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Results for “systems drift”

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At least 613 records · Page 34Linked to original sources

PubMed1999

Genetic diversity in peripheral and subcentral populations of corrigiola litoralis L. (Illecebraceae)

Genetic diversity and differentiation were studied in Corrigiola litoralis L., an annual plant species growing on seasonally flooded river banks. Plant species that are restricted to river systems may consist of highly isolated populations. For this species, pronounced genetic differentiation among rivers was expected. Plants were sampled from the river Loire (France) representing subcentral populations and the rivers Rhine, Weser and Elbe (Germany) representing peripheral ones. Allozyme electrophoresis revealed 17 putative loci in 11 enzyme systems. At the species level, percentage polymorphic loci, mean number of alleles, observed heterozygosity and expected heterozygosity were P=29%, A=1.5 +/- 0.2, Ho=0.007 +/- 0.005 and He=0.065 +/- 0.035, respectively. Peripheral populations were smaller in number and showed decreased levels of genetic diversity relative to central populations. Corrigiola litoralis was highly inbreeding as indicated by a mean FIS of 0.755. Genetic differentiation among populations was high with a mean FST-value of 0.585. Hierarchical F-statistics revealed that genetic variability was partitioned at 57% among sites, 52% among countries and 11% among sites within countries. Genetic distances between French and German populations were 0.08, indicative of considerable differentiation at the intraspecific level. The overall low level of allozyme diversity is attributed to the breeding system and to habitat conditions homogenized by regular flooding. The decrease in diversity from subcentral to peripheral populations is considered to be a result of drift and founder effects during postglacial recolonization. Peripheral populations were characterized by a single fixed allele at locus IDH, thus representing an evolutionarily significant unit.

Journal Article↗

PubMed1995

Extraordinarily high spider densities on islands: flow of energy from the marine to terrestrial food webs and the absence of predation.

Some islands in the Gulf of California support very high densities of spiders. Spider density is negatively correlated with island size; many small islands support 50-200 spiders per m3 of cactus. Energy for these spiders comes primarily from the ocean and not from in situ productivity by land plants. We explicitly connect the marine and terrestrial systems to show that insular food webs represent one endpoint of the marine web. We describe two conduits for marine energy entering these islands: shore drift and seabird colonies. Both conduits are related to island area, having a much stronger effect on smaller islands. This asymmetric effect helps to explain the exceptionally high spider densities on small islands. Although productivity sets the maximal potential densities, predation (by scorpions) limits realized spider abundance. Thus, prey availability and predation act in concert to set insular spider abundance.

Animals↗

PubMed2001

Nonlocal power deposition in inductively coupled plasmas.

Radiofrequency (rf) plasmas exhibit field penetration well beyond the classical skin depth. Two physical explanations are proposed. First, by tracing orbits of electrons through many rf cycles in a cylindrical system, it is shown that numerous ionizing electrons can reach the interior. Second, current-carrying electrons can form a long-lived torus that drifts toward the axis, causing frequently observed interference phenomena. The pressure dependence of this effect does not agree with collisionless theories of anomalous skin effect, but is consistent with the proposed mechanism.

Journal Article↗

PubMed1999

Semimajor axis mobility of asteroidal fragments

The semimajor axes of asteroids up to about 20 kilometers in diameter drift as a result of the Yarkovsky effect, a subtle nongravitational mechanism related to radiation pressure recoil on spinning objects that orbit the sun. Over the collisional lifetimes of these objects (typically, 10 to 1000 million years), orbital semimajor axes can be moved by a few hundredths of an astronomical unit for bodies between 1 and 10 kilometers in mean radius. This has implications for the delivery of multikilometer near-Earth asteroids, because the Yarkovsky drift drives many small main-belt asteroids into the resonances that transport them to the Mars-crossing state and eventually to near-Earth space. Recent work has shown that, without such a drift, the Mars-crossing population would be depleted over about 100 million years, a time scale much smaller than the age of the solar system. Moreover, the Yarkovsky semimajor axis mobility may spread in an observable way the tight semimajor axis clustering of small asteroids produced as a consequence of disruptive collisions.

