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Journal articles on the topic 'Crests'

Author: Grafiati

Published: 4 June 2021

Last updated: 29 July 2024

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1

Li, Yan-Hom, and Kuo-Lung Huang. "Effect of Rosensweig instability in a ferrofluid layer on reflection loss of a high-frequency electromagnetic wave." AIP Advances 12, no. 4 (2022): 045221. http://dx.doi.org/10.1063/5.0086107.

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A ferrofluid layer separates into numerous subscale crests, which is referred to as Rosensweig instability, whose shape and size depend on the field condition and the composition of the ferrofluid. A ferrofluid consisting of nanoscale magnetite particles is also used as an electromagnetic (EM) wave absorption and reflection material. For this study, oil-based and mixture ferrofluid layers that split into various shapes of crests in the presence of an external magnetic field are used to form a protruding structure to reflect and scatter the EM wave and decrease EM radiation energy. For an identical field strength, a mixture ferrofluid layer splits into more crests than an oil-based ferrofluid. A mixture crest shows a less uniform size and shape than the oil-based one. A high-power green laser light is used as a visual EM wave emitting to a crest, which has varying tip angles, and to demonstrate the reflection and scattering. The reflection loss increases as the field strength is increased to create a crest of a smaller tip angle. The reflection loss of an EM wave is significantly affected by the transmitting position on a crest and the shape of a crest. Inter-reflection arises if an EM wave is repeatedly reflected on the surfaces of crests, which contributes to a significant reflection loss. An EM wave incident at an angle of 45° on a crest resulting in a larger area of the inter-reflection zone without specular reflection in a trough gives the most significant reflection loss.

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2

Reese, Andrew J., and Stephen T. Maynord. "Design of Spillway Crests." Journal of Hydraulic Engineering 113, no. 4 (1987): 476–90. http://dx.doi.org/10.1061/(asce)0733-9429(1987)113:4(476).

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3

Boersma, Alexandra T., Matthew R. McCurry, and Nicholas D. Pyenson. "A new fossil dolphin Dilophodelphis fordycei provides insight into the evolution of supraorbital crests in Platanistoidea (Mammalia, Cetacea)." Royal Society Open Science 4, no. 5 (2017): 170022. http://dx.doi.org/10.1098/rsos.170022.

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Many odontocete groups have developed enlarged facial crests, although these crests differ in topography, composition and function. The most elaborate crests occur in the South Asian river dolphin ( Platanista gangetica ), in which they rise dorsally as delicate, pneumatized wings anterior of the facial bones. Their position wrapping around the melon suggests their involvement in sound propagation for echolocation. To better understand the origin of crests in this lineage, we examined facial crests among fossil and living Platanistoidea, including a new taxon, Dilophodelphis fordycei , nov. gen. and sp., described herein, from the Early Miocene Astoria Formation of Oregon, USA. We measured the physical extent and thickness of platanistoid crests, categorized their relative position and used computed tomography scans to examine their internal morphology and relative bone density. Integrating these traits in a phylogenetic context, we determined that the onset of crest elaboration or enlargement and the evolution of crest pneumatization among the platanistoids were separate events, with crest enlargement beginning in the Oligocene. However, we find no evidence for pneumatization until possibly the Early Miocene, although certainly by the Middle Miocene. Such an evolutionary context, including data from the fossil record, should inform modelling efforts that seek to understand the diversity of sound generation morphology in Odontoceti.

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4

Faivre, Sanja. "Analyses of the Velebit Mountain Ridge Crests." Hrvatski geografski glasnik/Croatian Geographical Bulletin 69, no. 02 (2008): 21–39. http://dx.doi.org/10.21861/hgg.2007.69.02.02.

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5

Krall, J., J. D. Huba, G. Joyce, and T. Yokoyama. "Density enhancements associated with equatorial spread <I>F</I>." Annales Geophysicae 28, no. 2 (2010): 327–37. http://dx.doi.org/10.5194/angeo-28-327-2010.

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Abstract. Forces governing the three-dimensional structure of equatorial spread-F (ESF) plumes are examined using the NRL SAMI3/ESF three-dimensional simulation code. As is the case with the equatorial ionization anomaly (IA), density crests within the plume occur where gravitational and diffusive forces are in balance. Large E×B drifts within the ESF plume place these crests on field lines with apex heights higher than those of the background IA crests. Large poleward field-aligned ion velocities within the plume result in large ion-neutral diffusive forces that support these ionization crests at altitudes higher than background IA crest altitudes. We show examples in which density enhancements associated with ESF, also called "plasma blobs," can occur within an ESF plume on density-crest field lines, at or above the density crests. Simulated ESF density enhancements reproduce all key features of those that have been observed in situ.

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6

Amaechi, P. O., E. O. Oyeyemi, and A. O. Akala. "Variability of the African equatorial ionization anomaly (EIA) crests during the year 2013." Canadian Journal of Physics 97, no. 2 (2019): 155–65. http://dx.doi.org/10.1139/cjp-2017-0985.

