Plastic Sections Research Articles

AAV-CRB2 protects against vision loss in an inducible CRB1 retinitis pigmentosa mouse model

Loss of Crumbs homolog 1 (CRB1) or CRB2 proteins in Müller cells or photoreceptors in the mouse retina results in a CRB dose-dependent retinal phenotype. In this study, we present a novel Müller cell-specific Crb1KOCrb2LowMGC retinitis pigmentosa mouse model (complete loss of CRB1 and reduced levels of CRB2 specifically in Müller cells). The Crb double mutant mice showed deficits in electroretinography, optokinetic head tracking, and retinal morphology. Exposure of retinas to low levels of dl-α-aminoadipate acid induced gliosis and retinal disorganization in Crb1KOCrb2LowMGC retinas but not in wild-type or Crb1-deficient retinas. Crb1KOCrb2LowMGC mice showed a substantial decrease in inner/outer photoreceptor segment length and optokinetic head-tracking response. Intravitreal application of rAAV vectors expressing human CRB2 (hCRB2) in Müller cells of Crb1KOCrb2LowMGC mice subsequently exposed to low levels of dl-α-aminoadipate acid prevented loss of vision, whereas recombinant adeno-associated viral (rAAV) vectors expressing human CRB1 (hCRB1) did not. Both rAAV vectors partially protected the morphology of the retina. The results suggest that hCRB expression in Müller cells is vital for control of retinal cell adhesion at the outer limiting membrane, and that the rAAV-cytomegalovirus (CMV)-hCRB2 vector is more potent than rAAV-minimal CMV (CMVmin)-hCRB1 in protection against loss of vision.

Polyester or epoxy: assessing embedding product efficacy in paleohistological methods.

Histological examination of bone microstructure provides insight into extant and extinct vertebrate physiology. Fossil specimens sampled for histological examination are typically first embedded in an inexpensive polyester resin and then cut into thin sections, mounted on slides, and polished for viewing. Modern undecalcified bone is chemically processed prior to embedding in plastic resin, sectioning, mounting, and polishing. Conversely, small fossil material and modern undecalcified bone are typically embedded in higher priced epoxy resin because these specimen types require final sections near or below 100 µm thick. Anecdotal evidence suggests thin sections made of polyester resin embedded material polished thinner than 100 µm increases likelihood of sample peeling, material loss, and is unsuitable for modern tissue and small fossil material. To test this assertion, a sample of modern bones and fossil bones, teeth, and scales were embedded in either polyester resin or epoxy resin. Embedded specimens were sectioned and mounted following standard published protocol. Thin sections were ground on a lapidary wheel using decreasing grit sizes until tissue microstructure was completely discernible when viewed under a polarizing light microscope. Additionally, eight prepared thin sections (four from polyester resin embedded specimens and four from epoxy resin embedded specimens) were continuously ground on a lapidary wheel using 600 grit carbide paper until peeling occurred or material integrity was lost. Slide thickness when peeling occurred was measured for comparing slide thickness when specimen integrity was lost between the two resin types. Final slide thickness ranged from 38 µm to 247 µm when tissue was identifiable using a polarizing microscope. Finished slide thickness varied between resin types despite similar tissue visibility. However, finished slide thickness appears more dependent on hard tissue composition than resin type. Additionally, we did not find a difference of slide thickness when material was lost between resin types. The results of this preliminary study suggest that polyester resins can be used for embedding undecalcified modern hard tissues and fossilized hard tissues without loss of tissue visibility or material integrity, at least in the short term.

The Prediction of Stiffness Reduction Non-Linear Phase in Bamboo Reinforced Concrete Beam Using the Finite Element Method (FEM) and Artificial Neural Networks (ANNs)

This paper discusses the reduction of the stiffness of bamboo reinforced concrete (BRC) beams to support the use of bamboo as an environmentally friendly building material. Calculation of cross-section stiffness in numerical analysis is very important, especially in the non-linear phase. After the initial crack occurs, the stiffness of the cross-section will decrease with increasing load and crack propagation. The calculation of the stiffness in the cross-section of the concrete beam in the non-linear phase is usually approximated by giving a reduction in stiffness. ACI 318-14 provides an alternative, reducing the stiffness of the plastic post-linear beam section through the moment of inertia (I) of the beam section for elastic analysis between 0.50Ig–0.25Ig. This study aims to predict the value of the reduction in the stiffness of the BRC beam section in the non-linear phase through the load-displacement relationship of experimental results validated by the Finite Element Method (FEM) and the Artificial Neural Networks (ANN) method. The experiment used 8 BRC beams and one steel-reinforced concrete (SRC) beam of singly reinforced with a size of 75 mm × 150 mm × 1100 mm. The beams were tested using a four-point loading method. The analysis results showed that the value of the stiffness reduction in the beam cross-sectional in the non-linear phase ranged from 0.5Ig–0.05Ig for BRC beams, and 0.75Ig–0.40Ig for SRC beams.

