Showing papers by "University of Potsdam published in 1999"

Multifractality in human heartbeat dynamics

Abstract: There is evidence that physiological signals under healthy conditions may have a fractal temporal structure. Here we investigate the possibility that time series generated by certain physiological control systems may be members of a special class of complex processes, termed multifractal, which require a large number of exponents to characterize their scaling properties. We report on evidence for multifractality in a biological dynamical system, the healthy human heartbeat, and show that the multifractal character and nonlinear properties of the healthy heart rate are encoded in the Fourier phases. We uncover a loss of multifractality for a life-threatening condition, congestive heart failure.

Quantum Games and Quantum Strategies

Abstract: We investigate the quantization of nonzero sum games. For the particular case of the Prisoners' Dilemma we show that this game ceases to pose a dilemma if quantum strategies are allowed for. We also construct a particular quantum strategy which always gives reward if played against any classical strategy.

A comparison of entanglement measures

Abstract: We compare the entanglement of formation with a measure defined as the modulus of the negative eigenvalue of the partial transpose. In particular we investigate whether both measures give the same ordering of density operators with respect to the amount of entanglement

Synchronization in the human cardiorespiratory system.

Abstract: We investigate synchronization between cardiovascular and respiratory systems in healthy humans under free-running conditions. For this aim we analyze nonstationary irregular bivariate data, namely, electrocardiograms and measurements of respiratory flow. We briefly discuss a statistical approach to synchronization in noisy and chaotic systems and illustrate it with numerical examples; effects of phase and frequency locking are considered. Next, we present and discuss methods suitable for the detection of hidden synchronous epochs from such data. The analysis of the experimental records reveals synchronous regimes of different orders n:m and transitions between them; the physiological significance of this finding is discussed.

Shaping Bipolar and Elliptical Planetary Nebulae: Effects of Stellar Rotation, Photoionization Heating, and Magnetic Fields

Abstract: We present two-dimensional hydrodynamical and magnetohydrodynamical simulations of the evolution of planetary nebulae formed through the interaction of two succeeding, time-independent stellar winds. Both winds are modeled according to a consistent physical prescription for the latitudinal dependence of their properties. We propose that single stars with initial masses above ~1.3 M☉ can achieve near-critical rotation rates during their "superwind" phase at the tip of the asymptotic giant branch (AGB). We show that the resulting equatorially confined winds and their subsequent inflation to a double lobe structure by the post-AGB wind leads to the typical hourglass shape found in many planetary nebulae, such as MyCn 18. Following Chevalier & Luo and Rozyczka & Franco, we then combine the effect of a magnetic field in the post-AGB wind with rotating AGB winds. We obtain highly collimated bipolar nebula shapes, reminiscent of M2-9 or He 2-437. For sufficiently strong fields, ansae and jets, similar to those observed in IC 4593 are formed in the polar regions of the nebula. Weaker fields are found to be able to account for the shapes of classical elliptical nebulae, e.g., NGC 6905, in the case of spherically symmetric AGB winds, which we propose for single stars with initial masses below ~1.3 M☉. Photoionization, via instabilities in the ionization-shock front, can generate irregularities in the shape of the simulated nebulae. In particular, it leads to the formation of cometary knots, similar to those seen in the Helix nebula (NGC 7293). This effect may also be responsible for large-scale irregularities like those found in Sh 2-71 or WeSb 4. We arrive at a scenario in which the majority of the planetary nebula with their diverse morphologies is obtained from single stars. This scenario is consistent with the Galactic distribution of the different nebula types, since spherical and elliptical nebulae—which have a distribution with a large scale height above the Galactic plane—are ascribed to progenitor masses below ~1.3 M☉, with magnetic effects introducing ellipticities. Bipolar nebulae, on the other hand—which are on average closer to the Galactic plane—are found to stem from progenitors with initial masses above ~1.3 M☉.

Effects of inulin on faecal bifidobacteria in human subjects.

