Hexagonal spiral growth in the absence of a substrate

Experiments on the formation of spiraling hexagons (350 - 1000 nm in width) from a solution of nanoparticles are presented. Transmission electron microscopy images of the reaction products of chemically synthesized cadmium nanocrystals indicate that the birth of the hexagons proceeds without assistance from static screw or edge dislocatons, that is, they spiral without constraints provided by an underlying substrate. Instead, the apparent growth mechanism relies on what we believe is a dynamical dislocation identified as a dense aggregate of small nanocrystals that straddles the spiraling hexagon at the crystal surface. This nanocrystal bundle, which we term the "feeder", also appears to release nanocrystals into the spiral during the growth process.Comment: 4 pages, 5 figure

An Application of the Two-Stage Model of Motor Learning to Speech Motor Control

Purpose: This study used a two-stage model of motor learning (Latash, 2012) to evaluate bad and good variance during a speech learning task. Stage 1 learning involves minimizing bad variance, or overall error, whereas Stage 2 learning involves changes in good variance while ceiling accuracy is maintained. Using two different variables to evaluate speech complexity (manner of articulation and syllable length), two hypotheses were evaluated: 1) A two-stage model exists during speech motor learning and 2) complexity of stimuli will alter the achievement and maintenance of each stage during learning. Methods: Twelve native English speakers with normal speech and hearing skills repeated stimuli that varied by manner of articulation (stops versus fricatives) and syllable length (4 versus 6-syllables) while having their tongue movements tracked using the WAVE Speech Research system. Complexity of the stimuli were ranked: simple = stops, 4-syllable, complex = fricative, 6-syllable. Results: Visual analysis was conducted by evaluating each participant’s productions for accuracy and duration per block. Results suggest there are two-stages of learning during a speech motor learning task. Three patterns of learning were observed in achievement of Stage 1 learning, and Stage 1 was achieved more quickly for simple stimuli. Additionally, differences in duration based on complexity of the stimuli were also observed during Stage 2 learning. Conclusion: A two-stage model was observed contrary to traditional speech motor learning theories. This study suggests variables other than accuracy may be related to learning and generalization. The complexity of stimuli also influences learning outcomes

A theoretical study of the aerodynamic characteristics of lifting-body entry vehicles Summary report, Mar. 1965 - Mar. 1966

Aerodynamic characteristics of lifting-body entry vehicle

Surface-directed spinodal decomposition in the pseudobinary alloy (HfO_2)_x(SiO_2)_{1-x}

Hf silicate films (HfO_2)_{0.25}(SiO_2)_{0.75} with thicknesses in the range 4-20 nm were grown on silicon substrate by atomic layer deposition at 350 deg.C.The Hf distributions in as-grown and 800 deg.C annealed films were investigated by high resolution transmission electron microscopy (HRTEM), angle-resolved x-ray photoelectron spectroscopy (ARXPS) and medium energy ion scattering (MEIS). HRTEM images show a layered structure in films thinner than 8 nm. The ARXPS data also reveal a non-uniform distribution of Hf throughout the film depth. Diffusion of SiO_2 to the film surface after a longer time anneal was observed by MEIS. All these observations provide evidence for surface-directed spinodal decomposition in the pseudobinary (HfO_2)_x(SiO_2)_{1-x} alloy system.Comment: 1o figures, one tabl

Cognition and violent behavior in psychotic disorders: a nationwide case-control study