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This paper discusses the variability of the position and magnitude of the crests of African Equatorial Ionization Anomaly during noon and post sunset periods. Total electron content data covered the year 2013, and were obtained from a chain of global positioning system receivers in both hemispheres around 37°E longitude. Local magnetometer data were used to infer the direction and magnitude of the E × B drift, while the solar extreme ultraviolet proxy index was used as a measure of solar activity. It was found that the time of formation of both crests varied from 1400 to 1700 local time. Additionally, the position of the crests was found to be asymmetric with respect to the magnetic equator. During the noon period, the position of the northern and southern crests varied from 4.91° to 7.36° and −9.17° to −12.62°, respectively. During the post-sunset period, it varied from 8° to 11.7° and −9° to −16°, respectively. Seasonally, with reference to the magnetic equator, both crests moved poleward during equinoxes and collapsed towards the equator during winter and summer. Equinoxes recorded the greatest crest magnitude followed by winter then summer over both hemispheres during the noon period. However, this trend persisted over the northern crest only during the post-sunset period. Overall, during the noon period, we recorded correlation coefficients of 0.67 and 0.68 between crest magnitudes and ΔH, a proxy for equatorial electrojet current, and 0.88 and 0.81 between crest positions and ΔH, for the northern and southern crests, respectively. During the Halloween day storm of 30 October 2013, a westward electric field inhibited the development of the post-sunset crests.

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7

ASHTON, E. H., and S. ZUCKERMAN. "CRANIAL CRESTS IN THE ANTHROPOIDEA." Proceedings of the Zoological Society of London 126, no. 4 (2009): 581–634. http://dx.doi.org/10.1111/j.1096-3642.1956.tb00454.x.

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8

Akylas, T. R. "Envelope solitons with stationary crests." Physics of Fluids A: Fluid Dynamics 5, no. 4 (1993): 789–91. http://dx.doi.org/10.1063/1.858626.

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9

Al-Humoud, J., M. A. Tayfun, and H. Askar. "Distribution of nonlinear wave crests." Ocean Engineering 29, no. 15 (2002): 1929–43. http://dx.doi.org/10.1016/s0029-8018(01)00101-9.

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10

Hone, David W. E. "Evolution: Convergence in Dinosaur Crests." Current Biology 25, no. 12 (2015): R494—R496. http://dx.doi.org/10.1016/j.cub.2015.04.051.

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11

Duckers, L. J. "Wave energy; crests and troughs." Renewable Energy 5, no. 5-8 (1994): 1444–52. http://dx.doi.org/10.1016/0960-1481(94)90186-4.

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12

Kriebel, D. L., and T. H. Dawson. "Distribution of Crest Amplitudes in Severe Seas With Breaking." Journal of Offshore Mechanics and Arctic Engineering 115, no. 1 (1993): 9–15. http://dx.doi.org/10.1115/1.2920097.

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A theoretical model is presented for the probability distribution of wave crest amplitudes in severe seas states with wave breaking. As the severity of a sea state increases, nonlinearities cause an increase in the amplitudes of the largest wave crests with a subsequent modification of the distribution of wave crest amplitudes from the linear Rayleigh theory. In this paper, a theory for the probabilities of these nonlinear crest amplitudes is first reviewed based on earlier work. The further limitations on these nonlinear crest amplitudes by wave breaking are then considered. As a result, a theoretical model is presented to account for both: 1) the nonlinear increase in the highest wave crests, and 2) the selective reduction of some fraction of these high crests due to wave breaking. This model is then verified using several sets of laboratory data for severe breaking seas having approximate JONSWAP wave spectra.

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13

Warrington, Curtis, Shiv Kapoor, and Richard DeVor. "Finite Element Modeling for Tap Design Improvement in Form Tapping." Journal of Manufacturing Science and Engineering 128, no. 1 (2005): 65–73. http://dx.doi.org/10.1115/1.2117427.

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The form tapping process typically yields unfinished threads known as split crests. Thread quality can be greatly improved by reducing the size and severity of split crest formation. This paper develops a finite element model to simulate form tapping with an eye towards the reduction of split crests. The model is validated against linear scratch experiments, and simulations are compared to actual tapping. The effects of various tap design parameters and tapping process conditions on the formation of split crests are investigated to strive toward an optimal tap design.

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14

Trochonowicz, Maciej, and Bogusław Szmygin. "Degradation processes and the methods of securing wall crests." Budownictwo i Architektura 16, no. 4 (2018): 209–33. http://dx.doi.org/10.24358/bud-arch_17_164_14.

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The protection of historical ruins requires solution of doctrinal and technical problems. Technical problems concern above all preservation of walls, which are exposed to the influence of atmospheric factors. The problem that needs to be solved in any historic ruin is securing of wall crests. Form of protection of the wall crests depends on many factors, mainly technical features of the wall and architectural and conservatory vision. The following article presents three aspects important for protection of wall crests. Firstly, analysis of features of the wall as a structure, secondly the characteristics of destructive agents, thirdly forms of protection of wall crests. In the summary of the following article, advantages and disadvantages of each method of preservation of the wall crests were presented.

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15

Goda, Y. "Statistics of Wave Crest Lengths Based on Directional Wave Simulations." Journal of Offshore Mechanics and Arctic Engineering 116, no. 4 (1994): 239–45. http://dx.doi.org/10.1115/1.2920158.

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Spatial surface elevations of directional random waves have numerically been simulated for various directional spectral conditions in deep water and finite uniform depth water. Individual wave crests are defined on the simulated surface data and the statistics of crest lengths are examined. The ratio of the mean crest length to the local wavelength is found to be governed by the directional spreading parameter. The average longitudinal profiles of high wave crests are presented for three typical values of directional spreading parameters.

