Central Filament Research Articles

Architecture and regulation of filamentous human cystathionine beta-synthase

Cystathionine beta-synthase (CBS) is an essential metabolic enzyme across all domains of life for the production of glutathione, cysteine, and hydrogen sulfide. Appended to the conserved catalytic domain of human CBS is a regulatory domain that modulates activity by S-adenosyl-L-methionine (SAM) and promotes oligomerisation. Here we show using cryo-electron microscopy that full-length human CBS in the basal and SAM-bound activated states polymerises as filaments mediated by a conserved regulatory domain loop. In the basal state, CBS regulatory domains sterically block the catalytic domain active site, resulting in a low-activity filament with three CBS dimers per turn. This steric block is removed when in the activated state, one SAM molecule binds to the regulatory domain, forming a high-activity filament with two CBS dimers per turn. These large conformational changes result in a central filament of SAM-stabilised regulatory domains at the core, decorated with highly flexible catalytic domains. Polymerisation stabilises CBS and reduces thermal denaturation. In PC-3 cells, we observed nutrient-responsive CBS filamentation that disassembles when methionine is depleted and reversed in the presence of SAM. Together our findings extend our understanding of CBS enzyme regulation, and open new avenues for investigating the pathogenic mechanism and therapeutic opportunities for CBS-associated disorders.

A low-frequency sub-arcsecond view of powerful radio galaxies in rich-cluster environments: 3C 34 and 3C 320

ABSTRACT Models of radio galaxy physics have been primarily based on high frequency (≥1 GHz) observations of their jets, hotspots, and lobes. Without highly resolved low-frequency observations, which provide information on older plasma, our understanding of the dynamics of radio galaxies and their interaction with their environment is limited. Here, we present the first sub-arcsecond (0.3 arcsec) resolution images at 144 MHz of two powerful radio galaxies situated in rich cluster environments, namely 3C 34 and 3C 320, using the International Low Frequency Array Telescope. We detect for the first time at low frequencies a plethora of structures in these objects, including strikingly large filaments across the base of the lobes in both sources, which are spatially associated with dense regions in the ambient medium. For 3C 34, we report a spectral flattening in the region of the central filament, suggesting that the origin of the filaments is related to the presence of large-scale ordered magnetic fields. We also report periodic total intensity and spectral index banding of diffuse emission in the eastern lobe, seen for the first time in radio galaxy lobes. The hotspot complexes are resolved into multiple fragments of varying structure and spectral index; we discuss the implications for particle acceleration and jet termination models. We find at most smooth gradients in the spectral behaviour of the hotspot structure suggesting that particle acceleration, if present, may be occurring throughout the complex, in contrast to simple models, but different jet termination models may apply to both sources.

Stabilization of membrane topologies by proteinaceous remorin scaffolds

In plants, the topological organization of membranes has mainly been attributed to the cell wall and the cytoskeleton. Additionally, few proteins, such as plant-specific remorins have been shown to function as protein and lipid organizers. Root nodule symbiosis requires continuous membrane re-arrangements, with bacteria being finally released from infection threads into membrane-confined symbiosomes. We found that mutations in the symbiosis-specific SYMREM1 gene result in highly disorganized perimicrobial membranes. AlphaFold modelling and biochemical analyses reveal that SYMREM1 oligomerizes into antiparallel dimers and may form a higher-order membrane scaffolding structure. This was experimentally confirmed when expressing this and other remorins in wall-less protoplasts is sufficient where they significantly alter and stabilize de novo membrane topologies ranging from membrane blebs to long membrane tubes with a central actin filament. Reciprocally, mechanically induced membrane indentations were equally stabilized by SYMREM1. Taken together we describe a plant-specific mechanism that allows the stabilization of large-scale membrane conformations independent of the cell wall.

