Regular Striations Research Articles

Salinity Fronts in the South Atlantic

Monthly climatology data for salinity fronts in the South Atlantic have been created from satellite SMOS sea surface salinity (SSS) measurements taken from 2011–2019, processed at the Barcelona Expert Center of Remote Sensing (BEC), and provided as high-resolution (1/20°) daily SSS data. The SSS fronts have been identified with narrow zones of enhanced horizontal gradient magnitude (GM) of SSS, computed using the Belkin–O’Reilly algorithm (BOA). The SSS gradient fields generated by the BOA have been log-transformed to facilitate feature recognition. The log-transformation of SSS gradients markedly improved the visual contrast of gradient maps, which in turn allowed new features to be revealed and previously known features to be documented with a monthly temporal resolution and a mesoscale (~100 km) spatial resolution. Monthly climatologies were generated and analyzed for large-scale open-ocean SSS fronts and for low-salinity regions maintained by the Rio de la Plata discharge, Magellan Strait outflow, Congo River discharge, and Benguela Upwelling. A 2000 km-long triangular area between Africa and Brazil was found to be filled with regular quasi-meridional mesoscale striations that form a giant ripple field with a 100 km wave length. South of the Tropical Front, within the subtropical high-salinity pool, a trans-ocean quasi-zonal narrow linear belt of meridional SSS maximum (Smax) was documented. The meridional Smax belt shifts north–south seasonally while retaining its well-defined linear morphology, which is suggestive of a yet unidentified mechanism that maintains this feature. The Subtropical Frontal Zone (STFZ) consists of two tenuously connected fronts, western and eastern. The Brazil Current Front (BCF) extends SE between 40 and 45°S to join the subantarctic front (SAF). The STFZ trends NW–SE across the South Atlantic, seemingly merging with the SAF/BCF south of Africa to form a single front between 40 and 45°S. In the SW Atlantic, the Rio de la Plata plume migrates seasonally, expanding northward in winter (June–July) from 39°S into the South Brazilian Bight, up to Cabo Frio (23°S) and beyond. The inner Plata front moves in and out seasonally. Farther south, the Magellan Strait outflow expands northward in winter (June–July) from 53°S up to 39–40°S to nearly join the Plata outflow. In the SE Atlantic, the Congo River plume spreads radially from the river mouth, with the spreading direction varying seasonally. The plume is often bordered from the south by a quasi-zonal front along 6°S. The diluted Congo River water spreads southward seasonally down to the Angola–Benguela Front at 16°S. The Benguela Upwelling is delineated by a meridional front, which extends north alongshore up to 20°S, where the low-salinity Benguela Upwelling water forms a salinity front, which is separate from the thermal Angola–Benguela Front at 16°S. The high-salinity tropical water (“Angola water”) forms a wedge between the low-salinity waters of the Congo River outflow and Benguela Upwelling. This high-salinity wedge is bordered by salinity fronts that migrate north–south seasonally.

LNOx Emission Model for Air Quality and Climate Studies Using Satellite Lightning Mapper Observations

AbstractA lightning nitrogen oxides (LNOx) emissions model using satellite‐observed lightning optical energy is introduced for utilization in Air Quality modeling systems. The effort supports assessments of air‐quality/climate coupling as related to the influence of LNOx on atmospheric chemistry. The Geostationary Lightning Mapper (GLM), International Space Station Lightning Imaging Sensor (ISS‐LIS), and the Tropical Rainfall Measuring Mission (TRMM) LIS data are used to examine the efficacy of the method, extend the previously derived LNOx record, and demonstrate a path for using ISS‐LIS observations to cross‐calibrate regional LNOx estimates from the future global constellation of geostationary lightning observations. A detailed evaluation of the GLM data set is provided to establish the robustness of observations for LNOx estimates and to make preliminary assessments of the LNOx emissions model. Seasonal and geographical variation, land/ocean contrast, and annual fluctuation in the GLM observed lightning activity and flash optical energy are provided. GLM detection substantially degrades with the increase in the field of view, resulting in 44% more flashes and 40% less optical energy observation by GLM‐16 (compared to GLM‐17) to the east of the middle‐longitude between the two mappers (106.2°W). Regular horizontal striations are found in the optical energy product. On average, GLM flashes matched to the cloud‐to‐ground flashes have ∼30% longer duration, 50%–70% more extension, and ≥100% higher optical energy compared to the unmatched flashes (assumed to be intra‐cloud). The results from summer‐long chemical transport simulations using LNOx generated from the emission model agrees with previous studies and shows consistency across the GLM/LIS data sets.

