Regular Cross-section Research Articles

Additional material feeding method by plunger shape design for hydroforming of triangular tubes

In this study, a hydroforming process is used for the manufacture of a bicycle frame tube, one side end of which is expanded to an acute-angled triangular shape from the initial tube, which has a regular triangular cross section. The end section of the expanding side is designed to be smoothly connected with the initial tube cross section to maintain sealing by the plunger. The tube hydroforming process is controlled using an axial feeding plunger and a pressure intensifier. Various load conditions can be applied to the initial tubes through these units. However, the experimental results showed that forming into the desired shape without bursting at the expanding area or shear cracking at other areas was not possible. These problems seem to occur because the circumferential propagation of plastic deformation is constrained by the triangular cross-sectional profile of the initial tube. To resolve this problem, less axial feeding should be supplied to the compressing zone compared with the expanding zone even in a single tube. In this work, besides conventional axial feeding, an additional axial feeding method by an end cam–shaped plunger is suggested to supply different axial feeding for each circumferential location of the tube. Finite element simulation and experimental studies are performed to verify the effectiveness of the concept.

Optimization design of prestressed concrete wind-turbine tower

Wind energy is a clean and renewable energy for which technology has developed rapidly in recent years. Wind turbines are commonly supported on tubular steel towers. As the turbine size is growing and the towers are rising in height, steel towers are required to be sufficiently strong and stiff, consequently leading to high construction costs. To tackle this problem, a new type of prestressed concrete tower was designed employing a novel tower concept having a regular octagon cross section with interior ribs on each side, which was optimized by comparing the natural frequency and stress difference under the same lateral load in different directions of the tower. The designed tower features a tapered profile that reduces the area subjected to wind; the tapered profile reduces the total weight, applied moment and the capital cost. An optimization method was developed employing ABAQUS software and a genetic algorithm. A target function was defined on the basis of the minimum cost of the concrete and prestressed tendon used, and constraints were applied by accounting for the stress, displacements and natural frequency of the tower. Employing the method, a 100 m prestressed concrete tower system for a 5 MW turbine was optimized and designed under wind and earthquake loads. The paper also reports a systematic design procedure incorporating the finite element method and the optimization method for the prestressed concrete wind-turbine towers.

Finitely presented monoids with linear Dehn function need not have regular cross-sections

This paper shows that a finitely presented monoid with linear Dehn function need not have a regular cross-section, strengthening the previously-known result that such a monoid need not be presented by a finite complete string rewriting system, and contrasting the fact that finitely presented groups with linear Dehn function always have regular cross-sections.

Absorption of planar massless scalar waves by Kerr black holes

We consider planar massless scalar waves impinging upon a Kerr black hole, for general angles of incidence. We compute the absorption cross section via the partial wave approach, and present a gallery of results. In the low-frequency regime, we show that the cross section approaches the horizon area; in the high-frequency regime, we show that the cross section approaches the geodesic capture cross section. In the aligned case, we extend the complex angular momentum method to obtain a `sinc' approximation, which relates the regular high-frequency oscillations in the cross section to the properties of the polar null orbit. In the non-aligned case, we show, via a semi-analytic approximation, that the reduction in symmetry generates a richer, less regular absorption cross section. We separate the absorption cross section into corotating and counterrotating contributions, showing that the absorption is larger for counterrotating waves, as expected.

Multiple states of finger propagation in partially occluded tubes

Recent experiments by Pailha et al. [Phys. Fluids 24, 021702 (2012)10.1063/1.3682772] uncovered a rich array of propagation modes when air displaces oil from axially uniform tubes that have local variations in flow resistance within their cross-sections. The behaviour is particularly surprising because only a single, symmetric mode has been observed in tubes of regular cross-section, e.g., circular, elliptical, rectangular, and polygonal. In this paper, we present experimental results describing a new mode, an asymmetric localised air finger, that persists in the limit of zero propagation speed. We show that the experimental observations are consistent with a model based on capillary static calculations within the tube's cross-section, and the observed bistability is a consequence of the existence of multiple solutions to the Young–Laplace equations. The model also provides an upper bound for the previously reported symmetry-breaking bifurcation [A. de Lózar, A. Heap, F. Box, A. L. Hazel, and A. Juel, Phys. Fluids 21, 101702 (2009)10.1063/1.3247879].

