Recent Dynamic Models Research Articles

Effects of instruction type and boredom proneness in vigilance: implications for boredom and workload.

The present study examined the effects of instruction type and boredom proneness (BP) on vigilance performance, workload, and boredom. Subjects completed the Boredom Proneness Scale and were assigned to high and low groups based on their scores. They then monitored a VDT for critical signals. Half the subjects were instructed to detect "critical" flickers (detection emphasis), and the remaining subjects were instructed to relax but to respond to any flickers observed (relaxation emphasis). Subjects also provided pre- and postvigil ratings of workload, stress, and boredom. A performance decrement was observed for all conditions. Low-BP subjects outperformed high-BP subjects and reported less boredom. Thus the results from the present study provide evidence for the long-sought, elusive link between trait boredom and performance in vigilance. In addition, subjects who received relaxation-emphasis instructions reported lower workload, frustration, and stress for the vigil than did those receiving detection-emphasis instructions. These results are discussed in terms of a recent dynamic model of stress as it relates to sustained attention.

Coarticulation and the accented/unaccented distinction: evidence from jaw movement data

Both coproduction and the more recent task dynamic models ofspeech production have advanced an explanation for certain kinds of vowel shortening in terms of coarticulatory overlap between neighbouring speech sounds. In this study, the extent to which coarticulatory overlap between opening and closing jaw movement gestures accompanies the accented/unaccented vowel distinction is considered. The authors begin by quantifying the salient differences between truncation, which is caused by a close phasing of articulatory gestures, and linear rescaling of jaw movements. In both truncation and linear rescaling, the duration and amplitude of movement decrease, and the peak velocities remain the same: the main differences occur in the resulting shape of the waveform between the temporal location of the peak velocities in the opening and closing gestures. Three parameters that encode these shape differences are then applied to the speech movements produced by three subjects. This study shows that the accented/unaccented differences are more appropriately modelled as a consequence of truncation, than linear rescaling.

The implications of picritic lavas for the mantle sources of terrestrial volcanism

The success of recent dynamic models of adiabatic partial melting of the Earth's mantle has lead to an increasing acceptance that much of the compositional spectrum of terrestrial basalts can be explained in terms of variations in the physical parameters of melting of a common anhydrous-lherzolite mantle source. A comparison of normalized compositions of terrestrial picritic lavas with the results of recent lherzolite melting experiments indicates, however, that picritic magmas from intraplate hot spots, such as Hawaii, can not be derived from the mantle source which gives rise to the picritic magmas associated with mid-ocean ridges or subduction zones. MORB picritic magmas could have equilibrated with a lherzolite residue wose composition resembles that of lherzolite xenoliths. Picritic magmas associated with subduction zones have compositions which range from those similar to MORB picrites to the ankaramitic picrites of the southwest Pacific, which appear to have equilibrated with a more-depleted harzburgite residue. The mantle sources for intraplate picritic magmas, on both the continents and in the oceans, are richer in Fe and Ti than the lherzolite mantle source which gives rise to the picritic magmas associated with plate boundaries. Moreover, the major and trace element compositions of hot spot picrites, such as those of Hawaii, present a paradox. The behaviour of the heavy rare earth elements has convinced geochemists (Hofmann et al., 1984; Frey and Roden, 1987) that residual garnet remains in their mantle source, yet melting experiments on both Hawaiian picrites (Eggins, 1992a) and model lherzolite mantles (Hirose and Kushiro, 1993) indicate that magmas of Hawaiian picrite composition have equilibrated with a Ca and Al-depleted harzburgite residue. The Hawaiian paradox is unresolved at present, but may indicate that garnet-equilibrated magmas have been forced to re-equilibrate with depleted harzburgite mantle or that the breakdown of amphibole in their mantle source resulted in melting under hydrous conditions. Alternatively, the existence of the paradox could be interpreted as evidence that hot spot picritic magmas are derived from piclogitic rather than lherzolitic mantle source regions (Anderson, 1984).

The implications of picritic lavas for the mantle sources of terrestrial volcanism