The Striation-Correlation-Based Beamforming for Estimating the Green’s Function in a Shallow Water Waveguide

In shallow water, there exist regular interference striations on the structured sound intensity pattern versus frequency and element location of a horizontal array. Beamforming along the striation with frequency-shifted pressure can improve the correlation among array signals, but the beam focusing performance is limited by the source spectrum (e.g. random phase spectrum generated from ship-radiated noise) and signal truncation. In this paper, the cross-correlation phase relationship among the array signals is deduced, and striation-based beamforming with such cross-correlated data can produce a similar directivity to the conventional beamforming, while the effect from signal truncation and source spectrum can be eliminated. This striation-correlation-based beamforming also outputs the signal corresponding to the Green’s function between the source and the reference array element, moreover, recovers the interference structure that characters the channel. The striation-based array signal processing also provides the proposed Greens function estimation method with the ability to work effectively under the condition of low signal-to-noise ratio. Simulation results are presented and performance variations related to signal frequency, signal-to-noise ratio, striation slope estimation error, element number and array aperture are also analyzed numerically.

A Review of Cluster Wideband Data Multi‐Spacecraft Observations of Auroral Kilometric Radiation

AbstractWe review important advances in the understanding of auroral kilometric radiation (AKR) resulting from observations by the Wideband Data instruments on the four Cluster spacecraft. AKR is an intense radio emission originating in the Earth's auroral regions with frequencies typically in the range 50–700 kHz, usually observed from space. It is now widely accepted that AKR is generated by the cyclotron maser instability (CMI) in density cavities in the auroral acceleration region. Multi‐point observations by the Cluster spacecraft with a time delay of arrival technique have allowed the source locations of many individual AKR bursts to be determined. The position uncertainty is around 500 km at the source region or about 200 km when mapped on to the auroral zone. AKR is emitted in a narrow beam close to the tangent to the magnetic field vector in the source region. This has important implications for the possible generation mechanisms, being incompatible with filled or hollow cone beaming models. It also implies that an observer at a given location can only see AKR from a fraction of possibly active source regions. The complex frequency time structure of AKR sometimes shows regular striations or pulsations. Cluster observations of these phenomena have been interpreted as modulation of the CMI by disturbances propagating through the generation region. Exceptionally, AKR can sometimes be observed from low altitude spacecraft or even on the ground. Recent work has involved simultaneous observations of AKR on the Cluster spacecraft and on the ground at the South Pole.

Rhodopsins build up the birefringent bodies of the dinoflagellate Oxyrrhis marina

