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At least 379 records · Page 21Linked to original sources

PubMed2005

New types of unstable step-flow growth on Si(111)-(7 x 7) during molecular beam epitaxy: scaling and universality.

New types of unstable homoepitaxial growth of vicinal surfaces are studied using ex situ atomic force microscopy. The growth features are two types of step bunching with straight step edges between 700 and 775 degrees C and one type of simultaneous bunching and meandering at 800 degrees C. The results of a quantitative size scaling analysis of the straight steps are discussed from the perspective of universality classes in bunching theory.

Journal Article↗

PubMed2006

Local electromigration model for crystal surfaces.

The dynamics of crystal surfaces in the presence of electromigration is analyzed. From a phase field model with a migration force which depends on the local geometry, a step model with additional contributions is derived in the kinetic boundary conditions. These contributions trigger various surface instabilities, such as step meandering, bunching, and pairing on vicinal surfaces. Experiments are discussed.

Journal Article↗

PubMed2006

Coherent control of harmonic generation in superlattices: single-mode response.

We study the harmonic generation spectrum in a semiconductor superlattice (a quantum-dot array) at slow relaxation. The effect of a single-mode response in an alternating rectangular (meander) electric field is demonstrated: For certain values of field parameters, the extremely wide discrete output spectrum with slowly decaying tails (multiharmonic generation) shrinks to one single harmonic (single-harmonic generation). Similarly, the effect is manifested in the transient continuous spectrum by diminishing the divergencies (peaks) at all odd harmonics but one. Substantial control over the spectrum is demonstrated.

Journal Article↗

PubMed2005

Rab11 GTPase-regulated membrane trafficking is crucial for tip-focused pollen tube growth in tobacco.

Pollen tube growth is a polarized growth process whereby the tip-growing tubes elongate within the female reproductive tissues to deliver sperm cells to the ovules for fertilization. Efficient and regulated membrane trafficking activity incorporates membrane and deposits cell wall molecules at the tube apex and is believed to underlie rapid and focused growth at the pollen tube tip. Rab GTPases, key regulators of membrane trafficking, are candidates for important roles in regulating pollen tube growth. We show that a green fluorescent protein-tagged Nicotiana tabacum pollen-expressed Rab11b is localized predominantly to an inverted cone-shaped region in the pollen tube tip that is almost exclusively occupied by transport vesicles. Altering Rab11 activity by expressing either a constitutive active or a dominant negative variant of Rab11b in pollen resulted in reduced tube growth rate, meandering pollen tubes, and reduced male fertility. These mutant GTPases also inhibited targeting of exocytic and recycled vesicles to the pollen tube inverted cone region and compromised the delivery of secretory and cell wall proteins to the extracellular matrix. Properly regulated Rab11 GTPase activity is therefore essential for tip-focused membrane trafficking and growth at the pollen tube apex and is pivotal to reproductive success.

Actins↗

PubMed2006

Germ cell atypia in undescended testes hinges on the aetiology of cryptorchidism but not the abdominal location per se.

Testicular carcinoma in situ (CIS), which precedes germ cell tumours, has been associated with coexistence or a history of testicular maldescent in 20-30% of human cases. The objective of this study was to determine if the abdominal location of the testis by itself affects differentiation of germ cells and why only some undescended testes manifest atypical germ cells. Groups (n = 4-6) of pregnant Dutch-Belted rabbits were treated on alternate days between gestation days 15 and 30 with anti-androgenic chemicals -- p,p' 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE; 100 mg/kg bw; oral), or flutamide (50 mg/kg; s.c.); oestrogenic chemical octylphenol (150 mg/kg; oral); or nothing. Groups (n = 4) of neonatal male pups from untreated litters were either implanted with oestradiol (0.5 mg; 60-day release), surgically rendered cryptorchid before testes transcended inguinal canal, or left untreated. Of the pups exposed in utero, four of the 12 DDE, two of the nine flutamide and one of the four octylphenol pups were unilaterally cryptorchid. All animals treated with oestradiol were bilaterally cryptorchid. Light and electron microscopic evaluation at 24-26 weeks revealed presence of atypical germ cells in the undescended testes of DDE-, octylphenol-, and oestradiol-exposed animals but not in flutamide-treated or surgical cryptorchids. These atypical cells exhibited morphological hallmarks of CIS, which included large nuclei with irregular contours, meandering nucleoli, swollen mitochondria, unusual cytoplasmic inclusions and occasional mitotic figures. As transformation of germ cells to CIS-like cells did not occur in flutamide or surgical groups, this phenomenon seems to be directly associated with the type of the chemical assault but not with the abdominal location of the testis per se.

