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To explore the physiological response characteristics of plant photosynthesis under acid precipitation stress (A stress), snow-melting agent stress (S stress), and freeze-thaw stress (F stress) as well as their various combinations, the net assimilation rate (NAR), intercellular CO2 concentration (Ci), stomatal conductance (Gs) and water use efficiency (WUE) of tall fescue (Festuca arundinacea Schreb.) under these three stresses respectively and four kinds of combined stresses were measured. The effects of these different kinds of stresses on the photosynthesis parameters were then evaluated, and the major mechanisms of main factors affecting the interactions between stresses were speculated. The experimental results indicated that both NAR and WUE decreased significantly in response to all stresses and Ci increased dramatically in response to all stresses, while Gs ascended under F stress but descended in response to A stress and S stress. The photosynthetic efficiency significantly decreased as the temperature decreased and did not clearly recover as the temperature increased. Moreover, the combination of A stress and S stress had fewer effects on photosynthesis than did the S stress alone, while the effects resulting from F stress were similar at low temperature. The major controlling mechanism is most likely the strong inhibition of photosystem II and the promotion of antioxidant enzymes resulting from acid precipitation as well as NaCl may strengthen the freezing tolerance of plants.

The shell transfer arm is a key component of gun automatic loading mechanism, the coordination speed and positioning accuracy have an important impact on gun ammunition delivery effect. Establishing an accurate dynamic model is the foundation for better control and prediction, therefore, it is necessary to identify the dynamic parameters of the shell transfer arm. In this paper, the dynamic model is established based on the topology method. The parameter identification model of the shell transfer arm is constructed by applying the dynamic model and unscented Kalman filter theory. Dynamic parameters of the shell transfer arm such as the mass, inertia and centroid position are estimated under unscented Kalman filter scheme. By comparing the parameter estimation results with the nominal design values, the feasibility and effectiveness of applying the proposed method to identify the dynamic parameters of the shell transfer arm are verified.

Building Information Modeling (BIM) models require sufficient semantic information and consistent modeling style to conduct Quantity Take-off (QTO) smoothly. However, BIM models created by different BIM modelers may have various mistakes about these requirements and auditing such BIM model behavior involves tremendous human effort for manual inspection or the development of rule sets. This study proposes an automatic and efficient BIM model auditing framework for QTO utilizing knowledge graph (KG) techniques. It begins at establishing a BIM-KG definition via identifying required information for auditing purposes. Subsequently, BIM data is automatically transformed into the BIM-KG representations, the embeddings of which are trained using a knowledge graph embedding model. Automatic mechanisms are then developed to utilize the computable embeddings to effectively identify mistake BIM elements. The framework is validated using illustrative examples and the results show that 100% mistake elements can be identified successfully without human intervention.

Uncut Roux-en-Y anastomosis is widely used in gastrointestinal reconstruction procedure after radical gastrectomy for distal gastric cancer. However, the proximal jejunal closure point recanalization of the input loop is an important complication of postoperative patients with prolonged time, resulting in pancreatic juice or bile reflux, which can lead to inflammatory lesions of the remnant stomach or esophagus. Poor selection of the location of the closure point during anastomosis causes a large amount of food deposited in the blind loop to be pushed and impacted, resulting in loosened threads or failed U-shaped staples, which may cause recanalization complications. Most scholars believe that the shortening of the jejunal tube closure point to the optimal position of 2 to 3 cm from the residual gastrojejunostomy can significantly reduce food retention, decrease the pressure of the closure point and the incidence of recanalization. At present, the application of new anastomotic techniques and materials such as four-row and six-row U-shaped staples and 7# wire ligation under laparoscopy can prevent the occurrence of recanalization of the closure point. Uncut Roux-en-Y anastomosis is safe and has few complications, and is expected to become one of the best ways of digestive tract reconstruction.非离断（Uncut）Roux-en-Y吻合术是目前远端胃癌根治术后应用比较广泛的消化道重建术式。但是，其输入袢近端空肠闭合点再通是患者术后随时间延长而易出现的重要并发症，引起的胰液或胆汁反流，可导致残胃或食管发生炎性病变。吻合时闭合点位置选择不佳，使盲袢中大量沉积食物受到推挤冲击以及丝线松脱、U型缝钉脱落等因素，均可导致再通并发症的发生。多数学者认为，空肠管闭合点缩短至距残胃空肠吻合口2~3 cm处位置最佳，可明显减少食物滞留量，减轻闭合点压力，降低再通率。目前，腹腔镜下四排、六排U型缝钉和7号丝线束扎等新的吻合技术和材料的应用，可预防闭合点再通的发生，Uncut Roux-en-Y安全、并发症少，有望成为消化道重建的最佳方式之一。.

