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1
Wen, Mingzheng, Huaibo Zhang, Shoujun Wang, Zhiwen Shang, Shaotong Zhang, Peng Yang, and Hong Wang. "Field Investigation on the Coastal Erosion and Progradation Evolution of the Binzhou Shelly Chenier in China: Comparisons between Normal and Typhoon Hydrodynamics." Journal of Marine Science and Engineering 10, no. 6 (May 30, 2022): 752. http://dx.doi.org/10.3390/jmse10060752.
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The shelly chenier is a dike-like accumulation formed by waves, currents, and other hydrodynamic forces pushing the shells and their debris in the intertidal zone to the high tide line. It is a special type of coastal dike. The shelly chenier located in Wangzi Island of northern Shandong Province is the last well-preserved chenier of the Bohai Bay with natural attributes exposed on the surface. It has unique and irreplaceable attributes among the shell beaches of China. Based on remote sensing interpretation, field investigation, and GPS-RTK (Real-Time Kinematic) measurement, this paper investigates the coastal erosion and progradation evolution of the Binzhou Shelly Chenier in China usingcomparisons between normal and typhoon hydrodynamics. The results show that: (1) There are two kinds of shelly chenier in the study area, the first is “the tidal channel shelly chenier” which is significantly affected by the tidal current, and the second is “the open shelly chenier”, which is significantly affected by direct scouring and silting of waves. The open shelly chenier is continuously eroding under the normal hydrodynamics and the shell beach is supplied by a large number of shells and their debris under the typhoon hydrodynamics, while the tidal channel shelly chenier is gradually developed due to the action of alongshore currents and in–out flows. (2) The energy of waves and currents under normal hydrodynamics is insufficient to transport the shells and their debris in the intertidal zone to the shell-beach. On the contrary, the continuous action of waves makes the shells and their debris on the open-shell beach finer and transports the shells and their debris to the sea causing erosion and retreat of the shelly chenier. (3) The action of typhoons and other strong winds and waves results in the original accumulation on the open shell-beach being further transported to the land and provides a large amount of shells and debris from the intertidal zone to the shelly chenier. Based on GPS-RTK monitoring data from 2020–2021, it was found that the transport volume of shells and debris caused by a typhoon storm surge is equivalent to the annual transport volume under normal ocean dynamics.
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Flessa, Karl W., Alan H. Cutler, and Keith H. Meldahl. "Time and taphonomy: quantitative estimates of time-averaging and stratigraphic disorder in a shallow marine habitat." Paleobiology 19, no. 2 (1993): 266–86. http://dx.doi.org/10.1017/s0094837300015918.
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We examined the radiocarbon age, taphonomic condition and stratigraphic position of shells of the venerid bivalveChionespp. from the tidal flats of Bahia la Choya, Sonora, Mexico. Shells in Bahia la Choya are time-averaged. Thirty shells yielded radiocarbon dates from modern (A.D. 1950 or younger) to 3569 years before present. The median calendar age of inner flat shells is 483 years; the median age of tidal channel shells is 427 years. We interpret such long shell survival to be the result of frequent shallow burial. Such burial retards bioerosion of shells.The taphonomic condition of shells varied with environment. Shells from the surface of the inner flats were better preserved than shells from the tidal channel. Shells are more likely to be physically worn and biologically degraded in the waters of the channel than on the quieter and more frequently exposed inner tidal flat. Taphonomic condition is an unreliable indicator of a shell's time-since-death. Poorly-preserved shells on the inner flats tended to be old, but in general shell condition was much more variable than shell age. A shell's condition is more likely the result of its total residence time on the surface than its time-since-death (surface time plus burial time).Two composite short (44 cm and 50 cm) cores revealed varying degrees of stratigraphic disorder (the departure from perfect correlation between relative stratigraphic position and relative age). One of eight shells in the inner flats core was disordered; four of nine shells in the tidal channel were disordered. The actual age range of surface shells approximates the age range of shells in cores. Stratigraphic disorder is a consequence of both time-averaging and physical and biogenic mixing.Time-averaging controls the degree of precision possible in paleoecological studies. Environmental changes and ecological phenomena occurring within a span of 3500 years would not be recognized in deposits like those of Bahia la Choya. Time-averaging and stratigraphic disorder also constrain the temporal resolution possible in microstratigraphic studies of evolution. The extent of time-averaging and stratigraphic disorder will dictate an appropriate sample interval. In order to prevent temporal overlap between successive samples in deposits like Bahia la Choya, sample spacing should not be less than approximately 0.5 m.
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Ayres-Peres, Luciane, Aline Ferreira Quadros, and Fernando L. Mantelatto. "Comparative analysis of shell occupation by two southern populations of the hermit crab Loxopagurus loxochelis (Decapoda, Diogenidae)." Brazilian Journal of Oceanography 60, no. 3 (September 2012): 299–310. http://dx.doi.org/10.1590/s1679-87592012000300003.
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The present study aimed to comparatively verify the relation between the hermit crabs and the shells they use in two populations of Loxopagurus loxochelis. Samples were collected monthly from July 2002 to June 2003, at Caraguatatuba and Ubatuba Bay, São Paulo, Brazil. The animals sampled had their sex identified, were weighed and measured; their shells were identified, measured and weighed, and their internal volume determined. To relate the hermit crab's characteristics and the shells' variables, principal component analysis (PCA) and a regression tree were used. According to the PCA analysis, the three gastropod shells most frequently used by L. loxochelis varied in size. The regression tree successfully explained the relationship between the hermit crab's characteristics and the internal volume of the inhabited shell. It can be inferred that the relationship between the morphometry of an individual hermit crab and its shell is not straightforward and it is impossible to explain only on the basis of direct correlations between the body's and the shell's attributes. Several factors (such as the morphometry and the availability of the shell, environmental conditions and inter- and intraspecific competition) interact and seem to be taken into consideration by the hermit crabs when they choose a shell, resulting in the diversified pattern of shell occupancy shown here and elsewhere.
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Theis, Christian. "Formation of Twin Clusters in a Galactic Tidal Field." Symposium - International Astronomical Union 207 (2002): 681–83. http://dx.doi.org/10.1017/s0074180900224534.
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The formation of globular clusters is still an unsolved problem. Though most scenarios assume a massive molecular cloud as the progenitor, it is unclear how the cloud is transformed into a star cluster. Here a scheme of supernova (SN) induced cluster formation is investigated. In this scenario the expanding SN shell accumulates the mass of the cloud. This is accompanied by fragmentation resulting in star formation in the shell. If this stellar shell expands sufficiently slowly, its self-gravity leads to a recollapsing shell, thus forming one or several stellar clusters.In this paper N-body simulations of collapsing shells moving on circular orbits in a galactic potential are presented. It is shown that typical shells (105 M⊙, 30 pc) evolve to twin clusters in the galactocentric distance range between 3 and 11 kpc. Their masses show a strong radial trend: on orbits inside 5 kpc both clusters have almost equal mass. Outside 5 kpc the more massive twin cluster contains about 55% of the shell's mass, whereas the mass of the smaller decreases linearily to 15% at 11 kpc. Outside 11 kpc the collapsing shells end up in a single cluster. Inside 3 kpc the shells are tidally disrupted and only fragments substantially less massive than the initial shell survive.
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Zhang, Shi, Yun Zhang, Zhigao Huang, Huamin Zhou, and Jianhui Li. "The inter-element coupling effect of triangular flat shells." Engineering Computations 32, no. 7 (October 5, 2015): 1959–80. http://dx.doi.org/10.1108/ec-11-2014-0230.
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Purpose – The purpose of this paper is to study the inter-element coupling effect of membrane and plate components between two adjacent shells occurring on the common boundary. Design/methodology/approach – In this paper, three triangular flat shells developed by combining an excellent membrane element (OPT) with three outstanding plate bending elements (DKT, RDKTM and DST-BK), respectively, are used to study this phenomenon. Benchmark tests are implemented to evaluate the performance of three selected plate elements and the formulated flat shells. Findings – The inter-element coupling effect of membrane and plate components belonging, respectively, to two adjacent shells deteriorate the performance of shells. Therefore, a shell’s performance cannot be guaranteed certainly by the superimposed membrane and plate behaviors. Practical implications – The “order matching” criterion is proposed to explain this phenomenon and it is concluded that the flat shell that follows this criterion explicitly may alleviate or even overcome the inter-element coupling effect. Originality/value – Previous studies mainly focus on formulation of high-performance membrane and plate elements. However, the inter-element coupling effect of membrane and plate components between two adjacent shells occurring on the common boundary, has attracted less attention. Thorough benchmark tests for three flat shells are implemented to investigate the phenomenon. The results shows that the inter-element coupling effect deteriorates the performance of shells. And the “order matching” criterion is proposed to explain this phenomenon and it is concluded that the flat shell that follows this criterion explicitly may alleviate or even overcome the inter-element coupling effect.
