Absence of localization in energy space of a Bloch electron driven by a constant electric force.
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Journal Article↗
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Results for “space driven”
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Real-space observation of current-driven domain wall motion in submicron magnetic wires.
We report direct observation of current-driven magnetic domain wall (DW) displacement by using a well-defined single DW in a microfabricated magnetic wire with submicron width. Magnetic force microscopy visualizes that a single DW introduced in a wire is displaced back and forth by positive and negative pulsed current, respectively. The direct observation gives quantitative information on the DW displacement as a function of the intensity and the duration of the pulsed current. The result is discussed in terms of the spin-transfer mechanism.
Journal Article↗
Hypoxia decreases proteins involved in epithelial electrolyte transport in A549 cells and rat lung.
Fluid reabsorption from alveolar space is driven by active Na reabsorption via epithelial Na channels (ENaCs) and Na-K-ATPase. Both are inhibited by hypoxia. Here we tested whether hypoxia decreases Na transport by decreasing the number of copies of transporters in alveolar epithelial cells and in lungs of hypoxic rats. Membrane fractions were prepared from A549 cells exposed to hypoxia (3% O(2)) as well as from whole lung tissue and alveolar type II cells from rats exposed to hypoxia. Transport proteins were measured by Western blot analysis. In A549 cells, alpha(1)- and beta(1)-Na-K-ATPase, Na/K/2Cl cotransport, and ENaC proteins decreased during hypoxia. In whole lung tissue, alpha(1)-Na-K-ATPase and Na/K/2Cl cotransport decreased. alpha- and beta-ENaC mRNAs also decreased in hypoxic lungs. Similar results were seen in alveolar type II cells from hypoxic rats. These results indicate a slow decrease in the amount of Na-transporting proteins in alveolar epithelial cells during exposure to hypoxia that also occurs in vivo in lungs from hypoxic animals. The reduced number of transporters might account for the decreased transport activity and impaired edema clearance in hypoxic lungs.
Adenocarcinoma, Bronchiolo-Alveolar↗
Uptake of methylchlorpromazine by brush-border membrane vesicles from rat small intestine.
The uptake of methylchlorpromazine (MCP), a quaternary derivative of chlorpromazine, was investigated using brush-border membrane vesicles isolated from rat small intestine. MCP was taken up rapidly by the vesicles, a major part of the uptake being due to binding to the membrane. Saturable MCP binding to the brush-border membrane was inhibited strongly by chlorpromazine, moderately by propantheline and imipramine, and slightly but significantly by methylbenactyzine and mepenzolate. However, choline and tetramethylammonium failed to exhibit any such inhibitory effect. The movement of MCP into the Intravesicular space was driven by an inside-negative transmembrane electrical potential difference (TEPD) induced by NaSCN or valinomycin. There was no effect of TEPD on MCP binding to the brush-border membrane. The data suggested that both rapid binding to the brush-border membrane and inside-negative TEPD, which is present physiologically across the membrane, play a significant role in the absorptive movements of MCP across intestinal epithelium.
Animals↗
Clinical brain MR imaging prescriptions in Talairach space: technologist- and computer-driven methods.
BACKGROUND AND PURPOSE: Variability in patient head positioning may yield substantial interstudy image variance in the clinical setting. We describe and test three-step technologist and computer-automated algorithms designed to image the brain in a standard reference system and reduce variance. METHODS: Triple oblique axial images obtained parallel to the Talairach anterior commissure (AC)-posterior commissure (PC) plane were reviewed in a prospective analysis of 126 consecutive patients. Requisite roll, yaw, and pitch correction, as three authors determined independently and subsequently by consensus, were compared with the technologists' actual graphical prescriptions and those generated by a novel computer automated three-step (CATS) program. Automated pitch determinations generated with Statistical Parametric Mapping '99 (SPM'99) were also compared. RESULTS: Requisite pitch correction (15.2 degrees +/- 10.2 degrees ) far exceeded that for roll (-0.6 degrees +/- 3.7 degrees ) and yaw (-0.9 degrees +/- 4.7 degrees ) in terms of magnitude and variance (P <.001). Technologist and computer-generated prescriptions substantially reduced interpatient image variance with regard to roll (3.4 degrees and 3.9 degrees vs 13.5 degrees ), yaw (0.6 degrees and 2.5 degrees vs 22.3 degrees ), and pitch (28.6 degrees, 18.5 degrees with CATS, and 59.3 degrees with SPM'99 vs 104 degrees ). CATS performed worse than the technologists in yaw prescription, and it was equivalent in roll and pitch prescriptions. Talairach prescriptions better approximated standard CT canthomeatal angulations (9 degrees vs 24 degrees ) and provided more efficient brain coverage than that of routine axial imaging. CONCLUSION: Brain MR prescriptions corrected for direct roll, yaw, and Talairach AC-PC pitch can be readily achieved by trained technologists or automated computer algorithms. This ability will substantially reduce interpatient variance, allow better approximation of standard CT angulation, and yield more efficient brain coverage than that of routine clinical axial imaging.
