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Results for “systems drift”

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At least 559 records · Page 31Linked to original sources

PubMed2006

High-resolution FMRI at 1.5T using balanced SSFP.

The resolution in conventional BOLD FMRI is considerably lower than can be achieved with other MRI methods, and is insufficient for many important applications. One major difficulty in robustly improving spatial resolution is the poor image quality in BOLD FMRI, which suffers from distortions, blurring, and signal dropout. This work considers the potential for increased resolution with a new FMRI method based on balanced SSFP. This method establishes a blood oxygenation sensitive steady-state (BOSS) signal, in which the frequency sensitivity of balanced SSFP is used to detect the frequency shift of deoxyhemoglobin. BOSS FMRI is highly SNR efficient and does not suffer from image distortions or signal dropout, making this method an excellent candidate for high-resolution FMRI. This study presents the first demonstration of high-resolution BOSS FMRI, using an efficient 3D stack-of-segmented EPI readout and combined acquisition at multiple center frequencies. BOSS FMRI is shown to enable high-resolution FMRI data (1 x 1 x 2 mm(3)) in both visual and motor systems using standard hardware at 1.5 T. Currently, the major limitation of BOSS FMRI is its sensitivity to temporal and spatial field drift.

Brain Mapping↗

PubMed2004

The evolutionary processes of mitochondrial and chloroplast genomes differ from those of nuclear genomes.

This paper first introduces our present knowledge of the origin of mitochondria and chloroplasts, and the organization and inheritance patterns of their genomes, and then carries on to review the evolutionary processes influencing mitochondrial and chloroplast genomes. The differences in evolutionary phenomena between the nuclear and cytoplasmic genomes are highlighted. It is emphasized that varying inheritance patterns and copy numbers among different types of genomes, and the potential advantage achieved through the transfer of many cytoplasmic genes to the nucleus, have important implications for the evolution of nuclear, mitochondrial and chloroplast genomes. Cytoplasmic genes transferred to the nucleus have joined the more strictly controlled genetic system of the nuclear genome, including also sexual recombination, while genes retained within the cytoplasmic organelles can be involved in selection and drift processes both within and among individuals. Within-individual processes can be either intra- or intercellular. In the case of heteroplasmy, which is attributed to mutations or biparental inheritance, within-individual selection on cytoplasmic DNA may provide a mechanism by which the organism can adapt rapidly. The inheritance of cytoplasmic genomes is not universally maternal. The presence of a range of inheritance patterns indicates that different strategies have been adopted by different organisms. On the other hand, the variability occasionally observed in the inheritance mechanisms of cytoplasmic genomes reduces heritability and increases environmental components in phenotypic features and, consequently, decreases the potential for adaptive evolution.

Animals↗

PubMed2001

Snakes and ladders: the role of temporal modulation in visual contour integration.

We investigated temporal aspects of the cortical mechanisms supporting visual contour integration by measuring observers' efficiency at detecting fragmented contours, composed of Gabor micropatterns, embedded in a field of distractor elements. Gabors consisted of a static Gaussian enveloping a sinusoidal carrier which was temporally modulated by motion or counter-phase flicker. The elements forming the path could be oriented either parallel ('snakes') or perpendicular to the contour orientation ('ladders'). Sensitivity to contour structure (estimated by measuring the maximum tolerable element orientation jitter supporting contour detection) was increased when the elements were drifting or flickering. Snakes were more detectable than ladders under all conditions. The increase in sensitivity conferred by drifting carriers was present even when the elements in the same stimulus were drifting at a range of speeds spanning almost three octaves. These results lend further support to the notion that the contour integration system receives separate transient and sustained input.

Discrimination, Psychological↗

PubMed2004

Influence of the ions on the dynamical response of a nematic cell submitted to a dc voltage.

The influence of the ions present in a liquid crystal on the dynamical response of a nematic slab submitted to a dc voltage is studied. The evolution of the system toward the equilibrium state is investigated by solving the continuity equation for the electric charge, taking into account the current of drift and of diffusion. Our analysis shows that the formation of the double layers close to the electrodes strongly modifies the distribution of the electric field across the sample. We evaluate the surface polarization due to the ions movements and the contribution to the anisotropic part of the surface energy having a dielectric origin. We show also that, even if the optical response of the liquid crystal is a slow phenomenon, the distribution of the ionic charge is rather fast. Consequently, the presence of the ions cannot be neglected in the determination of the flexoelectric coefficients when the nematic sample is submitted to a square wave having a period of the order of 1 s.