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Srichanachaichok, Wiranchana, and Dakrong Pissuwan. "Micro/Nano Structural Investigation and Characterization of Mussel Shell Waste in Thailand as a Feasible Bioresource of CaO." Materials 16, no. 2 (January 13, 2023): 805. http://dx.doi.org/10.3390/ma16020805.
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Mussel shell waste, which is regularly disposed by households, restaurants, markets, or farms, causes environmental problems worldwide, including in Thailand, because of its long decomposing time. Owing to a large amount of calcium (Ca) content from calcium carbonate (CaCO3) in mussel shell waste, many Thai local businesses grind the shell waste into powder and sell it as a source of Ca. Generally, these powdered waste shells are a mixture of various types of mussel shell waste. In this study, we investigated and characterized powdered mixed waste shells sold in a local Thai market (called mixed shell powder) and ground shells from waste green mussel shells (called green mussel shells) prepared in the laboratory after calcination at different temperatures (800 °C, 900 °C, and 1000 °C). Mixed shell powder containing five different types of mussel shells and green mussel shells were calcined for 2 h and 3 h, respectively. The time used for calcination of mixed shell powder and green mussel shells was different due to the different particle sizes of both shell wastes. We found that an optimal temperature of 1000 °C completely converted CaCO3 to CaO in both samples. The nanoscale size of CaO was detected at the surface of calcined shells. These shell wastes can be used as a bioresource of CaO.
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Yang, Yeong-Bin, and Jae-Hoon Kang. "Comparisons of Paraboloidal Shells and Sinusoidal-Shaped Shells in Natural Frequencies." Volume 24, No 3, September 2019 24, no. 3 (September 2019): 451–57. http://dx.doi.org/10.20855/ijav.2019.24.312.
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Natural frequencies and mode shapes are obtained for a sinusoidal-shaped shell of revolution by using the Ritz method from a three-dimensional (3-D) analysis instead of a mathematically two-dimensional (2-D) thin shell theory or high order thick shell theory. The present analysis uses circular cylindrical coordinates instead of 3-D shell coordinates, which have been used in traditional shell analyses. Convergence studies can analyze the first five frequencies to four-digit exactitude. Results are given for a variety of shallow and deep sinusoidal-shaped shells with different boundary conditions. The sinusoidal-shaped shells are very similar to paraboloidal shells in shape. The frequencies of the sinusoidal-shaped shells from the present 3-D method are compared with those from 2-D thin shell theories for paraboloidal shells. The present 3-D method is applicable to very thick as well as thin shells.
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Yang, Yeong-Bin, and Jae-Hoon Kang. "Comparisons of Paraboloidal Shells and Sinusoidal-Shaped Shells in Natural Frequencies." June 2019 24, no. 2 (September 2019): 451–57. http://dx.doi.org/10.20855/ijav.2019.24.31276.
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Natural frequencies and mode shapes are obtained for a sinusoidal-shaped shell of revolution by using the Ritz method from a three-dimensional (3-D) analysis instead of a mathematically two-dimensional (2-D) thin shell theory or high order thick shell theory. The present analysis uses circular cylindrical coordinates instead of 3-D shell coordinates, which have been used in traditional shell analyses. Convergence studies can analyze the first five frequencies to four-digit exactitude. Results are given for a variety of shallow and deep sinusoidal-shaped shells with different boundary conditions. The sinusoidal-shaped shells are very similar to paraboloidal shells in shape. The frequencies of the sinusoidal-shaped shells from the present 3-D method are compared with those from 2-D thin shell theories for paraboloidal shells. The present 3-D method is applicable to very thick as well as thin shells.
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Nurudin, La Ode, Lukas Kano Mangalla, and La Ode Ahmad Barata. "Analisis Karakteristik Biomassa Cangkang Kelapa Dan Kulit Mete Melalui Proses Torefaksi." Enthalpy : Jurnal Ilmiah Mahasiswa Teknik Mesin 7, no. 1 (April 3, 2022): 28. http://dx.doi.org/10.55679/enthalpy.v7i1.24559.
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In the face of the depletion of fossil fuels, alternative fuels such as biomass are needed. However, biomass has a fairly low calorific value and several other disadvantages compared to petroleum. Therefore, a new breakthrough is needed to correct these weaknesses, one of which is the Torrefaction process. The purpose of this study was to determine the effect of torrefaction of coconut shell and cashew shell biomass on the physical and chemical properties of the material. This research was conducted using coconut shells and cashew shells. The results of this study indicate that the calorific value of coconut shells and cashew shells after torrefaction is 5115,297-5147,021 cal/gr. The water content in coconut shells is 2.718% and the value of water content in cashew shells is 2.397%, the ash content of coconut shells is 6.853% and the value of cashew shell ash content is 6.600%, the value of volatile levels of coconut shells is 14.885% and the value of volatile levels of cashew shells of 14.557% and the value of fixed carbon content of coconut shell is 75.574% and the value of fixed carbon content of cashew shell is 76.447%. Keywords : Biomass, coconut shell, cashewnut shell, torrefaction
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Wang, Zhen, and Yang Zhao. "Buckling Strength of Tapered Cylindrical Shells under Partial Axial Compression: Effect of Circumferential Weld-Induced Imperfections." Advanced Materials Research 163-167 (December 2010): 49–54. http://dx.doi.org/10.4028/www.scientific.net/amr.163-167.49.
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Buckling is often the main design consideration for thin cylindrical shells. For most load cases, the stability behavior of the shell is acutely sensitive to circumferential weld-induced imperfections, and the corresponding residual stresses are some beneficial to buckling strength of the shell generally. However, these conclusions are all based on the cylinders with constant wall thickness, and the studies about the effect of residual stresses on buckling strength of tapered cylindrical shells under partial axial compression are few. This paper applies trapezoidal strain field approach to simulate circumferential weld-induced imperfections on tapered cylindrical shellls, and studies the stability behavior of the cylinders with single circumferential weld and multiple circumferential welds under partial axial compression respectively. By comparing the results derived from the models with/without circumferential welds and corresponding residual stresses, the effects of weld depressions and residual stresses on tapered cylindrical shells under partial axial compression are obtained.
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Laidre, Mark E., and Rebecca Trinh. "Unlike terrestrial hermit crabs, marine hermit crabs do not prefer shells previously used by conspecifics." Crustaceana 87, no. 7 (2014): 856–65. http://dx.doi.org/10.1163/15685403-00003320.
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Gastropod shells represent an essential resource for hermit crabs (Decapoda, Anomura). In many cases, hermit crabs acquire used shells from conspecifics who previously occupied the shell. Terrestrial hermit crabs (Coenobita compressus H. Milne Edwards, 1836) strongly prefer used shells. Here we test whether marine hermit crabs (Pagurus samuelis (Stimpson, 1857)) also exhibit a preference for used shells by providing them with matched pairs of (1) a used shell (previously occupied by either the choosing crab itself or by a conspecific) versus (2) a brand new shell (freshly derived from a predated gastropod). Unlike terrestrial hermit crabs, marine hermit crabs showed no preference for used shells (either their original shell or a shell from a conspecific). We suggest the divergent shell preferences of marine and terrestrial hermit crabs relate to the contrasting natural selection pressures in the sea versus on land. In particular, the used shells of terrestrial hermit crabs are architecturally remodeled by prior occupants and these remodeled shells represent a superior resource on land. In contrast, marine hermit crabs never remodel shells, and for them a used shell may be less protective than a new shell against the many specialized shell predators in the ocean.
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Alcaraz, Guillermina, and Karla Kruesi. "Niche overlap and resource partitioning between two intertidal hermit crab species." Journal of the Marine Biological Association of the United Kingdom 99, no. 1 (December 7, 2017): 135–42. http://dx.doi.org/10.1017/s0025315417001850.
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The gastropod shell influences important aspects of the hermit crab's life; however, the shells are commonly a limited resource. Therefore, different hermit crab species that coexist in intertidal areas are commonly involved in intraspecific and interspecific competition for shells. We assess if differences in shell preference, exploitation ability, or competition by interference can explain the partitioning of shells between the coexisting species Calcinus californiensis and Clibanarius albidigitus. Clibanarius preferred shells of Nerita funiculata among the six gastropod shells tested, while Calcinus did not establish a hierarchy in shell preference. Therefore, the preference for gastropod shell species does not seem to diminish the competition for shells in the wild. Clibanarius identified and attended to chemical cues signalling potential sites of available shells (chemical cues of dead gastropods); Calcinus did not respond to these cues (competition by exploitation). However, Calcinus was more successful in obtaining a new shell by interspecific shell fighting than Clibanarius. Consequently, the use of better quality shells (intact shells) by Calcinus in the wild can be explained by its greater fighting ability compared with Clibanarius. The bias in shell distributions through dominance by shell fighting, more than by exploitation ability, has also been suggested for other hermit crab species of these genera.