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16

M., L. "The case of the coarsened crests." Nature 365, no. 6448 (1993): 691. http://dx.doi.org/10.1038/365691b0.

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17

Michard, Annie, and Francis Albarede. "Hydrothermal uranium uptake at ridge crests." Nature 317, no. 6034 (1985): 244–46. http://dx.doi.org/10.1038/317244a0.

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18

Tayfun, M. Aziz. "Statistics of Wave Crests in Storms." Journal of Waterway, Port, Coastal, and Ocean Engineering 130, no. 4 (2004): 155–61. http://dx.doi.org/10.1061/(asce)0733-950x(2004)130:4(155).

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19

Fedele, Francesco. "Successive wave crests in Gaussian seas." Probabilistic Engineering Mechanics 20, no. 4 (2005): 355–63. http://dx.doi.org/10.1016/j.probengmech.2004.05.008.

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20

Dawson, T. H. "Maximum Wave Crests in Heavy Seas." Journal of Offshore Mechanics and Arctic Engineering 122, no. 3 (1999): 222–24. http://dx.doi.org/10.1115/1.1287039.

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Applicability of extreme-value theory in predicting the maximum crest amplitude in runs of ocean waves is demonstrated using data from extensive computer simulations of random linear waves. Extension of the theory to include wave crests in heavy seas is also made within the context of Stokes nonlinearities. Results are confirmed with scaled laboratory measurements. [S0892-7219(00)00803-7]

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21

Richter, R., and J. Bläsing. "Measuring magnetic liquid crests by radioscopy." PAMM 1, no. 1 (2002): 317. http://dx.doi.org/10.1002/1617-7061(200203)1:1<317::aid-pamm317>3.0.co;2-b.

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22

Barry, M. J., and I. A. E. Bayly. "Further Studies on Predator Induction of Crests in Australian Daphnia and the Effects of Crests on Predation." Marine and Freshwater Research 36, no. 4 (1985): 519. http://dx.doi.org/10.1071/mf9850519.

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The effects of notonectid predation on populations of Daphnia in a controlled seminatural environment were studied. Log crest size was positively correlated with predator density, suggesting that crest induction was not an all-or-nothing type of response. The size of the Daphnia population varied inversely with notonectid density. Laboratory studies indicated that a crest-induction factor was produced by all Anisops spp. and the one species of Enithares that were tested. Two forms of D. carinata s.1. differed in their ability to respond to the same species of notonectid. Non-notonectid predators did not induce crests. Results of predation experiments supported previously published indications that helmets reduce the efficiency of notonectid predation. The effect of the helmet varied, depending on the species of notonectid and the size and form of D. carinata s.1. The crest acted primarily to increase predator avoidance by evasion rather than by escape. A comparative study of an ecophenotypic morph and a permanently crested morph showed that the presence of a crest was associated with reduced fecundity. The growth rate of the permanently crested morph during this experiment was slower, although its intrinsic mortality was considerably higher.

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23

Taklo, Tore Magnus A., Karsten Trulsen, Harald E. Krogstad, and José Carlos Nieto Borge. "On dispersion of directional surface gravity waves." Journal of Fluid Mechanics 812 (January 5, 2017): 681–97. http://dx.doi.org/10.1017/jfm.2016.817.

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Using a nonlinear evolution equation we examine the dependence of the dispersion of directional surface gravity waves on the Benjamin–Feir index (BFI) and crest length. A parameter for describing the deviation between the dispersion of simulated waves and the theoretical linear dispersion relation is proposed. We find that for short crests the magnitude of the deviation parameter is low while for long crests the magnitude is high and depends on the BFI. In the present paper we also consider laboratory data of directional waves from the Marine Research Institute of the Netherlands (MARIN). The MARIN data confirm the simulations for three cases of BFI and crest length.

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24

Forristall, George Z. "KINEMATICS IN THE CRESTS OF STORM WAVES." Coastal Engineering Proceedings 1, no. 20 (1986): 16. http://dx.doi.org/10.9753/icce.v20.16.

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Uncertainty about kinematics in the crests of high waves has prevented random wave simulation from being accepted as a reliable method for computing wave forces for platform design. A theoretically defensible method of calculation for wave crest kinematics has been developed recently. The method produces a potential function which fits the kinematic boundary condition specified by second order wave theory and is thus named the Kinematic Boundary Condition Fitting (KBCF) method. KBCF agreed well with measurements of mechanically generated irregular waves made by a laser Doppler current meter in a wave tank. In order to obtain further data during high, short crested storm waves, instruments for the Fulmar Wave Crest Kinematics (FULWACK) experiment were installed in the North Sea early in November 1981. During a storm later in that month, good velocity measurements at heights up to 25 feet above mean water level were obtained in over 30 waves. For comparison with this data, KBCF was extended to three dimensions. Statistics of the velocities thus simulated agreed well with statistics of the measurements. KBCF has thus been verified as a accurate method for simulating the kinematics of natural storm waves.

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25

Aziz Tayfun, M. "Statistics of nonlinear wave crests and groups." Ocean Engineering 33, no. 11-12 (2006): 1589–622. http://dx.doi.org/10.1016/j.oceaneng.2005.10.007.

