Heterodyne dynamic light scattering for the characterization of particle dispersions.

Particle self-diffusivities in unimodal and bimodal aqueous dispersions are characterized by dynamic light scattering (DLS) applying a heterodyne detection scheme. For unimodal dispersions close to infinite dilution, it could be evidenced that pure homodyne conditions cannot be realized, leading to an increasing underestimation of diffusivity with a decreasing concentration. Even for bimodal dispersions and neglecting any local oscillator field, the coherent superposition of scattered light from different particle species hinders a clear assignment of the measured signals and their evaluation for diffusivity. In this case, the impact of a cross term on the determined diffusivities cannot be neglected. The results emphasize that the use of a heterodyne detection scheme in DLS experiments is a key aspect for an accurate determination of particle diffusivities in low-concentrated unimodal and bimodal dispersions.

Three Steps, Two Enzymes, One Pot, but a Multitude of Nanocompartments: Combined Cycles of Kinetic Resolutions and Re-racemization with Incompatible Biocatalysts.

Deracemizations are clearly preferable to kinetic resolutions in the production of chiral molecules from racemates, as they allow up to 100% chemical and optical yield. Here we present a new process route for multienzymatic deracemizations that is relevant for reaction systems with incompatible reaction conditions of the biocatalysts. This often applies to combinations of lipases used for stereoselective acylation and solvent-sensitive racemases. By encapsulating a model racemase in polymeric vesicles, it was protected from inactivation by the organic solvent up to phase proportions of 99%. As high yields in the lipase reaction required either water proportions well below 1% or racemase-denaturating acyl donor concentrations, a one-pot reaction was implemented through the sequential use of lipase and racemase-containing nanocompartments. This strategy allowed us to perform two kinetic resolutions with intermittent re-racemization in one pot yielding 72% (0.72 mM after 120 h) of an enantiopure product.

Material Characterization of AISI 316L Flexure Pivot Bearings Fabricated by Additive Manufacturing.

Recently, additive manufacturing (AM) by laser metal deposition (LMD) has become a key technology for fabricating highly complex parts without any support structures. Compared to the well-known powder bed fusion process, LMD enhances manufacturing possibilities to overcome AM-specific challenges such as process inherent porosity, minor build rates, and limited part size. Moreover, the advantages aforementioned combined with conventional machining enable novel manufacturing approaches in various fields of applications. Within this contribution, the additive manufacturing of filigree flexure pivots using 316L-Si by means of LMD with powder is presented. Frictionless flexure pivot bearings are used in space mechanisms that require high reliability, accuracy, and technical cleanliness. As a contribution to part qualification, the manufacturing process, powder material, and fabricated specimens were investigated in a comprehensive manner. Due to its major impact on the process, the chemical powder composition was characterized in detail by energy dispersive X-ray spectroscopy (EDX) and inductively coupled plasma optical emission spectrometry (ICP-OES). Moreover, a profound characterization of the powder morphology and flowability was carried out using scanning electron microscopy (SEM) and novel rheological investigation techniques. Furthermore, quantitative image analysis, mechanical testing, laser scanning microscopy, and 3D shape measurement of manufactured specimens were conducted. As a result, the gained knowledge was applied for the AM-specific redesign of the flexure pivot. Finally, a qualified flexure pivot has been manufactured in a hybrid manner to subsequently ensure its long-term durability in a lifetime test bench.

Simultaneous study of molecular and micelle diffusion in a technical microemulsion system by dynamic light scattering.

HYPOTHESIS: The application of dynamic light scattering (DLS) is well-established for measuring diffusion coefficients related to either molecular or translational micelle diffusion. The simultaneous determination of both transport properties should be feasible, but has not been reported in the literature yet. EXPERIMENTS: Different diffusion modes present in a microemulsion and selected subsystems consisting of a polyol mixture, a binary surfactant mixture, and carbon dioxide (CO2) were investigated systematically by DLS at temperatures of (314, 333, and 353) K and corresponding pressures of (10, 13, and 16) MPa. FINDINGS: Diffusion coefficients related to molecular and translational micelle diffusion could be measured simultaneously and increase with increasing temperature. From the translational diffusion coefficients, an increase in the hydrodynamic diameter of the micelles from their non-swollen to the CO2-swollen state being in agreement with literature data for the same and similar microemulsions was found. The effective diffusion coefficients related to the faster molecular diffusion process only observable in the presence of CO2 are not affected significantly by the surfactant. The time-dependent parts of the recorded intensity correlation functions related to molecular diffusion processes are heterodyne because the scattered light modulated by molecular concentration fluctuations is superimposed with light scattered by the micelles.

Self-expanding metal stents versus plastic prostheses in the palliation of malignant dysphagia: long-term outcome of 153 consecutive patients.

BACKGROUND: Malignant dysphagia due to esophagogastric cancer is associated with poor overall prognosis. Placements of self-expandable metal stents or plastic tubes are established methods as palliative treatment options. As an alternative and/or complementary therapy, radiologic techniques (external beam radiation/brachytherapy) and locally endoscopic techniques (laser, APC-beamer, PDT) are often used. STUDY AND GOALS: Retrospective trial of 153 patients treated in our department between 1993 and 2001. Forty-five patients received a plastic tube (Group A) and 108 patients were treated with metal stents (Group B). Both groups were compared for improvement of dysphagia score, survival, recurrent dysphagia and complications. RESULTS: Stent placement was successful in 41 of 45 (93%) patients of Group A and 107 of 108 (99%) of Group B. The median dysphagia score improved significantly in Group A (from 3.03 to 1.55, P = 0.010) and Group B (from 2.77 to 1.44, P = 0.009). Recurrent dysphagia was noted in 12 of 45 (27%) patients of Group A and 27 of 108 (25%) patients of Group B. Median survival time after stent insertion was 78 days (Group A) and 113 days (Group B). Overall complications occurred in 15 of 45 (33%) patients of Group A and 28 of 108 (26%) patients of Group B. However, significantly (P = 0.05) more major complications were seen in Group A than in Group B (22% vs. 9%). CONCLUSIONS: Our results indicate a marginal clinical benefit for metal stents versus plastic tubes in malignant dysphagia in the long run. However, metal stents seem to be safer and associated with a prolonged improvement of dysphagia score.