Journal Article↗

PubMed2005

Inhibition of saccade and vergence eye movements in 3D space.

Inhibitory capacity was investigated by measuring the eye movements of normal subjects asked to fixate a central point, and to suppress eye movements toward visual distracters appearing in the periphery or in depth. Eight right-handed young adults performed such a suppression or distracter task. In different conditions, the distracter could appear at 10 degrees left or right at a distance of 20, 40, or 150 cm (calling for horizontal saccades), or in a central position far or close (calling for convergence or divergence), or 7.5 degrees up or down at 40 or 150 cm (calling for vertical saccades). Eye movements were recorded binocularly with an infrared light eye-movement device. Results showed that (1) suppression performance was not perfect, as the subjects still produced eye movements; (2) errors were distributed unequally in three-dimensional space, with more frequent errors toward distracters calling for convergence, or leftward and downward saccades at a close distance; (3) distracters calling for saccade suppression yielded saccades in the direction of the distracter (that we called prosaccades), and saccades directed away from it (that we called spontaneous antisaccades); (4) for vergence, only distracters calling for convergence yielded errors, which were always promovements; (5) in addition, a small convergent drift was found for convergence distracters. Differences in the errors between saccade and vergence suggest that different inhibitory mechanisms may be involved in the two systems. Spatial left/right, up/down, and close/far asymmetries are interpreted in terms of attentional biases.

Adult↗

PubMed2005

Structure-function relations of parasol cells in the normal and glaucomatous primate retina.

PURPOSE: The purpose of this study was to examine the effect that chronic elevation of intraocular pressure has on the intrinsic and visual response properties of parasol cells in the primate retina. METHODS: A primate model of experimental glaucoma was combined with intracellular recording and staining techniques using an isolated retina preparation. Intrinsic electrical properties were examined by injection of depolarizing and hyperpolarizing currents. Visual responses were studied using drifting and counterphased gratings. Morphologic comparisons were made by injecting recorded cells with Neurobiotin and analyzing them quantitatively with a computer-based neuron reconstruction system. RESULTS: Structurally, parasol cells from glaucomatous eyes had smaller somata and smaller, less complex dendritic arbors, resulting in a significant reduction in total dendrite length and surface area. Functionally, these neurons did not differ from normal in their mean resting membrane potentials, input resistances, or thresholds to electrical activation, but did differ in membrane time constants and spike duration. Parasol cells from both normal and glaucomatous eyes preferred low-spatial-frequency stimuli, but significantly fewer glaucoma-related cells were driven visually-in particular, by patterned stimuli. Glaucomatous cells also did not respond as well to visual stimuli presented at increased temporal frequencies. CONCLUSIONS: Ganglion cells in the glaucomatous eye retain most of their normal intrinsic electrical properties, but are less responsive, both spatially and temporally, to visual stimuli. The reduction in visual responsiveness most likely results from significant changes in dendritic architecture, which affects their level of innervation by more distal retinal neurons.

Animals↗

PubMed2005

[Study on analytical method for alkaloids in Bulbus Fritillariae cirrhosae].

OBJECTIVE: To develop a HPLC-ELSD method for the quantitation of peimisine in Bulbus Fritillariae Cirrhosae. METHOD: HPLC equipped with ELSD was used for the analysis of peimisine in Bulbus Fritillariae Cirrhosae. The separation of peimisine was achieved on a reversed-phase Agilent Hypersil BDS-C18 column with an isocratic phase system consisting of acetonitrile-water-diethylamine (37:63:0. 03) under a flow rate at 1.0 mL x min(-1). Temperature for the detector drift tube was 115 degrees C. The air gas flow rate was 3.0 L x min(-1). RESULT: The analysis of peimissine showed good linearity between 0.031 88 - 1.020 mg x mL(-1). The average recovery was 102.1% (n = 5) with RSD 3.86%. According to the results of the 33 different Bulbus Fritillariae Cirrhosae obtained from various origins, the content limit of peimisine was determined to be 0.0070%. CONCLUSION: The assay was successfully utilized to quantify the major biologically active alkaloid in four species of Bulbus Fritillariae Cirrhosae. The developed method is simple, rapid, accurate and sensitive for determining the content of peimisine in crude Bulbus Fritillariae Cirrhosae.

