Critical Distance Model Research Articles

Rhetoric of natural law in the public discourse of Benedict XVI

The paper examines the rhetorical imagination of the Catholic speaker in public discourse on the basis of the parliamentary discourses of Pope Benedict XVI. According to this researcher, Pope Benedict XVI’s rhetorical model in the speeches is an extended version of Michael J. Hostetler’s critical distance model supported by the translation idea of Jurgen Habermas. This conclusion is reached by analysis of the constituent elements of the arguments in three parliamentary speeches given by Pope Benedict XVI. James B. Freeman’s updated version of Stephen Toulmin’s argumentation model is used to discern the constituent element of the argument.

Analyzing quasi-static fracture of notched magnesium ZK60 using notch fracture toughness and support vector machine

Magnesium alloys have drawn the attention of many industries due to their outstanding properties and lightweight. ZK60 is one of the most commonly used commercial magnesium alloy mainly due to its high strength and corrosion resistance. Such properties make magnesium alloys attractive materials for loading bearing components in various applications such as automotive, aerospace, and biomedical industries. However, notches such as holes, edges, grooves, and other geometrical irregularities are inevitable as they are integrated into structural components. Moreover, notches have a huge impact on the structural integrity due to the stress concentration regions around the notch tip geometry that can cause catastrophic failures. Therefore, an accurate prediction of the fracture behavior is necessary to avoid such failures. This work aims to investigate the ability of a combined notch stress intensity factor and the theory of critical distance method to predict the notch fracture toughness of notched ZK60 magnesium specimens. A support vector machine was also implemented to predict the notch fracture toughness and results from the support vector machine model were compared to that obtained from the combined notch stress intensity factor and theory of critical distance model. Eleven different U- and V-notched geometries were examined. Results with an accuracy between 2.8% and 22.5% were obtained using the combined notch stress intensity factor and theory of critical distance model while an accuracy between 1.8% and 27.6% were obtained using the support vector machine model.

Collision Avoidance Strategy for Self-Driving Vehicles Based on Drivers and Environmental Factors

In order to enhance the driving safety, various driving assistant systems are gradually developed and widely used. Based on the safe distance model related to the braking process, one warning/dangerous critical distance model for longitudinal control is proposed in this paper, considering the driver’s style and environment factors. The variable driver response time is obtained by employing fuzzy control theory. The author then establishes the vehicle dynamics model and its inverse model. Through the relative distance error and relative speed error, the upper controller is designed to obtain the expected acceleration based on sliding mode control, and the lower controller based on PID control is designed to track the acceleration. In order to solve the chattering problem of sliding mode controller, the author proposes variable gain coefficient control method. The fixed gain parameter in the expected acceleration formula is related to the negative exponential correlation formula, which can effectively depress the chattering of the expected acceleration. Finally, the author uses CarSim and Simulink to establish a co-simulation model of the collision avoidance warning system, and designs the test simulation conditions for typical traffic test scenarios to verify the control algorithm effectiveness.

A life prediction model coupled with residual stress and initial damage on aerofoil specimens subjected to foreign object damage

Foreign object damage (FOD) has been identified as one of the main concerns for fan blades. In this paper, systematic experimental and numerical investigations are conducted on aerofoil specimens subjected to FOD by a falling object. The failure mechanism is attributed to the combination of stress concentration, residual stress, and initial damage. Finite element analysis is carried out to simulate the stress field. Using the experimental data from smooth, typically notched, and FOD notched specimens, a novel theory of critical distance model coupling residual stress and initial damage is proposed, falling in a scatter band of 2.

Improving the Safe Operation of Platoon Lane Changing for Connected Automated Vehicles: A Novel Field-Driven Approach

Connected and automated vehicles (CAVs) platoons have been widely researched because of their efficiency advantages. However, most studies mainly focus on the stability control of platoon and there is a lack of in-depth consideration of platoon lane changing. In order to make up for this vacancy, this study focused on the dynamic gap in the platoon lane changing process. First, an intra-platoon potential field of vehicles in the platoon was established by combining the repulsive force under vehicle safety and the gravity inside the platoon, which can effectively characterize the risk distribution around vehicles. Second, the platoon lane changing process was designed and critical distances of platoon vehicles under different conflict situations were analyzed. Based on this, this study proposed a critical distance model of platoon lane changing. Furthermore, we also found that the critical distances for platoon lane changing were within an interval with upper and lower bounds, which was different from the minimum distance of non-platoon vehicles. Finally, experiments were conducted and the results showed that the proposed model could effectively represent the relationship between the distance between vehicles in the platoon and the motion state of the surrounding vehicles. Moreover, the proposed method could also be applied to the lane-changing maneuver of a self-organizing platoon at a strategic level in a CAVs system.

Critical distance model for the fatigue life analysis under low-velocity impacts of notched specimens

A fatigue life estimation method is proposed for the notched specimens under low-velocity repeated impact loadings. The stress concentration effect at the notch root is taken into account by the implementation of the Theory of Critical Distance, and the continuous variation of strain ranges at the critical point due to the plastic strain accumulation is considered by the mean strain modification. The impact fatigue experiment is conducted on the notched plate specimen of material S45C with the pendulum-type test machine, and the comparison with the numerical analysis results indicates that the proposed model gives a satisfactory prediction on the impact fatigue lives.

