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Results for “space driven”

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At least 253 records · Page 14Linked to original sources

PubMed1997

High-pressure replica technique for in vitro imaging of pore morphologies in teeth.

The presence of a natural pore morphology is an essential factor in chemical and mechanical stability of teeth. Common histological methods give only an insufficient picture of the three-dimensional pore distribution in sound or carious teeth. This paper describes a new technique to obtain complete images of the pore structure in teeth or other biological hard tissues. Whole extracted human teeth from orthodontic therapy are mechanically cleaned and organic remnants removed chemically. After being (partly) dried, the teeth are penetrated by a freshly prepared and colored (rhodamine B dye) two-component epoxy resin. The resin is pressed into the pores and cavities of the teeth with pressures of up to 2000 bar in a high-pressure vessel by means of a manually driven piston screw pump for pressure generation. The resin fills all hollow spaces of the tooth down to sizes below 0.1 micron. The pulp and the root canals are cast in massive forms of the hardened epoxy resin, giving an exact replica of the natural structure. The penetrated samples in the form of whole, intact teeth are investigated microscopically so that the pore morphology of the tooth surface, including carious defects, can be examined. The structure of the pores extending into the interior of the tooth can be made visible by dissolution of the hard tissue--for example, in acid solutions. Micro-cavities filled with the resin are observed in thin, ground, and polished cross- and longitudinal sections cut from the teeth. The colored resin induces a high contrast to the dental apatite material. In fluorescence microscopy, only the resin structures are visible.

Animals↗

PubMedDate not supplied

[The meaning of specialization for the nurse in the field of stomas].

This study aimed at knowing and understanding the meanings and perceptions of the enterostomal therapist (ET) about this specialty, using the methodological framework of Social Representation Theory. Three major Units were identified: the ET as a professional, the ET and the client, the ET as a person from an analysis of 12 ET's discourse. In relation to Enterostomal therapy, mainly positive representations were identified among nurses, such as: valorization, recognition, remuneration, promotion, satisfaction, ambition, professional prominence, improvement of care quality and client safety. On the other hand, demands and lack of recognition emerged as negative representations. These representations indicate specialty as an important dimension in professional evolution, a fact that has positively influenced the career of the nurse and that of the Enterostomal Therapist in particular. The ET's construct their existence, write their own history, driven towards autonomous and credible action, which allows them to conquer their space and give a new meaning to care--the basis of Nursing art and science.

Adult↗

PubMed2006

[Basic evaluation of the new pulse sequence for simultaneous acquisition of T1- and T2-weighted images].

A novel pulse sequence that enables simultaneous acquisition of T1-weighted (T1W) and T2-weighted (T2W) images is presented. In this new technique, the inversion recovery (IR) pulse of conventional fast inversion recovery (Fast IR) is replaced with a pulse train that consists of a fast spin echo (FSE) and 180 (y) +90 (x) for driven inversion (DI). By using a shorter TI and independent k-space ordering, the first part of the sequence provides T2W images and the second part provides T1W images, thereby enabling simultaneous acquisition in a single scan time comparable to that of Fast IR. Signal simulation also was conducted, and this was compared with conventional scanning techniques using normal volunteers. In the human studies, both T1W and T2W images showed the same image quality as conventional images, suggesting the potential for this technique to replace the combination of Fast IR and T2W FSE for scan-time reduction.

Adult↗

PubMed1994

A model of intrinsic and driven spindling in thalamocortical neurons.

We add a slow hyperpolarization-activated inward current IH = gHmH (v-vH) to our previous model of rebound bursting (Hindmarsh & Rose Phil. Trans. R. Soc. Lond. B 346, 129-150 (1994a)) to give a four-dimensional physiological model, and a corresponding four-dimensional model of the model. The physiological model generates periodic 'bursts of bursts' or 'spindles' resembling those recorded experimentally in thalamocortical (TC) neurons. The model of the model is simplified to a two-dimensional system having a limit cycle which corresponds to the slow spindle oscillation of the physiological model. Analysis of the stability of this two-dimensional model allows us to divide the parameter space of the slope (gamma mH) and shift (theta mH) parameters of mH infinity (v) into regions in which the model generates spindles or continuous bursting. This enables us to determine the parameter values required for spindling in the physiological model and to explain the experimentally observed effects of noradrenaline. Next we examine whether a cell at a stable equilibrium point can be driven into spindling by applying a sinusoidal input at the resonant frequency. This is done by averaging the equations for the driven model of the model. Analysis of the stability of these averaged equations shows how the regions of the (theta mH, gamma mH) parameter space change when the system is driven by a sinusoidal input. This enables us to choose parameter values for a physiological model of a driven spindle. We show that if the physiological model is modified to include a voltage-dependent time constant for mH, spindles, similar to those of TC cells, can be obtained with a small Ca(2+)-activated K+ current. Finally our knowledge of the form of the bifurcation diagram and the conditions for resonance leads to a new suggestion for the roles of GABAA and GABAB inhibitory postsynaptic potentials when TC cells are driven into spindling by neurons of the nucleus reticularis thalami.

