Overhang control in topology optimization: a comparison of continuous front propagation-based and discrete layer-by-layer overhang control

Although additive manufacturing (AM) allows for a large design freedom, there are some manufacturing limitations that have to be taken into consideration. One of the most restricting design rules is the minimum allowable overhang angle. To make topology optimization suitable for AM, several algorithms have been published to enforce a minimum overhang angle. In this work, the layer-by-layer overhang filter proposed by Langelaar (Struct Multidiscip Optim 55(3):871–883, 2017), and the continuous, front propagation-based, overhang filter proposed by van de Ven et al. (Struct Multidiscipl Optim 57(5):2075–2091, 2018) are compared in detail. First, it is shown that the discrete layer-by-layer filter can be formulated in a continuous setting using front propagation. Then, a comparison is made in which the advantages and disadvantages of both methods are highlighted. Finally, the continuous overhang filter is improved by incorporating complementary aspects of the layer-by-layer filter: continuation of the overhang filter and a parameter that had to be user-defined are no longer required. An implementation of the improved continuous overhang filter is provided.

Short-term fate of seagrass and macroalgal detritus in Arenicola marina bioturbated sediments

Seagrass meadows are globally important ecosystems for carbon (C) sequestration. However, bioturbation by benthic fauna can alter the distribution, degradation and overall preservation of C in the sediment. We performed a 4 wk laboratory experiment to investigate the short-term degradation and burial of 2 major C sources in bare sediments associated with seagrass ecosystems. Eelgrass Zostera marina and macroalgal (Fucus vesiculosus) detritus were amended in sediment with and without bioturbation by the common polychaete Arenicola marina. Bioturbation did not significantly affect the loss of eelgrass detritus (>0.5 mm), but caused a rapid burial of this material as a discrete layer (55% recovery) at sediment depths ranging from 8 to 14 cm. A. marina effects on macroalgal detritus were more pronounced, resulting, in total, in an 80% loss of macroalgal detritus by microbial degradation and worm ingestion. We conclude that A. marina bioturbation effectively buries eelgrass detritus into deep anoxic sediments, but we cannot confirm that this leads to enhanced C preservation in coastal ecosystems. In contrast, A. marina bioturbation significantly increases the degradation of macroalgal tissue, and it is unlikely that this detritus is a major source for permanent C burial.

Nanometer control in plasmonic systems through discrete layer-by-layer macrocycle–cation deposition

We demonstrate that cucurbit[7]uril coordinates Fe3+ to yield a novel and well-defined metallic nanopolymer with great potential as plasmonic system.

Discrete Layer Jamming for Variable Stiffness Co-Robot Arms

Continuous layer jamming is an effective tunable stiffness mechanism that utilizes vacuum to vary friction between laminates enclosed in a membrane. In this paper, we present a discrete layer jamming mechanism that is composed of a multilayered beam and multiple variable pressure clamps placed discretely along the beam; system stiffness can be varied by changing the pressure applied by the clamps. In comparison to continuous layer jamming, discrete layer jamming is simpler as it can be implemented with dynamic variable pressure actuators for faster control, better portability, and no sealing issues due to no need for an air supply. Design and experiments show that discrete layer jamming can be used for a variable stiffness co-robot arm. The concept is validated by quasi-static cantilever bending experiments. The measurements show that clamping 10% of the beam area with two clamps increases the bending stiffness by around 17 times when increasing the clamping pressure from 0 to 3 MPa. Computational case studies using finite element analysis for the five key parameters are presented, including clamp location, clamp width, number of laminates, friction coefficient, and number of clamps. Clamp location, number of clamps, and number of laminates are found to be most useful for optimizing a discrete layer jamming design. Actuation requirements for a variable pressure clamp are presented based on results from laminate beam compression tests.

