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An efficient and convenient protocol for the synthesis of γlactams has been developed. The selective C–N bond cleavage of aza-bridged pyridoazepines in the presence of NaIO4 and acetic acid smoothly proceeded to give the desired γlactams in good yields. This strategy possesses several advantages such as operational simplicity, safety, and environmental friendliness and therefore constitutes a promising tool for the synthesis of biologically active compounds. [ABSTRACT FROM AUTHOR]

We investigated the structural, electronic, chemical bonding, and optical properties of β-AgBiS2 crystal by using the Perdew-Burke-Ernzerhof (PBE) functional and the hybrid functional Heyd Scuseria Ernzerhof (HSE) within the DFT formalism. The electronic band structures obtained by both methods indicate that β-AgBiS2 is an indirect band gap semiconductor with band gap of 0.571 and 1.025 eV, respectively. The electron density difference and Mulliken overlap population show that the Ag-S bonds and Bi-S bonds are both ionic bonds. The calculated optical absorption spectrum prove that β-AgBiS2 is a promising material for solar photovoltaic conversion. [ABSTRACT FROM AUTHOR]

Atomistic simulations of the structures and stability of defect-free multiwalled carbon toroidal rings were performed using the second-generation empirical bond-order potential and a Morse-type van der Waals potential. It was found that a multiwalled toroidal ring improves the structural stability over its outermost single-walled counterpart, implying a stabilizing effect from the inner rings. This can be explained by the superlinear relation between the critical ring diameter and its tube diameter existing in single-walled rings. However, the findings that the critical diameter of an armchair ring is larger than that of a zigzag ring with the same tube diameters, and that the inclusion of torsion exhibits a negative effect on the stability of a multiwalled ring, are in contrast to that of a single-walled nanoring. In addition, the instability of a multiwalled nanoring always starts with the formation of many short-wavelength ripples on the compressed side of the outermost tube. Subsequently, some of the ripples develop into buckles, resulting in buckling failures. [ABSTRACT FROM AUTHOR]

Mechanical oscillatory behavior of multiwalled carbon-nanotube-based oscillators is investigated using molecular-dynamics simulations. The second-generation reactive bond-order potential and a Morse-type van der Waals potential based on the local-density approximation are used to describe bonding and nonbonding atomic interactions, respectively. It is found that the oscillatory frequency saturates as the number of outer tubes reaches three. The simulations show that the oscillatory frequency, amplitude decay rate, and stability of the oscillators depend on the diameter and helicity of the outer tubes, the extrusion distance, as well as the length of the outer tubes. [ABSTRACT FROM AUTHOR]

The mechanical oscillatory behavior of a C60 molecule tunneling through a carbon nanotube induced by van der Waals interaction are investigated by molecular-dynamics simulations. It is found that the C60 performs a decaying oscillation with a gradual decrease of the oscillatory amplitude and a gradual decrease of the oscillatory frequency. It is shown that this decay is due to the transformation of thermal energy and is sensitive to the change in the diameter and the degree of the helicity of the nanotube. In addition, the nanotube length can be used to tune the oscillation frequency of the C60-nanotube oscillators. [ABSTRACT FROM AUTHOR]

A three-dimensional concurrent atomistic/continuum analysis is performed to study the stress distributions in an epitaxial island. The island and the adjacent substrate are modeled by the molecular dynamics method, and the surrounding zone is modeled by the finite element method in which the nonlinear elasticity is governed by the atomic potential. An overlapping zone is defined to be the location where the atomistic and continuum models exchange necessary material information. It is found that the nonlinear elasticity based on the atomic potential is required for a smooth stress transition in the overlapping zone, and that the linear elasticity assumption significantly overestimates the stress levels at moderate and high loading levels. The implications of the present results on surface roughening driven by strain energy are discussed. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Many experimental observations have clearly shown that dislocation interaction plays a crucial role in the kinetics of strain relaxation in epitaxial thin films. A set of evolution equations are presented in this article. The key feature of the equations is the incorporation of dislocation interactions into the kinetic process by introducing a resistance term. The resistance to threading dislocation gliding is characterized by a hardening function, which depends only on the relaxed plastic strain. The evolution equations are tested on the Ge[sub x]Si[sub 1-x]/Si(100) materials system. Existing fundamental parameters are incorporated into the present model. The evolution equations successfully reproduce a wide range of experimental data on strain relaxation in Ge[sub x]Si[sub 1-x]/Si heterostructures. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Provides information on a study that analyzed the dynamic propagation of an atomistic crack tip using a molecular dynamics method. Methodology of the study; Results and discussion on the study.

Presents a study which analyzed the nucleation and emission of dislocations from the crack tip under mode II loading by the molecular dynamics method in which Finnis-Sinclair potential has been used. Experimental details; Results and discussion; Conclusions.