Liver and kidney serum profile abnormalities in workers exposed to aflatoxin B1 in urban solid waste management centers.

Many workers are exposed to health problems arising from molds, fungi, and their toxins during waste processing. Aflatoxin B1 (AFB1) level in airborne and settled dust, aflatoxin B1-albumin (AFB1-Alb) adduct in serum, liver and kidney biochemical tests, and body redox change of workers in municipal dry waste-processing sites were investigated. The surface, personal, and area air dust and the blood of workers' samples were collected from the plastic and bread waste-sorting sections in three recycling municipal dry waste sites. Digestion (only for serum samples), passed through SPE cartridge, elution, and collection with methanol, immune-affinity column clean-up, and HPLC system equipped with post-column derivatization method and fluorescence detection were performed for determination of AFB1 and AFB1-Alb levels in the samples. The mean level of dust and AFB1 in the personal and area air, and in the settled dust and the AFB1-Alb in the serum of workers in the bread waste sorting, was higher than plastic waste-sorting samples, in all of the sites. The differences in the biochemical profiles of subjects exposed to aflatoxin B1 as compared to the control group especially in liver and kidney function parameters as well as antioxidant factors of the serum were significant. The workers in handling of municipal waste may be exposed to potentially hazardous levels of aflatoxin B1. The adverse effects of AFB1 on the kidney and liver may be caused by changes in the redox system.

Dual-axis STEM tomography at 200 kV: Setup, performance, limitations

The interpretation of cell biological processes hinges on the elucidation of the underlying structures. Their three-dimensional analysis using electron tomography has extended our understanding of cellular organelles tremendously. The investigations depend on the availability of appropriate instruments for data recording. So far, such investigations have been done to a great extent on 300 keV transmission electron microscopes. Here we show the implementation of STEM tomography on a 200 kV FEG transmission electron microscope, including the tuning of the condenser for forming a beam with a small illumination aperture, dual-axis data recording, and evaluation of the maximum sample thickness and quality of the data. Our results show that the approach is accomplishable and promising, with high reliability, and reaching excellent data quality from plastic sections with a thickness of at least 900 nm.

Effects of strain rate and strain hardening on a cantilever under impact

An investigation is carried out to assess the response of elastic–plastic and ductile circular section cantilevers subjected to blast wave loading. A mathematical equation is formulated for the effects of strain rate and strain hardening for ductile (rigid–plastic) cantilever subjected to impact. It is assumed that the cantilever deforms when the moment produced by drag force about the clamped end exceeds the maximum resisting moment of the material, resulting in an equation for deformation. For the transient and modal phase, a correction factor is proposed, which improves the accuracy of response prediction. Full-scale explosion tests are carried out at Woomera (Australia) to investigate the response of cantilevers subjected to air-blast loading, where sixty cantilever test specimens were tested. The test specimens used were designed on the basis of different approaches such as elastic, elasto-plastic, quasi-static, impulse technique and plastic approach. Correction factor ‘K’ for the effects of strain rate and strain hardening were developed and used during the design of cantilever specimens. The prediction of a mathematical model for the response of cantilevers was in line with the response of test specimens during field explosion tests due to the modification factor for the effects of strain rate and strain hardening.