Animals↗

PubMed2005

Temporal properties of inputs to direction-selective neurons in monkey V1.

Motion in the visual scene is processed by direction-selective neurons in primary visual cortex. These cells receive inputs that differ in space and time. What are these inputs? A previous single-unit recording study in anesthetized monkey V1 proposed that the two major streams arising in the primate retina, the M and P pathways, differed in space and time as required to create direction selectivity. We confirmed that cortical cells driven by P inputs tend to have sustained responses. The M pathway, however, as assessed by recordings in layer 4Calpha and from cells with high contrast sensitivity, is not purely transient. The diversity of timing in the M stream suggests that combinations of M inputs, as well as of M and P inputs, create direction selectivity.

Action Potentials↗

PubMed2006

Spin-diffusion approach for relaxation in bi-spaced periodic one-dimensional systems.

A theoretical model for 1H-1H dipolar nuclear spin relaxation for a bi-spaced periodic one-dimensional array of spin 1/2 nuclei has been developed. A diffusion equation is formed for such a system by assuming nearest-neighbor interaction and isotropic random molecular reorientations. Under spin-diffusion conditions (omegatauc>>1), this equation has been solved using Laplace transform for an infinite chain. The results are presented for the boundary conditions described for truncated driven Nuclear Overhauser effect experiments. The solution is further generalized by making the inter-spin spacing as a random variable with a Gaussian distribution.

Nuclear Magnetic Resonance, Biomolecular↗

PubMed1992

Enhanced superoxide production by alveolar macrophages and air-space cells, airway inflammation, and alveolar macrophage density changes after segmental antigen bronchoprovocation in allergic subjects.

Airway inflammation is a principal determinant of airway responsiveness and function in asthma and allergic diseases. Alveolar macrophages (AM) may contribute to inflammation in multiple ways, including release of reactive oxygen species such as superoxide (SO) anion. We hypothesized that SO production by AM increases after segmental bronchoprovocation (SBP) with relevant antigen and contributes to airway injury. Eight ragweed-sensitive subjects with allergic rhinitis were studied by bronchoalveolar lavage and ragweed SBP to determine the SO production and characteristics of cells recruited after antigen challenge. No significant changes in cell numbers or total protein concentration were observed immediately after antigen challenge. Purification (to greater than 94%) of AM on discontinuous gradients of Percoll revealed significantly increased spontaneous and opsonized-zymosan-driven SO production immediately after antigen challenge. Forty-eight hours later, total air-space cells, AM, eosinophils, and total protein concentration were significantly increased in relationship to antigen dose given. Furthermore, both unfractionated air-space cells and purified AM obtained 48 h after antigen challenge released increased amounts of SO anion in response to activator compared with either cells obtained immediately after SBP or those obtained 48 h after saline challenge. In addition, significant increases in high density AM were also seen 48 h after antigen challenge. These data suggest that AM activation occurs immediately after antigen challenge, and that the late airway response to antigen is characterized by the appearance of high density AM, which have potentiated SO release. The increased oxidative burden thereby produced may contribute to increased airway injury.

Adult↗

PubMed1975

Possible mechanisms of the efflux of glutamate from kidney mitochondria generated by the activity of mitochondrial glutaminase.

