Long-range Motion Research Articles

Orientation sensitivity in human visual motion processing

Orientation tuning of receptive fields is well documented in the spatial domain, but considerable variability exists amongst published estimates of orientation sensitivity of motion receptive fields. We used a two-frame motion sequence, in which one frame was binary noise and the other was a horizontally displaced and filtered version of the same noise field, to examine the orientation sensitivity of human motion mechanisms. Initially, orientations orthogonal to the direction of motion were removed from each filtered frame. Observers indicated perceived direction of motion in a single interval, binary choice task. D max was determined for different amounts of removed orientations, and found to remain constant across the removal of energy up to approximately ±60 deg from vertical. In a second experiment, the orientations removed were now parallel to the direction of motion of the stimulus. D max fell as a cosine function with increasing removal of orientation information, in agreement with off-orientation looking or matched filtering predictions. The two experiments show the presence of mechanisms both broadly tuned and more narrowly tuned for orientation. A control experiment introduced an interstimulus interval between the two frames of our motion sequence. Performance on the direction discrimination task was severely degraded, indicating that the original results are not explicable in terms of a feature-tracking or long-range motion process. The presence of both broadly and narrowly tuned mechanisms implies multiple possible solutions to the processing of coherent plaid motion.

Fluctuating-frictionmolecular motors

We show that the correlated stochastic fluctuation of the frictioncoefficient can give rise to long-range directional motion of aparticle performing a Brownian random walk in the constant landscapeof a periodic potential energy. The occurrence of this motionrequires the presence of two additional independent bodiesinteracting with the particle via friction and via the energypotential, respectively, which can move relative to one another.Such a three-body system generalizes the classical Brownian ratchetmechanism, which requires only two interacting bodies. Inparticular, we describe a simple two-level model of afluctuating-friction molecular motor that can be solvedanalytically. In our previous work (Kreuzer M, Marrucci L andPaparo D 2000 J. Nonlinear Opt. Phys. Mater. 9 157)this model was applied, for the first time, in an effort tounderstand the fundamental mechanism of the photoinducedreorientation of dye-doped liquid crystals. Applications of thesame idea to other fields such as molecular biology andnanotechnology can be envisioned. As an example, in this paper wework out a model of the actin-myosin system based on thefluctuating-friction mechanism.

What does the Ternus display tell us about motion processing in human vision?

The Ternus display is a moving visual stimulus which elicits two very different percepts, according to the length of the interstimulus interval (ISI) between each frame of the motion sequence. These two percepts, referred to as element motion and group motion, have previously been analysed in terms of the operation of a low-level, dedicated short-range motion process (in the case of element motion), and of a higher-level, attentional long-range motion process (in the case of group motion). We used a novel Ternus configuration to show that both element and group motion are, in fact, mediated solely by a process sensitive to changes in the spatial appearance of the Ternus elements. In light of this, it appears that Ternus displays tell us nothing about low-level motion processing, implying that previous studies using Ternus displays, for instance those dealing with dyslexia, require reinterpretation. Further manipulations of the Ternus display revealed that the orientation and spatial-frequency discrimination of the process underlying the analysis of Ternus displays is far worse than thresholds for spatial vision. We conclude that Ternus displays are analysed via a long-range motion, or feature-tracking, process, and that this process is distinct from spatial vision.

Multiple regimes of constrained chromosome motion are regulated in the interphase Drosophila nucleus

Background: Increasing evidence indicates specific changes in the three-dimensional organization of chromosomes in the cell nucleus during the cell cycle and development. These changes may be linked to changes in both the coordinated regulation of gene transcription and the timing of chromosome replication. While there is cytological evidence for short-range diffusive motion of chromosomes during interphase, the mechanisms for large-scale chromosome remodeling inside the nucleus remain unknown.Results: Chromosome motion was tracked in Drosophila spermatocyte nuclei by 3D fluorescence microscopy. The Lac repressor/lac operator system was used to label specific chromosomal sites in live tissues, allowing extended observation of chromatin motion in different cell cycle stages. Our results reveal a highly dynamic chromosome organization governed by two types of motion: a fast, short-range component over a 1–2 s time scale and a slower component related to long-range chromosome motion within the nucleus. The motion patterns are consistent with a random walk. In early G2, short-range motion occurs within a small, approximately 0.5 μm radius domain, while long-range motion is confined to a much larger, chromosome-sized domain. Progression through G2 as cells approach meiotic prophase is accompanied by a complete arrest of long-range chromosome motion.Conclusions: Our analysis provides direct evidence for cell cycle-regulated changes in interphase chromatin motion. These changes are consistent with changes in local and long-range constraints on chromosome motility. We propose that dynamic interactions between chromosomes and internal nuclear structures modulate the range and rate of interphase chromatin diffusion and thereby regulate large-scale nuclear chromosome organization.