Adolescent↗
MARDER--multi-axes rotation device for experimental research. A new concept for investigations of the vestibular, oculomotor, and visual systems of humans in three-dimensional space.
A hydraulically driven, digitally servo-controlled multi-axes rotary chair is described. This device generates motion profiles with the subjects head in the center of rotation mainly in order to adequately stimulate the semicircular canals which are sensitive sensors for angular accelerations. This newly developed apparatus allows for motion stimuli which are below the vestibular threshold up to accelerations of 12 rad/s2 (688 degrees/s2) and is thus suitable for a variety of experiments in the field of vestibular, oculomotor, and intersensory research in 3-dimensional space.
Acceleration↗
Psychophysiological responding during script-driven imagery in people reporting abduction by space aliens.
Is recollection of highly improbable traumatic experiences accompanied by psychophysiological responses indicative of intense emotion? To investigate this issue, we measured heart rate, skin conductance, and left lateral frontalis electromyographic responses in individuals who reported having been abducted by space aliens. Recordings of these participants were made during script-driven imagery of their reported alien encounters and of other stressful, positive, and neutral experiences they reported. We also measured the psychophysiological responses of control participants while they heard the scripts of the abductees. We predicted that if "memories" of alien abduction function like highly stressful memories, then psychophysiological reactivity to the abduction and stressful scripts would be greater than reactivity to the positive and neutral scripts, and this effect would be more pronounced among abductees than among control participants. Contrast analyses confirmed this prediction for all three physiological measures (ps < .05). Therefore, belief that one has been traumatized may generate emotional responses similar to those provoked by recollection of trauma (e.g., combat).
Adult↗
Homeostatic expansion versus antigen-driven proliferation: common ends by different means?
The requirements for T-cell proliferation driven by "space-filling" (homeostatic expansion) differ significantly from those for antigen-driven responses. Here we review these differences and discuss their implications for regulation of T-cell responses and the size of the T-cell compartment.
Animals↗
The kinetics of recovery and development of potassium channel inactivation in perfused squid (Loligo pealei) giant axons.
K+ currents were studied at a normal (-69 mV) and at a depolarized (-49 mV) membrane potential in voltage-clamped squid giant axons perfused with 350 mM-K+ and bathed in K+-free artificial sea water containing tetrodotoxin to block the Na+ channels. Steady-state and instantaneous K+ currents were reduced by over 50% at corresponding voltages at the depolarized membrane potential. Instantaneous chord conductance-voltage curves showed that the depolarized membrane potential caused a uniform reduction of K+ conductance across the voltage range under study. The driving force for K+ ions was comparable at both membrane potentials when a short (2 ms) pre-pulse was used to open the K+ channels. When a longer (7.5 ms) pre-pulse was used, the driving force was actually larger at the depolarized membrane potential. The depolarized membrane potential did drive some K+ ions into the periaxonal space. The amount of K+ ions driven into the periaxonal space was estimated by two independent methods, with similar results. The resulting increase of K+ ions in the periaxonal space (10 mM) was about 40 times too small to account for the large reduction in currents in terms of a reduced driving force for K+ ions. The kinetics of recovery and development of inactivation were monitored by repeatedly applying a 7.5 ms test pulse followed by a long conditioning potential. Both recovery and development of inactivation, from the depolarized membrane potential, were described by the sum of two exponential terms plus a constant. The time constant-voltage curves for both phases of inactivation peaked at about -54 mV at 10 degrees C. The time constant of the slow phase of inactivation at -54 mV was about 12.4 s, while the corresponding time constant for the fast phase was about 2.3 s. The slow relaxation had an apparent plateau of about 11 s at more depolarized membrane potentials. Recovery from inactivation was rapid at hyperpolarized membrane potentials. The steady-state inactivation curve of the K+ channel was incomplete in the depolarizing region; and apparent plateau was reached with about 75% of the K+ current inactivated. The temperature sensitivity of both phases of inactivation corresponded to a Q10 of about 3. Elevated external concentrations of K+ ions did not block either phase of the inactivation process, although the kinetics of recovery from inactivation were slightly faster under these conditions.(ABSTRACT TRUNCATED AT 400 WORDS)
Animals↗
Readers' reality-driven and plot-driven analyses in narrative comprehension.
