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This article develops and empirically implements an arbitrage-free, dynamic term structure model with "priced" factor and regime-shift risks. The risk factors are assumed to follow a discrete-time Gaussian process, and regime shif...
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This article develops and empirically implements an arbitrage-free, dynamic term structure model with "priced" factor and regime-shift risks. The risk factors are assumed to follow a discrete-time Gaussian process, and regime shifts are governed by a discrete-time Markov process with state-dependent transition probabilities. This model gives closed-form solutions for zero-coupon bond prices, an analytic representation of the likelihood function for bond yields, and a natural decomposition of expected excess returns to components corresponding to regime-shift and factor risks. Using monthly data on U.S. Treasury zero-coupon bond yields, we show a critical role of priced, state-dependent regime-shift risks in capturing the time variations in expected excess returns, and document notable differences in the behaviors of the factor risk component of the expected returns across high and low volatility regimes. Additionally, the state dependence of the regime-switching probabilities is shown to capture an interesting asymmetry in the cyclical behavior of interest rates. The shapes of the term structure of volatility of bond yield changes are also very different across regimes, with the well-known hump being largely a low-volatility regime phenomenon.
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Sudden jumps in the crack tip velocity were revealed by numerical simulation (in both continuum/cohesive element and molecular dynamics approaches) and experiments for rapid shear cracking. The cracking velocity may accelerate fro...
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Sudden jumps in the crack tip velocity were revealed by numerical simulation (in both continuum/cohesive element and molecular dynamics approaches) and experiments for rapid shear cracking. The cracking velocity may accelerate from a sub-Rayleigh speed to the intersonic range, or from an intersonic speed to a higher one, when the reflected impact wave reloads the crack tip. On the other hand, the cracking velocity may decelerate from an intersonic speed to a lower one or recede to the sub-Rayleigh range when the fracture driving force declines. The velocity change encountered during intersonic cracking plays a different role from that in the acceleration or deceleration of a subsonic crack. A crack propagating at an intersonic speed would leave a shear wave trailing behind. When the crack decelerates or accelerates, the effect of the trailing wave will lead to a transition period from one steady-state solution of crack tip singularity to another. This investigation aims at quantifying these processes. The full field solution of an intersonic mode II crack whose speed changed suddenly from one velocity (intersonic or subsonic) to another (intersonic or subsonic) is given in closed form. The solution is facilitated via superposing a series of propagating crack problems that are loaded by dislocations to seal the unwanted crack-face sliding or by concentrated forces moving at various speeds to negate the crack-face traction. In contrast to the subsonic solution, the results in the intersonic case indicate that the elastic fields around the crack tip depend on the deceleration or acceleration history that is traced back over a long time. Singularity matching dictates the jump that may actually take place.
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Fracture of nanocrystalline metals with extremely small grain size is simulated in this paper by structural evolution. Two-dimensional scheme is formulated to study the competition between crack growth and blunting in nanocrystall...
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Fracture of nanocrystalline metals with extremely small grain size is simulated in this paper by structural evolution. Two-dimensional scheme is formulated to study the competition between crack growth and blunting in nanocrystalline samples with edge cracks. The scheme couples the creep deformation induced by grain boundary (GB) mechanisms and the intergranular crack growth. The effects of material properties, initial configurations and applied loads are explored. Either the enhancement in diffusion mobility, or the deterrence in the grain boundary damage, would blunt the crack and decelerate its growth, and vice versa. The simulations agree with the analytical predictions as modified from that of Yang and Yang [2008. Brittle versus ductile transition of nanocrystalline metal. Int. J. Solids Struct. 45,3897-3907]. Upon the suppression of dislocation activities, it is validated that the brittle versus ductile transition of nanocrystals is controlled by the development of grain boundary-dominated creep versus grain boundary decohesion. Further simulations found that either decreasing the grain sizes or increasing the dispersion of grain sizes would blunt the growing cracks.
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Fatigue crack growth has been observed recently in ferroelectrics under cyclic electric loading. Does the crack grow by electric breakdown, or by the stress field near the crack tip? The present paper provides a mechanistic explan...
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Fatigue crack growth has been observed recently in ferroelectrics under cyclic electric loading. Does the crack grow by electric breakdown, or by the stress field near the crack tip? The present paper provides a mechanistic explanation for the electric-field-induced fatigue crack growth. The non-uniform electric field near an insulated crack tip might cause domain switching which in turn produces a concentrated stress field characterized by a stress intensity factor. For ferroelectrics poled along a direction perpendicular to the crack, we are able to show quantitatively that: (1) the stress intensity factor under a negative electric field is nine times as large as the stress intensity factor under a positive electric field; (2) the crack starts to grow if the stress intensity factor is higher than the fracture toughness of the material, but the stress intensity factor decreases as the crack extends and eventually results in crack arrest; (3) by reversing the electric field, the stress intensity factor is increased and crack growth resumes; and (4) this model can predict the extent of fatigue crack growth. In contrast to the conventional perception of (mechanical) fatigue, the fatigue crack growth in ferroelectrics under cyclic electric loading is a step by step cleavage process caused by a domain switching sequence that generates a cyclic driving stress field near the crack tip.
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Recent experiments showed that nano-composite ceramics with particles distributed within the matrix grains and along the grain boundaries can acquire high toughening. The toughening of alumina ceramics with dispersed silicon carbi...
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Recent experiments showed that nano-composite ceramics with particles distributed within the matrix grains and along the grain boundaries can acquire high toughening. The toughening of alumina ceramics with dispersed silicon carbide nano-particles are studied in the present paper. Three toughening mechanisms are identified: switching from the intergranular cracking to the transgranular one by nano-particles along the grain boundaries, fracture surface roughening by zigzag crack path perturbed by the internal stresses of nano-particles within the grains, and shielding by clinched rough surfaces near the crack tip. For different volume fractions of nano-particles, the estimated gross toughening agrees with the experiments.
