726 research outputs found
Simulating the complex cell design of Trypanosoma brucei and its motility
The flagellate Trypanosoma brucei, which causes the sleeping sickness when infecting a mammalian host, goes through an intricate life cycle. It has a rather complex propulsion mechanism and swims in diverse microenvironments. These continuously exert selective pressure, to which the trypanosome adjusts with its architecture and behavior. As a result, the trypanosome assumes a diversity of complex morphotypes during its life cycle. However, although cell biology has detailed form and function of most of them, experimental data on the dynamic behavior and development of most morphotypes is lacking. Here we show that simulation science can predict intermediate cell designs by conducting specific and controlled modifications of an accurate, nature-inspired cell model, which we developed using information from live cell analyses. The cell models account for several important characteristics of the real trypanosomal morphotypes, such as the geometry and elastic properties of the cell body, and their swimming mechanism using an eukaryotic flagellum. We introduce an elastic network model for the cell body, including bending rigidity and simulate swimming in a fluid environment, using the mesoscale simulation technique called multi-particle collision dynamics. The in silico trypanosome of the bloodstream form displays the characteristic in vivo rotational and translational motility pattern that is crucial for survival and virulence in the vertebrate host. Moreover, our model accurately simulates the trypanosome's tumbling and backward motion. We show that the distinctive course of the attached flagellum around the cell body is one important aspect to produce the observed swimming behavior in a viscous fluid, and also required to reach the maximal swimming velocity. Changing details of the flagellar attachment generates less efficient swimmers. We also simulate different morphotypes that occur during the parasite's development in the tsetse fly, and predict a flagellar course we have not been able to measure in experiments so far
Emergence of geometrical optical nonlinearities in photonic crystal fiber nanowires
We demonstrate analytically and numerically that a subwavelength-core
dielectric photonic nanowire embedded in a properly designed photonic crystal
fiber cladding shows evidence of a previously unknown kind of nonlinearity (the
magnitude of which is strongly dependent on the waveguide parameters) which
acts on solitons so as to considerably reduce their Raman self-frequency shift.
An explanation of the phenomenon in terms of indirect pulse negative chirping
and broadening is given by using the moment method. Our conclusions are
supported by detailed numerical simulations.Comment: 5 pages, 3 figure
Gain in Three-Dimensional Metamaterials utilizing Semiconductor Quantum Structures
We demonstrate gain in a three-dimensional metal/semiconductor metamaterial
by the integration of optically active semiconductor quantum structures. The
rolling-up of a metallic structure on top of strained semiconductor layers
containing a quantum well allows us to achieve a three-dimensional superlattice
consisting of alternating layers of lossy metallic and amplifying gain
material. We show that the transmission through the superlattice can be
enhanced by exciting the quantum well optically under both pulsed or continuous
wave excitation. This points out that our structures can be used as a starting
point for arbitrary three-dimensional metamaterials including gain
Kinetics of Martensite Decomposition and Microstructure Stability of Ti-6246 during Rapid Heating to Service Temperatures
The aerospace alloy Ti-6246 was subjected to inductive heat treatments with high heating and quenching rates (up to 1500 K/s) while being applied to an in situ diffraction study at the HEMS beamline P07B at DESY. Thereby, the characterization of the emerging phases was possible at any point in the process. The heat treatment schedules include the preparation of Ti-6246 samples by means of a homogenization treatment and subsequent quenching to trigger α″-martensite formation. In order to simulate fast reheating within the scope of application, the samples were reheated to the upper range of possible service temperatures (550–650 °C) with a heating rate of 100 K/s. In a second heat treatment design, the homogenized and quenched sample state was exposed to high-temperature tempering at 840 °C, which aims for the elimination of α″. Again, fast reheating to the same service temperatures was executed. With the aim of this approach, the stability of the microstructure consisting of α-Ti, β-Ti and α″-martensite was characterized. Further, the martensite decomposition path was analyzed. It shows a two-tier nature, firstly approaching the bcc β-unit cell in the low-temperature range (<400 °C) but subsequently transforming into an hcp-like unit cell and later on into equilibrium α-Ti
Humidity Influence on Mechanics and Failure of Paper Materials: Joint Numerical and Experimental Study on Fiber and Fiber Network Scale
Paper materials are natural composite materials and well-known to be
hydrophilic unless chemical and mechanical processing treatments are
undertaken. The relative humidity impacts the fiber elasticity, the fiber-fiber
bonds and the failure mechanism. In this work, we present a comprehensive
experimental and computational study on the mechanical and failure behaviour of
the fiber and the fiber network under humidity influence. The manually
extracted cellulose fiber is exposed to different levels of humidity, and then
mechanically characterized using Atomic Force Microscopy, which delivers the
humidity dependent longitudinal Young's modulus. The obtained relationship
allows calculation of fiber elastic modulus at any humidity level. Moreover, by
using Confoncal Laser Scanning Microscopy, the coefficient of hygroscopic
expansion of the fibers is determined. On the other hand, we present a finite
element model to simulate the deformation and the failure of the fiber network.