Alkaloids↗

PubMed2005

[A rapid method for the measurement of major and minor elements in vanadium titanium magnetite sample].

A high resolution (203 eV/Mn Kalpha) portable X-ray fluorescence spectrometer has been developed and the measurement of major and minor elements in vanadium titanium magnetite sample was carried out. An 241Am radioactive source for X-ray excitation, a Si-PIN detector and a 2048 channel analyzer for the measurement of vanadium titanium magnetite direct powder sample were used. The correction methods for interferences, calibration and drift are presented. The method is simply, accurate and rapid. The detection limit is an order of magnitude lower compared with a sealed proportional counter system.

English Abstract↗

PubMed1997

[Zinc chloride smoke pollution. Effects of minimal exposure].

Thirteen patients were exposed to accidental zinc chloride inhalation during an army exercise. Smoke bombs were released in open air. The exposure was modest ranging from "taking a few inhalations" to "5-10 minutes in a house with smoke drifting in through unshuttered windows". Initial symptoms were scanty. All patients received inhalation steroid on admittance followed by i.v. bolus of hydrocortisone. Four patients continued systemic steroid treatment (prednisolone 40 mg with stepwise reduction to zero over four weeks) because exposure was judged significant (> 1 minute of unprotected inhalation). No respiratory symptoms developed within an eight week observation period. However, a gradual decline in pulmonary CO diffusion capacity (to 85% (76-99 of initial capacity) was observed within the first four weeks. It is concluded that a very modest inhalation of zinc chloride smoke may induce prolonged impairment of pulmonary function.

Adult↗

PubMed1998

Validity of oxygen uptake measurements during exercise under moderate hyperoxia.

PURPOSE: The validity of oxygen uptake in hyperoxia (FIO2 = 30%) measured by an automated system (MedGraphics, CPX/D system) was assessed during the simulation of gas exchanges during exercise with a mechanical system and during submaximal exercise by human subjects. METHODS: The simulation system reproduced a stable and accurate VO2 for 30 min (sim-test). This trial was repeated nine times in normoxia and nine times in hyperoxia. Ten subjects also performed two submaximal exercises (55% of normoxic VO2max) on a cycle ergometer at the same absolute power in normoxia and in hyperoxia (ex-test). RESULTS: There was a significant downward drift of the oxygen fraction measurement in hyperoxia (< or = 0.10% for FIO2 and FEO2) during sim-test, but VO2 measurement remained stable in the two conditions. There was also a downward drift of the oxygen fraction measurement in the two conditions (< or = 0.07% for FIO2) during ex-test. VO2 was significantly higher in hyperoxia (+4.6%), and this result was confirmed using a modified Douglas bag method. CONCLUSIONS: These findings show that the CPX/D system is stable and valid for assessing VO2 in moderate hyperoxia.

Adult↗

PubMed2001

Enzymatic acylation of hydroxypropyl cellulose in organic media and determination of ester formation by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy.

Esters were prepared by acylation of hydroxypropyl cellulose with fatty acid catalyzed by immobilized lipase from Candida antarctica in tert-butanol. The nature of the substrates used, the initial water activity of the system, and the molecular weight of the hydroxypropyl cellulose were investigated. Moreover, Fourier transform-infrared (FT-IR) spectroscopy was used for determination of ester content on hydroxypropyl cellulose. Specifically, a linear relationship was established between the peak height assigned to the absorption of the esterified carboxyl groups of the cellulose and the ester content. At optimum reaction conditions, the ester content on the hydroxypropyl cellulose was about 11%.