Experimental and numerical study on seismic performance of corroded steel frames in chloride environment

To investigate the seismic behavior of corroded steel frames in chloride environment, accelerated corrosion tests and lateral low cyclic loading tests were carried out on four steel frames. Firstly, a deterioration model of mechanical property with mass loss rate for corroded Q235B steel was proposed. Then, the failure process and mechanism of test steel frames were observed, the strain developments of potential plastic hinge sections at beam ends and column bases were analyzed, and the effects of corrosion level on the hysteretic curves, bearing capacity, stiffness degradation, ductility and energy dissipation capacity were studied in detail. The test results indicated that in relatively slight corrosion level, all specimens exhibited a hybrid yield dissipation mechanism, with the “beam end - column bottom - beam end” sequence of the plastic hinges occurring. However, an increase in corrosion level tended to accelerate plastic hinge formation and aggravate structural damage degree. Additionally, with the increase of corrosion level, the lateral bearing capacity reduced, stiffness degradation intensified, ductility and energy dissipation capacity decreased. Base on test data, the structural performance levels and performance index quantified thresholds of corroded steel frame were preliminarily determined. Moreover, a finite element model adopting a time-varying constitutive model of corroded steel and a stress triaxiality dependent failure criterion, was established using ABAQUS, and then verified to be valid by comparing the numerical and experimental results. The research results lay an experimental and theoretical foundation for the seismic performance evaluation of in-service steel frame structures in chloride environment.

EFFECT OF ADDING RECYCLED PLASTIC FIBERS TO CONCRETE ON THE STATIC PROPERTIES OF CONCRETE TILES

This research paper is an attempt to reuse plastic waste fibre resulting from plastic sections industry as an additive to concrete matrix. The relationship between fibre volume fraction and mechanical properties of concrete and re-inforced concrete tiles was investigated. Three volume fractions of fibre ( 0.5 % , 1 % and 1.5 % - by volume of concrete ) were used through the experi-mental program. Tests’ results proved a slight decrease in concrete compres-sive strength as plastic fibre was added compared with the reference mix. Flexural behaviour of concrete tiles was enhanced as adding fibres. Adding fibre to Concrete results in a negligible reduction in concrete density. Fibre with high volume fractions improved Splitting tensile strength compared to the reference mix.

New Medical Device and Therapeutic Approvals in Otolaryngology: State of the Art Review of 2019.

ObjectiveTo review new devices and drugs relevant to otolaryngology–head and neck surgery that were approved by the US Food and Drug Administration (FDA) in 2019.Data SourcesApproval notifications for 2019 were extracted from the ENT (ear, nose, and throat) and general and plastic surgery sections of the FDA’s medical devices and therapeutics listings.Review MethodsNew therapeutics and medical devices identified from the query were analyzed by members of the American Academy of Otolaryngology–Head and Neck Surgery’s Medical Devices and Drugs Committee. Technologies were assessed by 2 independent reviewers to ascertain relevance to otolaryngology, prioritized, and classified to subspecialty field with critical review based on extant scientific literature.ConclusionsQuery of the FDA drug and device database returned 105 ENT devices (50 cleared, 55 with premarket approval, and 0 de novo), 543 general and plastic surgery devices (372 cleared, 170 with premarket approval, and 1 de novo), and 46 new otolaryngology-relevant drug approvals that occurred in 2019. Advances spanned all subspecialty areas with otology predominating, primarily due to hearing-related technologies. While scientific evidence was available for all new devices, there was significant heterogeneity in rigor of supporting scientific data.Implications for PracticeTechnological and pharmaceutical innovation is an important catalyst for advances in the surgical specialties. Familiarity with new devices and therapeutics in otolaryngology–head and neck surgery ensures that clinicians keep abreast of developments with potential to improve prevailing standards of care.

Regional differences in the ependyma of the optic tectal ventricle of adult zebrafish with structures referring to brain hydrodynamics

Classical electron microscopic morphological studies provide detailed ultrastructural information, which may lend insights into cellular functions. As a follow-up to our morphological investigation of the adult zebrafish (Danio rerio) optic tectum, in this study, we have analyzed the ependymal structures lining the surfaces of the tectal ventricle: the torus, tegmental surface of the valvula cerebelli and the periventricular gray zone of the optic tectal cortex. We used toluidine blue stained plastic (semithin) sections for light microscopy and scanning electron microscopy. Our morphological findings of gated entrances and/or egresses indicate that, at least in the adult zebrafish brain, there may be a bidirectional direct flow communication between the ventricular cerebrospinal fluid and the parenchymal interstitial fluid.