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26

Dingyong, Yu, and Zhang Hanyuan. "Numerical simulation of 3-D wave crests." Journal of Ocean University of Qingdao 2, no. 1 (2003): 100–105. http://dx.doi.org/10.1007/s11802-003-0036-x.

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27

Brennan, A. J., and S. P. G. Madabhushi. "Amplification of seismic accelerations at slope crests." Canadian Geotechnical Journal 46, no. 5 (2009): 585–94. http://dx.doi.org/10.1139/t09-006.

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Earthquake accelerations can cause many problems in sloping ground. One such problem is that accelerations are greatly amplified at the crest of slopes. This topographic amplification can lead to acceleration gradients along the ground surface, which could create tensile forces in long surface structures that extend between areas of different amplifications. This paper uses centrifuge modelling to demonstrate and quantify this as a problem for a particular slope configuration. A special brittle structure has been constructed to undergo damage in the presence of large differential accelerations. The structure is seen to connect the crest to the level ground behind the crest during an earthquake, reducing the amplitude of the crest motion at the expense of structural tension. Topographic amplification is shown to be a clear function of frequency, and is especially serious for loading frequencies above the natural frequency of the soil layer.

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28

Ben-Zvi, Arie, Sylvie Massoth, and Asher P. Schick. "Travel time of runoff crests in Israel." Journal of Hydrology 122, no. 1-4 (1991): 309–20. http://dx.doi.org/10.1016/0022-1694(91)90185-k.

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29

Barry, MJ, and IAE Bayly. "c. Further studies on predator induction of crests in Australian Daphnia and the effects of crests on predation." Marine and Freshwater Research 36, no. 4 (1985): 519. http://dx.doi.org/10.1071/mf9850519c.

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30

JIANG, XUAN-KONG, ZU-XU ZHANG, HUI-MING CHEN, and ZHI-CAI XIE. "Description of Hypocambala zizhongi sp. nov. and the new combination, Glyphiulus polytrichus (Golovatch et al., 2011) comb. nov., based on morphological and molecular data (Spirostreptida: Cambalidea: Cambalopsidae)." Zootaxa 4903, no. 3 (2021): 405–18. http://dx.doi.org/10.11646/zootaxa.4903.3.6.

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The recent delimitation of the cambalopsid genera Hypocambala and Glyphiulus is debatable. The focus of controversy is whether the presence of crests on the trunk rings is an appropriate key character dividing these two genera. To address this issue, we conducted a molecular phylogenetic analysis including species with or without crests belonging to Hypocambala and species with crests belonging to Glyphiulus. The results of the phylogenetic analysis suggest that cambalopsids with crests are monophyletic and sister to a species without crests. Hypocambala polytricha, a cambalopsid with crests that is in a clade with crested Glyphiulus species, should be transferred to Glyphiulus. Therefore, a new combination is proposed, Glyphiulus polytrichus comb. nov. In addition, a discussion on the boundary between these two genera and a description of a new species, Hypocambala zizhongi sp. nov., are provided.

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JIANG, XUAN-KONG, ZU-XU ZHANG, HUI-MING CHEN, and ZHI-CAI XIE. "Description of Hypocambala zizhongi sp. nov. and the new combination, Glyphiulus polytrichus (Golovatch et al., 2011) comb. nov., based on morphological and molecular data (Spirostreptida: Cambalidea: Cambalopsidae)." Zootaxa 4903, no. 3 (2021): 405–18. http://dx.doi.org/10.11646/zootaxa.4903.3.6.

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The recent delimitation of the cambalopsid genera Hypocambala and Glyphiulus is debatable. The focus of controversy is whether the presence of crests on the trunk rings is an appropriate key character dividing these two genera. To address this issue, we conducted a molecular phylogenetic analysis including species with or without crests belonging to Hypocambala and species with crests belonging to Glyphiulus. The results of the phylogenetic analysis suggest that cambalopsids with crests are monophyletic and sister to a species without crests. Hypocambala polytricha, a cambalopsid with crests that is in a clade with crested Glyphiulus species, should be transferred to Glyphiulus. Therefore, a new combination is proposed, Glyphiulus polytrichus comb. nov. In addition, a discussion on the boundary between these two genera and a description of a new species, Hypocambala zizhongi sp. nov., are provided.

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32

Bolaji, Olawale, Oluwafisayo Owolabi, Elijah Falayi, et al. "Observations of equatorial ionization anomaly over Africa and Middle East during a year of deep minimum." Annales Geophysicae 35, no. 1 (2017): 123–32. http://dx.doi.org/10.5194/angeo-35-123-2017.

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Abstract. In this work, we investigated the veracity of an ion continuity equation in controlling equatorial ionization anomaly (EIA) morphology using total electron content (TEC) of 22 GPS receivers and three ground-based magnetometers (Magnetic Data Acquisition System, MAGDAS) over Africa and the Middle East (Africa–Middle East) during the quietest periods. Apart from further confirmation of the roles of equatorial electrojet (EEJ) and integrated equatorial electrojet (IEEJ) in determining hemispheric extent of EIA crest over higher latitudes, we found some additional roles played by thermospheric meridional neutral wind. Interestingly, the simultaneous observations of EIA crests in both hemispheres of Africa–Middle East showed different morphology compared to that reported over Asia. We also observed interesting latitudinal twin EIA crests domiciled at the low latitudes of the Northern Hemisphere. Our results further showed that weak EEJ strength associated with counter electrojet (CEJ) during sunrise hours could also trigger twin EIA crests over higher latitudes.

