Two-dimensional structures of ferroelectric domain inversion in LiNbO3 by direct electron beam lithography

We report on the fabrication of domain-reversed structures in LiNbO3 by means of direct electron beam lithography at room temperature without any static bias. The LiNbO3 crystals were chemically etched after the exposure of electron beam and then, the patterns of domain inversion were characterized by atomic force microscopy (AFM). In our experiment, an interesting phenomenon occurred when the electron beam wrote a one-dimensional (1-D) grating on the negative c-face: a two-dimensional (2-D) dotted array was observed on the positive c- face, which is significant for its potential to produce 2-D and three-dimensional photonic crystals. Furthermore, we also obtained 2-D ferroelectric domain inversion in the whole LiNbO3 crystal by writing the 2-D square pattern on the negative c-face. Such a structure may be utilized to fabricate 2-D nonlinear photonic crystal. AFM demonstrates that a 2-D domain-reversed structure has been achieved not only on the negative c-face of the crystal, but also across the whole thickness of the crystal.Comment: 17 pages, 4 figure

Comparison between architects and non-architects on perceptions of architectural acoustic environments

The perception of the architectural acoustic environment of both architects and non-architects is important. Through interviews with architects and non-architects, theoretical frameworks on acoustic environment perception for the two groups are created in the present study. The entire perception process is summarised into four steps for both groups: attitude towards the acoustic environment of the building, perception of the acoustic environment design, factors influencing the interpretation, and the outcome of the acoustic environment. Some obvious differences between the two groups were observed. Architects tend to focus on controlling the physical parameters of sound; they recognize that the active design of the acoustic environment is difficult and problematic. Non-architects pay more attention to interpreting and experiencing acoustic environments. They tend to create a good acoustic environment using ideal sound and have a positive attitude towards shaping the acoustic environment. Furthermore, compared to non-architects, architects do not pay enough attention to the various influencing factors that affect users’ interpretations of acoustic environments, and the multiple, long-term, and profound effects (e.g. behavioural, emotional, recovery, and health) of the architectural acoustic environment on users are usually ignored. Correlation analysis of these differences and phenomena reveals that the existing issues of the acoustic environment design initially focuses on two aspects: architects’ understanding of the active architectural acoustic environment design is not sufficient to overcome its inherent limitations, and architects’ understanding of public preferences and demands is insufficient. According to the interviews, the future development direction may lie in the combination of acoustic environment design and architecture, support for architects, effective communication and feedback mechanisms, and the transition of architects’ design thinking

The Alignment between Satellites and Central Galaxies: Theory vs. Observations

Recent studies have shown that the distribution of satellite galaxies is preferentially aligned with the major axis of their central galaxy. The strength of this alignment has been found to depend strongly on the colours of the satellite and central galaxies, and only weakly on the mass of the halo in which the galaxies reside. In this paper we study whether these alignment signals, and their dependence on galaxy and halo properties, can be reproduced in a hierarchical structure formation model of a $\Lambda$CDM concordance cosmology. To that extent we use a large $N$-body simulation which we populate with galaxies following a semi-analytical model for galaxy formation. We find that if the orientation of the central galaxy is perfectly aligned with that of its dark matter halo, then the predicted central-satellite alignment signal is much stronger than observed. If, however, the minor axis of a central galaxy is perfectly aligned with the angular momentum vector of its dark matter halo, we can accurately reproduce the observed alignment strength as function of halo mass and galaxy color. Although this suggests that the orientation of central galaxies is governed by the angular momentum of their dark matter haloes, we emphasize that any other scenario in which the minor axes of central galaxy and halo are misaligned by $\sim 40^{\circ}$ (on average) will match the data equally well. Finally, we show that dependence of the alignment strength on the color of the central galaxy is most likely an artefact due to interlopers in the group catalogue. The dependence on the color of the satellite galaxies, on the other hand, is real and owes to the fact that red satellites are associated with subhaloes that were more massive at their time of accretion.Comment: 13 Pages, 10 Figures, one figure replaced. added in discussion about comparison with others results, Updated version to match accepted version to MNRA