The transport of glutamate across the inner membrane of kidney mitochondria and the influx of glutamine into the mitochondria was studied using an oxygen electrode, the swelling technique and by continous recording of the activity of the mitochondrial glutaminase by an NH4+-sensitive electrode. It is well known that the enzyme is activated by inorganic phosphate and strongly inhibited by glutamate. 1. Avenaciolide, Bromocresal purple and Bromothymol blue inhibited the respiration of the mitochondria almost completely in the presence of glutamate as substrate but not in the presence of glutamine. Production of aspartate during the oxidation of glutamine was not significantly inhibited by avenaciolide but it was markedly suppressed by Bomocresol purple and Bromothymol blue. 2. Swelling of kidney mitochondria in an isosmotic solution of glutamine and ammonium phosphate was not inhibted by avenaciolide or Bromocresol purple indicating that these substances do not inhibit the penetration of the mitochondrial membrane by glutamine or phosphate. 3. The activity of the mitochondrial glutaminase was strongly inhibited by avenaciolide or Bromocresol purple in the presence of inhibitos of respiration or an uncoupler but not in ther absence. Experimental data suggest that this was caused by the inhibition of glutamate efflux. The addition of a detergent removed this inhibition. On the basis of these observations it was concluded that two mechanisms exist which enable glutamate to leave the inner space of kidney mitochondria: (a) an electrogenic efflux coupled to the respiration-driven proton translocation and the presence of a membrane potential (positive outside) and (b) an electroneutral glutamate-hydroxyl antiporter which is inhibted by avenaciolide and which operates in both directions. Our observations do not support the existence of the electrogenic glutamine-glutamate antiporter or glutamate-aspartate exchange in the mitochondria studied.

Animals↗

PubMed1989

Glutamine transport by rat basolateral membrane vesicles.

Glutamine, a neutral amino acid, is unlike most amino acids, has two amine moieties which underlies its importance as a nitrogen transporter and a carrier of ammonia from the periphery to visceral organs. The gastrointestinal tract utilizes glutamine as a respiratory substrate. The intestinal tract receives glutamine from the luminal side and from the arterial side through the basolateral membranes of the enterocyte. This study characterizes the transport of glutamine by basolateral membrane vesicles of the rat. Basolateral membranes were prepared by a well validated technique of separation on a percoll density gradient. Membrane preparations were enriched with Na+/K+-ATPase and showed no 'overshoot' phenomena with glucose under sodium-gradient conditions. Glutamine uptake represented transport into the intravesicular space as evident by an osmolality study. Glutamine uptake was temperature sensitive and driven by an inwardly directed sodium gradient as evident by transient accumulation of glutamine above the equilibrium values. Kinetics of glutamine uptake under both sodium and potassium gradients at glutamine concentrations between 0.01 and 0.6 mM showed saturable processes with Vmax of 0.39 +/- 0.008 and 0.34 +/- 0.05 nmol/mg protein per 15 s for both sodium-dependent and sodium-independent processes, respectively. Km values were 0.2 +/- 0.01 and 0.55 +/- 0.01 mM, respectively. pH optimum for glutamine uptake was 7.5. Imposition of negative membrane potential by valinomycin and anion substitution studies enhanced the sodium-dependent uptake of glutamine suggesting an electrogenic process, whereas the sodium-independent uptake was not enhanced suggesting an electroneutral process. Other neutral amino acids inhibited the initial uptake of glutamine under both sodium-dependent and sodium-independent conditions. We conclude that glutamine uptake by basolateral membranes occurs by carrier-mediated sodium-dependent and sodium-independent processes. Both processes exhibit saturation kinetics and are inhibited by neutral amino acids. The sodium-dependent pathway is electrogenic whereas the sodium-independent pathway is electroneutral.

Animals↗

PubMedDate not supplied

Using NMR displacement imaging to characterize electroosmotic flow in porous media.

Pulsed field gradient nuclear magnetic resonance (PFG-NMR) and NMR imaging were used to study temporal and spatial domains of an electrokinetically-driven mobile phase through open and packed segments of capillaries. Characteristics like velocity distribution and an asymptotic dispersion are contrasted to viscous flow behavior. We show that electroosmotic flow in microchannel geometries can offer a significant performance advantage over the pressure-driven flows at comparable Peclét numbers, indicating that velocity extremes in the pore space of open tubes and packed beds are drastically reduced. An inherent problem of capillary electrochromatography that we finally address is the existence of wall effects when in the general case the surface zeta-potentials of the capillary inner wall and the adsorbent particles are different. Using dynamic NMR microscopy we were able resolve this systematic velocity inequality of the flow pattern which strongly influences axial dispersion and may be responsible for long time-tails of velocity distribution in the mobile phase.

Magnetic Resonance Imaging↗

PubMed2001

A laminated, flex structure for electronic transport and hybridization of DNA.

