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This is a copy of the slides presented at the meeting but not formally written up for the volume.
We present a high-resolution transmission electron microscopy study, on the unit-cell scale, of the degree of tetragonality and the displacements of cations away from the centrosymmetry positions in an ultra-thin epitaxial PbZr0.2Ti0.8O3 film on a SrRuO3 electrode layer deposited on a SrTiO3 substrate. TEM results show that the lattice is highly tetragonal at the centre of the film with a c/a ratio of about 1.08, while it shows a reduced degree of tetragonality in the regions close to the interfaces. Most strikingly, we find that the maximum off-centre displacements for the central area of the film do not scale with the tetragonality in comparison with the bulk materials. The calculated switched polarization from the measured cationic displacement is 80 ìC/cm2 , and thus only half of the nominal bulk value. It is in very good agreement with electrical measurements of the switched polarization obtained via the PUND method. Furthermore, a systematic reduction of the atomic displacements is measured at the interfaces. This suggests that interface-induced suppression of the ferroelectric polarization plays a critical role in the size effect of nanoscale ferroelectrics. These issues will be discussed further in this presentation. This work was partially supported by the National Science Foundation (NSF) under Grants DMR-0132918, NSF-MRSEC DMR-0080008, and an NSF US-Europe program DMR-0244288. V.N also acknowledges the support of the Alexander von Humboldt Foundation for his stay in Germany and the financial support of an Australian Research Council Discovery Grant 0666231.
A numerical analysis of flow around a circular cylinder oscillating in-line with a steady flow is carried out over a range of driving frequencies
at relatively low amplitudes
and a constant Reynolds number of 175 (based on the free-stream velocity). The vortex shedding is investigated, especially when the shedding frequency
synchronises with the driving frequency. A series of modes of synchronisation are presented, which are referred to as the
are natural numbers. When a
is detuned to
, representing the shedding of
pairs of vortices over
cycles of cylinder oscillation. The
modes are further characterised by the periodicity of the transverse force over every
cycles of oscillation and a spatial–temporal symmetry possessed by the global wake. The synchronisation modes
with relatively small natural numbers are less sensitive to the change of external control parameters than those with large natural numbers, while the latter is featured with a narrow space of occurrence. Although the mode of synchronisation can be almost any rational ratio (as shown for
smaller than 10), the probability of occurrence of synchronisation modes with
being an even number is much higher than
being an odd number, which is believed to be influenced by the natural even distribution of vortices in the wake of a stationary cylinder.
Glacier surface melting can be described using energy-balance models. We conducted a surface energy budget experiment to quantify surface energy fluxes and to identify factors affecting glacial melt in the ablation zone of Laohugou glacier No. 12, western Qilian mountains. The surface energy budget was calculated based on data from an automatic weather station, and turbulent fluxes calculated using the bulk-aerodynamic approach were corrected using measurements from an eddy-covariance system. Simulated mass balances were validated by stake observations. Net shortwave radiation was the primary component of the surface energy balance (126Wm–2), followed by sensible heat flux. Net longwave radiation (–45Wm–2) and latent heat flux (–12.8 Wm–2) represented heat sinks. The bulk-aerodynamic method underestimated sensible and latent heat fluxes by 3.4 and 1.2 W m–2, respectively. The simulated total mass balance of –1703mmw.e. exceeded the observed total by 90 mm w.e. Daily positive accumulated temperature and low albedo were the main factors accelerating glacier melt. An uncertainty assessment showed that mass balance was very sensitive to albedo and varied by 36% when albedo changed by 0.1.
Bacillary dysentery continues to be a major health issue in developing countries and ambient temperature is a possible environmental determinant. However, evidence about the risk of bacillary dysentery attributable to ambient temperature under climate change scenarios is scarce. We examined the attributable fraction (AF) of temperature-related bacillary dysentery in urban and rural Hefei, China during 2006–2012 and projected its shifting pattern under climate change scenarios using a distributed lag non-linear model. The risk of bacillary dysentery increased with the temperature rise above a threshold (18·4 °C), and the temperature effects appeared to be acute. The proportion of bacillary dysentery attributable to hot temperatures was 18·74% (95 empirical confidence interval (eCI): 8·36–27·44%). Apparent difference of AF was observed between urban and rural areas, with AF varying from 26·87% (95% eCI 16·21–36·68%) in urban area to −1·90% (95 eCI −25·03 to 16·05%) in rural area. Under the climate change scenarios alone (1–4 °C rise), the AF from extreme hot temperatures (>31·2 °C) would rise greatly accompanied by the relatively stable AF from moderate hot temperatures (18·4–31·2 °C). If climate change proceeds, urban area may be more likely to suffer from rapidly increasing burden of disease from extreme hot temperatures in the absence of effective mitigation and adaptation strategies.