Sputtered metal-nonmetal granular films tend to exhibit growth-induced perpendicular magnetic anisotropy. In this work, Co/HfN multilayers were synthesized to suppress the development of columnar clusters along the deposition direction. The results reveal that a HfN interlayer thickness of less than 0.4 nm is insufficient to separate the columnar clusters; however, increasing the interlayer thickness to 0.8 nm with increasing the sputtering duration successfully led to typical in-plane magnetic anisotropy with a coercivity as low as 3 Oe. The Co(4 nm)/HfN(1.5 nm) multilayers exhibited high permeability of approximately 260 up to 1.6 GHz. The resonance frequency increased from 1.8 to 2.3 GHz with increasing annealing temperature, which is attributed to the increased magnetic anisotropy. Our results suggest that the multilayers still show high-frequency performance even after annealing at 450 °C, which would be a big advantage for complementary metal-oxide-semiconductor (CMOS) fabrication technology. [ABSTRACT FROM AUTHOR]

The article reports on the measurement of single-spin asymmetry in quasielastic scattering on a 3He gas target polarized normal to the lepton scattering plane with the asymmetry being zero for one-photon exchange when assuming time-reversal invariance. It mentions neutron asymmetries were obtained by using the effective polarization approximation and proton to-3He cross-section ratios. It states the measured neutron asymmetry agreed with a two-photon exchange prediction.

In present paper, the generalized fifth-order time-fractional Korteweg-de Vries (KdV) equation and the particular time-fractional Kaup-Kupershmidt equation are considered, a systematic investigation to derive Lie point symmetries of the equations are presented and compared. Each of them has been transformed into a nonlinear ordinary differential equation with a new independent variable are investigated. The derivative corresponding to time-fractional in the reduced formula is known as the Erdelyi-Kober fractional derivative. [ABSTRACT FROM AUTHOR]

An accurate model about the terahertz wave propagation in fluid-filled single-walled carbon nanotube, named non-local Euler-Bernoulli bean models, was studied in the past decade. The temperature is a key factor to study the mechanical properties of the nanostructures. This paper presents the thermal effect about single-walled carbon nanotubes. The governing equation for single-walled carbon nanotubes is developed through non-local Timoshenko beam theory, and size and surface effects are considered. The fluid flows quickly, and the terahertz wave propagation will be in the scope of the frequency. Thermal effect and liquid density significantly change the propagating frequency. [ABSTRACT FROM AUTHOR]

In order to study the influence of the plasma actuator on the air flow in more detail, the effect of the plasma actuator on the flow field was simplified to the volume force of the electric field. Reynolds Average Navier-Stokes method and transition SST turbulence model were used to simulate the air flow field at different loading voltage, power frequency and inflow velocity. The results show that the higher the loading voltage and power frequency of the plasma actuator, the stronger the effect of the actuator on the flow field. The induced velocity increases non-linearly with increasing loading voltage, however, the increasing rate is getting slower and slower. When the voltage rises to about 30 kV, the acceleration effect of the actuator to air reaches the limit. The induced velocity increases linearly with the increase of the power frequency, but the change of the power frequency does not affect the operating range of the actuator in the vertical direction. Provided that parameters such as loading voltage and power frequency are constant, the higher the inflow velocity, the weaker the actuator’s effect on the flow field. And the higher velocity inflow obviously suppresses the range of the actuator in the vertical direction. [ABSTRACT FROM AUTHOR]

Elastic waves propagating in graphene nanoribbons were studied using both continuum modeling and molecular dynamics simulations. The Mindlin's plate model was employed to model the propagation of interior waves of graphene, and a continuum beam model was proposed to model the propagation of edge waves in graphene. The molecular dynamics results demonstrated that the interior longitudinal and transverse wave speeds of graphene are about 18,450?m/s and 5640?m/s, respectively, in good agreement with the Mindlin's plate model. The molecular dynamics simulations also revealed the existence of elastic edge waves, which may be described by the proposed continuum beam model. [ABSTRACT FROM AUTHOR]

Precise positioning and packing of nanoscale building blocks is essential for the fabrication of many nanoelectro-mechanical devices. Carrying out such manipulations at the nanoscale still remains a challenge. Here we propose the use of graphone domain arrays embedded in a graphene sheet as a template to precisely position and pack molecules. Our atomistic simulations show that a graphone domain is able to adopt well-defined three-dimensional geometries, which in turn create 'energy wells' to trap molecules by means of physisorption. Using the C60 molecule as a model block, the stable trapping conditions are identified. The present work presents a novel route to position and pack molecules for nanoengineering applications. [ABSTRACT FROM AUTHOR]

