Sample records for mechanical burst element

  1. Formative mechanism of intracanal fracture fragments in thoracolumbar burst fractures: a finite element study

    ZENG Zhi-li; ZHU Rui; LI Shan-zhu; YU Yan; WANG Jian-jie; JIA Yong-wei; CHEN Bo


    Background Thoracolumbar burst fracture is a common clinical injury,and the fracture mechanism is still controversial.The aim of this research was to study the formation of intracanal fracture fragments in thoracolumbar burst fractures and to provide information for the prevention of thoracolumbar bursts fractures and reduction of damage to the nervous system.Methods A nonlinear three-dimensional finite element model of T11-L3 segments was established,and the injury processes of thoracolumbar bursts were simulated.The intact finite element model and the finite element model after the superior articular were impacted by 100 J of energy in different directions.The distribution and variation of stress in the superior posterior region of the L1 vertebral body were analyzed.Abaqus 6.9 explicit dynamic solver was used as finite element software in calculations.Results A three-dimensional nonlinear finite element model of the thoracolumbar spine was created.In the intact model,stress was concentrated in the superior posterior region of the L1 vertebral body.The stress peak was a maximum for the extension impact load and a minimum for the flexion impact load.The stress peak and contact force in the facet joint had close correlation with time.The stress peak disappeared after excision of the superior articular process.Conclusions The three-dimensional nonlinear finite element model was suitable for dynamic analysis.The contact force in the facet joint,which can be transferred to the superior posterior vertebral body,may explain the spinal canal fragment in thoracolumbar burst fractures.

  2. Burst Mechanisms in Hydrodynamics

    Knobloch, E


    Different mechanisms believed to be responsible for the generation of bursts in hydrodynamical systems are reviewed and a new mechanism capable of generating regular or irregular bursts of large dynamic range near threshold is described. The new mechanism is present in the interaction between oscillatory modes of odd and even parity in systems of large but finite aspect ratio, and provides an explanation for the bursting behavior observed in binary fluid convection. Additional applications of the new mechanism are proposed.

  3. A mechanism for fast radio bursts

    Romero, Gustavo E; Vieyro, Florencia L


    Fast radio bursts are mysterious transient sources likely located at cosmological distances. The derived brightness temperatures exceed by many orders of magnitude the self-absorption limit of incoherent synchrotron radiation, implying the operation of a coherent emission process. We propose a radiation mechanism for fast radio bursts where the emission arises from collisionless Bremsstrahlung in strong plasma turbulence excited by relativistic electron beams. We discuss possible astrophysical scenarios in which this process might operate. The emitting region is a turbulent plasma hit by a relativistic jet, where Langmuir plasma waves produce a concentration of intense electrostatic soliton-like regions (cavitons). The resulting radiation is coherent and, under some physical conditions, can be polarised and have a power-law distribution in energy. We obtain radio luminosities in agreement with the inferred values for fast radio bursts. The timescale of the radio flare in some cases can be extremely fast, of t...

  4. An Intelligent Segmented Burst Assembly Mechanism in Optical Burst Switching Networks

    XIE Yi-Yuan; ZHANG Jian-Guo


    We focus on the burst assembly mechanism and propose a new intelligent method in which the burst is assembled from several internet protocol (IP) packets in which the number of IP packets is changed according to the traffic load and the burst is segmented into several parts, called the ISOBS mechanism. The average burst assembly time of the ISOBS mechanism decreases as compared with the fixed-assembly-time and fixed-assembly-time-and-length mechanisms. The loss ratio decreases 50% as compared with the general optical burst switching (OBS) mechanism. The last segment can carry high quality of service (QOS) information. We can achieve that the loss ratio of the last segment is almost zero when the traffic load is less than 0.05. When the traffic load is 0.9, the loss ratio of the last segment is 0.0041. The ISOBS can support to transmit different QOS data.

  5. Analytical elements of mechanics

    Kane, Thomas R


    Analytical Elements of Mechanics, Volume 1, is the first of two volumes intended for use in courses in classical mechanics. The books aim to provide students and teachers with a text consistent in content and format with the author's ideas regarding the subject matter and teaching of mechanics, and to disseminate these ideas. The book opens with a detailed exposition of vector algebra, and no prior knowledge of this subject is required. This is followed by a chapter on the topic of mass centers, which is presented as a logical extension of concepts introduced in connection with centroids. A

  6. Rock Burst Mechanics: Insight from Physical and Mathematical Modelling

    J. Vacek


    Full Text Available Rock burst processes in mines are studied by many groups active in the field of geomechanics. Physical and mathematical modelling can be used to better understand the phenomena and mechanisms involved in the bursts. In the present paper we describe both physical and mathematical models of a rock burst occurring in a gallery of a coal mine.For rock bursts (also called bumps to occur, the rock has to possess certain particular rock burst properties leading to accumulation of energy and the potential to release this energy. Such materials may be brittle, or the rock burst may arise at the interfacial zones of two parts of the rock, which have principally different material properties (e.g. in the Poíbram uranium mines.The solution is based on experimental and mathematical modelling. These two methods have to allow the problem to be studied on the basis of three presumptions:· the solution must be time dependent,· the solution must allow the creation of cracks in the rock mass,· the solution must allow an extrusion of rock into an open space (bump effect. 

  7. Mechanical manifestations of bursting oscillations in slowly rotating systems

    Rakaric, Zvonko; Kovacic, Ivana


    This study is concerned with certain mechanical systems that comprise discrete masses moving along slowly rotating objects. The corresponding equation of relative motion is derived, with the rotating motion creating slowly varying external excitation. Depending on the system parameters, two cases are distinguished: two-well and single-well potential, i.e. the Duffing bistable oscillator and a pure cubic oscillator. It is illustrated that both systems can exhibit bursting oscillations, consisting of fast oscillations around the slow flow. Their mechanisms are explained in terms of bifurcation theory: the first one with respect to the existence of certain saddle-node bifurcation points, and the second one by creation of a certain hysteresis loop. The exact expressions for the slow flow are derived, in the first case as a discontinuous curve, and in the second one as a continuous curve. The influence of the excitation magnitude, which is a potential control parameter, on the characteristics of bursting oscillations is numerically illustrated.

  8. Selected elements of rock burst state assessment in case studies from the Silesian hard coal mines

    KABIESZ Józef; MAKóWKA Janusz


    Exploitation of coal seams in the Upper Silesian Coal Basin is conducted in complex and difficult conditions. These difficulties are connected with the occurrence of many natural mining hazards and limitations resulting from the existing in this area surface infrastructure. One of the most important problems of Polish mining is the rock burst hazard and reliable evaluation of its condition. During long-years' mining practice in Poland a comprehensive system of evaluation and control of this hazard was de-veloped. In the paper the main aspects of rock burst hazard state evaluation will be presented, comprising: 1) rock mass inclination for rock bursts, I.e., rock strength properties investigation, comprehensive parametric evaluation of rock mass inclination for rock bursts, prognosis of seismic events induced by mining operations, methods of computer-aided modelling of stress and rock mass deformation parameters distribution, strategic rock mass classification under rock burst degrees; 2) immediate seismic and rock burst hazard state evaluation, I.e., low diameter test drilling method, seismologic and seismoacoustic method, comprehensive method of rock burst hazard state evaluation, non-standard methods of evaluation; 3) legal aspects of rock burst hazard state evaluation. Selected elements of the hazard state evaluation system are illustrated with specific practical examples of their applica-tion.

  9. Determining hydrodynamic forces in bursting bubbles using DNA nanotube mechanics

    Hariadi, Rizal F.; Winfree, Erik; Yurke, Bernard


    Quantifying the mechanical forces produced by fluid flows within the ocean is critical to understanding the ocean’s environmental phenomena. Such forces may have been instrumental in the origin of life by driving a primitive form of self-replication through fragmentation. Among the intense sources of hydrodynamic shear encountered in the ocean are breaking waves and the bursting bubbles produced by such waves. On a microscopic scale, one expects the surface-tension–driven flows produced during bubble rupture to exhibit particularly high velocity gradients due to the small size scales and masses involved. However, little work has examined the strength of shear flow rates in commonly encountered ocean conditions. By using DNA nanotubes as a novel fluid flow sensor, we investigate the elongational rates generated in bursting films within aqueous bubble foams using both laboratory buffer and ocean water. To characterize the elongational rate distribution associated with a bursting bubble, we introduce the concept of a fragmentation volume and measure its form as a function of elongational flow rate. We find that substantial volumes experience surprisingly large flow rates: during the bursting of a bubble having an air volume of 10 mm3, elongational rates at least as large as ϵ˙=1.0×108 s−1 are generated in a fragmentation volume of ∼2×10−6 μL. The determination of the elongational strain rate distribution is essential for assessing how effectively fluid motion within bursting bubbles at the ocean surface can shear microscopic particles and microorganisms, and could have driven the self-replication of a protobiont. PMID:26504222

  10. Evidence of heavy-element ashes in thermonuclear X-ray bursts with photospheric superexpansion

    Zand, J J M in 't


    A small subset of thermonuclear X-ray bursts on neutron stars exhibit such a strong photospheric expansion that for a few seconds the photosphere is located at a radius r_ph greater than ~1000 km. Such `superexpansions' imply a large and rapid energy release, a feature characteristic of pure He burst models. Calculations have shown that during a pure He burst, the freshly synthesized heavy-element ashes of burning can be ejected in a strong radiative wind and produce significant spectral absorption features. We find 32 superexpansion bursts from 8 different systems with the following interesting features: (1) At least 7 out of 8 systems are (candidate) ultracompact X-ray binaries in which the neutron star accretes hydrogen-deficient fuel, suggesting that these bursts indeed ignite in a helium-rich layer. (2) In two bursts we detect strong absorption edges during the expansion phase. The edge energies and depths are consistent with the H-like edge of iron-peak elements with abundances greater than ~100 times s...

  11. Research on Mechanism of Rock Burst Generation and Development for High Stress Rock Tunnels

    高全臣; 赫建明; 王代华


    Through the investigation and analysis of high stress distribution in surrounding rock during the excavation of rock tunnels,the key factors to cause rock burst and the mechanism of rock burst generation and development are researched. The result shows that the scale and range of rock burst are related with elastic deformation energy storied in rock mass and the characteristics of unloading stress waves. The measures of preventing from rock burst for high stress rock tunnels are put forward.

  12. Finite element computational fluid mechanics

    Baker, A. J.


    Finite element analysis as applied to the broad spectrum of computational fluid mechanics is analyzed. The finite element solution methodology is derived, developed, and applied directly to the differential equation systems governing classes of problems in fluid mechanics. The heat conduction equation is used to reveal the essence and elegance of finite element theory, including higher order accuracy and convergence. The algorithm is extended to the pervasive nonlinearity of the Navier-Stokes equations. A specific fluid mechanics problem class is analyzed with an even mix of theory and applications, including turbulence closure and the solution of turbulent flows.

  13. Elements of Statistical Mechanics

    Sachs, Ivo; Sen, Siddhartha; Sexton, James


    This textbook provides a concise introduction to the key concepts and tools of modern statistical mechanics. It also covers advanced topics such as non-relativistic quantum field theory and numerical methods. After introducing classical analytical techniques, such as cluster expansion and Landau theory, the authors present important numerical methods with applications to magnetic systems, Lennard-Jones fluids and biophysics. Quantum statistical mechanics is discussed in detail and applied to Bose-Einstein condensation and topics in astrophysics and cosmology. In order to describe emergent phenomena in interacting quantum systems, canonical non-relativistic quantum field theory is introduced and then reformulated in terms of Feynman integrals. Combining the authors' many years' experience of teaching courses in this area, this textbook is ideal for advanced undergraduate and graduate students in physics, chemistry and mathematics. Analytical and numerical techniques in one text, including sample codes and solved problems on the web at Covers a wide range of applications including magnetic systems, turbulence astrophysics, and biology Contains a concise introduction to Markov processes and molecular dynamics

  14. Dynamics Analysis and Transition Mechanism of Bursting Calcium Oscillations in Non-Excitable Cells

    ZHANG Feng; LU Qi-Shao; DUAN Li-Xia


    A one-pool model with Ca2+-activated inositol-trisphosphate-concentration degradation is considered.For complex bursting Ca2+ oscillation,point-cycle bursting of subHopf-subHopf type is found to be in the intermediate state from quasi-periodic bursting to Point-point bursting of subHopf-subHopf type.The fast-slow burster analysis is used to study the transition mechanisms among simple periodic oscillation,quasi-periodic bursting,point-point and point-cycle burstings.The dynamics analysis of different oscillations provides better insight into the generation and transition mechanisms of complex intra- and inter-cellular Ca2+signalling.

  15. Mechanical Analogies of Fractional Elements

    HU Kai-Xin; ZHU Ke-Qin


    A Fractional element model describes a special kind of viscoelastic material.Its stress is proportional to the fractional-order derivative of strain. Physically the mechanical analogies of fractional elements can be represented by spring-dashpot fractal networks. We introduce a constitutive operator in the constitutive equations of viscoelastic materials.To derive constitutive operators for spring-dashpot fractal networks, we use Heaviside operational calculus, which provides explicit answers not otherwise obtainable simply.Then the series-parallel formulas for the constitutive operator are derived. Using these formulas, a constitutive equation of fractional element with 1/2-order derivative is obtained.Finally we find the way to derive the constitutive equations with other fractional-order derivatives and their mechanical analogies.

  16. Finite elements methods in mechanics

    Eslami, M Reza


    This book covers all basic areas of mechanical engineering, such as fluid mechanics, heat conduction, beams, and elasticity with detailed derivations for the mass, stiffness, and force matrices. It is especially designed to give physical feeling to the reader for finite element approximation by the introduction of finite elements to the elevation of elastic membrane. A detailed treatment of computer methods with numerical examples are provided. In the fluid mechanics chapter, the conventional and vorticity transport formulations for viscous incompressible fluid flow with discussion on the method of solution are presented. The variational and Galerkin formulations of the heat conduction, beams, and elasticity problems are also discussed in detail. Three computer codes are provided to solve the elastic membrane problem. One of them solves the Poisson’s equation. The second computer program handles the two dimensional elasticity problems, and the third one presents the three dimensional transient heat conducti...

  17. Mechanism of energy limit equilibrium of rock burst in coal mine

    Wang Jiong; Yan Yubiao; Jiang Zhengjun; Qi Ping; Chen Chen


    With the increase of mining depth, the effect of rock burst on coal mining is becoming more and more obvious and the rock burst mechanism becomes more and more complicated. Scholars from many countries had put forward different mechanisms, but no one gave a reasonable explanation to the mechanism of rock burst. In this paper, based on the energy theories, we studied the energy limit equilibrium (ELE) of coal mine rock burst. The coal seam with rock burst is divided into energy limit equilibrium zone (ELEZ) (A) and elastic zone (B); we also determined the position where the rock burst occurs, including the roof and floor of coal seams; in addition, we derived the limit width of ELEZ and the mathematic relationship between the limit width and occurrence mechanism of rock burst: the energy difference function (EDF), w(x) = wJ - wp because first-order derivative w'(x), is less than 0. So EDF is a monotonically decreasing function. The graph of the energy difference function was also determined,through which we analysed the occurrence mechanism of rock burst.

  18. Thermo-Mechanical Analysis of Water-Cooled Gun Barrel During Burst Firing

    FAN Li-xia; HU Zhi-gang; ZHAO Jian-bo


    The thermo-mechanical stress and deformation of water-cooled gun barrel during burst firing are studied by finite element analysis (FEA). The problem is modeled in two steps: 1) A transient heat transfer analysis is first carried out in order to determine temperature evolution and to predict the residual temperatures during the burst firing event; 2) The thermo-mecha-nical stresses and deformation caused by both the residual temperature field and the gas pressure are then calculated. The results show that the residual temperature field tends to a steady state with the increasing of rounds. The residual temperature field has much effect on the gun barrel stress and deformation, especially on the assembly area between barrel and water jacket. The gage between the barrel and water jacket is the critical factor to the thermo-mechanical stress and deformation. The results of this analysis will be very useful to develop the new strength design theory of the liquid-cooled gun barrel.

  19. Ionic mechanisms of burst firing in dissociated Purkinje neurons.

    Swensen, Andrew M; Bean, Bruce P


    Cerebellar Purkinje neurons have intrinsic membrane properties that favor burst firing, seen not only during complex spikes elicited by climbing fiber input but also with direct electrical stimulation of cell bodies. We examined the ionic conductances that underlie all-or-none burst firing elicited in acutely dissociated mouse Purkinje neurons by short depolarizing current injections. Blocking voltage-dependent calcium entry by cadmium or replacement of external calcium by magnesium enhanced burst firing, but it was blocked by cobalt replacement of calcium, probably reflecting block of sodium channels. In voltage-clamp experiments, we used the burst waveform of each cell as a voltage command and used ionic substitutions and pharmacological manipulations to isolate tetrodotoxin (TTX)-sensitive sodium current, P-type and T-type calcium current, hyperpolarization-activated cation current (Ih), voltage-activated potassium current, large-conductance calcium-activated potassium current, and small-conductance calcium-activated potassium (SK) current. Measured near the middle of the first interspike interval, TTX-sensitive sodium current carried the largest inward current, and T-type calcium current was also substantial. Current through P-type channels was large immediately after a spike but decayed rapidly. These inward currents were opposed by substantial components of voltage-dependent and calcium-dependent potassium current. Termination of the burst is caused partly by decay of sodium current, together with a progressive buildup of SK current after the first interspike interval. Although burst firing depends on the net balance between multiple large currents flowing after a spike, it is surprisingly robust, probably reflecting complex interactions between the exact voltage waveform and voltage and calcium dependence of the various currents.

  20. Spectral Structures and Their Generation Mechanisms for Solar Radio Type-I Bursts

    Iwai, Kazumasa; Masuda, Satoshi; Tsuchiya, Fuminori; Morioka, Akira; Misawa, Hiroaki


    The fine spectral structures of solar radio type-I bursts were observed by the solar radio telescope AMATERAS. The spectral characteristics, such as the peak flux, duration, and bandwidth, of the individual burst elements were satisfactorily detected by the highly resolved spectral data of AMATEAS with the burst detection algorithm that is improved in this study. The peak flux of the type-I bursts followed a power-law distribution with a spectral index of 2.9-3.3, whereas their duration and bandwidth were distributed more exponentially. There were almost no correlations between the peak flux, duration, and bandwidth. That means there were no similarity shapes in the burst spectral structures. We defined the growth rate of a burst as the ratio between its peak flux and duration. There was a strong correlation between the growth rate and peak flux. These results suggest that the free energy of type-I bursts that is originally generated by non-thermal electrons is modulated in the subsequent stages of the genera...

  1. Mechanism of Rock Burst Occurrence in Specially Thick Coal Seam with Rock Parting

    Wang, Jian-chao; Jiang, Fu-xing; Meng, Xiang-jun; Wang, Xu-you; Zhu, Si-tao; Feng, Yu


    Specially thick coal seam with complex construction, such as rock parting and alternative soft and hard coal, is called specially thick coal seam with rock parting (STCSRP), which easily leads to rock burst during mining. Based on the stress distribution of rock parting zone, this study investigated the mechanism, engineering discriminant conditions, prevention methods, and risk evaluation method of rock burst occurrence in STCSRP through setting up a mechanical model. The main conclusions of this study are as follows. (1) When the mining face moves closer to the rock parting zone, the original non-uniform stress of the rock parting zone and the advancing stress of the mining face are combined to intensify gradually the shearing action of coal near the mining face. When the shearing action reaches a certain degree, rock burst easily occurs near the mining face. (2) Rock burst occurrence in STCSRP is positively associated with mining depth, advancing stress concentration factor of the mining face, thickness of rock parting, bursting liability of coal, thickness ratio of rock parting to coal seam, and difference of elastic modulus between rock parting and coal, whereas negatively associated with shear strength. (3) Technologies of large-diameter drilling, coal seam water injection, and deep hole blasting can reduce advancing stress concentration factor, thickness of rock parting, and difference of elastic modulus between rock parting and coal to lower the risk of rock burst in STCSRP. (4) The research result was applied to evaluate and control the risk of rock burst occurrence in STCSRP.

  2. Mechanics analysis on the conditions of rock burst occurrence in the coal mass of roadway rib

    CHEN Xue-hua; DENG Xiao-lin; LI Zhong-hua


    According to the rock burst features occurred in the coal mass of roadway rib in one mine, the mechanics model of coal mass and roof structure system along the edge of goaf was founded to analyze the stress of roof rock layer, so the subside curve of roof rock layer was deduced. Furthermore, the stability of coal and rock system were analyzed, the critical load and critical resistance zone were used to judge the danger degree of rock burst occurrence. The influence of coal mass strength, brittleness degree, coal seam thickness, roof thickness, suspending length, equivalent shear module on the critical load,critical resistance zone was confirmed. So the rock burst occurrence conditions of coal mass in roadway rib mainly depend on mining depth, coal seam thickness and hard roof and floor, which are decided by the above studies, and successfully applied in prediction and prevention of rock burst in this mine.

  3. Bursting process of large- and small-scale structures in turbulent boundary layer perturbed by a cylinder roughness element

    Tang, Zhanqi; Jiang, Nan; Zheng, Xiaobo; Wu, Yanhua


    Hot-wire measurements on a turbulent boundary layer flow perturbed by a wall-mounted cylinder roughness element (CRE) are carried out in this study. The cylindrical element protrudes into the logarithmic layer, which is similar to those employed in turbulent boundary layers by Ryan et al. (AIAA J 49:2210-2220, 2011. doi: 10.2514/1.j051012) and Zheng and Longmire (J Fluid Mech 748:368-398, 2014. doi: 10.1017/jfm.2014.185) and in turbulent channel flow by Pathikonda and Christensen (AIAA J 53:1-10, 2014. doi: 10.2514/1.j053407). The similar effects on both the mean velocity and Reynolds stress are observed downstream of the CRE perturbation. The series of hot-wire data are decomposed into large- and small-scale fluctuations, and the characteristics of large- and small-scale bursting process are observed, by comparing the bursting duration, period and frequency between CRE-perturbed case and unperturbed case. It is indicated that the CRE perturbation performs the significant impact on the large- and small-scale structures, but within the different impact scenario. Moreover, the large-scale bursting process imposes a modulation on the bursting events of small-scale fluctuations and the overall trend of modulation is not essentially sensitive to the present CRE perturbation, even the modulation extent is modified. The conditionally averaging fluctuations are also plotted, which further confirms the robustness of the bursting modulation in the present experiments.

  4. Diversity of neural signals mediated by multiple, burst-firing mechanisms in rat olfactory tubercle neurons.

    Chiang, Elizabeth; Strowbridge, Ben W


    Olfactory information is processed by a diverse group of interconnected forebrain regions. Most efforts to define the cellular mechanisms involved in processing olfactory information have been focused on understanding the function of the olfactory bulb, the primary second-order olfactory region, and its principal target, the piriform cortex. However, the olfactory bulb also projects to other targets, including the rarely studied olfactory tubercle, a ventral brain region recently implicated in regulating cocaine-related reward behavior. We used whole cell patch-clamp recordings from rat tubercle slices to define the intrinsic properties of neurons in the dense and multiform cell layers. We find three common firing modes of tubercle neurons: regular-spiking, intermittent-discharging, and bursting. Regular-spiking neurons are typically spiny-dense-cell-layer cells with pyramidal-shaped, dendritic arborizations. Intermittently discharging and bursting neurons comprise the majority of the deeper multiform layer and share a common morphology: multipolar, sparsely spiny cells. Rather than generating all-or-none stereotyped discharges, as observed in many brain areas, bursting cells in the tubercle generate depolarizing plateau potentials that trigger graded but time-limited discharges. We find two distinct subclasses of bursting cells that respond similarly to step stimuli but differ in the role transmembrane Ca currents play in their intrinsic behavior. Calcium currents amplify depolarizing inputs and enhance excitability in regenerative bursting cells, whereas the primary action of Ca in nonregenerative bursting tubercle neurons appears to be to decrease excitability by triggering Ca-activated K currents. Nonregenerative bursting cells exhibit a prolonged refractory period after even short discharges suggesting that they may function to detect transient events.

  5. The diversity of progenitors and emission mechanisms for ultra-long bursts

    Gendre, B; Atteia, J L; Basa, S; Boer, M; Coward, D M; Cutini, S; D'Elia, V; Howell, E J; Klotz, A; Oates, S; De Pasquale, M; Piro, L


    GRB 111209A is the longest ever recorded burst. This burst was detected by Swift and Konus-Wind, and we obtained TOO time from XMM-Newton as well as prompt data from TAROT. We made a common reduction using data from these instruments together with other ones. This allows for the first time a precise study at high signal-to-noise ratio of the prompt to afterglow transition. We show that several mechanisms are responsible of this phase. In its prompt phase, we show that its duration is longer than 20 000 seconds. This, combined with the fact that the burst fluence is among the top 5% of what is observed for other events, makes this event extremely energetic. We discuss the possible progenitors that could explain the extreme duration properties of this burst as well as its spectral properties. We present evidences that this burst belong to a new, previously unidentified, class of GRBs. The most probable progenitor of this new class is a low metalicity blue super-giant star. We show that selection effects could p...

  6. Focal mechanism caused by fracture or burst of a coal pillar

    CAO An-ye; DOU Lin-ming; CHEN Guo-xiang; GONG Si-yuan; WANG Yu-gang; LI Zhi-hua


    As a regional, real-time and dynamic method, microseismic monitoring technology is quite an appropriate technology for forecasting geological hazards, such as rock bursts, mine tremors, coal and gas outbursts and can even be used to prevent or at least reduce these disasters. The study of the focal mechanisms of different seismic sources is the prerequisite and basis for forecasting rock burst by microseismic monitoring technology. Based on the analysis on the mechanism and fracture course of coal pillars where rock bursts occur mostly, the equivalent point source model of the seismicity caused by a coal pillar was created. Given the model, the seismic displacement equation of a coal pillar was analyzed and the seismic mechanism was pointed out by seismic wave theory. The course of the fracture of the coal pillar was simulated closely in the laboratory and the equivalent microseismic signals of the fractures of the coal pillar were acquired using a TDS-6 experimental system. The results show that, by the pressure and friction of a medium near the seismic source, both a compression wave and a shear wave will be emitted and shear fracture will be induced at the moment of breakage. The results can be used to provide an academic basis to forecast and prevent rock bursts or tremors in a coal pillar.

  7. Elements of mechanics of materials

    Olsen, G.A.


    The study of mechanics of materials as pursued in this text involves the development and application of those basic design relationships which occur in the more simple stress-resisting bodies. Chapters are included on stresses in members subjected to axial and central loads; stress-strain data and structural materials property data obtained by experimentation; stresses in thin-walled cylinders, spheres, and fabricated joints; shear- and bending-moment diagrams, beam design and deflections; stresses due to eccentrically applied loads; columns; combined stresses and strains; fatigue; and energy relationships and impact loads. This text was designed for use in a comprehensive one-semester undergraduate course in mechanics of materials. (LCL)

  8. Quantum mechanics and elements of reality

    Mohrhoff, Ulrich


    It is widely accepted that a Born probability of 1 is sufficient for the existence of a corresponding element of reality. Recently Vaidman has extended this idea to the ABL probabilities of the time-symmetrized version of quantum mechanics originated by Aharonov, Bergmann, and Lebowitz. Several authors have objected to Vaidman's time-symmetrized elements of reality without casting doubt on the widely accepted sufficiency condition for `ordinary' elements of reality. In this paper I show that ...

  9. Trainsient Accretion Disk and Energy Mechanism of Gamma Ray Bursts

    LU Ye; ZHENG Guang-Sheng; ZHAO Gang; YANG Lan-Tian


    We suggest that a rotating massive black hole (106M ) located at an inactive galaxy may convert its host into a transient active phase by capturing and disrupting a star. During this period, a transient accretion disk is formed and a strong transient magnetic field can be produced in the inner boundary of the accretion disk. A large amount of rotational energy of the black hole is extracted and released in the ultra relativistic jet with a bulk Lorentz factor larger than 103 via Blandford-Znajek process. The relativistic jet energy can be converted into γ-ray radiation in the shock region located at a distance of about 1.4 × 1016 cm via the external shock mechanism.The observed properties of GRB971214 is used to illustrate our model

  10. The anatomy of a long gamma-ray burst: a simple classification scheme for the emission mechanism(s)

    Bégué, Damien


    Ultra-relativistic motion and efficient conversion of kinetic energy to radiation are required by gamma-ray burst (GRB) observations, yet they are difficult to simultaneously achieve. Three leading mechanisms have been proposed to explain the observed emission emanating from GRB outflows: radiation from either relativistic internal or external shocks, or thermal emission from a photosphere. Previous works were dedicated to independently treating these three mechanisms and arguing for a sole, unique origin of the prompt emission of gamma-ray bursts. In contrast, herein, we first explain why all three models are valid mechanisms and that a contribution from each of them is expected in the prompt phase. Additionally, we show that a single parameter, the dimensionless entropy of the GRB outflow, determines which mechanism contributes the most to the emission. More specifically, internal shocks dominate for low values of the dimensionless entropy, external shocks for intermediate values and finally, photospheric e...

  11. Mosquitoes drink with a burst in reserve: explaining pumping behavior with a fluid mechanics model

    Chatterjee, Souvick; Socha, Jake; Stremler, Mark


    Mosquitoes drink using a pair of in-line pumps in the head that draw liquid food through the proboscis. Experimental observations with synchrotron x-ray imaging indicate two modes of drinking: a predominantly occurring continuous mode, in which the cibarial and pharyngeal pumps expand cyclically at a constant phase difference, and an occasional, isolated burst mode, in which the pharyngeal pump expansion is 10 to 30 times larger than in the continuous mode. We have used a reduced order model of the fluid mechanics to hypothesize an explanation of this variation in drinking behavior. Our model results show that the continuous mode is more energetically efficient, whereas the burst mode creates a large pressure drop across the proboscis, which could potentially be used to clear blockages. Comparisons with pump knock-out configurations demonstrate different functional roles of the pumps in mosquito feeding. This material is based upon work supported by the NSF under Grant No. #0938047.

  12. Detectivity of Fe Kα Lines in Gamma-Ray Bursts by Cerenkov Line Mechanism

    SU Jie; JIN Sheng-Zhen


    @@ The Fe Kα lines in gamma-ray bursts (GRBs) produced with the Cerenkov line mechan ism are studied. We theoretically predict the Fe Kα line luminosities in both the early (before 1 hour) and late (~ 1 day) afterglows. Assuming about 200 GRBs could be detected by Swift per year, we sampled the redshift of these GRBs using the Monte Carlo method according to the GRB formation rate derived from the statistical correlation between the spectral peak energy and the peak luminosity of GRBs.

  13. The anatomy of a long gamma-ray burst: a simple classification scheme for the emission mechanism(s).

    Bégué, Damien; Burgess, Michael


    Ultra-relativistic motion and efficient conversion of kinetic energy to radiation are required by gamma-ray burst (GRB) observations, yet they are difficult to simultaneously achieve. Three leading mechanisms have been proposed to explain the observed emission emanating from GRB outflows: radiation from either relativistic internal or external shocks, or thermal emission from a photosphere. Previous works were mechanisms and arguing for a sole, unique origin of the prompt emission of gamma-ray bursts. In contrast, herein, we first explain why all three models are valid mechanisms and that a contribution from each of them is expected in the prompt phase. Additionally, we show that a single parameter, the dimensionless entropy of the GRB outflow, determines which mechanism contributes the most to the emission. More specifically, internal shocks dominate for low values of the dimensionless entropy, external shocks for intermediate values and finally, photospheric emission for large values. We present a unified framework for the emission mechanisms of GRBs with easily testable predictions for each process.

  14. Elements of theoretical mechanics for electronic engineers

    Bultot, Franz


    Elements of Theoretical Mechanics for Electronic Engineers deals with theoretical mechanics, which is considered one of the fundamental branches of instruction essential to training an engineer. This book discusses the oscillatory motions and their counterparts in electrical circuits and radio, and provides an introduction to differential operators of vector field theory. Other topics covered include systems and functions of vectors; dynamics of a free point; vibrations and waves; and statics. Worked examples and many notes on the application of most sections of the theories to electrical deve

  15. Characterizing the mechanism(s) of heavy element synthesis reactions

    Loveland, Walter


    A review of the current state of our understanding of complete fusion reaction mechanisms is presented, from the perspective of an experimentalist. For complete fusion reactions, the overall uncertainties in predicting heavy element synthesis cross sections are examined in terms of the uncertainties associated with the calculations of capture cross sections, fusion probabilities and survival probabilities.

  16. Genotype-dependent Burst of Transposable Element Expression in Crowns of Hexaploid Wheat (Triticum aestivum L. during Cold Acclimation

    Debbie Laudencia-Chingcuanco


    Full Text Available The expression of 1,613 transposable elements (TEs represented in the Affymetrix Wheat Genome Chip was examined during cold treatment in crowns of four hexaploid wheat genotypes that vary in tolerance to cold and in flowering time. The TE expression profiles showed a constant level of expression throughout the experiment in three of the genotypes. In winter Norstar, the most cold-hardy of the four genotypes, a subset of the TEs showed a burst of expression after vernalization saturation was achieved. About 47% of the TEs were expressed, and both Class I (retrotransposons and Class II (DNA transposons types were well represented. Gypsy and Copia were the most represented among the retrotransposons while CACTA and Mariner were the most represented DNA transposons. The data suggests that the Vrn-A1 region plays a role in the stage-specific induction of TE expression in this genotype.

  17. Scaling of mechanical power output during burst escape flight in the Corvidae.

    Jackson, Brandon E; Dial, Kenneth P


    Avian locomotor burst performance (e.g. acceleration, maneuverability) decreases with increasing body size and has significant implications for the survivorship, ecology and evolution of birds. However, the underlying mechanism of this scaling relationship has been elusive. The most cited mechanistic hypothesis posits that wingbeat frequency alone limits maximal muscular mass-specific power output. Because wingbeat frequency decreases with body size, it may explain the often-observed negative scaling of flight performance. To test this hypothesis we recorded in vivo muscular mechanical power from work-loop mechanics using surgically implanted sonomicrometry (measuring muscle length change) and strain gauges (measuring muscle force) in four species of Corvidae performing burst take-off and vertical escape flight. The scale relationships derived for the four species suggest that maximum muscle-mass-specific power scales slightly negatively with pectoralis muscle mass (M(-0.18)(m), 95% CI: -0.42 to 0.05), but less than the scaling of wingbeat frequency (M(-0.29)(m), 95% CI: -0.37 to -0.23). Mean muscle stress was independent of muscle mass (M(-0.02)(m), 95% CI: -0.20 to 0.19), but total muscle strain (percent length change) scaled positively (M(0.12)(m), 95% CI: 0.05 to 0.18), which is consistent with previous results from ground birds (Order Galliformes). These empirical results lend minimal support to the power-limiting hypothesis, but also suggest that muscle function changes with size to partially compensate for detrimental effects of size on power output, even within closely related species. Nevertheless, additional data for other taxa are needed to substantiate these scaling patterns.

  18. FORTE antenna element and release mechanism design

    Rohweller, D.J. [Astro Aerospace Corp., Carpinteria, CA (United States); Butler, T.Af. [Los Alamos National Lab., NM (United States)


    The Fast On-Orbit Recording of Transient Events (FORTE) satellite being built by Los Alamos National Laboratory (LANL) and Sandia National Laboratories (SNL) has as its most prominent feature a large deployable (11 m by 5 m) log periodic antenna to monitor emissions from electrical storms on the Earth. This paper describes the antenna and the design for the long elements and explains the dynamics of their deployment and the damping system employed. It also describes the unique paraffin-actuated reusable tie-down and release mechanism employed in the system.

  19. Finite element modeling of retinal prosthesis mechanics

    Basinger, B. C.; Rowley, A. P.; Chen, K.; Humayun, M. S.; Weiland, J. D.


    Epiretinal prostheses used to treat degenerative retina diseases apply stimulus via an electrode array fixed to the ganglion cell side of the retina. Mechanical pressure applied by these arrays to the retina, both during initial insertion and throughout chronic use, could cause sufficient retinal damage to reduce the device's effectiveness. In order to understand and minimize potential mechanical damage, we have used finite element analysis to model mechanical interactions between an electrode array and the retina in both acute and chronic loading configurations. Modeling indicates that an acute tacking force distributes stress primarily underneath the tack site and heel edge of the array, while more moderate chronic stresses are distributed more evenly underneath the array. Retinal damage in a canine model chronically implanted with a similar array occurred in correlating locations, and model predictions correlate well with benchtop eyewall compression tests. This model provides retinal prosthesis researchers with a tool to optimize the mechanical electrode array design, but the techniques used here represent a unique effort to combine a modifiable device and soft biological tissues in the same model and those techniques could be extended to other devices that come into mechanical contact with soft neural tissues.

  20. The mechanism of bursting phenomena in Belousov-Zhabotinsky(BZ) chemical reaction with multiple time scales


    The dynamics of a typical Belousov-Zhabotinsky(BZ)reaction with multiple time scales is investigated in this paper.Different forms of periodic bursting phenomena,and specially,three types of chaotic bursters with different structures can be obtained,which are in common with the behaviors observed in experiments.The bifurcations connecting the quiescent state and the repetitive spikes are presented to account for the occurrence of the NKoscillations as well as the different forms of chaotic bursters.The mechanism of the period-adding bifurcation sequences is explored to reveal why the length of the periods in the sequences does not change continuously with the continuous variation of the parameters.

  1. Interindividual Variability and Intraindividual Reliability of Intermittent Theta Burst Stimulation-induced Neuroplasticity Mechanisms in the Healthy Brain

    Schilberg, Lukas; Schuhmann, Teresa; Sack, Alexander T


    We combined patterned TMS with EMG in several sessions of a within-subject design to assess and characterize intraindividual reliability and interindividual variability of TMS-induced neuroplasticity mechanisms in the healthy brain. Intermittent theta burst stimulation (iTBS) was applied over M1 to

  2. Corticosterone rapidly promotes respiratory burst of mouse peritoneal macrophages via non-genomic mechanism

    SHI Wen-lei; MA Qian; ZHANG Lu-ding; HUANG Jun-long; ZHOU Jian; LIU Lei; SHEN Xing-hua; JIANG Chun-lei


    Background The immunomodulatory effects of glucocorticoids (GCs) have been described as bimodal. High concentration of GCs exerts immunosuppressive effects and low levels of GCs are immunopermissive. While the immunosuppressive mechanisms of GCs have been investigated intensely, the immunopermissive effects of GCs remain unclear. A lot of studies showed GCs could exert rapid non-genomic actions. We herein studied the rapid immunopromoting effects of GCs.Methods We observed the rapid (within 30 minutes) effects of corticosterone on respiratory burst of mouse peritoneal macrophages and studied their mechanisms. The superoxide anions were measured by cytochrome C reduction assay.Protein kinase C phosphorylation was measured by Western blotting and membrane fluidity was evaluated by fluorescence polarization measurement.Results The 10-8 mol/L and 10-7 mol/L corticosterone rapidly increased the superoxide anions production by macrophages, which were insensitive to GC-receptor antagonist, mifepristone, and protein-synthesis inhibitor,cycloheximide. Corticosterone coupled to bovine serum albumin was able to mimic the effects of corticosterone. The effects were independent of protein kinase C pathway and the change in membrane fluidity.Conclusions The results indicate that corticosterone rapidly promote the superoxide anions production by mouse peritoneal macrophages may through non-genomic mechanisms. This study may contribute to understanding the effects of GCs under stress condition and the physiological significance of nongenomic effects of GCs.

  3. Central engines of Gamma Ray Bursts. Magnetic mechanism in the collapsar model

    Barkov, Maxim V


    In this study we explore the magnetic mechanism of hypernovae and relativistic jets of long duration gamma ray bursts within the collapsar scenario. This is an extension of our earlier work [1]. We track the collapse of massive rotating stars onto a rotating central black hole using axisymmetric general relativistic magnetohydrodynamic code that utilizes a realistic equation of state and takes into account the cooling associated with emission of neutrinos and the energy losses due to dissociation of nuclei. The neutrino heating is not included. We describe solutions with different black hole rotation, mass accretion rate, and strength of progenitor's magnetic field. Some of them exhibits strong explosions driven by Poynting-dominated jets with power up to $12\\times10^{51} {erg s}^{-1}$. These jets originate from the black hole and powered via the Blandford-Znajek mechanism. A provisional criterion for explosion is derived. A number of simulation movies can be downloaded from

  4. Examining the limits of cellular adaptation bursting mechanisms in biologically-based excitatory networks of the hippocampus.

    Ferguson, K A; Njap, F; Nicola, W; Skinner, F K; Campbell, S A


    Determining the biological details and mechanisms that are essential for the generation of population rhythms in the mammalian brain is a challenging problem. This problem cannot be addressed either by experimental or computational studies in isolation. Here we show that computational models that are carefully linked with experiment provide insight into this problem. Using the experimental context of a whole hippocampus preparation in vitro that spontaneously expresses theta frequency (3-12 Hz) population bursts in the CA1 region, we create excitatory network models to examine whether cellular adaptation bursting mechanisms could critically contribute to the generation of this rhythm. We use biologically-based cellular models of CA1 pyramidal cells and network sizes and connectivities that correspond to the experimental context. By expanding our mean field analyses to networks with heterogeneity and non all-to-all coupling, we allow closer correspondence with experiment, and use these analyses to greatly extend the range of parameter values that are explored. We find that our model excitatory networks can produce theta frequency population bursts in a robust fashion.Thus, even though our networks are limited by not including inhibition at present, our results indicate that cellular adaptation in pyramidal cells could be an important aspect for the occurrence of theta frequency population bursting in the hippocampus. These models serve as a starting framework for the inclusion of inhibitory cells and for the consideration of additional experimental features not captured in our present network models.

  5. Reliability Assessment Based on Design and Manufacturing Tolerances for Control Burst Mechanism of Small Arms

    S.K. Basu


    Full Text Available Very often specified tolerance is made greater than process tolerance, depending upon (i the manufacturing process capability, and (ii the 'aspiration level' of the designer in effecting a specified tolerance. This applies to multiple components merging into an assembly. In assembly tolerance, errors due to mating are inherent. Common errors arise due to clearance, misalignment in planes and distortion that may cause side stack. Such errors affect the functional performance of the subsystem and consequently become the main cause of failure. Probability distribution of the assembly tolerance and probability distribution of stacked up tolerance of the Components in actual practice leave a common zone of interaction, based on which the in-built reliability changes. From the designer's tolerance, one may have an idea about the 'aspiration level' of assembly tolerance stacking error. Assuming both these parameters, viz., actual stacking error and designer's aspiration level of stacking error to follow the normal probability distribution, it is possible to get the reliability of the product assembly. The paper presents a real life case study for assessing the reliability of sub-assembly at the initial stages of development for control burst mechanism (CBM of rifle.

  6. Will Finite Elements Replace Structural Mechanics?

    Ojalvo, I. U.


    This paper presents a personal view regarding the need for a continued interest and activity in structural methods in general, while viewing finite elements and the computer as simply two specific tools for assisting in this endeavor. An attempt is made to provide some insight as to why finite element methods seem to have "won the war," and to give examples of their more (and less) intelligent use. Items addressed include a highlight of unnecessary limitations of many existing standard finite element codes and where it is felt that further development work is needed.

  7. Control Mechanism of Rock Burst in the Floor of Roadway Driven along Next Goaf in Thick Coal Seam with Large Obliquity Angle in Deep Well

    Yunhai Cheng


    Full Text Available This paper deals with the theoretical aspects combined with stress analysis over the floor strata of coal seam and the calculation model for the stress on the coal floor. Basically, this research presents the relevant results obtained for the rock burst prevention in the floor of roadway driven along next goaf in the exploitation of thick coal seam with large obliquity in deep well and rock burst tendency. The control mechanism of rock burst in the roadway driven along next goaf is revealed in the present work. That is, the danger of rock burst can be removed by changing the stress environment for the energy accumulation of the floor and by reducing the impact on the roadway floor from the strong dynamic pressure. This result can be profitable being used at the design stage of appropriate position of roadway undergoing rock burst tendency in similar conditions. Based on the analysis regarding the control mechanism, this paper presents a novel approach to the prevention of rock burst in roadway floor under the above conditions. That is, the return airway is placed within the goaf of the upper working face that can prevent the rock burst effectively. And in this way, mining without coal pillar in the thick coal seam with large obliquity and large burial depth (over a thousand meters is realized. Practice also proves that the rock burst in the floor of roadway driven along next goaf is controlled and solved.

  8. Mechanisms underlying burst generation of the pyloric muscle in the mantis shrimp, Squilla oratoria.

    Tazaki, K; Chiba, C


    The pyloric constrictor muscles of the stomach in Squilla can generate spikes by synaptic activation via the motor nerve from the stomatogastric ganglion. Spikes are followed by slow depolarizing afterpotentials (DAPs) which lead to sustained depolarization during a burst of spikes. 1. The frequency of rhythmic bursts induced by continuous depolarization is membrane voltage-dependent. A brief depolarizing or hyperpolarizing pulse can trigger or terminate bursts, respectively, in a threshold-dependent manner. 2. The conductance increases during the DAP response. The amplitude of DAP decreases by imposed depolarization, whereas it increases by hyperpolarization. DAPs from successive spikes sum to produce a sustained depolarizing potential capable of firing a burst. 3. The spike and DAP are reduced in amplitude by decreasing [Ca]o, enhanced by Sr2+ or Ba2+ substituted for Ca2+, and blocked by Co2+ or Mn2+. DAPs are selectively blocked by Ni2+, and the spike is followed by a hyperpolarizing afterpotential. 4. The spike and DAP are prolonged by intracellular injection of the Ca2+ chelator EGTA. A hyperpolarizing afterpotential is abolished by EGTA and enhanced by increasing [Ca]o. The DAP is diminished in Na(+)-free saline and reduced by tetrodotoxin. 5. It is concluded that the muscle fiber is endowed with endogenous oscillatory properties and that the oscillatory membrane events result from changes of a voltage- and time-dependent conductance to Ca2+ and Na+ and a Ca2+ activated conductance to K+.

  9. Quantum mechanics and elements of reality inferred from joint measurements

    Cabello, Adan; Garcia-Alcaine, Guillermo


    The Einstein-Podolsky-Rosen argument on quantum mechanics incompleteness is formulated in terms of elements of reality inferred from joint (as opposed to alternative) measurements, in two examples involving entangled states of three spin-1/2 particles. The same states allow us to obtain proofs of the incompatibility between quantum mechanics and elements of reality.


    Lazzati, Davide [Department of Physics, NC State University, 2401 Stinson Drive, Raleigh, NC 27695-8202 (United States); Morsony, Brian J. [Department of Astronomy, University of Wisconsin-Madison, 3321 Sterling Hall, 475 N. Charter Street, Madison WI 53706-1582 (United States); Margutti, Raffaella [Harvard-Smithsonian Center for Astrophysics, ITC, 60 Garden Street, Cambridge, MA 02138 (United States); Begelman, Mitchell C. [JILA, University of Colorado and National Institute of Standards and Technology, Boulder, CO 80309-0440 (United States)


    We present the results of a set of numerical simulations of long-duration gamma-ray burst jets associated with massive, compact stellar progenitors. The simulations extend to large radii and allow us to locate the region in which the peak frequency of the advected radiation is set before the radiation is released at the photosphere. Light curves and spectra are calculated for different viewing angles as well as different progenitor structures and jet properties. We find that the radiation released at the photosphere of matter-dominated jets is able to reproduce the observed Amati and energy-Lorentz factor correlations. Our simulations also predict a correlation between the burst energy and the radiative efficiency of the prompt phase, consistent with observations.

  11. Hydraulic elements in reduction of vibrations in mechanical systems

    Białas, K.; Buchacz, A.


    This work presents non-classical method of design of mechanic systems with subsystem reducing vibrations. The purpose of this paper is also introduces synthesis of mechanic system with reducing vibrations understand as design of this type of systems. The synthesis may be applied to modify the already existing systems in order to achieve a desired result. Elements which reduce vibrations can be constructed with passive, semi-active or active components. These considerations systems have selected active items. A hallmark of active elements it is possible to change the parameters on time of these elements and their power from an external source. The implementation of active elements is very broad. These elements can be implemented through the use of components of electrical, pneumatic, hydraulic, etc. The system was consisted from mechanical and hydraulic elements. Hydraulic elements were used as subsystem reducing unwanted vibration of mechanical system. Hydraulic elements can be realized in the form of hydraulic cylinder. In the case of an active vibration reduction in the form of hydraulic cylinder it is very important to find the corresponding values of hydraulic components. The values of these elements affect the frequency of vibrations of this sub-system which is related to the effective vibration reduction [7,11].

  12. Magnetar Bursts

    Kouveliotou, Chryssa


    The Fermi/Gamma-ray Burst Monitor (GBM) was launched in June 2008. During the last five years the instrument has observed several hundreds of bursts from 8 confirmed magnetars and 19 events from unconfirmed sources. I will discuss the results of the GBM magnetar burst catalog, expand on the different properties of their diverse source population, and compare these results with the bursting activity of past sources. I will then conclude with thoughts of how these properties fit the magnetar theoretical models.

  13. Effect of wear on the burst strength of l-80 steel casing

    Irawan, S.; Bharadwaj, A. M.; Temesgen, B.; Karuppanan, S.; Abdullah, M. Z. B.


    Casing wear has recently become one of the areas of research interest in the oil and gas industry especially in extended reach well drilling. The burst strength of a worn out casing is one of the significantly affected mechanical properties and is yet an area where less research is done The most commonly used equations to calculate the resulting burst strength after wear are Barlow, the initial yield burst, the full yield burst and the rupture burst equations. The objective of this study was to estimate casing burst strength after wear through Finite Element Analysis (FEA). It included calculation and comparison of the different theoretical bursts pressures with the simulation results along with effect of different wear shapes on L-80 casing material. The von Misses stress was used in the estimation of the burst pressure. The result obtained shows that the casing burst strength decreases as the wear percentage increases. Moreover, the burst strength value of the casing obtained from the FEA has a higher value compared to the theoretical burst strength values. Casing with crescent shaped wear give the highest burst strength value when simulated under nonlinear analysis.


    Andrija P. Milojević


    Full Text Available A compliant mechanism is defined as a single piece structure that transfer motion or force through elastic deformation. The synthesis of this kind of mechanisms represents a challenging task, especially because their flexible segments usually must undergo large, nonlinear deflections which include difficult nonlinear analysis. In this paper the new software for synthesis of compliant mechanisms is developed. The software uses an improved topology optimization technique that is especially useful when the designer does not have a particular compliant mechanism already in mind. Intersection between elements in the compliant mechanisms obtained by using existing topology optimization technique often increases stiffness of the structure which need to be flexible. The topology optimization technique is improved in the software so that compliant mechanisms without intersecting elements are obtained. The methodology that software uses and its capability will be shown on the examples of synthesis of the compliant gripper and the compliant displacement inverter.

  15. The Calculation of Matrix Elements in Relativistic Quantum Mechanics

    Ilarraza-Lomelí, A. C.; Valdés-Martínez, M. N.; Salas-Brito, A. L.; Martínez-y-Romero, R. P.; Núñez-Yépez, H. N


    Employing a relativistic version of a hypervirial result, recurrence relations for arbitrary non-diagonal radial hydrogenic matrix elements have recently been obtained in Dirac relativistic quantum mechanics. In this contribution honoring Professor L\\"owdin, we report on a new relation we have recently discovered between the matrix elements $$ and $$---where $\\beta$ is a Dirac matrix and the numbers distiguish between different radial eigenstates--- that allow for a simplification and hence f...

  16. Comparison of the direct burst pressure and the ring tensile test methods for mechanical characterization of tissue-engineered vascular substitutes.

    Laterreur, Véronique; Ruel, Jean; Auger, François A; Vallières, Karine; Tremblay, Catherine; Lacroix, Dan; Tondreau, Maxime; Bourget, Jean-Michel; Germain, Lucie


    Tissue engineering provides a promising alternative for small diameter vascular grafts, especially with the self-assembly method. It is crucial that these grafts possess mechanical properties that allow them to withstand physiological flow and pressure without being damaged. Therefore, an accurate assessment of their mechanical properties, especially the burst pressure, is essential prior to clinical release. In this study, the burst pressure of self-assembled tissue-engineered vascular substitutes was first measured by the direct method, which consists in pressurizing the construct with fluid until tissue failure. It was then compared to the burst pressure estimated by Laplace׳s law using data from a ring tensile test. The major advantage of this last method is that it requires a significantly smaller tissue sample. However, it has been reported as overestimating the burst pressure compared to a direct measurement. In the present report, it was found that an accurate estimation of the burst pressure may be obtained from a ring tensile test when failure internal diameter is used as the diameter parameter in Laplace׳s law. Overestimation occurs with the method previously reported, i.e. when the unloaded internal diameter is used for calculations. The estimation of other mechanical properties was also investigated. It was demonstrated that data from a ring tensile test provide an accurate estimate of the failure strain and the stiffness of the constructs when compared to measurements with the direct method. Copyright © 2014 Elsevier Ltd. All rights reserved.

  17. Burst Suppression: A Review and New Insights

    Jonathan Dillon Kenny


    Full Text Available Burst suppression is a pattern of brain electrical activity characterized by alternating periods of high-amplitude bursts and electrical silence. Burst suppression can arise from several different pathological conditions, as well as from general anesthesia. Here we review current algorithms that are used to quantify burst suppression, its various etiologies, and possible underlying mechanisms. We then review clinical applications of anesthetic-induced burst suppression. Finally, we report the results of our new study showing clear electrophysiological differences in burst suppression patterns induced by two common general anesthetics, sevoflurane and propofol. Our data suggest that the circuit mechanisms that generate burst suppression activity may differ between different general anesthetics.

  18. Jet Luminosity of Gamma-ray Bursts: Blandford-Znajek Mechanism v.s. Neutrino Annihilation Process

    Liu, Tong; Xue, Li; Gu, Wei-Min


    A neutrino-dominated accretion flow (NDAF) around a rotating stellar-mass black hole (BH) is one of the plausible candidates for the central engine of gamma-ray bursts (GRBs). Two mechanisms, i.e., Blandford-Znajek (BZ) mechanism and neutrino annihilation process, are generally considered to power GRBs. Using the analytic solutions from Xue et al. (2013) and ignoring the effects of the magnetic field configuration, we estimate the BZ and neutrino annihilation luminosities as the functions of the disk masses and BH spin parameters to contrast the observational jet luminosities of GRBs. The results show that, although the neutrino annihilation processes could account for most of GRBs, the BZ mechanism is more effective, especially for long-duration GRBs. Actually, if the energy of afterglows and flares of GRBs is included, the distinction between these two mechanisms is more significant. Furthermore, massive disk mass and high BH spin are beneficial to power high luminosities of GRBs. Finally, we discuss possib...

  19. Element Verification and Comparison in Sierra/Solid Mechanics Problems

    Ohashi, Yuki; Roth, William


    The goal of this project was to study the effects of element selection on the Sierra/SM solutions to five common solid mechanics problems. A total of nine element formulations were used for each problem. The models were run multiple times with varying spatial and temporal discretization in order to ensure convergence. The first four problems have been compared to analytical solutions, and all numerical results were found to be sufficiently accurate. The penetration problem was found to have a high mesh dependence in terms of element type, mesh discretization, and meshing scheme. Also, the time to solution is shown for each problem in order to facilitate element selection when computer resources are limited.

  20. Single Element Excitation and Detection of (Micro-)Mechanical Resonators

    Tilmans, Harrie A.C.; IJntema, Dominicus .J.; Fluitman, Jan H.J


    The authors describe a single-element approach for the excitation and detection of the vibrational motion of (micro-)mechanical resonators. An equivalent electrical one-port network is derived for an electrostatically and a piezoelectrically driven resonator. In this way, the effect of the mechanica

  1. (Environmental and geophysical modeling, fracture mechanics, and boundary element methods)

    Gray, L.J.


    Technical discussions at the various sites visited centered on application of boundary integral methods for environmental modeling, seismic analysis, and computational fracture mechanics in composite and smart'' materials. The traveler also attended the International Association for Boundary Element Methods Conference at Rome, Italy. While many aspects of boundary element theory and applications were discussed in the papers, the dominant topic was the analysis and application of hypersingular equations. This has been the focus of recent work by the author, and thus the conference was highly relevant to research at ORNL.


    段成红; 吴祥; 罗翔鹏


    本文主要采用有限元法分析复合气瓶的爆破,按最大应力准则和最大应变准则预测爆破压力,并与《DOT CFFC》标准规定的最小爆破压力进行比较,计算误差百分比,由误差百分比分析得出,按最大应变准则预测爆破压力较为接近最小爆破压力,对工程实践有较大的指导意义.%In this paper, the bursting of composite cylinders is analyzed with the finite element method. The burst pressure is predicted according to the maximum stress criterion and the maximum strain criterion. The predicted results are compared with the minimum burst pressure regulated by the DOT CFFC standard, and the percentage error is calculated. By analyzing the percentage error, it can be concluded that the burst pressure predicted with maximum strain criterion is more approximate to the minimum burst pressure. The finite element analysis results in this paper are conducive to the engineering practice.

  3. Co-Evolutionary Mechanisms of Emotional Bursts in Online Social Dynamics and Networks

    Bosiljka Tadić


    Full Text Available Collective emotional behavior of users is frequently observed on various Web portals; however, its complexity and the role of emotions in the acting mechanisms are still not thoroughly understood. In this work, using the empirical data and agent-based modeling, a parallel analysis is performed of two archetypal systems—Blogs and Internet-Relayed-Chats—both of which maintain self-organized dynamics but not the same communication rules and time scales. The emphasis is on quantifying the collective emotions by means of fractal analysis of the underlying processes as well as topology of social networks, which arise and co-evolve in these stochastic processes. The results reveal that two distinct mechanisms, which are based on different use of emotions (an emotion is characterized by two components, arousal and valence, are intrinsically associated with two classes of emergent social graphs. Their hallmarks are the evolution of communities in accordance with the excess of the negative emotions on popular Blogs, on one side, and smooth spreading of the Bot’s emotional impact over the entire hierarchical network of chats, on the other. Another emphasis of this work is on the understanding of nonextensivity of the emotion dynamics; it was found that, in its own way, each mechanism leads to a reduced phase space of the emotion components when the collective dynamics takes place. That a non-additive entropy describes emotion dynamics, is further confirmed by computing the q-generalized Kolmogorov-Sinai entropy rate in the empirical data of chats as well as in the simulations of interacting emotional agents and Bots.

  4. Relating the Variability of Tone-Burst Otoacoustic Emission and Auditory Brainstem Response Latencies to the Underlying Cochlear Mechanics

    Verhulst, Sarah; Shera, Christopher A.


    Forward and reverse cochlear latency and its relation to the frequency tuning of the auditory filters can be assessed using tone bursts (TBs). Otoacoustic emissions (TBOAEs) estimate the cochlear roundtrip time, while auditory brainstem responses (ABRs) to the same stimuli aim at measuring the auditory filter buildup time. Latency ratios are generally close to two and controversy exists about the relationship of this ratio to cochlear mechanics. We explored why the two methods provide different estimates of filter buildup time, and ratios with large inter-subject variability, using a time-domain model for OAEs and ABRs. We compared latencies for twenty models, in which all parameters but the cochlear irregularities responsible for reflection-source OAEs were identical, and found that TBOAE latencies were much more variable than ABR latencies. Multiple reflection-sources generated within the evoking stimulus bandwidth were found to shape the TBOAE envelope and complicate the interpretation of TBOAE latency and TBOAE/ABR ratios in terms of auditory filter tuning. PMID:27175040

  5. Comparative Biochemistry of the Oxidative Burst Produced by Rose and French Bean Cells Reveals Two Distinct Mechanisms1

    Bolwell, G. Paul; Davies, Dewi R.; Gerrish, Chris; Auh, Chung-Kyoon; Murphy, Terence M.


    Cultured cells of rose (Rosa damascena) treated with an elicitor derived from Phytophthora spp. and suspension-cultured cells of French bean (Phaseolus vulgaris) treated with an elicitor derived from the cell walls of Colletotrichum lindemuthianum both produced H2O2. It has been hypothesized that in rose cells H2O2 is produced by a plasma membrane NAD(P)H oxidase (superoxide synthase), whereas in bean cells H2O2 is derived directly from cell wall peroxidases following extracellular alkalinization and the appearance of a reductant. In the rose/Phytophthora spp. system treated with N,N-diethyldithiocarbamate, superoxide was detected by a N,N′-dimethyl-9,9′-biacridium dinitrate-dependent chemiluminescence; in contrast, in the bean/C. lindemuthianum system, no superoxide was detected, with or without N,N-diethyldithiocarbamate. When rose cells were washed free of medium (containing cell wall peroxidase) and then treated with Phytophthora spp. elicitor, they accumulated a higher maximum concentration of H2O2 than when treated without the washing procedure. In contrast, a washing treatment reduced the H2O2 accumulated by French bean cells treated with C. lindemuthianum elicitor. Rose cells produced reductant capable of stimulating horseradish (Armoracia lapathifolia) peroxidase to form H2O2 but did not have a peroxidase capable of forming H2O2 in the presence of reductant. Rose and French bean cells thus appear to be responding by different mechanisms to generate the oxidative burst. PMID:9536055

  6. Comparative biochemistry of the oxidative burst produced by rose and french bean cells reveals two distinct mechanisms

    Bolwell; Davies; Gerrish; Auh; Murphy


    Cultured cells of rose (Rosa damascena) treated with an elicitor derived from Phytophthora spp. and suspension-cultured cells of French bean (Phaseolus vulgaris) treated with an elicitor derived from the cell walls of Colletotrichum lindemuthianum both produced H2O2. It has been hypothesized that in rose cells H2O2 is produced by a plasma membrane NAD(P)H oxidase (superoxide synthase), whereas in bean cells H2O2 is derived directly from cell wall peroxidases following extracellular alkalinization and the appearance of a reductant. In the rose/Phytophthora spp. system treated with N, N-diethyldithiocarbamate, superoxide was detected by a N, N'-dimethyl-9,9'-biacridium dinitrate-dependent chemiluminescence; in contrast, in the bean/C. lindemuthianum system, no superoxide was detected, with or without N,N-diethyldithiocarbamate. When rose cells were washed free of medium (containing cell wall peroxidase) and then treated with Phytophthora spp. elicitor, they accumulated a higher maximum concentration of H2O2 than when treated without the washing procedure. In contrast, a washing treatment reduced the H2O2 accumulated by French bean cells treated with C. lindemuthianum elicitor. Rose cells produced reductant capable of stimulating horseradish (Armoracia lapathifolia) peroxidase to form H2O2 but did not have a peroxidase capable of forming H2O2 in the presence of reductant. Rose and French bean cells thus appear to be responding by different mechanisms to generate the oxidative burst.

  7. Certain Discrete Element Methods in Problems of Fracture Mechanics

    P. P. Procházka


    Full Text Available In this paper two discrete element methods (DEM are discussed. The free hexagon element method is considered a powerful discrete element method, which is broadly used in mechanics of granular media. It substitutes the methods for solving continuum problems. The great disadvantage of classical DEM, such as the particle flow code (material properties are characterized by spring stiffness, is that they have to be fed with material properties provided from laboratory tests (Young's modulus, Poisson's ratio, etc.. The problem consists in the fact that the material properties of continuum methods (FEM, BEM are not mutually consistent with DEM. This is why we utilize the principal idea of DEM, but cover the continuum by hexagonal elastic, or elastic-plastic, elements. In order to complete the study, another one DEM is discussed. The second method starts with the classical particle flow code (PFC - which uses dynamic equilibrium, but applies static equilibrium. The second method is called the static particle flow code (SPFC. The numerical experience and comparison numerical with experimental results from scaled models are discussed in forthcoming paper by both authors.

  8. Transposable element recruitments in the mammalian placenta: impacts and mechanisms.

    Emera, Deena; Wagner, Günter P


    Transposable elements (TEs) are mobile DNA elements found at high frequency in mammalian genomes. Although these elements are generally perceived as genomic parasites, they have the potential to influence host genome function in many beneficial ways. This article discusses the role TEs have played in the evolution of the placenta and pregnancy in viviparous mammals. Using examples from our own research and the literature, we argue that frequent recruitment of TEs, in particular of retroelements, has facilitated the extreme diversification of tissues at the maternal-fetal interface. We also discuss the mechanisms by which TEs have been recruited for functions during pregnancy. We argue that retroelements are pre-adapted to becoming cis-regulatory elements for host genomes because they need to utilize host regulatory signals for their own life cycle. However, although TEs contain some of the signals necessary for host functions upon insertion, they often require modification before acquiring a biological role in a host tissue. We discuss the process by which one TE was transformed into a promoter for prolactin expression in the endometrium, describing a model for TE domestication called 'epistatic capture'.