New Continuum and Polarization Observations of the Cygnus Loop with FAST. II. Images and Analyses

We present total-intensity and polarized-intensity images of the Cygnus Loop supernova remnant (SNR) observed by the Five-hundred-meter Aperture Spherical radio Telescope. The high angular-resolution and high-sensitivity images enable us to thoroughly compare the properties of the northern part with the southern part of the SNR. The central filament in the northern part and the southern part have a similar foreground rotation measure, meaning their distances are likely similar. The polarization analysis indicates that the random magnetic field is larger than the regular field in the northern part, but negligible in the southern part. The total-intensity image is decomposed into components of various angular scales, and the brightness-temperature spectral index of the shell structures in the northern part is similar to that in the southern part in the component images. All the evidence suggests that the northern and southern parts of the Cygnus Loop are situated and thus evolved in different environments of interstellar medium, while belonging to the same SNR.

Comparison of Two Methods for Deriving the Magnetic Field in a Filament Channel

Understanding the magnetic structure of filament channels is difficult but essential for identifying the mechanism (s) responsible for solar eruptions. In this paper we characterize the magnetic field in a well-observed filament channel with two independent methods, prominence seismology and magnetohydrodynamics flux-rope modeling, and compare the results. In 2014 May and June, active region 12076 exhibited a complex of filaments undergoing repeated oscillations over the course of 12 days. We measure the oscillation periods in the region with both Global Oscillation Network Group Hα and Solar Dynamics Observatory (SDO) Advanced Imaging Assembly EUV images, and then utilize the pendulum model of large-amplitude longitudinal oscillations to calculate the radius of curvature of the fields supporting the oscillating plasma from the derived periods. We also employ the regularized Biot–Savart laws formalism to construct a flux-rope model of the field of the central filament in the region based on an SDO Helioseismic and Magnetic Imager magnetogram. We compare the estimated radius of curvature, location, and angle of the magnetic field in the plane of the sky derived from the observed oscillations with the corresponding magnetic-field properties extracted from the flux-rope model. We find that the two models are broadly consistent, but detailed comparisons of the model and specific oscillations often differ. Model observation comparisons such as these are important for advancing our understanding of the structure of filament channels.

Triggering Shock Wave Positions by Patterned Energy Deposition

The problem considered in this work is shock wave (SW) positioning control in shock-dominated flows. Experiments are conducted to investigate the triggering effect of patterned near-surface electrical discharges on SW reflection from plane walls. In the wind tunnel, M=4, P0 = 4 bar, a solid wedge SW generator is mounted on the upper wall. Q-DC filamentary electrical discharges were arranged on the opposite wall, so that the SW from the wedge impinged on the plasma filaments that are arranged flow-wise in either a row of three or a single central filament. Within the supersonic flow, narrow subsonic areas are actuated by electrical discharge thermal deposition, resulting in pressure redistribution, which, in turn, relocates the reflection of impinging SW to a predefined position. Mie scattering, schlieren imaging, and wall pressure measurements are used to explore the details of plasma-SW interaction. Using Mie scattering, the three-dimensional shape of the SW structure is mapped both before and after electrical discharge activation. Plasma-based triggering mechanisms are described in terms of the physical principles of flow control and a criterion for determining the effectiveness of the flowfield control.

Corncob structures in dental plaque reveal microhabitat taxon specificity

BackgroundThe human mouth is a natural laboratory for studying how bacterial communities differ across habitats. Different bacteria colonize different surfaces in the mouth—teeth, tongue dorsum, and keratinized and non-keratinized epithelia—despite the short physical distance between these habitats and their connection through saliva. We sought to determine whether more tightly defined microhabitats might have more tightly defined sets of resident bacteria. A microhabitat may be characterized, for example, as the space adjacent to a particular species of bacterium. Corncob structures of dental plaque, consisting of coccoid bacteria bound to filaments of Corynebacterium cells, present an opportunity to analyze the community structure of one such well-defined microhabitat within a complex natural biofilm. Here, we investigate by fluorescence in situ hybridization and spectral imaging the composition of the cocci decorating the filaments.ResultsThe range of taxa observed in corncobs was limited to a small subset of the taxa present in dental plaque. Among four major groups of dental plaque streptococci, two were the major constituents of corncobs, including one that was the most abundant Streptococcus species in corncobs despite being relatively rare in dental plaque overall. Images showed both Streptococcus types in corncobs in all individual donors, suggesting that the taxa have different ecological roles or that mechanisms exist for stabilizing the persistence of functionally redundant taxa in the population. Direct taxon-taxon interactions were observed not only between the Streptococcus cells and the central corncob filament but also between Streptococcus cells and the limited subset of other plaque bacteria detected in the corncobs, indicating species ensembles involving these taxa as well.ConclusionsThe spatial organization we observed in corncobs suggests that each of the microbial participants can interact with multiple, albeit limited, potential partners, a feature that may encourage the long-term stability of the community. Additionally, our results suggest the general principle that a precisely defined microhabitat will be inhabited by a small and well-defined set of microbial taxa. Thus, our results are important for understanding the structure and organizing principles of natural biofilms and lay the groundwork for future work to modulate and control biofilms for human health.DJxteJ7vGqLvWEg9EZAKHDVideo