Journal Article↗

PubMed1996

Fractal dynamics of human gait: stability of long-range correlations in stride interval fluctuations.

Fractal dynamics were recently detected in the apparently "noisy" variations in the stride interval of human walking. Dynamical analysis of these step-to-step fluctuations revealed a self-similar pattern: fluctuations at one time scale are statistically similar to those at multiple other time scales, at least over hundreds of steps, while healthy subjects walk at their normal rate. To study the stability of this fractal property, we analyzed data obtained from healthy subjects who walked for 1 h at their usual, slow, and fast paces. The stride interval fluctuations exhibited long-range correlations with power-law decay for up to 1,000 strides at all 3 walking rates. In contrast, during metronomically paced walking, these long-range correlations disappeared; variations in the stride interval were random (uncorrelated) and nonfractal. The long-range correlations observed during spontaneous walking were not affected by removal of drifts in the time series. Thus the fractal dynamics of spontaneous stride interval are normally quite robust and intrinsic to the locomotor system. Furthermore, this fractal property of neural output may be related to the higher nervous centers responsible for the control of walking rhythm.

Adult↗

PubMed2004

Spatiotemporal tuning of optic flow inputs to the vestibulocerebellum in pigeons: differences between mossy and climbing fiber pathways.

The pretectum, accessory optic system (AOS), and vestibulocerebellum (VbC) have been implicated in the analysis of optic flow and generation of the optokinetic response. Recently, using drifting sine-wave gratings as stimuli, it has been shown that pretectal and AOS neurons exhibit spatiotemporal tuning. In this respect, there are two groups: fast neurons, which prefer low spatial frequency (SF) and high temporal frequency (TF) gratings, and slow neurons, which prefer high SF-low TF gratings. In pigeons, there are two pathways from the pretectum and AOS to the VbC: a climbing fiber (CF) pathway to Purkinje cells (P cells) via the inferior olive and a direct mossy fiber (MF) pathway to the granular layer (GL). In the present study, we assessed spatiotemporal tuning in the VbC of ketamine-anesthetized pigeons using standard extracellular techniques. Recordings were made from 17 optic-flow-sensitive units in the GL, presumably granule cells or MF rosettes, and the complex spike activity (CSA) of 39 P-cells, which reflects CF input. Based on spatiotemporal tuning to gratings moving in the preferred direction, eight GL units were classified as fast units, with a primary response to low SF-high TF gratings (mean = 0.13 cpd/8.24 Hz), whereas nine were slow units preferring high SF-low TF gratings (mean = 0.68 cpd/0.30 Hz). CSA was almost exclusively tuned to slow gratings (mean = 0.67 cpd/0.35 Hz). We conclude that MF input to the VbC is from both fast and slow cells in the AOS and pretectum, whereas the CF input is primarily tuned to slow gratings.

Action Potentials↗

PubMed2005

Vaccine presentations and delivery technologies--what does the future hold?

There is an urgent need to change the presentations and delivery technologies of current vaccines. Until recently, these factors had not been key criteria in the selection of vaccines for program use. Recent and current changes in the field of vaccines and their delivery lead the authors to postulate that a major paradigm shift will take place over the next decade to revolutionize vaccine presentation and delivery in national immunization programs. The programmatic needs for certain vaccine presentations will increasingly dictate elements of vaccine development and manufacture. Over the next decade, an inexorable drift towards firstly, single-dose preparations, and secondly, delivery technologies other than the conventional needle and syringes is anticipated. A unified system capable of delivering multiple antigens as a single dose is urgently needed; however, changing the status quo of vaccine manufacture is not easy. The market predominantly produces vaccines delivered by needle and syringe. Profits for manufacturers from sales to developing countries are marginal at best, and there is little financial incentive to change. Global leaders will need to take bold decisions and begin demanding vaccines which have a presentation that lends them to safer, more practical delivery systems. If a strong enough case can be made to restructure the vaccine manufacturing industry, either through market forces, global bodies, such as the World Health Organization and the United Nations Children's Fund, or both, a dramatic change could be brought about that will make vaccine delivery simpler and safer. A globally coordinated approach to funding research and the introduction of a multiple-antigen, single-dose delivery system is urgently needed. The needs are clear, and this review argues that if the case is presented strongly enough, the resources will be found.