We suggest that when readers experience narratives, their expectations about the likelihood of narrative events are informed by two types of analyses. Reality-driven analyses incorporate real-world constraints involving, for example, time and space; plot-driven analyses incorporate concerns about outcomes that emerge from the plot. We explored the interaction of these two types of analyses in the application of temporal situation models. Participants read stories in which the final episode occurred after a minute time shift (i.e., "A minute later...") or hour time shift (i.e., "An hour later..."). Our experiments assessed participants' judgments and reading times for statements describing the state of events (e.g., the possibility that characters could carry out particular behaviors) following each type of time shift. Experiments 1A and 1B demonstrated that readers are appropriately sensitive to the real concomitants of time shifts. Experiments 2A and 2B demonstrated, even so, that plot-driven preferences modify judgments and reading times away from reality-driven expectations. Our results have implications for the role of the reader in theories of narrative comprehension.
Adult↗
Dynamic long-term anticipation of chaotic states.
Introducing a short time delay into the coupling of two synchronizing chaotic systems, it was shown recently that the driven system may anticipate the driving system in real time. Augmenting the phase space of the driven system, we accomplish anticipation times that are multiples of the coupling delay time and exceed characteristic time scales of the chaotic dynamics. The stability properties of the associated anticipatory synchronization manifold in certain cases turn out to be the same as for identically synchronizing oscillators.
Journal Article↗
Extraction and validation of correlation lengths from interstitial velocity fields using diffusion-weighted MRI.
Magnetic Resonance Imaging methods sensitive to individual molecular displacements (q-space MRI) provide a convenient means of measuring dispersion in complex interstitial spaces. Pressure-driven flow experiments through a water-saturated packed bed phantom have been conducted to prove the feasibility of using q-space MRI to measure the coherence length associated with the interstitial velocity field. The method involves measuring the dependence of the apparent dispersion coefficient on the distance along the mean flow by repeating a small number of pulsed-gradient stimulated-echo experiments with increasing gradient pulse separation times. Assuming homogeneous interstitial flow statistics inside the averaging volume, an integral spatial scale characterizing the Eulerian velocity auto-correlation coefficient is extracted via a stochastic convective model. The validity of the a priori statistical description of interstitial flow is verified by comparing with an independent MRI measurement of the Eulerian velocity field using phase contrast methods in the same phantom with pore-level resolution. The integral length scale obtained via q-space MRI agrees with the mean pore size in the present as well as in similar phantoms found in the literature. This method has direct applicability in the quantification of the interstitial morphology of fluid-saturated porous media with resolution independent of voxel size, assuming "perfectly reflecting pore walls" (no surface relaxation) and no contribution to the MR signal from outside the pore space.
Diffusion Magnetic Resonance Imaging↗
A study of the mechanisms by which potassium moves through brain tissue in the rat.