Abstract: We review the recent advances in the experimental and theoretical investigation of alloy distribution in semiconductor quantum dots (QDs). X-ray diffraction analysis, as well as wet chemical etching, represent two powerful techniques that are able to measure the alloy distribution inside the dots. From a theoretical point of view, determination of the alloy distribution follows from consideration of the thermodynamic quantities involved in the formation and stability of the QD: strain energy, surface energy, internal energy and entropy. Starting from the alloy distribution, the investigation of its role in influencing the electronic and optical properties of QDs is possible. Tight binding and ab initio calculation show the band structure of non-uniform alloyed Ge/Si and InAs/GaAs quantum dots. While for Ge/Si the indirect bandgap does not offer a strong photoluminescence spectra, direct-bandgap materials offer intense light emission, including the range for telecom applications (1.77–1.37μm). Control of alloying inside the QDs allows for the tailoring of their band structure and photoluminescence spectra, where high alloy gradients induce a blue-shift of the spectra, compared to a more uniform composition. [Copyright &y& Elsevier]

-In this paper, we study the unusual properties of electromagnetic waves on the interface between anisotropic metamaterials and conventional materials based on two dimensional periodic unloaded transmission lines. In a certain frequency region, the dispersion relation of the anisotropic metamaterials shows different behaviors separated by resonance frequency, while the shapes of wavevector surfaces are hyperbolic. The asymptotes of these hyperbolic surfaces are in the same directions as the wavevector surfaces in the resonance frequency. Therefore, with careful designing, the interface consisting of the anisotropic and the isotropic grids realizes the frequency selection of the microwave beams' direction. These phenomena can occur in a broad frequency range which is verified by the results of the simulations and experiments. [ABSTRACT FROM AUTHOR]

SUMMARY Published data on the long-term survival results of patients with localized esophageal carcinoma receiving late course accelerated hyper-fractionated radiotherapy (LCAF RT) versus conventional fractionated radiotherapy (CF RT) are inconclusive. In order to derive a more precise estimation of the both treatment-regimes, a meta-analysis based on systematic review of published articles was performed. A meta-analysis was performed using trials identified through Pubmed and Chinese national knowledge infrastructure. Results in 5-year survival and 5-year local control were collected from randomized trials comparing LCAF RT with CF RT. Review Manager (The Cochrane Collaboration, Oxford, England) and Stata software (Stata Corporation, College Station, TX, USA) were used for data management. A total of 11 trials were involved in this analysis with 572 cases and 567 controls. Our results showed that LCAF RT, compared with CF RT, significantly improved the 5-year survival (odds ratio [OR]= 2.93, 95% confidence interval [CI]: 2.15-4.00, P < 0.00001) and 5-year local control (OR = 3.96, 95% CI: 2.91-5.38, P < 0.00001). LCAF RT was more therapeutically beneficial than CF RT in the localized esophageal carcinoma. [ABSTRACT FROM AUTHOR]

Conflicting results on the effects of commensurability, overlap area, helicity and end configuration of double-walled carbon nanotubes (DWCNTs) on translational intertube friction have been reported. We perform molecular dynamics simulations on DWCNTs with different commensurabilities, overlap areas, helicities and end configurations to analyse the intertube friction behaviour and clarify these results. It is found that commensurability and overlap area play an insignificant role, while the atomic configurations of nanotube ends play a dominant role: armchair, normal and reconstructed zigzag ends contribute little to intertube friction; while the irregular ends with dangling atoms greatly increase the friction force. This end effect may also explain the role of helicity in the intertube friction. Implications of the end effect on experimental observations are also discussed. [ABSTRACT FROM AUTHOR]

Male and female nectar robbers may show significantly different behaviour on host plants and thus have different impacts on reproductive fitness of the plants. A 4-year study in natural populations of Glechoma longituba has shown that male carpenter bees ( Xylocopa sinensis) are responsible for most of the nectar robbing from these flowers, while female bees account for little nectar robbing, demonstrating distinct behavioural differentiation between male and female bees in visiting flowers. The smaller male bee spends less time visiting a single flower than the larger female bee, consequently, the male bee is capable of visiting more flowers per unit time and has a higher foraging efficiency. Moreover, the robbing behaviour of female carpenter bees is more destructive and affects flower structures (ovules and nectaries) and floral life-span more than that of the male bee. According to the energy trade-off hypothesis, the net energy gain for male bees during nectar robbing greatly surpasses energy payout (17.72 versus 2.43 J), while the female bee net energy gain is barely adequate to meet energy payout per unit time (3.78 versus 2.39 J). The differences in net energy gain for male and female bees per unit time in nectar robbing are the likely cause of observed behavioural differences between the sexes. The differences in food resource preference between male and female bees constitute an optimal resource allocation pattern that enables the visitors to utilise floral resources more efficiently. [ABSTRACT FROM AUTHOR]