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The existing framework of optimality criteria method is limited to the optimization of a simple energy functional with a single constraint on material resource. The present work extends the optimality criteria method to the case o...
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The existing framework of optimality criteria method is limited to the optimization of a simple energy functional with a single constraint on material resource. The present work extends the optimality criteria method to the case of multiple constraints. The difficulty in updating the Lagrangian multipliers is treated by gradient-split Taylor series expansion. Applications of the method are illustrated by computing the optimal structures under multiple displacement constraints, and by designing the material cells under given macroscopic elastic tensors that correspond to both positive and negative Possion's ratios.
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Microorganisms proliferate, consume nutrients, and produce many undesired metabolites, which are the main reason for the spoilage of fresh meat. Screening spoilage markers is of great significance for characterizing the freshness ...
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Microorganisms proliferate, consume nutrients, and produce many undesired metabolites, which are the main reason for the spoilage of fresh meat. Screening spoilage markers is of great significance for characterizing the freshness of fresh meat. At present, there are few studies on the volatile spoilage markers (VSMs) of lamb and their relationship with bacteria. In this study, the spoilage evolution of lamb was evaluated by multiple indicators. The changes of bacteria and volatile organic compounds (VOCs) in aerobic-packaged CAP) and vacuum-packaged (VP) lamb were measured by 16S next-generation sequencing (NGS) and headspace solid-phase microextraction (HS-SPME)-gas chromatography-mass spectrometry (GC-MS) respectively. The potential VSMs were also screened. Results showed that the shelf life of AP lamb at 4 ℃ was less than 10 d and VP lamb was less than 28 d. Pseudomonas was the dominant bacteria in AP lamb, while Latilactobacillus and Lactococcus were the dominant bacteria in VP lamb. Several VOCs could be recommended as potential spoilage markers, including 1-octen-3-ol, 1-hexanol, nonanal, methoxy-phenyloxime, 2,3-octanedione, acetoin and 1-pentanol for AP lamb; acetoin, 1-hexanol, 2,3-octanedione, hexanoic acid, 1-octen-3-ol, nonanal, hexanal and 2,3-octanediol for VP lamb. This study can provide information for characterizing and predicting the freshness of fresh lamb.
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A field study of student thermal comfort was conducted in the Chinese subtropics. Thermal comfort affects people's physical and psychological health. The study was performed in Hunan University in China from March 24 to April 23 i...
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A field study of student thermal comfort was conducted in the Chinese subtropics. Thermal comfort affects people's physical and psychological health. The study was performed in Hunan University in China from March 24 to April 23 in 2005.Two teaching buildings were selected as study sites. Thermal comfort was measured in naturally ventilated classrooms with ceiling fans. A total of 25 classrooms were surveyed and each classroom was visited two or three times and 1273 students responded to the questionnaire.Thermal comfort variables were measured at the same time: students answered a survey on their perception/sensation of the indoor climate. Objective data analysis showed that most respondents found thermal satisfaction during the sampling month, even though the indoor air temperature and relative humidity varied greatly, with average values at 20 ℃ and 71%, respectively.The thermal neutral temperature calculated by Thermal Sensation Vote (TSV) was at about 21.5 ℃ and the slope of
the regression line relating TSV with operative temperature was 0.0448/℃, which is quite different from that found in other similar thermal comfort studies.This difference is attributed to the different climate and adaptation and tolerance of students, who were the study subjects. There was a relatively large gap between studied TSV and Predicted Mean Vote (PMV). An extended PMV model that incorporated two common forms of adaptation - reducing activity pace and expectation - was also considered, but the discrepancy between predicted and studied thermal sensations did not reduce noticeably, especially at the lower temperatures.
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We describe the rational design of a novel class of magnetic resonance imaging (MRI) contrast agents with engineered proteins (CALCD2, i= 1, 2,..., 9) chelated with gadolinium. The design of protein-based contrast agents involves ...
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We describe the rational design of a novel class of magnetic resonance imaging (MRI) contrast agents with engineered proteins (CALCD2, i= 1, 2,..., 9) chelated with gadolinium. The design of protein-based contrast agents involves creating high-coordination Gd~(3+) binding sites in a stable host protein using amino acid residues and water molecules as metal coordinating ligands. Designed proteins show strong selectivity for Gd~(3+) over physiological metal ions such as Ca~(2+), Zn~(2+), and Mg~(2+). These agents exhibit a 20-fold increase in longitudinal and transverse relaxation rate values over the conventional small-molecule contrast agents, e.g., Gd-DTPA (diethylene triamine pentaacetic acid), used clinically. Furthermore, they exhibit much stronger contrast enhancement and much longer blood retention time than Gd-DTPA in mice. With good biocompatibility and potential functionalities, these protein contrast agents may be used as molecular imaging probes to target disease markers, thereby extending applications of MRI.
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Low fracture toughness of ferroelectric ceramics calls for a reliability concern in the development of smart structures. For ferrolelectrics under mechanical and electrical loadings, the intensified stress and electric fields in t...
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Low fracture toughness of ferroelectric ceramics calls for a reliability concern in the development of smart structures. For ferrolelectrics under mechanical and electrical loadings, the intensified stress and electric fields in the vicinity of a crack-like flaw led to domain reorientation. The switched domains induce incompatible strain near the flaw and consequently change the apparent fracture toughness. The present paper investigates toughness variation by small scale polarization switching under non-uniform electric and stress fields.
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