Radial Behavior Research Articles

Intravascular Ultrasound in the Determination of the Mechanical Properties of Diabetic Arteries

Abstract Cardiovascular disease is the leading cause of morbidity and mortality in diabetic individuals. Diabetes mellitus is associated with a two- to four-fold increase in risk of coronary heart disease. This risk is independent of other classical risk factors including age, smoking, elevated serum cholesterol levels, and hypertension, and the overall risk of cardiovascular disease increases proportionally with the number of risk factors. Many groups are currently investigating the aetiology of diabetic vascular disease, with particular interesting being paid to the processes involved in the formation of highly cross-linked carbohydrate-protein complexes known as melanoids. These complexes appear to be formed by glycation arising from reactions between glucose and the amino groups on proteins, and their formation within the vessel wall resqlts in a decrease in vascular elasticity. This decrease in elasticity has been implicated in the increased incidence of atherosclerosis in diabetic individuals. Previous testing modalities could not test in the radial direction and required assumptions based on incompressibility in order to determine the radial behavior of the artery.

Investigation of electron-distribution function and dynamo mechanisms in a reversed-field pinch by analysis of hydrogen-pellet deflection

In reversed-field pinches, two different mechanisms have been proposed to explain the dynamo process which drives the poloidal current needed to sustain the magnetic configuration: the kinetic dynamo theory and the magnetohydrodynamic (MHD) dynamo theory. Experimentally, they can be distinguished by the radial behavior of the electron distribution function. In this Letter the trajectory deflection of frozen hydrogen pellets has been used as a diagnostic of suprathermal electrons in the plasma. The classical Spitzer-Harm distortion of the electron distribution function consistent with the MHD dynamo electric field is found to give a better modeling of the pellet trajectory.

The Extended Narrow‐Line Region of the Seyfert 1 Galaxy ESO 362‐G18 versus That of the Seyfert 2 Galaxy ESO 362‐G8

We use long-slit spectroscopic data to study in detail the extended narrow-line regions (ENLRs) of the Seyfert 1 galaxy ESO 362-G18 and Seyfert 2 galaxy ESO 362-G8. These two galaxies have similar emission-line luminosities and extents of the ENLR (D4 kpc), whose shapes in previous narrowband (O III) images suggest anisotropic escape of the nuclear ionizing radiation as expected for shadowing by a nuclear torus in the framework of the uni—ed model. In the Seyfert 1 galaxy the high-excitation gas shows an approximately cone-shaped morphology. From the observed kinematics, we conclude that the gas within the cone most probably belongs to the galaxy disk, which implies that the collimation axis is closer to the disk than half the opening angle of the cone of ionizing radiation. In the Seyfert 2 galaxy, the main structure in the high-excitation gas is an emission blob which apparently consists of a high- latitude cloud being blown away from the nuclear region and ionized by the nuclear source. We use the radial distribution of stellar population features in order to extrapolate this population to the nucleus and isolate the optical continuum of the nuclear source. We obtain a featureless power-law continuum for the Seyfert 1 galaxy, while for the Seyfert 2 galaxy we conclude that the F l P l~0.76 nuclear bluer color and smaller equivalent widths of the absorption lines are due to an aging burst of star formation (age B 300 Myr) and that the nuclear source is hidden from direct view. Using the photoionization code MAPPINGS Ic and a mixture of matter-bounded (MB) and ionization-bounded (IB) clouds, we model the ENLRs of the two galaxies. We use all the observables, mostly the emission-line —uxes as a function of distance from the nucleus and the optical nuclear contin- uum observed in the Seyfert 1 galaxy as well as its X-ray —ux, to constrain the parameters of a self- consistent model for the ENLR. For both galaxies, we conclude that a power-law ionizing continuum better reproduces the high-excitation lines near the nucleus than a multisegmented power law F l P l~1.2 used in previous works. For the Seyfert 1 galaxy ESO 362-G18, the inferred luminosity of the ionizing continuum can be reconciled with the —ux observed in the optical, while in the X-rays the observed —ux is D100 times weaker than that necessary to reproduce the line —uxes, suggesting that the X-ray contin- uum is absorbed toward Earth. For the Seyfert 2 galaxy ESO 362-G8, the inferred ionizing continuum when extrapolated to the optical implies a minimum obscuration toward the nuclear source of A V B 4.0 mag. In the hypothesis of an isotropic nuclear source, in order to better constrain the model parameters, we have adopted symmetrical physical conditions as a function of distance on both sides of the nucleus: namely, the ionizing —ux, the temperature, density, and ionization parameter of the MB gas, and the metallicity. The radial density behavior of the IB gas was observationally inferred from the (S II) doublet ratio. The only free parameter, which was allowed to vary independently, was the relative proportion of the MB and IB emission-line components along the ENLR. The high-excitation gas within the cone of ESO 362-G18 and within the blob of ESO 362-G8 have been modeled as regions of larger mass contri- bution from the MB component relative to other locations of the ENLR. We derive the —lling factors, covering factors, and gas masses along the ENLR as a function of dis- tance from the nucleus. A comparison between the model results for the two galaxies shows that, around the nucleus, the Seyfert 1 galaxy has a larger excitation due to a larger contribution of the MB com- ponent. However, in the cone, the excitation is lower than in the blob of the Seyfert 2 galaxy due to a combination of a lower ionizing —ux and larger gas density in the disk of the Seyfert 1 galaxy. The total ionized gas mass derived for the blob in the Seyfert 2 galaxy is 105.8 consistent with its proposed M _ , origin in a nuclear superwind which probably occurred D300 Myr ago, while the ionized gas mass in the disk of the Seyfert 1 galaxy is 1 order of magnitude smaller. Subject headings: galaxies: activegalaxies: ISMgalaxies: nucleigalaxies: Seyfert

