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The Voyager 2 Photopolarimeter experiment has yielded the highest resolved data of Saturn's rings, exhibiting a wide variety of features. The B-ring region between 105000 km and 110000 km distance from Saturn has been investigated. It has a high matter density and contains no significance features visible by eye. Analysis with statistical methods has let us to the detection of two significant events. These features are correlated with the inner 3:2 resonances of the F-ring shepherd satellites Pandora and Prometheus, and may be evidence of large ring paricles caught in the corotation resonances.
Many methods have been proposed for the stabilization of higher index differential-algebraic equations (DAEs). Such methods often involve constraint differentiation and problem stabilization, thus obtaining a stabilized index reduction. A popular method is Baumgarte stabilization, but the choice of parameters to make it robust is unclear in practice. Here we explain why the Baumgarte method may run into trouble. We then show how to improve it. We further develop a unifying theory for stabilization methods which includes many of the various techniques proposed in the literature. Our approach is to (i) consider stabilization of ODEs with invariants, (ii) discretize the stabilizing term in a simple way, generally different from the ODE discretization, and (iii) use orthogonal projections whenever possible. The best methods thus obtained are related to methods of coordinate projection. We discuss them and make concrete algorithmic suggestions.
A Hamiltonian system in potential form (formula in the original abstract) subject to smooth constraints on q can be viewed as a Hamiltonian system on a manifold, but numerical computations must be performed in Rn. In this paper methods which reduce "Hamiltonian differential algebraic equations" to ODEs in Euclidean space are examined. The authors study the construction of canonical parameterizations or local charts as well as methods based on the construction of ODE systems in the space in which the constraint manifold is embedded which preserve the constraint manifold as an invariant manifold. In each case, a Hamiltonian system of ordinary differential equations is produced. The stability of the constraint invariants and the behavior of the original Hamiltonian along solutions are investigated both numerically and analytically.
Many methods have been proposed for the simulation of constrained mechanical systems. The most obvious of these have mild instabilities and drift problems. Consequently, stabilization techniques have been proposed A popular stabilization method is Baumgarte's technique, but the choice of parameters to make it robust has been unclear in practice. Some of the simulation methods that have been proposed and used in computations are reviewed here, from a stability point of view. This involves concepts of differential-algebraic equation (DAE) and ordinary differential equation (ODE) invariants. An explanation of the difficulties that may be encountered using Baumgarte's method is given, and a discussion of why a further quest for better parameter values for this method will always remain frustrating is presented. It is then shown how Baumgarte's method can be improved. An efficient stabilization technique is proposed, which may employ explicit ODE solvers in case of nonstiff or highly oscillatory problems and which relates to coordinate projection methods. Examples of a two-link planar robotic arm and a squeezing mechanism illustrate the effectiveness of this new stabilization method.
We have used techniques of nonlinear dynamics to compare a special model for the reversals of the Earth's magnetic field with the observational data. Although this model is rather simple, there is no essential difference to the data by means of well-known characteristics, such as correlation function and probability distribution. Applying methods of symbolic dynamics we have found that the considered model is not able to describe the dynamical properties of the observed process. These significant differences are expressed by algorithmic complexity and Renyi information.
In the modern industrialized countries every year several hundred thousands of people die due to the sudden cardiac death. The individual risk for this sudden cardiac death cannot be defined precisely by common available, non-invasive diagnostic tools like Holter-monitoring, highly amplified ECG and traditional linear analysis of heart rate variability (HRV). Therefore, we apply some rather unconventional methods of nonlinear dynamics to analyse the HRV. Especially, some complexity measures that are basing on symbolic dynamics as well as a new measure, the renormalized entropy, detect some abnormalities in the HRV of several patients who have been classified in the low risk group by traditional methods. A combination of these complexity measures with the parameters in the frequency domain seems to be a promising way to get a more precise definition of the individual risk. These findings have to be validated by a representative number of patients.