Acylation↗

PubMed2006

Improvement of bioprocess monitoring: development of novel concepts.

The advancement of bioprocess monitoring will play a crucial role to meet the future requirements of bioprocess technology. Major issues are the acceleration of process development to reduce the time to the market and to ensure optimal exploitation of the cell factory and further to cope with the requirements of the Process Analytical Technology initiative. Due to the enormous complexity of cellular systems and lack of appropriate sensor systems microbial production processes are still poorly understood. This holds generally true for the most microbial production processes, in particular for the recombinant protein production due to strong interaction between recombinant gene expression and host cell metabolism. Therefore, it is necessary to scrutinise the role of the different cellular compartments in the biosynthesis process in order to develop comprehensive process monitoring concepts by involving the most significant process variables and their interconnections. Although research for the development of novel sensor systems is progressing their applicability in bioprocessing is very limited with respect to on-line and in-situ measurement due to specific requirements of aseptic conditions, high number of analytes, drift, and often rather low physiological relevance. A comprehensive survey of the state of the art of bioprocess monitoring reveals that only a limited number of metabolic variables show a close correlation to the currently explored chemical/physical principles. In order to circumvent this unsatisfying situation mathematical methods are applied to uncover "hidden" information contained in the on-line data and thereby creating correlations to the multitude of highly specific biochemical off-line data. Modelling enables the continuous prediction of otherwise discrete off-line data whereby critical process states can be more easily detected. The challenging issue of this concept is to establish significant on-line and off-line data sets. In this context, online sensor systems are reviewed with respect to commercial availability in combination with the suitability of offline analytical measurement methods. In a case study, the aptitude of the concept to exploit easily available online data for prediction of complex process variables in a recombinant E. coli fed-batch cultivation aiming at the improvement of monitoring capabilities is demonstrated. In addition, the perspectives for model-based process supervision and process control are outlined.

Journal Article↗

PubMed2005

A machine learning evaluation of an artificial immune system.

ARTIS is an artificial immune system framework which contains several adaptive mechanisms. LISYS is a version of ARTIS specialized for the problem of network intrusion detection. The adaptive mechanisms of LISYS are characterized in terms of their machine-learning counterparts, and a series of experiments is described, each of which isolates a different mechanism of LISYS and studies its contribution to the system's overall performance. The experiments were conducted on a new data set, which is more recent and realistic than earlier data sets. The network intrusion detection problem is challenging because it requires one-class learning in an on-line setting with concept drift. The experiments confirm earlier experimental results with LISYS, and they study in detail how LISYS achieves success on the new data set.

Algorithms↗

PubMed2007

Language evolution as a Darwinian process: computational studies.

This paper presents computational experiments that illustrate how one can precisely conceptualize language evolution as a Darwinian process. We show that there is potentially a wide diversity of replicating units and replication mechanisms involved in language evolution. Computational experiments allow us to study systemic properties coming out of populations of linguistic replicators: linguistic replicators can adapt to specific external environments; they evolve under the pressure of the cognitive constraints of their hosts, as well as under the functional pressure of communication for which they are used; one can observe neutral drift; coalitions of replicators may appear, forming higher level groups which can themselves become subject to competition and selection.

Biological Evolution↗

PubMedDate not supplied

Genetic diversity in the Lithuanian rural population as illustrated by variation in the ABO and Rh(D) blood groups.

Regional and temporal variations in the ABO and Rh blood group gene frequencies were studied in the rural population of Lithuania. The total material, comprising blood group data for about 37,000 individuals, was subdivided according to place of residence into 401 parishes, 44 administrative districts and 6 ethnolinguistic regions. A significant regional heterogeneity was found. Gene diversity figures were higher than those observed in some other countries when studied at similar hierarchical levels. The gene frequency variation at the district level was compared to expected effects of genetic drift and migration and it was estimated that a migration rate of 5-10% would counter genetic drift in the rural population of Lithuania.

