Fluctuations, dissipation and the dynamical Casimir effect

Vacuum fluctuations provide a fundamental source of dissipation for systems coupled to quantum fields by radiation pressure. In the dynamical Casimir effect, accelerating neutral bodies in free space give rise to the emission of real photons while experiencing a damping force which plays the role of a radiation reaction force. Analog models where non-stationary conditions for the electromagnetic field simulate the presence of moving plates are currently under experimental investigation. A dissipative force might also appear in the case of uniform relative motion between two bodies, thus leading to a new kind of friction mechanism without mechanical contact. In this paper, we review recent advances on the dynamical Casimir and non-contact friction effects, highlighting their common physical origin.Comment: 39 pages, 4 figures. Review paper to appear in Lecture Notes in Physics, Volume on Casimir Physics, edited by Diego Dalvit, Peter Milonni, David Roberts, and Felipe da Rosa. Minor changes, a reference adde

3D + time blood flow mapping using SPIM-microPIV in the developing zebrafish heart

We present SPIM-μPIV as a flow imaging system, capable of measuring in vivo flow information with 3D micron-scale resolution. Our system was validated using a phantom experiment consisting of a flow of beads in a 50 μm diameter FEP tube. Then, with the help of optical gating techniques, we obtained 3D + time flow fields throughout the full heartbeat in a ∼3 day old zebrafish larva using fluorescent red blood cells as tracer particles. From this we were able to recover 3D flow fields at 31 separate phases in the heartbeat. From our measurements of this specimen, we found the net pumped blood volume through the atrium to be 0.239 nL per beat. SPIM-μPIV enables high quality in vivo measurements of flow fields that will be valuable for studies of heart function and fluid-structure interaction in a range of small-animal models

Spatio-Temporal Analysis of Flows Close to Free Water Surfaces

In order to examine the air-water gas exchange, a detailed knowledge is needed about the flow field within and beneath the water-side viscous boundary layer. Therefore a novel measurement technique is developed for the spatio-temporal analysis of flows close to free water surfaces. A fluid volume is illuminated by LEDs. Small spherical particles are added to the fluid, functioning as a tracer. A camera pointing to the water surface from above records the image sequences. The distance of the spheres to the surface is coded by means of a supplemented dye, which absorbs the light of the LEDs. By using LEDs flashing with two different wavelengths, it is possible to use particles variable in size. The velocity vectors are obtained by using an extension of the method of optical flow. The vertical velocity component is computed from the temporal change of brightness. Using 3D parametric motion models the shear stress at surfaces can be estimated directly, without previous calculation of the vector fields. Hardware and algorithmics are tested in several ways: A laminar falling film serves as reference flow. The predicted parabolic profile of this stationary flow can be reproduced very well. Buoyant convective turbulence acts as an example for an instationary inherently 3D flow. The direct estimation of the wall shear rate is applied to sequences recorded in the context of biofluidmechanics, revealing a substantial improvement compared to conventional techniques

A Review of Prosthetic Interface Stress Investigations

Over the last decade, numerous experimental and numerical analyses have been conducted to investigate the stress distribution between the residual limb and prosthetic socket of persons with lower limb amputation. The objectives of these analyses have been to improve our understanding of the residual limb/prosthetic socket system, to evaluate the influence of prosthetic design parameters and alignment variations on the interface stress distribution, and to evaluate prosthetic fit. The purpose of this paper is to summarize these experimental investigations and identify associated limitations. In addition, this paper presents an overview of various computer models used to investigate the residual limb interface, and discusses the differences and potential ramifications of the various modeling formulations. Finally, the potential and future applications of these experimental and numerical analyses in prosthetic design are presented

Advances in computational modelling for personalised medicine after myocardial infarction