Abstract: A controlled study with eight healthy free-living subjects was carried out, in which energy intake was adjusted to the individual energy requirements. On administration of inulin, blood lipids, the faecal microflora, short-chain fatty acids and accompanying gastrointestinal symptoms were characterized in order to investigate the long-term effect of inulin. During the run-in phase (8 d), subjects received a typical Western diet providing 45% energy as fat and 40% energy as carbohydrate. Subsequently, the subjects consumed a fat-reduced diet which provided 30% energy as fat and 55% energy as carbohydrate for a period of 64 d using inulin as a fat replacer. The amounts of inulin consumed by the subjects (up to 34 g/d) were based on individual energy requirements with the aim to keep the diet isoenergetic with that used in the run-in period. To assess the effects of inulin administration, a control study (run-in and intervention) was carried out in which subjects consumed the same diet but devoid of inulin during the whole course of the study. To investigate the effect of inulin on faecal flora composition total bacteria and bifidobacteria in the faeces were enumerated by in situ hybridization with 16S rRNA targeted oligonucleotide probes. Inulin significantly increased bifidobacteria from 9.8 to 11.0 log10/g dry faeces and caused a moderate increase in gastrointestinal symptoms such as flatulence and bloatedness, whereas blood lipids and short-chain fatty acids remained essentially unaffected.

Loss and heating of particles in small and noisy traps

Abstract: We derive the life time and loss rate for a trapped atom that is coupled to fluctuating fields in the vicinity of a room-temperature metallic and/or dielectric surface. Our results indicate a clear predominance of near-field effects over ordinary blackbody radiation. We develop a theoretical framework for both charged ions and neutral atoms with and without spin. Loss processes that are due to a transition to an untrapped internal state are included.

Molecular typing of global isolates of Cryptococcus neoformans var. neoformans by polymerase chain reaction fingerprinting and randomly amplified polymorphic DNA — a pilot study to standardize techniques on which to base a detailed epidemiological survey

Abstract: A total of 356 clinical isolates of the encapsulated basidiomycetous fungus Cryptococcus neoformans var. neoformans, obtained from Australia, Argentina, Brazil, India, Italy, New Zealand, Papua New Guinea, South Africa, Thailand and the USA, were analyzed to lay the basis for a comprehensive evaluation of the global genetic structure of C. neoformans. Two polymerase chain reaction (PCR)-based typing techniques were standardized: PCR fingerprinting using a single primer specific to minisatellite or microsatellite DNA, and randomly amplified polymorphic DNA (RAPD) analysis using two combinations of three 20- to 22-mer random primers. Previous studies showed that the resultant profiles are reproducible and stable over time. Identical results were obtained in two different laboratories and by different scientists in the same laboratory. Both typing techniques separated the isolates into four major groups (VNI and VNII, serotype A; VNIII, serotype A/D; and VNIV, serotype D). The majority (78%) of isolates belonged to VNI, compared with 18% VNII, 1% VNIII and 3% VNIV. All US isolates could be differentiated by a unique, strain-specific PCR fingerprint or RAPD pattern in contrast to most of the non-US isolates, which showed a substantially higher degree of genetic homogeneity, with some clonality, in different parts of the world. Isolates obtained from the same patient at different times and from different body sites, had identical banding patterns. Both typing techniques should provide powerful tools for epidemiological studies of medically important fungi.

Anaerobic transformation of quercetin-3-glucoside by bacteria from the human intestinal tract.

Abstract: From human feces two phenotypically different types of bacteria were isolated on quercetin-3-glucoside as carbon and energy source. Isolates of one type were identified as strains of Enterococcus casseliflavus. They utilized the sugar moiety of the glycoside, but did not degrade the aglycon further. The sugar moiety (4 mM) was fermented to 5.5 +/- 2.1 mM formate, 2.1 +/- 0.7 mM acetate, 1.6 +/- 0.3 mM l-lactate, and 1.3 +/- 0.4 mM ethanol. The second type of isolate was identified as Eubacterium ramulus. This organism was capable of degrading the aromatic ring system. Growing cultures of Eubacterium ramulus converted 5 mM quercetin-3-glucoside to 1.7 +/- 0.6 mM 3,4-dihydroxyphenylacetic acid, 7.6 +/- 1.0 mM acetate, and 4.0 +/- 0.4 mM butyrate. Molecular hydrogen, 3,4-dihydroxybenzaldehyde, and ethanol were detected in small amounts. Phloroglucinol was a transient intermediate in the breakdown of quercetin-3-glucoside. Eubacterium ramulus did not grow on the aglycon quercetin or the ring-fission intermediate phloroglucinol, but cleaved the flavonoid ring system when glucose was present as a cosubstrate. The most probable number of quercetin-3-glucoside-degrading bacteria determined in nine human fecal samples was 10(7)-10(9)/g dry mass. Isolates from these experiments were all identified as Eubacterium ramulus.

