Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Transformer model”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,369 records · Page 76Linked to original sources
PubMed1997

Venular oscillatory flow during hemorrhagic shock and NO inhibition in hamster cheek pouch microcirculation.

Blood flow oscillations (flowmotion) during hemorrhagic shock (HS) were recorded with laser Doppler perfusion monitoring (LDPM) and red blood cell (RBC) velocimetry in arterioles and venules in hamster cheek pouch microcirculation. Experiments were carried out after baroceptor denervation or inhibition of nitric oxide (NO) synthesis with NG-monomethyl-L-arginine prior to and during HS. Flowmotion was characterized by spectral analysis with fast Fourier transform and autoregressive modeling. Low frequency flowmotion was detected in LDPM and RBC velocity tracings derived from arterioles while high frequency oscillations dominated in venules under baseline conditions. Venular blood flow was significantly higher compared with arteriolar flow during HS, while large amplitude low frequency flowmotion was found in venules but not in arterioles where dominated small amplitude high frequency oscillations coincident with respiratory or heart rates. Baroceptor denervation did not affect venular blood flow and low frequency flowmotion during HS. NO inhibition reduced significantly venular blood flow compared with control and abolished low frequency flowmotion in venules. High frequency oscillations remained in arterioles during HS. In conclusion, LDPM low frequency flowmotion was not originated by variations in the diameter of vessels, but corresponded to RBC velocity changes. A compensatory higher blood flow and concomitant low frequency flowmotion in venules appeared to be related to NO production during HS, independently of neural mechanism.

Animals↗
PubMed1999

High-dimensional image registration using symmetric priors.

This paper is about warping a brain image from one subject (the object image) so that it matches another (the template image). A high-dimensional model is used, whereby a finite element approach is employed to estimate translations at the location of each voxel in the template image. Bayesian statistics are used to obtain a maximum a posteriori (MAP) estimate of the deformation field. The validity of any registration method is largely based upon the constraints or, in this instance, priors incorporated into the model describing the transformations. In this approach we assume that the priors should have some form of symmetry, in that priors describing the probability distribution of the deformations should be identical to those for the inverses (i.e., warping brain A to brain B should not be different probabilistically from warping B to A). The fundamental assumption is that the probability of stretching a voxel by a factor of n is considered to be the same as the probability of shrinking n voxels by a factor of n(-1). In the Bayesian framework adopted here, the priors are assumed to have a Gibbs form, where the Gibbs potential is a penalty function that embodies this symmetry. The penalty function of choice is based upon the singular values of the Jacobian having a lognormal distribution. This enforces a continuous one-to-one mapping. A gradient descent algorithm is presented that incorporates the above priors in order to obtain a MAP estimate of the deformations. We demonstrate this approach for the two-dimensional case, but the principles can be extended to three dimensions. A number of examples are given to demonstrate how the method works.

Bayes Theorem↗
PubMed2002

Transient dynamics in metapopulation response to perturbation.

Transient time in population dynamics refers to the time it takes for a population to return to population-dynamic equilibrium (or close to it) following a perturbation in the environment or in population size. Depending on the direction of the perturbation, transient time may either denote the time until extinction (or until the population has decreased to a lower equilibrium level), or the recovery time needed to reach a higher equilibrium level. In the metapopulation context, the length of the transient time is set by the interplay between population dynamics and landscape structure. Assuming a spatially realistic metapopulation model, we show that transient time is a product of four factors: the strength of the perturbation, the ratio between the metapopulation capacity of the landscape and a threshold value determined by the properties of the species, and the characteristic turnover rate of the species, adjusted by a factor depending on the structure of the habitat patch network. Transient time is longest following a large perturbation, for a species which is close to the threshold for persistence, for a species with slow turnover, and in a habitat patch network consisting of only a few dynamically important patches. We demonstrate that the essential behaviour of the n-dimensional spatially realistic Levins model is captured by the one-dimensional Levins model with appropriate parameter transformations.