Acute toxicity of trichlorfon and histological changes in the gills of Arapaima gigas, a neotropical fish from Amazon

Trichlorfon is a widely used drug to control ectoparasites in fish farming and is effective in treating protozoa, helminths, and crustaceans. However, prior to a concentration recommendation made for therapeutic purposes in aquaculture, it is necessary to establish its toxicity, behavioural and histological effects, and determine a safe use dose for each target species. Here we investigated the acute toxicity (LC50-12 h) of trichlorfon and its behavioural and histological effects on arapaima (Arapaima gigas) larvae and juveniles. For the acute toxicity tests (LC50), arapaima larvae and juveniles were exposed at 0, 50, 250, 500, 750, 1.000 and 1.250 mg L−1 of trichlorfon for 12 h. During this period, behavioural changes, mortality, and the water physico-chemical parameters were recorded. Immediately after a toxicity test, gills were collected for the histological analysis. The LC50–12 h for the arapaima larvae and juveniles were 411.8 mg L−1 and 587.3 mg L−1, respectively. The fish exposed for different times to the 250, 500, 750, 1.000 and 1.250 mg L−1 concentrations showed a dose-dependent effect with behavioural changes, such as erratic swimming, loss of balance, lethargy, gasping at the water surface and muscle spasms. Histological changes, such as lamellar hyperplasia and cell hypertrophy, total lamellar fusion, dilation, and vascular congestion in the central filament vessel, interlamellar hyperplasia, capillary congestion, proliferation of mucous cells, dilation of the venous sinus and capillaries, leukocyte infiltrate and haemorrhage, were observed and ranged from mild to diffuse lesions. However, branchial necrosis was presented only in the fish exposed to ≥ 500 mg L−1 of trichlorfon. In conclusion, sublethal trichlorfon concentrations (≤ 250 mg L−1) and short exposure times (up to 180 min) can be safely used in arapaima larvae and juveniles because they do not alter their normal behaviour nor induce mortalities and/or irreversible injuries to their gills.

Abstract OR-5: Helicobacter pylori Surface Structures

Background: Helicobacter pylori, which infects at least half of the human population, is an etiopathogenetic factor in the development of chronic gastritis (CG), gastric and duodenal ulcer disease (UD), and is also considered a risk factor in the occurrence of some forms of stomach cancer. Various surface structures of H. pylori are important pathogenic factors. Methods: Reference (NCTC 11637, NCTC 11639) and freshly isolated H. pylori strains as well as samples of the gastric mucosa were examined using transmission (TEM) and scanning electron microscopy (SEM) by means of “JEM-100 В” (JEOL, Japan) and “Quanta 200 3D” (FEI Company, USA) systems, respectively. Samples for SEM fixed with formalin and not subjected to dehydration were sprayed with an electrically conductive layer of gold. Samples for TEM were prepared using negative contrast (NC) with ammonium molybdate and ultrathin sections (US) contrasted by Reynolds; fixation by Ito-Karnovsky was used in both cases. Accelerating voltage at TEM and SEM was 80 and 10 kV, respectively. Results: Three types of H. pylori surface structures were found: flagella, fimbria, and vesicles. Flagella were found both in the material of cultures maintained in vitro and in each native sample of the gastric mucosa. SEM images suggest the involvement of flagella in biofilm formation. On longitudinal sections of the flagellum, the outer electron-dense layer and the inner content in the form of a filament were visualized; on cross sections, the flagellum looked like an annular structure with a centrally located point accumulation of electron-dense matter. Paradoxically, the H. pylori forms with a defective cell wall also possessed flagella. Freely located flagellar sheaths without central filament were often found in vitro only. Fimbriae were found exclusively in negatively contrasted pure bacterial cultures material. In addition, vesicles detaching from the surface of bacterial cells were found both in the material of aging H. pylori pure cultures and in native samples of the gastric mucosa under CG and UD. A small part of the vesicles retains their connection with the cell wall, while detached vesicles are present in excess in the surrounding space. Massive detachment of vesicles leads to the formation of spheroplasts, devoid of an outer membrane. Conclusion: H. pylori has a representative set of surface structures that play an important role in the onset and development of the infectious process in the gastroduodenal area.