Quasi-one-dimensional comb-like periodic and aperiodic structures composed of positive index materials branch resonators and negative index materials backbone waveguide are physically fabricated by using transmission line approach. It is theoretically shown that the structures possess a non-Bragg band-gap which is invariant with a change of scale length and robust against disorder. The gap edges are determined by zero average permittivity of the branch and the backbone and zero permeability of the backbone materials, respectively. The transmission properties of the structures are investigated by changing the (average) resonator size dBand the resonator spacing dArespectively. The experimental results agree well with the theoretical predictions and numerical simulations, which demonstrate the independence of the special gap on the scaling and disorder in the structures. [ABSTRACT FROM AUTHOR]

Nectar robbing not only affects the reproductive fitness of the plant but it may also potentially affect the pollination dynamics of the associated coflowering individuals. In this study, we established that the nectar robber Xylocopa sinensis robs nectar only from the hermaphrodite ramets of the gynodioecious plant Glechoma longituba but not from the female ramets. In populations with high rates of nectar robbing, this results in hermaphrodite ramets having reduced seed set whereas the female ramets have a slightly increased seed set. We hypothesize that selective nectar robbing confers an advantage to female individuals and thus ensures their maintenance in gynodioecious populations. Results of controlled experiments indicated that the reduction in the amounts of nectar available occasioned by nectar robbing resulted in some legitimate pollinators switching to visiting flowers on female rather than hermaphrodite ramets. This resulted in lower pollination rates and seed set for hermaphrodites and higher pollination rates and seed set for females. This study presents a previously unreported mechanism causing female advantage in gynodioecious plants. [ABSTRACT FROM AUTHOR]

It is still controversial whether adjuvant chemotherapy of cisplatin, 5-fluorouracil and leucovorin can increase the overall survival of esophageal cancer patients, and which subgroup of patients get most benefits from it. Between 1998 and 2004, 66 esophageal cancer patients with adjuvant chemotherapy and 160 well-matched patients without chemotherapy were included in this study. Nine markers were measured in the protein level to analyze prognostic significance. In the whole group, adjuvant chemotherapy did not improve the survival of esophageal cancer patients. There was also no significant difference for survival in stage I ( P=0.59 and P=0.59), stage II ( P=0.28 and P=0.28) and stage III patients ( P=0.144 and P=0.06) between the observation and the chemotherapy group. Chemotherapy was most effective for the patients who had metastases in cervical and/or celiac lymph nodes (IV subgroup). One and 3-year disease-free survival and overall survival were significantly better than for those who did not receive the chemotherapy( P=0.038, and 0.016, respectively). Bcl-2 expression was a bad prognostic factor, and was more predictive in the adjuvant chemotherapy group than in the no-chemotherapy group. Adjuvant chemotherapy significantly improved the treatment result of stage IV patients compared with the observation group. Bcl-2 could be used to analyze prognosis and guide the adjuvant treatment. [ABSTRACT FROM AUTHOR]

Survival of Monilinia fructicola on the surface of mummified fruit and in peduncles and shoots of stone fruit trees infected by M. fructicola in the previous season was studied from 2003 to 2006 in orchards in the agricultural region of Beijing. Viable conidia of M. fructicola were consistently detected on fruit mummies from mid-March to the end of April. During flowering (in mid-April), studies in five peach orchards showed that 33–87% of mummified fruit bore viable conidia. The germination rate of conidia on diseased fruit was about 64% in autumn. It decreased to 24% in mid-winter when the fruit was completely mummified, and in the following year to 2–4% in early spring. Viable M. fructicola was consistently detected in peach and nectarine shoots collected in winter and spring. In general, viable M. fructicola in peduncles was detected from mummified fruit of 11–27% branches and from asymptomatic plant tissues of 3–20% branches. Sporulation of M. fructicola was observed on peduncles in seven of eight surveys, and the percentage of branches containing viable M. fructicola in peduncles in contact with mummified fruits ranged from 18% to 40%. This study demonstrates that the tree-borne mummified fruit and the peduncles could be the parts of trees where M. fructicola can survive the winter in orchards in suburban Beijing. [ABSTRACT FROM AUTHOR]