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Li, Bing Ru, Xuan Yin Wang, Hui Liang Ge, and Yue Peng Jiang. "Study on Applicability of Sound Radiation Characteristics of Thin Finite Length Cylindrical Shells Using Wave Propagation Approach." Applied Mechanics and Materials 190-191 (July 2012): 1325–30. http://dx.doi.org/10.4028/www.scientific.net/amm.190-191.1325.
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Based on Donnell’s thin shell theory and basic equations, the wave propagation method is discussed here in detail, which is used to investigate the vibration and sound radiation characteristics of thin finite length circular cylindrical shells and ring stiffened shells under various boundary conditions. The effects of boundary conditions, mode truncation, shell’s length, thickness and rings on the acoustic radiation are explored. It is shown that the wave propagation method is more effective for the long cylindrical shell, and the mode truncation can satisfy the calculation accuracy. The conclusion is drawn that the stiffeners have a great influence on the total mechanical impedance while have a slight influence on radiation impedance. The work will give some guidelines for noise reduction of this kind of shell.
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Li, Bing Ru, Yue Peng Jiang, Xuan Yin Wang, and Hui Liang Ge. "Vibro-Acoustics Characteristics of Non-Uniform Ring Stiffened Cylindrical Shells Using Wave Propagation Approach." Advanced Materials Research 655-657 (January 2013): 562–67. http://dx.doi.org/10.4028/www.scientific.net/amr.655-657.562.
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Based on Donnell’s thin shell theory and basic equations, the wave propagation method is discussed here in detail, which is used to investigate the vibration and sound radiation characteristics of non-uniform ring stiffened cylindrical shells under various boundary conditions. The structure damp effects of cylindrical shells are investigated and the ring ribs were considered very narrow, and the rib forces are considered in radial direction. The conclusion are drawn that with the structural loss factor changing large, the whole pressure level are changed little, but the peak of resonance are slacking down obviously; The shell’s resonance frequency can be changed with irregular ring stiffened cylindrical shell .The work will give some guidelines for noise reduction of this kind of shell.
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Li, Dao Kui, and Yong Jun Lei. "Free Vibration of a Cylindrical Shell with Varied Initial Stresses in Different Longitudinal Sections." Applied Mechanics and Materials 52-54 (March 2011): 717–22. http://dx.doi.org/10.4028/www.scientific.net/amm.52-54.717.
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An exact and closed-form solution is obtained for free vibration problems of homogeneous isotropic cylindrical shells, which is under arbitrary boundary conditions and with varied initial stresses in different longitudinal sections. First, the cylindrical shell is divided into multiple sub-shells according to their thicknesses and initial stresses. And the displacement functions of the sub-shell’s middle plane are expanded as trigonometric series in circumferential direction. Then, based on the simplified Donnell shell theory, a set of fundamental dynamic equations, which take initial stresses into accounts, is derived through Hamilton’s principle for each sub-shell. Correspondingly, boundary conditions and connection conditions are derived too. These equations and conditions are simplified through setting the displacements varied in harmonic form. Finally, through defining the state vector, the dynamic equations and solution-determine conditions are described as state-space forms and solved conveniently. Numerical examples validate this method. Driving process of analytical solutions show that it is convenient for introducing and dealing with solution-determine conditions and solving the dynamic problems of cylindrical shells with varied initial stresses in different longitudinal sections.
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Tarn, Jiann-Quo, Yung-Ming Wang, and Shi-Horng Chang. "Theory of Multilayered Anisotropic Shells Based on an Asymptotic Variational Formulation." Journal of Mechanics 14, no. 4 (December 1998): 173–82. http://dx.doi.org/10.1017/s1727719100000204.
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ABSTRACTA general theory for multilayered anisotropic elastic shells is developed in an asymptotic variational framework of 3-D elasticity. The generic shell continuum considered is heterogeneous through the thickness. It is shown that the classical laminated shell theory based on Love's assumption arises naturally as the first-order approximation to the 3-D theory. Higher-order corrections can be determined by solving the 2-D shell equations hierarchically. The associated edge conditions at each level of approximation are derived. Various types of shells such as shells of revolution, conical shells, spherical shells, circular cylindrical shells can be treated within the context.
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Wang, Tsai-Yih, and Franklin A. Pokorny. "Pecan Shells as an Organic Component of Container Potting Media." HortScience 24, no. 1 (February 1989): 75–78. http://dx.doi.org/10.21273/hortsci.24.1.75.
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Abstract Pecan shells, a waste product of the nut processing industry, were evaluated as a potential container medium component. Raw shells need to be hammer-milled or otherwise transformed into a physically consistent product. Shells were acidic (pH 4.8) and low in soluble salts and water-extractable nutrients. Four shell-based media (100% milled pecan shells, 3 shells: 1 sand, 1 shells: 1 sand, and 1 shells: 3 sand, v/v) were evaluated. Control medium was 1.5 Canadian sphagnum peat: 1 perlite (v/v). Growth of begonia (Begonia semperflorens Link and Otto ‘Scarlet’) and tomato plants (Lycopersicon esculentum Mill. ‘Rutgers’) increased linearly as percentage of sand was increased from 0% to 75%. Begonias grown in the 1 shell : 3 sand mix equaled growth and quality of control plants. None of the tomato plants in shell-based media were comparable in growth to the control, because of phytotoxic substances associated with shells and the inadequacy of easily available water of shell-based media. Ilex × ‘Nellie R. Stevens’ grown in shell-based media were equivalent in size and quality to those in peat-perlite.
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Galletly, G. D., and J. Blachut. "Buckling Design of Imperfect Welded Hemispherical Shells Subjected to External Pressure." Proceedings of the Institution of Mechanical Engineers, Part C: Mechanical Engineering Science 205, no. 3 (May 1991): 175–88. http://dx.doi.org/10.1243/pime_proc_1991_205_108_02.
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Welded hemispherical or spherical shells in practice have initial geometric imperfections in them that are random in nature. These imperfections determine the buckling resistance of a shell to external pressure but their magnitudes will not be known until after the shell has been built. If suitable simplified, but realistic, imperfection shapes can be found, then a reasonably accurate theoretical prediction of a spherical shell's buckling/collapse pressure should be possible at the design stage. The main aim of the present paper is to show that the test results obtained at the David Taylor Model Basin (DTMB) on 28 welded hemispherical shells (having diameters of 0.75 and 1.68 m) can be predicted quite well using such simplified shape imperfections. This was done in two ways. In the first, equations for determining the theoretical collapse pressures of externally pressurized imperfect spherical shells were utilized. The only imperfection parameter used in these equations is δ0, the amplitude of the inward radial deviation of the pole of the shell. Two values for δ0 were studied but the best overall agreement between test and theory was found using δ0 = 0.05 ✓ (Rt). This produced ratios of experimental to numerical collapse pressures in the range 0.98–1.30 (in most cases the test result was the higher). The second approach also used simplified imperfection shapes, but in conjunction with the shell buckling program BOSOR 5. The arc length of the imperfection was taken as simp = k ✓ (Rt) (with k = 3.0 or 3.5) and its amplitude as δ0 = 0.05√(Rt). Using this procedure on the 28 DTMB shells gave satisfactory agreement between the experimental and the computer predictions (in the range 0.92–1.20). These results are very encouraging. The foregoing method is, however, only a first step in the computerized buckling design of welded spherical shells and it needs to be checked against spherical shells having other values of R/t. In addition, more experimental information on the initial geometric imperfections in welded spherical shells (and how they vary with R/t) is desirable. A comparison is also given in the paper of the collapse pressures of spherical shells, as obtained from codes, with those predicted by computer analyses when the maximum shape deviations allowed by the codes are employed in the computer programs. The computed collapse pressures are frequently higher than the values given by the buckling strength curves in the codes. On the other hand, some amplitudes of imperfections studied in the paper give acceptable results. It would be helpful to designers if agreement could be reached on an imperfection shape (amplitude and arc length) that was generally acceptable. Residual stresses are not considered in this paper. They might be expected to decrease a spherical shell's buckling resistance to external pressure. However, experimentally, this does not always happen.
