Braunschweig University of Technology

About: Braunschweig University of Technology is a education organization based out in Braunschweig, Germany. It is known for research contribution in the topics: Population & Computer science. The organization has 13268 authors who have published 26707 publications receiving 611590 citations.

The Growth Mechanisms of Macroscopic Bodies in Protoplanetary Disks

Abstract: The formation of planetesimals, the kilometer-sized planetary precursors, is still a puzzling process. Considerable progress has been made over the past years in the physical description of the first stages of planetesimal formation, owing to extensive laboratory work. This review examines the experimental achievements and puts them into the context of the dust processes in protoplanetary disks. It has become clear that planetesimal formation starts with the growth of fractal dust aggregates, followed by compaction processes. As the dust-aggregate sizes increase, the mean collision velocity also increases, leading to the stalling of the growth and possibly to fragmentation, once the dust aggregates have reached decimeter sizes. A multitude of hypotheses for the further growth have been proposed, such as very sticky materials, secondary collision processes, enhanced growth at the snow line, or cumulative dust effects with gravitational instability. We will also critically review these ideas.

A review on phase-field models of brittle fracture and a new fast hybrid formulation

Abstract: In this contribution we address the issue of efficient finite element treatment for phase-field modeling of brittle fracture. We start by providing an overview of the existing quasi-static and dynamic phase-field fracture formulations from the physics and the mechanics communities. Within the formulations stemming from Griffith's theory, we focus on quasi-static models featuring a tension-compression split, which prevent cracking in compression and interpenetration of the crack faces upon closure, and on the staggered algorithmic implementation due to its proved robustness. In this paper, we establish an appropriate stopping criterion for the staggered scheme. Moreover, we propose and test the so-called hybrid formulation, which leads within a staggered implementation to an incrementally linear problem. This enables a significant reduction of computational cost--about one order of magnitude--with respect to the available (non-linear) models. The conceptual and structural similarities of the hybrid formulation to gradient-enhanced continuum damage mechanics are outlined as well. Several benchmark problems are solved, including one with own experimental verification.

Dual Function of the Selenoprotein PHGPx During Sperm Maturation

Abstract: The selenoprotein phospholipid hydroperoxide glutathione peroxidase (PHGPx) changes its physical characteristics and biological functions during sperm maturation PHGPx exists as a soluble peroxidase in spermatids but persists in mature spermatozoa as an enzymatically inactive, oxidatively cross-linked, insoluble protein In the midpiece of mature spermatozoa, PHGPx protein represents at least 50 percent of the capsule material that embeds the helix of mitochondria The role of PHGPx as a structural protein may explain the mechanical instability of the mitochondrial midpiece that is observed in selenium deficiency

p140mDia, a mammalian homolog of Drosophila diaphanous, is a target protein for Rho small GTPase and is a ligand for profilin.

Abstract: Rho small GTPase regulates cell morphology, adhesion and cytokinesis through the actin cytoskeleton. We have identified a protein, p140mDia, as a downstream effector of Rho. It is a mammalian homolog of Drosophila diaphanous, a protein required for cytokinesis, and belongs to a family of formin-related proteins containing repetitive polyproline stretches. p140mDia binds selectively to the GTP-bound form of Rho and also binds to profilin. p140mDia, profilin and RhoA are co-localized in the spreading lamellae of cultured fibroblasts. They are also co-localized in membrane ruffles of phorbol ester-stimulated sMDCK2 cells, which extend these structures in a Rho-dependent manner. The three proteins are recruited around phagocytic cups induced by fibronectin-coated beads. Their recruitment is not induced after Rho is inactivated by microinjection of botulinum C3 exoenzyme. Overexpression of p140mDia in COS-7 cells induced homogeneous actin filament formation. These results suggest that Rho regulates actin polymerization by targeting profilin via p140mDia beneath the specific plasma membranes.