  9. Broadband Spectral Study of Magnetar Bursts

    Kirmizibayrak, Demet; Gogus, Ersin; Sasmaz Mus, Sinem; Kaneko, Yuki


    Magnetar bursts occur sporadically on random occasions, and every burst-active episode carries unique information about the bursting magnetar. Therefore, in-depth spectral and temporal analyses of each of the magnetar bursts provide new insights into the bursting and radiation mechanisms. There have been a number of studies over the last decade, investigating the spectral and temporal properties of magnetar bursts. The spectra of typical magnetar bursts were generally described with the Comptonized model or the sum of two blackbody functions. However, it was recently shown that the actual spectral nature of these bursts can be conclusively determined if the spectral analysis is performed on a wide energy coverage. We present the results of in-depth systematic broadband (2 - 250 keV) spectral analysis of a large number of bursts originated from three magnetars: SGR 1806-20, SGR 1900+14, and SGR J1550-5418, observed with the Rossi X-ray Timing Explorer.

  10. Finite elements in fracture mechanics theory, numerics, applications

    Kuna, Meinhard


    Fracture mechanics has established itself as an important discipline of growing interest to those working to assess the safety, reliability and service life of engineering structures and materials. In order to calculate the loading situation at cracks and defects, nowadays numerical techniques like finite element method (FEM) have become indispensable tools for a broad range of applications. The present monograph provides an introduction to the essential concepts of fracture mechanics, its main goal being to procure the special techniques for FEM analysis of crack problems, which have to date only been mastered by experts. All kinds of static, dynamic and fatigue fracture problems are treated in two- and three-dimensional elastic and plastic structural components. The usage of the various solution techniques is demonstrated by means of sample problems selected from practical engineering case studies. The primary target group includes graduate students, researchers in academia and engineers in practice.

  11. Formation of small-scale magnetic elements: surface mechanism

    Gadun, A S; Solanki, S K; 10.3103/50884591305030022


    We present the first results of a two-dimensional MHD simulation of the solar magnetogranulation. The medium was assumed to be compressible, gravitationally stratified, radiatively coupled, partially ionized, and turbulent. The simulated magnetogranulation evolved over the course of two hours of hydrodynamic (solar) time. A surface (magnetic plume-like) mechanism which forms thin magnetic elements was found to operate during the process of granule fragmentation. The activity of such a mechanism suggests that the magnetogranulation can concentrate and intensify the global magnetic flux at the boundaries of convective cells and can also form nearly vertical compact magnetic flux tubes by involving the weak horizontal photospheric field, which may be, in general, of local (turbulent) nature.

  12. Insights into dynamic strain aging under cyclic creep with reference to strain burst: Some new observations and mechanisms part-II: Microstructural aspects

    Sarkar, Aritra, E-mail: [Mechanical Metallurgy Division, Indira Gandhi Centre for Atomic Research, Kalpakkam, 603102 Tamil Nadu (India); Nagesha, A. [Mechanical Metallurgy Division, Indira Gandhi Centre for Atomic Research, Kalpakkam, 603102 Tamil Nadu (India); Parameswaran, P.; Murugesan, S. [Materials Synthesis and Structural Characterization Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, Tamil Nadu (India); Sandhya, R.; Laha, K. [Mechanical Metallurgy Division, Indira Gandhi Centre for Atomic Research, Kalpakkam, 603102 Tamil Nadu (India)


    Cyclic creep behavior of 316LN austenitic stainless steel (SS) was investigated at 823 K at different combinations of mean stress (σ{sub m}), stress amplitude (σ{sub a}) and stress rate. Characteristic strain bursts were observed being attributed to a pronounced influence of dynamic strain aging (DSA). Detailed microstructural investigation carried out through transmission electron microscope (TEM) revealed that dislocation substructure evolving under a process of strain burst during cyclic creep mainly consists of planar deformation bands. The number density of bands was found to be strongly sensitive to σ{sub m}- σ{sub a}-stress rate combination employed. An important substructural feature found in this study was the formation of microtwins. Either planar slip or twinning was found to dominate the substructure depending on the loading combination, which was demonstrated through a dislocation distribution map. Dislocation substructure was further correlated with evolution of surface relief studied through atomic force microscopy (AFM) and field emission gun-scanning electron microscopy (FEG-SEM), which depicts the formation of slip markings and nucleation of cracks from persistent slip markings during the course of a strain burst. Finally, well-known theoretical models explaining the mechanism of DSA during tensile deformation were suitably modified for load-controlled scenario and the origin of strain burst as a function of σ{sub m} or stress rate was explained based on the same. Dislocation density measurements were carried out for specimens undergoing strain burst during cyclic creep, which was utilized for reconstituting the models.

  13. Flexible Elements in the Mechanisms of Weaving Machines

    Žák, J.

    Weaving machines use several mechanisms to produce a fabric; their relative (mutual) position is exactly defined at any point of working cycle and must be maintained as accurately as possible. From that, it results some requirements on their design, such as stiffness of the joint frame, synchronization of their drives, accuracy and stiffness of particular links of those mechanisms and minimization of the clearances between them. In this paper, we have attempted to outline the possibility of replacing the binary links by using the flexible mechanism elements. In this step, we always removed one rotary constraint at least which is necessary when using a binary link, i.e., a rod, pitman or connecting rod. In practice, it means reducing the number of bearings which have a limited service life, require maintenance and when using them we cannot avoid the formation of clearances. In the case of a slay of the CAMEL weaving machine, it was furthermore possible to use the deformation energy to a relief of the drive, its better regulation and an overall reduction of energy consumption. Although this procedure is not subject to the use of special materials, there can be advantageously used fiber composites whose certain features make the design of such mechanisms easy to a great extent.

  14. Computationally efficient finite element evaluation of natural patellofemoral mechanics.

    Fitzpatrick, Clare K; Baldwin, Mark A; Rullkoetter, Paul J


    Finite element methods have been applied to evaluate in vivo joint behavior, new devices, and surgical techniques but have typically been applied to a small or single subject cohort. Anatomic variability necessitates the use of many subject-specific models or probabilistic methods in order to adequately evaluate a device or procedure for a population. However, a fully deformable finite element model can be computationally expensive, prohibiting large multisubject or probabilistic analyses. The aim of this study was to develop a group of subject-specific models of the patellofemoral joint and evaluate trade-offs in analysis time and accuracy with fully deformable and rigid body articular cartilage representations. Finite element models of eight subjects were used to tune a pressure-overclosure relationship during a simulated deep flexion cycle. Patellofemoral kinematics and contact mechanics were evaluated and compared between a fully deformable and a rigid body analysis. Additional eight subjects were used to determine the validity of the rigid body pressure-overclosure relationship as a subject-independent parameter. There was good agreement in predicted kinematics and contact mechanics between deformable and rigid analyses for both the tuned and test groups. Root mean square differences in kinematics were less than 0.5 deg and 0.2 mm for both groups throughout flexion. Differences in contact area and peak and average contact pressures averaged 5.4%, 9.6%, and 3.8%, respectively, for the tuned group and 6.9%, 13.1%, and 6.4%, respectively, for the test group, with no significant differences between the two groups. There was a 95% reduction in computational time with the rigid body analysis as compared with the deformable analysis. The tuned pressure-overclosure relationship derived from the patellofemoral analysis was also applied to tibiofemoral (TF) articular cartilage in a group of eight subjects. Differences in contact area and peak and average contact

  15. Finite element simulations on the mechanical properties of MHS materials

    Z.Y.Gao; T.X.Yu; D.Karagiozova


    Finite element simulations are carried out toexamine the mechanical behavior of the metallic hollowsphere (MHS) material during their large plastic defor-mation and to estimate the energy absorbing capac-ity of these materials under uniaxial compression.Asimplified model is proposed from experimental obser-vations to describe the connection between theneighboring spheres,which greatly improves the com-putation efficiency.The effects of the governing physi-cal and geometrical parameters are evaluated; whilst aspecial attention is paid to the plateau stress,which isdirectly related to the energy absorbing capacity.Finally,the empirical functions of the relative material densityare proposed for the elastic modulus,yield strength andplateau stress for FCC packing arrangement of hollowspheres,showing a good agreement with the experimen-tal results obtained in our previous study.

  16. Investigation of Burst Pressures in PWR Primary Pressure Boundary Components

    Ihn Namgung


    Full Text Available In a reactor coolant system of a nuclear power plant (NPP, an overpressure protection system keeps pressure in the loop within 110% of design pressure. However if the system does not work properly, pressure in the loop could elevate hugely in a short time. It would be seriously disastrous if a weak point in the pressure boundary component bursts and releases radioactive material within the containment; and it may lead to a leak outside the containment. In this study, a gross deformation that leads to a burst of pressure boundary components was investigated. Major components in the primary pressure boundary that is structurally important were selected based on structural mechanics, then, they were used to study the burst pressure of components by finite element method (FEM analysis and by number of closed forms of theoretical relations. The burst pressure was also used as a metric of design optimization. It revealed which component was the weakest and which component had the highest margin to bursting failure. This information is valuable in severe accident progression prediction. The burst pressures of APR-1400, AP1000 and VVER-1000 reactor coolant systems were evaluated and compared to give relative margins of safety.

  17. Finite Element Simulation of the Mechanical Properties of Mineralized Biomaterials

    Yuan, Fang

    Mineralized biomaterials are natural composite materials with both biomineral and biopolymer phases. They have attracted intense attention in the past decades, due to their outstanding mechanical properties and great potential as future materials. Such exceptional properties are believed to be attributed to their complex structures. Therefore, two different mineralized biomaterials (bone and sea urchin spine) were studied mainly by the finite element method and their structure-mechanical properties relationships were investigated. The research on bone was performed with a bottom-up approach. We focused on the nanoscale level structure-properties relationship first: the models of mineralized collagen fibril, consisting of hydroxyapatite platelets aligned within a collagen matrix, were created and the importance of the parameters defining its structure and constituent properties was evaluated. With the elastic model well established, the long-term mechanical behavior at nanoscale level was studied. The viscoelastic properties of undamaged collagen phase were deduced from low-irradiation-dosage creep measurements, then different damage scenarios were evaluated to explain the evolution of phase strains with larger irradiation dosage. The higher level structure-properties relationship of bone was simulated by two different approaches: 1) Assuming the macroscopic composite strain was comparable to nanoscale fibrillar strain, then based on nanoscale model, the macroscopic distributions of nanoscale phase strains were investigated; 2) Considering the structural complexity of bone at several length scales, the effective properties from lower scales were applied as the input properties at higher scales, and the elastic properties at each level were investigated. The computational results were validated by experimental data obtained by synchrotron X-ray diffraction and show the mechanical properties of bone are greatly influenced by its structure. The research on sea urchin

  18. Burst Encoding Mechanism for Low Delay and High Reliable Service in Optical Burst Switching Networks%光突发交换网络中面向低时延高可靠业务的突发编码机制

    黄胜; 李佳良; 李根; 李玲霞; 刘焕淋


    为了保证光突发交换( OBS)网络中业务高可靠性的同时,降低突发的端到端的时延,提出了一种基于不规则重复积累( IRA)码的突发编码机制。对IRA码校验矩阵结构进行了一定的调整,得到一种能对突发进行在线编解码的在线不规则重复累积( OL-IRA)码。利用OL-IRA码对信息突发进行编码,以便用产生的冗余突发来恢复丢失的信息突发。仿真结果表明,OL-IRA码在保证恢复丢包能力的同时,也能明显缩短丢包恢复的时延。%In order to guarantee high reliable service in optical burst switching ( OBS ) networks and re-duce the end-to-end delay of bursts, an online burst encoding mechanism based on irregular repeat accu-mulate( IRA) codes was proposed. The parity-check matrix of IRA codes was adjusted into a special structure, and then an on line IRA ( OL-IRA) code which can encode and decode burst online was con-structed. Information data bursts are encoded by OL-IRA codes to recover lost bursts with redundant bursts. Simulations show that OL-IRA codes will guarantee the performance of burst loss recovery, and can also shorten the delay of burst loss recovery.

  19. Applications of the discrete element method in mechanical engineering

    Fleissner, Florian, E-mail:; Gaugele, Timo, E-mail:; Eberhard, Peter [University of Stuttgart, Institute of Engineering and Computational Mechanics (Germany)], E-mail:


    Compared to other fields of engineering, in mechanical engineering, the Discrete Element Method (DEM) is not yet a well known method. Nevertheless, there is a variety of simulation problems where the method has obvious advantages due to its meshless nature. For problems where several free bodies can collide and break after having been largely deformed, the DEM is the method of choice. Neighborhood search and collision detection between bodies as well as the separation of large solids into smaller particles are naturally incorporated in the method. The main DEM algorithm consists of a relatively simple loop that basically contains the three substeps contact detection, force computation and integration. However, there exists a large variety of different algorithms to choose the substeps to compose the optimal method for a given problem. In this contribution, we describe the dynamics of particle systems together with appropriate numerical integration schemes and give an overview over different types of particle interactions that can be composed to adapt the method to fit to a given simulation problem. Surface triangulations are used to model complicated, non-convex bodies in contact with particle systems. The capabilities of the method are finally demonstrated by means of application examples.

  20. Research on experiment and calculation of foam bursting device


    This research presents experimental data on mechanical foam bursting device, based on the high speed of air fluid impinging insidethe foam bursting device, foam bubbles disrupted as a consequence of pressures changed very quickly as shear force and their impact forces. Experimental data on foam-bursting capacity have been presented. Designed device can provide effective foam bursting on collapse foam.

  1. An Analysis of Burst Disc Pressure Instability

    S. L. Robinson; B. C. Odegard, Jr.; N. r. Moody; S. H. Goods


    During the development stage of the 1X Acorn burst disc, burst pressure test results exhibited an unexpected increase of 8 to 14% over times of 90--100 days from initial fabrication. This increase is a concern where design constraints require stability. The disc material, 316L stainless steel sheet, is formed to a dome-like geometry and scored to produce a thin-walled, high-strength ligament. The fracture events controlling burst occur in that ligament. Thus it has been characterized both for tensile properties and microstructure through nanoindentation, magnetic measurements, optical and transmission electron microscopy. These results compare favorably with finite element simulation of the properties of the ligament. The ligament exhibits a highly heterogeneous microstructure; its small volume and microstructural heterogeneity make it difficult to identify which microstructural feature controls fracture and hence burst pressure. Bulk mechanical test specimens were fabricated to emulate mid-ligament properties, and aged at both room and elevated temperatures to characterize and accelerate the temporal behavior of the burst disc. Property changes included yield and ultimate tensile strength increases, and fracture strain decreases with aging. Specimens were subjected to a reversion anneal identical to that given the burst disc to eliminate the martensite phase formed during rolling. Reversion-annealed samples exhibited no change in properties in room temperature or accelerated aging, showing that the reversion-anneal eliminated the aging phenomenon. Aging was analyzed in terms of diffusion controlled precipitate growth kinetics, showing that carbon migration to dislocations is consistent with the strength increases. A vacancy-assisted diffusion mechanism for carbon transport is proposed, giving rise to rapid aging, which replaces interstitial carbon diffusion until excess vacancies from deformation are consumed. Mechanical activation parameters in stress relaxation

  2. Influence of alloying elements on mechanical properties of Al-Li plates

    杨守杰; 戴圣龙; 苏彬; 颜鸣皋


    The effect of alloying elements such as Cu, Mn and Zr on the mechanical properties of the Al-Li plates was studied, and the grain structure, crystallographic texture and precipitates were also investigated. It is found that the element Zr has a two-fold effect on the anisotropy of mechanical properties; the addition of element Mn can reduce the crystalline texture and the anisotropy of Al-Li plates. However, the effect of Cu element appears less pronounced.

  3. Application of gap element to nonlinear mechanics analysis of drillstring

    刘巨保; 丁皓江; 张学鸿


    This paper presents a nonlinear finite element method to resolve the problem of the nonlinear contact between the drillstring and hole wall by using a Multi-directional Contact Gap Element (MCGE) contacting at appropriate positi o ns in each beam element. The method was successfully applied to the Daqing Oil F ield GP1 well. It was shown that the drillstring's contact resistance at any wel l depth could be obtained by calculations and that as the error in the calculati on of the hole top load is below 10%, the calculation result can provide theoret ical basis for the design and operation of drillstrings.

  4. Spindle Bursts in Neonatal Rat Cerebral Cortex

    Jenq-Wei Yang


    Full Text Available Spontaneous and sensory evoked spindle bursts represent a functional hallmark of the developing cerebral cortex in vitro and in vivo. They have been observed in various neocortical areas of numerous species, including newborn rodents and preterm human infants. Spindle bursts are generated in complex neocortical-subcortical circuits involving in many cases the participation of motor brain regions. Together with early gamma oscillations, spindle bursts synchronize the activity of a local neuronal network organized in a cortical column. Disturbances in spindle burst activity during corticogenesis may contribute to disorders in cortical architecture and in the activity-dependent control of programmed cell death. In this review we discuss (i the functional properties of spindle bursts, (ii the mechanisms underlying their generation, (iii the synchronous patterns and cortical networks associated with spindle bursts, and (iv the physiological and pathophysiological role of spindle bursts during early cortical development.

  5. Spindle Bursts in Neonatal Rat Cerebral Cortex.

    Yang, Jenq-Wei; Reyes-Puerta, Vicente; Kilb, Werner; Luhmann, Heiko J


    Spontaneous and sensory evoked spindle bursts represent a functional hallmark of the developing cerebral cortex in vitro and in vivo. They have been observed in various neocortical areas of numerous species, including newborn rodents and preterm human infants. Spindle bursts are generated in complex neocortical-subcortical circuits involving in many cases the participation of motor brain regions. Together with early gamma oscillations, spindle bursts synchronize the activity of a local neuronal network organized in a cortical column. Disturbances in spindle burst activity during corticogenesis may contribute to disorders in cortical architecture and in the activity-dependent control of programmed cell death. In this review we discuss (i) the functional properties of spindle bursts, (ii) the mechanisms underlying their generation, (iii) the synchronous patterns and cortical networks associated with spindle bursts, and (iv) the physiological and pathophysiological role of spindle bursts during early cortical development.

  6. Mobile genetic elements in the genus Bacteroides, and their mechanism(s) of dissemination

    Nguyen, Mai


    Bacteroides spp organisms, the predominant commensal bacteria in the human gut have become increasingly resistant to many antibiotics. They are now also considered to be reservoirs of antibiotic resistance genes due to their capacity to harbor and disseminate these genes via mobile transmissible elements that occur in bewildering variety. Gene dissemination occurs within and from Bacteroides spp primarily by conjugation, the molecular mechanisms of which are still poorly understood in the genus, even though the need to prevent this dissemination is urgent. One current avenue of research is thus focused on interventions that use non-antibiotic methodologies to prevent conjugation-based DNA transfer. PMID:22479685

  7. Variation of microphysics in wind bubbles: an alternative mechanism for explaining the rebrightenings in Gamma-ray burst afterglows

    Kong, S. W.; Wong, A. Y. L.; Huang, Y. F.; Cheng, K. S.


    Conventionally, long Gamma-ray bursts (GRBs) are thought to be caused by the core collapses of massive stars. During the lifetime of a massive star, a stellar wind bubble environment should be produced. Furthermore, the microphysics shock parameters may vary along with the evolution of the fireball. Here, we investigate the variation of the microphysics shock parameters under the condition of wind bubble environment, and allow the microphysics shock parameters to be discontinuous at shocks in the ambient medium. It is found that our model can acceptably reproduce the rebrightenings observed in GRB afterglows, at least in some cases. The effects of various model parameters on rebrightenings are investigated. The rebrightenings observed in both the R-band and X-ray afterglow light curves of GRB 060206, GRB 070311 and GRB 071010A are reproduced in this model.

  8. Element transport in aquatic ecosystems – Modelling general and element-specific mechanisms

    Konovalenko, Lena


    Radionuclides are widely used in energy production and medical, military and industrial applications. Thus, understanding the behaviour of radionuclides which have been or may be released into ecosystems is important for human and environmental risk assessment. Modelling of radionuclides or their stable element analogues is the only tool that can predict the consequences of accidental release. In this thesis, two dynamic stochastic compartment models for radionuclide/element transfer in a mar...

  9. Innovative Application of Mechanical Activation for Rare Earth Elements Recovering: Process Optimization and Mechanism Exploration

    Tan, Quanyin; Deng, Chao; Li, Jinhui


    With the rapidly expanding use of fluorescent lamps (FLs) and increasing interest in conservation and sustainable utilization of critical metals such as rare earth elements (REEs), the recovering of REEs from phosphors in waste FLs is becoming a critical environmental and economic issue. To effectively recycle REEs with metallurgical methods, mechanical activation by ball milling was introduced to pretreat the waste phosphors. This current study put the emphasis on the mechanical activation and leaching processes for REEs, and explored the feasibility of the method from both theoretical and practical standpoints. Results showed physicochemical changes of structural destruction and particle size reduction after mechanical activation, leading to the easy dissolution of REEs in the activated samples. Under optimal conditions, dissolution yields of 89.4%, 93.1% and 94.6% for Tb, Eu and Y, respectively, were achieved from activated waste phosphors using hydrochloric acid as the dissolution agent. The shrinking core model proved to be the most applicable for the leaching procedure, with an apparent activation energy of 10.96 ± 2.79 kJ/mol. This novel process indicates that mechanical activation is an efficient method for recovering REEs from waste phosphors, and it has promising potential for REE recovery with low cost and high efficiency.

  10. Recent results of zebra patterns in solar radio bursts

    Gennady P.Chernov


    This review covers the most recent experimental results and theoretical research on zebra patterns(ZPs)in solar radio bursts.The basic attention is given to events with new peculiar elements of zebra patterns received over the last few years.All new properties are considered in light of both what was known earlier and new theoretical models.Large-scale ZPs consisting of small-scale fiber bursts could be explained by simultaneous inclusion of two mechanisms when whistler waves"highlight"the levels of double plasma resonance(DPR).A unique fine structure was observed in the event on 2006 December 13: spikes in absorption formed dark ZP stripes against the absorptive type Ⅲ-like bursts.The spikes in absorption can appear in accordance with well known mechanisms of absorptive bursts.The additional injection of fast particles filled the loss-cone(breaking the loss-cone distribution),and the generation of the continuum was quenched at these moments.The maximum absorptive effect occurs at the DPR levels.The parameters of millisecond spikes are determined by small dimensions of the particle beams and local scale heights in the radio source.Thus,the DPR model helps to understand several aspects of unusual elements of ZPs.However,the simultaneous existence of several tens of the DPR levels in the corona is impossible for any realistic profile of the plasma density and magnetic field.Three new theories of ZPs are examined.The formation of eigenmodes of transparency and opacity during the propagation of radio waves through regular coronal inhomogeneities is the most natural and promising mechanism.Two other models(nonlinear periodic space-charge waves and scattering of fast protons on ion-sound harmonics)could happen in large radio bursts.

  11. Physics of gamma-ray bursts

    Lamb, D. Q.


    Attention is given to the accumulating evidence for the view that gamma-ray bursts come from strongly magnetic neutron stars, discussing the physical properties of the emission region and the radiation processes expected in strong magnetic fields, and emphasizing that the observed burst spectra require that the emission region be optically thin. This entails that the energy of the emitting plasma and/or the plasma itself be continuously replenished during a burst, and that the cooling time scale of the emitting plasma be much shorter than the observed duration of the bursts. This characteristic of the cooling time scale implies that the burst intensity and spectrum can vary on extremely short time scales, and that the burst duration must have a separate explanation. It is emphasized that synchrotron emission is favored as the gamma-ray production mechanism; it is the only mechanism capable of satisfying the optical thinness constraint while producing the observed luminosity.

  12. Investigation of the surface generation mechanism of mechanical polishing engineering ceramics using discrete element method

    Han, Xuesong


    Machining technology about ceramics has been developed very fast over recent years due to the growing industrial demand of higher machining accuracy and better surface quality of ceramic elements, while the nature of hard and brittle ceramics makes it difficult to acquire damage-free and ultra-smooth surface. Ceramic bulk can be treated as an assemblage of discrete particles bonded together randomly as the micro-structure of ceramics consists of crystal particles and pores, and the inter-granular fracture of the ceramics can be naturally represented by the separation of particles due to breakage of bonds. Discrete element method (DEM) provides a promising approach for constructing an effective model to describe the tool-workpiece interaction and can serve as a predicting simulation tool in analyzing the complicated surface generation mechanism and is employed in this research to simulate the mechanical polishing process of ceramics and surface integrity. In this work, a densely packed particle assembly system of the polycrystalline Si3N4 has been generated using bonded-particle model to represent the ceramic workpiece numerically. The simulation results justify that the common critical depth of cut cannot be used as the effective parameters for evaluating brittle to ductile transformation in ceramic polishing process. Therefore, a generalized criterion of defining the range of ductile regime machining has been developed based on the numerical results. Furthermore, different distribution of pressure chain is observed with different depth of cut which ought to have intense relationship with special structure of ceramics. This study also justified the advantage of DEM model in its capability of revealing the mechanical behaviors of ceramics at micro-scale.

  13. Finite element based micro-mechanics modeling of textile composites

    Glaessgen, E. H.; Griffin, O. H., Jr.


    Textile composites have the advantage over laminated composites of a significantly greater damage tolerance and resistance to delamination. Currently, a disadvantage of textile composites is the inability to examine the details of the internal response of these materials under load. Traditional approaches to the study fo textile based composite materials neglect many of the geometric details that affect the performance of the material. The present three dimensional analysis, based on the representative volume element (RVE) of a plain weave, allows prediction of the internal details of displacement, strain, stress, and failure quantities. Through this analysis, the effect of geometric and material parameters on the aforementioned quantities are studied.

  14. SEACAS Theory Manuals: Part III. Finite Element Analysis in Nonlinear Solid Mechanics

    Laursen, T.A.; Attaway, S.W.; Zadoks, R.I.


    This report outlines the application of finite element methodology to large deformation solid mechanics problems, detailing also some of the key technological issues that effective finite element formulations must address. The presentation is organized into three major portions: first, a discussion of finite element discretization from the global point of view, emphasizing the relationship between a virtual work principle and the associated fully discrete system, second, a discussion of finite element technology, emphasizing the important theoretical and practical features associated with an individual finite element; and third, detailed description of specific elements that enjoy widespread use, providing some examples of the theoretical ideas already described. Descriptions of problem formulation in nonlinear solid mechanics, nonlinear continuum mechanics, and constitutive modeling are given in three companion reports.

  15. Two classes of gamma-ray bursts

    Katz, J I


    Data from the 3B Catalogue suggest that short and long GRB are the results of different classes of events, rather than different parameter values within a single class: Short bursts have harder spectra in the BATSE bands, but chiefly long bursts are detected at photon energies over 1 MeV, implying that their hard photons are radiated by a process not found in short bursts. The values of \\langle V/V_{max} \\rangle for short and long bursts differ by 4.3 \\sigma, implying different spatial distributions. Only the soft gamma-ray radiation mechanisms are the same in both classes.

  16. Continuum Mechanics Based Bi-linear Shear Deformable Shell Element Using Absolute Nodal Coordinate Formulation


    the convergent solution in the case of the continuum mechanics based bi- linear shear deformable ANCF shell element. 5.3 Slit Annular Plate Subjected...UNCLASSIFIED: Distribution Statement A. Approved for public release. #24515 CONTINUUM MECHANICS BASED BI- LINEAR SHEAR DEFORMABLE SHELL ELEMENT...MAR 2014 2. REPORT TYPE Technical Report 3. DATES COVERED 07-01-2014 to 04-03-2014 4. TITLE AND SUBTITLE CONTINUUM MECHANICS BASED BI- LINEAR

  17. Non-linear finite element analysis in structural mechanics

    Rust, Wilhelm


    This monograph describes the numerical analysis of non-linearities in structural mechanics, i.e. large rotations, large strain (geometric non-linearities), non-linear material behaviour, in particular elasto-plasticity as well as time-dependent behaviour, and contact. Based on that, the book treats stability problems and limit-load analyses, as well as non-linear equations of a large number of variables. Moreover, the author presents a wide range of problem sets and their solutions. The target audience primarily comprises advanced undergraduate and graduate students of mechanical and civil engineering, but the book may also be beneficial for practising engineers in industry.

  18. Avalanche Initiaition Mechanism - A Finite-element Approach

    S. Senthil


    Full Text Available The Himalayas, the longest chain of mountains in the world, experiences extensive snowfall and avalanche activity during winter. Some of these areas are densely populated, and death and destruction on large scale due to avalanche activity has been reported in these areas. One of the ways of reducing the loss of life and material due to avalanches is through prediction of avalanches. An understanding of weather forecasting, terrain, and avalanche initiation mechanism is a prerequisite for avalanche prediction. In the present paper mathematical modelling of avalanche initiation mechanism has been discussed.

  19. New numerical analysis method in computational mechanics: composite element method


    A new type of FEM, called CEM (composite element method), is proposed to solve the static and dynamic problems of engineering structures with high accuracy and efficiency. The core of this method is to define two sets of coordinate systems for DOF's description after discretizing the structure, i.e. the nodal coordinate system UFEM(ξ) for employing the conventional FEM, and the field coordinate system UCT(ξ) for utilizing classical theory. Then, coupling these two sets of functional expressions could obtain the composite displacement field U(ξ) of CEM. The computations of the stiffness and mass matrices can follow the conventional procedure of FEM. Since the CEM inherents some good properties of the conventional FEM and classical analytical method, it has the powerful versatility to various complex geometric shapes and excellent approximation. Many examples are presented to demonstrate the ability of CEM.

  20. New numerical analysis method in computational mechanics: composite element method



    A new type of FEM, called CEM (composite element method), is proposed to solve the static and dynamic problems of engineering structures with high accuracy and efficiency. The core of this method is to define two sets of coordinate systems for DOF’ s description after discretizing the structure, i.e. the nodal coordinate system UFEM(ζ) for employing the conventional FEM, and the field coordinate system UCT(ζ) for utilizing classical theory. Then, coupling these two sets of functional expressions could obtain the composite displacement field U(ζ) of CEM. The computations of the stiffness and mass matrices can follow the conventional procedure of FEM. Since the CEM inherents some good properties of the conventional FEM and classical analytical method, it has the powerful versatility to various complex geometric shapes and excellent approximation. Many examples are presented to demonstrate the ability of CEM.


    韩铁; 梁振刚; 马玉石


    As the spin tube gun has high firing rate, continuous shooting will not only use up the storage of ammunition quickly, but also reduce the tube’s life. In order to solve the problem, we analyzed the existing spin tube gun for the working principle of rotary ammunition supply system and designed a mechanism to control the burst firing based on the 23mm spin tube gun. The device made the electromagnetic as the core of the system,and used the photoelectric counter with the AT89C51 to control the number of burst firing of the gun. We used Pro/E software to model the device for 3D and dynamic simulation. Simulation results show that the structure is feasible on principle.%转管武器射速极高,连续射击不仅会过快消耗有限的备弹量,同时会严重降低身管寿命。针对这一问题,本文以内能源23mm 转管航炮为依据,分析了现有转管航炮供进弹部分的工作原理,设计了一种控制射击发数的射控装置。射控装置以电磁离合器为核心,运用光电计数器与单片机AT89C51来完成计数和整体控制的任务。利用Pro/E软件对所设计的离合机构进行三维实体建模、整体装配和机构运动仿真。通过对机构动作的仿真模拟,证明结构运动可行。

  2. Structural elements in particle physics and statistical mechanics

    Honerkamp, J.; Pohlmeyer, K.; Romer, H.


    The NATO Advanced Summer Institute on Theoretical Physics 1981 had as its main objective a thorough comparison of structures and methods of two different branches of Theoretical Physics, namely Elementary Particle Physics and Statistical Mechanics, and the idea was to exhibit the structural similarities, to trace them until their origins, to compare solution and approximation schemes and to report on those new results and methods in either of the two branches which are indicative of an intimate connection between them. Thus stimulation of a deeper understanding and development of new Methods could be hoped for in both fields. One group of contributions gives concise up-to-date information on basic topics in Statistical Mechanics and Phase Transitions, Dynamical Systems, Solvable Lattice Models and Lattice Gauge Theories. A second group is devoted to special topics which illustrate the interrelationship between Statistical Mechanics and Elementary Particle Physics, like topological quantum numbers on a lattice, model studies on the confinement problem, etc. Supplementary information on experimental implications and on neighbouring fields is provided in a third group.

  3. Mechanics of a crushable pebble assembly using discrete element method

    Annabattula, R.K., E-mail: [Institute for Applied Materials (IAM-WBM), Karlsruhe Institute of Technology (KIT), D-76344 Eggenstein-Leopoldshafen (Germany); Gan, Y., E-mail: [School of Civil Engineering, University of Sydney, 2006 NSW, Sydney (Australia); Zhao, S. [College of Mechanical and Electronics Engineering, Hebei University of Science and Technology, Shijiazhuang, Hebei 050018 (China); Kamlah, M., E-mail: [Institute for Applied Materials (IAM-WBM), Karlsruhe Institute of Technology (KIT), D-76344 Eggenstein-Leopoldshafen (Germany)


    The influence of crushing of individual pebbles on the overall strength of a pebble assembly is investigated using discrete element method. An assembly comprising of 5000 spherical pebbles is assigned with random critical failure energies with a Weibull distribution in accordance with the experimental observation. Then, the pebble assembly is subjected to uni-axial compression ({epsilon}{sub 33}=1.5%) with periodic boundary conditions. The crushable pebble assembly shows a significant difference in stress-strain response in comparison to a non-crushable pebble assembly. The analysis shows that a ideal plasticity like behaviour (constant stress with increase in strain) is the characteristic of a crushable pebble assembly with sudden damage. The damage accumulation law plays a critical role in determining the critical stress while the critical number of completely failed pebbles at the onset of critical stress is independent of such a damage law. Furthermore, a loosely packed pebble assembly shows a higher crush resistance while the critical stress is insensitive to the packing factor ({eta}) of the assembly.

  4. Burst Ductility of Zirconium Clads: The Defining Role of Residual Stress

    Kumar, Gulshan; Kanjarla, A. K.; Lodh, Arijit; Singh, Jaiveer; Singh, Ramesh; Srivastava, D.; Dey, G. K.; Saibaba, N.; Doherty, R. D.; Samajdar, Indradev


    Closed end burst tests, using room temperature water as pressurizing medium, were performed on a number of industrially produced zirconium (Zr) clads. A total of 31 samples were selected based on observed differences in burst ductility. The latter was represented as total circumferential elongation or TCE. The selected samples, with a range of TCE values (5 to 35 pct), did not show any correlation with mechanical properties along axial direction, microstructural parameters, crystallographic textures, and outer tube-surface normal ( σ 11) and shear ( τ 13) components of the residual stress matrix. TCEs, however, had a clear correlation with hydrostatic residual stress ( P h), as estimated from tri-axial stress analysis on the outer tube surface. Estimated P h also scaled with measured normal stress ( σ 33) at the tube cross section. An elastic-plastic finite element model with ductile damage failure criterion was developed to understand the burst mechanism of zirconium clads. Experimentally measured P h gradients were imposed on a solid element continuum finite element (FE) simulation to mimic the residual stresses present prior to pressurization. Trends in experimental TCEs were also brought out with computationally efficient shell element-based FE simulations imposing the outer tube-surface P h values. Suitable components of the residual stress matrix thus determined the burst performance of the Zr clads.


    王承强; 郑长良


    Based on the Hamiltonian governing equations of plane elasticity for sectorial domain, the variable separation and eigenfunction expansion techniques were employed to develop a novel analytical finite element for the fictitious crack model in fracture mechanics of concrete. The new analytical element can be implemented into FEM program systems to solve fictitious crack propagation problems for concrete cracked plates with arbitrary shapes and loads. Numerical results indicate that the method is more efficient and accurate than ordinary finite element method.

  6. Phantom bursting is highly sensitive to noise and unlikely to account for slow bursting in beta-cells

    Pedersen, Morten Gram


    Pancreatic beta-cells show bursting electrical activity with a wide range of burst periods ranging from a few seconds, often seen in isolated cells, over tens of seconds (medium bursting), usually observed in intact islets, to several minutes. The phantom burster model [Bertram, R., Previte, J...... and lowers the burst period dramatically in phantom bursters. It is therefore unlikely that slow bursting in single cells is driven by the slow phantom bursting mechanism, but could instead be driven by oscillations in glycolysis, which we show are stable to random ion channel fluctuations. Moreover, so...

  7. 49 CFR 236.560 - Contact element, mechanical trip type; location with respect to rail.


    ... SYSTEMS, DEVICES, AND APPLIANCES Automatic Train Stop, Train Control and Cab Signal Systems Rules and Instructions; Locomotives § 236.560 Contact element, mechanical trip type; location with respect to...

  8. State of the Art Report for Development of Control Element Drive Mechanism of the APR+ Reactor

    Lee, Jae Seon; Choi, Suhn; Song, Chul Hwa


    Recently newly-developed nuclear reactors with increased safety and enhanced performance by developed countries in the nuclear area are competing in the global nuclear market. Several reactors, for example AP600 and AP1000 by Westinghouse Electric Co. in USA, EPR by Areva in Europe, APWR by Mitsubishi Heavy Industry in Japan in the pressurized power reactor, are competing to preoccupy the nuclear market during Nuclear Renaissance. Dedicated control element drive mechanism with enhanced performance and increased safety are developed for these new reactors. And load follow capability is required, and it is estimated that load follow requirement make design requirement of a control element drive mechanism harsh. It is necessary to review the current technical state of a control element drive mechanism. This work is aimed to review the design characteristics of a past and current control element drive mechanism for a nuclear reactor and to check the direction and goal of CEDM design development recently.

  9. A Note on the Statistical Mechanics of Violent Relaxation of Phase Space Elements of Different Densities

    Kull, A.; R. A. Treumann; Böhringer, Hans


    The statistical mechanical investigation of Violent Relaxation of phase space elements of different densities first derived by Lynden-Bell (1967) is re-examined. It is found that the mass independence of the equations of motion of Violent Relaxation calls for a constraint on the volume of the phase space elements used to formulate the statistical mechanical description of Violent Relaxation. In agreement with observations of astrophysical objects believed to have been subject to Violent Relax...

  10. 政策议程设置中网民触发模式的基本要素分析%Basic Elements of Netizens’Burst Model in Policy Agenda-Setting



    Agenda-setting is the primary step of public policy.The rising of cyber society cre-ates a new model in public policy agenda-setting which is called netizens’burst model.Its basic elements include the igniting of focus event,the activation of common experience,the mobiliza-tion of opinion leaders,the following-up of traditional media and the ratification of decision-mak-ing authorities.The constitutive combination of these elements demonstrates that netizens’burst model possesses inherent attributions which are substantially different with traditional elites-dominant agenda-setting models,and represents a new trend of China’s public policy.%议程设置是公共政策的首要环节,网络社会的异军突起造就了政策议程设置的一种全新模式,即网民触发模式。网民触发模式的基本要素包括焦点事件的引爆、共同体验的激活、意见领袖的动员、传统媒体的跟进和决策当局的认同。这些基本要素的结构性组合表明网民触发模式具有自身的内在规定性,与传统的精英主义议程设置模式表现出本质上的不同,代表了中国公共政策发展的一种新趋势。

  11. Thalamic Bursts Down-regulate Cortical Theta and Nociceptive Behavior.

    LeBlanc, Brian W; Cross, Brent; Smith, Kelsey A; Roach, Catherine; Xia, Jimmy; Chao, Yu-Chieh; Levitt, Joshua; Koyama, Suguru; Moore, Christopher I; Saab, Carl Y


    We tested the relation between pain behavior, theta (4-8 Hz) oscillations in somatosensory cortex and burst firing in thalamic neurons in vivo. Optically-induced thalamic bursts attenuated cortical theta and mechanical allodynia. It is proposed that thalamic bursts are an adaptive response to pain that de-synchronizes cortical theta and decreases sensory salience.

  12. Finite Element Analysis of Mechanical Characteristics of Dropped Eggs Based on Fluid-Solid Coupling Theory

    Song Haiyan; Wang Fang; Zhang Jianguo; Zhang Yinong; Yang Shugang


    It is important to study the properties and mechanics of egg drop impacts in order to reduce egg loss during processing and logistics and to provide a basis for the protective packaging of egg products. In this paper, we present the results of our study of the effects of the structural parameters on the mechanical properties of an egg using a finite element model of the egg. Based on Fluid-Solid coupling theory, a finite element model of an egg was constructed using ADINA, a finite element ca...

  13. Finite element procedures for coupled linear analysis of heat transfer, fluid and solid mechanics

    Sutjahjo, Edhi; Chamis, Christos C.


    Coupled finite element formulations for fluid mechanics, heat transfer, and solid mechanics are derived from the conservation laws for energy, mass, and momentum. To model the physics of interactions among the participating disciplines, the linearized equations are coupled by combining domain and boundary coupling procedures. Iterative numerical solution strategy is presented to solve the equations, with the partitioning of temporal discretization implemented.

  14. Mechanism of Oxidative Burst in Tobacco Leaves and Cells Induced by Palmin from Phytophthora palmi%Palmin诱导烟草氧化猝发的机制

    王义华; 张宏明; 于中连; 陈珈; 王学臣


    In order to reveal the signaling pathways triggered by elicitor in plant-microbe interactions, the mechanisms of hypersensitive necrosis responses in Nicotiana tabacum L. cv. Gexin Ⅲ induced by palmin were studied at molecular and cellular level. The burst of superoxide, intercellular diffusion of hydrogen peroxide and process of cell death induced by palmin were investigated in tobacco plants by biochemical methods and Confocal microscopy. The results showed that a large amount of O*-2 was rapidly generated in tobacco cell elicited by palmin as a result of activation of NADPH oxidase, and the O*-2 was dismutated into H2O2 immediately by superoxide dismutase (SOD). Accumulation and intercellular diffusion of H2O2 were shown to be a trigger for hypersensitive cell death; and Ca2+ and some specific protein kinase were also shown to be involved in the activation of oxidative burst in tobacco cell induced by palmin.%为探讨植物对病原微生物的防御机制和激发子启动植物体内的信号转导应答过程,本文研究了Phytophthora palmi激发子palmin诱导其非寄主亲和性烟草的叶片和悬浮细胞系产生氧化猝发的分子机理.利用生化分析和激光共聚焦显微扫描技术动态观察palmin诱导烟草过敏反应中O*-2和H2O2的形成、胞间转移及引起细胞死亡的特性.结果表明:palmin诱导激活了烟草细胞内NADPH氧化酶,产生大量的O*-2;O*-2在SOD催化下迅速转变成H2O2,并且H2O2在一定范围的细胞间转移和积累,最后诱发烟草细胞的过敏性坏死反应.palmin诱导氧化猝发过程还有Ca2+和蛋白激酶的参与.

  15. A comparative study of the effects of constructional elements on the mechanical behaviour of dragonfly wings

    Rajabi, H.; Rezasefat, M.; Darvizeh, A.; Dirks, J.-H.; Eshghi, Sh.; Shafiei, A.; Mostofi, T. Mirzababaie; Gorb, S. N.


    Although wings of insects show a large variation in morphology, they are all made from a network of irregular veins interconnected through membranous areas. Depending on their shape, size, and position, wing veins are usually divided into three different groups: longitudinal veins, cross-veins and ambient veins. The veins together with the membrane and some other elements such as spines, nodus and pterostigma can be considered as the wing's "constructional elements". In spite of rather extensive literature on dragonfly wing structure, the role of each of these elements in determining the wing's function remains mostly unknown. As this question is difficult to answer in vivo using biomechanical experiments on actual wings, this study was undertaken to reveal the effects of the constructional elements on the mechanical behaviour of dragonfly wings by applying numerical simulations. An image processing technique was used to develop 12 finite element models of the insect wings with different constructional elements. The mechanical behaviour of these models was then simulated under normal and shear stresses due to tension, bending and torsion. A free vibration analysis was also performed to determine the resonant frequencies and the mode shapes of the models. For the first time, a quantitative comparison was carried out between the mechanical effects selectively caused by different elements. Our results suggest that the complex interactions of veins, membranes and corrugations may considerably affect the dynamic deformation of the insect wings during flight.

  16. A new burst assembly technique for supporting QoS in optical burst switching networks

    Xiaolong Yang(阳小龙); Mingrui Dang(党明瑞); Youju Mao(毛幼菊); Lemin Li(李乐民)


    This letter proposes a new burst assembly technique for supporting QoS in optical burst switching (OBS)networks. It consists of the adaptive-threshold burst assembly mechanism and QoS-based random offset-time scheme. The assembly mechanism, which is fit well to multi-class burst assembly, not only matcheswith IP QoS mechanism based on packet classification, and also utilizes fairly and efficiently assemblycapacity. Based on token-bucket model and burst segment selective discard (BSSD), the offset-time schemecan smooth the traffic to support OBS QoS. The simulation results show that the technique can improvethe performance in terms of packet loss probability (PLP).

  17. An equivalent finite element method to kinetics analysis of complex mechanism

    CHE Ren-wei; LU Nian-li


    The Finite Element Method was combined with the results from considerable analysis, producing a new kinetics analysis method of EFEM for a mechanism in truss, geared system, and assembled system. The equivalent principle and the motive differential equation of the system were derived by using an equivalent element, a virtual inertia matrix, and a systematic force matrix. The element' s mass matrix expression in the two dimensional and three dimensional mechanisms of the equivalent element was determined. The equivalent mass matrixes fashion of the Jacobin matrix, generalized coordinate matrix, and equivalent forces matrix were also determined. It was validated by two examples that the new method was normal, simple and direct, and had a higher efficiency than alternative methods; this is regardless of whether traditional methods are used with differential equations and calculated by using a computer.

  18. A coupled thermo-poro-mechanical finite element analysis of fractured porous rocks using a cohesive interface element

    Wang, W.; Regueiro, R. A.


    The coupling between multiphase flow, heat transfer, and poromechanics in fractured geomaterials has aroused great interest in the areas of geomechanics, geoenvironmental engineering, and petroleum engineering. Relevant applications include nuclear waste repositories, geological sequestration of CO2, geothermal systems, and exploitation of shale gas reservoirs. The paper presents a fully coupled thermo-poro-mechanical (TPM) cohesive interface element (CIE) model, which can represent fluid and heat flow along and across the fracture, and shear/normal deformation of the fracture surfaces. The proposed model is then applied to analyze two popular geological engineering problems using the finite element method (FEM) with a small strain formulation. The first application is the fracturing process in organic-rich shale due to heating. In the finite element analysis, multiple horizontal microcracks parallel to the bedding plane are assumed to preexist in the porous source rock, and are represented by coupled TPM cohesive interface elements. The porous bulk rock is assumed to be homogeneous, isotropic (for the time being, with transverse isotropy a natural extension), and linearly elastic. The excess pore fluid pressure, which mainly causes the development of the fractures, is actually induced by the rapid decomposition of organic matter during heating according to the literature. However, the involved complex chemical reaction process is beyond the scope of the paper, and is therefore substituted by a fluid injection process within the cracks under room temperature (25C) and high temperature (400C) in the paper. We investigate the fracture propagation due to pore fluid pressure increase and the development of fracture-induced permeability. The second application is a nuclear waste repository in a partially saturated fractured rock. Multiphase transport of moisture and heat, thermally-induced stress, as well as the change of fracture apertures are investigated due to short

  19. Adaptive implicit-explicit finite element algorithms for fluid mechanics problems

    Tezduyar, T. E.; Liou, J.


    The adaptive implicit-explicit (AIE) approach is presented for the finite-element solution of various problems in computational fluid mechanics. In the AIE approach, the elements are dynamically (adaptively) arranged into differently treated groups. The differences in treatment could be based on considerations such as the cost efficiency, the type of spatial or temporal discretization employed, the choice of field equations, etc. Several numerical tests are performed to demonstrate that this approach can achieve substantial savings in CPU time and memory.

  20. Finite element analysis of sliding distance and contact mechanics of hip implant under dynamic walking conditions.

    Gao, Yongchang; Jin, Zhongmin; Wang, Ling; Wang, Manyi


    An explicit finite element method was developed to predict the dynamic behavior of the contact mechanics for a hip implant under normal walking conditions. Two key parameters of mesh sensitivity and time steps were examined to balance the accuracy and computational cost. Both the maximum contact pressure and accumulated sliding distance showed good agreement with those in the previous studies using the implicit finite element analysis and analytical methods. Therefore, the explicit finite element method could be used to predict the contact pressure and accumulated sliding distance for an artificial hip joint simultaneously in dynamic manner.

  1. Computational contact and impact mechanics fundamentals of modeling interfacial phenomena in nonlinear finite element analysis

    Laursen, Tod A


    This book comprehensively treats the formulation and finite element approximation of contact and impact problems in nonlinear mechanics. Intended for students, researchers and practitioners interested in numerical solid and structural analysis, as well as for engineers and scientists dealing with technologies in which tribological response must be characterized, the book includes an introductory but detailed overview of nonlinear finite element formulations before dealing with contact and impact specifically. Topics encompassed include the continuum mechanics, mathematical structure, variational framework, and finite element implementations associated with contact/impact interaction. Additionally, important and currently emerging research topics in computational contact mechanics are introduced, encompassing such topics as tribological complexity, conservative treatment of inelastic impact interaction, and novel spatial discretization strategies.

  2. Elements of nonlinear quantum mechanics (Part II): Triple bracket generalization of quantum mechanics

    Czachor, Marek


    A new version of NLQM is formulated in terms of the generalized Nambu dynamics. The generalization is free from the difficulties of earlier approaches. The paper is a second part of "Elements of NLQM (I): NL Schrodinger equation and two-level atoms".

  3. Propeller tone bursts

    Succi, G. P.; Munro, D. H.; Ingard, K. U.


    Intense high frequency (25-38 kHz) tone bursts have been observed in acoustic tests of a scale model of a general aviation propeller. The amplitude of the tone burst is approximately equal to the amplitude of the propeller noise signature. The conditions necessary for the production of these tone bursts are described. The experiments indicate that the origin of these bursts is a periodic flow oscillation on the suction surface of the propeller blade tips which may be due to the interaction between an oscillating shock wave and a laminar boundary layer.

  4. On the Systematic Error in the Quantum Mechanical Calculations to the Periodic Table of Elements

    Khazan, Albert


    The scientists working on the problems of the Periodic Table of Elements regularly attempt to create models of the elements on the basis of the laws of Quantum Mechanics. One even attempted to use the calculation of the dependency ``atomic mass - element's number'' on this basis, in order to extend the Table by introducing two new Periods containing 50 elements each. The hyperbolic law we have found in the Periodic Table allows to find, first, the atomic mass of the last (heaviest stable) element (411.66), then - the number of the protons in it (155). Two functions were compared: the IUPAC 2007 function (elements 80-118) and another one created according the other data (elements 80-224). Both functions have a large deviation of data in No.104-118. Commencing in Period 8, there are three ``shifts'' of atomic mass for 17, 20, and 25 AMU. Also, our analysis manifests that there in all the aforementioned data is a single point with atomic mass 412 and number 155, where the parameters meet each other. This fact verifies our theory (Khazan A. Upper Limit in Mendeleev's Periodic Table - Element No.155. 2nd ed., Svenska fysikarkivet, Stockholm, 2010).

  5. Bursting neurons and ultrasound avoidance in crickets.

    Marsat, Gary; Pollack, Gerald S


    Decision making in invertebrates often relies on simple neural circuits composed of only a few identified neurons. The relative simplicity of these circuits makes it possible to identify the key computation and neural properties underlying decisions. In this review, we summarize recent research on the neural basis of ultrasound avoidance in crickets, a response that allows escape from echolocating bats. The key neural property shaping behavioral output is high-frequency bursting of an identified interneuron, AN2, which carries information about ultrasound stimuli from receptor neurons to the brain. AN2's spike train consists of clusters of spikes - bursts - that may be interspersed with isolated, non-burst spikes. AN2 firing is necessary and sufficient to trigger avoidance steering but only high-rate firing, such as occurs in bursts, evokes this response. AN2 bursts are therefore at the core of the computation involved in deciding whether or not to steer away from ultrasound. Bursts in AN2 are triggered by synaptic input from nearly synchronous bursts in ultrasound receptors. Thus the population response at the very first stage of sensory processing - the auditory receptor - already differentiates the features of the stimulus that will trigger a behavioral response from those that will not. Adaptation, both intrinsic to AN2 and within ultrasound receptors, scales the burst-generating features according to the stimulus statistics, thus filtering out background noise and ensuring that bursts occur selectively in response to salient peaks in ultrasound intensity. Furthermore AN2's sensitivity to ultrasound varies adaptively with predation pressure, through both developmental and evolutionary mechanisms. We discuss how this key relationship between bursting and the triggering of avoidance behavior is also observed in other invertebrate systems such as the avoidance of looming visual stimuli in locusts or heat avoidance in beetles.

  6. Structural elements of mechanical engineering 2. Power train elements. 6. ed.; Konstruktionselemente des Maschinenbaus 2. Grundlagen von Maschinenelementen fuer Antriebsaufgaben

    Steinhilper, W. [Kaiserslautern Univ. (Germany). Lehrstuhl fuer Maschinenelemente und Getriebetechnik; Sauer, B. (eds.) [Technische Univ. Kaiserslautern (Germany). Lehrstuhl fuer Maschinenelemente und Getriebetechnik


    The Steinhilper/Roeper textbooks have become standard textbooks of German technical universities. This is the 6th edition, published under the new name 'Structural elements of mechanical engineering' by Steinhilper/Sauer, a renowned team of expert authors, has been completely revised and re-edited. In Vol. 2, the standard chapters on friction, wear, lubrication, bearings, sliding bearings, rolling bearings, and seals, have been completely updated. There are new chapters on: Power train systems, transmission systems and brakes, toothed gears and toothed gear drives, traction drives, friction transmission, sensors and actuators. The two-volume textbook covers the whole spectrum of typical elements of mechanical engineering. The information, much of which goes deeper than just basic knowledge, addresses students of universities and technical universities. This makes the book also a useful reference manual for the daily work of practical engineers. (orig.) [German] Die Baende der Maschinen- und Konstruktionselemente von Steinhilper/Roeper haben sich als Standard-Lehrbuecher an Technischen Hochschulen durchgesetzt. Unter dem Titel Steinhilper/Sauer: Konstruktionselemente des Maschinenbaus wurde das Werk von einem ausgewiesenen Autorenteam aktualisiert und grundlegend ueberarbeitet. Im vorliegenden Band 2 sind die bisherigen Kapitel Reibung, Verschleiss und Schmierung, Lagerungen, Gleitlager und Waelzlager sowie Dichtungen komplett ueberarbeitet. Neu hinzu gekommen sind: Einfuehrung in Antriebssysteme, Kupplungen und Bremsen, Zahnraeder und Zahnradgetriebe, Zugmittelgetriebe, Reibradgetriebe sowie Sensoren und Aktoren. Die 6. Auflage stellt eine aktualisierte und berichtigte Fassung dar. Die beiden Baende des Lehrwerks umfassen das gesamte Spektrum der typischen Konstruktions- und Maschinenelemente. Die Inhalte sind auf die Ausbildung an Universitaeten und Technischen Hochschulen abgestimmt und gehen teilweise ueber das Grundlagenwissen hinaus. So stellen die


    Zhang Kai; Cui Yunjun; Xiong Chunyang; Wang Congshun; Fang Jing


    In this paper, we present the applications of Boundary Element Method (BEM)to simulate the electro-mechanical coupling responses of Micro-Electro-Mechanical systems (MEMS).The algorithm is programmed in our research group based on BEM modeling for electrostatics and elastostatics. Good agreement is shown while the simulation results of the pull-in voltages are compared with the theoretical/experimental ones for some examples.

  8. Wireless acceleration sensor of moving elements for condition monitoring of mechanisms

    Sinitsin, Vladimir V.; Shestakov, Aleksandr L.


    Comprehensive analysis of the angular and linear accelerations of moving elements (shafts, gears) allows an increase in the quality of the condition monitoring of mechanisms. However, existing tools and methods measure either linear or angular acceleration with postprocessing. This paper suggests a new construction design of an angular acceleration sensor for moving elements. The sensor is mounted on a moving element and, among other things, the data transfer and electric power supply are carried out wirelessly. In addition, the authors introduce a method for processing the received information which makes it possible to divide the measured acceleration into the angular and linear components. The design has been validated by the results of laboratory tests of an experimental model of the sensor. The study has shown that this method provides a definite separation of the measured acceleration into linear and angular components, even in noise. This research contributes an advance in the range of methods and tools for condition monitoring of mechanisms.

  9. Research on a special scarifier mechanism with Finite Element Analysis method.

    Jiandong Jian,; Hoogmoed, W.B.; GuoXing Tao,; Jie Gao,; Xian Zhang,


    A scarifier mechanism with rotary tillage and anti-rotary grubbing is proposed for inducing the power of tillage in hardens soil. MAT147 material modal is amended by experimental method and soil high-speed cutting finite element modal is build through SPH method, further, the tools parameter of prop

  10. Linearization of dynamic equations of flexible mechanisms - a finite element approach

    Jonker, Ben


    A finite element based method is presented for evaluation of linearized dynamic equations of flexible mechanisms about a nominal trajectory. The coefficient matrices of the linearized equations of motion are evaluated as explicit analytical expressions involving mixed sets of generalized co-ordinate

  11. Thermo-mechanical finite element analyses of bolted cask lid structures

    Wieser, G.; Qiao Linan; Eberle, A.; Voelzke, H. [Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin (Germany)


    The analysis of complex bolted cask lid structures under mechanical or thermal accident conditions is important for the evaluation of cask integrity and leak-tightness in package design assessment according to the Transport Regulations or in aircraft crash scenarios. In this context BAM is developing methods based on Finite Elements to calculate the effects of mechanical impacts onto the bolted lid structures as well as effects caused by severe fire scenarios. I n case of fire it might be not enough to perform only a thermal heat transfer analysis. The complex cask design in connection with a severe hypothetical time-temperature-curve representing an accident fire scenario will create a strong transient heating up of the cask body and its lid system. This causes relative displacements between the seals and its counterparts that can be analyzed by a so-called thermo-mechanical calculation. Although it is currently not possible to correlate leakage rates with results from deformation analyses directly an appropriate Finite Element model of the considered type of metallic lid seal has been developed. For the present it is possible to estimate the behaviour of the seal based on the calculated relative displacements at its seating and the behaviour of the lid bolts under the impact load or the temperature field respectively. Except of the lid bolts the geometry of the cask and the mechanical loading is axial-symmetric which simplifies the analysis considerably and a two-dimensional Finite Element model with substitute lid bolts may be used. The substitute bolts are modelled as one-dimensional truss or beam elements. An advanced two-dimensional bolt submodel represents the bolts with plane stress continuum elements. This paper discusses the influence of different bolt modelling on the relative displacements at the seating of the seals. Besides this, the influence of bolt modelling, thermal properties and detail in geometry of the two-dimensional Finite Element models on

  12. Burst and Outburst Characteristics of Magnetar 4U 0142+61

    Gogus, Ersin; Roberts, Oliver J; Chakraborty, Manoneeta; Kaneko, Yuki; Gill, Ramandeep; Granot, Jonathan; van der Horst, Alexander J; Watts, Anna L; Baring, Matthew; Kouveliotou, Chryssa; Huppenkothen, Daniela; Younes, George


    We have compiled the most comprehensive burst sample from magnetar 4U 0142+61, comprising 27 bursts from its three burst-active episodes in 2011, 2012 and the latest one in 2015 observed with Swift/BAT and Fermi/GBM. Bursts from 4U 0142+61 morphologically resemble typical short bursts from other magnetars. However, 4U 0142+61 bursts are less energetic compared to the bulk of magnetar bursts. We uncovered an extended tail emission following a burst on 2015 February 28, with a thermal nature, cooling over a time-scale of several minutes. During this tail emission, we also uncovered pulse peak phase aligned X-ray bursts , which could originate from the same underlying mechanism as that of the extended burst tail, or an associated and spatially coincident but different mechanism.

  13. Mechanism of interaction relation between the rare-earth element Ce and impurity elements Pb and Bi in Ag-based filler metal


    The mechanism of interaction relation between the rare-earth element Ce and elements Pb and Bi in Ag-based filler metal has been studied. The results show that the compounds CePb and CeBi with high melting point can be easily produced between these three elements in the filler metal, which greatly limited the formation of the isolated phase Pb or Bi and also eliminated the bad effect of impurity elements Pb and Bi on the spreading property of Ag-based filler metal. The metallurgical and quantum-mechanical bond formation analysis show that a strong chemical affinity was existed between the rare-earth element Ce and impurity elements Pb and Bi, which was proved by the XRD analysis results.

  14. 深井底板突水组合灰色物元判别系统及应用%Discrimination system of combined grey matter-element for water-bursting in seam floor of deep mine

    孙明; 郑文翔; 张文泉; 马凯


    Prediction of water outburst in seam floor of mines is a complex theoretic and technical problem, which has characters of fuzziness, grey and incompatibility. By building the factor index system and getting nine main factors through the grey correlation, the contribution weights are ascertained by the entropy adjustment. According to the grey matter-element analysis theory, it builds the linear grey matter-element and optimal grey matter-element model respectively, the discrimination system of combined grey matter-element for water outburst in seam floor of deep mines is exploited by VB 6.0. The two module in parallel operation and mutual verification can much raise the result precision, it is basically capable of forecasting deep seam mining faces which are all threatened by the Ordo-vician limestone water. The answer of simulation analysis applying this system to the realistic water-bursting cases is in good accordance with the truth condition. The system will be of some values for controlling and preventing deep seam water-bursting from coal floor in complex state.%深井底板突水预测是一个复杂的理论与技术问题,具有模糊性、灰色性和不相容性的特点.建立了深井底板突水的主控指标体系,通过灰色关联分析得到主控因素,应用熵值调整法确定了各主控因素在突水过程中的贡献权重.根据灰色物元分析理论,分别建立了线性灰色物元判别模型和最优灰色物元判别模型,采用VB6.0开发了深井底板突水组合灰色物元判别系统.该系统两种模块的并列运行和相互验证提高了判别结果的准确程度,使系统初步具备了受承压水威胁的深井工作面的危险度预测功能.应用该系统进行深井突水案例的模拟结果与实际情况比较吻合,这表明该系统对深井复杂条件下的矿井底板突水预测具有较好的应用价值.

  15. Effects of Crimping on Mechanical Performance of Nitinol Stent Designed for Femoral Artery: Finite Element Analysis

    Nematzadeh, F.; Sadrnezhaad, S. K.


    Nitinol stents are used to minimize improper dynamic behavior, low twistability, and inadequate radial mechanical strength of femoral artery stents. In this study, finite element method is used to investigate the effect of crimping and Austenite finish temperature ( A f) of Nitinol on mechanical performance of Z-shaped open-cell femoral stent under crimping conditions. Results show that low A f Nitinol has better mechanical and clinical performance due to small chronic outward force, large radial resistive force, and appropriate superelastic behavior.

  16. An efficient finite element with layerwise mechanics for smart piezoelectric composite and sandwich shallow shells

    Yasin, M. Yaqoob; Kapuria, S.


    In this work, we present a new efficient four-node finite element for shallow multilayered piezoelectric shells, considering layerwise mechanics and electromechanical coupling. The laminate mechanics is based on the zigzag theory that has only seven kinematic degrees of freedom per node. The normal deformation of the piezoelectric layers under the electric field is accounted for without introducing any additional deflection variables. A consistent quadratic variation of the electric potential across the piezoelectric layers with the provision of satisfying the equipotential condition of electroded surfaces is adopted. The performance of the new element is demonstrated for the static response under mechanical and electric potential loads, and for free vibration response of smart shells under different boundary conditions. The predictions are found to be very close to the three dimensional piezoelasticity solutions for hybrid shells made of not only single-material composite substrates, but also sandwich substrates with a soft core for which the equivalent single layer (ESL) theories perform very badly.