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Tzou, H. S., and J. P. Zhong. "Electromechanics and Vibrations of Piezoelectric Shell Distributed Systems." Journal of Dynamic Systems, Measurement, and Control 115, no. 3 (September 1, 1993): 506–17. http://dx.doi.org/10.1115/1.2899129.
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Smart piezoelectric structures, conventional passive materials integrated with piezoelectric sensors, actuators, and control electronics, have great potentials in many engineering applications. This paper is devoted to a new theoretical development of generic piezoelectric shell distributed systems. System electromechanical equations and boundary conditions for a thick piezoelectric shell continuum with symmetrical hexagonal structure (Class C6v = 6 mm) are derived using Hamilton’s principle and linear piezoelectric theory. Further simplification leads to a set of new electromechanical system equations, three translated coordinates and two rotary coordinates, for piezoelectric shell continua including rotary inertias and transverse shears. For thin piezoelectric shells, the second set system equations are further simplified using Kirchhoff-Love’s assumptions. The converse effect induced electric forces/moments and boundary conditions can be used to control system dynamics via open or closed-loop control systems. Applications of the theories to a plate and shells of revolution (spherical, cylindrical, and conical shells) are demonstrated in case studies.
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Meldahl, Keith H., Karl W. Flessa, and Alan H. Cutler. "Time-averaging and postmortem skeletal survival in benthic fossil assemblages: quantitative comparisons among Holocene environments." Paleobiology 23, no. 2 (1997): 207–29. http://dx.doi.org/10.1017/s0094837300016791.
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We used radiocarbon ages on dead Holocene shells of the venerid bivalveChionespp. to investigate how time-averaging and taphonomy in shallow marine benthic assemblages vary with sedimentary and tectonic setting. We compared shells collected from the sediment surface in five depositional environments from two regions of the Gulf of California, Mexico: Bahía Concepción, a young faulted rift basin with high rates of terrigenous and carbonate sedimentation; and Bahía la Choya, an intertidal system along a sediment-starved shelf. Frequency distributions of shell ages in all environments form a hollow curve, with a mode at young ages and a long tail toward older ages. This pattern suggests that shells are added to the taphonomically active zone (TAZ) at roughly constant rates (via continuous shell deaths), and removed from the TAZ at random, either through destruction or by achieving final burial. Shell half-lives (the amount of time to remove half the shells from the TAZ) provide a comparative measure of time-averaging. Time-averaging varies with sedimentary and tectonic setting. The lowest amounts of time-averaging (shell half-lives of 90 to 165 years) occur in Bahía Concepción, where rapid rates of terrigenous sedimentation (on fan-deltas) and carbonate sedimentation (in pocket bays) bury shells rapidly. Time-averaging is higher in the sediment-starved environments of Bahía la Choya (shell half-lives of 285 to 550 years). The highest amounts of time-averaging occur the inner tidal flats of Bahía la Choya (shell half-life of 550 years). Here the conjunction of low sedimentation rates with low rates of shell destruction (due to periodic tidal emergence) permits shells to persist in the TAZ for very long time spans.There is no systematic relationship between a shell's age and its taphonomic condition (taphonomic grade) in any environment, probably because of the complex and random nature of burial-exhumation in the TAZ. Agevariancetends to increase with increasing taphonomic alteration: highly altered shells range in age from young to several thousand years old, while less altered shells are mostly young. The correspondence between time-averaging and the taphonomic condition of entire shell assemblages is also weak, but might be resolved with further study.These results provide quantitative data on time-averaging in benthic assemblages as a function of sedimentary and tectonic setting, and suggest some guidelines for facies appropriate for particular studies. Shallow marine rift basins like Bahía Concepción can potentially contain within-horizon fossil assemblages representing time spans of only a few hundred years—time resolution often beyond reach in paleontology. In contrast, sediment-starved shelf habitats like Bahía la Choya are unlikely to yield assemblages with time resolution finer than several thousands of years.
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Godin, Oleg A. "Sound scattering and radiation suppression by pressurized spherical shells." Journal of the Acoustical Society of America 154, no. 5 (November 1, 2023): 3223–36. http://dx.doi.org/10.1121/10.0022416.
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Thin-shell models offer important insights into the complex process of sound-structure interaction but are found to be inconsistent with the rigorous thick-shell theory for fluid-loaded spherical shells. Here, linearized equations of motion of fluid-loaded, thin, spherical shells are re-derived from the first principles. The shell may be prestressed due to the difference in the static pressures in the internal and external fluids. Differences in the fluid-loading terms from previously proposed ad hoc models are identified and their significance is analyzed. Analytic solutions are derived of the problems of spherical sound wave scattering by a fluid-filled, prestressed spherical shell and resonant vibrations of the shell. The results reduce to a number of known exact and asymptotic solutions in appropriate limiting cases. The mathematical model of the shell vibrations is applied to characterize the influence of the shell's material properties and the prestress on passive suppression of low-frequency underwater sound radiation due to diffraction on an acoustically compliant sphere, such as an encapsulated gas bubble. Using soft rubber as the encapsulating membrane is found to preserve the sound suppression qualities of the free gas bubble.
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Muljani, Srie, Erwan Adi Saputra, and Ketut Sumada. "Transformation of Calcium Carbonate Polymorph From Various Type of Shells by Carbonation Methods." Reaktor 21, no. 1 (April 26, 2021): 27–34. http://dx.doi.org/10.14710/reaktor.21.1.27-34.
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The utilization of shells can reduce the accumulation of shell wastes and increase the value of shells to achieve ecological and economic incentives. This study examines the transformation of calcium carbonate polymorph from several types of shells to understand the causes of their characteristics in order to suitable for their use. The types of shells used in this experiment are selected based on consumable and their habitats such as snail shells, crab shells, eggshells, batik mussels shells, and golden conch shells. The prepared shells calcinate at 900 °C, the reaction with hydrochloric acid, and carbonation by flowing CO2 into a stirred reactor to produce precipitated CaCO3. The characteristics of polymorph CaCO3 in the sintering temperature of 30, 50, and 70 ℃ were identified by XRD, FTIR, and SEM morphological. The result is that the polymorphs formed from each shell are different in shape, size, and crystallinity. At the temperature of 70 ℃, the rhombohedral calcite was obtained from snail shells, the cubic calcite was obtained from batik mussel shell, while rhombohedral calcite multilayers obtained (100%) from golden conch shells. The aragonite was obtained from batik mussel shells at 30 and 70 ℃. The pure vaterite (100%) was obtained from snail shells and crab shells at 50 ℃. The characteristic of polymorph formed might be useful as information for more suitable applications, especially as nano-bio materials, optical, or filler
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Gönnenwein, Friedrich. "Shells, Anti-Shells and Modes in nuclear Fission." EPJ Web of Conferences 193 (2018): 01001. http://dx.doi.org/10.1051/epjconf/201819301001.
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Fission phenomena are surveyed where fragment properties are catching the eye. Beyond the Liquid Drop the relevant properties of fragments are shell effects and nuclear pairing. Shell effects influence on mass, charge, stability and deformability of fragments. Most often only the stabilizing effects of shells are discussed and the equally frequent destabilizing effects are not mentioned. For the present purpose the terms shells and anti-shells are used in case of stabilizing and destabilizing effects, respectively. Fragment shells and anti-shells lead to fission modes with characteristic properties. A special issue is where in the course of fission these modes assume their characteristic features. Surprisingly fragment angular distributions in above- and sub-barrier fission help elucidating this question. The discussion is focussed on fission in the standard actinides.
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Lim, Teik Cheng. "Spherical Auxetic Shells." Advanced Materials Research 804 (September 2013): 146–50. http://dx.doi.org/10.4028/www.scientific.net/amr.804.146.
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Materials that exhibit negative Poissons ratio are called auxetic materials. Although such materials are quite rare, they nevertheless exist as naturally occurring materials and artificially made materials. Due to their unique material properties, auxetic materials have been intensively investigated for the past 20 years. This paper studies the effect of auxeticity on the maximum stresses in spherical shells. The results suggest that auxetic materials are not suitable for shells with built-in edge, but highly suitable for shells that are simply supported. For the latter boundary condition, it was found that the ratio of maximum bending stress to the maximum membrane stress diminishes as the Poissons ratio of the shell material approaches-1. This means that under the boundary condition of simple supports, a geometrically thick shell is mechanically equivalent to a thin or membrane shell, and therefore the use of membrane shell theory suffices even for a reasonably thick shell if the shell material is highly auxetic.