In this paper, the recent studies of laboratory astrophysics with strong magnetic fields in China have been reviewed. On the Shenguang-II laser facility of the National Laboratory on High-Power Lasers and Physics, a laser-driven strong magnetic field up to 200 T has been achieved. The experiment was performed to model the interaction of solar wind with dayside magnetosphere. Also the low beta plasma magnetic reconnection (MR) has been studied. Theoretically, the model has been developed to deal with the atomic structures and processes in strong magnetic field. Also the study of shock wave generation in the magnetized counter-streaming plasmas is introduced.
Two-grid finite element methods for the steady Navier-Stokes/Darcy model are considered. Stability and optimal error estimates in the H1-norm for velocity and piezometric approximations and the L2-norm for pressure are established under mesh sizes satisfying h = H2. A modified decoupled and linearised two-grid algorithm is developed, together with some associated optimal error estimates. Our method and results extend and improve an earlier investigation, and some numerical computations illustrate the efficiency and effectiveness of the new algorithm.
Nanoporous carbon monoliths with different pore structures were obtained by carbonizing cured phenol–formaldehyde (PF) resin/poly(methyl methacrylate) (PMMA) blends. The effect of the molecular weight of PMMA, reaction activity of PF, and content ratio of compositions on the pore structure of carbon monoliths was systematically investigated, with emphasis on controlling the morphology of the nanostructure and pore size distribution. Nanostructures were an important factor in determining the compressive strength of porous carbon monoliths. The relationship between the nanoporous structure of carbon monoliths and compressive strength was revealed. Co-continuous pores provided escape channels for those volatile gases produced in the carbonization process to escape, reducing inner stress of the carbon materials. During compressive loading, co-continuous pores could also help to scatter and absorb the stress and energy. Porous carbon monoliths with a compressive strength of 34 MPa were obtained, and the compressive strength increased by 580% compared with that of carbon monoliths obtained from pure PF.
Sinusoidally oscillatory flow around four circular cylinders in an in-line square arrangement is numerically investigated at Keulegan–Carpenter numbers (
) ranging from 1 to 12 and at Reynolds numbers (
) from 20 to 200. A set of flow patterns is observed and classified based on known oscillatory flow regimes around a single cylinder. These include six types of reflection symmetry regimes to the axis of flow oscillation, two types of spatio-temporal symmetry regimes and a series of symmetry-breaking flow patterns. In general, at small gap distances, the four structures behave more like a single body, and the flow fields therefore resemble those around a single cylinder with a large effective cylinder diameter. With increasing gap distance, flow structures around each individual cylinder in the array start to influence the overall flow patterns, and the flow field shows a variety of symmetry and asymmetry patterns as a result of vortex and shear layer interactions. The characteristics of hydrodynamic forces on individual cylinders as well as on the cylinder group are also examined. It is found that the hydrodynamic forces respond in a similar manner to the flow field to the cylinder proximity and wake interference.
This paper presents a numerical study on steady flow around two identical circular cylinders of various arrangements at a low subcritical Reynolds number (
). The ratio of centre-to-centre pitch distance (
) to the diameter of the cylinder (
) ranges from 1.5 to 4, and the alignment angle
between the two cylinders and the direction of the cross-flow varies from 0 to 90°. The detailed flow information obtained from direct numerical simulation allows a comprehensive interpretation of the underlying physics responsible for some interesting flow features observed around two staggered cylinders. Four distinct vortex shedding regimes are identified and it is demonstrated that accurate classification of vortex shedding regimes around two staggered cylinders should consider the combination of the flow visualization with the analyses of lift forces and velocity signal in the wake. It is revealed that the change in pressure distribution, as a result of different vortex shedding mechanisms, leads to a variety of characteristics of hydrodynamic forces on both cylinders, including negative drag force, attractive and repulsive lift forces. Two distinct vortex shedding frequencies are identified and are attributed to the space differences based on the flow structures observed in the wake of the cylinders. It is also found that the three-dimensionality of flow in the gap and the shared wake region is significantly weakened in almost two of the classified flow regimes; however, compared with the flow around a single cylinder, active wake interaction at large
does not clearly increase the three-dimensionality.