Application of cross-correlated NMR spin relaxation to the zinc-finger protein CRP2(LIM2): evidence for collective motions in LIM domains.

The solution structure of quail CRP2(LIM2) was significantly improved by using an increased number of NOE constraints obtained from a 13C,15N-labeled protein sample and by applying a recently developed triple-resonance cross-correlated relaxation experiment for the determination of the backbone dihedral angle psi. Additionally, the relative orientation of the 15N(i)-1HN(i) dipole and the 13CO(i) CSA tensor, which is related to both backbone angles phi and psi, was probed by nitrogen-carbonyl multiple-quantum relaxation and used as an additional constraint for the refinement of the local geometry of the metal-coordination sites in CRP2(LIM2). The backbone dynamics of residues located in the folded part of CRP2(LIM2) have been characterized by proton-detected 13C'(i-1)-15N(i) and 15N(i)-1HN(i) multiple-quantum relaxation, respectively. We show that regions having cross-correlated time modulation of backbone isotropic chemical shifts on the millisecond to microsecond time scale correlate with residues that are structurally altered in the mutant protein CRP2(LIM2)R122A (disruption of the CCHC zinc-finger stabilizing side-chain hydrogen bond) and that these residues are part of an extended hydrogen-bonding network connecting the two zinc-binding sites. This indicates the presence of long-range collective motions in the two zinc-binding subdomains. The conformational plasticity of the LIM domain may be of functional relevance for this important protein recognition motif.

Context-sensitive binding by the laminar circuits of V1 and V2: A unified model of perceptual grouping, attention, and orientation contrast

A detailed neural model is presented of how the laminar circuits of visual cortical areas V1 and V2 implement context-sensitive binding processes such as perceptual grouping and attention. The model proposes how specific laminar circuits allow the responses of visual cortical neurons to be determined not only by the stimuli within their classical receptive fields, but also to be strongly influenced by stimuli in the extra-classical surround. This context-sensitive visual processing can greatly enhance the analysis of visual scenes, especially those containing targets that are low contrast, partially occluded, or crowded by distractors. We show how interactions of feedforward, feedback, and horizontal circuitry can implement several types of contextual processing simultaneously, using shared laminar circuits. In particular, we present computer simulations that suggest how top-down attention and preattentive perceptual grouping, two processes that are fundamental for visual binding, can interact, with attentional enhancement selectively propagating along groupings of both real and illusory contours, thereby showing how attention can selectively enhance object representations. These simulations also illustrate how attention may have a stronger facilitatory effect on low contrast than on high contrast stimuli, and how pop-out from orientation contrast may occur. The specific functional roles which the model proposes for the cortical layers allow several testable neurophysiological predictions to be made. The results presented here simulate only the boundary grouping system of adult cortical architecture. However, we also discuss how this model contributes to a larger neural theory of vision that suggests how intracortical and intercortical feedback help to stabilize development and learning within these cortical circuits. Although feedback plays a key role, fast feedforward processing is possible in response to unambiguous information. Model circuits are capable of synchronizing quickly, but context-sensitive persistence of previous events can influence how synchrony develops. Although these results focus on how the interblob cortical processing stream controls boundary grouping and attention, related modelling of the blob cortical processing stream suggests how visible surfaces are formed, and modelling of the motion stream suggests how transient responses to scenic changes can control long-range apparent motion and also attract spatial attention.

