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As a first step towards the next generation of computational tools for contact-impact applications, a robust consistent configuration dynamic formulation for frictional contact/impact dynamic problems is described based on a newly...
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As a first step towards the next generation of computational tools for contact-impact applications, a robust consistent configuration dynamic formulation for frictional contact/impact dynamic problems is described based on a newly developed decoupled point to segment gap vector projection and decoupled contact model, in conjunction with the so-called arbitrary reference configuration (ARC) formulation for finite elastic/inelastic deformation, and the forward incremental displacement central difference time integration scheme for the equation of motion. As a consequence, the resulting normal and tangential contact boundary formulations are easy to be solved, and the contact constraints are satisfied exactly. This formulation is highly robust and efficient for the numerical simulation of finite deformation elastic/inelastic frictional contact/impact dynamic applications. Numerical results with comparisons to available experimental data and those obtained from other codes are also presented, thereby demonstrating the inherent advantages.
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AbstractRemnant areas hosting natural vegetation in agricultural landscapes can impact the disease epidemiology and evolutionary dynamics of crop pathogens. However, the potential consequences for crop diseases of the composition,...
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AbstractRemnant areas hosting natural vegetation in agricultural landscapes can impact the disease epidemiology and evolutionary dynamics of crop pathogens. However, the potential consequences for crop diseases of the composition, the spatial configuration and the persistence time of the agro-ecological interface – the area where crops and remnant vegetation are in contact – have been poorly studied. Here, we develop a demographic–genetic simulation model to study how the spatial and temporal distribution of remnant wild vegetation patches embedded in an agricultural landscape can drive the emergence of a crop pathogen and its subsequent specialization on the crop host. We found that landscape structures that promoted larger pathogen populations on the wild host facilitated the emergence of a crop pathogen, but such landscape structures also reduced the potential for the pathogen population to adapt to the crop. In addition, the evolutionary trajectory of the pathogen population was determined by interactions between the factors describing the landscape structure and those describing the pathogen life histories. Our study contributes to a better understanding of how the shift of land-use patterns in agricultural landscapes might influence crop diseases to provide predictive tools to evaluate management practices.
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NUT midline carcinoma (NMC), a subtype of squamous cell cancer, is one of the most aggressive human solid malignancies known. NMC is driven by the creation of a translocation oncoprotein, BRD4-NUT, which blocks differentiation and...
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NUT midline carcinoma (NMC), a subtype of squamous cell cancer, is one of the most aggressive human solid malignancies known. NMC is driven by the creation of a translocation oncoprotein, BRD4-NUT, which blocks differentiation and drives growth of NMC cells. BRD4-NUT forms distinctive nuclear foci in patient tumors, which we found correlate with ～100 unprecedented, hyperacetylated expanses of chromatin that reach up to 2 Mb in size. These “megadomains” appear to be the result of aberrant, feed-forward loops of acetylation and binding of acetylated histones that drive transcription of underlying DNA in NMC patient cells and na?ve cells induced to express BRD4- NUT. Megadomain locations are typically cell lineage-specific; however, the cMYC and TP63 regions are targeted in all NMCs tested and play functional roles in tumor growth. Megadomains appear to originate from select pre-existing enhancers that progressively broaden but are ultimately delimited by topologically associating domain (TAD) boundaries. Therefore, our findings establish a basis for understanding the powerful role played by large-scale chromatin organization in normal and aberrant lineage-specific gene transcription.
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Concurrent tolerance allocation has been the focus of extensive research, yet very few researchers have considered how to concurrently allocate design and process tolerances for mechanical assemblies with interrelated dimension ch...
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Concurrent tolerance allocation has been the focus of extensive research, yet very few researchers have considered how to concurrently allocate design and process tolerances for mechanical assemblies with interrelated dimension chains. To address this question, this paper presents a new tolerance allocation method that applies the concept of concurrent engineering. The proposed method allocates the required functional assembly tolerances to the design and process tolerances by formulating the tolerance allocation problem into a comprehensive model and solving the model using a non-linear programming software package. A multivariate quality loss function of interrelated critical dimensions is first derived, each component design tolerance is formulated as the function of its related process tolerances according to the given process planning, both manufacturing cost and quality loss are further expressed as functions of process tolerances. And then, the objective function of the model, which is to minimize the sum of manufacturing cost and expected quality loss, is established and the constraints are formulated based on the assembly requirements and process constraints. The purpose of the model is to balance manufacturing cost and quality loss so that concurrent optimal allocation of design and process tolerances is realized and quality improvement and product cost reduction is achieved. The proposed method is tested on a practical example.
