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Sample records for machine screw equivalent

  1. Finite Element Analysis of Reciprocating Screw for Injection Molding Machine

    Directory of Open Access Journals (Sweden)

    Nagsen B. Nagrale

    2011-06-01

    Full Text Available This paper deals with, the solution of problem occurred for reciprocating screw of Injection molding machine. It identifies and solves the problem by using the modeling and simulation techniques. The problem occurred in the reciprocating screw of machine which was wearing of threads due to affect of temperature of mold materials(flow materials i.e. Nylon, low density polypropylene, polystyrene, PVC etc., The main work was to model the components of machine with dimensions, assemble those components and then simulate the whole assembly for rotation of the screw. The modeling software used is PRO-E wildfire 4.0 for modeling the machine components like body, movable platen, fixed platen, barrel, screw, nozzle, etc. The analysis software ANSYS is used to analyze the reciprocating screws. The objectives involved are:- • To model all the components using modeling software Pro-E 4.0 • To assemble all the components of the machine in the software. • To make the assembly run in Pro-E software.• Analysis of screw of machine using Ansys 11.0 software. • To identify the wearing of threads and to provide the possible solutions.This problem is major for all industrial injection molding machines which the industries are facing and they need the permanent solution, so if the better solution is achieved then the industries will think for implementing it. The industries are having temporary solution but it will affect the life of the screw, because the stresses will be more in machined screw on lathe machine as compared to normal screw. Also if the screw will fail after some years of operation, the new screw available in the market will have the same problem. Also the cost associated with new screw and its mounting is much more as it is the main component of machine.

  2. Technological Level of Machines in Production Process of Screws

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    Ingaldi Manuela

    2014-12-01

    Full Text Available The article focuses on analysing one of the elements of technological level in a company using the ABC method. The technological modernity of a machine used during the production process of screws was evaluated. In average, this machine was assigned the score 3.4, meaning that most parts of the machine were manufactured using more complex technologies requiring technical skills and knowledge, and many of them also with modern technologies. This means that the machine examined was quite modern

  3. Simulation and analysis of resin flow in injection machine screw

    Institute of Scientific and Technical Information of China (English)

    Ling-feng LI; Samir MEKID

    2008-01-01

    A method with simulation and analysis of the resin flow in a screw is presented to ease the control of some problems that may affect the efficiency and the quality of the product among existing screws in an injection machine. The physical model of a screw is established to represent the stress, the strain, the relationship between velocity and stress, and the temperature of the cells. In this paper, a working case is considered where the velocity and the temperature distributions at any section of the flow are obtained. The analysis of the computational results shows an ability to master various parameters depending on the specifications.

  4. Internally geared screw machines with ported end plates

    Science.gov (United States)

    Read, M. G.; Smith, I. K.; Stosic, N.

    2017-08-01

    It is possible to design cylindrical helical gearing profiles such that an externally lobed inner gear rotates inside an internally lobed outer gear while maintaining continuous lines of contact between the gears. The continuous contact between the inner and outer rotors (analogous to the main and gate rotors in a conventional screw machine) creates a series of separate working chambers. In this type of machine the rotors have parallel axes of rotation, and if both rotors are free to rotate about their own axes, these axes can be fixed in space. The use of ported end plates is proposed to control the period during which fluid is allowed to enter or leave the working chambers of the internally geared screw machine. As with conventional screw machines, these internally geared rotors can then be used to achieve compression or expansion of a trapped mass of fluid, and the machine geometry can be designed in order to optimise performance for particular applications. This paper describes the geometrical analysis of some simple rotor profiles and explores the effect on rotor torques for particular applications of this novel screw configuration.

  5. Screw Remaining Life Prediction Based on Quantum Genetic Algorithm and Support Vector Machine

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    Xiaochen Zhang

    2017-01-01

    Full Text Available To predict the remaining life of ball screw, a screw remaining life prediction method based on quantum genetic algorithm (QGA and support vector machine (SVM is proposed. A screw accelerated test bench is introduced. Accelerometers are installed to monitor the performance degradation of ball screw. Combined with wavelet packet decomposition and isometric mapping (Isomap, the sensitive feature vectors are obtained and stored in database. Meanwhile, the sensitive feature vectors are randomly chosen from the database and constitute training samples and testing samples. Then the optimal kernel function parameter and penalty factor of SVM are searched with the method of QGA. Finally, the training samples are used to train optimized SVM while testing samples are adopted to test the prediction accuracy of the trained SVM so the screw remaining life prediction model can be got. The experiment results show that the screw remaining life prediction model could effectively predict screw remaining life.

  6. Equivalence of History and Generator Epsilon-Machines

    CERN Document Server

    Travers, Nicholas F

    2011-01-01

    Epsilon-machines are minimal, unifilar representations of stationary stochastic processes. They were originally defined in the history machine sense---as machines whose states are the equivalence classes of infinite histories with the same probability distribution over futures. In analyzing synchronization, though, an alternative generator definition was given: unifilar edge-label hidden Markov models with probabilistically distinct states. The key difference is that history epsilon-machines are defined by a process, whereas generator epsilon-machines define a process. We show here that these two definitions are equivalent.

  7. ASCERTAINMENT OF THE EQUIVALENT CIRCUIT PARAMETERS OF THE ASYNCHRONOUS MACHINE

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    V. S. Safaryan

    2015-01-01

    Full Text Available The article considers experimental and analytical determination of the asynchronous machine equivalent-circuit parameters with application of the reference data. Transient processes investigation of the asynchronous machines necessitates the equivalent circuit parameters (resistance impedance, inductances and coefficient of the stator-rotor contours mutual inductance that help form the transitory-process mathematical simulation model. The reference books do not provide those parameters; they instead give the rated ones (active power, voltage, slide, coefficient of performance and capacity coefficient as well as the ratio of starting and nominal currents and torques. The noted studies on the asynchronous machine equivalent-circuits parametrization fail to solve the problems ad finem or solve them with admissions. The paper presents experimental and analytical determinations of the asynchronous machine equivalent-circuit parameters: the experimental one based on the results of two measurements and the analytical one where the problem boils down to solving a system of nonlineal algebraic equations. The authors investigate the equivalent asynchronous machine input-resistance properties and adduce the dependence curvatures of the input-resistances on the slide. They present a symbolic model for analytical parameterization of the asynchronous machine equivalent-circuit that represents a system of nonlineal equations and requires one of the rotor-parameters arbitrary assignment. The article demonstrates that for the asynchronous machine equivalent-circuit experimental parameterization the measures are to be conducted of the stator-circuit voltage, current and active power with two different slides and arbitrary assignment of one of the rotor parameters. The paper substantiates the fact that additional measurement does not discard the rotor-parameter choice arbitrariness. The authors establish that in motoring mode there is a critical slide by which the

  8. The Axial Nonlinear Vibration Analysis of Ball-screw about Machine Tool Feeding System

    Institute of Scientific and Technical Information of China (English)

    ZENG Hao-ran; LIU Nian-cong; YANG Jia-rui; CHEN Jian-long; GENG Wei-tao

    2016-01-01

    The forced state of the ball⁃screw of machine tool feeding system is analyzed. The ball⁃screw is simplified as Timoshenko beam and the differential equation of motion for the ball⁃screw is built. To obtain the axial vibration equation, the differential equation of motion is simplified using the assumed mode method. Axial vibration equation is in form of Duffing equation and has the characteristics of nonlinearity. The numerical simulation of Duffing equation is proceeded by MATLAB/Simulink. The effect of screw length, exciting force and damping coefficient are researched, and the axial vibration phase track diagram and Poincare section are obtained. The stability and period of the axial vibration are analyzed. The limit cycle of phase track diagram is enclosed. Axial vibration has two type⁃center singularity distributions on both sides of the origin. The singularity attracts vibration to reach a stable state, and Poincare section shows that axial vibration appears chaotic motion and quasi periodic motion or periodic motion. Singularity position changes with the vibration system parameters, while the distribution doesn′t change. The period of the vibration is enhanced with increasing frequency and damping coefficient. Test of the feeding system ball⁃screw axial vibration exists chaos movement. This paper provides a certain theoretical basis for the dynamic characteristic analysis of machine feeding system ball⁃screw and optimization of structural parameters.

  9. Magnetic equivalent circuit model for unipolar hybrid excitation synchronous machine

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    Kupiec Emil

    2015-03-01

    Full Text Available Lately, there has been increased interest in hybrid excitation electrical machines. Hybrid excitation is a construction that combines permanent magnet excitation with wound field excitation. Within the general classification, these machines can be classified as modified synchronous machines or inductor machines. These machines may be applied as motors and generators. The complexity of electromagnetic phenomena which occur as a result of coupling of magnetic fluxes of separate excitation systems with perpendicular magnetic axis is a motivation to formulate various mathematical models of these machines. The presented paper discusses the construction of a unipolar hybrid excitation synchronous machine. The magnetic equivalent circuit model including nonlinear magnetization curves is presented. Based on this model, it is possible to determine the multi-parameter relationships between the induced voltage and magnetomotive force in the excitation winding. Particular attention has been paid to the analysis of the impact of additional stator and rotor yokes on above relationship. Induced voltage determines the remaining operating parameters of the machine, both in the motor and generator mode of operation. The analysis of chosen correlations results in an identification of the effective control range of electromotive force of the machine.

  10. EQUIVALENT NORMAL CURVATURE APPROACH MILLING MODEL OF MACHINING FREEFORM SURFACES

    Institute of Scientific and Technical Information of China (English)

    YI Xianzhong; MA Weiguo; QI Haiying; YAN Zesheng; GAO Deli

    2008-01-01

    A new milling methodology with the equivalent normal curvature milling model machining freeform surfaces is proposed based on the normal curvature theorems on differential geometry. Moreover, a specialized whirlwind milling tool and a 5-axis CNC horizontal milling machine are introduced. This new milling model can efficiently enlarge the material removal volume at the tip of the whirlwind milling tool and improve the producing capacity. The machining strategy of this model is to regulate the orientation of the whirlwind milling tool relatively to the principal directions of the workpiece surface at the point of contact, so as to create a full match with collision avoidance between the workpiece surface and the symmetric rotational surface of the milling tool. The practical results show that this new milling model is an effective method in machining complex three- dimensional surfaces. This model has a good improvement on finishing machining time and scallop height in machining the freeform surfaces over other milling processes. Some actual examples for manufacturing the freeform surfaces with this new model are given.

  11. Sensorless compensation system for thermal deformations of ball screws in machine tools drives

    Science.gov (United States)

    Kowal, Michał

    2016-12-01

    The article presents constructional, technological and operational issues associated with the compensation of thermal deformations of ball screw drives. Further, it demonstrates the analysis of a new sensorless compensation method relying on coordinated computation of data fed directly from the drive and the control system in combination with the information pertaining to the operational history of the servo drive, retrieved with the use of an artificial neural networks (ANN)-based learning system. Preliminary ANN-based models, developed to simulate energy dissipation resulting from the friction in the screw-cap assembly and convection of heat are expounded upon, as are the processes of data selection and ANN learning. In conclusion, the article presents the results of simulation studies and preliminary experimental evidence confirming the applicability of the proposed method, efficiently compensating for the thermal elongation of the ball screw in machine tool drives.

  12. Process acceptance and adjustment techniques for Swiss automatic screw machine parts. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Robb, J.M.

    1976-01-01

    Product tolerance requirements for small, cylindrical, piece parts produced on swiss automatic screw machines have progressed to the reliability limits of inspection equipment. The miniature size, configuration, and tolerance requirements (plus or minus 0.0001 in.) (0.00254 mm) of these parts preclude the use of screening techniques to accept product or adjust processes during setup and production runs; therefore, existing means of product acceptance and process adjustment must be refined or new techniques must be developed. The purpose of this endeavor has been to determine benefits gained through the implementation of a process acceptance technique (PAT) to swiss automatic screw machine processes. PAT is a statistical approach developed for the purpose of accepting product and centering processes for parts produced by selected, controlled processes. Through this endeavor a determination has been made of the conditions under which PAT can benefit a controlled process and some specific types of screw machine processes upon which PAT could be applied. However, it was also determined that PAT, if used indiscriminately, may become a record keeping burden when applied to more than one dimension at a given machining operation. (auth)

  13. Finite element analysis of the equivalent stress distribution in Schanz screws during the use of a femoral fracture distractor.

    Science.gov (United States)

    Giordano, Vincenzo; Godoy-Santos, Alexandre Leme; Belangero, William Dias; Pires, Robinson Esteves Santos; Labronici, Pedro José; Koch, Hilton Augusto

    2017-01-01

    To evaluate the mechanical stress and elastic deformation exercised in the thread/shaft transition of Schanz screws in assemblies with different screw anchorage distances in the entrance to the bone cortex, through the distribution and location of tension in the samples. An analysis of 3D finite elements was performed to evaluate the distribution of the equivalent stress (triple stress state) in a Schanz screw fixed bicortically and orthogonally to a tubular bone, using two mounting patterns: (1) thread/shaft transition located 20 mm from the anchorage of the Schanz screws in the entrance to the bone cortex and (2) thread/shaft transition located 3 mm from the anchorage of the Schanz screws in entrance to the bone cortex. The simulations were performed maintaining the same direction of loading and the same distance from the force vector in relation to the center of the hypothetical bone. The load applied, its direction, and the distance to the center of the bone were constant during the simulations in order to maintain the moment of flexion equally constant. The present calculations demonstrated linear behavior during the experiment. It was found that the model with a distance of 20 mm between the Schanz screws anchorage in the entrance to the bone cortex and the thread/shaft transition reduces the risk of breakage or fatigue of the material during the application of constant static loads; in this model, the maximum forces observed were higher (350 MPa). The distance between the Schanz screws anchorage at the entrance to the bone cortex and the smooth thread/shaft transition of the screws used in a femoral distractor during acute distraction of a fracture must be farther from the entrance to the bone cortex, allowing greater degree of elastic deformation of the material, lower mechanical stress in the thread/shaft transition, and minimized breakage or fatigue. The suggested distance is 20 mm.

  14. EXPERIMENTAL EVALUATION OF A CONICAL-SCREW BRIQUETTING MACHINE FOR THE BRIQUETTING OF CARBONIZED COTTON STALKS IN SUDAN

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    YOUSIF A. ABAKR

    2006-12-01

    Full Text Available Briquetting of the carbonized agricultural residues represents one of the possible solutions to the local energy shortages in many developing countries. It constitutes a positive solution to the problem of increasing rates of desertification in many areas worldwide. Agricultural residues are not attractive as a household fuel source for urban areas because they are very bulky and have low energy intensity. Also, to eliminate the smoke generation when burning agricultural residues requires processing it by carbonization before being used as a house-hold indoor fuel. Previously investigated, briquetting machines lacked high productivity and were of complicated designs. The present study puts forward a machine of simple design which could be manufactured locally in Sudan and of much higher productivity. The local Sudanese briquetting experience was overviewed, studying all the alternative available options and the market potential. The study presents a detailed design study of the new briquetting machine. The prototype was made and tested in the field at Al-Gazeera area in Sudan. The investigation results show that the new machine has a production rate better than all the previous alternatives. This low pressure screw briquetting machine was found to have a production rate equivalent to about eight times better than the production rate of the best local competitor. The production cost was found to be lower due to the lower binder requirement for the new machine, which is lower by about 65%. The initial moisture content of the feed stock required for this machine is lower by about 30 % compared to the best alternative, which results in shorter drying time for the fuel briquettes produced. The quality of the produced briquettes was found to be better and of lower smoke generation when burned due to the lower binder content.

  15. Statistical Capability Study of a Helical Grinding Machine Producing Screw Rotors

    Science.gov (United States)

    Holmes, C. S.; Headley, M.; Hart, P. W.

    2017-08-01

    Screw compressors depend for their efficiency and reliability on the accuracy of the rotors, and therefore on the machinery used in their production. The machinery has evolved over more than half a century in response to customer demands for production accuracy, efficiency, and flexibility, and is now at a high level on all three criteria. Production equipment and processes must be capable of maintaining accuracy over a production run, and this must be assessed statistically under strictly controlled conditions. This paper gives numerical data from such a study of an innovative machine tool and shows that it is possible to meet the demanding statistical capability requirements.

  16. Universal geometric error modeling of the CNC machine tools based on the screw theory

    Science.gov (United States)

    Tian, Wenjie; He, Baiyan; Huang, Tian

    2011-05-01

    The methods to improve the precision of the CNC (Computerized Numerical Control) machine tools can be classified into two categories: error prevention and error compensation. Error prevention is to improve the precision via high accuracy in manufacturing and assembly. Error compensation is to analyze the source errors that affect on the machining error, to establish the error model and to reach the ideal position and orientation by modifying the trajectory in real time. Error modeling is the key to compensation, so the error modeling method is of great significance. Many researchers have focused on this topic, and proposed many methods, but we can hardly describe the 6-dimensional configuration error of the machine tools. In this paper, the universal geometric error model of CNC machine tools is obtained utilizing screw theory. The 6-dimensional error vector is expressed with a twist, and the error vector transforms between different frames with the adjoint transformation matrix. This model can describe the overall position and orientation errors of the tool relative to the workpiece entirely. It provides the mathematic model for compensation, and also provides a guideline in the manufacture, assembly and precision synthesis of the machine tools.

  17. Preliminary Design on Screw Press Model of Palm Oil Extraction Machine

    Science.gov (United States)

    Firdaus, Muhammad; Salleh, S. M.; Nawi, I.; Ngali, Z.; Siswanto, W. A.; Yusup, E. M.

    2017-01-01

    The concept of the screw press is to compress the fruit bunch between the main screw and travelling cones to extract the palm oil. Visual inspection, model development and simulation of screw press by using Solidworks 2016 and calculation of design properties were performed to support the investigation. The project aims to analyse different design of screw press which improves in reducing maintenance cost and increasing lifespan. The currently existing of screw press can endure between 500 to 900 hours and requires frequent maintenance. Different configurations have been tried in determination of best design properties in screw press. The results specify that screw press with tapered inner shaft has more total lifespan (hours) compared existing screw press. The selection of the screw press with tapered inner shaft can reduce maintenance cost and increase lifespan of the screw press.

  18. Run-in coatings for twin-screw machines; Einlaufschichten in Schraubenmaschinen

    Energy Technology Data Exchange (ETDEWEB)

    Kauder, K.; Bach, F.W. [Dortmund Univ. (Germany). Lehrstuhl fuer Werkstofftechnologie; Unterberg, W. [Dortmund Univ. (Germany). Lehrstuhl fuer Werkstofftechnologie; Dortmund Univ. (Germany). Fachgebiet Fluidenergiemaschinen

    1999-07-01

    In this paper new results of research regarding the efforts of run-in-coatings and corrosion resistant coatings for machines of the displacement type are described. The aim of the investigations are the development and testing of the new coating systems. In order to improve the reliability and operational behaviour of screw-type machines and to repair their machine's casing the procedure of atmospheric plasma spraying was used. The coatings developed for the rotors were deposited by a conventional plasma torch, while the coatings provided for the inside of the casing were deposited by the additional use of an internal torch. In both cases coating systems were manufactured, which consist of a NiCrAl bond coat and a ceramic top coat (7% yttria stabilized zirconia). In a first step parameter investigations concerning different powders were carried out. After this the coatings were applied to various substrate materials with different spraying distances in order to achieve a porous structure of the top coating. These porous structure turned out to be necessary for good run-in-properties. Furthermore corrosion testings of these coating systems were made. (orig.) [German] Im vorliegenden Beitrag wird ueber neue Forschungsergebnisse im Hinblick auf Einlauf- bzw. Korrosionsschutzschichten fuer den Einsatz in Rotationsverdraengermaschinen berichtet, wobei das Ziel der hier beschriebenen Untersuchungen in der Herstellung und Pruefung des hergestellten Werkstoffverbundes liegt. Um das Betriebsverhalten und die Betriebssicherheit von Schraubenmaschinen weiter verbessern zu koennen, als auch geometrieerhaltende Reparaturbeschichtungen an Schraubenmaschinengehaeusen durchzufuehren, werden in einem ersten Schritt mit Hilfe des atmosphaerischen Plasmaspritzens (APS) verschiedenartige Schichtsysteme auf Probekoerper aufgebracht. Dabei kommen ein konventioneller APS-Brenner fuer die Rotorbeschichtung und ein Innenbrenner fuer das Beschichten der Gehaeuse zur Anwendung. Als

  19. Gas flow research at a plane screw type machine model. Pt. 2; Gasspaltstroemungen in einem ebenen Schraubenmaschinenmodell. T. 2

    Energy Technology Data Exchange (ETDEWEB)

    Kauder, K.; Sachs, R. [Dortmund Univ. (Germany). FG Fluidenergiemaschinen

    1998-12-31

    Gas flows in screw-type machines are effecting the energy conversion of the machine by the leakage mass flows and entropy flows inside the machine. The profile meshing clearance and the housing gap have an essential influence. Here the gas flow at the housing gap with non moving gap bounds is investigated. The used and developed measuring and image analysis technique is explained. Qualitative Schlieren pictures of the flow at three different tooth tips, i.e. gap styles are following to enable a comparison of the flow shapes. The application of a plane screw type machine model with moving gap bounds will be meant to be a contribution towards the investigation of the gas flow conditions in the gaps. (orig.) [Deutsch] Gasspaltstroemungen in Schraubenmaschinen wirken als Leckmassen- und Entropiestroeme erheblich auf die Energiewandlungsguete der Maschine. Besonderen Einfluss haben der Profileingriffs- sowie der Gehaeusespalt. In diesem Beitrag wird die Gehaeusespaltstroemung am Nebenrotor mit feststehender Stroemungsberandung untersucht. Nach Erlaeuterungen zur verwendeten und entwickelten Mess- und Bildverarbeitungstechnik folgen qualitative Schlierenbilder der Stroemung an drei unterschiedlichen Zahnkopf- und damit Spaltformen, die einen Vergleich der Stroemungsformen ermoeglichen. Der naechste Schritt zur Klaerung der Stroemungsverhaeltnisse in den Spalten besteht aus der Einfuehrung eines ebenen Schraubenmaschinenmodells mit drehenden Rotorscheiben. (orig.)

  20. Skill for machining worm screw with NC lathe%数控车床上蜗杆的加工技巧

    Institute of Scientific and Technical Information of China (English)

    赵健

    2001-01-01

    介绍了一种在数控车床上加工大螺距蜗杆的切削技巧以及相应的数控程序。%The machining skill and relevant NC program of machining worm screw with large pitch using a NC lathe are introduced.

  1. Non-certainty Equivalent Adaptive Exciting Control of Multi-machine Power Systems

    OpenAIRE

    2013-01-01

    Transient stability problem for multi-machine infinite bus system with the generator excitation was addressed via the non-certainty equivalent nonlinear re-parameterization method. The system need not to be linearized. The damping coefficient uncertainty was considered. A non-certainty equivalent excitation controller and a novel parameter updating law were obtained simultaneously via adaptive backstepping and Lyapunov methods to achieve stability of the error systems. Simulation results show...

  2. Effect of Stiffness of Rolling Joints on the Dynamic Characteristic of Ball Screw Feed Systems in a Milling Machine

    Directory of Open Access Journals (Sweden)

    Dazhong Wang

    2015-01-01

    Full Text Available Dynamic characteristic of ball screw feed system in a milling machine is studied numerically in this work. In order to avoid the difficulty in determining the stiffness of rolling joints theoretically, a dynamic modeling method for analyzing the feed system is discussed, and a stiffness calculation method of the rolling joints is proposed based on the Hertz contact theory. Taking a 3-axis computer numerical control (CNC milling machine set ermined as a research object, the stiffness of its fixed joint between the column and the body together with the stiffness parameters of the rolling joints is evaluated according to the Takashi Yoshimura method. Then, a finite element (FE model is established for the machine tool. The correctness of the FE model and the stiffness calculation method of the rolling joints are validated by theoretical and experimental modal analysis results of the machine tool’s workbench. Under the two modeling methods of joints incorporating the stiffness parameters and rigid connection, a theoretical modal analysis is conducted for the CNC milling machine. The natural frequencies and modal shapes reveal that the joints’ dynamic characteristic has an important influence on the dynamic performance of a whole machine tool, especially for the case with natural frequency and higher modes.

  3. INFLUENCE OF SELF-TAPPING SCREW ELECTRO-ARC MACHINING ON ITS TWISTING-IN IN SPECIMENS MADE OF VARIOUS MATERIALS AND TWISTING-OUT PROCEDURE

    Directory of Open Access Journals (Sweden)

    M. G. Kiselev

    2015-01-01

    Full Text Available The paper provides an experimental evaluation pertaining to the influence of steel self-tapping screw on its twisting-in specimens made of various materials and its twisting-out process. Main principles of the investigation methodology including description of  technological scheme of self-tapping screw electro-arc machining and specimens applied while executing the experiments and hardware measuring tools used for fixation of torque which has been applied to the self-tapping screw during its twisting-in in the specimen  and its twisting-out process have been presented in the paper. It has been established that the self-tapping screw electro-arc machining initiates formation of dimples (holes which have solidified metal flows along their edges. The flows give a cutting ability to the screw and so they exert an influence on the conditions of screw’s interaction with the specimen during its twisting-in and twisting-out processes.The paper presents results of experimental investigations that demonstrate an impact of self-tapping screw electro-arc machining on its twisting-in in the specimens made of various materials and twisting-out procedure. In particular, it has been ascertained that torque value applied to the self-tapping screw with modified surface during twisting-in process is less in comparison with the self-tapping screw having an initial state of its surface and in the case of its twisting-out process the value is higher. In this respect difference between the indicated torque values is increasing when material hardness of the specimen becomes higher. 

  4. A Simple Application of Lightweight Fusion to Proving the Equivalence of Abstract Machines

    DEFF Research Database (Denmark)

    Danvy, Olivier; Millikin, Kevin

    2007-01-01

    We show how Ohori and Sasano's recent lightweight fusion by fixed-point promotion provides a simple way to prove the equivalence of the two standard styles of specification of abstract machines: (1) as a transition function together with a `driver loop' implementing the iteration of this transition...... function; and (2) as a function directly iterating upon a configuration until reaching a final state, if ever. The equivalence hinges on the fact that the latter style of specification is a fused version of the former one. The need for such a simple proof is motivated by our recent work on syntactic...

  5. 连续回转式拧盖机的创新设计%The Innovative Design for the Continuous Rotary Cap Screwing Machine

    Institute of Scientific and Technical Information of China (English)

    刘守谦

    2011-01-01

    According to the turning around of the cap screwing head in continuous rotary cap screwing machine, analyze the relationship between rotation movement, revolution movement, up and down movement of cap screwing head; Combining the main structure of the machine, summarize the key factor of the quality of cap screwing. Put forward a way of innovation design which is the process of production defines the principle of the transmission, the mode of cap fixing effects the machine' s structure.%根据连续回转式拧盖机中拧盖头公转一周的工艺过程,分析了拧盖头的自转运动、公转运动、上下往复运动之间相互关系;并结合拧盖机的主要结构,总结了影响拧盖质量的关键因素.提出了"工艺过程决定拧盖机的传动原理,瓶盖结构决定拧盖机的结构参数"的创新设计方法.

  6. Screw-Joints and Symmetries: Designing Nucleic Acid Nanotubes as Nano-Machines

    Science.gov (United States)

    Sherman, William

    2005-03-01

    In 2001, Mathieu et al.^1 presented the first nanotube constructed from DNA. Similar experimental techniques can be used to build a variety of other DNA nanotubes, but finding solutions to the structural constraint equations can be difficult. We show how symmetry based analysis can be used not only to find viable tube structures, but also to identify tube based devices. Such devices can pass through several states with varying tube profiles, inner and outer radii, and lengths. The theoretical basis for actuation of the devices is the screw-joint -- two double-helical domains joined by two or more symmetric Holliday junctions and one (or more) immobile Holliday junction(s). Two of the strands in the immobile junction can be pulled out of the system and replaced with different strands. This process changes the state of the device in a controlled and reversible manner. These devices are promising as gated pores, as well as stiff mechanical manipulators. This research supported by NIGMS, ONR, and NSF. ^1 F. Mathieu, C. Mao, N. C. Seeman, Journal of Biomolecular Structure & Dynamics, 18, p.907 (2001).

  7. The Engineering Research and Application of the Digital Screw Refrigerating Machine%数字化螺杆式启闭机的研究与应用

    Institute of Scientific and Technical Information of China (English)

    倪世江; 倪帅; 唐丽娜

    2012-01-01

    The screw refrigerating machine is one of the important device in water engineering.Recent years,because of some problem existed in screw refrigerating machine,such as large accuracy error in overload protection and opening equipment,leading to a low stability and some accident about screw bending.In order to solve these problem,we manufacture the digital screw refrigerating machine,this machine change the linear load on the worm into small bent axle torque with use of small bent axle.As a result,we can measure the opening power on the gate.In the super-speed shaft,using small module turbine worm,realize the axis rotation output to the encoder.As a result,we can measure the opening size on the gate.%螺杆式启闭机是水利工程上的重要设备之一。近年来由于螺杆式启闭机存在的问题,即过载保护和开度装置精度误差较大,造成性能不稳定,时有螺杆压弯或闸门启升越位等事故发生。为彻底解决螺杆机的技术难题,研究试制了数字化螺杆式启闭机。即利用小曲轴把蜗杆上的直线力变成小曲轴扭矩,从而达到测量闸门启闭力的目的;在高速轴上利用小模数涡轮蜗杆啮合,实现高速轴的转数输出给编码器,从而达到测量闸门开度的目的。

  8. 螺杆式制冷机维修质量控制实践%Quality Control of the Maintenance of Screw Refrigerating Machine

    Institute of Scientific and Technical Information of China (English)

    赵同惠

    2009-01-01

    螺杆机出现设备维修质量问题原因很多,现阶段存在极为普遍.文章结合实际案例,分析问题产生的原因,并提出成功解决问题的措施.%The paper mainly expounds on the malpractices during the maintenance of screw refrigerating machine and hereby puts forward effective cotmtermeasures.

  9. On the equivalence between small-step and big-step abstract machines: a simple application of lightweight fusion

    DEFF Research Database (Denmark)

    Danvy, Olivier; Millikin, Kevin

    2008-01-01

    We show how Ohori and Sasano’s recent lightweight fusion by fixed-point promotion provides a simple way to prove the equivalence of the two standard styles of specification of abstract machines: (1) in small-step form, as a state-transition function together with a ‘driver loop’, i.e., a function......-step specification. We illustrate this observation here with a recognizer for Dyck words, the CEK machine, and Krivine’s machine with call/cc. The need for such a simple proof is motivated by our current work on small-step abstract machines as obtained by refocusing a function implementing a reduction semantics (a...

  10. Economics of water injected air screw compressor systems

    Science.gov (United States)

    Venu Madhav, K.; Kovačević, A.

    2015-08-01

    There is a growing need for compressed air free of entrained oil to be used in industry. In many cases it can be supplied by oil flooded screw compressors with multi stage filtration systems, or by oil free screw compressors. However, if water injected screw compressors can be made to operate reliably, they could be more efficient and therefore cheaper to operate. Unfortunately, to date, such machines have proved to be insufficiently reliable and not cost effective. This paper describes an investigation carried out to determine the current limitations of water injected screw compressor systems and how these could be overcome in the 15-315 kW power range and delivery pressures of 6-10 bar. Modern rotor profiles and approach to sealing and cooling allow reasonably inexpensive air end design. The prototype of the water injected screw compressor air system was built and tested for performance and reliability. The water injected compressor system was compared with the oil injected and oil free compressor systems of the equivalent size including the economic analysis based on the lifecycle costs. Based on the obtained results, it was concluded that water injected screw compressor systems could be designed to deliver clean air free of oil contamination with a better user value proposition than the oil injected or oil free screw compressor systems over the considered range of operations.

  11. Machine Learning on Images: Combining Passive Microwave and Optical Data to Estimate Snow Water Equivalent

    Science.gov (United States)

    Dozier, J.; Tolle, K.; Bair, N.

    2014-12-01

    We have a problem that may be a specific example of a generic one. The task is to estimate spatiotemporally distributed estimates of snow water equivalent (SWE) in snow-dominated mountain environments, including those that lack on-the-ground measurements. Several independent methods exist, but all are problematic. The remotely sensed date of disappearance of snow from each pixel can be combined with a calculation of melt to reconstruct the accumulated SWE for each day back to the last significant snowfall. Comparison with streamflow measurements in mountain ranges where such data are available shows this method to be accurate, but the big disadvantage is that SWE can only be calculated retroactively after snow disappears, and even then only for areas with little accumulation during the melt season. Passive microwave sensors offer real-time global SWE estimates but suffer from several issues, notably signal loss in wet snow or in forests, saturation in deep snow, subpixel variability in the mountains owing to the large (~25 km) pixel size, and SWE overestimation in the presence of large grains such as depth and surface hoar. Throughout the winter and spring, snow-covered area can be measured at sub-km spatial resolution with optical sensors, with accuracy and timeliness improved by interpolating and smoothing across multiple days. So the question is, how can we establish the relationship between Reconstruction—available only after the snow goes away—and passive microwave and optical data to accurately estimate SWE during the snow season, when the information can help forecast spring runoff? Linear regression provides one answer, but can modern machine learning techniques (used to persuade people to click on web advertisements) adapt to improve forecasts of floods and droughts in areas where more than one billion people depend on snowmelt for their water resources?

  12. Design of In-line Filling Machine with Cap-screwing%直列式灌装旋盖机设计

    Institute of Scientific and Technical Information of China (English)

    王志学

    2012-01-01

    The design was made of the in-line filling machine with cap-screwing.The filling process,principle and total functions were decided and confirmed.Based on the above mentioned,every different function was put into decomposition.The program designs about containers transmission,positioning,filling and capping were all done.The productive efficiency of this machine can be up to 2400 bottles per hour.%对直列式灌装旋盖机进行了设计。确定了灌装的工艺原理方案及总功能,在此基础上进行了功能分解。对容器的输送、定位、灌装、旋盖等分能进行了方案设计。该机的生产效率可达到2 400瓶/h.

  13. 盾构螺旋输送机驱动密封故障处理与防护技术%Countermeasures for Malfunctions of Drive Sealing of Screw Conveyors of Shield Machines

    Institute of Scientific and Technical Information of China (English)

    吴朝来

    2012-01-01

    The causes for the malfunctions of the drive sealing of screw conveyors of shield machines, such as irrational screw conveyor design, inclining of screw rod, damage of contacting surface of the screw conveyor case, leaping forward of the screw rod and inadequate grease injection, are analyzed, and countermeasures, including screw conveyor structure optimization, ground conditioning, rationally selecting the screw conveyor speed, avoiding boring with empty chamber and controlling the manufacturing process, are proposed, with the practice in Chongqing as an example. The paper can provide reference for the coping with the malfunctions of the drive sealing of screw conveyors of shield machines in similar projects in the future.%为解决盾构螺旋机驱动密封故障问题,以重庆地区盾构施工情况为依托,结合多台盾构螺旋输送机驱动密封的修复经验,重点分析螺旋输送机驱动密封产生故障的原因:螺旋机设计不合理、螺旋机螺杆倾斜、筒体连接面磨损、螺杆向前蹿动、油脂注入量不足。总结出新的故障处理(螺旋机结构优化、渣土改良、合理选择螺旋机转速、防止空仓掘进、严控加工工艺等)与预防措施(螺旋机叶片修复、改善油脂注入量、更换损坏部件)。为今后盾构施工中处理螺旋输送机驱动密封故障处理与防护技术提供依据。

  14. Design for High-speed Ball Screw Running-life Test Machine Based on Linear Motor%基于直线电机的高速滚珠丝杠副寿命试验机设计

    Institute of Scientific and Technical Information of China (English)

    童亮; 王准

    2014-01-01

    A high-speed ball screw running-life test machine based on a linear motor was designed according to the testing requirements for the high-speed ball screw.A high-speed ball screw running-life test machine which used the linear motor as the loading mechanism,the rotation servo motor for the screw drive mechanism and the programmable multi-axis controller as motion controller,was de-signed and met the testing requirements of life testing and related parameters of the ball screw in the case of the long-running high-speed,high acceleration,big load under the conditions of continuous sta-ble varying loading.The test results demonstrate the feasibility of the system.%针对高速滚珠丝杠副性能指标的测量需求,设计了一套基于直线电机的高速滚珠丝杠副寿命测试试验系统,系统以直线电机为加载机构、旋转伺服电机为丝杠驱动机构、多轴运动控制卡为运动控制器。据此系统设计的滚珠丝杠副高速加载跑合寿命试验机在连续稳定变负载的情况下,可以对滚珠丝杠在高速、高加速度、大负荷等条件下进行长时间运行测试,满足寿命试验机对滚珠丝杠副寿命试验和相关参数的测试要求。试验结果证明了系统的可行性。

  15. 空心滚珠丝杠在数控机床伺服进给系统中的应用%Application on Hollow Ball Screw in Numerical Control Machine Tool Servo Feed System

    Institute of Scientific and Technical Information of China (English)

    常瑞丽; 韩军

    2016-01-01

    针对数控机床主轴和伺服传动系统的热误差阻碍进一步提高机床定位精度的问题,对数控机床伺服进给系统的热变形作了深入研究。结果表明:螺母摩擦和轴承摩擦是滚珠丝杠伺服进给系统的主要热源,其摩擦热量与滚珠丝杠转速及轴向载荷几乎成正比;采用空心丝杠和空心螺母有效抑制了滚珠丝杠在高速进给时的热变形量,减小伺服进给系统的稳态误差。%Aimed at the problem of the thermal error of numerical control ( NC) machine tool spindle and servo feed system hin-dered the raising of machine tool position precision , the thermal deformation of NC machine tool of servo feed system was researched in depth .The results show that the nut friction and bearing friction are the main heat sources of ball screw servo feed system , and the fric-tion heat is alomost proportional to rotational speed of ball screw and axial loading .Hollow ball screw and hollow nut were adopted , which effectively restraines the thermal deformation quantity when ball screw in high speed feeding , and the steady error of servo feed system is diminished .

  16. Twin-Screw Extruders in Ceramic Extrusion

    Science.gov (United States)

    Wiedmann, Werner; Hölzel, Maria

    The machines mainly used for compounding plastics, chemicals and food are co-rotating, closely intermeshing twin-screw extruders. Some 30 000 such extruders are in use worldwide, about 1/3 are ZSKs from Coperion Werner & Pfleiderer, Stuttgart. In the chemical industry more and more batch mixers are being replaced by continuous twin-screw kneaders.

  17. Pedicle screw placement in the lumbar spine: effect of trajectory and screw design on acute biomechanical purchase.

    Science.gov (United States)

    Wray, Steven; Mimran, Ronnie; Vadapalli, Sasidhar; Shetye, Snehal S; McGilvray, Kirk C; Puttlitz, Christian M

    2015-05-01

    testing were statistically significant between the 3 screw/trajectory combinations. The incidence of cortical wall breach with the cortical or traditional pedicle screw trajectories was not significantly different. CONCLUSIONS The data demonstrated that the cortical trajectory provides denser bone that allows for utilization of smaller screws to obtain mechanical purchase that is equivalent to long pedicle screws placed in traditional pedicle screw trajectories for both normal- and low-quality bone. Overall, this biomechanical study in cadavers provides evidence that the cortical screw trajectory represents a good option to obtain fixation for the lumbar spine with low-quality bone.

  18. A new compression design that increases proximal locking screw bending resistance in femur compression nails.

    Science.gov (United States)

    Karaarslan, Ahmet Adnan; Karakaşli, Ahmet; Karci, Tolga; Aycan, Hakan; Yildirim, Serhat; Sesli, Erhan

    2015-06-01

    The aim is to present our new method of compression, a compression tube instead of conventional compression screw and to investigate the difference of proximal locking screw bending resistance between compression screw application (6 mm wide contact) and compression tube (two contact points with 13 mm gap) application. We formed six groups each consisting of 10 proximal locking screws. On metal cylinder representing lesser trochanter level, we performed 3-point bending tests with compression screw and with compression tube. We determined the yield points of the screws in 3-point bending tests using an axial compression testing machine. We determined the yield point of 5 mm screws as 1963±53 N (mean±SD) with compression screw, and as 2929±140 N with compression tubes. We found 51% more locking screw bending resistance with compression tube than with compression screw (p=0,000). Therefore compression tubes instead of compression screw must be preferred at femur compression nails.

  19. 减少数控机床滚珠丝杆精度误差的措施与实践%Measures and Practice on Bridging Precision Errors of NC Machine Ball Screws

    Institute of Scientific and Technical Information of China (English)

    覃日强

    2011-01-01

    Improvement is made on the structure of NC machine ball screws by using a specially-made belleville spring or hydraulic cylinder as double nut preloaded device so as to automatically maintain zero axial clearance and reasonable pressure on ball raceways b%采用特制蝶形弹簧或液压缸作为双螺母的预紧装置,改进数控机床滚珠丝杆副的结构,使螺母与丝杆之间始终自动保持轴向间隙为零和合理的滚珠滚道间压力,从而达到降低数控机床精度误差。

  20. Simple machines

    CERN Document Server

    Graybill, George

    2007-01-01

    Just how simple are simple machines? With our ready-to-use resource, they are simple to teach and easy to learn! Chocked full of information and activities, we begin with a look at force, motion and work, and examples of simple machines in daily life are given. With this background, we move on to different kinds of simple machines including: Levers, Inclined Planes, Wedges, Screws, Pulleys, and Wheels and Axles. An exploration of some compound machines follows, such as the can opener. Our resource is a real time-saver as all the reading passages, student activities are provided. Presented in s

  1. Economics of water injected air screw compressor systems

    OpenAIRE

    Madhav, K. V.; Kovacevic, A.

    2015-01-01

    There is a growing need for compressed air free of entrained oil to be used in industry. In many cases it can be supplied by oil flooded screw compressors with multi stage filtration systems, or by oil free screw compressors. However, if water injected screw compressors can be made to operate reliably, they could be more efficient and therefore cheaper to operate. Unfortunately, to date, such machines have proved to be insufficiently reliable and not cost effective. This paper describes an in...

  2. Pullout strength of pedicle screws with cement augmentation in severe osteoporosis: A comparative study between cannulated screws with cement injection and solid screws with cement pre-filling

    Directory of Open Access Journals (Sweden)

    Lee Yen-Chen

    2011-02-01

    Full Text Available Abstract Background Pedicle screws with PMMA cement augmentation have been shown to significantly improve the fixation strength in a severely osteoporotic spine. However, the efficacy of screw fixation for different cement augmentation techniques, namely solid screws with retrograde cement pre-filling versus cannulated screws with cement injection through perforation, remains unknown. This study aimed to determine the difference in pullout strength between conical and cylindrical screws based on the aforementioned cement augmentation techniques. The potential loss of fixation upon partial screw removal after screw insertion was also examined. Method The Taguchi method with an L8 array was employed to determine the significance of design factors. Conical and cylindrical pedicle screws with solid or cannulated designs were installed using two different screw augmentation techniques: solid screws with retrograde cement pre-filling and cannulated screws with cement injection through perforation. Uniform synthetic bones (test block simulating severe osteoporosis were used to provide a platform for each screw design and cement augmentation technique. Pedicle screws at full insertion and after a 360-degree back-out from full insertion were then tested for axial pullout failure using a mechanical testing machine. Results The results revealed the following 1 Regardless of the screw outer geometry (conical or cylindrical, solid screws with retrograde cement pre-filling exhibited significantly higher pullout strength than did cannulated screws with cement injection through perforation (p = 0.0129 for conical screws; p = 0.005 for cylindrical screws. 2 For a given cement augmentation technique (screws without cement augmentation, cannulated screws with cement injection or solid screws with cement pre-filling, no significant difference in pullout strength was found between conical and cylindrical screws (p >0.05. 3 Cement infiltration into the open cell of

  3. TX1600G 数控镗铣加工中心滚珠丝杠热特性分析%Thermal Characteristics Analysis of Ball Screw of TX1600G CNC Boring and Milling Machining Center

    Institute of Scientific and Technical Information of China (English)

    孙军; 秦显军; 钱彬彬; 黄圆

    2015-01-01

    This paper takes TX1600G CNC bor-ing and milling machining center as example and mainly studies the impact of different feed speed and coolant flow on the system heat balance,under the conditions of the moving heat source.To un-derstand the ball screw in actual working condi-tions,ANSYS was first used to establish a simpli-fied three dimensional model of the ball screw, and then the heat source was moved to simulate heat transmission on nut and bearing,so the tem-perature model and thermal error compensation model of lead screw are established.Results show that the increase of feed speed can shorten the time for heat balance of the system,but the thermal e-quilibrium temperature was increased;coolant flu-id can effectively reduce the thermal equilibrium temperature and the thermal equilibrium time. Thermal error modeling and the analysis of tem-perature field also provide necessary theoretical ba-sis to the thermal compensation of the system.%以 TX1600G 数控镗铣加工中心为例,主要研究在移动热源施加条件下,不同的进给速度以及冷却液流量对系统热平衡的影响。为得到滚珠丝杠在实际工作中的状态,利用 ANSYS 建立丝杠的简化三维模型,施加移动热源来模拟螺母和轴承的传动热量,从而得到丝杠的温度模型,建立热误差补偿模型。结果表明,进给速度的增加可以缩短系统的热平衡时间,但热平衡温度有所升高;冷却液可以有效地降低热平衡温度和缩短热平衡时间。热误差模型建立和温度场分析,为系统的热补偿提供必要的理论依据。

  4. Biomechanical comparison of cervical fixation via transarticular facet screws without rods versus lateral mass screws with rods.

    Science.gov (United States)

    Yi, Seong; Rim, Dae-Cheol; Nam, Ki-Se; Keem, Sang-Hyun; Murovic, Judith A; Lim, Jesse; Park, Jon

    2015-04-01

    Transarticular facet screws restore biomechanical stability to the cervical spine when posterior cervical anatomy has been compromised. This study compares the more recent, less invasive, and briefer transarticular facet screw system without rods with the lateral mass screw system with rods. For this study, 6 human cervical spines were obtained from cadavers. Transarticular facet screws without rods were inserted bilaterally into the inferior articular facets at the C5-C6 and C5-C6-C7 levels. Lateral mass screws with rods were inserted bilaterally at the same levels using Magerl's technique. All specimens underwent range of motion (ROM) testing by a material testing machine for flexion, extension, lateral bending, and axial rotation. Both fixation methods, transarticular facet screws without rods and lateral mass screws with rods, reduced all ROM measurements and increased spinal stiffness. No statistically significant differences between the 2 stabilization methods were found in ROM measurements for 1-level insertions. However, in 2-level insertions, ROM for the nonrod transarticular facet screw group was significantly increased for flexion-extension and lateral bending. Transarticular facet screws without rods and lateral mass screws with rods had similar biomechanical stability in single-level insertions. For 2-level insertions, transarticular facet screws without rods are a valid option in cervical spine repair. Copyright © 2015 Elsevier Inc. All rights reserved.

  5. Screw Performance Degradation Assessment Based on Quantum Genetic Algorithm and Dynamic Fuzzy Neural Network

    Directory of Open Access Journals (Sweden)

    Xiaochen Zhang

    2015-01-01

    Full Text Available To evaluate the performance of ball screw, screw performance degradation assessment technology based on quantum genetic algorithm (QGA and dynamic fuzzy neural network (DFNN is studied. The ball screw of the CINCINNATIV5-3000 machining center is treated as the study object. Two Kistler 8704B100M1 accelerometers and a Kistler 8765A250M5 three-way accelerometer are installed to monitor the degradation trend of screw performance. First, screw vibration signal features are extracted both in time domain and frequency domain. Then the feature vectors can be obtained by principal component analysis (PCA. Second, the initialization parameters of the DFNN are optimized by means of QGA. Finally, the feature vectors are inputted to DFNN for training and then get the screw performance degradation model. The experiment results show that the screw performance degradation model could effectively evaluate the performance of NC machine screw.

  6. In vitro evaluation of force-expansion characteristics in a newly designed orthodontic expansion screw compared to conventional screws

    Directory of Open Access Journals (Sweden)

    Oshagh Morteza

    2009-01-01

    Full Text Available Objective : Expansion screws like Hyrax, Haas and other types, produce heavy interrupted forces which are unfavorable for dental movement and could be harmful to the tooth and periodontium. The other disadvantage of these screws is the need for patient cooperation for their regular activation. The purpose of this study was to design a screw and compare its force- expansion curve with other types. Materials and Methods : A new screw was designed and fabricated in the same dimension, with conventional types, with the ability of 8 mm expansion (Free wire length: 12 mm, initial compression: 4.5 mm, spring wire diameter: 0.4 mm, spring diameter: 3 mm, number of the coils: n0 ine, material: s0 tainless steel. In this in vitro study, the new screw was placed in an acrylic orthodontic appliance, and after mounting on a stone cast, the force-expansion curve was evaluated by a compression test machine and compared to other screws. Results : Force-expansion curve of designed screw had a flatter inclination compared to other screws. Generally it produced a light continuous force (two to 3.5 pounds for every 4 mm of expansion. Conclusion : In comparison with heavy and interrupted forces of other screws, the newly designed screw created light and continuous forces.

  7. Pullout strength of misplaced pedicle screws in the thoracic and lumbar vertebrae - A cadaveric study

    Directory of Open Access Journals (Sweden)

    Shyam K Saraf

    2013-01-01

    Full Text Available Background: The objective of this cadaveric study was to analyze the effects of iatrogenic pedicle perforations from screw misplacement on the mean pullout strength of lower thoracic and lumbar pedicle screws. We also investigated the effect of bone mineral density (BMD, diameter of pedicle screws, and the region of spine on the pullout strength of pedicle screws. Materials and Methods: Sixty fresh human cadaveric vertebrae (D10-L2 were harvested. Dual-energy X-ray absorptiometry (DEXA scan of vertebrae was done for BMD. Titanium pedicle screws of different diameters (5.2 and 6.2 mm were inserted in the thoracic and lumbar segments after dividing the specimens into three groups: a standard pedicle screw (no cortical perforation; b screw with medial cortical perforation; and c screw with lateral cortical perforation. Finally, pullout load of pedicle screws was recorded using INSTRON Universal Testing Machine. Results: Compared with standard placement, medially misplaced screws had 9.4% greater mean pullout strength and laterally misplaced screws had 47.3% lesser mean pullout strength. The pullout strength of the 6.2 mm pedicle screws was 33% greater than that of the 5.2 mm pedicle screws. The pullout load of pedicle screws in lumbar vertebra was 13.9% greater than that in the thoracic vertebra ( P = 0.105, but it was not statistically significant. There was no significant difference between pullout loads of vertebra with different BMD ( P = 0.901. Conclusion: The mean pullout strength was less with lateral misplaced pedicle screws while medial misplaced pedicle screw had more pullout strength. The pullout load of 6.2 mm screws was greater than that of 5.2 mm pedicle screws. No significant correlation was found between bone mineral densities and the pullout strength of vertebra. Similarly, the pullout load of screw placed in thoracic and lumbar vertebrae was not significantly different.

  8. 注塑机螺杆混炼元件混炼性能对比研究%Comparative Study on Plasticizing Properties of Screw Mixing Units for Injection Machine

    Institute of Scientific and Technical Information of China (English)

    柳天磊; 王建鸿; 杜遥雪

    2013-01-01

    Based on production process,three kinds of screw mixing units were designed:pin mixer,barrier mixer and pineapple mixer.Numerical simulation was carried out on the three mixing sections in the metering section based on the CFD software POLYFLOW,and comparative study was performed on the mixing properties and plasticizing quality among them.The results show that the differential pressure of exit and entrance in the barrier runner is minimum,that in the pin runner is maximum and the pressure dropdown in the pineapple between them.Moreover,the rate of stretching is larger in the pineapple mixer than in the other two mixers which are haply similar in curves.For the mixing index,the pineapple behaves best,the pin better and the barrier mixer worst.These conclusions provide a reference for the configuration of injection molding machine,selection of screws and their application.%根据生产实际设计销钉型、屏障型及菠萝型三种螺杆混炼元件,并借助于计算流体动力学软件POLYFLOW分别对位于计量段末端的三种类型混炼段进行数值仿真,对比分析其混炼性能和塑化质量。结果表明,三种构型混炼元件中,屏障型混炼元件出入口压力降最小,销钉型压力降最大,菠萝型压力降介于两者之间;菠萝型混炼元件拉伸速率最大,销钉型与屏障型相似;菠萝型混炼元件混合指数最大,销钉型次之,屏障型最小。

  9. The applicability of PEEK-based abutment screws.

    Science.gov (United States)

    Schwitalla, Andreas Dominik; Abou-Emara, Mohamed; Zimmermann, Tycho; Spintig, Tobias; Beuer, Florian; Lackmann, Justus; Müller, Wolf-Dieter

    2016-10-01

    The high-performance polymer PEEK (poly-ether-ether-ketone) is more and more being used in the field of dentistry, mainly for removable and fixed prostheses. In cases of screw-retained implant-supported reconstructions of PEEK, an abutment screw made of PEEK might be advantageous over a conventional metal screw due to its similar elasticity. Also in case of abutment screw fracture, a screw of PEEK could be removed more easily. M1.6-abutment screws of four different PEEK compounds were subjected to tensile tests to set their maximum tensile strengths in relation to an equivalent stress of 186MPa, which is aused by a tightening torque of 15Ncm. Two screw types were manufactured via injection molding and contained 15% short carbon fibers (sCF-15) and 40% (sCF-40), respectively. Two screw types were manufactured via milling and contained 20% TiO2 powder (TiO2-20) and >50% parallel orientated, continuous carbon fibers (cCF-50). A conventional abutments screw of Ti6Al4V (Ti; CAMLOG(®) abutment screw, CAMLOG, Wimsheim, Germany) served as control. The maximum tensile strength was 76.08±5.50MPa for TiO2-20, 152.67±15.83MPa for sCF-15, 157.29±20.11MPa for sCF-40 and 191.69±36.33MPa for cCF-50. The maximum tensile strength of the Ti-screws amounted 1196.29±21.4MPa. The results of the TiO2-20 and the Ti screws were significantly different from the results of the other samples, respectively. For the manufacturing of PEEK abutment screws, PEEK reinforced by >50% continuous carbon fibers would be the material of choice. Copyright © 2016 Elsevier Ltd. All rights reserved.

  10. Simple Machine Junk Cars

    Science.gov (United States)

    Herald, Christine

    2010-01-01

    During the month of May, the author's eighth-grade physical science students study the six simple machines through hands-on activities, reading assignments, videos, and notes. At the end of the month, they can easily identify the six types of simple machine: inclined plane, wheel and axle, pulley, screw, wedge, and lever. To conclude this unit,…

  11. A four lumen screwing device for multiparametric brain monitoring.

    Science.gov (United States)

    Feuerstein, T H; Langemann, H; Gratzl, O; Mendelowitsch, A

    2000-01-01

    We describe multiparametric monitoring in severe head trauma using a new screwing device. Our aim was to create a screw which would make the implantation of the probes and thus multiparametric monitoring easier. The new screw allows us to implant 3 probes (microdialysis, Paratrend and an intracranial pressure device) through one burr hole. The screw has four channels, the fourth being for ventricular drainage. We monitored 13 patients with severe head trauma (GCS = 3-8) for up to 7 days. Brain tissue pO2, pCO2, pH, and temperature were measured on-line with the Paratrend 7 machine. The microdialytic parameters glucose, lactate, pyruvate and glutamate were determined semi on-line with a CMA 600 enzymatic analyser. There were no complications in any of the patients that could be ascribed to the screw.

  12. Compressive Force With 2-Screw and 3-Screw Subtalar Joint Arthrodesis With Headless Compression Screws.

    Science.gov (United States)

    Matsumoto, Takumi; Glisson, Richard R; Reidl, Markus; Easley, Mark E

    2016-12-01

    Joint compression is an essential element of successful arthrodesis. Although subtalar joint compression generated by conventional screws has been quantified in the laboratory, compression obtainable with headless screws that rely on variable thread pitch to achieve bony contact has not been assessed. This study measured subtalar joint compression achieved by 2 posteriorly placed contemporary headless, variable-pitch screws, and quantified additional compression gained by placing a third screw anteriorly. Ten, unpaired fresh-frozen cadaveric subtalar joints were fixed sequentially using 2 diverging posterior screws (one directed into the talar dome, the other into the talar neck), 2 parallel posterior screws (both ending in the talar dome), and 2 parallel screws with an additional anterior screw inserted from the plantar calcaneus into the talar neck. Joint compression was quantified directly during screw insertion using a novel custom-built measuring device. The mean compression generated by 2 diverging posterior screws was 246 N. Two parallel posterior screws produced 294 N of compression, and augmentation of that construct with a third, anterior screw increased compression to 345 N (P < .05). Compression subsequent to 2-screw fixation was slightly less than that reported previously for subtalar joint fixation with 2 conventional lag screws, but was comparable when a third screw was added. Under controlled testing conditions, 2 tapered, variable-pitch screws generated somewhat less compression than previously reported for 2-screw fixation with conventional headed screws. A third screw placed anteriorly increased compression significantly. Because headless screws are advantageous where prominent screw heads are problematic, such as the load-bearing surface of the foot, their effectiveness compared to other screws should be established to provide an objective basis for screw selection. Augmenting fixation with an anterior screw may be desirable when conditions for

  13. 3D CFD analysis of a twin screw expander

    OpenAIRE

    Kovacevic, A.; S Rane

    2013-01-01

    Twin screw machines can be used as expanders for variety of applications. This paper describes how the performance of an oil free twin screw air expander of 3/5 lobe configuration was estimated by use of full 3D Computational Fluid Dynamics (CFD) applying a procedure similar to that used for screw compressors. The grid generator SCORG© was employed for pre-processing of the moving domains between the rotors while the stationary grids for the ports were derived from a commercial grid generator...

  14. DLC screw preload. Loosening prevention

    Directory of Open Access Journals (Sweden)

    Ivete Aparecida de Mattias Sartori

    2008-01-01

    Full Text Available The screw loosening is a reason to prosthetic rehabilitation failure. However, the DLC (Diamond-like carbon screw treatment lead thefriction decrease and sliding between the components, which increases the screw preload benefit and decreases the chance of looseningoccurrence. This case shows a clinical indication of the association of the correct preload applied and the DLC screw, which can be considered an optimized protocol to solve screw loosening recidivate of unitary prosthesis in anterior maxillary site.

  15. 3D CFD analysis of an oil injected twin screw expander

    OpenAIRE

    Papeš, Iva; Degroote, Joris; Vierendeels, Jan

    2014-01-01

    Small scale Organic Rankine Cycle (ORC) systems have a big potential for waste heat recovery in the market. Due to the smaller volume flows inside these systems, non-conventional expansion technologies such as screw expanders become more interesting. Recent economic studies have shown the important role of screw machines in such cycles. However, in order to get a better understanding of the expansion behaviour in an ORC, appropriate simulation models of screw expanders are necessary. The flow...

  16. Ball Screw Actuator Including a Compliant Ball Screw Stop

    Science.gov (United States)

    Wingett, Paul T. (Inventor); Hanlon, Casey (Inventor)

    2017-01-01

    An actuator includes a ball nut, a ball screw, and a ball screw stop. The ball nut is adapted to receive an input torque and in response rotates and supplies a drive force. The ball screw extends through the ball nut and has a first end and a second end. The ball screw receives the drive force from the ball nut and in response selectively translates between a retract position and a extend position. The ball screw stop is mounted on the ball screw proximate the first end to translate therewith. The ball screw stop engages the ball nut when the ball screw is in the extend position, translates, with compliance, a predetermined distance toward the first end upon engaging the ball nut, and prevents further rotation of the ball screw upon translating the predetermined distance.

  17. Design of Formed Milling Cutter for Double-Helix Screw Based on Noninstantaneous Envelope Method

    Directory of Open Access Journals (Sweden)

    Yun Li

    2013-01-01

    Full Text Available The design theory and method of formed milling cutter for double-helix screw of progressing cavity pump are presented. Through analyzing the shape and characteristic parameters of double-helix screw, the helicoids equation and axial curve equation of double-helix screw were established. According to the relative position relations between formed milling cutter and double-helix screw in the machining process, the geometric mapping relationship of screw coordinate system and formed milling cutter coordinate system was established by using the coordinate transformation theory. Based on noninstantaneous envelope method and the meshing conditions between formed milling cutter and double-helix screw, the contact line equations were established by minimum value method. By analyzing the machining errors caused by resharpening the formed milling cutter, the tooth back curve equation was established based on spiral of Archimedes, and the profile equation of formed milling cutter with constant back angle was got. On this basis, the formed milling cutter of processing double-helix screw was designed, and the cutter head and tool post were manufactured, respectively. The measuring results have shown that this method can satisfy the requirements of machining accuracy for double-helix screw. So this is an effective method to get formed milling cutter profile for double-helix screw.