Taxonomic revision of Saundersella (Ectocarpales s.l., Phaeophyceae) from the northwestern Pacific with description of Saundersella crassa sp. nov. and transfer of Heterosaundersella hattoriana to Saundersella

ABSTRACT Saundersella crassa sp. nov. (Ectocarpales s.l., Phaeophyceae) is newly described from cold-water regions of Japan and the northern Pacific. Saundersella crassa is similar to S. simplex (generitype) in morphology and has been identified as S. simplex in the area, but it has longer and thicker thalli, grows on different basiphytes (S. crassa on Chordaria spp vs S. simplex on Analipus spp) and is genetically distinct in the mitochondrial cox3 and chloroplast atpB, psaA, psbA and rbcL DNA sequences. The erect thalli of S. crassa were simple, filiform, soft and gelatinous, solid when young but later becoming hollow, cord-shaped, attenuated at the base to an indistinct stipe, at times twisted, yellowish to olive brown, and up to 50(–90) cm long and 5 mm wide. The erect thalli were composed of multiaxial colourless central medullary filaments and pigmented assimilatory filaments of 2–6 cells. Terminal cells of the assimilatory filaments were large and swollen, spherical or obovate. Unilocular zoidangia were sessile and obovate or irregular in shape, and were formed on erect thalli at the end of medullary cells or at the base of assimilatory filaments. In the molecular phylogeny, the type of the genus Heterosaundersella, H. hattoriana, was sister to S. crassa and was nested in the clade composed of S. simplex and S. crassa, irrespective of their differences in the habit and occurrence of basal prostrate thalli forming plurilocular zoidangia. Therefore, we propose the new combination S. hattoriana comb. nov. for H. hattoriana. Heterosaundersella thus becomes a taxonomic synonym of Saundersella.

Mechanism of filament formation in UPA-promoted CARD8 and NLRP1 inflammasomes

NLRP1 and CARD8 are related cytosolic sensors that upon activation form supramolecular signalling complexes known as canonical inflammasomes, resulting in caspase−1 activation, cytokine maturation and/or pyroptotic cell death. NLRP1 and CARD8 use their C-terminal (CT) fragments containing a caspase recruitment domain (CARD) and the UPA (conserved in UNC5, PIDD, and ankyrins) subdomain for self-oligomerization, which in turn form the platform to recruit the inflammasome adaptor ASC (apoptosis-associated speck-like protein containing a CARD) or caspase-1, respectively. Here, we report cryo-EM structures of NLRP1-CT and CARD8-CT assemblies, in which the respective CARDs form central helical filaments that are promoted by oligomerized, but flexibly linked, UPAs surrounding the filaments. Through biochemical and cellular approaches, we demonstrate that the UPA itself reduces the threshold needed for NLRP1-CT and CARD8-CT filament formation and signalling. Structural analyses provide insights on the mode of ASC recruitment by NLRP1-CT and the contrasting direct recruitment of caspase-1 by CARD8-CT. We also discover that subunits in the central NLRP1CARD filament dimerize with additional exterior CARDs, which roughly doubles its thickness and is unique among all known CARD filaments. Finally, we engineer and determine the structure of an ASCCARD–caspase-1CARD octamer, which suggests that ASC uses opposing surfaces for NLRP1, versus caspase-1, recruitment. Together these structures capture the architecture and specificity of the active NLRP1 and CARD8 inflammasomes in addition to key heteromeric CARD-CARD interactions governing inflammasome signalling.