The model includes the fiber anisotropy and the hygroscopic expansion using the
experimentally determined constants. In addition, it regards the fiber-fiber
bonding and damage by using a humidity dependent cohesive zone interface model.
Finite element simulations on exemplary fiber network samples are performed to
demonstrate the influence of different aspects including relative humidity and
fiber-fiber bonding parameters on the mechanical features such as
force-elongation curves, wet strength, extensiability and the local fiber-fiber
debonding. In meantime, fiber network failure in a locally wetted region is
revealed by tracking of individually stained fibers using in-situ imaging
techniques. Both the experimental data and the cohesive finite element
simulations demonstrate the pull-out of fibers and imply the significant role
of the fiber-fiber debonding in the failure process of the wet paper.Comment: 21 pages,10 figure
IL-17C and IL-17RE Promote Wound Closure in a Staphylococcus aureus-Based Murine Wound Infection Model
The epithelial cytokine interleukin-17C (IL-17C) mediates inflammation through the interleukin 17 receptor E (IL-17RE). Prior studies showed a detrimental role of IL-17C in the pathogenesis
of immune-mediated skin diseases (e.g., psoriasis). Here, we examined the role of IL-17C/IL-17RE
in wound closure in a Staphylococcus aureus wound infection model. We demonstrate that wound
closure is significantly delayed in IL-17RE (Il-17re−/−)- and 17C (Il-17c−/−)-deficient mice. There
was no significant difference between WT, Il-17re−/−, and Il-17c−/− mice in the absence of infection.
Deficiency for IL-17RE and IL-17C did not significantly affect the elimination of bacteria. IL-17C
expression was increased in the epidermis of human S. aureus-infected skin. Our results indicate that
the IL-17C/IL-17RE axis contributes to the closure of infected wounds but does not contribute to the
elimination of S. aureus
Symptomatic Diastasis Rectus Abdominis in Children: Review of Current Management Options and Presentation of a Novel Minimally Invasive Epifascial Repair Technique
Several surgical techniques are available for an adult patient collective with diastasis recti. Only few research papers addresses the treatment options of diastasis of the rectus abdominis in children. In this case series, we present a new technique of epifascial repair as a novel possibility in successfully repairing defects of the anterior abdominal wall using minimally invasive surgery. In this case series, we present an epifascial repair technique for patients with a diastasis recti with a dehiscence cranial of the umbilicus. Four pediatric patients with symptomatic rectus diastasis were treated with this new surgical technique. All procedures were conducted successfully, and no recurrence was observed in the follow up. All patients showed clinical regression of the rectus diastasis without any postoperative abdominal wall protrusion and good improvement of the symptoms. Intraoperative intraperitoneal air loss, postoperative scar keloid, thermal lesions due to Ultracision and one seroma/hematoma after the removal of the drain were minor complications observed during the follow-up
Preliminary assessment of the imaging capability of the YAP-(S)PET small animal scanner in neuroscience
The new and fully engineered version of the YAP–(S)PET small animal scanner has been tested at the University of Mainz for preliminary assessment of its imaging capability for studies related to neuropharmacology and psychiatry. The main feature of the scanner is the capability to combine PET and SPECT techniques. It allows the development of new and interesting protocols for the investigation of many biological phenomena, more effectively than with PET or SPECT modalities alone. The scanner is made up of four detector heads, each one composed of a 4 � 4c m 2 of YAlO3:Ce (or YAP:Ce) matrix, and has a field of view (FOV) of 4 cm axially � 4c m + transaxially. In PET mode, the volume resolution is less than 8 mm 3 and is nearly constant over the whole FOV, while the sensitivity is about 2%. The SPECT performance is not so good, due to the presence of the multi-hole lead collimator in front of each head. Nevertheless, the YAP–PET scanner offers excellent resolution and sensitivity for performing on the availability of D2-like dopamine receptors on mice and rats in both PET and SPECT modalities