mRNA stability and selenocysteine insertion sequence efficiency rank gastrointestinal glutathione peroxidase high in the hierarchy of selenoproteins

Abstract: The recently described gastrointestinal glutathione peroxidase (GI-GPx) is the fourth member of the family of the selenoenzymes glutathione peroxidases (GPx). In contrast to the more uniform distribution of, for example, the classical glutathione peroxidase (cGPx), it is expressed exclusively in the gastrointestinal tract and has, therefore, been suggested to function as a primary barrier against alimentary hydroperoxides. In order to get an idea of its relative importance we investigated its position in the hierarchy of selenoprotein expression. The selenium-dependent expression of GI-GPx was analyzed in comparison with that of other GPx types at the level of mRNA and protein in HepG2 and CaCo-2 cells. Furthermore, the selenocysteine insertion sequence (SECIS) efficiencies of GI-GPx, phospholipid hydroperoxide glutathione peroxidase (PHGPx) and cGPx in response to selenium were determined by a reporter-gene assay in human hepatoma cells and baby hamster kidney cells. GI-GPx mRNA levels increased during selenium deficiency, whereas cGPx mRNA levels decreased and PHGPx mRNA levels remained almost unaffected. In cells grown in selenium-poor media, all GPx-types were low in both activity and immunochemical reactivity. Upon selenium repletion immunoreactive GI-GPx protein reached a plateau after 10 h, whereas cGPx started to be expressed at 24 h and did not reach its maximum level before 3 days. SECIS efficiencies decreased in the order PHGPx > cGPx > GI-GPx. The augmentation of SECIS efficiencies by selenium was highest for cGPx and intermediate for PHGPx, whereas it was marginal for GI-GPx. The high mRNA stability under selenium restriction, the speed of biosynthesis upon selenium repletion and the marginal effect of selenium on the SECIS efficiency indicate that of the GPx isotypes, GI-GPx ranks highest in the hierarchy of selenoproteins and point to a vital role of GI-GPx in the gastrointestinal tract.

Structural and lithological controls on large Quaternary rock avalanches (sturzstroms) in arid northwestern Argentina

Abstract: Landsat thematic mapper (TM) analysis, aerial photograph interpretation, and field studies of the semiarid Puna Plateau, adjacent Eastern Cordillera, and Sierras Pampeanas of Argentina (lat 24°–28°S) have revealed the existence of at least 55 rock-avalanche deposits with volumes larger than 10 6 m 3 that formed by the collapse of entire mountain fronts. The spatial distribution of landslide deposits is not random, but it clusters along mountain fronts bounded by active faults. Inspection in the field reveals five principal controls on the distribution of these events. The source area of the rock avalanches has two topographic constraints: (1) vertical relief contrasts between the breakaway zone and the mountain front must exceed a threshold of 400 m, and (2) the slope inclinations must be steeper than 20°. Rock avalanches are restricted to three types of lithology: granites, low-grade metamorphic rocks, and coarse clastic sediments. Structural controls are very important. Rock avalanches are controlled by planar structures such as bedding planes, exfoliation joints, minor faults, and cleavage that all dip toward the valley. In addition, major slide clusters occur along mountain fronts that underwent Quaternary reverse-fault reactivation of former transfer faults with strike-slip kinematics. The trigger mechanism for the majority of these landslides is interpreted to be seismic, although the ages of some major slides are about 30 ka, and they may correspond to a more humid interval in southern South America.