We have developed the first prototypes of a three-dimensional, electrophoretically driven microlaboratory for the analysis of proteins and DNA. By selecting the appropriate spacing and geometrical configuration, oligonucleotides were transported, in a controlled, rapid fashion, by electrophoresis in free-space. Transport efficiencies over 2 mm distances exceeded 70%. Electrodes of similar design were combined with an electronically addressed DNA hybridization chip to form a fully electrophoretic microlaboratory. In this instance, gold-plated copper electrodes were patterned on a 2 mil thick polyimide substrate. This polyimide layer was stiffened with 20 mil of polyimide to provide support for flip-chip bonding of our standard 100-site Nanochip. This composite structure illustrated three-dimensional transport of target oligonucleotides, through a via in the polyimide, along a series of electrodes and onto the diagnostic chip. Upon reaching the diagnostic chip, electronic hybridization was performed for a competitive reverse dot blot assay. The electronic assay showed a specific to nonspecific ratio in excess of 20:1. These results suggested that this type of structure might be of practical consequence with the development of a microlaboratory for biowarfare applications.

Base Sequence↗

PubMed2004

Nicotinic acid adenine dinucleotide phosphate potentiates neurite outgrowth.

Ca(2+) regulates a spectrum of cellular processes including many aspects of neuronal function. Ca(2+)-sensitive events such as neurite extension and axonal guidance are driven by Ca(2+) signals that are precisely organized in both time and space. These complex cues result from both Ca(2+) influx across the plasma membrane and the mobilization of intracellular Ca(2+) stores. In the present study, using rat cortical neurons, we have examined the effects of the novel intracellular Ca(2+)-mobilizing messenger nicotinic acid adenine dinucleotide phosphate (NAADP) on neurite length and cytosolic Ca(2+) levels. We show that NAADP potentiates neurite extension in response to serum and nerve growth factor and stimulates increases in cytosolic Ca(2+) from bafilomycin-sensitive Ca(2+) stores. Simultaneous blockade of inositol trisphosphate and ryanodine receptors abolished the effects of NAADP on neurite length and reduced the magnitude of NAADP-mediated Ca(2+) signals. This is the first report demonstrating functional NAADP receptors in a mammalian neuron. Interplay between NAADP receptors and more established intracellular Ca(2+) channels may therefore play important signaling roles in the nervous system.

Animals↗

PubMed1994

The lumazine synthase/riboflavin synthase complex of Bacillus subtilis. X-ray structure analysis of hollow reconstituted beta-subunit capsids.

The lumazine synthase/riboflavin synthase complex of Bacillus subtilis consists of an icosahedral capsid of 60 beta subunits enclosing a triplet of alpha subunits. An X-ray structure of 0.32 nm resolution has been obtained for the icosahedral capsid of the native alpha 3 beta 60 complex [Ladenstein, R., Schneider, M., Huber, R., Bartunik, H. D., Wilson, K., Schott, K. & Bacher, A. (1988) J. Mol. Biol. 203, 1045-1070]. beta subunits were isolated after denaturation of the alpha 3 beta 60 complex and were subsequently reconstituted in a ligand-driven reaction yielding artifactual, hollow beta 60 capsids with icosahedral symmetry. Hexagonal crystals (space group P6(3)22) of the reconstituted capsids diffracted X-rays to a resolution of 0.32 nm. Crystallographic intensity data were obtained using synchrotron radiation. Freeze-etched electron-microscopic images and rotation function calculations showed that the hexagonal crystal forms of the artifactual beta 60 capsids and the native alpha 3 beta 60 complex are isomorphous. Orientation and translation parameters of the beta-subunit model were refined by XPLOR rigid-body refinement. The electron-density map was improved by cyclic icosahedral averaging and phase extension from 0.5-0.32 nm resolution. The beta-subunit structure was partially refined by energy minimization and crystallographic refinement (XPLOR) assuming strict icosahedral symmetry (final R factor 30.9% for data at 0.8-0.32 nm resolution). The topology and chain folding of the beta subunits in the artifactual beta 60 capsid are similar to the native alpha 3 beta 60 enzyme. Structural features of the substrate-binding site and the binding of the substrate-analogous ligand 5-nitro-6-ribitylamino-2,4(1H,3H)-pyrimidinedione are discussed. Ligand binding occurs at the pentamer interfaces and includes van der Waals' interactions and hydrogen bonding. The binding pocket shows a hydrophobic region which accomodates the pyrimidinedione ring and a hydrophilic region to which the ribityl side chain binds. Most amino acid residues involved in the active site are conserved as shown by sequence comparisons with the putative lumazine-synthase genes of Escherichia coli and Photobacterium leiognathi. In the final electron-density map, a residual density feature was tentatively assigned to a bound phosphate ion which mimics the binding of the second substrate, 3,4-dihydroxy-2-butanone 4-phosphate. This putative phosphate-binding site involves a highly conserved amino acid sequence containing three basic residues.

