Surrogate Models for the Prediction of Damping Ratios in Coupled Acoustoelastic Rotor-Cavity Systems

Centrifugal compressors are versatile machines that many industries employ for a wide range of different applications, including the production of highly compressed gases. During the last decades, comprehensive research was conducted on the impact of high-pressure operating conditions on the vibrational behavior of radial compressors. In various studies, acoustic modes building up in the side cavities were found to be a potential source of high cycle fatigue. Nowadays, it is well-known that an increase in gas pressure levels leads to a more pronounced fluid-structure interaction between the side cavities and the impeller resulting in a frequency shift of the acoustic and structural modes. In a recently published paper, the authors presented a generalized model which can predict this behavior. As it is not always possible to avoid operating close to or accelerating through a resonance, it is crucial to know the damping present within the system. Currently, only a few publications concentrate on the damping of radial impellers. Therefore, the authors present measurement data acquired from a test rig at the University of Duisburg-Essen, which reveals the damping behavior of a disk under varying operating conditions. Two surrogate models are proposed to predict the identified damping behavior. The first one is based solely on a one-dimensional piston model and the second approach uses an enhanced version of the generalized method. Finally, the measurement data is used to validate both surrogate systems.

Post-genomic progress in helminth parasitology

Helminth parasitology is an important discipline, which poses often unique technical challenges. One challenge is that helminth parasites, particularly those in humans, are often difficult to obtain alive and in sufficient quantities for study; another is the challenge of studying these organisms in vitro – no helminth parasite life cycle has been fully recapitulated outside of a host. Arguably, the key issue retarding progress in helminth parasitology has been a lack of experimental tools and resources, certainly relative to the riches that have driven many parasitologists to adopt free-living model organisms as surrogate systems. In response to these needs, the past 10–12 years have seen the beginnings of helminth parasitology's journey into the ‘omics’ era, with the release of abundant sequencing resources, and the functional genomics tools with which to test biological hypotheses. To reflect this progress, the 2019 Autumn Symposium of the British Society for Parasitology was held in Queen's University Belfast on the topic of ‘post-genomic progress in helminth parasitology’. This issue presents examples of the current state of play in the field, while this editorial summarizes how genomic datasets and functional genomic tools have stimulated impressive recent progress in our understanding of parasite biology.

The effect of hemicylindrical disruptors on the cell free layer thickness in animal blood flows inside microchannels

Blood-side resistance to oxygen transport in extracorporeal membrane blood oxygenators (MBO) depends on fluid mechanics governing the laminar flow in very narrow channels, particularly the hemodynamics controlling the cell free layer (CFL) built-up at solid/blood interfaces. The CFL thickness constitutes a barrier to oxygen transport from the membrane towards the erythrocytes. Interposing hemicylindrical CFL disruptors in animal blood flows inside rectangular microchannels, surrogate systems of MBO mimicking their hemodynamics, proved to be effective in reducing (ca. 20%) such thickness (desirable for MBO to increase oxygen transport rates to the erythrocytes). The blockage ratio (non-dimensional measure of the disruptor penetration into the flow) increase is also effective in reducing CFL thickness (ca. 10–20%), but at the cost of risking clot formation (undesirable for MBO) for disruptors with penetration lengths larger than their radius, due to large residence times of erythrocytes inside a low-velocity CFL formed at the disruptor/wall edge.

Fundamento Ontológico del Modelo en Hayek

In the debate on realism of models in economics, the Austrian School and Hayek in particular, seem to have, in a certain way, remained outside. Assuming neoclassical models as unrealistic, the theory of the market as a pro- cess looks like a more realistic proposal. However, one of the fundamental issues in Hayek’s dissent is not so much the unrealism of the assumptions, but that the market equilibrium theory was not correctly raised, especially with regards to the perfect knowledge assumption. Despite this, in this setting and in line with a previous paper (Zanotti & Borella, 2015), we will argue that Hayek’s spontaneous order may be understood as the Austrian School’s «model», assuming Mäki’s MISS version of models (Models as Isolations and Surrogate Systems) and emphasizing the place of the ontological foundation of Hayek’s proposal when assessing his model. Keywords: Realism of models, Hayek, spontaneous order, MISS version, onto- logical foundation. JEL classification: B31, B40, B53. Resumen: En el debate sobre el realismo de los modelos en economía, la Escuela Austríaca y en particular Hayek, parece haber quedado en algún sen- tido afuera. Asumiendo a los modelos neoclásicos como irrealistas, la teoría del mercado como proceso parece presentarse como una propuesta más rea- lista. Sin embargo, uno de los puntos fundamentales en el disenso de Hayek no es tanto el irrealismo de los supuestos, sino que la teoría del equilibrio de mer- cado estaba mal planteada, especialmente en relación al supuesto de conoci- miento perfecto. A pesar de esto, en este encuadre y en línea con un trabajo anterior (Zanotti & Borella, 2015), mostraremos que el orden espontáneo de Hayek puede ser entendido como «el modelo» de la Escuela Austríaca, tomando la consideración MISS de los modelos de Mäki (Models as Isolations and Surrogate Systems) y destacando el lugar del fundamento ontológico de la propuesta de Hayek a la hora de evaluar su modelo. Palabras clave: Realismo de los modelos, Hayek, orden espontáneo, conside- ración MISS, fundamento ontológico. Clasificación JEL: B31, B40, B53.

Mapping the Interactions of HBV cccDNA with Host Factors

Hepatitis B virus (HBV) infection is a major health problem affecting about 300 million people globally. Although successful administration of a prophylactic vaccine has reduced new infections, a cure for chronic hepatitis B (CHB) is still unavailable. Current anti-HBV therapies slow down disease progression but are not curative as they cannot eliminate or permanently silence HBV covalently closed circular DNA (cccDNA). The cccDNA minichromosome persists in the nuclei of infected hepatocytes where it forms the template for all viral transcription. Interactions between host factors and cccDNA are crucial for its formation, stability, and transcriptional activity. Here, we summarize the reported interactions between HBV cccDNA and various host factors and their implications on HBV replication. While the virus hijacks certain cellular processes to complete its life cycle, there are also host factors that restrict HBV infection. Therefore, we review both positive and negative regulation of HBV cccDNA by host factors and the use of small molecule drugs or sequence-specific nucleases to target these interactions or cccDNA directly. We also discuss several reporter-based surrogate systems that mimic cccDNA biology which can be used for drug library screening of cccDNA-targeting compounds as well as identification of cccDNA-related targets.

External Representations and Scientific Understanding

This paper provides an inferentialist account of modelKbased understanding by combining a counterfactual account of explanation and an inferentialist account of representation with a view of modeling as extended cognition. This account makes it understandable how the manipulation of surrogate systems like models can provide genuinely new empirical understanding about the world. Similarly, the account provides an answer to the question how models, that always incorporate assumptions that are literally untrue of the model target, can still provide factive explanations. Finally, the paper shows how the contrastive counterfactual theory of explanation can provide tools for assessing the explanatory power of models.