Clinical dilemmas in acute neurological disorders

This thesis introduces the evolving landscape of acute neurology and the challenges it presents to clinicians in the emergency department (ED).In Chapter 2, the focus is on mild traumatic brain injury (mTBI) in patients on anticoagulation therapy. The study, involving 905 patients, reveals that delayed intracranial hemorrhage within 24 hours is very rare after a normal cranial CT, suggesting that routine hospitalization may be unnecessary.Chapter 3 delves into alcohol intoxication as a stroke mimic, especially in posterior circulation cases. The study, involving 974 patients, emphasizes considering measuring blood ethanol levels in patients with a possible stroke of the posterior circulation presenting after working hours. Nevertheless, elevated blood ethanol levels should not withhold clinicians from administering reperfusion therapy.Chapter 4 explores the association between low blood pressure and outcomes after acute ischemic stroke (AIS). Analyzing data from 2124 patients, the study finds that low systolic blood pressure is linked to increased in-hospital mortality and complications, urging clinicians to investigate potential underlying conditions.In Chapter 5, the focus shifts to AIS patients with active cancer undergoing endovascular treatment. The study, involving 2583 patients, indicates that despite technical success, those with active cancer experience significantly worse outcomes and an increased risk of recurrent stroke after EVT. Still, about a quarter of the patients regained functional independence, and the risk of other complications was not increased.This thesis collectively highlights the importance of nuanced decision-making in acute neurology, offering insights into specific clinical dilemmas and proposing considerations for optimized patient care

Combining economic and social goals in the design of production systems by using ergonomics standards

In designing of production systems, economic and social goals can be combined, if ergonomics is integrated into the design process. More than 50 years of ergonomics research and practice have resulted in a large number of ergonomics standards for designing physical and organizational work environments. This paper gives an overview of the 174 international ISO and European CEN standards in this field, and discusses their applicability in design processes. The available standards include general recommendations for integrating ergonomics into the design process, as well as specific requirements for manual handling, mental load, task design, human-computer-interaction, noise, heat, body measurements, and other topics. The standards can be used in different phases of the design process: allocation of system functions between humans and machines, design of the work organization, work tasks and jobs, design of work environment, design of work equipment, hardware and software, and design of workspace and workstation. The paper is meant to inform engineers and managers involved in the design of production systems about the existence of a large number of ISO and CEN standards on ergonomics, which can be used to optimize human well-being and overall system performance.review;standard;standardization;ergonomics;CEN;ISO;human factors;production engineering;production planning

Periodically driven Taylor-Couette turbulence

We study periodically driven Taylor-Couette turbulence, i.e. the flow confined between two concentric, independently rotating cylinders. Here, the inner cylinder is driven sinusoidally while the outer cylinder is kept at rest (time-averaged Reynolds number is $Re_i = 5 \times 10^5$). Using particle image velocimetry (PIV), we measure the velocity over a wide range of modulation periods, corresponding to a change in Womersley number in the range $15 \leq Wo \leq 114$. To understand how the flow responds to a given modulation, we calculate the phase delay and amplitude response of the azimuthal velocity. In agreement with earlier theoretical and numerical work, we find that for large modulation periods the system follows the given modulation of the driving, i.e. the system behaves quasi-stationary. For smaller modulation periods, the flow cannot follow the modulation, and the flow velocity responds with a phase delay and a smaller amplitude response to the given modulation. If we compare our results with numerical and theoretical results for the laminar case, we find that the scalings of the phase delay and the amplitude response are similar. However, the local response in the bulk of the flow is independent of the distance to the modulated boundary. Apparently, the turbulent mixing is strong enough to prevent the flow from having radius-dependent responses to the given modulation.Comment: 12 pages, 6 figure

Bubble drag reduction requires large bubbles

In the maritime industry, the injection of air bubbles into the turbulent boundary layer under the ship hull is seen as one of the most promising techniques to reduce the overall fuel consumption. However, the exact mechanism behind bubble drag reduction is unknown. Here we show that bubble drag reduction in turbulent flow dramatically depends on the bubble size. By adding minute concentrations (6 ppm) of the surfactant Triton X-100 into otherwise completely unchanged strongly turbulent Taylor-Couette flow containing bubbles, we dramatically reduce the drag reduction from more than 40% to about 4%, corresponding to the trivial effect of the bubbles on the density and viscosity of the liquid. The reason for this striking behavior is that the addition of surfactants prevents bubble coalescence, leading to much smaller bubbles. Our result demonstrates that bubble deformability is crucial for bubble drag reduction in turbulent flow and opens the door for an optimization of the process.Comment: 4 pages, 2 figure