Myocardial infarction (MI) is a leading cause of premature morbidity and mortality worldwide. Determining which patients will experience heart failure and sudden cardiac death after an acute MI is notoriously difficult for clinicians. The extent of heart damage after an acute MI is informed by cardiac imaging, typically using echocardiography or sometimes, cardiac magnetic resonance (CMR). These scans provide complex data sets that are only partially exploited by clinicians in daily practice, implying potential for improved risk assessment. Computational modelling of left ventricular (LV) function can bridge the gap towards personalised medicine using cardiac imaging in patients with post-MI. Several novel biomechanical parameters have theoretical prognostic value and may be useful to reflect the biomechanical effects of novel preventive therapy for adverse remodelling post-MI. These parameters include myocardial contractility (regional and global), stiffness and stress. Further, the parameters can be delineated spatially to correspond with infarct pathology and the remote zone. While these parameters hold promise, there are challenges for translating MI modelling into clinical practice, including model uncertainty, validation and verification, as well as time-efficient processing. More research is needed to (1) simplify imaging with CMR in patients with post-MI, while preserving diagnostic accuracy and patient tolerance (2) to assess and validate novel biomechanical parameters against established prognostic biomarkers, such as LV ejection fraction and infarct size. Accessible software packages with minimal user interaction are also needed. Translating benefits to patients will be achieved through a multidisciplinary approach including clinicians, mathematicians, statisticians and industry partners

Structure-functionality relationship of collagen scaffolds for tissue engineering

Tissue engineering is a promising technology that enables scientists to create artificial organs or replace damaged tissues using animal cells and other components. For successful tissue regeneration, many factors should be taken into account, however, three components are most crucial: cell, scaffold, and soluble factor(s). In order to check the functionality after regeneration of desired tissues, various approaches have been attempted, depending on the physical, biological, and chemical properties of the tissues. Recently, the importance of the extracellular matrix (ECM) microstructure is being considered to be important in this regard. The ECM is closely associated with various functional properties of the tissues including mechanical properties, diffusivity, and hydraulic conductivity or permeability. Besides providing structural support and determining the physical and functional properties, the ECM plays various roles in tissue physiology by regulating cell morphology, growth and intercellular signaling. The ECM can also be reconfigured by cells during tissue remodeling and wound healing. In this thesis, in order to investigate the structure-functionality relationship of engineered tissues (ETs), computational modeling and experimental studies were performed based on the following three topics: (1) the effect of different ECM structures on the tissue transport property, (2) the effect of the different ECM structures on the cell functionality and subsequent tissue mechanical property, and (3) the evaluation of functionality of new vessel networks formed by modulation of ECM structures. ^ The first study developed computational models (i.e., parameter- and image-based models) using experimental data to predict transport properties (i.e.,permeability and diffusivity) of two different microstructural matrices (i.e., monomer and oligomer) for tissue functionality. The developed computational models underestimated the permeability result compared to what was obtained experimentally. The image- and parameter-based models developed in the present study were able to predict values closest to the experiment data, when compared with previously reported models of permeability. For diffusivity, the computational results showed a similar trend and magnitude to the experimental ones. ^ During cryopreservation of tissues, freezing-induced structural deformation of the tissues and cells occurs due to formation of ice within the intracellular and extracellular spaces. Several studies focused on developing optimal combinations of cryoprotective agent (CPA) and freeze/thaw (F/T) protocols for functional tissue and cell preservation. In the second study, a hypothesis was tested that the modulation of the cytoskeletal structure can mitigate the freezing-induced changes of the functionality, therefore, may reduce the amount of CPA necessary to preserve the tissue\u27s functionality during cryopreservation. In order to test the above hypothesis, the engineered tissues (ETs) were exposed to various F/T conditions with or without CPAs, and the freezing-induced cell-fluid-matrix interactions and subsequent functional properties of the ETs were assessed. Our result showed that, the use of only a small concentration of CPA was very successful in completely preserving the elastic modulus and the viscous friction to the state of the unfrozen 3D stressed structure (STR). This result underscores the importance of CPA in preserving the cytoskeleton structure and how that impacts functional properties of the tissue after freeze-thaw cycles. ^ The third study performed the parametric study to estimate endothelium hydraulic conductivity for vessel functionality. Currently, it is known that formation of vasculatures within the tissues is the most difficult aspect of tissue engineering. Moreover, a method to evaluate new vessel functionality has not been well-established to date. Therefore, a new method with the osmotic pressure-driven vessel deformation and the poroelastic theory was developed using new vessel networks formed by vasculogenesis for hydraulic conductivity estimation. Results showed that the hydraulic conductivity was more sensitive to the elastic modulus compared to other parameters. When the elastic modulus with 10 - 100 Pa and Possions\u27s ratio with 0.3 were applied, the hydraulic conductivity was well-matched with the previously reported hydraulic conductivity

