O2-Therapie im Notfall – Time to say goodbye?

Notfall + Rettungsmedizin - Die O2-Inhalationstherapie gehört zu den Standardmaßnahmen der Notfallmedizin und wird zunehmend kritisch diskutiert. Pathophysiologische Überlegungen und...     

A new method for cerclage wire fixation to maximal pre-tension with minimal elongation to failure

Objective. To develop and test a new cerclage wire tightening technique, yielding reproducibly maximal pre-tension, load to failure and minimal elongation to failure of the wire junction.

Design. Laboratory bench study.

Background. Cerclage wire fixation is difficult to perform by hand with reproducible quality and tightening tension, which are required for optimal performance.

Methods. With the new technique, 1, 1.25 and 1.5 mm steel wires were passed through a 9 × 18 mm steel tube, grasped using a modified ASIF wire-tightener and tightened by twisting until spontaneous failure of the wires in the tube. These fixations were compared to wires pre-tightened by hand to controlled high or low pre-tension using the simple twist, the knot twist and twist secured against untwisting, loaded to failure on a testing machine. The tests assessed pre-tension, ultimate failure load and elongation to failure.

Results. Wire twists performed with the new technique were always perfectly symmetrical and may be tightened to maximal pre-tension without weakening of the wire. The twist secured against untwisting combined high stiffness with high failure load.

The knot twist elongates to an unacceptable degree, unlike the secured twist. The simple twist untwists under little tension.

Conclusions. The new technique allows to obtain maximal pre-tension and thus minimal elongation to failure of simple wire twists, without having to worry about breaking the wire at the base of the twist due to over-tightening.Relevance

Cerclage wire fixation is an effective and cheap method to perform osteosynthesis. For adequate performance, maximal pre-tension, symmetrical twisting and high load to failure are necessary. The here presented technique combines all of these pre-requisites in a simple fashion.     

Acute oxygenator occlusion in two cases of polycythemia vera: Bailout strategies

Polycytemia vera (PV) is a rare myeloproliferative neoplasm associated with microcirculatory disturbances, thrombosis and bleeding. Patients suffering from PV have a high risk of perioperative adverse events, but the literature regarding on-pump procedures in PV patients is scarce. We report two cases of acute and severe oxygenator failure during cardiopulmonary bypass and present valid exit scenarios.     

Modeling T cell responses to antigenic challenge

T cell responses are a crucial part of the adaptive immune system in the fight against infections. This article discusses the use of mathematical models for understanding the dynamics of cytotoxic T lymphocyte (CTL) responses against viral infections. Complementing experimental research, mathematical models have been very useful for exploring new hypotheses, interpreting experimental data, and for defining what needs to be measured to improve understanding. This review will start with minimally parameterized models of CTL responses, which have generated some valuable insights into basic dynamics and correlates of control. Subsequently, more biological complexity is incorporated into this modeling framework, examining different mechanisms of CTL expansion, different effector activities, and the influence of T cell help. Models and results are discussed in the context of data from specific infections.     

FBG Strain Monitoring of a Road Structure Reinforced with a Geosynthetic Mattress in Cases of Subsoil Deformation in Mining Activity Areas

This paper presents implementation of purpose-designed optical fibre Bragg grating (FBG) sensors intended for the monitoring of real values of strain in reinforced road structures in areas of mining activity. Two field test stations are described. The first enables analysis of the geogrid on concrete and ground subgrades. The second models the situation of subsoil deformation due to mining activity at different external loads. The paper presents a system of optical fibre sensors of strain and temperature dedicated for the investigated mattress. Laboratory tests were performed to determine the strain characteristic of the FBG sensor-geogrid system with respect to standard load. As a result, it was possible to establish the dependence of the geogrid strain on the forces occurring in it. This may be the basis for the analysis of the mining activity effect on right-of-way structures during precise strain measurements of a geogrid using FBG sensors embedded in it. The analysis of the results of measurements in the aspect of forecasted and actual static and dynamic effects of mining on the stability of a reinforced road structure is of key importance for detailed management of the road investment and for appropriate repair and modernization management of the road structure.     