Fast CG-Based Methods for Tikhonov--Phillips Regularization

Abstract: Tikhonov--Phillips regularization is one of the best-known regularization methods for inverse problems. A posteriori criteria for determining the regularization parameter $\alpha$ require solving $$(*) (A^*A+\alpha I) x =A^* y^{\delta}$$ for different values of $\alpha$. We investigate two methods for accelerating the standard cg-algorithm for solving the family of systems (*). The first one utilizes a stopping criterion for the cg-iterations which depends on $\alpha$ and $\delta$. The second method exploits the shifted structure of the linear systems (*), which allows us to solve (*) simultaneously for different values of $\alpha$. We present numerical experiments for three test problems which illustrate the practical efficiency of the new methods. The experiments as well as theoretical considerations show that run times are accelerated by a factor of at least 3.

Putting ‘input’ in its proper place:

Abstract: Every theory of second language acquisition (SLA) hypothesizes that learners come to know the properties of a language by being exposed to instances of it in meaningful conversation. Within SLA, the standard analysis of the ‘input question’ appears to be that input equals objective properties of the stimulus array less the effects of selective attention (the intake). In this paper, I offer a critique of the standard analysis. I claim that it is not interpretable in the absence of a theory of mental representation, theories of speech perception and language parsing, and a theory of language learning. I show that it cannot account for aspects of signal detection, phonetic or phonological learning. The standard treatment is essentially pretheoretical. I define an alternative position which distinguishes input to speech processing and input to language-learning mechanisms, drawing on the Autonomous Induction Theory – a novel theory of learning which is compatible with a modular view of processing and a view o...

4-Hydroxynonenal induces dysfunction and apoptosis of cultured endothelial cells.

Abstract: Lipolytic products of triglyceride-rich lipoproteins, i.e., free fatty acids, may cause activation and dysfunction of the vascular endothelium. Mechanisms of these effects may include lipid peroxidation. One of the major and biologically active products of peroxidation of n-6 fatty acids, such as linoleic acid or arachidonic acid, is the aldehyde 4-hydroxynonenal (HNE). To study the hypothesis that HNE may be a critical factor in endothelial cell dysfunction caused by free fatty acids, human umbilical endothelial cells (HUVEC) were treated with up to160 microM of linoleic or arachidonic acid. HNE formation was detected by immunocytochemistry in cells treated for 24 h with either fatty acid, but more markedly with arachidonic acid. To study the cellulareffects of HNE, HUVEC were treated with different concentrations of this aldehyde, and several markers of endothelial cell dysfunction were determined. Exposure to HNE for 6 and 9 h resulted in increased cellular oxidative stress. However, short time treatment with HNE did not cause activation of nuclear factor-kappaB (NF-kappaB). In addition, HUVEC exposure to HNE caused a dose-dependent decrease in production of both interleukin-8 (IL-8) and intercellular adhesion molecule-1 (ICAM-1). On the other hand, HNE exerted prominent cytotoxic effects in cultured HUVEC, manifested by morphological changes, diminished cellular viability, and impaired endothelial barrier function. Furthermore, HNE treatment induced apoptosis of HUVEC. These data provide evidence that HNE does not contribute to NF-kappaB-related mechanisms of the inflammatory response in HUVEC, but rather to endothelial dysfunction, cytotoxicity, and apoptotic cell death.

Multifractality in Human Heartbeat Dynamics

Abstract: Recent evidence suggests that physiological signals under healthy conditions may have a fractal temporal structure. We investigate the possibility that time series generated by certain physiological control systems may be members of a special class of complex processes, termed multifractal, which require a large number of exponents to characterize their scaling properties. We report on evidence for multifractality in a biological dynamical system --- the healthy human heartbeat. Further, we show that the multifractal character and nonlinear properties of the healthy heart rate are encoded in the Fourier phases. We uncover a loss of multifractality for a life-threatening condition, congestive heart failure.

Preference of attractors in noisy multistable systems.