Role of hippocampal NMDA and nonNMDA receptors in radial maze behavior in rats

Role of hippocampal NMDA and nonNMDA receptors in radial maze behavior in rats

How is radial arm maze behavior in rats related to locomotor search tactics?

Norway rats have been shown to depend on short-term spatial memory to find food on a radial arm maze (RAM), but what locomotor search tactics are involved in using this memory effectively? Four experiments distinguished tactics of distance minimizing, central-place search, trail following, thigmotactic search, and random search by using different configurations of a RAM placed flat on the floor of an arena. These search tactics make similar predictions on an elevated RAM but predict different outcomes on a floor RAM because the rats are free to approach the food from any direction. After initial trials dominated by exploration, rats traveled along arms to food, even when the resultant distance was up to three times the minimum distance. With no food present, rats also traveled along arms; with no arms up to present, they traveled along walls to food. It appears that both maze arms and arena walls engage mechanisms related to trail following in rats.

Many-body exchange effects in clusters of rare gases with a chromophore: He2CO2

The many-body exchange effects up to the 5-body have been analyzed in terms of possible mechanisms by which the intermolecular electron exchange is carried out. The terms corresponding to single (SE), triple (TE), double (DE), and quadruple (QE) exchanges are identified, and their diagrammatic interpretation given. It is demonstrated that they require different physical interpretations, as well as display different angular and radial behaviors. The 3-body SE and TE terms were calculated ab initio, and analyzed for a variety of geometries of the He2CO2 cluster. The anisotropy of SE over the wide range of configurations is consistent with the electrostatic model of the exchange quadrupole of He2, interacting with the permanent quadrupole of CO2. The behavior of TE may be rationalized by considering the Pauli-principle-induced distortion of the monomers involved. The influence of the CO2 asymmetric stretch on the SE, TE, and on the total exchange non-additivity has also been evaluated and discussed. The TE 4-body term in He3CO2 has been calculated and compared with the SE 3-body terms.

Micromechanical modeling of load transfer in fibrous composites

A unified analytical treatment is presented for the study of micromechanical stress distribution in unidirectional fibrous composites loaded with various thermal and mechanical loads. Two models are considered to represent the composite. Both use a concentric cylindrical system with the difference that one requires laterally free while the other requires laterally constrained outer boundaries, broadly describing situations of plane stress and plane strain, respectively. The present work has been motivated by the recent work of McCartney (McCartney, Proc. Roy. Soc. London, Ser. A 425 (1989) 215–244) who analyzed the laterally free system, and by our previous work (Nayfeh, Fibre Sci. Technol. 10 (1977)) in which we analyzed the laterally constrained one. For axisymmetric loading, and upon adopting some appropriate restrictions on the radial behavior of some field quantities, an elasticity-based procedure reduces the two-dimensional field equations, which hold in both the fiber and matrix components, together with the appropriate interface and boundary conditions, to a quasi-one-dimensional system. The resulting system is capable of identifying the stress distribution in each component as influenced by the other component via the readily identifiable interaction (transfer) terms. The model is general and applicable to a large variety of situations. These include situations of matrix cracking, fiber break and even regions of slip at the fiber–matrix interface. As a by-product, the model was capable of obtaining the classical Lamé solutions (the iso-strain case) as a degenerate case. Confidence in the modeling was gained when it identically reproduced all of the numerical examples presented by McCartney. Numerical results that parallel some of the ones presented by McCartney are included in the form of comparisons between results obtained based upon the laterally constrained and the laterally free systems.