  17. The OSU Hydro-Mechanical Fuel Test Facility: Standard Fuel Element Testing

    Wade R. Marcum; Brian G. Woods; Ann Marie Phillips; Richard G. Ambrosek; James D. Wiest; Daniel M. Wachs


    Oregon State University (OSU) and the Idaho National Laboratory (INL) are currently collaborating on a test program which entails hydro-mechanical testing of a generic plate type fuel element, or standard fuel element (SFE), for the purpose of qualitatively demonstrating mechanical integrity of uranium-molybdenum monolithic plates as compared to that of uranium aluminum dispersion, and aluminum fuel plates due to hydraulic forces. This test program supports ongoing work conducted for/by the fuel development program and will take place at OSU in the Hydro-Mechanical Fuel Test Facility (HMFTF). Discussion of a preliminary test matrix, SFE design, measurement and instrumentation techniques, and facility description are detailed in this paper.

  18. Finite element 3D modeling of mechanical behavior of mineralized collagen microfibrils

    Barkaoui, Abdelwahed


    The aim of this work is to develop a 3D finite elements model to study the nanomechanical behaviour of mineralized collagen microfibrils, which consists of three phases, (i) collagen phase formed by five tropocollagen (TC) molecules linked together with cross links, (ii) a mineral phase (Hydroxyapatite) and (iii) impure mineral phase, and to investigate the important role of individual properties of every constituent. The mechanical and the geometrical properties (TC molecule diameter) of both tropocollagen and mineral were taken into consideration as well as cross-links, which was represented by spring elements with adjusted properties based on experimental data. In the present paper an equivalent homogenised model was developed to assess the whole microfibril mechanical properties (Young's modulus and Poisson's ratio) under varying mechanical properties of each phase. In this study both equivalent Young's modulus and Poisson's ratio which were expressed as functions of Young's modulus of each phase were obt...

  19. Burst Pressure Failure of Titanium Tanks Damaged by Secondary Plumes from Hypervelocity Impacts on Aluminum Shields

    Nahra, Henry; Ghosn, Louis; Christiansen, Eric; Davis, B. Alan; Keddy, Chris; Rodriquez, Karen; Miller, Joshua; Bohl, William


    Metallic pressure tanks used in space missions are inherently vulnerable to hypervelocity impacts from micrometeoroids and orbital debris; thereby knowledge of impact damage and its effect on the tank integrity is crucial to a spacecraft risk assessment. This paper describes tests that have been performed to assess the effects of hypervelocity impact (HVI) damage on Titanium alloy (Ti-6Al-4V) pressure vessels burst pressure and characteristics. The tests consisted of a pair of HVI impact tests on water-filled Ti-6Al-4V tanks (water being used as a surrogate to the actual propellant) and subsequent burst tests as well as a burst test on an undamaged control tank. The tanks were placed behind Aluminum (Al) shields and then each was impacted with a 7 km/s projectile. The resulting impact debris plumes partially penetrated the Ti-6Al-4V tank surfaces resulting in a distribution of craters. During the burst tests, the tank that failed at a lower burst pressure did appear to have the failure initiating at a crater site with observed spall cracks. A fracture mechanics analysis showed that the tanks failure at the impact location may have been due to a spall crack that formed upon impact of a fragmentation on the Titanium surface. This result was corroborated with a finite element analysis from calculated Von-Mises and hoop stresses.

  20. Numerical simulation of burst defects in cold extrusion process

    Labergère, C.; Lestriez, P.; Saanouni, K.


    The formation of the central bursts in axisymmetric cold extrusion is numerically simulated by using 2D finite element analysis (FEA) accounting for the mixed isotropic and kinematic hardening together with the ductile damage effect. The coupling between the ductile damage and the elastoplastic constitutive equations is formulated in the framework of the thermodynamics of irreversible processes together with the Continuum Damage Mechanics (CDM) theory. An isotropic ductile damage model is fully coupled with elastoplastic constitutive equations including non linear isotropic and kinematic hardening. A modified ductile damage criterion based on linear combination of the stress tensor invariants is used in order to predict the occurrence of micro-crack initiation as a discontinuous central bursts along the bar axis. The implicit integration scheme of the fully coupled constitutive equations and the Dynamic Explicit resolution scheme to solve the associated initial and boundary value problem are outlined. Application is made to the prediction of the chevron shaped cracks in cold extrusion of a round bar. The effect of various process parameters, as the diameter reduction ratio, the die semi-angle, the friction coefficient and the material ductility, on the central bursts occurrence are discussed.

  1. Bursting neurons and ultrasound avoidance in crickets

    Gary eMarsat


    Full Text Available Decision making in invertebrates often relies on simple neural circuits composed of only a few identified neurons. The relative simplicity of these circuits makes it possible to identify the key computation and neural properties underlying decisions. In this review, we summarize recent research on the neural basis of ultrasound avoidance in crickets, a response that allows escape from echolocating bats. The key neural property shaping behavioral output is high-frequency bursting of an identified interneuron, AN2, which carries information about ultrasound stimuli from receptor neurons to the brain. AN2's spike train consists of clusters of spikes –bursts– that may be interspersed with isolated, non-burst spikes. AN2 firing is necessary and sufficient to trigger avoidance steering but only high-rate firing, such as occurs in bursts, evokes this response. AN2 bursts are therefore at the core of the computation involved in deciding whether or not to steer away from ultrasound. Bursts in AN2 are triggered by synaptic input from nearly synchronous bursts in ultrasound receptors. Thus the population response at the very first stage of sensory processing –the auditory receptor- already differentiates the features of the stimulus that will trigger a behavioral response from those that will not. Adaptation, both intrinsic to AN2 and within ultrasound receptors, scales the burst-generating features according to the stimulus statistics, thus filtering out background noise and ensuring that bursts occur selectively in response to salient peaks in ultrasound intensity. Furthermore AN2’s sensitivity to ultrasound varies adaptively with predation pressure, through both developmental and evolutionary mechanisms. We discuss how this key relationship between bursting and the triggering of avoidance behavior is also observed in other invertebrate systems such as the avoidance of looming visual stimuli in locusts or heat avoidance in beetles.

  2. Modification Mechanism of Rare Earth Elements in ZA27 Casting Alloys

    刘贵立; 李荣德


    The model of the liquid-phase ZA27 alloys was set up by molecular dynamics theory. The atomic structure of phase, RE-compounds, and the phase-liquid interface in ZA27 alloys were constructed by computer programming. Electronic structures of phase with rare earth elements dissolved and of phase-liquid interfaces with rare earth elements enrichment in ZA27 casting alloys were investigated by using the Recursion method. The ESE energy of RE elements and the structure energy of RE-compounds, phase, and the liquid-phase ZA27 alloys were calculated. The results show that rare earth elements are more stable to be in the phase interface than in phase, which explains the fact of very small solid so lubility of rare earth elements in phase, and the enrichment in the solid-liquid growth front. This makes dendrite melt and break down, dissociate and propagate. RE-compounds can act as heterogeneous nuclei for phase, leading to phase refinement. All above elucidates the modification mechanism of rare earth elements in zinc-aluminum casting alloys at electronic level.

  3. A locus problem solved by using a mechanism with three dyads and two leading elements

    Popescu, I.; Sass, L.; Romanescu, A. E.


    In Geometry there are many types of loci, solved by means of classic geometrical considerations and yielding lines and arcs of circles or conics. Yet more complicated locus can be solved by means of the Theory of Mechanisms. Our research starts from a locus and provides a solution based on the Theory of Mechanisms, finding the equivalent mechanism. The structural and cinematic analysis of the mechanism is made, determining the trajectory of a point representing the locus which presents interest. The mechanism has three dyads and two leading elements, for which the movements were correlated by means of a coefficient q. For various values of q different loci were obtained, similar for close values of q but different for significantly different values of q.

  4. Mechanical characterization of soft viscoelastic gels via indentation and optimization-based inverse finite element analysis.

    Liu, Kaifeng; VanLandingham, Mark R; Ovaert, Timothy C


    Polymer gels are widely accepted as candidate materials for tissue engineering, drug delivery, and orthopedic load-bearing applications. In addition, their mechanical and physical properties can be tailored to meet a wide range of design requirements. For soft gels whose elastic modulus is in the kPa range, mechanical characterization by bulk mechanical testing methods presents challenges, for example, in sample preparation, fixture design, gripping, and/or load measurement accuracy. Nanoindentation, however, has advantages when characterizing the mechanical properties of soft materials. This study was aimed at investigating the application of an inverse finite element analysis technique to identify material parameters of polymer gels via nanoindentation creep testing, optimization, and finite element simulation. Nanoindentation experiments were conducted using a rigid circular flat punch, and then simulated using the commercial software ABAQUS. The optimization (error minimization) procedure was integrated in the parameter determination process using a Matlab shell program, which makes this approach readily adaptable to other test geometries and material models. The finite element results compare well with a derived analytical viscoelastic solution for a rigid circular flat punch on a Kelvin-Voigt half-space.

  5. The Drift Burst Hypothesis

    Christensen, Kim; Oomen, Roel; Renò, Roberto

    The Drift Burst Hypothesis postulates the existence of short-lived locally explosive trends in the price paths of financial assets. The recent US equity and Treasury flash crashes can be viewed as two high profile manifestations of such dynamics, but we argue that drift bursts of varying magnitude......, currencies and commodities. We find that the majority of identified drift bursts are accompanied by strong price reversals and these can therefore be regarded as “flash crashes” that span brief periods of severe market disruption without any material longer term price impacts....

  6. Hydro-mechanical modeling of impermeable discontinuity in rock by extended finite element method

    郑安兴; 罗先启


    The extended finite element method(XFEM) is a numerical method for modeling discontinuities within the classical finite element framework. The computation mesh in XFEM is independent of the discontinuities, such that remeshing for moving discontinuities can be overcome. The extended finite element method is presented for hydro-mechanical modeling of impermeable discontinuities in rock. The governing equation of XFEM for hydraulic fracture modeling is derived by the virtual work principle of the fracture problem considering the water pressure on crack surface. The coupling relationship between water pressure gradient on crack surface and fracture opening width is obtained by semi-analytical and semi-numerical method. This method simplifies coupling analysis iteration and improves computational precision. Finally, the efficiency of the proposed method for modeling hydraulic fracture problems is verified by two examples and the advantages of the XFEM for hydraulic fracturing analysis are displayed.

  7. Mechanical behavior of linear amorphous polymers: comparison between molecular dynamics and finite-element simulations.

    Solar, Mathieu; Meyer, Hendrik; Gauthier, Christian; Fond, Christophe; Benzerara, Olivier; Schirrer, Robert; Baschnagel, Jörg


    This paper studies the rheology of weakly entangled polymer melts and films in the glassy domain and near the rubbery domain using two different methods: molecular dynamics (MD) and finite element (FE) simulations. In a first step, the uniaxial mechanical behavior of a bulk polymer sample is studied by means of particle-based MD simulations. The results are in good agreement with experimental data, and mechanical properties may be computed from the simulations. This uniaxial mechanical behavior is then implemented in FE simulations using an elasto-viscoelasto-viscoplastic constitutive law in a continuum mechanics (CM) approach. In a second step, the mechanical response of a polymer film during an indentation test is modeled with the MD method and with the FE simulations using the same constitutive law. Good agreement is found between the MD and CM results. This work provides evidence in favor of using MD simulations to investigate the local physics of contact mechanics, since the volume elements studied are representative and thus contain enough information about the microstructure of the polymer model, while surface phenomena (adhesion and surface tension) are naturally included in the MD approach.

  8. Structural analysis of composite wind turbine blades nonlinear mechanics and finite element models with material damping

    Chortis, Dimitris I


    This book concerns the development of novel finite elements for the structural analysis of composite beams and blades. The introduction of material damping is also an important aspect of composite structures and it is presented here in terms of their static and dynamic behavior. The book thoroughly presents a new shear beam finite element, which entails new blade section mechanics, capable of predicting structural blade coupling due to composite coupling and/or internal section geometry. Theoretical background is further expanded towards the inclusion of nonlinear structural blade models and damping mechanics for composite structures. The models effectively include geometrically nonlinear terms due to large displacements and rotations, improve the modeling accuracy of very large flexible blades, and enable the modeling of rotational stiffening and buckling, as well as, nonlinear structural coupling. Validation simulations on specimen level study the geometric nonlinearities effect on the modal frequencies and...

  9. International Symposium on Boundary Element Methods : Advances in Solid and Fluid Mechanics

    Tseng, Kadin


    The Boundary Element Method (BEM) has become established as an effective tool for the solutions of problems in engineering science. The salient features of the BEM have been well documented in the open literature and therefore will not be elaborated here. The BEM research has progressed rapidly, especially in the past decade and continues to evolve worldwide. This Symposium was organized to provide an international forum for presentation of current research in BEM for linear and nonlinear problems in solid and fluid mechanics and related areas. To this end, papers on the following topics were included: rotary­ wing aerodynamics, unsteady aerodynamics, design and optimization, elasticity, elasto­ dynamics and elastoplasticity, fracture mechanics, acoustics, diffusion and wave motion, thermal analysis, mathematical aspects and boundary/finite element coupled methods. A special session was devoted to parallel/vector supercomputing with emphasis on mas­ sive parallelism. This Symposium was sponsored by United ...

  10. Modeling the mechanics of axonal fiber tracts using the embedded finite element method.

    Garimella, Harsha T; Kraft, Reuben H


    A subject-specific human head finite element model with embedded axonal fiber tractography obtained from diffusion tensor imaging was developed. The axonal fiber tractography finite element model was coupled with the volumetric elements in the head model using the embedded element method. This technique enables the calculation of axonal strains and real-time tracking of the mechanical response of the axonal fiber tracts. The coupled model was then verified using pressure and relative displacement-based (between skull and brain) experimental studies and was employed to analyze a head impact, demonstrating the applicability of this method in studying axonal injury. Following this, a comparison study of different injury criteria was performed. This model was used to determine the influence of impact direction on the extent of the axonal injury. The results suggested that the lateral impact loading is more dangerous compared to loading in the sagittal plane, a finding in agreement with previous studies. Through this analysis, we demonstrated the viability of the embedded element method as an alternative numerical approach for studying axonal injury in patient-specific human head models.

  11. Mechanical tests, static and modal finite element analysis for MWCNT composite materials

    Daniela BARAN


    Full Text Available The main purpose of this paper is to develop some numerical experiences based on mechanical tests performed on MWCNT (Multi-wall carbon nanotubes composites created in our Material compartment using finite element commercial codes (here NASTRAN. The results of numerical simulations are consistent with the laboratory tests and encourage us to continue to improve the models using NASTRAN capabilities in order to obtain a realistic simulation of aeronautical structures made of such composites, considering their special properties.

  12. A Kinematic Analysis of the Variable Valve Timing Mechanism with Three Elements and Continuous Valve Lift

    Stelian Mihalcea


    Full Text Available An innovating solution for throttle-free load control for spark-ignition engines is Variable Valve Timing system (VVT System, or VVA - Variable Valve Actuation System. In this paper is presented an analytic method for kinematic analysis of the valve timing mechanism with three elements, which mainly includes the camshaft, the roller rocker finger and an intermediate rocker arm. This type of mechanism ensures a continuous valve lift (VVL System between two extreme valve heights. It is also presented the numerical example for the variable valve lift mechanism’s motion.

  13. Fast Radio Bursts

    Akshaya Rane; Duncan Lorimer


    We summarize our current state of knowledge of fast radio bursts (FRBs) which were first discovered a decade ago. Following an introduction to radio transients in general, including pulsars and rotating radio transients, we discuss the discovery of FRBs. We then discuss FRB follow-up observations in the context of repeat bursts before moving on to review propagation effects on FRB signals, FRB progenitor models and an outlook on FRBs as potential cosmological tools.

  14. Numerical model for thermal and mechanical behaviour of a CANDU 37-element bundle

    Jiang, L.; MacKay, K. [Martec Limited, Halifax, Nova Scotia (Canada); Gibb, R. [Canadian Nuclear Safety Commission (CNSC), Ottawa, Ontario (Canada)


    Prediction of transient fuel bundle deformations is important for assessing the integrity of fuel and the surrounding structural components under different operating conditions including accidents. For numerical simulation of the interactions between fuel bundle and pressure tube, a reliable numerical bundle model is required to predict thermal and mechanical behaviour of the fuel bundle assembly under different thermal loading conditions. To ensure realistic representations of the bundle behaviour, this model must include all of the important thermal and mechanical features of the fuel bundle, such as temperature-dependent material properties, thermal viscoplastic deformation in sheath, fuel-to-sheath interactions, endplate constraints and contacts between fuel elements. In this paper, we present a finite element based numerical model for predicting macroscopic transient thermal-mechanical behaviour of a complete 37-element CANDU nuclear fuel bundle under accident conditions and demonstrate its potential for being used to investigate fuel bundle to pressure tube interaction in future nuclear safety analyses. This bundle model has been validated against available experimental and numerical solutions and applied to various simulations involving steady-state and transient loading conditions. (author)

  15. Phase analysis method for burst onset prediction

    Stellino, Flavio; Mazzoni, Alberto; Storace, Marco


    The response of bursting neurons to fluctuating inputs is usually hard to predict, due to their strong nonlinearity. For the same reason, decoding the injected stimulus from the activity of a bursting neuron is generally difficult. In this paper we propose a method describing (for neuron models) a mechanism of phase coding relating the burst onsets with the phase profile of the input current. This relation suggests that burst onset may provide a way for postsynaptic neurons to track the input phase. Moreover, we define a method of phase decoding to solve the inverse problem and estimate the likelihood of burst onset given the input state. Both methods are presented here in a unified framework, describing a complete coding-decoding procedure. This procedure is tested by using different neuron models, stimulated with different inputs (stochastic, sinusoidal, up, and down states). The results obtained show the efficacy and broad range of application of the proposed methods. Possible applications range from the study of sensory information processing, in which phase-of-firing codes are known to play a crucial role, to clinical applications such as deep brain stimulation, helping to design stimuli in order to trigger or prevent neural bursting.


    Weberg, Micah J. [PhD Candidate in Space Science, Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, 2134A Space Research Building, 2455 Hayward Street, Ann Arbor, MI 48109-2143, USA. (United States); Lepri, Susan T. [Associate Professor, Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, 2429 Space Research Building, 2455 Hayward Street, Ann Arbor, MI 48109-2143, USA. (United States); Zurbuchen, Thomas H., E-mail:, E-mail:, E-mail: [Professor, Space Science and Aerospace Engineering, Associate Dean for Entrepreneurship Senior Counselor of Entrepreneurship Education, Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, 2431 Space Research Building, 2455 Hayward Street, Ann Arbor, MI 48109-2143, USA. (United States)


    The elemental abundances of heavy ions (masses larger than He) in the solar wind provide information about physical processes occurring in the corona. Additionally, the charge state distributions of these heavy ions are sensitive to the temperature profiles of their respective source regions in the corona. Heavy ion dropouts are a relatively new class of solar wind events identified by both elemental and ionic charge state distributions. We have shown that their origins lie in large, closed coronal loops where processes such as gravitational settling dominate and can cause a mass-dependent fractionation pattern. In this study we consider and attempt to answer three fundamental questions concerning heavy ion dropouts: (1) 'where are the source loops located in the large-scale corona?'; (2) 'how does the interplay between coronal processes influence the end elemental abundances?'; and (3) 'what are the most probable release mechanisms'? We begin by analyzing the temporal and spatial variability of heavy ion dropouts and their correlation with heliospheric plasma and magnetic structures. Next we investigate the ordering of the elements inside dropouts with respect to mass, ionic charge state, and first ionization potential. Finally, we discuss these results in the context of the prevailing solar wind theories and the processes they posit that may be responsible for the release of coronal plasma into interplanetary space.

  17. Effects of Alloying Elements on the Microstructures and Mechanical Properties of Heavy Section Ductile Cast Iron

    G.S. Cho; K.H. Choe; K.W. Lee; A.Ikenaga


    The effects of alloying elements on the as-cast microstructures and mechanical properties of heavy section ductile cast iron were investigated to develop press die material having high strength and high ductility.Measurements of ultimate tensile strength, 0.2% proof strength, elongation and unnotched Charpy impact energy are presented as a function of alloy amounts within 0.25 to 0.75 wt pct range. Hardness is measured on the broken tensile specimens. The small additions of Mo, Cu, Ni and Cr changed the as-cast mechanical properties owing to the different as-cast matrix microstructures. The ferrite matrix of Mo and Ni alloyed cast iron exhibits Iow strength and hardness as well as high elongation and impact energy. The increase in Mo and Ni contents developed some fractions of pearlite structures near the austenite eutectic cell boundaries, which caused the elongation and impact energy to drop in a small range. Adding Cu and Cr elements rapidly changed the ferrite matrix into pearlite matrix, so strength and hardness were significantly increased. As more Mo and Cr were added. the size and fraction of primary carbides in the eutectic cell boundaries increased through the segregation of these elements into the intercellular boundaries.

  18. Finite Element Analysis of Mechanical Characteristics of Dropped Eggs Based on Fluid-Solid Coupling Theory

    Song Haiyan


    Full Text Available It is important to study the properties and mechanics of egg drop impacts in order to reduce egg loss during processing and logistics and to provide a basis for the protective packaging of egg products. In this paper, we present the results of our study of the effects of the structural parameters on the mechanical properties of an egg using a finite element model of the egg. Based on Fluid-Solid coupling theory, a finite element model of an egg was constructed using ADINA, a finite element calculation and analysis software package. To simplify the model, the internal fluid of the egg was considered to be a homogeneous substance. The egg drop impact was simulated by the coupling solution, and the feasibility of the model was verified by comparison with the experimental results of a drop test. In summary, the modeling scheme was shown to be feasible and the simulation results provide a theoretical basis for the optimum design of egg packaging and egg processing equipment.

  19. Study of transition mechanisms induced by an array of roughness elements

    Shrestha, Prakash; Candler, Graham V.; Computational Hypersonics Research Lab Team


    We study transition mechanisms of a Mach 5.92 laminar boundary layer due to an array of prismatic roughness elements using large-scale direct numerical simulations (DNS). We simulate a boundary layer tripped by arrays of different numbers of roughness elements, corresponding to experiments conducted at the Texas A & M University Actively Controlled Experimental (ACE) facility. We obtain solutions using a high-order, low-dissipation scheme for the convection terms in the Navier-Stokes equations. We perform separate 2D and 3D simulations. Flow parallel inflow acoustic disturbances are implemented in the 2D domain. We then interpolate spectral content obtained at 30 mm from the leading edge of the 2D domain to the inflow of the 3D domain. In the 3D domain, we compute optimal modes of pressure using dynamic mode decomposition (DMD). Using sparsity-promoting dynamic mode decomposition (SPDMD), we select the dominant modes to study the transition mechanisms. Recirculating vortices upstream and separated shear layers downstream of the roughness elements are observed to be the most dominant modes of transition. We compare streamwise mean mass flux and energy spectral densities at different streamwise locations to validate our simulations. Office of Naval Research.

  20. Mechanical Properties of Boehmite Evaluated by Atomic Force Microscopy Experiments and Molecular Dynamic Finite Element Simulations

    J. Fankhänel


    Full Text Available Boehmite nanoparticles show great potential in improving mechanical properties of fiber reinforced polymers. In order to predict the properties of nanocomposites, knowledge about the material parameters of the constituent phases, including the boehmite particles, is crucial. In this study, the mechanical behavior of boehmite is investigated using Atomic Force Microscopy (AFM experiments and Molecular Dynamic Finite Element Method (MDFEM simulations. Young’s modulus of the perfect crystalline boehmite nanoparticles is derived from numerical AFM simulations. Results of AFM experiments on boehmite nanoparticles deviate significantly. Possible causes are identified by experiments on complementary types of boehmite, that is, geological and hydrothermally synthesized samples, and further simulations of imperfect crystals and combined boehmite/epoxy models. Under certain circumstances, the mechanical behavior of boehmite was found to be dominated by inelastic effects that are discussed in detail in the present work. The studies are substantiated with accompanying X-ray diffraction and Raman experiments.

  1. Approximation of mechanical properties of sintered materials with discrete element method

    Dosta, Maksym; Besler, Robert; Ziehdorn, Christian; Janßen, Rolf; Heinrich, Stefan


    Sintering process is a key step in ceramic processing, which has strong influence on quality of final product. The final shape, microstructure and mechanical properties, e.g. density, heat conductivity, strength and hardness are depending on the sintering process. In order to characterize mechanical properties of sintered materials, in this contribution we present a microscale modelling approach. This approach consists of three different stages: simulation of the sintering process, transition to final structure and modelling of mechanical behaviour of sintered material with discrete element method (DEM). To validate the proposed simulation approach and to investigate products with varied internal structures alumina powder has been experimentally sintered at different temperatures. The comparison has shown that simulation results are in a very good agreement with experimental data and that the novel strategy can be effectively used for modelling of sintering process.

  2. Layerwise mechanics and finite element for the dynamic analysis of piezoelectric composite plates

    Saravanos, Dimitris A.; Heyliger, Paul R.; Hopkins, Dale A.


    Laminate and structural mechanics for the analysis of laminated composite plate structures with piezoelectric actuators and sensors are presented. The theories implement layerwise representations of displacements and electric potential, and can model both the global and local electromechanical response of smart composite laminates. Finite-element formulations are developed for the quasi-static and dynamic analysis of smart composite structures containing piezoelectric layers. Comparisons with an exact solution illustrate the accuracy, robustness and capability of the developed mechanics to capture the global and local response of thin and/or thick laminated piezoelectric plates. Additional correlations and numerical applications demonstrate the unique capabilities of the mechanics in analyzing the static and free-vibration response of composite plates with distributed piezoelectric actuators and sensors.

  3. Cis-regulatory elements: molecular mechanisms and evolutionary processes underlying divergence.

    Wittkopp, Patricia J; Kalay, Gizem


    Cis-regulatory sequences, such as enhancers and promoters, control development and physiology by regulating gene expression. Mutations that affect the function of these sequences contribute to phenotypic diversity within and between species. With many case studies implicating divergent cis-regulatory activity in phenotypic evolution, researchers have recently begun to elucidate the genetic and molecular mechanisms that are responsible for cis-regulatory divergence. Approaches include detailed functional analysis of individual cis-regulatory elements and comparing mechanisms of gene regulation among species using the latest genomic tools. Despite the limited number of mechanistic studies published to date, this work shows how cis-regulatory activity can diverge and how studies of cis-regulatory divergence can address long-standing questions about the genetic mechanisms of phenotypic evolution.

  4. Finite Element Analysis of Flat Spiral Spring on Mechanical Elastic Energy Storage Technology

    Jingqiu Tang


    Full Text Available Energy storage technology has become an effective way of storing energy and improving power output controllability in modern power grid. The mechanical elastic energy storage technology on flat spiral spring is a new energy storage technology. This study states the mechanical elastic energy storage technology, models the mechanical model. Aimed to three kinds of structure and size of flat spiral spring, the finite element model are modeled, modal analysis is completed and the natural frequencies and the first 10-order vibration modes of the spring are analyzed, the relationship of natural frequency and vibration mode of spiral spring and structure and size is analyzed. The research results can provide the reference for the structure design and dynamics analysis.

  5. The long and the short of gamma-ray bursts

    Katz, J I


    We report evidence from the 3B Catalogue that long (T_{90} > 10 s) and short (T_{90} 1 MeV. This implies different spatial origin and physical processes for long and short bursts. Long bursts may be explained by accretion-induced collapse. Short bursts require another mechanism, for which we suggest neutron star collisions. These are capable of producing neutrino bursts as short as a few ms, consistent with the shortest observed time scales in GRB. We briefly investigate the parameters of clusters in which neutron star collisons may occur, and discuss the nuclear evolution of expelled and accelerated matter.

  6. Evaluation of the thermal-hydraulic response and fuel rod thermal and mechanical deformation behavior during the power burst facility test LOC-3. [PWR

    Yackle, T.R.; MacDonald, P.E.; Broughton, J.M.


    An evaluation of the results from the LOC-3 nuclear blowdown test conducted in the Power Burst Facility is presented. The test objective was to examine fuel and cladding behavior during a postulated cold leg break accident in a pressurized water reactor (PWR). Separate effects of rod internal pressure and the degree of irradiation were investigated in the four-rod test. Extensive cladding deformation (ballooning) and failure occurred during blowdown. The deformation of the low and high pressure rods was similar; however, the previously irradiated test rod deformed to a greater extent than a similar fresh rod exposed to identical system conditions.

  7. Wet Friction-Elements Boundary Friction Mechanism and Friction Coefficient Prediction

    WANG Yanzhong


    Full Text Available The friction mechanism for the boundary friction course of friction elements engagement was explicitly expressed. The boundary friction model was built up by the surface topography. The model contained the effect of boundary film, adhesion, plough and lubrication. Based on the model, a coefficient for weakening plough for the lubrication was proposed. The modified model could fit for the working condition of wet friction elements. The friction coefficient as a function curve of rotating speed could be finally obtained by the data k and s/sm. The method provides a well interpretation of friction condition and friction coefficient prediction and the agreement between theoretical and experimental friction coefficients is reasonably good.

  8. Synthesis of amorphous Ti-Al alloys by mechanical alloying of elemental powders

    张俊红; 黄伯云; 贺跃辉; 周科朝; 刘咏


    Blended elemental powders with the nominal compositions (mole fraction, %) of Ti54Al46, Ti52Al48 and Ti50Al50 were mechanically alloyed in a planetary ball milling system for up to 100h.The structure evolution in these powders was characterized by scanning electron microscope, X-ray diffraction and differential thermal a nalysis techniques. It was found that elemental powders were progressively trans formed into nanocrystalline Ti(Al) supersaturated solid solution, then into amor phous phase. With increasing Al content, the formation of a fully Ti(Al) supersa turated solid solution and amorphous phase were accelerated, which are attributed to the fine grain size. And the grain size condition for formation of amorpho us phase in this system is ≤16 nm.

  9. Tolerance design of mechanical assembly using NSGA II and finite element analysis

    Govindarajalu, Jayaprakash [Saranathan College of Engineering, Tamil Nadu (India); Karuppan, Sivakumar [Bannari Amman Institute of Technology, Tamil Nadu (India); Manoharan, Thilak [TRP Engineering College, Tamil Nadu (India)


    The technological and financial limitations in the manufacturing process are the reason for non achievability of nominal dimension. Therefore, tolerance allocation is of significant importance for assembly. Conventional tolerance allocation methods are limited by an assumption that all parts are rigid. Every mechanical assembly consists of at least one or more flexible parts which undergo significant deformation due to inertia effect. Finite element analysis is used to determine the deformation of components in an assembly. Therefore, integration of statistical tolerance design with finite element analysis will guarantee that the optimal tolerance values of various components of the assembly obtained as end product of the tolerance design will remain within tolerance variation. Then the product can function as intended under a wide range of operating conditions for the duration of its life. In this paper, tolerance design of a piston cylinder assembly is done to demonstrate the proposed methodology.

  10. Dynamic encoding of natural luminance sequences by LGN bursts.

    Nicholas A Lesica


    Full Text Available In the lateral geniculate nucleus (LGN of the thalamus, visual stimulation produces two distinct types of responses known as tonic and burst. Due to the dynamics of the T-type Ca(2+ channels involved in burst generation, the type of response evoked by a particular stimulus depends on the resting membrane potential, which is controlled by a network of modulatory connections from other brain areas. In this study, we use simulated responses to natural scene movies to describe how modulatory and stimulus-driven changes in LGN membrane potential interact to determine the luminance sequences that trigger burst responses. We find that at low resting potentials, when the T channels are de-inactivated and bursts are relatively frequent, an excitatory stimulus transient alone is sufficient to evoke a burst. However, to evoke a burst at high resting potentials, when the T channels are inactivated and bursts are relatively rare, prolonged inhibitory stimulation followed by an excitatory transient is required. We also observe evidence of these effects in vivo, where analysis of experimental recordings demonstrates that the luminance sequences that trigger bursts can vary dramatically with the overall burst percentage of the response. To characterize the functional consequences of the effects of resting potential on burst generation, we simulate LGN responses to different luminance sequences at a range of resting potentials with and without a mechanism for generating bursts. Using analysis based on signal detection theory, we show that bursts enhance detection of specific luminance sequences, ranging from the onset of excitatory sequences at low resting potentials to the offset of inhibitory sequences at high resting potentials. These results suggest a dynamic role for burst responses during visual processing that may change according to behavioral state.

  11. Three-dimensional Finite Element Analysis of the Mechanical Stress on Root from Orthodontic Tooth Movement by Sliding Mechanics

    LI Ping; MAO Jing; PENG Zhou; XIE Hui


    In order to study mechanical stress on root from orthodontic tooth movement by sliding mechanics, a 3-dimensional finite element model incorporating all layers of a human mandibular dental arch with orthodontic appliance has been developed to simulate mechanical stress on root from the orthodontic tooth movement. Simulated orthodontic force of 2 N at 0, 30 and 45 degree from the horizontal axis was applied to the crown of the teeth. The finite element analysis showed when or- thodontic forces were applied to the tooth, the stress was mainly concentrated at the neck of the tooth decreasing uniformly to the apex and crown. The highest stress on the root was 0.621 N/ram2 for cer- vical margin of the canine, and 0.114 N/mm2 for apical region of the canine. The top of canine crown showed the largest amount of displacement (2.417 μm), while the lowest amount of displacement was located at the apical region of canine (0.043 μm). In conclusion, this model might enable one to simulate orthodontic tooth movements clinically. Sliding force at 2 N is ideal to ensure the bodily or- thodontic tooth movement. The highest stress concentration in the roots was always localized at the cervical margin when orthodontic force of 2 N at 0, 30 and 45 degree from the horizontal axis, so there may be the same risk of root resorption when orthodontic force of 2 N at 0, 30 and 45 degree was used in clinic cases.

  12. Interplanetary Type IV Bursts

    Hillaris, Alexander; Nindos, Alexander


    In this work we study the characteristics of moving type IV radio bursts which extend to the hectometric wavelengths (interplanetary type IV or type IV IP bursts) and their relationship with energetic phenomena on the Sun. Our dataset comprised 48 Interplanetary type IV bursts observed by the Wind/WAVES in the 13.825 MHz?20 KHz frequency range. The dynamic spec tra of the RSTN, DAM, ARTEMIS-IV, CULGOORA, Hiraiso and IZMIRAN Radio-spectrographs were used to track the evolution of the events in the low corona; these were supplemented with SXR ?ux recordings from GOES and CME data from LASCO. Positional information for the coronal bursts were obtained by the Nan\\c{c}ay radioheliograph (NRH). We examined the relationship of the type IV events with coronal radio bursts, CMEs and SXR ?ares. The majority of the events (45) were characterized as compact; their duration was on average 106 min. This type of events were, mostly, associated with M and X class ?ares (40 out of 45) and fast CMEs; 32 of these events had CME...

  13. Mechanical analysis on individualized finite element of temporal-mandibular joint under overlarge jaw opening status.

    Sun, Mingxu; Yang, Jianjun; Zhou, Ruizhi; Li, Ningyi; Xia, Junnan; Gu, Fang


    Analyze the stress status of temporal-mandibular joint (TMJ) of a healthy volunteer under the overlarge jaw opening status through the finite element method, with the purpose of clarifying the loading features of each structure in the joint area, and achieving further understanding of the pathogenesis of the temporomandibular disorders (TMD). Collect the CBCT and MRI data of a volunteer respectively under the maximum jaw opening, establish the finite element model (FEM) of TMJ under the maximum jaw opening status through a series of software, image segmentation, rectification, meshing, material evaluation and other related processing, simulate the mechanical environment of this joint area under this status, and analyze the stress status of the articular disc, condyle cartilage, and condyle process. Based on CT and MRI image data, build 3D model and FEM of TMJ, fully simulate the mechanical environment under the large jaw opening status, and calculate the stress value of the articular disc, condyle process and condylar cartilage. This research result reminds us that the normal people's articular disc are easy to generate stress concentration under large jaw opening, but its stress is far less than the one under the tight biting status. Perhaps the TMJ symptom induced under the large jaw opening status is mainly caused by the displacement of the articular disc. Under the large jaw opening status, the condylar cartilage plays a vital role in dispersing the stress. This method can be applied for carrying out individualized mechanical analysis on the patients with TMD.

  14. Development of an algorithm for the analysis of surface defects in mechanical elements

    Fargione, Giovanna A.; Geraci, Alberto L.; Pennisi, Luigi; Risitano, Antonino


    The non-destructive tests allow to establish the physical and structural conditions of a mechanical part, to verify its condition, the superficial wear and tear and then evaluate its `remaining' efficiency. The non-destructive tests are applied in all those fields of engineering in which the determination of the mechanical and structural characteristics of elements in use is requested, without making them undergo destructive or damaging tests. In the present work an application program has been developed which, examining the surface of mechanical parts under an optical microscope and a blaster video, is able to characterize the material and to recognize and identify the possible presence of a superficial crack. The program constitutes the first step towards the realization of an industrial prototype which, thanks to the utilization of a plan moved by step-by-step motors, allowing the scanning of the whole surface of a part and the recognition of the crack in an automatic way, that is without the presence of an operator, and its characterization, in case it is identified, through the determination of some geometric parameters useful to ascertain the structural integrity of the element under examination. For the realization of the program different techniques of image analysis have been applied and the use of an artificial neural network preset for the recognition of the crack has been necessary. The program has been realized in C language and it works in Linux system.

  15. A three-dimensional finite element model for the mechanics of cell-cell interactions.

    Viens, Denis; Brodland, G Wayne


    Technical challenges, including significant ones associated with cell rearrangement, have hampered the development of three-dimensional finite element models for the mechanics of embryonic cells. These challenges have been overcome by a new formulation in which the contents of each cell, assumed to have a viscosity mu, are modeled using a system of orthogonal dashpots. This approach overcomes a stiffening artifact that affects more traditional models, in which space-filling viscous elements are used to model the cytoplasm. Cells are assumed to be polyhedral in geometry, and each n-sided polygonal face is subdivided into n triangles with a common node at the face center so that it needs not remain flat. A constant tension gamma is assumed to act along each cell-cell interface, and cell rearrangements occur through one of two complementary topological transformations. The formulation predicts mechanical interactions between pairs of similar or dissimilar cells that are consistent with experiments, two-dimensional simulations, contact angle theory, and intracellular pressure calculations. Simulations of the partial engulfment of one tissue type by another show that the formulation is able to model aggregates of several hundred cells without difficulty. Simulations carried out using this formulation suggest new experimental approaches for measuring cell surface tensions and interfacial tensions. The formulation holds promise as a tool for gaining insight into the mechanics of isolated or aggregated embryonic cells and for the design and interpretation of experiments that involve them.

  16. Electricity Generation Characteristics of Energy-Harvesting System with Piezoelectric Element Using Mechanical-Acoustic Coupling

    Hirotarou Tsuchiya


    Full Text Available This paper describes the electricity generation characteristics of a new energy-harvesting system with piezoelectric elements. The proposed system is composed of a rigid cylinder and thin plates at both ends. The piezoelectric elements are installed at the centers of both plates, and one side of each plate is subjected to a harmonic point force. In this system, vibration energy is converted into electrical energy via electromechanical coupling between the plate vibration and piezoelectric effect. In addition, the plate vibration excited by the point force induces a self-sustained vibration at the other plate via mechanical-acoustic coupling between the plate vibrations and an internal sound field into the cylindrical enclosure. Therefore, the electricity generation characteristics should be considered as an electromechanical-acoustic coupling problem. The characteristics are estimated theoretically and experimentally from the electric power in the electricity generation, the mechanical power supplied to the plate, and the electricity generation efficiency that is derived from the ratio of both power. In particular, the electricity generation efficiency is one of the most appropriate factors to evaluate a performance of electricity generation systems. Thus, the effect of mechanical-acoustic coupling is principally evaluated by examining the electricity generation efficiency.

  17. Research on the Working Mechanism and Virtual Design for Cleaning Element in Brush Shape of the Sugarcane Harvester


    The cleaning element is the key part to the small w ho le-stall sugarcane harvester, which is suitable to the highland. And it is the bottleneck of the design of the small sugarcane harvester. The working mechanism of centrifugal cleaning method of the cleaning element in brush shape is based on the high speed rotating cleaning element that push, scrub, and strike the sta lk to separate the leaves from the sugarcane. The paper elaborated the worki ng mechanism of cleaning element in brush shape of the ...

  18. Mechanical stress induces biotic and abiotic stress responses via a novel cis-element.

    Justin W Walley


    Full Text Available Plants are continuously exposed to a myriad of abiotic and biotic stresses. However, the molecular mechanisms by which these stress signals are perceived and transduced are poorly understood. To begin to identify primary stress signal transduction components, we have focused on genes that respond rapidly (within 5 min to stress signals. Because it has been hypothesized that detection of physical stress is a mechanism common to mounting a response against a broad range of environmental stresses, we have utilized mechanical wounding as the stress stimulus and performed whole genome microarray analysis of Arabidopsis thaliana leaf tissue. This led to the identification of a number of rapid wound responsive (RWR genes. Comparison of RWR genes with published abiotic and biotic stress microarray datasets demonstrates a large overlap across a wide range of environmental stresses. Interestingly, RWR genes also exhibit a striking level and pattern of circadian regulation, with induced and repressed genes displaying antiphasic rhythms. Using bioinformatic analysis, we identified a novel motif overrepresented in the promoters of RWR genes, herein designated as the Rapid Stress Response Element (RSRE. We demonstrate in transgenic plants that multimerized RSREs are sufficient to confer a rapid response to both biotic and abiotic stresses in vivo, thereby establishing the functional involvement of this motif in primary transcriptional stress responses. Collectively, our data provide evidence for a novel cis-element that is distributed across the promoters of an array of diverse stress-responsive genes, poised to respond immediately and coordinately to stress signals. This structure suggests that plants may have a transcriptional network resembling the general stress signaling pathway in yeast and that the RSRE element may provide the key to this coordinate regulation.

  19. Finite element analysis of mechanical behavior of human dysplastic hip joints: a systematic review.

    Vafaeian, B; Zonoobi, D; Mabee, M; Hareendranathan, A R; El-Rich, M; Adeeb, S; Jaremko, J L


    Developmental dysplasia of the hip (DDH) is a common condition predisposing to osteoarthritis (OA). Especially since DDH is best identified and treated in infancy before bones ossify, there is surprisingly a near-complete absence of literature examining mechanical behavior of infant dysplastic hips. We sought to identify current practice in finite element modeling (FEM) of DDH, to inform future modeling of infant dysplastic hips. We performed multi-database systematic review using PRISMA criteria. Abstracts (n = 126) fulfilling inclusion criteria were screened for methodological quality, and results were analyzed and summarized for eligible articles (n = 12). The majority of the studies modeled human adult dysplastic hips. Two studies focused on etiology of DDH through simulating mechanobiological growth of prenatal hips; we found no FEM-based studies in infants or children. Finite element models used either patient-specific geometry or idealized average geometry. Diversities in choice of material properties, boundary conditions, and loading scenarios were found in the finite-element models. FEM of adult dysplastic hips demonstrated generally smaller cartilage contact area in dysplastic hips than in normal joints. Contact pressure (CP) may be higher or lower in dysplastic hips depending on joint geometry and mechanical contribution of labrum (Lb). FEM of mechanobiological growth of prenatal hip joints revealed evidence for effects of the joint mechanical environment on formation of coxa valga, asymmetrically shallow acetabulum and malformed femoral head associated with DDH. Future modeling informed by the results of this review may yield valuable insights into optimal treatment of DDH, and into how and why OA develops early in DDH.

  20. A Burst to See


    On 19 March, Nature was particularly generous and provided astronomers with the wealth of four gamma-ray bursts on the same day. But that was not all: one of them is the most luminous object ever observed in the Universe. Despite being located in a distant galaxy, billions of light years away, it was so bright that it could have been seen, for a brief while, with the unaided eye. ESO PR Photo 08a/08 ESO PR Photo 08a/08 The REM Telescope and TORTORA Camera Gamma-ray bursts (GRBs) are short flashes of energetic gamma-rays lasting from less than a second to several minutes. They release a tremendous quantity of energy in this short time making them the most powerful events since the Big Bang. It is now widely accepted that the majority of the gamma-ray bursts signal the explosion of very massive, highly evolved stars that collapse into black holes. Gamma-ray bursts, which are invisible to our eyes, are discovered by telescopes in space. After releasing their intense burst of high-energy radiation, they become detectable for a short while in the optical and in the near-infrared. This 'afterglow' fades very rapidly, making detailed analysis possible for only a few hours after the gamma-ray detection. This analysis is important in particular in order to determine the GRB's distance and, hence, intrinsic brightness. The gamma-ray burst GRB 080319B was detected by the NASA/STFC/ASI Swift satellite. "It was so bright that it almost blinded the Swift instruments for a while," says Guido Chincarini, Italian principal investigator of the mission. A bright optical counterpart was soon identified in the Boötes Constellation (the "Bear Driver" or "Herdsman"). A host of ground-based telescopes reacted promptly to study this new object in the sky. In particular, the optical emission was detected by a few wide-field cameras on telescopes that constantly monitor a large fraction of the sky, including the TORTORA camera in symbiosis with the 0.6-m REM telescope located at La Silla

  1. Structural integrity assessment by using finite element analysis based on damage mechanics

    Oh, Chang Sik; Kim, Nak Hyun; Kim, Yun Jae [Korea University, Seoul (Korea, Republic of)


    This paper introduces structural integrity assessment by using Finite Element analysis based on damage mechanics. Several FE damage methods as like GTN model have been proposed up to the present. These damage models have their own advantages and disadvantages. It is important to select the proper damage model for the integrity assessment of the structure in interest. In this paper, selected several damage models are apply to simulate fracture behaviours of structures with various geometries, and the FE results are compared with the experimental results. These models are implemented to general purpose FE program, ABAQUS, via user-defined subroutines.

  2. Fracture mechanics analysis of damaged turbine rotor discs using finite element method

    Vasović Ivana V.


    Full Text Available This paper presents evaluation fracture mechanics parameters in low pressure turbine components. Critical locations such as keyway and dovetail area are experiencing stress concentration leading to crack initiation. Stress intensity factors were evaluated using the J-Integral approach available within ANSYS software code. The finite element method allowed the prediction of the point of crack initiation and the crack propagation using the orientations of the maximum principal stresses. Special attention in this investigation is focused to develop analytic expressions for stress intensity factors at critical location of low pres-sure steam turbine disc. [Projekat Ministarstva nauke Republike Srbije, br. I-174001 i br. TR-35045

  3. Finite element simulation for mechanical response of surface mounted solder joints under different temperature cycling

    马鑫; 钱乙余


    Nonlinear finite element simulation for mechanical response of surface mounted solder joint under different temperature cycling was carried out. Seven sets of parameters were used in order to evaluate the influence of temperature cycling profile parameters. The results show that temperature cycling history has significant effect on the stress response of the solder joint. Based on the concept of relative damage stress proposed by the authors, it is found that enough high temperature holding time is necessary for designing the temperature cycling profile in accelerated thermal fatigue test.

  4. Determination of Mechanical Properties of Porous Silicon with Image Analysis and Finite Element

    Rahmoun, K.; Faraoun, H. I.; Bassou, G.; Mathieu, C.; Sari, N. E. Chabane

    In order to create equivalent images, a series of SEM micrographs of porous silicon were treated with the image analysis procedure, developed using public domain software "ImageJ". A morphological description was used to reduce the complexity of the microstructure of porous silicon and an image analysis procedure has been established to quantify different geometrical parameters related to the shape, size and orientation distribution. This description allows performing predictive calculation of mechanical properties of porous silicon using finite element analysis. Results are compared with experiment and a good agreement is observed

  5. The Glast Burst Monitor

    Meegan, Charles


    The Gamma-Ray Large Area Space Telescope (GLAST) will include a secondary instrument to augment the observatory's capabilities for GRB studies. The GLAST Burst Monitor (GBK is a collaboration between Marshall Space Flight Center, the University of Huntsville, Alabama, and the Max Plank Institute for Extraterrestrial Physics. The purpose of the GBM is to extend energy coverage below the main instrument's lower limit of about 20 MeV, and to provide an on-board burst trigger and approximate location. The instrument consists of twelve NaI detectors and two BGO detectors. This combination provides energy coverage from a few keV up to about 30 MeV.

  6. Interplanetary Type IV Bursts

    Hillaris, A.; Bouratzis, C.; Nindos, A.


    We study the characteristics of moving type IV radio bursts that extend to hectometric wavelengths (interplanetary type IV or type {IV}_{{IP}} bursts) and their relationship with energetic phenomena on the Sun. Our dataset comprises 48 interplanetary type IV bursts observed with the Radio and Plasma Wave Investigation (WAVES) instrument onboard Wind in the 13.825 MHz - 20 kHz frequency range. The dynamic spectra of the Radio Solar Telescope Network (RSTN), the Nançay Decametric Array (DAM), the Appareil de Routine pour le Traitement et l' Enregistrement Magnetique de l' Information Spectral (ARTEMIS-IV), the Culgoora, Hiraso, and the Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation (IZMIRAN) Radio Spectrographs were used to track the evolution of the events in the low corona. These were supplemented with soft X-ray (SXR) flux-measurements from the Geostationary Operational Environmental Satellite (GOES) and coronal mass ejections (CME) data from the Large Angle and Spectroscopic Coronagraph (LASCO) onboard the Solar and Heliospheric Observatory (SOHO). Positional information of the coronal bursts was obtained by the Nançay Radioheliograph (NRH). We examined the relationship of the type IV events with coronal radio bursts, CMEs, and SXR flares. The majority of the events (45) were characterized as compact, their duration was on average 106 minutes. This type of events was, mostly, associated with M- and X-class flares (40 out of 45) and fast CMEs, 32 of these events had CMEs faster than 1000 km s^{-1}. Furthermore, in 43 compact events the CME was possibly subjected to reduced aerodynamic drag as it was propagating in the wake of a previous CME. A minority (three) of long-lived type {IV}_{{IP}} bursts was detected, with durations from 960 minutes to 115 hours. These events are referred to as extended or long duration and appear to replenish their energetic electron content, possibly from electrons escaping from the corresponding coronal

  7. Discrete element modeling of indentation tests to investigate mechanisms of CO2-related chemomechanical rock alteration

    Sun, Zhuang; Espinoza, D. Nicolas; Balhoff, Matthew T.


    During CO2 injection into geological formations, petrophysical and geomechanical properties of host formations can be altered due to mineral dissolution and precipitation. Field and laboratory results have shown that sandstone and siltstone can be altered by CO2-water mixtures, but few quantitative studies have been performed to fully investigate underlying mechanisms. Based on the hypothesis that CO2-water mixtures alter the integrity of rock structure by attacking cements rather than grains, we attempt to explain the degradation of cementation due to long-term contact with CO2 and water and mechanisms for changes in rock mechanical properties. Many sandstones, including calcite-cemented quartzitic sandstone, chlorite-cemented quartzitic sandstone, and hematite-cemented quartzitic sandstone, contain interparticle cements that are more readily affected by CO2-water mixtures than grains. A model that couples the discrete element method and the bonded-particle model is used to perform simulations of indentation tests on synthetic rocks with crystal and random packings. The model is verified against the analytical cavity expansion model and validated against laboratory indentation tests on Entrada sandstone with and without CO2 alteration. Sensitivity analysis is performed for cementation microscopic parameters including stiffness, size, axial, and shear strength. The simulation results indicate that the CO2-related degradation of mechanical properties in bleached Entrada sandstone can be attributed to the reduction of cement size rather than cement strength. Our study indicates that it is possible to describe the CO2-related rock alteration through particle-scale mechanisms.

  8. The supernova-gamma-ray burst-jet connection.

    Hjorth, Jens


    The observed association between supernovae and gamma-ray bursts represents a cornerstone in our understanding of the nature of gamma-ray bursts. The collapsar model provides a theoretical framework for this connection. A key element is the launch of a bipolar jet (seen as a gamma-ray burst). The resulting hot cocoon disrupts the star, whereas the (56)Ni produced gives rise to radioactive heating of the ejecta, seen as a supernova. In this discussion paper, I summarize the observational status of the supernova-gamma-ray burst connection in the context of the 'engine' picture of jet-driven supernovae and highlight SN 2012bz/GRB 120422A--with its luminous supernova but intermediate high-energy luminosity--as a possible transition object between low-luminosity and jet gamma-ray bursts. The jet channel for supernova explosions may provide new insights into supernova explosions in general.

  9. A Hierarchical of Security Situation Element Acquisition Mechanism in Wireless Sensor Network

    Li Fangwei


    Full Text Available In wireless sensor network, the processing ability of the sensor nodes is poor. And the security situational element acquisition is also a serious problem. Thus, this paper proposes a hierarchical framework of security situational elements acquisition mechanism. In this framework, support vector machine hyper sphere multi class algorithm is introduced as basic classifier. The method of attribute reduction uses non negative matrix factorization algorithm. The fuzzy classification algorithm used to initialize non negative matrix factorization, in order to avoid the local optimal which is caused by non negative matrix factorization random initialization. In the sink node classification rules and attribute reduction rules are formed by learning. The classification analyses respectively focus on the cluster head and sink node, which can reduce the requirement of the sensor node properties. Attribute reduction before the data transmission, which reduces communication consumption data transmission, improves the performance of classifiers. By simulation analysis, the scheme has preferably accuracy in the situation elements acquisiton, and smaller communication overhead in the process of information transmission.

  10. Matrix elements for sum of power-law potentials in quantum mechanic using generalized hypergeometric functions

    Ma'zoozeh E. Abu-Amra


    Full Text Available In this paper we derive close form for the matrix elements for $hat H=-Delta +V$, where $V$ is a pure power-law potential. We use trial functions of the form $$ psi _n(r= sqrt{{frac{2eta ^{gamma/2}(gamma _n} {n!Gamma(gamma }}} r^{gamma - 1/2} e^{-frac{sqrt{eta }}{2}r^q} _pF_1 ( -n,a_2,ldots ,a_p;gamma;sqrt {eta } r^q, $$ for $eta, q,gamma >0$ to obtain the matrix elements for $hat H$. These formulas are then optimized with respect to variational parameters $eta ,q$ and $gamma $ to obtain accurate upper bounds for the given nonsolvable eigenvalue problem in quantum mechanics. Moreover, we write the matrix elements in terms of the generalized hypergeomtric functions. These results are generalization of those found earlier in [2], [8-16] for power-law potentials. Applications and comparisons with earlier work are presented.

  11. Determination of mechanical properties from depth-sensing indentation data and results of finite element modeling

    Isaenkova, M. G.; Perlovich, Yu A.; Krymskaya, O. A.; Zhuk, D. I.


    3D finite element model of indentation process with Berkovich tip was created. Using this model with different type of test materials, several series of calculations were made. These calculations lead to determination of material behavior features during indentation. Relations between material properties and its behavior during instrumented indentation were used for construction of dimensionless functions required for development the calculation algorithm, suitable to determine mechanical properties of materials by results of the depth-sensing indentation. Results of mechanical properties determination using elaborated algorithm for AISI 1020 steel grade were compared to properties obtained with standard compression tests. These two results differ by less than 10% for yield stress that evidence of a good accuracy of the proposed technique.

  12. A methodology for semiautomatic generation of finite element models: Application to mechanical devices

    Jesús López


    Full Text Available In this work, a methodology to create parameterized finite element models is presented, particularly focusing on the development of suitable algorithms in order to generate models and meshes with high computational efficiency. The methodology is applied to the modeling of two common mechanical devices: an optical linear encoder and a gear transmission. This practical application constitutes a tough test to the methodology proposed, given the complexity and the large number of components that set up this high-precision measurement device and the singularity of the internal gears. The geometrical and mechanical particularities of the components lead to multidimensional modeling, seeking to ensure proper interaction between the different types of finite elements. Besides, modeling criteria to create components such as compression and torsion springs, sheet springs, bearings, or adhesive joints are also presented in the article. The last part of the work aims to validate the simulation results obtained with the methodology proposed with those derived from experimental tests through white noise base-driven vibration and hammer impact excitation modal analysis.

  13. Finite element analysis of stress transfer mechanism from matrix to the fiber in SWCN reinforced nanocomposites

    Günay, E.


    This study defined as micromechanical finite element (FE) approach examining the stress transfer mechanism in single-walled carbon nanotube (SWCN) reinforced composites. In the modeling, 3D unit-cell method was evaluated. Carbon nanotube reinforced composites were modeled as three layers which comprises CNT, interface and matrix material. Firstly; matrix, fiber and interfacial materials all together considered as three layered cylindrical nanocomposite. Secondly, the cylindrical matrix material was assumed to be isotropic and also considered as a continuous medium. Then, fiber material was represented with zigzag type SWCNs. Finally, SWCN was combined with the elastic medium by using springs with different constants. In the FE modeling of SWCN reinforced composite model springs were modeled by using ANSYS spring damper element COMBIN14. The developed interfacial van der Waals interaction effects between the continuous matrix layer and the carbon nanotube fiber layer were simulated by applying these various spring stiffness values. In this study, the layered composite cylindrical FE model was presented as the equivalent mechanical properties of SWCN structures in terms of Young's modulus. The obtained results and literature values were presented and discussed. Figures, 16, 17, and 18 of the original article PDF file, as supplied to AIP Publishing, were affected by a PDF-processing error. Consequently, a solid diamond symbol appeared instead of a Greek tau on the y axis labels for these three figures. This article was updated on 17 March 2017 to correct the PDF-processing error, with the scientific content remaining unchanged.

  14. A Repeating Fast Radio Burst

    Spitler, L G; Hessels, J W T; Bogdanov, S; Brazier, A; Camilo, F; Chatterjee, S; Cordes, J M; Crawford, F; Deneva, J; Ferdman, R D; Freire, P C C; Kaspi, V M; Lazarus, P; Lynch, R; Madsen, E C; McLaughlin, M A; Patel, C; Ransom, S M; Seymour, A; Stairs, I H; Stappers, B W; van Leeuwen, J; Zhu, W W


    Fast Radio Bursts are millisecond-duration astronomical radio pulses of unknown physical origin that appear to come from extragalactic distances. Previous follow-up observations have failed to find additional bursts at the same dispersion measures (i.e. integrated column density of free electrons between source and telescope) and sky position as the original detections. The apparent non-repeating nature of the fast radio bursts has led several authors to hypothesise that they originate in cataclysmic astrophysical events. Here we report the detection of ten additional bursts from the direction of FRB121102, using the 305-m Arecibo telescope. These new bursts have dispersion measures and sky positions consistent with the original burst. This unambiguously identifies FRB121102 as repeating and demonstrates that its source survives the energetic events that cause the bursts. Additionally, the bursts from FRB121102 show a wide range of spectral shapes that appear to be predominantly intrinsic to the source and wh...

  15. Gamma-ray bursts at high redshift

    R.A.M.J. Wijers


    Gamma-ray bursts are much brighter than supernovae, and could therefore possibly probe the Universe to high redshift. The presently established GRB redshifts range from 0.83 to 5, and quite possibly even beyond that. Since most proposed mechanisms for GRB link them closely to deaths of massive stars

  16. Gamma-ray bursts at high redshift

    Wijers, R.A.M.J.


    Gamma-ray bursts are much brighter than supernovae, and could therefore possibly probe the Universe to high redshift. The presently established GRB redshifts range from 0.83 to 5, and quite possibly even beyond that. Since most proposed mechanisms for GRB link them closely to deaths of massive stars

  17. Finite element analysis of surface cracks in the Wilkins Ice Shelf using fracture mechanics

    Plate, Carolin; Müller, Ralf; Gross, Dietmar; Humbert, Angelika; Braun, Matthias


    Ice shelves, located between the warming atmosphere and the ocean, are sensitive elements of the climate system. The Wilkins Ice Shelf is situated in the south-western part of the Antarctic Peninsula, a well known hot spot of global warming. Recent break-up events exemplified the potential of disintegration of the ice shelf. A multi interdisciplinary project consisting of remote sensing, modeling of the ice dynamics and fracture mechanics intends to improve the understanding of the impacts of temperature increase on ice shelf stability. As a part of this project the aim of this presentation is to demonstrate the fracture mechanical approach using finite elements and configurational forces. For fracture mechanical purposes the material behavior of ice is treated as a brittle solid, and linear fracture mechanics is used. Crucial to all methods in linear fracture mechanics is the evaluation of the stress intensity factor K which is a measure for the load concentration at the crack tip and which depends on the geometry of the body and on the applied loading. The computed value of K can be compared to the critical stress intensity factor Kc, a material property obtained from experimental examinations, to judge whether a crack will propagate. One very effective procedure to obtain the stress intensity factor takes advantage of configurational forces, which can be easily obtained in the finite element analysis. An initial investigation is based on a 2-dimensional analysis of a single crack with a mode-I load type using a static plane strain model in the finite element analysis software COMSOL and additional routines to compute and evaluate the configurational forces. Analytical solutions of simple geometry and load cases are called on in comparison. The application to the Wilkins Ice Shelf follows by using material parameters, geometries and loading situations, which are obtained from literature values, remote sensing data analysis and modeling of the ice dynamics

  18. Finite element simulation for the mechanical characterization of soft biological materials by atomic force microscopy.

    Valero, C; Navarro, B; Navajas, D; García-Aznar, J M


    The characterization of the mechanical properties of soft materials has been traditionally performed through uniaxial tensile tests. Nevertheless, this method cannot be applied to certain extremely soft materials, such as biological tissues or cells that cannot be properly subjected to these tests. Alternative non-destructive tests have been designed in recent years to determine the mechanical properties of soft biological tissues. One of these techniques is based on the use of atomic force microscopy (AFM) to perform nanoindentation tests. In this work, we investigated the mechanical response of soft biological materials to nanoindentation with spherical indenters using finite element simulations. We studied the responses of three different material constitutive laws (elastic, isotropic hyperelastic and anisotropic hyperelastic) under the same process and analyzed the differences thereof. Whereas linear elastic and isotropic hyperelastic materials can be studied using an axisymmetric simplification, anisotropic hyperelastic materials require three-dimensional analyses. Moreover, we established the limiting sample size required to determine the mechanical properties of soft materials while avoiding boundary effects. Finally, we compared the results obtained by simulation with an estimate obtained from Hertz theory. Hertz theory does not distinguish between the different material constitutive laws, and thus, we proposed corrections to improve the quantitative measurement of specific material properties by nanoindentation experiments.

  19. Effects of Frequency and Acceleration Amplitude on Osteoblast Mechanical Vibration Responses: A Finite Element Study

    Liping Wang


    Full Text Available Bone cells are deformed according to mechanical stimulation they receive and their mechanical characteristics. However, how osteoblasts are affected by mechanical vibration frequency and acceleration amplitude remains unclear. By developing 3D osteoblast finite element (FE models, this study investigated the effect of cell shapes on vibration characteristics and effect of acceleration (vibration intensity on vibrational responses of cultured osteoblasts. Firstly, the developed FE models predicted natural frequencies of osteoblasts within 6.85–48.69 Hz. Then, three different levels of acceleration of base excitation were selected (0.5, 1, and 2 g to simulate vibrational responses, and acceleration of base excitation was found to have no influence on natural frequencies of osteoblasts. However, vibration response values of displacement, stress, and strain increased with the increase of acceleration. Finally, stress and stress distributions of osteoblast models under 0.5 g acceleration in Z-direction were investigated further. It was revealed that resonance frequencies can be a monotonic function of cell height or bottom area when cell volumes and material properties were assumed as constants. These findings will be useful in understanding how forces are transferred and influence osteoblast mechanical responses during vibrations and in providing guidance for cell culture and external vibration loading in experimental and clinical osteogenesis studies.

  20. Bubble bursting as an aerosol generation mechanism during an oil spill in the deep-sea environment: laboratory experimental demonstration of the transport pathway.

    Ehrenhauser, Franz S; Avij, Paria; Shu, Xin; Dugas, Victoria; Woodson, Isaiah; Liyana-Arachchi, Thilanga; Zhang, Zenghui; Hung, Francisco R; Valsaraj, Kalliat T


    Oil spills in the deep-sea environment such as the 2010 Deep Water Horizon oil spill in the Gulf of Mexico release vast quantities of crude oil into the sea-surface environment. Various investigators have discussed the marine transport and fate of the oil into different environmental compartments (air, water, sediment, and biota). The transport of the oil into the atmosphere in these previous investigations has been limited to only evaporation, a volatility dependent pathway. In this work, we studied the aerosolization of oil spill matter via bursting bubbles as they occur during whitecaps in a laboratory aerosolization reactor. By evaluating the alkane content in oil mousse, crude oil, the gas phase, and particulate matter we clearly demonstrate that aerosolization via bursting bubbles is a solubility and volatility independent transport pathway for alkanes. The signature of alkane fractions in the native oil and aerosolized matter matched well especially for the less volatile alkanes (C20-C29). Scanning electron microscope interfaced with energy dispersive X-ray images identified the carbon fractions associated with salt particles of aerosols. Theoretical molecular dynamics simulations in the accompanying paper lend support to the observed propensity for alkanes at air-salt water interfaces of breaking bubbles and the produced droplets. The presence of a dispersant in the aqueous phase increased the oil ejection rate at the surface especially for the C20-C29 alkanes. The information presented here emphasizes the need to further study sea-spray aerosols as a possible transport vector for spilled oil in the sea surface environment.

