The Experts below are selected from a list of 321 Experts worldwide ranked by ideXlab platform

Robert A. Dickson - One of the best experts on this subject based on the ideXlab platform.

  • Unilateral spondylolysis and the presence of facet joint tropism.
    Spine, 2010
    Co-Authors: James J. Rankine, Robert A. Dickson
    Abstract:

    STUDY DESIGN: Retrospective review of the CT scans performed in a group of patients examined for a possible spondylolysis. OBJECTIVE: To investigate whether there is an association between unilateral spondylolysis and facet joint tropism. SUMMARY OF BACKGROUND DATA: Spondylolysis is a fatigue fracture of the pars interarticularis of great importance in sports injury. The demonstration of a unilateral spondylolysis is important because there is a potential for full healing if the athletic activity is modified, whereas bilateral spondylolysis frequently leads to established nonunion. Coronally orientated facet joints are known to predispose to spondylolysis by increasing the point loading of the pars interarticularis. The importance of this finding has not been investigated in unilateral spondylolysis. METHODS: A review of patients with low back pain and a possible diagnosis of spondylolysis who were investigated with multislice CT was performed. The coronal orientation of the facet joints at L4/5 and L5/S1 was measured and comparison was done between those with and without a spondylolysis. RESULTS: The coronal angle of 140 facet joints in 35 patients was recorded. Of 35 patients, 23 had a spondylolysis which was unilateral in 12 patients. The facet joint angle was significantly more coronally orientated in the presence of a spondylolysis when compared with an intact pars (means, 53° and 43°, respectively; P < 0.01). In the presence of a unilateral spondylolysis, the facet joint was significantly more coronally orientated on the side of the spondylolysis (means, 52° and 45°, respectively; P < 0.01). CONCLUSION.: This study is the first investigation of facet joint anatomy in unilateral spondylolysis. Asymmetric facet joints do increase the force through one side of the spine, with a unilateral spondylolysis occurring on the side of the more coronally orientated facet joint.

  • Unilateral spondylolysis and the presence of facet joint tropism.
    Spine, 2010
    Co-Authors: James J. Rankine, Robert A. Dickson
    Abstract:

    Retrospective review of the CT scans performed in a group of patients examined for a possible spondylolysis. To investigate whether there is an association between unilateral spondylolysis and facet joint tropism. Spondylolysis is a fatigue fracture of the pars interarticularis of great importance in sports injury. The demonstration of a unilateral spondylolysis is important because there is a potential for full healing if the athletic activity is modified, whereas bilateral spondylolysis frequently leads to established nonunion. Coronally orientated facet joints are known to predispose to spondylolysis by increasing the point loading of the pars interarticularis. The importance of this finding has not been investigated in unilateral spondylolysis. A review of patients with low back pain and a possible diagnosis of spondylolysis who were investigated with multislice CT was performed. The coronal orientation of the facet joints at L4/5 and L5/S1 was measured and comparison was done between those with and without a spondylolysis. The coronal angle of 140 facet joints in 35 patients was recorded. Of 35 patients, 23 had a spondylolysis which was unilateral in 12 patients. The facet joint angle was significantly more coronally orientated in the presence of a spondylolysis when compared with an intact pars (means, 53° and 43°, respectively; P < 0.01). In the presence of a unilateral spondylolysis, the facet joint was significantly more coronally orientated on the side of the spondylolysis (means, 52° and 45°, respectively; P < 0.01). CONCLUSION.: This study is the first investigation of facet joint anatomy in unilateral spondylolysis. Asymmetric facet joints do increase the force through one side of the spine, with a unilateral spondylolysis occurring on the side of the more coronally orientated facet joint.

Deepika Janakiraman - One of the best experts on this subject based on the ideXlab platform.

