An Easy Method to Determine the Effective Conductivity of Carbon Fiber Composites Using a Wall Perturbation Approach

Carbon-fiber-reinforced plastics (CFRPs) are of increasing popularity in a wide range of applications, and microwave curing promises significant reduction in processing times. However, for the design of an efficient microwave curing system, the composites’ effective material parameters must be known. This work presents a measurement system using a wall perturbation approach with a coaxial cavity to determine the effective conductivity of a CFRP along the fiber direction

Small-Size Coaxial Resonant Applicator for Microwave Heating Assisted Additive Manufacturing

This article introduces the design and analysis of a small-size coaxial resonant applicator for high-speed microwave heating-assisted additive manufacturing of multiple materials, such as continuous carbon fiber reinforced polymer composites, thermoplastic, and metal parts. The elaborated coaxial resonant applicator reduces the size and has a resonant frequency between 2.4 and 2.5 GHz. A TEM wave is stimulated in the applicator where the electrical field is polarized perpendicular to the filaments and, therefore, allows a maximum penetration depth. The electrical conductive filament is designed as a part of the inner conductor to enhance coupling efficiency. To prevent microwave leakage induced by the conductive material, a compact quarter wavelength filter was developed. The equivalent circuit of the filter was used to analyze the influence of structural parameters on the resonance frequency. The filter has been tested and good agreement between measured and simulated results is obtained. The heating behavior with varying input power has been investigated for polyamide, polylactic acid, and continuous carbon fiber reinforced polyamide filaments

The Potential of UAV Imagery for the Detection of Rapid Permafrost Degradation: Assessing the Impacts on Critical Arctic Infrastructure

Ground subsidence and erosion processes caused by permafrost thaw pose a high risk to infrastructure in the Arctic. Climate warming is increasingly accelerating the thawing of permafrost, emphasizing the need for thorough monitoring to detect damages and hazards at an early stage. The use of unoccupied aerial vehicles (UAVs) allows a fast and uncomplicated analysis of sub-meter changes across larger areas compared to manual surveys in the field. In our study, we investigated the potential of photogrammetry products derived from imagery acquired with off-the-shelf UAVs in order to provide a low-cost assessment of the risks of permafrost degradation along critical infrastructure. We tested a minimal drone setup without ground control points to derive high-resolution 3D point clouds via structure from motion (SfM) at a site affected by thermal erosion along the Dalton Highway on the North Slope of Alaska. For the sub-meter change analysis, we used a multiscale point cloud comparison which we improved by applying (i) denoising filters and (ii) alignment procedures to correct for horizontal and vertical offsets. Our results show a successful reduction in outliers and a thorough correction of the horizontal and vertical point cloud offset by a factor of 6 and 10, respectively. In a defined point cloud subset of an erosion feature, we derive a median land surface displacement of (Formula presented.) m from 2018 to 2019. Projecting the development of the erosion feature, we observe an expansion to NNE, following the ice-wedge polygon network. With a land surface displacement of (Formula presented.) m and an alignment root mean square error of (Formula presented.) m, we find our workflow is best suitable for detecting and quantifying rapid land surface changes. For a future improvement of the workflow, we recommend using alternate flight patterns and an enhancement of the point cloud comparison algorithm

Combination of Scattering Matrix Code and Process Model to Optimize a Microwave Applicator Suitable for the Stabilization of PAN Fibers

Carbon fiber production is an energy intensive process requiring new approaches for energy efficient heating. One possible option might be the dielectric heating. A basic requirement to design an efficient applicator is the knowledge of the variation of dielectric properties during processing. The experience shows strongly increasing dielectric loss of a Polyacrylonitrile (PAN) fiber with increasing temperatures while it decreases during the chemical transformation in the stabilization stage. For the applicator design an electrical field that counteracts the variation of the dielectric loss is a suitable choice. In this presentation the focus is on the combination of the generalized scattering matrix (GSM) code with a process model. It shall allow for the optimization of the geometry of a cylindrical resonator usable during the stabilization stage of the PAN fiber. The scattering matrix code is utilized to calculate the field profile of a cylindrical resonator with step-wise changing diameter that acts as applicator. The number of steps can be varied, depending on the ability of production and spacial requirements

Condensate formation and multiscale dynamics in two-dimensional active suspensions

The collective effects of microswimmers in active suspensions result in active turbulence, a spatiotemporally chaotic dynamics at mesoscale, which is characterized by the presence of vortices and jets at scales much larger than the characteristic size of the individual active constituents. To describe this dynamics, Navier-Stokes-based one-fluid models driven by small-scale forces have been proposed. Here, we provide a justification of such models for the case of dense suspensions in two dimensions (2d). We subsequently carry out an in-depth numerical study of the properties of one-fluid models as a function of the active driving in view of possible transition scenarios from active turbulence to large-scale pattern, referred to as condensate, formation induced by the classical inverse energy cascade in Newtonian 2d turbulence. Using a one-fluid model it was recently shown (Linkmann et al., Phys. Rev. Lett. (in press)) that two-dimensional active suspensions support two non-equilibrium steady states, one with a condensate and one without, which are separated by a subcritical transition. Here, we report further details on this transition such as hysteresis and discuss a low-dimensional model that describes the main features of the transition through nonlocal-in-scale coupling between the small-scale driving and the condensate

Phase Transition to Large Scale Coherent Structures in Two-Dimensional Active Matter Turbulence