The ultrastructure of the birefringent bodies of the dinoflagellate Oxyrrhis marina was investigated by transmission electron microscopy. Ultrathin sectioning revealed that the bodies consist of highly ordered and densely packed lamellae, which show a regular striation along their longitudinal axis. A lattice distance of 6.1 nm was measured for the densely packed lamellae by FFT (Fast Fourier Transformation) analysis. In addition, a rather faint and oblique running striation was registered. Lamellae sectioned rather oblique or almost close to the surface show a honeycombed structure with a periodicity of 7.2–7.8 nm. Freeze-fracture transmission electron microscopy revealed that the lamellae are composed of highly ordered, crystalline arrays of particles. Here, FFT analysis resulted in lattice distances of 7.0–7.6 nm. Freeze-fracture transmission electron microscopy further revealed that the bodies remained intact after cell rupture followed by ascending flotation of the membrane fractions on discontinuous sucrose gradients. The birefringent bodies most likely are formed by evaginations of membranes, which separate the cytoplasm from the food vacuoles. Distinct, slightly reddish-colored areas, which resembled the birefringent bodies with respect to size and morphology, were registered by bright field light microscopy within Oxyrrhis marina cells. An absorbance maximum at 540 nm was registered for these areas, indicating that they are composed of rhodopsins. This was finally proven by immuno-transmission electron microscopy, as antisera directed against the C-terminal amino acid sequences of the rhodopsins AEA49880 and ADY17806 intensely immunolabeled the birefringent bodies of Oxyrrhis marina.

Influence of the laser cutting front geometry on the striation formation analysed with high-speed synchrotron X-ray imaging

The generation of low surface roughness of the cut edge during laser beam cutting is a challenge. The striation pattern, which determines the surface roughness, can be distinguished into regular and interrupted striations, the latter resulting in an increased surface roughness. In order to analyse their formation, the space- and time-resolved cutting front geometry and melt film thickness were captured during laser beam fusion cutting of aluminium sheets with a framerate of 1000 Hz by means of high-speed synchrotron X-ray imaging. The comparison of the contours of the cutting fronts for a cut result with regular und interrupted striations shows that the contour fluctuates significantly more in case of interrupted striations. This leads to a strong fluctuation of the local angle of incidence. In addition, the average angle of incidence decreases, which results in an increase of the average absorbed irradiance. Both phenomena, local increase of absorbed irradiance and its dynamic fluctuation, result in a local increase of the melt film thickness at the cutting front which is responsible for the formation of the interrupted striations.

Abnormal interference of very low frequency sound field in shallow water

In a multi-channel seismic exploration experiment in the South Yellow Sea, a tuned air gun array with a shooting interval of 37.5m was used as broadband pulse source, and a horizontal line array with 336 elements is used to receive transmitted signals. The received single shot records in the range-time domain are transformed into an interference pattern in the range-frequency domain using Fourier transform. It is found that there is an abnormal interference pattern of the very low frequency (VLF) sound field in the stratified shallow water environment. It is a complex nonlinear structure, no longer regular striations in the range-frequency domain. The mechanism of this particular interference pattern is interpreted according to normal mode theory. In shallow water stratified leaky waveguide, VLF sound propagates as waterborne modes and bottom-trapped modes. These two kinds of normal mode interfere with each other and form the particular stable interference pattern. In the experimental environment, the group speeds for these two type normal modes change differently with frequency. And it causes slope of interference striations change from positive to negative with increase of frequency. The theoretical simulation results are in good agreement with the experimental data. It is shown that the structure of interference pattern is sensitive to bottom structure and geoacoustic parameters.

Skeletal Muscles: Insight into Embryonic Development, Satellite Cells, Histology, Ultrastructure, Innervation, Contraction and Relaxation, Causes, Pathophysiology, and Treatment of Volumetric Muscle I

