Filament-like Structures Research Articles

Evolution of filament-like compact structures in small 3 kJ dense plasma focus discharges

Evolution of filament-like compact structures in small 3 kJ dense plasma focus discharges

The cytoplasmic tail of myelin protein zero induces morphological changes in lipid membranes

The major myelin protein expressed by the peripheral nervous system Schwann cells is protein zero (P0), which represents 50% of the total protein content in myelin. This 30-kDa integral membrane protein consists of an immunoglobulin (Ig)-like domain, a transmembrane helix, and a 69-residue C-terminal cytoplasmic tail (P0ct). The basic residues in P0ct contribute to the tight packing of myelin lipid bilayers, and alterations in the tail affect how P0 functions as an adhesion molecule necessary for the stability of compact myelin. Several neurodegenerative neuropathies are related to P0, including the more common Charcot-Marie-Tooth disease (CMT) and Dejerine-Sottas syndrome (DSS) as well as rare cases of motor and sensory polyneuropathy. We found that high P0ct concentrations affected the membrane properties of bicelles and induced a lamellar-to-inverted hexagonal phase transition, which caused bicelles to fuse into long, protein-containing filament-like structures. These structures likely reflect the formation of semicrystalline lipid domains with potential relevance for myelination. Not only is P0ct important for stacking lipid membranes, but time-lapse fluorescence microscopy also shows that it might affect membrane properties during myelination. We further describe recombinant production and low-resolution structural characterization of full-length human P0. Our findings shed light on P0ct effects on membrane properties, and with the successful purification of full-length P0, we have new tools to study the role of P0 in myelin formation and maintenance in vitro.

Physicochemical analysis of deterioration affecting the darkening of rock art in Maros-Pangkep, South Sulawesi, Indonesia

This study investigates the darkening processes affecting Maros-Pangkep rock art through a comprehensive multianalytical approach. We integrate in-situ color index measurements using Nix color Pro 2 with various physicochemical characterization techniques, including optical microscopy, XRF, SEM-EDS, Raman spectroscopy, and FTIR. By examining microbial, geochemical, and anthropogenic factors on rock art pigment samples, we establish a clear correlation between the formation of blackish-gray layers and reduced chromaticity values, indicating a significant darkening process. The shift in pigment color from vibrant red or purple to a prevailing blackish-gray hue is attributed to surface accumulation. Surface morphology analysis reveals distinct blackish deposits and delicate white fibrous structures on darkened rock art. Elemental composition analysis demonstrates heightened blackish deposit formation and increased phosphorus content in darkened samples. SEM-EDS characterization exposes gypsum morphology, with filament-like structures prevailing in heavily darkened samples, highlighting the role of both geochemical and microbial factors in deposit layer formation. FTIR spectra results confirm the presence of gypsum minerals, which are attributed to the substrate minerals and/or mineral weathering product, and unveil the existence of organic compounds, indicating microbial activity. Additionally, Raman spectroscopy reveals the anthropogenic contribution, notably soot deposition produced by human activities, to the darkening of rock art. This study underscores the need for a holistic preservation approach addressing natural, human, and microbial impacts on cultural heritage sites. Further research is also needed to conduct cross-sectional stratigraphical analysis to understand the accurate mechanism of the deterioration process on the rock art. Moreover, excavation measures regarding the possible relationship of soot deposition with human activities are also important to be carried out at the sites.

Understanding the influence of β-glucan-based superabsorbent hydrogel on the digestibility of wheat starch: Gelatinization, rheological and structural properties

This study aims to evaluate the effects of β-glucan-based superabsorbent hydrogel (βCHY) on wheat starch digestibility and elucidate the underlying mechanism. The results revealed that the incorporation of βCHY led to a significant reduction in rapidly digestible starch content of wheat starch from 71% to 44%, while concurrently increasing the levels of slowly digestible starch and resistant starch in a dose-dependent manner. From a mechanistic perspective, incorporating βCHY into wheat starch notably affected their pasting behavior and influenced the rheological properties and gel strength of resulting gels. Moreover, the addition of βCHY increased the relative crystallinity, short-range ordered degree (R1047/1024), molecular order (the full width at half maximum at 480 cm−1), and thermal stability of the starch, suggesting the formation of a more stable and ordered structure. Furthermore, the wheat starch-βCHY gel complexes exhibited large, discrete layered structures with thicker layer walls, accompanied by interspersed filament-like structures. These structural alterations may collectively contribute to the reduced digestibility of wheat starch. These findings confirmed the positive effects of βCHY on the starch digestibility, offering valuable insights into the development of innovative starch-based foods with slow digestion characteristics.