Abdomen↗

PubMed2005

Large regenerative nodule perfused by the portal vein.

In a 42-year-old Japanese woman with esophageal varices, abdominal ultrasound (US) demonstrated a hyperechoic lesion 3 cm in diameter in segment 4 (S4). This nodular lesion had high intensity on T1-weighted magnetic resonance imaging (MRI), low intensity on T2, and very high intensity on superparamagnetic iron oxide (SPIO) enhanced MRI. Angiography showed sparse distribution of arterial branches and dense distribution of portal branches in S4. Meandering, thin arteries were seen in the peripheral area of the right lobe. The second branches of the portal vein were hardly visualized anywhere in the liver. Computed tomography arterioportography (CTAP) revealed portal blood flow dominance in this nodular lesion. There was no evidence of ischemic liver damage, such as thromboembolic episodes, laboratory data of liver damage, coagulation abnormalities etc. Therefore this abnormality was more likely to be caused by anomalous changes than thrombotic changes. Needle biopsy revealed no atypical cells. Two years later, the nodule size was reduced to 1.9 cm, showing its benign nature. Based on these findings, this lesion was classified as a new type of large regenerative nodule (LRN) associated with anomalies in the portal veins and arteries. This is the first report of an LRN of this size in which portal vein perfusion was dominant. Moreover, this lesion was difficult to differentiate from hepatocellular carcinoma (HCC) by imaging. Analysis of the images and pathological features of this case would contribute to a better understanding of the pathogenesis of nodular lesions of the liver.

Adult↗

PubMed1975

A case of Déjerine-Sottas disease with schizophrenic symptoms. A clinical and pathological study.

A case of hypertrophic interstitial neuritis with a disturbance of intelligence and schizophrenic symptoms was reported. The patient, a 41-year-old male, showed monologia at the age of 14 and auditory hallucination at the age of 21. He was diagnosed as schizophrenia. Torsion of the head to the right side and muscular atrophy were also noticed at 21 years. Atrophy of the muscles progressed gradually, particularly in the distal parts of the upper and lower extremeties. Psychiatric examination revealed schizophrenic symptoms such as auditory hallucination, thought disorder, lack of spontaneity, autism, apathy, etc. There was also a disturbance of intelligence (imbecility). In neurological examination, the torsion of the head to the right side, slight exaggeration of the peripheral reflexes, muscular atrophy in the distal parts of the extremeties were noted. The bilateral ulnar nerves were markedly hypertrophied. The biopsy of the right ulnar nerve revealed a remarkable thickening of the endoneuria and "onion bulb" formations. A large amount of the interstitial accumulation of PAS positive substance, which showed metachromasia in cresyl violet staining, was also noted. Schwann cell processes were proved electron-microscopically to surround the myelin sheaths and some of them meandered and extended and into the metachromatic substance. The basement membrane of the sheath cell was hypertrophic in some portions and elongated into interstitium. The nucleus of the sheath cell was hyperchromic and showed marked atrophy. Histological examination of the biopsy specimen obtained from the gastrocnemius muscle suggested neurogenic muscular atrophy. The relationship among the hypertrophic interstitial neuritis, schizophrenic symptoms, disturbance of intelligence and torsion of the head was also discussed.

Adult↗

PubMed1979

The effect of hyperthyroidism induced by thyroideum siccatum on the central nervous system: an electron microscopic study.