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HNO_3 with the marine NaCl), as well as generally increasing dry dust resuspension under a semi-arid climate. Average trace metal concentrations rise with the highest levels at industrial and traffic hotspots sites, in some cases ...
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HNO_3 with the marine NaCl), as well as generally increasing dry dust resuspension under a semi-arid climate. Average trace metal concentrations rise with the highest levels at industrial and traffic hotspots sites, in some cases (Ti, Cr, Mn, Cu, Zn, As, Sn, W, and Pb) exceeding rural background levels by over an order of magnitude.
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The Roccamonfina volcanic complex (RVC), in southern Italy, is an Early to Middle Pleistocene stratovolcano sharing temporal and morphological characteristics with the Somma-Vesuvius and the Alban Hills; both being associated with...
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The Roccamonfina volcanic complex (RVC), in southern Italy, is an Early to Middle Pleistocene stratovolcano sharing temporal and morphological characteristics with the Somma-Vesuvius and the Alban Hills; both being associated with high volcanic hazard for the cities of Naples and Rome, respectively. The RVC is important for the understanding of volcanic evolution in the Roman and Campanian volcanic provinces. We report a comprehensive study of its evolution based on morphological, geochemical and K-Ar geochronological data. The RVC was active from c.a. 550 ka to 150 ka. Its evolution is divided into five stages, defining a volcanic pulse recurrence time of c.a. 90-100 kyr. The two initial stages, consisted in the construction of two successive stratovolcanoes of the tephrite-phonolite, namely "High-K series". The first stage was terminated by a major plinian eruption emplacing the trachytic Rio Rava pumices at 439 ±9 ka. At the end of the second stage, the last High-K series stratovolcano was destroyed by a large sector collapse and the emplacement of the Brown Leucitic Tuff (BLT) at 353 ± 5 ka. The central caldera of the RVC is the result of the overlapping of the Rio Rava and of the BLT explosions. The plinian eruption of the BLT is related to the emptying of a stratified, deep-seated HKS magma chamber during the upwelling of K series (KS) magma, marking a major geochemical transition and plumbing system re-organization. The following stage was responsible for the emplacement of the Lower White Trachytic Tuff at 331 ±2 ka, and of basaltic-trachytic effusive products erupted through the main vent. The subsequent activity was mainly restricted to the emplacement of basaltic-shoshonitic parasitic cones and lava flows, and of minor subplinian deposits of the Upper White Trachytic Tuff between 275 and 230 ka. The northern crater is most probably a maar that formed by the phreatomagmatic explosion of the Yellow Trachytic Tuff at 230 ka. The latest stage of activity featured the edification of the central shoshonitic domes at c.a. 150 ka.
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This paper presents the full-order and multimode methods for analyzing coupled flutter of long-span bridges using commercial finite element (FB) package ANSYS. In the full-order method of flutter analysis, a novel FE model is deve...
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This paper presents the full-order and multimode methods for analyzing coupled flutter of long-span bridges using commercial finite element (FB) package ANSYS. In the full-order method of flutter analysis, a novel FE model is developed to model the coupled wind-bridge system, in which a specific user-defined Matrix27 element in ANSYS is adapted to model the aeroelastic forces and its stiffness or damping matrices are parameterized by wind velocity and vibration frequency. Variation of complex eigenvalues of the coupled system with wind velocity is then depicted by using this model together with complex eigenvalue analysis, and flutter instability can be determined from the variation diagram. In the multimode method, equations of motion for the coupled wind-bridge system are first represented using a modal superposition technique. This formulation leads to a single-parameter searching technique without iteration to determine the conditions of flutter instability when structural damping is not considered in solution. The contribution of participating modes to flutter instability is given in terms of modal amplitude and modal energy in the multimode method. Numerical studies are provided to validate the developed methods as well as to demonstrate both the procedures for flutter analysis using ANSYS. The proposed methods enable the bridge designers and engineering practitioners to analyze bridge flutter in commercial FE package ANSYS.