The major inducible small heat shock protein HSP20-3 in the tardigrade Ramazzottius varieornatus forms filament-like structures and is an active chaperone.

The tardigrade Ramazzottius varieornatus has remarkable resilience to a range of environmental stresses. In this study, we have characterised two members of the small heat shock protein (sHSP) family in R. varieornatus, HSP20-3 and HSP20-6. These are the most highly upregulated sHSPs in response to a 24h heat shock at 35 0C of adult tardigrades with HSP20-3 being one of the most highly upregulatedgene in the whole transcriptome. Both R. varieornatus sHSPs and the human sHSP, CRYAB (HSPB5), were produced recombinantly for comparative structure-function studies. HSP20-3 exhibited a superior chaperone activity than human CRYAB in a heat-induced protein aggregation assay. Both tardigrade sHSPs also formed larger oligomers than CRYAB as assessed by size exclusion chromatography and transmission electron microscopy of negatively stained samples. Whilst both HSP20-3 and HSP20-6 formed particles that were variable in size and larger than the particles formed by CRYAB, only HSP20-3 formed filament-like structures. The particles and filament-like structures formed by HSP20-3 appear inter-related as the filament-like structures often had particles located at their ends. Sequence analyses identified two unique features; an insertion in the middle region of the N-terminal domain (NTD) and preceding the critical-sequence identified in CRYAB, as well as a repeated QNTN-motif located in the C-terminal domain of HSP20-3. The NTD insertion is expected to affect protein-protein interactions and subunit oligomerisation. Removal of the repeated QNTN-motif abolished HSP20-3 chaperone activity and also affected the assembly of the filament-like structures. We discuss the potential contribution of HSP20-3 to protein condensate formation.

Filamentary-like structures of plasma in a small 3-kJ dense plasma-focus discharge in pure deuterium

Filament-like structures were observed during discharges in a small 3-kJ plasma focus device operated with pure deuterium. These structures were recorded by means of two different laser diagnostic techniques: a schlieren system and a differential laser interferometry. They present the novel fine-scale (submillimeter) plasma structures recorded during the radial implosion, at the pinch stagnation, at the development of instabilities, and during a decay of the dense plasma column, when hard x-rays and fusion-produced neutrons were generated. The temporal uncertainty of these observations was about 2 ns, and the spatial one amounted to 40 μm. The filamentation seems be a natural and spontaneous process which occurs in high-current, hot, and dense plasmas produced in plasma focus devices. The observed filaments have usually longitudinal and/or azimuthal orientations. Their higher plasma density and appearance in regions of the measured and assumed current flows can be interpreted as the formation of plasma-current filaments with concentrated magnetic energy. These filamentary effects should be studied due to their possible role during the evolution of instabilities and the formation of small sources emitting fast electrons and ions.

Viscoelastic response of confined powder under large strain oscillations, characterized by its noise temperature

We report a study on granular matter with and without small additions of silicon oil, under low-frequency and large amplitude oscillatory shear strain under constant normal pressure, by running experiments with a rotational rheometer with a cup-and-plate geometry. We analysed the expansion with the Chebyshev polynomials of the orthogonal decomposition of stress–strain Lissajous–Bowditch loops. We found the onset of the strain amplitude for the yielding regime indicated a regime change from filament-like structures of grains to grain rearrangements for the dry granulate and from oscillations to the breaking and regeneration of liquid bridges for wet granulates. We have shown that this viscoelastic dynamics can be characterized by a noise temperature following Sollich et al. (Phys Rev Lett https://doi.org/10.1103/PhysRevLett.78.2020, 1997). The analysis of the first harmonics of the Chebyshev expansion showed that the state of disorder of dry and wet granular matter in pre-yielding and yielding regimes involved ensembles of different inherent states; thus, each of them was governed by a different noise temperature. The higher-order harmonics of the Chebyshev expansion revealed a proportionality between the viscous nonlinearity and the variation in the elastic nonlinearity induced by the deformation, which shows the coupling between the elastic deformation and the viscous flow of mesoscopic-scale structures.Graphic abstract