Structural and transient internal friction due to thermal expansion mismatch between matrix and reinforcement in Al–SiC particulate composite

Microyield phenomena during thermocycling of Al 7075 alloy/15 vol.% SiC metal-matrix composite due to mismatch of the thermal expansion coefficients of the matrix and the SiC particles are studied over the temperature range from ∼50 to 300 K by means of internal friction techniques. The transient component of the internal friction is measured in the infrasonic frequency range, whereas the structural strain amplitude-independent and strain amplitude-dependent internal friction is investigated at ultrasonic frequencies. Combining the two techniques enables us to follow the variation of the defect structure during thermocycling as well as to evaluate basic contributions to the microyield phenomenon. The following conclusions are drawn: (1) thermal stresses are responsible for creation of fresh, i.e. mobile dislocations, whose density does not differ significantly, for the same temperature, during heating and cooling or in consecutive thermocycles; (2) yielding is much more pronounced during the first cooling from a stress-free state than in the consecutive thermocycles; this pronounced yielding is due to long-range motion of approximately the same amount of fresh dislocations as in consecutive thermocycles; and (3) during thermocycling, the matrix undergoes dynamic strain ageing; its intensity depends strongly on temperature and therefore varies continuously in a thermocycle.

Dielectric Relaxation of Poly(ester-block-amide) Multiblock Copolymers

A series of poly(ester-block-amide)s, composed of crystallized sequences of poly(butylene terephthalate) (PBT) and an amorphous, aliphatic oligoamide (PA 36.6) obtained by the reaction of diamines and dimerized fatty acids, has been synthesized by polycondensation in the melt. The dielectric properties of these multiblock copolymers have been investigated as a function of temperature and PBT/PA ratio in the frequency range from 5·102 to 106 Hz. The melting and glass transition temperatures as well as the degree of crystallinity were characterized by means of DSC. The dielectric properties vary with temperature due to two relaxation processes: a) the β-relaxation process, associated with the local motion of polar groups attached to the soft and hard segments of the copolymer chain, and b) the α-relaxation process, associated with long-range molecular motions near the glass-transition temperature. This behaviour is discussed by means of the Havriliak-Negami analysis.

Evidence for light-induced long-range hydrogen motion in a-Si:H using Raman scattering of a-WO 3

We demonstrate that one can detect minuscule amounts of hydrogen diffusion out of a-Si:H under illumination at room temperature by monitoring the changes in the Raman spectrum of a-WO 3 as a function of illumination. The Staebler–Wronski effect, the light-induced creation of metastable defects in hydrogenated amorphous silicon (a-Si:H), has been one of the major problems that has limited the performance of solar cells based on this material. The recently suggested ‘hydrogen collision model’ can explain many aspects of the Staebler–Wronski effect, but assumes that the photogenerated mobile hydrogen atoms can move a long distance at room temperature. However, light-induced hydrogen motion in a-Si:H has not been experimentally observed at room temperature. We utilized the high sensitivity of the Raman spectrum of electrochromic a-WO 3 to hydrogen insertion to probe the long-range motion of hydrogen at room temperature. We deposited a thin (200 nm) layer of a-WO 3 on top of a-Si:H, and under illumination a change in the Raman spectrum was detected. By comparing the Raman signal changes with those for control experiments where hydrogen is electrochemically inserted into a-WO 3, we can estimate semi-quantitatively the amount of hydrogen that diffuses out of the a-Si:H layer.

Evidence for Long-range Hydrogen Motion in a-Si:H under Room-temperature Illumination Using Raman Scattering of Amorphous Tungsten Oxide Overlayer

ABSTRACTWe demonstrate that one can detect minuscule amounts of hydrogen diffusion out of a-Si:H under illumination at room temperature, by monitoring the changes in the Raman spectrum of amorphous tungsten oxide as a function of illumination. The Staebler-Wronski effect, the light-induce creation of metastable defects in hydrogenated amorphous silicon (a-Si:H), has been one of the major problems that has limited the performance of such devices as solar cells. Recently, Branz suggested the hydrogen collision model that can explain many aspects of the Staebler-Wronski effect. One of the main predictions of this model is that the photogenerated mobile hydrogen atoms can move a long distance at room temperature. However, light-induced hydrogen motion in a-Si:H has not been experimentally observed at room temperature. We utilized the high sensitivity of the Raman spectrum of electrochromic a-WO3 to hydrogen insertion to probe the long-range motion of hydrogen at room temperature. We deposited a thin (200 nm) layer of a-WO3 on top of a-Si:H, and under illumination, a change in the Raman spectrum was detected. By comparing the Raman signal changes with those for control experiments where hydrogen is electrochemically inserted into a-WO3, we can estimate semiquantitatively the amount of hydrogen that diffuses out of the a-Si:H layer.