Morphology transition from diffuse to diffuse-and-filamentary for an argon plume with varying sinusoidal frequency or voltage amplitude

With increasing sinusoidal frequency or its voltage amplitude, a central filament emerges in a diffuse plume downstream of an argon jet with a single-electrode geometry. The plume with a co-existing filament and diffuse part, also referred to as a diffuse-and-filamentary (DAF) plume, is formed after a sudden length increment from a diffuse plume. Only one negative discharge appears per voltage cycle for the diffuse plume. Besides the negative discharge, there is one positive discharge per voltage cycle for the DAF plume. By fast photography, negative discharge behaves as plump plasma bullets propagating along the argon flow, which results in diffuse plume or the diffuse part of the DAF plume. Comparatively, positive discharge behaves as slim bullets, leading to the filament formation. Based on optical emission spectroscopy, it is found that both electron density and electron temperature increase with increasing sinusoidal frequency or voltage amplitude for negative and positive discharges. Moreover, there are abrupt increments in them for negative discharge during the morphology transition. Compared with negative discharge, the positive one has higher electron density and electron temperature. All of the experimental phenomena mentioned above are qualitatively explained through considering the discharge enhancement by residual active species.

Pulling-force generation by ensembles of polymerizing actin filaments

The process by which actin polymerization generates pulling forces in cellular processes such as endocytosis is less well understood than pushing-force generation. To clarify the basic mechanisms of pulling-force generation, we perform stochastic polymerization simulations for a square array of polymerizing semiflexible actin filaments, having different interactions with the membrane. The filaments near the array center have a strong attractive component. Filament bending and actin-network elasticity are treated explicitly. We find that the outer filaments push on the membrane and the inner filaments pull, with a net balance of forces. The total calculated pulling force is maximized when the central filaments have a very deep potential well, and the outer filaments have no well. The steady-state force is unaffected by the gel rigidity, but equilibration takes longer for softer gels. The force distributions are flat over the pulling and pushing regions. Actin polymerization is enhanced by softening the gel or reducing the filament binding to the membrane. Filament-membrane detachment can occur for softer gels, even if the total binding energy of the filaments to the membrane is 100 or more. It propagates via a stress-concentration mechanism similar to that of a brittle crack in a solid, and the breaking stress is determined by a criterion similar to that of the ‘Griffith’ theory of crack propagation.

Star Formation Efficiencies at Giant Molecular Cloud Scales in the Molecular Disk of the Elliptical Galaxy NGC 5128 (Centaurus A)

Abstract We present ALMA CO (1−0) observations toward the dust lane of the nearest elliptical and radio galaxy, NGC 5128 (Centaurus A), with high angular resolution (∼1″, or 18 pc), including information from large to small spatial scales and total flux. We find a total molecular gas mass of 1.6 × 109 M ⊙ and reveal the presence of filamentary components more extended than previously seen, up to a radius of 4 kpc. We find that the global star formation rate is ∼1 M ⊙ yr−1, which yields a star formation efficiency (SFE) of 0.6 Gyr−1 (depletion time τ = 1.5 Gyr), similar to those in disk galaxies. We show the most detailed view to date (40 pc resolution) of the relation between molecular gas and star formation within the stellar component of an elliptical galaxy, from a scale of several kiloparsecs to the circumnuclear region close to the powerful radio jet. Although on average the SFEs are similar to those of spiral galaxies, the circumnuclear disk (CND) presents SFEs of 0.3 Gyr−1, lower by a factor of 4 than the outer disk. The low SFE in the CND is in contrast to the high SFEs found in the literature for the circumnuclear regions of some nearby disk galaxies with nuclear activity, probably as a result of larger shear motions and longer active galactic nucleus feedback. The higher SFEs in the outer disk suggest that only central molecular gas or filaments with sufficient density and strong shear motions will remain in ∼1 Gyr, which will later result in the compact molecular distributions and low SFEs usually seen in other giant ellipticals with cold gas.

