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Sample records for dislocation density-based constitutive

  1. Dislocation Density-Based Constitutive Model for the Mechanical Behavior of Irradiated Cu

    SciTech Connect

    Arsenlis, A; Wirth, B D; Rhee, M

    2003-04-10

    Performance degradation of structural steels in nuclear environments results from the development of a high number density of nanometer scale defects. The defects observed in copper-based alloys are composed of vacancy clusters in the form of stacking fault tetrahedra and/or prismatic dislocation loops, which impede dislocation glide and are evidenced in macroscopic uniaxial stress-strain curves as increased yield strengths, decreased total strain to failure, decreased work hardening and the appearance of a distinct upper yield point above a critical defect concentration (neutron dose). In this paper, we describe the development of an internal state variable model for the mechanical behavior of materials subject to these environments. This model has been developed within an information-passing multiscale materials modeling framework, in which molecular dynamics simulations of dislocation--radiation defect interactions, inform the final coarse-grained continuum model. The plasticity model includes mechanisms for dislocation density growth and multiplication and for radiation defect density evolution with dislocation interaction. The general behavior of the constitutive (single material point) model shows that as the defect density increases, the initial yield point increases and the initial strain hardening decreases. The final coarse-grained model is implemented into a finite element framework and used to simulate the behavior of tensile specimens with varying levels of irradiation induced material damage. The simulation results compare favorably with the experimentally observed mechanical properties of irradiated materials in terms of their increased strength, decreased hardening, and decreased ductility with increasing irradiation dose.

  2. Dislocation density-based finite element method modeling of ultrasonic consolidation

    NASA Astrophysics Data System (ADS)

    Pal, Deepankar

    A dislocation density-based constitutive model has been developed and implemented into a crystal plasticity quasi-static finite element framework. This approach captures the statistical evolution of dislocation structures and grain fragmentation at the bonding interface when sufficient boundary conditions pertaining to the Ultrasonic Consolidation (UC) process are prescribed. The hardening is incorporated using statistically stored and geometrically necessary dislocation densities (SSDs and GNDs), which are dislocation analogs of isotropic and kinematic hardening, respectively. Since the macroscopic global boundary conditions during UC involves cyclic sinosuidal simple shear loading along with constant normal pressure, the cross slip mechanism has been included in the evolution equation for SSDs. The inclusion of cross slip promotes slip irreversibility, dislocation storage, and hence, cyclic hardening during the UC. The GND considers strain-gradient and thus renders the model size-dependent. The model is calibrated using experimental data from published refereed literature for simple shear deformation of single crystalline pure aluminum alloy and uniaxial tension of polycrystalline Aluminum 3003-H18 alloy. The model also incorporates various local and global effects such as (1) friction, (2) thermal softening, (3) acoustic softening, (4) surface texture of the sonotrode and initial mating surfaces, and (6) presence of oxide-scale at the mating surfaces, which further contribute significantly specifically to the grain substructure evolution at the interface and to the anisotropic bulk deformation away from the interface during UC in general. The model results have been predicted for Al-3003 alloy undergoing UC. A good agreement between the experimental and simulated results has been observed for the evolution of linear weld density and anisotropic global strengths macroscopically. Similarly, microscopic observations such as embrittlement due to grain substructure

  3. A novel unified dislocation density-based model for hot deformation behavior of a nickel-based superalloy under dynamic recrystallization conditions

    NASA Astrophysics Data System (ADS)

    Lin, Y. C.; Wen, Dong-Xu; Chen, Ming-Song; Chen, Xiao-Min

    2016-09-01

    In this study, a novel unified dislocation density-based model is presented for characterizing hot deformation behaviors in a nickel-based superalloy under dynamic recrystallization (DRX) conditions. In the Kocks-Mecking model, a new softening item is proposed to represent the impacts of DRX behavior on dislocation density evolution. The grain size evolution and DRX kinetics are incorporated into the developed model. Material parameters of the developed model are calibrated by a derivative-free method of MATLAB software. Comparisons between experimental and predicted results confirm that the developed unified dislocation density-based model can nicely reproduce hot deformation behavior, DRX kinetics, and grain size evolution in wide scope of initial grain size, strain rate, and deformation temperature. Moreover, the developed unified dislocation density-based model is well employed to analyze the time-variant forming processes of the studied superalloy.

  4. A dislocation density-based continuum model of the anisotropic shock response of single crystal α-cyclotrimethylene trinitramine

    DOE PAGESBeta

    Luscher, Darby Jon; Addessio, Francis L.; Cawkwell, Marc Jon; Ramos, Kyle James

    2016-09-20

    Here, we have developed a model for the finite deformation thermomechanical response of α-cyclotrimethylene trinitramine (RDX). Our model accounts for nonlinear thermoelastic lattice deformation through a free energy-based equation of state developed by Cawkwell et al. (2016) in combination with temperature and pressure dependent elastic constants, as well as dislocation-mediated plastic slip on a set of slip systems motivated by experimental observation. The kinetics of crystal plasticity are modeled using the Orowan equation relating slip rate to dislocation density and the dislocation velocity developed by Austin and McDowell (2011), which naturally accounts for transition from thermally activated to dislocation dragmore » limited regimes. Evolution of dislocation density is specified in terms of local ordinary differential equations reflecting dislocation–dislocation interactions. This paper presents details of the theory and parameterization of the model, followed by discussion of simulations of flyer plate impact experiments. Impact conditions explored within this combined simulation and experimental effort span shock pressures ranging from 1 to 3 GPa for four crystallographic orientations and multiple specimen thicknesses. Simulation results generated using this model are shown to be in strong agreement with velocimetry measurements from the corresponding plate impact experiments. Finally, simulation results are used to motivate conclusions about the nature of dislocation-mediated plasticity in RDX.« less

  5. Dislocation

    MedlinePlus

    Joint dislocation ... It may be hard to tell a dislocated joint from a broken bone . Both are emergencies that ... to repair a ligament that tears when the joint is dislocated is needed. Injuries to nerves and ...

  6. Description of tantalum deformation behavior by dislocation mechanics based constitutive relations

    NASA Astrophysics Data System (ADS)

    Zerilli, Frank J.; Armstrong, Ronald W.

    1990-08-01

    Dislocation mechanics based constitutive equation constants are determined for temperature, strain rate, work hardening, and polycrystal grain size influences on the deformation behavior of various tantalum materials. An analysis of the maximum load point strain provides a useful method of determining the work hardening constants. Different athermal stress constants and thermal activation related constants are obtained for certain groupings of the different tantalum materials. The variation are correlated with the annealing history of the materials and related to dislocation model parameters involved in the thermal activation strain rate analysis. Computed tantalum deformation results based on these constants are shown to agree with Gourdin's reported expanding ring test measurements and with the deformed shape of a Taylor cylinder impact test specimen.

  7. Dislocations

    MedlinePlus

    Dislocations are joint injuries that force the ends of your bones out of position. The cause is often a fall or a ... one, seek medical attention. Treatment depends on which joint you dislocate and the severity of the injury. It might include manipulations to reposition your bones, ...

  8. Dislocation-Radiation Obstacle Interactions: Developing Improved Mechanical Property Constitutive Models

    SciTech Connect

    Ian Robertson

    2008-10-10

    The objective of this program was to understand the interaction of dislocations with a wide range of obstacles commonly produced in materials under irradiation (dislocation loops, voids, helium bubbles, stacking fault tetrahedra and radiation-induced precipitates). The approach employed in this program combined multi-scale modeling and dynamic in-situ and static ex-situ transmission electron microscopy experiments.

  9. Constitutive Model Modification of Titanium Alloy Ti-6Al-4V Based on Dislocation Pile-up Theory

    NASA Astrophysics Data System (ADS)

    Zhang, Yi-Chuan; Zhou, Tian-Feng; Che, Jiang-Tao; Liang, Zhi-Qiang; Wang, Xi-Bin

    2016-05-01

    Through the Split Hopkinson Pressure Bar (SHPB) test and the quasi-static tensile test on non-standard specimen of titanium alloy Ti-6Al-4V, the rules of the mechanical property changing with the specimen size under different temperatures are summarized, and the parameters of the classical constitutive Johnson-Cook (JC) model are determined. Based on the dislocation pile-up theory, the classical constitutive JC model is modified by considering the influence of grain size, and the modified JC model is established by adding a functional term Δσ into the classical constitutive model to describe the influence of the grain. The tensile testis analyzed by the finite element method (FEM) simulation. Comparing with the experimental results, the simulation results based on the modified JC model show much better accuracy than that by the classical JC model.

  10. Coupling the Phase Field Method for diffusive transformations with dislocation density-based crystal plasticity: Application to Ni-based superalloys

    NASA Astrophysics Data System (ADS)

    Cottura, M.; Appolaire, B.; Finel, A.; Le Bouar, Y.

    2016-09-01

    A phase field model is coupled to strain gradient crystal plasticity based on dislocation densities. The resulting model includes anisotropic plasticity and the size-dependence of plastic activity, required when plasticity is confined in region below few microns in size. These two features are important for handling microstructure evolutions during diffusive phase transformations that involve plastic deformation occurring in confined areas such as Ni-based superalloys undergoing rafting. The model also uses a storage-recovery law for the evolution of the dislocation density of each glide system and a hardening matrix to account for the short-range interactions between dislocations. First, it is shown that the unstable modes during the morphological destabilization of a growing misfitting circular precipitate are selected by the anisotropy of plasticity. Then, the rafting of γ‧ precipitates in a Ni-based superalloy is investigated during [100] creep loadings. Our model includes most of the important physical phenomena accounted for during the microstructure evolution, such as the presence of different crystallographic γ‧ variants, their misfit with the γ matrix, the elastic inhomogeneity and anisotropy, the hardening, anisotropy and viscosity of plasticity. In agreement with experiments, the model predicts that rafting proceeds perpendicularly to the tensile loading axis and it is shown that plasticity slows down significantly the evolution of the rafts.

  11. Constitutive modeling of hot horming of austenitic stainless steel 316LN by accounting for recrystallization in the dislocation evolution

    NASA Astrophysics Data System (ADS)

    Kooiker, H.; Perdahcioğlu, E. S.; van den Boogaard, A. H.

    2016-08-01

    Hot compression test data taken from Zhang [1] of metastable austenitic stainless steel AISI 316LN over a range of strain rates and temperatures shows typical dynamic recovery and recrystallization behavior. It is proposed to model this behavior by incorporating not only the hardening and recovery into the Bergstrom dislocation evolution equation, but also the recrystallization. It is shown that the initial mechanical response before recrystallization can be accurately represented by assuming that the mean free path evolves as the microstructure evolves from homogeneously spaced dislocations to cell-pattern. Results show that this novel continuum mechanical model can predict the observed behavior, showing a good match to the experimental data and capturing the transition from recrystallization to (almost) no recrystallization.

  12. Knee Dislocations

    PubMed Central

    Schenck, Robert C.; Richter, Dustin L.; Wascher, Daniel C.

    2014-01-01

    Background: Traumatic knee dislocation is becoming more prevalent because of improved recognition and increased exposure to high-energy trauma, but long-term results are lacking. Purpose: To present 2 cases with minimum 20-year follow-up and a review of the literature to illustrate some of the fundamental principles in the management of the dislocated knee. Study Design: Review and case reports. Methods: Two patients with knee dislocations who underwent multiligamentous knee reconstruction were reviewed, with a minimum 20-year follow-up. These patients were brought back for a clinical evaluation using both subjective and objective measures. Subjective measures include the following scales: Lysholm, Tegner activity, visual analog scale (VAS), Short Form–36 (SF-36), International Knee Documentation Committee (IKDC), and a psychosocial questionnaire. Objective measures included ligamentous examination, radiographic evaluation (including Telos stress radiographs), and physical therapy assessment of function and stability. Results: The mean follow-up was 22 years. One patient had a vascular injury requiring repair prior to ligament reconstruction. The average assessment scores were as follows: SF-36 physical health, 52; SF-36 mental health, 59; Lysholm, 92; IKDC, 86.5; VAS involved, 10.5 mm; and VAS uninvolved, 2.5 mm. Both patients had excellent stability and were functioning at high levels of activity for their age (eg, hiking, skydiving). Both patients had radiographic signs of arthritis, which lowered 1 subject’s IKDC score to “C.” Conclusion: Knee dislocations have rare long-term excellent results, and most intermediate-term studies show fair to good functional results. By following fundamental principles in the management of a dislocated knee, patients can be given the opportunity to function at high levels. Hopefully, continued advances in the evaluation and treatment of knee dislocations will improve the long-term outcomes for these patients in the

  13. Perilunar carpal dislocations treatment outcome.

    PubMed

    Gagała, Jacek; Tarczyńska, Marta; Kosior, Piotr

    2006-06-30

    Background. The aim of the study was to analyze late outcomes of perilunar carpal dislocations, depending on the type of the injury, time of the diagnosis and the treatment methods. Material and methods. The material is constituted by 37 patients treated in our department between 1981-2004 because of perilunar dislocation. In group were 2 women and 35 men, aged 19-56 (mean 31 years). All patients were asked for control visit. DASH and Mayo score were used to evaluate the outcome. Range of wrist motion, its stability, grip strength and X-ray pictures were analyzed. Results. Better follow-up results were observed in persons with early diagnosed dislocations of the wrist. The best outcomes were observed in group with perilunar early diagnosed dislocations, which were treated by open reduction. Posttraumatic wrist instability often was diagnosed in patients with dislocation of lunar bone and late-diagnosed transscaphoid perilunar carpal dislocations. Conclusions. The data we obtained show, that the consequences of late-diagnosed and late-treated injuries of the wrist are instability, pain, decrease in range of motion and hand skills. PMID:17592406

  14. Lateral subtalar dislocation.

    PubMed

    Sharda, Praveen; DuFosse, Julian

    2008-07-01

    Subtalar dislocations are rare in routine orthopedic practice. While many of these dislocations are a result of high-energy injuries such as fall from a height or traffic accidents, it is not uncommon for patients to present after slipping down a few stairs. Two types of dislocation have been described, medial and lateral. The type of dislocation is described according to the position of the foot. In lateral subtalar dislocation the head of talus is found medially and the calcaneus is dislocated laterally. The navicular may lie dorsolateral to the talus. The reverse is true of lateral dislocation. Medial dislocation has been referred to as "basketball foot" due to its preponderance in basketball players.4 The deciding factor is the inverted or everted position of the foot when the force is dissipated through the weak talonavicular and talocalcaneal ligaments. This article presents a case of an adult with lateral subtalar dislocation following a fall.

  15. Dislocation motion and instability

    NASA Astrophysics Data System (ADS)

    Zhu, Yichao; Chapman, Stephen Jonathan; Acharya, Amit

    2013-08-01

    The Peach-Koehler expression for the stress generated by a single (non-planar) curvilinear dislocation is evaluated to calculate the dislocation self stress. This is combined with a law of motion to give the self-induced motion of a general dislocation curve. A stability analysis of a rectilinear, uniformly translating dislocation is then performed. The dislocation is found to be susceptible to a helical instability, with the maximum growth rate occurring when the dislocation is almost, but not exactly, pure screw. The non-linear evolution of the instability is determined numerically, and implications for slip band formation and non-Schmid behavior in yielding are discussed.

  16. Dislocation dynamics in hexagonal close-packed crystals

    NASA Astrophysics Data System (ADS)

    Aubry, S.; Rhee, M.; Hommes, G.; Bulatov, V. V.; Arsenlis, A.

    2016-09-01

    Extensions of the dislocation dynamics methodology necessary to enable accurate simulations of crystal plasticity in hexagonal close-packed (HCP) metals are presented. They concern the introduction of dislocation motion in HCP crystals through linear and non-linear mobility laws, as well as the treatment of composite dislocation physics. Formation, stability and dissociation of < c + a > and other dislocations with large Burgers vectors defined as composite dislocations are examined and a new topological operation is proposed to enable their dissociation. The results of our simulations suggest that composite dislocations are omnipresent and may play important roles both in specific dislocation mechanisms and in bulk crystal plasticity in HCP materials. While fully microscopic, our bulk DD simulations provide wealth of data that can be used to develop and parameterize constitutive models of crystal plasticity at the mesoscale.

  17. Sports-related shoulder dislocations: a state-hospital experience.

    PubMed

    Hazmy, C H Wan; Parwathi, A

    2005-07-01

    This retrospective study was conducted in a state hospital set-up and aimed at identifying the incidence of sports-related shoulder dislocations and their characteristics and the sports events involved. All patients with shoulder dislocation related to sporting activities admitted to the hospital from January 1999 to December 2002 were included in the study. There were 18 sports-related shoulder dislocations out of 106 all shoulder dislocations admitted during this 4-year period. The average age of the patients was 25.4 years. All but two were male. All were anterior dislocations. Recurrent dislocation constitutes 78% of the cases with an average of 3 times re-dislocation. Rugby and badminton were the major contributors to the injuries followed by volleyball, soccer and swimming. Conservative treatment was successfully instituted for 88% of the patients and 12% opted for surgical intervention.

  18. Dislocation dynamics in hexagonal close-packed crystals

    DOE PAGESBeta

    Aubry, S.; Rhee, M.; Hommes, G.; Bulatov, V. V.; Arsenlis, A.

    2016-04-14

    Extensions of the dislocation dynamics methodology necessary to enable accurate simulations of crystal plasticity in hexagonal close-packed (HCP) metals are presented. They concern the introduction of dislocation motion in HCP crystals through linear and non-linear mobility laws, as well as the treatment of composite dislocation physics. Formation, stability and dissociation of and other dislocations with large Burgers vectors defined as composite dislocations are examined and a new topological operation is proposed to enable their dissociation. Furthermore, the results of our simulations suggest that composite dislocations are omnipresent and may play important roles both in specific dislocation mechanisms and in bulkmore » crystal plasticity in HCP materials. While fully microscopic, our bulk DD simulations provide wealth of data that can be used to develop and parameterize constitutive models of crystal plasticity at the mesoscale.« less

  19. Sports-related shoulder dislocations: a state-hospital experience.

    PubMed

    Hazmy, C H Wan; Parwathi, A

    2005-07-01

    This retrospective study was conducted in a state hospital set-up and aimed at identifying the incidence of sports-related shoulder dislocations and their characteristics and the sports events involved. All patients with shoulder dislocation related to sporting activities admitted to the hospital from January 1999 to December 2002 were included in the study. There were 18 sports-related shoulder dislocations out of 106 all shoulder dislocations admitted during this 4-year period. The average age of the patients was 25.4 years. All but two were male. All were anterior dislocations. Recurrent dislocation constitutes 78% of the cases with an average of 3 times re-dislocation. Rugby and badminton were the major contributors to the injuries followed by volleyball, soccer and swimming. Conservative treatment was successfully instituted for 88% of the patients and 12% opted for surgical intervention. PMID:16381278

  20. Temporomandibular joint dislocation

    PubMed Central

    Sharma, Naresh Kumar; Singh, Akhilesh Kumar; Pandey, Arun; Verma, Vishal; Singh, Shreya

    2015-01-01

    Temporomandibular joint (TMJ) dislocation is an uncommon but debilitating condition of the facial skeleton. The condition may be acute or chronic. Acute TMJ dislocation is common in clinical practice and can be managed easily with manual reduction. Chronic recurrent TMJ dislocation is a challenging situation to manage. In this article, we discuss the comprehensive review of the different treatment modalities in managing TMJ dislocation. PMID:26668447

  1. Bilateral Anterior Shoulder Dislocation

    PubMed Central

    Siu, Yuk Chuen; Lui, Tun Hing

    2014-01-01

    Introduction: Unilateral anterior shoulder dislocation is one of the most common problems encountered in orthopedic practice. However, simultaneous bilateral anterior dislocation of the shoulders is quite rare. Case Presentation: We report a case of a 75-year-old woman presented with simultaneous bilateral anterior shoulder dislocation following a trauma, complicated with a traction injury to the posterior cord of the brachial plexus. Conclusions: Bilateral anterior shoulder dislocation is very rare. The excessive traction force during closed reduction may lead to nerve palsy. Clear documentation of neurovascular status and adequate imaging before and after a reduction should be performed. PMID:25685749

  2. Traumatic proximal tibiofibular dislocation.

    PubMed

    Burgos, J; Alvarez-Montero, R; Gonzalez-Herranz, P; Rapariz, J M

    1997-01-01

    Proximal tibiofibular dislocation is an exceptional lesion. Rarer still is its presentation in childhood. We describe the clinical case of a 6-year-old boy, the victim of a road accident. He had a tibiofibular dislocation associated with a metaphyseal fracture of the tibia.

  3. Parallel Dislocation Simulator

    2006-10-30

    ParaDiS is software capable of simulating the motion, evolution, and interaction of dislocation networks in single crystals using massively parallel computer architectures. The software is capable of outputting the stress-strain response of a single crystal whose plastic deformation is controlled by the dislocation processes.

  4. Electromechanical simulations of dislocations

    NASA Astrophysics Data System (ADS)

    Skiba, Oxana; Gracie, Robert; Potapenko, Stanislav

    2013-04-01

    Improving the reliability of micro-electronic devices depends in part on developing a more in-depth understanding of dislocations because dislocations are barriers to charge carriers. To this end, the quasi-static simulation of discrete dislocations dynamics in materials under mechanical and electrical loads is presented. The simulations are based on the extended finite element method, where dislocations are modelled as internal discontinuities. The strong and weak forms of the boundary value problem for the coupled system are presented. The computation of the Peach-Koehler force using the J-integral is discussed. Examples to illustrate the accuracy of the simulations are presented. The motion of the network of the dislocations under different electrical and mechanical loads is simulated. It was shown that even in weak piezoelectric materials the effect of the electric field on plastic behaviour is significant.

  5. Crushed Salt Constitutive Model

    SciTech Connect

    Callahan, G.D.

    1999-02-01

    The constitutive model used to describe the deformation of crushed salt is presented in this report. Two mechanisms -- dislocation creep and grain boundary diffusional pressure solution -- are combined to form the basis for the constitutive model governing the deformation of crushed salt. The constitutive model is generalized to represent three-dimensional states of stress. Upon complete consolidation, the crushed-salt model reproduces the Multimechanism Deformation (M-D) model typically used for the Waste Isolation Pilot Plant (WIPP) host geological formation salt. New shear consolidation tests are combined with an existing database that includes hydrostatic consolidation and shear consolidation tests conducted on WIPP and southeastern New Mexico salt. Nonlinear least-squares model fitting to the database produced two sets of material parameter values for the model -- one for the shear consolidation tests and one for a combination of the shear and hydrostatic consolidation tests. Using the parameter values determined from the fitted database, the constitutive model is validated against constant strain-rate tests. Shaft seal problems are analyzed to demonstrate model-predicted consolidation of the shaft seal crushed-salt component. Based on the fitting statistics, the ability of the model to predict the test data, and the ability of the model to predict load paths and test data outside of the fitted database, the model appears to capture the creep consolidation behavior of crushed salt reasonably well.

  6. Medial subtalar dislocation.

    PubMed

    Kinik, H; Oktay, O; Arikan, M; Mergen, E

    1999-01-01

    We report a medial subtalar dislocation without fracture in an eighteen year old male injured during basketball game. He was successfully treated with closed reduction and cast immobilization. At one year follow-up he was symptomless.

  7. Acute traumatic patellar dislocation.

    PubMed

    Duthon, V B

    2015-02-01

    Inaugural traumatic patellar dislocation is most often due to trauma sustained during physical or sports activity. Two-thirds of acute patellar dislocations occur in young active patients (less than 20 years old). Non-contact knee sprain in flexion and valgus is the leading mechanism in patellar dislocation, accounting for as many as 93% of all cases. The strong displacement of the patella tears the medial stabilizing structures, and notably the medial patellofemoral ligament (MPFL), which is almost always injured in acute patellar dislocation, most frequently at its femoral attachment. Lateral patellar glide can be assessed with the knee in extension or 20° flexion. Displacement by more than 50% of the patellar width is considered abnormal and may induce apprehension. Plain X-ray and CT are mandatory to diagnose bony risk factors for patellar dislocation, such as trochlear dysplasia or increased tibial tubercle-trochlear groove distance (TT-TG), and plan correction. MRI gives information on cartilage and capsulo-ligamentous status for treatment planning: free bodies or osteochondral fracture have to be treated surgically. If patellar dislocation occurs in an anatomically normal knee and osteochondral fracture is ruled out on MRI, non-operative treatment is usually recommended.

  8. Supersonic Dislocation Bursts in Silicon

    PubMed Central

    Hahn, E. N.; Zhao, S.; Bringa, E. M.; Meyers, M. A.

    2016-01-01

    Dislocations are the primary agents of permanent deformation in crystalline solids. Since the theoretical prediction of supersonic dislocations over half a century ago, there is a dearth of experimental evidence supporting their existence. Here we use non-equilibrium molecular dynamics simulations of shocked silicon to reveal transient supersonic partial dislocation motion at approximately 15 km/s, faster than any previous in-silico observation. Homogeneous dislocation nucleation occurs near the shock front and supersonic dislocation motion lasts just fractions of picoseconds before the dislocations catch the shock front and decelerate back to the elastic wave speed. Applying a modified analytical equation for dislocation evolution we successfully predict a dislocation density of 1.5 × 1012 cm−2 within the shocked volume, in agreement with the present simulations and realistic in regards to prior and on-going recovery experiments in silicon. PMID:27264746

  9. Supersonic Dislocation Bursts in Silicon

    DOE PAGESBeta

    Hahn, E. N.; Zhao, S.; Bringa, E. M.; Meyers, M. A.

    2016-06-06

    Dislocations are the primary agents of permanent deformation in crystalline solids. Since the theoretical prediction of supersonic dislocations over half a century ago, there is a dearth of experimental evidence supporting their existence. Here we use non-equilibrium molecular dynamics simulations of shocked silicon to reveal transient supersonic partial dislocation motion at approximately 15 km/s, faster than any previous in-silico observation. Homogeneous dislocation nucleation occurs near the shock front and supersonic dislocation motion lasts just fractions of picoseconds before the dislocations catch the shock front and decelerate back to the elastic wave speed. Applying a modified analytical equation for dislocation evolutionmore » we successfully predict a dislocation density of 1.5 x 10(12) cm(-2) within the shocked volume, in agreement with the present simulations and realistic in regards to prior and on-going recovery experiments in silicon.« less

  10. Behavior of dislocations in silicon

    SciTech Connect

    Sumino, Koji

    1995-08-01

    A review is given of dynamic behavior of dislocations in silicon on the basis of works of the author`s group. Topics taken up are generation, motion and multiplication of dislocations as affected by oxygen impurities and immobilization of dislocations due to impurity reaction.

  11. Congenital hip dislocation (image)

    MedlinePlus

    ... by a blow, fall, or other trauma, a dislocation can also occur from birth. The cause is unknown but genetic factors may play a role. Problems resulting from very mild developmental dysplasia of the hip may not become apparent until the person is ...

  12. Dislocated Worker Project.

    ERIC Educational Resources Information Center

    1988

    Due to the severe economic decline in the automobile manufacturing industry in southeastern Michigan, a Dislocated Workers Program has been developed through the partnership of the Flint Area Chamber of Commerce, three community colleges, the National Center for Research in Vocational Education, the Michigan State Department of Education, the…

  13. Dorsal radiocarpal fracture dislocation.

    PubMed

    Tanzer, T L; Horne, J G

    1980-11-01

    A case of a rare radiocarpal fracture dislocation in a 17-year-old girl, with persisting loss of radiocarpal joint space following reduction under hematoma block, is described. The wrist joint was exposed, and two osteochondral fragments were rotated 90 degrees and secured with 2.7-mm AO screws. Satisfactory healing followed 3 months postinjury.

  14. Phonon Drag Dislocations at High Pressures

    SciTech Connect

    Wolfer, W.G.

    1999-10-19

    Phonon drag on dislocations is the dominant process which determines the flow stress of metals at elevated temperatures and at very high plastic deformation rates. The dependence of the phonon drag on pressure or density is derived using a Mie-Grueneisen equation of state. The phonon drag is shown to increase nearly linearly with temperature but to decrease with density or pressure. Numerical results are presented for its variation for shock-loaded copper and aluminum. In these cases, density and temperature increase simultaneously, resulting in a more modest net increase in the dislocation drag coefficient. Nevertheless, phonon drag increases by more than an order of magnitude during shock deformations which approach melting. Since the dependencies of elastic moduli and of the phonon drag coefficient on pressure and temperature are fundamentally different, the effect of pressure on the constitutive law for plastic deformation can not simply be accounted for by its effect on the elastic shear modulus.

  15. Single crystal plasticity by modeling dislocation density rate behavior

    SciTech Connect

    Hansen, Benjamin L; Bronkhorst, Curt; Beyerlein, Irene; Cerreta, E. K.; Dennis-Koller, Darcie

    2010-12-23

    The goal of this work is to formulate a constitutive model for the deformation of metals over a wide range of strain rates. Damage and failure of materials frequently occurs at a variety of deformation rates within the same sample. The present state of the art in single crystal constitutive models relies on thermally-activated models which are believed to become less reliable for problems exceeding strain rates of 10{sup 4} s{sup -1}. This talk presents work in which we extend the applicability of the single crystal model to the strain rate region where dislocation drag is believed to dominate. The elastic model includes effects from volumetric change and pressure sensitive moduli. The plastic model transitions from the low-rate thermally-activated regime to the high-rate drag dominated regime. The direct use of dislocation density as a state parameter gives a measurable physical mechanism to strain hardening. Dislocation densities are separated according to type and given a systematic set of interactions rates adaptable by type. The form of the constitutive model is motivated by previously published dislocation dynamics work which articulated important behaviors unique to high-rate response in fcc systems. The proposed material model incorporates thermal coupling. The hardening model tracks the varying dislocation population with respect to each slip plane and computes the slip resistance based on those values. Comparisons can be made between the responses of single crystals and polycrystals at a variety of strain rates. The material model is fit to copper.

  16. Dislocation Mechanics of High-Rate Deformations

    NASA Astrophysics Data System (ADS)

    Armstrong, Ronald W.; Li, Qizhen

    2015-10-01

    Four topics associated with constitutive equation descriptions of rate-dependent metal plastic deformation behavior are reviewed in honor of previous research accomplished on the same issues by Professor Marc Meyers along with colleagues and students, as follow: (1) increasing strength levels attributed to thermally activated dislocation migration at higher loading rates; (2) inhomogeneous adiabatic shear banding; (3) controlling mechanisms of deformation in shock as compared with shock-less isentropic compression experiments and (4) Hall-Petch-based grain size-dependent strain rate sensitivities exhibited by nanopolycrystalline materials. Experimental results are reviewed on the topics for a wide range of metals.

  17. Congenital Dislocation of the Hip

    PubMed Central

    Premi, J. M.

    1976-01-01

    The implications of a diagnosis of congenital dislocation of the hip and the importance of the role of the family physician in early detection and treatment are identified. A review of the salient clinical features of congenital dislocation of the hip is undertaken. The results of a survey carried out in the author's practice on an unusual incidence of congenital dislocated hip are reviewed. PMID:21308053

  18. Dislocation and fracture-dislocation of the carpometacarpal joints.

    PubMed

    Jebson, P J; Engber, W D; Lange, R H

    1994-02-01

    Dislocations and fracture-dislocations of the carpometacarpal joints are rare. Diagnosis requires a high index of suspicion, careful examination, and appropriate radiography. Treatment is controversial and is based upon the injury pattern and the surgeon's experience and preference. This article reviews the pertinent anatomy, mechanism of injury, evaluation, and treatment of patients with carpometacarpal joint injuries.

  19. Misfit dislocations in epitaxy

    NASA Astrophysics Data System (ADS)

    van der Merwe, Jan H.

    2002-08-01

    This article on epitaxy highlights the following: the definition and some historical milestones; the introduction by Frenkel and Kontorowa (FK) of a truncated Fourier series to model the periodic interaction at crystalline interfaces; the invention by Frank and van der Merwe (FvdM)—using the FK model—of (interfacial) misfit dislocations as an important mechanism in accommodating misfit at epilayer-substrate interfaces; the generalization of the FvdM theory to multilayers; the application of the parabolic model by Jesser and van der Merwe to describe, for growing multilayers and superlattices, the impact of Fourier coefficients in the realization of epitaxial orientations and the stability of modes of misfit accommodation; the involvement of intralayer interaction in the latter—all features that impact on the attainment of perfection in crystallinity of thin films, a property that is so vital in the fabrication of useful uniformly thick epilayers (uniformity being another technological requirement), which also depends on misfit accommodation through the interfacial energy that function strongly in the criterion for growth modes, proposed by Bauer; and the ingenious application of the Volterra model by Matthews and others to describe misfit accommodation by dislocations in growing epilayers.

  20. Moving Dislocations in Disordered Alloys.

    SciTech Connect

    Marian, J; Caro, A

    2006-11-18

    Using atomistic simulations of dislocation motion in Ni and Ni-Au alloys we report a detailed study of the mobility function as a function of stress, temperature and alloy composition. We analyze the results in terms of analytic models of phonon radiation and their selection rules for phonon excitation. We find a remarkable agreement between the location of the cusps in the {sigma}-v relation and the velocity of waves propagating in the direction of dislocation motion. We identify and characterize three regimes of dissipation whose boundaries are essentially determined by the direction of motion of the dislocation, rather than by its screw or edge character.

  1. Dislocation after total knee arthroplasty.

    PubMed

    Wazir, N N; Shan, Y; Mukundala, V V; Gunalan, R

    2007-05-01

    Two cases of dislocation of total knee arthroplasty presented to us within the same week. The first patient is a 71-year-old woman who underwent bilateral primary total knee arthroplasty. The left knee dislocated three weeks after the surgery. Due to failure of conservative measures, she underwent revision total knee arthroplasty. The other patient is a 72-year-old woman presenting ten years after primary total knee arthroplasty, with a traumatic dislocation of the knee joint. She was treated as an outpatient with closed manipulative reduction.

  2. Buckling of dislocation in graphene

    NASA Astrophysics Data System (ADS)

    Yao, Yin; Wang, Shaofeng; Bai, Jianhui; Wang, Rui

    2016-10-01

    The buckling of dislocation in graphene is discussed through the lattice theory of dislocation and elastic theory. The approximate solution of the buckling is obtained based on the inner stress distribution caused by different structure of dislocations and is proved to be suitable by the simulation. The position of the highest buckling is predicted to be at the vertex of the pentagon far away from the heptagon. The buckling is strongly influenced by the internal stress and the distance between the extrusive area and stretching area, as well as the critical stress σc. The SW defect is proved to be unbuckled due to its strong interaction between extrusion and stretching.

  3. Dislocation Detection Through Harmonic Generation

    NASA Astrophysics Data System (ADS)

    Reinhardt, B. T.; Kropf, M.; Boudraeu, K.; Guers, M. J.; Tittmann, B. R.

    2010-02-01

    A fundamental goal of ultrasonic nondestructive evaluation is to characterize material defects before failure. During material fatigue, dislocations tend to nucleate, becoming sources of stress concentration. Eventually, cracks start to form and lead to material failure. Recent research has indicated that nonlinear harmonic generation can be used to distinguish between materials of high and low dislocation densities. This research reports nonlinear harmonic generation measurements to distinguish between those areas of high and low dislocation densities in copper bars. The copper bars were subjected to flexural fatigue. Periodic scans were taken in order to track dislocation development during the fatigue life of the material. We show that this technique provides improved early detection for critical components of failure.

  4. Dislocation sources in ordered intermetallics

    SciTech Connect

    Yoo, M.H.; Appel, F.; Wagner, R.; Mecking, H.

    1996-09-01

    An overview on the current understanding of dislocation sources and multiplication mechanisms is made for ordered intermetallic alloys of the L1{sub 2}, B2, and D0{sub 19} structures. In L1{sub 2} alloys, a large disparity of edge/screw segments in their relative mobility reduces the efficiency of a Frank-Read Type multiplication mechanism. In Fe-40%Al of the B2 structure, a variety of dislocation sources are available for <111> slip, including ones resulting from condensation of thermal vacancies. In NiAl with the relatively high APB energy, <100> dislocations may result from the dislocation decomposition reactions, the prismatic punching out from inclusion particles, and/or steps and coated layers of the surface. Internal interfaces often provide sites for dislocation multiplication, e.g., grain boundaries, sub-boundaries in Ni{sub 3}Ga, NiAl and Ti{sub 3}Al, and antiphase domain boundaries in Ti{sub 3}Al. As for the crack tip as a dislocation source, extended SISFs trailed by super-Shockley partials emanating form the cracks in Ni{sub 3}Al and Co{sub 3}Ti are discussed in view of a possible toughening mechanism.

  5. Discrete dislocation plasticity analysis of the wedge indentation of films

    NASA Astrophysics Data System (ADS)

    Balint, D. S.; Deshpande, V. S.; Needleman, A.; Van der Giessen, E.

    2006-11-01

    The plane strain indentation of single crystal films on a rigid substrate by a rigid wedge indenter is analyzed using discrete dislocation plasticity. The crystals have three slip systems at ±35.3∘ and 90∘ with respect to the indentation direction. The analyses are carried out for three values of the film thickness, 2, 10 and 50 μm, and with the dislocations all of edge character modeled as line singularities in a linear elastic material. The lattice resistance to dislocation motion, dislocation nucleation, dislocation interaction with obstacles and dislocation annihilation are incorporated through a set of constitutive rules. Over the range of indentation depths considered, the indentation pressure for the 10 and 50 μm thick films decreases with increasing contact size and attains a contact size-independent value for contact lengths A>4 μm. On the other hand, for the 2 μm films, the indentation pressure first decreases with increasing contact size and subsequently increases as the plastic zone reaches the rigid substrate. For the 10 and 50 μm thick films sink-in occurs around the indenter, while pile-up occurs in the 2 μm film when the plastic zone reaches the substrate. Comparisons are made with predictions obtained from other formulations: (i) the contact size-independent indentation pressure is compared with that given by continuum crystal plasticity; (ii) the scaling of the indentation pressure with indentation depth is compared with the relation proposed by Nix and Gao [1998. Indentation size effects in crystalline materials: a law for strain gradient plasticity. J. Mech. Phys. Solids 43, 411-423]; and (iii) the computed contact area is compared with that obtained from the estimation procedure of Oliver and Pharr [1992. An improved technique for determining hardness and elastic-modulus using load and displacement sensing indentation experiments, J. Mater. Res. 7, 1564-1583].

  6. Congenital dislocation of the knee.

    PubMed

    Ko, J Y; Shih, C H; Wenger, D R

    1999-01-01

    Between February 1988 and June 1995, 24 congenital dislocations of the knee joints (17 patients) were reduced with closed methods including immediate reduction, serial casting, or traction in patients from 10 min to 26 days old. At an average follow-up of 4 years and 10 months, an excellent or good result was achieved if there were no associated anomalies. Fair or poor results were the result of delayed treatment or associated musculoskeletal anomalies including arthrogryposis multiplex congenita or Larsen's syndrome. Routine check of the hip dislocation is suggested. Diagnosis with manual testing was difficult, and other methods such as radiography or sonography were suggested in combination to detect hip dysplasia. The dislocated knee should be reduced before treating the hip dislocation. Concomitant treatment of the congenital dislocation of the knee and the hip with Pavlik harness provided satisfactory results. When late, progressive, genu valgus deformity occurred because of global instability of the knee and asymmetric physeal growth, reconstruction of the medial structures of the knee and prolonged bracing provided good results. PMID:10088699

  7. Modeling hydrogen transport by dislocations

    NASA Astrophysics Data System (ADS)

    Dadfarnia, Mohsen; Martin, May L.; Nagao, Akihide; Sofronis, Petros; Robertson, Ian M.

    2015-05-01

    Recent experimental studies of the microstructure beneath fracture surfaces of specimens fractured in the presence of high concentrations of hydrogen suggest that the dislocation structure and hydrogen transported by mobile dislocations play important roles in establishing the local conditions that promote failure. The experiments demonstrate that hydrogen is responsible for the copious plasticity in large volumes of material before the onset of fracture and further afield from a crack tip. A revised model for hydrogen transport that accounts for hydrogen carried by dislocations along with stress driven diffusion and trapping at other microstructural defects is proposed. With the use of this new model, numerical simulation results for transient hydrogen profiles in the neighborhood of a crack tip are presented. Based on hydrogen-enhanced dislocation mobility and density, the results indicate that dislocation transport can contribute to the elevation of the local hydrogen concentrations ahead of the crack to levels above those predicted by the classical diffusion model and to distributions that extend farther afield.

  8. Dislocations and other topological oddities

    NASA Astrophysics Data System (ADS)

    Pieranski, Pawel

    2016-03-01

    We will show that the book Dislocations by Jacques Friedel, published half a century ago, can still be recommended, in agreement with the author's intention, as a textbook "for research students at University and for students at engineering schools as well as for research engineers". Indeed, today dislocations are known to occur not only in solid crystals but also in many other systems discovered more recently such as colloidal crystals or liquid crystals having periodic structures. Moreover, the concept of dislocations is an excellent starting point for lectures on topological defects occurring in systems equipped with order parameters resulting from broken symmetries: disclinations in nematic or hexatic liquid crystals, dispirations in chiral smectics or disorientations in lyotropic liquid crystals. The discussion of dislocations in Blue Phases will give us an opportunity to call on mind Sir Charles Frank, friend of Jacques Friedel since his Bristol years, who called these ephemeral mesophases "topological oddities". Being made of networks of disclinations, Blue Phases are similar to Twist Grain Boundary (TGB) smectic phases, which are made of networks of screw dislocations and whose existence was predicted by de Gennes in 1972 on the basis of the analogy between smectics and superconductors. We will stress that the book by Jacques Friedel contains seeds of this analogy.

  9. Dislocation-density function dynamics - An all-dislocation, full-dynamics approach for modeling intensive dislocation structures

    NASA Astrophysics Data System (ADS)

    Leung, H. S.; Ngan, A. H. W.

    2016-06-01

    It has long been recognized that a successful strategy for computational plasticity will have to bridge across the meso scale in which the interactions of high quantities of dislocations dominate. In this work, a new meso-scale scheme based on the full dynamics of dislocation-density functions is proposed. In this scheme, the evolution of the dislocation-density functions is derived from a coarse-graining procedure which clearly defines the relationship between the discrete-line and density representations of the dislocation microstructure. Full dynamics of the dislocation-density functions are considered based on an "all-dislocation" concept in which statistically stored dislocations are preserved and treated in the same way as geometrically necessary dislocations. Elastic interactions between dislocations in a 3D space are treated in accordance with Mura's formula for eigen stress. Dislocation generation is considered as a consequence of dislocations to maintain their connectivity, and a special scheme is devised for this purpose. The model is applied to simulate a number of intensive microstructures involving discrete dislocation events, including loop expansion and shrinkage under applied and self stress, dipole annihilation, and Orowan looping. The scheme can also handle high densities of dislocations present in extensive microstructures.

  10. The Constitutional Amendment Process

    ERIC Educational Resources Information Center

    Chism, Kahlil

    2005-01-01

    This article discusses the constitutional amendment process. Although the process is not described in great detail, Article V of the United States Constitution allows for and provides instruction on amending the Constitution. While the amendment process currently consists of six steps, the Constitution is nevertheless quite difficult to change.…

  11. Continuum Dislocation Dynamics (CDD) Modeling of Thin Film Micro-Plasticity

    NASA Astrophysics Data System (ADS)

    Nikitas, Nikolaos; Zaiser, Michael

    2009-09-01

    Using continuum modeling to describe the plastic deformation of micron-sized structures has been a long standing problem. The major pitfall to overcome consists of finding a description of the material state that is still adequate after the necessary step of averaging over microscopic properties. In this paper we utilize a dislocation density based formulation, cast in terms of averaged evolution equations for screw and edge dislocation densities, in order to confront two benchmark problems of confined micro-plasticity, namely the bending and shearing of a thin film. The method captures the size dependence of micron-scale deformation and achieves good agreement with experimental results and with much more computationally cumbersome 3D Dislocation Dynamics simulations (3DDD).

  12. Irreducible dislocation of the knee.

    PubMed

    Schaefer, R A; Bellafiore, V A; Corzatt, R D

    1999-11-01

    Irreducible knee dislocation is a rare injury. This case report describes a knee dislocation in a 39-year-old male U.S. Army noncommissioned officer who was injured while playing in a softball game. Arthroscopy showed the medial collateral ligament and capsule to be locked in the intercondylar notch, covering the medial femoral condyle. Arthrotomy and open reduction were required. Staged posterior cruciate ligament reconstruction using patellar tendon autograft was later performed. Review of the magnetic resonance imaging scan showed the irreducible lesion. The diagnostic clinical and radiographic features of this unusual injury are described.

  13. Bipolar dislocation of the clavicle.

    PubMed

    Jiang, Wei; Gao, Shu-Guang; Li, Yu-Sheng; Lei, Guang-Hua

    2012-11-01

    Bipolar dislocation of the clavicle at acromioclavicular and sternoclavicular joint is an uncommon traumatic injury. The conservative treatments adopted in the past is associated with redislocation dysfunction and deformity. A 41 years old lady with bipolar dislocation of right shoulder is treated surgically by open reduction and internal fixation by oblique T-plate at sternoclavicular joint and Kirschner wire stabilization at acromioclavicular joint. The patient showed satisfactory recovery with full range of motion of the right shoulder and normal muscular strength. The case reported in view of rarity and at 2 years followup. PMID:23325981

  14. Dislocation nonlinearity and nonlinear wave processes in polycrystals with dislocations

    NASA Astrophysics Data System (ADS)

    Nazarov, V. E.

    2016-09-01

    Based on the modification of the linear part of the Granato-Lücke dislocation theory of absorption, the equation of state of polycrystalline solids with dissipative and reactive nonlinearity has been derived. The nonlinear effects of the interaction and self-action of longitudinal elastic waves in such media have been theoretically studied.

  15. Drift of dislocation tripoles under ultrasound influence.

    PubMed

    Murzaev, R T; Bachurin, D V; Nazarov, A A

    2016-01-01

    Numerical simulations of dynamics of different stable dislocation tripoles under influence of monochromatic standing sound wave were performed. The basic conditions necessary for the drift and mutual rearrangements between dislocation structures were investigated. The dependence of the drift velocity of the dislocation tripoles as a function of the frequency and amplitude of the external influence was obtained. The results of the work can be useful in analysis of motion and self-organization of dislocation structure under ultrasound influence. PMID:26278625

  16. Simultaneous double interphalangeal dislocation in one finger.

    PubMed

    Takami, H; Takahashi, S; Ando, M

    2000-01-01

    Isolated dislocation of the proximal or distal interphalangeal joint of a finger is common, but simultaneous dislocation of both joints is rare. Three cases of simultaneous dislocations of both interphalangeal joints in the same finger are reported. Closed reduction was easily achieved in all cases.

  17. Dislocated Workers: Neighbors, Friends, Relatives.

    ERIC Educational Resources Information Center

    Blessington, Robert

    1989-01-01

    Worker dislocation is a major problem in Wisconsin. Services needed include provision of coping mechanisms, job search methods, and retraining. A partnership between the state and the Wisconsin American Federation of Labor-Congress of Industrial Organizations was created to provide these services and referrals, as well as preventive training…

  18. Financial Dislocations among Divorcing Families.

    ERIC Educational Resources Information Center

    Little, Marilyn J.

    Extensive economic changes may be brought about by divorce. In an attempt to demonstrate that the degree of financial dislocation following divorce depends on three factors--custody arrangements, wife's employment, and social class--data on men's and women's employment, income, and support payments were gathered for 222 divorcing families. Total…

  19. An atomistically validated continuum model for strain relaxation and misfit dislocation formation

    NASA Astrophysics Data System (ADS)

    Zhou, X. W.; Ward, D. K.; Zimmerman, J. A.; Cruz-Campa, J. L.; Zubia, D.; Martin, J. E.; van Swol, F.

    2016-06-01

    In this paper, molecular dynamics (MD) calculations have been used to examine the physics behind continuum models of misfit dislocation formation and to assess the limitations and consequences of approximations made within these models. Without compromising the physics of misfit dislocations below a surface, our MD calculations consider arrays of dislocation dipoles constituting a mirror imaged "surface". This allows use of periodic boundary conditions to create a direct correspondence between atomistic and continuum representations of dislocations, which would be difficult to achieve with free surfaces. Additionally, by using long-time averages of system properties, we have essentially reduced the errors of atomistic simulations of large systems to "zero". This enables us to deterministically compare atomistic and continuum calculations. Our work results in a robust approach that uses atomistic simulation to accurately calculate dislocation core radius and energy without the continuum boundary conditions typically assumed in the past, and the novel insight that continuum misfit dislocation models can be inaccurate when incorrect definitions of dislocation spacing and Burgers vector in lattice-mismatched systems are used. We show that when these insights are properly incorporated into the continuum model, the resulting energy density expression of the lattice-mismatched systems is essentially indistinguishable from the MD results.

  20. A modified density-based clustering algorithm and its implementation

    NASA Astrophysics Data System (ADS)

    Ban, Zhihua; Liu, Jianguo; Yuan, Lulu; Yang, Hua

    2015-12-01

    This paper presents an improved density-based clustering algorithm based on the paper of clustering by fast search and find of density peaks. A distance threshold is introduced for the purpose of economizing memory. In order to reduce the probability that two points share the same density value, similarity is utilized to define proximity measure. We have tested the modified algorithm on a large data set, several small data sets and shape data sets. It turns out that the proposed algorithm can obtain acceptable results and can be applied more wildly.

  1. Solute drag on perfect and extended dislocations

    NASA Astrophysics Data System (ADS)

    Sills, R. B.; Cai, W.

    2016-04-01

    The drag force exerted on a moving dislocation by a field of mobile solutes is studied in the steady state. The drag force is numerically calculated as a function of the dislocation velocity for both perfect and extended dislocations. The sensitivity of the non-dimensionalized force-velocity curve to the various controlling parameters is assessed, and an approximate analytical force-velocity expression is given. A non-dimensional parameter S characterizing the strength of the solute-dislocation interaction, the background solute fraction ?, and the dislocation character angle ?, are found to have the strongest influence on the force-velocity curve. Within the model considered here, a perfect screw dislocation experiences no solute drag, but an extended screw dislocation experiences a non-zero drag force that is about 10 to 30% of the drag on an extended edge dislocation. The solutes can change the spacing between the Shockley partials in both stationary and moving extended dislocations, even when the stacking fault energy remains unaltered. Under certain conditions, the solutes destabilize an extended dislocation by either collapsing it into a perfect dislocation or causing the partials to separate unboundedly. It is proposed that the latter instability may lead to the formation of large faulted areas and deformation twins in low stacking fault energy materials containing solutes, consistent with experimental observations of copper and stainless steel containing hydrogen.

  2. Theory of interacting dislocations on cylinders

    NASA Astrophysics Data System (ADS)

    Amir, Ariel; Paulose, Jayson; Nelson, David R.

    2013-04-01

    We study the mechanics and statistical physics of dislocations interacting on cylinders, motivated by the elongation of rod-shaped bacterial cell walls and cylindrical assemblies of colloidal particles subject to external stresses. The interaction energy and forces between dislocations are solved analytically, and analyzed asymptotically. The results of continuum elastic theory agree well with numerical simulations on finite lattices even for relatively small systems. Isolated dislocations on a cylinder act like grain boundaries. With colloidal crystals in mind, we show that saddle points are created by a Peach-Koehler force on the dislocations in the circumferential direction, causing dislocation pairs to unbind. The thermal nucleation rate of dislocation unbinding is calculated, for an arbitrary mobility tensor and external stress, including the case of a twist-induced Peach-Koehler force along the cylinder axis. Surprisingly rich phenomena arise for dislocations on cylinders, despite their vanishing Gaussian curvature.

  3. Dislocation structures and electrical conduction properties of low angle tilt grain boundaries in LiNbO3

    NASA Astrophysics Data System (ADS)

    Furushima, Yuho; Nakamura, Atsutomo; Tochigi, Eita; Ikuhara, Yuichi; Toyoura, Kazuaki; Matsunaga, Katsuyuki

    2016-10-01

    Dislocations in crystalline materials constitute unique, atomic-scale, one-dimensional structure and have a potential to induce peculiar physical properties that are not found in the bulk. In this study, we fabricated LiNbO3 bicrystals with low angle tilt grain boundaries and investigated the relationship between the atomic structure of the boundary dislocations and their electrical conduction properties. Observations by using transmission electron microscopy revealed that dislocation structures at the (0001) low angle tilt grain boundaries depend on the tilt angle of the boundaries. Specifically, the characteristic dislocation structures with a large Burgers vector were formed in the boundary with the tilt angle of 2°. It is noteworthy that only the grain boundary of 2° exhibits distinct electrical conductivity after reduction treatment, although LiNbO3 is originally insulating. This unique electrical conductivity is suggested to be due to the characteristic dislocation structures with a large Burgers vector.

  4. Dislocation of the knee: imaging findings.

    PubMed

    Shearer, Damon; Lomasney, Laurie; Pierce, Kenneth

    2010-01-01

    Dislocations of the knee are relatively uncommon injuries. However, the incidence of this injury appears to be increasing. Knee dislocations are most often high velocity blunt injuries, with motor vehicle accidents being a frequent etiology. Other causes include falls from height, athletic injuries, farming and industrial accidents, and even low velocity mechanisms such as a misstep into a hole. Likewise, minor trauma in the morbidly obese is increasingly recognized as a mechanism of knee dislocation. Multiple forms of dislocation exist, with the common factor being disruption of the tibiofemoral articulation. Dislocation can occur in a variety of directions depending on the mechanism of injury. The most common dislocation is anterior, which may be seen in hyperextension injuries such as martial arts kicking. The "dashboard injury" of motor vehicle accidents can result in a posterior dislocation of the knee. Lateral and rotary dislocations are less common. Knee dislocation is more commonly diagnosed in men, with a mean age of 23 to 31 years old. This is the very patient population encountered by Special Operations Forces (SOF) healthcare providers. Given the mechanisms of injury noted above, it is reasonable to conclude that knee dislocations may be seen in a young, active SOF patient population, particularly those engaged in parachuting, fast-roping/rappelling, driving at high speeds during military operations, and mixed martial arts. PMID:20306414

  5. Three-dimensional formulation of dislocation climb

    NASA Astrophysics Data System (ADS)

    Gu, Yejun; Xiang, Yang; Quek, Siu Sin; Srolovitz, David J.

    2015-10-01

    We derive a Green's function formulation for the climb of curved dislocations and multiple dislocations in three-dimensions. In this new dislocation climb formulation, the dislocation climb velocity is determined from the Peach-Koehler force on dislocations through vacancy diffusion in a non-local manner. The long-range contribution to the dislocation climb velocity is associated with vacancy diffusion rather than from the climb component of the well-known, long-range elastic effects captured in the Peach-Koehler force. Both long-range effects are important in determining the climb velocity of dislocations. Analytical and numerical examples show that the widely used local climb formula, based on straight infinite dislocations, is not generally applicable, except for a small set of special cases. We also present a numerical discretization method of this Green's function formulation appropriate for implementation in discrete dislocation dynamics (DDD) simulations. In DDD implementations, the long-range Peach-Koehler force is calculated as is commonly done, then a linear system is solved for the climb velocity using these forces. This is also done within the same order of computational cost as existing discrete dislocation dynamics methods.

  6. Parallel Density-Based Clustering for Discovery of Ionospheric Phenomena

    NASA Astrophysics Data System (ADS)

    Pankratius, V.; Gowanlock, M.; Blair, D. M.