The aim of this study was to research the potential mechanism of INHBC and CSF1R in diabetic nephropathy.30 SD rats were selected and randomly divided into Con group, Sham group, and DN group. In the DN group, intraperitoneal injection of the streptozotocin-citrate solution was conducted to construct the DN model. In the Sham group, intraperitoneal injection of equal citrate solution was conducted. The Con group did not do anything. After successful modeling, blood glucose, insulin, biochemical indexes, and levels of inflammatory cytokines in blood samples were detected. The expression levels of INHBC, CSF1R, apoptosis-related proteins and IGF-1 were detected by Western blot. MRNA expression levels of INHBC, CSF1R, IGF-1 and inflammatory cytokines were detected by qPCR.Compared with the Con group, the expression levels of blood glucose, insulin, biochemical indexes, INHBC, CSF1R, IGF-1, IL-6, TNF-α and Bcl2 increased in the DN group, while the expression levels of IL-10, Caspase 3, Caspase 9, and Bax decreased. INHBC mRNA was positively correlated with IGF-1 mRNA. CSF1R was negatively correlated with Caspase 3, Caspase 9, Bax, and IL-10, and positively correlated with IL-6, TNF-α, and Bcl2.NHBC and CSF1R induced the secretion of IL-6 and TNF-α, inhibited the production of IL-10, inhibited apoptosis of cells, and promoted the proliferation of renal cells during DN disease. Therefore, INHBC and CSF1R can be used as target objects of DN treatment strategies.

This paper reviews the evolution of offsite construction methods in UK housing over the past 15 years and puts this in an international context. Long-standing themes include targets for construction productivity, challenges of labour shortages and skills, desire to learn across sectors and a need to develop new business models. Newer developments include research and development funding through the UK government’s ‘transforming construction’ initiative, higher pre-manufactured value and increased digitisation. The paper concludes with recommendations for practice, policy and research.

With development of smart grid, the stable operation of grid has put forward higher requirements for system dispatch. In particular, short-term load forecasting of power systems is a key factor of power grid management systems, which is related to the safety, economy, and stable operation of the smart grid. However, short-term electricity forecasting is affected by many external factors. It has complex characteristics, especially non-linear relationships, so it cannot be accurately predicted. Recently, Recurrent Neural Network based models have good performance in electricity forecasting because of their excellent ability to capture non-linear relationships. However, they cannot fully capture historical information, especially local historical information, which has an impact on prediction accuracy. In order to address these problems, we propose a scheme by combining STL decomposition and GRU model. Specifically, we first decompose the original time series into three different components by STL. The decomposition results are separately imported into the main prediction module, which uses two GRU networks with different structures to obtain the local and global dependencies of the data. We also add an autoregressive method to make the model more robust. The proposed scheme is validated based on real-world data, and the simulation results show that our proposed method can perfectly capture local and global information and achieve higher prediction accuracy than traditional models.