A Simple Microbiome in the European Common Cuttlefish,Sepia officinalis

ABSTRACTThe European common cuttlefish,Sepia officinalis, is used extensively in biological and biomedical research, yet its microbiome remains poorly characterized. We analyzed the microbiota of the digestive tract, gills, and skin in mariculture-raisedS. officinalisusing a combination of 16S rRNA amplicon sequencing, quantitative PCR (qPCR), and fluorescence spectral imaging. Sequencing revealed a highly simplified microbiota consisting largely of two single bacterial amplicon sequence variants (ASVs) ofVibrionaceaeandPiscirickettsiaceae. The esophagus was dominated by a single ASV of the genusVibrio. Imaging revealed bacteria in the familyVibrionaceaedistributed in a discrete layer that lines the esophagus. ThisVibriowas also the primary ASV found in the microbiota of the stomach, cecum, and intestine, but occurred at lower abundance, as determined by qPCR, and was found only scattered in the lumen rather than in a discrete layer via imaging analysis. Treatment of animals with the commonly used antibiotic enrofloxacin led to a nearly 80% reduction of the dominantVibrioASV in the esophagus but did not significantly alter the relative abundance of bacteria overall between treated versus control animals. Data from the gills were dominated by a single ASV in the familyPiscirickettsiaceae, which imaging visualized as small clusters of cells. We conclude that bacteria belonging to theGammaproteobacteriaare the major symbionts of the cuttlefishSepia officinaliscultured from eggs in captivity and that the esophagus and gills are major colonization sites.IMPORTANCEMicrobes can play critical roles in the physiology of their animal hosts, as evidenced in cephalopods by the role ofVibrio(Aliivibrio)fischeriin the light organ of the bobtail squid and the role ofAlpha- andGammaproteobacteriain the reproductive system and egg defense in a variety of cephalopods. We sampled the cuttlefish microbiome throughout the digestive tract, gills, and skin and found dense colonization of an unexpected site, the esophagus, by a microbe of the genusVibrio, as well as colonization of gills byPiscirickettsiaceae. This finding expands the range of organisms and body sites known to be associated withVibrioand is of potential significance for understanding host-symbiont associations, as well as for understanding and maintaining the health of cephalopods in mariculture.

Free vibration and buckling analysis of composite sandwich plates in thermal environment

In this work, a first-order discrete layer model is performed to deal with the free vibration and buckling analysis of composite sandwich plates in thermal environment. Owing to considering the effect of rotary inertias and shear deformation, thin-to-moderately thick shells can be analyzed. The differential equations of motion are derived from Hamilton’s principle, and account for the nonlinear variation of the in-plane and transverse displacements through the thickness due to temperature variation. These equations are solved by means of the closed-form Navier method, and validated by comparing the numerical results obtained by the present method with the findings published in literatures. Finally, the variation tendency of critical buckling temperature with material parameters is evaluated and shown graphically.

A simple microbiome in the European common cuttlefish, Sepia officinalis

ABSTRACTThe European common cuttlefish, Sepia officinalis, is used extensively in biological and biomedical research yet its microbiome remains poorly characterized. We analyzed the microbiota of the digestive tract, gills, and skin in mariculture-raised S. officinalis using a combination of 16S rRNA amplicon sequencing, qPCR and fluorescence spectral imaging. Sequencing revealed a highly simplified microbiota consisting largely of two single bacterial amplicon sequence variants (ASVs) of Vibrionaceae and Piscirickettsiaceae. The esophagus was dominated by a single ASV of the genus Vibrio. Imaging revealed bacteria in the family Vibrionaceae distributed in a discrete layer that lines the esophagus. This Vibrio was also the primary ASV found in the microbiota of the stomach, cecum, and intestine, but occurred at lower abundance as determined by qPCR and was found only scattered in the lumen rather than in a discrete layer via imaging analysis. Treatment of animals with the commonly-used antibiotic enrofloxacin led to a nearly 80% reduction of the dominant Vibrio ASV in the esophagus but did not significantly alter the relative abundance of bacteria overall between treated versus control animals. Data from the gills was dominated by a single ASV in the family Piscirickettsiaceae, which imaging visualized as small clusters of cells. We conclude that bacteria belonging to the Gammaproteobacteria are the major symbionts of the cuttlefish Sepia officinalis cultured from eggs in captivity, and that the esophagus and gills are major colonization sites.IMPORTANCEMicrobes can play critical roles in the physiology of their animal hosts, as evidenced in cephalopods by the role of Vibrio (Aliivibrio) fischeri in the light organ of the bobtail squid and the role of Alpha- and Gammaproteobacteria in the reproductive system and egg defense in a variety of cephalopods. We sampled the cuttlefish microbiome throughout the digestive tract, gills, and skin and found dense colonization of an unexpected site, the esophagus, by a microbe of the genus Vibrio, as well as colonization of gills by Piscirickettsiaceae. This finding expands the range of organisms and body sites known to be associated with Vibrio and is of potential significance for understanding host-symbiont associations as well as for understanding and maintaining the health of cephalopods in mariculture.