  1. Study on fault induced rock bursts

    LI Zhi-hua; DOU Lin-ming; LU Cai-ping; MU Zong-long; CAO An-ye


    In order to study the rules of rock bursts caused by faults by means of mechanical analysis of a roof rock-mass balanced structure and numerical simulation about fault slip destabilization, the effect of coal mining operation on fault plane stresses and slip displacement were studied. The results indicate that the slip displacement sharply increases due to the decrease of normal stress and the increase of shear stress at the fault plane when the working face advances from the footwall to the fault itself, which may induce a fault rock burst. However, this slip displacement will be very small due to the increase of normal stress and the decrease of shear stress when the working face advances from the hanging wall to the fault itself, which results in a very small risk of a fault rock burst.

  2. Evaluation of Tissue Interactions with Mechanical Elements of a Transscleral Drug Delivery Device

    Jeffrey T. Borenstein


    Full Text Available The goal of this work was to evaluate tissue-device interactions due to implantation of a mechanically operated drug delivery system onto the posterior sclera. Two test devices were designed and fabricated to model elements of the drug delivery device—one containing a free-spinning ball bearing and the other encasing two articulating gears. Openings in the base of test devices modeled ports for drug passage from device to sclera. Porous poly(tetrafluoroethylene (PTFE membranes were attached to half of the gear devices to minimize tissue ingrowth through these ports. Test devices were sutured onto rabbit eyes for 10 weeks. Tissue-device interactions were evaluated histologically and mechanically after removal to determine effects on device function and changes in surrounding tissue. Test devices were generally well-tolerated during residence in the animal. All devices encouraged fibrous tissue formation between the sclera and the device, fibrous tissue encapsulation and invasion around the device, and inflammation of the conjunctiva. Gear devices encouraged significantly greater inflammation in all cases and a larger rate of tissue ingrowth. PTFE membranes prevented tissue invasion through the covered drug ports, though tissue migrated in through other smaller openings. The torque required to turn the mechanical elements increased over 1000 times for gear devices, but only on the order of 100 times for membrane-covered gear devices and less than 100 times for ball bearing devices. Maintaining a lower device profile, minimizing microscale motion on the eye surface and covering drug ports with a porous membrane may minimize inflammation, decreasing the risk of damage to surrounding tissues and minimizing disruption of device operation.

  3. A Fault-Cored Anticline Boundary Element Model Incorporating the Combined Fault Slip and Buckling Mechanisms

    Wen-Jeng Huang


    Full Text Available We develop a folding boundary element model in a medium containing a fault and elastic layers to show that anticlines growing over slipping reverse faults can be significantly amplified by mechanical layering buckling under horizontal shortening. Previous studies suggested that folds over blind reverse faults grow primarily during deformation increments associated with slips on the fault during and immediately after earthquakes. Under this assumption, the potential for earthquakes on blind faults can be determined directly from fold geometry because the amount of slip on the fault can be estimated directly from the fold geometry using the solution for a dislocation in an elastic half-space. Studies that assume folds grown solely by slip on a fault may therefore significantly overestimate fault slip. Our boundary element technique demonstrates that the fold amplitude produced in a medium containing a fault and elastic layers with free slip and subjected to layer-parallel shortening can grow to more than twice the fold amplitude produced in homogeneous media without mechanical layering under the same amount of shortening. In addition, the fold wavelengths produced by the combined fault slip and buckling mechanisms may be narrower than folds produced by fault slip in an elastic half space by a factor of two. We also show that subsurface fold geometry of the Kettleman Hills Anticline in Central California inferred from seismic reflection image is consistent with a model that incorporates layer buckling over a dipping, blind reverse fault and the coseismic uplift pattern produced during a 1985 earthquake centered over the anticline forelimb is predicted by the model.

  4. Delayed Nickel Decay in Gamma Ray Bursts

    McLaughlin, G C


    Recently observed emission lines in the X-ray afterglow of gamma ray bursts suggest that iron group elements are either produced in the gamma ray burst, or are present nearby. If this material is the product of a thermonuclear burn, then such material would be expected to be rich in Nickel-56. If the nickel remains partially ionized, this prevents the electron capture reaction normally associated with the decay of Nickel-56, dramatically increasing the decay timescale. Here we examine the consequences of rapid ejection of a fraction of a solar mass of iron group material from the center of a collapsar/hypernova. The exact rate of decay then depends on the details of the ionization and therefore the ejection process. Future observations of iron, nickel and cobalt lines can be used to diagnose the origin of these elements and to better understand the astrophysical site of gamma ray bursts. In this model, the X-ray lines of these iron-group elements could be detected in suspected hypernovae that did not produce ...

  5. A High-order Eulerian-Lagrangian Finite Element Method for Coupled Electro-mechanical Systems

    Brandstetter, Gerd

    The main focus of this work is on the development of a high-order Eulerian-Lagrangian finite element method for the simulation of electro-mechanical systems. The coupled problem is solved by a staggered scheme, where the mechanical motion is discretized by standard Lagrangian finite elements, and the electrical field is solved on a fixed Eulerian grid with embedded boundary conditions. Traditional Lagrangian-Lagrangian or arbitrary Lagrangian-Eulerian (ALE) methods encounter deficiencies, for example, when dealing with mesh distortion due to large deformations, or topology changes due to contacting bodies. The presented Eulerian-Lagrangian approach addresses these issues in a natural way. Within this context we develop a high-order immersed boundary discontinuous-Galerkin (IB-DG) method, which is shown to be necessary for (i) the accurate representation of the electrical gradient along nonlinear boundary features such as singular corners, and (ii) to achieve full convergence during the iterative global solution. We develop an implicit scheme based on the mid-point rule, as well as an explicit scheme based on the centered-difference method, with the incorporation of energy conserving, frictionless contact algorithms for an elastic-to-rigid-surface contact. The performance of the proposed method is assessed for several benchmark tests: the electro-static force vector around a singular corner, the quasi-static pull-in of an electro-mechanically actuated switch, the excitation of a carbon nanotube at resonance, and the cyclic impact simulation of a micro-electro-mechanical resonant-switch. We report improved accuracy for the high-order method as compared to low-order methods, and linear convergence in the iterative solution of the staggered scheme. Additionally, we investigate a Newton-Krylov shooting scheme in order to directly find cyclic steady states of electro-mechanical devices excited at resonance-- as opposed to a naive time-stepping from zero initial

  6. Study of gap conductance model for thermo mechanical fully coupled finite element model

    Kim, Hyo Cha; Yang, Yong Sik; Kim, Dae Ho; Bang, Je Geon; Kim, Sun Ki; Koo, Yang Hyun [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)


    A light water reactor (LWR) fuel rod consists of zirconium alloy cladding and uranium dioxide pellets, with a slight gap between them. Therefore, the mechanical integrity of zirconium alloy cladding is the most critical issue, as it is an important barrier for fission products released into the environment. To evaluate the stress and strain of the cladding during operation, fuel performance codes with a one-dimensional (1D) approach have been reported since the 1970s. However, it is difficult for a 1D model to simulate the stress and strain of the cladding accurately owing to a lack of degree of freedom. A LWR fuel performance code should include thermo-mechanical coupled model owing to the existence of the fuel-cladding gap. Generally, the gap that is filled with helium gas results in temperature drop along radius direction. The gap conductance that determines temperature gradient within the gap is very sensitive to gap thickness. For instance, once the gap size increases up to several microns in certain region, difference of surface temperatures increases up to 100 Kelvin. Therefore, iterative thermo-mechanical coupled analysis is required to solve temperature distribution throughout pellet and cladding. Consequently, the Finite Element (FE) module, which can simulate a higher degree of freedom numerically, is an indispensable requirement to understand the thermomechanical behavior of cladding. FRAPCON-3, which is reliable performance code, has iterative loop for thermo-mechanical coupled calculation to solve 1D gap conductance model. In FEMAXI-III, 1D thermal analysis module and FE module for stress-strain analysis were separated. 1D thermal module includes iterative analysis between them. DIONISIO code focused on thermal contact model as function of surface roughness and contact pressure when the gap is closed. In previous works, gap conductance model has been developed only for 1D model or hybrid model (1D and FE). To simulate temperature, stress and strain

  7. The Double Firing Burst


    Astronomers from around the world combined data from ground- and space-based telescopes to paint a detailed portrait of the brightest explosion ever seen. The observations reveal that the jets of the gamma-ray burst called GRB 080319B were aimed almost directly at the Earth. Uncovering the disc ESO PR Photo 28/08 A Gamma-Ray Burst with Two Jets Read more on this illuminating blast in the additional story. GRB 080319B was so intense that, despite happening halfway across the Universe, it could have been seen briefly with the unaided eye (ESO 08/08). In a paper to appear in the 11 September issue of Nature, Judith Racusin of Penn State University, Pennsylvania (USA), and a team of 92 co-authors report observations across the electromagnetic spectrum that began 30 minutes before the explosion and followed it for months afterwards. "We conclude that the burst's extraordinary brightness arose from a jet that shot material almost directly towards Earth at almost the speed of light - the difference is only 1 part in 20 000," says Guido Chincarini, a member of the team. Gamma-ray bursts are the Universe's most luminous explosions. Most occur when massive stars run out of fuel. As a star collapses, it creates a black hole or neutron star that, through processes not fully understood, drives powerful gas jets outward. As the jets shoot into space, they strike gas previously shed by the star and heat it, thereby generating bright afterglows. The team believes the jet directed toward Earth contained an ultra-fast component just 0.4 degrees across (this is slightly smaller than the apparent size of the Full Moon). This jet is contained within another slightly less energetic jet about 20 times wider. The broad component is more typical of other bursts. "Perhaps every gamma-ray burst has a narrow jet, but astronomers miss it most of the time," says team member Stefano Covino. "We happened to view this monster down the barrel of the very narrow and energetic jet, and the chance for

  8. Investigating feedback mechanisms between stress and grain-size: preliminary findings from finite-element modelling

    Cross, A. J.; Prior, D. J.; Ellis, S. M.


    It is widely accepted that changes in stress and grain size can induce a switch between grain-size insensitive (GSI) and sensitive (GSS) creep mechanisms. Under steady-state conditions, grains evolve to an equilibrium size in the boundary region between GSS and GSI, described by the paleopiezometer for a given material. Under these conditions, significant rheological weakening is not expected, as grain size reduction processes are balanced by grain growth processes. However, it has been shown that the stress field surrounding faults varies through the seismic cycle, with both rapid loading and unloading of stress possible in the co- and post-seismic stages. We propose that these changes in stress in the region of the brittle-ductile transition zone may be sufficient to force a deviation from the GSI-GSS boundary and thereby cause a change in grain size and creep mechanism prior to system re-equilibration. Here we present preliminary findings from numerical modelling of stress and grain size changes in response to loading of mechanical inhomogeneities. Our results are attained using a grain-size evolution (GSE) subroutine incorporated into the SULEC finite-element code developed by Susan Ellis and Susanne Buiter, which utilises an iterative approach of solving for spatial and temporal changes in differential stress, grain size and active creep mechanism. Preliminary models demonstrate that stress changes in response to the opening of a fracture in a flowing medium can be significant enough to cause a switch from GSI to GSS creep. These results are significant in the context of understanding spatial variations and feedback between stress, grain size and deformation mechanisms through the seismic cycle.

  9. Thermal-mechanical study of functionally graded dental implants with the finite element method.

    Wang, F; Lee, H P; Lu, C


    This article investigates the thermal-mechanical performance of hydroxyapatite/titanium (HA/Ti) functionally graded (FG) dental implants with the three-dimensional finite element method. The stresses induced by occlusal force for the present HA/Ti FG implant are calculated to compare with the corresponding stresses for the titanium dental implant. Thermal-mechanical effect of temperature variation due to daily oral activity is also studied. The HA/Ti FG dental implant performance is evaluated against the maximum von Mises stress, which is the general performance indicator, the first principal/tensile stress for mechanical failure of implant-bone-bond and the third principal/compressive stress for bone absorption. Simulation results indicate that under the influence of occlusal force only, the FG implants with different HA fraction along the implant length perform almost equally well, while the titanium implant sustains much higher von Mises stress. However, when thermal stress is also considered, the FG implant having HA fraction exponential index of m = 2 with temperature decrease of 20 degrees C yields the highest first principal and von Mises stresses among all the FG and titanium implants.

  10. Influence of superstructure geometry on the mechanical behavior of zirconia implant abutments: a finite element analysis.

    Geringer, Alexander; Diebels, Stefan; Nothdurft, Frank P


    To predict the clinical performance of zirconia abutments, it is crucial to examine the mechanical behavior of different dental implant-abutment connection configurations. The international standard protocol for dynamic fatigue tests of dental implants (ISO 14801) allows comparing these configurations using standardized superstructure geometries. However, from a mechanical point of view, the geometry of clinical crowns causes modified boundary conditions. The purpose of this finite element (FE) study was to evaluate the influence of the superstructure geometry on the maximum stress values of zirconia abutments with a conical implant-abutment connection. Geometry models of the experimental setup described in ISO 14801 were generated using CAD software following the reconstruction of computerized tomography scans from all relevant components. These models served as a basis for an FE simulation. To reduce the numerical complexity of the FE model, the interaction between loading stamp and superstructure geometry was taken into account by defining the boundary conditions with regard to the frictional force. The results of the FE simulations performed on standardized superstructure geometry and anatomically shaped crowns showed a strong influence of the superstructure geometry and related surface orientations on the mechanical behavior of the underlying zirconia abutments. In conclusion, ISO testing of zirconia abutments should be accompanied by load-bearing capacity testing under simulated clinical conditions to predict clinical performance.

  11. Studying the influence of substitutional elements on mechanical behavior of Alloy 718

    Max Bertrand


    Full Text Available In nickel-based superalloys, substitutional solute species have a strong impact on in service mechanical properties as well as on oxidation and corrosion resistances. In alloy 718, recent studies carried out by tensile tests highlighted the fact that refractory solute species are able to interact strongly with mobile dislocations during plastic deformation, generating dynamic strain ageing, and, in wide ranges of tests temperatures and strain rates, Portevin-Le Chatelier effect. The precise nature of the substitutional element responsible for such a dynamic interaction is still subject to debate. We addressed this question by means of mechanical spectroscopy studies of alloy 718 and various related alloys corresponding to monitored changes in the chemical composition. Only a single internal friction relaxation peak has been observed for all the studied alloys. By analyzing the damping behavior of these alloys at different imposed solicitation frequencies by sweeping a large temperatures range, the activation energies of the relaxation process and the type of mechanism involved have been determined. The process is a “Zener relaxation” in the alloys, i.e. a substitutional atoms dipole reorientation under applied stress. The results tend to prove that Niobium is not involved in the relaxation process whereas Molybdenum content seems to play an important role in the relaxation intensity.

  12. Sensitivity of left ventricular mechanics to myofiber architecture: A finite element study.

    Nikou, Amir; Gorman, Robert C; Wenk, Jonathan F


    The goal of this study was to investigate the sensitivity of computational models of the heart to their incorporated myofiber architecture during diastole. This architecture plays a critical role in the mechanical and electrical function of the heart and changes after myocardial tissue remodeling, which is associated with some of the most common heart diseases. In this study, a left ventricular finite element model of the porcine heart was created using magnetic resonance imaging, which represents the in vivo geometry. Various myofiber architectures were assigned to the finite element mesh, in the form of fiber and sheet angles. A structural-based material law was used to model the behavior of passive myocardium and its parameters were estimated using measured in vivo strains and cavity volume from magnetic resonance imaging. The final results showed noticeable sensitivity of the stress distribution to both the fiber and sheet angle distributions. This implies that a structural-based material law that takes into account the effect of both fiber and sheet angle distributions should be used. The results also show that although the simulation results improve using available data from histological studies of myocardial structure, the need for individualized myofiber architecture data is crucial.

  13. Partition of unity finite element method for quantum mechanical materials calculations

    Pask, John E


    The current state of the art for large-scale quantum-mechanical simulations is the planewave (PW) pseudopotential method, as implemented in codes such as VASP, ABINIT, and many others. However, since the PW method uses a global Fourier basis, with strictly uniform resolution at all points in space, it suffers from substantial inefficiencies in calculations involving atoms with localized states, such as first-row and transition-metal atoms, and requires significant nonlocal communications, which limit parallel efficiency. Real-space methods such as finite-differences and finite-elements have partially addressed both resolution and parallel-communications issues but have been plagued by one key disadvantage relative to PW: excessive number of degrees of freedom needed to achieve the required accuracies. We present a real-space partition of unity finite element (PUFE) method to solve the Kohn-Sham equations of density functional theory. In the PUFE method, we build the known atomic physics into the solution proc...

  14. Analysis of Composite Transverse Mechanical Properties Based on Micromechanical Finite Element Method

    LIU Wan-lei


    Full Text Available Transverse fracture often occurs early in the loading history and is one of the key issues limiting the composite structural design. However, the mechanical behavior under transverse loading can not be represented by traditional micromechanical model which does not consider the influence of constituent properties, fiber volume fraction and fiber distribution. A new computational micromechanics finite element method, which the microstructure was idealized as a random dispersion of parallel fibers embedded in the polymeric matrix using improved random sequence absorption algorithm, was presented. The plasticity of matrix and interface decohesion of the composite were included in this model and the residual stress caused by the cooling of composite after the curing process was also taken into consideration. The transverse tension, compression and shear of composite were analyzed by the micromechanical finite element method. Compared with the experiment results, the prediction errors of transverse module were less than 7%, and the transverse compression strength and shear strength were less than 8%. The results demonstrate that the method proposed here can be used to predict the composite transverse behavior.

  15. Effect of alloying elements on mechanical properties in Cu-15%Cr in-situ composites

    H. G. Suzukit; J. Ma; K. Mihara; S. Sakai; S. Sun


    The effects of alloying elements on the mechanical properties as well as electrical conductivity in Cu-15 %Cr(mass fraction) in-situ composites were systematically studied and high strength and high electrical conductive Cu base in-situ composites have been developed. The best combination is the addition of 0.1% to 0.2% Zr, Ti, or Sn in Cu 15 %Cr in-situ composite, thermomechanical treatment to refine the microstructure and optimizing the precipitation of second phase. The strength is controlled by high density of dislocations in the Cu matrix, the lamellar spacing of the second phase, and the fine Cr precipitates. The aging treatment to reduce solute atoms has a beneficial effect on the increase of electrical conductivity. The addition of Zr, or Ti of about 0.15% to 0.2% promotes the precipitation of Cr particles.

  16. Modeling of the mechanical behavior of fiber-reinforced ceramic composites using finite element method (FEM

    Dimitrijević M.M.


    Full Text Available Modeling of the mechanical behavior of fiber-reinforced ceramic matrix composites (CMC is presented by the example of Al2O3 fibers in an alumina based matrix. The starting point of the modeling is a substructure (elementary cell which includes on a micromechanical scale the statistical properties of the fiber, matrix and fiber-matrix interface and their interactions. The numerical evaluation of the model is accomplished by means of the finite element method. The numerical results of calculating the elastic modulus of the composite dependance on the quantity of the fibers added and porosity was compared to experimental values of specimens having the same composition. [Projekat Ministarstva nauke Republike Srbije, br. ON174004 i TVH to project III45012

  17. Investigation of 1-Dimensional ultrasonic vibration compliance mechanism based on finite element analysis

    Latif, A. Afiff; Ibrahim, M. Rasidi; Rahim, E. A.; Cheng, K.


    The conventional milling has many difficulties in the processing of hard and brittle material. Hence, ultrasonic vibration assisted milling (UVAM) was proposed to overcome this problem. The objective of this research is to study the behavior of compliance mechanism (CM) as the critical part affect the performance of the UVAM. The design of the CM was investigated and focuses on 1-Dimensional. Experimental result was obtained from a portable laser digital vibrometer. While the 1-Dimensional value such as safety factor, deformation of hinges and stress analysis are obtained from finite elements simulation. Finally, the findings help to find the best design judging from the most travelled distance of the piezoelectric actuators. In addition, this paper would provide a clear picture the behavior of the CM embedded in the UVAM, which can provide good data and to improve the machining on reducing tool wear, and lower cutting force on the workpiece surface roughness.

  18. Homogenized Finite Element Analysis on Effective Elastoplastic Mechanical Behaviors of Composite with Imperfect Interfaces

    Wu-Gui Jiang


    Full Text Available A three-dimensional (3D representative volume element (RVE model was developed for analyzing effective mechanical behavior of fiber-reinforced ceramic matrix composites with imperfect interfaces. In the model, the fiber is assumed to be perfectly elastic until its tensile strength, and the ceramic material is modeled by an elasto-plastic Drucker-Prager constitutive law. The RVE model is then used to study the elastic properties and the tensile strength of composites with imperfect interfaces and validated through experiments. The imperfect interfaces between the fiber and the matrix are taken into account by introducing some cohesive contact surfaces. The influences of the interface on the elastic constants and the tensile strengths are examined through these interface models.

  19. Homogenized finite element analysis on effective elastoplastic mechanical behaviors of composite with imperfect interfaces.

    Jiang, Wu-Gui; Zhong, Ren-Zhi; Qin, Qing H; Tong, Yong-Gang


    A three-dimensional (3D) representative volume element (RVE) model was developed for analyzing effective mechanical behavior of fiber-reinforced ceramic matrix composites with imperfect interfaces. In the model, the fiber is assumed to be perfectly elastic until its tensile strength, and the ceramic material is modeled by an elasto-plastic Drucker-Prager constitutive law. The RVE model is then used to study the elastic properties and the tensile strength of composites with imperfect interfaces and validated through experiments. The imperfect interfaces between the fiber and the matrix are taken into account by introducing some cohesive contact surfaces. The influences of the interface on the elastic constants and the tensile strengths are examined through these interface models.

  20. Influence of Rare Earth Elements on Microstructure and Mechanical Properties of Mg-Li Alloys


    A series of α-based Mg-Li-Al-Zn-xRE alloys were prepared. These alloys have low density ranging from 1.5 to 1.7 g·cm-3 and high strength properties. The influence of RE element on the microstructure and the mechanical properties of these alloys were studied. The results indicate that the addition of RE (La, Pr, Ce) leads to the formation of rod-shaped intermetallic compound Al2Zn2La distributed in the matrix. Al2Zn2La induces reduction of the laminar spacing and causes refinement of the microstructure. Therefore, this compound improves the strength of alloys at a high temperature.

  1. Discrete Element Method Numerical Modelling on Crystallization of Smooth Hard Spheres under Mechanical Vibration

    AN Xi-Zhong


    The crystallization, corresponding to the fcc structure (with packing density p ≈ 0.74), of smooth equal hard spheres under batch-wised feeding and three-dimensional interval vibration is numerically obtained by using the discrete element method. The numerical experiment shows that the ordered packing can be realized by proper control of the dynamic parameters such as batch of each feeding § and vibration amplitude A. The radial distribution function and force network are used to characterize the ordered structure. The defect formed during vibrated packing is characterized as well The results in our work fill the gap of getting packing density between random close packing and fcc packing in phase diagram which provides an effective way of theoretically investigating the complex process and mechanism of hard sphere crystallization and its dynamics.

  2. Design development of linear pulse motor type control element drive mechanism

    Kim, Ji Ho; Yu, Je Yong; Kim, Jong In [Korea Atomic Energy Research Institute, Taejon (Korea)


    The integral reactor SMART is designed for soluble boron free operation and nuclear heating during reactor startup. These design features require the CEDM to have fine-step movement capability as well as high reliability for the fine reactivity control. This report describes the design characteristics of linear pulse motor (LPM) type control element drive mechanism which meets the SMART design requirements. Following items are discussed in this report : - Design concept of LPM type CEDM -Design Requirements - System descriptions -Materials -Design of linear pulse motor -Design of position indicator -Manufacturability of LPM. The results of this report are to be utilized as the starting point for design development of CEDM for SMART. 13 refs., 38 figs., 2 tabs. (Author)

  3. Fiber bundle models for stress release and energy bursts during granular shearing

    Michlmayr, Gernot; Or, Dani; Cohen, Denis


    Fiber bundle models (FBMs) offer a versatile framework for representing transitions from progressive to abrupt failure in disordered material. We report a FBM-based description of mechanical interactions and associated energy bursts during shear deformation of granular materials. For strain-controlled shearing, where elements fail in a sequential order, we present analytical expressions for strain energy release and failure statistics. Results suggest that frequency-magnitude characteristics of fiber failure vary considerably throughout progressive shearing. Predicted failure distributions were in good agreement with experimentally observed shear stress fluctuations and associated bursts of acoustic emissions. Experiments also confirm a delayed release of acoustic emission energy relative to shear stress buildup, as anticipated by the model. Combined with data-rich acoustic emission measurements, the modified FBM offers highly resolved contact-scale insights into granular media dynamics of shearing processes.

  4. Analysis of 3-D Frictional Contact Mechanics Problems by a Boundary Element Method

    KEUM Bangyong; LIU Yijun


    The development of two boundary element algorithms for solving 3-D, frictional, and linear elastostatic contact problems is reported in this paper. The algorithms employ nonconforming discretizations for solving 3-D boundary element models, which provide much needed flexibility in the boundary element modeling for 3-D contact problems. These algorithms are implemented in a new 3-D boundary element code and verified using several examples. For the numerical examples studied, the results using the new boundary element algorithms match very well with the results using a commercial finite element code, and clearly demonstrate the feasibility of the new boundary element approach for 3-D contact analysis.

  5. Connecting mechanics and bone cell activities in the bone remodeling process: an integrated finite element modeling.

    Hambli, Ridha


    Bone adaptation occurs as a response to external loadings and involves bone resorption by osteoclasts followed by the formation of new bone by osteoblasts. It is directly triggered by the transduction phase by osteocytes embedded within the bone matrix. The bone remodeling process is governed by the interactions between osteoblasts and osteoclasts through the expression of several autocrine and paracrine factors that control bone cell populations and their relative rate of differentiation and proliferation. A review of the literature shows that despite the progress in bone remodeling simulation using the finite element (FE) method, there is still a lack of predictive models that explicitly consider the interaction between osteoblasts and osteoclasts combined with the mechanical response of bone. The current study attempts to develop an FE model to describe the bone remodeling process, taking into consideration the activities of osteoclasts and osteoblasts. The mechanical behavior of bone is described by taking into account the bone material fatigue damage accumulation and mineralization. A coupled strain-damage stimulus function is proposed, which controls the level of autocrine and paracrine factors. The cellular behavior is based on Komarova et al.'s (2003) dynamic law, which describes the autocrine and paracrine interactions between osteoblasts and osteoclasts and computes cell population dynamics and changes in bone mass at a discrete site of bone remodeling. Therefore, when an external mechanical stress is applied, bone formation and resorption is governed by cells dynamic rather than adaptive elasticity approaches. The proposed FE model has been implemented in the FE code Abaqus (UMAT routine). An example of human proximal femur is investigated using the model developed. The model was able to predict final human proximal femur adaptation similar to the patterns observed in a human proximal femur. The results obtained reveal complex spatio-temporal bone

  6. Elements of Adaptation of Organizational and Economic Mechanism of Vegetable Companies to the External Environment

    Korobeynikov Dmitriy Aleksandrovich


    Full Text Available In this article the authors note that the priorities of improving the organizational and economic mechanism of agricultural enterprises specializing in vegetable production belong to the sphere of management. It is connected with the need to adapt their management systems to dynamic environmental conditions in order to minimize the risk factors. On the basis of the systematic approach and such scientific methods as analysis, synthesis and simulation, the authors elaborate a model of adaptation of management system of vegetable-growing enterprises to the external environment. The model includes three elements: 1 the principles of adaptation; 2 the elements of adaptation mechanism, including specific functions and structural features of monitoring; 3 assessment indicators. They explain why the essence of management should be considered in the unity of its two aspects: the process (general and specific control functions and structure (hierarchy and organization of management system of vegetable-growing enterprises. Within the context of the process approach they prove the need to supplement the general and specific management functions by the complementary risk management procedures, which provide the adaptivity of control system to risky environmental conditions. They give the substantial characteristics of the proposed procedures and methods of risk management, which complete the specific control function in the context of the three stages of the management cycle – adoption, implementation and monitoring of management decisions realization. The proposed approach links the technological aspects of management to its basic manifestations as functions realized in the environment of mutual influence of external (macroeconomic and industrial environment and internal (sphere of interaction of managing and managed subsystems risks. They complete the principles of structural optimization of management system by strengthening the role of elements that

  7. Burst pressure predictions of pipelines with longitudinal cracks

    Dotta, Fernando; Riggieri, Claudio [Sao Paulo Univ., SP (Brazil). Dept. de Engenharia Naval e Oceanica


    This study extends a micro mechanics approach based upon the computational cell methodology to model ductile crack extension of longitudinal crack-like defects in a high strength pipeline steel. Laboratory testing of an API 5L X60 steel at room temperature using standard, deep crack C(T) specimens provides the data needed to measure the crack growth resistance curve for the material. In the computational cell model, ductile crack extension occurs through void growth and coalescence (by cell extinction) within a thin layer of material ahead of crack tip. A simple scheme to calibrate material-specific parameters for the cells is also described. A central focus of the paper is the application of the cell methodology to predict experimentally measured burst pressures for pre-cracked pipe specimens with different crack sizes. The experimental program includes longitudinally pre cracked 20'' (508 mm) O.D. pipe specimens with 15.8 mm thickness and varying crack geometries. Plane-strain computations are conducted on detailed finite element models for the pipe specimens to describe crack extension with increased pressure. The numerical simulations demonstrate the effectiveness of the cell approach to describe crack growth response and to predict the burst pressure for the tested pipes. (author)

  8. Do Gamma-Ray Bursts Come from the Oort Cloud?

    Clarke, T E; Tremaine, S; Tremaine, adn S.


    We examine the possibility that gamma-ray bursts arise from sources in the Oort comet cloud, basing most of our arguments on accepted models for the formation and spatial distribution of the cloud. We identify three severe problems with such models: (1) There is no known mechanism for producing bursts that can explain the observed burst rate and energetics without violating other observational constraints. (2) The bright source counts cannot be reconciled with standard models for the phase-space distribution of objects in the Oort cloud. (3) The observed isotropy of the available burst data is inconsistent with the expected angular distribution of sources in the Oort cloud. We therefore assert that Oort cloud models of gamma-ray bursts are extremely implausible.

  9. Evaluating the risk of coal bursts in underground coal mines

    Mark Christopher⇑; Gauna Michael


    Coal bursts involve the sudden, violent ejection of coal or rock into the mine workings. They are almost always accompanied by a loud noise, like an explosion, and ground vibration. Bursts are a particular haz-ard for miners because they typically occur without warning. Despite decades of research, the sources and mechanics of these events are not well understood, and therefore they are difficult to predict and control. Experience has shown, however, that certain geologic and mining factors are associated with an increased likelihood of a coal burst. A coal burst risk assessment consists of evaluating the degree to which these risk factors are present, and then identifying appropriate control measures to mitigate the hazard. This paper summarizes the U.S. and international experience with coal bursts, and describes the known risk factors in detail. It includes a framework that can be used to guide the risk assessment process.

  10. Experimental and finite element analysis of fracture criterion in general yielding fracture mechanics

    D M Kulkarni; Ravi Prakash; A N Kumar


    Efforts made over the last three decades to understand the fracture behaviour of structural materials in elastic and elasto-plastic fracture mechanics are numerous, whereas investigations related to fracture behaviour of materials in thin sheets or general yielding fracture regimes are limited in number. Engineering simulative tests are being used to characterize formability and drawability of sheet metals. However, these tests do not assure consistency in quality of sheet metal products. The prevention of failure in stressed structural components currently requires fracture mechanics based design parameters like critical load, critical crack-tip opening displacement or fracture toughness. The present attempt would aim to fulfill this gap and generate more information thereby increased understanding on fracture behaviour of sheet metals. In the present investigation, using a recently developed technique for determining fracture criteria in sheet metals, results are generated on critical CTOD and fracture toughness. Finite element analysis was performed to support the results on various fracture parameters. The differences are within 1 to 4%. At the end it is concluded that magnitude of critical CTOD and/or critical load can be used as a fracture criterion for thin sheets.

  11. Mechanical property analysis of kenaf–glass fibre reinforced polymer composites using finite element analysis

    M Ramesh; S Nijanthan


    Nowadays, natural fibres are used as a reinforcing material in polymer composites, owing to severe environmental concerns. Among many different types of natural resources, kenaf plants have been extensively exploited over the past few years. In this experimental study, partially eco-friendly hybrid composites were fabricated by using kenaf and glass fibres with two different fibre orientations of 0° and 90°. The mechanical properties such as tensile, flexural and impact strengths of these composites have been evaluated. From the experiment, it was observed that the composites with the 0° fibre orientation can withstand the maximum tensile strength of 49.27 MPa, flexural strength of 164.35 MPa, and impact strength of 6 J. Whereas, the composites with the 90° fibre orientation hold the maximum tensile strength of 69.86 MPa, flexural strength of 162.566 MPa and impact strength of 6.66 J. The finite element analysis was carried out to analyse the elastic behaviour of the composites and to predict the mechanical properties by using NX Nastran 9.0 software. The experimental results were compared with the predicted values and a high correlation between the results was observed. The morphology of the fractured surfaces of the composites was analysed using a scanning electron microscopy analysis. The results indicated that the properties were in the increasing trend and comparable with pure synthetic fibre reinforced composites, which shows the potential for hybridization of kenaf fibre with glass fibre.

  12. 3D Finite Element Simulation of Graphene Nano-Electro-Mechanical Switches

    Jothiramalingam Kulothungan


    Full Text Available In this paper, we report the finite element method (FEM simulation of double-clamped graphene nanoelectromechanical (NEM switches. Pull-in and pull-out characteristics are analyzed for graphene NEM switches with different dimensions and these are consistent with the experimental results. This numerical model is used to study the scaling nature of the graphene NEM switches. We show the possibility of achieving a pull-in voltage as low as 2 V for a 1.5-μm-long and 3-nm-thick nanocrystalline graphene beam NEM switch. In order to study the mechanical reliability of the graphene NEM switches, von Mises stress analysis is carried out. This analysis shows that a thinner graphene beam results in a lower von Mises stress. Moreover, a strong electrostatic force at the beam edges leads to a mechanical deflection at the edges larger than that around the center of the beam, which is consistent with the von Mises stress analysis.

  13. Laboratory and 3-D-distinct element analysis of failure mechanism of slope under external surcharge

    N. Li


    Full Text Available Landslide is a major disaster resulting in considerable loss of human lives and property damages in hilly terrain in Hong Kong, China and many other countries. The factor of safety and the critical slip surface for slope stabilization are the main considerations for slope stability analysis in the past, while the detailed post-failure conditions of the slopes have not been considered in sufficient details. There are however increasing interest on the consequences after the initiation of failure which includes the development and propagation of the failure surfaces, the amount of failed mass and runoff and the affected region. To assess the development of slope failure in more details and to consider the potential danger of slopes after failure has initiated, the slope stability problem under external surcharge is analyzed by the distinct element method (DEM and laboratory model test in the present research. A more refined study about the development of failure, microcosmic failure mechanism and the post-failure mechanism of slope will be carried out. The numerical modeling method and the various findings from the present work can provide an alternate method of analysis of slope failure which can give additional information not available from the classical methods of analysis.

  14. Consideration of reinforcement mechanism in the short fiber mixing granular materials by granular element simulations

    Mori, Kentaro; Kaneko, Kenji; Hashizume, Yutaka


    The short fiber mixing method is well known as one of the method to improve the strength of gran- ular soils in geotechnical engineering. Mechanical properties of the short fiber mixing granular materials are influenced by many factors, such as the mixture ratio of the short fiber, the material of short fiber, the length, and the orientation. In particular, the mixture ratio of the short fibers is very important in mixture design. In the past study, we understood that the strength is reduced by too much short fiber mixing by a series of tri-axial compression experiments. Namely, there is "optimum mixture ratio" in the short fiber mixing granular soils. In this study, to consider the mechanism of occurrence of the optimum mixture ratio, we carried out the numerical experiments by granular element method. As the results, we can understand that the strength decrease when too much grain-fiber contact points exist, because a friction coefficient is smaller than the grain-grain contact points.

  15. Supernovae and Gamma-Ray Bursts

    Livio, Mario; Panagia, Nino; Sahu, Kailash


    Participants; Preface; Gamma-ray burst-supernova relation B. Paczynski; Observations of gamma-ray bursts G. Fishman; Fireballs T. Piran; Gamma-ray mechanisms M. Rees; Prompt optical emission from gamma-ray bursts R. Kehoe, C. Akerlof, R. Balsano, S. Barthelmy, J. Bloch, P. Butterworth, D. Casperson, T. Cline, S. Fletcher, F. Frontera, G. Gisler, J. Heise, J. Hills, K. Hurley, B. Lee, S. Marshall, T. McKay, A. Pawl, L. Piro, B. Priedhorsky, J. Szymanski and J. Wren; X-ray afterglows of gamma-ray bursts L. Piro; The first year of optical-IR observations of SN1998bw I. Danziger, T. Augusteijn, J. Brewer, E. Cappellaro, V. Doublier, T. Galama, J. Gonzalez, O. Hainaut, B. Leibundgut, C. Lidman, P. Mazzali, K. Nomoto, F. Patat, J. Spyromilio, M. Turatto, J. Van Paradijs, P. Vreeswijk and J. Walsh; X-ray emission of Supernova 1998bw in the error box of GRB980425 E. Pian; Direct analysis of spectra of type Ic supernovae D. Branch; The interaction of supernovae and gamma-ray bursts with their surroundings R. Chevalier; Magnetars, soft gamma-ray repeaters and gamma-ray bursts A. Harding; Super-luminous supernova remnants Y. -H. Chu, C. -H. Chen and S. -P. Lai; The properties of hypernovae: SNe Ic 1998bw, 1997ef, and SN IIn 1997cy K. Nomoto, P. Mazzali, T. Nakamura, K. Iwanmoto, K. Maeda, T. Suzuki, M. Turatto, I. Danziger and F. Patat; Collapsars, Gamma-Ray Bursts, and Supernovae S. Woosley, A. MacFadyen and A. Heger; Pre-supernova evolution of massive stars N. Panagia and G. Bono; Radio supernovae and GRB 980425 K. Weiler, N. Panagia, R. Sramek, S. Van Dyk, M. Montes and C. Lacey; Models for Ia supernovae and evolutionary effects P. Hoflich and I. Dominguez; Deflagration to detonation A. Khokhlov; Universality in SN Iae and the Phillips relation D. Arnett; Abundances from supernovae F. -K. Thielemann, F. Brachwitz, C. Freiburghaus, S. Rosswog, K. Iwamoto, T. Nakamura, K. Nomoto, H. Umeda, K. Langanke, G. Martinez-Pinedo, D. Dean, W. Hix and M. Strayer; Sne, GRBs, and the

  16. Experimental approach and modelling of the mechanical behaviour of graphite fuel elements subjected to compression pulses

    Forquin, P.


    Among the activities led by the Generation IV International Forum (GIF) relative to the future nuclear systems, the improvement of recycling of fuel elements and their components is a major issue. One of the studied systems by the GIF is the graphite-moderated high-temperature gas cooled reactor (HTGR). The fuel elements are composed of fuel roads half-inch in diameter named compacts. The compacts contain spherical particles made of actinide kernels about 500 m in diameter coated with three layers of carbon and silicon carbide, each about 50 m thick, dispersed in a graphite matrix. Recycling of compacts requires first a separation of triso-particles from the graphite matrix and secondly, the separation of the triso-coating from the kernels. This aim may be achieved by using pulsed currents: the compacts are placed within a cell filled by water and exposed to high voltage between 200 - 500 kV and discharge currents from 10 to 20 kA during short laps of time (about 2 µs) [1-2]. This repeated treatment leads to a progressive fragmentation of the graphite matrix and a disassembly of the compacts. In order to improve understanding of the fragmentation properties of compacts a series of quasi-static and dynamic experiments have been conducted with similar cylindrical samples containing 10% (volume fraction) of SiC particles coated in a graphite matrix. First, quasi-static compression tests have been performed to identify the mechanical behaviour of the material at low strain-rates (Fig.1). The experiments reveal a complex elasto-visco-plastic behaviour before a brittle failure. The mechanical response is characterised by a low yield stress (about 1 MPa), a strong strain-hardening in the loading phase and marked hysteresis-loops during unloading-reloading stages. Brittle failure is observed for axial stress about 13 MPa. In parallel, a series of flexural tests have been performed with the aim to characterise the quasi-static tensile strength of the particulate

  17. Experimental approach and modelling of the mechanical behaviour of graphite fuel elements subjected to compression pulses

    Forquin P.


    Full Text Available Among the activities led by the Generation IV International Forum (GIF relative to the future nuclear systems, the improvement of recycling of fuel elements and their components is a major issue. One of the studied systems by the GIF is the graphite-moderated high-temperature gas cooled reactor (HTGR. The fuel elements are composed of fuel roads half-inch in diameter named compacts. The compacts contain spherical particles made of actinide kernels about 500 m in diameter coated with three layers of carbon and silicon carbide, each about 50 m thick, dispersed in a graphite matrix. Recycling of compacts requires first a separation of triso-particles from the graphite matrix and secondly, the separation of the triso-coating from the kernels. This aim may be achieved by using pulsed currents: the compacts are placed within a cell filled by water and exposed to high voltage between 200 – 500 kV and discharge currents from 10 to 20 kA during short laps of time (about 2 µs [1-2]. This repeated treatment leads to a progressive fragmentation of the graphite matrix and a disassembly of the compacts. In order to improve understanding of the fragmentation properties of compacts a series of quasi-static and dynamic experiments have been conducted with similar cylindrical samples containing 10% (volume fraction of SiC particles coated in a graphite matrix. First, quasi-static compression tests have been performed to identify the mechanical behaviour of the material at low strain-rates (Fig.1. The experiments reveal a complex elasto-visco-plastic behaviour before a brittle failure. The mechanical response is characterised by a low yield stress (about 1 MPa, a strong strain-hardening in the loading phase and marked hysteresis-loops during unloading-reloading stages. Brittle failure is observed for axial stress about 13 MPa. In parallel, a series of flexural tests have been performed with the aim to characterise the quasi-static tensile strength of the

  18. A Retroactive-Burst Framework for Automated Intrusion Response System

    Alireza Shameli-Sendi


    Full Text Available The aim of this paper is to present an adaptive and cost-sensitive model to prevent security intrusions. In most automated intrusion response systems, response selection is performed locally based on current threat without using the knowledge of attacks history. Another challenge is that a group of responses are applied without any feedback mechanism to measure the response effect. We address these problems through retroactive-burst execution of responses and a Response Coordinator (RC mechanism, the main contributions of this work. The retroactive-burst execution consists of several burst executions of responses with, at the end of each burst, a mechanism for measuring the effectiveness of the applied responses by the risk assessment component. The appropriate combination of responses must be considered for each burst execution to mitigate the progress of the attack without necessarily running the next round of responses, because of the impact on legitimate users. In the proposed model, there is a multilevel response mechanism. To indicate which level is appropriate to apply based on the retroactive-burst execution, we get help from a Response Coordinator mechanism. The applied responses can improve the health of Applications, Kernel, Local Services, Network Services, and Physical Status. Based on these indexes, the RC gives a general overview of an attacker’s goal in a distributed environment.

  19. Solar Partial N-burst

    Zong-Jun Ning; Yu-Ying Liu; Qi-Jun Fu; Fu-Ying Xu


    We present a new sub-class of type III solar radio burst at the highfrequencies around 6.0 GHz. In addition to a descending and an ascending branchon the dynamic spectrum, it has an inverted morphology different from the simpletype U-burst. We call it "partial N-burst" because it is interpreted as the knownN-burst minus its first branch. The partial N-burst presented here was detectedamong a reverse slope type III (RS-III) burst group prior to the type V solar radiocontinuum and was simultaneously recorded by two spectrometers at the NationalAstronomical Observatories, Chinese Academy of Sciences (NAOC, 5.20-7.60 GHz)and at Purple Mountain Observatory (PMO, 4.50-7.50 GHz) on 1999 August 25.After the N-burst and M-burst, the partial N-burst is a third piece of evidence for amagnetic mirror effect in solar radio observation, when the same electron is reflectedat a pinched foot of a flare loop.

  20. Gamma-ray burst spectra

    Teegarden, B. J.


    A review of recent results in gamma-ray burst spectroscopy is given. Particular attention is paid to the recent discovery of emission and absorption features in the burst spectra. These lines represent the strongest evidence to date that gamma-ray bursts originate on or near neutron stars. Line parameters give information on the temperature, magnetic field and possibly the gravitational potential of the neutron star. The behavior of the continuum spectrum is also discussed. A remarkably good fit to nearly all bursts is obtained with a thermal-bremsstrahlung-like continuum. Significant evolution is observed of both the continuum and line features within most events.

  1. Simulation and evaluation of rupturable coated capsules by finite element method.

    Yang, Yan; Fang, Jie; Shen, Lian; Shan, Weiguang


    The objective of this study was to simulate and evaluate the burst behavior of rupturable coated capsules by finite element method (FEM). Film and coated capsules were prepared by dip-coating method and their dimensions were determined by stereomicroscope. Mechanical properties of the film were measured by tensile test and used as material properties of FEM models. Swelling pressure was determined by restrained expansion method and applied to the internal surface of FEM models. Water uptake of coated capsules was determined to study the formation of internal pressure. Burst test and in vitro dissolution was used to verify the FEM models, which were used to study and predict the coating burst behavior. Simulated results of coating burst behavior were well agreed with the experiment results. Swelling pressure, material properties and dimensions of coating had influence on the maximum stress. Burst pressure and critical L-HPC content were calculated for burst prediction and formulation optimization. FEM simulation was a feasible way to simulate and evaluate the burst behavior of coated capsules. Copyright © 2017 Elsevier B.V. All rights reserved.

  2. A parallel finite element scheme for thermo-hydro-mechanical (THM) coupled problems in porous media

    Wang, Wenqing; Kosakowski, Georg; Kolditz, Olaf


    Many applied problems in geoscience require knowledge about complex interactions between multiple physical and chemical processes in the sub-surface. As a direct experimental investigation is often not possible, numerical simulation is a common approach. The numerical analysis of coupled thermo-hydro-mechanical (THM) problems is computationally very expensive, and therefore the applicability of existing codes is still limited to simplified problems. In this paper we present a novel implementation of a parallel finite element method (FEM) for the numerical analysis of coupled THM problems in porous media. The computational task of the FEM is partitioned into sub-tasks by a priori domain decomposition. The sub-tasks are assigned to the CPU nodes concurrently. Parallelization is achieved by simultaneously establishing the sub-domain mesh topology, synchronously assembling linear equation systems in sub-domains and obtaining the overall solution with a sub-domain linear solver (parallel BiCGStab method with Jacobi pre-conditioner). The present parallelization method is implemented in an object-oriented way using MPI for inter-processor communication. The parallel code was successfully tested with a 2-D example from the international DECOVALEX benchmarking project. The achieved speed-up for a 3-D extension of the test example on different computers demonstrates the advantage of the present parallel scheme.

  3. Finite element simulation of the gating mechanism of mechanosensitive ion channels

    Bavi, Navid; Qin, Qinghua; Martinac, Boris


    In order to eliminate limitations of existing experimental or computational methods (such as patch-clamp technique or molecular dynamic analysis) a finite element (FE) model for multi length-scale and time-scale investigation on the gating mechanism of mechanosensitive (MS) ion channels has been established. Gating force value (from typical patch clamping values) needed to activate Prokaryotic MS ion channels was applied as tensional force to the FE model of the lipid bilayer. Making use of the FE results, we have discussed the effects of the geometrical and the material properties of the Escherichia coli MscL mechanosensitive ion channel opening in relation to the membrane's Young's modulus (which will vary depending on the cell type or cholesterol density in an artificial membrane surrounding the MscL ion channel). The FE model has shown that when the cell membrane stiffens the required channel activation force increases considerably. This is in agreement with experimental results taken from the literature. In addition, the present study quantifies the relationship between the membrane stress distribution around a `hole' for modeling purposes and the stress concentration in the place transmembrane proteins attached to the hole by applying an appropriate mesh refinement as well as well defining contact condition in these areas.

  4. Human skeletal muscle behavior in vivo: Finite element implementation, experiment, and passive mechanical characterization.

    Clemen, Christof B; Benderoth, Günther E K; Schmidt, Andreas; Hübner, Frank; Vogl, Thomas J; Silber, Gerhard


    In this study, useful methods for active human skeletal muscle material parameter determination are provided. First, a straightforward approach to the implementation of a transversely isotropic hyperelastic continuum mechanical material model in an invariant formulation is presented. This procedure is found to be feasible even if the strain energy is formulated in terms of invariants other than those predetermined by the software's requirements. Next, an appropriate experimental setup for the observation of activation-dependent material behavior, corresponding data acquisition, and evaluation is given. Geometry reconstruction based on magnetic resonance imaging of different deformation states is used to generate realistic, subject-specific finite element models of the upper arm. Using the deterministic SIMPLEX optimization strategy, a convenient quasi-static passive-elastic material characterization is pursued; the results of this approach used to characterize the behavior of human biceps in vivo indicate the feasibility of the illustrated methods to identify active material parameters comprising multiple loading modes. A comparison of a contact simulation incorporating the optimized parameters to a reconstructed deformed geometry of an indented upper arm shows the validity of the obtained results regarding deformation scenarios perpendicular to the effective direction of the nonactivated biceps. However, for a valid, activatable, general-purpose material characterization, the material model needs some modifications as well as a multicriteria optimization of the force-displacement data for different loading modes.

  5. Mechanical blind gap measurement tool for alignment of the JWST Optical Telescope Element

    Liepmann, Till


    This paper describes a novel gap gauge tool that is used to provide an independent check of the James Webb Space Telescope (JWST) Optical Telescope Element (OTE) primary mirror alignment. Making accurate measurements of the mechanical gaps between the OTE mirror segments is needed to verify that the segments were properly aligned relative to each other throughout the integration and test of the 6.6 meter telescope. The gap between the Primary Mirror Segment Assemblies (PMSA) is a sensitive indicator of the relative clocking and decenter. Further, the gap measurements are completely independent of all the other measurements use in the alignment process (e.g. laser trackers and laser radar). The gap measurement is a challenge, however, that required a new approach. Commercial gap measurements tools were investigated; however no suitable solution is available. The challenge of this measurement is due to the required 0.1 mm accuracy, the close spacing of the mirrors segments (approximately 3-9mm), the acute angle between the segment sides (approximately 4 degrees), and the difficult access to the blind gap. Several techniques were considered and tested before selecting the gauge presented here. This paper presents the theory, construction and calibration of the JWST gap gauge that is being used to measure and verify alignment of the OTE primary mirror segments.

  6. Radiative recombination mechanisms in CdTe thin films deposited by elemental vapor transport

    Collins, Shamara [Department of Electrical Engineering, University of South Florida, 4202 East Fowler Ave, Tampa, FL 33620 (United States); Vatavu, Sergiu, E-mail: [Department of Electrical Engineering, University of South Florida, 4202 East Fowler Ave, Tampa, FL 33620 (United States); Faculty of Physics and Engineering, Moldova State University, 60 A. Mateevici str., Chisinau, MD-2009, Republic of Moldova (Moldova, Republic of); Evani, Vamsi; Khan, Md; Bakhshi, Sara; Palekis, Vasilios [Department of Electrical Engineering, University of South Florida, 4202 East Fowler Ave, Tampa, FL 33620 (United States); Rotaru, Corneliu [Faculty of Physics and Engineering, Moldova State University, 60 A. Mateevici str., Chisinau, MD-2009, Republic of Moldova (Moldova, Republic of); Ferekides, Chris [Department of Electrical Engineering, University of South Florida, 4202 East Fowler Ave, Tampa, FL 33620 (United States)


    A photoluminesence (PL) study of the radiative recombination mechanisms for CdTe films deposited under different Cd and Te overpressure by elemental vapor transport is presented. The experiment and analysis have been carried out in the temperature range of 12-130 K. The intensity of the PL laser excitation beam was varied by two orders of magnitude. It has been established that the bands in the 1.47-1.50 eV are determined by transitions involving shallow D and A states and the 1.36x-1.37x eV band is due to band to level transitions. Deep transitions at 1.042 eV and 1.129 eV are due to radiative transitions to levels determined by CdTe native defects. - Highlights: • Photoluminescense (PL) of CdTe thin films is present in the 0.8-1.6 eV spectral region. • High intensity excitonic peaks are among the main radiative paths. • Radiative transitions at 1.36x eV are assisted by dislocations caused levels. • Extremal Cd/Te overpressure ratios enhance PL for 1.497 eV, 1.486 eV, 1.474 eV bands. • PL intensity reaches its max value for the 0.45 and 1.25 Cd/Te overpressure ratios.

  7. Finite Element Model of the Knee for Investigation of Injury Mechanisms: Development and Validation

    Kiapour, Ali; Kiapour, Ata M.; Kaul, Vikas; Quatman, Carmen E.; Wordeman, Samuel C.; Hewett, Timothy E.; Demetropoulos, Constantine K.; Goel, Vijay K.


    Multiple computational models have been developed to study knee biomechanics. However, the majority of these models are mainly validated against a limited range of loading conditions and/or do not include sufficient details of the critical anatomical structures within the joint. Due to the multifactorial dynamic nature of knee injuries, anatomic finite element (FE) models validated against multiple factors under a broad range of loading conditions are necessary. This study presents a validated FE model of the lower extremity with an anatomically accurate representation of the knee joint. The model was validated against tibiofemoral kinematics, ligaments strain/force, and articular cartilage pressure data measured directly from static, quasi-static, and dynamic cadaveric experiments. Strong correlations were observed between model predictions and experimental data (r > 0.8 and p knee joint as well as the complex, nonuniform stress and strain fields that occur in biological soft tissue. Such a model will facilitate the in-depth understanding of a multitude of potential knee injury mechanisms with special emphasis on ACL injury. PMID:24763546

  8. Quantum chemistry investigation on the reaction mechanism of the elemental mercury, chlorine, bromine and ozone system.

    Gao, Zhengyang; Lv, Shaokun; Yang, Weijie; Yang, Pengfei; Ji, Shuo; Meng, Xinxin


    Ab initio calculations were performed to study the quantum chemistry reactions mechanisms among Hg(0), elemental halogen and O3. The geometry of reactions, transition states (TS), intermediates (M) and products were optimized using the MP2 method at the SDD basis function level for Hg, and using 6-311++G (3df, 3pd) for other species. Molecular energies were calculated at QCISD (T) level with zero point energy. Activation energies were calculated along with pre-exponential factors . The reaction rate constants within 298-1800 K were calculated according to transition state theory (TST). The influences of O3 on the reaction of Hg(0) with halogen are discussed. Hg(0) can be oxidized to Hg(1+) by halogen and O3, and halogen and O3 can be arranged in decreasing order as: Br2 > BrO > O3 > Br > Cl, BrCl > HBr > HCl, Br2 > Cl2 according to reaction rate constants. When O3 is presented, Br2, HBr, BrCl, Cl2 and HCl react with O3 and are initially converted to BrO and ClO. O3 is unfavorable for oxidation of Hg(0) by Br2. The mixture of HBr and O3 has better oxidizing Hg(0) performance than HBr and O3. Cl is less effective than Br for oxidation of Hg(0).

  9. Interface mechanics in lower-limb external prosthetics: a review of finite element models.

    Zachariah, S G; Sanders, J E


    The distribution of mechanical stress at the interface between a residual limb and prosthetic socket is an important design consideration in lower-limb prosthetics. Stresses must be distributed so that the amputee is stable and comfortable, while avoiding trauma to the tissues of the residual limb. Numerical estimation of the stresses at the interface through finite element (FE) modeling can potentially provide researchers and prosthetists with a tool to aid in the design of the prosthetic socket. This review addresses FE modeling of interface stresses in lower-limb external prosthetics. The modeling methodologies adopted by analysts are described. Verification of FE estimates of interface stress against experimental data by different analysts is presented and the likely sources of error discussed. While the performance of the models is encouraging, there are definite limitations to all of them, necessitating further improvements. Parametric analysis of the sensitivity of interface stress to model parameters provides a tool to identify model weaknesses and to suggest possible refinements. Parametric analyses by different analysts are also presented and potential refinements discussed. Finally, directions for future work in prosthetic FE modeling are suggested.


    F. Panteleenko


    Full Text Available The paper presents results of investigations on structure and mechanical properties of technological equipment elements made of heat-resistant steels. A scale of chrome and molybdenum steel microstructure degradation based on evaluation of  coagulated carbide size and material mechanical properties (a point from 0-operation without time limits, up to 4-operation prohibition has been proposed in the paper. It has been  established that an analysis of  steel microstructure directly on equipment elements by means of a portable microscope is an efficient express method for evaluation of equipment condition and structures due to control of material structure degradation rate of a diagnosed object.

  11. Short Gamma-Ray Bursts with Extended Emission

    Norris, J. P.; Bonnell, J. T.


    The recent association of several short gamma-ray bursts (GRBs) with early type galaxies with low star formation rate demonstrates that short bursts arise from a different progenitor mechanism than long bursts. However, since the duration distributions of the two classes overlap, membership is not always easily established. The picture is complicated by the occasional presence of softer, extended emission lasting tens of seconds after the initial spike- like emission comprising an otherwise short burst. Using the large BATSE sample with time-tagged event (TTE) data, we show that the fundamental defining characteristic of the short burst class is that the initial spike exhibits negligible spectral evolution at energies above approx. 25 keV. This is behavior is nearly ubiquitous for the 260 bursts with T(sub 90) less than 2s where the BATSE TTE data type completely included the initial spike: Their spectral lags measured between the 25-50 keV and 100-300 energy ranges are consistent with zero in 90-95% of the cases, with most outliers probably representing the tail of the long burst class. We also analyze a small sample of "short" BATSE bursts - those with the most fluent, intense extended emission. The same lack of evolution on the pulse timescale obtains for the extended emission in the brighter bursts where significant measurements can be made. One possible inference is that both emission components may arise in the same region. We also show that the dynamic range in the ratio of peak intensities, spike : extended, is at least approx. l0(exp 3), and that for some bursts, the extended emission is only a factor of 2-5 lower. However, for our whole sample the total counts fluence of the extended component equals or exceeds that in the spike by a factor of several.

  12. Dark Gamma Ray Bursts

    Brdar, Vedran; Liu, Jia


    Many theories of dark matter (DM) predict that DM particles can be captured by stars via scattering on ordinary matter. They subsequently condense into a DM core close to the center of the star and eventually annihilate. In this work, we trace DM capture and annihilation rates throughout the life of a massive star and show that this evolution culminates in an intense annihilation burst coincident with the death of the star in a core collapse supernova. The reason is that, along with the stellar interior, also its DM core heats up and contracts, so that the DM density increases rapidly during the final stages of stellar evolution. We argue that, counterintuitively, the annihilation burst is more intense if DM annihilation is a p-wave process than for s-wave annihilation because in the former case, more DM particles survive until the supernova. If among the DM annihilation products are particles like dark photons that can escape the exploding star and decay to Standard Model particles later, the annihilation bu...

  13. Inverse period-doubling bifurcations determine complex structure of bursting in a one-dimensional non-autonomous map.

    Han, Xiujing; Chen, Zhenyang; Bi, Qinsheng


    We propose a simple one-dimensional non-autonomous map, in which some novel bursting patterns (e.g., "fold/double inverse flip" bursting, "fold/multiple inverse flip" bursting, and "fold/a cascade of inverse flip" bursting) can be observed. Typically, these bursting patterns exhibit complex structures containing a chain of inverse period-doubling bifurcations. The active states related to these bursting can be period-2(n) (n = 1, 2, 3,…) attractors or chaotic attractors, which may evolve to quiescence by a chain of inverse period-doubling bifurcations when the slow excitation decreases through period-doubling bifurcation points of the map. This accounts for the complex inverse period-doubling bifurcation structures observed in bursting patterns. Our findings enrich the possible routes to bursting as well as the underlying mechanisms of bursting.

  14. Arbuscular mycorrhizal fungi in phytoremediation of contaminated areas by trace elements: mechanisms and major benefits of their applications.

    Cabral, Lucélia; Soares, Claúdio Roberto Fonsêca Sousa; Giachini, Admir José; Siqueira, José Oswaldo


    In recent decades, the concentration of trace elements has increased in soil and water, mainly by industrialization and urbanization. Recovery of contaminated areas is generally complex. In that respect, microorganisms can be of vital importance by making significant contributions towards the establishment of plants and the stabilization of impacted areas. Among the available strategies for environmental recovery, bioremediation and phytoremediation outstand. Arbuscular mycorrhizal fungi (AMF) are considered the most important type of mycorrhizae for phytoremediation. AMF have broad occurrence in contaminated soils, and evidences suggest they improve plant tolerance to excess of certain trace elements. In this review, the use of AMF in phytoremediation and mechanisms involved in their trace element tolerance are discussed. Additionally, we present some techniques used to study the retention of trace elements by AMF, as well as a summary of studies showing major benefits of AMF for phytoremediation.

  15. Identifying Type Ia Supernova Mechanisms in Dwarf Spheroidal Galaxies through Analysis of Iron-peak Elemental Abundances

    Guo, Rachel; Xie, Justin Long; Kirby, Evan N.


    Through the fusion of nucleons to produce elements heavier than hydrogen and helium, stellar nucleosynthesis produces most of the elements in the universe. Such is the case in a supernova explosion, which creates most of the elements on the periodic table—including iron-peak elements, atomic numbers 21 through 30—through nucleosynthesis and ejects them into the interstellar medium. In this study, we determine the best theoretical supernova model appropriate for the stars in the dwarf spheroidal galaxies Sculptor, Fornax, Ursa Minor, and Leo II by calculating the abundances of iron-peak elements in these stars. To determine iron-peak elemental abundances, we compare synthesized spectra with observed spectra from medium-resolution spectroscopy and determine the best-fitting spectrum by way of a chi-squared minimization. Through inspecting the relationship between the iron-peak element abundances and the abundance of iron itself and by comparing them to previously hypothesized supernova model theories, we discover that the near-Chandrasekhar mass “n1” model, as predicted by Seitenzahl et al., most accurately represents the trends and patterns within our data, presenting new insight into Type Ia supernovae mechanisms within the Milky Way and beyond.

  16. Study of rare earth element effect on microstructures and mechanical properties of an Al-Cu-Mg-Si cast alloy

    WAN Weiwei; HAN Jianmin; LI Weijing; WANG Jinhua


    The improvements of microstructures and properties of a high strength aluminum cast alloy were studied.The effects of rare earth elements on the microstructures and mechanical properties of the high strength cast alloy Al-Cu-Mg-Si were investigated.The result shows that the addition of rare earth elements can change the microstructures in refining the grain size of the alloy and making the needle-like and laminar eutectic Si to a granular Si.With the increase of the rare earth, the tensile strength and elongation of the alloy increase first and then fall down.The mechanical properties of the alloy will reach the highest value when the content of rare earth elements is about 0.7%.

  17. Planning of designing and installation of mechanical elements at the gear speed reducer on the basis of the parameter technology

    D. Letić


    Full Text Available The development and implementation of the computer methods at project managing in the part of the planning of designing and installation of mechanical elements with the fit (assembly block of the gear speed reducer is significant and at present irreplaceable engineering task if it has been realized by the modern parameter technology. There are multifunction uses of this organized group of activities, beginning from the quick changeability of elements still in the phase of designing and constructing, thanks to the characteristics of their associativity, still to the wide basis of standard elements that are incorporated in the very program package. Meanwhile, these activities are not simple, so their realization has to be planned from the stand - point of time, resource and cost of realization. For the very designing and constructing was used AutoCAD Mechanical, and for the design managing Microsoft Project.

  18. Effect of the additions of carbide-forming elements on the microstructure and mechanical properties of steel shot

    Shchennikova, T. L.; Zalazinskii, G. G.; Leont'ev, L. I.; Rybalko, O. F.