    2015-12-01

    Ionospheric total electron content maps derived from global networks of dual-frequency GPS receivers can reveal a plethora of ionospheric features in real-time and are key to space weather studies and natural hazard monitoring. However, growing data volumes from expanding sensor networks are making manual exploratory studies challenging. As the community is heading towards Big Data ionospheric science, automation and Computer-Aided Discovery become indispensable tools for scientists. One problem of machine learning methods is that they require domain-specific adaptations in order to be effective and useful for scientists. Addressing this problem, our Computer-Aided Discovery approach allows scientists to express various physical models as well as perturbation ranges for parameters. The search space is explored through an automated system and parallel processing of batched workloads, which finds corresponding matches and similarities in empirical data. We discuss density-based clustering as a particular method we employ in this process. Specifically, we adapt Density-Based Spatial Clustering of Applications with Noise (DBSCAN). This algorithm groups geospatial data points based on density. Clusters of points can be of arbitrary shape, and the number of clusters is not predetermined by the algorithm; only two input parameters need to be specified: (1) a distance threshold, (2) a minimum number of points within that threshold. We discuss an implementation of DBSCAN for batched workloads that is amenable to parallelization on manycore architectures such as Intel's Xeon Phi accelerator with 60+ general-purpose cores. This manycore parallelization can cluster large volumes of ionospheric total electronic content data quickly. Potential applications for cluster detection include the visualization, tracing, and examination of traveling ionospheric disturbances or other propagating phenomena. Acknowledgments. We acknowledge support from NSF ACI-1442997 (PI V. Pankratius).

  7. Crushed-salt constitutive model update

    SciTech Connect

    Callahan, G.D.; Loken, M.C.; Mellegard, K.D.

    1998-01-01

    Modifications to the constitutive model used to describe the deformation of crushed salt are presented in this report. Two mechanisms--dislocation creep and grain boundary diffusional pressure solutioning--defined previously but used separately are combined to form the basis for the constitutive model governing the deformation of crushed salt. The constitutive model is generalized to represent three-dimensional states of stress. New creep consolidation tests are combined with an existing database that includes hydrostatic consolidation and shear consolidation tests conducted on Waste Isolation Pilot Plant and southeastern New Mexico salt to determine material parameters for the constitutive model. Nonlinear least-squares model fitting to data from the shear consolidation tests and a combination of the shear and hydrostatic consolidation tests produced two sets of material parameter values for the model. The change in material parameter values from test group to test group indicates the empirical nature of the model but demonstrates improvement over earlier work with the previous models. Key improvements are the ability to capture lateral strain reversal and better resolve parameter values. To demonstrate the predictive capability of the model, each parameter value set was used to predict each of the tests in the database. Based on the fitting statistics and the ability of the model to predict the test data, the model appears to capture the creep consolidation behavior of crushed salt quite well.

  8. Mobility Laws in Dislocation Dynamics Simulations

    SciTech Connect

    Cai, W; Bulatov, V V

    2003-10-21

    Prediction of the plastic deformation behavior of single crystals based on the collective dynamics of dislocations has been a challenge for computational materials science for a number of years. The difficulty lies in the inability of existing dislocation dynamics (DD) codes to handle a sufficiently large number of dislocation lines, to establish a statistically representative model of crystal plasticity. A new massively-parallel DD code is developed that is capable of modeling million-dislocation systems by employing thousands of processors. We discuss an important ingredient of this code--the mobility laws dictating the behavior of individual dislocations. They are materials input for DD simulations and are constructed based on the understanding of dislocation motion at the atomistic level.

  9. Strain hardening in 2D discrete dislocation dynamics simulations: A new '2.5D' algorithm

    NASA Astrophysics Data System (ADS)

    Keralavarma, S. M.; Curtin, W. A.

    2016-10-01

    The two-dimensional discrete dislocation dynamics (2D DD) method, consisting of parallel straight edge dislocations gliding on independent slip systems in a plane strain model of a crystal, is often used to study complicated boundary value problems in crystal plasticity. However, the absence of truly three dimensional mechanisms such as junction formation means that forest hardening cannot be modeled, unless additional so-called '2.5D' constitutive rules are prescribed for short-range dislocation interactions. Here, results from three dimensional dislocation dynamics (3D DD) simulations in an FCC material are used to define new constitutive rules for short-range interactions and junction formation between dislocations on intersecting slip systems in 2D. The mutual strengthening effect of junctions on preexisting obstacles, such as precipitates or grain boundaries, is also accounted for in the model. The new '2.5D' DD model, with no arbitrary adjustable parameters beyond those obtained from lower scale simulation methods, is shown to predict athermal hardening rates, differences in flow behavior for single and multiple slip, and latent hardening ratios. All these phenomena are well-established in the plasticity of crystals and quantitative results predicted by the model are in good agreement with experimental observations.

  10. The Constitution by Cell

    ERIC Educational Resources Information Center

    Greenhut, Stephanie; Jones, Megan

    2010-01-01

    On their visit to the National Archives Experience in Washington, D.C., students in Jenni Ashley and Gay Brock's U.S. history classes at the Potomac School in McLean, Virginia, participated in a pilot program called "The Constitution by Cell." Armed with their cell phones, a basic understanding of the Constitution, and a willingness to participate…

  11. Interpreting the Constitution.

    ERIC Educational Resources Information Center

    Brennan, William J., Jr.

    1987-01-01

    Discusses constitutional interpretations relating to capital punishment and protection of human dignity. Points out the document's effectiveness in creating a new society by adapting its principles to current problems and needs. Considers two views of the Constitution that lead to controversy over the legitimacy of judicial decisions. (PS)

  12. Teaching the Constitution.

    ERIC Educational Resources Information Center

    Weatherman, Donald V.

    1987-01-01

    Courses on the Constitution must focus on the principles of government. Those principles and how the understanding of those principles shaped the document are appropriate subjects for consideration. The best sources for an examination of the Constitution are "The Records of the Federal Convention of 1787" and "The Federalist." (MLW)

  13. Worker Dislocation. Case Studies of Causes and Cures.

    ERIC Educational Resources Information Center

    Cook, Robert F., Ed.

    Case studies were made of the following dislocated worker programs: Cummins Engine Company Dislocated Worker Project; GM-UAW Metropolitan Pontiac Retraining and Employment Program; Minnesota Iron Range Dislocated Worker Project; Missouri Dislocated Worker Program Job Search Assistance, Inc.; Hillsborough, North Carolina, Dislocated Worker Project;…

  14. Robust atomistic calculation of dislocation line tension

    NASA Astrophysics Data System (ADS)

    Szajewski, B. A.; Pavia, F.; Curtin, W. A.

    2015-12-01

    The line tension Γ of a dislocation is an important and fundamental property ubiquitous to continuum scale models of metal plasticity. However, the precise value of Γ in a given material has proven difficult to assess, with literature values encompassing a wide range. Here results from a multiscale simulation and robust analysis of the dislocation line tension, for dislocation bow-out between pinning points, are presented for two widely-used interatomic potentials for Al. A central part of the analysis involves an effective Peierls stress applicable to curved dislocation structures that markedly differs from that of perfectly straight dislocations but is required to describe the bow-out both in loading and unloading. The line tensions for the two interatomic potentials are similar and provide robust numerical values for Al. Most importantly, the atomic results show notable differences with singular anisotropic elastic dislocation theory in that (i) the coefficient of the \\text{ln}(L) scaling with dislocation length L differs and (ii) the ratio of screw to edge line tension is smaller than predicted by anisotropic elasticity. These differences are attributed to local dislocation core interactions that remain beyond the scope of elasticity theory. The many differing literature values for Γ are attributed to various approximations and inaccuracies in previous approaches. The results here indicate that continuum line dislocation models, based on elasticity theory and various core-cut-off assumptions, may be fundamentally unable to reproduce full atomistic results, thus hampering the detailed predictive ability of such continuum models.

  15. Microdiffraction Analysis of Hierarchical Dislocation Organization

    SciTech Connect

    Barabash, R.I.; Ice, G.E.

    2007-12-19

    This article describes how x-ray microdiffraction is influenced by the number, kind, and organization of dislocations. Particular attention is placed on micro-Laue diffraction, where polychromatic x-rays are diffracted into characteristic Laue patterns that are sensitive to the dislocation content and arrangement. Diffraction is considered for various stages of plastic deformation. For early stages of plastic deformation with random dislocation spacing, the intensity in reciprocal space is redistributed about Laue spots with a length scale proportional to the number of dislocations within the sample volume and with a characteristic shape that depends on the kinds of dislocations and the momentum transfer vector. Unpaired dislocations that contribute to lattice rotations cause the largest redistribution of scattered intensity. In later stages of plastic deformation, strong interactions between individual dislocations cause them to organize into correlated arrangements. Here again, xray diffraction Laue spots are broadened in proportion to the number of excess (unpaired) dislocations inside the wall and to the total number of unpaired walls, but the broadening can be discontinuous. With microdiffraction it is possible to quantitatively test models of dislocation organization.

  16. Enabling Strain Hardening Simulations with Dislocation Dynamics

    SciTech Connect

    Arsenlis, A; Cai, W

    2006-12-20

    Numerical algorithms for discrete dislocation dynamics simulations are investigated for the purpose of enabling strain hardening simulations of single crystals on massively parallel computers. The algorithms investigated include the /(N) calculation of forces, the equations of motion, time integration, adaptive mesh refinement, the treatment of dislocation core reactions, and the dynamic distribution of work on parallel computers. A simulation integrating all of these algorithmic elements using the Parallel Dislocation Simulator (ParaDiS) code is performed to understand their behavior in concert, and evaluate the overall numerical performance of dislocation dynamics simulations and their ability to accumulate percents of plastic strain.

  17. Congenital dislocation of the patella - clinical case.

    PubMed

    Miguel Sá, Pedro; Raposo, Filipa; Santos Carvalho, Manuel; Alegrete, Nuno; Coutinho, Jorge; Costa, Gilberto

    2016-01-01

    Congenital patellar dislocation is a rare condition in which the patella is permanently dislocated and cannot be reduced manually. The patella develops normally as a sesamoid bone of the femur. This congenital dislocation results from failure of the internal rotation of the myotome that forms the femur, quadriceps muscle and extensor apparatus. It usually manifests immediately after birth, although in some rare cases, the diagnosis may be delayed until adolescence or adulthood. Early diagnosis is important, thereby allowing surgical correction and avoiding late sequelae, including early degenerative changes in the knee. A case of permanent dislocation of the patella is presented here, in a female child aged seven years.

  18. Multiscale modeling of dislocation-precipitate interactions in Fe: From molecular dynamics to discrete dislocations.

    PubMed

    Lehtinen, Arttu; Granberg, Fredric; Laurson, Lasse; Nordlund, Kai; Alava, Mikko J

    2016-01-01

    The stress-driven motion of dislocations in crystalline solids, and thus the ensuing plastic deformation process, is greatly influenced by the presence or absence of various pointlike defects such as precipitates or solute atoms. These defects act as obstacles for dislocation motion and hence affect the mechanical properties of the material. Here we combine molecular dynamics studies with three-dimensional discrete dislocation dynamics simulations in order to model the interaction between different kinds of precipitates and a 1/2〈111〉{110} edge dislocation in BCC iron. We have implemented immobile spherical precipitates into the ParaDis discrete dislocation dynamics code, with the dislocations interacting with the precipitates via a Gaussian potential, generating a normal force acting on the dislocation segments. The parameters used in the discrete dislocation dynamics simulations for the precipitate potential, the dislocation mobility, shear modulus, and dislocation core energy are obtained from molecular dynamics simulations. We compare the critical stresses needed to unpin the dislocation from the precipitate in molecular dynamics and discrete dislocation dynamics simulations in order to fit the two methods together and discuss the variety of the relevant pinning and depinning mechanisms. PMID:26871192

  19. Quantum dislocations in solid Helium-4

    NASA Astrophysics Data System (ADS)

    Aleinikava, Darya

    In this thesis the following problems on properties of solid 4He are considered: (i) the role of long-range interactions in suppression of dislocation roughening at T = 0; (ii) the combined effect of 3He impurities and Peierls potential on shear modulus softening; (iii) the dislocation superclimb and its connection to the phenomenon of "giant isochoric compressibility"; (iv) non-linear dislocation response to the applied stress and stress-induces dislocation roughening as a I-order phase transition in 1D at finite temperature. First we investigate the effect of long-range interactions on the state of edge dislocation at T = 0. Such interactions are induced by elastic forces of the solid. We found that quantum roughening transition of a dislocation at T = 0 is completely suppressed by arbitrarily small long-range interactions between kinks. A heuristic argument is presented and the result has been verified by numerical Monte-Carlo simulations using Worm Algorithm in J-current model. It was shown that the Peierls potential plays a crucial role in explaining the elastic properties of dislocations, namely shear modulus softening phenomenon. The crossover from T = 0 to finite temperatures leads to intrinsic softening of the shear modulus and is solely controlled by kink typical energy. It was demonstrated that the mechanism, involving only the binding of 3He impurities to the dislocations, requires an unrealistically high concentrations of defects (or impurities) in order to explain the shear modulus phenomenon and therefore an inclusion of Peierls potential in consideration is required. Superclimbing dislocations, that is the edge dislocations with the superfluidity along the core, were investigated. The theoretical prediction that superclimb is responsible for the phenomenon of "giant isochoric compressibility" was confirmed by Monte-Carlo simulations. It was demonstrated that the isochoric compressibility is suppressed at low temperatures. The dependence of

  20. The form of a constitutive equation of plastic deformation compatible with stress relaxation data

    SciTech Connect

    Fortes, M.A.; Rosa, M.E.

    1984-05-01

    Hart's approach to constitutive equations of plasticity and experimental results relevant to his formalism are reanalyzed, with special emphasis on the consequences of the scaling relation observed in the relaxation curves of a large number of materials. Complete constitutive equations containing a single structure variable are proposed which describe the experimentally determined relaxation and tensile test curves. An interpretation of the structure variable is given in terms of the density of obstacles to dislocations. The equations are generalized to include recovery and applied to dislocation creep.

  1. Dislocated interests and climate change

    NASA Astrophysics Data System (ADS)

    Davis, Steven J.; Diffenbaugh, Noah

    2016-06-01

    The predicted effects of climate change on surface temperatures are now emergent and quantifiable. The recent letter by Hansen and Sato (2016 Environ. Res. Lett. 11 034009) adds to a growing number of studies showing that warming over the past four decades has shifted the distribution of temperatures higher almost everywhere, with the largest relative effects on summer temperatures in developing regions such as Africa, South America, southeast Asia, and the Middle East (e.g., Diffenbaugh and Scherer 2011 Clim. Change 107 615-24 Anderson 2011 Clim. Change 108 581; Mahlstein et al 2012 Geophys. Res. Lett. 39 L21711). Hansen and Sato emphasize that although these regions are warming disproportionately, their role in causing climate change—measured by cumulative historical CO2 emissions produced—is small compared to the US and Europe, where the relative change in temperatures has been less. This spatial and temporal mismatch of climate change impacts and the burning of fossil fuels is a critical dislocation of interests that, as the authors note, has ‘substantial implications for global energy and climate policies.’ Here, we place Hansen and Sato’s ‘national responsibilities’ into a broader conceptual framework of problematically dislocated interests, and briefly discuss the related challenges for global climate mitigation efforts.

  2. Dislocated interests and climate change

    NASA Astrophysics Data System (ADS)

    Davis, Steven J.; Diffenbaugh, Noah

    2016-06-01

    The predicted effects of climate change on surface temperatures are now emergent and quantifiable. The recent letter by Hansen and Sato (2016 Environ. Res. Lett. 11 034009) adds to a growing number of studies showing that warming over the past four decades has shifted the distribution of temperatures higher almost everywhere, with the largest relative effects on summer temperatures in developing regions such as Africa, South America, southeast Asia, and the Middle East (e.g., Diffenbaugh and Scherer 2011 Clim. Change 107 615–24 Anderson 2011 Clim. Change 108 581; Mahlstein et al 2012 Geophys. Res. Lett. 39 L21711). Hansen and Sato emphasize that although these regions are warming disproportionately, their role in causing climate change—measured by cumulative historical CO2 emissions produced—is small compared to the US and Europe, where the relative change in temperatures has been less. This spatial and temporal mismatch of climate change impacts and the burning of fossil fuels is a critical dislocation of interests that, as the authors note, has ‘substantial implications for global energy and climate policies.’ Here, we place Hansen and Sato’s ‘national responsibilities’ into a broader conceptual framework of problematically dislocated interests, and briefly discuss the related challenges for global climate mitigation efforts.

  3. Constitution and Bylaws.

    ERIC Educational Resources Information Center

    Journal of Dental Education, 1981

    1981-01-01

    Constitutions and bylaws of the American Association of Dental Schools are presented, covering organization name, statement of purpose, administrative organization, offices, membership, legislative and administrative bodies, elected and appointed officers, regular and special sessions, sections, publications, election, and finance. (MSE)

  4. Dislocation generation during early stage sintering.

    NASA Technical Reports Server (NTRS)

    Sheehan, J. E.; Lenel, F. V.; Ansell, G. S.

    1973-01-01

    Discussion of the effects of capillarity-induced stresses on dislocations during early stage sintering. A special version of Hirth's (1963) theoretical calculation procedures modified to describe dislocation nucleation on planes meeting the sintering body's neck surface obliquely is shown to predict plastic flow at stress levels know to exist between micron size metal particles in the early stages of sintering.

  5. Statistics of dislocation pinning at localized obstacles

    NASA Astrophysics Data System (ADS)

    Dutta, A.; Bhattacharya, M.; Barat, P.

    2014-10-01

    Pinning of dislocations at nanosized obstacles like precipitates, voids, and bubbles is a crucial mechanism in the context of phenomena like hardening and creep. The interaction between such an obstacle and a dislocation is often studied at fundamental level by means of analytical tools, atomistic simulations, and finite element methods. Nevertheless, the information extracted from such studies cannot be utilized to its maximum extent on account of insufficient information about the underlying statistics of this process comprising a large number of dislocations and obstacles in a system. Here, we propose a new statistical approach, where the statistics of pinning of dislocations by idealized spherical obstacles is explored by taking into account the generalized size-distribution of the obstacles along with the dislocation density within a three-dimensional framework. Starting with a minimal set of material parameters, the framework employs the method of geometrical statistics with a few simple assumptions compatible with the real physical scenario. The application of this approach, in combination with the knowledge of fundamental dislocation-obstacle interactions, has successfully been demonstrated for dislocation pinning at nanovoids in neutron irradiated type 316-stainless steel in regard to the non-conservative motion of dislocations. An interesting phenomenon of transition from rare pinning to multiple pinning regimes with increasing irradiation temperature is revealed.

  6. A rare variant of knee dislocation

    PubMed Central

    HUSSIN, P.; MAWARDI, M.; AB HALIM, A.H.

    2016-01-01

    Knee dislocation is a rare injury. It represents less than 0.2% of orthopaedic injuries. This case reports a rare form of knee dislocation caused by the impact of a high-energy trauma. In these cases the appropriate assessment and management is needed to ensure that patient receives the proper treatment. PMID:27381692

  7. Obesity. A risk factor for knee dislocation.

    PubMed

    Marin, E L; Bifulco, S S; Fast, A

    1990-06-01

    Complete dislocation of the knee joint is a severe injury that is commonly the result of high-velocity injuries and often associated with disruption of the popliteal artery. We report two cases in which obesity appeared to be the principal cause of knee dislocation with vascular compromise. Preventive measures in extremely obese patients are recommended.

  8. Community College Adjustment among Dislocated Workers

    ERIC Educational Resources Information Center

    Schwitzer, Alan M.; Duggan, Molly H.; Laughlin, Janet T.; Walker, Martha A.

    2011-01-01

    Community colleges often are catalysts for economic and workforce development in localities with high unemployment or large numbers of dislocated workers. Increasingly, dislocated workers--individuals who have experienced job loss due to occupational closings, reduced workforces, or severe local economic downturns--are enrolling in educational and…

  9. Dislocation of the cuboid bone without fracture.

    PubMed

    Gough, D T; Broderick, D F; Januzik, S J; Cusack, T J

    1988-10-01

    A 37-year-old man presented following an inversion plantar flexion injury to the left foot and ankle. Dislocation of the cuboid without associated fracture was identified and successfully treated by closed reduction. The patient was immobilized in a walking cast for seven weeks after surgery and no further dislocation occurred.

  10. Statistics of dislocation pinning at localized obstacles

    SciTech Connect

    Dutta, A.; Bhattacharya, M. Barat, P.

    2014-10-14

    Pinning of dislocations at nanosized obstacles like precipitates, voids, and bubbles is a crucial mechanism in the context of phenomena like hardening and creep. The interaction between such an obstacle and a dislocation is often studied at fundamental level by means of analytical tools, atomistic simulations, and finite element methods. Nevertheless, the information extracted from such studies cannot be utilized to its maximum extent on account of insufficient information about the underlying statistics of this process comprising a large number of dislocations and obstacles in a system. Here, we propose a new statistical approach, where the statistics of pinning of dislocations by idealized spherical obstacles is explored by taking into account the generalized size-distribution of the obstacles along with the dislocation density within a three-dimensional framework. Starting with a minimal set of material parameters, the framework employs the method of geometrical statistics with a few simple assumptions compatible with the real physical scenario. The application of this approach, in combination with the knowledge of fundamental dislocation-obstacle interactions, has successfully been demonstrated for dislocation pinning at nanovoids in neutron irradiated type 316-stainless steel in regard to the non-conservative motion of dislocations. An interesting phenomenon of transition from rare pinning to multiple pinning regimes with increasing irradiation temperature is revealed.

  11. Geometric approach to dislocation and disclination theory

    SciTech Connect

    Nesterov, A.I.; Ovchinnikov, S.G.

    1988-05-01

    Cartan structure equations are used to create a four-dimensional geometric description of dislocations in continuum theory. It is shown that the dislocation distribution is determined by the torsion tensor, while the disclination distribution is determined by the curvature tensor. An analogy to electrodynamics is offered.

  12. [Bipolar forearm dislocation or floating forearm (a case report)].

    PubMed

    Daoudi, A; Elibrahimi, A; Loudiyi, W D; Elmrini, A; Chakour, K; Boutayeb, F

    2009-02-01

    Bipolar dislocation of the forearm or floating forearm is a rare injury. It combines concomitant elbow and wrist dislocation. Only six cases have been reported in the literature. The diagnosis of wrist dislocation may initially be missed and therefore the prognosis will be worse. The authors report a case of a bipolar dislocation with a posterior dislocation of the elbow and a perilunate dislocation of the wrist.

  13. Initial dislocation structure and dynamic dislocation multiplication in Mo single crystals

    SciTech Connect

    Hsiung, L M; Lassila, D H

    2000-03-22

    Initial dislocation structure in annealed high-purity Mo single crystals and deformation substructure in a crystal subjected to 1% compression have been examined and studied in order to investigate dislocation multiplication mechanisms in the early stages of plastic deformation. The initial dislocation density is in a range of 10{sup 6} {approx} 10{sup 7} cm{sup -2}, and the dislocation structure is found to contain many grown-in superjogs along dislocation lines. The dislocation density increases to a range of 10{sup 8} {approx} 10{sup 9} cm{sup -2}, and the average jog height is also found to increase after compressing for a total strain of 1%. It is proposed that the preexisting jogged screw dislocations can act as (multiple) dislocation multiplication sources when deformed under quasi-static conditions. Both the jog height and length of link segment (between jogs) can increase by stress-induced jog coalescence, which takes place via the lateral migration (drift) of superjogs driven by unbalanced line-tension partials acting on link segments of unequal lengths. Applied shear stress begins to push each link segment to precede dislocation multiplication when link length and jog height are greater than critical lengths. This dynamic dislocation multiplication source is subsequently verified by direct simulations of dislocation dynamics under stress to be crucial in the early stages of plastic deformation in Mo single crystals.

  14. Double Dislocation of Interphalangeal Joints Accompanied with Contralateral Shoulder Dislocation: A Case Report.

    PubMed

    Raval, Pradyumna Ramchandra; Jariwala, Arpit

    2016-02-01

    Dislocation of any joint is an orthopaedic emergency and needs immediate attention by the attending physician. A delay in reducing a dislocated joint can lead to disastrous complications both immediately as well as in the long run. Although anterior dislocation of a shoulder joint is by far the commonest dislocation encountered by any emergency care physician, other joints may also get dislocated. In certain cases two joints may get dislocated simultaneously. Such dislocation is known as a double dislocation. Double dislocation of the proximal interphalangeal joint and the distal interphalangeal joint in the same finger is a rare injury. High impact loading at the fingertip is the primary cause in most cases and it is often associated with younger individuals playing contact sports. The right little finger is the digit commonly involved and this injury is evident in football players more often than not. Although closed reduction is a preferred treatment, it may not be always successful. Time of presentation, tendon interposition, associated swelling and co-existent phalangeal fractures are certain key impediments to a successful closed reduction manoeuvre. In patients with an open injury, a thorough wash out and appropriate antibiotic cover is mandatory. We report a rare case of double dislocation of the interphalangeal joints accompanied with contralateral shoulder dislocation in an elderly man sustained after a fall which was treated successfully with closed reduction and early mobilization. PMID:27028386

  15. Dislocation patterning in a two-dimensional continuum theory of dislocations

    NASA Astrophysics Data System (ADS)

    Groma, István; Zaiser, Michael; Ispánovity, Péter Dusán

    2016-06-01

    Understanding the spontaneous emergence of dislocation patterns during plastic deformation is a long standing challenge in dislocation theory. During the past decades several phenomenological continuum models of dislocation patterning were proposed, but few of them (if any) are derived from microscopic considerations through systematic and controlled averaging procedures. In this paper we present a two-dimensional continuum theory that is obtained by systematic averaging of the equations of motion of discrete dislocations. It is shown that in the evolution equations of the dislocation densities diffusionlike terms neglected in earlier considerations play a crucial role in the length scale selection of the dislocation density fluctuations. It is also shown that the formulated continuum theory can be derived from an averaged energy functional using the framework of phase field theories. However, in order to account for the flow stress one has in that case to introduce a nontrivial dislocation mobility function, which proves to be crucial for the instability leading to patterning.

  16. Glide dislocation nucleation from dislocation nodes at semi-coherent {111} Cu–Ni interfaces

    SciTech Connect

    Shao, Shuai; Wang, Jian; Beyerlein, Irene J.; Misra, Amit

    2015-07-23

    Using atomistic simulations and dislocation theory on a model system of semi-coherent {1 1 1} interfaces, we show that misfit dislocation nodes adopt multiple atomic arrangements corresponding to the creation and redistribution of excess volume at the nodes. We identified four distinctive node structures: volume-smeared nodes with (i) spiral or (ii) straight dislocation patterns, and volume-condensed nodes with (iii) triangular or (iv) hexagonal dislocation patterns. Volume-smeared nodes contain interfacial dislocations lying in the Cu–Ni interface but volume-condensed nodes contain two sets of interfacial dislocations in the two adjacent interfaces and jogs across the atomic layer between the two adjacent interfaces. Finally, under biaxial tension/compression applied parallel to the interface, we show that the nucleation of lattice dislocations is preferred at the nodes and is correlated with the reduction of excess volume at the nodes.

  17. Glide dislocation nucleation from dislocation nodes at semi-coherent {111} Cu–Ni interfaces

    DOE PAGESBeta

    Shao, Shuai; Wang, Jian; Beyerlein, Irene J.; Misra, Amit

    2015-07-23

    Using atomistic simulations and dislocation theory on a model system of semi-coherent {1 1 1} interfaces, we show that misfit dislocation nodes adopt multiple atomic arrangements corresponding to the creation and redistribution of excess volume at the nodes. We identified four distinctive node structures: volume-smeared nodes with (i) spiral or (ii) straight dislocation patterns, and volume-condensed nodes with (iii) triangular or (iv) hexagonal dislocation patterns. Volume-smeared nodes contain interfacial dislocations lying in the Cu–Ni interface but volume-condensed nodes contain two sets of interfacial dislocations in the two adjacent interfaces and jogs across the atomic layer between the two adjacent interfaces.more » Finally, under biaxial tension/compression applied parallel to the interface, we show that the nucleation of lattice dislocations is preferred at the nodes and is correlated with the reduction of excess volume at the nodes.« less

  18. Internal stresses, dislocation mobility and ductility

    NASA Astrophysics Data System (ADS)

    Saada, G.

    1991-06-01

    The description of plastic deformation must take into account individual mechanisms and heterogeneity of plastic strain. Influence of dislocation interaction with forest dislocations and of cross slip are connected with the organization of dipole walls. The latter are described and their development is explained as a consequence of edge effects. Applications are discussed. La description de la déformation plastique doit prendre en compte les interactions individuelles des dislocations et l'hétérogénéité à grande échelle de la déformation plastique. Les interactions des dislocations mobiles avec la forêt de dislocations, le glissement dévié, ont pour effet la création de parois dipolaires. Celles-ci sont décrites et leur développement est appliqué à partir des effets de bord.

  19. Constitution, 15 August 1982.

    PubMed

    1987-01-01

    This document reprints major provisions of the 1982 Constitution of Equatorial Guinea. The Constitution calls for protection of the family as the basic building block of society. Foreigners are afforded the same civil rights as citizens and may seek asylum but may not exercise political rights. The Constitution guarantees equality before the law and prohibits discrimination based on ethnic background, race, sex, language, religion, filiation, political or other views, social origin, economic position, or birth. Women are afforded the same rights as men regardless of their marital status. The Constitution also guarantees citizens freedom to travel nationally and internationally and to choose a place of residence. Equatoguineans are also entitled to a standard of living that insures health, nutrition, education, clothing, housing, medical care, and necessary social services. The family policy contained in the Constitution protects all types of legal marriages equally and recognizes nonattachable and inalienable family patrimony. Children are protected from the time of conception, and all inhabitants are guaranteed a basic state education which is compulsory and free. Efforts are also being made to eradicate illiteracy. Women are insured training and promotion for their integration into the active life and development of the country, and farmers are guaranteed traditional ownership of the lands they possess, although the state retains the right of eminent domain. PMID:12346662

  20. Atlantoaxial dislocation and Down's syndrome.

    PubMed Central

    Whaley, W J; Gray, W D

    1980-01-01

    The phenotypic features of Down's syndrome are easily recognized and include characteristic facial features, hypotonia, ligament laxity, transverse palmar creases and mental subnormality. Associated manifestations and complications are also familiar and involve almost every organ system. Congenital heart defects, bowel malformations and a tendency to leukemia are common attendant problems. Less common, however, are defects of the skeletal system; in fact, the most recent edition of a standard pediatric textbook makes no mention of anomalies of the vertebral column. The purpose of this paper is to call attention to the association between Down's syndrome and atlantoaxial dislocation, which in our patient resulted in quadriplegia and eventually death. Images FIG. 1 FIG. 2 PMID:6448087

  1. Recurrent Dislocation of the Patella

    PubMed Central

    Benítez, Gustavo

    2015-01-01

    Purpose: To evaluate results of medial patellofemoral ligament (MPFL) reconstruction associated with lateral release and advancement of vastus medialis in recurrent dislocation of the patella. Methods: We retrospectively evaluated 11 patients with a mean follow-up of 19 months. Mean age was 23, mainly women. We did MPFL reconstruction with semitendinosus or gracilis tendon depending on BMI, associated with advancement of vastus medialis and lateral release. Results: Mean Kujala score improved from 46,54 pts. preoperative to 88,36 postoperative. Our main complication was 1 patient with rigid knee, who required movilization under anesthesia and arthroscopic arthrolisis to improve her outcome. Conclusion: The combination of this techniques are a good alternative to treat patients with recurrent patella disclocation, with good short and mid-term results. Biomechanic intra and postop complications of MPFL reconstruction are related to patellar fixation, anatomic positioning of femoral tunnel and knee position of the graft fixation.

  2. Dislocation-obstacle interactions in aluminum alloys

    NASA Astrophysics Data System (ADS)

    Clark, Blythe Gore

    Dislocation-obstacle interactions play a significant role in determining the mechanical response of a material. Because higher stresses are needed for dislocations to bypass obstacles, these interactions reduce dislocation mobility and increase the yield strength of a material, as well as improve the work-hardening rate and the resistance to coarsening. The phenomenon of dislocation-obstacle interactions can be advantageous, as in the case of particle-strengthening to increase the creep strength of a material, or disadvantageous, as in embrittlement of a metal due to radiation-induced defects. In order to accelerate the time from development to implementation of a new material, optimize production parameters, and accurately predict the behavior of a material while in service, it is necessary to develop robust material models based on fundamental physical inputs. Through careful experimentation, the nature of dislocation-obstacle interactions can be assessed, allowing key physical parameters to be identified and clarified. These can serve as the basis for developing new and accurate material models. This thesis examines two types of dislocation-obstacle interactions: dislocation-particle interactions during creep deformation, and dislocation-loop interactions during deformation at room temperature. Dislocation-particle interaction studies in Al-Zn-Mg-Cu-Zr, Al-4Mg-0.3Sc, and Al-0.3Sc showed that temperature, coherency, and particle size play a role in determining the dominant bypass mechanism, and that interactions are more complex than what is considered in current models. A new mechanism for elevated temperature bypass of particles during creep deformation was revealed, in which dislocations interact directly with the particle-matrix interface, altering the interfacial structure, and affecting subsequent dislocation interactions. These results are discussed in relation to macroscopic behavior in steady-state creep experiments. In addition, dislocation

  3. Dislocation Creep in Magnesium Calcite

    NASA Astrophysics Data System (ADS)

    Xu, L.; Xiao, X.; Evans, B. J.

    2003-12-01

    To investigate the effect of dissolved Mg on plastic deformation of calcite, we performed triaxial deformation experiments on synthetic calcite with varying amount of Mg content. Mixtures of powders of calcite and dolomite were isostatically hot pressed (HIP) at 850° C and 300 MPa confining pressure for different intervals (2 to 20hrs) resulting in homogeneous aggregates of high-magnesium calcite; Mg content varied from 0.07 to 0.17 mol%. Creep tests were performed at differential stresses from 20 to 160 MPa at 700 to 800° C. Grain sizes before and after deformation were determined from the images obtained from scanning electron microscope (SEM) and optical microscope. Grain sizes are in the range of 5 to 20 microns depending on the HIP time, and decrease with increasing magnesium content. Both BSE images and chemical analysis suggest that all dolomite are dissolved and the Mg distribution is homogeneous through the sample, after 2 hrs HIP. At stresses below 40 MPa, the samples deformed in diffusion region (Coble creep), as described previously by Herwegh. The strength decreases with increasing magnesium content, owing to the difference of grain size. At stresses above 80 MPa, the stress exponent is greater than 3, indicating an increased contribution of dislocation creep. The transition between diffusion to dislocation creep occurs at higher stresses for the samples with higher magnesium content and smaller grain size. Preliminary data suggests a slight increase in strength with increasing magnesium content, but more tests are needed to verify this effect. In a few samples, some strain weakening may have been evident. The activation energy in the transition region (at 80 MPa) is ˜200 KJ/mol with no dependence on magnesium content, agreeing with previous measurements of diffusion creep in natural and synthetic marbles.

  4. Evolution, Interaction, and Intrinsic Properties of Dislocations in Intermetallics: Anisotropic 3D Dislocation Dynamics Approach

    SciTech Connect

    Chen, Qian

    2008-01-01

    The generation, motion, and interaction of dislocations play key roles during the plastic deformation process of crystalline solids. 3D Dislocation Dynamics has been employed as a mesoscale simulation algorithm to investigate the collective and cooperative behavior of dislocations. Most current research on 3D Dislocation Dynamics is based on the solutions available in the framework of classical isotropic elasticity. However, due to some degree of elastic anisotropy in almost all crystalline solids, it is very necessary to extend 3D Dislocation Dynamics into anisotropic elasticity. In this study, first, the details of efficient and accurate incorporation of the fully anisotropic elasticity into 3D discrete Dislocation Dynamics by numerically evaluating the derivatives of Green's functions are described. Then the intrinsic properties of perfect dislocations, including their stability, their core properties and disassociation characteristics, in newly discovered rare earth-based intermetallics and in conventional intermetallics are investigated, within the framework of fully anisotropic elasticity supplemented with the atomistic information obtained from the ab initio calculations. Moreover, the evolution and interaction of dislocations in these intermetallics as well as the role of solute segregation are presented by utilizing fully anisotropic 3D dislocation dynamics. The results from this work clearly indicate the role and the importance of elastic anisotropy on the evolution of dislocation microstructures, the overall ductility and the hardening behavior in these systems.

  5. Increasing preoperative dislocations and total time of dislocation affect surgical management of anterior shoulder instability

    PubMed Central

    Denard, Patrick J.; Dai, Xuesong; Burkhart, Stephen S.

    2015-01-01

    Purpose: Our purpose was to determine the relationship between number of preoperative shoulder dislocations and total dislocation time and the need to perform bone deficiency procedures at the time of primary anterior instability surgery. Our hypothesis was that need for bone deficiency procedures would increase with the total number and hours of dislocation. Materials and Methods: A retrospective review was performed of primary instability surgeries performed by a single surgeon. Patients with <25% glenoid bone loss were treated with an isolated arthroscopic Bankart repair. Those who also had an engaging Hill-Sachs lesion underwent arthroscopic Bankart repair with remplissage. Patients with >25% glenoid bone loss were treated with Latarjet reconstruction. Number of dislocations and total dislocation time were examined for their relationship with the treatment method. Results: Ten arthroscopic Bankart repairs, 13 arthroscopic Bankart plus remplissage procedures, and 9 Latarjet reconstructions were available for review. Total dislocations (P = 0.012) and total hours of dislocation (P = 0.019) increased from the Bankart, to the remplissage, to the Latarjet groups. Patients with a total dislocation time of 5 h or more were more likely to require a Latarjet reconstruction (P = 0.039). Patients with only 1 preoperative dislocation were treated with an isolated Bankart repair in 64% (7 of 11) of cases, whereas those with 2 or more dislocations required a bone loss procedure in 86% (18 of 21) of cases (P = 0.013). Conclusion: Increasing number of dislocations and total dislocation time are associated with the development of glenoid and humeral head bony lesions that alter surgical management of anterior shoulder instability. The necessity for the addition of a remplissage to an arthroscopic Bankart repair or the use of a Latarjet reconstruction increases with only 1 recurrent dislocation. Level of evidence: Level III, retrospective comparative study. PMID:25709237

  6. Thermodynamic forces in single crystals with dislocations

    NASA Astrophysics Data System (ADS)

    Van Goethem, Nicolas

    2014-06-01

    A simple model for the evolution of macroscopic dislocation regions in a single crystal is presented. This model relies on maximal dissipation principle within Kröner's geometric description of the dislocated crystal. Mathematical methods and tools from shape optimization theory provide equilibrium relations at the dislocation front, similarly to previous work achieved on damage modelling (J Comput Phys 33(16):5010-5044, 2011). The deformation state variable is the incompatible strain as related to the dislocation density tensor by a relation involving the Ricci curvature of the crystal underlying elastic metric. The time evolution of the model variables follows from a novel interpretation of the Einstein-Hilbert flow in terms of dislocation microstructure energy. This flow is interpreted as the dissipation of non-conservative dislocations, due to the climb mechanism, modelled by an average effect of mesoscopic dislocations moving normal to their glide planes by adding or removing points defects. The model equations are a fourth-order tensor parabolic equation involving the operator "incompatibility," here appearing as a tensorial counterpart of the scalar Laplacian. This work encompasses and generalizes results previously announced (C R Acad Sci Paris Ser I 349:923-927, 2011), with in addition a series of physical interpretations to give a meaning to the newly introduced concepts.

  7. Numerical implementation of a crystal plasticity model with dislocation transport for high strain rate applications

    NASA Astrophysics Data System (ADS)

    Mayeur, Jason R.; Mourad, Hashem M.; Luscher, Darby J.; Hunter, Abigail; Kenamond, Mark A.

    2016-05-01

    This paper details a numerical implementation of a single crystal plasticity model with dislocation transport for high strain rate applications. Our primary motivation for developing the model is to study the influence of dislocation transport and conservation on the mesoscale response of metallic crystals under extreme thermo-mechanical loading conditions (e.g. shocks). To this end we have developed a single crystal plasticity theory (Luscher et al (2015)) that incorporates finite deformation kinematics, internal stress fields caused by the presence of geometrically necessary dislocation gradients, advection equations to model dislocation density transport and conservation, and constitutive equations appropriate for shock loading (equation of state, drag-limited dislocation velocity, etc). In the following, we outline a coupled finite element–finite volume framework for implementing the model physics, and demonstrate its capabilities in simulating the response of a [1 0 0] copper single crystal during a plate impact test. Additionally, we explore the effect of varying certain model parameters (e.g. mesh density, finite volume update scheme) on the simulation results. Our results demonstrate that the model performs as intended and establishes a baseline of understanding that can be leveraged as we extend the model to incorporate additional and/or refined physics and move toward a multi-dimensional implementation.

  8. Distribution of distances between dislocations in different types of dislocation substructures in deformed Cu-Al alloys

    NASA Astrophysics Data System (ADS)

    Trishkina, L.; Cherkasova, T.; Zboykova, N.; Koneva, N.; Kozlov, E.

    2016-01-01

    The aim of the investigation was the determination of the statistic description of dislocation distribution in each dislocation substructures component forming after different deformation degrees in the Cu-Al alloys. The dislocation structures were investigated by the transmission diffraction electron microscopy method. In the work the statistic description of distance distribution between the dislocations, dislocation barriers and dislocation tangles in the deformed Cu-Al alloys with different concentration of Al and test temperature at the grain size of 100 µm was carried out. It was established that the above parameters influence the dislocation distribution in different types of the dislocation substructures (DSS): dislocation chaos, dislocation networks without disorientation, nondisoriented and disoriented cells, in the walls and inside the cells. The distributions of the distances between dislocations in the investigated alloys for each DSS type formed at certain deformation degrees and various test temperatures were plotted.

  9. Monteggia fracture-dislocations: A Historical Review

    PubMed Central

    Rehim, Shady A.; Maynard, Mallory A.; Sebastin, Sandeep J.; Chung, Kevin C.

    2014-01-01

    The eponym Monteggia fracture-dislocation originally referred to a fracture of the shaft of the ulna accompanied by anterior dislocation of the radial head that was described by Giovanni Battista Monteggia of Italy in 1814. Subsequently, a further classification system based on the direction of the radial head dislocation and associated fractures of the radius and ulna was proposed by Jose Luis Bado of Uruguay in 1958. This article investigates the evolution of treatment, classification, and outcomes of the Monteggia injury and sheds light on the lives and contributions of Monteggia and Bado. PMID:24792923

  10. South Africa's Constitutional Change.

    ERIC Educational Resources Information Center

    Getman, Thomas

    1987-01-01

    Describes the striking dichotomy of South Africa's beauty and the squalor resulting from the apartheid policies of the government. Reviews reactions of black South Africans to recent constitutional changes and details efforts to secure more sweeping reform. Includes stories of several individuals who have taken actions which oppose the system of…

  11. Sexuality and the Constitution.

    ERIC Educational Resources Information Center

    Copelon, Rhonda

    1987-01-01

    Argues for abortion rights and protection of intimate decisions and relationships. Describes the role and position of women in eighteenth century American society as a means of exposing the fallacy of the anti-abortion movement's insistence on adherence to constitutional text. Discusses the recent attempts to overturn the Roe v. Wade ruling. (PS)

  12. The Constitution in Action

    ERIC Educational Resources Information Center

    Potter, Lee Ann

    2007-01-01

    In this article, the author describes the experiences middle school students on a field trip to the new Constitution in Action Learning Lab in the Boeing Learning Center at the National Archives can expect. There, middle school students take on the roles of archivists and researchers collecting and analyzing primary sources from the holdings of…

  13. Instabilities and constitutive modelling.

    PubMed

    Wilson, Helen J

    2006-12-15

    The plastics industry today sees huge wastage through product defects caused by unstable flows during the manufacturing process. In addition, many production lines are throughput-limited by a flow speed threshold above which the process becomes unstable. Therefore, it is critically important to understand the mechanisms behind these instabilities. In order to investigate the flow of a molten plastic, the first step is a model of the liquid itself, a relation between its current stress and its flow history called a constitutive relation. These are derived in many ways and tested on several benchmark flows, but rarely is the stability of the model used as a criterion for selection. The relationship between the constitutive model and the stability properties of even simple flows is not yet well understood. We show that in one case a small change to the model, which does not affect the steady flow behaviour, entirely removes a known instability. In another, a change that makes a qualitative difference to the steady flow makes only tiny changes to the stability.The long-term vision of this research is to exactly quantify what are the important properties of a constitutive relation as far as stability is concerned. If we could understand that, not only could very simple stability experiments be used to choose the best constitutive models for a particular material, but our ability to predict and avoid wasteful industrial instabilities would also be vastly improved.

  14. The Constitutional Heritage.

    ERIC Educational Resources Information Center

    Baxter, Maurice

    Changing political, social, economic, and intellectual conditions over the past two hundred years have demanded innovation and adjustment of legal doctrine, thus giving the United States Constitution a character which the framers of the document could not have predicted. Historically, one must not only understand developments since 1787 but also…

  15. “Conjugate Channeling” Effect in Dislocation Core Diffusion: Carbon Transport in Dislocated BCC Iron

    PubMed Central

    Ishii, Akio; Li, Ju; Ogata, Shigenobu

    2013-01-01

    Dislocation pipe diffusion seems to be a well-established phenomenon. Here we demonstrate an unexpected effect, that the migration of interstitials such as carbon in iron may be accelerated not in the dislocation line direction , but in a conjugate diffusion direction. This accelerated random walk arises from a simple crystallographic channeling effect. is a function of the Burgers vector b, but not , thus a dislocation loop possesses the same everywhere. Using molecular dynamics and accelerated dynamics simulations, we further show that such dislocation-core-coupled carbon diffusion in iron has temperature-dependent activation enthalpy like a fragile glass. The 71° mixed dislocation is the only case in which we see straightforward pipe diffusion that does not depend on dislocation mobility. PMID:23593255

  16. Fundamentals in generalized elasticity and dislocation theory of quasicrystals: Green tensor, dislocation key-formulas and dislocation loops

    NASA Astrophysics Data System (ADS)

    Lazar, Markus; Agiasofitou, Eleni

    2014-12-01

    The present work provides fundamental quantities in generalized elasticity and dislocation theory of quasicrystals. In a clear and straightforward manner, the three-dimensional Green tensor of generalized elasticity theory and the extended displacement vector for an arbitrary extended force are derived. Next, in the framework of dislocation theory of quasicrystals, the solutions of the field equations for the extended displacement vector and the extended elastic distortion tensor are given; that is, the generalized Burgers equation for arbitrary sources and the generalized Mura-Willis formula, respectively. Moreover, important quantities of the theory of dislocations as the Eshelby stress tensor, Peach-Koehler force, stress function tensor and the interaction energy are derived for general dislocations. The application to dislocation loops gives rise to the generalized Burgers equation, where the displacement vector can be written as a sum of a line integral plus a purely geometric part. Finally, using the Green tensor, all other dislocation key-formulas for loops, known from the theory of anisotropic elasticity, like the Peach-Koehler stress formula, Mura-Willis equation, Volterra equation, stress function tensor and the interaction energy are derived for quasicrystals.

  17. Automated identification and indexing of dislocations in crystal interfaces

    DOE PAGESBeta

    Stukowski, Alexander; Bulatov, Vasily V.; Arsenlis, Athanasios

    2012-10-31

    Here, we present a computational method for identifying partial and interfacial dislocations in atomistic models of crystals with defects. Our automated algorithm is based on a discrete Burgers circuit integral over the elastic displacement field and is not limited to specific lattices or dislocation types. Dislocations in grain boundaries and other interfaces are identified by mapping atomic bonds from the dislocated interface to an ideal template configuration of the coherent interface to reveal incompatible displacements induced by dislocations and to determine their Burgers vectors. Additionally, the algorithm generates a continuous line representation of each dislocation segment in the crystal andmore » also identifies dislocation junctions.« less

  18. Automated identification and indexing of dislocations in crystal interfaces

    SciTech Connect

    Stukowski, Alexander; Bulatov, Vasily V.; Arsenlis, Athanasios

    2012-10-31

    Here, we present a computational method for identifying partial and interfacial dislocations in atomistic models of crystals with defects. Our automated algorithm is based on a discrete Burgers circuit integral over the elastic displacement field and is not limited to specific lattices or dislocation types. Dislocations in grain boundaries and other interfaces are identified by mapping atomic bonds from the dislocated interface to an ideal template configuration of the coherent interface to reveal incompatible displacements induced by dislocations and to determine their Burgers vectors. Additionally, the algorithm generates a continuous line representation of each dislocation segment in the crystal and also identifies dislocation junctions.

  19. Developmental Dislocation (Dysplasia) of the Hip (DDH)

    MedlinePlus

    ... developmental dysplasia (dislocation) of the hip (DDH), the hip joint has not formed normally. The ball is loose ... be taken to provide detailed pictures of the hip joint. Treatment When DDH is detected at birth, it ...

  20. Analysis of dislocation pile-ups using a dislocation-based continuum theory

    NASA Astrophysics Data System (ADS)

    Schulz, K.; Dickel, D.; Schmitt, S.; Sandfeld, S.; Weygand, D.; Gumbsch, P.

    2014-03-01

    The increasing demand for materials with well-defined microstructure, accompanied by the advancing miniaturization of devices, is the reason for the growing interest in physically motivated, dislocation-based continuum theories of plasticity. In recent years, various advanced continuum theories have been introduced, which are able to described the motion of straight and curved dislocation lines. The focus of this paper is the question of how to include fundamental properties of discrete dislocations during their motion and interaction in a continuum dislocation dynamics (CDD) theory. In our CDD model, we obtain elastic interaction stresses for the bundles of dislocations by a mean-field stress, which represents long-range stress components, and a short range corrective stress component, which represents the gradients of the local dislocation density. The attracting and repelling behavior of bundles of straight dislocations of the same and opposite sign are analyzed. Furthermore, considering different dislocation pile-up systems, we show that the CDD formulation can solve various fundamental problems of micro-plasticity. To obtain a mesh size independent formulation (which is a prerequisite for further application of the theory to more complex situations), we propose a discretization dependent scaling of the short range interaction stress. CDD results are compared to analytical solutions and benchmark data obtained from discrete dislocation simulations.

  1. Dislocation dynamics simulations of interactions between gliding dislocations and radiation induced prismatic loops in zirconium

    NASA Astrophysics Data System (ADS)

    Drouet, Julie; Dupuy, Laurent; Onimus, Fabien; Mompiou, Frédéric; Perusin, Simon; Ambard, Antoine

    2014-06-01

    The mechanical behavior of Pressurized Water Reactor fuel cladding tubes made of zirconium alloys is strongly affected by neutron irradiation due to the high density of radiation induced dislocation loops. In order to investigate the interaction mechanisms between gliding dislocations and loops in zirconium, a new nodal dislocation dynamics code, adapted to Hexagonal Close Packed metals, has been used. Various configurations have been systematically computed considering different glide planes, basal or prismatic, and different characters, edge or screw, for gliding dislocations with -type Burgers vectors. Simulations show various interaction mechanisms such as (i) absorption of a loop on an edge dislocation leading to the formation of a double super-jog, (ii) creation of a helical turn, on a screw dislocation, that acts as a strong pinning point or (iii) sweeping of a loop by a gliding dislocation. It is shown that the clearing of loops is more favorable when the dislocation glides in the basal plane than in the prismatic plane explaining the easy dislocation channeling in the basal plane observed after neutron irradiation by transmission electron microscopy.

  2. Unloading behavior of dislocations emitted from a crack

    NASA Astrophysics Data System (ADS)

    Zhao, Rui-Huan; Li, J. C. M.

    1985-12-01

    Upon unloading, dislocations emitted from a crack can be retracted partially (stationary crack with lattice friction for dislocation motion) or completely (moving crack or zero friction for dislocation motion). The behavior of the plastic zone, the dislocation distribution, and the dislocation-free zone during the retraction process are studied by computer simulation. A propagating crack always moves forward upon unloading until all the dislocations are retracted. Its speed could be much faster during retraction than during the emission of dislocations. The rate of dislocation retraction or crack motion is slow in the beginning but then suddenly the crack jumps forward to retract all the rest of dislocations. This incubation period before the sudden crack surge seems to depend on the size of the dislocation-free zone.

  3. Density-based crystal plasticity: From the discrete to the continuum

    NASA Astrophysics Data System (ADS)

    Valdenaire, Pierre-Louis; Le Bouar, Yann; Appolaire, Benoît; Finel, Alphonse

    2016-06-01

    Because of the enormous range of time and space scales involved in dislocation dynamics, plastic modeling at macroscale requires a continuous formulation. In this paper, we present a rigorous formulation of the transition between the discrete, where plastic flow is resolved at the scale of individual dislocations, and the continuum, where dislocations are represented by densities. First, we focus on the underlying coarse-graining procedure. Our work reveals that both a spatiotemporal convolution and an ensemble average are required and that the emerging correlation-induced stresses are scale dependent. Each of these stresses can be expanded into the sum of two components. The first one depends on the local values of the dislocation densities and always opposes the sum of the applied stress and long-range mean field stress generated by the geometrically necessary dislocation (GND) density; this stress acts as a friction stress. The second component depends on the local gradients of the dislocation densities and is inherently associated to a translation of the elastic domain; therefore, it acts as a back stress. Finally, we show that that these friction and back stresses contain symmetry-breaking components that were missing in previous continuous formulations and that make, at mesoscale, the local stress experienced by dislocations depend on the sign of their Burgers vectors.

  4. Atomistic modeling of dislocation-interface interactions

    SciTech Connect

    Wang, Jian; Valone, Steven M; Beyerlein, Irene J; Misra, Amit; Germann, T. C.

    2011-01-31

    Using atomic scale models and interface defect theory, we first classify interface structures into a few types with respect to geometrical factors, then study the interfacial shear response and further simulate the dislocation-interface interactions using molecular dynamics. The results show that the atomic scale structural characteristics of both heterophases and homophases interfaces play a crucial role in (i) their mechanical responses and (ii) the ability of incoming lattice dislocations to transmit across them.

  5. Dislocation shielding of a cohesive crack

    NASA Astrophysics Data System (ADS)

    Bhandakkar, Tanmay K.; Chng, Audrey C.; Curtin, W. A.; Gao, Huajian

    2010-04-01

    Dislocation interaction with a cohesive crack is of increasing importance to computational modelling of crack nucleation/growth and related toughening mechanisms in confined structures and under cyclic fatigue conditions. Here, dislocation shielding of a Dugdale cohesive crack described by a rectangular traction-separation law is studied. The shielding is completely characterized by three non-dimensional parameters representing the effective fracture toughness, the cohesive strength, and the distance between the dislocations and the crack tip. A closed form analytical solution shows that, while the classical singular crack model predicts that a dislocation can shield or anti-shield a crack depending on the sign of its Burgers vector, at low cohesive strengths a dislocation always shields the cohesive crack irrespective of the Burgers vector. A numerical study shows the transition in shielding from the classical solution of Lin and Thomson (1986) in the high strength limit to the solution in the low strength limit. An asymptotic analysis yields an approximate analytical model for the shielding over the full range of cohesive strengths. A discrete dislocation (DD) simulation of a large (>10 3) number of edge dislocations interacting with a cohesive crack described by a trapezoidal traction-separation law confirms the transition in shielding, showing that the cohesive crack does behave like a singular crack at very high cohesive strengths (˜7 GPa), but that significant deviations in shielding between singular and cohesive crack predictions arise at cohesive strengths around 1GPa, consistent with the analytic models. Both analytical and numerical studies indicate that an appropriate crack tip model is essential for accurately quantifying dislocation shielding for cohesive strengths in the GPa range.