Gill Monogeneans (Platyhelminthes) Parasitic on <i>Gnathopogon elongatus elongatus</i> and <i>G</i>. <i>caerulescens</i> (Cypriniformes: Gobionidae) from Japan, with Descriptions of One New Species of <i>Dactylogyrus</i> and Three New Species of <i>Bivaginogyrus</i> (Dactylogyridae)

In this study we describe one new species of Dactylogyrus Diesing, 1850 and three new species of Bivaginogyrus Gussev and Gerasev in Gussev, 1985 (Monogenea: Dactylogyridae) from two freshwater fishes Gnathopogon elongatus elongatus (Temminck and Schlegel, 1846) and G. caerulescens (Sauvage, 1883) (Cypriniformes: Gobionidae) endemic to Japan. Further, G. elongatus is a new host record for Paradiplozoon skrjabini Achmerov, 1974 (Monogenea: Diplozoidae). Dactylogyrus tamoroko n. sp. is most similar to D. chenjiagengi Zhang in Zhang, Zhou, and Wen, 1990, D. clypeatus Gussev, 1955, and D. gnathopogonis Yamaguti, 1963; it differs from these three congeners by the bifurcate base of the accessory piece. Bivaginogyrus japonicus n. sp. is close to D. polylepidis Alvarez Pellitero, Simon Vicente, and Gonzalez Lanza, 1981, but it can be separated from the latter species based on its uniform-sized marginal hooks. The new species was connected to the cartilage tissue of the gill using filament-like structures, which are assumed to be derived from secretions of the reservoirs associated with each marginal hook. Bivaginogyrus cingulatus n. sp. resembles D. navicularis Gussev, 1955, D. trullaeformis Gussev, 1955, and D. imberbis Wu and Wang, 1983, but the new species is distinguished from these three species by having its inconspicuous outer roots. Bivaginogyrus exiguus n. sp. is comparable to D. pandus Wu and Wang, 1983 and D. colpodes Wu, Wang, and Song, 1983, but differs from these two species in having a shorter penis. Molecular phylogenetic analysis indicates that Bivaginogyrus is a paraphyletic group and shows affinity to “Dactylogyrus” species parasitic on gobionid fishes. However, most of those closely related Dactylogyrus species are yet to be described for their internal morphology and should accordingly be redescribed. The three new species of Bivaginogyrus are assumed to have been co-introduced along with G. e. elongatus into non-native regions of this host.

Structure and function of Plasmodium actin II in the parasite mosquito stages.

Actins are filament-forming, highly-conserved proteins in eukaryotes. They are involved in essential processes in the cytoplasm and also have nuclear functions. Malaria parasites (Plasmodium spp.) have two actin isoforms that differ from each other and from canonical actins in structure and filament-forming properties. Actin I has an essential role in motility and is fairly well characterized. The structure and function of actin II are not as well understood, but mutational analyses have revealed two essential functions in male gametogenesis and in the oocyst. Here, we present expression analysis, high-resolution filament structures, and biochemical characterization of Plasmodium actin II. We confirm expression in male gametocytes and zygotes and show that actin II is associated with the nucleus in both stages in filament-like structures. Unlike actin I, actin II readily forms long filaments in vitro, and near-atomic structures in the presence or absence of jasplakinolide reveal very similar structures. Small but significant differences compared to other actins in the openness and twist, the active site, the D-loop, and the plug region contribute to filament stability. The function of actin II was investigated through mutational analysis, suggesting that long and stable filaments are necessary for male gametogenesis, while a second function in the oocyst stage also requires fine-tuned regulation by methylation of histidine 73. Actin II polymerizes via the classical nucleation-elongation mechanism and has a critical concentration of ~0.1 μM at the steady-state, like actin I and canonical actins. Similarly to actin I, dimers are a stable form of actin II at equilibrium.