Nanoindentation using atomic force microscopy (AFM) has found a wide range of applications in characterizing the mechanical properties of cells. However, both conventional Hertz theory and Sneddon's solution face difficulties in interpreting cell indentation data due to lack of considerations of the bilayered structure of cells, the pre-stress of cell membranes and the intrinsic viscoelasticity of cell interior phases. In the present study, the indentation of a cell using AFM is modelled as that of a pre-tensed elastic shell supported by a viscoelastic half-space. Analytical solutions are derived for the shallow indentation of the elastic counterpart of the bilayered structure and then extended to moderate-depth indentation. The cell membrane and its pre-tension are important in interpreting the indentation data if a small indenter is used. Based on the elastic solutions, viscoelastic solutions are derived for creep tests, relaxation tests and linear loading tests, and verified by finite element analysis. Parametric studies were performed to investigate the effects of the membrane pre-stress and the intrinsic viscoelasticity of the cell on the relation between the indentation load vs. indentation depth. In addition, an inverse analysis was performed to extract the viscoelastic parameters of the cell interior phase and the uniqueness of the extraction was assessed. [ABSTRACT FROM AUTHOR]

Mitogen-inducible gene 6 (MIG-6) is located in human chromosome 1p36, a locus frequently associated with human lung cancer. MIG-6 is a negative regulator of epidermal growth factor (EGF) signaling, and we show that Mig-6 – like EGF – is induced by hepatocyte growth factor/scatter factor (HGF/SF) in human lung cancer cell lines. Frequently, the receptors for both factors, EGFR and Met, are expressed in same lung cancer cell line, and MIG-6 is induced by both factors in a mitogen-activated protein kinase-dependent fashion. However, not all tumor lines express MIG-6 in response to either EGF or HGF/SF. In these cases, we find missense and nonsense mutations in the MIG-6 coding region, as well as evidence for MIG-6 transcriptional silencing. Moreover, germline disruption of Mig-6 in mice leads to the development of animals with epithelial hyperplasia, adenoma, and adenocarcinoma in organs like the lung, gallbladder, and bile duct. These data suggests that MIG-6 is a tumor-suppressor gene and is therefore a candidate gene for the frequent 1p36 genetic alterations found in lung cancer.Oncogene (2007) 26, 269–276. doi:10.1038/sj.onc.1209790; published online 3 July 2006 [ABSTRACT FROM AUTHOR]

A constitutive model for thermoplastic polymeric materials and its finite element implementation are presented. The model was verified by both tensile and indentation experimental results. In addition, a five-step indentation scheme, which is able to separate time-dependent plastic deformation from elastic and visco-elastic–plastic deformations, was formulated to extract the complete list of parameters in the constitutive model. Four types of indentation tests on polymethylmethacrylate (PMMA), following the five-step and other schemes, were performed. Experimental data were used to extract all the parameters in the model and verify the five-step test scheme. Good agreement between the experimental results and model prediction indicate that the five-step indentation scheme is a practical approach to determine the mechanical properties of thermoplastic polymers. [ABSTRACT FROM AUTHOR]

Adenosine levels increase in brain during cerebral ischemia, and adenosine has receptor-mediated neuroprotective effects. This study was performed to test the hypothesis that nitrobenzylthioinosine (NBMPR), a selective and potent inhibitor of one adenosine transporter subtype termed ENT1, or es, can protect against ischemic neuronal injury by enhancing adenosine levels and potentiating adenosine receptor-mediated effects, including attenuation of the cellular production and release of tumor necrosis factor-α (TNF-α). In rats, the phosphorylated prodrug form of NBMPR, NBMPR-phosphate, or saline was administered by intracerebroventricular injection 30 min before forebrain ischemia. Seven days following the ischemic episode, rats were killed, and neuronal damage in the CA1 region of the hippocampus was assessed. The number of pyramidal neurons was significantly (p < 0.001) greater in the NBMPR-P treatment group. A trend toward protection was still evident at 28 days postreperfusion. Adenosine increased significantly during ischemia to levels eight- to 85-fold above basal. NBMPR-P treatment did not cause statistically significant increases in ischemic adenosine levels ; however, this treatment tended to increase adenosine levels in all brain regions at 7 min postreperfusion. Ischemia-induced expression of TNF-α was not altered by NBMPR-P treatment, and the nonselective adenosine receptor antagonist 8-(p-sulfophenyl) theophylline did not abolish the neuroprotective effects of NBMPR-P treatment. These data indicate that NBMPR can protect CA1 pyramidal neurons from ischemic death without statistically significant effects on adenosine levels or adenosine receptor-mediated inhibition of the proinflammatory cytokine TNF-α. [ABSTRACT FROM AUTHOR]

Tungsten heavy alloy is a kind of two-phase alloy composed of highstrength tungsten phase and binder phase with good-plasticity. Its mechanical properties and damage evolution are affected by both phases. The static and dynamic mechanical tests of 92.5W-4.9Ni-2.1Fe-0.5Co are carried out. According to the characteristics of stress-strain curves, KHL model is selected as the constitutive model of the material. Then, combined with Eshelby equivalent inclusion theory and Mori Tanaka mean field theory, the stress-strain relationship of each phase in tungsten heavy alloy is studied by introducing representative volume element (RVE). The damage evolution model considering the strain rate effect is proposed, and according to the different loading states, a two-phase constitutive model with damage is established. By compiling the UMAT subroutine, the test conditions of different strain rates are calculated in ABAQUS software. The simulation results are in good agreement with the test results, and the validity of the proposed model is verified. [ABSTRACT FROM AUTHOR]

The article focuses on a study on leaf blotch that is caused by parastagonospora nodorum on Leymus chinensis in a farm in China.