  6. Medial dislocation of the medial meniscus.

    PubMed

    Chan, S K L; Robb, C A; Singh, T; Chugh, S

    2010-01-01

    We present the first reported case of symptomatic medial dislocation of the medial meniscus in a patient who had no previous history of trauma and who had an otherwise normal knee. The treatment of instability of the medial meniscus is controversial and studies have indicated that certain individuals without a firm meniscal bony insertion may be predisposed to meniscal dislocation. In our patient, the meniscal instability interfered with daily activities. Operative stabilisation by reconstruction of the meniscotibial ligaments cured the symptoms.

  7. Congenital Dislocation of the Hip

    PubMed Central

    Specht, Elmer E.

    1976-01-01

    Congenital dislocation or subluxation of the hip (congenital acetabular dysplasia) is a complete or partial displacement of the femoral head out of the acetabulum. The physical signs essential for diagnosis are age related. In newborns the tests for instability are the most sensitive. After the neonatal period, and until the age of walking, tightness of the adductor muscles is the most reliable sign. Early diagnosis is vital for successful treatment of this partially genetically determined condition. Various therapeutic measures, ranging from abduction splinting to open reduction and osteotomy, may be required. Following diagnosis in the first month of life, the average treatment time in one recent series was only 2.3 months from initiation of therapy to attainment of a normal hip. When the diagnosis was not made until 3 to 6 months of age, ten months of treatment was required to achieve the same outcome. When the diagnosis is not made, or the treatment is not begun until after the age of 6, a normal hip will probably not develop in any patient. ImagesFigure 1.Figure 2.Figure 3.Figure 4.Figure 5.Figure 6.Figure 7.Figure 8.Figure 9. PMID:1251603

  8. Dislocation electrical conductivity of synthetic diamond films

    SciTech Connect

    Samsonenko, S. N. Samsonenko, N. D.

    2009-05-15

    A relationship between the electric resistance of single-crystal homoepitaxial and polycrystalline diamond films and their internal structure has been investigated. It is established that the electrical conductivity of undoped homoepitaxial and polycrystalline diamond films is directly related to the dislocation density in them. A relation linking the resistivity {rho} ({approx}10{sup 13}-10{sup 15} {omega} cm) with the dislocation density {gamma} ({approx}10{sup 14}-4 x 10{sup 16} m{sup -2}) is obtained. The character of this correlation is similar for both groups of homoepitaxial and polycrystalline diamond films. Thin ({approx}1-8 {mu}m) homoepitaxial and polycrystalline diamond films with small-angle dislocation boundaries between mosaic blocks exhibit dislocation conductivity. The activation energy of dislocation acceptor centers was calculated from the temperature dependence of the conductivity and was found to be {approx}0.3 eV. The conduction of thick diamond films (h > 10 {mu}m) with the resistivity {rho} {approx} 10{sup 8} {omega} cm is determined by the conduction of intercrystallite boundaries, which have a nondiamond hydrogenated structure. The electronic properties of the diamond films are compared with those of natural semiconductor diamonds of types IIb and Ic, in which dislocation acceptor centers have activation energies in the range 0.2-0.35 eV and are responsible for hole conduction.

  9. Chronic Knee Dislocation After Total Knee Arthroplasty.

    PubMed

    Ross, John P; Brown, Nicholas M; Levine, Brett R

    2015-12-01

    Knee dislocation after total knee arthroplasty (TKA), although rare, is a dangerous injury that can lead to neurovascular compromise and permanent disability. Chronic dislocation after TKA is even less common and is defined as dislocation that is present for 4 weeks or more. There are few reports of its management. Chronic dislocation may be complicated further by concomitant extensor mechanism disruption, ligamentous instability, and/or capsular contracture. This article describes 3 cases of chronically dislocated TKAs and the challenges encountered in treating this difficult problem. A higher level of constraint was required to maintain knee stability, and an extensor mechanism allograft was needed in 2 of the 3 reported patients. The preferred technique at the authors' institution is a complete allograft composite, tensioned in full extension. In the setting of a chronically dislocated TKA, the authors now recommend revision surgery with an enhanced measure of constraint (constrained condylar device or hinged knee prosthesis), reconstruction of the extensor mechanism when necessary, and restoration of the joint while compensating for concomitant bony defects. Even when surgeons follow these principles, it is important to inform the patient that long-term outcomes will likely be inferior to those of revision surgery for other causes.

  10. Investigation of the Dynamics of a Screw Dislocation in Copper

    NASA Astrophysics Data System (ADS)

    Kolupaeva, S. N.; Petelina, Yu. P.; Polosukhin, K. A.; Petelin, A. E.

    2015-08-01

    A modification of the mathematical model of forming the crystallographic shear band is proposed in which the strength of elastic interaction between all dislocations of the forming dislocation pileups is taken into account in addition to the Peach-Keller force; lattice, impurity, and dislocation friction; linear tension; viscous braking; and intensity of generation of point defects behind kinks. The model is used to investigate the influence of the dislocation density on the time characteristics of the formation of dislocation loops in copper.

  11. Thomas Jefferson and the Constitution.

    ERIC Educational Resources Information Center

    Peterson, Merrill D.

    1987-01-01

    Examines Thomas Jefferson's role in the making and interpretation of the United States Constitution. Discusses the dominant features of Jefferson's constitutional theory; the character of Jefferson's presidency; and Jefferson's ongoing concern about constitutional preservation and change. Lists important dates in the history of the constitution.…

  12. The Constitution in Other Lands.

    ERIC Educational Resources Information Center

    Bill of Rights in Action, 1987

    1987-01-01

    Designed for classroom teaching, this document contains articles on the new constitutions of Japan, South Korea, and the Philippine Islands which were modeled in part on the U.S. Constitution. These countries' experiences with constitutional government are examined, and whether or not the U.S. Constitution can be a suitable model for other…

  13. Quantum dynamics of a single dislocation

    NASA Astrophysics Data System (ADS)

    de Gennes, Pierre-Gilles

    We discuss the zero temperature motions of an edge dislocation in a quantum solid (e.g., He4). If the dislocation has one kink (equal in length to its Burgers vector b) the kink has a creation energy U and can move along the line with a certain transfer integral t. When t and U are of comparable magnitude, two opposite kinks can form an extended bound state, with a size l. The overall shape of the dislocation in the ground state is then associated with a random walk of persistence length l (along the line) and hop sizes b. We also discuss the motions of kinks under an applied shear stress σ: the glide velocity is proportional to exp(-σ*/σ), where σ* is a characteristic stress, controlled by tunneling processes. Mouvements quantiques d'une dislocation. On analyse le mouvement à température nulle d'une dislocation coin dans un solide quantique (He4). La dislocation peut avoir un cran (d'énergie U) dans son plan de glissement. Le cran peut avancer ou reculer le long de la dislocation par effet tunnel, avec une certaine intégrale de transfert t. Deux crans de signe opposé peuvent former un état lié. En présence d'une contrainte extérieure σ, la ligne doit avancer avec une vitesse ~exp(-σ*/σ) où σ* est une contrainte seuil, contrôlée par l'effet tunnel.

  14. Constitution, 30 September 1987.

    PubMed

    1987-01-01

    This document reprints provisions of Suriname's 1987 Constitution relating to freedom of movement, equality of the sexes, the right to life, the right to physical integrity, equal opportunity in employment, the family, children, maternity benefits, the right to health care, parental responsibilities, free and compulsory education, illiteracy, and housing. All citizens enjoy freedom of movement within the bounds of the law. All people within the territory may claim protection of their person and property, and discrimination is forbidden on the basis of birth, sex, race, language, religion, education, political beliefs, economic position, or other status. Torture or inhuman treatment and punishment is banned, and the right to life is protected by the law. The state guarantees the right to work, and all employees have the right to equal remuneration for equal work, safe working conditions, and sufficient rest and recreation. The family is protected, and husbands and wives are equal before the law. Children have the right to protection, and working women are entitled to paid maternity leave. The state promotes the right to good health by systematic improvements in living and working conditions and dissemination of health education. The right to education is protected by the provision of free general primary education and efforts of the state to enable all citizens to achieve the highest educational levels possible. The Constitution also calls for the institution of a plan to allow the state to create public housing.

  15. The key role of dislocation dissociation in the plastic behaviour of single crystal nickel-based superalloy with low stacking fault energy: Three-dimensional discrete dislocation dynamics modelling

    NASA Astrophysics Data System (ADS)

    Huang, Minsheng; Li, Zhenhuan

    2013-12-01

    To model the deformation of single crystal nickel based superalloys (SCNBS) with low stacking fault energy (SFE), three-dimensional discrete dislocation dynamics (3D-DDD) is extended by incorporating dislocation dissociation mechanism. The present 3D-DDD simulations show that, consistent with the existing TEM observation, the leading partial can enter the matrix channel efficiently while the trailing partial can hardly glide into it when the dislocation dissociation is taken into account. To determine whether the dislocation dissociation can occur or not, a critical percolation stress (CPS) based criterion is suggested. According to this CPS criterion, for SCNBS there exists a critical matrix channel width. When the channel width is lower than this critical value, the dislocation tends to dissociate into an extended configuration and vice versa. To clarify the influence of dislocation dissociation on CPS, the classical Orowan formula is improved by incorporating the SFE. Moreover, the present 3D-DDD simulations also show that the yielding stress of SCNBSs with low SFE may be overestimated up to 30% if the dislocation dissociation is ignored. With dislocation dissociation being considered, the size effect due to the width of γ matrix channel and the length of γ‧ precipitates on the stress-strain responses of SCNBS can be enhanced remarkably. In addition, due to the strong constraint effect by the two-phase microstructure in SCNBS, the configuration of formed junctions is quite different from that in single phase crystals such as Cu. The present results not only provide clear understanding of the two-phase microstructure levelled microplastic mechanisms in SCNBSs with low SFE, but also help to develop new continuum-levelled constitutive laws for SCNBSs.

  16. Ethics and constitutional government.

    PubMed

    Albright, James A

    2007-01-01

    The term ethics refers to a set of principles that govern acceptable, proper conduct. Attacks on the Constitution of the United States pose the most serious breach of ethics today. Our country was founded as a republic, not as a democracy. Our Founding Fathers' main concern was to protect citizens from the power of the federal government, so constitutionally, the central government has little or no authority over individual citizens except on federal property. One of the major problems today is the fact that we now have professional politicians. This is due in large part to the lure of financial gain from countless special interest groups. This would change under constitutional law because the federal budget would decrease drastically. Article 1 states that all legislative power is vested in Congress. Congress has only 18 enumerated powers, and almost half of these pertain to defense of the country. Many of our current problems are due to regulatory agencies that have become independent fiefdoms with unconstitutional legislative, as well as executive and judicial, powers. The regulatory agency most relevant to medicine, both clinical care and research, is the FDA. It is now obvious that its basic structure needs to be changed or abolished because its actions are identical to those inherent in authoritarian systems. Constructive change could come from Congress, but it would be most desirable if the Supreme Court would take the lead and reestablish the authority of the Constitution as the Supreme Law of the Land. The FDA's function could be limited to the determination of safety, but preferably its mission would be altered to that of product certification. Defenders of the current system claim that such a drastic change would be too dangerous and their prime example is thalidomide. But it is now known that the market has already solved that problem prior to the government-imposed sanctions. Realistically, market forces and their ramifications, including our legal

  17. Ethics and constitutional government.

    PubMed

    Albright, James A

    2007-01-01

    The term ethics refers to a set of principles that govern acceptable, proper conduct. Attacks on the Constitution of the United States pose the most serious breach of ethics today. Our country was founded as a republic, not as a democracy. Our Founding Fathers' main concern was to protect citizens from the power of the federal government, so constitutionally, the central government has little or no authority over individual citizens except on federal property. One of the major problems today is the fact that we now have professional politicians. This is due in large part to the lure of financial gain from countless special interest groups. This would change under constitutional law because the federal budget would decrease drastically. Article 1 states that all legislative power is vested in Congress. Congress has only 18 enumerated powers, and almost half of these pertain to defense of the country. Many of our current problems are due to regulatory agencies that have become independent fiefdoms with unconstitutional legislative, as well as executive and judicial, powers. The regulatory agency most relevant to medicine, both clinical care and research, is the FDA. It is now obvious that its basic structure needs to be changed or abolished because its actions are identical to those inherent in authoritarian systems. Constructive change could come from Congress, but it would be most desirable if the Supreme Court would take the lead and reestablish the authority of the Constitution as the Supreme Law of the Land. The FDA's function could be limited to the determination of safety, but preferably its mission would be altered to that of product certification. Defenders of the current system claim that such a drastic change would be too dangerous and their prime example is thalidomide. But it is now known that the market has already solved that problem prior to the government-imposed sanctions. Realistically, market forces and their ramifications, including our legal

  18. A review of nonlinear constitutive models for metals

    NASA Technical Reports Server (NTRS)

    Allen, David H.; Harris, Charles E.

    1990-01-01

    Over the past two decades a number of thermomechanical constitutive theories have been proposed for viscoplastic metals. These models are in most cases similar in that they utilize a set of internal state variables which provide locally averaged representations of microphysical phenomena such as dislocation rearrangement and grain boundary sliding. The state of development of several of these models is now at the point where accurate theoretical solutions can be obtained for a wide variety of structural problems at elevated temperatures. The fundamentals of viscoplasticity are briefly reviewed and a general framework is outlined. Several of the more prominent models are reviewed, and predictions from models are compared to experimental results.

  19. Visualizing dislocation nucleation by indenting colloidal crystals.

    PubMed

    Schall, Peter; Cohen, Itai; Weitz, David A; Spaepen, Frans

    2006-03-16

    The formation of dislocations is central to our understanding of yield, work hardening, fracture, and fatigue of crystalline materials. While dislocations have been studied extensively in conventional materials, recent results have shown that colloidal crystals offer a potential model system for visualizing their structure and dynamics directly in real space. Although thermal fluctuations are thought to play a critical role in the nucleation of these defects, it is difficult to observe them directly. Nano-indentation, during which a small tip deforms a crystalline film, is a common tool for introducing dislocations into a small volume that is initially defect-free. Here, we show that an analogue of nano-indentation performed on a colloidal crystal provides direct images of defect formation in real time and on the single particle level, allowing us to probe the effects of thermal fluctuations. We implement a new method to determine the strain tensor of a distorted crystal lattice and we measure the critical dislocation loop size and the rate of dislocation nucleation directly. Using continuum models, we elucidate the relation between thermal fluctuations and the applied strain that governs defect nucleation. Moreover, we estimate that although bond energies between particles are about fifty times larger in atomic systems, the difference in attempt frequencies makes the effects of thermal fluctuations remarkably similar, so that our results are also relevant for atomic crystals.

  20. Vascular and orthopedic complications of knee dislocation.

    PubMed

    Jones, R E; Smith, E C; Bone, G E

    1979-10-01

    Experience with complete dislocation of the knee in 22 consecutive patients during a six year period was analyzed. Major vascular complications occurred in nine of 13 extremities with anterior dislocation, one of seven extremities with posterior dislocation and none of two extremities with lateral dislocation. Liberal use of trans-femoral ateriography for diagnosis disclosed significant arterial injuries in four of 15 limbs, despite postreduction pedal pulses which were apparently normal. Limb salvage was accomplished in 20 of 21 survivors and in eight of nine with associated vascular complications. All patients demonstrated severe instability of the ligamentous structures of the knee consistent with the type of dislocation. Posterior instability was severe in all patients, an indication of disruption of the posterior cruciate ligament in every instance. Adequate follow-up information was available on 12 knees that had primary ligamentous repair, ten of which were stable to stress testing. Postoperative immobilization was accomplished by external skeletal fixation, skeletal traction or long leg posterior plaster splint. PMID:483133

  1. Use of cervical collar in temporomandibular dislocation.

    PubMed

    Jaisani, Mehul R; Pradhan, Leeza; Sagtani, Alok

    2015-06-01

    Dislocation of the temporomandibular joint represents 3 % of all reported dislocated joints. In the last 3 decades many cases of TMJ dislocation have been reported with a wide variety of treatment options ranging from non-surgical conservative approaches to open joint procedures. The question remains whether one method is superior to the others. Conservative treatments are still the option in this part of the continent due to financial constraints and as well as due to availability of skilled manpower. A variety of conservative techniques have been described for reducing dislocations, all of which require 10-14 days of immobilization of the jaw post reduction so as to prevent further episodes of dislocation. Immobilization of the jaw can be done in the form of barrel bandage, barton bandage, head chin cap or maxillomandibular fixation using arch bars. We suggest the use of a cervical collar as a form of post reduction immobilization technique to overcome the inherent disadvantages of conventional forms of immobilization techniques.

  2. Isolated dorsal dislocation of the tarsal naviculum

    PubMed Central

    Hamdi, Kaziz; Hazem, Ben Ghozlen; Yadh, Zitoun; Faouzi, Abid

    2015-01-01

    Isolated dislocation of the tarsal naviculum is an unusual injury, scarcely reported in the literature. The naviculum is surrounded by the rigid bony and ligamentous support hence fracture dislocation is more common than isolated dislocation. The mechanism and treatment options remain unclear. In this case report, we describe a 31 year old man who sustained an isolated dorsal dislocation of the left tarsal naviculum, without fracture, when he was involved in a motor vehicle collision. The reported mechanism of the dislocation is a hyper plantar flexion force applied to the midfoot, resulting in a transient disruption of the ligamentous support of the naviculum bone, with dorsal displacement of the bone. The patient was treated with open reduction and Krischner-wire fixation of the navicular after the failure of closed reduction. The wires were removed after 6 weeks postoperatively. Physiotherapy for stiffness and midfoot pain was recommended for 2 months. At 6 months postoperatively, limping, midfoot pain and weakness were reported, no X-ray abnormalities were found. The patient returned to his obvious activities with a normal range of motion. PMID:26806978

  3. Proximal interphalangeal joint dislocations without fractures.

    PubMed

    Vicar, A J

    1988-02-01

    Injuries to the proximal interphalangeal joint are extremely common. An understanding of the complex anatomy of this joint is essential for diagnosis and treatment of proximal interphalangeal joint sprains and dislocations. Lateral injuries are among the commonest injuries in the hand. These are often stable after reduction, requiring only closed treatment. Occasionally, however, the collateral ligament can be trapped in the joint and require open reduction. Dorsal dislocations represent the most common dislocation in the hand. These, too, are usually stable after reduction and can be treated by closed methods. On occasion, however, these dislocations will be open or irreducible by closed means, requiring surgical intervention and repair of damaged structures. Complex rotary dislocations are exactly that: complex. An exact understanding of the damaged structures and causes of irreducibility frequently makes this an injury often requiring open reduction and selective repair of damaged soft tissue structures. Fortunately, prompt diagnosis, reduction, and institution of appropriate treatment can usually afford the patient good function after these injuries. It must be noted that stiffness is more common than instability, and active range-of-motion exercises instituted at the proper time are essential. These joints will often remain permanently thicker after injury in spite of optimal care, and tenderness and soreness with use may persist for 6 to 12 months.

  4. Dislocation-Radiation Obstacle Interactions: Developing Improved Mechanical Property Constitutive Models

    SciTech Connect

    B.D. WIrth; Ian M. Robertson

    2007-11-29

    Radiation damage to structural and cladding materials, including austenitic stainless steels, ferritic steels, and zirconium alloys, in nuclear reactor environments results in significant mechanical property degradation, including yield strength increases, severe ductility losses and flow localization, which impacts reliability and performance. Generation IV and advanced fuel cycle concepts under consideration will require the development of advanced structural materials, which will operate in increasingly hostile environments. The development of predictive models is required to assess the performance and response of materials in extreme Gen IV reactor operating conditions (temperature, stress, and pressure), to decrease the time to rapidly assess the properties of new materials and insert them into technological applications (Gen IV and Advanced Fuel Cycle Operations).

  5. On the use of internal state variables in thermoviscoplastic constitutive equations

    NASA Technical Reports Server (NTRS)

    Allen, D. H.; Beek, J. M.

    1985-01-01

    The general theory of internal state variables are reviewed to apply it to inelastic metals in use in high temperature environments. In this process, certain constraints and clarifications will be made regarding internal state variables. It is shown that the Helmholtz free energy can be utilized to construct constitutive equations which are appropriate for metallic superalloys. Internal state variables are shown to represent locally averaged measures of dislocation arrangement, dislocation density, and intergranular fracture. The internal state variable model is demonstrated to be a suitable framework for comparison of several currently proposed models for metals and can therefore be used to exhibit history dependence, nonlinearity, and rate as well as temperature sensitivity.

  6. Screw dislocation-driven epitaxial solution growth of ZnO nanowires seeded by dislocations in GaN substrates.

    PubMed

    Morin, Stephen A; Jin, Song

    2010-09-01

    In the current examples of dislocation-driven nanowire growth, the screw dislocations that propagate one-dimensional growth originate from spontaneously formed highly defective "seed" crystals. Here we intentionally utilize screw dislocations from defect-rich gallium nitride (GaN) thin films to propagate dislocation-driven growth, demonstrating epitaxial growth of zinc oxide (ZnO) nanowires directly from aqueous solution. Atomic force microscopy confirms screw dislocations are present on the native GaN surface and ZnO nanowires grow directly from dislocation etch pits of heavily etched GaN surfaces. Furthermore, transmission electron microscopy confirms the existence of axial dislocations. Eshelby twist in the resulting ZnO nanowires was confirmed using bright-/dark-field imaging and twist contour analysis. These results further confirm the connection between dislocation source and nanowire growth. This may eventually lead to defect engineering strategies for rationally designed catalyst-free dislocation-driven nanowire growth for specific applications.

  7. High dislocation density of tin induced by electric current

    SciTech Connect

    Liao, Yi-Han; Liang, Chien-Lung; Lin, Kwang-Lung; Wu, Albert T.

    2015-12-15

    A dislocation density of as high as 10{sup 17} /m{sup 2} in a tin strip, as revealed by high resolution transmission electron microscope, was induced by current stressing at 6.5 x 10{sup 3} A/ cm{sup 2}. The dislocations exist in terms of dislocation line, dislocation loop, and dislocation aggregates. Electron Backscattered Diffraction images reflect that the high dislocation density induced the formation of low deflection angle subgrains, high deflection angle Widmanstätten grains, and recrystallization. The recrystallization gave rise to grain refining.

  8. Constitution, 5 May 1989.

    PubMed

    1989-01-01

    This document contains provisions of Cambodia's Constitution of May 5, 1989. Article 7 gives men and women equal rights in marriage and the family, calls for monogamous marriages, and affords social protection to mothers and children. Article 8 guides parent-child relationships. The 14th article defines state property, and the 15th gives citizens full rights to own, use, and inherit land. The use of agricultural and forested land can only be changed with permission. Article 22 assigns educational responsibilities to the state, including free elementary education and a gradual expansion of higher education. Adult literacy classes are also promoted. Article 26 guarantees free medical consultations, and article 27 gives women a 90-day paid maternity leave. Breast-feeding women are also given special privileges. Article 33 guarantees the right to pay equity and to social security benefits. Article 36 grants the freedom to travel, the inviolability of homes, and privacy in correspondence of all types.

  9. Constitution, 5 October 1988.

    PubMed

    1989-01-01

    This document contains major provisions of the constitution adopted by Brazil on 5 October 1988. This constitution seeks to promote the welfare of all citizens without discrimination. The equality of all citizens is guaranteed, and the equal rights of women are specifically mentioned. Property rights are also guaranteed and defined. Female inmates are granted the right to remain with their children while breast feeding. Workers are guaranteed a minimum wage, a family allowance for dependents, maternity/paternity leave, specific incentives to protect the labor market for women, retirement benefits, free day care for preschool-age children, pay equity, and equal rights between tenured and sporadically employed workers. Agrarian reform provisions are given, including the authority to expropriate land. Social and economic policies to promote health are called for, and public health services are to be decentralized, to be integrated, and to foster community participation. Pension plan and social assistance provisions are outlined as are duties of the state in regard to education. The amount of money to be dedicated to education is set out, and a national educational plan is called for to achieve such goals as the eradication of illiteracy, the universalization of school attendance, the improvement of instruction, and the provision of vocational training. Specific measures are set out to protect and preserve the environment. Family policy deals with issues of marriage, the definition of a family, divorce, the right to family planning services, and the deterrence of domestic violence. Social protection provisions cover mothers and children, handicapped persons, and protection of minors. Finally, the customs and rights of Indians are protected, with special provisions given to protect land tenure and to protect the rights of Indians in water resource development and prospecting and mining activities. PMID:12344286

  10. Constitution, 5 October 1988.

    PubMed

    1989-01-01

    This document contains major provisions of the constitution adopted by Brazil on 5 October 1988. This constitution seeks to promote the welfare of all citizens without discrimination. The equality of all citizens is guaranteed, and the equal rights of women are specifically mentioned. Property rights are also guaranteed and defined. Female inmates are granted the right to remain with their children while breast feeding. Workers are guaranteed a minimum wage, a family allowance for dependents, maternity/paternity leave, specific incentives to protect the labor market for women, retirement benefits, free day care for preschool-age children, pay equity, and equal rights between tenured and sporadically employed workers. Agrarian reform provisions are given, including the authority to expropriate land. Social and economic policies to promote health are called for, and public health services are to be decentralized, to be integrated, and to foster community participation. Pension plan and social assistance provisions are outlined as are duties of the state in regard to education. The amount of money to be dedicated to education is set out, and a national educational plan is called for to achieve such goals as the eradication of illiteracy, the universalization of school attendance, the improvement of instruction, and the provision of vocational training. Specific measures are set out to protect and preserve the environment. Family policy deals with issues of marriage, the definition of a family, divorce, the right to family planning services, and the deterrence of domestic violence. Social protection provisions cover mothers and children, handicapped persons, and protection of minors. Finally, the customs and rights of Indians are protected, with special provisions given to protect land tenure and to protect the rights of Indians in water resource development and prospecting and mining activities.

  11. Electron paramagnetic resonance at dislocations in germanium

    SciTech Connect

    Pakulis, E.J.

    1982-06-01

    The first observation of the paramagnetic resonance of electrons at dislocations in germanium single crystals is reported. Under subband gap optical excitation, two sets of lines are detected: four lines about the <111> axes with g/sub perpendicular to/ = 0.34 and g/sub parallel/ = 1.94, and 24 lines with g/sub perpendicular to/ = 0.73 and g/sub parallel/ = 1.89 about <111> axes with the six-fold 1.2/sup 0/ distortion. This represents the first measurement of the disortion angle of a dislocation dangling bond. The possibility that the distortion results from a Peierls transition along the dislocation line is discussed.

  12. Dislocation filtering in GaN nanostructures.

    PubMed

    Colby, Robert; Liang, Zhiwen; Wildeson, Isaac H; Ewoldt, David A; Sands, Timothy D; García, R Edwin; Stach, Eric A

    2010-05-12

    Dislocation filtering in GaN by selective area growth through a nanoporous template is examined both by transmission electron microscopy and numerical modeling. These nanorods grow epitaxially from the (0001)-oriented GaN underlayer through the approximately 100 nm thick template and naturally terminate with hexagonal pyramid-shaped caps. It is demonstrated that for a certain window of geometric parameters a threading dislocation growing within a GaN nanorod is likely to be excluded by the strong image forces of the nearby free surfaces. Approximately 3000 nanorods were examined in cross-section, including growth through 50 and 80 nm diameter pores. The very few threading dislocations not filtered by the template turn toward a free surface within the nanorod, exiting less than 50 nm past the base of the template. The potential active region for light-emitting diode devices based on these nanorods would have been entirely free of threading dislocations for all samples examined. A greater than 2 orders of magnitude reduction in threading dislocation density can be surmised from a data set of this size. A finite element-based implementation of the eigenstrain model was employed to corroborate the experimentally observed data and examine a larger range of potential nanorod geometries, providing a simple map of the different regimes of dislocation filtering for this class of GaN nanorods. These results indicate that nanostructured semiconductor materials are effective at eliminating deleterious extended defects, as necessary to enhance the optoelectronic performance and device lifetimes compared to conventional planar heterostructures. PMID:20397703

  13. Mesoscale modeling of dislocations in molecular crystals

    NASA Astrophysics Data System (ADS)

    Lei, Lei; Koslowski, Marisol

    2011-02-01

    Understanding the inelastic deformation of molecular crystals is of fundamental importance to the modeling of the processing of drugs in the pharmaceutical industry as well as to the initiation of detonation in high energy density materials. In this work, we present dislocation dynamics simulations of the deformation of two molecular crystals of interest in the pharmaceutical industry, sucrose and paracetamol. The simulations calculate the yield stress of sucrose and paracetamol in good agreement with experimental observation and predict the anisotropy in the mechanical response observed in these materials. Our results show that dislocation dynamics is an effective tool to study plastic deformation in molecular crystals.

  14. Elbow Dislocation with Complete Triceps Avulsion

    PubMed Central

    Karuppiah, S. V.; Knox, D.

    2014-01-01

    Radio-ulnar Fracture dislocation of the elbow is a high-energy trauma which can be associated with significant ligamentous injury in adults. We report an unusual triad of injury in a patient with avulsion injury of the triceps. This injury can be thought of as a variant of “terrible triad” with dislocation of radio-ulnar joint, radial head fracture, and medial collateral ligament injury with avulsion of the triceps. Elbow has to be stabilized with early repair of the ligaments for a successful outcome. PMID:24876982

  15. Screw dislocation in functionally graded magnetoelectroelastic solids

    NASA Astrophysics Data System (ADS)

    Wang, Yi-Ze; Kuna, Meinhard

    2014-02-01

    A screw dislocation in a functionally graded magnetoelectroelastic material is investigated. The material properties exponentially changing along both x and y directions are considered and the mechanical-electric-magnetic coupling is discussed. Closed-form expressions for the mechanical, electric and magnetic components are derived using the general stress function method. The solutions can be applied as a fundamental result and reduced into the classic and piezoelectric cases. The study puts forth a direct way for screw dislocation analysis in inhomogeneous structures with multifield coupling.

  16. Geometry of dislocated de Broglie waves

    SciTech Connect

    Holland, P.R.

    1987-04-01

    The geometrical structures implicit in the de Broglie waves associated with a relativistic charged scalar quantum mechanical particle in an external field are analyzed by employing the ray concept of the causal interpretation. It is shown how an osculating Finslerian metric tensor, a torsion tensor, and a tetrad field define respectively the strain, the dislocation density, and the Burgers vector in the natural state of the wave, which is a non-Riemannian space of distant parallelism. A quantum torque determined by the quantum potential is introduced and the example of a screw dislocated wave is discussed.

  17. Rotator Cuff Tear Consequent to Glenohumeral Dislocation.

    PubMed

    Gilotra, Mohit N; Christian, Matthew W; Lovering, Richard M

    2016-08-01

    The patient was a 21-year-old collegiate running back who was tackled during a football game and sustained a posterior glenohumeral dislocation. He was referred to an orthopaedist and presented 3 weeks after the injury, and, following examination, further imaging was ordered by the orthopaedist due to rotator cuff weakness. Magnetic resonance imaging showed a complete tear of the supraspinatus and infraspinatus, as well as a posterior Bankart lesion, a subscapularis tear, and a dislocation of the biceps long head tendon into the reverse Hill-Sachs lesion. J Orthop Sports Phys Ther 2016;46(8):708. doi:10.2519/jospt.2016.0413. PMID:27477475

  18. Surgical hip dislocation: techniques for success.

    PubMed

    Ricciardi, Benjamin F; Sink, Ernest L

    2014-01-01

    Surgical hip dislocation (SHD) is a versatile approach used to address both intra-articular and extra-articular pathology around the hip joint in both pediatric and adult patients. It allows anterior dislocation of the femoral head for direct visualization of the hip joint while preserving femoral head vascularity and minimizing trauma to the abductor musculature. Previously described indications for SHD include femoroacetabular impingement, deformity resulting from Legg-Calve-Perthes disease, slipped capital femoral epiphysis, periarticular trauma, benign lesions of the hip joint, and osteochondral lesions. In this review, we will describe current surgical techniques, indications, and clinical outcomes for SHD. PMID:25207733

  19. Subtalar Dislocation in a Basketball Player.

    PubMed

    Crosby, L A

    1989-10-01

    In brief: Easily mistaken for an ankle fracture during the initial examination, medial subtalar dislocation-also known as 'basketball foot'-requires plaster immobilization for no more than 3 weeks. To extend immobilization beyond this time can lead to reduced range of motion in the subtalar joint, making it difficult for the athlete to resume sports activities. Encouraging toe motion while the patient is still in the cast prevents tendon adhesions. In this case report, the author discusses the importance of short-term immobilization and early rehabilitation for a 21-year-old basketball player recovering from medial subtalar dislocation.

  20. Constitutive models in LAME.

    SciTech Connect

    Hammerand, Daniel Carl; Scherzinger, William Mark

    2007-09-01

    The Library of Advanced Materials for Engineering (LAME) provides a common repository for constitutive models that can be used in computational solid mechanics codes. A number of models including both hypoelastic (rate) and hyperelastic (total strain) constitutive forms have been implemented in LAME. The structure and testing of LAME is described in Scherzinger and Hammerand ([3] and [4]). The purpose of the present report is to describe the material models which have already been implemented into LAME. The descriptions are designed to give useful information to both analysts and code developers. Thus far, 33 non-ITAR/non-CRADA protected material models have been incorporated. These include everything from the simple isotropic linear elastic models to a number of elastic-plastic models for metals to models for honeycomb, foams, potting epoxies and rubber. A complete description of each model is outside the scope of the current report. Rather, the aim here is to delineate the properties, state variables, functions, and methods for each model. However, a brief description of some of the constitutive details is provided for a number of the material models. Where appropriate, the SAND reports available for each model have been cited. Many models have state variable aliases for some or all of their state variables. These alias names can be used for outputting desired quantities. The state variable aliases available for results output have been listed in this report. However, not all models use these aliases. For those models, no state variable names are listed. Nevertheless, the number of state variables employed by each model is always given. Currently, there are four possible functions for a material model. This report lists which of these four methods are employed in each material model. As far as analysts are concerned, this information is included only for the awareness purposes. The analyst can take confidence in the fact that model has been properly implemented

  1. How Democratic Is the Constitution?

    ERIC Educational Resources Information Center

    Goldwin, Robert A., Ed.; Schambra, William A., Ed.

    Designed to help prepare the nation for a thoughtful observance of the Constitutional bicentennial, this publication contains seven essays on the topic of democracy and the Constitution. "Democracy and the Constitution" (Gordon S. Wood) looks at the popular and democratic rhetoric used to justify the federalist system in the late 1700's. "Decent,…

  2. Dislocation Content of Micropipes in SiC

    NASA Astrophysics Data System (ADS)

    Heindl, J.; Dorsch, W.; Strunk, H. P.; Müller, St. G.; Eckstein, R.; Hofmann, D.; Winnacker, A.

    1998-01-01

    Silicon carbide, a potentially powerful device material, suffers from microscopic hollow defects called micropipes. Their nature is not satisfactorily clarified yet. Our analysis shows that they are hollow core dislocations according to Frank's model, but contain dislocations of mixed type.

  3. Constitution, 3 February 1987.

    PubMed

    1987-01-01

    This document contains provisions of the 1987 Constitution of the Philippines. The state policies reprinted from Article 2 note that the state recognizes the sanctity of family life and protects the life of the mother and of the unborn from conception. Women and men are afforded equality before the law. The state prioritizes education, science and technology, arts, culture, and sports and promotes comprehensive rural development and agrarian reform. Provisions reprinted from Article 13 (Social Justice and Human Rights) cover agrarian and natural resources reform, urban land reform and housing, health, and protection of women in the workforce. Sections from Article 14 (Education, Science and Technology, Arts, Culture, and Sports) set forth the state's duty to make quality education accessible to all citizens through a compulsory system of free public education, provision of incentives to deserving students, encouragement of informal education, and provision of adult education. Article 15, on the family, recognizes the family as the foundation of the nation and marriage as the foundation of the family. Spouses have the right to found a family, children have the right to appropriate care, the family has the right to a living wage and income, families or family associations have the right to participate in the planning and implementation of policies and programs that affect them, and the family has the duty to care for its elderly.

  4. Amendment to the Constitution.

    PubMed

    1988-01-01

    This Amendment rewrites Clause 4 of Article 10 of the Chinese Constitution to permit the right of land use to be transferred by lease in accordance with the law. In December 1988, the Government also enacted legislation amending the Land Management Law so as to allow for the transfer of Land. See Renmin Ribao (Beijing), 31 December 1988, p. 4; Foreign Broadcast Information Service, FBIS-CHI-89-003, 5 January 1989, pp. 38-39. Provisional Regulations on the Land Use Tax in Urban Areas were promulgated on 27 September 1988. See Xinhua Domestic Service (Beijing), 4 October 1988, Foreign Broadcast Information Service, FBIS-CHI-88-197, 12 October 1988, pp. 26-27, and Xinhua (Beijing), 4 October 1988, FBIS-CHI-88-193, 5 October 1988, pp. 20. Provisional Tax Regulations on Farmland Occupation and Use were proclaimed on 1 April 1987. See Xinhua Domestic Service (Beijing), 19 April 1987; Joint Publications Research Service, China, 22 April 1987, pp. K33-K35. PMID:12289449

  5. On the auxiliary lattices and dislocation reactions at triple junctions.

    PubMed

    Gertsman, V Y

    2002-03-01

    Coincidence site and displacement shift complete lattices of triple junctions are analysed. Dislocation reactions at triple junctions are considered. It is shown that in alpha=1 junctions no trapped residual triple-junction dislocation is geometrically necessary for dislocation transmission between adjoining grain boundaries. However, the situation is different for alpha (unequal) 1 triple junctions, where in some cases the residual dislocation cannot leave the triple junction for a grain boundary without generating a stacking-fault-like defect.

  6. Dislocations in magnetohydrodynamic waves in a stellar atmosphere.

    PubMed

    López Ariste, A; Collados, M; Khomenko, E

    2013-08-23

    We describe the presence of wave front dislocations in magnetohydrodynamic waves in stratified stellar atmospheres. Scalar dislocations such as edges and vortices can appear in Alfvén waves, as well as in general magnetoacoustic waves. We detect those dislocations in observations of magnetohydrodynamic waves in sunspots in the solar chromosphere. Through the measured charge of all the dislocations observed, we can give for the first time estimates of the modal contribution in the waves propagating along magnetic fields in solar sunspots.

  7. Dislocation dynamics in solid solutions of covalent crystals

    NASA Astrophysics Data System (ADS)

    Petukhov, B. V.

    2016-09-01

    The dislocation mechanism of solid solution strengthening of covalent semiconductor crystals has been studied. The change in the regularities of dislocation dynamics in solid solutions from those in the components of the solution is connected with the manifestation of the nonlinear drift of dislocation kinks. The theory developed suggests an explanation of specificities of the dislocation mobility in a Ge1- c Si c solid solution.

  8. Dislocation-mediated relaxation in nanograined columnar palladium films revealed by on-chip time-resolved HRTEM testing

    PubMed Central

    Colla, M. -S.; Amin-Ahmadi, B.; Idrissi, H.; Malet, L.; Godet, S.; Raskin, J. -P.; Schryvers, D.; Pardoen, T.

    2015-01-01

    The high-rate sensitivity of nanostructured metallic materials demonstrated in the recent literature is related to the predominance of thermally activated deformation mechanisms favoured by a large density of internal interfaces. Here we report time-resolved high-resolution electron transmission microscopy creep tests on thin nanograined films using on-chip nanomechanical testing. Tests are performed on palladium, which exhibited unexpectedly large creep rates at room temperature. Despite the small 30-nm grain size, relaxation is found to be mediated by dislocation mechanisms. The dislocations interact with the growth nanotwins present in the grains, leading to a loss of coherency of twin boundaries. The density of stored dislocations first increases with applied deformation, and then decreases with time to drive additional deformation while no grain boundary mechanism is observed. This fast relaxation constitutes a key issue in the development of various micro- and nanotechnologies such as palladium membranes for hydrogen applications. PMID:25557273

  9. The Use of Ultrasound to Measure Dislocation Density

    NASA Astrophysics Data System (ADS)

    Barra, Felipe; Espinoza-González, Rodrigo; Fernández, Henry; Lund, Fernando; Maurel, Agnès; Pagneux, Vincent

    2015-08-01

    Dislocations are at the heart of the plastic behavior of materials yet they are very difficult to probe experimentally. Lack of a practical nonintrusive measuring tool for, say, dislocation density, seriously hampers modeling efforts, as there is little guidance from data in the form of quantitative measurements, as opposed to visualizations. Dislocation density can be measured using transmission electron microscopy (TEM) and x-ray diffraction (XRD). TEM can directly show the strain field around dislocations, which allows for the counting of the number of dislocations in a micrograph. This procedure is very laborious and local, since samples have to be very small and thin, and is difficult to apply when dislocation densities are high. XRD relies on the broadening of diffraction peaks induced by the loss of crystalline order induced by the dislocations. This broadening can be very small, and finding the dislocation density involves unknown parameters that have to be fitted with the data. Both methods, but especially TEM, are intrusive, in the sense that samples must be especially treated, mechanically and chemically. A nonintrusive method to measure dislocation density would be desirable. This paper reviews recent developments in the theoretical treatment of the interaction of an elastic wave with dislocations that have led to formulae that relate dislocation density to quantities that can be measured with samples of cm size. Experimental results that use resonant ultrasound spectroscopy supporting this assertion are reported, and the outlook for the development of a practical, nonintrusive, method to measure dislocation density is discussed.

  10. Dislocation core fields and forces in FCC metals

    SciTech Connect

    Henager, Charles H.; Hoagland, Richard G.

    2004-04-01

    Atomistic models were used to obtain dislocation core fields for edge, screw, and mixed dislocations in Al and Cu using EAM. Core fields are analyzed using a line force dipole representation, with dilatant and dipole terms. The core field contribution to the force between dislocations is shown to be significant for interactions within 50b.

  11. Metatarsal Shaft Fracture with Associated Metatarsophalangeal Joint Dislocation.

    PubMed

    Tung, Taranjit Singh

    2016-01-01

    Metatarsophalangeal joint dislocations of lesser toes are often seen in the setting of severe claw toes. Traumatic irreducible dislocations have been reported in rare cases following both low-energy and high-energy injuries to the forefoot. In this case report, I present a previously unreported association of a metatarsal shaft fracture with metatarsophalangeal joint dislocation of a lesser toe. PMID:27597914

  12. Metatarsal Shaft Fracture with Associated Metatarsophalangeal Joint Dislocation

    PubMed Central

    2016-01-01

    Metatarsophalangeal joint dislocations of lesser toes are often seen in the setting of severe claw toes. Traumatic irreducible dislocations have been reported in rare cases following both low-energy and high-energy injuries to the forefoot. In this case report, I present a previously unreported association of a metatarsal shaft fracture with metatarsophalangeal joint dislocation of a lesser toe. PMID:27597914

  13. The Perceptions of Dislocated Workers under the Workforce Investment Act

    ERIC Educational Resources Information Center

    Wilson, Michael S.; Brown, James M.

    2012-01-01

    This descriptive qualitative case study investigated the perceptions of dislocated workers offered program services through the Workforce Investment Act's (WIA) Dislocated Worker program in Minnesota. This research focused on recently dislocated workers who lost their jobs through no fault of their own and hence were eligible for unemployment…

  14. [Open total dislocation of the talus].

    PubMed

    Grabski, R S; Sosiński, R

    1992-01-01

    A case of 35 years old patient with open, total, fixed dislocation of the talus reduced with heel traction is presented. The Sudeck syndrome subsided after one year. Weight bearing was not allowed for 7 months. An examination after 2.5 years revealed minor osteoarthritis, full range of movement in the foot but limited walking capability. PMID:7555299

  15. An unusual variant of perilunate fracture dislocations

    PubMed Central

    Morin, Matthew L.; Becker, Giles W.

    2016-01-01

    Abstract Trans-scaphoid, trans-radial styloid, trans-triquetral perilunate fracture dislocations are rare. We describe a 19-year-old male who suffered this injury after crashing his bicycle. He underwent open reduction internal fixation and percutaneous pinning. Scaphoid union was achieved at 8 weeks. Near complete range of painless motion was achieved by 4 months. PMID:27583261

  16. An unusual variant of perilunate fracture dislocations.

    PubMed

    Morin, Matthew L; Becker, Giles W

    2016-01-01

    Trans-scaphoid, trans-radial styloid, trans-triquetral perilunate fracture dislocations are rare. We describe a 19-year-old male who suffered this injury after crashing his bicycle. He underwent open reduction internal fixation and percutaneous pinning. Scaphoid union was achieved at 8 weeks. Near complete range of painless motion was achieved by 4 months. PMID:27583261

  17. The origin of dislocations in multilayers

    NASA Astrophysics Data System (ADS)

    Humphreys, C. J.; Maher, D. M.; Eaglesham, D. J.; Kvam, E. P.; Salisbury, I. G.

    1991-06-01

    This paper will consider some fundamental questions concerning the source, nucleation and propagation of dislocations in multilayers, particularly semiconductor epilayers. The concept of a “critical thickness” for the introduction of misfit dislocations in a strained layer will be considered, and X-ray topography and electron microscopy results will be presented which demonstrate that the concept of a critical thickness is not as well defined as previously supposed. Theoretical considerations for the source of misfit dislocations in epilayers grown on dislocation free substrates indicate that surface sources are improbable in low mismatched systems at typical growth temperatures, however the experimental evidence is that the nucleation of misfit dislocations is relatively easy. A new regenerative source with unique properties has been identified in the GeSi/Si system and we have called this source the diamond defect because of its diamond shape (it is a four-sided planar fault on a {111} plane with <110> sides so that two opposing internal angles are 60° and the other two are 120°). This defect operates like a FrankRead source, but it has the unique property that it can repetitively produce dislocations with two different Burgers vectors on the same glide plane, and it can generate orthogonal bundles of misfit dislocations. Whether this source exists more widely in other materials systems requires further assessment. The important role of misfit dislocations in trace impurity gettering is demonstrated. Cet article aborde des questions fondamentales qui concernent la germination et la propagation des dislocations dans les multicouches, et en particulier dans les semiconducteurs épitaxiés. Nous considérons le concept d'épaisseur critique pour l'apparition des dislocations de désadaptation de réseau dans les couches contraintes. Les résultats de topographie X et de microscopie électronique qui sont présentés montrent que le concept d

  18. Temporomandibular joint dislocation: experiences from Zaria, Nigeria

    PubMed Central

    Fomete, Benjamin; Obiadazie, Athanasius Chukwudi; Idehen, Kelvin; Okeke, Uche

    2014-01-01

    Objectives Dislocation of the temporomandibular joint may occur for various reasons. Although different invasive methods have been advocated for its treatment, this study highlights the value of non-invasive treatment options even in chronic cases in a resource-poor environment. Materials and Methods A seven-year retrospective analysis of all patients managed for temporomandibular joint dislocation in our department was undertaken. Patient demographics, risk factors associated with temporomandibular joint dislocation and treatment modalities were retrieved from patient records. Results In all, 26 patients were managed over a seven-year period. Males accounted for 62% of the patients, and yawning was the most frequent etiological factor. Conservative treatment methods were used successfully in 86.4% of the patients managed. Two (66.7%) of the three patients who needed surgical treatment developed complications, while only one (5.3%) patient who was managed conservatively developed complications. Conclusion Temporomandibular joint dislocation appears to be associated with male sex, middle age, yawning, and low socio-economic status, although these observed relationships were not statistically significant. Non-invasive methods remain an effective treatment option in this environment in view of the low socio-economic status of the patients affected. PMID:25045637

  19. Simultaneous dislocation of all five carpometacarpal joints.

    PubMed

    Fayman, M; Hugo, B; de Wet, H

    1988-07-01

    A case of unique combination of simultaneous dislocation of all five carpometacarpal joints is presented. The mechanism of injury in this case seems to be some manner of punching with a closed fist rather than direct violence. Satisfactory results were achieved using simple principles of manipulation under anesthesia, open reduction, and skeletal fixation, followed by intensive physiotherapy.

  20. Assessment of hardening due to dislocation loops in bcc iron: Overview and analysis of atomistic simulations for edge dislocations

    NASA Astrophysics Data System (ADS)

    Bonny, G.; Terentyev, D.; Elena, J.; Zinovev, A.; Minov, B.; Zhurkin, E. E.

    2016-05-01

    Upon irradiation, iron based steels used for nuclear applications contain dislocation loops of both < 100 > and ½ < 111 > type. Both types of loops are known to contribute to the radiation hardening and embrittlement of steels. In the literature many molecular dynamics works studying the interaction of dislocations with dislocation loops are available. Recently, based on such studies, a thermo-mechanical model to threat the dislocation - dislocation loop (DL) interaction within a discrete dislocation dynamics framework was developed for ½ < 111 > loops. In this work, we make a literature review of the dislocation - DL interaction in bcc iron. We also perform molecular dynamics simulations to derive the stress-energy function for < 100 > loops. As a result we deliver the function of the activation energy versus activation stress for < 100 > loops that can be applied in a discrete dislocation dynamics framework.

  1. Constitution, 1989. [Selected provisions].

    PubMed

    1989-01-01

    Chapter XII of the Hungarian Constitution, 1989, details the Fundamental Rights and Duties of Citizens. Everyone lawfully within the territory of Hungary has the right to liberty of movement and the freedom to choose his or her residence, except when restricted by law, including the right to leave his or her residence or county. The Republic of Hungary grants asylum to foreign citizens who were persecuted for racial, religious ethnic, linguistic, or political reasons. Men and women shall equally enjoy all civil, political, economic, social and political rights. Mothers are entitled to special care and protection before and after childbirth; women and juveniles are protected at work by special regulations. Every child has the right to special care an assistance from his or her family, the State, and society, for appropriate physical, spiritual, and moral development. Parents shall decide the kind of education their children receive. Hungary grants equal rights to all person within its territories, without regard to race, color, sex, language, religion, political, or other opinion, national, and social origin, property, birth and other status. Prejudicial discrimination shall be severely punished. Everyone has the right to work, to the free choice of employment and profession and to equal pay for equal work. Citizens have the right to social security, including social services necessary in old age, sickness, disability, widowhood, orphanhood an unemployment through no fault of their own. Hungary guarantees the right to culture for its citizens and realized this right by free and compulsory elementary education, by secondary and higher education which is accessible to all on the basis of capacity, and by the financial support of those receiving an education.

  2. Screw dislocation driven growth of nanomaterials.

    PubMed

    Meng, Fei; Morin, Stephen A; Forticaux, Audrey; Jin, Song

    2013-07-16

    Nanoscience and nanotechnology impact our lives in many ways, from electronic and photonic devices to biosensors. They also hold the promise of tackling the renewable energy challenges facing us. However, one limiting scientific challenge is the effective and efficient bottom-up synthesis of nanomaterials. We can approach this core challenge in nanoscience and nanotechnology from two perspectives: (a) how to controllably grow high-quality nanomaterials with desired dimensions, morphologies, and material compositions and (b) how to produce them in a large quantity at reasonable cost. Because many chemical and physical properties of nanomaterials are size- and shape-dependent, rational syntheses of nanomaterials to achieve desirable dimensionalities and morphologies are essential to exploit their utilities. In this Account, we show that the dislocation-driven growth mechanism, where screw dislocation defects provide self-perpetuating growth steps to enable the anisotropic growth of various nanomaterials at low supersaturation, can be a powerful and versatile synthetic method for a wide variety of nanomaterials. Despite significant progress in the last two decades, nanomaterial synthesis has often remained an "art", and except for a few well-studied model systems, the growth mechanisms of many anisotropic nanostructures remain poorly understood. We strive to go beyond the empirical science ("cook-and-look") and adopt a fundamental and mechanistic perspective to the anisotropic growth of nanomaterials by first understanding the kinetics of the crystal growth process. Since most functional nanomaterials are in single-crystal form, insights from the classical crystal growth theories are crucial. We pay attention to how screw dislocations impact the growth kinetics along different crystallographic directions and how the strain energy of defected crystals influences their equilibrium shapes. Furthermore, such inquiries are supported by detailed structural investigation to

  3. Essential Medicines in National Constitutions

    PubMed Central

    Toebes, Brigit; Hogerzeil, Hans

    2016-01-01

    Abstract A constitutional guarantee of access to essential medicines has been identified as an important indicator of government commitment to the progressive realization of the right to the highest attainable standard of health. The objective of this study was to evaluate provisions on access to essential medicines in national constitutions, to identify comprehensive examples of constitutional text on medicines that can be used as a model for other countries, and to evaluate the evolution of constitutional medicines-related rights since 2008. Relevant articles were selected from an inventory of constitutional texts from WHO member states. References to states’ legal obligations under international human rights law were evaluated. Twenty-two constitutions worldwide now oblige governments to protect and/or to fulfill accessibility of, availability of, and/or quality of medicines. Since 2008, state responsibilities to fulfill access to essential medicines have expanded in five constitutions, been maintained in four constitutions, and have regressed in one constitution. Government commitments to essential medicines are an important foundation of health system equity and are included increasingly in state constitutions. PMID:27781006

  4. Partial Dislocations in Graphene and Their Atomic Level Migration Dynamics.

    PubMed

    Robertson, Alex W; Lee, Gun-Do; He, Kuang; Fan, Ye; Allen, Christopher S; Lee, Sungwoo; Kim, Heeyeon; Yoon, Euijoon; Zheng, Haimei; Kirkland, Angus I; Warner, Jamie H

    2015-09-01

    We demonstrate the formation of partial dislocations in graphene at elevated temperatures of ≥500 °C with single atom resolution aberration corrected transmission electron microscopy. The partial dislocations spatially redistribute strain in the lattice, providing an energetically more favorable configuration to the perfect dislocation. Low-energy migration paths mediated by partial dislocation formation have been observed, providing insights into the atomistic dynamics of graphene during annealing. These results are important for understanding the high temperature plasticity of graphene and partial dislocation behavior in related crystal systems, such as diamond cubic materials.

  5. The dynamics of an edge dislocation in a ferromagnetic crystals

    NASA Astrophysics Data System (ADS)

    Dezhin, V. V.; Nechaev, V. N.

    2016-08-01

    The system of equations describing the bending vibrations of the dislocation in the ferromagnetic crystal is written. Elastic and magnetostrictive properties of the ferromagnetic crystals are considered isotropic. The linearization of the resulting system produced a relatively small contribution to the magnetization from the influence of dislocation. In the linear approximation of the dislocation displacement system of equation describing vibrations of a ferromagnetic crystal with an edge dislocation is obtained. The equation of motion of an edge dislocation in a ferromagnetic crystal is found.

  6. Radiation enhanced basal plane dislocation glide in GaN

    NASA Astrophysics Data System (ADS)

    Yakimov, Eugene B.; Vergeles, Pavel S.; Polyakov, Alexander Y.; Lee, In-Hwan; Pearton, Stephen J.

    2016-05-01

    A movement of basal plane segments of dislocations in GaN films grown by epitaxial lateral overgrowth under low energy electron beam irradiation (LEEBI) was studied by the electron beam induced current (EBIC) method. Only a small fraction of the basal plane dislocation segments were susceptible to irradiation and the movement was limited to relatively short distances. The effect is explained by the radiation enhanced dislocation glide (REDG) in the structure with strong pinning. A dislocation velocity under LEEBI with a beam current lower than 1 nA was estimated as about 10 nm/s. The results assuming the REDG for prismatic plane dislocations were presented.