  18. Biomechanical comparison of cervical transfacet pedicle screws versus pedicle screws

    Institute of Scientific and Technical Information of China (English)

    LIU Guan-yi; XU Rong-ming; MA Wei-hu; SUN Shao-hua; HUANG Lei; YING Jiang-wei; JIANG Wei-yu

    2008-01-01

    Background Transfacet pedicle screws provide another alternative for standard pedicle screw placement for plate fixation in the Iumbar spine. However, few studies looking at transfacet pedicle screw fixation in the cervical spine are available. Therefore, cervical transfacet pedicle screw fixation and standard pedicle screw fixation techniques were biomechanically compared in this study.Methods Ten fresh human cadaveric cervical spines were harvested. On one side, transfacet pedicle screws were placed at the C3-4, C5-6, and C7-T1 levels. On the other side, pedicle screws were placed at the C3, C5, and C7 levels. The screw insertion technique at each level was randomized for right or left. The starting point for the transfacet pedicle screw insertion was located at the midpoint of the inferolateral quadrant of the lateral mass and the direction of the screw was about 50° caudally in the sagittal plane and about 45° toward the midline in the axial plane. Screws were placed from the inferior articular process, across the facet complex and the pedicle into the body of the caudal vertebra. The entry point for the pedicle screw was located at the midpoint of the superolateral quadrant of the lateral mass, and the direction of the screw was about 45° toward the midline in the axial plane and toward the upper third of the vertebral body in the sagittal plane. After screw placement we performed axial pullout testing.Results All the cervical transfacet pedicle screws and the pedicle screws were inserted successfully. The mean pullout strength for the transfacet pedicle screws was 694 N, while for the pedicle screws 670 N (P=-0.013). In all but six instances (10%), the pedicle screw pullout values exceeded the values for the transfacet pedicle screws; this occurred three times at the C3/C4 level, twice at the C5/C6 level and once at the C7/T1 level. The greatest pullout strength difference at a single level was observed at the C5/C6 level, with a mean difference of 38 N (t

  19. Equivalent Magnetic Circuit Model of Flux-switching Hybrid Excitation Machine%混合励磁磁通切换电机等效磁路模型

    Institute of Scientific and Technical Information of China (English)

    许泽刚; 谢少军; 毛鹏

    2011-01-01

    混合励磁磁通切换电机(flux-switching hybrid excitationmachine,FSHM)是一种新型定子励磁型交流无刷电机,具有磁链双极性、结构简单、功率密度高、运行可靠等优点。改变电励磁绕组电流的大小和方向,实现了对永磁气隙磁场的有效调节与控制,而引入导磁磁桥可提升气隙磁场调节范围。以建立电枢绕组磁链最大位置的等效磁路模型为切入点,推导了峰值磁通表达式,探索了磁桥段相对磁导率的估算方法,结合有限元仿真分析了磁桥厚度变化与磁桥式FSHM初始气隙磁密、磁桥磁密、气隙磁场调节能力、磁力线路径转移等特性的关系。样机的有限元仿真及实验结果与等效磁路模型预测趋势基本一致,验证了建模方法与理论分析的正确性,可用于指导磁通切换电机的设计与性能分析。%Flux-switching hybrid excitation machine(FSHM) was an interesting brushless machine with magnets in the stator,which offered the advantages of bipolar flux linkage,simple and robust rotor structure and high power density.Adjustment and control of the PM air gap magnetic field could be achieved by means of controlling the field winding current,and magnetic bridge amplified the effect of field flux on PM flux.This paper took equivalent magnetic circuit model(EMCM) of maximum phase flux-linkage position as point of penetration,deduced the equation of peak magnetic flux,and explored a method for estimating the relative permeability of magnetic bridge.The characteristic relation between the thickness of magnetic bridge and initial air gap flux density,magnetic bridge flux density,regulating capacity of air gap magnetic field,and magnetic lines transfer were studied combined with finite element analysis(FEA).The estimation results based on EMCM agreed well with the FEA and experiment data,which confirmed the correctness of modeling method and theoretical analysis.It provided reference for

  20. Optimization of Twin-Screw Superchargers for Combined Compressor - Expander Performance (SCREW); Optimierung von Schraubenladern fuer den kombinierten Verdichtungs- und Expansionsbetrieb (SCREW)

    Energy Technology Data Exchange (ETDEWEB)

    Romba, M. [Dortmund Univ. (Germany). Fachgebiet Fluidenergiemaschinen

    2005-07-01

    During the last years the use of mechanical superchargers has gained increasing interest in a bid to combine attractive emission- and fuel consumption values with dynamic driving performance. Based on an analysis of available supercharging systems the development potential of twin screw superchargers is assessed. A concept using inlet slide valves is developed which allows at the same time to control the mass flow delivered by the supercharger and achieve an expansion of the transported charge under part load conditions when the delivered pressure is lower than ambient pressure, achieving a reduction in necessary shaft power or even the delivery of shaft power. To distinguish it from conventional superchargers the new device is called ''SCREW'' - screw type machine with compressor respectively expander working mode. The effect of several design parameters on the SCREW'S performance is evaluated by extensive simulation calculations, showing that a suitable design varies considerably from conventional supercharger designs and that a significant amount of further research, especially covering the development of rotor profiles suited for the specific task, is still needed to fully utilize the concept's potential. As a proof of concept prototype SCREW'S, based on a conventional twin screw supercharger, have been built and tested. The results obtained made clear the general suitability of the concept but also underlined the shortcomings of the prototype as they had already been predicted by the simulations. (orig.)

  1. In vitro evaluation of flexural strength of different brands of expansion screws

    Directory of Open Access Journals (Sweden)

    Kádna Fernanda Mendes de Oliveira

    2012-06-01

    Full Text Available OBJECTIVE: The objective of this study was to compare the flexural strength of the stems of three maxillary expanders screws of Morelli, Forestadent and Dentaurum brands. METHODS: The sample consisted of nine expander screws (totalizing of 36 stems, three from each brand, all stainless steel and 12 mm of expansion capacity. The stems of the expander screws were cut with cutting pliers close to the weld region with screw body, then fixed in a universal testing machine Instron 4411 for tests of bending resistance of three points. The ultimate strength in kgF exerted by the machine to bend the stem of the 5 mm screw was recorded and the flexural strength was calculated using a mathematical formula. During the flexural strength test it was verified the modulus of elasticity of the stems by means of Bluehill 2 software. The flexural strength data were subjected to ANOVA with one criterion and Tukey's test, with significance level of 5%. RESULTS: Forestadent screw brand showed the greatest bending strength, significantly higher than Dentaurum. Morelli showed the lowest resistance. CONCLUSION: The flexural strength of the screws varied according to the brand. Forestadent screw showed the greatest resistance and Morelli the lowest. All the three screws were found adequate for use in procedures for rapid maxillary expansion.

  2. Twin screw two-phase expanders in large chiller units

    Energy Technology Data Exchange (ETDEWEB)

    Smith, I.K.; Stosic, N.; Aldis, C.A.; Kovacevic, A. [City Univ., Dept. of Mechanical Engineering and Aeronautics, London (United Kingdom)

    1999-07-01

    An investigation was carried out to determine the feasibility of the use of a twin screw expander as a throttle valve replacement in a 500 ton chiller. The aim was to produce a demonstration unit with an overall machine adiabatic efficiency of not less that 70%. The efficiency target was effectively met but further analytical work is needed to predict mass flow rates reliably and hence the exact machine size required when refrigerant enters the expander as subcooled liquid. (Author)

  3. Biomechanical comparison of three-point bending resistance of titanium and stainless steel locking screws in intramedullary nails.

    Science.gov (United States)

    Karaarslan, Ahmet Adnan; Karakaşlı, Ahmet; Aycan, Hakan; Ertem, Fatih; Sesli, Erhan

    2015-01-01

    This study aims to investigate whether there is any significant difference in bending resistance between titanium and stainless steel locking screws of femur nails and to review deformation of locking screws which is a common problem in interlocking nailing. In this study, a total of 60 pieces of 5 mm major diameter titanium and stainless steel locking screws were used as six groups in three different thread depth structures (high threaded, low threaded, and unthreaded). Three-point bending tests were conducted on steel screws placed inside stainless steel tube with 30 mm inner diameter, which imitated the level of lesser trochanter. We used an axial compression testing machine in order to determine the yield points that permanent deformation occurred in the locking screws. For low threaded locking screws, which are the most frequently used thread type for locking screws, the mean bending yield points were 1413 N on the titanium screws and this level was below 1922 N (2.8 BW) of level walking loading on femur for 70 kg person. On low threaded stainless screws, bending resistance was 2071 N, which was above the value of 1922 N. For high threaded locking screws, the mean bending yield points were 874 N on the titanium screws and 556 N on stainless screws. In comminuted femur shaft fractures (in full load bearing conditions), using stainless steel locking screws is better instead of titanium screws to avoid locking screw deformation since low threaded stainless steel screws were 46.5% more resistant to bending deformation than titanium ones. Stainless steel or titanium high threaded locking screws may only be carefully used in non-comminuted fractures.

  4. Screw bondgraph contact dynamics

    NARCIS (Netherlands)

    Visser, Martijn; Stramigioli, Stefano; Heemskerk, Cock

    2002-01-01

    This paper presents an elegant contact dynamics model in screw bondgraph form. It can model the contact between any two objects of finite curvature. It does so by defining a Gauss frame on the surfaces of both objects in the points that are closest to each other. Then it describes how the Gauss fram

  5. Bending strength and holding power of tibial locking screws.

    Science.gov (United States)

    Lin, J; Lin, S J; Chiang, H; Hou, S M

    2001-04-01

    The bending strength and holding power of two types of specially designed tibial locking devices, a both-ends-threaded screw and an unthreaded bolt, were studied and compared with four types of commercially available tibial interlocking screws: Synthes, Howmedica, Richards, and Osteo AG. To test bending strength, the devices were inserted into a high molecular weight polyethylene tube and loaded at their midpoint by a materials testing machine to simulate a three point bending test. Single loading yielding strength and cyclic loading fatigue life were measured. To test holding power, the devices were inserted into tubes made of polyurethane foam, and their tips were loaded axially to measure pushout strength. The devices were tested with two different densities of foam materials and two different sizes of pilot holes. Insertion torque and stripping torque of the screws were measured first. Pushout tests were performed with each screw inserted with a tightness equal to 60% of its stripping torque. Test results showed that the yielding strength and the fatigue life were related closely to the inner diameter of the screws. The stripping torque predicted the pushout strength more reliably than did the insertion torque. All tested devices showed greater holding power in the foam with the higher density and with the smaller pilot holes. The both-ends-threaded screw had the highest pushout strength and a satisfactory fatigue strength. The unthreaded bolt had the highest fatigue strength but only fair holding power. Clinical studies of the use of these two types of locking devices are worthwhile.

  6. Wet granulation in a twin-screw extruder: implications of screw design.

    Science.gov (United States)

    Thompson, M R; Sun, J

    2010-04-01

    Wet granulation in twin-screw extrusion machinery is an attractive technology for the continuous processing of pharmaceuticals. The performance of this machinery is integrally tied to its screw design yet little fundamental knowledge exists in this emerging field for granulation to intelligently create, troubleshoot, and scale-up such processes. This study endeavored to systematically examine the influence of different commercially available screw elements on the flow behavior and granulation mechanics of lactose monohydrate saturated at low concentration (5-12%, w/w) with an aqueous polyvinyl-pyrrolidone binder. The results of the work showed that current screw elements could be successfully incorporated into designs for wet granulation, to tailor the particle size as well as particle shape of an agglomerate product. Conveying elements for cohesive granular flows were shown to perform similar to their use in polymer processing, as effective transport units with low specific mechanical energy input. The conveying zones provided little significant change to the particle size or shape, though the degree of channel fill in these sections had a significant influence on the more energy-intensive mixing elements studied. The standard mixing elements for this machine, kneading blocks and comb mixers, were found to be effective for generating coarser particles, though their mechanisms of granulation differed significantly.

  7. NUT SCREW MECHANISMS

    Science.gov (United States)

    Glass, J.A.F.

    1958-07-01

    A reactor control mechanism is described wherein the control is achieved by the partial or total withdrawal of the fissile material which is in the form of a fuel rod. The fuel rod is designed to be raised and lowered from the reactor core area by means of two concentric ball nut and screw assemblies that may telescope one within the other. These screw mechanisms are connected through a magnetic clutch to a speed reduction gear and an accurately controllable prime motive source. With the clutch energized, the fuel rod may be moved into the reactor core area, and fine adjustments may be made through the reduction gearing. However, in the event of a power failure or an emergency signal, the magnetic clutch will become deenergized, and the fuel rod will drop out of the core area by the force of gravity, thus shutting down the operation of the reactor.

  8. ROTARY SCREW SYSTEMS IN CEMENT

    OpenAIRE

    2016-01-01

    The article presents results of research of rotary-screw systems in relation to the creation of rotary kilns for the annealing of-cuttings in the preparation of cement clinker. Using the proposed design, in comparison with known designs of similar purpose, it significantly improves performance, reduces size and power consumption through the use of rotary screw systems in the form of screw rotors and drums made hollow with sidewalls assembled from separate strips or plates of different geometr...

  9. New concept single screw compressors and their manufacture technology

    Science.gov (United States)

    Feng, Q.; Liu, F.; Chang, L.; Feng, C.; Peng, C.; Xie, J.; van den Broek, M.

    2017-08-01

    Single screw compressors were generally acknowledged as one of the nearly perfect machines by compressor researchers and manufacturers. However the rapid wear of the star-wheel in a single screw compressor during operation is a key reason why it hasn’t previously joined the main current compressors’ market. After more than ten years of effective work, the authors of this paper have proposed a new concept single screw compressor whose mesh-couple profile is enveloped with multi-column. Also a new design method and manufacture equipment for this kind of compressor have been developed and are described in this paper. A lot of prototype tests and a long period of industrial operations under full loading conditions have shown that the mesh-couple profiles of the new concept single compressors have excellent anti-wearness.

  10. A screwing device for handling and assembly of micro screws

    DEFF Research Database (Denmark)

    Gegeckaite, Asta; Hansen, Hans Nørgaard; Eriksson, Torbjörn Gerhard

    2007-01-01

    Nowadays, the application of specially designed handling devices in micro technology is an important topic and a necessity for the industry. Conventional methods for screwing can not be applied directly to micro screws. This is caused by the 3D micro object geometry and dimensions which inducing ...

  11. Numerical simulation of a twin screw expander for performance prediction

    Science.gov (United States)

    Papes, Iva; Degroote, Joris; Vierendeels, Jan

    2015-08-01

    With the increasing use of twin screw expanders in waste heat recovery applications, the performance prediction of these machines plays an important role. This paper presents a mathematical model for calculating the performance of a twin screw expander. From the mass and energy conservation laws, differential equations are derived which are then solved together with the appropriate Equation of State in the instantaneous control volumes. Different flow processes that occur inside the screw expander such as filling (accompanied by a substantial pressure loss) and leakage flows through the clearances are accounted for in the model. The mathematical model employs all geometrical parameters such as chamber volume, suction and leakage areas. With R245fa as working fluid, the Aungier Redlich-Kwong Equation of State has been used in order to include real gas effects. To calculate the mass flow rates through the leakage paths formed inside the screw expander, flow coefficients are considered as constant and they are derived from 3D Computational Fluid Dynamic calculations at given working conditions and applied to all other working conditions. The outcome of the mathematical model is the P-V indicator diagram which is compared to CFD results of the same twin screw expander. Since CFD calculations require significant computational time, developed mathematical model can be used for the faster performance prediction.

  12. Comparison of organic rankine cycle systems under varying conditions using turbine and twin-screw expanders

    OpenAIRE

    Read, M. G.; Smith, I K; Stosic, N.; Kovacevic, A.

    2016-01-01

    A multi-variable optimization program has been developed to investigate the performance of Organic Rankine Cycles (ORCs) for low temperature heat recovery applications using both turbine and twin-screw expanders when account is taken of performance variation due to changes in ambient conditions. The cycle simulation contains thermodynamic models of both types of expander. In the case of the twin-screw machine, the methods used to match the operation of the expander to the requirements of the ...

  13. Analysis of Indicator Diagrams of a Water Injected Twin-shaft Screw-type Expander

    OpenAIRE

    Nikolov, Alexander; Brümmer, Andreas

    2016-01-01

    Twin-shaft screw-type expanders offer a high potential for energy conversion in the lower and medium power range, for instance as expansion engines in Rankine cycles for exhaust heat recovery. With regard to minimizing internal leakages and lubricating moving machine parts, an auxiliary liquid or liquid working fluid can be fed to the screw expander. In this paper, indicator diagrams of a twin-shaft screw-type expander prototype designed at the Chair of Fluidics at TU Dortmund University are ...

  14. Numerical and Experimental Investigation of Pressure Losses at Suction of a Twin Screw Compressor

    Science.gov (United States)

    Arjeneh, M.; Kovacevic, A.; Rane, S.; Manolis, M.; Stosic, N.

    2015-08-01

    Rotary twin screw machines are used in the wide range of industrial applications and are capable of handling single and multiphase fluids as compressors, expanders and pumps. Concentration of liquid in the inlet flow can influence the performance of the machine significantly. Characteristics of the multiphase flow at the suction of a screw compressor depend on the local flow velocities and concentration. Local flow velocity measurements inside the screw compressors are difficult to obtain. However other flow properties such as local pressures are easier to attain. It is therefore useful to carry out experiments with local pressure variations in the suction which can be used to validate the 3D numerical Computational Fluid Dynamic (CFD) models that could help in studying the single and multiphase flow behaviour in screw compressors. This paper presents experimental efforts to measure the local pressure losses inside the suction plenum of the screw compressor. Pressure variations are measured at 23 locations in the suction port at various operating conditions and compared with 3D CFD model. The grid generator SCORGTM was used for generating numerical mesh of rotors. The flow calculations were carried out using commercial 3D solver ANSYS CFX. It was found that the local pressure changes predicted by the CFD model are in the good agreement with measured pressures. This validated the use of CFD for modelling of the single phase flows in suction of screw machines.

  15. Mechanical strength, fatigue life, and failure analysis of two prototypes and five conventional tibial locking screws.

    Science.gov (United States)

    Hou, Sheng-Mou; Wang, Jaw-Lin; Lin, Jinn

    2002-01-01

    To investigate the effects of the design and microstructure on the mechanical strength of tibial locking devices. The mechanical strength of two prototypes of specially developed locking devices (a both-ends-threaded screw and an unthreaded bolt) was tested and compared with that of five types of commercially available tibial locking screws (Synthes, Howmedica, Richards, Osteo AG, and Zimmer) with similar dimensions. The devices were inserted into a polyethylene tube and loaded at their midpoint by a materials testing machine to simulate a three-point bending test. Single-loading yielding strength and cyclic-loading fatigue life were then measured. Failure analysis of the fractured screws was performed to investigate the microstructure and potential causes of the fatigue fracture. Test results showed that both yielding strength and fatigue life were closely related to the section modulus of the inner diameter of screws. Among the threaded screws, the both-ends-threaded screws had a higher yielding strength and longer fatigue life than the Osteo AG, Howmedica, Richards, and Zimmer screws. The unthreaded bolts had a lower yielding strength than Synthes screws, but they demonstrated the longest fatigue life among all. In failure analysis of broken screws, no metallurgical or manufacturing defects were found except for surface microimperfections. The implants investigated in this study are manufactured with high-quality materials and manufacturing processes. The main cause of hardware failure was mechanical overloading. The five commercially used tibial locking screws had a relatively short fatigue life under high loading. Removing the screw threads might substantially increase the fatigue life of the locking devices. In unthreaded bolts, this increase might be tenfold to a hundredfold.

  16. The pullout performance of pedicle screws

    CERN Document Server

    Demir, Teyfik

    2015-01-01

    This brief book systematically discusses all subjects that affect the pullout strength of pedicle screws. These screws are used in spinal surgeries to stabilize the spine. The holding strength of the pedicle screw is vital since loosening of the pedicle screws can cause revision surgeries. Once the pedicle screw is pulled out, it is harder to obtain same stabilization for the fused vertebrae. The book reviews the effect of screw designs, application techniques, cement augmentation, coating of the screw and test conditions on the pullout strength. The studies with finite element analysis were also included.

  17. Carbon nanotube Archimedes screws.

    Science.gov (United States)

    Oroszlány, László; Zólyomi, Viktor; Lambert, Colin J

    2010-12-28

    Recently, nanomechanical devices composed of a long stationary inner carbon nanotube and a shorter, slowly rotating outer tube have been fabricated. In this paper, we study the possibility of using such devices as nanoscale transducers of motion into electricity. When the outer tube is chiral, we show that such devices act like quantum Archimedes screws, which utilize mechanical energy to pump electrons between reservoirs. We calculate the pumped charge from one end of the inner tube to the other, driven by the rotation of a chiral outer nanotube. We show that the pumped charge can be greater than one electron per 360° rotation, and consequently, such a device operating with a rotational frequency of 10 MHz, for example, would deliver a current of ≈1 pAmp.

  18. The Study of Vibration Processes in Oil Flooded Screw Compressors

    Directory of Open Access Journals (Sweden)

    I. V. Filippov

    2014-01-01

    Full Text Available Vibration processes that accompany most of machines and mechanisms are of interest to the researcher, as a source of information about the technical condition and the nature of the business processes flow. Vibration-based diagnostics of oil flooded screw compressors allows us to estimate the deviation of their operation from the main mode in accordance with changing the settings of vibration processes.The oil flooded screw compressor transition from the main mode of operation to the abnormal one is accompanied by complex gas-dynamic phenomena i.e. the initial gaps and their decays. This leads to changes in the nature of vibration processes, prompting suggestions that there is a relationship to a change of vibration parameters and mode of compressor operation.Studies were conducted by combined method using an analytical calculation of the decay parameters of the initial discontinuity and an experimental one based on the measurement of acceleration on the body of the real oil flooded screw compressor. A virtually adequate reaction of the decay parameters of the initial gap and the peak values of vibration acceleration to the change of operation mode of oil flooded screw compressor has been received. The peak value of the vibration acceleration was selected by the method of Gating being time-coinciding with the beginning discharge phase of the oil flooded screw compressor, and therefore, with the decay time of the initial discontinuity.This indicates a large degree of hypothesis likelihood on an existing initial break in oil flooded screw compressor when operating in abnormal conditions. This work contains the study results of vibration processes and their relationship to the operating mode of the oil flooded screw compressor, which distinguish it from the other works studied vibration processes in reciprocating compressors. The vibration parameters control of operating oil flooded screw compressor allows us to create an automatic capacity control

  19. How Reliable Are The Threaded Locking Screws?

    OpenAIRE

    Karaarslan, Ahmet; Karakaslı, Ahmet; Karcı, Tolga; Aycan, Hakan; Sesli, Erhan

    2015-01-01

    Objectives: A frequent problem for interlocking nailing, that affects the treatment of the fracture is locking screw deformation. The research question is whether bending resistance is different between high, low and unthreaded locking screws of interlocking femoral nails. Materials and methods. : We used 90 screws for nine groups, ten screws for each group in this experimental study. We performed three-point bending tests on six group of 5 mm screws (titanium, stainless steel, crossed with u...

  20. Torsional stiffness after subtalar arthrodesis using second generation headless compression screws: Biomechanical comparison of 2-screw and 3-screw fixation.

    Science.gov (United States)

    Riedl, Markus; Glisson, Richard R; Matsumoto, Takumi; Hofstaetter, Stefan G; Easley, Mark E

    2017-06-01

    Subtalar joint arthrodesis is a common operative treatment for symptomatic subtalar arthrosis. Because excessive relative motion between the talus and calcaneus can delay or prohibit fusion, fixation should be optimized, particularly in patients at risk for subtalar arthrodesis nonunion. Tapered, fully-threaded, variable pitch screws are gaining popularity for this application, but the mechanical properties of joints fixed with these screws have not been characterized completely. We quantified the torsion resistance of 2-screw and 3-screw subtalar joint fixation using this type of screw. Ten pairs of cadaveric subtalar joints were prepared for arthrodesis and fixed using Acutrak 2-7.5 screws. One specimen from each pair was fixed with two diverging posterior screws, and the contralateral joint was fixed using two posterior screws and a third screw directed through the anterior calcaneus into the talar neck. Internal and external torsional loads were applied and joint rotation and torsional stiffness were measured at two torque levels. Internal rotation was significantly less in specimens fixed with three screws. No difference was detectable between 2-screw and 3-screw fixation in external rotation or torsional stiffness in either rotation direction. Both 2-screw and 3-screw fixation exhibited torsion resistance surpassing that reported previously for subtalar joints fixed with two diverging conventional lag screws. Performance of the tapered, fully threaded, variable pitch screws exceeded that of conventional lag screws regardless of whether two or three screws were used. Additional resistance to internal rotation afforded by a third screw placed anteriorly may offer some advantage in patients at risk for nonunion. Copyright © 2017. Published by Elsevier Ltd.

  1. Gyrokinetic equivalence

    Energy Technology Data Exchange (ETDEWEB)

    Parra, Felix I; Catto, Peter J [Plasma Science and Fusion Center, MIT, Cambridge, MA 02139 (United States)], E-mail: fparra@mit.edu, E-mail: catto@psfc.mit.edu

    2009-06-15

    We compare two different derivations of the gyrokinetic equation: the Hamiltonian approach in Dubin D H E et al (1983 Phys. Fluids 26 3524) and the recursive methodology in Parra F I and Catto P J (2008 Plasma Phys. Control. Fusion 50 065014). We prove that both approaches yield the same result at least to second order in a Larmor radius over macroscopic length expansion. There are subtle differences in the definitions of some of the functions that need to be taken into account to prove the equivalence.

  2. Gyrokinetic equivalence

    Science.gov (United States)

    Parra, Felix I.; Catto, Peter J.

    2009-06-01

    We compare two different derivations of the gyrokinetic equation: the Hamiltonian approach in Dubin D H E et al (1983 Phys. Fluids 26 3524) and the recursive methodology in Parra F I and Catto P J (2008 Plasma Phys. Control. Fusion 50 065014). We prove that both approaches yield the same result at least to second order in a Larmor radius over macroscopic length expansion. There are subtle differences in the definitions of some of the functions that need to be taken into account to prove the equivalence.

  3. Drilling head for tunnelling machines. Bohrkopf fuer Tunnelvortriebsmaschinen

    Energy Technology Data Exchange (ETDEWEB)

    1978-03-08

    The drilling head for cutting tunnelling machines described is fixed so as to rotate via a sleeve on the machine and is equipped with tools to remove the face on the front. The drilling head is flanged on the free front of the sleeve and screwed to it. It is supported by at least one bearing directly on a journal of the machine.

  4. Helical Screw Expander Evaluation Project. Final report

    Energy Technology Data Exchange (ETDEWEB)

    McKay, R.

    1982-03-01

    A functional 1-MW geothermal electric power plant that featured a helical screw expander was produced and then tested in Utah in 1978 to 1979 with a demonstrated average performance of approximately 45% machine efficiency over a wide range of test conditions in noncondensing operation on two-phase geothermal fluids. The Project also produced a computer-equipped data system, an instrumentation and control van, and a 1000-kW variable load bank, all integrated into a test array designed for operation at a variety of remote test sites. Additional testing was performed in Mexico in 1980 under a cooperative test program using the same test array, and machine efficiency was measured at 62% maximum with the rotors partially coated with scale, compared with approximately 54% maximum in Utah with uncoated rotors, confirming the importance of scale deposits within the machine on performance. Data are presented for the Utah testing and for the noncondensing phases of the testing in Mexico. Test time logged was 437 hours during the Utah tests and 1101 hours during the Mexico tests.

  5. Self-energized screw coupling

    Science.gov (United States)

    Lefever, A. E.; Totah, R. S.

    1980-01-01

    Threaded coupling carries its own store of rotational energy. Originally developed to ease task of astronauts assembling structures in space, coupling offers same advantages in other hazardous operations, such as underwater and in and around nuclear reactors. Coupling consists of two parts: crew portion and receptacle. When screw portion is inserted into receptacle and given slight push by operator, trigger pins release ratchet, allowing energy stored in springs to rotate screw into nut in receptacle.

  6. Study of the Dynamic Characteristics of Ball Screw with a Load Disturbance

    Directory of Open Access Journals (Sweden)

    Zhe Du

    2016-01-01

    Full Text Available The dynamic character of ball screw is the key factor that influences the machining accuracy of numerical control (NC machine tool. To improve the dynamic characteristics of the NC machine tool, it is necessary to study the dynamic characteristics of a ball screw. In this paper, the kinematics of a ball screw mechanism (BSM are studied to expound the dynamic process of the drive, and the load disturbance is considered to analyze the contact deformation based on the Hertzian contact theory. The velocity relationships among the ball, screw, and nut are analyzed, and the influence of the contact deformation on the dynamic characteristics is simulated and investigated experimentally. The results show that the relationships between the contact deformation, which is affected by the material characteristics, the contact angle, and the load of nut are nonlinear. The contact deformation is a factor that cannot be ignored when considering the dynamic machining error of high-speed and high-precision machine tools.

  7. Optimisation of two-stage screw expanders for waste heat recovery applications

    Science.gov (United States)

    Read, M. G.; Smith, I. K.; Stosic, N.

    2015-08-01

    It has previously been shown that the use of two-phase screw expanders in power generation cycles can achieve an increase in the utilisation of available energy from a low temperature heat source when compared with more conventional single-phase turbines. However, screw expander efficiencies are more sensitive to expansion volume ratio than turbines, and this increases as the expander inlet vapour dryness fraction decreases. For singlestage screw machines with low inlet dryness, this can lead to under expansion of the working fluid and low isentropic efficiency for the expansion process. The performance of the cycle can potentially be improved by using a two-stage expander, consisting of a low pressure machine and a smaller high pressure machine connected in series. By expanding the working fluid over two stages, the built-in volume ratios of the two machines can be selected to provide a better match with the overall expansion process, thereby increasing efficiency for particular inlet and discharge conditions. The mass flow rate though both stages must however be matched, and the compromise between increasing efficiency and maximising power output must also be considered. This research uses a rigorous thermodynamic screw machine model to compare the performance of single and two-stage expanders over a range of operating conditions. The model allows optimisation of the required intermediate pressure in the two- stage expander, along with the rotational speed and built-in volume ratio of both screw machine stages. The results allow the two-stage machine to be fully specified in order to achieve maximum efficiency for a required power output.

  8. Machine Transliteration

    CERN Document Server

    Knight, K; Knight, Kevin; Graehl, Jonathan

    1997-01-01

    It is challenging to translate names and technical terms across languages with different alphabets and sound inventories. These items are commonly transliterated, i.e., replaced with approximate phonetic equivalents. For example, "computer" in English comes out as "konpyuutaa" in Japanese. Translating such items from Japanese back to English is even more challenging, and of practical interest, as transliterated items make up the bulk of text phrases not found in bilingual dictionaries. We describe and evaluate a method for performing backwards transliterations by machine. This method uses a generative model, incorporating several distinct stages in the transliteration process.

  9. CAD/CAM-fabricated template for locating implant abutment screws in cement-retained anatomic zirconia restorations.

    Science.gov (United States)

    Lee, Du-Hyeong

    2015-09-01

    Currently, appropriate access to the abutment screw within cement-retained implant restorations is determined using labor-intensive techniques. The introduction of computer-aided design/computer-aided manufacture technology has facilitated a digitized fabrication process to yield a template that can enhance the accuracy of drilling a screw channel. This article describes the method used to create these guide templates by using advanced dental design programs and machining.

  10. Mobility analysis of parallel mechanisms based on screw theory and mechanism topology

    Directory of Open Access Journals (Sweden)

    Liping Wang

    2015-11-01

    Full Text Available A practical method for mobility analysis of mechanisms is presented in this article, which is based on the screw theory and the topology structure of mechanisms. The proposed method can be summarized as one core principle and two key techniques. The core principle is that the series connection of kinematic pairs is equivalent to the superposition of corresponding degrees of freedom, and the parallel connection of kinematic pairs is equivalent to the superposition of corresponding constraints. The first key technique for analyzing the mobility of mechanisms is to correctly identify the series and parallel connection relationship between all kinematic pairs, that is, the mechanism topology structure. Another key technique is transforming the screws and reciprocal screws from local coordinate systems to the global coordinate system. First, the above-mentioned method is presented in theory. Then, several examples are analyzed using it, which validate its effectiveness and universality.

  11. Cancellous Screws Are Biomechanically Superior to Cortical Screws in Metaphyseal Bone.

    Science.gov (United States)

    Wang, Tim; Boone, Christopher; Behn, Anthony W; Ledesma, Justin B; Bishop, Julius A

    2016-09-01

    Cancellous screws are designed to optimize fixation in metaphyseal bone environments; however, certain clinical situations may require the substitution of cortical screws for use in cancellous bone, such as anatomic constraints, fragment size, or available instrumentation. This study compares the biomechanical properties of commercially available cortical and cancellous screw designs in a synthetic model representing various bone densities. Commercially available, fully threaded, 4.0-mm outer-diameter cortical and cancellous screws were tested in terms of pullout strength and maximum insertion torque in standard-density and osteoporotic cancellous bone models. Pullout strength and maximum insertion torque were both found to be greater for cancellous screws than cortical screws in all synthetic densities tested. The magnitude of difference in pullout strength between cortical and cancellous screws increased with decreasing synthetic bone density. Screw displacement prior to failure and total energy absorbed during pullout strength testing were also significantly greater for cancellous screws in osteoporotic models. Stiffness was greater for cancellous screws in standard and osteoporotic models. Cancellous screws have biomechanical advantages over cortical screws when used in metaphyseal bone, implying the ability to both achieve greater compression and resist displacement at the screw-plate interface. Surgeons should preferentially use cancellous over cortical screws in metaphyseal environments where cortical bone is insufficient for fixation. [Orthopedics.2016; 39(5):e828-e832.].

  12. Metalworking defects in surgery screws as a possible cause of post-surgical infections

    Science.gov (United States)

    Spector, Mario; Peretti, Leandro E.; Romero, Gustavo

    2016-04-01

    In the first phase of this work, surface defects (metalworking) in stainless steel implantable prostheses and their possible relation to infections that can be generated after surgery was studied. In a second phase, the results obtained in the aforementioned stage were applied to knee cruciate ligaments surgery screws, considering the fact that a substantial number of Mucormycetes infections have been reported after arthroscopic surgery in Argentina since the year 2005. Two types of screws, transverse and interference screws, were analyzed. The Allen heads presented defects such as burrs and metalworking bending as a result of the machining process. These defects allow the accumulation of machining oil, which could be contaminated with fungal spores. When this is the case, the gaseous sterilization by ethylene oxide may be jeopardized. Cortical screws were also analyzed and were found to present serious metalworking defects inside their heads. To reduce the risk of infection in surgery, the use of screws with metalworking defects on the outer surface, analyzed with stereomicroscope and considering the inside part of the Allen as an outer surface, should be avoided altogether.

  13. Recognizing knee pathologies by classifying instantaneous screws of the six degrees-of-freedom knee motion.

    Science.gov (United States)

    Wolf, Alon; Degani, Amir

    2007-05-01

    We address the problem of knee pathology assessment by using screw theory to describe the knee motion and by using the screw representation of the motion as an input to a machine learning classifier. The flexions of knees with different pathologies are tracked using an optical tracking system. The instantaneous screw parameters which describe the transformation of the tibia with respect to the femur in each two successive observation is represented as the instantaneous screw axis of the motion given in its Plücker line coordinates along with its corresponding pitch. The set of instantaneous screw parameters associated with a particular knee with a given pathology is then identified and clustered in R(6) to form a "signature" of the motion for the given pathology. Sawbones model and two cadaver knees with different pathologies were tracked, and the resulting screws were used to train a classifier system. The system was then tested successfully with new, never-trained-before data. The classifier demonstrated a very high success rate in identifying the knee pathology.

  14. "Rolling" phenomenon in twin screw granulation with controlled-release excipients.

    Science.gov (United States)

    Thompson, M R; O'Donnell, K P

    2015-03-01

    The developed knowledge regarding use of twin screw granulators for continuous wet granulation has been primarily limited to immediate release formulations in the literature. The present study highlights an issue previously unreported for wet granulation with twin screw extruders when using formulations containing controlled-release (CR) excipients. Long (3-10 mm), twisted noodle-like granules can be produced in the presence of these excipients that are difficult to control and are anticipated to create complications in downstream unit operations to the granulator. Working with two different CR excipients, METHOCEL™ K4M and Kollidon® SR, each blended at different ratios with a mixture of 80% α-lactose monohydrate/20% microcrystalline cellulose, these unique particles were found to be produced in the conveying elements of the extruder, arising from a rolling action at the top of the screw flights. The CR excipients adhesively strengthen the wetted mass, forming this undesired granule shape such that they persisted to the exit of the machine; the shape appeared most strongly affected by screw speed, producing particles of higher aspect ratio as speed was increased. Adjusting the concentration of these CR excipients in the formulation, the flow rate or the type of compression element used in the screws proved ineffective in controlling the problem. Rather, a re-design of the extruder screws was required to prevent generation of these extended-form granules.

  15. The mechanical stability of extra-articular distal radius fractures with respect to the number of screws securing the distal fragment.

    Science.gov (United States)

    Crosby, Samuel N; Fletcher, Nicholas D; Yap, Erwin R; Lee, Donald H

    2013-06-01

    The treatment of distal radius fractures with volar locked plating (VLP) has gained popularity. Many different designs and sizes of plates afford a wide variety of configurations of locking screws that can be placed into the distal fracture fragment. The purpose of this study was to determine whether using half of the distal locking screws decreased stability when compared with using all possible distal locking screws with 4 different VLP systems. Twenty-four identical synthetic distal radius sawbone models were instrumented with 1 of 4 designs of VLP devices over a standardized dorsal wedge osteotomy to simulate a dorsally comminuted, extra-articular distal radius fracture. Distal locking screws were placed in varying configurations. Six radii per plate model with different screw configurations then underwent axial loading, volar bending, and dorsal bending using a servohydraulic machine. Distal fragment displacement was recorded using a differential variable reluctance transducer. There was no significant difference in fracture fragment displacement when using half of the distal locking screw set compared with using the full screw set. Mean differences in displacement between half and full screws were less than 0.1 mm. All configurations had the greatest magnitude of displacement during axial loading. Mean displacement was less in plates containing 2 rows of distal locking screws (-0.4 mm) compared with plates containing 1 row (-0.6 mm). Using half of the distal locking screws in VLP in an extra-articular, nonosteoporotic distal radial fracture model with noncyclical, nondestructive loading does not decrease construct stability compared with using all of the screws. Not filling all holes in VLP is more cost effective and does not sacrifice plate stiffness or construct stability. Plates with 2 rows of distal locking screws create more stable fixation than plates with 1 row of distal locking screws. Copyright © 2013 American Society for Surgery of the Hand

  16. Stability of the prosthetic screws of three types of craniofacial prostheses retention systems.

    Science.gov (United States)

    Lanata-Flores, Antonio Gabriel; Sigua-Rodriguez, Eder Alberto; Goulart, Douglas Rangel; Bomfim-Azevedo, Veber Luiz; Olate, Sergio; de Albergaria-Barbosa, José Ricardo

    2016-12-01

    This study aimed to evaluate the stability of prosthetic screws from three types of craniofacial prostheses retention systems (bar-clip, ball/O-ring, and magnet) when submitted to mechanical cycling. Twelve models of acrylic resin were used with implants placed 20 mm from each other and separated into three groups: (1) bar-clip (Sistema INP, São Paulo, Brazil), (2) ball/O-ring (Sistema INP), and (3) magnet (Metalmag, São Paulo, Brazil), with four samples in each group. Each sample underwent a mechanical cycling removal and insertion test (f=0.5 Hz) to determine the torque and the detorque values of the retention screws. A servo-hydraulic MTS machine (810-Flextest 40; MTS Systems, Eden Prairie, MN, USA) was used to perform the cycling with 2.5 mm and a displacement of 10 mm/s. The screws of the retention systems received an initial torque of 30 Ncm and the torque values required for loosening the screw values were obtained in three cycles (1,080, 2,160, and 3,240). The screws were retorqued to 30 Ncm before each new cycle. The sample was composed of 24 screws grouped as follows: bar-clip (n=8), ball/O-ring (n=8), and magnet (n=8). There were significant differences between the groups, with greater detorque values observed in the ball/O-ring group when compared to the bar-clip and magnet groups for the first cycle. However, the detorque value was greater in the bar-clip group for the second cycle. The results of this study indicate that all prosthetic screws will loosen slightly after an initial tightening torque, also the bar-clip retention system demonstrated greater loosening of the screws when compared with ball/O-ring and magnet retention systems.

  17. Biomechanical properties of a novel biodegradable magnesium-based interference screw

    Directory of Open Access Journals (Sweden)

    Marco Ezechieli

    2016-06-01

    Full Text Available Magnesium-based interference screws may be an alternative in anterior/posterior cruciate ligament reconstruction. The well-known osteoconductive effects of biodegradable magnesium alloys may be useful. It was the purpose of this study to evaluate the biomechanical properties of a magnesium based interference screw and compare it to a standard implant. A MgYREZr-alloy interference screw and a standard implant (Milagro®; De Puy Mitek, Raynham, MA, USA were used for graft fixation. Specimens were placed into a tensile loading fixation of a servohydraulic testing machine. Biomechanical analysis included pretensioning of the constructs at 20 N for 1 min following cyclic pretensioning of 20 cycles between 20 and 60 N. Biomechanical elongation was evaluated with cyclic loading of 1000 cycles between 50 and 200 N at 0.5 Hz. Maximum load to failure was 511.3±66.5 N for the Milagro® screw and 529.0±63.3 N for magnesium-based screw (ns, P=0.57. Elongations after preload, during cyclical loading and during failure load were not different between the groups (ns, P>0.05. Stiffness was 121.1±13.8 N/mm for the magnesiumbased screw and 144.1±18.4 for the Milagro® screw (ns, P=0.32. MgYREZr alloy interference screws show comparable results in biomechanical testing to standard implants and may be an alternative for anterior cruciate reconstruction in the future.

  18. Comparison of crossed screw versus plate fixation for radial neck fractures.

    Science.gov (United States)

    Gutowski, Christina J; Darvish, Kurosh; Ilyas, Asif M; Jones, Christopher M

    2015-11-01

    Fixation of radial neck fractures can be achieved with a plate and screw construct or, in absence of comminution, with two obliquely-oriented screws. This study investigated the mechanical properties, specifically the stiffness and load to failure, of these two fixation strategies in a cadaver model. Ten matched-pair radii were removed from fresh cadaver arms. A transverse osteotomy was created at the neck of each radius. Right-sided radii were fixed with two oblique headless compression screws; left-sided radii were fixed with a radial neck plate. The distal aspect of each radius was potted in urethane casting resin. The radial head was loaded in shear in 4 different planes (medial to lateral, lateral to medial, posterior to anterior, and anterior to posterior) using an Instron machine. Stiffness and load to failure were recorded. The stiffness of both constructs was similar in all planes except for loading from medial to lateral where the screw construct was 1.8 times stiffer. Average ultimate failure occurred at 229N for the screws and 206N for the plate. Failure strength was not statistically different. However, mode of failure differed for both fixation constructs, the plate failed in bending while the screws failed by pullout and fracture. The two strategies provide similar strength and stiffness for the fixation of transverse, non-comminuted radial neck fractures. While plate and screw constructs are more appropriate for axially unstable or comminuted fractures, two oblique screws might be preferred for simple transverse neck fractures since this strategy requires less exposure and the implant is buried. Copyright © 2015 Elsevier Ltd. All rights reserved.

  19. On Equivalence And Evaluation

    Institute of Scientific and Technical Information of China (English)

    孙贝

    2013-01-01

      Equivalence, a central and controversial issue in translation, has been studied, discussed and disputed by many scholars. For this reason, they employed various approaches and have yielded fruitful and remarkable theories. Three representative equivalence theories are selected in the thesis to elaborate equivalence:Nida’s reader-response based dynamic equivalence, Catford’s textual equivalence, Qiu Maoru’s empirical formula on equivalence. Equivalence is an applicable tool to analyze and evaluate translation.

  20. MODIFIED PERIODONTAL EXPLORER FOR EXPANSION SCREW ACTIVATION

    Directory of Open Access Journals (Sweden)

    Srinivasan

    2012-08-01

    Full Text Available INTRODUCTION: Accidents with expansion screw activation keys are r eported in the literature 1,2 . A simple method to prevent such accident is to use a modified periodontal explorer as a key for expansion screw activation. A no.17 per iodontal explorer (fig 1 is cut at its first terminal bend (fig 2. The second section is bent m ore vertically to the long axis of the shaft (fig 3. This part which is tapered and stiff enough to ac tivate the screw is tried extra orally into the screw. It is further trimmed in such a way that onl y a mm of instrument can project through the screw hole (fig 4. Now a safe key for activating t he maxillary expansion screw is ready to use (fig 5. Once the patient’s parent or guardian succes sfully repeat the activation procedure in office, the instrument can be given to them for hom e use

  1. Biomechanical Analysis of Latarjet Screw Fixation: Comparison of Screw Types and Fixation Methods.

    Science.gov (United States)

    Shin, Jason J; Hamamoto, Jason T; Leroux, Timothy S; Saccomanno, Maristella F; Jain, Akshay; Khair, Mahmoud M; Mellano, Christen R; Shewman, Elizabeth F; Nicholson, Gregory P; Romeo, Anthony A; Cole, Brian J; Verma, Nikhil N

    2017-09-01

    To compare the initial fixation stability, failure strength, and mode of failure of 5 different screw types and fixation methods commonly used for the classic Latarjet procedure. Thirty-five fresh-frozen cadaveric shoulder specimens were allocated into 5 groups. A 25% anteroinferior glenoid defect was created, and a classic Latarjet coracoid transfer procedure was performed. All grafts were fixed with 2 screws, differing by screw type and/or fixation method. The groups included partially threaded solid 4.0-mm cancellous screws with bicortical fixation, partially threaded solid 4.0-mm cancellous screws with unicortical fixation, fully threaded solid 3.5-mm cortical screws with bicortical fixation, partially threaded cannulated 4.0-mm cancellous screws with bicortical fixation, and partially threaded cannulated 4.0-mm captured screws with bicortical fixation. All screws were stainless steel. Outcomes included cyclic creep and secant stiffness during cyclic loading, as well as load and work to failure during the failure test. Intergroup comparisons were made by a 1-way analysis of variance. There were no significant differences among different screw types or fixation methods in cyclic creep or secant stiffness after cyclic loading or in load to failure or work to failure during the failure test. Post-failure radiographs showed evidence of screw bending in only 1 specimen that underwent the Latarjet procedure with partially threaded solid cancellous screws with bicortical fixation. The mode of failure for all specimens analyzed was screw cutout. In this biomechanical study, screw type and fixation method did not significantly influence biomechanical performance in a classic Latarjet procedure. When performing this procedure, surgeons may continue to select the screw type and method of fixation (unicortical or bicortical) based on preference; however, further studies are required to determine the optimal method of treatment. Surgeons may choose the screw type and

  2. Shock-Absorbent Ball-Screw Mechanism

    Science.gov (United States)

    Hirr, Otto A., Jr.; Meneely, R. W.

    1986-01-01

    Actuator containing two ball screws in series employs Belleville springs to reduce impact loads, thereby increasing life expectancy. New application of springs increases reliability of equipment in which ball screws commonly used. Set of three springs within lower screw of ball-screw mechanism absorbs impacts that result when parts reach their upper and lower limits of movement. Mechanism designed with Belleville springs as shock-absorbing elements because springs have good energy-to-volume ratio and easily stacked to attain any stiffness and travel.

  3. Analysis of synchronous machines

    CERN Document Server

    Lipo, TA

    2012-01-01

    Analysis of Synchronous Machines, Second Edition is a thoroughly modern treatment of an old subject. Courses generally teach about synchronous machines by introducing the steady-state per phase equivalent circuit without a clear, thorough presentation of the source of this circuit representation, which is a crucial aspect. Taking a different approach, this book provides a deeper understanding of complex electromechanical drives. Focusing on the terminal rather than on the internal characteristics of machines, the book begins with the general concept of winding functions, describing the placeme

  4. When Machines Design Machines!

    DEFF Research Database (Denmark)

    2011-01-01

    Until recently we were the sole designers, alone in the driving seat making all the decisions. But, we have created a world of complexity way beyond human ability to understand, control, and govern. Machines now do more trades than humans on stock markets, they control our power, water, gas...... and food supplies, manage our elevators, microclimates, automobiles and transport systems, and manufacture almost everything. It should come as no surprise that machines are now designing machines. The chips that power our computers and mobile phones, the robots and commercial processing plants on which we...... depend, all are now largely designed by machines. So what of us - will be totally usurped, or are we looking at a new symbiosis with human and artificial intelligences combined to realise the best outcomes possible. In most respects we have no choice! Human abilities alone cannot solve any of the major...

  5. Derived equivalence of algebras

    Institute of Scientific and Technical Information of China (English)

    杜先能

    1997-01-01

    The derived equivalence and stable equivalence of algebras RmA and RmB are studied It is proved, using the tilting complex, that RmA and RmB are derived-equivalent whenever algebras A and B are derived-equivalent

  6. Anatomic comparison of transarticular screws with lateral mass screws in cervical vertebrae

    Institute of Scientific and Technical Information of China (English)

    LIU Guan-yi; XU Rong-ming; MA Wei-hu; RUAN Yong-ping; SUN Shao-hua; HUANG Lei

    2007-01-01

    Objective: To compare the potential incidence of nerve root (ventral and dorsal ramus) injury caused by cervical transarticular screws and Roy-Camille lateral mass screws.Methods: Insertion techniques with Klekamp transarticular screws and Roy-Camille lateral mass screws were respectively performed in this study. Each technique involved four specimens and 40 screws, which were inserted from C3 to C7. And 20-mm-long screws were used to overpenetrate the ventral cortex. The anterolateral aspect of the cervical spine was carefully dissected to allow observation of the screw-ramus relationship.Results: The overall percentage of nerve invasion was significantly lower with Klekamp (45%) technique than with Roy-Camille (85%) technique (P<0.05). The largest percentage of nerve invasion for Klekamp transarticular screws was found at the dorsal ramus (25%), followed by the ventral ramus (15%) and the bifurcation of the ventral dorsal ramus (5%). The largest percentage of nerve invasion for Roy-Camille lateral mass screws was found at the ventral ramus (80%).Conclusion: The potential risk of nerve root invasion is lower with Klekamp transarticular screws than with Roy-Camille lateral mass screws.

  7. Study on Hardware-in-loop Simulation of Twin-screw Extruder Experiment System

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    <正>In order to facilitate the teaching of industrial processes and experiments on the twin-screw extruder control debugging,and be closer to the actual testing,to reduce the debugging costs and the risk of debugging process,the paper designs a hardware-in-loop simulation of twin-screw extruder experiment system which is closer to scene,low cost and high safety.The system through the establishment of twin-screw extruder’s mathematical model on computer to simulate the realistic system and there is hardware practicality in the computer simulation loop.The hardware based on C8051F020 can operate in the simulation loop in real time.In computer software design, we desigh man-machine interface that is intuitive and easy to operate,can reflect twin-screw extruder main operation information vividly.Finally,twin-screw extruder’s 3 heater temperature mathematical model and PID incremental control algorithm are presented.

  8. Research on the thermal load of CNC milling machine

    Science.gov (United States)

    Nie, Xue-Jun; Wu, Ping-Dong

    2011-05-01

    Machine tool accuracy is the assurance of top-quality products in machining processes. In the all kinds of errors related to machine tools, thermal errors of machine tools' parts play an important role in machining accuracy and directly influence both the surface finish and the geometric shape of the finished workpiece. Therefore the objective of this work was to analyze the temperature field and thermal deformation in some parts of CNC machine tools. In this paper, the thermal boundary condition of main spindle and driving ball screw in CNC milling machine are discussed, some parameters in heat transfer process are calculated. Based on steady heat transfer process, the thermal analysis about spindle and ball screw is carried out under ANSYS environment, and their temperature fields are obtained when milling machine is working. Then the deformations of main spindle and ball screw are acquired by applying the thermal structure coupling element. Furthermore, in order to decrease main parts' deformations and improve the accuracy of CNC milling machine, some suggests are proposed.

  9. DEVELOPMENT OF ARCHIMEDEAN’S PIPE-SCREW FOR THAI SAIL WINDPUMP

    Directory of Open Access Journals (Sweden)

    Ronnakorn Thepwong

    2014-01-01

    Full Text Available This study describes new considerations in the design and development of Archimedean’s Pipe-Screw especially for water pumping in case of low head high volume form open farm pond at Rajamangala University of Technology Rattanakosin, Thailand. The objectives of this research is to develop an Archimedean’s Pipe-Screw especially for water pumping in case of low head high volume form open farm pond used for water pumping with Thai sail windmill, at any location of low wind speed of Thailand and tests the performance of an Archimedean’s Pipe-Screw Model (APSM. The experimental was carried out on diameter of Archimedean’s Pipe-Screw is Φ5/8”, the pitch Archimedean’s Pipe-Screw (P is 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8 and 2.0 D for angle slope of the screw with the horizontal (α is 20, 25, 30°C in laboratory scale Archimedean’s Pipe-Screw model. Archimedean’s Pipe-Screw tests were conducted to assess the performance of characteristics of Archimedean’s Pipe-Screw model. A model of pump has been manufactured; 1.0 m long with the blade small rubber tube was constructed. The output of the experiments recommenced for development the prototype of Archimedean’s Pipe-Screw for the Thai sail wind pump. The prototype of pump has been manufactured, 4.0 m long, 8 m diameter. This wind pump has twelve triangular sails sweeping a circle of 8 m diameter. For the construction of this Archimedean’s Pipe-Screw wind pump all efforts were made to use maximize materials and local parts available in the market for large scale of Archimedean’s screw-pipe for Thai sail wind pump. The cost of material and parts is 145,000 Baht excluding the cost of machining and fabrication. Water discharge was in the range 0.005-0.081 lps. It can be seen maximum water discharge of pitch Archimedean’s Pipe-Screw (P is 1.4D at 80 rpm for α = 20° was 0.081 lps. For the result of prototype of Archimedean’s Pipe-Screw for Thai sail wind pump, it was found that the

  10. Biomechanical comparison of translaminar versus pedicle screws at T1 and T2 in long subaxial cervical constructs.

    Science.gov (United States)

    McGirt, Matthew J; Sutter, Edward G; Xu, Risheng; Sciubba, Daniel M; Wolinsky, Jean-Paul; Witham, Timothy F; Gokaslan, Ziya L; Bydon, Ali

    2009-12-01

    The first in vitro biomechanical investigation comparing the immediate and postcyclical rigidities of thoracic translaminar versus pedicle screws in posterior constructs crossing the cervicothoracic junction (CTJ). Ten human cadaveric spines underwent C4-C6 lateral mass screw and T1-T2 translaminar (n = 5) versus pedicle (n = 5) screw fixation. Spines were then potted in polymethylmethacrylate bone cement and placed on a materials testing machine. Rotation about the axis of bending was measured using passive retroreflective markers and infrared motion capture cameras. The motion of C6 relative to T2 in flexion-extension and lateral bending was assessed uninstrumented, immediately after instrumentation, and after 40,000 cycles of 4 N.m flexion-extension and lateral bending moments at 1 Hz. The effect of instrumentation and cyclical loading on rotational motion across the CTJ was analyzed for significance. Compared with preinstrumented spines, pedicle and translaminar screw constructs significantly (P bending. After cyclical loading, rotational motion at the CTJ was significantly increased (P bending in both groups. With flexion-extension, the mean rotational motion across the CTJ was similar in the translaminar and pedicle constructs immediately after fixation, but slightly greater (P = 0.03) after cyclical loading in the translaminar versus the pedicle screw constructs (0.39 degrees versus 0.26 degrees). Nevertheless, after cyclical loading, the mean angular motion across the CTJ remained less than one half of a degree in both groups. With lateral bending, the mean rotational motion was similar in both translaminar and pedicle screw constructs. Both upper thoracic translaminar and pedicle screws allow for rigid fixation at the CTJ. Although translaminar screw constructs demonstrated one eighth of a degree more motion at the CTJ after cycling, this minimal difference is likely less than would influence the biological fusion process. Upper thoracic translaminar

  11. Simple Technique for Removing Broken Pedicular Screws

    Directory of Open Access Journals (Sweden)

    A Agrawal

    2014-03-01

    Full Text Available The procedure for removing a broken pedicle screw should ideally be technically easy and minimally invasive, as any damage to the pedicle, during removal of the broken screw, may weaken the pedicle, thus compromising on the success of re-instrumentation. We describe the case of a 32-year old man who had undergone surgery for traumatic third lumbar vertebral body fracture three years prior to current admission and had developed the complication of pedicle screw breakage within the vertebral body. The patient underwent re-exploration and removal of the distal screws. Through a paravertebral incision and muscle separation, the screws and rods were exposed and the implants were removed.

  12. Twin screw granulation: steps in granule growth.

    Science.gov (United States)

    Dhenge, Ranjit M; Cartwright, James J; Hounslow, Michael J; Salman, Agba D

    2012-11-15

    The present work focuses on the study of the progression of granules in different compartments along the length of screws in a twin screw granulator (TSG). The effects of varying powder feed rate; liquid to solid ratio and viscosity of granulation liquid on properties of granules was studied. The bigger granules produced at the start of the process were found to change in terms of size, shape and strength along the screw length at all the conditions investigated. The granules became more spherical and their strength increased along the screw length. Tracer granules were also introduced in order to understand the role of kneading and conveying elements in the TSG. The kneading elements promoted consolidation and breakage while the conveying elements led to coalescence, breakage and some consolidation. The results presented here help to provide a qualitative and quantitative understanding of the twin screw granulation process.

  13. Twin screw subsurface and surface multiphase pumps

    Energy Technology Data Exchange (ETDEWEB)

    Dass, P. [CAN-K GROUP OF COMPANIES, Edmonton, Alberta (Canada)

    2011-07-01

    A new subsurface twin screw multiphase pump has been developed to replace ESP and other artificial lift technologies. This technology has been under development for a few years, has been field tested and is now going for commercial applications. The subsurface twin screw technology consists of a pair of screws that do not touch and can be run with a top drive or submersible motor; and it carries a lot of benefits. This technology is easy to install and its low slippage makes it highly efficient with heavy oil. In addition twin screw multiphase pumps are capable of handling high viscosity fluids and thus their utilization can save water when used in thermal applications. It also induces savings of chemicals because asphaltenes do not break down easily as well as a reduction in SOR. The subsurface twin screw multiphase pump presented herein is an advanced technology which could be used in thermal applications.

  14. Cutting temperature measurement and material machinability

    Directory of Open Access Journals (Sweden)

    Nedić Bogdan P.

    2014-01-01

    Full Text Available Cutting temperature is very important parameter of cutting process. Around 90% of heat generated during cutting process is then away by sawdust, and the rest is transferred to the tool and workpiece. In this research cutting temperature was measured with artificial thermocouples and question of investigation of metal machinability from aspect of cutting temperature was analyzed. For investigation of material machinability during turning artificial thermocouple was placed just below the cutting top of insert, and for drilling thermocouples were placed through screw holes on the face surface. In this way was obtained simple, reliable, economic and accurate method for investigation of cutting machinability.

  15. Effect of screw access hole preparation on fracture load of implant-supported zirconia-based crowns: an in vitro study

    Science.gov (United States)

    Mokhtarpour, Hadi; Eftekhar Ashtiani, Reza; Mahshid, Minoo; Tabatabaian, Farhad; Alikhasi, Marzieh

    2016-01-01

    Background. Fracture load of implant-supported restorations is an important factor in clinical success. This study evaluated the effect of two techniques for screw access hole preparation on the fracture load of cement-screw-retained implant-supported zirconia-based crowns. Methods. Thirty similar cement-screw-retained implant-supported zirconia-based maxillary central incisor crowns were evaluated in three groups of 10. Group NH: with no screw access holes for the control; Group HBS: with screw access holes prepared with a machine before zirconia sintering; Group HAS: with screw access holes prepared manually after zirconia sintering. In group HBS, the access holes were virtually designed and prepared by a computer-assisted design/computer-assisted manufacturing system. In group HAS, the access holes were manually prepared after zirconia sintering using a diamond bur. The dimensions of the screw access holes were equal in both groups. The crowns were cemented onto same-size abutments and were then subjected to thermocycling. The fracture load values of the crowns were measured using a universal testing machine. Data were analyzed with ANOVA and Tukey test (P zirconia-based crowns decreased the fracture load. PMID:27651885

  16. Effect of screw access hole preparation on fracture load of implant-supported zirconia-based crowns: an in vitro study.

    Science.gov (United States)

    Mokhtarpour, Hadi; Eftekhar Ashtiani, Reza; Mahshid, Minoo; Tabatabaian, Farhad; Alikhasi, Marzieh

    2016-01-01

    Background. Fracture load of implant-supported restorations is an important factor in clinical success. This study evaluated the effect of two techniques for screw access hole preparation on the fracture load of cement-screw-retained implant-supported zirconia-based crowns. Methods. Thirty similar cement-screw-retained implant-supported zirconia-based maxillary central incisor crowns were evaluated in three groups of 10. Group NH: with no screw access holes for the control; Group HBS: with screw access holes prepared with a machine before zirconia sintering; Group HAS: with screw access holes prepared manually after zirconia sintering. In group HBS, the access holes were virtually designed and prepared by a computer-assisted design/computer-assisted manufacturing system. In group HAS, the access holes were manually prepared after zirconia sintering using a diamond bur. The dimensions of the screw access holes were equal in both groups. The crowns were cemented onto same-size abutments and were then subjected to thermocycling. The fracture load values of the crowns were measured using a universal testing machine. Data were analyzed with ANOVA and Tukey test (P zirconia-based crowns decreased the fracture load.

  17. Equivalent thermal conductivity of heat pipes

    Institute of Scientific and Technical Information of China (English)

    Zesheng LU; Binghui MA

    2008-01-01

    In precision machining, the machining error from thermal distortion carries a high proportion of the total errors. If a precision machining tool can transfer heat fast, the thermal distortion will be reduced and the machining precision will be improved. A heat pipe working based on phase transitions of the inner working liquid transfers heat with high efficiency and is widely applied in spaceflight and chemical industries. In mechanics, applications of heat pipes are correspondingly less. When a heat pipe is applied to a hydrostatic motor-ized spindle, the thermal distortion cannot be solved dur-ing the heat transfer process because thermal conductivity or equivalent thermal conductivity should be provided first for special application in mechanics. An equivalent thermal conductivity model based on equivalent thermal resistances is established. Performance tests for a screen wick pipe, gravity pipe, and rotation heat pipe are done to validate the efficiency of the equivalent thermal conduc-tivity model. The proposed model provides a calculation method for the thermal distortion analysis of heat pipes applied in the motorized spindle.

  18. Politico-economic equivalence

    DEFF Research Database (Denmark)

    Gonzalez Eiras, Martin; Niepelt, Dirk

    2015-01-01

    Traditional "economic equivalence'' results, like the Ricardian equivalence proposition, define equivalence classes over exogenous policies. We derive "politico-economic equivalence" conditions that apply in environments where policy is endogenous and chosen sequentially. A policy regime...... and a state are equivalent to another such pair if both pairs give rise to the same allocation in politico-economic equilibrium. The equivalence conditions help to identify factors that render institutional change non-neutral and to construct politico-economic equilibria in new policy regimes. We exemplify...... their use in the context of several applications, relating to social security reform, tax-smoothing policies and measures to correct externalities....