A dynamic route finder for the cognitive map.

Cognitive behaviorist E. C. Tolman (1932) proposed many years ago that rats and men navigate with the aid of cognitive maps, but his theory was incomplete. Critic E. R. Guthrie (1935) pointed out that Tolman's maps lack a rule for action, a route finder. We show that a dynamic model for stimulus generalization based on an elementary diffusion process can reproduce the qualitative properties of spatial orientation in animals: area-restricted search in the open field, finding shortcuts, barrier learning (the Umweg problem), spatial insight in mazes, and radial maze behavior. The model provides a behavioristic reader for Tolman's cognitive map. The cognitive behaviorist Edward Tolman spent much of his career devising clever experiments to show that stimulus-response accounts of rat behavior cannot be correct. Some of his most striking demonstrations involve spatial learning. One such example is shown in Figure 1, which depicts a maze apparatus used in a famous experiment by Tolman and Honzik (1930). The maze has three paths from the Start box to the Goal box. The paths differ in length: 1 (heavy vertical line) shorter than 2 (intermediate line) shorter than (light line). In preliminary training, the rats were allowed to become familiar with all three paths to the Goal box. They also had experience with a block at Point A, which permits access to the Goal only via Paths 2 and 3. In the test condition, the block was moved to Point B--so that only is open. The question is, Will the rats choose as soon as they encounter the block at B, or will they choose 2, which is normally preferred to 3--indicating that they do not know Paths 1 and 2 share a common, blocked, segment? Tolman and Honzik's rats behaved intelligently and usually went straight to after encountering the block at B. Tolman took this as evidence that the rats knew something about the topography of the maze. They were not just operating on a fixed hierarchy of preferences ( Path 1 better than 2 better than 3 ), nor were they responding reflexively to local cues. Tolman considered this behavior to be an example of insight, although he did not specify exactly what that means. He did say that some kind of cognitive map

Radial behavior of gradient expansion approximation to atomic Fukui function and shell structure of atoms

Radial behavior of gradient expansion approximation to atomic Fukui function and shell structure of atoms

Radial behavior of gradient expansion approximation to atomic Fukui function and shell structure of atoms

Radial behavior of gradient expansion approximation to atomic Fukui function and shell structure of atoms

Memory of radial maze behavior in pigeons after ablations of the presumed equivalent of mammalian prefrontal cortex.

Pigeons were trained and postoperatively tested in an 8-arm radial maze in which 1 arm was always used for start, 3 were never baited, and 4 were always baited. Of 2 groups of pigeons, 1 (n = 6) received ablations of the postero-dorso-lateral neostriatum (PDLNS) as well as the corticoid, and the other (n = 8) was sham operated. After the surgery, in the PDLNS group the number of reference memory errors (entering the never-baited arms) was significantly increased, but the number of working memory errors (entering previously visited baited arms) was not. Two of 6 pigeons with PDLNS ablations did not show any impairment, 3 were impaired in the reference memory, and 1 was impaired in working memory. This outcome resembles behavioral effects obtained in rats with prefrontal lesions. In pigeons and rats, the lesion seems to "release" the normal "win-shift" tendency and/or impair the ability to choose correctly in simultaneous multiple-choice situations.

Composition- and history-dependent radial compressive behavior of human atherosclerotic plaque.

Invasive procedures to revascularize occluded blood vessels rely on the mechanical response of the diseased tissue. Failure rates associated with such procedures show the need for improvement. to understand the associated mechanics, the material properties of atherosclerotic plaque should be known; yet data are scant. The purpose of this study was to investigate the different mechanical responses exhibited by plaques with different compositions, focusing specifically on radial compressive behavior. A custom-built experimental system was developed that was fully computer controlled with a broad range of loading capabilities. A temperature-controlled, physiologic specimen bath allowed testing at 37 degrees C. Monotonically loaded specimens showed that plaque behavior was nonlinear under finite deformations. A multiple cycle protocol, executed in two phases, distinguished three types of mechanical response of different plaques. The differences in behavior were associated with histologic differences in plaque composition, and mechanically characterized by different "repeatability" (the stabilization of the cyclic response) and "recoverability" (the second loading phase retracing the first loading phase behavior). Type 1 behavior was categorized by repeatability and recoverability. Type 2 behavior displayed repeatability but only partial recovery during the second loading phase. Recovery was absent in type 3 behavior. The histologic observations demonstrated that calcified tissue was present only in specimens displaying type 1 behavior. Fibrous tissue and part of a modified media (due to disease) were present in specimens displaying type 2 behavior. An atheroma, along with a relatively thin modified media, was present in specimens displaying type 3 behavior. The differences in the maximum stretches attained at the end of phase I loading, the stretch offset from the first to the 15th cycle of phase I loading, and the hysteresis in the first and 15th cycles of phase I loading distinguished the specimen behaviors with statistical significance. These compression data showed that plaques exhibit composition- and history-dependent nonlinear and inelastic responses under finite deformations.