  7. Observation of Dislocation Dynamics in the Electron Microscope

    SciTech Connect

    Lagow, B W; Robertson, I M; Jouiad, M; Lassila, D H; Lee, T C; Birnbaum, H K

    2001-08-21

    Deformation experiments performed in-situ in the transmission electron microscope have led to an increased understanding of dislocation dynamics. To illustrate the capability of this technique two examples will be presented. In the first example, the processes of work hardening in Mo at room temperature will be presented. These studies have improved our understanding of dislocation mobility, dislocation generation, and dislocation-obstacle interactions. In the second example, the interaction of matrix dislocations with grain boundaries will be described. From such studies predictive criteria for slip transfer through grain boundaries have been developed.

  8. Observation of dislocation dynamics in the electron microscope

    SciTech Connect

    Lagow, B W; Robertson, I M; Jouiad, M; Lassila, D H; Lee, T C; Birnbaum, H K

    2001-01-17

    Deformation experiments performed in-situ in the transmission electron microscope have led to an increased understanding of dislocation dynamics. To illustrate the capability of this technique two examples will be presented. In the first example, the processes of work hardening in Mo at room temperature will be presented. These studies have improved our understanding of dislocation mobility, dislocation generation, and dislocation-obstacle interactions. In the second example, the interaction of matrix dislocations with grain boundaries will be described. From such studies predictive criteria for slip transfer through grain boundaries have been developed.

  9. Empirical potential simulations of interstitial dislocation loops in uranium dioxide

    NASA Astrophysics Data System (ADS)

    Le Prioux, Arno; Fossati, Paul; Maillard, Serge; Jourdan, Thomas; Maugis, Philippe

    2016-10-01

    Stoichiometric circular shaped interstitial dislocation loop energies are calculated in stoichiometric UO2 by empirical potential simulation. The Burgers vector directions studied are <110> and <111>. The main structural properties of each type of interstitial dislocation loop are determined, including stacking fault energy. Defect energies are compared and a maximum size for stable <111> dislocation loops before transition to <110> dislocation loops is given. A model of dislocation loop energy based on elasticity theory is then fitted on the basis of these simulation results.

  10. Observation of dislocations and twins in explosively compacted alumina

    SciTech Connect

    Yust, C.S.; Harris, L.A.

    1980-01-01

    The microstructure at the half-radius position of a polycrystalline alumina rod formed by explosive compaction has been studied by transmission electron microscopy. The as-compacted lattice is composed of differently misoriented bands aligned predominantly in one direction. Such bands may correspond to frequently observed shock lamellae. The band edges are defined by dislocation arrays lying on the basal planes of the hexagonal alumina lattice. The dislocations have Burgers vectors of the type (1120) and (1010), which are the Burgers vectors of slip dislocations in the basal plane. Basal plane twinning is also observed, and the twin boundaries are found to contain interfacial dislocations. While dislocation generation occurs primarily on basal planes, some dislocation activity is also noted on prism, (1100), and on rhombohedral, (1101), planes. Nonbasal twinning, however, has not been detected. The lattice damage is discussed in terms of possible dislocation and twinning mechanisms.

  11. A fast density-based clustering algorithm for real-time Internet of Things stream.

    PubMed

    Amini, Amineh; Saboohi, Hadi; Wah, Teh Ying; Herawan, Tutut

    2014-01-01

    Data streams are continuously generated over time from Internet of Things (IoT) devices. The faster all of this data is analyzed, its hidden trends and patterns discovered, and new strategies created, the faster action can be taken, creating greater value for organizations. Density-based method is a prominent class in clustering data streams. It has the ability to detect arbitrary shape clusters, to handle outlier, and it does not need the number of clusters in advance. Therefore, density-based clustering algorithm is a proper choice for clustering IoT streams. Recently, several density-based algorithms have been proposed for clustering data streams. However, density-based clustering in limited time is still a challenging issue. In this paper, we propose a density-based clustering algorithm for IoT streams. The method has fast processing time to be applicable in real-time application of IoT devices. Experimental results show that the proposed approach obtains high quality results with low computation time on real and synthetic datasets.

  12. A Fast Density-Based Clustering Algorithm for Real-Time Internet of Things Stream

    PubMed Central

    Ying Wah, Teh

    2014-01-01

    Data streams are continuously generated over time from Internet of Things (IoT) devices. The faster all of this data is analyzed, its hidden trends and patterns discovered, and new strategies created, the faster action can be taken, creating greater value for organizations. Density-based method is a prominent class in clustering data streams. It has the ability to detect arbitrary shape clusters, to handle outlier, and it does not need the number of clusters in advance. Therefore, density-based clustering algorithm is a proper choice for clustering IoT streams. Recently, several density-based algorithms have been proposed for clustering data streams. However, density-based clustering in limited time is still a challenging issue. In this paper, we propose a density-based clustering algorithm for IoT streams. The method has fast processing time to be applicable in real-time application of IoT devices. Experimental results show that the proposed approach obtains high quality results with low computation time on real and synthetic datasets. PMID:25110753

  13. Constitutional Issues--Watergate and the Constitution. Teaching with Documents.

    ERIC Educational Resources Information Center

    National Archives and Records Administration, Washington, DC.

    When U.S. President Richard Nixon resigned in 1974 in the wake of the Watergate scandal, it was only the second time that impeachment of a president had been considered. Although the U.S. Constitution has provisions for a person removed from office to be indicted, there are no guidelines in the Constitution about a President who has resigned. The…

  14. Superclimb of Dislocations in Solid 4He

    NASA Astrophysics Data System (ADS)

    Kuklov, Anatoly

    2011-03-01

    Edge dislocation with superfluid core can perform superclimb -- non-conservative motion (climb) assisted by superflow along its core. Such dislocation, with Burgers vector along the C-axis, has been found in ab initio simulations of hcp solid 4. Uniform network of superclimbing dislocations can induce isochoric compressibility which is finite (in contrast to ideal solid where it vanishes) and, practically, independent of the network density. Here N is total number of atoms and is chemical potential. Such giant response has been observed by Ray and Hallock during superfluid flow events through solid He4. Study of superclimbing dislocation within the model of Granato-Lücke string, subjected to Peierls potential and to vanishing bias by , has found that exhibits wide peak in the intermediate range of temperatures (T) - above some determined by Peierls energy and below above which superfluidity of the core essentially vanishes. Non-Luttinger type behavior characterized by K scaling as some power χ of dislocation length is observed in the wide peak region. Biasing superclimbing dislocation by finite μ (due to a contact with liquid through vycor electrodes,) can induce core roughening caused by thermally assisted tunneling of jog-antijog pairs through the barrier produced by combination of Peierls potential and the bias. The threshold for this effect scales as with some power a~ 1.7. The roughening is found to be hysteretic below some temperature Thyst , with TR determining temperature of thermal roughening, He exhibits strong and narrow resonant peak leading to a dip in the core superfluid sound velocity. This mechanism is proposed as an explanation for a strong and narrow dip observed in critical superflow rate. It is found that the dip characteristics are sensitive to the bias by μ and, therefore, this can be used as a test for the proposed mechanism. It is also predicted that the dip depth at given μc ~ 1 /La should be periodic in χ with the period T . This

  15. First principles determination of dislocation properties.

    SciTech Connect

    Hamilton, John C.

    2003-12-01

    This report details the work accomplished on first principles determination of dislocation properties. It contains an introduction and three chapters detailing three major accomplishments. First, we have used first principle calculations to determine the shear strength of an aluminum twin boundary. We find it to be remarkably small ({approx}17 mJ/m{sup 2}). This unexpected result is explained and will likely pertain for many other grain boundaries. Second, we have proven that the conventional explanation for finite grain boundary facets is wrong for a particular aluminum grain boundary. Instead of finite facets being stabilized by grain boundary stress, we find them to originate from kinetic effects. Finally we report on a new application of the Frenkel-Kontorova model to understand reconstructions of (100) type surfaces. In addition to the commonly accepted formation of rectangular dislocation arrays, we find numerous other possible solutions to the model including hexagonal reconstructions and a clock-rotated structure.

  16. Transtriquetral perihamate fracture-dislocation: case report.

    PubMed

    Moraes, Frederico Barra de; Ferreira, Rodrigo Cunha; Geraldino, Stéphanie Zago; Farias, Renato Silva; Silva, Ricardo Pereira da; Kuwae, Mário Yoshihide

    2016-01-01

    The wrist is a region that is very vulnerable to injuries of the extremities. Among these injuries, fractures of the pyramidal bone (or triquetrum) in association with dislocation of the hamate and carpal instability are uncommon. They are generally correlated with high-energy trauma and may be associated with neurovascular deficits, muscle-tendon disorders, skin lesions or injuries to other carpal bones. Thus, in this report, one of these rare cases of transtriquetral perihamate fracture-dislocation with carpal instability is presented, diagnosed by means of radiography on the right wrist of the patient who presented pain, edema and limitation of flexion-extension of the carpus after trauma to the region. The stages of attending to the case are described, from the initial consultation to the surgical treatment and physiotherapy, which culminated in restoration of the strength and range of motion of the wrist.

  17. The Origins of the Constitution.

    ERIC Educational Resources Information Center

    Grindle, Diane

    1987-01-01

    Maintains that there were three forces operating in colonial American culture which led to the drafting of the Constitution. These were: English law and tradition, the lifestyle of the colonies, and the Enlightenment. Provides examples of how these forces were expressed in the events surrounding the birth of the United States Constitution. (JDH)

  18. Constitution And Bylaws: 2004 Edition

    ERIC Educational Resources Information Center

    Distance Education and Training Council, 2004

    2004-01-01

    This document contains the constitution and bylaws of the Distance Education and Training Council. The constitution and bylaws include 13 articles. Sections include: Name; Mission and Goals; Administration of the Council; Membership; Meetings; The Commission; Terms of Office; Officers; Committees; Compensation; Dues and Assessments; Miscellaneous…

  19. The Constitution and Its Critics

    ERIC Educational Resources Information Center

    Main, Thomas J.

    2011-01-01

    In planning a freshman undergraduate curriculum with colleagues recently, the question arose as to what type of understanding educators wanted to impart to their students about the Constitution. The alleged defects of the Constitution that these books point to are wide-ranging and can be classified into various categories. Some problems--such as…

  20. The Constitution and American Radicalism.

    ERIC Educational Resources Information Center

    Lobel, Jules

    1987-01-01

    Discusses the history of the following movements' attitudes towards the Constitution: (1) abolition; (2) feminism; (3) trade unions; (4) socialism and communism; and (5) civil rights and anti-war. Maintains that the tensions in these movements' towards the Constitution represent basic contradictions in the document itself. (PS)

  1. Constitutional Change: A Case Study.

    ERIC Educational Resources Information Center

    Christofferson, Walter D.; Pergande, Donald J.

    1987-01-01

    Presents a lesson for secondary students which teaches that the U.S. Constitution has changed in a variety of ways and that it has a direct effect upon the lives of citizens. Provides a worksheet and a lecture outline covering three methods of constitutional change and Supreme Court cases such as Dred Scott and Brown vs. Board of Education. (GEA)

  2. Dislocations: 75 years of Deformation Mechanisms

    NASA Technical Reports Server (NTRS)

    Schneider, Judy

    2009-01-01

    The selection of papers presented in this section reflect on themes to be explored at the "Dislocations: 75 years of Deformation Mechanisms" Symposium to be held at the Annual 2009 TMS meeting. The symposium was sponsored by the Mechanical Behavior of Materials Committee to give tribute to the evolution of a concept that has formed the basis of our mechanistic understanding of how crystalline solids plastically deform and how they fail.

  3. Energetics and Noise in dislocation patterning.

    SciTech Connect

    Thomson, R. M.; Koslowski, M.; LeSar, R. ,

    2004-01-01

    The competition between energy and noise in the patterning transition in deformation is explored by employing a 2D model of parallel straight edge dislocations. We define a generalized force for ordering and show that at mechanical equilibrium, the ordering force is equal to the average back stress noise on the slip plane. We consider a system subjected to a total external strain that is a uniform linear function of time. When the external stress reaches a critical value that depends on the instantaneous state of strain and dislocation content, a discrete strain event occurs (what we have called elsewhere a percolation event) with the formation of one or perhaps a few micro slip steps on the surface. Within these micro slip bands, the dislocation content increases in a time short compared to the time between strain events. After the stress drop associated with the stain event, the strain stops. During the time between events, the configuration relaxes to a new equilibrium configuration, which may include thermally generated recovery. As the stress again builds owing to the continuously increasing total strain, it reaches a new critical stress determined by the newly achieved dislocation configuration. Our modeling addresses the changes during the relaxation of the system in the time between events. In our model, the initial state is a random configuration i.e., it does not contain any memory of the previous state of the deforming system. This is an extreme assumption, because in a real system, the order will evolve from one event to the next. Nevertheless, if the real system does order, we expect this to be captured in the model - we will simply be careful not to predict the quantitative order in the evolving system from our modeling.

  4. Dislocation Microstructures in Experimentally Deformed wet Olivine

    NASA Astrophysics Data System (ADS)

    Sharp, T. G.; Jung, H.; Karato, S.

    2002-12-01

    Seismic anisotropy in the upper mantle is generally considered to be the result of lattice preferred orientations (LPOs) of olivine as a result of mantle flow. Therefore seismic anisotropy in the upper mantle can be used to probe fabrics and therefore flow directions. Jung and Karato (2001) have demonstrated that fabrics developed in experimentally deformed olivine are dependent on H2O fugacity and stress. Fabric type C, which develops at moderate experimental stresses and high H2O fugacities, has [001] subparallel to the slip direction and (100) subparallel to the shear plane. Fabric type B, which develops at high stresses and high H2O fugacities has [001] subparallel to the slip direction and (010) subparallel to the shear plane. To investigate the role of H2O in olivine fabric transitions, we are using high-resolution and conventional transmission electron microscopy (HRTEM and TEM) to characterize the dislocation microstructures and core structures in experimentally deformed samples of Fabric types B and C. Initial results for Fabric type C (sample JK11 of Jung and Karato, 2001) show a dominance of mixed-character and screw dislocations with Burgers vectors b = [001]. This Burgers vector, combined with the (100) being subparallel to the shear plane, is consistent with the (100)[001] slip system being dominant in the C-type fabric. This slip system, which is of minor importance in dry olivine, may be favored in wet samples by changes in the dislocation core structure. We are currently using HRTEM imaging to characterize the dislocation core structures in deformed samples with type C and type B fabrics.

  5. Open Galeazzi fracture with ipsilateral elbow dislocation.

    PubMed

    Adanır, Oktay; Yüksel, Serdar; Beytemur, Ozan; Güleç, M Akif

    2016-08-01

    Combination of the Galeazzi fracture and dislocation of the elbow joint in same extremity is very rare. In this article, we report a 26-year-old male patient with a posterolateral dislocation of the elbow and ipsilateral volar type Galeazzi fracture. We performed closed reduction for the elbow dislocation during admission to the emergency department. Patient was taken to the operating room in the sixth hour of his application to emergency department and open wound on the ulnovolar region of the wrist was closed primarily after irrigation and debridement. We performed open reduction and internal fixation of the radial fracture with a dynamic compression plate. After fixation, we evaluated the stability of the elbow joint and distal radioulnar joint. Distal radioulnar joint was unstable under fluoroscopic examination and fixed with one 1.8 mm Kirschner wire in a pronated position. Then, elbow joint was stable. One year after surgery, patient had no pain or sings of instability. At the last follow-up, range of motion of the elbow was 10°-135° and forearm pronation and supination were 70°.

  6. Open Galeazzi fracture with ipsilateral elbow dislocation.

    PubMed

    Adanır, Oktay; Yüksel, Serdar; Beytemur, Ozan; Güleç, M Akif

    2016-08-01

    Combination of the Galeazzi fracture and dislocation of the elbow joint in same extremity is very rare. In this article, we report a 26-year-old male patient with a posterolateral dislocation of the elbow and ipsilateral volar type Galeazzi fracture. We performed closed reduction for the elbow dislocation during admission to the emergency department. Patient was taken to the operating room in the sixth hour of his application to emergency department and open wound on the ulnovolar region of the wrist was closed primarily after irrigation and debridement. We performed open reduction and internal fixation of the radial fracture with a dynamic compression plate. After fixation, we evaluated the stability of the elbow joint and distal radioulnar joint. Distal radioulnar joint was unstable under fluoroscopic examination and fixed with one 1.8 mm Kirschner wire in a pronated position. Then, elbow joint was stable. One year after surgery, patient had no pain or sings of instability. At the last follow-up, range of motion of the elbow was 10°-135° and forearm pronation and supination were 70°. PMID:27499325

  7. Dislocation movement and hysteresis in Maraging blades

    NASA Astrophysics Data System (ADS)

    Di Cintio, Arianna; Marchesoni, Fabio; Ascione, Maria; Bhawal, Abhik; De Salvo, Riccardo

    2009-10-01

    All seismic isolation systems developed for gravitational-wave interferometric detectors, such as LIGO, Virgo and TAMA, make use of Maraging steel blades. The dissipation properties of these blades have been studied at low frequencies, by using a geometric anti-spring (GAS) filter, which allowed the exploration of resonant frequencies below 100 mHz. At this frequency an anomalous transfer function was observed in the GAS filter: this is one of several motivations for this work. The many unexpected effects observed and measured are explainable by the collective movement of dislocations inside the material described with the statistic of self-organised criticality. At low frequencies, below 200 mHz, the dissipation mechanism can subtract elasticity from the system even leading to sudden collapse. While Young's modulus is weaker, excess dissipation is observed. At higher frequencies the applied stress is probably too fast to allow the full growth of dislocation avalanches, and less losses are observed, thus explaining the higher Q-factor in this frequency range. The domino effect that leads to the release of entangled dislocations allows the understanding of the random walk of the Virgo and TAMA inverted pendula, the anomalous GAS filter transfer function as well as the loss of predictability of the ring-down decay in the LIGO seismic attenuation system inverted pendula.

  8. Atomistic simulation of oxide dislocations and interfaces

    NASA Astrophysics Data System (ADS)

    Parker, S. C.; de Leeuw, N. H.; Harris, D. J.; Higgins, F. M.; Oliver, Pe M.; Redfern, S. E.; Watson, G. W.

    Atomistic simulation techniques have been used to study screw dislocations, grain boundaries, thin films and surfaces. The results show that the a/2<110> screw dislocations in bulk MgO and NiO are more stable than the a<100> although the latter are stabilised by vacancies. Adsorption of MgO units at the a<100> spiral dislocation shows a complicated two-layer growth mechanism. Self-diffusion through MgO grain boundaries is shown to be faster than in the bulk crystal, with pipe diffusion the energetically most favourable route. Study of thin iron oxide films on MgO found that the most stable MgO/Fe3O4 /(001) interface is an open structure with closely matching spacing between substrate Mg ions and oxygens of the film. The interaction of water with oxides MgO and SiO2 has been investigated. The dominance of the MgO surface is shown through facetting of the less stable and surfaces. The low-coordinated surface sites hence formed are the most reactive towards adsorption of water and dissolution. Similarly, α-quartz surfaces with dangling bonds are more reactive towards water and NaOH than the fully-coordinated surface sites.

  9. Dislocation Theory of the Fatigue of Metals

    NASA Technical Reports Server (NTRS)

    Machlin, E S

    1949-01-01

    A dislocation theory of fatigue failure for annealed solid solutions is presented. On the basis of this theory, an equation giving the dependence of the number of cycles for failure on the stress, the temperature, the material parameters, and the frequency is derived for uniformly stressed specimens. The equation is in quantitative agreement with the data. Inasmuch as one material parameter is indicated to be temperature-dependent and its temperature dependence is unknown, it is impossible to predict the temperature dependence of the number of cycles for failure. A predicted quantitative correlation between fatigue and creep was found to exist, which suggests the practical possibility of obtaining fatigue data for annealed solid solutions and elements from steady-state creep-rate data for these materials. As a result of this investigation, a modification of the equation for the steady-state creep rate previously developed on the basis of the dislocation theory is suggested. Additional data are required to verify completely the dislocation theory of fatigue.

  10. Types of Traumatic Lens Dislocations at Larkana.

    PubMed

    Shah, Syed Imtiaz Ali; Shah, Shujaat Ali; Rai, Partab; Siddiqui, Shahid Jamal; Abbasi, Safdar Ali; Katpar, Naeem Akhtar

    2016-08-01

    The objective of this study was to determine the pattern of traumatic lens dislocations presenting at our institute. This may help develop the preventive strategies. The number of cases of traumatic lens dislocations, presented at the Department of Ophthalmology, Chandka Medical College, Larkana, Pakistan, from January 2002 to June 2015, were 59 including 61.02% (n=36) males and 38.98% (n=23) females. Cause of trauma was wood or plant impalement in 35.6% (n=21) cases, cracker blast in 13.55% (n=8) cases, fall on ground in 11.86% (n=7) cases, penetrating injuries with needle, scissors or knife in 10.16% (n=6) cases, road traffic accidents in 10.16% (n=6) cases, sports injuries (cricket ball and gulle danda) in 8.47% (n=5) cases, firearm injuries in 5.1% (n=3) cases, and fist hitting in 5.1% (n=3) cases. Lens was dislocated posteriorly in 33.90% (n=20) cases, anteriorly in 25.42% (n=15) cases, inferiorly in 11.86% (n=7) cases, medially in 10.17% (n=6) cases, laterally in 10.17% (n=6) cases, superiorly in 6.78% (n=4) cases, and a single (1.69%) case of lenticele was seen. PMID:27539772

  11. BBilateral Neglected Anterior Shoulder Dislocation with Greater Tuberosity Fractures

    PubMed Central

    Upasani, Tejas; Bhatnagar, Abhinav; Mehta, Sonu

    2016-01-01

    Introduction: Shoulder dislocations are a very common entity in routine orthopaedic practice. Chronic unreduced anterior dislocations of the shoulder are not very common. Neurological and vascular complications may occur as a result of an acute anterior dislocation of the shoulder or after a while in chronic unreduced shoulder dislocation. Open reduction is indicated for most chronic shoulder dislocations. We report a case of neglected bilateral anterior shoulder dislocation with bilateral displaced greater tuberosity fracture. To the best of our knowledge, only a handful cases have been reported in literature with bilateral anterior shoulder dislocation with bilateral fractures. Delayed diagnosis/reporting is a scenario which makes the list even slimmer and management all the more challenging. Case Report: We report a case of a 35-year-old male who had bilateral anterior shoulder dislocation and bilateral greater tuberosity fracture post seizure and failed to report it for a period of 30 days. One side was managed conservatively with closed reduction and immobilization and the other side with open reduction. No neurovascular complications pre or post reduction of shoulder were seen. Conclusion: Shoulder dislocations should always be suspected post seizures and if found should be treated promptly. Treatment becomes difficult for any shoulder dislocation that goes untreated for considerable period of time PMID:27703939

  12. Probing the character of ultra-fast dislocations.

    PubMed

    Ruestes, C J; Bringa, E M; Rudd, R E; Remington, B A; Remington, T P; Meyers, M A

    2015-01-01

    Plasticity is often controlled by dislocation motion, which was first measured for low pressure, low strain rate conditions decades ago. However, many applications require knowledge of dislocation motion at high stress conditions where the data are sparse, and come from indirect measurements dominated by the effect of dislocation density rather than velocity. Here we make predictions based on atomistic simulations that form the basis for a new approach to measure dislocation velocities directly at extreme conditions using three steps: create prismatic dislocation loops in a near-surface region using nanoindentation, drive the dislocations with a shockwave, and use electron microscopy to determine how far the dislocations moved and thus their velocity at extreme stress and strain rate conditions. We report on atomistic simulations of tantalum that make detailed predictions of dislocation flow, and find that the approach is feasible and can uncover an exciting range of phenomena, such as transonic dislocations and a novel form of loop stretching. The simulated configuration enables a new class of experiments to probe average dislocation velocity at very high applied shear stress.

  13. Probing the character of ultra-fast dislocations

    NASA Astrophysics Data System (ADS)

    Ruestes, C. J.; Bringa, E. M.; Rudd, R. E.; Remington, B. A.; Remington, T. P.; Meyers, M. A.

    2015-11-01

    Plasticity is often controlled by dislocation motion, which was first measured for low pressure, low strain rate conditions decades ago. However, many applications require knowledge of dislocation motion at high stress conditions where the data are sparse, and come from indirect measurements dominated by the effect of dislocation density rather than velocity. Here we make predictions based on atomistic simulations that form the basis for a new approach to measure dislocation velocities directly at extreme conditions using three steps: create prismatic dislocation loops in a near-surface region using nanoindentation, drive the dislocations with a shockwave, and use electron microscopy to determine how far the dislocations moved and thus their velocity at extreme stress and strain rate conditions. We report on atomistic simulations of tantalum that make detailed predictions of dislocation flow, and find that the approach is feasible and can uncover an exciting range of phenomena, such as transonic dislocations and a novel form of loop stretching. The simulated configuration enables a new class of experiments to probe average dislocation velocity at very high applied shear stress.

  14. Probing the character of ultra-fast dislocations

    PubMed Central

    Ruestes, C. J.; Bringa, E. M.; Rudd, R. E.; Remington, B. A.; Remington, T. P.; Meyers, M. A.

    2015-01-01

    Plasticity is often controlled by dislocation motion, which was first measured for low pressure, low strain rate conditions decades ago. However, many applications require knowledge of dislocation motion at high stress conditions where the data are sparse, and come from indirect measurements dominated by the effect of dislocation density rather than velocity. Here we make predictions based on atomistic simulations that form the basis for a new approach to measure dislocation velocities directly at extreme conditions using three steps: create prismatic dislocation loops in a near-surface region using nanoindentation, drive the dislocations with a shockwave, and use electron microscopy to determine how far the dislocations moved and thus their velocity at extreme stress and strain rate conditions. We report on atomistic simulations of tantalum that make detailed predictions of dislocation flow, and find that the approach is feasible and can uncover an exciting range of phenomena, such as transonic dislocations and a novel form of loop stretching. The simulated configuration enables a new class of experiments to probe average dislocation velocity at very high applied shear stress. PMID:26592764

  15. Probing the character of ultra-fast dislocations

    DOE PAGESBeta

    Rudd, R. E.; Ruestes, C. J.; Bringa, E. M.; Remington, B. A.; Remington, T. P.; Meyers, M. A.

    2015-11-23

    Plasticity is often controlled by dislocation motion, which was first measured for low pressure, low strain rate conditions decades ago. However, many applications require knowledge of dislocation motion at high stress conditions where the data are sparse, and come from indirect measurements dominated by the effect of dislocation density rather than velocity. Here we make predictions based on atomistic simulations that form the basis for a new approach to measure dislocation velocities directly at extreme conditions using three steps: create prismatic dislocation loops in a near-surface region using nanoindentation, drive the dislocations with a shockwave, and use electron microscopy tomore » determine how far the dislocations moved and thus their velocity at extreme stress and strain rate conditions. We report on atomistic simulations of tantalum that make detailed predictions of dislocation flow, and find that the approach is feasible and can uncover an exciting range of phenomena, such as transonic dislocations and a novel form of loop stretching. Furthermore, the simulated configuration enables a new class of experiments to probe average dislocation velocity at very high applied shear stress.« less

  16. Probing the character of ultra-fast dislocations

    SciTech Connect

    Rudd, R. E.; Ruestes, C. J.; Bringa, E. M.; Remington, B. A.; Remington, T. P.; Meyers, M. A.

    2015-11-23

    Plasticity is often controlled by dislocation motion, which was first measured for low pressure, low strain rate conditions decades ago. However, many applications require knowledge of dislocation motion at high stress conditions where the data are sparse, and come from indirect measurements dominated by the effect of dislocation density rather than velocity. Here we make predictions based on atomistic simulations that form the basis for a new approach to measure dislocation velocities directly at extreme conditions using three steps: create prismatic dislocation loops in a near-surface region using nanoindentation, drive the dislocations with a shockwave, and use electron microscopy to determine how far the dislocations moved and thus their velocity at extreme stress and strain rate conditions. We report on atomistic simulations of tantalum that make detailed predictions of dislocation flow, and find that the approach is feasible and can uncover an exciting range of phenomena, such as transonic dislocations and a novel form of loop stretching. Furthermore, the simulated configuration enables a new class of experiments to probe average dislocation velocity at very high applied shear stress.

  17. Bertram Hopkinson's pioneering work and the dislocation mechanics of high rate deformations and mechanically induced detonations.

    PubMed

    Armstrong, Ronald W

    2014-05-13

    Bertram Hopkinson was prescient in writing of the importance of better measuring, albeit better understanding, the nature of high rate deformation of materials in general and, in particular, of the importance of heat in initiating detonation of explosives. This report deals with these subjects in terms of post-Hopkinson crystal dislocation mechanics applied to high rate deformations, including impact tests, Hopkinson pressure bar results, Zerilli-Armstrong-type constitutive relations, shock-induced deformations, isentropic compression experiments, mechanical initiation of explosive crystals and shear banding in metals.

  18. Sternoclavicular dislocation: case report and surgical technique.

    PubMed

    Terra, Bernardo Barcellos; Rodrigues, Leandro Marano; Pádua, David Victoria Hoffmann; Martins, Marcelo Giovanini; Teixeira, João Carlos de Medeiros; De Nadai, Anderson

    2015-01-01

    Sternoclavicular dislocations account for less than 5% of all dislocations of the scapular belt. Most cases of anterior dislocation of the sternoclavicular joint do not present symptoms. However, some patients may develop chronic anterior instability and remain symptomatic, and surgical treatment is indicated in these cases. There is a scarcity of reports in the literature relating to reconstruction using the long palmar tendon in cases of traumatic anterior instability. Although rare, these injuries deserve rapid diagnosis and efficient treatment in order to avoid future complications. The aim of this report was to report on a case of a motocross competitor who developed chronic traumatic anterior instability of the sternoclavicular joint and underwent surgical reconstruction using the autogenous long palmar tendon. The patient was a 33-year-old man with a history of anterior dislocation of the sternoclavicular subsequent to a fall during a maneuver in a motocross competition. Conservative treatment was instituted initially, consisting of use of a functional sling to treat the symptoms for 3 weeks, along with physiotherapeutic rehabilitation for 3 months. We chose to use a modification of the "figure of eight" technique based on the studies by Spencer and Kuhn. A longitudinal incision of approximately 10 cm was made at the level of the sternoclavicular joint. The graft from the ipsilateral long palmar tendon was passed through the orifices in the form of a modified "figure of eight" and its ends were sutured together. The patient was immobilized using an American sling for 4 weeks. After 6 months of follow-up, the patient no longer presented pain or instability when movement of the sternoclavicular joint was required. Minor discomfort and slight prominence of the sternoclavicular joint continued to be present but did not affect the patient's activities. Thus, the patient was able to return to racing 6 months after the operation. Our study presented a case of

  19. Constitutive model for the dynamic response of a NiTi shape memory alloy

    NASA Astrophysics Data System (ADS)

    Shi, Xiaohong; Zeng, Xiangguo; Chen, Huayan

    2016-07-01

    In this paper, based on irreversible thermodynamic theory, the Helmholtz free energy function, was selected to deduce both the master equations and evolution equations of the constitutive model of a NiTi alloy under high strain. The Helmholtz free energy function contains the parameters of the reflecting phase transition and plastic property. The constitutive model for a NiTi alloy was implemented using a semi-implicit stress integration algorithm. Four successive stages can be differentiated and simulated: parent phase elasticity, martensitic phase transition, martensitic elasticity, and dislocation yield. The simulation results are in good agreement with the experimental results.

  20. Remarks on turbulent constitutive relations

    NASA Technical Reports Server (NTRS)

    Shih, Tsan-Hsing; Lumley, John L.

    1993-01-01

    The paper demonstrates that the concept of turbulent constitutive relations can be used to construct general models for various turbulent correlations. Some of the Generalized Cayley-Hamilton formulas for relating tensor products of higher extension to tensor products of lower extension are introduced. The combination of dimensional analysis and invariant theory can lead to 'turbulent constitutive relations' (or general turbulence models) for, in principle, any turbulent correlations. As examples, the constitutive relations for Reynolds stresses and scalar fluxes are derived. The results are consistent with ones from Renormalization Group (RNG) theory and two-scale Direct-Interaction Approximation (DIA) method, but with a more general form.

  1. Bilateral dorsal trans-scaphoid perilunate fracture–dislocation: A case report

    PubMed Central

    Yildirim, Cengiz; Unuvar, Fatih; Keklikci, Kenan; Demirtas, Mehmet

    2014-01-01

    INTRODUCTION Perilunate dislocations represent one of the most devastating injuries to the carpus. Fortunately, these injuries are relatively rare, constituting approximately 10% of all carpal injuries. One of the problems associated with this injury is the difficulty of its accurate and early recognition. PRESENTATION OF CASE In this study, an uncommon case of bilateral dorsal trans-scaphoid perilunate fracture–dislocation following trauma has been reported. The injury was missed initially and the patient was subsequently operated after two weeks. Anatomic reduction was achieved by closed reduction. After closed reduction, percutaneous pin fixation of the carpus was performed using Kirschner wires. Finally, the scaphoid was stabilized with a headless screw percutaneously. The same procedure was repeated for the other wrist. This was followed by an uneventful post-operative period, with a satisfactory functional outcome at the two-year follow-up, despite non-union of the scaphoid in one side. DISCUSSION The case was examined in detail, and compared to the findings in the literature; observations regarding fracture prognosis were also made. Most authors agree that closed reduction is the initial treatment of choice for trans-scaphoid perilunate fracture–dislocations. In addition, treatment often requires intercarpal fixation within the proximal carpal row. CONCLUSION We believe that closed reduction in these cases should be attempted regarding the potential risks of avascular necrosis and non-union of the affected carpal bones due to open reduction. PMID:24705189

  2. High resolution detection of solute segregation to the cores of dislocations in grain boundaries

    NASA Astrophysics Data System (ADS)

    Michael, J. R.; Lin, C. H.; Sass, S. L.

    1988-03-01

    Thin film Fe -0.8 at. percent Au bicrystals, approximately 60 nm thick, containing (001) twist boundaries were prepared. The average compositon of the bicrystal was determined by Rutherford backscattering spectroscopy (RBS), which also showed that the Au was nonuniformly distributed along the direction normal to the interface, with a large amount concentrated at the (001) twist boundary. This observation constitutes direct evidence that the Au is segregated to the vicinity of the grain boundary. The Au distribution within the plane of the interface was analyzed in a Vacuum Generators HB-501 Scanning Transmission Electron Microscope (STEM) equipped with a field emission electron source and a Link Analytical windowless X-ray detector. The boundary plane was oriented perpendicular to the electron beam. Digital line scans were performed across the dislocation network. Au segregates extensively to the cores of the (100)-type dislocations in small angle (001) twist boundaries in Fe-Au alloys. Our observations demonstrate that the (110) network is favored in pure Fe, which leads to the suggestion that the dislocation core energy plays an important role in determining the stable boundary structure.

  3. Pathogeny and natural history of congenital dislocation of the hip.

    PubMed

    Seringe, R; Bonnet, J-C; Katti, E

    2014-02-01

    Based on a review of the literature, the authors have made a critical study of several etiological factors. Endogenous factors such as acetabular dysplasia, increased anteversion of the femoral neck, and capsular laxity support the genetic theory but are neither constant nor necessary and are only facilitating factors. The major factor seems to be a mechanical one linked to the position in the uterus: hyperflexion with adduction and external rotation constituting the dislocating foetal posture combined with abnormal pressure on the greater trochanter and leading to expulsion of the head upward and backward. This theory can explain the natural history of C D H which is first, at birth a hip instability followed by two possible evolutions: either persistent luxation becoming irreducible or spontaneous stabilisation leading sometimes to complete healing or to residual abnormalities (subluxation or dysplasia). This concept suggests practical conclusions: the importance of an early diagnosis, the selection of the signs of the hip at risk, the pattern of prevention, the role for non-clinical investigations, the principles of the treatment based on postures, the indications for the different types of treatment. PMID:24456762

  4. Atomistic simulations of dislocation pileup: Grain boundaries interaction

    DOE PAGESBeta

    Wang, Jian

    2015-05-27

    Here, using molecular dynamics (MD) simulations, we studied the dislocation pileup–grain boundary (GB) interactions. Two Σ11 asymmetrical tilt grain boundaries in Al are studied to explore the influence of orientation relationship and interface structure on dislocation activities at grain boundaries. To mimic the reality of a dislocation pileup in a coarse-grained polycrystalline, we optimized the dislocation population in MD simulations and developed a predict-correct method to create a dislocation pileup in MD simulations. MD simulations explored several kinetic processes of dislocations–GB reactions: grain boundary sliding, grain boundary migration, slip transmission, dislocation reflection, reconstruction of grain boundary, and the correlation ofmore » these kinetic processes with the available slip systems across the GB and atomic structures of the GB.« less

  5. Thermally Induced Dynamics of Dislocations in Graphene at Atomic Resolution.

    PubMed

    Gong, Chuncheng; Robertson, Alex W; He, Kuang; Lee, Gun-Do; Yoon, Euijoon; Allen, Christopher S; Kirkland, Angus I; Warner, Jamie H

    2015-10-27

    Thermally induced dislocation movements are important in understanding the effects of high temperature annealing on modifying the crystal structure. We use an in situ heating holder in an aberration corrected transmission electron microscopy to study the movement of dislocations in suspended monolayer graphene up to 800 °C. Control of temperature enables the differentiation of electron beam induced effects and thermally driven processes. At room temperature, the dynamics of dislocation behavior is driven by the electron beam irradiation at 80 kV; however at higher temperatures, increased movement of the dislocation is observed and provides evidence for the influence of thermal energy to the system. An analysis of the dislocation movement shows both climb and glide processes, including new complex pathways for migration and large nanoscale rapid jumps between fixed positions in the lattice. The improved understanding of the high temperature dislocation movement provides insights into annealing processes in graphene and the behavior of defects with increased heat.

  6. Lens dislocation has a possible relationship with laser iridotomy.

    PubMed

    Mutoh, Tetsuya; Barrette, Kevin F; Matsumoto, Yukihiro; Chikuda, Makoto

    2012-01-01

    We report our recent experience of four eyes with spontaneous lens dislocation in four patients with no history of trauma or any systemic disease associated with zonular dialysis. Lens dislocation developed with 0.5 to 6 months following laser iridotomy. All patients were male and two eyes were complicated with acute primary angle closure glaucoma preoperatively. Case 1 showed bilateral lens dislocation, while cases 2 and 3 involved unilateral lens dislocation. Cases 2 and 3 showed lenses completely dislocated into the vitreous cavity. All cases needed lens removal and scleral fixation of intraocular lenses. Final visual acuity was 1.2 in all cases. We suspect that laser iridotomy may induce localized zonular dialysis that results in progressive zonular weakness, leading to lens dislocation. PMID:23271880

  7. Atomistic simulations of dislocation pileup: Grain boundaries interaction

    SciTech Connect

    Wang, Jian

    2015-05-27

    Here, using molecular dynamics (MD) simulations, we studied the dislocation pileup–grain boundary (GB) interactions. Two Σ11 asymmetrical tilt grain boundaries in Al are studied to explore the influence of orientation relationship and interface structure on dislocation activities at grain boundaries. To mimic the reality of a dislocation pileup in a coarse-grained polycrystalline, we optimized the dislocation population in MD simulations and developed a predict-correct method to create a dislocation pileup in MD simulations. MD simulations explored several kinetic processes of dislocations–GB reactions: grain boundary sliding, grain boundary migration, slip transmission, dislocation reflection, reconstruction of grain boundary, and the correlation of these kinetic processes with the available slip systems across the GB and atomic structures of the GB.

  8. Pattern formation in a minimal model of continuum dislocation plasticity

    NASA Astrophysics Data System (ADS)

    Sandfeld, Stefan; Zaiser, Michael

    2015-09-01

    The spontaneous emergence of heterogeneous dislocation patterns is a conspicuous feature of plastic deformation and strain hardening of crystalline solids. Despite long-standing efforts in the materials science and physics of defect communities, there is no general consensus regarding the physical mechanism which leads to the formation of dislocation patterns. In order to establish the fundamental mechanism, we formulate an extremely simplified, minimal model to investigate the formation of patterns based on the continuum theory of fluxes of curved dislocations. We demonstrate that strain hardening as embodied in a Taylor-type dislocation density dependence of the flow stress, in conjunction with the structure of the kinematic equations that govern dislocation motion under the action of external stresses, is already sufficient for the formation of dislocation patterns that are consistent with the principle of similitude.

  9. Abnormal human sex chromosome constitutions

    SciTech Connect

    1993-12-31

    Chapter 22, discusses abnormal human sex chromosome constitution. Aneuploidy of X chromosomes with a female phenotype, sex chromosome aneuploidy with a male phenotype, and various abnormalities in X chromosome behavior are described. 31 refs., 2 figs.

  10. The Constitution's Prescription for Freedom.

    ERIC Educational Resources Information Center

    Peach, Lucinda

    1986-01-01

    Examines how the framers of the Constitution came to choose our system of government, how that system was designed to function, and how the separation of powers has served to maintain our democracy despite attempts to violate it. (JDH)

  11. Head size and dislocation rate in primary total hip arthroplasty

    PubMed Central

    Singh, Somesh P; Bhalodiya, Haresh P

    2013-01-01

    Background: Dislocation after total hip arthroplasty (THA) has a multifactorial etiology with variables such as surgical approach, component orientation and position, type of cup, stem and head size. Review of the literature regarding the relationship of head size and dislocation rate in THA is suggestive that large femoral head size is associated with lower dislocation rate after THA. However, limited data is available as a proof of this hypothesis. The purpose of this study was to determine that the use of large head size would lead to a decreased incidence of dislocations following THA. Materials and Methods: 317 primary THAs were performed using the posterolateral approach with posterior soft-tissue repair between January 2006 and December 2009. Cases were divided into two groups (A and B). Femoral head diameter size 36 mm was used in 163 THA in group A and 28 mm in 154 THA in group B. Average period of followup being 2 years (6 month to 4 years). Patients were routinely followed at definite intervals and were specifically assessed for dislocation. Results: One or more dislocations occurred in 11 out of 317 hips with the overall rate of dislocation being 3.47%. Dislocation rate was 0.6% in 36 mm head size and 6.49% with 28 mm head size (P value is 0.0107). Keeping the stem design variable as a constant, the difference in the rate of dislocation between the two groups was again found to be statistically significant for both un-cemented and cemented stem. Conclusion: Dislocation rate decreased significantly as the size of the head increased in primary THA. However, longer followup is necessary as rate of dislocation or in vivo highly cross linked poly failure or fracture may increase in future affecting the rate of dislocations in primary THA. PMID:24133302

  12. Dislocations: do you want them moving or in 3D ?

    NASA Astrophysics Data System (ADS)

    Cordier, Patrick; Boioli, Francesca; Bollinger, Caroline; Idrissi, Hosni; Mussi, Alexandre; Clitton Nzogang, Billy; Schryvers, Dominique

    2016-04-01

    Plastic deformation of minerals and rocks can be explained in most cases by the presence of crystal defects. Among those, dislocations represent the most efficient strain-producing actors of deformation. The physics of deformation by dislocations is complex since it is intrinsically multiscale. At the atomic scale, the dislocation core structure controls a fundamental property: their mobility. However, the plastic strain results from the collective behavior of dislocations which can be understood only at the mesoscopic scale. Multiscale numerical modeling has provided a lot of insights on these aspects in the recent years, also in mineral physics. These progress were calling for parallel developments in experiments and characterization. Here we present two studies on dislocations in olivine deformed under lithospheric conditions based in recent developments in transmission electron microscopy. We present plastic deformation experiments performed on olivine in situ, in the transmission electron microscope, at room temperature. The ductile behavior is made possible thanks to the very small size of the specimens (maximum dimension < 5μm) which are prepared by focused ion beam and strained in a special Micro-Electro-Mechanical-System (MEMS) device called push-to-pull (PI 95 TEM PicoIndenter from Hysitron). By performing experiments under constant load, the velocity of [001] screw dislocations has been measured as a function of stress. This mobility law has then been introduced in a Dislocation Dynamics model to determine the stress strain curves. We present also some recent developments on electron tomography of dislocations performed on olivine. The difficulty is here to keep diffraction conditions strictly constant over a wide range of tilt acquisitions. We present some examples obtained by imaging dislocations in weak-beam dark-field using precession electron diffraction. The analysis of dislocation microstructures in 3D is used to characterize dislocations glide

  13. Dislocation of the Temporomandibular Joint and Relocation Procedures.

    PubMed

    White, Thomas; Hedderick, Viki; Ramponi, Denise R

    2016-01-01

    Temporomandibular joint (TMJ) dislocation requires prompt medical attention due to the crucial impact of airway, nutrition acquisition, and communication. Recognition of this injury by the practitioner, based on clinical presentation and history, is paramount for identification of accurate diagnosis and prompt treatment of TMJ dislocation. Relocation or reduction methods vary on the basis of the severity of the injury and whether it is an acute or chronic dislocation. PMID:27482989

  14. New mechanism for dislocation blocking in strained layer epitaxial growth

    SciTech Connect

    Stach, E.A.; Schwarz, K.W.; Hull, R.; Ross, F.M.; Tromp, R.M.

    1999-09-14

    Dislocation interactions play a critical role in plasticity and heteroepitaxial strain relaxation. We use real time transmission electron microscopy observations of the interaction between threading and misfit dislocations in SiGe heterostructures to investigate interactions quantitatively. In addition to the expected long range blocking of threading segments, we observe a new short range mechanism which is significantly more effective. Simulations show that this reactive blocking occurs when two dislocations with the same Burgers vector reconnect.

  15. The equivalence between dislocation pile-ups and cracks

    NASA Technical Reports Server (NTRS)

    Liu, H. W.; Gao, Q.

    1990-01-01

    Cracks and dislocation pile-ups are equivalent to each other. In this paper, the physical equivalence between cracks and pile-ups is delineated, and the relationshps between crack-extension force, force on the leading dislocation, stress-intensity factor, and dislocation density are reviewed and summarized. These relations make it possible to extend quantitatively the recent advances in the concepts and practices of fracture mechanics to the studies of microfractures and microplastic deformations.

  16. Jaw Dislocation as an Unusual Complication of Upper Endoscopy

    PubMed Central

    Dellon, Evan S.; Steele, David

    2016-01-01

    This case report presents an unusual complication of upper endoscopy, resulting in jaw dislocation. Temporomandibular joint dislocation is commonly reported in association with anesthesia and intubation, but it is not widely recognized as a complication of gastrointestinal endoscopy. This report also reviews the current literature regarding this complication and discusses the potential causes of dislocation, differential diagnoses for jaw pain following endoscopy, and recommendations for prevention. PMID:27403117

  17. Constitutive modeling for isotropic materials

    NASA Technical Reports Server (NTRS)

    Ramaswamy, V. G.; Vanstone, R. H.; Dame, L. T.; Laflen, J. H.

    1984-01-01

    The unified constitutive theories for application to typical isotropic cast nickel base supperalloys used for air-cooled turbine blades were evaluated. The specific modeling aspects evaluated were: uniaxial, monotonic, cyclic, creep, relaxation, multiaxial, notch, and thermomechanical behavior. Further development of the constitutive theories to model thermal history effects, refinement of the material test procedures, evaluation of coating effects, and verification of the models in an alternate material will be accomplished in a follow-on for this base program.

  18. Dislocations in magnetohydrodynamic waves in a stellar atmosphere.

    PubMed

    López Ariste, A; Collados, M; Khomenko, E

    2013-08-23

    We describe the presence of wave front dislocations in magnetohydrodynamic waves in stratified stellar atmospheres. Scalar dislocations such as edges and vortices can appear in Alfvén waves, as well as in general magnetoacoustic waves. We detect those dislocations in observations of magnetohydrodynamic waves in sunspots in the solar chromosphere. Through the measured charge of all the dislocations observed, we can give for the first time estimates of the modal contribution in the waves propagating along magnetic fields in solar sunspots. PMID:24010425

  19. Dislocation luminescence in GaN single crystals under nanoindentation.

    PubMed

    Huang, Jun; Xu, Ke; Fan, Ying Min; Wang, Jian Feng; Zhang, Ji Cai; Ren, Guo Qiang

    2014-01-01

    This work presents an experimental study on the dislocation luminescence in GaN by nanoindentation, cathodoluminescence, and Raman. The dislocation luminescence peaking at 3.12 eV exhibits a series of special properties in the cathodoluminescence measurements, and it completely disappears after annealing at 500°C. Raman spectroscopy shows evidence for existence of vacancies in the indented region. A comprehensive investigation encompassing cathodoluminescence, Raman, and annealing experiments allow the assignment of dislocation luminescence to conduction-band-acceptor transition involving Ga vacancies. The nanoscale plasticity of GaN can be better understood by considering the dislocation luminescence mechanism.

  20. Lateral subtalar dislocation: Case report and review of the literature

    PubMed Central

    Veltman, Ewout S; Steller, Ernst JA; Wittich, Philippe; Keizer, Jort

    2016-01-01

    A case of complicated lateral subtalar dislocation is presented and the literature concerning this injury is reviewed. Subtalar joint dislocations are rare and often the result of a high-energy trauma. Complications include avascular necrosis of the talus, infection, posttraumatic osteoarthritis requiring arthrodesis and chronic subtalar instability. Negative prognostic factors include lateral and complicated dislocations, total talar extrusions, and associated fractures. A literature search was performed to identify studies describing outcome after lateral subtalar joint dislocation. Eight studies including fifty patients could be included, thirty out of 50 patients suffered a complicated injury. Mean follow-up was fifty-five months. Ankle function was reported as good in all patients with closed lateral subtalar dislocation. Thirteen out of thirty patients with complicated lateral subtalar joint dislocation developed a complication. Avascular necrosis was present in nine patients with complicated injury. Four patients with complicated lateral subtalar dislocation suffered deep infection requiring treatment with antibiotics. In case of uncomplicated lateral subtalar joint dislocation, excellent functional outcome after closed reduction and immobilization can be expected. In case of complicated lateral subtalar joint dislocation immediate reduction, wound debridement and if necessary (external) stabilisation are critical. Up to fifty percent of patients suffering complicated injury are at risk of developing complications such as avascular talar necrosis and infection. PMID:27672576

  1. Exploring the limit of dislocation based plasticity in nanostructured metals.

    PubMed

    Hughes, D A; Hansen, N

    2014-04-01

    A twofold decrease to an unexplored scale of 5 nm was produced in Cu by applying a large sliding load in liquid nitrogen. Statistical and universal scaling analyses of deformation induced high angle boundaries, dislocation boundaries, and individual dislocations observed by high resolution electron microscopy reveal that dislocation processes still dominate. Dislocation based plasticity continues far below the transition suggested by experiment and molecular dynamics simulations, with a limit below 5 nm. Very high strength metals may emerge based on this enhanced structural refinement. PMID:24745438

  2. Lateral subtalar dislocation: Case report and review of the literature.

    PubMed

    Veltman, Ewout S; Steller, Ernst Ja; Wittich, Philippe; Keizer, Jort

    2016-09-18

    A case of complicated lateral subtalar dislocation is presented and the literature concerning this injury is reviewed. Subtalar joint dislocations are rare and often the result of a high-energy trauma. Complications include avascular necrosis of the talus, infection, posttraumatic osteoarthritis requiring arthrodesis and chronic subtalar instability. Negative prognostic factors include lateral and complicated dislocations, total talar extrusions, and associated fractures. A literature search was performed to identify studies describing outcome after lateral subtalar joint dislocation. Eight studies including fifty patients could be included, thirty out of 50 patients suffered a complicated injury. Mean follow-up was fifty-five months. Ankle function was reported as good in all patients with closed lateral subtalar dislocation. Thirteen out of thirty patients with complicated lateral subtalar joint dislocation developed a complication. Avascular necrosis was present in nine patients with complicated injury. Four patients with complicated lateral subtalar dislocation suffered deep infection requiring treatment with antibiotics. In case of uncomplicated lateral subtalar joint dislocation, excellent functional outcome after closed reduction and immobilization can be expected. In case of complicated lateral subtalar joint dislocation immediate reduction, wound debridement and if necessary (external) stabilisation are critical. Up to fifty percent of patients suffering complicated injury are at risk of developing complications such as avascular talar necrosis and infection. PMID:27672576

  3. Interfacial dislocation motion and interactions in single-crystal superalloys

    SciTech Connect

    Liu, B.; Raabe, D.; Roters, F.; Arsenlis, A.

    2014-10-01

    The early stage of high-temperature low-stress creep in single-crystal superalloys is characterized by the rapid development of interfacial dislocation networks. Although interfacial motion and dynamic recovery of these dislocation networks have long been expected to control the subsequent creep behavior, direct observation and hence in-depth understanding of such processes has not been achieved. Incorporating recent developments of discrete dislocation dynamics models, we simulate interfacial dislocation motion in the channel structures of single-crystal superalloys, and investigate how interfacial dislocation motion and dynamic recovery are affected by interfacial dislocation interactions and lattice misfit. Different types of dislocation interactions are considered: self, collinear, coplanar, Lomer junction, glissile junction, and Hirth junction. The simulation results show that strong dynamic recovery occurs due to the short-range reactions of collinear annihilation and Lomer junction formation. The misfit stress is found to induce and accelerate dynamic recovery of interfacial dislocation networks involving self-interaction and Hirth junction formation, but slow down the steady interfacial motion of coplanar and glissile junction forming dislocation networks. The insights gained from these simulations on high-temperature low-stress creep of single-crystal superalloys are also discussed.

  4. Lateral subtalar dislocation: Case report and review of the literature

    PubMed Central

    Veltman, Ewout S; Steller, Ernst JA; Wittich, Philippe; Keizer, Jort

    2016-01-01

    A case of complicated lateral subtalar dislocation is presented and the literature concerning this injury is reviewed. Subtalar joint dislocations are rare and often the result of a high-energy trauma. Complications include avascular necrosis of the talus, infection, posttraumatic osteoarthritis requiring arthrodesis and chronic subtalar instability. Negative prognostic factors include lateral and complicated dislocations, total talar extrusions, and associated fractures. A literature search was performed to identify studies describing outcome after lateral subtalar joint dislocation. Eight studies including fifty patients could be included, thirty out of 50 patients suffered a complicated injury. Mean follow-up was fifty-five months. Ankle function was reported as good in all patients with closed lateral subtalar dislocation. Thirteen out of thirty patients with complicated lateral subtalar joint dislocation developed a complication. Avascular necrosis was present in nine patients with complicated injury. Four patients with complicated lateral subtalar dislocation suffered deep infection requiring treatment with antibiotics. In case of uncomplicated lateral subtalar joint dislocation, excellent functional outcome after closed reduction and immobilization can be expected. In case of complicated lateral subtalar joint dislocation immediate reduction, wound debridement and if necessary (external) stabilisation are critical. Up to fifty percent of patients suffering complicated injury are at risk of developing complications such as avascular talar necrosis and infection.

  5. Mobility of edge dislocations in stressed iron crystals during irradiation

    SciTech Connect

    Korchuganov, A. V. Zolnikov, K. P.; Kryzhevich, D. S.; Chernov, V. M.; Psakhie, S. G.