  • Lévy flights in the presence of a point sink of finite strength.
    Physical review. E, 2017
    Co-Authors: Deepika Janakiraman
    Abstract:

    In this paper, the absorption of a particle undergoing Lévy flight in the presence of a point sink of arbitrary strength and position is studied. The motion of such a particle is given by a modified Fokker-Planck equation whose exact solution in the Laplace domain can be described in terms of the Laplace transform of the unperturbed (absence of the sink) Green's function. This solution for the Green's function is a well-studied, generic result which applies to both fractional and usual Fokker-Planck equations alike. Using this result, the propagator and the absorption-time distribution are obtained for free Lévy flight and Lévy flight in linear and harmonic potentials in the presence of a delta function sink, and their dependence on the sink strength is analyzed. Analytical results are presented for the long-time behavior of the absorption-time distribution in all three above-mentioned potentials. Simulation results are found to corroborate closely with analytical results.

  • l e vy flights in the presence of a point sink of finite strength
    arXiv: Statistical Mechanics, 2017
    Co-Authors: Deepika Janakiraman
    Abstract:

    In this paper, the absorption of a particle undergoing L\'{e}vy flight in the presence of a point sink of arbitrary strength and position is studied. The motion of such a particle is given by a modified Fokker-Planck equation whose exact solution in the Laplace domain can be described in terms of the Laplace transform of the unperturbed (absence of the sink) Green's function. This solution for the Green's function is a well-studied, generic result which applies to both fractional and usual Fokker-Planck equations alike. Using this result, the propagator and the absorption time distribution are obtained for free L\'{e}vy flight and L\'{e}vy flight in linear and harmonic potentials in the presence of a delta function sink, and their dependence on the sink strength is analyzed. Analytical results are presented for the long-time behaviour of the absorption time distribution in all the three above mentioned potentials. Simulation results are found to corroborate closely with the analytical results.

  • L\'{e}vy flights in the presence of a point sink of finite strength
    arXiv: Statistical Mechanics, 2017
    Co-Authors: Deepika Janakiraman
    Abstract:

    In this paper, the absorption of a particle undergoing L\'{e}vy flight in the presence of a point sink of arbitrary strength and position is studied. The motion of such a particle is given by a modified Fokker-Planck equation whose exact solution in the Laplace domain can be described in terms of the Laplace transform of the unperturbed (absence of the sink) Green's function. This solution for the Green's function is a well-studied, generic result which applies to both fractional and usual Fokker-Planck equations alike. Using this result, the propagator and the absorption time distribution are obtained for free L\'{e}vy flight and L\'{e}vy flight in linear and harmonic potentials in the presence of a delta function sink, and their dependence on the sink strength is analyzed. Analytical results are presented for the long-time behaviour of the absorption time distribution in all the three above mentioned potentials. Simulation results are found to corroborate closely with the analytical results.

  • levy flights in the presence of a point sink of finite strength
    Physical Review E, 2017
    Co-Authors: Deepika Janakiraman
    Abstract:

    In this paper, the absorption of a particle undergoing Levy flight in the presence of a point sink of arbitrary strength and position is studied. The motion of such a particle is given by a modified Fokker-Planck equation whose exact solution in the Laplace domain can be described in terms of the Laplace transform of the unperturbed (absence of the sink) Green's function. This solution for the Green's function is a well-studied, generic result which applies to both fractional and usual Fokker-Planck equations alike. Using this result, the propagator and the absorption-time distribution are obtained for free Levy flight and Levy flight in linear and harmonic potentials in the presence of a delta function sink, and their dependence on the sink strength is analyzed. Analytical results are presented for the long-time behavior of the absorption-time distribution in all three above-mentioned potentials. Simulation results are found to corroborate closely with analytical results.

J. Quiñones - One of the best experts on this subject based on the ideXlab platform.

  • Diffusion bonding of alumina to steel using soft copper interlayer
    Journal of Materials Science, 1992
    Co-Authors: A. Ureña, J. M. Gómez Salazar, J. Quiñones
    Abstract:

    The diffusion bonding of a low steel to alumina has been studied in the present work. Thin foils of a soft metal (copper) were used to reduce the effects of the residual stresses produced in the joint by thermal expansion mismatch. The strength of the joint was found to be influenced by the bonding parameters, but principally by the oxygen content both on the surface and in the copper matrix. The diffusion bonds have been mechanically tested using a three-point bending test. Maximum bending strengths of 100 MPa were achieved by using a 0.1 mm copper foil, and bonding in a oxidizing atmosphere ( P _O _2=10_4Pa). SEM and EDS investigations have shown the presence of reaction products in the copper-alumina interface which controls the mechanical properties of the joint.

