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Results for “Meanders”

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At least 433 records · Page 24Linked to original sources

PubMed2005

Slow-moving predatory gastropods track prey odors in fast and turbulent flow.

Olfactory searching by aquatic predators is reliant upon the hydrodynamic processes that transport and modify chemical signals. Previous studies indicate that the search behavior of some benthic crustaceans is hindered by rapid water flow and turbulent mixing of prey chemicals, but different sensory strategies employed by other taxa might offset such detrimental effects. Using a laboratory flume, we investigated the odor-tracking behavior of a marine gastropod whelk (Busycon carica) to test the generalization that turbulence interferes with chemically mediated navigation. We exposed individual whelks to turbulent odor plumes in free-stream velocities of 1.5, 5, 10 or 15 cm s(-1), or with one of two obstructions placed upstream of the odor source in an intermediate flow of 5 cm s(-1). Measurements of velocity and stimulus properties confirmed that obstruction treatments increased turbulence intensity and altered the fine-scale structure of downstream odor plumes. In all conditions tested, between 36-63% of test animals successfully located the odor source from 1.5 m downstream with no significant effect of flow treatment. Search behaviors, such as cross-stream meander were reduced at higher flow velocities and in the presence of obstructions, allowing whelks to reach the odor source significantly more quickly than in slower, less turbulent conditions. Our results demonstrate that whelks can respond to chemical information in fast and turbulent flow, and we suggest that these slow-moving predators can forage in hydrodynamic environments where the olfactory abilities of other taxa are limited.

Analysis of Variance↗

PubMed2001

A study of helical and planar waves on sea urchin sperm flagella, with a theory of how they are generated.

When the spermatozoon of Echinus esculentus swims in sea water containing methyl cellulose (viscosity 1.5--4 Pa s), its flagellum may generate either a helical or a planar waveform, each type being stable. The helical wave, which is dextral, is complicated by the concurrent passage of miniature waves along it. These miniature waves have a pulsatile origin in the neck region of the spermatozoon. Our videotape analysis indicates that there are two pulses of mechanical activity for each true cycle of the helical wave. (The true helical frequency was obtained from the apparent wave frequency and the roll frequency of the sperm head, the latter being detectable in some sperm when lit stroboscopically.) The planar wave has a meander shape. During the propagation of planar waves, the sliding displacements are adjustable in either direction; moribund flagella can undergo unrestricted sliding. The planar waves are, in fact, exactly planar only at interfaces. Otherwise, there tend to be torsions in the interbend segments between planar bends. Mechanical stimulation of the flagellum can cause a sudden transition from the helical to the planar waveform. To account for the two modes of beating, we advance the hypothesis that circumferential linkages yield beyond a threshold strain. Whether this yield point is exceeded, we suggest, depends upon the balance between the active shear force and the external viscosity (among other factors). We propose that a subthreshold force originates in one array and then triggers the other dynein arrays circumferentially, but unidirectionally, around the base of the flagellum; whereas a suprathreshold force provokes bi-directional circumferential triggering. These may be the two patterns of activation that result in helical and planar waveforms, respectively. The transition from helical to planar bending may result from an increment in the force produced by the dynein motors. The pulsatile origin of the helical wave resembles behaviour described previously for spermatozoa of Ciona intestinalis and of the quail Coturnix coturnix.

Animals↗

PubMed1976

Effects of calcium on flagellar movement in the trypanosome Crithidia oncopelti.

1. The effects of calcium on the motility of different preparations of flagella from Crithidia oncopelti were studied using stroboscopic and high-speed cine photographic techniques. 2. By varying the concentration of calcium in suspensions of chemically treated samples of the organism it was found that changes occurred in bend shape, wave direction and frequency. 3. Waves on the flagellum of the organisms in vivo possess the unusual ability to propagate from tip to base, but reverse in direction during an avoiding response. In chemically extracted and reactivated preparations tip to base propagation was observed only at low concentrations (less than 10(-4) mol m-3) of calcium ion; at high concentrations base to tip propagation only was seen. In cells treated with ion across membranes, tip to base propagation was seen only in the presence of EGTA; when calcium was added the majority of organisms propagated waves from base to tip. 4. At certain values (ca. 10(-3) mol m-3) of the calcium concentration the wave shape had meander-like characteristics, whereas at higher and lower concentrations it was more sinsoidal. At high calcium concentrations only one wave appeared on the flagellum whereas at low values two or three were observed. 5. A reduction in frequency at high calcium concentrations was probably due to competitive inhibition of magnesium ions. 6. The results suggest that wave reversal in living Crithidia is induced by the release of calcium ions within the flagellum following stimulation of the membrane. In terms of the sliding filament model of flagellar activity the effects of calcium suggest that the ion is effective in modifying the interaction between the spoke head and central sheath and may control the relative direction of microtubular sliding.