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33

FEDELE, FRANCESCO, and M. AZIZ TAYFUN. "On nonlinear wave groups and crest statistics." Journal of Fluid Mechanics 620 (February 10, 2009): 221–39. http://dx.doi.org/10.1017/s0022112008004424.

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We present a second-order stochastic model of weakly nonlinear waves and develop theoretical expressions for the expected shape of large surface displacements. The model also leads to an exact theoretical expression for the statistical distribution of large wave crests in a form that generalizes the Tayfun distribution (Tayfun, J. Geophys. Res., vol. 85, 1980, p. 1548). The generalized distribution depends on a steepness parameter given by μ = λ3/3, where λ3 represents the skewness coefficient of surface displacements. It converges to the Tayfun distribution in narrowband waves, where both distributions describe the crests of all waves well. In broadband waves, the generalized distribution represents the crests of large waves just as well whereas the Tayfun distribution appears as an upper bound and tends to overestimate them. However, the theoretical nature of the generalized distribution presents practical difficulties in oceanic applications. We circumvent these by adopting an appropriate approximation for the steepness parameter. Comparisons with wind-wave measurements from the North Sea suggest that this approximation allows both distributions to assume an identical form with which we can describe the distribution of large wave crests fairly accurately. The same comparisons also show that third-order nonlinear effects do not appear to have any discernable effect on the statistics of large surface displacements or wave crests.

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Bailey, G. J., M. H. Denton, R. A. Heelis, and S. Venkatraman. "A modelling study of the latitudinal variations in the nighttime plasma temperatures of the equatorial topside ionosphere during northern winter at solar maximum." Annales Geophysicae 18, no. 11 (2000): 1435–46. http://dx.doi.org/10.1007/s00585-000-1435-6.

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Abstract. Latitudinal variations in the nighttime plasma temperatures of the equatorial topside ionosphere during northern winter at solar maximum have been examined by using values modelled by SUPIM (Sheffield University Plasmasphere Ionosphere Model) and observations made by the DMSP F10 satellite at 21.00 LT near 800 km altitude. The modelled values confirm that the crests observed near 15° latitude in the winter hemisphere are due to adiabatic heating and the troughs observed near the magnetic equator are due to adiabatic cooling as plasma is transported along the magnetic field lines from the summer hemisphere to the winter hemisphere. The modelled values also confirm that the interhemispheric plasma transport needed to produce the required adiabatic heating/cooling can be induced by F-region neutral winds. It is shown that the longitudinal variations in the observed troughs and crests arise mainly from the longitudinal variations in the magnetic meridional wind. At longitudes where the magnetic declination angle is positive the eastward geographic zonal wind combines with the northward (summer hemisphere to winter hemisphere) geographic meridional wind to enhance the northward magnetic meridional wind. This leads to deeper troughs and enhanced crests. At longitudes where the magnetic declination angle is negative the eastward geographic zonal wind opposes the northward geographic meridional wind and the trough depth and crest values are reduced. The characteristic features of the troughs and crests depend, in a complicated manner, on the field-aligned flow of plasma, thermal conduction, and inter-gas heat transfer. At the latitudes of the troughs/crests, the low/high plasma temperatures lead to increased/decreased plasma concentrations.Key words: Ionosphere (equatorial ionosphere; ionosphere-atmosphere interactions)

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35

Seniczak, Stanisław, Otilia Ivan, Sławomir Kaczmarek, and Anna Seniczak. "Morphological ontogeny of Lopheremaeus mirabilis (Acari: Oribatida: Plateremaeidae), and comments on Lopheremaeus Paschoal." Systematic and Applied Acarology 25, no. 12 (2020): 2147–64. http://dx.doi.org/10.11158/saa.25.12.1.

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The morphological ontogeny of Lopheremaeus mirabilis (Csiszár 1962), the type species of Lopheremaeus Paschoal, 1988 (Plateremaeidae) is described and illustrated. The adult of this species has six pairs of notogastral setae (lp, h1, h2 and p-series), epimeral and anogenital hypertrichy, and 4–5 pairs of anal setae. The cuticle of juveniles is plicate, the larva lacks the gastronotal setae c3, la, lm and h3, the nymphs are multideficient (they lack also setae of d-series) and eupheredermous, i.e. they carry the exuvial scalps of previous instars on the gastronotum. In the adult, dorsal and ventral crests are present on all femora and trochanter III, and dorsal crest is present on trochanter IV, the nymphs have also dorsal and ventral crests on genua, whereas the larva has no crests. In all instars, seta d on all genua and tibiae is present, and all tarsi have basal bulb (containing muscles) and uniformly narrow distal stalk (with only tendons) at about mid-length. This species was reported only from Bulgaria, Bosnia-Herzegovina and North Macedonia, Romania and Georgia.

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36

Prevosto, Marc, and George Z. Forristall. "Statistics of Wave Crests From Models vs. Measurements." Journal of Offshore Mechanics and Arctic Engineering 126, no. 1 (2004): 43–50. http://dx.doi.org/10.1115/1.1641795.