  19. Actively suspended counter-rotating machine

    Science.gov (United States)

    Studer, Philip A. (Inventor)

    1983-01-01

    A counter-rotating machine, such as a positive displacement pump having a pair of meshed, non-contacting helical screws (10,12), subjects its rotating members to axial and radial thrust forces when used for such purposes as compression of liquid or gaseous phase fluids while transporting them through a pump cavity (11,13). Each helical screw (10,12) has a shaft (17,17') which is actively suspended at opposite ends (11a,11b) of the pump cavity by a servo-controlled magnetic bearing assembly (19) and a servo-controlled rotary drive motor (20). Both bearing assemblies and drive motors are mounted on the outside of the pump cavity (11,13). Opto-electric angular position sensors (250) provide synchronization between radial orientation of the drive motors. The bearing assemblies and drive motors conjugately provide axial stabilization and radial centering of the helical screws during volumetric compression of aspirated liquid or gaseous phase fluids.

  20. Comprehensive Model of a Single-screw Expander for ORC-Systems

    OpenAIRE

    Ziviani, Davide; Bell, Ian; van den Broek, Martijn; Paepe, Michel De

    2014-01-01

    The Organic Rankine Cycle (ORC) system is considered one of the leading technologies for waste heat recovery applications. In order to increase the overall efficiency, design improvements and optimization analyses are necessary. The expander is the key component to convert the thermal energy in useful work. Several volumetric and turbine expanders have been investigated. Among volumetric machines, scroll, twin-screw and vane-type expanders are the main technologies. Recently, a number of expe...

  1. CFD simulation of a screw compressor including leakage flows and rotor heating

    Science.gov (United States)

    Spille-Kohoff, Andreas, Dr.; Hesse, Jan; El Shorbagy, Ahmed

    2015-08-01

    Computational Fluid Dynamics (CFD) simulations have promising potential to become an important part in the development process of positive displacement (PD) machines. CFD delivers deep insights into the flow and thermodynamic behaviour of PD machines. However, the numerical simulation of such machines is more complex compared to dynamic pumps like turbines or fans. The fluid transport in size-changing chambers with very small clearances between the rotors, and between rotors and casing, demands complex meshes that change with each time step. Additionally, the losses due to leakage flows and the heat transfer to the rotors need high-quality meshes so that automatic remeshing is almost impossible. In this paper, setup steps and results for the simulation of a dry screw compressor are shown. The rotating parts are meshed with TwinMesh, a special hexahedral meshing program for gear pumps, gerotors, lobe pumps and screw compressors. In particular, these meshes include axial and radial clearances between housing and rotors, and beside the fluid volume the rotor solids are also meshed. The CFD simulation accounts for gas flow with compressibility and turbulence effects, heat transfer between gas and rotors, and leakage flows through the clearances. We show time- resolved results for torques, forces, interlobe pressure, mass flow, and heat flow between gas and rotors, as well as time- and space-resolved results for pressure, velocity, temperature etc. for different discharge ports and working points of the screw compressor. These results are also used as thermal loads for deformation simulations of the rotors.

  2. A geometrical introduction to screw theory

    Science.gov (United States)

    Minguzzi, E.

    2013-05-01

    This work introduces screw theory, a venerable but little known theory aimed at describing rigid body dynamics. This formulation of mechanics unifies in the concept of screw the translational and rotational degrees of freedom of the body. It captures a remarkable mathematical analogy between mechanical momenta and linear velocities, and between forces and angular velocities. For instance, it clarifies that angular velocities should be treated as applied vectors and that, under the composition of motions, they sum with the same rules of applied forces. This work provides a short and rigorous introduction to screw theory intended for an undergraduate and general readership.

  3. Vertical-Screw-Auger Conveyer Feeder

    Science.gov (United States)

    Walton, Otis (Inventor); Vollmer, Hubert J. (Inventor)

    2016-01-01

    A conical feeder is attached to a vertically conveying screw auger. The feeder is equipped with scoops and rotated from the surface to force-feed regolith the auger. Additional scoops are possible by adding a cylindrical section above the conical funnel section. Such then allows the unit to collect material from swaths larger in diameter than the enclosing casing pipe of the screw auger. A third element includes a flexible screw auger. All three can be used in combination in microgravity and zero atmosphere environments to drill and recover a wide area of subsurface regolith and entrained volatiles through a single access point on the surface.

  4. Equivalence principles and electromagnetism

    Science.gov (United States)

    Ni, W.-T.

    1977-01-01

    The implications of the weak equivalence principles are investigated in detail for electromagnetic systems in a general framework. In particular, it is shown that the universality of free-fall trajectories (Galileo weak equivalence principle) does not imply the validity of the Einstein equivalence principle. However, the Galileo principle plus the universality of free-fall rotation states does imply the Einstein principle.

  5. Equivalence in Translation

    Institute of Scientific and Technical Information of China (English)

    李良杰

    2013-01-01

    There are many researches about translation theories and methods in western translation history. Equivalence in transla⁃tion has always been the central issue for discussion. This paper gives a general review and comment on equivalence in translation in terms of three representative translation theorists and their views about equivalence in translation.

  6. Biomechanical comparison of intramedullary cortical button fixation and interference screw technique for subpectoral biceps tenodesis.

    Science.gov (United States)

    Buchholz, Arne; Martetschläger, Frank; Siebenlist, Sebastian; Sandmann, Gunther H; Hapfelmeier, Alexander; Lenich, Andreas; Millett, Peter J; Stöckle, Ulrich; Elser, Florian

    2013-05-01

    The purpose of this study was to biomechanically evaluate a new technique of intramedullary cortical button fixation for subpectoral biceps tenodesis and to compare it with the interference screw technique. We compared intramedullary unicortical button fixation (BicepsButton; Arthrex, Naples, FL) with interference screw fixation (Bio-Tenodesis screw; Arthrex) for subpectoral biceps tenodesis using 10 pairs of human cadaveric shoulders and ovine superficial digital flexor tendons. After computed tomography analysis, the specimens were mounted in a testing machine. Cyclic loading was performed (preload, 5 N; 5 to 70 N at 1.5 Hz for 500 cycles), recording the displacement of the tendon. Load to failure and stiffness were subsequently evaluated with a load-to-failure test (1 mm/s). Cyclic loading showed a displacement of 11.3 ± 2.8 mm for intramedullary cortical button fixation and 9 ± 1.7 mm for interference screw fixation (P = .112). All specimens within the cortical button group passed the cyclic loading test, whereas 3 of 10 specimens within the interference screw group failed by tendon slippage at the screw-tendon-bone interface after a mean of 252 cycles (P = .221). Load-to-failure testing showed a mean load to failure of 218.8 ± 40 N and stiffness of 27.2 ± 7.2 N/mm for the intramedullary cortical button technique. For the interference screw, the mean load to failure was 212.1 ± 28.3 N (P = .625) and stiffness was 40.4 ± 13 N/mm (P = .056). We could not find any major differences in load to failure when comparing the tested techniques for subpectoral biceps tenodesis. Intramedullary cortical button fixation showed no failure during cyclic testing. However, we found a 30% failure rate (3 of 10) for the interference screw fixation. Intramedullary cortical button fixation provides an alternative technique for subpectoral biceps tenodesis with comparable and, during cyclic loading, even superior biomechanical properties to interference screw fixation

  7. A Biomechanical Comparison of Expansive Pedicle Screws for Severe Osteoporosis: The Effects of Screw Design and Cement Augmentation.

    Directory of Open Access Journals (Sweden)

    Ching-Lung Tai

    Full Text Available Expansive pedicle screws significantly improve fixation strength in osteoporotic spines. However, the previous literature does not adequately address the effects of the number of lengthwise slits and the extent of screw expansion on the strength of the bone/screw interface when expansive screws are used with or without cement augmentation. Herein, four designs for expansive pedicle screws with different numbers of lengthwise slits and different screw expansion levels were evaluated. Synthetic bones simulating severe osteoporosis were used to provide a comparative platform for each screw design. The prepared specimens were then tested for axial pullout failure. Regardless of screw design, screws with cement augmentation demonstrated significantly higher pullout strength than pedicle screws without cement augmentation (p 0.05. Taken together, our results show that pedicle screws combined with cement augmentation may greatly increase screw fixation regardless of screws with or without expansion. An increase in both the number of slits and the extent of screw expansion had little impact on the screw-anchoring strength. Cement augmentation is the most influential factor for improving screw pullout strength.

  8. Biomechanical assessment of unilateral pedicle screws plus contralateral transfacetopedicular screws after transforaminal lumbar interbody fusion with two cages.

    Science.gov (United States)

    Xue, Zhong-Lin; Chen, Zhong-Xian; Fu, Chao-Hua; Lei, Hong-Jun; Yuan, Xiang-Wei

    2013-11-01

    To assess the biomechanical stability of unilateral pedicle screws (UPS) plus contralateral transfacetopedicular screws (TFPS) after transforaminal lumbar interbody fusion (TLIF) with two cages. Range of motion (ROM) testing was performed in 28 fresh-frozen human cadaveric lumbar spine motion segments. The sequential test configurations included supplemental constructs after TLIF such as UPS, UPS plus contralateral TFPS and bilateral pedicle screws (BPS). All test specimens were fixated in the normal lordotic lignment, then mounted in a three-dimensional (3-D) motion testing machine and fixed to the load frame of a six degrees of freedom spine simulator. Each of the test constructs were subjected to three load-unload cycles in each of the physiologic planes generating flexion-extension, right-left lateral bending and right-left axial rotation load-displacement curves. Statistical analysis was performed on the ROM data. Comparison of data was performed by repeated-measures analysis of variance for independent samples followed by Bonferroni analysis for multiple comparison procedures. The ROMs for UPS, BPS and UPS plus TFPS fixation after TLIF were significantly smaller than those of the intact spine in all modes. The ROM for UPS plus TFPS fixation was between the largest for UPS and the smallest for BPS. The differences between ROMs of UPS and UPS plus TFPS were significant for both lateral bending and rotation. There were no significant differences between BPS and UPS plus TFPS in any mode. Because the UPS construct provides the least stability, especially during lateral bending and rotation, it should be used prudently. After TLIF with two cages, UPS plus TFPS provides stability comparable to that of TLIF with BPS. It is thus an acceptable option in minimally invasive surgery. © 2013 Chinese Orthopaedic Association and Wiley Publishing Asia Pty Ltd.

  9. Micro-CT evaluation of in vivo osteogenesis at implants processed by wire-type electric discharge machining.

    Science.gov (United States)

    Yamaki, Koichi; Kataoka, Yu; Ohtsuka, Fukunaga; Miyazaki, Takashi

    2012-01-01

    Titanium surfaces processed by wire-type electric discharge machining (EDM) are microfabricated surfaces with an irregular morphology, and they exhibited excellent in vitro bone biocompatibility. In this study, the efficiency of in vivo osteogenesis on EDM surfaces was investigated by surgically placing screw-shaped EDM-processed and machined-surface implants into the femurs of four Japanese white rabbits. The volume and process of new bone formation were evaluated by an X-ray micro-CT scanner, coupled with histopathological observations at 1, 2, and 4 weeks post-implantation. Before surgical implantation, the surface topography and contact angle of each implant surface were examined. Bone formation increased over time on both implant surfaces, with both implant types yielding statistically equivalent bone volume at 4 weeks post-implementation. However, at 1 week post-implantation, amount of new bone at EDM-processed implant was markedly greater than that at machined-surface implant. Moreover, new bone appeared to initiate directly from the EDM surfaces, while new bone appeared to generate from pre-existing host bone to the machined surfaces. Thus, EDM seemed to be a promising method for surface modification of titanium implants to support enhanced osteogenesis.

  10. Turing Automata and Graph Machines

    Directory of Open Access Journals (Sweden)

    Miklós Bartha

    2010-06-01

    Full Text Available Indexed monoidal algebras are introduced as an equivalent structure for self-dual compact closed categories, and a coherence theorem is proved for the category of such algebras. Turing automata and Turing graph machines are defined by generalizing the classical Turing machine concept, so that the collection of such machines becomes an indexed monoidal algebra. On the analogy of the von Neumann data-flow computer architecture, Turing graph machines are proposed as potentially reversible low-level universal computational devices, and a truly reversible molecular size hardware model is presented as an example.

  11. An Equivalent Gauge and the Equivalence Theorem

    CERN Document Server

    Wulzer, Andrea

    2014-01-01

    I describe a novel covariant formulation of massive gauge theories in which the longitudinal polarization vectors do not grow with the energy. Therefore in the present formalism, differently from the ordinary one, the energy and coupling power-counting is completely transparent at the level of individual Feynman diagrams, with obvious advantages both at the conceptual and practical level. Since power-counting is transparent, the high-energy limit of the amplitudes involving longitudinal particles is immediately taken, and the Equivalence Theorem is easily demonstrated at all orders in perturbation theory. Since the formalism makes the Equivalence Theorem self-evident, and because it is based on a suitable choice of the gauge, we can call it an "Equivalent Gauge".

  12. Twin Screw Mixer/Fine Grind Facility

    Data.gov (United States)

    Federal Laboratory Consortium — The 40-mm Twin-Screw Mixer/Extruder (TSE) pilot plant is a continuous, remotely operated, flexible facility that can significantly enhance safety and environmental...

  13. Building a Successful Machine Safeguarding Program

    Energy Technology Data Exchange (ETDEWEB)

    McConnell, S

    2003-03-06

    Safeguarding hazards associated with machines is a goal common to all health and safety professionals. Whether the individual is new to the safety field or has held associated responsibilities for a period of time, safeguarding personnel who work with or around machine tools and equipment should be considered an important aspect of the job. Although significant progress has been made in terms of safeguarding machines since the era prior to the organized safety movement, companies continue to be cited by the Occupational Safety and Health Administration (OSHA) and workers continue to be injured, even killed by machine tools and equipment. In the early 1900s, it was common practice to operate transmission machinery (gears, belts, pulleys, shafting, etc.) completely unguarded. At that time, the countersunk set screw used on shafting had not been invented and projecting set screws were involved in many horrific accidents. Manufacturers built machines with little regard for worker safety. Workers were killed or seriously injured before definitive actions were taken to improve safety in the workplace. Many states adopted legislation aimed at requiring machine guarding and improved injury reduction. The first patent for a machine safeguard was issued in 1868 for a mechanical interlock. Other patents followed. As methods for safeguarding machinery and tools were developed, standards were written and programs were set up to monitor factories for compliance. Many of those standards continue to govern how we protect workers today. It is common to see machine tools built in the forties, fifties and sixties being used in machine shops today. In terms of safeguarding, these machines may be considered poorly designed, improperly safeguarded or simply unguarded. In addition to the potential threat of an OSHA citation, these conditions expose the operator to serious hazards that must be addressed. The safety professional can help line management determine workable solutions for

  14. Design and biomechanical study of a modified pedicle screw

    Institute of Scientific and Technical Information of China (English)

    LIU Tao; ZHENG Wen-jie; LI Chang-qing; LIU Guo-dong; ZHOU Yue

    2010-01-01

    Objective: In pedicle screw fixation,the heads of monoaxial screws need to be directed in the same straight line to accommodate the rod placement by backing out during operation, which decreases the insertional torque and internal fixation strength. While polyaxial screws facilitate the assembly of the connecting rod, but its ball-in-cup locking mechanism reduces the static compressive bending yield strength as compared with monoaxial screws. Our study aimed to assess the mechanical performance of a modified pedicle screw.Methods: In this study, the tail of the screw body of the modified pedicle screw was designed to be a cylindershaped structure that well matched the inner wall of the screw head and the screw head only rotated around the cyclinder. Monoaxial screws, modified screws and polyaxial screws were respectively assembled into 3 groups ofvertebrectomy models simulated by ultra high molecular weight polyethylene (UHMWPE) blocks. This model was developed according to a standard for destructive mechanical testing published by the American Society for Testing Materials (ASTM F1717-04). Each screw design had 6 subgroups, including 3 for static tension, load compression and torsion tests, and the rest for dynamic compression tests. In dynamic tests, the cyclic loads were 25%, 50%, and 75% of the compressive bending ultimate loads respectively.Yield load, yield ultimate load, yield stiffness, torsional stiffness, cycles to failure and modes of failure for the 3 types of screws were recorded. The results of modified screws were compared with those ofmonoaxial and polyaxial screws.Results: In static tests, results of bending stiffness,yield load, yield torque and torsional stiffness indicated no significant differences between the modified and monoaxial screws (P>0.05), but both differed significantly from those ofpolyaxial screws (P<0.05). In dynamic compression tests,both modified and monoaxial screws showed failures that occurred at the insertion point of screw

  15. Ball Screw Actuator Including a Stop with an Integral Guide

    Science.gov (United States)

    Wingett, Paul T. (Inventor); Perek, John (Inventor); Geck, Kellan (Inventor)

    2015-01-01

    An actuator includes a housing assembly, a ball nut, a ball screw, and a ball screw stop. The ball nut is rotationally mounted in the housing assembly, is adapted to receive an input torque, and is configured, upon receipt thereof, to rotate and supply a drive force. The ball screw is mounted within the housing assembly and extends through the ball nut. The ball screw has a first end and a second end, and is coupled to receive the drive force from the ball nut. The ball screw is configured, upon receipt of the drive force, to selectively translate between a stow position and a deploy position. The ball screw stop is mounted on the ball screw to translate therewith and is configured to at selectively engage the housing assembly while the ball screw is translating, and engage the ball nut when the ball screw is in the deploy position.

  16. [Odontoid bending stiffness after anterior fixation with a single lag screw: biomechanical study].

    Science.gov (United States)

    Buchvald, P; Čapek, L; Barsa, P

    2015-01-01

    PURPOSE OF THE STUDY The aim of the experiment was to compare the bending stiffness of an intact odontoid process with bending stiffness after its simulated type II fracture was fixed with a single lag screw. The experiment was done with a desire to answer the question of whether a single osteosynthetic screw is sufficient for good fixation of a type II odontoid fracture. MATERIAL AND METHODS The C2 vertebrae of six cadavers were used. With simultaneous measurement of odontoid bending stiffness, the occurrence of a fracture (type IIA, Grauer's modification of the Anderson- D'Alonzo classification) was simulated using action exerted by a tearing machine in the direction perpendicular to the odontoid axis. Each odontoid fracture was subsequently treated by direct osteosynthesis with a single lag screw inserted in the axial direction by a standard surgical procedure in order to provide conditions similar to those achieved by routine surgical management. The treated odontoid process was subsequently subjected to the same tearing machine loading as applied to it at the start of the experiment. The bending stiffness measured was then compared with that found before the fracture occurred. The results were statistically evaluated by the t-test for paired samples at the level of significance α = 0.05. RESULTS The average value of bending stiffness for odontoid processes of intact vertebrae at the moment of fracture occurrence was 318.3 N/mm. After single axial lag screw fixation of the fracture, the average bending stiffness for the odontoid processes treated was 331.3 N/mm. DISCUSSION Higher values of bending stiffness after screw fixation were found in all specimens and, in comparison with the values recorded before simulated fractures, the increase was statistically significant. CONCLUSIONS The results of our measurements suggest that the single lag screw fixation of a type IIA odontoid fracture will provide better stability for the fracture fragment-C2 body complex on

  17. Biomechanical Analysis Of The Proximal Femoral Locking Compression Plate: Do Quality Of Reduction And Screw Orientation Influence Construct Stability?

    Science.gov (United States)

    Zderic, Ivan; Oh, Jong-Keon; Stoffel, Karl; Sommer, Christoph; Helfen, Tobias; Camino, Gaston; Richards, R Geoff; Nork, Sean E; Gueorguiev, Boyko

    2017-08-22

    To investigate biomechanically in a human cadaveric model the failure modes of the Proximal Femoral Locking Compression Plate (PF-LCP) and explore the underlying mechanism. Twenty-four fresh-frozen paired human cadaveric femora with simulated unstable intertrochanteric fractures (AO/OTA 31-A3.3) were assigned to four groups with six specimens each for plating with PF-LCP. The groups differed in the quality of fracture reduction and plating fashion of the first and second proximal screws as follows: 1) anatomical reduction with on-axis screw placement; 2) anatomical reduction with off-axis screw placement; 3) malreduction with on-axis screw placement; 4) malreduction with off-axis screw placement. The specimens were tested until failure using a protocol with combined axial and torsional loading. Mechanical failure was defined as abrupt change in machine load-displacement data. Clinical failure was defined as 5° varus tilting of the femoral head as captured with optical motion tracking. Initial axial stiffness (N/mm) in groups 1 to 4 was 213.6±65.0, 209.5±134.0, 128.3±16.6 and 106.3±47.4, respectively. Numbers of cycles to clinical and mechanical failure were 16642±10468 and 8695±1462 in group 1, 14076±3032 and 7449±5663 in group 2, 8800±8584 and 4497±2336 in group 3 and 9709±3894 and 5279±4119 in group 4. Significantly higher stiffness as well as numbers of cycles to both clinical and mechanical failure were detected in group 1 in comparison to group 3, P≤0.044. Generally, malreduction led to significantly earlier construct failure. The observed failures were cut-out of the proximal screws in the femoral head, followed by either screw bending, screw loosening or screw fracture. Proper placement of the proximal screws in anatomically reduced fractures led to significantly higher construct stability. Our data also indicates that once the screws are placed off-axis (>5 degrees), the benefit of an anatomic reduction is lost.

  18. Preset Electrodes for Electrical-Discharge Machining

    Science.gov (United States)

    Coker, Bill E.

    1987-01-01

    New electrode holder for electrical-discharge machining (EDM) provides for repeatable loading and setting of many electrodes. New holder is rotating-index tool carrying six, eight, or more electrodes. Before use, all electrodes set with aid of ring surrounding tool, and locked in position with screws. When electrode replaced, EDM operator pulls spring-loaded pin on tool so it rotates about center pin. Fresh electrode then rotated into position against workpiece.

  19. Flow characteristics of screws and special mixing enhancers in a co-rotating twin screw extruder

    NARCIS (Netherlands)

    Brouwer, T.; Todd, D.B.; Janssen, L.P.B.M.

    2002-01-01

    The flow behavior of a Newtonian fluid through special mixing enhancers in a modular intermeshing co-rotating twin screw extruder has been examined. The mixing enhancers are slotted screws and gear mixing elements. Particular attention has been directed to drag and pressure flow characteristics and

  20. Experimental Investigation into Pull-Out Strength of Foamed Concrete Using Different Types of Screw

    Directory of Open Access Journals (Sweden)

    Othuman Mydin M.A.

    2014-01-01

    Full Text Available This study focuses on the results of the comprehensive strength test to quantify the mechanical properties of the screw’s pullout strength on foamed concrete. Foamed concrete is classified as lightweight concrete that been produced by cement paste or mortar in which air-voids are entrapped in the mortar by a suitable foaming agent. These days, the use of foamed concrete has been recognized in the construction industry as wall blocks, wall panels and also material floor and roof screeds. Hence, the applications of this material should be maximized as it is multi-functional. As we know, the use of screws on the wall or ceiling is common in a building. The objective of this research is to examine and determine the pullout strength of various properties and types of screws in lightweight foamed concrete with various densities that may depict the best result of the pullout strength on foamed concrete. To visualize the different results of pullout strength, screws with and without wall plug will be used as well. The pullout strength will be tested using the Universal Testing Machine where it shall measure the ultimate load of the screws attached to the foamed concrete may resist.

  1. Influence of liquid in clearances on the operational behaviour of twin screw expanders

    Science.gov (United States)

    Gräßer, Melanie; Brümmer, Andreas

    2015-08-01

    A lot of effort has been expended on understanding the influences of an injected auxiliary liquid on a twin screw expander's performance. Sealed clearances improve performance on the one hand, but involve considerable frictional losses on the other hand. This paper contributes to an evaluation of these opposing effects with regard to the efficiency of screw expanders. First, thermodynamic analyses using the multi-chamber model-based simulation tool KaSim, developed at the Chair of Fluidics, are presented for a test screw expander in order to show the maximum potential of clearance sealing. This analysis involves thermodynamic simulations for sealed and unsealed clearances and leads to an order of priorities for different clearance types. Second, hydraulic losses within front and housing clearances are calculated, applying an analytical model of incompressible one-phase clearance flow. Subsequently dry and wet screw expanders are evaluated while both clearance sealing and frictional losses are considered for the simulation of a liquid-injected machine.

  2. Biomechanical comparison between C-7 lateral mass and pedicle screws in subaxial cervical constructs. Presented at the 2009 Joint Spine Meeting. Laboratory investigation.

    Science.gov (United States)

    Xu, Risheng; McGirt, Matthew J; Sutter, Edward G; Sciubba, Daniel M; Wolinsky, Jean-Paul; Witham, Timothy F; Gokaslan, Ziya L; Bydon, Ali

    2010-12-01

    The aim of this study was to conduct the first in vitro biomechanical comparison of immediate and postcyclical rigidities of C-7 lateral mass versus C-7 pedicle screws in posterior C4-7 constructs. Ten human cadaveric spines were treated with C4-6 lateral mass screw and C-7 lateral mass (5 specimens) versus pedicle (5 specimens) screw fixation. Spines were potted in polymethylmethacrylate bone cement and placed on a materials testing machine. Rotation about the axis of bending was measured using passive retroreflective markers and infrared motion capture cameras. The motion of C-4 relative to C-7 in flexion-extension and lateral bending was assessed uninstrumented, immediately after instrumentation, and following 40,000 cycles of 4 Nm of flexion-extension and lateral bending moments at 1 Hz. The effect of instrumentation and cyclical loading on rotational motion across C4-7 was analyzed for significance. Preinstrumented spines for the 2 cohorts were comparable in bone mineral density and range of motion in both flexion-extension (p = 0.33) and lateral bending (p = 0.16). Lateral mass and pedicle screw constructs significantly reduced motion during flexion-extension (11.3°-0.26° for lateral mass screws, p = 0.002; 10.51°-0.30° for pedicle screws, p = 0.008) and lateral bending (7.38°-0.27° for lateral mass screws, p = 0.003; 11.65°-0.49° for pedicle screws, p = 0.03). After cyclical loading in both cohorts, rotational motion over C4-7 was increased during flexion-extension (0.26°-0.68° for lateral mass screws; 0.30°-1.31° for pedicle screws) and lateral bending (0.27°-0.39° and 0.49°-0.80°, respectively), although the increase was not statistically significant (p > 0.05). There was no statistical difference in postcyclical flexion-extension (p = 0.20) and lateral bending (0.10) between lateral mass and pedicle screws. Both C-7 lateral mass and C-7 pedicle screws allow equally rigid fixation of subaxial lateral mass constructs ending at C-7

  3. The Comparison of Water Absorption Analysis between Counterrotating and Corotating Twin-Screw Extruders with Different Antioxidants Content in Wood Plastic Composites

    Directory of Open Access Journals (Sweden)

    Mohd Hafizuddin Ab Ghani

    2011-01-01

    Full Text Available Water absorption is a major concern for natural fibers as reinforcement in wood plastic composites (WPCs. This paper presents a study on the comparison analysis of water absorption between two types of twin-screw extruders, namely, counterrotating and corotating with presence of variable antioxidants content. Composites of mixed fibres between rice husk and saw dust with recycled high-density polyethylene (rHDPE were prepared with two different extruder machines, namely, counterrotating and corotating twin screw, respectively. The contents of matrix (30 wt% and fibres (62 wt% were mixed with additives (8 wt% and compounded using compounder before extruded using both of the machines. Samples were immersed in distilled water according to ASTM D 570-98. From the study, results indicated a significant difference among samples extruded by counterrotating and corotating twin-screw extruders. The counterrotating twin-screw extruder gives the smallest value of water absorption compared to corotating twin-screw extruder. This indicates that the types of screw play an important role in water uptake by improving the adhesion between natural fillers and the polymer matrix.

  4. Standard Waste Box Lid Screw Removal Option Testing

    Energy Technology Data Exchange (ETDEWEB)

    Anast, Kurt Roy [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2016-03-11

    This report provides results from test work conducted to resolve the removal of screws securing the standard waste box (SWB) lids that hold the remediated nitrate salt (RNS) drums. The test work evaluated equipment and process alternatives for removing the 42 screws that hold the SWB lid in place. The screws were secured with a red Loctite thread locker that makes removal very difficult because the rivets that the screw threads into would slip before the screw could be freed from the rivet, making it impossible to remove the screw and therefore the SWB lid.

  5. Transpedicular screw fixation in the thoracic and lumbar spine with a novel cannulated polyaxial screw system

    Directory of Open Access Journals (Sweden)

    Lutz Weise

    2008-10-01

    Full Text Available Lutz Weise, Olaf Suess, Thomas Picht, Theodoros KombosNeurochirurgische Klinik, Charité – Universitätsmedizin Berlin, Berlin, GermanyObjective: Transpedicular screws are commonly and successfully used for posterior fixation in spinal instability, but their insertion remains challenging. Even using navigation techniques, there is a misplacement rate of up to 11%. The aim of this study was to assess the accuracy of a novel pedicle screw system.Methods: Thoracic and lumbar fusions were performed on 67 consecutive patients for tumor, trauma, degenerative disease or infection. A total of 326 pedicular screws were placed using a novel wire-guided, cannulated, polyaxial screw system (XIA Precision®, Stryker. The accuracy of placement was assessed post operatively by CT scan, and the patients were followed-up clinically for a mean of 16 months.Results: The total medio-caudal pedicle wall perforation rate was 9.2% (30/326. In 19 of these 30 cases a cortical breakthrough of less than 2 mm occurred. The misplacement rate (defined as a perforation of 2 mm or more was 3.37% (11/326. Three of these 11 screws needed surgical revision due to neurological symptoms or CSF leakage. There have been no screw breakages or dislocations over the follow up-period.Conclusion: We conclude that the use of this cannulated screw system for the placement of pedicle screws in the thoracic and lumbar spine is accurate and safe. The advantages of this technique include easy handling without a time-consuming set up. Considering the incidence of long-term screw breakage, further investigation with a longer follow-up period is necessary.Keywords: spinal instrumentation, pedicle screws, misplacement, pedicle wall perforation

  6. Machine Translation

    Institute of Scientific and Technical Information of China (English)

    张严心

    2015-01-01

    As a kind of ancillary translation tool, Machine Translation has been paid increasing attention to and received different kinds of study by a great deal of researchers and scholars for a long time. To know the definition of Machine Translation and to analyse its benefits and problems are significant for translators in order to make good use of Machine Translation, and helpful to develop and consummate Machine Translation Systems in the future.

  7. On translation equivalence

    Institute of Scientific and Technical Information of China (English)

    石雏凤

    2009-01-01

    Nida's translation theories, especially for his "Dynamic equivalence theory", are highly praised and adopted in Chinese translation circle. Howev-er, there are a lot of criticism and misunderstanding at the same time. This paper explores the issue on translation equivalence so as to benefit our translation studies on both theory and practice level.

  8. Sustainable machining

    CERN Document Server

    2017-01-01

    This book provides an overview on current sustainable machining. Its chapters cover the concept in economic, social and environmental dimensions. It provides the reader with proper ways to handle several pollutants produced during the machining process. The book is useful on both undergraduate and postgraduate levels and it is of interest to all those working with manufacturing and machining technology.

  9. Equivalence principles exotica

    Institute of Scientific and Technical Information of China (English)

    C.S. UNNIKRISHNAN; George T. GILLIES

    2008-01-01

    This is a short review of the different prin-ciples of equivalence stated and used in the context of the gravitational interaction. We emphasize the need for precision in stating and differentiating these different equivalence principles, especially in the context of preva-lent confusion regarding the applicability of the weak equivalence principle in quantum mechanics. We discuss several empirical results pertaining to the validity of the equivalence principle in exotic physical sitautions not di-rectly amenable to experimental tests. We conclude with a section on the physical basis of the universal validity of the equivalence principle, as manifest in the universality of free fall, and discuss its link to cosmic gravity.

  10. Kinematics and dynamics of deployable structures with scissor-like-elements based on screw theory

    Science.gov (United States)

    Sun, Yuantao; Wang, Sanmin; Mills, James K.; Zhi, Changjian

    2014-07-01

    Because the deployable structures are complex multi-loop structures and methods of derivation which lead to simpler kinematic and dynamic equations of motion are the subject of research effort, the kinematics and dynamics of deployable structures with scissor-like-elements are presented based on screw theory and the principle of virtual work respectively. According to the geometric characteristic of the deployable structure examined, the basic structural unit is the common scissor-like-element(SLE). First, a spatial deployable structure, comprised of three SLEs, is defined, and the constraint topology graph is obtained. The equations of motion are then derived based on screw theory and the geometric nature of scissor elements. Second, to develop the dynamics of the whole deployable structure, the local coordinates of the SLEs and the Jacobian matrices of the center of mass of the deployable structure are derived. Then, the equivalent forces are assembled and added in the equations of motion based on the principle of virtual work. Finally, dynamic behavior and unfolded process of the deployable structure are simulated. Its figures of velocity, acceleration and input torque are obtained based on the simulate results. Screw theory not only provides an efficient solution formulation and theory guidance for complex multi-closed loop deployable structures, but also extends the method to solve dynamics of deployable structures. As an efficient mathematical tool, the simper equations of motion are derived based on screw theory.

  11. Introductory study to mathematics modelling of fluid flow in the screw compressors; Einfuehrungsstudie zur mathematischen Modellierung der Stroemungen in Schraubenkompressoren

    Energy Technology Data Exchange (ETDEWEB)

    Svigler, J.; Vimmr, J. [Westboehmische Univ. Pilsen (Czechoslovakia). Lehrstuhl fuer Mechanik

    2000-07-01

    A fast development of the screw machines leads to the investigation of the physical processes, which take place in the work space of the screw machine and in the gaps on its boundary. These processes have a great influence on the performance of the screw machine especially with regard to its efficiency, therefore its knowledge is very important. It is necessary to turn our attention to the fluid dynamics of the screw machines. This paper deals with the preliminary analysis of the fluid flow in the screw machines. In this paper numerical computation of the compressible inviscid fluid flow in the work space of the screw machines and through the sealing gaps which are situated between the stator and the head of the female rotor tooth, is presented. The mathematical model of two- and three-dimensional inviscid compressible flow is described by the conservative system of the Euler equations. This problem was solved by the cell-centred finite volume method on a structured quadrilateral mesh. (orig.) [German] Die schnelle Entwicklung der Schraubenmaschinen fuehrt zur Notwendigkeit einer Untersuchung der physikalischen Vorgaenge, die im Arbeitsraum und in den arbeitsraumbegrenzenden Spalten der Schraubenmaschine ablaufen. Diese Vorgaenge beeinflussen nachhaltig das Betriebsverhalten sowie die Energiewandlungsguete, womit deren Kenntnis und der Information ueber die Details eine ausserordentliche Bedeutung zukommt. Einen Ausgangspunkt fuer die Analyse stellen die Kenntnisse im Bereich der kompressiblen Fluide dar. Der Zustand kann vor allem durch das Geschwindigkeits-, Druck-, und Temperaturfeld beurteilt werden. Der Beitrag beschaeftigt sich mit der Problematik der Stroemungsuntersuchungen des Gases im Arbeitsraum der Schaubenmaschine und im Gehaeusespalt. Die Aufgabe wird dreidimensional behandelt und auf eine Art und Weise formuliert, dass sie die Voraussetzung fuer die Erstellung eines raeumlichen Modells und der damit gekoppelten mathematischen Loesung schafft. Die

  12. Twin screw wet granulation: Binder delivery.

    Science.gov (United States)

    Saleh, Mohammed F; Dhenge, Ranjit M; Cartwright, James J; Hounslow, Michael J; Salman, Agba D

    2015-06-20

    The effects of three ways of binder delivery into the twin screw granulator (TSG) on the residence time, torque, properties of granules (size, shape, strength) and binder distribution were studied. The binder distribution was visualised through the transparent barrel using high speed imaging as well as quantified using offline technique. Furthermore, the effect of binder delivery and the change of screw configuration (conveying elements only and conveying elements with kneading elements) on the surface velocity of granules across the screw channel were investigated using particle image velocimetry (PIV). The binder was delivered in three ways; all solid binder incorporated with powder mixture, 50% of solid binder mixed with powder mixture and 50% mixed with water, all the solid binder dissolved in water. Incorporation of all solid binder with powder mixture resulted in the relatively longer residence time and higher torque, narrower granule size distribution, more spherical granules, weaker big-sized granules, stronger small-sized granules and better binder distribution compared to that in other two ways. The surface velocity of granules showed variation from one screw to another as a result of uneven liquid distribution as well as shown a reduction while introducing the kneading elements into the screw configuration.

  13. Effect of twist-orientation on mechanical properties of self-reinforced poly(lactic acid) screws in simulated body environment

    Science.gov (United States)

    Sakaguchi, Masato; Kobayashi, Satoshi; composite engineering lab Team

    Poly(lactic acid) (PLA) attracts much attention as a typical biodegradable polymer, and has been applied as a bone fixation device. As one of the methods to improve mechanical properties of PLA bone fixation device, orientations of molecular chains have been investigated. However, conventional uniaxial drawing could not improve mechanical properties along the other loading direction than the drawing direction, such as torsion. In this study, screw is treated as a bone fixation device. In order to improve torsional strength of a bioabsorbable PLA screw, twist-orientation method has been developed. PLA screw is prepared through a series of routes including extrusion molding, extrusion drawing, twist-orientation and forging. This screw was immersed in the phosphate buffer solution for 0, 8, 16 and 24 weeks, then shear strength, orientation function, crystallinity and molecular weight were measured. As a result, twist-orientation improves the initial torsional strength of PLA screw without the decrease in initial shear strength. In addition, the shear strength on twist-oriented screw is equivalent that of non-twist oriented screw during immersion until 24 weeks. This result shown that the twist-orientation does not decrease shear strength after immersion.

  14. Characteristic analysis on screw conveyor used for lignite molding%褐煤成型用螺旋输送机的特性分析

    Institute of Scientific and Technical Information of China (English)

    郝兵; 崔郎郎; 李聪杰; 白爱民; 蒋惠民; 刘正魁; 高洁

    2013-01-01

    根据褐煤成型机用螺旋输送机的工作特点,通过对螺旋轴结构进行分析及试验研究,确定一种合理的螺旋结构.通过试验数据得出螺旋输送机输送能力受煤粉的水分、温度和粒度的影响.物料水分增加,会增加螺旋输送机的功耗;物料水分下降,既能降低螺旋输送机功耗,又能提升成型机的成型压力.因此,合理设计螺旋输送机的结构,可为成型机运行参数的确定提供参考.%Based on the operating features of the screw conveyor used for lignite molding machine,after the structure of the screw shaft was analyzed and tested,a screw with reasonable structure was determined.Test data showed the influences of moisture,temperature and granularity of pulverized coal on the transportation capacity of the screw conveyor.The moisture raise led to increase in power consumption of the screw conveyor; the moisture reduction led to decrease in power consumption of the screw conveyor and increase in molding pressure of the molding machine.The screw conveyor with reasonable structure could offer foundation for determining the operating parameters of the molding machine.

  15. The accuracy and the safety of individualized 3D printing screws insertion templates for cervical screw insertion.

    Science.gov (United States)

    Deng, Ting; Jiang, Minghui; Lei, Qing; Cai, Lihong; Chen, Li

    2016-12-01

    Clinical trial for cervical screw insertion by using individualized 3-dimensional (3D) printing screw insertion templates device. The objective of this study is to evaluate the safety and accuracy of the individualized 3D printing screw insertion template in the cervical spine. Ten patients who underwent posterior cervical fusion surgery with cervical pedicle screws, laminar screws or lateral mass screws between December 2014 and December 2015 were involved in this study. The patients were examined by CT scan before operation. The individualized 3D printing templates were made with photosensitive resin by a 3D printing system to ensure the screw shafts entered the vertebral body without breaking the pedicle or lamina cortex. The templates were sterilized by a plasma sterilizer and used during the operation. The accuracy and the safety of the templates were evaluated by CT scans at the screw insertion levels after operation. The accuracy of this patient-specific template technique was demonstrated. Only one screw axis greatly deviated from the planned track and breached the cortex of the pedicle because the template was split by rough handling and then we inserted the screws under the fluoroscopy. The remaining screws were inserted in the track as preoperative design and the screw axis deviated by less than 2 mm. Vascular or neurologic complications or injuries did not happen. And no infection, broken nails, fracture of bone structure, or screw pullout occurred. This study verified the safety and the accuracy of the individualized 3D printing screw insertion templates in the cervical spine as a kind of intraoperative screw navigation. This individualized 3D printing screw insertion template was user-friendly, moderate cost, and enabled a radiation-free cervical screw insertion.

  16. [Cement augmentation of pedicle screws : Pros and cons].

    Science.gov (United States)

    Schnake, K J; Blattert, T R; Liljenqvist, U

    2016-09-01

    Cement augmentation of pedicle screws biomechanically increases screw purchase in the bone. However, clinical complications may occur. The pros and cons of the technique are discussed from different clinical perspectives.

  17. Impact of screw configuration on the particle size distribution of granules produced by twin screw granulation.

    Science.gov (United States)

    Vercruysse, J; Burggraeve, A; Fonteyne, M; Cappuyns, P; Delaet, U; Van Assche, I; De Beer, T; Remon, J P; Vervaet, C

    2015-02-01

    Twin screw granulation (TSG) has been reported by different research groups as an attractive technology for continuous wet granulation. However, in contrast to fluidized bed granulation, granules produced via this technique typically have a wide and multimodal particle size distribution (PSD), resulting in suboptimal flow properties. The aim of the current study was to evaluate the impact of granulator screw configuration on the PSD of granules produced by TSG. Experiments were performed using a 25 mm co-rotating twin screw granulator, being part of the ConsiGma™-25 system (a fully continuous from-powder-to-tablet manufacturing line from GEA Pharma Systems). Besides the screw elements conventionally used for TSG (conveying and kneading elements), alternative designs of screw elements (tooth-mixing-elements (TME), screw mixing elements (SME) and cutters) were investigated using an α-lactose monohydrate formulation granulated with distilled water. Granulation with only conveying elements resulted in wide and multimodal PSD. Using kneading elements, the width of the PSD could be partially narrowed and the liquid distribution was more homogeneous. However, still a significant fraction of oversized agglomerates was obtained. Implementing additional kneading elements or cutters in the final section of the screw configuration was not beneficial. Furthermore, granulation with only TME or SME had limited impact on the width of the PSD. Promising results were obtained by combining kneading elements with SME, as for these configurations the PSD was narrower and shifted to the size fractions suitable for tableting.

  18. Pull-out strength comparison of a novel expanding fastener against an orthopaedic screw in an ovine vertebral body: an ex-vivo study.

    Science.gov (United States)

    Oldakowski, Matthew; Oldakowska, Intan; Kirk, Thomas B; Ford, Chris T; Sercombe, Tim B; Hardcastle, Philip; Day, Robert E

    2016-01-01

    The purpose of this study was to mechanically test a novel Unthreaded Expandable Fastener (UEF), manufactured using Selective Laser Melting, which was designed for fixation in the cervical lateral mass. The pull-out strength and stiffness of the prototype UEFs was evaluated in a non-osteoporotic ovine bone model against equivalent screws. The prototype UEF demonstrated a 41% increase in failure force and a 60% reduction in failure force standard deviation compared to the screws. All bone samples were micro CT-scanned and no significant differences in bone microstructural properties was found between the screw and UEF sample sets, indicating that the UEFs may be less sensitive to bone quality variation. This increased performance can potentially translate into improved surgical outcome and reduced surgical risk for lateral mass fixation. With further design optimisation, additional improvement in performance over screws may be possible in future studies.

  19. Comparative endurance testing of the Biomet Matthews Nail and the Dynamic Compression Screw, in simulated condylar and supracondylar femoral fractures

    Directory of Open Access Journals (Sweden)

    Davies Benjamin M

    2008-01-01

    Full Text Available Abstract Background The dynamic compression screw is a plate and screws implant used to treat fractures of the distal femur. The Biomet Matthews Nail is a new retrograde intramedullary nail designed as an alternative surgical option to treat these fractures. The objective of this study was to assess the comparative endurance of both devices. Method The dynamic compression screw (DCS and Biomet Matthews Nail (BMN were implanted into composite femurs, which were subsequently cyclically loaded using a materials testing machine. Simulated fractures were applied to each femur prior to the application of load. Either a Y type fracture or a transverse osteotomy was prepared on each composite femur using a jig to enable consistent positioning of cuts. Results The Biomet Matthews Nail demonstrated a greater endurance limit load over the dynamic compression screw in both fracture configurations. Conclusion The distal locking screws pass through the Biomet Matthews Nail in a unique "cruciate" orientation. This allows for greater purchase in the bone of the femoral condyle and potentially improves the stability of the fracture fixation. As these fractures are usually in weak osteoporotic bone, the Biomet Matthews Nail represents a favourable surgical option in these patients.

  20. A modified technique for removing a failed abutment screw from an implant with a custom guide tube.

    Science.gov (United States)

    Taira, Yohsuke; Sawase, Takashi

    2012-04-01

    Fracture of abutment screw is a serious prosthodontic complication. When the abutment screw is fractured at the junction of the screw shank and screw thread, removal of the fractured screw fragment from the screw hole can be difficult. This article describes a modified technique for removing the failed abutment screw with a custom guide tube and tungsten carbide bur. The failed screw can be removed speedily without damaging the screw hole of the implant body or the screw threads.

  1. A processing method for orthodontic mini-screws reuse

    Directory of Open Access Journals (Sweden)

    Saeed Noorollahian

    2012-01-01

    Conclusion: Cleaning of used mini-screws with phosphoric acid 37% (10 minutes and sodium hypochlorite 5.25% (30 minutes reduces tissue remnants to the level of as-received mini-screws. So it can be suggested as a processing method of used mini-screws. Previous insertion of mini-screws into the bone and above-mentioned processing method and resterilization with autoclave had no adverse effects on insertion, removal, and fracture torque values as mechanical properties indices.

  2. Guided pedicle screw insertion: techniques and training.

    Science.gov (United States)

    Manbachi, Amir; Cobbold, Richard S C; Ginsberg, Howard J

    2014-01-01

    In spinal fusion surgery, the accuracy with which screws are inserted in the pedicle has a direct effect on the surgical outcome. Accurate placement generally involves considerable judgmental skills that have been developed through a lengthy training process. Because the impact of misaligning one or more pedicle screws can directly affect patient safety, a number of navigational and trajectory verification approaches have been described and evaluated in the literature to provide some degree of guidance to the surgeon. To provide a concise review to justify the need and explore the current state of developing navigational or trajectory verification techniques for ensuring proper pedicle screw insertion along with simulation methods for better educating the surgical trainees. Recent literature review. To justify the need to develop new methods for optimizing pedicle screw paths, we first reviewed some of the recent publications relating to the statistical outcomes for different types of navigation along with the conventional freehand (unassisted) screw insertion. Second, because of the importance of providing improved training in the skill of accurate screw insertion, the training aspects of relevant techniques are considered. The third part is devoted to the description of specific navigational assist methods or trajectory verification techniques and these include computer-assisted navigation, three-dimensional simulations, and also electric impedance and optical and ultrasonic image-guided methods. This article presents an overview of the need and the current status of the guidance methods available for improving the surgical outcomes in spinal fusion procedures. It also describes educational aids that have the potential for reducing the training process. Copyright © 2014 Elsevier Inc. All rights reserved.

  3. Performance Study on a Single-Screw Expander for a Small-Scale Pressure Recovery System

    Directory of Open Access Journals (Sweden)

    Guoqiang Li

    2016-12-01

    Full Text Available A single-screw expander with 195 mm diameter is developed to recover pressure energy in letdown stations. An experiment system is established using compressed air as a working fluid instead of natural gas. Experiments are conducted via measurements for important parameters, such as inlet and outlet temperature and pressure, volume flow rate and power output. The influence of inlet pressure and rotational speed on the performance are also analyzed. Results indicate that the single-screw expander achieved good output characteristics, in which 2800 rpm is considered the best working speed. The maximum volumetric efficiency, isentropic efficiency, overall efficiency, and the lowest air-consumption are 51.1 kW, 83.5%, 66.4%, 62.2%, and 44.1 kg/(kW·h, respectively. If a single-screw expander is adopted in a pressure energy recovery system applied in a certain domestic natural gas letdown station, the isentropic efficiency of the single-screw expander and overall efficiency of the system are found to be 66.4% and 62.2%, respectively. Then the system performances are predicted, in which the lowest methane consumption is 27.3 kg/(kW·h. The installed capacity is estimated as 204.7 kW, and the annual power generation is 43.3 MWh. In the next stage, a pressure energy recovery demonstration project that recycles natural gas will be established within China, with the single-screw expander serving as the power machine.

  4. Experimental determination of the dynamic properties of screw compressors; Die experimentelle Bestimmung der dynamischen Eigenschaften von Schraubenkompressoren

    Energy Technology Data Exchange (ETDEWEB)

    Rinder, L. [Technische Univ., Wien (Austria). Abt. Maschinenelemente; Svigler, J.; Pasek, M.; Albl, P. [Westboehmische Univ., Pilsen (Czech Republic). Lehrstuhl fuer Mechanik

    1998-12-31

    The demand for continuing improvements of screw machines leads to a vibration research of these machines. The presented paper deals with the experimental measurement of screw compressor operational vibrations and the determination of vibration sources. The measuring of operational vibrations, modal analysis and the determination of mode shape forms of a screw compressor were performed. The main sources of the operational vibrations were determined and the screw compressor eigenfrequencies were found in the frequency spectrum. This contribution forms a basis for the comparison of the theoretical and experimental results. This work was done in cooperation between the University of West Bohemia Pilsen and the Technical University Vienna. (orig.) [Deutsch] Staendig steigende Anforderungen an die Laufruhe von Schraubenkompressoren machen Schwingungsuntersuchungen an diesen Maschinen notwendig. Die vorliegende Arbeit beschreibt Messungen des Betriebs-Schwingungszustandes und die Bestimmung der Erregerquellen an einem oeleingespritzten Schraubenverdichter. Es wird der Schwingungszustand mit Beschleunigungsaufnehmern gemessen, eine Modalanalyse beider Rotoren durchgefuehrt und es werden die Eigenformen der Laeufer bestimmt. Die Haupterregerquellen fuer die Schwingungen koennen ermittelt werden. Die Eigenfrequenzen des Kompressors sind im Frequenzspektrum festzustellen. Die Ergebnisse dienen als Basis fuer den Vergleich zwischen experimenteller Schwingungsanalyse und theoretischen Schwingungsuntersuchungen. Ueber theoretische Ergebnisse soll in naechster Zukunft berichtet werden. Die Arbeit entstand im Rahmen einer Zusammenarbeit zwischen der Westboehmischen Universitaet Pilsen und der Technischen Universitaet Wien. Die Schwingungsmessungen wurden am Schraubenverdichterpruefstand des Instituts fuer Maschinenelemente der TU Wien durchgefuehrt. (orig.)

  5. Topics in orbit equivalence

    CERN Document Server

    Kechris, Alexander S

    2004-01-01

    This volume provides a self-contained introduction to some topics in orbit equivalence theory, a branch of ergodic theory. The first two chapters focus on hyperfiniteness and amenability. Included here are proofs of Dye's theorem that probability measure-preserving, ergodic actions of the integers are orbit equivalent and of the theorem of Connes-Feldman-Weiss identifying amenability and hyperfiniteness for non-singular equivalence relations. The presentation here is often influenced by descriptive set theory, and Borel and generic analogs of various results are discussed. The final chapter is a detailed account of Gaboriau's recent results on the theory of costs for equivalence relations and groups and its applications to proving rigidity theorems for actions of free groups.

  6. General Dynamic Equivalent Modeling of Microgrid Based on Physical Background

    Directory of Open Access Journals (Sweden)

    Changchun Cai

    2015-11-01

    Full Text Available Microgrid is a new power system concept consisting of small-scale distributed energy resources; storage devices and loads. It is necessary to employ a simplified model of microgrid in the simulation of a distribution network integrating large-scale microgrids. Based on the detailed model of the components, an equivalent model of microgrid is proposed in this paper. The equivalent model comprises two parts: namely, equivalent machine component and equivalent static component. Equivalent machine component describes the dynamics of synchronous generator, asynchronous wind turbine and induction motor, equivalent static component describes the dynamics of photovoltaic, storage and static load. The trajectory sensitivities of the equivalent model parameters with respect to the output variables are analyzed. The key parameters that play important roles in the dynamics of the output variables of the equivalent model are identified and included in further parameter estimation. Particle Swarm Optimization (PSO is improved for the parameter estimation of the equivalent model. Simulations are performed in different microgrid operation conditions to evaluate the effectiveness of the equivalent model of microgrid.

  7. Drag and Torque on Locked Screw Propeller

    Directory of Open Access Journals (Sweden)

    Tomasz Tabaczek

    2014-09-01

    Full Text Available Few data on drag and torque on locked propeller towed in water are available in literature. Those data refer to propellers of specific geometry (number of blades, blade area, pitch and skew of blades. The estimation of drag and torque of an arbitrary propeller considered in analysis of ship resistance or propulsion is laborious. The authors collected and reviewed test data available in the literature. Based on collected data there were developed the empirical formulae for estimation of hydrodynamic drag and torque acting on locked screw propeller. Supplementary CFD computations were carried out in order to prove the applicability of the formulae to modern moderately skewed screw propellers.

  8. Screw Extruder for Pellet Injection System

    Directory of Open Access Journals (Sweden)

    Sharadkumar K. Chhantbar

    2014-05-01

    Full Text Available Solid hydrogenic pellets are used as fuel for fusion energy reactor. A technique for continuous production of solid hydrogen and its isotopes by a screw extruder is suggested for the production of an unlimited number of pellets. The idea was developed and patented by PELIN laboratories, Inc. (Canada. A Gifford McMahon cryocooler is used for the generation of solid hydrogenic fluid pellets. Requirements of the pellets is depends upon the energy to be produced by tokamak. This review paper focuses on the model for the screw extruder for solidification of hydrogen ice having high injection reliability.

  9. A geometrical introduction to screw theory

    CERN Document Server

    Minguzzi, E

    2012-01-01

    Since the addition of applied forces must take into account the line of action, applied forces do not belong to a vector space. Screw theory removes this geometrical limitation and solves other mechanical problems by unifying, in a single concept, the translational and rotational degrees of freedom. Although venerable this theory is little known. By introducing some innovations, I show how screw theory can help us to rapidly develop several standard and less standard results in classical mechanics. The connection with the Lie algebra of the group of rigid maps is clarified.

  10. Energy self-sufficient sensory ball screw drive; Energieautarker sensorischer Kugelgewindetrieb

    Energy Technology Data Exchange (ETDEWEB)

    Bertram, Oliver

    2012-07-01

    Nowadays the availability of machine tools plays a decisive role in competition to increase in productivity. From state of the art it arises, that ball screw drives are the most abusive component in feed drives because of abrasive wear. Furthermore condition monitoring enables avoiding unplanned machine failure and increasing the availability of the deployed production facility. Thereby the application of additional sensors allows the direct acquisition of wear correlative measurements. To reduce the required effort for integration and increase the robustness, reliability and clarity in industrial environment energy self-sufficient sensor systems can be applied. In this thesis the development and investigation of an energy self-sufficient sensory ball screw drive with direct measurement of wear correlative pretension for condition monitoring application is described. The prototype measures the pretension with force sensors based on strain gauges. The sensor system includes microcontroller-based electronics for signal processing as well as wireless data transmission with ZigBee-standard. A hybrid system assures the energy supply of the sensor system. On the one hand a stepper motor generator produces electrical energy from the motion energy of the ball screw drive. On the other hand an energy buffer based on super caps is reloaded in stationary position by wireless energy transmission. For verification a prototype system is build up. In measurements the sensory and energetic characteristics of the energy self-sufficient sensor systems are analyzed. Moreover, the functionality of the ball screw drive as well as the signal characteristics of the force sensors are examined for different pretensions. In addition, pretension losses due to wear are established in realized endurance trials, which means that timely maintenance can be planned.

  11. Biomechanical evaluation of an expansive pedicle screw in calf vertebrae

    Institute of Scientific and Technical Information of China (English)

    雷伟; 吴子祥

    2005-01-01

    Objective: To obtain a comprehensive understanding of the effect of the improvement of fixation strength of a newly designed expansive pedicle screw through biomechanical analyses.Metheds: 100 (200 pedicles) fresh calf lumber vertebrae were used. A total of four instrumentation systems were tested including CDH (CD Horizon), USS (Universal Spine System pedicle screw), Tenor (Sofamor Denek) and expansive pedicle screw (EPS). Pullout and turning-back tests were performed to compare the holding strength of the expansive pedicle screw with conventional screws, i.e. USS, CDH and Tenor. Revision tests were performed to evaluate the mechanical properties of the expansive pedicle screw as a "rescue" revision screw. A fatigue simulation using perpendicular load up to 1 500 000 cycles was carried out.Results: The turning back torque (Tmax) and pull-out force (Fmax) of EPS were significantly greater than those of USS, Tenor and CDH screws (6.5 mm×40 mm). In revision tests, the Fmax of both kinds of EPS (6.5 mm×40 mm; 7.0 mm×40 mm) were greater than that of CDH, USS and Tenor screws significantly (P<0.05). No screws were broken or bent at the end of fatigue tests.Conclusions: EPS can significantly improve the bone purchase and the pull-out strength compared to USS, Tenor and CDH screws with similar dimensions before and after failure simulation. The fatigue characteristic of EPS is similar to that of CDH, USS and Tenor screws.

  12. Dual-worm screw compressors; Compresseurs bi-vis

    Energy Technology Data Exchange (ETDEWEB)

    Baleydier, J.P. [Bitzer France, 69 - Lyon (France)

    1997-12-31

    Low power worm-screw moto-compressors are used in any king of refrigerating machineries and more and more in air conditioning systems. This paper presents the principle of dual-screw moto-compressors: worm-screw technology, role of oil (lubrication, tightness, cooling), compression, internal pressure, power reduction, lubrication, economizer, operation, model selection and accessories. (J.S.)

  13. 21 CFR 872.4880 - Intraosseous fixation screw or wire.

    Science.gov (United States)

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Intraosseous fixation screw or wire. 872.4880... (CONTINUED) MEDICAL DEVICES DENTAL DEVICES Surgical Devices § 872.4880 Intraosseous fixation screw or wire. (a) Identification. An intraosseous fixation screw or wire is a metal device intended to be...

  14. The additon of screws and the axodes of gear pairs

    Institute of Scientific and Technical Information of China (English)

    ZHANG Wen-xiang

    2001-01-01

    In the light of screw addition, the distribution of instantaneous axes along the common perpendicular of the two screws is determined and all possible sorts of axodes are derived cinematically with the pitch of the relative-motio n screw in the gear pair as the basis and the transmission ratio i as an inde pendent variable.

  15. The additon of screws and the axodes of gear pairs

    Institute of Scientific and Technical Information of China (English)

    张文祥

    2001-01-01

    In the light of screw addition, the distribution of instantaneous axes along the common perpendicular of the two screws is determined and all possible sorts of axodes are derived cinematically with the pitch of the relative-motion screw in the gear pair as the basis and the transmission ratio i as an independent variable.

  16. Design of a magnetic lead screw for wave energy conversion

    DEFF Research Database (Denmark)

    Holm, Rasmus Koldborg; Berg, Nick Ilsø; Rasmussen, Peter Omand

    2012-01-01

    This paper deals with the development of a magnetic lead screw (MLS) for wave energy conversion. Initially, a brief state-of-the-art regarding linear PM generators and magnetic lead screws is given, leading to an introduction of the magnetic lead screw and a presentation of the results from...

  17. A Novel Pedicle Screw with Mobile Connection: A Pilot Study

    Directory of Open Access Journals (Sweden)

    Yasuaki Tokuhashi

    2014-01-01

    Full Text Available To prevent adjacent disc problems after spinal fusion, a pedicle screw with a mobile junction between the head and threaded shaft was newly developed. The threaded shaft of the screw has 10 degrees mobility in all directions, but its structure is to prevent abnormal translation and tilting. This screw was evaluated as follows: (1 endurance test: 106 times rotational stress was applied; (2 biological reactions: novel screws with a mobile head and conventional screws with a fixed head were inserted into the bilateral pedicles of the L3, L4, and L5 in two mini pigs with combination. Eight months after surgery, vertebral units with the screw rod constructs were collected. After CT scan, the soft and bony tissues around the screws were examined grossly and histologically. As a result, none of the screws broke during the endurance test stressing. The mean amount of abrasion wear was 0.0338 g. In the resected mini pig section, though zygapophyseal joints between fixed-head screws showed bony union, the amount of callus in the zygapophyseal joints connected with mobile-head screws was small, and joint space was confirmed by CT. No metalloses were noted around any of the screws. Novel screws were suggested to be highly durable and histologically safe.

  18. Design Research on Drive System of Underwater Tapping Machine

    Institute of Scientific and Technical Information of China (English)

    YU Kai-an

    2009-01-01

    The underwater tapping machine is composed of a center bit,a tapping cutter,a sesl box,a main drive box,aboring bar assembly,a envelop,a gear case,a counter and so on.The drive system in underwater tapping machine consists of a worm drive,a gear drive system and a screw drive.The worm drive is in the main drive box.The worm is connected with a hydraulic motor and driven by the hydraulic motor.The gear drive system is a combined gear train which is the combinations of the fixed axes and differential gear train in the gear case.On the one hand,by means of the fixed axes gear trains the turn and power of transmission shaft are transferred to the boring bar and the screw rod,causing differential tam between the boring bar and the screw rod.On the other hand,the turns of the boring bar and the screw rod are transferred to the differential gear train.The differential gear train is used to drive a special counter to count axial travel of the boring bar.The screw drive is composed of a feed screw and a nut on the boring bar.There is the differential turn between the boring bar and the feed screw.By means of the nut,the boring bar can feed automatically.With the movement of the sliding gear 7 in the gear case,the designed drive system can also be provided with the ability of fast forward and fast backward movement of the boring bar in its idle motion,restdting in the increase of the tapping efficiency.