Animals↗

PubMed2005

Combined effects of nifekalant and lidocaine on the spiral-type re-entry in a perfused 2-dimensional layer of rabbit ventricular myocardium.

BACKGROUND: Spiral re-entry plays the principal role in the genesis of ventricular tachycardia and ventricular fibrillation (VT/VF). The specific I(Kr) blocker, nifekakant (NIF) has, often in combination with lidocaine (LID), recently been used in Japan to prevent recurrent VT/VF, but the combined effects of these drugs on spiral re-entry had never been investigated. METHODS AND RESULTS: A ventricular epicardial sheet was obtained from 13 Langendorff-perfused rabbit hearts by means of a cryoprocedure, and epicardial excitations were analyzed with a high-resolution optical mapping system. Nifekakant (0.5 micromol/L) caused significant prolongation of action potential duration (APD) and LID (3 micromol/L) attenuated the APD prolongation without affecting the conduction velocity. VT were induced in 6 hearts by cross-field stimulation, and single- or double-loop spirals circulating around variable functional block lines were visualized during the VT. Nifekakant reduced VT cycle length and caused early termination in association with destabilization of the spiral dynamics (prolongation of functional block line, frequent local conduction block, and extensive meandering). These modifications of spiral-type re-entrant VT by NIF were prevented by addition of LID. CONCLUSIONS: The effects of NIF on the spiral excitations are reversed by LID. This interaction should be taken into account when these drugs are used in combination to treat VT/VF.

Animals↗

PubMed2006

Pancreatic arteriovenous malformation involving adjacent duodenum with gastrointestinal bleeding: report of a case.

A 54-year-old man was admitted to our hospital with the symptoms of palpitation, dyspnea, and tarry stool. Upper gastroduodenal endoscopy revealed submucosal lesions with vascular ectasia in the second part of the duodenum. Dynamic computed tomography (CT) detected a hypervascular lesion in the pancreatic head and the duodenum. Selective angiography showed proliferation of a vascular network and early filling of the portal vein at the early arterial phase. With a diagnosis of pancreatic arteriovenous malformation (AVM), we performed pylorus-preserving pancreaticoduodenectomy. At laparotomy, localized and meandering vessels were seen on the surface of the head of the pancreas. Histological examination showed dilated tortuous vessels accompanied by severed elastic fibers in the vessel media and blood clot formation. The incidence of pancreatic AVM remains extremely low, and recurrent gastrointestinal bleeding is a frequent complication. To prevent recurrent bleeding and progressive portal hypertension, surgery may be the definitive management of symptomatic AVM.

Arteriovenous Malformations↗

PubMed1992

Pregnancy and lactation affect the microvasculature of the mammary gland in mice.

Microvascular changes in the mammary gland in mice during pregnancy and lactation were investigated by scanning electron microscopy (SEM) with a corrosion cast method, transmission electron microscopy (TEM) and morphometry. By SEM, duct-associated capillary plexuses were sparsely distributed to branch into adipocytes during virgin period. With advance in pregnancy, both branches from the capillary plexuses and branches from the vessels surrounding adipocytes extended further to form capillary networks. The basket-like architecture was completed by day 18 of pregnancy. These findings may indicate that angiogenesis occurs frequently during this period. During lactation, the basket-like architecture still remained and the capillaries surrounding alveoli meandered. After weaning, the regression of microvasculature followed the degeneration of alveoli. By TEM and morphometry, the density of pinocytotic vesicles (PVs) (number of PVs per microns 2 of endothelium cytoplasm) increased twofold from day 18 of pregnancy to day 5 of lactation, furthermore increased threefold from days 10 to 20 of lactation, and subsequently decreased after weaning. Marginal folds and microvillous processes gradually increased in length with advance in pregnancy, reached the maximum from days 5 to 15 of lactation, and thereafter decreased. In addition, the capillaries with thinner walls were in close contact with alveoli during the late stage of pregnancy and during lactation. Furthermore, the alveolar epithelial cells had well-developed basal infoldings during lactation. These findings suggest that the capillaries play an important role in transporting materials necessary for milk production.