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Preliminary analyses have shown that membrane materials, connecting mastic asphalt surfacings to plates of orthotropic steel deck bridges, play an extremely important role in determining the structural response of these types of b...
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Preliminary analyses have shown that membrane materials, connecting mastic asphalt surfacings to plates of orthotropic steel deck bridges, play an extremely important role in determining the structural response of these types of bridges. This necessitates search for a realistic representation of the behaviour of membrane materials. For this purpose, an extensive experimental program was carried out, and a nonlinear constitutive model was developed to describe the behaviour of membrane materials. This is the second part of two papers on characterization of the behaviour of a bituminous-based membrane material in an orthotropic steel deck bridge. In this paper, the details of the constitutive model will be discussed. Furthermore, an unconditionally stable, implicit Euler backward algorithm for the integration of the constitutive equations will be presented in details. Comparisons of model predictions and laboratory measurements at different temperatures, deformation rates and confining stresses are presented. Some numerical examples, in which various aspects of the finite elements response of a 3D orthotropic steel deck bridge subjected to stationary and moving loads, are presented. The importance of the damage distribution on the membrane material is demonstrated as well as the role of other influencing factors, such as loading speed and temperature.
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Guangzhou (GZ) is one of the highly industrialized and economically vibrant cities in China, yet it remains relatively understudied in terms of its air quality, which has become severely degraded. In this study, extensive air samp...
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Guangzhou (GZ) is one of the highly industrialized and economically vibrant cities in China, yet it remains relatively understudied in terms of its air quality, which has become severely degraded. In this study, extensive air sampling campaigns had been conducted at GZ urban sites and in Dinghu Mountain (DM), a rural site, in the Pearl River Delta (PRD) during the spring of 2001 and 2005. Additionally, roadside and tunnel samples were collected in GZ in 2000 and 2005. Later, exhaust samples from liquefied petroleum gas (LPG)- and gasoline-fueled taxis were collected in 2006. All samples were analyzed for C_2-C_(10) non-methane hydrocarbons (NMHCs). NMHC profiles showed significant differences in the exhaust samples between gasoline- and LPG-fueled taxis. Propane (47%) was the dominant hydrocarbon in the exhaust of the LPG-fueled taxis, while ethene (35%) was the dominant one in that of gasoline-fueled taxis. The use of LPG-fueled buses and taxis since 2003 and the leakage from these LPG-fueled vehicles were the major factors for the much higher level of propane in GZ urban area in 2005 compared to 2001. The mixing ratios of toluene, ethylbenzene, m/p-xylene and o-xylene decreased at the GZ and DM sites between 2001 and 2005, especially for toluene in GZ, despite the sharp increase in the number of registered motor vehicles in GZ. This phenomenon was driven in part by the closure of polluting industries as well as the upgrading of the road network in urban GZ and in part by the implementation of more stringent emission standards for polluting industries and motor vehicles in the PRD region.
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In this paper, the meshless integral method based on regularized boundary integral equation [A. Bodin, J. Ma, X.J. Xin, P. Krishnaswami, A meshless integral method based on regularized boundary integral equation, Comput. Methods A...
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In this paper, the meshless integral method based on regularized boundary integral equation [A. Bodin, J. Ma, X.J. Xin, P. Krishnaswami, A meshless integral method based on regularized boundary integral equation, Comput. Methods Appl. Mech. Engrg. 195 (2006) 6258-6286] has been extended to elastoplastic materials. In the formulation, the domain of interest is populated with a set of nodes using an automatic node generation algorithm. The sub-domain and support domain associated with each node are also generated automatically using algorithms that have been developed for this purpose. The governing integral equation is obtained from the weak form of elastoplasticity over a local sub-domain, and the moving least-squares approximation is used for meshless function approximation. The constitutive law is the small deformation, rate-independent flow theory based on von Mises yielding criterion with isotropic hardening. The generalized collocation method is employed to enforce the essential boundary conditions exactly, which is simple and computationally efficient. Natural boundary conditions are incorporated in the system governing equation and require no special handling. The solution algorithm for elastoplastic analysis is discussed in detail. The proposed method can handle any prescribed loading profile, including unloading and reversed loading. Numerical examples show that the elastoplastic integral meshless method is accurate and robust.
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