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B., Neeraja. "Molluscan Shell Diversity of Ennore Creek, Chennai, India." International Journal of Zoological Investigations 08, no. 01 (2022): 120–23. http://dx.doi.org/10.33745/ijzi.2022.v08i01.015.
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Molluscs are the soft bodied invertebrates, which are protected by calcium carbonate shells. The shells are coated mostly with calcium carbonate and protein matrix in a process called bio-mineralization. Apart from playing a major role in the aquatic ecosystem, they are considered to be best bio-indicators of environmental pollution, as their soft tissues, and their shells are known to accumulate the pollutants. The divers patterns and different shell morphologies of the clams, snails and oysters, seem to be influenced by the solar radiation, predator stress and various environmental factors, which seem to regulate the gene expression patterns of the shell formation. In the present study, different molluscan shells were collected and studied for their diverse patterns. They were collected from Ennore, creek of Tamil Nadu, India as it is known to be a lagoon type of ecosystem and plays an important role in maintenance of the aquatic ecosystem surrounding it. The present study showed a diverse shell patterns mostly with reference to clam shells. A few, oyster shells, cerithiid shells and potaminind shells were also observed. A detailed analysis of the shell patterns under the influence of various external environmental cues may be investigated in future.
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Sun, Jianliang, Xu Zhang, Yuanhe Zhang, Xianghui Lu, and Yan Peng. "Failure Behavior of Corrugated Pressure Cylindrical Shells with Variable Wall Thickness under Uniform External Pressure." Journal of Marine Science and Engineering 12, no. 3 (February 23, 2024): 385. http://dx.doi.org/10.3390/jmse12030385.
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The main load-bearing structure of submarines is the pressure shell. Shell failures are usually caused by high hydrostatic pressure and its own potential geometric imperfections. This paper proposes a cylindrical shell with a strong corrugated stiffening structure. Two theoretically geometrically identical shells are fabricated using CNC machining to ensure the reproducibility and reasonableness of the results. Firstly, the point cloud data of all the geometric parameters of the corrugated pressure cylindrical shells were obtained using a 3D scanner. Geomagic Control X 3D inspection software was used to determine the geometric deviations of the shells. Geometric reconstruction was performed using Geomagic Design X reverse modeling software to capture potential imperfections of the shells. The aluminum shells were then welded and placed in the pressure chamber. Failure loads were obtained for all shells by constant water injection and pressurization. Considering the confined nature of the pressure chamber, a nonlinear finite element analysis of the corrugated pressure cylindrical shell was carried out using Abaqus/Riks, taking into account actual fabrication imperfections. Finally, the failure behavior of the shells under uniform external pressure was determined. The results show that both corrugated pressure cylindrical shells have high machining accuracy. The numerical simulation results of the critical buckling load of the corrugated pressure cylindrical shells were in good agreement with the test results. The corrugated structure has additional advantages in retarding the generation and expansion of shell surface defects. The equilibrium path of the corrugated pressure cylindrical shell can be maintained in a smooth and continuous state, showing stable buckling behavior. This study will provide new inspiration for the structural design and failure prediction of the submarine pressure shell.
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Zannon, Mohammad, and Hussam Alrabaiah. "Mathematical Formulation of Laminated Composite Thick Conical Shells." Journal of Mathematics Research 8, no. 4 (July 25, 2016): 166. http://dx.doi.org/10.5539/jmr.v8n4p166.
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<span lang="EN-US">The </span><span lang="EN-US">mathematical formulation</span><span lang="EN-US">of thick conical shells using third order shear deformation of thick shell theory are presented. The equations of motion are obtained using Hamilton’s principle. For present analysis, we consider shell's system transverse normal stress, rotary inertia and shear deformation.</span>
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Charpentier, Victor, and Sigrid Adriaenssens. "Effect of Gravity on the Scale of Compliant Shells." Biomimetics 5, no. 1 (January 27, 2020): 4. http://dx.doi.org/10.3390/biomimetics5010004.
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Thin shells are found across scales ranging from biological blood cells to engineered large-span roof structures. The engineering design of thin shells used as mechanisms has occasionally been inspired by biomimetic concept generators. The research goal of this paper is to establish the physical limits of scalability of shells. Sixty-four instances of shells across length scales have been organized into five categories: engineering stiff and compliant, plant compliant, avian egg stiff, and micro-scale compliant shells. Based on their thickness and characteristic dimensions, the mechanical behavior of these 64 shells can be characterized as 3D solids, thick or thin shells, or membranes. Two non-dimensional indicators, the Föppl–von Kármán number and a novel indicator, namely the gravity impact number, are adopted to establish the scalability limits of these five categories. The results show that these shells exhibit similar mechanical behavior across scales. As a result, micro-scale shell geometries found in biology, can be upscaled to engineered shell geometries. However, as the characteristic shell dimension increases, gravity (and its associated loading) becomes a hindrance to the adoption of thin shells as compliant mechanisms at the larger scales-the physical limit of compliance in the scaling of thin shells is found to be around 0.1 m.
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Floeter, S. R., R. C. Nalesso, M. M. P. Rodrigues, and A. Turra. "Patterns of shell utilization and selection in two sympatric hermit crabs (Anomura: Diogenidae) in south-eastern Brazil." Journal of the Marine Biological Association of the United Kingdom 80, no. 6 (December 2000): 1053–59. http://dx.doi.org/10.1017/s0025315400003118.
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The present study evaluated shell utilization and preference of two sympatric hermit crab species, Calcinus tibicen and Clibanarius antillensis, from Ilha Galheta de Dentro, Vitória Bay, south-eastern Brazil. Distribution of individuals and use and availability of shells were estimated in the field, where micro-habitat and shell partitioning were demonstrated between the two species of crabs. Calcinus occurred in higher numbers in the infralittoral fringe and shallow subtidal, while Clibanarius was found mainly in the midlittoral zone. The crabs used shells of different architectures and sizes. Calcinus used mainly globose and low spired shells (Tegula viridula and Cymatium parthenopeum), while Clibanarius utilized predominantly the elongated and high spired ones (mainly Cerithium atratum). Clibanarius used shells with smaller volume, weight, and aperture. Free access experiments were conducted in the laboratory and showed that Calcinus and Clibanarius had a high satisfaction rate, i.e. only 50% of the crabs exchanged their shells. From those that exchanged, they chose shells with higher internal volume than that used in the field, while shell weight did not present any increase. Clibanarius was found in shells closer to the preferred ones and in a very different proportion from shell availability, contrasting to Calcinus, which followed shell availability instead of their preferences. Shell internal volume was more important as a choice factor than the weight for both hermit crab species, showing that crabs optimized shell volume in relation to shell weight in the free access experiments.
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Yan, Qing Song, Xu Xiong, Gang Lu, Hong Wan, Can Cheng Liu, Fang Wang, and Xun Zou. "Comparison of Dimensional Accuracy for Different Investment Casting Shells and Binders Based on Selective Laser Sintering." Applied Mechanics and Materials 120 (October 2011): 243–47. http://dx.doi.org/10.4028/www.scientific.net/amm.120.243.
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The dimensional accuracy of shells and binders of investment casting which incorporation with selective laser sintering is investigated. The results show that the dimensional accuracy of colloidal silica is higher than that of ethyl silicate, and the dimensional variation rate of investment casting shells produced with colloidal silica is much lower than ethyl silicate shells. Moreover, colloidal silica possesses better performance on environmental protection and production cost control. These indicate that the comprehensive properties of colloidal silica are better than that of ethyl silicate. Meanwhile, the average dimensional variation rate of the single colloidal silica shell and the ethyl silicate-colloidal silica alteration shell was almost identical and it was much lower than that of the other shells which were produced in this study. This means two kinds of shells are optimized in all five types of shells studied in the aspect of dimensional accuracy. The unique properties of two shells show clearly direction to choose the type of shell.
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Meng, Yuan, Zhenbin Guo, Susan C. Fitzer, Abhishek Upadhyay, Vera B. S. Chan, Chaoyi Li, Maggie Cusack, Haimin Yao, Kelvin W. K. Yeung, and Vengatesen Thiyagarajan. "Ocean acidification reduces hardness and stiffness of the Portuguese oyster shell with impaired microstructure: a hierarchical analysis." Biogeosciences 15, no. 22 (November 16, 2018): 6833–46. http://dx.doi.org/10.5194/bg-15-6833-2018.