Background: The excess risk of violence in psychotic disorders may partly be explained by impairments in executive functions (EFs) and theory of mind (ToM). However, previous studies have been limited by composite measures of EFs and small samples of inpatients. Methods: Data were collected for the research project Genetic Risk and Outcome of Psychosis (GROUP). Patients with psychotic disorders (N=891) were recruited from various care settings in the Netherlands. The following neuropsychological tests were administered (targeted cognitive function in parentheses): (i) Continuous Performance Test-HQ (inhibition); (ii) Response Shifting Task (cognitive flexibility); (iii) Wechsler Adult Intelligence Scale, Third Edition (WAIS-III) Block Design subtest (fluid intelligence); (iv) Neuropsychological Assessment Battery (NAB) Mazes Test (planning); (v) Degraded Facial Affect Recognition Task (affective ToM); and (vi) Hinting Task (cognitive ToM). Lifetime violence was ascertained from medical records and patient interviews. We used analysis of covariance to compare the mean scores of violent and nonviolent patients on each test, adjusting for age and sex. Results: Violent patients performed significantly worse than nonviolent patients on the WAIS-III Block Design subtest (F [1, 847]=5.12, p=.024), NAB Mazes Test (F [1, 499]=5.32, p=.022) and Hinting Task (F [1, 839]=9.38, p=.002). For the other tests, the between-group differences were nonsignificant. Violent behavior explained no more than 1% of the variance in performance on each test. Conclusion: Impairments in EFs and ToM are unlikely to provide useful targets for risk assessment and interventions

Phase-field crystal study of grain-boundary premelting

We study the phenomenon of grain-boundary premelting for temperatures below the melting point in the phase-field crystal model of a pure material with hexagonal ordering in two dimensions. We investigate the structures of symmetric tilt boundaries as a function of misorientation for two different inclinations and compute in the grand canonical ensemble the disjoining potential V(w) that governs the fundamental interaction between crystal-melt interfaces as a function of the premelted layer width w. The results reveal qualitatively different behaviors for high-angle grain boundaries that are uniformly wetted, with w diverging logarithmically as the melting point is approached from below, and low-angle boundaries that are punctuated by liquid pools surrounding dislocations, separated by solid bridges. This qualitative difference between high and low angle boundaries is reflected in the w-dependence of the disjoining potential that is purely repulsive (V'(w)<0 for all w) above a critical misorientation, but switches from repulsive at small w to attractive at large w for low angles. In the latter case, V(w) has a minimum that corresponds to a premelted boundary of finite width at the melting point. Furthermore, we find that the standard wetting condition (the grain boundary energy is equal to twice the solid-liquid free energy) gives a much too low estimate of the critical misorientation when a low-temperature value of the grain boundary energy is used. In contrast, a reasonable estimate is obtained if the grain boundary energy is extrapolated to the melting point, taking into account both the elastic softening of the material at high temperature and local melting around dislocations.Comment: 24 pages, 13 figures, some figure files with reduced resolution because of submission size limitations. In the 2nd version, some parts (and figures) have been modified, especially in Sec. V (discussion

Phase-ordering of conserved vectorial systems with field-dependent mobility

The dynamics of phase-separation in conserved systems with an O(N) continuous symmetry is investigated in the presence of an order parameter dependent mobility M(\phi)=1-a \phi^2. The model is studied analytically in the framework of the large-N approximation and by numerical simulations of the N=2, N=3 and N=4 cases in d=2, for both critical and off-critical quenches. We show the existence of a new universality class for a=1 characterized by a growth law of the typical length L(t) ~ t^{1/z} with dynamical exponent z=6 as opposed to the usual value z=4 which is recovered for a<1.Comment: RevTeX, 8 pages, 13 figures, to be published in Phys. Rev.

Radiative corrections to single Higgs boson production in e+e−e^+ e^- annihilation

For energies relevant to future linear colliders, \sqrt{s} \gsim 500 GeV, the WW fusion channel dominates the Higgs boson production cross section $e^+ e^- \to \bar{\nu} \nu h^0$. We have calculated the one-loop corrections to this process due to fermion and sfermion loops in the context of the MSSM. As a special case, the contribution of the fermion loops in the SM has also been studied. In general, the correction is negative and sizeable of the order of 10 percent, the bulk of it being due to fermion loops.Comment: Version to appear in Phys. Lett.