    2015-10-27

    The behavior of a/2(111)(110) edge dislocations in iron in shear loading and irradiation conditions was studied by means of molecular dynamics simulation. Edge dislocations were exposed to shock waves formed by atomic displacement cascades of different energies. It was shown that starting from a certain threshold amplitude shock waves cause displacement of edge dislocations in the loaded samples. Calculations showed that the larger the shear load and the amplitude of the shock wave, the greater the displacement of dislocations in the crystallite.

  6. Surface dislocation nucleation controlled deformation of Au nanowires

    SciTech Connect

    Roos, B.; Kapelle, B.; Volkert, C. A.; Richter, G.

    2014-11-17

    We investigate deformation in high quality Au nanowires under both tension and bending using in-situ transmission electron microscopy. Defect evolution is investigated during: (1) tensile deformation of 〈110〉 oriented, initially defect-free, single crystal nanowires with cross-sectional widths between 30 and 300 nm, (2) bending deformation of the same wires, and (3) tensile deformation of wires containing coherent twin boundaries along their lengths. We observe the formation of twins and stacking faults in the single crystal wires under tension, and storage of full dislocations after bending of single crystal wires and after tension of twinned wires. The stress state dependence of the deformation morphology and the formation of stacking faults and twins are not features of bulk Au, where deformation is controlled by dislocation interactions. Instead, we attribute the deformation morphologies to the surface nucleation of either leading or trailing partial dislocations, depending on the Schmid factors, which move through and exit the wires producing stacking faults or full dislocation slip. The presence of obstacles such as neutral planes or twin boundaries hinder the egress of the freshly nucleated dislocations and allow trailing and leading partial dislocations to combine and to be stored as full dislocations in the wires. We infer that the twins and stacking faults often observed in nanoscale Au specimens are not a direct size effect but the result of a size and obstacle dependent transition from dislocation interaction controlled to dislocation nucleation controlled deformation.

  7. [Bilateral elbow dislocation related to Essex-Lopresti injury].

    PubMed

    Romero Pérez, B; Marcos García, A; Medina Henríquez, J A; Muratore Moreno, G

    2012-01-01

    Elbow dislocation is second in frequency, after the shoulder, whereas bilateral dislocation is uncommon, even less than dislocations with concurrent associated fractures. One of the least frequent associations is the Essex-Lopresti injury which consists of a fracture of the radial head affecting the distal radioulnar joint with injury to the interosseous membrane. This is a case of bilateral elbow dislocation, one of the elbows associated with the Essex-Lopresti injury. During treatment, the premature closed reduction prevails, previously making sure the elbow is stable, the premise which will determine the orthopedic or surgical treatment of the injury.

  8. High-resolution three-dimensional imaging of dislocations.

    PubMed

    Barnard, J S; Sharp, J; Tong, J R; Midgley, P A

    2006-07-21

    Dislocations and their interactions govern the properties of many materials, ranging from work hardening in metals to device pathology in semiconductor laser diodes. However, conventional electron micrographs are simply two-dimensional projections of three-dimensional (3D) structures, and even stereo microscopy cannot reveal the true 3D complexity of defect structures. Here, we describe an electron tomographic method that yields 3D reconstructions of dislocation networks with a spatial resolution three orders of magnitude better than previous work. We illustrate the method's success with a study of dislocations in a GaN epilayer, where dislocation densities of 1010 per square centimeter are common.

  9. Anterior Shoulder Dislocations in Busy Emergency Departments

    PubMed Central

    Janitzky, Angelika A.; Akyol, Can; Kesapli, Mustafa; Gungor, Faruk; Imak, Arefe; Hakbilir, Oktay

    2015-01-01

    Abstract Shoulder joint is the most common joint requiring reduction by emergency physicians. Successful reduction is based on the overcoming of resistance of the shoulder muscles. Pain is the most important factor in resistance increase and sedation; analgesia and, in certain cases, intra-articular anesthesia are preferred for reduction. The external rotation (ER) method can provide successful reduction without causing an increase in muscle resistance if applied slowly and gently. The aim of this study was, therefore, to determine the usefulness of the ERWOSA method in the reduction of acute anterior shoulder dislocations (AASDs). This was a retrospective descriptive study. The records of patients admitted to the emergency department with anterior shoulder dislocation between 2009 and 2011 were reviewed for demographic data, sedation, analgesia, and discharge times. Patients were then divided into ERWOSA (n = 80) and external rotation and sedation-analgesia (ERASA, n = 59) groups, with regard to the application of SA (sedation-analgesia). The study data were analyzed using SPSS version 22.0 software for Windows. Numerical data were presented as mean ± standard deviation and categorical data as rates. A total of 139 patients were included in the study. The patients’ average age was 35 ± 14 years, 108 (77.7%) were male. Successful reduction rates for 59 male and 21 female patients in the ERWOSA group were 83% and 66.7% (78.7% total success), respectively. Successful reduction rates for 49 male and 10 female patients in the ERASA group were 87.7% and 90% (88.1% total success), respectively. The length of stay of the ERWOSA and ERASA groups in emergency services were found to be significantly different, with 55 ± 17 and 118 ± 23 minutes for each group, respectively. There were no complications. The ER method can be used in reduction of anterior shoulder dislocations without sedation and analgesia, if applied slowly enough to overcome

  10. [Acute perilunar dislocations: algorithm for treatment].

    PubMed

    Towfigh, H

    2001-01-01

    In most cases, perilunar dislocations of the wrist are caused by high speed accidents. Usually these injuries occur by a fall on the dorsiflexed superextension of the hand. The instability caused by injuries of various erticular structures (ligament, bone) show various developmental stages. Clinical symptoms are reduced and painful movement, instability of the carpus, snapping and swelling. The diagnosis is established by X-ray, cinematography, arthrography MRT or CT. Perilunar instability with or without associated fractures and particularly de Quervain must be reduced and treated operatively including suture of the ligament and stabilization of the fracture. PMID:11824286

  11. A computational method for dislocation-precipitate interaction

    NASA Astrophysics Data System (ADS)

    Takahashi, Akiyuki; Ghoniem, Nasr M.

    A new computational method for the elastic interaction between dislocations and precipitates is developed and applied to the solution of problems involving dislocation cutting and looping around precipitates. Based on the superposition principle, the solution to the dislocation-precipitate interaction problem is obtained as the sum of two solutions: (1) a dislocation problem with image stresses from interfaces between the dislocation and the precipitate, and (2) a correction solution for the elastic problem of a precipitate with an initial strain distribution. The current development is based on a combination of the parametric dislocation dynamics (PDD) and the boundary element method (BEM) with volume integrals.The method allows us to calculate the stress field both inside and outside precipitates of elastic moduli different from the matrix, and that may have initial coherency strain fields. The numerical results of the present method show good convergence and high accuracy when compared to a known analytical solution, and they are also in good agreement with molecular dynamics (MD) simulations. Sheared copper precipitates (2.5 nm in diameter) are shown to lose some of their resistance to dislocation motion after they are cut by leading dislocations in a pileup. Successive cutting of precipitates by the passage of a dislocation pileup reduces the resistance to about half its original value, when the number of dislocations in the pileup exceeds about 10. The transition from the shearable precipitate regime to the Orowan looping regime occurs for precipitate-to-matrix elastic modulus ratios above approximately 3-4, with some dependence on the precipitate size. The effects of precipitate size, spacing, and elastic modulus mismatch with the host matrix on the critical shear stress (CSS) to dislocation motion are presented.

  12. Implicit integration methods for dislocation dynamics

    DOE PAGESBeta

    Gardner, D. J.; Woodward, C. S.; Reynolds, D. R.; Hommes, G.; Aubry, S.; Arsenlis, A.

    2015-01-20

    In dislocation dynamics simulations, strain hardening simulations require integrating stiff systems of ordinary differential equations in time with expensive force calculations, discontinuous topological events, and rapidly changing problem size. Current solvers in use often result in small time steps and long simulation times. Faster solvers may help dislocation dynamics simulations accumulate plastic strains at strain rates comparable to experimental observations. Here, this paper investigates the viability of high order implicit time integrators and robust nonlinear solvers to reduce simulation run times while maintaining the accuracy of the computed solution. In particular, implicit Runge-Kutta time integrators are explored as a waymore » of providing greater accuracy over a larger time step than is typically done with the standard second-order trapezoidal method. In addition, both accelerated fixed point and Newton's method are investigated to provide fast and effective solves for the nonlinear systems that must be resolved within each time step. Results show that integrators of third order are the most effective, while accelerated fixed point and Newton's method both improve solver performance over the standard fixed point method used for the solution of the nonlinear systems.« less

  13. Implicit integration methods for dislocation dynamics

    SciTech Connect

    Gardner, D. J.; Woodward, C. S.; Reynolds, D. R.; Hommes, G.; Aubry, S.; Arsenlis, A.

    2015-01-20

    In dislocation dynamics simulations, strain hardening simulations require integrating stiff systems of ordinary differential equations in time with expensive force calculations, discontinuous topological events, and rapidly changing problem size. Current solvers in use often result in small time steps and long simulation times. Faster solvers may help dislocation dynamics simulations accumulate plastic strains at strain rates comparable to experimental observations. Here, this paper investigates the viability of high order implicit time integrators and robust nonlinear solvers to reduce simulation run times while maintaining the accuracy of the computed solution. In particular, implicit Runge-Kutta time integrators are explored as a way of providing greater accuracy over a larger time step than is typically done with the standard second-order trapezoidal method. In addition, both accelerated fixed point and Newton's method are investigated to provide fast and effective solves for the nonlinear systems that must be resolved within each time step. Results show that integrators of third order are the most effective, while accelerated fixed point and Newton's method both improve solver performance over the standard fixed point method used for the solution of the nonlinear systems.

  14. Congenital dislocation of the hip. A review.

    PubMed

    Sherk, H H; Pasquariello, P S; Watters, W C

    1981-08-01

    Congenital dislocation of the hip usually results from capsular stretching caused by fetal malposition and crouching late in the third trimester. Early recognition of hip dislocation or instability soon after birth permits prompt treatment. Ortolani's and Barlow's maneuvers, respectively, reduce into and displace from the acetabulum a femoral head that is insecurely contained therein. The diagnosis of CDH in the first month of life usually depends on these clinical components of the physical examination of the newborn, because similar device, in this age group can usually maintain the displaced hip in sufficient flexion and abduction to permit reduction and normal development. By 3 months of age, the nuclei of the pelvis and upper femur have ossified enough to permit radiologic diagnosis of CDH. Problems related to treatment increase as the child grows older. In infants up to 6 months of age, closed methods with a harness usually succeed. Beyond 6 months, the soft tissues shorten and prevent easy reduction. These patients almost always require pre-reduction traction. An adductor tenotomy also facilitates reduction and apparently lessens compressive forces on the femoral head, an important consideration in preventing avascular necrosis of the head. Children over 1 year old develop bony changes, such as excessive femoral valgus and anteversion and deformity of the acetabulum. Treatment in these patients requires realignment of bony deformities with femoral or pelvic osteotomies in addition to the measures noted previously. The gentleness and high success rate of early treatment make early diagnosis of CDH an important consideration in infants and newborns.

  15. Concept of healing of recurrent shoulder dislocation.

    PubMed

    D'Angelo, Donato

    2014-01-01

    This paper presents the main surgical techniques applied in the treatment of anterior recurrent shoulder dislocation, aiming the achievement of the normality of articulate movements. This was obtained by combining distinct surgical procedures, which allowed the recovery of a complete functional capacity of the shoulder, without jeopardizing the normality of movement, something that has not been recorded in the case of the tense sutures of the surgical procedures of Putti-Platt, Bankart, Latarjet, Dickson-O'Dell and others. The careful review of the methods applied supports the conclusion that recurrent shoulder dislocation can be cured, since cure has been obtained in 97% of the treated cases. However, some degree of limitation in the shoulder movement has been observed in most of the treated cases. Our main goal was to achieve a complete shoulder functional recovery, by treating simultaneously all of the anatomical-pathological lesions, without considering the so-called essential lesions. The period of post-operatory immobilization only last for the healing of soft parts; this takes place in a position of neutral shoulder rotation, since the use of vascular bone graft eliminates the need for long time immobilization, due to the shoulder stabilization provided by rigid fixation of the coracoid at the glenoid edge, as in the Latarjet's technique. Our procedure, used since 1959, comprises the association of several techniques, which has permitted shoulder healing without movement limitation. That was because of the tension reduction in the sutures of the subescapularis, capsule, and coracobraquialis muscles.

  16. Void growth by dislocation-loop emission

    NASA Astrophysics Data System (ADS)

    Ahn, D. C.; Sofronis, P.; Kumar, M.; Belak, J.; Minich, R.

    2007-03-01

    Experimental results from spall tests on aluminum reveal the presence of a dense dislocation structure in an annulus around a void that grew under the tensile pulse when a shock wave was reflected at the free surface of the specimen. The proposition is that dislocation emission from the void surface under load is a viable mechanism for void growth. To understand void growth in the absence of diffusive effects, the interstitial-loop emission mechanism under tensile hydrostatic stress is investigated. First, the micromechanics of pile-up formation when interstitial loops are emitted from a void under applied macroscopic loading is reviewed. Demand for surface energy expenditure upon void-surface change is taken into consideration. It is demonstrated that in face-centered cubic metals loop emission from voids with a radius of ˜10 nm is indeed energetically possible in the hydrostatic stress environment generated by shock loading. On the other hand, the levels of hydrostatic stress prevalent in common structural applications are not sufficient to drive loops at equilibrium positions above a ˜10 nm void. However, for voids larger than about 100 nm, the energetics of loop emission are easily met as a necessary condition even under the low stress environment prevalent in structural applications.

  17. Extensor Mechanism Disruption in Knee Dislocation.

    PubMed

    O'Malley, Michael; Reardon, Patrick; Pareek, Ayoosh; Krych, Aaron; Levy, Bruce A; Stuart, Michael J

    2016-05-01

    Disruption of the knee extensor mechanism is a challenging injury with no clear consensus on optimal treatment. Although rare in the setting of knee dislocations, these injuries should not be overlooked. Acute, complete rupture of either the quadriceps or patellar tendon necessitates primary repair with or without augmentation. Surgical management may also be required in the setting of a partial tear if a significant extensor lag is present or nonoperative treatment has failed. Tendon augmentation is used during primary repair if the native tissue is inadequate or after a failed primary repair. The purpose of this study is to evaluate extensor mechanism disruption incidence, injury patterns, associated injuries, and surgical options, including a novel tendon augmentation technique. This procedure consists of primary patellar or quadriceps tendon repair with semitendinosus autograft augmentation utilizing a distal or proximal patellar socket. Advantages of repair with tendon augmentation include accelerated rehabilitation, decreased risk of patellar fracture from transverse or longitudinal bone tunnels, and less hardware complications. We recommend consideration of this technique for selected cases of acute extensor mechanism disruption in the setting of tibiofemoral dislocation. PMID:26636488

  18. Novel Presentation of Uncommon Wrist Injury: Simultaneous Lunate and Perilunate Fracture Dislocation (scapho-capitate Syndrome) of Both Wrists

    PubMed Central

    Bhat, Anil K.; A, Nishanth; Acharya, Ashwath; Kumar, Yogesh

    2016-01-01

    Introduction: Perilunate and lunate dislocations are uncommon high energy injuries and have extensive soft tissue, cartilaginous and bony damage. The most common pattern is trans-scaphoid perilunate fracture dislocation which constitutes approximately 50% of these injuries. Unusual injury pattern like Scaphocapitate syndrome can occur with fracture through scaphoid waist and capitate that rotates the proximal capitate 180° so that its proximal articular surface points distally. With this case report, we would like to present a novel presentation of an uncommon wrist injury. Case report: We present a case of simultaneous lunate dislocation in one wrist and perilunate fracture dislocation (Scapho- capitate syndrome) in the contralateral wrist which occurred simultaneously in a young male following a two wheeler accident. The injury was missed initially at the primary treating centre. Upon diagnosis, the patient underwent open reduction and internal fixation along with ligament repair. The patient was subsequently followed up for a period of four years and was found to have very good clinical and radiological outcome. Conclusion: These injuries occurring simultaneously in contralateral wrists are exceptionally rare and unusual as the mechanisms of injury are different. These are high velocity injuries and are often missed, especially in presence of other major injuries. These high energy injuries need accurate diagnosis, early and aggressive treatment in order to prevent complications PMID:27703938

  19. Immigration, naturalization and the Constitution.

    PubMed

    Vecoli, R J

    1987-03-01

    This essay focuses upon major decisions made by the US government affecting aliens and the constitutional bases for them. These include: 1) the admission and exclusion of aliens, 2) the deportation of aliens, 3) the rights of aliens within the US, and 4) naturalization and denaturalization. The recourse to the extra-constitutional doctrine of sovereignty by the Supreme Court was the source of the plenary power of the Congress over immigration, thus denying the authority of the judiciary to extend the guarantees of due process of law and the equal protection of the law to aliens. The courts in the last 2 decades have assumed a more activist posture with respect to the rights of aliens, extending a greater degree of constitutional protection to the security of acquired citizenship and to the rights of due process and equal protection of foreigners, even to undocumented aliens.

  20. The Dislocated Worker: When Training Is Not Enough.

    ERIC Educational Resources Information Center

    Blong, John T.; Shultz, Rose M.

    1990-01-01

    Discusses the socioeconomic effects of plant closings, focusing on the problems faced by dislocated workers who lack the financial resources to complete a retraining program. Describes the Eastern Iowa Community College District's efforts to train and counsel dislocated workers through its Caterpillar Worker Assistance Center. (DMM)

  1. Effective mobility of dislocations from systematic coarse-graining

    NASA Astrophysics Data System (ADS)

    Kooiman, M.; Hütter, M.; Geers, MGD

    2015-06-01

    The dynamics of large amounts of dislocations governs the plastic response of crystalline materials. In this contribution we discuss the relation between the mobility of discrete dislocations and the resulting flow rule for coarse-grained dislocation densities. The mobilities used in literature on these levels are quite different, for example in terms of their intrinsic the stress dependence. To establish the relation across the scales, we have derived the macroscopic evolution equations of dislocation densities from the equations of motion of individual dislocations by means of systematic coarse-graining. From this, we can identify a memory kernel relating the driving force and the flux of dislocations. This kernel can be considered as an effective macroscopic mobility with two contributions; a direct contribution related to the overdamped motion of individual dislocations, and an emergent contribution that arises from time correlations of fluctuations in the Peach-Koehler force. Scaling analysis shows that the latter contribution is dominant for dislocations in metals at room temperature. We also discuss several concerns related to the separation of timescales.

  2. Dynamics of discrete screw dislocations on glide directions

    NASA Astrophysics Data System (ADS)

    Alicandro, R.; De Luca, L.; Garroni, A.; Ponsiglione, M.

    2016-07-01

    We consider a simple discrete model for screw dislocations in crystals. Using a variational discrete scheme we study the motion of a configuration of dislocations toward low energy configurations. We deduce an effective fully overdamped dynamics that follows the maximal dissipation criterion introduced in Cermelli and Gurtin (1999) and predicts motion along the glide directions of the crystal.

  3. A field theory of piezoelectric media containing dislocations

    SciTech Connect

    Taupin, V. Fressengeas, C.; Ventura, P.; Lebyodkin, M.

    2014-04-14

    A field theory is proposed to extend the standard piezoelectric framework for linear elastic solids by accounting for the presence and motion of dislocation fields and assessing their impact on the piezoelectric properties. The proposed theory describes the incompatible lattice distortion and residual piezoelectric polarization fields induced by dislocation ensembles, as well as the dynamic evolution of these fields through dislocation motion driven by coupled electro-mechanical loading. It is suggested that (i) dislocation mobility may be enhanced or inhibited by the electric field, depending on the polarity of the latter, (ii) plasticity mediated by dislocation motion allows capturing long-term time-dependent properties of piezoelectric polarization. Due to the continuity of the proposed electro-mechanical framework, the stress/strain and polarization fields are smooth even in the dislocation core regions. The theory is applied to gallium nitride layers for validation. The piezoelectric polarization fields associated with bulk screw/edge dislocations are retrieved and surface potential modulations are predicted. The results are extended to dislocation loops.

  4. [Dislocation-disassembly of bipolar hip arthroplasty--case report].

    PubMed

    Gagała, Jacek; Blacha, Jan

    2005-01-01

    Bipolar hip arthroplasty dislocation is rare. A case of bipolar hip arthroplasty dislocation in patient treated because of femoral neck fracture was described. Patient had neurological problems. The arthroplasty was made with posterolateral approach. Disassembly of bipolar prosthesis occurred during closed reduction. Open reduction with bipolar head exchange was necessary. To avoid this complication reduction should be made in anesthesia with muscles relaxation.

  5. Computation of the lattice Green function for a dislocation

    NASA Astrophysics Data System (ADS)

    Tan, Anne Marie Z.; Trinkle, Dallas R.

    2016-08-01

    Modeling isolated dislocations is challenging due to their long-ranged strain fields. Flexible boundary condition methods capture the correct long-range strain field of a defect by coupling the defect core to an infinite harmonic bulk through the lattice Green function (LGF). To improve the accuracy and efficiency of flexible boundary condition methods, we develop a numerical method to compute the LGF specifically for a dislocation geometry; in contrast to previous methods, where the LGF was computed for the perfect bulk as an approximation for the dislocation. Our approach directly accounts for the topology of a dislocation, and the errors in the LGF computation converge rapidly for edge dislocations in a simple cubic model system as well as in BCC Fe with an empirical potential. When used within the flexible boundary condition approach, the dislocation LGF relaxes dislocation core geometries in fewer iterations than when the perfect bulk LGF is used as an approximation for the dislocation, making a flexible boundary condition approach more efficient.

  6. Non-reducible palmar dislocation of the distal radioulnar joint

    PubMed Central

    Zannou, Rupestre S.; Rezzouk, Joel; Ruijs, Aleid C.J.

    2015-01-01

    Abstract A rare case of an isolated traumatic palmar dislocation of the distal radioulnar joint is presented. Clinically, there is a loss of pronation and supination. The dislocation was treated using an open reduction, reinsertion of the capsule-ligamentous complex and temporary stabilization using K-wires. PMID:26158121

  7. Acute shoulder and elbow dislocations in the athlete.

    PubMed

    Burra, Giridhar; Andrews, James R

    2002-07-01

    Dislocations of the elbow are less common than shoulder dislocations. The primary treatment is conservative, with a conscious effort toward early mobilization. Recurrence is rare, and improvement in function and motion can be expected for up to 1 year. Operative treatment should be reserved for baseball pitchers and cases of complex instability.

  8. High purity, low dislocation GaAs single crystals

    NASA Technical Reports Server (NTRS)

    Chen, R. T.; Holmes, D. E.; Kirkpatrick, C. G.

    1983-01-01

    Liquid encapsulated Czochralski crystal growth techniques for producing undoped, high resistivity, low dislocation material suitable for device applications is described. Technique development resulted in reduction of dislocation densities in 3 inch GaAs crystals. Control over the melt stoichiometry was determined to be of critical importance for the reduction of twinning and polycrystallinity during growth.

  9. Method to reduce dislocation density in silicon using stress

    DOEpatents

    Buonassisi, Anthony; Bertoni, Mariana; Argon, Ali; Castellanos, Sergio; Fecych, Alexandria; Powell, Douglas; Vogl, Michelle

    2013-03-05

    A crystalline material structure with reduced dislocation density and method of producing same is provided. The crystalline material structure is annealed at temperatures above the brittle-to-ductile transition temperature of the crystalline material structure. One or more stress elements are formed on the crystalline material structure so as to annihilate dislocations or to move them into less harmful locations.

  10. Dislocated ankle fracture complicated by near total distal ischaemia

    PubMed Central

    Duygun, Fatih; Sertkaya, Omer; Aldemir, Cengiz; Dogan, Ali

    2013-01-01

    Total arterial ischaemia is rarely seen following a dislocated ankle fracture but if it does and intervention is not made, it can lead to serious morbidity. We present a 39-year-old woman with almost total occlusion in the arteria tibialis and arteria dorsalis pedis following a dislocated ankle fracture as a result of a bicycle fall. PMID:24248319

  11. Moment tensors of a dislocation in a porous medium

    NASA Astrophysics Data System (ADS)

    Wang, Zhi; Hu, Hengshan

    2016-06-01

    A dislocation can be represented by a moment tensor for calculating seismic waves. However, the moment tensor expression was derived in an elastic medium and cannot completely describe a dislocation in a porous medium. In this paper, effective moment tensors of a dislocation in a porous medium are derived. It is found that the dislocation is equivalent to two independent moment tensors, i.e., the bulk moment tensor acting on the bulk of the porous medium and the isotropic fluid moment tensor acting on the pore fluid. Both of them are caused by the solid dislocation as well as the fluid-solid relative motion corresponding to fluid injection towards the surrounding rocks (or fluid outflow) through the fault plane. For a shear dislocation, the fluid moment tensor is zero, and the dislocation is equivalent to a double couple acting on the bulk; for an opening dislocation or fluid injection, the two moment tensors are needed to describe the source. The fluid moment tensor only affects the radiated compressional waves. By calculating the ratio of the radiation fields generated by unit fluid moment tensor and bulk moment tensor, it is found that the fast compressional wave radiated by the bulk moment tensor is much stronger than that radiated by the fluid moment tensor, while the slow compressional wave radiated by the fluid moment tensor is several times stronger than that radiated by the bulk moment tensor.

  12. Conservative treatment of the isolated dislocation of the pisiform bone.

    PubMed

    Saleh, Waleed Riad; Yajima, Hiroshi; Nakanishi, Akito

    2014-08-01

    We report isolated dislocation of the right pisiform bone dislocated distal and medial to the triquetrum bone in a young adult after a fall. Manipulation and closed reduction under intravenous regional anaesthesia resulted in full functional recovery and a good radiological outcome.

  13. The relationship between strain geometry and geometrically necessary dislocations

    NASA Astrophysics Data System (ADS)

    Hansen, Lars; Wallis, David

    2016-04-01

    The kinematics of past deformations are often a primary goal in structural analyses of strained rocks. Details of the strain geometry, in particular, can help distinguish hypotheses about large-scale tectonic phenomena. Microstructural indicators of strain geometry have been heavily utilized to investigate large-scale kinematics. However, many of the existing techniques require structures for which the initial morphology is known, and those structures must undergo the same deformation as imposed macroscopically. Many deformed rocks do not exhibit such convenient features, and therefore the strain geometry is often difficult (if not impossible) to ascertain. Alternatively, crystallographic textures contain information about the strain geometry, but the influence of strain geometry can be difficult to separate from other environmental factors that might affect slip system activity and therefore the textural evolution. Here we explore the ability for geometrically necessary dislocations to record information about the deformation geometry. It is well known that crystallographic slip due to the motion of dislocations yields macroscopic plastic strain, and the mathematics are established to relate dislocation glide on multiple slip systems to the strain tensor of a crystal. This theoretical description generally assumes that dislocations propagate across the entire crystal. However, at any point during the deformation, dislocations are present that have not fully transected the crystal, existing either as free dislocations or as dislocations organized into substructures like subgrain boundaries. These dislocations can remain in the lattice after deformation if the crystal is quenched sufficiently fast, and we hypothesize that this residual dislocation population can be linked to the plastic strain geometry in a quantitative manner. To test this hypothesis, we use high-resolution electron backscatter diffraction to measure lattice curvatures in experimentally deformed

  14. Dislocation of the distal radioulnar joint associated with a transstyloid radiocarpal fracture dislocation. A case report and review of the literature.

    PubMed

    Stoffelen, D; Fortems, Y; De Smet, L; Broos, P

    1996-03-01

    Dislocations of the distal radio-ulnar joint (DRUJ) can be isolated or combined with fractures. Cases of DRUJ dislocations have been described with Galleazi fractures, open radius and ulna fractures and intraarticular fractures of the distal radius. We report a case of a volar DRUJ dislocation combined with a transstyloid radio-carpal dislocation. Because of severe instability of the wrist, open reduction of the radial styloid combined with an open reduction of the dislocated DRUJ is advised. PMID:8669257

  15. Room-temperature dislocation climb in copper-niobium interfaces

    SciTech Connect

    Wang, Jian; Hoagland, Richard G; Hirth, John P; Misra, Amit

    2008-01-01

    Using atomistic simulations, we show that dislocations climb efficiently in metallic copper-niobium interfaces through absorption and emission of vacancies in the dislocation core, as well as an associated counter diffusion of Cu atoms in the interfacial plane. The high efficiency of dislocation climb in the interface is ascribed to the high vacancy concentration of 0.05 in the interfacial plane, the low formation energy of 0.12 e V with respect to removal or insertion of Cu atoms, as well as the low kinetic barrier of 0.10 eV for vacancy migration in the interfacial Cu plane. Dislocation climb in the interface facilitates reactions of interfacial dislocations, and enables interfaces to be in the equilibrium state with respect to concentrations ofpoint defects.

  16. Dislocation injection in strontium titanate by femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Titus, Michael S.; Echlin, McLean P.; Gumbsch, Peter; Pollock, Tresa M.

    2015-08-01

    Femtosecond laser ablation is used in applications which require low damage surface treatments, such as serial sectioning, spectroscopy, and micromachining. However, dislocations are generated by femtosecond laser-induced shockwaves and consequently have been studied in strontium titanate (STO) using transmission electron microscopy (TEM) and electron backscatter diffraction analysis. The laser ablated surfaces in STO exhibit dislocation structures that are indicative of those produced by uniaxial compressive loading. TEM analyses of dislocations present just below the ablated surface confirm the presence of ⟨110 ⟩ dislocations that are of approximately 35° mixed character. The penetration depth of the dislocations varied with grain orientation relative to the surface normal, with a maximum depth of 1.5 μm. Based on the critical resolved shear stress of STO crystals, the approximate shockwave pressures experienced beneath the laser irradiated surface are reported.

  17. Charge accumulation at a threading edge dislocation in gallium nitride

    SciTech Connect

    Leung, K.; Wright, A.F.; Stechel, E.B.

    1999-04-01

    We have performed Monte Carlo calculations to determine the charge accumulation on threading edge dislocations in GaN as a function of the dislocation density and background dopant density. Four possible core structures have been examined, each of which produces defect levels in the gap and may therefore act as electron or hole traps. Our results indicate that charge accumulation, and the resulting electrostatic interactions, can change the relative stabilities of the different core structures. Structures having Ga and N vacancies at the dislocation core are predicted to be stable under nitrogen-rich and gallium-rich growth conditions, respectively. Due to dopant depletion at high dislocation density and the multitude of charge states, the line charge exhibits complex crossover behavior as the dopant and dislocation densities vary. {copyright} {ital 1999 American Institute of Physics.}

  18. Scapular dislocation from trivial trauma: a rare case.

    PubMed

    Landge, Vikrant; Vaishya, Raju; Aggarwal, Anurag

    2012-01-01

    Dislocation of the scapula between the ribs and into the thoracic cage is a very rare event. Scapulothoracic dissociation though has been reported, usually occurs after a severe injury and is often associated with other serious injuries like brachial plexus or chest injury, etc. Ainscow has described a rare type that may occur due to slight violence with a pre-existing condition. Cases of isolated scapular dislocation after minor trauma have not been reported frequently in the literature. It is a distinct clinical entity and needs to be differentiated from other similar conditions. Here, we present a case of painless scapular dislocation associated with trivial trauma followed by spontaneous reduction in a 10 years old girl. The patient had a recurrence of the dislocation before presenting to us. But she did not have any pre-existing condition for scapular dislocation.

  19. Conservative Treatment of Carpometacarpal Dislocation of the Three Last Fingers

    PubMed Central

    2016-01-01

    Posterior carpometacarpal (CMC) dislocation is a rare condition. Treatment is usually surgical though no strict consensus can be found upon literature review. If diagnosed early and no associated fractures are found, CMC dislocation could benefit from conservative treatment comprising closed reduction and splint immobilisation. We report the case of a 26-year-old man diagnosed with a posterior dislocation of the third, fourth, and fifth CMC joints after a fall of 1.5 meters, treated by external reduction under procedural sedation and immobilisation with a cast for 6 weeks. Evolution was excellent with no relapse observed during follow-up. Our aim is to increase physician awareness of CMC dislocation so that they seek this injury in the emergency department. Unrecognised CMC dislocation can lead to neurovascular injuries as well as chronic instability and early articular degeneration. PMID:27703817

  20. Second yield via dislocation-induced premelting in copper

    NASA Astrophysics Data System (ADS)

    Wang, L.; Cai, Y.; He, A. M.; Luo, S. N.

    2016-05-01

    Premelting or virtual melting was proposed previously as an important deformation mechanism for high strain-rate loading. However, two questions remain outstanding: how premelting occurs exactly, and whether it plays a role in plastic deformation independent of, parasitic on, or synergetic with, dislocation motion. By virtue of double-shock compression, our large-scale molecular dynamics simulations reveal two yields in single-crystal copper, with the first yield achieved via dislocation motion, and the second, via dislocation-induced premelting as well. The clean capture of melting during dislocation motion suggests that premelting occurs on slip planes and at their intersections, facilitating gliding and leading to yield together with dislocation motion.

  1. Ripple dislocation slip in wrinkled gold film deposited on polydimethylsiloxane

    NASA Astrophysics Data System (ADS)

    Lin, C. B.; Chuang, Y. F.; Liu, Y. H.; Lee, Sanboh; Chou, Y. T.

    2011-07-01

    The motion of ripple dislocations in a wrinkled thin film of gold deposited on polydimethylsiloxane (PDMS) was investigated. The deposition was made under tensile load along the first direction on the PDMS plate. After the tensile load was released, a ripple pattern and ripple dislocations were formed on the surface. Upon reloading in the second direction, these ripple dislocations were able to slip. At a given tensile load, the speed of slip decreased as the loading time increased, and finally reached a constant value, which was increasing with the applied load. The measured data were interpreted with a dynamic model based on Newton's law of motion. Interaction of ripple dislocations was also observed. It was shown that a pair of positive and negative ripple dislocations of equal strength could annihilate each other or form a dipole, depending on the magnitude of the applied load.

  2. Neglected Posterior Dislocation of Hip in Children - A Case Report

    PubMed Central

    Pal, Chandra Prakash; Kumar, Deepak; Sadana, Ashwani; Dinkar, Karuna Shankar

    2014-01-01

    Introduction: Traumatic dislocation of the hip in children is a rare injury. We report the outcome of 2 patients of neglected hip dislocation which were treated by open reduction and internal fixation by k-wires. Case Report: We treat 2 children both girls (one was of 4 years and other was 7 years of age). In both cases dislocation was unilateral and was not associated with any facture. Both cases were of posterior dislocation. in both cases open reduction and internal fixation was done by k wires. Hip spica was applied post operatively in both cases. The k wire was removed at 3 to 4 weeks. Patients were allowed to bear weight from gradual to full weight bearing after 6 weeks. Conclusion: We conclude that open reduction is a satisfactory treatment for neglected hip dislocation. It prevents not only deformity but also maintains limb length. PMID:27298953

  3. Constitutional Reform of School Finance.

    ERIC Educational Resources Information Center

    Alexander, Kern, Ed.; Jordan, K. Forbis, Ed.

    This book contains conference papers by experts in educational administration, law, and economics. Six of the papers are devoted to a legal analysis of fiscal inequality among school attendance units, school districts, and States. These contributions are: (1) K. Forbis Jordan and Kern Alexander, "Constitutional Methods of Financing Public…

  4. Civil Liberties under State Constitutions.

    ERIC Educational Resources Information Center

    Tarr, G. Alan

    1988-01-01

    Discusses "new judicial federalism" as the rediscovery of state bills of rights for protecting civil liberties. Analyzes the differences in protection under state and federal bills of rights. Recommends that the growing importance of state constitutions be included in the political science curriculum and suggests bibliographic sources to be used.…

  5. Take Advantage of Constitution Day

    ERIC Educational Resources Information Center

    McCune, Bonnie F.

    2008-01-01

    The announcement of the mandate for Constitution and Citizenship Day shortly before September, 2005, probably led to groans of dismay. Not another "must-do" for teachers and schools already stressed by federal and state requirements for standardized tests, increasingly rigid curricula, and scrutiny from the public and officials. But the idea and…

  6. Lazy Elephants and the Constitution.

    ERIC Educational Resources Information Center

    Hantula, James

    1989-01-01

    Depicts an eighth grade unit utilizing the production of a newspaper to teach U.S. history, 1787 to 1791, in a combined social studies and language arts class at Malcolm Price Laboratory School (Iowa). Two teachers used both large- and small-group instruction to focus on the development of the U.S. Constitution. (LS)

  7. Comparison of dislocation density tensor fields derived from discrete dislocation dynamics and crystal plasticity simulations of torsion

    DOE PAGESBeta

    Jones, Reese E.; Zimmerman, Jonathan A.; Po, Giacomo; Mandadapu, Kranthi

    2016-02-01

    Accurate simulation of the plastic deformation of ductile metals is important to the design of structures and components to performance and failure criteria. Many techniques exist that address the length scales relevant to deformation processes, including dislocation dynamics (DD), which models the interaction and evolution of discrete dislocation line segments, and crystal plasticity (CP), which incorporates the crystalline nature and restricted motion of dislocations into a higher scale continuous field framework. While these two methods are conceptually related, there have been only nominal efforts focused at the global material response that use DD-generated information to enhance the fidelity of CPmore » models. To ascertain to what degree the predictions of CP are consistent with those of DD, we compare their global and microstructural response in a number of deformation modes. After using nominally homogeneous compression and shear deformation dislocation dynamics simulations to calibrate crystal plasticity ow rule parameters, we compare not only the system-level stress-strain response of prismatic wires in torsion but also the resulting geometrically necessary dislocation density fields. To establish a connection between explicit description of dislocations and the continuum assumed with crystal plasticity simulations we ascertain the minimum length-scale at which meaningful dislocation density fields appear. Furthermore, our results show that, for the case of torsion, that the two material models can produce comparable spatial dislocation density distributions.« less

  8. A Comparison of Starting Wages and Job Satisfaction for Reemployed Dislocated Workers Participating in the Rock County Dislocated Worker Program.

    ERIC Educational Resources Information Center

    Borremans, Robert T.

    Following the economic recession of the early 1980's and the consequent high levels of unemployment in Rock County, a program was created at the Blackhawk Technical Institute (BTI) to assist dislocated workers reentering the labor force. The Rock County Dislocated Worker Program was intended as a comprehensive program with two principal activities…

  9. Dislocation-induced chirality of semiconductor nanocrystals.

    PubMed

    Baimuratov, Anvar S; Rukhlenko, Ivan D; Gun'ko, Yurii K; Baranov, Alexander V; Fedorov, Anatoly V

    2015-03-11

    Optical activity is a common natural phenomenon, which occurs in individual molecules, biomolecules, biological species, crystalline solids, liquid crystals, and various nanosized objects, leading to numerous important applications in almost every field of modern science and technology. Because this activity can hardly be altered, creation of artificial active media with controllable optical properties is of paramount importance. Here, for the first time to the best of our knowledge, we theoretically demonstrate that optical activity can be inherent to many semiconductor nanowires, as it is induced by chiral dislocations naturally developing during their growth. By assembling such nanowires in two- or three-dimensional periodic lattices, one can create optically active quantum supercrystals whose activity can be varied in many ways owing to the size quantization of the nanowires' energy spectra. We believe that this research is of particular importance for the future development of semiconducting nanomaterials and their applications in nanotechnology, chemistry, biology, and medicine.

  10. Painful Spastic Hip Dislocation: Proximal Femoral Resection

    PubMed Central

    Albiñana, Javier; Gonzalez-Moran, Gaspar

    2002-01-01

    The dislocated hip in a non-ambulatory child with spastic paresis tends to be a painful interference to sleep, sitting upright, and perineal care. Proximal femoral resection-interposition arthroplasty is one method of treatment for this condition. We reviewed eight hips, two bilateral cases, with a mean follow-up of 30 months. Clinical improvement was observed in all except one case, with respect to pain relief and sitting tolerance. Some proximal migration was observed in three cases, despite routine post-operative skeletal traction in all cases and careful soft tissue interposition. One case showed significant heterotopic ossification which restricted prolonged sitting. This patient needed some occasional medication for pain. PMID:12180614

  11. Density-based parallel skin lesion border detection with webCL

    PubMed Central

    2015-01-01

    Background Dermoscopy is a highly effective and noninvasive imaging technique used in diagnosis of melanoma and other pigmented skin lesions. Many aspects of the lesion under consideration are defined in relation to the lesion border. This makes border detection one of the most important steps in dermoscopic image analysis. In current practice, dermatologists often delineate borders through a hand drawn representation based upon visual inspection. Due to the subjective nature of this technique, intra- and inter-observer variations are common. Because of this, the automated assessment of lesion borders in dermoscopic images has become an important area of study. Methods Fast density based skin lesion border detection method has been implemented in parallel with a new parallel technology called WebCL. WebCL utilizes client side computing capabilities to use available hardware resources such as multi cores and GPUs. Developed WebCL-parallel density based skin lesion border detection method runs efficiently from internet browsers. Results Previous research indicates that one of the highest accuracy rates can be achieved using density based clustering techniques for skin lesion border detection. While these algorithms do have unfavorable time complexities, this effect could be mitigated when implemented in parallel. In this study, density based clustering technique for skin lesion border detection is parallelized and redesigned to run very efficiently on the heterogeneous platforms (e.g. tablets, SmartPhones, multi-core CPUs, GPUs, and fully-integrated Accelerated Processing Units) by transforming the technique into a series of independent concurrent operations. Heterogeneous computing is adopted to support accessibility, portability and multi-device use in the clinical settings. For this, we used WebCL, an emerging technology that enables a HTML5 Web browser to execute code in parallel for heterogeneous platforms. We depicted WebCL and our parallel algorithm design. In

  12. Sex Differences in Constitutive Autophagy

    PubMed Central

    Oliván, Sara; Calvo, Ana Cristina; Manzano, Raquel; Zaragoza, Pilar

    2014-01-01

    Sex bias has been described nowadays in biomedical research on animal models, although sexual dimorphism has been confirmed widely under pathological and physiological conditions. The main objective of our work was to study the sex differences in constitutive autophagy in spinal cord and skeletal muscle tissue from wild type mice. To examine the influence of sex on autophagy, mRNA and proteins were extracted from male and female mice tissues. The expressions of microtubule-associated protein 1 light chain 3 (LC3) and sequestosome 1 (p62), markers to monitor autophagy, were analyzed at 40, 60, 90, and 120 days of age. We found significant sex differences in the expression of LC3 and p62 in both tissues at these ages. The results indicated that sex and tissue specific differences exist in constitutive autophagy. These data underlined the need to include both sexes in the experimental groups to minimize any sex bias. PMID:24719882

  13. Period-doubling reconstructions of semiconductor partial dislocations

    SciTech Connect

    Park, Ji -Sang; Huang, Bing; Wei, Su -Huai; Kang, Joongoo; McMahon, William E.

    2015-09-18

    Atomic-scale understanding and control of dislocation cores is of great technological importance, because they act as recombination centers for charge carriers in optoelectronic devices. Using hybrid density-functional calculations, we present period-doubling reconstructions of a 90° partial dislocation in GaAs, for which the periodicity of like-atom dimers along the dislocation line varies from one to two, to four dimers. The electronic properties of a dislocation change drastically with each period doubling. The dimers in the single-period dislocation are able to interact, to form a dispersive one-dimensional band with deep-gap states. However, the inter-dimer interaction for the double-period dislocation becomes significantly reduced; hence, it is free of mid-gap states. The Ga core undergoes a further period-doubling transition to a quadruple-period reconstruction induced by the formation of small hole polarons. Lastly, the competition between these dislocation phases suggests a new passivation strategy via population manipulation of the detrimental single-period phase.

  14. Period-doubling reconstructions of semiconductor partial dislocations

    DOE PAGESBeta

    Park, Ji -Sang; Huang, Bing; Wei, Su -Huai; Kang, Joongoo; McMahon, William E.

    2015-09-18

    Atomic-scale understanding and control of dislocation cores is of great technological importance, because they act as recombination centers for charge carriers in optoelectronic devices. Using hybrid density-functional calculations, we present period-doubling reconstructions of a 90° partial dislocation in GaAs, for which the periodicity of like-atom dimers along the dislocation line varies from one to two, to four dimers. The electronic properties of a dislocation change drastically with each period doubling. The dimers in the single-period dislocation are able to interact, to form a dispersive one-dimensional band with deep-gap states. However, the inter-dimer interaction for the double-period dislocation becomes significantly reduced;more » hence, it is free of mid-gap states. The Ga core undergoes a further period-doubling transition to a quadruple-period reconstruction induced by the formation of small hole polarons. Lastly, the competition between these dislocation phases suggests a new passivation strategy via population manipulation of the detrimental single-period phase.« less

  15. On the electronic properties of a single dislocation

    SciTech Connect

    Reiche, Manfred Erfurth, Wilfried; Pippel, Eckhard; Sklarek, Kornelia; Blumtritt, Horst; Haehnel, Angelika; Kittler, Martin

    2014-05-21

    A detailed knowledge of the electronic properties of individual dislocations is necessary for next generation nanodevices. Dislocations are fundamental crystal defects controlling the growth of different nanostructures (nanowires) or appear during device processing. We present a method to record electric properties of single dislocations in thin silicon layers. Results of measurements on single screw dislocations are shown for the first time. Assuming a cross-section area of the dislocation core of about 1 nm{sup 2}, the current density through a single dislocation is J = 3.8 × 10{sup 12} A/cm{sup 2} corresponding to a resistivity of ρ ≅ 1 × 10{sup −8} Ω cm. This is about eight orders of magnitude lower than the surrounding silicon matrix. The reason of the supermetallic behavior is the high strain in the cores of the dissociated dislocations modifying the local band structure resulting in high conductive carrier channels along defect cores.

  16. A Conservative Surgical Approach in the Management of Longstanding Chronic Protracted Temporomandibular Joint Dislocation: A Case Report and Review of Literature.

    PubMed

    Jeyaraj, Priya; Chakranarayan, Ashish

    2016-07-01

    Chronic protracted dislocation of the TMJ is a relatively uncommon but extremely unpleasant and distressing condition for a patient. It is also particularly challenging and difficult to treat as it worsens with time due to continuing spasm of the masticatory muscles and progressive fibrosis, adhesions and consolidation in and around the dislocated joint. No definite guidelines or treatment protocols have been laid down in literature till date, towards management of such dislocations. A range of extensive and invasive surgical procedures such as eminectomy, condylectomy, menisectomy, and various osteotomies of the mandibular ramus and body have been performed to reduce these dislocations. A chronic longstanding unilateral TMJ dislocation in a 64-year-old woman was managed successfully and effectively using a modified, rather conservative surgical technique. The aim was to reduce the dislocated condyle (without excessive manipulation of the intra-articular space or extra-articular joint components); and at the same time, to limit further excessive translation of the condyle and restore physiological TMJ biomechanical constraints, to prevent future recurrence. This was achieved by surgically exposing the dislocated joint and manipulating the anterosuperiorly positioned condyle back into the glenoid fossa, aided by a downward distraction of the mandible; followed by soft tissue tethering of the meniscus and fibrous capsule of the joint to the temporal fascia above. The procedure yielded excellent results without any functional limitations or recurrence, and can hence constitute a viable and effective treatment option which can be attempted prior to resorting to the more invasive surgical procedures as described in literature. PMID:27408471

  17. [Women, gender, and the Constitution].

    PubMed

    1993-12-01

    Although all the constitutions of Latin America directly or indirectly acknowledge the juridical equality of the sexes, these patriarchal societies continue to maintain institutional power in male hands and to neutralize legal actions favoring women. International instruments such as the Convention on Elimination of All Forms of Discrimination Against Women, approved by the UN in 1979, have given a firmer basis to policies and actions to improve the status of women. Obstacles to full equality of Latin American women are rooted in economic and sociopolitical factors, but lack of true political will also plays a significant role. A number of new laws in the past several years as well as the new Constitution have improved the legal position of Colombian women. The new Constitution recognizes fundamental rights that may be claimed directly before a judge, and social, economic, and collective rights requiring legislative development. Article 43 of the new Constitution states that women will not be subjected to any form of discrimination. Another norm states that women will enjoy special assistance and protection before and after childbirth, in recognition of the social functions of maternity. Article 43 also states that women who are heads of households will receive special assistance, but the corresponding regulations have not yet been promulgated. The mechanism of tutelage has become an important recourse that has been used in several cases in which fundamental rights of women have been violated or threatened because of their sex. The order of tutelage has been used in cases of adolescents expelled from school for pregnancy and of abused wives, as well as to force recognition of the social and economic contributions of housework.

  18. [Women, gender, and the Constitution].

    PubMed

    1993-12-01

    Although all the constitutions of Latin America directly or indirectly acknowledge the juridical equality of the sexes, these patriarchal societies continue to maintain institutional power in male hands and to neutralize legal actions favoring women. International instruments such as the Convention on Elimination of All Forms of Discrimination Against Women, approved by the UN in 1979, have given a firmer basis to policies and actions to improve the status of women. Obstacles to full equality of Latin American women are rooted in economic and sociopolitical factors, but lack of true political will also plays a significant role. A number of new laws in the past several years as well as the new Constitution have improved the legal position of Colombian women. The new Constitution recognizes fundamental rights that may be claimed directly before a judge, and social, economic, and collective rights requiring legislative development. Article 43 of the new Constitution states that women will not be subjected to any form of discrimination. Another norm states that women will enjoy special assistance and protection before and after childbirth, in recognition of the social functions of maternity. Article 43 also states that women who are heads of households will receive special assistance, but the corresponding regulations have not yet been promulgated. The mechanism of tutelage has become an important recourse that has been used in several cases in which fundamental rights of women have been violated or threatened because of their sex. The order of tutelage has been used in cases of adolescents expelled from school for pregnancy and of abused wives, as well as to force recognition of the social and economic contributions of housework. PMID:12287889

  19. Constitutive Law and Flow Mechanism in Diamond Deformation

    DOE PAGESBeta

    Yu, Xiaohui; Raterron, Paul; Zhang, Jianzhong; Lin, Zhijun; Wang, Liping; Zhao, Yusheng

    2012-11-19

    Constitutive laws and crystal plasticity in diamond deformation have been the subjects of substantial interest since synthetic diamond was made in 1950's. To date, however, little is known quantitatively regarding its brittle-ductile properties and yield strength at high temperatures. In this paper, we report, for the first time, the strain-stress constitutive relations and experimental demonstration of deformation mechanisms under confined high pressure. The deformation at room temperature is essentially brittle, cataclastic, and mostly accommodated by fracturing on {111} plane with no plastic yielding at uniaxial strains up to 15%. At elevated temperatures of 1000°C and 1200°C diamond crystals exhibit significantmore » ductile flow with corresponding yield strength of 7.9 and 6.3 GPa, indicating that diamond starts to weaken when temperature is over 1000°C. Finally, at high temperature the plastic deformation and ductile flow is meditated by the <110>{111} dislocation glide and a very active {111} micro-twinning.« less

  20. Constitutive Law and Flow Mechanism in Diamond Deformation

    SciTech Connect

    Yu, Xiaohui; Raterron, Paul; Zhang, Jianzhong; Lin, Zhijun; Wang, Liping; Zhao, Yusheng

    2012-11-19

    Constitutive laws and crystal plasticity in diamond deformation have been the subjects of substantial interest since synthetic diamond was made in 1950's. To date, however, little is known quantitatively regarding its brittle-ductile properties and yield strength at high temperatures. In this paper, we report, for the first time, the strain-stress constitutive relations and experimental demonstration of deformation mechanisms under confined high pressure. The deformation at room temperature is essentially brittle, cataclastic, and mostly accommodated by fracturing on {111} plane with no plastic yielding at uniaxial strains up to 15%. At elevated temperatures of 1000°C and 1200°C diamond crystals exhibit significant ductile flow with corresponding yield strength of 7.9 and 6.3 GPa, indicating that diamond starts to weaken when temperature is over 1000°C. Finally, at high temperature the plastic deformation and ductile flow is meditated by the <110>{111} dislocation glide and a very active {111} micro-twinning.

  1. Constitutive modeling for isotropic materials

    NASA Technical Reports Server (NTRS)

    Chan, K. S.; Lindholm, U. S.; Bodner, S. R.

    1988-01-01

    The third and fourth years of a 4-year research program, part of the NASA HOST Program, are described. The program goals were: (1) to develop and validate unified constitutive models for isotropic materials, and (2) to demonstrate their usefulness for structural analysis of hot section components of gas turbine engines. The unified models selected for development and evaluation were those of Bodner-Partom and of Walker. The unified approach for elastic-viscoplastic constitutive equations is a viable method for representing and predicting material response characteristics in the range where strain rate and temperature dependent inelastic deformations are experienced. This conclusion is reached by extensive comparison of model calculations against the experimental results of a test program of two high temperature Ni-base alloys, B1900+Hf and Mar-M247, over a wide temperature range for a variety of deformation and thermal histories including uniaxial, multiaxial, and thermomechanical loading paths. The applicability of the Bodner-Partom and the Walker models for structural applications has been demonstrated by implementing these models into the MARC finite element code and by performing a number of analyses including thermomechanical histories on components of hot sections of gas turbine engines and benchmark notch tensile specimens. The results of the 4-year program have been published in four annual reports. The results of the base program are summarized in this report. The tasks covered include: (1) development of material test procedures, (2) thermal history effects, and (3) verification of the constitutive model for an alternative material.

  2. Strength and Dislocation Structure Evolution of Small Metals under Vibrations

    NASA Astrophysics Data System (ADS)

    Ngan, Alfonso

    2015-03-01

    It is well-known that ultrasonic vibration can soften metals, and this phenomenon has been widely exploited in industrial applications concerning metal forming and bonding. In this work, we explore the effects of a superimposed small oscillatory load on metal plasticity, from the nano- to macro-size range, and from audible to ultrasonic frequency ranges. Macroscopic and nano-indentation were performed on aluminum, copper and molybdenum, and the results show that the simultaneous application of oscillatory stresses can lower the hardness of these samples. More interestingly, EBSD and TEM observations show that subgrain formation and reduction in dislocation density generally occurred when stress oscillations were applied. These findings point to an important knowledge gap in metal plasticity - the existing understanding of ultrasound softening in terms of the vibrations either imposing additional stress waves to augment the quasi-static applied load, or heating up the metal, whereas the metal's intrinsic deformation resistance or dislocation interactive processes are assumed unaltered by the ultrasound, is proven wrong by the present results. Furthermore, in the case of nanoindentation, the Continuous Stiffness Measurement technique for contact stiffness measurement assumes that the imposed signal-carrier oscillations do not intrinsically alter the material properties of the specimen, and again, the present results prove that this can be wrong. To understand the enhanced subgrain formation and dislocation annihilation, Discrete Dislocation Dynamics (DDD) simulations were carried out and these show that when an oscillatory stress is superimposed on a quasi-static applied stress, reversals of motion of dislocations may occur, and these allow the dislocations to revisit repeatedly suitable configurations for annihilation. DDD, however, was unable to predict the observed subgrain formation presumably because the number of dislocations that can be handled is not large

  3. Dislocation following total knee arthroplasty: A report of six cases

    PubMed Central

    Villanueva, Manuel; Ríos-Luna, Antonio; Pereiro, Javier; Fahandez-Saddi, Homid; Pérez-Caballer, Antonio

    2010-01-01

    Background: Dislocation following total knee arthroplasty (TKA) is the worst form of instability. The incidence is from 0.15 to 0.5%. We report six cases of TKA dislocation and analyze the patterns of dislocation and the factors related to each of them. Materials and Methods: Six patients with dislocation of knee following TKA are reported. The causes for the dislocations were an imbalance of the flexion gap (n=4), an inadequate selection of implants (n=1), malrotation of components (n=1) leading to incompetence of the extensor mechanism, or rupture of the medial collateral ligament (MCC). The patients presented complained of pain, giving way episodes, joint effusion and difficulty in climbing stairs. Five patients suffered posterior dislocation while one anterior dislocation. An urgent closed reduction of dislocation was performed under general anaesthesia in all patients. All patients were operated for residual instability by revision arthroplasty after a period of conservative treatment. Results: One patient had deep infection and knee was arthrodesed. Two patients have a minimal residual lag for active extension, including a patient with a previous patellectomy. Result was considered excellent or good in four cases and fair in one, without residual instability. Five out of six patients in our series had a cruciate retaining (CR) TKA designs: four were revised to a posterior stabilized (PS) TKA and one to a rotating hinge design because of the presence of a ruptured MCL. Conclusion: Further episodes of dislocation or instability will be prevented by identifying and treating major causes of instability. The increase in the level of constraint and correction of previous technical mistakes is mandatory. PMID:20924487

  4. Galeazzi fracture with volar dislocation of the distal radioulnar joint.

    PubMed

    Kim, Suezie; Ward, James P; Rettig, Michael E

    2012-11-01

    Galeazzi fracture dislocations are fractures of the distal one-third of the radial diaphysis with traumatic disruption of the distal radioulnar joint (DRUJ). This injury results in subluxation or dislocation of the ulnar head. We present a case of a Galeazzi fracture with a volar dislocation of the DRUJ. Open reduction of the DRUJ with Kirschner wire fixation in pronation was necessary to reduce the joint and maintain anatomic alignment. Repair of the triangular fibrocartilage complex was also necessary to maintain stability of the DRUJ.