β-Sheet Structure Formation within Binary Blends of Two Spider Silk Related Peptides.

Intrinsically disordered proteins (IDPs) play an important role in molecular biology and medicine because their induced folding can lead to so-called conformational diseases, where β-amyloids play an important role. Still, the molecular folding process into the different substructures, such as parallel/antiparallel or extended β-sheet/crossed β-sheet is not fully understood. The recombinant spider silk protein eADF4(Cx) consisting of repeating modules C, which are composed of a crystalline (pep-c) and an amorphous peptide sequence (pep-a), can be used as a model system for IDP since it can assemble into similar structures. In this work, blend films of the pep-c and pep-a sequences were investigated to modulate the β-sheet formation by varying the molar fraction of pep-c and pep-a. Dichroic Fourier-transform infrared spectroscopy (FTIR), circular dichroism, spectroscopic ellipsometry, atomic force microscopy, and IR nanospectroscopy were used to examine the secondary structure, the formation of parallel and antiparallel β-sheets, their orientation, and the microscopic roughness and phase formation within peptide blend films upon methanol post-treatment. New insights into the formation of filament-like structures in these silk blend films were obtained. Filament-like structures could be locally assigned to β-sheet-rich structures. Further, the antiparallel or parallel character and the orientation of the formed β-sheets could be clearly determined. Finally, the ideal ratio of pep-a and pep-c sequences found in the fibroin 4 of the major ampullate silk of spiders could also be rationalized by comparing the blend and spider silk protein systems.

MeTACAST: Target- and Context-Aware Spatial Selection in VR.

We propose three novel spatial data selection techniques for particle data in VR visualization environments. They are designed to be target- and context-aware and be suitable for a wide range of data features and complex scenarios. Each technique is designed to be adjusted to particular selection intents: the selection of consecutive dense regions, the selection of filament-like structures, and the selection of clusters-with all of them facilitating post-selection threshold adjustment. These techniques allow users to precisely select those regions of space for further exploration-with simple and approximate 3D pointing, brushing, or drawing input-using flexible point- or path-based input and without being limited by 3D occlusions, non-homogeneous feature density, or complex data shapes. These new techniques are evaluated in a controlled experiment and compared with the Baseline method, a region-based 3D painting selection. Our results indicate that our techniques are effective in handling a wide range of scenarios and allow users to select data based on their comprehension of crucial features. Furthermore, we analyze the attributes, requirements, and strategies of our spatial selection methods and compare them with existing state-of-the-art selection methods to handle diverse data features and situations. Based on this analysis we provide guidelines for choosing the most suitable 3D spatial selection techniques based on the interaction environment, the given data characteristics, or the need for interactive post-selection threshold adjustment.

Polarization power spectra and dust cloud morphology

Context In the framework of studying cosmic microwave background polarization and characterizing its Galactic foregrounds, the angular power spectrum analysis of the thermal dust polarization map has led to intriguing evidence of an E/B asymmetry and a positive TE correlation. The interpretation of these observations is the subject of theoretical and simulation-driven studies in which the correlation between the density structure of the interstellar medium (ISM) and the magnetic field appears to be a key aspect. In this context, and when the magnetized ISM structures are modeled in three dimensions, dust clouds are generally considered to be filamentary structures only, but both filamentary and sheet-like shapes are supported by observational and theoretical evidence. Aims. We aim to study the influence of the cloud shape and its connection to the local magnetic field, as well as the influence from the viewing angle, on the angular power spectra measured on thermal dust polarization maps; we specifically focus on the dependence of the E/B power asymmetry and TE correlation. Methods. To this end, we simulated realistic interstellar clouds with both filament-like and sheet-like shapes using the software Asterion, which also allowed us to generate synthetic maps of thermal dust polarized emission with an area of 400 square degrees. Then, we computed their polarization power spectra in the multipole range ℓ ϵ [100, 500] and focused on the E/B power asymmetry, quantified through the ℛEB ratio, and the correlation coefficient rTE between Τ and Ε modes. We quantified the dependence of ℛEB and rTE values on the offset angle (between the longest cloud axis and local magnetic field lines) and inclination angle (between the line of sight and the magnetic field) for both types of cloud shapes, either embedded in a regular magnetic field or coupled to a nonregular field to mimic turbulence. Results. We find that both types of cloud shapes cover the same regions of the (ℛEB, rTE) parameter space. The dependence on the inclination and offset angles is similar for both shapes, although sheet-like structures generally show larger scatter than filamentary structures. In addition to the known dependence on the offset angle, we find a strong dependence of ℛEB and rTE on the inclination angle. Conclusions. The very fact that filament-like and sheet-like structures may lead to polarization power spectra with similar (ℛEB,rTE) values complicates their interpretation. We argue that interpreting them solely in terms of filament characteristics is risky, and in future analyses, this degeneracy should be accounted for, as should the connection to the magnetic field geometry. Our results based on maps of 400 square degrees clarify that the overall geometrical arrangement of the magnetized ISM surrounding the observer leaves its marks on polarization power spectra.