Ten adult male rats were administered orally with thyroideum siccatum every day to produce a hyperfunctional state of thyroid hormone. They were examined electron microscopically for the fine structure of the brain. Clinically, experimental rats lost in weight, manifested a hyperactive, irritative attitude, and were in an aggressive state. Electron microscopically, the nerve cells showed a slight increase in the number of mitochondria in the frontal cortex, spiral and petaloid variation of ER in the thalamus. The specific findings in the experimental rats were variations of synapse observed in the frontal and temporal cortex, gyrus hippocampi, and thalamus, centering around the hypothalamus. They included meandering of the presynaptic membrane, formation of vacuoles by the presynaptic membrane, saccate projection of this membrane to the postsynapse, and changes in vacuoles which were torn off and fell into the dendrite. These variations occurred in the synaptic membrane and ER, probably because synthesis of the membrane had been accelerated remarkably by the action of thyroid hormones. They were considered to have brought about abnormalities to the conductive and transmission system. They seemed to be closely related with emotional disturbances and psychic symptoms, since such variations were particularly apparent in the hypothalamus.

Aggression↗

PubMed1986

Adrenocortical adenoma with Cushing's syndrome. Scanning electron microscopic observations.

Adrenocortical adenomas with Cushing's syndrome (Cushing's adenoma) consisted of two different features, which intermingled in various proportions and were related with each other. The first feature showed long-columnar or trabecular arrangement and a vacuolar appearance which correspond to lipid droplets of clear-type cells. In the second feature, the sinusoid was well developed and meandering, and the perisinusoidal space was prominent and contained collagen fibrils, bleb-like structures, and granules. The collagen fibrils were entangled with the parenchymal cells. The sinusoid was lined by a sinusoidal wall with fenestrations or pores. Bleb-like structures and granules traversed them. Two different features were speculated to be consistent with areas of clear-type cells and compact-type cells, respectively, observed light and transmission electron microscopies.

Adenoma↗

PubMed1986

Structural change of adrenocortical adenoma in Cushing's syndrome.

Eight adrenocortical adenomata from patients with Cushing's syndrome were examined by light and electron microscopy. Light microscopically, the reticulin fibers were markedly prominent in areas of the compact-type cells and ran tangentially to the adenoma cells or parenchymal cells. Electron microscopically, adrenocortical adenoma was composed of parenchymal cells, interstitial cells, and endothelial cells. In areas of the clear-type cells, the parenchymal cells were arranged in long columns and covered by the sinusoidal wall. In areas of the compact-type cells, the sinusoid was well-developed and meandering. The dilated intercellular space was conspicuous and filled with filamentous substance and collagen fibrils. The parenchymal cells appeared to produce the filamentous substance and collagen fibrils, and underwent fragmentation. Interstitial cells and fragmented cytoplasm of the parenchymal cells were found in the intercellular and perisinusoidal space. It was likely that the fragmented cytoplasm flowed into the sinusoid. Experimental study using cell culture methods revealed these phenomena, especially a production of collagen fibrils.

Adenoma↗

PubMed1990

Vascular abnormalities in congenital cutis laxa--report of two cases.

Two cases of Japanese girls with congenital cutis laxa associated with cardiovascular abnormalities are described. Case 1: A 12-year-old girl has been under our observation from the age of 6 months. Cardioangiogram revealed dilatation of the ascending aorta, meandering of the descending aorta and the coronary arteries, coiling of the carotid and innominate (brachiocephalic) arteries, and hypoplasia of the pulmonary arteries. Case 2: A 2.8/12-year-old girl died after our follow-up from the age of 3 months. The cause of death was congestive heart failure secondary to peripheral stenosis of the pulmonary arteries. In both cases, skin biopsy revealed a decreased number of elastic fibers and an increased amount of acidic mucopolysaccharides. The same histological features were observed in the pulmonary arteries and other arteries as well. Electron microscopic findings were diffuse thinning of elastic fibers and reduced elastic content. The high blood level of elastase (167.8 micrograms/l) in case 1 may cast a light on the unknown etiology of the disease.

Abnormalities, Multiple↗

PubMed2006

Preventive effects of glycaemic control on ocular complications of Spontaneously Diabetic Torii rat.