Composition profile across an interface in a core/shell or axial heterojunction nanowire often plays an important role in dictating its electronic, optical and magnetic properties. The control of composition profiles to achieve optimal performance still remains a challenge. In the present work, we formulate a theoretical model which accounts for three key factors that completely control the interface composition profile: the deposition flux of individual components, the atomic exchange rate between the surface and its sub-surface layer, and the thermodynamic driving force for surface segregation. We validate the model by matching its predictions with the experimental results for thin film growth. We then apply the model to the growth of core/shell and axial heterojunction nanowires and show that both abrupt and diffuse interface composition profiles can be achieved by tuning the growth parameters, providing a predictive approach for controlling interface composition distribution. [ABSTRACT FROM AUTHOR]

We investigate the bifurcation instabilities of swelling circular hydrogel plates programed with a space-varying cross-linking density along the radial direction. Depending on the distribution of the cross-linking density and the aspect ratio of the plate, different buckling patterns are observed. When the cross-linking density is lower at the center and increases monotonically outwards, a global buckling occurs, and the hydrogel plate forms an axisymmetric bowl-shaped container. When the cross-linking density is higher at the center and decreases monotonically outwards, edge wrinkling occurs. These wrinkles can be either localized near the edge or penetrate deep into the plate, depending on the detailed distribution of the cross-linking density. The rich post-buckling morphologies exhibited by the programed hydrogel plate provide a powerful route to fabricate smart hydrogel components, such as, self-adjusting containers and microlenses. [ABSTRACT FROM AUTHOR]

Both previous theoretical and experimental work showed that the bending rigidity of a liquid membrane decreases with increasing temperature. We demonstrate that the elastic energy forms for a solid membrane and a liquid membrane are identical under equal-biaxial stretching, implying the bending rigidity of a solid membrane should decrease with increasing temperature. We perform molecular dynamics simulations to study how thermal fluctuation affects the bending rigidity of graphene, and find that the bending rigidity decreases exponentially with increasing temperature. This is in contrast with recent atomistic Monte Carlo simulation result that the bending rigidity of graphene increases with increasing temperature. [ABSTRACT FROM AUTHOR]

We examine the dynamics of surface pattern formation during both annealing and vapor deposition of a heteroepitaxial thin film on prepatterned substrate surfaces, predicting a sustained propagation of regular surface waves via surface diffusion driven by strain relaxation. Both the wavelength and propagation speed are found to be insensitive to the surface prepatterns, growth rate and film thickness. [ABSTRACT FROM AUTHOR]

The variation in dot density, dot size, and photoluminescence intensity in two series of 1.8 and 2.5 ML InAs quantum dots (QDs) as a function of InAs growth rate has been investigated. As the growth rate increases from 0.14 to 3.60 ML/s, the average dot lateral size reduces by half, whereas the dot density increases five times. Nonlinear relationships were observed between dot density, dot size, and growth rate. The dot density is found to saturate at a growth rate of 3 ML/s. High dot density of 7.76×1011 cm-2 has been demonstrated and is beneficial for applications in high power QD devices. [ABSTRACT FROM AUTHOR]

Three-dimensional computer simulations are performed to obtain the phase diagrams for heteroepitaxially grown ordered quantum dots and quantum rings by surface prepatterning. Concave patterning in a squared array may lead to the formation of ordered dots, whereas convex patterning in a squared array may initially lead to the formation of ordered quantum rings, then a transition into quantum dots with further growth. The evolution of the surface chemical potential during growth explains the formation of the ordered surface structures. [ABSTRACT FROM AUTHOR]

The formation, self-assembly, and shape transition of heteroepitaxial islands during Stranski-Kranstonov growth are studied by three-dimensional computer simulations. It is shown that calculations considering surface energy anisotropy and elastic anisotropy reproduce many features of experimental results, and demonstrate the significance of their influence on island formation and self-assembly in epitaxial growth. [ABSTRACT FROM AUTHOR]