Decoding ultrafast polarization responses in lead halide perovskites by the two-dimensional optical Kerr effect

The ultrafast polarization response to incident light and ensuing exciton/carrier generation are essential to outstanding optoelectronic properties of lead halide perovskites (LHPs). A large number of mechanistic studies in the LHP field to date have focused on contributions to polarizability from organic cations and the highly polarizable inorganic lattice. For a comprehensive understanding of the ultrafast polarization response, we must additionally account for the nearly instantaneous hyperpolarizability response to the propagating light field itself. While light propagation is pivotal to optoelectronics and photonics, little is known about this in LHPs in the vicinity of the bandgap where stimulated emission, polariton condensation, superfluorescence, and photon recycling may take place. Here we develop two-dimensional optical Kerr effect (2D-OKE) spectroscopy to energetically dissect broadband light propagation and dispersive nonlinear polarization responses in LHPs. In contrast to earlier interpretations, the below-bandgap OKE responses in both hybrid CH₃NH₃PbBr₃ and all-inorganic CsPbBr₃ perovskites are found to originate from strong hyperpolarizability and highly anisotropic dispersions. In both materials, the nonlinear mixing of anisotropically propagating light fields results in convoluted oscillatory polarization dynamics. Based on a four-wave mixing model, we quantitatively derive dispersion anisotropies, reproduce 2D-OKE frequency correlations, and establish polarization-dressed light propagation in single-crystal LHPs. Moreover, our findings highlight the importance of distinguishing the often-neglected anisotropic light propagation from underlying coherent quasiparticle responses in various forms of ultrafast spectroscopy.

Understanding the ultrafast polarization response to light fields and the subsequent generation of charge carriers or excitons is key to establishing the photophysical mechanisms in the excellent optoelectronic material system of lead halide perovskites (LHPs) (1). The two ionic polarization contributions by the reorientational motion of organic cations and the deformation of the inorganic cages have been discussed within dynamic screening models (2–4) and large polaron formation (5), respectively and jointly, whereas the immediate electronic polarization response to the light field itself has been neglected so far. In many optoelectronic applications, nevertheless, not only charge carrier transport but also light propagation right below the bandgap is essential. In LHP nanowire lasers, the lasing modes are known to be redshifted from excitonic resonances due to efficient coupling to plasmon emission (6). In LHP-based exciton–polariton devices, light–matter coupling redshifts the hybrid state on the lower polariton branch (7). Propagation of subgap light is known to boost the efficiency of LHP photovoltaic cells and light-emitting devices by the so-called “photon recycling” (8). Light propagation strongly influences the function of LHP photonic devices in general (9, 10). A key feature of light propagation near the bandgap is its strong photon energy dependence, as is obvious from the classic Lorentzian model for the dielectric function near an optical resonance (11). However, most photophysical experiments probing carrier/exciton formation, screening, scattering, and nonlinear optical responses employ ultrashort excitation pulses with inherently broad energy distribution and thus convoluted spectral responses. Here, we develop a Fourier-transform-based laser spectroscopy technique, two-dimensional optical Kerr effect (2D-OKE), to investigate light propagation and nonlinear polarization responses directly in the time domain with superior excitation energy resolution near the electronic bandgap.The third-order nonlinear electric polarization P(3) serves as an in situ probe of a material’s polarizability and governs the ultrafast macroscopic response to an incident light field. This is employed in a variety of spectroscopies, such as (magneto-) OKE (12, 13), coherent phonon spectroscopy (14, 15), and four-wave mixing (FWM) in general (11). Recently, OKE has been applied to LHP single crystals: Below the bandgap, the dominating nonoscillatory Kerr response of MAPbBr₃ (MA = CH₃NH₃) compared to its all-inorganic counterpart CsPbBr3 was previously attributed to the transient polarization anisotropy caused by liquidlike reorientation dynamics of organic cations (2) and lattice disorder (5). The exponentially decaying responses with above-gap excitations were discussed in relation to polaron formation in both materials (5). Interestingly, for excitation energies close to the bandgap in CsPbBr₃ at room temperature, time-resolved OKE reveals complex oscillatory features. Such oscillatory transient birefringence signals are usually attributed to coherently excited collective modes, such as phonons (15–17) or magnons (18, 19), but the strong dependence of the oscillatory frequency on pump-photon energy in OKE seems to contradict these origins in LHPs (5). In this work, we unveil a unified source for the Kerr responses in single-crystal LHPs by tracing contributions from hyperpolarizability and the peculiar light propagation close to electronic transitions.