Variations of multi-parameter observations in atmosphere related to earthquake

Anomalies of multi-parameters (outgoing longwave radiation, surface latent heat flux, air temperature, relative humidity, and air pressure) before the 12 May 2008 Wenchuan <i>M</i><sub>s</sub> =8.0 earthquake were discussed in order to obtain the seismic precursors. Multi-parameter data were computed based on multi-year background data. The results indicated that these parameters had significant variations prior to this event. The anomaly of outgoing longwave radiation was observed firstly, which gives an early warning. Next were air temperature, relative humidity, and air pressure, which had quasi-simultaneous variations in the basin and the mountain region close to the epicenter. The last was surface latent heat flux, which happened the day before this event. The characteristics of the parameter variations for this event are similar to other earthquakes, which is demonstrated in some other publications. The variations can be attributed to solid earth degassing and chemical reactions in the atmosphere. Additionally, the emission of gases from solid earth into the atmosphere could be ascribed to the tectonic stress of the Wenchuan earthquake

Crowd noise and vocal power level in large college canteens in China

Both the noise and the vocal power level of the crowd are parameters for evaluating the acoustic environment. The former is from the perspective of the environment, and the latter is from the perspective of the user's needs. This paper aims to explore the crowd noise and vocal power level of diners in large college canteens in China. Measurements were conducted in two typical Chinese college canteens. Videos were also recorded to analyse the diners’ behaviour. The results showed that the noise in canteens varied from 61 dBA to 73 dBA during the meal. It was noted that although the noise level had a strong correlation with the number of occupants, the relationship between this two was not simply the superposition of equal-intensity sound sources. The speaking ratio and the Lombard effect played a significant role during the meal. The average speaking ratio was 0.12, which was far less than the practical value, 1/3. A prediction model for vocal power level under crowd noise was introduced into Chinese college canteens, which considered direct and reverberant sound energy using the parameters of room information, the location of the diners, and the speaking ratio. Based on this model, the vocal power level was found to vary from 59 dBA to 97 dBA. According to Pearson's evaluation criterion, 17.1% of the data fell between “Raised” and “Loud”, and 71.8% of the data fell between “Loud” and “Shout”. It indicated that the crowd noise in Chinese college canteens had a significant impact on communication and some acoustic treatment was necessary

Tri-band spectroscopic optical coherence tomography based on optical parametric amplification for lipid and vessel visualization

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Selective laser melting of an Al(86)Ni(6)Y(4.5)Co(2)La(1.5) metallic glass: processing, microstructure evolution and mechanical properties

In this study, single line scans at different laser powers were carried out using selective laser meting (SLM) equipment on a pre-fabricated porous Al86Ni6Y4.5Co2La1.5 metallic glass (MG) preform. The densification, microstructural evolution, phase transformation and mechanical properties of the scan tracks were systematically investigated. It was found that the morphology of the scan track was influenced by the energy distribution of the laser beam and the heat transfer competition between convection and conduction in the melt pool. Due to the Gaussian distribution of laser energy and heat transfer process, different regions of the scan track experienced different thermal histories, resulting in a gradient microstructure and mechanical properties. Higher laser powers caused higher thermal stresses, which led to the formation of cracks; while low power reduced the strength of the laser track, also inducing cracking. The thermal fluctuation at high laser power produced an inhomogeneous chemical distribution which gave rise to severe crystallization of the MG, despite the high cooling rate. The crystallization occurred both within the heat affected zone (HAZ) and at the edge of melt pool. However, by choosing an appropriate laser power crack-free scan tracks could be produced with no crystallization. This work provides the necessary fundamental understanding that will lead to the fabrication of large-size, crack-free MG with high density, controllable microstructure and mechanical properties using SLM. (C) 2014 Elsevier B.V. All rights reserved