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Abstract. The rapidly intensifying process of ocean acidification (OA) due to anthropogenic CO2 is not only depleting carbonate ions necessary for calcification but also causing acidosis and disrupting internal pH homeostasis in several marine organisms. These negative consequences of OA on marine calcifiers, i.e. oyster species, have been very well documented in recent studies; however, the consequences of reduced or impaired calcification on the end-product, shells or skeletons, still remain one of the major research gaps. Shells produced by marine organisms under OA are expected to show signs of dissolution, disorganized microstructure and reduced mechanical properties. To bridge this knowledge gap and to test the above hypothesis, we investigated the effect of OA on juvenile shells of the commercially important oyster species, Magallana angulata, at ecologically and climatically relevant OA levels (using pH 8.1, 7.8, 7.5, 7.2). In lower pH conditions, a drop of shell hardness and stiffness was revealed by nanoindentation tests, while an evident porous internal microstructure was detected by scanning electron microscopy. Crystallographic orientation, on the other hand, showed no significant difference with decreasing pH using electron back-scattered diffraction (EBSD). These results indicate the porous internal microstructure may be the cause of the reduction in shell hardness and stiffness. The overall decrease of shell density observed from micro-computed tomography analysis indicates the porous internal microstructure may run through the shell, thus inevitably limiting the effectiveness of the shell's defensive function. This study shows the potential deterioration of oyster shells induced by OA, especially in their early life stage. This knowledge is critical to estimate the survival and production of edible oysters in the future ocean.
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RYAN, EMILY K., MICHAEL J. SOREGHAN, MICHAEL M. MCGLUE, JONATHAN A. TODD, ELLINOR MICHEL, DARRELL S. KAUFMAN, and ISMAEL KIMIREI. "PALEOENVIRONMENTAL IMPLICATIONS OF TIME-AVERAGING AND TAPHONOMIC VARIATION OF SHELL BEDS IN LAKE TANGANYIKA, AFRICA." PALAIOS 35, no. 2 (February 4, 2020): 49–66. http://dx.doi.org/10.2110/palo.2019.037.
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ABSTRACT The lake bottom along structural platforms in Lake Tanganyika, Africa, is carpeted with numerous large shell beds, known to be of late Holocene age, but of uncertain assemblage process. The shell beds may be the result of sedimentological (physical) assembly processes, or biological processes, or both. Previous work focused on the distribution of shell-rich facies, and showed time averaging of the surficial shell bioclasts over the last ∼ 1600 calendar years BP. We focus on an extensive shell deposit along a deltaic platform in Kungwe Bay, Tanzania and examine time-averaging and taphonomy of Neothauma tanganyicense shells to constrain sedimentological and biological processes forming concentrations of shells. New radiocarbon dating indicates that Neothauma shells are time-averaged over the last ∼ 3000 calendar years. Younger shells predominate shallow-water and exhibit unimodal age distributions, while shells from deeper-water exhibit a broader age distribution. Taphonomic results indicate that water depth and distance from the delta river mouth influence shell abrasion and encrustation with more encrustation developing away from sediment input points. Shells with black coatings and reddish-orange oxidation patinas suggest local burial and exposure. The age-frequency distributions of the shells suggest production rates of the shells vary over time and with water depth, tracking climatically driven lake-level changes (e.g., Little Ice Age, ∼ 100–650 BP). In addition, age-distributions suggest that (1) mixing of different populations are more prevalent along the steeper deltaic slopes, and (2) recent decreasing production rates may reflect anthropogenic land-use change and attendant sedimentation, which has implications for Neothauma itself, and for organisms that are obligate occupants of the shell beds. These results suggest both climatic and depositional processes play unique roles in the distribution and accumulation of shell beds in Lake Tanganyika, which informs interpretation of similar paleoenvironments in the geologic record.
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Odyuo, Aronthung S., and P. Mercy. "On Fibonacci Range Labeling for Standard Shell Graphs." Journal of Advances in Mathematics and Computer Science 38, no. 7 (April 24, 2023): 67–75. http://dx.doi.org/10.9734/jamcs/2023/v38i71773.
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A shell C[n, (n - 3)] of size n is a graph obtained by taking (n - 3) concurrent chords in a cycle \(C_n\) on n vertices. Deb and Limaye (2002) have conjectured that all multiple shells are harmonious. The conjecture has prove to be true for uniform double shells, uniform triple shells and uniform quadruple shells. Here, we prove for a non- uniform double shells with order m and n, where n = (m - 1) and \(\kappa\)-copies of a shell C[n, (n - 3)]\(\kappa\) with a union of \(K_2\) for n = 4, 2\(K_2\) for n = 6 and 3\(K_2\) for n = 8, having a common end vertex joined to the apex of the shell are Fibonacci range labeling.
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LaBarbera, Michael, and Rachel Ann Merz. "Postmortem changes in strength of gastropod shells: evolutionary implications for hermit crabs, snails, and their mutual predators." Paleobiology 18, no. 4 (1992): 367–77. http://dx.doi.org/10.1017/s0094837300010940.
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Calliostoma ligatum shells inhabited by hermit crabs were weaker than shells inhabited by snails collected at the same locality. When shells of C. ligatum were loaded repetitively to 80% of their predicted failure load, hermit crab-inhabited shells showed an immediate drop in shell strength followed by a progressive further loss of shell strength over the next 18 days. Snailinhabited C. ligatum shells exhibited a decrease in strength after 9 days, but returned to initial values within 18 days of loading.Hermit crabs thus bear shells significantly weaker than they were when borne by the gastropods that produced them. Reported similarities in vulnerability of gastropods and hermit crabs to shell-crushing predators may be artifacts of the metric (critical size) used to compare vulnerabilities. Hermit crabs probably were a significant factor in the diversification of durophagous predators in the Mesozoic, supplying a prey base identical in size and shape to gastropods but with significantly lower resistance to crushing. The unpredictability of strength in hermit-crab inhabited shells may maintain the apparently inefficient indiscriminate attacks common among durophagous predators.
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Yang, Yi, Katherine Vella, and Douglas P. Holmes. "Grasping with kirigami shells." Science Robotics 6, no. 54 (May 12, 2021): eabd6426. http://dx.doi.org/10.1126/scirobotics.abd6426.
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The ability to grab, hold, and manipulate objects is a vital and fundamental operation in biological and engineering systems. Here, we present a soft gripper using a simple material system that enables precise and rapid grasping, and can be miniaturized, modularized, and remotely actuated. This soft gripper is based on kirigami shells—thin, elastic shells patterned with an array of cuts. The kirigami cut pattern is determined by evaluating the shell’s mechanics and geometry, using a combination of experiments, finite element simulations, and theoretical modeling, which enables the gripper design to be both scalable and material independent. We demonstrate that the kirigami shell gripper can be readily integrated with an existing robotic platform or remotely actuated using a magnetic field. The kirigami cut pattern results in a simple unit cell that can be connected together in series, and again in parallel, to create kirigami gripper arrays capable of simultaneously grasping multiple delicate and slippery objects. These soft and lightweight grippers will have applications in robotics, haptics, and biomedical device design.
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Eslami, M. R., and M. Shariyat. "Elastic, Plastic, and Creep Buckling of Imperfect Cylinders Under Mechanical and Thermal Loading." Journal of Pressure Vessel Technology 119, no. 1 (February 1, 1997): 27–36. http://dx.doi.org/10.1115/1.2842263.
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Based on the concept of secant and tangent modulus, the nonlinear equilibrium and stability equations of thin cylindrical shells under axial compression, external pressure, or external fluid pressure are derived. The resulting equations are applicable to shells without length limitation as the rotations and transverse shears are included in the derivations. The reduction factors for plastic and creep buckling are then obtained. A procedure for determining secant and tangent modulus in the very general case of elastic, plastic, or creep stress in the presence of temperature gradient is proposed. Then, using Donnell’s nonlinear theory of shells, the effect of initial imperfection on the strength of the elastic shell is discussed. The foregoing results are extended to plastic and creep buckling of cylindrical shells of arbitrary length and temperature gradient. Some design curves are proposed using the obtained equations. Finally, the present results are compared with available results in the literature and the accuracy of the method is examined.
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Crofts, S. B., and A. P. Summers. "How to best smash a snail: the effect of tooth shape on crushing load." Journal of The Royal Society Interface 11, no. 92 (March 6, 2014): 20131053. http://dx.doi.org/10.1098/rsif.2013.1053.
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Organisms that are durophagous, hard prey consumers, have a diversity of tooth forms. To determine why we see this variation, we tested whether some tooth forms break shells better than others. We measured the force needed with three series of aluminium tooth models, which varied in concavity and the morphology of a stress concentrating cusp, to break a shell. We created functionally identical copies of two intertidal snail shells: the thicker shelled Nucella ostrina and the more ornamented Nucella lamellosa using a three-dimensional printer. In this way, we reduced variation in material properties between test shells, allowing us to test only the interaction of the experimental teeth with the two shell morphologies. We found that for all tooth shapes, thicker shells are harder to break than the thinner shells and that increased ornamentation has no discernible effect. Our results show that for both shell morphologies, domed and flat teeth break shells better than cupped teeth, and teeth with tall or skinny cusps break shells best. While our results indicate that there is an ideal tooth form for shell breaking, we do not see this shape in nature. This suggests a probable trade-off between tooth function and the structural integrity of the tooth.