The site of confluence of the artery and the portal vein in the liver still appears to be controversial. Anatomical studies suggested a presinusoidal or an intrasinusoidal confluence in the first, second or even final third of the sinusoids. The objective of this investigation was to study the problem with functional biochemical techniques. Rat livers were perfused through the hepatic artery and simultaneously either in the orthograde direction from the portal vein to the hepatic vein or in the retrograde direction from the hepatic vein to the portal vein. Arterial how was linearly dependent on arterial pressure between 70 cm H2O and 120 cm H2O at a constant portal or hepatovenous pressure of 18 cm H2O. An arterial pressure of 100 cm H2O was required for the maintenance of a homogeneous orthograde perfusion of the whole parenchyma and of a physiologic ratio of arterial to portal how of about 1:3. Glucagon was infused either through the artery or the portal vein and hepatic vein, respectively, to a submaximally effective ''calculated'' sinusoidal concentration after mixing of 0.1 nmol/L. During orthograde perfusions, arterial and portal glucagon caused the same increases in glucose output. Yet during retrograde perfusions, hepatovenous glucagon elicited metabolic alterations equal to those in orthograde perfusions, whereas arterial glucagon effected changes strongly reduced to between 10% and 50%. Arterially infused trypan blue was distributed homogeneously in the parenchyma during orthograde perfusions, whereas it reached clearly smaller areas of parenchyma during retrograde perfusions. Finally, arterially applied acridine orange was taken up by all periportal hepatocytes in the proximal half of the acinus during orthograde perfusions but only by a much smaller portion of periportal cells in the proximal third of the acinus during retrograde perfusions. These findings suggest that in rat liver, the hepatic artery and the portal vein mix before and within the first third of the sinusoids, rather than in the middle or even last third.
Earlier investigations at South Creek in northeastern Queensland established the importance of overland flow as a hydrologic pathway in this tropical rainforest environment. Since this pathway is ‘fast’, transmitting presumably ‘new’ water, its importance should be reflected in the stormflow chemistry of South Creek: the greater the volumentric contribution to the stormflow hydrograph, the more similarity between the chemical composition of streamwater and of overland flow is to be expected. Water samples were taken during two storm events in an ephemeral gully (gully A), an intermittent gully (gully B) and at the South Creek catchment outlet; additional spot checks were made in several poorly defined rills. The chemical composition of ‘old’ water was determined from 45 baseflow samples collected throughout February. The two events differed considerably in their magnitudes, intensities and antecedent moisture conditions. In both events, the stormflow chemistry in South Creek was characterized by a sharp decrease in Ca, Mg, Na, Si, Cl, EC, ANC, alkalinity and total inorganic carbon. pH remained nearly constant with discharge, whereas K increased sharply, as did sulfate in an ill-defined manner. In event 1, this South Creek stormflow pattern was closely matched by the pattern in gully A, implying a dominant contribution of ‘new’ water. This match was confirmed by the spot samples from rills. Gully B behaved like South Creek itself, but with a dampened ‘new’ water signal, indicating less overland flow generation in its subcatchment. In event 2, which occurred five days later, the initial ‘new’ water signal in gully A was rapidly overwhelmed by a different signal which is attributed to rapid drainage from a perched water table. This study shows that stormflow in this rainforest catchment consists predominantly of ‘new’ water which reaches the stream channel via ‘fast’ pathways. Where the ephemeral gullies delivering overland flow are incised deeply enough to intersect a perched water table, a delayed, ‘old’ water-like signal may be transmitted.
Increase in prostanoid formation in rat liver macrophages (Kupffer cells) by human anaphylatoxin C3a
(1993)
Human anaphylatoxin C3a increases glycogenolysis in perfused rat liver. This action is inhibited by prostanoid synthesis inhibitors and prostanoid antagonists. Because prostanoids but not anaphylatoxin C3a can increase glycogenolysis in hepatocytes, it has been proposed that prostanoid formation in nonparenchymal cells represents an important step in the C3a-dependent increase in hepatic glycogenolysis. This study shows that (a) human anaphylatoxin C3a (0.1 to 10 mug/ml) dose-dependently increased prostaglandin D2, thromboxane B, and prostaglandin F2alpha formation in rat liver macrophages (Kupffer cells); (b) the C3a-mediated increase in prostanoid formation was maximal after 2 min and showed tachyphylaxis; and (c) the C3a-elicited prostanoid formation could be inhibited specifically by preincubation of C3a with carboxypeptidase B to remove the essential C-terminal arginine or by preincubation of C3a with Fab fragments of a neutralizing monoclonal antibody. These data support the hypothesis that the C3a-dependent activation of hepatic glycogenolysis is mediated by way of a C3a-induced prostanoid production in Kupffer cells.