Osteosarcoma is a malignant bone tumor with high incidence. The prognosis of osteosarcoma is very poor when it is diagnosed with metastasis. Numerous studies have demonstrated that aberrant expressions of microRNAs are involved in cancer initiation and development. However, the potential role of miR-214 in osteosarcoma remains largely unrevealed. The current study investigated the relationship between the miR-214 and TNF receptor-associated factor 3 (TRAF3) in osteosarcoma tissues and cell lines. We also aimed to evaluate the potential roles of miR-214 on the occurrence and metastasis in osteosarcoma and verify its effect on the regulation of TRAF3.The miR-214 expression and TRAF3 expression in osteosarcoma tissue samples and cell line were measured using quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR). Followed by transfection assays, transwell assay was conducted to detect the migration and invasion abilities of osteosarcoma cells. Subsequently, Western blotting and luciferase reporter assay were performed in osteosarcoma cells to confirm the target of miR-214.The results showed that miR-214 expression levels were significantly increased not only in osteosarcoma tissues but also in osteosarcoma cell lines as compared with adjacent normal tissues and matched cell lines, respectively. On the contrary, the TRAF3 expression levels in osteosarcoma tissues and cell lines were frequently decreased compared to the control group. Moreover, TRAF3 was identified as a direct target of miR-214 and the inverse relationship between them was also observed in osteosarcoma tissues. Additionally, we found that miR-214 restoration could significantly promote osteosarcoma cell invasion and migration via targeting TRAF3.MicroRNA-214 functioned as an oncogene in osteosarcoma via targeting TRAF3, which may provide new insights into osteosarcoma prevention and treatment.

Detached eddy simulation (DES) of the liquid-phase turbulent flow in an unbaffled stirred tank agitated by a six-blade, 45°-pitched blade turbine was performed in this study. The tank wall is cylindrical with no baffle and the fluid flow problem was solved in a single reference frame (SRF) rotating with the impeller. For the purpose of comparison, computation based on large eddy simulation (LES) was also carried out. The commercial code Fluent was used for all simulations. Predictions of the phase-averaged turbulent flow quantities and power consumption were conducted. Results obtained by DES were compared with experimental laser Doppler velocimetry (LDV) data from the literature and with the predictions obtained by LES. It was found that numerical results of mean velocity and turbulent kinetic energy profiles as well as the power consumption are in good agreement with the LDV data. When performed on the same computational grid, which is under-resolved in the sense of LES, DES allows better accuracy than ...

We demonstrate GaN-based double-layer electrode flip-chip light-emitting diodes (DLE-FCLED) with highly reflective indium-tin oxide (ITO)/distributed bragg reflector (DBR) p-type contact and via hole-based n-type contacts. Transparent thin ITO in combination with TiO2/SiO2 DBR is used for reflective p-type ohmic contact, resulting in a significant reduction in absorption of light by opaque metal electrodes. The finely distributed via hole-based n-type contacts are formed on the n-GaN layer by etching via holes through p-GaN and multiple quantum well (MQW) active layer, leading to reduced lateral current spreading length, and hence alleviated current crowding effect. The forward voltage of the DLE-FCLED is 0.31 V lower than that of the top-emitting LED at 90 mA. The light output power of DLE-FCLED is 15.7% and 80.8% higher than that of top-emitting LED at 90 mA and 300 mA, respectively. Compared to top- emitting LED, the external quantum efficiency (EQE) of DLE-FCLED is enhanced by 15.4% and 132% at 90 mA and 300 mA, respectively. The maximum light output power of the DLE-FCLED obtained at 195.6 A/cm2 is 1.33 times larger than that of the top-emitting LED obtained at 93 A/cm2.

Mildew resistance locus o (MLO) is a plant-specific seven-transmembrane (TM) gene family. Several studies have revealed that certain members of the MLO gene family mediate powdery mildew susceptibility in three plant species, namely, Arabidopsis, barley, and tomato. The sequenced cucumber genome provides an opportunity to conduct a comprehensive overview of the MLO gene family. Fourteen genes (designated CsMLO01 through CsMLO14) have been identified within the Cucumis sativus genome by using an in silico cloning method with the MLO amino acid sequences of Arabidopsis thaliana and rice as probes. Sequence alignment revealed that numerous features of the gene family, such as TMs, a calmodulin-binding domain, peptide domains I and II, and 30 important amino acid residues for MLO function, are well conserved. Phylogenetic analysis of the MLO genes from cucumber and other plant species reveals seven different clades (I through VII). Three of these clades comprised MLO genes from A. thaliana, rice, maize, and cucumber, suggesting that these genes may have evolved after the divergence of monocots and dicots. In silico mapping showed that these CsMLOs were located on chromosomes 1, 2, 3, 4, 5, and 6 without any obvious clustering, except CsMLO01. To our knowledge, this paper is the first comprehensive report on MLO genes in C. sativus. These findings will facilitate the functional characterization of the MLOs related to powdery mildew susceptibility and assist in the development of disease resistance in cucumber.