Theory of critical distance combined with the generalized strain energy density criterion for mixed mode fracture assessment of PMMA dental materials

Polymethylmethacrylate (PMMA) is one of the well-known dental materials generally used for restoration, extension and relining of dental prostheses. Being subjected to periodic loads, while sustaining inherent voids and microcracks, dental materials are prone to the nucleation and extension of cracks under mixed mode loading condition. In this paper, the mixed mode fracture behavior of PMMA dental materials is studied both experimentally and theoretically. The experiments are carried out using a modified single edge notched bend (SENB) specimen. To theoretically assess the onset of fracture, the theory of critical distance (TCD) along with the generalized strain energy density (GSED) criterion is utilized. This fracture model includes the effect of the second stress term in the William’s series expansion, known as the T-stress, in addition to the stress intensity factors (SIFs) to estimate the onset of fracture. Based on the theoretical model, crack propagation commences once the strain energy W reaches its critical value Wc over a critical distance rc, with Wc and rc both being material parameters. This article also suggests the implementation of a new critical distance model, derived from the GSED criterion, which ameliorates the theoretical estimates when compared to the traditional models for the critical distance devised specifically for stress-based fracture models. It is eventually demonstrated that the GSED criterion provides superior fracture predictions for the tested PMMA dental material in comparison with the classical SED criterion, mainly in view of the contribution of the T-stress and the critical distance concept.

On the necessity of using critical distance model in mixed mode brittle fracture prediction of V-notched Brazilian disk specimens under negative mode І conditions

Fracture load is experimentally measured for round-tip V-notched Brazilian disk (RV-BD) specimen made of PMMA and loaded under mixed mode І/ІІ with negative mode І components. The experimental results are obtained for 90° notch angle and various notch tip radii. The experimental observations show that in some cases, fracture does not initiate from the notch border and it occurs from the edge of the central square hole of the specimen, which is not usually expected. It is shown by the finite element (FE) analysis that although the notch is under mixed mode І/ІІ loading with negative mode І conditions and the notch bisector line experiences compressive stresses, the notch round border is divided into two compressive and tensile sides, suggesting that two critical points may exist on the notch border. Moreover, the FE analysis shows that in some cases, the value of tangential stress on the notch border is larger than that on the edge of the central square hole; but according to the maximum tangential stress (MTS) criterion, which is based on the Theory of Critical Distances (TCD), because the value of tangential stress at the critical distance from the notch border is lower than that on the edge of the hole, fracture is not expected to occur from the notch border. In such cases, the experimental observations are consistent well with predictions of the MTS criterion for the fracture initiation points. The results demonstrate the necessity of using the critical distance in brittle failure prediction of engineering components weakened by blunt V-notches.

A combined critical distance and energy density model to predict high temperature fatigue life in notched single crystal superalloy members

The formation of short cracks at notched members of superalloy single crystals under high temperature low cycle fatigue is analysed. AM1 superalloy at 950°C is studied for [001] and [111] loading axis under fully reversed strain loading. An anomalous crack growth rate regime is observed that depends upon test frequency. Local strain gradient is computed using a finite element model and crystal viscoplasticity constitutive equations. A damage model based on viscoplastic strain energy density and dilation energy density is used to describe short crack growth and fatigue life of smooth specimens. Finite element results are used to identify a critical distance model for notched specimens. A good correlation between experimental results and model predictions is achieved for all test orientations and frequencies.

Critical distance model for the energy of activation of the Bergman cyclization of enediynes

AbstractThe reaction profile of the Bergman cyclization of enediynes is written as a cubic polynomial expansion about the critical distance. Using the “simple sewing” approximation, a relationship is derived that expresses the energy of activation as a function of the critical distance, with the effect of other geometric and electronic factors accounted for in the expansion coefficients. A training set of 10 representative enediynes were selected and input parameters were calculated by density functional theory at the B3LYP/6‐311G* level of theory. All calculations were corrected for zero‐point energy. All singlet biradical calculations were also checked for wave function stability. Calibration curves were then constructed that correlate the activation energy of cyclization of the molecules in the test set with the critical distance parameter. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003

Homing Strategy of the Eastern Chipmunk,Tamias striatus(Mammalia: Rodentia): Validation of the Critical Distance Model

AbstractFifteen eastern chipmunks,Tamias striatus, were displaced and released 500m away from their nest sites, and their eventual behavior was monitored by means of radio‐assisted surveillance. As a rule (allowing for some interindividual variability), the chipmunks left the release site area along a relatively straight course, made a U‐turn at a median 60 m from the release site, returned closer to the latter and initiated a pattern of systematic search based on relatively straight forays from and back to the release site area. This overall strategy is consistent with the critical distance model of homing, which was originally proposed on the basis of the homing behavior of another sciund, the red squirrel,Tamiasciurus hudsonicus.