Animals↗
PubMed1990

Superposition of arteriolar vasomotion waves and regulation of blood flow in skeletal muscle microcirculation.

In skin muscle microcirculation of Syrian hamsters, rhythmic diameter changes were studied along the arteriolar network, under normoxic conditions, at rest. A teflon coated-aluminum chamber was implanted in the dorsum skin of animals. The microcirculation was investigated using intravital microscopy technique. Vessel diameters were determined by a computer-assisted method. Power spectrum analysis of vasomotion recordings was carried out with Fast Fourier Transform and Autoregressive modelling. To determine vasomotion waveform spreading, cross-spectral data (amplitude and phase) were computed, using the modified periodogram method (FFT). The arterioles were classified according to Strahler's method. Order 1 vessels (diameter: 7.50 +/- 1.16 microns) showed the highest frequency, 4-15 cycles per min, and percentage amplitude in the range 60-100%. Order 2 and 3 arterioles had intermediate frequencies, and amplitude in the range 50-100%, and 15-50%, respectively. The largest order 4 vessels (diameter: 28.97 +/- 9.55 microns) had the lowest frequency, 0.3-3 cpm, and amplitude in the range 5-20%. In most networks, cross-correlation analysis revealed two groups of frequency components. Low frequency group was propagated from order 4 and 3 vessels downstream. High frequency components were transmitted upstream from order 1 and 2 arterioles. Therefore, a complex superposition of waveforms resulted from the activity of discrete points along the microvasculature. In conclusion, rhythmic diameter changes of arterioles in skeletal muscle microcirculation regulate blood flow distribution in capillary units and control tissue oxygenation.

Animals↗
PubMed1990

Spontaneous phenotypic and karyotypic progression in the SV40 transfected cell line SVG during prolonged passage in vitro.

Transfection of primary cultures of human cells with origin of replication deficient SV40 DNA has been carried out by others to generate in vitro models of malignant transformation in vivo. The present work describes progressive alterations in karyotype and phenotype in one such transfected (neuroglial) cell line (SVG). After repeated passage, recognisable marker chromosomes evolved. These may be related to karyotypic anomalies found in human glial tumors. Accompanying the evolution in karyotype were changes in phenotype. Although presaging malignant transformation, these stopped short of actual tumorigenicity.

Animals↗
PubMed1996

Tissue-level biomarkers and biological effect of mercury on sentinel slugs, Arion ater.

The present investigation was to determine the extent to which mercury (Hg) provokes measurable effects on the structure of the digestive gland of slugs as well as to relate the extent of these effects to the cell and tissue distribution of Hg. For this purpose, slugs (Arion ater) received various dietary concentrations of Hg (from 0 to 1,000 microg Hg/g food) as chloride for 30 days and were histologically examined every third day. Autometallography was used to demonstrate Hg as black silver deposits (BSD) in paraffin sections. The lysosomes and residual bodies of digestive cells resulted to be the major accumulation sites. In addition, Hg was also evidenced in lipofuscine granules of vacuoles in excretory cells but, however, it was rarely observed within calcium cells. Generally, the extent of BSD increased with dietary Hg concentration and exposure time but, however, it became significant lowered after exposure to 1,000 microg Hg/g food for 30 when the digestive epithelium appeared almost devoid of digestive cells. On the other hand, significant changes were recorded in the quantitative structure of digestive tubules. Mean Epithelial Thickness (MET), Mean Luminal Radius (MLR) and Mean Diverticular Radius (MDR) were recorded as measures of the sublethal biological effect of Hg. MET, MLR/MET and MET/MDR were affected by Hg concentration (C), exposure time (T) and CxT interaction, changes in MET, MLR, MLR/MET and MET/MDR being explained by regression models after logarithmic transformation of the data. In order to explain the nature of the changes in the quantitative structure of the digestive tubules this investigation was complemented with qualitative histological observations. According to them, the excretory activity in digestive cells was initially enhanced. Afterwards, the relative numbers of digestive cells declined until the extreme cases of exposure to 1, 000 microg Hg/g for 27 to 30 days in which the digestive epithelium was mostly comprised of calcium and excretory cells. Concomitantly, some changes took place in blood vessels where Leydig cells became disrupted and the connective tissue layers thickened. Finally, it is suggested to use slugs in soil quality assessment as sentinel organisms ("Slug Watch") in which biomarkers of exposure to metallic pollutants and of biological effect are recorded.