Nitride-based high power LEDs with finger-like SiO2 current blocking layer (CBL), three-dimensional (3D) patterned step-like ITO double layers and wavy sidewalls were fabricated. The finger-like SiO2 CBL beneath finger-like p-electrode was designed to prevent current crowding effect, thereby facilitating uniform current spreading over the entire chip. In addition, 3D patterned step-like ITO double layers, including alternating 230 nm thick patterned upper step ITO layer and 100 nm thick lower step ITO layer, were formed by combining photolithography and aqua regia etchant. We showed that the top light extraction efficiency of high power LEDs can be significantly enhanced by taking 3D patterned step-like ITO. The light output power of high power LEDs with 3D patterned step-like ITO double layers is 13.9% higher than that of LEDs with smooth ITO layer. High-power LEDs with wavy sidewalls was fabricated by an optimized mask design in conjunction with dry etching process based on Cl2/BCl3 to improve light extraction efficiency at the horizontal direction. We demonstrated that light output power of high power LEDs with wavy sidewalls can be improved by 11% as compared to LEDs with flat sidewalls.

A study was carried out on the deformation of nanocrystalline cobalt. For cold-rolled nanocrystalline cobalt, the X-ray diffraction peaks narrowed instead of broadened on deformation. The results of transmission electron microscopy showed that grain size (17.8 nm on average) was not increased. The results can be explained in terms of the production and activity of vacancies and vacancy clusters.

Numerical simulations based on the RANS model are known to have drawbacks of low accuracy in predicting the turbulence quantities of the flow fields in stirred tanks. For this purpose, the detached eddy simulation (DES) model was employed to simulate the turbulent flow in an unbaffled dish-bottom stirred tank. The free-surface deformation was modelled by the volume of fluid (VOF) method. The numerical predictions were validated with LDV measurements reported by Haque et al. (Haque, J. N., Mahmud, T., Roberts, K. J., Liang, J. K., White, G., Wilkinson, D., Rhodes, D., Can. J. Chem. Eng. 89 (2011) 745)11. The results show that the predicted surface profiles using the combination of DES and VOF are generally better than their counterparts obtained by the k-ε model. The mean velocity components and turbulent kinetic energy are in good agreement with the experimental results. By comparison, the differences between the k-ε predictions and the LDV data are much greater. These findings indicate that DES works better than k-ε model in the prediction of the free-surface hydrodynamics in stirred tanks.

Decohesion is an important failure mode associated with layered composite materials. Here, the energy implications of material softening are explored in a thermodynamic framework with the result that the dissipated energy (fracture energy) is greater than the plastic work of the traction on the failure surface. It is also argued that if the traction and continuum constitutive equations are solved simultaneously, the resulting algorithm is as simple as that for conventional plasticity. For numerical simulations, the material point method displays the attributes of no mesh deformation so that remeshing is not necessary and the continuous tracking of material points avoids the need for remapping history variables such as decohesion. Compatibility is invoked in a weak sense with the result that no special algorithms are needed for mesh realignment along crack surfaces or for double nodes. Example solutions exhibit no sensitivity of delamination propagation with mesh orientation.

The elastic displacement field of a jogged screw dislocation is obtained analytically from Burgers equation. With this analytic solution, a pair of jogs in a screw dislocation is implemented into molecular-dynamics simulations. The dislocation line bows out between two jog pinning points and breaks away when the line tension of the dislocation exceeds a certain critical value. The creation of vacancies and interstitials is observed during the non-conservative motion of the jogged screw dislocation in γ-TiAl. The structures of vacancies and interstitials are discussed.