Animals↗

PubMed2000

[Computer system for simulating population dynamic patterns of polygenes and mobile genetic elements upon truncation selection for a quantitative trait].

A computer system was developed for simulation of population dynamics of interacting polygene patterns and mobile genetic elements (MGEs) under selection for a quantitative trait. The system is stochastic (Monte Carlo) and takes into account the main sources of random change in the patterns (recombinations, transpositions, excisions), genetic drift, and determined trends of selection and other genetic processes in a finite population. Using this model, it is possible to analyze the dynamics of many population parameters that cannot be experimentally estimated: frequencies of polygenic alleles, proportions of adaptive and random fixations, average heterozygosities of polygenes and MGEs, coefficient of inbreeding, heritability, etc. In addition, the model can be used to test various hypotheses on polygene-MGE interaction.

Adaptation, Physiological↗

PubMedDate not supplied

[The creation of a new pathology in Paris. The case of deinstitutionalized patients].

The development of attitudes towards the mentally ill, the progress of psychotherapeutic care and medicines, allowed the looking after of psychotic patients outside of the hospital institution, while keeping their social links with their personal environment. The setting up of alternative structures in the context of the communitary psychiatry was supposed to enable the reinsertion of the stabilized psychotic patients. In Paris, the lack of such structures, and the difficult socio-economic context condemn these patients to drifting aimlessly, locked out of any institution, which worsen their pathological state. These "deinstitutionalized" patients cause a serious problem for the Health system.

Community Mental Health Services↗

PubMed1984

Sustained upgaze in coma.

Sustained upgaze is a rare phenomenon that is observed primarily in those patients with coma secondary to cardiac arrest or prolonged hypotension. Because of "selective vulnerability" of the brain, cardiac arrest or prolonged hypotension may produce both cerebral and cerebellar cortical damage sparing the brain stem vestibulo-ocular reflex (VOR) pathways. This selective damage may be responsible for the generation of sustained upgaze. The VORs receive their selective inhibition from the cerebellar flocculus. This inhibition is exerted on only one of the two VOR pathways converging on each extra-ocular muscle, so that total disinhibition of the VOR pathway activities will result in a tonic upward bias. The underlying neuronal mechanism of sustained upgaze appears to be due to total floccular disinhibition resulting in upward drift produced by the biased VOR and the lack of correcting saccades due to cerebral dysfunction releasing the brain stem ocular motor systems from their control.

Cerebellar Cortex↗

PubMedDate not supplied

[Torsional movements of the human eye. I. Torsional movements on inclining the head towards the shoulder].

The characteristics of the torsional eye movements during head tilting were investigated. Different conditions were used in the experiments. The subjects were in sitting and lying positions in the light and in the dark. A new method of recording with the suction device of Yarbus and the simple optical system allowed to have records without some redundant components of movement. This made record processing less complex and more accurate. The torsional drift in the slow phase of the eye movement was found present under any conditions. When being recorded simultaneously both eyes in man were in identical and synchronous movement.

Eye Movements↗

PubMed2006

Effective stochastic dynamics on a protein folding energy landscape.

We present an approach to protein folding kinetics using stochastic reaction-coordinate dynamics, in which the effective drift velocities and diffusion coefficients are determined from microscopic simulation data. The resultant Langevin equation can then be used to directly simulate the folding process. Here, we test this approach by applying it to a toy two-state dynamical system and to a funnellike structure-based (Go-type) model. The folding time predictions agree very well with full simulation results. Therefore, we have in hand a fast numerical tool for calculating the folding kinetic properties, even when full simulations are not feasible. In addition, the local drift and diffusion coefficients provide an alternative way to compute the free energy profile in cases where only local sampling can be achieved.

Chemistry, Physical↗

PubMedDate not supplied

Rural water safety from the source to the on-farm tap.