滑模施工混凝土筒仓结构的缺陷原因分析

混凝土筒仓采用滑模施工相对简便快捷，模板投资较低，可连续作业，该施工方法普遍用于混凝土烟囱、冷却塔、广播电视发射塔等高耸体形且截面规则壳体结构的浇注成型，多年来,作为专项成套技术在国内外得到了广泛应用。近年的国内工程调查表明，滑模施工混凝土筒仓的筒壳易出现以下缺陷：表层强度不同程度低于内部及设计强度,混凝土粘结握裹配筋状况较差,不规则与环向水平裂缝，对结构各项性能有明显不利影响。为此，对混凝土筒仓因滑模施工可能导致质量劣化的问题进行了分析研究，提出了相关技术建议，可供结构设计与施工人员参考。 For the slipforming construction to built reinforced concrete silos, it is not only faster and easier relatively than that in usual, but also less template investment and it brings about continuous operation. The method is still widely used to built this kind of tall and regular cross-section concrete shells, such as chimneys, cooling towers, radio and TV towers etc. and it is token as special sets of construction technology at home and abroad for many years. In recent years, a number of engineering surveys in the domestic showed that the following shell defects appeared easily in slipforming construction and affected them badly, such as surface concrete strength which was less generally than that of the internal and the design requirement, poor concrete adhesive around reinforcements, more irregular and annular cracks on silo walls. To resolve these problems, careful analysis and research are done for the quality deterioration of reinforced concrete silos due to slipforming techniques, and then some improved suggestions are proposed to the reference for relative structural designers and workers.

Significance of Low Desmin Expression in Cardiomyocytes in Patients With Idiopathic Dilated Cardiomyopathy

Desmin plays an essential role in maintaining cell cytoarchitecture, positioning and functioning of organelles, and the intercellular signaling pathway. It has been suggested that remodeling of desmin cytoskeleton might contribute to the progression of idiopathic dilated cardiomyopathy and might affect patients' long-term prognosis. We performed endomyocardial biopsy in 200 patients with idiopathic dilated cardiomyopathy. A total of 5 to 6 specimens were collected from the left ventricular (LV) wall. Desmin was detected with immunohistochemical staining and Western blotting. Immunohistochemistry revealed 4 types of desmin expression: I, normal staining at Z-lines and intercalated disks, giving a regular cross-section pattern; IIA, increased desmin staining at Z-lines and intercalated disks; IIB, increased desmin staining with irregular pattern of cross-striation and/or with presence of aggregates; and III, decreased or lack of desmin staining. Patients with type III had a greater New York Heart Association class and N-terminal pro-brain natriuretic peptide level, larger LV end-diastolic diameter, and lower LV ejection fraction than patients with type I (p <0.001). At the end of follow-up (mean duration 59 ± 33 months), 44 patients (22%) had died and 5 (2.5%) had undergone heart transplantation. Patients with type III had an increased risk of death or heart transplantation in univariate Cox proportional hazard regression models (adjusted hazard ratio 7.18, 95% confidence interval 2.96 to 17.40, p <0.001) and multivariate models (New York Heart Association class, LV end-diastolic diameter, LV ejection fraction, N-terminal pro-brain natriuretic peptide, gender, and age; hazard ratio 5.24, 95% confidence interval 1.58 to 17.38, p = 0.007). In conclusion, in patients with idiopathic dilated cardiomyopathy, a decrease or lack of desmin expression seems to be a strong, independent predictor of an unfavorable prognosis. Our outcomes support the relevance of exploring desmin expression as a potential target to treat heart failure progression.

Investigations on Forced Convection in Compact Passages With Surface Irregularities

Two-dimensional, fully developed, convective heat transfer in compact passages is investigated numerically, incorporating the effects of the surface irregularities, to analyze the influence of these irregularities on fluid flow and heat transfer. This analysis helps to bring out the differences in the performance evaluation if regular cross sections are assumed in analyzing compact and mini channels. Forced convection in compact passages with an apparent rectangular shape is analyzed using a finite-difference method. The calculation is validated experimentally using Michelson interferometry. The numerical results for the channel, incorporating surface irregularities, are compared with those assuming a regular cross-sectional geometry. The results indicate that the coefficient of friction and the Nusselt number calculated for channels, considering the irregular cross section, are less than those predicted using an assumption of regular geometry. The results provide some insight into the reasons for the observed deviations in the comparisons. The observations are attributed to the influence of the surface irregularities on the relative dominance of the surface area to the cross-sectional area, which gets pronounced in compact passages. The findings suggest that some of the observed deviations in the performance of compact passages, compared to theoretical results, may be due to the use of regular geometries to define domain shapes while performing theoretical analysis.