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Turra, Alexander, and Fosca P. P. Leite. "Shell utilization patterns of a tropical intertidal hermit crab assemblage." Journal of the Marine Biological Association of the United Kingdom 82, no. 1 (February 2002): 97–107. http://dx.doi.org/10.1017/s0025315402005210.
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The shell selection and utilization patterns of three sympatric hermit crab populations (Clibanarius antillensis, C. sclopetarius, and C. vittatus) and shell availability were studied in a tropical intertidal low energy area. Shell availability (except for C. antillensis) was low and the hermit crabs showed overlap in size (mainly C. sclopetarius and C. vittatus). The influence of shell availability and selection on shell use was dependent on crab species. Clibanarius antillensis used mainly shells of Cerithium atratum, the most available shell species, while Clibanarius sclopetarius and C. vittatus occupied shells with lower availability in the studied area such as Chicoreus senegalensis, Stramonita haemastoma, Leucozonia nassa and Cymatium parthenopeum. The three species selected different gastropod shells with only Clibanarius antillensis using almost exclusively its preferred shell species in nature. The relationship between shield length and the weight of the used shell was not dependent on crab species or shell species, indicating that the size (not species) of the shells defines what size (not species) of crabs will occupy them.
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Ovesy, Hamid Reza, and Jamshid Fazilati. "Lay-Up Effects on the Dynamic Instability of Moderately Thick Stiffened Curved Panels." Applied Mechanics and Materials 152-154 (January 2012): 1477–82. http://dx.doi.org/10.4028/www.scientific.net/amm.152-154.1477.
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The dynamic instability of cylindrical shell panels having longitudinal stiffener is studied by using the developed finite strip method (FSM). The method is formulated using the third order shear deformation shell's theory of Reddy's form and the Koiter-Sanders theory for cylindrical shells is implemented. The lay-up effects of skin as well as the stiffener are investigated.
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Suárez-Rodríguez, Monserrat, Karla Kruesi, and Guillermina Alcaraz. "The shadow of the shell: a cue for a new home." Journal of the Marine Biological Association of the United Kingdom 99, no. 5 (March 11, 2019): 1165–69. http://dx.doi.org/10.1017/s0025315419000122.
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AbstractHermit crabs use different senses to search for and find shells. In most cases, chemical cues have been proven to act as a very efficient way of finding new shells. However, in intertidal environments, the water transports chemical signals in different directions and velocities may make it harder to track the source of the cue, so visual stimuli may be a more precise source of information. The hermit crab Calcinus californiensis shows a preference for the biconical shells of Stramonita biserialis, although the crabs may also use the less preferred shell of Nerita scabricosta. We were interested in exploring if C. californiensis identify the preferred shell species through vision in the absence of chemical stimuli. We presented both shell species to hermit crabs in two different sets of experiments. In one experiment, we presented to the hermit crabs real shells of N. scabricosta and S. biserialis, and in another, we presented only the silhouettes of the same shells. The hermit crabs discriminated between the real shells and the silhouettes of N. scabricosta and S. biserialis. Females attended with higher frequency to real shells and silhouettes of S. biserialis; while males attended more to shells and silhouettes of N. scabricosta. Although, larger males biased their attendance toward shells of S. biserialis. Our results show that visual perception may be more important than we have thought in intertidal animals.
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Sadygov, I. "FREE AND FORCED VIBRATIONS OF SHELLS OF VARIOUS SHAPES, TAKING INTO ACCOUNT THE VARIABILITY OF THE NON-LINEAR ELASTIC MATERIAL." Construction Materials and Products 3, no. 1 (July 8, 2020): 70–75. http://dx.doi.org/10.34031/2618-7183-2020-3-1-70-75.
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the article considers issues of shell vibrations, which are widely used in various industries and construction. Shells serve as elements of building structures with large spans.
The chapter “Introduction” discussed issues related to the use of shells in all areas of industry, in aviation, rocket and space technology, railway transport, in the oil and gas industry and provides examples of shells for use in ceilings of circuses, stations, hangars; in industry: shells of rotation used as tanks, containers, columns, reactors, etc. In the section “Materials and research methods” free and forced vibrations of shells of variable thickness made out of nonlinear elastic material reviewed. In shell calculations the Kirchhoff – Law hypothesis was used. It was found that, during vibrations, the shells experience relative deformation of elongation and shear of the surface with coordinates (x, y), as well as bending and torsion strains. It is established that vibrations in the shells lead to a rotation of the main directions of elasticity and regarding to the adopted coordinate axis to angle θ, and the elastic constants of the material depend on the elastic constant Biy – the main directions of the nonlinear elastic shells.
When solving the system of equations of motion of the shell relative to the displacements arising in it during vibration, based on theory R and various methods. The values of the dimensionless frequency parameter for a spherical shell taking into account changes in its curvature, variability and thickness of elastic properties are obtained.
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Li, Wenliang, Xudong Zhi, and Feng Fan. "Influence of the Roofing System on the Seismic Performance of Single-Layer Spherical Reticulated Shell Structures." Buildings 12, no. 2 (February 1, 2022): 155. http://dx.doi.org/10.3390/buildings12020155.
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The seismic performance of a single-layer spherical reticulated shell is the key problem to be solved in the design and analysis of this structure. In previous studies, the influences of roofing systems on the seismic performance of shells were usually ignored, resulting in large discrepancies between the results of analyses and the actual stress states of shells. In this paper, the finite element analysis method is applied to a shell with a roofing system, and the applicability of the method is proven by static loading experiments. The influences of roofing systems on the seismic performance of shells are obtained from seismic response curves, the proportions and distributions of plastic members and the failure behaviours of the shells during strong earthquakes. The mechanism of the influence of the roofing system on the seismic response of a shell is revealed by analysing the damage of purlin joints and the energy consumption of the components of the shell. The relationships that describe the influence of different parameters of reticulated shells and roofing systems on the seismic response of the shells are studied, and the results show that the roofing system can greatly change the seismic response and failure of a shell under strong earthquake conditions.
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Van Dung, Dao, Nguyen Thi Nga, and Pham Minh Vuong. "Nonlinear stability analysis of stiffened functionally graded material sandwich cylindrical shells with general Sigmoid law and power law in thermal environment using third-order shear deformation theory." Journal of Sandwich Structures & Materials 21, no. 3 (April 18, 2017): 938–72. http://dx.doi.org/10.1177/1099636217704863.
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This paper investigates analytically nonlinear buckling and postbuckling of functionally graded sandwich circular thick cylindrical shells filled inside by Pasternak two-parameter elastic foundations under thermal loads and axial compression loads. Shells are reinforced by closely spaced functionally graded material (FGM) rings and stringers. The temperature field is taken into account. Two general Sigmoid law and general power law, with four models of stiffened FGM sandwich cylindrical shell, are proposed. Using the Reddy’s third-order shear deformation shell theory (TSDT), stress function, and Lekhnitsky’s smeared stiffeners technique, the governing equations are derived. The closed form to determine critical axial load and postbuckling load-deflection curves are obtained by the Galerkin method. The effects of the face sheet thickness to total thickness ratio, stiffener, foundation, material, and dimensional parameters on critical thermal loads, critical mechanical loads and postbuckling behavior of shells are analyzed. In addition, this paper shows that for thin shells we can use the classical shell theory to investigate stability behavior of shell, but for thicker shells the use of TSDT for analyzing nonlinear stability of shell is necessary and suitable.
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Ko, Soo-Min, and Jae-Hoon Kang. "Vibration of Hemispherical-Cylindrical-Hemispherical Shells and Complete Hollow Spherical Shells with Variable Thickness." International Journal of Structural Stability and Dynamics 19, no. 03 (March 2019): 1950018. http://dx.doi.org/10.1142/s0219455419500184.