First-order perturbation analysis has been performed to investigate the stability and the fastest growth mode of a biaxially strained epitaxial thin film surface by stress-induced surface diffusion. It is found that the normalized critical wavelength along one principal direction depends on the Poisson’s ratio of the film, and also the perturbed wavelength and stress level along the other principal direction. The fastest growth analysis shows that when the absolute value of the ratio of the two principal stresses deviates from unity, a gradual transition from nanoisland formation to nanowire formation occurs. The larger the deviation, the stronger the tendency for the formation of a nanowire; finite element simulations confirm the tendency. [ABSTRACT FROM AUTHOR]

We report long-wavelength photoluminescence emission (∼1.6–1.7 μm) from self-organized InAs surface quantum dots (SQDs) grown on GaAs substrate without any capping layers. Photoluminescence (PL) properties of these quantum dots (QDs) are strongly affected by the surface states and strain relaxation mechanism. Compared to the case of capped InAs QDs, a large redshift of about 466 nm observed in the PL spectrum of SQDs can be attributed to the strain relaxation and the strong coupling of the confined states with the surface states. The PL properties of these SQDs can also be influenced by the presence of quasi-infinite surface potential. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations are performed to investigate the bending behavior of tubular graphite cones (TGCs). The second-generation reactive bond-order potential and four different van der Waals potentials are used to describe bonding and nonbonding atomic interactions, respectively. It is shown that the bending behavior is insensitive to the choice of the van der Waals potentials. An increase in the cone apex angle of TGCs moderately improves the bending stiffness due to the low shear resistance between the nanotube walls. A TGC with a high cone apex angle is preferred to a TGC with a low cone apex angle in terms of bending stiffness and stress level. It is also shown that an increase in the diameter of the innermost nanotube effectively increases the bending stiffness of TGCs. [ABSTRACT FROM AUTHOR]

Dislocation formation in homoepitaxial pyramidal [001] Cu islands under tensile stress is studied using molecular dynamics simulations. It is found that 90° Shockley partial dislocations are dominant in the island strain relaxation. For a low-aspect-ratio island, the dislocations are nucleated from the island surface and propagate downwards to form misfit dislocations. For a high-aspect-ratio island, a pair of the dislocations on the same slip plane are simultaneously nucleated respectively from the two island edges, propagate inwards, and react to form a 90° Shockley misfit partial dislocation. These dislocations can form sequentially and cooperatively. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The self-organization of three-dimensional quantum-dot superlattices that spontaneously form during heteroepitaxial growth is investigated by using a three-dimensional kinetic model. The model predictions show that the multilayer arrays of quantum dots can be fully or partially aligned vertically, or completely misaligned with respect to the buried islands, depending on the thickness of the spacer layer and the growth interruption time. In particular, there is a growth window in which a nearly uniform and regular array of dots is arranged in a squared lattice with an alternating stacking sequence; namely, the A-B-A-B stacking sequence. [ABSTRACT FROM AUTHOR]

A continuum model of shape transitions in strained heteroepitaxial islands predicts that small islands are hut shaped, while larger islands are domed. The volume of a stable hut can exceed that of a stable dome, however, indicating that the stability of hut-shaped islands plays an important role in shape transition, in addition to energy changes associated with the transition. A hut-shaped island loses stability upon reaching a critical volume, which depends on the anisotropy in surface energy. Impingement between islands reduces the critical volume by nucleating new facets at the base of a hut, which subsequently trigger a shape transition. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Bulk waves radiated into an anisotropic half-space by an interdigital transducer are studied theoretically. The mechanical displacements of excited waves are obtained by asymptotic evaluation of an integral whose singularities give rise to both Rayleigh surface waves and angularly focused bulk waves. By applying the analysis to singly rotated Y cuts of quartz with propagation normal to the x axis, it is shown that the orientation and width of the main lobe are very sensitive to frequency and crystal orientation. [ABSTRACT FROM AUTHOR]

In order to reduce dynamic loss and improve the performance of low-pressure turbines, the technology of active flow control of a dielectric barrier discharge plasma actuator was used to control the internal flow of a low-pressure turbine using a numerical simulation method. In this paper, the effect of plasma actuation on the cascade flow field with different actuator positions and applied voltages was studied. The results show that the closer the plasma actuator is to the leading edge of the cascade, the better the control effect of the plasma actuation. When the actuator is aligned with the leading edge of the cascade, the total pressure loss at the outlet is reduced by 4.5%. Plasma actuation has a greater ability to restrain outlet loss at higher voltage, but the control effect tends to saturation as the applied voltage increases. Total pressure loss is reduced by 8.2% for U0 = 15 kV. The plasma actuation decreases the lateral pressure gradient in the cascade passage thus suppresses the lateral movement of low energy fluids from the pressure side to the suction side. The height of the passage vortex and total pressure loss are restrained, which is an important reason for decreasing outlet loss. [ABSTRACT FROM AUTHOR]