Numerical Simulation in Biomechanics and Biomedical Engineering

In the first contribution, Morbiducci and co-workers discuss the theoretical and methodological bases supporting the Lagrangian- and Euler-based methods, highlighting their application to cardiovascular flows. The second contribution, by the Ansón and van Lenthe groups, proposes an automated virtual bench test for evaluating the stability of custom shoulder implants without the necessity of mechanical testing. Urdeitx and Doweidar, in the third paper, also adopt the finite element method for developing a computational model aim to study cardiac cell behavior under mechano-electric stimulation. In the fourth contribution, Ayensa-Jiménez et al. develop a methodology to approximate the multidimensional probability density function of the parametric analysis obtained developing a mathematical model of the cancer evolution. The fifth paper is oriented to the topological data analysis; the group of Cueto and Chinesta designs a predictive model capable of estimating the state of drivers using the data collected from motion sensors. In the sixth contribution, the Ohayon and Finet group uses wall shear stress-derived descriptors to study the role of recirculation in the arterial restenosis due to different malapposed and overlapping stent conditions. In the seventh contribution, the research group of Antón demonstrates that the simulation time can be reduced for cardiovascular numerical analysis considering an adequate geometry-reduction strategy applicable to truncated patient specific artery. In the eighth paper, Grasa and Calvo present a numerical model based on the finite element method for simulating extraocular muscle dynamics. The ninth paper, authored by Kahla et al., presents a mathematical mechano-pharmaco-biological model for bone remodeling. Martínez, Peña, and co-workers propose in the tenth paper a methodology to calibrate the dissection properties of aorta layer, with the aim of providing useful information for reliable numerical tools. In the eleventh contribution, Martínez-Bocanegra et al. present the structural behavior of a foot model using a detailed finite element model. The twelfth contribution is centered on the methodology to perform a finite, element-based, numerical model of a hydroxyapatite 3D printed bone scaffold. In the thirteenth paper, Talygin and Gorodkov present analytical expressions describing swirling jets for cardiovascular applications. In the fourteenth contribution, Schenkel and Halliday propose a novel non-Newtonian particle transport model for red blood cells. Finally, Zurita et al. propose a parametric numerical tool for analyzing a silicone customized 3D printable trachea-bronchial prosthesis

Seismic shear and acceleration demands in multi-storey cross-laminated timber buildings

A realistic estimation of seismic shear demands is essential for the design and assessment of multi-storey buildings and for ensuring the activation of ductile failure modes during strong ground-motion. Likewise, the evaluation of seismic floor accelerations is fundamental to the appraisal of damage to non-structural elements and building contents. Given the relative novelty of tall timber buildings and their increasing popularity, a rigorous evaluation of their shear and acceleration demands is all the more critical and timely. For this purpose, this paper investigates the scaling of seismic shear and acceleration demands in multi- storey cross-laminated timber (CLT) buildings and its dependency on various structural properties. Special attention is given to the influence of the frequency content of the ground-motion. A set of 60 CLT buildings of varying heights representative of a wide range of structural configurations is subjected to a large dataset of 1656 real earthquake records. It is demonstrated that the mean period (Tm) of the ground-motion together with salient structural parameters such as building aspect ratio (λ), design force reduction factor (q) and panel subdivision (β) influence strongly the variation of base shear, storey shears and acceleration demands. Besides, robust regression models are used to assess and quantify the distribution of force and acceleration demands on CLT buildings. Finally, practical expressions for the estimation of base shears, inter-storey shears and peak floor accelerations are offered