Full textAbstract:
The natural frequencies and mode shapes of enclosed shell typed structures with variable thickness (hemispherical-cylindrical-hemispherical shells and complete hollow spherical shells) are determined by the Ritz method using a three-dimensional (3D) analysis. However, in the conventional shell analysis, mathematically two-dimensional (2D) thin shell theories or higher order thick shell theories are often employed, which adopt limiting assumptions about the displacement variation through the shell thickness. While most researchers have adopted the 3D shell coordinates that are normal and tangential to the shell mid-surface, the present analysis is based upon the circular cylindrical coordinates. By the Ritz method, the Legendre polynomials, which are mathematically orthonormal and minimal, are used as the admissible functions, instead of the ordinary algebraic polynomials. The strain and kinetic energies of the combined shell structures are formulated, and upper bound solutions of the frequencies are obtained by minimizing the solution for frequencies. As the degree of the Legendre polynomials is increased, frequencies converge to the exact values. Convergence to four-digit exactitude is demonstrated for the first five frequencies. The frequencies from the present 3D method are compared with those from other 3D approach and 2D thin and thick shell theories existing in the literature. The present 3D analysis is applicable to both very thick shells and very thin shells.
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Grant, Chrissy. "Beautiful shells and their connection to the Reef." Queensland Review 28, no. 2 (December 2021): 80–81. http://dx.doi.org/10.1017/qre.2022.2.
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Shells are beautiful! They are really ingenious in the way that they are made and the animals they house. The shells grow with the animal, from tiny little shells to a great big shell. An animal wasn’t born that big, so the large shells have been there for years.
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Langer, G., G. Nehrke, C. Baggini, R. Rodolfo-Metalpa, J. M. Hall-Spencer, and J. Bijma. "Limpets counteract ocean acidification induced shell corrosion by thickening of aragonitic shell layers." Biogeosciences 11, no. 24 (December 20, 2014): 7363–68. http://dx.doi.org/10.5194/bg-11-7363-2014.
Full textAbstract:
Abstract. Specimens of the patellogastropod limpet Patella caerulea were collected within (pHlow-shells) and outside (pHn-shells) a CO2 vent site at Ischia, Italy. Four pHlow-shells and four pHn-shells were sectioned transversally and scanned for polymorph distribution by means of confocal Raman microscopy. The pHlow-shells displayed a twofold increase in aragonite area fraction and size-normalised aragonite area. Size-normalised calcite area was halved in pHlow-shells. Taken together with the increased apical and the decreased flank size-normalised thickness of the pHlow-shells, these data led us to conclude that low-pH-exposed P. caerulea specimens counteract shell dissolution by enhanced shell production. This is different from normal elongation growth and proceeds through addition of aragonitic parts only, while the production of calcitic parts is confined to elongation growth. Therefore, aragonite cannot be regarded as a disadvantageous polymorph per se under ocean acidification conditions.
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Langer, G., G. Nehrke, C. Baggini, R. Rodolfo-Metalpa, J. Hall-Spencer, and J. Bijma. "Limpets counteract ocean acidification induced shell corrosion by thickening of aragonitic shell layers." Biogeosciences Discussions 11, no. 8 (August 25, 2014): 12571–90. http://dx.doi.org/10.5194/bgd-11-12571-2014.
Full textAbstract:
Abstract. Specimens of the patellogastropod limpet Patella caerulea were collected within (pHlow-shells) and outside (pHn-shells) a CO2 vent site at Ischia, Italy. Four pHlow-shells and four pHn-shells were sectioned transversally and scanned for polymorph distribution by means of confocal Raman microscopy. The pHlow-shells displayed a twofold increase in aragonite area fraction and size normalised aragonite area. Size normalised calcite area was halved in pHlow-shells. Taken together with the increased apical and the decreased flank size normalised thickness of the pHlow-shells, these data led us to conclude that low pH exposed P. caerulea specimens counteract shell dissolution by enhanced shell production. The latter is different from normal elongation growth and proceeds through addition of aragonitic layers only, while the production of calcitic layers is confined to elongation growth. Therefore aragonite cannot be regarded as a per se disadvantageous polymorph under ocean acidification conditions.
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O'Neill, M., R. Mala, D. Cafiso, C. Bignardi, and D. Taylor. "Repair and remodelling in the shells of the limpet Patella vulgata." Journal of The Royal Society Interface 15, no. 145 (August 2018): 20180299. http://dx.doi.org/10.1098/rsif.2018.0299.
Full textAbstract:
Limpets and other molluscs rely on shells to protect them from physical damage, predation, dehydration, etc. If the shell becomes damaged, this may significantly impair its function. In this work, experiments were carried out to investigate the effect of damage on the strength of shells of the common limpet ( Patella vulgata ) and their ability to repair this damage effectively. Shells were damaged in three ways: (i) low-energy impacts; (ii) abrasion of the outer layer; and (iii) creation of a small hole in the apex of the shell. Shells were left to repair for several time periods (0, 10, 30 and 60 days). The mechanical strength was evaluated by impacting the shells with a weight dropped from a known height. The damage reduced the strength (defined as impact energy to failure) by 50–70% depending on damage type. After 60 days, limpets in all three groups had repaired their shells significantly, bringing their strength to 79–91% of the control value (in each case, samples were statistically indistinguishable from their control counterparts). Measurements of the thickness of the shell at the apex suggest that the main effect of low-energy impact and abrasion is reduction in thickness, which correlates linearly with the impact energy needed for failure. The method of repair is believed to be by the growth of fresh shell material on the inside of the shell, though we could not identify this new material specifically. Even after 60 days, the shells were still statistically thinner than the controls. Consequently, there may be some other strengthening mechanism at work. This work has demonstrated the remarkable ability of limpets to detect the mechanical weakening of their shells caused by relatively subtle forms of damage and to take appropriate action to restore shell strength.
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Yasuda, Chiaki I., Yuki Takiya, Masaya Otoda, Reiko Nakano, and Tsunenori Koga. "Is the seasonal change of sexual differences in shell use by the hermit crabPagurus minutusconsidered to be driven by growth or reproduction?" Journal of the Marine Biological Association of the United Kingdom 99, no. 4 (November 15, 2018): 901–10. http://dx.doi.org/10.1017/s0025315418000905.
Full textAbstract:
AbstractSexual differences in behaviours are often affected by the difference in individual interests between the sexes: growth in males and egg production in females. Some hermit crabs show sexual differences in shell use patterns during the reproductive season. In the non-reproductive season, however, when both sexes are focused on increasing growth, this sexual difference is expected to be reduced. In this study, we compared the pattern of shell use in the hermit crabPagurus minutusbetween seasons, while focusing on the effects of shell shape on growth or egg production. As we predicted, sexual differences in shell use inP. minutusshowed seasonal change. In the non-reproductive season, both sexes appeared to use shells well suited for growth. In the reproductive season, sexual differences became more evident, especially in larger solitary crabs and guarding pairs; males monopolized round-type shells such as those ofUmbonium moniliferum, whereas more than 80% of females relied on high-spiredBatillaria-type shells such as those ofBatillaria zonalis. A lack of advantage for egg number in females usingBatillaria-type shells suggests that female shell use is explained by factors other than maximizing clutch size. Both sexes can moult during the reproductive season, and larger body size is advantageous for reproduction. Given thatBatillaria-type shells resulted in a lower growth increment and males have an advantage in shell fights in congeneric crabs, our findings suggest the importance of intersexual competition for shells and female compromise in determining the seasonal change of shell use patterns inP. minutus.
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Cheng, Yu-Qiang, Lin He, Chang-Geng Shuai, Hua Gao, and Jian-Guo Ma. "Free vibration characteristics of cord-reinforced air spring with winding formation under preload conditions." AIP Advances 13, no. 3 (March 1, 2023): 035230. http://dx.doi.org/10.1063/5.0137600.
Full textAbstract:
A precise transfer matrix was employed to analyze the free vibration characteristics of a cord-reinforced air spring with winding formation under preload conditions. The air spring was abstracted as a rotary combined shell structure with variable winding trajectory characteristics. The rotary structure, which consisted of cylindrical and toroidal shells, was analyzed for its shell pre-stress under preload conditions. The shell pre-stress was combined with the theory of thin shells to create the rotary shell vibration control equations under preload effect. The Helmholtz equation was used to analyze the influence of sound pressure inside shells under the fluid–structure coupling boundary conditions. The rotary shell transfer matrix was derived from the variable winding trajectory equation, geometrical equation, and physical equation of shells. Under the continuous conditions of state vector between the cylindrical and toroidal shells, the shells were combined into a rotary combined shell structure to obtain its total free vibration equation. The shell boundary conditions were considered to solve the natural frequency of the air spring. The calculation results were compared with the prototype test and simulation results to verify the effectiveness and accuracy of the theoretical model. On this basis, we explored the influence of axial half wave number, circumferential wave number, geometrical structure, and material characteristics on the free vibration characteristics of the air spring. The research findings would provide important and significant guidance for the structural design of cord-reinforced air springs with winding formation.