Analysis of Workspace for the 4-PUU Parallel Manipulator

4-PUU parallel manipulator with three-dimensional translations and one rotational motion about Z axis was presented. The Workspace of boundary point was obtained by searching in Polar Coordinates,the workspace of standing pose was analyzed by programming with MATLAB and LabVIEW. The research indicated that the workspace of the 4-PUU parallel mechanism has advantages of smooth boundary, big volume, no cavity and regular cross section in the fields of industrial robots, micromanipulators, virtual axis machine tools, damping platform, rehabilitation robot and etc.

A simple CAD method for constructing sand-heap formations as an analogous means of determining the fully plastic torque capacity of various structural sections

A brief review is presented of the sand-heap analogy as a means of determining the ultimate plastic torque capacity of a ductile metallic prismatic bar of known cross-section. A novel method using an industry-standard computer-aided design (CAD) tool is then described for determining the shape and corresponding sand-heap volume for a general cross-section that can include the presence of keyways, fillets, rebates, and holes. Existing solutions for simple regular cross-section shapes are used as a benchmark for the solutions from the new method, and perfect agreement is found. Subsequent examples are presented which demonstrate the ease with which sand-heap formations and their corresponding volumes can be found for more general cross-sections that are more representative of those used in practical engineering applications.

Periodic orbits in the gravity field of a fixed homogeneous cube

In the current study, the existence of periodic orbits around a fixed homogeneous cube is investigated, and the results have powerful implications for examining periodic orbits around non-spherical celestial bodies. In the two different types of symmetry planes of the fixed cube, periodic orbits are obtained using the method of the Poincar\'e surface of section. While in general positions, periodic orbits are found by the homotopy method. The results show that periodic orbits exist extensively in symmetry planes of the fixed cube, and also exist near asymmetry planes that contain the regular Hex cross section. The stability of these periodic orbits is determined on the basis of the eigenvalues of the monodromy matrix. This paper proves that the homotopy method is effective to find periodic orbits in the gravity field of the cube, which provides a new thought of searching for periodic orbits around non-spherical celestial bodies. The investigation of orbits around the cube could be considered as the first step of the complicated cases, and helps to understand the dynamics of orbits around bodies with complicated shapes. The work is an extension of the previous research work about the dynamics of orbits around some simple shaped bodies, including a straight segment, a circular ring, an annulus disk, and simple planar plates.

Effect of catalyst layer on morphology and optical properties of zinc-oxide nanostructures fabricated by carbothermal evaporation method

Zinc-oxide nanostructures were synthesised by carbothermal evaporation of ZnO+C at elevated temperatures. Substrates were silicon wafers, and different materials such as SiO2, Al2O3, Au and silica-gel were used as the catalyst layer. Characterisation of morphology by scanning electron microscopy showed that the catalyst layer has a major role in controlling of geometrical shape and dimensions of the resultant nanostructures. The long and narrow nanowires with a regular cross-section were formed on the substrate coated by Au particles. On the substrate coated by silica-gel, the authors achieved the capillary microtubes with the hexagonal cross-section, nanometre-thick walls and also radial sheets inside them. Such nanostructures are believed to be reported for the first time. The electro-optical specifications of the samples were investigated by measurement of their optical absorption spectra using ultraviolet/visible (UV/VIS) spectrophotometry. Determination of the optical band gap from Tauc's plot showed that, in contrary to different shapes, the samples have identical band gap energy. This phenomenon revealed that the optical behaviour of the nanostructures grown by the proposed method does not depend to their morphology.

Localized meshless point collocation method for time-dependent magnetohydrodynamics flow through pipes under a variety of wall conductivity conditions

In this article a numerical solution of the time dependent, coupled system equations of magnetohydrodynamics (MHD) flow is obtained, using the strong-form local meshless point collocation (LMPC) method. The approximation of the field variables is obtained with the moving least squares (MLS) approximation. Regular and irregular nodal distributions are used. Thus, a numerical solver is developed for the unsteady coupled MHD problems, using the collocation formulation, for regular and irregular cross sections, as are the rectangular, triangular and circular. Arbitrary wall conductivity conditions are applied when a uniform magnetic field is imposed at characteristic directions relative to the flow one. Velocity and induced magnetic field across the section have been evaluated at various time intervals for several Hartmann numbers (up to 105) and wall conductivities. The numerical results of the strong-form MPC method are compared with those obtained using two weak-form meshless methods, that is, the local boundary integral equation (LBIE) meshless method and the meshless local Petrov–Galerkin (MLPG) method, and with the analytical solutions, where they are available. Furthermore, the accuracy of the method is assessed in terms of the error norms L 2 and L ∞, the number of nodes in the domain of influence and the time step length depicting the convergence rate of the method. Run time results are also presented demonstrating the efficiency and the applicability of the method for real world problems.