Animals↗
PubMed1979

Ultrastructural morphometry of blastogenesis I: transformation of small lymphocytes stimulated in vivo with dinitrochlorobenzene.

Changes in the volumes and surfaces of subcellular compartments of unstimulated small lymphocytes and immunoblasts in mouse axillary lymph nodes have been established using stereological techniques. Blast transformation was induced in vivo with dinitrochlorobenzene (DNCB). Cell samples were obtained by random sampling regimes applied at light and electron microscopic levels. From electron micrographs the volume densities of euchromatin, heterochromatin, nucleoli, mitochondria, Golgi apparatus and rough endoplasmic reticulum were determined. Cell surface/volume ratios were also computed. By estimating mean nuclear volumes using light microscopy, it was possible to calculate absolute compartmental volumes and to evaluate the plasma membrane surface areas of average cells. Transformation in this model was characterized by a considerable cellular hypertrophy and a substantial increase in plasmalemma surface. Hypertrophy was the consequence of increases in the volumes of all measured intracellular compartments, notably euchromatin and "residual cytoplasm" (including ground cytoplasm and free ribosomes). These changes are discussed in the context of the altered metabolic status of cells.

Animals↗
PubMed1994

Narcissism in the novels of Herman Melville.

The nineteenth-century novels of Herman Melville, in their exploration of the theme of the conflict of man's godlike aspirations with his all-too-human limitations, anticipate the twentieth-century psychoanalytic understanding of narcissism, as developed by Sigmund Freud and Hans Kohut, specifically its psychodynamic model of the ego ideal in conflict with reality and the finiteness of human life. Captain Ahab in Moby-Dick is a vivid portrait of a narcissistic character, while Captain Vere in Billy Budd stands as a model of the "transformations of narcissism" in a mature individual. Melville's imaginative fiction is still capable of giving us valuable insights into the human condition.

Humans↗
PubMed1989

Selection of a spectral analysis method for the assessment of velocity distribution based on the spectral distribution of ultrasonic Doppler signals.

The direct Fourier transform method, autoregressive modelling, the maximum likelihood method and the Wigner-Ville distribution were applied to the Doppler signal obtained from a fully insonated laminar model flow. The appreciation of the spectral method was based on the properties of the ratio variance/(fmean)2 (INT) of the spectrum. The basic criterion was the sensitivity of INT to the analysis parameters, especially the data window. The results of spectral analysis, as well as the properties of INT, were strongly affected by the method applied. The maximum likelihood method appeared best suited for the purpose of assessment of velocity distribution and is expected to give the best results in the case of in vivo blood flow. The performances of other discussed methods were inferior, due to their stronger incompatibility with the signal properties.

Blood Flow Velocity↗
PubMed1999

[Rationing in medicine from the economic viewpoint].

The rationing of medical care is inevitable. The economic term "rationing" describes in a value-neutral manner that goods and services have to be withhold if financial means are limited. A changing demographic structure of society, rising expectations of patients as well as relatives and medical-technological progress are the main reasons for the rising rationing pressure and these developments can, if at all, be influenced only to a minor degree. Rationalization, i.e. to increase efficiency is a prerequisite before any rationing should be initiated and it often combines cost-savings with improved patient care. Rationalisation, however, cannot render rationing unnecessary. Rationing should take place in an explicit manner, with open discussions and comprehensible modes of discussion. One has to ask, a) which ideas about justice prevail in a society, b) which philosophical theory could provide a widely accepted and coherent basis for a rationing calculus and c) how a theoretical model can be transformed into applicable social politics and decision modes.