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The analysis phase of the Wave Crest Sensor Intercomparison Study (WACSIS) focussed on the interpretation of the wave data collected by the project during the winter of 1997–98. Many aspects of wave statistics have been studied, but the main emphasis has been on crest height distributions, and recommendations for crest heights to be used in air gap calculations. In this paper, we first describe comparisons of the crest height distributions derived from the sensors (radars, wave staffs, laser) and from simulations based on 3-D second-order irregular wave models. These comparisons permit us to make conclusions on the quality of these models and to qualify the ability of some sensors to measure the crest heights accurately. In the second part, two new parametric models of the crest height distributions are discussed and their superiority to standard parametric models is demonstrated.

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37

Rodriguez Lopez, Hanzel, Roberto Rodriguez Morales, and Augusto de Jesus Gonzalez Garcia. "Distances Between Wave Crests Obtained From Satellite Images." IEEE Latin America Transactions 17, no. 08 (2019): 1276–82. http://dx.doi.org/10.1109/tla.2019.8932336.

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38

Presta, Ivan, Annalidia Donato, Domenico Chirchiglia, Natalia Malara, and Giuseppe Donato. "Cardiac myxoma and neural crests: a tense relationship." Cardiovascular Pathology 44 (January 2020): 107163. http://dx.doi.org/10.1016/j.carpath.2019.107163.

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39

Roychoudhury, Anita. "Elementary students’ reasoning: Crests and troughs of learning." Journal of Elementary Science Education 19, no. 2 (2007): 25–43. http://dx.doi.org/10.1007/bf03173661.

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40

Tayfun, M. Aziz, and Jasem Al-Humoud. "Least Upper Bound Distribution for Nonlinear Wave Crests." Journal of Waterway, Port, Coastal, and Ocean Engineering 128, no. 4 (2002): 144–51. http://dx.doi.org/10.1061/(asce)0733-950x(2002)128:4(144).

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41

Lugt, J. S. de, S. Thomson, and D. M. Cruden. "A suggested method for estimating setbacks from the crests of slopes on the Interior Plains in Alberta." Canadian Geotechnical Journal 30, no. 5 (1993): 863–75. http://dx.doi.org/10.1139/t93-077.

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A method of estimating safe setbacks from the crests of river valley slopes in Alberta was evaluated for 39 slopes, of which eight are presented to illustrate the method and assess its reliability. The slope at each site is compared with angles of nearby stable, abandoned slopes with similar geology. An abandoned slope is a slope not being eroded by a river at present. The terrain behind the valley crest is often level. However, if the terrain rises or falls away from the crest, the setback should be corrected by a simply determined factor. Setbacks include an allowance for lateral river erosion, though this component is difficult to determine precisely. Ideally, site-specific rates of erosion should be determined and then applied to the model. In the eight cases discussed, no damage would have occurred had the structures been built behind the setback guideline. The suggested method for determining setbacks appears to be a prudent guideline for development along valley crests. The crests of slopes that have reached their ultimate angle are available for development with a small setback. For any slope that has not attained its ultimate angle, the setback represents land that is not available for development without detailed geotechnical analyses and remedial work. Key words : setback, slope, landslide, abandoned slope, angle of ultimate stability.

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42

Valladares, C. E., J. Villalobos, R. Sheehan, and M. P. Hagan. "Latitudinal extension of low-latitude scintillations measured with a network of GPS receivers." Annales Geophysicae 22, no. 9 (2004): 3155–75. http://dx.doi.org/10.5194/angeo-22-3155-2004.

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Abstract. A latitudinal-distributed network of GPS receivers has been operating within Colombia, Peru and Chile with sufficient latitudinal span to measure the absolute total electron content (TEC) at both crests of the equatorial anomaly. The network also provides the latitudinal extension of GPS scintillations and TEC depletions. The GPS-based information has been supplemented with density profiles collected with the Jicamarca digisonde and JULIA power maps to investigate the background conditions of the nighttime ionosphere that prevail during the formation and the persistence of plasma depletions. This paper presents case-study events in which the latitudinal extension of GPS scintillations, the maximum latitude of TEC depletion detections, and the altitude extension of radar plumes are correlated with the location and extension of the equatorial anomaly. Then it shows the combined statistics of GPS scintillations, TEC depletions, TEC latitudinal profiles, and bottomside density profiles collected between September 2001 and June 2002. It is demonstrated that multiple sights of TEC depletions from different stations can be used to estimate the drift of the background plasma, the tilt of the plasma plumes, and in some cases even the approximate time and location of the depletion onset. This study corroborates the fact that TEC depletions and radar plumes coincide with intense levels of GPS scintillations. Bottomside radar traces do not seem to be associated with GPS scintillations. It is demonstrated that scintillations/depletions can occur when the TEC latitude profiles are symmetric, asymmetric or highly asymmetric; this is during the absence of one crest. Comparison of the location of the northern crest of the equatorial anomaly and the maximum latitude of scintillations reveals that for 90% of the days, scintillations are confined within the boundaries of the 50% decay limit of the anomaly crests. The crests of the anomaly are the regions where the most intense GPS scintillations and the deepest TEC depletions are encountered. In accord with early results, we observe that GPS scintillations/TEC depletions mainly occur when the altitude of the magnetic equator F-region is above 500km. Nevertheless, in many instances GPS scintillations and TEC depletions are observed to exist when the F-layer is well below 500km or to persist when the F-layer undergoes its typical nighttime descent. Close inspection of the TEC profiles during scintillations/depletions events that occur when the equatorial F-layer peak is below 500km altitude reveals that on these occasions the ratio of the crest-to-equator TEC is above 2, and the crests are displaced 10° or more from the magnetic equator. When the equatorial F-layer is above 500km, neither of the two requirements is needed, as the flux tube seems to be inherently unstable. We discuss these findings in terms of the Rayleigh-Taylor instability (RTI) mechanism for flux-tube integrated quantities. We advance the idea that the seeming control that the reverse fountain effect exerts on inhibiting or suppressing GPS scintillations may be related to the redistribution of the density and plasma transport from the crests of the anomaly toward the equatorial region and then to much lower altitudes, and the simultaneous decrease of the F-region altitude. These two effects originate a decrease in the crest/trough ratio and a reduction of the crests separation, making the whole flux tube more stable to the RTI. The correspondence between crest separation, altitude of the equatorial F-region, the onset of depletions, and the altitude (latitude) extension of plumes (GPS scintillations) can be used to track the fate of the density structures.