Elasto-plastic behaviour and design of semi-compact circular hollow sections

Previous research has revealed shortcomings in the current Eurocode 3 (EC3) provisions for the design of semi-compact (Class 3) cross-sections. These shortcomings arise primarily from the lack of utilisation of partial plastification in bending, leading to a step in the design resistance function at the boundary between Class 2 and 3 cross-sections and an underestimation of the available capacity. This affects the accuracy of resistance predictions in bending and under combined loading, and applies at both cross-sectional and member level. To address this issue, the use of an elasto-plastic section modulus, which lies between the plastic and elastic section moduli, has been proposed and employed in the design of semi-compact I- and box sections. The aim of the present study is to develop new cross-section and member buckling design rules incorporating the elasto-plastic section modulus for semi-compact circular hollow sections (CHS), and to assess their accuracy against existing experimental and freshly generated numerical data. Firstly, an experimental database, consisting of previous cross-section and member buckling test results on steel CHS, was established. A comprehensive numerical simulation programme was subsequently carried out; in this programme, finite element (FE) models were developed, validated and used for parametric studies, where over 600 numerical structural performance data on semi-compact CHS were generated. New sets of cross-section and member buckling design expressions featuring elasto-plastic section properties were then proposed and assessed against the test and numerical data. The proposals were shown to offer improved accuracy and design efficiency over the elastic EC3 methods. The reliability of the proposed elasto-plastic design rules was then confirmed through statistical analyses in accordance with EN 1990, demonstrating their suitability for inclusion into the next revision of EN 1993-1-1. • Existing cross-section and member buckling test data on CHS were collected. • Numerical simulation was conducted to generate further data on CHS. • New design rules were developed to capture the elasto-plastic behaviour of semi-compact CHS. • Accuracy of the current Eurocode 3 and proposed methods were assessed and compared. • Reliability of the proposed design rules was confirmed through statistical analyses.

Experimental and numerical evaluation of rigid connection with reduced depth section

After medium or strong earthquakes, damage in the reduced portion of RBS connections occurs due to plastic deformations. The purpose of this paper is to numerically and experimentally investigate the reduced depth section connection as a replaceable fuse. In this regard, three commonly used rigid connections with RBS, a replaceable fuse with RBS, and a replaceable fuse with Reduced Depth Section (RDS-F) were evaluated. All specimens were subjected to quasi-static cyclic load until failure. Although the final strength of the RDS-F is lower than that of the other two, laboratory results showed that it had the maximum ductility among the three samples. The numerical models of all three laboratory samples were constructed in ABAQUS, and the results were verified with great accuracy. The results of more than 28 numerical analyses showed that the RDS-F sample is more ductile than the other specimens. Moreover, the thickness of the web and the plastic section modulus increasing, the final strength would be equal to the other specimens. Therefore, the modified RDS-F with replaceability after an earthquake can be a better alternative for RBS connections.

Electron Tomography and Immunogold Labeling as Tools to Analyze De Novo Assembly of Plant Cell Walls.

High-resolution imaging of the membranous intermediates and cytoskeletal arrays involved in the assembly of a new cell wall during plant cytokinesis requires state-of-the-art electron microscopy techniques. The combination of cryofixation/freeze-substitution methods with electron tomography (ET) has revealed amazing structural details of this unique cellular process. This chapter deals with the main steps associated with these imaging techniques: selection of samples suitable for studying plant cytokinesis, sample preparation by high-pressure freezing/freeze substitution, and ET of plastic sections. In addition, immunogold approaches for identification of proteins and polysaccharides during cell wall assembly are discussed.

Simplified Bending Capacity Formulation Based on the Continuous Strength Method

ABSTRACTIn the frame of the current revision of the Eurocodes, there is a trend to simplify the existing design formulae while, at the same time, providing higher efficiency and reliability. To consider the effect of strain hardening present in the material behaviour of stainless steel, advanced design formulae are proposed in the 4th edition of the Design Manual for Structural Stainless Steel. The method called the continuous strength method (CSM), is a deformation‐based design approach that uses a bilinear hardening material model, leading to the introduction of several new parameters depending on which stainless steel family is considered and one additional design formula for the cross‐section verification. The CSM was proven to be accurate for austenitic, duplex and ferritic grades.The idea developed in the present paper is that there exists a reasonable and equally accurate approximation of the cross‐section capacity considering hardening through the combination of the elastic and plastic section modulus. The concept uses the current well‐known plastic section modulus and, to deal with the hardening effect, an additional contribution is added for which an equation is proposed. This equation only combines the elastic section modulus, the yield‐to‐ultimate strength ratio as well as their difference. Then, the cross section bending resistance is determined through well‐known cross‐section geometrical parameters.The presented approach is compared to the formulation of the CSM for I‐section and rectangular hollow sections beams, for austenitic, duplex and ferritic grades. It is shown to be only slightly more conservative for hollow sections. The formulation deals with tangible concepts, is easy to apply for daily engineering practice and guarantees a more rational use of the material benefit.