  19. Suture Button Fixation Versus Syndesmotic Screws in Supination-External Rotation Type 4 Injuries: A Cost-Effectiveness Analysis.

    Science.gov (United States)

    Neary, Kaitlin C; Mormino, Matthew A; Wang, Hongmei

    2017-01-01

    %. Furthermore, fixation with a single suture button continued to be the dominant treatment strategy compared with 2 suture buttons, 1 screw, and 2 screws for syndesmotic fixation. This cost-effectiveness analysis suggests that for unstable SER IV ankle fractures, suture button fixation is more cost-effective than syndesmotic screws not removed on a routine basis. Suture button fixation was a dominant treatment strategy, because patients spent on average $1482 less and had a higher quality of life by 0.058 QALYs compared with patients who received fixation with 2 syndesmotic screws. Assuming that functional outcomes and failure rates were equivalent, screw fixation only became more cost-effective when the screw hardware removal rate was reduced to less than 10% or when the suture button cost exceeded $2000. In addition, fixation with a single suture button device proved more cost-effective than fixation with either 1 or 2 syndesmotic screws.

  20. Application of static pressure guide screw and screw nut in vertical lathe%静压丝杆螺母在立式车床的应用

    Institute of Scientific and Technical Information of China (English)

    吴晓明; 海燕

    2011-01-01

    针对现有的重型立式车床中存在的升降传动问题,探讨超重型立式车床的横梁升降机构所采用的静压丝杆螺母的设计及制造工艺,以减少传动系统的摩擦和磨损,提高机床运动精度和传动效率,详细介绍了丝杆螺母的设计与计算,在加工工艺中还从多个方面保证了产品的制造精度,经过定量叶片泵和变量叶片泵的验证实验,还对制造结果进行了讨论与分析,对存在的问题提出了有效的解决办法.%With regard to up and down transmission problem available in the heavy-duty vertical lathe, the design and manufacturing technology of static pressure guide screw and screw nut adopted by lifting mechanism of the heavy-duty vertical lathe is discussed in it in order to decrease friction and wear of transmission system,improve kinematic accuracy of the machine tool and transmission efficiency.Then the design and calculation of the guide screw and screw nut are introduced in detail. The processing technology ensures product manufacturing accuracy in many aspects,and it is rectified through validating experiment of ration pump and variable pump.Above all efficient solutions are put forward to the problems available.

  1. Clinical pedicle screw accuracy and deviation from planning in robot-guided spine surgery: robot-guided pedicle screw accuracy

    NARCIS (Netherlands)

    Dijk, van Joris D.; Ende, Roy P.J.; Stramigioli, Stefano; Köchling, Matthias; Höss, Norbert

    2015-01-01

    STUDY DESIGN: A retrospective chart review was performed for 112 consecutive minimally invasive spinal surgery patients who underwent pedicular screw fixation in a community hospital setting. OBJECTIVE: To assess the clinical accuracy and deviation in screw positions in robot-assisted pedicle screw

  2. Nylon screws make inexpensive coil forms

    Science.gov (United States)

    Aucoin, G.; Rosenthal, C.

    1978-01-01

    Standard nylon screws act as coil form copper wire laid down in spiral thread. Completed coil may be bonded to printed-circuit board. However, it is impossible to tune coil by adjusting spacing between windings, technique sometimes used with air-core coils.

  3. Nylon screws make inexpensive coil forms

    Science.gov (United States)

    Aucoin, G.; Rosenthal, C.

    1978-01-01

    Standard nylon screws act as coil form copper wire laid down in spiral thread. Completed coil may be bonded to printed-circuit board. However, it is impossible to tune coil by adjusting spacing between windings, technique sometimes used with air-core coils.

  4. A phenomenological study on twin screw extruders

    NARCIS (Netherlands)

    Janssen, L.P.B.M.

    1976-01-01

    Although more and more twin screw extruders are being used in the polymer industry, the theoretical background is relatively undeveloped. The literature abounds in contradictions and often informs the reader that all extrusion problems can be solved if a certain new design is considered. The develop

  5. The Integration of an API619 Screw Compressor Package into the Industrial Internet of Things

    Science.gov (United States)

    Milligan, W. J.; Poli, G.; Harrison, D. K.

    2017-08-01

    The Industrial Internet of Things (IIoT) is the industrial subset of the Internet of Things (IoT). IIoT incorporates big data technology, harnessing the instrumentation data, machine to machine communication and automation technologies that have existed in industrial settings for years. As industry in general trends towards the IIoT and as the screw compressor packages developed by Howden Compressors are designed with a minimum design life of 25 years, it is imperative this technology is embedded immediately. This paper provides the reader with a description on the Industrial Internet of Things before moving onto describing the scope of the problem for an organisation like Howden Compressors who deploy multiple compressor technologies across multiple locations and focuses on the critical measurements particular to high specification screw compressor packages. A brief analysis of how this differs from high volume package manufacturers deploying similar systems is offered. Then follows a description on how the measured information gets from the tip of the instrument in the process pipework or drive train through the different layers, with a description of each layer, into the final presentation layer. The functions available within the presentation layer are taken in turn and the benefits analysed with specific focus on efficiency and availability. The paper concludes with how packagers adopting the IIoT can not only optimise their package but by utilising the machine learning technology and pattern detection applications can adopt completely new business models.

  6. Rotating Drive for Electrical-Arc Machining

    Science.gov (United States)

    Fransen, C. D.

    1986-01-01

    Rotating drive improves quality of holes made by electrical-arc machining. Mechanism (Uni-tek, rotary head, or equivalent) attached to electrical-arc system. Drive rotates electrode as though it were mechanical drill, while an arc disintegrates metal in workpiece, thereby creating hole. Rotating electrode method often used in electric-discharge machining. NASA innovation is application of technique to electrical-arc machining.

  7. Rotational Efficiency of Photo-Driven Archimedes Screws for Micropumps

    Directory of Open Access Journals (Sweden)

    Chih-Lang Lin

    2015-06-01

    Full Text Available In this study, we characterized the rotational efficiency of the photo-driven Archimedes screw. The micron-sized Archimedes screws were fabricated using the two-photon polymerization technique. Free-floating screws trapped by optical tweezers align in the laser irradiation direction and rotate spontaneously. The influences of the screw pitch and the number of screw blades have been investigated in our previous studies. In this paper, the blade thickness and the central rod of the screw were further investigated. The experimental results indicate that the blade thickness contributes to rotational stability, but not to rotational speed, and that the central rod stabilizes the rotating screw but is not conducive to rotational speed. Finally, the effect of the numerical aperture (NA of the optical tweezers was investigated through a demonstration. The NA is inversely proportional to the rotational speed.

  8. A Review of Screw Conveyors Performance Evaluation During Handling Process

    Directory of Open Access Journals (Sweden)

    Hemad Zareiforoush

    2010-04-01

    Full Text Available This paper reviews recent work on screw conveyors performance evaluation during handling process, especially in the case of agricultural grains and bulk materials. Experimental work has been mainly carried out to determine a range of parameters, such as auger dimension, screw rotational speed, screw clearance, conveyor intake length and conveying angle for horizontal, inclined and vertical screw conveyors. Several measurement techniques including theoretical models and DEM have been utilized to study the screw conveyors performance. However, each of these techniques is limited in its application. Difficulties in representing vortex motion and interactions among conveying grains and between the particles and screw rotating flight have so far limited the success of advanced modeling. Further work is needed to be conducted on screw augers performance to understand and improve the agricultural grains and bulk materials handling process.

  9. Atlantoaxial stabilization using multiaxial C-1 posterior arch screws.

    Science.gov (United States)

    Donnellan, Michael B; Sergides, Ioannis G; Sears, William R

    2008-12-01

    The authors present a novel technique of atlantoaxial fixation using multiaxial C-1 posterior arch screws. The technique involves the insertion of bilateral multiaxial C-1 posterior arch screws, which are connected by crosslinked rods to bilateral multiaxial C-2 pars screws. The clinical results are presented in 3 patients in whom anomalies of the vertebral arteries, C-1 lateral masses, and/or posterior arch of C-1 presented difficulty using existing fixation techniques with transarticular screws, C-1 lateral mass screws, or posterior wiring. The C-1 posterior arch screws achieved solid fixation and their insertion appeared to be technically less demanding than that of transarticular or C-1 lateral mass screws. This technique may reduce the risk of complications compared with existing techniques, especially in patients with anatomical variants of the vertebral artery, C-1 lateral masses, or C-1 posterior arch. This technique may prove to be an attractive fixation option in patients with normal anatomy.

  10. Electric machine

    Science.gov (United States)

    El-Refaie, Ayman Mohamed Fawzi [Niskayuna, NY; Reddy, Patel Bhageerath [Madison, WI

    2012-07-17

    An interior permanent magnet electric machine is disclosed. The interior permanent magnet electric machine comprises a rotor comprising a plurality of radially placed magnets each having a proximal end and a distal end, wherein each magnet comprises a plurality of magnetic segments and at least one magnetic segment towards the distal end comprises a high resistivity magnetic material.

  11. Current Conveyor Equivalent Circuits

    Directory of Open Access Journals (Sweden)

    Tejmal S. Rathore

    2012-02-01

    Full Text Available An equivalence between a class of (current conveyor CC II+ and CC II- circuits is established. CC IIequivalent circuit uses one extra element. However, under certain condition, the extra element can be eliminated. As an illustration of the application of this equivalence, minimal first and second order all-pass filters are derived. Incertain cases, it is possible to compensate the effect of the input resistor of CC at port X. At the end, an open problem of realizing an Nth order (N > 2 minimal all-pass filter is stated.

  12. Feed Drive Based upon Linear Motor for Ultraprecision Turning Machine

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    The characteristics of several different linear motors have been investigated, and the feed drive system with linear motor instead of screw-nut mechanism has been built for a submicro ultraprecision turning machine. In the control system for the feed drive system arranged as "T", both P-position and PI-speed control loops are used. The feedback variable is obtained from a double frequecy laser interferometor. Experiments show that the feed drive with linear motor is simple in construction, and that its dynamics is better than others. So the machining accuracy of the workpiece machined has been successfully improved.

  13. Research and application of absorbable screw in orthopedics: a clinical review comparing PDLLA screw with metal screw in patients with simple medial malleolus fracture

    Directory of Open Access Journals (Sweden)

    TANG Jin

    2013-02-01

    Full Text Available 【Abstract】Objective: To observe the therapeutic effect of absorbable screw in medial malleolus fracture and discuss its clinical application in orthopedics. Methods: A total of 129 patients with simple medial malleolus fracture were studied. Among them, 64 patients were treated with poly-D, L-lactic acid (PDLLA absorbable screws, while the others were treated with metal screws. All the patients were followed up for 12-20 months (averaged 18.4 months and the therapeutic effect was evaluated ac-cording to the American Orthopaedic Foot and Ankle Soci-ety clinical rating systems. Results: In absorbable screw group, we obtained excel-lent and good results in 62 cases (96.88%; in steel screw group, 61 cases (93.85% achieved excellent and good results. There was no significant difference between the two groups. Conclusion: In the treatment of malleolus fracture, absorbable screw can achieve the same result compared with metal screw fixation. Absorbable screw is preferred due to its advantages of safety, cleanliness and avoiding the removal procedure associated with metallic implants. Key words: Ankle; Bone screws; Fractures, bone

  14. Vector grammars and PN machines

    Institute of Scientific and Technical Information of China (English)

    蒋昌俊

    1996-01-01

    The concept of vector grammars under the string semantic is introduced.The dass of vector grammars is given,which is similar to the dass of Chomsky grammars.The regular vector grammar is divided further.The strong and weak relation between the vector grammar and scalar grammar is discussed,so the spectrum system graph of scalar and vector grammars is made.The equivalent relation between the regular vector grammar and Petri nets (also called PN machine) is pointed.The hybrid PN machine is introduced,and its language is proved equivalent to the language of the context-free vector grammar.So the perfect relation structure between vector grammars and PN machines is formed.

  15. A new type of axial-flux magnetic lead screw with inherent spring characteristic

    DEFF Research Database (Denmark)

    Lu, Kaiyuan; Xia, Yongming; Pan, Haipeng

    2016-01-01

    of MLS is proposed, where all the permanent magnets of the rotor and translator are magnetized along the axial direction and it utilizes the propelling force between two opposite magnetic polarity poles for driving. It is a new topology for realizing MLS. The rotor and translator magnets can be made......Magnetic Lead Screw (MLS) can transfer slow linear motion into fast rotary motion offering much higher force density than that of traditional linear permanent magnet machines. It has been developed for ocean wave energy harvester and active damper for electrical vehicles. In this paper, a new type...

  16. Mass Equivalent Dyads

    NARCIS (Netherlands)

    van der Wijk, V.; Bai, Shaoping; Ceccarelli, Marco

    2015-01-01

    In this paper it is shown how a general 2-DoF dyad can be designed mass equivalent to a general (1-DoF) link element. This is useful in the synthesis of balanced mechanisms, for instance to increase or reduce the number of DoFs of a balanced mechanism maintaining its balance. Also it can be used as

  17. Mass equivalent triads

    NARCIS (Netherlands)

    van der Wijk, V.

    2015-01-01

    In this paper it is shown how a general 3-DoF triad can be designed mass equivalent to a general (1-DoF) link element. This is useful in the synthesis of shaking force balanced and statically balanced mechanisms, for instance to add or remove a number of DoFs of a balanced mechanism maintaining its

  18. Equivalence of Differential System

    Institute of Scientific and Technical Information of China (English)

    Zheng-xin Zhou

    2004-01-01

    Using refiecting function of Mironenko we construct some differential systems which are equivalent to the given differential system.This gives us an opportunity to find out the monodromic matrix of these periodi csystems which are not integrable in finite terms.

  19. Biomechanical performance of subpectoral biceps tenodesis: a comparison of interference screw fixation, cortical button fixation, and interference screw diameter.

    Science.gov (United States)

    Sethi, Paul M; Rajaram, Arun; Beitzel, Knut; Hackett, Thomas R; Chowaniec, David M; Mazzocca, Augustus D

    2013-04-01

    Subpectoral biceps tenodesis with interference screw fixation allows reproducible positioning of the tendon to help maintain the length-tension relationship. The aim of our study was to evaluate the role of cortical button fixation in isolation or as an augment to interference screw fixation and to determine if the diameter of the interference screw affected fixation strength. Thirty-two cadaveric shoulders were dissected and randomized to 1 of 4 groups: (1) 7-mm interference screw and cortical button, (2) cortical button alone, (3) 7-mm interference screw, or (4) 8-mm interference screw. Testing was performed on a materials testing system with a 100-N load cycled at 1 Hz for 5000 cycles, followed by an axial load to failure test. Cyclic displacement, ultimate load to failure, and site of failure were recorded for each specimen. The mean ultimate failure loads were 7-mm interference screw with cortical button augmentation, 237.8 ± 120.4 N; cortical button alone, 99.4 ± 16.9 N; 7-mm interference screw, 275.5 ± 56 N; 8-mm interference screw, 277.1 ± 42.1 N. All specimens failed through tendon failure at the screw-tendon-bone interface. The biomechanical performance of subpectoral biceps tenodesis with interference screw fixation was not improved with cortical button augmentation. In addition, cortical button fixation alone yielded a significantly lower ultimate load to failure compared with interference screws. Finally, the biomechanical performance of smaller-diameter interference screws with matching bone tunnels was not affected by interference screw diameter. Copyright © 2013 Journal of Shoulder and Elbow Surgery Board of Trustees. Published by Mosby, Inc. All rights reserved.

  20. The Machine within the Machine

    CERN Multimedia

    Katarina Anthony

    2014-01-01

    Although Virtual Machines are widespread across CERN, you probably won't have heard of them unless you work for an experiment. Virtual machines - known as VMs - allow you to create a separate machine within your own, allowing you to run Linux on your Mac, or Windows on your Linux - whatever combination you need.   Using a CERN Virtual Machine, a Linux analysis software runs on a Macbook. When it comes to LHC data, one of the primary issues collaborations face is the diversity of computing environments among collaborators spread across the world. What if an institute cannot run the analysis software because they use different operating systems? "That's where the CernVM project comes in," says Gerardo Ganis, PH-SFT staff member and leader of the CernVM project. "We were able to respond to experimentalists' concerns by providing a virtual machine package that could be used to run experiment software. This way, no matter what hardware they have ...

  1. Strategy for salvage pedicle screw placement: A technical note.

    Science.gov (United States)

    Fujibayashi, Shunsuke; Takemoto, Mitsuru; Neo, Masashi; Matsuda, Shuichi

    2013-01-01

    Salvage surgery for failed lumbar spine fusion with a loosened pedicle screw is challenging. In general, the strategy includes replacement with larger and longer pedicle screws, augmentation with polymethylmethacrylate cement or hydroxyapatite granules, and extension of fused segments. The purpose of this study is to introduce a new technique for pedicle screw replacement after failed lumbar spine fusion. Five salvage operations were performed using a different trajectory (DT) pedicle screw replacement technique based on 3-dimensional radiological information. Position of the alternative pedicle screws was planned carefully on the computer screen of a computed tomography-based navigation system before the operation. To obtain sufficient initial stability, 1 of 2 techniques was chosen, depending on the patient. One technique created a completely new route, which did not interfere with the existing screw hole, and the other involved penetration of the existing screw hole. DT pedicle screws were replaced successfully according to the preoperative plan. In all patients, bony union were achieved at the final follow-up period without any instrument failure. Extension of the fused segments could be avoided by using the DT pedicle screw replacement technique combined with transforaminal lumbar interbody fusion. The DT pedicle screw replacement technique is a treatment option for salvage lumbar spine surgery. The current technique is a treatment option for salvage operations that can both avoid extension of a fused segment and achieve successful bony union.

  2. Impact of screw elements on continuous granulation with a twin-screw extruder.

    Science.gov (United States)

    Djuric, Dejan; Kleinebudde, Peter

    2008-11-01

    The influence of different screw element types on wet granulation process with a twin-screw extruder was investigated. Lactose granules were prepared with different screw configurations such as conveying, combing mixer and kneading elements. The use of kneading blocks led to an almost complete agglomeration of lactose, whereas kneading and combing mixer elements resulted in smaller granules in comparison. Granule porosity varied between 17.4% and 50.6%. Granule friability values ranged from 1.2% to 38.5%. Conveying elements led to the most porous and friable granules, whereas kneading blocks produced the densest and least friable granules. Combing mixer elements produced granules with median properties. A linear correlation between granule porosity and the natural logarithm of granule friability was detected. Flowability of granules was also influenced by the element type. Compressed granules with higher granule porosities resulted in tablets with higher tensile strength values and vice versa. Twin-screw extruders proved to be a versatile tool for wet granulation. By the choice of a suitable screw element granule and tablet characteristics were influenced.

  3. Analysis of Modeling Parameters on Threaded Screws.

    Energy Technology Data Exchange (ETDEWEB)

    Vigil, Miquela S. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Brake, Matthew Robert [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Vangoethem, Douglas [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

    2015-06-01

    Assembled mechanical systems often contain a large number of bolted connections. These bolted connections (joints) are integral aspects of the load path for structural dynamics, and, consequently, are paramount for calculating a structure's stiffness and energy dissipation prop- erties. However, analysts have not found the optimal method to model appropriately these bolted joints. The complexity of the screw geometry cause issues when generating a mesh of the model. This paper will explore different approaches to model a screw-substrate connec- tion. Model parameters such as mesh continuity, node alignment, wedge angles, and thread to body element size ratios are examined. The results of this study will give analysts a better understanding of the influences of these parameters and will aide in finding the optimal method to model bolted connections.

  4. Translaminar facetal screw (magerl′s fixation

    Directory of Open Access Journals (Sweden)

    Rajasekaran S

    2005-01-01

    Full Text Available Translaminar facet screw fixation (TLFS achieves stabilization of the vertebral motion segment by screws inserted at the base of the spinous process, through the opposite lamina, traversing the facet joint, and ending in the base of the transverse process. It is simple, does not require any specialized equipment, and has the advantages of being a procedure of lesser magnitude, lesser operative time, less cost and few complication rate. Recently there is growing interest in this technique to augment the anterior lumbar fusions to achieve global fusion less invasively. In this review article, we discuss the clinical and biomechanical considerations, surgical technique, indications, contraindications and recent developments of TLFS fixation in lumbar spine fusion.

  5. Twin screw granulation - review of current progress.

    Science.gov (United States)

    Thompson, M R

    2015-01-01

    Twin screw granulation (TSG) is a new process of interest to the pharmaceutical community that can continuously wet granulate powders, doing so at lower liquid concentrations and with better product consistency than found by a high shear batch mixer. A considerable body of research has evolved over the short time since this process was introduced but generally with little comparison of results. A certain degree of confidence has been developed through these studies related to how process variables and many attributes of machinery configuration will affect granulation but some major challenges still lay ahead related to scalability, variations in the processing regimes related to degree of channel fill and the impact of wetting and granulation of complex powder formulations. This review examines the current literature for wet granulation processes studied in twin screw extrusion machinery, summarizing the influences of operational and system parameters affecting granule properties as well as strives to provide some practical observations to newly interested users of the technique.

  6. Machine Learning

    CERN Document Server

    CERN. Geneva

    2017-01-01

    Machine learning, which builds on ideas in computer science, statistics, and optimization, focuses on developing algorithms to identify patterns and regularities in data, and using these learned patterns to make predictions on new observations. Boosted by its industrial and commercial applications, the field of machine learning is quickly evolving and expanding. Recent advances have seen great success in the realms of computer vision, natural language processing, and broadly in data science. Many of these techniques have already been applied in particle physics, for instance for particle identification, detector monitoring, and the optimization of computer resources. Modern machine learning approaches, such as deep learning, are only just beginning to be applied to the analysis of High Energy Physics data to approach more and more complex problems. These classes will review the framework behind machine learning and discuss recent developments in the field.

  7. Equivalence Between Squirrel Cage and Sheet Rotor Induction Motor

    Science.gov (United States)

    Dwivedi, Ankita; Singh, S. K.; Srivastava, R. K.

    2016-06-01

    Due to topological changes in dual stator induction motor and high cost of its fabrication, it is convenient to replace the squirrel cage rotor with a composite sheet rotor. For an experimental machine, the inner and outer stator stampings are normally available whereas the procurement of rotor stampings is quite cumbersome and is not always cost effective. In this paper, the equivalence between sheet/solid rotor induction motor and squirrel cage induction motor has been investigated using layer theory of electrical machines, so as to enable one to utilize sheet/solid rotor in dual port experimental machines.

  8. From equivalence to adaptation

    Directory of Open Access Journals (Sweden)

    Paulina Borowczyk

    2009-01-01

    Full Text Available The aim of this paper is to illustrate in which cases the translators use the adaptation when they are confronted with a term related to sociocultural aspects. We will discuss the notions of equivalence and adaptation and their limits in the translation. Some samples from Arte TV news and from the American film Shrek translated into Polish, German and French will be provided as a support for this article.

  9. MOVING SCREW DISLOCATION IN CUBIC QUASICRYSTAL

    Institute of Scientific and Technical Information of China (English)

    ZHOU Wang-min; SONG Yu-hai

    2005-01-01

    The elasticity theory of the dislocation of cubic quasicrystals is developed.The governing equations of anti-plane elasticity dynamics problem of the quasicrystals were reduced to a solution of wave equations by introducing displacement functions,and the analytical expressions of displacements, stresses and energies induced by a moving screw dislocation in the cubic quasicrystalline and the velocity limit of the dislocation were obtained. These provide important information for studying the plastic deformation of the new solid material.

  10. Biomechanical comparison of interference screw and cortical button with screw hybrid technique for distal biceps brachii tendon repair.

    Science.gov (United States)

    Arianjam, Afshin; Camisa, William; Leasure, Jeremi M; Montgomery, William H

    2013-11-01

    Various fixation techniques have been described for ruptured distal biceps tendons. The authors hypothesized that no significant differences would be found between the mean failure strength, maximum strength, and stiffness of the interference screw and hybrid technique. Fourteen fresh-frozen human cadaveric elbows were prepared. Specimens were randomized to either interference screw or hybrid cortical button with screw fixation. The tendon was pulled at a rate of 4 mm/s until failure. Failure strength, maximum strength, and stiffness were measured and compared. Failure strength, maximum strength, and stiffness were 294±81.9 N, 294±82.1 N, and 64.4±40.5 N/mm, respectively, for the interference screw technique and 333±129 N, 383±121 N, and 56.2±40.5 N/mm, respectively, for the hybrid technique. No statistically significant difference existed between the screw and hybrid technique in failure strength, maximum strength, or stiffness (P>.05). The interference screws primarily failed by pullout of the screw and tendon, whereas in the hybrid technique, failure occurred with screw pullout followed by tearing of the biceps tendon. The results suggest that this hybrid technique is nearly as strong and stiff as the interference screw alone. Although the hybrid technique facilitates tensioning of the reconstructed tendon, the addition of the cortical button did not significantly improve the failure strength of the interference screw alone. Copyright 2013, SLACK Incorporated.

  11. Research and application of absorbable screw in orthopedics: a clinical review comparing PDLLA screw with metal screw in patients with simple medial malleolus fracture

    Institute of Scientific and Technical Information of China (English)

    TANG Jin; HU Jin-feng; GUO Wei-chun; YU Ling; ZHAO Sheng-hao

    2013-01-01

    Objective:To observe the therapeutic effect of absorbable screw in medial malleolus fracture and discuss its clinical application in orthopedics.Methods:A total of 129 patients with simple medial malleolus fracture were studied.Among them,64 patients were treated with poly-D,L-lactic acid (PDLLA) absorbable screws,while the others were treated with metal screws.All the patients were followed up for 12-20 months (averaged 18.4 months) and the therapeutic effect was evaluated according to the American Orthopaedic Foot and Ankle Society clinical rating systems.Results:In absorbable screw group,we obtained excellent and good results in 62 cases (96.88%); in steel screw group,61 cases (93.85%) achieved excellent and good results.There was no significant difference between the two groups.Conclusion:In the treatment of malleolus fracture,absorbable screw can achieve the same result compared with metal screw fixation.Absorbable screw is preferred due to its advantages of safety,cleanliness and avoiding the removal procedure associated with metallic implants.

  12. Reciprocal screw theory based singularity analysis of a novel 3-DOF parallel manipulator

    Science.gov (United States)

    Fang, Hairong; Fang, Yuefa; Zhang, Ketao

    2012-07-01

    Singularity analysis is an essential issue for the development and application of parallel manipulators. Most of the existing researches focus on the singularity of parallel manipulators are carried out based on the study of Jacobian matrices. A 3-DOF parallel manipulator with symmetrical structure is presented. The novel parallel manipulator employs only revolute joints and consists of four closed-loop subchains connecting to both base and platform via revolute joints. The closed-loop subchain in each chain-leg is a spherical 6R linkage. The motion characteristics of the output link in the spherical 6R linkage with symmetrical structure are analyzed based on the interrelationships between screw systems. The constraints that are exerted on the platform by each chain-leg are investigated applying the concept of generalized kinematic pair in terms of equivalent screw system. Considering the geometric characteristics of the parallel manipulator, the singularity criteria of the parallel manipulator corresponding to different configurations are revealed based on the dependency of screw system and line geometry. The existing conditions of certain configuration that a singularity must occur are determined. This paper presents a new way of singularity analysis based on disposition of constraint forces on the geometrically identified constraint plane and the proposed approach is capable of avoiding the complexity in solving the Jacobian matrices.

  13. Equivalence Relations of -Algebra Extensions

    Indian Academy of Sciences (India)

    Changguo Wei

    2010-04-01

    In this paper, we consider equivalence relations of *-algebra extensions and describe the relationship between the isomorphism equivalence and the unitary equivalence. We also show that a certain group homomorphism is the obstruction for these equivalence relations to be the same.

  14. Biomechanical evaluation of a unicortical button versus interference screw for subpectoral biceps tenodesis.

    Science.gov (United States)

    Arora, Amarpal S; Singh, Anshu; Koonce, Ryan C

    2013-04-01

    The purpose of this study was to evaluate and compare the biomechanical properties of a unicortical button with an interference screw used for subpectoral biceps tenodesis. We also describe the anatomic dangers of bicortical button use in the subpectoral location. Twenty-eight fresh-frozen human cadaveric shoulders with a mean age of 52 years were studied. The specimens were randomly divided into 4 experimental biceps tenodesis groups (n = 7): unicortical button, interference screw, bicortical suspensory button, and bicortical suspensory with interference screw (Arthrex, Naples, FL). Each tenodesis specimen was mounted on a mechanical testing machine, preloaded for 2 minutes at 5 N, cycled from 5 to 70 N for 500 cycles (1 Hz), and loaded to failure (1 mm/s). We determined the mode of failure and computed the ultimate load to failure, yield load, pullout stiffness, and displacement at peak load. Calculations of the distance between the axillary and radial nerves with respect to the bicortical buttons were also calculated in 6 specimens. There was no statistically significant difference (P > .05) among groups in terms of age, ultimate load to failure, pullout stiffness, or displacement at peak load. Suture-tendon interface failure was the most commonly observed mode of failure. The axillary nerve was on average 7.8 mm from the bicortical button; however, in 6 specimens the nerve was less than 3 mm away. The use of a unicortical button for subpectoral biceps tenodesis provides biomechanical properties similar to the use of an interference screw. In addition, the use of a bicortical button in this area of the proximal humerus puts the axillary nerve at risk. Using a unicortical button subpectoral biceps method may provide a surgeon with a safe and technically easy and reproducible technique while providing similar biomechanical properties to a known standard implant. Copyright © 2013 Arthroscopy Association of North America. Published by Elsevier Inc. All rights

  15. Discrete element modelling of screw conveyor-mixers

    Directory of Open Access Journals (Sweden)

    Jovanović Aca

    2015-01-01

    Full Text Available Screw conveyors are used extensively in food, plastics, mineral processing, agriculture and processing industries for elevating and/or transporting bulk materials over short to medium distances. Despite their apparent simplicity in design, the transportation action is very complex for design and constructors have tended to rely heavily on empirical performance data. Screw conveyor performance is affected by its operating conditions (such as: the rotational speed of the screw, the inclination of the screw conveyor, and its volumetric fill level. In this paper, horizontal, several single-pitch screw conveyors with some geometry variations in screw blade was investigated for mixing action during transport, using Discrete Element Method (DEM. The influence of geometry modifications on the performance of screw conveyor was examined, different screw designs were compared, and the effects of geometrical variations on mixing performances during transport were explored. During the transport, the particle tumbles down from the top of the helix to the next free surface and that segment of the path was used for auxiliary mixing action. The particle path is dramatically increased with the addition of three complementary helices oriented in the same direction as screw blades (1458.2 mm compared to 397.6 mm in case of single flight screw conveyor Transport route enlarges to 1764.4 mm, when installing helices oriented in the opposite direction from screw blades. By addition of straight line blade to single flight screw conveyor, the longest particle path is being reached: 2061.6 mm [Projekat Ministarstva nauke Republike Srbije, br. TR-31055

  16. Double insurance transfacetal screws for lumbar spinal stabilization

    Directory of Open Access Journals (Sweden)

    Atul Goel

    2014-01-01

    Full Text Available Aim: The authors report experience with 14 cases where two screws or ′′double insurance′′ screws were used for transfacetal fixation of each joint for stabilization of the lumbar spinal segment. The anatomical subtleties of the technique of insertion of screws are elaborated. Materials and Methods: During the period March 2011 to June 2014, 14 patients having lumbar spinal segmental instability related to lumbar canal stenosis were treated by insertion of two screws into each articular assembly by transfacetal technique. After a wide surgical exposure, the articular cartilage was denuded and bone chips were impacted into the joint cavity. For screw insertion in an appropriate angulation, the spinous process was sectioned at its base. The screws (2.8 mm in diameter and 18 mm in length were inserted into the substance of the medial or inferior articular facet of the rostral vertebra via the lateral limit of the lamina approximately 6-8 mm away from the edge of the articular cavity. The screws were inserted 3 mm below the superior edge and 5 mm above the inferior edge of the medial (inferior facets and directed laterally and traversed through the articular cavity into the lateral (superior articular facet of the caudal vertebra toward and into the region of junction of base of transverse process and of the pedicle. During the period of follow-up all treated spinal levels showed firm bone fusion. There was no complication related to insertion of the screws. There was no incidence of screw misplacement, displacementor implant rejection. Conclusions: Screw insertion into the firm and largely cortical bones of facets of lumbar spine can provide robust fixation and firm stabilization of the spinal segment. The large size of the facets provides an opportunity to insert two screws at each spinal segment. The firm and cortical bone material and absence on any neural or vascular structure in the course of the screw traverse provides strength and

  17. Comments on TNT Equivalence

    Energy Technology Data Exchange (ETDEWEB)

    Cooper, P.W.

    1994-07-01

    The term ``TNT Equivalence`` is used throughout the explosives and related industries to compare the effects of the output of a given explosive to that of TNT. This is done for technical design reasons in scaling calculation such as for the prediction of blast waves, craters, and structural response, and is also used as a basis for government regulations controlling the shipping, handling and storage of explosive materials, as well as for the siting and design of explosive facilities. TNT equivalence is determined experimentally by several different types of tests, the most common of which include: plate dent, ballistic mortar, trauzl, sand crush, and air blast. All of these tests do not necessarily measure the same output property of the sample explosive. As examples of this, some tests depend simply upon the CJ pressure, some depend upon the PV work in the CJ zone and in the Taylor wave behind the CJ plane, some are functions of the total work which includes that from secondary combustion in the air mixing region of the fireball and are acutely effected by the shape of the pressure-time profile of the wave. Some of the tests incorporate systematic errors which are not readily apparent, and which have a profound effect upon skewing the resultant data. Further, some of the tests produce different TNT Equivalents for the same explosive which are a function of the conditions at which the test is run. This paper describes the various tests used, discusses the results of each test and makes detailed commentary on what the test is actually measuring, how the results may be interpreted, and if and how these results can be predicted by first principals based calculations. Extensive data bases are referred to throughout the paper and used in examples for each point in the commentaries.

  18. Magnet management in electric machines

    Energy Technology Data Exchange (ETDEWEB)

    Reddy, Patel Bhageerath; El-Refaie, Ayman Mohamed Fawzi; Huh, Kum Kang

    2017-03-21

    A magnet management method of controlling a ferrite-type permanent magnet electrical machine includes receiving and/or estimating the temperature permanent magnets; determining if that temperature is below a predetermined temperature; and if so, then: selectively heating the magnets in order to prevent demagnetization and/or derating the machine. A similar method provides for controlling magnetization level by analyzing flux or magnetization level. Controllers that employ various methods are disclosed. The present invention has been described in terms of specific embodiment(s), and it is recognized that equivalents, alternatives, and modifications, aside from those expressly stated, are possible and within the scope of the appending claims.

  19. Magnet management in electric machines

    Science.gov (United States)

    Reddy, Patel Bhageerath; El-Refaie, Ayman Mohamed Fawzi; Huh, Kum Kang

    2017-03-21

    A magnet management method of controlling a ferrite-type permanent magnet electrical machine includes receiving and/or estimating the temperature permanent magnets; determining if that temperature is below a predetermined temperature; and if so, then: selectively heating the magnets in order to prevent demagnetization and/or derating the machine. A similar method provides for controlling magnetization level by analyzing flux or magnetization level. Controllers that employ various methods are disclosed. The present invention has been described in terms of specific embodiment(s), and it is recognized that equivalents, alternatives, and modifications, aside from those expressly stated, are possible and within the scope of the appending claims.

  20. SHEARING STRENGTH TEST OF ORTOPEDIC TITANIUM ALLOY SCREW PRODUCED IN THE PROCESS OF 3D TECHNOLOGY PRINTING

    Directory of Open Access Journals (Sweden)

    Patrycja Ruszniak

    2016-03-01

    Full Text Available The aim of the present dissertation is the assessment of technical shear resistance (technological shear of orthopedic screw made of titanium alloy Ti6Al4V, produced using incremental technology in the process of 3D printing process. The first part of the work presents incremental techniques in production engineering. The second part of the present work contains specification of the 3D printing process of samples as well as the description of the used material. The fundamental part of the article is composed out of endurance tests for orthopaedic screws as well as the analysis of the obtained results and conclusions. The method of incremental production SLM using SLM 280HL metal printer was used during the technological process. The resistance tests were performed using ZWICK/ROELL Z150 machines. Identical endurance trials were performed for monolithic bars made of titanium alloys (of bar core size made on a wire electric discharge machine Sodick SL600Q for comparative purposes. The obtained test results enabled comparative assessment of the value of shear resistance Rt in the conditions of technological shear. According to the performed tests, the shear resistance Rt of orthopaedic screws is nearly 33% lower than of monolithic bars of the same core size.

  1. Machine Learning

    Energy Technology Data Exchange (ETDEWEB)

    Chikkagoudar, Satish; Chatterjee, Samrat; Thomas, Dennis G.; Carroll, Thomas E.; Muller, George

    2017-04-21

    The absence of a robust and unified theory of cyber dynamics presents challenges and opportunities for using machine learning based data-driven approaches to further the understanding of the behavior of such complex systems. Analysts can also use machine learning approaches to gain operational insights. In order to be operationally beneficial, cybersecurity machine learning based models need to have the ability to: (1) represent a real-world system, (2) infer system properties, and (3) learn and adapt based on expert knowledge and observations. Probabilistic models and Probabilistic graphical models provide these necessary properties and are further explored in this chapter. Bayesian Networks and Hidden Markov Models are introduced as an example of a widely used data driven classification/modeling strategy.

  2. Designing of monitoring setup for vibration signature analysis of steam turbine driven high capacity rotary screw compressor

    Energy Technology Data Exchange (ETDEWEB)

    Pyne, T.; Vinod, J. [Birla VXL Ltd., Porbandar (India)

    1997-12-31

    Tracking the behaviour by signature analysis of machines like Screw Compressor having large number of auxiliaries, high power transmissions, variation of process gas properties, changes of load condition, fluctuating revolutions is truly a challenging job. These unavoidable process conditions often disturb the whole setup and there is every possibility to miss important and relevant information. Standards for overall monitoring as well as for peak-amplitudes responsible for root cause identification are not always available because these machines are `custom designed` and manufacturer`s standards are of paramount importance to consider. The health of these machines cannot be assessed by simply comparing with the international standards unlike most common machines such as fans, pumps, motors etc. with minimum number of auxiliaries. There may also be limitations in the features of the instruments used for the purpose. In this presentation, an attempt has been made to setup a monitoring approach for screw compressor which will help the industries initially setting base-line data to implement vibration analysis based off-line predictive maintenance programme either with the help of an analyser or with a latest software. (orig.) 3 refs.

  3. Load-induced error identification of hydrostatic turntable and its influence on machining accuracy

    Institute of Scientific and Technical Information of China (English)

    程强; 任伟达; 刘志峰; 陈东菊; 顾佩华

    2016-01-01

    In heavy duty machine tools, hydrostatic turntable is often used as a means for providing rotational motion and supporting workpiece, so the accuracy of turntable is crucial for part machining. In order to analyze the influence of load-indcued errors on machining accuracy, an identification model of load-induced errors based on the deformation caused by applied load of hydrostatic turntable of computerized numerical control (CNC) gantry milling heavy machine is proposed. Based on multi-body system theory and screw theory, the space machining accuracy model of heavy duty machine tool is established with consideration of identified load-induced errors. And then, the influence of load-induced errors on space machining accuracy and the roundness error of a milled hole is analyzed. The analysis results show that load-induced errors have a big influence on the roundness error of machined hole, especially when the center of the milled hole is far from that of hydrostatic turntable.

  4. Fluid Flow Phenomenon in a Three-Bladed Power-Generating Archimedes Screw Turbine

    OpenAIRE

    Tineke Saroinsong; Rudy Soenoko; Slamet Wahyudi; Mega N Sasongko

    2016-01-01

    Experimental studies of the Archimedes screw turbine are applied as a micro hydro power plant for low head focused on the fluid flow. Fluid flow on a screw turbine is not completely filled water flow there is still a free surface between the water fluid and atmospheric air. Except the screw geometry, the turbine screw free surface allows the flow phenomena that are important in the process of turbine screw power generation. The Archimedes screw turbine main driving force is the fl...

  5. Fluid Flow Phenomenon in a Three-Bladed Power-Generating Archimedes Screw Turbine

    OpenAIRE

    2016-01-01

    Experimental studies of the Archimedes screw turbine are applied as a micro hydro power plant for low head focused on the fluid flow. Fluid flow on a screw turbine is not completely filled water flow there is still a free surface between the water fluid and atmospheric air. Except the screw geometry, the turbine screw free surface allows the flow phenomena that are important in the process of turbine screw power generation. The Archimedes screw turbine main driving force is the fl...

  6. Theoretical and practical equivalents in multimachine power systems. Part 1: Construction of coherency power systems. Part 1: Construction of coherency based theoretical equivalent

    Energy Technology Data Exchange (ETDEWEB)

    Di Caprio, U.

    1982-10-01

    Taking account of the structural conditions for theoretical coherency, a single machine equivalent circuit is determined. This is an extension of the Thevenin theorem to electromechanic circuits and will be used as the basis for constructing a practical dynamic equivalent in the second part of the paper.

  7. Posterior spinal fusion using pedicle screws.

    Science.gov (United States)

    Athanasakopoulos, Michael; Mavrogenis, Andreas F; Triantafyllopoulos, George; Koufos, Spiros; Pneumaticos, Spiros G

    2013-07-01

    Few clinical studies have reported polyetheretherketone (PEEK) rod pedicle screw spinal instrumentation systems (CD-Horizon Legacy PEEK rods; Medtronic, Minneapolis, Minnesota). This article describes a clinical series of 52 patients who underwent posterior spinal fusion using the PEEK Rod System between 2007 and 2010. Of the 52 patients, 25 had degenerative disk disease, 10 had lateral recess stenosis, 6 had degenerative spondylolisthesis, 6 had lumbar spine vertebral fracture, 4 had combined lateral recess stenosis and degenerative spondylolisthesis, and 1 had an L5 giant cell tumor. Ten patients had 1-segment fusion, 29 had 2-segment fusion, and 13 had 3-segment fusion. Mean follow-up was 3 years (range, 1.5-4 years); no patient was lost to follow-up. Clinical evaluation was performed using the Oswestry Disability Index and a low back and leg visual analog pain scale. Imaging evaluation of fusion was performed with standard and dynamic radiographs. Complications were recorded. Mean Oswestry Disability Index scores improved from 76% preoperatively (range, 52%-90%) to 48% at 6 weeks postoperatively, and to 34%, 28%, and 30% at 3, 6, and 12 months postoperatively, respectively. Mean low back and leg pain improved from 8 and 9 points preoperatively, respectively, to 6 and 5 points immediately postoperatively, respectively, and to 2 points each thereafter. Imaging union of the arthrodesis was observed in 50 (96%) patients by 1-year follow-up. Two patients sustained screw breakage: 1 had painful loss of sagittal alignment of the lumbar spine and underwent revision spinal surgery with pedicle screws and titanium rods and the other had superficial wound infection and was treated with wound dressing changes and antibiotics for 6 weeks. No adjacent segment degeneration was observed in any patient until the time of this writing. Copyright 2013, SLACK Incorporated.

  8. Establishing Substantial Equivalence: Proteomics

    Science.gov (United States)

    Lovegrove, Alison; Salt, Louise; Shewry, Peter R.

    Wheat is a major crop in world agriculture and is consumed after processing into a range of food products. It is therefore of great importance to determine the consequences (intended and unintended) of transgenesis in wheat and whether genetically modified lines are substantially equivalent to those produced by conventional plant breeding. Proteomic analysis is one of several approaches which can be used to address these questions. Two-dimensional PAGE (2D PAGE) remains the most widely available method for proteomic analysis, but is notoriously difficult to reproduce between laboratories. We therefore describe methods which have been developed as standard operating procedures in our laboratory to ensure the reproducibility of proteomic analyses of wheat using 2D PAGE analysis of grain proteins.

  9. Comparison between Bilateral C2 Pedicle Screwing and Unilateral C2 Pedicle Screwing, Combined with Contralateral C2 Laminar Screwing, for Atlantoaxial Posterior Fixation

    OpenAIRE

    Miyakoshi, Naohisa; HONGO, MICHIO; Kobayashi, Takashi; Suzuki, Tetsuya; Abe, Eiji; Shimada, Yoichi

    2014-01-01

    Study Design A retrospective study. Purpose To compare clinical and radiological outcomes between bilateral C2 pedicle screwing (C2PS) and unilateral C2PS, combined with contralateral C2 laminar screwing (LS), for posterior atlantoaxial fixation. Overview of Literature Posterior fixation with C1 lateral mass screwing (C1LMS) and C2PS (C1LMS-C2PS method) is an accepted procedure for rigid atlantoaxial stabilization. However, conventional bilateral C2PS is not always allowed in this method due ...

  10. The fluid–solid coupling analysis of screw conveyor in drilling fluid centrifuge based on ANSYS

    Directory of Open Access Journals (Sweden)

    Hongbin Liu

    2015-09-01

    Full Text Available In the centrifugal separations of drilling fluid, screw conveyor is a critical component to push and separate the sediment. The work performance and structural parameters of conveyor are immediately related to the production capability, the working life and the separating effect of the centrifuge. The existing researches always use the theoretical calculation of the approximate loads to analyze the strength of conveyor, and it cannot reflect the stress situations accurately. In order to ensure the precise mastery of the working performance, this article obtained pressure distribution under working conditions from CFX evaluation and gained equivalent stress and deformation under several load conditions by using the ANSYS Workbench platform to check the strength of conveyor. The results showed that the influence of centrifugal hydraulic pressure was less than that of centrifugal force on the strength and deformation of conveyor. Besides, the maximum equivalent stress occurred at the inside of the feed opening, while the maximum deformation occurred at the conveyor blade edge of taper extremity. Furthermore, whether considered the feed opening or not, the computing model had a great influence on the analysis results, and the simplified loads had a great influence on the deformation analysis results. The methods and results from this article can provide reference for the design and the improvement of screw conveyor.

  11. [Intraosseous screw splinting of mandibular fragments].

    Science.gov (United States)

    Erle, A

    1978-12-01

    Fractures in the frontal region of the mandible may be treated by intra-ossal splinting without the risk of injuring nerves or vessels. Function-stable fixation of the reposited fragments was achieved in 15 patients by means of a transfragmental screw with metric thread. The advantages of this procedure consist in the easy removability of the material and the superfluidity of new developments of material or instruments. As the possibility of early functional treatment prevents the late impairment of the articular function, this procedure is particularly indicated in case of concurrent paramedian and articular fractures.

  12. Machine testning

    DEFF Research Database (Denmark)

    De Chiffre, Leonardo

    This document is used in connection with a laboratory exercise of 3 hours duration as a part of the course GEOMETRICAL METROLOGY AND MACHINE TESTING. The exercise includes a series of tests carried out by the student on a conventional and a numerically controled lathe, respectively. This document...

  13. Representational Machines

    DEFF Research Database (Denmark)

    Petersson, Dag; Dahlgren, Anna; Vestberg, Nina Lager

    to the enterprises of the medium. This is the subject of Representational Machines: How photography enlists the workings of institutional technologies in search of establishing new iconic and social spaces. Together, the contributions to this edited volume span historical epochs, social environments, technological...

  14. Stuttering Equivalence for Parity Games

    CERN Document Server

    Cranen, Sjoerd; Willemse, Tim A C

    2011-01-01

    We study the process theoretic notion of stuttering equivalence in the setting of parity games. We demonstrate that stuttering equivalent vertices have the same winner in the parity game. This means that solving a parity game can be accelerated by minimising the game graph with respect to stuttering equivalence. While, at the outset, it might not be clear that this strategy should pay off, our experiments using typical verification problems illustrate that stuttering equivalence speeds up solving parity games in many cases.

  15. Determination of the of rate cross slip of screw dislocations

    DEFF Research Database (Denmark)

    Vegge, Tejs; Rasmussen, Torben; Leffers, Torben;

    2000-01-01

    The rate for cross slip of screw dislocations during annihilation of screw dipoles in copper is determined by molecular dynamics simulations. The temperature dependence of the rate is seen to obey an Arrhenius behavior in the investigated temperature range: 225-375 K. The activation energy...

  16. Reliability of predictors for screw cutout in intertrochanteric hip fractures

    NARCIS (Netherlands)

    K.M.J. de Bruijn (Kirstin); D. den Hartog (Dennis); W.E. Tuinebreijer (Wim); G.R. Roukema (Gert)

    2012-01-01

    textabstractBackground: Following internal fixation of intertrochanteric hip fractures, tip apex distance, fracture classification, position of the screw in the femoral head, and fracture reduction are known predictors for screw cutout, but the reliability of these measurements is unknown. We invest

  17. KINEMATICS OF 3-DOF PYRAMID MANIPULATOR BY PRINCIPAL SCREWS

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Kinematics of a 3-RPS parallel pyramid manipulator are investigated by principal screw. Firstly, the principal screws are identified by quadric degeneration. The planar conics representing the relations between the pitches and the three linear inputs are described, and the three-dimensional distribution of the axes of all the twists is illustrated. Finally, a numerical example is given successfully.

  18. [Loosening of a Calcaneo-Stop Screw after Trampolining].

    Science.gov (United States)

    Trieb, K; Fingernagel, T; Petershofer, A; Hofstaetter, S G

    2015-06-01

    Flexible flatfoot is a common malalignment in the paediatric population. Arthroereisis with a calcaneo-stop screw is an effective surgical procedure for treating juvenile flexible flatfoot after conservative measures have been fully exploited. In the present report, we describe the case of a loosening of a calcaneo-stop screw in a 12-year-old youth after excessive trampolining.

  19. OPTIMAL DISTAL SCREW ALIGNMENT IN THE GAMMA NAIL

    Institute of Scientific and Technical Information of China (English)

    Ching-KongChao; Chun-ChingHsiao; Po-QuangChen

    2002-01-01

    The effect of stress distribution due to the changes of the distal screw alignment in relation to the Gamma nail and the femoral shaft is thoroughly studied in this paper. Failure of the Gamma nail composite occurs through the cranial aperture of the distal screws and the insertion hole for the lag screw due to nonunion, delayed-union and continued weight-bearing. A three-dimensional finite element model was used to study the fractured femur, the Gamma nail, the lag screw and the distal locking screws. The first and the second distal screws were inserted into the Gamma nail in four different configurations. We found that the stress of the Gamma nail composite was substantially reduced with the two screws configured in the anterior to posterior direction. This alignment can bear greater loading in the more demanding fracture types. In the subtrochanteric fracture or the comminuted fractures at the proximal femur, the optimal alignment of the two distal screws was in the anterior to posterior direction.

  20. USING OF OBJECT-ORIENTED DESIGN PRINCIPLES IN ELECTRIC MACHINES DEVELOPMENT

    OpenAIRE

    Zablodskii, N. N.; V.E. Pliugin; A.N. Petrenko

    2016-01-01

    Purpose. To develop the theoretical basis of electrical machines object-oriented design, mathematical models and software to improve their design synthesis, analysis and optimization. Methodology. We have applied object-oriented design theory in electric machines optimal design and mathematical modelling of electromagnetic transients and electromagnetic field distribution. We have correlated the simulated results with the experimental data obtained by means of the double-stator screw dryer wi...

  1. The Analysis of Soil Resistance During Screw Displacement Pile Installation

    Directory of Open Access Journals (Sweden)

    Krasinski Adam

    2015-02-01

    Full Text Available The application of screw displacement piles (SDP is still increasing due to their high efficiency and many advantages. However, one technological problem is a serious disadvantage of those piles. It relates to the generation of very high soil resistance during screw auger penetration, especially when piles are installed in non-cohesive soils. In many situations this problem causes difficulties in creating piles of designed length and diameter. It is necessary to find a proper method for prediction of soil resistance during screw pile installation. The analysis of screw resistances based on model and field tests is presented in the paper. The investigations were carried out as part of research project, financed by the Polish Ministry of Science and Higher Education. As a result of tests and analyses the empirical method for prediction of rotation resistance (torque during screw auger penetration in non-cohesive subsoil based on CPT is proposed.

  2. On Helical Projection and Its Application in Screw Modeling

    Directory of Open Access Journals (Sweden)

    Riliang Liu

    2014-04-01

    Full Text Available As helical surfaces, in their many and varied forms, are finding more and more applications in engineering, new approaches to their efficient design and manufacture are desired. To that end, the helical projection method that uses curvilinear projection lines to map a space object to a plane is examined in this paper, focusing on its mathematical model and characteristics in terms of graphical representation of helical objects. A number of interesting projective properties are identified in regard to straight lines, curves, and planes, and then the method is further investigated with respect to screws. The result shows that the helical projection of a cylindrical screw turns out to be a Jordan curve, which is determined by the screw's axial profile and number of flights. Based on the projection theory, a practical approach to the modeling of screws and helical surfaces is proposed and illustrated with examples, and its possible application in screw manufacturing is discussed.

  3. The Analysis of Soil Resistance During Screw Displacement Pile Installation

    Science.gov (United States)

    Krasinski, Adam

    2015-02-01

    The application of screw displacement piles (SDP) is still increasing due to their high efficiency and many advantages. However, one technological problem is a serious disadvantage of those piles. It relates to the generation of very high soil resistance during screw auger penetration, especially when piles are installed in non-cohesive soils. In many situations this problem causes difficulties in creating piles of designed length and diameter. It is necessary to find a proper method for prediction of soil resistance during screw pile installation. The analysis of screw resistances based on model and field tests is presented in the paper. The investigations were carried out as part of research project, financed by the Polish Ministry of Science and Higher Education. As a result of tests and analyses the empirical method for prediction of rotation resistance (torque) during screw auger penetration in non-cohesive subsoil based on CPT is proposed.

  4. Ball Screw Actuator Including an Axial Soft Stop

    Science.gov (United States)

    Wingett, Paul T. (Inventor); Forrest, Steven Talbert (Inventor); Abel, Steve (Inventor); Woessner, George (Inventor); Hanlon, Casey (Inventor)

    2016-01-01

    An actuator includes an actuator housing, a ball screw, and an axial soft stop assembly. The ball screw extends through the actuator housing and has a first end and a second end. The ball screw is coupled to receive a drive force and is configured, upon receipt of the drive force, to selectively move in a retract direction and an extend direction. The axial soft stop assembly is disposed within the actuator housing. The axial soft stop assembly is configured to be selectively engaged by the ball screw and, upon being engaged thereby, to translate, with compliance, a predetermined distance in the extend direction, and to prevent further movement of the ball screw upon translating the predetermined distance.

  5. Formation of technical requirements for flexible rotary machine nodes

    Science.gov (United States)

    Bulenkov, Y.; Mikhaylov, A.

    2016-11-01

    The method of parameters determining for the flexible rotary machines and lines and its individual components is described in this article. The method is based on the analysis of the fail safe performance probability. It allows determining the fail safe performance probability for tools, transportation and tool changing device nodes, elements of flexible rotary machine and is based on the analysis of flexible rotor line structure. The relationships between rational flexible rotary line structure and parameters of the individual nodes are shown on the flexible rotor line for the screws processing.

  6. Supermassive screwed cosmic string in dilaton gravity

    Energy Technology Data Exchange (ETDEWEB)

    Bezerra, V B [Departamento de Fisica, Universidade Federal da ParaIba, 58059-970, Joao Pessoa, PB (Brazil); Ferreira, Cristine N [Nucleo de Fisica, Centro Federal de Educacao Tecnologica de Campos, Rua Dr Siqueira, 273-Parque Dom Bosco, 28030-130, Campos dos Goytacazes, RJ (Brazil); Cuesta, H J Mosquera [Instituto de Cosmologia, Relatividade e AstrofIsica (ICRA-BR), Centro Brasileiro de Pesquisas Fisicas, Rua Dr Xavier Sigaud 150, Urca 22290-180, Rio de Janeiro, RJ (Brazil)

    2006-06-21

    The early universe might have undergone phase transitions at energy scales much higher than the one corresponding to the grand unified theories (GUT) scales. At these higher energy scales, the transition at which gravity separated from all other interactions, the so-called Planck era, more massive strings called supermassive cosmic strings could have been produced, with energy of about 10{sup 19} GeV. The dynamics of strings formed with this energy scale cannot be described by means of the weak-field approximation, as in the standard procedure for ordinary GUT cosmic strings. As suggested by string theories, at this extreme energy, gravity may be transmitted by some kind of scalar field (usually called the dilaton) in addition to the tensor field of Einstein's theory of gravity. It is then permissible to tackle the issue regarding the dynamics of supermassive cosmic strings within this framework. With this aim, we obtain the gravitational field of a supermassive screwed cosmic string in a scalar-tensor theory of gravity. We show that for the supermassive configuration, exact solutions of scalar-tensor screwed cosmic strings can be found in connection with the Bogomol'nyi limit. We show that the generalization of Bogomol'nyi arguments to the Brans-Dicke theory is possible when torsion is present and we obtain an exact solution in this supermassive regime, with the dilaton solution obtained by consistency with internal constraints.

  7. Lumbar pedicle cortical bone trajectory screw

    Institute of Scientific and Technical Information of China (English)

    Song Tengfei; Wellington K Hsu; Ye Tianwen

    2014-01-01

    Objective The purpose of this study was to demonstrate the lumbar pedicle cortical bone trajectory (CBT) screw fixation technique,a new fixation technique for lumbar surgery.Data sources The data analyzed in this review are mainly from articles reported in PubMed published from 1994 to 2014.Study selection Original articles and critical reviews relevant to CBT technique and lumbar pedicle fixation were selected.Results CBT technique was firstly introduced as a new fixation method for lumbar pedicle surgery in 2009.The concepts,morphometric study,biomechanical characteristics and clinical applications of CBT technique were reviewed.The insertional point of CBT screw is located at the lateral point of the pars interarticularis,and its trajectory follows a caudocephalad path sagittally and a laterally directed path in the transverse plane.CBT technique can be used for posterior fixation during lumbar fusion procedures.This technique is a minimally invasive surgery,which affords better biomechanical stability,fixation strength and surgical safety.Therefore,CBT technique has the greatest benefit in lumbar pedicle surgery for patients with osteoporosis and obesity.Conclusion CBT technique is a better alternative option of lumbar pedicle fixation,especially for patients with osteoporosis and obesity.

  8. Asymmetric distribution in twin screw granulation.

    Science.gov (United States)

    Chan Seem, Tim; Rowson, Neil A; Gabbott, Ian; de Matas, Marcel; Reynolds, Gavin K; Ingram, Andy

    2016-09-01

    Positron Emission Particle Tracking (PEPT) was successfully employed to validate measured transverse asymmetry in material distribution in the conveying zones of a Twin Screw Granulator (TSG). Flow asymmetry was established to be a property of the granulator geometry and dependent on fill level. The liquid distribution of granules as a function of fill level was determined. High flow asymmetry at low fill level negatively affects granule nucleation leading to high variance in final uniformity. Wetting of material during nucleation was identified as a critical parameter in determining final granule uniformity and fill level is highlighted as a crucial control factor in achieving this. Flow asymmetry of dry material in conveying zones upstream of binder fluid injection leads to poor non-uniform wetting at nucleation and results in heterogeneous final product. The granule formation mechanism of 60°F kneading blocks is suggested to be primarily breakage of agglomerates formed during nucleation. Optimisation of screw configuration would be required to provide secondary growth. This work shows how fill dependent flow regimes affect granulation mechanisms.

  9. Adding machine and calculating machine

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    In 1642 the French mathematician Blaise Pascal(1623-1662) invented a machine;.that could add and subtract. It had.wheels that each had: 1 to 10 marked off along its circumference. When the wheel at the right, representing units, made one complete circle, it engaged the wheel to its left, represents tens, and moved it forward one notch.

  10. Evaluation the treatment outcomes of intracapsular femoral neck fractures with closed or open reduction and internal fixation by screw in 18-50-year-old patients in Isfahan from Nov 2010 to Nov 2011

    Directory of Open Access Journals (Sweden)

    Mohammad Javdan

    2013-01-01

    Conclusion: This study showed that femoral neck fracture is associated with several complications, especially if open reduction was necessary. So, the surgical method and necessary equipments such as radiolucent bed, C-ARM machine, and implant cannulated screw set should be considered.

  11. Influence of hooks and a lag screw on internal fixation plates for lateral malleolar fracture: a biomechanical and ergonomic study.

    Science.gov (United States)

    Sakai, Rina; Uchino, Masataka; Yoneo, Terumasa; Ohtaki, Yasuaki; Minehara, Hiroaki; Matsuura, Terumasa; Gomi, Tsutomu; Ujihira, Masanobu

    2017-02-23

    For internal fixation of AO classification Type B lateral malleolar fracture, insertion of lag screws into the fracture plane and fixation with a one-third tubular plate as a neutralization plate are the standard treatment procedures. The one-third tubular plate is processed to a hook shape and hung on the distal end of the fibula. In this study, to compare the function of the hook and lag screws of a one-third tubular plate and LCP for osteosynthesis of lateral malleolar fracture, mechanical indices of internal fixation were compared among the one-third tubular plates with lag screws with and without the hook and a locking compression plate. As mechanical tests, a compression test was performed in which compression in the bone axis direction produced by supporting the body weight was simulated, and a torsion test was performed in which external rotation of the bone axis caused by plantar flexion of the ankle joint was simulated. Muscle strength during walking and the force and torque acting on the ankle and knee joints were determined using inverse dynamic analysis. Finite element analysis was performed to analyze the function of hooks and lag screws. The joint reaction force determined by inverse dynamic analysis was adopted as the loading condition of finite element analysis. A stiffness equivalent to that of healthy bone could be achieved by all three internal fixations. It was clarified that the presence of the hook does not make a difference in stiffness. Displacement of the one-third tubular plate was small regardless of the presence or absence of the hook compared with those of locking compression plates. The presence of the hook did not make any difference in stiffness, suggesting that active preparation of the hook is unnecessary. We also clarified that lag screws inhibit displacement.

  12. Genesis machines

    CERN Document Server

    Amos, Martyn

    2014-01-01

    Silicon chips are out. Today's scientists are using real, wet, squishy, living biology to build the next generation of computers. Cells, gels and DNA strands are the 'wetware' of the twenty-first century. Much smaller and more intelligent, these organic computers open up revolutionary possibilities. Tracing the history of computing and revealing a brave new world to come, Genesis Machines describes how this new technology will change the way we think not just about computers - but about life itself.