Molecular dynamics simulations of sputtering involving clusters

In this paper we reported the results of our molecular-dynamics simulations on core-excitation effects during the early stages of high-energy clusters of light atoms (Al) colliding with a high-Z metal surface (Au(100)). In these simulations a simple critical distance model (Re = 0.44 A) was used for L-shell core excitation in Al. The threshold for core-excitation was found to be near 0.4 ke V /atom for pure Al clusters, and significantly lower (~0.11 keV/Al-atom) for mixed Al-Au clusters. Core-excitation was found to be most probable during the early, compressional phase of the cluster impacts, and the probability for a core excited atom being ejected from the cluster-target system was found to be quite high (~40%). Using realistic lifetimes for the core-excited states in the solid, it was estimated that the rate of atomiclike Auger emission from core-excited atoms decaying in the vacuum would be quite high (>0.1 per incident cluster).

The role of a critical distance in RMn/sub 2/ compounds

In the RMn/sub 2/ system, the antiferromagnetically ordered Mn moments are reported to disappear at a reduction of the Mn-Mn distance, either by applying external pressure or by alloying. We illustrate the phenomena for the hexagonal NdMn/sub 2/ compound. The Neel temperature in the (Nd,Lu)Mn/sub 2/ system is found to vanish; at substitution of 30% of Nd by Lu, considered to be equivalent-to applying a pressure of 24.5 kbar. Antiferromagnetic order of the Mn sublattice, however, vanishes already at substitution of 7% of Mn by Cu and of 3% of Mn by Fe in the NdMn/sub 2/, being equivalent to an external pressure of only 4 kbar. High-pressure studies on the Nd(Mn,Cu)2 system show that the effect of an external pressure on the Neel temperature decreases markedly with increasing Cu concentration, in contrast to what is expected in a critical distance model. >

Simulations of core excitation in energetic cluster impacts on metallic surfaces

A modified version of the SPUT2 molecular dynamics sputtering code was used to investigate core excitation in Al atoms following the impact of pure Al clusters and composite AlAu clusters on Au surfaces. Information was obtained on distances-of closest-approach times-of-closest-approach, and ejection properties of cluster-atoms undergoing hard collisions for 32-, 63-, and 108-atom Al clusters impacting Au(100) targets with energies/atom ranging from 0.2 keV to 1.0 keV. Similar information was obtained for composite AlAu clusters (38 Al atoms, 25 Au atoms) with comparable total cluster energies. Using a simple critical distance model (R c = 0.44 A ̊ ) for L-shell core excitation in Al, the threshold for core excitation in pure Al clusters was found to be at approximately 0.4 keV/atom. For the composite clusters, the threshold was at approximately 0.11 keV/Al-atom. Core excitation was most probable during the early, compressional phase of the cluster impacts. A significant fraction (typically ∼40%) of core-excited Al atoms were found to eject from the cluster-target system. Elapsed times between excitation and ejection typically were less than 80 fs, and significant numbers of Al atoms ejected within 20–30 fs after excitation. Our results suggest that line spectra of Auger electrons from sputtered, excited cluster-atoms can be used as a diagnostic tool to investigate the early stages of energetic cluster collisions with surfaces.

Comment on "Fusion of 32S+27Al and 19F+40Ca and the nucleus-nucleus potential"

The purpose of the present Comment is twofold. First, we stress that the fusion cross section in region II of the critical distance model is not determined by the potential alone, but that dynamical effects (friction and deformation) play an essential role. Second, we point out that a proper single-folding potential accounts well for the fusion cross section in region I.

The “elastic” model for heavy-ion reactions

In the present work the “elastic” model for the heavy-ion reactions is presented. Following this model the total reaction cross-section is determined from Rutherford scattering. This cross-section coincides with that obtained using the generalized critical distance model for heavy-ion reactions, yet the hypotheses of the “elastic” model are less restrictive than those of the generalized critical distance model.

The “elastic” model applied to heavy-ion fusion

In the present work the “elastic” model for heavy-ion reactions is applied to fusion. Following this model the fusion cross-section is determined from Rutherford scattering. This cross-section coincides with that obtained using the generalized critical distance model, yet the hypotheses of the “elastic” model are less restrictive than those of the generalized critical distance model.

Calculation of the real part of the interaction potential between two heavy ions from the generalized critical-distance model

In the present work the nuclear partVN of the nucleus-nucleus potential is obtained in the framework of the generalized critical-distance model. It is compared with an analytical formula for the nuclear part of the interaction potential which is closely related to an energy density formalism calculation. By using theVN potential it is found that the proximity theorem is satisfied.

Determination of the nucleus-nucleus potential from the generalized critical-distance model

In the present work we get an analytical expression of the nuclear part VN of the nucleus-nucleus potential in terms of the critical-distance and entrancechannel parameters. The critical distance is obtained in the framework of the generalized critical-distance model. By using VN, we derive for several reactions the universal function U(s), which displays the known scaling behaviour.

Measurement of nuclear potentials from fusion excitation functions

Difficulties associated with the determination of the nuclear potential at distances inside the fusion barrier radius are discussed. The critical distance model analysis of fusion excitation functions at high bombarding energies does not give a model independent measurement of the internuclear potential at small separations of interacting heavy nuclei.