  • Diffusion bonding of alumina to steel using soft copper interlayer
    Journal of Materials Science, 1992
    Co-Authors: A. Ureña, J. M. Gómez Salazar, J. Quiñones
    Abstract:

    The diffusion bonding of a low steel to alumina has been studied in the present work. Thin foils of a soft metal (copper) were used to reduce the effects of the residual stresses produced in the joint by thermal expansion mismatch. The strength of the joint was found to be influenced by the bonding parameters, but principally by the oxygen content both on the surface and in the copper matrix. The diffusion bonds have been mechanically tested using a three-point bending test. Maximum bending strengths of 100 MPa were achieved by using a 0.1 mm copper foil, and bonding in a oxidizing atmosphere ( P _O _2=10_4Pa). SEM and EDS investigations have shown the presence of reaction products in the copper-alumina interface which controls the mechanical properties of the joint.

James J. Rankine - One of the best experts on this subject based on the ideXlab platform.

  • Unilateral spondylolysis and the presence of facet joint tropism.
    Spine, 2010
    Co-Authors: James J. Rankine, Robert A. Dickson
    Abstract:

    STUDY DESIGN: Retrospective review of the CT scans performed in a group of patients examined for a possible spondylolysis. OBJECTIVE: To investigate whether there is an association between unilateral spondylolysis and facet joint tropism. SUMMARY OF BACKGROUND DATA: Spondylolysis is a fatigue fracture of the pars interarticularis of great importance in sports injury. The demonstration of a unilateral spondylolysis is important because there is a potential for full healing if the athletic activity is modified, whereas bilateral spondylolysis frequently leads to established nonunion. Coronally orientated facet joints are known to predispose to spondylolysis by increasing the point loading of the pars interarticularis. The importance of this finding has not been investigated in unilateral spondylolysis. METHODS: A review of patients with low back pain and a possible diagnosis of spondylolysis who were investigated with multislice CT was performed. The coronal orientation of the facet joints at L4/5 and L5/S1 was measured and comparison was done between those with and without a spondylolysis. RESULTS: The coronal angle of 140 facet joints in 35 patients was recorded. Of 35 patients, 23 had a spondylolysis which was unilateral in 12 patients. The facet joint angle was significantly more coronally orientated in the presence of a spondylolysis when compared with an intact pars (means, 53° and 43°, respectively; P < 0.01). In the presence of a unilateral spondylolysis, the facet joint was significantly more coronally orientated on the side of the spondylolysis (means, 52° and 45°, respectively; P < 0.01). CONCLUSION.: This study is the first investigation of facet joint anatomy in unilateral spondylolysis. Asymmetric facet joints do increase the force through one side of the spine, with a unilateral spondylolysis occurring on the side of the more coronally orientated facet joint.

  • Unilateral spondylolysis and the presence of facet joint tropism.
    Spine, 2010
    Co-Authors: James J. Rankine, Robert A. Dickson
    Abstract:

    Retrospective review of the CT scans performed in a group of patients examined for a possible spondylolysis. To investigate whether there is an association between unilateral spondylolysis and facet joint tropism. Spondylolysis is a fatigue fracture of the pars interarticularis of great importance in sports injury. The demonstration of a unilateral spondylolysis is important because there is a potential for full healing if the athletic activity is modified, whereas bilateral spondylolysis frequently leads to established nonunion. Coronally orientated facet joints are known to predispose to spondylolysis by increasing the point loading of the pars interarticularis. The importance of this finding has not been investigated in unilateral spondylolysis. A review of patients with low back pain and a possible diagnosis of spondylolysis who were investigated with multislice CT was performed. The coronal orientation of the facet joints at L4/5 and L5/S1 was measured and comparison was done between those with and without a spondylolysis. The coronal angle of 140 facet joints in 35 patients was recorded. Of 35 patients, 23 had a spondylolysis which was unilateral in 12 patients. The facet joint angle was significantly more coronally orientated in the presence of a spondylolysis when compared with an intact pars (means, 53° and 43°, respectively; P < 0.01). In the presence of a unilateral spondylolysis, the facet joint was significantly more coronally orientated on the side of the spondylolysis (means, 52° and 45°, respectively; P < 0.01). CONCLUSION.: This study is the first investigation of facet joint anatomy in unilateral spondylolysis. Asymmetric facet joints do increase the force through one side of the spine, with a unilateral spondylolysis occurring on the side of the more coronally orientated facet joint.

