1,289 research outputs found
Multiple cracking events in metal bi-layers on polymer substrates
Metal films on polymer substrates are used in a variety of applications such as flexible electronics, sensors, medical devices and aerospace including multilayer insulators and surface mirrors on satellites. A common way to assess the mechanical behavior of metal-polymer systems is with fragmentation testing, which strains the system under uniaxial tension. During straining cracks or localized deformation (necks) develop perpendicular to the loading direction and buckle delaminations occur parallel to the loading. From the crack spacing the fracture behavior can be determined and the interface adhesion energy can be measured from the buckles. Fragmentation testing has been used on single and multilayer films and has shown that brittle adhesion layers next to the substrate, can cause brittle cracking of normally ductile overlying films. A similar fracture behavior was observed here for the Inconel-Ag-Teflon system, but in this system, the top 30 nm Inconel film is the brittle layer inducing brittle cracking of the underlying 150 nm Ag film. Inconel acts as a corrosion protection for the Ag layer in surface mirrors on satellites in low earth orbit, where the material should not develop cracks upon mechanical loading. Observation of the Inconel surface during in-situ tensile straining revealed crack formation in the Inconel layer at less than 1% strain, which continues with increasing strain (primary cracks). At approximately 3% strain, the primary cracks in the Inconel overcoat act as stress concentrators and generate through thickness cracks in the Ag film (secondary cracks). The primary Inconel cracks had a saturation spacing of 1.5 µm, while the secondary Inconel-Ag saturation crack spacing was much larger at 12 µm. In-situ fragmentation experiments performed through the transparent Teflon substrate revealed only the secondary through thickness cracks and cross-sectional focused ion beam characterization provides further evidence for the two-stage cracking behavior. Using the shear lag model the interfacial shear stresses of the Inconel and Inconel-Ag layers were determined from the saturation crack spacings and observed fracture strains. These results further illustrate that brittle layers at any position are detrimental to the functionality of multi-layered metal-polymer systems and should be carefully considered for any application.
Please click Additional Files below to see the full abstract
Swimmer-tracer scattering at low Reynolds number
Understanding the stochastic dynamics of tracer particles in active fluids is
important for identifying the physical properties of flow generating objects
such as colloids, bacteria or algae. Here, we study both analytically and
numerically the scattering of a tracer particle in different types of
time-dependent, hydrodynamic flow fields. Specifically, we compare the tracer
motion induced by an externally driven colloid with the one generated by
various self-motile, multi-sphere swimmers. Our results suggest that force-free
swimmers generically induce loop-shaped tracer trajectories. The specific
topological structure of these loops is determined by the hydrodynamic
properties of the microswimmer. Quantitative estimates for typical experimental
conditions imply that the loops survive on average even if Brownian motion
effects are taken into account.Comment: 14 pages, to appear in Soft Matte
The Energy-Momentum Tensor in Noncommutative Gauge Field Models
We discuss the different possibilities of constructing the various
energy-momentum tensors for noncommutative gauge field models. We use Jackiw's
method in order to get symmetric and gauge invariant stress tensors--at least
for commutative gauge field theories. The noncommutative counterparts are
analyzed with the same methods. The issues for the noncommutative cases are
worked out.Comment: 11 pages, completed reference
Moregrasp: Restoration of Upper Limb Function in Individuals with High Spinal Cord Injury by Multimodal Neuroprostheses for Interaction in Daily Activities
The aim of the MoreGrasp project is to develop a noninvasive, multimodal user interface including a brain-computer interface (BCI) for intuitive control of a grasp neuroprosthesis to support individuals with high spinal cord injury (SCI) in everyday activities. We describe the current state of the project, including the EEG system, preliminary results of natural movements decoding in people with SCI, the new electrode concept for the grasp neuroprosthesis, the shared control architecture behind the system and the implementation of a user-centered design
CIS is a potent checkpoint in NK cell-mediated tumor immunity
The detection of aberrant cells by natural killer (NK) cells is controlled by the integration of signals from activating and inhibitory ligands and from cytokines such as IL-15. We identified cytokine-inducible SH2-containing protein (CIS, encoded by Cish) as a critical negative regulator of IL-15 signaling in NK cells. Cish was rapidly induced in response to IL-15, and deletion of Cish rendered NK cells hypersensitive to IL-15, as evidenced by enhanced proliferation, survival, IFN-γ production and cytotoxicity toward tumors. This was associated with increased JAK-STAT signaling in NK cells in which Cish was deleted. Correspondingly, CIS interacted with the tyrosine kinase JAK1, inhibiting its enzymatic activity and targeting JAK for proteasomal degradation. Cish -/- mice were resistant to melanoma, prostate and breast cancer metastasis in vivo, and this was intrinsic to NK cell activity. Our data uncover a potent intracellular checkpoint in NK cell-mediated tumor immunity and suggest possibilities for new cancer immunotherapies directed at blocking CIS function
Computed tomography-osteoabsorptiometry for assessing the density distribution of subchondral bone as a measure of long-term mechanical adaptation in individual joints
To estimate subchondral mineralisation patterns which represent the long-term loading history of individual joints, a method has been developed employing computed tomography (CT) which permits repeated examination of living joints. The method was tested on 5 knee, 3 sacroiliac, 3 ankle and 5 shoulder joints and then investigated with X-ray densitometry. A CT absorptiometric presentation and maps of the area distribution of the subchondral bone density areas were derived using an image analyser. Comparison of the results from both X-ray densitometry and CT-absorptiometry revealed almost identical pictures of distribution of the subchondral bone density. The method may be used to examine subchondral mineralisation as a measure of the mechanical adaptability of joints in the living subject
Avaliação do incremento em volume de madeira de Quassia amara L.- Simaroubaceae, em cultivo agroecológico no trópico úmido da Costa Rica.
Quassia amara é arbusto de 3 a 6 metros de altura, tendo sido retirado indiscriminadamente das florestas para extrair do caule as quassinas usadas na indústria farmacêutica e como inseticida em agricultura orgânica. Não se tem muita informação técnica acerca do crescimento desta espécie para subsidiar estratégias de manejo sustentado. Este trabalho tem como objetivo avaliar o crescimento de Q. amara L. em cultivo agroecológico na Costa Rica. O trabalho consistiu em realizar avaliações do desenvolvimento de indivíduos de Q. amara em parcelas permanentes de medições, instaladas em meio às plantações desta espécie em consórcio com essências arbóreas. Foram efetuadas medições de diâmetro do caule a 10 cm do solo e altura total. Foi observado que em função das taxas de crescimento vegetal e incrementos médio e corrente anuais (IMA e ICA), mesmo após cinco anos de plantio, a madeira de Quassia amara para extração de quassinas não está pronta para colheita
- …