The flux of K+ produced by electric current across the pia-arachnoid surface of the neocortex of anaesthetized rats has been studied with K+-selective electrodes in a cup at the surface and with flame photometry. The potential differences developed across three regions of the rat brain (neocortex, cerebellum, hippocampus) have been measured as [K+] was altered in fluid at the surface. The experimental results have been related to those that would be expected (i) if K+ moved principally by diffusion in extracellular space and (ii) if current flow through cells makes a significant contribution to K+ transfer. K movement produced by current across the neocortical surface accounted for 0.06 of the transfer of electric charge with small currents in either direction (ca. 5 microA mm-2) and with larger currents out of the tissue. Large currents (ca. 20 microA mm-2) into the tissue produced less K+ movement, but still more than the fraction 0.012 expected for purely extracellular flux. Alternating current pulses (5 Hz) with zero net transfer of charge produced no flux of K+ across the surface, while alternation with unequal durations produced the same effects as the equivalent steady charge transfer. The K+ flux lagged behind the onset and cessation of current with a time constant ca. 45 sec, approximately as expected from calculations with a model of the tissue. A surface-negative potential shift averaging 2 mV was observed when [K+ ]at the brain surface was increased from 3 to 12 mM. The time for development of half of the full potential change was 20 sec, with the solution changes complete in less than 4 sec. These results are inconsistent with the hypothesis that K+ movement through brain tissue occurs principally through intercellular clefts, except where these movements involve very localized gradients. They are consistent with the conclusion that ca. 5 times as much K+ flux passes through cells (probably largely glial cells) as through extracellular space, with fluxes driven by either extracellular voltage or concentration gradients.
Animals↗
Experimental targeting and control of spatiotemporal chaos in nonlinear optics.
We demonstrate targeting and control over spatiotemporal chaos in an optical feedback loop experiment. Different stationary target patterns are stabilized in real time by means of a two dimensional space extended perturbation field driven by an interfaced computer and applied in real space to a liquid crystal display device inserted within a control optical loop. The flexibility of the system in switching between different target patterns is also demonstrated.
Journal Article↗
Arterial pulsation-driven cerebrospinal fluid flow in the perivascular space: a computational model.
This study was conducted to determine whether local arterial pulsations are sufficient to cause cerebrospinal fluid (CSF) flow along perivascular spaces (PVS) within the spinal cord. A theoretical model of the perivascular space surrounding a "typical" small artery was analysed using computational fluid dynamics. Systolic pulsations were modelled as travelling waves on the arterial wall. The effects of wave geometry and variable pressure conditions on fluid flow were investigated. Arterial pulsations induce fluid movement in the PVS in the direction of arterial wave travel. Perivascular flow continues even in the presence of adverse pressure gradients of a few kilopascals. Flow rates are greater with increasing pulse wave velocities and arterial deformation, as both an absolute amplitude and as a proportion of the PVS. The model suggests that arterial pulsations are sufficient to cause fluid flow in the perivascular space even against modest adverse pressure gradients. Local increases in flow in this perivascular pumping mechanism or reduction in outflow may be important in the etiology of syringomyelia.
Arteries↗
Space science. Bumpy ride for data-driven NASA chief.
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News↗
Establishing through-bond connectivity in solids with NMR: structure and dynamics in HC(60)(+).
We present a novel nuclear magnetic resonance experiment for establishing through-bond connectivity in solids using scalar coupling-driven correlation. This method, a variant of the popular double-quantum-filtered correlation spectroscopy experiment in liquids, is robust under fast magic-angle-spinning conditions and in the presence of dynamics. In HC(60)(+), where anisotropic molecular motion renders through-space dipolar-driven correlation ineffective, this through-bond correlation method answers a significant structural question by accurately identifying the direct bond between the protonated sp(3) hybridized carbon site and the sp(2) hybridized cationic site.
Magnetic Resonance Spectroscopy↗
Intrinsic localized modes and chaos in damped driven rotator lattices.
It is shown that intrinsic localized rotational modes (ILRMs) in parametrically driven damped lattices of coupled classical dipole rotators can become chaotic without losing their localized character. Insight into this behavior is obtained by means of a nonlinear stability analysis. Moreover, we discuss a robust scheme for exploiting a spatially extended chaotic state to generate stationary randomly spaced arrays of driven ILRMs, and show that the associated absorption exhibits unusual signatures.
Journal Article↗