Feature Extraction of 3T3 Fibroblast Microtubule Based on Discrete Wavelet Transform and Lucy-Richardson Deconvolution Methods.

Accompanied by the increasing requirements of the probing micro/nanoscopic structures of biological samples, various image-processing algorithms have been developed for visualization or to facilitate data analysis. However, it remains challenging to enhance both the signal-to-noise ratio and image resolution using a single algorithm. In this investigation, we propose a composite image processing method by combining discrete wavelet transform (DWT) and the Lucy–Richardson (LR) deconvolution method, termed the DWDC method. Our results demonstrate that the signal-to-noise ratio and resolution of live cells’ microtubule networks are considerably improved, allowing the recognition of features as small as 120 nm. The method shows robustness in processing the high-noise images of filament-like biological structures, e.g., the cytoskeleton networks captured by fluorescent microscopes.

Structural Organization of Human Full-Length PAR3 and the aPKC–PAR6 Complex

The tripartite partition defect (PAR) polarity complex, which includes the proteins PAR3, atypical protein kinase C (aPKC), and PAR6, is a major regulator of cellular polarity. It is highly conserved and expressed in various tissues. Its largest component, PAR3, controls protein–protein interactions of the PAR complex with a variety of interaction partners, and PAR3 self-association is critical for the formation of filament-like structures. However, little is known about the structure of the PAR complex. Here, we purified non-filamentous PAR3 and the aPKC–PAR6 complex and characterized them by single-particle electron microscopy (EM). We expressed and purified an oligomerization-deficient form of PAR3, PAR3V13D,D70K, and the active aPKC–PAR6 dimer. For PAR3, engineering at two positions is sufficient to form stable single particles with a maximum dimension of 20 nm. aPKC–PAR6 forms a complex with a maximum dimension of 13.5 nm that contains single copies of aPKC. Thus, the data present a basis for further high-resolution studies of PAR proteins and PAR complex formation.

A slender body theory for the motion of special Cosserat filaments in Stokes flow

The motion of filament-like structures in fluid media has been a topic of interest since long. In this regard, a well known slender body theory exists, wherein the fluid flow is assumed to be Stokesian while the filament is modeled as a Kirchhoff rod which can bend and twist but remains inextensible and unshearable. In this work, we relax the inextensibility and unshearability constraints on filaments, i.e., the filament is modeled as a special Cosserat rod. Starting with the boundary integral formulation of Stokes flow involving the filament’s surface velocity and fluid traction that acts on the filament surface, the method of matched asymptotic expansion is used to first obtain a leading-order representation of the boundary integral kernels in the filament’s aspect ratio. We then substitute Fourier series expansion (in filament’s circumferential coordinate) of both the filament’s surface velocity and fluid traction in the aforementioned leading-order representation and further linearize it in the rod’s shear strains to reduce the two-dimensional boundary integral over the filament surface into a line integral over the filament’s centerline. Upon further collecting the coefficients of sine and cosine terms, the zeroth-order Fourier mode yields a line integral equation relating the rod’s centerline velocity with the distributed fluid force that acts on the filament. The presence of line integral makes the relation non-local in nature. On the contrary, the first-order Fourier mode yields a simpler local relation between the rod’s angular velocity and the distributed fluid couple. The line integral equation is shown to reduce to the classical slender body theory when shear strains and axial strain are set to zero. The non-dimensional governing equations of the special Cosserat rod are also derived accounting for the distributed fluid force and distributed fluid couple in them which are solved to obtain the filament motion. The presented theory is demonstrated with an example problem of the tumbling of filaments in background shear flow. We show that for relatively shorter filaments where the effect of shear and axial stretch is more dominant, the obtained results deviate from the ones based on the classical slender body theory.