  5. Dislocations in extruded Co-49.3 at. pct Al

    NASA Technical Reports Server (NTRS)

    Yaney, D. L.; Nix, W. D.; Pelton, A. R.

    1986-01-01

    Polycrystalline Co-49.3 at. pct Al, which had been extruded at 1505 K, was examined using transmission electron microscopy. Diffraction contrast analysis showed that b = 100 as well as b = 111 line dislocations contribute to elevated temperature deformation in CoAl. Therefore, it was concluded that sufficient slip systems exist in CoAl to allow for general plasticity in the absence of diffusional mechanisms. Line dislocations of the type b = 001 were observed on both 110 and 100 planes while b = 111 line dislocations were observed on 1 -1 0 planes.

  6. The dislocation free zone model of fracture by symbolic programming

    SciTech Connect

    Chang, Shih-Jung

    1997-09-01

    The dislocation free zone (DFZ) model of fracture was developed by Chang and Ohr after a series of experimental observations on the crack tip dislocation structures that invariably showed the existence of the dislocation free region. The DFZ model is a modified BCS crack model that is supplemented with the Rice-Thomson crack tip dislocation emission mechanism. This dislocation emission mechanism imposes a finite energy barrier to the crack tip for emitting dislocations into the plastic zone, in contrast to a zero energy barrier for the BCS model. This finite energy barrier results in the formation of the DFZ and a stress-singular crack tip region. This resistance was expressed in terms of a dislocation emission toughness K{sub e} as a material constant. Because of the emission toughness K{sub e} the crack tip has the choice either to emit dislocation or to fracture in brittle mode. The model, therefore, was first used to explain the fundamental phenomenon of brittle versus ductile fracture. Brittle fracture occurs if K{sub Ic} < K{sub e}, that is, the crack tip breaks before the dislocation can be emitted. Ductile fracture is possible if K{sub Ic} > K{sub e} so that dislocation will be generated before brittle fracture toughness K{sub Ic} is reached. The distribution function for the dislocations was solved from the dislocation pile-up equation. It was expressed in terms of the complete elliptic integrals. Although the analytical nature of the model is clear and precise, the numerical values of the model may not always be obtained readily. Attempts have been made to simplify and approximate the model by elementary mathematical functions. In this paper the distribution function is written in terms of a symbolic programming language MAPLE. The analytical and numerical manipulations can be made easily. An improvement of the program that accounts for the technique of calculating the elliptic integral of the third kind in different regions of the model is presented here.

  7. Role of oxygen at screw dislocations in GaN.

    PubMed

    Arslan, I; Browning, N D

    2003-10-17

    Here we report the first direct atomic scale experimental observations of oxygen segregation to screw dislocations in GaN using correlated techniques in the scanning transmission electron microscope. The amount of oxygen present in each of the three distinct types of screw dislocation core is found to depend on the evolution and structure of the core, and thus gives rise to a varying concentration of localized states in the band gap. Contrary to previous theoretical predictions, the substitution of oxygen for nitrogen is observed to extend over many monolayers for the open core dislocation. PMID:14611410

  8. Dynamic phases, pinning, and pattern formation for driven dislocation assemblies

    DOE PAGESBeta

    Zhou, Caizhi; Reichhardt, Charles; Olson Reichhardt, Cynthia J.; Beyerlein, Irene J.

    2015-01-23

    We examine driven dislocation assemblies and show that they can exhibit a set of dynamical phases remarkably similar to those of driven systems with quenched disorder such as vortices in superconductors, magnetic domain walls, and charge density wave materials. These phases include pinned-jammed, fluctuating, and dynamically ordered states, and each produces distinct dislocation patterns as well as specific features in the noise fluctuations and transport properties. Lastly, our work suggests that many of the results established for systems with quenched disorder undergoing plastic depinning transitions can be applied to dislocation systems, providing a new approach for understanding pattern formation andmore » dynamics in these systems.« less

  9. Dynamic phases, pinning, and pattern formation for driven dislocation assemblies

    SciTech Connect

    Zhou, Caizhi; Reichhardt, Charles; Olson Reichhardt, Cynthia J.; Beyerlein, Irene J.

    2015-01-23

    We examine driven dislocation assemblies and show that they can exhibit a set of dynamical phases remarkably similar to those of driven systems with quenched disorder such as vortices in superconductors, magnetic domain walls, and charge density wave materials. These phases include pinned-jammed, fluctuating, and dynamically ordered states, and each produces distinct dislocation patterns as well as specific features in the noise fluctuations and transport properties. Lastly, our work suggests that many of the results established for systems with quenched disorder undergoing plastic depinning transitions can be applied to dislocation systems, providing a new approach for understanding pattern formation and dynamics in these systems.

  10. Discrete dislocation dynamics study of strained-layer relaxation.

    PubMed

    Schwarz, K W

    2003-10-01

    Numerical simulations are performed to follow the evolution of an initial density of dislocation loops in an infinite strained layer to the point where the dislocations have stopped moving. Several unexpected results are obtained. First, many of the threading arms are either annihilated or prematurely immobilized by hardening interactions such as jogging and junction formation. Second, the remaining dislocation arms are eventually trapped by stress fluctuations that arise more from local overrelaxation than from the blocking mechanisms usually considered. Third, the degree of relaxation that can be attained depends strongly on the initial density of threading arms. PMID:14611535

  11. Concentric reduction of the dislocated hip: computed tomographic evaluation

    SciTech Connect

    Hernandez, R.J.

    1984-01-01

    Concentric reduction of a dislocated hip can be evaluated by anteroposterior views or linear tomography. Anterior relationships, however, may be difficult to evaluate from a frontal radiograph despite good visibility. Computed tomography (CT), because of its cross-sectional imaging capabilities, is superior in demonstrating these relationships. The CT appearance of two types of dislocations (posterior and lateral ) is described. A posterior dislocation should be suspected if the femoral metaphysis approximates the acetabulum, a mass projects behind the ischium, or the fat plane anterior to the gluteus maximus is deformed or displaced posteriorly.

  12. Management of arterial and venous injuries in the dislocated knee.

    PubMed

    Gray, John L; Cindric, Matthew

    2011-06-01

    Although uncommonly encountered, knee dislocation is frequently associated with major vascular injury. Serious injuries resulting in ischemia demand prompt recognition and efficient management to prevent devastating long-term sequelae. In this review, we detail mechanisms of knee dislocation and associated popliteal vascular injuries. Diagnostic modalities used to evaluate the extent of vascular injury are individually discussed. Appropriate initial management of vascular injuries is crucial and an algorithm for diagnosis and management will be reviewed. We elaborate on the salient points of vascular reconstruction in the context of the dislocated knee: surgical approach, conduct of the procedure, and adjunctive maneuvers are described.

  13. Discrete Dislocation Dynamics Study of Strained-Layer Relaxation

    NASA Astrophysics Data System (ADS)

    Schwarz, K. W.

    2003-10-01

    Numerical simulations are performed to follow the evolution of an initial density of dislocation loops in an infinite strained layer to the point where the dislocations have stopped moving. Several unexpected results are obtained. First, many of the threading arms are either annihilated or prematurely immobilized by hardening interactions such as jogging and junction formation. Second, the remaining dislocation arms are eventually trapped by stress fluctuations that arise more from local overrelaxation than from the blocking mechanisms usually considered. Third, the degree of relaxation that can be attained depends strongly on the initial density of threading arms.

  14. Tibial-talar dislocation without fracture: treatment principles and outcome.

    PubMed

    Finkemeier, C; Engebretsen, L; Gannon, J

    1995-01-01

    The incidence of tibial-talar dislocations without fracture is unknown and has been sparsely reported in the literature. The diagnosis of the injury is straightforward with the appropriate examination and roentgenograms. Good to excellent results can be achieved with open or closed dislocations treated by closed reduction and immobilization for 4-6 weeks. Although open dislocations require irrigation, debridement, and possibly delayed closure, controversy exists with regard to acute ligament repair. Because good to excellent results are possible without acute ligament repair, and delayed repair on reconstruction can be accomplished with good outcomes, we recommend treating these injuries without ligament repair.

  15. Simulation of the interaction between an edge dislocation and a 1 0 0 interstitial dislocation loop in -iron

    SciTech Connect

    Terentyev, Dmitry; Grammatikopoulos, P.; Bacon, D; Osetsky, Yu N

    2008-01-01

    Atomic-level simulations are used to investigate the interaction of an edge dislocation with h100i interstitial dislocation loops in airon at 300 K. Dislocation reactions are studied systematically for different loop positions and Burgers vector orientations, and results are compared for two different interatomic potentials. Reactions are wide-ranging and complex, but can be described in terms of conventional dislocation reactions in which Burgers vector is conserved. The fraction of interstitials left behind after dislocation breakaway varies from 25 to 100%. The nature of the reactions requiring high applied stress for breakaway is identified. The obstacle strengths of h100i loops, 1/2h111i loops and voids containing the same number (169) of point defects are compared. h100i loops with Burgers vector parallel to the dislocation glide plane are slightly stronger than h100i and 1/2h111i loops with inclined Burgers vector: voids are about 30% weaker than the stronger loops. However, small voids are stronger than small 1/2h111i loops. The complexity of some reactions and the variety of obstacle strengths poses a challenge for the development of continuum models of dislocation behaviour in irradiated iron. 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

  16. Density-based load estimation using two-dimensional finite element models: a parametric study.

    PubMed

    Bona, Max A; Martin, Larry D; Fischer, Kenneth J

    2006-08-01

    A parametric investigation was conducted to determine the effects on the load estimation method of varying: (1) the thickness of back-plates used in the two-dimensional finite element models of long bones, (2) the number of columns of nodes in the outer medial and lateral sections of the diaphysis to which the back-plate multipoint constraints are applied and (3) the region of bone used in the optimization procedure of the density-based load estimation technique. The study is performed using two-dimensional finite element models of the proximal femora of a chimpanzee, gorilla, lion and grizzly bear. It is shown that the density-based load estimation can be made more efficient and accurate by restricting the stimulus optimization region to the metaphysis/epiphysis. In addition, a simple method, based on the variation of diaphyseal cortical thickness, is developed for assigning the thickness to the back-plate. It is also shown that the number of columns of nodes used as multipoint constraints does not have a significant effect on the method. PMID:17132530

  17. The influence of the dislocation distribution heterogeneity degree on the formation of a non-misoriented dislocation cell substructures in f.c.c. metals

    NASA Astrophysics Data System (ADS)

    Cherepanov, D. N.; Selivanikova, O. V.; Matveev, M. V.

    2016-06-01

    Dislocation loops emitted by Frank-Reed source during crossing dislocations of the non-coplanar slip systems are accumulates jogs on the own dislocation line, resulting in the deceleration of the segments of dislocation loops with high jog density. As a result, bending around of the slowed segments the formation of dynamic dipoles in the shear zone occurs. In the present paper we consider formation mechanism of non-misoriented dislocation cell substructure during plastic deformation of f.c.c. metals and conclude that the increase in the degree heterogeneity of dislocation distribution leads to an increase in the jog density and reduce the mean value of arm dynamic dipoles.

  18. The Constitution: Perspectives on Contemporary American Democracy.

    ERIC Educational Resources Information Center

    Close Up Foundation, Arlington, VA.

    Four articles expressing the views of nine prominent United States citizens about the Constitution provide a context for reflecting on the meaning of the Constitution in present-day America. In "Why Has the Constitution Endured So Long?" Don Edwards, chairman of the House Civil and Constitutional Rights Subcommittee, discusses why the Constitution…

  19. Quantifying dislocation microstructure evolution and cyclic hardening in fatigued face-centered cubic single crystals

    NASA Astrophysics Data System (ADS)

    Hussein, Ahmed M.; El-Awady, Jaafar A.

    2016-06-01

    Discrete dislocation dynamics simulations were performed to investigate the dislocation microstructure evolution and cyclic hardening during the early stages of fatigue loading in nickel single crystals. The effects of the crystal size and initial dislocation densities on both the mechanical response and the evolution of dislocation microstructure were quantified. Crystals having an initial dislocation density of 1012 m-2 and diameter less than 2.0 μm do not show any dislocation density multiplication or cyclic hardening. In contrast, crystals having the same initial dislocation density and diameters larger than 2.0 μm show a significant dislocation density accumulation in the form of dislocation cell-like structures, even after only a few number of loading cycles. This dislocation density accumulation was also accompanied by considerable cyclic hardening. The dislocation cell size and its wall thickness increase with increasing crystal size. With increasing dislocation density the critical crystal size, at which dislocation cell-structures form, decreases. The information theoretic entropy is utilized as a metric to quantify the extent of dislocation patterning and the formation and evolution of dislocation cell structures over time. Cross-slip was found to play a dominant role in the dislocation cell-structure formation. Further insights on the mechanisms contributing to the observed behavior are presented and discussed.

  20. The effect of length scale on the determination of geometrically necessary dislocations via EBSD continuum dislocation microscopy.

    PubMed

    Ruggles, T J; Rampton, T M; Khosravani, A; Fullwood, D T

    2016-05-01

    Electron backscatter diffraction (EBSD) dislocation microscopy is an important, emerging field in metals characterization. Currently, calculation of geometrically necessary dislocation (GND) density is problematic because it has been shown to depend on the step size of the EBSD scan used to investigate the sample. This paper models the change in calculated GND density as a function of step size statistically. The model provides selection criteria for EBSD step size as well as an estimate of the total dislocation content. Evaluation of a heterogeneously deformed tantalum specimen is used to asses the method. PMID:26986021

  1. Microscopic Structure of Stepwise Threading Dislocation in 4H-SiC Substrate

    NASA Astrophysics Data System (ADS)

    Ishikawa, Yukari; Sugawara, Yoshihiro; Saitoh, Hiroaki; Danno, Katsunori; Suzuki, Hiroshi; Bessho, Takeshi; Kawai, Yoichiro; Shibata, Noriyoshi

    2012-04-01

    The dislocation structure that forms the caterpillar-shaped etch pit upon molten KOH etching is investigated by transmission electron microscopy employing a weak-beam dark-field method. The observed dislocation has the Burgers vector 1/3[bar 12bar 10], and its structure was transformed from a basal plane dislocation to a threading edge dislocation. In the basal plane dislocation region, it propagated parallel to the [10bar 10] direction. On the basis of the measured dislocation structure, the caterpillar pit formation is explained. The process of dislocation formation is discussed by analyzing the relationship between sample types and the detection of the caterpillar pits.

  2. Constitutive equations for solid propellants

    SciTech Connect

    Oezuepek, S.; Becker, E.B.

    1997-04-01

    Mechanical behavior of the Space Shuttle redesigned solid rocket motor (RSRM) propellant is studied from a phenomenological point of view. Motivated by the study of the experimental data three initially isotropic constitutive models have been developed. All models represent the effect of strain rate, superimposed hydrostatic pressure, and cyclic loading on the stress and dilatation response of the material. A particular emphasis is given to the prediction of volume dilatation. The model resulting in the best representation of the available data is calibrated using only a few tests. The predictions of the model are compared with experiments for several loading conditions not used in the calibration.

  3. Traumatic testicular dislocation a review of 36 cases.

    PubMed

    Kochakarn, W; Choonhaklai, V; Hotrapawanond, P; Muangman, V

    2000-02-01

    We retrospectively reviewed 36 patients who were treated in our institutes with traumatic testicular dislocation from 1975 to 1997. The mean patient age was 25 years old (18-38). Average time to present at the emergency room was 1 hour (0.5-6). Bilateral dislocation was found in thirty cases and unilateral dislocation was found in six cases. The sites of dislocation included: 34 cases (64 testes) at superficial inguinal area, one case (one testis) at acetabular area, and one case (one testis) at the perineal area. Closed reduction under general anesthesia was successful in 14 cases, open reduction after failed closed reduction in 10 cases, open exploration and repaired testis with reposition in 11 cases and orchiectomy only in one case. The overall results after treatment showed the normal size and position of the testis. PMID:10710892

  4. Plastic anisotropy and dislocation trajectory in BCC metals

    PubMed Central

    Dezerald, Lucile; Rodney, David; Clouet, Emmanuel; Ventelon, Lisa; Willaime, François

    2016-01-01

    Plasticity in body-centred cubic (BCC) metals at low temperatures is atypical, marked in particular by an anisotropic elastic limit in clear violation of the famous Schmid law applicable to most other metals. This effect is known to originate from the behaviour of the screw dislocations; however, the underlying physics has so far remained insufficiently understood to predict plastic anisotropy without adjustable parameters. Here we show that deviations from the Schmid law can be quantified from the deviations of the screw dislocation trajectory away from a straight path between equilibrium configurations, a consequence of the asymmetrical and metal-dependent potential energy landscape of the dislocation. We propose a modified parameter-free Schmid law, based on a projection of the applied stress on the curved trajectory, which compares well with experimental variations and first-principles calculations of the dislocation Peierls stress as a function of crystal orientation. PMID:27221965

  5. Dislocation Structure and Mobility in hcp ^{4}He.

    PubMed

    Landinez Borda, Edgar Josué; Cai, Wei; de Koning, Maurice

    2016-07-22

    Using path-integral Monte Carlo simulations, we assess the core structure and mobility of the screw and edge basal-plane dislocations in hcp ^{4}He. Our findings provide key insights into recent interpretations of giant plasticity and mass flow junction experiments. First, both dislocations are dissociated into nonsuperfluid Shockley partial dislocations separated by ribbons of stacking fault, suggesting that they are unlikely to act as one-dimensional channels that may display Lüttinger-liquid-like behavior. Second, the centroid positions of the partial cores are found to fluctuate substantially, even in the absence of applied shear stresses. This implies that the lattice resistance to motion of the partial dislocations is negligible, consistent with the recent experimental observations of giant plasticity. Further results indicate that both the structure of the partial cores and the zero-point fluctuations play a role in this extreme mobility. PMID:27494477

  6. Measuring surface dislocation nucleation in defect-scarce nanostructures.

    PubMed

    Chen, Lisa Y; He, Mo-rigen; Shin, Jungho; Richter, Gunther; Gianola, Daniel S

    2015-07-01

    Linear defects in crystalline materials, known as dislocations, are central to the understanding of plastic deformation and mechanical strength, as well as control of performance in a variety of electronic and photonic materials. Despite nearly a century of research on dislocation structure and interactions, measurements of the energetics and kinetics of dislocation nucleation have not been possible, as synthesizing and testing pristine crystals absent of defects has been prohibitively challenging. Here, we report experiments that directly measure the surface dislocation nucleation strengths in high-quality 〈110〉 Pd nanowhiskers subjected to uniaxial tension. We find that, whereas nucleation strengths are weakly size- and strain-rate-dependent, a strong temperature dependence is uncovered, corroborating predictions that nucleation is assisted by thermal fluctuations. We measure atomic-scale activation volumes, which explain both the ultrahigh athermal strength as well as the temperature-dependent scatter, evident in our experiments and well captured by a thermal activation model. PMID:25985457

  7. Atomistic Simulation of Dislocation-Defect Interactions in Cu

    SciTech Connect

    Wirth, B D; Bulatov, V V; Diaz de la Rubia, T

    2001-01-01

    The mechanisms of dislocation-defect interactions are of practical importance for developing quantitative structure-property relationships, mechanistic understanding of plastic flow localization and predictive models of mechanical behavior in metals under irradiation. In copper and other face centered cubic metals, high-energy particle irradiation produces hardening and shear localization. Post-irradiation microstructural examination in Cu reveals that irradiation has produced a high number density of nanometer sized stacking fault tetrahedra. Thus, the resultant irradiation hardening and shear localization is commonly attributed to the interaction between stacking fault tetrahedra and mobile dislocations, although the mechanism of this interaction is unknown. In this work, we present a comprehensive molecular dynamics simulation study that characterizes the interaction and fate of moving dislocations with stacking fault tetrahedra in Cu using an EAM interatomic potential. This work is intended to produce atomistic input into dislocation dynamics simulations of plastic flow localization in irradiated materials.

  8. In-game Management of Common Joint Dislocations

    PubMed Central

    Skelley, Nathan W.; McCormick, Jeremy J.; Smith, Matthew V.

    2014-01-01

    Context: Sideline management of sports-related joint dislocations often places the treating medical professional in a challenging position. These injuries frequently require prompt evaluation, diagnosis, reduction, and postreduction management before they can be evaluated at a medical facility. Our objective is to review the mechanism, evaluation, reduction, and postreduction management of sports-related dislocations to the shoulder, elbow, finger, knee, patella, and ankle joints. Evidence Acquisition: A literature review was performed using the PubMed database to evaluate previous and current publications focused on joint dislocations. This review focused on articles published between 1980 and 2013. Study Design: Clinical review. Level of Evidence: Level 4. Results: The clinician should weigh the benefits and risks of on-field reduction based on their knowledge of the injury and the presence of associated injuries. Conclusion: When properly evaluated and diagnosed, most sports-related dislocations can be reduced and initially managed at the game. PMID:24790695

  9. Arytenoid dislocation after uneventful endotracheal intubation: a case report

    PubMed Central

    Oh, Tak Kyu; Ryu, Chang Hwan; Park, Yu Na; Kim, Nam Woo

    2016-01-01

    Arytenoid dislocation is an unusual complication of endotracheal intubation. We reported a case of a 48-year-old female with arytenoid dislocation after uneventful endotracheal intubation, which was successfully treated with arytenoid reduction. The patient complained of persistent hoarseness until the fourth day after an uneventful gynecologic surgery under general anesthesia. On laryngoscopic examination, paralyzed left vocal cord with minimal arytenoid movement was observed. An anteromedial dislocation of the left arytenoid cartilage was suspected and surgical reduction was performed by the laryngologist. The hoarseness was immediately resolved after surgical intervention. Anesthesiologists should be careful not to cause laryngeal trauma in anesthetized patients. In addition, early diagnosis and prompt surgical reduction are essential for a better prognosis for arytenoid dislocation. PMID:26885311

  10. Dislocation Structure and Mobility in hcp 4He

    NASA Astrophysics Data System (ADS)

    Landinez Borda, Edgar Josué; Cai, Wei; de Koning, Maurice

    2016-07-01

    Using path-integral Monte Carlo simulations, we assess the core structure and mobility of the screw and edge basal-plane dislocations in hcp 4He. Our findings provide key insights into recent interpretations of giant plasticity and mass flow junction experiments. First, both dislocations are dissociated into nonsuperfluid Shockley partial dislocations separated by ribbons of stacking fault, suggesting that they are unlikely to act as one-dimensional channels that may display Lüttinger-liquid-like behavior. Second, the centroid positions of the partial cores are found to fluctuate substantially, even in the absence of applied shear stresses. This implies that the lattice resistance to motion of the partial dislocations is negligible, consistent with the recent experimental observations of giant plasticity. Further results indicate that both the structure of the partial cores and the zero-point fluctuations play a role in this extreme mobility.

  11. ParaDiS-FEM dislocation dynamics simulation code primer

    SciTech Connect

    Tang, M; Hommes, G; Aubry, S; Arsenlis, A

    2011-09-27

    The ParaDiS code is developed to study bulk systems with periodic boundary conditions. When we try to perform discrete dislocation dynamics simulations for finite systems such as thin films or cylinders, the ParaDiS code must be extended. First, dislocations need to be contained inside the finite simulation box; Second, dislocations inside the finite box experience image stresses due to the free surfaces. We have developed in-house FEM subroutines to couple with the ParaDiS code to deal with free surface related issues in the dislocation dynamics simulations. This primer explains how the coupled code was developed, the main changes from the ParaDiS code, and the functions of the new FEM subroutines.

  12. Dislocation Interactions with Voids and Helium Bubbles in FCC Metals

    SciTech Connect

    Robertson, I; Robach, J; Wirth, B; Young, J

    2003-11-18

    The formation of a high number density of helium bubbles in FCC metals irradiated within the fusion energy environment is well established. Yet, the role of helium bubbles in radiation hardening and mechanical property degradation of these steels remains an outstanding issue. In this paper, we present the results of a combined molecular dynamics simulation and in-situ straining transmission electron microscopy study, which investigates the interaction mechanisms between glissile dislocations and nanometer-sized helium bubbles. The molecular dynamics simulations, which directly account for dislocation core effects through semi-empirical interatomic potentials, provide fundamental insight into the effect of helium bubble size and internal gas pressure on the dislocation/bubble interaction and bypass mechanisms. The combination of simulation and in-situ straining experiments provides a powerful approach to determine the atomic to microscopic mechanisms of dislocation-helium bubble interactions, which govern the mechanical response of metals irradiated within the fusion environment.

  13. Dislocation processes and deformation twinning in nanocrystalline Al.

    SciTech Connect

    Yamakov, V.; Wolf, D.; Phillpot, S.R.; Gleiter, H.

    2002-01-29

    Using a recently developed, massively parallel molecular-dynamics (MD) code for the simulation of polycrystal plasticity, we analyze for the case of nanocrystalline Al the complex interplay among various dislocation and grain-boundary processes during low-temperature deformation. A unique aspect of this work, arising from our ability to deform to rather large plastic strains and to consider a rather large grain size, is the observation of deformation under very high grain-boundary and dislocation densities, i.e., in a deformation regime where they compete on an equal footing. We are thus able to identify the intra- and intergranular dislocation and grain-boundary processes responsible for the extensive deformation twinning observed in our simulations. This illustrates the ability of this type of simulations to capture novel atomic-level insights into the underlying deformation mechanisms not presently possible experimentally. smaller grain size, mobile dislocations must be nucleated from other sources, such as the GBs or grain junctions.

  14. Dislocation Structure and Mobility in hcp He4

    DOE PAGESBeta

    Landinez Borda, Edgar Josue; Cai, Wei; de Koning, Maurice

    2016-07-20

    We assess the core structure and mobility of the screw and edge basal-plane dislocations in hcp 4He using path-integral Monte Carlo simulations. Our findings provide key insights into recent interpretations of giant plasticity and mass flow junction experiments. First, both dislocations are dissociated into nonsuperfluid Shockley partial dislocations separated by ribbons of stacking fault, suggesting that they are unlikely to act as one-dimensional channels that may display Lüttinger-liquid-like behavior. Second, the centroid positions of the partial cores are found to fluctuate substantially, even in the absence of applied shear stresses. This implies that the lattice resistance to motion of themore » partial dislocations is negligible, consistent with the recent experimental observations of giant plasticity. Our results indicate that both the structure of the partial cores and the zero-point fluctuations play a role in this extreme mobility.« less

  15. Posteromedial dislocation of the ankle without fracture or diastasis.

    PubMed

    Wang, L C; Love, M B

    1993-02-01

    This case report describes a patient with posteromedial dislocation of the ankle without fracture and without disruption of the tibiofibular syndesmosis. The pathogenesis of this uncommon lesion is discussed.

  16. Theoretical investigations of compositional inhomogeneity around threading dislocations in III-nitride semiconductor alloys

    NASA Astrophysics Data System (ADS)

    Sakaguchi, Ryohei; Akiyama, Toru; Nakamura, Kohji; Ito, Tomonori

    2016-05-01

    The compositional inhomogeneity of group III elements around threading dislocations in III-nitride semiconductors are theoretically investigated using empirical interatomic potentials and Monte Carlo simulations. We find that the calculated atomic arrangements around threading dislocations in Al0.3Ga0.7N and In0.2Ga0.8N depend on the lattice strain around dislocation cores. Consequently, compositional inhomogeneity arises around edge dislocation cores to release the strain induced by dislocation cores. In contrast, the compositional inhomogeneity in screw dislocation is negligible owing to relatively small strain induced by dislocation cores compared with edge dislocation. These results indicate that the strain relief around dislocation cores is decisive in determining the atomic arrangements and resultant compositional inhomogeneity around threading dislocations in III-nitride semiconductor alloys.

  17. Unusual upward closed tibiotalar dislocation without fracture: A case report.

    PubMed

    Lamraski, Guyve; Clegg, Emilie

    2010-06-01

    Pure tibiotalar dislocations without associated fracture are rare. The authors report a case of an unusual closed tibiotalar dislocation without fracture, involving proximal ascension of the talus. Despite immediate closed reduction, a tibiofibular diastasis remained, therefore two syndesmosis screws were inserted, followed by six weeks of plaster casting. After 5 years of follow-up, functional results were excellent, MRI showed slight arthritic degenerative changes. PMID:20483130

  18. Plastic dislocation motion via nonequilibrium molecular and continuum dynamics

    SciTech Connect

    Hoover, W.G.; Ladd, A.J.C.; Hoover, N.E.

    1980-09-29

    The classical two-dimensional close-packed triangular lattice, with nearest-neighbor spring forces, is a convenient standard material for the investigation of dislocation motion and plastic flow. Two kinds of calculations, based on this standard material, are described here: (1) Molecular Dynamics simulations, incorporating adiabatic strains described with the help of Doll's Tensor, and (2) Continuum Dynamics simulations, incorporating periodic boundaries and dislocation interaction through stress-field superposition.

  19. Posterior dislocation of the hip while playing basketball.

    PubMed

    Tennent, T D; Chambler, A F; Rossouw, D J

    1998-12-01

    Injuries in basketball are usually to the ankles and knees. Dislocation of the hip is usually associated with severe trauma--for example, road traffic accidents. A case is reported here in which a 22 year old club basketball player slipped on landing from a jump shot, forcing him into a side splits position from which he sustained a posterior dislocation of the hip resulting in a sciatic nerve palsy.

  20. Pure closed posteromedial dislocation of the tibiotalar joint without fracture.

    PubMed

    Wang, Yun-tao; Wu, Xiao-tao; Chen, Hui

    2013-08-01

    Pure tibiotalar dislocation without an associated fracture is an extremely rare injury. We present three cases of closed posteromedial tibiotalar dislocation without any associated fractures to the foot, ankle, or leg. All patients were treated conservatively with immediate closed reduction under general or local anaesthesia and immobilised in a short leg cast for six weeks without weight-bearing resulting in a satisfactory outcome at the final follow-up. A review of the literature is also presented in this paper.

  1. Dislocation theory of melting for iron, revisited

    SciTech Connect

    Poirier, J.P.; Shankland, T.J.

    1993-11-01

    Melting point T{sub m} of iron at conditions of the Earth`s inner core boundary (ICB) has been calculated from dislocation theory of melting in metals. Monte Carlo calculations were used to estimate uncertainties introduced by uncertainty in the geophysical parameters that are used in the calculations. These calculations take into account the effects of pressure at ICB conditions and of possible freezing point depression resulting from dilution of pure iron in the outer core. With this approach T{sub m} of pure {var_epsilon}-Fe at a pressure of 330 GPa and without freezing point depression is 6160 {plus_minus} 250 K; for a 1000 K freezing point depression it is 6110 K. T{sub m} of pure {gamma}-Fe is 6060 K, a value that is not significantly different. A possible {alpha}{prime} phase would melt at 5600 K. These values agree with calculated shock wave determinations of T{sub m}. Although calculated T{sub m} of the pure phase is little affected by assumptions about the extent of freezing point depression, the estimated temperature of the inner core boundary is lower by the breezing point depression, perhaps 500--1000 K less than T{sub m} of a pure phase.

  2. Reactivity of pyrites and dislocation density

    SciTech Connect

    Pollack, S.S.; Martello, D.V.; Diehl, J.R.; Tamilia, J.V. ); Graham, R.A. )

    1991-01-01

    Highly reactive coal pyrites and unstable museum specimens are easily distinguished from the stable pyrites by the growth of white crystals that cover samples exposed to room atmosphere for short periods of time. Continued exposure to the atmosphere will eventually cause the specimens to fall apart. The term rotten pyrite has been applied to museum specimens that fall apart in this way. SEM studies show that reactive (rotten) pyrites contain between 100 and 10,000 times more dislocations than stable pyrites. Shock-loading of a stable pyrite to 7.5 GPa and 17 GPa increased its reactivity by a factor of two, probably caused by an increase in the number of imperfections. However, shock-loading at 22 GPa decreased the reactivity of pyrite because the imperfections produced at the higher pressure were removed during annealing the sample received at the higher temperature. Although there was a factor of six difference between the most and least reactive shocked MCB (commercial pyrite) samples, shock-loading did not increase the reactivity of the MCB pyrite to that of the Queensland coal pyrite. The results in hand show that while shock-loading produces sufficient imperfections to increase the reactivity of pyrites, there is insufficient data to show that imperfections are the main reason why some coal pyrites are highly reactive. 9 refs., 1 fig., 1 tab.

  3. Dislocation theory of melting for iron, revisited

    SciTech Connect

    Poirier, J. ); Shankland, T.J. )

    1994-07-10

    The melting point T[sub m] of iron at conditions of the Earth's inner core boundary (ICB) has been calculated from the dislocation theory of melting in metals. Monte Carlo calculations were used to estimate uncertainties introduced by uncertainty in the geophysical parameters that are used in the calculations. These calculations take into account the effects of pressure at ICB conditions and of possible freezing point depression resulting from dilution of pure iron in the outer core. With this approach T[sub m] of pure [epsilon]-Fe at a pressure of 330 GPa and without freezing point depression is 6160[plus minus]250 K; for a 1000 K freezing point depression it is 6110 K. T[sub m] of pure [gamma]-Fe is 6060 K, a value that is not significantly different. A possible [alpha][prime] phase would melt at 5600 K. These values agree with calculated shock wave determinations of T[sub m]. Although calculated T[sub m] of the pure phase is little affected by assumptions about the extent of freezing point depression, the estimated temperature of the inner core boundary is lower by the freezing point depression, perhaps 500--1000 K less than T[sub m] of a pure phase. [copyright] 1994 American Institute of Physics

  4. Constitutive modeling for isotropic materials

    NASA Technical Reports Server (NTRS)

    Lindholm, Ulric S.; Chan, Kwai S.

    1986-01-01

    The objective of the program is to evaluate and develop existing constitutive models for use in finite-element structural analysis of turbine engine hot section components. The class of constitutive equation studied is considered unified in that all inelastic deformation including plasticity, creep, and stress relaxation are treated in a single term rather than a classical separation of plasticity (time independent) and creep (time dependent) behavior. The unified theories employed also do not utilize the classical yield surface or plastic potential concept. The models are constructed from an appropriate flow law, a scalar kinetic relation between strain rate, temperature and stress, and evolutionary equations for internal variables describing strain or work hardening, both isotropic and directional (kinematic). This and other studies have shown that the unified approach is particularly suited for determining the cyclic behavior of superalloy type blade and vane materials and is entirely compatible with three-dimensional inelastic finite-element formulations. The behavior was examined of a second nickel-base alloy, MAR-M247, and compared it with the Bodner-Partom model, further examined procedures for determining the material-specific constants in the models, and exercised the MARC code for a turbine blade under simulated flight spectrum loading. Results are summarized.

  5. The energetics of dislocation array stability in strained epitaxial layers

    NASA Astrophysics Data System (ADS)

    Gosling, T. J.; Willis, J. R.; Bullough, R.; Jain, S. C.

    1993-06-01

    Two aspects of the energetics of dislocation array stability in lattice-mismatched strained layers are addressed. The first concerns criteria for determining equilibrium dislocation distributions in strained layers; the second concerns the difference between the energies of arrays of dislocations in which the Burgers vectors of all dislocations are identical, and those in which the screw components of the Burgers vectors alternate. The conclusions reached are at variance with those of recent work by Feng and Hirth on periodic arrays of dipoles in an infinite body [X. Feng and J. P. Hirth, J. Appl. Phys. 72, 1386 (1992); J. P. Hirth and X. Feng, J. Appl. Phys. 67, 3343 (1990)]. In particular, it is emphasized that if layers remain in equilibrium then there is always a residual mean strain; in other words, the mismatch strain is never completely relaxed. Also it is shown, via a direct calculation, that although alternating the screw components of the Burgers vectors of dislocations within a single array is energetically favorable, it is preferable to have all screw components of the same sign within an array if two orthogonal arrays are considered. Although for comparison with the work of Feng and Hirth arrays of dipoles in an infinite body are considered in more detail, the stated conclusions are also shown to hold for arrays of unpaired dislocations near a free surface.

  6. Inferior hip dislocation after falling from height: A case report

    PubMed Central

    Tekin, Ali Çağrı; Çabuk, Haluk; Büyükkurt, Cem Dinçay; Dedeoğlu, Süleyman Semih; İmren, Yunus; Gürbüz, Hakan

    2016-01-01

    Introduction Traumatic inferior hip dislocation is the least common of all hip dislocations. Adult inferior hip dislocations usually occur after high-energy trauma, very few cases are reported without fracture. Presentation of case A 26-year-old female was brought to the emergency department with severe pain in the left hip, impaired posture and restricted movement following a fall from 15 m height. The hip joint was fixed in 90° flexion, 15° abduction, and 20° external rotation. No neurovascular impairment was determined. On radiologic examination, a left ischial type inferior hip dislocation was detected. Hemorrhagic shock which developed due to acute blood loss to thoracic and abdominal cavity and patient died at third hour after she was brought to the hospital. Discussion Traumatic hip dislocations have high morbidity and mortality rates due to multiple organ damage, primarily of the extremities, chest and abdomen. In the treatment of traumatic hip dislocation, closed reduction is recommended through muscle relaxation under general anesthesia or sedation. This procedure should be applied before any intervention for concomitant extremity injuries. A detailed evaluation on emergency presentation, a multi-disciplinary approach and early diagnosis with the rapid application of imaging methods could be life-saving for such patients. PMID:27058153

  7. How to identify dislocations in molecular dynamics simulations?

    NASA Astrophysics Data System (ADS)

    Li, Duo; Wang, FengChao; Yang, ZhenYu; Zhao, YaPu

    2014-12-01

    Dislocations are of great importance in revealing the underlying mechanisms of deformed solid crystals. With the development of computational facilities and technologies, the observations of dislocations at atomic level through numerical simulations are permitted. Molecular dynamics (MD) simulation suggests itself as a powerful tool for understanding and visualizing the creation of dislocations as well as the evolution of crystal defects. However, the numerical results from the large-scale MD simulations are not very illuminating by themselves and there exist various techniques for analyzing dislocations and the deformed crystal structures. Thus, it is a big challenge for the beginners in this community to choose a proper method to start their investigations. In this review, we summarized and discussed up to twelve existing structure characterization methods in MD simulations of deformed crystal solids. A comprehensive comparison was made between the advantages and disadvantages of these typical techniques. We also examined some of the recent advances in the dynamics of dislocations related to the hydraulic fracturing. It was found that the dislocation emission has a significant effect on the propagation and bifurcation of the crack tip in the hydraulic fracturing.

  8. Dislocation Starvation and Exhaustion Hardening in Mo-alloy Nanofibers

    SciTech Connect

    Chisholm, Claire; Bei, Hongbin; Lowry, M. B.; Oh, Jason; Asif, S.A. Syed; Warren, O.; Shan, Zhiwei; George, Easo P; Minor, Andrew

    2012-01-01

    The evolution of defects in Mo alloy nanofibers with initial dislocation densities ranging from 0 to 1.6 1014 m2 were studied using an in situ push-to-pull device in conjunction with a nanoindenter in a transmission electron microscope. Digital image correlation was used to determine stress and strain in local areas of deformation. When they had no initial dislocations the Mo alloy nanofibers suffered sudden catastrophic elongation following elastic deformation to ultrahigh stresses. At the other extreme fibers with a high dislocation density underwent sustained homogeneous deformation after yielding at much lower stresses. Between these two extremes nanofibers with intermediate dislocation densities demonstrated a clear exhaustion hardening behavior, where the progressive exhaustion of dislocations and dislocation sources increases the stress required to drive plasticity. This is consistent with the idea that mechanical size effects ( smaller is stronger ) are due to the fact that nanostructures usually have fewer defects that can operate at lower stresses. By monitoring the evolution of stress locally we find that exhaustion hardening causes the stress in the nanofibers to surpass the critical stress predicted for self-multiplication, supporting a plasticity mechanism that has been hypothesized to account for the rapid strain softening observed in nanoscale bcc materials at high stresses.

  9. Bilateral posterior shoulder dislocation after electrical shock: A case report

    PubMed Central

    Ketenci, Ismail Emre; Duymus, Tahir Mutlu; Ulusoy, Ayhan; Yanik, Hakan Serhat; Mutlu, Serhat; Durakbasa, Mehmet Oguz

    2015-01-01

    Introduction Posterior dislocation of the shoulder is a rare and commonly missed injury. Unilateral dislocations occur mostly due to trauma. Bilateral posterior shoulder dislocations are even more rare and result mainly from epileptic seizures. Electrical injury is a rare cause of posterior shoulder dislocation. Injury mechanism in electrical injury is similar to epileptic seizures, where the shoulder is forced to internal rotation, flexion and adduction. Presentation of case This report presents a case of bilateral posterior shoulder dislocation after electrical shock. We were able to find a few individual case reports describing this condition. The case was acute and humeral head impression defects were minor. Our treatment in this case consisted of closed reduction under general anesthesia and applying of orthoses which kept the shoulders in abduction and external rotation. A rehabilitation program was begun after 3 weeks of immobilization. After 6 months of injury the patient has returned to work. 20 months postoperatively, at final follow-up, he was painless and capable of performing all of his daily activities. Discussion The amount of bilateral shoulder dislocations after electrical injury is not reported but is known to be very rare. The aim of this case presentation is to report an example for this rare entity, highlight the difficulties in diagnosis and review the treatment options. Conclusion Physical examination and radiographic evaluation are important for quick and accurate diagnosis. PMID:26904192

  10. Material yielding and irreversible deformation mediated by dislocation motion

    NASA Astrophysics Data System (ADS)

    Miguel, M.-Carmen; Laurson, L.; Alava, M. J.

    2008-08-01

    We study the collective behavior of dislocation assemblies in simplified models of plastic deformation. We first review several numerical results on long range dislocation interactions with simplified dislocation motion constraints. These typically give rise to a yielding transition separating stationary and moving dislocation phases. Furthermore, we discuss the intermittent relaxation of the plastic strain-rate observed around this transition at mesoscopic scales, and how this intermittent behavior gives rise to an average slow power law relaxation in time known in the literature as Andrade’s creep. We analyze the coherent dynamics and the average stress-strain relationship in the steady regime of plastic deformation. In this steady regime, plastic deformation proceeds in the form of plastic avalanches whose size and duration are broadly distributed and statistically characterized. One signature of the time correlations of this heterogeneous collective dislocation dynamics is a power spectrum scaling with frequency as f - a with an exponent α close to 1.5. This feature appears to be peculiar of dislocation and grain boundary motion as has been observed in other physical situations in the vicinity of a yielding transition.

  11. Current concepts in the diagnosis and management of acromioclavicular dislocations.

    PubMed

    Post, M

    1985-11-01

    Not all complete dislocations of the acromioclavicular joint should be treated by one method alone. A classification of acromioclavicular dislocation is presented and is based upon the pathology of the injury. Grade I sprain results from a mild force that causes tearing of only a few fibers of the acromioclavicular joint. Grade II sprains are caused by a moderate force with a rupture of the capsule and acromioclavicular ligament. Grade III sprains result from a severe force that ruptures both the acromioclavicular and coracoclavicular ligaments and causes a dislocation of the joint. Grade IV dislocation may be associated with an avulsion fracture of the coracoclavicular ligament from the inferior lateral clavicle, severe tearing or other injury to the soft-tissue envelope about the lateral clavicle, or a buttonhole injury of the lateral clavicle. Grade V dislocation refers to a posterior displacement of the lateral clavicle from any cause, while Grade VI relates to an inferior lateral clavicle displacement. Grades I, II, and most Grade III injuries can be treated conservatively. The indications for open treatment of Grade III injuries are reviewed. It is recommended that Grade IV and most Grade V and VI dislocations be managed with open methods.

  12. In Situ TEM Observation of Dislocation Evolutionin Polycrystalline UO2

    SciTech Connect

    L. F. HE; 1 M. A. KIRK; Argonne National Laboratory; J. Gan; T. R. ALLEN

    2014-10-01

    In situ transmission electron microscopy observation of polycrystalline UO2 (with average grain size of about 5 lm) irradiated with Kr ions at 600C and 800C was conducted to understand the radiation-induced dislocation evolution under the influence of grain boundaries. The dislocation evolution in the grain interior of polycrystalline UO2 was similar under Kr irradiation at different ion energies and temperatures. As expected, it was characterized by the nucleation and growth of dislocation loops at low irradiation doses, followed by transformation to extended dislocation lines and tangles at high doses. For the first time, a dislocation-denuded zone was observed near a grain boundary in the 1-MeV Kr-irradiated UO2 sample at 800C. The denuded zone in the vicinity of grain boundary was not found when the irradiation temperature was at 600C. The suppression of dislocation loop formation near the boundary is likely due to the enhanced interstitial diffusion toward grain boundary at the high temperature.

  13. Dislocation characterization in cold rolled stainless steel using nonlinear ultrasonic techniques: A comprehensive model

    NASA Astrophysics Data System (ADS)

    Zhang, Jianfeng; Xuan, Fu-zhen; Xiang, Yanxun

    2013-09-01

    Both dislocation density and character in cold rolled stainless steel cause the change of acoustic nonlinearity. An analytical model considering the different oscillating motion of edge and screw dislocations is presented for the generation of ultrasonic harmonic wave during the process of multiplication and motion of dislocation. Results reveal that the edge dislocation induces stronger acoustic nonlinearity response than screw dislocation. The new model is certified by the application to the cold rolled stainless steel.

  14. A constitutive model for representing coupled creep, fracture, and healing in rock salt

    SciTech Connect

    Chan, K.S.; Bodner, S.R.; Munson, D.E.; Fossum, A.F.

    1996-03-01

    The development of a constitutive model for representing inelastic flow due to coupled creep, damage, and healing in rock salt is present in this paper. This model, referred to as Multimechanism Deformation Coupled Fracture model, has been formulated by considering individual mechanisms that include dislocation creep, shear damage, tensile damage, and damage healing. Applications of the model to representing the inelastic flow and fracture behavior of WIPP salt subjected to creep, quasi-static loading, and damage healing conditions are illustrated with comparisons of model calculations against experimental creep curves, stress-strain curves, strain recovery curves, time-to-rupture data, and fracture mechanism maps.

  15. Type IIA Monteggia Fracture Dislocation with Ipsilateral Distal Radius Fracture in Adult – A Rare Association

    PubMed Central

    James, Boblee

    2016-01-01

    Monteggia fracture constitutes about 5-10% of the forearm fractures. Monteggia fracture by definition is proximal ulnar fracture with disruption of proximal radioulnar joint. Bado classified Monteggia fracture dislocation into four types and Jupiter subclassified type II Bado’s fractures into four types. The associated injury in the form of distal radial fractures and distal humerus fractures are rare though many cases of distal radial physeal injuries have been reported in paediatric population. Hereby we report a rare association of type IIA Monteggia fracture dislocation with ipsilateral distal radius fracture in an adult patient. This case report also highlights on proper examination and full length radiographs of forearm to avoid missing injury at wrist in cases of elbow injuries. Management of such complex injuries included open reduction and internal fixation of olecronon fracture, distal radius fracture and radial head resection. Functional outcome at six months was good at wrist whereas at elbow, stiffness was a major concern with elbow range of movement from 40°-110°. PMID:27656518

  16. Type IIA Monteggia Fracture Dislocation with Ipsilateral Distal Radius Fracture in Adult - A Rare Association.

    PubMed

    Kembhavi, Raghavendra S; James, Boblee

    2016-08-01

    Monteggia fracture constitutes about 5-10% of the forearm fractures. Monteggia fracture by definition is proximal ulnar fracture with disruption of proximal radioulnar joint. Bado classified Monteggia fracture dislocation into four types and Jupiter subclassified type II Bado's fractures into four types. The associated injury in the form of distal radial fractures and distal humerus fractures are rare though many cases of distal radial physeal injuries have been reported in paediatric population. Hereby we report a rare association of type IIA Monteggia fracture dislocation with ipsilateral distal radius fracture in an adult patient. This case report also highlights on proper examination and full length radiographs of forearm to avoid missing injury at wrist in cases of elbow injuries. Management of such complex injuries included open reduction and internal fixation of olecronon fracture, distal radius fracture and radial head resection. Functional outcome at six months was good at wrist whereas at elbow, stiffness was a major concern with elbow range of movement from 40°-110°. PMID:27656518

  17. A dislocation-based, strain–gradient–plasticity strengthening model for deformation processed metal–metal composites

    SciTech Connect

    Tian, Liang; Russell, Alan; Anderson, Iver

    2014-01-03

    Deformation processed metal–metal composites (DMMCs) are high-strength, high-electrical conductivity composites developed by severe plastic deformation of two ductile metal phases. The extraordinarily high strength of DMMCs is underestimated using the rule of mixture (or volumetric weighted average) of conventionally work-hardened metals. A dislocation-density-based, strain–gradient–plasticity model is proposed to relate the strain-gradient effect with the geometrically necessary dislocations emanating from the interface to better predict the strength of DMMCs. The model prediction was compared with our experimental findings of Cu–Nb, Cu–Ta, and Al–Ti DMMC systems to verify the applicability of the new model. The results show that this model predicts the strength of DMMCs better than the rule-of-mixture model. The strain-gradient effect, responsible for the exceptionally high strength of heavily cold worked DMMCs, is dominant at large deformation strain since its characteristic microstructure length is comparable with the intrinsic material length.

  18. A dislocation-based, strain–gradient–plasticity strengthening model for deformation processed metal–metal composites

    DOE PAGESBeta

    Tian, Liang; Russell, Alan; Anderson, Iver

    2014-01-03

    Deformation processed metal–metal composites (DMMCs) are high-strength, high-electrical conductivity composites developed by severe plastic deformation of two ductile metal phases. The extraordinarily high strength of DMMCs is underestimated using the rule of mixture (or volumetric weighted average) of conventionally work-hardened metals. A dislocation-density-based, strain–gradient–plasticity model is proposed to relate the strain-gradient effect with the geometrically necessary dislocations emanating from the interface to better predict the strength of DMMCs. The model prediction was compared with our experimental findings of Cu–Nb, Cu–Ta, and Al–Ti DMMC systems to verify the applicability of the new model. The results show that this model predicts themore » strength of DMMCs better than the rule-of-mixture model. The strain-gradient effect, responsible for the exceptionally high strength of heavily cold worked DMMCs, is dominant at large deformation strain since its characteristic microstructure length is comparable with the intrinsic material length.« less

  19. A dislocation-based, strain–gradient–plasticity strengthening model for deformation processed metal-metal composites

    SciTech Connect

    Tian, Liang; Russell, Alan; Anderson, Iver

    2014-01-03

    Deformation processed metal–metal composites (DMMCs) are high-strength, high-electrical conductivity composites developed by severe plastic deformation of two ductile metal phases. The extraordinarily high strength of DMMCs is underestimated using the rule of mixture (or volumetric weighted average) of conventionally work-hardened metals. In this article, a dislocation-density-based, strain–gradient–plasticity model is proposed to relate the strain-gradient effect with the geometrically necessary dislocations emanating from the interface to better predict the strength of DMMCs. The model prediction was compared with the experimental findings of Cu–Nb, Cu–Ta, and Al–Ti DMMC systems to verify the applicability of the new model. The results show that this model predicts the strength of DMMCs better than the rule-of-mixture model. The strain-gradient effect, responsible for the exceptionally high strength of heavily cold worked DMMCs, is dominant at large deformation strain since its characteristic microstructure length is comparable with the intrinsic material length.

  20. Cloud Computing Application for Hotspot Clustering Using Recursive Density Based Clustering (RDBC)

    NASA Astrophysics Data System (ADS)

    Santoso, Aries; Khiyarin Nisa, Karlina

    2016-01-01

    Indonesia has vast areas of tropical forest, but are often burned which causes extensive damage to property and human life. Monitoring hotspots can be one of the forest fire management. Each hotspot is recorded in dataset so that it can be processed and analyzed. This research aims to build a cloud computing application which visualizes hotspots clustering. This application uses the R programming language with Shiny web framework and implements Recursive Density Based Clustering (RDBC) algorithm. Clustering is done on hotspot dataset of the Kalimantan Island and South Sumatra Province to find the spread pattern of hotspots. The clustering results are evaluated using the Silhouette's Coefficient (SC) which yield best value 0.3220798 for Kalimantan dataset. Clustering pattern are displayed in the form of web pages so that it can be widely accessed and become the reference for fire occurrence prediction.

  1. A density-based adaptive quantum mechanical/molecular mechanical method.

    PubMed

    Waller, Mark P; Kumbhar, Sadhana; Yang, Jack

    2014-10-20

    We present a density-based adaptive quantum mechanical/molecular mechanical (DBA-QM/MM) method, whereby molecules can switch layers from the QM to the MM region and vice versa. The adaptive partitioning of the molecular system ensures that the layer assignment can change during the optimization procedure, that is, on the fly. The switch from a QM molecule to a MM molecule is determined if there is an absence of noncovalent interactions to any atom of the QM core region. The presence/absence of noncovalent interactions is determined by analysis of the reduced density gradient. Therefore, the location of the QM/MM boundary is based on physical arguments, and this neatly removes some empiricism inherent in previous adaptive QM/MM partitioning schemes. The DBA-QM/MM method is validated by using a water-in-water setup and an explicitly solvated L-alanyl-L-alanine dipeptide. PMID:24954803

  2. A density-based adaptive quantum mechanical/molecular mechanical method.

    PubMed

    Waller, Mark P; Kumbhar, Sadhana; Yang, Jack

    2014-10-20

    We present a density-based adaptive quantum mechanical/molecular mechanical (DBA-QM/MM) method, whereby molecules can switch layers from the QM to the MM region and vice versa. The adaptive partitioning of the molecular system ensures that the layer assignment can change during the optimization procedure, that is, on the fly. The switch from a QM molecule to a MM molecule is determined if there is an absence of noncovalent interactions to any atom of the QM core region. The presence/absence of noncovalent interactions is determined by analysis of the reduced density gradient. Therefore, the location of the QM/MM boundary is based on physical arguments, and this neatly removes some empiricism inherent in previous adaptive QM/MM partitioning schemes. The DBA-QM/MM method is validated by using a water-in-water setup and an explicitly solvated L-alanyl-L-alanine dipeptide.