This study was designed to determine the effect of melatonin on the in vitro maturation (IVM) and developmental potential of bovine oocytes denuded of the cumulus oophorus (DOs). DOs were cultured alone (DOs) or with 10−9 M melatonin (DOs + MT), cumulus–oocyte complexes (COCs) were cultured without melatonin as the control. After IVM, meiosis II (MII) rates of DOs, and reactive oxygen species (ROS) levels, apoptotic rates and parthenogenetic blastocyst rates of MII oocytes were determined. The relative expression of ATP synthase F0 Subunit 6 and 8 (ATP6 and ATP8), bone morphogenetic protein 15 (BMP-15) and growth differentiation factor 9 (GDF-9) mRNA in MII oocytes and IFN-tau (IFN-τ), Na+/K+-ATPase, catenin-beta like 1 (CTNNBL1) and AQP3 mRNA in parthenogenetic blastocysts were quantified using real-time polymerase chain reaction (PCR). The results showed that: (1) melatonin significantly increased the MII rate of DOs (65.67 ± 3.59 % vs. 82.29 ± 3.92%; P < 0.05), decreased the ROS level (4.83 ± 0.42 counts per second (c.p.s) vs. 3.78 ± 0.29 c.p.s; P < 0.05) and apoptotic rate (36.99 ± 3.62 % vs. 21.88 ± 2.08 %; P < 0.05) and moderated the reduction of relative mRNA levels of ATP6, ATP8, BMP-15 and GDF-9 caused by oocyte denudation; (2) melatonin significantly increased the developmental rate (24.17 ± 3.54 % vs. 35.26 ± 4.87%; P < 0.05), and expression levels of IFN-τ, Na+/K+-ATPase, CTNNBL1 and AQP3 mRNA of blastocyst. These results indicated that melatonin significantly improved the IVM quality of DOs, leading to an increased parthenogenetic blastocyst formation rate and quality.
We investigated the effect mouse cumulus cells (mCCs) on the in vitro maturation (IVM) and developmental potential of bovine denuded germinal vesicle oocytes (DOs). Cumulus–oocyte complexes (COCs), DOs and DOs cocultured with either mCCs (DOs + mCCs) or bovine cumulus cells (bCCs; DOs + bCCs) were subjected to IVM. The meiosis II (MII) rates of DOs, glutathione (GSH) contents, zona pellucida (ZP) hardening and parthenogenetic blastocyst rates of MII oocytes were determined. The relative expression levels of bone morphogenetic protein 15 (BMP-15) and growth differentiation factor 9 (GDF-9) in MII oocytes were measured using quantitative real-time polymerase chain reaction (PCR). mCCs significantly increased the MII rate of DOs from 53.5 ± 3.58% to 69.67 ± 4.72% (p < 0.05) but had no effect on the GSH content (2.17 ± 0.31 pmol/oocyte with mCCs, 2.14 ± 0.53 pmol/oocyte without mCCs). For the DOs + mCCs group, the BMP-15 and GDF-9 expression levels were significantly higher and the ZP dissolution time was significantly lower (162.49 ± 12.51 s) than that of the DOs group (213.95 ± 18.87 s; p < 0.05). The blastocyst rate of the DOs + mCCs group (32.56 ± 4.94%) was similar to that of the DOs group (31.75 ± 3.65%) but was significantly lower than that of the COCs group (43.52 ± 5.37%; p < 0.05). In conclusion, mCCs increased the MII rate of DOs and expression of certain genes in MII oocytes, and decreased the ZP hardening of MII oocytes, but could not improve their GSH content or developmental potential.
A novel rheo-rolling process for producing A356 alloy sheet was developed. The influence
of parameters on the microstructure of A356 alloy sheets was investigated. The eutectic
fraction and primary α globule size increase with the increment in the
roll speed. The globule size and eutectic fraction of A356 alloy sheet increase with the
increment in the casting temperature. The primary α globule size
decreases and the solid fraction increases with the increment in vibration frequency from
30 Hz to 80 Hz. With a roll speed of 0.069 m.s-1, a casting temperature of 660
°C, and a vibration frequency of 80 Hz, A356 alloy sheet with a cross-section
size of 4 × 160 mm was prepared. The microstructure is mainly composed of fine spherical
or rosette α globules, and the average α globule size is
20.5 μm. The ultimate tensile strength of the A356 alloy sheet was 260
MPa, and the elongation to failure was 7.9%, which were 2.5 and 3.7 times greater than
those of the as-cast material.