AIM: Spontaneously Diabetic Torii (SDT) rat is a new model of non-obese type 2 diabetes. SDT rats show severe ocular complications such as cataracts, tractional retinal detachment with fibrous proliferation and massive haemorrhaging in the anterior chamber. In the present study, blood glucose levels of SDT rats were controlled in order to examine whether these ocular complications are caused by hyperglycaemia. METHODS: SDT rats were treated with an insulin implant to control blood glucose. To evaluate retinal function, we used electroretinograms (ERG) and measured vascular endothelial growth factor (VEGF) concentrations within the aqueous humour. Finally, we studied retinal flat-mounts and trypsin digestion to evaluate vascular abnormalities in SDT rats. RESULTS: Forty-four-week-old SDT rats displayed an increase in VEGF concentrations within the aqueous humour and significant prolongation of the peak latencies in ERG (Sigma(OP(1)-OP(4)); Sprague-Dawley (SD): 146.2 +/- 1.06 ms; SDT: 166.3 +/- 2.38 ms; SDT + insulin: 149.2 +/- 1.83 ms). Retinal flat-mounts of SDT rats showed venous dilation and meandering vascular networks. Furthermore, acellular capillaries were observed in the retinal trypsin digestion. Insulin treatment prevented these ocular abnormalities in SDT rats. CONCLUSIONS: These findings indicate that ocular complications of SDT rats are caused by hyperglycaemia. The features of SDT rats indicate their usefulness for the future study of diabetic retinopathy.

Animals↗

PubMed2005

Defining dangerous anthropogenic interference: the role of science, the limits of science.

Defining "dangerous anthropogenic interference with the climate system" in the context of Article 2 of the UN Framework Convention on Climate Change (UNFCCC) presents a complex challenge for those developing long-term climate policy. Natural science has a key role to play in quantifying vulnerabilities of elements of the Earth system and estimating the risks from a changing climate. But attempts to interpret Article 2 will inevitably draw on understanding from social science, psychology, law, and ethics. Here I consider the limits of science in defining climate "danger" by focusing on the potential disintegration of the major ice sheets as an example of an extreme impact. I show that considerations of timescale, uncertainty, and learning preclude a definition of danger drawn purely from natural science. Decision makers will be particularly challenged by one characteristic of global problems: answers to some scientific questions become less accurate over decadal timescales, meandering toward the wrong answer, a feature I call negative learning. I argue for a precautionary approach to Article 2 that would be based initially on current, limited scientific understanding of the future of the ice sheets.

Journal Article↗

PubMed1998

Transmembrane potential properties of atrial cells at different sites of a spiral wave reentry: cellular evidence for an excitable but nonexcited core.

Transmembrane action potentials (TAPs) were recorded during simultaneous mapping of a reentrant wavefront induced in canine isolated atria. The activation pattern was visualized dynamically using a high resolution electrode catheter mapping system. During functional reentry (spiral wave), cells in the core of the spiral wave remained quiescent near their resting membrane potential. Cells away from the core progressively gained TAP amplitude and duration, and at the periphery of the spiral wave the cells generated TAPs with full height and duration. During anatomical reentry, when the tip of the wavefront remained attached to the obstacle (a condition of high source-to-sink ratio), the TAP near the obstacle had normal amplitude and duration. However, when the tip of the wavefront detached from the obstacle (condition of lowered source-to-sink ratio) the TAP lost amplitude and duration. These results are consistent with the theory that the source-to-sink ratio determines the safety factor for wave propagation and wave block near the core. With decreasing source-to-sink ratio, TAP progressively decreases in amplitude and duration. In the center of the core, the cells, while excitable, remain quiescent near their resting potential. This decrease reflects a progressive decrease in the source-to-sink ratio. TAP vanishes in the core where cells remain quiescent near their resting potential. Functional and meandering reentrant wavefronts are compatible with the spiral mechanism of reentry where block at the rotating point is provided by the steep curvature of the wave tip.

Animals↗

PubMed1991

The development and structure of principal fibers and cellular cementum in rat molars.

