Dense Tangles Research Articles

SHEET WEBS OF LINYPHIOID SPIDERS (ARANEAE: LINYPHIIDAE, PIMOIDAE): THE LIGHT OF DIVERSITY HIDDEN UNDER A LINGUISTIC BASKET

Photographs of the webs of approximately 113 species in 52 genera show that the web architecture of linyphioid spiders (Linyphiidae and Pimoidae) present many variations on a single basic pattern. Nearly all species built webs with a more or less horizontal, continuous sheet with an open space just below the sheet. However, the details in the designs showed great diversity; we recognized >50 web traits, including positions relative to the ground or large objects; sheet shapes and orientations; secondary sheets; “slime” on the sheet; patterns and densities of lines in sheets; visible droplets on sticky lines; upward and downward directed dimples in the sheet with tensor lines; primary and secondary frame lines; retreats; and the presence, location, and designs of associated tangles. This survey probably substantially underestimates both intraspecific and intrageneric diversity of web forms. Intrageneric comparisons in just over 20 genera documented varying degrees of intrageneric variation; some genera show striking differences. Several web designs were widely distributed: sheets with dense tangles above commonly had arrays of lines attached to the sheet's upper surface; downward dimples in sheets commonly occurred at sites where the sheet curved upward, but upward-directed dimples were rare and small; and sheets built next to the surface of the ground almost always lacked extensive tangles above them. New web patterns not previously reported for linyphiid webs include: sandwich webs (pairs of closely spaced, otherwise naked sheets); extensive vertical sheets next to tree trunks; tubular retreats at the edges of the sheet where the spider rests; trough-like sheets just above the upper surface of a curled leaf; sizeable, apparently sticky droplets densely covering many lines that were apparently placed in pairs in the sheet; long sheet lines that converge at one corner; runways to a sheltered site where the spider waits beyond the sheet's edge; and apparent skeleton lines in the sheet (probably from early stages of construction). Patterns of lines within the sheet may reflect patterns of movement during sheet construction behavior. We propose that some webs on the substrate function to extend the spider's sensory field rather than detain prey and that some tangles below and perhaps some above the sheet may function to defend the spider from enemies. A suite of linyphiid traits, including leg, chelicera, and spinneret morphology; details of web design, such as numerous small upward-directed dimples in dome-shaped sheets but fewer, large downward-directed dimples in cup-shaped sheets; and attack behavior, appears to function to increase the speed with which spiders attack prey. The functions of many architectural features remain obscure.

The View From the Tree.

The View From the Tree.

Contribution of dislocation substructures developed during cold rolling to the formation of rolling textures in Al–Mg alloys

Abstract In order to investigate the mechanism of the development of rolling textures in Al –Mg alloys, hot bands of high-purity Al, Al-3 wt. %Mg and Al-5 wt. %Mg alloys were solution-treated at 450 °C and cold-rolled by varying rolling reductions up to 97%. Rolling textures of these specimens were investigated with the orientation distribution function analysis. Comparisons of the results of the texture analysis with those of the hardness measurement and transmission electron microscopy observations revealed that, in all specimens, the texture development occurred mainly at the later half of work hardening, i. e., at rolling reductions above 80 %, where dislocation substructures were well developed. In pure Al, in which well defined, elongated cell structures were developed, {112}<111> and {123}<634> components developed remarkably, whereas in the Al-5% Mg alloys, in which only dense dislocation tangles and ill defined small cells were developed, the development of {112}<111> and {123}<634> components was strongly suppressed. All these observations thus suggested that the development of rolling textures was strongly affected by the development of dislocation substructures, which occurred concurrently during rolling, and that the formation of elongated cell structures was more favorable for the development of rolling textures. In cold rolling, elongated cell structures may be the final form of dislocation substructures, providing both mechanical stability and orientation stability.

Ubiquity of particle–vortex interactions in turbulent counterflow of superfluid helium

Abstract

Novel methods for dislocation density estimation in highly compacted tangles

Dislocation lines are usually observed in thin foil images obtained by transmission electron microscopy (TEM). Based on conventional methods involving stereological relationship and line counting, dislocation densities have been calculated in distinct materials, mostly in plastically deformed metals and alloys. However, under certain plastic deformation conditions, such as those associated with dynamic strain aging (DSA), dislocation arrangements may develop highly compact tangles. Inside DSA dense tangles, the individual identification of lines for stereological counting becomes impracticable. In the present work, two novel methods to estimate dislocation densities in highly compact tangles are proposed. The first method is exemplified in TEM images of cells and banded walls substructure of an austenitic stainless steel plastically deformed under DSA condition. In a second method, the average dislocation density of such TEM images is proposed to be calculated by the proportional sum of area fractions multiplied by corresponding dislocation densities of visible dislocation and highly compact tangle areas as well as dislocation-free area.