An analytical approach for elastic and non-elastic buckling of pipes under external/internal pressures

Abstract An analytical model is presented to evaluate the buckling pressure of pipes subjected to external/internal pressures. At firstly, a set of stability equations was solved mathematically and the elastic buckling solution was established. By introducing the inner plastic section and the middle non-linear elastic section, the analytical approach was then extended to the critical pressure evaluation of the thick pipes in non-elastic buckling and the effect of the initial ovality on the critical pressure is considered. Details of the analytical formulations and the required parameters are defined. The results are presented to show that the initial ovality has a significant influence on the bifurcation pressure and, however, its effect becomes trivial as the pipes become thicker. Compared to the plastic hinge approach, the proposed solution represents a lower critical pressure, which indicates that the pipes would collapse before the formation of the plastic hinges. Furthermore, some factors that affect the pressure capacity of the pipes are discussed, the results from the proposed analytical solution are compared with those of other solutions and experiments.

TEKNOLOGI PROSES PENGECATAN MENGGUNAKAN SISTEM ATOMISASI PADA PRODUK BERBAHAN PLASTIK DI INDUSTRI PERAKITAN SEPEDAMOTOR

Motorcycles are a type of transportation that is familiar in Indonesia. Cost product and speed for mobilization are the main reasons for choosing this transportation. Demand for motorcycles that are still large in Indonesia and encouraged motorcycles manufacturing industries to deliver products according to consumer needs. To be able to meet the varied needs of consumers, motorcycle manufacturers always make improvements in all of their production area. There are two main components in the motorcycle, engine and frame. These two components are produced by several parts of production based on the characteristics of each product. The production section of the motorcycle industry that do paintingactivities on plastic products is painting plastic section. The coating technology used in painting plastic is atomization . This technology is a converting liquid material into mist or granules used to coat the product. This technology has many challenges in terms of material transfer to products. The selection of the right material is the key to the atomization process, besides that human factors are also important because the operator's competence or expertise during the painting process can affect product yield. From these problems the author tries to map some of the problems caused by paintings, including technological materials, production systems, product quality and problems caused by painting processes to the environment. However with the level of complexity of the problems faced by the plastic paintingsection, not many studies have focused on the problems in the paintingprocess of plastic products. Therefore the author tries to give a detailed description of the production process in the painting plastic section. The author divides this article into several sub-chapters including paintingtechnology, technology material, production system and Quality properties. Furthermore, the authors hope that this article can be used as a basis for developing the paintingprocess on plastic products.

Decreased Expression of Synaptophysin 1 (SYP1 Major Synaptic Vesicle Protein p38) and Contactin 6 (CNTN6/NB3) in the Cerebellar Vermis of reln Haplodeficient Mice.

Reeler heterozygous mice (reln+/-) are seemingly normal but haplodeficient in reln, a gene implicated in autism. Structural/neurochemical alterations in the reln+/- brain are subtle and difficult to demonstrate. Therefore, the usefulness of these mice in translational research is still debated. As evidence implicated several synapse-related genes in autism and the cerebellar vermis is structurally altered in the condition, we have investigated the expression of synaptophysin 1 (SYP1) and contactin 6 (CNTN6) within the vermis of reln+/- mice. Semi-thin plastic sections of the vermis from adult mice of both sexes and different genotypes (reln+/- and reln+/+) were processed with an indirect immunofluorescence protocol. Immunofluorescence was quantified on binary images and statistically analyzed. Reln+/- males displayed a statistically significant reduction of 11.89% in the expression of SYP1 compared to sex-matched wild-type animals, whereas no differences were observed between reln+/+ and reln+/- females. In reln+/- male mice, reductions were particularly evident in the molecular layer: 10.23% less SYP1 than reln+/+ males and 5.84% < reln+/+ females. In reln+/- females, decrease was 9.84% versus reln+/+ males and 5.43% versus reln+/+ females. Both reln+/- males and females showed a stronger decrease in CNTN6 expression throughout all the three cortical layers of the vermis: 17-23% in the granular layer, 24-26% in the Purkinje cell layer, and 9-14% in the molecular layer. Altogether, decrease of vermian SYP1 and CNTN6 in reln+/- mice displayed patterns compatible with the structural modifications of the autistic cerebellum. Therefore, these mice may be a good model in translational studies.