  13. 基于约束图谱旋量分析方法的调平机构约束设计%Constraint Design of a Leveling Mechanism via a Screw Theory Approach for Constraint Pattern Analysis

    Institute of Scientific and Technical Information of China (English)

    王大志; 何凯; 杜如虚

    2011-01-01

    约束图谱分析方法从自由度和约束的视角处理机械设计问题,由于自由度和约束概念的一般性,因而该方法对机械设计问题具有广泛的指导意义.从刚性机构及机械接口通用设计方法角度,将旋量理论应用于约束图谱分析方法研究,采用纯力旋量表示点接触约束,采用运动旋量表示自由度,给出约束图谱分析几何概念的旋量描述;基于互易旋量,提出自由度超平面的概念,用以描述点接触约束的单向性,给出并联机构自由度分析及串联机构约束分析方法;在此基础上,提出自由度线等价原则及自由度约束互补原则的代数基础,由此形成集成几何概念的约束图谱旋量分析方法.以光刻机调平机构为例开展应用研究,指出常用2-SPS&1-SP调平机构欠约束和欠确定运动问题,进而提出1-PSV&1-PSE&1-S调平机构,介绍约束图谱旋量分析方法在机构约束设计问题中的应用.%Constraint pattern analysis handles the mechanical design problem from a viewpoint of freedom and constraint, because of the generality for the concept of freedom and constraint, the method is a wide guide for machine design. From a viewpoint of a general design method for rigid mechanisms and mechanical interfaces, screw theory is applied in constraint pattern analysis. Point contact constraint and degree of freedom are denoted as a pure wrench and a twist, respectively. The geometrical concept for constraint pattern analysis is provided. The freedom hyper-plane is presented via reciprocal screw, and the analytical approach for freedom of parallel connections and constraint of serial connections are provided. The screw algebra basis for the equivalence rule for a freedom line and the rule of complementary pattern are proposed, a screw theory approach for constraint pattern analysis is formed. The application for the approach is carried out by a leveling mechanism for an optical projection exposure machine

  14. Why scalar-tensor equivalent theories are not physically equivalent?

    CERN Document Server

    Sk., Nayem

    2016-01-01

    Whether Jordan's and Einstein's frame descriptions of F(R) theory of gravity are physically equivalent, is a long standing debate. However, none questioned on true mathematical equivalence, since classical field equations may be translated from one frame to the other following a transformation relation. Nevertheless, true mathematical equivalence is only established, if all the mathematical results derived from one frame may be translated to the other. Here we show that, neither Noether equations, nor quantum equations may be translated from one frame to the other. The reason being the momenta can't be translated. This appears to be the cause for dynamical in-equivalence.

  15. Positioning of pedicle screws in adolescent idiopathic scoliosis using electromyography

    Directory of Open Access Journals (Sweden)

    Bruno Moreira Gavassi

    2015-06-01

    Full Text Available OBJECTIVE: To analyze the occurrence of poor positioning of pedicle screws inserted with the aid of intraoperative electromyographic stimulation in the treatment of Adolescent Idiopathic Scoliosis (AIS.METHODS: This is a prospective observational study including all patients undergoing surgical treatment for AIS, between March and December 2013 at a single institution. All procedures were monitored by electromyography of the inserted pedicle screws. The position of the screws was evaluated by assessment of postoperative CT and classified according to the specific AIS classification system.RESULTS: Sixteen patients were included in the study, totalizing 281 instrumented pedicles (17.5 per patient. No patient had any neurological deficit or complaint after surgery. In the axial plane, 195 screws were found in ideal position (69.4% while in the sagittal plane, 226 screws were found in ideal position (80.4%. Considering both the axial and the sagittal planes, it was observed that 59.1% (166/281 of the screws did not violate any cortical wall.CONCLUSION: The use of pedicle screws proved to be a safe technique without causing neurological damage in AIS surgeries, even with the occurrence of poor positioning of some implants.

  16. Engineering Aspects of Single- and Twin-screw Extrusion-cooking of Biopolymers

    NARCIS (Netherlands)

    Zuilichem, D.J. van; Stolp, W.; Janssen, L.P.B.M.

    1983-01-01

    A survey is given of the properties of single- and twin-screw extruders. The influence on the design of the different leakage gaps existing in co-rotating, counter-rotating, self-wiping, twin-screw extruders and single-screw equipment is discussed. The mixing effects in single- and twin-screw equipm

  17. Comparison of expansive pedicle screw and polymethylmethacrylate-augmented pedicle screw in osteoporotic sheep lumbar vertebrae: biomechanical and interfacial evaluations.

    Directory of Open Access Journals (Sweden)

    Da Liu

    Full Text Available BACKGROUND: It was reported that expansive pedicle screw (EPS and polymethylmethacrylate-augmented pedicle screw (PMMA-PS could be used to increase screw stability in osteoporosis. However, there are no studies comparing the two kinds of screws in vivo. Thus, we aimed to compare biomechanical and interfacial performances of EPS and PMMA-PS in osteoporotic sheep spine. METHODOLOGY/PRINCIPAL FINDINGS: After successful induction of osteoporotic sheep, lumbar vertebrae in each sheep were randomly divided into three groups. The conventional pedicle screw (CPS was inserted directly into vertebrae in CPS group; PMMA was injected prior to insertion of CPS in PMMA-PS group; and the EPS was inserted in EPS group. Sheep were killed and biomechanical tests, micro-CT analysis and histological observation were performed at both 6 and 12 weeks post-operation. At 6-week and 12-week, screw stabilities in EPS and PMMA-PS groups were significantly higher than that in CPS group, but there were no significant differences between EPS and PMMA-PS groups at two study periods. The screw stability in EPS group at 12-week was significantly higher than that at 6-week. The bone trabeculae around the expanding anterior part of EPS were more and denser than that in CPS group at 6-week and 12-week. PMMA was found without any degradation and absorption forming non-biological "screw-PMMA-bone" interface in PMMA-PS group, however, more and more bone trabeculae surrounded anterior part of EPS improving local bone quality and formed biological "screw-bone" interface. CONCLUSIONS/SIGNIFICANCE: EPS can markedly enhance screw stability with a similar effect to the traditional method of screw augmentation with PMMA in initial surgery in osteoporosis. EPS can form better biological interface between screw and bone than PMMA-PS. In addition, EPS have no risk of thermal injury, leakage and compression caused by PMMA. We propose EPS has a great application potential in augmentation of

  18. Simulating Turing machines on Maurer machines

    NARCIS (Netherlands)

    Bergstra, J.A.; Middelburg, C.A.

    2008-01-01

    In a previous paper, we used Maurer machines to model and analyse micro-architectures. In the current paper, we investigate the connections between Turing machines and Maurer machines with the purpose to gain an insight into computability issues relating to Maurer machines. We introduce ways to

  19. Environmentally Friendly Machining

    CERN Document Server

    Dixit, U S; Davim, J Paulo

    2012-01-01

    Environment-Friendly Machining provides an in-depth overview of environmentally-friendly machining processes, covering numerous different types of machining in order to identify which practice is the most environmentally sustainable. The book discusses three systems at length: machining with minimal cutting fluid, air-cooled machining and dry machining. Also covered is a way to conserve energy during machining processes, along with useful data and detailed descriptions for developing and utilizing the most efficient modern machining tools. Researchers and engineers looking for sustainable machining solutions will find Environment-Friendly Machining to be a useful volume.

  20. An obstacle to building a time machine

    Science.gov (United States)

    Carroll, Sean M.; Farhi, Edward; Guth, Alan H.

    1992-01-01

    Gott (1991) has shown that a spacetime with two infinite parallel cosmic strings passing each other with sufficient velocity contains closed timelike curves. An attempt to build such a time machine is discussed. Using the energy-momentum conservation laws in the equivalent (2 + 1)-dimensional theory, the spacetime representing the decay of one gravitating particle into two is explicitly constructed; there is never enough mass in an open universe to build the time machine from the products of decays of stationary particles. More generally, the Gott time machine cannot exist in any open (2 + 1)-dimensional universe for which the total momentum is timelike.

  1. A power recirculating test rig for ball screw endurance tests

    Directory of Open Access Journals (Sweden)

    Giberti Hermes

    2016-01-01

    Full Text Available A conceptual design of an innovative test rig for endurance tests of ball screws is presented in this paper. The test rig layout is based on the power recirculating principle and it also allows to overtake the main critical issues of the ball screw endurance tests. Among these there are the high power required to make the test, the lengthy duration of the same and the high loads between the screw and the frame that holds it. The article describes the test rig designed scheme, the kinematic expedients to be adopted in order to obtain the required performance and functionality and the sizing procedure to choose the actuation system.

  2. Electromagnetic Lead Screw for Potential Wave Energy Application

    DEFF Research Database (Denmark)

    Lu, Kaiyuan; Wu, Weimin

    2014-01-01

    This paper presents a new type electromagnetic lead screw (EMLS) intended for wave energy application. Similar to the mechanical lead screw, this electromagnetic version can transfer slow linear motion to high-rotational motion, offering gearing effects. Compared with the existing pure magnetic...... lead screw (MLS) employing permanent magnets only, the new EMLS proposed uses dc current to provide the required helical-shape magnetic field, offering a much simpler, robust structure compared with the MLS. The working principle and the performances of this EMLS are analyzed in this paper. Comparison...

  3. Migration of polyethylene fixation screw after total knee arthroplasty.

    Science.gov (United States)

    Cho, Woo-Shin; Youm, Yoon-Seok

    2009-08-01

    Duracon (Howmedica, Rutherford, NJ) posterior stabilized total knee system has a snap fit locking mechanism of a tibial polyethylene, including an additional locking screw for further fixation of polyethylene. We report 13 cases of locking screw migration from tibial component after Duracon posterior stabilized primary total knee arthroplasty. Among 13 knees, screw migration in 10 asymptomatic cases was incidentally detected during regular follow-up, and they were just observed in the outpatient clinic. Only 3 knees had moderate pain, swelling, and instability, and revision was done on 2 of 3 knees.

  4. Test Research on Special Sucker Rod for Screw Pump

    Institute of Scientific and Technical Information of China (English)

    Zhang Mingyi; Chen Mingzhan; Li Zhi

    2006-01-01

    @@ According to the statistics of straight thread sucker rods' application in screw pump in Daqing Oilfield before2000, the proportion of sucker rods' yearly breakaway reached to 41.6%, taking up 70% of the total wells that were checked. Thus it can be seen that the rods breakaway problem was becoming the main barrier restricting screw pump large-scale population and application. Since then,the development work on the special sucker rods for screw pump had been carried on. Through the analysis on the failure position and failure form of the sucker rods',the following conclusions arepresented:

  5. Noninvasive method for retrieval of broken dental implant abutment screw

    Directory of Open Access Journals (Sweden)

    Jagadish Reddy Gooty

    2014-01-01

    Full Text Available Dental implants made of titanium for replacement of missing teeth are widely used because of ease of technical procedure and high success rate, but are not free of complications and may fail. Fracturing of the prosthetic screw continues to be a problem in restorative practice and great challenge to remove the fractured screw conservatively. This case report describes and demonstrates the technique of using an ultrasonic scaler in the removal of the fracture screw fragment as a noninvasive method without damaging the hex of implants.

  6. Testing statistical hypotheses of equivalence

    CERN Document Server

    Wellek, Stefan

    2010-01-01

    Equivalence testing has grown significantly in importance over the last two decades, especially as its relevance to a variety of applications has become understood. Yet published work on the general methodology remains scattered in specialists' journals, and for the most part, it focuses on the relatively narrow topic of bioequivalence assessment.With a far broader perspective, Testing Statistical Hypotheses of Equivalence provides the first comprehensive treatment of statistical equivalence testing. The author addresses a spectrum of specific, two-sided equivalence testing problems, from the

  7. A Comparison of Different Machine Transliteration Models

    CERN Document Server

    Choi, K; Oh, J; 10.1613/jair.1999

    2011-01-01

    Machine transliteration is a method for automatically converting words in one language into phonetically equivalent ones in another language. Machine transliteration plays an important role in natural language applications such as information retrieval and machine translation, especially for handling proper nouns and technical terms. Four machine transliteration models -- grapheme-based transliteration model, phoneme-based transliteration model, hybrid transliteration model, and correspondence-based transliteration model -- have been proposed by several researchers. To date, however, there has been little research on a framework in which multiple transliteration models can operate simultaneously. Furthermore, there has been no comparison of the four models within the same framework and using the same data. We addressed these problems by 1) modeling the four models within the same framework, 2) comparing them under the same conditions, and 3) developing a way to improve machine transliteration through this com...

  8. Discussion on the Processing and Manufacturing of Screw Conveyor’s Screw Axis%浅谈盾构螺旋输送机螺旋轴的加工制造

    Institute of Scientific and Technical Information of China (English)

    杨永

    2014-01-01

    Screw conveyor is one of the key parts and components of earth pressure balance shield machine to implementing the transportation of sludge and the function of earth pressure balance.In order to reduce the occurrence of failure caused by exces-sive wearing and breaking under the changeable and adverse geological conditions,excellent welding performance of materials is selected and the welding of advanced technology is used to ensure concentricity.These measures together with different measures of wear resistance can improve the performance of screw conveyor and prolong the service life of the screw conveyor.%螺旋输送机作为土压平衡盾构机实现渣土输送及土压平衡功能的关键零部件之一,为了减少其在多变且恶劣地质工况下因过度磨损和断裂而引起故障发生,通过选择焊接性能优良的材料、采用先进的焊接工艺技术保证同心度以及不同的耐磨措施,改善螺旋输送机的性能,达到了延长螺旋输送机使用寿命的效果。

  9. Effect of twin-screw extrusion parameters on mechanical hardness of direct-expanded extrudates

    Indian Academy of Sciences (India)

    M Brnčić; B Tripalo; D Ježek; D Semenski; N Drvar; M Ukrainczyk

    2006-10-01

    Mechanical properties of cereal (starch-based) extrudates are perceived by the final consumer as criteria of quality. We investigate one of the important characteristics of extrudates, mechanical hardness, which is one of the main texture parameters. Texture quality has an influence on taste sensory evaluation, and thus on the acceptability of the product. Characteristics that have great influence on acceptability are crispness, elasticity, hardness and softness. These attributes are narrowly related to, and affected by, the process parameters. A 2-level–4-factor factorial experimental design was used to investigate the influence of temperature of expansion, screw speed, feed moisture content and feed rate, and their interactions, on the mechanical hardness of extrudates. Feed moisture content, screw speed and temperature are found to influence, while feed rate does not have significant effect on extrudate hardness. Mechanical properties of specimens were measured by means of compression testing, based on the concept of nominal stress, using a universal testing machine and special grips that were constructed for this purpose.

  10. Failure Diagnosis System for a Ball-Screw by Using Vibration Signals

    Directory of Open Access Journals (Sweden)

    Won Gi Lee

    2015-01-01

    Full Text Available Recently, in order to reduce high maintenance costs and to increase operating ratio in manufacturing systems, condition-based maintenance (CBM has been developed. CBM is carried out with indicators, which show equipment’s faults and performance deterioration. In this study, indicator signal acquisition and condition monitoring are applied to a ball-screw-driven stage. Although ball-screw is a typical linearly reciprocating part and is widely used in industry, it has not gained attention to be diagnosed compared to rotating parts such as motor, pump, and bearing. First, the vibration-based monitoring method, which uses vibration signal to monitor the condition of a machine, is proposed. Second, Wavelet transform is used to analyze the defect signals in time-frequency domain. Finally, the failure diagnosis system is developed using the analysis, and then its performance is evaluated. Using the system, we estimated the severity of failure and detect the defect position. The low defect frequency (≈58.7 Hz is spread all over the time in the Wavelet-filtered signal with low frequency range. Its amplitude reflects the progress of defect. The defect position was found in the signal with high frequency range (768~1,536 Hz. It was detected from the interval between abrupt changes of signal.

  11. Machine Protection

    CERN Document Server

    Schmidt, R

    2014-01-01

    The protection of accelerator equipment is as old as accelerator technology and was for many years related to high-power equipment. Examples are the protection of powering equipment from overheating (magnets, power converters, high-current cables), of superconducting magnets from damage after a quench and of klystrons. The protection of equipment from beam accidents is more recent. It is related to the increasing beam power of high-power proton accelerators such as ISIS, SNS, ESS and the PSI cyclotron, to the emission of synchrotron light by electron–positron accelerators and FELs, and to the increase of energy stored in the beam (in particular for hadron colliders such as LHC). Designing a machine protection system requires an excellent understanding of accelerator physics and operation to anticipate possible failures that could lead to damage. Machine protection includes beam and equipment monitoring, a system to safely stop beam operation (e.g. dumping the beam or stopping the beam at low energy) and an ...

  12. Saponification equivalent of dasamula taila.

    Science.gov (United States)

    Saxena, R B

    1994-07-01

    Saponification equivalent values of Dasamula taila are very useful for the technical and analytical work. It gives the mean molecular weight of the glycerides and acids present in Dasamula Taila. Saponification equivalent values of Dasamula taila are reported in different packings.

  13. An Intensional Concurrent Faithful Encoding of Turing Machines

    Directory of Open Access Journals (Sweden)

    Thomas Given-Wilson

    2014-10-01

    Full Text Available The benchmark for computation is typically given as Turing computability; the ability for a computation to be performed by a Turing Machine. Many languages exploit (indirect encodings of Turing Machines to demonstrate their ability to support arbitrary computation. However, these encodings are usually by simulating the entire Turing Machine within the language, or by encoding a language that does an encoding or simulation itself. This second category is typical for process calculi that show an encoding of lambda-calculus (often with restrictions that in turn simulates a Turing Machine. Such approaches lead to indirect encodings of Turing Machines that are complex, unclear, and only weakly equivalent after computation. This paper presents an approach to encoding Turing Machines into intensional process calculi that is faithful, reduction preserving, and structurally equivalent. The encoding is demonstrated in a simple asymmetric concurrent pattern calculus before generalised to simplify infinite terms, and to show encodings into Concurrent Pattern Calculus and Psi Calculi.

  14. 滚珠丝杠副静力学特性分析%Analysis on statics characteristic of ball screw

    Institute of Scientific and Technical Information of China (English)

    翁健光; 袁军堂; 汪振华; 夏亮亮

    2012-01-01

    Based on the Hertz Contact Theory, the mathematical model of the ball screw's axial contact deformation and stiffness is established considering the factor of lead angle and using traversal method to calculate the dimensionless contact displacement. The calculation results show that the axial contact deformation of double nut ball screw than nut ball screw reduces by 60% , stiffness increases by 80% , increasing the lead angle is helpful to improve the positional accuracy of machine.%以赫兹接触理论为基础,考虑螺旋角的影响,通过遍历法计算量纲为1的接触位移,建立滚珠丝杠副轴向接触变形与刚度的数学模型.计算结果表明:双螺母滚珠丝杠副的轴向接触变形量比单螺母的减小60%,刚度提高80%,增大螺旋角,有利于提高机床进给系统的定位精度.

  15. Centrifuging Step-Screw Conveyor for Regolith Project

    Data.gov (United States)

    National Aeronautics and Space Administration — A variety of ISRU operations will utilize lunar regolith as feedstock. The proposed centrifuging step-screw conveyor concept will provide a well controlled robust,...

  16. Kinematic analysis of parallel manipulators by algebraic screw theory

    CERN Document Server

    Gallardo-Alvarado, Jaime

    2016-01-01

    This book reviews the fundamentals of screw theory concerned with velocity analysis of rigid-bodies, confirmed with detailed and explicit proofs. The author additionally investigates acceleration, jerk, and hyper-jerk analyses of rigid-bodies following the trend of the velocity analysis. With the material provided in this book, readers can extend the theory of screws into the kinematics of optional order of rigid-bodies. Illustrative examples and exercises to reinforce learning are provided. Of particular note, the kinematics of emblematic parallel manipulators, such as the Delta robot as well as the original Gough and Stewart platforms are revisited applying, in addition to the theory of screws, new methods devoted to simplify the corresponding forward-displacement analysis, a challenging task for most parallel manipulators. Stands as the only book devoted to the acceleration, jerk and hyper-jerk (snap) analyses of rigid-body by means of screw theory; Provides new strategies to simplify the forward kinematic...

  17. Biomechanical analysis of titanium fixation plates and screws in ...

    African Journals Online (AJOL)

    Key words: Bone plates, bone screws, finite element analysis, jaw fixation techniques, mandible, mandibular .... model is built up, in similar way to building block construction, .... shows advantages, such as granting intraoral route, minimal.

  18. Lumbar pedicle screw placement: Using only AP plane imaging

    Directory of Open Access Journals (Sweden)

    Anil Sethi

    2012-01-01

    Conclusion: Placement of pedicle screws under fluoroscopic guidance using AP plane imaging alone with tactile guidance is safe, fast, and reliable. However, a good understanding of the radiographic landmarks is a prerequisite.

  19. Screw-matrix method in dynamics of multibody systems

    Science.gov (United States)

    Yanzhu, Liu

    1988-05-01

    In the present paper the concept of screw in classical mechanics is expressed in matrix form, in order to formulate the dynamical equations of the multibody systems. The mentioned method can retain the advantages of the screw theory and avoid the shortcomings of the dual number notation. Combining the screw-matrix method with the tool of graph theory in Roberson/Wittenberg formalism. We can expand the application of the screw theory to the general case of multibody systems. For a tree system, the dynamical equations for each j-th subsystem, composed of all the outboard bodies connected by j-th joint can be formulated without the constraint reaction forces in the joints. For a nontree system, the dynamical equations of subsystems and the kinematical consistency conditions of the joints can be derived using the loop matrix. The whole process of calculation is unified in matrix form. A three-segment manipulator is discussed as an example.

  20. Intermaxillary Fixation Screw Morbidity in Treatment of Mandibular Fractures

    DEFF Research Database (Denmark)

    Florescu, Vlad-Andrei; Kofod, Thomas; Pinholt, Else Marie

    2016-01-01

    Surgery, Rigshospitalet, University Hospital of Copenhagen, Copenhagen, Denmark). The fracture type, radiographic findings, treatment modality, screw type and number, and root damage were recorded. For the outcome comparison, a review of the published data regarding iatrogenic dental root damage caused......Purpose The aim of the present retrospective study was to investigate the morbidity of screws used for intermaxillary fixation (IMF) in the treatment of mandibular fractures. A review of the published data was also performed for a comparison of outcomes. Our hypothesis was that the use of screws...... for IMF of mandibular fractures would result in minimal morbidity. Materials and Methods Patients treated for mandibular fractures from 2007 to 2013, using screws for IMF, using the international diagnosis code for mandibular fracture, DS026, were anonymously selected (Department of Oral and Maxillofacial...

  1. Unitary equivalence of quantum walks

    Energy Technology Data Exchange (ETDEWEB)

    Goyal, Sandeep K., E-mail: sandeep.goyal@ucalgary.ca [School of Chemistry and Physics, University of KwaZulu-Natal, Private Bag X54001, 4000 Durban (South Africa); Konrad, Thomas [School of Chemistry and Physics, University of KwaZulu-Natal, Private Bag X54001, 4000 Durban (South Africa); National Institute for Theoretical Physics (NITheP), KwaZulu-Natal (South Africa); Diósi, Lajos [Wigner Research Centre for Physics, Institute for Particle and Nuclear Physics, H-1525 Budapest 114, P.O.B. 49 (Hungary)

    2015-01-23

    Highlights: • We have found unitary equivalent classes in coined quantum walks. • A single parameter family of coin operators is sufficient to realize all simple one-dimensional quantum walks. • Electric quantum walks are unitarily equivalent to time dependent quantum walks. - Abstract: A simple coined quantum walk in one dimension can be characterized by a SU(2) operator with three parameters which represents the coin toss. However, different such coin toss operators lead to equivalent dynamics of the quantum walker. In this manuscript we present the unitary equivalence classes of quantum walks and show that all the nonequivalent quantum walks can be distinguished by a single parameter. Moreover, we argue that the electric quantum walks are equivalent to quantum walks with time dependent coin toss operator.

  2. Analysis of machining and machine tools

    CERN Document Server

    Liang, Steven Y

    2016-01-01

    This book delivers the fundamental science and mechanics of machining and machine tools by presenting systematic and quantitative knowledge in the form of process mechanics and physics. It gives readers a solid command of machining science and engineering, and familiarizes them with the geometry and functionality requirements of creating parts and components in today’s markets. The authors address traditional machining topics, such as: single and multiple point cutting processes grinding components accuracy and metrology shear stress in cutting cutting temperature and analysis chatter They also address non-traditional machining, such as: electrical discharge machining electrochemical machining laser and electron beam machining A chapter on biomedical machining is also included. This book is appropriate for advanced undergraduate and graduate mechani cal engineering students, manufacturing engineers, and researchers. Each chapter contains examples, exercises and their solutions, and homework problems that re...

  3. 单螺母滚珠丝杠副静刚度可靠性及灵敏度分析%Reliability and sensitivity of static stiffness of single nut ball screw pair

    Institute of Scientific and Technical Information of China (English)

    张义民; 石晏霖; 李常有; 邓强

    2016-01-01

    为提高数控机床整机可靠度,基于赫兹接触理论,对单螺母滚珠丝杠副静刚度可靠性及灵敏度进行研究,利用单螺母滚珠丝杠副的导程、接触角、丝杠公称直径、滚道曲率比、工作载荷等技术参数建立了轴向接触变形的理论模型。根据滚珠丝杠副的轴向接触变形小于加工精度的原则,建立滚珠丝杠副可靠性模型。利用改进一次二阶矩法分析和计算单螺母滚珠丝杠副的可靠度和灵敏度。结果表明:适当增大滚珠丝杠副的导程以及减小滚道曲率比可提高滚珠丝杠副的刚度,减小工作载荷可以降低滚珠丝杠副的轴向接触变形,提高滚珠丝杠副的可靠度。%To improve the reliability of numerical-controlled machine tool, the reliability and sensitivity of static stiffness of single nut ball screw pair were studied. Based on the Hertz Contact Theory, a model of axial contact deformation was established using the lead, contact angle, nominal diameter of ball screw, raceway curvature ratio, working load and other technical parameters of single nut ball screw pair. According to the principle that the inaccuracy of axial contact deformation for nut ball screw pair is less than the machining accuracy, a nut ball screw pair reliability model was established. The reliability and sensitivity of single nut ball screw pair were analyzed and calculated using the modified first order second moment method. The results show that the static stiffness of nut ball screw pair can be improved by increasing the lead of nut ball screw and decreasing the raceway curvature ratio appropriately, and the reliability of nut ball screw pair can be improved by decreasing the working load to reduce axial contact deformation of nut ball screw pair.

  4. Density of Plutonium Turnings Generated from Machining Activities

    Energy Technology Data Exchange (ETDEWEB)

    Gonzales, John Robert [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Vigil, Duane M. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Jachimowski, Thomas A. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Archuleta, Alonso [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Arellano, Gerald Joseph [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Melton, Vince Lee [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2016-10-20

    The purpose of this project was to determine the density of plutonium (Pu) turnings generated from the range of machining activities, using both surrogate material and machined Pu turnings. Verify that 500 grams (g) of plutonium will fit in a one quart container using a surrogate equivalent volume and that 100 grams of Pu will fit in a one quart Savy container.

  5. Study of the Service Reliability of Machines Based on Safety

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    From the point of safety being the basic requirement of machine operation, equivalent failure number, which is employed to replace the actual statistical failure number, is introduced. Calculating theory of service reliability indexes of machines based on safety is developed. The method proposed in this paper can reflect the damage degree of failure.

  6. Optimization design of drilling string by screw coal miner based on ant colony algorithm

    Institute of Scientific and Technical Information of China (English)

    ZHANG Qiang; MAO Jun; DING Fei

    2008-01-01

    It took that the weight minimum and drive efficiency maximal were as double optimizing target,the optimization model had built the drilling string,and the optimization solution was used of the ant colony algorithm to find in progress.Adopted a two-layer search of the continuous space ant colony algorithm with overlapping or variation global ant search operation strategy and conjugated gradient partial ant search operation strategy.The experiment indicates that the spiral drill weight reduces 16.77% and transports the efficiency enhance 7.05% through the optimization design,the ant colony algorithm application on the spiral drill optimized design has provided the basis for the system research screw coal mine machine.

  7. Optimization design of drilling string by screw coal miner based on ant colony algorithm

    Institute of Scientific and Technical Information of China (English)

    ZHANG Qiang; MAO Jun; DING Fei

    2008-01-01

    It took that the weight minimum and drive efficiency maximal were as double optimizing target, the optimization model had built the drilling string, and the optimization solution was used of the ant colony algorithm to find in progress. Adopted a two-layer search of the continuous space ant colony algorithm with overlapping or variation global ant search operation strategy and conjugated gradient partial ant search operation strat-egy. The experiment indicates that the spiral drill weight reduces 16.77% and transports the efficiency enhance 7.05% through the optimization design, the ant colony algorithm application on the spiral drill optimized design has provided the basis for the system re-search screw coal mine machine.

  8. Immediate loading of titanium hexed screw-type implants in the edentulous patient: case report.

    Science.gov (United States)

    Calvo, M P; Muller, E; Garg, A K

    2000-01-01

    Histologic and histomorphometric studies in both animals and humans have shown that more rapid and greater bone-to-implant contact can be achieved with implants that incorporate certain surface characteristics compared with the original machined-surface implants. Such findings are significant because various implant designs may allow the fixtures to sufficiently resist functional loading sooner than originally thought. The case report presented here indicates that immediate loading of hexed titanium screw-type implants in the anterior mandible can lead to successful osseointegration and clinical outcome. The number of implants placed, their distribution, and the type of rigid connection are critical considerations for immediate loading. A bone height that can accommodate dental implants > or = 10 mm long is recommended. Biomechanically, the implants to be immediately loaded must be stable and resistant to macromovement to ensure good osseointegration.

  9. FORWARDER DEPRICIATION ANALYSIS APPLIED TO EQUIVALENT UNIFORM ANNUAL COST

    OpenAIRE

    DANILO SIMÕES; RICARDO GHANTOUS CERVI; PAULO TORRES FENNER

    2013-01-01

    Depreciation is considered a necessary fixed cost to replace a machinery or goods at the end of its useful life thus interfering directly on the Equivalent Annual Cost (EAC). This paper aimed at analyzing different methods used to calculate depreciation over the useful economic life of a Forwarder, a machine used in eucalyptus harvesting process, evaluating the influence of such methods in estimating EAC. Five depreciation methods were evaluated: Straight-line, Declining Balanc...

  10. Rapid prototyping drill guide template for lumbar pedicle screw placement

    Institute of Scientific and Technical Information of China (English)

    LU Sheng; XU Yong-qing; ZHANG Yuan-zhi; LI Yan-bing; SHI Ji-hong; CHEN Guo-ping; CHEN Yu-bing

    2009-01-01

    To develop a novel method of spinal pedical stereotaxy by reverse engineering and rapid prototyping techniques, and to validate its accuracy by experimental and clinical studies. Methods: A 3D reconstruction model for the desired lumbar vertebra was generated by using the Mimics 10.11 software, and the optimal screw size and orientation were determined using the reverse engineering software. Afterwards, a drill template was created by reverse engi-neering principle, whose surface was the antitemplate of the vertebral surface. The drill template and its correspond-ing vertebra were manufactured using the rapid prototyping technique. Results: The accuracy of the drill template was con-firmed by drilling screw trajectory into the vertebral biomodel preoperatively. This method also showed its ability to cus-tomize the placement and size of each screw based on the unique morphology of the lumbar vertebra.The drill tem-plate fits the postural surface of the vertebra very well in the cadaver experiment. Postoperative CT scans for controlling the pedicle bore showed that the personalized template had a high precision in cadaver experiment and clinical application. No misplacement occurred by using the per-sonalized template. During surgery, no additional computer assistance was needed.Conclusions: The authors have developed a novel drill template for lumbar pedicle screw placement with good applicability and high accuracy. The potential use of drill templates to place lumbar pedicle screws is promising. Our methodology appears to provide an accurate technique and trajectory for pedicle screw placement in the lumbar spine.

  11. Pedicle screw fixation against burst fracture of thoracolumbar vertebrae

    Institute of Scientific and Technical Information of China (English)

    L(U) Fu-xin; HUANG Yong; ZHANG Qiang; SHI Feng-lei; ZHAO Dong-sheng; HU Qiao

    2007-01-01

    Objective: To analyze the application of vertebral pedicle screw fixation in the treatment of burst fracture of thoracolumbar vertebrae.Methods: A total of 48 cases (31 males and 17 females, aged from 18-72 years, mean: 41.3 years) with thoracolumbar vertebrae burst fracture were treated by pedicle screw system since January 2004. According to the AO classification of thoracolumbar vertebrae fracture,there are 36 cases of Type A, 9 of Type B and 3 of Type C.Results: All patients were followed up for 6-25 months (average 12 months ), no secondary nerve root injury, spinal cord injury, loosening or breakage of pedicle screw were observed. The nerve function of 29 patients with cauda equina nerve injury was restored to different degrees. The vertebral body height returned to normal level and posterior process angle was rectified after operation.Conclusions: The vertebral pedicle screw internal fixation was technologically applicable, which can efficiently reposition and stablize the bursting fractured vertabrae,indirectly decompress canalis spinalis, maintain spine stablity, scatter stress of screw system, reduce the risk of loosening or breakage of screw and loss of vertebral height,and prevent the formation of posterior convex after operation.

  12. Far cortical locking screws in distal femur fractures.

    Science.gov (United States)

    Adams, John D; Tanner, Stephanie L; Jeray, Kyle J

    2015-03-01

    Distal femur fractures routinely heal by secondary bone healing, which relies on interfragmentary motion. Periarticular locking plates are commonly used for fixation in distal femur fractures but are associated with a high nonunion rate, likely due to the stiffness of the constructs. Far cortical locking (FCL) screws are designed to allow micromotion at the near cortex while maintaining purchase in only the far cortex. Although clinical data are limited, these screws have been shown in biomechanical studies to provide excellent interfragmentary motion, and animal models have shown increased callus formation compared with traditional locking screws. The purpose of this study was to examine the clinical effects that FCL screws have on healing in distal femur fractures treated with locked constructs. In this retrospective case series, 15 patients with a distal femur fracture treated with MotionLoc screws (Zimmer, Warsaw, Indiana) were analyzed. Serial radiographs were evaluated for callus presence and time to union. All fractures were either 33-A3 or 33-C2 according to the AO classification system, and 5 (33%) were open. Bone loss was recorded in 2 patients. There were no nonunions, and average time to union was 24 weeks. There were no implant failures, and all 5 open fractures, including the 2 with bone loss, healed without intervention. There was 1 reoperation due to painful hardware. Although this is a small case series, these results are promising. Far cortical locking screws may provide the answer to the high nonunion rate associated with distal femur fractures treated with traditional locked constructs.

  13. Robot-assisted Anterior Odontoid Screw Fixation: A Case Report.

    Science.gov (United States)

    Tian, Wei; Wang, Han; Liu, Ya-Jun

    2016-08-01

    Anterior odontoid screw fixation has been proved to be effective but technically challenging because the difficult approach is associated with high risks of screw malposition and damage to surrounding vital structures. Navigation techniques are therefore increasingly being used to improve safety and accuracy. However, no robot-assisted odontoid screw fixation has yet been reported. We here report a 61-year-old woman with a type II dens fracture on whom anterior odontoid screw fixation was performed under the guidance of a newly developed robotic system (TiRobot, co-designed by Beijing Jishuitan Hospital and TINAVI Medical Technologies). One odontoid screw was safely and accurately placed, the calculated deviation between the planned and actual positions being 0.9 mm. No intraoperative complications were identified and the patient was discharged on Day 5. Follow-up studies after 2 weeks showed good clinical and radiological results. We believe this is the first reported case of robot-assisted anterior odontoid screw fixation. We consider that complicated procedures can become feasible, safe and accurate using TiRobot systems.

  14. Vectorial Formalism of Polyphase Synchronous Machine With Permanents Magnets

    Directory of Open Access Journals (Sweden)

    Nacéra Bachir Bouiadjra

    2013-04-01

    Full Text Available This paper presents a mathematical model that transforms the real machine to fictitious machines and our goal is to simulate these and see the behavior of these machines in load. The polyphase machines are developed mainly in the field of variable speed drives of high power because increasing the number of phases on the one hand allows to reduce the dimensions of the components in power modulators energy and secondly to improve the operating safety. By a vector approach (vector space, it is possible to find a set of single-phase machine and / or two-phase fictitious equivalent to polyphase synchronous machine. These fictitious machines are coupled electrically and mechanically but decoupled magnetically. This approach leads to introduce the concept of the equivalent machine (multimachine multiconverter system MMS which aims to analyze systems composed of multiple machines (or multiple converters in electric drives. A first classification multimachine multiconverter system follows naturally from MMS formalism. We present an example of a pentaphase (polyphase synchronous machine for a simulation and study the behavior of the machine load

  15. A finite element analysis of the pelvic reconstruction using fibular transplantation fixed with four different rod-screw systems after transplantation fixed with four different rod-screw systems after type Ⅰ resection

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Background The pelvis often needs to be reconstructed after bone tumor resection.A major challenge here for the orthopedic surgeons is to choose a method that gives the best performance which depends upon its biomechanical properties.In this study,a 3-dimensional finite element analysis(FEA)was used to analyze the biomechanical properties of reconstructed pelvis using fibula transplant fixed by four commonly used rod-screw systems.Methods A total pelvic finite-element model including the lumbar-sacral spine and proximal femur was constructed based on the geometry of CT image from a healthy volunteer.Three-dimensional finite element models of different implants including fibula,rod and screw were simulated using ways of solid modeling.Then various reconstructed finite element models were assembled with different finite element implant model and type Ⅰ resected pelvic finite element model.The load of 500 N was imposed vertically onto the superior surface of L3 vertebral body,and the pelvis was fixed in bilateral leg standing positions.FEA was performed to account for the stress distribution on the bones and implants.The pelvis displacement of the different rod-screw fixation methods and the maximum equivalent stress(max EQV)on all nodes and element were figured out to evaluate the advantages and disadvantages of different reconstructive methods.Results Stress concentration in the fibula transplant was extremely high in the reconstructed pelvis,but could be substantially decreased by internal fixation,which partially transferred the stress from the fibula to the rod-screw systems.High stress concentration was also found in the implants,especially in the connection sites between screw and rod.Among the four methods of fixation,a double rod system with L5-S1 pedicle and ilium screws(L5-S1 HR)produced the best performance:least stress concentrations and least total displacement.Conclusion According to the stability and stress concentration,the method of L5-S1 HR

  16. EVALUATION OF PULP AND PAPER MAKING CHARACTERISTICS OF RICE STEM FIBERS PREPARED BY TWIN-SCREW EXTRUDER PULPING

    Directory of Open Access Journals (Sweden)

    Alireza Talebizadeh

    2010-06-01

    Full Text Available Twin-screw extrusion pulping is a new approach to the manufacture of pulp for paper production, designed for non-wood feedstocks. In this research, the production of pulp from rice stem with a newly fabricated twin-screw extruder was investigated. Extrusion pulping of rice stem was conducted following a central composite design using a two-level factorial plan involving three process variables (pretreatment NaOH concentration: 0.4, 0.8, 1.2%; extrusion temperature: 40, 60, 80 oC; and extruder rotational speed: 55, 70, 85 rpm. Responses of pulp and handsheets properties to the process variables were analyzed using statistical software (MINITAB 15. As the results show, pulping of rice stem fiber can be done at a relatively short pretreatment time about 4 hours and a low NaOH concentration about 0.8% by twin-screw extruder with limit extrusion temperature of about 80 oC and extruder rotational speed about 85 rpm. The effect of pretreatment solvent, NaOH, is greatly enhanced by increases in the extrusion temperature. Analysis of the results revealed that this process has suitable potential to be used to obtain a pulp with yields approximately equivalent to neutral sulfite semi-chemical pulping at fixed kappa number, which is applicable for fluting paper and linerboard production.

  17. Fixation strength of biocomposite wedge interference screw in ACL reconstruction: effect of screw length and tunnel/screw ratio. A controlled laboratory study

    Directory of Open Access Journals (Sweden)

    Herrera Antonio

    2010-06-01

    Full Text Available Abstract Background Primary stability of the graft is essential in anterior cruciate ligament surgery. An optimal method of fixation should be easy to insert and provide great resistance against pull-out forces. A controlled laboratory study was designed to test the primary stability of ACL tendinous grafts in the tibial tunnel. The correlation between resistance to traction forces and the cross-section and length of the screw was studied. Methods The tibial phase of ACL reconstruction was performed in forty porcine tibias using digital flexor tendons of the same animal. An 8 mm tunnel was drilled in each specimen and two looped tendons placed as graft. Specimens were divided in five groups according to the diameter and length of the screw used for fixation. Wedge interference screws were used. Longitudinal traction was applied to the graft with a Servohydraulic Fatigue System. Load and displacement were controlled and analyzed. Results The mean loads to failure for each group were 295,44 N (Group 1; 9 × 23 screw, 564,05 N (Group 2; 9 × 28, 614,95 N (Group 3; 9 × 35, 651,14 N (Group 4; 10 × 28 and 664,99 (Group 5; 10 × 35. No slippage of the graft was observed in groups 3, 4 and 5. There were significant differences in the load to failure among groups (ANOVA/P Conclusions Longer and wider interference screws provide better fixation in tibial ACL graft fixation. Short screws (23 mm do not achieve optimal fixation and should be implanted only with special requirements.

  18. Prediction of Deformity Correction by Pedicle Screw Instrumentation in Thoracolumbar Scoliosis Surgery

    Science.gov (United States)

    Kiriyama, Yoshimori; Yamazaki, Nobutoshi; Nagura, Takeo; Matsumoto, Morio; Chiba, Kazuhiro; Toyama, Yoshiaki

    In segmental pedicle screw instrumentation, the relationship between the combinations of pedicle screw placements and the degree of deformity correction was investigated with a three-dimensional rigid body and spring model. The virtual thoracolumbar scoliosis (Cobb’s angle of 47 deg.) was corrected using six different combinations of pedicle-screw placements. As a result, better correction in the axial rotation was obtained with the pedicle screws placed at or close to the apical vertebra than with the screws placed close to the end vertebrae, while the correction in the frontal plane was better with the screws close to the end vertebrae than with those close to the apical vertebra. Additionally, two screws placed in the convex side above and below the apical vertebra provided better correction than two screws placed in the concave side. Effective deformity corrections of scoliosis were obtained with the proper combinations of pedicle screw placements.

  19. Three-dimensional comparison of alternative screw positions versus actual fixation of scaphoid fractures.

    Science.gov (United States)

    Volk, Ido; Gal, Jonathan; Peleg, Eran; Almog, Gil; Luria, Shai

    2017-06-01

    The recommended technique for the fixation of a scaphoid waist fracture involves a headless compression screw placed in the proximal fragment center. This is usually accomplished by placing a longitudinal axis screw as visualized by fluoroscopy. The screw length has been shown to have a biomechanical advantage. An alternative to these options, which has been debated in the literature, is a screw placed perpendicular to the fracture plane and in its center. The perpendicular screw may have a biomechanical advantage despite the fact that it may be shorter. This study examined the differences in location and length in actual patients between a screw in the center of the proximal fragment with a longitudinal axis screw, and the actual fixating screw. These were then compared to a perpendicular axis screw. Pre- and post-operative CT scans of 10 patients with scaphoid waist fractures were evaluated using a 3D computer model. Comparisons were made between the length, location and angle of actual and virtual screw alternatives; namely, a screw along the central third of the proximal fragment (central screw axis) where the scaphoid longitudinal axis was calculated mathematically (longitudinal screw axis) and a screw placed at 90° to the fracture plane and in its center (perpendicular screw axis). The longitudinal axis screw was found to be significantly longer than the other axes (28.3mm). There was a significant difference between the perpendicular axis screw and the location and angle of the other screw axis, but it was only shorter than the longitudinal screw (23.6mm versus 25.5mm for the actual screw; ns.). A computed longitudinal axis screw is longer than a central or actual screw placed longitudinally by visual inspection by the surgeon. Although it needs to be placed using computer assisted (CAS) techniques, it may have the biomechanical advantages of a longer screw in a similar trajectory. The perpendicular screw was found to be significantly different in position

  20. Usefulness of absorbable screws in the Sauvé-Kapandji procedure for rheumatoid wrist reconstruction.

    Science.gov (United States)

    Nakamura, K; Oda, H; Tanaka, S; Kuga, Y; Yamamoto, M; Nishikawa, T; Juji, T; Shimizu, M

    2002-06-01

    Abstract  In the Sauvé-Kapandji (S-K) procedure for rheumatoid wrist reconstruction, the distal end of the ulna is fixed to the radius with screws. Recently, absorbable screws have increasingly been used instead of metal ones. However, the clinical usefulness of absorbable screws in S-K procedures for rheumatoid patients is still unknown. The purpose of this article is to evaluate the effect of absorbable screws in this procedure by comparing their clinical results with those of metal screws. Poly-l-lactic acid (PLLA) absorbable screws were used in 23 wrists, and metal screws were used in 20 wrists. We evaluated the presence of general or local reactions to PLLA, the stability of the ulnar head, the time to bone union, changes in the shape of the distal ulna, and the presence of bone resorption around the screws. There were no complications with the use of PLLA screws, and their fixation stability was adequate to form sufficient bone union. In five cases in the metal screw group, bone resorption around the screws occurred between 1 and 2 years after surgery. Bone resorption around the PLLA screws was not observed. We conclude that absorbable screws may be more useful than metal screws in the S-K procedure for rheumatoid wrist reconstruction.

  1. Biomechanical analysis of pedicle screw density in spinal instrumentation for scoliosis treatment: first results.

    Science.gov (United States)

    Wang, Xiaoyu; Aubin, Carl-Eric; Larson, A Noelle; Labelle, Hubert; Parent, Stefan

    2012-01-01

    Clinical studies reveal remarkable variation in screw patterns, or screw density in spinal instrumentation. Screw density may have a great impact on blood loss, operative time, radiation, risk of screw malposition, and cost. Thus, there is a need to understanding of the biomechanical effects of screw density so as to minimize the number of pedicle screws while ensuring safe and effective instrumentation. The objective of this study was to compare the deformity correction effects and bone-screw loadings of different pedicle screw densities in spinal instrumentation for scoliosis treatment. Spinal instrumentation simulations were performed on three scoliosis patients using 3 screw density patterns (low, preferred, and high screw density) proposed by two experienced surgeons and basic correction techniques: concave rod attachment, rod derotation, apical vertebral derotation, and convex side rod attachment. Simulation results showed that all tested screw densities generated quite similar correction, with differences between the achieved corrections all below 3°. The average bone-screw forces were 244±67N, 214±66 N, and 210±71 N, respectively for low, preferred, and high densities. It remains a complex challenge balancing the benefit of load sharing between more implants with the overconstraints and limited degrees of freedom introduced by the increased number of implants. Studies on additional screw densities and patterns proposed by more surgeons for a variety of cases, and using more diverse correction techniques are necessary to draw stronger conclusions and to recommend the optimal screw density.

  2. Development and Testing of X-Ray Imaging-Enhanced Poly-L-Lactide Bone Screws.

    Directory of Open Access Journals (Sweden)

    Wei-Jen Chang

    Full Text Available Nanosized iron oxide particles exhibit osteogenic and radiopaque properties. Thus, iron oxide (Fe3O4 nanoparticles were incorporated into a biodegradable polymer (poly-L-lactic acid, PLLA to fabricate a composite bone screw. This multifunctional, 3D printable bone screw was detectable on X-ray examination. In this study, mechanical tests including three-point bending and ultimate tensile strength were conducted to evaluate the optimal ratio of iron oxide nanoparticles in the PLLA composite. Both injection molding and 3D printing techniques were used to fabricate the PLLA bone screws with and without the iron oxide nanoparticles. The fabricated screws were implanted into the femoral condyles of New Zealand White rabbits. Bone blocks containing the PLLA screws were resected 2 and 4 weeks after surgery. Histologic examination of the surrounding bone and the radiopacity of the iron-oxide-containing PLLA screws were evaluated. Our results indicated that addition of iron oxide nanoparticles at 30% significantly decreased the ultimate tensile stress properties of the PLLA screws. The screws with 20% iron oxide exhibited strong radiopacity compared to the screws fabricated without the iron oxide nanoparticles. Four weeks after surgery, the average bone volume of the iron oxide PLLA composite screws was significantly greater than that of PLLA screws without iron oxide. These findings suggested that biodegradable and X-ray detectable PLLA bone screws can be produced by incorporation of 20% iron oxide nanoparticles. Furthermore, these screws had significantly greater osteogenic capability than the PLLA screws without iron oxide.

  3. Biopolymer augmentation of the lag screw in the treatment of femoral neck fractures - a biomechanical in-vitro study

    Directory of Open Access Journals (Sweden)

    Paech A

    2010-04-01

    Full Text Available Abstract The cut-out of the sliding screw is one of the most common complications in the treatment of intertrochanteric fractures. The reasons for the cut-out are: a suboptimal position of the hip-screw in the femoral head, the type of fracture and poor bone quality. The aim of this study was to reproduce the cut-out event biomechanically and to evaluate the possible prevention of this event by the use of a biopolymer augmentation of the hip screw. Concerning the density and compression force of osteoporotic femoral bone polyurethane foam according to the terms of the Association for Standard Testing Material (ASTMF 1839-97 was used as test material. The polyurethane foam Lumoltan 200 with a compression force of 3.3 Mpa and a density of 0.192 g/cm3 was used to reproduce the osteoporotic bone of the femoral fragment (density 12 lbm/ft3. A cylinder of 50 mm of length and 50 mm of width was produced by a rotary splint raising procedure with planar contact. The axial load of the system was performed by a hydraulic force cylinder of a universal test machine type Zwick 1455, Ulm, Germany. The CCD-angle of the used TGN-System was preset at 130 degrees. The migration pattern of the hip screw in the polyurethane foam was measured and expressed as a curve of the distance in millimeter [mm] against the applied load in Newton [N] up to the cut-out point. During the tests the implants reached a critical changing point from stable to unstable with an increased load progression of steps of 50 Newton. This unstable point was characterized by an increased migration speed in millimeters and higher descending gradient in the migration curve. This peak of the migration curve served as an indicator for the change of the hip screw position in the simulated bone material. The applied load in the non-augmented implant showed that in this group for a density degree of 12 (0,192 g/cm3 the mean force at the failure point was 1431 Newton (± 52 Newton. In the augmented

  4. Ipsilateral pedicle screw placement with contralateral percutaneous facet screws: Early results with an alternative in lumbar arthrodesis

    Directory of Open Access Journals (Sweden)

    Richard B Rhiew

    2009-03-01

    Full Text Available Richard B Rhiew, Sunil Manjila, Andrew M Lozen, David Hong, Murali Guthikonda, S S RengacharyDepartment of Neurosurgery, Wayne State University, Detroit, MI, USAAbstract: Transforaminal lumbar interbody fusion (TLIF is a widely used method of surgical treatment for a variety of lumbar spinal disorders. Bilateral transpedicular instrumentation is routinely used in conjunction with an interbody graft to provide additional stability. In this technical note, we describe our fusion construct using ipsilateral pedicle screw placement on the side of TLIF and contralateral facet screw placement. We performed this construct at six levels in four patients. Suggested advantages include: low morbidity, small incision and lower cost. Outcomes parameters included radiographic evidence of solid union at four months and improvement in Oswestry Disability Index. A mean improvement from a preoperative score of 73 to 26 after surgery was observed at one-year follow-up. There were no instrument-related complications. In conclusion, this hybrid screw system minimizes contralateral dissection and is an attractive alternative to standard bilateral pedicle screw fixation.Keywords: TLIF, facet screw, pedicle screw, lumbar spine fusion

  5. The influence of screw configuration on the pretreatment performance of a continuous twin screw-driven reactor (CTSR).

    Science.gov (United States)

    Choi, Chang Ho; Um, Byung-Hwan; Oh, Kyeong Keun

    2013-03-01

    A combination of a continuous twin screw-driven reactor (CTSR) and a dilute acid pretreatment was used for the pretreatment of biomass with a high cellulose content and high monomeric xylose hydrolyzate. With the newly modified CTSR screw configuration (Config. 3), the influences of the screw rotational speed (30-60 rpm), of the pretreatment conditions such as acid concentration (1-5%) and reaction temperature (160-175 °C) at the operating condition of biomass feeding rate (1.0 g/min) and acid feeding rate (13.4 mL/min) on the pretreatment performance were investigated. The cellulose content in the pretreated rape straw was 67.1% at the following optimal conditions: barrel temperature of 165 °C, acid concentration of 3.0% (w/v), and screw rotational speed of 30 rpm. According to the three screw configurations, the glucose yields from enzymatic hydrolysis were 70.1%, 72.9%, and 78.7% for screw Configs. 1, 2, and 3, respectively.

  6. Investigation of an 11mm diameter twin screw granulator: Screw element performance and in-line monitoring via image analysis.

    Science.gov (United States)

    Sayin, Ridade; Martinez-Marcos, Laura; Osorio, Juan G; Cruise, Paul; Jones, Ian; Halbert, Gavin W; Lamprou, Dimitrios A; Litster, James D

    2015-12-30

    As twin screw granulation (TSG) provides one with many screw element options, characterization of each screw element is crucial in optimizing the screw configuration in order to obtain desired granule attributes. In this study, the performance of two different screw elements - distributive feed screws and kneading elements - was studied in an 11 mm TSG at different liquid-to-solid (L/S) ratios. The kneading element configuration was found to break large granules more efficiently, leading to narrower granule size distributions. While pharmaceutical industry shifts toward continuous manufacturing, inline monitoring and process control are gaining importance. Granules from an 11 mm TSG were analysed using the Eyecon™, a real-time high speed direct imaging system, which has been used to capture accurate particle size distribution and particle count. The size parameters and particle count were then assessed in terms of their ability to be a suitable control measure using the Shewhart control charts. d10 and particle count were found to be good indicators of the change in L/S ratio. However, d50 and d90 did not reflect the change, due to their inherent variability even when the process is at steady state.

  7. Evaluation of Occipitocervical Arthrodesis Rates with Screw-based Fixation and Osteoinductive Fusion Adjuncts.

    Science.gov (United States)

    Stone, Jeremy G; Panczykowski, David M; Tempel, Zachary J; Tormenti, Matthew; Kanter, Adam S; Okonkwo, David O

    2015-09-01

    not significantly different between adjunct cohorts (local autograft 92%, ICBG 77%, BMP 88%, and combination of ICBG and BMP 83%; p = 0.79). This finding persisted despite adjustment for age, pathology, number of levels instrumented, and attendant procedures. Importantly, neither the presence of arthrodesis nor fusion adjunct was significantly associated with functional outcome in both univariate and adjusted regression models. Additionally, perioperative adverse events occurred in 23% of cases and did not vary significantly in incidence or severity between fusion adjunct cohorts. We present a large series of patients treated for OC instability with rigid fixation utilizing modern segmental screw-based constructs. The use of adjuvant osteoinductive agents (BMP, ICBG, or a combination) produced equivalent rates of arthrodesis, functional outcome, and adverse events compared with use of local autograft alone.

  8. Effect of Crosslinks on the Stability of the Spine and the Pedicle Screw Fixation.

    Science.gov (United States)

    Xiang-Yu, Zhang; Feng, S U; Shi, Yan; Zhi-Min, Zhang; Pei-Nan, Zhang

    2015-06-01

    To evaluate the effect of crosslinks on the stability of the spine and pedicle screws. Compression fracture of the L1 vertebra was produced in 30 fresh thoracic and lumbar vertebrae samples obtained from adult sheep, which were divided into 3 groups (n=10)with lot-drawing method. Four screws were fixed onto the superior and inferior pedicles of vertebral arch close to the fractured vertebrae, with different number of crosslinks (0 in Group A,1 in Group B, and 2 in Group C) on the rods. After fixation, the samples were subject to 10 000 times of fatigue test with 1.5 Hz load on the HY-3080 computer-control electronic universal test machine and HY-1000NM computer-control torsion test machine. The axial compressive stiffness, maximum pullout strength,and range of motion (ROM) of 6 directions, i.e., flexion, extension, left and right lateral bending, and left and right axial rotation of the 3 groups were measured and compared. There were no statistically significant differences in axial compressive stiffness as well as the ROM of flexion, extension, and left and right lateral bending (all P>0.05). The maximum pullout strength was significantly smaller in Group A and Group B than in Group C [(129.56±29.63)N vs.(294.67±23.25) N,P=0.000;(254.02±36.29)vs.(294.67±23.25)N, P=0.006]. The ROM of left axial rotation was the highest in Group A(13.35°±1.06°), followed by Group B(12.23°±1.06°)and Group C (11.04°±0.74°)(F=13.44, P=0.000; Group B vs. Group A, P=0.000; Group B vs. Group C, P=0.001; Group C vs. Group A,P=0.000). The ROM of right axial rotation was also the highest in Group A(13.56°±1.15°), lower in Group B (12.39°±1.01°) and the lowest in Group C (10.81°±0.51°) (F=21.91, P=0.000; Group B vs. Group A,P=0.002; Group B vs. Group C, P=0.001; Group C vs. Group A, P=0.000). Crosslinks may reinforce the pullout strength of the screws and improve the axial stability of the spine.

  9. Automation of printing machine

    OpenAIRE

    Sušil, David

    2016-01-01

    Bachelor thesis is focused on the automation of the printing machine and comparing the two types of printing machines. The first chapter deals with the history of printing, typesettings, printing techniques and various kinds of bookbinding. The second chapter describes the difference between sheet-fed printing machines and offset printing machines, the difference between two representatives of rotary machines, technological process of the products on these machines, the description of the mac...

  10. Pullout performance comparison of novel expandable pedicle screw with expandable poly-ether-ether-ketone shells and cement-augmented pedicle screws.

    Science.gov (United States)

    Aycan, Mehmet Fatih; Tolunay, Tolga; Demir, Teyfik; Yaman, Mesut Emre; Usta, Yusuf

    2017-02-01

    Aim of this study is to assess the pullout performance of various pedicle screws in different test materials. Polyurethane foams (Grade 10 and Grade 40) produced in laboratory and bovine vertebrae were instrumented with normal, cannulated (cemented), novel expandable and normal (cemented) pedicle screws. Test samples were prepared according to the ASTM F543 standard testing protocols and surgical guidelines. To examine the screw placement and cement distribution, anteriosuperior and oblique radiographs were taken from each sample after insertion process was completed. Pullout tests were performed in an Instron 3369 testing device. Load versus displacement graphs were recorded and the ultimate pullout force was defined as the maximum load (pullout strength) sustained before failure of screw. Student's t-test was performed on each group whether the differences between pullout strength of pedicle screws were significant or not. While normal pedicle screws have the lowest pullout strength in all test materials, normal pedicle screws cemented with polymethylmethacrylate exhibit significantly higher pullout performance than others. For all test materials, there is a significant improvement in pullout strength of normal screws by augmentation. While novel expandable pedicle screws with expandable poly-ether-ether-ketone shells exhibited lower pullout performance than normal screws cemented with polymethylmethacrylate, their pullout performances in all groups were higher than the ones of normal and cannulated pedicle screws. For all test materials, although cannulated pedicle screws exhibit higher pullout strength than normal pedicle screws, there are no significant differences between the two groups. The novel expandable pedicle screws with expandable poly-ether-ether-ketone shells may be used instead of normal and cannulated pedicle screws cemented with polymethylmethacrylate due to their good performances.

  11. PEACH POMACE PROCESSING USING TWIN SCREW EXTRUSION

    Directory of Open Access Journals (Sweden)

    Preetam Sarkar

    2014-02-01

    Full Text Available Fruit by-products have found limited applications in the food industry. They have been primarily used as animal feed, applied to agricultural land for soil amendment or composted and applied to farms for growing crops. Some of these disposal methods are not environment friendly, while others are costly. This study was undertaken to examine the possibility of utilizing peach pomace as a source of soluble dietary fiber in expanded extruded food products. Peach pomace was combined with rice flour at four different levels. The four blends were mixed, dried to a moisture level of 13.5% (w/w and ground to flour. These blends were extruded in a twin-screw extruder (Clextral EV-25 at a feed flow rate of 15 kg/h. The extruded products were analyzed for physical and textural properties. The apparent and true densities for the extrudates decreased from 183.93 to 133.94 kg/m3 and 1275.31 to 1171.2 kg/m3, respectively. A linear increase in extrudate porosity (85.11-88.54% and radial expansion ratio (13.5-19.3 and a steady decrease in breaking strength (104-50.74 kPa were observed with increasing peach pomace level in the blends. This study demonstrates the potential of extrusion processing as a tool for fruit by-product utilization, which will not only enhance consumption of soluble dietary fiber but will also increase the overall fruit utilization.

  12. Full Static Output Feedback Equivalence

    Directory of Open Access Journals (Sweden)

    Aristotle G. Yannakoudakis

    2013-01-01

    Full Text Available We present a constructive solution to the problem of full output feedback equivalence, of linear, minimal, time-invariant systems. The equivalence relation on the set of systems is transformed to another on the set of invertible block Bezout/Hankel matrices using the isotropy subgroups of the full state feedback group and the full output injection group. The transformation achieving equivalence is calculated solving linear systems of equations. We give a polynomial version of the results proving that two systems are full output feedback equivalent, if and only if they have the same family of generalized Bezoutians. We present a new set of output feedback invariant polynomials that generalize the breakaway polynomial of scalar systems.

  13. Tissue Engineered Human Skin Equivalents

    Directory of Open Access Journals (Sweden)

    Zheng Zhang

    2012-01-01

    Full Text Available Human skin not only serves as an important barrier against the penetration of exogenous substances into the body, but also provides a potential avenue for the transport of functional active drugs/reagents/ingredients into the skin (topical delivery and/or the body (transdermal delivery. In the past three decades, research and development in human skin equivalents have advanced in parallel with those in tissue engineering and regenerative medicine. The human skin equivalents are used commercially as clinical skin substitutes and as models for permeation and toxicity screening. Several academic laboratories have developed their own human skin equivalent models and applied these models for studying skin permeation, corrosivity and irritation, compound toxicity, biochemistry, metabolism and cellular pharmacology. Various aspects of the state of the art of human skin equivalents are reviewed and discussed.