Background: Skeletal muscles are attached to bone and are responsible for the axial and appendicular movement of the skeleton and for maintenance of body position and posture. Objectives: The present review aimed to high light on embryonic development of skeletal muscles, histological and ultrastructure, innervation, contraction and relaxation, causes, pathophysiology, and treatment of volumetric muscle injury. The heterogeneity of the muscle fibers is the base of the flexibility which allows the same muscle to be used for various tasks from continuous low-intensity activity, to repeated submaximal contractions, and to fast and strong maximal contractions. The formation of skeletal muscle begins during the fourth week of embryonic development as specialized mesodermal cells, termed myoblasts. As growth of the muscle fibers continues, aggregation into bundles occurs, and by birth, myoblast activity has ceased. Satellite cells (SCs), have single nuclei and act as regenerative cells. Satellite cells are the resident stem cells of skeletal muscle; they are considered to be self-renewing and serve to generate a population of differentiation-competent myoblasts that will participate as needed in muscle growth, repair, and regeneration. Based on various structural and functional characteristics, skeletal muscle fibres are classified into three types: Type I fibres, Type II-B fibres, and type II-A fibres. Skeletal muscle fibres vary in colour depending on their content of myoglobin. Each myofibril exhibits a repeating pattern of cross-striations which is a product of the highly ordered arrangement of the contractile proteins within it. The parallel myofibrils are arranged with their cross-striations in the register, giving rise to the regular striations seen with light microscopy in longitudinal sections of skeletal muscle. Each skeletal muscle receives at least two types of nerve fibers: motor and sensory. Striated muscles and myotendinous junctions contain sensory receptors that are encapsulated proprioceptors. The process of contraction, usually triggered by neural impulses, obeys the all-or-none law. During muscle contraction, the thin filaments slide past the thick filaments, as proposed by Huxley's sliding filament theory. In response to a muscle injury, SCs are activated and start to proliferate; at this stage, they are often referred to as either myogenic precursor cells (MPC) or myoblasts. In vitro, evidence has been presented that satellite cells can be pushed towards the adipogenic and osteogenic lineages, but contamination of such cultures from non-myogenic cells is sometimes hard to dismiss as the underlying cause of this observed multipotency. There are, however, other populations of progenitors isolated from skeletal muscle, including endothelial cells and muscle-derived stem cells (MDSCs), blood-vessel-associated mesoangioblasts, muscle side-population cells, CD133+ve cells, myoendothelial cells, and pericytes. Volumetric muscle loss (VML) is defined as the traumatic or surgical loss of skeletal muscle with resultant functional impairment. It represents a challenging clinical problem for both military and civilian medicine. VML results in severe cosmetic deformities and debilitating functional loss. In response to damage, skeletal muscle goes through a well-defined series of events including; degeneration (1 to 3days), inflammation, and regeneration (3 to 4 weeks), fibrosis, and extracellular matrix remodeling (3 to 6 months).. Mammalian skeletal muscle has an impressive ability to regenerate itself in response to injury. During muscle tissue repair following damage, the degree of damage and the interactions between muscle and the infiltrating inflammatory cells appear to affect the successful outcome of the muscle repair process. The transplantation of stem cells into aberrant or injured tissue has long been a central goal of regenerative medicine and tissue engineering. Conclusion: It can be concluded that the formation of skeletal muscle begins during the fourth week of embryonic development as specialized mesodermal cells, termed myoblasts, by birth myoblast activity has ceased. Satellite cells are considered to be self-renewing, and serve to generate a population of differentiation-competent myoblasts. Skeletal muscle fibres are classified into three types. The process of contraction, usually triggered by neural impulses, obeys the all-or-none law. VML results in severe cosmetic deformities and debilitating functional loss. Mammalian skeletal muscle has an impressive ability to regenerate itself in response to injury. The transplantation of stem cells into aberrant or injured tissue has long been a central goal of regenerative medicine and tissue engineering.

Tailored Bonded Interfacial Intermolecular Entanglement of Polyethylene/Ultrahigh-Molecular-Weight Polyethylene Blends: Enhancing Miscibility, Reinforcement, and Friction Reduction