  3. Unborn children as constitutional persons.

    PubMed

    Roden, Gregory J

    2010-01-01

    In Roe v. Wade, the state of Texas argued that "the fetus is a 'person' within the language and meaning of the Fourteenth Amendment." To which Justice Harry Blackmun responded, "If this suggestion of personhood is established, the appellant's case, of course, collapses, for the fetus' right to life would then be guaranteed specifically by the Amendment." However, Justice Blackmun then came to the conclusion "that the word 'person,' as used in the Fourteenth Amendment, does not include the unborn." In this article, it is argued that unborn children are indeed "persons" within the language and meaning of the Fourteenth and Fifth Amendments. As there is no constitutional text explicitly holding unborn children to be, or not to be, "persons," this argument will be based on the "historical understanding and practice, the structure of the Constitution, and thejurisprudence of [the Supreme] Court." Specifically, it is argued that the Constitution does not confer upon the federal government a specifically enumerated power to grant or deny "personhood" under the Fourteenth Amendment. Rather, the power to recognize or deny unborn children as the holders of rights and duties has been historically exercised by the states. The Roe opinion and other Supreme Court cases implicitly recognize this function of state sovereignty. The states did exercise this power and held unborn children to be persons under the property, tort, and criminal law of the several states at the time Roe was decided. As an effect of the unanimity of the states in holding unborn children to be persons under criminal, tort, and property law, the text of the Equal Protection Clause of the Fourteenth Amendment compels federal protection of unborn persons. Furthermore, to the extent Justice Blackmun examined the substantive law in these disciplines, his findings are clearly erroneous and as a whole amount to judicial error. Moreover, as a matter of procedure, according to the due process standards recognized in

  4. Detailed formation processes of stable dislocations in graphene

    NASA Astrophysics Data System (ADS)

    Lee, Gun-Do; Yoon, Euijoon; He, Kuang; Robertson, Alex W.; Warner, Jamie H.

    2014-11-01

    We use time-dependent HRTEM to reveal that stable dislocation pairs in graphene are formed from an initial complex multi-vacancy cluster that undergoes multiple bond rotations and adatom incorporation. In the process, it is found that the transformation from the formed complex multi-vacancy cluster can proceed without the increase of vacancy because many atoms and dimers are not only evaporated but also actively adsorbed. In tight-binding molecular dynamics simulations, it is confirmed that adatoms play an important role in the reconstruction of non-hexagonal rings into hexagonal rings. From density functional theory calculations, it is also found from simulations that there is a favorable distance between two dislocations pointing away from each other (i.e. formed from atom loss). For dislocation pairs pointing away from each other, the hillock-basin structure is more stable than the hillock-hillock structure for dislocation pairs pointing away from each other (i.e. formed from atom loss).We use time-dependent HRTEM to reveal that stable dislocation pairs in graphene are formed from an initial complex multi-vacancy cluster that undergoes multiple bond rotations and adatom incorporation. In the process, it is found that the transformation from the formed complex multi-vacancy cluster can proceed without the increase of vacancy because many atoms and dimers are not only evaporated but also actively adsorbed. In tight-binding molecular dynamics simulations, it is confirmed that adatoms play an important role in the reconstruction of non-hexagonal rings into hexagonal rings. From density functional theory calculations, it is also found from simulations that there is a favorable distance between two dislocations pointing away from each other (i.e. formed from atom loss). For dislocation pairs pointing away from each other, the hillock-basin structure is more stable than the hillock-hillock structure for dislocation pairs pointing away from each other (i.e. formed from

  5. Written Constitution or None: Which Works Better?

    ERIC Educational Resources Information Center

    Cowen, Zelman

    1987-01-01

    Explores the differences between the U.S. Constitution and British constitutional law. Specifically examines the concept of the U.S. Bill of Rights in relation to the United Kingdom common law doctrine of parliamentary sovereignty. (BSR)

  6. Monteggia fracture-dislocation: a case report, its' initial management and review of bado's classification.

    PubMed

    Musa, Abdullahi Agaba-Idu

    2006-12-01

    Fracture of proximal ulna and dislocation of the proximal radio-ulna joint in the same arm is called Monteggia fracture- dislocation. Four clinical variants of this fracture- dislocation have been described in literature. This is a report and description of initial management of a fracture- dislocation, which was consequent to a sideswipe injury and consisted of a combination of the following injuries; lateral dislocation of the radial head, fractures of the olecranon and proximal ulna in the left forearm. The radial head dislocation and fracture of the olecranon were open. The head of the radius was exposed through the same wound. This fracture-dislocation resembled type 3 Bado's classification of Monteggia fracture-dislocation because of fracture of the olecranon close to the coronoid process and lateral dislocation of the head of radius.

  7. Theoretical Issues of the Constitutional Regulation Mechanism

    ERIC Educational Resources Information Center

    Zhussupova, Guldaray B.; Zhailyaubayev, Rassul T.; Ukin, Symbat K.; Shunayeva, Sylu M.; Nurmagambetov, Rachit G.

    2016-01-01

    The purpose of this research is to define the concept of "constitutional regulation mechanism." The definition of the concept of "constitutional regulation mechanism" will give jurists and legislators a theoretical framework for developing legal sciences, such as the constitutional law and the theory of state and law. The…

  8. Antithetical Ethics: Kenneth Burke and the Constitution.

    ERIC Educational Resources Information Center

    Anderson, Virginia

    1995-01-01

    Shows how the textuality of the United States Constitution, the most venerable of classic democratic icons, might be exploited to nurture postmodern ethics. Shows how Kenneth Burke's reading of the Constitution accords with and augments the postmodern theories of J.-F. Lyotard and S. Jarratt. Discusses a postmodern Constitution and the…

  9. About Our Constitution: 1787-1987.

    ERIC Educational Resources Information Center

    National Council for the Social Studies, Washington, DC.

    Designed to assist elementary school teachers, these materials present a series of lessons about the United States Constitution. Ten lesson plans and appropriate work sheets are included for grades K-3. The topics covered include the age of the Constitution, a constitutional convention, elected representatives, majority rule, voting, law making,…

  10. 32 CFR 536.42 - Constitutional torts.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... National Defense Department of Defense (Continued) DEPARTMENT OF THE ARMY CLAIMS AND ACCOUNTS CLAIMS AGAINST THE UNITED STATES Investigation and Processing of Claims § 536.42 Constitutional torts. A claim for violation of the U.S. Constitution does not constitute a state tort and is not cognizable...

  11. 32 CFR 536.42 - Constitutional torts.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... National Defense Department of Defense (Continued) DEPARTMENT OF THE ARMY CLAIMS AND ACCOUNTS CLAIMS AGAINST THE UNITED STATES Investigation and Processing of Claims § 536.42 Constitutional torts. A claim for violation of the U.S. Constitution does not constitute a state tort and is not cognizable...

  12. 32 CFR 536.42 - Constitutional torts.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... National Defense Department of Defense (Continued) DEPARTMENT OF THE ARMY CLAIMS AND ACCOUNTS CLAIMS AGAINST THE UNITED STATES Investigation and Processing of Claims § 536.42 Constitutional torts. A claim for violation of the U.S. Constitution does not constitute a state tort and is not cognizable...

  13. 32 CFR 536.42 - Constitutional torts.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... National Defense Department of Defense (Continued) DEPARTMENT OF THE ARMY CLAIMS AND ACCOUNTS CLAIMS AGAINST THE UNITED STATES Investigation and Processing of Claims § 536.42 Constitutional torts. A claim for violation of the U.S. Constitution does not constitute a state tort and is not cognizable...

  14. 7 CFR 718.201 - Farm constitution.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 7 Agriculture 7 2011-01-01 2011-01-01 false Farm constitution. 718.201 Section 718.201 Agriculture... Reconstitution of Farms, Allotments, Quotas, and Bases § 718.201 Farm constitution. (a) In order to implement... this section. The constitution and identification of land as a farm for the first time and...

  15. 7 CFR 718.201 - Farm constitution.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 7 Agriculture 7 2014-01-01 2014-01-01 false Farm constitution. 718.201 Section 718.201 Agriculture... Reconstitution of Farms, Allotments, Quotas, and Bases § 718.201 Farm constitution. (a) In order to implement... this section. The constitution and identification of land as a farm for the first time and...

  16. 29 CFR 452.18 - Constitutional officers.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... officer refers to a person holding a position identified as an officer by the constitution and bylaws of... constitution identifies the holder of such a position as an officer. On the other hand, legislative representatives who are required to be elected by the constitution and bylaws of a labor organization are...

  17. 29 CFR 452.18 - Constitutional officers.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... officer refers to a person holding a position identified as an officer by the constitution and bylaws of... constitution identifies the holder of such a position as an officer. On the other hand, legislative representatives who are required to be elected by the constitution and bylaws of a labor organization are...

  18. 7 CFR 718.201 - Farm constitution.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 7 Agriculture 7 2013-01-01 2013-01-01 false Farm constitution. 718.201 Section 718.201 Agriculture... Reconstitution of Farms, Allotments, Quotas, and Bases § 718.201 Farm constitution. (a) In order to implement... this section. The constitution and identification of land as a farm for the first time and...

  19. 29 CFR 452.18 - Constitutional officers.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... officer refers to a person holding a position identified as an officer by the constitution and bylaws of... constitution identifies the holder of such a position as an officer. On the other hand, legislative representatives who are required to be elected by the constitution and bylaws of a labor organization are...

  20. 7 CFR 718.201 - Farm constitution.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 7 Agriculture 7 2012-01-01 2012-01-01 false Farm constitution. 718.201 Section 718.201 Agriculture... Reconstitution of Farms, Allotments, Quotas, and Bases § 718.201 Farm constitution. (a) In order to implement... this section. The constitution and identification of land as a farm for the first time and...

  1. American Focus on World Constitutions. Teacher's Guide.

    ERIC Educational Resources Information Center

    Holmes, Stanley T., III

    This curriculum project was designed to familiarize high school students with their own constitutional roots while gaining a better understanding of governmental systems developed by other nations. The project uses the U.S. Constitution as a baseline for analyzing the constitutions of other nations, and is intended to supplement courses in such…

  2. Atomistically determined phase-field modeling of dislocation dissociation, stacking fault formation, dislocation slip, and reactions in fcc systems

    NASA Astrophysics Data System (ADS)

    Rezaei Mianroodi, Jaber; Svendsen, Bob

    2015-04-01

    The purpose of the current work is the development of a phase field model for dislocation dissociation, slip and stacking fault formation in single crystals amenable to determination via atomistic or ab initio methods in the spirit of computational material design. The current approach is based in particular on periodic microelasticity (Wang and Jin, 2001; Bulatov and Cai, 2006; Wang and Li, 2010) to model the strongly non-local elastic interaction of dislocation lines via their (residual) strain fields. These strain fields depend in turn on phase fields which are used to parameterize the energy stored in dislocation lines and stacking faults. This energy storage is modeled here with the help of the "interface" energy concept and model of Cahn and Hilliard (1958) (see also Allen and Cahn, 1979; Wang and Li, 2010). In particular, the "homogeneous" part of this energy is related to the "rigid" (i.e., purely translational) part of the displacement of atoms across the slip plane, while the "gradient" part accounts for energy storage in those regions near the slip plane where atomic displacements deviate from being rigid, e.g., in the dislocation core. Via the attendant global energy scaling, the interface energy model facilitates an atomistic determination of the entire phase field energy as an optimal approximation of the (exact) atomistic energy; no adjustable parameters remain. For simplicity, an interatomic potential and molecular statics are employed for this purpose here; alternatively, ab initio (i.e., DFT-based) methods can be used. To illustrate the current approach, it is applied to determine the phase field free energy for fcc aluminum and copper. The identified models are then applied to modeling of dislocation dissociation, stacking fault formation, glide and dislocation reactions in these materials. As well, the tensile loading of a dislocation loop is considered. In the process, the current thermodynamic picture is compared with the classical mechanical

  3. A parallel algorithm for 3D dislocation dynamics

    NASA Astrophysics Data System (ADS)

    Wang, Zhiqiang; Ghoniem, Nasr; Swaminarayan, Sriram; LeSar, Richard

    2006-12-01

    Dislocation dynamics (DD), a discrete dynamic simulation method in which dislocations are the fundamental entities, is a powerful tool for investigation of plasticity, deformation and fracture of materials at the micron length scale. However, severe computational difficulties arising from complex, long-range interactions between these curvilinear line defects limit the application of DD in the study of large-scale plastic deformation. We present here the development of a parallel algorithm for accelerated computer simulations of DD. By representing dislocations as a 3D set of dislocation particles, we show here that the problem of an interacting ensemble of dislocations can be converted to a problem of a particle ensemble, interacting with a long-range force field. A grid using binary space partitioning is constructed to keep track of node connectivity across domains. We demonstrate the computational efficiency of the parallel micro-plasticity code and discuss how O(N) methods map naturally onto the parallel data structure. Finally, we present results from applications of the parallel code to deformation in single crystal fcc metals.

  4. Irreducible Lateral Patellar Dislocation: A Case Report and Literature Review

    PubMed Central

    Grewal, Balvinder; Elliott, Devlin; Daniele, Luca; Reidy, James

    2016-01-01

    Background: Acute patellar dislocation is a common injury in young people, especially in adolescent females and athletes. Lateral dislocation is the most common form of patellar dislocation and often reduces spontaneously or with simple manipulation and closed reduction. We report a rare circumstance in which the patella was irreducible and required manipulation and closed reduction in the operating room. Case Report: While dancing, a 32-year-old female was knocked by a fellow dancer on her left knee, and she fell to the nightclub floor. She was unable to stand or bear weight because of the pain, and her knee was in fixed flexion with lateral displacement of the patella. Multiple attempts at closed reduction under sedation failed in the emergency department. Computed tomography (CT) images revealed a medial border patellar fracture and lipohemarthrosis that required closed reduction and manipulation in the operating room. The patient was placed in a Richards splint for follow-up and referred to a physiotherapist for conservative management. Conclusion: This case highlights the fact that some lateral patellar dislocations are irreducible on initial attempts, particularly if a fracture is present or another mechanism of impingement impedes relocation. CT imaging is a valuable diagnostic tool, and manipulation under anesthesia or open reduction in the operating room may be necessary. Our review of the literature further highlights the complexity and potential problems associated with treatment of locked lateral patellar dislocations. PMID:27303231

  5. Theoretical study of kinks on screw dislocation in silicon

    NASA Astrophysics Data System (ADS)

    Pizzagalli, L.; Pedersen, A.; Arnaldsson, A.; Jónsson, H.; Beauchamp, P.

    2008-02-01

    Theoretical calculations of the structure, formation, and migration of kinks on a nondissociated screw dislocation in silicon have been carried out using density functional theory calculations as well as calculations based on interatomic potential functions. The results show that the structure of a single kink is characterized by a narrow core and highly stretched bonds between some of the atoms. The formation energy of a single kink ranges from 0.9to1.36eV , and is of the same order as that for kinks on partial dislocations. However, the kinks migrate almost freely along the line of an undissociated dislocation unlike what is found for partial dislocations. The effect of stress has also been investigated in order to compare with previous silicon deformation experiments which have been carried out at low temperature and high stress. The energy barrier associated with the formation of a stable kink pair becomes as low as 0.65eV for an applied stress on the order of 1GPa , indicating that displacements of screw dislocations likely occur via thermally activated formation of kink pairs at room temperature.

  6. Dislocation core structures in Si-doped GaN

    SciTech Connect

    Rhode, S. L. Fu, W. Y.; Sahonta, S.-L.; Kappers, M. J.; Humphreys, C. J.; Horton, M. K.; Pennycook, T. J.; Dusane, R. O.; Moram, M. A.

    2015-12-14

    Aberration-corrected scanning transmission electron microscopy was used to investigate the core structures of threading dislocations in plan-view geometry of GaN films with a range of Si-doping levels and dislocation densities ranging between (5 ± 1) × 10{sup 8} and (10 ± 1) × 10{sup 9} cm{sup −2}. All a-type (edge) dislocation core structures in all samples formed 5/7-atom ring core structures, whereas all (a + c)-type (mixed) dislocations formed either double 5/6-atom, dissociated 7/4/8/4/9-atom, or dissociated 7/4/8/4/8/4/9-atom core structures. This shows that Si-doping does not affect threading dislocation core structures in GaN. However, electron beam damage at 300 keV produces 4-atom ring structures for (a + c)-type cores in Si-doped GaN.

  7. Dislocation dynamics simulations of plasticity at small scales

    SciTech Connect

    Zhou, Caizhi

    2010-01-01

    As metallic structures and devices are being created on a dimension comparable to the length scales of the underlying dislocation microstructures, the mechanical properties of them change drastically. Since such small structures are increasingly common in modern technologies, there is an emergent need to understand the critical roles of elasticity, plasticity, and fracture in small structures. Dislocation dynamics (DD) simulations, in which the dislocations are the simulated entities, offer a way to extend length scales beyond those of atomistic simulations and the results from DD simulations can be directly compared with the micromechanical tests. The primary objective of this research is to use 3-D DD simulations to study the plastic deformation of nano- and micro-scale materials and understand the correlation between dislocation motion, interactions and the mechanical response. Specifically, to identify what critical events (i.e., dislocation multiplication, cross-slip, storage, nucleation, junction and dipole formation, pinning etc.) determine the deformation response and how these change from bulk behavior as the system decreases in size and correlate and improve our current knowledge of bulk plasticity with the knowledge gained from the direct observations of small-scale plasticity. Our simulation results on single crystal micropillars and polycrystalline thin films can march the experiment results well and capture the essential features in small-scale plasticity. Furthermore, several simple and accurate models have been developed following our simulation results and can reasonably predict the plastic behavior of small scale materials.

  8. Hip arthroscopy versus open surgical dislocation for femoroacetabular impingement

    PubMed Central

    Zhang, Dagang; Chen, Long; Wang, Guanglin

    2016-01-01

    Abstract Background: This meta-analysis aims to evaluate the efficacy and safety of hip arthroscopy versus open surgical dislocation for treating femoroacetabular impingement (FAI) through published clinical trials. Methods: We conducted a comprehensive literature search using PUBMED, EMBASE, and the Cochrane Central Register of Controlled Trials databases for relevant studies on hip arthroscopy and open surgical dislocation as treatment options for FAI. Results: Compared with open surgical dislocation, hip arthroscopy resulted in significantly higher Nonarthritic Hip Scores (NAHS) at 3- and 12-month follow-ups, a significant improvement in NAHS from preoperation to 3 months postoperation, and a significantly lower reoperation rate. Open surgical dislocation resulted in a significantly improved alpha angle by the Dunn view in patients with cam osteoplasty from preoperation to postoperation, compared with hip arthroscopy. This meta-analysis demonstrated no significant differences in the modified Harris Hip Score, Hip Outcome Score-Activities of Daily Living, or Hip Outcome Score-Sport Specific Subscale at 12 months of follow-up, or in complications (including nerve damage, wound infection, and wound dehiscence). Conclusion: Hip arthroscopy resulted in higher NAHS and lower reoperation rates, but had less improvement in alpha angle in patients with cam osteoplasty, than open surgical dislocation. PMID:27741133

  9. Thermal stress induced dislocation distribution in directional solidification of Si for PV application

    NASA Astrophysics Data System (ADS)

    Jiptner, Karolin; Gao, Bing; Harada, Hirofumi; Miyamura, Yoshiji; Fukuzawa, Masayuki; Kakimoto, Koichi; Sekiguchi, Takashi

    2014-12-01

    This paper presents the limitation of the cast technique for silicon growth and the obstacle to reduce the dislocation density below 103 cm-2. The thermal stress induced dislocation density, independent of other dislocation sources, is determined and the result suggests that local dislocation densities as high as 104 cm-2 are readily introduced alone in the cooling period of the crystal growth. Areas of high residual strain and dislocation densities are identified and presented. The experimental results are correlated with numerical simulation based on a three-dimensional Haasen-Alexander-Sumino (HAS) model. The dislocation introduction is caused by an activation of different slip systems in different ingot areas.

  10. Density-based Energy Decomposition Analysis for Intermolecular Interactions with Variationally Determined Intermediate State Energies

    SciTech Connect

    Wu, Q.; Ayers, P.W.; Zhang, Y.

    2009-10-28

    The first purely density-based energy decomposition analysis (EDA) for intermolecular binding is developed within the density functional theory. The most important feature of this scheme is to variationally determine the frozen density energy, based on a constrained search formalism and implemented with the Wu-Yang algorithm [Q. Wu and W. Yang, J. Chem. Phys. 118, 2498 (2003) ]. This variational process dispenses with the Heitler-London antisymmetrization of wave functions used in most previous methods and calculates the electrostatic and Pauli repulsion energies together without any distortion of the frozen density, an important fact that enables a clean separation of these two terms from the relaxation (i.e., polarization and charge transfer) terms. The new EDA also employs the constrained density functional theory approach [Q. Wu and T. Van Voorhis, Phys. Rev. A 72, 24502 (2005)] to separate out charge transfer effects. Because the charge transfer energy is based on the density flow in real space, it has a small basis set dependence. Applications of this decomposition to hydrogen bonding in the water dimer and the formamide dimer show that the frozen density energy dominates the binding in these systems, consistent with the noncovalent nature of the interactions. A more detailed examination reveals how the interplay of electrostatics and the Pauli repulsion determines the distance and angular dependence of these hydrogen bonds.

  11. Improved parameterization of interatomic potentials for rare gas dimers with density-based energy decomposition analysis

    NASA Astrophysics Data System (ADS)

    Zhou, Nengjie; Lu, Zhenyu; Wu, Qin; Zhang, Yingkai

    2014-06-01

    We examine interatomic interactions for rare gas dimers using the density-based energy decomposition analysis (DEDA) in conjunction with computational results from CCSD(T) at the complete basis set (CBS) limit. The unique DEDA capability of separating frozen density interactions from density relaxation contributions is employed to yield clean interaction components, and the results are found to be consistent with the typical physical picture that density relaxations play a very minimal role in rare gas interactions. Equipped with each interaction component as reference, we develop a new three-term molecular mechanical force field to describe rare gas dimers: a smeared charge multipole model for electrostatics with charge penetration effects, a B3LYP-D3 dispersion term for asymptotically correct long-range attractions that is screened at short-range, and a Born-Mayer exponential function for the repulsion. The resulted force field not only reproduces rare gas interaction energies calculated at the CCSD(T)/CBS level, but also yields each interaction component (electrostatic or van der Waals) which agrees very well with its corresponding reference value.

  12. Probability density based gradient projection method for inverse kinematics of a robotic human body model.

    PubMed

    Lura, Derek; Wernke, Matthew; Alqasemi, Redwan; Carey, Stephanie; Dubey, Rajiv

    2012-01-01

    This paper presents the probability density based gradient projection (GP) of the null space of the Jacobian for a 25 degree of freedom bilateral robotic human body model (RHBM). This method was used to predict the inverse kinematics of the RHBM and maximize the similarity between predicted inverse kinematic poses and recorded data of 10 subjects performing activities of daily living. The density function was created for discrete increments of the workspace. The number of increments in each direction (x, y, and z) was varied from 1 to 20. Performance of the method was evaluated by finding the root mean squared (RMS) of the difference between the predicted joint angles relative to the joint angles recorded from motion capture. The amount of data included in the creation of the probability density function was varied from 1 to 10 subjects, creating sets of for subjects included and excluded from the density function. The performance of the GP method for subjects included and excluded from the density function was evaluated to test the robustness of the method. Accuracy of the GP method varied with amount of incremental division of the workspace, increasing the number of increments decreased the RMS error of the method, with the error of average RMS error of included subjects ranging from 7.7° to 3.7°. However increasing the number of increments also decreased the robustness of the method.

  13. Acute finger injuries: part II. Fractures, dislocations, and thumb injuries.

    PubMed

    Leggit, Jeffrey C; Meko, Christian J

    2006-03-01

    Family physicians can treat most finger fractures and dislocations, but when necessary, prompt referral to an orthopedic or hand surgeon is important to maximize future function. Examination includes radiography (oblique, anteroposterior, and true lateral views) and physical examination to detect fractures. Dislocation reduction is accomplished with careful traction. If successful, further treatment focuses on the concomitant soft tissue injury. Referral is needed for irreducible dislocations. Distal phalanx fractures are treated conservatively, and middle phalanx fractures can be treated if reduction is stable. Physicians usually can reduce metacarpal bone fractures, even if there is a large degree of angulation. An orthopedic or hand surgeon should treat finger injuries that are unstable or that have rotation. Collateral ligament injuries of the thumb should be examine with radiography before physical examination. Stable joint injuries can be treated with splinting or casting, although an orthopedic or hand surgeon should treat unstable joints.

  14. Dislocation Dynamics in Multishell Carbon Nano-Onions

    NASA Astrophysics Data System (ADS)

    Dumitrica, Traian; Akatyeva, Evgeniya; Huang, Jianyu

    2011-03-01

    Graphite has long served as a model material to understand dislocations. An early work on natural graphite provided factual evidence for the existence of screw dislocations. Recently, synthetic carbon nanostructures began to be explored in order to understand dislocations at the nanoscale. Here we study the 1/ 2 0001 > edgedislocationinnestedmultishellcarbononions [ 1 ] . Wereportinsituelectronmicroscopyobservationsofdislocationdissociationandannihilationprocessesinindividualnanometer - sizedcarbononions . Essentialfortheseprocessesisthecounterintuitivemotionofthe 1 / 2 0001 edge from the outer surface to the inner region, which cross-links or unlinks a large number of shells. The correlation with atomistic simulations and analysis of the energy, which separates the strain and edge components, indicates that this inward glide originates in the reduction of edge with each inwards glide step, an effect specific to the spherical topology. We thank NSF CAREER Grant No. CMMI-0747684, NSF Grant No. DMR-1006706, and NSF MRSEC Grants No. DMR-0212302 and No. DMR-0819885.

  15. Posterolateral dislocation of the knee: Recognizing an uncommon entity.

    PubMed

    Woon, Colin Yl; Hutchinson, Mark R

    2016-06-18

    Posterolateral dislocations of the knee are rare injuries. Early recognition and emergent open reduction is crucial. A 48-year-old Caucasian male presented with right knee pain and limb swelling 3 d after sustaining a twisting injury in the bathroom. Examination revealed the pathognomonic anteromedial "pucker" sign. Ankle-brachial indices were greater than 1.0 and symmetrical. Radiographs showed a posterolateral dislocation of the right knee. He underwent emergency open reduction without an attempt at closed reduction. Attempts at closed reduction of posterolateral dislocations of the knee are usually impossible because of incarceration of medial soft tissue in the intercondylar notch and may only to delay surgical management and increase the risk of skin necrosis. Magnetic resonance imaging is not crucial in the preoperative period and can lead to delays of up to 24 h. Instead, open reduction should be performed once vascular compromise is excluded. PMID:27335816

  16. Posterolateral dislocation of the knee: Recognizing an uncommon entity

    PubMed Central

    Woon, Colin YL; Hutchinson, Mark R

    2016-01-01

    Posterolateral dislocations of the knee are rare injuries. Early recognition and emergent open reduction is crucial. A 48-year-old Caucasian male presented with right knee pain and limb swelling 3 d after sustaining a twisting injury in the bathroom. Examination revealed the pathognomonic anteromedial “pucker” sign. Ankle-brachial indices were greater than 1.0 and symmetrical. Radiographs showed a posterolateral dislocation of the right knee. He underwent emergency open reduction without an attempt at closed reduction. Attempts at closed reduction of posterolateral dislocations of the knee are usually impossible because of incarceration of medial soft tissue in the intercondylar notch and may only to delay surgical management and increase the risk of skin necrosis. Magnetic resonance imaging is not crucial in the preoperative period and can lead to delays of up to 24 h. Instead, open reduction should be performed once vascular compromise is excluded. PMID:27335816

  17. Dislocation dynamical approach to force fluctuations in nanoindentation experiments

    NASA Astrophysics Data System (ADS)

    Ananthakrishna, G.; Katti, Rohit; K, Srikanth

    2014-09-01

    We develop an approach that combines the power of nonlinear dynamics with the evolution equations for the mobile and immobile dislocation densities and force to explain force fluctuations in nanoindentation experiments. The model includes nucleation, multiplication, and propagation thresholds for mobile dislocations, and other well known dislocation transformation mechanisms. The model predicts all the generic features of nanoindentation such as the Hertzian elastic branch followed by several force drops of decreasing magnitudes, and residual plasticity after unloading. The stress corresponding to the elastic force maximum is close to the yield stress of an ideal solid. The predicted values for all the quantities are close to those reported by experiments. Our model allows us to address the indentation-size effect including the ambiguity in defining the hardness in the force drop dominated regime. At large indentation depths, the hardness remains nearly constant with a marginal decreasing trend.

  18. Acute Dislocation of the Metacarpal-Trapezoid Joint

    PubMed Central

    Plata, Guillermo Varón; Casas, Jairo Antonio Camacho; Rodríguez, Natalia Sauza

    2016-01-01

    The trapezoid metacarpal dislocation is a rare event. In the literature, it is found in case reports. This injury is caused by direct or indirect high energy trauma. In most cases, the dislocation is dorsal and is difficult to reproduce because the joint is not very mobile. Given the low incidence and little evidence supported in the literature regarding the management, this injury can be treated by open or closed reduction; however, it has been published that most authors use Kirschner wire fixation with good results. Here we present our experience in the management of a male patient with acute trapezoid metacarpal dislocation handled with a splint with good functional results at 6 weeks. PMID:27247751

  19. Role of dislocation theory in the design of engineering materials

    SciTech Connect

    Morris, J.W. Jr.

    1980-06-01

    The science of materials development has progressed to a stage in which it is possible to compose a recipe for new materials. The recipe has three steps: given a desirable set of properties and material constraints, one identifies a composition and microstructure to achieve them; given a desirable composition and microstructure, one identifies a processing sequence to achieve them; given a trial alloy, one conducts analytical testing to identify its shortcomings and overcomes them. In effecting each stage of this recipe, it is usually necessary to be aware of and understand the role of the dislocations which determine material properties, define material microstructure, and control its evolution. The role of dislocations is discussed. The text contains examples of particular alloy development efforts, and suggestions for research in dislocation theory which might contribute to the solution of significant problems in materials development.

  20. Quantitative observations of dislocation mechanisms in gamma TiAl

    SciTech Connect

    Viguier, B.; Cieslar, M.; Martin, J.L.; Hemker, K.J.

    1995-08-01

    Quantitative TEM observations have been made on a series of gamma Ti{sub 47}Al{sub 51}Mn{sub 2} polycrystals that were deformed at different temperatures. Special attention has been given to determining the statistical variation of defect densities that occur at the different temperatures. The results, which are in good agreement with mechanical testing, indicate that three different mechanisms control deformation in this alloy: lattice friction and the formation of faulted dipoles at low temperatures, the pinning of ordinary dislocations at intermediate temperatures, and the bowing and looping of dislocations at high temperatures. The anomalous flow strength of this alloy has been found to be related to the intrinsic pinning of ordinary dislocations. Details of this pinning and subsequent unzipping process, which are the basis for the new local-pinning-unzipping (LPU) models, are outlined within.

  1. A general numerical method to solve for dislocation configurations

    NASA Astrophysics Data System (ADS)

    Xin, X. J.; Wagoner, R. H.; Daehn, G. S.

    1999-08-01

    The shape of a mechanically equilibrated dislocation line is of considerable interest in the study of plastic deformation of metals and alloys. A general numerical method for finding such configurations in arbitrary stress fields has been developed. Analogous to the finite-element method (FEM), a general dislocation line is approximated by a series of straight segments (elements) bounded by nodes. The equilibrium configuration is found by minimizing the system energy with respect to nodal positions using a Newton-Raphson procedure. This approach, termed the finite-segment method (FSM), confers several advantages relative to segment-based, explicit formulations. The utility, generality, and robustness of the FSM is demonstrated by analyzing the Orowan bypass mechanism and a model of dislocation generation and equilibration at misfitting particles. Energy differences from previous analytical methods based on simple loop shapes are significant, up to 80 pct. Explicit expressions for the coordinate transformations, energies, and forces required for numerical implementation are presented.

  2. Dislocation of the distal phalanx epiphysis in toddlers.

    PubMed

    Waters, P M; Benson, L S

    1993-07-01

    Two cases of physeal fracture dislocation of the distal phalanx are reviewed. Each injury occurred in a toddler, was originally undiagnosed, and appeared years later as a dorsal mass in a fore-shortened digit with decreased distal interphalangeal joint motion. In each case x-ray films revealed a dislocated epiphysis, accounting for the enlarging dorsal prominence and the phalangeal growth disturbance. These cases demonstrate that dislocation of the distal phalanx epiphysis can occur with a crush injury and may be difficult to detect before development of the ossification center. Careful physical examination and a high index of suspicion will increase the likelihood of early diagnosis. Early open reduction may prevent the late complications of deformity and stiffness. PMID:8349960

  3. Silicon based light emitters utilizing radiation from dislocations; electric field induced shift of the dislocation-related luminescence

    NASA Astrophysics Data System (ADS)

    Arguirov, T.; Mchedlidze, T.; Kittler, M.; Reiche, M.; Wilhelm, T.; Hoang, T.; Holleman, J.; Schmitz, J.

    2009-05-01

    Dislocation rich regions can be controllably formed at a certain location inside a silicon wafer. We studied the light emission properties of such regions located in an electric field of a p-n junction under different excitation conditions. It was found that the luminescence spectra of the dislocations are significantly influenced by the presence of the junction. The dislocation-related luminescence peak position appears red-shifted due to the built-in electric field. A suppression of that field by photo-generation of carriers or by applying a forward bias voltage at the junction leads to a gradual decrease in the energy position of the peaks. The dependence of the peak position on the electric field was found to be a quadratic function, similar to that observed for semiconductor nanostructures. We show that the shift of the peak position is due to the Stark effect on dislocation-related excitonic states. The characteristic constant of the shift, obtained by fitting the data with the quadratic Stark effect equation, was 0.0186 meV/(kV/cm) 2. The observed effect opens new possibilities for integration of a silicon based light emitter, combining the radiation from dislocations with a Stark effect based modulator.

  4. TEM characterization of dislocations in TiB2 particles after hypervelocity impact.

    PubMed

    Guo, Q; Li, J F; Hou, L L; Sun, D L

    2014-12-01

    Characteristic of dislocations in TiB2 particles associated with hypervelocity impact craters in 65 vol.% TiB2/Al composite were investigated by transmission electron microscopy (TEM). Two kinds of dislocation networks in as-impacted TiB2 particles were identified. One is hexagonal dislocation networks including 1/3〈1̄21̄0〉, 〈0001〉, 1/3〈1̄21̄3〉 type dislocations on {0001}, {101̄0}, and {123̄0} planes. Another one is the hexagonal dislocation networks including 1/3〈112̄0〉, 〈0001〉, and 1/3〈112̄3〉 type dislocations on {0001}, {101̄0}, and {11̄00} planes. Formation of dislocation network should be contributed to the parallel sets of "a" type dislocations (1/3〈112̄0〉 or 1/3〈1̄21̄0〉 type dislocations) reacting with parallel sets of "b" type dislocations (〈0001〉 type dislocations) to form "c" type dislocations (1/3〈112̄3〉 or 1/3〈1̄21̄3〉 type dislocations). Moreover, dislocations reaction processes do not result in an energy reduction, and are called quasi-equilibrium configurations. Formation of dislocations may result from high temperature or pressure generated by hypervelocity impact. During the cooling from high temperature and unloading from high pressure, dislocations in TiB2 particles rearranged and transformed to dislocation networks to lower the defect energy. PMID:25108104

  5. Impingement and Dislocation in Total HIP Arthroplasty: Mechanisms and Consequences

    PubMed Central

    Brown, Thomas D; Elkins, Jacob M; Pedersen, Douglas R; Callaghan, John J

    2014-01-01

    In contemporary total hip arthroplasty, instability has been a complication in approximately 2% to 5% of primary surgeries and 5% to 10% of revisions. Due to the reduction in the incidence of wear-induced osteolysis that has been achieved over the last decade, instability now stands as the single most common reason for revision surgery. Moreover, even without frank dislocation, impingement and subluxation are implicated in a set of new concerns arising with advanced bearings, associated with the relatively unforgiving nature of many of those designs. Against that backdrop, the biomechanical factors responsible for impingement, subluxation, and dislocation remain under-investigated relative to their burden of morbidity. This manuscript outlines a 15-year program of laboratory and clinical research undertaken to improve the scientific basis for understanding total hip impingement and dislocation. The broad theme has been to systematically evaluate the role of surgical factors, implant design factors, and patient factors in predisposing total hip constructs to impinge, sublux, and/or dislocate. Because this class of adverse biomechanical events had not lent itself well to study with existing approaches, it was necessary to develop (and validate) a series of new research methodologies, relying heavily on advanced finite element formulations. Specific areas of focus have included identifying the biomechanical challenges posed by dislocation-prone patient activities, quantifying design parameter effects and component surgical positioning effects for conventional metal-on-polyethylene implant constructs, and the impingement/dislocation behavior of non-conventional constructs, quantifying the stabilizing role of the hip capsule (and of surgical repairs of capsule defects), and systematically studying impingement and edge loading of hard-on-hard bearings, fracture of ceramic liners, confounding effects of patient obesity, and subluxation-mediated worsening of third body

  6. Including dislocation flux in a continuum crystal plasticity model to produce size scale effects

    SciTech Connect

    Becker, R; Arsenlis, A; Bulatov, V V; Parks, D M

    2004-02-13

    A novel model has been developed to capture size scale and gradient effects within the context of continuum crystal plasticity by explicitly incorporating details of dislocation transport, coupling dislocation transport to slip, evolving spatial distributions of dislocations consistent with the flux, and capturing the interactions among various dislocation populations. Dislocation flux and density are treated as nodal degrees of freedom in the finite element model, and they are determined as part of the global system of equations. The creation, annihilation and flux of dislocations between elements are related by transport equations. Crystallographic slip is coupled to the dislocation flux and the stress state. The resultant gradients in dislocation density and local lattice rotations are analyzed for geometrically necessary and statistically stored dislocation contents that contribute to strength and hardening. Grain boundaries are treated as surfaces where dislocation flux is restricted depending on the relative orientations of the neighboring grains. Numerical results show different behavior near free surfaces and non-deforming surfaces resulting from differing levels of dislocation transmission. Simulations also show development of dislocation pile-ups at grain boundaries and an increase in flow strength reminiscent of the Hall-Petch model. The dislocation patterns have a characteristic size independent of the numerical discretization.

  7. Grain Boundary Traction Signatures: Quantitative Predictors of Dislocation Emission

    NASA Astrophysics Data System (ADS)

    Li, Ruizhi; Chew, Huck Beng

    2016-08-01

    We introduce the notion of continuum-equivalent traction fields as local quantitative descriptors of the grain boundary interface. These traction-based descriptors are capable of predicting the critical stresses to trigger dislocation emissions from ductile ⟨110 ⟩ symmetrical-tilt nickel grain boundaries. We show that Shockley partials are emitted when the grain boundary tractions, in combination with external tensile loading, generate a resolved shear stress to cause dislocation slip. The relationship between the local grain boundary tractions and the grain boundary energy is established.

  8. Grain Boundary Traction Signatures: Quantitative Predictors of Dislocation Emission.

    PubMed

    Li, Ruizhi; Chew, Huck Beng

    2016-08-19

    We introduce the notion of continuum-equivalent traction fields as local quantitative descriptors of the grain boundary interface. These traction-based descriptors are capable of predicting the critical stresses to trigger dislocation emissions from ductile ⟨110⟩ symmetrical-tilt nickel grain boundaries. We show that Shockley partials are emitted when the grain boundary tractions, in combination with external tensile loading, generate a resolved shear stress to cause dislocation slip. The relationship between the local grain boundary tractions and the grain boundary energy is established. PMID:27588865

  9. Electronic selection rules controlling dislocation glide in bcc metals.

    PubMed

    Jones, Travis E; Eberhart, Mark E; Clougherty, Dennis P; Woodward, Chris

    2008-08-22

    The validity of the structure-property relationships governing the low-temperature deformation behavior of many bcc metals was brought into question with recent ab initio density functional studies of isolated screw dislocations in Mo and Ta. These relationships were semiclassical in nature, having grown from atomistic investigations of the deformation properties of the group V and VI transition metals. We find that the correct form for these structure-property relationships is fully quantum mechanical, involving the coupling of electronic states with the strain field at the core of long a/<2111> screw dislocations. PMID:18764636

  10. Electronic Selection Rules Controlling Dislocation Glide in bcc Metals

    NASA Astrophysics Data System (ADS)

    Jones, Travis E.; Eberhart, Mark E.; Clougherty, Dennis P.; Woodward, Chris

    2008-08-01

    The validity of the structure-property relationships governing the low-temperature deformation behavior of many bcc metals was brought into question with recent ab initio density functional studies of isolated screw dislocations in Mo and Ta. These relationships were semiclassical in nature, having grown from atomistic investigations of the deformation properties of the group V and VI transition metals. We find that the correct form for these structure-property relationships is fully quantum mechanical, involving the coupling of electronic states with the strain field at the core of long a/2⟨111⟩ screw dislocations.

  11. Modelling dislocation cores in MgSiO3 perovskite

    NASA Astrophysics Data System (ADS)

    Cordier, P.; Carrez, P.; Gouriet, K.; Kraych, A.

    2012-12-01

    MgSiO3 perovskite is the most abundant mineral of the Earth's lower mantle (i.e. between 700 and 2900 km depth) and accounts for half of Earth's mass. At lower mantle pressures (25-135 GPa) MgSiO3 crystallises in a distorted (orthorhombic) perovskite structure (described in the following using the Pbnm space group). In this structure, SiO6 octahedra are tilted with tilt angles increasing with increasing pressure. Since it is very difficult to perform deformation experiments under the extreme P, T conditions of the lower mantle, little is known about plastic deformation of MgSiO3 perovskite and its slip systems are still a matter of debate. To overcome this difficulty, we model dislocation core structures in this mineral taking into account the influence of pressure. In this study, we focus on dislocation core structures of dislocations with [100] and [010] Burgers vectors (which derive from <110> Burgers vectors of the underlying pseudo-cubic structure). Atomistic calculations are performed using pair-wise potentials as implemented in the LAMMPS code. The choice of potentials was initially validated by comparing generalized stacking fault (GSF) energies to similar calculations performed with the density functional theory (DFT). The core structures of screw dislocations are calculated using two independent methods. The first one is based on Peierls-Nabarro-Galerkin simulations involving GSF as an input. Direct calculations have also bee performed using cluster approach. It turns out that screw dislocations with [100] Burgers vector are characterised by a core mostly spread in the (010) plane. The core exhibits two edge-sharing octahedra in a configuration very similar to that modelled in SrTiO3 cubic perovskite. The structure of [010] screw dislocations is more complex with dissociation into two, non-collinear partial dislocations with a significant non-screw component. Both dislocations exhibit high Peierls stresses. This illustrates the effect of orthorhombic

  12. Hall Conductivity in the Cosmic Defect and Dislocation Spacetime

    NASA Astrophysics Data System (ADS)

    Ma, Kai; Wang, Jian-Hua; Yang, Huan-Xiong; Fan, Hua-Wei

    2016-10-01

    Influences of topological defect and dislocation on conductivity behavior of charge carries in external electromagnetic fields are studied. Particularly the quantum Hall effect is investigated in detail. It is found that the nontrivial deformations of spacetime due to topological defect and dislocation produce an electric current at the leading order of perturbation theory. This current then induces a deformation on the Hall conductivity. The corrections on the Hall conductivity depend on the external electric fields, the size of the sample and the momentum of the particle.

  13. [Couch-netting operation for dislocation of adult lens].

    PubMed

    Jiang, B L; Tang, Y Z

    1992-06-01

    Clinical data of 12 adult cases of dislocation of lens treated with couching-netting operating were analysed, including cases of traumatic cataracts with complications of glaucoma and cataract couching surgical complication of phacolysis. The result was rather satisfactory. Eye sight was corrected, most of the corrective vision was over 0.5 level, intraocular pressure was controlled and no serious complication was found. According to the authors experience, couching-netting was recommended as a simple and effective method for treating dislocation of adult lens.

  14. A Universal Approach Towards Computational Characterization of Dislocation Microstructure

    NASA Astrophysics Data System (ADS)

    Steinberger, Dominik; Gatti, Riccardo; Sandfeld, Stefan

    2016-06-01

    Dislocations—linear defects within the crystal lattice of, e.g., metals—have been directly observed and analyzed for nearly a century. While experimental characterization methods can nowadays reconstruct three-dimensional pictures of complex dislocation networks, simulation methods are at the same time more and more able to predict the evolution of such systems in great detail. Concise methods for analyzing and comparing dislocation microstructure, however, are still lagging behind. We introduce a universal microstructure "language" which could be used for direct comparisons and detailed analysis of very different experimental and simulation methods.

  15. Treatment of chronic radial head dislocations in children.

    PubMed

    Belangero, W D; Livani, B; Zogaib, R K

    2007-04-01

    From 1990 to 2005 our department treated nine patients with chronic radial head dislocation by an ulnar osteotomy and indirect reduction by interosseous membrane. The patients varied in age from 2 years and 8 months to 10 years, and the time from the injury to operation ranged from 40 days to 3 years. The range of functional motion and carrying angle was restored in all nine patients, and no complications, such as recurrent dislocation, infection, or neurovascular injury were observed. This technique has proven to be a successful approach to treating such cases, with a low range of complications and good functional results. PMID:16741732

  16. Weak indices and dislocations in general topological band structures

    NASA Astrophysics Data System (ADS)

    Ran, Ying

    2011-03-01

    It has recently been shown that crystalline defects - dislocation lines - in three dimensional topological insulators, can host protected one dimensional modes propagating along their length. We generalize this observation to the case of topological superconductors and other insulators of the Altland Zirnbauer classification, in d=2,3 dimensions. In general, protected dislocation modes are controlled by the topological indices in (d-1) dimensions. This is shown by relating this feature to characteristic properties of surface states of these topological phases. This observation also allows us to constrain these surface states properties, which is illustrated by an addition formula for (d-1) and (d-2) indices of a topological superconductor.

  17. A Universal Approach Towards Computational Characterization of Dislocation Microstructure

    NASA Astrophysics Data System (ADS)

    Steinberger, Dominik; Gatti, Riccardo; Sandfeld, Stefan

    2016-08-01

    Dislocations—linear defects within the crystal lattice of, e.g., metals—have been directly observed and analyzed for nearly a century. While experimental characterization methods can nowadays reconstruct three-dimensional pictures of complex dislocation networks, simulation methods are at the same time more and more able to predict the evolution of such systems in great detail. Concise methods for analyzing and comparing dislocation microstructure, however, are still lagging behind. We introduce a universal microstructure "language" which could be used for direct comparisons and detailed analysis of very different experimental and simulation methods.

  18. Radial head dislocation with acute plastic bowing of the ulna.

    PubMed

    Sai, Shigaku; Fujii, Katsuyuki; Chino, Hiroyuki; Inoue, Junichi

    2005-01-01

    Five radial head dislocations with acute plastic bowing of the ulna in patients aged 6-12 years were reviewed. Closed reduction was successful in two, and open reduction was required in three patients in whom treatment was started more than 2 weeks after injury. In one child who presented 2 months after injury, realignment by osteotomy of the ulna as well as open reduction of the radial head was necessary. Follow-up evaluations at 6-24 months revealed good clinical outcomes in all patients. Awareness of this type of radial head dislocation is important to avoid delays in diagnosis and treatment. PMID:15666132

  19. A distinct form of spondyloepimetaphyseal dysplasia with multiple dislocations.

    PubMed Central

    Hall, C M; Elçioglu, N H; Shaw, D G

    1998-01-01

    Three unrelated patients with identical radiological features are presented. Hypotonia was noted at birth and one patient was diagnosed as having congenital fibre type disproportion in the neonatal period. Later muscle biopsies, however, were entirely normal. All patients, now in their teens and twenties, are of normal intelligence, show striking epiphyseal and metaphyseal changes of the long bones, and have joint laxity and multiple dislocations of large joints, which are particularly incapacitating at the knees. These three cases represent a sporadic, previously unreported skeletal dysplasia with spondyloepimetaphyseal distribution and multiple large joint dislocations. Images PMID:9678701

  20. Dislocation mechanism of deuterium retention in tungsten under plasma implantation.

    PubMed

    Dubinko, V I; Grigorev, P; Bakaev, A; Terentyev, D; van Oost, G; Gao, F; Van Neck, D; Zhurkin, E E

    2014-10-01

    We have developed a new theoretical model for deuterium (D) retention in tungsten-based alloys on the basis of its being trapped at dislocations and transported to the surface via the dislocation network with parameters determined by ab initio calculations. The model is used to explain experimentally observed trends of D retention under sub-threshold implantation, which does not produce stable lattice defects to act as traps for D in conventional models. Saturation of D retention with implantation dose and effects due to alloying of tungsten with, e.g. tantalum, are evaluated, and comparison of the model predictions with experimental observations under high-flux plasma implantation conditions is presented.

  1. ACUTE ISOLATED ANTEROLATERAL DISLOCATION OF THE PROXIMAL TIBIOFIBULAR JOINT.

    PubMed

    Almeida Silvares, Paulo Roberto de; Fernandes Guerreiro, Joao Paulo; Müller, Sergio Swain; Pereira, Ricardo Violante; Vannini, Rodrigo

    2010-01-01

    Isolated traumatic dislocation of the proximal tibiofibular joint is rare. This injury may go unrecognized or be misdiagnosed at the initial presentation. Lack of clinical suspicion can cause diagnostic problems. The diagnosis requires an accurate history of the mechanism and symptoms of the injury, and adequate clinical and radiographic evaluation of both knees. Unrecognized cases are a source of chronic abnormalities. The treatment consists of closed reduction and immobilization or, in non-reducible or unstable cases, open reduction with temporary internal fixation. A rare case of isolated proximal tibiofibular dislocation in a basketball player is reported to illustrate this injury.

  2. 78 FR 39721 - Constitution Pipeline Company, LLC; Notice of Application

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-07-02

    ... Energy Regulatory Commission Constitution Pipeline Company, LLC; Notice of Application Take notice that on June 13, 2013, Constitution Pipeline Company, LLC (Constitution), having its principal place of...\\ Constitution further requests that the Commission grant Constitution a blanket certificate...

  3. 3 CFR 8562 - Proclamation 8562 of September 16, 2010. Constitution Day and Citizenship Day, Constitution Week...

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    .... Constitution Day and Citizenship Day, Constitution Week, 2010 8562 Proclamation 8562 Presidential Documents Proclamations Proclamation 8562 of September 16, 2010 Proc. 8562 Constitution Day and Citizenship Day... the States, the Framers advanced our national journey. On Constitution Day and Citizenship Day,...

  4. 75 FR 57835 - Constitution Day and Citizenship Day, Constitution Week, 2010

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-09-22

    ... two hundred and thirty-fifth. (Presidential Sig.) [FR Doc. 2010-23898 Filed 9-21-10; 11:15 am] Billing... Proclamation 8562--Constitution Day and Citizenship Day, Constitution Week, 2010 Proclamation 8563--National... President ] Proclamation 8562 of September 16, 2010 Constitution Day and Citizenship Day, Constitution...

  5. Constitutional and Non-Constitutional Governments...Similarities and Differences throughout History. Resource Packet.

    ERIC Educational Resources Information Center

    Pallasch, Brian Thomas

    This civic education resource packet is designed to provide teachers, community leaders, and other civic educators with an understanding of the differences between constitutional and non-constitutional governments. Six papers discussing the topic are included: "The Differences bewteen Constitutional and Non-Constitutional Governments" (John…

  6. Closed-form density-based framework for automatic detection of cellular morphology changes

    PubMed Central

    Duong, Tarn; Goud, Bruno; Schauer, Kristine

    2012-01-01

    A primary method for studying cellular function is to examine cell morphology after a given manipulation. Fluorescent markers attached to proteins/intracellular structures of interest in conjunction with 3D fluorescent microscopy are frequently exploited for functional analysis. Despite the central role of morphology comparisons in cell biological approaches, few statistical tools are available that allow biological scientists without a high level of statistical training to quantify the similarity or difference of fluorescent images containing multifactorial information. We transform intracellular structures into kernels and develop a multivariate two-sample test that is nonparametric and asymptotically normal to directly and quantitatively compare cellular morphologies. The asymptotic normality bypasses the computationally intensive calculations used by the usual resampling techniques to compute the P-value. Because all parameters required for the statistical test are estimated directly from the data, it does not require any subjective decisions. Thus, we provide a black-box method for unbiased, automated comparison of cell morphology. We validate the performance of our test statistic for finite synthetic samples and experimental data. Employing our test for the comparison of the morphology of intracellular multivesicular bodies, we detect changes in their distribution after disruption of the cellular microtubule cytoskeleton with high statistical significance in fixed samples and live cell analysis. These results demonstrate that density-based comparison of multivariate image information is a powerful tool for automated detection of cell morphology changes. Moreover, the underlying mathematics of our test statistic is a general technique, which can be applied in situations where two data samples are compared. PMID:22586080

  7. Dislocation motion and grain boundary migration in two-dimensional tungsten disulphide.

    PubMed

    Azizi, Amin; Zou, Xiaolong; Ercius, Peter; Zhang, Zhuhua; Elías, Ana Laura; Perea-López, Néstor; Stone, Greg; Terrones, Mauricio; Yakobson, Boris I; Alem, Nasim

    2014-01-01

    Dislocations have a significant effect on mechanical, electronic, magnetic and optical properties of crystals. For a dislocation to migrate in bulk crystals, collective and simultaneous movement of several atoms is needed. In two-dimensional crystals, in contrast, dislocations occur on the surface and can exhibit unique migration dynamics. Dislocation migration has recently been studied in graphene, but no studies have been reported on dislocation dynamics for two-dimensional transition metal dichalcogenides with unique metal-ligand bonding and a three-atom thickness. This study presents dislocation motion, glide and climb, leading to grain boundary migration in a tungsten disulphide monolayer. Direct atomic-scale imaging coupled with atomistic simulations reveals a strikingly low-energy barrier for glide, leading to significant grain boundary reconstruction in tungsten disulphide. The observed dynamics are unique and different from those reported for graphene. Through strain field mapping, we also demonstrate how dislocations introduce considerable strain along the grain boundaries and at the dislocation cores.

  8. Strange behavior of dislocations of a certain type: Self-locking

    NASA Astrophysics Data System (ADS)

    Greenberg, B. A.; Ivanov, M. A.

    2016-04-01

    The results of studying the self-locking of dislocations, namely, the transformation of glissile dislocations into blocked dislocations in the absence of an applied stress, are generalized. The existence of selflocking is theoretically grounded and experimentally proved via the observation of dislocation extension along a preferred direction upon loading-free heating after preliminary plastic deformation. The following concept is developed to explain the experimental results: an effective force appears in the case of a two-valley dislocation potential relief; it is proportional to the difference between the valley depths and causes the transformation of a dislocation into an indestructible barrier. The temperature anomaly of yield strength and the dislocation self-locking are shown to have the same nature—a two-valley dislocation potential relief. Both effects were observed in Ni3Al- and TiAl-type intermetallics and a pure metal (magnesium).