  14. Analysis on Accuracy of Bias, Linearity and Stability of Measurement System in Ball screw Processes by Simulation

    Directory of Open Access Journals (Sweden)

    Fan-Yun Pai

    2015-11-01

    Full Text Available To consistently produce high quality products, a quality management system, such as the ISO9001, 2000 or TS 16949 must be practically implemented. One core instrument of the TS16949 MSA (Measurement System Analysis is to rank the capability of a measurement system and ensure the quality characteristics of the product would likely be transformed through the whole manufacturing process. It is important to reduce the risk of Type I errors (acceptable goods are misjudged as defective parts and Type II errors (defective parts are misjudged as good parts. An ideal measuring system would have the statistical characteristic of zero error, but such a system could hardly exist. Hence, to maintain better control of the variance that might occur in the manufacturing process, MSA is necessary for better quality control. Ball screws, which are a key component in precision machines, have significant attributes with respect to positioning and transmitting. Failures of lead accuracy and axial-gap of a ball screw can cause negative and expensive effects in machine positioning accuracy. Consequently, a functional measurement system can incur great savings by detecting Type I and Type II errors. If the measurement system fails with respect to specification of the product, it will likely misjudge Type I and Type II errors. Inspectors normally follow the MSA regulations for accuracy measurement, but the choice of measuring system does not merely depend on some simple indices. In this paper, we examine the stability of a measuring system by using a Monte Carlo simulation to establish bias, linearity variance of the normal distribution, and the probability density function. Further, we forecast the possible area distribution in the real case. After the simulation, the measurement capability will be improved, which helps the user classify the measurement system and establish measurement regulations for better performance and monitoring of the precision of the ball screw.

  15. Design and Construction of a Spring Stiffness Testing Machine

    Directory of Open Access Journals (Sweden)

    Olugboji Oluwafemi Ayodeji

    2015-04-01

    Full Text Available A spring stiffness testing machine was produced which differentiates a good spring from bad one using hydraulic principle and locally sourced materials were used to produce at relative low cost and high efficiency. It also categories each spring by stiffness into one of several distinct categories based on its performance under test. This is to ensure that in the final assembly process, springs with similar performance characteristics are mated to ensure a better ride, more précised handling and improved overall vehicle or equipment performance. The construction of the machine involves basically the fabrication process which includes such operation as cutting, benching, welding, grinding, drilling, machining, casting and screw fastening. Taken into consideration under test, were types of compression springs with varying spring loading and their different displacement recorded at different pressures to compare their stiffness.

  16. Machine musicianship

    Science.gov (United States)

    Rowe, Robert

    2002-05-01

    The training of musicians begins by teaching basic musical concepts, a collection of knowledge commonly known as musicianship. Computer programs designed to implement musical skills (e.g., to make sense of what they hear, perform music expressively, or compose convincing pieces) can similarly benefit from access to a fundamental level of musicianship. Recent research in music cognition, artificial intelligence, and music theory has produced a repertoire of techniques that can make the behavior of computer programs more musical. Many of these were presented in a recently published book/CD-ROM entitled Machine Musicianship. For use in interactive music systems, we are interested in those which are fast enough to run in real time and that need only make reference to the material as it appears in sequence. This talk will review several applications that are able to identify the tonal center of musical material during performance. Beyond this specific task, the design of real-time algorithmic listening through the concurrent operation of several connected analyzers is examined. The presentation includes discussion of a library of C++ objects that can be combined to perform interactive listening and a demonstration of their capability.

  17. Sacroiliac secure corridor: analysis for safe insertion of iliosacral screws

    Directory of Open Access Journals (Sweden)

    Henrique Alves Cruz

    2013-08-01

    Full Text Available OBJECTIVE: Posterior pelvic lesions, especially of the sacral-iliac joint, have high mortality and morbidity risks. Definitive fixation is necessary for the joint stabilization, and one option is the sacral percutaneous pinning with screws. Proximity to important structures to this region brings risks to the fixation procedure; therefore, it is important to know the tridimensional anatomy of the pelvis posterior region. Deviations of the surgeon's hand of four degrees may target the screws to those structures; dimorphisms of the upper sacrum and a poor lesion reduction may redound in a screw malpositioning. This study is aimed to evaluate the dimensions of a safe surgical corridor for safe sacroiliac screw insertion and relations with age and sex of the patients. METHOD: One hundred randomly selected pelvis CTs of patients with no pelvic diseases, seen at a tertiary care teaching Hospital. Measurements were made by computer and the safest area for screw insertion was calculated by two methods. The results were expressed in mm (not in degrees, in order to be a further surgical reference. RESULTS: There was a significant size difference in the analyzed sacral vertebra, differing on a wider size in men than in women. There was no significant statistical difference between vertebral size and age. By both methods, a safe area for screw insertion could be defined. CONCLUSION: Age does not influence the width of the surgical corridor. The surgeon has a safe corridor considered narrower when inserting screws in a female pelvis than when in a male one. However, as the smallest vertebra found (feminine was considered for statics, it was concluded that this corridor is 20 mm wide in any direction, taking as a reference the centrum of the vertebra.

  18. Evaluation of roundness error using a new method based on a small displacement screw

    Science.gov (United States)

    Nouira, Hichem; Bourdet, Pierre

    2014-04-01

    In relation to industrial need and the progress of technology, LNE would like to improve the measurement of its primary pressure, spherical and flick standards. The spherical and flick standards are respectively used to calibrate the spindle motion error and the probe which equips commercial conventional cylindricity measuring machines. The primary pressure standards are obtained using pressure balances equipped with rotary pistons with an uncertainty of 5 nm for a piston diameter of 10 mm. Conventional machines are not able to reach such an uncertainty level. That is why the development of a new machine is necessary. To ensure such a level of uncertainty, both stability and performance of the machine are not sufficient, and the data processing should also be done with accuracy less than a nanometre. In this paper, a new method based on the small displacement screw (SDS) model is proposed. A first validation of this method is proposed on a theoretical dataset published by the European Community Bureau of Reference (BCR) in report no 3327. Then, an experiment is prepared in order to validate the new method on real datasets. Specific environment conditions are taken into account and many precautions are considered. The new method is applied to analyse the least-squares circle, minimum zone circle, maximum inscribed circle and minimum circumscribed circle. The results are compared to those done by the reference Chebyshev best-fit method and reveal perfect agreement. The sensibilities of the SDS and Chebyshev methodologies are investigated, and it is revealed that results remain unchanged when the value of the diameter exceeds 700 times the form error.

  19. The differential induction machine: Theory and performance

    Indian Academy of Sciences (India)

    Sumita Sinha; Nirmal K Deb; Nikhil Mondal; Sujit K Biswas

    2008-10-01

    This paper presents the theory and performance of a differential induction machine, which is a special type of induction machine having two shafts projected from the two ends of a single stator. Application of a differential load on the two shafts cause them to run at different speed as a motor, which permits true differential movement and thus can meet the requirements of a differential drive in an electric vehicle. The machine is also capable of regeneration in the differential mode. This paper presents the construction of the above machine and performance of the same based on experimental results from a laboratory prototype. The equivalent circuit of the motor has been presented and verified experimentally.

  20. Electrical machines mathematical fundamentals of machine topologies

    CERN Document Server

    Gerling, Dieter

    2015-01-01

    Electrical Machines and Drives play a powerful role in industry with an ever increasing importance. This fact requires the understanding of machine and drive principles by engineers of many different disciplines. Therefore, this book is intended to give a comprehensive deduction of these principles. Special attention is given to the precise mathematical derivation of the necessary formulae to calculate machines and drives and to the discussion of simplifications (if applied) with the associated limits. The book shows how the different machine topologies can be deduced from general fundamentals, and how they are linked together. This book addresses graduate students, researchers, and developers of Electrical Machines and Drives, who are interested in getting knowledge about the principles of machine and drive operation and in detecting the mathematical and engineering specialties of the different machine and drive topologies together with their mutual links. The detailed - but nevertheless compact - mat...

  1. Preoperative CT planning of screw length in arthroscopic Latarjet.

    Science.gov (United States)

    Hardy, Alexandre; Gerometta, Antoine; Granger, Benjamin; Massein, Audrey; Casabianca, Laurent; Pascal-Moussellard, Hugues; Loriaut, Philippe

    2016-08-25

    The Latarjet procedure has shown its efficiency for the treatment of anterior shoulder dislocation. The success of this technique depends on the correct positioning and fusion of the bone block. The length of the screws that fix the bone block can be a problem. They can increase the risk of non-union if too short or be the cause of nerve lesion or soft tissue discomfort if too long. Suprascapular nerve injuries have been reported during shoulder stabilisation surgery up to 6 % of the case. Bone block non-union depending on the series is found around 20 % of the cases. The purpose of this study was to evaluate the efficiency of this CT preoperative planning to predict optimal screws length. The clinical importance of this study lies in the observation that it is the first study to evaluate the efficiency of CT planning to predict screw length. Inclusion criteria were patients with chronic anterior instability of the shoulder with an ISIS superior to 4. Exclusion criteria were patients with multidirectional instability or any previous surgery on this shoulder. Thirty patients were included prospectively, 11 of them went threw a CT planning, before their arthroscopic Latarjet. Optimal length of both screws was calculated, adding the size of the coracoid at 5 and 15 mm from the tip to the glenoid. Thirty-two-mm screws were used for patients without planning. On a post-operative CT scan with 3D reconstruction, the distance between the screw tip and the posterior cortex was measured. A one-sample Wilcoxon test was used to compare the distance from the tip of the screw to an acceptable positioning of ±2 mm from the posterior cortex. In the group without planning, screw 1 tended to differ from the acceptable positioning: mean 3.44 mm ± 3.13, med 2.9 mm, q1; q3 [0.6; 4.75] p = 0.1118, and screw 2 differed significantly from the acceptable position: mean 4.83 mm ± 4.11, med 3.7 mm, q1; q3 [1.7; 5.45] p = 0.0045. In the group with planning, position of

  2. A biomechanical study of two different pedicle screw methods for fixation in osteoporotic and nonosteoporotic vertebrae.

    Science.gov (United States)

    Higashino, Kosaku; Kim, Jin Hwan; Horton, William C; Hutton, William C

    2012-01-01

    In reconstruction of the osteoporotic spine, patients often show poor outcome because of pedicle screw failure. This study used osteoporotic and nonosteoporotic vertebrae to determine the difference in fixation strength between pedicle screws inserted straight forward and pedicle screws inserted in an upward trajectory toward the superior end plate (i.e., end-plate screws). There is some evidence to suggest that end-plate screws have a strength advantage. The particular focus was on osteoporotic vertebrae. Thirty-three vertebrae (T10-L2) were harvested. The bone mineral density (BMD) was measured: 15 vertebrae were greater than 0.8 g/cm(2) and designated as nonosteoporotic (average BMD 1.146 ± 0.186 g/cm(2)) and 18 vertebrae were designated as osteoporotic (average BMD 0.643 ± 0.088 g/cm(2)). On one pedicle the screw was inserted straight forward and on the other pedicle the screw was inserted as an end-plate screw. The torque of insertion was measured (Proto 6106 torque screwdriver). Using an MTS Mini Bionix, two types of mechanical testing were carried out on each pedicle: (a) cephalocaudad toggling was first carried out to simulate some physiological type loading: 500 cycles at 0.3 Hz, at ±50 N; and (b) then each pedicle screw was pulled out at a displacement rate of 12.5 cm/min.There was no difference in pullout force between the pedicle screws inserted straight forward and the pedicle screws inserted as end-plate screws. This result applies whether the vertebrae were osteoporotic or nonosteoporotic. For both the straight-forward screws and the end-plate screws, a statistically significant correlation was observed between torque of insertion and pullout force. The results of this experiment indicate that pedicle screws inserted as end-plate screws do not provide a strength advantage over pedicle screws inserted straight forward, whether the vertebrae are osteoporotic or not.

  3. Pediatric lumbar pedicle screw placement using navigation templates: A cadaveric study

    Directory of Open Access Journals (Sweden)

    Xing Wang

    2017-01-01

    Full Text Available Background: Pedicle screw technique is commonly used treatment of adult spinal trauma, tumor, degeneration. The application of pedicle screws is very challenging in children because children have a fast growing spine and spinal pedicle morphology of children and adult has large difference. 3 D reconstruction individual navigation templates improve the success rate of pediatric pedicle screw system. This study is aimed to provide a precise method for lumbar spine pedicle screw placement in children using computer-aided design and rapid prototyping technology. Materials and Methods: Computed tomography (CT scans of cadaver specimens of 4 children were obtained, and the raw data were reconstructed using three-dimensional reconstruction software. Pedicle screws were placed using the conventional method or by using individually designed navigation templates based on the principles of reverse engineering and rapid prototyping technology. Results: We evaluated the accuracy of the pedicle screws placed using the two methods by CT scan. Ten navigation templates were designed for placement of 20 lumbar pedicle screws in the navigation group, and CT scan confirmed that all the screws were placed accurately in the corresponding pedicle. Conversely, of the 20 lumbar pedicle screws placed using the conventional method, 3 screws perforated the pedicle. The findings showed that lumbar pedicle screw placement was successful using navigation templates in children. Conclusions: This technique is simple, easy to master, and allows personalized screw placement, thus providing a new and feasible method for lumbar pedicle screw placement in children.

  4. Interfragmentary compression forces of scaphoid screws in a sawbone cylinder model.

    Science.gov (United States)

    Hausmann, J T; Mayr, W; Unger, E; Benesch, T; Vécsei, V; Gäbler, C

    2007-07-01

    Various screws have been developed to stabilise fractures of the scaphoid. Commonly used are the Herbert, the HBS, the 3-mm AO and the Acutrak screws. Not long ago a new screw, the Twin Fix, was introduced. This is cannulated and similar in shape and appearance to the classical Herbert screw. In our test series we compared the maximum achievable compression forces of the Twin Fix screw with that of three other screws (AO, HBS and Acutrak screws). To avoid the variations of density, stiffness and rigidity in natural bone, a polyurethane sawbone-based test setup was used. The test series included 10 screws of each type. The compression force was measured using a special strain gauge. The mean compression force was significantly higher for the Twin Fix screw (8+/-1N) and the Acutrak screw (7.6+/-0.4/0.6N) in relation to the AO screw (6.8+/-1.0/1.4N) and HBS screw (2+/-1N). We found the Twin Fix and Acutrak screws to be promising in the treatment of scaphoid fractures.

  5. Anatomic considerations of costotransverse screw placement in the thoracic spine.

    Science.gov (United States)

    Xu, R; Ebraheim, N A; Ou, Y; Skie, M; Yeasting, R A

    2000-04-01

    Numerous techniques have been reported to restore spinal stability and to correct spinal deformities, including rods with wires/hooks, and rods or plates with pedicular screws. It was thought that posterior fixation of the thoracic spine through the costotransverse joint may be another alternative. Nine cadavers were obtained for study of screw fixation of the costotransverse joint for posterior thoracic instrumentation. The entrance point for screw insertion was designed to be at the posterior center of the clubbed extremity of the transverse process. From this point, a 3-mm drill bit was used to create the screw path penetrating the costotransverse joint and the ventral cortex of the rib. Under direct visualization of the costotransverse joint, the drill bit was directed parallel to the sagittal plane and toward the upper portion of the rib. Measurements included the screw path length and sagittal angulation. Also, the distance between the superior borders of the transverse process and the tubercle of the rib and the anatomic relationship of the drill bit exit to the intercostal vessels and nerves were evaluated. The maximum length of the screw path was found at T1 (19.7 mm), whereas the minimum length was noted at T4-T5 (13.9 mm). This value decreased gradually from T1 to T4-T5, and slightly increased to T10. The larger sagittal angles of the screw path were found at the levels of T1-T4 (78-86 degrees ), whereas the smaller were noted at the levels below T5 (53-61 degrees ). The mean distance between the superior borders of the transverse process and the tubercle of the rib was smaller at T1-T5 (0.2-0.4 mm), and significantly increased to T8 (5. 1 mm), and then slightly decreased to T10. The variation of this parameter was remarkable. All of the exit points for the drill bit were located in the upper half of the rib, and away from the intercostal vessels. The ideal screw orientation is parallel to the sagittal plane, and angled 80-90 degrees relative to the

  6. Laser machining of advanced materials

    CERN Document Server

    Dahotre, Narendra B

    2011-01-01

    Advanced materialsIntroductionApplicationsStructural ceramicsBiomaterials CompositesIntermetallicsMachining of advanced materials IntroductionFabrication techniquesMechanical machiningChemical Machining (CM)Electrical machiningRadiation machining Hybrid machiningLaser machiningIntroductionAbsorption of laser energy and multiple reflectionsThermal effectsLaser machining of structural ceramicsIntrodu

  7. Numerical and experimental study of an Archimedean Screw Generator

    Science.gov (United States)

    Dellinger, G.; Garambois, P.-A.; Dufresne, M.; Terfous, A.; Vazquez, J.; Ghenaim, A.

    2016-11-01

    Finding new, safe and renewable energy is becoming more and more of a priority with global warming. One solution that is gaining popularity is the Archimedean Screw Generator (ASG). This kind of hydroelectric plant allows transforming potential energy of a fluid into mechanical energy and is convenient for low-head hydraulic sites. As it is a new and growing technology, there are few references dealing with their design and performance optimization. The present contribution proposes to investigate experimentally and numerically the ASG performances. The experimental study is performed for various flow conditions and a laboratory scale screw device installed at the fluid mechanics laboratory of the INSA of Strasbourg. The first results show that the screw efficiencies are higher than 80% for various hydraulic conditions. In order to study the structure of 3D turbulent flows and energy losses in a screw, the 3D Navier Stokes equations are solved with the k-w SST turbulence model. The exact geometry of the laboratory-scale screw was used in these simulations. Interestingly, the modeled values of efficiency are in fairly good agreement with experimental results while any friction coefficient is involved.

  8. Treatment of scaphoid waist fractures with the HCS screw

    Directory of Open Access Journals (Sweden)

    Gehrmann, Sebastian V.

    2014-11-01

    Full Text Available The aim of the study was to evaluate the clinical results of the Headless Compression Screw (HCS, Synthes when used for treatment of acute scaphoid waist fractures. The new screw design generates interfragmentary compression with use of a compression sleeve. Twenty-one patients were treated for acute scaphoid waist fractures type B2 with HCS screws. The average time to the final follow-up examination was 12.8 months. All 21 fractures united after a mean time of 7.2 weeks. The mean DASH score was 7.1. The average motion of the wrist in extension was 61°, flexion was 46°, radial abduction reached 25° and the ulnar abduction was 31°. The maximally achieved grip strength was 86% compared to the uninjured side. Treatment of type B2 scaphoid fractures with the Headless Compression Screw showed good functional and radiographic results. The results are similar to those identified using other screw fixation systems.

  9. Percutaneous Iliac Screws for Minimally Invasive Spinal Deformity Surgery

    Directory of Open Access Journals (Sweden)

    Michael Y. Wang

    2012-01-01

    Full Text Available Introduction. Adult spinal deformity (ASD surgeries carry significant morbidity, and this has led many surgeons to apply minimally invasive surgery (MIS techniques to reduce the blood loss, infections, and other peri-operative complications. A spectrum of techniques for MIS correction of ASD has thus evolved, most recently the application of percutaneous iliac screws. Methods. Over an 18 months 10 patients with thoracolumbar scoliosis underwent MIS surgery. The mean age was 73 years (70% females. Patients were treated with multi-level facet osteotomies and interbody fusion using expandable cages followed by percutaneous screw fixation. Percutaneous iliac screws were placed bilaterally using the obturator outlet view to target the ischial body. Results. All patients were successfully instrumented without conversion to an open technique. Mean operative time was 302 minutes and the mean blood loss was 480 cc, with no intraoperative complications. A total of 20 screws were placed successfully as judged by CT scanning to confirm no bony violations. Complications included: two asymptomatic medial breaches at T10 and L5, and one patient requiring delayed epidural hematoma evacuation. Conclusions. Percutaneous iliac screws can be placed safely in patients with ASD. This MIS technique allows for successful caudal anchoring to stress-shield the sacrum and L5-S1 fusion site in long-segment constructs.

  10. Theoretical investigation of flash vaporisation in a screw expander

    Science.gov (United States)

    Vasuthevan, Hanushan; Brümmer, Andreas

    2017-08-01

    In the present study flash vaporisation of liquid injection in a twin screw expander for a Trilateral Flash Cycle (TFC) is examined theoretically. The TFC process comprises a pressure increase in the working fluid, followed by heating the liquid close to boiling point. The hot liquid is injected into the working chamber of a screw expander. During this process the pressure of the liquid drops below the saturation pressure, while the temperature of the liquid remains virtually constant. Hence the liquid is superheated and in a metastable state. The liquid jet seeks to achieve a stable state in thermodynamic equilibrium and is therefore partially vaporised. This effect is referred to as flash vaporisation. Accordingly, a two-phase mixture, consisting of vapour and liquid, exists in the working chamber. Thermodynamic simulations were carried out using water as the working fluid for representative screw expander geometry. The simulations presented are performed from two different aspects during the filling process of a screw expander. The first case is the vaporisation of the injected liquid in a state of thermodynamic equilibrium, whereby the two-phase mixture is treated entirely as a compressible and homogeneous gas. The second case considers flashing efficiency. It describes the quantity of flashed vapour and consists of a liquid and vapour domain. Both models are compared and analysed with respect to the operational behaviour of a screw expander.

  11. Studies on positive conveying in helically channeled single screw extruders

    Directory of Open Access Journals (Sweden)

    L. Pan

    2012-07-01

    Full Text Available A solids conveying theory called double-flight driving theory was proposed for helically channeled single screw extruders. In the extruder, screw channel rotates against static barrel channel, which behaves as cooperative embedded twin-screws for the positive conveying. They turn as two parallel arc plates, between which an arc-plate solid-plug was assumed. By analyzing the forces on the solid-plug in the barrel channel and screw channel, the boundary conditions when the solid-plug is waived of being cut off on barrel wall, were found to have the capacity of the positive conveying. Experimental data were obtained using a specially designed extruder with a helically channeled barrel in the feeding zone and a pressure-adjustable die. The effects of the barrel channel geometry and friction coefficients on the conveying mechanism were presented and compared with the experimental results. The simulations showed that the positive conveying could be achieved after optimizing extruder designs. Compared with the traditional design with the friction-drag conveying, the throughput is higher while screw torque and energy consumption are decreased. Besides, the design criteria of the barrel channel were also discussed.

  12. Screw dislocations in GaN grown by different methods

    Energy Technology Data Exchange (ETDEWEB)

    Liliental-Weber, Z.; Zakharov, D.; Jasinski, J.; O' Keefe, M.A.; Morkoc, H.

    2003-05-27

    A study of screw dislocations in Hydride-Vapor-Phase-Epitaxy (HVPE) template and Molecular-Beam-Epitaxy (MBE) over-layers was performed using Transmission Electron Microscopy (TEM) in plan-view and in cross-section. It was observed that screw dislocations in the HVPE layers were decorated by small voids arranged along the screw axis. However, no voids were observed along screw dislocations in MBE overlayers. This was true both for MBE samples grown under Ga-lean and Ga-rich conditions. Dislocation core structures have been studied in these samples in the plan-view configuration. These experiments were supported by image simulation using the most recent models. A direct reconstruction of the phase and amplitude of the scattered electron wave from a focal series of high-resolution images was applied. It was shown that the core structures of screw dislocations in the studied materials were filled. The filed dislocation cores in an MBE samples were stoichiometric. However, in HVPE materials, single atomic columns show substantial differences in intensities and might indicate the possibility of higher Ga concentration in the core than in the matrix. A much lower intensity of the atomic column at the tip of the void was observed. This might suggest presence of lighter elements, such as oxygen, responsible for their formation.

  13. Screw theoretic view on dynamics of spatially compliant beam

    Institute of Scientific and Technical Information of China (English)

    Xi-lun DING; J.M.SELIG

    2010-01-01

    Beams with spatial compliance can be deformed as bending in a plane,twisting,and extending.In terms of the screw theory on rigid body motions,the concept of"deflection screw"is introduced,a spatial compliant beam theory via the deflection screw is proposed,and the spatial compliance of such a beam system is presented and analysed based on the material theory and fundamental kinematic assumptions.To study the dynamics of the spatially compliant beam,the potential energy and the kinetic energy of the beam are discussed by using the screw theory to obtain the Lagrangian.The Rayleigh-Ritz method is used to compute the vibrational frequencies based on discussions of boundary conditions and shape functions.The eigenfrequencies of the beam with spatial compliance are compared with those of individual deformation cases,pure bending,extension,or torsion.Finally,dynamics of a robot with two spatial compliant links and perpendicular joints is studied using the spatial compliant beam theory.Coupling between the joint rigid body motions and the deformations of spatial compliant links can easily be found in dynamic simulation.The study shows the effectiveness of using the screw theory to deal with the problems of dynamic modeling and analysis of mechanisms with spatially compliant links.

  14. Morita Equivalence for Factorisable Semigroups

    Institute of Scientific and Technical Information of China (English)

    Yu Qun CHEN; K. P. SHUM

    2001-01-01

    Recall that the semigroups S and R are said to be strongly Morita equivalent if there exists a unitary Morita context (S,R,S PR,RQs, <, []) with < and [] surjective. For a factorisable semigroup S, we denote s = {(s1, s2) ∈ S× S | ss1 =ss2,s ∈ S}, S' = S/s and US-FAct= {sM ∈S- Act|SM = M and SHoms(S, M) ≌ M}. We show that, for factorisable semigroups S and R, the categories US-FAct and UR-FAct are equivalent if and only if the semigroups S' and R' are strongly Morita equivalent. Some conditions for a factorisable semigroup to be strongly Morita equivalent to a sandwich semigroup, local units semigroup, monoid and group separately are also given. Moreover, we show that a semigroup S is completely simple if and only if S is strongly Morita equivalent to a group and for any index set I, S SHoms(S,Ⅱi∈ S)→Ⅱi∈S, s t·f→(st)f is an S-isomorphism.

  15. The deleuzian abstract machines

    DEFF Research Database (Denmark)

    Werner Petersen, Erik

    2005-01-01

    production. In Kafka: Toward a Minor Literature, Deleuze and Guatari gave the most comprehensive explanation to the abstract machine in the work of art. Like the war-machines of Virilio, the Kafka-machine operates in three gears or speeds. Furthermore, the machine is connected to spatial diagrams...

  16. Matching of equivalent field regions

    DEFF Research Database (Denmark)

    Appel-Hansen, Jørgen; Rengarajan, S.B.

    2005-01-01

    screen, having the same homogeneous medium on both sides and an impressed current on one aide, an alternative procedure is relevant. We make use of the fact that in the aperture the tangential component of the magnetic field due to the induced currents in the screen is zero. The use of such a procedure......In aperture problems, integral equations for equivalent currents are often found by enforcing matching of equivalent fields. The enforcement is made in the aperture surface region adjoining the two volumes on each side of the aperture. In the case of an aperture in a planar perfectly conducting...... shows that equivalent currents can be found by a consideration of only one of the two volumes into which the aperture plane divides the space. Furthermore, from a consideration of an automatic matching at the aperture, additional information about tangential as well as normal field components...

  17. Teleparallel Equivalent of Lovelock Gravity

    CERN Document Server

    Gonzalez, P A

    2015-01-01

    There is a growing interest in modified gravity theories based on torsion due to these theories prove to exhibit interesting cosmological implications. In this work, inspired by the teleparallel formulation of General Relativity we present its extension to Lovelock Gravity known as the most natural extension of general relativity in higher-dimensional spacetimes. First, we review Teleparallel Equivalent of General Relativity and Teleparallel Equivalent of Gauss-Bonnet Gravity, and then we construct Teleparallel Equivalent of Lovelock Gravity. In order to achieve this goal we use the vielbein and the connection, without imposing the Weitzenb\\"ock connection. Then, we extract the teleparallel formulation of the theory by setting the curvature to be null.

  18. Mathematically Equivalent, Computationally Non-equivalent Formulas and Software Comprehensibility

    Science.gov (United States)

    2016-06-07

    and Software Comprehensibility Marvin J. Goldstein Surface Ship Sonar Department Approved for public release; distribution unlimited Report...equivalent Formulas and Software Comprehensibility 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) Marvin Goldstein...13. SUPPLEMENTARY NOTES NUWC2015 14. ABSTRACT In the development of mathematical software , often the formula that defines the mathematical purpose

  19. Influence of bacterial colonization of the healing screws on peri-implant tissue

    Directory of Open Access Journals (Sweden)

    Simonetta D'Ercole

    2013-06-01

    Conclusion: The healing screws left in situ for a period of 90 days caused a peri-implant inflammation and the presence of periodontal pathogenic bacteria in the peri-implant sulcus, due to the plaque accumulation on screw surfaces.

  20. Instantaneous screws of weight-bearing knee: what can the screws tell us about the knee motion.

    Science.gov (United States)

    Wolf, Alon

    2014-07-01

    There are several ways to represent a given object's motion in a 3D space having 6DOF i.e., three translations and three rotations. Some of the methods that are used are mathematical and do not provide any geometrical insight into the nature of the motion. Screw theory is a mathematical, while at the same time, geometrical method in which the 6DOF motion of an object can be represented. We describe the 6DOF motion of a weight-bearing knee by its screw parameters, that are extracted from 3D Optical Reflective motion capture data. The screw parameters which describe the transformation of the shank with respect to the thigh in each two successive frames, is represented as the instantaneous screw axis of the motion given in its Plücker line coordinate, along with its corresponding pitch and intensity values. Moreover, the Striction curve associated with the motion provides geometrical insight into the nature of the motion and its repeatability. We describe the theoretical background and demonstrate what the screw can tell us about the motion of healthy subjects' knee.

  1. Teleparallel equivalent of Lovelock gravity

    Science.gov (United States)

    González, P. A.; Vásquez, Yerko

    2015-12-01

    There is a growing interest in modified gravity theories based on torsion, as these theories exhibit interesting cosmological implications. In this work inspired by the teleparallel formulation of general relativity, we present its extension to Lovelock gravity known as the most natural extension of general relativity in higher-dimensional space-times. First, we review the teleparallel equivalent of general relativity and Gauss-Bonnet gravity, and then we construct the teleparallel equivalent of Lovelock gravity. In order to achieve this goal, we use the vielbein and the connection without imposing the Weitzenböck connection. Then, we extract the teleparallel formulation of the theory by setting the curvature to null.

  2. Augmentation of Pedicle Screw Fixation with Calcium Phosphate Cement

    Institute of Scientific and Technical Information of China (English)

    YANG Shu-hua; FU De-hao; LI Jin; XU Wei-hua; YANG Cao; YE Zhe-wei; ZUO Xiao-yan

    2004-01-01

    To determine whether a biodegradable calcium phosphate cement(CPC) provides significant augmentation of pedicle screw fixation or not,an in vitro biomechanical study was carried out to evaluate the biomechanical effect of CPC in the restoration and augmentation of pedicle screw fixation.Axial pullout test and cyclic bending resistance test were employed in the experiment,and polymethylmethacrylate (PMMA) was chosen as control.The results demonstrate that the pullout strengths following CPC restoration and augmentation are 74% greater on an average than those of the control group,but less than those of PMMA restoration group and augmentation group respectively (increased by 126% versus control).In cyclic bending resistance test,the CPC augmented screws are found to withstand a greater number of cycles or greater loading with less displacement before loosening,but the augmentation effect of PMMA is greater than that of CPC.

  3. [Midcarpal fusion using break-away compression screw].

    Science.gov (United States)

    Maire, N; Facca, S; Gouzou, S; Liverneaux, P

    2012-02-01

    Indication of midcarpal fusion is SNAC or SLAC wrist grade 3. The main complication of circular plate (most common technique) is non-union. In this context, the purpose of our work was to propose the use of break-away compression screws to decrease the rate of non-union. Our series included ten patients. The fusion was fixed using two break-away compression screws (2mm diameter). No bone graft was used. As assessment, subjective (pain, Quick-DASH) and objective (strength, mobility) criteria were reviewed at follow-up. All the criteria were significantly improved after operation except mobility. Among the complications, we noticed one delayed bone-healing with a good outcome and a radiological consolidation. Midcarpal fusion by dorsal approach using break-away compression screws appears to us a technique of interest, not requiring a bone graft, with good cost effectiveness.

  4. Error Analysis of Robotic Assembly System Based on Screw Theory

    Institute of Scientific and Technical Information of China (English)

    韩卫军; 费燕琼; 赵锡芳

    2003-01-01

    Assembly errors have great influence on assembly quality in robotic assembly systems. Error analysis is directed to the propagations and accumula-tions of various errors and their effect on assembly success.Using the screw coordinates, assembly errors are represented as "error twist", the extremely compact expression. According to the law of screw composition, relative position and orientation errors of mating parts are computed and the necessary condition of assembly success is concluded. A new simple method for measuring assembly errors is also proposed based on the transformation law of a screw.Because of the compact representation of error, the model presented for error analysis can be applied to various part- mating types and especially useful for error analysis of complexity assembly.

  5. Optically driven Archimedes micro-screws for micropump application.

    Science.gov (United States)

    Lin, Chih-Lang; Vitrant, Guy; Bouriau, Michel; Casalegno, Roger; Baldeck, Patrice L

    2011-04-25

    Archimedes micro-screws have been fabricated by three-dimensional two-photon polymerization using a Nd:YAG Q-switched microchip laser at 532nm. Due to their small sizes they can be easily manipulated, and made to rotate using low power optical tweezers. Rotation rates up to 40 Hz are obtained with a laser power of 200 mW, i.e. 0.2 Hz/mW. A photo-driven micropump action in a microfluidic channel is demonstrated with a non-optimized flow rate of 6 pL/min. The optofluidic properties of such type of Archimedes micro-screws are quantitatively described by the conservation of momentum that occurs when the laser photons are reflected on the helical micro-screw surface.

  6. Experimental determination of bone cortex holding power of orthopedic screw

    Directory of Open Access Journals (Sweden)

    Bolliger Neto Raul

    1999-01-01

    Full Text Available Cylindrical specimens of bone measuring 15 mm in diameter were obtained from the lateral cortical layer of 10 pairs of femurs and tibias. A central hole 3.2 mm in diameter was drilled in each specimen. The hole was tapped, and a 4.5 mm cortical bone screw was inserted from the outer surface. The montage was submitted to push-out testing up to a complete strip of the bone threads. The cortical thickness and rupture load were measured, and the shear stress was calculated. The results were grouped according to the bone segment from which the specimen was obtained. The results showed that bone cortex screw holding power is dependent on the bone site. Additionally, the diaphyseal cortical bone tissue is both quantitatively and qualitatively more resistant to screw extraction than the metaphyseal tissue.

  7. Odontoid screw fixation for fresh and remote fractures

    Directory of Open Access Journals (Sweden)

    Rao Ganesh

    2005-01-01

    Full Text Available Fractures of the odontoid process are common, accounting for 10% to 20% of all cervical spine fractures. Odontoid process fractures are classified into three types depending on the location of the fracture line. Various treatment options are available for each of these fracture types and include application of a cervical orthosis, direct anterior screw fixation, and posterior cervical fusion. If a patient requires surgical treatment of an odontoid process fracture, the timing of treatment may affect fusion rates, particularly if direct anterior odontoid screw fixation is selected as the treatment method. For example, type II odontoid fractures treated within the first 6 months of injury with direct anterior odontoid screw fixation have an 88% fusion rate, whereas fractures treated after 18 months have only a 25% fusion rate. In this review, we discuss the etiology, biomechanics, diagnosis, and treatment (including factors affecting fusion such as timing and fracture orientation options available for odontoid process fractures.

  8. 滚珠丝杠副轴向静刚度测试方案研究%Study on Test Program for Axial Static Stiffness of Ball Screw

    Institute of Scientific and Technical Information of China (English)

    李东君

    2011-01-01

    随着滚珠丝杠副向高速、高精度方向发展,对其刚度特性提出了越来越高的要求.研究滚珠丝杠副轴向静刚度测试方案,并设计专用夹具,可以方便地在材料试验机上完成滚珠丝杠副轴向静刚度的测试而不需要增加其他辅助设备.%The demand on ball screw stiffness is increasingly high when it is developed toward high-speed and high-precision direction.The testing program for axis static stiffness of ball screw was studied.A special fixtures was designed.The test can be easily completed in material testing machine without adding other auxiliary equipment.

  9. 准等壁厚螺杆钻具马达断面型线设计%Section Line Designing of Screw Drill Motor with Quasi Thickness Rubber Bush

    Institute of Scientific and Technical Information of China (English)

    李增亮; 姜明云; 禹超; 盛文慧

    2014-01-01

    分析了等壁厚螺杆钻具马达的性能优点和马达金属外壳的加工方法。针对等壁厚螺杆钻具马达金属外壳内表面存在的加工难题,提出了准等壁厚螺杆钻具马达的设计思路。阐述了准等壁厚螺杆钻具马达金属外壳断面型线的绘制方法,并给出了设计实例。试验分析了准等壁厚和等壁厚螺杆钻具马达的性能。结果表明:准等壁厚螺杆钻具马达不仅具有等壁厚螺杆钻具马达的性能优点,还解决了等壁厚螺杆钻具马达金属外壳电解加工的难题。%The performance benefits of the screw drill motor with the uniform thickness rubber bush and the processing methods of the motor metal shell were analyzed.The screw drill motor with quasi thickness rubber bush was proposed to solve the problems of processing the inner sur-face of the metal shell of the screw drill motor with the uniform thickness rubber bush.The draw-ing method of the metal shell cross section type line of the screw drill motor with quasi thickness rubber bush was elaborated and the section line designing of the screw drill motor with quasi thickness rubber bush was given.Finally,the properties of the screw drill motor with quasi thick-ness rubber bush and the screw drill motor with the uniform thickness rubber bush were analy zed.The result shows that the screw drill motor with quasi thickness rubber bush not only has the same performance advantages with the screw drill motor with the uniform thickness rubber bush but also solves the problems of the electrochemical machining of metal shell of the screw drill mo-tor with the uniform thickness rubber bush.

  10. 单螺杆膨化机磨损计算模型建立及分析%Establish ment and analysis of the wear-calculating model for single screw extruder

    Institute of Scientific and Technical Information of China (English)

    孙春一; 石彬

    2011-01-01

    In the high temperature and high pressure extrusion work after a period of timethe single screw extruder produces wear, starting from analyzing wear mechanism, determine the extrusion machine wear form mainly for screw surface and inner surface of cylinder fatigue wear, establish a mathematic model of wear, derive and determine in the wear model the calculation formula of the maximum pressure of flow cutout and extrusion, surface characteristic parameters and the real contact pressure,through example,discuss influence of each parameter to wear and production capacity, the results of analysis have definite effect to design and use of the Single screw Extruder,for extruder wear problem of twin screw and triple screw extruder to lay the foundation.%从分析磨损机理入手,确定膨化机的磨损形式主要为螺杆表面和机筒内表面的疲劳磨损,建立磨损计算数学模型,推导和确定模型中断流挤出状态时的杌头最大压力、表面特性参数和真实接触压力等参数的计算公式.

  11. Free-hand thoracic pedicle screws placed by neurosurgery residents: a CT analysis

    OpenAIRE

    Wang, Vincent Y.; Chin, Cynthia T.; Lu, Daniel C.; Smith, Justin S.; Chou, Dean

    2010-01-01

    Free-hand thoracic pedicle screw placement is becoming more prevalent within neurosurgery residency training programs. This technique implements anatomic landmarks and tactile palpation without fluoroscopy or navigation to place thoracic pedicle screws. Because this technique is performed by surgeons in training, we wished to analyze the rate at which these screws were properly placed by residents by retrospectively reviewing the accuracy of resident-placed free-hand thoracic pedicle screws u...

  12. Biomechanical and histological evaluation of roughened surface titanium screws fabricated by electron beam melting.

    Directory of Open Access Journals (Sweden)

    Jun Yang

    Full Text Available BACKGROUND: Various fabrication methods are used to improve the stability and osseointegration of screws within the host bone. The aim of this study was to investigate whether roughened surface titanium screws fabricated by electron beam melting can provide better stability and osseointegration as compared with smooth titanium screws in sheep cervical vertebrae. METHODS: Roughened surface titanium screws, fabricated by electron beam melting, and conventional smooth surface titanium screws were implanted into sheep for 6 or 12 weeks (groups A and B, respectively. Bone ingrowth and implant stability were assessed with three-dimensional imaging and reconstruction, as well as histological and biomechanical tests. RESULTS: No screws in either group showed signs of loosening. Fibrous tissue formation could be seen around the screws at 6 weeks, which was replaced with bone at 12 weeks. Bone volume/total volume, bone surface area/bone volume, and the trabecular number were significantly higher for a define region of interest surrounding the roughened screws than that surrounding the smooth screws at 12 weeks. Indeed, for roughened screws, trabecular number was significantly higher at 12 weeks than at 6 weeks. On mechanical testing, the maximum pullout strength was significantly higher at 12 weeks than at 6 weeks, as expected; however, no significant differences were found between smooth and roughened screws at either time point. The maximum torque to extract the roughened screws was higher than that required for the smooth screws. CONCLUSIONS: Electron beam melting is a simple and effective method for producing a roughened surface on titanium screws. After 12 weeks, roughened titanium screws demonstrated a high degree of osseointegration and increased torsional resistance to extraction over smooth titanium screws.

  13. Biomechanical and histological evaluation of roughened surface titanium screws fabricated by electron beam melting.

    Science.gov (United States)

    Yang, Jun; Cai, Hong; Lv, Jia; Zhang, Ke; Leng, Huijie; Wang, Zhiguo; Liu, Zhongjun

    2014-01-01

    Various fabrication methods are used to improve the stability and osseointegration of screws within the host bone. The aim of this study was to investigate whether roughened surface titanium screws fabricated by electron beam melting can provide better stability and osseointegration as compared with smooth titanium screws in sheep cervical vertebrae. Roughened surface titanium screws, fabricated by electron beam melting, and conventional smooth surface titanium screws were implanted into sheep for 6 or 12 weeks (groups A and B, respectively). Bone ingrowth and implant stability were assessed with three-dimensional imaging and reconstruction, as well as histological and biomechanical tests. No screws in either group showed signs of loosening. Fibrous tissue formation could be seen around the screws at 6 weeks, which was replaced with bone at 12 weeks. Bone volume/total volume, bone surface area/bone volume, and the trabecular number were significantly higher for a define region of interest surrounding the roughened screws than that surrounding the smooth screws at 12 weeks. Indeed, for roughened screws, trabecular number was significantly higher at 12 weeks than at 6 weeks. On mechanical testing, the maximum pullout strength was significantly higher at 12 weeks than at 6 weeks, as expected; however, no significant differences were found between smooth and roughened screws at either time point. The maximum torque to extract the roughened screws was higher than that required for the smooth screws. Electron beam melting is a simple and effective method for producing a roughened surface on titanium screws. After 12 weeks, roughened titanium screws demonstrated a high degree of osseointegration and increased torsional resistance to extraction over smooth titanium screws.

  14. Posterior atlantoaxial transpedicle screw fixation for traumatic atlatoaxial instability

    Directory of Open Access Journals (Sweden)

    Zheng-lei WANG

    2015-10-01

    Full Text Available Objective To explore the clinical efficacy of posterior atlantoaxial pedicle screw fixation for traumatic atlantoaxial instability. Methods From September 2009 to March 2013, 17 patients with atlantoaxial instability received posterior atlantoaxial pedicle screw fixation. There were 12 males and 5 females, with a mean age of 42 years old (ranged from 19 to 63 years old. Transpedicle screw fixation was employed in 8 patients with atlantoaxial fracture and dislocation, in 2 with traumatic disruption of transverse atlantal ligament, and in 7 with odontoid fracture. The Japanese Orthopaedic Association (JOA score before operation was from 5 to 14, with a mean of 11.2. Preoperative CT, MRI and radiographs, as well as intraoperative screw placement and bone graft were administered in all the patients. Results In all the patients, complete reduction was achieved without injury to the vertebral artery, spinal cord or never root, and they started to be ambulatory on the first day after the operation. The patients were followed up for 6-36 months (mean 21 months, and clinical symptoms were seen to be improved significantly. Imaging reexamination 6 months after the surgery showed satisfactory healing of implanted bone and position of all the screws without loosening of the implant. The mean JOA scores was 15.5(11.0-17.0 twelve months after the operation. Conclusion Atlantoaxial pedicle screw fixation for traumatic atlantoaxial instability is safe and reliable with a favorable clinical result. DOI: 10.11855/j.issn.0577-7402.2015.09.14

  15. Blocking screws for the treatment of distal femur fractures.

    Science.gov (United States)

    Seyhan, Mustafa; Cakmak, Selami; Donmez, Ferdi; Gereli, Arel

    2013-07-01

    Intramedullary nailing is one of the most convenient biological options for treating distal femoral fractures. Because the distal medulla of the femur is wider than the middle diaphysis and intramedullary nails cannot completely fill the intramedullary canal, intramedullary nailing of distal femoral fractures can be difficult when trying to obtain adequate reduction. Some different methods exist for achieving reduction. The purpose of this study was determine whether the use of blocking screws resolves varus or valgus and translation and recurvatum deformities, which can be encountered in antegrade and retrograde intramedullary nailing. Thirty-four patients with distal femoral fractures underwent intramedullary nailing between January 2005 and June 2011. Fifteen patients treated by intramedullary nailing and blocking screws were included in the study. Six patients had distal diaphyseal fractures and 9 had distal diaphyseo-metaphyseal fractures. Antegrade nailing was performed in 7 patients and retrograde nailing was performed in 8. Reduction during surgery and union during follow-up were achieved in all patients with no significant complications. Mean follow-up was 26.6 months. Mean time to union was 12.6 weeks. The main purpose of using blocking screws is to achieve reduction, but they are also useful for maintaining permanent reduction. When inserting blocking screws, the screws must be placed 1 to 3 cm away from the fracture line to avoid from propagation of the fracture. When applied properly and in an adequate way, blocking screws provide an efficient solution for deformities encountered during intramedullary nailing of distal femur fractures. Copyright 2013, SLACK Incorporated.

  16. Screw-in forces during instrumentation by various file systems

    Science.gov (United States)

    2016-01-01

    Objectives The purpose of this study was to compare the maximum screw-in forces generated during the movement of various Nickel-Titanium (NiTi) file systems. Materials and Methods Forty simulated canals in resin blocks were randomly divided into 4 groups for the following instruments: Mtwo size 25/0.07 (MTW, VDW GmbH), Reciproc R25 (RPR, VDW GmbH), ProTaper Universal F2 (PTU, Dentsply Maillefer), and ProTaper Next X2 (PTN, Dentsply Maillefer, n = 10). All the artificial canals were prepared to obtain a standardized lumen by using ProTaper Universal F1. Screw-in forces were measured using a custom-made experimental device (AEndoS-k, DMJ system) during instrumentation with each NiTi file system using the designated movement. The rotation speed was set at 350 rpm with an automatic 4 mm pecking motion at a speed of 1 mm/sec. The pecking depth was increased by 1 mm for each pecking motion until the file reach the working length. Forces were recorded during file movement, and the maximum force was extracted from the data. Maximum screw-in forces were analyzed by one-way ANOVA and Tukey's post hoc comparison at a significance level of 95%. Results Reciproc and ProTaper Universal files generated the highest maximum screw-in forces among all the instruments while M-two and ProTaper Next showed the lowest (p < 0.05). Conclusions Geometrical differences rather than shaping motion and alloys may affect the screw-in force during canal instrumentation. To reduce screw-in forces, the use of NiTi files with smaller cross-sectional area for higher flexibility is recommended. PMID:27847752

  17. Fabrication of titanium implant-retained restorations with nontraditional machining techniques.

    Science.gov (United States)

    Schmitt, S M; Chance, D A

    1995-01-01

    Traditional laboratory techniques are being supplemented by modern precision technologies to solve complex restorative problems. Electrical discharge machining combined with laser scanning and computer aided design-computer aided manufacturing can create very precise restorations without the lost wax method. A laser scanner is used to create a three-dimensional polyline data model that can then be converted into a stereolithography file format for output to a stereolithography apparatus or other rapid prototyping device. A stereolithography-generated model is used to create an electric discharge machining electrode via copper electroforming. This electrode is used to machine dental restorations from an ingot of titanium, bypassing the conventional lost wax casting process. Retaining screw access holes are machined using conventional drilling procedures, but could be accomplished with electric discharge machining if desired. Other rapid prototyping technologies are briefly discussed.

  18. Virtual estimates of fastening strength for pedicle screw implantation procedures

    Science.gov (United States)

    Linte, Cristian A.; Camp, Jon J.; Augustine, Kurt E.; Huddleston, Paul M.; Robb, Richard A.; Holmes, David R.

    2014-03-01

    Traditional 2D images provide limited use for accurate planning of spine interventions, mainly due to the complex 3D anatomy of the spine and close proximity of nerve bundles and vascular structures that must be avoided during the procedure. Our previously developed clinician-friendly platform for spine surgery planning takes advantage of 3D pre-operative images, to enable oblique reformatting and 3D rendering of individual or multiple vertebrae, interactive templating, and placement of virtual pedicle implants. Here we extend the capabilities of the planning platform and demonstrate how the virtual templating approach not only assists with the selection of the optimal implant size and trajectory, but can also be augmented to provide surrogate estimates of the fastening strength of the implanted pedicle screws based on implant dimension and bone mineral density of the displaced bone substrate. According to the failure theories, each screw withstands a maximum holding power that is directly proportional to the screw diameter (D), the length of the in-bone segm,ent of the screw (L), and the density (i.e., bone mineral density) of the pedicle body. In this application, voxel intensity is used as a surrogate measure of the bone mineral density (BMD) of the pedicle body segment displaced by the screw. We conducted an initial assessment of the developed platform using retrospective pre- and post-operative clinical 3D CT data from four patients who underwent spine surgery, consisting of a total of 26 pedicle screws implanted in the lumbar spine. The Fastening Strength of the planned implants was directly assessed by estimating the intensity - area product across the pedicle volume displaced by the virtually implanted screw. For post-operative assessment, each vertebra was registered to its homologous counterpart in the pre-operative image using an intensity-based rigid registration followed by manual adjustment. Following registration, the Fastening Strength was computed

  19. Posterior cervical spine arthrodesis with laminar screws: a report of two cases

    Directory of Open Access Journals (Sweden)

    Sugimoto,Yoshihisa

    2007-04-01

    Full Text Available We performed fixation using laminar screws in 2 patients in whom lateral mass screws, pedicle screws or transarticular screws could not be inserted. One was a 56-year-old woman who had anterior atlantoaxial subluxation (AAS. When a guide wire was inserted using an imaging guide, the hole bled massively. We thought the re-insertion of a guide wire or screw would thus increase the risk of vascular injury, so we used laminar screws. The other case was an 18-year-old man who had a hangman fracture. Preoperative magnetic resonance angiography showed occlusion of the left vertebral artery. A laminar screw was inserted into the patent side (i.e., the right side of C2. Cervical pedicle screws are the most biomechanically stable screws. However, their use carries a high risk of neurovascular complications during screw insertion, because the cervical pedicle is small and is adjacent laterally to the vertebral artery, medially to the spinal cord, and vertically to the nerve roots. Lateral mass screws are also reported to involve a risk of neurovascular injuries. The laminar screw method was thus thought to be useful, since arterial injuries could thus be avoided and it could also be used as a salvage modality for the previous misinsertion.

  20. 46 CFR 154.524 - Piping joints: Welded and screwed couplings.

    Science.gov (United States)

    2010-10-01

    ... 46 Shipping 5 2010-10-01 2010-10-01 false Piping joints: Welded and screwed couplings. 154.524... Equipment Cargo and Process Piping Systems § 154.524 Piping joints: Welded and screwed couplings. Pipe... warmer. (d) Screwed couplings are allowed for instrumentation and control piping that meets §...

  1. The best location for proximal locking screw for femur interlocking nailing: A biomechanical study

    Directory of Open Access Journals (Sweden)

    Ahmet A Karaarslan

    2016-01-01

    Conclusion: According to our findings, there is twice as much difference in locking screw bending resistance between these two application levels. To avoid proximal locking screw deformation, locking screws should be placed in the level of the lesser trochanter in nailing of 1/3 middle and distal femur fractures.

  2. ALGORITHM OF DETERMINATION OF POWER AND ENERGY INDEXES OF SCREW INTENSIFIER ON THE BULLDOZER WORKING EQUIPMENT AT TRENCH REFILLINGS

    Directory of Open Access Journals (Sweden)

    KROL R. N.

    2016-03-01

    Full Text Available Raising of problem. A bulldozer work at trench refilings is conducted by cyclic, machine shuttle motions that increases a right-of-way; increasing of time charges, fuel and labour by the side of the continuous refilling method. Besides the indicated defects gets worse also the quality of the trench refilling: the uneven soil output into a trench with large portions results the damages of pipes isolation and emptinesses formation, in consequence  settling and washing of soil. A bulldozer with the screw intensifier (SI, is deprived lacks of an odinary bulldozer  moving along a trench, it moves the loose soil that does not fall on a pipeline, but rolles on it. Thus the circuitous speed of a cutting edge of SI exceeds the speed of the base machine moving that provides the strong soil treatment (before dispersion before output into a trench. Purpose. The algorithm development of the rotational moment determination on the SI driveshaft, the consumable energy, the energy intensity and the working process productivity of the reverse trench refillings depending on physical and mechanical properties of soil, geometrical parameters of SI and bulldozer optimal speed. Conclusion. The developed algorithm allows to define that at the fixed value of the rotational speed the rotational moment and indicated efficiency of SI at the optimum speed increasing of the base machine change on a linear law; the optimum speed change of the base machine practically does not influence on the energy intensity at the considered change of the rotational speed .

  3. Acquired Equivalence Changes Stimulus Representations

    Science.gov (United States)

    Meeter, M.; Shohamy, D.; Myers, C. E.

    2009-01-01

    Acquired equivalence is a paradigm in which generalization is increased between two superficially dissimilar stimuli (or antecedents) that have previously been associated with similar outcomes (or consequents). Several possible mechanisms have been proposed, including changes in stimulus representations, either in the form of added associations or…

  4. USEPA PATHOGEN EQUIVALENCY COMMITTEE RETREAT

    Science.gov (United States)

    The Pathogen Equivalency Committee held its retreat from September 20-21, 2005 at Hueston Woods State Park in College Corner, Ohio. This presentation will update the PEC’s membership on emerging pathogens, analytical methods, disinfection techniques, risk analysis, preparat...

  5. Comments on field equivalence principles

    DEFF Research Database (Denmark)

    Appel-Hansen, Jørgen

    1987-01-01

    It is pointed Out that often-used arguments based on a short-circuit concept in presentations of field equivalence principles are not correct. An alternative presentation based on the uniqueness theorem is given. It does not contradict the results obtained by using the short-circuit concept...

  6. Screw angulation affects bone-screw stresses and bone graft load sharing in anterior cervical corpectomy fusion with a rigid screw-plate construct: a finite element model study.

    Science.gov (United States)

    Hussain, Mozammil; Natarajan, Raghu N; Fayyazi, Amir H; Braaksma, Brian R; Andersson, Gunnar B J; An, Howard S

    2009-12-01

    Anterior corpectomy and reconstruction with bone graft and a rigid screw-plate construct is an established procedure for treatment of cervical neural compression. Despite its reliability in relieving symptoms, there is a high rate of construct failure, especially in multilevel cases. There has been no study evaluating the biomechanical effects of screw angulation on construct stability; this study investigates the C4-C7 construct stability and load-sharing properties among varying screw angulations in a rigid plate-screw construct. A finite element model of a two-level cervical corpectomy with static anterior cervical plate. A three-dimensional finite element (FE) model of an intact C3-T1 segment was developed and validated. From this intact model, a fusion model (two-level [C5, C6] anterior corpectomy) was developed and validated. After corpectomy, allograft interbody fusion with a rigid anterior screw-plate construct was created from C4 to C7. Five additional FE models were developed from the fusion model corresponding to five different combinations of screw angulations within the vertebral bodies (C4, C7): (0 degrees, 0 degrees), (5 degrees, 5 degrees), (10 degrees, 10 degrees), (15 degrees, 15 degrees), and (15 degrees, 0 degrees). The fifth fusion model was termed as a hybrid fusion model. The stability of a two-level corpectomy reconstruction is not dependent on the position of the screws. Despite the locked screw-plate interface, some degree of load sharing is transmitted to the graft. The load seen by the graft and the shear stress at the bone-screw junction is dependent on the angle of the screws with respect to the end plate. Higher stresses are seen at more divergent angles, particularly at the lower level of the construct. This study suggests that screw divergence from the end plates not only increases load transmission to the graft but also predisposes the screws to higher shear forces after corpectomy reconstruction. In particular, the inferior screw

  7. Biomechanics and stability of the spine after implantation with pedicle screw and cervical vertebral screw fixation%椎弓根螺钉及颈椎体螺钉置入内固定后的生物力学及稳定性比较

    Institute of Scientific and Technical Information of China (English)

    刘淼; 尚显文; 宁旭; 庄勇; 许顺恩

    2016-01-01

    BACKGROUND:From the point of view of human anatomy, the load of the spine is more. When the body moves, the range of activities, and activity are relatively large. After screws were implanted in the spine, if biomechanical properties and stability are not up to the standard, it easily leads to lack of grip force of screw and screw loosening so as to increase the incidence of complications after treatment. OBJECTIVE:To compare biomechanical properties and stability of the spine after insertion of pedicle screw and cervical vertebral screw into the spine. METHODS:100 vertebrae under human cervical spine specimens were analyzed and randomly divided into cervical vertebral screw fixation group and pedicle screw fixation group. Cervical vertebral screws and pedicle screws were implanted in lower cervical spine specimens. Electro Force 3510 material testing machine was used to test axial pul-out force, axial pul-out strength after the fatigue loading, and fixed stability. The biomechanical properties and stability were compared after two kinds of screws were implanted in the spine. RESULTS AND CONCLUSION:(1) Instantaneous pul out force and immediate pul out stiffness were significantly higher in the pedicle screw fixation group than in the cervical vertebral screw fixation group (P  目的:对比内固定椎弓根螺钉与颈椎体螺钉置入脊柱后的生物力学性能及其稳定性。  方法:选取100个人体下颈椎椎体标本进行分析,随机分为颈椎体螺钉组与内固定椎弓根螺钉组。分别将内固定椎弓根螺钉与颈椎体螺钉置入人体下颈椎标本中,采用Electro Force 3510材料试验机对标本进行轴向拔出力、疲劳加载后轴向拔出力、固定稳定性等生物力学测试,比较2种螺钉置入脊柱后的生物力学性能及其稳定性。  结果与结论:①内固定椎弓根螺钉组即时拔出力、即时拔出刚度均显著高于颈椎体螺钉组(P<0.05);②2组虽然疲劳

  8. Matching Derived Functionally-Same Stimulus Relations: Equivalence-Equivalence and Classical Analogies

    National Research Council Canada - National Science Library

    Carpentier, Franck; Smeets, Paul M; Barnes-Holmes, Dermot; Stewart, Ian

    2004-01-01

    ... (equivalence-equivalence). Similar performances are required in classical analogies (a : b :: c : d). Therefore, some researchers have argued that equivalence-equivalence can serve as a behavior analytic model for analogical reasoning...

  9. A new scale-up approach for dispersive mixing in twin-screw compounding

    Science.gov (United States)

    Fukuda, Graeme; Bigio, David I.; Andersen, Paul; Wetzel, Mark

    2015-05-01

    Scale-up rules in polymer processing are critical in ensuring consistency in product quality and properties when transitioning from low volume laboratory mixing processes to high volume industrial compounding. The scale-up approach investigated in this study evaluates the processes with respect to dispersive mixing. Demand of polymer composites with solid additives, such as carbon microfibers and nanotubes, has become increasingly popular. Dispersive mixing breaks down particles that agglomerate, which is paramount in processing composites because solid additives tend to collect and clump. The amount of stress imparted on the material governs the degree of dispersive mixing. A methodology has been developed to characterize the Residence Stress Distribution (RSD) within a twin-screw extruder in real time through the use of polymeric stress beads. Through this technique, certain mixing scale-up rules can be analyzed. The following research investigated two different scale-up rules. The industry standard for mixing scale-up takes the ratio of outer diameters cubed to convert the volumetric flow rate from the smaller process to a flow rate appropriate in the larger machine. This procedure then resolves both operating conditions since shear rate remains constant. The second rule studied is based on percent drag flow, or the fraction of pumping potential, for different elements along the screw configuration. The percent drag flow rule aims to bring greater focus to operating conditions when scaling-up with respect to dispersive mixing. Through the use of the RSD methodology and a Design of Experiment (DOE) approach, rigorous statistical analysis was used to determine the validity between the scale-up rules of argument.

  10. EQUIVALENCE VERSUS NON-EQUIVALENCE IN ECONOMIC TRANSLATION

    Directory of Open Access Journals (Sweden)

    Cristina, Chifane

    2012-01-01

    Full Text Available This paper aims at highlighting the fact that “equivalence” represents a concept worth revisiting and detailing upon when tackling the translation process of economic texts both from English into Romanian and from Romanian into English. Far from being exhaustive, our analysis will focus upon the problems arising from the lack of equivalence at the word level. Consequently, relevant examples from the economic field will be provided to account for the following types of non-equivalence at word level: culturespecific concepts; the source language concept is not lexicalised in the target language; the source language word is semantically complex; differences in physical and interpersonal perspective; differences in expressive meaning; differences in form; differences in frequency and purpose of using specific forms and the use of loan words in the source text. Likewise, we shall illustrate a number of translation strategies necessary to deal with the afore-mentioned cases of non-equivalence: translation by a more general word (superordinate; translation by a more neutral/less expressive word; translation by cultural substitution; translation using a loan word or loan word plus explanation; translation by paraphrase using a related word; translation by paraphrase using unrelated words; translation by omission and translation by illustration.