Abstract: A model system exhibiting a large number of attractors is investigated under the influence of noise. Several methods for discriminating two qualitatively different regions of the noise intensity are presented, and the phenomenon of noise-induced preference of attractors is reported. Finally, the relevance of our findings for detection of multiple stable states of systems occurring in nature or in the laboratory is pointed out.

Interspecies differences in cancer susceptibility and toxicity

Abstract: One of the most complex challenges to the toxicologist represents extrapolation from laboratory animals to humans. In this article, we review interspecies differences in metabolism and toxicity of heterocyclic amines, aflatoxin B1, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), and related compounds, endocrine disrupters, polycyclic aromatic hydrocarbons, tamoxifen, and digitoxin. As far as possible, extrapolations to human toxicity and carcinogenicity are performed. Humans may be more susceptible to the carcinogenic effect of heterocyclic amines than monkeys, rats, and mice. Especially, individuals with high CYP1A2 and 3A4 activities and the rapid acetylator phenotype may be expected to have an increased risk. Striking interspecies variation in susceptibility to aflatoxin B1 carcinogenesis is known, with rats representing the most sensitive and mice the most resistant species, refractory to dietary levels three orders of magnitude higher than rats. An efficient conjugation with glutathione, catalyzed by glutathione S-transferase mYc, confers aflatoxin B1 resistance to mice. Extremely large interspecies differences in TCDD-induced toxicity are known. The guinea pig is the most susceptible mammal known, with an LD50 in the range 1-2 micrograms TCDD/kg, whereas the hamster is the most resistant species with an LD50 greater than 3000 micrograms/kg. A number of experts have pointed out to the fact that humans appear to be less sensitive to TCDD than most laboratory animals. Human exposure to background levels of TCDD is not likely to cause an incremental cancer risk. A clear cause--effect relationship has been shown between environmental endocrine-disrupting contaminants and adverse health effects in wildlife, whereas the effects seem to be less critical for humans. Studies on DNA adduct formation and metabolism of the nonsteroidal antiestrogen tamoxifen indicate that rats and mice are orders of magnitude more susceptible than humans.

Long-term neuropsychological consequences of maternal epilepsy and anticonvulsant treatment during pregnancy for school-age children and adolescents.

Abstract: Summary: Purpose: Antiepileptic drugs (AEDs) are potential teratogenic agents. The purpose of this study was to examine the long-term effects of intrauterine AED exposure on neurologic and psychological functioning. Methods: Of a prospective study, “Epilepsy, pregnancy, and child development,” children could be retraced at school age and adolescence. Sixty-seven were born to mothers with epilepsy [no drugs during pregnancy (n = 13), monotherapy (n = 31), polytherapy (n = 23)]; 49 were nonafflicted control children. Assessments included an intelligence test (Wechsler), a neurologic examination (Touwen), and an EEG. Data analyses were performed, controlling for parental social status, type of maternal drug therapy and drug dosage, type of epilepsy, frequency of seizures during pregnancy, the original subgroups, and specific drug effects. Results: Type of maternal epilepsy and type and kind of AED therapy, but not maternal seizures during pregnancy correlated with an increase in abnormal EEG patterns. Minor neurologic dysfunction was diagnosed, with increased frequency from the control to the risk/no drug or monotherapy to the polytherapy group. The compromised intelligence score of the polytherapy group was primarily due to those children who had been exposed to primidone (PRM). Level of IQ was negatively associated with PRM dosage. Conclusions: Maternal epilepsy and AED therapy during pregnancy appear to have long-term effects on the offspring well into adolescence, as evinced in EEG patterns, minor neurologic dysfunction, and intellectual performance. Severity of effects increased from control group to epilepsy/no-drug group to monotherapy group and was most marked in the polytherapy group. These group differences are assumed to reflect differential neural vulnerability to social and family factors.

Endothelial cell functions. relationship to atherogenesis

Abstract: The vascular endothelium plays a critical role in the preservation of normal vessel wall structure and function. In particular endothelial cells control vascular permeability, vessel tone, coagulation, fibrinolysis, and inflammatory responses. These functions are accomplished by production of a variety of biologically active substances. However, endothelial cell-mediated reactions may also lead to the development of pathological stages within the vessel wall. The current review is focused on endothelial cell metabolism in relationship to the development of atherosclerosis.