The collective motion of microswimmers in suspensions induce patterns of vortices on scales that are much larger than the characteristic size of a microswimmer, attaining a state called bacterial turbulence. Hydrodynamic turbulence acts on even larger scales and is dominated by inertial transport of energy. Using an established modification of the Navier-Stokes equation that accounts for the small scale forcing of hydrodynamic flow by microswimmers, we study the properties of a dense supensions of microswimmers in two dimensions, where the conservation of enstrophy can drive an inverse cascade through which energy is accumulated on the largest scales. We find that the dynamical and statistical properties of the flow show a sharp transition to the formation of vortices at the largest length scale. The results show that 2d bacterial and hydrodynamic turbulence are separated by a subcritical phase transition.Comment: postprint versio

Increased vegetative development and sturdiness of storekeeper-transgenic tobacco

The STOREKEEPER (STK) family of DNA-binding proteins work as transcription factors and the ectopic expression of two stk-like genes from Arabidopsis thaliana, stk01 (At1g61730) and stk03 (At4g00238), in tobacco increased the number of vegetative internodes and promoted plant and leaf size, stem diameter and sturdiness. The development of these plants started with rosette formation while pronounced shoot elongation and flowering was delayed. Moreover, when the STK01 and STK03 proteins were fused to the Herpes Simplex Virus VP16 transcriptional activation domain and expressed in tobacco the vigorous storekeeper-phenotype did not appear indicating that transgenic STK-like proteins in part worked as repressors of tobacco reproductive development. Furthermore, Yeast Two-Hybrid screenings proved that STK01 and STK03 can form homodimers and heterodimers with further members of the STKlike family. Therefore, we assume that interactions between transgenic Arabidopsis STKs and resident tobacco STKs could have contributed to the observed developmental changes in transgenic tobacco. Our findings open up promising applications for overexpression of stk-like genes in crops that benefit from increased sturdiness and vegetative organ development, such as tobacco in molecular farming approaches, biomass-based energy crops and medicinal plants that produce bioactive compounds in leaves

Intraperitoneal Mesh Implantation for Fascial Dehiscence and Open Abdomen

Background: Postoperative fascial dehiscence and open abdomen are severe postoperative complications and are associated with surgical site infections, fistula, and hernia formation at long-term follow-up. This study was designed to investigate whether intraperitoneal implantation of a composite prosthetic mesh is feasible and safe. Methods: A total of 114 patients with postoperative fascial dehiscence and open abdomen who had undergone surgery between 2001 and 2009 were analyzed retrospectively. Contaminated (wound class 3) or dirty wounds (wound class 4) were present in all patients. A polypropylene-based composite mesh was implanted intraperitoneally in 51 patients, and in 63 patients the abdominal wall was closed without mesh implantation. The primary endpoint was incidence of incisional hernia, and the incidence of enterocutaneous fistula was a secondary endpoint. Results: The incidence of enterocutaneous fistulas after wound closure post-fascial dehiscence (13% vs. 6% without and with mesh, respectively) or post-open abdomen (22% vs. 28% without and with mesh, respectively) was not significantly different. The incidence of incisional hernia was significantly lower with mesh implantation compared with no-mesh implantation in both contaminated (4% vs. 28%; p=0.025) and dirty abdominal cavities (5% vs. 34%; p=0.01). Conclusions: Intra-abdominal contamination is not a contraindication for intra-abdominal mesh implantation. The incidence of enterocutaneous fistula is not elevated despite the presence of contamination. The rate of incisional hernias is significantly reduced after intraperitoneal mesh implantation for postoperative fascial dehiscence or open abdome

Synchro-Modality and Slow Steaming: New Business Perspectives in Freight Transportation

The logistics sector faces substantial challenges in meeting customer demands for higher service quality, speed and flexibility under conditions of continued growth in world trade and worldwide transportation movements, increasing distances and vulnerabilities of the supply chain. Additional challenges relate to the economic and environmental sustainability of logistics operations. While a lot of attention was devoted in the past decades to the operational and technical aspects, the business development phase has been put aside, causing the market failure of several projects. The paper presents the SYNCHRO-modal supply chain eco-NET (SYNCHRO-NET) project, which will demonstrate the effectiveness of slow steaming combined with synchro-modality in reducing the cost and the emissions of international supply chains and improving reliability and sustainability through the optimization of the planning process. Differently from other similar projects, SYNCHRO-NET combines operational aspects with a business perspective and represents a stakeholder-driven approach aimed at developing a close-to-market solution over the timeframe of the project

Towards representing thermokarst processes in land surface models

Large-scale Earth system and land surface models often lack an adequate representation of subgrid-scale processes in permafrost landscapes. Small-scale processes such as thermokarst formation might, however, considerably impact the energy and carbon budgets in way which is not resolved within large-scale models. Since a spatially high-resolved simulation of such processes is not feasible, novel techniques for up-scaling subgrid processes are demanded. Within this work a one-dimensional model of the ground thermal regime of land surfaces, CryoGrid 3, is employed to conceptually represent small-scale features of permafrost landscapes, particularly those related to thermokarst. For example, the model has been shown to adequately describe the degradation of permafrost underneath waterbodies in a warming climate. Using tiling approaches such point-wise realizations can be up-scaled in a statistical way in order to represent larger land surface units. The model development is closely linked to field campaigns to the Lena River Delta in Siberia which offers very diverse land surface features such as polygonal tundra and thermos-erosional valleys. These features are related to the region’s diverse soil stratigraphies, in particular the occurrence of ice-rich ground. Combining field measurements with modelling ultimately allows an improvement in the qualitative and quantitative understanding of the typical geomorphological processes in permafrost landscapes and their representation in large-scale models