Melanothamnus maniticola sp. nov. (Ceramiales, Rhodophyta): an epizoic species evolved for living on the West Indian Manatee.

Over 35 macroalgae have been documented growing epizoically on sea turtles, and macroalgae are also known to grow on the West Indian Manatee, but the number and identity of these latter species have not been determined. Analysis of DNA sequences of 12 samples collected from different manatees captured in three areas of Florida indicated that they represented a single undescribed species within the Rhodomelaceae genus Melanothamnus. Morphological analysis revealed Melanothamnus characteristics but also a previously undescribed combination of character states. These include eight to nine, but as many as 11, pericentral cells; heavy cortication restricted to the base of thalli, and a sharp transition between the corticated and ecorticate sections of the thallus; cells surrounding the ostiole being similar in size to the outer pericarp cells immediately below, and robust rhizoids that have no terminal lobes and develop from central axial cell filaments instead of pericentral cells. The unique characteristics of the rhizoids may be evolutionary adaptations for anchoring the thalli to manatee epidermis. This species is described as M. maniticola sp. nov.

Standing Waves of Fixed Period for $$n+1$$ Vortex Filaments

The $$n+1$$ vortex filament problem has explicit solutions consisting of n parallel filaments of equal circulation in the form of nested polygons uniformly rotating around a central filament which has circulation of opposite sign. We show that when the relation between temporal and spatial periods is fixed at certain rational numbers, these configurations have an infinite number of homographic time dependent standing wave patterns that bifurcate from these uniformly rotating central configurations.

In-Service Microstructural Modifications caused by Fatigue Phenomena leading to the Failure of a High-Voltage Cable

Abstract This study analyses the causes leading to the failure of a high-voltage cable in regions close to it “mooring” at the end near to one of the high-voltage towers. The horizontal span of the cable between moorings was over 1040 m, with a difference in elevation between high-voltage towers of approximately 300 m. The conductor was made up of 30 aluminium strands with a 7 strands eutectoid steel core. The aluminium filaments were distributed in 2 layers, an outer layer with 18 filaments and an inner layer with 12. The steel filaments were distributed in a layer composed of 6 filaments surrounding a single central filament. All the filaments had a diameter of 2.6 mm. Cold drawn and twisted aluminium and the possible presence of recovery substructures in regions close to the fracture were analysed by means of optical microscopy. The steel was similarly studied, verifying its pearlitic nature and assessing the existence of softening phenomena due to recovery or recrystallization. The thicknesses of the zinc coating on the steel filaments were determined. The fracture faces of the aluminium and steel filaments were analysed by scanning electron microscopy and the fused remains resulting from possible arcs between the aluminium filaments were examined. In order to assess the deterioration of the filaments, tensile tests were performed on all the individual filament in regions adjacent to and at a certain distance from the fracture. The failure of the conductor had its origin in the outer aluminium filaments due to causes imputable to fatigue phenomena. The reduction in the cross-section of the conductor led to an increase in temperature, leading to the weakening of the remaining aluminium filaments and their subsequent failure, the electrical current being subsequently transferred to the steel core. The increase in electrical resistivity characteristic of steel led to a significant increase in temperature that drastically decreased the mechanical strength of the steel cables.

Magnetic field structure in Serpens South

Abstract We made near-infrared polarimetric observations toward Serpens South. This region contains three dense filaments that are roughly parallel to one another. Using the histogram of relative orientations, the three filaments are found to be roughly perpendicular to the global magnetic field. The morphology of the plane-of-sky (POS) magnetic field and molecular gas suggests that the magnetic field plays an important role in the filament formation and evolution. Applying the Davis–Chandrasekhar–Fermi method, the POS magnetic field strengths are estimated to be 10–80$\, \mu$G. The evaluated mass-to-flux ratios indicate that the center filament is magnetically supercritical, while the others are approximately magnetically critical. We speculate that the filaments are formed by fragmentation of a sheet-like cloud that was created through the gravitational contraction of a magnetized, turbulent cloud.