Teacher gender‐related influences in Greek schools

Abstract: Background. Although there is a wealth of empirical studies examining the effects and the correlates of student gender in school, teacher gender has rarely been a research focus. Since Greece is one of the few Western countries with an about equal percentage of male and female teachers at primary and secondary levels of public education, it offers itself as a well-suited context for exploring teacher gender-related influences. Aims. The aim of the study was to examine gender-related differences in Greek classrooms focusing on teacher gender. It was hypothesised that due to the societal context clear gender effects could be detected. It was also assumed that teacher-student interaction patterns would be influenced by teacher gender not so much as a main effect but as interaction effects involving variables such as student gender, student achievement, grade, and teacher specialisation. Samples. The samples consisted of 1041 elementary school (mean age = 11.4 years) and 862 secondary school (mean age = 14.3 years) students in public schools in Greece. Methods. A multi-informant and multiperspective approach to academic and psychosocial competence was used, involving teacher, peer, and self-ratings. Achievement data were also obtained. Results. Several significant teacher gender differences were found in teachers' assessment of students' competence at both age groups. Furthermore, various domains of children's self-concept were found to be different in classes of female and male teachers. Conclusions. The findings indicate the need to use teacher gender as a relevant variable in future research.

Alternating Locking Ratios in Imperfect Phase Synchronization

Abstract: In periodically driven chaotic dynamical systems with a broad distribution of intrinsic time scales, perfect phase synchronization cannot be reached. Long segments of evolution during which the phase of a chaotic variable follows the phase of the driving force are interrupted by short segments of phase drift. We demonstrate that this drift is another short-lived synchronized state; its onset is caused by the passage near the long unstable periodic orbits whose frequencies are locked by external force in ratios different from 1:1.

High surface-charge stability of porous polytetrafluoroethylene electret films at room and elevated temperatures

Abstract: Porous polytetrafluoroethylene films were positively or negatively corona-charged at room or elevated temperatures and their charge-storage behaviour was investigated by means of isothermal surface-potential and thermally stimulated discharge-current measurements. In addition, electron micrographs of the sample morphology were taken and the influence of high humidities on the surface-charge decay was investigated. For comparison, nominally non-porous polytetrafluoroethylene films were studied in the same manner. It was found that porosity may lead to significantly enhanced surface-charge stability for both polarities if the relative humidity is not too high. Further investigations are under way in order to better understand this behaviour and to employ it for electret applications.

Development of Cellulose Sulfate-based Polyelectrolyte Complex Microcapsules for Medical Applications

Abstract: Microencapsulation, as a tool for immunoisolation for allogenic or xenogenic implants, is a rapidly growing field. However most of the approaches are based on alginate/polylysine capsules, despite this system's obvious disadvantages such as its pyrogenicity. Here we report a different encapsulation system based on sodium cellulose sulfate and polydiallyldimethyl ammonium chloride for the encapsulation of mammalian cells. We have characterized this system regarding capsule formation, strength and size of the capsules as well as viability of the cells after encapsulation. In addition, we demonstrate the efficacy of these capsules as a "microfactory" in vitro and in vivo. Using encapsulated hybridoma cells we were able to demonstrate long-term release of antibodies up to four months in vivo. In another application we could show the therapeutic relevance of encapsulated genetically modified cells as an in vivo activation center for cytostatic drugs during tumor therapy.

Seismotectonic range-front segmentation and mountain-belt growth in the Pamir-Alai region, Kyrgyzstan (India-Eurasia collision zone)