In this paper we prove an existence theorem of global smooth solutions for the Cauchy problem of a class of quasilinear hyperbolic systems with nonlinear dissipative terms under the assumption that only the C0-norm of the initial data is sufficiently small, while the C1-norm of the initial data can be large. The analysis is based on a priori estimates, which are obtained by a generalised Lax transformation.
This paper is concerned with a stabilized finite element method based on two local Gauss integrations for the two-dimensional non-stationary conduction-convection equations by using the lowest equal-order pairs of finite elements. This method only offsets the discrete pressure space by the residual of the simple and symmetry term at element level in order to circumvent the inf-sup condition. The stability of the discrete scheme is derived under some regularity assumptions. Optimal error estimates are obtained by applying the standard Galerkin techniques. Finally, the numerical illustrations agree completely with the theoretical expectations.
The present work proposes a Dugdale type model to theoretically predict the multiple cracks of a residually tensile stressed thin film on a ductile substrate. The results show that there exists a critical value, Rc, of the cracking resistance number, R. When R < R, the film > c cracks and the normalized crack spacing is determined by cracking resistance number and the stress ratio of the residual stress to the yield strength of the substrate.
Vickers indentation tests were carried out at room temperature with a microhardness tester on ZnO thin films deposited on (100) Si wafers. The films with thicknesses ranging from 0.202 to 1.535 νm were tested under indentation loads varying from 50 mN to 2.0 N. The experiments exhibited a film thickness dependent deformation behavior. When the film thickness is smaller than a critical value, only indentation-induced radical cracking occurred and for a given load, the radical crack size decreased with film thickness. On the other hand, indentation-induced delamination was observed if the film thickness was larger than the critical value. In this case, the radial crack, if induced, had a size smaller than the size of delamination or even smaller than the size of indentation impression. Under a same indentation load, the delamination size increased with the film thickness.
Films of the Tl‐Ba‐Ca‐Cu‐O high‐Tc superconductor can be prepared by several organometallic chemical vapor deposition routes. Two of these involve Ba‐Ca‐Cu‐0 films that are first prepared using the volatile metal‐organic precursors Ba(heptafluorodimethyloctanedionate)2, Ca(dipivaloylmethanate)2, and Cu(acetylacetonate)2‐ Deposition is carried out at a pressure of 5 Torr with argon as the carrier gas and water vapor as the reactant gas. Thallium is next incorporated into these films either by organometallic chemical vapor deposition using Tl(cyclopentadienide) as the source, or by vapor diffusion using bulk Tl‐Ba‐Ca‐Cu‐O as the source. Thallium deposition is carried out at atmospheric pressure with an argon carrier and water‐saturated oxygen reactant gas, followed by rapid thermal annealing. Both procedures yield films that consist primarily of the TlBa2Ca2Cu3Ox phase, have preferential orientation of the Cu‐O planes parallel to the substrate surface, and exhibit onset of superconductivity at ∼125 K with zero resistance by 100 K.
We report here a plasma‐enhanced organometallic chemical vapor deposition process for the preparation of YBa2Cu3O7‐x thin films using two rf plasma coupling configurations. For the films grown under a direct plasma glow, the YBa2Cu3O7‐x phase is not found in the as‐deposited state. However, by employing plasma‐activated nitrous oxide as the reactant gas, superconducting YBa2Cu3O7‐x films having a low carbon content and a mirror‐like surface have been prepared in‐situ at a substrate temperature of 610°C using an organometallic chemical vapor deposition process.
Interactions between fluorinated polyimide and aluminum under different thermal treatment conditions have been investigated using transmission electron microscopy (TEM) and x-ray diffractometry (XRD) techniques over a wide temperature range. Our results suggest that the oxygen from the dielectric materials may result in the oxidation of the underlying aluminum either on the surface or along the grain boundary. This work implies that processing conditions, such as curing temperature and time, may play critical roles in affecting the performance of polymeric dielectric materials.