ABO Blood-Group System↗

PubMed1996

Quantitative three-dimensional confocal imaging of the cornea in situ and in vivo: system design and calibration.

A new depth encoding system (DES) is presented, which makes it possible to calculate, display, and record the z-axis position continuously during in vivo imaging using tandem scanning confocal microscopy (TSCM). In order to verify the accuracy of the DES for calculating the position of the focal plane in the cornea both in vitro and in vivo, we compared TSCM measurements of corneal thickness to measurements made using an ultrasonic pachymeter (UP, a standard clinical instrument) in both enucleated rabbit, cat, and human eyes (n = 15), and in both human patients (n = 7). Very close agreement was found between the UP and TSCM measurements in enucleated eyes; the mean percent difference was 0.50 +/- 2.58% (mean +/- SD, not significant). A significant correlation (R = 0.995, n = 15, p < 0.01) was found between UP and TSCM measurements. These results verify that the theoretical equation for calculating focal depth provided by the TSCM manufacturer is accurate for corneal imaging. Similarly, close agreement was found between the in vivo UP and TSCM measurements; the mean percent differences was 1.67 +/- 1.38% (not significant), confirming that z-axis drift can be minimized with proper applanation of the objective. These results confirm the accuracy of the DES for imaging of the cornea both ex vivo and in vivo. This system should be of great utility for applications where quantitation of the three-dimensional location of cellular structures is needed.

Adult↗

PubMed1978

Saccadic system plasticity in humans.

A subject with a medial rectus paresis secondary to a partial third nerve palsy was forced to use the affected eye for six days while the good eye was constantly patched. Saccadic eye movements were carefully measured each day; the grain increased, with a time constant of 0.85 day. The patch was then switched to the paretic eye and the gain decreased, with a time constant of 0.85 day. The patch was then switched to the paretic eye and the gain decreased, with a time constant of 1.54 days. This demonstrated central nervous system plasticity of the pulse and step of neural activity responsible for the generation of saccades in the adult human. In addition to gain changes, postsaccadic drift velocity and saccadic velocity/amplitude relationship alterations during the patching are reported. A major conclusion that can be drawn from analysis fo these data is that the gain changing is accomplished by pulse width changes rather than pulse height (firing frequency), which was not markedly altered.

Eye Movements↗

PubMed2005

Mechanical response analysis and power generation by single-cell stretching.

To harvest useful information about cell response due to mechanical perturbations under physiological conditions, a cantilever-based technique was designed, which allowed precise application of arbitrary forces or deformation histories on a single cell in vitro. Essential requirements for these investigations are a mechanism for applying an automated cell force and an induced-deformation detection system based on fiber-optical force sensing and closed loop control. The required mechanical stability of the setup can persist for several hours since mechanical drifts due to thermal gradients can be eliminated sufficiently (these gradients are caused by local heating of the cell observation chamber to 37 degrees C). During mechanical characterization, the cell is visualized with an optical microscope, which enables the simultaneous observation of cell shape and intracellular morphological changes. Either the cell elongation is observed as a reaction against a constant load or the cell force is measured as a response to constant deformation. Passive viscoelastic deformation and active cell response can be discriminated. The active power generated during contraction is in the range of Pmax= 10(-16) Watts, which corresponds to 2500 ATP molecules s(-1) at 10 k(B)T/molecule. The ratio of contractive to dissipative power is estimated to be in the range of 10(-2). The highest forces supported by the cell suggest that about 10(4) molecular motors must be involved in contraction. This indicates an energy-conversion efficiency of approximately 0.5. Our findings propose that, in addition to the recruitment of cell-contractile elements upon mechanical stimulation, the cell cytoskeleton becomes increasingly crosslinked in response to a mechanical pull. Quantitative stress-strain data, such as those presented here, may be employed to test physical models that describe cellular responses to mechanical stimuli.

3T3 Cells↗