Influence of surface recombination on the longitudinal Shubnikov-de Haas oscillation amplitude

Longitudinal magnetoresistance has been measured for various sizes of pure bismuth single crystals in magnetic fields up to 5 T at a temperature of 4.2K in order to investigate the sample size dependence of the longitudinal Shubnikov-de Haas (SdH) oscillation. The samples used were sticks with regular square cross section elongate along the bisectrix axis of bismuth. Dimensions of the samples were in the range of 0.80 - 3.8 mm thick and about 20 mm long. When the sample thickness d ≤ 2.5 mm, the amplitude of the longitudinal SdH oscillation reduces rapidly, while d ≥ 2.5 mm it tends to saturate. This can be qualitatively explained by assuming that the gradient of carrier concentrations, even in the case of longitudinal magnetoresistance, is established near at surface by a balance of the Lorentz force, the counter diffusion force and the generation and recombination of carriers. The surface recombination time obtained from our data was found to be 2.6 x 10-7 sec. The fact that the non-oscillatory part of magnetoresistance became gradually less in magnitude with decreasing in sample size was also found.

A simple hydrothermal route to GaOOH intersecting-rods with regular diamond-like cross section

GaOOH crystals were synthesized by a simple hydrothermal method at 90–200 °C for 18 h. The products were characterized by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscope (HRTEM). The rods synthesized at 110–150 °C exhibited intersecting morphology and regular diamond-like cross section with a diagonal length ratio of 2:1, and those synthesized at 180–200 °C exhibited nunchakus-like architecture. The formation of diamond-like cross section was due to homogeneous growth of lattice planes, namely {1 1 0}, along [4 1 0], [4 1¯ 0], [4¯ 1 0], and [4¯ 1¯ 0] directions of orthorhombic GaOOH. Moreover, the formation of the trunk was due to the growth along [0 0 1] direction.

OTOSCLEROSIS IN THE INCUS

To the Editor: The last issue of the journal (Otology & Neurotology, 28:301-3) published a paper titled "Otosclerosis of the Incus." Escada et al. (1) describes a bony lesion in the incus that is considered to be otosclerotic upon hematoxylin-eosin staining and a single light microscopic histological examination (1). A series of articles have been published during the last 3 years about the pathogenesis of otosclerosis (Karosi et al. 2-4). These reports clearly call the attention to the fact that all histologically otosclerotic stapes fixations are associated with the presence of measles virus genomic RNA. Otosclerotic stapes fixations are, however, only two thirds of the stapes fixations in a series of more than 300 stapes footplates consecutively operated on during the last 4 years (3,4). Similar histological lesions and/or presence of measles virus in the stapes superstructure or other bones are not found. Those ankylotic stapes that do not represent otosclerosis show heterogeneous histological pattern of localized hemosiderosis, lymphocytic-plasmocytic infiltration with thickened stapedial mucosal layer, globular fibrosis, or annular calcification (3,4). The otic capsule shows inevitable affinity to persisting measles virus infection and replication, which coincides with the organ-specific localization of otosclerotic foci. The subsequent inflammatory process is characterized by pseudovascular, irregular, and hypercellular absorption lacunae bordered by numerous osteoclasts and multi-nucleated giant cells in the active stage. In contrast, the inactive phase of otosclerosis is featured by almost total absence of bone-derived cells with woven and mosaiclike pattern of cement lines. In these cases, the osteoid substance represents homogeneous eosinophilia. Nevertheless, cement lines cannot be visualized without polarizing light microscopic analysis (3,4), and cement line pattern is a structure of inorganic bony material that is not identical with the osteoid rings bordered by osteocytes. The presented histological section of the incus in the cited article shows no sign of the aforementioned histological features; rather, it shows regular vascular cross sections and Haversian lacunae (1). The section shows normal cellularity and concentric disposition of regular osteocytes. No osteoclasts or giant cells can be identified. The osteoid substance is eosinophilic, only the bulky perivascular connective tissue and vascular endothelial cells are characterized by basophilia. It does not represent information about the pattern of osteoid cement lines. It would be helpful to identify the sectioned part of the incus because intraosseal vascular network is different in the long process and in the body. In addition, the serological diagnosis of otosclerosis is based upon the antimeasles immunoglobulin G low concentration (<12 IU/mL) in the sera of these patients versus healthy immunized individuals' high titer (>100 IU/mL) (5). The specificity and sensitivity of this test for otosclerosis in conductive hearing loss are around 95% (5). Today, we do think, that the diagnosis of otosclerosis cannot be established without detecting low antimeasles immunoglobulin G in the serum and/or detecting measles virus RNA in the affected bone specimen. István Sziklai, M.D., D.Sc. Tamás Karosi, M.D., Ph.D. Department of Otolaryngology- Head and Neck Surgery University Medical School of Debrecen Debrecen, Hungary