    The effect of the additions of carbide-forming elements (vanadium, titanium, chromium, molybdenum) on the microstructure and mechanical properties of the steel shot produced by the atomization of an iron-carbon melt (0.8% C) by water at a low pressure (0.2 MPa) is studied. The introduction of alloying elements is shown to affect the sizes of the structural constituents that form during the solidification of shot particles and, hence, the mechanical properties (hardness, wear resistance) of the shot. The additions can decrease the grain size in the shot by a factor of 2.5-3. The formation of the MC ( M is a carbide-forming element), VC, TiC, or M 2C (e.g., Mo2C) carbide increases the hardness of the shot material. Chromium and molybdenum form solid solutions with iron and complex (Fe, M)3C carbides.

  19. Short duration gamma ray bursts

    Patrick Das Gupta


    After a short review of gamma ray bursts (GRBs), we discuss the physical implications of strong statistical correlations seen among some of the parameters of short duration bursts (90 < 2 s). Finally, we conclude with a brief sketch of a new unified model for long and short GRBs.

  20. Dynamic finite element knee simulation for evaluation of knee replacement mechanics.

    Baldwin, Mark A; Clary, Chadd W; Fitzpatrick, Clare K; Deacy, James S; Maletsky, Lorin P; Rullkoetter, Paul J


    In vitro pre-clinical testing of total knee replacement (TKR) devices is a necessary step in the evaluation of new implant designs. Whole joint knee simulators, like the Kansas knee simulator (KKS), provide a controlled and repeatable loading environment for comparative evaluation of component designs or surgical alignment under dynamic conditions. Experimental testing, however, is time and cost prohibitive for design-phase evaluation of tens or hundreds of design variations. Experimentally-verified computational models provide an efficient platform for analysis of multiple components, sizes, and alignment conditions. The purpose of the current study was to develop and verify a computational model of a dynamic, whole joint knee simulator. Experimental internal-external and valgus-varus laxity tests, followed by dynamic deep knee bend and gait simulations in the KKS were performed on three cadaveric specimens. Specimen-specific finite element (FE) models of posterior-stabilized TKR were created from magnetic resonance images and CAD geometry. The laxity data was used to optimize mechanical properties of tibiofemoral soft-tissue structures on a specimen-specific basis. Each specimen was subsequently analyzed in a computational model of the experimental KKS, simulating both dynamic activities. The computational model represented all joints and actuators in the experimental setup, including a proportional-integral-derivative (PID) controller to drive quadriceps actuation. The computational model was verified against six degree-of-freedom patellofemoral (PF) and tibiofemoral (TF) kinematics and actuator loading during both deep knee bend and gait activities, with good agreement in trends and magnitudes between model predictions and experimental kinematics; differences were less than 1.8 mm and 2.2° for PF and TF translations and rotations. The whole joint FE simulator described in this study can be applied to investigate a wide range of clinical and research questions.

  1. On the Source of the Systematic Errors in the Quatum Mechanical Calculation of the Superheavy Elements

    Khazan A.


    Full Text Available It is shown that only the hyperbolic law of the Periodic Table of Elements allows the exact calculation for the atomic masses. The reference data of Periods 8 and 9 manifest a systematic error in the computer software applied to such a calculation (this systematic error increases with the number of the elements in the Table.

  2. On the Source of the Systematic Errors in the Quantum Mechanical Calculation of the Superheavy Elements

    Khazan A.


    Full Text Available It is shown that only the hyperbolic law of the Periodic Table of Elements allows the exact calculation for the atomic masses. The reference data of Periods 8 and 9 manifest a systematic error in the computer software applied to such a calculation (this systematic error increases with the number of the elements in the Table.

  3. Short Gamma-Ray Bursts with Extended Emission

    Norris, J P; Bonnell, Jerry T.; Norris, Jay P.


    The recent association of several short gamma-ray bursts (GRBs) with early type galaxies with low star formation rate demonstrates that short bursts arise from a different progenitor mechanism than long bursts. However, since the duration distributions of the two classes overlap, membership is not always easily established. The picture is complicated by the occasional presence of softer, extended emission lasting tens of seconds after the initial spike-like emission. We show that the fundamental defining characteristic of the short burst class is that the initial spike exhibits negligible spectral evolution at energies above ~ 25 keV. This behavior is nearly ubiquitous for the 260 bursts with T90 < 2 s, where the BATSE TTE data completely included the initial spike. The same signature obtains for one HETE-2 and six Swift/BAT short bursts. Analysis of a small sample of "short" BATSE bursts with the most intense extended emission shows that the same lack of evolution on the pulse timescale obtains for the ex...

  4. Bursts de raios gama

    Braga, J.


    Nos últimos anos, graças principalmente aos dados obtidos pelo Compton Gamma-Ray Observatory e pelo satélite ítalo-holandês BeppoSAX, grandes avanços foram obtidos no nosso conhecimento sobre os fascinantes e enigmáticos fenômenos conhecidos por "bursts"de raios gama. Neste trabalho é feita uma revisão sobre a fenomenologia desses misteriosos objetos e são apresentados os desenvolvimentos recentes nessa área palpitante da astrofísica moderna, ressaltando tanto os resultados observacionais obtidos até o momento quanto os modelos teóricos propostos para explixá-los.

  5. Quantum Key Based Burst Confidentiality in Optical Burst Switched Networks

    A. M. Balamurugan


    Full Text Available The optical burst switching (OBS is an emergent result to the technology concern that could achieve a feasible network in future. They are endowed with the ability to meet the bandwidth requirement of those applications that require intensive bandwidth. There are more domains opening up in the OBS that evidently shows their advantages and their capability to face the future network traffic. However, the concept of OBS is still far from perfection facing issues in case of security threat. The transfer of optical switching paradigm to optical burst switching faces serious downfall in the fields of burst aggregation, routing, authentication, dispute resolution, and quality of service (QoS. This paper deals with employing RC4 (stream cipher to encrypt and decrypt bursts thereby ensuring the confidentiality of the burst. Although the use of AES algorithm has already been proposed for the same issue, by contrasting the two algorithms under the parameters of burst encryption and decryption time, end-to-end delay, it was found that RC4 provided better results. This paper looks to provide a better solution for the confidentiality of the burst in OBS networks.

  6. Quantum key based burst confidentiality in optical burst switched networks.

    Balamurugan, A M; Sivasubramanian, A


    The optical burst switching (OBS) is an emergent result to the technology concern that could achieve a feasible network in future. They are endowed with the ability to meet the bandwidth requirement of those applications that require intensive bandwidth. There are more domains opening up in the OBS that evidently shows their advantages and their capability to face the future network traffic. However, the concept of OBS is still far from perfection facing issues in case of security threat. The transfer of optical switching paradigm to optical burst switching faces serious downfall in the fields of burst aggregation, routing, authentication, dispute resolution, and quality of service (QoS). This paper deals with employing RC4 (stream cipher) to encrypt and decrypt bursts thereby ensuring the confidentiality of the burst. Although the use of AES algorithm has already been proposed for the same issue, by contrasting the two algorithms under the parameters of burst encryption and decryption time, end-to-end delay, it was found that RC4 provided better results. This paper looks to provide a better solution for the confidentiality of the burst in OBS networks.

  7. Prediction and control of rock burst of coal seam contacting gas in deep mining

    WANG En-yuan; LIU Xiao-fei; ZHAO En-lai; LIU Zhen-tang


    By analyzing the characteristics and the production mechanism of rock burst that goes with abnormal gas emission in deep coal seams, the essential method of elimi-nating abnormal gas emission by eliminating the occurrence of rock burst or depressing the magnitude of rock burst was considered. The No.237 working face was selected as the typical working face contacting gas in deep mining; aimed at this working face, a sys-tem of rock burst prediction and control for coal seam contacting gas in deep mining was established. This system includes three parts: ① regional prediction of rock burst hazard before mining, ② local prediction of rock burst hazard during mining, and ③ rock burst control.

  8. Transcriptional bursting is intrinsically caused by interplay between RNA polymerases on DNA

    Fujita, Keisuke; Iwaki, Mitsuhiro; Yanagida, Toshio


    Cell-to-cell variability plays a critical role in cellular responses and decision-making in a population, and transcriptional bursting has been broadly studied by experimental and theoretical approaches as the potential source of cell-to-cell variability. Although molecular mechanisms of transcriptional bursting have been proposed, there is little consensus. An unsolved key question is whether transcriptional bursting is intertwined with many transcriptional regulatory factors or is an intrinsic characteristic of RNA polymerase on DNA. Here we design an in vitro single-molecule measurement system to analyse the kinetics of transcriptional bursting. The results indicate that transcriptional bursting is caused by interplay between RNA polymerases on DNA. The kinetics of in vitro transcriptional bursting is quantitatively consistent with the gene-nonspecific kinetics previously observed in noisy gene expression in vivo. Our kinetic analysis based on a cellular automaton model confirms that arrest and rescue by trailing RNA polymerase intrinsically causes transcriptional bursting.

  9. The isotope composition of selenium in chondrites constrains the depletion mechanism of volatile elements in solar system materials

    Vollstaedt, Hauke; Mezger, Klaus; Leya, Ingo


    Solar nebula processes led to a depletion of volatile elements in different chondrite groups when compared to the bulk chemical composition of the solar system deduced from the Sun's photosphere. For moderately-volatile elements, this depletion primarily correlates with the element condensation temperature and is possibly caused by incomplete condensation from a hot solar nebula, evaporative loss from the precursor dust, and/or inherited from the interstellar medium. Element concentrations and interelement ratios of volatile elements do not provide a clear picture about responsible mechanisms. Here, the abundance and stable isotope composition of the moderately- to highly-volatile element Se are investigated in carbonaceous, ordinary, and enstatite chondrites to constrain the mechanism responsible for the depletion of volatile elements in planetary bodies of the inner solar system and to define a δ 82 / 78 Se value for the bulk solar system. The δ 82 / 78 Se of the studied chondrite falls are identical within their measurement uncertainties with a mean of - 0.20 ± 0.26 ‰ (2 s.d., n = 14, relative to NIST SRM 3149) despite Se abundance depletions of up to a factor of 2.5 with respect to the CI group. The absence of resolvable Se isotope fractionation rules out a kinetic Rayleigh-type incomplete condensation of Se from the hot solar nebula or partial kinetic evaporative loss on the precursor material and/or the parent bodies. The Se depletion, if acquired during partial condensation or evaporative loss, therefore must have occurred under near equilibrium conditions to prevent measurable isotope fractionation. Alternatively, the depletion and cooling of the nebula could have occurred simultaneously due to the continuous removal of gas and fine particles by the solar wind accompanied by the quantitative condensation of elements from the pre-depleted gas. In this scenario the condensation of elements does not require equilibrium conditions to avoid isotope

  10. Hybrid-finite-element analysis of some nonlinear and 3-dimensional problems of engineering fracture mechanics

    Atluri, S. N.; Nakagaki, M.; Kathiresan, K.


    In this paper, efficient numerical methods for the analysis of crack-closure effects on fatigue-crack-growth-rates, in plane stress situations, and for the solution of stress-intensity factors for arbitrary shaped surface flaws in pressure vessels, are presented. For the former problem, an elastic-plastic finite element procedure valid for the case of finite deformation gradients is developed and crack growth is simulated by the translation of near-crack-tip elements with embedded plastic singularities. For the latter problem, an embedded-elastic-singularity hybrid finite element method, which leads to a direct evaluation of K-factors, is employed.

  11. Alteration of local adipose tissue trace element homeostasis as a possible mechanism of obesity-related insulin resistance.

    Tinkov, Alexey A; Sinitskii, Anton I; Popova, Elizaveta V; Nemereshina, Olga N; Gatiatulina, Evgenia R; Skalnaya, Margarita G; Skalny, Anatoly V; Nikonorov, Alexandr A


    The mechanisms of association between obesity and the related metabolic disturbances in general and insulin resistance in particular are extensively studied. Taking into account a key role of adipose tissue insulin resistance in the development of systemic obesity-related insulin resistance, the estimation of mechanisms linking increased adiposity and impaired insulin signaling in adipocytes will allow to develop novel prophylactic and therapeutic approaches to treatment of these states. A number of trace elements like chromium, zinc, and vanadium have been shown to take part in insulin signaling via various mechanisms. Taking into account a key role of adipocyte in systemic carbohydrate homeostasis it can be asked if trace element homeostasis in adipose tissue may influence regulatory mechanisms of glucose metabolism. We hypothesize that caloric excess through currently unknown mechanisms results in decreased chromium, vanadium, and zinc content in adipocytes. Decreased content of trace elements in the adipose tissue causes impairment of intra-adipocyte insulin signaling subsequently leading to adipose tissue insulin resistance. The latter significantly contributes to systemic insulin resistance and further metabolic disruption in obesity. It is also possible that decreased adipose tissue trace element content is associated with dysregulation of insulin-sensitizing and proinflammatory adipokines also leading to insulin resistance. We hypothesize that insulin resistance and adipokine dysbalance increase the severity of obesity subsequently aggravating alteration of adipose tissue trace element balance. Single indications of high relative adipose tissue trace element content, decreased Cr, V, and Zn content in obese adipose tissue, and tight association between fat tissue chromium, vanadium, and zinc levels and metabolic parameters in obesity may be useful for hypothesis validation. If our hypothesis will be confirmed by later studies, adipose tissue chromium

  12. Finite element modelling of the mechanics of discrete carbon nanotubes filled with ZnS and comparison with experimental observations

    Monteiro, André O.


    The mechanical response to a uniaxial compressive force of a single carbon nanotube (CNT) filled (or partially-filled) with ZnS has been modelled. A semi-empirical approach based on the finite element method was used whereby modelling outcomes were closely matched to experimental observations. This is the first example of the use of the continuum approach to model the mechanical behaviour of discrete filled CNTs. In contrast to more computationally demanding methods such as density functional theory or molecular dynamics, our approach provides a viable and expedite alternative to model the mechanics of filled multi-walled CNTs. © 2013 Springer Science+Business Media New York.

  13. Influence of Rare Earth Elements on Microstructure and Mechanical Properties of Cast High-Speed Steel Rolls

    Wang Mingjia; Mu Songmei; Sun Feifei; Wang Yan


    The influence of rare earth (RE) elements on the solidification process and eutectic transformation and mechanical properties of the high-V type cast, high-speed steel roll was studied. Test materials with different RE additions were prepared on a horizontal centrifugal casting machine. The solidification process, eutectic structure transformation, carbide morphology, and the elements present, were all investigated by means of differential scanning calorimetry (DSC) and scanning electron microscopy energy dispersive spectrometry (SEM-EDS). The energy produced by crack initiation and crack extension was analyzed using a digital impact test machine. It was found that rare earth elements increased the tensile strength of the steel by inducing crystallization of earlier eutectic γ-Fe during the solidification process, which in turn increased the solidification temperature and thinned the dendritic grains. Rare earth elements with large atomic radius changed the lattice parameters of the MC carbide by forming rare earth carbides. This had the effect of dispersing long-pole MC carbides to provide carbide grains, thereby, reducing the formation of the gross carbide and making more V available, to increase the secondary hardening process and improve the hardness level. The presence of rare earth elements in the steel raised the impact toughness by changing the mechanism of MC carbide formation, thereby increasing the crack initiation energy.

  14. Burst Detector X-Ray IIR



    The Burst Detector X-Ray (BDX) instrument for the Block IIR series of Global Positioning System satellites is described. The BDX instrument can locate and characterize exoatmospheric nuclear detonations by using four sensors consisting of sets of filters over silicon diodes to detect x rays of various energies from the burst. On the BDX-IIR, a fifth sensor with a response spanning those of the other sensors confirms coincidences among the four main channels. The mechanical and electronic features of the BDX-IIR and its sensors are described. The calibrations and the system tests used in flight are presented. The commands for the BDX-IIR are given. The messages sent from the BDX-IIR are described in detail.


    张洪武; 韩炜; 陈金涛; 段庆林


    Two kinds of variational principles for numerical simulation of heat transfer and contact analyses are respectively presented. A finite element model for numerical simulation of the thermal contact problems is developed with a pressure dependent heat transfer constitutive model across the contact surface. The numerical algorithm for the finite element analysis of the thermomechanical contact problems is thus developed. Numerical examples are computed and the results demonstrate the validity of the model and algorithm developed.

  16. Quality Assessment of the Physico-Mechanical and Elemental Composition of Three Pencil Grades and Eraser Types Produced in Nigeria

    K. I. Omoniyi


    Full Text Available The quality assessment of the physical (pH, electrical conductivity, density, writeability, eraseability, mechanical (compression test and break strength and elemental composition of the pencil grades HB, 2B and 3B and eraser types of brand names Ben 10, Tiky 20 and the commonest White eraser in Nigerian primary school (Gummes Co. China was carried out. The diameter of the graphite part increased in the order HB Cr > Cd. Though, the levels of the trace metals and essential elements detected in the school items are below the recommended limits, regulatory measures should be directed towards maintaining the standards of school items.

  17. Three-dimensional finite element analyses of the local mechanical behavior of riveted lap joints

    Iyer, Kaushik Arjunan

    Three-dimensional elastic-plastic finite element models of single and double rivet-row lap joints have been developed to evaluate local distortions and the mechanics of airframe-type 7075-T6 aluminum alloy riveted assemblies. Loading induced distortion features such as the excess assembly compliance, rivet tilt, local in- and out-of-plane slips and stress concentration factors are evaluated as functions of rivet countersinking, rivet material and friction coefficient. Computed features are examined to identify alterations in the proportions of in-plane and out-of-plane load transmission across rivet-panel interfaces and isolate global and lower-order effects present in the complex response of these multi-body assemblies. Analytical procedures are validated by comparing calculated and measured values of excess assembly compliance and local panel bending. Direct out-of-plane load transmission between the rivet heads and panels affects global deformation features such as remote panel bending and local features such as the panel stress concentration factor. The increase in stress concentration due to panel bending is self-limiting owing to decreasing in-plane load bearing with increasing rivet tilt, which is a composite reflection of the basic rivet deformation modes of shear and rotation. Calculations have also been performed to define approximate steady-state fretting fatigue conditions that lead to crack initiation at a panel hole surface in single and double rivet-row assemblies for countersunk and non-countersunk rivets. These account for and isolate effects of interference and clamping forces on fatigue performance by comparing computed circumferential variations of bulk residual stresses, cyclic stress range and mean stress. With interference, a non-countersunk assembly is shown to be as prone to crack initiation as a countersunk assembly. Frictional work due to fretting is evaluated and the physical location of fretting fatigue crack initiation is predicted by

  18. Size limits the formation of liquid jets during bubble bursting.

    Lee, Ji San; Weon, Byung Mook; Park, Su Ji; Je, Jung Ho; Fezzaa, Kamel; Lee, Wah-Keat


    A bubble reaching an air-liquid interface usually bursts and forms a liquid jet. Jetting is relevant to climate and health as it is a source of aerosol droplets from breaking waves. Jetting has been observed for large bubbles with radii of R≫100 μm. However, few studies have been devoted to small bubbles (Rbubbles in sea water. Here we show that jet formation is inhibited by bubble size; a jet is not formed during bursting for bubbles smaller than a critical size. Using ultrafast X-ray and optical imaging methods, we build a phase diagram for jetting and the absence of jetting. Our results demonstrate that jetting in bubble bursting is analogous to pinching-off in liquid coalescence. The coalescence mechanism for bubble bursting may be useful in preventing jet formation in industry and improving climate models concerning aerosol production.

  19. Extracellular calcium modulates persistent sodium current-dependent burst-firing in hippocampal pyramidal neurons.

    Su, H; Alroy, G; Kirson, E D; Yaari, Y


    The generation of high-frequency spike bursts ("complex spikes"), either spontaneously or in response to depolarizing stimuli applied to the soma, is a notable feature in intracellular recordings from hippocampal CA1 pyramidal cells (PCs) in vivo. There is compelling evidence that the bursts are intrinsically generated by summation of large spike afterdepolarizations (ADPs). Using intracellular recordings in adult rat hippocampal slices, we show that intrinsic burst-firing in CA1 PCs is strongly dependent on the extracellular concentration of Ca(2+) ([Ca(2+)](o)). Thus, lowering [Ca(2+)](o) (by equimolar substitution with Mn(2+) or Mg(2+)) induced intrinsic bursting in nonbursters, whereas raising [Ca(2+)](o) suppressed intrinsic bursting in native bursters. The induction of intrinsic bursting by low [Ca(2+)](o) was associated with enlargement of the spike ADP. Low [Ca(2+)](o)-induced intrinsic bursts and their underlying ADPs were suppressed by drugs that reduce the persistent Na(+) current (I(NaP)), indicating that this current mediates the slow burst depolarization. Blocking Ca(2+)-activated K(+) currents with extracellular Ni(2+) or intracellular chelation of Ca(2+) did not induce intrinsic bursting. This and other evidence suggest that lowering [Ca(2+)](o) may induce intrinsic bursting by augmenting I(NaP). Because repetitive neuronal activity in the hippocampus is associated with marked decreases in [Ca(2+)](o), the regulation of intrinsic bursting by extracellular Ca(2+) may provide a mechanism for preferential recruitment of this firing mode during certain forms of hippocampal activation.

  20. The GLAST Burst Monitor (GBM)

    Lichti, G. G.; Briggs, M.S.; Diehl, R.; Fishman, G.; Georgii, R.; Kippen, R. M.; Kouveliotou, C.; Meegan, C.; Paciesas, W.; Preece, R.; Schoenfelder, V.; von Kienlin, A.


    The selection of the GLAST burst monitor (GBM) by NASA will allow the investigation of the relation between the keV and the MeV-GeV emission from gamma-ray bursts. The GBM consists of 12 NaI and 2 BGO crystals allowing a continuous measurement of the energy spectra of gamma-ray bursts from ~5 keV to \\~30 MeV. One feature of the GBM is its high time resolution for time-resolved gamma-ray spectroscopy. Moreover the arrangement of the NaI crystals allows a rapid on-board location (

  1. Concept for LEU Burst Reactor

    Klein, Steven Karl [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Kimpland, Robert Herbert [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)


    Design and performance of a proposed LEU burst reactor are sketched. Salient conclusions reached are the following: size would be ~1,500 kg or greater, depending on the size of the central cavity; internal stresses during burst require split rings for relief; the reactor would likely require multiple control and safety rods for fine control; the energy spectrum would be comparable to that of HEU machines; and burst yields and steady-state power levels will be significantly greater in an LEU reactor.

  2. A mixed Eulerian-Lagrangian finite element method for simulation of thermo-mechanical forming processes

    Huetink, J.; Vanderlugt, J.


    A mixed Eulerian-Lagrangian finite element method is developed by which nodal point locations can be adapted independently from the actual material displacements. Numerical difficulties due to large element distortions, as many occur when the updated Lagrange method is applied, can be avoided by this method. Movement of (free) surfaces can be taken into account by adapting nodal surface points in a way that they remain on the surface. Hardening and other deformation path dependent properties are determined by incremental treatment of convective terms. A local and a weighed global smoothing procedure is introduced in order to avoid numerical instabilities. The method has been applied to simulations of an upsetting process, a wire drawing process and a cold rolling process. In the simulation of the rolling process, both workpiece and roll are simultaneously analyzed in order to predict the flattening of the roll. Special contact-slip elements are developed for the tool-workpiece interface.

  3. Slip as the basic mechanism for formation of deformation relief structural elements

    Lychagin, D. V.; Alfyorova, E. A.


    The experimental results of investigation of the nickel single crystal surface morphology after compression deformation are presented. The quasi-periodic character of the deformation profile, common for shear deformation of different types of relief structural elements, is found. It is demonstrated that the morphological manifestation of these structural elements is determined by local shear systems along octahedral planes. The regularities of the deformation structure in these regions defining the material extrusion and intrusion regions and the specific features of disorientation accumulation are established. If reorientation of local regions takes part in the relief element formation, along with octahedral slip, much stronger growth of the surface area is observed. The possibility of application of two-dimensional and three-dimensional surface roughness parameters for description of deformation relief is considered.

  4. Influence of Alloying Elements Corrosion Resistance of Cold on Mechanical Properties and Rolled C-Mn-Si TRIP Steels

    ZHANG Ling-yun; WU Di; LI Zhuang


    The rust layer plays an important role in the corrosion of steel in chlorinated environments. Salt spray, po- tentiodynamic polarization curve and tensile test were conducted in laboratory for the specimens after two-stage heat treatment. The influence of the alloying elements on mechanical properties and corrosion resistance of three kinds of steels was investigated by observing the microstructure and the morphologies of rust layer. The results show that the highest value (29%) of total elongation for steel A is obtained. The mechanical property of the specimen for steel C exhibits best strength ductility balance (21 384 MPa ·%) because of the presence of the multiphase microstructures after a two-stage heat treatment and the addition of the alloying elements. The corrosion products are known to be a complex mixture of Fe3O4 , Fe2O3 and α-FeOOH for steel C. The presence of the alloying elements results in the for mation of compact and dense rust layers in steel B and C. Passive film protects the substrate of TRIP (transformation induced plasticity) steel containing a complex mix of multiphase. Superior corrosion performance is exhibited for steel C with low alloying contents due to the enrichment of alloying elements within the rust layers.

  5. The influence of selected elements upon mechanical properties of ductile iron EN-GJS-500-7

    M. S. Soiński


    Full Text Available On the basis of chemical composition and mechanical properties analyses of EN-GJS-500-7 spheroidal graphite cast iron (as per PN-EN1563 standard, an attempt to determine the relations between the changes in the contents of elements included in alloy (such as: C, Si, Mn, P, S, Cr, Ni, Mo, Cu, Mg, and its tensile strength (Rm, proof stress (Rp0,2, elongation (A5 and hardness (HB, has been made. Cast iron subjected to the tests came from 291 heats, conducted in one of the domestic foundries. Cast iron was melted in medium-frequency induction furnace, spheroidized with bell method and modified with “in-stream” method.It results from conducted calculations that in a number of cases even small changes of the elements contents lead to statistically significant increases or decreases in examined mechanical properties of cast iron.

  6. Effects of Deep Cryogenic Treatment on Wear Mechanisms and Microthermal Expansion for the Material of Drive Elements

    Yuh-Ping Chang


    Full Text Available By the composite heat treatments, the strength and the surface hardness of the materials of drive elements can be improved. Moreover, the high accurate and capable machines can be obtained. For the numerous composite heat treatments, the deep cryogenic treatment has been used widely for the purpose of low thermal expansion in the industry. Therefore, this paper is further to investigate the low friction, wear resistance, and low thermal expansion for the carburizing steels of drive elements with deep cryogenic treatment. According to the experimental results, martensitic transformation occurred after the deep cryogenic treatment. The effects of deep cryogenic treatment on wear mechanisms are significant. The shape of wear particles changes from slip tongue to smooth stratification. Moreover, the surface magnetization is smaller for the case of Carburizing-Deep cryogenic treatment. Hence, the wear mechanism becomes simple. Besides, the thermal expansion is significantly smaller for the case of Carburizing-Deep cryogenic treatment.

  7. Numerical simulation of mechanical deformation of semi-solid material using a level-set based finite element method

    Sun, Zhidan; Bernacki, Marc; Logé, Roland; Gu, Guochao


    In this work, a level-set based finite element method was used to numerically evaluate the mechanical behavior in a small deformation range of semi-solid materials with different microstructure configurations. For this purpose, a finite element model of the semi-solid phase was built based on Voronoï diagram. Interfaces between the solid and the liquid phases were implicitly described by level-set functions coupled to an anisotropic meshing technique. The liquid phase was considered as a Newtonian fluid, whereas the behavior of the solid phase was described by a viscoplastic law. Simulations were performed to study the effect of different parameters such as solid phase fraction and solid bridging. Results show that the macroscopic mechanical behavior of semi-solid material strongly depends on the solid fraction and the local microstructure which play important roles in the formation of hot tearing. These results could provide valuable information for the processing of semi-solid materials.

  8. 30 CFR 57.3461 - Rock bursts.


    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Rock bursts. 57.3461 Section 57.3461 Mineral...-Underground Only § 57.3461 Rock bursts. (a) Operators of mines which have experienced a rock burst shall— (1) Within twenty four hours report to the nearest MSHA office each rock burst which: (i) Causes persons...

  9. ESA's X-ray space telescope proves supernovae can cause mysterious gamma-ray bursts


    By analysing the afterglow of the gamma-ray burst in the X-ray light, scientists produced the first ever evidence of the presence of chemical elements which were the unmistakable remnants of a supernova explosion which had occurred just a few days before. "We can now confidently say that the death of a massive star, a supernova, was the cause of a gamma-ray burst. However we still don't know exactly how and why these bursts, the most energetic phenomena in the Universe, are triggered," says ESA astronomer Norbert Schartel, a co-author of the original paper, published today in Nature. Gamma-ray bursts were first discovered in 1967 by chance, when satellites designed to look for violations of the Nuclear Test Ban Treaty detected strong gamma-ray emissions coming from sources not in the vicinity of Earth, but from outer space. They have been a mystery ever since. They occur as often as several times a day but last for no longer than a couple of minutes, and there is no way to predict when or where the next burst will occur. Consequently they are very difficult to study. For three decades it was not even known whether the explosions were close, in our own Milky Way galaxy, or far away in distant galaxies. But astronomers set up an 'alert system'. This allows them to see the 'afterglow' of the burst before it fades away, by quickly aiming their telescopes at the precise location in the sky shortly after a detector triggers the alert. It is now clear that the bursts occur in galaxies millions of light-years away. The longest burst Technically called 'GRB 011211', it was first detected on 11 December 2001 at 19:09:21 (Universal Time), by the Italian-Dutch satellite BeppoSAX. The burst lasted for 270 seconds - the longest one observed by the satellite. A few hours afterwards, when a first analysis confirmed that a burst had indeed been registered, the BeppoSAX team alerted the rest of the astronomical community. ESA's XMM-Newton arrived on the scene 11 hours after the

  10. Dihydroxyoctadecamonoenoate esters inhibit the neutrophil respiratory burst

    David Alan Thompson; Bruce D Hammock


    The leukotoxins [9(10)- and 12(13)-EpOME] are produced by activated inflammatory leukocytes such as neutrophils. High EpOME levels are observed in disorders such as acute respiratory distress syndrome and in patients with extensive burns. Although the physiological significance of the EpOMEs remains poorly understood, in some systems, the EpOMEs act as a protoxin, with their corresponding epoxide hydrolase metabolites, 9,10- and 12,13-DiHOME, specifically exerting toxicity. Both the EpOMEs and the DiHOMEs were also recently shown to have neutrophil chemotactic activity. We evaluated whether the neutrophil respiratory burst, a surge of oxidant production thought to play an important role in limiting certain bacterial and fungal infections, is modulated by members of the EpOME metabolic pathway. We present evidence that the DiHOMEs suppress the neutrophil respiratory burst by a mechanism distinct from that of respiratory burst inhibitors such as cyclosporin H or lipoxin A4, which inhibit multiple aspects of neutrophil activation.

  11. Investigation of wrinkling failure mechanics in metal spinning by Box-Behnken design of experiments using finite element method

    Watson, M.; Van Long, H.; Lu, B


    An investigation into material wrinkling failure mechanics of conventional metal spinning and the effects of process parameters and material properties are presented in this paper. By developing finite element (FE) models using the Box-Behnken design of experiments, the effects of six key process and material parameters on the start of material wrinkling have been investigated. These key factors include roller feed per pass, feed rate, blank thickness, tool path profile, material Young’s modu...

  12. Mechanisms involved in carbachol-induced Ca2+ sensitization of contractile elements in rat proximal and distal colon

    Takeuchi, Tadayoshi; Kushida, Masahiko; Hirayama, Nobue; Kitayama, Muneyoshi; Fujita, Akikazu; Hata, Fumiaki


    Mechanisms involved in Ca2+ sensitization of contractile elements induced by the activation of muscarinic receptors in membrane-permeabilized preparations of the rat proximal and distal colon were studied.In α-toxin-permeabilized preparations from the rat proximal and distal colon, Ca2+ induced a rapid phasic and subsequent tonic component. After Ca2+-induced contraction reached a plateau, guanosine 5′-triphosphate (GTP) and carbachol (CCh) in the presence of GTP further contracted preparatio...

  13. Disinhibition Bursting of Dopaminergic Neurons

    Collin J Lobb


    Full Text Available Substantia nigra pars compacta (SNpc dopaminergic neurons receive strong tonic inputs from GABAergic neurons in the substantia nigra pars reticulata (SNpr and globus pallidus (GP, and glutamatergic neurons in the subthalamic nucleus. The presence of these tonic inputs raises the possibility that phasic disinhibition may trigger phasic bursts in dopaminergic neurons. We first applied constant NMDA and GABAA conductances onto a two-compartment single cell model of the dopaminergic neuron (Kuznetsov et al., 2006. The model exhibited disinhibition bursting upon stepwise removal of inhibition. A further bifurcation analysis suggests that disinhibition may be more robust than excitation alone in that for most levels of NMDA conductance, the cell remains capable of bursting even after a complete removal of inhibition, whereas too much excitatory input will drive the cell into depolarization block. To investigate the network dynamics of disinhibition, we used a modified version of an integrate-and-fire based model of the basal ganglia (Humphries et al., 2006. Synaptic activity generated in the network was delivered to the two-compartment single cell dopaminergic neuron. Phasic activation of the D1-expressing medium spiny neurons in the striatum (D1STR produced disinhibition bursts in dopaminergic neurons through the direct pathway (D1STR to SNpr to SNpc. Anatomical studies have shown that D1STR neurons have collaterals that terminate in GP. Adding these collaterals to the model, we found that striatal activation increased the intra-burst firing frequency of the disinhibition burst as the weight of this connection was increased. Our studies suggest that striatal activation is a robust means by which disinhibition bursts can be generated by SNpc dopaminergic neurons, and that recruitment of the indirect pathway via collaterals may enhance disinhibition bursting.

  14. Study of the Internal Mechanical response of an asphalt mixture by 3-D Discrete Element Modeling

    Feng, Huan; Pettinari, Matteo; Hofko, Bernhard


    In this paper the viscoelastic behavior of asphalt mixture was investigated by employing a three-dimensional Discrete Element Method (DEM). The cylinder model was filled with cubic array of spheres with a specified radius, and was considered as a whole mixture with uniform contact properties for ...

  15. Thermal mechanically coupled finite element analysis in metal-forming processes

    Lugt, van der J.; Huetink, J.


    A combined Eulerian-Lagrangian finite element formulation is presented for the analysis of metal-forming, coupled with thermal effects. The procedure developed involves incrementally solving a coupled set of equations for both the displacement and the temperature. The material properties may be temp

  16. A possible mechanism of origin of heavy elements in the solar system

    Tito, E. P.; V. I. Pavlov


    We advance a hypothesis that a collision of a neutron-rich compact object (NRCO) with a massive dense object of the early solar system was responsible for the heavy element enrichment of the system and for the formation of the terrestrial planets.

  17. Element uptake, accumulation, and resorption in leaves of mangrove species with different mechanisms of salt regulation

    E. Medina; W. Fernandez; F. Barboza


    Element uptake from substrate and resorption capacity of nutrients before leaf shedding are frequently species-specific and difficult to determine in natural settings. We sampled populations of Rhizophora mangle (salt-excluding species) and Laguncularia racemosa (salt-secreting species) in a coastal lagoon in the upper section of the Maracaibo strait in western...

  18. Thermal mechanically coupled finite element analysis in metal-forming processes

    van der Lugt, J.; Huetink, Han


    A combined Eulerian-Lagrangian finite element formulation is presented for the analysis of metal-forming, coupled with thermal effects. The procedure developed involves incrementally solving a coupled set of equations for both the displacement and the temperature. The material properties may be

  19. Stress recovery techniques for natural element method in 2-D solid mechanics

    Cho, Jin Rae [Dept. of Naval Architecture and Ocean Engineering, Hongik University, Sejong (Korea, Republic of)


    This paper is concerned with the stress recovery for the natural element method in which the problem domain is discretized with Delaunay triangles and the structural behavior is approximated with Laplace interpolation functions. Basically, the global and local patch recovery techniques based on the L2-projection method are adopted. For the local patch recovery, the local element patches are defined by the supports of each Laplace interpolation function. For the comparison purpose, the local stress recovery is also performed using Lagrange-type basis functions that are used for 3- and 6-node triangular elements. The stresses that are recovered by the present global and local recovery techniques are compared each other and compared with the available analytic solution, in terms of their spatial distributions and the convergence rates. As well, the dependence of the recovered stress field on the type of test basis functions that are used forbnov-Galerkin (BG) and Petrov-Galerkin (PG) natural element methods is also investigated.

  20. Off-diagonal elements of the DeWitt expansion from the quantum mechanical path integral

    Dilkes, F A


    The DeWitt expansion of the matrix element M_{xy} = , (p=-i\\partial) in powers of t can be made in a number of ways. For x=y (the case of interest when doing one-loop calculations) numerous approaches have been employed to determine this expansion to very high order; when x \

  1. Gamma-ray burst models.

    King, Andrew


    I consider various possibilities for making gamma-ray bursts, particularly from close binaries. In addition to the much-studied neutron star+neutron star and black hole+neutron star cases usually considered good candidates for short-duration bursts, there are also other possibilities. In particular, neutron star+massive white dwarf has several desirable features. These systems are likely to produce long-duration gamma-ray bursts (GRBs), in some cases definitely without an accompanying supernova, as observed recently. This class of burst would have a strong correlation with star formation and occur close to the host galaxy. However, rare members of the class need not be near star-forming regions and could have any type of host galaxy. Thus, a long-duration burst far from any star-forming region would also be a signature of this class. Estimates based on the existence of a known progenitor suggest that this type of GRB may be quite common, in agreement with the fact that the absence of a supernova can only be established in nearby bursts.

  2. Extending Mechanical Construction Kits to Incorporate Passive and Compliant Elements for Educational Robotics

    Assaf, Dorit; Larsen, Jørgen Christian; Reichardt, Markus


    artificial intelligence and biomechanics to students with different backgrounds. The robots we use both for research and education are usually built incorporating compliant materials as well as passive dynamics. These kind of properties are often not available in classical robot kits or mechanical...... and mechanical construction kits we describe interface solutions between several kits. Further we show some solutions to incorporate compliant materials and passive dynamics to traditional mechanical construction kits by using cheap and widely available materials....

  3. Damage Model of Brittle Coal-Rock and Damage Energy Index of Rock Burst

    尹光志; 张东明; 魏作安; 李东伟


    Based on the mechanical experiment of brittle coal-rock and the damage mechanical theory, a damage model was established. Coal-Rock damage mechanical characteristic was researched. Furthermore, interior energy transformation mechanism of rock was analyzed from the point of view of damage mechanics and damage energy release rate of brittle coal rock was derived. By analyzing the energy transformation of rock burst, a new conception, damage energy index of rock burst, was put forward. The condition of rock burst was also established.

  4. Do Gamma-Ray Burst Sources Repeat?

    Meegan, Charles A.; Hartmann, Dieter H.; Brainerd, J. J.; Briggs, Michael S.; Paciesas, William S.; Pendleton, Geoffrey; Kouveliotou, Chryssa; Fishman, Gerald; Blumenthal, George; Brock, Martin


    The demonstration of repeated gamma-ray bursts from an individual source would severely constrain burst source models. Recent reports (Quashnock and Lamb 1993; Wang and Lingenfelter 1993) of evidence for repetition in the first BATSE burst catalog have generated renewed interest in this issue. Here, we analyze the angular distribution of 585 bursts of the second BATSE catalog (Meegan et al. 1994). We search for evidence of burst recurrence using the nearest and farthest neighbor statistic and...

  5. Detection of bursts and pauses in spike trains.

    Ko, D; Wilson, C J; Lobb, C J; Paladini, C A


    Midbrain dopaminergic neurons in vivo exhibit a wide range of firing patterns. They normally fire constantly at a low rate, and speed up, firing a phasic burst when reward exceeds prediction, or pause when an expected reward does not occur. Therefore, the detection of bursts and pauses from spike train data is a critical problem when studying the role of phasic dopamine (DA) in reward related learning, and other DA dependent behaviors. However, few statistical methods have been developed that can identify bursts and pauses simultaneously. We propose a new statistical method, the Robust Gaussian Surprise (RGS) method, which performs an exhaustive search of bursts and pauses in spike trains simultaneously. We found that the RGS method is adaptable to various patterns of spike trains recorded in vivo, and is not influenced by baseline firing rate, making it applicable to all in vivo spike trains where baseline firing rates vary over time. We compare the performance of the RGS method to other methods of detecting bursts, such as the Poisson Surprise (PS), Rank Surprise (RS), and Template methods. Analysis of data using the RGS method reveals potential mechanisms underlying how bursts and pauses are controlled in DA neurons.

  6. A biomechanical study of three kinds of internal fixation methods in the treatment of lumbar burst fracture based on a finite element method%三维有限元模型分析3种内固定方式治疗严重腰椎不稳定型骨折的生物力学特点

    农鲁明; 周栋; 徐南伟


    背景:严重腰椎不稳定型骨折的内固定修复方法未形成统一的观点.目的:应用三维有限元模型对比分析不同内固定方式治疗严重腰椎不稳定型骨折的生物力学性能.方法:选取1个健康成年志愿者,用CT图像和Mimics软件建立T12~L2椎体三维模型,模拟L1椎体爆裂性骨折,并分别模拟后路减压短节段椎弓根钉固定、前路减压钛网置入内固定和后路减压内固定+前路椎体次全切除钛网置入内固定3种治疗方法.将模型导入到有限元分析软件Abaqus,施加约束和载荷分别加载260 N压力和10 N?m转矩,模拟3种模型在不同工况下的椎体位移、应力传导情况,以及前后路固定器械的受力情况.结果与结论:从椎体位移分布情况来看,前后联合内固定方式下的位移要较其他两种内固定方式小.从应力分布情况来看,前后联合内固定方式更加符合载荷分布原则.从生物力学角度来看,前后联合内固定方式优于其他两种内固定方式.%BACKGROUND: No reports have been found about comparative study among three different methods to treat lumbar burst fracture th rough finite element model, which leads to the different ideas of treatment.OBJECTIVE: To introduce and evaluate the biomechanical features of different internal fixation for treatment of lumbar burst fractu re based on a three-dimensional finite element model.METHODS: A youth volunteer without chronic low back pain and trauma of lumbar was chosen. The CT data were obtained by DICOM format. We used Mimics software to build a three-dimensional finite element model to mimic the fracture of L1 burst fracture , then three different approaches of posterior decompression internal fixation , anterior decompression combined with titanium mush im plantation internal fixation and posterior decompression combined with anterior reconstruction internal fixation were performed by the three-dimensional finite element model. These three

  7. A comparison of the jaw mechanics in hadrosaurid and ceratopsid dinosaurs using finite element analysis.

    Bell, Phil R; Snively, Eric; Shychoski, Lara


    Hadrosaurid and ceratopsid dentaries display traits that suggest divergent functions toward broadly similar diets of fibrous plants. Computed tomographic scans of dentaries of a lambeosaurine and a centrosaurine (Centrosaurus aptertus) were used to compare feeding function of these animals using finite element analysis (FEA). In the hadrosaur, mediolateral expansion of the dentary and elongation of the coronoid process of the surangular were optimally developed to withstand torsion associated with transverse-isognathous jaw occlusion. FEA results strongly suggest longitudinal rotation of the hadrosaurid mandible. Mediolaterally compressed mandibles and FEA stress for the ceratopsid are in compliance with purely isognathous jaw adduction, although palinal retraction during the powerstroke cannot be ruled out. The ceratopsid dentary is further reinforced by a longitudinal ridge on the lateral surface of that element. Surface texture indicating Sharpey's fibers within the ceratopsid coronoid process suggests greater bite force than in lambeosaurines. These findings corroborate previous interpretations and suggest complementary or alternative kinematics to maxillary pleurokinesis in hadrosaurs.

  8. A comparison of classical mechanics models and finite element simulation of elastically tailored wing boxes

    Rehfield, Lawrence W.; Pickings, Richard D.; Chang, Stephen; Holl, Michael


    Structural tailoring concepts were developed to create wings with elastically produced camber for the purpose of increasing lift during takeoff conditions. Simple models based upon enhancements to the thin walled composite beam theory of Rehfield were developed to investigate prospects for elastic tailoring of the chordwise deformation of wing structures. The purpose here is to provide a comparison of the theoretical results with a finite element model for the bending method of producing camber. Finite element correlation studies were completed for two cases: a bonded unstiffened structural box, and a bolted unstiffened structural box. Results from these studies show an error of less than one percent for the bonded case and less than six percent for the bolted case in predicting camber curvature for the structural box. Examination of the results shows that the theory is very accurate for the cases studied and will provide an excellent basis for conducting further tailoring studies.

  9. Explicit mixed strain-displacement finite element for dynamic geometrically non-linear solid mechanics

    Lafontaine, N. M.; Rossi, R.; Cervera, M.; Chiumenti, M.


    Low-order finite elements face inherent limitations related to their poor convergence properties. Such difficulties typically manifest as mesh-dependent or excessively stiff behaviour when dealing with complex problems. A recent proposal to address such limitations is the adoption of mixed displacement-strain technologies which were shown to satisfactorily address both problems. Unfortunately, although appealing, the use of such element technology puts a large burden on the linear algebra, as the solution of larger linear systems is needed. In this paper, the use of an explicit time integration scheme for the solution of the mixed strain-displacement problem is explored as an alternative. An algorithm is devised to allow the effective time integration of the mixed problem. The developed method retains second order accuracy in time and is competitive in terms of computational cost with the standard irreducible formulation.

  10. [Dislocation of the closing element of the disk mechanical graft at aortic valve replacement].

    Korostelev, A N; Kuntsevich, G I; Zotikov, A E; Chernyak, B B; Il'ina, M V; Ter-Khachaturova, I E; Solopova, G V


    Presented herein is the first case of dislocation of the closing element of the artificial low-profile aortic valve to the abdominal aorta, which happened during replacement. Toward completion of extracorporeal circulation a 37-year-old man showed the signs of aortic insufficiency because of dislocation of the closing element. After resumption of extracorporeal circulation repeated replacement was accomplished. To detect the site of graft cusp embolism, transesophageal echocardiography and duplex scanning of the abdominal aorta were employed. On the 18th day following the first intervention the patient developed thromboembolism to the distal arterial bed. Emergency thrombectomy from the arteries of the right lower extremity was performed and a foreign body was removed from the abdominal aorta, using left-sided thoracophrenolumbotomy. The patient was discharged from the clinic in a satisfactory condition.

  11. Dynamic characterization of hysteresis elements in mechanical systems. I. Theoretical analysis

    Al-Bender, F.; Symens, W.


    The pre-sliding-pre-rolling phase of friction behavior is dominated by rate-independent hysteresis. Many machine elements in common engineering use exhibit, therefore, the characteristic of "hysteresis springs," for small displacements at least. Plain and rolling element bearings that are widely used in motion guidance of machine tools are typical examples. While the presence of a hysteresis element may mark the character of the resulting dynamics, little is to be found about this topic in the literature. The study of the nonlinear dynamics caused by such elements becomes imperative if we wish to achieve accurate control of such machines. In this Part I of the investigation, we examine a single-degree-of-freedom mass-hysteresis-spring system and show that, while the free response case is amenable to an exact solution, the more important case of forced response has no closed form solution and requires other methods of treatment. We consider harmonic-balance analysis methods (which are common analysis tools in engineering) suitable for frequency-domain treatment, in particular the approximate describing function (DF) method, and compare those results with "exact" numerical simulations. The DF method yields basically a linear equation with amplitude-dependent modal parameters. We find that agreement in the frequency response function, between DF and exact solution, is good for small excitation amplitudes and for very large amplitudes. Intermediate values, however, show high sensitivity to amplitude variations and, consequently, no regular solution is obtainable by either approach. This appears to be an inherent property of the system pointing to the need for developing further analysis methods. Experimental verification of the analysis outlined in this Part I is given in Part II of the paper.

  12. Main formulations of the finite element method for the problems of structural mechanics. Part 3

    Ignat’ev Aleksandr Vladimirovich


    Full Text Available In this paper the author offers is the classification of the formulae of Finite Element Method. This classification help to orient in a huge number of published articles, as well as those to be published, which are dedicated to the problem of enhancing the efficiency of the most commonly used method. The third part of the article considers the variation formulations of FEM and the energy principles lying in the basis of it. If compared to the direct method, which is applied only to finite elements of a simple geometrical type, the variation formulations of FEM are applicable to the elements of any type. All the variation methods can be conventionally divided into two groups. The methods of the first group are based on the principle of energy functional stationarity - a potential system energy, additional energy or on the basis of these energies, which means the full energy. The methods of the second group are based on the variants of mathematical methods of weighted residuals for solving the differential equations, which in some cases can be handled according to the principle of possible displacements or extreme energy principles. The most widely used and multipurpose is the approach based on the use of energy principles coming from the energy conservation law: principle of possible changes in stress state, principle of possible change in stress-strain state.

  13. Main formulations of the finite element method for the problems of structural mechanics. Part 2

    Ignat’ev Aleksandr Vladimirovich

    Full Text Available The author offers a classification of Finite Element formulations, which allows orienting in a great number of the published and continuing to be published works on the problem of raising the efficiency of this widespread numerical method. The second part of the article offers examination of straight formulations of FEM in the form of displacement approach, area method and classical mixed-mode method. The question of solution convergence according to FEM in the form of classical mixed-mode method is considered on the example of single-input single-output system of a beam in case of finite element grid refinement. The author draws a conclusion, that extinction of algebraic equations system of FEM in case of passage to the limit is not a peculiar feature of this method in general, but manifests itself only in some particular cases. At the same time the obtained results prove that FEM in mixed-mode form provides obtaining more stable results in case of finite element grid refinement in comparison with FEM in the form of displacement approach. It is quite obvious that the same qualities will appear also in two-dimensional systems.

  14. Carbon allocation and element composition in four Chlamydomonas mutants defective in genes related to the CO2 concentrating mechanism.

    Memmola, Francesco; Mukherjee, Bratati; Moroney, James V; Giordano, Mario


    Four mutants of Chlamydomonas reinhardtii with defects in different components of the CO2 concentrating mechanism (CCM) or in Rubisco activase were grown autotrophically at high pCO2 and then transferred to low pCO2, in order to study the role of different components of the CCM on carbon allocation and elemental composition. To study carbon allocation, we measured the relative size of the main organic pools by Fourier Transform Infrared spectroscopy. Total reflection X-ray fluorescence was used to analyze the elemental composition of algal cells. Our data show that although the organic pools increased their size at high CO2 in all strains, their stoichiometry was highly homeostatic, i.e., the ratios between carbohydrates and proteins, lipid and proteins, and carbohydrates and lipids, did not change significantly. The only exception was the wild-type 137c, in which proteins decreased relative to carbohydrates and lipids, when the cells were transferred to low CO2. It is noticeable that the two wild types used in this study responded differently to the transition from high to low CO2. Malfunctions of the CCM influenced the concentration of several elements, somewhat altering cell elemental stoichiometry: especially the C/P and N/P ratios changed appreciably in almost all strains as a function of the growth CO2 concentration, except in 137c and the Rubisco activase mutant rca1. In strain cia3, defective in the lumenal carbonic anhydrase (CA), the cell quotas of P, S, Ca, Mn, Fe, and Zn were about 5-fold higher at low CO2 than at high CO2. A Principle Components Analysis showed that, mostly because of its elemental composition, cia3 behaved in a substantially different way from all other strains, at low CO2. The lumenal CA thus plays a crucial role, not only for the correct functioning of the CCM, but also for element utilization. Not surprisingly, growth at high CO2 attenuated differences among strains.

  15. Estimation of periodontal ligament’s equivalent mechanical parameters for finite element modeling

    Xia, Zeyang; Jiang, Feifei; Chen, Jie


    Introduction Young’s modulus (E) and Poisson’s ratio (v) of the periodontal ligament are needed in a finite element analysis for investigating the biomechanical behavior of a tooth, periodontal ligament, and bone complex. However, large discrepancies in E (0.01–1,750 MPa) and v (0.28–0.49) were reported previously. The objective of this study was to narrow the ranges and to provide equivalent E and v pairs suitable for finite element modeling of a tooth, periodontal ligament, and bone complex by using a reported crown load-displacement relationship as the criterion. Methods A 3-dimensional finite element model of a 3-tooth, periodontal ligament, and bone complex, consisting of a maxillary central incisor with 2 adjacent teeth, from a cone-beam computed tomography scan was created. The dimensions, constraints, and loading condition were kept similar to those reported in the human study. With the load applied to the crown, both v and E were adjusted independently, and the corresponding crown displacements were calculated. The resulting load-displacement curves were compared with those reported in the human study. The mean absolute displacement difference method was used to find the best fit. The E and v pairs that generated the minimum mean absolute displacement difference were identified. Results The finite element model with 1 of the 3 E and v pairs (v = 0.35, E = 0.87 MPa; v = 0.4, E = 0.71 MPa; and v = 0.45, E = 0.47 MPa) simulated the tooth, periodontal ligament, and bone complex well. The mean absolute displacement differences were 0.0135, 0.0138, and 0.0138 mm, respectively; these are less than 8% of 0.175 mm, which was the crown displacement of the tooth, periodontal ligament, and bone complex under the load of 500 cN. Conclusions The E and v values close to the 3 pairs might be used for finite element modeling of the tooth, periodontal ligament, and bone complex. PMID:23561409

  16. Numerical investigations of the mechanical properties of a braided non-vascular stent design using finite element method.

    Ni, Xiao-Yu; Pan, Chang-Wang; Gangadhara Prusty, B


    This paper discusses various issues relating to the mechanical properties of a braided non-vascular stent made of a Ni-Ti alloy. The design of the stent is a major factor which determines its reliability after implantation into a stenosed non-vascular cavity. This paper presents the effect of the main structural parameters on the mechanical properties of braided stents. A parametric analysis of a commercial stent model is developed using the commercial finite element code ANSYS. As a consequence of the analytical results that the pitch of wire has a greater effect than other structural parameters, a new design of a variable pitch stent is presented to improve mechanical properties of these braided stents. The effect of structural parameters on mechanical properties is compared for both stent models: constant and variable pitches. When the pitches of the left and right quarters of the stent are 50% larger and 100% larger than that of the central portion, respectively, the radial stiffness in the central portion increases by 10% and 38.8%, while the radial stiffness at the end portions decreases by 128% and 164.7%, the axial elongation by 25.6% and 56.6% and the bending deflection by 3.96% and 10.15%. It has been demonstrated by finite element analysis that the variable pitch stent can better meet the clinical requirements.

  17. Effect of elemental interaction on microstructure and mechanical properties of FeCoNiCuAl alloys

    Zhuang, Y.X., E-mail: [Key Laboratory of Electromagnetic Processing of Materials, Ministry of Education, Northeastern University, Shenyang 110819 (China); Liu, W.J.; Chen, Z.Y.; Xue, H.D.; He, J.C. [Key Laboratory of Electromagnetic Processing of Materials, Ministry of Education, Northeastern University, Shenyang 110819 (China)


    FeCoNiCuAlX (X refers to Si, Cr, Ti, Zr and Nd) alloys were prepared using a suck-casting method. The effect of various elements on phase constituents, microstructures and mechanical properties of the alloys was investigated using X-ray diffraction (XRD), scanning electron microscopy, and compressive tests. It has been found that the microstructure and phase constituents remain unchanged when the Si, Cr and Ti are added into the FeCoNiCuAl alloy, which have a typical cast dendrite microstructure consisting of a dominated body-centered-cubic (BCC) solid solution and a face-centered-cubic (FCC) solid solution. However, the intermetallic compounds are formed in the alloys with the addition of Zr or Nd element. The compressive strength and plasticity of the alloys are enhanced by the addition of the Si, Cr and Ti, and retarded by the addition of the Zr or Nd element. The results have been discussed in aspects of atomic size difference, electronegativity difference, valance electron concentration and the mixing enthalpy among the elements in the alloys.

  18. Importance of greenstick lamina fractures in low lumbar burst fractures

    Ersozlu, S.; Aydinli, U.


    Lumbar burst fractures (L3–L5) represent a small percentage of all spinal fractures. The treatment of fractures involving the lumbar spine has been controversial. Lamina fractures may be complete or of the greenstick type. Dural tears and nerve root entrapment may accompany these lamina fractures. The aim of this retrospective study was to determine the incidence of dural tear in patients who had lumbar burst fractures with greenstick lamina fractures and the importance of these lamina fractures when choosing the optimum treatment. Twenty-six patients with 28 lumbar burst fractures were treated from 1995 through 2002. The average follow-up was 60 months (range 32–110 months). The male to female ratio was 21:5 and the mean age was 37 years (17–64). Dural tear was detected in seven (25%) out of 28 burst fractures. The functional outcome of the entire study group was assessed using the Smiley-Webster Scale. Good to excellent results were obtained in 24 (92%) of 26 patients. Lumbar burst fractures with greenstick lamina fractures occur mostly in the L2–L4 area. In the surgical treatment, any reduction manoeuvre will close the fracture and crush the entrapped neural elements. Therefore, it may be better to explore the greenstick lamina fracture whether there is any neural entrapment or not, before any reduction manoeuvre is attempted. PMID:16501977

  19. Validation of predicted patellofemoral mechanics in a finite element model of the healthy and cruciate-deficient knee.

    Ali, Azhar A; Shalhoub, Sami S; Cyr, Adam J; Fitzpatrick, Clare K; Maletsky, Lorin P; Rullkoetter, Paul J; Shelburne, Kevin B


    Healthy patellofemoral (PF) joint mechanics are critical to optimal function of the knee joint. Patellar maltracking may lead to large joint reaction loads and high stresses on the articular cartilage, increasing the risk of cartilage wear and the onset of osteoarthritis. While the mechanical sources of PF joint dysfunction are not well understood, links have been established between PF tracking and abnormal kinematics of the tibiofemoral (TF) joint, specifically following cruciate ligament injury and repair. The objective of this study was to create a validated finite element (FE) representation of the PF joint in order to predict PF kinematics and quadriceps force across healthy and pathological specimens. Measurements from a series of dynamic in-vitro cadaveric experiments were used to develop finite element models of the knee for three specimens. Specimens were loaded under intact, ACL-resected and both ACL and PCL-resected conditions. Finite element models of each specimen were constructed and calibrated to the outputs of the intact knee condition, and subsequently used to predict PF kinematics, contact mechanics, quadriceps force, patellar tendon moment arm and patellar tendon angle of the cruciate resected conditions. Model results for the intact and cruciate resected trials successfully matched experimental kinematics (avg. RMSE 4.0°, 3.1mm) and peak quadriceps forces (avg. difference 5.6%). Cruciate resections demonstrated either increased patellar tendon loads or increased joint reaction forces. The current study advances the standard for evaluation of PF mechanics through direct validation of cruciate-resected conditions including specimen-specific representations of PF anatomy.

  20. Mechanical and Microstructural Effects of Thermal Aging on Cast Duplex Stainless Steels by Experiment and Finite Element Method

    Schwarm, Samuel C.; Mburu, Sarah N.; Kolli, Ratna P.; Perea, Daniel E.; Liu, Jia; Ankem, Sreeramamurthy


    Cast duplex stainless steel piping in light water nuclear reactors expe- rience thermal aging embrittlement during operational service. Interest in extending the operational life to 80 years requires an increased understanding of the microstructural evolution and corresponding changes in mechanical behavior. We analyze the evolution of the microstructure during thermal aging of cast CF-3 and CF-8 stainless steels using electron microscopy and atom probe tomography. The evolution of the mechanical properties is measured concurrently by mechanical methods such as tensile tests, Charpy V-notch tests, and instrumented nanoinden- tation. A microstructure-based finite element method model is developed and uti- lized in conjunction with the characterization results in order to correlate the local stress-strain effects in the microstructure with the bulk measurements. This work is supported by the DOE Nuclear Energy University Programs (NEUP), contract number DE-NE0000724.

  1. Investigation of mechanical responses to the tactile perception of surfaces with different textures using the finite element method

    Wei Tang


    Full Text Available Tactile perception is essential for humans to perceive the world, and it usually results in mechanical responses from the finger. In this study, a nonlinear, viscoelastic, and multilayered finite element model of the finger was developed. The relationship between the mechanical responses within the finger and tactile perception while the finger scanned different surface textures was studied. The results showed that the sensitivity of tactile perception is affected by the peak value of von Mises stress, which is itself determined by the shape and density of a given texture. The von Mises stress varies periodically with time, and this variation depends on the periodicity of the texture. Displacement signals around Pacinian corpuscles have periodic variation. The period of displacement decreases as the density of the texture increases. The spectral centroid increases as the spacing of the texture decreases. The related mechanisms are discussed in this article.

  2. Factors influencing in vitro respiratory burst assays with head kidney leucocytes from rainbow trout, Oncorhynchus mykiss (Walbaum)

    Chettri, Jiwan Kumar; Holten-Andersen, Lars; Buchmann, Kurt

    Head kidney leukocytes are central elements in a number of in vivo and in vitro assays elucidating innate and adaptive immune mechanisms in teleosts following stimulation with various antigens. These systems are sensitive to a number of factors affecting the outcome of the assays. The present work...... describes the importance of temperature, cell concentration, immunostimulant, exposure time and immune-modulatory molecules on the respiratory burst activity of rainbow trout head kidney leukocytes in vitro. Some variation in RBA was observed among individual fish. However, use of cells pooled from four...

  3. On current aspects of finite element computational fluid mechanics for turbulent flows

    Baker, A. J.


    A set of nonlinear partial differential equations suitable for the description of a class of turbulent three-dimensional flow fields in select geometries is identified. On the basis of the concept of enforcing a penalty constraint to ensure accurate accounting of ordering effects, a finite element numerical solution algorithm is established for the equation set and the theoretical aspects of accuracy, convergence and stability are identified and quantized. Hypermatrix constructions are used to formulate the reduction of the computational aspects of the theory to practice. The robustness of the algorithm, and the computer program embodiment, have been verified for pertinent flow configurations.

  4. Postanoxic Burst Suppression Electroencephalogram in a Comatose Child Associated with Spontaneous Eyelid Opening

    John R. Crawford


    Full Text Available Spontaneous eye opening associated with burst suppression electroencephalogram has been reported in adults following postanoxic injury. Previous reports have correlated the onset of epileptiform bursts with the eye opening and attribute it to a brainstem-release phenomenon associated with poor prognosis. The author presents a case of a 12-year-old boy with burst suppression electroencephalogram following severe anoxic injury where the eye opening occurred at the conclusion of the bursts that has never been previously reported. These electroencephalographic findings are important for intensive care physicians to recognize and may provide further insight into the pathophysiological mechanism of this rare phenomenon.

  5. LOFAR tied-array imaging and spectroscopy of solar S bursts

    Morosan, D E; Zucca, P; O'Flannagain, A; Fallows, R; Reid, H; Magdalenic, J; Mann, G; Bisi, M M; Kerdraon, A; Konovalenko, A A; MacKinnon, A L; Rucker, H O; Thide, B; Vocks, C; Alexov, A; Anderson, J; Asgekar, A; Avruch, I M; Bentum, M J; Bernardi, G; Bonafede, A; Breitling, F; Broderick, J W; Brouw, W N; Butcher, H R; Ciardi, B; de Geus, E; Eisloffel, J; Falcke, H; Frieswijk, W; Garrett, M A; Griessmeier, J; Gunst, A W; Hessels, J W T; Hoeft, M; Karastergiou, A; Kondratiev, V I; Kuper, G; van Leeuwen, J; McKay-Bukowski, D; McKean, J P; Munk, H; Orru, E; Paas, H; Pizzo, R; Polatidis, A G; Scaife, A M M; Sluman, J; Tasse, C; Toribio, M C; Vermeulen, R; Zarka, P


    Context. The Sun is an active source of radio emission that is often associated with energetic phenomena ranging from nanoflares to coronal mass ejections (CMEs). At low radio frequencies (<100 MHz), numerous millisecond duration radio bursts have been reported, such as radio spikes or solar S bursts (where S stands for short). To date, these have neither been studied extensively nor imaged because of the instrumental limitations of previous radio telescopes. Aims. Here, Low Frequency Array (LOFAR) observations were used to study the spectral and spatial characteristics of a multitude of S bursts, as well as their origin and possible emission mechanisms. Methods. We used 170 simultaneous tied-array beams for spectroscopy and imaging of S bursts. Since S bursts have short timescales and fine frequency structures, high cadence (~50 ms) tied-array images were used instead of standard interferometric imaging, that is currently limited to one image per second. Results. On 9 July 2013, over 3000 S bursts were ob...

