Nucleation and growth of a quasicrystalline monolayer: Bi adsorption on the five-fold surface of i-Al70Pd21Mn9

Scanning tunnelling microscopy has been used to study the formation of a Bi monolayer deposited on the five-fold surface of i-Al70Pd21Mn9. Upon deposition of low sub-monolayer coverages, the nucleation of pentagonal clusters of Bi adatoms of edge length 4.9 A is observed. The clusters have a common orientation leading to a film with five-fold symmetry. By inspection of images where both the underlying surface and the Bi atoms are resolved, the pentagonal clusters are found to nucleate on pseudo-Mackay clusters truncated such that a Mn atom lies centrally in the surface plane. The density of these sites is sufficient to form a quasiperiodic framework, and subsequent adsorption of Bi atoms ultimately leads to the formation of a quasicrystalline monolayer. The initial nucleation site is different to that proposed on the basis of recent density functional theory calculations.Comment: 6 pages, 5 figure

Opportunities for promoting physical activity in rural communities by understanding the interests and values of community members

Purpose. Physical activity (PA) has well-established health benefits, but most Americans do not meet national guidelines. In southeastern Missouri, trails have been developed to increase rates of PA. Although this has had success, broad-scale interventions will be needed to improve rates further. In this study, we surveyed residents of southeastern Missouri to identify ways to improve rates of PA. Methods. We conducted a telephone survey in 2015 of adults (n=524) from eight rural Missouri towns that had walking trails, regarding their activities and interests. Findings. Forty percent of respondents reported both walking and meeting PA recommendations, 29% reported walking but not meeting PA recommendations, and the remainder did not walk or did not answer. Respondents who used the trails were significantly more likely to meet PA recommendations (odds ratio = 2.7; 95% confidence interval = 1.7, 4.5). Certain values and interests that may encourage PA or draw people to trails were common. Conclusions. The group that walked but did not meet PA recommendations would be the ideal group to target for intervention, which could focus on their reported values and interests (e.g., personal relationships, being outdoors). Use of walking trails was associated with meeting PA recommendations

Gauge Coupling Unification via A Novel Technicolor Model

We show that the recently proposed minimal walking technicolor theory together with a small modification of the Standard Model fermionic matter content leads to an excellent degree of unification of the gauge couplings. We compare the degree of unification with various time-honored technicolor models and the minimal supersymmetric extension of the Standard Model. We find that, at the one-loop level, the new theory provides a degree of unification higher than any of the other extensions above. The phenomenology of the present model is very rich with various potential dark matter candidates.Comment: Final version to match the published on

Promoting Reflection During Practice Teaching in an Australian University : Clarifying the Rhetoric and the Reality

This paper focuses on the promotion of reflectivity during practice teaching amongst student teachers at a university in Australia. By way of background, current criticisms of what is termed the technocratic approach to teacher education are outlined and the emphasis which is placed on the development of the reflective teacher as a counterforce to this approach is considered. It is then argued that the technocratic position and the reflective teacher position need not necessarily be viewed as being in conflict. Rather, the contention is that they are both satisfactorily accommodated within Van Manen\u27s (1977) theory of reflectivity . For the study reported in the remainder of the paper, Van Manen\u27s levels of reflectivity provided a helpful framework for the concepts, language and practices of reflection. The study details an investigation of the reality and rhetoric of promoting reflectivity amongst student teachers engaged in one practice teaching period of their Bachelor of Teaching (Primary) pre-service programme at an Australian university. Firstly, the paper reports on the extent to which the process of reflection was mentioned and clarified in the university\u27s official practice teaching literature, and on the stated priority for its development as a practicum aim. The paper then goes on to outline the findings of the second phase of the research which explored the extent to which reflectivity was promoted in the practice of university lecturers supervising students on practice teaching

Sequential Flavour Symmetry Breaking

The gauge sector of the Standard Model (SM) exhibits a flavour symmetry which allows for independent unitary transformations of the fermion multiplets. In the SM the flavour symmetry is broken by the Yukawa couplings to the Higgs boson, and the resulting fermion masses and mixing angles show a pronounced hierarchy. In this work we connect the observed hierarchy to a sequence of intermediate effective theories, where the flavour symmetries are broken in a step-wise fashion by vacuum expectation values of suitably constructed spurion fields. We identify the possible scenarios in the quark sector and discuss some implications of this approach.Comment: 22 pages latex, no figure

Comparability of Functional MRI Response in Young and Old During Inhibition

When using fMRI to study age-related cognitive changes, it is important to establish the integrity of the hemodynamic response because, potentially, it can be affected by age and disease. However, there have been few attempts to document such integrity and no attempts using higher cognitive rather than perceptual or motor tasks. We used fMRI with 28 healthy young and older adults on an inhibitory control task. Although older and young adults differed in task performance and activation patterns, they had comparable hemodynamic responses. We conclude that activation during cognitive inhibition, which was predominantly increased in elders, was not due to vascular confounds or specific changes in hemodynamic coupling