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Hogue, Aaron S., and Shakila ZiaShakeri. "Molar crests and body mass as dietary indicators in marsupials." Australian Journal of Zoology 58, no. 1 (2010): 56. http://dx.doi.org/10.1071/zo09084.

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The discovery of ecomorphological relationships in mammals is important not only in its own right, but also for its potential in shedding light on the ecology of extinct and poorly known species. Two such potential relationships are the proposed connection between molar shear crests and body mass to diet. Research on primates suggests that, owing to the digestive challenges of structural carbohydrates (in foliage and insects), folivores and insectivores differ from other species in needing relatively long molar shear crests. These studies also suggest that metabolic constraints force folivores to be consistently larger than insectivores, with 500–700 g being the proposed body mass boundary between the two. This study tests these proposed ecomorphological links in a diverse sample of 64 marsupial species. As predicted, folivores and insectivores have significantly relatively longer molar shear crests than other species. Similarly, folivores are significantly larger than insectivores, as predicted, though the proposed body mass boundary was not supported. These results suggest that shear crest length and body mass are indeed linked to diet in the proposed manner. It may now be possible to use these findings to gain a greater understanding of the feeding behaviours of a variety of extinct marsupials and other therians.

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LONGUET-HIGGINS, MICHAEL S., and DAVID A. DRAZEN. "On steep gravity waves meeting a vertical wall: a triple instability." Journal of Fluid Mechanics 466 (September 10, 2002): 305–18. http://dx.doi.org/10.1017/s0022112002001246.

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Theoretical arguments suggest that progressive gravity waves incident on a vertical wall can produce periodic standing waves only if the incident wave steepness ak is quite small, certainly less than 0.284. Laboratory experiments are carried out in which an incident wave train of almost uniform amplitude meets a vertical barrier. At wave steepnesses greater than 0.236 the resulting motion near the barrier is non-periodic. A growing instability is observed in which every third wave crest is steeper than its neighbours. The steep waves develop sharp crests, or vertical jets. The two neighbouring crests are rounded, at-topped, or of intermediate form. The instability grows by a factor of about 2.2 for every three wave periods, almost independently of the incident wave steepness.

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Kriebel, D. L., and T. H. Dawson. "Nonlinear Effects on Wave Groups in Random Seas." Journal of Offshore Mechanics and Arctic Engineering 113, no. 2 (1991): 142–47. http://dx.doi.org/10.1115/1.2919910.

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Laboratory simulations of extreme random seas reveal that high wave crests occur more frequently than predicted by the Rayleigh distribution. In this paper, a theory is presented to account for nonlinearities in the sea state to second order resulting in a non-Rayleigh distribution of wave crest and trough amplitudes based on the narrow-band assumption. The resulting probability density functions are then used to predict average wave group characteristics through a modification of linear wave envelope theory which accounts, for example, for a significant decrease in the time intervals between successive runs of high crests compared to linear theory. The nonlinear theory is then verified based on a laboratory data set on deep water wave group statistics for severe seas described by Bretschneider and JONSWAP spectra.

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Alcolado, Pedro M., Darlenys Hernández-Muñoz, Hansel Caballero, Linnet Busutil, Susana Perera, and Gema Hidalgo. "EFECTOS DE UN INUSUAL PERÍODO DE ALTA FRECUENCIA DE HURACANES SOBRE EL BENTOS DE ARRECIFES CORALINOS." Revista Ciencias Marinas y Costeras 1 (December 11, 2009): 73. http://dx.doi.org/10.15359/revmar.1.4.