Bacillus subtilis↗

PubMed1987

Na+-dependent transport of taurine by membrane vesicles of neuroblastoma x glioma hybrid cells.

The transport of taurine into membrane vesicles prepared from neuroblastoma x glioma hybrid cells 108CC5 was studied. A great part of the taurine uptake by the membrane preparation is due to the transport into an osmotically sensitive space of membrane vesicles. Taurine uptake by membrane vesicles is an active transport driven by the concentration gradient of Na+ across the membrane (outside concentration greater than inside). The Km value of 36 microM for Na+-dependent taurine uptake indicates a high-affinity transport system. The rate of taurine transport by the membrane vesicles is enhanced by the K+ gradient (inside concentration greater than outside) and the K+ ionophore valinomycin. Taurine transport is inhibited by several structural analogs of taurine: hypotaurine, beta-alanine, and taurocyamine. All these results indicate that the taurine transport system of the membrane vesicles displays properties almost identical to those of intact neuroblastoma X glioma hybrid cells.

Animals↗

PubMed2001

Transition path sampling: throwing ropes over rough mountain passes, in the dark.

This article reviews the concepts and methods of transition path sampling. These methods allow computational studies of rare events without requiring prior knowledge of mechanisms, reaction coordinates, and transition states. Based upon a statistical mechanics of trajectory space, they provide a perspective with which time dependent phenomena, even for systems driven far from equilibrium, can be examined with the same types of importance sampling tools that in the past have been applied so successfully to static equilibrium properties.

Journal Article↗

PubMed2001

Shift changes, updates, and the on-call architecture in space shuttle mission control.

In domains such as nuclear power, industrial process control, and space shuttle mission control, there is increased interest in reducing personnel during nominal operations. An essential element in maintaining safe operations in high risk environments with this 'on-call' organizational architecture is to understand how to bring called-in practitioners up to speed quickly during escalating situations. Targeted field observations were conducted to investigate what it means to update a supervisory controller on the status of a continuous, anomaly-driven process in a complex, distributed environment. Sixteen shift changes, or handovers, at the NASA Johnson Space Center were observed during the STS-76 Space Shuttle mission. The findings from this observational study highlight the importance of prior knowledge in the updates and demonstrate how missing updates can leave flight controllers vulnerable to being unprepared. Implications for mitigating risk in the transition to 'on-call' architectures are discussed.

Communication↗

PubMed1994

Artifact-free application of drugs into the avian endolymphatic space.

A push-pull system is described that allows artifact-free application of drugs into very small volumes such as, e.g., the endolymphatic space of the inner ear. The system consists of two syringes, the pistons of which are fixed together and driven by an Oriel motordrive. The syringes are connected to the pipette holders and microcapillaries by PVC tubes. One capillary is used to expel a certain volume, whilst the other one aspirates the same volume. A balanced exchange of fluids within a given space without an overall change in volume is therefore possible.

Action Potentials↗

PubMed2004

Mixing, volatile loss and compositional change during impact-driven accretion of the Earth.

The degree to which efficient mixing of new material or losses of earlier accreted material to space characterize the growth of Earth-like planets is poorly constrained and probably changed with time. These processes can be studied by parallel modelling of data from different radiogenic isotope systems. The tungsten isotope composition of the silicate Earth yields a model timescale for accretion that is faster than current estimates based on terrestrial lead and xenon isotope data and strontium, tungsten and lead data for lunar samples. A probable explanation for this is that impacting core material did not always mix efficiently with the silicate portions of the Earth before being added to the Earth's core. Furthermore, tungsten and strontium isotope compositions of lunar samples provide evidence that the Moon-forming impacting protoplanet Theia was probably more like Mars, with a volatile-rich, oxidized mantle. Impact-driven erosion was probably a significant contributor to the variations in moderately volatile element abundance and oxidation found among the terrestrial planets.

Journal Article↗