Burrow morphology of the ghost shrimp Nihonotrypaea petalura (Decapoda: Thalassinidea: Callianassidae) from western Kyushu, Japan

The callianassid shrimp Nihonotrypaea petalura (Stimpson, 1860) is a common member on boulder beaches in Japanese waters. Its burrow morphology was investigated, based on 28 resin casts collected from a steeply sloping beach with dense boulders and 30 from a more gently sloping beach with less dense boulders in Ariake Sound, southern Japan. The structure and dimensions of the burrows from the two beaches were basically the same, and thus a combined mean value could be given to most of their constituent elements. In its entire dimensions, the burrow is greater in lateral extent than depth, with a mean maximum horizontal extension of 145 mm and a mean maximum depth of 119 mm for the shrimp with a mean total length of 31.8 mm. The burrow winds along boulders or cobbles and consists of, from top to bottom, a single surface opening with an ejected mound, a top shaft leading to the uppermost chamber at a mean depth of 48–56 mm, a passage with a regular cross section that is wider than that of the top shaft, and bulbous chambers (mean no.=4.7) with an irregular cross section associated with branches (mean no. per burrow=1.2). Bulbous chambers are much larger than the uppermost chamber and are usually connected by passages, with some directly attached to each other. The combined architecture of these features is unique and relatively simple among the burrows of all callianassid species, the majority of which inhabit bare soft sediments. The structure and function of the N. petalura burrow are discussed in relation to lifestyle.

Undecidable properties of monoids with word problem solvable in linear time. Part II— cross sections and homological and homotopical finiteness conditions

Using a particular simulation of single-tape Turing machines by finite string-rewriting systems the first two authors have shown that all linear Markov properties are undecidable for the class of finitely presented monoids with linear-time decidable word problem. Expanding on this construction it is shown here that also many properties that are not known to be linear Markov properties are undecidable for this class of monoids. These properties include the existence of context-free or regular cross-sections, the existence of finite convergent presentations, the property of being automatic, and the homological and homotopical finiteness properties left- and right-FPn(n⩾3), FHT, and FDT.

Exact Riemann Solution and Weighted Average Flux Method for Power-law Channel Section

The aim of this work is to extend the Weighted Averaged Flux (WAF) method by E.F. Toro from rectangular to generic regular cross sections, in order to represent the geometric effects of the cross-section on wave propagation along channels. Assuming a power-law variation of the channel width, the 1D conservative shallow water equations, their characteristic form and the shock propagation equations are presented. The exact Riemann solver is derived and is applied to the dam-break problem in valleys with different shape in order to test its efficiency and to check the accuracy order of solutions obtained by approximating the real cross-section with an equivalent rectangle. The WAF method is extended to a power-law channel section and is used to solve the 1D proposed equations taking into account all the source terms that are incorporated into the local Riemann problem. A code based on this method has been developed and results of numerical applications to a Venturi channel and to the attenuation of waves are presented, in order to verify, for well known situations, how accurately the source terms are represented. The code is applied to reproduce one of Brock's experiments (1969; 1970) on roll waves generation in a rectangular channel and results are compared with those obtained with a Godunov-type code developed at CEMAGREF, which is based on a Roe scheme with a later average evaluation of source terms.

Performance of a rectangular secondary concentrator with an asymmetric heliostat field

Secondary concentrators with non-regular cross section have been proposed to permit additional degrees of freedom in heliostat field design, free of the limitations imposed by conventional rotationally symmetric concentrators. A new class of concentrators with a rectangular cross section was found by numerical optimization for heliostat fields having an elliptic contour with high eccentricity. An example of such a rectangular concentrator was constructed and tested at the Weizmann Institute, where the heliostat field has a strong asymmetry and is poorly suited for symmetric (having regular cross section) concentrators. The performance of the new concentrator has been tested using calorimetric and radiometric measurements. The tests were carried out for several heliostats, located in representative positions relative to the predicted acceptance contours of the concentrator. The results of the tests show an agreement with the prediction, and validate the new design for use with highly eccentric fields. A more general conclusion is the validation of the approach of optimizing faceted secondary concentrators with flexible geometry to match heliostat fields having a wide range of possible contours.