  6. FAST TCP over optical burst switched networks: Modeling and stability analysis

    Shihada, Basem


    FAST TCP is important for promoting data-intensive applications since it can cleverly react to both packet loss and delay for detecting network congestion. This paper provides a continuous time model and extensive stability analysis of FAST TCP congestion-control mechanism in bufferless Optical Burst Switched Networks (OBS). The paper first shows that random burst contentions are essential to stabilize the network, but cause throughput degradation in FAST TCP flows when a burst with all the packets from a single round is dropped. Second, it shows that FAST TCP is vulnerable to burst delay and fails to detect network congestion due to the little variation of round-trip time, thus unstable. Finally it shows that introducing extra delays by implementing burst retransmission stabilizes FAST TCP over OBS. The paper proves that FAST TCP is not stable over barebone OBS. However, it is locally, exponentially, and asymptotically stable over OBS with burst retransmission.

  7. Decameter type III bursts with positive and negative frequency drift rates

    Melnik, V. N.; Brazhenko, A. I.; Konovalenko, A. A.; Briand, C.; Dorovskyy, V. V.; Zarka, P.; Frantzusenko, A. V.; Rucker, H. O.; Rutkevych, B. P.; Panchenko, M.; Zaqarashvili, T.; Shergelashvili, B.


    We report about observations of decameter type III bursts whose frequency drift rates vary their signs from negative to positive. Moreover drift rates of some bursts vary the sign some times. Positive drift rates for some bursts are changed from 0.44 MHz/s to 12 MHz/s. At the same time the negative drift rates of these bursts are standard values for decameter type III bursts. A possible interpretation of such phenomenon on the base of plasma mechanism of type III burst generation is discussed. The sense of this interpretation is that group velocity of type III electromagnetic waves generated by fast electrons at some conditions can be smaller than velocity of these electrons.

  8. Amplitude-Modulated Bursting: A Novel Class of Bursting Rhythms

    Vo, Theodore; Kramer, Mark A.; Kaper, Tasso J.


    We report on the discovery of a novel class of bursting rhythms, called amplitude-modulated bursting (AMB), in a model for intracellular calcium dynamics. We find that these rhythms are robust and exist on open parameter sets. We develop a new mathematical framework with broad applicability to detect, classify, and rigorously analyze AMB. Here we illustrate this framework in the context of AMB in a model of intracellular calcium dynamics. In the process, we discover a novel family of singularities, called toral folded singularities, which are the organizing centers for the amplitude modulation and exist generically in slow-fast systems with two or more slow variables.

  9. Contact mechanics of pad of grasshopper (Insecta: ORTHOPTERA) by finite element methods

    DAI ZhenDong; GORB Stanislav


    During locomotion, insect feet endure dramatic impact force and generate adhesive force which is controlled by the architecture of the foot. The patterns of smooth attachment pads in insect feet vary widely among insect orders and families. The functional significance of the micro-structure and geo-metric design of insect feet remains largely unknown. In this study, we developed a two-dimensional finite element model of a grasshopper's attachment pad. Realistic geometric microstructure and mate-rial properties are applied in the biomechanical analysis of the structural behavior during contact. Here we use scanning electronic microscopy to study the microstructure of the grasshopper's pad, and then use the finite element method to calculate the deformation vector fields, contact stiffness, contact area, function of the airbag and strain fields during the contact process. The results reveal that the geometric design and material topology of a grasshopper's pads are very effective in reducing contact stiffness, increasing contact area and generating high friction force during the contact procedure. The rod-containing structure supporting the soft exocuticle makes the pads highly adaptive to various surfaces and decreases the stress inside the pads.

  10. Performance of mixed formulations for the particle finite element method in soil mechanics problems

    Monforte, Lluís; Carbonell, Josep Maria; Arroyo, Marcos; Gens, Antonio


    This paper presents a computational framework for the numerical analysis of fluid-saturated porous media at large strains. The proposal relies, on one hand, on the particle finite element method (PFEM), known for its capability to tackle large deformations and rapid changing boundaries, and, on the other hand, on constitutive descriptions well established in current geotechnical analyses (Darcy's law; Modified Cam Clay; Houlsby hyperelasticity). An important feature of this kind of problem is that incompressibility may arise either from undrained conditions or as a consequence of material behaviour; incompressibility may lead to volumetric locking of the low-order elements that are typically used in PFEM. In this work, two different three-field mixed formulations for the coupled hydromechanical problem are presented, in which either the effective pressure or the Jacobian are considered as nodal variables, in addition to the solid skeleton displacement and water pressure. Additionally, several mixed formulations are described for the simplified single-phase problem due to its formal similitude to the poromechanical case and its relevance in geotechnics, since it may approximate the saturated soil behaviour under undrained conditions. In order to use equal-order interpolants in displacements and scalar fields, stabilization techniques are used in the mass conservation equation of the biphasic medium and in the rest of scalar equations. Finally, all mixed formulations are assessed in some benchmark problems and their performances are compared. It is found that mixed formulations that have the Jacobian as a nodal variable perform better.

  11. Performance of mixed formulations for the particle finite element method in soil mechanics problems

    Monforte, Lluís; Carbonell, Josep Maria; Arroyo, Marcos; Gens, Antonio


    This paper presents a computational framework for the numerical analysis of fluid-saturated porous media at large strains. The proposal relies, on one hand, on the particle finite element method (PFEM), known for its capability to tackle large deformations and rapid changing boundaries, and, on the other hand, on constitutive descriptions well established in current geotechnical analyses (Darcy's law; Modified Cam Clay; Houlsby hyperelasticity). An important feature of this kind of problem is that incompressibility may arise either from undrained conditions or as a consequence of material behaviour; incompressibility may lead to volumetric locking of the low-order elements that are typically used in PFEM. In this work, two different three-field mixed formulations for the coupled hydromechanical problem are presented, in which either the effective pressure or the Jacobian are considered as nodal variables, in addition to the solid skeleton displacement and water pressure. Additionally, several mixed formulations are described for the simplified single-phase problem due to its formal similitude to the poromechanical case and its relevance in geotechnics, since it may approximate the saturated soil behaviour under undrained conditions. In order to use equal-order interpolants in displacements and scalar fields, stabilization techniques are used in the mass conservation equation of the biphasic medium and in the rest of scalar equations. Finally, all mixed formulations are assessed in some benchmark problems and their performances are compared. It is found that mixed formulations that have the Jacobian as a nodal variable perform better.

  12. Finite element simulation of the mechanical impact of computer work on the carpal tunnel syndrome.

    Mouzakis, Dionysios E; Rachiotis, George; Zaoutsos, Stefanos; Eleftheriou, Andreas; Malizos, Konstantinos N


    Carpal tunnel syndrome (CTS) is a clinical disorder resulting from the compression of the median nerve. The available evidence regarding the association between computer use and CTS is controversial. There is some evidence that computer mouse or keyboard work, or both are associated with the development of CTS. Despite the availability of pressure measurements in the carpal tunnel during computer work (exposure to keyboard or mouse) there are no available data to support a direct effect of the increased intracarpal canal pressure on the median nerve. This study presents an attempt to simulate the direct effects of computer work on the whole carpal area section using finite element analysis. A finite element mesh was produced from computerized tomography scans of the carpal area, involving all tissues present in the carpal tunnel. Two loading scenarios were applied on these models based on biomechanical data measured during computer work. It was found that mouse work can produce large deformation fields on the median nerve region. Also, the high stressing effect of the carpal ligament was verified. Keyboard work produced considerable and heterogeneous elongations along the longitudinal axis of the median nerve. Our study provides evidence that increased intracarpal canal pressures caused by awkward wrist postures imposed during computer work were associated directly with deformation of the median nerve. Despite the limitations of the present study the findings could be considered as a contribution to the understanding of the development of CTS due to exposure to computer work.

  13. Cosmological Gamma-Ray Bursts and Hypernovae Conclusively Linked


    . Thousands of years prior to this explosion, a very massive star, running out of hydrogen fuel, let loose much of its outer envelope, transforming itself into a bluish Wolf-Rayet star [3]. The remains of the star contained about 10 solar masses worth of helium, oxygen and heavier elements. In the years before the explosion, the Wolf-Rayet star rapidly depleted its remaining fuel. At some moment, this suddenly triggered the hypernova/gamma-ray burst event. The core collapsed, without the outer part of the star knowing. A black hole formed inside, surrounded by a disk of accreting matter. Within a few seconds, a jet of matter was launched away from that black hole. The jet passed through the outer shell of the star and, in conjunction with vigorous winds of newly formed radioactive nickel-56 blowing off the disk inside, shattered the star. This shattering, the hypernova, shines brightly because of the presence of nickel. Meanwhile, the jet plowed into material in the vicinity of the star, and created the gamma-ray burst which was recorded some 2,650 million years later by the astronomers on Earth. The detailed mechanism for the production of gamma rays is still a matter of debate but it is either linked to interactions between the jet and matter previously ejected from the star, or to internal collisions inside the jet itself. This scenario represents the "collapsar" model, introduced by American astronomer Stan Woosley (University of California, Santa Cruz) in 1993 and a member of the current team, and best explains the observations of GRB 030329. " This does not mean that the gamma-ray burst mystery is now solved ", says Woosley . " We are confident now that long bursts involve a core collapse and a hypernova, likely creating a black hole. We have convinced most skeptics. We cannot reach any conclusion yet, however, on what causes the short gamma-ray bursts, those under two seconds long ."

  14. Intraflagellar transport dynein is autoinhibited by trapping of its mechanical and track-binding elements.

    Toropova, Katerina; Mladenov, Miroslav; Roberts, Anthony J


    Cilia are multifunctional organelles that are constructed using intraflagellar transport (IFT) of cargo to and from their tip. It is widely held that the retrograde IFT motor, dynein-2, must be controlled in order to reach the ciliary tip and then unleashed to power the return journey. However, the mechanism is unknown. Here, we systematically define the mechanochemistry of human dynein-2 motors as monomers, dimers, and multimotor assemblies with kinesin-II. Combining these data with insights from single-particle EM, we discover that dynein-2 dimers are intrinsically autoinhibited. Inhibition is mediated by trapping dynein-2's mechanical 'linker' and 'stalk' domains within a novel motor-motor interface. We find that linker-mediated inhibition enables efficient transport of dynein-2 by kinesin-II in vitro. These results suggest a conserved mechanism for autoregulation among dimeric dyneins, which is exploited as a switch for dynein-2's recycling activity during IFT.

  15. Mechanisms of inclusion evolution and intra-granular acicular ferrite formation in steels containing rare earth elements

    Xiaoxuan DENG; Min JIANG; Xinhua WANG


    Inclusion characteristic and microstructure of rare earth (RE) elements containing steel were evaluated with scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS),element-mapping,optical microscopy (OM),and automated feature analysis (AFA) option equipped with ASPEX PSEM.Factsage was used tocalculate the equilibrium inclusion composition.Based on the calculation,an inclusion evolution mechanism was proposed.Furthermore,line scanning analysis was used to elucidate the intra-granular acicular ferrite (IAF) nucleation mechanism.The result showed that two different inclusions exist in sample steel:(Mn-Al-Si-Ti-La-Ce-O)+MnS complex inclusion and isolated MnS inclusion.Almost all nucleation sites for IAF are complex inclusions,while single MnS inclusion cannot induce IAF.A possible formation mechanism of complex inclusion is proposed based on calculated results using Factsage,which agrees well with experimental results.A Mn-depletion zone (MDZ) which exists adjacent to the (Mn-A1-Si-Ti-La-Ce-O) +-MnS complex inclusion can account for the IAF formation.However,the low volume fraction (1.49× 10-7)of effective inclusion may result in onlv 10% (volume fraction) IAF.

  16. Bursts in intermittent aeolian saltation

    Carneiro, M V; Herrmann, H J


    Close to the onset of Aeolian particle transport through saltation we find in wind tunnel experiments a regime of intermittent flux characterized by bursts of activity. Scaling laws are observed in the time delay between each burst and in the measurements of the wind fluctuations at the critical Shields number $\\theta_c$. The time delay between each burst decreases on average with the increase of the Shields number until saltation becomes non-intermittent and the sand flux becomes continuous. A numerical model for saltation including the wind-entrainment from the turbulent fluctuations can reproduce these observations and gives insight about their origin. We present here also for the first time measurements showing that with feeding it becomes possible to sustain intermittent flux even below the threshold $\\theta_c$ for natural saltation initiation.

  17. A Parallel Multigrid Method for the Finite Element Analysis of Mechanical Contact

    Hales, J D; Parsons, I D


    A geometrical multigrid method for solving the linearized matrix equations arising from node-on-face three-dimensional finite element contact is described. The development of an efficient implementation of this combination that minimizes both the memory requirements and the computational cost requires careful construction and storage of the portion of the coarse mesh stiffness matrices that are associated with the contact stiffness on the fine mesh. The multigrid contact algorithm is parallelized in a manner suitable for distributed memory architectures: results are presented that demonstrates the scheme's scalability. The solution of a large contact problem derived from an analysis of the factory joints present in the Space Shuttle reusable solid rocket motor demonstrates the usefulness of the general approach.

  18. An investigation into the mechanics of double-sided incremental forming using finite element methods

    Moser, Newell; Zhang, Zixuan; Ren, Huaqing; Ehmann, Kornel; Cao, Jian


    Double-Sided Incremental Forming (DSIF) is a developing sheet metal manufacturing process that has gained a lot of attention in recent years due to its inherent flexibility, low-overhead cost, and die-less nature. However, it can be challenging to define the tool gap so as to achieve a desired pressure through the sheet thickness since one must first predict sheet thinning. In this investigation, a novel part design is proposed which varies in-plane curvature as a function of depth. A finite element model for DSIF is developed and the strain histories in various regions are extracted. It was concluded that if the supporting tool loses contact with the sheet, localized necking can occur prior to part failure. Additionally, part geometry can have significant effects on the tool contact area which, consequently, affects the evolution of strain.

  19. Finite element analysis of seal mechanism using SMA for Mars sample return

    Bao, Xiaoqi; Younse, Paulo


    Returning Martian samples to Earth for extensive analysis is of great interest to planetary science community. Current Mars sample return architecture would require leaving the acquired samples on Mars for several years before being retrieved by subsequent mission. Each sample would be sealed securely to keep its integrity. A reliable seal technique that does not affect the integrity of the samples and uses simple low-mass tool is required. The shape memory alloy (SMA) seal technique is a promising candidate. The performances of several primary designs of SMA seal for sample tubes were analyzed by finite element (FE) modeling. The results of thermal heating characteristics had been reported in a previous presentation this paper focus on the preparation and actuation of SMA plugs, the seal pressure, and the stress and strain induced in the sealing procedure with various designs.

  20. Dynamic Response of a Planetary Gear System Using a Finite Element/Contact Mechanics Model

    Parker, Robert G.; Agashe, Vinayak; Vijayakar, Sandeep M.


    The dynamic response of a helicopter planetary gear system is examined over a wide range of operating speeds and torques. The analysis tool is a unique, semianalytical finite element formulation that admits precise representation of the tooth geometry and contact forces that are crucial in gear dynamics. Importantly, no a priori specification of static transmission error excitation or mesh frequency variation is required; the dynamic contact forces are evaluated internally at each time step. The calculated response shows classical resonances when a harmonic of mesh frequency coincides with a natural frequency. However, peculiar behavior occurs where resonances expected to be excited at a given speed are absent. This absence of particular modes is explained by analytical relationships that depend on the planetary configuration and mesh frequency harmonic. The torque sensitivity of the dynamic response is examined and compared to static analyses. Rotation mode response is shown to be more sensitive to input torque than translational mode response.

  1. A review on the mechanical design elements of ankle rehabilitation robot.

    Khalid, Yusuf M; Gouwanda, Darwin; Parasuraman, Subramanian


    Ankle rehabilitation robots are developed to enhance ankle strength, flexibility and proprioception after injury and to promote motor learning and ankle plasticity in patients with drop foot. This article reviews the design elements that have been incorporated into the existing robots, for example, backdrivability, safety measures and type of actuation. It also discusses numerous challenges faced by engineers in designing this robot, including robot stability and its dynamic characteristics, universal evaluation criteria to assess end-user comfort, safety and training performance and the scientific basis on the optimal rehabilitation strategies to improve ankle condition. This article can serve as a reference to design robot with better stability and dynamic characteristics and good safety measures against internal and external events. It can also serve as a guideline for the engineers to report their designs and findings.

  2. Usage of mechanically switching devices for HV electrostatic elements of beam optics

    Mikhailichenko, Alexander


    We are considering usage of gas-filled mechanical relays-Kilovacs and Gigavacs- for power supply of HV electrical dipoles, quadrupoles etc., where even a time dependent regime required. One can expect the physical switching time on few nanosecond level with such devices operating up to 70kV with currents~50A.


    Dialyzable plasma phosphorous is not incorporated into erythrocyte lipids. Plasma phospholipids emulsified in aqueous media by ultrasonic vibration...Acanthocytosis show marked reductions in their content of lecithin and linoleic acid. In vivo removal mechanisms, in addition to the metabolic defect

  4. A displacement-based finite element formulation for incompressible and nearly-incompressible cardiac mechanics.

    Hadjicharalambous, Myrianthi; Lee, Jack; Smith, Nicolas P; Nordsletten, David A


    The Lagrange Multiplier (LM) and penalty methods are commonly used to enforce incompressibility and compressibility in models of cardiac mechanics. In this paper we show how both formulations may be equivalently thought of as a weakly penalized system derived from the statically condensed Perturbed Lagrangian formulation, which may be directly discretized maintaining the simplicity of penalty formulations with the convergence characteristics of LM techniques. A modified Shamanskii-Newton-Raphson scheme is introduced to enhance the nonlinear convergence of the weakly penalized system and, exploiting its equivalence, modifications are developed for the penalty form. Focusing on accuracy, we proceed to study the convergence behavior of these approaches using different interpolation schemes for both a simple test problem and more complex models of cardiac mechanics. Our results illustrate the well-known influence of locking phenomena on the penalty approach (particularly for lower order schemes) and its effect on accuracy for whole-cycle mechanics. Additionally, we verify that direct discretization of the weakly penalized form produces similar convergence behavior to mixed formulations while avoiding the use of an additional variable. Combining a simple structure which allows the solution of computationally challenging problems with good convergence characteristics, the weakly penalized form provides an accurate and efficient alternative to incompressibility and compressibility in cardiac mechanics.

  5. High Redshift Gamma Ray Bursts

    Gehrels, Neil


    The Swift Observatory has been detecting 100 gamma-ray bursts per year for 7 years and has greatly stimulated the field with new findings. Observations are made of the X-ray and optical afterglow from 1 minute after the burst, continuing for days. GRBs are providing a new tool to study the high redshift universe. Swift has detected several events at z>5 and one at z=9.4 giving information on metallicity, star formation rate and reionization. The talk will present the latest results.

  6. Burst and Persistent Emission Properties during the Recent Active Episode of the Anomalous X-Ray Pulsar 1E 1841-045

    Lin, Lin; Kouveliotou, Chryssa; Gogus, Ersin; van der Horst, Alexander J.; Watts, Anna L.; Baring, Matthew G.; Kaneko, Yuki; Wijers, Ralph A. M. J.; Woods, Peter M.; Barthelmy, Scott; Burgess, J. Michael; Chaplin, Vandiver; Gehrels, Neil; Goldstein, Adam; Granot, Jonathan; Guiriec, Sylvain; Mcenery, Julie; Preece, Robert D.; Tierney, David; van der Klis, Michiel; von Kienlin, Andreas; Zhang, Shuang Nan


    SWift/BAT detected the first burst from 1E 1841-045 in May 2010 with intermittent burst activity recorded through at least July 2011. Here we present Swift and Fermi/GBM observations of this burst activity and search for correlated changes to the persistent X-ray emission of the source. The T90 durations of the bursts range between 18 - 140 ms, comparable to other magnetar burst durations, while the energy released in each burst ranges between (0.8-25) x 1038 erg, which is in the low side of SGR bursts. We find that the bursting activity did not have a significant effect on the persistent flux level of the source. We argue that the mechanism leading to this sporadic burst activity in IE 1841-045 might not involve large scale restructuring (either crustal or magnetospheric) as seen in other magnetar sources.

  7. Burst and Persistent Emission Properties during the Recent Active Episode of the Anomalous X-ray Pulsar 1E 1841-045

    Lin, Lin; Gogus, Ersin; van der Horst, Alexander J; Watts, Anna L; Baring, Matthew G; Kaneko, Yuki; Wijers, Ralph A M J; Woods, Peter M; Barthelmy, Scott; Burgess, J Michael; Chaplin, Vandiver; Gehrels, Neil; Goldstein, Adam; Granot, Jonathan; Guiriec, Sylvain; Mcenery, Julie; Preece, Robert D; Tierney, David; van der Klis, Michiel; von Kienlin, Andreas; Zhang, Shuang Nan


    Swift/BAT detected the first burst from 1E 1841-045 in May 2010 with intermittent burst activity recorded through at least July 2011. Here we present Swift and Fermi/GBM observations of this burst activity and search for correlated changes to the persistent X-ray emission of the source. The T90 durations of the bursts range between 18-140 ms, comparable to other magnetar burst durations, while the energy released in each burst ranges between (0.8 - 25)E38 erg, which is in the low side of SGR bursts. We find that the bursting activity did not have a significant effect on the persistent flux level of the source. We argue that the mechanism leading to this sporadic burst activity in 1E 1841-045 might not involve large scale restructuring (either crustal or magnetospheric) as seen in other magnetar sources.

  8. Mechanical behaviour of pressed and sintered titanium alloys obtained from prealloyed and blended elemental powders.

    Bolzoni, L; Esteban, P G; Ruiz-Navas, E M; Gordo, E


    The applicability of irregular prealloyed Ti-6Al-4V powder for the fabrication of titanium products by pressing and sintering and its employment as a master alloy to obtain the Ti-3Al-2.5V alloy was studied. To this end, the starting powders were characterised by dilatometry, differential thermal analysis and XRD. Green samples were obtained by cold uniaxial pressing, and the evolution of the microstructure over the sintering temperature range 900-1400°C was studied. The variation of the final density and mechanical properties with the sintering temperature was considered. Based on the study carried out, it can be stated that more reliable powders are needed to open the titanium market to new applications. A relative density of 95% and diverse microstructural features and mechanical properties equivalent to those of biomedical devices can be obtained by the pressing and sintering route.

  9. Mounting of the electro-mechanical elements of Flamanville Power Plant Support

    Cerdan Fernandez, Gabriel


    In this multidisciplinary internship at Sofinel, an EDF and AREVA subsidiary created for the construction of the EPRs around the world, I performed multiple tasks. Working on the mechanical equipment group I learned how a magnificent project like the construction of a nuclear power plant is managed. A strong, rigorous and standardized engineering change management has to be implemented in order to maintain the safety level and the technical and cost consistency of the project. In fact, ...

  10. Study of the mechanical behavior of cortical bone microstructure by the finite element method

    Arango Villegas, Camila


    [EN] Cortical bone tissue is the responsible of giving support and structure to vertebrates. For that reason, understanding and analyzing its behavior is needed from each different hierarchical level that composes it. The lower the structural scale is, the greater the complexity and scarcity of studies in literature. These studies are relevant for understanding, preventing and solving important health problems that affect human beings. From a mechanical point of view is interesting to eval...

  11. Intraflagellar transport dynein is autoinhibited by trapping of its mechanical and track-binding elements

    Toropova, K.; Mladenov, M; Roberts, Anthony


    Cilia are multi-functional organelles that are constructed using intraflagellar transport (IFT) of cargo to and from their tip. It is widely held that the retrograde IFT motor, dynein-2, must be controlled in order to reach the ciliary tip and then unleashed to power the return journey. However, the mechanism is unknown. Here, we systematically define the mechanochemistry of human dynein-2 motors as monomers, dimers, and multi-motor assemblies with kinesin-II. Combining these data with insigh...

  12. A three-dimensional finite-element thermal/mechanical analytical technique for high-performance traveling wave tubes

    Shalkhauser, Kurt A.; Bartos, Karen F.; Fite, E. B.; Sharp, G. R.


    Current research in high-efficiency, high-performance traveling wave tubes (TWT's) has led to the development of novel thermal/mechanical computer models for use with helical slow-wave structures. A three-dimensional, finite element computer model and analytical technique used to study the structural integrity and thermal operation of a high-efficiency, diamond-rod, K-band TWT designed for use in advanced space communications systems. This analysis focused on the slow-wave circuit in the radiofrequency section of the TWT, where an inherent localized heating problem existed and where failures were observed during earlier cold compression, or 'coining' fabrication technique that shows great potential for future TWT development efforts. For this analysis, a three-dimensional, finite element model was used along with MARC, a commercially available finite element code, to simulate the fabrication of a diamond-rod TWT. This analysis was conducted by using component and material specifications consistent with actual TWT fabrication and was verified against empirical data. The analysis is nonlinear owing to material plasticity introduced by the forming process and also to geometric nonlinearities presented by the component assembly configuration. The computer model was developed by using the high efficiency, K-band TWT design but is general enough to permit similar analyses to be performed on a wide variety of TWT designs and styles. The results of the TWT operating condition and structural failure mode analysis, as well as a comparison of analytical results to test data are presented.

  13. Static and Dynamic Mechanics Analysis on Artificial Hip Joints with Different Interface Designs by the Finite Element Method

    Hai-bo Jiang


    Four different structural models of artificial joints were developed and the finite element method (FEM) was employed to investigate their mechanical characteristics under static and dynamic conditions. The materials used in the FEM calculation were ultra-high molecular weight polyethylene (UHMWPE), 316L stainless steel, CoCrMo alloy and Ti6A14V alloy. The stress distribution, strain, and elastic deformation under static and dynamic conditions were obtained. Analysis and comparison of the calculation results of different models were conducted. It is shown that with the same parameters the model of a metallic femur head covered with an artificial cartilage layer is more similar to the structure of the natural human joint and its mechanical characteristics are the best of the four models.

  14. Multi-scale finite element modeling allows the mechanics of amphibian neurulation to be elucidated

    Chen, Xiaoguang; Brodland, G. Wayne


    The novel multi-scale computational approach introduced here makes possible a new means for testing hypotheses about the forces that drive specific morphogenetic movements. A 3D model based on this approach is used to investigate neurulation in the axolotl (Ambystoma mexicanum), a type of amphibian. The model is based on geometric data from 3D surface reconstructions of live embryos and from serial sections. Tissue properties are described by a system of cell-based constitutive equations, and parameters in the equations are determined from physical tests. The model includes the effects of Shroom-activated neural ridge reshaping and lamellipodium-driven convergent extension. A typical whole-embryo model consists of 10 239 elements and to run its 100 incremental time steps requires 2 days. The model shows that a normal phenotype does not result if lamellipodium forces are uniform across the width of the neural plate; but it can result if the lamellipodium forces decrease from a maximum value at the mid-sagittal plane to zero at the plate edge. Even the seemingly simple motions of neurulation are found to contain important features that would remain hidden, they were not studied using an advanced computational model. The present model operates in a setting where data are extremely sparse and an important outcome of the study is a better understanding of the role of computational models in such environments.

  15. The mechanical significance of the temporal fasciae in Macaca fascicularis: an investigation using finite element analysis.

    Curtis, Neil; Witzel, Ulrich; Fitton, Laura; O'higgins, Paul; Fagan, Michael


    Computational finite element analyses (FEAs) of the skull predict structural deformations under user specified loads and constraints, with results normally presented as stress and strain distributions over the skull's surface. The applied loads are generally a representation of the major adductor musculature, with the skull constrained at bite positions and at the articulating joints. However, virtually all analyses ignore potentially important anatomical structures, such as the fasciae that cover the temporalis muscle and attach onto the zygomatic arch. In vivo experimental studies have shown that removal of the temporal fasciae attachment onto the zygomatic arch in Cebus monkeys results in significant bone adaptation and remodeling in this region, suggesting the fasciae play an important role in stabilising the arch during biting. Here we investigate this potential stabilising role by carrying out FEAs of a macaque skull with and without temporal fasciae included. We explore the extent to which the zygomatic arch might be stabilized during biting by a synchronized tensioning of the temporal fasciae, acting to oppose masseteric contraction forces. According to our models, during temporalis muscle bulging the forces generated within the tensioned temporal fasciae are large enough to oppose the pull of the masseter. Further, a near bending-free state of equilibrium within the arch can be reached, even under forceful biting. We show that it is possible to eliminate the high strain gradients in and around the zygomatic arch that are present in past computational studies, with strains being more uniform in magnitude than previously thought.

  16. Unusual seeding mechanism for enhanced performance in solid-phase magnetic extraction of Rare Earth Elements

    Polido Legaria, Elizabeth; Rocha, Joao; Tai, Cheuk-Wai; Kessler, Vadim G.; Seisenbaeva, Gulaim A.


    Due to the increasing demand of Rare Earth Elements (REE or RE), new and more efficient techniques for their extraction are necessary, suitable for both mining and recycling processes. Current techniques such as solvent extraction or solid adsorbents entail drawbacks such as using big volumes of harmful solvents or limited capacity. Hybrid nanoadsorbents based on SiO2 and highly stable γ-Fe2O3-SiO2 nanoparticles, proved recently to be very attractive for adsorption of REE, yet not being the absolute key to solve the problem. In the present work, we introduce a highly appealing new approach in which the nanoparticles, rather than behaving as adsorbent materials, perform as inducers of crystallization for the REE in the form of hydroxides, allowing their facile and practically total removal from solution. This induced crystallization is achieved by tuning the pH, offering an uptake efficiency more than 20 times higher than previously reported (up to 900 mg RE3+/g vs. 40 mg RE3+/g). The obtained phases were characterized by SEM-EDS, TEM, STEM and EFTEM and 13C and 29Si solid state NMR. Magnetic studies showed that the materials possessed enough magnetic properties to be easily removed by a magnet, opening ways for an efficient and industrially applicable separation technique.

  17. Chemical enrichment mechanisms in Omega Centauri: clues from neutron-capture elements

    D'Orazi, Valentina; Pancino, Elena; Bragaglia, Angela; Carretta, Eugenio; Lucatello, Sara; Sneden, Chris


    In the complex picture of multiple stellar populations in globular clusters (GCs), a special role is played by NGC 5139 Omega Centauri. At variance with the majority of GCs, Omega Cen exhibits significant star-to-star variations in metallicity and in relative neutron-capture element abundance ratios with respect to Fe, along with split evolutionary sequences as revealed from colour-magnitude diagrams. Combining information from photometry and spectroscopy, several studies suggested that an age spread of several Gyr has to be invoked to explain (at least partially) some of the observed features. However, a comprehensive understanding of the formation, evolution and chemical enrichment processes is still not at hand. Relatively metal-rich Omega cen stars display neutron-capture abundance distributions dominated by contributions from the s-process, but it is not clear what roles have been played by the so-called main and weak s-process components in generating these abundances. To gain better insight into this q...

  18. Evaluating knee replacement mechanics during ADL with PID-controlled dynamic finite element analysis.

    Fitzpatrick, Clare K; Baldwin, Mark A; Clary, Chadd W; Maletsky, Lorin P; Rullkoetter, Paul J


    Validated computational knee simulations are valuable tools for design phase development of knee replacement devices. Recently, a dynamic finite element (FE) model of the Kansas knee simulator was kinematically validated during gait and deep flexion cycles. In order to operate the computational simulator in the same manner as the experiment, a proportional-integral-derivative (PID) controller was interfaced with the FE model to control the quadriceps actuator excursion and produce a target flexion profile regardless of implant geometry or alignment conditions. The controller was also expanded to operate multiple actuators simultaneously in order to produce in vivo loading conditions at the joint during dynamic activities. Subsequently, the fidelity of the computational model was improved through additional muscle representation and inclusion of relative hip-ankle anterior-posterior (A-P) motion. The PID-controlled model was able to successfully recreate in vivo loading conditions (flexion angle, compressive joint load, medial-lateral load distribution or varus-valgus torque, internal-external torque, A-P force) for deep knee bend, chair rise, stance-phase gait and step-down activities.

  19. Study on micro hydro-mechanical deep drawing using finite element method

    Ma Xiaoguang


    Full Text Available A numerical model was established to investigate the micro hydro-mechanical deep drawing process of austenitic stainless steel 304 foil (0.05 mm thickness. Due to the miniaturisation of the specimen size, the effect of grain size, gap distance and radial pressure during drawing process could be prominent. The results indicate that the appropriate radial pressure and gap distance could improve the limit drawing ratio (LDR of manufactured cylindrical cups by reducing the friction resistance. The maximum LDR obtained in the present work reaches 3.2, which is much higher than that obtained by conventional deep drawing process.

  20. Field Simulations and Mechanical Implementation of Electrostatic Elements for the ELENA Transfer Lines

    Barna, D; Borburgh, J; Carli, C; Vanbavinckhove, G


    The Antiproton Decelerator (AD) complex at CERN will be extended by an extra low energy anti-proton ring (ELENA) [1] further decelerating the anti-protons thus improving their trapping. The kinetic energy of 100 keV at ELENA extraction facilitates the use of electrostatic transfer lines to the experiments. The mechanical implementation of the electrostatic devices are presented with focus on their alignment, bakeout compatibility, ultra-high vacuum compatibility and polarity switching. Field optimisations for an electrostatic crossing device of three beam lines are shown.

  1. Reaction mechanism in high Nb containing TiAl alloy by elemental powder metallurgy

    WANG Yan-hang; LIN Jun-pin; HE Yue-hui; WANG Yan-li; LIN Zhi; CHEN Guo-liang


    High Nb containing TiAl alloy was fabricated in argon atmosphere by reactive hot pressing process. Reaction mechanism was investigated by means of microstructural analyses and thermodynamic calculations. The results show that it is feasible to prepare high Nb containing TiAl alloy with fine lamellar colonies by reactive hot pressing process. The reaction between Ti and Al powders is dominant in Ti-Al-Nb system. Nb powders dissolve into the Ti-Al matrix by diffusion. Pore nests are formed in situ after Nb powders diffusion. The hot pressing atmosphere is optimized by thermodynamic calculations. Vacuum or argon protective atmosphere should be adopted.

  2. Modelling of URM Walls Retrofitted with Cable:A Comparison Between a Basic Mechanical Model and Distinct Element Method

    ZHUGE Yan; CHUANG Shihwei


    The Australian love of "heritage" buildings (most of them are unreinforced masonry (URM)) means that greater attention is required to secure their performance under seismic or impact loading in the future.A research project has been carried out to develop a new,economic and high strength retrofitting technique for masonry structures.A series of experimental testing on URM walls retrofitted with an innovative technique by cable system have been conducted.In this paper,an analytical model which is based on distinct element method(DEM) is developed to simulate the behaviour of retrofitted walls.In DEM,a solid is represented as an assembly of discrete blocks.Joints are modelled as interface between distinct bodies.It is a dynamic process and specially designed to model the behaviour of discontinuities.In order to assist the practising engineers to design this new retrofitted wall system,a simple mechanical model was also developed to predict the strength of the retrofitted walls.The results obtained from this simple mechanical model are compared with those from both experiments and distinct element model.

  3. Investigation of Micro-mechanical Response of Asphalt Mixtures by a Three-dimensional Discrete Element Model

    HOU Shuguang; ZHANG Dong; HUANG Xiaoming; ZHAO Yongli


    The micro-mechanical response of asphalt mixtures was studied using the discrete element method. The discrete element sample of stone mastic asphalt was generated first and the vehicle load was applied to the sample. A user-written program was coded with the FISH language in PFC3D to extract the contact forces within the sample and the displacements of the particles. Then, the contact forces within the whole sample, in asphalt mastic, in coarse aggregates and between asphalt mastic and coarse aggregates were investigated. Finally, the movement of the particles in the sample was analyzed. The sample was divided into 15 areas and a figure was drawn to show how the balls move in each area according to the displacements of the balls in each area. The displacements of asphalt mastic balls and coarse aggregates were also analyzed. The experimental results explain how the asphalt mixture bears vehicle load and the potential reasons why the rutting forms from a micro-mechanical view.

  4. Alterations of erythrocyte antioxidant mechanisms: antioxidant enzymes, lipid peroxidation and serum trace elements associated with anemia in bovine tropical theileriosis.

    Razavi, S M; Nazifi, S; Bateni, M; Rakhshandehroo, E


    In order to investigate the alterations of erythrocyte protective antioxidant mechanisms, lipid peroxidation and trace elements associated with anemia in bovine tropical theileriosis, an infected group comprised of 50 crossbred Holstein cattle, about 1-2 years old, naturally infected with Theileria annulata, were divided into 4 subgroups according to their parasitemia rates (5%) and also 10 healthy cattle as control were selected. Blood samples were taken and hematological parameters, the activities of antioxidant enzymes including superoxide dismutase (SOD), glutathione peroxidase (GPX) and catalase and serum concentrations of some antioxidant trace elements (copper, iron, zinc, manganese and selenium) were measured. As an index of lipid peroxidation, the level of Malondialdehyde (MDA) was also determined. The results showed a conspicuous decrease in the activities of SOD, GPX and catalase (P<0.01), and a significant decrease in the serum concentrations of Cu, Zn, Mn and Se in cattle with higher than 1% parasitemia (P<0.05) compared to the control. In addition, remarkable elevations in the MDA level (P<0.01) and serum concentration of iron (P<0.05) were observed in the infected animals. These findings pointed to the occurrence of exacerbating oxidative injuries to erythrocytes during parasitemia. Furthermore, it can be concluded that infection with T. annulata can interfere with protective antioxidant mechanisms of RBCs against oxidative damages, which promote the development of anemia.

  5. Mechanical properties of silicon nanobeams with an undercut evaluated by combining the dynamic resonance test and finite element analysis

    Zhang Jia-Hong; Mao Xiao-Li; Liu Qing-Quan; Gu Fang; Li Min; Liu Heng; Ge Yi-Xian


    Mechanical properties of silicon nanobeams are of prime importance in nanoelectromechanical system applications.A numerical experimental method of determining resonant frequencies and Young's modulus of nanobeams by combining finite element analysis and frequency response tests based on an electrostatic excitation and visual detection by using a laser Doppler vibrometer is presented in this paper.Silicon nanobeam test structures are fabricated from silicon-on-insulator wafers by using a standard lithography and anisotropic wet etching release process,which inevitably generates the undercut of the nanobeam clamping.In conjunction with three-dimensional finite element numerical simulations incorporating the geometric undercut,dynamic resonance tests reveal that the undercut significantly reduces resonant frequencies of nanobeams due to the fact that it effectively increases the nanobeam length by a correct value △L,which is a key parameter that is correlated with deviations in the resonant frequencies predicted from the ideal Euler-Bernoulli beam theory and experimentally measured data.By using a least-square fit expression including △L,we finally extract Young's modulus from the measured resonance frequency versus effective length dependency and find that Young's modulus of a silicon nanobeam with 200-nm thickness is close to that of bulk silicon.This result supports that the finite size effect due to the surface effect does not play a role in the mechanical elastic behaviour of silicon nanobeams with thickness larger than 200 nm.

  6. Discrete Element Modelling of the Influence of Reinforcement in Structurally Controlled Squeezing Mechanisms in a Hard Rock Mine

    Karampinos, Efstratios; Hadjigeorgiou, John; Turcotte, Pascal


    Structurally defined squeezing mechanisms in hard rock mining often result in buckling failures and large deformations. In mining drives, the primary objective is to mitigate and manage, in a cost-effective way, as opposed to arrest the deformation. This paper is a contribution to an improved understanding of the impact of several reinforcement scenarios in structurally controlled deformations in hard rock mines. The influence of reinforcement in the 3D discrete element method is explored, extending previous numerical work that has captured the squeezing buckling mechanism driven by foliation and high stresses in the selected mine site. A comprehensive strategy for explicitly modelling rock reinforcement using the DEM was developed and implemented in a series of 3D numerical models. The models were calibrated based on field testing of reinforcement and observations at the LaRonde Mine. They were used to investigate the influence of different reinforcement strategies at different deformation stages. The numerical results were in agreement with the field observations and demonstrated the practical implications of using yielding reinforcement elements. This was supported by field data where the use of yielding bolts reduced the drift convergence and rehabilitation. The methodology is applicable to other mine sites facing structurally controlled large deformations.

  7. Thermo-hydro-mechanical-air coupling finite element method and its application to multi-phase problems

    Feng Zhang; Yonglin Xiong; Sheng Zhang; Bin Ye


    In this paper, a finite element method (FEM)-based multi-phase problem based on a newly proposed thermal elastoplastic constitutive model for saturated/unsaturated geomaterial is discussed. A program of FEM named as SOFT, adopting unified field equations for thermo-hydro-mechanical-air (THMA) behavior of geomaterial and using finite element-finite difference (FE-FD) scheme for soilewatereair three-phase coupling problem, is used in the numerical simulation. As an application of the newly proposed numerical method, two engineering problems, one for slope failure in unsaturated model ground and another for in situ heating test related to deep geological repository of high-level radioactive waste (HLRW), are simulated. The model tests on slope failure in unsaturated Shirasu ground, carried out by Kitamura et al. (2007), is simulated in the framework of soilewatereair three-phase coupling under the condition of constant temperature. While the in situ heating test reported by Munoz (2006) is simulated in the same framework under the conditions of variable temperature but constant air pressure. © 2014 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. All rights reserved.

  8. Light Dawns on Dark Gamma-ray Bursts


    [1] Gamma-ray bursts lasting longer than two seconds are referred to as long bursts and those with a shorter duration are known as short bursts. Long bursts, which were observed in this study, are associated with the supernova explosions of massive young stars in star-forming galaxies. Short bursts are not well understood, but are thought to originate from the merger of two compact objects such as neutron stars. [2] The Gamma-Ray burst Optical and Near-infrared Detector (GROND) was designed and built at the Max-Planck Institute for Extraterrestrial Physics in collaboration with the Tautenburg Observatory, and has been fully operational since August 2007. [3] Other studies relating to dark gamma-ray bursts have been released. Early this year, astronomers used the Subaru Telescope to observe a single gamma-ray burst, from which they hypothesised that dark gamma-ray bursts may indeed be a separate sub-class that form through a different mechanism, such as the merger of binary stars. In another study published last year using the Keck Telescope, astronomers studied the host galaxies of 14 dark GRBs, and based on the derived low redshifts they infer dust as the likely mechanism to create the dark bursts. In the new work reported here, 39 GRBs were studied, including nearly 20 dark bursts, and it is the only study in which no prior assumptions have been made and the amount of dust has been directly measured. [4] Because the afterglow light of very distant bursts is redshifted due to the expansion of the Universe, the light that left the object was originally bluer than the light we detect when it gets to Earth. Since the reduction of light intensity by dust is greater for blue and ultraviolet light than for red, this means that the overall dimming effect of dust is greater for the more distant gamma-ray bursts. This is why GROND's ability to observe near-infrared radiation makes such a difference. More information This research is presented in a paper to appear in the

  9. Optical telescope BIRT in ORIGIN for gamma ray burst observing

    Content, Robert; Sharples, Ray; Page, Mathew J.


    The ORIGIN concept is a space mission with a gamma ray, an X-ray and an optical telescope to observe the gamma ray bursts at large Z to determine the composition and density of the intergalactic matter in the line of sight. It was an answer to the ESA M3 call for proposal. The optical telescope i...... length. All 3 instruments use the same 2k x 2k detector simultaneously so that telescope pointing and tip-tilt control of a fold mirror permit to place the gamma ray burst on the desired instrument without any other mechanism. © 2012 SPIE....

  10. Gamma-Ray Bursts and Population III Stars

    Toma, Kenji; Yoon, Sung-Chul; Bromm, Volker


    Gamma-ray bursts (GRBs) are ideal probes of the epoch of the first stars and galaxies. We review the recent theoretical understanding of the formation and evolution of the first (so-called Population III) stars, in light of their viability of providing GRB progenitors. We proceed to discuss possible unique observational signatures of such bursts, based on the current formation scenario of long GRBs. These include signatures related to the prompt emission mechanism, as well as to the afterglow radiation, where the surrounding intergalactic medium might imprint a telltale absorption spectrum. We emphasize important remaining uncertainties in our emerging theoretical framework.

  11. Varying Faces of Photospheric Emission in Gamma-Ray Bursts

    Axelsson, M


    Among the more than 1000 gamma-ray bursts observed by the Fermi Gamma-ray Space Telescope, a large fraction show narrow and hard spectra inconsistent with non-thermal emission, signifying optically thick emission from the photosphere. However, only a few of these bursts have spectra consistent with a pure Planck function. We will discuss the observational features of photospheric emission in these GRBs as well as in the ones showing multi-component spectra. We interpret the observations in light of models of subphotospheric dissipation, geometrical broadening and multi-zone emission, and show what we can learn about the dissipation mechanism and properties of GRB jets.

  12. An Instability-driven Dynamo for $\\gamma$ Ray Bursts

    Araya-Gochez, R A


    We show that an MHD-instability driven dynamo (IDD) operating in a hot accretion disk is capable of generating energetically adequate magnetic flux deposition rates above and below a mildly advective accretion disk structure. The dynamo is driven by the magnetorotational instability (MRI) of a toroidal field in a shear flow and is limited by the buoyancy of `horizontal' flux and by reconnection in the turbulent medium. The efficiency of magnetic energy deposition is estimated to be comparable to the neutrino losses although an MHD collimation mechanism may deem this process a more viable alternative to neutrino-burst-driven models of gamma ray bursts.

  13. Gamma-ray bursts and Population III stars

    Toma, Kenji; Bromm, Volker


    Gamma-ray bursts (GRBs) are ideal probes of the epoch of the first stars and galaxies. We review the recent theoretical understanding of the formation and evolution of the first (so-called Population III) stars, in light of their viability of providing GRB progenitors. We proceed to discuss possible unique observational signatures of such bursts, based on the current formation scenario of long GRBs. These include signatures related to the prompt emission mechanism, as well as to the afterglow radiation, where the surrounding intergalactic medium might imprint a telltale absorption spectrum. We emphasize important remaining uncertainties in our emerging theoretical framework.

  14. INTEGRAL monitoring of unusually long X-ray bursts

    of the known X-ray bursters are frequently observed by INTEGRAL, in particular in the frame of the Key Programmes. Taking advantage of the INTEGRAL instrumentation, an international collaboration led by the JEM-X team at the Danish National Space Institute has been monitoring the occurrence of uncommon burst...... be triggered by the helium flash. Half of the 15 intermediate long bursts known to date have been observed by INTEGRAL, and the mechanisms up to high energies of these unusual events have been investigated. Observation results will be presented that lead to an advanced description of the relationship between...

  15. Focal mechanisms in the southern Dead Sea basin and related structural elements based on seismological data

    Hofstetter, A.; Dorbath, C.; Dorbath, L.


    A dense temporary local seismological network was operated from 10/2006 to 3/2008 in the southern Dead Sea basin also outside the basin within the framework of the DESIRE (DEad Sea Integrated REsearch) project, providing many recordings of local earthquakes. We used the recordings of DESIRE and also the recordings of the permanent networks of Israel Seismic Network, Israel, and Jordan Seismic Observatory, Jordan. We determined high quality focal plane solutions of 490 events, using at least 6 stations (normally >10 stations) with a good station distribution around the epicenters. In the southern Dead Sea basin and adjacent regions there are several clusters of earthquakes. Most of the activity occurred along the eastern bordering fault of the basin, in the Lisan Peninsula and just south and north of it. Along the eastern and western bordering faults we observe mainly strike slip mechanism, probably supporting the left lateral motion along the Dead Sea fault. The nodal planes of many of focal mechanisms inside the basin are parallel to the transverse faults crossing the basin, i.e., Bokek and Ein-Gedi faults, and also parallel to faults that border the Lisan Peninsula on the north-western and south-western sides.

  16. FERMIGBRST - Fermi GBM Burst Catalog

    National Aeronautics and Space Administration — This table lists all of the triggers observed by a subset of the 14 GBM detectors (12 NaI and 2 BGO) which have been classified as gamma-ray bursts (GRBs). Note that...

  17. Finite element analysis of traction force microscopy: influence of cell mechanics, adhesion, and morphology.

    Zielinski, Rachel; Mihai, Cosmin; Kniss, Douglas; Ghadiali, Samir N


    The interactions between adherent cells and their extracellular matrix (ECM) have been shown to play an important role in many biological processes, such as wound healing, morphogenesis, differentiation, and cell migration. Cells attach to the ECM at focal adhesion sites and transmit contractile forces to the substrate via cytoskeletal actin stress fibers. This contraction results in traction stresses within the substrate/ECM. Traction force microscopy (TFM) is an experimental technique used to quantify the contractile forces generated by adherent cells. In TFM, cells are seeded on a flexible substrate and displacements of the substrate caused by cell contraction are tracked and converted to a traction stress field. The magnitude of these traction stresses are normally used as a surrogate measure of internal cell contractile force or contractility. We hypothesize that in addition to contractile force, other biomechanical properties including cell stiffness, adhesion energy density, and cell morphology may affect the traction stresses measured by TFM. In this study, we developed finite element models of the 2D and 3D TFM techniques to investigate how changes in several biomechanical properties alter the traction stresses measured by TFM. We independently varied cell stiffness, cell-ECM adhesion energy density, cell aspect ratio, and contractility and performed a sensitivity analysis to determine which parameters significantly contribute to the measured maximum traction stress and net contractile moment. Results suggest that changes in cell stiffness and adhesion energy density can significantly alter measured tractions, independent of contractility. Based on a sensitivity analysis, we developed a correction factor to account for changes in cell stiffness and adhesion and successfully applied this correction factor algorithm to experimental TFM measurements in invasive and noninvasive cancer cells. Therefore, application of these types of corrections to TFM

  18. Microscopic characteristics of burst coal seams

    Zhang, H.; Wang, C. [Shandong University of Science and Technology (China)


    Based on the analytical results of coal samples with microscope and scanning electron microscope, the paper explains the petrographic characteristics and microscopic depredation of burst coal. Quantitative analysis on the components and microstructures of the burst coal is conducted. The influence of the microscopic characteristics on coal burst is discussed. For coal seams with burst tendency, it has provided the necessary forecasting parameters. 2 refs., 1 fig., 2 tabs.

  19. Millisecond extragalactic radio bursts as magnetar flares

    Popov, S B


    Properties of the population of millisecond extragalactic radio bursts discovered by Thornton et al. (2013) are in good correspondence with the hypothesis that such events are related to hyperflares of magnetars, as was proposed by us after the first observation of an extragalactic millisecond radio burst by Lorimer et al. (2007). We also point that some of multiple millisecond radio bursts from M31 discovered by Rubio-Herrera et al. (2013) also can be related to weaker magnetar bursts.

  20. Modeling gamma-ray bursts

    Maxham, Amanda

    Discovered serendipitously in the late 1960s, gamma-ray bursts (GRBs) are huge explosions of energy that happen at cosmological distances. They provide a grand physical playground to those who study them, from relativistic effects such as beaming, jets, shocks and blastwaves to radiation mechanisms such as synchrotron radiation to galatic and stellar populations and history. Through the Swift and Fermi space telescopes dedicated to observing GRBs over a wide range of energies (from keV to GeV), combined with accurate pinpointing that allows ground based follow-up observations in the optical, infrared and radio, a rich tapestry of GRB observations has emerged. The general picture is of a mysterious central engine (CE) probably composed of a black hole or neutron star that ejects relativistic shells of matter into intense magnetic fields. These shells collide and combine, releasing energy in "internal shocks" accounting for the prompt emission and flaring we see and the "external shock" or plowing of the first blastwave into the ambient surrounding medium has well-explained the afterglow radiation. We have developed a shell model code to address the question of how X-ray flares are produced within the framework of the internal shock model. The shell model creates randomized GRB explosions from a central engine with multiple shells and follows those shells as they collide, merge and spread, producing prompt emission and X-ray flares. We have also included a blastwave model, which can constrain X-ray flares and explain the origin of high energy (GeV) emission seen by the Fermi telescope. Evidence suggests that gamma-ray prompt emission and X-ray flares share a common origin and that at least some flares can only be explained by long-lasting central engine activity. We pay special attention to the time history of central engine activity, internal shocks, and observed flares. We calculate the gamma-ray (Swift/BAT band) and X-ray (Swift/XRT band) lightcurves for arbitrary

  1. Simulation-based Estimation of Thermal Behavior of Direct Feed Drive Mechanism with Updated Finite Element Model

    LIN Xiankun; LI Yanjun; LI Haolin


    Linear motors generate high heat and cause significant deformation in high speed direct feed drive mechanisms. It is relevant to estimate their deformation behavior to improve their application in precision machine tools. This paper describes a method to estimate its thermal deformation based on updated finite element(FE) model methods. Firstly, a FE model is established for a linear motor drive test rig that includes the correlation between temperature rise and its resulting deformation. The relationship between the input and output variables of the FE model is identified with a modified multivariate input/output least square support vector regression machine. Additionally, the temperature rise and displacements at some critical points on the mechanism are obtained experimentally by a system of thermocouples and an interferometer. The FE model is updated through intelligent comparison between the experimentally measured values and the results from the regression machine. The experiments for testing thermal behavior along with the updated FE model simulations is conducted on the test rig in reciprocating cycle drive conditions. The results show that the intelligently updated FE model can be implemented to analyze the temperature variation distribution of the mechanism and to estimate its thermal behavior. The accuracy of the thermal behavior estimation with the optimally updated method can be more than double that of the initial theoretical FE model. This paper provides a simulation method that is effective to estimate the thermal behavior of the direct feed drive mechanism with high accuracy.

  2. Study on Monitoring Rock Burst through Drill Pipe Torque

    Zhonghua Li


    Full Text Available This paper presents a new method to identify the danger of rock burst from the response of drill pipe torque during drilling process to overcome many defects of the conventional volume of drilled coal rubble method. It is based on the relationship of rock burst with coal stress and coal strength. Through theoretic analysis, the change mechanism of drill pipe torque and the relationship of drill pipe torque with coal stress, coal strength, and drilling speed are investigated. In light of the analysis, a new device for testing drill pipe torque is developed and a series of experiments is performed under different conditions; the results show that drill pipe torque linearly increases with the increase of coal stress and coal strength; the faster the drilling speed, the larger the drill pipe torque, and vice versa. When monitoring rock burst by drill pipe torque method, the index of rock burst is regarded as a function in which coal stress index and coal strength index are principal variables. The results are important for the forecast of rock burst in coal mine.

  3. Regulatory mechanisms that prevent re-initiation of DNA replication can be locally modulated at origins by nearby sequence elements.

    Christopher D Richardson


    Full Text Available Eukaryotic cells must inhibit re-initiation of DNA replication at each of the thousands of origins in their genome because re-initiation can generate genomic alterations with extraordinary frequency. To minimize the probability of re-initiation from so many origins, cells use a battery of regulatory mechanisms that reduce the activity of replication initiation proteins. Given the global nature of these mechanisms, it has been presumed that all origins are inhibited identically. However, origins re-initiate with diverse efficiencies when these mechanisms are disabled, and this diversity cannot be explained by differences in the efficiency or timing of origin initiation during normal S phase replication. This observation raises the possibility of an additional layer of replication control that can differentially regulate re-initiation at distinct origins. We have identified novel genetic elements that are necessary for preferential re-initiation of two origins and sufficient to confer preferential re-initiation on heterologous origins when the control of re-initiation is partially deregulated. The elements do not enhance the S phase timing or efficiency of adjacent origins and thus are specifically acting as re-initiation promoters (RIPs. We have mapped the two RIPs to ∼ 60 bp AT rich sequences that act in a distance- and sequence-dependent manner. During the induction of re-replication, Mcm2-7 reassociates both with origins that preferentially re-initiate and origins that do not, suggesting that the RIP elements can overcome a block to re-initiation imposed after Mcm2-7 associates with origins. Our findings identify a local level of control in the block to re-initiation. This local control creates a complex genomic landscape of re-replication potential that is revealed when global mechanisms preventing re-replication are compromised. Hence, if re-replication does contribute to genomic alterations, as has been speculated for cancer cells, some

  4. Thermo-mechanical interaction effects in foam cored sandwich panels-correlation between High-order models and Finite element analysis results

    Palleti, Hara Naga Krishna Teja; Santiuste, Carlos; Thomsen, Ole Thybo;


    Thermo-mechanical interaction effects including thermal material degradation in polymer foam cored sandwich structures is investigated using the commercial Finite Element Analysis (FEA) package ABAQUS/Standard. Sandwich panels with different boundary conditions in the form of simply supported...

  5. Numerical Simulations of Gamma-Ray Burst Explosions

    Lazzati, Davide; López-Cámara, Diego


    Gamma-ray bursts are a complex, non-linear system that evolves very rapidly through stages of vastly different conditions. They evolve from scales of few hundred kilometers where they are very dense and hot to cold and tenuous on scales of parsecs. As such, our understanding of such a phenomenon can truly increase by combining theoretical and numerical studies adopting different numerical techniques to face different problems and deal with diverse conditions. In this review, we will describe the tremendous advancement in our comprehension of the bursts phenomenology through numerical modeling. Though we will discuss studies mainly based on jet dynamics across the progenitor star and the interstellar medium, we will also touch upon other problems such as the jet launching, its acceleration, and the radiation mechanisms. Finally, we will describe how combining numerical results with observations from Swift and other instruments resulted in true understanding of the bursts phenomenon and the challenges still lyi...

  6. Relativistic Precessing Jets and Cosmological $\\gamma$ Ray Bursts

    Blackman, E G; Field, G B; Blackman, Eric G.; Yi, Insu; Field, George B.


    We discuss the possibility that gamma-ray bursts may result from cosmological relativistic blob emitting neutron star jets that precess past the line of sight. Beaming reduces the energy requirements, so that the jet emission can last longer than the observed burst duration. One precession mode maintains a short duration time scale, while a second keeps the beam from returning to the line of sight, consistent with the paucity of repeaters. The long life of these objects reduces the number required for production as compared to short lived jets. Blobs can account for the time structure of the bursts. Here we focus largely on kinematic and time scale considerations of beaming, precession, and blobs--issues which are reasonably independent of the acceleration and jet collimation mechanisms. We do suggest that large amplitude electro-magnetic waves could be a source of blob acceleration.

  7. Nonlinear electronic circuit with neuron like bursting and spiking dynamics.

    Savino, Guillermo V; Formigli, Carlos M


    It is difficult to design electronic nonlinear devices capable of reproducing complex oscillations because of the lack of general constructive rules, and because of stability problems related to the dynamical robustness of the circuits. This is particularly true for current analog electronic circuits that implement mathematical models of bursting and spiking neurons. Here we describe a novel, four-dimensional and dynamically robust nonlinear analog electronic circuit that is intrinsic excitable, and that displays frequency adaptation bursting and spiking oscillations. Despite differences from the classical Hodgkin-Huxley (HH) neuron model, its bifurcation sequences and dynamical properties are preserved, validating the circuit as a neuron model. The circuit's performance is based on a nonlinear interaction of fast-slow circuit blocks that can be clearly dissected, elucidating burst's starting, sustaining and stopping mechanisms, which may also operate in real neurons. Our analog circuit unit is easily linked and may be useful in building networks that perform in real-time.

  8. On the three harmonics of solar type III bursts at the decameter wavelengths

    Brazhenko, Anatolii; Pylaev, Oleg; Melnik, Valentin; Konovalenko, Alexandr; Zaqarashvili, Teimuraz; Rucker, Helmut; Frantsuzenko, Anatolii; Dorovskyy, Vladimir


    Harmonic structure of type III bursts are explained in terms of plasma emission mechanism. The second harmonic emission is well known. But there are theoretical papers about the third harmonic of type III bursts. And there were observations of the third harmonic of such types of bursts as U, J, V, II. We observed triple type III bursts where frequency ratio is close to 1:2:3. They are structures where type III emission is repeated at the double and triple frequencies. Incidentally, components of triple type III bursts are not only standard type III but also type IIIb bursts. We registered 30 triple bursts during 2011 and 2012 years. Observations were made by radio telescope URAN-2, Poltava, Ukraine. It enables polarization measurements at the frequencies 8 - 32 MHz. URAN-2 allows registration of radio emission with time and frequency resolution 10 ms and 4 kHz correspondingly. We analyze properties of the components of triple bursts and their dependencies on frequency, type of burst and on the position of the component within the triplet. The main properties of the components of triple bursts such as duration and drift rate are similar to those of standard type III and IIIb bursts. We find usual for type III bursts dependencies such as follow: duration decreases with frequency, the type IIIb bursts have always smaller duration at the same frequencies, all bursts drift from high to low frequencies. But we also find the linear dependence of drift rate on frequency. All components of a trio have the same sign of polarization. Polarization of the first component is always the highest in triple bursts. It corresponds to the generally accepted viewpoint about the first harmonic emission. The second and the third components of trio have low polarization. It is typical for the second and the third harmonics according to the plasma radiation mechanism. We discuss possible emission mechanisms and theoretical aspects of observed dependencies. The most of detected regularities

  9. Extending Mechanical Construction Kits to Incorporate Passive and Compliant Elements for Educational Robotics

    Assaf, Dorit; Larsen, Jørgen Christian; Reichardt, Markus


    Robots are a popular educational tool to introduce science, technology, and engineering to students. The field of educational robotics is growing and consequently a number of ducational robot kits have been developed within the last decade. Our laboratories have radition of teaching embodied...... artificial intelligence and biomechanics to students with different backgrounds. The robots we use both for research and education are usually built incorporating compliant materials as well as passive dynamics. These kind of properties are often not available in classical robot kits or mechanical...... construction kits. In this paper we describe some of the robots we use for education. So far we built the robots using 3D printing technology which is convenient but too expensive for class use. Our aim is to find cheaper, commercially available solutions. After a short review on educational robot kits...

  10. Elements for the expected mechanisms on 'reduced emissions from deforestation and degradation, REDD' under UNFCCC

    Mollicone, D.; Freibauer, A.; Schulze, E. D.; Braatz, S.; Grassi, G.; Federici, S.


    Carbon emissions from deforestation and degradation account for about 20% of global anthropogenic emissions. Strategies and incentives for reduced emissions from deforestation and degradation (REDD) have emerged as one of the most active areas in the international climate change negotiations under the United Nations Framework Convention on Climate Change (UNFCCC). While the current negotiations focus on a REDD mechanism in developing countries, it should be recognized that risks of carbon losses from forests occur in all climate zones and also in industrialized countries. A future climate change agreement would be more effective if it included all carbon losses and gains from land use in all countries and climate zones. The REDD mechanism will be an important step towards reducing emissions from land use change in developing countries, but needs to be followed by steps in other land use systems and regions. A national approach to REDD and significant coverage globally are needed to deal with the risk that deforestation and degradation activities are displaced rather than avoided. Favourable institutional and governance conditions need to be established that guarantee in the long-term a stable incentive and control system for maintaining forest carbon stocks. Ambitious emission reductions from deforestation and forest degradation need sustained financial incentives, which go beyond positive incentives for reduced emissions but also give incentives for sustainable forest management. Current data limitations need—and can be—overcome in the coming years to allow accurate accounting of reduced emissions from deforestation and degradation. A proper application of the conservativeness approach in the REDD context could allow a simplified reporting of emissions from deforestation in a first phase, consistent with the already agreed UNFCCC reporting principles.

  11. Numerical simulation with finite element and artificial neural network of ball indentation for mechanical property estimation

    Kamal Sharma; Vivek Bhasin; K K Vaze; A K ghosh


    A combined mechanical property evaluation methodology with ABI (Automated Ball Indentation) simulation and Artificial Neural Network (ANN) analysis is evolved to evaluate the mechanical properties for Carbon Manganese Steel (SA-333 Grade-6) and Stainless Steel (SS-304LN). The experimental load deflection data is converted into meaningful mechanical properties for these materials and their evaluated property is verified with experimental tensile specimen results. An ANN database is generated with the help of contact type finite element analysis by numerically simulating the ABI process for various magnitudes of yield strength $(\\sigma_{yp})$ (200 MPa–400 MPa) with a range of strain hardening exponent (n) (0.05–0.5)$and strength coefficient (K) (600 MPa–1600 MPa). For the present problem, a ball indenter of 1.57 mm diameter having Young’s modulus higher than test piece is used to minimize the error due to indenter deformation. Test piece dimension is kept large enough in comparison to the indenter configuration in the simulation to minimize the deflection at the outer edge of the test piece. Further, this database after the neural network training; is used to analyse measured material properties of different test pieces. The ANN predictions are reconfirmed with contact type finite element analysis for an arbitrary selected test sample. The methodology evolved in this work can be extended to predict material properties for any irradiated nuclear material in the service. Extensions of the ABI tests and the associated database analysis could lead to evaluation of the indentation energy to fracture needed for the structural integrity assessment of aged components.