  11. Simulation and experimental results of hybrid electric machine with a novel flux control strategy

    Directory of Open Access Journals (Sweden)

    Paplicki Piotr

    2015-03-01

    Full Text Available The paper presents selected simulation and experimental results of a hybrid ECPMS-machine (Electric Controlled Permanent Magnet Synchronous Machine. This permanent magnets (PMs excited machine offers an extended magnetic field control capability which makes it suitable for battery electric vehicle (BEV drives. Rotor, stator and the additional direct current control coil of the machine are analyzed in detail. The control system and strategy, the diagram of power supply system and an equivalent circuit model of the ECPMS-machine are presented. Influence of the additional excitation on the performance parameters of the machine, such as: torque, efficiency, speed limits and back-EMF have also been discussed.

  12. Machine tool structures

    CERN Document Server

    Koenigsberger, F

    1970-01-01

    Machine Tool Structures, Volume 1 deals with fundamental theories and calculation methods for machine tool structures. Experimental investigations into stiffness are discussed, along with the application of the results to the design of machine tool structures. Topics covered range from static and dynamic stiffness to chatter in metal cutting, stability in machine tools, and deformations of machine tool structures. This volume is divided into three sections and opens with a discussion on stiffness specifications and the effect of stiffness on the behavior of the machine under forced vibration c

  13. Role of rod diameter in comparison between only screws versus hooks and screws in posterior instrumentation of thoracic curve in idiopathic scoliosis.

    Science.gov (United States)

    Lamartina, Claudio; Petruzzi, Maria; Macchia, Marcello; Stradiotti, Paola; Zerbi, Alberto

    2011-05-01

    Since the introduction of Cotrel-Dubousset instrumentation in 1984, the correction techniques in scoliosis surgery have changed from Harrington principles of concave distraction to segmental realignment to a variety of possibilities including the rod rotation manoeuvres, and to segmental approximation via cantilever methods. Additionally, pedicle screw utilization in lumbar curves enhanced correction and stabilization of various deformities, and various studies have strongly supported the clinical advantages of lumbar pedicle screws versus conventional hook instrumentation. Pedicle screw constructs have become increasingly popular in the treatment of patients with spinal deformity. When applied to adolescent idiopathic scoliosis patients, pedicle screw fixation has demonstrated increased corrective ability compared with traditional hook/hybrid instrumentation. In our study, we do a retrospective review of idiopathic scoliosis patients (King 2-Lenke 1 B/C) treated with a selective thoracic posterior fusion using an all-screw construct versus a hybrid (pedicle screws and hooks) construct and, compare the percentage of correction of the scoliotic curves obtained with screws alone and screws and hooks. Special attention was given to the rod diameter and correction technique. Our results show that the percentage of correction of idiopathic thoracic scoliosis is similar when treating the scoliosis with rods and screws alone or with rods, screws and hooks; therefore, we and the majority of authors in the literature do not consider the rod section. This can be an important parameter in the evaluation of the superiority of treatment with screws only or screws and hooks. In our study, even if not of statistical significance, the better thoracic curve correction obtained with the hybrid group should be ascribed to the fact that in this group mostly 6 mm rods were used.

  14. Atomistic simulations of jog migration on extended screw dislocations

    DEFF Research Database (Denmark)

    Vegge, T.; Leffers, T.; Pedersen, O.B.;

    2001-01-01

    We have performed large-scale atomistic simulations of the migration of elementary jogs on dissociated screw dislocations in Cu. The local crystalline configurations, transition paths. effective masses. and migration barriers for the jogs are determined using an interatomic potential based on the...

  15. 21 CFR 888.3070 - Pedicle screw spinal system.

    Science.gov (United States)

    2010-04-01

    ... treatment of the following acute and chronic instabilities or deformities of the thoracic, lumbar, and... conditions are significant mechanical instability or deformity of the thoracic, lumbar, and sacral spine... screw spinal system because this is a technically demanding procedure presenting a risk of...

  16. Sacroiliac screw fixation: A mini review of surgical technique

    Directory of Open Access Journals (Sweden)

    Hernando Raphael Alvis-Miranda

    2014-01-01

    Full Text Available The sacral percutaneous fixation has many advantages but can be associated with a significant exposure to X-ray radiation. Currently, sacroiliac screw fixation represents the only minimally invasive technique to stabilize the posterior pelvic ring. It is a technique that should be used by experienced surgeons. We present a practical review of important aspects of this technique.

  17. Sacroiliac screw fixation: A mini review of surgical technique

    Science.gov (United States)

    Alvis-Miranda, Hernando Raphael; Farid-Escorcia, Hector; Alcalá-Cerra, Gabriel; Castellar-Leones, Sandra Milena; Moscote-Salazar, Luis Rafael

    2014-01-01

    The sacral percutaneous fixation has many advantages but can be associated with a significant exposure to X-ray radiation. Currently, sacroiliac screw fixation represents the only minimally invasive technique to stabilize the posterior pelvic ring. It is a technique that should be used by experienced surgeons. We present a practical review of important aspects of this technique. PMID:25336831

  18. Ankle fusion using a 2-incision, 3-screw technique

    NARCIS (Netherlands)

    R.P.M. Hendrickx; G.M.M.J. Kerkhoffs; S.A.S. Stufkens; C.N. van Dijk; R.K. Marti

    2011-01-01

    Reliable fusion and optimal correction of the alignment of the ankle joint using a 2-incision, 3-screw technique. Symptomatic osteoarthritis of the ankle joint after insufficient other treatment, severe deformity of the osteoarthritic ankle joint, or salvation procedure after failed arthroplasty. Ac

  19. Are inclined screw blades for vertical grain augers advantageous?

    NARCIS (Netherlands)

    Rademacher, F.J.C.

    1978-01-01

    Due to modern technology, screw blades are often manufactured by rolling them out of one single strip of steel. When simultaneously some blade inclination is applied, less residual stresses and/or larger possible ratios between outer and shaft diameter are claimed by some manufacturers, which seems

  20. Coupled Thermodynamic Behavior of New Screw Compressors Rotors Profile

    Directory of Open Access Journals (Sweden)

    Arístides Rivera Torres

    2010-05-01

    Full Text Available The article displays an evaluation of the thermodynamic behavior of screw compressor rotors with new profiles, obtained with the help of the Scorpath 2000 software. This allows predicting precisely the operation of the compressor, as well as its thermodynamic evaluation, under equal conditions, with the work of other compressors fitted with rotor profiles of other kinds.

  1. Residence time distribution in twin-screw extruders.

    NARCIS (Netherlands)

    Jager, T.

    1992-01-01

    For the twin-screw extruders used in the food industry at short time high temperature processes the knowledge of their reactor properties is incomplete for mass- and heat flow. Therefore each process change such as: scale-up or product development requires a great number of measurements before an ac

  2. Kinematics of a Hybrid Manipulator by Means of Screw Theory

    Energy Technology Data Exchange (ETDEWEB)

    Gallardo-Alvarado, J [Department of Mechanical Engineering, Instituto Tecnologico de Celaya (Mexico)

    2005-11-15

    In this work the kinematics of a hybrid manipulator, namely a fully parallel-serial manipulator, with a particular topology is approached by means of the theory of screws. Given the length of the six independent limbs, the forward position analysis of the mechanism under study, indeed the computation of the resulting pose, position and orientation, of the end-platform with respect to the fixed platform, is carried out in closed-form solution. Therefore conveniently this initial analysis avoids the use of a numerical technique such as the Newton-Raphson method. Writing in screw form the reduced acceleration state of the translational platform, with respect to the fixed platform, a simple expression for the computation of the acceleration of the translational platform is derived by taking advantage of the properties of reciprocal screws, via the Klein form, a bilinear symmetric form of the Lie algebra e(3). Following a similar procedure, a simple expression for the computation of the angular acceleration of the end-platform, with respect to the translational platform, is easily derived. Naturally, as an intermediate step, this contribution also provides the forward and inverse velocity analyses of the chosen parallel-serial manipulator. Finally, in order to prove the versatility of the expressions obtained via screw theory for solving the kinematics, up to the acceleration analysis, of the proposed spatial mechanism, a numerical example is solved with the help of commercial computer codes.

  3. Residence time distribution in twin-screw extruders

    NARCIS (Netherlands)

    Jager, T.

    1992-01-01

    For the twin-screw extruders used in the food industry at short time high temperature processes the knowledge of their reactor properties is incomplete for mass- and heat flow. Therefore each process change such as: scale-up or product development requires a great number of measurements

  4. Design of new silencers for a screw compressor

    NARCIS (Netherlands)

    Lier, L.J. van; Korst, H.J.C.; Smeulers, J.P.M.

    2014-01-01

    Two screw compressors used for the recycling of waste gas showed high vibration in the discharge piping. To mitigate the vibration problems new silencers had to be designed. A great challenge was the large variation in operating conditions, especially the variation of the molecular weight of the

  5. Optimisation of acoustic silencer for the screw compressor system

    NARCIS (Netherlands)

    Swamy, M.; Lier, L.J. van; Smeulers, J.P.M.

    2014-01-01

    In one of the screw compressor system, designed silencer was not optimal. A great challenge was the large variation in operating conditions, especially the variation of the molecular weight of the gas. There was need to optimize the silencer. This paper describes the acoustic modelling tools to

  6. Local mixing effects of screw elements during extrusion

    NARCIS (Netherlands)

    Einde, van den R.M.; Kroon, P.J.; Goot, van der A.J.; Boom, R.M.

    2005-01-01

    An in-line method was applied to determine local residence time distribution (RTD) at two places in a completely filled corotating twin screw extruder. Axial mixing effects of different types of elements were evaluated. Paddles +90 degrees induced flow patterns that appear to be circular, both

  7. Optimisation of acoustic silencer for the screw compressor system

    NARCIS (Netherlands)

    Swamy, M.; Lier, L.J. van; Smeulers, J.P.M.

    2014-01-01

    In one of the screw compressor system, designed silencer was not optimal. A great challenge was the large variation in operating conditions, especially the variation of the molecular weight of the gas. There was need to optimize the silencer. This paper describes the acoustic modelling tools to opti

  8. Kinematics Analysis Based on Screw Theory of a Humanoid Robot

    Institute of Scientific and Technical Information of China (English)

    MAN Cui-hua; FAN Xun; LI Cheng-rong; ZHAO Zhong-hui

    2007-01-01

    A humanoid robot is a complex dynamic system for its idiosyncrasy. This paper aims to provide a mathematical and theoretical foundation for the design of the configuration, kinematics analysis of a novel humanoid robot. It has a simplified configuration and design for entertainment purpose. The design methods, principle and mechanism are discussed. According to the design goals of this research, there are ten degrees of freedom in the two bionic arms.Modularization, concurrent design and extension theory methods were adopted in the configuration study and screw theory was introduced into the analysis of humanoid robot kinematics. Comparisons with other methods show that: 1) only two coordinates need to be established in the kinematics analysis of humanoid robot based on screw theory; 2) the spatial manipulator Jacobian obtained by using twist and exponential product formula is succinct and legible; 3) adopting screw theory to resolve the humanoid robot arms kinematics question can avoid singularities; 4) using screw theory can solve the question of specification insufficiency.

  9. [Posterior atlantoaxial fixation using vertex multiaxial screw system].

    Science.gov (United States)

    Zhong, Dejun; Song, Yueming

    2007-06-01

    This study aims to assess the effectiveness and advantages of Vertex multiaxial screw system in use for stabilizing the atlanto-axial junction. The entry point of the atlas was located 18-20 mm lateral to the midline and 2.0 mm superior to the inferior border of posterior arch, and the direction of screw was chosen to be about 10 degrees medial to the sagittal plane and about 5 degrees cephalad to the transverse plane. In odontoid vertebra (C2), the direction of the drill bit was guided directly by the medial and superior aspect of the individual C2 pedicle. All screws were placed properly without incidence of nerve or blood vessel injury, and no complication appeared in operation and after surgery. All cases were followed up for an average of 9 months, all cases achieved well reposition and fixation of atlantoaxial joint, average JOA grade was 9.6 before preoperation and 15.9 after operation. Fixation of the atlantoaxial complex using Vertex multiaxial screw system seemed to be a reliable technique and should be considered a good alternative in atlantoaxial fusion. The technique could be used in young patiens.

  10. Granulation of increasingly hydrophobic formulations using a twin screw granulator.

    Science.gov (United States)

    Yu, Shen; Reynolds, Gavin K; Huang, Zhenyu; de Matas, Marcel; Salman, Agba D

    2014-11-20

    The application of twin screw granulation in the pharmaceutical industry has generated increasing interest due to its suitability for continuous processing. However, an understanding of the impact of formulation properties such as hydrophobicity on intermediate and finished product quality has not yet been established. Hence, the current work investigated the granulation behaviour of three formulations containing increasing amounts of hydrophobic components using a Consigma™-1 twin screw granulator. Process conditions including powder feed rate, liquid to solid ratio, granulation liquid composition and screw configuration were also evaluated. The size of the wet granules was measured in order to enable exploration of granulation behaviour in isolation without confounding effects from downstream processes such as drying. The experimental observations indicated that the granulation process was not sensitive to the powder feed rate. The hydrophobicity led to heterogeneous liquid distribution and hence a relatively large proportion of un-wetted particles. Increasing numbers of kneading elements led to high shear and prolonged residence time, which acted to enhance the distribution of liquid and feeding materials. The bimodal size distributions considered to be characteristic of twin screw granulation were primarily ascribed to the breakage of relatively large granules by the kneading elements.

  11. Design of a magnetic lead screw for wave energy conversion

    DEFF Research Database (Denmark)

    Holm, Rasmus Koldborg; Berg, Nick Ilsoe; Walkusch, Morten

    2013-01-01

    This paper deals with the development of a magnetic lead screw (MLS) for wave energy conversion. Initially, a brief state of the art regarding linear permanent-magnet generators and MLSs is given, leading to an introduction of the MLS and a presentation of the results from a finite-element analysis...

  12. STRUCTURE SYNTHESIS OF 4-DOF PARALLEL ROBOT MECHANISMS BASED ON SCREW THEORY

    Institute of Scientific and Technical Information of China (English)

    Fang Hairong; Fang Yuefa; Guo Sheng

    2004-01-01

    Structural synthesis for 4-DOF parallel manipulators using screw theory is systematically studied. Motion properties and constraint conditions of 4-DOF parallel manipulators according to the relationship between screw and reciprocal screw are analyzed. Mathematical expressions for constraint screws and twist screws of moving platform are constructed, and all possible limbs, which provide one or more force constraints, are enumerated. Finally, a parallel manipulator with 3-rotation-DOF and 1-translation-DOF is used as an example to describe the synthesis procedure for symmetrical and non-symmetrical 4-DOF parallel manipulators.

  13. Effects of lag screw design and lubrication on sliding in trochanteric nails.

    Science.gov (United States)

    Kummer, Frederick J

    2010-01-01

    This study compared the sliding characteristics of three lag screw designs used with trochanteric nails and determined the effects of lubrication on sliding. They were tested by an established method to measure initiation and ease of lag screw sliding. These tests were then repeated with calf serum lubrication. There were significant differences (p Lubrication did not affect either parameter. Lag screw design aspects, such as diameter and, particularly, surface finish, affect sliding. Due to the small contact area between the lag screw and nail creating high interface stresses, lubrication had no effect on lag screw sliding.

  14. Use of computational fluid dynamics simulations for design of a pretreatment screw conveyor reactor.

    Science.gov (United States)

    Berson, R Eric; Hanley, Thomas R

    2005-01-01

    Computational fluid dynamics simulations were employed to compare performance of various designs of a pretreatment screw conveyor reactor. The reactor consisted of a vertical screw used to create cross flow between the upward conveying solids and the downward flow of acid. Simulations were performed with the original screw design and a modified design in which the upper flights of the screw were removed. Results of the simulations show visually that the modified design provided favorable plug flow behavior within the reactor. Pressure drop across the length of the reactor without the upper screws in place was predicted by the simulations to be 5 vs 40 kPa for the original design.

  15. A technique for the management of screw access opening in cement-retained implant restorations

    Directory of Open Access Journals (Sweden)

    Hamid Kermanshah

    2014-01-01

    Full Text Available Introduction: Abutment screw loosening has been considered as a common complication of implant-supported dental prostheses. This problem is more important in cement-retained implant restorations due to their invisible position of the screw access opening. Case Report: This report describes a modified retrievability method for cement-retained implant restorations in the event of abutment screw loosening. The screw access opening was marked with ceramic stain and its porcelain surface was treated using hydrofluoric acid (HF, silane, and adhesive to bond to composite resin. Discussion: The present modified technique facilitates screw access opening and improves the bond between the porcelain and composite resin.

  16. Covering the screw-access holes of implant restorations in the esthetic zone: a clinical report.

    Directory of Open Access Journals (Sweden)

    Abolfazl Saboury

    2014-12-01

    Full Text Available Screw-retained implant restorations have an advantage of predictable retention as well as retrievability, and obviate the risk of excessive sub-gingival cement commonly associated with cement retained implant restorations. Screw-retained restorations generally have screw access holes, which can compromise esthetics and weaken the porcelain around the holes. The purpose of this study is to describe the use of a separate overcasting crown design to cover the screw access hole of implant screw-retained prosthesis for improved esthetics.

  17. Placement of thoracic transvertebral pedicle screws using 3D image guidance.

    Science.gov (United States)

    Nottmeier, Eric W; Pirris, Stephen M

    2013-05-01

    Transvertebral pedicle screws have successfully been used in the treatment of high-grade L5-S1 spondylolisthesis. An advantage of transvertebral pedicle screws is the purchase of multiple cortical layers across 2 vertebrae, thereby increasing the stability of the construct. At the lumbosacral junction, transvertebral pedicle screws have been shown to be biomechanically superior to pedicle screws placed in the standard fashion. The use of transvertebral pedicle screws at spinal levels other than L5-S1 has not been reported in the literature. The authors describe their technique of transvertebral pedicle screw placement in the thoracic spine using 3D image guidance. Twelve patients undergoing cervicothoracic or thoracolumbar fusion had 41 thoracic transvertebral pedicle screws placed across 26 spinal levels using this technique. Indications for placement of thoracic transvertebral pedicle screws in earlier cases included osteoporosis and pedicle screw salvage. However, in subsequent cases screws were placed in patients undergoing multilevel thoracolumbar fusion without osteoporosis, particularly near the top of the construct. Image guidance in this study was accomplished using the Medtronic StealthStation S7 image guidance system used in conjunction with the O-arm. All patients were slated to undergo postoperative CT scanning at approximately 4-6 months for fusion assessment, which also allowed for grading of the transvertebral pedicle screws. No thoracic transvertebral pedicle screw placed in this study had to be replaced or repositioned after intraoperative review of the cone beam CT scans. Review of the postoperative CT scans revealed all transvertebral screws to be across the superior disc space with the tips in the superior vertebral body. Six pedicle screws were placed using the in-out-in technique in patients with narrow pedicles, leaving 35 screws that underwent breach analysis. No pedicle breach was noted in 34 of 35 screws. A Grade 1 (fusion was observed

  18. Biomechanical comparison of 2 anterior cruciate ligament graft preparation techniques for tibial fixation: adjustable-length loop cortical button or interference screw.

    Science.gov (United States)

    Mayr, Raul; Heinrichs, Christian Heinz; Eichinger, Martin; Coppola, Christian; Schmoelz, Werner; Attal, René

    2015-06-01

    Cortical button fixation at the femoral side and interference screws within the tibial bone tunnel are widely used for anterior cruciate ligament graft fixation. Using a bone socket instead of a full tunnel allows cortical button fixation on the tibial side as well. If adjustable-length loop cortical button devices are used for femoral and tibial fixation, the tendon graft has to be secured with sutures in a closed tendon loop. The increased distance of fixation points and potential slippage of the tendon strands at the securing sutures might lead to greater risk of postoperative graft elongation when compared with conventional graft preparation with tibial interference screw fixation. Compared with an anterior cruciate ligament graft with tibial adjustable-length loop cortical button fixation, a graft with tibial interference screw fixation will show less graft elongation during cyclic loading and lower ultimate failure loads. Controlled laboratory study. Grafts with tibial adjustable-length loop cortical button fixation and grafts with tibial interference screw fixation were biomechanically tested in calf tibiae (n = 10 per group). Femoral fixation was equivalent for both groups, using an adjustable-length loop cortical button. Specimens underwent cyclic loading followed by a load-to-failure test. Grafts with screw fixation showed significantly less initial elongation (cycles 1-5: 1.46 ± 0.26 mm), secondary elongation (cycles 6-1000: 1.87 ± 0.67 mm), and total elongation (cycles 1-1000: 3.33 ± 0.83 mm) in comparison with grafts with button fixation (2.47 ± 0.26, 3.56 ± 0.39, and 6.03 ± 0.61 mm, respectively) (P button fixation were able to withstand significantly higher ultimate failure loads (908 ± 74 vs 693 ± 119 N) (P button fixation resulted in higher graft elongation during cyclic loading and showed higher ultimate failure loads in comparison with conventional graft preparation with tibial interference screw fixation at time zero. The results of this

  19. Equivalence problem for Bishop surfaces

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    The paper has two parts. We first briefly survey recent studies on the equivalence problem for real submanifolds in a complex space under the action of biholomorphic transformations. We will mainly focus on some of the recent studies of Bishop surfaces, which, in particular, includes the work of the authors. In the second part of the paper, we apply the general theory developed by the authors to explicitly classify an algebraic family of Bishop surfaces with a vanishing Bishop invariant. More precisely, we let M be a real submanifold of C 2 defined by an equation of the form w = zz + 2Re(z s + az s+1 ) with s≥ 3 and a a complex parameter. We will prove in the second part of the paper that for s≥ 4 two such surfaces are holomorphically equivalent if and only if the parameter differs by a certain rotation. When s = 3, we show that surfaces of this type with two different real parameters are not holomorphically equivalent.

  20. Equivalent statistics and data interpretation.

    Science.gov (United States)

    Francis, Gregory

    2016-10-14

    Recent reform efforts in psychological science have led to a plethora of choices for scientists to analyze their data. A scientist making an inference about their data must now decide whether to report a p value, summarize the data with a standardized effect size and its confidence interval, report a Bayes Factor, or use other model comparison methods. To make good choices among these options, it is necessary for researchers to understand the characteristics of the various statistics used by the different analysis frameworks. Toward that end, this paper makes two contributions. First, it shows that for the case of a two-sample t test with known sample sizes, many different summary statistics are mathematically equivalent in the sense that they are based on the very same information in the data set. When the sample sizes are known, the p value provides as much information about a data set as the confidence interval of Cohen's d or a JZS Bayes factor. Second, this equivalence means that different analysis methods differ only in their interpretation of the empirical data. At first glance, it might seem that mathematical equivalence of the statistics suggests that it does not matter much which statistic is reported, but the opposite is true because the appropriateness of a reported statistic is relative to the inference it promotes. Accordingly, scientists should choose an analysis method appropriate for their scientific investigation. A direct comparison of the different inferential frameworks provides some guidance for scientists to make good choices and improve scientific practice.

  1. The general theory of blade screws including propellers, fans, helicopter screws, helicoidal pumps, turbo-motors, and different kinds of helicoidal blades

    Science.gov (United States)

    De Bothezat, George

    1920-01-01

    Report presents a theory which gives a complete picture and an exact quantitative analysis of the whole phenomenon of the working of blade screws, but also unites in a continuous whole the entire scale of states of work conceivable for a blade screw. Chapter 1 is devoted to the establishment of the system of fundamental equations relating to the blade screw. Chapter 2 contains the general discussion of the 16 states of work which may establish themselves for a blade screw. The existence of the vortex ring state and the whirling phenomenon are established. All the fundamental functions which enter the blade-screw theory are submitted to a general analytical discussion. The general outline of the curve of the specific function is examined. Two limited cases of the work of the screw, the screw with a zero constructive pitch and the screw with an infinite constructive pitch, are pointed out. Chapter 3 is devoted to the study of the propulsive screw or propeller. (author)

  2. Investigation of Equivalent Unsprung Mass and Nonlinear Features of Electromagnetic Actuated Active Suspension

    Directory of Open Access Journals (Sweden)

    Jun Yin

    2015-01-01

    Full Text Available Electromagnetic actuated active suspension benefits active control and energy harvesting from vibration at the same time. However, the rotary type electromagnetic actuated active suspension introduces a significant extra mass on the unsprung mass due to the inertia of the rotating components of the actuator. The magnitude of the introduced unsprung mass is studied based on a gearbox type actuator and a ball screw type actuator. The geometry of the suspension and the actuator also influence the equivalent unsprung mass significantly. The suspension performance simulation or control logic derived should take this equivalent unsprung mass into account. Besides, an extra force should be compensated due to the nonlinear features of the suspension structure and it is studied. The active force of the actuator should compensate this extra force. The discovery of this paper provides a fundamental for evaluating the rotary type electromagnetic actuated active suspension performance and control strategy derived as well as controlling the electromagnetic actuated active suspension more precisely.

  3. Design of Demining Machines

    CERN Document Server

    Mikulic, Dinko

    2013-01-01

    In constant effort to eliminate mine danger, international mine action community has been developing safety, efficiency and cost-effectiveness of clearance methods. Demining machines have become necessary when conducting humanitarian demining where the mechanization of demining provides greater safety and productivity. Design of Demining Machines describes the development and testing of modern demining machines in humanitarian demining.   Relevant data for design of demining machines are included to explain the machinery implemented and some innovative and inspiring development solutions. Development technologies, companies and projects are discussed to provide a comprehensive estimate of the effects of various design factors and to proper selection of optimal parameters for designing the demining machines.   Covering the dynamic processes occurring in machine assemblies and their components to a broader understanding of demining machine as a whole, Design of Demining Machines is primarily tailored as a tex...

  4. Applied machining technology

    CERN Document Server

    Tschätsch, Heinz

    2010-01-01

    Machining and cutting technologies are still crucial for many manufacturing processes. This reference presents all important machining processes in a comprehensive and coherent way. It includes many examples of concrete calculations, problems and solutions.

  5. Machining with abrasives

    CERN Document Server

    Jackson, Mark J

    2011-01-01

    Abrasive machining is key to obtaining the desired geometry and surface quality in manufacturing. This book discusses the fundamentals and advances in the abrasive machining processes. It provides a complete overview of developing areas in the field.

  6. Women, Men, and Machines.

    Science.gov (United States)

    Form, William; McMillen, David Byron

    1983-01-01

    Data from the first national study of technological change show that proportionately more women than men operate machines, are more exposed to machines that have alienating effects, and suffer more from the negative effects of technological change. (Author/SSH)

  7. Machine medical ethics

    CERN Document Server

    Pontier, Matthijs

    2015-01-01

    The essays in this book, written by researchers from both humanities and sciences, describe various theoretical and experimental approaches to adding medical ethics to a machine in medical settings. Medical machines are in close proximity with human beings, and getting closer: with patients who are in vulnerable states of health, who have disabilities of various kinds, with the very young or very old, and with medical professionals. In such contexts, machines are undertaking important medical tasks that require emotional sensitivity, knowledge of medical codes, human dignity, and privacy. As machine technology advances, ethical concerns become more urgent: should medical machines be programmed to follow a code of medical ethics? What theory or theories should constrain medical machine conduct? What design features are required? Should machines share responsibility with humans for the ethical consequences of medical actions? How ought clinical relationships involving machines to be modeled? Is a capacity for e...

  8. Brain versus Machine Control.

    Directory of Open Access Journals (Sweden)

    Jose M Carmena

    2004-12-01

    Full Text Available Dr. Octopus, the villain of the movie "Spiderman 2", is a fusion of man and machine. Neuroscientist Jose Carmena examines the facts behind this fictional account of a brain- machine interface

  9. Bioresorbable screws reinforced with phosphate glass fibre: manufacturing and mechanical property characterisation.

    Science.gov (United States)

    Felfel, R M; Ahmed, I; Parsons, A J; Rudd, C D

    2013-01-01

    Use of bioresorbable screws could eliminate disadvantages associated with metals such as removal operations, corrosion, MRI interference and stress shielding. Mechanical properties of bioresorbable polymers alone are insufficient for load bearing applications application as screws. Thus, reinforcement is necessary to try and match or surpass the mechanical properties of cortical bone. Phosphate based glass fibres were used to reinforce polylactic acid (PLA) in order to produce unidirectionally aligned (UD) and unidirectionally plus randomly distributed (UD/RM) composite screws (P40 UD and P40 UD/RM). The maximum flexural and push-out properties for the composite screws (P40 UD and P40 UD/RM) increased by almost 100% in comparison with the PLA screws. While the pull-out strength and stiffness of the headless composite screws were ∼80% (strength) and ∼130% (stiffness) higher than for PLA, those with heads exhibited properties lower than those for PLA alone as a result of failure at the heads. An increase in the maximum shear load and stiffness for the composite screws (∼30% and ∼40%) in comparison to the PLA screws was also seen. Maximum torque for the PLA screws was ∼1000 mN m, while that for the composite screws were slightly lower. The SEM micrographs for P40 UD and P40 UD/RM screws revealed small gaps around the fibres, which were suggested to be due to buckling of the UD fibres during the manufacturing process.

  10. Sauvé-Kapandji procedure with headless compression screw in patients with rheumatoid arthritis.

    Science.gov (United States)

    Maeda, Atsushi; Suzuki, Taku; Hasegawa, Masaki; Kuroiwa, Takashi; Shizu, Kanae; Hayakawa, Katsuhiko; Tsuji, Takashi; Suzuki, Katsuji; Yamada, Harumoto

    2017-04-11

    We examined the surgical outcomes of the Sauvé-Kapandji (S-K) procedure using a headless compression screw and a metal cancellous screw in patients with rheumatoid arthritis (RA). This retrospective study included 41 RA patients who underwent the S-K procedure for distal radioulnar joint disorders with two screws: headless compression screws (HCS group, n = 20) and cannulated cancellous screws (CCS group, n = 21). Clinical and radiographic outcomes were assessed 1 year after surgery. Radiographic outcomes included bony union of the distal radioulnar joint (DRUJ), bone resorption around the screw, a screw back-out, and use of additional K-wire. We investigated any complications related to the screw head. All 20 patients in the HCS group showed bone fusion of the DRUJ. In the CCS group, an asymptomatic non-union was observed in one patient and additional K-wire was needed to stabilize the DRUJ in three patients. No patients complained of any complications related to the screw head in the HCS group, while the CCS group demonstrated the hardware protrusion in two patients who complained of tenderness or discomfort at the screw head. The use of a headless compression screw in the S-K procedure is useful in patients with RA.

  11. A rationale method for evaluating unscrewing torque values of prosthetic screws in dental implants

    Directory of Open Access Journals (Sweden)

    Felipe Miguel Saliba

    2011-02-01

    Full Text Available OBJECTIVES: Previous studies that evaluated the torque needed for removing dental implant screws have not considered the manner of transfer of the occlusal loads in clinical settings. Instead, the torque used for removal was applied directly to the screw, and most of them omitted the possibility that the hexagon could limit the action of the occlusal load in the loosening of the screws. The present study proposes a method for evaluating the screw removal torque in an anti-rotational device independent way, creating an unscrewing load transfer to the entire assembly, not only to the screw. MATERIAL AND METHODS: Twenty hexagonal abutments without the hexagon in their bases were fixed with a screw to 20 dental implants. They were divided into two groups: Group 1 used titanium screws and Group 2 used titanium screws covered with a solid lubricant. A torque of 32 Ncm was applied to the screw and then a custom-made wrench was used for rotating the abutment counterclockwise, to loosen the screw. A digital torque meter recorded the torque required to loosen the abutment. RESULTS: There was a significant difference between the means of Group 1 (38.62±6.43 Ncm and Group 2 (48.47±5.04 Ncm, with p=0.001. CONCLUSION: This methodology was effective in comparing unscrewing torque values of the implant-abutment junction even with a limited sample size. It confirmed a previously shown significant difference between two types of screws.

  12. [Finite element analysis of the initial stability of subtalar arthrodesis with double-screw fixation].

    Science.gov (United States)

    Cui, Zhuang; Yu, Bin; Li, Xue; Xu, Changpeng; Song, Jinqi; Ouyang, Hanbin; Diao, Xicai; Chen, Liguang

    2012-11-01

    To assess the optimal configuration of double-screw fixation for subtalar arthrodesis using finite element analysis. Three-dimensional finite element double-screw models of subtalar arthrodesis were reconstructed using Mimics 13.0, Geomagic 10.0 and solid works software based on the 3-D images of the volunteer's right foot. The external and internal rotation torques of 4 N·m were applied, and the micromotion at the bone-to-bone interface were measured to evaluate the initial stability of subtalar arthrodesis. A neck screw plus an anterolateral dome screw was the most stable model. The peak micromotion at the fusion site of this fixation configuration were 41.67mnplus;0.49 and 42.64mnplus;0.75 µm in response to the respectively. A neck screw plus a posteromedial dome screw was the least stable model, with peak micromotion at the bone-to-bone interface of 61.76mnplus;1.00 and 62.32mnplus;0.90 µm, respectively. A neck screw plus an anterolateral dome screw is the best fixation configuration while a neck screw plus a posteromedial screw provides the least stability of subtalar arthrodesis. Three-dimensional finite element models allow effective preoperative planning of the screw number and placement.

  13. 21 CFR 26.9 - Equivalence determination.

    Science.gov (United States)

    2010-04-01

    ... 21 Food and Drugs 1 2010-04-01 2010-04-01 false Equivalence determination. 26.9 Section 26.9 Food... Specific Sector Provisions for Pharmaceutical Good Manufacturing Practices § 26.9 Equivalence determination... document insufficient evidence of equivalence, lack of opportunity to assess equivalence or a determination...

  14. Biomechanical testing of bioabsorbable cannulated screws for slipped capital femoral epiphysis fixation.

    Science.gov (United States)

    Kroeber, Markus W; Rovinsky, David; Haskell, Andrew; Heilmann, Moira; Llotz, Jeff; Otsuka, Norman

    2002-06-01

    This study compared cannulated 4.5-mm bioabsorbable screws made of self-reinforced poly-levolactic acid to cannulated 4.5-mm steel and titanium screws for resistance to shear stress and ability to generate compression in a polyurethane foam model of slipped capital femoral epiphysis fixation. The maximum shear stress resisted by the three screw types was similar (self-reinforced poly-levolactic acid 371 +/- 146 MPa, steel 442 +/- 43 MPa, and titanium 470 +/- 91 MPa). The maximum compression generated by both the self-reinforced poly-levolactic acid screw (68.5 +/- 3.3 N) and the steel screw (63.3 +/- 5.9 N) was greater than that for the titanium screw (3 +/- 1.4 N, P <.05). These data suggest cannulated self-reinforced poly-levolactic acid screws can be used in the treatment of slipped capital femoral epiphysis because of their sufficient biomechanical strength.

  15. Easy retrieval of polyaxial tulip-head pedicle screws by “U” rod technique

    Science.gov (United States)

    Isik, Cengiz; Altinel, Levent; Ates, Ali; Ozdemir, Mustafa

    2009-01-01

    The number of fusion surgeries increase each year which also increase the need for implant removal. In some cases, it can be extremely hard to remove a pedicle screw especially when there is a mismatch of the screw and the screwdriver. Also the screwdrivers can be contaminated during the operation, and this will cause a delay till the instruments are re-sterilized. There is a need for the removal of screws without special instruments. We describe a method for removing tulip-head polyaxial pedicle screws without special instruments. The screws are removed using an Allen key, a rod bender and a “U” shaped rod. We successfully removed 76 screws in 11 recent cases without any complications. The “U” rod technique is a simple and useful technique for the removal of tulip-head polyaxial screws. PMID:19618219

  16. Easy retrieval of polyaxial tulip-head pedicle screws by "U" rod technique.

    Science.gov (United States)

    Kose, Kamil Cagri; Isik, Cengiz; Altinel, Levent; Ates, Ali; Ozdemir, Mustafa

    2010-01-01

    The number of fusion surgeries increase each year which also increase the need for implant removal. In some cases, it can be extremely hard to remove a pedicle screw especially when there is a mismatch of the screw and the screwdriver. Also the screwdrivers can be contaminated during the operation, and this will cause a delay till the instruments are re-sterilized. There is a need for the removal of screws without special instruments. We describe a method for removing tulip-head polyaxial pedicle screws without special instruments. The screws are removed using an Allen key, a rod bender and a "U" shaped rod. We successfully removed 76 screws in 11 recent cases without any complications. The "U" rod technique is a simple and useful technique for the removal of tulip-head polyaxial screws.

  17. Time analysis for screw application: traditional lag technique versus self-tapping lag technique.

    Science.gov (United States)

    Gonzalez, J V; Trout, B M; Stuck, R M; Vrbos, L A

    1997-01-01

    A study was conducted to compare the procedural time of a 2.7-mm. fully threaded cortical screw versus a self-tapping, 2.4-mm. lag screw, which is reported to eliminate the need for overdrilling and tapping. The screws were applied by four board-certified podiatric and orthopedic physicians and four second-year podiatric and orthopedic residents. Each screw was placed through two 8-mm. layers of Last-a-foam, and the participants were timed for length of application of four screws from each system per week. The trials were repeated weekly for 4 weeks. The results showed a statistically significant difference between the length of time for insertion between a traditional cortical screw and a self-tapping lag screw, regardless of physician experience.

  18. Evaluation of different screw fixation techniques and screw diameters in sagittal split ramus osteotomy: finite element analysis method.

    Science.gov (United States)

    Sindel, A; Demiralp, S; Colok, G

    2014-09-01

    Sagittal split ramus osteotomy (SSRO) is used for correction of numerous congenital or acquired deformities in facial region. Several techniques have been developed and used to maintain fixation and stabilisation following SSRO application. In this study, the effects of the insertion formations of the bicortical different sized screws to the stresses generated by forces were studied. Three-dimensional finite elements analysis (FEA) and static linear analysis methods were used to investigate difference which would occur in terms of forces effecting onto the screws and transmitted to bone between different application areas. No significant difference was found between 1·5- and 2-mm screws used in SSRO fixation. Besides, it was found that 'inverted L' application was more successful compared to the others and that was followed by 'L' and 'linear' formations which showed close rates to each other. Few studies have investigated the effect of thickness and application areas of bicortical screws. This study was performed on both advanced and regressed jaws positions.

  19. A Universal Reactive Machine

    DEFF Research Database (Denmark)

    Andersen, Henrik Reif; Mørk, Simon; Sørensen, Morten U.

    1997-01-01

    Turing showed the existence of a model universal for the set of Turing machines in the sense that given an encoding of any Turing machine asinput the universal Turing machine simulates it. We introduce the concept of universality for reactive systems and construct a CCS processuniversal...

  20. Nonlinear Modeling of a High Precision Servo Injection Molding Machine Including Novel Molding Approach

    Institute of Scientific and Technical Information of China (English)

    何雪松; 王旭永; 冯正进; 章志新; 杨钦廉

    2003-01-01

    A nonlinear mathematical model of the injection molding process for electrohydraulic servo injection molding machine (IMM) is developed.It was found necessary to consider the characteristics of asymmetric cylinder for electrohydraulic servo IMM.The model is based on the dynamics of the machine including servo valve,asymmetric cylinder and screw,and the non-Newtonian flow behavior of polymer melt in injection molding is also considered.The performance of the model was evaluated based on novel approach of molding - injection and compress molding,and the results of simulation and experimental data demonstrate the effectiveness of the model.

  1. The Design of a Novel Prismatic Drive for a Three-DOF Parallel-Kinematics Machine

    CERN Document Server

    Renotte, Jérome; Angeles, Jorge

    2004-01-01

    The design of a novel prismatic drive is reported in this paper. This transmission is based on Slide-O-Cam, a cam mechanism with multiple rollers mounted on a common translating follower. The design of Slide-O-Cam was reported elsewhere. This drive thus provides pure-rolling motion, thereby reducing the friction of rack-and-pinions and linear drives. Such properties can be used to design new transmissions for parallel-kinematics machines. In this paper, this transmission is optimized to replace ball-screws in Orthoglide, a three-DOF parallel robot optimized for machining applications.

  2. The Design of a Novel Prismatic Drive for a Three-DOF Parallel-Kinematics Machine

    CERN Document Server

    Chablat, Damien

    2011-01-01

    The design of a novel prismatic drive is reported in this paper. This transmission is based on Slide-o-Cam, a cam mechanism with multiple rollers mounted on a common translating follower. The design of Slide-o-Cam was reported elsewhere. This drive thus provides pure-rolling motion, thereby reducing the friction of rack-and-pinions and linear drives. Such properties can be used to design new transmissions for parallel-kinematics machines. In this paper, this transmission is intended to replace the ball-screws in Orthoglide, a three-dof parallel robot intended for machining applications.

  3. Biomechanical Evaluation of Plate Versus Lag Screw Only Fixation of Distal Fibula Fractures.

    Science.gov (United States)

    Misaghi, Amirhossein; Doan, Josh; Bastrom, Tracey; Pennock, Andrew T

    2015-01-01

    Traditional fixation of unstable Orthopaedic Trauma Association type B/C ankle fractures consists of a lag screw and a lateral or posterolateral neutralization plate. Several studies have demonstrated the clinical success of lag screw only fixation; however, to date no biomechanical comparison of the different constructs has been performed. The purpose of the present study was to evaluate the biomechanical strength of these different constructs. Osteotomies were created in 40 Sawbones(®) distal fibulas and reduced using 1 bicortical 3.5-mm stainless steel lag screw, 2 bicortical 3.5-mm lag screws, 3 bicortical 3.5-mm lag screws, or a single 3.5-mm lag screw coupled with a stainless steel neutralization plate with 3 proximal cortical and 3 distal cancellous screws. The constructs were tested to determine the stiffness in lateral bending and rotation and failure torque. No significant differences in lateral bending or rotational stiffness were detected between the osteotomies fixed with 3 lag screws and a plate. Constructs fixed with 1 lag screw were weaker for both lateral bending and rotational stiffness. Osteotomies fixed with 2 lag screws were weaker in lateral bending only. No significant differences were found in the failure torque. Compared with lag screw only fixation, plate fixation requires larger incisions and increased costs and is more likely to require follow-up surgery. Despite the published clinical success of treating simple Orthopaedic Trauma Association B/C fractures with lag screw only fixation, many surgeons still have concerns about stability. For noncomminuted, long oblique distal fibula fractures, lag screw only fixation techniques offer construct stiffness similar to that of traditional plate and lag screw fixation.

  4. Latarjet Fixation: A Cadaveric Biomechanical Study Evaluating Cortical and Cannulated Screw Fixation.

    Science.gov (United States)

    Alvi, Hasham M; Monroe, Emily J; Muriuki, Muturi; Verma, Rajat N; Marra, Guido; Saltzman, Matthew D

    2016-04-01

    Attritional bone loss in patients with recurrent anterior instability has successfully been treated with a bone block procedure such as the Latarjet. It has not been previously demonstrated whether cortical or cancellous screws are superior when used for this procedure. To assess the strength of stainless steel cortical screws versus stainless steel cannulated cancellous screws in the Latarjet procedure. Controlled laboratory study. Ten fresh-frozen matched-pair shoulder specimens were randomized into 2 separate fixation groups: (1) 3.5-mm stainless steel cortical screws and (2) 4.0-mm stainless steel partially threaded cannulated cancellous screws. Shoulder specimens were dissected free of all soft tissue and a 25% glenoid defect was created. The coracoid process was osteomized, placed at the site of the glenoid defect, and fixed in place with 2 parallel screws. All 10 specimens failed by screw cutout. Nine of 10 specimens failed by progressive displacement with an increased number of cycles. One specimen in the 4.0-mm screw group failed by catastrophic failure on initiation of the testing protocol. The 3.5-mm screws had a mean of 274 cycles (SD, ±171 cycles; range, 10-443 cycles) to failure. The 4.0-mm screws had a mean of 135 cycles (SD, ±141 cycles; range, 0-284 cycles) to failure. There was no statistically significant difference between the 2 types of screws for cycles required to cause failure (P = .144). There was no statistically significant difference in energy or cycles to failure when comparing the stainless steel cortical screws versus partially threaded cannulated cancellous screws. Latarjet may be performed using cortical or cancellous screws without a clear advantage of either option.

  5. Subaxial cervical pedicle screw insertion with newly defined entry point and trajectory: accuracy evaluation in cadavers.

    Science.gov (United States)

    Zheng, Xiujun; Chaudhari, Rahul; Wu, Chunhui; Mehbod, Amir A; Transfeldt, Ensor E

    2010-01-01

    Successful placement of cervical pedicle screws requires accurate identification of both entry point and trajectory. However, literature has not provided consistent recommendations regarding the direction of pedicle screw insertion and entry point location. The objective of this study was to define a guideline regarding the optimal entry point and trajectory in placing subaxial cervical pedicle screws and to evaluate the screw accuracy in cadaver cervical spines. The guideline for entry point and trajectory for each vertebra was established based on the recently published morphometric data. Six fresh frozen cervical spines (C3-C7) were used. There were two men and four women. After posterior exposure, the entry point was determined and the cortical bone of the entry point was removed using a 2-mm burr. Pilot holes were created with a cervical probe based on the guideline using fluoroscopy. After tapping, 3.5-mm screws with appropriate length were inserted. After screw insertion, every vertebra was dissected and inspected for pedicle breach. The pedicle width, height, pedicle transverse angulation and actual screw insertion angle were measured. A total of 60 pedicle screws were inserted. No statistical difference in pedicle width and height was found between the left and right sides for each level. The overall accuracy of pedicle screws was 83.3%. The remaining 13.3% screws had noncritical breach, and 3.3% had critical breach. The critical breach was not caused by the guideline. There was no statistical difference between the pedicle transverse angulation and the actual screw trajectory created using the guideline. There was statistical difference in pedicle width between the breach and non-breach screws. In conclusion, high success rate of subaxial cervical pedicle screw placement can be achieved using the recently proposed operative guideline and oblique views of fluoroscopy. However, careful preoperative planning and good surgical skills are still required to

  6. Biomechanical Evaluation of Strength and Stiffness of Subtalar Joint Arthrodesis Screw Constructs.

    Science.gov (United States)

    Jastifer, James R; Alrafeek, Saif; Howard, Peter; Gustafson, Peter A; Coughlin, Michael J

    2016-04-01

    Subtalar arthrodesis is a common treatment for end-stage subtalar joint arthritis as well as many other clinical problems. The best method of subtalar arthrodesis fixation is unknown. The purpose of this study was to compare the strength of subtalar arthrodesis fixation methods including a single posterior screw (SP), 2 posterior minimally divergent screws (MD) and a 2 screw highly divergent screw (HD) construct for subtalar arthrodesis. A biomechanical study was performed including the three different screw configurations (SP, MD, HD). These surrogate bone specimens were subjected to applied inversion and eversion torques about the subtalar joint axis on a servo-hydraulic load frame. Torsional stiffness of the construct and the maximum torque for each configuration were measured. Additionally, a cadaver study was performed using 5 fresh-frozen cadaver specimens. The perpendicular distance from the divergent screw guide-wire placement was measured from anatomic structures. The HD screw configuration was found to have the highest torsional stiffness in both inversion and eversion, followed by the MD construct and then the SP construct. Similarly, the HD construct had the highest maximum torque versus the MD and SP constructs. All between-group differences were statistically significant (P < .05). The mean distance from key structures to the divergent screw included the sural nerve (13 mm), peroneus brevis tendon (18 mm), tibialis anterior tendon (8 mm), and tibialis posterior tendon (21 mm). This biomechanical and cadaver study supports the use of 2 screws for fixation of subtalar arthrodesis over a single posterior screw. Additionally, we describe a biomechanically superior and potentially safe, alternative 2-screw divergent construct. This study gives biomechanical support for 2 screw, divergent fixation of subtalar arthrodesis or a single over a single screw or two screw minimally divergent construct. © The Author(s) 2015.

  7. Accuracy of robot-assisted pedicle screw placement for adolescent idiopathic scoliosis in the pediatric population.

    Science.gov (United States)

    Macke, Jeremy J; Woo, Raymund; Varich, Laura

    2016-06-01

    This is a retrospective review of pedicle screw placement in adolescent idiopathic scoliosis (AIS) patients under 18 years of age who underwent robot-assisted corrective surgery. Our primary objective was to characterize the accuracy of pedicle screw placement with evaluation by computed tomography (CT) after robot-assisted surgery in AIS patients. Screw malposition is the most frequent complication of pedicle screw placement and is more frequent in AIS. Given the potential for serious complications, the need for improved accuracy of screw placement has spurred multiple innovations including robot-assisted guidance devices. No studies to date have evaluated this robot-assisted technique using CT exclusively within the AIS population. Fifty patients were included in the study. All operative procedures were performed at a single institution by a single pediatric orthopedic surgeon. We evaluated the grade of screw breach, the direction of screw breach, and the positioning of the patient for preoperative scan (supine versus prone). Of 662 screws evaluated, 48 screws (7.2 %) demonstrated a breach of greater than 2 mm. With preoperative prone position CT scanning, only 2.4 % of screws were found to have this degree of breach. Medial malposition was found in 3 % of screws, a rate which decreased to 0 % with preoperative prone position scanning. Based on our results, we conclude that the proper use of image-guided robot-assisted surgery can improve the accuracy and safety of thoracic pedicle screw placement in patients with adolescent idiopathic scoliosis. This is the first study to evaluate the accuracy of pedicle screw placement using CT assessment in robot-assisted surgical correction of patients with AIS. In our study, the robot-assisted screw misplacement rate was lower than similarly constructed studies evaluating conventional (non-robot-assisted) procedures. If patients are preoperatively scanned in the prone position, the misplacement rate is further

  8. A Vectorial modeling for the pentaphase Permanent Magnet Synchronous Machine based on multimachine approach

    Directory of Open Access Journals (Sweden)

    Abdelkrim Sellam

    2012-12-01

    Full Text Available The polyphase [1] machines are developed mainly in the field of variable speed drives of high power because increasing the number of phases on the one hand allows to reduce the dimensions of the components in power modulators energy and secondly to improve the operating safety. By a vector approach (vector space, it is possible to find a set of single-phase machine and / or two-phase fictitious equivalent to polyphase synchronous machine.These fictitious machines are coupled electrically and mechanically but decoupled magnetically. This approach leads to introduce the concept of the equivalent machine (multimachine multiconverter system MMS which aims to analyze systems composed of multiple machines (or multiple converters in electric drives. A first classification multimachine multiconverter system follows naturally from MMS formalism. We present an example of a synchronous machine pent phase.

  9. Biomechanical effect of the iliac screw insertion depth on lumboiliac taxation construct%髂骨钉置入深度对腰椎-骨盆重建结构的生物力学影响

    Institute of Scientific and Technical Information of China (English)

    陈辉; 于滨生; 郑召民; 吕游; 张奎渤; 刘辉; 李佛保

    2008-01-01

    Objective To biomechanically compare the stability of the short and long iliae screw fixation constructs in lumboiliac reconstruction. Methods Seven adult human embalmed cadavers (L3- pelvis) were used. Using posterior spinal fixation system, L4-S1 pedicle screw fixation was performed. This was defined as intact state of the sacroiliac joint. After the intact test, total sacrum resection and L4-L5- pelvis reconstruction by pediele screw and iliac screw with different lengths were performed as follow: short screw group (as the length of exceeding 2 mm over ischial notch) and long screw group (as the length of exceeding 2 mm over anterior inferior iliac spine ). Using the 858 MTS material testing machine, biomechanical testing was performed under 800 N compression and 7 Nm torsion loading modes. At last, the axial pullout test of two iliac screws was executed. Construct stiffness in compression and torsion test, and maximum pullout force were analyzed. Results Insertion lengths of the short and long iliac screw were (70±2) mm and (138±4) mm respectively. The lumbopelvic reconstruction using short and long iliac screw, respectively restored 53.3%±13.6% and 57.6%±16.2% of the initial stiffness in compression testing, and respectively harvested 55.1%±11.9% and 62.5%±9.2% of the initial stiffness in torsion testing. No significant difference was detected between the two reconstructions (P>0.05), however, the compressive and torsional stiffness of the two techniques were markedly less than the intact condition (P0.05);但是,两者的轴向压缩及旋转刚度均显著低于完整状态组(P<0.05).髂骨长钉的最大拔出力显著高于髂骨短钉(P<0.05).结论 在生理载荷下,髂骨短钉的脊柱-骨盆重建结构可获得与髂骨长钉同等的力学稳定性;髂骨短钉的置入深度仅为长钉的一半,可降低置入的风险.但是,无论髂骨长钉或短钉的脊柱.骨盆重建装置均难以恢复局部的初始稳定性.

  10. On the Translation Equivalence of Literature Works

    Institute of Scientific and Technical Information of China (English)

    吴娟

    2013-01-01

    As for translation principle, people have different opinions. The principle of equivalent translation may be is one of the most reason-able ones in today's translation world in my eyes. This paper focuses on the possibility and thec ondition to be achieved the biggest equivalence of the semantic, pragmatic and culture in order to get the conclusion that the translation equivalence is the proper principle. Besides,this paper has also discussed the pragmatic equivalence and cultural equivalence.

  11. On the Translation Equivalence of Literature Works

    Institute of Scientific and Technical Information of China (English)

    吴娟

    2013-01-01

    As for translation principle,people have different opinions.The principle of equivalent translation maybe is one of the most reasonable ones in today’s translation world in my eyes.This paper focuses on the possibility and the condition to be achieved the biggest equivalence of the semantic,pragmatic and culture in order to get the conclusion that the translation equivalence is the proper principle.Besides,this paper has also discussed the pragmatic equivalence and cultural equivalence.

  12. On an equivalence of fuzzy subgroups III

    Directory of Open Access Journals (Sweden)

    V. Murali

    2003-01-01

    Full Text Available This paper is the third in a series of papers studying equivalence classes of fuzzy subgroups of a given group under a suitable equivalence relation. We introduce the notion of a pinned flag in order to study the operations sum, intersection and union, and their behavior with respect to the equivalence. Further, we investigate the extent to which a homomorphism preserves the equivalence. Whenever the equivalences are not preserved, we have provided suitable counterexamples.

  13. Research on temperature rise and thermal distortion of hollow cooling ball screw based on finite element method%基于有限元法的中空冷却滚珠丝杠温升及热变形研究

    Institute of Scientific and Technical Information of China (English)

    芮执元; 张传辉; 郭俊锋

    2011-01-01

    Aiming at heat generation and thermal deformation problems during the working process of ball screw feeding system in high speed machine, a mathematical model for temperature field and thermal distortion of hollow cooling ball screw drive was established based on heat transfer theory. The model was validated through the finite element simulation and screw cooling running simulation test. The results show that the screw temperature rise and thermal deformation of the screw increases gradually and tends to be a steady value with the screw speed increases and operation time e-lapses.%针对高速机床工作过程中滚珠丝杠进给系统的发热及热变形问题,基于传热学理论,建立了中空冷却滚珠丝杠传动过程中温度场和热变形的数学模型,并通过有限元仿真模拟和丝杠冷却模拟运行试验对该模型进行验证.结果表明,随着丝杠转速的提高和运行时间的增加,丝杠温升和热变形先是逐渐增大,然后趋于一个稳定值.

  14. Technological advances of compressors in refrigerating machines. Evolutions technologiques des compresseurs de machines frigorifiques

    Energy Technology Data Exchange (ETDEWEB)

    Sartre, V.; Lallemand, M. (Centre National de la Recherche Scientifique, 69 - Villleurbanne (France)); Chiaffi, M. (Societe Bertin et Compagnie, 78 - Plaisir (France))

    1994-03-01

    The present study is related to the development of compressors for heat pumps and refrigerating machines. For a given application, various compressor technologies are possible. The choice is often dictated by the experience acquired on a compressor type, ensuring good reliability and a reasonable cost of the plant. In our study, we examine the limits of various compressor types: piston, screw, scroll, rotary vane, rolling piston and centrifugal. A comparison of the theoretical and practical limits of the compressors' operating ranges shows the necessity of better adaptation of the compressor type to each application. Finally, we suggest the main research focus for the development of future compressors. The new technologies should evolve towards a variable-speed operation, without lubricating oil or with refrigerant lubrication. Acoustic comfort is also an important criterion. (author)

  15. Conformal dynamical equivalence and applications

    Science.gov (United States)

    Spyrou, N. K.

    2011-02-01

    The "Conformal Dynamical Equivalence" (CDE) approach is briefly reviewed, and some of its applications, at various astrophysical levels (Sun, Solar System, Stars, Galaxies, Clusters of Galaxies, Universe as a whole), are presented. According to the CDE approach, in both the Newtonian and general-relativistic theories of gravity, the isentropic hydrodynamic flows in the interior of a bounded gravitating perfect-fluid source are dynamically equivalent to geodesic motions in a virtual, fully defined fluid source. Equivalently, the equations of hydrodynamic motion in the former source are functionally similar to those of the geodesic motions in the latter, physically, fully defined source. The CDE approach is followed for the dynamical description of the motions in the fluid source. After an observational introduction, taking into account all the internal physical characteristics of the corresponding perfect-fluid source, and based on the property of the isentropic hydrodynamic flows (quite reasonable for an isolated physical system), we examine a number of issues, namely, (i) the classical Newtonian explanation of the celebrated Pioneer-Anomaly effect in the Solar System, (ii) the possibility of both the attractive gravity and the repulsive gravity in a non-quantum Newtonian framework, (iii) the evaluation of the masses - theoretical, dynamical, and missing - and of the linear dimensions of non-magnetized and magnetized large-scale cosmological structures, (iv) the explanation of the flat-rotation curves of disc galaxies, (v) possible formation mechanisms of winds and jets, and (vi) a brief presentation of a conventional approach - toy model to the dynamics of the Universe, characterized by the dominant collisional dark matter (with its subdominant luminous baryonic "contamination"), correctly interpreting the cosmological observational data without the need of the notions dark energy, cosmological constant, and universal accelerating expansion.

  16. Asynchronized synchronous machines

    CERN Document Server

    Botvinnik, M M

    1964-01-01

    Asynchronized Synchronous Machines focuses on the theoretical research on asynchronized synchronous (AS) machines, which are "hybrids” of synchronous and induction machines that can operate with slip. Topics covered in this book include the initial equations; vector diagram of an AS machine; regulation in cases of deviation from the law of full compensation; parameters of the excitation system; and schematic diagram of an excitation regulator. The possible applications of AS machines and its calculations in certain cases are also discussed. This publication is beneficial for students and indiv

  17. Quantum machine learning.

    Science.gov (United States)

    Biamonte, Jacob; Wittek, Peter; Pancotti, Nicola; Rebentrost, Patrick; Wiebe, Nathan; Lloyd, Seth

    2017-09-13

    Fuelled by increasing computer power and algorithmic advances, machine learning techniques have become powerful tools for finding patterns in data. Quantum systems produce atypical patterns that classical systems are thought not to produce efficiently, so it is reasonable to postulate that quantum computers may outperform classical computers on machine learning tasks. The field of quantum machine learning explores how to devise and implement quantum software that could enable machine learning that is faster than that of classical computers. Recent work has produced quantum algorithms that could act as the building blocks of machine learning programs, but the hardware and software challenges are still considerable.

  18. Precision machine design

    CERN Document Server

    Slocum, Alexander H

    1992-01-01

    This book is a comprehensive engineering exploration of all the aspects of precision machine design - both component and system design considerations for precision machines. It addresses both theoretical analysis and practical implementation providing many real-world design case studies as well as numerous examples of existing components and their characteristics. Fast becoming a classic, this book includes examples of analysis techniques, along with the philosophy of the solution method. It explores the physics of errors in machines and how such knowledge can be used to build an error budget for a machine, how error budgets can be used to design more accurate machines.

  19. Continuous twin screw melt granulation of glyceryl behenate: Development of controlled release tramadol hydrochloride tablets for improved safety.

    Science.gov (United States)

    Keen, Justin M; Foley, Connor J; Hughey, Justin R; Bennett, Ryan C; Jannin, Vincent; Rosiaux, Yvonne; Marchaud, Delphine; McGinity, James W

    2015-06-20

    Interest in granulation processes using twin screw extrusion machines is rapidly growing. The primary objectives of this study were to develop a continuous granulation process for direct production of granules using this technique with glyceryl behenate as a binder, evaluate the properties of the resulting granules and develop controlled release tablets containing tramadol HCl. In addition, the granulation mechanism was probed and the polymorphic form of the lipid and drug release rate were evaluated on stability. Granules were prepared using a Leistritz NANO16 twin screw extruder operated without a constricting die. The solid state of the granules were characterized by differential scanning calorimetry and X-ray diffraction. Formulated tablets were studied in 0.1N HCl containing 0-40% ethanol to investigate propensity for alcohol induced dose dumping. The extrusion barrel temperature profile and feed rate were determined to be the primary factors influencing the particle size distribution. Granules were formed by a combination immersion/distribution mechanism, did not require subsequent milling, and were observed to contain desirable polymorphic forms of glyceryl behenate. Drug release from tablets was complete and controlled over 16 h and the tablets were determined to be resistant to alcohol induced dose dumping. The drug release rate from the tablets was found to be stable at 40°C and 75% relative humidity for the duration of a 3 month study.

  20. Equivalence principle in Chameleon models .

    Science.gov (United States)

    Kraiselburd, L.; Landau, S.; Salgado, M.; Sudarsky, D.

    Most theories that predict time and/or space variation of fundamental constants also predict violations of the Weak Equivalence Principle (WEP). Khoury and Weltmann proposed the chameleon model in 2004 and claimed that this model avoids experimental bounds on WEP. We present a contrasting view based on an approximate calculation of the two body problem for the chameleon field and show that the force depends on the test body composition. Furthermore, we compare the prediction of the force on a test body with Eötvös type experiments and find that the chameleon field effect cannot account for current bounds.