Rainfall erosivities as defined by the R factor from the universal soil loss equation were determined for all events during a two-year period at the station La Cuenca in western Amazonia. Three methods based on a power relationship between rainfall amount and erosivity were then applied to estimate event and daily rainfall erosivities from the respective rainfall amounts. A test of the resulting regression equations against an independent data set proved all three methods equally adequate in predicting rainfall erosivity from daily rainfall amount. We recommend the Richardson model for testing in the Amazon Basin, and its use with the coefficient from La Cuenca in western Amazonia.
The topography of first-order catchments in a region of western Amazonia was found to exhibit distinctive, recurrent features: a steep, straight lower side slope, a flat or nearly flat terrace at an intermediate elevation between valley floor and interfluve, and an upper side slope connecting interfluve and intermediate terrace. A detailed survey of soil-saturated hydraulic conductivity (K sat)-depth relationships, involving 740 undisturbed soil cores, was conducted in a 0.75-ha first-order catchment. The sampling approach was stratified with respect to the above slope units. Exploratory data analysis suggested fourth-root transformation of batches from the 0–0.1 m depth interval, log transformation of batches from the subsequent 0.1 m depth increments, and the use of robust estimators of location and scale. The K sat of the steep lower side slope decreased from 46 to 0.1 mm/h over the overall sampling depth of 0.4 m. The corresponding decrease was from 46 to 0.1 mm/h on the intermediate terrace, from 335 to 0.01 mm/h on the upper side slope, and from 550 to 0.015 mm/h on the interfluve. A depthwise comparison of these slope units led to the formulation of several hypotheses concerning the link between K sat and topography.
4-Phenylphenoxazinones were isolated after biomimetic oxidation, using diphenoloxidases of insect cuticle, mushroom tyrosinase, or after autoxidation of N-acetyldopamine (Image ) in the presence of β-alanine, β-alanine methyl ester or N-acetyl-L-lysine. They are formed presumably by addition of 2-aminoalkyl-5-alkylphenols to the o-quinone of biphenyltetrol which, in turn, arises from oxidative coupling of. The structures of present the first examples for the assembly of reasonably stable intermediates in the rather complex process of chemical modifications of aliphatic amino acid residues by o-quinones.
The complement fragments C3a and C5a were purified from zymosan-activated human serum by column chromatographic procedures after the bulk of the proteins had been removed by acidic polyethylene glycol precipitation. In the isolated in situ perfused rat liver C3a increased glucose and lactate output and reduced flow. Its effects were enhanced in the presence of the carboxypeptidase inhibitor DL-mercaptomethyl-3-guanidinoethylthio-propanoic acid (MERGETPA) and abolished by preincubation of the anaphylatoxin with carboxypeptidase B or with Fab fragments of an anti-C3a monoclonal antibody. The C3a effects were partially inhibited by the thromboxane antagonist BM13505. C5a had no effect. It is concluded that locally but not systemically produced C3a may play an important role in the regulation of local metabolism and hemodynamics during inflammatory processes in the liver.
Amphiphilic derivatives of octadiene and docosadiene were investigated in monolayers and Langmuir-Blodgett multilayers, with respect to their self-organization and their polymerization behavior. All amphiphiles investigated form monolayers. However, only acid and alcohol derivatives were able to build up multilayers. Those multilayers are rapidly photopolymerized in the layers via a two-step process: Irradiation with long-wavelength UV light yields soluble polymers, whereas additional irradiation with sfiort-wavelength UV light produces insoluble and presumably cross-linked polymers. The reaction meclianism is discussed according to the polymer characterization by UV spectroscopy, small-angle X-ray scattering, NMR spectroscopy, and gel permeation chromatography. All multilayers undergo structural changes during the polymerization; substantial changes result in defects in the polymerized layers as observed by scanning electron microscopy. In contrast to the acids and alcohols, the deposition of monolayers of the aldehyde derivatives did not yield well-ordered multilayers, but rather amorphous films. In this different film structure, the photopolymerization process differs from the one observed in multilayers.
In the isolated rat liver perfused in situ stimulation of the nerve bundles around the portal vein and the hepatic artery caused an increase of urate formation that was inhibited by the α1-blocker prazosine and the xanthine oxidase inhibitor allopurinol. Moreover, nerve stimulation increased glucose and lactate output and decreased perfusion flow. Infusion of noradrenaline had similar effects. Compared to nerve stimulation infusion of glucagon led to a less pronounced increase of urate formation and a twice as large increase in glucose output but a decrease in lactate release without affecting the flow rate. Insulin had no effect on any of the parameters studied.