  12. Bursting dynamics of in vitro neural networks and their stimulation driven learning.

    Choi, Joon Ho; Hoan Kim, June; Lee, Kyoung J.


    Recent studies have indicated that recurring neural ``bursts'' may play an essential role in neural information processing and memory. One key element of this hypothesis involves the translation of temporal patterns of stimuli into spatiotemporally distributed information. One ideal system to investigate this issue is cultured network of neurons grown on multi-electrode array (MEA). Based on such in vitro systems, we have investigated the changes incurred by extrinsic stimuli in the spontaneously recurring bursting activities. We have employed, in particular, two-channel paired, delayed, tetanic stimuli to evoke different patterns of bursting activities. Our preliminary data suggests that the neural network can exhibit some learning behavior.

  13. Bursting Bubbles and Bilayers

    Steven P. Wrenn, Stephen M. Dicker, Eleanor F. Small, Nily R. Dan, Michał Mleczko, Georg Schmitz, Peter A. Lewin


    Full Text Available This paper discusses various interactions between ultrasound, phospholipid monolayer-coated gas bubbles, phospholipid bilayer vesicles, and cells. The paper begins with a review of microbubble physics models, developed to describe microbubble dynamic behavior in the presence of ultrasound, and follows this with a discussion of how such models can be used to predict inertial cavitation profiles. Predicted sensitivities of inertial cavitation to changes in the values of membrane properties, including surface tension, surface dilatational viscosity, and area expansion modulus, indicate that area expansion modulus exerts the greatest relative influence on inertial cavitation. Accordingly, the theoretical dependence of area expansion modulus on chemical composition - in particular, poly (ethylene glyclol (PEG - is reviewed, and predictions of inertial cavitation for different PEG molecular weights and compositions are compared with experiment. Noteworthy is the predicted dependence, or lack thereof, of inertial cavitation on PEG molecular weight and mole fraction. Specifically, inertial cavitation is predicted to be independent of PEG molecular weight and mole fraction in the so-called mushroom regime. In the “brush” regime, however, inertial cavitation is predicted to increase with PEG mole fraction but to decrease (to the inverse 3/5 power with PEG molecular weight. While excellent agreement between experiment and theory can be achieved, it is shown that the calculated inertial cavitation profiles depend strongly on the criterion used to predict inertial cavitation. This is followed by a discussion of nesting microbubbles inside the aqueous core of microcapsules and how this significantly increases the inertial cavitation threshold. Nesting thus offers a means for avoiding unwanted inertial cavitation and cell death during imaging and other applications such as sonoporation. A review of putative sonoporation mechanisms is then presented

  14. Resilient and Corrosion-Proof Rolling Element Bearings Made from Superelastic Ni-Ti Alloys for Aerospace Mechanism Applications

    DellaCorte, Christopher; Noebe, Ronald D.; Stanford, Malcolm; Padula, Santo A.


    Mechanical components (bearings, gears, mechanisms) typically utilize hard materials to minimize wear and attain long life. In such components, heavily loaded contact points (e.g., meshing gear teeth, bearing ball-raceway contacts) experience high contact stresses. The combination of high hardness, heavy loads and high elastic modulus often leads to damaging contact stress. In addition, mechanical component materials, such as tool steel or silicon nitride exhibit limited recoverable strain (typically less than 1 percent). These material attributes can lead to Brinell damage (e.g., denting) particularly during transient overload events such as shock impacts that occur during the launching of space vehicles or the landing of aircraft. In this paper, a superelastic alloy, 60NiTi, is considered for rolling element bearing applications. A series of Rockwell and Brinell hardness, compressive strength, fatigue and tribology tests are conducted and reported. The combination of high hardness, moderate elastic modulus, large recoverable strain, low density, and intrinsic corrosion immunity provide a path to bearings largely impervious to shock load damage. It is anticipated that bearings and components made from alloys with such attributes can alleviate many problems encountered in advanced aerospace applications.

  15. Cancer cell mechanics with altered cytoskeletal behavior and substrate effects: A 3D finite element modeling study.

    Katti, Dinesh R; Katti, Kalpana S


    A robust computational model of a cancer cell is presented using finite element modeling. The model accurately captures nuances of the various components of the cellular substructure. The role of degradation of cytoskeleton on overall elastic properties of the cancer cell is reported. The motivation for degraded cancer cellular substructure, the cytoskeleton is the observation that the innate mechanics of cytoskeleton is disrupted by various anti-cancer drugs as therapeutic treatments for the destruction of the cancer tumors. We report a significant influence on the degradation of the cytoskeleton on the mechanics of cancer cell. Further, a simulations based study is reported where we evaluate mechanical properties of the cancer cell attached to a variety of substrates. The loading of the cancer cell is less influenced by nature of the substrate, but low modulus substrates such as osteoblasts and hydrogels indicate a significant change in unloading behavior and also the plastic deformation. Overall, softer substrates such as osteoblasts and other bone cells result in a much altered unloading response as well as significant plastic deformation. These substrates are relevant to metastasis wherein certain type of cancers such as prostate and breast cancer cells migrate to the bone and colonize through mesenchymal to epithelial transition. The modeling study presented here is an important first step in the development of strong predictive methodologies for cancer progression. Copyright © 2017 Elsevier Ltd. All rights reserved.

  16. Clarification of the mechanical behaviour of spinal motion segments through a three-dimensional poroelastic mixed finite element model.

    Wu, J S; Chen, J H


    The purpose of this study is to clarify the mechanical behaviour of spinal motion segments through a proper numerical model. The model constructed can give correct information and provide medical fields with valuable guidance in solving clinical problems occurring in the spine. A three-dimensional poroelastic finite element model of spinal motion segments is constructed and a mixed formulation is introduced. The geometry of the model is automatically formed from a series of CT-scanning images. Vertebral column, intervertebral joint, facet joints and ligaments are all included in the model. The contact surface of facet joints is considered as the inclined boundary. Such inclination is imposed when the contact surface is under compression. Ligaments surrounding the vertebral body and the intervertebral disc are put into the model when they are under tension. Iteration is implemented in the computing process to meet such boundary characteristics of facet joints and ligaments. Prediction of the mechanical behaviour in the segment under long term creep loading, is demonstrated using the current algorithm. Results show that the model and corresponding numerical procedures developed here can simulate the mechanical behaviour of the spinal motion segments properly.

  17. Time dependent voiding mechanisms in polyamide 6 submitted to high stress triaxiality: experimental characterisation and finite element modelling

    Selles, Nathan; King, Andrew; Proudhon, Henry; Saintier, Nicolas; Laiarinandrasana, Lucien


    Double notched round bars made of semi-crystalline polymer polyamide 6 (PA6) were submitted to monotonic tensile and creep tests. The two notches had a root radius of 0.45 mm, which imposes a multiaxial stress state and a state of high triaxiality in the net (minimal) section of the specimens. Tests were carried out until the failure occurred from one of the notches. The other one, unbroken but deformed under steady strain rate or steady load, was inspected using the Synchrotron Radiation Computed Tomography (SRCT) technique. These 3D through thickness inspections allowed the study of microstructural evolution at the peak stress for the monotonic tensile test and at the beginning of the tertiary creep for the creep tests. Cavitation features were assessed with a micrometre resolution within the notched region. Spatial distributions of void volume fraction ( Vf) and void morphology were studied. Voiding mechanisms were similar under steady strain rates and steady loads. The maximum values of Vf were located between the axis of revolution of the specimens and the notch surface and voids were considered as flat cylinders with a circular basis perpendicular to the loading direction. A model, based on porous plasticity, was used to simulate the mechanical response of this PA6 material under high stress triaxiality. Both macroscopic behaviour (loading curves) and voiding micro-mechanisms (radial distributions of void volume fraction) were accurately predicted using finite element simulations.

  18. $\\gamma$-Ray Bursts the Four Crises

    Tavani, M


    We discuss some open problems concerning the origin and the emission mechanism of gamma-ray bursts (GRBs) in light of recent developments. If GRBs originate at extragalactic distances, we are facing four crises: (1) an energy crisis, models have to account for more than 10^{53} ergs of energy emitted in the gamma-ray energy band; (2) a spectral crisis, emission models have to account for the surprising `smoothness' of GRB broad-band spectra, with no indication of the predicted spectral `distorsions' caused by inverse Compton scattering in large radiation energy density media, and no evidence for beaming; (3) an afterglow crisis, relativistic shock models have to explain the complexity of the afterglow behavior, the longevity of optical transients detectable up to six months after the burst, the erratic behavior of the radio emission, and the lack of evidence for substantial beaming as indicated by recent searches for GRB afterglows in the X-ray band; (4) a population crisis, from data clearly indicating that ...

  19. Combining the finite element method with structural connectome-based analysis for modeling neurotrauma: connectome neurotrauma mechanics.

    Reuben H Kraft

    Full Text Available This article presents the integration of brain injury biomechanics and graph theoretical analysis of neuronal connections, or connectomics, to form a neurocomputational model that captures spatiotemporal characteristics of trauma. We relate localized mechanical brain damage predicted from biofidelic finite element simulations of the human head subjected to impact with degradation in the structural connectome for a single individual. The finite element model incorporates various length scales into the full head simulations by including anisotropic constitutive laws informed by diffusion tensor imaging. Coupling between the finite element analysis and network-based tools is established through experimentally-based cellular injury thresholds for white matter regions. Once edges are degraded, graph theoretical measures are computed on the "damaged" network. For a frontal impact, the simulations predict that the temporal and occipital regions undergo the most axonal strain and strain rate at short times (less than 24 hrs, which leads to cellular death initiation, which results in damage that shows dependence on angle of impact and underlying microstructure of brain tissue. The monotonic cellular death relationships predict a spatiotemporal change of structural damage. Interestingly, at 96 hrs post-impact, computations predict no network nodes were completely disconnected from the network, despite significant damage to network edges. At early times (t < 24 hrs network measures of global and local efficiency were degraded little; however, as time increased to 96 hrs the network properties were significantly reduced. In the future, this computational framework could help inform functional networks from physics-based structural brain biomechanics to obtain not only a biomechanics-based understanding of injury, but also neurophysiological insight.

  20. Correlation between mechanical stress by finite element analysis and 18F-fluoride PET uptake in hip osteoarthritis patients.

    Hirata, Yasuhide; Inaba, Yutaka; Kobayashi, Naomi; Ike, Hiroyuki; Yukizawa, Yohei; Fujimaki, Hiroshi; Tezuka, Taro; Tateishi, Ukihide; Inoue, Tomio; Saito, Tomoyuki


    18F-fluoride positron emission tomography (18F-fluoride PET) is a functional imaging modality used primarily to detect increased bone metabolism. Increased 18F-fluoride PET uptake suggests an association between increased bone metabolism and load stress at the subchondral level. This study therefore examined the relationship between equivalent stress distribution calculated by finite element analysis and 18F-fluoride PET uptake in patients with hip osteoarthritis. The study examined 34 hips of 17 patients who presented to our clinic with hip pain, and were diagnosed with osteoarthritis or pre-osteoarthritis. The hips with trauma, infection, or bone metastasis of cancer were excluded. Three-dimensional models of each hip were created from computed tomography data to calculate the maximum equivalent stress by finite element analysis, which was compared with the maximum standardized uptake value (SUVmax) examined by 18F-fluoride PET. The SUVmax and equivalent stress were correlated (Spearman's rank correlation coefficient ρ=0.752), and higher equivalent stress values were noted in higher SUVmax patients. The correlation between SUVmax and maximum equivalent stress in osteoarthritic hips suggests the possibility that 18F-fluoride PET detect increased bone metabolism at sites of stress concentration. This study demonstrates the correlation between mechanical stress and bone remodeling acceleration in hip osteoarthritis.

  1. Digital image correlation and finite element modelling as a method to determine mechanical properties of human soft tissue in vivo

    Moerman, Kevin M; Evans, Sam L; Simms, Ciaran K


    The mechanical properties of human soft tissue are crucial for impact biomechanics, rehabilitation engineering and surgical simulation. Validation of these constitutive models using human data remains challenging and often requires the use of non-invasive imaging and inverse finite element (FE) analysis. Post processing data from imaging methods such as tagged magnetic resonance imaging (MRI) can be challenging. Digital Image Correlation (DIC) however is a relatively straightforward imaging method and thus the goal of this study was to assess the use of DIC in combination with FE modelling to determine the bulk material properties of human soft tissue. Indentation experiments were performed on a silicone gel soft tissue phantom. A two camera DIC setup was then used to record the 3D surface deformation. The experiment was then simulated using a FE model.

  2. Investigation on mechanism of magnetization reversal for nanocrystalline Pr-Fe-B permanent magnets by micromagnetic finite element methods

    ZHENG Bo; ZHAO Sufen


    Magnetization configurations were calculated under various magnetic fields for nanocrystalline Pr-Fe-B permanent magnets by micromagnetic finite element method. According to the configurations during demagnetization process, the mechanism of magnetization reversal was analyzed. For the Pr2Fe14B with 10 nm grains or its composite with 10vol.% α-Fe, the coercivity was determined by nucleation of reversed domain that took place at grain boundaries. However, for Pr2Fe14B with 30 nm grains, coercivity was controlled by pinning of the nucleated domain. For Pr2Fe14B/α-Fe with 30vol.% α-Fe, the demagnetization behavior was characterized by continuous reversal of α-Fe moment.

  3. Effect of Co element on microstructure and mechanical properties of FeCoxNiCuAl alloys

    Yanxin ZHUANG; Wenjie LIU; Pengfei XING; Fei WANG; Jicheng HE


    FeCoxNiCuAl (x values in molar ratio,x=0.2,0.5,1,1.5,2 and 3) alloys were prepared using a suck-casting method.The effect of Co element on phase constituents,microstructure and mechanical properties of the FeCoxNiCuAl alloys was investigated using X-ray diffraction,scanning electron microscopy,optical microscopy and compressive tests.It was found that the Co addition has a significant influence on the structure and properties of the FeCoxNiCuAl alloys.The alloys have typical dendrite microstructure,and are composed of a simple fcc structure and bcc structure.The addition of Co promotes the formation of fcc phase in the alloys,retards the compressive strength and hardness of the alloys,and enhances the plasticity of the alloys.

  4. Effect of Residual Stresses and Prediction of Possible Failure Mechanisms on Thermal Barrier Coating System by Finite Element Method

    Ranjbar-Far, M.; Absi, J.; Mariaux, G.; Shahidi, S.


    This work is focused on the effect of the residual stresses resulting from the coating process and thermal cycling on the failure mechanisms within the thermal barrier coating (TBC) system. To reach this objective, we studied the effect of the substrate preheating and cooling rate on the coating process conditions. A new thermomechanical finite element model (FEM) considering a nonhomogeneous temperature distribution has been developed. In the results, we observed a critical stress corresponding to a low substrate temperature and high cooling rate during spraying of the top-coat material. Moreover, the analysis of the stress distribution after service shows that more critical stresses are obtained in the case where residual stresses are taken into account.

  5. Finite Element Analysis of voltage effect in the MechanicalBehavior of Diaphragm of Electrostatic Micro-pumps

    Hamid masoudi sadaghiani


    Full Text Available Micro-pumps are one of the most important devices in the field of micro-fluids which have many applications in biomedical engineering. Electrostatic stimulation is one of the mechanisms of stimulation in the micro-pumps that due to low power consumption and comfortable control have very much application in this field. Various phenomena occurs in micro-pumps, electrostatic induction that influence the efficiency and efficacy of this devices. One of these phenomena have been Pull-in instability which is a static phenomenon and occurs when the applied voltage exceeds a critical level. In this case, the diaphragm of micro pump get absorbed into opposite fixed electrode and instability occurs in the system. Therefore, understanding the relationship between pull-in voltage by external factors (for example, the physical characteristics of the device help designers to customize these factors in order to take their required output from device. To estimate the pull-in voltage, for an electrostatic diaphragm computer simulation of finite elements were used. According to the results obtained from the Software, the voltage in steps of 0.025, V = 313/925 which is best answer to unstable Static voltage.The amount of voltage for dynamic mode is approximately 0.91 of static value that is v = 284.41v obtained by software. Comparing the results it can be observed that in the case of unstable Static voltage there is little difference between results. So with this software Mechanical Behavior of Micro Analytical review pages that is difficult and time-consuming can be studied.And the results are used in the design of MEMS that these elements are used in the micro-plates.

  6. Gamma ray bursts, neutron star quakes, and the Casimir effect

    Carlson, C; Pérez-Mercader, J; Carlson, C; Goldman, T; Perez-Mercader, J


    We propose that the dynamic Casimir effect is a mechanism that converts the energy of neutron starquakes into \\gamma--rays. This mechanism efficiently produces photons from electromagnetic Casimir energy released by the rapid motion of a dielectric medium into a vacuum. Estimates based on the cutoff energy of the gamma ray bursts and the volume involved in a starquake indicate that the total gamma ray energy emission is consonant with observational requirements.

  7. 蔚县矿区北阳庄矿东二采区皮带巷里段突水机理探讨%Probe into Belt Way Inside Water Bursting Mechanism in E2 Winning District, Beiyangzhuang Coalmine, Yuxian Mining Area

    李万阳; 贾立新; 张树胜


    A water bursting accident has been happened during Sep 27~Nov 1, 2014 in the E2 winning district, Beiyangzhuang coalmine. The peak water inflow was 2015 m3/h, large amount gangue and fragments burst out at the same time. The water bursting pro⁃cess was long, with water temperature 30℃above, higher 3~4℃than previous two in the coalmine. The contents of Ga++and Mg++in the water are higher than in Ordovician limestone water, and basically consistent with the regional Jixian System limestone water quality type. Through the analyses of the area’s geological and hydrogeological conditions, discussed water bursting mechanism, have consid⁃ered that the main causation of this water bursting is structurally formed water conducted zone has led through the deep part paleokarst subsided column made the Jixian System Wumishan limestone karst water pass through subsided column and water conducted zone in⁃to the coalmine. The study has provided geological basis for mine water control works.%北阳庄矿东二采区皮带巷里段2014年9月27日~11月1日发生突水事故,峰值涌水量达2015 m3/h,同时喷出大量矸石和碎屑,突水过程时间长,水温高达30℃以上,比本矿井前两次突水水温高3~4℃,水中Ga++、Mg++含量也高于奥灰水,且与区域蓟县系灰岩水水质类型基本一致。通过对本区地质和水文地质条件分析,探讨了突水机理,认为本次突水主要是由于构造形成的导压裂隙带导通了深部古岩溶陷落柱,使蓟县系雾迷山岩溶水通过古陷落柱及导压构造裂隙带进入矿井而形成。该研究为矿井防治水工作提供了地质依据。

  8. A comparison of computational methods for detecting bursts in neuronal spike trains and their application to human stem cell-derived neuronal networks.

    Cotterill, Ellese; Charlesworth, Paul; Thomas, Christopher W; Paulsen, Ole; Eglen, Stephen J


    Accurate identification of bursting activity is an essential element in the characterization of neuronal network activity. Despite this, no one technique for identifying bursts in spike trains has been widely adopted. Instead, many methods have been developed for the analysis of bursting activity, often on an ad hoc basis. Here we provide an unbiased assessment of the effectiveness of eight of these methods at detecting bursts in a range of spike trains. We suggest a list of features that an ideal burst detection technique should possess and use synthetic data to assess each method in regard to these properties. We further employ each of the methods to reanalyze microelectrode array (MEA) recordings from mouse retinal ganglion cells and examine their coherence with bursts detected by a human observer. We show that several common burst detection techniques perform poorly at analyzing spike trains with a variety of properties. We identify four promising burst detection techniques, which are then applied to MEA recordings of networks of human induced pluripotent stem cell-derived neurons and used to describe the ontogeny of bursting activity in these networks over several months of development. We conclude that no current method can provide "perfect" burst detection results across a range of spike trains; however, two burst detection techniques, the MaxInterval and logISI methods, outperform compared with others. We provide recommendations for the robust analysis of bursting activity in experimental recordings using current techniques.

  9. Correlated bursts and the role of memory range

    Jo, Hang-Hyun; Kaski, Kimmo; Kertesz, Janos


    Inhomogeneous temporal processes in natural and social phenomena have been described by bursts that are rapidly occurring events within short time periods alternating with long periods of low activity. In addition to the analysis of heavy-tailed inter-event time distributions, higher-order correlations between inter-event times, called \\emph{correlated bursts}, have been studied only recently. As the possible mechanisms underlying such correlated bursts are far from being fully understood, we devise a simple model for correlated bursts by using a self-exciting point process with variable memory range. Here the probability that a new event occurs is determined by a memory function that is the sum of decaying memories of the past events. In order to incorporate the noise and/or limited memory capacity of systems, we apply two memory loss mechanisms, namely either fixed number or variable number of memories. By using theoretical analysis and numerical simulations we find that excessive amount of memory effect ma...

  10. Mechanical behaviour of a fibrous scaffold for ligament tissue engineering: finite elements analysis vs. X-ray tomography imaging.

    Laurent, Cédric P; Latil, Pierre; Durville, Damien; Rahouadj, Rachid; Geindreau, Christian; Orgéas, Laurent; Ganghoffer, Jean-François


    The use of biodegradable scaffolds seeded with cells in order to regenerate functional tissue-engineered substitutes offers interesting alternative to common medical approaches for ligament repair. Particularly, finite element (FE) method enables the ability to predict and optimise both the macroscopic behaviour of these scaffolds and the local mechanic signals that control the cell activity. In this study, we investigate the ability of a dedicated FE code to predict the geometrical evolution of a new braided and biodegradable polymer scaffold for ligament tissue engineering by comparing scaffold geometries issued from FE simulations and from X-ray tomographic imaging during a tensile test. Moreover, we compare two types of FE simulations the initial geometries of which are issued either from X-ray imaging or from a computed idealised configuration. We report that the dedicated FE simulations from an idealised reference configuration can be reasonably used in the future to predict the global and local mechanical behaviour of the braided scaffold. A valuable and original dialog between the fields of experimental and numerical characterisation of such fibrous media is thus achieved. In the future, this approach should enable to improve accurate characterisation of local and global behaviour of tissue-engineering scaffolds.

  11. The dynamic excitation of a granular chain for biomedical ultrasound applications: contact mechanics finite element analysis and validation

    Gélat, P.; Yang, J.; Thomas, P. J.; Hutchins, D. A.; Akanji, O.; Davis, L. A. J.; Freear, S.; Harput, S.; Saffari, N.


    There has been recent interest in the transmission of acoustic signals along granular chains of spherical beads to produce waveforms of relevance to biomedical ultrasound applications. Hertzian contact between adjacent beads can introduce different harmonic content into the signal as it propagates. This transduction mechanism has the potential to be of use in both diagnostic and therapeutic ultrasound applications, and is the object of the study presented here. Although discrete dynamics models of this behaviour exist, a more comprehensive solution must be sought if changes in shape and deformation of individual beads are to be considered. Thus, the finite element method was used to investigate the dynamics of a granular chain of six, 1 mm diameter chrome steel spherical beads excited at one end using a sinusoidal displacement signal at 73 kHz. Output from this model was compared with the solution provided by the discrete dynamics model, and good overall agreement obtained. In addition, it was able to resolve the complex dynamics of the granular chain, including the multiple collisions which occur. It was demonstrated that under dynamic excitation conditions, the inability of discrete mechanics models to account for elastic deformation of the beads when these lose contact, could lead to discrepancies with experimental observations.

  12. LOFAR tied-array imaging and spectroscopy of solar S bursts

    Morosan, D. E.; Gallagher, P. T.; Zucca, P.; O'Flannagain, A.; Fallows, R.; Reid, H.; Magdalenić, J.; Mann, G.; Bisi, M. M.; Kerdraon, A.; Konovalenko, A. A.; MacKinnon, A. L.; Rucker, H. O.; Thidé, B.; Vocks, C.; Alexov, A.; Anderson, J.; Asgekar, A.; Avruch, I. M.; Bentum, M. J.; Bernardi, G.; Bonafede, A.; Breitling, F.; Broderick, J. W.; Brouw, W. N.; Butcher, H. R.; Ciardi, B.; de Geus, E.; Eislöffel, J.; Falcke, H.; Frieswijk, W.; Garrett, M. A.; Grießmeier, J.; Gunst, A. W.; Hessels, J. W. T.; Hoeft, M.; Karastergiou, A.; Kondratiev, V. I.; Kuper, G.; van Leeuwen, J.; McKay-Bukowski, D.; McKean, J. P.; Munk, H.; Orru, E.; Paas, H.; Pizzo, R.; Polatidis, A. G.; Scaife, A. M. M.; Sluman, J.; Tasse, C.; Toribio, M. C.; Vermeulen, R.; Zarka, P.


    Context. The Sun is an active source of radio emission that is often associated with energetic phenomena ranging from nanoflares to coronal mass ejections (CMEs). At low radio frequencies (<100 MHz), numerous millisecond duration radio bursts have been reported, such as radio spikes or solar S bursts (where S stands for short). To date, these have neither been studied extensively nor imaged because of the instrumental limitations of previous radio telescopes. Aims: Here, LOw Frequency ARray (LOFAR) observations were used to study the spectral and spatial characteristics of a multitude of S bursts, as well as their origin and possible emission mechanisms. Methods: We used 170 simultaneous tied-array beams for spectroscopy and imaging of S bursts. Since S bursts have short timescales and fine frequency structures, high cadence (~50 ms) tied-array images were used instead of standard interferometric imaging, that is currently limited to one image per second. Results: On 9 July 2013, over 3000 S bursts were observed over a time period of ~8 h. S bursts were found to appear as groups of short-lived (<1 s) and narrow-bandwidth (~2.5 MHz) features, the majority drifting at ~3.5 MHz s-1 and a wide range of circular polarisation degrees (2-8 times more polarised than the accompanying Type III bursts). Extrapolation of the photospheric magnetic field using the potential field source surface (PFSS) model suggests that S bursts are associated with a trans-equatorial loop system that connects an active region in the southern hemisphere to a bipolar region of plage in the northern hemisphere. Conclusions: We have identified polarised, short-lived solar radio bursts that have never been imaged before. They are observed at a height and frequency range where plasma emission is the dominant emission mechanism, however, they possess some of the characteristics of electron-cyclotron maser emission. A movie associated to Fig. 3 is available in electronic form at

  13. Suppression of the Early Optical Afterglow of Gamma-Ray Bursts

    Roming, P W A; Fox, D B; Zhang, B; Liang, E; Mason, K O; Rol, E; Burrows, D N; Blustin, A J; Boyd, P T; Brown, P; Holland, S T; McGowan, K; Landsman, W B; Page, K L; Rhoads, J E; Rosen, S R; Barthelmy, S D; Breeveld, A A; Cucchiara, A; De Pasquale, M; Fenimore, E E; Gehrels, N; Gronwall, C; Grupe, D; Goad, M R; Ivanushkina, M; James, C; Kennea, J A; Kobayashi, S; Mangano, V; Mészáros, P; Morgan, A N; Nousek, J A; Osborne, J P; Palmer, D M; Poole, T; Still, M D; Tagliaferri, G; Zane, S


    Recent observations of gamma-ray bursts (GRBs) are providing prompt few-arcminute gamma-ray localizations, rapid few-arcsecond X-ray positions, and rapid and extensive follow-up in the X-ray, UV, optical, and radio bands. Thirteen of these bursts include extraordinary optical upper limits at very early epochs after the burst, in marked contrast to the bright optical flashes previously believed to be the norm. Although host extinction can explain the properties of some bursts, and the natural range of burst energies and distances can explain some others, comparison of our optical, X-ray, and gamma-ray data sets reveals that these considerations alone cannot explain the full diversity of the burst population. Instead, one or more mechanisms must act to suppress the optical flash and provide a significantly enhanced efficiency of the prompt gamma-ray emission for some bursts. One possibility is that a fraction of the burst population is powered by Poynting flux-dominated outflows, resulting in a very inefficient...

  14. A Different Cone: Bursting Drops in Solids

    Zhao, Xuanhe


    Drops in fluids tend to be spheres--a shape that minimizes surface energy. In thunderstorm clouds, drops can become unstable and emit thin jets when charged beyond certain limits. The instability of electrified drops in gases and liquids has been widely studied and used in applications including ink-jet printing, electrospinning nano-fibers, microfluidics and electrospray ionization. Here we report a different scenario: drops in solids become unstable and burst under sufficiently high electric fields. We find the instability of drops in solids morphologically resembles that in liquids, but the critical electric field for the instability follows a different scaling due to elasticity of solids. Our observations and theoretical models not only advance the fundamental understanding of electrified drops but also suggest a new failure mechanism of high-energy-density dielectric polymers, which have diverse applications ranging from capacitors for power grids and electric vehicles to muscle-like transducers for soft robots and energy harvesting.

  15. Relativistic Outflows in Gamma-Ray Bursts

    Aloy, M A


    The possibility that gamma-ray bursts (GRBs) were not isotropic emissions was devised theoretically as a way to ameliorate the huge energetic budget implied by the standard fireball model for these powerful phenomena. However, the mechanism by which after the quasy-isotropic release of a few $10^{50} $erg yields a collimated ejection of plasma could not be satisfactory explained analytically. The reason being that the collimation of an outflow by its progenitor system depends on a very complex and non-linear dynamics. That has made necessary the use of numerical simulations in order to shed some light on the viability of some likely progenitors of GRBs. In this contribution I will review the most relevant features shown by these numerical simulations and how they have been used to validate the collapsar model (for long GRBs) and the model involving the merger of compact binaries (for short GRBs).

  16. Hybrid Finite-Discrete Element Simulation of the EDZ Formation and Mechanical Sealing Process Around a Microtunnel in Opalinus Clay

    Lisjak, Andrea; Tatone, Bryan S. A.; Mahabadi, Omid K.; Grasselli, Giovanni; Marschall, Paul; Lanyon, George W.; Vaissière, Rémi de la; Shao, Hua; Leung, Helen; Nussbaum, Christophe


    The analysis and prediction of the rock mass disturbance around underground excavations are critical components of the performance and safety assessment of deep geological repositories for nuclear waste. In the short term, an excavation damaged zone (EDZ) tends to develop due to the redistribution of stresses around the underground openings. The EDZ is associated with an increase in hydraulic conductivity of several orders of magnitude. In argillaceous rocks, sealing mechanisms ultimately lead to a partial reduction in the effective hydraulic conductivity of the EDZ with time. The goal of this study is to strengthen the understanding of the phenomena involved in the EDZ formation and sealing in Opalinus Clay, an indurated claystone currently being assessed as a host rock for a geological repository in Switzerland. To achieve this goal, hybrid finite-discrete element method (FDEM) simulations are performed. With its explicit consideration of fracturing processes, FDEM modeling is applied to the HG-A experiment, an in situ test carried out at the Mont Terri underground rock laboratory to investigate the hydro-mechanical response of a backfilled and sealed microtunnel. A quantitative simulation of the EDZ formation process around the microtunnel is first carried out, and the numerical results are compared with field observations. Then, the re-compression of the EDZ under the effect of a purely mechanical loading, capturing the increase of swelling pressure from the backfill onto the rock, is considered. The simulation results highlight distinctive rock failure kinematics due to the bedded structure of the rock mass. Also, fracture termination is simulated at the intersection with a pre-existing discontinuity, representing a fault plane oblique to the bedding orientation. Simulation of the EDZ re-compression indicates an overall reduction of the total fracture area as a function of the applied pressure, with locations of ineffective sealing associated with self

  17. Mechanical properties of UO2 thin films under heavy ion irradiation using nanoindentation and finite element modeling

    Elbakhshwan, Mohamed S.; Miao, Yinbin; Stubbins, James F.; Heuser, Brent J.


    The mechanical response of UO2 to irradiation is becoming increasingly important due to the shift to higher burn-up rates in the next generation of nuclear reactors. In the current study, thin films of UO2 were deposited on YSZ substrates using reactive-gas magnetron sputtering. Nanoindentation was used to measure the mechanical properties of the as-grown and irradiated films. Finite element modeling was used to account for the substrate effect on the measurements. In order to study the effect of displacement cascades accompanying gas bubbles, 5000 Å UO2 films were irradiated with 600 keV Kr+ ions at 25 °C and 600 °C. These irradiation conditions were used to confine radiation damage effects and implanted gas within the film. Results showed an increase in the film hardness and yield strength with dose, while elastic modulus initially decreased with irradiation and then kept increasing with dose. The change in hardness and elastic modulus is attributed to the introduction of gas bubbles and displacement cascade damage. Irradiation at 600 °C resulted in a decrease in the hardness and elastic modulus after irradiation using 600 keV Kr+ at a dose of 1E14 ions/cm2. Both hardness and elastic modulus then increased with irradiation dose. This behavior is attributed to recrystallization during irradiation at 600 °C and the formation of nanocrystallite regions with diameter and density that increase with dose. The calculation of the critical resolved shear stress (CRSS) demonstrated that nanocrystals are the primary cause for film hardening based on the Orowan hardening mechanism.

  18. The oxidative burst reaction in mammalian cells depends on gravity.

    Adrian, Astrid; Schoppmann, Kathrin; Sromicki, Juri; Brungs, Sonja; von der Wiesche, Melanie; Hock, Bertold; Kolanus, Waldemar; Hemmersbach, Ruth; Ullrich, Oliver


    Gravity has been a constant force throughout the Earth's evolutionary history. Thus, one of the fundamental biological questions is if and how complex cellular and molecular functions of life on Earth require gravity. In this study, we investigated the influence of gravity on the oxidative burst reaction in macrophages, one of the key elements in innate immune response and cellular signaling. An important step is the production of superoxide by the NADPH oxidase, which is rapidly converted to H2O2 by spontaneous and enzymatic dismutation. The phagozytosis-mediated oxidative burst under altered gravity conditions was studied in NR8383 rat alveolar macrophages by means of a luminol assay. Ground-based experiments in "functional weightlessness" were performed using a 2 D clinostat combined with a photomultiplier (PMT clinostat). The same technical set-up was used during the 13th DLR and 51st ESA parabolic flight campaign. Furthermore, hypergravity conditions were provided by using the Multi-Sample Incubation Centrifuge (MuSIC) and the Short Arm Human Centrifuge (SAHC). The results demonstrate that release of reactive oxygen species (ROS) during the oxidative burst reaction depends greatly on gravity conditions. ROS release is 1.) reduced in microgravity, 2.) enhanced in hypergravity and 3.) responds rapidly and reversible to altered gravity within seconds. We substantiated the effect of altered gravity on oxidative burst reaction in two independent experimental systems, parabolic flights and 2D clinostat / centrifuge experiments. Furthermore, the results obtained in simulated microgravity (2D clinorotation experiments) were proven by experiments in real microgravity as in both cases a pronounced reduction in ROS was observed. Our experiments indicate that gravity-sensitive steps are located both in the initial activation pathways and in the final oxidative burst reaction itself, which could be explained by the role of cytoskeletal dynamics in the assembly and function

  19. Statistics of gamma ray burst temporal asymmetry

    Link, B; Link, Bennett; Epstein, Richard


    We study the temporal asymmetry of over 600 bursts from the BATSE 3B catalog, encompassing a 200-fold range in peak flux. By comparing the rates of rise and fall of the flux near the highest burst peak, we find that about two-thirds of the bursts exhibit a preferred asymmetry in the sense that the flux rises more rapidly than it falls, confirming the conclusions of previous studies employing smaller databases. The statistical significance of the average time asymmetry of the sample is >99.999\\%; therefore, models that predict time symmetry of the burst profile are ruled out. We find no statistically significant correlation between burst temporal asymmetry and peak. This result is consistent with both cosmological and local interpretations of the gamma ray burst phenomenon.

  20. Stirling Colgate and Gamma-Ray Bursts

    Lamb, Donald


    Even before the discovery of gamma-ray bursts (GRBs), Stirling Colgate proposed that bursts of x rays and gamma rays might be produced by a relativistic shock created in the supernova explosion of a massive star. We trace the scientific story of GRBs from their detection to the present, highlighting along the way Stirling's interest in them and his efforts to understand them. We summarize our current understanding that short, soft, repeating bursts are produced by magnetic neutron stars; short, hard bursts are produced by the mergers of neutron star-neutron star binaries; and long, hard bursts are produced by the core collapse of massive stars that have lost their hydrogen and helium envelopes. We then discuss some important open questions about GRBs and how they might be answered. We conclude by describing the recent serendipitous discovery of an x-ray burst of exactly the kind he proposed, and the insights into core collapse supernovae and GRBs that it provided.

  1. Hardness/intensity correlations among BATSE bursts

    Paciesas, William S.; Pendleton, Geoffrey N.; Kouveliotou, Chryssa; Fishman, Gerald J.; Meegan, Charles A.; Wilson, Robert B.


    Conclusions about the nature of gamma-ray bursts derived from the size-frequency distribution may be altered if a significant correlation exists between burst intensity and spectral shape. Moreover, if gamma-ray bursts have a cosmological origin, such a correlation may be expected to result from the expansion of the universe. We have performed a rudimentary search of the BATSE bursts for hardness/intensity correlations. The range of spectral shapes was determined for each burst by computing the ratio of the intensity in the range 100-300 keV to that in 55-300 keV. We find weak evidence for the existence of a correlation, the strongest effect being present when comparing the maximum hardness ratio for each burst with its maximum rate.

  2. Three types of $\\gamma$-ray bursts

    Mukherjee, S; Babu, G J; Murtagh, F; Fraley, C; Raftery, A E; Mukherjee, Soma; Feigelson, Eric D.; Babu, Gutti Jogesh; Murtagh, Fionn; Fraley, Chris; Raftery, Adrian


    A multivariate analysis of gamma-ray burst (GRB) bulk properties is presented to discriminate between distinct classes of GRBs. Several variables representing burst duration, fluence and spectral hardness are considered. Two multivariate clustering procedures are used on a sample of 797 bursts from the Third BATSE Catalog: a nonparametric average linkage hierarchical agglomerative clustering procedure validated with Wilks' $\\Lambda^*$ and other MANOVA tests; and a parametric maximum likelihood model-based clustering procedure assuming multinormal populations calculated with the EM Algorithm and validated with the Bayesian Information Criterion. The two methods yield very similar results. The BATSE GRB population consists of three classes with the following Duration/Fluence/Spectrum bulk properties: Class I with long/bright/intermediate bursts, Class II with short/hard/faint bursts, and Class III with intermediate/intermediate/soft bursts. One outlier with poor data is also present. Classes I and II correspond...

  3. Pulse Phase Dependence of the Magnetar Bursts

    Chetana Jain; Anjan Dutta; Biswajit Paul


    We report here results from a study of X-ray bursts from 3 magnetar candidates (SGR 1806–20, SGR 1900+14 and AXP 1E 2259+586). We have searched for a pulse phase dependence of the X-ray burst rate from these sources. X-ray light curves were obtained with the Proportional Counter Array on-board the Rossi X-ray Timing Explorer during the periods of intense burst activity in these sources. On detailed analysis of the three sources, we found a very significant burst rate for all pulsar phases. However, some locations appear to produce bursts slightly more often, rendering the non-isotropic distribution. Only in the case of SGR 1900+14, there is a clear pulse phase dependence of burst rate.

  4. Ballerina - pirouettes in search of gamma bursts

    Brandt, S.; Lund, N.; Pedersen, H.; Hjorth, J.; BALLERINA Collaboration


    The cosmological origin of gamma ray bursts has now been established with reasonable certainty. Many more bursts will need to be studied to establish the typical distance scale, and to map out the large diversity in properties which have been indicated by the first handful of events. We are proposing Ballerina, a small satellite to provide accurate positions and new data on the gamma-ray bursts. We anticipate a detection rate an order of magnitude larger than obtained from Beppo-SAX.

  5. United assembly algorithm for optical burst switching

    Jinhui Yu(于金辉); Yijun Yang(杨教军); Yuehua Chen(陈月华); Ge Fan(范戈)


    Optical burst switching (OBS) is a promising optical switching technology. The burst assembly algorithm controls burst assembly, which significantly impacts performance of OBS network. This paper provides a new assembly algorithm, united assembly algorithm, which has more practicability than conventional algorithms. In addition, some factors impacting selections of parameters of this algorithm are discussed and the performance of this algorithm is studied by computer simulation.

  6. Fast Radio Burst/Gamma-Ray Burst Cosmography

    Gao, He; Li, Zhuo; Zhang, Bing


    Recently, both theoretical arguments and observational evidence suggested that a small fraction of fast radio bursts (FRBs) could be associated with gamma-ray bursts (GRBs). If such FRB/GRB association systems are commonly detected in the future, the combination of dispersion measures (DM) derived from FRBs and redshifts derived from GRBs makes these systems a plausible tool to conduct cosmography. We quantify uncertainties in deriving the redshift-dependent DM_{IGM} as a function of z and test how well dark energy models can be constrained with Monte Carlo simulations. We show that with several tens of FRB/GRB systems potentially detected in a decade or so, one may reach reasonable constraints on wCDM models. When combined with Type Ia supernova (SN Ia) data, unprecedented constraints on the dark energy equation of state may be achieved, thanks to the prospects of detecting FRB/GRB systems at relatively high redshifts. The ratio between the mean value \\lt {DM_IGM} (z)\\gt and luminosity distance (D L(z)) is insensitive to dark energy models. This gives the prospect of applying SN Ia data to calibrate \\lt {DM_IGM} (z)\\gt using a relatively small sample of FRB/GRB systems, allowing a reliable constraint on the baryon inhomogeneity distribution as a function of redshift. The methodology developed in this paper can also be applied if the FRB redshifts can be measured by other means. Some caveats of putting this method into practice are also discussed.

  7. Fast radio burst/gamma-ray burst cosmography

    Gao, He; Zhang, Bing [Department of Physics and Astronomy, University of Nevada Las Vegas, NV 89154 (United States); Li, Zhuo, E-mail:, E-mail:, E-mail: [Department of Astronomy, School of Physics, Peking University, Beijing 100871 (China)


    Recently, both theoretical arguments and observational evidence suggested that a small fraction of fast radio bursts (FRBs) could be associated with gamma-ray bursts (GRBs). If such FRB/GRB association systems are commonly detected in the future, the combination of dispersion measures (DM) derived from FRBs and redshifts derived from GRBs makes these systems a plausible tool to conduct cosmography. We quantify uncertainties in deriving the redshift-dependent DM{sub IGM} as a function of z and test how well dark energy models can be constrained with Monte Carlo simulations. We show that with several tens of FRB/GRB systems potentially detected in a decade or so, one may reach reasonable constraints on wCDM models. When combined with Type Ia supernova (SN Ia) data, unprecedented constraints on the dark energy equation of state may be achieved, thanks to the prospects of detecting FRB/GRB systems at relatively high redshifts. The ratio between the mean value and luminosity distance (D {sub L}(z)) is insensitive to dark energy models. This gives the prospect of applying SN Ia data to calibrate using a relatively small sample of FRB/GRB systems, allowing a reliable constraint on the baryon inhomogeneity distribution as a function of redshift. The methodology developed in this paper can also be applied if the FRB redshifts can be measured by other means. Some caveats of putting this method into practice are also discussed.

  8. Prediction of Burst Pressure in Multistage Tube Hydroforming of Aerospace Alloys.

    Saboori, M; Gholipour, J; Champliaud, H; Wanjara, P; Gakwaya, A; Savoie, J


    Bursting, an irreversible failure in tube hydroforming (THF), results mainly from the local plastic instabilities that occur when the biaxial stresses imparted during the process exceed the forming limit strains of the material. To predict the burst pressure, Oyan's and Brozzo's decoupled ductile fracture criteria (DFC) were implemented as user material models in a dynamic nonlinear commercial 3D finite-element (FE) software, ls-dyna. THF of a round to V-shape was selected as a generic representative of an aerospace component for the FE simulations and experimental trials. To validate the simulation results, THF experiments up to bursting were carried out using Inconel 718 (IN 718) tubes with a thickness of 0.9 mm to measure the internal pressures during the process. When comparing the experimental and simulation results, the burst pressure predicated based on Oyane's decoupled damage criterion was found to agree better with the measured data for IN 718 than Brozzo's fracture criterion.

  9. Bistability of silence and seizure-like bursting.

    Barnett, William; O'Brien, Gabrielle; Cymbalyuk, Gennady


    Neuronal circuits exhibiting seizure episodes have been shown to be prone to multistability. The coexistence of normal and pathological regimes could explain why seizures suddenly start and stop. Methods developed in dynamical systems theory are powerful tools for determining the cellular mechanisms that underlie multistable seizure dynamics. Here, we present two different approaches to assess multistability in a model neuron. In this model, we identified a bursting regime and a silent regime. First, we investigated properties of a square pulse of injected current which produced a switch from seizure-like bursting into silence. By systematically varying the phase and amplitude of the pulse, we found contiguous pulse parameter sets, so-called windows, that satisfied this criterion, and we determined the dependence of these windows on the parameter gleak. As gleak increased, the size of each window scaled according to the same law as the amplitude of the saddle orbit. Second, we examined the role of each current in supporting bistability of bursting and silence. We defined the index of propensity for multistability as the range of gleak for which bursting and silence coexisted. We computed this quantity while iteratively varying the maximal conductance of each voltage-gated current one at a time. Increasing the maximal conductance of the slow potassium current or the hyperpolarization-activated current increased the range of bistability. In contrast, decreasing the maximal conductance of the persistent sodium current increased the range of bistability. Copyright © 2013 Elsevier B.V. All rights reserved.

  10. Bubble burst as jamming phase transition

    Nishinari, Katsuhiro; Saito, Yukiko Umeno; Watanabe, Tsutomu


    Recently research on bubble and its burst attract much interest of researchers in various field such as economics and physics. Economists have been regarding bubble as a disorder in prices. However, this research strategy has overlooked an importance of the volume of transactions. In this paper, we have proposed a bubble burst model by focusing the transactions incorporating a traffic model that represents spontaneous traffic jam. We find that the phenomenon of bubble burst shares many similar properties with traffic jam formation by comparing data taken from US housing market. Our result suggests that the transaction could be a driving force of bursting phenomenon.

  11. Multiple conductances cooperatively regulate spontaneous bursting in mouse olfactory bulb external tufted cells.

    Liu, Shaolin; Shipley, Michael T


    External tufted (ET) cells are juxtaglomerular neurons that spontaneously generate bursts of action potentials, which persist when fast synaptic transmission is blocked. The intrinsic mechanism of this autonomous bursting is unknown. We identified a set of voltage-dependent conductances that cooperatively regulate spontaneous bursting: hyperpolarization-activated inward current (I(h)), persistent Na+ current (I(NaP)), low-voltage-activated calcium current (I(L/T)) mediated by T- and/or L-type Ca2+ channels, and large-conductance Ca2+-dependent K+ current (I(BK)). I(h) is important in setting membrane potential and depolarizes the cell toward the threshold of I(NaP) and I(T/L), which are essential to generate the depolarizing envelope that is crowned by a burst of action potentials. Action potentials depolarize the membrane and induce Ca2+ influx via high-voltage-activated Ca2+ channels (I(HVA)). The combined depolarization and increased intracellular Ca2+ activates I(BK), which terminates the burst by hyperpolarizing the membrane. Hyperpolarization activates I(h) and the cycle is regenerated. A novel finding is the role of L-type Ca2+ channels in autonomous ET cells bursting. A second novel feature is the role of BK channels, which regulate burst duration. I(L) and I(BK) may go hand-in-hand, the slow inactivation of I(L) requiring I(BK)-dependent hyperpolarization to deactivate inward conductances and terminate the burst. ET cells receive monosynaptic olfactory nerve input and drive the major inhibitory interneurons of the glomerular circuit. Modulation of the conductances identified here can regulate burst frequency, duration, and spikes per burst in ET cells and thus significantly shape the impact of glomerular circuits on mitral and tufted cells, the output channels of the olfactory bulb.

  12. An Artificial Intelligence Classification Tool and Its Application to Gamma-Ray Bursts

    Hakkila, Jon; Haglin, David J.; Roiger, Richard J.; Giblin, Timothy; Paciesas, William S.; Pendleton, Geoffrey N.; Mallozzi, Robert S.


    Despite being the most energetic phenomenon in the known universe, the astrophysics of gamma-ray bursts (GRBs) has still proven difficult to understand. It has only been within the past five years that the GRB distance scale has been firmly established, on the basis of a few dozen bursts with x-ray, optical, and radio afterglows. The afterglows indicate source redshifts of z=1 to z=5, total energy outputs of roughly 10(exp 52) ergs, and energy confined to the far x-ray to near gamma-ray regime of the electromagnetic spectrum. The multi-wavelength afterglow observations have thus far provided more insight on the nature of the GRB mechanism than the GRB observations; far more papers have been written about the few observed gamma-ray burst afterglows in the past few years than about the thousands of detected gamma-ray bursts. One reason the GRB central engine is still so poorly understood is that GRBs have complex, overlapping characteristics that do not appear to be produced by one homogeneous process. At least two subclasses have been found on the basis of duration, spectral hardness, and fluence (time integrated flux); Class 1 bursts are softer, longer, and brighter than Class 2 bursts (with two second durations indicating a rough division). A third GRB subclass, overlapping the other two, has been identified using statistical clustering techniques; Class 3 bursts are intermediate between Class 1 and Class 2 bursts in brightness and duration, but are softer than Class 1 bursts. We are developing a tool to aid scientists in the study of GRB properties. In the process of developing this tool, we are building a large gamma-ray burst classification database. We are also scientifically analyzing some GRB data as we develop the tool. Tool development thus proceeds in tandem with the dataset for which it is being designed. The tool invokes a modified KDD (Knowledge Discovery in Databases) process, which is described as follows.

  13. Role of persistent sodium current in bursting activity of mouse neocortical networks in vitro.

    van Drongelen, Wim; Koch, Henner; Elsen, Frank P; Lee, Hyong C; Mrejeru, Ana; Doren, Erin; Marcuccilli, Charles J; Hereld, Mark; Stevens, Rick L; Ramirez, Jan-Marino


    Most types of electrographic epileptiform activity can be characterized by isolated or repetitive bursts in brain electrical activity. This observation is our motivation to determine mechanisms that underlie bursting behavior of neuronal networks. Here we show that the persistent sodium (Na(P)) current in mouse neocortical slices is associated with cellular bursting and our data suggest that these cells are capable of driving networks into a bursting state. This conclusion is supported by the following observations. 1) Both low concentrations of tetrodotoxin (TTX) and riluzole reduce and eventually stop network bursting while they simultaneously abolish intrinsic bursting properties and sensitivity levels to electrical stimulation in individual intrinsically bursting cells. 2) The sensitivity levels of regular spiking neurons are not significantly affected by riluzole or TTX at the termination of network bursting. 3) Propagation of cellular bursting in a neuronal network depended on excitatory connectivity and disappeared on bath application of CNQX (20 microM) + CPP (10 microM). 4) Voltage-clamp measurements show that riluzole (20 microM) and very low concentrations of TTX (50 nM) attenuate Na(P) currents in the neural membrane within a 1-min interval after bath application of the drug. 5) Recordings of synaptic activity demonstrate that riluzole at this concentration does not affect synaptic properties. 6) Simulations with a neocortical network model including different types of pyramidal cells, inhibitory interneurons, neurons with and without Na(P) currents, and recurrent excitation confirm the essence of our experimental observations that Na(P) conductance can be a critical factor sustaining slow population bursting.

  14. Local axial compressive mechanical properties of human carotid atherosclerotic plaques-characterisation by indentation test and inverse finite element analysis.

    Chai, Chen-Ket; Akyildiz, Ali C; Speelman, Lambert; Gijsen, Frank J H; Oomens, Cees W J; van Sambeek, Marc R H M; van der Lugt, Aad; Baaijens, Frank P T


    The fibrous cap of an atherosclerotic plaque may be prone to rupture if the occurring stresses exceed the strength of the cap. Rupture can cause acute thrombosis and subsequent ischaemic stroke or myocardial infarction. A reliable prediction of the rupture probability is essential for the appropriate treatment of atherosclerosis. Biomechanical models, which compute stresses and strain, are promising to provide a more reliable rupture risk prediction. However, these models require knowledge of the local biomechanical properties of atherosclerotic plaque tissue. For this purpose, we examined human carotid plaques using indentation experiments. The test set-up was mounted on an inverted confocal microscope to visualise the collagen fibre structure during the tests. By using an inverse finite element (FE) approach, and assuming isotropic neo-Hookean behaviour, the corresponding Young's moduli were found in the range from 6 to 891kPa (median 30kPa). The results correspond to the values obtained by other research groups who analysed the compressive Young's modulus of atherosclerotic plaques. Collagen rich locations showed to be stiffer than collagen poor locations. No significant differences were found between the Young's moduli of structured and unstructured collagen architectures as specified from confocal collagen data. Insignificant differences between the middle of the fibrous cap, the shoulder regions, and remaining plaque tissue locations indicate that axial, compressive mechanical properties of atherosclerotic plaques are independent of location within the plaque. Copyright © 2013 Elsevier Ltd. All rights reserved.

  15. Fractionation of Rare Earth Elements in Plants Ⅰ. Fractionation Patterns and Their Forming Mechanisms in Different Organs of Triticum Aestivum

    Liang Tao; Ding Shiming; Zhang Chaosheng; Zhang Zili; Yan Juncai; Li Haitao


    Fractionations of rare earth elements (REEs) and the forming mechanisms in plants were studied using Triticum aestivum as plant material with application of exogenous REEs and hydroponic culture. REEs were significantly fractionated in different parts of Triticum aestivum. M-type tetrad effect could be observed in both root and shoot of Triticum aestivum, which might result from the different abilities of REEs to form phosphate precipitation. Middle REEs (MREEs), light REEs (LREEs) and heavy REEs (HREEs) were enriched in root, stem and leaf of Triticum aestivum, respectively. REE speciation calculations using VMINTEQ program show REEs in simulated xylem solution mainly exist as REE-EDTA- and RE3+, but only HREEs are enriched in REE-EDTA-, while LREEs are enriched in the other REE species. It is suggested that the fractionation between LREEs and HREEs might be caused by the uptake of REE-EDTA- in Triticum aestivum leaves, but might result from the uptake of the other REE species in their stems.

  16. A potential-of-mean-force approach for fracture mechanics of heterogeneous materials using the lattice element method

    Laubie, Hadrien; Radjaï, Farhang; Pellenq, Roland; Ulm, Franz-Josef


    Fracture of heterogeneous materials has emerged as a critical issue in many engineering applications, ranging from subsurface energy to biomedical applications, and requires a rational framework that allows linking local fracture processes with global fracture descriptors such as the energy release rate, fracture energy and fracture toughness. This is achieved here by means of a local and a global potential-of-mean-force (PMF) inspired Lattice Element Method (LEM) approach. In the local approach, fracture-strength criteria derived from the effective interaction potentials between mass points are shown to exhibit a scaling commensurable with the energy dissipation of fracture processes. In the global PMF-approach, fracture is considered as a sequence of equilibrium states associated with minimum potential energy states analogous to Griffith's approach. It is found that this global approach has much in common with a Grand Canonical Monte Carlo (GCMC) approach, in which mass points are randomly removed following a maximum dissipation criterion until the energy release rate reaches the fracture energy. The duality of the two approaches is illustrated through the application of the PMF-inspired LEM for fracture propagation in a homogeneous linear elastic solid using different means of evaluating the energy release rate. Finally, by application of the method to a textbook example of fracture propagation in a heterogeneous material, it is shown that the proposed PMF-inspired LEM approach captures some well-known toughening mechanisms related to fracture energy contrast, elasticity contrast and crack deflection in the considered two-phase layered composite material.

  17. The Power Spectra of Two Classes of Long-duration Gamma-ray Bursts

    Shen, R F


    We have studied the averaged power density spectra (PDSs) of two classes of long-duration gamma-ray bursts in the recent classification by Balastegui et al.(2001) based on neural network analysis. Both PDSs follow a power law over a wide frequency range with approximately the same slope, which indicates that a process with a self-similar temporal property may underlie the emission mechanisms of both. The two classes of bursts are divided into groups according to their brightness and spectral hardness respectively and each group's PDS was calculated; For both classes, the PDS is found to flatten both with increasing burst brightness and with increasing hardness.

  18. Real-Time Supernova Neutrino Burst Monitor at Super-Kamiokande

    Abe, K; Hayato, Y; Ikeda, M; Iyogi, K; Kameda, J; Kishimoto, Y; Miura, M; Moriyama, S; Nakahata, M; Nakano, Y; Nakayama, S; Sekiya, H; Shiozawa, M; Suzuki, Y; Takeda, A; Tanaka, H; Tomura, T; Ueno, K; Wendell, R A; Yokozawa, T; Irvine, T; Kajita, T; Kametani, I; Kaneyuki, K; Lee, K P; McLachlan, T; Nishimura, Y; Richard, E; Okumura, K; Labarga, L; Fernandez, P; Berkman, S; Tanaka, H A; Tobayama, S; Gustafson, J; Kearns, E; Raaf, J L; Stone, J L; Sulak, L R; Goldhaber, M; Carminati, G; Kropp, W R; Mine, S; Weatherly, P; Renshaw, A; Smy, M B; Sobel, H W; Takhistov, V; Ganezer, K S; Hartfiel, B L; Hill, J; Keig, W E; Hong, N; Kim, J Y; Lim, I T; Akiri, T; Himmel, A; Scholberg, K; Walter, C W; Wongjirad, T; Ishizuka, T; Tasaka, S; Jang, J S; Learned, J G; Matsuno, S; Smith, S N; Hasegawa, T; Ishida, T; Ishii, T; Kobayashi, T; Nakadaira, T; Nakamura, K; Oyama, Y; Sakashita, K; Sekiguchi, T; Tsukamoto, T; Suzuki, A T; Takeuchi, Y; Bronner, C; Hirota, S; Huang, K; Ieki, K; Kikawa, T; Minamino, A; Murakami, A; Nakaya, T; Suzuki, K; Takahashi, S; Tateishi, K; Fukuda, Y; Choi, K; Itow, Y; Mitsuka, G; Mijakowski, P; Hignight, J; Imber, J; Jung, C K; Yanagisawa, C; Wilking, M J; Ishino, H; Kibayashi, A; Koshio, Y; Mori, T; Sakuda, M; Yamaguchi, R; Yano, T; Kuno, Y; Tacik, R; Kim, S B; Okazawa, H; Choi, Y; Nishijima, K; Koshiba, M; Suda, Y; Totsuka, Y; Yokoyama, M; Martens, K; Marti, Ll; Vagins, M R; Martin, J F; de Perio, P; Konaka, A; Chen, S; Zhang, Y; Connolly, K; Wilkes, R J


    We present a real-time supernova neutrino burst monitor at Super-Kamiokande (SK). Detecting supernova explosions by neutrinos in real time is crucial for giving a clear picture of the explosion mechanism. Since the neutrinos are expected to come earlier than light, a fast broadcasting of the detection may give astronomers a chance to make electromagnetic radiation observations of the explosions right at the onset. The role of the monitor includes a fast announcement of the neutrino burst detection to the world and a determination of the supernova direction. We present the online neutrino burst detection system and studies of the direction determination accuracy based on simulations at SK.

  19. Analysis of historic bursts and burst detection in water supply areas of different size

    Bakker, M.; Trietsch, E.A.; Vreeburg, J.H.G.; Rietveld, L.C.


    Pipe bursts in water distribution networks lead to water losses and a risk of damaging the urban environment. We studied hydraulic data and customer contact records of 44 real bursts for a better understanding of the phenomena. We found that most bursts were reported to the water company shortly aft

  20. Bifurcations of emergent bursting in a neuronal network.

    Yu Wu

    Full Text Available Complex neuronal networks are an important tool to help explain paradoxical phenomena observed in biological recordings. Here we present a general approach to mathematically tackle a complex neuronal network so that we can fully understand the underlying mechanisms. Using a previously developed network model of the milk-ejection reflex in oxytocin cells, we show how we can reduce a complex model with many variables and complex network topologies to a tractable model with two variables, while retaining all key qualitative features of the original model. The approach enables us to uncover how emergent synchronous bursting can arise from a neuronal network which embodies known biological features. Surprisingly, the bursting mechanisms are similar to those found in other systems reported in the literature, and illustrate a generic way to exhibit emergent and multiple time scale oscillations at the membrane potential level and the firing rate level.

  1. Magnetars and Gamma Ray Bursts

    Bucciantini, N


    In the last few years, evidences for a long-lived and sustained engine in Gamma Ray Bursts (GRBs) have increased the attention to the so called millisecond-magnetar model, as a competitive alternative to the standard collapsar scenario. I will review here the key aspects of the {\\it millisecond magnetar} model for Long Duration Gamma Ray Bursts (LGRBs). I will briefly describe what constraints, present observations put on any engine model, both in term of energetic, outflow properties, and the relation with the associated Supernova (SN). For each of these I will show how the millisecond magnetar model satisfies the requirements, what are the limits of the model, how can it be further tested, and what observations might be used to discriminate against it. I will also discuss numerical results that show the importance of the confinement by the progenitor star in explaining the formation of a collimated outflow, how a detailed model for the evolution of the central engine can be built, and show that a wide varie...

  2. Closest Gamma Ray Burst Providing Scientists With Crucial Test for Burst Physics


    The closest Gamma Ray Burst (GRB) yet known is providing astronomers with a rare opportunity to gain information vital to understanding these powerful cosmic explosions. Extremely precise radio-telescope observations already have ruled out one proposed mechanism for the bursts. "This is the closest and brightest GRB we've ever seen, and we can use it to decipher the physics of how these bursts work," said Greg Taylor of the National Radio Astronomy Observatory (NRAO) in Socorro, NM. Taylor worked with Dale Frail, also of the NRAO, along with Prof. Shri Kulkarni and graduate student Edo Berger of Caltech in studying a GRB detected on March 29, 2003. The scientists presented their findings to the American Astronomical Society's meeting in Nashville, TN. VLBA image of GRB 030329 VLBA IMAGE of GRB 030329 CREDIT: NRAO/AUI/NSF (Click on Image for Larger Version) Taylor and Frail used the National Science Foundation's (NSF) Very Long Baseline Array (VLBA) and other radio telescopes to study the burst, known as GRB 030329. In a series of observations from April 1 to May 19, they determined the size of the expanding "fireball" from the burst and measured its position in the sky with great precision. At a distance of about 2.6 billion light-years, GRB 030329 is hardly next door. However, compared to other GRBs at typical distances of 8-10 billion light-years, it presents an easier target for study. "We only expect to see one burst per decade this close," said Frail. The precise measurement of the object's position allowed the scientists to show that one theoretical model for GRBs can be ruled out. This model, proposed in 2000, says that the radio-wave energy emitted by the GRB comes from "cannonballs" of material shot from the explosion at extremely high speeds. "The 'cannonball model' predicted that we should see the radio-emitting object move across the sky by a specific amount. We have not seen that motion," Taylor said. The currently standard "fireball model" of GRBs


    FRYER, CHRISTOPHER LEE [Los Alamos National Laboratory


    The authors review the different engines behind supernova (SNe) and gamma-ray bursts (GRBs), focusing on those engines driving explosions in massive stars: core-collapse SNe and long-duration GRBs. Convection and rotation play important roles in the engines of both these explosions. They outline the basic physics and discuss the wide variety of ways scientists have proposed that this physics can affect the supernova explosion mechanism, concluding with a review of the current status in these fields.

  4. A nonlinear, implicit, three-dimensional finite element code for solid and structural mechanics - User`s Manual

    Maker, B.N.


    This report provides a user`s manual for NIKE3D, a fully implicit three-dimensional finite element code for analyzing the finite strain static and dynamic response of inelastic solids, shells, and beams. Spatial discretization is achieved by the use of 8-node solid elements, 2-node truss and beam elements, and 4-node membrane and shell elements. Over twenty constitutive models are available for representing a wide range of elastic, plastic, viscous, and thermally dependent material behavior. Contact-impact algorithms permit gaps, frictional sliding, and mesh discontinuities along material interfaces. Several nonlinear solution strategies are available, including Full-, Modified-, and Quasi-Newton methods. The resulting system of simultaneous linear equations is either solved iteratively by an element-by-element method, or directly by a factorization method, for which case bandwidth minimization is optional. Data may be stored either in or out of core memory to allow for large analyses.