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En arrecifes coralinos del suroeste de Cuba, se evaluaron los impactos de la inusitada frecuencia e intensidad de huracanes entre el 2001 y el 2007, y de las enfermedades de corales, ambos factores asociados al cambio climático. En las crestas arrecifales, la reducción de la cobertura de coral duro vivo varió de nula a 21%, mientras que la reducción del diámetro máximo promedio de los corales varió de 16 a 40 cm. En los arrecifes frontales, la reducción de la cobertura de coral varió de nula a 14%, mientras que la reducción del diámetro máximo promedio varió de nula a 26 cm. Sin embargo, en todos los sitios se observaron grandes cambios en el predominio numérico de las especies. En las crestas, este se desplazó de Acropora palmata y otros corales duros hacia Millepora complanata, Porites astreoides o Acropora prolifera. En los arrecifes frontales, el cambio ocurrió de la dominancia de Montastraea annularis (complejo de especies), Diploria strigosa y Agaricia agaricites a la de P. astreoides o Siderastrea siderea. Con esos cambios, las crestas están perdiendo efectividad como refugios y como disipadoras del oleaje, a causa de la reducción de complejidad estructural. La densidad del erizo Diadema antillarum se mantuvo insignificante y sin cambio en el sur del Golfo de Batabanó, mientras que se incrementó de manera importante en la cresta de Faro Cazones. Los porcentajes de mortalidad reciente y de incidencia de enfermedades de corales se mantuvieron bajos, lo que sugiere una influencia dominante de los huracanes en la condición de los arrecifes coralinos evaluados.In coral reefs of southwestern Cuba, we assessed the impacts from unprecedented frequent and intense hurricanes during the period 2001-2007, and from coral diseases, which are both factors considered to be associated with climate change.. At the reef crests, live hard coral cover reduction varied from null to 21%, while maximum average coral diameter reduction varied from 16 to 40 cm. In the fore-reefs, the reduction of coral cover varied from null to 14%, while diameter reduction varied from null to 26 cm. However, at all sites, great shifts in species dominance patterns were observed. In reef crests, numerical dominance of Acropora palmata and other hard corals shifted towards increases of Millepora complanata or, to a lesser extent, of Porites astreoides or Acropora prolifera. At the fore-reefs, the shifts occurred from the dominance of Montastraea annularis complex, Diploria strigosa and Agaricia agaricites, towards combined increases of P. astreoides or Siderastrea siderea. With those ongoing changes, reef crests are losing effectiveness as refuges and wave dissipators because of reduction of structural complexity. The population density of the sea-urchin Diadema antillarum remained negligible and unchanged in the southern Gulf of Batabanó, while it increased significantly at the Faro Cazones reef crest. Percentages of recent mortality and percentages of disease incidence in corals remained low, suggesting a dominant influence from hurricanes on assessed coral reef decline.

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Benetazzo, Alvise, Francesco Barbariol, Filippo Bergamasco, Andrea Torsello, Sandro Carniel, and Mauro Sclavo. "Observation of Extreme Sea Waves in a Space–Time Ensemble." Journal of Physical Oceanography 45, no. 9 (2015): 2261–75. http://dx.doi.org/10.1175/jpo-d-15-0017.1.

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AbstractIn this paper, an observational space–time ensemble of sea surface elevations is investigated in search of the highest waves of the sea state. Wave data were gathered by means of a stereo camera system, which was installed on top of a fixed oceanographic platform located in the Adriatic Sea (Italy). Waves were measured during a mature sea state with an average wind speed of 11 m s−1. By examining the space–time ensemble, the 3D wave groups have been isolated while evolving in the 2D space and grabbed “when and where” they have been close to the apex of their development, thus exhibiting large surface displacements. The authors have selected the groups displaying maximal crest height exceeding the threshold adopted to define rogue waves in a time record, that is, 1.25 times the significant wave height (Hs). The records at the spatial positions where such large crests occurred have been analyzed to derive the empirical distributions of crest and wave heights, which have been compared against standard statistical linear and nonlinear models. Here, the maximal observed wave crests have resulted to be outliers of the standard statistics, behaving as isolated members of the sample, apparently uncorrelated with other waves of the record. However, this study has found that these unexpectedly large wave crests are better approximated by a space–time model for extreme crest heights. The space–time model performance has been improved, deriving a second-order approximation of the linear model, which has provided a fair agreement with the empirical maxima. The present investigation suggests that very large waves may be more numerous than generally expected.

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Warrington, Curtis, Shiv Kapoor, and Richard DeVor. "Experimental Investigation of Thread Formation in Form Tapping." Journal of Manufacturing Science and Engineering 127, no. 4 (2005): 829–36. http://dx.doi.org/10.1115/1.1951784.

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In form tapping, the generation of unfinished thread forms results in the appearance of split crests. An experimental technique is developed to study the nature of split crest formation. Custom tools are modeled after tap tooth geometry to perform the forming process in a vertical milling machine. Single-tooth experiments replicate the initial deformation stages and determine the tap geometry and tapping process parameters that significantly affect ridge size and shape. This method is then expanded to consider two axially consecutive tap teeth and the interaction of consecutive ridges to create the final thread form. It is found that certain tap geometrical characteristics are important to the final thread form and, therefore, determine the size and shape of the resulting split crest.

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Smith, David R., and Meicai Wei. "A New AsianMonophadnoidesAshmead (Hymenoptera: Tenthredinidae) with High Antennal Crests." Proceedings of the Entomological Society of Washington 117, no. 2 (2015): 203–8. http://dx.doi.org/10.4289/0013-8797.117.2.203.

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UDA, Takaaki, Shinji SATO, Kenji NOGUCHI, Makoto SHIBASAKI, and Takayuki KUMADA. "Experimental Study on Improvement of Artificial Reef with Crests." Journal of Japan Society of Civil Engineers, Ser. B2 (Coastal Engineering) 69, no. 2 (2013): I_596—I_600. http://dx.doi.org/10.2208/kaigan.69.i_596.

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