The Webs ofNeoantistea riparia(Araneae: Hahniidae): Are Dew Drops Helpful in Prey Capture?

The webs of hahniid spiders are poorly known. Those of Neoantistea riparia (Keyserling, 1887) all included sheets near the surface of the ground, but were more complex and variable than the simple sheets mentioned in previous accounts. Additional components included: sparse tangles of variable size above the sheet; lines below the sheet; small, dense tangles near some edges of the sheet; and a temporary feeding chamber below the sheet built near a recently captured prey. Webs were close to the surface of damp ground and, as a result, spent long periods coated with droplets of water. These droplets may aid in prey capture, as water accumulated on struggling prey and may have hindered their escape. In contrast, droplets seldom adhered to the spiders.

Sleep patterns, daytime predation, and the evolution of diurnal sleep site selection in lorisiforms.

Synthesize information on sleep patterns, sleep site use, and daytime predation at sleep sites in lorisiforms of Asia and Africa (10 genera, 36 species), and infer patterns of evolution of sleep site selection. We conducted fieldwork in 12 African and six Asian countries, collecting data on sleep sites, timing of sleep and predation during daytime. We obtained additional information from literature and through correspondence. Using a phylogenetic approach, we established ancestral states of sleep site selection in lorisiforms and traced their evolution. The ancestral lorisiform was a fur-clinger and used dense tangles and branches/forks as sleep sites. Use of tree holes and nests as sleep sites emerged ∼22 Mya (range 17-26 Mya) in Africa, and use of bamboo emerged ∼11 (7-14) Mya in Asia and later in Africa. Fur clinging and some sleep sites (e.g., tree holes, nests, but not bamboo or dense tangles) show strong phylogenetic signal. Nests are used by Galagoides, Paragalago, Galago and Otolemur; tree holes by Galago, Paragalago, Sciurocheirus and Perodicticus; tangles by Nycticebus, Loris, Galagoides, Galago, Euoticus, Otolemur, Perodicticus and Arctocebus; all but Sciurocheirus and Otolemur additionally sleep on branches/forks. Daytime predation may affect sleep site selection and sleep patterns in some species of Nycticebus, Galago, Galagoides, Otolemur and Perodicticus. Most lorisiforms enter their sleep sites around sunrise and leave around sunset; several are active during twilight or, briefly, during daytime. Variations in sleep behavior, sleep patterns and vulnerability to daytime predation provide a window into the variation that was present in sleep in early primates. Overall, lorisiforms use the daytime for sleeping and no species can be classified as cathemeral or polycyclic.

Visualization of quantum turbulence in superfluid He3−B : Combined numerical and experimental study of Andreev reflection

We present a combined numerical and experimental study of Andreev scattering from quantum turbulence in superfluid $^3$He-B at ultralow temperatures. We simulate the evolution of moderately dense, three-dimensional, quasiclassical vortex tangles and the Andreev reflection of thermal quasiparticle excitations by these tangles. This numerical simulation enables us to generate the two-dimensional map of local Andreev reflections for excitations incident on one of the faces of a cubic computational domain, and to calculate the total coefficient of Andreev reflection as a function of the vortex line density. Our numerical simulation is then compared with the experimental measurements probing quantum turbulence generated by a vibrating grid. We also address the question of whether the quasiclassical and ultraquantum regimes of quantum turbulence can be distinguished by their respective total Andreev reflectivities. We discuss the screening mechanisms which may strongly affect the total Andreev reflectivity of dense vortex tangles. Finally, we present combined numerical-experimental results for fluctuations of the Andreev reflection from a quasiclassical turbulent tangle and demonstrate that the spectral properties of the Andreev reflection reveal the nature and properties of quantum turbulence.