Steven Chamberland - One of the best experts on this subject based on the ideXlab platform.

  • Designing Two-Level IP Networks Including the Points of Presence
    2008 Next Generation Internet Networks, 2008
    Co-Authors: Steven Chamberland
    Abstract:

    In this paper, we propose a heuristic algorithm based on the tabu search principle for the topological design problem of two-level Internet protocol (IP) networks including the design of the points of presence. This global problem consists in selecting the number of routers and their types to install in each point of presence, selecting the interface card types to install in each router, finding the access and backbone networks and finally, interconnecting the co-located routers in each point of presence. The numerical results show that "good" solutions can be found rapidly with the proposed approach.

  • Incorporating the Points of Presence within the Two-Level Topological Network Design Problem
    Networks 2006. 12th International Telecommunications Network Strategy and Planning Symposium, 2006
    Co-Authors: Steven Chamberland
    Abstract:

    In this paper, we propose to tackle the topological design problem of two-level networks including the design of the points of presence. The problem consists in selecting the number of routers and their types to install in each point of presence, selecting the interface card types to install in each router, finding the access and backbone networks and finally, interconnecting the co-located routers in each point of presence. Instead of partitioning the problem into subproblems and solving them successively, we propose a mathematical programming model that addresses it as a whole. Finally, we present a detailed network design example.

  • On the point-of-presence optimization problem in IP networks
    Canadian Journal of Electrical and Computer Engineering, 2005
    Co-Authors: Steven Chamberland, Marc St-hilaire, Samuel Pierre
    Abstract:

    This paper presents a model for the point-of-presence (POP) optimization problem in Internet protocol (IP) networks, where a POP is a node composed of several interconnected co-located backbone routers. This problem consists of selecting the number of routers and their types, selecting the interface card types, connecting the access and the backbone links to the ports, selecting the link types between the co-located routers, and routing the traffic within the POP. A detailed example solved by using a branch-and-bound algorithm is presented along with results for a set of randomly generated problems. The results show that fair-sized problems can be solved to optimality within a reasonable amount of time.

  • Point of presence design in Internet protocol networks with performance guarantees
    Computers & Operations Research, 2005
    Co-Authors: Steven Chamberland
    Abstract:

    In this paper, we propose a model for the point of presence (POP) design problem in Internet protocol (IP) networks with performance guarantees, where a POP is a node composed of several interconnected co-located backbone routers within a central office. This problem consists of selecting the number of routers and their types, selecting the interface card types, connecting the access and the backbone links to the ports and selecting the link types between the co-located routers. Furthermore, the model considers the routing of the IP traffic. The performance guarantees we refer to are bandwidth guarantees between the routers for the normal state of the POP and also for all failure scenarios of interest to the network planner. A tabu search heuristic to find solutions for real-size instances of the problem is proposed. Finally, we present a systematic set of experiments designed to assess the performance of the proposed heuristic.

  • On the point-of-presence optimization problem in IP networks Sur le probl` eme de l'optimisation des points de pr´ esence dans les r´
    2005
    Co-Authors: Steven Chamberland, Marc St-hilaire, Samuel Pierre
    Abstract:

    This paper presents a model for the point-of-presence(POP) optimizationproblemin Internet protocol(IP) networks, where a POP is a node composedof several interconnected co-located backbone routers. This problem consists of selecting the number of routers and their types, selecting the interface card types, connecting the access and the backbonelinks to the ports, selecting the link types between the co-located routers, and routing the traffic within the POP. A detailed example solved by using a branch-and-bound algorithm is presented along with results for a set of randomly generated problems. The results show that fair-sized problemscan be solved to optimality within a reasonableamountof time.