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Self-Assembly of Polymer-Modified FePt Magnetic Nanoparticles and Block Copolymers
The fabrication of nanocomposites containing magnetic nanoparticles is gaining interest as a model for application in small electronic devices. The self-assembly of block copolymers (BCPs) makes these materials ideal for use as a soft matrix to support the structural ordering of the nanoparticles. In this work, a high-molecular-weight polystyrene-b-poly(methyl methacrylate) block copolymer (PS-b-PMMA) was synthesized through anionic polymerization. The influence of the addition of different ratios of PMMA-coated FePt nanoparticles (NPs) on the self-assembled morphology was investigated using transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). The self-assembly of the NPs inside the PMMA phase at low particle concentrations was analyzed statistically, and the negative effect of higher particle ratios on the lamellar BCP morphology became visible. The placement of the NPs inside the PMMA phase was also compared to theoretical descriptions. The magnetic addressability of the FePt nanoparticles inside the nanocomposite films was finally analyzed using bimodal magnetic force microscopy and proved the magnetic nature of the nanoparticles inside the microphase-separated BCP films
Motility-induced clustering and meso-scale turbulence in active polar fluids
Meso-scale turbulence was originally observed experimentally in various suspensions of swimming bacteria, as well as in the collective motion of active colloids. The corresponding large scale dynamical patterns were reproduced in a simple model of a polar fluid, assuming a constant density of active particles. Recent, more detailed studies in a variety of experimental realizations of active polar fluids revealed additional interesting aspects, such as anomalous velocity statistics and clustering phenomena. Those phenomena cannot be explained by currently available models for active polar fluids. Herein, we extend the continuum model suggested by Dunkel et al to include density variations and a local feedback between the local density and self-propulsion speed of the active polar particles. If the velocity decreases strong enough with the density, a linear stability analysis of the resulting model shows that, in addition to the short-wavelength instability of the original model, a long-wavelength instability occurs. This is typically observed for high densities of polar active particles and is analogous to the well-known phenomenon of motility-induced phase separation (MIPS) in scalar active matter. We determine a simple phase diagram indicating the linear instabilities and perform systematic numerical simulations for the various regions in the corresponding parameter space. The interplay between the well understood short-range instability (leading to meso-scale turbulence) and the long-range instability (associated with MIPS) leads to interesting dynamics and novel phenomena concerning nucleation and coarsening processes. Our simulation results display a rich variety of novel patterns, including phase separation into domains with dynamically changing irregularly shaped boundaries. Anomalous velocity statistics are observed in all phases where the system segregates into regions of high and low densities. This offers a simple explanation for their occurrence in recent experiments with bacterial suspensions.DFG, 163436311, SFB 910: Kontrolle selbstorganisierender nichtlinearer Systeme: Theoretische Methoden und Anwendungskonzept
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