Cost Control↗
PubMed2004

[Primary gastric lymphoma].

Primary gastric lymphoma derives from a secondary MALT system developing after a reaction of the immune system, e.g. following chronic gastritis induced by Helicobacter pylori. Morphologically, follicular hyperplasia is found in the gastric mucosa. The pathoetiologic model confirms the transformation of a malignant lymphoma from low grade to high grade by demonstrating increasing autonomous proliferation and, finally, uncontrolled dissemination. Modern diagnostic tools are essential for staging and planning an adequate therapeutic strategy. At present, the therapeutic strategies regarding primary lymphoma are under discussion. Nevertheless, the consensus of international medical and surgical associations still recommends surgical therapy with curative intention for low-grade malignant lymphomas staged I 2-II 2. In cases of high-grade malignant lymphoma, conservative therapy is supposed to be similarly successful. The recent success of noninvasive therapeutic concepts seems to justify the application of triple eradication medication in case of Hp infection as well as radio- and chemotherapy in low- and high-grade malignant lymphomas. However, in cases of nonremission or therapy-associated complications such as uncontrollable bleeding or tumor perforation, surgery is the only therapeutic option. Regarding the oncological aspects of lymphoma growth, surgery should then be performed in order to achieve R0 resection.

Anti-Ulcer Agents↗
PubMed1999

Integration of visual and somatosensory target information in goal-directed eye and arm movements.

In this study, we compared separate and coordinated eye and hand movements towards visual or somatosensory target stimuli in a dark room, where no visual position information about the hand could be obtained. Experiment 1 showed that saccadic reaction times (RTs) were longer when directed to somatosensory targets than when directed to visual targets in both single- and dual-task conditions. However, for hand movements, this pattern was only found in the dual-task condition and not in the single-task condition. Experiment 1 also showed that correlations between saccadic and hand RTs were significantly higher when directed towards somatosensory targets than when directed towards visual targets. Importantly, experiment 2 indicated that this was not caused by differences in processing times at a perceptual level. Furthermore, hand-pointing accuracy was found to be higher when subjects had to move their eyes as well (dual task) compared to a single-task hand movement. However, this effect was more pronounced for movements to visual targets than to somatosensory targets. A schematic model of sensorimotor transformations for saccadic eye and goal-directed hand movements is proposed and possible shared mechanisms of the two motor systems are discussed.

Goals↗
PubMed2003

Reference values of ductus venosus blood flow velocities and waveform indices from 10 to 20 weeks of gestation.

OBJECTIVE: Our objective was to establish reference values for ductus venosus flow velocities during ventricular systole (S wave) and diastole (D wave), the lowest forward velocity during atrial contraction (A wave) and different calculated indices [(S-A)/D), (S-A)/Vmean, (S-A)/S, S/A, S/D)]. METHODS: Ductus venosus flow velocity waveforms were obtained from 329 singleton pregnancies at 10-20 weeks of gestation by pulsed-wave color Doppler. Reference values were constructed by means of a quadratic regression model after logarithmic transformation of original data. RESULTS: A significant increase in blood flow velocity during atrial contraction [A-wave, (3.5 cm/s to 9.9 cm/s and 12.9 cm/s to 66.3 cm/s respectively, 5-95% centile)], during ventricular systole [S-wave, (19.2 cm/s to 30.1 cm/s and 45.1 cm/s to 84.9 cm/s respectively, 5-95% centile)] and during early ventricular diastole [D-wave, (15.7 cm/s to 26.1 cm/s and 37.9 cm/s to 77.9 cm/s respectively, 5-95% centile)]. The venous indices values decreased with increasing gestational age. In 3 of 329 fetuses (0.91%) a reversed flow during atrial contraction was seen. CONCLUSION: Assessment of ductus venosus blood flow velocities during first and second trimester is feasible by means of color Doppler flow. The reference ranges and calculated velocities established in this study may be utilized in studies dealing with the role of ductus venosus blood flow in chromosomal abnormal fetuses, fetuses with congenital heart disease or fetal myocardial insufficiency of hypoxic origin.