For those Canadians who live in metropolitan areas, good quality water for domestic use and consumption is readily available, and perhaps taken for granted. However, for over 4 million Canadians who rely on private water supplies, access to water that is safe for consumption and suitable for domestic use is a very real issue. This is also true in the agriculture and agri-food sector. Many of these private water supplies are in rural areas, where water is taken from surface or ground sources. These supplies may be of naturally poor quality, or may have had their quality affected by municipal, industrial, or agricultural activities. Options to protect and enhance the quality of private water supplies include source protection using best management practices (BMPs), source enhancement, and water treatment using innovative small-scale systems. With funding from the Canada-Saskatchewan Agri-Food Innovation Fund, Agriculture and Agri-Food Canada has conducted applied research into effective and affordable BMPs (remote livestock watering, low-drift nozzles for spraying farm chemicals, methods to reduce agro-chemical runoff or leaching, etc.). Source enhancement strategies were studied using aeration for farm ponds or preventive maintenance procedures for ground water wells. Various water treatment technologies were adapted to the small-scale needs of farms, including coagulation, biological sand and biological carbon filtration, membrane filtration using microfilters, nanofilters or reverse osmosis processes, and disinfection systems using chlorination or ultra violet light. Each research project included a technology transfer component, to ensure that the knowledge gained from the research was available to those that needed the information, and to help decision makers address rural water quality problems.

Agriculture↗

PubMedDate not supplied

Blood group variation in the Isle of Lewis.

Blood groups and protein and enzyme polymorphism distributions were studied in 285 residents on the Isle of Lewis, in the Outer Hebrides. As well as gene frequency calculations for individual loci, genetic distance estimations were made and a phylogenetic tree was constructed. The results indicated several major differences from North-west European populations, with high values of R2(CDe), Rz(CDE) and P1. Among protein and enzyme polymorphisms Hp1, EAPA and PGM1(1) had very high frequencies. Genetic distances show Lewis to be unlike both Western and Eastern North European populations, while the phylogenetic tree shows a common, but rather distant, ancestry with Icelanders. This genetic uniqueness of Lewis as a whole is accompanied by a considerable degree of heterogeneity within the island itself, especially in the ABO and Rh systems. Stornoway, with a greater proportion of residents descended from immigrant stock, shows a greater degree of similarity with neighbouring populations. The reasons for both the overall uniqueness and the heterogeneity within Lewis are discussed, but in the absence of a large time-depth and adequate vital records, the various roles of selection, drift and migration in producing them are difficult to establish.

ABO Blood-Group System↗

PubMed2005

A novel continuous subcutaneous lactate monitoring system.

A novel continuous lactate monitoring system has been developed modifying the GlucoDay portable medical device (A. Menarini Diagnostics), already present in the European market, and used to continuously measure glucose levels. Lactate oxidase based biosensors have been developed immobilising the enzyme on nylon net and placing it on a Pt electrode. The biosensor was connected to the portable device provided with a micro-pump and coupled to a microdialysis system. It is capable to record subcutaneous lactate every 3 min. In vitro analytical results confirmed that the sensors respond linearly in the interval of concentration between 0.1 and 10 mmol/L, covering the whole physiological range. During prolonged monitoring periods, the response of the biosensors remained stable, showing a limited drift of 8%, within 60 h. Stability tests are still on route. However, preliminary results have shown a shelf life of about 10 months. In vivo experiments performed on healthy rabbits have demonstrated the good accuracy and reproducibility of the system. A correlation coefficient equal to 0.9547 (N=80) was found, which represents a good correlation between the GlucoDay and the laboratory reference analyser. A 16 h in vivo monitoring on a healthy volunteer has been also performed.

Animals↗

PubMed2005

Clinical experience with the intraparenchymal intracranial pressure monitoring Codman MicroSensor system.

