Goal-oriented error estimation and adaptivity for fluid–structure interaction using exact linearized adjoints

We develop duality-based a posteriori error estimates for functional outputs of solutions of steady fluid–structure-interaction problems. The crucial complication in obtaining these estimates pertains to the derivation of the coupled dual (exact linearized adjoint) problem owing to the free-boundary character of fluid–structure interaction. We present two approaches to derive the dual problem. In the domain-map linearization approach, the fluid subproblem is first transformed to a fixed reference domain, after which one essentially linearizes with respect to the domain transformation map. In the shape-linearization approach, fluid unknowns are fixed in the current configuration and a very weak formulation of the fluid subproblem is then linearized using shape-derivative techniques. We show that the dual problems correspond to coupled fluid–structure problems with nonstandard coupling conditions. Furthermore, we present numerical experiments that demonstrate the consistency of the dual-based error estimates and their usefulness in goal-oriented adaptive mesh-refinement.     

Adaptive isogeometric analysis for phase-field modeling of anisotropic brittle fracture

The surface energy a phase-field approach to brittle fracture in anisotropic materials is also anisotropic and gives rise to second-order gradients in the phase field entering the energy functional. This necessitates C¹ continuity of the basis functions which are used to interpolate the phase field. The basis functions which are employed in isogeometric analysis (IGA), such as nonuniform rational B-splines and T-splines naturally possess a higher order continuity and are therefore ideally suited for phase-field models which are equipped with an anisotropic surface energy. Moreover, the high accuracy of spline discretizations, also relative to their computational demand, significantly reduces the fineness of the required discretization. This holds a fortiori if adaptivity is included. Herein, we present two adaptive refinement schemes in IGA, namely, adaptive local refinement and adaptive hierarchical refinement, for phase-field simulations of anisotropic brittle fracture. The refinement is carried out using a subdivision operator and exploits the Bézier extraction operator. Illustrative examples are included, which show that the method can simulate highly complex crack patterns such as zigzag crack propagation. An excellent agreement is obtained between the solutions from global refinement and adaptive refinement, with a reasonable reduction of the computational effort when using adaptivity.     

On the numerical integration of isogeometric interface elements

Zero‐thickness interface elements are commonly used in computational mechanics to model material interfaces or to introduce discontinuities. The latter class requires the existence of a non‐compliant interface prior to the onset of fracture initiation. This is accomplished by assigning a high dummy stiffness to the interface prior to cracking. This dummy stiffness is known to introduce oscillations in the traction profile when using Gauss quadrature for the interface elements, but these oscillations are removed when resorting to a Newton‐Cotes integration scheme 1. The traction oscillations are aggravated for interface elements that use B‐splines or non‐uniform rational B‐splines as basis functions (isogeometric interface elements), and worse, do not disappear when using Newton‐Cotes quadrature. An analysis is presented of this phenomenon, including eigenvalue analyses, and it appears that the use of lumped integration (at the control points) is the only way to avoid the oscillations in isogeometric interface elements. New findings have also been obtained for standard interface elements, for example that oscillations occur in the relative displacements at the interface irrespective of the value of the dummy stiffness. Copyright © 2015 John Wiley & Sons, Ltd.     

CD95 (Fas/APO-1) induces ceramide formation and apoptosis in the absence of a functional acid sphingomyelinase

CD95 is a potent inducer of apoptosis. It activates the caspase cascade, but also induces ceramide (Cer) production, reportedly involving acid sphingomyelinase (aSMase) activity. A role for Cer as a second messenger for apoptosis induction was proposed, based on the finding that synthetic Cer analogues can induce cell death. We have tested whether aSMase is required for 1) apoptosis induction and 2) Cer production by CD95. For this purpose, we have used cultured Niemann-Pick disease (NPD) lymphoid cells with a defined mutation (R600H) in the aSMase protein. Despite their inherited deficiency of aSMase, we found that these cells readily undergo apoptosis upon CD95 stimulation. After retrovirus-mediated gene transfer of the aSMase cDNA, the transduced (i.e. "corrected") NPD cells showed neither increased levels of apoptosis nor altered kinetics of caspase-8 and caspase-3 activation and apoptosis induction as compared with empty vector-transduced cells. The slow sustained elevation of Cer levels in response to CD95, which we have previously documented for Jurkat T cells (Tepper, A. D., Boesen-de Cock, J. G. R., de Vries, E., Borst, J., and van Blitterswijk, W. J. (1997) J. Biol. Chem. 272, 24308-24312), was similarly found in NPD cells. Moreover, the kinetics of Cer formation remained unaffected after aSMase transduction. These results indicate that this Cer does not result from aSMase activity. We conclude that aSMase is not required for and does not facilitate CD95-mediated apoptosis and that it is not responsible for the late Cer response.     