The surface stress distribution in an ordered quantum dot superlattice is investigated using classical molecular dynamics simulations. We find that the surface stress field induced by various numbers~ from 1t o 9! of Ge islands embedded in a Si~001! substrate is in good agreement with analytical expressions based on pointlike embedded force dipoles, explaining the tendency of layered arrays to form vertically aligned columns. The short-ranged nature of this stress field implies that only the uppermost layers affect the surface growth and that their influence decreases rapidly with layer depth. @S0163-1829~99!52028-6#

We examined the Sun's shadow by 10 TeV cosmic rays observed with the Tibet air shower array during the period from 1991 through 1997. The results suggest that there is a causal relation between the shadow's movement and the changing inclination of the heliospheric current sheet of the large-scale solar magnetic field. Thus, further observations with higher statistics may provide direct information on the relation between a time variation of the large-scale structure of the solar and interplanetary magnetic fields and the phase of solar activity cycle.

The problem of dry friction between two metallic interfaces is discussed from the perspective of large scale molecular dynamics (MD) simulations. For flat interfaces between identical metals, two-dimensional MD simulations using embedded-atom-method potentials for copper have shown a variety of phenomena associated with a velocity weakening of the tangential force at high relative velocities (approaching significant fractions of the transverse sound speed). These include dislocation generation, dislocation motion both parallel and normal to the sliding interface, large plastic deformation, nucleation of microstructure, diffusive coarsening of microstructure, and material mixing. The early time behavior of a flat sliding interface is dominated by dislocation motion parallel to the interface. For this early stage, lower-dimensional models are useful in interpreting some of the simulation data. A two-chain forced Frenkel-Kontorova model reproduces some of the behavior of the larger scale simulations when the phenomenological damping is taken to be consistent with the MD simulations. This model exhibits four velocity regimes of steady state flow which will be discussed. Some of the implications for the nucleation of microstructure will be addressed.

Molecular-dynamics simulations of dynamic fracture show that local shear deformation at the crack tip increases, and local potential energy builds up, eventually triggering dislocation emission — the instability that leads to crack branching. Neither the build-up nor the instability can be predicted by linear-continuum theories. We propose a simple nonlinear-discrete model, which demonstrates that the excitation of nonlinear modes generates this instability.

We describe the historical development of large-scale nonequilibrium molecular-dynamics (NEMD) computer simulations of fracture at Los Alamos. We have found that dynamic crack propagation leads to energy buildup that seeds instabilities, such as dislocation emission and branching. Recent three-dimensional simulations have shed light on ductile fracture mechanisms, including sequences of dislocation emission in various modes that are strikingly different from anything previously conjectured. The future for constitutive modeling, based on observations of dynamical features in such NEMD simulations is quite bright, and one such example is discussed.

We briefly present recent results obtained with our parallel molecular dynamics (MD) code, SPaSM, performing large-scale multi-million atom simulations to study crack blunting and dislocation generation in copper. We also discuss some recent work addressing the problems associated with analyzing and visualizing the data generated from multi-million particle MD simulations.

A series of molecular-dynamics simulations has been performed in order to evaluate the effects of several physical factors on dynamic crack stability. These factors are the crystalline structure and the interatomic interaction modeled by various empirical potentials. For brittle crack propagation at low temperature we find that steady-state crack velocities are limited to a band of accessible values. Increasing the overload beyond ${\mathrm{K}}_{\mathrm{Ic}}$, the crack can propagate with a steady-state velocity, which quickly reaches the terminal velocity of about 0.4 of the Rayleigh wave speed. The magnitude of the terminal velocity can be related to the nonlinearity of the interatomic interaction. Further increasing the overload does not change the steady-state velocity dramatically, but significantly increases the amplitude of acoustic emission from the crack tip. Loading the crack even further leads to instabilities which take the form of cleavage steps, dislocation emission, or branching. The instability is closely related to the buildup of a localized coherent, phononlike field generated by the bond-breaking events. The form of the instability depends critically on crystal structure and on the crystallographic orientation of the crack system but can also be correlated with the relative ease of dislocation generation (and motion).