LETTER TO THE EDITOR: General-Relativistic Model of Magnetically Driven Jet

The general scheme for the construction of the general-relativistic model of the magnetically driven jet is suggested. The method is based on the usage of the 3+1 MHD formalism. It is shown that the critical points of the flow and the explicit radial behavior of the physical variables may be derived through the jet ``profile function."

Memory of radial maze behavior in pigeons after ablations of the presumed equivalent of mammalian prefrontal cortex.

Memory of radial maze behavior in pigeons after ablations of the presumed equivalent of mammalian prefrontal cortex.

Detection and Behavior of Pan Wakes in Saturn's A Ring

Six previously unseen Pan wakes are found interior and exterior to the Encke gap in Saturn's A ring, one in the Voyager 2 photopolarimeter (PPS) stellar occultation data and five in the Voyager 1 radio science (RSS) earth occultation data. Pan orbits at the center of the Encke gap and maintains it. Originally it was hypothesized that a wake would be completely damped by the time it reached a longitude of 360° relative to Pan. However, five of the six newly detected wakes are at longitudes in excess of 360° and are a result of earlier encounters with Pan. The sixth is the first detection of the RSS outer Pan wake. The new PPS inner wake is at a longitude of 389.8°. The new RSS inner wakes are at longitudes of 519.4° ± 1.6° and 879.4° ± 1.6°. The RSS outer wakes are at longitudes of 200.6° ± 1.6°, 560.6° ± 1.6°, and 920.6° ± 1.6°. Because of the time needed for a wake to develop after encountering Pan, the higher order wakes (longitude >360°) can be more prominent than their lower order counterparts which are superimposed at the same location.The radial dispersion behavior of the Pan wakes are characterized using a Burg autoregressive power spectral algorithm. The wake radial wavelength behavior is compared to a simple model which ignores collisions and self-gravity. The four wakes with longitudes below 360° show an average deviation of 0–3% from the predicted wavelengths, indicative of the strength of collective effects.The detection of Pan wakes at longitudes greater than 360° demonstrates that wakes persist for much longer than originally hypothesized and may interact with one another. The presence and characteristics of these wakes will provide an important test of kinetic theory models.

Parabolic-hyperspherical approach to the fragmentation of three-particle Coulomb systems.

In this work the three-body Coulomb continuum problem is reformulated in a set of parabolic-hyperspherical coordinates. It is shown how this procedure yields additional information on the angular and radial behavior of correlated three-body Coulomb continuum wave functions. For two electrons receding from a nucleus it is shown that three-body coupling is essential in describing the dependence of the fragmentation dynamics on the ratio of the electronic distances from the nucleus whereas the angular distribution of these electrons is less sensitive to this coupling. The spin asymmetry in the total cross section for electron-impact ionization of atomic hydrogen is analyzed and found to be sensitive to the radial correlation of the outgoing electrons. \textcopyright{} 1996 The American Physical Society.

Influence of oxygen and nitrogen on point defect aggregation in silicon single crystals

Oxygen- and nitrogen-doped floating zone (FZ) crystals were investigated with regard to radial oxygen precipitation, D-defect formation and gate oxide integrity (GOI) behavior as a function of the nitrogen content. It is shown that the inactivation of the nitrogen-enhanced D-defect suppression and GOI improvement is not a result of the reduction of the N-pair concentration due to nitrogen-oxygen interaction. Instead, it is suggested that the diffusivity of vacancies, Si interstitials and nitrogen is reduced due to interaction with oxygen. This leads to a considerable decrease in the nitrogen- enhanced recombination between vacancies and interstitials, which was previously proposed to explain the simultaneous suppression of vacancy- and Si interstitial-type defects by nitrogen doping. The radial oxygen precipitation behavior is explained by applying the formula of Vanhellemont and Claeys (J. Appl. Phys., 62 (9) (1987) 3960; 71 (2) (1992) 1073) for the critical radius of oxygen precipitates which accounts for the influence of vacancies and self- interstitials. A qualitative picture of the radial variation of the vacancy and interstitial concentrations is derived assuming that D-defect formation occurs before the onset of oxygen precipitation.