Animals↗

PubMed1995

Congenital anophthalmia with caudal vertebral anomalies in Japanese Brown cattle.

Anophthalmia and caudal vertebral anomalies such as taillessness or wry tail were morphologically examined in ten Japanese Brown calves obtained in Kumamoto Prefecture. The anomalous calves lacked eyeball bilaterally or unilaterally but had small-sized eyelids and narrow palpebral fissures. A small cystic, solid or spot-like remnant of eyeball (REB) was buried in the mixture of vestigial extraocular muscles, lacrimal gland and adipose tissue of the orbit. The REB was composed of irregularly arranged elements of ocular wall such as sclera, choroid and retina. The retina was often dysplastic and connected to the hypoplastic optic nerve. These morphological changes might represent the defective processes after the formation of the optic vesicle or cup. Therefore, this eye defect may be defined as degenerative anophthalmia. The defects of the vertebral body such as wedge vertebra, hemivertebra, and sagittal cleft vertebra seen in the lumbar, sacral, and coccygial regions and the meandering of the axial line of abnormal vertebrae may suggest the failure of notochord formation in the early fetal period. From the embryological point of view, it seemed possible that the calves were exposed to teratogen at the critical time of optic organogenesis and notochordal formation. The cause of anomalies could not be determined in this study.

Animals↗

PubMed1999

Computerized digital image processing on radiographs of canine filariosis.

For objective evaluation in the lung arterial lesions, density histogram revealed by survey thoracic radiographies of fifteen canine filariosis and five normal canine were digitally analyzed, and preparation of pulmonary artery angiogram with inflated-fixed lung, the changes in the histogram and the pulmonary arterial lesion by a soft x-ray examination were compared. In the lung areas affected by filariosis, the density histogram increased the white level and decreased the black level in each part compared to a normal lung. In comparison with the normal parameters, those of the filariosis it were significantly increased in minimum grey level values (Min), maximum grey level values (Max), and the maximum frequency grey level values (Mode) and, it was significantly decreased in maximum frequency values (MaF). The pulmonary arterial lesion of the filariosis showed obvious morphological changes such as in distinction, pruning, angiectasis, and meandering. In the grade of pulmonary arterial lesion, the parameter Min, Max, Mode and MaF were changed significantly. From these results, it was clear that the methods for the lung arterial lesions analysis of x-ray images were confirmed to be highly beneficial in the lung arterial lesions for objective diagnosis.

Animals↗

PubMed2004

Polarization singularities in optical lattices.

Polarization singularities are shown to be unavoidable features of three-dimensional optical lattices. These singularities take the form of lines of circular polarization, C lines, and lines of linear polarization, L lines. The polarization figures surrounding a C line (L line) rotate about the line with winding number +/-1/2 (+/-1). C and L lines permeate the lattice, meander throughout the unit cell, and form closed loops. Surprisingly, every point in a linearly polarized optical lattice is found to be a singularity about which the surrounding polarization vectors rotate with an integer winding number.

Journal Article↗

PubMed2006

Amplified optical window for three-dimensional images.

A proposed amplified optical window can form an observable three-dimensional image of an object in darkness. The window comprises two gradient-index (GRIN) lens arrays with an image intensifier between them. The length of the individual GRIN lenses that constitute the arrays is three fourths of the cycle of the meandering optical path on the input side and one fourth of the cycle on the output side. A primitive experimental result proved that the method produces three-dimensional images to be observed. This device would be used as a viewer for observing three-dimensional objects in a dark space without a camera and display equipment.

Journal Article↗

PubMed1994

Two cases of scimitar variant.