Virtual grasp release method and evaluation

We address a “sticking object” problem for the release of whole-hand virtual grasps. The problem occurs when grasping techniques require fingers to be moved outside an object's boundaries after a user's (real) fingers interpenetrate virtual objects due to a lack of physical motion constraints. This may be especially distracting for grasp techniques that introduce mismatches between tracked and visual hand configurations to visually prevent interpenetration. Our method includes heuristic analysis of finger motion and a transient incremental motion metaphor to manage a virtual hand during grasp release. We integrate the method into a spring model for whole-hand virtual grasping to maintain the physically-based pickup and manipulation behavior of such models. We show that the new spring model improves release speed and accuracy based on pick-and-drop, targeted ball-drop, and cube-alignment experiments. In contrast to a standard spring-based grasping method, measured release quality does not depend notably on object size. Users subjectively prefer the new approach and it can be tuned to avoid potential side effects such as increased drops or visual distractions. We further investigated a convergence speed parameter to find the subjectively good range and to better understand tradeoffs in subjective artifacts on the continuum between pure incremental motion and rubber-band-like convergence behavior.     

Handling of particulate solids on the International Space Station

We present the principles of a particle-handling system for the International Space Station (ISS) with which experiments with astrophysical and planetological applications will be performed. The principle of dust deagglomeration and dispersion was successfully tested in short-duration microgravity experiments. The flight of the systems on the ISS is planned for 2012.     

Intravascular ultrasound-guided percutaneous fenestration of the intimal flap in the dissected aorta

BACKGROUND: Aortic dissection with branch obstruction is associated with high morbidity and mortality. Fenestration of the dissection flap to relieve distal vessel ischemia is at present largely performed surgically. The surgical mortality and morbidity are high, because most patients are poor candidates for anesthesia or surgery. METHODS AND RESULTS: Nine percutaneous fenestrations (one with additional stenting of the infrarenal true aortic lumen) were performed under local anesthesia in seven patients with aortic dissection. The presenting symptoms were abdominal angina or claudication. By the transfemoral approach, the intimal flap was initially punctured with a needle-catheter combination through which a guidewire was placed across the dissection flap. The fenestration was carried out with a balloon catheter introduced over the guidewire. The procedure was performed under on-line guidance with intravascular ultrasound imaging. The procedure was performed successfully and without complications in all patients. After intervention, symptoms resolved in all seven patients. CONCLUSIONS: Intravascular ultrasound-guided percutaneous fenestration of the intimal flap in symptomatic aortic dissections with distal vessel involvement is a technically feasible and safe procedure that can effectively relieve the patient's symptoms.     

Extraanatomic thoracic aortic bypass grafts: indications, techniques, and results

A polymorphism in the UL42-UL43 region of the human cytomegalovirus genome has been characterized by nucleotide sequence analysis, revealing a 929-bp insertion following nt 54,612 relative to the published strain AD169-UK genome sequence (M.S. Chee et al., 1990, Curr. Top. Microbiol Immunol. 154, 125-170). Although AD169-UK exhibited polymorphism in this genomic region, other CMV strains (Towne, Toledo, and AD169-ATCC) carried only the newly characterized longer form. The additional sequence altered the assignment of UL42 and UL43 open reading frames. UL42 decreased in size from 157 to 125 codons, retaining 76 of the previously reported carboxyl terminal codons, and UL43 increased in size from 187 to 423 codons, retaining 185 of the previously reported amino terminal codons. This additional sequence makes UL43 a more conserved betaherpesvirus US22 family member. Only AD169-UK exhibited restriction fragment length polymorphism in this region, suggesting that a deletion occurred during the propagation of this strain in cell culture. The additional sequence should be considered a bona fide part of the cytomegalovirus genome and the AD169 genome size should be corrected to 230,283 bp.     

Comparison of the internal transcribed spacer, ITS 1, from Toxoplasma gondii isolates and Neospora caninum

Limited data about homicide in Australia have been published. Data on homicide occurring in the state of Victoria, Australia, are presented. Since 1945 there has been a doubling of the population and an increase in the rate of homicide. The most common method of killing was shooting, and most homicide victims were known to their assailants. Male assailants far outnumber female assailants. Men are the most frequent victims, but female victims far outnumber female assailants. The data are compared with data on other Australian states and published data from other countries.