Identification of 16SrII-V Phytoplasma Associated with Mungbean Phyllody Disease in Taiwan.

Mungbean (Vigna radiata (L.) R. Wilczek), an important legume crop in Asia, is primarily cultivated in the central-southern region of western Taiwan. In 2020, mungbean exhibiting typical phytoplasma-induced disease symptoms such as witches' broom, phyllody, virescence, and proliferation was observed in Yunlin County, Taiwan. Moreover, the seed harvested from diseased plants displayed premature germination. Transmission electron microscopy examination of leaf veins prepared from symptomatic mungbean demonstrated that the occlusion of sieve tubes resulted from the accumulation of phytoplasma-like bodies in sieve elements along with filament-like structures in sieve pores. The association of phytoplasma in symptomatic mungbean was confirmed by PCR analyses of the 16S ribosomal RNA (rRNA) and immunodominant membrane protein genes. Further analyses of the 16S rRNA-based phylogenetic tree and the iPhyClassifier-based virtual restriction fragment length polymorphism study demonstrated that the phytoplasma-associated mungbean phyllody disease identified in this study belongs to the 16SrII-V subgroup. BLAST analysis and the phylogenetic analysis indicated that the SAP11-like protein identified in mungbean phyllody disease is identical to peanut witches' broom phytoplasma SAP11, which explains the witches' broom phenotype observed in symptomatic mungbean. The results described in this report confirm that the 16SrII-V phytoplasma, a widely distributed phytoplasma associated with peanut witches' broom disease in Taiwan, has also infected mungbean. This is not only the first instance of mungbean phyllody disease found in Taiwan but also the first instance of mungbean phyllody disease caused by 16SrII-V subgroup phytoplasma.

Fragmentation and kinematics in high-mass star formation

Context. The formation of high-mass star-forming regions from their parental gas cloud and the subsequent fragmentation processes lie at the heart of star formation research. Aims. We aim to study the dynamical and fragmentation properties at very early evolutionary stages of high-mass star formation. Methods. Employing the NOrthern Extended Millimeter Array and the IRAM 30 m telescope, we observed two young high-mass star-forming regions, ISOSS22478 and ISOSS23053, in the 1.3 mm continuum and spectral line emission at a high angular resolution (~0.8″). Results. We resolved 29 cores that are mostly located along filament-like structures. Depending on the temperature assumption, these cores follow a mass-size relation of approximately M ∝ r2.0 ± 0.3, corresponding to constant mean column densities. However, with different temperature assumptions, a steeper mass-size relation up to M ∝ r3.0 ± 0.2, which would be more likely to correspond to constant mean volume densities, cannot be ruled out. The correlation of the core masses with their nearest neighbor separations is consistent with thermal Jeans fragmentation. We found hardly any core separations at the spatial resolution limit, indicating that the data resolve the large-scale fragmentation well. Although the kinematics of the two regions appear very different at first sight – multiple velocity components along filaments in ISOSS22478 versus a steep velocity gradient of more than 50 km s−1 pc−1 in ISOSS23053 – the findings can all be explained within the framework of a dynamical cloud collapse scenario. Conclusions. While our data are consistent with a dynamical cloud collapse scenario and subsequent thermal Jeans fragmentation, the importance of additional environmental properties, such as the magnetization of the gas or external shocks triggering converging gas flows, is nonetheless not as well constrained and would require future investigation.