Microstructure and hot corrosion behavior of the Ni-based superalloy GH202 treated by laser shock processing

The effects of laser shock processing on microstructure, the residual stress, and hot corrosion behavior of the Ni-based superalloy GH202 were investigated. The microstructures of GH202 before and after laser shock processing (LSP) were characterized by electron backscattered diffraction (EBSD) and transmission electron microscope (TEM). A large number of crystal defects (twins, dislocation arrays, and high dense tangles) were generated on the surface of GH202 treated with LSP. The cross-sectional compressive residual stress and micro-hardness of specimens treated by LSP were improved significantly. The corrosion kinetics of GH202 with or without LSP treatment at 800°C and 900°C were investigated. Analysis by X-ray diffraction (XRD) revealed that the corrosion products mainly consist of Cr2O3, TiO2, Al2O3, NiO, CrS, Ni3S2, and Na2CrO4. The surface and cross-section morphologies were observed by scanning electron microscope (SEM) combined with energy dispersive spectroscopy (EDS). The results confirmed that the crystal defects induced by LSP promotes the creation of diffusion paths for elements (Cr, Al, and Ti), allowing the formation of tiny homogeneous oxidation films in a very short time. Additionally, the spallation of oxidation film on the treated specimens was alleviated significantly. Overall, the hot corrosion resistance of Ni-based GH202 induced by LSP was improved in Na2SO4 and NaCl molten salt from 800°C to 900°C.

Do Collared Peccaries Negatively Impact Understory Insectivorous Rain Forest Birds Indirectly Via Lianas and Vines?

AbstractTropical rain forest understory insectivorous birds are declining, even in large forest reserves, yet the mechanisms remain unclear. Abundant large mammals can reshape forest structure, which degrades foraging microhabitat. We used six sites in Nicaragua, Costa Rica, and Panama with varying collared peccary (Pecari tajacu) density to test three linked hypotheses: (1) locally declining understory insectivores forage preferentially in liana tangles; (2) vine and liana density, cover, and frequency of dense tangles are lower in the presence of abundant collared peccaries; and consequently (3) abundant collared peccaries are associated with reduced understory insectivorous bird abundance. Three insectivores that declined at La Selva preferentially foraged in liana tangles: Checker‐throated Antwren (Epinecrophylla fulviventris), Dot‐winged Antwren (Microrhopias quixensis), and Ruddy‐tailed Flycatcher (Terenotriccus erythrurus). Vine density, liana cover, liana tangle frequency, and forest cover were lower in the presence of collared peccaries relative to experimental mammal exclosures, with the greatest differences at La Selva Biological Station, Costa Rica. Across sites, five of seven vine and liana measures showed negative, curvilinear relationships with peccary densities. Vine and liana measures peaked at sites with intermediate peccary density, and were low at La Selva. Structural equation models suggest negative indirect effects of the collared peccaries on focal bird densities, mediated by vine and liana density, cover, or tangle frequency. Forest area and rainfall affected both lianas and birds, but collared peccaries also contributed to the reduced abundance of understory insectivores. Indirect effects such as that suggested here may occur even in large, protected forest reserves where large mammal communities are changing.

Hot deformation behavior and microstructural evolution of homogenized 7050 aluminum alloy during compression at elevated temperature

Hot compression tests of homogenized 7050 aluminum alloy were carried out on the Gleeble-1500 thermal simulation machine, and the associated microstructure was studied using electron back scattered diffraction technique and transmission electron microscopy. The results showed that the peak stress levels decreased with the increase of deformation temperatures or the decrease of strain rates, which can be represented by the Zener–Hollomon parameter in the exponent-type equation with the hot deformation activation energy of 160.3kJ/mol. With the decrease of Z values, results showed a continuous decrease in very low angle boundaries, exhibiting a misorientation between 2° and 5°, associated to substructure, and a steady increase in the other higher angle boundaries, especially with the misorientation angles between 30° and 60°. And such an evolution is due to the increase of subgrain size with the decrease of Z values. At lower Z, the dislocations collected into more widely spaced and less dense tangles. As strain rose, the tangles reorganized into subgrains with walls that were more widely spaced and straighter; they had fewer, more regularly arranged dislocations. The main softening mechanism of homogenized 7050 aluminum alloy is dynamic recovery.

Population Density and Habitat Preferences Of the Kenya Lesser Galago (Galago senegalensis braccatus) Along The Ewaso Nyiro River, Laikipia, Kenya

Surveys of the Kenya lesser galago (or bushbaby) Galago senegalensis braccatus on Mpala Ranch near the Mpala Research Centre, Kenya, were conducted in June and July 1995. Data were collected along two transects. Galago s. braccatus reached its highest density in Fever Tree Acacia xanthophloea riverine woodland and was found primarily at a height of 4–6 m above the ground, followed by 14–16 m. Within A. xanthophloea, G. s. braccatus was closely associated with trees having dense liana tangles. We suggest that lianas provide G. s. braccatus with protection both while sleeping during the day and while foraging at night.