  5. 气爆式核桃破壳有限元力学分析%Finite Element Mechanics Analysis for Breaking Walnut Shell in Gas Explosion Type

    周军; 史建新


    Breaking walnut shell is the key of processing walnut .According to the geometry parameters of walnut , a wal-nut finite element analysis model is established with software .Through the analysis of the load stress state stress and strain distribution under three kinds of pneumatic loading ways , we have obtained the analysis results that when a load is loaded at hole A at 0 .55 Mpa , the walnut shell burst open position is the best and it is the optimal solution .More rupture positions more conducive to breaking hull work and being able to get a higher breaking rate and a lower loss rate .We have proved the feasibility of this finite element analysis model .%核桃破壳取仁技术是核桃深加工工艺中的重点。为此,根据核桃的几何尺寸参数,用软件建立了核桃有限元分析模型,对核桃在3种气压载荷加载方式下的受力状态进行应力与应变分布分析。分析结果表明,在0.55 MPa载荷时核桃结蒂位置加载是最优解,核桃壳体爆开位置较好,多处破裂有利于取仁工作,可以得到较高的破壳率和较低的碎仁率,证明此有限元分析模型具有可行性。

  6. The Most Remote Gamma-Ray Burst


    years, the look-back time indicates that the explosion took place around the time our own galaxy, the Milky Way, was formed and at least 6,000 million years before the solar system was born. GRB 000131 and other gamma-ray bursts are believed to have taken place in remote galaxies. However, due to the huge distance, it has not yet been possible to see the galaxy in which the GRB 000131 event took place (the "host" galaxy). From the observed fading of the afterglow it is possible to estimate that the maximum brightness of this explosion was at least 10,000 times brighter than the host galaxy. Future studies of gamma-ray bursts The present team of astronomers has now embarked upon a detailed study of the surroundings of GRB 000131 with the VLT. A main goal is to observe the properties of the host galaxy. From the observations of about twenty optical counterparts of gamma-ray bursts identified until now, it is becoming increasingly clear that these very rare events are somehow related to the death of massive, short-lived stars . But despite the accumulating amount of excellent data, the details of the mechanism that leads to such dramatic explosions still remain a puzzle to astrophysicists. The detection and present follow-up observations of GRB 000131 highlight the new possibilities for studies of the extremely distant (and very early) Universe, now possible by means of gamma-ray bursts. When observed with the powerful instruments at a large ground-based telescope like the VLT, this incredibly bright class of cosmological objects may throw light on the fundamental processes of star formation in the infant universe. Of no less interest is the opportunity to analyse the chemical composition of the gas clouds at the epoch galaxies formed, by means of the imprints of the corresponding absorption lines on the afterglow spectrum. Waiting for the opportunity In this context, it would be extremely desirable to obtain very detailed (high-dispersion) spectra of the afterglow of a

  7. Search for Gravitational Wave Bursts from Six Magnetars

    Abadie, J.; Abbott, B. P.; Abbott, R.; Abernathy, M.; Accadia, T.; Acernese, F.; Adams, C.; Adhikari, R.; Affeldt, C.; Allen, B.; Allen, G. S.; Amador Ceron, E.; Amariutei, D.; Amin, R. S.; Anderson, S. B.; Anderson, W. G.; Antonucci, F.; Arai, K.; Arain, M. A.; Araya, M. C.; Aston, S. M.; Astone, P.; Atkinson, D.; Aufmuth, P.; Aulbert, C.; Aylott, B. E.; Babak, S.; Baker, P.; Ballardin, G.; Ballmer, S.; Barker, D.; Barnum, S.; Barone, F.; Barr, B.; Barriga, P.; Barsotti, L.; Barsuglia, M.; Barton, M. A.; Bartos, I.; Bassiri, R.; Bastarrika, M.; Basti, A.; Bauchrowitz, J.; Bauer, Th. S.; Behnke, B.; Beker, M. G.; Bell, A. S.; Belletoile, A.; Belopolski, I.; Benacquista, M.; Bertolini, A.; Betzwieser, J.; Beveridge, N.; Beyersdorf, P. T.; Bilenko, I. A.; Billingsley, G.; Birch, J.; Birindelli, S.; Biswas, R.; Bitossi, M.; Bizouard, M. A.; Black, E.; Blackburn, J. K.; Blackburn, L.; Blair, D.; Bland, B.; Blom, M.; Bock, O.; Bodiya, T. P.; Bogan, C.; Bondarescu, R.; Bondu, F.; Bonelli, L.; Bonnand, R.; Bork, R.; Born, M.; Boschi, V.; Bose, S.; Bosi, L.; Bouhou, B.; Boyle, M.; Braccini, S.; Bradaschia, C.; Brady, P. R.; Braginsky, V. B.; Brau, J. E.; Breyer, J.; Bridges, D. O.; Brillet, A.; Brinkmann, M.; Brisson, V.; Britzger, M.; Brooks, A. F.; Brown, D. A.; Brummit, A.; Budzyński, R.; Bulik, T.; Bulten, H. J.; Buonanno, A.; Burguet-Castell, J.; Burmeister, O.; Buskulic, D.; Buy, C.; Byer, R. L.; Cadonati, L.; Cagnoli, G.; Cain, J.; Calloni, E.; Camp, J. B.; Campagna, E.; Campsie, P.; Cannizzo, J.; Cannon, K.; Canuel, B.; Cao, J.; Capano, C.; Carbognani, F.; Caride, S.; Caudill, S.; Cavaglià, M.; Cavalier, F.; Cavalieri, R.; Cella, G.; Cepeda, C.; Cesarini, E.; Chaibi, O.; Chalermsongsak, T.; Chalkley, E.; Charlton, P.; Chassande-Mottin, E.; Chelkowski, S.; Chen, Y.; Chincarini, A.; Christensen, N.; Chua, S. S. Y.; Chung, C. T. Y.; Chung, S.; Clara, F.; Clark, D.; Clark, J.; Clayton, J. H.; Cleva, F.; Coccia, E.; Colacino, C. N.; Colas, J.; Colla, A.; Colombini, M.; Conte, R.; Cook, D.; Corbitt, T. R.; Cornish, N.; Corsi, A.; Costa, C. A.; Coughlin, M.; Coulon, J.-P.; Coward, D. M.; Coyne, D. C.; Creighton, J. D. E.; Creighton, T. D.; Cruise, A. M.; Culter, R. M.; Cumming, A.; Cunningham, L.; Cuoco, E.; Dahl, K.; Danilishin, S. L.; Dannenberg, R.; D'Antonio, S.; Danzmann, K.; Das, K.; Dattilo, V.; Daudert, B.; Daveloza, H.; Davier, M.; Davies, G.; Daw, E. J.; Day, R.; Dayanga, T.; De Rosa, R.; DeBra, D.; Debreczeni, G.; Degallaix, J.; del Prete, M.; Dent, T.; Dergachev, V.; DeRosa, R.; DeSalvo, R.; Dhurandhar, S.; Di Fiore, L.; Di Lieto, A.; Di Palma, I.; Emilio, M. Di Paolo; Di Virgilio, A.; Díaz, M.; Dietz, A.; Donovan, F.; Dooley, K. L.; Dorsher, S.; Douglas, E. S. D.; Drago, M.; Drever, R. W. P.; Driggers, J. C.; Dumas, J.-C.; Dwyer, S.; Eberle, T.; Edgar, M.; Edwards, M.; Effler, A.; Ehrens, P.; Engel, R.; Etzel, T.; Evans, M.; Evans, T.; Factourovich, M.; Fafone, V.; Fairhurst, S.; Fan, Y.; Farr, B. F.; Fazi, D.; Fehrmann, H.; Feldbaum, D.; Ferrante, I.; Fidecaro, F.; Finn, L. S.; Fiori, I.; Flaminio, R.; Flanigan, M.; Foley, S.; Forsi, E.; Forte, L. A.; Fotopoulos, N.; Fournier, J.-D.; Franc, J.; Frasca, S.; Frasconi, F.; Frede, M.; Frei, M.; Frei, Z.; Freise, A.; Frey, R.; Fricke, T. T.; Friedrich, D.; Fritschel, P.; Frolov, V. V.; Fulda, P.; Fyffe, M.; Galimberti, M.; Gammaitoni, L.; Garcia, J.; Garofoli, J. A.; Garufi, F.; Gáspár, M. E.; Gemme, G.; Genin, E.; Gennai, A.; Ghosh, S.; Giaime, J. A.; Giampanis, S.; Giardina, K. D.; Giazotto, A.; Gill, C.; Goetz, E.; Goggin, L. M.; González, G.; Gorodetsky, M. L.; Goßler, S.; Gouaty, R.; Graef, C.; Granata, M.; Grant, A.; Gras, S.; Gray, C.; Greenhalgh, R. J. S.; Gretarsson, A. M.; Greverie, C.; Grosso, R.; Grote, H.; Grunewald, S.; Guidi, G. M.; Guido, C.; Gupta, R.; Gustafson, E. K.; Gustafson, R.; Hage, B.; Hallam, J. M.; Hammer, D.; Hammond, G.; Hanks, J.; Hanna, C.; Hanson, J.; Harms, J.; Harry, G. M.; Harry, I. W.; Harstad, E. D.; Hartman, M. T.; Haughian, K.; Hayama, K.; Hayau, J.-F.; Hayler, T.; Heefner, J.; Heitmann, H.; Hello, P.; Hendry, M. A.; Heng, I. S.; Heptonstall, A. W.; Herrera, V.; Hewitson, M.; Hild, S.; Hoak, D.; Hodge, K. A.; Holt, K.; Hong, T.; Hooper, S.; Hosken, D. J.; Hough, J.; Howell, E. J.; Huet, D.; Hughey, B.; Husa, S.; Huttner, S. H.; Ingram, D. R.; Inta, R.; Isogai, T.; Ivanov, A.; Jaranowski, P.; Johnson, W. W.; Jones, D. I.; Jones, G.; Jones, R.; Ju, L.; Kalmus, P.; Kalogera, V.; Kandhasamy, S.; Kanner, J. B.; Katsavounidis, E.; Katzman, W.; Kawabe, K.; Kawamura, S.; Kawazoe, F.; Kells, W.; Kelner, M.; Keppel, D. G.; Khalaidovski, A.; Khalili, F. Y.; Khazanov, E. A.; Kim, H.; Kim, N.; King, P. J.; Kinzel, D. L.; Kissel, J. S.; Klimenko, S.; Kondrashov, V.; Kopparapu, R.; Koranda, S.; Korth, W. Z.; Kowalska, I.; Kozak, D.


    Soft gamma repeaters (SGRs) and anomalous X-ray pulsars (AXPs) are thought to be magnetars: neutron stars powered by extreme magnetic fields. These rare objects are characterized by repeated and sometimes spectacular gamma-ray bursts. The burst mechanism might involve crustal fractures and excitation of non-radial modes which would emit gravitational waves (GWs). We present the results of a search for GW bursts from six galactic magnetars that is sensitive to neutron star f-modes, thought to be the most efficient GW emitting oscillatory modes in compact stars. One of them, SGR 0501+4516, is likely ~1 kpc from Earth, an order of magnitude closer than magnetars targeted in previous GW searches. A second, AXP 1E 1547.0-5408, gave a burst with an estimated isotropic energy >1044 erg which is comparable to the giant flares. We find no evidence of GWs associated with a sample of 1279 electromagnetic triggers from six magnetars occurring between 2006 November and 2009 June, in GW data from the LIGO, Virgo, and GEO600 detectors. Our lowest model-dependent GW emission energy upper limits for band- and time-limited white noise bursts in the detector sensitive band, and for f-mode ringdowns (at 1090 Hz), are 3.0 × 1044 d 2 1 erg and 1.4 × 1047 d 2 1 erg, respectively, where d_{1} = \\frac{d_{{0501}}}{1\\,{kpc}} and d 0501 is the distance to SGR 0501+4516. These limits on GW emission from f-modes are an order of magnitude lower than any previous, and approach the range of electromagnetic energies seen in SGR giant flares for the first time.

  8. Inhibitory activity of lipid fractions myobacterium avium complex against macrophage respiratory burst

    Shimizu, Toshiaki; 冨岡, 治明


    To explore possible mechanisms of the resistance of Mycobacterium avium complex (MAC) intracellular parasites to the antimicrobial activity of macrophages (MΦs), effects of the lipid components of these parasites on the MΦ respiratory burst were investigated. In this study, the MΦ respiratory burst was measured by luminoldependent chemiluminescence generated through the peroxidase-mediated halogenation reaction in murine peritoneal MΦs in response to phorbol myristate acetate (PMA) triggering...

  9. A new prediction method at the edge of optical burst switching network

    Zhicheng Sui; Qingji Zeng; Shilin Xiao


    To achieve lower assembly delay at optical burst switching edge node, this paper proposes an approach called current weight length prediction (CWLP) to improve existing estimate mechanism in burst introduced to make a dynamic tradeoff between the current and past traffic under different offset time.Simulation results show that CWLP can achieve a significant improvement in terms of traffic estimation in various offset time and offered load.

  10. Coding Bounds for Multiple Phased-Burst Correction and Single Burst Correction Codes

    Fong, Wai Han


    In this paper, two upper bounds on the achievable code rate of linear block codes for multiple phased-burst correction (MPBC) are presented. One bound is constrained to a maximum correctable cyclic burst length within every subblock, or equivalently a constraint on the minimum error free length or gap within every phased-burst. This bound, when reduced to the special case of a bound for single burst correction (SBC), is shown to be the Abramson bound when the cyclic burst length is less than half the block length. The second MPBC bound is developed without the minimum error free gap constraint and is used as a comparison to the first bound.

  11. Coupling and noise induced spiking-bursting transition in a parabolic bursting model.

    Ji, Lin; Zhang, Jia; Lang, Xiufeng; Zhang, Xiuhui


    The transition from tonic spiking to bursting is an important dynamic process that carry physiologically relevant information. In this work, coupling and noise induced spiking-bursting transition is investigated in a parabolic bursting model with specific discussion on their cooperation effects. Fast/slow analysis shows that weak coupling may help to induce the bursting by changing the geometric property of the fast subsystem so that the original unstable periodical solution are stabilized. It turned out that noise can play the similar stabilization role and induce bursting at appropriate moderate intensity. However, their cooperation may either strengthen or weaken the overall effect depending on the choice of noise level.

  12. Gamma-Ray Burst at the extreme: "the naked-eye burst" GRB 080319B

    Wozniak, P R; Panaitescu, A D; Wren, J A; Davis, H R; White, R R


    On 19 March 2008, the northern sky was the stage of a spectacular optical transient that for a few seconds remained visible to the naked eye. The transient was associated with GRB 080319B, a gamma-ray burst at a luminosity distance of about 6 Gpc (standard cosmology), making it the most luminous optical object ever recorded by human kind. We present comprehensive sky monitoring and multi-color optical follow-up observations of GRB 080319B collected by the RAPTOR telescope network covering the development of the explosion and the afterglow before, during, and after the burst. The extremely bright prompt optical emission revealed features that are normally not detectable. The optical and gamma-ray variability during the explosion are correlated, but the optical flux is much greater than can be reconciled with single emission mechanism and a flat gamma-ray spectrum. This extreme optical behavior is best understood as synchrotron self-Compton model (SSC). After a gradual onset of the gamma-ray emission, there is ...

  13. Using temporal bursts for query modeling

    Peetz, M.H.; Meij, E.; de Rijke, M.


    We present an approach to query modeling that leverages the temporal distribution of documents in an initially retrieved set of documents. In news-related document collections such distributions tend to exhibit bursts. Here, we define a burst to be a time period where unusually many documents are pu

  14. Photospheric radius expansion during magnetar bursts

    A.L. Watts; C. Kouveliotou; A.J. van der Horst; E. Göğüş; Y. Kaneko; M. van der Klis; R.A.M.J. Wijers; A.K. Harding; M.G. Baring


    On 2008 August 24 the new magnetar SGR 0501+4516 (discovered by Swift) emitted a bright burst with a pronounced double-peaked structure in hard X-rays, reminiscent of the double-peaked temporal structure seen in some bright thermonuclear bursts on accreting neutron stars. In the latter case this is

  15. Astronomy: Radio burst caught red-handed

    Falcke, Heino


    For almost a decade, astronomers have observed intense bursts of radio waves from the distant cosmos whose origins were unknown. The source of one such burst has now been identified, but this has only deepened the mystery. See Letter p.58

  16. The transposon-like Correia elements encode numerous strong promoters and provide a potential new mechanism for phase variation in the meningococcus.

    Siddique, Azeem; Buisine, Nicolas; Chalmers, Ronald


    Neisseria meningitidis is the primary causative agent of bacterial meningitis. The genome is rich in repetitive DNA and almost 2% is occupied by a diminutive transposon called the Correia element. Here we report a bioinformatic analysis defining eight subtypes of the element with four distinct types of ends. Transcriptional analysis, using PCR and a lacZ reporter system, revealed that two ends in particular encode strong promoters. The activity of the strongest promoter is dictated by a recurrent polymorphism (Y128) at the right end of the element. We highlight examples of elements that appear to drive transcription of adjacent genes and others that may express small non-coding RNAs. Pair-wise comparisons between three meningococcal genomes revealed that no more than two-thirds of Correia elements maintain their subtype at any particular locus. This is due to recombinational class switching between elements in a single strain. Upon switching subtype, a new allele is available to spread through the population by natural transformation. This process may represent a hitherto unrecognized mechanism for phase variation in the meningococcus. We conclude that the strain-to-strain variability of the Correia elements, and the large number of strong promoters encoded by them, allows for potentially widespread effects within the population as a whole. By defining the strength of the promoters encoded by the eight subtypes of Correia ends, we provide a resource that allows the transcriptional effects of a particular subtype at a given locus to be predicted.

  17. Mechanisms of extracellular signal-regulated kinase/cAMP response element-binding protein/brain-derived neurotrophic factor signal transduction pathway in depressive disorder.

    Wang, Hongyan; Zhang, Yingquan; Qiao, Mingqi


    The extracellular signal-regulated kinase/cAMP response element-binding protein/brain-derived neurotrophic factor signal transduction pathway plays an important role in the mechanism of action of antidepressant drugs and has dominated recent studies on the pathogenesis of depression. In the present review we summarize the known roles of extracellular signal-regulated kinase, cAMP response element-binding protein and brain-derived neurotrophic factor in the pathogenesis of depression and in the mechanism of action of antidepressant medicines. The extracellular signal-regulated kinase/cAMP response element-binding protein/brain-derived neurotrophic factor pathway has potential to be used as a biological index to help diagnose depression, and as such it is considered as an important new target in the treatment of depression.

  18. Mechanisms of extracellular signal-regulated kinase/cAMP response element-binding protein/brain-derived neurotrophic factor signaltransduction pathway in depressive disorder

    Hongyan Wang; Yingquan Zhang; Mingqi Qiao


    The extracellular signal-regulated kinase/cAMP response element-binding protein/brain-derived neurotrophic factor signal transduction pathway plays an important role in the mechanism of action of antidepressant drugs and has dominated recent studies on the pathogenesis of depression. In the present review we summarize the known roles of extracellular signal-regulated kinase, cAMP response element-binding protein and brain-derived neurotrophic factor in the pathogenesis of depression and in the mechanism of action of antidepressant medicines. The extracellular signal-regulated kinase/cAMP response element-binding protein/brain-derived neurotrophic factor pathway has potential to be used as a biological index to help diagnose depression, and as such it is considered as an important new target in the treatment of depression.

  19. Regulation of the CDP-choline pathway by sterol regulatory element binding proteins involves transcriptional and post-transcriptional mechanisms.

    Ridgway, Neale D; Lagace, Thomas A


    The synthesis of phosphatidylcholine (PtdCho) by the CDP-choline pathway is under the control of the rate-limiting enzyme CTP:phosphocholine cytidylyltransferase (CCT). Sterol regulatory element binding proteins (SREBPs) have been proposed to regulate CCT at the transcriptional level, or via the synthesis of lipid activators or substrates of the CDP-choline pathway. To assess the contributions of these two mechanisms, we examined CCTalpha expression and PtdCho synthesis by the CDP-choline pathway in cholesterol and fatty acid auxotrophic CHO M19 cells inducibly expressing constitutively active nuclear forms of SREBP1a or SREBP2. Induction of either SREBP resulted in increased expression of mRNAs for sterol-regulated genes, elevated fatty acid and cholesterol synthesis (>10-50-fold) and increased PtdCho synthesis (2-fold). CCTalpha mRNA was increased 2-fold by enforced expression of SREBP1a or SREBP2. The resultant increase in CCTalpha protein and activity (2-fold) was restricted primarily to the soluble fraction of cells, and increased CCTalpha activity in vivo was not detected. Inhibition of the synthesis of fatty acids or their CoA esters by cerulenin or triacsin C respectively following SREBP induction effectively blocked the accompanying elevation in PtdCho synthesis. Thus PtdCho synthesis was driven by increased synthesis of fatty acids or a product thereof. These data show that transcriptional activation of CCTalpha is modest relative to that of other SREBP-regulated genes, and that stimulation of PtdCho synthesis by SREBPs in CHO cells is due primarily to increased fatty acid synthesis.

  20. A molecular, morphometric and mechanical comparison of the structural elements of byssus from Mytilus edulis and Mytilus galloprovincialis.

    Lucas, Jared M; Vaccaro, Eleonora; Waite, J Herbert


    Marine mussels are renowned for their ability to produce an extra-organismic tendon-like structure that can withstand the wave forces associated with the intertidal habitat. Initial characterization of byssal properties has focused on Mytilus edulis, with few detailed comparisons with other mussels. M. galloprovincialis, a closely related species, provides an opportunity for a thorough comparison. Three full-length cDNA clones encoding the byssal collagens, precollagen D (preCol-D), preCol-NG and preCol-P, were isolated from M. galloprovincialis. Comparisons with M. edulis preCol-D, preCol-NG and preCol-P reveal a 91.3 %, 88.6 % and 90.1 % identity with the cDNA and an 89.0 %, 88.1 % and 89.0 % identity with the deduced protein sequences, respectively. Key elements are maintained between the species: in particular, modeled bends in the collagen helix due to breaks in the Gly-X-Y pattern and the location of cysteine and putative 3,4-dihydroxyphenylalanine (DOPA) residues. A potentially important difference between the two is that, in all cases, M. galloprovincialis byssal collagens contain additional histidine residues in their flanking domains. The significance of this may lie in the ability of M. galloprovincialis to utilize more metal chelate cross-links, which have been implicated in byssal thread stability. M. edulis threads are typically twice the length and diameter of M. galloprovincialis threads and appear to contain nearly 10 % more collagen. These differences are maintained even when the different thread portions are compared. Despite differences in a number of parameters, most notably that whole M. galloprovincialis threads are stiffer, threads whether whole or separated into proximal and distal portions, have similar mechanical behaviors. It is apparent from this comparison that M. galloprovincialis and M. edulis are seemingly interchangeable models for byssal research.

  1. Mechanical behavior of ProTaper universal F2 finishing file under various curvature conditions: a finite element analysis study.

    Gao, Yuan; Cheung, Gary S P; Shen, Ya; Zhou, Xuedong


    The purpose of this study was to visualize the stresses and strain distribution patterns in ProTaper Universal F2 files (Dentsply Maillefer, Ballaigues, Switzerland) and to establish the stress- and strain-curvature relationship for this instrument under various conditions by using a dynamic, three-dimensional finite-element model. An accurate geometric model of a ProTaper Universal F2 instrument was created. Two short, straight tubes were also modeled to represent the parts of root canal apical and coronal to the curvature. Then, the file was constrained to a curve of varying degree, curve length, and position. The maximum von Mises stress and strain on the tension side of the instrument was measured at 5-degree intervals in a numerical simulation package (LS-DYNA; Livermore Software Technology, Livermore, CA). The mechanical performance of the ProTaper F2 file under various conditions was simulated. A long curvature length produced lower values of stress and strain under the same angle of curvature. An increase in the curvature angle generally induces higher stress and strain. For the same degree and curve length, the stress and strain increased if the curved portion was situated further up the shaft of the instrument (ie, with a larger diameter). The dynamic, numerical model may be used to evaluate and compare the effect of various root canal curvatures on the behavior of different designs of root canal instrument. The magnitude of stress and strain imposed on the instrument is influenced by the abruptness and degree of curvature as well as the location of the curved portion. Crown Copyright © 2011. Published by Elsevier Inc. All rights reserved.

  2. Defining Elemental Imitation Mechanisms: A Comparison of Cognitive and Motor-Spatial Imitation Learning across Object- and Computer-Based Tasks

    Subiaul, Francys; Zimmermann, Laura; Renner, Elizabeth; Schilder, Brian; Barr, Rachel


    During the first 5 years of life, the versatility, breadth, and fidelity with which children imitate change dramatically. Currently, there is no model to explain what underlies such significant changes. To that end, the present study examined whether task-independent but domain-specific--elemental--imitation mechanism explains performance across…

  3. Influence of formwork surface on the orientation of steel fibres within self-compacting concrete and on the mechanical properties of cast structural elements

    Svec, Oldrich; Zirgulis, Giedrius; Bolander, John E.;


    The influences of formwork surface on the final orientation of steel fibres immersed in self-compacting concrete and on the resulting mechanical response of the cast structural elements are investigated. Experimental observations of fibre orientation within cast slabs, obtained via computed tomog...

  4. An Evaluation Method for the Bursting Characteristics of Coal Under the Effect of Loading Rate

    Haitao, Li; Hongwei, Zhou; Yaodong, Jiang; Hongwei, Wang


    Changes in loading rate can affect the strength performance and bursting characteristics of coal. Coal samples from the same source were subject to mechanical tests for multi-loading rates. These tests were carried out to determine changes in evaluation indicators for the law of bursting liability due to increases in the loading rate. The results show that indicators, including the uniaxial compressive strength and the bursting energy index, first increased and then decreased with the increase in loading rate. The value of the loading rate, which corresponds to the strength turning point, is named the "critical loading rate". The results of evaluating the bursting liability of coal (from the same source) show all the possibilities. The critical loading rate corresponds to the highest bursting liability. The "loading rate sensitivity" is proposed to describe the comprehensive response of the bursting characteristics to the loading rate. This index, combined with the scale conversion method, makes the field application of laboratory experimentation possible. This method for evaluating the bursting liability of coal under the effect of loading rate was systematically established and shows good applicability.


    Li-yang Dai


    Objective To review imaging use in the diagnosis ofthoracolumbar burst fractures and to determine the diagnostic value of different imaging methods.Methods One hundred and fourteen patients with 120 thoracolumbar burst fractures were retrospectively reviewed. Plain radiographs were available in all cases; CT scans and MRI were obtained in 96 and 74 cases, respectively.Results A total of 27 burst fractures were misdiagnosed as other types of fractures on radiographs alone, and accounted for 22.5% of all fractures. The results indicated that plain radiographs often fail to delineate the pathological features of thoracolumbar burst fractures, leading to delay in diagnosis.Conclusion In regard to thoracolumbar injury diagnosis, burst fractures should be differentiated from compression fractures. CT should be routinely indicated and MRI examination, when necessary, may be simultaneously considered.

  6. Bright 30 THz Impulsive Solar Bursts

    Kaufmann, P; Marcon, R; Kudaka, A S; Cabezas, D P; Cassiano, M M; Francile, C; Fernandes, L O T; Ramirez, R F Hidalgo; Luoni, M; Marun, A; Pereyra, P; de Souza, R V


    Impulsive 30 THz continuum bursts have been recently observed in solar flares, utilizing small telescopes with a unique and relatively simple optical setup concept. The most intense burst was observed together with a GOES X2 class event on October 27, 2014, also detected at two sub-THz frequencies, RHESSI X-rays and SDO/HMI and EUV. It exhibits strikingly good correlation in time and in space with white light flare emission. It is likely that this association may prove to be very common. All three 30 THz events recently observed exhibited intense fluxes in the range of 104 solar flux units, considerably larger than those measured for the same events at microwave and sub-mm wavelengths. The 30 THz burst emission might be part of the same spectral burst component found at sub-THz frequencies. The 30 THz solar bursts open a promising new window for the study of flares at their origin

  7. FRBCAT: The Fast Radio Burst Catalogue

    Petroff, E.; Barr, E. D.; Jameson, A.; Keane, E. F.; Bailes, M.; Kramer, M.; Morello, V.; Tabbara, D.; van Straten, W.


    Here, we present a catalogue of known Fast Radio Burst sources in the form of an online catalogue, FRBCAT. The catalogue includes information about the instrumentation used for the observations for each detected burst, the measured quantities from each observation, and model-dependent quantities derived from observed quantities. To aid in consistent comparisons of burst properties such as width and signal-to-noise ratios, we have re-processed all the bursts for which we have access to the raw data, with software which we make available. The originally derived properties are also listed for comparison. The catalogue is hosted online as a Mysql database which can also be downloaded in tabular or plain text format for off-line use. This database will be maintained for use by the community for studies of the Fast Radio Burst population as it grows.

  8. Detection of burning ashes from thermonuclear X-ray bursts

    Kajava, J. J. E.; Nättilä, J.; Poutanen, J.; Cumming, A.; Suleimanov, V.; Kuulkers, E.


    When neutron stars (NS) accrete gas from low-mass binary companions, explosive nuclear burning reactions in the NS envelope fuse hydrogen and helium into heavier elements. The resulting thermonuclear (type-I) X-ray bursts produce energy spectra that are fit well with black bodies, but a significant number of burst observations show deviations from Planck spectra. Here we present our analysis of RXTE/PCA observations of X-ray bursts from the NS low-mass X-ray binary HETE J1900.1-2455. We have discovered that the non-Planckian spectra are caused by photoionization edges. The anticorrelation between the strength of the edges and the colour temperature suggests that the edges are produced by the nuclear burning ashes that have been transported upwards by convection and become exposed at the photosphere. The atmosphere model fits show that occasionally the photosphere can consist entirely of metals, and that the peculiar changes in blackbody temperature and radius can be attributed to the emergence and disappearance of metals in the photosphere. As the metals are detected already in the Eddington-limited phase, it is possible that a radiatively driven wind ejects some of the burning ashes into the interstellar space.

  9. Detection of burning ashes from thermonuclear X-ray bursts

    Kajava, J J E; Poutanen, J; Cumming, A; Suleimanov, V; Kuulkers, E


    When neutron stars (NS) accrete gas from low-mass binary companions, explosive nuclear burning reactions in the NS envelope fuse hydrogen and helium into heavier elements. The resulting thermonuclear (type-I) X-ray bursts produce energy spectra that are fit well with black bodies, but a significant number of burst observations show deviations from Planck spectra. Here we present our analysis of RXTE/PCA observations of X-ray bursts from the NS low-mass X-ray binary HETE J1900.1-2455. We have discovered that the non-Planckian spectra are caused by photo-ionization edges. The anti-correlation between the strength of the edges and the colour temperature suggests that the edges are produced by the nuclear burning ashes that have been transported upwards by convection and become exposed at the photosphere. The atmosphere model fits show that occasionally the photosphere can consist entirely of metals, and that the peculiar changes in black body temperature and radius can be attributed to the emergence and disappea...

  10. Prediction of Central Burst Defects in Copper Wire Drawing Process

    Vega, G.; Haddi, A.; Imad, A.


    In this study, the prediction of chevron cracks (central bursts) in copper wire drawing process is investigated using experimental and numerical approaches. The conditions of the chevron cracks creation along the wire axis depend on (i) the die angle, the friction coefficient between the die and the wire, (ii) the reduction in crosssectional area of the wire, (iii) the material properties and (iv) the drawing velocity or strain rate. Under various drawing conditions, a numerical simulation for the prediction of central burst defects is presented using an axisymmetric finite element model. This model is based on the application of the Cockcroft and Latham fracture criterion. This criterion was used as the damage value to estimate if and where defects will occur during the copper wire drawing. The critical damage value of the material is obtained from a uniaxial tensile test. The results show that the die angle and the reduction ratio have a significant effect on the stress distribution and the maximum damage value. The central bursts are expected to occur when the die angle and reduction ratio reach a critical value. Numerical predictions are compared with experimental observations.

  11. A density-functional-theory-based finite element model to study the mechanical properties of zigzag phosphorene nanotubes

    Ansari, R.; Shahnazari, A.; Rouhi, S.


    In this paper, the density functional theory calculations are used to obtain the elastic properties of zigzag phosphorene nanotubes. Besides, based on the similarity between phosphorene nanotubes and a space-frame structure, a three-dimensional finite element model is proposed in which the atomic bonds are simulated by beam elements. The results of density functional theory are employed to compute the properties of the beam elements. Finally, using the proposed finite element model, the elastic modulus of the zigzag phosphorene nanotubes is computed. It is shown that phosphorene nanotubes with larger radii have larger Young's modulus. Comparing the results of finite element model with those of density functional theory, it is concluded that the proposed model can predict the elastic modulus of phosphorene nanotubes with a good accuracy.

  12. Are Fast Radio Bursts the Birthmark of Magnetars?

    Lieu, Richard


    A model of fast radio bursts, which enlists young, short period extragalactic magnetars satisfying B/P > 2 × 1016 G s‑1 (1 G = 1 statvolt cm‑1) as the source, is proposed. When the parallel component {{\\boldsymbol{E}}}\\parallel of the surface electric field (under the scenario of a vacuum magnetosphere) of such pulsars approaches 5% of the critical field {E}c={m}e2{c}3/(e{\\hslash }), in strength, the field can readily decay via the Schwinger mechanism into electron–positron pairs, the back reaction of which causes {{\\boldsymbol{E}}}\\parallel to oscillate on a characteristic timescale smaller than the development of a spark gap. Thus, under this scenario, the open field line region of the pulsar magnetosphere is controlled by Schwinger pairs, and their large creation and acceleration rates enable the escaping pairs to coherently emit radio waves directly from the polar cap. The majority of the energy is emitted at frequencies ≲ 1 {GHz} where the coherent radiation has the highest yield, at a rate large enough to cause the magnetar to lose spin significantly over a timescale ≈ a few × {10}-3 s, the duration of a fast radio burst. Owing to the circumstellar environment of a young magnetar, however, the ≲1 GHz radiation is likely to be absorbed or reflected by the overlying matter. It is shown that the brightness of the remaining (observable) frequencies of ≈ 1 {GHz} and above are on a par with a typical fast radio burst. Unless some spin-up mechanism is available to recover the original high rotation rate that triggered the Schwinger mechanism, the fast radio burst will not be repeated again in the same magnetar.

  13. Methods of rock burst prediction

    Genkin, V.A.; Minin, Yu.Ya.; Morozov, G.D.; Proskuryakov, V.M.; Cmirnov, V.A.


    Some methods of predicting rock bursts in underground coal and iron ore mines are evaluated: using BP-18 indenters and the MGD indenter with automatic recording; seismic method consisting in measuring the speed of shock waves travelling through various layers (apparatus SB-20 is designed for use in coal mines); electrometric method (measuring resistance between two electrodes when electric currents flow through coal and rocks). The design of the AEhSSh-1 measuring instrument, used in the electrometric method in coal mines is also described. Each of the methods is described and mathematical fomulae used as their theoretical basis are presented. The calculating process is explained and brief information on the design and use of the measuring instrument is given. The methods are evaluated from the viewpoint of precision. (In Russian)

  14. Solar Micro-Type III Burst Storms and Long Dipolar Magnetic Field in the Outer Corona

    Morioka, A.; Miyoshi, Y.; Iwai, K.; Kasaba, Y.; Masuda, S.; Misawa, H.; Obara, T.


    Solar micro-type III radio bursts are elements of the so-called type III storms and are characterized by short-lived, continuous, and weak emissions. Their frequency of occurrence with respect to radiation power is quite different from that of ordinary type III bursts, suggesting that the generation process is not flare-related, but due to some recurrent acceleration processes around the active region. We examine the relationship of micro-type III radio bursts with coronal streamers. We also explore the propagation channel of bursts in the outer corona, the acceleration process, and the escape route of electron beams. It is observationally confirmed that micro-type III bursts occur near the edge of coronal streamers. The magnetic field line of the escaping electron beams is tracked on the basis of the frequency drift rate of micro-type III bursts and the electron density distribution model. The results demonstrate that electron beams are trapped along closed dipolar field lines in the outer coronal region, which arise from the interface region between the active region and the coronal hole. A 22 year statistical study reveals that the apex altitude of the magnetic loop ranges from 15 to 50 RS. The distribution of the apex altitude has a sharp upper limit around 50 RS suggesting that an unknown but universal condition regulates the upper boundary of the streamer dipolar field.

  15. Observing a Burst with Sunglasses


    Unique Five-Week VLT Study of the Polarisation of a Gamma-Ray Burst Afterglow "Gamma-ray bursts (GRBs)" are certainly amongst the most dramatic events known in astrophysics. These short flashes of energetic gamma-rays, first detected in the late 1960's by military satellites, last from less than one second to several minutes. GRBs have been found to be situated at extremely large ("cosmological") distances. The energy released in a few seconds during such an event is larger than that of the Sun during its entire lifetime of more than 10,000 million years. The GRBs are indeed the most powerful events since the Big Bang known in the Universe, cf. ESO PR 08/99 and ESO PR 20/00. During the past years circumstantial evidence has mounted that GRBs signal the collapse of extremely massive stars, the so-called hypernovae. This was finally demonstrated some months ago when astronomers, using the FORS instrument on ESO's Very Large Telescope (VLT), documented in unprecedented detail the changes in the spectrum of the light source ("the optical afterglow") of the gamma-ray burst GRB 030329 (cf. ESO PR 16/03). A conclusive and direct link between cosmological gamma-ray bursts and explosions of very massive stars was provided on this occasion. Gamma-Ray Burst GRB 030329 was discovered on March 29, 2003 by NASA's High Energy Transient Explorer spacecraft. Follow-up observations with the UVES spectrograph at the 8.2-m VLT KUEYEN telescope at the Paranal Observatory (Chile) showed the burst to have a redshift of 0.1685 [1]. This corresponds to a distance of about 2,650 million light-years, making GRB 030329 the second-nearest long-duration GRB ever detected. The proximity of GRB 030329 resulted in very bright afterglow emission, permitting the most extensive follow-up observations of any afterglow to date. A team of astronomers [2] led by Jochen Greiner of the Max-Planck-Institut für extraterrestrische Physik (Germany) decided to make use of this unique opportunity to study the

  16. TRIO: Burst Buffer Based I/O Orchestration

    Wang, Teng [Auburn University; Oral, H Sarp [ORNL; Pritchard, Michael [Auburn University; Wang, Bin [Auburn University; Yu, Weikuan [Auburn University


    The growing computing power on leadership HPC systems is often accompanied by ever-escalating failure rates. Checkpointing is a common defensive mechanism used by scientific applications for failure recovery. However, directly writing the large and bursty checkpointing dataset to parallel filesystem can incur significant I/O contention on storage servers. Such contention in turn degrades the raw bandwidth utilization of storage servers and prolongs the average job I/O time of concurrent applications. Recently burst buffer has been proposed as an intermediate layer to absorb the bursty I/O traffic from compute nodes to storage backend. But an I/O orchestration mechanism is still desired to efficiently move checkpointing data from bursty buffers to storage backend. In this paper, we propose a burst buffer based I/O orchestration framework, named TRIO, to intercept and reshape the bursty writes for better sequential write traffic to storage severs. Meanwhile, TRIO coordinates the flushing orders among concurrent burst buffers to alleviate the contention on storage server bandwidth. Our experimental results reveal that TRIO can deliver 30.5% higher bandwidth and reduce the average job I/O time by 37% on average for data-intensive applications in various checkpointing scenarios.

  17. Ultra-high Burst Strength of CVD Graphene Membranes

    Wang, Luda; Boutilier, Michael; Kidambi, Piran; Karnik, Rohit; Microfluidics; Nanofluidics Research Lab Team


    Porous graphene membranes have significant potential in gas separation, water desalination and nanofiltration. Understanding the mechanical strength of porous graphene is crucial because membrane separations can involve high pressures. We studied the burst strength of CVD graphene membrane placed on porous support at applied pressures up to 100 bar by monitoring the gas flow rate across the membrane as a function of pressure. Increase of gas flow rate with pressure allowed for extraction of the burst fraction of graphene as it failed under increasing pressure. We also studied the effect of sub-nanometer pores on the ability of graphene to withstand pressure. The results showed that porous graphene membranes can withstand pressures comparable to or even higher than the >50 bar pressures encountered in water desalination, with non-porous CVD graphene exhibiting even higher mechanical strength. Our study shows that porous polycrystalline CVD graphene has ultra-high burst strength under applied pressure, suggesting the possibility for its use in high-pressure membrane separations. Principal Investigator

  18. Mechanics

    Chester, W


    When I began to write this book, I originally had in mind the needs of university students in their first year. May aim was to keep the mathematics simple. No advanced techniques are used and there are no complicated applications. The emphasis is on an understanding of the basic ideas and problems which require expertise but do not contribute to this understanding are not discussed. How­ ever, the presentation is more sophisticated than might be considered appropri­ ate for someone with no previous knowledge of the subject so that, although it is developed from the beginning, some previous acquaintance with the elements of the subject would be an advantage. In addition, some familiarity with element­ ary calculus is assumed but not with the elementary theory of differential equations, although knowledge of the latter would again be an advantage. It is my opinion that mechanics is best introduced through the motion of a particle, with rigid body problems left until the subject is more fully developed. Howev...

  19. Nanoemulsions obtained via bubble bursting at a compound interface

    Feng, Jie; Vigolo, Daniele; Arnaudov, Luben N; Stoyanov, Simeon D; Gurkov, Theodor D; Tsutsumanova, Gichka G; Stone, Howard A


    The bursting of bubbles at an air/liquid interface is a familiar occurrence important to foam stability, cell cultures in bioreactors and mass transfer between the sea and atmosphere. Here we document the hitherto unreported formation and dispersal into the water column of submicrometre oil droplets following bubble bursting at a compound air/oil/water-with-surfactant interface. We show that dispersal results from the detachment of an oil spray from the bottom of the bubble towards water during bubble collapse. We provide evidence that droplet size is selected by physicochemical interactions between oil molecules and the surfactants rather than by hydrodynamic effects. We illustrate the unrecognized role that this dispersal mechanism may play in the fate of the sea surface micro-layer and of pollutant spills by dispersing petroleum in the water column. Finally, our system provides an energy-efficient route, with potential upscalability and wide applicability, for applications in drug delivery, food production...

  20. Trace and minor element variations and sulfur isotopes in crystalline and colloform ZnS: Incorporation mechanisms and implications for their genesis

    Pfaff, Katharina; Koenig, Alan; Wenzel, Thomas; Ridley, Ian; Hildebrandt, Ludwig H.; Leach, David L.; Markl, Gregor


    Various models have been proposed to explain the formation mechanism of colloform sphalerite, but the origin is still under debate. In order to decipher influences on trace element incorporation and sulfur isotope composition, crystalline and colloform sphalerite from the carbonate-hosted Mississippi-Valley Type (MVT) deposit near Wiesloch, SW Germany, were investigated and compared to sphalerite samples from 52 hydrothermal vein-type deposits in the Schwarzwald ore district, SW Germany to study the influence of different host rocks, formation mechanisms and fluid origin on trace element incorporation. Trace and minor element incorporation in sphalerite shows some correlation to their host rock and/or origin of fluid, gangue, paragenetic minerals and precipitation mechanisms (e.g., diagenetic processes, fluid cooling or fluid mixing). Furthermore, crystalline sphalerite is generally enriched in elements like Cd, Cu, Sb and Ag compared to colloform sphalerite that mainly incorporates elements like As, Pb and Tl. In addition, sulfur isotopes are characterized by positive values for crystalline and strongly negative values for colloform sphalerite. The combination of trace element contents, typical minerals associated with colloform sphalerite from Wiesloch, sulfur isotopes and thermodynamic considerations helped to evaluate the involvement of sulfate-reducing bacteria in water-filled karst cavities. Sulfate-reducing bacteria cause a sulfide-rich environment that leads in case of a metal-rich fluid supply to a sudden oversaturation of the fluid with respect to galena, sphalerite and pyrite. This, however, exactly coincides with the observed crystallization sequence of samples involving colloform sphalerite from the Wiesloch MVT deposit.

  1. Observational properties of decameter type IV bursts

    Melnik, Valentin; Brazhenko, Anatoly; Rucker, Helmut; Konovalenko, Alexander; Briand, Carine; Dorovskyy, Vladimir; Zarka, Philippe; Frantzusenko, Anatoly; Panchenko, Michael; Poedts, Stefan; Zaqarashvili, Teimuraz; Shergelashvili, Bidzina


    Oscillations of decameter type IV bursts were registered during observations of solar radio emission by UTR-2, URAN-2 and NDA in 2011-2012. Large majority of these bursts were accompanied by coronal mass ejections (CMEs), which were observed by SOHO and STEREO in the visible light. Only in some cases decameter type IV bursts were not associated with CMEs. The largest periods of oscillations P were some tens of minutes. There were some modes of long periods of oscillations simultaneously. Periods of oscillations in flux and in polarization profiles were close. Detailed properties of oscillations at different frequencies were analyzed on the example of two type IV bursts. One of them was observed on April 7, 2011 when a CME happened. Another one (August 1, 2011) was registered without any CME. The 7 April type IV burst had two periods in the frames 75-85 and 35-85 minutes. Interesting feature of these oscillations is decreasing periods with time. The observed decreasing rates dP/dt equaled 0.03-0.07. Concerning type IV burst observed on August 1, 2011 the period of its oscillations increases from 17 min. at 30 MHz to 44 min. at 10 MHz. Connection of type IV burst oscillations with oscillations of magnetic arches and CMEs at corresponding altitudes are discussed. The work is fulfilled in the frame of FP7 project "SOLSPANET".

  2. Finite Element Simulation of Mechanical Behavior of TRIP800 Steel Under Different Loading Conditions Using an Advanced Microstructure-Based Model

    Hosseinabadi, F.; Rezaee-Bazzaz, A.; Mazinani, M.


    The mechanical behavior of a low alloy multiphase TRIP steel has been predicted by an advanced microstructure-based finite element method. A representative volume element chosen based on the actual microstructure has been utilized for simulating the mechanical behavior of the studied steel. The parameters describing the martensitic transformation kinetics have been estimated using both crystallographic and thermodynamic theories of martensitic transformation. The mechanical behavior of each of the constituent phases required for the prediction of mechanical behavior of the studied material has been extracted from those reported in the literature. Comparison of the predicted mechanical behavior of the investigated TRIP800 steel with those reported in the literature shows that there is good agreement between simulated and experimental results. Therefore, it can be said that, the utilized microstructure-based model can be used for the prediction of both mechanical and transformation behaviors of the TRIP800 steels. It is worth noting that all of the parameters used in the model, except the sensitivity of the martensitic transformation to the stress state, can be estimated theoretically; thus, the number of parameters obtained by correlating the simulated and experimental results reduces to one. This is the unique characteristic of the utilized model, which makes the application of the model for simulation of the mechanical behavior of TRIP steels simpler than that of the similar ones.

  3. Modeling of fluid injection and withdrawal induced fault activation using discrete element based hydro-mechanical and dynamic coupled simulator

    Yoon, Jeoung Seok; Zang, Arno; Zimmermann, Günter; Stephansson, Ove


    Operation of fluid injection into and withdrawal from the subsurface for various purposes has been known to induce earthquakes. Such operations include hydraulic fracturing for shale gas extraction, hydraulic stimulation for Enhanced Geothermal System development and waste water disposal. Among these, several damaging earthquakes have been reported in the USA in particular in the areas of high-rate massive amount of wastewater injection [1] mostly with natural fault systems. Oil and gas production have been known to induce earthquake where pore fluid pressure decreases in some cases by several tens of Mega Pascal. One recent seismic event occurred in November 2013 near Azle, Texas where a series of earthquakes began along a mapped ancient fault system [2]. It was studied that a combination of brine production and waste water injection near the fault generated subsurface pressures sufficient to induced earthquakes on near-critically stressed faults. This numerical study aims at investigating the occurrence mechanisms of such earthquakes induced by fluid injection [3] and withdrawal by using hydro-geomechanical coupled dynamic simulator (Itasca's Particle Flow Code 2D). Generic models are setup to investigate the sensitivity of several parameters which include fault orientation, frictional properties, distance from the injection well to the fault, amount of fluid withdrawal around the injection well, to the response of the fault systems and the activation magnitude. Fault slip movement over time in relation to the diffusion of pore pressure is analyzed in detail. Moreover, correlations between the spatial distribution of pore pressure change and the locations of induced seismic events and fault slip rate are investigated. References [1] Keranen KM, Weingarten M, Albers GA, Bekins BA, Ge S, 2014. Sharp increase in central Oklahoma seismicity since 2008 induced by massive wastewater injection, Science 345, 448, DOI: 10.1126/science.1255802. [2] Hornbach MJ, DeShon HR

  4. Effect of MgO nanofillers on burst release reduction from hydrogel nanocomposites.

    Hezaveh, Hadi; Muhamad, Ida Idayu


    In this study, MgO nanoparticles are applied to control the initial burst release by modification of matrix structure, thereby affecting the release mechanism. The effects of MgO nanofiller loading on the in vitro release of a model drug are investigated. Surface topography and release kinetics of hydrogel nanocomposites are also studied in order to have better insight into the release mechanism. It was found that the incorporation of MgO nanofillers can significantly decrease the initial burst release. The effect of genipin (GN) on burst release was also compared with MgO nanoparticles, and it was found that the impact of MgO on burst release reduction is more obvious than GN; however, GN cross-linking caused greater final release compared to blanks and nanocomposites. To confirm the capability of nanocomposite hydrogels to reduce burst release, the release of β-carotene in Simulated Gastric Fluid and Simulated Intestinal Fluid was also carried out. Thus, the application of MgO nanoparticles seems to be a promising strategy to control burst release.

  5. The Arecibo Fast Radio Burst: Dense Circum-burst Medium

    Kulkarni, S R; Neill, J D


    The nature of fast radio bursts (FRB) has been extensively debated. Here we investigate FRB121102, detected at Arecibo telescope and remarkable for its unusually large spectral index. After extensive study we conclude that the spectral index is caused by a nebula with free-free absorption. We find that putative nebula must lie beyond the Milky Way. We conclude that FRBs are of extra-galactic origin and that they arise in dense star-forming regions. The challenge with extra-galactic models is the the high volumetric rate of FRBs. This high rate allows us to eliminate all models of catastrophic stellar deaths. Hyper-giant flares from young magnetars emerge as the most likely progenitors. Some of the consequences are: (i) Intergalactic FRB models can be safely ignored. (ii) The rich ISM environment of young magnetars can result in significant contribution to DM, Rotation Measure (RM) and in some cases to significant free-free optical depth. (iii) The star-forming regions in the host galaxies can contribute signi...

  6. Ballerina - pirouettes in search of gamma bursts

    Brandt, Søren Kristian; Lund, Niels; Pedersen, Henrik


    The cosmological origin of gamma ray bursts has now been established with reasonable certainty, Many more bursts will need to be studied to establish the typical distance scale, and to map out the large diversity in properties which have been indicated by the first handful of events. We are propo...... are proposing Ballerina, a small satellite to provide accurate positions and new data on the gamma-ray bursts. We anticipate a detection rate an order of magnitude larger than obtained from Beppo-SAX....

  7. Principles of rock mechanics

    Turchaninov, I.A.; Iofis, M.A.; Kasparyan, E.V.


    This book presents the principles of rock mechanics in a systematic way, reflecting both the historic development and the contemporary status of theoretical and experimental techniques used for the determination of the properties and stress state of rock masses, calculation of elements of systems for exploitation of useful mineral deposits and the design of mine openings. The subject of rock mechanics is discussed and methods and basic approaches are analyzed. The most widely used methods for determining the properties of rock in specimens and in situ are described. Problems of determining the stress strain state of the rock around mine openings by both experimental and analytic methods are discussed. The primary results of the study of the stress state of rock around main, development and production openings are presented. Problems of the movement of rock due to extraction of minerals are analyzed in detail, as are the conditions and causes of the development of rock bursts and sudden release of rock and gas in both surface and underground mines. Procedures for preventing or localizing rock bursts or sudden outbursts are described. (313 refs.)

  8. Effects of the sp element additions on the microstructure and mechanical properties of NiCoFeCr based high entropy alloys

    Vida, Adam, E-mail: [Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, H-1525 Budapest, P.O. Box 49 (Hungary); Department of Matefrials Physics, Eötvös University Budapest, H-1117 Budapest, Pázmány P. sétány 1/A (Hungary); Varga, Lajos K. [Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, H-1525 Budapest, P.O. Box 49 (Hungary); Chinh, Nguyen Quang [Department of Matefrials Physics, Eötvös University Budapest, H-1117 Budapest, Pázmány P. sétány 1/A (Hungary); Molnar, David [Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, H-1525 Budapest, P.O. Box 49 (Hungary); Department of Matefrials Physics, Eötvös University Budapest, H-1117 Budapest, Pázmány P. sétány 1/A (Hungary); Huang, Shuo [Applied Materials Physics, Department of Materials Science and Engineering, Royal Institute of Technology, Stockholm SE-100 44 (Sweden); Vitos, Levente [Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, H-1525 Budapest, P.O. Box 49 (Hungary); Applied Materials Physics, Department of Materials Science and Engineering, Royal Institute of Technology, Stockholm SE-100 44 (Sweden)


    The effects of the sp (Al, Ga, Ge, Sn) element additions on the microstructure and mechanical properties of equimolar NiCoFeCr High Entropy Alloys (HEAs) are investigated. The results of X-ray diffraction measurements combined with scanning electron microscopy SEM investigations, as well as the results of nanoindentation test revealed that while the structure of the basic alloy is full FCC, the addition of sp elements has changed it to a multiphase containing both FCC and BCC components, but in different scales. Accordingly, the addition of sp elements strongly increases the strength of the basic state, especially in the case of alloys where the BCC phase is dominant in the microstructure. The physical properties as the Young’s- and shear moduli of the investigated HEAs were also determined using ultrasound methods. The correlation between these two moduli suggests a general relationship for metallic alloys.


    ZHENG Chuanxiang


    In order to get more precise bursting pressure formula of mild steel, hundreds of bursting experiments of mild steel pressure vessels such as Q235(Gr.D) and 20R(1020) are done. Based on statistical data of bursting pressure and modification of Faupel formula, a more precise modified formula is given out according to the experimental data. It is proved to be more accurate after examining other bursting pressure value presented in many references. This bursting formula is very accurate in these experiments using pressure vessels with different diameter and shell thickness.Obviously, this modified bursting formula can be used in mild steel pressure vessels with different diameter and thickness of shell.

  10. Evolution of the bursting-layer wave during a Type 1 X-ray burst

    Berkhout, R G


    In a popular scenario due to Heyl, quasi periodic oscillations (QPOs) which are seen during type 1 X-ray bursts are produced by giant travelling waves in neutron-star oceans. Piro and Bildsten have proposed that during the burst cooling the wave in the bursting layer may convert into a deep crustal interface wave, which would cut off the visible QPOs. This cut-off would help explain the magnitude of the QPO frequency drift, which is otherwise overpredicted by a factor of several in Heyl's scenario. In this paper, we study the coupling between the bursting layer and the deep ocean. The coupling turns out to be weak and only a small fraction of the surface-wave energy gets transferred to that of the crustal-interface wave during the burst. Thus the crustal-interface wave plays no dynamical role during the burst, and no early QPO cut-off should occur.

  11. Cosmic Forensics Confirms Gamma-Ray Burst And Supernova Connection


    Scientists announced today that they have used NASA's Chandra X-ray Observatory to confirm that a gamma-ray burst was connected to the death of a massive star. This result is an important step in understanding the origin of gamma-ray bursts, the most violent events in the present-day universe. "If a gamma-ray burst were a crime, then we now have strong circumstantial evidence that a supernova explosion was at the scene," said Nathaniel Butler of Massachusetts Institute of Technology in Cambridge, lead author of a paper presented today at the meeting of the High Energy Division of the American Astronomical Society. Chandra was able to obtain an unusually long observation (approximately 21 hours) of the afterglow of GRB 020813 (so named because the High-Energy Transient Explorer, HETE, discovered it on August 13, 2002.) A grating spectrometer aboard Chandra revealed an overabundance of elements characteristically dispersed in a supernova explosion. Narrow lines, or bumps, due to silicon and sulfur ions (atoms stripped of most of their electrons) were clearly identified in the X-ray spectrum of GRB 020813. "Our observation of GRB 020813 supports two of the most important features of the popular supra-nova model for gamma-ray bursts," said Butler. "An extremely massive star likely exploded less than two months prior to the gamma-ray burst, and the radiation from the gamma-ray burst was beamed into a narrow cone." An analysis of the data showed that the ions were moving away from the site of the gamma-ray burst at a tenth the speed of light, probably as part of a shell of matter ejected in the supernova explosion. The line features were observed to be sharply peaked, indicating that they were coming from a narrow region of the expanding shell. This implies that only a small fraction of the shell was illuminated by the gamma-ray burst, as would be expected if the burst was beamed into a narrow cone. The observed duration of the afterglow suggests a delay of about 60 days

  12. Neuronal networks and energy bursts in epilepsy.

    Wu, Y; Liu, D; Song, Z


    Epilepsy can be defined as the abnormal activities of neurons. The occurrence, propagation and termination of epileptic seizures rely on the networks of neuronal cells that are connected through both synaptic- and non-synaptic interactions. These complicated interactions contain the modified functions of normal neurons and glias as well as the mediation of excitatory and inhibitory mechanisms with feedback homeostasis. Numerous spread patterns are detected in disparate networks of ictal activities. The cortical-thalamic-cortical loop is present during a general spike wave seizure. The thalamic reticular nucleus (nRT) is the major inhibitory input traversing the region, and the dentate gyrus (DG) controls CA3 excitability. The imbalance between γ-aminobutyric acid (GABA)-ergic inhibition and glutamatergic excitation is the main disorder in epilepsy. Adjustable negative feedback that mediates both inhibitory and excitatory components affects neuronal networks through neurotransmission fluctuation, receptor and transmitter signaling, and through concomitant influences on ion concentrations and field effects. Within a limited dynamic range, neurons slowly adapt to input levels and have a high sensitivity to synaptic changes. The stability of the adapting network depends on the ratio of the adaptation rates of both the excitatory and inhibitory populations. Thus, therapeutic strategies with multiple effects on seizures are required for the treatment of epilepsy, and the therapeutic functions on networks are reviewed here. Based on the high-energy burst theory of epileptic activity, we propose a potential antiepileptic therapeutic strategy to transfer the high energy and extra electricity out of the foci.

  13. Gamma-Ray Burst Progenitors

    Levan, Andrew; Crowther, Paul; de Grijs, Richard; Langer, Norbert; Xu, Dong; Yoon, Sung-Chul


    We review our current understanding of the progenitors of both long and short duration gamma-ray bursts (GRBs). Constraints can be derived from multiple directions, and we use three distinct strands; (i) direct observations of GRBs and their host galaxies, (ii) parameters derived from modelling, both via population synthesis and direct numerical simulation and (iii) our understanding of plausible analog progenitor systems observed in the local Universe. From these joint constraints, we describe the likely routes that can drive massive stars to the creation of long GRBs, and our best estimates of the scenarios that can create compact object binaries which will ultimately form short GRBs, as well as the associated rates of both long and short GRBs. We further discuss how different the progenitors may be in the case of black hole engine or millisecond-magnetar models for the production of GRBs, and how central engines may provide a unifying theme between many classes of extremely luminous transient, from luminous and super-luminous supernovae to long and short GRBs.

  14. On Gamma-Ray Bursts

    Ruffini, Remo; Bianco, Carlo Luciano; Caito, Letizia; Chardonnet, Pascal; Cherubini, Christian; Dainotti, Maria Giovanna; Fraschetti, Federico; Geralico, Andrea; Guida, Roberto; Patricelli, Barbara; Rotondo, Michael; Hernandez, Jorge Armando Rueda; Vereshchagin, Gregory; Xue, She-Sheng


    (Shortened) We show by example how the uncoding of Gamma-Ray Bursts (GRBs) offers unprecedented possibilities to foster new knowledge in fundamental physics and in astrophysics. After recalling some of the classic work on vacuum polarization in uniform electric fields by Klein, Sauter, Heisenberg, Euler and Schwinger, we summarize some of the efforts to observe these effects in heavy ions and high energy ion collisions. We then turn to the theory of vacuum polarization around a Kerr-Newman black hole, leading to the extraction of the blackholic energy, to the concept of dyadosphere and dyadotorus, and to the creation of an electron-positron-photon plasma. We then present a new theoretical approach encompassing the physics of neutron stars and heavy nuclei. It is shown that configurations of nuclear matter in bulk with global charge neutrality can exist on macroscopic scales and with electric fields close to the critical value near their surfaces. These configurations may represent an initial condition for the...

  15. Gamma-ray burst progenitors

    Levan, Andrew; de Grijs, Richard; Langer, Norbert; Xu, Dong; Yoon, Sung-Chul


    We review our current understanding of the progenitors of both long and short duration gamma-ray bursts (GRBs). Constraints can be derived from multiple directions, and we use three distinct strands; i) direct observations of GRBs and their host galaxies, ii) parameters derived from modeling, both via population synthesis and direct numerical simulation and iii) our understanding of plausible analog progenitor systems observed in the local Universe. From these joint constraints, we describe the likely routes that can drive massive stars to the creation of long GRBs, and our best estimates of the scenarios that can create compact object binaries which will ultimately form short GRBs, as well as the associated rates of both long and short GRBs. We further discuss how different the progenitors may be in the case of black hole engine or millisecond-magnetar models for the production of GRBs, and how central engines may provide a unifying theme between many classes of extremely luminous transient, from luminous an...

  16. Gamma-ray Burst Cosmology

    Wang, F Y; Liang, E W


    Gamma-ray bursts (GRBs) are the most luminous electromagnetic explosions in the Universe, which emit up to $8.8\\times10^{54}$ erg isotropic equivalent energy in the hard X-ray band. The high luminosity makes them detectable out to the largest distances yet explored in the Universe. GRBs, as bright beacons in the deep Universe, would be the ideal tool to probe the properties of high-redshift universe: including the cosmic expansion and dark energy, star formation rate, the reionization epoch and the metal enrichment history of the Universe. In this article, we review the luminosity correlations of GRBs, and implications for constraining the cosmological parameters and dark energy. Observations show that the progenitors of long GRBs are massive stars. So it is expected that long GRBs are tracers of star formation rate. We also review the high-redshift star formation rate derived from GRBs, and implications for the cosmic reionization history. The afterglows of GRBs generally have broken power-law spectra, so it...

  17. Bursting Smoke as an Infrared Countermeasure

    Amarjit Singh; P. J. Kamale; S. A. Joshi; L. K. Bankar


    ...) using cadmium-mercury-telluride (CMI) detector cooled by liquid nitrogen. The particle size and shape of the powders used in the bursting smokes were determined microscopically using Carl Zeiss Jena Neophot- 21...

  18. Expected Performance of the GLAST Burst Monitor

    Meegan, Charles; Fishman, Gerald; Kouveliotou, Chryssa; Wilson-Hodge, Colleen; Paciesas, William; Preece, Robert; Briggs, Michael; Bhat, Narayana; Connaughton, Valerie; Greiner, Jochen; vonKienlin, Andreas; Diehl, Roland; Steinle, Helmut; Bissaldi, Elisabetta; Kippen, R. Marc


    The GLAST Burst Monitor (GBM) will enhance LAT observations of GRBs by extending the spectral coverage from the LAT threshold down to approx. 8 kev, and will provide a trigger for re-orienting the spacecraft to observe delayed emission from selected bursts outside the LAT field of view. GBM consists of twelve NaI scintillation detectors operating in the 8 kev to 1 MeV energy range and two BGO scintillation detectors operating in the 150 keV to 30 MeV energy range. Detector resolution, effective area, and angular response have been determined by calibrations. Analyses indicate that the on-board burst threshold will be approx. 0.7 photon/cm2/s and the on-board burst localization accuracy will typically be better than 8 degrees.

  19. Plasma Bursts in Deep Penetration Laser Welding

    Mrňa, L.; Šarbort, M.

    We present an experimental study of the deep penetration laser welding process which aims to analyze the plasma plume oscillations on a short time scale. Using the high-speed camera we show that the plasma comes out of the keyhole in the form of short bursts rather than the continuous flow. We detect these bursts as the short-time intensity oscillations of light emissions coming from the plasma plume. We determine the period of bursts using the statistical signal processing methods and the short-time frequency analysis. Finally, we compare the characteristics of plasma bursts and the geometry of resulting welds carried out on a 2 kW Yb:YAG laser welding machine for the steel workpiece and various welding parameters settings.

  20. Long Burst Error Correcting Codes Project

    National Aeronautics and Space Administration — Long burst error mitigation is an enabling technology for the use of Ka band for high rate commercial and government users. Multiple NASA, government, and commercial...