We have performed massively parallel 3D molecular dynamics simulations with up to 35 million atoms to investigate ductile failure, obtaining mechanistic information at the atomistic level inaccessible to experiment. We observe dislocation loops emitted from the crack front{emdash}the first time this has been seen in computer simulations. The sequence of dislocation emission events, essential for establishing an intrinsic ductility criterion, strongly depends on the crystallographic orientation of the crack front and differs strikingly from anything previously conjectured. {copyright} {ital 1997} {ital The American Physical Society}

We performed embedded atom method calculations of surface energies and unstable stacking fault energies for a series of intermetallics for which interatomic potentials of the embedded atom type have recently been developed. These results were analyzed and applied to the prediction of relative ductility of these materials using the various current theories. Series of alloys with the B2 ordered structure were studied, and the results were compared to those in pure body-centered cubic (bcc) Fe. Ordered compounds with L12 and L10 structures based on the face-centered cubic (fcc) lattice were also studied. It was found that there is a correlation between the values of the antiphase boundary (APB) energies in B2 alloys and their unstable stacking fault energies. Materials with higher APB energies tend to have higher unstable stacking fault energies, leading to an increased tendency to brittle fracture.

Few studies look into cerebral blood flow (CBF) changes during emergence from general anaesthesia for craniotomy. The purpose of this study was to assess CBF changes during emergence from general anaesthesia for craniotomy, through monitoring blood oxygen saturation of jugular vein bulb (SjvO2 ) and transcranial Doppler (TCD).We enrolled 30 patients undergoing selective craniotomy (group C) for supratentorial brain tumour resection and 30 patients undergoing selective abdominal surgery (group A). Mean velocity of middle cerebral artery (Vmca), mean arterial pressure (MAP), SjvO2 (only measured in group C), and arterial CO2 partial pressure were measured before anaesthesia, at tracheal extubation, and 30, 60, 90, 120 min after extubation.Vmca of the same side of tumour was significantly higher than contralateral Vmca before anaesthesia and at all times after extubation in group C. The ipsilateral Vmca increased significantly (95.7 ± 16.9 cm/s vs. 63.7 ± 6.7 cm/s, P 0.01) at extubation in group C, then declined but still above baseline significantly in the first 2 h after extubation. While Vmca of the right side changed only slightly (63.6 ± 7.7 cm/s vs. 61.8 ± 8.1 cm/s, P 0.01) but significantly at extubation in group A. SjvO2 increased significantly (81.4% ± 7.4% vs. 60.9% ± 3.7%, P 0.01) at extubation in group C, and remained above baseline significantly for 2 h. There was no significant correlation between Vmca and MAP at any time.Cerebral hyperaemia occurs after supratentorial brain tumour resection surgery. The hyperaemia is more pronounced on the same side as the tumour.

We have discussed the prospects of applying massively parallel molecular dynamics simulation to investigate brittle versus ductile fracture behaviors and dislocation intersection. This idea is illustrated by simulating dislocation emission from a three-dimensional crack. Unprecedentedly, the dislocation loops emitted from the crack fronts have been observed. It is found that dislocation-emission modes, jogging or blunting, are very sensitive to boundary conditions and interatomic potentials. These 3D phenomena can be effectively visualized and analyzed by a new technique, namely, plotting only those atoms within the certain ranges of local potential energies.

From large-scale molecular-dynamics simulations of dynamic crack propagation, we find that cracks accelerate quickly to a relatively steady velocity. Energy released by bond breaking accumulates in a local phonon field that moves with the crack tip and promotes the emission of dislocations. Branching follows dislocation emission along a slip plane. The branching instability requires the crack to achieve a critical velocity, as well as in induction time for energy buildup at the crack tip. {copyright} {ital 1996 The American Physical Society.}

The effect of processing-induced fiber damage, or equivalently the effect of fiber length in discontinuously-reinforced composites, on the tensile stress-strain behavior of a fiber-reinforced ceramic or metal matrix is determined as a function of the extent of initial fiber damage and the pristine fiber strength distribution. The analysis combines a generalization of the analysis employed for the undamaged fiber problem [Curtin, W. A. (1991) Theory of mechanical properties of ceramic-matrix composites. J. Am. Ceram. Sec. 74, 2837-2845] and numerical simulations to predict the stress-strain curve, ultimate tensile strength and strain, fiber pullout, and work of pullout in terms of the underlying micromechanical material parameters. The results show that the characteristic scale of initial damage required to weaken the composite substantially is always of the order of one fiber break per length delta(c), where delta(c) is the critical fiber slip length in the undamaged composite (typically similar to 1 mm). Overall, the effect of damage on tensile strength, failure strain, and pullout is found to be fairly small, which is attributed to the load carrying capacity of broken fibers due to the sliding resistance of the fiber/matrix interface. However, the detailed stress-strain behavior of the composite is modified. The analysis is applied to a Nicalon/CAS composite in which ''premature'' fiber damage has been observed. The inclusion of initial fiber damage into the theory accurately accounts for the excess strain, lower tangent modulus, and lower ultimate strength (relative to the predictions in the absence of initial fiber damage) observed in this material.