Alternative perceptual states ‘apparent motion’ and ‘perceived simultaneity’ lead to differences of induced EEG rhythms

An investigation of the cortical response (EEG) to periodically presented stimuli producing an ambiguity between long-range apparent motion and flicker is reported. ERPs to stimulus onsets differed slightly between the two percepts, in accordance with the results of Manning et al. (1988), Selmes et al. (1997). Induced rhythms exhibited a strong increase in induced beta and gamma powers at electrode positions T7 and T8 during the perception of apparent motion in two out of 10 participants. In addition, a small overall increase in alpha power at 12–13 Hz and a decrease in delta power below 3.5 Hz during perceived motion were found. The results indicate that a variety of different neural rhythms are involved in the perception of long-range apparent motion.

Ionic conductivity of silica gels and dynamic properties of their pore liquids studied by impedance spectroscopy and polarized-light spectrofluorimetry

Long-range transport and local molecular motions in the sol/gel system have been studied during an acid-catalyzed sol–gel process in the silicate system. Tetramethoxy orthosilicate (TMOS, Si(OCH 3) 4) was used as an alkoxide precursor. The long-range ionic transport was studied by impedance spectroscopy, and local dynamics of molecules were monitored by polarized-light spectrofluorimetry. A slow, but steady decrease of the ionic conductivity and a similar time-dependence of the reciprocal microviscosity were observed during the sol–gel process. The changes of local and long-range transport properties are ascribed to interactions of molecules of the pore liquid with highly ramified surfaces of pore walls and to geometrical constraints on the freedom of their local motion.

Light-induced long-range hydrogen motion in hydrogenated amorphous silicon at room temperature

We present evidence for long-range hydrogen motion in hydrogenated amorphous silicon (a-Si:H) under room-temperature illumination, by monitoring the changes in the Raman spectrum of an a-WO3 overlayer with illumination. We observe that illumination causes hydrogen to diffuse out of the a-Si:H layer into the a-WO3 layer. This hydrogen motion is observed to saturate after about 30 min when the a-Si:H is illuminated with 15 W/cm2 of the 514.5 nm laser line at room temperature. The amount of hydrogen that diffuses out of the a-Si:H layer is estimated semiquantitatively to be approximately 9×10−4 at. %.

Hindering the light-induced instability in a-Si:H by hydrogen clusters

The effects of hydrogen clusters, relating to the hydrogen effusion peak around 350°C, on the light-induced stability in hydrogenated amorphous silicon (a-Si:H) have been investigated. The hydrogen clusters were removed by increasing the temperature up to 400°C with an increase rate of 12°C/min. After removing the hydrogen clusters, a reduction in hydrogen content and weak Si–Si bond density was observed but the light-induced instability increased by a factor of 4 for the completely degraded state. The increase of the instability is consistent with a model of suppression of the long-range motion of atomic hydrogen by the hydrogen clusters.

Critical Beha vior of a Depinning Dislocation

ABSTRACTThe dynamics of dislocations at yield can be understood within the framew ork of the depinning transition of elastic manifolds in random media. Close to the threshold stress for their long-range motion, the geometry and dynamics of dislocations are characterized by a set of critical exponents. We consider a single flexible dislocation gliding through a random stress field, taking in to account long-range self stresses, and estimate the critical stress where depinning takes place. Simulations of a discretized lattice model confirm the analytical estimate and yield numerical values of the critical exponents which are in agreement with theoretical predictions for an elastic string mo ving on a plane.