For achieving a well-miscible and highly enhanced polyethylene/ultrahigh-molecular-weight polyethylene (PE/UHMWPE) blend, which is an important blend for polyolefin materials with wide applications, tailored bonded interfacial intermolecular entanglement between the two phases was innovatively constructed via a facile reactive melt process through reaction between epoxy and carboxyl groups grafted onto polymer chains. The UHMWPE phase with obvious decreasing size and distribution was tightly embedded in a PE matrix, and the interfacial transition area increased dramatically, leading to forming a homogeneous and miscible blend. Meanwhile, the viscoelasticity and molecular entanglement density were improved remarkably, indicating an enhanced interfacial intermolecular diffusion, and a tight and robust dual network structure with covalent linkage and intermolecular entanglements was constructed in the blend. Obvious deformation with regular striation and many pulling-out UHMWPE fibrils were observed on an impact-fractured surface, and mechanical strength/toughness of the blend was remarkably enhanced. Furthermore, the wear rate and the friction coefficient were reduced significantly, and the worn surface presented smooth and flat features, confirming highly improved mechanical and tribological properties of the blend. This work provided a facile method to fabricate an enhanced PE/UHMWPE blend with application potential.

A combined Langendorff-injection technique for simultaneous isolation of single cardiomyocytes from atria and ventricles of the rat heart

Single cardiomyocytes are widely used for investigations of the cellular and molecular mechanisms of regulation and modulation of cardiac performance. Intact cardiomyocytes allow one to study in detail cell function avoiding the effects of extracellular matrix and neighboring cells. The most established protocols of cardiomyocyte isolation are based on the isolated heart perfusion using a Langendorff-apparatus or on intraventricular perfusion using a syringe. However, the yield of single cardiomyocytes obtained by these methods may be low due to the cell injury following non-uniform enzyme digestion of connective tissue in different heart chambers. Moreover, isolation of atrial cardiomyocytes is challenging because of their small size and complex geometric shape. Here we present a new protocol for simultaneous isolation of high quality cardiomyocytes from the atria, ventricular free walls and interventricular septum. The protocol is based on the combination of the Langendorff perfusion method with the intraventricular and intra-atrial injection technique taking into account the collagen content variation between the different heart chambers. Obtained cells demonstrate rod-shaped morphology, a clear and regular sarcomere striation pattern and rat-specific frequency-dependence of contraction and calcium transient parameters. Our protocol provides gentle cell isolation that increases the yield of single cardiomyocytes suitable for biophysical researches .

Performance Metrics for Striation-based Beamforming and Application Requirements with the Horizontal Line Array in Shallow Water

Due to the dispersion of normal modes in shallow water, there exist regular striations on the interference spectrogram in space-frequency domain. Based on the range-frequency domain striations, waveguide invariant can be estimated with the prior knowledge of source range. Utilizing striations along the array, Rouseff and Zurk [J. Acoust. Soc. Amer. 130 (2011) EL76–EL81] proposed the striation-based beamforming (SBF), which shows a theoretical possibility to estimate waveguide invariant that is independent of source range. To make this beamforming technique more practical, its application requirements and performance limitation should be defined. These two issues are researched with the phase and amplitude relationships deduced by the frequency-shift compensation theory. It shows the source whose spectrum varies slowly and received signals that contain the complete information of transmission time are keys for applying SBF to real work. The azimuth limitation can lead to the degradation of array gain and distortion of interference structure. Matching parameters of waveguide invariant and source range, respectively, two modified striation-based beamformers are developed to eliminate the azimuth limitation. Simulation and experimental results are presented.