A numerical and experimental study of the compression uniaxial properties of PLA manufactured with FDM technology based on product specifications

This paper presents a numerical and experimental study of the compression uniaxial properties of PLA material manufactured with FDM based on product specifications. A first experimental test in accordance with the requirements and conditions established in the ISO 604 standard characterizes the mechanical and elastic properties of PLA manufactured with FDM technology and product requirements in a uniaxial compression stress field by testing six specimens. A second experimental test allows analyzing the structural behavior of the industrial case, evaluating the compression stiffness, the compression yield stress, the field of displacements, and stress along its elastic area until reaching the compression yield stress and the ultimate yield stress data. To improve the structural analysis of the case study, a numerical validation was carried out using two analytical models. The first analytical model applies an interpolation procedure to the experimental results of the tested specimens in order to characterize the uniaxial tension-compression curve versus the nominal deformations by means of an 8-degree polynomial function. The second model defines the plastic material as elastic and isotropic with Young’s compression modulus constant and according to the guidelines established in ISO standard 604. The comparison between experimental tests and numerical simulation results for the study case verify that the new model that uses the proposed polynomial function is closer to the experimental solution with only an 0.36% error, in comparison with the model with Young’s compression modulus constant that reaches an error of 4.27%. The results of the structural analysis of the mechanical element indicate that the elastic region of the plastic material PLA manufactured with FDM can be modeled numerically as an isotropic material, using the elastic properties from the experimental results of the specimens tested according to ISO standard 604. In this way, it is possible to characterize the PLA FDM material as isotropic, obtaining as an advantage its easy definition in the numerical simulation software as it does not require the modification of the constitutive equations in the material database. SEM micrographs have indicated that the fracture of the failed test specimens is of the brittle type, mainly caused by the separation between the central plastic filament layers of the specimens. The results presented suggest that the use of FDM technology with PLA material is promising for the manufacture of low volume industrial components that are subject to compression efforts or for the manufacture of components by the user.

Dust spectrum and polarisation at 850 μm in the massive IRDC G035.39-00.33

Context. The sub-millimetre polarisation of dust emission from star-forming clouds carries information on grain properties and on the effects that magnetic fields have on cloud evolution. Aims. Using observations of a dense filamentary cloud G035.39-00.33, we aim to characterise the dust emission properties and the variations of the polarisation fraction. Methods. JCMT SCUBA-2/POL-2 observations at 850 μm were combined with Planck 850 μm(353 GHz) data to map polarisation fraction at small and large scales. With previous total intensity SCUBA-2 observations (450 and 850 μm) and Herschel data, the column densities were determined via modified black-body fits and via radiative transfer modelling. Models were constructed to examine how the observed polarisation angles and fractions depend on potential magnetic field geometries and grain alignment processes. Results. POL-2 data show clear changes in the magnetic field orientation. These are not in contradiction with the uniform orientation and almost constant polarisation fraction seen by Planck, because of the difference in the beam sizes and the POL-2 data being affected by spatial filtering. The filament has a peak column density of N(H2) ~ 7 × 1022 cm−2, a minimum dust temperature of T ~ 12 K, and a mass of ~4300 M⊙ for the area N(H2) > 5 × 1021 cm−2. The estimated average value of the dust opacity spectral index is β ~ 1.9. The ratio of sub-millimetre and J-band optical depths is τ (250 μm)∕τ (J) ~ 2.5 × 10−3, more than four times the typical values for diffuse medium. The polarisation fraction decreases as a function of column density to p ~ 1% in the central filament. Because of noise, the observed decrease of p(N) is significant only at N(H2) > 2 × 1022 cm−2. The observations suggest that the grain alignment is not constant. Although the data can be explained with a complete loss of alignment at densities above ~104 cm−3 or using the predictions of radiative torques alignment, the uncertainty of the field geometry and the spatial filtering of the SCUBA-2 data prevent strong conclusions. Conclusions. The G035.39-00.33 filament shows strong signs of dust evolution and the low polarisation fraction is suggestive of a loss of polarised emission from its densest parts.