A series of atomistic calculations is performed in order to explore dislocation core-core interactions and the Peierls stress in a model hexagonal lattice. The method of calculation is the lattice Green`s function method, using several pair potentials with variable parameters. We confirm that dislocation cores broaden as a pair of dislocations with opposite sign move closer to each other. Continuum theories are surprisingly accurate in describing the dislocation-dislocation interaction force even in the range of strong core-core overlap. However, our atomistic calculations show that while the relation between the Peierls stress and dislocation width is exponential as the Peierls-Nabarro model predicts, that model underestimates the Peierls stress by nearly a factor of 10{sup 4}.

Using the lattice Green function approach, we study the crack-dislocation effects in the fracture of crystalline materials. Firstly, we calculate the Green function for the defective lattice, with dislocation and crack, by solving the Dyson equation. After the lattice Green functions have been determined, the relaxation problem for the reconstituted bonds in the cohesive zone is solved. The external force F with tensile and shear components is applied, as a pair of forces, to the atoms at the center of the crack. In this calculation the dislocation emission is chosen to be on a cleavage plane as well as on a glide plane of the two-dimensional lattice (hexagonal and graphite lattices). We compare the cleavage and dislocation emission criteria of the atomistic simulation with those of linear elasticity theory.

A series of atomistic calculations is performed in order to evaluate the effects of several physical factors on dislocation emission in a model hexagonal lattice. The method of calculation is the lattice Green's-function method, together with several pair potentials with variable parameters. The physical factors of interest are the dislocation width (or, more precisely, maximum strain) and ``unstable stacking energy'' suggested by several continuum-based calculations, as well as the mode-I loading. We find that the continuum theories are surprisingly accurate, provided that some modifications are made. Typical discrepancies are of order 10% in the emission stress intensity. However, the atomistic calculations indicate that several of the assumptions underlying the continuum theories are inaccurate. In addition, we find strong mode-I--mode-II interactions, which are summarized in the form of a crack-stability diagram.

This paper explores the use of lattice Green's functions for calculating the static structure of defects in lattices, in that the atoms of the lattice interact with their neighbors with an arbitrary nonlinear (short-range) potential. The method is hierarchical, in which Green's functions are calculated for the perfect lattice, for increasingly complicated defect lattices, and finally the nonlinear structure problem is iterated until a converged solution is found. For the case where the defect must be embedded within a very large linear system, and the slip plane, cleavage plane, nonlinear zone, etc., can be made small compared to the system size, Green's functions are a very powerful method for studying the physics of defects and their interactions. As an illustration of the method, we report numerical calculations for an interfacial crack emitting dislocations from an interface between two joined two-dimensional hexagonal lattices. The supercell size was 4{times}10{sup 6}, and the crack length was 101 lattice spacings. After the Green's functions were obtained for the defective lattice, the dislocation and crack structures were obtained in a minute or less, making possible detailed studies of the defects with various external loads, force laws, defect relative positions, etc., with negligible computer time. Withmore » practical supercomputer times, supercell and defect sizes one or two orders larger are feasible, thus making possible a realistic calculation of three-dimensional nucleation events on cracks, etc.« less

In this paper, we address some fundamental questions regarding the response of a crack to externally generated dislocations. We note that since dislocations that formed at external sources in the material must be in the form of loops or dipoles, the theory must be couched in terms of crack shielding in a plastically polarizable medium. There are strong analogies to dielectric theory. We prove two general theorems: (1) Dipoles formed in the emission geometry relative to a crack tip always antishield the crack and (2) when dipoles are induced during uniform motion of a crack through a uniformly plastically polarizable material, then the net shielding is always positive. We illustrate these general theorems with a number of special cases for fixed and polarizable sources. Finally, we simulate the self consistent time dependent response of a crack to a polarizable source as the crack moves past it. The results show that the crack is initially antishielded, but that positive shielding always dominates during later stages of configuration evolution. The crack may be arrested by the source, or it may break away from it, depending upon the various parameters (source strength and geometry, dislocation mobility, Griffith condition for the crack, etc.). The results indicate that the time dependence of crack shielding in the presence of a nonuniform density of sources will be very important in practical cases of brittle transitions in materials.