Adolescent↗
PubMed2004

Reference values of fetal ductus venosus, inferior vena cava and hepatic vein blood flow velocities and waveform indices during the second and third trimester of pregnancy.

OBJECTIVE: Our objective was to establish reference values for ductus venosus, inferior vena cava and hepatic vein flow velocities during ventricular systole (S-wave) and diastole (D-wave), the lowest forward velocity during atrial contraction (a-wave), the intensity-weighted mean flow velocity (Vmean) and different calculated indices. METHODS: Venous flow velocity waveforms were obtained from 329 singleton pregnancies at 20-42 weeks of gestation by pulsed-wave color Doppler. Reference values were constructed by means of a quadratic regression model after logarithmic transformation of original data. RESULTS: With advancing gestational age the peak velocity index for the vein (PVIV) and pulsatility index for the vein (PIV) decreased whereas blood flow velocities increased. Blood flow velocities were highest in the ductus venosus and lowest in the right hepatic vein. Values for PVIV and PIV were highest in the hepatic vein and lowest in the ductus venosus. During atrial contraction there was a blood flow towards the fetal heart in the ductus venosus, whereas in the inferior vena cava and in the hepatic vein blood flow was either in the opposite from the fetal heart (reverse flow), or there was absent flow (zero flow) or flow was towards the fetal heart (positive flow). CONCLUSIONS: The reference ranges and calculated velocities established in this study may be utilized in studies dealing with the role of ductus venosus and inferior vena cava blood flow in fetuses with chromosomal abnormalities or congenital heart disease as well as hypoxic conditions. We speculate, that the reduction in PVIV and PIV with advancing gestational age may reflect a decrease in cardiac afterload as a result of maturation of diastolic ventricular function.

Blood Flow Velocity↗
PubMed1979

A data analysis microcomputer package (DAMP) for biomedical signals.

The advent of cheap, powerful microcomputer systems makes the analysis of data via sophisticated techniques available to the personnel who are non-specialists in computing systems. The DAMP package described here is intended for use on personal computers and has therefore been written in BASIC for portability. The analysis techniques are powerful, comprising algorithms to perform sample-data generation, plotting displays, digital data filtering, auto-correlation functions, fast Fourier transforms and autoregressive modelling. The last technique contains a number of options including the display of z-plane plots, frequency response of the model, residual plotting and auto-correlation of the residuals. Illustrative results are shown from psychological mood data and rat locomotor activity. The package is designed both to instruct a user in the techniques of spectral analysis, and also to provide a range of methods for investigating time and frequency behaviour of biomedical data.

Biomedical Engineering↗
PubMed1996

A marker-free method for tracking human lower limb segments based on model matching.

A 2D marker-free method for tracking the human lower limb segments has been developed and tested. The method is based on model matching using distance transformations, and is intended for use in analysis of human gait. The model used consists of five line segments, which are matched to the contours of the lower limb segments. Experiments have been made on two different kinds of objects: a rigid model of a leg and a human leg. Only movement in the sagittal plane has been considered. An image sequence of the moving object was captured, and the method was used for tracking the segments of the object in each image. The results were then compared to data obtained using markers mounted at the ankle joint, the knee joint and the hip joint. The experiments on the rigid body were done to assess the accuracy of the method under perfect conditions. The average difference between the estimated joint positions and the reference positions was found to be less than 2 mm for all three joints, with a standard deviation of less than 1 mm. To test the method in a more realistic situation, it was applied to a human leg during the stance phase of walking. Measurements were made on three healthy male subjects. The average differences between the estimated joint positions and the reference marker positions were less than 6 mm, 10 mm and 22 mm, for the ankle joint, the knee joint, and the hip joint, respectively. The corresponding standard deviations were less than 4 mm, 7 mm and 9 mm, respectively. The satisfying results, though obtained controlled laboratory conditions, show that this method might be useful in gait analysis.