Microstructure and hydrogen dynamics in hydrogenated amorphous silicon carbides

Small angle x-ray scattering (SAXS) and deuterium secondary-ion-mass spectrometry (DSIMS) studies of the microstructure and hydrogen dynamics in undoped rf-sputter-deposited (RFS) and undoped and boron-doped electron-cyclotron-resonance-deposited (ECR) hydrogenated amorphous silicon carbides $(a\ensuremath{-}{\mathrm{Si}}_{1\ensuremath{-}x}{\mathrm{C}}_{x}:\mathrm{H})$ are described. In the RFS carbides with $xl~19 \mathrm{at}.%,$ the SAXS indicated that the films contained elongated features larger than 20 nm with preferred orientation, consistent with a residual columnarlike growth of the films. In addition, the SAXS also included a clear nanostructural component consistent with roughly spherical nanovoids $\ensuremath{\sim}1.1 \mathrm{nm}$ in diameter, of total content $0.5l~{C}_{\mathrm{nV}}l~1.0 \mathrm{vol}.%.$ ${C}_{\mathrm{nV}}$ increased by $\ensuremath{\sim}100%$ after isochronal 1-h annealing at 300, 350, and $375\ifmmode^\circ\else\textdegree\fi{}\mathrm{C},$ followed by further annealing for 2--15 hours at $375\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}.$ The growth of ${C}_{\mathrm{nV}}$ was apparently due largely to a $\ensuremath{\sim}20%$ increase in the average void diameter. This growth was noticeably weaker than in similarly fabricated $a\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}.$ In RFS carbides with $xl~3$ at. %, the DSIMS yielded power-law time dependent H diffusion constants ${D(t)=D}_{00}(\ensuremath{\omega}{t)}^{\ensuremath{-}\ensuremath{\alpha}},$ where the dispersion parameter $\ensuremath{\alpha}$ varied from 0 to $\ensuremath{\sim}0.5\ifmmode\pm\else\textpm\fi{}0.1$ among the samples, but was temperature independent at $350\ifmmode^\circ\else\textdegree\fi{}l~Tl~475\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}.$ The moderate values of $\ensuremath{\alpha}$ are consistent with the moderate initial nanovoid contents ${C}_{\mathrm{nV}}l~1.0$ vol. % determined by SAXS. The weak dependence of $\ensuremath{\alpha}$ on T is consistent with the weaker growth of the SAXS with annealing as compared to $a\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}.$ The values of activation energy ${E}_{a}(1000 \mathrm{\AA{}}\mathrm{})$ for a diffusion length $L=1000 \mathrm{\AA{}}\mathrm{}$ among the different films were $\ensuremath{\sim}1.7,$ $\ensuremath{\sim}1.4,$ and $\ensuremath{\sim}0.65 \mathrm{eV}.$ While the first two values are similar to those found in $a\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H},$ the nature of the anomalously low value of $\ensuremath{\sim}0.65 \mathrm{eV}\mathrm{}$ is not clear. In undoped ECR $a\ensuremath{-}{\mathrm{Si}}_{0.86}{\mathrm{C}}_{0.14}:\mathrm{H},$ $D(t)$ exhibited a similar power-law time dependence, but $\ensuremath{\alpha}$ decreased from $\ensuremath{\sim}0.3$ at $350\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ and 400$\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ to $\ensuremath{\sim}0.1$ at $450\ifmmode^\circ\else\textdegree\fi{}\mathrm{C},$ also consistent with a low ${C}_{\mathrm{nV}}.$ Thus, in spite of the high-C content, the behavior of $\ensuremath{\alpha}$ was similar to that of typical $a\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}$ at lower temperatures, where it decreases at $Tl~350\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}.$ However, ${E}_{a}(1000 \mathrm{\AA{}}\mathrm{})$ was an anomalously low $\ensuremath{\sim}1.0 \mathrm{eV}.$ The evolution of the infrared (IR) spectra of both the RFS and ECR films showed that during annealing the Si-bonded H content decreases relative to the C-bonded H content, consistent with a transfer of H from Si- to C-bonded sites or hydrogen evolution. In addition, the reduction in the $2000\ensuremath{-}{\mathrm{cm}}^{\ensuremath{-}1}$ band characteristic of bulk-like Si-H group was much greater than the reduction of the $2100\ensuremath{-}{\mathrm{cm}}^{\ensuremath{-}1}$ band characteristic of surface Si-H, O-Si-H, and C-Si-H groups. Boron doping of the ECR carbides also reduced the bulklike Si-bonded H content, suggesting that it induces nanovoids, consistent with the observed suppression of long-range motion of most of the H and D atoms. However, a small fraction of the H atoms appeared to undergo fast diffusion, reminiscent of the fast diffusion in B-doped $a\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}.$

Polaronic effects on lithium motion in intercalated perovskite lithium lanthanum titanate observed by 7Li NMR and impedance spectroscopy