Fatigue behaviour of an additively manufactured ductile gas turbine superalloy

Additive manufacturing (AM) offers new possibilities in gas turbine technology by allowing for more complex geometries. However, the fatigue performance, including crack initiation and crack propagation of AM gas turbine material, is not fully known. In addition, AM materials shows anisotropic properties due to the columnar grain growth in the building direction during the AM process, which needs to be accounted for. Also, an AM component often solidifies with a cellular dendritic structure during the manufacturing process. In the present study, the bulk material of an AM adopted nickel-based superalloy based on Hastelloy X was subjected to low-cycle fatigue (LCF) loading at room temperature. The LCF tests were conducted in strain control on additively manufactured smooth bars,with two different build orientations (with an angle of 0° and 90° relative to the building platform). The LCF results showed that the major part of the fatigue life is spent in the crack initiation phase, namely 78% to 99% of the total fatigue life. Based on the experiments, a model to predict the crack initiation life was developed that takes the anisotropic material behaviour into account. The last part of the fatigue life, the crack propagation phase, was studied on a microstructural level, where initial fractography of the ruptured LCF specimens revealed that the dendritic structure was visible on the fracture surface. It was noted that the dendritic structure could easily be mistaken for regular striations although they represent a different fracture mechanism. The fracture surfaces were therefore cross sectioned and possible correlations between fracture surface characteristics and underlying microstructure were studied using electron backscatter diffraction and electron channelling contrast imaging. The outcome showed that the dendritic structure had some effect on the LCF crack propagation behaviour by interdendritic tearing, which was discussed.

Effect of additive manufacturing on fatigue crack propagation of a gas turbine superalloy

Additive manufacturing (AM) offers new possibilities in gas turbine technology by, for example, allowing for more complex internal cooling channels. One such application, where AM can improve the function by new designs, is burners. However, the fatigue performance, especially the fatigue crack propagation of AM gas turbine material, is not fully known. In the present study, an AM adopted nickel-based superalloy Hastelloy X was subjected to low-cycle fatigue (LCF) loading at room temperature. The LCF tests were conducted in strain control on additive manufactured smooth bars with two different build orientations (with an angle of 0° and 90° relative to the building platform). During the the manufacturing process, an AM component often solidifies with a dendritic structure. Initial fractography of the ruptured LCF specimens revealed that the dendritic structure was visible on the fracture surface. It was noted that the dendritic structure could easily be mistaken for regular striations although they represent a different fracture mechanism. The fracture surfaces were therefore cross sectioned and possible correlations between fracture surface characteristics and underlying microstructure were studied using electron backscatter diffraction and electron channelling contrast imaging. The outcome was used to discuss the effect of AM microstructure on the LCF crack propagation.

Effect of morphology development on mechanical properties and fracture behavior of PP/EPDM/SiO2 blend-nanocomposites

The main objective of the present work was to study the effects of dispersion and distribution of the silica nanoparticles in ternary PP/EPDM/SiO2 systems. Different morphologies were developed via applying different feeding orders (one-step or two-step) as well as alteration in functionality of the rubbery phase (EPDM or EPDM-g-MA). Morphological characterizations were performed using direct SEM observation and indirect dynamic-mechanical analysis. The results showed that the main toughening mechanism of the ternary systems was shear yielding of the PP matrix, while the corresponding binary reference PP/EPDM or PP/EPDM-g-MA blends underwent internal cavitation of the rubbery phases. This led to increased toughness and stiffness of the ternary blend-nanocomposites compared to the binary blends, representative of the synergistic effects of the soft rubber phase and the rigid silica nanoparticles. This synergy effect was much more obvious when the silica nanoparticles were preferentially localized around the rubber domains, leading to the overlapping of the stress fields within the PP matrix which, in turn, led to the formation of regular striations during impact testing. On the contrary, localization of most of the nanoparticles within the rubbery phase masked the stiffness and rigidity of the silica phase and, as a consequence, led to lower mechanical performance compared to other ternary systems.

Heteromorphism in seeds ofLeptocereus scopulophilus(Cactaceae) from Pan de Matanzas, Cuba