DESI Commissioning Instrument Metrology

The Dark Energy Spectroscopic Instrument (DESI) is under construction to measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique. The spectra of 35 million galaxies and quasars over 14000 sq deg will be measured during the life of the experiment. A new prime focus corrector for the KPNO Mayall telescope will deliver light to 5000 fiber optic positioners. The fibers in turn feed ten broad-band spectrographs. We will describe the methods and results for the commissioning instrument metrology program. The primary goals of this program are to calculate the transformations and further develop the systems that will place fibers within 5um RMS of the target positions. We will use the commissioning instrument metrology program to measure the absolute three axis Cartesian coordinates of the five CCDs and 22 illuminated fiducials on the commissioning instrument

Linear thermal expansivity (1–300 K), specific heat (1–108 K), and electrical resistivity of the icosahedral quasicrystal i-Al61.4Cu25.4Fe13.2

Linear thermal expansivity (α, 1–300 K), heat capacity (Cp, 1–108 K), and electrical resistivity (ρ, 1–300 K) measurements are reported for single grain i-Al61.4Cu25.4Fe13.2 quasicrystals as a function of sample processing. While ρ(T) is sensitive to sample treatment, both Cp and α are relatively insensitive (to a few percent) except at the lowest temperatures (below 4 K), where an inverse correlation between ρ and the electronic Cp coefficient γ appears to exist. Dispersion effects (deviations from Debye-like behavior) in both Cp and the lattice Grüneisen parameter Γ are large and comparable with those for single grain i-Al71Pd21Mn08quasicrystal and its Al72Pd25Mn03 approximant [Phys. Rev. B 65, 184206 (2002)]. Since the 0-K Debye temperature [Θ0=536(2)K] is in reasonable agreement with that from 4-K elastic constants [548(8) K], a previous postulate for AlPdMn that these large dispersion effects are associated with high dispersion lattice modes in off-symmetry directions also appears to apply to i-Al-Cu-Fe. A comparison with other Cp data suggests that the major effects of sample treatment (and composition) are reflected, with a few exceptions, in the values of γ, with remarkably similar lattice contributions

Neural signatures of cognitive flexibility and reward sensitivity following nicotinic receptor stimulation in dependent smokers : a randomized trial

IMPORTANCE Withdrawal from nicotine is an important contributor to smoking relapse. Understanding how reward-based decision making is affected by abstinence and by pharmacotherapies such as nicotine replacement therapy and varenicline tartrate may aid cessation treatment. OBJECTIVE To independently assess the effects of nicotine dependence and stimulation of the nicotinic acetylcholine receptor on the ability to interpret valence information (reward sensitivity) and subsequently alter behavior as reward contingencies change (cognitive flexibility) in a probabilistic reversal learning task. DESIGN, SETTING, AND PARTICIPANTS Nicotine-dependent smokers and nonsmokers completed a probabilistic reversal learning task during acquisition of functional magnetic resonance imaging (fMRI) in a 2-drug, double-blind placebo-controlled crossover design conducted from January 21, 2009, to September 29, 2011. Smokers were abstinent from cigarette smoking for 12 hours for all sessions. In a fully Latin square fashion, participants in both groups underwent MRI twice while receiving varenicline and twice while receiving a placebo pill, wearing either a nicotine or a placebo patch. Imaging analysis was performed from June 15, 2015, to August 10, 2016. MAIN OUTCOME AND MEASURES A well-established computational model captured effects of smoking status and administration of nicotine and varenicline on probabilistic reversal learning choice behavior. Neural effects of smoking status, nicotine, and varenicline were tested for on MRI contrasts that captured reward sensitivity and cognitive flexibility. RESULTS The study included 24 nicotine-dependent smokers (12 women and 12 men; mean [SD] age, 35.8 [9.9] years) and 20 nonsmokers (10 women and 10 men; mean [SD] age, 30.4 [7.2] years). Computational modeling indicated that abstinent smokers were biased toward response shifting and that their decisions were less sensitive to the available evidence, suggesting increased impulsivity during withdrawal. These behavioral impairments were mitigated with nicotine and varenicline. Similarly, decreased mesocorticolimbic activity associated with cognitive flexibility in abstinent smokers was restored to the level of nonsmokers following stimulation of nicotinic acetylcholine receptors (familywise error-corrected P<.05). Conversely, neural signatures of decreased reward sensitivity in smokers (vs nonsmokers; familywise error-corrected P<.05) in the dorsal striatum and anterior cingulate cortex were not mitigated by nicotine or varenicline. CONCLUSIONS AND RELEVANCE There was a double dissociation between the effects of chronic nicotine dependence on neural representations of reward sensitivity and acute effects of stimulation of nicotinic acetylcholine receptors on behavioral and neural signatures of cognitive flexibility in smokers. These chronic and acute pharmacologic effects were observed in overlapping mesocorticolimbic regions, suggesting that available pharmacotherapies may alleviate deficits in the same circuitry for certain mental computations but not for others