-displacement (P-h) relationship and stress intensity factor (SIF) in experiments. Therefore, we attempt at enhancing the analytical solutions based on three-dimensional extended finite element (XFE) analysis to obtain reproducible results from DT tests. As a result, the P-h relationship in DT test can be efficiently described by combining the bending deformation of a DT specimen with torsional deformation. Weighting factors are proposed as functions of thickness, moment arm and crack length. DT experiments are conducted with sodalime glass specimens to further validate the proposed weighting factors. Finally, correction terms are provided for SIF and fracturs toughness evaluation in DT specimen with straight and curved crack fronts. Fracturs toughness values of sodalime glass specimens with various thickness are consistent, and in good agreement with literature values.     

PEGylated Cationic Serum Albumin for Boosting Retroviral Gene Transfer

Retroviral vectors are common tools for introducing genes into the genome of a cell. However, low transduction rates are a major limitation in retroviral gene transfer, especially in clinical applications. We generated cationic human serum albumin (cHSA) protected by a shell of poly(ethylene glycol) (PEG); this significantly enhanced retroviral gene transduction with potentially attractive pharmacokinetics and low immunogenicity. By screening a panel of chemically optimized HSA compounds, we identified a very potent enhancer that boosted the transduction rates of viral vectors. Confocal microscopy revealed a drastically increased number of viral particles attached to the surfaces of target cells. In accordance with the positive net charge of cationic and PEGylated HSA, this suggests a mechanism of action in which the repulsion of the negatively charged cellular and viral vector membranes is neutralized, thereby promoting attachment and ultimately transduction. Importantly, the transduction‐enhancing PEGylated HSA derivative evaded recognition by HSA‐specific antibodies and macrophage activation. Our findings hold great promise for facilitating improved retroviral gene transfer.     

Bildgebende UV/VIS-Spektroskopie zur Untersuchung des Einflusses der Fluiddynamik auf die Entstehung von Haupt- und Nebenprodukt in schnellen konkurrierenden konsekutiven Gas-Flüssig-Reaktionen

To form many bulk chemicals, gaseous substances must be mixed and reacted with a continuous liquid phase. In this research work, we systematically investigate to what extent the formation of a side product in a fast competing consecutive reaction can be influenced by the time scales of mixing. For this purpose, a Taylor bubble experiment is used, in which the time scales of mixing can be varied systematically and reproducibly. It is shown, that the mixing in the wake of a bubble is of great importance for the formation of by-products.     

Quick screening method for the photocatalytic activity of nanoparticles and powdery materials

A new quantitative screening method for the photocatalytic activity of nanoparticles and powdery materials was developed. With a custom-built apparatus the measurement of the photodegradation of non-volatile organic compounds in dependence of the inorganic photocatalyst and experimental factors like irradiation time, temperature, organic compound, spectral distribution and irradiance is possible. By applying various spectral distributions and irradiances slightly lower than in outdoor conditions, the described method uses application-oriented testing conditions. It can be used for the screening of the photocatalytic activity of newly developed materials towards any carbon containing non-volatile compounds.     

Multidimensional, mapping-based complex wavelet transforms.

Although the discrete wavelet transform (DWT) is a powerful tool for signal and image processing, it has three serious disadvantages: shift sensitivity, poor directionality, and lack of phase information. To overcome these disadvantages, we introduce multidimensional, mapping-based, complex wavelet transforms that consist of a mapping onto a complex function space followed by a DWT of the complex mapping. Unlike other popular transforms that also mitigate DWT shortcomings, the decoupled implementation of our transforms has two important advantages. First, the controllable redundancy of the mapping stage offers a balance between degree of shift sensitivity and transform redundancy. This allows us to create a directional, nonredundant, complex wavelet transform with potential benefits for image coding systems. To the best of our knowledge, no other complex wavelet transform is simultaneously directional and nonredundant. The second advantage of our approach is the flexibility to use any DWT in the transform implementation. As an example, we exploit this flexibility to create the complex double-density DWT: a shift-insensitive, directional, complex wavelet transform with a low redundancy of (3M - 1)/(2M - 1) in M dimensions. No other transform achieves all these properties at a lower redundancy, to the best of our knowledge. By exploiting the advantages of our multidimensional, mapping-based complex wavelet transforms in seismic signal-processing applications, we have demonstrated state-of-the-art results.     

Limitations to beam quality of mid-infrared angled-gratingdistributed-feedback lasers

The far-field characteristics of mid-infrared angled-grating distributed-feedback (α-DFB) lasers with W active regions are studied as a function of etch depth, stripe width, and optical pumping intensity. Whereas near-diffraction-limited output is obtained for 50 μm stripes at ten times threshold, the beam quality degrades rapidly when either the stripe width or the pump intensity is increased. A key finding is that most of the degradation may be attributed to the onset of Fabry-Perot-like lasing modes that propagate along the direct path normal to the facets. We further show that these parasitic modes may be effectively eliminated by using ion-bombardment to create angled virtual mesas surrounded by loss regions. The bombarded structures show substantial improvement of the beam quality for wide pump stripes and high pump intensities, although in this first demonstration the efficiency decrease was greater than expected