The success of recent dynamic models of adiabatic partial melting of the Earth's mantle has lead to an increasing acceptance that much of the compositional spectrum of terrestrial basalts can be explained in terms of variations in the physical parameters of melting of a common anhydrous-lherzolite mantle source. A comparison of normalized compositions of terrestrial picritic lavas with the results of recent lherzolite melting experiments indicates, however, that picritic magmas from intraplate hot spots, such as Hawaii, can not be derived from the mantle source which gives rise to the picritic magmas associated with mid-ocean ridges or subduction zones. MORB picritic magmas could have equilibrated with a lherzolite residue wose composition resembles that of lherzolite xenoliths. Picritic magmas associated with subduction zones have compositions which range from those similar to MORB picrites to the ankaramitic picrites of the southwest Pacific, which appear to have equilibrated with a more-depleted harzburgite residue. The mantle sources for intraplate picritic magmas, on both the continents and in the oceans, are richer in Fe and Ti than the lherzolite mantle source which gives rise to the picritic magmas associated with plate boundaries. Moreover, the major and trace element compositions of hot spot picrites, such as those of Hawaii, present a paradox. The behaviour of the heavy rare earth elements has convinced geochemists (Hofmann et al., 1984; Frey and Roden, 1987) that residual garnet remains in their mantle source, yet melting experiments on both Hawaiian picrites (Eggins, 1992a) and model lherzolite mantles (Hirose and Kushiro, 1993) indicate that magmas of Hawaiian picrite composition have equilibrated with a Ca and Al-depleted harzburgite residue. The Hawaiian paradox is unresolved at present, but may indicate that garnet-equilibrated magmas have been forced to re-equilibrate with depleted harzburgite mantle or that the breakdown of amphibole in their mantle source resulted in melting under hydrous conditions. Alternatively, the existence of the paradox could be interpreted as evidence that hot spot picritic magmas are derived from piclogitic rather than lherzolitic mantle source regions (Anderson, 1984).

Stochastic model of chemoattractant receptor dynamics in leukocyte chemosensory movement.

Mammalian white blood cells are known to bias the direction of their movement along concentration gradients of specific chemical stimuli, a phenomenon called chemotaxis. Chemotaxis of leukocyte cells is central to the acute inflammatory response in living organisms and other critical physiological functions. On a molecular level, these cells sense the stimuli termed chemotactic factor (CF) through specific cell surface receptors that bind CF molecules. This triggers a complex signal transduction process involving intracellular biochemical pathways and biophysical events, eventually leading to the observable chemotactic response. Several investigators have shown theoretically that statistical fluctuations in receptor binding lead to "noisy" intracellular signals, which may explain the observed imperfect chemotactic response to a CF gradient. The most recent dynamic model (Tranquillo and Lauffenburger, J. Math. Biol. 25, 229-262. 1987) couples a scheme for intracellular signal transduction and cell motility response with fluctuations in receptor binding. However, this model employs several assumptions regarding receptor dynamics that are now known to be oversimplifications. We extend the earlier model by accounting for several known and speculated chemotactic receptor dynamics, namely, transient G-protein signaling, cytoskeletal association, and receptor internalization and recycling, including statistical fluctuations in the numbers of receptors among the various states. Published studies are used to estimate associated constants and ensure the predicted receptor distribution is accurate. Model analysis indicates that directional persistence in uniform CF concentrations is enhanced by increasing rate constants for receptor cytoskeletal inactivation, ternary complex dissociation, and binary complex dissociation, and by decreasing rate constants for receptor internalization and recycling. For most rate constants, we have detected an optimal range that maximizes orientation bias in CF gradients. We have also examined different desensitization and receptor recycling mechanisms that yield experimentally documented orientation behavior. These yield novel insights into the relationship between receptor dynamics and leukocyte chemosensory movement behavior.

Comparison between two recent large-signal dynamic DFB laser models

Two large-signal dynamic DFB laser models have been developed recently: the transmission-line laser model and the power matrix method. The paper presents quantitative comparisons between these two models and demonstrates good agreement between results for L—I characteristics, transient response, time-resolved spectra and spatial hole-burning of the longitudinal carrier density. The models are also compared in terms of applicability.

The effect of two dimensions on the atomic vibrations at the (0001) graphite surface

The recent dynamical model suggested by the present authors is modified to explain the observed experimental results on atomic vibrations of carbon atoms perpendicular to (0001) graphite surface ((uz2)T) in the temperature range 0-300 K. The model also yields the detailed calculated values of (uz2)T given by Firey et al. (1983). It is found that in both cases the atomic vibrations are predominantly two dimensional in character.

Black holes or dark clusters in M31 and M32?

Recent spectroscopic data and dynamical modeling indicate the presence of dark matter within the nuclei of M31 and M32. If these nuclei do not contain massive black holes, the most likely alternative form for the dark matter is a cluster of low-mass stars or degenerate remnants. Here it is shown that simple physical considerations place lower limits of about 0.1 arcsec on the half-mass radii of such clusters if they have survived in their present form over much of the age of the universe. Therefore, Space Telescope observations should rule out such clusters, or resolve them. 42 references.