Software tools for automated transmission electron microscopy.

The demand for high-throughput data collection in electron microscopy is increasing for applications in structural and cellular biology. Here we present a combination of software tools that enable automated acquisition guided by image analysis for a variety of transmission electron microscopy acquisition schemes. SerialEM controls microscopes and detectors and can trigger automated tasks at multiple positions with high flexibility. Py-EM interfaces with SerialEM to enact specimen-specific image-analysis pipelines that enable feedback microscopy. As example applications, we demonstrate dose reduction in cryo-electron microscopy experiments, fully automated acquisition of every cell in a plastic section and automated targeting on serial sections for 3D volume imaging across multiple grids.

Cyclic Seismic Performance of Weak-Axis RBS Welded Steel Moment Connections

In this study, cyclic seismic performance of weak-axis reduced beam section (RBS) welded steel moment connections was experimentally investigated. Experimental results of this study again showed that the weak-axis RBS moment connection designed based on the procedure proposed by Gilton and Uang (J Struct Eng 122:1292–1299, 2002) performs well and developed an excellent seismic performance much better than 4% story drift with 80% of beam plastic capacity. However, it was also shown that the sharp corner of C-shaped fillet weld, used for attaching the beam web to the shear plate, can be the origin of crack propagation owing to stress concentration there. Slight trimming of the sharp corner is recommended to reduce notch effect. One specimen in this study eventually failed due to low cycle fatigue fracture as a result of cyclic flange local buckling that occurred at the butt joint between the beam flange and the horizontal continuity plate. The size of the weld access hole beneath the butt joint should be minimized if possible to suppress the occurrence of flange local buckling around the butt joint. The factors affecting the size of C-shaped fillet weld and the beam shear eccentricity for the weld design were also examined through a case study and simple analytical modeling. The sectional factor governing the beam shear eccentricity was shown to be the plastic section modulus ratio of beam section at RBS center to the beam flanges at welded joint. The elastic method neglecting the ductile behavior of the C-shaped fillet weld group was shown to be too conservative and should not be used in design in order to minimize welding heat affection to the thin beam web as well.

Towards a Solution of the A-B-Z Question using Z-Disks Isolated from the Flight Muscle of Lethocerus Indicus

The recent publication of a 3-D image of isolated Z-disks from Apis mellifera, flight muscle[Rusu et al., J. Muscle Res Cell Motil (2017)], the first of its kind utilizing isolated Z-disks, confirmed many details of the previously 3-D image obtained from plastic sections[Cheng and Deatherage, J. Cell Biol. (1989)]. However, they used relatively harsh treatment of high KCl/KI to isolate Z-disks. Here we combine 1.4M NaCl and 10mM pyrophosphate applied to Lethocerus indicus flight muscle to remove the thick filaments and 4.5min exposure to calcium insensitive gelsolin to remove the thin filaments from the remaining of the I-Z-I-brushes. We are improving the resolution by adding more tilt-series to our previous analysis. By comparing the Fourier transforms and subvolume averages, we conclude that Z-disks from honey-bee and Lethocerus indicus are similar but not identical. The large solvent channel that characterizes the honey-bee Z-disk is less prominent in Lethocerus, which is reflected in a much weaker to nearly absent 1,0 spot intensity in transforms of Lethocerus Z-disks, whereas the corresponding spots in the honey-bee transform are strong. There is ample evidence that the actin filaments in the overlap zone of both bee and waterbug flight muscle present a helical array of target zones around each thick filament. However, Squire[J. Molec. Biol. 72, (1972)] has pointed out that the P312 symmetry assumed for the honey-bee Z-disk reconstruction from plastic sections when extrapolated into the A-band, implies rings rather than helices of target zones surrounding the thick filament. This discrepancy might be resolved if there are three-fold screw axes instead of three-fold rotation axes at the lattice and trigonal positions of the flight muscle Z-band; corresponding more to space group symmetry P3121.