Adult↗
PubMed1993

Extension of a generalized state-vector model of radiation carcinogenesis to consideration of dose rate.

Mathematical models for radiation carcinogenesis typically employ transition rates that either are a function of the dose to specific cells or are purely empirical constructs unrelated to biophysical theory. These functions either ignore or do not explicitly model interactions between the fates of cells in a community. This paper extends a model of mitosis, cell transformation, promotion, and progression to cases in which interacting cellular communities are irradiated at specific dose rates. The model predicts that lower dose rates are less effective at producing cancer when irradiation is by X- or gamma rays but are generally more effective in instances of irradiation by alpha particles up to a dose rate in excess of 0.01 Gy/day. The resulting predictions are compared with existing experimental data.

Animals↗
PubMed1976

Sequential alterations in the hepatic content and metabolism of cyclic AMP and cyclic GMP induced by DL-ethionine: evidence for malignant transformation of liver with a sustained increase in cyclic AMP.

There is evidence than adenosine 3',5'-monophosphate (cAMP) and guanosine 3',5'-monophosphate (cGMP) may have antagonistic actions on cell growth, with cAMP inhibiting and cGMP stimulating this process. However, reductions in cAMP and increases in cGMP are not charactersitic of all neoplastic tissues. Thus, benign and malignant tissues from hepatoma-bearing rats exposed to the hepatic carcinogen DL-ethionine have elevated rather than depressed cAMP, compared to control liver, and parenteral administration of this drug increases hepatic cAMP within hours. In the present study, the effects of ethionine ingestion on the hepatic content and metabolism of both cAMP and cGMP were examined sequentially in rats at 2 and then 6 wk intervals, from the initiation of drug administration until the development of hepatomas. After 2 wk, cAMP content of quick-frozen liver from rats receiving ethionine (E) was significantly increased (826 +/- 91 pmole/g wet weight) above that of liver from pair-fed controls (C, 415 +/- 44), whether calculated by tissue wet weight, protein, or DNA content. In benign tissue from E, higher cAMP was still evident after in vitro incubations of slices with 2 mM 1-methyl-3-iso-butylxanthine (MIX) and was associated with enhanced adenylate cyclase and unchanged high or low Km cAMP-phosphodiesterase activities. These findings are compatible with accelerated cAMP generation in liver from E. Protein kinase activity ratios were significantly increased in frozen liver from E (0.52 +/- 0.04 versus 0.36 +/- 0.03 in C), and the percent glycogen synthetase in the I form was clearly reduced (19% +/- 2% in E versus 47% +/- 5% in c). incubation of hepatic slices from E or C with MIX and/or 10 muM glucagon further increased cAMP and protein kinase activity ratios, data which imply higher effective, as well as total, cellular cAMP in E. Changes in cAMP metabolism and action observed at 2 wk persisted throughout the 38-wk period of drug ingestion. Adenylate cyclase activity, cAMP content, and protein kinase activity ratios of ethionine-induced hepatomas exceeded those of both the surrounding liver from tumor-bearing rats and that of control liver, but alterations in these parameters were qualitatively similar in both tissues from E. By contrast, while cGMP in quick-frozen surrounding liver from tumor-bearing rats (36 +/- 4 pmole/g wet weight) did not differ from that of control liver (30 +/- 3), cGMP in the hepatomas was increased. This change was evident in both frozen tumor (89 +/- 10) and in tumor slices incubated in vitro with MIX (C, 90 +/- 11; surrounding liver, 85 +/- 10; hepatoma 231 +/- 29). These results indicate that malignant conversion can occur in liver with a sustained elevation of both total and effective cAMP during the premalignant phase. The increase in cGMP detected in ethionine-induced hepatomas could also be a key determinant of malignant transformation in the model, although premalignant changes in cGMP were not apparent.

3',5'-Cyclic-AMP Phosphodiesterases↗