The scimitar sign is characteristic of partial anomalous pulmonary venous drainage into the inferior vena cava (IVC). We encountered two variant cases of scimitar sign. In one case, the scimitar vein entered both the IVC and the left atrium (LA) without any intracardiac shunts. Surgical repair was made by simple ligation of the scimitar vein to correct the left to right shunt. Retrograde balloon occlusion angiography of the scimitar vein was diagnostic. In the other case, the scimitar vein showed a meandering course, and then drained into the LA without any connection with the IVC, and surgical intervention was not required.

Adult↗

PubMed1997

[Group process in nursing: possibilities and limits].

This work shows studies and reflections about the utilisation of groups in nursing assistance. As an aim sought to identify, through nurses perspective, aspects about their motivations to work with groups, their source of knowledge and relevant points of their experience with groups. The results demonstrates that nurses recognise the therapeutic value of groups in assistance and provide suitable conditions to its development. However, difficulties to handling groupal situations are limiting elements to develop this activity that reveal the human sentiment meander, indicating that nurse group co-ordinator needs, beyond theoretical establishment, to practice by their self-knowledge to provide an ambient and a interpersonal relationship able to obtain the real significance of this activity.

Attitude of Health Personnel↗

PubMed1996

Nuclear domains involved in RNA synthesis, RNA processing, and replication.

Two main principles of nuclear organization have been outlined on the basis of contributions by many research groups in recent years. The first principle is that interphase chromosomes occupy discrete territories in the nucleus, with no intermingling of the DNA from different chromosomes. Within a chromosome territory the DNA is organized in chromatin fibers at several levels of folding, that meander through the territory. Transcription and replication take place at the surface of these higher order chromatin fibers, probably on locally unfolded DNA templates. The second principle is that different types of nuclear domains are associated with several specific gene loci. This holds for clusters of interchromatin granules, coiled bodies, RNA 3'-cleavage factor-containing nuclear bodies (cleavage bodies) and probably PML-containing nuclear bodies. These domains may play an important role in the spatial arrangement of genes in the interphase nucleus. Despite these new insights, our knowledge of the function of many nuclear compartments and the molecular interactions responsible for the dynamic organization of a compartmentalized nucleus is still in its infancy.

Animals↗

PubMed1993

Scanning electron microscopic study of the collagen networks of the normal mucosa, hyperplastic polyps, tubular adenoma, and adenocarcinoma of the human large intestine.

The three-dimensional structure of the collagen network of normal mucosa, hyperplastic polyps, tubular adenoma, villous adenoma and adenocarcinoma of the human large intestine was examined by scanning electron microscopy after cell-maceration with a low temperature NaOH solution. In the normal large intestine, the surface of the sub-basal laminar collagen sheath lining the crypts was generally smooth. In hyperplastic polyps, the crypts extended and the sub-basal collagen network protruded from the surrounding normal tissue. The sub-basal laminar collagen sheath was more densely arranged near the openings of the crypts and on the luminal surface than in deeper regions of the crypts. In tubular adenoma, the tumor glands showed meandering, bending, and divisions. The sub-basal laminar collagen sheath was composed of densely packed collagen fibrils. In villous adenoma, the sub-basal laminar collagen sheath formed foliate or linguiform villous cores projecting sharply into the lumen. In adenocarcinoma, the sub-basal laminar collagen sheath exhibited a dense arrangement of fibrils in the central region of the tumor. Toward the marginal region, the collagen sheaths surrounding tumor glands became thinner, and at the edge of the marginal region, basket-like collagen sheaths were observed around individual tumor cells infiltrating the interstitium. Such a tumor lesion was frequently surrounded by a thick collagen fiber zone.

Adenocarcinoma↗

PubMed1987

A transmission electron microscopic study of rabbit liver sinusoids with special remarks on an experimentally induced canalicular system and the "pored domes" in the endothelial cells.