The optical density of human macular pigment was measured for 50 observers ranging in age from 10 to 90 years. The psychophysical method required adjusting the radiance of a 1°, monochromatic light (400–550 nm) to minimize flicker (15 Hz) when presented in counterphase with a 460 nm standard. This test stimulus was presented superimposed on a broad-band, short-wave background. Macular pigment density was determined by comparing sensitivity under these conditions for the fovea, where macular pigment is maximal, and 5° temporally. This difference spectrum, measured for 12 observers, matched Wyszecki and Stiles's standard density spectrum for macular pigment. To study variation in macular pigment density for a larger group of observers, measurements were made at only selected spectral points (460, 500 and 550 nm). The mean optical density at 460 nm for the complete sample of 50 subjects was 0.39. Substantial individual differences in density were found (ca. 0.10–0.80), but this variation was not systematically related to age.
Cinnamic acid moieties were incorporated into amphiphilic compounds containing one and two alkyl chains. These lipid-like compounds with photoreactive units undergo self-organization to form monolayers at the gas-water interface and bilayer structures (vesicles) in aqueous solutions. The photoreaction of the cinnamic acid moiety induced by 254 nm UV light was investigated in the crystalline state, in monolayers, in vesicles and in solution in organic solvents. The single-chain amphiphiles undergo dimerization to yield photoproducts with twice the molecular weight of the corresponding monomers in organized systems. The photoreaction of amphiphiles containing two cinnamic acid groups occurs via two mechanisms: The intramolecular dimerization produces bicycles, with retention of the molecular weight of the corresponding monomer. The intermolecular reaction leads to oligomeric and polymeric photoproducts. In contrast to the single-chain amphiphiles, photodimerization processes of lipoids containing two cinnamic acid moieties also occur in solution in organic solvents.
Monolayers of rod-shaped and disc-shaped liquid crystalline compounds at the air-water interface
(1986)
Calamitic (rod-shaped) and discotic (disc-shaped) thermotropic liquid crystalline (LC) compounds were spread at the air-water interface, and their ability to form monolayers was studied. The calamitic LCs investigated were found to form monolayers which behave analogously to conventional amphiphiles such as fatty acids. The spreading of the discotic LCs produced monolayers as well, but with a behaviour different from classical amphiphiles. The areas occupied per molecule are too small to allow the contact of all hydrophilic groups with the water surface and the packing of all hydrophobic chains. Various molecular arrangements of the discotics at the water surface to fit the spreading data are discussed.
The development of phonetic codes in memory of 141 pairs of normal and disabled readers from 7.8 to 16.8 years of age was tested with a task adapted from L. S. Mark, D. Shankweiler, I. Y. Liberman, and C. A. Fowler (Memory & Cognition, 1977, 5, 623–629) that measured false-positive errors in recognition memory for foil words which rhymed with words in the memory list versus foil words that did not rhyme. Our younger subjects replicated Mark et al., showing a larger difference between rhyming and nonrhyming false-positive errors for the normal readers. The older disabled readers' phonetic effect was comparable to that of the younger normal readers, suggesting a developmental lag in their use of phonetic coding in memory. Surprisingly, the normal readers' phonetic effect declined with age in the recognition task, but they maintained a significant advantage across age in the auditory WISC-R digit span recall test, and a test of phonological nonword decoding. The normals' decline with age in rhyming confusion may be due to an increase in the precision of their phonetic codes.
Linguistic and psycholinguistic accounts based on the study of English may prove unreliable as guides to sentence processing in even closely related languages. The present study illustrates this claim in a test of sentence interpretation by German-, Italian-, and English-speaking adults. Subjects were presented with simple transitive sentences in which contrasts of (1) word order, (2) agreement, (3) animacy, and (4) stress were systematically varied. For each sentence, subjects were asked to state which of the two nouns was the actor. The results indicated that Americans relied overwhelming on word order, using a first-noun strategy in NVN and a second-noun strategy in VNN and NNV sentences. Germans relied on both agreement and animacy. Italians showed extreme reliance on agreement cues. In both German and Italian, stress played a role in terms of complex interactions with word order and agreement. The findings were interpreted in terms of the “competition model” of Bates and MacWhinney (in H. Winitz (Ed.), Annals of the New York Academy of Sciences Conference on Native and Foreign Language Acquisition. New York: New York Academy of Sciences, 1982) in which cue validity is considered to be the primary determinant of cue strength. According to this model, cues are said to be high in validity when they are also high in applicability and reliability.