In this paper, we propose that, depending on their height, ledges on cracks can be efficient sources of dislocations at loadings well below the critical loading for homogeneous emission. Detailed 3-D elastic calculations are presented supporting this proposition. There are two configurations for emission: one which blunts the crack, and one we call a jogging configuration. By our calculations, the blunting configuration should be the more efficient source; however, jogging dislocations are more frequently observed, experimentally. We find that the ledge is only a finite source of dislocations, in the sense that the ledge height decreases as the dislocations are emitted. The atomic configuration at the ledge is composed of finite lengths of real dislocations, which is the reason why such dislocations can be emitted easier than homogeneously produced dislocations. The stresses at the ledge tip produce a cloud of bound dislocations near the ledge, pinned at the ledge ends, so that the ledge crack configuration becomes delocalized. Delocalization of the pileup dislocations in the jogging direction may explain why the jogging dislocations are more frequently seen. Implications for dislocation free zones and ductile transitions are discussed.

Emission source functions are extracted from correlation functions constructed from charged pions produced at midrapidity in Au+Au collisions at sqrt[s(NN)]=200 GeV. The source parameters extracted from these functions at low k(T) give first indications of a long tail for the pion emission source. The source extension cannot be explained solely by simple kinematic considerations. The possible role of a halo of secondary pions from resonance emissions is explored.

Inclusive transverse momentum spectra of eta mesons have been measured within p(T) = 2-10 GeV/c at midrapidity by the PHENIX experiment in Au + Au collisions at square root S(NN) = 200 GeV. In central Au+Au the eta yields are significantly suppressed compared to peripheral Au + Au, d + Au, and p + p yields scaled by the corresponding number of nucleon-nucleon collisions. The magnitude, centrality, and p(T) dependence of the suppression is common, within errors, for eta and pi0. The ratio of eta to pi0 spectra at high p(T) amounts to 0.40R(eta/pi)00.48 for the three systems, in agreement with the world average measured in hadronic and nuclear reactions and, at large scaled momentum, in e+e- collisions.

Transverse single-spin asymmetries to probe the transverse-spin structure of the proton have been measured for neutral pions and nonidentified charged hadrons from polarized proton-proton collisions at midrapidity and root s = 200 GeV. The data cover a transverse momentum (pT) range 1.0-5.0 GeV/c for neutral pions and 0.5-5.0 GeV/c for charged hadrons, at a Feynman-x value of approximately zero. The asymmetries seen in this previously unexplored kinematic region are consistent with zero within errors of a few percent. In addition, the inclusive charged hadron cross section at midrapidity from 0.5 < P-T < 7.0 GeV/c is presented and compared to next-to-leading order perturbative QCD ( pQCD) calculations. Successful description of the unpolarized cross section above similar to 2 GeV/c suggests that pQCD is applicable in the interpretation of the asymmetry results in the relevant kinematic range.

The PHENIX experiment has measured midrapidity ([FORMULA: SEE TEXT]) transverse momentum spectra ([FORMULA: SEE TEXT]) of electrons as a function of centrality in Au+Au collisions at [FORMULA: SEE TEXT]. Contributions from photon conversions and from light hadron decays, mainly Dalitz decays of pi0 and eta mesons, were removed. The resulting nonphotonic electron spectra are primarily due to the semileptonic decays of hadrons carrying heavy quarks. Nuclear modification factors were determined by comparison to nonphotonic electrons in p+p collisions. A significant suppression of electrons at high pT is observed in central Au+Au collisions, indicating substantial energy loss of heavy quarks.