Rabbits were starved for a week and then allowed to take the standard diet; the animals were sacrificed after 20 or 24 hr. One group of the animals were treated in winter, and the other, in summer. Control animals were fed solid rabbit food ad libitum. In the control rabbits, short rudimentary canaliculi and occasional small-sized pored domes were found in the thicker portions of the endothelial extension. In the animals experimentally treated in winter, well-developed meandering canaliculi with vacuolar expansions and constrictions appeared in the thicker portions and perikaryonal cytoplasm. In addition prominent pored domes were produced. The canaliculi often formed sponge-like networks with openings both to the sinusoid and the Disse's space. The development of the canalicular system and pored domes correlated to an increased blood flow through the sinusoids; this seemed to be induced upon sudden feedings after lengthy starvation. The rabbits subjected to the experimental treatment in summer exhibited no distinct development of the canaliculi and pored domes. This result was ascribed to the inhibited functions of the rabbit liver during this season.

Animals↗

PubMed2000

Histometrical and three-dimensional analyses of liver hematopoiesis in the mouse embryo.

The development and cytoarchitectures of liver hematopoiesis in the mouse from 10 to 19 days of gestation were examined by light and electron microscopy. In fetal liver hematopoiesis, four stages were identified: Stage I, the onset of hematopoiesis at 10 days; Stage II, expansion of the volume of the hematopoietic compartment at 11 and 12 days; Stage III, the peak in the volume of the hematopoietic compartment at 13 and 14 days; and Stage IV, the involution of hematopoiesis after 15 days. During Stages I-II, hematopoietic stem cells appeared to move from the sinusoidal lumina into primitive hepatic cell cords through the sinusoidal endothelium to give rise to colonies among hepatoblasts. At Stage III, the hematopoietic colonies formed ellipsoidal foci as a structural unit of hematopoiesis. These foci were 35-70 x 20-40 microm in size, and erythroblastic islands could be observed in the center of each. Each island contained central macrophages surrounded by a ring of erythroblasts. The macrophages underwent mitosis, showing close contact with the erythroblasts, after which the hematopoietic foci appeared as cords. At Stage IV, these cord-shaped hematopoietic foci became disrupted, and round solitary foci including macrophages appeared within the hepatic cell cords on meandering sinusoids. In fetal liver hematopoiesis, macrophages could be one of the major cell components comprising the hematopoietic microenvironment, especially at Stages II and III.

Animals↗

PubMed2005

Fine-scale tracking of marine turtles using GPS-Argos PTTs.

High-accuracy location data of wildlife telemetry using conventional satellite location systems are difficult to obtain. However, such data are necessary to clarify the nature of movements and home range sizes of animals. In order to measure the high-accuracy location data, we developed new GPS-Argos Platform Terminal Transmitters (PTTs) which transmit both the conventional location and GPS location simultaneously. Two experiments, one in an artificial rearing pond and the other in the open sea, were performed. First, two hawksbill turtles were tracked with the PTTs in a 5 ha breeding pond in Thailand. Their home ranges using both data were calculated and found to be 2.96 ha and 0.93 ha by the GPS data, and 156,740 ha and 184,478 ha by a conventional data. Secondly, a female green turtle attached with the GPS-Argos was released from the coast of Pangnga Province, Thailand. There was a relationship between depth and speed of travel based on the GPS data. The data from the PTT showed that the turtle moved south along the coastline at the depth of less than 20 m for 5 days, and then stayed at a depth of less than 10 m for 4 days. However, we could not find any clear relationship using conventional data. Only a meandering movement at a variety of depths was observed. The results of the two experiments indicated the PTTs have an enormous potential for enhancing our understanding of fine-scale movement patterns and home ranges of marine turtles.

Animals↗

PubMed1990

Fusiform superior cerebellar artery aneurysm presenting with contralateral abducens nerve paresis--case report.

A 25-year-old female suddenly developed headache and diplopia. On admission, neurological examination revealed neck stiffness and left abducens nerve paresis. A computed tomographic scan suggested subarachnoid hemorrhage. Left vertebral angiogram showed an aneurysm on the anterior pontine segment of the right superior cerebellar artery (SCA) and marked flexion and meandering of the basilar artery to the left. At surgery, an atherosclerotic, fusiform aneurysm was found through the right subtemporal transtentorial approach, and the right SCA was clipped just proximal to the aneurysm. Thirteen cases of SCA aneurysm have been described in the literature, but none was a fusiform aneurysm.

Abducens Nerve↗