Abstract: The Trans Alai Range along the northern perimeter of the Pamir region of Kyrgyzstan is at the northern edge of the India-Eurasia collision zone. The range defines a section of Main Pamir thrust, which is divided into eastern, central, and western segments that record differential absorption of plate convergence. The 50-km-long, east-west–striking, central fault segment of the Main Pamir thrust has dip-slip thrust fault offsets (with a minimum Holocene dip-slip rate of ∼6 mm/yr) and is linked to the other segments via northwest-striking dextral transfer. The western transfer faults are well characterized geomorphically, and the westernmost records the predominant transition to north-vergent thrusting along the western segment via north-vergent, low-angle thrust faults rooted in a steeply south-dipping dextral shear zone. In contrast, the eastern segment deformation is widely distributed and geomorphically less evident, but the transfer also takes place in a structurally complex zone. Asymmetric offset of a regionally correlated terrace, geomorphic zonation, and the distribution of historic earthquakes suggest that the central segment is mechanically linked with the western segment, but not with the eastern segment. The progressive closure of the Alai Valley by the northward advance of thrusting exemplifies the annihilation of an intramontane basin. If the high surface uplift rates implied by these geologic observations have been maintained for the last few million years, they attest to the high level of tectonic activity and the recency of construction of the Trans Alai Range.

Heating of trapped atoms near thermal surfaces

Abstract: We study the electromagnetic coupling and concomitant heating of a particle in a miniaturized trap close to a solid surface. Two dominant heating mechanisms are identified: proximity fields generated by thermally excited currents in the absorbing solid and time-dependent image potentials due to elastic surface distortions (Rayleigh phonons). Estimates for the lifetime of the trap ground state are given. Ions are particularly sensitive to electric proximity fields: for a silver substrate, we find a lifetime below one second at distances closer than some ten μm to the surface. Neutral atoms may approach the surface more closely: if they have a magnetic moment, a minimum distance of one μm is estimated in tight traps, the heat being transferred via magnetic proximity fields. For spinless atoms, heat is transferred by inelastic scattering of virtual photons off surface phonons. The corresponding lifetime, however, is estimated to be extremely long compared to the timescale of typical experiments.

Amplitude Equations from Spatiotemporal Binary-Fluid Convection Data

Abstract: We apply a recently developed method for the analysis of spatiotemporal data to extract the dynamical equations that describe an experiment on traveling-wave convection in a binary fluid. The technique is based on nonlinear regression analysis and allows the nonparametric estimation of the functions involved in these equations. We find that the system is well described by a pair of coupled complex Ginzburg-Landau equations, and the coefficient of the term that describes the interaction between the two oppositely propagating waves can be determined.

Superoxide Dismutase Activity Measurement Using Cytochrome c-Modified Electrode.

Abstract: SOD activity was quantified by the use of a cytochrome c-modified gold electrode. The electrode responded rapidly to superoxide radicals in solution. Steady-state superoxide concentrations were established by control of the calibration conditions. On this basis very low SOD activities were detected (10-200 munits/mL). This method showed good correlation with the standard photometric test and was applied for the determination of SOD activity entrapped into liposomes. Interference by hydrogen peroxide and uric acid was characterized and minimized using long-chain thiols for the first electrode modification step. The complete modification proved to be stable for several days.

Giant Outbursts of Luminous Blue Variables and the Formation of the Homunculus Nebula around η Carinae

Abstract: The observed giant outbursts of luminous blue variables (LBVs) may occur when these massive stars approach their Eddington limits. When this happens, they must reach a point at which the centrifugal force and the radiative acceleration cancel out gravity at the equator. We call this the Ω limit. When stars are close to the Ω limit, strong nonspherical mass loss should occur. This suggests a scenario in which a slow and very dense wind, strongly confined to the equatorial plane, is followed by a fast and almost spherical wind. We compute two-dimensional hydrodynamic models of the evolution of the nebula formed from such interacting winds, using parameters consistent with the outburst of η Carinae in the last century. This outburst gave birth to the Homunculus, the hourglass-shaped inner part of a highly structured circumstellar nebula. Assuming the star was very close to the Ω limit during outburst, our models produce gas distributions that strongly resemble the Homunculus on large and small scales. This supports the general conjecture that giant outbursts in LBVs occur when they approach the Eddington limit. Our models constrain the average mass-loss rate since the outburst to values smaller than the present-day mass-loss rate and suggest that η Car is approaching another outburst. Our models imply that the occurrence of giant LBV outbursts depends on the initial stellar rotation rate and that the initial angular momentum is as important to the evolution of very massive stars as their initial mass or metallicity.