OBJECTIVE: Our main objective was to study the reliability of the Codman MicroSensor (CMS), used for intracranial pressure (ICP) measurements, as it is used in a clinical setting. In particular, the drift from zero was studied. METHODS: The investigation is a prospective study of 128 patients with a need for neurointensive care who have been treated for various diseases. The patients received an intraparenchymal CMS device, and the zero drift was measured at explantation of the sensor. In another 22 patients, the ICP was recorded simultaneously from a ventriculostomy and a CMS, and the values were compared. The general data of complications and pitfalls are collected from close to 1000 CMS devices implanted. RESULTS: The CMS was used, on average, 7.2 +/- 0.4 days per patient. The total time of ICP measurement was 20,040 hours, resulting in at least 7.2 x 10(7) measuring values displayed. The drift from zero was 0.9 +/- 0.2 mm Hg, and no correlation with duration of use was found (P = 0.9, r = 0.002). There was a good correlation between ICP measured by CMS and by ventriculostomy (P < 0.0001, r = 0.79). The average ICP measured with the ventriculostomy was 18.3 +/- 0.3 mm Hg, and with the CMS, it was 19.0 +/- 0.2 mm Hg. A few minor hematomas were identified, and no infections directly connected to the device were observed. Some pitfalls in handling and problems during magnetic resonance imaging investigations are discussed. CONCLUSION: In our hands, the CMS device is reliable and easy to use. The ICP recordings are stable over time, and there is only a minor zero drift. The device is today our standard method for ICP measurements.

Brain↗

PubMed2006

Spreeta-based biosensor assays for endocrine disruptors.

The construction and performance of an automated low-cost Spreeta-based prototype biosensor system for the detection of endocrine disrupting chemicals (EDCs) is described. The system consists primarily of a Spreeta miniature liquid sensor incorporated into an aluminum flow cell holder, dedicated to support a Biacore chip frame, in combination with a simple pressurized air-driven fluid system. During the optimization, a monoclonal antibody (MAb)-based immunoassay for the estrogenic compound bisphenol A (BPA) was used as a model. After the optimization two thyroxine transport protein inhibition assays for thyroid endocrine disruptors were implemented. The average noise of the system for 1 min of baseline was 1.1 microRIU (refractive index units) and it could be operated in the range of 18-22 degrees C with a minimum baseline drift (5-10 microRIU/100 min). Optimum signal to noise ratio (S/N R) was obtained using a flow cell height of 100 microm and a flow rate of 180 microl/min. The sensitivity of the Spreeta-based biosensor inhibition assays implemented (50% inhibition concentration (IC50) of 30.2 nM for BPA using MAb12 and 12.3 and 11.6 nM for thyroxine (T4) using thyroxine-binding globulin (TBG) and recombinant transthyretin (rTTR), respectively) was comparable to the sensitivity previously obtained using a Biacore 3000 (IC50 of 39.9 nM for BPA and 8.6 and 13.7 nM, respectively, for T4). The results indicate that the alternative prototype system can be used in combination with ready-to-use biosensor chip surfaces and it is potentially a useful tool for the bioeffect-related screening of EDCs.

Benzhydryl Compounds↗

PubMed2005

Validity and stability of a computerized metabolic system with mixing chamber.

The aim of this study was to validate a computerized metabolic system with mixing chamber (Oxycon Pro, Erich Jaeger GmbH, Hoechberg, Germany) against the Douglas bag method (1) over a large range of ventilations and (2) for drift during shorter (25-min time trial) and longer (approximately three months) test periods. Eighteen well-trained/elite cyclists performed graded exercise tests, maximal oxygen uptake tests and time trial tests on an electromagnetic braked cycle ergometer. Respiratory variables were measured simultaneously, once or several times in every test by the Oxycon Pro and the Douglas bag method. (1) Overall, oxygen uptake was 0.8 % (0.03 l x min(-1)) lower with the Oxycon Pro than with the Douglas bag method with a coefficient of variation of 1.2 % (n = 802) (p < 0.05). (2) During the time trials, oxygen uptake measured with the Oxycon Pro gradually decreased from 0.5 % (0.02 l) lower than the Douglas bag method at 5 min to 1.0 % (0.05 l) lower at 25 min (p < 0.05). Over the period of three months of testing, oxygen uptake measured with the Oxycon Pro gradually increased from 1.1 % (0.04 l) lower than the Douglas bag method at the start to 0.5 % (0.02 l) lower at the end (p < 0.05). This study demonstrates that a computerized metabolic system with mixing chamber is an accurate system for measuring oxygen uptake. This applies to testing over a large range of ventilations and for stability both during shorter and longer test periods.

Adult↗