Air cavities at the inner cylinder of turbulent Taylor-Couette flow

Air cavities, i.e. air layers developed behind cavitators, are seen as a promising drag reducing method in the maritime industry. Here we utilize the Taylor-Couette (TC) geometry, i.e. the flow between two concentric, independently rotating cylinders, to study the effect of air cavities in this closed setup, which is well-accessible for drag measurements and optical flow visualizations. We show that stable air cavities can be formed, and that the cavity size increases with Reynolds number and void fraction. The streamwise cavity length strongly depends on the axial position due to buoyancy forces acting on the air. Strong secondary flows, which are introduced by a counter-rotating outer cylinder, clearly decrease the stability of the cavities, as air is captured in the Taylor rolls rather than in the cavity. Surprisingly, we observed that local air injection is not necessary to sustain the air cavities; as long as air is present in the system it is found to be captured in the cavity. We show that the drag is decreased significantly as compared to the case without air, but with the geometric modifications imposed on the TC system by the cavitators. As the void fraction increases, the drag of the system is decreased. However, the cavitators itself significantly increase the drag due to their hydrodynamic resistance (pressure drag): In fact, a net drag increase is found when compared to the standard smooth-wall TC case. Therefore, one must first overcome the added drag created by the cavitators before one obtains a net drag reduction.Comment: 14 pages, 13 figure

The influence of wall roughness on bubble drag reduction in Taylor-Couette turbulence

We experimentally study the influence of wall roughness on bubble drag reduction in turbulent Taylor-Couette flow, i.e.\ the flow between two concentric, independently rotating cylinders. We measure the drag in the system for the cases with and without air, and add roughness by installing transverse ribs on either one or both of the cylinders. For the smooth wall case (no ribs) and the case of ribs on the inner cylinder only, we observe strong drag reduction up to $DR=33\%$ and $DR=23\%$, respectively, for a void fraction of $\alpha=6\%$. However, with ribs mounted on both cylinders or on the outer cylinder only, the drag reduction is weak, less than $DR=11\%$, and thus quite close to the trivial effect of reduced effective density. Flow visualizations show that stable turbulent Taylor vortices --- large scale vortical structures --- are induced in these two cases, i.e. the cases with ribs on the outer cylinder. These strong secondary flows move the bubbles away from the boundary layer, making the bubbles less effective than what had previously been observed for the smooth-wall case. Measurements with counter-rotating smooth cylinders, a regime in which pronounced Taylor rolls are also induced, confirm that it is really the Taylor vortices that weaken the bubble drag reduction mechanism. Our findings show that, although bubble drag reduction can indeed be effective for smooth walls, its effect can be spoiled by e.g.\ biofouling and omnipresent wall roughness, as the roughness can induce strong secondary flows.Comment: 10 pages, 5 figure

Fragmenting the Chieftain – Catalogue

There is a cluster of Early Iron Age (800–500 BC) elite burials in the Low Countries in which bronze vessels, weaponry, horse-gear and wagons were interred as grave goods. Mostly imports from Central Europe, these objects are found brought together in varying configurations in cremation burials generally known as chieftains’ graves or princely burials. In terms of grave goods they resemble the Fürstengräber of the Hallstatt Culture of Central Europe, with famous Dutch and Belgian examples being the Chieftain’s grave of Oss, the wagon-grave of Wijchen and the elite cemetery of Court-St-Etienne. The majority of the Dutch and Belgian burials were found several decades to several centuries ago and context information tends to be limited. They also tend to be published in Dutch or French or otherwise difficult to access publications. This research went back to the original reports and studied the objects found in these graves in detail. This generated new and evidence-based insights and interpretations into these exceptional burials and allowed for the reconstruction of the individual burial rituals. Fragmenting the Chieftain – Catalogue presents the first comprehensive overview of the Dutch and Belgian elite graves (in English) and the objects they contain. The results of an in-depth and practice-based archaeological analysis of the Dutch and Belgian elite graves and the burial practice through which they were created can be found in Fragmenting the Chieftain. A practice-based study of Early Iron Age Hallstatt C elite burials in the Low Countries

Self-similar decay of high Reynolds number Taylor-Couette turbulence

We study the decay of high-Reynolds number Taylor-Couette turbulence, i.e. the turbulent flow between two coaxial rotating cylinders. To do so, the rotation of the inner cylinder (Re$_i=2 \times 10^6$, the outer cylinder is at rest) is stopped within 12 s, thus fully removing the energy input to the system. Using a combination of laser Doppler anemometry and particle image velocimetry measurements, six decay decades of the kinetic energy could be captured. First, in the absence of cylinder rotation, the flow-velocity during the decay does not develop any height dependence in contrast to the well-known Taylor vortex state. Second, the radial profile of the azimuthal velocity is found to be self-similar. Nonetheless, the decay of this wall-bounded inhomogeneous turbulent flow does not follow a strict power law as for decaying turbulent homogeneous isotropic flows, but it is faster, due to the strong viscous drag applied by the bounding walls. We theoretically describe the decay in a quantitative way by taking the effects of additional friction at the walls into account.Comment: 7 pages, 6 figure