  1. Thermodynamic equivalence of spin systems

    Energy Technology Data Exchange (ETDEWEB)

    Beltman, J.M. (Katholieke Universiteit Nijmegen (Netherlands))

    1975-01-01

    The thermodynamic equilibrium properties of systems composed of classical spin /sup 1///sub 2/ particles (Ising spins) are studied. Given an interaction pattern between the Ising spins the main problem is to calculate the equilibrium state(s) of the system. The point put forward here is the existence of many thermodynamical equivalent spin coordinate systems. As a consequence of this phenomenon the interaction pattern of a system may be very intricate when described with respect to one spin coordinate system whereas it may become simple with respect to another one and vice versa. A systematic investigation of this phenomenon is made. (FR)

  2. Blast Wave Characteristics and Equivalency

    OpenAIRE

    Sochet, Isabelle; Schneider, Helmut

    2010-01-01

    ISBN 978-5-94588-079-5; The characteristics of blast waves generated by detonation of gas clouds are studies theoretically and validated by both small-scale and large-scale experiments with ethylene-air mixtures of different equivalence ratio. The mixtures were confined in hemispherical or spherical balloons made from thin polyethylene foils of 0.75 m³ and 15 m³ in volume. The detonation of gas mixtures was initiated by a solid explosive. The characteristics of the blast wave in terms of over...

  3. Equivalence Principle in Chameleon Models

    CERN Document Server

    Kraiselburd, Lucila; Salgado, Marcelo; Sudarsky, Daniel

    2013-01-01

    Most theories that predict time and/or space variation of fundamental constants also predict violations of the Weak Equivalence Principle (WEP). Khoury and Weltmann proposed the chameleon model in 2004 and claimed that this model avoids experimental bounds on WEP. We present a contrasting view based on an approximate calculation of the two body problem for the chameleon field and show that the force depends on the test body composition. Furthermore, we compare the prediction of the force on a test body with E\\"otv\\"os type experiments and find that the chameleon field effect cannot account for current bounds.

  4. On Vasyliunas's equivalent conductivity formalism

    Science.gov (United States)

    Pontius, D. H., Jr.

    1992-01-01

    The Vasyliunas's (1972) equivalent conductivity formalism (ECF) for representing the coupling of the ionosphere and the magnetosphere is discussed, and a new, simpler, derivation is presented of the ECF, in which certain of the underlying assumptions and their implications are made transparent. The derivation presented indicates that the only role of the ions in the ECF is to insure quasi-neutrality. It is shown that the ECF is not as robust as usually assumed and that caution must be used to insure that reasonable results are obtained.

  5. Nano-scale machining of polycrystalline coppers - effects of grain size and machining parameters.

    Science.gov (United States)

    Shi, Jing; Wang, Yachao; Yang, Xiaoping

    2013-11-22

    In this study, a comprehensive investigation on nano-scale machining of polycrystalline copper structures is carried out by molecular dynamics (MD) simulation. Simulation cases are constructed to study the impacts of grain size, as well as various machining parameters. Six polycrystalline copper structures are produced, which have the corresponding equivalent grain sizes of 5.32, 6.70, 8.44, 13.40, 14.75, and 16.88 nm, respectively. Three levels of depth of cut, machining speed, and tool rake angle are also considered. The results show that greater cutting forces are required in nano-scale polycrystalline machining with the increase of depth of cut, machining speed, and the use of the negative tool rake angles. The distributions of equivalent stress are consistent with the cutting force trends. Moreover, it is discovered that in the grain size range of 5.32 to 14.75 nm, the cutting forces and equivalent stress increase with the increase of grain size for the nano-structured copper, while the trends reserve after the grain size becomes even higher. This discovery confirms the existence of both the regular Hall-Petch relation and the inverse Hall-Petch relation in polycrystalline machining, and the existence of a threshold grain size allows one of the two relations to become dominant. The dislocation-grain boundary interaction shows that the resistance of the grain boundary to dislocation movement is the fundamental mechanism of the Hall-Petch relation, while grain boundary diffusion and movement is the reason of the inverse Hall-Petch relation.

  6. Note on the equivalence of hierarchical variational models and auxiliary deep generative models

    OpenAIRE

    Brümmer, Niko

    2016-01-01

    This note compares two recently published machine learning methods for constructing flexible, but tractable families of variational hidden-variable posteriors. The first method, called "hierarchical variational models" enriches the inference model with an extra variable, while the other, called "auxiliary deep generative models", enriches the generative model instead. We conclude that the two methods are mathematically equivalent.

  7. Accuracy and safety of free-hand pedicle screw fixation in age less than 10 years

    Directory of Open Access Journals (Sweden)

    Hyoung Yeon Seo

    2013-01-01

    Full Text Available Background: Pedicle screws are being used commonly in the treatment of various spinal disorders. However, use of pedicle screws in the pediatric population is not routinely recommended because of the risk of complications. The present study was to evaluate the safety of pedicle screws placed in children aged less than 10 years with spinal deformities and to determine the accuracy and complication (early and late of pedicle screw placement using the postoperative computed tomography (CT scans. Materials and Methods: Thirty one patients (11 males and 20 females who underwent 261 pedicle screw fixations (177 in thoracic vertebrae and 84 in lumbar vertebrae for a variety of pediatric spinal deformities at a single institution were included in the study. The average age of patients was 7 years and 10 months. These patients underwent postoperative CT scan which was assessed by two independent observers (spine surgeons not involved in the treatment. Results: Breach rate was 5.4% (14/261 screws for all pedicles. Of the 177 screws placed in the thoracic spine, 13 (7.3% had breached the pedicle, that is 92.7% of the screws were accurately placed within pedicles. Seven screws (4% had breached the medial pedicle wall, 4 screws (2.3% had breached the lateral pedicle wall and 2 screws (1.1% had breached the superior or inferior pedicle wall respectively. Of the 84 screws placed in the lumbar spine, 83 (98.8% screws were accurately placed within the pedicle. Only 1 screw (1.2% was found to be laterally displaced. In addition, the breach rate was found to be 4.2% (11/261 screws with respect to the vertebral bodies. No neurological, vascular or visceral complications were encountered. Conclusions: The accuracy of pedicle screw placement in pedicles and vertebral bodies were 94.6% and 95.8% respectively and there was no complication related to screw placement noted until the last followup. These results suggest that free-hand pedicle screw fixation can be safely

  8. Comparison of migration behavior between single and dual lag screw implants for intertrochanteric fracture fixation

    Directory of Open Access Journals (Sweden)

    Katonis Pavlos G

    2009-05-01

    Full Text Available Abstract Background Lag screw cut-out failure following fixation of unstable intertrochanteric fractures in osteoporotic bone remains an unsolved challenge. This study tested if resistance to cut-out failure can be improved by using a dual lag screw implant in place of a single lag screw implant. Migration behavior and cut-out resistance of a single and a dual lag screw implant were comparatively evaluated in surrogate specimens using an established laboratory model of hip screw cut-out failure. Methods Five dual lag screw implants (Endovis, Citieffe and five single lag screw implants (DHS, Synthes were tested in the Hip Implant Performance Simulator (HIPS of the Legacy Biomechanics Laboratory. This model simulated osteoporotic bone, an unstable fracture, and biaxial rocking motion representative of hip loading during normal gait. All constructs were loaded up to 20,000 cycles of 1.45 kN peak magnitude under biaxial rocking motion. The migration kinematics was continuously monitored with 6-degrees of freedom motion tracking system and the number of cycles to implant cut-out was recorded. Results The dual lag screw implant exhibited significantly less migration and sustained more loading cycles in comparison to the DHS single lag screw. All DHS constructs failed before 20,000 cycles, on average at 6,638 ± 2,837 cycles either by cut-out or permanent screw bending. At failure, DHS constructs exhibited 10.8 ± 2.3° varus collapse and 15.5 ± 9.5° rotation around the lag screw axis. Four out of five dual screws constructs sustained 20,000 loading cycles. One dual screw specimens sustained cut-out by medial migration of the distal screw after 10,054 cycles. At test end, varus collapse and neck rotation in dual screws implants advanced to 3.7 ± 1.7° and 1.6 ± 1.0°, respectively. Conclusion The single and double lag screw implants demonstrated a significantly different migration resistance in surrogate specimens under gait loading simulation with

  9. Error Modeling and Sensitivity Analysis of a Five-Axis Machine Tool

    Directory of Open Access Journals (Sweden)

    Wenjie Tian

    2014-01-01

    Full Text Available Geometric error modeling and its sensitivity analysis are carried out in this paper, which is helpful for precision design of machine tools. Screw theory and rigid body kinematics are used to establish the error model of an RRTTT-type five-axis machine tool, which enables the source errors affecting the compensable and uncompensable pose accuracy of the machine tool to be explicitly separated, thereby providing designers and/or field engineers with an informative guideline for the accuracy improvement by suitable measures, that is, component tolerancing in design, manufacturing, and assembly processes, and error compensation. The sensitivity analysis method is proposed, and the sensitivities of compensable and uncompensable pose accuracies are analyzed. The analysis results will be used for the precision design of the machine tool.

  10. The design of the test apparatus of heavy load ball-screw%重载滚珠丝杠试验仪的设计

    Institute of Scientific and Technical Information of China (English)

    黄宽; 殷爱华

    2012-01-01

    Introduce the design of the system of the test apparatus of heavy load ball-screw, which includes the project of the system, testing theory and flow chart of the software. The test apparatus can dynamically measure the reverse interval, friction moment, temperature rising of heavy load ball screw and provide the experiment data for the optimization design of the heavy load ball screw. The system can measure reliably and has worked steadily in Hanjiang Machine Tool Co. , Ltd..%介绍了重载滚珠丝杠试验仪的系统设计,包括系统方案、测量原理和软件流程图等.该试验仪可以动态测量重载滚珠丝杠的反向间隙、摩擦力矩和温升,为重载滚珠丝杠副的优化设计提供实验数据.该系统测量可靠,已经在陕西汉江机床有限公司稳定运行.

  11. Highly viscous fluid flow in the kneading zone of a corotating twin-screw extruder; Die Stroemung hochviskoser Fluessigkeiten im Knetbereich einer Gleichdralldoppelschnecke

    Energy Technology Data Exchange (ETDEWEB)

    Wuensch, O.; Boehme, G. [Universitaet der Bundeswehr, Hamburg (Germany). Inst. fuer Stroemungslehre und Stroemungsmaschinen

    2001-05-01

    Peoples running screw machines are strongly interested in a detailed theoretical analysis of the transport processes for real highly viscous liquids which are non-Newtonian in general. The paper deals with an unconventional strategy which enables to simulate the three-dimensional unsteady flow in the kneading zone of intermeshing twin-screw extruders numerically. The concept is pointed at a finite element approximation of the flow field at particular times well chosen after the computation domain has been minimized with the aid of periodicities and symmetries existing in space and time. The method has been realized numerically and proved by means of a typical kneading geometry. Selected results show that the flow and deformation processes in the kneading element differ substantially from those in a screwed segment. (orig.) [German] Es besteht ein erhebliches Interesse daran, die Transportprozesse in Schneckenmaschinen fuer reale hochviskose, nichtnewtonsche Fluessigkeiten im Detail theoretisch zu analysieren und berechenbar zu machen. In der Arbeit wird eine unkonventionelle Strategie beschrieben, nach der die dreidimensionale instationaere Stroemung im Knetbereich kaemmender Doppelschnecken numerisch simuliert werden kann. Das theoretisch fundierte Konzept zielt auf eine Finite-Elemente-Approximation des Stroemungsfelds zu gewissen Zeitpunkten, wobei das Berechnungsgebiet mit Hilfe raeumlicher und zeitlicher Periodizitaeten und Symmetrien minimiert wird. Das Konzept wurde numerisch realisiert und an einer typischen Knetgeometrie erprobt. Ausgewaehlte Ergebnisse machen deutlich, da paragraph sich die Stroemungs- und Deformationsprozesse in einem Knetelement wesentlich von denen in einem Schraubenelement gleicher Geometrie unterscheiden. (orig.)

  12. PROSPECTS OF USE OF RELATIVE SCREW AND COMBINED REELS FOR MIXING BULKS

    Directory of Open Access Journals (Sweden)

    Marchenko A. Y.

    2015-11-01

    Full Text Available The article reveals a possibility of using equipment based on relative screw and combined drums for mixing of bulks. Change of relative positioning of flat elements of sidewalls of internal surfaces in relative screw drums allows operating the difficult and spatial movement of streams of bulks. In relative screw drums we have developed effective processes of mixing and sets of the equipment, which are characterized by that fact the difficult and spatial screw movement taking place in relative screw drums is dismembered on rather simple, in the kinematic relation, in the movements. The difficult and spatial screw movement with a big amplitude of 15-1000 mm and more, in the offered equipment constructions on the basis of relative screw or combined drums, is reported to bulks by elements of the relative screw or combined drums of various parameters and configurations which becomes complicated also screw lines on perimeter of a relative screw drum with various number of calling and the directions from each other or rounds of the springs fixed in the relative combined drums

  13. Cytotoxicity of a new antimicrobial coating for surgical screws: an in vivo study

    Science.gov (United States)

    Güzel, Yunus; Elmadag, Mehmet; Uzer, Gokcer; Yıldız, Fatih; Bilsel, Kerem; Tuncay, İbrahim

    2017-01-01

    INTRODUCTION The risk of surgery-related infection is a persistent problem in orthopaedics and infections involving implants are particularly difficult to treat. This study explored the responses of bone and soft tissue to antimicrobial-coated screws. We investigated whether such screws, which have never been used to fix bony tissues, would result in a cytotoxic effect. We hypothesised that the coated screws would not be toxic to the bone and that the likelihood of infection would be reduced since bacteria are not able to grow on these screws. METHODS Titanium screws were inserted into the left supracondylar femoral regions of 16 rabbits. The screws were either uncoated (control group, n = 8) or coated with a polyvinylpyrrolidone-polyurethane interpolymer with tertiary amine functional groups (experimental group, n = 8). At Week 6, histological samples were obtained and examined. The presence of necrosis, fibrosis and inflammation in the bony tissue and the tissue surrounding the screws was recorded. RESULTS Live, cellular bone marrow was present in all the rabbits from the experimental group, but was replaced with connective tissue in four rabbits from the control group. Eight rabbits from the control group and two rabbits from the experimental group had necrosis in fatty bone marrow. Inflammation was observed in one rabbit from the experimental group and five rabbits from the control group. CONCLUSION Titanium surgical screws coated with polyvinylpyrrolidone-polyurethane interpolymer were associated with less necrosis than standard uncoated screws. The coated screws were also not associated with any cytotoxic side effect. PMID:26805670

  14. A novel approach to navigated implantation of S-2 alar iliac screws using inertial measurement units.

    Science.gov (United States)

    Jost, Gregory F; Walti, Jonas; Mariani, Luigi; Cattin, Philippe

    2016-03-01

    The authors report on a novel method of intraoperative navigation with inertial measurement units (IMUs) for implantation of S-2 alar iliac (S2AI) screws in sacropelvic fixation of the human spine and its application in cadaveric specimens. Screw trajectories were planned on a multiplanar reconstruction of the preoperative CT scan. The pedicle finder and screwdriver were equipped with IMUs to guide the axial and sagittal tilt angles of the planned trajectory, and navigation software was developed. The entry points were chosen according to anatomical landmarks on the exposed spine. After referencing, the sagittal and axial orientation of the pedicle finder and screwdriver were wirelessly monitored on a computer screen and aligned with the preoperatively planned tilt angles to implant the S2AI screws. The technique was performed without any intraoperative imaging. Screw positions were analyzed on postoperative CT scans. Seventeen of 18 screws showed a good S2AI screw trajectory. Compared with the postoperatively measured tilt angles of the S2AI screws, the IMU readings on the screwdriver were within an axial plane deviation of 0° to 5° in 15 (83%) and 6° to 10° in 2 (11%) of the screws and within a sagittal plane deviation of 0° to 5° in 15 (83%) and 6° to 10° in 3 (17%) of the screws. IMU-based intraoperative navigation may facilitate accurate placement of S2AI screws.

  15. SU-E-T-609: Perturbation Effects of Pedicle Screws On Radiotherapy Dose Distributions

    Energy Technology Data Exchange (ETDEWEB)

    Bar-Deroma, R; Borzov, E; Nevelsky, A [Rambam Medical Center, Haifa (Israel)

    2015-06-15

    Purpose: Radiation therapy in conjunction with surgical implant fixation is a common combined treatment in case of bone metastases. However, metal implants generally used in orthopedic implants perturb radiation dose distributions. Carbon-Fiber Reinforced (CFR) PEEK material has been recently introduced for production of intramedullary screws and plates. Gold powder can be added to the CFR-PEEK material in order to enhance visibility of the screws during intraoperative imaging procedures. In this work, we investigated the perturbation effects of the pedicle screws made of CFR-PEEK, CFR-PEEK with added gold powder (CFR-PEEK-AU) and Titanium (Ti) on radiotherapy dose distributions. Methods: Monte Carlo (MC) simulations were performed using the EGSnrc code package for 6MV beams with 10×10 fields at SSD=100cm. By means of MC simulations, dose distributions around titanium, CFR- PEEK and CFR-PEEK-AU screws (manufactured by Carbo-Fix Orthopedics LTD, Israel) placed in a water phantom were calculated. The screw axis was either parallel or perpendicular to the beam axis. Dose perturbation (relative to dose in homogeneous water phantom) was assessed. Results: Maximum overdose due to backscatter was 10% for the Ti screws, 5% for the CFR-PEEK-AU screws and effectively zero for the CFR-PEEK screws. Maximum underdose due to attenuation was 25% for the Ti screws, 15% for the CFR-PEEK-AU screws and 5% for the CFR-PEEK screws. Conclusion: Titanium screws introduce the largest distortion on the radiation dose distribution. The gold powder added to the CFR-PEEK material improves visibility at the cost of increased dose perturbation. CFR-PEEK screws caused minimal alteration on the dose distribution. This can decrease possible over and underdose of adjacent tissue and thus favorably influence treatment efficiency. The use of such implants has potential clinical advantage in the treatment of neoplastic bone disease.

  16. Determination of Screw and Nail Withdrawal Resistance of Some Important Wood Species

    Directory of Open Access Journals (Sweden)

    Alper Aytekin

    2008-04-01

    Full Text Available In this study, screw and nail withdrawal resistance of fir (Abies nordmanniana, oak (Quercus robur L. black pine (Pinus nigra Arnold and Stone pine (Pinus pinea L. wood were determined and compared. The data represent the testing of withdrawal resistance of three types of screws as smart, serrated and conventional and common nails. The specimens were prepared according to TS 6094 standards. The dimensions of the specimens were 5x5x15cm and for all of the directions. Moreover, the specimens were conditioned at ambient room temperature and 65±2% relative humidity. The screws and nails were installed according to ASTM-D 1761 standards. Nail dimensions were 2.5mm diameter and 50 mm length, conventional screws were 4x50mm, serrated screws were 4x45mm and smart screws were 4x50mm. Results show that the maximum screw withdrawal resistance value was found in Stone pine for the serrated screw. There were no significant differences between Stone pine and oak regarding screw withdrawal resistance values. Conventional screw yielded the maximum screw withdrawal resistance value in oak, followed by Stone pine, black pine and fir. Oak wood showed the maximum screw withdrawal resistance value for the smart screw, followed by Stone pine, black pine, and fir. Oak wood showed higher nail withdrawal resistances than softwood species. It was also determined that oak shows the maximum nail withdrawal resistance in all types. The nail withdrawal resistances at the longitudinal direction are lower with respect to radial and tangential directions.

  17. Perspex machine: VII. The universal perspex machine

    Science.gov (United States)

    Anderson, James A. D. W.

    2006-01-01

    The perspex machine arose from the unification of projective geometry with the Turing machine. It uses a total arithmetic, called transreal arithmetic, that contains real arithmetic and allows division by zero. Transreal arithmetic is redefined here. The new arithmetic has both a positive and a negative infinity which lie at the extremes of the number line, and a number nullity that lies off the number line. We prove that nullity, 0/0, is a number. Hence a number may have one of four signs: negative, zero, positive, or nullity. It is, therefore, impossible to encode the sign of a number in one bit, as floating-point arithmetic attempts to do, resulting in the difficulty of having both positive and negative zeros and NaNs. Transrational arithmetic is consistent with Cantor arithmetic. In an extension to real arithmetic, the product of zero, an infinity, or nullity with its reciprocal is nullity, not unity. This avoids the usual contradictions that follow from allowing division by zero. Transreal arithmetic has a fixed algebraic structure and does not admit options as IEEE, floating-point arithmetic does. Most significantly, nullity has a simple semantics that is related to zero. Zero means "no value" and nullity means "no information." We argue that nullity is as useful to a manufactured computer as zero is to a human computer. The perspex machine is intended to offer one solution to the mind-body problem by showing how the computable aspects of mind and, perhaps, the whole of mind relates to the geometrical aspects of body and, perhaps, the whole of body. We review some of Turing's writings and show that he held the view that his machine has spatial properties. In particular, that it has the property of being a 7D lattice of compact spaces. Thus, we read Turing as believing that his machine relates computation to geometrical bodies. We simplify the perspex machine by substituting an augmented Euclidean geometry for projective geometry. This leads to a general

  18. Numerical Simulation and Performance Analysis of Twin Screw Air Compressors

    Directory of Open Access Journals (Sweden)

    W. S. Lee

    2001-01-01

    Full Text Available A theoretical model is proposed in this paper in order to study the performance of oil-less and oil-injected twin screw air compressors. Based on this model, a computer simulation program is developed and the effects of different design parameters including rotor profile, geometric clearance, oil-injected angle, oil temperature, oil flow rate, built-in volume ratio and other operation conditions on the performance of twin screw air compressors are investigated. The simulation program gives us output variables such as specific power, compression ratio, compression efficiency, volumetric efficiency, and discharge temperature. Some of the above results are then compared with experimentally measured data and good agreement is found between the simulation results and the measured data.

  19. Analysis of Eyring-Powell Fluid in Helical Screw Rheometer

    Directory of Open Access Journals (Sweden)

    A. M. Siddiqui

    2014-01-01

    Full Text Available This paper aims to study the flow of an incompressible, isothermal Eyring-Powell fluid in a helical screw rheometer. The complicated geometry of the helical screw rheometer is simplified by “unwrapping or flattening” the channel, lands, and the outside rotating barrel, assuming the width of the channel is larger as compared to the depth. The developed second order nonlinear differential equations are solved by using Adomian decomposition method. Analytical expressions are obtained for the velocity profiles, shear stresses, shear at wall, force exerted on fluid, volume flow rates, and average velocity. The effect of non-Newtonian parameters, pressure gradients, and flight angle on the velocity profiles is noticed with the help of graphical representation. The observation confirmed the vital role of involved parameters during the extrusion process.

  20. Analysis of Eyring-Powell fluid in helical screw rheometer.

    Science.gov (United States)

    Siddiqui, A M; Haroon, T; Zeb, M

    2014-01-01

    This paper aims to study the flow of an incompressible, isothermal Eyring-Powell fluid in a helical screw rheometer. The complicated geometry of the helical screw rheometer is simplified by "unwrapping or flattening" the channel, lands, and the outside rotating barrel, assuming the width of the channel is larger as compared to the depth. The developed second order nonlinear differential equations are solved by using Adomian decomposition method. Analytical expressions are obtained for the velocity profiles, shear stresses, shear at wall, force exerted on fluid, volume flow rates, and average velocity. The effect of non-Newtonian parameters, pressure gradients, and flight angle on the velocity profiles is noticed with the help of graphical representation. The observation confirmed the vital role of involved parameters during the extrusion process.

  1. HA/UHMWPE Nanocomposite Produced by Twin-screw Extrusion

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    The HA/UHMWPE nanocomposite is compounded by twin-screw extrusion of the HA and UHMWPE powder mixture in paraffin oil and then compression molded to a sheet form. TGA measurement shows the HA weight loss after processing is about 1%-2% . FTIR spectra indicate the paraffin oil residue is trivial and UHMWPE is not oxidized. SEM reveals the HA nano particles are homogeneously dispersed by twin- screw extrusion and the inter-particle spaces are penetrated with UHMWPE fibrils by swelling treatment. HRTEM image indicates the HA particles and UHMWPE are intimately contacted by mechanical interlocking. Compared with the unfilled UHMWPE, stiffness of the composite with the HA volume fraction 0.23 was significantly enhanced to 9 times without detriment of the yield strength and the ductility.

  2. Accuracy of spinal navigation for Magerl-screws

    CERN Document Server

    Herz, T

    2001-01-01

    Study design: assessment of the accuracy of frameless stereotactic navigation at the second cervical vertebra. Objectives: to assess the influence of the protocol of preoperative CT-scan and the registration technique on the accuracy of navigation for implanting Magerl-screws. Summary of background data: the use of navigation systems for implanting Magerl-screws could help to decrease the risk of complications and to reduce the required skin incision. Two parameters conceivably affecting the accuracy are the protocol of the preoperative CT-scan and the registration technique. Methods: four cervical spine segments of human cadavers were scanned with two different protocols (3 mm slice thickness/2 mm table increment, 1 mm slice thickness/1 mm table increment). Registration was performed either based on anatomical landmarks or using a specially designed percutaneous registration device. For the accuracy-check, the pointer tip was exactly placed on markers. The distance between the pointer and the marker displaye...

  3. PERFORMANCE OPTIMIZATION OF AN ORGANIC MUD AGITATOR SCREW

    Directory of Open Access Journals (Sweden)

    Mircea Dimitrie CAZACU

    2009-11-01

    Full Text Available Due to the special performances obtained by means of the optimisation method applied to the axial runners of run-of-river hydraulic turbines and of wind turbines, as well as in the case of the screws for boat propulsion, perfected by the first of the authors [1] - [10], in this work one extend the application of this method at the case of an organic mud agitator screw for fermentation and biogas production. One presents the obtaining of the bio liquid circulation minimal velocity in the two possible cases [3]: extracting the fluid velocity from the peripheral force exerted by the runner, as well as from the mechanical power consumed for its driving. After the obtaining of the optimal relative peripheral angle one determines also the optimal incidence angles of the profile for other blade radii. This method permits in the same time to find the optimal profile, using the multitude of the profile characteristics, experimentally studied.

  4. Modeling the Parker instability in a rotating plasma screw pinch

    CERN Document Server

    Khalzov, I V; Katz, N; Forest, C B; 10.1063/1.3684240

    2012-01-01

    We analytically and numerically study the analogue of the Parker (magnetic buoyancy) instability in a uniformly rotating plasma screw pinch confined in a cylinder. Uniform plasma rotation is imposed to create a centrifugal acceleration, which mimics the gravity required for the classical Parker instability. The goal of this study is to determine how the Parker instability could be unambiguously identified in a weakly magnetized, rapidly rotating screw pinch, in which the rotation provides an effective gravity and a radially varying azimuthal field is controlled to give conditions for which the plasma is magnetically buoyant to inward motion. We show that an axial magnetic field is also required to circumvent conventional current driven magnetohydrodynamic (MHD) instabilities such as the sausage and kink modes that would obscure the Parker instability. These conditions can be realized in the Madison Plasma Couette Experiment (MPCX). Simulations are performed using the extended MHD code NIMROD for an isothermal...

  5. EQUIVALENT EXCITATION METHOD FOR VIBRATION ISOLATION DESIGN:THEORETICAL ANALYSIS AND EXPERIMENTAL RESULTS

    Institute of Scientific and Technical Information of China (English)

    Huo Rui; Shi Yin

    2005-01-01

    In view of difficulties concerned with direct measurement of excitations inside source equipments and their significant influence on vibration isolation effectiveness, a dynamical model, for vibration isolation of a rigid machine with six-degree-of-freedom mounted on a flexible foundation through multiple mounts, is analyzed, in which the complicated and multiple disturbances inside the machine are described as an equivalent excitation spectrum. And a method for the estimation of the equivalent excitation spectrum according to system dynamic responses is discussed for the quantitative prediction of isolation effectiveness.Both theoretical analysis and experimental results are demonstrated. Further work shows the quantitative prediction of transmitted power flow in a flexible vibration isolation experiment system using the proposed equivalent excitation spectrum method, by comparison with its testing results.

  6. Smallest Archimedean Screw: Facet Dynamics and Friction in Multiwalled Nanotubes.

    Science.gov (United States)

    Guerra, Roberto; Leven, Itai; Vanossi, Andrea; Hod, Oded; Tosatti, Erio

    2017-08-28

    We identify a new material phenomenon, where minute mechanical manipulations induce pronounced global structural reconfigurations in faceted multiwalled nanotubes. This behavior has strong implications on the tribological properties of these systems and may be the key to understand the enhanced interwall friction recently measured for boron-nitride nanotubes with respect to their carbon counterparts. Notably, the fast rotation of helical facets in these systems upon coaxial sliding may serve as a nanoscale Archimedean screw for directional transport of physisorbed molecules.

  7. The human sacrum and safe approaches for screw placement.

    Science.gov (United States)

    Arman, Candan; Naderi, Sait; Kiray, Amaç; Aksu, Funda Taştekin; Yilmaz, Hakan Sinan; Tetik, Süleyman; Korman, Esin

    2009-08-01

    The human sacrum is the target of lumbosacral instrumentation and decompression procedures. Such surgical interventions require detailed knowledge of the anatomy of the human sacrum. The aim of this study was to measure surgically relevant parameters. Several factors, including the one-piece composition of the sacrum, the angles of the sacral pedicles and the anteroposterior diameter of the sacral vertebral bodies distinguish the sacrum from other parts of spine. Thirty-two measurements of shape, angles and distances between parts were taken of the sacra of 100 adult West Anatolian people using a Vernier caliper accurate to 0.1 mm and goniometer. According to this morphometric study, when measured from the sagittal, the S1 facet angle was measured as 35.71 degrees +/-9.59 and 34.70 degrees +/-9.66, the sacral pedicle anteromedial screw trajectory angle was 35.65 degrees +/-4.73 and 31.95 degrees +/-3.95 and the anterolaterally oriented sacral wing screw trajectory angle was 32.65 degrees +/-3.51 and 29.10 degrees +/-3.14, on the right and left sides, respectively. The distance of the midline oriented S1 pedicle screw was 51.12 mm and 51.26 mm on the right and left side, respectively. The distance for sacral wing oriented screw placement was 50.13 mm and 50.46 mm on the right and left side, respectively. The anteroposterior and transverse diameter of the sacral spinal canal were 21.81 mm and 31.31 mm, respectively. Thus, this study describes anatomical specifications of the sacrum. These defined morphometric details should be taken into consideration during surgical procedures. This study also describes anatomical landmarks which will allow injury of the sacrum during surgery to be avoided.

  8. Biomechanical comparison of bilateral pedicle screw and unilateral pedicle screw fixation%双侧钉棒及同侧单钉棒置入内固定的生物力学比较

    Institute of Scientific and Technical Information of China (English)

    陈立业; 夏虹; 王建华; 尹庆水

    2011-01-01

    BACKGROUND: Most of lumbar degenerative diseases, such as lumbar instability and lumbar spondylolisthesis, need lumbarspinal fusion for the spine stability, but the choice of internal fixation approaches is an argument.OBJECTIVE: To investigate the biomechanical difference of unilateral and bilateral minimally I nvasive transforaminal lumbarinterbody fusion (TLIF) for the treatment of lumbar degenerative diseases.METHODS: Minimally invasive TLIF with different internal fixations were performed on L4-5 segments from six fresh frozenhuman lumbar cadaveric specimens. Then, the specimens were divided into two groups according to different internal fixationmethods: bilateral pedicle screw group and unilateral pedicle screw group. Range of motion (ROM) for the lumbar function unitwas measured on the biomechanical machine and compared between the two groups.RESULTS AND CONCLUSION: Compared with the compact lumbar function unit, the ROM of the two fixation groups weresignificantly lower (P < 0.05). The ROM value of the bilateral pedicle screw group was significantly lower than that of the unilateralpedicle screw group in all working states (P < 0.05). Biomechanical experiments show that unilateral TLIF provides favorablebiomechanical effect and stiffness, which offers the dependable stability of the lumbar vertebra e. However, compared with thebilateral pedicle screw fixation, there are still gaps in the unilateral pedicle screw fixation.%背景:腰椎失稳、腰椎滑脱等腰椎退行性疾病常常需要实施腰椎融合,其目标是稳定脊柱,但究竟采取何种内固定方式仍存在争论.目的:比较单侧与双侧经椎间孔减压椎体间融合治疗腰椎退行性病变的生物力学差异.方法:人新鲜尸体腰椎标本6具,L4~5模拟微创经椎间孔减压椎体间融合,根据不同的内固定组合方式分为2组,即双侧钉棒组及同侧单钉棒组.在生物力学试验机上测量各种固定方式不同工况下的运动范围(ROM

  9. Historical and Epistemological Reflections on the Culture of Machines around the Renaissance: Machines, Machineries and Perpetual Motion

    Directory of Open Access Journals (Sweden)

    Raffaele Pisano

    2015-05-01

    Full Text Available This paper is the second part of our recent paper ‘Historical and Epistemological Reflections on the Culture of Machines around the Renaissance: How Science and Technique Work’ (Pisano & Bussotti 2014a. In the first paper—which discussed some aspects of the relations between science and technology from Antiquity to the Renaissance—we highlighted the differences between the Aristotelian/Euclidean tradition and the Archimedean tradition. We also pointed out the way in which the two traditions were perceived around the Renaissance. The Archimedean tradition is connected with machines: its relationship with science and construction of machines should be made clear. It is enough to think that Archimedes mainly dealt with three machines: lever, pulley and screw (and a correlated principle of mechanical advantage. As underlined in the first part, our thesis is that many machines were constructed by people who ignored theory, even though, in other cases, the knowledge of the Archimedean tradition was a precious help in order to build machines. Hence, an a priori idea as to the relations between the Archimedean tradition and construction of machines cannot exist. In this second part we offer some examples of functioning machines constructed by people who ignored any physical theory, whereas, in other cases, the ignorance of some principles—such as the impossibility of a perpetuum mobile—induced the attempt to construct impossible machines. What is very interesting is that these machines did not function, of course, as a perpetuum mobile, but anyway had their functioning and were useful for certain aims, although they were constructed on an idea which is completely wrong from a theoretical point of view. We mainly focus on the Renaissance and early modern period, but we also provide examples of machines built before and after this period. We have followed a chronological order in both parts, starting from the analysis of the situation in

  10. Einstein's equivalence principle in cosmology

    CERN Document Server

    Kopeikin, Sergei M

    2013-01-01

    We study physical consequences of the Einstein equivalence principle (EEP) for a Hubble observer in FLRW universe. We introduce the local inertial coordinates with the help of a special conformal transformation. The local inertial metric is Minkowski flat and materialized by a congruence of time-like geodesics of static observers. The static observers are equipped with the ideal clocks measuring the proper time that is synchronized with the clocks of the Hubble observer. The local inertial metric is used for physical measurements of spacetime intervals with the ideal clocks and rulers. The special conformal transformation preserves null geodesics but does not keep invariant time-like geodesics. Moreover, it makes the rate of the local time coordinate dependent on velocity of the particle which makes impossible to rich the uniform parameterization of the world lines of static observers and light geodesics with a single parameter - they differ by the conformal factor of FLRW metric. The most convenient way to s...

  11. ROMANIC EQUIVALENTS FOR LATIN IDIOMS

    Directory of Open Access Journals (Sweden)

    Dr. Stefan DUMITRU

    2010-11-01

    Full Text Available In this study we set forth to present several of the most important aspects regarding the contrastive analysis of a well-defined number of Latin idioms in parallel with their Romanic counterparts (in French, Italian, Spanish and Romanian. Our intent was not to discover, in the Romanic space, all the equivalents of the phrases that form the corpus we work with, for reasons pertaining to material restrictions, but to discuss, based on a certain number of units, the different types of issues they may point to. The most important is to establish the relation between the idiomatic expressions in Latin and their correspondents in the above mentioned languages, regarding their inner form, their meaning and their structure.

  12. Electroweak Vortices and Gauge Equivalence

    Science.gov (United States)

    MacDowell, Samuel W.; Törnkvist, Ola

    Vortex configurations in the electroweak gauge theory are investigated. Two gauge-inequivalent solutions of the field equations, the Z and W vortices, have previously been found. They correspond to embeddings of the Abelian Nielsen-Olesen vortex solution into a U(1) subgroup of SU(2)×U(1). It is shown here that any electroweak vortex solution can be mapped into a solution of the same energy with a vanishing upper component of the Higgs field. The correspondence is a gauge equivalence for all vortex solutions except those for which the winding numbers of the upper and lower Higgs components add to zero. This class of solutions, which includes the W vortex, corresponds to a singular solution in the one-component gauge. The results, combined with numerical investigations, provide an argument against the existence of other vortex solutions in the gauge-Higgs sector of the Standard Model.

  13. Fluid Flow Phenomenon in a Three-Bladed Power-Generating Archimedes Screw Turbine

    Directory of Open Access Journals (Sweden)

    Tineke Saroinsong

    2016-05-01

    Full Text Available Experimental studies of the Archimedes screw turbine are applied as a micro hydro power plant for low head focused on the fluid flow. Fluid flow on a screw turbine is not completely filled water flow there is still a free surface between the water fluid and atmospheric air. Except the screw geometry, the turbine screw free surface allows the flow phenomena that are important in the process of turbine screw power generation. The Archimedes screw turbine main driving force is the fluid-gravity weight, which is affected by the inflow depth, inflow velocity and the turbine shaft’s slope. The dimensionless parameter Froude number (Fr is connected to analyze the screw turbine efficiency. The purpose of this study is to figure out the fluid flow role when power generated by a three blades Archimedes screw turbine observed visualized, and also observed the turbine rotation and torque. The observed parameters are varied in inflow depth as the characteristic length (y of Froude Number, inflow velocity (co, and the turbine shaft slope (α. The screw turbine model, were made under a laboratory scale and made from acrylic material. The geometric form is the three bladed screws which have seven screw respectively, the number of helix turns is 21, the angle of screw blade is 30°, radius ratio of 0.54 with a pitch distance of 2,4 Ro. The result from this study revealed a phenomenon of fluid flow between the screw blades a whirlpool wave occurs or vortex due to the linear momentum in a form of the hydrostatic force against the blade screw which occurs in two opposite directions and the effect of the turbine shaft angular momentum. The vortex would affect the screw turbine power generation process as most of the kinetic energy that goes into the screw turbine sucked into the vortex between the screw blades, but this phenomenon can be reduced by reducing the turbine shaft slope. The highest turbine efficiency of 89% occurred in the turbine shaft’s slope of 25

  14. Expanding the Interaction Equivalency Theorem

    Directory of Open Access Journals (Sweden)

    Brenda Cecilia Padilla Rodriguez

    2015-06-01

    Full Text Available Although interaction is recognised as a key element for learning, its incorporation in online courses can be challenging. The interaction equivalency theorem provides guidelines: Meaningful learning can be supported as long as one of three types of interactions (learner-content, learner-teacher and learner-learner is present at a high level. This study sought to apply this theorem to the corporate sector, and to expand it to include other indicators of course effectiveness: satisfaction, knowledge transfer, business results and return on expectations. A large Mexican organisation participated in this research, with 146 learners, 30 teachers and 3 academic assistants. Three versions of an online course were designed, each emphasising a different type of interaction. Data were collected through surveys, exams, observations, activity logs, think aloud protocols and sales records. All course versions yielded high levels of effectiveness, in terms of satisfaction, learning and return on expectations. Yet, course design did not dictate the types of interactions in which students engaged within the courses. Findings suggest that the interaction equivalency theorem can be reformulated as follows: In corporate settings, an online course can be effective in terms of satisfaction, learning, knowledge transfer, business results and return on expectations, as long as (a at least one of three types of interaction (learner-content, learner-teacher or learner-learner features prominently in the design of the course, and (b course delivery is consistent with the chosen type of interaction. Focusing on only one type of interaction carries a high risk of confusion, disengagement or missed learning opportunities, which can be managed by incorporating other forms of interactions.

  15. The Kelastic variable wall mining machine. Interim final report

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1995-11-12

    This machine cuts coal along a longwall face extending up to 500 feet by a rotating auger with bits. The machine also transports the coal that is cut acting as screw conveyor. By virtue of an integral shroud comprising part of the conveyor the machine is also amenable to a separation of the zones where men work from air being contaminated by dust and methane gas by the cutting action. Beginning as single intake air courses, the air separates at the working section where one split provides fresh air to the Occupied Zone (OZ) for human needs and the other split purges and carries away dust and methane from face fragmentation in the Cutting Zone (CZ). The attractiveness of the Variable Wall Mining Machine is that it addresses the limitations of current longwall mining equipment: it can consistently out-produce continuous mining machines and most longwall shearing machines. It also is amenable to configuring an environment, the dual-duct system, where the air for human breathing is separated from dust-laden ventilating air with methane mixtures. The objective of the research was to perform a mathematical and experimental study of the interrelationships of the components of the system so that a computer model could demonstrate the workings of the system in an animation program. The analysis resulted in the compilation of the parameters for three different configurations of a dual aircourse system of ventilating underground mines. In addressing the goal of an inherently safe mining system the dual-duct adaptation to the Variable Wall Mining Machine appears to offer the path to solution. The respirable dust problem is solvable; the explosive dust problem is nearly solvable; and the explosive methane problem can be greatly reduced. If installed in a highly gassy mine, the dual duct models would also be considerably less costly.

  16. Machining of a bioactive nanocomposite orthopedic fixation device.

    Science.gov (United States)

    Sparnell, Amie; Aniket; El-Ghannam, Ahmed

    2012-08-01

    Bioactive ceramics bond to bone and enhance bone formation. However, they have poor mechanical properties which restrict their machinability as well as their application as load bearing implants. The goal of this study was to machine bioactive fixation screws using a silica-calcium phosphate nanocomposite (SCPC50). The effect of compact pressure, holding time, and thermal treatment on the microstructure, machinability, and mechanical properties of SCPC50 cylinders were investigated. Samples prepared by powder metallurgy technique at compact pressure range of 100-300 MPa and treated at 900°C/1 h scored a poor machinability rating of (1/5) due to the significant formation of amorphous silicate phase at the grain boundaries. On the other hand, lowering of compact pressure and sintering temperature to 30 MPa/3 h and 700°C/2 h, respectively, minimized the formation of the amorphous phase and raised the machinability rating to (5/5). The modulus of elasticity and ultimate strength of machinable SCPC50 were 10.8 ± 2.0 GPa and 72.8 ± 22.8 MPa, respectively, which are comparable to the corresponding values for adult human cortical bone. qRT-PCR analyses showed that bone cells attached to SCPC50 significantly upregulated osteocalcin mRNA expression as compared to the cells on Ti-6Al-4V. Moreover, cells attached to SCPC50 produced mineralized bone-like tissue within 8 days. On the other hand, cells attached to Ti-6Al-4V failed to produce bone mineral under the same experimental conditions. Results of the study suggest that machinable SCPC50 has the potential to serve as an attractive new material for orthopedic fixation devices.

  17. Intramedullary Screw and Kirschner Wire Fixation for Unstable Scaphoid Nonunion.

    Science.gov (United States)

    Allon, Raviv; Kramer, Aviv; Wollstein, Ronit

    2016-12-01

    Surgical treatment of scaphoid nonunion is not always successful, often requiring stabilization and bone grafting to achieve healing. Even after intramedullary screw fixation, residual instability may still hinder union. The purpose of this study was to describe the addition of Kirschner wires (KWs) through the capitate and the lunate to supplement an intramedullary screw for temporary enhanced stability, possibly improving healing of unstable fractures. A case-control study reviewing 25 cases with addition of KWs and 19 controls was performed. Demographic and fracture information, time to diagnosis, and healing time were documented. We found no differences in population characteristics, fracture characteristics, or outcome measures between patients treated with this method and those treated with a screw alone. We had no complications related to the addition of KWs. Preoperative lunate type and scapholunate gapping was suggestive but not significantly associated with KW insertion. Addition of KWs is safe and may be considered in scaphoid nonunion in the presence of intraoperative suboptimal stability. Intraoperative stability may possibly be inferred by reviewing preoperative radiographs for signs of instability.

  18. Equivalent damage of loads on pavements

    CSIR Research Space (South Africa)

    Prozzi, JA

    2009-05-26

    Full Text Available This report describes a new methodology for the determination of Equivalent Damage Factors (EDFs) of vehicles with multiple axle and wheel configurations on pavements. The basic premise of this new procedure is that "equivalent pavement response...

  19. Recognition of Kinematic Joints of 3D Assembly Models Based on Reciprocal Screw Theory

    Directory of Open Access Journals (Sweden)

    Tao Xiong

    2016-01-01

    Full Text Available Reciprocal screw theory is used to recognize the kinematic joints of assemblies restricted by arbitrary combinations of geometry constraints. Kinematic analysis is common for reaching a satisfactory design. If a machine is large and the incidence of redesign frequent is high, then it becomes imperative to have fast analysis-redesign-reanalysis cycles. This work addresses this problem by providing recognition technology for converting a 3D assembly model into a kinematic joint model, which is represented by a graph of parts with kinematic joints among them. The three basic components of the geometric constraints are described in terms of wrench, and it is thus easy to model each common assembly constraint. At the same time, several different types of kinematic joints in practice are presented in terms of twist. For the reciprocal product of a twist and wrench, which is equal to zero, the geometry constraints can be converted into the corresponding kinematic joints as a result. To eliminate completely the redundant components of different geometry constraints that act upon the same part, the specific operation of a matrix space is applied. This ability is useful in supporting the kinematic design of properly constrained assemblies in CAD systems.

  20. International test and demonstration of a 1-MW wellhead generator: Helical screw expander power plant

    Science.gov (United States)

    McKay, R. A.

    1984-06-01

    A 1-MW wellhead generator was tested in 1980, 1981, and 1982 by Mexico, Italy, and New Zealand at Cerro Prieto, Cesano, and Broadlands, respectively. The total flow helical screw expander portable power plant, Model 76-1, had been built for the U.S. Government and field-tested in Utah, USA, in 1978 and 1979. The expander had oversized internal clearances designed for self-cleaning operation on fluids that deposit adherent scale normally detrimental to the utiliation of liquid dominated fields. Conditions with which the expander was tested included inlet pressures of 64 to 220 psia, inlet qualities of 0% to 100%, exhaust pressures of 3.1 to 40 psia, electrial loads of idle and 110 to 933 kW, electrical frequencies of 50 and 60 Hz, male rotor speeds of 2500 to 4000 rpm, and fluid characteristics to 310,000 ppm total dissolved solids and noncondensables to 38 wt % of the vapor. Some testing was done on-grid. Typical expander isentropic efficiency was 40% to 50% with the clearances not closed, and 5 percentage points or more higher with the clearances partly closed. The expander efficiency increased approximately logarithmically with shaft power for most operations, while inlet quality, speed, and pressure ratio across the machine had only small effects. These findings are all in agreement with the Utah test results.

  1. Archimedes in Cephalonia and in Euripus Strait: Modern Horizontal Archimedean Screw Turbines for Recovering Marine Power

    Directory of Open Access Journals (Sweden)

    A. Stergiopoulou

    2013-01-01

    Full Text Available The possibility of exploiting sea and tidal currents for power generation has given little attention in Mediterranean countries despite the fact that these currents representing a large renewable energy resource could be exploited by “modern old technologies” to provide important levels of electric power. It is also well known that one of the oldest machines still in use is the Archimedes screw, a device for lifting water for irrigation and drainage, invention credited to Archimedes. The main aim of this paper is to present a new small hydro philosophy of recovering the unexploited coastal and tidal hydraulic potential by following an efficient “Archimedean philosophy” and by using modern horizontal-axis unconventional cochlear turbines. Our work proposes “the presence of Archimedes in Cephalonia and in Euripus Strait” and the optimal “Archimedean” exploitation of the Euripus tidal current and of the Cephalonia coastal paradox cross flowing continuously from Livadi Gulf to the Gulf of Sami. The present paper intends to prove the useful modern rediscovering of some old Archimedean ideas concerning spiral water wheel technologies under the form of new and efficient horizontal-axis Archimedean hydropower turbines.

  2. Discovering Classes of Strongly Equivalent Logic Programs

    OpenAIRE

    Chen, Y.; Lin, F.

    2011-01-01

    In this paper we apply computer-aided theorem discovery technique to discover theorems about strongly equivalent logic programs under the answer set semantics. Our discovered theorems capture new classes of strongly equivalent logic programs that can lead to new program simplification rules that preserve strong equivalence. Specifically, with the help of computers, we discovered exact conditions that capture the strong equivalence between a rule and the empty set, between two rules, between t...

  3. Machinability of advanced materials

    CERN Document Server

    Davim, J Paulo

    2014-01-01

    Machinability of Advanced Materials addresses the level of difficulty involved in machining a material, or multiple materials, with the appropriate tooling and cutting parameters.  A variety of factors determine a material's machinability, including tool life rate, cutting forces and power consumption, surface integrity, limiting rate of metal removal, and chip shape. These topics, among others, and multiple examples comprise this research resource for engineering students, academics, and practitioners.

  4. Pattern recognition & machine learning

    CERN Document Server

    Anzai, Y

    1992-01-01

    This is the first text to provide a unified and self-contained introduction to visual pattern recognition and machine learning. It is useful as a general introduction to artifical intelligence and knowledge engineering, and no previous knowledge of pattern recognition or machine learning is necessary. Basic for various pattern recognition and machine learning methods. Translated from Japanese, the book also features chapter exercises, keywords, and summaries.

  5. Support vector machines applications

    CERN Document Server

    Guo, Guodong

    2014-01-01

    Support vector machines (SVM) have both a solid mathematical background and good performance in practical applications. This book focuses on the recent advances and applications of the SVM in different areas, such as image processing, medical practice, computer vision, pattern recognition, machine learning, applied statistics, business intelligence, and artificial intelligence. The aim of this book is to create a comprehensive source on support vector machine applications, especially some recent advances.

  6. Machining of titanium alloys

    CERN Document Server

    2014-01-01

    This book presents a collection of examples illustrating the resent research advances in the machining of titanium alloys. These materials have excellent strength and fracture toughness as well as low density and good corrosion resistance; however, machinability is still poor due to their low thermal conductivity and high chemical reactivity with cutting tool materials. This book presents solutions to enhance machinability in titanium-based alloys and serves as a useful reference to professionals and researchers in aerospace, automotive and biomedical fields.

  7. Classroom Activities for Introducing Equivalence Relations

    Science.gov (United States)

    Brandt, Jim

    2013-01-01

    Equivalence relations and partitions are two interconnected ideas that play important roles in advanced mathematics. While students encounter the informal notion of equivalence in many courses, the formal definition of an equivalence relation is typically introduced in a junior level transition-to-proof course. This paper reports the results of a…

  8. An electric charge has no screw sense--a comment on the twistfree formulation of electrodynamics by da Rocha & Rodrigues

    CERN Document Server

    Itin, Yakov; Hehl, Friedrich W

    2009-01-01

    Da Rocha and Rodigues (RR) claim (i) that in classical electrodynamics in vector calculus the distinction between polar and axial vectors and in exterior calculus between twisted and untwisted forms is inappropriate and superfluous, and (ii) that they can derive the Lorentz force equation from Maxwell's equations. As to (i), we point out that the distinction of polar/axial and twisted/untwisted derives from the property of the electric charge of being a pure scalar, that is, not carrying any screw sense. Therefore, the mentioned distinctions are necessary ingredients in any fundamental theory of electrodynamics. If one restricted the allowed coordinate transformations to those with positive Jacobian determinants (or prescribed an equivalent constraint), then the RR scheme could be accommodated; however, such a restriction is illegal since electrodynamics is, in fact, also covariant under transformations with negative Jacobians. As to (ii), the "derivation" of the Lorentz force from Maxwell's equations, we poi...

  9. 纤维增强C/SiC复合陶瓷材料小螺纹孔攻丝工艺研究%Study on Small Screw Hole Tapping Technology of Fiber Reinforced C/SiC Ceramic Composites

    Institute of Scientific and Technical Information of China (English)

    王振来; 刘迎春; 周大华

    2015-01-01

    针对C/SiC复合陶瓷材料加工过程中掉渣严重、螺牙成型困难、加工合格率较低等问题,通过大量的工艺试验,摸索出非金属材料小螺纹攻丝螺牙成型的变化规律,从工艺方案的确定、钻头材质的选择、丝锥材质的选择、丝锥攻丝受力等方面总结出在非金属纤维增强C/SiC陶瓷材料上的小螺纹孔攻丝的工艺加工方法.提高了非金属材料小螺纹孔攻丝的合格率.%Focusing on the problems of serious scaling-off,screw tooth forming difficulty,and low qualified rate in the machining process of C/SiC composite ceramics,massive experiments were conducted.Forming rules of small screw tooth of C/SiC composite ceramic material were found and processing technology of small screw hole tapping for the material was summarized from aspects of scheme,drill and tap material,and tap force.The qualified rate of small screw hole tapping of C/SiC composite ceramics was improved.

  10. Twin screw wet granulation: the study of a continuous twin screw granulator using Positron Emission Particle Tracking (PEPT) technique.

    Science.gov (United States)

    Lee, Kai T; Ingram, Andy; Rowson, Neil A

    2012-08-01

    In this paper, Positron Emission Particle Tracking (PEPT) techniques are utilised to track the trajectory of single particles through the mixing and conveying zones of a Twin Screw Granulator (TSG). A TSG consisting of conveying zones and mixing zones is used in this study. The mixing zones are arranged with kneading discs at an angle of 30°, 60° or 90°. Experiments were carried out using different mixing configurations with various screw speed and total mass flow rate. The PEPT data obtained were then utilised to obtain the residence time distribution (RTD) and the Peclet number in an attempt to gain some insight into the mixing of the process. The fill level of the granulator was also estimated to study the mechanism of granulation. As might be expected, it was shown that the residence time of the granulation process increases with decreasing screw speed. It also increases with increasing angle of the arrangement of kneading blocks in the mixing zones, but will decreases when powder feed rate is increased. The fill level of the mixing zone in particular increases when the screw speed decreases or when powder feed rate increases. Furthermore, the fill level of the granulator will increase when the mixing zone configuration changes from 30° to 90°. It is shown that the granulator is never fully filled, even using 90° mixer elements implying limited compaction which may explain why the granules produced are porous compared with those from a high shear mixer. Interestingly, the RTD analysis reveals that the extent of axial mixing in the mixing zone of the granulator does not change significantly for different configurations and process conditions. There is evidence of a tail in the RTD which implies some material hold up and channelling.

  11. Influence of Induction Machine and Mechanism Parameters on Starting Transient Processes in Case of Constant Load Conditions

    Directory of Open Access Journals (Sweden)

    Dimitar Spirov

    2005-10-01

    Full Text Available Two-phase induction machine dynamic model in a coordinate system which rotates at synchronous speed and one-mass dynamic model of mechanism driven in relative units describing transient processes when starting an induction machine in case of constant load conditions are developed.The influence of equivalent circuit parameters of induction machine and mechanism parameters on impact currents and torques and starting time of common used induction machines is studied by means of design of experiment method.

  12. Rotating electrical machines

    CERN Document Server

    Le Doeuff, René

    2013-01-01

    In this book a general matrix-based approach to modeling electrical machines is promulgated. The model uses instantaneous quantities for key variables and enables the user to easily take into account associations between rotating machines and static converters (such as in variable speed drives).   General equations of electromechanical energy conversion are established early in the treatment of the topic and then applied to synchronous, induction and DC machines. The primary characteristics of these machines are established for steady state behavior as well as for variable speed scenarios. I

  13. Chaotic Boltzmann machines.

    Science.gov (United States)

    Suzuki, Hideyuki; Imura, Jun-ichi; Horio, Yoshihiko; Aihara, Kazuyuki

    2013-01-01

    The chaotic Boltzmann machine proposed in this paper is a chaotic pseudo-billiard system that works as a Boltzmann machine. Chaotic Boltzmann machines are shown numerically to have computing abilities comparable to conventional (stochastic) Boltzmann machines. Since no randomness is required, efficient hardware implementation is expected. Moreover, the ferromagnetic phase transition of the Ising model is shown to be characterised by the largest Lyapunov exponent of the proposed system. In general, a method to relate probabilistic models to nonlinear dynamics by derandomising Gibbs sampling is presented.

  14. Tribology in machine design

    CERN Document Server

    Stolarski, Tadeusz

    1999-01-01

    ""Tribology in Machine Design is strongly recommended for machine designers, and engineers and scientists interested in tribology. It should be in the engineering library of companies producing mechanical equipment.""Applied Mechanics ReviewTribology in Machine Design explains the role of tribology in the design of machine elements. It shows how algorithms developed from the basic principles of tribology can be used in a range of practical applications within mechanical devices and systems.The computer offers today's designer the possibility of greater stringen

  15. Debugging the virtual machine

    Energy Technology Data Exchange (ETDEWEB)

    Miller, P.; Pizzi, R.

    1994-09-02

    A computer program is really nothing more than a virtual machine built to perform a task. The program`s source code expresses abstract constructs using low level language features. When a virtual machine breaks, it can be very difficult to debug because typical debuggers provide only low level machine implementation in formation to the software engineer. We believe that the debugging task can be simplified by introducing aspects of the abstract design into the source code. We introduce OODIE, an object-oriented language extension that allows programmers to specify a virtual debugging environment which includes the design and abstract data types of the virtual machine.

  16. Electrical machines & drives

    CERN Document Server

    Hammond, P

    1985-01-01

    Containing approximately 200 problems (100 worked), the text covers a wide range of topics concerning electrical machines, placing particular emphasis upon electrical-machine drive applications. The theory is concisely reviewed and focuses on features common to all machine types. The problems are arranged in order of increasing levels of complexity and discussions of the solutions are included where appropriate to illustrate the engineering implications. This second edition includes an important new chapter on mathematical and computer simulation of machine systems and revised discussions o

  17. Machine learning with R

    CERN Document Server

    Lantz, Brett

    2013-01-01

    Written as a tutorial to explore and understand the power of R for machine learning. This practical guide that covers all of the need to know topics in a very systematic way. For each machine learning approach, each step in the process is detailed, from preparing the data for analysis to evaluating the results. These steps will build the knowledge you need to apply them to your own data science tasks.Intended for those who want to learn how to use R's machine learning capabilities and gain insight from your data. Perhaps you already know a bit about machine learning, but have never used R; or

  18. Induction machine handbook

    CERN Document Server

    Boldea, Ion

    2002-01-01

    Often called the workhorse of industry, the advent of power electronics and advances in digital control are transforming the induction motor into the racehorse of industrial motion control. Now, the classic texts on induction machines are nearly three decades old, while more recent books on electric motors lack the necessary depth and detail on induction machines.The Induction Machine Handbook fills industry's long-standing need for a comprehensive treatise embracing the many intricate facets of induction machine analysis and design. Moving gradually from simple to complex and from standard to

  19. CT-based bone density assessment for iliosacral screw trajectories

    Directory of Open Access Journals (Sweden)

    Andreas Schicho

    2016-01-01

    Full Text Available Introduction: Sacroiliac screw placement is one standard treatment option for stabilization of posterior pelvic ring injuries encountering high intra- and inter-individual variations of bone stock quality as well as a vast variety and prevalence of sacral dysmorphism. An individual, easy-to-use preoperative bone stock quality estimation would be of high value for the surgeon. Materials and Methods: We analyzed 36 standard computed tomography datasets with the uninjured pelvic ring. Using a two-plane cross-referencing technique, we assessed the Hounsfield unit (HU mean values as well as standard deviation and minimum/maximum values within selected region of interests (ROIs at five key areas: os ilium left and right, massa lateralis of os sacrum left and right, and central vertebral body on levels S1 and S2. Results: Results showed no difference in mean HU at any ROI when comparing male and female data. For all ROIs set on S1 and S2, there was an age-related decline of HU with a calculated slope significantly different from zero. There was no statistical difference of slopes when comparing S1- and S2-level with respect to any distinct ROI. Comparison of levels S1 and S2 revealed differences at the vertebral body and at the right os ilium. The right and left massa lateralis of os sacrum had lower bone density than the center of the vertebral body, the right, or left os ilium on S1; right and left massa lateralis density did not differ significantly. On level S2, results were comparable with no difference of massa lateralis density. Conclusion: With our easy-to-use preoperative assessment of bone density of five key areas of sacroiliac screw anchoring we were able to find the lowest bone density in both the left and right massa lateralis on levels S1 and S2 with high inter- and intra-individual variations. Significantly lower bone density was found in the center of the vertebral bodies S2 in comparison to S1, which both are crucial for iliosacral

  20. Accuracy and complications of transpedicular C2 screw placement without the use of spinal navigation.

    Science.gov (United States)

    Mueller, Christian-Andreas; Roesseler, Lukas; Podlogar, Martin; Kovacs, Attlila; Kristof, Rudolf Andreas

    2010-05-01

    The objective of the study was to describe the technique, accuracy of placement and complications of transpedicular C2 screw fixation without spinal navigation. Patients treated by C2 pedicle screw fixations were identified from the surgical log book of the department. Clinical data were extracted retrospectively from the patients' charts. Pedicle screw placement accuracy was assessed on postoperative CT scans according to Gertzbein and Robbins (GRGr). A total of 27 patients were included in the study. The mean age of the patients was 56 +/- 22.0 years; 51.9% of them were female. As much as 17 patients suffered from trauma, 5 of degenerative disease, 3 of inflammations and 2 of metastatic disease. A total of 47 C2 transpedicular screw fixations were performed. The canulated screws were inserted under visual control following the preparation of the superior surface of the isthmus and of the medial surface of the pedicles of the C2. Intraoperative fluoroscopy was additionally used. The postoperative CT findings showed in 55.3% GRGr 1, in 27.7% GRGr 2, in 10.6% GRGr 3, and in 6.3% GRGr 4 pedicle screw insertion accuracy. Screw insertions GRGr 5 were not observed. Screw malpositioning (i.e., GRGr 3 and 4) was significantly associated with thin (C2 fractures. In the three patients with screw insertions GRGr 4, postoperative angiographies were performed to exclude vertebral artery affections. In one of these three cases, the screw caused a clinically asymptomatic vertebral artery compression. Hardware failures did not occur. In one patient, postoperative pneumonia resulted in the death of the patient. Careful patient selection and surgical technique is necessary to avoid vertebral artery injury in C2 pedicle screw fixation without spinal navigation. A slight opening of the vertebral artery canal (Gertzbein and Robbins grade C2 pedicle screw insertions.