AbstractSeed heteromorphism is the formation of different seed morphs from the same individual. Two seed morphs have been preliminarily observed inLeptocereus scopulophilus. One morph shows an apparent natural scarification of its coat. Herein we describe the seeds, taking into account shape, coat integrity, surface, dimensions, mass and the position of germination cracks. We defined two seed morphs using the integrity of the spermoderma: fragmented seed coats (FSC) and complete seed coats (CSC). We also evaluated minimum germination time, germination rate and germinability. The seed morphs did not differ significantly in traits; however, regular striations along the cuticle of the periclinal walls were more visible in the FSC compared with the CSC. Both seed morphs displayed anticlinal cell boundaries in the border region that are channelled and straight in the dorsal-ventral region but difficult to define in the lateral region. We found four morphological variations in different positions where the radicle or cotyledons emerge and variations in cuticle thickness in different regions of the seed that could determine the formation of cracks during germination. All germination variants occurred in both seed morphs, albeit in different proportions. Germination was higher and faster for the FSC compared with the CSC. These germination differences could be related to a thinner cuticle in the FSC and the punctual release of its spermoderma, which facilitates a quick imbibition of the embryo and the breaking of the seed coat. Our results indicate that differences in germination parameters between the two seed morphs relate to differences in the percentage of dormant seeds, which favour the temporal expansion of germination and reduce competition between siblings. To propagate the species for conservation purposes, we recommend using FSC, while CSC may be used to establish a seed collectionex situ.

Effect of ultrasonic vibration on fatigue performance of AA 2024-T3 friction stir weld joints

Fatigue test of conventional friction stir welding (FSW) joints, ultrasonic vibration enhanced friction stir welding (UVeFSW) joints and base metal in 2024-T3 aluminum alloys are performed to investigate the influence of ultrasonic vibration on the fatigue strength and life of joints. It is found that for 50% survival probability the fatigue strength of UVeFSW joint is greatly improved, up to 96.13% of the base metal. On the advancing side, there exists a weak bonding region at upper part of transverse cross section of welds due to material flow. The stress concentration reaches maximum in the weak bonding region, which usually becomes the fatigue crack initiation site of FSW weld. The application of ultrasonic vibration narrows the weak bonding region and reduces the stress concentration there. In the crack propagation zone, the fatigue striations of UVeFSW joints fracture are parallel with each other and spaced apart, while the regular fatigue striations are not obvious but with larger spacing and poorer parallelism for FSW joint fracture. In the final fracture region, the application of ultrasonic vibration makes the secondary-phase particles smaller in size, more in quantity, and more uniform in distribution. All these contribute the improvement of fatigue performance in UVeFSW.

Thin Filament Pointed Ends Redistribute in Response to Altered Thick Filaments

Striated muscle generates contractile force and shortens as polar actin (thin) filaments slide past bipolar myosin (thick) filaments. Maximal force is able to be produced when thin filaments completely overlap the motor domains (heads) which occurs when the thin filament slow-growing (pointed) ends extend to the central (∼0.2 micrometer) thick filament bare zone devoid of myosin heads. The assembly of thin and thick filaments into regular contractile units (sarcomeres) is complex and highly-regulated, yet also robust; allowing diverse vertebrate and invertebrate animals to produce a variety of sarcomeric architectures with specific physiological contractile properties. Maximal thin-thick filament overlap in vivo is highly conserved among all types of striated muscle examined and highlights its importance. How thin-thick filament overlap is specified and maintained in different muscles is uncertain, but it manifests as the uniform and precise specification of thin filament lengths and involves the exchange of actin subunits at pointed ends and dynamic pointed-end capping by tropomodulin (Tmod). Here, we use CRISPR-Cas9 gene editing and fluorescence microscopy to investigate whether interactions between myosin heads and pointed ends are necessary for specifying thin filament lengths in C. elegans obliquely striated body wall muscle. To determine the position of thin filament pointed ends, we inserted the green fluorescent protein (GFP) coding sequence in-frame with the C. elegans Tmd1 gene to generate a GFP-Tmod fusion protein. Homozygous GFP-Tmod worms are indistinguishable from wildtype worms demonstrating that the GFP fusion is completely functional. In body wall muscle, GFP-Tmod appears as regular striations that co-localize with myosin thick filaments. GFP-Tmod striations appear as single bands (singlets) or closely spaced double bands (doublets) in living worms confirming that thin-thick filament overlap is complete. In contrast, GFP-Tmod striations appear as more broadly-spaced doublets in headless-myoA transgenic worms that were designed to have an expanded (∼2 micrometer) thick filament bare zone. Our results show that thin filament pointed ends redistribute their location in response to changing the size of the thick filament bare zone. The response of pointed ends suggests that interactions with myosin heads stabilize pointed ends, increasing thin filament lengths until they fully overlap with thick filaments and permit optimal force generation.