Atomic oxygen in the lower thermosphere

We measured in thermal emission the 63‐μm line due to thermospheric atomic oxygen O(3P), using a far‐infrared spectrometer on a balloon platform at 37 km altitude over Palestine, Texas (32°N), on June 20, 1983. From measurements of the equivalent width of this line at two elevation angles, we find a weak angular dependence: the equivalent width increases by a factor of 1.5 ±0.3 as the angle decreases from +30° to +1°. Since the optical depth of the O(3P) line is large, we cannot directly convert the measured line intensity to a column abundance. Instead, we interpret the measurements in terms of radiative transfer through a 16‐layer atmosphere extending to 200 km. We use a model atmosphere for summer at 30°N, with an exospheric temperature of 1300 K, including (1) an assumed daytime atomic oxygen abundance profile constructed from recent chemical and dynamical models and (2) a water vapor abundance profile constructed from recent experimental and model results. For this assumed O(3P) vertical profile shape we determine from our spectra at two elevation angles a multiplicative scaling factor of 0.8, with an altitude‐dependent uncertainty. In the best‐determined layer the uncertainty in the multiplier is ±0.2 at 119 km. The model‐dependent peak atomic oxygen density is 3.6 (±1.9) × 1011 cm−3 at an altitude of about 101 km.

Temperature Dependence of the Anharmonic Debye-Waller Factor for Cubic Metals

Temperature dependence of the anharmonic Debye-Waller factor for some cubic metals are calculated by employing our recent dynamical model. Willis anharmonic approach has been followed to estimate the effect of anharmonic terms in the crystal potential. A comparative study of the computed values and the experimental data in terms of the Debye-Waller temperature parameter Y and the X-ray Debye temperature \(\varTheta_{M}\), reveal the fact that the anharmonic consideration in the crystal potential has greatly improved the results compared with those due to the harmonic and quasi-harmonic approximations.

Lattice vibrations and thermophysical properties of aluminium

An equilibrium condition which preserves the crystal stability is derived by incorporating the Fermi, exchange and correlation energy of conduction electrons perturbed under ionic motion. The condition in conjunction with a recent dynamical model for f.c.c. metals is employed to study the phonon dispersion and temperature dependence of the Debye temperature, the Debye-Waller factor, the characteristic Debye temperature, the mean square displacement of the atoms and the Gruneisen parameter of Al. The theoretical results are in good agreement with the experimental values.

Crystal dynamics of face centered cubic cobalt

An equilibrium condition which preserves the crystal stability is derived. This condition in conjunction with recent dynamical model is employed to study the crystal dynamics of f.c.c. Co. The agreement between theory and experiment is good.

Nuclear structure studies in the medium mass (A ≈ 70) region

The in-beam γ-ray studies on several nuclei in A ≈ 70 region, have revealed highly collective band structures of the following types: 1) ground state band, 2) one or two even spin positive parity bands with 8 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> as band head, 3) odd and even spin negative parity bands, 4) ΔJ = 1 even parity bands with 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> as band heads, 5) deformed bands built on the first excited 0 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> states. Not all these types of bands have been observed in all of the nuclei in this mass region. The even spin positive parity bands with 8 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> as band head and the negative parity bands can be understood in terms of rotational alignment model. The Interacting Boson Model calculations reproduce the negative parity bands and the ΔJ = 1 even parity bands with 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> as band head. Both these models have to be further investigated as to the validity of them in describing nuclei in the mass region A ≈ 70. Recent dynamic deformation model calculations of Kumar support the shape coexistence picture for <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">72</sup> Se, which explains the deformed bands built on the first excited 0 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> states.

Sharp-line absorption, luminescence, Raman studies for the 5d3hexafluororhenate(IV) ion in pure and host crystal environments

Five electronic transitions have been observed by absorption spectroscopy at liquid helium temperature for the ReF6 -2 ion in a single Cs2ReF6 crystal and in a Cs2GeF6 cubic host lattice. Also, luminescence has been observed from the Γ7(2 T 2g ) electronic state to the Γ8(4 A 2g ) ground state in the pure Cs2ReF6 system. Temperature dependent absorption hot bands, Raman and luminescence results provide information about the symmetry of the ReF6 -2 ion in a pure Cs2ReF6 crystal. The observed electronic transitions can be assigned with a crystal field model to give B, C, Dq and λso values for ReF6 -2. The detailed phonon structure observed for the t 2g 3 →t 2g 3 transitions in both the pure and mixed crystal cases, can be assigned to lattice modes, internal modes of the ReF6 -2 entity, and combination modes of the proper symmetry. We have assigned the low energy lattice modes by use of recent rigid ion lattice dynamical model results for Cs2SiF6.

Leibenstein on the benefits and costs of birth control programmes

Abstract Enke draws attention particularly to his recent dynamic models of the effects of birth prevention. He argues that the result of birth prevention is, typically, to leave future G.N.P. almost unaffected, with a smaller population and a reduction in the ratio of dependent children to the active age groups. G.N.P. per head is thus raised. Leibenstein accepts the relevance of population control and family planning programmes. He argues, however, that in its present form benefit-cost analysis does not provide a sound basis for estimating the value of such programmes.