The long-range and short-range motion of lithium ions into an electrochemically intercalated Li3xLa2/3-xTiO3 (LLTO) sintered pellet has been studied by ac impedance spectroscopy and 7Li solid state nuclear magnetic resonance (NMR). The temperature dependence of the dc conductivity and the intercalation ratio dependence of the chemical shift, the relative intensity of the resonance line, the spin-lattice and the spin-spin relaxation times of 7Li NMR experiments are indicative of polaron formation at the initial stage of intercalation. The total dc conductivity measured in the temperature range 45-600 K and the shape of the impedance diagrams show that after intercalation the conductivity is both ionic and electronic in nature. However for temperatures lower than 300 K the total conductivity is mainly dominated by the electronic one and for temperatures higher than 400 K the total conductivity is dominated by the ionic one. Moreover at low temperatures, when electronic conductivity dominates, the temperature dependence of the conductivity agrees well with a polaron model for conduction in these intercalated oxides. The NMR experiments clearly show that the resonance peak decreases strongly as intercalation occurs. This is explained by a coupling between the electronic and the Li+ nuclear spins leading to an unobservability of some Li+ nuclei in NMR. The other Li+ nuclei, which do not interact directly with the electronic spins, are responsible for the observed NMR signal. If the static effect of the intercalation is weak and leads to a very small chemical shift variation, variable temperature 7Li NMR spin-lattice and spin-spin relaxation measurements show that the presence of electrons acts essentially on the dynamics of the Li+ nuclei through the lattice modification induced by the polaron formation. At the beginning of the intercalation the inverse of the relaxation time T1 of the observed Li+ nuclei decreases by one order of magnitude. At the same time the linewidth of the resonance peak (1/T2) decreases abruptly. The motion of the lithium ions is sharply enhanced. For further intercalation, 1/T1 decreases and the linewidth of the central peak increases indicating that the variations of the relaxation times are mostly governed by the variations of the spectral densities of the Li+ motion. Consequently, the lithium motion decreases gradually as intercalation proceeds. These results are in good agreement with a lattice modification due to polaron formation during intercalation.

Local and long-range hydrogen diffusion in Nb(OH)0.011

The quantum diffusion of hydrogen trapped by oxygen interstitials in niobium is well studied in the temperature range below 150 K. The studies demonstrate that the hydrogen is trapped by the oxygen impurity atoms and that the trapped hydrogen performs a rapid local diffusion process between two nearest-neighbour tetrahedral interstitial sites. With temperatures rising above 150 K, the probability that the hydrogen leaves the trap sites increases. The hydrogen dissociates from its original oxygen trapping atom and carries out a long-range diffusional motion before it is trapped again by an oxygen impurity. We studied this situation by neutron scattering in the temperature range from 100 to 300 K. In our experiment we found a continuous transition from local diffusion at low temperatures to a predominantly long-range diffusion at higher temperatures. This behaviour can successfully be described by a two-state model: one state describes the local diffusion of the hydrogen in the trapped state. The other state describes the long-range diffusion process. Each of these states has a characteristic lifetime, which is also a measure for the probability of the hydrogen to be in this state.

Structural ordering and dynamics of LaH3−x

Abstract The structural arrangements, optic-vibrational density of states, and diffusive motions of hydrogen (and deuterium) in the light-rare-earth hydride LaH 3− x (for small hydrogen-vacancy fractions x ) have been measured by neutron powder diffraction, neutron vibrational spectroscopy, and quasielastic neutron scattering. Diffraction measurements of LaD 3− x indicate preparation-dependent changes in structural ordering below room temperature. Vibrational spectra of both pure and isotopically mixed samples reflect the presence of significant H–H interactions involving the hydrogen located in the octahedral and tetrahedral interstices of the fcc metal sublattice. Quasielastic scattering measurements above room temperature reveal two types of hydrogen motions: a localized ‘rattling’ motion of the octahedrally coordinated hydrogen and a long-range diffusional motion via the hydrogen vacancies. A sample color change from black to copperish-orange observed in the vicinity of the highest hydrogen concentrations likely reflects a transition from optical opacity to optical transparency, as reported for LaH 3− x thin films.

Analyses on the Background of Dynamic Internal Friction and the Modulus Defect during Plastic Deformation

An analysis on the background of dynamic internal friction (DIF) and the modulus defect (ΔG/G) at low frequency during plastic deformation in single crystal specimens is given. The background Q b -1 is considered to be associated with the string vibration of immobile dislocations under a combined action of a unidirectional stress and an alternating stress. It is shown that the frequency dependence of Q b -1 is different from that of the components associated with multiplication and long-range motion of mobile dislocations. Hence Q b -1 can be resolved from the total DIF with measurements of different frequencies. It is found that the resolved Q b -1 is not a constant as usually treated in the literature, but is variable with strain (or time). A detailed analysis shows that the variation of Q b -1 during deformation is associated with the variation of dislocation density. The variation of modulus defect ΔG/G during deformation is shown to be also associated with the variation of dislocation density.