A sequential filtering algorithm for range estimation of a moving ship based on striation geometric features

There exist regular striation pattern in the broad-band noise field excited by a moving ship in shallow waters, whose time (range) frequency structure can be interpreted by the waveguide invariant theory. The striation characteristics have been exploited for underwater acoustic inversion problems, e.g., sediment geoacoustic parameter characterization. In this paper, the geometrical features of specific striations are observed for continuously ship ranging by a sequential algorithm. Comparing to matched-field processing techniques, this approach also has no requirements prior knowledge of environmental properties and burden of forward sound field calculation, which is similar to virtual receiver approach. The technique is tested on the striation fragments extracted from the ship noise data collected in Dalian 2008, and the outputs are in high agreement with in-situ GPS measurements. The results from independent runs with different initial values also suggest that this approach is robust to initial conditions in the sense of all runs can converge to the true values rapidly.

On the extrusomes of Oxyrrhis marina (Dinophyceae).

Oxyrrhis marina was subjected to conventional transmission electron microscopy, with emphasis being laid on its extrusomes. Mainly regular trichocysts were obvious in ultrathin sections. They were highly abundant, approximately 2μm in length and 200nm in width, and composed of the characteristic features, i.e., an anterior tip and the posterior crystalline body. The tip measures approximately 440nm in length and is built by an outer less electron-dense concentric layer followed by an inner electron-dense core with a translucent center in the middle. The less electron-dense layer most likely ends up in a bundle of filaments which are concentrically placed around the electron-dense core in the transition zone between the tip and body. Trichocyst bodies which are sectioned along the longitudinal axis are approximately 1.5μm in length and show a regular striation of electron-dense and electron-translucent lines with a spacing of 9nm. Cross-sectioned bodies are square-shaped and show a crystalline lattice composed of particles which are 8-9nm in size. Discharge of regular trichocysts results in long rigid rods. They are square-shaped, 54nm broad, and with a regular striation of approximately 54nm along their longitudinal axes. Besides regular trichocysts, an additional type of extrusome was registered. It is not as abundant as regular trichocysts, membrane-enclosed, 2μm in length and 180nm in width, and resembles two bullets adjacent to each other with the tips facing in opposite directions. The two parts are slightly of different lengths (anterior part, 740nm; posterior part, 590nm) and widths (anterior part, 126nm; posterior part, 117nm) and separated from each other by a gap of 30nm. The anterior part is more electron-dense than the posterior one. A faint electron-dense sheet-like structure was registered between the envelope membrane and these two inner structures. In extrusomes which had been arrested in the process of discharge, the anterior part gives rise to an oozing, amorphous, fibrous blob, while the posterior part consists of twisted filaments which most likely function as the charge of a gun for the release of the anterior part.

Erratum to: The acrosome of eutherian mammals.

Fig. 2 PB appearance in corpus epididymal spermatozoa. a. Regular striations of the two PBs in a transverse section of a sperm head. Bar 0.2 μm (×30,000) b. High magnification of the striations in a part of a consecutive section of the same sperm head. Bar 0.1 μm (×70,000) The PBs can be more easily observed by increasing the magnification on the screen Fig. 3 Sagittal section of an ejaculated sperm head observed with the goniometer stage. Bar 0.1μm (×80,000). a. – 15° inclination: alignments almost perpendicular to the sperm axis in the large PB. b. + 20° inclination: alignments almost parallel to the sperm axis in the large PB. The PBs can be more easily observed by increasing the magnification on the screen