Upheaval Dome, Utah, USA: Impact origin confirmed

Research Article| March 01, 2008 Upheaval Dome, Utah, USA: Impact origin confirmed Elmar Buchner; Elmar Buchner 1Institut für Planetologie, Universität Stuttgart, 70174 Stuttgart, Germany Search for other works by this author on: GSW Google Scholar Thomas Kenkmann Thomas Kenkmann 2Museum für Naturkunde-Mineralogie, Humboldt-Universität zu Berlin, 10115 Berlin, Germany Search for other works by this author on: GSW Google Scholar Geology (2008) 36 (3): 227–230. https://doi.org/10.1130/G24287A.1 Article history received: 27 Jul 2007 rev-recd: 02 Nov 2007 accepted: 06 Nov 2007 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Elmar Buchner, Thomas Kenkmann; Upheaval Dome, Utah, USA: Impact origin confirmed. Geology 2008;; 36 (3): 227–230. doi: https://doi.org/10.1130/G24287A.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Upheaval Dome is a unique circular structure on the Colorado Plateau in SE Utah, the origin of which has been controversially discussed for decades. It has been interpreted as a crypto volcanic feature, a salt diapir, a pinched-off salt diapir, and an eroded impact crater. While recent structural mapping, modeling, and analyses of deformation mechanisms strongly support an impact origin, ultimate proof, namely the documentation of unambiguous shock features, has yet to be successfully provided. In this study, we document, for the first time, shocked quartz grains from this crater in sandstones of the Jurassic Kayenta Formation. The investigated grains contain multiple sets of decorated planar deformation features. Transmission electron microscopy (TEM) reveals that the amorphous lamellae are annealed and exhibit dense tangles of dislocations as well as trails of fluid inclusions. The shocked quartz grains were found in the periphery of the central uplift in the northeastern sector of the crater, which most likely represents the cross range crater sector. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Life history of the Mato Grosso Antbird Cercomacra melanaria in the Brazilian Pantanal

Here we describe the habitat use, reproductive biology, diet and details of the life history of the Mato Grosso Antbird Cercomacra melanaria, one of the least studied Cercomacra species. We located 30 nests, of which 22 became active and were monitored. The nest consists of a deep cup, placed among dense tangles of vegetation, almost always in forests of Vochysia divergens (Cambarazal). Eggs are pinkish‐cream coloured, covered with reddish brown to purple spots and blotches that are concentrated around its centre and larger end. Average nest success was 32%. The Mayfield method indicated daily survival rates during egg and nestling periods of 0.94 and 0.96, respectively, and a success rate of 26%. Examination of 24 stomach contents revealed a diet based exclusively on arthropods.

Contribution of dislocation substructures developed during cold rolling to the formation of rolling textures in Al–Mg alloys

Abstract In order to investigate the mechanism of the development of rolling textures in Al–Mg alloys, hot bands of high-purity Al, Al-3 wt. % Mg and Al-5 wt. % Mg alloys were solution-treated at 450 °C and cold-rolled by varying rolling reductions up to 97 %. Rolling textures of these specimens were investigated with the orientation distribution function analysis. Comparisons of the results of the texture analysis with those of the hardness measurement and transmission electron microscopy observations revealed that, in all specimens, the texture development occurred mainly at the later half of work hardening, i. e., at rolling reductions above 80 %, where dislocation substructures were well developed. In pure Al, in which well defined, elongated cell structures were developed, {112} and {123} components developed remarkably, whereas in the Al-5 % Mg alloys, in which only dense dislocation tangles and ill defined small cells were developed, the development of {112} and {123} components...

Energy Spectrum of Vortex Tangle

The energy spectrum of superfluid turbulence in the absence of the normal fluid is studied numerically. In order to discuss the statistical properties, we calculate the energy spectra of the 3D velocity field induced by both dilute and dense vortex tangles, whose dynamics are calculated by the full nonlocal Biot-Savart law. In the case of a dense tangle, the slope of the energy spectrum changes at k=2π/l, where l is the intervortex spacing. For k>2π/l, the energy spectrum has a k−1 behavior in the same manner as the dilute vortex tangle, while otherwise the slope of the energy spectrum deviates from the k−1 behavior. We compare the behavior for k<2π/l with the Kolmogorov law.