Deficits in radial arm maze performance in kindled rats: evidence for long-lasting memory dysfunction induced by repeated brief seizures

Repeated activation of neural pathways by kindling induces brief seizures, permanent increases in seizure susceptibility, neuronal loss in the hippocampus, and mossy fiber sprouting in the dentate gyrus. Because kindling induces permanent cellular alterations in hippocampal pathways that have been implicated in memory, it was of interest to determine if kindling also induces long-lasting impairments in a spatial memory task in rats. In this study, the effects of kindling on memory were investigated by assessing kindled rats in a radial arm maze behavior that is impaired by hippocampal damage. Kindled rats studied at 1 month after the last of 30-134 evoked generalized tonic-clonic seizures acquired competence in the performance of the radial arm maze task at a rate that was indistinguishable from age-matched normal controls, but demonstrated a deficit in the ability to repeat the task on consecutive days. The repetition deficit was not observed in rats that experienced three afterdischarges or three generalized tonic-clonic seizures, and the severity of the deficit varied directly with the number of evoked kindled seizures. Repeated brief seizures evoked by kindling induced a long-lasting deficit in a radial arm maze task that is a rodent model of memory. The observation of a long-lasting deficit in radial arm maze performance in kindled rats suggests that the cellular alterations induced in the hippocampus by seizures could contribute to the memory dysfunction in human epilepsy.

Biaxial mechanical behavior of excised porcine mitral valve leaflets.

Anterior and posterior leaflets from excised porcine mitral valves were mechanically tested under cyclic equibiaxial and strip biaxial stretch protocols at a strain rate of 4-12%/s after preconditioning. Cauchy stress and Lagrangian strain were calculated for both membrane and three-dimensional cases. The leaflets exhibited nonlinearly elastic, anisotropic behavior. Both anterior and posterior leaflets were less extensible in the circumferential than in the radial direction under equibiaxial stretch, with stress ratios of 5.7 and 4.3, respectively. The posterior leaflets exhibited greater extensibility in both directions and lower circumferential posttransitional moduli (ranges 690-820 vs. 2,500-3,200 N/m for anterior). This larger posterior extensibility may be due to the greater number of chordal attachments, which provide additional mechanical stability to this structure. Coupling of radial and circumferential mechanical behavior was evidenced by the response to different stretch protocols, indicating a complex microstructural coupling between individual collagen fibers or bundles. These are the first biaxial data for mitral valves and are a foundation for the development of a more detailed quantitative material description.

A Gradient in the Surface Brightness Fluctuations of NGC 3379

view Abstract Citations (29) References (41) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Gradient in the Surface Brightness Fluctuations of NGC 3379 Sodemann, Marianne ; Thomsen, Bjarne Abstract We present an investigation of the radial behavior of the surface brightness fluctuations of the standard elliptical galaxy NGC 3379, and we demonstrate that it is possible to measure radial changes accurately. Our results are based on a thorough procedure, which takes into account that the unwanted point sources, such as foreground stars, background galaxies, and globular clusters, are located in a background of varying amounts of luminosity and photon fluctuations. Our reduction procedure leaves no systematic effects due to the varying detection threshold of point sources, and we arrive at a significant radial gradient in the surface brightness fluctuations {DELTA}m^bar^_I_/{DELTA} log R = - 0.29 +/- 0.08. If our broadband surface brightness profile of NGC 3379 in I is combined with a corresponding profile in B taken from the literature, the radial behavior of m^bar^_I_, may be expressed as {DELTA}m^bar^_J_,/{DELTA}(B - I) = 1.9 +/- 0.5. The weighted mean of the measured fluctuation magnitudes is m^bar^_I_ = 28.67+/-0.04. Our results have implications on the distance measurements based on surface brightness fluctuations and the discussion of the degenerate effects of age and metallicity on stellar populations of elliptical galaxies. The linear relationship between m^bar^_I_, and B - I establishes an empirical calibration, which is needed for the distance measurements based on surface brightness fluctuations. The slope of the calibration obtained for NGC 3379 seems to be in agreement with the slope achieved earlier by others for Local Group galaxies and the Fornax and Eridanus clusters. The fluctuation magnitude m^bar^_I_, proves to be a sensitive indicator for radial changes in the underlying stellar population. However, the correlation between m^bar^_I_, and B -I together with state-of-the-art synthesized models indicates that these two observables do not give independent information on the underlying stellar population. Publication: The Astronomical Journal Pub Date: July 1995 DOI: 10.1086/117505 Bibcode: 1995AJ....110..179S Keywords: GALAXIES: INDIVIDUAL: NGC 3379; GALAXIES: ELLIPTICAL AND LENTICULAR full text sources ADS | data products SIMBAD (1) NED (1)