The principal fibers and cellular cementum were examined in various developmental stages in rat molars by light and electron microscopy, and their development and structure were studied. The principal fibers increased in thickness with root development. At any given stage, the principal fibers consisted of small fiber bundles on the cementum surface and showed a branching structure. Sharpey's fibers also showed a similar branching structure and increased in thickness, as traced superficially in the cementum. It was suggested that the principal fibers increased in thickness by means of the aggregation of fiber bundles. The development of cellular cementum was divided into two (early and late) phases on the basis of the fiber arrangement. The early cementum was believed to contain a few Sharpey's fibers and many randomly arranged intrinsic fibers. The late cementum contained thicker Sharpey's fibers with branches and the intrinsic fibers which appeared to encircle Sharpey's fibers and/or meander among them.

Animals↗

PubMedDate not supplied

Delineating alluvial aquifer heterogeneity using resistivity and GPR data.

Conceptual geological models based on geophysical data can elucidate aquifer architecture and heterogeneity at meter and smaller scales, which can lead to better predictions of preferential flow pathways. The macrodispersion experiment (MADE) site, with >2000 measurements of hydraulic conductivity obtained and three tracer tests conducted, serves as an ideal natural laboratory for examining relationships between subsurface flow characteristics and geophysical attributes in fluvial aquifers. The spatial variation of hydraulic conductivity measurements indicates a large degree of site heterogeneity. To evaluate the usefulness of geophysical methods for better delineating fluvial aquifer heterogeneities and distribution of preferential flow paths, a surface grid of two-dimensional ground penetrating radar (GPR) and direct current (DC) resistivity data were collected. A geological model was developed from these data that delineate four stratigraphic units with distinct electrical and radar properties including (from top to bottom) (1) a meandering fluvial system (MFS); (2) a braided fluvial system (BFS); (3) fine-grained sands; and (4) a clay-rich interval. A paleochannel, inferred by other authors to affect flow, was mapped in the MFS with both DC resistivity and GPR data. The channel is 2 to 4 m deep and, based on resistivity values, is predominantly filled with clay and silt. Comparing previously collected hydraulic conductivity measurements and tracer-plume migration patterns to the geological model indicates that flow primarily occurs in the BFS and that the channel mapped in the MFS has no influence on plume migration patterns.

Geological Phenomena↗

PubMedDate not supplied

Comparison of local grid refinement methods for MODFLOW.

Many ground water modeling efforts use a finite-difference method to solve the ground water flow equation, and many of these models require a relatively fine-grid discretization to accurately represent the selected process in limited areas of interest. Use of a fine grid over the entire domain can be computationally prohibitive; using a variably spaced grid can lead to cells with a large aspect ratio and refinement in areas where detail is not needed. One solution is to use local-grid refinement (LGR) whereby the grid is only refined in the area of interest. This work reviews some LGR methods and identifies advantages and drawbacks in test cases using MODFLOW-2000. The first test case is two dimensional and heterogeneous; the second is three dimensional and includes interaction with a meandering river. Results include simulations using a uniform fine grid, a variably spaced grid, a traditional method of LGR without feedback, and a new shared node method with feedback. Discrepancies from the solution obtained with the uniform fine grid are investigated. For the models tested, the traditional one-way coupled approaches produced discrepancies in head up to 6.8% and discrepancies in cell-to-cell fluxes up to 7.1%, while the new method has head and cell-to-cell flux discrepancies of 0.089% and 0.14%, respectively. Additional results highlight the accuracy, flexibility, and CPU time trade-off of these methods and demonstrate how the new method can be successfully implemented to model surface water-ground water interactions.

Computer Simulation↗

PubMed2003

Evidence for persistent flow and aqueous sedimentation on early Mars.

Landforms representative of sedimentary processes and environments that occurred early in martian history have been recognized in Mars Global Surveyor Mars Orbiter Camera and Mars Odyssey Thermal Emission Imaging System images. Evidence of distributary, channelized flow (in particular, flow that lasted long enough to foster meandering) and the resulting deposition of a fan-shaped apron of debris indicate persistent flow conditions and formation of at least some large intracrater layered sedimentary sequences within fluvial, and potentially lacustrine, environments.

Exobiology↗