Here, we present a preselected small set of ordered structures (PSSOS) method, a first principles-based high fidelity (HF), high throughput (HT) approach, for fast screening of the large composition space of high entropy alloys (HEAs) to select the most energetically stable, single-phase HEAs. Taking quinary AlCoCrFeNi HEA as an example system, we performed PSSOS calculations on the formation energies and mass densities of 8801 compositions in both FCC and BCC lattices and selected five most stable FCC and BCC HEAs for detailed analysis. The calculation results from the PSSOS approach were compared with existing experimental and first-principles data, and the good agreement was achieved. We also compared the PSSOS with the special quasi-random structures (SQS) method, and found that with a comparable accuracy, the PSSOS significantly outperforms the SQS in efficiency, making it ideal for HF, HT calculations of HEAs. [ABSTRACT FROM AUTHOR]

Submerged close-range impinging jets (CRIJs) are widely applied to numerous engineering fields; however, the research on the dynamic flowfield of close-range impinging jets, especially when the impinging distance is very small, is not yet sufficient in the numerical simulation and experiment. In the present study, the time-resolved particle image velocimetry (TR-PIV) is used to measure the dynamic flowfield of an impinging jet with the impinging distance of H/D = 1. Here, H is the nozzle inner diameter and D is the impinging distance. The effects of the Reynolds number Re and the nozzle end-profile (wall constraints) on the vortex generation and migration inside and outside the gap are investigated. The obtained experimental data are further analyzed using the vorticity analysis and the proper orthogonal decomposition (POD) method. It is found that the Reynolds number affects the vortex generation and migration in different ways for nozzles with different end-profiles. The Reynolds number affects only slightly the flow pattern of the basic nozzle (nozzle I). On the contrary, the Reynolds number can strongly affect the flow pattern of the bevel nozzle (nozzle II) and dynamic vortices can appear when the value of Re increases to 1600. The dynamic vortex migration from the gap to the outside exhibits significant periodic characteristics. The vorticity analysis determines the vorticity size and distribution of the time-averaged field. Further, the energy distribution and variation in the vortices outside the gap are revealed based on the distribution of the large-scale structure of the transient field in the POD analysis. The transient pulsating velocity fields of the first four modes illustrate the abrupt and periodic characteristics of the velocity field at the microscopic time-scale. [ABSTRACT FROM AUTHOR]

The effect of Hf and Ta on the microstructure of powder metallurgy Ni-based superalloys after heat treatment was investigated. Hf and Ta change the distribution and main components of MC carbides, inhibiting TiC carbides precipitate along prior particle boundaries by forming stable Hf- and Ta-rich carbides inside powders during the process of hot isostatic pressing. The partition of Hf and Ta in γ′ phase causes the repartition of other elements in γ and γ′ phases, which leads to the change of the lattice mismatch of γ and γ′ phases. The size of secondary γ′ precipitates increases and their shapes transform from spheres to cuboids when Hf or Ta content is raised, and some secondary γ′ precipitates begin to split in high Hf and Ta content. This transformation of morphology is related to the increase of the lattice mismatch of γ and γ′ phases, and the increase in size and volume fraction of secondary γ′ precipitates. [ABSTRACT FROM AUTHOR]

Interfacial adhesion between polymer matrix and reinforcing silica nanoparticles plays an important role in strengthening polypropylene (PP) composite. To improve the adhesion strength, the surface of silica nanoparticles can be modified by grafted functional molecules. Using atomistic simulations, we examined the effect of functionalization of silica nanoparticles by hexamethyldisilazane (HMDS) and octyltriethoxysilane (OTES) molecules on the deformation and failure of silica-reinforced PP composite. We found that the ultimate tensile strength (UTS) of PP composite functionalized by OTES (28 MPa) is higher than that of HMDS (25 MPa), which is in turn higher than that passivated only by hydrogen (22 MPa). To understand the underlying mechanistic origin, we calculated the adhesive energy and interfacial strength of the interphase region, and found that both the adhesive energy and interfacial strength are the highest for the silica nanoparticles functionalized by OTES molecules, while both are the lowest by hydrogen. The ultimate failure of the polymer composite is initiated by the cavitation in the interphase region with the lowest mass density, and this cavitation failure mode is common for all the examined PP composites, but the cavitation position is dependent on the tail length of the functional molecules. The present work provides interesting insights into the deformation and cavitation failure mechanisms of the silica-reinforced PP composites, and the findings can be used as useful guidelines in selecting chemical agents for surface treatment of silica nanoparticles. [ABSTRACT FROM AUTHOR]