Lagrangian flow effects on phytoplankton abundance and composition along filament-like structures

Influence of frontal dynamics on phytoplankton distribution and composition was studied combining in situ observations and Lagrangian computations from altimetry satellite derived currents. Four transects during the SHEBEX cruise (May 2015) over the Western Mediterranean were examined identifying a region with high spatial variability in the dynamical and biogeochemical properties. The dynamical situation unraveled from the Lagrangian analysis is dominated by filaments originated by an anticyclonic–cyclonic eddy interaction that organize the transport, modifying the biogeochemical properties of the water column and shaping the satellite derived surface Chlorophyll a (chla) distribution. The properties of the water column have been analyzed in relation to the dynamical properties of the filaments showing that local variation of the mixed layer and nutricline depths are correlated with the spatial variability of finite size Lyapunov exponents. Furthermore, the composition of phytoplankton community was studied regarding the path-accumulated properties of the flow during the formation of the filaments. In this regard new metrics accounting the Lagrangian evolution of the turbulent and topological properties of the flow along fluid parcel trajectories have been developed. Here we provide observational evidence that fluid parcels associated with high Lagrangian turbulent kinetic energy and Lagrangian positive vorticity host higher presence of larger pennate diatoms (i.e. Pseudo-nitzschia spp). Our findings indicate that the combination of these diagnostics provides an improved description of the turbulent dynamics showing that the Lagrangian properties of the flow have important biological consequences for phytoplankton to high ecological levels.

Nanoscale oligopeptide adsorption behaviour on chlorite as revealed by scanning probe microscopy and density functional simulations

In the present work, the interaction between simple oligopeptides of L-alanine (di-L-alanine) and the (001) surface of clinochlore was characterized in details by employing cross-correlated atomic force microscopy (AFM) observations and Density Functional Theory (DFT) simulations. The AFM results showed that the mineral surface is able to stably bind L-alanine peptides preferentially onto the brucite-like sheets of clinochlore during an interaction in a water suspension. In particular, the (001) surface acted as a condensing and agglomerating system, where AFM evidenced di-L-alanine oligopeptides organized in dot-like, agglomerates and filament-like structures up to more than 160 nm in length, in the experimental conditions here used. DFT simulations were conducted to analyse at the atomic scale the interaction between di-L-alanine oligopeptides and the mineral, finding the molecular conformation with the lowest energy, the adsorption (binding) energy between the oligopeptide and the brucitic surface and also the hydrogen bonding scheme. The reported findings constitute a further step towards the comprehension of the interaction mechanisms between fundamental biomolecules and clay mineral surfaces, of paramount importance for environmental sequestration and biotechnological purposes, but also for prebiotic chemistry research.

The Importance of a Filament-like Structure in Aerial Dispersal and the Rarefaction Effect of Air Molecules on a Nanoscale Fiber: Detailed Physics in Spiders' Ballooning.

Many flying insects utilize a membranous structure for flight, which is known as a "wing." However, some spiders use silk fibers for their aerial dispersal. It is well known that spiders can disperse over hundreds of kilometers and rise several kilometers above the ground in this way. However, little is known about the ballooning mechanisms of spiders, owing to the lack of quantitative data. Recently, Cho et al. discovered previously unknown information on the types and physical properties of spiders' ballooning silks. According to the data, a crab spider weighing 20 mg spins 50-60 ballooning silks simultaneously, which are about 200 nm thick and 3.22 m long for their flight. Based on these physical dimensions of ballooning silks, the significance of these filament-like structures is explained by a theoretical analysis reviewing the fluid-dynamics of an anisotropic particle (like a filament or a high-slender body). (1) The filament-like structure is materially efficient geometry to produce (or harvest, in the case of passive flight) fluid-dynamic force in a low Reynolds number flow regime. (2) Multiple nanoscale fibers are the result of the physical characteristics of a thin fiber, the drag of which is proportional to its length but not to its diameter. Because of this nonlinear characteristic of a fiber, spinning multiple thin ballooning fibers is, for spiders, a better way to produce drag forces than spinning a single thick spider silk, because spiders can maximize their drag on the ballooning fibers using the same amount of silk dope. (3) The mean thickness of fibers, 200 nm, is constrained by the mechanical strength of the ballooning fibers and the rarefaction effect of air molecules on a nanoscale fiber, because the slip condition on a fiber could predominate if the thickness of the fiber becomes thinner than 100 nm.