Cranial Ultrasonography

Cranial Ultrasonography

Metallographic study on rolling contact fatigue of 0.44%C–1.71 %Mn induction-hardened bearing steels

Microstructural changes and propagation of subsurface cracks during rolling contact have been studied to clarify rolling contact fatigue of 0.44%C–1.71%Mn induction-hardened bearing steels, using the specimens with different induction-hardened layer. The specimens were pre-treated to form lower bainite and induction-hardened to form fine martensite in shallow induction-hardened layer or coarse martensite in deep hardened layer. Rolling contact fatigue tests were conducted under maximum a Hertzian contact stress of 508 kgf mm −2 with circulating lubricant through a filtered-pump feed system. Heavy plastic deformation of fine martensite in shallow induction-hardened layer and propagation of subsurface crack across grain boundaries were observed with superior resistance to fatigue. On the other hand, intergranular crack along grain boundaries in coarse martensite of deep hardened layer were observed with poor resistance to fatigue. Deformed martensite and dense tangles of dislocations in ferrite were observed by transmission electron microscopy for a shallow induction-hardened layer which was heavily deformed during rolling contact fatigue.

Selective expression and rapid regulation of GABAA receptor subunits in geniculocortical neurons of macaque dorsal lateral geniculate nucleus

Monocular deprivation in adult macaques produces a rapid down-regulation in GABA and GABAA receptor subunit immunoreactivity in deprived-eye columns of primary visual cortex (VI) but a significantly delayed GABA reduction in deprived layers of the dorsal lateral geniculate nucleus (LGN). These findings, suggesting that normal inhibitory neurotransmission persists in LGN at a time when VI inhibitory mechanisms are greatly altered, are consistent with physiological studies that have demonstrated a greater degree of functional plasticity in VI than in LGN. Nonetheless, functional adaptation to partial loss of visual input has been detected in the LGN, indicating that synaptic plasticity takes place in this nucleus. In the present study, evidence for early changes in inhibitory neurotransmission were examined with immunocytochemical methods to determine if, in the absence of early GABA regulation, GABAA receptor subunits in macaque LGN are affected by adult deprivation. Immunoreactivity for alpha 1 and beta 2/3 subunits of the GABAA receptor was intense within the magnocellular layers and more modest in the parvocellular layers and intercalated layers. In all layers, immunoreactivity was present in the cytoplasm and along the surfaces of relatively large somata and in dense tangles of processes in the neuropil. Double-labeling experiments demonstrated that somata and processes immunoreactive for alpha 1 and beta 2/3 were surrounded by GABA terminals but no cell intensely immunoreactive for either subunit expressed immunoreactivity for GABA, itself. Following periods of monocular deprivation by tetrodotoxin (TTX) injection for 4 days or longer, layers deprived of visual activity displayed levels of alpha 1 and beta 2/3 immunoreactivity markedly lower than those displayed by the adjacent, normally active layers. Such changes were greater as the period of deprivation increased. The changes included a loss of immunostaining in and around somata and in many neuropil elements of deprived layers. These data indicate that GABA and GABAA receptor subunits alpha 1 and beta 2/3 are expressed by separate populations of neurons in macaque LGN that are differentially regulated by visual activity. The findings suggest that rapid, activity-dependent regulation of postsynaptic receptors represents one mechanism for altering synaptic strength in the adult macaque visual system.

Sleeping habits of tamarins, Saguinus mystax and Saguinus fuscicollis (Mammalia; Primates; Callitrichidae), in north‐eastern Peru

The sleeping habits of moustached tamarins, Saguinus mystax, and saddle‐back tamarins, Saguinus fuscicollis, were studied in northeastern Peru. Five types of sleeping sites were distinguished: 1) Jessenia bataua palms; 2) tree hollows; 3) dense tangles of vegetation; 4) crotches; 5) open horizontal branches. Both tamarin species used Jesseniu‐palms most frequently. Tree hollows ranked second in the saddle‐back tamarins, but were never used by moustached tamarins. Sleeping sites of moustached tamarins were located significantly higher than those of saddle‐back tamarins. Jessenia‐palms used by moustached tamarins were significantly higher than palms from a random transect sample, but this was not the case for Jessenia‐palms used by saddle‐back tamarins. For both species, concealment seems to be more important than height above ground. The maximum number of subsequent nights spent in the same sleeping site was two in moustached tamarins and six in saddle‐back tamarins. The two tamarin species did not compete for sleeping sites. While the general pattern of sleeping site selection conforms to hypotheses predicting safety from predators as a major factor, differences between the two tamarin species reflect general niche differences between them. Most sleeping sites are located in exclusively used parts of the home range. Moustached tamarins generally use sleeping sites that are close to the last feeding site of the afternoon. The distance between simultaneously used sleeping sites of moustached and saddle‐back tamarins are generally close together, which helps to minimize time spent out of interspecific association.