  9. Volar perilunate dislocation in an ununited scaphoid of a child: a case report.

    PubMed

    Ramesh, Balasundaram; Shetty, Sanathkumar; Clay, Nigel R

    2010-07-01

    Volar perilunate dislocations of the wrist are rare. An unusual case of volar perilunate dislocation in the presence of an ununited scaphoid in a skeletally immature patient is presented. PMID:20386327

  10. The definition of recurrent shoulder dislocation in tramadol induced seizure patients

    PubMed Central

    Nakhaei Amroodi, Morteza; Iri, Abdolrazzagh; Akhoondi, Salehe

    2015-01-01

    Background: Prevalence of recurrent shoulder dislocation in patients taking tramadol has not been studied yet; so, this study aims to study the recurrent shoulder dislocation following tramadol induced seizure. Methods: In this cross-sectional study, 205 patients with recurrent shoulder dislocation complaints (2 or more) referred to Shafa Orthopedic and Iranmehr hospitals Tehran, Iran, from October 2012 to October 2014 were studied. Data on patient history and physical examination, patient demographic information such as age, sex, age at first dislocation, total number of dislocation, cause of the first dislocation, history of tramadol use, number of dislocation following tramadol induced seizure, history of other drugs use, the dominant hand, involved side, direction of dislocations and greater tuberosity fracture was recorded using a pre-designed questionnaire. Categorical variables were compared by chi-square test and the means were compared with student T-test. Results: In this study, 50 patients (24.4%) suffered from tramadol induced seizures and recurrent shoulder dislocation. Results showed that there was a significant relationship between the number of dislocation and tramadol use (P = 0.02). Recurrent shoulder dislocation following tramadol induced seizure was significantly associated with greater tuberosity fracture of humerus (P = 0.04); in 49 out of 50 patients (98%) dislocation was of anterior type. Conclusion: The findings of this study suggest that tramadol induced seizure may increase the risk of recurrent shoulder dislocation. Furthermore, the prevalence of greater tuberosity fracture in shoulder dislocation increases following tramadol induced seizure; and anterior shoulder dislocation is the most common type of dislocation following tramadol induced seizure. PMID:26913261

  11. The molecular structure within dislocations in Cannabis sativa fibres studied by polarised Raman microspectroscopy.

    PubMed

    Thygesen, Lisbeth G; Gierlinger, Notburga

    2013-06-01

    Polarised Raman micrsospectroscopy was employed to study the molecular structure within dislocations (slip planes) in the cell walls of Hemp fibre cells (Cannabis sativa (L.)). It was found that the cellulose microfibrils within dislocations have a different orientation than in the surrounding cell wall, and that the cellulose in the transition zones between a large dislocation and the surrounding wall may have yet another orientation. Furthermore, cellulose orientation seemed to be less uniform within dislocations than in the surrounding cell wall.

  12. Defining the criteria for identifying constitutional epimutations.

    PubMed

    Sloane, Mathew A; Ward, Robyn L; Hesson, Luke B

    2016-01-01

    In the January 2016 issue of Clinical Epigenetics, Quiñonez-Silva et al. (Clin Epigenetics 8:1, 2016) described a possible constitutional epimutation of the RB1 gene as a cause of hereditary predisposition to retinoblastoma. The term constitutional epimutation describes an epigenetic aberration in normal tissues that predisposes to disease. The data presented by Quiñonez-Silva et al. are interesting, but further analysis is required to demonstrate a constitutional epimutation in this family. Here, we define the criteria and describe the experimental approach necessary to identify an epigenetic aberration as a constitutional epimutation. PMID:27096027

  13. Testing of constitutive models in LAME.

    SciTech Connect

    Hammerand, Daniel Carl; Scherzinger, William Mark

    2007-09-01

    Constitutive models for computational solid mechanics codes are in LAME--the Library of Advanced Materials for Engineering. These models describe complex material behavior and are used in our finite deformation solid mechanics codes. To ensure the correct implementation of these models, regression tests have been created for constitutive models in LAME. A selection of these tests is documented here. Constitutive models are an important part of any solid mechanics code. If an analysis code is meant to provide accurate results, the constitutive models that describe the material behavior need to be implemented correctly. Ensuring the correct implementation of constitutive models is the goal of a testing procedure that is used with the Library of Advanced Materials for Engineering (LAME) (see [1] and [2]). A test suite for constitutive models can serve three purposes. First, the test problems provide the constitutive model developer a means to test the model implementation. This is an activity that is always done by any responsible constitutive model developer. Retaining the test problem in a repository where the problem can be run periodically is an excellent means of ensuring that the model continues to behave correctly. A second purpose of a test suite for constitutive models is that it gives application code developers confidence that the constitutive models work correctly. This is extremely important since any analyst that uses an application code for an engineering analysis will associate a constitutive model in LAME with the application code, not LAME. Therefore, ensuring the correct implementation of constitutive models is essential for application code teams. A third purpose of a constitutive model test suite is that it provides analysts with example problems that they can look at to understand the behavior of a specific model. Since the choice of a constitutive model, and the properties that are used in that model, have an enormous effect on the results of an

  14. A modified surgical technique for reconstruction of an acute acromioclavicular joint dislocation

    PubMed Central

    Marchie, Anthony; Kumar, Arun; Catre, Melanio

    2009-01-01

    We report a modified surgical technique for reconstruction of coracoclavicular and acromioclavicular ligaments after acute dislocation of acromioclavicular joint using suture anchors. We have repaired 3 consecutive type III acromioclavicular dislocations with good results. This technique is simple and safe and allows anatomical reconstruction of the ligaments in acute dislocations. PMID:20671868

  15. Scaphoid dislocation associated with axial carpal dissociation during volar flexion of the wrist: a case report.

    PubMed

    Kanaya, Kohei; Wada, Takuro; Yamashita, Toshihiko

    2010-01-01

    We present the first report of a patient with an isolated scaphoid dislocation with axial carpal dissociation sustained during volar flexion of the wrist. The scaphoid was dislocated to the radial side of the radial styloid process and was slightly shifted to the dorsal side. It was shown that the position of the wrist played an irrelevant role for occurring scaphoid dislocation.

  16. 20 CFR 663.105 - When must adults and dislocated workers be registered?

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 20 Employees' Benefits 3 2011-04-01 2011-04-01 false When must adults and dislocated workers be... LABOR ADULT AND DISLOCATED WORKER ACTIVITIES UNDER TITLE I OF THE WORKFORCE INVESTMENT ACT Delivery of Adult and Dislocated Worker Services Through the One-Stop Delivery System § 663.105 When must adults...

  17. 20 CFR 663.105 - When must adults and dislocated workers be registered?

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 20 Employees' Benefits 4 2013-04-01 2013-04-01 false When must adults and dislocated workers be... LABOR (CONTINUED) ADULT AND DISLOCATED WORKER ACTIVITIES UNDER TITLE I OF THE WORKFORCE INVESTMENT ACT Delivery of Adult and Dislocated Worker Services Through the One-Stop Delivery System § 663.105 When...

  18. 20 CFR 663.105 - When must adults and dislocated workers be registered?

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 20 Employees' Benefits 4 2014-04-01 2014-04-01 false When must adults and dislocated workers be... LABOR (CONTINUED) ADULT AND DISLOCATED WORKER ACTIVITIES UNDER TITLE I OF THE WORKFORCE INVESTMENT ACT Delivery of Adult and Dislocated Worker Services Through the One-Stop Delivery System § 663.105 When...

  19. 20 CFR 663.105 - When must adults and dislocated workers be registered?

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 20 Employees' Benefits 4 2012-04-01 2012-04-01 false When must adults and dislocated workers be... LABOR (CONTINUED) ADULT AND DISLOCATED WORKER ACTIVITIES UNDER TITLE I OF THE WORKFORCE INVESTMENT ACT Delivery of Adult and Dislocated Worker Services Through the One-Stop Delivery System § 663.105 When...

  20. 76 FR 43729 - Notice of Random Assignment Study To Evaluate Workforce Investment Act Adult and Dislocated...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-07-21

    ... Adult and Dislocated Worker Programs; Request for Comment AGENCY: Employment and Training Administration... intensive services and training provided under the Workforce Investment Act (WIA) Adult and Dislocated... WIA Adult and Dislocated Worker programs will be required to participate in the study during a...

  1. 20 CFR 663.105 - When must adults and dislocated workers be registered?

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 20 Employees' Benefits 3 2010-04-01 2010-04-01 false When must adults and dislocated workers be... LABOR ADULT AND DISLOCATED WORKER ACTIVITIES UNDER TITLE I OF THE WORKFORCE INVESTMENT ACT Delivery of Adult and Dislocated Worker Services Through the One-Stop Delivery System § 663.105 When must adults...

  2. Uncovertebral joint injury in cervical facet dislocation: the headphones sign.

    PubMed

    Palmieri, Francesco; Cassar-Pullicino, Victor N; Dell'Atti, Claudia; Lalam, Radhesh K; Tins, Bernhard J; Tyrrell, Prudencia N M; McCall, Iain W

    2006-06-01

    The purpose of our study is to demonstrate the uncovertebral mal-alignment as a reliable indirect sign of cervical facet joint dislocation. We examined the uncovertebral axial plane alignment of 12 patients with unilateral and bilateral cervical facet joint dislocation (UCFJD and BCFJD, respectively), comparing its frequency to the reverse hamburger bun sign on CT and MR axial images. Of the seven cases with BCFJD, five clearly demonstrated the diagnostic reverse facet joint hamburger bun sign on CT and MR images, but in two cases this sign was not detectable. In the five cases with UCFJD, four demonstrated the reverse hamburger bun sign on both CT and MRI. In one case the reverse hamburger bun sign was not seen adequately with either image modality, but the facet dislocation was identified on sagittal imaging. The uncovertebral mal-alignment was detected in all 12 cases. Normally, the two components of the uncovertebral joint enjoy a concentric relationship that in the axial plane is reminiscent of the relationship of headphones with the wearer's head. We name this appearance the 'headphones' sign. Radiologists should be aware of the headphones sign as a reliable indicator of facet joint dislocation on axial imaging used in the assessment of cervical spine injuries.

  3. Method of inhibiting dislocation generation in silicon dendritic webs

    DOEpatents

    Spitznagel, John A.; Seidensticker, Raymond G.; McHugh, James P.

    1990-11-20

    A method of tailoring the heat balance of the outer edge of the dendrites adjacent the meniscus to produce thinner, smoother dendrites, which have substantially less dislocation sources contiguous with the dendrites, by changing the view factor to reduce radiation cooling or by irradiating the dendrites with light from a quartz lamp or a laser to raise the temperature of the dendrites.

  4. Dislocation of stapes with footplate fracture caused by indirect trauma.

    PubMed

    Kagoya, Ryoji; Ito, Ken; Kashio, Akinori; Karino, Shotaro; Yamasoba, Tatsuya

    2010-09-01

    We report the first case of isolated stapedial dislocation caused by indirect head trauma, and present imaging and surgical findings in the case of a 25-year-old woman who suffered hearing loss and dizziness after head trauma caused by a traffic accident. The pure tone average was 60 dB, with an air-bone gap of 50 dB. The stapedial reflex was positive with the probe on the affected ear. Computed tomography scans revealed a longitudinal fracture of the temporal bone and a dislocated stapedial superstructure in the tympanic cavity, adhering to the tympanic membrane. During surgery, it was found that the stapes was broken at the base of the posterior crus and at the anterior one third of the footplate and that the stapedial superstructure was dislocated outward and downward, with the anterior one third of the footplate adhering to the tympanic membrane. The stapedial tendon was connected to the superstructure. Ossicular chain reconstruction was performed with success. In the present case, two mechanisms may have acted together: 1) an increase in perilymphatic pressure that caused the footplate to fracture, and 2) a distorting force that broke the posterior crus, disconnecting the incudostapedial joint, and finally dislocating the stapedial superstructure together with the anterior part of the footplate.

  5. Non-singular dislocation loops in gradient elasticity

    NASA Astrophysics Data System (ADS)

    Lazar, Markus

    2012-04-01

    Using gradient elasticity, we give in this Letter the non-singular fields produced by arbitrary dislocation loops in isotropic media. We present the ‘modified’ Mura, Peach-Koehler and Burgers formulae in the framework of gradient elasticity theory.

  6. [A Case of Traumatic Dislocation of the Penis].

    PubMed

    Taguchi, Makoto; Inoue, Takaaki; Nishida, Teruhisa; Kawakita, Shigenari; Muguruma, Kouei; Murota, Takashi; Kinoshita, Hidefumi; Matsuda, Tadashi

    2016-08-01

    We report a rare case of a traumatic dislocation of the penis. The patient was a 39-year-old man who was ambulanced to our hospital because of a motorbike accident. He was diagnosed to have a pelvic fracture. He was admitted to our department because of his urinary retention and lower abdominal pain. Only the penile skin was left as the genital organ, and neither the penis nor the glans penis was palpable. As the computed tomography scan of the abdomen revealed the dislocation of the penis under the skin in the foreside of the pubic bone, urinary retention due to the traumatic dislocation of the penis was diagnosed, and a percutaneous cystostomy was performed. After improvement of his general condition, the patient was transferred to our department for the evaluation of the perineal region, including the lower urinary tract, and for the treatment of the traumatic dislocation of the penis. First, as hematoma and abscess in the left spermatic cord were suspected by magnetic resonance imaging of the pelvic region, removal of the hematoma and abscess in the left spermatic cord as well as an anterograde cystoscopy were performed under lumbar anesthesia, and the absence of urethral injury was confirmed. After infection control, repositioning of the penis was jointly performed with the Department of Plastic Surgery of our hospital under general anesthesia. After the operation, spontaneous urination was observed and erectile function was observed to be normal.

  7. Continuum simulation of dislocation dynamics: Predictions for internal friction response

    SciTech Connect

    Greaney, P. Alex; Friedman, Lawrence H.; Chrzan, D.C.

    2002-02-19

    The amplitude dependent mechanical loss due to bosing of an idealized Frank-Read Source is studied using both simulation and analytical techniques. Dislocations are modeled within isotropic elasticity theory, and are assumed to be in the over-damped limit.

  8. White Beam Microdiffraction and Dislocations Gradients (Chapter 79)

    SciTech Connect

    Ice, Gene E; Barabash, Rozaliya

    2007-03-01

    Dislocations are lines of irregularity in the structure of a solid analogous to the bumps in a badly laid carpet. Like these bumps they can be easily moved, and they provide the most important mechanism by which the solid can be deformed. They also have a strong influence on crystal growth and on the electronic properties of semiconductors.

  9. A Qualitative Study of the Dislocated Working Class

    ERIC Educational Resources Information Center

    Fouad, Nadya A.; Cotter, Elizabeth W.; Carter, Laura; Bernfeld, Steven; Gray, India; Liu, Jane P.

    2012-01-01

    This qualitative study examines factors that influence the career decisions of dislocated workers. The research focuses on individuals identified as working class, as this group has been relatively ignored in past research compared to individuals from higher socioeconomic statuses. Participants include 13 individuals (10 females and 3 males)…

  10. Distal Radius Radiographic Indices and Perilunate Fracture Dislocation

    PubMed Central

    Bagherifard, Abolfazl; Jafari, Davod; Keihan Shokouh, Hassan; Motavallian, Ebrahim; Najd Mazhar, Farid

    2016-01-01

    Background Distal radius radiographic indices may play a role as risk factors in pathogenesis of Kienbock’s disease, scaphoid fracture and nonunion. Perilunate fracture dislocations are devastating wrist injuries, and their relationship and distal radius indices have not been addressed in the literature. Objectives The aim of this study was to evaluate the possible role of distal radius radiographic indices including radial height, radial inclination, ulnar variance and volar tilt as risk factors in the perilunate fracture dislocation injury of the wrist. Patients and Methods We studied distal radius radiographic indices including radial height, radial inclination, ulnar variance and volar tilt in 43 patients with perilunate fracture dislocations and compared them with 44 wrists in the control group. Results The mean values of the radial height, radial inclination, ulnar variance and volar tilt were 12.74 (5 - 18), 24.20 (7 - 35), -0.73 (-5 - 4) and 12.28 (2 - 20) in the patient group. These values were 12.68 (9 - 22), 23.22 (17 - 30), -0.11 (-4 - 3) and 11.05 (-3 - 20), respectively in the control group. There was no statistically significant difference between the two groups. Conclusions This study did not show that distal radius anatomical indices including the radial height, radial inclination, ulnar variance and volar tilt influence perilunate fracture dislocation as risk factors.

  11. Temporomandibular joint dislocation and deafness from a cricket ball injury.

    PubMed

    Murthy, P; Bandasson, C; Dhillon, R S

    1994-05-01

    Cricket is a national sport in some countries and can be potentially hazardous. We report an incident of a cricket ball impact to the chin, which resulted in posterior dislocation of both temporomandibular joints and bilateral mixed deafness. There appear to be no similar case reports in the literature.

  12. Edge Stabilized Ribbon (ESR); Stress, Dislocation Density and Electronic Performance

    NASA Technical Reports Server (NTRS)

    Sachs, E. M.

    1984-01-01

    The edge stabilized ribbon (ESR) silicon ribbon was grown in widths of 1, 2.2 and 4.0 inches at speeds ranging from .6 to 7 in/min, which result in ribbon thicknesses of 5 to 400 microns. One of the primary problems remaining in ESR growth is that of thermally induced mechanical stresses. This problem is manifested as ribbon with a high degree of residual stress or as ribbon with buckled ribbon. Thermal stresses result in a high dislocation density in the grown material, resulting in compromised electronic performance. Improvements in ribbon flatness were accomplished by modification of the ribbon cooling profile. Ribbon flatness and other experimental observations of ESR ribbon are discussed. Laser scanner measurements show a good correlation between diffusion length and dislocation density which indicates that the high dislocation densities are the primary cause of the poor current performance of ESR materials. Dislocation densities were reduced and improved electronic performance resulted. Laser scanner data on new and old material are presented.

  13. Plastic deformation of tubular crystals by dislocation glide

    NASA Astrophysics Data System (ADS)

    Beller, Daniel A.; Nelson, David R.

    2016-09-01

    Tubular crystals, two-dimensional lattices wrapped into cylindrical topologies, arise in many contexts, including botany and biofilaments, and in physical systems such as carbon nanotubes. The geometrical principles of botanical phyllotaxis, describing the spiral packings on cylinders commonly found in nature, have found application in all these systems. Several recent studies have examined defects in tubular crystals associated with crystalline packings that must accommodate a fixed tube radius. Here we study the mechanics of tubular crystals with variable tube radius, with dislocations interposed between regions of different phyllotactic packings. Unbinding and separation of dislocation pairs with equal and opposite Burgers vectors allow the growth of one phyllotactic domain at the expense of another. In particular, glide separation of dislocations offers a low-energy mode for plastic deformations of solid tubes in response to external stresses, reconfiguring the lattice step by step. Through theory and simulation, we examine how the tube's radius and helicity affects, and is in turn altered by, the mechanics of dislocation glide. We also discuss how a sufficiently strong bending rigidity can alter or arrest the deformations of tubes with small radii.

  14. Limits of Dislocation-based Deformation of Ni

    NASA Astrophysics Data System (ADS)

    Follstaedt, David; Knapp, James; Hugo, Richard; Kung, Harriet

    2001-11-01

    How small can metallic grains be and still deform by dislocation glide? This question is critical to understanding the mechanical properties of nanocrystalline Ni and for enhancing yield strength and hardness while maintaining ductility. As grain size is reduced in the micrometer range, the hardness of Ni scales as H = Ho + kd-1/2 in accordance with the dislocation-based Hall-Petch relation; however, below 100-50 nm the observed hardness no longer increases. Theoretical treatments indicate that intergranular types of deformation will replace dislocation motion at a few 10's of nanometers. To probe this limit, we have prepared a nearly ideal Ni material with very fine, uniform grain size and uncontaminated grain boundaries by using pulsed laser deposition. In situ tensile straining in the TEM directly shows dislocation motion in grains as small as 20 nm. Moreover, the material exhibits excellent ductility, consistent with this mechanism. We also find high yield strengths (2.4 GPa) and hardnesses (10 GPa) that agree with extensions of the Hall-Petch mechanism down to 12 nm grain-size. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94AL85000.

  15. 21 CFR 890.3665 - Congenital hip dislocation abduction splint.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Congenital hip dislocation abduction splint. 890.3665 Section 890.3665 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES PHYSICAL MEDICINE DEVICES Physical Medicine Prosthetic Devices §...

  16. 21 CFR 890.3665 - Congenital hip dislocation abduction splint.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Congenital hip dislocation abduction splint. 890.3665 Section 890.3665 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES PHYSICAL MEDICINE DEVICES Physical Medicine Prosthetic Devices §...

  17. 21 CFR 890.3665 - Congenital hip dislocation abduction splint.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Congenital hip dislocation abduction splint. 890.3665 Section 890.3665 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES PHYSICAL MEDICINE DEVICES Physical Medicine Prosthetic Devices §...

  18. 21 CFR 890.3665 - Congenital hip dislocation abduction splint.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Congenital hip dislocation abduction splint. 890.3665 Section 890.3665 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES PHYSICAL MEDICINE DEVICES Physical Medicine Prosthetic Devices §...

  19. 21 CFR 890.3665 - Congenital hip dislocation abduction splint.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Congenital hip dislocation abduction splint. 890.3665 Section 890.3665 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES PHYSICAL MEDICINE DEVICES Physical Medicine Prosthetic Devices §...

  20. [A Case of Traumatic Dislocation of the Penis].

    PubMed

    Taguchi, Makoto; Inoue, Takaaki; Nishida, Teruhisa; Kawakita, Shigenari; Muguruma, Kouei; Murota, Takashi; Kinoshita, Hidefumi; Matsuda, Tadashi

    2016-08-01

    We report a rare case of a traumatic dislocation of the penis. The patient was a 39-year-old man who was ambulanced to our hospital because of a motorbike accident. He was diagnosed to have a pelvic fracture. He was admitted to our department because of his urinary retention and lower abdominal pain. Only the penile skin was left as the genital organ, and neither the penis nor the glans penis was palpable. As the computed tomography scan of the abdomen revealed the dislocation of the penis under the skin in the foreside of the pubic bone, urinary retention due to the traumatic dislocation of the penis was diagnosed, and a percutaneous cystostomy was performed. After improvement of his general condition, the patient was transferred to our department for the evaluation of the perineal region, including the lower urinary tract, and for the treatment of the traumatic dislocation of the penis. First, as hematoma and abscess in the left spermatic cord were suspected by magnetic resonance imaging of the pelvic region, removal of the hematoma and abscess in the left spermatic cord as well as an anterograde cystoscopy were performed under lumbar anesthesia, and the absence of urethral injury was confirmed. After infection control, repositioning of the penis was jointly performed with the Department of Plastic Surgery of our hospital under general anesthesia. After the operation, spontaneous urination was observed and erectile function was observed to be normal. PMID:27624112

  1. Energetics of dislocation dipoles in capped epitaxially strained layers

    NASA Astrophysics Data System (ADS)

    Atkinson, A.; Jain, S. C.

    1994-08-01

    Most device structures based on strained epitaxial layers are capped by a second, unstrained layer to increase the mechanical stability of the structure. In order to calculate the energies of these structures it is necessary to synthesize the total energy from the energies of the line defects they contain (interfacial dislocations and dislocation dipoles). The self energies and interaction energies of dislocations and dipoles are calculated and their behavoir examined as a function of their spacing and the thicknesses of the strained and capping layers. The results confirm the observations that capped strained layers are more stable than uncapped ones (of the same strained layer thickness) and that capping layers do not need to be thicker than approximately three times the strained layer thickness. An expression is deduced for the total energy of finite, nonuniform arrays of dipoles in capped layers and, by analogy with a similar earlier expression for dislocation in uncapped layers, it is concluded that the effect of a nonuniformity in the dipole spacing will be to increase the energy of the system compared with that of a uniform array having the same average spacing. The results in this paper can be used to assess the stability of devices and their rate of degradation by strain relaxation.

  2. Double dislocation of the interphalangeal joints in the finger.

    PubMed

    Mesmar, M A

    2000-05-01

    A case of simultaneous dislocation of the proximal and distal interphalangeal joints of the same digit is described. The case presented at Princess Basma Teaching Hospital after athletic trauma. It was treated successfully with close reduction followed by two weeks immobilization in slight flexion position. The condition is described in this report with review of the relevant literature.

  3. Isolated acute dislocation of the proximal tibiofibular joint.

    PubMed

    Iosifidis, Michael I; Giannoulis, Ioannis; Tsarouhas, Alexandros; Traios, Stavros

    2008-06-01

    Lesions of knee's lateral side are less common than medial injuries. The anatomy of the lateral ligaments and the presence of additional structures (eg, fibula head) can cause diagnostic problems. Isolated dislocation of the proximal tibiofibular joint is unusual; therefore, it may be overlooked in the emergency department. Many cases are missed due to failure of diagnosis. This type of injury is common in athletes whose sports require twisting motions of the flexed knee (eg, wrestling, parachute jumping, judo, gymnastics, skiing, rugby, football, soccer, track, baseball, basketball, racquetball, and roller-skating). Anterolateral dislocation of the proximal tibiofibular joint is seemingly rare in soccer players, as less than a handful cases have been reported in the literature. The diagnosis can be made by clinical examination, plain knee radiographs, and, sometimes, computed tomography (CT) scanning for further confirmation. Treatment usually consists of closed or open reduction. In complicated cases, however, arthrodesis or resection of the fibular head may be required. This article reports a rare case of acute isolated anterolateral dislocation of the proximal tibiofibular joint in a soccer player and discusses the joint anatomy, types of dislocations, mechanisms of injury, and treatment options.

  4. A Unified Constitutive Equation of a Bainite Steel During Hot Deformation

    NASA Astrophysics Data System (ADS)

    Li, Lixin; Ye, Ben; Liu, Sheng; Hu, Shengde; Liao, Hanqing

    2016-10-01

    A constitutive model has been established based on dislocation theory, work hardening and dynamic recovery theory, and softening mechanisms of dynamic recrystallization. The stress-strain curves of a bainite steel have been measured with hot compression experiments at temperatures of 1173, 1273, 1373 and 1473 K with strain rates of 0.01, 0.1, 1 and 10 s-1 on a thermo-mechanical simulator (Gleeble-1500). The material constants involved in the constitutive model have been optimized by an inverse analysis of the stress-strain curves using the method of coordinate rotation, determining the strain-stress relationship or the constitutive equation, the kinetic models of dynamic recovery and dynamic recrystallization, and a few material constants of the investigated steel. Comparison of the calculated flow stress with the experimental data suggests that the relationship between the flow stress and the strain rate, temperature, strain of the steel during hot deformation can be described by the constitutive model, and that the underlying materials science can be captured from the material constants determined by the stress-strain curves.

  5. A Unified Constitutive Equation of a Bainite Steel During Hot Deformation

    NASA Astrophysics Data System (ADS)

    Li, Lixin; Ye, Ben; Liu, Sheng; Hu, Shengde; Liao, Hanqing

    2016-08-01

    A constitutive model has been established based on dislocation theory, work hardening and dynamic recovery theory, and softening mechanisms of dynamic recrystallization. The stress-strain curves of a bainite steel have been measured with hot compression experiments at temperatures of 1173, 1273, 1373 and 1473 K with strain rates of 0.01, 0.1, 1 and 10 s-1 on a thermo-mechanical simulator (Gleeble-1500). The material constants involved in the constitutive model have been optimized by an inverse analysis of the stress-strain curves using the method of coordinate rotation, determining the strain-stress relationship or the constitutive equation, the kinetic models of dynamic recovery and dynamic recrystallization, and a few material constants of the investigated steel. Comparison of the calculated flow stress with the experimental data suggests that the relationship between the flow stress and the strain rate, temperature, strain of the steel during hot deformation can be described by the constitutive model, and that the underlying materials science can be captured from the material constants determined by the stress-strain curves.

  6. Column-by-column observation of dislocation motion in CdTe: Dynamic scanning transmission electron microscopy

    NASA Astrophysics Data System (ADS)

    Li, Chen; Zhang, Yu-Yang; Pennycook, Timothy J.; Wu, Yelong; Lupini, Andrew R.; Paudel, Naba; Pantelides, Sokrates T.; Yan, Yanfa; Pennycook, Stephen J.

    2016-10-01

    The dynamics of partial dislocations in CdTe have been observed at the atomic scale using aberration-corrected scanning transmission electron microscopy (STEM), allowing the mobility of different dislocations to be directly compared: Cd-core Shockley partial dislocations are more mobile than Te-core partials, and dislocation cores with unpaired columns have higher mobility than those without unpaired columns. The dynamic imaging also provides insight into the process by which the dislocations glide. Dislocations with dangling bonds on unpaired columns are found to be more mobile because the dangling bonds mediate the bond exchanges required for the dislocations to move. Furthermore, a screw dislocation has been resolved to dissociate into a Shockley partial-dislocation pair along two different directions, revealing a way for the screw dislocation to glide in the material. The results show that dynamic STEM imaging has the potential to uncover the details of dislocation motion not easily accessible by other means.

  7. Continuum dynamics of the formation, migration and dissociation of self-locked dislocation structures on parallel slip planes

    NASA Astrophysics Data System (ADS)

    Zhu, Yichao; Niu, Xiaohua; Xiang, Yang

    2016-11-01

    In continuum models of dislocations, proper formulations of short-range elastic interactions of dislocations are crucial for capturing various types of dislocation patterns formed in crystalline materials. In this article, the continuum dynamics of straight dislocations distributed on two parallel slip planes is modelled through upscaling the underlying discrete dislocation dynamics. Two continuum velocity field quantities are introduced to facilitate the discrete-to-continuum transition. The first one is the local migration velocity of dislocation ensembles which is found fully independent of the short-range dislocation correlations. The second one is the decoupling velocity of dislocation pairs controlled by a threshold stress value, which is proposed to be the effective flow stress for single slip systems. Compared to the almost ubiquitously adopted Taylor relationship, the derived flow stress formula exhibits two features that are more consistent with the underlying discrete dislocation dynamics: (i) the flow stress increases with the in-plane component of the dislocation density only up to a certain value, hence the derived formula admits a minimum inter-dislocation distance within slip planes; (ii) the flow stress smoothly transits to zero when all dislocations become geometrically necessary dislocations. A regime under which inhomogeneities in dislocation density grow is identified, and is further validated through comparison with discrete dislocation dynamical simulation results. Based on the findings in this article and in our previous works, a general strategy for incorporating short-range dislocation correlations into continuum models of dislocations is proposed.

  8. Influence of misfit stresses on dislocation glide in single crystal superalloys: A three-dimensional discrete dislocation dynamics study

    NASA Astrophysics Data System (ADS)

    Gao, Siwen; Fivel, Marc; Ma, Anxin; Hartmaier, Alexander

    2015-03-01

    In the characteristic γ / γ ‧ microstructure of single crystal superalloys, misfit stresses occur due to a significant lattice mismatch of those two phases. The magnitude of this lattice mismatch depends on the chemical composition of both phases as well as on temperature. Furthermore, the lattice mismatch of γ and γ ‧ phases can be either positive or negative in sign. The internal stresses caused by such lattice mismatch play a decisive role for the micromechanical processes that lead to the observed macroscopic athermal deformation behavior of these high-temperature alloys. Three-dimensional discrete dislocation dynamics (DDD) simulations are applied to investigate dislocation glide in γ matrix channels and shearing of γ ‧ precipitates by superdislocations under externally applied uniaxial stresses, by fully taking into account internal misfit stresses. Misfit stress fields are calculated by the fast Fourier transformation (FFT) method and hybridized with DDD simulations. For external loading along the crystallographic [001] direction of the single crystal, it was found that the different internal stress states for negative and positive lattice mismatch result in non-uniform dislocation movement and different dislocation patterns in horizontal and vertical γ matrix channels. Furthermore, positive lattice mismatch produces a lower deformation rate than negative lattice mismatch under the same tensile loading, but for an increasing magnitude of lattice mismatch, the deformation resistance always diminishes. Hence, the best deformation performance is expected to result from alloys with either small positive, or even better, vanishing lattice mismatch between γ and γ ‧ phase.

  9. Microstructural evidence for the transition from dislocation creep to dislocation-accommodated grain boundary sliding in naturally deformed plagioclase

    NASA Astrophysics Data System (ADS)

    Miranda, Elena A.; Hirth, Greg; John, Barbara E.

    2016-11-01

    We use quantitative microstructural analysis including misorientation analysis based on electron backscatter diffraction (EBSD) data to investigate deformation mechanisms of naturally deformed plagioclase in an amphibolite gabbro mylonite. The sample is from lower oceanic crust exposed near the Southwest Indian Ridge, and it has a high ratio of recrystallized matrix grains to porphyroclasts. Microstructures preserved in porphyroclasts suggest that early deformation was achieved principally by dislocation creep with subgrain rotation recrystallization; recrystallized grain (average diameter ∼8 μm) microstructures indicate that subsequent grain boundary sliding (GBS) was active in the continued deformation of the recrystallized matrix. The recrystallized matrix shows four-grain junctions, randomized misorientation axes, and a shift towards higher angles for neighbor-pair misorientations, all indicative of GBS. The matrix grains also exhibit a shape preferred orientation, a weak lattice preferred orientation consistent with slip on multiple slip systems, and intragrain microstructures indicative of dislocation movement. The combination of these microstructures suggest deformation by dislocation-accommodated GBS (DisGBS). Strain localization within the recrystallized matrix was promoted by a transition from grain size insensitive dislocation creep to grain size sensitive GBS, and sustained by the maintenance of a small grain size during superplasticity.

  10. The United States and the Indian Constitution.

    ERIC Educational Resources Information Center

    Weil, Jonathan S.

    India, a huge land with the second largest population in the world, socially and economically poor, and culturally and linguistically diverse, became the largest democracy in the world on November 26, 1949 with the adoption of the Indian Constitution. The goals of that constitution are: (1) the achievement of national unity and stability; (2) the…

  11. From Confederation to Constitution: 1781-1789.

    ERIC Educational Resources Information Center

    Urofsky, Melvin I.; Cox, Nancy

    Students should achieve a higher level of understanding and appreciation of the evolving nature of the U.S. Constitution and its relevance to contemporary societal issues by studying historical documents from the period of time between the Articles of Confederation and the Constitution. This document begins with a history of that period and of the…

  12. The Constitution in the Twentieth Century.

    ERIC Educational Resources Information Center

    Murphy, Paul L.

    1987-01-01

    Investigates the development of the United States Constitution in the twentieth century up to and including the Burger Court. Contends that interpreting the Constitution is an important issue of our times. Consequently argues that we should teach students about the development of this document. (RKM)

  13. 32 CFR 536.42 - Constitutional torts.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 32 National Defense 3 2010-07-01 2010-07-01 true Constitutional torts. 536.42 Section 536.42 National Defense Department of Defense (Continued) DEPARTMENT OF THE ARMY CLAIMS AND ACCOUNTS CLAIMS AGAINST THE UNITED STATES Investigation and Processing of Claims § 536.42 Constitutional torts. A...

  14. Liberty, Power, and the American Constitutional Heritage.

    ERIC Educational Resources Information Center

    Madison, James H.

    The principles, values, and issues of our constitutional heritage that should be emphasized in citizenship education are based on the concepts of liberty and power. The Constitution is not a sacred icon formulated by immortals, but rather a changing and controversial framework guided by a diverse group of practical politicians, sensitive to their…

  15. An Internet Guide to Teaching the Constitution

    ERIC Educational Resources Information Center

    Risinger, C. Frederick

    2005-01-01

    In 2004, Congress passed and President Bush signed legislation designating every September 17 as Constitution Day and suggesting that all schools teach about the Constitution on that day. There are innumerable websites, countless lesson plans and a multitude of other teaching resources on the topic. Teachers were inundated with brochures,…

  16. An unusual variety of simultaneous fracture dislocation pattern: medial swivel dislocation of talonavicular joint with displaced fractures of the fourth and fifth metatarsals.

    PubMed

    Inal, Sermet; Inal, Canan

    2013-01-01

    In published studies, a very rare, special type of Chopart dislocation termed a swivel dislocation has been reported. This injury is characterized by dislocation of the talonavicular joint, but the calcaneocuboid joint remains intact. The foot creates a typical rotational movement without inversion or eversion. The axis of rotation is the interosseous talocalcaneal ligament, which remains intact. We report the case of an 18-year-old male who had experienced a medial swivel dislocation of the talonavicular joint associated with displaced fractures of the fourth and fifth metatarsals. The occurrence, features, and method of treatment of this rare injury are presented.

  17. Total Hip Arthroplasty Dislocations Are More Complex Than They Appear: A Case Report of Intraprosthetic Dislocation of an Anatomic Dual-Mobility Implant After Closed Reduction

    PubMed Central

    Waddell, Bradford S.; De Martino, Ivan; Sculco, Thomas; Sculco, Peter

    2016-01-01

    Background: Total hip arthroplasty is a successful operation for the treatment of hip pain. One of the common complications of hip arthroplasty is dislocation. While reduction of standard prosthetic dislocations is highly successful, new prostheses add the potential for new complications. Case Report: We present the case of a patient who experienced intraprosthetic dislocation of an anatomic dual-mobility total hip prosthesis after a closed hip reduction and include the prereduction and postreduction radiographic findings. Conclusion: Emergency department physicians should be aware of intraprosthetic dislocation. This complication can be easily missed because the metal/ceramic femoral head appears to be reduced in the acetabulum. PMID:27303232

  18. Spatial organization of plastic deformation in single crystals with different structure of slip dislocation

    SciTech Connect

    Kunitsyna, T. S.; Teplyakova, L. A. Koneva, N. A.; Poltaranin, M. A.

    2015-10-27

    It is established that different structure of slip dislocation at the end of the linear hardening stage results in different distribution of dislocation charges in the volume of a single crystal. In the alloy with a near atomic order the slip of single dislocations leads to formation of planar structures—layers with the excess density of dislocations. In the alloy with long-range atomic order the slip of superdislocations brings the formation of the system of parallel rod-like charged dislocation linking.

  19. A complete absorption mechanism of stacking fault tetrahedron by screw dislocation in copper

    NASA Astrophysics Data System (ADS)

    Fan, Haidong; Wang, Qingyuan

    2013-10-01

    It was frequently observed in experiments that stacking fault tetrahedron (SFT) can be completely absorbed by dislocation and generate defect-free channels in irradiated materials, but the mechanism is still open. In this paper, molecular dynamics (MD) was used to explore the dislocation mechanism of reaction between SFT and screw dislocation in copper. Our computational results reveal that, at high temperature, the SFT is completely absorbed by screw dislocation with the help of Lomer-Cottrell (LC) lock transforming into Lomer dislocation. This complete absorption mechanism is very helpful to understand the defect-free channels in irradiated materials.

  20. Midline mandibulotomy for reduction of long-standing temporomandibular joint dislocation.

    PubMed

    Rattan, Vidya; Rai, Sachin; Sethi, Amit

    2013-06-01

    Long-standing temporomandibular joint (TMJ) dislocation is an uncommon condition, and due to its rarity, no definitive guidelines have been developed for its management. Various reduction techniques ranging from indirect traction techniques to direct exposure of the TMJ have been used. Indirect traction techniques for reduction may fail in long-standing dislocation. Management of two cases of long-standing TMJ dislocation with midline mandibulotomy is discussed in which other indirect reduction techniques had failed. Midline osteotomy of the mandible can be used for reduction in difficult TMJ dislocations. An algorithm for the management of long-standing TMJ dislocation is proposed and related literature is reviewed.

  1. Dislocation density evolution during high pressure torsion of a nanocrystalline Ni-Fe alloy

    SciTech Connect

    Li, Hongqi; Wang, Y B; Ho, J C; Cao, Y; Liao, X Z; Ringer, S P; Zhu, Y T; Zhao, Y H; Lavernia, E J

    2009-01-01

    High-pressure torsion (HPT) induced dislocation density evolution in a nanocrystalline Ni-20wt.%Fe alloy was investigated using X-ray diffraction and transmission electron microscopy. Results suggest that the dislocation density evolution is different from that in coarse-grained materials. An HPT process first reduces the dislocation density within nanocrystalline grains and produces a large number of dislocations located at small-angle sub grain boundaries that are formed via grain rotation and coalescence. Continuing the deformation process eliminates the sub grain boundaries but significantly increases the dislocation density in grains. This phenomenon provides an explanation of the mechanical behavior of some nanostructured materials.

  2. Dislocation pileup as a representation of strain accumulation on a strike-slip fault

    USGS Publications Warehouse

    Savage, J.C.

    2006-01-01

    The conventional model of strain accumulation on a vertical transform fault is a discrete screw dislocation in an elastic half-space with the Burgers vector of the dislocation increasing at the rate of relative plate motion. It would be more realistic to replace that discrete dislocation by a dislocation distribution, presumably a pileup in which the individual dislocations are in equilibrium. The length of the pileup depends upon the applied stress and the amount of slip that has occurred at depth. I argue here that the dislocation pileup (the transition on the fault from no slip to slip at the full plate rate) occupies a substantial portion of the lithosphere thickness. A discrete dislocation at an adjustable depth can reproduce the surface deformation profile predicted by a pileup so closely that it will be difficult to distinguish between the two models. The locking depth (dislocation depth) of that discrete dislocation approximation is substantially (???30%) larger than that (depth to top of the pileup) in the pileup model. Thus, in inverting surface deformation data using the discrete dislocation model, the locking depth in the model should not be interpreted as the true locking depth. Although dislocation pileup models should provide a good explanation of the surface deformation near the fault trace, that explanation may not be adequate at greater distances from the fault trace because approximating the expected horizontally distributed deformation at subcrustal depths by uniform slip concentrated on the fault is not justified.

  3. Effects of edge dislocations on interstitial helium and helium cluster behavior in α-Fe

    NASA Astrophysics Data System (ADS)

    Wang, Y. X.; Xu, Q.; Yoshiie, T.; Pan, Z. Y.

    2008-05-01

    The properties of interstitial He in the vicinity of an edge dislocation were studied using molecular dynamics (MD) simulation. The distribution of the binding energy of a single interstitial He to the dislocation with and without a jog is calculated. The results show that the distribution of the binding energy is governed by the elastic interaction between the interstitial He and the dislocation. The interstitial He is strongly attracted to the dislocation in the tensile region of the dislocation. The jog acts as a stronger sink to absorb interstitial He. The binding energy to the jog is even larger than that of the dislocation. A small He cluster (composed of three interstitial He atoms) was trapped by the dislocation core in the form of a chain along the dislocation line. The dislocation changes the migration behavior of the He cluster, and provides a pipe for the small cluster to exhibit one-dimensional motion. The diffusion of the He cluster in the dislocation is faster than in the defect-free iron, where the He cluster migrates three-dimensionally (3D). If the dislocation is decorated by a jog, the small cluster sinks deep into the jog. The jog prevents the He cluster from escaping.

  4. Dislocation Multiplication in the Early Stage of Deformation in Mo Single Crystals

    SciTech Connect

    Hsiung, L.; Lassila, D.H.

    2000-03-02

    Initial dislocation structure in annealed high-purity Mo single crystals and deformation substructure in a crystal subjected to 1% compression have been examined and studied using transmission electron microscopy (TEM) techniques in order to investigate dislocation multiplication mechanisms in the early stage of plastic deformation. The initial dislocation density is in a range of 10{sup 6} {approx} 10{sup 7} cm{sup -2}, and the dislocation structure is found to contain many grown-in superjogs along dislocation lines. The dislocation density increases to a range of 10{sup 8} {approx} 10{sup 9} cm{sup -2}, and the average jog height is also found to increase after compressing for a total strain of 1%. It is proposed that the preexisting jogged screw dislocations can act as (multiple) dislocation multiplication sources when deformed under quasi-static conditions. The jog height can increase by stress-induced jog coalescence, which takes place via the lateral migration (drift) of superjogs driven by unbalanced line-tension partials acting on link segments of unequal lengths. The coalescence of superjogs results in an increase of both link length and jog height. Applied shear stress begins to push each link segment to precede dislocation multiplication when link length and jog height are greater than critical lengths. This ''dynamic'' dislocation multiplication source is suggested to be crucial for the dislocation multiplication in the early stage of plastic deformation in Mo.

  5. Sessile dislocations by reactions in NiAl severely deformed at room temperature

    SciTech Connect

    Geist, D.; Gammer, C.; Rentenberger, C.; Karnthaler, H. P.

    2015-02-05

    B2 ordered NiAl is known for its poor room temperature (RT) ductility; failure occurs in a brittle like manner even in ductile single crystals deforming by single slip. In the present study NiAl was severely deformed at RT using the method of high pressure torsion (HPT) enabling the hitherto impossible investigation of multiple slip deformation. Methods of transmission electron microscopy were used to analyze the dislocations formed by the plastic deformation showing that as expected dislocations with Burgers vector a(100) carry the plasticity during HPT deformation at RT. In addition, we observe that they often form a(110) dislocations by dislocation reactions; the a(110) dislocations are considered to be sessile based on calculations found in the literature. It is therefore concluded that the frequently encountered 3D dislocation networks containing sessile a(110) dislocations are pinned and lead to deformation-induced embrittlement. In spite of the severe deformation, the chemical order remains unchanged.

  6. Formation of helical dislocations in ammonothermal GaN substrate by heat treatment

    NASA Astrophysics Data System (ADS)

    Horibuchi, Kayo; Yamaguchi, Satoshi; Kimoto, Yasuji; Nishikawa, Koichi; Kachi, Tetsu

    2016-03-01

    GaN substrate produced by the basic ammonothermal method and an epitaxial layer on the substrate was evaluated using synchrotron radiation x-ray topography and transmission electron microscopy. We revealed that the threading dislocations present in the GaN substrate are deformed into helical dislocations and the generation of the voids by heat treatment in the substrate for the first observation in the GaN crystal. These phenomena are formed by the interactions between the dislocations and vacancies. The helical dislocation was formed in the substrate region, and not in the epitaxial layer region. Furthermore, the evaluation of the influence of the dislocations on the leakage current of Schottky barrier diodes fabricated on the epitaxial layer is discussed. The dislocations did not affect the leakage current characteristics of the epitaxial layer. Our results suggest that the deformation of dislocations in the GaN substrate does not adversely affect the epitaxial layer.

  7. 3 CFR 8418 - Proclamation 8418 of September 16, 2009. Constitution Day and Citizenship Day, Constitution Week...

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    .... Constitution Day and Citizenship Day, Constitution Week, 2009 8418 Proclamation 8418 Presidential Documents Proclamations Proclamation 8418 of September 16, 2009 Proc. 8418 Constitution Day and Citizenship Day... citizenship, the Congress, by joint resolution of February 29, 1952 (36 U.S.C. 106), designated September...

  8. 77 FR 57981 - Constitution Day and Citizenship Day, Constitution Week, 2012

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-09-18

    ... of the United States of America the two hundred and thirty- seventh. (Presidential Sig.) [FR Doc... September 18, 2012 Part VI The President Proclamation 8862--Constitution Day and Citizenship Day... ] Proclamation 8862 of September 13, 2012 Constitution Day and Citizenship Day, Constitution Week, 2012 By...

  9. 3 CFR 8714 - Proclamation 8714 of September 16, 2011. Constitution Day and Citizenship Day, Constitution Week...

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    .... Constitution Day and Citizenship Day, Constitution Week, 2011 8714 Proclamation 8714 Presidential Documents Proclamations Proclamation 8714 of September 16, 2011 Proc. 8714 Constitution Day and Citizenship Day... because they believed in what our country stands for. Every year, thousands of candidates for...

  10. 78 FR 57777 - Constitution Day and Citizenship Day, Constitution Week, 2013

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-09-19

    .... (Presidential Sig.) [FR Doc. 2013-23014 Filed 9-18-13; 11:15 am] Billing code 3295-F3 ... September 19, 2013 Part IV The President Proclamation 9019--Constitution Day and Citizenship Day... September 16, 2013 Constitution Day and Citizenship Day, Constitution Week, 2013 By the President of...

  11. 3 CFR 8862 - Proclamation 8862 of September 13, 2012. Constitution Day and Citizenship Day, Constitution Week...

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    .... Constitution Day and Citizenship Day, Constitution Week, 2012 8862 Proclamation 8862 Presidential Documents Proclamations Proclamation 8862 of September 13, 2012 Proc. 8862 Constitution Day and Citizenship Day... candidates for citizenship who will commemorate this day by joining our American family. For more than...

  12. 20 CFR 663.115 - What are the eligibility criteria for core services for dislocated workers in the adult and...

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... services for dislocated workers in the adult and dislocated worker programs? 663.115 Section 663.115 Employees' Benefits EMPLOYMENT AND TRAINING ADMINISTRATION, DEPARTMENT OF LABOR ADULT AND DISLOCATED WORKER ACTIVITIES UNDER TITLE I OF THE WORKFORCE INVESTMENT ACT Delivery of Adult and Dislocated Worker...

  13. Low-dislocation-density epitatial layers grown by defect filtering by self-assembled layers of spheres

    DOEpatents

    Wang, George T.; Li, Qiming

    2013-04-23

    A method for growing low-dislocation-density material atop a layer of the material with an initially higher dislocation density using a monolayer of spheroidal particles to bend and redirect or directly block vertically propagating threading dislocations, thereby enabling growth and coalescence to form a very-low-dislocation-density surface of the material, and the structures made by this method.

  14. Dislocation locking versus easy glide in titanium and zirconium.

    PubMed

    Clouet, Emmanuel; Caillard, Daniel; Chaari, Nermine; Onimus, Fabien; Rodney, David

    2015-09-01

    The ease of a metal to deform plastically in selected crystallographic planes depends on the core structure of its dislocations. As the latter is controlled by electronic interactions, metals with the same valence electron configuration usually exhibit a similar plastic behaviour. For this reason, titanium and zirconium, two transition metals of technological importance from the same column of the periodic table, have so far been assumed to deform in a similar fashion. However, we show here, using in situ transmission electron microscopy straining experiments, that plasticity proceeds very differently in these two metals, being intermittent in Ti and continuous in Zr. This observation is rationalized using first-principles calculations, which reveal that, in both metals, dislocations may adopt the same set of different cores that are either glissile or sessile. An inversion of stability of these cores between Zr and Ti is shown to be at the origin of the profoundly different plastic behaviours. PMID:26147845

  15. A Newtonian interpretation of configurational forces on dislocations and cracks

    NASA Astrophysics Data System (ADS)

    Ballarini, Roberto; Royer-Carfagni, Gianni

    2016-10-01

    Configurational forces are fundamental concepts in the description of the motion of dislocations, cracks and other defects that introduce singularities within the solid state. They are defined by considering variations in energies associated with the movement of such defects, and are therefore different from the classical forces that enter the balance laws of classical Newtonian mechanics. Here, it is demonstrated how a configurational force can be viewed as the resultant of the (Newtonian) contact forces acting on the perturbed shape of an object of substance equivalent to the defect, and evaluated in the limit of the shape being restored to the primitive configuration. The expressions for the configurational forces on the paradigmatic examples of cracks and dislocations are in agreement with those determined using classical variational arguments. This finding opens a new prospective in the use of configurational forces by permitting their physical and intuitive visualization.

  16. Atomic-scale details of dislocation - stacking fault tetrahedra interaction.

    SciTech Connect

    Osetskiy, Yury N; Stoller, Roger E; Rodney, David; Bacon, David J

    2005-01-01

    Stacking fault tetrahedra (SFTs) are formed during irradiation of fcc. metals and alloys with low stacking fault energy. The high number density of SFTs observed suggests that they should contribute to radiation-induced hardening and, therefore, be taken into account when estimating mechanical property changes of irradiated materials. The key issue is to describe the interaction between a moving dislocation and an individual SFT, which is characterized by a small physical scale of about 100 nm. In this paper we present results of an atomistic simulation of edge and screw dislocations interacting with small SFTs at different temperatures and strain rates and present mechanisms which can explain the formation of defect-free channels observed experimentally.

  17. Treatment of chronic radial head dislocations in children

    PubMed Central

    Belangero, W. D.; Zogaib, R. K.

    2006-01-01

    From 1990 to 2005 our department treated nine patients with chronic radial head dislocation by an ulnar osteotomy and indirect reduction by interosseous membrane. The patients varied in age from 2 years and 8 months to 10 years, and the time from the injury to operation ranged from 40 days to 3 years. The range of functional motion and carrying angle was restored in all nine patients, and no complications, such as recurrent dislocation, infection, or neurovascular injury were observed. This technique has proven to be a successful approach to treating such cases, with a low range of complications and good functional results. PMID:16741732

  18. Interstitial iron impurities at cores of dissociated dislocations in silicon

    NASA Astrophysics Data System (ADS)

    Ziebarth, Benedikt; Mrovec, Matous; Elsässer, Christian; Gumbsch, Peter

    2015-11-01

    Dislocations play an important role in semiconductor devices made of crystalline silicon (Si). They are known to be strongly performance-limiting defects in solar cell applications, since they act as preferred segregation sites for metallic impurities. In this work we investigate the segregation of iron (Fe) to the cores of the 30° and 90° partial dislocations in Si using atomistic calculations based on first-principles density functional theory. Our simulations show that interstitial Fe impurities segregate readily to all investigated cores and the driving force for the segregation increases with impurity concentration. Moreover, our analysis of the electronic structure reveals the existence of deep defect levels within the band gap that can be related to experimental observations by deep-level transient spectroscopy.

  19. Dislocation Majorana zero modes in perovskite oxide 2DEG

    NASA Astrophysics Data System (ADS)

    Chung, Suk Bum; Chan, Cheung; Yao, Hong

    2016-05-01

    Much of the current experimental efforts for detecting Majorana zero modes have been centered on probing the boundary of quantum wires with strong spin-orbit coupling. The same type of Majorana zero mode can also be realized at crystalline dislocations in 2D superconductors with the nontrivial weak topological indices. Unlike at an Abrikosov vortex, at such a dislocation, there is no other low-lying midgap state than the Majorana zero mode so that it avoids usual complications encountered in experimental detections such as scanning tunneling microscope (STM) measurements. We will show that, using the anisotropic dispersion of the t2g orbitals of Ti or Ta atoms, such a weak topological superconductivity can be realized when the surface two-dimensional electronic gas (2DEG) of SrTiO3 or KTaO3 becomes superconducting, which can occur through either intrinsic pairing or proximity to existing s-wave superconductors.

  20. Atomic-level level dislocation dynamics in irradiated metals

    SciTech Connect

    Osetskiy, Yury N; Bacon, David J

    2015-01-01

    Primary damage and microstructure evolution in structural nuclear materials operating under conditions of a high flux of energetic atomic particles and high temperature and stress lead to formation of a high concentration, non-homogeneous distribution of defect clusters in the form of dislocation loops, voids, gas-filled bubbles and radiation-induced precipitates of nanometer scale. They cause changes in many material properties. Being obstacles to dislocation glide, they strongly affect mechanical properties in particular. This gives rise to an increase in yield and flow stress and a reduction in ductility. Atomic-scale computer simulation can provide details of how these effects are influenced by obstacle structure, applied stress, strain rate and temperature. Processes such as obstacle cutting, transformation, absorption and drag are observed. Some recent results for body-centered and face-centered cubic metals are described in this review and, where appropriate, comparisons drawn with predictions based on elasticity theory of crystal defects.